Articles from 1999 In January

Products Featured on the Cover of MPMN

Products Featured on the Cover of MPMN

Close-tolerance production of wire and tubing components and assemblies

An ISO 9002–certified company manufactures close-tolerance precision wire components and assemblies in diameters from 0.001 to 0.100 in. In-house operations include wire straightening and cutting, centerless and multitaper grinding, coil winding, wire forming, flattening, precision welding, and vacuum heat treating. In addition, the company specializes in the assembly of wire and tubing components using its expertise in laser welding, resistance welding, brazing, and other joining technologies. The company works with most alloys, including stainless steel, MP35N, nitinol, tungsten, titanium, and platinum. Star Guide Corp., 5000 Independence St., Arvada, CO 80002.

Custom electronics manufacturing services for medical device OEMs

A variety of custom electronics manufacturing services for medical devices including cabling, cable assemblies, wire harnesses, electromechanical assemblies, printed circuit assemblies, and power supplies are available. Capabilities include design, prototyping, high- or low-volume production, packaging, and warehouse and freight services. Manufacturing facilities are ISO 9001 and EN 46001 certified with CE marking pending. Additional services include computerized testing, software development and production, design for manufacturability and engineering, and 3-D modeling. Burron OEM Div., B. Braun Medical Inc., 824 12th Ave., Bethlehem, PA 18018.

Custom-made balls available in a variety of colors and sizes

Custom-made specialty balls can be precision fabricated in specific sizes, colors, and weights for use with medical scanning equipment and other applications. The specialty balls are custom made in diameters from 1.375 to 8.5 in. with ±0.003-in. tolerances and ±0.002 TIR in. roundness, hardness from 65 to 89 D, and high-gloss finishes to 7–8 rms. Manufactured from Partek thermoset resins, the balls can feature precise weights from 1.2 to 1.75 specific gravity, be custom color-matched, and incorporate embedded type or logos. Depending on resin formulation, the balls provide high impact resistance and durability. They are available in solid opaque colors as well as marbleized, glowing, pearlescent, neon pearlescent, fluorescent, sparkling, transparent, and clear finishes. E. Parrella Company, Inc., 36 Alder St., Medway, MA 02053.

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Investing in Good Design

Editor's Page

Investing in Good Design

Last year MPMN's publisher, Canon Communications, teamed up with the Industrial Designers Society of America (ISDA) to establish the Medical Design Excellence Awards to honor the innovators, risk takers, and creative thinkers who characterize the medical device industry. Following the program's inaugural success, Canon is again sponsoring the design and engineering competition.

Next month an eight-member panel with expertise in product design and development, medicine, ergonomics and human factors, biomedical engineering, and industrial design will convene to evaluate the entries for the second annual awards program.

The jurors have a challenging task ahead of them. With such an impressive showing of entries anticipated, the jury is likely to engage in significant debate in choosing the top products. "I expect spirited discussion on such issues as design, innovation, engineering, and quality as we come to some accord in our selection process," says juror and former award winner Matt Duncan, president of Morphix Design (San Clemente, CA). For Duncan, winning a 1998 Medical Design Excellence Award proved to be a gratifying experience. "As one of the recipients of last year's Medical Design Excellence Awards, I've enjoyed the exposure that Medical Product Manufacturing News and other magazines have given the product and my client—not to mention my own practice."

As for this year's competition, juror Robert Hall, principal of GVO Design (Palo Alto, CA), had this to say about the judging: "One aspect I will be looking at is how well the product addresses the economics of modern healthcare. I think designers need to realize that usability includes affordability and affordability includes cost and reimbursement issues." For juror Christoph Böeninger, vice president of Siemens Design & Messe GmbH (Munich), the practicality of the devices will be of primary importance. "The product should meet the intended user's physical requirements and be easy to operate, and should contain features that prevent fatigue," he says. "A product's originality and design and harmony with its surroundings are also important."

As a user-interface designer, juror Michael Wiklund, director of the Usability Engineering Group at the American Institutes of Research (Concord, MA), will be looking at ergonomics and usability. "A high-quality design will not seem overly complex on first impression and will provide rapid and intuitive access to frequently used and critical functions. I think companies should be rewarded for investing in good design. And clearly, winning a Medical Design Excellence Award can help a company market its product, thereby providing another reinforcement to investing in good design."

Perhaps you've been instrumental in the design, engineering, development, or manufacture of a medical or healthcare product that has reached the marketplace. If so, I encourage you to enter the competition, which has a fast-approaching deadline of February 8. To learn more about the awards program, or to view the 1998 winning products, stop by Booth #2345 at the Medical Design & Manufacturing Exposition January 26–28 in Anaheim, CA. You can also pick up an entry form for this year's competition at the booth.

Entry forms are available in PDF or by calling the fax-on-demand number at 800/588-8527 or by calling Sally Lane of Canon Communications at 310/392-5509 or Kathy Leftwich of IDSA at 703/759-0100.

Amy Allen

Printing and labeling equipment

Printing and labeling equipment

Label-counting table

A label-counting table with a visual setup mode and a moving plate–to–moving plate system facilitates accurate counts. A plate-to-plate feature maintains uniform web tension, allowing even narrow rolls to be moved without telescoping. The table can be customized according to user requirements with retrofits available for previously installed systems. Specifications include up to 6-in. label heights on 13-in. disks, 3-in.-diam x 4-in.-high mechanical core locks, a 24 x 48-in. steel table, a reversing motor, and a mechanical brake. HB Registration Corp., 12 Sherman St., Linden, NJ 07036.

Label printer/applicator

A high-speed printer/applicator prints and applies bar code labels to the tops of packages traveling along a conveyor. The LSX-12 can accommodate package heights ranging from 0.25 to 36 in., with a maximum throughput of 3600 packages per hour, or 60 packages per minute. The system consists of an embedded high-speed printer, a system controller, a high-speed vertical linear transport system, and a label pick-and-apply mechanism. Separate detection devices include a light curtain, a belt encoder (tachometer), and a package-tracking photo eye. Accu-Sort Systems Inc., 511 School House Rd., Telford, PA 18969.


The Autoprint system combines ink-jet and thermal-transfer printing, labeling, scanning, and product-handling equipment, as well as message-management software. The system transports, prints, bar codes, and counts cartons for many thousands of different products or stock-keeping units. Line speeds of up to 100 cartons per minute are possible. Setup time is minimal; messages for each product and/or customer can be changed in a few seconds. AT Information Products Inc., 575 Corporate Dr., Mahwah, NJ 07430-2004.

Tabletop printer/applicator

The speed and efficiency of hand packing and labeling operations can be maximized with a tabletop printer/applicator. The Label Mill 1200TPA provides a cost-effective, semiautomatic method of printing and tamp-applying labels to a large variety of products in large or small batches. It can print batch, lot, and date codes, as well as bar codes, text, and graphics, on a variety of label materials at speeds of up to 6 in./sec. The swing tamp applies the labels accurately and efficiently. MMI Automated Systems, 2416 Jackson St., Savanna, IL 61074.

Bar code imprinter

A 60-page/min bar code imprinter is specifically designed for high-volume bar code tag, label, and form imprinting. The LIS-1660 features a patented technology that uses fiber optics in conjunction with a high-speed digital shuttering system—along with 400-dpi rectangular dot technology—to achieve sharp edge definition and high print quality. The system also features an ergonomic operator panel with convenient, easy-to-use graphical backlit displays. Meto Inc., 1200 The American Rd., Morris Plains, NJ 07950.

Tamp-type label applicator

Suitable for delicate, high-precision print-and-apply applications, a tamp-type applicator applies small labels with an accuracy of ±0.02 in. According to the manufacturer, field tests for placement accuracy of the Apollo 1 have recorded a best of 0.008 in. and a worst case of 0.031 in. The unit attaches to a 300-dpi thermal or thermal-transfer printer. Tharo Systems Inc., P.O. Box 798, Brunswick, OH 44212.

Thermal transfer printer

A thermal transfer printer applies variable information directly onto package substrates such as poly, films, foil, Tyvek, and paper. The EasyPrint printer is designed as a replacement for conventional hot-stamp coders on form-fill-seal packaging machines, baggers, and label applicators. A traversing coding system moves on a linear rail to code up to 30 packages in one pass—eliminating the need for multiple coders—and has a print area up to 5 in. wide. This traversing feature increases production and provides cost savings by replacing a hot-stamp ribbon and metal type. Bell-Mark Corp., P.O. Box 2007, Pine Brook, NJ 07058-2007.


Small and difficult applications can be handled with a unit that provides print-and-apply capability for labels as small as 0.5 x 0.5 in. at speeds up to 30 labels per minute. The ValuePro 3240 is especially suitable for applying small labels to medical devices, surgical supplies, and similar products with limited space. It can be installed on-line or as a stand-alone system. When installed on-line, start-up is as simple as plugging in a photo eye to the external port or connecting a PLC to an Opto 22 module. Off-line applications use a foot switch or photo eye for initiation of the label cycle. Imtec Inc., 1 Imtec Ln., Bellows Falls, VT 05101.

Printing system

A printing system integrates a pad printer with a UV ink-curing system. Features of the Model UV340PP include digital conveyor-speed readout, a precision x-y jig table, an ergonomic design, and print-and-cure speeds up to 1900 marks per hour. The system is suitable for all marking, identification, and decoration needs. Automated Industrial Systems Inc., 4238 W. 12th St., Erie, PA 16505.

All-electric label applicator

No compressed air is required for an all-electric label application system for thermal-transfer printers. The ELA-100 applies up to 40 labels per minute and is suitable for shipping labels and warehouse and inventory identification labels. The system works in conjunction with most customer-supplied thermal-transfer printers. Because the printer and applicator are separate, printer changes can be made rapidly. Technomation Inc., 3408 South 1400 West, Salt Lake City, UT 84119.

Laser marking

Plastics, metals, ceramics, glass, and many other substrates can be marked with a high-speed sealed CO2 laser. Suitable applications include graphics, alphanumerics, bar codes, logos, geometric shapes, and intricate designs. In addition to marking directly onto the substrate, the system offers a unique laser technology that allows high-contrast permanent color marking. The system is designed to process both static materials as well as materials on the fly at speeds of up to 90 in./sec. A marking head, a PC, software, and optics are included. The Industrial Laser Source Inc., 7 Fitzgerald Dr., Hopedale, MA 01747.

Flexographic printer

Manufacturers using any brand of horizontal form-fill-seal packaging machinery for their products can now retrofit their equipment with an in-line flexographic rotary printer that will print directly onto their product packaging. According to its manufacturer, the Black Max printer is the smallest and fastest in the industry, and offers the lowest costs per impression. It prints total product information on any substrate at speeds of up to 35 cycles per minute. A lightweight stainless-steel covered PVC print drum allows operators to make print plate changes in seconds without using tools. Greydon Inc., 2083 Springwood Rd., Box 301, York, PA 17403.

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Composite Board Allows the Fast Machining of Injection Molds

Injection Molding

Composite Board Allows the Fast Machining of Injection Molds

The molds can produce hundreds of accurate parts

A NEW COMPOSITE BOARD allows the machining of thermoplastic injection molds in just hours. Molds milled with Cibatool-Express composite board from Ciba Specialty Chemicals Corp. (East Lansing, MI) are durable enough to run hundreds of dimensionally accurate parts with high-quality surface finishes from production plastics such as ABS, polypropylene, and polycarbonate.

"Cibatool-Express can produce tools in 15 to 20% of the time needed to generate aluminum molds," says Linda Chamberlain, director of advanced manufacturing for Prince (Holland, MI). In 1997, Prince established a research partnership with Ciba to develop a series of composite boards for machining injection molds. The objective of the program was to reduce product development lead times by generating production-quality parts for engineering and marketing evaluation very early in the design process. The Cibatool-Express mold-making system created through this partnership exhibits the physical performance characteristics required for such a demanding application.

Rapid production is possible because the machined composite board exhibits a surface finish that virtually eliminates the need for the time-consuming benching required to produce aluminum molds. Once mounted in an aluminum support structure, the composite tool can withstand the temperatures and pressures needed to run many thermoplastics and form hundreds of production-quality parts that hold tolerances to ±0.005 in.

For more information, contact Ciba Specialty Chemicals Corp. at 517/351-5900.

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Software Developed for the Design of Implantable Devices

Allows designers to explore interactions between a device and the body

REMCOM INC. (State College, PA), an electromagnetics software developer, has released a native Windows 95/98/NT version 5.0 of XFDTD to complement its existing line of UNIX products.

Key features of the finite-difference time-domain software include steady-state/transient field analysis, S-parameters, complex media, and specific absorption rate (SAR) for biomedical applications.

The new Windows release features an easy-to-use graphical user interface that will allow engineers to perform sophisticated analyses previously available only from UNIX-based versions. The software's flexibility and ease of use, combined with its more advanced capabilities, may help companies increase productivity and shorten design cycles.

The new features enhance the variety and scale of analyses that can be done, especially for antennas, microwave devices, and biological applications. Enhanced biological analysis capabilities allow designers of implantable medical devices to explore the complex interactions between the hardware and the human body.

For more information, contact Remcom Inc. at 814/861-1299.

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Injection Molding

Microinjection Molding Machine Produces Small Plastic Parts

Fits onto a standard laboratory benchtop

MURRAY INC. of Buffalo Grove, IL, has introduced a microinjection molding machine that is specifically designed to fit into the process flow for cleanroom manufacturing of medical devices.

Examples of applications targeted for the Sesame .020 include molding tips directly onto catheters, molding luer fittings onto catheters, assembling components (plastic and metal), integrating sensors into devices, and producing small plastic parts. The machine fits onto a standard laboratory benchtop and requires only compressed air and 115-V-ac power for operation. Plastic shot capacity can be as small as 1.0 mm3 to mold parts with a wall thickness down to 0.025 mm.

When the machine was demonstrated at MD&M Minnesota in November, part sizes were illustrated by molding a sesame seed with a volume of 2.0 mm3 and a weight of 0.0022 g. The company's logo in 0.3-mm-high letters was molded into the surface of the sesame seed and could be seen under a microscope.

For more information, contact Murray Inc. at 847/419-0090.

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Go for the Gold : Packaging Solutions Found at Pack Expo

Go for the Gold

The deadline for the second annual Medical Design Excellence Awards is approaching

Canon Communications, publisher of Medical Product Manufacturing News, is accepting applications for the second annual Medical Design Excellence Awards. The awards program, endorsed by the Industrial Designers Society of America (IDSA; Great Falls, VA), recognizes 13 categories of finished medical devices and device packaging. This year, the competition is open to designers and manufacturers worldwide. Entries must be submitted by February 8, 1999.

Kent Ritzel, director of Metaphase Design Group, will chair the Medical Design Excellence Awards jury for a second time.

An eight-member jury with expertise in product design and development, human factors, engineering, medicine, ergonomics, and R&D, will be judging the awards. The jury will evaluate entries based on such factors as benefits to users and patients, safety, cost-effectiveness, innovation, and advancement of the state of the art. Participants will be eligible for two levels of awards--gold and silver. Winners will be notified by mail by March 24, 1999, and invited to attend a gala dinner ceremony during MD&M East 99 in New York City, May 25-27. Also, the award-winning products will be displayed at the show.

"Last year, as a group, we were all pretty impressed with the amount of background work and research that had been done in the development of these products," says jury chair Kent Ritzel, director of Metphase Design Group (St. Louis). Ritzel, who will be chairing the jury for a second time, believes opening the awards program to the global community will make this year's competition "all the more challenging and exciting."

For information on how to submit an entry or to obtain an entry form, call Sally Lane of Canon Communications at 310/392-5509, or Kathy Leftwich of IDSA at 703/759-0100. The entry form is also available in PDF. Forms are also available through a 24-hour fax-on-demand line, 800/588-8527 or by e-mailing requests to

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Packaging Solutions Found at Pack Expo

Medical device packaging engineers continue to struggle with validating their packaging. At Pack Expo in Chicago, November 8-12, many firms were on hand to offer solutions to packaging validation challenges. Alloyd, Packaging Aids Corp., and True Technology were just a few of the many companies displaying products designed to simplify medical device packaging validation.

Alloyd (De Kalb, IL) displayed its Model 2SM1216 heat sealer, which features a PC hookup through which 33 parameters are recorded, including the temperature, pressure, and duration of the heat-sealing process. A complete record for every packaged item is thus available. The unit features an LCD touch screen interface with numeric controls, which allows the operator to select and download project setup parameters from PC-based software.

Attendees at Pack Expo were able to view products from more than 1600 exhibitors.

For manufacturers with limited space, budget, or production requirements who nevertheless require medical seal integrity, Packaging Aids Corp. (San Rafael, CA) showed its Med Pac pouch sealer. Although the unit cannot be connected to a PC, it features sealing parameters that are set by validatable controls. An alarm system aborts the cycle if either the temperature or pressure fall out of range, and the machine goes into lockout mode to prevent the operator from putting any more pouches through. The two heat sealers provide process control.

True Technology Inc. (Newton, MA) displayed its Sealcheck 210 system, which allows packagers to test and document the sterile integrity of every package rather than taking random samples from a large batch. The tester also shows the location of leaks as small as 0.001 to 0.002 in. diam. In the testing operation, a temporary barrier layer is applied over the package membrane using a special tape. Helium tracer gas is then introduced into the package through a port in the barrier tape. A probe maps the helium concentration using a mass spectrometer leak and reports the location of any leaks detected.

Overall, 75,000 people attended Pack Expo. This year's show is scheduled to be held October 18-20, 1999, in Las Vegas.

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Firms Offer One-Stop Services

Through a merger of five companies based in Massachusetts and New Hampshire, the Brookfield Group (West Brookfield, MA) holding company offers rapid prototyping, tooling, and production manufacturing of injection-molded parts. The companies that make up the Brookfield Group are Brookfield Rapid Solutions (Hudson, NH), Wilderness Mold (West Hatfield, MA), Mill Valley Molding (West Hatfield, MA), Brookfield Machine (Brookfield, MA), and Brookfield Innovations (Hudson, NH).

"The merger allows member companies to leverage their financial strength for continued capital investment in new technologies," said Christopher S. Nesbitt, Brookfield Group chairman and CEO. "Other benefits include reduced overhead, increased customer service and sales coverage, and opportunities to sell existing services to a broader customer base."

The new corporation has four locations and about 260 employees.

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Business and Acquisition News

Testing-instrumentation maker Thwing-Albert Instrument Co. (Philadelphia) has acquired Karl Frank GmbH. The acquired company, renamed Thwing-Albert Frank GmbH, will maintain its corporate headquarters in Germany. Davis-Standard Corp. (Pawcatuck, CT) acquired a line of blown-film dies, air rings, towers, and winders for small production and laboratory film systems from Film Master (Passaic, NJ), and will transfer the line to Davis-Standard's Laboratory and Specialty Systems Group (Cedar Grove, NJ). Specialty extruder Natvar Co. (Wakefield, MA) has formed a strategic alliance with Rubicon Medical (Salt Lake City), as well as a joint venture with Valnet Medical Corp. (Santa Isabel, Puerto Rico), to run an extrusion production line at Valnet's facility. The Texwipe Co. LLC (Upper Saddle River, NJ) opened a cleanroom products manufacturing facility in Cabayao in the Philippines. Sparton Corp. (Jackson, MI) and Contract Assembly Inc. (Lawrence, MI) have created a business alliance to provide front-end manufacturing services, including SMT, SMT prototype manufacturing, autoinsertion PCB assembly, through-hole manufacturing, cable and harness fabrication, electromechanical assembly, and total subsystems assembly. Prudential Cleanroom Services (Irvine, CA) has opened a Milpitas, CA, Class 1 cleanroom laundry processing facility. Schurter Group (Lucerne, Switzerland) has acquired Rendar Ltd. (Bognor Regis, West Sussex, UK) from the Advance Group (Witney, Oxfordshire, UK).

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Combined PNC and Virtual Camshaft Machining Give Research Instrument Maker an Edge

Combined PNC and Virtual Camshaft Machining Give Research Instrument Maker an Edge

Reducing machine setup time while attaining cost-effective production, accuracy, and ease of operation were the primary goals of the Hamilton Co. (Reno, NV) when it sought to acquire machining systems to produce high-precision components for its fluid-measuring products. Specifically, the firm was seeking equipment to machine components for its precision pipettes and positive-displacement syringes. The systems that Hamilton selected have paid off with a dramatic reduction in setup time—from 18 hours down to between 2 and 4 hours—and have eliminated the need for secondary part finishing.

Hamilton recently introduced the Softgrip Precision pipette, a liquid-transfer device that requires precise mating of a stainless-steel piston with a spring-loaded shaft, as well as a nearly zero-tolerance fit within a Teflon seal to maintain sampling accuracy and precision.

Hamilton installed three Tornos-Bechler DECO 2000 systems to reduce setup time and increase efficiency.

The syringes are used for accurate liquid dispensing in DNA testing and gas and liquid chromatography, as well as for chemical mixing and adhesive dispensing. The company's syringes require tiny Teflon ferrules to seal removable needles into the stainless-steel housings glued to the syringe bodies. Hamilton engineers specified Teflon for the ferrules because the syringes must be inert to the constituents drawn into them. However, machining the Teflon presents technical challenges because of the abrasive nature of the material and its flexibility.

Acquiring the Machining System

To produce the tiny ferrules and accurate pistons, Hamilton purchased three Tornos-Bechler (Tornos Technologies U.S. Corp., Brookfield, CT) DECO 2000 single-spindle Swiss automatic systems. The DECO systems run at cycle times that rival camshaft-driven machines, producing exceedingly close tolerances on the steel parts and eliminating hours of Teflon deburring. "We took a bit of a risk in buying the first Tornos DECO 2000s in this country in 1996," says Randy Barron, a manufacturing engineer for Hamilton. "New cutting tools and workpiece materials for higher and higher rpm are in constant development, but we knew the DECOs operated up to 16,000 rpm. We were certain the system had a platform robust enough in terms of rpm to take almost any new tooling and material. That's particularly important since we try to retain machine tools for their useful life."

Taking Advantage of System Features

The Hamilton manufacturing engineers adjusted to programming the DECOs using Tornos's proprietary TB-DECO software, which runs in Windows 95 on any 486 DX2/66 or faster PC. Some programming is done on a DECO-dedicated PC on the manufacturing floor, but to save time, Barron and the NC programmer sometimes program the systems from their office PCs while the equipment is running.

Barron says that the Hamilton staff has become very comfortable with the program's user-friendly design. "They can make changes much more quickly on the PC. They know exactly which tables to change. They can just click an icon in the program instead of searching through all the program lines," Barron says.

The NC program created on a PC is transferred directly to the DECO controls. Using an RS-232 link, programmers can run a direct transfer from the programming office to the system, notes Tom Dierks, president of Tornos. Users can also obtain a step-by-step, interactive programming course on a CD-ROM from Tornos to learn how to use all the system's features.

To attain the high productivity of camshaft-controlled automatic systems, the program calculates axis paths and stores them on tables, creating "virtual cams" synchronized by the internal time clock—the "virtual camshaft." The measuring unit of the virtual camshaft is milliseconds and not degrees, replacing the usual 360° angular limits of actual camshafts with nearly infinite units within the program's calculations.

A stainless-steel pipette piston emerges from the oil bath of the DECO 2000.

Because the program controls each table independently, enabling parallel processing, Tornos refers to the technology as parallel numerical control (PNC). The ability to direct simultaneous operations for each DECO's spindles and nine axes also gives Hamilton an edge over camshaft machines for producing a number of small precision parts.

Attaining Accuracy

When the first DECO unit arrived, Barron employed it to produce Teflon ferrules, which Hamilton manufactures in annual volumes exceeding 100,000 pieces. Barron chose to use 0.25-in. PTFE Teflon bar stock to run the 0.125-in.-diam ferrules to prevent the soft material from bunching up in the bar feeder "like a rope being pushed," as he describes it. The DECO program first faces the front of the stock, then center-drills it before drilling the 0.0068-in. shaft hole with the end-working attachment.

"The DECO system's small-tool capability allowed the use of a tiny drill with a shank of only 0.009 in.," Barron says. "Because the tooling is so close to the spindle, it's suitable for running our small parts." When producing other ferrules for the same syringe family, Barron needs only to change the diameter of the drill and modify two or three lines of the NC code specific to that operation.

Although Teflon is soft, it wears tools almost like stainless steel does, Barron notes. For this reason, the system's automatic tool corrector feature is a distinct advantage for Hamilton. Operators can adjust the tool correctors from the control panel while the machine is running. In addition, with this electronic control, operators can manually run the program forward or backward with a virtual handwheel function.

Currently the DECOs deliver two ferrules per minute. Barron anticipates that by changing the program and bar-feed tube, Hamilton engineers can use a higher rpm, thereby increasing surface speeds and ultimately increasing productivity.

By acquiring the DECO systems, Hamilton realized additional efficiencies. Each system's counter spindle is programmed to pick off each part and drop it into a finished-part bin, rather than "our having to pick through a rat's nest of chips to retrieve the parts," Barron says. This feature saved the company about 44 hours of deburring time on the initial run of 6000 ferrules.

In addition to machining the Teflon ferrules, Hamilton also employs the DECO systems to produce stainless-steel pipette pistons. The pipette relies on the 0.0005-in. tolerance of the piston, and its exact relationship to the lead of the threaded shaft, for proper performance. The 1.8-in.-long part is machined to a 0.375-in. diam plus 0.002–0.004 in. of excess material for a subsequent centerless-grinding operation.

Once the stock is faced and the OD turned, the workpiece is center-drilled, shaft-drilled, and rough ID-tapered with a form tool. The final 5°, 56-minute taper is generated with a very small boring bar, which is also used for the fine surface-finish requirement. Then a 2-56UNC-2B thread is tapped at the bottom of the taper. All features are on a common centerline, so there is minimal runout. The part's current cycle time is about 90 seconds for a run of 4200 parts.

The pipette is part of a family of products for which "we're only changing the PNC program from setup to setup, and perhaps modifying bar-stock sizes. All of the tooling is the same, so setups require about 2 hours for the family of parts, including first-article QC signoff, which is about 4 to 6 hours for a unique or new part," Barron says.

Because product performance, accuracy, and production capabilities are vital to the Hamilton Co., investment in the DECO 2000s was made only after considerable research. Since the purchase, Hamilton's manufacture of small parts has taken a big step forward. How much further the company will take Tornos Technologies' PNC programming remains to be seen, but as with the virtual camshafts, the variations appear to be limitless.

MPMN is actively seeking success stories like this. If your company has one to tell, please contact managing editor Karim Marouf at 11444 W. Olympic Blvd., Ste. 900, Los Angeles, CA 90064, phone: 310/445-4200, fax: 310/445-4299, or E-mail

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Streamlining Innovation : Thinking in 3-D

Streamlining Innovation

At Interpore Cross International, a new software package was instrumental in helping engineers create an expandable spinal implant.

By Mark E. Apgar, Project Engineer, Interpore Cross International, Dublin, OH

Interpore Cross International had been designing spinal implants for years when it was presented with a new challenge: designing an expandable spinal implant. A neurosurgeon with a patent for a cage-type device had approached the corporation about developing his design. After careful consideration, Cross decided to accept the challenge and, in order to meet it, employed a variety of software programs to optimize the device's development.

The Challenge

Surgeons may opt to use an expandable spinal implant when performing certain types of spinal fusions. When spinal disks collapse, they can press on nerves, resulting in pain and loss of nerve signal to the limbs. In a spinal fusion procedure, a surgeon moves the vertebral bodies apart to relieve pressure on the nerves, then places bone graft material in the disk spaces between the vertebrae. An expandable vertebral device is used in place of a strut graft to hold the vertebral bodies apart and stabilize the spine while the bone graft placed inside the device takes hold, a process that usually takes several months.

The difference between an expandable vertebral device and a standard spinal cage is that after the expandable device is installed (in a compressed position) it can be lengthened to move vertebral bodies apart. The device is then locked in the expanded position. One of the challenges Cross faced in designing an expandable device was devising a locking mechanism that would hold securely. The device needed to be able to resist the dynamic loads placed on it—that is, be strong enough to support the weight of a person's head when used for treating cervical (neck) tumors.

Using the neurosurgeon's sketches, Cross created a solid model with Solid Modeling from Unigraphics Solutions Inc. (St. Louis). When the model was ready, Cross invited the surgeon to its offices. Under the surgeon's supervision, the engineers went through five different iterations of the design on the computer. Because Cross had parameterized the model, it was easy to make changes in response to the surgeon's suggestions. For example, when the surgeon wanted to change the angle of a flange to better meet the angle of a vertebral body, engineers simply changed a number and regenerated a model with the new flange angle. The surgeon was impressed with the speed at which Cross was able to incorporate his suggestions. Prior to this, he had worked out bugs by building and evaluating prototypes, which often took months to create.

How Did They Do It?

A spinal implant system consists of bone screws, hooks that attach to the vertebra, lateral connectors, and rods, as well as the tools needed to install these components. To be effective, a spinal implant must be strong, small, and easy to install. These were the guiding factors in the design of Cross's original Synergy spinal implant system, which has been on the market since 1995. For that design, Cross used an earlier generation of 2-D computer-aided design (CAD) technology to create drawings.

Engineers at Interpore Cross used Unigraphics CAD/CAM software to redesign the threads of a spinal implant screw. The software allowed design engineers to easily vary the model's parameters and run an analysis on the updated models until they found a thread design that met their requirements.

Although the 2-D CAD allowed Cross to create drawings quickly and to revise them easily, its effectiveness was limited. This is because Cross also used a finite-element analysis (FEA) program, Nastran, from MacNeal Schwendler Corp. (MSC), to simulate the performance of implant components. Nastran requires the use of a 3-D computer model to replicate real-world conditions. Working from the 2-D drawings, the Cross analyst had to recreate designs in 3-D in Nastran, a process that could take weeks and that limited the use of FEA. Despite its limitations, the system helped Cross fine-tune several components of the first implant system. It demonstrated the effect on stiffness and strength of changing bone screw variables such as pitch, ratio between major and minor diameter, and minor diameter taper. Using FEA as a guide, Cross created a new screw design in which the first five threads below the screw head are tapered for optimal performance.

Although these insights were valuable and helped Cross create a better product, the design of the original implant required a great deal of prototype testing. Here, too, someone had to work from the 2-D drawings—in this case, to program a CNC machine for cutting the metal prototype parts. Each prototype took 2 to 8 weeks to make.

Because Cross wished to reduce reliance on metal prototypes and allow greater use of FEA, the engineers decided to move from 2-D CAD to solid modeling. The benefits would be twofold: solid models could be transferred to Nastran, sparing the analyst the task of recreating designs for FEA, and it would allow Cross to replace metal prototypes with rapid prototyping techniques such as stereolithography. Cross also wanted parametric modeling capabilities, which would allow them to vary designs by plugging in new values for design variables. Because Cross creates a large number of screws, finding a program to simplify this task was a high priority. In a program such as 2-D CAD, laying out the threads was tedious and time-consuming. Cross wanted something more efficient and wanted the ability to export files directly into Nastran.

Cross found that Unigraphics' Solid Modeling met these requirements. The program's law curve capability proved to be an efficient way of modeling screws. Creating a path that a helix follows, a designer can simply attach the helix to a sketch of a screw thread, and the program removes the thread pattern from the solid mass of the screw. In addition, because MSC is a Unigraphics Solutions Alliance Program member, the company's products have a tight integration that allows solid models created in Unigraphics to be transferred to Nastran without data translation for the finite-element mesh.

Taking a Test Drive

The "test drive" of the new system was not as beneficial as it could have been because Cross did not have the new software from the very start of the project. The plan was to convert the corporation's original implant system from stainless steel into titanium. The engineers hoped they would be able to convert their original implant design to titanium without much reengineering; the fact that titanium is twice as flexible as stainless steel, however, complicated the matter. Because the engineering team did not have a solid modeler initially, they were required to do extensive prototype testing to investigate how the titanium threads that are inserted into bone would perform under physiological loading. This is when engineers decided to use the Unigraphics software to look for a solution.

The first step was to create the original screw design as a Unigraphics' solid model. Cross created a sketch, constrained parametrically, so that modifications would be easy to make later. Some of the parameterized values included major diameter, minor diameter, and pitch. The law curve function helped speed the process.

Next, Cross exported the solid model to Nastran to simulate the loads the screw would be subjected to inside a patient. Nastran results allowed engineeres to compare the performance of different thread designs. After analyzing one design in Nastran, Cross went back to Unigraphics to change the screw model by varying one or more of the model's parameters. Engineers then ran the analysis with the updated model, repeating the process until they had found a thread design that met their requirements.

New Product, New Process

Using the new software on the titanium conversion helped the engineering team complete the transition sooner than it normally could have. By allowing Cross to use FEA to solve the problems caused by the more flexible material, the software reduced the time-consuming prototyping process. Following this experience, it was clear to the engineers that solid modeling had a lot to offer, and that they had tapped only a fraction of its potential.

Designing the expandable vertebral cage would enable the engineers to use the full range of the software's capabilities. On this project, developed entirely in the new system, Cross also made good use of the ability to turn solid models into rapid prototypes. Cross used a stereolithography (STL) process provided by an outside service. When Cross wanted an evaluation part, the engineers simply converted a Unigraphics model to STL format (the conversion routine is included as part of Unigraphics), which is then read by the stereolithography machine. Cross would send an STL file to the service bureau via modem and in 1 or 2 days would receive a part. This was especially helpful when dealing with the surgeon, who liked to have solid model parts to examine.

As in other projects, Cross used Nastran to evaluate stresses on the various parts of the new device, which enabled design engineers to work out problems while the device was still in software, meaning fewer prototypes were needed. Although the engineers still had to build prototypes for final testing, by the time they built them, they were confident the prototypes would work.

Cross estimates use of the software saved more than $100,000 in prototyping and testing costs and reduced development time on this project by a year. Purchasing the new equipment (software and computers) cost $250,000, but Cross estimates it paid for itself after just two projects, including the expandable spinal implant.

Thinking in 3-D

New software packages are giving designers a more complete picture of their creations on screen, reducing the need for costly prototypes.

By Sally Lane, MPMN Senior Editor

Parametric Technology Corp. Delivers Enhanced Usability

Continued user-interface improvements and automation tools are some of the Pro/ENGINEER development projects currently under way to combine usability and interoperability within the design environment. "The large focus on productivity through the user-interface improvements for Pro/ENGINEER Release 20 will continue to be enhanced as we move forward," says Laurie Stefanov, technical marketing director, Parametric Technology Corp. (PTC; Waltham, MA). Future development plans for Pro/ENGINEER will introduce enhanced usability for the engineering environment in conjunction with a Microsoft Windows—compliant user interface.

Insight Product Development used Pro/ENGINEER product development software to create its EyeSys Vista handheld corneal topographer. The software enabled Insight to assemble the laser, optics, digital camera, and LCD into a compact handheld unit.

PTC will soon be introducing NC-EXPERT, which expands the usability of the programming tools of Pro/NC by focusing the functionality on the production machining of prismatic parts. NC-EXPERT allows numerical control programmers and process planners to take existing Pro/ENGINEER solid models and define them in terms of manufacturing features, such as "faces" and "pockets." Once the features have been defined and the process order specified, customized tool paths are easily applied.

Another recent enhancement from PTC is the associative topology bus (ATB), which allows users in the continuum of PTC Solutions to access, share, and modify design information dynamically and concurrently. "Our customers work with different tools in the design environment, and we are trying to promote interoperability in this environment," Stefanov says. "For example, parts created in Pro/ENGINEER can now be associativity leveraged within Pro/DESKTOP, enabling users to optimize their work environment while maintaining time and effort invested in other systems." The ATB goes beyond standard data interchange by automatically updating the geometry, topology, and assembly structure in models created in other applications. The ATB will eventually facilitate associativity among other product design and development software, Stefanov says.

SolidWorks 98Plus Promises Speedy Access to Assemblies

The newest 3-D mechanical design software release from SolidWorks Corp. (Concord, MA) boasts more than 200 customer-driven enhancements, including user-interface improvements, detailing, assembly design, surfacing, and sheet-metal design capabilities.

SolidWorks 98Plus's detailing tools make it easy to generate complete production-level engineering drawings that comply with major international standards. Users can create fully associative drawings—the model, drawing view, and assembly update automatically when modifications are made. The assembly design allows users to refer to the surrounding geometry, associating all of the relationships directly and propagating changes automatically throughout the design, eliminating the need to export parameters or build equations. A "lightweight" components capability allows users to open large assemblies up to 300% faster without loading any unnecessary data.

The part-modeling feature enhances design flexibility and includes drag-and-drop capabilities, while the sheet-metal design capabilities allow designers to create in 3-D or "in the flat."

"We are particularly excited about the new assembly features, including the ability to easily manage the entire assembly process with the enhanced configuration manager and the new lightweight components feature, which will reduce design time," says Paul McDonnell, a mechanical CAD coordinator for Automation Tooling Systems Inc. (Cambridge, ON, Canada).

Instant Communication the Goal of OneSpace

The ability to simultaneously communicate with customers, suppliers, and internal divisions is the key to developing sophisticated products vital to any company's success. Until recently, however, having real-time access to all of these groups was not possible.

Now geographical distance needn't be a barrier to the creative process. CoCreate Software Inc. (Fort Collins, CO) has introduced OneSpace, a Web-enabled product development program that allows all members of a mechanical design team to interact in real time so they can share information and simultaneously work on and modify a model in electronic space. OneSpace, which targets the emerging virtual product development management (VPDM) market, functions on top of most 3-D computer-aided design (CAD) environments so users do not have to invest in new CAD technology to reap the benefits.

OneSpace's Java-based user interface provides many intuitive features including drag-and-drop context-sensitive menus and a structured browser. Users have access to different data sources, such as the local file system, during the real-time session. Image courtesy of RKS Design.

"The VPDM market is going to experience rapid growth during the next five years as manufacturers look for ways to leverage their intellectual capital in real time, instead of simply capturing design intent," says Dave Burdick, vice president of Gartner Group, a Stamford, CT–based market research firm.

By giving companies the capability to bring together the right people at the right time, OneSpace allows for immediate problem solving, helping minimize delays.

"With OneSpace, companies can make innovation a part of their culture by encouraging people from different disciplines to explore ideas together," says Tilman F. Schad, CoCreate's president and CEO.

Structural Research & Analysis to Debut Three New Packages

COSMOS/Works, a design-analysis program first introduced in 1997 that is tightly integrated with SolidWorks CAD, is getting a new twist. An updated version, COSMOS/Works 5.0, is due out this March from Structural Research & Analysis (Los Angeles). The updated version's capabilities will include gap/contact-in-assembly analysis, design optimization, new sparse matrix direct solver, optional UAI/NASTRAN linear static solver, transfer of motion loads from Dynamic Designer/Motion and Working Model 3D, and transitional meshing with mesh controls.

Cosmos/Edge 3.0 features a Windows-native multiple-document environment, allowing designers to tile the screen and run several analyses simultaneously.

COSMOS/DesignSTAR, a new architecture that features a native Windows interface powered by the Parasolid modeling kernel from Unigraphics Solutions, is due to hit the market in February. It incorporates Spatial Technology's ACIS modeling kernel and an ACIS-to-Parasolid translator. In addition, it is compliant with object linking and embedding (OLE) for design and modeling programs, allowing associativity and enabling the designer to drag models from any compliant design program and drop them into COSMOS/DesignSTAR. The software has its own applications program interface, which will make it easy for third-party analysis developers, value-added resellers, and other users to add their own capabilities. It also allows designers to tile the screen and perform several analyses simultaneously.

Due for release in January, COSMOS/Edge 3.0, based on the COSMOS/DesignSTAR architecture, is an associative design-analysis program for the Solid Edge CAD program. It allows for the analysis of assemblies as well as individual parts, real-time visualization of results, and the use of drag-and-drop techniques to select objects for analysis. The software also includes a Design Check Wizard to help users ensure a design meets all yield-strength criteria, and is capable of automatically preparing Web-enabled design reports in text and HTML with embedded virtual reality modeling language (VRML) and AVI visualization tools.

Autodesk Unites 2- and 3-D Design

At Baxter International's Fenwal Div., Autodesk has proven to be a real lifesaver—the software is helping designers to more quickly and efficiently develop specialized medical devices such as flexible and disposable blood-collection containers.

"We need to refine our designs quickly and then move the devices on for clinical trials," says Tony Poventud, an engineer technician in the technical services group. "Autodesk software helps us answer this urgent call to save lives around the world."

Release 14 Mechanical Desktop from Autodesk (San Rafael, CA) combines the 2-D capabilities of AutoCAD with advanced 3-D tools, including parametric feature-based solid modeling, nonuniform rational B-spline (NURBS) surface modeling, and assembly modeling. Component and assembly models are fully associative, and automatic interference checking can help pinpoint design errors. In particular, Autodesk allows Baxter's engineers to design parts to tolerances within 0.0001 in., Poventud notes. The software also makes it easier to share external files, while an MTEXT editor allows designers to annotate drawings and edit text easily, Poventud says. Mechanical Desktop's native AutoCAD compatibility also enables designers to easily create 3-D designs from existing 2-D data. Other features include a mechanical applications initiative that allows for finite-element analysis, sheet-metal design, NC programming, and analysis of kinematics, tolerance, and plastic flow, allowing designers to take their product from concept through production without ever leaving their desktop PC.

Something for Everyone: CATIA Version 5

CATIA Version 5, a reengineered, next-generation, computer-aided design, manufacturing, and engineering program for both native Microsoft Windows NT and UNIX platforms, is the latest offering from Dassault Systémes S.A. (Suresnes, France) and marketed worldwide by IBM. The unique feature of CATIA 5 is its ability to be adapted to any level of design complexity and CAD/CAM experience. Occasional users with limited training can easily operate the Windows interface, while more experienced users can access its more advanced, process-based applications. CATIA Version 5 was designed to deliver intuitive part and assembly modeling. Generative drafting automatically creates associative drawings from 3-D mechanical designs and assemblies, while the real-time rendering applications produce photorealistic images by using technological material textures. The Knowledge Advisor feature assists designers in reaching informed decisions quickly.

CATIA Version 5 finite-element analysis tools allow designers to quickly conduct stress vibration analysis on part designs early in the process.

CATIA Version 5 also provides easy-to-use designer-oriented part stress and modal analysis for early part prevalidation. Advance Smart Shape Designer tools allow designers to quickly create innovative, free-form shape design deformation. Advanced functions extend the shape- and surface-modeling functions to morphing complex multisurface shapes. "The thing to remember is that CATIA can benefit designers and manufacturers of everything from simple disposables to prosthetic devices," says Patrick Kieffer, who handles marketing communications at IBM Engineering Solutions.

Software Focus is a new feature. If you are interested in having your product appear in an upcoming issue, please contact MPMN's editors by fax, 310/392-4920 or e-mail,

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Rapid Prototyping

Rapid Prototyping

Rapid prototyping for electronics

Minimizing time to market and improving design cycles are imperative for success in today's competitive market. Many electronic contract manufacturers, however, are using the same processes that they have always used. A company has sought to address this problem by defining its rapid prototyping process as a continuous one that begins with the fabrication of the raw board and ends with the placement of the components. It designed a facility around this concept and then installed the hardware and software systems to make it work. The company even developed a patented infrared job-tracking system to instill a first-up mentality in every department and to continuously monitor the progress of an order through all process operations. The assembled boards are delivered 3 days from receipt of CAD data and are made to production standards. Diversified Systems Inc., 3939 W. 56th St., Indianapolis, IN 46254.

Plastic parts

Prototypes or limited production runs of plastic injection-molded parts can be provided in less than 3 weeks. The company also provides rubber molds, polyurethane duplicates, metal castings, and patterns for investment casting, sand casting, and vacuum molding. 3D-Cam Inc., 9139 Lurline Ave., Chatsworth, CA 91311.

Prototyping services

Located in Neenah, WI, and Milpitas, CA, two ProtoCenters provide full turnkey and consigned-material assembly services and are supported by dedicated materials teams and prototype-testing capabilities. The facilities provide Plus Services, addressing customers' staffing, training, tools, time-to-market, and technology needs. Manufacturability assessments, automated testing services as a part of prototyping, comprehensive printed circuit design services, and complete production realization services are also provided. Plexus Corp., 55 Jewelers Park Dr., Neenah, WI 54957- 0156.

Precision prototyping

Accurate prototype tooling can be used later for high-volume production runs. The company offering this rapid prototyping service is equipped with computerized 3-D and CAD/CAM software, coupled with numerically controlled metal-fabrication processes. It can produce precision tooling using multiaxis CNC mills, CNC lathes, and EDM capabilities. A full range of measuring equipment, including coordinate-measuring machinery that features digitizing capabilities, aids in the development of the prototype tooling. Specialty Silicone Fabricators Inc., 3077 Rollie Gates Rd., Paso Robles, CA 93446.

Sheet-metal prototypes

With the use of CAD/CAM and water-jet cutting technology, a company can quickly produce sheet-metal prototypes. Bending can be done after the flat blank is cut, and no heat is introduced to the material edges. The thickness of metallic and nonmetallic materials worked ranges from 0.010 to 4.0 in. Forming the part to the final shape, spot welding, and plating or painting are also performed. Crenshaw Die & Mfg., 1959 N. Main St., Orange, CA 92865.

Rapid prototyping technologies

Specific rapid prototyping requirements may be matched to the potential advantages of more than 20 different technologies. These include CNC machining of prehardened steel, aluminum, and plastic; injection molding; cast urethane; nonmachined bridge tooling; composition epoxy; spray metal; rubber molds; stereolithography; powder metal; silicon vapor conversion; and sand, die, investment, plaster-mold, MCP vacuum, and resin casting. Brookfield Rapid Solutions, 13 Hampshire Dr., Hudson, NH 03051.


A vacuum and pressure former now offers rapid prototyping. Its vacuum casting process produces exact and complicated prototype components in plastic materials. Prototype molds can be produced in less than a day. Close tolerances, thin-wall parts, good surface aesthetics, and part-to-part consistency are possible. A wide range of casting resins are available to suit most applications. Cardinal Products Inc., 2840 Croddy Way, Santa Ana, CA 92704.

Prototype parts

A company's rapid prototyping parts can be used for testing, creating automation systems, establishing assembly lines, building fixtures and gauges, conducting focus group studies, and establishing accurate production tooling and part estimates. The parts are made from specification materials—including medical-grade plastics—and can be finished in just days. Using the prototype parts to identify design, moldability, and assembly issues prior to making production tools can save both time and money. Phillips Plastics Corp., Technical Center, N4660 1165th St., Prescott, WI 54021.

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Outcomes Research: Documenting the Value of a Medical Device

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

An MD&DI January 1999 Column


Evidence gathered from outcomes research conducted from the beginning of product development can help convince purchasers and end-users of a device's economic value, regardless of its cost, and give manufacturers a competitive edge.

In the increasingly competitive struggle for healthcare dollars, the market for new medical technologies is more austere, more demanding, and more scrutinized than in the past. Buyers and end-users want to know what value a new technology provides, what advantages it offers compared to what has been available, how much it costs, and what coverage of this device will do to a budget.

Medical device manufacturers should start anticipating these questions and determine the value of their products during the planning stages to help smooth the way for product development, marketing, and acceptance.

Figure 1. Treatment functions assessed in cost-benefit and cost-effectiveness analysis (CBA/CEA) studies during the past 18 years, broken into four medical-related interventions.

In the past decade, the pharmaceutical industry has grappled with many of the issues that currently face medical device manufacturers (Figure 1). Research-oriented drug companies have dominated the effort to establish the value of their products. This effort has been so potent that a new discipline—pharmacoeconomics—has developed, as exemplified by the founding of the journal Pharmacoeconomics and of the International Society of Pharmacoeconomics and Outcomes Research. Both the journal and the society are dedicated to assessing the health, economic, and quality-of-life outcomes associated with use of drugs. Outcomes is defined as the impact of the intervention beyond safety and efficacy —for example, effectiveness, health status, satisfaction, quality of life, and cost. (Efficacy is how well an intervention achieves measured improvements in clinical outcomes under the highly controlled setting of a clinical study, and effectiveness is how well the intervention works under routine clinical conditions.)

The drug industry also lobbied Congress for section 114 of the FDA Modernization Act, which requires FDA to relax promotional regulatory standards concerning healthcare economic information for decision makers. The device industry can learn from this process and build on it to customize outcomes research for its own particular circumstances.


Defining the Customers. In the past, the physician or surgeon was the individual making the decisions about purchasing and using a therapeutic medical device. A hospital purchasing manager then negotiated price, and third-party insurers paid what was billed. Today, physicians and surgeons are still important end-users, and purchasing agents still negotiate costs, but they have much less influence on the purchasing decisions and must yield to entities such as technology assessment committees (TACs). In addition, the customer base includes patients, the federal government, the courts, and even public opinion.

What Are the Customers Seeking? Physicians and patients primarily seek effective therapies and good outcomes and can be frustrated by lack of access to new technologies they consider potentially valuable. They need evidence of cost-effectiveness to support their advocacy for access to and use of technologies and services. Similarly, the courts are interested in ensuring them fair access to beneficial technologies.

FDA requires evidence to support claims. In order to promote a technology as being safe and effective, a manufacturer must have evidence of that. Similarly, FDA requires scientific evidence to back up a claim of a technology's cost-effectiveness, which is defined as providing more value for the money spent when compared with the most reasonable alternative. The term is usually expressed as cost divided by good outcome, such as cost per year of life saved, cost per case detected, or cost per case cured. The term cost-effective is often confused with cost-saving, which means that a technology saves money. A cost-effective technology may actually cost more, but the improvement in outcomes is judged to be worth the extra cost.

Institutional decision makers seek to control expenditures while keeping their physicians, patients, and beneficiaries satisfied. They want—or at least should want—good value for their money, but they seldom generate their own information concerning value.

How Can Customers Improve the Situation? Healthcare customers are becoming more informed about the value of medical technologies. Managed-care organizations, indemnity insurers, and other institutional providers are establishing TACs or are subscribing to technology assessment services (Table I).

Health Care Financing Administration's Technology Advisory
Medicare is a critical customer for the device industry. Thus, HCFA consults its TAC, which it treats as an internal advisory committee, and does not require input from outside parties such as physicians or manufacturers.
Blue Cross/Blue Shield Technology Evaluation Comm (TEC)
This committee began TAs for internal use, but now offers reports through a subscription service.
A "clinical and coverage policy" unit performs TAs on procedures and devices for coverage policy decisions.
ECRI Health Technology Assessment Information Service
Performs TAs and provides reports through a subscription service.
Group Health Cooperative of Puget Sound
The committee on medically emerging technologies conducts TAs using cost as a primary end point, although costs do not dominate other outcomes. Published information is primary data source.
Harvard Pilgrim Health Plan
The committee for appropriate technology reviews technologies based on published literature, taking safety, efficacy, effectiveness, and cost-effectiveness into consideration. Uses outside data sources ECRI, Technology Management Information Exchange (TEMINIX).
Provides managed-care organizations with rapid-turnaround TAs based on published literature—Hayes Directory of New Technologies' Status and Hayes Directory of Legal Precedence Reports—which are periodically updated.
Institute for Clinical Systems Integration
Funded by medical groups and HMOs to research coverage decisions from other organizations to obtain the most balanced, unbiased reports. Develops guidelines based on TAs.
Kaiser Permanente of Northern California
Relies on TAs from outside organizations (ECRI, Blue Cross/Blue Shield Technology Evaluation Committee) but conducts them when none are available.
The HMO Group members founded TEMINIX as a service to its customers. The group conducts TAs based on literature reviews.
United Healthcare
Conducts literature review of devices and procedures to assess safety, efficacy, and outcomes. TA document is used in coverage policy statements.

Table I. A listing of selected organizations that conduct, use, or offer subscription services that include technology assessments (TAs).

The hallmark of the organizations listed in Table I is their use of evidence-based decision making. The evidence-based decision-making process requires systematically gathering and analyzing scientifically valid evidence of the efficacy of a new product or procedure. This evidence comes primarily from published literature, although review committees will include information from other sources. Available evidence usually includes cost of the device and clinical evidence of its effect, but relatively little information on concomitant procedures and virtually no information on cost offsets.


Until recently, the device industry has responded to the radical changes in the healthcare environment and to purchasers' demands mainly by negotiating discounts with insurers and providers. However, this process of discounting tends to focus on price rather than value, and places manufacturers at enormous disadvantage.

To level the negotiating playing field, manufacturers need to examine the relative value of a device and its cost offsets. For example, would use of an intervention reduce other healthcare costs, decrease the length of hospitalization, or limit the number of tests and procedures, perhaps eliminating some completely? Most effective therapeutic medical technologies offer these or other cost offsets.

Directly attributable costs are only half of the equation. It is important to consider how a device or treatment protocol compares with other available alternatives. A device that costs more than its competitors will still be a better value if it results in higher detection rates, thus allowing the condition to be better controlled or increasing survival rates. Other value factors to consider include the number and severity of side effects, and if use of the device allows patients to return to normal functioning earlier or otherwise improves their physical, mental, or social well-being.

Without these kinds of information, decision makers focus on price rather than value, and decisions about use and coverage are often made with incomplete knowledge of the facts, which can be detrimental to patients, physicians, and manufacturers.

For their part, manufacturers are responding to the increasing power of TACs by investing in health and economic outcomes assessment studies to gather evidence of product benefits. Manufacturers will thus have at their disposal during negotiations not only price information but also data on cost offsets and health benefits, including improvements in quality of life.


The value equation is a key tool in determining evidence of value. This equation shows how much it costs to achieve a particular outcome. The equation numerator comprises costs, and the denominator comprises effectiveness or the impact on health (Figure 2).

Figure 2. The value equation used to determine the economic and health consequences of a specific health intervention.

The Intervention. The first and most critical input into the value equation is the intervention, or the technology under study. The most critical question being addressed about the technology is how well it works. Acquiring firm evidence of a product's effectiveness is the first step in conducting an outcomes study.

The Numerator. The numerator of the value equation measures costs or the changes in dollar values of the following variety of resources.

  • Healthcare resources. Examples of these resources include hospitalization; physician visits; emergency room visits; use of drugs; use of other devices, tests, and laboratories; procedures; rehabilitation; long-term care; and home healthcare.
  • Nonhealthcare resources. Special education, costs to modify the home because of disability or other limitations, travel time, and day-care costs for children while parents seek medical care are included in this category.
  • Informal caregiver time.
  • Patient time for seeking care and undergoing treatment. This item and the following one are assigned monetary values that reflect the next best use of the person's time.

Note that the numerator of the equation does not include only healthcare resources. Some outcomes studies consider only healthcare resource costs dictated by the perspective of the analysis and the client for whom the study was conducted. Healthcare insurers or managed-care organizations might only concern themselves with those costs relevant to health-care services. The government might consider healthcare costs as well as nonhealthcare resources for which it would be responsible. Studies examining the benefit to society should consider all cost components.

The Denominator. The denominator of a value equation measures effectiveness or the impact of the technology on health status. One way of measuring health-status changes is to examine their intrinsic value. Some of these can be disease-specific, such as cardiovascular events avoided. Others are technology-specific, such as improved images. Still others are generic, such as number of lives or years saved or quality-adjusted life-years saved.

Another way of measuring health status changes is to examine the impact of health on production output. Reductions in illness or averted mortality can be translated into productivity gains—these individuals will continue to contribute to society and that contribution is most often measured in terms of production output, or wages.


Cost analysis: Economic evaluation that focuses on the costs of the intervention and does not consider health outcomes.

Cost-benefit analysis (CBA): Economic analysis in which both the inputs to produce the intervention (or costs) and its consequences or benefits are expressed in monetary terms of net savings or a benefit-cost ratio. A positive net savings or a benefit-cost ratio greater than 1 indicates that the intervention saves money.

Cost-effectiveness analysis (CEA): Economic analysis in which the consequences or effects of the intervention are expressed in natural units such as years of life saved, lives saved, cases detected, cases successfully treated, or some other improvement in health specific to the intervention.

Cost-effectiveness (CE) ratio: The results of CEA are expressed as the cost per health outcome (for example, cost per year of life saved):

CostIntervention A — CostIntervention B


EffectivenessIntervention A — EffectivenessIntervention B

Cost-of-illness study (COI): An analysis that computes the total costs incurred by society as a consequence of a specified health-care problem, typically including both the direct and the indirect costs—such as medical costs and lost productivity—associated with an illness. There is no comparison of treatment alternatives.

Cost-minimization analysis (CMA): When two alternatives have been shown to have equivalent clinical effectiveness, only their costs need to be compared to identify the most economically desirable alternative.

Cost-utility analysis (CUA): Economic analysis in which the consequences are expressed as the utility or quality of the health outcome. CUA results are generally expressed as cost per quality-adjusted life year (QALY) gained, recognizing that all life years are not equivalent and taking into account pain, discomfort, and other factors.

Quality of life (QOL): The social, physical, emotional, psychological, and general well-being of individuals, typically measured using standardized questionnaires or interviews, such as the Medical Outcomes Study (MOS) SF-36 or EuroQOL (EQ-5D). When assessed in the context of health and medicine, QOL is termed health-related quality of life (HRQL).

Technology assessment: An evaluation of the impact of a technology or intervention on a broad array of costs and consequences, including some that may not be quantifiable. The purpose is to identify hidden costs and outcomes that, if known, might change resource allocation or purchasing decisions.


When a device is as effective as its most likely alternative, it is only necessary to examine costs. The following situations illustrate the importance of studying cost offsets for a device undergoing outcomes assessment and of comparing results with those for alternative products.

  • If the device in question has lower acquisition and use costs than its alternative, an excellent argument exists for replacing the alternative, as long as there are no cost offsets in the latter's favor.
  • If the device has higher or equivalent acquisition costs but would result in a reduction in total medical costs, there is an excellent argument for replacing the alternative. However, this argument will be persuasive only if the decision maker involved is concerned with a global health-care budget, as opposed to a narrow budget such as an institution's capital expenditures budget.
  • Some devices may have higher or equivalent acquisition costs, offer no reduction in other healthcare costs, but have a beneficial effect on nonhealthcare resources or patient time. In such a case, use of a device may still be supported from certain perspectives, such as that of an employer who is concerned about lost productivity or a patient facing significant out-of-pocket expenses with use of the traditional treatment.


Not all products require a strategic outcomes research program. Outcomes research should be targeted at those devices that are expected to provide a significant therapeutic impact or that will result in changes in resource use. New devices that incorporate only minor or incremental changes compared with previous generations or competitors generally do not warrant an outcomes research program. The one exception is if a competitor's product has not established itself as a cost-effective choice, and outcomes research could potentially provide evidence that the new device is cost-effective.

Diagnostic technologies are a special challenge, since by definition they provide information that will be used to determine subsequent treatment choices. As such, they are one step removed from the treatment intervention and two steps removed from the final outcome. If there is reason to believe that the information provided by a diagnostic technology is likely to contribute to measurable differences in treatment, economic, or quality-of-life consequences, then it is a candidate for outcomes research.

Figure 3. Strategic product development for market acceptance shows the progression of the regulatory, product development, and outcomes research tracks.

Outcomes research should be introduced as early as possible, and product developers should conceive, design, and test devices with the value equation in mind. Outcomes research will help to ensure that only cost-effective products will be developed, that they will be marketed with emphasis on their perceived value, that coverage decisions will be made more quickly with higher reimbursement levels, and that commercial success is maximized. Outcomes research and health economics have a role in every stage of product development and can be used to orchestrate a well-coordinated and effective product launch (Figure 3).


Product Design and Early Development. During the product conception phase, outcomes research can help clarify the nature of the condition for which the device is indicated. At this stage, outcomes research can establish baseline practice patterns and costs for the condition based on its epidemiology, expected patterns, and outcomes. It is important to determine whether patients will be treated in hospitals or as outpatients and whether the device can be used only by a physician or by other medical professionals or even patients—perhaps at some cost savings.

At this early phase of the product development cycle, outcomes research can also be used to make go/no-go decisions. Factors to consider include whether the product has a health, economic, or quality-of-life advantage over its alternatives or whether its clinical advantages are significant enough to convince healthcare decision makers to change from established therapies or devices. Such decisions can be especially difficult to influence when significant capital expenditures are involved.

Early Clinical Studies. Outcomes research can be used to develop early models of the disease and of practice patterns, based on current diagnosis and treatment. Such models are built using published literature and the input of clinicians.

Early models can be used to predict the cost drivers—resources that determine the overall costs of treating a condition. These are associated with both relatively high unit costs such as hospitalization, use of ICU versus regular beds, and emergency room visits, and with relatively low-cost resources that are used very frequently, such as physician visits and use of other products or medications.

In addition to cost drivers, early health outcomes research should identify the effects of current treatment and how they are measured. Every study is not necessarily going to examine the same effects but may choose among clinical outcomes, functional status, and quality of life, to name a few. In determining what factors to measure and how, an examination of past studies can reveal potential flaws in study design.

Early models of the disease and its treatment are critical in determining which key health and economic outcomes data need to be collected in later clinical studies. These models also help determine which data are not necessary, thus helping to streamline later studies.

Later Clinical Studies. Collecting outcomes data in a clinical study is one of the most powerful ways of examining the cost-effectiveness of an intervention. Adding an outcomes assessment component often means modifying only slightly the case-report forms or adding a patient questionnaire. The marginal cost of adding an outcomes assessment component can be quite small in proportion to the expense of the entire clinical study.

At this stage, it is also possible to adapt the early models—taking into account the introduction of the new technology—by measuring effectiveness rather than efficacy. Clinical studies tend to assess efficacy rather than effectiveness, but both forms of information are necessary for TACs to make the most informed decisions.

Another reason to study effectiveness is that a device can be expected to affect costs and health outcomes well beyond the short time frame of most clinical studies. By using decision analytic modeling, results from the study can be extrapolated to approximate the long-term effects of the intervention when epidemiological information is available to support the analysis.

Dissemination of Health Outcomes Information. The preparation of a dissemination plan is a critical parallel to the product development track. Information generated during each product development stage can be part of a strategic information dissemination plan. Early models depicting current treatment patterns and costs can lay the foundation for disseminating subsequent work that supports the device's health outcomes benefits.

The questions of how to go public with health outcomes information can be complicated. Many conferences and journals will be restricted to a particular medical specialty; however, managed-care conferences and journals may be an advantageous choice for some presentations and published work.

Product Launch. The collection of information demonstrating the health, economic, and quality-of-life value of a device should be available for dissemination at product launch in the form of articles and clinical reports. Given a TAC's heavy reliance on published literature, it is imperative that high-quality outcomes research reports are available when adoption and coverage decisions are to be made.

The early-stage model can now be adapted for other major audiences pertinent to the device—the customers or payers. The primary model should be conducted from the perspective of the device's most relevant audience, and subsequent analyses can then be conducted to consider other perspectives.


A manufacturer's success in the health-care marketplace will increasingly depend on its being able to provide evidence of the health and cost outcomes associated with a device. The device industry has hesitated to embrace technology assessment and outcomes evaluation, and as a result has limited internal capacity to address the needs and demands of health-care decision makers. Nonetheless, the concepts and methods of technology assessment and outcomes research are well established, and solidly trained economists and health services researchers are available to work with the industry.

Device company personnel often lament that they do not have the financial resources of pharmaceutical manufacturers and that devices should not be held to the same standards as drugs. The market nevertheless demands evidence of value before devices will be accepted at premium prices and adopted to their fullest potential.

Recent events have heralded a more active approach on the part of industry and others to demonstrating the value of healthcare devices. Two recently formed entities epitomize these changes:

  • The Medical Technology Leadership Forum is comprised of leaders from medical device firms, academic and professional organizations, and consumer or patient groups and is working to evaluate coverage policies and to promote the conduct of value assessments of medical technologies. Reports on both these subjects are available upon request (202/661-3584).
  • The task force for technology assessment of medical devices met in Seattle in 1997 and included representatives from device manufacturers, HIMA, academic institutions, managed-care organizations, employers, and the federal government. Its mission was to identify strategies to improve technology assessment of medical devices and to promulgate guidelines for the process. The task force developed a set of guidelines for information exchange between device manufacturers and managed-care organizations and insurers. A special issue of the American Journal of Managed Care will be devoted to papers emanating from the task force's work.

The efforts of these groups signal the beginning of a process to establish guidelines for outcomes research of devices. The device industry can contribute to this process so that outcomes research reflects the unique characteristics, challenges, and opportunities of this sector of the health-care marketplace. Individual firms and their leaders must also rise to the challenge by conducting assessments and providing information to healthcare decision makers. Integrating outcomes research into the product development process will allow device manufacturers to meet marketplace demands, while simultaneously ensuring that their products provide healthcare benefits and enjoy commercial success.


Drummond MF et al., Methods for the Economic Evaluation of Health Care Programmes. 2nd ed. Oxford, England: Oxford University Press, 1997.

Evidence of Value: Building a New Paradigm. Washington, DC: Medical Technology Leadership Forum, March 1998.

Gold MR et al., Cost-Effectiveness in Health and Medicine. New York: Oxford University Press, 1996.

Medicare Coverage: Time for a Public Policy Dialogue. Washington, DC: Medical Technology Leadership Forum, March 1998.

Bryan R. Luce, PhD, is CEO and senior research leader at MEDTAP International (Bethesda, MD). Anne Elixhauser, PhD, is a social science analyst at the Agency for Health Care Policy and Research (AHCPR), U.S. Public Health Service. A version of this paper was previously presented at the Medical Device Executive Forum, Anaheim, CA, in January 1998.

Copyright ©1999 Medical Device & Diagnostic Industry

Choosing Motion Control Components

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

An MD&DI January 1999 Column


Designers of motion control systems today must choose from among an ever-expanding array of components and technologies.

With the continuing advances in microprocessors, programmable logic technology, power semiconductors, and software, designers of motion control systems can achieve more reliable, accurate, and sophisticated results than ever before. But to realize these improvements, the designers must be able to choose the most suitable motion control components and technologies from among a wide variety of products and suppliers.

Making these choices involves not just picking the highest-quality components, such as controllers, motors, motor drives, and feedback sensors, but also planning how all of these components and others will work together in the finished system.

A typical multiaxis x-y-z motion platform applied to a sample analyzer.


The first step for choosing motion control components is to clearly define the system requirements. Does the system need to control force, speed, position, or a combination of these? Is accuracy the most important goal or is repeatability more critical? How many motors or axes of control are required? Do multiple axes need to be coordinated, as they are in an x-y-z arrangement, or can they be treated as independent axes? A common mistake is not taking into account the unique needs of an application when choosing components.

Once the designer has taken the time to gain a complete understanding of the requirements, he or she is ready to determine which products will best meet the needs of the system.

Mechanical factors have much more effect on the electronic design of motion control systems than the electronic design has on mechanics. Product flow and throughput, human operator requirements, and maintenance issues help determine mechanics, which in turn help decide electronic and software requirements. Therefore, electronics engineers must understand the mechanics of motion control systems to achieve successful electronics designs.

Mechanical Actuators. Actuators provide a method of converting a motor's rotary motion into linear motion. Options include leadscrews, ball screws, rack and pinion, or belt/cable/chain drives. Some actuators have backlash and all have finite levels of torsional and axial stiffness, which directly affect the system's frequency response characteristics.

Linear Guides and Linear Bearings. These bearings keep a translating load constrained to a single degree of freedom. Technologies include recirculating and nonrecirculating rolling elements; sliding (friction) type; round and profile- shaped guides; and air, hydrostatic, and magnetic bearings. Important attributes are dynamic and static friction, rigidity, straightness, flatness, smoothness, load capacity, and amount of mounting surface preparation for installation.

Machine Structure. Machine structure directly affects a motion system's performance in ways that aren't always obvious. A properly designed structure will minimize the injection of external disturbances by incorporating a highly damped and compliant barrier to isolate the motion system from its environment, yet have a stiff enough and sufficiently damped structure to avoid resonance problems. A high static mass–to–reciprocating mass ratio can also prevent the motion system from exciting the structure it is mounted on.

Other Components. Other moving mechanical components include cable carriers that retain moving cables, end stops that restrict travel, shock absorbers to dissipate energy during a crash, and way covers that protect against dirt. Any components that move will affect a system's response by changing the amount of inertia, damping, friction, stiffness, or resonance.


Most electronic motion control systems consist of several key elements: a controller, motor drive, motor, and feedback sensor.

The brain of the motion control system, the motion controller is responsible for all the computational requirements of motion path planning, servo loop closure, and sequence execution. Essentially a computer dedicated to motion control, the controller is programmed by the end-user to perform desired tasks. The controller outputs a low-power motor command signal in digital or analog format to the motor drive.

Brushless servomotors with integral feedback are shown here in several frame sizes, stack lengths, and windings.

The motor drive takes this low-power signal and amplifies it to deliver the appropriate current to the motor windings. The motor produces torque proportional to its winding current and sets the load in motion.

The feedback sensor provides position or velocity information back to the controller, which determines whether to change the current requested from the drive. In a typical closed-loop system, the sequence of reading the feedback and updating the motor current is done at 1 kHz or faster. This fast sampling frequency (or servo update rate) allows the motor to smoothly follow varying velocity profiles as well as react quickly to external disturbances.


The wide variety of motion controllers available gives a designer considerable flexibility; however, of all the component choices made in designing a motion control system, the choice of the motion controller can have the most serious ramifications. The selection of most motors, drives, feedback devices, and mechanical components can often be tweaked or changed midway through the equipment design process or even much later as part of a field upgrade (albeit with great inconvenience). However, the motion controller usually involves a software component, and changing it represents much more than just a parts replacement--it also includes a learning curve and a test-and-debug process. Also, controllers can differ in their feature sets, communication protocols, and hardware interfaces.

Motion controllers have evolved considerably in the last few years, following the trend of improving price/performance ratios for microprocessors, digital signal processors, and programmable logic devices. Equipment designers faced with a build-or-buy decision usually realize quickly that the level of development time and technical expertise contained in the hardware, firmware, and software of these specialized products often rules out a competitive in-house design. Selecting a vendor focused on motion control is typically the best choice.

Software configuration utilities allow checking of status and variables for troubleshooting and diagnostics.

Servo frequency response and stability may be evaluated by today's advanced software tools without using traditional test equipment such as oscilloscopes.

For those rare applications that require unique embedded solutions, a designer may consider using specialized motion control chip sets incorporating application-specific firmware and hardware logic. Such chip sets require printed circuit board designs that include the component-level hardware and software interfaces to host microprocessors and input/output (I/O). Considering the amount of work required and the need to obtain the latest features and performance to remain competitive, most users decide to purchase an appropriate controller.

Motion controllers are typically available as bus-based cards or in stand-alone configurations. Designed to be incorporated within a host computer, bus-based cards are available in most popular formats, including ISA, PCI, compact PCI, STD, PC-104, and VME. By residing on the computer's internal expansion bus, the cards can provide communication speed and flexibility.

Unlike bus-based cards, stand-alone controllers operate without requiring installation in a computer. They have their own power supplies and enclosures. Communications take place via RS-232 serial links.

Space requirements and cost are usually about the same whether a designer chooses a stand-alone or card controller. A bus-based card typically requires an external breakout board to allow the many signals from its single high-density edge connector to be transmitted to the outside environment. In many cases, a powerful stand-alone motion controller with significant analog and digital I/O can function as the entire machine controller and eliminate the need for a computer.

Whether choosing a bus-based or stand-alone motion controller, a manufacturer needs to ensure that the controller can not only control the number of motors required, but also the types of motors. For example, some multiaxis controllers control both step and servomotors, allowing a designer to easily use both motor technologies in one system.

Additional considerations for choosing motion controllers include the ease of use and power of the programming language and setup software tools; multitasking capabilities; number of I/O points; coordinated motion requirements, such as linear and circular interpolation, electronic gearing, or camming; synchronization to internal and external events; and error-handling capabilities.


The most popular of the many types of motors available are step, permanent magnet (PM) brush, and PM brushless (Table I).

  Step Brush Brushless
Cost Low Moderate Higher
Smoothness Low to moderate Good to excellent Good to excellent
Speed range 0–1500 rpm typical (higher speeds possible with special drive schemes) 0–6000 rpm 0–100,000 rpm
Torque High, but rapid falloff with speed Moderate High
Required feedback None Position or velocity Commutation and position or velocity
Maintenance None Yes None
Cleanliness Excellent Brush dust Excellent

Table I. A comparison of step and permanent-magnet motor types.

Step motors are often selected simply because they can be run open loop; that is, without any feedback sensor. A step motor is designed with a number of discrete positions where the shaft will rest while producing a holding torque. The lack of feedback plus a relatively simple motor drive design makes step motors a cost-effective and reliable choice for many applications.

Digital servo drives are software configurable for torque, velocity, position, and follower modes of operation.

However, performance demands often require that designers consider either brush or brushless servomotors. Both can typically achieve higher top speeds, smoother low-speed operation, and finer resolution than step motors, but the required feedback sensor and relative complexity imparts a cost disadvantage when compared to step motors.

Brush servomotors are constructed with a wire-wound armature rotating within a magnetic field produced by a stationary PM assembly. As the motor rotates, current is sequentially applied to the appropriate armature windings by a mechanical commutator consisting of multiple brushes sliding on a ring of copper segments. Brush motor technology is quite mature and can provide very high performance. However, the mechanical commutator often becomes a limiting factor.

Brushless motors incorporate electronics to eliminate the need for mechanical commutation. Essentially an inside-out brush motor, a brushless motor consists of a PM rotor with windings distributed about the outer stationary housing. The mechanical commutator is replaced by either extra transistors and logic in the motor drive and noncontact Hall effect sensors in the motor; a commutating encoder; or, in some cases, extra software in the controller or drive.

Compared to brush motors, brushless motors typically exhibit lower rotor inertia, lower winding thermal resistance, and no sliding mechanical contacts. These motors can offer higher top speeds, higher continuous torque, and faster acceleration without the brush dust, commutator wear, contamination, arcing, and electromagnetic interference (EMI) or radio-frequency interference (RFI) of a brush assembly. Recent advances in semiconductors, specifically in power devices and microprocessors, have significantly reduced the cost disadvantage of brushless motor systems. The majority of new designs employ brushless technology.

Lately there has also been increasing market interest in linear motors. Although these motors have been around for many years, recent trends in digital drives, software commutation, performance requirements, and competition in the linear motor industry have increased the popularity of this motor type.

A linear motor can be envisioned as a rotary motor that has been sliced open and unrolled. Linear motors are available in many of the same designs as rotary motors: step, brush, brushless, and induction. Linear motors can replace conventional mechanical actuators, such as leadscrews and belt drives, and eliminate most moving and wearing of mechanical components. Their noncontact design offers advantages in speed, acceleration, cleanliness, and maintenance. Additionally, linear motors do not experience performance degradation commensurate with system length, as do most other methods of mechanical actuation.

However, linear motors typically require a more expensive feedback device than rotary motors do. They also require moving cables and often use exposed high-energy magnets, which may present safety hazards by attracting loose ferrous objects. Also, the only way to obtain greater force is to choose a larger motor. There are no other options, such as reducing gears or changing screw pitch or pulley size.


Motor drives, also referred to as motor amplifiers, must match the type of motor that is used, such as step, brush, or brushless.

Basic step motor drives are fairly simple devices consisting of several power transistors that sequentially energize the motor phases according to the number of digital step pulses received from the controller. More advanced microstepping versions, which are common, control the phase currents in a staircase sinusoidal fashion, permitting a motor to operate with a much greater resolution and reducing a step motor's inherent resonance problem.

  • Accuracy
  • Repeatability
  • Resolution
  • Bandwidth (frequency response)
  • Step response
  • Settling time
  • Stability over time
  • Environmental sensitivity
  • Disturbance rejection
  • Power (torque and speed)
  • EMI/RFI emissions and immunity
  • Regulatory compliance
  • Reliability (mean time between failures)
  • Error handling
  • Product throughput
  • Safety


Brush motor drives typically accept a ±10-V analog signal from the controller. This signal corresponds to a current or voltage command. Four power transistors arranged in an H-bridge control both the direction and magnitude of current in the motor windings.

Like a brush drive, a brushless motor drive typically accepts a ±10-V analog signal from the controller. However, just as the typical brushless motor has a three-phase winding (delta or wye), brushless drives typically contain six power transistors arranged in three half–H-bridges as well as additional logic to control their timing as a function of rotor-position feedback. This logic is often expanded upon to employ advanced commutation schemes, such as sinusoidal current control and phase advance, to extract even more performance.

Drives are either linear, which have power transistors that operate in the active region, or pulse width modulated (PWM), which have power transistors that switch between full on and full off. PWM drives are by far the most common and offer advantages in efficiency, size, and cooling requirements. Linear drives, however, produce much less EMI/RFI and may offer performance advantages when used with low-inductance motors.

For optimum performance, drives must suit the motor's characteristics. For example, a motor has a peak current limit before demagnetization occurs and a continuous current limit before it exceeds its thermal limit. The drive must be set to avoid exceeding these limits. Many drives use closed-loop feedback of winding current, and this loop must be tuned. Also, the scaling of the drive must be set so that it operates over its full dynamic range.

Considering all of these factors, it is often in the designer's best interest to procure both motor and drive from the same vendor to ensure easy setup. Many of today's drives are digitally controlled by microprocessors, which can tremendously simplify configuration through the use of Windows-based utilities.


While step motors are often run open loop, not requiring feedback sensors, all servomotors must use these components.

The most common feedback sensor is the incremental encoder. An incremental encoder produces a number of pulses proportional to the distance moved (a linear encoder) or the rotation of a shaft (a rotary encoder). These pulses are counted by the controller to determine the motor's position and direction of travel at any time. Motor speed is determined by the controller mathematically differentiating pulses in real time. Systems that require very smooth, low-speed operation are usually fitted with a high-resolution encoder that provides accurate velocity data. However, some systems incorporate an analog tachometer that produces an analog signal directly proportional to speed.

In addition to incremental encoders, other types of feedback sensors include resolvers, linear variable-differential transformers (LVDTs), potentiometers, absolute encoders, sinusoidal encoders, capacitive sensors, inductive sensors, and laser interferometers. Selection criteria include accuracy, repeatability, environmental concerns, operating temperature, cost, and physical envelope.

Because a sensor can rarely be mounted directly to the end effector, feedback is usually taken from a mechanically coupled component with the assumption of a robust connection. In actuality, how a feedback sensor is mounted can have a far greater effect on accuracy than the type of sensor that is chosen. Care must be taken, because mechanical linkages between the feedback sensor and the moving load can have backlash and compliance, introducing both static and dynamic errors into the system.


Motion controllers, feedback sensors, motor drives, and motors are the most significant components of motion control systems that designers must choose. But there are many other elements that contribute to the success of the design. For example, cabling must be chosen for signal integrity, flex life, bend radius, and exposure to chemicals.

Travel-limit switches should be used to avoid end-of-stroke collisions and home switches employed to establish a zero-reference position. To avoid unacceptable levels of EMI/RFI emissions and to minimize susceptibility, attention needs to be given to choosing line filters, connectors, cable shielding, and grounding methods.

Any relevant regulatory compliance issues must be addressed, and safety issues must be dealt with. For instance, designers must address what might happen in the event of component failure, power failure, or programming errors. Maintenance and diagnostic features should also be incorporated to ease troubleshooting and service. Finally, the method by which a human operator or other system controllers and computers will interface with the motion control system must be addressed.


Although the number and variety of choices in motion control components and their vendors give designers considerable flexibility, they also increase the likelihood of compatibility problems.

A component may seem to be the ideal choice when considered alone, but is it really best when its interdependency on other components in the system is taken into account? For example, a low-inductance motor may seem suitable, but designers must consider whether the low PWM switching frequency of a digital drive could lead to excessive ripple currents, effectively derating the motor. Perhaps a linear drive or external inductors would better suit such an application.

One common problem when choosing components is that designers often assume that the products will operate as advertised even under less than ideal conditions. For example, the speed-torque envelope listed in a motor manufacturer's data sheet is generated under optimal conditions: using a drive that has a particular peak current, continuous current, switching frequency, and minimum bus voltage; cables of minimum resistance; particular motor heat sinks, and ideal ambient temperature conditions. If the motor will not operate under these conditions in an application, its published performance cannot be expected for that application.

Typically, the performance requirements for a motion system cannot be defined in terms of one component's specifications. For example, if a positioning system requires an accuracy of 0.0002 in. and an encoder with 0.0002-in. resolution is being used, several problems may still occur. All digital servo systems can hunt plus and minus one count, microprocessor controllers may experience round-off error, there are no perfect couplings between the feedback sensor and the end effector, and both dynamic and static accuracy is partly governed by system tuning.

Considering the system as a whole and keeping all the requirements of the system in mind can help designers to choose from among the increasing variety of motion control components.

Michael Backman is manager of the Motion Control Division of Thomson Industries Inc. (Port Washington, NY).

Copyright ©1999 Medical Device & Diagnostic Industry