More Than Just General Motors

Originally Published MPMN July 2004

PRODUCT UPDATE

More Than Just General Motors

Motion control devices fulfill a variety of needs

SusanWallace

Motors are the heartbeat of many medical devices. They come in all kinds of sizes and shapes, and are capable of varying speeds to power a myriad of products. In this article, MPMN takes a look at the latest in the world of motors and motion control devices. 

Tachometer Uses Both Analog and Digital Signals 

A tachometer encoder combination offers both analog velocity and digital position signals in one device. The dc tachometer from Servo-Tek (Hawthorne, NJ) has an encoder that uses high-quality optical sensors and electronics to provide a square wave output. Having the tachometer and encoder on one common shaft reduces mounting and coupling requirements. The tachometer generator can provide an analog signal from 12,000 rpm down to zero speed. Since the unit reverses polarity from clockwise to counterclockwise rotation, direction can be sensed almost instantaneously. 

Brushless Motors Minimize Cogging Torque

Intended for direct-drive applications in large inertia and high torque load systems, brushless torque motors deliver stall torque ranging from 2 to 1490 lb/ft. Motor diameter sizes range from 6.7 to 31.2 in. Megaflux motors from Emoteq Corp. (Tulsa, OK) can be provided with special mounting features to ease integration into the user's machine. The company also offers high-resolution encoders that are incorporated directly into the motor and are capable of delivering rotary precision to sub-arc-second levels. Although engineered to maximize output torque, the motors also minimize cogging torque, thereby enhancing their precision in applications sensitive to parasitic torque perturbations.

Optical Linear Encoders Are Made for Speed

Noncontact linear position encoders use low-mass, ultra-low-profile design and self-tuning electronics to bring 5-µm to 10-nm resolution to machine applications. The encoders from Renishaw Inc. (Hoffman Estates, IL) are engineered for high-speed, short-travel processing where space is at a premium. They can achieve speeds up to 300 mm/sec at 20 nm, and 150 mm/sec at 10 nm. A noncontact, no-wear design eliminates hysteresis and friction for reliability and repeatability. The machine's read head measures 36 ¥ 14.3 ¥ 12.5 mm and weighs 22 g. Patented filtering optics provide immunity to dust, scratches, and light oils on the tape scale to ensure signal stability. The 20-µm pitch scale is made of gold-plated steel tape, lacquered to protect against dirt. It provides linearity better than 1 µm.

The scale's adhesive backing mounts to all common material types, including granite, ceramic, steel, aluminum, iron, and invar. By mounting directly to the machine, the scale thermally replicates the base material, eliminating the need to compensate for multiple coefficients of expansion. The tape can be applied quickly and easily at any stage of machine building, with a special applicator ensuring parallelism with axis guideways. No drilling is required.

The RGH25F is available with either digital or analog outputs. Digital read heads produce differential line-driven quadature signals to industry standard EIA/RS422. Differential line driver outputs offer noise immunity in harsh electrical and magnetic environments. It is enhanced by self-tuning adaptive control and double-shielded, highly flexible cable. 

A signal condition monitoring circuit drives an integral two-color LED and an alarm signal for remote monitoring at the control. The LED facilitates quick installation with visual confirmation of optimum scale alignment, while the alarm signal alerts the control of low-signal amplitude, eliminating the danger of unrecognized encoder-count loss.

Encoders Are Suitable for Light Applications

Optical rotary incremental encoders are designed for light industrial applications that require high resolution in a small package. Available from Gurley Precision Instruments (Troy, NY) in either shafted or blind-hollow shaft versions, the models R112S and R112B measure 12 ¥ 25 mm long with resolutions up to 8000 c/rev. The encoders are suitable for miniature robots, precision pumps, and fine instrumentation. 

Hybrid Motors Are Suitable for High-Speed Applications 

To satisfy requirements of high-speed applications, Moons' Industries America Inc. (Elmhurst, IL) offers the 17HE 3.6° hybrid stepping motor series. Compared with the company's 0.9°and 1.8° motors, the new unit has a higher running speed, making it suitable for high-speed applications. The company isalso introducing a new Series 3 phase stepping motor. Smooth running makes thismotor useful for micro step systems.

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