Originally Published MPMN September 2005

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Durable Motion Control System Withstands Rigorous Daily Use by Multiple Users

A heavy-duty motor and gearbox were strategically positioned to endure harsh usage.

Susan Shepard

The Clinitek Status analyzer from Bayer HealthCare (Tarrytown, NY; www.labnews.de/ en/products/pr_clist.php) automatically analyzes urine strips. This eliminates errors that happen with human visual judgments. It has a touch screen user interface, and a motorized drawer that accepts the reagent strip or cassette and automatically positions it under the instrument’s optical-analysis sensors.

Previous sample drawer systems worked perfectly under normal conditions with operators who were familiar with the instrument. However, prototype testing uncovered a potential problem with new users. When manually pushing the drawer in, it was possible that they could use too much force and damage the motor’s gear teeth.

"We required a motorized table that could withstand the rigors of daily use by multiple different operators, using different kinds of reagents," says Trevor Allison, R&D director at Bayer Diagnostics’ product development and manufacturing facility in the UK. "We were concerned that they would not meet our desired reliability specification. To address the requirement, we needed both a fast answer, and preferably one that could fit easily within our existing investments in production tooling and processes."

Bayer sought help from Cambridge Consultants (Cambridge, UK; www.cambridgeconsultants.com). The firm "worked in parallel with us and provided the answer within a matter of weeks, keeping an important product launch on schedule," Allison says.

The problem was relatively simple to define as a design task, Allison notes. "The major issues were how fast it could be produced, and the desire for the design to fit with current production tools and processes."

To begin the project, "we started with a detailed analysis of the specific motion control problem, both in isolation and in the context of the overall product," says Richard Snell of Cambridge Consultants.

The motion control system that the firm created involved a heavier-duty motor and gearbox than had been used in previous systems. It was also specifically located to ensure that force on the drawer could never damage it. Cambridge Consultants also provided electronic circuit advice to assist the Bayer team in designing an improved control and drive strategy. This involved sensing the insertion of the drawer by feedback from the motor windings and driving the motor in a more sophisticated way. Additionally, a special motion profile improves both the engagement process and the final positioning of the reagent under the optics.

The sample drawer itself and the mouth of the enclosure were also designed to make the table insertion intuitive, with mechanical shaping and visual indication of the right orientation. These mechanical changes were achieved using modifications to existing molding tools, thus avoiding the time and costs associated with making new ones.

"On tasks like this, with demand to complete in a short time period, our project control scheme called for all the mechanical specifications and tolerances to be meticulously verified, to ensure that everything would fit perfectly, and for rigorous tests to prove the design’s robustness and reliability," says Snell. This gave the client the confidence to put the design modification straight into manufacturing, he continues.

After 18 months on the market, the Clinitek Status analyzer has thousands of installations worldwide. It undergoes high-frequency daily use in hospital wards and healthcare practices, and there have been no failures attributable to design problems with the new moving-part mechanism.

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