2008

Motion Control Components Lend Hand to Biomedical Applications

The worlds of biomedical and motion control are joining at the hip, with motors, controllers, actuators, and other motion control components becoming key elements in advanced biomedical applications ranging from fluid dispensers to imaging tables to surgical simulation systems.

altThe increasing use of sophisticated electromechanical and electronics technology in patient monitoring, laboratory, and other biomedical applications is opening the doors to the motion control industry, which has been developing smaller, higher precision motion components for industrial applications for years. But biomedical applications impose their own stringent needs.

Though speeds are lower and motion sequences are sometimes simpler, the need to gently move patients or accurately dispense samples requires motors to start and stop smoothly, with very high precision. Vibration, noise, and heat must be carefully controlled, and motion control components must often fit space-constrained products.

Reliability is the arguably the key requirement for the motion control system, because biomedical OEMS want to ensure that a product performs reliably for extended operating cycles in a laboratory or operating room environment. Given those constraints, cost becomes less of a primary concern.

“Our products are not the cheapest, but for what we provide they’re cost-effective,” said Joe Martino, a sales engineer for Maxon Precision Motors. Maxon makes a number of design modifications, such as using ceramic rather than metal inside gearboxes, for improved reliability. “You won’t find these materials in consumer applications,” he said.

Martino notes that roughly half of the company’s business comes from biomedical applications. One application for Maxon’s motors is a surgical simulator, developed by Immersion Medical, that enables the surgeon to simulate laparo-scopic procedures through a virtual reality system.

Johnson Medtech, the medical products network of Johnson Electric, supplied its Nanomotion motors to help the University of Calgary and MacDonald, Dettwiler and Associates Ltd. create the neuroArm, reportedly the world’s first MRI-compatible, image-guided surgical robot. The neuroArm uses 16 Nanomotion HR2-1-N-3 cermaic piezo ultrasonic motors, coupled with the company’s AB5 drive module.

The key advantage of Nanomotion’s motors for MRI applications is their non-magnetic design, unlike more common permanent magnet motors, according to Alan Feinstein, Nanomotion’s president. Motors that generate magnetic fields would lead to misleading images on the MRI.

The motors are used to regulate the motion of six rotary joints. Using the real-time visibility into the human body provided by the MRI, the neuroArm enables the surgeon to manipulate tools at a microscopic scale, performing surgeries previously deemed difficult or impossible.

Many biomedical applications call for simple, repetitive motion rather than executing complex sequences. David Goodin, president of Allmotion, which manufactures stepper drives, stepper controllers, servo drives and servo controllers, said, “All customers want to do is draw a sample, not machine a contour. There are controller designs we are working on for multi-axis configurations that don’t necessarily require coordinated motion.”

Other performance aspects are more critical. For one, vibration must be controlled to ensure patient stability. Motors and controllers that drive a patient table, for instance, must minimize vibrations that could make the patient uncomfortable and possibly upset sensitive organs. Likewise, motion control components regulating imaging systems must maintain stability, or images will be inaccurate. Galil Motion Control adapted its single-axis, DMC-1412 controller into an ultrasound system from Philips Medical Systems that can identify, for instance, distinct anatomic features of a developing infant. The controller incorporates a proportional-integral-derivative (PID) filter with acceleration and velocity feed-forward functionality for accurate control and smooth motion. The controller helps the ultrasound system probe with high accuracy and stability between frames, eliminating wobbly or bouncing images.

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