ABB motor parts help alleviate pain, raise quality of life

Electric motors are often regarded as "commodity items" despite examples to the contrary like motors that make Segway’s Human Transporter "hum". Here’s another novel example from the versatile world of motors.

By Control Engineering Staff December 17, 2003

Electric motors are often regarded as “commodity items” despite examples to the contrary, like motors that make Segway’s Human Transporter “hum” (see ” Propelling the Human Transporter ” in Dec 2001 Motors archive) or motors that power a self-contained artificial heart (see ” Motor with a heart ” in Nov. 2001 Motors archive). Here’s another novel example from the versatile world of motors:

ABB’s non-invasive stator turns the implanted rotor at 3,000 rpm, driving a rotary-to-linear actuator to extend the prosthesis by one millimeter in four minutes. Stator-to-rotor magnetic coupling is reportedly excellent, despite the asymmetrical air gap and differences in fit of the patient’s limb within the stator.

ABB ’s office in the U.K. announced in December 2003 that it has supplied synchronous motor stators to a pioneering research team at the University College London (UCL), helping children to walk again using a novel prosthesis. Children being treated at the Royal National Orthopaedic Hospital, (Stanmore, U.K.) have lost part of their leg bones due to cancer. The revolutionary procedure eliminates the need for further surgery associated with conventional prosthesis implanted in a patient’s leg to support the remaining bone.

Conventional implants must be extended to keep pace with the child’s skeletal growth, requiring as many as three or four additional operations a year over a five-year period. Pain and recovery treatment for the patient are major negatives with the prior procedures, along with added medical costs.

The new procedure places a miniature rare-earth magnet synchronous “rotor” in the patient’s leg, which is linked to the prosthetic implant by a miniature gearbox and rotary-to-linear actuator that extends when an external ring-shaped stator is placed over the patient’s leg and energized by a rotating magnetic field. “A typical treatment extends the prosthesis by four millimeters over the course of 16 minutes,” according to ABB. The implant is extended in small increments several times, depending on a patient’s growth rate to full height. The non-invasive procedure to extend is quick, painless, and can be completed on an outpatient basis.

Researchers from the Centre for Biomedical Engineering at UCL, working at the Royal National Orthopaedic Hospital, developed the device. The stator cores—based on ABB’s standard 180-frame motor in a 2-pole stack—were series-wound with 552 turns of 1.06-mm gauge wire in a star connection. as specified by UCL and supplied through an ABB Motor Service Partner, EMR Silverthorn (Wembley, U.K.).

This stator core configuration was a design refinement “that had produced the best performance during
tests at Stanmore,” says Chris Fletcher, EMR’s managing director. “Our role was to interpret the UCL team’s needs and bring our expertise in motor winding to solve the problem,” he explains. “ABB gave the stator cores free of charge and, working with the UCL research team, we helped to develop a winding to meet the specifications.”

Five patients have been treated so far since the new procedure started in November 2002. UCL’s commercial arm—Stanmore Implants Worldwide Ltd.—has ordered five more windings from EMR Silverthorn. Initial results with the device promise a bright future.

—Frank J. Bartos, executive editor, Control Engineering,