Medical professionals at University College in London, England, have found a unique use for motor technology: They are using a small magnetic rotor in a patient's leg to extend a prosthesis to keep up with the patient's growth.
The patients, all children, have lost part of their leg bones after suffering from bone cancer. The prostheses support the remaining bone. But as the children grow, the implants have to extend with to accommodate their growth. That usually involves three or four operations a year over a five-year period.
Using the magnetic rotor is non-invasive. The rotor links to the implant through a gearbox. A separate stator turns the rotor. Medical professionals place the patient's leg inside the stator core. The stator turns the rotor at 3,000 rpm, driving the gearbox and extending the prostheses by one millimeter every four minutes.
The original design included six air-cored coils configured as a two-pole, three-phase winding. That design required oil cooling.
Five patients have received the treatment, which can be administered on an outpatient basis. EMR Silverthorne, a UK partner of ABB Motor Service, supplied the stator cores. It's based on ABB's standard 180-frame-size motor in a two-pole stack. The stator is series-wound with 552 turns of 1.06 mm wire.
Growing Gains: The stator drives the rotor to extend the prosthesis one millimeter every four minutes. It's a painless and non-invasive way to make sure prostheses keep up with the growing skeletel frames of children.