Intelligent prosthetics make use of maxon dc motors

It can be difficult for amputees, particularly lower limb amputees, to be able to walk uninhibited and with comfort as their prosthesis can’t adapt in real-time to changing walking conditions, such as walking up and down slopes and avoiding obstacles.

The élan foot uses two microprocessors to automatically alter the resistance around the artificial ankle joint so that it replicates how a human ankle works and allows amputees to walk more easily on inclines.

The microprocessors work in tandem with the hydraulic ankle, which sits on top of carbon-fibre foot springs. The ankle control ensures silent operation and sinuous movement that biomimetically matches the user’s body and walking style.

The system uses dc motors, gearheads and encoders from maxon motor. Two brushed dc motors from the RE family, which use precious metal brushes to give the advantage of low stiction at low speed plus a low current draw, noiselessly operate the precision hydraulic valves. A maxon motor Mencencoder (Magneto-Hall-Effect) is used as it requires little space and is has a low power draw for this battery powered application. 

Endolite is the products division of Blatchford, who have been involved in the design, manufacture and innovation of lower limb prosthetics for over a century. Head of research, Dr David Moser, says the maxon motors have operated flawlessly from the start, with great technical support from the maxon team during the design, development release phase.

As the motors and gearheads run on every step an active user can easily generate several million movements. Ian Bell, Senior Sales Engineer at maxon motor uk, says that to date there have been no failures. "The precise nature of the valve requires tight tolerances to be maintained, which we are set up to achieve," says Mr Bell. "If the tolerances couldn’t be maintained the motor would have to be larger, the product heavier and the battery life shorter."

Ian Bell has been working with Blatchford since the development of the first microprocessor controlled joint in the early 1990s . Then the valve motor in the artificial knee was 15mm diameter; in future, it will be possible to do the same work with the new 10mm DCX.