The prosthesis provides controllable torque about the ankle axis. The keel portion of the device is controlled by an external actuator unit, while a passive heel spring provides compliance in the early stance phase of the walking cycle.The amount of applied torque is measured with a load cell, and the joint angle is measured with an optical encoder. The external actuator unit was also designed by HuMoTech and consists of a servo-motor, a servo-drive and a drive pulley. Torque is transmitted to the prosthesis via a Bowden cable: a cable guided inside a flexible sheath.
The control signals for the high-performance torque control are determined using the actual torque applied at the ankle prosthesis together with the prosthesis joint angle. The Speedgoat Performance real-time target machine measures such torque and angle using realtime measurements from a load cell and an encoder, respectively, and computes motor commands to regulate ankle joint impedance.The interface and control code was developed in MATLAB & Simulink. Simulink Coder was used to automatically generate the code to run on the target machine.