Intelligent power management enables autonomous power supply of sensor systems for modern prostheses

Modern intelligent prosthesis or robotic extremities use a combination of mechanically, hydraulically and electronically controlled components and joints for motion. For precise controlling, stepping motors are used. Here, passive movement of the extremity, like the lowering of the arm caused by the gravity, produces unexploited energy. Utilization of this normally lost energy expands the lifetime of non-rechargeable batteries or the time for recharging the accumulators. Main component of the energy harvesting system is a double-layer capacitor (ultracap) for storing the electrical energy. This energy buffer is necessary, because a switching converter needs a startup time to work properly. A MOSFET switch is used to avoid a backflow into the motor or the motor driving unit. Charging up a RC-element indicates the stored energy and represents the load of the ultracap. It activates a high efficient DC/DC buck boost converter for stabilizing the voltage and driving a microcontroller or another sensor circuit. The rotation of the rotor through the limb produces a sinusoidal output voltage. The input energy is irregular and aperiodic. Its amplitudes are in the range of 2 V to 4 V with current pulses about 30 μA depending on the type of the used stepping motor and the rotation speed of the rotor. The built energy harvesting system enables recovering of unused energy for driving a sensor circuit. Furthermore, it supports the power supplies by improving the efficiency. The advantages are that this system will be activated when enough energy is gathered and that there is no running out of power in comparison to a battery powered system.