Development of Multi-axis Motor Control Systems for Lower Limb Robotic Exoskeleton

Abstract

The aim of this study was to establish a control system with multi-axis motors for a lower limb robotic exoskeleton (LLRE). This LLRE structure was built by using an aluminum alloy designed with an adjustable mechanism. A four-motor control system with four Maxon brushless direct current motors was developed and installed in the hips and knees of the LLRE, respectively. In addition, four harmonic reducers were connected to the motors to increase the torque. A master controller which commands the four-axis motors was developed by using Texas Instruments (TI) embedded chip (TMS320F28069). The walking gait parameters were established to support the LLRE movement. The controller local area network protocol was used to communicate between the master and slave motor controllers. The slave motor controllers were developed by using TI embedded chip (DRV8301/TMS320F28069) for each joint by a high bandwidth control strategy. A high dynamic response system was obtained by considering the LLRE inertia, external variable load induced by the LLRE and delay in a digital control system. The result showed that this high bandwidth control with the experimental ones, the trajectory of each joint demonstrated a high response bandwidth and the tracking gait errors were significantly eliminated. This study indicated that the development of this LLRE with a master controller/the slave motor controllers strategy through controller local area network protocol was feasible for healthcare applications.