COMPLIANCE CONTROL OF ROBOTIC WALK ASSIST DEVICE VIA INTEGRAL SLIDING MODE CONTROL

The existing robotic walk assist devices (RWAD) are not affordable for everyone particularly in low income countries like Pakistan. In addition, convincing people to adopt such devices is somehow challenging due to lack of trust, dependability and cultural constraints. Safety of the users is also a major concern. Many researchers are currently working in this area to come up with better mechanical design along with safe and trust worthy control techniques. Some aspects of safety can be addressed with the help of compliance (low-stiffness and flexibility) control. Compliance(low stiffness) control will make RWAD more user friendly by limiting the forces RWAD applied on the human user. In this paper a model reference compliance control scheme is suggested for a robotic walk assist device based on integral sliding mode control (ISMC) coupled with a dynamic model based feedback linearization controller. Joint torques feedback from the knee and hip joints are used to make the robotic walk assist device compliant via ISMC. A mass-spring-damper system is used as a compliant reference model. Simulation results are presented to show the effectiveness of the suggested scheme.