The SoftGait: A simple and powerful weight-support device for walking and squatting

Abstract

When designing a lower-limb assisting robot with body-weight support (BWS), it is important to achieve high force fidelity to support body weight at standing phase. Low impedance operation at swing phase is also required not to disturb leg motions for users. The SoftGait is designed to achieve both performances with a simple mechanical structure based on a pneumatic actuator and low cost sensor development. The SoftGait generates large force for body-weight-supporting in squatting mode corresponding to user's body weight. In fact, in walking mode, it enables a user to experience more comfortable walking with support from intrinsic compliance. The SoftGait uses two pneumatic linear actuators. Two different types of force sensors are designed to measure forces from both the seat and the pneumatic actuators. Two magnetic encoders attached to hip joints are designated to differentiate between a standing mode and a walking mode. In addition, two force sensing resistor (FSR) sensors are positioned in one shoe molded out of silicon for detecting gait phases in a walking mode and its availability as a gait phase detector is verified. A control strategy is established to operate the device using three modes: standing, walking and squatting. Mode transitions are conducted by using information from the sensors. All the modes are controlled by a simple PD controller while their target references are set to be different among modes. Experimental results tested with a healthy user show its effectiveness as a body-weight-support device targeting rehabilitation for the old and the obese.