Servo and Force Control with Improved Robustness and Accuracy for An Active Body Weight Support System

Active body weight support (ABWS) is of great importance for lower limb rehabilitation. We have built up an ABWS system to simultaneously follow the patient's horizontal movement and provide the designed vertical body weight support force to the patient. However, the patient's movement is highly dynamic and there exist disturbance and other uncertainties in the system, making it challenging for the position servo and force control. Two improved control strategies are respectively proposed, using disturbance observer (DOB) along with one-step prediction and dynamics compensation, to achieve accurate and robust horizontal position servo as well as vertical force control of the ABWS system. Experiments were conducted to verify the efficacy of the proposed methods, and the results were significantly improved in comparison with PID control.