Controller design and simulation of a one-degree-of-freedom power assist system for lifting objects

Abstract

This paper presents a controller design and simulation of a one-degree-of-freedom power assist robot for lifting objects. The research is conducted through a simulation of the control system of power assist devices, without determining friction of the system, but allowing for time delay at 150 μs. To this end, a force sensor-less method, a calculation of the disturbance torque from the actual weight of an object which can be estimated from a disturbance observer in place of a force sensor is employed. The disturbance torque obtained is then converted to force signal and reference motion to control the power assist system. Both, force signal and reference motion are generated by the PID controller, which is designed for the power assist system to maintain its stability. From the simulation, the controller enables the robot to efficiently lift an object with ease of use; the operator perceives a load applied 10 times lighter than the actual weight (assist ratio, a = 10). In practice, however, there might be other limitations to be taken into account: for example, strength of the power assist robot’s structure which has to be suitable for a certain task.