Force sensorless power assist control using operation force observer for nursing lift

This paper proposes a power assist control methodology based on an operation force observer for a nursing lift, where operation force of nurse applying to the nursing lift is estimated using an operation force observer. In order to improve estimation performance for the operation force, a position information based disturbance observer is applied, in which no differentiators are needed to calculate acceleration for the system. As for the power assist algorithm, a position control based power assist system is applied, where the position reference for the nursing lift is generated based on an impedance control method using assist force calculated by the estimated force of nurse. The effectiveness of the proposed power assist system has been verified by experiments using a prototype of a nursing lift.