Object Weight Compensation Of A Manipulator

Whenever a manipulator handles an unknown object, it is necessary to compensate for the weight as it causes position errors. Although the integral function of an PID control law eliminates position errors, it takes a lot of time to converge to a set point. Sometimes, it also causes the system to go unstable by increasing its order. Therefore, a feedforward control method is usually used to compensate for this weight. In the weight compensation method which does not use a force sensor, the servostiffnesses of the manipulator joints are used to identify the load mass. However, this method needs the calibration of the servostiffnesses. This paper presents a weight compensation method using only joint servo-inputs corresponding to the object weight. Therefore, it does not need the complicated calibration of the joint servostiffnesses. This paper clarifies the compensation algarithm which cancels the joint servostiffneses and presents experimental results to compensate for an object weight.