End point position control of a single link, two-degree-of-freedom manipulator with joint compliance and actuator dynamics

One problem which limits the cycle time of typical industrial manipulators is the vibration which results if the modes of vibration of a manipulator with significant joint compliance are excited. In this paper the effects of joint compliance in a two-degree-of-freedom manipulator are modeled and a study of several possible controller structures is conducted for the problem of end point position control. Controller structures considered include independent joint control neglecting compliance and independent joint control including actuator dynamics and joint compliance. A nonlinear observer which reduces the number of state measurements required is developed. Simulation of various controllers is performed utilizing ACSL, Advanced Continuous Simulation Language. It is shown that the closed loop frequency response of the manipulator can be increased beyond the typical industrial limit of 50% of the manipulator's natural frequency while maintaining desirable response characteristics by considering the joint compliance in the design and providing suitable feedback measurements. Simulations suggest satisfactory performance can be obtained as high as the limit imposed by the manipulators unmodeled higher vibration modes. The effects of motor torque limiting are investigated via simulation. The results demonstrate that the advantage of including actuator dynamics and compliance in the design is maintained when practicalmore » torque limitations of the motors are considered.« less