Sliding Mode Compensation for Model Uncertainty, Payload Variation and Actuator Dynamics for Inverse Dynamics Velocity Control of Direct Drive Robot Manipulator

The robot manipulator joint actuator dynamics and the payload variation are major factors that severely affect the overall dynamics and hence the tracking performance of the direct drives manipulator. This paper proposes a robust and computationally simple approach aimed at compensating the tracking error due to model uncertainty, actuator dynamics, and payload variation for the inverse dynamics velocity control of direct drive robot manipulator. The proposed scheme employs a simple Proportional-Integral (PI) type sliding mode control scheme for the design of the compensation control signal. In this scheme, the sliding mode compensation control input can be calculated from the nominal model of the manipulator, provided the bound on the model uncertainty can be estimated. Thus, for the proposed control method, unlike the classical inverse dynamics controller, calculation of the parameters of the dynamic model very accurately in real-time is not a serious requirement. The effectiveness of the proposed control algorithm has been validated in simulation studies considering the model of a 3-DOF direct drive robot manipulator with different loading conditions. KeywordsSliding Mode Compensation; Inverse Dynamics; Velocity Control; Direct Drive Manipulator; Robust Tracking