Sliding Mode Control with Extended State Observer for Multi-axis Motion Control System

In this paper, the position servo control problem of multi-axis motion control system is studied. In terms of our multi-axis motion control platform, the dynamic disturbance between axes is formed due to the simultaneous movement of the motion axes. The dynamic disturbance between axes have a certain influence on the tracking accuracy of the multi-axis servo system, but such disturbance is often neglected. In addition, the accurate model of the mentioned disturbance is difficult to be obtained. Therefore, in order to solve the above problem, the extended state observer (ESO) is introduced. For each axis, friction torque, load torque, current tracking error and, particularly, the disturbance from other axes are regarded as the lumped disturbance to be estimated via a three-order ESO. Then the lumped disturbance can be compensated in the controller, thus enhancing the disturbance resistance ability of the system. Furthermore, the sliding mode control scheme is employed in the single-axis control to ensure a strong robustness of the system. And the sign function in the control law is replaced by the saturation function to alleviate the chattering. As simulation and experiment results indicate, the composite control scheme proposed by this paper has a better tracking precision and higher disturbance resistance performance than the traditional three-loop PI control method for multi-axis servo system.