Robust Control of a MIMO Laboratory Motion System Using Variable Structure Control and the Computed Torque Method With the Velocity Limitation

In this study, we experimentally verified a robust control law based on variable structure control and the computed torque method on a laboratory motion system. Variable structure control is characterized by high-frequency switching control, which does not have to be applicable to real motion systems. Therefore, we used a suitable reaching law to create a continuous substitution for the discontinuous nonlinear control law. This continuous substitution caused the loss of control invariance to parametric and signal disturbances, but the control loop remained robust, with bounded position errors. We augmented the variable structure control with the computed torque method, which ensured the feedback linearization of the dynamic system. The proposed design of the control law also considered the velocity constraints of the system. Both components of the control law needed to be considered in the velocity limitation, otherwise, the system constraints would be violated. We designed a velocity limitation algorithm for variable structure control to be compatible with the computed torque method, with regard to the desired performance, with exponential convergence and no overshoot. The control law is shown to satisfy the control objectives, and the results are discussed.