Rearch Of Model Predictive Control Algorithm For Motion Control Of Manipulators Based On Double-layered Structure

Predictive control has shown its advantage in handling the optimal control problems for complex systems. However, with the expansion of the scale of industrial processes, the single-layer predictive control usually does not satisfy various demands of complex systems. So a hierarchical control structure of model predictive control(MPC) is commonly used in industrial processes. It divides a complex task into several parts, and realizes respective functions in different layers. It has characteristics of simple structures a good performance in improving the robustness and stability of large-scale systems. The work of this paper concentrates on applying the concept of hierarchical control structure into the motion control of the manipulator, which comprises of the following parts:1) A double-layered control structure for manipulator motion control is proposed. The control structure is composed of planning layer and tracking layer. The planning layer designs an optimal reference trajectory for the tracking controller. The tracking layer mainly computes optimal control torque to make the manipulator accurately track the reference trajectory. We introduce the dynamic equations of the manipulator, and obtain linear equations by linearization and discretization. Based on this prediction model, constrained predictive planner and tracking controller is designed respectively corresponding to the planning layer and tracking layer.2) The double-layered control structure is applied to vibration control of flexible manipulators. The dynamic equations for flexible manipulators are created and the motion analysis is carried out based on simulations. Furthermore, the coupling relationship between flexible deformation of manipulators and rotation movement is determined. Based on this relationship, special function is added to the design of constrained predictive planner to improve the vibration control. A simulation environment is built in Matlab environment to verify effectiveness of the algorithm.3) The double-layered control structure is applied to motion control of six-degree-of-freedom manipulators. For the control objective PUMA560, the control algorithm ensures the manipulator to reach the target fast and steadily. For the disturbance in the output of the manipulator, a feed-forward control strategy is integrated into the double-layer structure. The disturbance is identified and its effects on the predicted model is evaluated and compensated in the design procedure, which accomplishes disturbance attenuation.