A Synchronized Position Control Architecture for Parallel Manipulator-based Positioning Stage of Coordinate Measuring Machine (CMM)

The structure of the positioning stage consists of two parts - the structural frame and the metrology frame. These two parts are separated from each other to resist the error interference from the structural frame to the metrology frame. The overview of the structural frame along with kinematic analysis is presented. The overall plant parameters are found analytically from the forward and inverse kinematic equations based on kinematic analysis. Based on these parameters, control architecture is designed for the movement of three kinematic sub-chains and ultimately to control the position of the positioning stage. Here this positioning stage is defined as central stage assembly (CSA). It needs the synchronous movements of three motors with the requirement of synchronization between associated joint movements in the dynamic environment. Hence, contour error analysis in a 3-D plane is crucial. For that, the contour error realization is implemented along with the tracking controller. To investigate the control architecture, implementation has been carried out in MATLAB/Simulink environment. The feed-forward control algorithm is implemented for pre-compensation of position errors of different axis before synchronization. A Synchronized controller (SC) (Cc) takes care of the synchronization effort for the overall contour tracking of the wedge plane in a cross-coupled manner.