A model based feedforward regulator improving PI control of an ice-clamping device activated by thermoelectric cooler

Ice-clamping devices are of great advantage in deformation-free and sustainable workpiece clamping by using frozen water to fix pieces during machining operations. The adhesive bonding of ice generates high forces, encapsulating the piece form-fitted around and underneath its surface. The freezing is generated by thermoelectric coolers (TECs), placed under a clamping plate. The colder the plate is chilled, the higher the total forces of ice bonding are, guaranteeing a secure grip during machining. However, process heat generated by machining tools pose the risk of thawing the ice, illustrating an external disturbance which is needed to be controlled. Traditional control strategies for TECs use PID algorithm due to its simplicity. To attenuate disadvantages of a PID controller, such as oscillations, overshoots and settling time as well as to attain a better performance and robustness in the presence of parameter uncertainties and disturbances, a model based feedforward regulator including Anti-windup method is proposed additionally to a PI controller for the nonlinear thermal system. Furthermore, a technical requirement is formulated mathematically proving the existence of a structural stability of the thermal system. Simulation results, performed in MATLAB Simulink, are shown and are validated with experimental data.