Feed-forward pressure control of balancing cylinder for hybrid electric-pneumatic ultra-precision vertical positioning device

Abstract

One of the positioning methods in vertical direction of machine tools, a hybrid electric-pneumatic ultra-precision vertical positioning device has been developed and utilized. In this method, because the weight of the stage is supported by the pneumatic pressure of the balancing cylinder, the linear motor can drive the stage motion without so much affected by the weight of the stage. Therefore, lower electric energy consumption, less heat generation, higher power and speed, can be expected with the linear motor. However, hybrid electric-pneumatic ultra-precision vertical positioning device has a drawback. When the tool change occurs, the total weight of the stage changes. Then the pressure in the balancing cylinder should be adjusted accordingly. But the pressure adjustment takes a bit of time with the conventional method that uses a diaphragm type pressure regulator. In this paper, in order to enhance the performance of the hybrid electric-pneumatic ultra-precision vertical positioning device, a new pressure adjustment method in the balancing cylinder when the tool change occurred is proposed. The proposed method utilizes a feed-forward control and a high precision quick response pneumatic regulator (HPQR) that was developed in our previous research. By the experimental results using a hybrid electric-pneumatic ultra-precision vertical positioning device, the validity of the proposed control method is evaluated and its superiority is indicated.