Study of Pneumatic Servo Loading System in Double-Sided Polishing

Abstract

The precise double-sided polishing process is one of the main methods to get the ultra-smooth surface of workpiece. In double-sided polishing machine, a loading system is required to be able to precisely control the load superimposed on the workpiece, while the polishing is being carried out. A pneumatic servo loading system is proposed for this purpose. In the pneumatic servo system, the servo valve, which acts both the electrical to mechanical converter and the power amplifier, has a substantial influence on the performance of the loading system. Therefore a specially designed pneumatic digital servo valve is applied in the control system. In this paper, the construction of the pneumatic servo loading system in double-sided polishing machine and control strategy associated with the digital servo valve are first addressed. The mathematical model of the system established and the hardware of the pneumatic servo system is designed. Finally, the experiments are carried out by measuring the practical load on the workpiece and the quality of the surface finish. It is demonstrated that the error rate of load is less than 5% and a super-smooth surface of silicon wafer with roughness Ra 0.401 nm can be obtained.