The Development of an Displacement Sensor Embedded Voice Coil Motor Based Fast-Tool-Servo for the Machining of Micro-Structure

Abstract

The Fast Tool Servo (FTS) is widely used for the machining of micro-structures, especially for optical micro lens array. The working principle of FTS is that a voice coil motor or a piezoelectric (PZT) actuator is used as the driving elements, and the flexure hinges are developed as the guide mechanisms. In addition, an optical encoder is applied to measure the displacement. However, the existing design of FTS is too complicated and expensive. One reason is that the stroke of the FTS for the fabrication of optical micro lens array is only a few hundred micrometers, while its precision reaches to nanometric range, thus the optical encoder in not applicable. On the other hand, there exists sluggish and creep for piezoelectric materials, which makes the control of displacement difficult. This paper develops a displacement sensor embedded voice coil motor. In the design, the driving element is ampere force of the voice coil motor which is a linear ratio to the input current. Both the two covers are thin plates which serve as compliant mechanism by supporting the deformation at the Radial direction and provide linear stiffness in the axial direction. Therefore, the output displacement is proportional to the ampere force. The existence of external force affects the actual displacement, an embedded capacitor serves as displacement sensor will detects the real displacement, and the external force can be estimated by the current and measured displacement, which makes the motion control easy. At the same time, a multiphysics model of the developed FTS is built in this study by using finite element method and the displacement control under different cutting force is studied. The experimental results show that the developed FTS is efficient for achieving short stroke with high precision.