Development of a Non-contacting Capacitive Displacement Sensor for Integrated Chatter Prediction on High Speed Machining Centers

Abstract

Chatter is an unstable forced vibration of the cutting tool during machining processes that can limit the productivity of high-speed machining. Chatter increases tool and machine wear rates, reduces tolerances, degrades surface finish, and can result in tool breakage. For these reasons, its avoidance is critical. Researchers at N.C. State University are focusing on the development of technologies to detect and avoid this dynamic instability. The primary objective of this project is to develop accurate, high bandwidth, low cost capacitive displacement sensors for use with a prototype electromechanically actuated chatter prediction device. These application-specific sensors are required to have at least 1.0 µm resolution, 1.0 kHz bandwidth, and linearity over the desired measurement ranges. These sensors must output analog DC voltages proportional to the vertical and horizontal displacements of a specifically engineered machine tool. A simulation-based design process is utilized to optimize the mechanical and electrical aspects of these capacitive probes, the electrical circuits, and the mechanical mounting hardware. Performance and stability are simulated using MATLAB® and SPICE® modeling software and are validated experimentally using static and dynamic test rigs.