Estimation of Milling Forces From Compliant Sensors Using a Harmonic Force Model and Kalman Filter

Force transducers such as the piezoelectric Kistler dynamometer and the wireless strain gage Smart Tool are used to monitor the cutting force during CNC machining. Due to sensor dynamics, there are differences between the actual cutting force and the measured force, characterized by phase delay and additional vibrations in the cutting profile. In this work, actual cutting forces are estimated from the measured sensor data using a Kalman filter. Since cutting forces are composed of harmonics of the tooth passing frequency and runout frequency, both a sensor dynamic model and harmonic cutting force model are included in the Kalman filter model in order to improve performance of the filter. The harmonic computations of the measured cutting force are used to self-tune the Kalman filter. Comparisons between the measured and estimated force show the ability of the Kalman filter to reduce sensor vibration and noise with no phase delay.