Development of an optimized smart tool holder using symmetrical structure for three-axis cutting force measurement in diamond cutting

Cutting force measurement is an important technique for monitoring the machining process in diamond cutting. This paper presents an optimized smart tool holder using the symmetrical structure of a fast tool servo (FTS) for three-axis cutting force measurement by utilizing six piezoelectric force sensors. The cutting force along each axis was measured by using the differential result of two sensors to eliminate the influence from environmental noise, bias current of charge amplifier, and temperature drift on the measured forces. The symmetrical structure of the tool holder was designed based on a flexible hinge, and the theoretical model was constructed and optimized for high stiffness and low coupling. An improved algorithm combining differential and dynamic accumulation method was developed for stable and accurate static force measurement. Tests were carried out to verify the effectiveness of the algorithm in improving the stability and accuracy of output voltage and static force measurement. The results demonstrated that the influence from environmental noise, bias current, and temperature drift on measured force could be effectively reduced. Subsequently, the smart tool holder was integrated on an FTS for cutting experiments. Compared with a commercial dynamometer, the proposed tool holder system was verified to have excellent performance of high sensitivity and high accuracy in three-axis cutting force measurement, and have capacity of identification of nanometric scale microdefects.