Investigation of an indirect measurement method of ultrasonic bone cutting forces based on strain sensors

Abstract The measurement model of ultrasonic bone cutting force is an urgent problem to be solved in the application of ultrasonic osteotomy in robot assisted orthopedic surgery, which is of great significance for achieving bone layer perception and cutting force control during the surgical process. This article proposes an indirect measurement method of ultrasonic bone cutting force based on strain. Firstly, according to the axial vibration strain distribution curve of the ultrasonic osteotomy, the optimal measurement position for the strain gauge is selected as the high strain position (with a high signal-to-noise ratio), and the temperature compensation strategy of the dual strain gauge method is used to reduce or eliminate the thermal effects during the strain measurement. Then, the Pearson correlation coefficient between strain and cutting force in different cutting directions is calculated, and there is a strong positive correlation between strain and cutting force. Finally, the least squares method was used to obtain indirect measurement models of ultrasonic bone cutting force based on strain in different cutting directions. The experimental results showed that the waveform of cutting force measured indirectly based on strain was in good agreement with the waveform of cutting force measured directly by the force sensor. The error between the effective value of indirect measurement of cutting force and the effective value of direct measurement of cutting force did not exceed 13%, which verified the feasibility and effectiveness of this method. The indirect measurement models of ultrasonic bone cutting force based on strain will become a cost-effective choice with good accuracy and high sensitivity, providing a theoretical basis for orthopedic robots to perceive and control cutting force, and promoting the clinical application of ultrasonic osteotomy in orthopedic robots.