Strain gauges attached to the driving pulleys of the instrument of surgical robots allow estimation of the torque between the instrument and environment. Transmission of torque applied to the instrument tip is analyzed, and the result confirms that the friction and the gap existing between the driving pulleys and the torque sensor are significant factors inducing estimation error. Characteristics of the friction in each degree-of-freedom also vary.
This paper attempts to provide better estimation of the interaction force and torque between the instrument and environment in multi-degree-of-freedom motion. The gap is eliminated by incorporating the torque sensor into a single part. This torque sensor is designed base on the beam theory. Performance test of designed torque sensor such as linearity, hysteresis is carried out. The characteristics of the friction are analyzed by comparing the torque estimated from the strain gauge and the torque actually measured at the instrument tip. It can be confirmed the direction of the wrist motion should be considered to estimate grip torque in the multi-degree-of-freedom motion. A friction model is developed based on Dahl model and reflects the characteristics of the particular driving mechanism.
Contact experiments using springs that simulate the elasticity of a tissue interaction are performed to verify the accuracy of the proposed model. The each pulley is driven to motion of a sine wave in single-degree-of-freedom motion. The results show relative error of roll, wrist, right grip, left grip torque can be reduced to 8.43%, 1.89%, 3.49%, 1.37%, respectively. The pulleys corresponding to wrist and right grip motion are driven to the motion that mixed with sine, constant, linear, quadratic, and logarithmic functions in multi-degree-of-freedom motion The results show relative error of wrist and right grip torque can be reduced to 1.34%, 2.34%, respectively.
본 논문에서는 로봇 수술 시 의사에게 신뢰성 높은 햅틱 감각을 제공해주기 위해 수술용 기구와 인체 조직 간 발생하는 다자유도 상호작용 힘과 토크 추정의 정확도를 향상시키는 방법에 대하여 논의한다. 수술용 기구의 메커니즘을 자유물체도를 그려 분석한 결과 구동 풀리에 가해지는 토크를 측정하여 상호작용 힘과 토크를 추정할 때 토크 센서의 유격, 마찰이 오차 요인임을 확인하였다. 센서의 유격은 빔 이론을 기반으로 한 일체형의 토크센서를 제작함으로 해결하였고, 마찰모델은 토크센서로 수술용 기구의 말단의 토크를 추정한 결과와 직접 말단에 가해지는 토크를 측정한 결과를 비교함으로써 실험적으로 도출하였다. 수술용 기구의 각 자유도 별로 접촉 동작 실험을 수행한 결과 제안된 마찰모델로 보상하여 추정한 토크의 오차가 최소 1.37%, 최대 8.41%임을 확인하였다.
