手持式脊椎微創手術機器人結合力量感測之伺服控制

Abstract

本實驗室將所開發之六軸史都華平台手持機器人結合電腦輔助導引系統，用於補償椎弓釘植入手術之手術器械與病灶徒手對位時因非自主性的手部偏移與振顫所造成的對位誤差。本研究將手持機器人之影像伺服層與馬達伺服層進行控制系統改良，使馬達輸出能夠平滑化以減少回饋給操作者手部的反作用力並提升機器人追蹤性能以補償徒手對位時之誤差。首先針對底層馬達伺服控制系統重新設計，透過對六軸史都華平台進行摩擦力分析建模與補償、系統鑑別、與控制器設計，並透過電腦模擬與實驗來驗證其伺服性能。影像伺服層則針對光學量測儀量測訊號進行分析，並以非線性濾波方式減少量測雜訊之影響。最後透過安裝於機器人末端致動器上之力量感測器量測鑽頭與接觸面的力量回饋，將機器人末端致動器模擬成質量阻尼彈簧之阻抗控制系統順應外力而伸縮，使鑽頭沿著接觸面到達下鑽點與減少接觸面給予之反作用力。實驗證明機器人開啟補償功能後能夠減少約50%的誤差，其方均根誤差小於1 mm。加入力量控制後亦使鑽頭著陸時操作者手部不會因為接觸面反作用力造成機器人偏移，提升手持機器人之操作容易度與穩定度，以達到精準定位與穩定下鑽的能力。

A handheld Stewart platform-based surgical robotics manipulator for minimally invasive surgery (MIS) pedicle screw placement was previously developed by Robots and Medical Mechatronics Lab (RMML), National Taiwan University and combined with computer-aided surgical (CAS) system. The handheld robot is used for compensating the position error between a surgical tool and a planned path that results from the involuntary hand offset and tremor of a surgeon. In this research, the visual servo loop and motor servo loop were improved to smooth the motor outputs and reduce the reaction force fed back to operator’s hand. In this research, the motor servo system was redesigned first by friction compensation, system identification, and trajectory planning, improving the transient tracking performance and reducing the steady-state error of robotics manipulator. Second, the measurement noise of an optical tracker in the visual servo system was analyzed and was suppressed by a non-linear filter. Finally, the force feedback between the drill bit and the contact surface was measured by a force sensor installed on the end effector of the robot. The end effector of the robot was simulated as a mass-spring-damper system to reduce the contact force and kept the drill bit move along the contact surface. The experiment results show that the error between the drill bit and the path was compensated and reduced by about 50%, and the root mean square error was less than 1 mm. The robot and operator’s hand were not shifted due to the reduction of the reaction force under force control when the drill bit contacting with the surface.