Safety Motion Control and End Force Estimation Based on Angle Information in Robotic Flexible Endoscopy

Precise motion control and clear contact force information play an important role in robot-assisted endoscopy. It allows the surgeon to estimate soft tissue stiffness, understand the anatomy, and enables the robot to perform the surgeon’s movement intentions more accurately. However, the ability of surgeon to perceive contact force information and motion status through the flexible endoscope is severely impaired. In this work, we proposed a rotational joint with torque estimation functions based on angle information to achieve the motion control and end force estimation of the flexible endoscope during the robot-assisted endoscopy. Furthermore, the joint consists of two wheels, which are connected with cables and springs. And then, two encoders have been utilized to check the joint positions. In the meantime, a feedforward PID control strategy has been proposed to realize an accurate position control for the designed joint. According to the force estimation study, the perception performance of the proposed joint was characterized with an excellent linearity error (0.53%), a high resolution (7.778 × 10–3 $${\text{N}} \cdot {\text{mm}}$$ ) and a wide measurement range ( $$- 500{\text{ N}} \cdot {\text{mm}}$$ to $$+ 500{\text{ N}} \cdot {\text{mm}}$$ ), while the tracking performance demonstrates high sensitivity of the control strategy. The proposed joint has the capability to observe the external interference by estimating the change of the torque. Thus, the proposed method has important application potential in force detection, force feedback and control strategy with enhanced safety during Natural Orifice Transluminal Endoscopic Surgery (NOTES).