A Soft Inflatable Cable-Driven Parallel Robot with A Variable Stiffness End-Effector for Advanced Interventional Endoscopy

Objective: This paper presents a cable-driven parallel robot (CDPR) with a variable stiffness end-effector for Advanced Interventional Endoscopy. Methods: The CDPR consists of a soft inflatable scaffold that is made from plastic laminate sheets, capable of deploying into a hollow triangular prism. The end-effector comprises multiple units linked by two cables, which also actuate the rolling joint on the end-effector tip. Variable stiffness of the end-effector is achieved by adjusting the tensions in the two cables. Results: Through master-slave control tests, the mean manual tracking error of the robot is approximately 0.5 mm. Simulated endoscopic surgical tasks, including peg transfer, wire threading, and needle threading, demonstrate the robot's performance. Additionally, the two cables double up as force-transmission elements to estimate the contact force acting on the end-effector tip. A force estimation strategy is proposed, and preprogrammed palpation tests reveal a mean force estimation error of 0.026 N when the cable pretension is 1 N and the Bowden cable's bending angle is 90°. A study involving ten users indicates a 100% accuracy in ranking the stiffness of four blocks with visual feedback. Conclusion: We demonstrated a variable stiffness end-effector with rolling degree of freedom and force sensing function based on a CDPR platform. Significance: The method for achieving variable stiffness and force sensing is cost-effective and holds significant potential for application in gastrointestinal endoscopy.