Design and analytical modeling of a double-joint flexible surgical instrument with hand-held isomorphic actuation

In catheter reduction surgeries, surgical instruments with multi-joint end effectors are employed to improve surgery qualities, where implementations of miniaturization design and isomorphic actuation are challenging. In this work, a miniaturized double-joint end effector is designed using a novel multi-backbone mechanism. The backbones are made of spiral-notched tubes that have good axial stiffness and large bending flexibility, and a co-placed backbone arrangement is used to avoid double-joint actuation coupling. A double-joint handle is developed to implement isomorphic actuation of the end effector, where local reinforcement design of the handle is proposed to reduce torsional disturbances on the end effector. A recursive kinematic model of the multi-backbone mechanism is firstly established by relating friction with bending angles in a beam model of the backbones, and forward kinematics from the handle to the end effector is developed. Performance tests show that the double-joint end effector has good actuation decoupling characteristics. Parameter identification is conducted and model accuracy is validated. Phantom model experiments show that the end effector can reach the target position with the double-joint configuration.