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Utilization of 2N +1 Units for 2-DOF Discrete Bending Joint to Transmit Perfect Axial Rotation for Laparoscopic Instruments

Jungwook Suh
International Journal of Control, Automation, and Systems, vol. 18, no. 1, pp.186-195, 2020

Abstract : Laparoscopic instruments, which have traditionally been long and straight, have been equipped with wrist joints for executing complex procedures. Among the many methods for constructing a cable-driven wrist joint for such instruments, the use of pulleyless rolling unit joints has recently been demonstrated to be effective and applied to various surgical robots. Although it is a common practice to alternately stack 2N one-degree-of-freedom (1-DOF) units to form a 2-DOF bending joint, it is cumbersome to determine the optimal stacking sequence, and the determined sequence might not satisfy performance requirements. Therefore, in this paper, we propose a new method to construct a 2-DOF discrete bending joint by using 2N +1 units. The advantages of the proposed method over the previous method of determining the optimal structure by using 2N units are demonstrated quantitatively through kinematic modeling and calculation. As a result, the behavior of the proposed discrete bending joint becomes increasingly similar to that of a continuum joint as the number of units employed in the construction increases. In addition, it is confirmed that the 2N +1 model can accurately transfer proximal rotation to the distal tip, similarly to a constant velocity joint. It is expected that the proposed simple method for constructing bending joints will be applied to develop various surgical robot structures in the future.

Keyword : Continuum joint, discrete bending joint, isotropic bending, laparoscopic instrument, stacking sequence, surgical robot, 2N +1 unit joints

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