Novel block mechanism for rolling joints in minimally invasive surgery

This study developed a rolling joint including blocks to improve the stiffness of a manipulator. We defined the design parameters of the block mechanism and derived the joint moments when an external force is applied to the distal link of the manipulator. As the joint moments were not zero at the initial position, the equilibrium position for minimizing the joint moments was calculated via sequential quadratic programming in Matlab. We found that the design parameters affected the manipulator displacement and optimized them to minimize the displacement using the complete enumeration survey method. The stiffness calculated using the displacement of the optimized block mechanism was 47.3% to 268.2% higher than the conventional rolling joint on changing the operating cable tension and external force during simulations. Furthermore, we fabricated the prototype and validated the stiffness improvement of the manipulator experimentally. Although the required tension to move the block increased slightly because of friction, the stiffness of the block mechanism was 140.4% to 353.9% higher than the conventional rolling joint under the same external force and cable tensions. (C) 2020 Elsevier Ltd. All rights reserved.