Safe Manipulation in Robotic Surgery Using Compliant Constant-Force Mechanism

Safe manipulation of soft tissue in robotic-assisted minimally invasive surgery (RMIS) is a challenging task for surgeons. The conventional solution is to introduce tactile sensors to measure the tool-tissue interaction force, and then transmit the signal back to the surgeon to enable manual force control. However, since the RMIS-forceps is very small, even the hand tremor of the surgeon could lead to unstable force applied to the tissue. To cope with this problem, we present a compliant constant-force mechanism (CFM) in this article to achieve stable force regulation of RMIS forceps. The proposed CFM is comprised of a pair of symmetrical compliant slider-crank mechanisms, whose mechanical behavior can be described by a pseudo-rigid-body (PRB) model. Cross-spring-based compliant joints are also introduced to improve the model accuracy, while the magnitude of the generated constant force can be adjusted by using detachable slider-crank mechanisms with different force configurations. In this work, the proposed CFM is selective-laser-sintered with polyamide (PA2200) and is actuated by a linear motor. Experiments were also conducted and successfully validated the constant-force performance of the proposed CFM. Furthermore, a grasping test of artificial artery was also performed, which demonstrated the application of the developed CFM system in RMIS.