A new circular-guided remote center of motion mechanism for assistive surgical robots

Remote center of motion (RCM) mechanisms are widely used in surgical robots to mechanically constrain the position of a certain point in the operation space. Examples of well-known RCM mechanisms include parallelogram mechanisms, spherical linkages, circular guiding arcs, etc. In this paper, a reinforced circular-guided RCM mechanism is presented. In the mechanism, a closed-looped circular-guiding arc instead of an open-looped one is used to improve rigidity. In addition, with this linearly-actuated RCM mechanism, we can avoid moving the actuator along with its link. This provides an alternative to the use of tendon-driven mechanisms. The proposed mechanism is then further extended to a 3-degree-of-freedom (DOF) configuration for surgical robots. In contrast to most applications where the RCM is designed to be placed out of the patient´s body, our new RCM is designed to be placed inside body, which is more preferable in some applications, for example, uterus positioning during laparoscopic hysterectomy. In this paper, the design, dynamic model, static analysis and the extended application of the linearly-actuated-arc-guided RCM mechanism is presented. A prototype is built to validate the feasibility of the mechanism and experiments are conducted.