Design and analysis of a novel metamorphic remote-centre-of-motion mechanism with parallelogram joints

Owing to their movements through a fixed point, remote-centre-of-motion (RCM) mechanisms can be widely used in applications such as surgery robotics, exoskeleton robots, haptic devices, pointing mechanisms. Most existing RCM mechanisms only have a constant mobility and RCM point. To adapt to more situations with variable motion requirements, a novel metamorphic RCM mechanism is proposed in this paper based on an analysis of the fundamental methods for metamorphic and RCM mechanisms. The mechanism is composed of two limbs with parallelogram joints and has three motion branches with different RCMs and two furcation points. The screw constraint multisets of the end-effector are utilized to analyse the mobilities and motions of reconfigurations by spanning different screw constraint systems. For the two furcation points and three motion branches, kinematic models and branch transformations are established. In addition, one actuation arrangement and its combined Jacobian are proposed and analysed. The workspace with no singularities except for the furcation points is shown at the end. The mechanism can move with three types of RCMs, which expands the design method of both RCM and metamorphic mechanisms.