A New Family of Near-Zero Parasitic Shift Remote Center of Motion Flexure-based Pivots

Abstract

Remote Center of Motion (RCM) pivots mechanisms are 1-DOF pivots whose axis of rotation is located outside of the physical structure of the mechanism. They are widely used in surgical manipulators and precision optical-mechanical systems. This paper introduces a new family of planar mechanical linkages that generate a geometrically exact RCM. The adaptability of this linkage family is leveraged to extend the performance limits of flexure-based RCM pivots by compensating for parasitic motion, improving restoring torque linearity, and enhancing radial stiffness and angular stroke. Three planar flexure-based kinematic implementations are investigated. The first realizes an exactly constrained flexure-based RCM pivot with no second-order parasitic motion and nearly constant angular stiffness. The second exploits redundant topologies to suppress parasitic motion while increasing radial stiffness without compromising angular stroke or restoring moment linearity, thereby overcoming a longstanding trade-off in overconstrained flexure pivot design. The third enables a large-stroke flexure pivot allowing ±45° rotation without internal degrees of freedom and minimized parasitic motion. By intentionally exploiting parasitic effects, the stiffness of this large-stroke pivot can be continuously tuned. For each configuration, a direct analytical model is developed to predict its key kinetostatic properties. The models are validated through numerical simulations and demonstrate how parasitic motion can be treated as a controllable design parameter to extend the performance limits of flexure-based RCM pivots.