Development of a Base-Actuated Three-Rhombus Configured Remote Center of Motion Mechanism for Lumbar Puncture

Owing to the advantages of safety and reproducibility, remote center of motion (RCM) mechanisms are widely adopted in lumbar puncture (LP) procedures to guide the insertion angle and depth of the end effector. However, the proximal-actuated pattern in existing RCM mechanisms occupies a large space near the end effector, which obstructs the visual field and increases the system inertia. In this work, a base-actuated three-rhombus configured RCM mechanism for LP operation is first proposed, where the symmetric three-rhombus scheme is designed for motion transmission. As a result, the rotational and translational motions of the needle are respectively realized through the homodromous and heterodromous actuation of the two base-mounted motors. Kinematic models are established to analyze the manipulability, singularity, and workspace of the RCM mechanism theoretically. The parameter optimization procedure is provided to minimize the footprint of the RCM mechanism. Experimental results show that the mechanism reaches an insertion angle from −29.2 deg to 29.2 deg, a maximum insertion depth of 60.02 mm, and a footprint of 4.98 × 10⁴ mm². The relative error of the RCM point is 1.1 mm.