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Owing to the advantages of safety and reproducibility, remote center of motion (RCM) mechanisms are adopted in lumbar puncture (LP) procedures to guide the insertion angle and depth. However, the proximal-actuated pattern in existing RCM mechanisms occupies 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 the LP operation is firstly proposed, where the symmetric three-rhombus scheme is designed for the motion transmission. As a result, the rotational and translational motions of the mechanism are respectively realized through the homodromous and heterodromous actuations of the two base-mounted motors. Kinematic models are established to analyze the manipulability, singularity, and workspace of the RCM mechanism theoretically. 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° to 29.2°, a maximum insertion depth of 60.02 mm, and a footprint of 4.98 × 104 mm2. The maximum error of the RCM point is 1.1 mm.

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