Design, prototype and control of a 3R1T robot with RCM for eye surgery

Minimally invasive surgery has significantly improved patient outcomes but, access to ophthalmic procedures such as cataract surgery remains constrained by high skill requirements and a limited number of surgeons. Eye surgery is particularly challenging due to physiological tremor, limited dexterity, and the fulcrum effect, which compromise precision. Robotic systems incorporating a remote centre of motion (RCM) can stabilise instruments and enhance precision, yet robotic eye surgery remains an unsolved challenge. This thesis presents the design, development, and experimental validation of a novel 3R1T parallel robot with distant RCM. A comprehensive literature review identified a clear gap in the state of the art. There are no reported 3R1T spherical parallel mechanisms (SPM) with coaxial input shafts, a distant RCM, and all actuators mounted on the base. Eleven key design requirements were derived through clinician engagement, surgical observation and video analysis. Based on these requirements, a 3R1T robot providing three rotational (3R) degrees of freedom for tool orientation and one translational (1T) degree of freedom for insertion was designed, prototyped and controlled. Forward and inverse kinematic models were developed, alongside singularity analysis and dimensional synthesis, confirming the presence of an RCM and a singularity-free workspace during normal operation. To address the stringent geometric constraints inherent to parallel RCM mechanisms, an error model and a novel metrology-assisted fabrication and assembly methodology were developed and implemented. This approach ensured the RCM geometric constraints were maintained within ±0.052 mm. A physical prototype comprising 62 bespoke components and 341 standard parts was manufactured and assembled. A new dynamic motor-sizing methodology was also introduced to account for varying load conditions across the robot’s operational cycle. Hardware and control integration was achieved using a MicroMACS6 master controller and EPOS4 motor controllers communicating via CAN, with a preliminary control strategy implemented in Cyclic Synchronous Position mode. Experimental evaluation demonstrated ±40° pitch and yaw rotation, a 50 mm translational stroke, and tool orientation repeatability of ±22.86 μm. This performance is superior or comparable to reported results from existing surgical robotic systems and meets the workspace and precision requirements for cataract surgery. The results demonstrate that the proposed 3R1T parallel robot is a viable and promising platform for robotic eye surgery. The thesis concludes by identifying current limitations and presenting a structured roadmap for future development towards clinical deployment. Thesis is embargoed until 31 July 2031.