Robotic Relay of Free-Space Optical Beams for Medical Applications

Abstract

Medical robotic laser systems require precise positioning and movements to control laser beam paths associated with sensors and other optical systems in many applications (e.g., laser surgery, laser-based tissue diagnosis). While existing robotic laser beam control systems were developed for microscale control to achieve highly precise steering and focusing, they assume a single robot which is limiting in applications where the beam path must cover large areas and angles (e.g., 360-degree full-view object scanning). To expand imaging flexibility, we propose a novel robot-mirror framework to use robot-attached mirrors to control a 3D free-space laser beam, which is referred to as “N-mirror-N-robot system” where N is the number of mirrors and robots. This framework allows for general laser beam planning to trace targets based on geometric constraints of 3D obstacles and fixed orientations and positions with unlimited number of robot-and-mirror combinations. We develop a prototype for the special case with a single mirror attached to the robot (N = 1). This prototype integrates an RGB-D depth camera for object tracking, a 6- DOF robot-attached mirror, and a laser diode source. We propose a computational framework for system kinematics and calibration. Simulation and real experiments are conducted to track specified paths, markers, phantoms, and real tissue to verify the system feasibility. The results show an average object tracking error of approximately 2.0 mm that is close to the depth accuracy of the camera. This N = 1 prototype shows promise for N > 1 case and the potential for general 3D laser planning under arbitrary geometric constraints.