Determining the threshold of time-delay for teleoperation accuracy and efficiency in relation to telesurgery

Advances in robotics have made teleoperated surgical procedures a feasible means of treating patients in remote locations. In this study a suite of experiments was performed to investigate the influence of time-delay on teleoperation accuracy and efficiency during a path-following task.

Subjects used a Phantom Omni 6-degrees of freedom (dof) input device (Sensable, Triangle Park, NC) to move the end-effector of a Mitsubishi (Tokyo, Japan) PA-10 7-dof robotic manipulator along a prescribed path. End-effector motion was recorded using a video motion capture system. Time-delays ranging from 0 to 2.5 s were artificially imposed. Performance was quantified by time to complete the task, path length, and square root-mean-square (RMS) error. Randomization of time-delay order and allowance for practice runs reduced the learning effect. An imposed time limit and pacing were used to negate the move-and-pause strategy that emerged in early trials.

Time to complete the task and RMS error generally increased with increasing time-delay. Path length also generally increased, but not as consistently. With imposed pacing, RMS error continued to increase beyond 1.5 s, and some subjects were not able to complete the task in the allotted 90 s.

The results suggest a threshold of time-delay in the range of 1.5-2.0 s. Beyond 1.5 s, subjects adopted a move-and-pause strategy that increased completion time to preserve path-tracking accuracy. If paced, tracking accuracy tended to degrade substantially beyond 1.5 s. A strong learning effect was evident, and experienced teleoperators performed substantially better than novices.