Small Gripper Scaling Deteriorates Transparency of Telegrasping in Unilateral Robot-Assisted Surgery

To increase accuracy in robot-assisted minimally-invasive surgery (RAMIS), the movements of the instruments are often down-scaled relative to the movements of the hand-held manipulator, used by the surgeon. An important design goal in RAMIS is transparency, i.e. the actions of the surgeons are natural and similar to their movements in open surgery, and their perception is of directly interacting with the tissue. Perception of the size of an object is affected by visual illusions, and size discrimination sensitivity is proportional to the size of the objects. However, natural reach to grasp movements are robust to the perceptual distortions, and their variability does not depend on object size. We suggest that a transparent RAMIS system should maintain this disassociation between perception and action. We studied the effect of grip aperture scaling on the coordination of object grasping, and found that teleoperated grip aperture trajectories during actual and perceptual tasks are similar to natural grasping. However, smaller scaling of the mapping between finger and instrument gripper apertures deteriorates transparency and drives users to adopt a different grasping strategy.