A Passive Force Amplifier

The proposed robotic system provides the surgeon with an augmented sensation of the interaction forces between the instrument and the organ. Such a system aims at increasing the surgeon's dexterity for tasks requiring that only small forces be applied on the organ (eg. for micro-surgery). In the proposed setup, the surgeon manipulates a handle mounted on the instrument. This is a comanipulation system because the surgeon and the robot simultaneously manipulate the instrument. The proposed control scheme allows an augmented force control: the control law ensures that the instrument applies on the organ the same forces that the surgeon applies on the handle but decreased by a scale factor. As a consequence, the forces sensed by the surgeon are the forces between the instrument and the organ amplified by a scale factor. This control scheme is proved stable thanks to a passivity study. Indeed, passivity analysis is a useful tool for the stability analysis of a robot interacting with the environment. Experimental results are presented on a robot dedicated to minimally invasive surgery.