In laparoscopic surgery, forceps are stuck through trocars into the abdominal cavity, and dissect and grasp internal organs. Because of their straight shapes, the current forceps suffer from the narrow range of operation and limit the skill of surgeons. In this paper, we propose active forceps actuated by unconventional use of shape memory alloy. In developing active forceps, we utilize two properties of shape memory alloy, shape memory effect and super elasticity The forceps possess both stiffness for transmitting operation forces from surgeons and flexibility in changing their shapes.

Power grasp is redefined as a type of grasp that its mechanism can resist passively against external forces without relying on feedback control of joint torques. A computational algorithm is invented to calculate the critical external force, a force which is requisite to move the grasped object in a definite direction. Virtual work is proposed as the quality measure of the robustness of power grasp. Because this measure is a scalar, it is convenient and suitable for the planning of power grasp. The effectiveness of the computational algorithm of critical external force and quality measure of robustness of power grasp is verified with a numerical example.>