Design and Characterization of a Novel Hybrid Actuator Using Shape Memory Alloy and DC Micromotor for Minimally Invasive Surgery Applications

The end-effectors in the state-of-the-art robotic tools for minimally invasive surgery (MIS) are actuated by actuator packs located outside the patient's body, with the power transmitted from the actuator pack to the end-effector by means of sliding link or tendon-driven mechanisms. This method of power transmission limits the number of degrees-of-freedom (DOFs) in these systems, as the design of a spherical wrist gets complicated. The design of the spherical wrists can be simplified, and the number of DOFs increased, if local actuation is used for the end-effector. However, there are no suitable actuation systems available in the literature. In this paper, a novel design idea for developing a millimeter-scale actuator is presented for locally actuating the end-effector (5-mm-diameter laparoscopic needle driver) for a robot performing MIS. This actuator is designed by combining a dc micromotor and a shape memory alloy actuator in series. The designed actuator is 5.14 mm in diameter (including casing) and 40 mm in length, and is used to actuate a 20-mm-long needle driver assembly, while generating a force of 24 N, resulting in a gripping force of 8 N. The total stroke length of the actuator is 1 mm, which results in a 45 $^{\circ}$ opening of the needle driver jaw with a gap of 8 mm in between the jaws.