Design of SMA micro-gripper for minimally invasive surgery

Application of robotic instruments in minimally invasive surgery (MIS) has been developing in recent years. The urge to implement biocompatible and less invasive devices found way in use of materials like shape memory alloys. However such designs presented the idea of using heat control actuation in the MIS surgery and some have found noticeable position in robotic surgery. Yet the problems relating to insufficient stroke, slow motion and unfavorable generated heat have to be defeated. In this work it is focused to overcome these problems by a new design. Modern SMA grippers take advantage of two techniques: Net SMA and Spiral SMA. Both of these actuators demand application of high electric power to raise the wire temperature, which consequently is accompanied by heating of the gripper, slow actuation, etc. While in this paper, we propose the use of one SMA braided-wire in a spiral sheath cut inside the covering tube capable of using longer SMA wire. The outer diameter of the gripper is 3 mm with the total length of 9.5 mm. It demands less electric pulses to actuate, easily controlled and is applicable in heart surgeries with limited trocar aperture. The other design features together with the complete simulation of the device are addressed in the article. A full scale prototype of this SMA gripper capable of using in operation room will be produced by the end of year 2012.