Medical and welfare applications of shape memory alloy microcoil actuators

We have successfully developed several mechanisms using Ti-Ni shape memory alloy (SMA) microcoil actuators, for example, a bending mechanism, an extension/contraction mechanism, a torsional mechanism and a stiffness control mechanism. The principles involved in these mechanisms and the structure of each mechanism are detailed, and medical and welfare applications are presented. One of the devices which has been developed is an active bending soft tube using an SMA microcoil actuator. Doctors can control the bending motion of the tip of the tube from outside the body. One application of this tube is the treatment of intestinal obstruction. The tube consists of a bending tip (external diameter, 6 mm; length, 40 mm) and a 3 m long silicone rubber tube. It enables easier and more reliable passage at the lower end of the stomach (pylorus). The maximum bending angle is 110 degrees. Another device we have developed using SMA microcoil actuators is a dynamic tactile pin display which displays Braille characters and graphic information by dynamic up-and-down movement of an array of pins. SMA microcoil actuators enable up-and-down movement of the pins and a magnetic latch mechanism keeps the pins in an up or down state. This two-dimensional pin display consists of 100 (10 x 10) pins with a pin pitch of 2.5 rum, the actuation length of each pin being 2 mm. The tactile information can be displayed sequentially every 0.3 s.