Development of a shape memory alloy actuator. Measurement of material characteristics and development of active endoscopes

Endoscopes are nowadays playing a very important role in the medical and industrial fields, and will further increase their importance and applications if they are provided with more flexibility or freedom of flexure at probing into, for instance, human internal organs. The purpose of this study was to realize more pliable endoscopes which can be actively operated by using a shape memory alloy (SMA). First, the characteristics of an SMA as an actuator are clarified in this paper. For this purpose, four variables of temperature, stress, strain, and electrical resistance are measured simultaneously on SMA coil spring samples. Subsequently, a new method is introduced to express the measured characteristics, and temperature-stress diagrams are drawn so that conditions of optimal use and heat-processing can be determined for using SMA as actuators from the viewpoint of phase transition. Based on analytical techniques, the resistance feedback characteristic is enhanced and the fatigue problem resulting from the...