1987 Volume 5 Issue 2 Pages 87-101
Today the endoscope has become an indispensable inspection tool in the field of medical diagnosis and engineering non-destructive test. However the conventional type endoscope is not flexible enough so as to be inserted with ease inside narrow and complex path. In case of the fibersigmoidoscope, one of the typical example of the endoscope, the limited flexibility causes a great amount of pain to the patient and requires special skill to the doctor in its operation inside the lower intestine. The limited flexibility is caused by the fact that the fibersigmoidoscope has manipulatable segments only on its tip end and the rest of the stem have to follow the shape of colon by deforming itself using the force reaction from the colon wall.
The purpose of this paper is to realize what we call an“active endoscope”, the endoscope with the stem all of which can be actively manipulated, by using Shape Memory Alloy (SMA) actuators.
The paper first clarifies the basic characteristics of the SMA from the standpoint of its application for the servo-actuator. The simultaneous measurements of four parameters, i. e. temperature, stress, strain and electric resistance of SMA are done. The results of the SMA's four parameters are expressed in a newly introduced diagram. Based on the measurements, other diagram named temperature-stress phase are derived and the effect of the phase transformation is evaluated for the SMA's actuation performance.
The optimal operational and annealing conditions of the SMA are made clear. The specifications of the formally proposed SMA servo actuator based on its electric resistance feedback are improved and some of the fatigue problems are solved by using these considerations.
Based on these basic experiments and considerations, a prototype model of the active endoscope with SMA are constructed. It is 13 mm in diameter, 215 mm in length and consists of 5 active segments with array of SMA coil springs as the servo actuator under micro computer control. Each segments has 60 degree of maximum bending angle. Fiber optics are mounted at the core of the endoscope. By the joystick control of the front segments and coordination control of all the segments to shift the bending signals from tip end to the rear by the computer, the SMA active endoscope showed smooth insertion motion inside model colon path. The validity to realize the SMA active endoscope is thus demonstrated.
