Development and Characteristics of Servo Motor for Use under High Temperature and Radiation Flux Conditions

Abstract

Recently, robots have been required to inspect the insides of nuclear reactors with an environment of high temperature and radiation flux. In a FBR (fast breeder reactor), the viewing system of the robot is particularly important because the reactor vessel of the FBR is filled with opaque liquid sodium. To drive the robot, servo motors have to meet such special requirements. Above 220°C, organic materials cannot maintain their properties for long periods. In addition, the air gap length of the motor varies, because metals expand at high temperature. Thus, the characteristics of induction motors with an air gap length of 0.2_??_0.4 mm may vary. Furthermore, the rotor may come into contact with the stator.
In this paper, a newly developed permanent magnet motor which can withstand high temperature and radiation is presented and the characteristics of the motor at high temperature are discussed.
Coils which wind ceramic magnetic wires are installed in the stator. Sm₂Co₁₇ permanent magnets are embedded in the rotor yoke. This motor is suitable for application at up to 400°C because of the use of inorganic materials. In addition, the permanent magnet motor can have a long air gap length, which has little effect on the characteristics of the motor.
The test results show that the motor has excellent characteristics at high temperature.