CHARACTERISTICS OF UHV STEPPING MOTORS

Characteristics of an ultrahigh vacuum (UHV) stepping motor have been examined for practical use. The temperature rise of the motor in the energized-and-rest condition was measured as a function of the coil current. The result showed that it is approximately proportional to the electric power fed to the coil. The outgassing from the motor increased significantly at temperatures above 100-degrees-C. The components of the released gas were the usual species in vacuum such as H-2, H2O, CO, CO2, and hydrocarbons. Initially a small amount of NH3 was also observed at temperatures higher than 150-degrees-C. This gas might originate from a small amount of the epoxy resin used for bonding the rotor and the permanent magnets. It decreased rapidly during the test operation. In the running mode, the outgassing of H-2, CH4, H2O, CO, and CO2 increased with the revolution rate. The amount of the H-2 released from the motor with the silver-ion plated ball bearings was larger than that with the MoS2 coated ball bearings. The lifetime of the MoS2-coated ball bearings was longer than that of the Ag ion plated ones.