Frictional torque characteristics of PFPE lubricated ball bearings under oscillatory motion in vacuum

Using a pointable observation sensor, the Greenhouse Gases Observing Satellite (GOSAT) monitors greenhouse gases from space. During observation operations, an anomaly occurred in which the settling time of the pointing mechanism worsened due to an increase in the frictional torque of the ball bearings caused by repetitive small-angle oscillations. To suppress this, four types of ball bearings lubricated with a perfluoropolyether oil were subjected to 1.5–2.0 × 10 7 cycles of oscillation in vacuum with different oscillation angles, and the frictional torque characteristics were investigated. It was found that a bearing using spacer balls instead of a cage slightly suppressed the increase in frictional torque due to oscillation compared to a standard bearing with 440C stainless steel balls and a cage. The test showed that changing the ball material from 440C stainless steel to silicon nitride could suppress the increased frictional torque. In addition, reducing the ball diameter and the contact ellipse between the balls and rings could suppress the increase in frictional torque.