Mechanical shocks caused by brakes on electric motors

When a mechanical brake on an electric motor engages or releases, a damaging shock load is generated (brake shock). The shock propagates through the motor and harms electric components, particularly rotary encoders. According to the current state of science, brake shocks are not sufficiently understood. Therefore, in the first part of this paper, the mech-anisms and influencing factors of brake shocks are analysed. It is also shown that brake shocks are comparable to pyroshocks in key aspects. In the second part, it is reasoned that current shock testing procedures do not consider the special requirements that are necessary to test rotary encoders, and the fundamentals of an optimized procedure are developed. The procedure enables the identification of valid shock limits, cutting down the number of necessary full lifecycle tests and reducing development cost and time. Further, a clear assessment of whether the encoder is used according to functional safety specifications is possible.