Simulation and Mathematical Description of Mechanical Shocks Caused by Brake Actuation on Electric Motors

When a brake engages or releases on an electric motor, a mechanical shock is generated. These so-called brake shocks propagate across the motor housing and the motor shaft, affecting safety relevant mechanical and electronic components. The nature of the interference may be irreversible, i.e. mechanical damage, or reversible, e.g. interference of signal measurement or data transmission. Especially component failures or faulty signal values on rotary encoders are undesirable from a safety point of view. Current shock testing procedures are insufficient to simulate real brake shock characteristics and to identify valid shock limits regarding these shocks. In the first part of this paper, the characteristics of brake shocks are presented and compared to pyroshocks with similar characteristics. Furthermore, it shows that the Pseudo-Velocity Shock Response Spectrum (PVSRS) appears to be the best mathematical method to describe the severity of brake shocks with respect to their potential of damaging encoder components or influencing electrical signals. In the second part a testing machine will be introduced, which is able to generate mechanical shocks with comparable characteristics of real mechanical brake shocks for up to several million cycles. During further research, endurance tests shall be performed with the machine to determine the resilience of safety-related components against mechanical brake shocks. The long-term goal is to define scientifically confirmed test criteria for a standardized shock testing procedure to be applied on safety-related components on electric motors. It is intended to include this testing procedure in an international safety-related standard, like IEC 61800-5-3.