Permanent-Magnetically Amplified Brake Mechanism Compensated and Stroke-Shortened by a Multistage Nonlinear Spring

Abstract

Electromagnetic (EM) brakes are widely used but consume electricity continuously to maintain their activated state. In this letter, for efficient braking and idling of robots and vehicles, we proposed a concept of a brake mechanism using a permanent magnet for the amplification of the pressing force between brake pads, allowing for the brake torque to be steplessly regulated by a minimal external force. The prototype of the proposed mechanism was developed with a newly devised compensation spring - not the conventional conical coil springs - comprising two linear springs to shorten the pad-detaching stroke. For proof of concept, evaluation experiments based on the Japanese Industrial Standards were conducted. Both the maximum static and average dynamic friction torques increased to 161.0% and 192.9%, respectively, when identical pads of an EM brake were used for comparison. Power saving was also achieved when braking for longer than 0.43 s; the torque-energy efficiency increased by 8.7 when measured for 1.0 s, successfully revealing the effectiveness of the proposed principle. Further, based on the force-displacement characteristic of the compensated magnet, the theoretical response time was numerically analyzed as 13.6 ms - comparable to the contrasted EM brake - validating the actual behavior of 14.0 ms.