Design and analysis of a hollow-ring permanent magnet brake for robot joints

Abstract

An electromagnetic brake is the key basic component to ensure the safety of robot joints. The conventional electromagnetic brake mostly uses a set of springs to provide braking force and solenoid power to provide a recovery force, which makes this kind of brake with large thickness and small braking torque that is not conducive to the application in light and small joint components. In many design processes, unclear understanding of the machine-electric-magnetic coupling characteristics leads to relatively simple theoretical models and inaccurate theoretical results, which do not provide more help for subsequent designs. In this paper, a hollow-ring type permanent magnetic power-loss protection brake, integrated inside a joint assembly, is designed. The brake uses rare earth Nd–Fe–B permanent magnets to provide braking suction instead of ordinary spring packs, and achieves motion guidance and braking torque transmission by means of leaf spring. Combined with the deformation model of the leaf spring and the magnetic circuit models of the brake under the power-on and power-off conditions, the overall coupling dynamics model of the brake is established. The theoretical results are compared through finite-element software, and a prototype is produced for experimental testing. Finally, the accuracy and validity of the theoretical model are verified, providing a theoretical and experimental basis for the design of this type of brake.