A linear magnetorheological brake with multipole outer coil structure for high on-state and low off-state force outputs

Abstract

A wide range of braking forces, from near zero to high values, is required in specific applications such as forces in haptic devices or steering stability in motorcycles. Classical piston cylinder type magnetorheological (MR) brakes are not suitable for these applications due to their high off-state forces. In this paper, a new linear type MR brake employing shear mode braking principle with a multipole outer coil structure is presented for high on-state and low off-state force outputs. To implement this device, an analytical model of the brake is derived by using magnetic circuit analysis to determine braking force. Magnetic finite element models are developed and coupled with an optimization algorithm to determine the optimal set of parameters of the brake design. A prototype is manufactured and tested experimentally to characterize the device's force response, transient response, hysteresis, force tracking, and damping performance. The proposed brake achieved a maximum braking force of 480 N and a low off-state force of 6 N with infinite stroke. The results show that the ratio of maximum force to off-state force for our device is about 80, even though it is a maximum of 32 for the best linear brakes in the literature.