Magnetorheological (MR) brake is a sort of electromagnetic brake that uses the controllable output characteristics of MR fluid for braking. In this paper, an MR brake with a double brake disc was developed to improve the braking performance of conventional MR brakes. The effective damping gaps were increased from the traditional two sections to four sections by increasing the single brake disc of the conventional MR brake to a double brake disc. By reasonably arranging the non-magnetic sleeve inside the MR brake, the magnetic flux lines were better guided to the effective damping gaps, which increased the utilization rate of the magnetic field, effectively enhanced the braking performance, and also reduced the braking power consumption. The structure and working principle of the MR brake with double brake disc were discussed. The magnetic field of the proposed MR brake was analyzed by ANSYS software, and the theoretical result of braking performance was obtained by combining the established mechanical model. The braking performance test rig was setup to investigate the torque performance of the MR brake. The experimental results show that the maximum braking torque is 18.01 N·m at the applied current of 2.0 A and the rotational speed of 400 r·min⁻¹, and the simulation values are basically verified. In addition, the results indicate that the constant torque characteristic of the MR brake is relatively stable, and the torque is almost unaffected by the changes of rotational speed. The results can provide some guidance for the structural design and optimization of the MR actuators.

In order to solve the problems of low magnetic field utilization rate and low volume-torque ratio of the traditional magnetorheological (MR) brake under a volume constraint, a rotary MR brake with multiple fluid flow channels was proposed. The magnetic flux was guided into the external axial fluid flow channel by inserting a non-magnetic ring in the middle of the magnetic conduction sleeves which could improve the magnetic circuit structure greatly, the working area where the MR brake producing rheological effect was increased, and the effective damping gaps were also increased from two sections to four sections. The working principle of rotary MR brake was expounded and torque mathematical model was also deduced. The electromagnetic field was modeled and the distribution of magnetic flux density in multiple fluid flow channels was analyzed using finite element method. The prototypes of initial and optimal design were fabricated by using the obtained optimal geometric parameters. An experimental test system was setup to investigate the dynamic performance of the proposed rotary MR brake. The experimental results show that the maximum braking torque and torque ratio of the optimal MR brake are increased by 13.5% and 2.3% compared with the initial MR brake at the applied current of 1.8 A, respectively. At the same time, the variation trend of experimental and simulation results is basically consistent, and the rotational speed has almost no effect on the torque performance, which is conducive to the application of MR brakes under different working conditions.

Magnetorheological (MR) damper performance is evaluated only by single-field analysis in the design process, which can easily lead to larger design errors. Based on this, a simulation method of MR damper considering multiphysics coupling was proposed. According to a certain automobile shock absorber requirement, an MR damper suitable for automobile suspension was designed. The mechanical model, electromagnetic field model, flow field model, and structural stress field model of the MR damper were deduced and established. To investigate the damping performance of the MR damper more accurately, the multiphysics coupling simulation model was established by COMSOL software, and coupling analysis of the electromagnetic field, flow field, and structural stress field was also carried out. The static magnetic field characteristics, dynamic flow field characteristics, stress distribution, and dynamic performance of the proposed MR damper under the action of multiphysics coupling were obtained. The simulation results show that the damping force is 1134.6 N, and the damping adjustable coefficient is 9.1 at an applied current of 1.4 A. A test system was established to analyze the dynamic performance of the MR damper, and the simulation results were compared with the experimental results. The results show that the simulated and experimental results have the same change rule. Moreover, the damping force increases with the applied current, and different external excitations have little effect on the damping force. The damper can output appropriate damping force and has a wide adjustable damping range. The experimental results illustrate that the damping force is 1200.0 N, and the damping adjustable coefficient is 10.1 when the current is 1.4 A. The error between simulation and experiment of the damping force and damping adjustable coefficient is only 5.5% and 9.9%, respectively.

In order to improve the environmental adaptability and interaction stability of industrial robotic arms, a flexible joint with variable damping and stiffness based on magnetorheological (MR) technology was proposed. The mechanical models for variable stiffness and damping of MR flexible joint were established, and the relationship between cam surface and variable stiffness element was derived based on the energy method. Subsequently, the variation patterns of equivalent stiffness and damping of the prototype under different excitations were experimentally tested, and the test results show that its mechanical properties meet the design requirements. To further verify the performance of the MR flexible joint on the robotic arm, we setup a collision buffering test system and investigated the buffering performance of the system under different working conditions. The buffering test results indicate that when the current of variable stiffness element is 2.0 A, the peak collision acceleration of the system after installing the MR flexible joint decreases by about 40.19% compare with the rigid collision.

In this paper, magnetorheological (MR) porous fabric composites were prepared by using non-woven fabrics pretreated with lithium stearate. Due to the porous structure of non-woven fabric and the good stability of lithium stearate, the mechanical properties and sedimentation stability of the composite have been improved. The viscosity, shear stress and dynamic viscoelasticity of different samples were analyzed by rheological properties tests. The results indicate that the mechanical properties of the composite samples containing lithium stearate are improved compared with the MRF (magnetorheological fluid) sample, and its sedimentation stability under non-working conditions is also improved. However, with the increase of lithium stearate content, the improving effect of material performance gradually decreased. The experimental results show that when the magnetic flux density is 0.31 T, the shear stress of the MR porous fabric composite with 1 wt% lithium stearate is about 27 kPa, which increases by 51.1% compared with the MRF sample.