Based on magnetorheological fluid, magnetorheological brake can exhibit promising characteristics in haptics such as intrinsic passiveness and high torque density. The main difficulty in applying magnetorheological brake lies in the magnetic hysteresis. To deal with the magnetic hysteresis, a magnetorheological brake was combined with a micromotor to construct a hybrid actuator in this article. A novel hollowed multi-drum architecture was adopted for the brake so that the micromotor could be placed inside the brake to obtain a compact structure. The brake produced the maximum torque of 1263.39 mN m with 40 mm diameter and 28 mm length. Through the closed-loop control, no obvious hysteresis loop was observed in the hybrid actuator current–torque figure. The maximum difference between the forward and backward torque was reduced from 7.2% to 1.94% of the total torque range. The dynamic range was increased from 41.17 to 45.42 dB. Furthermore, the experimental results proved that the hybrid actuator could track the reference signals more accurately than the brake.

Wearable fingertip device is a promising form to display haptic stimuli since it provides a lightweight and natural way for operators to grasp or manipulate the objects in the virtual environment. This paper focuses on the analysis and performance evaluation of a wearable fingertip device for haptic applications. The device is equipped with three small servo motors and can provide 3-DOF (degree of freedom) force feedback at fingertip with contact/non-contact capability. It combines a five-bar linkage and a slider-crank linkage, and these two linkages are decoupled, leading to simpler kinematics than some devices with coupled structures. In order to present the device, its mechanical analysis, kinematics analysis, and static force analysis were carried out at first. Then, four experiments were designed and conducted to evaluate the device performance quantitatively. The first experiment aimed to verify the effectiveness in rendering variable stiffness. The second experiment investigated its capability in providing different skin stretch directions for operators. The third experiment evaluated its performance improvement during virtual manipulation. The last experiment aimed to verify the effectiveness in displaying mass information during remote manipulation. The experimental results indicated that this device was capable of rendering various stiffness. It could generate eight clear skin stretch directions. The subjects had better performance during virtual manipulation with cutaneous feedback provided by the device than without cutaneous feedback. The device was also capable of displaying mass information during remote manipulation.INDEX TERMS Haptics, wearable fingertip device, cutaneous feedback, performance evaluation.

Under the same excitation, the multi-drum magnetorheological brake has a nonuniform distribution of flux density over fluid gaps. Each fluid gap has its own flux density and shear area. Therefore, the number of drums and the fluid gap selection in optimization are two important parameters to be considered in a multi-drum brake design. When a fluid gap is selected in optimization, the brake is optimized to reach the maximum required flux density over this gap. This article focuses on evaluating the influence of these two parameters on the performance of the multi-drum brake. According to the number of drums and the fluid gap selection in optimization, the brakes were marked and optimized via finite element analysis. After all optimal designs were obtained, the performance in terms of torque, volume, mass, and power consumption as well as the torque–volume, torque–mass, and torque–power ratios were calculated and compared. Based on the evaluation results, suggestions on the number of drums and the fluid gap selection in optimization are given.

Based on the rheological effect of magnetorheological (MR) fluid, MR brake is a promising actuator due to its passiveness, high torque density, and low power consumption. This paper focuses on a unique hollowed multi-drum MR brake which has a hollow casing and several drum-like rotors and stators and evaluates the influence of the hollow casing radius on the performance of this brake. First, the brakes with different hollow casing radii were optimized via finite element analysis to obtain the optimal designs. Then, the torque, volume, mass, and power consumption including torque volume, torque mass, and torque power ratios were calculated to conduct the performance evaluation. According to the results, the suggestion on the hollow casing radius was given in the hollowed multi-drum brake design. To validate finite element analysis, the brake with 8-mm hollow casing radius was fabricated, assembled, and tested. The test results were generally consistent with the results of finite element analysis.INDEX TERMS Hollowed multi-drum MR brake, hollow casing radius, finite element analysis, performance evaluation.

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