Compact and Wide-Force-Range Magnetorheological Hand Exoskeleton for Kinesthetic Feedback in Teleoperation
TL;DR A hand exoskeleton with a 39.8 g magnetorheological brake per finger gives kinesthetic feedback while teleoperating a robot hand. It renders fingertip forces up to 21 N with about 1 N of back-driving force, and 12 users gripped more gently with it (3.50 N vs 4.61 N).
What they do
Force-feedback gloves for teleoperating robot hands have to trade force range against size and weight. This paper builds a five-finger hand exoskeleton whose feedback comes from small magnetorheological (MR) brakes, and tests it with users teleoperating a 3-DoF robot hand (Cora Hand) on a UR-5 arm.
How it works
- MR bearing brake. Magnetorheological grease is injected into the ball gaps of a deep-groove ball bearing. A coil next to it sets the magnetic field, and with it the resistance of the shaft, with no gear reduction.
- Exoskeleton. A 3D-printed linkage per finger transmits the brake torque to the fingertip; a potentiometer on the same shaft tracks finger motion. The whole device weighs 495 g.
- Teleoperation loop. Finger angles drive the robot fingers. Pressure sensors on the robot’s finger pads measure contact force, which is sent over Wi-Fi and mapped to brake current.
- Demagnetization. A decaying sine voltage on the coil removes residual torque before the user releases.
Results
- Braking torque ranges from 0.01 N·m at 0 A to 0.918 N·m at 1.5 A, with a 33.26 ms response time. The brake has a mass of 39.8 g.
- Fingertip force reaches 21 N at 1.25 A; the mean peak back-driving force after demagnetization is about 1 N. The kinematic model predicts fingertip force within 5% from 0.5 A to 1.25 A.
- Blindfolded users told air and a rigid cube apart reliably, but classified the sponge and foam cubes with 61.1% and 72.2% accuracy.
- In a grasp-and-lift task with 12 participants, mean grip force fell from 4.61 N with vision only to 3.50 N with added feedback, while operation time rose from 9.37 s to 10.87 s.
Limitations
Objects of similar stiffness are hard to tell apart, and users rated the realism of the feedback only moderately. Feedback slows the task, and the user must press a button to demagnetize the brake before releasing. Fingertip force output was measured on a single participant, and the robot hand has only three degrees of freedom, so the middle exoskeleton finger drives three coupled robot fingers.
Figures
Abstract
Hand kinesthetic feedback is crucial for restoring and enhancing human perception of force and displacement in robotic hand teleoperation. Wide perception range of force feedback is vital in rendering objects of different stiffness, especially for high-stiffness rendering. However, existing approaches struggle to achieve wide range of force feedback while maintaining compact and wearable design. This paper presents a hand exoskeleton system employing magnetorheological (MR) brakes to provide a wide range kinesthetic feedback during teleoperation. The MR brake provides a braking torque ranging from 0.01 to 0.918 Nm, while maintaining a compact structure with a total mass of only 39.8 g. The proposed exoskeleton can render fingertip forces up to 21 N while maintaining back-driving force of 1.01 N. Experimental results show that the system allows users to discriminate object stiffness using kinesthetic feedback alone. In a tele-grasping task, when both conditions achieved a 100% success rate, kinesthetic feedback led to a 28.2% reduction in object contact force compared to visual feedback only, enhancing object safety and operator immersion. Questionnaire results further indicate that kinesthetic feedback improves reliability, realism, and user confidence during teleoperation.
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