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. 2021 Apr 8:15:664062.
doi: 10.3389/fnbot.2021.664062. eCollection 2021.

A Cable-Driven Three-DOF Wrist Rehabilitation Exoskeleton With Improved Performance

Ke Shi  1 , Aiguo Song  1 , Ye Li  1 , Huijun Li  1 , Dapeng Chen  1 , Lifeng Zhu  1
Affiliations

A Cable-Driven Three-DOF Wrist Rehabilitation Exoskeleton With Improved Performance

Ke Shi et al. Front Neurorobot. .

Abstract

This paper developed a cable-driven three-degree-of-freedom (DOF) wrist rehabilitation exoskeleton actuated by the distributed active semi-active (DASA) system. Compared with the conventional cable-driven robots, the workspace of this robot is increased greatly by adding the rotating compensation mechanism and by optimizing the distribution of the cable attachment points. In the meanwhile, the efficiency of the cable tension is improved, and the parasitic force (the force acting on the joint along the limb) is reduced. Besides, in order to reduce the effects of compliant elements (e.g., cables or Bowden cables) between the actuators and output, and to improve the force bandwidth, we designed the DASA system composed of one geared DC motor and four magnetorheological (MR) clutches, which has low output inertia. A fast unbinding strategy is presented to ensure safety in abnormal conditions. A passive training algorithm and an assist-as-needed (AAN) algorithm were implemented to control the exoskeleton. Several experiments were conducted on both healthy and impaired subjects to test the performance and effectiveness of the proposed system for rehabilitation. The results show that the system can meet the needs of rehabilitation training for workspace and force-feedback, and provide efficient active and passive training.

Keywords: cable-driven robot; distributed drive system; human-robot interaction; mechanism design; rehabilitation robot.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
The definition of the parasitic force: Ow is the center of the wrist joint, Oh is the center of the hand, A1−4 are four cable attachments of the forearm module, B1−4 are four cable attachments of the hand ring, T1−4 is the cable tension, and Fp is the parasitic force.
Figure 2
Figure 2
(A) close-up of the robot on a healthy subject, (B) the exploded view of the robot: A1−4 are four cable attachments of the forearm module, and B1−4 are four cable attachments of the hand ring.
Figure 3
Figure 3
The schematic of two different drive systems: (A) the DASA system based on MRs, (B) the conventional electric motor drive system.
Figure 4
Figure 4
The power box: (A) the upper layer, (B) the bottom layer, (C) the exploded view of the MR-Cable unit, (D) the MR clutch assembly.
Figure 5
Figure 5
(A) anatomy of the wrist joint and the coordinate frames, (B) the optimization process of the workspace.
Figure 6
Figure 6
The MR-Cable tension control block diagram.
Figure 7
Figure 7
Three work modes for safety.
Figure 8
Figure 8
(A) the MR performance test platform, (B) the MR-Cable system performance test platform, (C) the MR current-torque curve, (D) the MR step response curve, (E) the MR-Cable closed-loop force control Bode diagram.
Figure 9
Figure 9
The passive training experiment: (A) the tracking error, (B) the tension, parasitic force, and actual assistive torque curve. D/A/E/M-Angle represent the desired angle, the actual angle, the tracking error of the angle, and the angle of the Z-axis, respectively. E-Position means the tracking error of the position. The red area in (A) is the infeasible area of CDWRR.
Figure 10
Figure 10
The actual workspace in experiment.
Figure 11
Figure 11
(A,C,E) show the visual interface, adaptive KD and average error for FE experiment, respectively; (B,D,F) show the visual interface, adaptive KD and average error for PS experiment, respectively; (G,H) demonstrate the average tension and max parasitic force in task no. 15–30 of S3, respectively. The red bar is the average value of SER-WRE in the large range, the green bar is its average value in the small range, and the blue bar is the average value of CDWRR in the small range.
Figure 12
Figure 12
The healthy subject performs a safety mode test. The damping coefficient BD is 1 Nm·s/rad. The subject actively exceeds the safe range near the 9th s, and then returns to the safe range. Near the 12th s, the drive system is powered off and the robot enters Safety Mode II. Then, the drive system is powered on near the 15th s, the robot returns to Normal Work Mode. The blue and red regions are Safe Mode I and Safe Mode II, respectively.
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