A compact wrist rehabilitation robot with accurate force/stiffness control and misalignment adaptation


Robots have been demonstrated to assist the rehabilitation of patients with upper or lower limb disabilities. To make exoskeleton robots more friendly and accessible to patients, they need to be lightweight and compact without major performance tradeoffs. Existing upper-limb exoskeleton robots focus on the assistance of the coarse-motion of the upper arm while the fine-motion rehabilitation of the forearm is often ignored. This paper presents a wrist robot with three degrees-of-freedom. Using a geared bearing, slider crank mechanisms, and a spherical mechanism, this robot can provide the complete motion assistance for the forearm. The optimized robot dimensions allow large torque and rotation output while the motors are placed parallel to the forearm. Thus lightweight, compactness, and better inertia properties can be achieved. Linear and rotary series elastic actuators (SEAs) with high torque-to-weight ratios are proposed to accurately measure and control the interaction force and impedance between the robot and the wrist. The resulting 1.5-kg robot can be used alone or easily in combination with other robots to provide various robot-aided upper limb rehabilitation.

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  1. Andrews, J.G., Youm, Y.: A biomechanical investigation of wrist kinematics. J. Biomech. 12(1), 83–93 (1979)

    Article  Google Scholar 

  2. Bian, H., et al.: Mechanical design of EFW Exo II: a hybrid exoskeleton for elbow-forearm-wrist rehabilitation.” In: 2017 International Conference on Rehabilitation Robotics (ICORR), pp. 689–694. IEEE (2017)

  3. Brooks, T.L.: Telerobotic response requirements. In: IEEE International Conference on Systems, man and cybernetics, 1990. Conference Proceedings. IEEE (1990)

  4. Buongiorno, D., et al.: WRES: a novel 3DoF wrist ExoSkeleton with tendon-driven differential transmission for neuro-rehabilitation and teleoperation. IEEE Robot. Autom. Lett. (2018)

  5. Chandler, R. F., et al. Investigation of inertial properties of the human body. No. AMRL-TR-74-137. Air Force Aerospace Medical Research Lab Wright-Patterson AFB OH, 1975

  6. Choi, W., et al.: Low stiffness design and hysteresis compensation torque control of SEA for active exercise rehabilitation robots. Autonom. Robots 41(5), 1221–1242 (2017)

    Article  Google Scholar 

  7. Dong, W., et al.: Soft human–machine interfaces: design, sensing and stimulation. Int. J. Intell. Robot. Appl. 1–26 (2018)

  8. French, J.A. et al.: System characterization of MAHI Exo-II: a robotic exoskeleton for upper extremity rehabilitation. In: Proceedings of the ASME Dynamic Systems and Controls Conference, October (2014)

  9. Hope, James, McDaid, Andrew: Development of wearable wrist and forearm exoskeleton with shape memory alloy actuators. J. Intell. Rob. Syst. 3(3), 2152–2159 (2017)

    Google Scholar 

  10. Hsieh, H.-C., et al.: Design of a parallel actuated exoskeleton for adaptive and safe robotic shoulder rehabilitation. IEEE/ASME Trans. Mechatron. 22(5), 2034–2045 (2017)

    Article  Google Scholar 

  11. Hu, X.L., et al.: A comparison between electromyography-driven robot and passive motion device on wrist rehabilitation for chronic stroke. Neurorehabilit. Neural Repair 23(8), 837–846 (2009)

    Article  Google Scholar 

  12. Khokhar, Zeeshan O., Xiao, Zhen G., Menon, Carlo: Surface EMG pattern recognition for real-time control of a wrist exoskeleton. Biomed. Eng. Online 9(1), 41 (2010)

    Article  Google Scholar 

  13. Kim, Bongsu, Deshpande, Ashish D.: An upper-body rehabilitation exoskeleton Harmony with an anatomical shoulder mechanism: design, modeling, control, and performance evaluation. Int. J. Robot. Res. 36(4), 414–435 (2017)

    Article  Google Scholar 

  14. Krebs, H.I., et al.: Robot-aided neurorehabilitation: a robot for wrist rehabilitation. IEEE Trans. Neural Syst. Rehabilit. Eng. 15(3), 327–335 (2007)

    Article  Google Scholar 

  15. Lambelet, C., et al.: The eWrist—a wearable wrist exoskeleton with sEMG-based force control for stroke rehabilitation. In: 2017 International Conference on Rehabilitation Robotics (ICORR), IEEE (2017)

  16. Lee, Y.-F., et al.: A Humanoid robotic wrist with two-dimensional series elastic actuation for accurate force/torque interaction. IEEE/ASME Trans. Mechatron. 21(3), 1315–1325 (2016)

    Article  Google Scholar 

  17. Lee, J., et al.: A robust control method of multi-DOF power-assistant robots for unknown external perturbation using sEMG signals. In: Intelligent Robots and Systems (IROS), 2015 IEEE/RSJ International Conference on. IEEE (2015)

  18. Lin, K.-Y., et al.: High-performance series elastic stepper motors for interaction force control. In: 2017 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), IEEE (2017)

  19. Mehling, J.S.: Impedance control approaches for series elastic actuators. Diss. Rice University (2015)

  20. Meng, W., et al.: Recent development of mechanisms and control strategies for robot-assisted lower limb rehabilitation. Mechatronics 31, 132–145 (2015)

    Article  Google Scholar 

  21. Oh, Sehoon, Kong, Kyoungchul: High-precision robust force control of a series elastic actuator. IEEE/ASME Trans. Mechatron. 22(1), 71–80 (2017)

    Article  Google Scholar 

  22. Omarkulov, N., et al.: Preliminary mechanical design of NU-Wrist: A 3-DOF self-aligning Wrist rehabilitation robot. In: 2016 6th IEEE International Conference on Biomedical Robotics and Biomechatronics (BioRob). IEEE, Singapore (2016). https://doi.org/10.1109/BIOROB.2016.7523753

  23. Patil, G., et al.: Momentum-based trajectory planning for lower-limb exoskeletons supporting sit-to-stand transitions. Int. J. Intell. Robot. Appl. 2(2), 180–192 (2018)

    Article  Google Scholar 

  24. Pehlivan, A.U., et al.: Design and validation of the RiceWrist-S exoskeleton for robotic rehabilitation after incomplete spinal cord injury. Robotica 32(8), 1415–1431 (2014)

    Article  Google Scholar 

  25. Perry, J.C., et al.: Upper-limb powered exoskeleton design. IEEE/ASME Trans. Mechatron. 12(4), 408–417 (2007)

    MathSciNet  Article  Google Scholar 

  26. Pezent, E., et al.: Design and characterization of the openwrist: a robotic wrist exoskeleton for coordinated hand-wrist rehabilitation. In: 2017 International Conference on Rehabilitation Robotics (ICORR), IEEE (2017)

  27. Pu, S.-W., Sung-Yu, T., Jen-Yuan, C.: Design and development of the wearable hand exoskeleton system for rehabilitation of hand impaired patients. In: 2014 IEEE International Conference onAutomation Science and Engineering (CASE). IEEE (2014)

  28. Saadatzi, M., David, C. L., Ozkan, C.: Comparison of human-robot interaction torque estimation methods in a wrist rehabilitation exoskeleton. J. Intell. Robot. Syst. 1–17 (2018)

  29. Squeri, V., et al.: Wrist rehabilitation in chronic stroke patients by means of adaptive, progressive robot-aided therapy. IEEE Trans. Neural Syst. Rehabilit. Eng. 22(2), 312–325 (2014)

    Article  Google Scholar 

  30. Su, Y.-Y, et al.: Design of a lightweight forearm exoskeleton for fine-motion rehabilitation. In: 2018 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM). IEEE (2018)

  31. Vitiello, N., et al.: NEUROExos: A powered elbow exoskeleton for physical rehabilitation. IEEE Trans. Robot. 29(1), 220–235 (2013)

    Article  Google Scholar 

  32. Wu, K.-Y. et al.: Series elastic actuation of an elbow rehabilitation exoskeleton with axis misalignment adaptation. In: 2017 International Conference on Rehabilitation Robotics (ICORR), IEEE (2017)

  33. Xu, D., et al.: Development of a Reconfigurable Wrist Rehabilitation Device with an Adaptive Forearm Holder. In: 2018 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM), IEEE (2018)

  34. Yin, K., et al.: Fuzzy iterative learning control strategy for powered ankle prosthesis. Int. J. Intell. Robot. Appl. 2(1), 122–131 (2018)

    Article  Google Scholar 

  35. Yu, H., et al.: Human–robot interaction control of rehabilitation robots with series elastic actuators. IEEE Trans. Robot. 25(2), 95–106 (2015)

    Google Scholar 

  36. Zhang, T., He H.H.: Lower-back robotic exoskeleton. IEEE Robot. Autom. Mag. (2018)

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This work was supported by the Ministry of Science and Technology, Taiwan (with Project No. MOST 107-2221-E-006-137-MY2).

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Correspondence to Chao-Chieh Lan.

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The coefficients in Eq. (11) can be expressed as in Eqs. (2125) while the nomenclature of the paper is listed in Table 5.

Table 5 List of nomenclature
$$ h_{01} = (C\alpha_{2} C\alpha_{3} - C\alpha_{1} C\alpha_{4} C\alpha_{5} + S\alpha_{1} S\alpha_{4} S\alpha_{5} C_{5} )/S\alpha_{2} S\alpha_{3} $$
$$ h_{02} = (C\alpha_{1} S\alpha_{4} S\alpha_{5} + S\alpha_{1} S\alpha_{4} C\alpha_{5} C_{5} )/S\alpha_{2} S\alpha_{3} $$
$$ h_{03} = - S\alpha_{1} S\alpha_{4} S_{5} /S\alpha_{2} S\alpha_{3} $$
$$ h_{13} = - C\alpha_{2} S\alpha_{2} S_{1} - C\alpha_{4} S\alpha_{5} S_{5} - S\alpha_{4} C_{5} S_{4} - S\alpha_{4} C\alpha_{5} S_{5} C_{4} $$
$$ \begin{aligned} h_{14} = S\alpha_{2} C\alpha_{3} C_{1} - C\alpha_{4} (S\alpha_{1} C\alpha_{5} - C\alpha_{1} S\alpha_{5} C_{5} ) \hfill \\ + S\alpha_{4} (C\alpha_{1} C\alpha_{5} C_{5} + S\alpha_{1} S\alpha_{5} ) - C\alpha_{1} S_{4} S_{5} \hfill \\ \end{aligned} $$

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Su, Y., Yu, Y., Lin, C. et al. A compact wrist rehabilitation robot with accurate force/stiffness control and misalignment adaptation. Int J Intell Robot Appl 3, 45–58 (2019). https://doi.org/10.1007/s41315-019-00083-6

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  • Rehabilitation robot
  • Wrist exoskeleton
  • Torque-to-weight ratio
  • Series elastic actuator
  • Parallel spherical mechanism
  • Misalignment adaptation
  • Impedance control