Employing variable impedance (stiffness/damping) hybrid actuators on lower limb exoskeleton robots for stable and safe walking trajectory tracking


Compliant actuators are employed in exoskeleton robots instead of stiff actuators for safe human-robot interaction. In parallel with this idea, we previously constructed a biomimetic compliant exoskeleton robot (BioComEx). In this study, to provide more stable and safe trajectory tracking even under disturbances, magneto-rheological (MR) brakes were added to all joints of BioComEx as variable damping actuators and a PID+D controller was proposed. To evaluate the robot and controller, first, BioComEx was hung on a platform and the controller was applied without device user under external forces. This primary test results showed that the proposed design and controller can effectively minimize disturbance effects and consequently reduce trajectory tracking oscillations. In the rest of the study, the similar control experiments were repeated with a user who has unilateral lower limb movement disorders. In these experiments, the movements of the user’s healthy leg were detected by force feedback impedance control algorithm and then were used as reference for the impaired leg with walking cycle delay in real time. The secondary test results showed that the variable impedance exoskeleton robot design with PID+D controller can ensure effective walking assistance for the impaired human legs.

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The authors thank the Scientific and Technological Research Council of Turkey for the financial support of a research project titled as “Design and Control of a Biomimetic Exoskeleton Robot” and numbered 213M297.

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Correspondence to Ozgur Baser.

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Recommended by Editor Ja Choon Koo

Ozgur Baser received the M.S. and Ph.D. from Middle East Technical University, Turkey, in 2006 and 2012, respectively, all in mechanical engineering. He is currently an Associate Professor of Mechanical Engineering at Suleyman Demirel University, Turkey. His research interests include control systems, exoskeleton robots, MR brakes and haptic devices.

Ergin Kilic received the M.S. and Ph.D. from Middle East Technical University, Turkey, in 2007 and 2012, respectively, all in mechanical engineering. He is currently an Associate Professor of Mechanical Engineering at Suleyman Demirel University, Turkey. His research interests include fuzzy-logic control, artificial neural networks, rehabilitation robots and EMG signal processing.

Hasbi Kizilhan received the M.S. from Department of Mechanical Engineering of Süleyman Demirel University, Turkey, in 2015. He is currently a Research Assistant and studying for his Ph.D. at the same department and university. His research interests include robotics, exoskeleton robots and human-robot interaction.

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Baser, O., Kizilhan, H. & Kilic, E. Employing variable impedance (stiffness/damping) hybrid actuators on lower limb exoskeleton robots for stable and safe walking trajectory tracking. J Mech Sci Technol 34, 2597–2607 (2020). https://doi.org/10.1007/s12206-020-0534-4

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  • Lower limb exoskeleton
  • Variable stiffness actuator
  • Variable damping actuator
  • Magneto-rheological brake
  • Hybrid actuator
  • Walking trajectory tracking