4.3 Article

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

Journal

JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY
Volume 34, Issue 6, Pages 2597-2607

Publisher

KOREAN SOC MECHANICAL ENGINEERS
DOI: 10.1007/s12206-020-0534-4

Keywords

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

Funding

  1. Scientific and Technological Research Council of Turkey [213M297]

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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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