Validation of An Elbow Position Super-Twisting Sliding-Mode Controller for Upper-Limb Exosuit Using A Soft Position Sensor

Abstract

Flexible exoskeletons, also known as exosuits, are robotic wearable devices intended to help healthy and unhealthy subjects in different tasks, such as daily life activities, load lifting or rehabilitation. A position control is required to assure stability and compliance in all assisted movements. In this paper, the authors propose the use of a flexible position sensor based on differential capacitance measurement as position feedback for the elbow joint in the flexible exoskeleton LUXBIT. This exosuit is controlled in position by a super-twisting sliding mode controller (SMC), which is robust against disturbances. Different movements involved in rehabilitation therapies are performed over three healthy subjects in order to evaluate the exosuit performance using this motion sensor. The measures given by the flexible sensor are compared to the ones obtained by OptiTrack motion capture system, which are used as ground truth.

Robust Motion Control Architecture for an Upper-Limb Rehabilitation Exosuit

“…Assuming that the transmission cables are not deformable, the linear speed v of the cable in the motor side is the same of the anchor-point side. Considering, for example, the shoulder cable, the cable speed is defined in terms of the shoulder actuator angular variation in (9) and in relation to the shoulder angular variation in (10):…”

“…An elegant trajectory-tracking control for a rigid elbow and shoulder exoskeleton that consists on a fuzzy approximation-based adaptive backstepping controller was proposed in [8]. Position controllers for trajectory tracking in exosuits have also been used, where a SMC-based control with adaptive backlash compensation was designed for elbow control in [9]; and a supertwisting SMC was implemented for the elbow joint, obtaining high robustness to external disturbances in [10]. To the knowledge of the authors, there do not exist yet international standards regarding the required tracking accuracy for upper-limb rehabilitation.…”

Validation of a Hybrid Exoskeleton for Upper Limb Rehabilitation. A Preliminary Study

“…A super twisting slider mode controller [29] has been simulated and implemented previously for elbow and shoulder flexion and extension movements [30]. In the study conducted previously by the authors, the use of a supertwisting controller is proposed, which stands out from other controllers in sliding mode due to its attenuation of chattering, a high frequency noise coupled to the control signals due to the discontinuous nature of SMC.…”

Exoesqueleto híbrido para rehabilitación de las extremidades superiores.

“…Además, se ha desarrollado un exoesqueleto flexible que está equipado con una transmisión por cable en la que el par es generado por dos motores de corriente continua. Se ha simulado e implementado un controlador de modo de deslizante super twisting [14] para los movimientos de flexión y extensión de codos y hombros [15]. Finalmente, se han estudiando métodos para estimar la orientación y posición del hombro utilizando diferentes tipos de sensores y algoritmos [16][17].…”