Integrated control method for power-assisted rehabilitation: Ellipsoid regression and impedance control

Abstract

This paper proposes an integrated control method including learning with an ellipsoid function and impedance controller for rehabilitation using power-assisted robotic de- vices. The proposed controller consists of two parts of a primary algorithm, which are ellipsoid regression method for re-designing trajectory and impedance controller with pseudo mass/inertia. The ellipsoid regression method generates refer- ence impedance profiles though acquiring motion and force trajectories during rehabilitation tasks assisted by therapists. The assisted force is controlled by impedance controller during execution of rehabilitation task using a concept of pseudo mass/inertia. The proposed method offers the power-assisted rehabilitation as guided by therapist, without consistent help from the therapist or other assisters. The proposed control method is validated by experiments throughout a 2-DOF reha- bilitation robot, KULEX-2DOF(KIST Upper Limb Exoskeleton - 2DOF). I. INTRODUCTION The importance of rehabilitation robots, one of the repre- sentative applications of interactive robots, has been growing. After stroke or injuring upper limbs, the patients requires a consistent rehabilitation for recovering functions of the upper limb. Especially, approximately 50% of stroke suffers requires special care and rehabilitation as soon and regular as possible after the stroke (1). Additionally, repetitive training or implementing remedial motion are helpful to improve the performance of rehabilitation in motor system of suffers (2). As conventional researches have reported that the repetitive practice of movements and specific functional activities with external assisting force can be effective for stroke suffers (3), robot-assisted rehabilitation becomes more important and remarkable. In this sense, the robotic system can contribute to reha- bilitation for not only stroke suffers but also elderly and disabled by assisting behavior. As shown in Fig. 1. (a), the therapist or the physiatrist are demanded to guide a remedial exercise of suffers with proper therapeutic program considering physical condition of them. It means that a self-rehabilitation can be impossible or inefficient when the therapist is absent. However, the rehabilitation robot can help rehabilitation while the therapist is absent as Fig. 1. (b). For safe and effective rehabilitation, it is an interesting issue to learn and to reproduce the therapeutic behavior with training motion and assisting power for rehabilitation, simultaneously. The power-assisted exoskeleton robot is able to be used to improve performance of daily tasks for the old, infirm and