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A 4-DOF Upper Limb Exoskeleton for Stroke Rehabilitation: Kinematics Mechanics and Control

Anan Sutapun and Viboon Sangveraphunsiri
Department of Mechanical Engineering, Faculty of Engineering, Chulalongkorn University, 254 Phyathai, Patumwan, Bangkok, Thailand 10330

Abstract—A 4-DOF power-assist exoskeleton for stroke rehabilitation is developed in this research work. Its configuration consists of three degrees of freedom, two of them are adjustable to suit patient arm, at the shoulder joint and one degree of freedom at the elbow joint. The mechanical system is designed based on low friction, no backlash, low inertia, large dynamic range, and backdrivable. Kinematics, link-configuration, and control strategies are detailed here. Two control strategies: assistive-resistive mode, based on impedance force control, for a patient who has some difficulty in moving his hand or physically weak persons. An impedance model, based on the concept of virtual wall, has been purposed in the torque control scheme. The resistive mode for a patient who want to improve his hand motion or after finishing the assistive-resistive operation training program. Each jointed of the exoskeleton arm is actuated by brushless DC servomotor. To simplify torque measurement, each joint torques in the feedback loop are obtained by measuring the input current of the motor drivers multiply by the motors torque constant. Otherwise, sophisticate procedure needed, if we measure current in the armature coil. Both operation modes have been tested with patients, the feedback from patients and medical doctors are very positive.
Index Terms—exoskeleton arm, stroke rehabilitation, force control, backdrivability

Cite: Anan Sutapun and Viboon Sangveraphunsiri, "A 4-DOF Upper Limb Exoskeleton for Stroke Rehabilitation: Kinematics Mechanics and Control," International Journal of Mechanical Engineering and Robotics Research, Vol.4, No. 3, pp. 269-272, July 2015. DOI: 10.18178/ijmerr.4.3.269-272