DESIGN, DEVELOPMENT AND CONTROL OF HAND EXOSKELETON SYSTEM

Abstract

Numerous people around the world suffer from hand paralysis which results in loss of motor function. Along with the disability, comes the burden of care towards caretakers. With paralysis, the dependency of the inflicted is seriously increased and the even performing simple operations is a challenge. To avoid further damage to the hand in the form of muscle atrophy etc. the hand is subjected to certain exercises where each muscle is involved to avoid further deterioration. Aside from this, various practical exercises are part of the physical therapy for regain of motor control. These activities have been found to yield very reasonable results and are recommended on all patients suffering from paralysis. These exercises involve certain prescribed movements and are often limited to specialized training centers where specific training equipment and personnel are equipped for overseeing the whole process and conducting the exercises. The complete regain of motor function is a time-consuming process and often is abandoned due to its boring and localized nature. Research (ref) shows that performing daily activities with the affected hand actually yields better results as compared to relying solely on trainings. Employing the hand in daily activities removes the burden of dependency and also improves the moral state of the patient. Through this technique the patient experiences his prior state and tries to stand perform his basic daily activities. Through this, the patient rehabilitates himself in a familiar environment and continuous manner. Therefore, we propose an exoskeleton hand that is aimed towards enabling the person with paralyzed hand to perform some basic day to day tasks such as drinking water and lifting things with ease and familiarity. Our design incorporates a compliant solution to control the paralyzed hand in a natural, efficient and effective way. Our target is to provide new therapy solutions to the patients by increasing the comfort and time devoted to hand rehabilitation. This system can potentially provide long-term therapy and assistance in a familiar environment. The prevalent hand exoskeleton systems can be distinguished into soft and hard exoskeleton systems. The control mechanism and strength of the hard exoskeleton systems is better than soft systems however the soft systems are bio inspired and compliant. Thus, the soft systems offer great physical Human-Robot-Interaction but at the expense of effective control. The exact iii control mechanisms of soft mechanisms is seriously lacking and is the subject of ongoing research. The proposed exoskeleton hand is a hybrid of soft and hard exoskeleton systems. The proposed design is controlled by rigid hard structures near the actuation. The mechanism is mounted on the hand through soft Velcro strips for the ease and compliance with the finger. This pseudo hybrid system offers a soft system for physical interaction and offers a hard system for control of finger control mechanism. The exoskeleton hand offers five degrees of freedom spread over five fingers. Three basic joints of each finger are controlled by an underactuated mechanism which is connected to servo motors through inextensible string. The wrist motion is locked through employing a rigid plastic splint spread over the hand which is also the base for servo motors. The main focus has been towards the finger mechanism. Each finger employs a multi linkages structure composed of multiple four and five bar linkages. Through this mechanism, certain unique and essential characteristics of the physical hand are embodied such as the natural curve followed by the finger during flexion and extension. The mechanical compliance of the finger around different shaped objects is achieved through dual compounded five bar mechanisms. The hand exoskeleton system offers a hybrid structure that is light weight, top-mounted, energy efficient, smooth, compliant and adjustable. an exoskeleton hand should have the ability to allow the user to grasp a wide range of objects having different shapes i.e. it should be capable of conformance. Our system provides us the freedom required to grasp/hold different shapes of objects. Studying the existing prevalent linkage-based designs, an improvisation has been proposed in the mechanics to provided better energy efficiency and force transmittivity to the hand. Current designs achieve maximum force in non-grasping position i.e. when the fingers are straight (not bent). Our focus of research was to increase the efficiency of the hand exoskeleton systems through optimizing the design towards a grasping posture. Therefore, our design is based on achieving maximum force/torque at end effector when the fingers are in grasping position. This helps in achieving energy efficiency while performing various holding and lifting activities. The designed hand exoskeleton system is to be controlled through an EMG sensor which reads the muscle activity and moves the hand according to the input.