DESIGN AND DEVELOPMENT OF A HAND EXOSKELETON

Abstract

Paralysis is a common affliction in the world today and has been for ages. The historical bias against it can be judged from the famous case of the German Emperor Wilhelm III. New terminologies such as differently-abled have begun to be used to reduce the stigma around to encourage acceptance of it. As much as it is difficult for the person to live through the ordeal, it is harder still for society to handle paralyzed patients with care; hence it is always a point of interest for all those involved with someone with paralysis, for the patient to regain some form of autonomy to assist them in their activities of daily living. A prolonged period of paralysis spawns other challenges, such that prolonged disuse of muscles can cause atrophy. To stop paralysis in its track or better still recover function, is therefore highly sought. Stroke patients are usually undergoing physiotherapy and medication to help through the process. Physiotherapy involves rehabilitative exercises aimed at restoring motor function. The aforementioned rehabilitative exercises often involve prescribed movements and are limited to specialized training centers where specific training equipment is made use of use of. The process of completely regaining motor function while quite desirable soon becomes a boon, and its repetitive nature and the confinement that comes with it being carried out in small spaces can render it frustrating. It has been observed that almost sixty percent of all patients suffering from paralysis, present with upper extremity dysfunction [1]. This is acutely traumatizing to the patient because it nibbles away at the most recognizable sign of autonomy – hands, and as such renders the patient too dependent. Any sort of recovery with regards to hands is highly welcome because it acts as a step towards reclaiming autonomy for the patient and improves their mental state. Hand exoskeletons are a recent innovation and have been adopted to assist in the process of rehabilitation. Hand exoskeletons can be considered a piece of portable equipment and thus the patient can easily engage in ‘rehabilitation’ 3 without the need of being in a specialized training center which the patient might discompose patients owing to their unpleasant associations with it. The present thesis presents the design and development of a hand exoskeleton. While the primary aim is to assist in the process of rehabilitation for patients suffering from paralysis. It does not preclude the possibility of its being used in other areas where an application may be found to exist. Rock climbing or other sports that may require a large amount of force from the hands, cannot do away with the possibility of a device that may assist in force augmentation. This feature of force augmentation may also render it very useful in military exercises. The force of recoil from a rifle or any such personnel may be easily countered by way of force augmentation achieved through a hand exoskeleton. This military application just cited can be appreciated, when you realize that the force from recoil can in the worst-case scenario even cause a fracture in the clavicle – or ‘beauty bone’. The design presented in the present thesis proposes a unique solution that caters to the design of the linkages. The dimensions of the links in a hand exoskeleton, if not selected properly can make for unnatural trajectories of the hand, which may introduce undesirable stresses in the hand and at any point, thus rendering the process of rehabilitation more painful. The design in this paper makes use of differential evolution to overcome this problem. With the natural trajectory of the finger identified, the process of finding the right dimensions of the link to make the exoskeleton more user-friendly becomes easy. With the right trajectory identified through software like Kinovea, and feeding the data in a code, the algorithm gives the dimensions most likely to efficiently approximate the given trajectory. With the development of such a hand exoskeleton, that is portable and user-friendly, its deployment could work wonders. Exoskeletons in existence usually make use of either soft or hard robotics. Soft robotics involves shape-memory alloys or Bowden cables that 4 are actuated with fluids. Hard robotics involves mechanisms that operate on linkages and transmit power mechanically rather than through fluids as is the case with soft robotics. The hand exoskeleton in the present thesis bases its design on hard robotics and optimizes the dimensions of the linkages to make it follow the natural motion of the finger. The control of hand exoskeletons is an ongoing area of research and as such there are a few options that exoskeletons operate on to achieve control. There is the approach of using electromyographic (EMG) signals which pick up signals from healthy nerves. One of the approaches involves sensors mounted on a healthy hand, to replicate its motion onto the other hand – this presupposes a healthy hand. FSR rehabilitation is another method and it involves the use of FSRs – force-sensitive resistors. FSR rehabilitation leads to better monitoring of the patient’s progress which helps the concerned physiotherapists to modify the plan of exercises.