Wearable exoskeletons represent electro-mechanical mechanisms designed to assist, aid, strengthen, help people, and have a range of human movement practices and scenarios in order to provide potential supplementation and argumentation to the patients. The applications include a wide variety of domains:
- medical devices to compensate impairments or instruments for rehabilitation coaching of people recovering from stress or trauma;
- movement support for disabled patients;
- personal care androids for providing support for normal daily life to healthy persons;
- decrease in physical burden during commercial and military implementation.
The efficient and affordable design of wearable exoskeletons and their development challenges the researchers and producers in the part of the mechanical configuration, ergonomic interfaces for comfort, and successfulness, human-adaptive controllers to provide symbiotic support and human modeling and biomechanics. Modern materials and composition, adaptive movement controllers, human-robot interplay control, biomechanical sensors, and new lightweight actuators require new technologies.
Exoskeleton research and development requires a wide range of knowledge, including mechanism design and control involving consideration of close human-robot interaction scenarios, advanced human motion intention detection, support, comfort, and ergonomics and safety regulation in various wearable devices.
This article presents modern development work on walking assistant exoskeletons for gait training of patients and exercise promotion for the elderly.
The first existing model of the exoskeleton is a whole leg assisting device using a unique parallel link mechanism. For gait training of motor palsy patients, it has a weight-bearing lifter attached. For the elderly, a torque controller was developed, taking into account the dynamics of both a user and the apparatus with real-time acceleration data.
The second model of the exoskeleton is a whole-body assisting suit developed by adding arm assistance to the whole leg apparatus. Assisting not only legs but also swinging arms increases the cerebral activity of all areas. Such an effect can be expected through rehabilitation with the entire body exoskeleton.
Finally, there is a close-fitting type exoskeleton assisting only the ankle joint. By utilizing the structure of the bi-articular muscle and the physiological phenomenon of the stretch reflex, the user’s leg can be raised, assisting only the ankle joint. Experiments with hemiplegic (with one side of the body paralyzed) patients show that abduct variation of the hip joint is decreased. At the same time, the stride length is increased by using the device.
For many apoplexy patients (over 1 million people per year in the US), recovering and regaining an independent life through neuro-rehabilitation is highly demanded. If the patients start training immediately after the incident, they have a high possibility to recover compared to no training. In walking, when the ideal leg gait motion for a motor palsy patient is input by using an assistive gait device, the patient regains their motor function. The movement activates the subject’s brain in the undamaged area. Then the neural network of the brain is reconstructed.
Neuro-rehabilitation, which repairs the neural circuits by directly inputting movement into the body, requires a programable training device to perform this movement and treatment. Novel training machines and methods have been developed in recent years.
NIRS (Near-Infrared Spectroscopy) is a useful approach to evaluate cerebral activity during walking. It suggests that the alternating leg movements seen during gait are controlled by the leg regions of the primary motor cortex (PMC) and other related motor areas. Suzuki found that the prefrontal and premotor cortices are involved in adapting walking and running speed on the treadmill using NIRS. They also indicated that preparation for walking cued by verbal instruction enhanced frontal activations both during the preparation and execution of walking as well as walking performance. Furthermore, Yano developed a footpad-type locomotion interface. Using NIRS, they confirmed it activated the user’s brain more effectively than walking on a treadmill. Therefore, it is more effective to use the assistive motion device than regular training. However, most of these machines require the motor palsy patient to remain stationary during use. Many conventional devices are tightly fixed to arms and legs. Most of these devices do not equip the actuator to assist the ankle joint.
The comparison between ideal gait and hemiplegic gait
Ideal gait has four points of feature: straight posture, long stride, heel contact by dorsiflexion (bending upwards), and kicking ground by plantarflexion (bending downwards).
On the other hand, hemiplegic gait also has four features: droopy posture, specific toe contact, the inadequacy of plantarflexion, and circumductive foot. The equinus foot (with limited ankle joint movement) is dangerous for walking because it is easy to stumble and fall. It is essential for hemiplegic patients to recover heel contact; therefore, it is necessary to develop the ankle motion support type of walking assistive apparatus.
The popular research topic is the rapidly aging population. Most of the elderly’s muscles become weak with age. Especially, TA muscle (Tibialis Anterior muscle), used in the dorsiflexion of the ankle joint, is the most fatigable muscle. It is more likely to stumble and fall even though there may only be a slight step. Therefore, they lose confidence in walking alone. If they don’t walk, it will become easy to fracture their bone, and finally, they will be bedridden.
Several exoskeletons were developed to meet the different training requirements to address the needs and problems noted above. Furthermore, a whole-body motion support type mobile suit was designed. By utilizing NIRS, we evaluated the cerebral activity while walking and compared the difference assisting only legs or both legs and swinging arms and walking on a treadmill or in a corridor. However, patients hesitated to use this apparatus because it was bulky and afraid of going out of control. For gait training of hemiplegic patients, it is necessary to reduce the apparatus’s weight attached to the patient’s leg. A close-fitting type of walking assistive device was developed to address this problem. It was improved and sold as a product, RE-Gait, in 2016. It is very lightweight, low cost, and tiny so that you can hide it in the hem of the pants. By using this apparatus, both dorsiflexion and plantarflexion increased, and the gait got improved. RE-Gait can be used not only for gait training of patients but also for walking exercise promotion. However, even though the user is assisted with the apparatus physically, they should mentally maintain the exercise. Therefore, the developers suggested evaluating the user’s emotion two-dimensionally and developed a device controlled by using the relation between the two-dimensional emotion map and the walking condition map.
Nowadays, the industry has been developing walking assistive apparatus for gait training patients and promotion exercise for the elderly. One of them is already utilized by many patients to improve their gait. Furthermore, they are now developing an automatic emotion evaluation system. By connecting to the walking assistive device, many elderly will be able to promote exercise easily. By that, they will regain their independent life.