Research and development in the area of exoskeletons, either partial or full body, is well represented in literature. Early development of powered human exoskeletons started in the late 1960s. These early projects were undertaken by groups in the USA, Generally intended for able bodied users to augment their abilities in applications such as the military, while groups from the former Yugoslavia developed devices for the physically challenged [21]. The general focus of the research and development of exoskeletons has had minimal change since the first developments with the prominent recent projects in this field still being developed for amplifying the abilities of able bodied persons, substantially increasing the carrying capacity and range of the user. While many of these exoskeletons are intended for use by military personnel and search and rescue teams [22, 23], others are being developed to help the elderly and infirm, or the nursing staff who care for these people [24].
This section will discuss the exoskeleton projects presented in literature that are targeted for amplifying human ability, while exoskeleton type devices intended for rehabilitation of patients, who have lost some of their function due to sickness or injury, will be discussed in the following robotic rehabilitation section.
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Figure 2.1 - The HAL-5 (Hybrid Assistive Limb) [25]
HAL (Hybrid Assistive Limb) is an exoskeleton device developed by a team at the University of Tsukuba in Japan and is the first to be released commercially by Cyberdyne Inc. [24-26]. An initial development model, the HAL 3 was designed as a lower body exoskeleton, with its successor, the HAL 5 (which is the first commercialised design) including upper body assistance in its development, is a full body exoskeleton. The HAL suit uses the myoelectric signals from the operator’s muscles to anticipate the intentions of the user, and produce appropriate torque at the joints to achieve this motion [27]. The intended purpose of the HAL suit is to aid the elderly, weak and disabled by increasing their mobility when they are too weak to support their own weight, it is also proposed that this exoskeleton will be useful for carers of these people, such as nurses.
This exoskeleton has an estimated battery life of 5 hours between charges and can increase the strength of the user by a magnitude of between 2 and 10 times their own strength [25]. By comparison, the HAL suit has the most aesthetically refined designed of any of the current exoskeletons in development.
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Figure 2.2 - The Ratheon Sarcos XOS exoskeleton [28]
The XOS, developed by Ratheon Sarcos with funding from DARPA (Defence Advanced Research Projects Agency) [24, 28], future developments this exoskeleton are intended for use by the American defence force in the future. The current model of this project is electrically powered, with the exoskeleton currently tethered to its power supply via a cable, which can be seen in Figure 2.2.
Another full body exoskeleton is the Kanagawa Power Suit developed at the Kanagawa Institute of Technology in Japan [29]. The suit is pneumatically powered, with the pneumatic supply provided by battery operated air compressors mounted within the suit. It is intended for use by nurses caring for patients [30]. This suit is able to assist nurses to lift patients weighing up to 85kg with ease.
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Figure 2.3 - The HULC exoskeleton - a development from the BLEEX exoskeleton [24]
Initially developed as a project at Berkeley University, which later commercialised through Berkeley Bionics, the BLEEX (Berkeley Lower Extremity Exoskeleton) is an exoskeleton for the lower limbs designed to augment human abilities, namely strength and endurance [23, 31]. It was developed under DARPA funding, and became the first load carrying lower extremity exoskeleton in the world [24]. Berkeley Bionics went on to develop this technology further in the HULC (Human Universal Load Carrier), the ExoHiker and ExoClimber) [24].
MIT have developed an exoskeleton based assistive device for carrying heavy loads over uneven terrain. This project is also DARPA funded [24], and the exoskeleton is similar in appearance to the BLEEX exoskeleton. As with the BLEEX, this exoskeleton was developed for military and emergency services use. Whilst it improves carrying capacity by 80%, there is some extra energy required on the part of the pilot due to alteration in gait because of the suit. This increases oxygen usage by 10% as compared to normal walking [22, 32].
The RoboKnee is a developmental exoskeleton device worn at the knee, and designed to enhance strength and endurance, particularly when climbing stairs or lifting heavy
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loads. The device uses an innovative elastic actuator to add compliance to the system and achieve a low impedance actuator. This is a relatively light device that enhances performance while not hindering natural walking gait on a steady surface or ascending stairs. However the device causes the user to employ unnatural muscle groups when descending stairs, therefore hindering natural motion. The current design is cumbersome to put on and take off, requiring up to ten minutes, and prevents the user from sitting due to the location of the actuator [33].
The projects discussed above are representative of the current developments in exoskeleton technologies for non-therapeutic applications.