POWERED EXOSKELETONi-What is exoskeleton and how it works?ii-History and application iii-Practical examplesiv-Limitations and design issues

What is exoskeleton?• An exoskeleton is a hard, protective outer-body

covering of an animal. Although exoskeletons provide support they are not comprised of bones.

Powered exoskeletonA powered exoskeleton is a mobile machine consisting primarily of an outer framework worn by a person, and a powered system of motors orhydraulics that delivers atleast part of the energy forlimb movement.

Powered exoskeletonThe main function of a powered exoskeleton is to assist the wearer by boosting their strength and endurance.

Application Powered exoskeletons are commonly designed for military use, also in civilian areas, similar exoskeletons could be used to help firefighters and other rescue workers survive dangerous environments.The medical field is another prime area for exoskeletontechnology, where it can be used for enhanced precisionduring surgery, or as an assist to allow nurses to move heavy patients. Exoskeletons could also be applied in the area of rehabilitation of stroke or Spinal cord injury patients.

History The first attempt to build a practical powered exoskeleton, by general electric in 1965.The suit was made lifting 110Kg feel like lifting4.5Kg,it weighs 680Kg, powered by both hydraulics an electricity the suit allowed the wearer to amplify their strength by a factor of 25.the project was not successful.

HULC(Human Universal Load Carrier), The HULC is a battery powered, lower extremity exoskeleton. The innovative hydraulic architecture is highly efficient enabling the system to run on batteries, It carries up to 90 kg, An onboard micro-computer ensures the exoskeleton moves in concert with the individual.

Powered by Four lithium ion batteries, 48-hour operation

HAL-5 The Hybrid Assistive Limb It has been designed to support and expand the physical capabilities of its users, particularly people with physical disabilities. Double-leg model/approximately 12kg, hip joint: extension 20˚/flexion 120˚ | knee joint: extension 6˚/flexion 120,made of nickel molybdenum and ammonium alloy.

Powered by 100-volt battery pack

Ekso bionicsEkso provides functional based rehabilitation, over ground gait training, and upright, weight bearing exercise unlike any other. Provides a means for people with as much as complete paralysis, and minimal forearm strength, to stand and walk

Raytheon XOS 2The XOS is similar to the HULC in that it allows the wearer to lift upwards of 90kg without feeling any strain, thanks to hydraulic assistance and sensors attached to the hands and feet, Powered by External power supply via cable.

Limitations and design issuesEngineers of powered exoskeletons face a number of large technological challenges to build a suit that is capable of quick and agile movements, yet is also safe to operate without extensive training.

Power supplyOne of the largest problems facing designers of powered exoskeletons is the power supply. Power supplies being used:1-Li-ion or Li-Po rechargeable cells2-Alkaline or silver-oxide non-rechargeable cells3-Internal combustion engine4-solid oxide fuel cells5-Direct external power(cable)Future trend: wireless energy transfer

Skeleton materialInitial exoskeleton experiments are commonly done using inexpensive and easy to mold materials such as steel andAluminum. As the design moves past the initial exploratory steps, the engineers move to progressively more expensive andstrong but lightweight materials such as titanium, and use more complex component construction methods, such asmolded carbon-fiber plates.

Actuators The powerful but lightweight design issues are also true of the joint actuators, actuators being used:1-pneumatic cylinders2-hydraulic cylinders3-electronic servomotorsFuture trend: elastic actuators like SMP

Joint flexibilitySeveral human joints such as the hips and shoulders are ball and socket joints, with the center of rotation inside the body. It is difficult for an exoskeleton to exactly match the motions of this ball joint using a series of external single-axis hinge points, limiting flexibility of the wearer. Possible solutions: 1-Separate exterior ball joint alongside the shoulder or hip2-Hollow spherical ball joint that encloses the human joint3-Spinal flexibility

Power control and modulationIt is not enough to build a simple single-speed assist motor, with forward/hold/reverse position controls and no on-board computer control. Such a mechanism can be too fast for the user's desired motion, with the assisted motion overshooting the desired position. Sudden unexpected movements such as tripping or being pushed over requires fast precise movements to recover and prevent falling over, Fast and accurate assistive positioning is typically done using a range of speeds controlled using computer position sensing of both the exoskeleton and the wearer, so that the assistive motion only moves as fast or as far as the motion of the wearer and does not overshoot or undershoot.

Other possible problems• Detection of unsafe/invalid motions• Pinching and joint fouling• Adaptation to user size variations

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