How Does An Exoskeleton Work?
What is an exoskeleton? Exo is a Greek word which means outside. As opposed to the normal human skeleton which supports the body from the inside, an exoskeleton supports the body from the outside. Exoskeletons are usually designed to allow people with mobility disorders to walk or to augment strength and endurance.
Exoskeletons have several key components:
Frame: Usually made of lightweight materials, the frame must be strong enough to support the weight of body as well as the weight of the exoskeleton and its components. The frame must also be able to hold the body securely in place without the risk of the wearer falling out. The frame will usually have a series of joints which match the joints of the body, at the hip, knee and ankle.
Batteries: Must either power the exoskeleton for most of the day or be easily replaceable so that depleted batteries can be quickly removed and replaced with charged batteries during the day. The batteries should be lightweight and small so that the exoskeleton is neither heavy nor bulky. The batteries must also be quickly rechargeable so that the exoskeleton is ready to go again the next day.
Sensors: These gather information about how the user wants to move. Sensors may be manual, such as a joystick, or sensors may be bio-electrical and detect the physiological impulses generated by the body, or the sensors may be a combination of devices such as a remote control and motion detector which allows the wearer to change the motion from a walk to a climb. The information gathered by the sensors is sent to the computer for analysis.
Controller: Acting as the brains of the device, the controller is on-board computer which takes the information gathered by the sensors and controls the actuators. The computer coordinates the various actuators in the exoskeleton and enables the exoskeleton and its wearer to stand, walk or climb or descend.
Actuators: If the frame is like the bones of the body and the controller is the brain, then the actuators are like the muscles driving the movement. The actuators are usually electric or hydraulic motors. Using the power from the batteries and the information sent by the computer, actuators move the exoskeleton and the person who is wearing it.
Balance and Gait Control: Most current exoskeletons provide neither balance nor gait control. Current exoskeletons require the wearer to have sufficient upper body strength so that the exoskeleton and the wearer do not topple over. Balance of current exoskeletons is usually controlled with the use of crutches. Also, most current exoskeletons do not mimic normal human gait. Walking has been described as “controlled falling forward”. With each step, we throw our bodies forward and move the other foot to catch us and prevent our bodies from hitting the ground. The normal human step moves from heel to foot to toe when we are walking. Our stride changes when we walk forwards or backwards or climb a step or descend a hill. Current exoskeletons can not mimic these functions and are less efficient and less comfortable. Exoskeletons of the future will certainly have built in balance control systems, such as gyroscopes, to keep the wearer from falling and built in gait control which will mimic normal human physiological movement.