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The exoskeleton is composed by two main supports (calf and thigh) which are fixed to the leg by means of velcro closures. The two supports are linked with a four-bars system (which will be described later) that also provides a path which follows the knee motion. The four-bars mechanism is covered inside a protecting box.

The power is provided by a linear actuator which works like the mechanism of the crane to impose a roto-translational motion to the system.

On the lower part, there is a system which allows the customer to change the length to better suit the leg. The pedal was added with a rotational joint to allow the ankle to rotate. It can also discharge part of the force onto the ground.

Between the leg and the exoskeleton there is a soft part which can provides comfort to the user.

Four-bar System

The idea of the four-bar system was taken from a thesis on the mechanism simulation of knee motion. (The link is shown as following). We refined the existing four-bars system used for the inner knee substution, and managed to apply it on the external support.

The movement of the mechanism is powered by an linear actuator, which is driven by a proper program, and provides the power to achieve the movement of the leg.

We found some useful information on the internet, which helped us to understand better how the other commercial companies faced with similar problems. They are shown in this "Inspiration" section:

1、Eksobionics:

Ekso Bionics develop and manufacture powered exoskeleton bionic devices that can be strapped on as wearable robots to enhance the strength, mobility, and endurance of soldiers and paraplegics. These assistive robots have a variety of applications in the medical, military, industrial, and consumer markets. It enables individuals with any amount of lower extremity weakness, including those who are paralyzed, to stand up and walk.

The company's first commercially available product is called called Ekso. Ekso Bionics is the original developer of HULC, now under military development by Lockheed Martin, and the current developers of Ekso (formerly eLEGS), which allows wheelchair users to stand and walk.

http://www.eksobionics.com/

2、Four-bar Internal Knee System

More than 100 individual knee mechanisms are commercially available for the North American amputee population. Classifications for prosthetic knees have been proposed previously, but there are two basic knee categories of kinematic function into which prosthetic knees fall: single-axis knees and polycentric knees. Prosthetists should be aware of several key differences between these two classes of knees to make informed decisions regarding prescriptions of prosthetic knees for their patients.

Single-axis knees have a single axis of rotation about which the shank rotates with respect to the thigh. Polycentric knees, on the other hand, are characterized by a center of rotation that varies with the knee-flexion angle. The center of rotation, more appropriately called the instantaneous center of rotation, is simply the point about which the shank and foot rotate as the knee flexes. Polycentric knees are becoming increasingly popular among prosthetists for transfemoral amputee prostheses.

The most common type of polycentric knee is the four-bar linkage knee, so-called because it has four axes of rotation connected by four rigid linkages. The polycentric nature of four-bar linkage knees accounts for two key advantages: stance-phase stability and knee-flexion cosmesis. A lesser known distinction of four-bar linkage knees is their inherent ability to provide greater foot clearance than single-axis knees for a given knee-flexion angle. This additional floor clearance allows the amputee to walk with less concern for floor clearance during prosthetic swing. This article focuses primarily on floor clearance issues of four-bar and single-axis knees but also includes brief discussions of stance-phase stability and cosmesis.

-Copied From "The Influence of Four-Bar Linkage Knees on Prosthetic Swing-Phase Floor Clearance"