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The second iteration of the overall CAD design has been improved in four main ways. First, the Watt 6-bar mechanism is actuated by a crank-rocker. Second, the new crank-rocker is timed mechanically by means of a Geneva mechanism. Third, a detailed and improved human-exoskeleton interface is detailed. Fourth, the nut and bolt fasteners from the previous design are replaced with shafts, bearings, spacers, and retaining rings to ensure a more robust and frictionless interface between linkages.
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As can be seen from Figure 1, the Watt 6-bar mechanism now has an additional linkage attached to the bicep. This linkage is the middle link of a four-bar crank-rocker mechanism. The four-bar crank-rocker is comprised of the body as ground, the upper circular gear as the driver link, the middle linkage attaches to the bicep, and the bicep linkage becomes the driven link.
Figure 1: Side view View of Prototype 2 exoskeletonExoskeleton
The purpose of this additional crank-rocker was to simplify the actuation of the system. In the previous iteration of the design, the exoskeleton had to move between two discrete angles. This required starting, stopping, and changing positions of the motor during each cycle of motion. This means a more complicated control system and the need for either a damper or compliant element to absorb the momentum change of the system. In the new design with the crank-rocker, the motor merely has to rotate the upper gear (or driven link) continuously in order to rotate the bicep linkage the appropriate range of motion.
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The next addition to the design was the exoskeleton interface with the human body. In the first iteration, most of the design emphasis was placed upon the kinematics of the linkages and less upon the interface with the wearer. In this design, we developed a exoskeleton spine that will serve numerous purposes. First, it will connect to the exoskeleton linkages, thus providing a ground for the mechanism. Second, it will provide a place to attached the motor and circuits to control the mechanism. Finally, velcro straps will be used to securely attach the exoskeleton spine to the users shoulders and torso. The spine component is shown in Figure 2.
Figure 2: Back view View of exoskeletonExoskeleton
