VOHS 2.0
Voluntary Open-Hook System 2.0
Towards a Solution
CREATIVITY
The Prosthetic:
In order to solve the problem of the excess amount of activation force required to lift an object, this idea features a newer extension of the lever, which joins both hooks using a bar. The bar is attached to the circular adjustor that the black arrow points to. This adjustor is ridged with three levels, low, medium and high, each corresponding to varying degrees of force. These forces are adjusted by the displacement of the cable-four whel pulley system shown here with gray circles(pulleys) and a black line(cable). For the level to move the distance between these ridges on the adjustor, the cable must displace one-fourth of the distance between the ridges. This allows for increased efficiency, a smaller activation force, and the ability of the user to adjust the amount of force they're exerting for various objects.
The Hook:
The terminal device is also altered in that the cable which is attached to the lever adjoining both hooks allows the hooks to move up and down. The thumb pointed at by the neon green arrow is set between 90 and 120 degrees, allowing for a more advance imitation of the real human hand. While the thumb is set at a certain angle, the two hooks which move up and down allow for a firm grasp on the object. Also, like current hooks, the terminal device can be rotated to any set orientation by the user.
Pulley and Adjuster
In order to allow force adjustment so that the user can easily grip various objects (instead of being restricted to only one level of output force), this idea introduces a level adjuster shown in the third drawing below. This level adjuster has three ridges, each signifying a level of force: low, medium and high. The black rectangular prism attached is the lever where its default position is the first ridge, allowing for the hooks to remain closed in a relaxed position, as shown in the first drawing. When the cable displaces from the pulleys at one-fourth of the distance between each of the ridges, the lever (indicated by the red arrow) is pulled back, allowing the left hook to move a distance specified by the lever's displacement between the ridges. This pulley system allows its pivot point to be the elbow around which the cable will be wrapped so that even small movements of the arm can open the hooks while using less force.
The Proposed Solution:
The Prosthetic:The final solution shown to the right reduces the number of pulleys from four to one. Although this threatens to decrease the efficiency of the above stated ideas, this is balanced out by the fact that the lever can be made longer to increase the moment, thus, also contricbuting to the reduction of the activation force to require the hooks of the terminal device. Morever,efficiency is increased by replacing the metal housing with that of teflon, which lighter in weight with less friction.
The Hook: This solution also innovates the terminal device by attaching a thumb digit to the level adjuster on one side, while on the bottom of the adjuster, the lever is attached to the cable. Thus, when the cable becomes taut due to the extension of the arm, the lever is pulled up from its starting position at the third ridge, allowing the thumb digit to lower. The two hooks themselves are stationary. When the arm relaxes to grip an object, the lever returns below the third ridge, while the thumb digit ascends grasping the object between itself and the two hooks firmly.