Double the Force!

Updated: Sep 1, 2019

The Victoria Hand Project’s mission is to work with local communities to provide low-cost, functional prosthetic devices to upper-limb amputees who lack access to their own. In addition to providing amputees with prosthetics on demand where they need them, the Victoria Hand Project works very closely with our clinical partners in-country after the hands are distributed to get feedback, from both clinicians and amputees, that we can use to make the Victoria Hand even better.

The VC200 device is capable of an Adaptive Grasp, a Moveable Thumb and a Lockable Grip to make carrying loads and picking up objects easy for the user. Taking into account all suggestions and inquiries by users and professionals, we began brainstorming ways to make the grip strength of the V200 hand stronger without drastically changing the design. This led our design team to the idea of the Force Doubler.

The Victoria Hand Project has developed a new Force Doubler mechanism to give users more control over their prosthetic limb. This device, which fits on the Tricep Brace of the harness, doubles the pinch force exerted by the Victoria Hand and allows for smoother, more controlled hand motions. ​​

 Figure 2: Arrow describing where Force Doubler sits on the Tricep Brace

The Force Doubler uses a moving-pulley system to increase the input force. When lifting 1 unit of load (in our case, applying 1 unit of pinch force on the hand) the pulley splits the load between the fixed cable and the free cable, so the user only needs to apply ½ a unit of force. The mechanical advantage is 2 and the force is effectively “doubled”.

Figure 3: Schematic diagram of the moving pulley

The Force Doubler is designed to be lightweight and compact , ensuring a comfortable fit for the user. The Force Doubler is also able to rotate so it can move with the user when they lift or extend their arm. 

Figure 4: The Force Doubler in the neutral position and rotated approx. 20°

As an added bonus: since the device is incorporated into the tricep brace, and not the hand or socket, this force doubling mechanism can be easily implemented with all previously deployed Victoria Hands. All amputees fit with the Victoria Hand will soon have access to a stronger, more functional hand without needing any adjustments to the terminal device.

We are very excited to deploy the Force Doubler as soon as possible!

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