Note: This text is a work in progress. If you find any inaccuracies or material that needs to be included, please contact us.
Background
Due to their reliability, durability, and relatively low cost, body powered hooks and hands are the most popular upper extremity prostheses. They are controlled by a harness that captures an unrelated movement of the user’s body, such as a shrugging of the shoulders, and transfers this movement through a cable system to a terminal device such as a hand or hook. Body power is also used to control elbows and other motions in hybrid electronic/mechanical systems.
There are two major types of body powered terminal devices. A voluntary opening device is held closed by springs or rubber bands and the user moves to open it. This mechanism makes it easy to hold and move objects without effort, but has a grip strength limited to the strength of the springs. A voluntary closing device is held open by springs and the user moves to close it. This allows for a strong grip but requires effort to hold and move objects.
To get a feel for the range of available terminal devices, see the following manufacturer catalog pages:
An interesting prototype hook, the vector prehensor, is a voluntary opening device with highly adjustable grip force. It works by adjusting the angle between the spring and the hook. The authors filed for a patent but the prior art search turned up a similar 1954 German patent. Authors Lawrence Carlson and Dan Frey have generously agreed to let us publish their design on this website. It looks like a great product, and we can’t wait to see it become available for use. Carlson and Frey did get patents on some other interesting ideas: a locking mechanism and a hand that grips by rotating the thumb.
All content and designs on this site are in the public domain, and we place no restrictions on their use. We encourage any derivative works, but all designs are registered periodically so that our work cannot be kept from the public by patents.