Livny: Developement of a Cosmetic Hand Prosthesis Activated by Compressed Air (1969)

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ABSTRACT IN HEBREW

● TITLE: Development of a Cosmetic Hand Prosthesis Activated by Compressed Air
● AUTHORS: Livny, Avinoam
avinoam.livni@gmail.com
● SOURCE: M.Sc. thesis, Technion, Haifa, Israel (1969).
● LANGUAGE: Hebrew with English synopsis
● SUPERVISOR: Dino Bousso (1933-1971).
● 12 references:
[1] Bousso, Dino (1933-1971), A six degree of freedom experimental limb for thalidomide children, Bio Medical Engineering, v. 4, No. 7, pp. 313-321 (1969)
[2] Bousso, Dino (1933-1971), A new rotary actuator, Journal of the Association of Engineers and Architects in Israel, v. 26, No. 4, Nov.-Dec. (1969)
[6] Russell, Harold (1914-2002), Victory in my Hands, (1949).
Hebrew translation: Nitzahti et Yaday, Argaman, Tel-Aviv, Israel (1954)
and more 9 references.
● SYNOPSIS in English:
The aim of this project was to develop cosmetic multiple degrees of freedom, powered hand prosthesis.

There exists a variety of hand prostheses, but there are serious mechanical problems associated with them such as complicated design, large weight, sensitivity to the environment, and a limited number of degrees of freedom. The aim of the research was to develop a hand that would be free from these drawbacks.

Another severe problem in prostheses is control. This can be mechanical, through body movements, or myoelectric. In both cases, it is difficult to control many degrees of freedom because of the limited number of control sites. It was decided to limit ourselves to three degrees of freedom which would allow a considerable variety of movements and not present excessive demands on the limited number of control sites available.

In order to initiate the hand to the maximum extent, the anatomy, bones, joints, and structure of the human hand were studied and the range of movement and forces developed by its various parts was determined.

A number of available hand prostheses were studied regarding their use, advantages, and drawbacks. It seems that the various types of hooks are the most practical for heavy work and quite efficient for daily use. However, from the social and psychological viewpoint of the amputee, a cosmetic hand is preferable [6].

The study made indicated the desirability of compressed gas as an energy source together with the rotary pouch actuator developed by Bousso [1, 2] for powering the joints.

The actuator performance regarding weight, moment, space requirements and springiness was determined and found to be suitable when the gas pressure is 10 Kg/cm². Single-acting actuators were used.

The return spring and movement limiting straps were combined together in the form of nylon fabric-covered rubber bands. The material best suited for the structure is some high-strength polymer. It is possible to slip a glove onto the hand, thus improving it cosmetically.

A prosthesis was built and tested in the laboratory for a variety of everyday applications such as holding eating utensils, shaving razors, pens, suitcases, briefcases, door handles, etc. In every case, the appearance is quite natural and the performance was very good. The angular range of movement and forces developed were determined.

It seems that this prosthesis has a number of advantages compared to other available artificial hands. These advantages are:

1. Three degrees of freedom.
2. Low weight – 180 grams.
3. High efficiency.
4. An extremely simple design made up of nine structural elements and five actuators.
5. Insensitivity to the environment.
6. Self-adaptation of the fingers to the object grasped.
7. Fast response time = 0.25 second.

Other details include:
Maximum opening between thumb and fingers: 85 mm
Range of joint movement - 90^o
Force at the beginning of stroke (per finger): 2.4 Kg
Force at the end of the stroke (per finger): 1.0 Kg

The prosthesis is extremely versatile from the design viewpoint. The number of degrees of freedom can be reduced if the number of control signals is less than three or increased if additional control sites are available. In both cases, the self-adaptation feature is preserved.

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