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Personalized, Low Cost Prosthetics for Above and Below the Wrist Amputations

Nirel Kakon

Introduction:

Prosthetic development is a field dating back to 950 B.C., with the goal of helping those who are disabled return, as close as they can, to an unhindered life. In recent years this field has taken off tremendously, incorporating new technologies in order to bring a level of control and complexity to prosthetics that has never been possible before. Nowadays these prosthetics can range anywhere from mechanically operated, powered by the movement of a person’s arm, to myoelectric prosthetics, controlled by sensors that detect the muscle movements beneath the skin. To make this technology available to anyone, these prosthetics have to be made simple, user friendly, maintenance friendly and most importantly non expensive. This proposal is all about that.

 

The Problem

            Currently, most of the prosthetic hands available on the market are somewhat bulky and very expensive and therefore non affordable. Furthermore, in order to get a hand, the user needs to go to a a special manufacturing lab to get it custom made for his use. A mechanical prosthetic in the form of a hook that opens and closes, or an aesthetic prosthetic, costs in the range of thousands of dollars. A more complicated prosthetic with sensors and motors able to do more than simply motions costs in the range of tens of thousands of dollars. These prosthetics allow for a much larger range of motions and provide a great deal of freedom for the user. The high cost is affected by the manufacturing of custom made pieces, since otherwise the prosthetic can cause severe discomfort, and even phantom pains when in use. Additionally for electric prosthetics, the use of expensive motors and microchips capable of the calculations necessary for controlling the hand increases price dramatically. Lastly all of these prosthetics are made by individual companies seeking to make a profit. Consequently,  only limited number of people can afford these arms, and they are usually unobtainable to children (even in households that can afford it) since they will have to be replaced often when the child develops. Furthermore, despite the amount of custom made parts in these prosthetics, they have very few cosmetic options if the user wants anything other than the standard shape the prosthetics come in. While this may not seem like a problem at first, it’s important to keep in mind the psychological aspect of wearing a prosthetic, especially for children. If they aren’t comfortable with what they are wearing, it will hinder their development and ability to integrate socially as well as others who don’t need a prosthetic.

 

Our goal is to design and manufacture low cost, custom made, user specific, easy to maintain prosthetic hands. Furthermore, our designs will be available to anyone(open access) such that it could be modified and manufactured anywhere around the world.  To do that we will make our designs compatible with 3D printing technologies for manufacturing.

 

On-going work

 

Our low-cost prosthetics are made using 3D printing technology in order to custom fit a mechanical hand and its cosmetic design to the user. Custom fitting of the prosthetic hand is very important in order to prevent pressure wounds, phantom pains and constant discomfort. Therefore, our hand designs are parametric and can be deformed and adjusted per user. To do that we also developed a scanning tool in-which the user’s hand is scanned and 3D modeled using low cost 3D cameras (such as Microsoft Kinect). The collected scans are then introduced to an algorithm we developed (Figure 1 and 2). The results of this algorithm is a user friendly 3D reconstruction of the user limb (Figure 2). The geometric data extracted from this model are then used to modify the specific hand design to a specific user anatomy.   

Our hand models very in complexity. The most simple model is able just to open and close its fingers (grasp) by using mechanical motions of upper body parts such as bending or extending the wrist or elbow. A more complex prosthetics uses micro motors and sensors to recognize muscle activation in the arm and translate these, using an algorithms developed by us, to motor commands and hand motion. These prosthetics allow for a much larger range of motions and provide a great deal of freedom for the wearer, yet are still affordable due too the low manufacturing cost.  We have already developed and provided users with several hands – see example in figure 3 and Figure 4

 

Future propose

 

We propose to further develop a portfolio of prosthetic arms that are both affordable and cover a large range of use, styles, and that can be as simple as mechanical opening and closing hands, or as complicated as the high level electric prosthetics. The hand designs will be parametric so that with our scanning and measurement software they could be scaled to fit a specific user. This scaling method will allow even those who don’t know how to use or have access to 3D modeling software to still get a proper, user-specific, prosthetic. Our designs will be 3D printing compatible to lower production costs, and make replacing broken parts as easy as clicking print on your computer instead of getting in touch with a company overseas and waiting for a new part to arrive.

Most importantly, we will make all our designs and tools available online (open access) for others to be use so that people around the world would be able to execute the developed procedure and print a user tailored prosthetic hand.

 

 

 

 

 

Click on images to enlarge
Four motion demo
Two motion demo