Smart Hand project

October 24, 2009 Wolf Schweitzer

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Smart Hand project; published October 24, 2009, 12:58; URL: https://www.swisswuff.ch/tech/?p=231.

BibTeX: @MISC{schweitzer_wolf_1571392106, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Smart Hand project}}, month = {October},year = {2009}, url = {https://www.swisswuff.ch/tech/?p=231}}

A very ambitious hand project builds a new bionic anatomic looking and directly nerve connected hands. It is advertised to achieve at least 80% of grips necessary for daily living but not manipulation:

http://www-arts.sssup.it/newCyberhand/smarthand/index.htm [now defunct probably due to raging success they moved to patents and commercialization fast] - http://www-arts.sssup.it/

From a functional point of view, the hand will be able to perform at least the 80% of the grips necessary in activities of daily living (ADLs) , i.e. palm opposition grasps (power grasps), a small set of pad opposition grasps (precision grasps) and lateral grasps. For this reason, the developed hand will be a fine device for grasping tasks but not for manipulation. In fact, the hand transmission and actuator system based on underactuated mechanisms do not permit the direct control of all degrees of freedom.

This in my eyes is a relevant statement as it means that someone would - first of all - not even complete all actions necessary for ADL with that hand and still put up with all that surgery and drama required to actuate this nerve connector controlled hand. Up[ to 20% of ADL related grips unsolved by that technology. Amazing!

One particular terminal device delivers significantly less than 100% of the grips necessary for ADL? Then first and foremost I'd require a fast sturdy quick release mechanism. As one terminal device does not do it all we are talking about using two or more to cover significantly over 80% of the grips required. At that point, it does not matter any more, whether it is two, three or four terminal devices. So with a second priority I would require different suitably constructed and functional terminal devices and - seeing as if I am going to swap devices anyway - with a third priority I will want to get the right kind and type of devices that make all of these happy: me, friends and family, employer, insurance. Good looking, sturdy and reliable, affordable and light weight. That is the logical consequence of only covering only 80% of grips required for ADL with only one lead-anchor type of terminal device.

So quite logically as derived from the above description I would aim for these:

First priority: sturdy quick release mechanism,
Second priority: suitably constructed and functional terminal devices - that means: for work, manipulate and lift heavy weights, withstand chemicals and operate under a wide temperature range; for going out, this should be a fashion item similar to glasses or a watch - functional but hip, and not too expensive; for sports and outdoors, full speed parts that survive heavy loads.
Third priority: price and quality relative to performance (above).

Now I would ask is whether the statement "at least 80% of the grips necessary in activities of daily living (but not manipulation)" is a sufficient goal for a huge undertaking such as this project. Why exclude manipulation? After all my own current setup - total cost around 7000 CHF, no microsurgery and no associated risks or discomfort, no batteries, no rechargers, except cleaning and occasional liner replacement no maintenance - already performs well within that range and with the current modifications, it runs stable and sturdy for weeks and months. It is not an untrained out of the box experience that I have but a trained and optimized experience. But that is what you should compare new stuff with.

I'm not saying don't do it. I'm saying, evaluate carefully.

So, let's look at the grips necessary in activities of daily living (including manipulation).
And let's look at what modifications were done to make it run stable - wrist, socket, harness, cable control and terminal device choice all were significantly improved with our own developments.

Now, this project still is extremely cool in terms of getting a feeling for a hand back. However there are some questions. Will the implants on the nerves keep functioning? Will they not cause inflammation and get useless due to fibrosis? What about the nervous system: how will it adapt? If the hand is to work well with an active body, and if it is meant for working, how will it be attached so I can lift 10 and 20 kg with it? How do these things perform under temperature variation, humidity, heat?

So far I don't think they are going anywhere. With really limited two-point discrimination on my stump, I can get almost all my everyday stuff done without prosthetic arm, and really all of it with my prosthetic arm. Open and close works extremely well using body powered arms, no need to toad around heavy schlepp anchors with batteries, motors and stuff. If I would consider a schlepp anchor (i.e., myo arm), it would have to offer manipulation and dextrous hand control, non-invasively. That is the requirement. And as I know these control strategies are under development, I will wait for these.