Precision grip enhancement of prosthetic hand [close-up, detail, technical aspect]

The problem is, that by far not all grip geometries of prosthetic hands actually deliver actual, true, reliable precision grips. Hooks, mostly yes, hands, not so much.

From a hard utilitarian view, however, a true, small-scaled precise precision grip is the only true reason from my view as a below elbow amputee to really wear a prosthetic arm as far as grips or grip functions are concerned (that is, notwithstanding asymmetry of shoulders, back, total load, end of day feeling, overuse for repetitive or heavy activities, like, real work, et cetera).  So in other words, the everyday dichotomy - either I wear a prosthetic hook if I mean business, or no prosthesis - remains intact. This also relates to the fact that the body-powered arm has an error rate so low it is far, far, far beyond reach for myoelectric technology to match. It is a few powers of ten away. When they said in five or ten years, five or ten years ago, they were dreaming - a few things such as inherently low SNR based on polyvalent muscle activity cannot be easily fixed [link].

There are a few technical things to know, or consider, to put this into context.

    1. My arm is easily able to perform a soft tight fitted "adaptive" cylinder/power grip by using the elbow, the cubital fossa, the joint between upper arm and forearm stump, for a real lot of situations or grip applications. It does not cost me any extra equipment, it is by and large totally care free, and readily available at all times. It is the most convenient way to grip, ever, as no extra materials, negotiations, repairs, drama, etc. are required, ever. That aspect is mostly ignored and underestimated at once, by most players in the field. Which is why I put it here in writing. The function on a functional level (where else?) is so good that one could cite a study where unilateral below elbow amputee children perform better than two-handed peers; so from that and my description alone, it could not have been all that bad to begin with, right?
    2. The only technical grip that is far out, totally impossible, not within reach even with the best of intentions, without a prosthetic arm, is a very focused detailed small-scaled precision grip. Which is the exact reason why I either wear a hook or no prosthesis, for the most part. The precision grip is the single most important ergonomic add-on any prosthetic arm brings to the table. If a prosthetic arm with all its bells and whistles has no superbly perfect precision grip, it can virtually stay home. No real need; admitted, maybe a nice ornament, who knows, but no real dire sore need.

So, that is why most other things are junk and the body-powered split hook wins [link].

The general problem of precision grip planning and gripper geometry has been laid out in all detail [link]. The iLimb, for example, systematically fails a reliable grip geometry by design, by hand control design [link]. No surprises there. The only robust prosthetic hand that offers a truly reliable precision grip from my personal view and knowledge, combined with a smooth sweet adaptive grip, is the Becker Hand [link].

And now, that just got a whole lot better!

I started to tune my gripper surfaces with rubbery and deformable add-ons a while back now, with great success [link]. So now, I bought these GRIPEEZ rubber finger tips by Swingline [link]:

And I put the onto my Becker Mechanical Hand [link].

This gives the concept of Blue Light Special a new spin [link].

Here is lifting a small hex key off the workbench.

Here is lifting a relatively small nut off workbench surface.

Here is lifting a rather small screw off workbench surface.

Here is lifting a tiny nut off workbench surface.

Here is lifting a small plastic part off workbench.

Here is picking up a small dowel. Off workbench surface.

Here is getting a tiny washer off workbench surface.

Here is lifting a set of stapler staples, delicate thing thingies really, off workbench.

Here is grasping a pen out of tin jammed with other stuff there, to show off power of powerful precision grip here.

Here is lifting three sticky tape rolls separately, to show just how good grip control is.

And if I think, this type of precision grip is "the best", after all, the type of objects one gets to grip is astonishing, hold your horses ... this seems uncanny only for a prosthetic hand. And even there, Becker Mechanical Hands have always delivered great precision grips. The thing is, that prosthetic split hooks deliver that type of performance already since a long time. No need to worry there. But, we were not worried, either.

If at all you are after embodying a closer-to-life instance of "bionic" hand function, why not consider to adopt a more cynical practical utilitarian view just as I do? The total cost of a body-powered arm (maybe 3000-9000 USD depending on specifics) and a Becker Mechanical Hand (up to maybe 650 USD, lasts very long usually) (including a few bucks for rubber stuff, work glove, etc.) will be there where amateur developers all around the world attempt to go, but they still seem to struggle with far higher control error rates and far, far, far higher hardware costs. Sure, if you are after drama, why not pursue the high road. But if all you want is a prosthetic hand that works, and works really well, here is one.

What really is new and very, very cool for (some of) us is that a "relevant upgrade" of the hand that I showed off here, is colored blue. You know what that means [link]. With that, we are "officially allowed" to touch (with?) all things colored blue, and we can call ourselves "pilot" ; ) off to painting my tool grips and light bulbs blue now ; )

#cybathlon #precisiongrip #amputee #cyborg #truecyborg #bettercyborg #bluelightspecial #beckerhand #prosthetichand #bionichand

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Precision grip enhancement of prosthetic hand [close-up, detail, technical aspect]; published 22/11/2020, 14:30; URL: https://www.swisswuff.ch/tech/?p=11231.

BibTeX: @MISC{schweitzer_wolf_1610951435, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Precision grip enhancement of prosthetic hand [close-up, detail, technical aspect]}}, month = {November},year = {2020}, url = {https://www.swisswuff.ch/tech/?p=11231}}