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Category: Design principles

Angular constraints of prosthetic grippers and functional success correlation [technical evaluation]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Angular constraints of prosthetic grippers and functional success correlation [technical evaluation]; published February 11, 2019, 04:55; URL: https://www.swisswuff.ch/tech/?p=9322.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Angular constraints of prosthetic grippers and functional success correlation [technical evaluation]}}, month = {February},year = {2019}, url = {https://www.swisswuff.ch/tech/?p=9322}}


I had evaluated, subjectively, the grip performance of various prosthetic options that I have. These have been already analysed in the context of grip taxonomy, where so far, research has largely focused on grip geometry as such, using some idiosyncratic logic that I found not too relevant.

Using a more relevant logic, I approached the question of grip mechanic from a different angle, both verbally and proverbially speaking: from a user angle, both actually geometrically and subjectively speaking.

I realized that most of my frequently used grips and grip situations fall into a far more narrow range of angle distributions than I had ever assumed.  So I sat down to add "typical object angles" to my already present grip success statistics over a list of my most frequently or typically used grips. Then I did that in theory and THEN I figured, why not go and video some. Thereby, a prosthetic hook as gripper device appears to be a lot more advanced, design wise, geometrically, in reducing device materials, bulk and design to approximate a really good overall use performance than the iLimb (which I have here also for as much testing as I like) and with that, many current commercial (or other) multi articulated hands.

In fact, prosthetic hands appear to be by far the older (and thus possibly less reflected) geometric design idea of a prosthetic arm's terminal device than the definitely more modern split hook. I may also go history hunting, but the claim that a split hook is old or outdated, and that therefore by inference a prosthetic hand is automatically new or more modern, as an idea, is wrong, particularly technically speaking. But also historically, to replace a hand with a hand is a straightforward design idea, that does not take any imagination, thus it is reportedly old, very old.

The far more elegant reduction, also of angles and controls, to fit into the limited action and option constraints of an arm amputee, is certainly that of a body powered split hook. It boils down the prosthetic needs to a successful sleek elegant reduction of a functional minimum, making it the ideal choice for anyone that wants a maximum of performance from a minimum of failure, cost, decay, bulk, futile grip attempts and total overhead. The subtle distinction is that a "body powered split hook" is an entirely different beast than a passive hook, obviously, which probably no one ever noticed, particularly not the people that assumed that a body powered split hook is best portrayed by installing a "Captain Hook" metaphor.

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Real work - Real Men Don't Eat Quiche - Real Programmers Don't Use PASCAL [reference to popular culture]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Real work - Real Men Don't Eat Quiche - Real Programmers Don't Use PASCAL [reference to popular culture]; published December 6, 2018, 08:37; URL: https://www.swisswuff.ch/tech/?p=8850.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Real work - Real Men Don't Eat Quiche - Real Programmers Don't Use PASCAL [reference to popular culture]}}, month = {December},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=8850}}


When I mention real work as opposed to work one does in the role of a pansy boy, I certainly mean this both seriously and tongue in cheek.

Only if you spend your days with real work will you ever understand. You will be dripping wet from sweating. Your clothes will be so entirely smelly from external causes. Your materials will be in dire need for cleaning ever so comprehensively. You have worked for many hours. And you will go back to do it all over again. A prosthetic arm that is built to last 3 years dies within 5 seconds, 15 minutes, or 2 months - using stock commercial parts, it burns and dies like paper consumed by a slow fire, component by component.

Welcome to the world of real work.

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Understanding and informing design issues of a prosthetic arm for below elbow amputation by way of "taxonomy" [literature review, reality check]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Understanding and informing design issues of a prosthetic arm for below elbow amputation by way of "taxonomy" [literature review, reality check]; published July 26, 2018, 21:18; URL: https://www.swisswuff.ch/tech/?p=7651.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Understanding and informing design issues of a prosthetic arm for below elbow amputation by way of "taxonomy" [literature review, reality check]}}, month = {July},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=7651}}


The academic and industrial attempts to approach prosthetic arms so far have been met with less success than the providers must have hoped for. Far less, in fact so little that we wonder what is going on.

Possibly, design issues are the key to this as however vaguely put, some analytic approach needs to inform better design - but how to really inform better design from issues based on analysis? What is a suitable analysis? If we cannot see any better designs anywhere in practice, real life, then what is the analysis worth? Can we analyze analyses to get a better understanding of what might be going on there?

We might best start with what we know to be true.

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3D-print molded Protosil RTV 245 (durometer shore 40A) silicone covers for Toughware Equilux [proof of concept, demo of "bionic" grip]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - 3D-print molded Protosil RTV 245 (durometer shore 40A) silicone covers for Toughware Equilux [proof of concept, demo of "bionic" grip]; published February 4, 2018, 11:50; URL: https://www.swisswuff.ch/tech/?p=8248.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - 3D-print molded Protosil RTV 245 (durometer shore 40A) silicone covers for Toughware Equilux [proof of concept, demo of "bionic" grip]}}, month = {February},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=8248}}


It is sometimes more fun to present the technical results before or even instead of explaining exactly why.  So in short, I 3d-designed and then printed molds to make grip covers for really serious grip performance of a Toughware Equilux device.

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Towards a more sustainable cosmetic covering / glove for the iLimb Revolution

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Towards a more sustainable cosmetic covering / glove for the iLimb Revolution; published January 24, 2018, 09:56; URL: https://www.swisswuff.ch/tech/?p=8159.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Towards a more sustainable cosmetic covering / glove for the iLimb Revolution}}, month = {January},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=8159}}


The fragility (and cost) of the gloves or coverings of the Touchbionics iLimb is legendary. No prosthetic hands smokes off expensive gloves faster.

That is in part because the relatively weak but lightweight motors will stop if the glove offers extensive resistance to the hand. So only the thinnest of gloves are given out by Touch Bionics for reasons of grip strength.

Only, as proficient user, that aspect greatly sucks.

Luckily, there is a bit of competition on the glove market - not as much as we wish to be, but some.

This reminds us of the times back in the days, when computer manufacturers issued proprietary video and monitor plugs. And when we got ourselves dip-switch setting modified video plug adapters to hook up Sun monitors on Apple or PC computers despite manufacturers' attempts to dominate device combinations. Growing into an industry that generally gives users only "their own" add-ons, consumables or other prosthetic extensions of any general kind, I was fast to see this as issue here as well.

And while the Bebionic hand's cosmetic glove allegedly may give Bebionic users a difficult time because it restricts or affects the thumb of the Bebionic too much, that glove is thick and sturdy enough to survive and yet sufficiently compliant to work with the iLimb. One will want it when one sees it, it is so good. So I got one because I wanted one when I saw one. Cosmetically, it sucks as it folds up and so on, but then, hiding one's handicap has not been approximated by the "bionic" trend currently happening in the realm of prosthetic hands.

The drawback is that the Bebionic covering's fingers are a bit too long for the iLimb. Here is how I fixed that.

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Case-study of a user-driven prosthetic arm design: bionic hand versus customized body-powered technology in a highly demanding work environment [article out]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Case-study of a user-driven prosthetic arm design: bionic hand versus customized body-powered technology in a highly demanding work environment [article out]; published January 4, 2018, 14:29; URL: https://www.swisswuff.ch/tech/?p=8066.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Case-study of a user-driven prosthetic arm design: bionic hand versus customized body-powered technology in a highly demanding work environment [article out]}}, month = {January},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=8066}}


 


This is a blog post of one of the rare focused and well based scientific journal articles that really explains how real work, body powered and myoelectric arms relate and go together for a unilateral right below elbow amputee in a physically demanding work environment.

The prior presentation of this paper [poster at Cybathlon symposium 2016], which had been more pragmatically worded (with me thinking people would know anyway), this was now written up as article and published. During that process, the reviewers clearly made great points of all kinds of aspects I never knew were not sky clear to everyone.

So maybe, writing a ~ 30 page case study with > 210 references does clarify stuff, at least potentially and for those that actually read it. But possibly, it still requires attention to even just read it.

Knowledge does not come easy, Highlander! (Nakano, in: Highlander III The Final Dimension)

 

If you are more interested in visionary posts, read about the gadget features of the prosthetic arm in Kingsmen: The Golden Circle [link]. And technically, myoelectric control did have it coming. That technology remained uncool for four decades [link].

Publication [link]

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Scientific approach taken for implementing a successfully marketable microprocessor-controlled knee - history of Otto Bock C-leg [lessons for prosthetic arms?]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Scientific approach taken for implementing a successfully marketable microprocessor-controlled knee - history of Otto Bock C-leg [lessons for prosthetic arms?]; published January 2, 2018, 15:10; URL: https://www.swisswuff.ch/tech/?p=7790.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Scientific approach taken for implementing a successfully marketable microprocessor-controlled knee - history of Otto Bock C-leg [lessons for prosthetic arms?]}}, month = {January},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=7790}}


This blog post takes a few relevant observations, and assumptions, throws them up in the air and sees if they turn into sunshine.

  • If anything has brought us forward, it is also the ability to find relevant short cuts. We do not always have to invent the wheel when really we just want a variation of it.
  • If there is any acutal success story where academic research was required to leverage consumer market for a prosthetic limb, it is that of Otto Bock's C-leg.
  • If we can understand what the concepts are for getting a C-leg successfuly built, marketed and sold, we should be able to take generalized aspects of it to formulate success elements for prosthetic hands, grippers or arms.

Background

While the idea of a microprocessor controlled knee was created earlier [link], no marketable solution was available in due course. "In the early 1990s, Kelly James, an engineer at the University of Alberta, Edmonton, Canada, developed the C-Leg, the first leg with microprocessor-controlled swing and stance phases. Buying the rights from the university, he traveled around the world to interest prosthetic manufacturers in his invention ("A Leg Up," by Isabelle Gallant, U of A Engineer, Spring 2011). However, he didn't receive any commercial interest until German manufacturer Ottobock bought the patent in 1992 and launched the groundbreaking technology.".

Then, based on work betweeen 1995 and 1998, a doctoral thesis at the ETH Zurich described an intelligently, microprocessor controlled knee for above knee prostheses built from available and affordable materials [1].

That research was performed 1995 to 1998, financially supported by Otto Bock, and Otto Bock presented its first C-Leg in 1997.

The rest is history. If ever there was a leap in performance of prosthetic function, ever, it was the C-Leg. No prosthetic hand ever came close to achieving this level of success.

So this particular doctoral thesis seems to contain some possibly interesting ingredients worthwhile looking at. As any doctoral thesis here is public record, and a copy of it must be made available at the public library, I borrowed a copy for further information.

There are some other prosthetic developments, however, nowhere else is academic research anywhere near that successful as in the instance of the C-leg:

  • Otto Bock Michelangelo hand; the mechanism seems to come from American DARPA or other army research and probably was just built, the first glove was a great design work. So there is no analytical approach comparable to the C-Leg. It is too heavy, it does not work with prosthetic gloves really, it is not sturdy.
  • i-Limb: This cannot possibly have suffered too much analytical thought. The device looks more like it was born out of something else. While it does not always function as maybe intended, it is really lovable. It does not have a reliable precision grip, it is really weak, it tears up its paper thin gloves within minutes.
  • TRS prosthetics: Bob Radocy as end-user himself developed by far the greatest useful solutions. But they are not the result of extensive academic efforts, so they cannot be compared to the C-Leg. They are extremely good though and any analysis must start there.
  • Toughware PRX: These devices are extremely well made, mechanics wise - but we lack an analytical model that precedes the engineering there as well, comparing this to the C-leg approach.
  • Becker Mechanical Hand: Also the Becker hand was clearly built by someone with great practical and pragmatic understanding. No analytical effort of the magnitude of a C-Leg preceded it though.
  • Hosmer hooks: they came out of a practical development, no scholarly work appeared to be prepared for these either.

 

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[1] D. Zlatnik, "Intelligently controlled above knee prosthesis," PhD Thesis, 1998.
[Bibtex]
@phdthesis{zlatnik1998intelligently,
  title={Intelligently controlled above knee prosthesis},
  author={Zlatnik, Daniel},
  year={1998},
 school={ETH Zuerich, Switzerland}
}

Grip performance enhancement through modifying terminal device gripper surface [overview]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Grip performance enhancement through modifying terminal device gripper surface [overview]; published July 19, 2017, 16:00; URL: https://www.swisswuff.ch/tech/?p=7431.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Grip performance enhancement through modifying terminal device gripper surface [overview]}}, month = {July},year = {2017}, url = {https://www.swisswuff.ch/tech/?p=7431}}


When using a prosthetic arm with a terminal device, grip performance is a key issue.

Usually, a bare steel hook such as the Hosmer model 5 works through just about every situation. That is just because that is how it is. A closer look reveals, however, that that view may be overly simplistic. If anything, it requires explanation.

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Guitar pick holder for iLimb / Dunlop TORTEX picks [3d printed solution]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Guitar pick holder for iLimb / Dunlop TORTEX picks [3d printed solution]; published February 12, 2017, 17:23; URL: https://www.swisswuff.ch/tech/?p=7198.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Guitar pick holder for iLimb / Dunlop TORTEX picks [3d printed solution]}}, month = {February},year = {2017}, url = {https://www.swisswuff.ch/tech/?p=7198}}


As we all know, I just recently designed and rapid prototyped a guitar pick holder for my prosthetic hook.

And guess what, this guitar pick holder also perfectly fits my iLimb revolution, certainly making me the first official "Cyborg AND 3d-print" endowing prosthetic arm guitar player, like, ever ; ) That just got to be raising hell, getting all these new hyped up slogan words lined up, like, together. Plus, this is just a really first test, as in, first minutes. I put in on, and 5 minutes later, this.

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Guitar pick holder for Hosmer 5 hook /Dunlop TORTEX picks [3d printed solution]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Guitar pick holder for Hosmer 5 hook /Dunlop TORTEX picks [3d printed solution]; published February 11, 2017, 00:08; URL: https://www.swisswuff.ch/tech/?p=7189.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Guitar pick holder for Hosmer 5 hook /Dunlop TORTEX picks [3d printed solution]}}, month = {February},year = {2017}, url = {https://www.swisswuff.ch/tech/?p=7189}}


I was searching for a practical way to get back to playing guitar with a pick for quite a while. I knew what I wanted - I just had to make it happen.

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Bowden cable mount for prosthetic arm [patent, explained]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Bowden cable mount for prosthetic arm [patent, explained]; published February 3, 2017, 14:30; URL: https://www.swisswuff.ch/tech/?p=7172.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Bowden cable mount for prosthetic arm [patent, explained]}}, month = {February},year = {2017}, url = {https://www.swisswuff.ch/tech/?p=7172}}


Explaining Swiss patent CH 703 982 B1 (PDF also here).

The motivation for this patent was to avoid frequent cable tears, cable rips or cable damage when using metal cables such as the ones used for gear or brake control on bicycles.

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Trautmann hook [3D printed steel parts, assembly, first use]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Trautmann hook [3D printed steel parts, assembly, first use]; published December 28, 2016, 17:53; URL: https://www.swisswuff.ch/tech/?p=7037.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Trautmann hook [3D printed steel parts, assembly, first use]}}, month = {December},year = {2016}, url = {https://www.swisswuff.ch/tech/?p=7037}}


First, I had performed a feasibility test using a PLA model that I had printed myself to see whether I really wanted a Trautman hook. After that, I had decided that I wanted one.

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Freebasing 3D shapes: wine glass holder [way to go]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Freebasing 3D shapes: wine glass holder [way to go]; published November 29, 2016, 06:09; URL: https://www.swisswuff.ch/tech/?p=6926.

BibTeX: @MISC{schweitzer_wolf_1571761454, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Freebasing 3D shapes: wine glass holder [way to go]}}, month = {November},year = {2016}, url = {https://www.swisswuff.ch/tech/?p=6926}}


While the "bionic" hands are the current darlings of the hypsters, the hooks are the darlings of real people, i.e., those that actually work [definitions here / tongue in cheek / GOH DTE type stuff].

And with that, the real avenue for home improvement are the hooks.

That is where it's at, that is where the future lies, that is where the bear steps (hier steppt der Bär), that is where the pope boxes wearing a chain armour (da boxt der Papst im Kettenhemd).

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