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Category: Cable control

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_1571767438, 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 I may also go history hunting, but the claim that a split hook is old or outdated, and that therefore by inference a prosthetic hand is automatically new or more modern, as an idea, is wrong, particularly technically speaking.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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Disability and the public - prosthetic arms and more: do we appear "competent"? (review)

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Disability and the public - prosthetic arms and more: do we appear "competent"? (review); published December 7, 2018, 15:50; URL: https://www.swisswuff.ch/tech/?p=8812.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Disability and the public - prosthetic arms and more: do we appear "competent"? (review)}}, month = {December},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=8812}}


The current view of us, what the general public thinks of us, seems to be a major aspect. Of "us", yes.

The research question for this armchair analyst thus will be: are we - arm amputees in specific, and, as people with a visible physical handicap more generally, more broadly as disabled people generally, seen as competent people?

Generally, the answer seems to be a clear "NO" right from the outset.

This should not come as a shock. There are good reasons to believe that, great reasons to make that plausible, perfect reasons to justify that statement. With that, there may be exceptions to that -  people that see through society's fairytales of disability, horror and fears, but they are usually the exception.

As I had figured out quite early into my enquiries into that issue, that this aspect is of absolutely no further practical concern not because it is not disconcerting - but because I cannot change it. And that is a rapid, lean and cynical logical consequence, that I stopped caring about what other people think of me based on, say, visual impression of my prosthetic arm. I may thus safely focus on function and comfort, sustainability and cost, without worrying too much about whether other people treat me as more or less competent based on my looks. Not because it would not be cool to take influence but because it is of no matter as to the target dimension: the tendendy to disregard any mental capacity of people with physical handicap appears to be implemented in many people's thinking outside of any actual experiences. And regardless of what type of prosthesis I wear.

If anything, I might optimize my appearance by simply trying to look reasonably neat.

But to bend over backwards for what really we have to concede are actually strange people? If anything, can we hack their brains?

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Embodiment of a prosthetic arm [reflections, thoughts, considerations]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Embodiment of a prosthetic arm [reflections, thoughts, considerations]; published September 16, 2018, 15:42; URL: https://www.swisswuff.ch/tech/?p=8513.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Embodiment of a prosthetic arm [reflections, thoughts, considerations]}}, month = {September},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=8513}}


So, apparently I had been "identified" as a "super prosthesis user" by a group of researchers. And I was invited to talk about embodiment in context of the "rubber hand illusion" at a user interface or robotic control workshop [link].

So is that what I am: a "user"?

Tsk.

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Experienced user based advice for investors in the domain of prosthetic arms [technical guide for understanding the field]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Experienced user based advice for investors in the domain of prosthetic arms [technical guide for understanding the field]; published July 26, 2018, 15:17; URL: https://www.swisswuff.ch/tech/?p=8702.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Experienced user based advice for investors in the domain of prosthetic arms [technical guide for understanding the field]}}, month = {July},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=8702}}


Investors may need to understand what prosthetic arms really are, how they come about, and what is there to be considered, before investing into a prosthetic arm component manufacturer or research spin off.

With a realistic estimate of around 85% rejection rate, the prosthetic arm industry so far is one of the most unsuccessful industries that there are both in high-tech and medicine technology.

Now, what usually keeps developments, market introductions and user feedback as well as improvement circles going is a successful social setting. Such a really successful circle, where respect combines with a striving for technical proficiency, in the context of prosthetic arms, appears to be largely absent. To a great part, this explains why the current status with regard to marketing, improving or successfully selling prosthetic arms is not a lot better than maybe sixty years ago.

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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_1571767438, 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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Modifying Shimano Ultegra road bike setup on a Colnago C40 for left handed use - second approach [technical right below elbow amputee core focus work / bike adaptation]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Modifying Shimano Ultegra road bike setup on a Colnago C40 for left handed use - second approach [technical right below elbow amputee core focus work / bike adaptation]; published January 27, 2018, 15:30; URL: https://www.swisswuff.ch/tech/?p=8196.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Modifying Shimano Ultegra road bike setup on a Colnago C40 for left handed use - second approach [technical right below elbow amputee core focus work / bike adaptation]}}, month = {January},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=8196}}


After a first approach, where also the history and idea where it came from is detailed [link], I now set up and tested a second approach to modifying my Colnago C40 carbon bike with a triple chainring Shimano Ultegra chainset.

The extensive testing of my first approach that I had performed there lead to a range of concise detailed issues and problems. There were now addressed, all, and thus a second (and significantly better) approach resulted.

As stated before, no disability sports advocate specializing in road bikes and no bicycle mechanic specializing in individualization and custom solutions over the years ever thought this was possible in this way. They all said it could not be done. And I had asked a few of them, since it had bugged me a lot. And as I had sold my Cannondale road bike after the amputation, thinking there was no way, I now got myself a road bike back and decided to go down my own path to really use it the way it is meant to be used.

Generally and as part of riding a road bike, I wanted fast and comfortable gear switching, fast and accessible and comfortable braking, and I wanted to be able to enjoy various and if possible equally comfortable sitting positions or body positions. A great road bike trip may be a lot longer than a fast mountain bike trip into the forest. Last but not the least, as amputee my stump usually would suffer from vibration induced pain after 20 minutes  particularly with hard connectors such as the Mert or Freelock adapters, so padding definitely was an issue.

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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_1571767438, 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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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_1571767438, 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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ADL learning and body powered prosthesis control [paper review]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - ADL learning and body powered prosthesis control [paper review]; published October 9, 2016, 11:42; URL: https://www.swisswuff.ch/tech/?p=6484.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - ADL learning and body powered prosthesis control [paper review]}}, month = {October},year = {2016}, url = {https://www.swisswuff.ch/tech/?p=6484}}


Learning to use a body-powered prosthesis: changes in functionality and kinematics. Laura H. B. Huinink, Hanneke Bouwsema, Dick H. Plettenburg, Corry K. van der Sluis and Raoul M. Bongers. Journal of NeuroEngineering and Rehabilitation 2016 13:90.

Abstract [1]

Background: Little is known about action-perception learning processes underlying prosthetic skills in body-powered prosthesis users. Body-powered prostheses are controlled through a harness connected by a cable that might provide for limited proprioceptive feedback. This study aims to test transfer of training basic tasks to functional tasks and to describe the changes over time in kinematics of basic tasks of novice body-powered prosthesis users. Methods: Thirty able-bodied participants and 17 controls participated in the study, using a body-powered prosthetic simulator. Participants in the training group were divided over four groups and practiced during a 2-week-period either direct grasping, indirect grasping, fixation, or a combination of these tasks. Deformable objects with different compliances had to be manipulated while kinematic variables and grip force control were assessed. Functional performance was measured with the Southampton Hand Assessment Procedure (SHAP) prior to and after the training sessions, and after 2 weeks and 3 months retention. The control group only performed the SHAP tests. Results: All four training groups and the control group improved on the SHAP, also after a period of non-use. Type of training had a small but significant influence on the improvements of the SHAP score. On a kinematic level movement times decreased and hook closing velocities increased over time. The indirect grasping group showed significantly shorter plateau times than the other training groups. Grip force control only improved a little over training. Conclusions: Training action-perception couplings of body-powered prosthesis in basic tasks transferred to functional tasks and this lasted after a period of non-use. During training movement times decreased and the indirect grasping group showed advantages. It is advisable to start body-powered training with indirect grasping tasks but also to practice hook-object orientations. Keywords: Upper-limb prosthesis, Body-powered prosthetic

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[1] [doi] L. H. B. Huinink, H. Bouwsema, D. H. Plettenburg, C. K. van der Sluis, and R. M. Bongers, "Learning to use a body-powered prosthesis: changes in functionality and kinematics," Journal of NeuroEngineering and Rehabilitation, vol. 13, iss. 1, pp. 1-12, 2016.
[Bibtex]
@Article{Huinink2016,
author="Huinink, Laura H. B.
and Bouwsema, Hanneke
and Plettenburg, Dick H.
and van der Sluis, Corry K.
and Bongers, Raoul M.",
title="Learning to use a body-powered prosthesis: changes in functionality and kinematics",
journal="Journal of NeuroEngineering and Rehabilitation",
year="2016",
volume="13",
number="1",
pages="1--12",
abstract="Little is known about action-perception learning processes underlying prosthetic skills in body-powered prosthesis users. Body-powered prostheses are controlled through a harness connected by a cable that might provide for limited proprioceptive feedback. This study aims to test transfer of training basic tasks to functional tasks and to describe the changes over time in kinematics of basic tasks of novice body-powered prosthesis users.",
issn="1743-0003",
doi="10.1186/s12984-016-0197-7",
url="http://dx.doi.org/10.1186/s12984-016-0197-7"
}

#userdrivendesign Prosthetic arm design: i-Limb Revolution versus customized body powered arm in a work environment combining bodily exertion, wide temperature ranges, wide body motion ranges, heavy workload and subtle grips [Cybathlon Symposium, Oct 6 2016, Poster A12]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - #userdrivendesign Prosthetic arm design: i-Limb Revolution versus customized body powered arm in a work environment combining bodily exertion, wide temperature ranges, wide body motion ranges, heavy workload and subtle grips [Cybathlon Symposium, Oct 6 2016, Poster A12]; published October 2, 2016, 13:05; URL: https://www.swisswuff.ch/tech/?p=6342.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - #userdrivendesign Prosthetic arm design: i-Limb Revolution versus customized body powered arm in a work environment combining bodily exertion, wide temperature ranges, wide body motion ranges, heavy workload and subtle grips [Cybathlon Symposium, Oct 6 2016, Poster A12]}}, month = {October},year = {2016}, url = {https://www.swisswuff.ch/tech/?p=6342}}


PDF of poster presentation @ Cybathlon Symposium Oct 06 2016 @ Kloten.

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Hosmer Model 6 Work Hook [tweak / improvement / backlock feature]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Hosmer Model 6 Work Hook [tweak / improvement / backlock feature]; published June 2, 2016, 11:47; URL: https://www.swisswuff.ch/tech/?p=6102.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Hosmer Model 6 Work Hook [tweak / improvement / backlock feature]}}, month = {June},year = {2016}, url = {https://www.swisswuff.ch/tech/?p=6102}}


The Hosmer Model 6 Work Hook is by far the most robust, powerful and useful commercially available terminal device for real work, besides the Toughware PRX V2P Prehensor and the Toughware PRX Retro. This Hosmer device is particularly useful due to the backlock feature that allows the user to reliably hold also relatively heavy machines for an extended period of time (such as hedge cutters).

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Trimming hedges with Hosmer 6 work hook and 2,7 kg cutter in 37 deg C sunny summer [achievement / benchmark report]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Trimming hedges with Hosmer 6 work hook and 2,7 kg cutter in 37 deg C sunny summer [achievement / benchmark report]; published July 4, 2015, 23:33; URL: https://www.swisswuff.ch/tech/?p=5013.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Trimming hedges with Hosmer 6 work hook and 2,7 kg cutter in 37 deg C sunny summer [achievement / benchmark report]}}, month = {July},year = {2015}, url = {https://www.swisswuff.ch/tech/?p=5013}}


Bimanual activities that require a prosthetic arm (one with industrial qualities) often times evade the prosthetist, the societal arm chair citizen, the academic researchers, the media makers that "use" amputees as stereotypes, in many aspects - one risks to overlook the simple glory, the sunshine that goes with doing it, the hardness of it, the pride. And the fact that it requires putting one's mind to something that is not just as self understood as it may appear.

What seems to be never considered is the fact that I really need a prosthetic arm for actual bimanual activities. It is for these situations where there is a need to work two-handedly, where a prosthetic arm attains a deeper relevance and importance. And it is not just me, that as a need there, actually. That is the type of stuff one generally needs a prosthetic arm for. Those activities are the ones where insurances usually tend to agree to pay for a prosthetic arm - a prosthetic arm that works through these tasks, mind you: hard work, repetitive work, two hands required, very hot, very cold, dangerous. Leaving the amputee totally intact, by the way.

Operating a hedge cutter is just not possible, safe, or easy with just one hand. In other words, we talk about real work. And no, you cannot "just put your mind to it". Sure with a small tiny clipper you can approximate the sound and feel - but with 2-3 kg and overhead work with a long powerful cutter, one-handed is a big risk, and operating the switch together with directing the blade is very hard.

That, as opposed to drinking coffee, reading news paper, just going for lunch with a food tray, cutting pizza or meat, shopping with bags or baskets, tying shoe laces, talk past a Bialetti when making remarks about "making coffee", opening a fridge, wearing correctly sized trousers, walking a dog, drinking alcohol, or such  - all of these work with a Becker hand, with a passive arm, with a hook or without prosthesis quite well, too.

Not, like, hedge cutting. This requires, like, a real prosthetic arm. It cannot be done without prosthetic arm, with a passive arm, with the "bionic" stuff (their control paradigm is just not safe for that type of work), certainly not with "3d printed" gadgetry that risks to scratch up your stump in no time. I talk about reliability, comfort, overuse, asymmetry, grip function, the stuff that hopefully, my real sustainable living future is made of.

To show what is required, or done, with a prosthetic arm in 2015, I cut the outer and inner perimeter of my hedges in the early afternoon of what turned out to be the hottest day in July in Switzerland since a long time, at over 37 deg C, using a Bosch AHS 55-16 (2,7kg) 450W electric cutter and a super tweaked body powered prosthetic arm with a Hosmer model 6 (back lock containing) work hook. The work contains overhead as well as low down feet height cutting.

 

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The "Russian arm" control paradigm for myoelectric prostheses [still relabeled as "bionic" or "thought controlled" arm] {what we have been withholding from you so far}

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - The "Russian arm" control paradigm for myoelectric prostheses [still relabeled as "bionic" or "thought controlled" arm] {what we have been withholding from you so far}; published June 1, 2014, 13:38; URL: https://www.swisswuff.ch/tech/?p=3151.

BibTeX: @MISC{schweitzer_wolf_1571767438, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - The "Russian arm" control paradigm for myoelectric prostheses [still relabeled as "bionic" or "thought controlled" arm] {what we have been withholding from you so far}}}, month = {June},year = {2014}, url = {https://www.swisswuff.ch/tech/?p=3151}}


The "Russian arm" [link] was introduced so many years ago. Then, it fulfilled a different role than just getting amputees back on track. Really, it was a modern version of the Carnes arm, that also was leveraged as somewhat political tool. And quite possibly, for finances.

Because, see, every age has its gadget arm.

Also, these (our) times have their "gadget arms". And their actual real shortcomings? They are ever so gloriously evaded, ignored, dismissed, forgotten, not mentioned and unknown.

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