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Fast and furious - speed of prosthetic hands and hook [slamming the "bionic" myth once again]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Fast and furious - speed of prosthetic hands and hook [slamming the "bionic" myth once again]; published May 1, 2012, 16:30; URL: https://www.swisswuff.ch/tech/?p=545.

BibTeX: @MISC{schweitzer_wolf_1571789216, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Fast and furious - speed of prosthetic hands and hook [slamming the "bionic" myth once again]}}, month = {May},year = {2012}, url = {https://www.swisswuff.ch/tech/?p=545}}


There are a range of extremely expensive prosthetic hands that are sold under the wrongfully and deceitfully used advertising term "bionic". I did address my concerns with that term before [see: inflated language].

We will now look at the speed aspect a bit more closely.

I contend that the concept "body powered" is far more healthy than the concept "myoelectric" also because delay is practically Zilch. There is no wait time, no tension space time hold death to be died, and life being one continuous rage can be lived better than by wearing an insane asylum's rubber room  inversely projected by the world onto your stump - in form of a battery driven gadget - to serve as a buffer for their assumed normality. I mean, get in touch with that big German prosthetic parts manufacturers customer service once, as an end-user, and experience it yourself. Nevertheless, a contention, so far.

However, I admit that I am somewhat biased. I am also a competitive swimmer with an IPC classification as S9 / SB9 / SM9 and as that, I recently qualified for the FINA Masters World Championship (non-disabled swimmers, mind you). Given that S9 is a significant handicap - one that has the capacity to slow one down quite a bit - that will give you a rough idea about the technical advantage that I have when addressing (a) speed, (b) force and power, (c) coordination and (d) training drills. So, I am biased with regard to some aspects of motion. There are performance aspects that I expect my prosthetic arm to deliver other people may not know or care about at all. Your mileage may vary.

Furthermore and before you are getting all worked up over nothing - this blog is called what? Correct, ".. below elbow amputee issues...". No one forces you to read it either - you came here, all by yourself. Alright? All you get here is my rants and raves, and my angle on things. I am not saying myoelectric arms are generally useless. I mean, there might be some real issues with these, true, but all I am saying is that I am ever so thoroughly investigating what is or is not good for ... me. So, here we go.

What set this off here, was the fact that a recent study titled "Performance Characteristics of Anthropomorphic Prosthetic Hands" [1] conveniently omitted speed details of the Becker hand or other devices that do have the potential to be actually kind of fast.

In short, the human hand can be relatively fast [2].

Now, the terms "bionic"or "lifelike" mean, "lifelike".

To be "like" a human hand, a prosthetic hand must necessarily be about as fast.

Not trying to diminish the massive achievement that the Otto Bock Michelangelo or Touch Bionics iLimb hand represent, here is me wrecking my Becker hand over a few demo grips - far faster and more responsive than any "bionic" hand will be in the near future:

So, how fast is fast?

Simply put, we can measure how "bionic" a prosthetic hand is, with regard to speed.

So far, you can follow this line of argument?

Now, before we will deface their pretentious speed claims, let us look at the advertising texts:

[touchbionics] With the i-limb ultra, your prosthesis looks and moves more like a natural hand than any other powered prosthetic hand.. Each finger moves independently and bends at the natural joints so that it can accurately adapt to fit around the shape of the object you want to grasp.

[bebionic] bebionic v2 myoelectric hands feature new motor technology which allows the user to react very quickly, with smooth, proportional control.

[Otto Bock] As a system provider, Ottobock is offering a completely new prosthetic system that assures fast and secure data transmission thanks to digital data transfer technology [..] Very high gripping force and speed [..] ([x] approx. 325mm/s, opening width approx. 120mm) .

Estimated closing times of current "bionic" myoelectric arms:

  • iLimb: 600ms [1].
  • Michelangelo hand: 370ms [x].
  • Bebionic: 800ms (tripod graps), 1900ms (power grasp), 1500ms (key grasp) [1]

My own measurements: background

I now used my Casio EX-ZR100 camera (with its 1000 frame per second option) and a flash clock showing milliseconds to estimate the closing speed of some of my own prosthetic devices just to see how bionic I was feeling myself today.

I am almost not wearing a prosthetic arm since January this year because of problems with the new prosthetic and its construction. The customized parts my prosthetic technician was about to provide require a lot of trial and error so we are working on these. In the meantime though, I started to appreciate the practical aspects of my disabled arm as such. For one, it is extremely affordable - I have not wasted one second at anyone else's office waiting for repairs. I have not wasted one second typing up insurance applications. Sure, I rammed it up a few times but seems like it healed by itself, a feature none of the "lifelike" (healing is part of life, royte?) seem to feature. And gripping works relatively well with the bare stump - even though in a rather limited way - and now for the first time, I am *really* fast. I am twice as fast or faster than the fastest prosthetic arms on earth - without a prosthetic.

I included a typical stump grab in the speed measurements that consists in pressing my stump against my thigh over the same ~12 cm that prosthetic hands maximally grip.

As you can see, we are far below any times as found with the clumsy anchors sold as "bionic arms".

Method

I conducted speed performance in front of my computer screen that showed a running millisecond flash application and recorded the event using my camera that was set on 1000fps (one thousand frames per second).

Results

Measurement results (closing times in milliseconds):

  • Hosmer 5X / 3 used up old rubbers: 76ms (average)
  • Becker Imperial / older PVC glove: 77ms (average)
  • Becker Lock Grip / fabric work glove: 71ms (average)
  • Stump against knee (approx. 12 cm): 33ms (measured just once for curiosity)
  • My own old Otto Bock myoelectric hand: 540ms (average)

Averages / class comparison:

  • Stump against knee: 33ms
  • Body powered: 75 +/- 25 ms
  • Myoelectric: 564 +/- 143 ms
How much faster:
  • Using the stump requires a mere 5% (five percent) of the closing time a myo arm requires.
  • Using a body powered device requires a mere 13% of the closing time a myo arm requires.
  • Using the stump requires a mere 44% of the closing time a body powered arm requires.

'

Figure (above): x-axis: stump versus thigh closing time ('anatomical') based on own measurement, body powered terminal devices ('body powered terminal group') measured myself, and myoelectric devices based on published and measured results ('myoelectric'); y-axis: logarithmic scale for closing time in milliseconds.

As one can easily see, no prosthetic arm is a whole dimension faster than any prosthetic. Among prostheses, the immediacy and speed of body powered arms is ever so entirely unsurpassed.

Discussion

It has so far remained a mystery to some academic or industrial researchers why the lifestyle of upper extremity amputees every now and so often evaded their attempts to load them with more gadgetry. And that just ever so completely.

Well, so far, academic research comprehensively fails the amputee. This is a lot of things - dumb, blind, ego centric, autistic, anti social - but it is also extremely funny in one peculiar way: everybody and their freaking grandmother pays for speed these days. Just about everybody.

With an extreme focus, all that is done with all things gadget - mobile phones, urban transport, e-bikes, cars, motorbikes, ADSL lines, computers, laptops, - is being measured, rated, and sold for speed. Speed matters, and it does so a great deal.

And here we are, dealing with academic as well as industrial research in what the upper extremity amputee may or may not need - and our all times favorite choices - bare stump, body powered arms - have not yet been quantitatively analyzed by these folks. I am sorry, but this simply cannot be taken serious.

Luckily, I can provide y'all with some starting figures to play with. I neither overdid it with reaction times, I toodled around with a real el-cheapo consumer camera and I just wanted to see what a real simple armchair type diagnostic would yield in terms of speed measurements here. Given that the academic and industrial research - people we pay for that type of stuff, people that abuse the 'upper extremity prosthesis research' tag to waste that money - failed to provide these measurement I figured that a true blue gummi bear approach would entirely suffice to drive home these rather embarrassing and clear, obvious and easy to understand results.

For one, these delays are relevant. You may wish otherwise but they are.

The longer things take on a device or system that is supposed to deliver instantaneously, the more profoundly users tend to suffer from it [2].

The relation is non-linear in that already relatively small delays already can have a big effect [2]. This is a fact well studied and well known from other research domains, such as computer-user-interaction.

With my left hand being my left hand and very fast, I will want symmetry for stuff that I do - and a body powered arm or the bare stump provide that symmetry in speed action.

It is established - and on no way controversial or mere guesswork - that users are extremely sensitive to delay [2]. It remains an unsolved mystery however why users reject prosthetic arms with staggeringly high quotes but delays and prices do weigh in. Regardless of other factors, delays alone may explain up to 20% of users attitudes [2] even though they might not even consciously point these out themselves.

This means that inherent signal acquisition related delays such as in myoelectric arms [2] as well as weight related issues all are problems that identify a doomed product design. Was that hard to figure out? All base on wrong assumptions - hanging on to the old stereotype that the average amputee as being endlessly patient, and endlessly happy to lug a 3 kg device, such are fairy tales just as dumb as a bag of hammers. I guess new signal acquisition paradigms - such as immediately available measurements like accelerometers or ultrasound - and new energy solutions - such as fuel cells - will pave the way into the future but then, who knows what happens.

So far, one aspect more than any other has solved a lot of practical problems for me: the raising numbers of octogenarians will cause all kinds of product packaging to get to be opened easier. The last two years saw marmalade and apple sauce glasses reduce their pressure so I can now easily open them with one hand. Wait for another five years and raising awareness for public presence of disabilities of all kinds - hearing, visually or otherwise disabled - will further make prosthetic arms obsolete. I am waiting for the carbon fiber vacuum cleaner, and I already have a 900g steaming iron that is extremely well built. And there is yet another approach that tends to render prosthetic arms obsolete: other people. Ever thought about what in hell the term "can you lend me a hand" could mean, practically, for me as an arm amputee? Ever considered what happened if amputees, instead of learning how to use a heavy and slow device that costs 50'000$ every three or four years, started to learn how to ask other people for their help?

And I don't need an even heavier so-called "sensitive prosthetic myoelectric arm" device to deliver painful or strange signals as "feedback", when I can have perfectly adequate feedback with very limited 2-point-discrimination using my bare stump or a very stiff coupling with a body powered prosthetic arm both of which do provide the ~"lightning" speed grasp that the term "bionic" actually should contain.

For now, I advise the current myoelectric hand sales people to correct their wording, given the fact they are not fast with their hands, and, not even near the term "fast". They should use terms such as "sluggish" or "less sluggish" (if they improve their slow speeds a tad). So right now these are massively overpriced sluggish anchors - not fast bionic prostheses. Please correct any other preconceived notions : )

Reference:

[1] Belter JT, Dollar AM (2011) Performance Characteristics of Anthropomorphic Prosthetic Hands. 2011 IEEE International Conference on Rehabilitation Robotics, Rehab Week Zurich, ETH Zurich Science City, Switzerland, June 29 - July 1, 2011 [link]

[2] I read that somewhere while browsing papers on Google Scholar. I didn't make it up but was too lazy to provide all references. Sorry about that.

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