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How does a Helping Hand / LN 4 hand work [test report]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - How does a Helping Hand / LN 4 hand work [test report]; published December 17, 2018, 05:44; URL: https://www.swisswuff.ch/tech/?p=9027.

BibTeX: @MISC{schweitzer_wolf_1574160334, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - How does a Helping Hand / LN 4 hand work [test report]}}, month = {December},year = {2018}, url = {https://www.swisswuff.ch/tech/?p=9027}}


I organized myself the opportunity to test a "Helping Hand" (also known as LN 4 hand) myself.

You know, the one that are being built as a feel-good exercise by business people and others, and that are given away to people that seem in need. It has its own website [link]. The Ellen Meadows Foundation specifically empowers not amputees, but non-disabled people. Verbally, they claim in their mission statement: "Inspire change in the world by empowering individuals to use their hands to support putting hands on people in need. We will not stop until anyone who needs a prosthetic hand has access to one". About the hand, they write: "Originally Ernie intended to design a functional prosthetic hand for children and adolescent land mine victims. Over time he developed a design for a low-cost, light, durable, functional prosthetic hand. He knew that this would help all who need a prosthetic hand and who could not afford the available alternatives".

That means:

  • They empower non-disabled people that have hands to use their hands. That is noble, I guess.
  • They will not stop until anyone that needs a prosthetic hand has access to one. The definition of a prosthetic hand is wide open, I guess,  but they precisely state their hand is functional and durable. That? We will see about that.

The smiles speak for themselves. The non-disabled people, by their looks, definitely feel empowered.

(C) Copyright Odyssey Teams

 

The hand mechanism may seem a bit wiggly really.  Can you write with this, really?

(C) Copyright Odyssey Teams

Contents

Assembly

The assembly was flawless as far as I was concerned. I had ordered the full single hand kit with parts, and built it without problems, thanks to the well made instructions.

Function

What can it really do?

It has two fingers. These can be fixed into a closed or grip position by using externally applied force. The fingers then appear to be locked. They are released by a slight swivel at the base of the prosthetic gripper.

Snugness of fit

The LN-4 has a truly wobbly fit. It wiggles in any direction at any time. That is a part of its problem: you cannot use it to really write well as that would require a far stiffer coupling to the stump. Also, hammering or other tool work is not possible, also for other (grip) reasons, but, also, because of the extensive wiggle.

Compare with iLimb: snugness of fit

My myoelectric iLimb suspension also is rather unstable. There are true constraints there, technically, among other constraints there is not sufficient space, length wise, to use a pin lock. That is because manufacturers do not provide a myoelectric wrist that allows for a pin lock to be stacked inside to provide a correct length. So we had to employ a lanyard system. And we used a relatively soft Ohio Willowwood Alpha liner because stiffer liners were not able to provide a slip prevention while not being painful.

Compare with hook: snugness of fit

(The hook has a rock steady fit).

What actually works at least a little bit: writing with pen or pencil

It is actually possible to write with this prosthesis. However, the writing is weirdly wobbly. That is because the whole thing has a very wobbly fit.

Compare with: writing with iLimb

My myoelectric iLimb, as the LN-4, has a wobbly quality to writing, and so the pen or pencil is never held too firmly with this device. It is possible to write with it but it is a weirdly unprecise and somewhat jittery experience.

Compare with: writing with prosthetic hook

A prosthetic hook on a regular body powered arm is by far the better solution, also for writing, than an LN-4 or an iLimb. The fit is absolutely snug and the coupling to the pen or pencil is stiff.

What somehow works but not quite as well: sorting soft balls on a table

LN-4 can be used to sort soft balls but not on its own. It is more work to use this, than, to do it with the (own, human, other) hand. So really, no one would realistically sort soft balls using the LN-4 prosthesis.

Compare with: sorting soft balls using iLimb

What can be seen here also, is the issue that the extra fingers of an iLimb, compared to a two-fingered hook or gripper, can be in the way in that they are often outside the visually covered area. I cannot avoid the middle and ring finger providing ill-controlled grip aspects as they are too much in this unstable fast object placement situation.

The iLimb and its competitors are currently still at a relatively early stage of development. Their grasp functionality is not mature. In 5, 10, 20 or 50 years, one might see an improvement if R&D manages to move outside the current comfort zone.

Compare with: sorting soft balls using TRS Prehensor

Compare with: sorting soft balls using hook - blazing!

The hook is visually and mechanically top notch in terms of grip planning, execution and control. Top notch. You cannot recommend a prosthetic hook to anyone, only to people that really know about the need for robust, lightweight and very reliable grasp control. There is an elite aspect to this advanced level of function that many do not understand that are not directly involved with the use of these.

Compare with: sorting soft balls using Becker hand - blazing!

The Becker Mechanical hands are inexpensive, very sturdy prosthetic hands. If any supporting association were to hand out prosthetic hands to people that would need these, Becker Hands would be my first recommendation, in conjunction with a good prosthetic body powered setup that really holds up.

What does not work: lifting a small box

The LN-4 seems to open, by itself, when one lifts an item that is a bit heavier. There is no way to avoid this. The box is not very heavy, it is just a box with some stuff inside. But the LN-4 cannot lift it.

What does not work: hammering with a light small hammer

I could not get the LN-4 to even reliably hold on to a hammer.

Compare with: human own natural hand holding on to a hammer - gold standard!

One easily forgets just how vast the difference to using a hammer in a normal way is. Do you understand why I would hammer with my left and regardless of just how approximate the prosthetic hand can offer this? It is just SO MUCH better.

What is problematic: gripping and lifting scissors

Gripping and lifting a pair of scissors from a table is far easier with any other prosthesis than with an LN-4. That device manages, but not too well.

Compare to: lift scissors with hook - versatile, error correcting, subtle!

The hook is a dream come true, with regard to actually handling a pair of scissors, compared to a whole range of other devices. It can be used to balance, to grip change, and to generally just snatch an object such as, also, scissors.

Compare to: lift scissors with TRS Prehensor - easy!

The TRS Prehensor is the lion of control subtlety. It manages most precise grips at lowest cable forces ever.

What works more or less: grasping and holding a small USB memory-stick

The carrying of a small USB memory-stick is not a true benchmark for prosthetic grippers. Not even academic testers have identified this task as relevant for, say, a controversial test such as the SHAP. But as we are really using grip testing to find out, a USB memory-stick such as this offers a great opportunity to watch and observe, and that is more than can be said about a whole range of other attempts in that domain.

Compare with: lifting a small USB memory-stick with an iLimb - difficult, real tricky!

My myoelectric iLimb suffers from limb positioning effect and from an ill-configured grip geometry. In combination, grips are possible, or in other words, one does manage to perform an actual grip eventually. But how that plays out, can be observed in more detail here.

Image 1 (left) shows how limb positioning effect rapidly closes the hand while I try to keep it open, forcing me to navigate a stubborn device into a grip situation which, eventually, succeeds.

Image 2 (middle) shows how I am unable to keep a lifted hand and a bent elbow on the right arm, which in itself triggers the and close command constantly, preventing me from successfully grasping the item.

Image 3 (right) shows the ultimately successful grasp whereas the item gets stuck on the index finger. Overall, that is a reality with the iLimb, that its grasp is a bit freestyle. As stated above, the iLimb is a device that still, functionally, needs a lot of further development until one may consider it mature.

Compare with: lifting a small USB memory-stick with a TRS Prehensor - competent!

The TRS Prehensor offers a vast range of grip power subtlety, from the very delicate and subtle to the fully powerful grip. Despite relatively wide grippers, it easily lifts the USB memory-stick in a superbly controlled fashion.

Compare with: lifting a small USB memory-stick with a hook - blazing!

The top device for precision grips is the body-powered hook.

Here, I manipulate, sucessfully, various shape details of the USB memory-stick. I can grab it by this or by that part.

 

What does not work: vacuum cleaning

The LN-4 cannot really grip and hold on to a vacuum cleaner hose in any usefully reliable way. It detaches by itself all the time. This was a rather annoying experience.

What does not work: lifting a simple garbage bag

Lifting garbage bags are an activity any prosthetic hand or gripper should be able to perform, always, and fully reliably.

I mean, who wants their garbage bag dropped? If you consider amputees as people that want to drop their garbage bags, then you will never understand how, given the current produce of prosthetic arm quality, of which the LN-4 is quite symptomatic, has a realistic ~85% rejection rate in a country such as Switzerland where insurance actually covers a prosthesis.

So, the LN-4 does not hold on to a garbage bag.

The LN-4 also does not hold on to a strap of a garbage bag. It lets go, or detaches, by itself. You get dropped garbage bags with this one so much that this will make your ears flap.

What does work with an LN-4: waving around an empty bag

To wave around an empty bag, the LN-4 can be used with ease and precision. It is just that I can handle empty bags also without prosthesis.

What does not work well: wiping table with sponge or towel

The LN-4 showed difficulty to vigorously wipe a table due to the occurrence of frequent loss of contact. Thereby, the non-snug fit of the arm and the wiggly setup allowed the sponge to work its way from underneath the prosthetic gripper of the LN-4.

Compare with: wiping table using bare stump - solid!

Even just using the stump provided a more fluent experience when wiping a table with a cloth or sponge.

 

What does not work: grasping, lifting, holding, handling dishes

The grip is far too weak and unreliable, the dishes are far too critical to allow for the many drops ahead for an LN-4, so, no, dishes won't work a bit here.

Compare with: dish washer unloading with Toughware Equilux - blazing!

Generally, prosthetic arms can very well handle dishes, and that reliably as well. Here a few test shots of a Toughware Equilux device at work unloading my dish washer.

What does not work: handle power drill

The LN-4 does not, at all, hold on to a power drill. There is no way, no way at all.

What does not work: lifting a metal basket

Similarly to failing lift test for garbage bag, lifting a metal basket clearly is beyond the capability of an LN-4 device.

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What does not really work well: using brush to sweep surface dirt into shovel

Holding on to a brush for sweeping dirty surfaces requires the handle to remain sturdy and not swivel.

The insufficient grasp of an LN-4 will not result in a good fluent and productive sweeping experience. The sweeping experience really is quite annoying and cumbersome.

Compare with: sweeping surface with brush using a hook - blazing!

The grasp of this hook is far more sturdy and reliable. There is no wiggle. That is how to really sweep a surface using a brush and shovel and a prosthetic arm.

Conclusion

The LN-4 is very, very annoying. It is one bit of wiggly something. Its visual appearance does promise at least a low level function on a sturdy simple application level. But, I never wore something that was that low on overall function. It does not lift even light boxes. It does not lift garbage bags. It does not help sweeping a surface with a brush. It fails to keep a sponge or towel stable for surface cleaning. You cannot trust it with any dishes. To stabilize an item, no prosthesis is mostly better. To grip would be good - but the mechanism really lets go so early, it is really astonishing. One can hold an empty plastic bag though, but not a full one. If at all, one may use it to attempt to write with a pencil. I will have to find a good killer application for that one, this needs better justification for its existence, I guess, but, I have not found one yet.

I cannot see how anyone regards this device as a sign of good will. It is a sign to exert power over the disenfranchised, sure: take this truly crappy arm as a sign that you will be socially unable to reject this crap. It is a very clear sign that one group of people powerfully dominates over others. But really? Don't do it. Don't make arm amputees wiggle with discomfort by presenting them this piece of, well, questionable engineering, as sign of true good-will. Good prosthetic arms are really different even when they are "simple". I wear a body powered hook for a lot of the things that I do, and as I tried to show, their function is so much better than this LN-4 device.

And with that, I will say that it is, indeed, possible to also "test" devices that are basically non-functional.

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