I was offered the privilege to provide a first usage test and report for a new body powered device. This device allows an “on the fly” switch between VC (voluntary closing) and VO (voluntary opening) control mode.

If you use a prosthetic arm recreationally, for fun, for “the little things that count”, such as opening the odd envelope, holding the odd water bottle while filling it with tap water, or pushing the odd knob on your coffee machine, then it probably does not matter what device you wear, or how it would hold up. But if you usually demand performances of your prosthesis that are in the domain of the “unreal”, the difficult to cover for existing devices, then having a terminal device that allows on the fly switching between these two control modes really is a big thing. It means that I can switch between the most popular passive grasp mode (VO) – used to carry or hold on to items without thinking – and the most powerful dynamic and forceful grasp mode that ever exists for prosthetic arms (VC).

The device is called “Equilux” and it is (or will be) manufactured by Toughware PRX.

Toughware PRX
2514 West 104th Circle
Westminster, Colorado 80234-3508
Telephone:303-635-1619
FAX:303-635-1621
E-mail: info@toughwareprx.com

An outstanding feature is that the device also provides for the fact that normally, VO works better with slightly longer control cables, whereas the VC system requires mildly shorter ones. This device’s flip / switch design does away with this by way of clever design. So with one good control cable length, you are set.

As a further feature, it contains an interface for exchangeable grip pads. As we will see, this is a relevant aspect, that will have to be followed up in the future.

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Description

Voluntary closing (VC) mode: open by default, closes with cable pull / actuation, maximal force usually over 200N; with slightly deformable grip surfaces, form closure is approximated, and objects can be gripped with serious reliability.

Voluntary opening (VO) mode: closed by default, opens with cable pull / actuation; typical grip force around 20-40N (it is possible to add rubbers, I found a trick); with slightly deformable grip surfaces, form closure is approximated and objects can be gripped with serious reliability.

Switch from VO to VC:

Switch from VC to VO:

Tube grip

Description: The tube shaped object (concise examples below) stays within the grip opening of the claws. The claws’ rounded shape is similar to the Trautman Hook, Hosmer model 6 or V2P, and that shape is instrumental for that grip feature. The object (round, red) finds it hard to open the hook because the vector of that force is always at an angle to the closing vectors of the device. So the force to keep it closed can be disproportionally low.

These problems occur here:

• Vacuum cleaning
• Mopping floor
• Garden work, cleaning street
• Awning handles to lower or lift store or projection wall in presentation rooms

At lower forces:

• Handling cables when setting up a laptop etc
• Biking
• Carrying heavy grocery shopping basket
• Carrying laundry basket

Test – vacuum cleaning

Not once did the tube fall out of the Toughware Equilux in the VO setting.

Test – mopping floor

Slightly thinner handle angles against claws, prying them slightly open; instrumental for grip maintenance is the shape of the opening vs. right angle of grippers.

Test – riding bike around the block with just a few bumps

• Mert hand for riding a bike as “gold standard” is an extremely hard connection – all handle bar vibration is transmitted to the prosthesis. A second problem is that of lifting: when riding in deep winter or after a storm, frequently lifting the bike by pulling the handle bar risks to disconnect the adapter unless one resorts to ridiculously high spring settings. Also, the body position is entirely fixed with relation to the handlebar, causing strain over longer rides. Handlebar control while riding is superb.
• The Freelock (Wilfried Mijnheer, NL) fixes around regular handlebar padding (see chafed appearance of my handle bar rubbers). It thus solves the vibration problem to a large degree. But the connector, as the Mert hand, fixes posture and back without a rapid option to let go and stretch. Handling is superb.
• TRS Prehensor and Toughware Equilux (TE) under VC setting (NOT VO!!! NO!!!!!) currently the best option for dynamic riding, given above experiences. Vibration may be reduced by using any thick handlebar grip padding. Position of the gripper can be changed dynamically, making for far more comfortable longer rides. And control is, again, superb.

Wearing a versatile hook rather than a one-trick pony for bike riding has comprehensive advantages. Like, when you want to stop riding and do something entirely different.

This is a demo of the Toughware Equilux with a short ride around the block with two small bumps on regular mountain bike with front shocks; watch the video loop below, check for the real time counteraction in VC cable control. There is a small bump going off the lawn here; body powered VC has complete proprioception control to handle this.

Anyone interested in understanding why I laugh off real time proprioception with a hosed arm stump, that by itself offers little but enough concerning immediate feedback, may put an effort into academically establishing just why this works so damned well. I am just a user and my body knows this works too well.

Another bit of a bump here.

Two far bumpier rides from a trail in a forest with tree roots running across.

The significant advantage of the Toughware Equilux is that it can be switched to VO mode in an instant.

With regard to pure VC use for biking, the TRS Evolution 5 Prehensor as shown here is just as useful.

Even the Becker hand holds up well, here on really bumpy uphill sections.

An i-Limb could, in theory, also be used for biking, but maybe more for a “show ride” rather than a real one [puppetry / AUA vs WIFUCD]. Not everyone that can hint at, intend, wave at or show off a bike ride is routinely able to perform that activity. The internet with various “demonstrations” of sorts contains many interesting “show rides”, when really, no routine use is possible or sensible. On the other hand, we all learn (only?) from mistakes – so please ride for a few hours, straining yourself, with your myoelectric arm on. When the electrodes start to mess with your skin in a nasty way once you started sweating and keep riding and activating the electrodes  [link], time to start taking notes and making these public too.

Disclaimer: this was needlessly cynical and satirical. Please be careful with your prosthesis. Please follow manufacturers and medical personnel’s indications at all times.

Comparison – grip for hedge cutting

Consider the grip geometry of back locking Hosmer 6 work hook when cutting hedges. Static holding action of a dangerous device; here you want maximal passive closing action.

Disclaimer: I do not advise any amputee or non-amputee to operate dangerous machinery, or, ride bikes, or, clean up at home. I do not enocurage any academic researcher to even consider this, not in their remote dreams. Use, overuse, training, pain and recovery and, worse, lots of sweat will be involved. People that prefer clean chlorine smell to sweat should be particularly alarmed. Only for those that don’t read disclaimers, you want to be careful and go about the path that you walk, and act with caution, with diligence and responsibly. This is exactly why I am extremely picky about my prosthetic devices. I can name companies that never understood that by name, and I have customer “care” correspondence that makes you want to puke. But the videos below are real footage of real use of real devices. The red wrist connector is a PUPPCHEN wrist that runs service free for over 4 years or so. Under exactly these if not far, far (far!) worse conditions. Just saying.

Next image: showing just how robust the back-locking grip of this work hook is. I do not shake the machine because of a magical belief or ritual, and not because I intrinsically think these machines had it coming and all need to be shaken vigorously. This is simply to imply a bit of trust into such a grip and to visually illustrate what possibly could be asked from a prosthetic device. From one spirit to another, maybe.

And the following is a very short video loop of the hedge cutting that in full length took me maybe 2 hours or so, in blistering summer heat. This is to illustrate, visually, what could be asked of a prosthetic suspension. Here, tube gauze (directly on the skin; Molnlycke green stripe Tubifast) and gel liner (Alpha liner, Ohio Willowwood) with a pin lock were used with very good success. You could attempt a humanistic angle for this: not everyone gets some other person to cut their hedges, and if so, maybe that other person wears a prosthetic arm. Who are you to judge?  If you build bionic hands and hope for myoelectric controls to survive here, I very strongly recommend you wear really, really, really, really good protection when you start your first trials with that type of work.

Test – shopping basket

Shopping baskets tend to pry open a slanted Hosmer 5 hook. After loading the basket with 4-5 kg, accelerations brought about by swinging risk to open that hook. And you do not want the eggs to go ‘poof’. You want a near 100% reliability for the grip to maintain its closed state.

Alright, admitted, maybe you are totally cool with 90% (drop the basket one out of every ten super market visits, become real friends with customer service) or 99% (drop it three times a year, become at least a good acquaintance of customer service), but let me tell you how it is here: I am not keen on such drops.

The Trautman style hook shape (let someone explain if you do not know) gives a bar shaped object no angle to pry open the grasp just so easily. The V2P, Retro and now Equilux (all by Toughware) and the Hosmer work hook (model 6) embody that design. It is extremely useful.

Test – carrying laundry basket

Evaluation of devices for tube shaped grips

Vacuum, mopping

	Toughware Equilux	V2P	Hosmer 5	Hosmer 6	iLimb Rev	Becker Imperial	Otto Bock hand	TRS Prehensor
Vacuum, mopping	10 (VO)	10	4	10	2	10	3	10 mod

Comment:

• The Hosmer 5 series hooks are great because of their slender shape, but, great for other stuff. The Otto Bock hand has a similar slit shaped grip. The slender shape allows the round vacuum tube to press the gripper open with relatively little force.
• The roundness of the Trautman derived grippers prevents that, so forces are distributed far better. The same is true for the Becker hand and the Hosmer 6 series (“work hooks”) that make it hard if not impossible for a machine or object to open against the hook grip. To saw the hedges with a machine, the Hosmer 6 hook with the back locking feature is by far the best choice, and the TE is not far away.
• The iLimb has a useful grip per se but due to myoelectric control crapping out after 10 minutes of sweating, it cannot be used for serious house cleaning. Also, the glove perforates after 10 minutes of holding a tube (tested in car wash, water tube).
• The TRS Prehensor only works beautifully once one tweaks it (carbid drill, rod, modification) to lock it for vacuuming (or such).

Riding bike

	Toughware Equilux	V2P	Hosmer 5	Hosmer 6	iLimb Rev	Becker Imperial	Otto Bock hand	TRS Prehensor
Riding bike	10 (VC) / 7 (VO)	7	3	7	5	10	3	10

Comment:

• The VC modes (TE, TRS Prehensor) as well as back locking VO devices (Hosmer 6, Becker hand) work very well; round shape of opening for VO somewhat but not ideally suited (TE in VO mode, V2P).
• iLimb sufficient for short ride to gas station but damages glove too fast and dies after 10 mins of sweat.
• Slit shaped opening of VO devices not suitable (Otto Bock hand, Hosmer 5). Possibly for VO devices, a Trautman hook shape is better (see V2P and Hosmer 6). .

Tube grip – exceptions

Before we start to make a religion out of tube grips having to be secure (you realized that te above section was all about that, right?) – there is a distinct tube grip type that has to necessarily be sliding, where the tube cross section of the item being held is intended to pry the hook claws open, and where the device must not fully close in onto the item.

Quite possibly, driving and riding bikes may have to be attributed to the dynamic grip section (below).

Driving and steering wheel handling

This website does not ask you, or encourage you, to do anything dangerous. Like driving.

But it is this website author’s personal experience across many thousand kilometers, including many on also German freeway and Swiss or Italian winding pass roads, that a steering wheel needs to be secured from rotating while at the same time interference must be possible at all times. Thus, I use a soft steering wheel cover, and I wear a Hosmer 5 hook with slanted claws, that fixes the steering wheel safely but at the same time does not impede me from letting go, or from turning against a bit more force all the same, using the left hand. There, having the grip to be a partially squeezing grip is a feature and not a bug.

Riding bike in particular circumstances

Also, riding a bicycle will entail a possibly sudden need to let go.

What exact hook or gripper shape turns out to be the best versus others is an open question at the moment. I have not excessively worn any device except the Mert hand, and the Mert hand is problematic in a few ways – it fixes the arm and shoulder to the handle bar without option to easily stretch or shift position slightly; I find however that riding larger distances require frequent minimal position changes or short stretches to reduce back pain.

So a voluntary closing device seems to be better than a device that locks firmly onto the handle bar, and first tests to that direction seem to confirm this.

How grip pad thickness and device can be optimized, whether the TRS Prehensor with its slightly more elegant opening that appears to allows a particularly fast release, or whether an Equilux with a more angled Trautman style grip that howevermuch seems to sit on handle bars with similar elegance, is better, and if yes, for what exact ride (difficult technical mountain bike uphill; difficult technical mountain bike downhill; road bike distance; biking to go grocery shopping), will remain open until I can perform more extensive testing there. If anything seems obvious, then it is the everyday trip to shopping or train station that will benefit tremendously from a single device that allows for both VO and VC modes.

Hard grip – scrubbing, shaking, varying forces

The object causes erratic and peaking forces while being held and moved. Using VC cable control allows to feel these and to exert counter force, in real time.

Using VC is the only way to counter these situations efficiently (or deal with any situation with freaky force peaks) because it is the only control system that allows for fully proprioceptive real time control over closing forces.

Using VO, scrubbing or other shaking etc force application requires maximal forces on the device (many rubbers, spring on maximal load).

These issues exist for:

• Scrubbing
• Holding and maybe shaking a heavy juice bottle
• Putting food from frying pan onto plate
• Cutting bread

Test – scrubbing (comparison: V2P)

Test – scrubbing frying pan

• Wide grippers are important for large objects such as frying pan, so an advantage over the smaller TRS grippers.
• Gripper surface must be at least minimally soft.
• Gripper really gets dirty so cleaning gripper is an issue.
• Preferrably, there will be a set of many (smallest set of 50?) rubbers to go through that don’t cost much.

 

Test – use scraper to remove food from pan

• Scraper with long handle bar experiences varying forces in different directions.
• Fast counteraction necessary.
• Analog permanent real time proprioception of force transmitted via VC cable is ideal.
• Wide grippers of TE better suited than small surfaces of TRS prehensor.

Test – hold and shake heavy juice bottle

• Definitely not a necessary ADL; total nonsense but a great “eat my dust” show off (and for that reason a perfect candidate for academic “testing” such as SHAP, clothespin or Cybathlon).
• But: wide grippers, VC  control for rapidly changing forces, and large forces with 2L bottle (about ½ gallon).

The juice was well mixed after that.

 

Evaluation across devices for heavy grips

	Toughware Equilux	V2P	Hosmer 5	Hosmer 6	iLimb Rev	Becker Imperial	Otto Bock hand	TRS Prehensor
Scrubbing, cleaning	10	6	4	3	1	5	3	8
Get food from frying pan	10	9	4	3	2	4	3	4

Comment:

• All VO devices (V2P, Hosmer hooks, Becker hand, Otto Bock hand) have too limited grip violence to efficiently scrub full force.
• So grip geometry plays a considerable role there; the V2P enhanced with rubbers and nitrile covers still grips well howevermuch it gets really dirty in the process.
• The Hosmer hooks, without silicone tubing over the claws, really scratch dishes and do not hold on to many kitchen tools (except knives) and thus have a bad grip.
• The Becker hand is surprisingly good with a PVC glove that cleans well, and a reasonably well back locking grip.
• The iLimb perforates its glove and is not water proof; really it is not built for any work.
• The TRS prehensor, with added soft covers, is great but its gripper surfaces are a bit small, which makes rotational stabilization harder than the TE.

Rotational forces grip

Force needs to be increased until the rotation stops. Force may have to be high.

Applications

• Open large jar maybe slippery
• Pepper mill

Test – open large slippery jar

Most devices fail to open that far; this is our supermarket coconut oil jar, and the TRS prehensor does not even open that wide.

Most devices fail to grab that hard.

VO devices will need permanently insane amounts of rubbers or spring setting; at that level they wear out conventional cable sheaths within about 3 days (however, an  engineeringwise correct installation will still last > 9 months).

Here the grip is perfect with the VC setting.

Test – pepper mill

Pepper mills tend to be very hard to use devices because the mills are typically cheap and block, causing resistance.

Test – professional i-Limb user and trainer fails jar opening task at Cybathlon entirely (i-Limb comparison)

And that jar was not even slippery.

People may not understand that the i-Limb is built that way – so the user has not the slightest chance. It is not the user that is at fault here, not the slightest bit. It is the hand that is totally overwhelmed.

(C) Copyright Swiss Television

Evaluation – rotational force grip across devices

 

	Toughware Equilux	V2P	Hosmer 5	Hosmer 6	iLimb Rev	Becker Imperial	Otto Bock hand	TRS Prehensor
Rotational forces such as large jar or pepper mill	10 (VC)	5	3	2	1	4	4	10*

Comments:

• Large jars clearly require large forces only realistically available with VC devices.
• All others fail the average pepper mill. Try one that jams hard.

Knife grip – form closure

Cutting with a knife during meal eatings is not just practical but symbolic. One must not splash the table. Due to the knife blade force vector being perpendicular to the hook geometry there exists a problem.

Form closure with knife

The hook does have a small shape curve that protrudes downwards, as shown in the above picture.

One can place a knife so its blade-grip connection rests there.

Owing to the shallow knife shape curve (and missing a rectangular shape for the knife – handle connection) in the above image, it becomes clear that not every knife locks in there.

So holding an elegant knife for cutting that way may be very risky. This is exacerbated by the fact that most such knives do not cut well.

No video, because really that failed.

Test – slice potato

Form closure with this particular knife and Toughware Equilux: ridge at TE inside interacts with knife handle/blade connection because of rectangular shape of the handle/blade connection in this instance of a large kitchen knife.

Test – cut meat at table

• Tilt knife by 90 degrees. With rigid claw up (to exert downward pressure) cutting meat can be approximated.
• For more pressure, knife will swivel though. Thus there is a need for cover inserts that have grooves to stabilize a knife in that perpendicular way. The rigid claw up is the correct start though.

Developing new pads

I just tested whether I could slap on some 3D designed and printed pads by myself.

An afternoon and a test PLA print later, I got these via Shapeways as “rubber like” material.

Way to go.

 

These are perfect for the task here, but we want to go a lot further than that.

Like so – bike brake pads. After I made frames to mount brake pads they really were too hard. No way around it – brake pads do not work as grippers. No brake pad manufacturer that I called would offer to produce a small series of soft rubber thingies for me so I am / was on my own. Also the manufacturer of the Toughware Equilux did not come forward to produce lush soft vastly superbly gripping grip covers. So again the website here is where you read how to do this first – here are the first 3D printed molded soft silicone made prosthetic arm specific add-ons. With an insanely great grip performance.

Updates for Toughware Equilux here.

Evaluation of meat cutting across devices

 

	Toughware Equilux	V2P	Hosmer 5	Hosmer 6	iLimb Rev	Becker Imperial	Otto Bock hand	TRS Prehensor
Cutting with knife	5 (VO) 7 (VC)	5	8	10	7	7	3	1

Comments:

• Key to performing here is to be able to lock a knife so it cannot escape because edge forces can be large.
• Hosmer 6 hook has a little feature for that; the Hosmer 5 hook series also has a way to fix a knife that works well.
• The prosthetic hands allow to cross place a knife so one can cut.
• TRS Prehensor totally tanks here, both TE and V2P are not ideal but it can be rigged perhaps. But so far it is not ideal.
• You do not want to negotiate failure rates here. You will go for 100% success rates here. 100,00000000%, so we understand each other.

Dynamic use – swift control along time and space

• Dynamic applications may really be difficult to understand from a control design view. Not if you are into freebasing slick body powered hardware, not if you do like race bikes, not if you play guitar or tenns or so – then you at least subconsciously understand immediate body-device interactions. But if you prefer the remote type of control like artillery – press button, wait a few minutes, listen for bang, then turn on the news to hear what happened. Which is how myoelectric control tends to feel – remote and lost, confused and you have to see it on the internet by someone else, before it feels real.
• VC (voluntary closing) offers best grip force feedback and thus fastest option for user to directly react. A cable across your back and you feel its tension always – no matter just how hosed the stump is.
• Gripper configuration needs to be rigid for forseeable and plannable action; uncoordinated grips are not sustainable in a dynamic forward action setting.
• Gripper surfaces soft and deformable a necessity for reliable forward planning.

Test – thin plastic cup

• VC control for continuous analog force perception.
• Grab plastic cup.
• Keep cable tension as you can feel it.
• Elevate cup.
• Put cup to mouth and drink.
• At the same time go down in knees so camera can see you.
• Back to start while keeping cable tension stable.

Test – compare this to i-Limb demonstration on public Swiss TV with Robert Riener (Cybathlon aftermath)

• No real control.
• This device does not effectively hide the handicap either.
• Professional i-Limb user and trainer.

(C) Copyright Swiss Television

Comparison across other situations with dynamic control requirements

Body powered VO hook to test spaghetti for aldente status. This shows just how dynamic an uninterrupted action sequence can go.

Body powered VC control, locked down, in Cybathlon wire loop test winner Bob Radocy’s performance. This shows a perfect integration of body motion and terminal device use.

(C) Copyright Swiss TV

Tried at home with TRS Prehensor, worked instantly – grab clothespin off floor and in a single sweeping motion, I placed it onto the line.

Myoelectric control – at Cybathlon with professional iLimb users/trainers – succumbs to limb positioning artifact even despite extensive training and professional user status. They are not really to blame, even though an experienced user that is used to open up locked doors wearing boxing gloves and soft boiled spaghetti as only “tool” will invariably have some tricks up their sleeves.

The limb positioning effect disrupts all sweeping or dynamic motion sooner or later, and it does so particularly with heated, stressful and overwhelming situations. To counteract it, one will have to understand myoelectric control as, in essence, another way of “body powered” control. One then has to understand the origin of limb positioning effect or posture interference. Then one has to go and stop exactly these interference signals, by actively working with one’s body. Only by performing the comprehensive step of accepting that myoelectric control is just as essentially body powered as “body powered” arms are, but far less intuitive, can one start to employ better control concepts that avoid that interference. When you reach that point, in your reflection on what is and what is not a good control system, then you will sooner or later embrace actual body powered control. It is a pure matter of cognition and understanding of true dynamics to acknowledge that.

The following animated sequence shows that towards the end of the motion where the error is made, a slight leftward leaning or back motion of the shoulder with minimal elbow extension triggers the positional interference (all details here). Watch the body frame in reference to the wire structure, and watch for the last second of the video loop. The polo shirt opening at the front with its V-shape suddenly tilts to the body’s left – exactly then the i-Limb device opens. You may have to stare at it for a while before you “see” it.

This is a typical myoelectric control glitch that is system inherent. It is not the fault of the user, or Touch Bionics. It still really messes up your day, like, if you want to take the garbage out but the damned bag drops and causes a mess.

Only embracing these postural aspects will pave a way out of these, and if only in part. Denying it is a real liability though and here, you can see what happens when you deny problems of inherent proportions. You will succumb and no one can comment. The Touch Bionics instructors (including both Cybathlon performers) talked me out of regarding this as a problem, told me that occupational therapy would teach me, but look at them. They have not embodied their own “solutions”.

(C) Copyright Swiss TV

Cybathlon failure by professional i-Limb wearers to provide competent device control across full body and arm motion (sweeps).

The grab for the clothespin out of a body motion with a free walk of the pilot towards the clothes line and then a freely approaching arm motion fails. If one looks closely, the thumb is a bit too far towards the middle finger and its tip closes before the index tip closes. The iLimb does not coordinate its grip, so a full grip reset, and finding a solid stand before starting this as a full embodied body control maneuver, would have been required to solve this problem with this device.

(C) Copyright Swiss TV

To succeed with failing devices, one must embrace their problems. Again the thumb and the fingers are not aligned properly and the pilot does not perform a full grip reset. Resetting an i-Limb to a “start precision grip” position will give you a high chance (not a guarantee) of a successful precision grip. During any grip, the hand may and will change configuration. Then it is wise to reset it again, and again, and again. Then of course there are reasons why the hand may be bought but not worn to often.

 

Test – cutting bread

• Bread loaf is soft and compressible.
• Force and grip form closure need to be found carefully and cautiously so as to leave a minimally deformed bread loaf behind.
• It is a Cybathlon challenge that many failed gloriously.

 

Comparison – bread cutting at Cybathlon by osseointegrated pilot with neural implant control

• This pilot just presses down on the loaf with an osseointegrated prosthesis that is controlled via nerve implants.
• The bread slice then is shoved off the table and thrown on the ground.
• Not acceptable for most family breakfast or hotel breakfast buffet styles.

(C) Copyright Swiss TV

Comparison – professional iLimb trainer butchering loaf with elbow at Cybathlon

• This pilot just presses down very hard on the loaf with her elbow, wearing an i-Limb; she is a professional i-Limb trainer and works for Touch Bionics.
• Not acceptable for most family breakfast or hotel breakfast buffet styles.

(C) Copyright Swiss TV

Comparison – multielectrode control at Cybathlon

• This pilot just presses down on the loaf with a sophisticated multi-electrode control system; Canadian contestant.
• Not acceptable for most family breakfast or hotel breakfast buffet styles.

(C) Copyright Swiss TV

Comparison – VC TRS Prehensor at Cybathlon

This pilot is Bob Radocy of TRS with a very decent handling of the bread loaf. This is suitable for breakfast at hotels or when one is invited somewhere. The loaf survives the gripper contact relatively well.

(C) Copyright Swiss TV

 

Test – cracking an egg

• Help to carefully cracking an egg may be one of the difficult things a prosthesis can provide.
• Here, I damage the shell with my (left) hand. Ha, ha.
• But that’s alright, no shell fragments dropped.

 

Evaluation of dynamic grip, sweeping forward grip execution and arm motion across devices

	Toughware Equilux	V2P	Hosmer 5	Hosmer 6	iLimb Rev	Becker Imperial	Otto Bock hand	TRS Prehensor
Swift dynamic forward grip sweeps	10 sc (VC)	8 sc	8 sc	8 sc	1	8	5	10 sc

Comments:

• All body powered devices are good but these activities are ruled by the VC devices.
• Soft covers (sc) massively aid these activities, see next section.

Soft covers for grip enhancement

Accommodate any hard object shape, and thus reduce the amount of gripper fingers or claws. Jack up and maximize form closure. Reduce need for high actuation forces, often massively, and thus essential for each and every device unless it has to be permanently disinfected or super clean. Avoids scratches.

Test – unloading dish washer

• Unloading dish washer will present contact with many non deformable objects.
• See how it integrates with fast dynamic forward grip planning.

Test – lift bicycle around

• Lifting bike around garage.
• Soft grip covers do not impede lifting large weights.
• Soft grip covers also, as here, protect soft objects such as leather saddle.

Mounting soft covers

Adding sheet rubber (red) and double sided tape (white), then a work glove finger with nitrile cover (fabric stuff) taped to claw.

Massively increases grip power.

Required to comfortably type with a pencil stuck between claws in VO mode.

Step 1 – check screw mount

Step 2 – cut sheet rubber to size

Step 3 – put layers together using double sided sticky tape

Step 4 – prepare for mounting on claw

Step 5 – use work glove finger with nitrile cover for perfect combination of deformability aspects of various materials that are used

Test – typing

The ability to type over extended periods of time requires a good posture. Normally, hooks provide that posture. With the wider claws, a V2P Prehensor or Equilux may have difficulties precisely hitting keys, so I usually grab a pencil or pen when typing with one of these devices, or when typing with a prosthetic hand.

Then, a maximal grip function combined with low actuation forces is a key aspect in having the pen or pencil remain stationary within these claws rather than move, dislodge or fall out.

This is typically achieved with soft grip covers. Conversely, typing this way is a good test to see whether the grip covers are useful. With a bit of a head start over others (I now look back on a few years of surface modding for such use), I can safely say that the Equilux has a configuration that lends itself very well to modification of this kind.

A next step will be to find simplified, if possible industrially produced, surface add-ons that we can easily mount, and swap, here. One option will be to order manufacturer issued surface add-ons, but another option is to add a variety of third-party add-ons that may be of use. Seeing as if the market for surface tweaking for this type of device will be small, open access, open source and shared developments seem a viable way to go.

Oh, and if you manage to watch this video loop with attention: you certainly have noticed that I managed to smuggle in some extra rubbers to increase VO closing power ; ) May the force be with you ; )

Soft covers for grippers – overview of cost and options

Covers are so relevant that it pays off – literally – to be outspoken about them. Do not write research papers and not put what you used in the method section. Put what you used into the method section. These are grip determining, if used correctly.

Gripper	Material used	Survival [hours]	Material replacement  cost [CHF]	Swap effort [h]	Cost per hour swap effort [CHF]	Cost per 8 hours of work a day [CHF]	Cost per year [CHF]	Bottom line
i-Limb	Touch Bionics glove required	0.2	400	3	30	16090	4,000,090	Extremely expensive if used for real work
Hosmer 5	Stock silicone tubing	42	1	0.2	30	6	53	Great performance cost ratio
Becker Imperial hand	PVC glove	480	120	0.5	30	17	515	Pricey but good value
Toughware Equilux Toughware V2P TRS Prehensor	Sheet rubber, double sided sticky tape, nitrile glove fingers	84	5	0.5	30	15	134	Better grip makes up for higher cost
Hosmer 5XA built in soft lining	Nitrile	2000	450	0	0	1.8	450	Costs more per year but no maintenance
Stump	Skin	160	2	0	0	0.1	25	Wear  down of skin costs consumption of skin care product (shea butter or skin creme)

• For gripper cover replacement, there exists a given situation with various options.
• Within that, convenience and cost are the factors to be weighed against grip performance.

Final rating

• This table sums up the above tables.
• There are no weightings. Add weightings to modify the results.
• The list is not comprehensive and lacks activities of other people. Add these if you feel like this makes a difference.
• However, it squares up some everyday essentials.

Qualitative appreciation

The Toughware Equilux is one hell of a device.

It delivers better what others deliver good, and it offers a combination of VC/VO in a degree of technical elegance that the market has not seen so far.

For bike riding, we can argue that it is not necessarily better than existing devices, but with the right covers you can keep it on to eat a steak.

Its covers are currently under development. I developed a first own set and will work on these further, with some own ideas. Check back on this site later to see about any new ideas. Such as a slide-in mount for bike brake pads ; )

Other devices also have weaknesses that can be remedied. The TRS Prehensor line would tremendously benefit from large quantity manufacturing of silicone or PVC glove type covers. Small tricks or add-ons on how to reliably cut pizza or meat are a necessity.

Ultimately, this device has great capabilities and even more, great potential.

Ultimate frontiers

• Mechanical hands that take the Becker hand design to VC/VO switch AND that fit standard(work, PVC, rubber, ..) gloves available everywhere
• High-end manufacturing and materials for these grippers or hands with no wiggle and tunable spring forces
• Trade-off between grip softness, cover wear-down rate, and replacement price

Becker hand demonstration

For those that enjoy real time control. Obviously, we did a lot of right things with harness, cable, and wrist. To take that further, we may need to first understand it.

Becker hand demonstration – grip / hand cover – standard hardware store work glove performance

The hand obviously has a repetitively precise precision grip. But this is greatly aided by the widely available standard glove size fit.

No conflict of interest though

The user is partial to small and fragile item handling and heavy work applications.

This blog leans on performance and no nonsense hardware shredding. This blog author developed a few things with his friends or himself, but the author of this blog has no financial gains or interest of this other than actually providing for his own extremely durable setups, obviously.

There are no contracts or business obligations between any prosthetic part manufacturer and the author here. He provides advice and feedback for a few component builders, however, as well as providing clear answers to researchers that ask him questions. He privately invests in both myoelectric and body powered technologies and performs his own assessments and tests, and works on possible solutions.

He is interested in next generation prostheses that provide industry level quality grip grades under “expedition style” conditions (i.e., that manage to approximate a grip failure rate lower than one in a million or thereabouts with wide ambient temperature ranges and full sweat over the whole skin, heavy and delicate objects).

He also studies social aspects of prosthetic arms.