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DUCK : A Device for Upper-limb Cycling Kit

DUCK : A Device for Upper-limb Cycling Kit

26 Jan, 2024 | English text, Non classé

Team Gre-Nable is keen to present a project done by a group of students from INP Grenoble collaborating with members of our team. team Gre-nable has the ability to promote and use the outcomes of the study to answer all needs required by E-Nable members.

 

This post is an excerpt of the project’s final report presented by the students for their diploma and is available here in pdf format.

 

Intro

As part of the product development project our team [the students’ group] is working on the design of a device that helps a young child [Noé] riding his bike. He doesn’t have a fully functioning hand, which makes this a difficult task for him to perform. Our team needs to design a functional final prototype to help Noé ride a bike, which includes testing and prototyping in real conditions to ensure the safety and reliability of the final product.

Our team is tasked with developing this system for Noé because he does not have any fingers on his right hand, which makes him unable to ride a bike accordingly due to his inability to grip the handlebar. The project took place over the course of one academic year and we are currently at the final phase, which is the validation and verification of the final prototype. The group has been working with APF France handicap, an association dedicated to helping handicapped people and children like Noé, who also work in collaboration with Gre-nable, local E-nable members that specialize in creating functional prosthetics. The group has also been working in collaboration with two engineering school teachers Philippe and Marie-Laure [who are members of team Gre-nable].

 

General Overview

Our project started from a first attempt by the occupational therapist of designing an adaptation for Noé’s handlebar with thermoformed plastic sheets. This deviced proved to really help Noé in biking, but also led to the identifiation of some potential improvements.

Prior to the second meeting with the client, the occupational therapist told us that the main problem with the previous system’s function was Noé’s position and posture while on his bike. His elbow was too high compared to the other arm, creating an imbalance and bad posture resulting in poor alignment of his back. Since the system awkwardly positioned his arm, it was not serving him properly and didn’t have much utility as a consequence. 

Another important point we faced was to provide Noé with the ability to move his hand quite freely on the handlebar, even if his wrist is firmly maintained in the socket. This is the reason why we proposed a kinematic made of both a ball joint for free rotation, and a rotary sliding link which made it possible for the wrist to move up and down when cycling on uneven path. The analysis of this kinematics is shown on the picture below.

 

On the aesthetic side, it was also necessary to reduce the size of the system, principally the hand rest or plank, and the system housing as they were visually bulky and not very discreet for Noé’s preferences. In the end, though, we were able to correct the size and form of the final system to achieve a much better, working prototype, which is more adapted for Noé’s helbow and his back posture. Our system’s shape ended up resembling the shape of a duck, which is where inspiration for the name came from.

An overview of the new system should be briefly introduced prior to talking about the new functions and features. As we can see in figure below, the system has been modeled showing the new system in blue, mounted to a rough estimation of Noé’s handlebar. The device is simply slid over the righthandlebar and tightened using two screws to prevent it from slipping off or rotating.

For a closer look at each component we can reference in the image below.

The system features a plank with a ball in the middle, where Noé attaches his wrist when that part of the system is configured to his arm. This piece is able to move up and down via two guide arms (or rails) that slide within the larger housing component attached directly to the handlebars.

Our first prototype featured a stopper in the form of a pin that was installed through the bottom of the rails to prevent the rails and the plank from sliding up and out of the housing once installed, but new components were added to accomplish this in a more discrete way. Instead, internal stoppers were added along the tracks in the housing (shown in orange below). The L-shape of these stoppers catches on the new C-shape of the guides so that when the plank and guides are at their maximum height, they are not able to slide out of the housing. Not only did this save material, but it also removed some unnecessary clunkiness and potentially sharp or pointy aspects from the design that could have posed a safety issue.

The shape of both components were also strategically designed to hold springs on both sides at the same interface in this region, stacked on top of each other, where the design was then able to be more easily reduced in size.

The interaction of these components can be more clearly seen in next figure, where it will be discussed in detail.

 

 

Another set of new components includes covers on the sides of the housing, which is shown as transparent in both figures to more clearly see how the system has been redesigned. One purpose of the covers on both the left and right sides is to contain the guides, stoppers, and springs from moving during operation. Another aspect of designing these covers came out of necessity, since inserting the guides and stoppers would make it very difficult to install the springs in any other way. If one imagines installing the guides attached to the plank and then the stoppers, it would be challenging to compress the springs
enough to install them from the top of the housing.

The covers allow the user to first install each component from the sides of the system, where they can then all be nicely encased in a way that they will not escape during operation. At the same time, the springs have a much harder time accidentally coming out or becoming dislodged while riding. Figure below provides a side view of the system that makes it easier to visualize this concept (and it should be noted that the handlebar in both images is not shown to make the images less crowded). This image of DUCK also highlights how the movement of the rails work in this version.

Once everything is in place, the covers retain the components in conjunction with the stoppers, where the L and C-shaped features of the stoppers and guides create a retention point at the location in the dashed yellow box.

Again, this is how the plank and guides are free to move up and down with help from the spring, but do not become dislodged during use. To better imagine the movement, a black double-sided arrow is shown at the bottom of the guide rail. This is how the new design was able to reduce its size and become more sleek, which we will discuss in the next section.

Ball Joint Coupling – Tests and Experimentations

The ball joint coupling is the primary connection point between the bike and the rider.
These two parts, the ball and the socket, allows the rider to easily disengage with the system in case of a fall. It is therefore very important to size it properly in order to ensure the security of Noé. To reduce the lever arm, which provides better solidity and more stability for Noé, we changed our ball joint coupling system slightly. Instead of having more mobility in the socket, the ball will be the soft piece that can deform and enable more movement. The socket can now be integrated in a bigger part, saving space and materials. The socket is now completely solid, printed in ABS and does not have any mobility (completely rigid). Due to these changes it was necessary to size the system properly for Noé, so we then developed an experiment plan.

 

Several parameters have an influence on the force needed to separate both parts when
engaged, so we will call this force the “release force”. The radius of the ball and the socket
were made to the same dimensions to ensure good mobility.

Socket depth : Changing the depth of the socket will make the ball harder to remove, and because the system is round, making it deeper will allow more plastic to wrap around the ball, which will need to be squeezed more to be released. We need to have at least the depth of half a sphere (14.1mm), or its radius, to have a release force (and for retention, too). For better comprehension, we will say for example that a socket offset of 3mm from the surface has a depth of 14.1 + 3 = 17.1mm. Please see section view with 3 sample depths (3, 4, 5mm) for better understanding.

Softness of the ball : To change the softness, we changed the infill percentage when 3D printing this component. We could have changed the interior geometry of the balls but changing the infill % allows us to keep a resilient structure for the piece, and this makes it easier to classify the different balls after printing.

Materials used : Changing the materials for 3D printing will change the properties of the materials and how they influence the system. For the socket, we chose not to change it and keep it as ABS V2 (from Zortrax company) because we needed a solid piece. Having this piece made of a single material makes testing simpler, too. The ball is printed in SemiFlex, and there are different types of SemiFlex usable in GI-Nova such as: Ninja Cheetah and Zortrax SemiFlex.

There are more parameters that could influence the release force, such as the friction between both parts, the form of the system (not perfectly round) etc… But we chose to do our experiment plan on those parameters because we thought they were the main ones with the largest consequences on the release force.

Improvements

Although the project in the end was successful in providing a useful product for our client, there are some points that could have been improved upon. For example, the design changes in version two of the system were well executed but could have been adapted for more adjustability. More specifically, the design aspect with regard to the adjustment of the height of the wrist could have been improved slightly. In the second version, the wrist is situated at nearly the system’s lowest position and is able to move up and down several millimeters. If the position of the L-shape of the stoppers was redesigned so that the point of contact between them and the guides was higher up, the height of the wrist and the amount of movement could be increased. With the covers, offering several different stoppers could make the system more adjustable since these pieces could be swapped and installed relatively easily. However, since the current stoppers worked well for Noé, it was decided to leave the design the way it was.

Considering the second design worked much better than the first and met nearly all of our client’s needs, we can definitely consider the system a success despite the small design improvement opportunities. Nearly all designs and products in general could be improved in some way, even if only to a minimal degree. It is good to recognize and reflect on these improvements for future projects that require similar methodologies, too, especially as our group continues studies in engineering and eventually more professional experiences.

In the end, the team was very satisfied to have met our goals when faced with the challenges presented by this project. Our group managed our time very well, and was able to equally distribute the work throughout the year in a way that made it possible to have a successful outcome. This has proven to be a very interesting subject to work on that taught us valuable lessons and skills that can be taken away and used in our futures, too.

Ski pole

Ski pole

5 May, 2022 | English text, Hand, Non classé, Prosthesis, Technical tutorial

Manon, hope for the 2030 Olympics ?

Our previous design of the ski pole aimed at Pierre-Luc, based on the principle of ball joint that enclosed his palm, does not seem appropriate to us in Manon’s case, because her clamp function can be performed by his thumb and his pinky. Of course the strength of this clamp is clearly not sufficient to hold a ski pole, so we keep the principle of using a socket build around her hand.

We therefore define new specifications intending the left hand palm to have the same feelings of touch as her right hand.

Scan of the left hand, equipped with a muffle

Pour ce nouveau projet, nous essayons de nous passer de l’étape moulage, en réalisant un scan de la main in-situ, en position de maintien du bâton de ski. La main étant équipée d’une moufle qui sera ensuite bien adaptée par la couturière de la famille.

For this new project, we are trying to work without the molding stage, by performing an in-situ live hand scan, right in the position of holding the ski pole. The hand being equipped with a muffle which will then be well adapted by her family’s seamstress (grand’ma).

The scanning operation is not as easy as expected, but after 3 attempts we got a good quality mesh file.

 

Another evolution of our process, we will not transform the resulting mesh (STL format) into a B-rep file for importing into our usual CAD software (Onshape).

Once the STL is imported into an ONshape’s “part studio”, an enveloping surface is made around the mesh, made of multiple ‘Spline’ curves (generalization of Bezier curves) drawn over successive cut planes. These curves, building a group of sections, each of them wrapping the glove, are then connected (joined) to each other by ‘lofts’. A loft is a surface obtained by interpolation between the different curves, in the form of a NURBS surface (cf wikipedia).

 

A pile of parallel planes will slice the fist holding the pole. All plans are referenced on remarkable points of the muffle.
On each plane, a closed curve is drawn to surround all boundaries of the displayed STL, thus creating a section. By interconnecting the successive parallel sections by lofts (3D loft function), we obtain the blue envelope (as a surface) which will then be transformed into volume using the “thicken” function.
After having created thickness to the developed surface, having cut the end of the socket to allow the thumb to come out of it, the socket is ready for integration into the new holding system.

Highlights of the device including a (simple) system.

The new device is therefore no longer based on the ball joint principle but on a two-element system :

  • an element on the stick (host)
  • a detachable socket for Manon’s hand.

The cohesion of the two elements is achieved by neodymium magnets, powerful enough for the stick to follow each hand’s movements, but detachable enough to allow the release of the socket in case of fall.

The host frame is attached to the stick. The vertical side of the host is on the outside to allow ejection of the interlocking (inwards) in case of any fall. On the inner side of the host, we can see the location where the small circular neodymium magnet aimed at vertical support will be screwed, and the rectangular magnet, more powerful, dedicated to lateral support.
L’emboitement est “collé” sur le bâti grâce aux forces d’attraction des deux aimants.
The hand-socket is “glued” to the host-frame thanks to the forces of attraction of the two magnets.
  1. The correct positioning of the interlocking is ensured by a centering dome, and a calibrated location
  2. The holding of the interlocking on the frame is the attractive forces of the main rectangular magnet (40x40x4)
  3. The second magnet (circular) facilitates vertical support and centering of the hand-socket.
-The first prototype validated the functionality of holding the ski pole and its test on a ski slope confirmed our technical choices.

Some small improvements were made to give more room for the thumb and the final version of the interlocking was printed using semi-flexible material (BASF Fusion, with shore mark 65D).

The success of this new concept quickly attracted other parents. So we reviewed (cleaning) the design scripts, so any new requests would be made quickly. The frame (HOST on the drawing) is almost generic, its adaptation to the hand-socket is minimal. On the other hand, the hand-socket being 100% adapted to the size/aspect of the hand and the type of agenesis of the child, its design will be a little more touchy.

Ces adaptations de système à la main d’un autre enfant nécessitent de maitriser l’outil de conception CAO, mais n’est pas aussi compliqué qu’il y paraît. Les fichiers STL du système développé pour Manon ne seraient d’aucune utilité pour un autre enfant. Par contre, nos développements sont open-sources et disponibles sur la plate-forme Onshape, et nous sommes toujours prêts à donner un coup de main 🙂 [© E-nable France]

These system’s adaptations for another child’s hand will require some skill using a CAD design tool, but are not as complicated as it seems. The STL files of the system developed for Manon would be of no use for another child. On the other hand, our designs are open-source and available on the Onshape platform, and we are always ready to give a helpful hand 🙂

Let’s keep in touch.

 

 

Multi Tool Holder with Ball Joint

Multi Tool Holder with Ball Joint

5 May, 2022 | English text, Non classé

Pen/Pencil MTH Holder Evolution

 

During the delivery of our first MultiToolHlder [MTH] dedicated to writing, it came to us that our method for positioning the pen was not necessarily that desired by the wearer of the prosthesis.

Every person who writes has his own habits, so we have to design an MTH that will suit needs well without the need to design a new support.

We got inspired by GPS mounting system that we used to suck on our car windshields.

No sooner said than done, the specifications were simple to write:

  • to redesign the existing pen sleeve
  • to graft a ball joint on the sleeve
  • to redesign the socket whilst grafting a self-tightening screw to lock the ball joint.

Design

 

According to our development process, our design is naturally open source, available through Onshape the online application at the following URL: https://cad.onshape.com/documents/a8c6f5401b2ae5574858ee9a/w/103408f60b9c74886ceb3f5d/e/f94eb28f22ddfaab4354a469

The folder can also be found with the Search (target) function targeting the Public domain, with the string: ” team Gre-Nable.fr : MultiToolHolder“.

Visitor can discover the assembly as we simulated it, to correctly place the different elements.

 

and the designs of the parts constituting the MTH are grouped in the PartStudio directory “PenHolder_rotule “.

As usual to modify the file, it will first be necessary to make a copy in your personal space, folder that you can then change to wish, including to adapt the MTH to your target nesting.

 

The Socket

This element is the heritage of a previous development that we described in our post:https://www.gre-nable.fr/creation-dun-multi-tool-holder/

At the end of this socket must be created and “solder” a thread that will tighten the ball.

 

Design of the thread

The aim is to realize a cylinder, whose periphery will be dug (extrusion with removal of matter – extrude remove)a triangular profile corresponding to the thread, sweept along a helical path, image of the screw.

Step#1

Le profil en triangle (jaune) dont le plan de construction est normal au chemin hélicoïdal, va définir un volume qui sera retiré de l’enveloppe cylindrique de la vis.

Step #2

Extrusion du cylindre complet de la vis, puis extrusion (remove) du profil du pas de vis suivant le chemin hélicoïdal.

Etape #3

On creuse l’intérieur de la vis pour y insérer la rotule, puis on “conifie” le début de la vis pour permettre un effet de serrage (l’écrou aura une conification inverse).

Etape #4

On fragilise la vis avec 8 fentes pour créer des lamelles un peu souples qui emprisonneront la rotule lors du serrage.

Etape #5

Enfin, on assouplit la base de chaque lamelle pour faciliter la flexion et le serrage autour de la bille.

3D Prints

Socket printing

The socket is a complex shape, to ensure the printings with high quality, printing will be done vertically, the socket laying on the flat section of the screw using supports to maintain a smooth appearance of the socket.

To ensure that the thread is properly stick on the printing mirror, a trick is used which consists in the existence of a small extruded flat part (thickness = 2 layers) in the same plan as the end plane of the thread. This piece (trick) is exported to the slicer at the same time as the socket, so it is she who imposes the collage of the whole on the plate.

Printing of the socket

Toute la complexité de l’impression réside dans l’impression de la rotule qui est orthogonale avec l’axe du manchon.

Dans une première version, le manchon avait été imprimé en appuyant la section coupée de la rotule sur le plateau. Lors d’un essai avec un bénéficiaire, la section du raccord entre la rotule et le manchon s’est cassé suite à un essai de rotation du manchon sans dé-serrer l’écrou. Essai concluant de résistance des matériaux et de la capacité de serrage de l’écrou!.

Nous avons donc orienté l’ensemble pour que la rotule, le raccord et le manchon soient imprimés dans le même plan.

Simplify3D, génère des supports de qualité qui se décollent sans laisser de traces. L’expérience montre qu’une épaisseur de couche de 20/100ème génère une rotule suffisamment précise pour l’utilisation.

Printing of the screw

Quelques essais d’écrous en PLA ont mis en évidence la présence de frottements (PLA sur PLA) importants lors du dé-serrage ce qui rend l’utilisation moins aisée pour une personne n’ayant qu’une main valide.

Un essai avec du filament Iglidur, (fabriqué par Igus) réputé pour ses qualités de frottements réduits, confirme le choix. L’écrou sera donc en Iglidur (https://www.igus.eu/product/703), c’est cher mais on peut en demander quelques mètres en échantillon.

Par contre, l’impression n’est pas triviale, une température élevée pour la buse (260 à 265°C) avec un plateau à 70°C, et une vitesse d’impression faible (20 mm/s) comme pour du flex.

Printing of the inserts

Les stylos, crayons, pinceaux … ayant tous des diamètres différents, il faut donc imprimer un jeu de bouchons de diamètres différents, avec du filament flexible. Nous utilisons deux filaments : ninjaFlex et SmarFlex.

A partir d’un design paramétrable (paramètre  Pen_diameter dans le Part Studio ‘manchon_a_rotule‘), on exporte autant de bouchons que l’on veut pour constituer le jeu. Pour cette livraison, les diamètres choisis sont 9,5 mm, 8,5 mm, 8mm et 7 mm (crayon de papier courant).

et pour terminer, une coupe générale du MTH à rotule assemblé;

… and finally the Multi Tool Holder on stage.

Nathalie ré-apprend à se servir de sa main droite pour écrire, pour dessiner. Les réflexes vont revenir rapidement.

 

Afin que Nathalie puisse tenir des outils de plus petits diamètres, Patrick imprime et lui envoie quelques manchons encore plus petits que les précédents.

Et peu de temps après, nous recevons des nouvelles… et des photos : Nathalie s’est mise à peindre, cela faisait tellement longtemps qu’elle en rêvait ! Et on doit dire qu’elle se débrouille plutôt très bien …  

Nathalie peint

…  et immédiatement après la livraison, conception d’une nouvelle extension articulée !!

 

Le porte fourchette

Maintenant que la base est construite, il devient aisé de concevoir d’autres extensions articulées et spécialisées.

En repartant du concept de porte fourchette décrit dans un article précédent (www.gre-nable.fr/creation-dun-multi-tool-holder/) pour réutiliser et améliorer le bloc “coinceur” de fourchette, imprimé en flexible. La réalisation de cette extension a été très rapide.

On retrouve les primitives de conception dans le Part Studio ‘fourchette_a_rotule‘ du même dossier team Gre-Nable.fr:MultiToolHolder

A l’attention de tous les membres d’e-Nable France (Makers ou Demandeurs d’appareil)

Nos développements sont en open source, disponibles à tous pour être reproduits. L’adaptation de l’emboitement demande un peu plus de technicité qu’une simple compétence en impression. Mais, nous sommes là pour vous aider à acquérir cette compétence.

Soumettez-nous vos besoins et nous vous aiderons à réaliser votre MTH personnalisé. La seule petite contrainte, est que le design est trop complexe pour être réalisé avec le logiciel Openscad (surtout du fait de la forme non modélisable par simples primitives de l’emboitement).

Heureusement il existe une solution gratuite pour résoudre nos besoins, celle que nous maitrisons : l’application en ligne OnShape.com. Son usage n’est pas plus compliqué qu’appréhender Openscad. Prenez quelques minutes pour lire notre article ‘https://www.gre-nable.fr/pourquoi-team-gre-nable-utilise-onshape/’

 

Terminal Socket for Keyboard Typing & Smartphone Use

Terminal Socket for Keyboard Typing & Smartphone Use

10 Mar, 2019 | Arm, English text, Technical tutorial

Open source project:

This design, like all those made by Team Gre-Nable, is open source. We explain in these articles why and how they were done, the reasons for our technical choices like the means and tools we used. All 3D models are available under the Onshape environment (free access for public models). This design is accessible on Onshape by using the Search tool with team Gre-Nable.fr : manchon Jean“.

Jean’s Situation …

Jean is an adult suffering from agenesis of the right arm. He has his elbow and forearm only 9cm long, with very conical form and ending with a small “bud” … he has become accustomed to use among others to typing his MacBook’s. And we must admit that it is impressive with his “dexterity”. But the more and more intensive use of his computer for his work ends up hurting him and generating pain from his little “finger”. He would like to protect his skin while maintaining his dexterity he has acquired in the usage of the keyboard. He has already consulted two or three professionals who made him special appliances, which ultimately did not suit him. He then contacts Team Gre-Nable.

 

Molding & Casting

An alginate molding session provides a plaster model of Jean’s forearm and elbow. Note on the image below many bubbles that have been trapped in the hair of his arm during molding, which generates these small “balls” distributed on the surface of the plaster model. These were removed very easily with a cutter blade on the plaster. We can distinguish very well in the upper part the “bud finger” Jean used until now to type on the keyboard of his computer. In the lower part of this molding, the slight restriction of section is due to the presence of an elastic band we place intendely to clearly mark the location of his elbow during molding. This restriction will be removed (smoothed) between the 3D scanning operation and the CAD volume reconstruction.

Plaster model cast from the alginate mold.

Comparison of 2 brand/types of 3D scanners.

This plaster model is digitized with a 3D scanner. We took this opportunity to compare the iSense (see also  https://3dscanexpert.com/structure-sensor-review-part-1/)  with a high-end HandyScan 700 professional scanner. HandyScan 700 .

The Handyscan will be considered as the reference tool, with a reported accuracy well below 0.05mm on this type of object.

Results of scan shows the iSense giving efficient results for this application (accuracy less than 0.7mm, average around 0.5mm) in most areas with few variation of curvature, however, in more rugged areas, errors can reach nearly 2mm. But since we foresee the insertion of a comfort glove with thickness of 3mm (blue 3D fabric visible on the featured image near the Jean’s elbow: the process of designing this comfort glove is fully described in his post), and that we can also count on the adaptability of the flesh in contact with the socket, it seems that the quality of the iSense will be sufficient to digitize this model in plaster.

Please note that a direct digitization of the arm would probably have generated larger dimensional variations. We will keep the accurate scan made with the Handyscan as we have it.

A CAD model will be created based on this 3D scanning (obviously a mesh file), and exported in STEP format for use by Onshape online webapp.

 

Socket Design

Two new models are generated thanks to VXelements application (associated app with Handyscan scanner of Creaform)), with offsets of surfaces of 3mm then of 5mm. We wanted to test these features in VXelements (and we were very satisfied with the results) nevertheless these surface offsets and the generation of the new volumes could have been done with other modeling tools, either on the STL model (with Meshmixer for example) , or on the reconstructed STEP model (Fusion360, Onshape, etc …). You can read our post “Création d’un Multi-tool holder“for an example of using the “Surface Offset” function in Onshape.

The three volume models obtained, which we will call “ arm “, “ arm + 3 ” and “arm + 5” are imported into Onshape in STEP format. A boolean (volum) subtraction operation between “arm + 3” and “arm + 5” makes it possible to obtain a socket with a thickness of 2 mm thick, 3 mm away from the arm.

emboiture

ARM and initial socket

 

Clearance around pinky

An additional offset of the surface, followed by some cuts and re-assemblies of volumes allow us at this stage to release a significant clearance at the end of socket, which will avoid the contact between the Jean’s finger and the socket. This protection is the main element of his design “specifications” transmitted to us, so we pay special care for this!

Then we add an artificial “finger”, which will be equipped with a flexible tip ( made of NinjaFlex) to allow a soft touch with keyboard’s keys.

Socket and finger, external view.

Preparing 3D fabric, and clearance provided around Jean’s bud to prevent any injury.

Socket and finger, section view on.

3D fabric : finger clearance.

Adaptation for touch screen

Like most of us Jean uses a smartphone or tablet and thus a touch screen.Could he take advantage of this artificial finger to manipulate the apps on this type of screen ?

I had studied this issue few months ago, and I came to the conclusion that it should be possible. Indeed most of the current touch screens are capacitive, and speaking without too technical terms (which I would not control for that matter!) the touch screen detects a variation of potential generated by a slight leak of electrons when the finger touches the sensitive surface. It “would be enough” therefore that the end of our plastic finger (in this case the foam cap) would be connected to a sufficient electrical mass to provoke a slight electrically discharge during contact with the screen. The solution is …

  • drilling a small channel inside the artificial finger to insert a flexible electrical wire,
  • to replace the current printed tip (made of Ninjaflex) with an conductive tip retrieved from a smartphone stylus,
  • and to connect the wire to a metal mass, and possibly touching the skin of the user.

Channel to end of the tip for the wire

Wire exiting toward conducting tip

Former stylus tip placed on the finger

Electric mass made of aluminium foil (kitchen product)

Electric wire as an alternate solution

The smartphone stylus tip was taken on a stylus of this type.  Tests show that direct contact with the user’s skin is not necessary and good news as well ! What’s more, aluminum foil is not essential either. The system works very well with just a turn of wire in the socket, wire which is located about 3mm (the thickness of foam “3D fabrics” of comfort) of Jean’s arm.

Results of first tests

The second meeting with Jean (after the molding) was really satisfying.
remaining point was to imagine a way to maintain the socket well in place around his forearm. The first tests were done by placing two pieces of adhesive Velcro on the edge of the socket, and placing another strip of Velcro around his arm. The following videos taken during the first minute of use in each context (keyboard and touch screen) show that Jean will undoubtedly succeed in appropriating this new tool … if it is already done from this moment.

 

Very first try, Jean typing on his Mac.

Jean’s first test on his touch screen. See how smoothly he zooms with his left thumb and right “index”!

Holding the socket on the arm

The very conical shape of the Jean’s forearm does not allow effective hold by simply clamping in this area. The first tests showed the feasibility of maintaining a strap around the arm, but we are looking for a solution that would be easier to handle, and that would avoid a localized tightening certainly not comfortable.

It seems then that the proposal made by Dominick Scalise to use a fabric sleeve for some prostheses would fit here.
A first test is done by cutting a sock … it seems to work well, and we propose to Jean, by email, to test himself this solution with the socket it uses.  

Meanwhile, we also offer a socket version printed in TPU (semi-flexible material) rather than PLA, to further improve comfort. Let’s not forget that John wants to use this device every day for several hours. 

In our third meeting, Jean introduced us to the fixation solution he found : he replaced the idea of ​​the sock with an ankle (usually used in the case of a sprain) that provides homogeneous and very efficient clamping. Just find the right dimension, and he will use or not the complementary elastic straps that come with it.

The TPU version seems to seduce him on the comfort side, and he plans to reduce the length, or even cut a slot on the side … what we do on the spot.

Printed release with TPU with slots. Please note the “glove” made of 3D fabric.

Hold with ankle (it may be necessary to use the size below)

Orthosis for a Cook

Orthosis for a Cook

26 Nov, 2018 | English text, Non classé, Orthesis, Technical tutorial

Yann’s Life Status :

Yann is an adult suffering from a pathology of the nerves (an NMMBC [1] for topic’s specialist) which in particular renders ineffective the control of a muscle of his left thumb, the one which brings the thumb into the position of opposition towards the other fingers (aptly named “opposing thumb muscle”, see image below). The muscle atrophies. Yann can therefore no longer have a normal grip with his left hand, which is inconvenient for a cook (to hold a bread, a sausage, an onion … while his right hand cuts slices for example).

[image en provenance du site Doctissimo]

A need for an orthosis

He would therefore need a mechanical assistance to place his thumb in opposition, but he also needs to be able to move back his thumb when needed in the plane of the palm for other manipulations (like cutting thin slices of salmon for example).

Occupational therapists in the hand surgery department at Grenoble University Hospital can build a rigid orthosis that will keep Yann’s thumb in opposition, but this will prevent him from raising it to put his hand flat back on the working table. The orthosis to be designed must also be compatible with the hygienic constraints associated with the cooking profession, and to be as compact or invasive as possible to minimize the inconvenience of wearing over a long period. So his occupational therapist advised him to contact our team (“makers” of e-Nable France) to envision if 3D printing technology could produce an adapted orthosis to his situation.

Methodology

The project was first entrusted to a group of engineering students from Grenoble-INP Génie Industriel [2]. After a very detailed study of the needs, and the usage of a 3D scanner to model Yann’s hand, they carried out a benchmark which confirmed that most of the existing orthosis for hands are made from thermo plastic mesh which remains rigid after shaping. Unfortunately this would prevent Yann from bringing his thumb back into the plane of the palm. But the scanned model made it possible to print an exact copy of Yann’s hand to quickly test the placement of various orthosis prototypes. However, this does not make it possible to judge the effectiveness of maintaining the thumb in the desired position. Recurrent interviews with Yann were necessary to fully understand the solution. All this work resulted in a printed orthosis made from a flexible material (TPU) which wraps around the hand, hooks to the base of the index-middle fingers, and maintains the thumb in an opposable position, without preventing the return of the thumb to the flat hand position. The result of this study is promising, but keeping the thumb in opposition still seems insufficient to Yann, the orthosis is a little too bulky to be used over a long period by Yann as part of his job.

 

Design Steps

For this development we followed an iterative user-centered design process, which steps are defined below.

Step 1 :

During a meeting with Yann, the observation of the previous prototype on his hand, and gathering his feelings and expectations as the final user, we generally come out with a drawing on a paper, which provides the raw aspect of the future orthosis, highlighting the evolution compared to the previous version. See two examples of such sketches on the pictures opposite.

Step 2 :

Uploading the hand drawing into the CAD system then allows sketching a digital model of the outlines of the orthosis (mainly by Spline curves).

Step 3 :

After adjustment of the sketch curved lines to achieve a ‘nice’ appearance, the base shape is obtained by extrusion with a thickness of 1.6mm to 2mm depending on the flexibility we expect.

Step 4 :

Parallel line cut allow keeping only the contour boundaries (3mm to 4mm width). The holes will later be replaced by honeycomb structure.

 

 

Step 5 :

Design of a matrix with honeycomb shape. Various parameters are adapted to properly fill the orthosis. Not too much material and not too much holes.

 

 

Step 6 :

Extrusion of the honeycomb structure, removing of the outer extrusion to keep only inner elements, and finally merging with the boundaries.

 

 

Step 7 :

Designing, extruding (thickness of 3mm to 4mm) and merging the blocking “blade” that will push on the back of the thumb.

Note also the small link added on the left side of the blade, to help pushing the thumb.

 

 

How it works

The idea is that the honeycomb orthosis fits the hand of the patient, and the thicker tongue, that is more rigid, pushes the thumb towards the opposition configuration. So wearing this device maintains the thumb in this position. But simultaneously, the whole orthosis being printed with quite flexible material, the person can overcome the small force provided by the tongue to extend his thumb and get the hand flat when needed.

The way to wear it is presented on the series of pictures below.

 

About the material we use

For this kind of device we use either TPE (thermoplastic elastomer) which is a “flexible filament” or TPU (Thermoplastic Polyurethane) which is a “semi-flexible” filament.
The specific behavior of these materials is characterized by its hardness, expressed on a standard “Shore” scale. Be careful there are several scales. The ‘A’ scale is used for softer materials (like rubber band), and the ‘D’ scale for much harder ones (like solid truck tires).
The TPE filaments we use here feature between around 86 Shore A.
The other type, TPU, generally features a hardness of more than 95 Shore A, and up to 98, which is really more rigid.
So depending on what behaviour you want, you can change the material, but don’t forget the other main parameter you can adapt to get a more or less flexible part is the thickness (and infill percentage) of the printed part, and the thickness has a huge influence on the part’s flexibility or stiffness.

Improvements

 

This first draft of project having given interesting results and allowing to consider still some improvements, team Gre-Nable ensure the follow-up, and two additional interviews with Yann made it possible to reach a usable orthosis with a slightly thicker support tab behind the thumb.

The orthosis is also smaller and therefore less invasive than the first versions, more flexible, it clings to the middle-ring fingers (which makes it possible to better pull the thumb in opposition). The Velcro straps are also reduced in width for less discomfort.

Yann seems satisfied with the help provided by this orthosis, while leaving him the freedom of bringing his hand flat when he wishes. The fact remains, however, that the crossing of the plastic filaments between the fingers is still troublesome.

Yann therefore returned visiting his occupational therapist who placed a protection consisting of a very thin adhesive tissue, which should avoid injuring the skin between his fingers.

Achievements

Note that the following images are made on the hand of one of the designers, and the orthosis does not really fit, but this is mainly for demonstration purpose.

Picture 1 :

Here is the orthosis ready to be used, with two Velcro straps.

Picture 2 :

How to put the orthosis on the middle and ring finger, then on the thumb.

Picture 3 :

How the Velcro straps are fixed on the back side of the hand.

Picture 3 :

When the Velcro straps are tied, the configuration of the thumb is naturally opposed to other fingers…

Picture 4 :

… and allowing a heavy grasp on an object.

Picture 5 :

But the flexibility of the TPE material still allows the user to extend his thumb,

Picture 6 :

… and put the hand flat on the table.

Testimonies

“Regarding the orthosis, all improvements made the orthosis efficient and more comfortable, however, it’s still not sufficient to wear it for a long time (duration greater than 1 hour). I therefore only use it on well-defined tasks that I group together as much as possible, and efficiency is there ! […]

Thank you to the whole team, thank you for your actions which allow a few happy people to retrieve a part of their autonomy. “

Yann.

Cook

“The orthosis developed by the Gre-Nable team:

  • it frees the mobility of the wrist compared to the first draft,
  • it allows passive opposition (by the splint) and the active feedback of the thumb in the plane of the hand,
  • no bulk in the palm – disinfection is possible by immersion,
  • not very bulky: fits within a vinyl glove

Yann retrieves a function without it being to the detriment of another.

This is where it is powerful ! “

Yann's occupational therapist

Grenoble hospital

To access the orthosis model we developed

For all our developments, we use a professional web-application with free access for makers named : Onshape .
If you want to use it, you only have to register. It is a very powerful and rather easy to learn Parametric CAD application developed by the former designers of SolidWorks.
All the projects developed using Onshape’s free license are public, therefore accessible to everyone for reading and copying in their environment.

orthese

Orthosis seen in Onshape

After logging into Onshape, just search for the word “Orthosis” to find all versions of this orthosis (among a few others), or “orthosis_Gre-Nable_Yann_V6” for the series of latest modifications shown in the images above.

Notes :

1) Multifocal Motor Neuropathy With Conduction Blocks causing motor deficit in part of the left hand.

2) Many thanks to the entire team of engineering students for their significant contribution to this project : Valeria Baghin, Adriana Camacho, Lucas Delaire, Dorian Gomez, Orianne Kassis, Bhargav Patel