Tag: printable prosthetics

Printable Prosthetics: Brainstorming

An illustrative hand
An illustrative hand

My overall designs for a printable parametric hand are still far from done.  And, yet, I’ve come a long long way since jumping headfirst into the realm of open source prosthetics a little more than 30 days ago.12

Forgive the digression, dear reader, before I return you to considerations of prosthetics. After visiting the Asian Art Museum today with the family, I am feeling particularly inspired to discuss dualities.3 I find I am an often-inspired person. This is a very charitable way to describe myself by what would otherwise colloquially and clinically be considered ADHD. When I am inspired by a new topic, I tend to jump right into it – reading voraciously and trying to learn as much about it as I can. When this happens, I also tend to set aside whatever thing I was most recently working on. This means that recently I’ve done little work on drawing robots (big and small) and a multitude of other small projects that would otherwise be just amazing. However, such inspirations/distractions are not only external to a project – but can also be very much internal to a project. Consider, for instance, feature creep – the adding of ever more features to a project, usually at a faster rate than which features are resolved and refined. In order to combat this aspect of my nature, the wanting to add more and better features, I have developed a coping mechanism. To prevent myself from falling down the rabbit hole of features and improvements, I jot them down someplace – either in a blog post4 , in an email to myself, or in a notebook.5 I find that once I’ve externalized and memorialized an idea, I can continue working on a project unfettered and undistracted these other ideas.

To this end, and in the spirit of open source ideals, I will jot down some ideas while I have them:

  • How large and how small are prosthetic designs typically scaled?
    • I wanted to have a range of sizes for which my designs were optimized.  My guess would be no smaller than 85% and not much more than 160% of the size of the existing  Cyborg Beast.  Jorge Zuniga was, again, patient enough to discuss this with me.  His estimate of a range would be between about 105 – 150%.
  • What is the diameter of the Chicago Screws typically used in the creation of a Cyborg Beast?
    • From the retailer’s website, it appears the “barrel” diameter is 0.2 inches, or 5.08mm.  I’ll need to make some adjustments to holes for the Chicago Screws in the designs.
  • How important is hyperextension of these fingers?
    • The designs of the Cyborg Beast include fingers that can bend “backwards” very slightly.  Each finger joint includes a “stop” at the back of the joint.  While certainly useful, I question their necessity.  I previously designed a connection system for printable snap-fit parts ((For use in an equally noble project)) that connect very tightly and/or bend with a user specified degree of movement.  The point with me mentioning these parts is that the “stop” used at the back of each knuckle and joint in the Cyborg Beast may not be necessary at all.
  • How necessary are metal Chicago Screws to strength and durability of the hand and fingers?  
    • Before you laugh, consider this question – what is the weakest point of any given finger which uses a metal Chicago Screw when having to deal with lateral forces?  I would postulate the weakest points would be those thin plastic parts surrounding the Chicago Screws themselves.  Thus, even though the hand incorporates metal pins, I have to wonder just how much strength they are providing to the overall device.  It would be easy to conceive of a plastic prosthetic hand that was so small that there wasn’t a lot of plastic around each metal screw6.  In such a case, the weakest points would be plastic surrounding the metal parts.  Extending this conjecture, of what use are metal fasteners to a design that is primarily plastic?  The best guess I can offer is that they allow reliable and smooth operation.
  • Work on proportional fingers
    • In designing the fingers, I worked to be able to make them customizable in several different ways.  The user may specify whether the fingers have the “star grip” pads, whether the finger should be slightly shorter or longer, and scale the finger up or down – without distortion to the hardware and cord channels.
    • I need to add at least three additional options to these parametric designs.  The designs should include the option to add “mouse ears” and easily removable support structures.  Additionally, the design should also allow the user to change the diameter of the finger.  I did implement this, somewhat, in part of the design.  Without implementation throughout the entire design, these partial attempts aren’t helpful.
    • In creating the fingers shown above, I adjusted their lengths to conform to the measurements of my own hand.7 Next time, I think I would also measure finger diameters.
    • I think I should create a way to prevent finger parts from being mixed up accidentally while printing.  A possible solution is to include “mouse ears” with each finger – but embed an identifying mark in each mouse ear to label the parts.
  • Ideas on making a better parametric palm
    • The palm should be redesigned so that the fingers, at the appropriate lengths, would fit into it.  I designed the fingers quite a while since working on the palm.  I haven’t had a chance to ensure the parts would mesh well without adjustment to the scale.
    • On an entirely different note, I have an idea to redesign the entire palm.  By carefully placing deformed spheres, I was able to design a palm.  Using a similar process, I subtracted out a void for the user’s hand.  The result is a palm with an uneven thickness throughout.  Uniform thickness isn’t necessarily an interesting or useful goal.  That said, it could lead to a reduction in unnecessary plastic.  If I were to redesign the palm, I could design the internal area first8 – and then use the “Minkowski” function to create a uniformly thick shell around the internal form.  The bottom would have to be sliced off and the original internal area would need to be subtracted from it.
  • Ideas on making a more realistic hand
    • My designs so far are based primarily on the Cyborg Beast, with some minor changes.  The “Flexy-Hand” appears to be very organic and realistic.  It also features flexible printed connections between each finger segment.  Additionally, each finger is comprised of three segments – rather than two like the Cyborg Beast.  Interestingly, since the flexible connections between segments allows the hand to return to an “open” position, the hand only requires five tension cords – rather than five tension cords and five elastic cords.  The fingers appear to not have any “stops” behind each joint.  I have to wonder how having three segments to each finger impacts the function.  Does it allow the hand to better grip things?  Does it make the hand less sturdy?
  • Masculine/Feminine hands
    • One well-intentioned comment to my latest designs is that they are “pretty.”9 While I accept the compliment with the spirit in which it was given, it immediately made me wonder – is the hand I designed “feminine?”  Then it occurred to me that with more design effort, I could make “feminine” and “masculine” version of these hands.  I think the primary differences would be two-fold – thinner fingers and a less “hefty” palm for a more feminine version and a thicker and perhaps more “blocky” palm for a more masculine hand.
  • New developments
    • There have been a number of interesting and new developments and experiments of late.10 In no particular order, these ideas are:
  • Discussions with a 7-year-old
    • A few days ago my daughter and I were jotting down some ideas in my sketchbook.  As we did so, she saw some of the notes from the e-NABLE meeting on 3/21/2014 – including several sketches.  We discussed the problem – affordable, customized, and comfortable prosthetics.  We talked about amniotic band syndrome, how fibrous amniotic bands affect fetuses, and the different ways in which these bands can cause11 deformities to single fingers, whole hands, and a range of changes in between.  I explained how Mr. Jose Delgado Jr. had a $42,000.00 myoelectric prosthetic, the problems he has with that prosthetic, how and why he prefers his $50.00 printed replacement, and how for the price of his one prosthetic people could make 840 more prosthetics.12 She asked, “Why can’t someone use a stump to operate a hand?” I replied that this was exactly how these prosthetics worked – and I drew a few simplified sketches of the Cyborg Beast.  Her next question was, “Why can’t it move side to side?”  I said that Mr. David Ogreman had designed such a prosthetic.
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  1. My first concrete step was going to an e-NABLE meeting in San Francisco on 3/21/2014. [↩]
  2. The above picture is slightly misleading.  I haven’t confirmed that the fingers I’ve designed will properly fit into the palm that I’ve designed – or that the thumb would work at all.  Thus, the picture is partially a parlor trick and partially an indication of where I hope to take this design. [↩]
  3. Many of the gods and goddesses in Eastern religions embody dual natures – creation/destruction, life/death, etc [↩]
  4. In one of my several different blogs. Besides, what could be more ADHD than having 3+ blogs?!? [↩]
  5. You may not find this as amusing as I do – but I probably have about four different sketch/notebooks. [↩]
  6. Say, only 1mm [↩]
  7. From pinky finger to thumb, the non-scientific measurements from knuckle to finger/thumb tip were 77mm, 102mm, 106mm, 92mm, and 72mm [↩]
  8. Using the deformed spheres and hull trick [↩]
  9. Thanks Erik! [↩]
  10. I don’t even know why I’m saying “of late” when I’ve really only been involved a little over 30 days.  I guess becuase these developments are new to me? [↩]
  11. Please forgive my lack of a more politically correct term.  If you’ve got a better or more sensitive phrase, please let me know as I will gladly adopt it [↩]
  12. She wanted to know if he could get a refund! [↩]

Printable Prosthetics: A Mock Hand

More progress on a fully parametric prosthetic design
More progress on a fully parametric prosthetic design

Here you can see the fingers placed appropriately with the palm. I’ve used the same “finger” designs to add a thumb.

For right now, this is just to demonstrate the progress so far.  Theoretically, the only thing left to do is crank out an appropriate gauntlet to bring the entire design together.  In reality, there’s still a fair amount of work to do.  The design for the prosthetic palms was… not elegant.  Also, I want to create a separate (but very similar) design for the thumb.1 It is possible that if I improved the finger designs, I might be able to get away without designing a separate thumb.

In the meantime, I think it looks good and would probably be functional as-is.

Onwards and upwards!

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  1. I feel like the thumb should be stubbier, so I’ll go back and adjust the designs accordingly. [↩]

Printable Parametric Prosthetics: Design Features

Parametric fingers - different lengths, same scale, with no distortion to hardware
Parametric fingers – different lengths, same scale, with no distortion to hardware

I’m not ashamed to admit it – I’m proud of these parametric designs like few of my other designs.  I’ve worked to make this design as customizable and organic as possible.  The two modules that define each finger can be customized in two important ways – they can be lengthened1 as well as scaled up or down – without any distortion or change in the size of the holes for the hardware, elastic cords, or tension cords.

Parametric fingers - with grippy bits
Parametric fingers – with grippy bits

Being able to lengthen2 the finger segments is important because it allows the user to create fingers of different lengths, as normal fingers are of different lengths, all without having to actually scale the fingers to different sizes and without causing a change in each finger’s diameter.

As I’ve discussed in earlier posts, being able to scale the parts up and down without distortion to the hardware holes is important because it allows users to use standard hardware throughout different designs.

For now, it’s back to work on the parametric palm to ensure a proper fit with these parts.

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  1. Or shortened [↩]
  2. Or shorten [↩]

Printable Prosthetics R&D Q&A FAQ: Part 1 – The Questioning

Top down view, extension view, and flexion view
Top down view, extension view, and flexion view

Marc Petrykowski of Creighton University was kind enough to provide some additional practical experience and information about the university’s research study into printable prosthetics.  For anyone looking to dive into this project, I’m cross-posting the information from the e-NABLE Google Plus group here.1 I’ve adjusted the formatting slightly, but otherwise everything below are Marc’s words.

  1. What exact measurements do you need (e.g., hand-length from where to where?) 
    1. Below are photos of all of the measurements I use for designing a hand.2 Yes it does seem like a lot, but all of them are needed to ensure the best custom fit for the hand we make for the user. When making a custom hand, it is important to make the 3D printed hand as similar to the non effect hand (fingers, width, length, etc). Each hand also has to be custom because of the size (length, width, height) or the stump. Some are very tiny and some are much bigger, so that also plays a big role when you have to design a hand. There are two photos that are measuring angle of flexion and extension. Those are important to see how tight or how loose the hand has to be for the power and strength of the individual and to make the hand as functional as possible.
  2. How do you get them from scans etc.
    1. Scans from our 3D scanner are in the format .STL which can be imported into programs such as blender (Shown below). Then I can lay it into the preexisting hand design and see an image of how it will fit, including the gauntlet size. If there are further changes to be made, I can do it all in blender before the print.
  3. How do you apply those measurements to your model
    1. As stated above, the measurements matter for the size of the hand. You can’t have a hand that is much smaller then the opposite hand, but you also can’t have a hand that is too small or large for the stump. Everything has to be customize depending on each case. This is where the designing takes the longest. My goal as the designer and printer is to make the hand as near perfect as the other hand so it feels the same to the body and brain, thus they will respond with the effected hand like it was their real non effected hand. Also as stated above, the degrees of flexion and extension and the size/length of the fingers are all incorporated into the final design before the printing the hand.
    2. And if, as +Jorge Zuniga suggests, ALL parts can be pre-printed, I’m hoping you guys will take the lead in helping us make it easy.  (As easy as buying shoes at a shoe store)
    3. This is possible because all of the redesigning and redoing of the measurements are all done in blender. Remember, if you resize a finger to a certain percentage, then you have to do the same for the rest of the fingers, thumb, phalanges, palm, and the gauntlet. That is how you can print everything off as one complete print.
  4. What are the pre-printed unit descriptors and dimensions small medium large XL? Narrow/wide?
    1. Pre Print units are based off of the measurements and how you converted them in blender. Instead of having small, medium, large, XL, etc. I have converted that into being resizing percentages. I use makerware since we use makerbots (2x and 2) so for a hand such as below picture measurements, I would classify that as a small or (110-130%), an extra small would be closer to 100-110% (which is super small like a 4 year old or so), a medium hand will be around 130-150%, a large will be around 150-170%, and an extra large is around 170%-190%+. Again, the percentage matters from the sizes that correspond the non effected hand as you want to make it as close to the other hand as possible.
  5. Does a Medium finger always go with a Medium hand?  If not, what’s the deal?
    1. Yes, whenever you print a certain size of one finger, you do that same size for the rest of the print. For example, if I printed a palm at 110%, I would have to make the fingers, phalanges, thumb, thumb phalanger, and the gauntlet all at 110%.
  6. Where are  the models for printing S M L XL hands or fingers, etc..
    1. The problem is that there are no models. Each hand is supposed to be custom depending on each case scenario.

I have several follow up questions, but I’ll leave those for the next post.

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  1. The Google Plus group is private and you have to request an invitation, freely given, to be included.  While discussing discrete issues is easy enough, without the ability to quote original text, a detailed multi-issue open design discussion is very difficult. [↩]
  2. Note:  I’ve removed the photographs.  I am not sure I have permission to post these pictures publicly. [↩]

Progress on Parametric Printable Prosthetic

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So, I’ve been hacking away at an OpenSCAD sketch of the Cyborg Beast 3D printable DIY prosthetic.  At the moment I’m working on designing the left palm.1 I’m reasonably happy with the version so far.  I’ve also managed to separate out the cutouts for the hardware from the design of the hand itself.  The benefit to doing so is that it should later be possible to scale the hand up or down, but keep the hareware cutouts the same size.

It’s easy to print a hand, fingers, and thumb scaled to 110%, but finding Chicago screws that is 110% may be more difficult.  There’s still a LOT of work to do here, but I think this is a good start.  Below are the same three views of the two versions (OpenSCAD parametric and original Cyborg Beast).

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As I’m going through and replicating the design aspects of the Cyborg Beast, more design issues crop up:

  1. The grooves where the fingers fit into the palm are either tapered or flared in a non-uniform manner.  To get a better idea of this by reviewing the two pictures below.
  2. The holes for the elastic cord to cause the fingers to return to the open position do not appear to be of uniform diameter, uniform distance apart, or equally centered in the knuckle blocks.

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I can’t tell if these are critical design features2 or just design elements that don’t provide additional function or utility.  If you happen to know, your input would be greatly appreciated.

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  1. And, really, once the left palm is done it’s an easy to mirror this part to make a “right palm.” [↩]
  2. I’m guessing not [↩]