3D Printed Biomimetic Mechatronic Hand Explained Part 1

so let me start off by talking about some of the joints in the Bionic hand so the vast majority of the joints that you'll see are just simple hinge joints and that includes all of the joints in the thumb most of the joints in the finger and a few others here and there so the way that these work is they have a simple pivot which in this case is just a ball now having a ball as a pivot is obviously in no way ideal the bolts are just kind of there as a placeholder obviously in a final thing I'd have the ball only threaded at the very end so that would have a nice long shaft to rotate around but as a sort of proof of concept piece they're just the pivots are across just these threaded bolts now the way that they're actuated is by using a sort of cable and spring arrangement so all the motors are mounted in the forearm and those motors have little pulleys on them which pulled some cable through a cable sheath if you think of like a brick cable in a bike you pull the brick which pulls a little bit of wire through the cable sheath which actuates the brake callipers are another part of the bike that's a sim kind of idea here except instead of manual brake lever that you pull with your hand if a motor pulling the way over the pulley so when the motor pulls the cable through the sheath and that contracts the finger by using the inner cable to pull the the finger joint downwards and then when the motor relaxes a little torsional spring in the center of the join wrapped around the around the pivot point returns the finger back to a neutral position and maintains tension on the wire at all times so you'll see there's a little animation of this working hopefully that sort of clarifies it if that explanation want satisfactory now this sort of cable arrangement is something that's used quite often in animatronics because this is quite easy and simple to actuate something and make it do some quite complex motion without having to have any actuators in the joint or narrow even it can be as far away as you like but obviously there are some inherent problems with this so the further the distance you put between your actuator and the thing that you move in there's a lot of wiggle room between all the sort of components in that in that chain and so eventually is inevitable that component will sort of come out at calibration so eventually the fingers will be not they'll not be in quite the same positions as the way to start with and because the inner cable has room to move in the inner feith as the fingers move around and the the outer cable is moved around there's the potential for the fingers to move slightly just as the tension of the inner cable is just like moved slightly if you had an inner cable that was the exact same diameter as the inner diameter of the outer cable if that made any sense at all then you wouldn't have to worry about it but you would obviously have to worry about friction so so for something where you're trying to just get a really lifelike motion and you're not too concerned about the accuracy then it's not too much of a problem the solution would be 12a feedback sensor in the join itself like a feedback sensor in every single joint and then it could be more or less perfectly accurate every time but obviously that would have a lot of complexity to the assembly it is something that could be done it wouldn't be too much trouble but using the kind of really small potentiometers that are used in the controller there's no reason why you couldn't have something like that or maybe in a future redesign that will be something to think about if this was used as a real prosthetic hand you wouldn't need something like that absolutely because he couldn't be recalibrating it all the time and it wouldn't be practical so having a feedback potentiometer every single drone would probably make the design a lot more reliable but regardless that still be some problems with the pulley mechanism most of them you could make a lot better just by using tighter tolerances between the inner cable and our sheath things like a better poly and a bear securing mechanism on both the pulley and the the point that you're actuated there's a million little tweaks that you could make that would make this a lot better but in the demonstration that did seem to work sort of okay as a as a proof-of-concept you know so one quick other point I want to make about the hinge assembly looking at the exploded view you can see there's like an unbelievable amount of components in this hinge when really there only needs to be the two parts that are moving relative to each other and the pivot point which is the bolt that's going through the center there isn't really too much need for any other components and that it's just cuz they're this really weird idea of how strong 3d printed parts were based on the sort of bad experiences that I've had with my cheap printer which is now running a lot better because of some upgrades I've made it's also just because I wanted it to be as strong as it possibly could be and I didn't really realize that PLA can actually be really strong but when I was designing it I made it so that very few parts that printed would have any sort of holes running through any side faces and the vast majority of the holes it'd just be op through their Zed axis of the 3d printer and I also tried to print everything in really simple shapes no overhangs you know just a simple basic shapes as possible so I'm a 3d printer be able to print them quickly and strong but was I think I was seriously overcompensating for the limitations of 3d printing because I've ended up with this design that has way too many parts and where so many fasteners and the other thing was that because I had to do so much 3d printing during this project my 3d printing skills actually increased massively to the point where I'm much more confident printing odd shaped parts now and really even on my cheap printer there's nothing wrong with doing that sort of thing and it can be made really strong but honestly it probably makes it look a bit cooler than it it really is in the renders having all these bulbs but I think in a future redesign I definitely wanted redesign it's I have like as few fasteners as possible like I was thinking even the shell components could be like snap fit become a lot more confident with designing two different 3d printed parts to fit together and the sort of tolerances you need between them to be able to achieve that this also leads into another really big problem with the design and that's that I have limited myself almost entirely to 3d printed parts I'm going to talk about that in more detail a bit later on so going down to the knuckles of the fingers these are MCP joints I believe the called metacarpophalangeal joints in a real hand these are these are candlelight joints which is like it's like a weird ball socket joint but rather than being a ball it's kind of like a sort of or voyage ship so when the finger moves it's got obviously the two axes of motion are quite easy to see you can see it can go up and down I can do a left and right but you'll also notice that the finger tends inward slightly it sort of points inwards towards its towards its axis of rotation when it's moving left to right this is something that I thought would be quite important for certain grip types and things like if you wanted to pick up a ball and display your fingers to go and pick up you know like a large bowl you'll see that your your little finger and your index finger sort of quell inwards and I thought that would be quite an important sort of grip configurations are able to pick up something like a ball so I thought for a really really long time about how I could how I could make a mechanism to without really over complicating it and then too many actuators sort of automatically have the finger twist inwards as it did the lateral side to side motion in the mCP joint so I drafted a few ideas and I decided that it'd be best just to simplify it to two axes like a double hinge joint although I still sort of bothers me that I didn't manage to find a solution to that and I feel more confident now that if I went back I could think of a better way to do it I'm fairly certain it would be possible I thought of some ideas of how you could do it with some sort of linkage assembly but I couldn't think of a way to make it strong enough and definitely not with 3d printed parts it just wouldn't be strong enough well that's actually where I started designing the assembly because I was really keen on having that that little twist in words and that's that that's the point that I started building the hand from just because I was so insistent on getting that that range of motion but I couldn't figure out I'd admit some assemblies and had some ideas and I got something that sort of worked okay when I simulated in SolidWorks but it wouldn't really have been strong enough to have any real force going through it and it of just simplifying it to this double hinge joint there's nothing really special about this design there's a joint in the center that allows it to move left to right and a joint that allows it to curl it should be noted that the lateral movement rather than using this torsional spring like all the other joints it has cable from both ends of the pulley so rather than use a spring to return it back to a neutral position it sort of pulls from both sides so that's useful because I wouldn't know which side would necessarily need to be exerting more force so you know the left and right movement should move with an equal amount of force so most of the joints in the thumb work exactly the same as the hinge joints that I talked about earlier except just a little bit larger apart from the base of the thumb now the base of the thumb is a subtle joint it's the only one of his kind in the human body of when I was looking through the literature it seems like a lot of people disagree about how to classify what this joint is at the base of the thumb but it's a really complex joint it said Candice it's like a concave surface interacting with a convex surface and it allows the thumb to move through some quite complex ranges of motion but if you look at your thumb you'll see there's two joint sorry there's two segments of the thumb that I saw protruding from the palm and then there's a another burn that sort of built into the palm and it's surrounded by a muscle as a mention this a little bit in the previous video when I was talking about the control glove all that muscle around the the botton burner the thumb makes it quite difficult to measure how it moves but I believe there's something ridiculous like eight muscles or something in the thumb there's ones that connect to like the the carpal bones and in the base of the hand and then I believe them the metacarpal bones of the index finger on both sides by the looks of it basically it was way to sort of complicated trying directly Emilia I couldn't just have a cable for each one of the muscles because I think that'd just be ridiculous and I'd have way too many actuators so I tried to approximate the movement of the thumb as best I could at this that join and he ended up having two axes immersion I could have put another on but when I did the grip tape testing for the hand I found that it was more or less all I needed so yeah so having one axis of motion being the sort of swing around the fingers from from all the way from opposing most of the fingers to swinging back and sort of being facing the same direction as the fingers and this uses a little assembly with two little bearings that allows it to swing round deep groove bearings so they can have a little bit of force through through their axes of rotation and then a little sort of spring piston assembly to bring the thumb in towards the fingers so that that piston is a little bit jammy really not too pleased with it it's the kind of thing that really just probably shouldn't be 3d printed I could make it on a lathe or just buy something that do that that task bought it just canned away at least it's a proof concept but also presented some problems about the management of the cables through it so probably more development more focus is needed at the base of the thumb to try and and merely at that joint better because it is just so complex but it's also so critical it's just so important to have the thumb working properly you know without the opposing thumb wouldn't be able to do anything with the hand really and then at the same time you're also limited by how much you can measure it with the control glove so the base the thumb was definitely a challenge and something that still needs work so there is another sort of weird range of motion that I wanted to have the metacarpal bones are slightly flexible and you'll notice that if you just sort of play around with your palm you'll notice that you can move your little and ring finger metacarpal bones by sort of squeezing the muscles below your little finger in your palm so this was another thing that I thought would be important I wasn't able to find much research into that specific sort of degree of freedom but I feel like it is quite important even though it's something that you don't really pick up on whenever you go and grasp something your there's your knuckles sort of move downward and depending on what you're picking up I feel like that might be quite an important quite an important range of motion but there's something that I'm sort of a little bit unclear of it just seems to be like quite a Polly researched and probably understood things to happen and it might just be something that sort of locked to other movements might not be something that you can really control individually but I want you to put it in anywhere because because I guess my intention was to just cram as much degrees of freedom and degrees of actuation as possible and just try and cram everything in there so it could be as organic looking and moving as possible so this is the one thing that just didn't really work because I'd used a little bit of soft inner tube going across the knuckles to try and be the elastic thing that would return it back to back to a neutral position yeah the the inner shoe weren't really good enough for bringing it back and it just kind of like made it more difficult to actually something that MA directly opposes being bent like a little stripper spring steel something like that would have been a lot better in place of that inner tube this is this is something that I'm just not sure if it's necessary at all I don't if it adds anything really to the hand is something that I'd be tempted to just completely take away because yeah it's so much instability to the structure of the hand and there's kind of like no benefit to it being there it was kind of just because you know as I've said at the beginning the idea is just to design a hand that's as close to a real hand as possible with kind of like no regard really for how easy it would be to control you know like the pitch was just in the future when there's no restrictions on how we can control by on accounts like myoelectric technology detecting nerve impulses in the residual limb like I said we could just detect everything in like super fine detail what kind of amazing the complex hands would we use rather than the you know the limited ones that we have now but yeah that's something I could probably just get rid of honestly I have seen Bionic hand designs that kind of integrate like one or two hinges sort of in the palm to sort of it sort of combines the motion of moving the metacarpal bone with the the sort of inwards twisting that I was describing earlier and it does allow the little finger to sort of oppose the thumb more directly it's something that I need to sort of research in more detail maybe I was in too much of a rush to sort of start designing and I sort of neglected certain joints even though I did produce a wealth of research and my thesis was marked very highly in fact but the hand is such an enormous ly complicated biological mechanism that there's just just so much you could look into and trying to emulate every single drawing is something it's just a really complicated process CERN is the wrist the wrist was kind of challenging because I want you to make it as small as possible the wrist in our hands I'm just talking about the the flexion and the left-to-right I'm not talking about turning your palm over as of yet but that motion in our hand is just controlled by muscles in the forearm just like the the fingers didn't really have any more space in the forearm because all of the forum was taken up with the actors for the fingers so I ended up sort of integrate in sever mothers into the wrist right where it bends and then using using like timing belts and pulleys to try and get a little bit more torque out of the motors and obviously transfer the transfer the fossa cross I did have a little bit of trouble fitting these quite bulky Murs into a small enough space and ideally I'd like to the wrist to be a little bit more streamlined but it did seem to wear her care even if it was maybe maybe the motors where quite as strong as they needed to be but that's also a problem with the the weight of the hand which is a problem with the design sort of overcompensating for the limitations of of my idea of the limitations of 3d printing so you know people asking me you know how can it be fixed and I can get it working but realistically the the problem sort of deep-rooted and it needs to just be started from scratch to be able to you know have it working perfectly because it is just too heavy and there's like a thousand little tweaks that need to be made it's just like one step in a iterative design and prototyping process yeah the restaurant worked too but now the ten in over of the palm this is something to fart about for a while because in a real hand you have to burns a radius and an ulnar burn you all know burn forms most of the elbow joint well as the radius bone forms most of the wrist joint so when you turn your palm over the radius burn moved across the ulna burn which stays stationary so effectively you turn your palm over while your elbow stays stationary this is something that just didn't have time to figure out I was looking at this great big massive off stephannie and trying to imagine how I could get it to turn the entire thing over but in the end I just didn't have time to figure out how I mean obviously you could just have one more just sort of twisting the entire arm through the center and that's why I was thinking of doing what in the end I just wasn't happy with anything other than the saw of radius telling over the ulnar assembly cuz it it just wouldn't be biomimetic and I wouldn't have been happy with it but that's something that in the future I'd like to figure out so thanks for watching there's gonna be another part on this because there's still a lot more to cover on the Bionic hand there's also a video about the control glove and which is a was another important part of the project so check that out if you're interested and I'll see you in the next video

Channel: Will Cogley

Views: 735,491

Rating: 4.9285364 out of 5

Keywords: 3d, 3d printing, 3d printing animatronics, animatronic, animatronics, arduino, arduino animatronics, arduino robot, arduino robotics, cad, cad animatronics, diy, diy animatronics, diy robotics, how, how to, instructables, make, maker, making, mechanism, robot hand, robot arm, bionic hand, bionic arm, prosthetic arm, prosthetic hand, arduino robot hand, arduino bionic hand, diy robot hand, diy bionic hand, 3d printed robot, 3d printed hand, 3d printed prosthetics, robot, diy robot

Id: l6xqTcLXXC8

Length: 20min 32sec (1232 seconds)

Published: Sun Oct 28 2018

Reddit Comments

[u/crua9]

I figure this is worth a share since a lot of this could be used on other mechanical parts you might design

[u/Bmarquez1997]

Interesting. This reminds me of the 3d printed hands I've printed through the Enable program! They don't really use any "mechanical" parts, but they do piece together to form a functioning prosthetic hand that works quite well