Precision on a Budget: DIY Displacement Sensor for under $10
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- เผยแพร่เมื่อ 17 มี.ค. 2024
- ---Video Overview---
Join me as I build and test out the performance of an electronic displacement sensor. It uses a 3d printed, plastic flexure to guide the motion and an opto-interrupter to get that motion into an electrical signal. I set out to design it to get digital data collection on tasks where I've been using a dial indicator and notebook to date.
Based on my testing, it is repeatable to better than 5 microns (it's actually closer to 2 microns based on the data, but I added some head room to account for some of the drift and such that wasn't captured over the limited measurement time.)
To help visualize the movement of the flexure, I show a couple of fusion 360 simulations.
---Build yourself one!---
If you'd like to build one, links to the models along with the rest of the details are all here: jfs-agri.com/index.php/bubsbu...
If you have a resin printer (you could try it with FDM, but no promises), and want to try out a different take on this same basic concept. A while back I also made this displacement sensor using diaphram flexures instead of the leaf flexures shown in the video. I haven't tested this one in detail, but I would expect it to perform similarly, if not a tad better: www.printables.com/model/4432...
---Alternate use case - Displacement sensor as Load Cell ---
These sensors can also be used as a load cell. I'm working on a project currently using the same sensors shown to make a mass balance. It's a work in progress, but additional info here: jfs-agri.com/index.php/bubsbu... - วิทยาศาสตร์และเทคโนโลยี
as a career metrologist, I saw microns in the title and had to take a look. Nice video, and project. If you are going to start talking about tenths of a micron, as in the uncertainty of the Mitutoyo slip gauges, or indeed the couple of microns on the feeler gauges then you had better also start talking temperature and temperature stability. 20 degrees ambient with no more than 1 degree change in 24 hours is a good enough starting point to enter in to those discussions. Excellent.
Thank you! And absolutely, I definitely did a bit of a disservice by not touching on the temperature sensitivity! Especially given that I've got a whole collection of mismatched materials, and cheap electrical components. I'm going to set up a couple of thermal drift measurement tests that I'll share as a follow up. I have no doubt they'll result in a nice big asterisk alongside that '5 micron' number :)
Very much appreciate the kind words and clarifications! Coming from an experienced hand in the field makes them feel all the more appreciated. Thanks again.
Good comment. 20 degrees C = 68 degrees F for those of us who still need to convert to have a feel for the thing..
@@bubsbuilds Not sure if it is mentioned later in the comments but I thought I should warn you that it will be essential to add light shielding to your innovative project.
Printing a hole though the middle of the plunger and reaming it out to be replaced by an Invar screw/rod might go a long way to fixing likely thermal error and drift. If you have it a sliding fit in the hole except at one point the plastic expansion will not even matter. A slit for a interruptor vane (and screwdriver slot) in one end and a hole for the steel ball in the other end makes it look like a old world set screw might fit the bill.
I had a look and there were lots of linear displacement transducers on eBay for US$15-40 that might have long term stability and enough resolution and accuracy out of the box.
3:23 What?! Is that a fractal vise made AS a compliant mechanism?! Dude, that's amazing!
It is indeed, and thanks! It's a concept I've been playing around with for a bit, but still haven't been able to get one that checks all the boxes for me. I've got some info on the variations I've tried thus far here: jfs-agri.com/index.php/bubsbuilds-projects/just-playin-and-concept-demo-projects/flexure-fun/63-flexure-fractal-vise-jaws.
@@bubsbuilds That's really awesome. I've seen the fractal vise and compliant mechanisms but never thought to link the two together. I may try printing one or a modified version for my normal vise. Thanks for sharing! Or as Max from The Flight of the Navigator would say, "Compliance!".
Hahaha, what a perfectly appropriate close, nice :) Thank you, and if you decide to go for it, I'd love to see what ya cook up!
Fantastic work. It's not often I come across somebody on youtube who seems to /actually/ know about metrology. Liked, subbed, commented. All hail the algorithm
Why thank ya! I should confess I'm by no means a metrologist, but I do have much love/respect for their field! And, on the flip side of determinism, all hail the algorithm indeed! :)
Wonderful. There is probably some noise from the lights, which a cover would help, since the peak wavelength is around 940nm. Also there is a 0.5% current drift per degree Celcius around room temperature for that opto-interruptor, plus whatever the TCR on your current sensing resistors are. Finally the datasheet alludes to using a higher amperage pulse for sensing, which would help overcome the noise from the incident light or other noise sources.
PLA is transparent to the wavelength of interest so you are relying on the pigment in the plastic for absorbing the IR. The non-linearity of your voltage-displacement curve suggests that the plastic isn't fully opaque, the knife-edge is not knife-edging. Some black acrylic paint or even just black filament should pretty much erase this effect if it's there at all.
...a chemist, eh? I dunno, I'm starting to doubt it :)
Great points all around! Room light interference is definitely a potential error source on these guys. For pulsing the current, I'm guessing they're recommending the high current to bring down the response time....maybe? What I've done in the past is to use a high(ish) frequency signal and then a band pass filter on the read side. The frequency depending on the response time of the sensor I was using. Works great, but does require a fair bit less laziness than I showcased in my circuit here :) Also, one thing to keep an eye out for with that is if you're measuring anything dynamic. Just have to make sure whatever frequency content you're hoping to measure is less than half your pulse frequency and also not cut out by the band pass.
Temp is a BIG one. Without quite a bit of care, anything measuring in micro or below is probably as good of a temp sensor as it is a sensor for whatever it was purchased for :) The resistor drift is one I had completely overlooked (by the way, I had to Google TCR...again...chemist? mm hmm). And it's very much a big one with the simple circuit I'm using! An additional significant influence from temp will be with the 50mm of PETG between the contact point at the knife edge. I think it has a CTE somewhere between 50 and 100 ppm, so that'll add quite quickly. Really just need one of those super stable, 20 deg C rooms!
Damn, I think you're right! I hadn't considered that at all as the potential source of the non-linearity...I just immediately jumped to taking the easy way out and putting it in a lookup table. I printed it in PETG, but I'm pretty sure it also transmits just fine in that range. In the past, I've always just added a razor blade, since they are cheap and have well-defined edges. So these printed knife edges are still relatively new for me. I like the idea of an acrylic paint. I have some UV cure acrylic, I'll give it a shot! I also like that this should smooth out that edge a bit.
Thanks for the good stuff to think on, and for pointing out some of the big time-dependent stuff I didn't cover at all in the video!!
Great comment and response comment. This type of open sharing of thoughts is how we all advance our collective learning.
How about using a real knife as the edge? You could insert a piece of a razor blade into the print. This would make the edge crisper and block the IR better :)
Awesome video!
@@bubsbuildsMy guess on the current is to drown out other potential sources of interference. LEDs and resistors are similar in that their current rating is for DC steady state. Just using AC increases the peak voltage to Vrms * sqrt(2). Short high current pulses would produce an extremely strong signal, and in the off time you could measure the ambient and subtract it in software.
I wish it would let me post the "the more you know" thing here! I hadn't considered anything even close to that. Very much appreciate the insight, thanks for sharing!
"Ultimately, the best tools, are the ones you got!", that's great!
I would highly recommend watching Breaking Taps video on the cryogenic mirror actuators for the JWST. Using gearing and flexors they are able to create repeatable nanometer precision movement using stepper motors. I'm sure that the same design could be used to create repeatable motion for close to nanometer level precision displacement measurement. If I am wrong I would love to hear where I went wrong! Awesome video though, keep it up!
BIG fan of Breaking Taps! And agreed, the JWST is a showcase of beautiful precision engineering....so damn cool... th-cam.com/video/5MxH1sfJLBQ/w-d-xo.htmlfeature=shared . Although I think my favorite video on Break Taps is still the electron microscope metal cutting. th-cam.com/video/aF7ltBT_atA/w-d-xo.htmlfeature=shared
You definitely CAN use similar concepts in making a nano-scale sensor. But you start to run in to quite a few challenges on that path to shave a few more decimal points :) For example, for an optical sensor like the one I used in the video, you'll start coming up against the diffraction limit of the light at a few hundred nanometers (exact limit will depend on the wavelength and optics being used). At nano, the deformation of the steel stylus and gauge block also start to matter (Hertzian contact, ifn ya want some fun googlin). Working at 10s of nanometers, I've even had ambient humidity changes between seasons cause me to chase my tail for a while. The full list of all these extra 'little' factors can become pretty challenging to manage/account for. Not at all trying to imply it's not possible to overcome all the wonkiness that comes with sub-micron, but in my experience it's a non-trivial design project. Admittedly, I'm far from being a Nasa satellite builder that people call 'Dr.', so they may very well have some more tricks up their sleeve than I do :) But I think maybe they just make it LOOK 'easy'. I'd guess there's a Moby Dick sized book of calculations supporting those JWST beauts.
Aluminium foil has a thickness in the 15-35 micron range. The thickness is printed on the box and is a good low-budget reference for calibration.
Very cool, the additional comments to enhance accuracy were also nice.
Accuracy is typically given in 2x standard deviation not 1x.
At that level youre workin at viscoelastic effects of the plstic and temperature stability come into effect. Pla is very very bad at having a homogenic temperature. So touching the part takes literal minutes to dissapate the heat. I design air bearing and when i measure Nanometers or microns its best practice to work in a temperature stable environment and let your experiment sit for like 10-15 minutes after you touched it. Interesting design! Thanks for sharing.
That’s really clever using an optointerrupter as a jank displacement sensor. How is the thermal stability? I’m sure you’d only see a few degrees C but some cheap sensors can get totally thrown by that
I haven't done any characterization of the thermal drift, but I agree, I should! One bit of data on it that I can give, the calibration runs that I referenced/showed in the video were done over multiple days and at different times of day. So there is thermal drift somewhat wrapped in to the repeatability numbers shown. There are a couple of follow up tests that I was thinking of running on it based on some of the feedback thus far. I'll definitely put this one high on the list. My plan will be to see if I can set it up such that I can isolate the drift coming from the sensor side and the driver circuit (since I suspect both are pretty temp sensitive for this setup.)
@@bubsbuildsoh nice sounds like it may not be a huge issue then. Well if you want to go sub-micron one day perhaps you can actively compensate with a thermistor or thermocouple. A little extra calibration never hurt anyone 😅
Oh I didn't mean to give that impression! I think you're spot on! My guess is when I try again in summer I won't be so lucky :) But exactly, who doesn't love a few extra fitting functions! :D
This is amazing! Will be really tempted to make one - (note: I have absolutely no need for one)
Thanks! To play a part in encouraging someone (other than myself, for once) to make random stuff they don't need is very much the dream! Maybe it's one of those "if you build it..." situations. Once you have it, just all sorts of stuff will need measurin!
Or, if distance measurement isn't your thing, you can also use it as a load cell. I used three of them to make a 'little' (it's quite large....oops) mass balance. But, full disclosure, I already had a perfectly good one... kind of circling back to your comment :)
Still a work in progress, but more info on that mass balance, ifn you're curious: jfs-agri.com/administrator/index.php?option=com_content&view=article&layout=edit&id=71
wow that is SO cool!!! thank you for sharing
flexures are amazing
Another possible way to measure the distance is to use magnets and Hall effect sensors. Put the analogue Hall effect sensor between two opposing magnets (push each other apart) and you can measure the position of the Hall effect sensor between the two magnets by measuring the voltage, so if you attach the magnets to the flexure and attach the hall sensor fixed to the frame it should work quite well.
I've never tried using hall effects for something like this, but I've now heard a couple of times that I'm missing out! I'll definitely have to give it a try. And I like that suggested configuration. Should make it easy to convert the same basic design over, thank ya! If you have any specific models of hall effects that you have found work well, I'd welcome recommendations!
This is fantastic, thanks for sharing the OnShape model!
@AK-xb9ke Thanks, and glad to hear the model is helpful for ya! Although sorry you have to deal with my terrible modeling practices :)
This is amazing.
now that i'm thinking about the whole assembly, this is basically a super cheap load cell! if you increased the wall thickness you could modify the range of the load cell
Yep! I had the same realization after I built the first one, and so naturally I stuck a few of them together and made a mass balance :) jfs-agri.com/index.php/bubsbuilds-projects/just-playin-and-concept-demo-projects/flexure-fun/71-mass-balance
@@bubsbuilds that's awesome :OOO and it seems pretty linear too
Thanks! I'm not convinced it's practical, but I must admit, I do like how it looks...always an important engineering consideration :D
This is awesome! I never thought of using those interrupters for anything other than simple object detection. Really cool!
I'm glad I'm not the only one that had that reaction! I was first introduced to using them in their linear range a few years ago, and it's still a personal favorite!
Awesome build!
That is good work , very practical .
Thank you, I very much take 'practical' as quite the compliment!
I wish that voltage was a bit lower on the sensor, I haven't done low enough level electronics for a bit, but when I was playing with adc's and such, a 4.096 volt voltage reference was my best friend for making reading voltage easy on an adc, as I'm sure anyone who's worked with raw adc setups understands why and hopefully many have also experienced.
@glennmcgurrin8397 well then, have I got good news for you! :) The receiver side of the opto is just an NPN transistor, and the output voltage (in my setup) is just the voltage drop across the load resistor. So you can change the voltage range pretty easily by just changing the Collector-Emitter voltage.
I think at 0:56 You are simulating an off-axis force in the y direction, but the physical model recieves the force in the x direction.
Also You shoud try covering the photo-sensor with aluminium foil, or a plastic cover, as there are some infrared light in ambient lighting.
nice solution, wondering if you need to be inline of the object, or could move this around with a lever so you could increase the performance to maybe 1:2 or 1:3 or even more 😅
Would be cool to see if you can make a probe for 3d printing with this, so that you don't have to do the constant up and down movement. You could just move it across the bed to get measurements. Like the beacon probe, but that uses induction and doesn't touch the plate.
Thank you! I will make this for sure! Will reach out if I manage it. Subscribed!
Can't wait to see how it comes out, and thanks!
Very cool. I do have to ask- did linear hall effect sensors come up as a contender for the photogate? They are cheaper/same price and wouldnt have offset issues from ambient light, and wouldnt need to use a knife edge either
I have never tried building a version with a hall effect in place of the opto, but I'm quite curious now to know how it would compare. I'll add it to my list of things to give a go! If you happen to know of any specific models of sensors that have good linear performance and dynamic range, I'd love to take a look.
i love these simulations. wish i could calculate that on paper, seems so cool
If doing the hand calcs for flexures like this is really something you'd be interested in tackling, it may be more doable than you think! There are some simplified equation sets that just require some algebra to solve that can cover a huge range of flexure designs. They do include some assumptions and limitations in terms of things like range of motion, some aspect ratios of features may need to be inside of a range, etc., but in general I personally would trust the numbers resulting from those hand calcs more than I would for those in the simulation. My goto book for this kind of thing is "Ultraprecision Mechanism Design" by Stuart Smith (amzn.to/4aAwyJf ). I think his newer, more comprehensive "Basics of Precision Engineering" also has a section that covers similar turf, but I haven't familiarized myself with that one as much.
If you are more math-savy than myself, and enjoy diving into calculus in your paper calcs, you could then skip the simplified calcs and get a solution that can be extremely close to actual. If you want to dive into that deep end, I'd yet again point you to Stuart Smith...what can I say, the man literally wrote the book on flexures...aka, this book is just called "Flexures". It's not for the faint of heart, but if flexure calculatin is your jam.... :)
BUT, one big exception to all of the above....3d printed parts are not your friend if you want predictable/deterministic performance, especially FDM printed parts. So you'll want to pad those errors bars a smidge accordingly. Not only do they have direction-dependent properties, they also don't tend to act predictably compared to their bulk-material counterparts in other ways. Like in my sensor, the thin regions of the flexure webs are only two strands wide. So it tends to (at least in my experience) act like something in between solid plastic, and two strands of plastic. I'm sure there are folks out there that know how to calculate that....but it aint me!
Sorry for the ramble, but if you decide to give it a shot, I'd love to hear how it goes for ya!
@@bubsbuilds thanks for the huge reply!! this is awesome information. nice to see that you can skip calculus here, lol, the things we do at my mechatronics high school are kinda mysterious to me, it isn't explained veey deeply and so we just have some stresses of a cross section that we're comparing with the max stresses for a material etc. i don't like how everything has some kind of coefficient, but i guess that's just how it goes in mechanics... nevertheless still thanks for help, all the mechanics books have some math that's certainly not for me lol
@king_james_official If you're already into mechatronics in highschool, then you're well ahead of where I was then! Although all of the books I recommended to you are ones I didn't encounter until at least grad school...so I may still have gone a bit overboard, haha. But I do very much remember Statics! Which sounds similar, "all beams, all the time"! If it makes you feel any better, you'll definitely have options along the way to take classes where you can get to the bottom of those coefficients! And hey, if you're someone that's first instinct in seeing a flexure simulation is, "I wish I could calculate that!", I'm guessing you won't find that math 'not for you' for long :)
@@bubsbuilds yeah i hope i'll do some cool shit :D
That's fantastic work, many thanks for all the information displayed ! I am wondering if your concept could be tweaked and used to make a test indicator instead of a dial indicator, to measure the surface variation of your rotary plate. The limitation might be the material to fix the axe needed for the lever- type contact and the probe sturdiness.
Looking forward to your motorized rotary table posted on your blog and displayed at the beginning of the video ! With your digital dial indicator and a stepped motor and accurate coordinates you could display a height variation graph as for 3D printer bed with cr touch/bl touch
Ya know, I think ya could! I actually just made a sensor last weekend that may be a good starting place. I'll toss it on the list of upcoming stuff to take a shot at, thanks for the suggestion! Although probably won't make it's way into the video on the rotary table. I've been dragging my feet on that one for a bit (got sidetracked playing with the new load tester :) ), but I'm hoping to finish it up in the next week or two. Hearing that someone other than myself is interested in it may very well be just the motivation I needed! Thank you!
Excellent-SUBSCRIBED 😊
Why thank ya! :)
The entirety of the viewership of this video are people irresponsible enough with our money to have purchased "AA" or "00" Gage blocks (Since apparently companies can agree on standards for measurement but not what to name them) lol. Fantastic video!
Haha, thank you YT for finding me my kind of people! :) And seriously! Why the hell is it so hard to pick a naming convention!
Thanks!
Oh, don’t even get me started on naming!
I use a ton of data for my analysis work and every bit of it has been renamed by IT to meet THEIR standards.
Note 1, the IT standards don’t match industry standard names used by the people relying on the data. If IT was building systems for the military they would call the Army the Land Force, and the Navy the Sea Force, ignoring Navy planes because that doesn’t make sense as there is already an Air Force. Renaming the Marines would involve months of discussion because they go about everywhere but space.
Note 2, “Standards? Sure, we have lots of them.” Unfortunately, different groups within IT have different standards, and no interest in standardizing on one standard. IT has fairly vague understanding of what any of the business terms mean, so after they’ve renamed something to their standard they write a vague description of it - obscuring what it really IS.
I need to expand my rant out to an article one of these days. Thanks for reading this far!
what if you turned the tip area from a rectangle to a cylinder profile, and then added another cylindrical sleeve around it to constrain it? would that not reduce off-axis flexing error in most cases? (given proper tolerancing and 3D printer accuracy)
@ulamss5 Not sure I'm correctly envisioning what you have in mind, so please feel free to correct me! But my read is that you are asking about having nesting cylinders with a running fit to allow them to slide relative to one another....? If so, it's certainly possible to build a sensor this way (for example, these spring-loaded LVDTs: www.omega.com/en-us/control-monitoring/motion-and-position/displacement-transducers/p/LDI-G19 ), but they have some limitations compared to a flexure-based design.
The first being that there will be a limit to how tight of a running fit can be reasonably achieved. Even with precision ground parts, you'll still have a clearance of 10s of microns (and this would be a fairly pricey set of parts in comparison to something printed). So there will be some unconstrained lateral movement in that gap, and it will also allow for some pitch and roll rotations (the amount of which depending on the length of the bore.) And because it's not constrained at all in that gap, the movement around that gap will be somewhat random and so can't be calibrated out. You could add a preload to force the probe to always sit on one side of the gap, but that is only going to make issue 2 worse...
The second issue is the friction. Unless you go with something like an air bearing, there will be a non-negligible amount of bearing friction, both static and dynamic. The static friction is likely to cause some 'stiction' any time there is a change between static positions, and the dynamic friction is going to result in additional hysteresis. Depending on the application, these can be dealt with, but they can definitely present problems. For example, in applications where I've used sensors like the LVDT referenced above, we would only use them for measurements from a single direction. So they work just fine for something like bed leveling, where you can lift the sensor, move to the point you want to measure, and then lower the sensor to collect a measurement while moving only in negative Z direction. Then lift, move, repeat. However, they wouldn't work well if you wanted to leave the Z in position, and move the sensor across the surface to collect values continuously.
If I totally missed the mark on what you meant, and just ranted for no reason, please feel free to say so! :)
COMPLIMENT MECHANISMS ARE COOOOOL
I wonder if using a linear rail or a differently shaped compliant mechanism can make it more compact and at least equally accurate. I really want one of these and have them attached to an arm, but I'd need a really strong arm or really light dial for that
You can definitely make a much more compact version, but how difficult that'll be will depend on what kinds of tools and materials you have at your disposal. The stiffness in the direction of movement goes with the cube of the leaf spring thickness. So every bit you can remove from those web thicknesses will pay large dividends in reduced stiffness. If you have access to a resin printer, you could easily make the same design, just scaled down. With standard resins, it may be too brittle to give you the full range of motion, but if you mix in some elastomer to up the ductility, you should be able to get the full range out of it. I've done similar with mixing SirayaTech's Fast ABS-Like with their "Tenacious" resin. You can also make variations on this same design concept out of aluminum plate (or other machinable material of your liking) on a mill. Using notch-type flexures in place of the leaf flexures I used, you just have to drill and ream some well-positioned holes, then the rest of the material removal can generally be done pretty loose. I've done webs as thin as 0.010" (~0.25mm) like that on a decent hobby mill. You just have to make sure to fixture it down fully so it doesn't chatter you to death when the flexure gets free :)
...oops, sorry, got me on a rant there! If you want to chat about what you're aiming for in some more detail, feel free to reach out!
@@bubsbuilds I love it when I get people to rant about interesting stuff :D. Yeah, if I am gonna make on emyself, it'll probably be another design. I think I might go for a linear rail version. Maybe just some guides to a pin in general. I feel like linear rails should be relatively easy to 3d print as well (given you already have ball bearings), and would have similar side-to-side inaccuracy to this flexible design, but won't have the consistent movement of compliant mechanisms and will be more complex to put together. I think that's worth it though, for the sake of compactness and weight. I'll probably make the spring a compliant mechanism attaching the pin to the main body.
Oh man! I build stuff with cylindrical magnets with a press fit and while overall the tolerance of the magnets is very good, I get about 1 of 150-200 that is either undersized or oversized by about .005-.012. It is just enough that an occasional loose magnet doesn’t stay pressed or an occasional tight magnet is stressed to the point of cracking the chrome plating. This would help me build something to easily measure the magnets one at a time in a stack and do it quickly.
I don’t even need an accurate measurement just an accurate relative measurement. Hmmm.
I tried it with very accurate calipers but the magnets make maneuvering the calipers clumsy and slow. Now I want to work all weekend making this!
Soo?? Did you find yourself a solution?? :)
@@bubsbuilds I think my solution will be to design and build my own device leaning heavily on what you've done here. I'd probably have two silicon carbide bearings spaced close together so the cylindrical magnets would contact those and then a third carbide bearing in the flexing part of the device. I think I could just take a big stack of magnets stuck end to end and slide them slowly through, pausing just long enough to see the diameter. Centering the cylinder tangent to the 3 carbide balls would allow for some variability in the angle of the cylinder that wouldn't affect the reading much for the first 4-5 degrees. I think it can work.
For all Americans out there it just few inches, yards, pounds etc etc...
They are also moving to a more scientific unit system, inch by inch.
Oh wow, thank you for pointing out the oversight!! The sensor should be good to about 0.0000055 yards.
And, in light of that glaring omission, a couple of additional conversions in the interest of inclusiveness:
For equestrians in the audience: 0.000000025 furlongs
For the seamen: 0.0000000027 nautical miles
And for those somehow even more ancient than the US: 0.000011 cubits
:)
@@bubsbuilds Awesome. 😀
How many football fields is that? Where "foot ball" means "hand egg", of course.
Did you do the Voltage over thickness curve for more than just those 6 values? Because it might not be linear, but if the repeatability is that good it would be easy to use the correct function to map voltage to thickness. There is no need for that to be linear as long as it is known.
I did indeed only calibrate it with a relatively small number of points, and very true! I don't have any tools on hand at home that I could use for finer cal, but if you do, that will absolutely work! One of these days I'd like to splurge and get myself a Mitutoyo Calibration Tester, that'd be great for exactly that sort of thing.
I should clarify a bit, even though I only used the handful of points, the 5 microns I mention was assuming/using interpolating values between the cal points. So the linearity error impacting them is quite a bit less than the full scale linearity error I showed in the plot in the video. But it is still contributing a little under a micron of the uncertainty, and that's an appreciable percentage improvement if you can reduce it.
One additional benefit you may be able to get from finer resolution on cal points would potentially be a bit of extended useful range. There's some additional noise that comes out near the edges, but even with it, you should be able to get some usable range in the highly nonlinear bits at both ends.
@@bubsbuilds Should you ever get those values but have no way to get a good fit (like if the few functions excel comes with do not happen to work): Just post the values here, I can do that.
Super neat little gizmo. I'd be worried about temperature and especially humidity changes (stupid plastic is so hydrophilic) completely borking the calibration all the time, but I bet it would work GREAT for stuff like centering a workpiece or tramming, stuff where you only need a relative measurement. Honestly I didn't know those little sensors were that repeatable.
Thanks, and that's exactly the sort of stuff I'm aiming for! And great point on the humidity, I hadn't really considered the swelling of the plastic! I've currently got some thermal stability/drift tests going....I may have to cook up some humidity sensitivity measurements too...also, ugh, that's gonna be a tad more of a PIA than controlling temp :)
They really are surprisingly impressive little things. Someone first introduced me to them for this sort of use a while back, and I still think they're just great little tools to have in the box.
Can an extensometer with an accuracy of 10 microns be made using this electronics and 3D printing? The maximum travel would be up to 20 mm for a Type I specimen according to ASTM D638 standard. I am developing a plastic tensile testing machine, and I still need to measure the deformations.
Sounds like a fun project! I've actually been tinkering on a mechanical tester project lately too, must be the thing to do :)
For the accuracy* and range you're looking for, you need 1 part in 2000, which I think may be pushing it with printed parts and an opto-interrupter. I think you could probably get 10 microns on 10mm, or 20 microns on 20mm....but even that isn't likely to be an easy task. One challenge is going to be that you won't be able to get an opto that has a 20+mm measurement range (or at least I'm not aware of any, and it seems like to make one with a beam this wide would mean arrayed emitters and detectors, which I would think would make them less suitable for measurement.) You can definitely still use them, but you'll need to add some 'gearing' in the flexure mechanism. Since you only need 10 microns, and the opto can very much be made stable to 1 micron with a good knife edge (I'd glue in a razor blade, instead of printing the edge), you should be able to gear it 10:1 with a lever arm, and 1mm range optos are widely available. Adding in this sort of lever mechanism into a printed flexure should definitely be doable, but it will add a fair bit of complexity.
Some alternative options:
A few folks in the comments have recommended using Hall Effect sensors in place of the opto interrupter that I used in the video. I haven't worked with them myself, so I can't speak to whether they'd be well-suited, but may be worth a look. They generally do have a much longer working range, but given the fun that are field lines, I would guess they get pretty nonlinear. If you end up going that route, I'd very much like to hear how it goes! Folks have me intrigued.
If you are somewhat comfortable with electronics (nothing too crazy, but does require a little bit of working with AC signals) then I think a good candidate sensor for an extensometer would be an LVDT (Linear Variable Differential Transformer... the name sounds way fancier than it is...it's a few coils of wire and a steel slug :) ). They can have extremely good dynamic range, well beyond the 2000:1 you're aiming for...but yeah, little bit of electronics involved.
And an alternative option that you could use that also uses an opto interrupter. You set it up as a linear encoder. You could print a sawtooth pattern (or maybe even just embed a piece of actual saw blade), and have it move through the U of the opto. You can then also add more than one opto directly alongside the first (just make sure not to space them at an even interval of the sawtooth wavelength). If you're familiar with a quadrature encoder, it's the same basic idea. In addition to giving direction (which you don't care so much about) it will also help quite a bit in averaging out some of the noise.
Circling back to that 'accuracy asterisk' above, my answer really somewhat depends on what you mean by that goal. My guess is that for an extensometer you're mainly concerned with the relative movement as it's loaded, and don't care so much about the absolute accuracy....? Meaning if the actual length was 10.03mm long when it starts, and is stretched to 15.05. My assumption would be you want that delta of 5.02 good to that 2, and if the sensor was off on the absolutes, that'd be ok (say it read 9.08 to 15.00, but still gives the same 5.02). If you are indeed looking for the absolute accuracy, then I'd probably push my "challenging" to "pretty unlikely" :)
You can't reference an ASTM standard and NOT expect me to write a novella :) Hope at least somethin in that long-winded reply is useful!
Nice. I recommend adding a flexure lever between the ball and the sensor, to get better precision. Why not even with 2 sensors? coarse, and fine ?
@chargehanger I'm not sure if you could get much better precision out of it with a lever, but I've been wrong more than once :). The only configurations I can readily picture would either cause a fair bit of stiffness increase or introduce a pretty significant Abbe offset. If you've got some specific designs in mind, I'd welcome takin a look at em! Same with the coarse/fine idea! I think I can roughly picture the direction you're thinking, but each way I picture it, either they both read the same, or the fine sensor gets chopped in half :)
Love the suggestions, thanks! I may have to just test out a version with a lever to see how my assumptions above pan out.
I wonder if the consistency would be better if you wrap the sensor in foil or something opaque and shielding
Depending on the ambient lighting, it definitely can! A sometimes easier option though is to do it on the electronics side. Using a pulsed signal on the detector side along with a band pass filter can be really effective.
you can attach an adc and do a bit of nonlinear correction stuff in software, improves linearity by a bit (not much though)
Absolutely! I have a couple paired with Arduinos for something similar (admittedly, a higher bit depth ADC would probably be wise) . Although I didn't go with a nonlinear curve fit or the like, instead I just put the calibration data points in to two lists in the program, and then interpolate for the Displacement (aka a "lookup table", I suppose). Probably not the best if trying to do something high speed...but then again, this sensor probably isn't either :)
Hi! I was wondering where you learned about flexure design. Do you know of any good resources to learn about it? Besides the obvious of college.
Hi there cool guy! (love the handle)
I was fortunate enough to learn about them during school, but there are some great resources out there that you can access without that. If you're comfortable with diving in to text books, I can't recommend enough, "Ultraprecision Mechanisms" by Stuart Smith. It has great info spanning a LOT of precision design concepts, and the flexures section has fairly straightforward approaches to analyzing leaf-type, notch-type, and cartwheel flexures. Stuart Smith also has literally written the book on flexures...in a book called 'Flexures", but it goes through more detailed derivations that can be a bit more involved. It's great if you really want to design something to the last decimal point, but at least for me it's a bit harder to look to for quick guidance.
There's also a great book called "Compliant Mechanisms", by Larry Howell. I like this one as more of a 'get some ideas for options' kind of book. Like one of those books that just has a bunch of cam mechanism designs. It shows a number of compliant mechanisms and how they operate, but it doesn't really dive into the theory (at least not compared to the previous ones).
And on TH-cam, there's a channel run by Jonathan Hopkins, who is a researcher that has done a LOT of work with flexures: www.youtube.com/@TheFACTsofMechanicalDesign They have some really cool videos showcasing quite a few flexure designs.
And, last but not least, there's 3d printers :) play around and have some fun with bendy things!
Thank you so much! This is the exact kind of response I was hoping for!
Glad to hear it! If you have a specific design you're working through and can't find what you're looking for, feel free to shoot me a message. Enjoy the flexure fun!
It is funny that the ten dollar digital micrometer is calibrated with gauge blocks that cost more than the dial indicators you're replacing. still, very impressive, especially if similar results can be achieved with feeler gauges
Haha, yeah, I found that kinda funny too :) but hey, they lived to gauge another day
If you want to calibrate down to microns, I think it's gonna be tough to not find an expensive tool somewhere in the chain. If you have access to a half-decent coordinate measuring machine, you could use it to get some good 'actual' values for a set of feeler gauges to be your "Cal Feelers"....admittedly, this does sound a bit excessive. But with tools available in the shop, you should be able to calibrate it to better than 50 micron pretty easily. Half that with some effort. Not amazing, but not useless :)
Looks like an application for some Origami folding. Did you consider that?
It would be interesting make one of these using EDM and some metal, im sure it could be made significantly smaller. Also, i wonder if you could get a finer resolution using strain gauges compared to your solution. At least youd have a more linear accuracy around the extremes
That would be cool indeed! I think the form factor could definitely be quite a bit smaller. I'm not sure what the minimum wall thickness is for most wire EDM machines, but I'd guess they could get the webs pretty dern thin.
As an alternative option for a metal variant, in the past I've machined a fair number of similar flexures on a manual mill. If you replace the leaf flexures with notch-type flexures then you just have to drill and ream some well placed holes. Adding in some holes in the moving bits to secure them down to a sacrificial plate, you then just hog out the remaining bits....but not gonna lie, the EDM option sounds WAY cooler :)
On the strain gauges, I don't see any reason that wouldn't work just fine. I am usually a bit hesitant with using strain gauges personally just because I've had a couple of bad experiences with not getting proper surface adhesion and such causing me to chase my tail for a bit. However, that's very much a me problem. As long as you could get them attached correctly in the load path, they should be good to go....I wonder if you could use some conductive filament to just make the flexure a strain gauge itself...hmmm
Or you could buy a dial indicator for $50.
You would need to set up a ruby sphere as the contact surface. Well, or polish a piece of carbide or tungsten.
Would "need to" for what? :)
@@bubsbuilds contact hardness dude
BTW ..more yammering ( but, I do actually have some experience with precision/resolution/accuracy, and the differences therein)
Just thinking that one might reasonably apply the linear tape from an inkjet printer for the "range", measuring the number of ticks of the tape system for coarse distance, with a "hard stop" index to measure the tape for temperature compensation and "sanity check" for possible catastrophic failure modes... So, given that you have the known-good tape measurement for 50 mm, say, then interpolation for the "in-between-ticks" maybe even with a second optical sensor with know offset.... If you have established*linearity* of the optical/voltage change over the fine span, you can then increase *resolution* by introducing known "noise" into the measurement via change in the light level of the sensor, mechanical movement of the sensor "block" (piezoelectric or electromagnetic? Tiny earphone speaker? SMA element, maybe an SMA wire "baked in" the flexure, so that a small current will drive the SMA wire to change length in a "well-controlled" manner...)
Sorry, there I go, again...
Is stray sun light going to affect the measurement?
It absolutely can! A lot of indoor lighting sources can also have some content in the sensor's range. If putting a shade over it is easy, then that takes care of it without much trouble. A more robust option can also be implemented on the electronics side by using an AC signal on the sensor along with a high pass filter. That will knock out any DC signal from the ambient light.
@@bubsbuilds that's a fine solution
Once you made one you should be able to use it to calibrate additional ones very easily. Would make for some nice low-cost gifts for friends. Nerdy friends, at least...
Very true!....well, except for the 'nice' gift part, as much as I would love to believe otherwise :) The ones calibrated off of the first will be calibrated to the uncertainty of the original, so they'll all be a bit worse than the first. Choose recipients accordingly!
oh you better believe i subscribed
may try this as hall effect
I'd very much love to hear how that comes out! I've never tried using a hall effect for this, but I don't see why it wouldn't work. And it could definitely have some benefits. If you build it, please keep me posted!
👏 👏 👏
👍👍👍
Frankly, I Prefer mechanical devices because they are ( sturdy, powerful, smart, simple, accurate, and it is easy to notice changes in them, and they do not require a battery ).
Please what is the name of the program you used for the simulation ?
Not sure we agree fully on the 'why', but hey, preference is preference, so you do you! Purely mechanical devices are something of beauty though, I'm pretty fond of them myself!
Those simulations were just in Fusion360's Simulation Extension.
This would be a project where a linear regression would actually be really useful apart from university xD
Linear regression used to bring food to my table
What about using a cheap load cell?
Not sure I can picture it. Can you describe what you have in mind a little more?
Have you seen Adam the Machinist’s video on high resolution machinists jacks? I think you might enjoy it!
I had not, but I have now! And working my way through all of his other videos as I type....awesome!! He has some super clever designs and some gorgeous machining! Thanks for sharing!
If anyone comes across this and also hasn't seen it, do yourself a favor: th-cam.com/video/AdJzY1XF08A/w-d-xo.htmlfeature=shared
not sure the plastic backing plate is the best idea for calibration, I'd want something less ductile (steel block) as you are measuring microns, otherwise nice
Thank you! I was wondering when someone was going to call me out on that! Couldn't agree more. The corrugations from printing also aren't the ideal reference surface against the gauge blocks. Not gonna lie, when I first made it, I was just expected to use it for a quick test....but when the numbers came out down around where I was targeting, I just ran with it :)
For the thermal drift tests that I'm currently setting up, I'm going to go aim for a more suitable fixture. Although, it occurs to me as I write this that the plastic frame may actually have been helping me a bit since it has the same high thermal expansion as the sensor body...hmmm, well, guess I'll know soon enough!
Thanks for highlighting this, I very much appreciate the clarifications and additional context that I either forgot or completely overlooked!
woahhhhh
Totally not in the head space to be able to pay attention to this, much less appreciate/enjoy it but i can tell i will at some point. So ill subscribe and add to watch later as a lil treat for different times lol
Hope the head space is back to a place for enjoyin! whether you ended up watching or not :)
dude how are those amazing opto-interruptors only a buck each...
Great video Bubs. I think you might be addicted to flextures. Seek help 😁
Thanks bud, and hey, it's just so much easier to make things bendy than it is to make them stable :)
One parameter to improve would be size, but I lack a 3d printer.
Well hell, I've got a printer! Send your design on over and I'll give it a go!
i'm getting motion sickness from all that camera wobble.
How do you think I felt?? I had to edit that crap! ¯\_(ツ)_/¯
@@bubsbuilds haha nice reply :)
Thanks :)
Unfortunately, photodiode & transistor loop gain is a function of temperature and age. 💩
Wrong comment se section
Well....I tried Google Translate, but I'm now even more confused....So I'll go with, 'nah, I wouldn't recommend it for that'....¯\_(ツ)_/¯
@@bubsbuilds sorry man, I think the video changed but the comment section didn't. Lol, that was weird for sure.
Haha, no worries, just glad to confirm I'm not havin a stroke :)
If you are doing this for TH-cam views, then fine. If you are doing this to help yourself or others with measurement, you could have bought a $49 digital dial indicator from Amazon that reads to 1 micron, and saved a few days of effort.
How to say 'I didn't listen to the intro'....
I know, I know, BubsBuys just never took off :( . So I had to resort to wasting days of effort to crank out that sweet, sweet click bait....Thanks for the engagement!
Why do you want to prevent people from innovating ??
@RasTona_ Thanks :)
I've been looking and wasn't able to find a micron resolution gauge for $49. Care to share a link? Thank You.
Crap