16 ms·

Show HN: I made a new sensor out of 3D printer filament for my PhD

886 points by 00702 2y ago

Here's a "behind-the-scenes" look at my development of a cool sensor during my PhD (electrical engineering). This sensor is only about 1/3 of my total research for my degree and took about a year. I've been on HN for a while now and I've seen my fair share of posts about the woes of pursuing a PhD. Now that I'm done with mine I wanna share some anecdotal evidence that doing a PhD can actually be enjoyable (not necessarily easy) and also be doable in 3 years. When I started I knew I didn't want to work on something that would never leave the lab or languish in a dissertation PDF no one will ever read. Thanks to an awesome advisor I think I managed to thread the needle between simplicity and functionality. Looking back, the ideas and methods behind it are pretty straightforward, but getting there took some doing. It’s funny how things seem obvious once you've figured them out! Oh, I love creating GUIs for sensor data and visualizations as you'll see -- it's such a game changer! pyqtgraph is my go-to at the moment - such a great library.

Balvarez 2y ago
Wow that's super cool! Very nice work
- 00702 2y ago
  Thanks!
JackFr 2y ago
Made me think of Navin R. Johnson’s invention of the Opti-Grab.
klysm 2y ago
> Thanks to an awesome advisor And there you have it! The difference between a miserable experience and a good one
- 00702 2y ago
  Very much so!
porphyra 2y ago
That's super cool and I hope you don't mind a little bit of unsolicited feedback but the first question everyone's asking is "what does it do?" At present the blog post starts out with two paragraphs talking about the format of the blog post and the applications but not what the sensor actually measures.
- 00702 2y ago
  Good point -- I need to better explain what "bend localization" means on a more practical level pretty early on.
  - porphyra 2y ago
    Yeah. I guess in layman's terms it's a long squishy cable that knows where it's being bent.
  - oersted 2y ago
    > This means the sensor can tell you where you bent it, with a predefined (and coarse) resolution. > OptiGap’s application is mainly within the realm of soft robotics, which typically involves compliant (or ‘squishy’) systems, where the use of traditional sensors is often not practical. This explanation is already quite clear. If I understood correctly, by "predefined resolution" you mean that it detects which silicone sleeve was bent on a tube with a series of them, correct? Can you provide more concrete examples for how you envision it being used? The first application that comes to mind is sensing how fingers bend in a glove controller.
    - 00702 2y ago
      The finger bending example is certainly a classic for something like this but I think it truly shines in soft robot examples like flapping wing robots or swimming finned robot, where it's critical for sensors to be mechanically transparent so as to not impact the usually delicate dynamics. The "soft" robotic arm in my earlier paper is another good example https://ieeexplore.ieee.org/document/9763962 https://ieeexplore.ieee.org/document/9763962
  - 2y ago
szundi 2y ago
This guy knows how to find shit out, I like this!
blkhawk 2y ago
on first blush that sounds like a better version of the way the Nintendo power-glove detected finger bending.
moralestapia 2y ago
Paul, what an amazing project, this is what hacking is all about. Congratulations! Definitely try to explore the commercial side of your invention. It wouldn't hurt to talk to an IP lawyer, if you're still in Uni they usually have people there doing this and you can just go talk to them, free of charge (for you!). I'm generally against the idea of patents, mainly because of people who came to know to game the system and exploit it (patent trolls etc...) Your project is a real thing with real applications, you definitely deserve a share of whatever commercial benefit this could bring to the world, :D.
- 00702 2y ago
  My (former) school is actually already in the process of doing that! My dissertation committee thought it was novel enough that it needed some IP protection and encouraged me to pursue that.
  - moralestapia 2y ago
    Hey, that's great to hear. Best of luck with everything!
- kobalsky 2y ago
  Maybe I'm not understanding the blog post so bear with me. Isn't what he is described what a time domain reflectometer does? [1]. I mean that's what it's used to detect breaks or kinks in fiber optics cables. The same tech is used to detect problems in civil infrastructure with embbeded fiber optics. [1]: https://en.wikipedia.org/wiki/Optical_time-domain_reflectometer https://en.wikipedia.org/wiki/Optical_time-domain_reflectome...
  - 00702 2y ago
    Oh yeah cable companies have long been able to do that - I wasn't trying to compete with or replace that technology. My work was soft robotics-focused with simplicity in mind.
  - georgeburdell 2y ago
nimish 2y ago
hell yeah, this is super cool!
lttlrck 2y ago
This is really really cool, but why does it depend on TPU? Wouldn't it work with regular fiber optic? Or does it come down to economics?
- 00702 2y ago
  It doesn't! I heavily used TPU to drive home the point that it can work with almost any light-transmitting fiber. I used PMMA optical fiber for the more fine demos.
  - lttlrck 2y ago
    That's great! Well done.
- deleted 2y ago
  [deleted]
Projectiboga 2y ago
Hi, what kind of sensor? When posting to the public you should mention the subject of what can be sensed or scanned early on.
- bobberkarl 2y ago
  Have you been to Gabon recently?
Projectiboga 2y ago
Solid job, and congratulations on doing something useful and hitting the program with the goal to make something tangible and getting out promptly.
- 00702 2y ago
  Thanks -- I definitely relied heavily on my wife in order to maintain that pace.
ericdfoley 2y ago
Not quite the same thing, but this reminds me of DAS using fiber optic cable for various acoustic sensing tasks--basically as an alternative to geophones/hydrophones. There have been a number of papers using transoceanic fibers for various monitoring tasks. That is also used for various industrial applications, e.g. for strain sensing by Luna Innovations. I know that Schlumberger has various patents on fiber-optic sensing relating to towed streamers (e.g. for marine seismic acquisition.) But I haven't seen it used for soft robotics before.
- 00702 2y ago
  Yeah initially doing literature review was a bit daunting because of all this existing work, especially FBG-type sensors, but this idea is so fundamentally simple that its been mostly bypassed by the smarter minds
  - ericdfoley 2y ago
    Yeah, it makes a lot of sense to just create those gaps when you're specifically installing the fiber for sensing.
bythreads 2y ago
Congrats and if I may; your blog post should be how ph.d's are done - readable, understandable and devoid of techno mumbling.
- 00702 2y ago
  Thank you!
lifeisstillgood 2y ago
“I stuck a piece of plastic to my desk, it bent as I did it, I had time to investigate and skills to get a whole PhD out of that” And this dear worker drones, is why schedule destroys quality :-) Loving the write up. Clear and simple. Good luck with squishy robots. :-)
- 00702 2y ago
  Haha this made me laugh -- thanks!
raphman 2y ago
Very beautiful research and thorough documentation. I initially wanted to comment that this looks a lot like time-domain reflectometry on a conceptual level - but as Cindy Harnett seems to be your advisor, you probably know that already :)
- 00702 2y ago
  Indeed! How do you know her?
  - raphman 2y ago
    Oh, just from reading her papers. I have been playing with TDR a long time ago [1] and try to follow current developments. [1] https://dl.acm.org/doi/10.1145/2047196.2047264 https://dl.acm.org/doi/10.1145/2047196.2047264
- smoyer 2y ago
  I did some work on TDR analysis when analyzing CATV fraud detection but it turns out that we generally know where on the fiber plant each CPE is and collecting the DOCS IS timing data from those devices is essentially free.
teucris 2y ago
I wonder if by using a large nozzle, you could print out the entire sensor by laying out lengths of TPU with flexible joints at each air gap. It would depend on how well light traveled through the printed part though.
- 00702 2y ago
  3D printing does affect the light passing through significantly. There are a number of options for fabricating these but most of the successful ones involve cutting (can even use a laser cutter).
adversaryIdiot 2y ago
incredible work. good job!
- 00702 2y ago
  Thanks!
uoaei 2y ago
Similar concept but for temperature (linked on HN a while back): https://en.m.wikipedia.org/wiki/Distributed_temperature_sensing https://en.m.wikipedia.org/wiki/Distributed_temperature_sens...
poyu 2y ago
Great job, this is so cool!! Can't wait to see where this will be used in.
wholinator2 2y ago
As sometime about to start a PhD in theoretical physics, how did you do 3 years? I've been told a doctorate is 2 years of classes followed by 3 to 5 years of research. Did you already have a masters that you're doctorate college accepted to override class requirements?
- 00702 2y ago
  The short answer? Weekly meetings with my advisor! Long answer: I also had 2 years of classes but I started working on my research immediately, while taking classes. By the time I finished all my classes and became a candidate I had one paper already published and another one accepted, so I was able to get a 3rd paper out and defend by the end of the 3rd year.
  - atlas_hugged 2y ago
    Wow
  - fpgamlirfanboy 2y ago
    With all do respect, I think you're telling a half-truth here. Your LinkedIn profile shows you had two MS degrees before starting your PhD. Undoubtedly you got some of the requirements waived for the PhD course requirements. That means your total time post BS was 5 years. I did the same thing - 1.5 years (3 semesters) MS and then came back later (different school) to do a PhD and got half the course requirements waived. Finished the PhD in 4 years but total time post BS was a more humble 5.5.
wantsanagent 2y ago
Isn't total internal reflection affected by surface defects? Aka, scratch the filament rather than air-gap it.
- 00702 2y ago
  I was aiming for significant attenuation when bending, so scratching wouldn't be enough.
crote 2y ago
What an absolutely amazing idea, great work! Your sensor data seems to have quite large "dead zones" - those should be trivially fixable by reducing the inter-sensor distance, right? Would it be useful to sense the direction of the bend? I reckon this might be possible by dividing the tube like a Mercedes logo, and having three sets of the sensor in one outer tube. Is there a way to sense multiple bends? With the current setup that'd result in invalid readings as you're essentially OR-ing the value. Are there any good solutions for this?
- 00702 2y ago
  Great ideas! Even though I haven't implemented it fully it is possible to sense multiple bends because each bend will always have the same relative attenuation (across the strands) so it would just be a matter of matching on the relative deltas from one reading to another. The catch, though, is at that at some point no light will reach the end if every joint bends a lot. There are ways to mitigate that, but my comment is too long already!
  - gaudystead 2y ago
    No need to cut your comments short! You clearly have a passion, and passion is the best way to get other people interested! :D (also, nice work!)
  - liamwire 2y ago
    Could you increase power output through the fibre in response to a loss of signal, or one that falls below a given threshold? Using reasonable bounds to account for errors where attenuation isn’t the cause of no signal being received.
datadrivenangel 2y ago
Love the use of lower cost materials and nice jankier DIY SCIENCE. 00702, 4th photo caption appears to be missing the word gap. :)
- 00702 2y ago
  Fixed -- thanks! And yes exactly! I had access to basically any piece of equipment I could want (including a cleanroom that can create ICs) but then basically no one would be able to recreate what I would make.
maxnoe 2y ago
Very Cool! Since you mentioned the visualization part, let me comment on my pet pieve: The rainbow / jet color map should not be used for anything. It distorts your data and is not accessible for people with color vision deficiencies. If you want to know more, have a look here: https://matplotlib.org/stable/users/explain/colors/colormaps.html https://matplotlib.org/stable/users/explain/colors/colormaps... and this talk here: https://youtu.be/xAoljeRJ3lU https://youtu.be/xAoljeRJ3lU
npace12 2y ago
This is such a clever project, and a great write up! Thanks for sharing!
itissid 2y ago
I recall first haring and reading about soft robot application from veritasium: https://www.youtube.com/watch?v=058hRtaCWC0 https://www.youtube.com/watch?v=058hRtaCWC0 I think you must have heard of it? In the realm of rescuing or assisting people unreachable otherwise, could this bend and flex as much as those highly compliant robots?
bobberkarl 2y ago
This makes me think of so many possible industrial applications. I believe you are onto something great!
skoocda 2y ago
This is awesome! Presumably you can make this work with any interface that doesn't enforce the total internal reflectivity of a fiber optic cable, and therefore allows light to leak out. Instead of an air gap, have you tried experimenting with removing the cladding of the fiber optic cable, but keeping the core intact? Alteratively, could you use a short segment of colored cladding that allows certain wavelengths to leak out more than others? I think that would allow you to encode each bend point as a different color-- which might require a different (more expensive) rx sensor, but could be useful for certain applications.
- 00702 2y ago
  I did experiment with various ways of allowing light to escape but nothing came close to the properties of a total air gap. You can actually measure (relative) bend angle with it like a protractor since the attenuation is very linear! There is already existing work that uses colored segments for something similar but those techniques are hard to do outside a well equipped lab.
jjk166 2y ago
This is fantastic! One can easily imagine some minor refinements that would allow this to be mass producible with very high accuracy. And the applications are abundant. I imagine you could use space filling curves to make 2D or 3D sensors that could cost-efficiently give robots a sense of touch. Wrapped around something like a flexible tube you could make it directionally sensitive for proprioception. It's easily possible that other things that affect the air gaps like say temperature differences could be detected and localized as well.
- 00702 2y ago
  There are a lot of cool applications indeed! I was able to use it to do gait for a soft robot "leg", but I have to wait for the paper to be published later this year before going into too much detail.
mhb 2y ago
Thanks for sharing your work. Would you be able to compare your device to the fiber optic one used in the data glove (e.g., https://iopscience.iop.org/article/10.1088/1742-6596/2464/1/012022/pdf https://iopscience.iop.org/article/10.1088/1742-6596/2464/1/...).
- hypercube33 2y ago
  Isn't this sensor a lot or exactly like how the Powerglove works?
  - mhb 2y ago
    It's how Jaron Lanier's DataGlove worked. The Power Glove used cheaper flex sensors instead of fiber optics. https://en.wikipedia.org/wiki/Power_Glove https://en.wikipedia.org/wiki/Power_Glove
- 00702 2y ago
  There are a lot of similarities in the approach to the linked paper (which is a very cool concept) and I saw a lot of similar concepts in my lit review. At a high level, my sensor targets bend localization with simple fabrication techniques while the linked paper is doing more general camera-based gesture recognition. I have a more thorough comparison to existing work in my actual dissertation. Our lab has done a good bit of work around elastomers similar to the linked paper, such as multitouch pressure sensing (https://ieeexplore.ieee.org/abstract/document/9674750 https://ieeexplore.ieee.org/abstract/document/9674750). The authors of your linked paper can actually achieve what they've done with a single light source by using one of these! The zones are key (https://www.st.com/en/imaging-and-photonics-solutions/time-of-flight-sensors.html https://www.st.com/en/imaging-and-photonics-solutions/time-o...)
hervature 2y ago
> also be doable in 3 years I would like to add more color to this. 3 year PhD is very possible for a motivated individual at, what I'll call, the low end of R1 universities. That doesn't mean you cannot do good research (the OP is a counterexample) but that there is a fundamental difference between the program that the OP went to and top-tier universities. Think Harvard, Berkeley, Stanford, etc. It is normally pretty easy to distinguish these programs because they focus a lot on the course requirements and that the thesis counts as a course. From the OP's institution, you can see that the course load is at least 15 courses and I would not be surprised if some students do 20 [1]. These programs are more or less an advanced undergraduate with a real independent research project that spans multiple years. Conversely, top-tier universities typically operate under the "publish 3 things and you have satisfied the thesis requirements". This cannot be explicitly written and this is normally difficult to ascertain online. For example, Harvard has similar requirements [2] but you can still find it for some departments [3]. The Catch-22 with this is that someone who can publish 3 things in 3 years can publish 6 things (or more) in 5 years which will greatly increase their academic job prospects. Thus, at top-tier universities, even the best students stay for 5 years at a minimum to start working the job market. You need to be at Dantzig's level to finish at a top-tier in 3 years [4]. To summarize, if you want to finish a PhD in 3 years, look for course-heavy programs and don't expect to get hired into academia. Edit: I see the OP commented somewhere else that they published 3 papers. The OP is obviously a standout but I think most people have to be realistic that very few areas of research allow for publications in your first year PhD. For example, if you are doing research in LLMs, you are looking at a couple of years just to be brought up to speed. [1] - https://catalog.louisville.edu/graduate/programs-study/doctor-philosophy-electrical-engineering/#degreerequirementstext https://catalog.louisville.edu/graduate/programs-study/docto... [2] - https://seas.harvard.edu/office-academic-programs/graduate-policies-procedures-and-forms/phd-degree-requirements/phd-course-requirements https://seas.harvard.edu/office-academic-programs/graduate-p... [3] - https://www.math.harvard.edu/graduate/graduate-program-timeline/ https://www.math.harvard.edu/graduate/graduate-program-timel... [4] - https://en.wikipedia.org/wiki/George_Dantzig https://en.wikipedia.org/wiki/George_Dantzig
- kiwih 2y ago
  In my experience in computer engineering in the academic systems of the USA, New Zealand, and Australia, a very large proportion of students will write their first paper in their first year. It is field dependent, but when I was a postdoc at a top US R1, 100% of the students I interacted with had their first paper in their first year. These even included students working on LLMs :-) Also, top non-US universities often graduate their engineering students within 3-4 years of commencing, with 3-4 papers being a very common international expectation as well. If you want to finish a PhD in 3 years and are interested in academia, in addition to following the path the OP has laid out you may also look to good international universities and then get your next 3-4 papers as a postdoc.
yogurtboy 2y ago
This is cool as hell! I hope your PhD continues well, and that this invention serves you in the future. Do you put any lube on the interface between the silicone sleeve and optical cable? I imagine the bending action will cause displacement, and friction there could rub and/or cause the nominal position to shift around.
- 00702 2y ago
  Since the sleeve is a stretchy rubber as long as the inner diameter of it is a bit smaller than the outer diameter of the fiber it holds just fine. For more dynamic applications, though, a silicone adhesive, or even super glue for more permanent strands, helps!
  - yogurtboy 2y ago
    Oh cool, that kind of robustness is not what I was expecting. Very cool project!
riedel 2y ago
Have you explored fiber bragg grating. 10 years ago a student of mine semi successfully explored sensing the shape of firefighter hose using that technique. Seems to gain new traction again lately for optical shape sensing.
- 00702 2y ago
  I explored FBG sensors early on and they are very cool -- I was aiming for a less expensive and more robotics-oriented application. Something that can be seamlessly integrated into a design at a lower level without the complexity of FBG technology.
  - Prcmaker 2y ago
    I think you made the right choice. You've come up with a great sensor topology. FBGs are good, but there's so much to them that is just infuriating. I ended up late in my optics work spending most of my time finding ways to avoid them.
- Prcmaker 2y ago
  The perpetual issue with FBGs is cost, in my experience. For quality sensors, you can use cheap fibre with expensive detectors, or cheap detectors with expensive fibre. There's been a perpetual promise of the tech getting cheaper, but never seems to really drop significantly. We always struggled to find buyers once they saw the price tag.
  - araes 2y ago
    Reading about them, the main reason is because you have to manufacture regularly repeating slices of glass in a column over large distances whose thicknesses are usually on the order of the wavelength you're dealing with. So visible light requires some really small slices. I could probably make fiber bragg gratings in my ceramics studio, yet it would require buying some Very specific thickness glass sheet, setting up a bunch of hole punch jigs to get 1 m worth out of 1 um slices, figuring out some way to actually layer 1,000,000 slices correctly, and then not just melting them to slag accidentally.
knodi123 2y ago
This is interesting! Although the way you have to have log2 fibers, and a different encoding in each junction, presents quite a manufacturing challenge. Oh well, it's not a problem at the research/POC phase!
rcarmo 2y ago
This, sir, is sheer genius. I genuinely loved your approach and the way you wrote it down.
deleted 2y ago
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rationalfaith 2y ago
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doug_life 2y ago
Very cool to see how it all came together. Can you elaborate on why you chose to use a Kalman filter in your signal chain?
- 00702 2y ago
  I used it more for future-proofing in case I wanted to do sensor fusion or something like that later on -- currently it's just 1D filtering so I could have used anything. Also I'm just way more familiar with using Kalman filters so it was also a comfort thing!
sabujp 2y ago
is the idea to eventually make muscle fibers with lots of these stranded together?
- 00702 2y ago
  No I actually didn't have muscle fibers in mind -- there's quite a bit of ongoing research specifically in that area.
beachy 2y ago
I've been looking for a sensor that can accurately detect a golf club sweeping over the top of it (how close, how quickly, arc of swing). The idea being to create a golf launch monitor that doesn't require hitting a ball, so you can play sim golf inside. Think playing alongside the Masters as you watch on TV in the lounge - without smashing a golf ball through your TV. I am wondering if this could be suitable (or a number of them ganged together).
- cglace 2y ago
  My dad had something like this that hooked up to his computer in the 90's.
- risenshinetech 2y ago
  This already exists, its called the Optishot, and it doesn't work very well when compared to any modern radar or camera based sensors.
  - beachy 2y ago
    The opportunity is for something that can accurately measure your golf swing without a ball. Optishot is not that: > Since no ball data is recorded, the OptiShot 2 cannot accurately read how your club impacts the ball, so if you top the ball or even miss entirely, the OptiShot 2 will show that you made solid contact.
- speps 2y ago
  The risk of hitting the sensor and seeing it flying across the room into the TV seems too risky. As mentioned, a high FPS camera along with the Kinect tech to extract a skeleton would work so much better. You could make that in your garage using a PlayStation Eye and existing open source tech.
  - beachy 2y ago
    Yep, the sensor would need to be buried/encased in a mat. The club needs to make contact with the mat realistically (i.e. like taking a divot on a real grass surface). Most launch monitors today use high cameras or doppler radar. Neither of them really works without a ball. The difference between a good shot and a crap shot is a few millimetres. The technology can measure a bit of data from the club alone (club speed, angle of attack) but that's not enough to accurately extrapolate actual ball flight, since it's all about the quality of the contact of club on ball before ground.
Prcmaker 2y ago
Very cool! I used to build sensors similar in construction, but in all glass. Was a great challenge and a lot of fun. I like your spin on things. Well done completing the Phd!
- 00702 2y ago
  Thanks!
Glyptodon 2y ago
Could you get a similar effect by cutting dimples or notches in patterns (like a helical line of small conical holes) along the whole length in a sleeve instead of using separate pieces and infer overall curve shape? Or do the segments need to be cut completely through?
- 00702 2y ago
  Yes! The catch is any notch you make will weaken the material significantly and you'll have fatigue failures. That's the sneaky part of using a flexible sleeve, you don't introduce any undesired weaknesses.
robryk 2y ago
I don't understand what happens when the sensor is bent in more than one location. At the beginning you mention a ToF sensor, which made me think that you're looking at reflections from the bends and measuring distance to them, but this seems not to be the case. ISTM that if you bend the sensor in two places, you'll simply get the sum of the logattenuations from both. If we assume that the "strength" of the bend continuously changes attenuation, ISTM that you need as many strands as there are gap locations to be able to disambiguate between any two sets of bends. Am I misreading something or is this intended to operate in cases where we know only one bend is present?
- mariusor 2y ago
  In the paragraph "Visualization of the OptiGap Sensor System" looks like the gap pattern from multiple sensors is providing a unique signature that can be translated into the exact location on the length of the sensors. The mechanism for translating the wave forms to actual location seems to be based on a bayesian model, according to the "Realtime Machine Learning on a Microcontroller" paragraph.
Valerie_Wilson 2y ago
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downrightmike 2y ago
Isn't this just the same tech as the first Nintendo Power Glove had? https://www.youtube.com/watch?v=3g8JiGjRQNE https://www.youtube.com/watch?v=3g8JiGjRQNE They put light down a tube and then measured the light to trigger a key press. That's why bending your fingers/hand did anything. The revised the mechanism in the later generations.
- Doxin 2y ago
  I think at least one novelty here is that there's multiple "bend points" it can detect without needing a fiber for each bend point.
OisinMoran 2y ago
This is really neat—thanks for sharing! I love the general idea of making materials more "self-aware" or inspectable. It's very sci fi! The research I did before my current job touched ever so slightly on this too, so even cooler to see it on the front page. What we were doing was using complex valued neural nets to learn the transmission matrix of an optical fibre. It was previously done in the optics community by propagating Maxwell's equations, but we were able to beat the state of the art by a few orders of magnitude with a very simple architecture (the actual physics just boils down to a single complex matrix multiplication!). The connection to your work here is that if the fibre is bent you have to relearn a new matrix. It could even be possible to learn some parameterized characterisation of the fibre, so you could say do some input/output measurements and use that to model a spline of the fibre. We did not get that far though! Here are the papers if you're interested: CS-focussed one: https://papers.nips.cc/paper_files/paper/2018/hash/148510031349642de5ca0c544f31b2ef-Abstract.html https://papers.nips.cc/paper_files/paper/2018/hash/148510031... Physics-focussed one: https://www.nature.com/articles/s41467-019-10057-8 https://www.nature.com/articles/s41467-019-10057-8
- spiderxxxx 2y ago
  could it detect a twist instead of a bend?
  - OisinMoran 2y ago
    Interesting! I'm not sure to be honest. I imagine in practice it's hard to get a pure twist without any bending, and if the system can't detect any difference with a twist then the need to detect it is also nullified as it is effectively the same system.
  - wcrossbow 2y ago
    Maybe with polarization maintaining fiber? If at the gap they are aligned a teist will make them more perpendicular reducing mode coupling. Disclaimer: I know nothing about this field but have spent a lot of time in a dark lab surrounded by various types of optical fiber.
karambahh 2y ago
It seems to me that the refractive index plays a role: couldn't you increase resolution by replacing air by another medium every other cut? Say air, water, air, etc. My reasoning is that you'd increase the resolution without adding too much technical complexity. My maths is too rusty to evaluate how it would mess with the gray code though. Very nice idea
- 00702 2y ago
  I didn't include this in my article but I did some experiments early on (for a different idea) with air bubbles in oil inside a Teflon coated tube but that presented a lot of challenges (mainly the bubble breaking up) that made it not ideal for something like this. This can certainly be miniaturized with the right manufacturing techniques but I left that for the future.
tjtang2019 2y ago
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Lucas-YANG 2y ago
Great! Really enjoyed that, thanks
qtwhat 2y ago
very clever idea! if you know how OTDR works, location is known by high speed modulation and high speed sampling components, which means high costs, if you want to achieve higher resolution. Usually the laser pusle will be in the level of nano seconds. what's being introduced in the article is using multiple fibers with coded location info. therefore no need to have sophisticated OTDRA-like equipment to get the location info. not sure if my understanding is right, but good job: from a simple idea to sophisticated design, optimization and even commercialization.congrats.
markisus 2y ago
How does it work if there is more than one bend? Is it able to localize both bends? And what about the bend directionality? Anyway nice project. I could see it being used for a mesh to give robots a tactile skin covering.
eigenvalue 2y ago
Awesome work. Would be cool to make a really long one and tape it all along the links of an industrial robot arm and see if you can train a neural net to predict the location of the end effector (which you would already know precisely from the angles of the linkages) from the readings of your sensor.
jallmann 2y ago
What an excellent write-up. Very clearly explained, and the use of gifs and visuals to illustrate concepts was spot-on. I'm only a software engineer with a limited understanding of this field, but really enjoyed reading this and learned a lot. Well done and congrats on the PhD.
- 00702 2y ago
  Thank you!
grobbyy 2y ago
This has inspired about a hundred ideas in my head. Thank you! (They're all ways which on paper seem like I might be able to do things better, but if the sort where 95% don't pan out in practice. Everything from machine learning algorithms to identify shapes to fancy encoding with spectra of what reflects along the path to other ways to engineer changes in the path)

886 points by 00702 2y ago

Balvarez 2y ago

Wow that's super cool! Very nice work

00702 2y ago
Thanks!

JackFr 2y ago

Made me think of Navin R. Johnson’s invention of the Opti-Grab.

klysm 2y ago

> Thanks to an awesome advisor And there you have it! The difference between a miserable experience and a good one

00702 2y ago
Very much so!

porphyra 2y ago

That's super cool and I hope you don't mind a little bit of unsolicited feedback but the first question everyone's asking is "what does it do?" At present the blog post starts out with two paragraphs talking about the format of the blog post and the applications but not what the sensor actually measures.

00702 2y ago
Good point -- I need to better explain what "bend localization" means on a more practical level pretty early on.
- porphyra 2y ago
  Yeah. I guess in layman's terms it's a long squishy cable that knows where it's being bent.
- oersted 2y ago
  > This means the sensor can tell you where you bent it, with a predefined (and coarse) resolution. > OptiGap’s application is mainly within the realm of soft robotics, which typically involves compliant (or ‘squishy’) systems, where the use of traditional sensors is often not practical. This explanation is already quite clear. If I understood correctly, by "predefined resolution" you mean that it detects which silicone sleeve was bent on a tube with a series of them, correct? Can you provide more concrete examples for how you envision it being used? The first application that comes to mind is sensing how fingers bend in a glove controller.
  - 00702 2y ago
    The finger bending example is certainly a classic for something like this but I think it truly shines in soft robot examples like flapping wing robots or swimming finned robot, where it's critical for sensors to be mechanically transparent so as to not impact the usually delicate dynamics. The "soft" robotic arm in my earlier paper is another good example https://ieeexplore.ieee.org/document/9763962 https://ieeexplore.ieee.org/document/9763962
- 2y ago

szundi 2y ago

This guy knows how to find shit out, I like this!

blkhawk 2y ago

on first blush that sounds like a better version of the way the Nintendo power-glove detected finger bending.

moralestapia 2y ago

Paul, what an amazing project, this is what hacking is all about. Congratulations! Definitely try to explore the commercial side of your invention. It wouldn't hurt to talk to an IP lawyer, if you're still in Uni they usually have people there doing this and you can just go talk to them, free of charge (for you!). I'm generally against the idea of patents, mainly because of people who came to know to game the system and exploit it (patent trolls etc...) Your project is a real thing with real applications, you definitely deserve a share of whatever commercial benefit this could bring to the world, :D.

00702 2y ago
My (former) school is actually already in the process of doing that! My dissertation committee thought it was novel enough that it needed some IP protection and encouraged me to pursue that.
- moralestapia 2y ago
  Hey, that's great to hear. Best of luck with everything!
kobalsky 2y ago
Maybe I'm not understanding the blog post so bear with me. Isn't what he is described what a time domain reflectometer does? [1]. I mean that's what it's used to detect breaks or kinks in fiber optics cables. The same tech is used to detect problems in civil infrastructure with embbeded fiber optics. [1]: https://en.wikipedia.org/wiki/Optical_time-domain_reflectometer https://en.wikipedia.org/wiki/Optical_time-domain_reflectome...
- 00702 2y ago
  Oh yeah cable companies have long been able to do that - I wasn't trying to compete with or replace that technology. My work was soft robotics-focused with simplicity in mind.
- georgeburdell 2y ago

nimish 2y ago

hell yeah, this is super cool!

lttlrck 2y ago

This is really really cool, but why does it depend on TPU? Wouldn't it work with regular fiber optic? Or does it come down to economics?

00702 2y ago
It doesn't! I heavily used TPU to drive home the point that it can work with almost any light-transmitting fiber. I used PMMA optical fiber for the more fine demos.
- lttlrck 2y ago
  That's great! Well done.
deleted 2y ago
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Projectiboga 2y ago

Hi, what kind of sensor? When posting to the public you should mention the subject of what can be sensed or scanned early on.

bobberkarl 2y ago
Have you been to Gabon recently?

Projectiboga 2y ago

Solid job, and congratulations on doing something useful and hitting the program with the goal to make something tangible and getting out promptly.

00702 2y ago
Thanks -- I definitely relied heavily on my wife in order to maintain that pace.

ericdfoley 2y ago

Not quite the same thing, but this reminds me of DAS using fiber optic cable for various acoustic sensing tasks--basically as an alternative to geophones/hydrophones. There have been a number of papers using transoceanic fibers for various monitoring tasks. That is also used for various industrial applications, e.g. for strain sensing by Luna Innovations. I know that Schlumberger has various patents on fiber-optic sensing relating to towed streamers (e.g. for marine seismic acquisition.) But I haven't seen it used for soft robotics before.

00702 2y ago
Yeah initially doing literature review was a bit daunting because of all this existing work, especially FBG-type sensors, but this idea is so fundamentally simple that its been mostly bypassed by the smarter minds
- ericdfoley 2y ago
  Yeah, it makes a lot of sense to just create those gaps when you're specifically installing the fiber for sensing.

bythreads 2y ago

Congrats and if I may; your blog post should be how ph.d's are done - readable, understandable and devoid of techno mumbling.

00702 2y ago
Thank you!

lifeisstillgood 2y ago

“I stuck a piece of plastic to my desk, it bent as I did it, I had time to investigate and skills to get a whole PhD out of that” And this dear worker drones, is why schedule destroys quality :-) Loving the write up. Clear and simple. Good luck with squishy robots. :-)

00702 2y ago
Haha this made me laugh -- thanks!

raphman 2y ago

Very beautiful research and thorough documentation. I initially wanted to comment that this looks a lot like time-domain reflectometry on a conceptual level - but as Cindy Harnett seems to be your advisor, you probably know that already :)

00702 2y ago
Indeed! How do you know her?
- raphman 2y ago
  Oh, just from reading her papers. I have been playing with TDR a long time ago [1] and try to follow current developments. [1] https://dl.acm.org/doi/10.1145/2047196.2047264 https://dl.acm.org/doi/10.1145/2047196.2047264
smoyer 2y ago
I did some work on TDR analysis when analyzing CATV fraud detection but it turns out that we generally know where on the fiber plant each CPE is and collecting the DOCS IS timing data from those devices is essentially free.

teucris 2y ago

I wonder if by using a large nozzle, you could print out the entire sensor by laying out lengths of TPU with flexible joints at each air gap. It would depend on how well light traveled through the printed part though.

00702 2y ago
3D printing does affect the light passing through significantly. There are a number of options for fabricating these but most of the successful ones involve cutting (can even use a laser cutter).

adversaryIdiot 2y ago

incredible work. good job!

00702 2y ago
Thanks!

uoaei 2y ago

Similar concept but for temperature (linked on HN a while back): https://en.m.wikipedia.org/wiki/Distributed_temperature_sensing https://en.m.wikipedia.org/wiki/Distributed_temperature_sens...

poyu 2y ago

Great job, this is so cool!! Can't wait to see where this will be used in.

wholinator2 2y ago

As sometime about to start a PhD in theoretical physics, how did you do 3 years? I've been told a doctorate is 2 years of classes followed by 3 to 5 years of research. Did you already have a masters that you're doctorate college accepted to override class requirements?

00702 2y ago
The short answer? Weekly meetings with my advisor! Long answer: I also had 2 years of classes but I started working on my research immediately, while taking classes. By the time I finished all my classes and became a candidate I had one paper already published and another one accepted, so I was able to get a 3rd paper out and defend by the end of the 3rd year.
- atlas_hugged 2y ago
  Wow
- fpgamlirfanboy 2y ago
  With all do respect, I think you're telling a half-truth here. Your LinkedIn profile shows you had two MS degrees before starting your PhD. Undoubtedly you got some of the requirements waived for the PhD course requirements. That means your total time post BS was 5 years. I did the same thing - 1.5 years (3 semesters) MS and then came back later (different school) to do a PhD and got half the course requirements waived. Finished the PhD in 4 years but total time post BS was a more humble 5.5.

wantsanagent 2y ago

Isn't total internal reflection affected by surface defects? Aka, scratch the filament rather than air-gap it.

00702 2y ago
I was aiming for significant attenuation when bending, so scratching wouldn't be enough.

crote 2y ago

What an absolutely amazing idea, great work! Your sensor data seems to have quite large "dead zones" - those should be trivially fixable by reducing the inter-sensor distance, right? Would it be useful to sense the direction of the bend? I reckon this might be possible by dividing the tube like a Mercedes logo, and having three sets of the sensor in one outer tube. Is there a way to sense multiple bends? With the current setup that'd result in invalid readings as you're essentially OR-ing the value. Are there any good solutions for this?

00702 2y ago
Great ideas! Even though I haven't implemented it fully it is possible to sense multiple bends because each bend will always have the same relative attenuation (across the strands) so it would just be a matter of matching on the relative deltas from one reading to another. The catch, though, is at that at some point no light will reach the end if every joint bends a lot. There are ways to mitigate that, but my comment is too long already!
- gaudystead 2y ago
  No need to cut your comments short! You clearly have a passion, and passion is the best way to get other people interested! :D (also, nice work!)
- liamwire 2y ago
  Could you increase power output through the fibre in response to a loss of signal, or one that falls below a given threshold? Using reasonable bounds to account for errors where attenuation isn’t the cause of no signal being received.

datadrivenangel 2y ago

Love the use of lower cost materials and nice jankier DIY SCIENCE. 00702, 4th photo caption appears to be missing the word gap. :)

00702 2y ago
Fixed -- thanks! And yes exactly! I had access to basically any piece of equipment I could want (including a cleanroom that can create ICs) but then basically no one would be able to recreate what I would make.

maxnoe 2y ago

Very Cool! Since you mentioned the visualization part, let me comment on my pet pieve: The rainbow / jet color map should not be used for anything. It distorts your data and is not accessible for people with color vision deficiencies. If you want to know more, have a look here: https://matplotlib.org/stable/users/explain/colors/colormaps.html https://matplotlib.org/stable/users/explain/colors/colormaps... and this talk here: https://youtu.be/xAoljeRJ3lU https://youtu.be/xAoljeRJ3lU

npace12 2y ago

This is such a clever project, and a great write up! Thanks for sharing!

itissid 2y ago

I recall first haring and reading about soft robot application from veritasium: https://www.youtube.com/watch?v=058hRtaCWC0 https://www.youtube.com/watch?v=058hRtaCWC0 I think you must have heard of it? In the realm of rescuing or assisting people unreachable otherwise, could this bend and flex as much as those highly compliant robots?

bobberkarl 2y ago

This makes me think of so many possible industrial applications. I believe you are onto something great!

skoocda 2y ago

This is awesome! Presumably you can make this work with any interface that doesn't enforce the total internal reflectivity of a fiber optic cable, and therefore allows light to leak out. Instead of an air gap, have you tried experimenting with removing the cladding of the fiber optic cable, but keeping the core intact? Alteratively, could you use a short segment of colored cladding that allows certain wavelengths to leak out more than others? I think that would allow you to encode each bend point as a different color-- which might require a different (more expensive) rx sensor, but could be useful for certain applications.

00702 2y ago
I did experiment with various ways of allowing light to escape but nothing came close to the properties of a total air gap. You can actually measure (relative) bend angle with it like a protractor since the attenuation is very linear! There is already existing work that uses colored segments for something similar but those techniques are hard to do outside a well equipped lab.

jjk166 2y ago

This is fantastic! One can easily imagine some minor refinements that would allow this to be mass producible with very high accuracy. And the applications are abundant. I imagine you could use space filling curves to make 2D or 3D sensors that could cost-efficiently give robots a sense of touch. Wrapped around something like a flexible tube you could make it directionally sensitive for proprioception. It's easily possible that other things that affect the air gaps like say temperature differences could be detected and localized as well.

00702 2y ago
There are a lot of cool applications indeed! I was able to use it to do gait for a soft robot "leg", but I have to wait for the paper to be published later this year before going into too much detail.

mhb 2y ago

Thanks for sharing your work. Would you be able to compare your device to the fiber optic one used in the data glove (e.g., https://iopscience.iop.org/article/10.1088/1742-6596/2464/1/012022/pdf https://iopscience.iop.org/article/10.1088/1742-6596/2464/1/...).

hypercube33 2y ago
Isn't this sensor a lot or exactly like how the Powerglove works?
- mhb 2y ago
  It's how Jaron Lanier's DataGlove worked. The Power Glove used cheaper flex sensors instead of fiber optics. https://en.wikipedia.org/wiki/Power_Glove https://en.wikipedia.org/wiki/Power_Glove
00702 2y ago
There are a lot of similarities in the approach to the linked paper (which is a very cool concept) and I saw a lot of similar concepts in my lit review. At a high level, my sensor targets bend localization with simple fabrication techniques while the linked paper is doing more general camera-based gesture recognition. I have a more thorough comparison to existing work in my actual dissertation. Our lab has done a good bit of work around elastomers similar to the linked paper, such as multitouch pressure sensing (https://ieeexplore.ieee.org/abstract/document/9674750 https://ieeexplore.ieee.org/abstract/document/9674750). The authors of your linked paper can actually achieve what they've done with a single light source by using one of these! The zones are key (https://www.st.com/en/imaging-and-photonics-solutions/time-of-flight-sensors.html https://www.st.com/en/imaging-and-photonics-solutions/time-o...)

hervature 2y ago

> also be doable in 3 years I would like to add more color to this. 3 year PhD is very possible for a motivated individual at, what I'll call, the low end of R1 universities. That doesn't mean you cannot do good research (the OP is a counterexample) but that there is a fundamental difference between the program that the OP went to and top-tier universities. Think Harvard, Berkeley, Stanford, etc. It is normally pretty easy to distinguish these programs because they focus a lot on the course requirements and that the thesis counts as a course. From the OP's institution, you can see that the course load is at least 15 courses and I would not be surprised if some students do 20 [1]. These programs are more or less an advanced undergraduate with a real independent research project that spans multiple years. Conversely, top-tier universities typically operate under the "publish 3 things and you have satisfied the thesis requirements". This cannot be explicitly written and this is normally difficult to ascertain online. For example, Harvard has similar requirements [2] but you can still find it for some departments [3]. The Catch-22 with this is that someone who can publish 3 things in 3 years can publish 6 things (or more) in 5 years which will greatly increase their academic job prospects. Thus, at top-tier universities, even the best students stay for 5 years at a minimum to start working the job market. You need to be at Dantzig's level to finish at a top-tier in 3 years [4]. To summarize, if you want to finish a PhD in 3 years, look for course-heavy programs and don't expect to get hired into academia. Edit: I see the OP commented somewhere else that they published 3 papers. The OP is obviously a standout but I think most people have to be realistic that very few areas of research allow for publications in your first year PhD. For example, if you are doing research in LLMs, you are looking at a couple of years just to be brought up to speed. [1] - https://catalog.louisville.edu/graduate/programs-study/doctor-philosophy-electrical-engineering/#degreerequirementstext https://catalog.louisville.edu/graduate/programs-study/docto... [2] - https://seas.harvard.edu/office-academic-programs/graduate-policies-procedures-and-forms/phd-degree-requirements/phd-course-requirements https://seas.harvard.edu/office-academic-programs/graduate-p... [3] - https://www.math.harvard.edu/graduate/graduate-program-timeline/ https://www.math.harvard.edu/graduate/graduate-program-timel... [4] - https://en.wikipedia.org/wiki/George_Dantzig https://en.wikipedia.org/wiki/George_Dantzig

kiwih 2y ago
In my experience in computer engineering in the academic systems of the USA, New Zealand, and Australia, a very large proportion of students will write their first paper in their first year. It is field dependent, but when I was a postdoc at a top US R1, 100% of the students I interacted with had their first paper in their first year. These even included students working on LLMs :-) Also, top non-US universities often graduate their engineering students within 3-4 years of commencing, with 3-4 papers being a very common international expectation as well. If you want to finish a PhD in 3 years and are interested in academia, in addition to following the path the OP has laid out you may also look to good international universities and then get your next 3-4 papers as a postdoc.

yogurtboy 2y ago

This is cool as hell! I hope your PhD continues well, and that this invention serves you in the future. Do you put any lube on the interface between the silicone sleeve and optical cable? I imagine the bending action will cause displacement, and friction there could rub and/or cause the nominal position to shift around.

00702 2y ago
Since the sleeve is a stretchy rubber as long as the inner diameter of it is a bit smaller than the outer diameter of the fiber it holds just fine. For more dynamic applications, though, a silicone adhesive, or even super glue for more permanent strands, helps!
- yogurtboy 2y ago
  Oh cool, that kind of robustness is not what I was expecting. Very cool project!

riedel 2y ago

Have you explored fiber bragg grating. 10 years ago a student of mine semi successfully explored sensing the shape of firefighter hose using that technique. Seems to gain new traction again lately for optical shape sensing.

00702 2y ago
I explored FBG sensors early on and they are very cool -- I was aiming for a less expensive and more robotics-oriented application. Something that can be seamlessly integrated into a design at a lower level without the complexity of FBG technology.
- Prcmaker 2y ago
  I think you made the right choice. You've come up with a great sensor topology. FBGs are good, but there's so much to them that is just infuriating. I ended up late in my optics work spending most of my time finding ways to avoid them.
Prcmaker 2y ago
The perpetual issue with FBGs is cost, in my experience. For quality sensors, you can use cheap fibre with expensive detectors, or cheap detectors with expensive fibre. There's been a perpetual promise of the tech getting cheaper, but never seems to really drop significantly. We always struggled to find buyers once they saw the price tag.
- araes 2y ago
  Reading about them, the main reason is because you have to manufacture regularly repeating slices of glass in a column over large distances whose thicknesses are usually on the order of the wavelength you're dealing with. So visible light requires some really small slices. I could probably make fiber bragg gratings in my ceramics studio, yet it would require buying some Very specific thickness glass sheet, setting up a bunch of hole punch jigs to get 1 m worth out of 1 um slices, figuring out some way to actually layer 1,000,000 slices correctly, and then not just melting them to slag accidentally.

knodi123 2y ago

This is interesting! Although the way you have to have log2 fibers, and a different encoding in each junction, presents quite a manufacturing challenge. Oh well, it's not a problem at the research/POC phase!

rcarmo 2y ago

This, sir, is sheer genius. I genuinely loved your approach and the way you wrote it down.

deleted 2y ago

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rationalfaith 2y ago

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doug_life 2y ago

Very cool to see how it all came together. Can you elaborate on why you chose to use a Kalman filter in your signal chain?

00702 2y ago
I used it more for future-proofing in case I wanted to do sensor fusion or something like that later on -- currently it's just 1D filtering so I could have used anything. Also I'm just way more familiar with using Kalman filters so it was also a comfort thing!

sabujp 2y ago

is the idea to eventually make muscle fibers with lots of these stranded together?

00702 2y ago
No I actually didn't have muscle fibers in mind -- there's quite a bit of ongoing research specifically in that area.

beachy 2y ago

I've been looking for a sensor that can accurately detect a golf club sweeping over the top of it (how close, how quickly, arc of swing). The idea being to create a golf launch monitor that doesn't require hitting a ball, so you can play sim golf inside. Think playing alongside the Masters as you watch on TV in the lounge - without smashing a golf ball through your TV. I am wondering if this could be suitable (or a number of them ganged together).

cglace 2y ago
My dad had something like this that hooked up to his computer in the 90's.
risenshinetech 2y ago
This already exists, its called the Optishot, and it doesn't work very well when compared to any modern radar or camera based sensors.
- beachy 2y ago
  The opportunity is for something that can accurately measure your golf swing without a ball. Optishot is not that: > Since no ball data is recorded, the OptiShot 2 cannot accurately read how your club impacts the ball, so if you top the ball or even miss entirely, the OptiShot 2 will show that you made solid contact.
speps 2y ago
The risk of hitting the sensor and seeing it flying across the room into the TV seems too risky. As mentioned, a high FPS camera along with the Kinect tech to extract a skeleton would work so much better. You could make that in your garage using a PlayStation Eye and existing open source tech.
- beachy 2y ago
  Yep, the sensor would need to be buried/encased in a mat. The club needs to make contact with the mat realistically (i.e. like taking a divot on a real grass surface). Most launch monitors today use high cameras or doppler radar. Neither of them really works without a ball. The difference between a good shot and a crap shot is a few millimetres. The technology can measure a bit of data from the club alone (club speed, angle of attack) but that's not enough to accurately extrapolate actual ball flight, since it's all about the quality of the contact of club on ball before ground.

Prcmaker 2y ago

Very cool! I used to build sensors similar in construction, but in all glass. Was a great challenge and a lot of fun. I like your spin on things. Well done completing the Phd!

00702 2y ago
Thanks!

Glyptodon 2y ago

Could you get a similar effect by cutting dimples or notches in patterns (like a helical line of small conical holes) along the whole length in a sleeve instead of using separate pieces and infer overall curve shape? Or do the segments need to be cut completely through?

00702 2y ago
Yes! The catch is any notch you make will weaken the material significantly and you'll have fatigue failures. That's the sneaky part of using a flexible sleeve, you don't introduce any undesired weaknesses.

robryk 2y ago

I don't understand what happens when the sensor is bent in more than one location. At the beginning you mention a ToF sensor, which made me think that you're looking at reflections from the bends and measuring distance to them, but this seems not to be the case. ISTM that if you bend the sensor in two places, you'll simply get the sum of the logattenuations from both. If we assume that the "strength" of the bend continuously changes attenuation, ISTM that you need as many strands as there are gap locations to be able to disambiguate between any two sets of bends. Am I misreading something or is this intended to operate in cases where we know only one bend is present?

mariusor 2y ago
In the paragraph "Visualization of the OptiGap Sensor System" looks like the gap pattern from multiple sensors is providing a unique signature that can be translated into the exact location on the length of the sensors. The mechanism for translating the wave forms to actual location seems to be based on a bayesian model, according to the "Realtime Machine Learning on a Microcontroller" paragraph.

Valerie_Wilson 2y ago

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downrightmike 2y ago

Isn't this just the same tech as the first Nintendo Power Glove had? https://www.youtube.com/watch?v=3g8JiGjRQNE https://www.youtube.com/watch?v=3g8JiGjRQNE They put light down a tube and then measured the light to trigger a key press. That's why bending your fingers/hand did anything. The revised the mechanism in the later generations.

Doxin 2y ago
I think at least one novelty here is that there's multiple "bend points" it can detect without needing a fiber for each bend point.

OisinMoran 2y ago

This is really neat—thanks for sharing! I love the general idea of making materials more "self-aware" or inspectable. It's very sci fi! The research I did before my current job touched ever so slightly on this too, so even cooler to see it on the front page. What we were doing was using complex valued neural nets to learn the transmission matrix of an optical fibre. It was previously done in the optics community by propagating Maxwell's equations, but we were able to beat the state of the art by a few orders of magnitude with a very simple architecture (the actual physics just boils down to a single complex matrix multiplication!). The connection to your work here is that if the fibre is bent you have to relearn a new matrix. It could even be possible to learn some parameterized characterisation of the fibre, so you could say do some input/output measurements and use that to model a spline of the fibre. We did not get that far though! Here are the papers if you're interested: CS-focussed one: https://papers.nips.cc/paper_files/paper/2018/hash/148510031349642de5ca0c544f31b2ef-Abstract.html https://papers.nips.cc/paper_files/paper/2018/hash/148510031... Physics-focussed one: https://www.nature.com/articles/s41467-019-10057-8 https://www.nature.com/articles/s41467-019-10057-8

spiderxxxx 2y ago
could it detect a twist instead of a bend?
- OisinMoran 2y ago
  Interesting! I'm not sure to be honest. I imagine in practice it's hard to get a pure twist without any bending, and if the system can't detect any difference with a twist then the need to detect it is also nullified as it is effectively the same system.
- wcrossbow 2y ago
  Maybe with polarization maintaining fiber? If at the gap they are aligned a teist will make them more perpendicular reducing mode coupling. Disclaimer: I know nothing about this field but have spent a lot of time in a dark lab surrounded by various types of optical fiber.

karambahh 2y ago

It seems to me that the refractive index plays a role: couldn't you increase resolution by replacing air by another medium every other cut? Say air, water, air, etc. My reasoning is that you'd increase the resolution without adding too much technical complexity. My maths is too rusty to evaluate how it would mess with the gray code though. Very nice idea

00702 2y ago
I didn't include this in my article but I did some experiments early on (for a different idea) with air bubbles in oil inside a Teflon coated tube but that presented a lot of challenges (mainly the bubble breaking up) that made it not ideal for something like this. This can certainly be miniaturized with the right manufacturing techniques but I left that for the future.

tjtang2019 2y ago

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Lucas-YANG 2y ago

Great! Really enjoyed that, thanks

qtwhat 2y ago

very clever idea! if you know how OTDR works, location is known by high speed modulation and high speed sampling components, which means high costs, if you want to achieve higher resolution. Usually the laser pusle will be in the level of nano seconds. what's being introduced in the article is using multiple fibers with coded location info. therefore no need to have sophisticated OTDRA-like equipment to get the location info. not sure if my understanding is right, but good job: from a simple idea to sophisticated design, optimization and even commercialization.congrats.

markisus 2y ago

How does it work if there is more than one bend? Is it able to localize both bends? And what about the bend directionality? Anyway nice project. I could see it being used for a mesh to give robots a tactile skin covering.

eigenvalue 2y ago

Awesome work. Would be cool to make a really long one and tape it all along the links of an industrial robot arm and see if you can train a neural net to predict the location of the end effector (which you would already know precisely from the angles of the linkages) from the readings of your sensor.

jallmann 2y ago

What an excellent write-up. Very clearly explained, and the use of gifs and visuals to illustrate concepts was spot-on. I'm only a software engineer with a limited understanding of this field, but really enjoyed reading this and learned a lot. Well done and congrats on the PhD.

00702 2y ago
Thank you!

grobbyy 2y ago

This has inspired about a hundred ideas in my head. Thank you! (They're all ways which on paper seem like I might be able to do things better, but if the sort where 95% don't pan out in practice. Everything from machine learning algorithms to identify shapes to fancy encoding with spectra of what reflects along the path to other ways to engineer changes in the path)