Proprioceptive string microscopy

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D-503
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Proprioceptive string microscopy

Postby D-503 » Wed Nov 14, 2018 7:33 am UTC

Proprioception is generally thought of as an organism's ability to sence the relative positions of its body parts. I am interested in the applicability of this type of internal displacement sensing to scientific measurement. To do this I propose the proprioceptive string, a device that modulates EM signals passed along it based on how it is bent such that the signals can be used to determine its shape. Would it be possible to construct such a string capable of mapping microscopic surfaces by being draped across them? Are there theoretical limits to the resolution it could achieve? Would it be possible to go beyond the diffraction limit?

Nicias
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Re: Proprioceptive string microscopy

Postby Nicias » Wed Nov 14, 2018 3:09 pm UTC


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Eebster the Great
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Re: Proprioceptive string microscopy

Postby Eebster the Great » Thu Nov 15, 2018 9:46 am UTC

Detecting the roughness of a surface by touching it isn't proprioception, that's touch. Proprioception is a sense that uses nerves in muscles, tendons, and joints to determine the relative orientation of your head, body, and all your limbs and digits. Pretty much by definition, you can't use proprioception to figure out anything about the outside world, just your own body. So it doesn't sound like a very useful sense to model a microscope off of.

SuicideJunkie
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Re: Proprioceptive string microscopy

Postby SuicideJunkie » Thu Nov 15, 2018 2:51 pm UTC

It sounds more like figuring out the shape of a room by walking around and wondering why your elbows are bent every now and then.

Did anybody else do those experiments where you stand in a doorway and push your arms against the sides for a minute, then walk around with your arms floating where they shouldn't be? That seems like a case where you've thrown off your calibration of effort vs expected results, and your proprioceptive calculations are visibly wrong.

D-503
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Re: Proprioceptive string microscopy

Postby D-503 » Thu Nov 15, 2018 3:17 pm UTC

Eebster the Great wrote:Detecting the roughness of a surface by touching it isn't proprioception, that's touch. Proprioception is a sense that uses nerves in muscles, tendons, and joints to determine the relative orientation of your head, body, and all your limbs and digits. Pretty much by definition, you can't use proprioception to figure out anything about the outside world, just your own body. So it doesn't sound like a very useful sense to model a microscope off of.


A body analogy would be laying across a mattress and finding a lump in it. You can build up a picture of the outside world based on the internal displacement of your body when pressed against it, although, the human body isn't very good for this purpose since it didn't have very many joints.

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Re: Proprioceptive string microscopy

Postby Soupspoon » Thu Nov 15, 2018 7:10 pm UTC

My original thought when I first found this thread (NPI!) unanswered was that maybe an optical fibre thread could, bowed by the pressure of the changing surface topography it was forced at an angle against, produce a readable change of bounced-through-and-back light according to how it is disturbed. Maybe needs to be worked via some combination of Rayleigh Scattering and Raman Spectrometry (may be difficult to map a 'reading' from the detector directly, or even simple calibration, but by comparing new signatures detected with signatures recorded for known surface 'feels' you could probably correlate an equivalence).

As a robot's "touch" sensor* maybe it could be developed into a large area 'skin' sensor, very much like a cat's whiskers or even just my not-overly-hairy arms, where more direct but increasingly awkward microdevices cannot so easily be installed with enough coverage. Though whether it'd be my ideas of fibreoptics (or velcro) or something else… I can't rightfully say I know.

* - I've seen a hairy "velcro hook" pad hooked up with a sensitive microphone directly behind the finger used as a primitive but resilient(ish) pressure-sensor to estimate how much force is being used and/or detect the start of slippage out of the grip, according to the scratchy noise transmitted back through the gripper

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Re: Proprioceptive string microscopy

Postby Eebster the Great » Thu Nov 15, 2018 7:47 pm UTC

D-503 wrote:A body analogy would be laying across a mattress and finding a lump in it. You can build up a picture of the outside world based on the internal displacement of your body when pressed against it, although, the human body isn't very good for this purpose since it didn't have very many joints.


OK, but you can't find a lump in a mattress by lying on it using proprioception, only using pressure. But SuicideJunkie is right, by dead reckoning, you could in principle use proprioception alone to determine the shape and size of a room and your current position in it. The reason is that when your arm pushes against a wall, it will bend, and you will notice it bend even if for some reason you cannot feel the wall itself.

D-503
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Re: Proprioceptive string microscopy

Postby D-503 » Sat Nov 17, 2018 6:38 pm UTC

Soupspoon wrote:My original thought when I first found this thread (NPI!) unanswered was that maybe an optical fibre thread could, bowed by the pressure of the changing surface topography it was forced at an angle against, produce a readable change of bounced-through-and-back light according to how it is disturbed. Maybe needs to be worked via some combination of Rayleigh Scattering and Raman Spectrometry (may be difficult to map a 'reading' from the detector directly, or even simple calibration, but by comparing new signatures detected with signatures recorded for known surface 'feels' you could probably correlate an equivalence).

Using modulations to a light signal seems like the optimal design, but I'm not sure if it's possible to do it in such a way that many bends in different sections of the fiber could be detected. Maybe each section could effect a different wavelength of light when it is bent?

A digital circuit approach might be more feasible with current fabrication technologies, although it would probably require the string to be at least a micrometer wide and have limited flexibility. It might be possible to print a ”chip" with cuts in it that would let it unfold into a string. Transistors could be positioned along the string so that 2^(number of wires running along it) points could be separately queried to determine if they are bent. An etching process similar to the one used for embedded gyroscopes (planks that stick out over holes in the silicon) could be used to create bend sensors at each point.

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Re: Proprioceptive string microscopy

Postby Soupspoon » Sat Nov 17, 2018 7:43 pm UTC

I was thinking along the lines of either a simple elastic bowing* of a (semi-stiff) strand length, or else a sort of Mean Free Path signature (albeit constrained within the current kinks) as photons navigate whatever compound kinks currently kink in the kinkily kinked strand.

But, as loose a concept as it was, it didn't seem right to be first-responder to the thread with such ill-formed ideas. Now though, it seems as good a hogswash as anybody's. ;)



* may be asymmetric, but still a curve without inflection within the first one or more orders.

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Eebster the Great
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Re: Proprioceptive string microscopy

Postby Eebster the Great » Sun Nov 18, 2018 5:43 am UTC

What if you just had two electrified wire meshes separated by a short gap of air. When the outer mesh presses against a surface, the two meshes contact and complete a circuit. It's very imprecise, but it is also very simple. As with proprioception, this can only detect the amount of deflection (in this case, as a binary "deflected" vs. "not deflected"), not the magnitude of the pressure.

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Re: Proprioceptive string microscopy

Postby SuicideJunkie » Mon Nov 19, 2018 5:48 pm UTC

That sounds like a pressure sensor, but if it was kept to joint internals and measured if the bone angle was small or large it would be fair.

How about a "micro GPS" mesh of arbitrary receivers along the limbs, which pick up pings from the main body. The timing determines how far apart they are and thus determines the position and orientation of all the hardware.


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