[HN Gopher] Making Electronic Calipers
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Making Electronic Calipers
Author : surprisetalk
Score : 65 points
Date : 2024-11-08 15:29 UTC (7 hours ago)
(HTM) web link (kevinlynagh.com)
(TXT) w3m dump (kevinlynagh.com)
| satiric wrote:
| I don't actually see an accuracy number, only the claim of
| "millimeter precision", which is actually pretty bad for
| calipers. Looks like a fun project though. Basically a linear
| resolver sensor I guess. From how much effort the author has put
| into the project I'd estimate the accuracy is much better than
| +/- 0.5mm.
| Arcanum-XIII wrote:
| Which is quite low. My manual caliper is precise to the 1/10 of
| a mm, my electronic to 1/100 (but I would say 0,02 is the more
| realistic) The manual one is not good, harbor freight quality,
| electronic is a mituyo (not an entry level). Still - good ROI
| on both, got the electronic one because my eyesight is not that
| good anymore.
| jcgrillo wrote:
| With a decent set of vernier calipers (I have Brown and
| Sharpe ones) they're accurate to 0.001" (0.02mm) every time.
| But what's nice about analog measuring tools is you can
| actually reliably achieve better accuracy--like 0.0005" +/-
| 0.00025"--by "reading between the lines". I can reliably take
| finishing cuts accurately to a few ten thousandths of an inch
| using vernier calipers (confirmed by checking with a
| micrometer accurate to 0.0001").
|
| The only application I've encountered where digital tools
| work better for me is having a DRO on a mill is extremely
| convenient.
| varjag wrote:
| You really want to use a mike on this kind of precision.
| Calipers can be repeatable in a certain range but even then
| a readout from vernier gives too much error. Measuring a
| tenth of mm is acceptable (tho I'd never trust a vernier
| caliper measurement beyond 0.2). A hundredth IMO is wishful
| thinking.
| jcgrillo wrote:
| Looking at my calipers now I noticed that the imperial
| side is twice as precise as the metric side. Graduations
| of 0.05mm vs 0.001". I wonder why that is.
| genewitch wrote:
| tenths and hundredths of an inch "don't mean anything"
| because we don't divide inches that way in common use,
| but in subtractive manufacturing and the like they do use
| "thou" - and 0.001" is a thou.
|
| Personally, i use microns instead of 0.001mm, too, when
| measuring that small. I forget the accuracy of my good
| calipers, but i could detect errors of around 2 microns
| if memory serves. It's been a long time since i cared
| about anything that accurate so i have two pairs of cheap
| plastic ones - scale and digital.
| jcgrillo wrote:
| Yeah I only use calipers and micrometers for machining--I
| haven found any use for additive manufacturing--and never
| in metric units because all my tools are imperial. Just
| strange the calipers punish metric users by giving them
| only half the precision.
| varjag wrote:
| A typical metric micrometer is accurate to 0.01mm (tho
| you can find more precise ones at premium). It's really
| unlikely you'll get a micron precision from any calipers.
| Even an angry glance warms up the instrument enough to
| make this meaningless.
|
| Microns are the domain of grinding and lapping, you
| rarely ever need to go there with cutting.
| eth0up wrote:
| The proper term for calipers, for me, is Mitutoyo. I really
| want one of the solar models.
| HeyLaughingBoy wrote:
| Interesting that you say that. My current backburner project
| is a display (TFT or PC) for Mitutoyo Digimatic. I can read
| the bright VFD display, but it struck me that others might
| find it difficult to read from across a workbench.
| deskr wrote:
| > Have you ever wished for a 500 Hz, millimeter-precise linear
| position sensing system
|
| Kind of, but I'd like an 0.01mm precision please. It can be just
| a few Hz, I don't need 500 Hz.
|
| Great project though!
| tonyarkles wrote:
| I'd be super curious to see how the accuracy changes with
| averaging out/low-pass filtering the measurements. Accuracy
| usually improves proportional to sqrt(N) when you take N
| samples so your higher precision desire might just be a bit of
| code to write.
|
| The other side of it though is that you're starting to get down
| into the "everything needs to be temperature controlled" region
| as you squeeze that precision number. FR-4 and copper have
| thermal expansion coefficients around 15-20ppm/C. If I'm doing
| this mental math correctly, a 5 deg temperature rise would make
| a 1m long piece of FR4 expand by 0.1mm, or a 10cm piece of FR4
| expand by 0.01mm.
| foobarian wrote:
| One time I wanted to demonstrate thermal expansion to my kid
| (1st grade or so) so I made some marks with a steel ruler and
| put it in the freezer. Imagine my surprise when we took it
| out and there was no perceptible difference :-D
| satiric wrote:
| With some microcontrollers you can do this "averaging out"
| just by changing ADC parameters, you don't even have to write
| the low-pass-filter code.
| contingencies wrote:
| TLDR: <0.02mm should be possible w/open source using cheap fabs.
|
| Interesting project. The hardware guy earlier built a rotary
| encoder and a vape pen. I am no metrologist (though by chance I
| once worked for the UK guy who brought Hexagon to China and made
| bank), this looks overall like quite a complex scheme that was
| probably referenced from an existing implementation. These days
| you can get 0.10mm pitch tracks and offsets ("4 mil") or 0.09mm
| ("3.5 mil") from JLC on 2 layer/4+ layer. With flex PCBs you can
| get still smaller pitch ("3 mil"). Combining a few rows of these
| with basic multi-track rotary encoder theory should give you
| portions thereof, ~0.01-0.02mm.
|
| This back of hand calculation aligns well with my Mitutoyo's test
| report, which states maximum permissible error is 0.04mm @ 5mm
| diameter, 0.02mm @ 0-200mm, and 0.03mm @ 300mm. Indicated errors
| on the test report are all in the range of 0mm-0.02mm except
| inside radius which is 0.03mm. This would be a standard high
| grade caliper level of precision.
|
| In practice, achieving these levels is going to require machining
| high grade steels and mounting them at high levels of
| parallelism, not simply working out the electronics.
|
| See also: https://www.eevblog.com/forum/projects/absolute-
| capacitive-r... (see animation, GC7626C datasheet)
| https://github.com/littleboot/ACRE
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