How cheap digital verniers work (2017)
mjt.me.uk
mjt.me.uk
Can that be done with analog circuitry or does the signal need to be digitised?
They are absolute for a single rotation meaning if power is lost and reapplied, you still know the angle of the shaft (good for robot arms). This absolute positioning is not possible with a quadrature encoder.
Very cool bit of work and writeup, I use these all the time but never did a teardown — thanks!
https://www.youtube.com/watch?v=fKSSY1gzCEs
I'd like to adapt the concept using flexible pcbs to make a largish Nest-style rotary encoder.
To understand Vernier measurement conceptually, the Wikipedia article is actually not bad: https://en.wikipedia.org/wiki/Vernier_scale
That was driving me nuts.
Honestly it’s a much more ‘vernier’-like mechanism than I’d given it credit for.
The reason this is annoying in a shop environment is that there are likely other tools around with a vernier scale. That being said, I've also been around older machinists & engineers who exclusively refer to gauge blocks as "jo blocks", even when there wasn't a single set manufactured by the Johansson company in the building. This is common enough that searching for "jo blocks" returns a dedicated page on mc-master: https://www.mcmaster.com/products/jo-blocks
--Henry M. Leland, Founder of Cadillac and Lincoln automobile companies
From Machine Thinking video "Origins of Precision": https://youtu.be/gNRnrn5DE58?t=652
I guess this is a car engineer's version of "that thing you call the Internet is actually the web."
Dashboards were kept, and as gauges fell into use the gauges were mounted on or about the dashboard. So the dashboard is the ancestor to the gauge display holder, and to the firewall.
Patent US652940 (1900) shows a water-level gauge mounted to a dashboard in a "Whitney motor wagon".
That said, they absolutely do eat batteries faster than the expensive calipers.
"Turns out they pull almost as much current off (15uA) as they do on (17uA)."
https://www.reddit.com/r/harborfreight/comments/z7j8hp/fixed...
that's true but a physical switch needs to be placed and soldered while the soft on/off just needs to be placed atop it on the traces on the pcb. cost just probably was the biggest issue.
I bought a €20 digital caliper (this one[1]) and the battery is still fine, 2½ years later.
Cheap verniers are 'absolute modulo 10mm' as the T-shaped bar pattern repeats itself. They produce 'absolute' measurements by reading fast enough to keep track of how many whole bars they've moved.
Fancier verniers instead have two tracks in parallel, with slightly different pitches. Checking the offset between the two patterns at the current location gives an absolute measurement. This of course requires them to be factory calibrated etc.
They might also have slightly better electronics (some of these cheap verniers need a new battery every 3 months or so) or other differences.
In your article you link to a patent on the cheaper T shaped coatings, do you also have a reference to a patent specifically using this system of parallel + different pitch tracks?
Great write up by the way!
Gray codes[1]?
[1]: https://en.wikipedia.org/wiki/Gray_code#Position_encoders
I feel like the cash spent on replacing batteries in my 'crappy environment' calipers (usually harbor freight or equivalent brands) could've easily paid for keeping Mitutoyos in the bad environments, anyway.
It's one of those from-my-cold-dead-hands kinds of tools.
At the same time, I soldered a tiny power switch into my cheap calipers to stop the battery drain issue.
https://www.amazon.com/Imperial-Stainless-Accurate-Shockproo...
Fortunately that phase seems to have passed and it's now possible to buy very good digital calipers that consistently match my $300 Mitatoyos, stay off when turned off, and automatically turn off after a few minutes of inactivity.
I was so impressed I bought another two and gave them away, saves pulling out the Mitatoyos when someone at work wants to borrow 'em.
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m...
From Wikipedia:
A vernier scale, named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, thereby increasing resolution and reducing measurement uncertainty by using vernier acuity to reduce human estimation error.
This is because the cheap ones never power off, only turn off the lcd. They can’t power down without losing the position/calibration because they need to be aware when they move to a different section.
>The comb on the vernier shaft has a tooth pitch of 5mm. In other words, if the slider instantly moved 5mm, it would be undetectable, or 'ambiguous'.
You would imagine that you could use some kind of registration pattern(s) to solve this, but sadly nearly all mouse sensors are made by Avago, and Avago runs their own algorithm on the raw sensor data, and won't let you have the full data stream (you can only receive it via a debug API which only lets you get the data out super slowly). The avago ROM's are built into the sensor, and run a little 8080 CPU with a neat DSP for processing the image data, but sadly the system has too little RAM for any exploit to run your own code on it.
See also https://en.wikipedia.org/wiki/Very-long-baseline_interferome..., where the wavelengths are typically larger than light.