Linear scale resolution increase

[geshka]

Hello folks. 

I've got my hands on linear scale with optical strip encoder and reading sensor made around  Avago. HEDS-9720 with quadrature output. It is encoder that provides up to 150 LPI resolution according to spec, which makes it rather useless for precise measurements (like on mill or lathe) .  There are, however, two sensors  that are mounted in the same scale and they can be moved synchronously or independently  - mechanically they are not connected to each other.
My question  - is there way to make it , let's say differential, move it synchronously but with some shift between each other, and then to increase resolution by subtracting signal in MCU?  Any other bright idea ?

Thanks. 

[moffy]

Could you please elaborate as to what the second sensor is?

[thm_w]

Could you please elaborate as to what the second sensor is?

Sounds like its a second of the same sensor. In which case yes, you could offset it by 45 degrees and then read that into a micro to get 300 LPI.
Is it worth the time, probably not, as thats still not amazing resolution.

[TimFox]

Very high resolution linear encoders take the analog signals from two sensors 90^o apart and do a mathematical interpolation between physical lines.
See pp 18-21 of this Heidenhain brochure:  https://www.heidenhain.us/wp-content/uploads/2022/07/PR_Interfaces_ID1078628_en.pdf

[geshka]

Yes, second sensor is exactly the same.  Sure, still not a great resolution, but for the experiment sake...  I was thinking following - quadrature encoder can give four transitions per one division on scale  , so this is 150 x4 and then differential readings is another x2 which si already something... what do ya think ?

[thm_w]

Yeah you are right, LPR would translate to 4x CPR so x8 as you say.
Which would give a resolution of 1"/1200 = 0.0008" which is not too bad.

Looks like there are also parts like TimFox is talking about to interpolate but you'd essentially be replacing the encoders: https://www.broadcom.com/products/motion-control-encoders/incremental-encoders/reflective-encoders/aedr-871x

[mzzj]

Sounds like its a second of the same sensor. In which case yes, you could offset it by 45 degrees and then read that into a micro to get 300 LPI.
Is it worth the time, probably not, as thats still not amazing resolution.

Indeed. Linear scales prices have dropped to dirt cheap compared what they used to be ages ago.
Fully packaged 500mm linear scale with 5080 LPI or 0,005mm resolution is something like 50 usd and half of the price is already shipping fees. 0.001mm resolution is also commodity item, maybe 70 usd.