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low-cost 2D position sensor/encoder
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low-cost 2D position sensor/encoder

by bludin on Sat May 28, 2022 5:17 am

i have a mechanism that includes a disk/wheel, 95mm in diameter, 10mm thick. The disk can rotate 360° and shift axially by 5mm. i only have access to the outer surface of the disk. I need a low-cost solution to determine the rotational and axial position in standstill with an accuracy of 0.1° and 0.1mm. My current idea is to have a small camera detect a pattern printed on the outer surface of disk, but that would mean a significant amount of development work. Would anybody here know a more off-the-shelf solution?
TIA, beat

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Re: low-cost 2D position sensor/encoder

by sj_remington on Sat May 28, 2022 7:23 pm

Sensors that report angular position to +/- 0.1 degree or distance to +/- 0.1 mm are certainly available, but rarely, if ever, "low-cost".

A rough rule of thumb when comparing measuring instruments is that a 10X increase in accuracy is associated with at least a 10X increase in cost. Here is a glance at Mouser's collection of 3600 PPR shaft encoders: https://www.mouser.com/c/electromechani ... 3600%20PPR

Let us know if you find a solution.

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Re: low-cost 2D position sensor/encoder

by adafruit_support_bill on Sat May 28, 2022 8:39 pm

Detecting the axial shift should be reasonably straightforward assuming careful alignment and a camera of sufficient resolution. As noted above, off-the-shelf rotational encoders of that resolution are available - at a price. Rolling your own would be a substantial engineering effort. If you can get away with relative rotation readings, that is easier to do than absolute positioning.

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Re: low-cost 2D position sensor/encoder

by bludin on Sun May 29, 2022 9:36 am

Thanks for your thoughts. The usual kind of encoders are not really suitable because I only have access to the outer surface of the disk. Also, they are geared towards high resolution at high speed and i need medium to low resolution at very low speed only. I know there used to be optical mice that could determine their absolute position on a patterened mouse mat. I think, that kind of sensor could fit my application perfectly, but i can‘t seem to find it anywhere (anymore)

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Re: low-cost 2D position sensor/encoder

by adafruit_support_bill on Sun May 29, 2022 9:48 am

Do you need to measure the full 360 rotation, or just part of it? If you search for "linear encoder tape" there are various types available. You might be able to wrap one of those around the edge of your disk,

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Re: low-cost 2D position sensor/encoder

by sj_remington on Sun May 29, 2022 11:05 am

i need medium to low resolution

Please put that in terms of numbers with measurement units.

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Re: low-cost 2D position sensor/encoder

by bludin on Sun May 29, 2022 11:42 am

sj_remington wrote:
i need medium to low resolution

Please put that in terms of numbers with measurement units.

0.1mm in both directions (which translates to about 0.1° at a diameter of 95mm)

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Re: low-cost 2D position sensor/encoder

by bludin on Sun May 29, 2022 11:49 am

adafruit_support_bill wrote:Do you need to measure the full 360 rotation, or just part of it? If you search for "linear encoder tape" there are various types available. You might be able to wrap one of those around the edge of your disk,

That will give me only one of the two required dimensions. In addition, i haven‘t found any low-cost absolute tape-based encoders. I can get an ESP32 based camera module for less than $20, I just don‘t want to invest a lot of development work into something that probably has been done before.

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Re: low-cost 2D position sensor/encoder

by adafruit_support_bill on Sun May 29, 2022 12:59 pm

I doubt that it has been done before at anywhere near that price-point. In my experience, >95% of positioning applications use relative encoders and a 'home' sensor to establish a known starting reference. Absolute encoders - especially the high resolution ones - are only used when absolutely necessary due to their high cost.

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