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Author Topic: Any one know how to build a cheap linear encoder?  (Read 7777 times)

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Any one know how to build a cheap linear encoder?
« on: March 10, 2008, 02:25:05 PM »
Any one know how to build a cheap linear encoder?  Just looking for a simple cheap way to build up a linear encoder.  Ideas?

Offline jimpinder

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Re: Any one know how to build a cheap linear encoder?
« Reply #1 on: March 10, 2008, 03:59:36 PM »
There are many ways to build a linear encoder - but if you are talking, as I am sure you are, of something that can measure movement to, say, half a thousanth of an inch, I would have thought it in the realms of "too hard" for the average person. I don't know how the ones I have seen even work, but I would imagine some sort of wire matrix laid along the measuring distance. The machinery to lay down such a thing to that accuracy must be specialised.

A simple way, (without me thinking too much) would be to have a "stepper" motor connected to the moving part, so that it rotates, and some sort of "computer" counting the pulses it gives out. If it were free running, as on some of these sepcialist "fifth wheel" measuring devices it would be accurate.

Another way would be a disc which spins as the part moves - with a number of slots in it - and , of course, some form, probably an optical, counter.

The best linear encoders I ever saw were on the coal mine winding gear at the local pit. This was a worm drive on the winding engine moving a marker. When this lined up with a chalk mark on the wall the "driver" knew the cage was accurately aligned. (There were two marks - one to wind with men in, and one to wind with coal tubs in - the latter stretched the cable further). The distance involved was between 200 and 500 meters. Most miners would only "travel" with a driver they knew.
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Re: Any one know how to build a cheap linear encoder?
« Reply #2 on: March 10, 2008, 04:16:12 PM »
Hi, What resolution would you expect from a home made encoder perhaps 0.1mm at best.  Are you good at electronics?

If yes then 2 ideas could be,

Using a wheel and optical sensor on a computer mouse. You could print lines on a clear film and use the optical sensor with a bit of electronics.

Or you could hook the mouse wheel to a toothed cog with a toothed belt laid out flat.

Using the clear film idea will probably be the most accurate but you may need a laser printer to give the best result.

Or wait for an encoder to come up on e-bay.


Hope this helps
Re: Any one know how to build a cheap linear encoder?
« Reply #3 on: March 10, 2008, 04:33:48 PM »
Looking for something around 0.2mm (0.01in), or better.   Not bad with electronics and can build up any basic circuit, and cut then needed PCB board.  How about using the sensor from an optical/laser mouse?

Offline Whacko

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Re: Any one know how to build a cheap linear encoder?
« Reply #4 on: March 10, 2008, 06:16:53 PM »
Depends on the lenght. You can hack an inkjet printer. It has a high resolution film strip with lines and a sensor. But there is also a method to increase the accuracy of a home made linear encoder. But this will also be limited by lenght. Then you can use ferromagnetic strip from an old audio cassette, with spans of lenght. This can give you four channels. You need to pre record an accurate frequency on the tape, the whole lenght will give you about 500 meters. Then you can use the tape head with it's preamp for the signal. I've done this years ago to prove a pointless point to a hapless fellow!

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Re: Any one know how to build a cheap linear encoder?
« Reply #5 on: March 10, 2008, 06:29:15 PM »
Looking for a max distance of 48in.  So, I would have to hack apart a big printer/plotter.

Offline Whacko

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Re: Any one know how to build a cheap linear encoder?
« Reply #6 on: March 10, 2008, 06:32:37 PM »
Why does it have to be linear?

Whacko
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Re: Any one know how to build a cheap linear encoder?
« Reply #7 on: March 10, 2008, 06:42:36 PM »
I am not fussy.  But, I know that my lead screws can shift a little and I miss steps.  So what ever I use, I would like it to be independent of the drive system.
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vmax549

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Re: Any one know how to build a cheap linear encoder?
« Reply #8 on: March 10, 2008, 10:04:37 PM »
SO just attach the encoders on the lead screws?????  (;-) TP

Offline Whacko

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Re: Any one know how to build a cheap linear encoder?
« Reply #9 on: March 11, 2008, 12:22:54 AM »
If you have play in the lead screw and you use servo drives with the loop closed in the drive, you must be carefull of resonant feedback using direct coupled encoders. This is because the play in the lead screw can account for some encoder counts which the motors do not have direct control of.
I suppose a walk through the local scrap dealer might yield something too. You'de be amazed at what people chuck! Lots of equipment use linear encoders, like plotters and automation equipment.
The link you provided don't look like a 48" application, the inkjet hack could work on that, or are you building an upscaled model?

Whacko
Nothing's impossible