i'm working on project I need to measure the position with a rotary encoder millimeters (mm) I don't know what kind of rotary encoder to use?
A rotary encoder recordes the number of turns, not the distance (someone please correct me if I'm wrong), so you mainly need the type of encoder that resets itself to zero everytime it finishes a full rotation. After that, it just depends on the circumference of the wheel you attach to it.
Hello macantelecom
Provide detailed information wrt your project to see how we can help.
I need to get the position of the rail from the 3D printer
you can apply gears with known ratio so your encoder does multiple turns per wheel turn, but that will make it harder to turn the wheel
Use a linear scale rather than rotary encoder. Google capacitive scales.
It kind of depends on what sort of setup you want. Is this something you intend to keep, which has to be robust enough to last for a while? Or is it just an experimental setup which you'd use for a short time?
Linear encoders are pretty expensive, but you could look on eBay, and maybe you'd find something. Or you could substitute a rotary encoder with a timing belt to drive it. A quick-and-dirty substitute might be replacing the belt with a cord wrapped around a pulley. That would generate pulses, but it wouldn't be 100% repeatable.
There is a project which I think uses Arduino to read and display from low-cost capacitive scales. These are the type of scale used for example in all the cheap electronic "vernier" calipers - indeed you can use many of these as they have a data interface. See:
The scales are available from many hobby machine tool suppliers as well as on eBay and doubtless Aliexpress. They generally have a resolution of 0.01mm though accuracy probably won't be that good. For more money you can get magnetic scales that will read to 5 microns; or optical ones that will do a micron are even more.
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