Shaft encoder application

[justwhy2003]

Hi Im looking into an application where a shaft is rotating in a lathe (slowly) and i want to design a controller that will allow the required number of revs to be entered and the controller stops the lathe when they have been completed. I can do the controller side easily enough but i havent much expereince with shaft encoders. What should i be looking for? If i have 6 inputs on my controller say, should i be looking for an encoder that produces a 4 or 5 or 6 bit grey code/binary word that i can use in my controller? to compare? My original simple idea was to have a point on the lathe chuck that a sensor looks for and pulses the controller eac time it passes but this means the lathe has to start with the point under the sensor at the start of the cycle. Im hoping that with an encoder i can check the parallel input word at start up and increment a counter each time the same code is encountered (each full revolution) meaning the counter can start when any point on the shaft is encountered. Any ideas? am i making sense? justwhy2003

[Kiwi Nate]

it seems like over kill but your idea will work. i take it you want to stop the chuck EXACTLY where it was started from?

[justwhy2003]

yeah probably exactly where it started from. Im thinking now that maybe a small notch on the chuck and a small microswitch might be an easier cheaper method. Ill look into both.

[Kiwi Nate]

If you wanted to make the simplier option with the micro sitch or prox, then if you wanted, insert some self teaching code that logs how long it took to reach the switch on start up, and applies those values when you press the stop button, to have a good shot at getting it roughly where it was before hand. A few intelligent lines of code and a little bit of inertia masking, I think you would get a good result. You might as well try and jazz it up a little if you got some spare hours on it...makes things more interesting.