Originally Posted by
Rocketman
I realize I'm coming to the party a little late but after viewing the photos I'd say it's an optical encoder. I could not see a part number on the thing to find out what model and who made it? I'd love to hack one of these someday! That black thing the disk revolves in probably has an L.E.D.(light emitting diode) in it that shines light through the disk and a photo resistor on the other side of the disk. Usually set up in pairs out of phase from one another. The photo resistor varies it's resistance by the amount of light being shown on it's surface. The printed bands on the disk break up the light beam being shown on the photo resistor and thus we are able to count R.P.M.'s and determine location by counting how many light blinks or variances in resistance from the photo resistor have transpired. With the photo resistors in pairs and out of phase helps determine the direction the motor is spinning.
If anybody has one of these encoders apart there may be a product number or manufacturer name on the black plastic housing somewhere.
I did a product search using the numbers on the circuit board but came up empty handed. The only encoder sold separately is kind of in the board sensor assembly and it's $35 bucks at the time of this writing. Too much money for me to order one just to play with. It may or may not be the same as the ones installed on the other axis I don't know. Encoders come in all sizes and flavors depending on your needs. Lines per inch (lpi) sometimes listed as pulses per revolution (ppr) is just one of the things that come into play when your trying to make things accurate and hopefully fast too.