Linear encoder from HP printer?

[jeffs555]

I took apart an HP inkjet printer expecting to retrieve a small stepper motor. What I found instead was that the carriage position was driven by a DC motor with a linear encoder for feedback.

The encoder consists of a mylar strip with very fine lines etched or printed on it. I assume there is some kind of optical quadrature sensor in the print head. This printer spec'd 1200 DPI, so the resolution on the encoder must be very high.

I have several small projects in mind where a high resolution linear encoder would fit right in. Does anyone have any experience using these encoders?

Jeff

[BushmanLA]

They are generally an Infra Red Emitter and Receiver pair in a little black plastic housing. The strip passes in the gap between the pair and the black lines block the light and the clear parts allow it to pass.

Usually there are 4 wires for each pair. Two for the emitter and two for the reciever. You will need to provide your own current limiting resistor for the emitter in most cases. Limit it to 20mA or less and you should be ok.

The receiver end will let current pass when the emitter is shining on it, and will block current when it is not. Polarity matters here, so be careful, and don't let too much current pass through the receiver or it will fry too.

[darkith]

IIRC, most printers have "home" switch on one side, then (I presume) count pulses from there...so they may not actually be quadrature encoded. Also, I wonder if the resolution of the strip may not match the printer resolution...it may use the strip to find a consistent speed and use that to determine the timing for the print heads to spew.

D.

[jeffs555]

I found this thread which says it is a quadrature detector.
http://sci.tech-archive.net/Archive/sci.electronics.components/2006-11/msg00141.html

I tried to count the stripes on the mylar and the best I can tell there are 200 lines per inch. With a quadrature detector, that would give a resolution of 1/800 inch. I need to find a source for a few more printers.

[darkith]

Perhaps posting on Kijiji.com might net you a few junkers from people's closets.

D.

[Unterhausen]

I have a couple of these in my junk closet. But I prefer to go on ebay and buy linear encoders, the small ones go cheap sometimes.

[BushmanLA]

I have a couple of these in my junk closet. But I prefer to go on ebay and buy linear encoders, the small ones go cheap sometimes.

I know what you say is true, but its so haaaaaaaaaaaaaard! :(

Its like I have this disease, and I can't throw any old electronics away without gutting them and seeing how they tick first. :)