Re: [CAD_CAM_EDM_DRO] Re: First note-Help

> Yes, its distressing. But, you have to look at the applications this
> type of sensor was really designed for. It was designed as a shaft
> encoder for instrument panels, where the microcontroller was probably
> only 2 - 5 inches away, in a relatively noise-free environment,
> or in small mechanical devices like tape cartridge libraries, etc.
> where things are a little noisier, but still nothing like a machine tool
> control where the encoder counter (and power source) is on the other
> end of 20+ feet of cable from the encoder.

My guess is that HP developed the HEDS-style modules to use in their
printers. Older deskjets contain a QEDS rotary encoder (something
like 512 CPR) on the traverse servomotor (which is the same as the HEDS
as far as I can tell) while newer ones contain a tiny linear encoder that
reads a mylar strip stretched in free space across the width of the printer.

In the case of the rotary encoder the cable is short. But the linear
encoder read head travels with the carriage, and is mounted on a small
PC board containing a capacitor. Some attention must have been payed
to noise performance as the power and signal lines run through the
same flex cable as the signals for the HP deskjet head, which takes
around a 400 milliamp pulse a mere 3 microseconds or so long to fire.
(It's possible they slow the edges of that pulse some to reduce
emissions).

I've re-used these rotary encoders on machine tools, but the linear
encoders seem too coarse to be of much interest (which it too bad, as
the tiny modules would be nice on small machines)

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT