idea for cheap but very accurate linear scale

[henry_phd]

I'm building a 3d printer and the first step was building an XY
inkjet. Basically I ripped out the X axis on a printer and strapped
it to a linear positioner. I'm planning to emulate the pulses of the
DC servo motor inside the inkjet to control the linear positioner.
I've been using steppers like most of you out there but one thing I
hate is not knowing what position I'm at because there's no linear
encoder on one of my ballscrew linear positioners.

Anyway, when I was examining the inkjet I found that they have a
linear encoder on the X axis. This is made very easily. There's a
plastic strip with very tiny lines on it which is suspended by pieces
of sheet metal which act like a spring. There is also a rotary
encoder on the paper drive with a thin optical disc.

You can rip these off for your home built CNC machine and get a DRO or
convert any big brushed DC motor + geckodrive into a very accurate and
expensive servo motor!

One of the sensors is on the inkjet head and not that easily removed
but the optical disc sensor is very easily removed and on a small pcb.

There are 4 wires on it, +V, GND, A, B encoder outputs. These inputs
can go directly into a linear positioner output to give a digital
output. I have a National Instruments DAQ card and I just used
Labview to get a digital position reading on my computer. I can make
a package for people with a microcontroller that don't have a daq card
for around $100 if there is any interest. Just plug it into the USB
slot and run the program and convert your inkjet + computer into an 8
axis DRO.

Really it is effortless. Just steal the encoder strip + encoder board
from a $10 inkjet (doesn't even need to work), no soldering required!

If you want a longer encoder then what you can do is print the lines
on a large format 36" blueprint printer at Kinkos onto mylar film.
Printers get easily get 2400 dpi so you should be able to get better than .001
lines (.001 dot then .001 space). If you want to stiff it up (not
necessary) then you can put two pieces of thin glass over the strip.

I'll put some info on my website when I have time to take some
pictures of it all.

Henry
www.fullspectrumengineering.com

[budP]

Thanks for a great idea.

budP