Re: [CAD_CAM_EDM_DRO] canibalising old printers

Hi Peter,

You might look for some LARGE plotter chassis. Try to find one with
schematics available. What you want to do is find the motor wires,
backtrack into the transistor "outputs", and find their LOGIC inputs
(I'm expecting the "processor" part of the controller/driver to be
digital, if not, you're on your own!). to simplify the hardware,
unipolar drive with four "output" transistors are often used. An 'H'
bridge drive will have eight "output" transistors (per motor), often a
pair of "transistor types" (for the high and low side of the bridge),
and a driver IC(s). Bipolar power supplies are also often seen with 'H'
bridge drivers.

Anyway, by looking at the logic signals feeding the "driver" ('scope
them or use a logic analyzer while the motor is being driven), you
should be able to get an idea of what signals are needed. Four channels
(phases), driving four darlington transistors (sometimes a cascade pair
of transistors) would be a tip off of a unipolar, 4-phase drive. The
four signals are what you want to duplicate for your use! An L297, PAL,
PIC, or even a pair of F/F's can generate this for you.

The HPGL is not connected to whether the motors/drivers are step/dir or
4-phase. 4-phase "out of the processor" is simply doing the "state
machine" (which generates a 4-phase signal) in SOFTWARE. Software is
often cheaper then hardware.

For printers and plotters, the "driver" will seldom be step/dir, usually
to cut costs. You might even see what may be called cw/ccw drive
signals, and a pair of F/F's or a counter, connected so that it "counts"
up or down, (a step), and four Q's (output of counter stages) are used
to drive simple darlington transistors (4-phase).

Hope this wasn't too confusing. In short, get a printer/plotter and
it's schematics, open it up and see what it's doing!

STANDARD CAUTIONARY NOTE on DANGERS HERE!

Best way to learn! I've got a big plotter in my garage (along with a
laser printer or two) WAITING for attention!

I think Randy has some hardware to sell, If I don't get over there
first!

Have fun, learn!

Alan KM6VV


cadcamcenter@... wrote:

>
> Hi,
>
> Just wondering if there are any motor driver board that accept step
> and direction signals that can be cannibalised for lightweight CNC
> work.
>
> I understand that most printers are controlled using HPGL rather than
> G-code. I understand also that some controller accept steps and
> direction signal and others phase (whatever does this mean?). Are
> these two (language and controller) related or independent, and how
> so?
>
> Thanks
>
> Peter