Re: HP plotter servo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<davemucha@j...> wrote:

>
> Hi all,
>
> I pulled apart an old HP plotter ......
> Has anyone ever tried to use the plotter motors ?
> > Has anyone ever hacked the controller board for these for CNC

use ?

> Any ideas what to do with them ?
> Since I have three more plotters I'm not sure if I should pull them
> apart for parts or just junk them.
>
> Dave.

Dave,
This is the idea that gave me the CNC bug many moons ago.
I still haven't shaken it and a relapse was brought on recently with
the imminent delivery of a free HP 7475A Graphics Plotter. I already
received the (Operator's) Manual.
Hopefully, the motors in mine are steppers, for simplicity.
To keep things simple, I will use the output motor phase signals and
add a simple Driver Stage (eg. Higher Voltage stage with 4x
darlingtons to bigger steppers). I intend to stick with the HPGL and
drive it as a Plotter as designed.
The original cheap Plotter that I first played with was on a SHARP
MZ700 64kB computer circa 1978. It had 4 wee coloured ballpoint pens
in a rotating chamber. Motors were driven by 5V TTL Hi levels on the
phase wires!
A BASIC command such as "CIRCLE 5,46,0,360,0.2" (Draw a circle with
centre at X=5,Y=46, Radius:123,Start Angle:0,End Angle:360,Step
Angle:0.2 degrees) involved sending ASCII codes
for "C","comma","5","comma","4","6","comma","0","comma","3","6","0","c
omma","0",".","2" to an onboard interpreter).
HPGL may well be interpreted onboard in vintage plotters in a similar
way. Axis co-ordination being done onboard.(A reason to stick with
that command format.)
There are a few different ways of achieving extra controls. Pen-
Up /Down is readily available (including successive Pen-Dns!)and the
pen change movements can be modified also. (The SHARP simply drove
the pen carousel against an off-plot-area stop with the pen up. Each
motion against the stop indexed the carousel to the next pen by a
simple mechanical ratchet.)
Pen cleaning movement routines are often available for playing with,
too.
I scrapped the SHARP project because it only addressed -480 to +480
clicks on X-axis. HP7475A does -32767 to +32767 clicks per axis, so
32" at 0.001" resolution is possible!
Don't throw those boards out yet! They may be smarter than you think.
(Or throw them my way.)
Anyone wanting to share manuals/info/hardware/ideas on plotters,
please keep in touch. Hurry, though, because I just ordered a 4 axis
Xylotex Driver, and am in danger of going mainstream unless
encouraged. :)

Cheers, Don.

P.S. Photos will be forthcoming, Dave, but I don't seem able to post
to Files area ....