Simple text plotter

DennisFletcher

I was thinking of trying to build a small 1 line by ~15 chars text plotter that would use a couple of Parallax hobby servo's to move a sharpie marker to write a line of text.
Does anyone have ideas on how to get a basic stamp to control the servos in an x-y configuration to output the characters?· I know there are lots of pic controllers out there, but since the stamp can control the servo directly why over-compicate things.· I really need ideas on the software part - given the letter 'A' how do you convert that into movments to draw the letter?

Dennis

K de Jong

Hi Dennis,

I have the feeling that the Stamp code will depend strongly on the plotters design. What servo's are you using and how are the positioned and connected to the pen. Things like that.

But it will not be too difficult. Knowing nothing about the geometry of your plotter I would write:

MoveTo 0,0
LineTo 10,30
LineTo 20,0
MoveTo 5,15
LineTo 15,15

This should give you an 'A'.


MoveTo and LineTo are subroutines you have to write in order to move your servo's.

Regards,

Klaus

DennisFletcher

Thanks for the response·Klaus,

I was actually thinking of using Futaba Continuous Rotation Servo's from the Parallax web site, and wire them·to a BS2 and connect them to the pen (holder) via some kind of geared system.· The pen (holder) could move back and forth on very small rails using a belt or screw and nut (or something) to drive it.

If you look at the inside of a floppy drive; the Read/Write head moves on small rails and uses brass bushings to glide on.· Simple and easy...· This is what gave me the idea.

The thing I'm having trouble getting me head around is this:· A real cnc control handles moving the X and Y axis at the right speeds to make the diagonal line of the letter 'A' (ex. the X axis might have to move faster the the Y axis for both to end up at the right location at the same time).· How do I do this in a BS2 myself?

Dennis
·

K de Jong

Hi Dennis,

Small plotters often use stepper motors, then you can say:

Stepper 1: do 2 steps
Stepper 2: do 1 step

Another way is this: I took apart a color inkjet printer and there they use DC motors and encoder wheels, transparent with fine black radial lines on them so the printer knows where the ink goes. The same princple as used in the classical PC mouse, but much smaller lines and more accurate.

Maybe you can take apart an old mouse and use the encoder wheels + the optical detectors for your design.

With the BS2 you can run into the problem that it can not detect movements in both directions at the same time. But there will be a work around for tha, I' sure.

Regards,

Klaus

DennisFletcher

Hi Klaus,

Mouse optics and encoder wheels, hmmm... I didn't think of that. That's a good idea... I'm getting a screw driver right now and finding a victim, ah I mean a mouse...


Thanks,

Dennis

Chris Savage

Dennis,

·· In a plotter, I would think the Stepper Motors would be the better way to go...Many plotters that I have seen use Stepper Motors already, so it would seem to be the tried & true way to go.· And you wouldn't really need to use an encoder to track position, since it's not a critical application, and the likelyhood of the stepper motor getting hung up is low.· Two stepper motors would be very easy to calibrate for your application, and some sort of solenoid maybe, for the pen.

·· Many early Hard Drives used Stepper Motors for moving the drive's r/w head.· Most had no encoder.



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Chris Savage

Knight Designs
324 West Main Street
P.O. Box 97
Montour Falls, NY 14865
(607) 535-6777

Business Page:·· http://www.knightdesigns.com
Personal Page:··· http://www.lightlink.com/dream/chris
Designs Page:··· http://www.lightlink.com/dream/designs
·

Bean

FYI:
Find an old junk dot matrix printer. There are two decent stepper motors in them. One moves the paper up and the other moves the head back and forth.
You can probably get one for $5 at a thrift store.

Terry