I love plotters and plotter art and if you’re into robots or other machines that draw, you should check out #PlotterTwitter and DrawingBots.net
While I’m still working on my new plotter (which is really an old HP7475A) I figured I’d have fun with Processing and write some code to generate some nice vector art. This is something I do every now and then. I’m someone who believes in writing code for pleasure, and sometimes I actually do that!
I’ve also released this code in case someone else wants to generate some art for use with their own plotter or whatever device they have that can do something with it. (Like a laser cutter, for instance.) And yes, the sample images you see on the page were generated by the sketch. There are a few variables you can change to adjust things, like the spacing between circles, steps between circles inside of circles, and setting the limit on the smallest circle.
We recently got a uArm Swift Pro robot arm at Brinn Labs and I’ve been putting it through its paces. It comes with software called uArm Studio that lets you do a lot of things, but for this post I’ll focus on drawing (or “plotting”) using a pen.
One of the tools I’ve used in the past with the Egg-Bot was StippleGen2 from our friends at Evil Mad Scientist Laboratories. StippleGen2 is a program written in Processing that takes an image and converts it into a series of lines, or more specifically, a single line, which is suitable for plotting.
Above is the image I started with, an “8-bit heart” as I call it. It’s a simple black and white image of a low-res heart. (Great for Valentine’s Day, right?)
After running the heart through StippleGen2 and choosing the appropriate complexity of the line drawing I wanted, I saved out the file as an SVG format vector file. Perfect for plotting. (In fact, since it’s a single line, the z axis never has to move up once it starts.)
I fired up uArm Studio and chose the Draw/Laser feature, and then loaded in the SVG file. I did have to scale it up a bit, as I still don’t have the exact dimensions I should use for artwork in uArm Studio.
Once the file is loaded, you hit start and there’s a step where you set the z axis so it know where the pen hits the paper. At this step, I wish there was a little more control over how the z axis moves. I think the smallest increment is one millimeter, and I think it should be smaller. (Most CNC software has some adjustment to how much you move things, so I can see adding in 0.5mm and perhaps 0.2mm as well.)
While the uArm Swift Pro is awesome, I’m still going to be a little critical… One of the issues I’ve come across in the Draw/Laser part of the software is that the speed seems to be hard-coded, with no way to adjust it to go faster (or slower.) As someone who understands G-code and how CNC machines work, I found this a little annoying…
So I set about to find a solution. I first posted a message on the forum, but then Chinese New Year hit and it seemed as though it would be two weeks (or more) before I got an answer. I had dug around and found that the G-code created by the Draw/Laser part of the software generates a file and drops it at ~/uarm/Temp/files/gcode/tmp_pen.gcode and I assumed that by editing the feedrate in that file, I could speed things up… I was right!
My first attempt was to connect with the arm using Universal Gcode Sender, which in this case was not universal, and failed to properly talk to the arm. I dug around a bit more and found simple_stream.py which is a Python script to stream G-code to a device. Sadly, it was not compatible with Python3, but luckily, I’ve been writing a lot of Python lately, so I fixed it.
After I got it working (that is, after much hacking at the original code) I found that I could easily speed up the drawing to half the time. In this case, 5 minutes with the Python script versus 10 minutes with uArm Studio. For TSP art, great precision tends not to matter too much, and I think I could speed it up even more.
I’ll work on cleaning up my Python code and seeing if I can get it online in case others want to muck around with it.
I started playing around with the #plottertwitter thing and wanted to do some creative coding with Processing, and at least one person asked about the code, so I’ve included it below.
Instead of drawing a rectangle, I’m creating a shape, and then varying the position of it a bit more with each row that is drawn. I reused some code I’ve used plenty of times before that keeps track of where things are drawn so the code knows when to start a new row, and when the screen is filled. After it draws a screen full it will save a PDF and exit.
Once you have a PDF (which is a vector file) you can make your plotter (or laser cutter, or CNC machine) do what you want with it. I typically bring the PDF into Inkscape and make any adjustments needed before I save it out in a format suitable for the machine I’ll be sending it to.
