Table of Contents
I have some spare V-Slot linear extrusions along with accessories. Let’s use them to build a simple pen plotter. It could later be rebuilt into a general purpose 2.5-3 axis CNC machine, which would likely require a more rigid design in most cases.
Design
Currently, i’m thinking of a simple “T” style design with only one linear actuator per axis. As we’re not building a heavy-duty CNC machine, but rather just a plotter, forces should be small enough to allow for that kind of setup.
Parts Library
The design is developed around the V-Slot extrusions, so using the Openbuilds OpenSCAD library can save us some time.
A quick test to see if it’s working:
Process
- Design a common linear actuator
- Design the Y-axis
- Design the X-axis
- Design the Z-axis (end effector)
- Assemble everything
- Animate
Linear actuator
A linear actuator consists of:
- a length of extrusion
- a “passive end” with the idler pulley
- an “active end” with the stepper motor
- the gantry
- the belt (maybe omit that from the CAD)
The motor stems from the MCAD library, which is bundeled with OpenSCAD. The pulleys are included in openscad-openbuilds. I couldn’t find a model of the end mount for the motor and idler pulley, so i designed it myself. I likely would have needed that custom model anyway, because i want to print them, instead of buying them for 10€ each.
X and Y axis
After modelling the linear actuator, “assembling the axes” is quite simple: Just put two of them on top of each other:
The X motor kind of acts as a counterweight
End effector
The end effector (Z axis) will slide on cheap 8mm smooth rod with LM8UU linear bearings. It will push the pen downwards using a spring and be able to lift it with a servo. The assembly could be mounted upside down to inverse this logic so that the pen would be pushed up by the spring and down by the servo. I prefer the former approach because this way the spring acts as a suspension while drawing, smoothing out any irregularities in the drawing surface and reducing forces at the pen tip.
Build Steps
Building with Openbuilds parts is quite straight forward and requires not much explanation:
Linear Actuator Build
End Effector Build
Manual Operation
Individual Contribution
Though this assignment is a group assignment (and requires to describe the individual’s contribution), i did the design and build by myself, as i didn’t find the time to visit to the lab and coordinate with the other student.
Improvements
- Add end stops
- Smarter pen holder
- Increase counterweight or add wheel to the loose end of the X axis
- Use thinner rod for the end effector 4 or 6mm (8mm is what i happened to have around)