Drawbot using Cartesian method

x axis

I’ve got a drawbot on my drawing board.

I was thinking of having a Cartesian version that would not rely on gravity to keep line tension.

My theory with this is that the speed and accuracy of the drawbot may be increased.

I realize it’s much more complex but this could be mounted to a picture frame.

Further, many of the pulleys would share the same axle.

In the x-axis drawing at the right you can see a stationary pulley system. The x stepper motor will drive the cable/belt from the spot marked with “x”. The large vertical beam (gantry) is attached to the very top belt and the 2nd from the bottom.

So the gantry is driven from both sides and the system is under a constant tension.

y axis

I’ve added the y-axis in the diagram at the right. The y-belt is attached at a point at the top left of the diagram.

It runs over a pulley on the gantry then down to a pulley on the truck that rides the gantry. Back up then around the right perimeter.

The y-stepper position is marked with a “y”. I’ve only done this in my head but I figure that we would have x and y control with constant tension.

It’s not as complicated as it looks in my diagram. All pulleys freewheel.

Top Left: Y-anchor, X pulley.

Top Right: Y-pulley, two X pulleys all on one axis.

Bottom Right: Y-pulley, two X pulleys all on one axis.

Bottom Left: Y-anchor, X pulley.

Gantry: 4 pulleys at it’s corners. Top and bottom pulleys share same axis.

Truck: Two pulleys sharing one axis.

So the actuation system has 4 stationary axles sharing 8 pulleys, the gantry has 2 axles sharing 4 pulleys and the truck has 2 pulleys sharing one axle. That’s 7 axles and 14 pulleys.

Linear guides can be simpler than a standard gantry since the gantry is driven from both sides in constant tension.

I figure for X and Y stability the gantry could run on two ball bearings. One at the top and one at the bottom of a frame. This would prevent vertical play. Horizontal play and alignment is taken care of by the constant tension system. The truck could ride on 4 or three ball bearings that are at the left and right of the gantry. So for X and Y stability that’s just 6 bearings.

Z stability might require 4 bearings for the gantry and 2 for the truck. Sot the total is 12 ball bearings.

Unanswered questions:

1) What sort of cable or belt to use? XL timing belt? Bicycle brake cable? Spaghetti?

2) How to control the pen or drawing apparatus? There is no Z axis. I figured a multiple pen cartridge could be designed instead of a Z axis but how to control it?