Can't make round circles

Added by leotuorto almost 8 years ago

I made a custom laser cutter using laos to control it but it has a problem with circles and some complex geometries they always get deformed no matter the speed and acceleration of the cutter. Here is some photos of the issue.
Sorry for my bad english, thanks for the assistance!

Replies (6)

RE: Can't make round circles - Added by Springuin almost 8 years ago

Looks like your stepper motors are skipping steps. What kind of stepper motors and stepper drivers are you using? Can you increase the stepper driver current?

RE: Can't make round circles - Added by KalleP almost 8 years ago

Those circles and squares look like a lot of backlash (slop, slack, play) present in one axis. You may have the carriage loose on the rail or a very loose belt or some other mechanical problem, perhaps even extreme sticktion in the bearings as the error occurs when the carriage changes direction.

You can test to see if it is a electrical ot mechanical problem by swapping your X and Y stepper and limit wires and seeing if the error rotates 90 degrees with the changing of the electronics or if it remains with the mechanics.

Nice job on your cutter.

RE: Can't make round circles - Added by leotuorto almost 8 years ago

Thanks for the fast response and sorry for my delay.
Springuin, I use the pololu DRV8825 as stepper drivers, I tested several current levels and I set the speed of the cutter for only 10%.
KalleP, the cutter is using only Igus linear guides, all axis are very light and the belts are with adequate tension.
None of this solution work. Can the firmware not understand correctly all the commands?

RE: Can't make round circles - Added by Springuin over 7 years ago

Set the current as high as possible, but so that the motors don't overheat (keep temperature below 50-60 degrees C) and that you don't exceed the maximum current of these stepper drivers.

Why are the lines dashed? Is the machine engraving (same kind of motion as an inkjet printer) or cutting (following the contours)?

Are the power supplies (5V and motor supply) stable? If you have an oscilloscope, use that or check the fluctuation of the voltage using a multimeter.

I don't expect firmware problems, because then other users would have the same problems.

RE: Can't make round circles - Added by jaap over 7 years ago

The DRV8825 stepper drivers are a bit odd, when I used them in an Ultimaker, they would block on high currents, while they work great on (very) low currents. I guess you will have to experiment a bit, or maybe try orther stepper drivers if the problem persists.

RE: Can't make round circles - Added by leotuorto over 7 years ago

I figure out what the problem are, actually the problem is mechanical, the igus drylin N linear guide that I choose for the X carriage is wobbling a little inside the rail when the X axis change the direction. I think changing the linear guide will fix the problem.
Thanks all for the help!