Random printhead movement and crashing  

RE: Random printhead movement and crashing

Posted by: @dzar

For the past couple of months I've had this issue with increasing frequency. Today, I could not even do a first-layer calibration.

The issue is that at some point during a print, the printhead will simply move to a random spot on the bed and continue printing from there. It loses its X-axis home spit (moving to X=0 puts the printhead somewhere in the middle of the X-axis, not the far left) as well. Sometimes, this is accompanied by a "crash detected" message, but not always. I've come back to visit a print after 30 minutes to see that it has shifted everything over several centimeters. 

Nothing I do fixes this, permanently. I reset the printer, perform all calibrations and it usually fixes it for a week or two. But not today. The first layer calibration had the issue! Started printing the pattern, then after the first leg, it stopped, moved the head to some weird spot, and then completed the pattern on the right half of the bed. TWICE. I have never seen it so deterministic. 

 

Any thoughts on what I should check? Does it seem like a controller issue or a bad sensor? 

Thanks

Have you checked your belt tension and lubrication of bearings and rods as well as pulleys are fixed onto motor shafts correctly, and idlers are moving freely.

Sounds like a mechanical issue somewhere 

RE: Random printhead movement and crashing

@clarmrrsn

This was my issue with an older printer.  It is worth a try!

RE: Random printhead movement and crashing

From my understanding, the printer records the home position at the very beginning of the print process. After that, the printer head only knows where it is by the number of steps (motor steps) it took since the initial homing. i.e. after homing, move x right 150, then left 100, then right 25. the head is now 150-100+25=75 steps to the right of home.

During printing, if the x position has done an offset, the reason for this might be, the x stepper wanted to step 50 to the right, which the board did send to it and the motor tried, but if the belt slipped due to too much friction on the head, the position relative to the number of steps to get there has now altered the position. Other causes for this misstep could be the pulley on the x-motor end is loose, and as mentioned before, the friction of the x-axis is too high. Check that the head can move from left to right easily with no grabbing along the way. If you feel it, lube and check that the belt is not touching the housing on either end and there is a clear path for the belt to pass through, including the head. A couple of other things that could cause this friction, is the idler pulley on the right side is binding against the housing and not aloud to spin freely, or its bearings are shot. Belt could be too loose as well. I found that the belt test numbers are not a true indication of belt tension. With this device https://www.prusaprinters.org/prints/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus even though my x and y numbers where the same, the y belt was tensioned higher than the x belt. So, your x-belt might be too loose. Finally, if none of these appear to be your issue, the stepper motor itself could be the problem. Ensure that it is fully seated in the RAMBO.

Run the belt test a few times and see if you are getting consistent numbers on the x-belt. If it fluctuates on each try, there is definitely something going on as described above.