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Using a Gearman RepRap with Slic3r, printing from an SD card, with an uniterupted power supply (UPS), and both PLA and ABS filaments, short power outages often result in x/y-axis offsets (see image). During an outage the power is not as clear from a UPS as from a power conditioner. If both x and y axes offset the results look like Why did my print fall off its raft?. Are you experiencing these same issues? Have you solved the issue.

Shows x-axis offset (ABS)

The image above shows an x-axis shift that occurred evenly across eight parts distributed across the bed. The filament was ABS. The parts still adhered to the bed. Note: the G-code file normally prints well. Thus, the file is not corrupt.

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  • $\begingroup$ If the UPS does not work optimally, what can the 3D Printing.SE community advice? A better UPS may be an option, one that doesn't cause power ripples maybe? The question does ask for experience of other users, that is not specifically an SE question. $\endgroup$ – 0scar♦ Jul 20 '19 at 7:05
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    $\begingroup$ Was the shift at the moment power failed? Seems likely the switchover just wasn't fast enough to keep sufficient current to the motors. $\endgroup$ – R.. GitHub STOP HELPING ICE Jul 20 '19 at 14:04
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    $\begingroup$ Note that "an x-axis shift that occurred evenly across eight parts" is nothing special. A shift is a one-time event where the logical and physical position of the axis become desynced due to inability of a motor to accelerate or decelerate at the rate the controller is attempting (missing steps). After that event, everything will be offset by the same amount (unless/until another such event occurs). $\endgroup$ – R.. GitHub STOP HELPING ICE Jul 20 '19 at 15:28
  • $\begingroup$ @R.. So, you're saying the robot motors temporarily lost power while the computer kept stepping through the program. In this case the x motor. So, we need a UPS rated for robotics not just computers. $\endgroup$ – Perry Webb Jul 20 '19 at 18:34
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Part of your self-answer:

What is puzzling is why did the 3D printer run as if the computer was still operating it, when is was printing from the SD card? Was the circuitry getting power from the USB cable from the computer?

is more of an extension of the question, which I'll answer. Generally, yes, the logic of many (most?) 3D printers can be powered by the USB connection. You can try it sometime with the printer not plugged in to the AC power source at all. Under such a power configuration, the motors (not to mention the heating elements) should not operate at all, and I think the firmware has logic to detect this condition and not try to print under it, but I may be mistaken. However, in any case, in the event of an outage during printing, the logic board will remain powered if it's connected by USB, and especially if the outage is short enough, it might not even notice that the motors and heating elements are not functioning, yielding a result like what you saw.

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I believe I resolved this issue. The next power outage will tell. After getting a larger UPS used for robotic testers, when swapping out the UPS, I noticed the 3D printer was plugged in to the surge protector side without the battery, probably because the smaller UPS was only rated for power to the computer. Now, with the larger UPS, the 3D printer also has power backup. What is puzzling is why did the 3D printer run as if the computer was still operating it, when is was printing from the SD card? Was the circuitry getting power from the USB cable from the computer?

Note: If one is running their 3D printer using a notebook with a charged battery and the 3D printer doesn't have a UPS, it would have similar behavior.

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  • $\begingroup$ Yes, most likely the logic components were getting their power from the computer during the brown out event. The steppers may have turned off while the micro controller kept sending out step commands. $\endgroup$ – user77232 Jul 23 '19 at 14:17

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