Z axes do not home correctly anymore

Hi!

I have totally no idea where best to post this, but I thought it might have something to do with the RAMPS 1.4 microprocessor that I use.

I have been quite happily printing for a while now. Today, I printed a big part (about 8 hrs printing), but I had to stop it prematurily (emergency shutdown). I did this using the emergency shutdown of the Repetier software. However, after that, I hit the Z axis home button. While this should have homed the Z axis (to the top), the axis only moved for a small distance down?... Then it stopped. I can keep on doing this, and always the same happened.

BTW: I use 2 Z axes, so the motors themselves shouldn't be to blame (would be strange if both be broken)?

I did the following:

• Reboot RAMPS 1.4
• Reboot controlling PC
• Reinstall the firmware (marlin)
• Replace the motor driver for my two motors of the 2 Z axes
• Try to print something

Always the same problem... For now, printing is out of the question :-(

Did anyone have such a problem? Could it be that my RAMPS board is fried for some reason? Maybe using the "emergency shutdown" function of the Repetier Software is extremely unhealthy?

Thanks for any ideas!

Normally happens when your Z axis end stop has become disconnected. Check the wiring and send M119 to the printer to see end stop status.

That's correct. I did also check the wiring, but didn't do the M119 command. After checking the wiring again, I still get the same problem. This is what I get when I execute the M119 command:

00:55:19.201 : Reporting endstop status
00:55:19.201 : x_min: TRIGGERED
00:55:19.201 : x_max: open
00:55:19.201 : y_min: TRIGGERED
00:55:19.201 : y_max: open
00:55:19.201 : z_min: open
00:55:19.201 : z_max: open

Both X and Y axes actually are at home position. Z axis is not yet at home position, however it still moves down about 2mm when I do "G28 Z". Note that it does not perform the home positioning (slowing down and then moving down and up) but only moves down 2mm. Also, I now notice that if I do the homing, the Z axis cannot move down below that point. It seems as if the 0 point of the Z axis has been changed...

Note that this all started without any changes to firmware or any hardware...

I have manually moved up the Z axis to the end trigger and it seems to work correctly:

01:00:06.680 : Reporting endstop status
01:00:06.680 : x_min: TRIGGERED
01:00:06.680 : x_max: open
01:00:06.680 : y_min: TRIGGERED
01:00:06.680 : y_max: open
01:00:06.680 : z_min: open
01:00:06.680 : z_max: TRIGGERED

Could there be another reason for the malfunctioning?

Thanks!

Maybe try M503 to see if a Z offset has been set in EEPROM, or send M206 Z0 to set 0 Z offset?

I couldn't sleep so I did some more testing. I found another optical switch laying around, and exchanged that with the old one. And miraculously, it works again!

I switched back to the old one, and things go wrong again...

So it seems like the optical switch itself is broken. However, the light still goes on and off when I wave something in front of it, but it seems for some reason the info is not sent to the RAMPS board.

Do you guys have experience with the reliability of such optical switches (like this one)? The reliability of this one is crap (only a few months), and the fail mechanism is strange to say the least...

I will perform more tests on it tomorrow to try and find more about the fail mechanism. Hope it'll help another guy having these issues!

Steph

BTW: I exchanged the optical switch for the Z axis by a mechanical switch now. Hope that'll prove to be more reliable (and easier to notice if it is broken)!

Thanks all!!