LitePlacer.com forums

Hi All,

I almost have my Liteplacer going...

Sometimes when It goes to pick up a part, it probes that part (slow down till limit switch trips). It then moves up till the limit switch trips again and generates the "Attempt to move while nozzle is down" error (the part is still in the tray). I click OK a few times and I then get "Debug: CNC_BlockingWrite: Timeout on command {"hp":""}". The only way to recover appears to be to reset the TinyG controller.

Any suggestions on how to avoid the original error please?

Thanks.
Regards,
Les Grant.

I had a similar issue when my pickup tube wasn't free enough. When the pickup head makes contact with table it pushes down until the limit switch triggers, and then backs off. The backing off should cause the limit switch to untrigger.

If the pickup tube is sticky the limit switch will trigger when it tries to raise the head. Since a limit switch is not expected to be triggered while the head is jogging up (should have already untriggered the switch during the backoff) it causes the error that requires a reset to clear. The reset being needed after any unexpected limit switch being triggered is general behavior of the software (or the TinyG perhaps).

Checkout this thread for more details on a sticky pickup tube:

https://liteplacer.com/phpBB/viewtopic.php?f=4&t=6088

Thanks Stefan. I had seen that post and I had a lot of trouble with my pickup tube originally. I removed the curved spring to reduce the friction - it worked much better after that. However, I just checked and my nozzle adaptor was compressing slightly before the limit switch switched. So, I lowered the collar for the spring below the top bearing and it now operates the limit switch before compressing the nozzle adaptor.

Why is that spring there anyway? I am thinking of removing it so I can positively limit the travel of the limit switch arm (to avoid it moving or being damaged). I can't see why the spring above the top bearing is there either...

I have 2.2 mm of backoff. I will repeat the nozzle height calibration in the morning. Given the spring settings, my backoff may have been variable.

Thanks for your help.
Regards,
Les.

Ok, I couldn't wait till morning (only 4AM here!).
The springs above and below the top bearing are disabled and nozzle hight calibration completed.
The collar from the top spring is now about 4mm below the top bearing to limit the pickup tube upward movement.
Backoff is now 1.65mm which tells me the top springs were acting against the nozzle adaptor spring.
I will test later this morning. Bed time.

Cheers,
Les.

> Why is that spring there anyway? I am thinking of removing it so I can positively limit the travel of the limit switch arm (to avoid it moving or being damaged). I can't see why the spring above the top bearing is there either.

The springs around the tube are for trimming the pickup force. There are two, so you can increase and decrease the effective weight of the tube. The weight of the tube alone, with the springs disengaged seems to be fine, though.

The flat spring that pushes the tube sideways is taking out any slack in the bearings for front-back direction. The rotation belt does the same for left-right.