Homing -- No pull off
- Thread starter flytyree
- Start date
breezy
Moderator
What is your homing speed? Try slowing it down.
What is happening is that the Z axis is over shooting the limit switch and when it pulls off, the limit switch is still operated, hence the alarm.
I sometimes have an hard limit alarm on the X or Y axis and just pulling the relevant axis (they are belt driven) off the switch and rerunning the homing fixes it.
Guy,
I disagree here, you need some pull off to allow for the hysteresis in the limit switch, sometimes set pull off to a large value and then work to reducing it. But I agree that homing is a combination of speed and pull off.
Regards,
Arie.
What is happening is that the Z axis is over shooting the limit switch and when it pulls off, the limit switch is still operated, hence the alarm.
I sometimes have an hard limit alarm on the X or Y axis and just pulling the relevant axis (they are belt driven) off the switch and rerunning the homing fixes it.
Guy,
I disagree here, you need some pull off to allow for the hysteresis in the limit switch, sometimes set pull off to a large value and then work to reducing it. But I agree that homing is a combination of speed and pull off.
Regards,
Arie.
breezy
Moderator
When I set up homing, I have the machine sitting in the middle of its axis and set the homing sequence to individual homing moves so that I could stop homing if the axis moved in wrong direction. The first time I homed the machine I had the homing speed set same as rapid speed and the machine slammed into the end of the axis, I quickly adjusted the homing speed down to a crawl. Then I worked the speed and pull off until I was happy the homing speed was as high as possible and the pull off was as short as possible. (Why waste axis travel).
Pull off is in the opposite direction to the homing direction.
If your homing position is not the 0,0,0 position, then you have to set the coordinates so that when you issue G0/G1 X0 Y0 Z0 it will travel to the machines 0,0,0 position. And those coordinates need to match or be less than the values set in each axis travel settings, else you will get soft limit alarms and homing failures. How do I know, because that happened to me. So now I home to the 0,0,0 position.
Regards,
Arie.
There is a limited distance (about 10mm) the axis will back off a sensor and if it cannot clear it in that distance it will give a homing alarm. This initial distance is not the pull off distance. The pull off distance is the additional distance it backs off after the sensor or switch goes low.
As Arie says speed is the main cause of these issues and causes the axis to overshoot by a distance that will not allow the sensor to clear in the initial back off.
In extreme cases it will overshoot a sensor and actually clear the sensor entirely causing it to go low so it doesn't need to do the back off but when it starts to do the pull off it trips the sensor and you get the hard limit.
Hope this helps
Cheers
Peter
As Arie says speed is the main cause of these issues and causes the axis to overshoot by a distance that will not allow the sensor to clear in the initial back off.
In extreme cases it will overshoot a sensor and actually clear the sensor entirely causing it to go low so it doesn't need to do the back off but when it starts to do the pull off it trips the sensor and you get the hard limit.
Hope this helps
Cheers
Peter
Gentlemen. Thank you for your input.
The pull-off is now working. I slowed the rate down but I think the biggest issue was I had a "-" in front of the pull off values. Bad move. I removed the "-" from the Z axis and the Y axis and left the "-" in front of the X axis. Z and Y pulled-off. The X did not. Changed the X axis by removing the "-" and then all three axis function properly.
My bad. Again thank you for your input.
Clifford
The pull-off is now working. I slowed the rate down but I think the biggest issue was I had a "-" in front of the pull off values. Bad move. I removed the "-" from the Z axis and the Y axis and left the "-" in front of the X axis. Z and Y pulled-off. The X did not. Changed the X axis by removing the "-" and then all three axis function properly.
My bad. Again thank you for your input.
Clifford
breezy
Moderator
Well I tested this and here is what I found.
Set back off to zero and homed the machine. It backed off the sensors and stopped as the sensor went low, but this left the sensor in a flickering state when watching the MASSO homing inputs. So when returning to MCS 0,0,0 position 9 out 10 times it would trip HARD LIMIT alarm.
I just needed to set back off to 0.1mm to prevent HARD LIMIT alarm from occurring when returning to 0,0,0 position.
Final back off was set to 0.5mm just be sure.
Regards,
Arie.