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Author Topic: Backing off homing switches  (Read 3020 times)

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Backing off homing switches
« on: August 28, 2012, 03:55:04 PM »
I have the problem that a few people seem to have had of the gantries not backing off the homing switches properly.
The z homes but when it touches the home switch it stops. The diagnostics show that the switch is clear but the other axis will not home or just jerk a bit and stop. If I lower the z then they will home. Only the x, thats the english x btw the long axis  ;), backs of a few steps. neither the y or the z do. Can this backing off be adjusted?

Bruce

Just reading a thread I had missed and realise that I have not connected the earthing to ground. I will correct this tomorrow and see what happens.
« Last Edit: August 28, 2012, 04:01:18 PM by motoxy »
Re: Backing off homing switches
« Reply #1 on: August 29, 2012, 12:55:20 PM »
This is a copy of a post I just made on the other board. Thought I would share it here as well.

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okay I think I have got to the bottom of the problem.....crappy switches.
When a homing switch is triggered then the motor will back off until the switch clears, as was said earlier. You can test this by homing an axis and the pressing the switch manually. If you hold it in the motor will keep backing off until you let go. Because these switches are, cannot think of the right word, flicking off then the motor winds back until it flicks back. Trouble with these switches is that they start to lift off the connection before they fully flick off. Therefore the circuit is broken and the motor only goes back a very small amount to make the switch. This means that the switch is resting on the gantry and any vibration at all will lift it off and so the next homing is reset early. Thats why when I backed off the offending axis the rest homed perfectly. This also explains why one switch, which must flick as it breaks, allows the motors to rewind a small amount before it flicks back.

Hope this makes sense to anyone else and serves as a warning on cheap switches.

Bruce
Re: Backing off homing switches
« Reply #2 on: November 17, 2013, 01:50:51 PM »
I have a problem with auto homing.  I installed a set of npn prox switches. I used the pmdx 126 boart, the 134 mother board, and gecko 203's. I configured everything correctly
and get all the lights for x,y, (z is not being homed)  The machine begins with the Y axis homing and reaches the switch and stops and backs off. Then the x axis homes towards
the switchs, the A axis (slaved axis) hits the switch and backs off, the x- hits the switch, backs off, and continues to ram in a back and forth fashion?    What am I doing wrong?
Re: Backing off homing switches
« Reply #3 on: November 17, 2013, 03:42:34 PM »
Another way to deal with crappy limit switches is to increase your debounce time in General Config to maybe 500 units at 40 microseconds per unit equaling a .02 seconds delay. That may be just enough time (distance) to clear the switch. If your slow speed zone speed was 25"/min you would be .008" off the switch.

Tony
Re: Backing off homing switches
« Reply #4 on: November 17, 2013, 03:59:09 PM »
I have a problem with auto homing.  I installed a set of npn prox switches. I used the pmdx 126 boart, the 134 mother board, and gecko 203's. I configured everything correctly
and get all the lights for x,y, (z is not being homed)  The machine begins with the Y axis homing and reaches the switch and stops and backs off. Then the x axis homes towards
the switchs, the A axis (slaved axis) hits the switch and backs off, the x- hits the switch, backs off, and continues to ram in a back and forth fashion?    What am I doing wrong?

Maybe

From Gerry: " You need to make sure to UNCHECK "Home Slave with Master" in General Config. You may also need to modify your Ref All script to use RefCombination() to get the two sides to move together."
« Last Edit: November 17, 2013, 04:02:19 PM by Tony Bullard »