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Author Topic: Slave Y axis getting behind in time.  (Read 1187 times)

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Offline FiveO

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Slave Y axis getting behind in time.
« on: March 22, 2022, 11:05:14 AM »
Hi

I found that my Y slave axis is getting out of square with time. At 10 days its getting 1.5mm to Y++ side, 0.1..mm per day. I measured that after I turn on the machine and ref. all axes.

What could be the problem?
Re: Slave Y axis getting behind in time.
« Reply #1 on: March 22, 2022, 03:20:28 PM »
Hi,
one possibility is that the forward/reverse signalling is not symmetric. If the slave were losing or gaining steps you would expect it to happen in bunches,
not just slowly accumulating over time.

Typically a slave motor turns in the opposite direction to the master motor. Thus if the Master is in FWD the slave will be in REV.
If the stepper drivers have say a pull up resistor on the Step signal it might be that the master stepper motor goes 1000 steps FWD and then 1000 steps REV
to end up in the same spot. The slave axis may go 1000 steps REV but then only 999 steps FWD. Over a period of time the slave will lag behind.

To test this you need a long stroke dial indicator, and even then you must be very particular to get the accuracy required to tell whether this is happening or not.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'

Offline MN300

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Re: Slave Y axis getting behind in time.
« Reply #2 on: March 23, 2022, 08:17:23 AM »
Quote
Typically a slave motor turns in the opposite direction to the master motor. Thus if the Master is in FWD the slave will be in REV.

If you reverse one of the windings of the slave stepper it can be fed with the same polarity signals as the master. That should make the two motors behave the same.

Offline FiveO

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Re: Slave Y axis getting behind in time.
« Reply #3 on: March 24, 2022, 10:22:19 AM »
Hi,
one possibility is that the forward/reverse signalling is not symmetric. If the slave were losing or gaining steps you would expect it to happen in bunches,
not just slowly accumulating over time.

Typically a slave motor turns in the opposite direction to the master motor. Thus if the Master is in FWD the slave will be in REV.
If the stepper drivers have say a pull up resistor on the Step signal it might be that the master stepper motor goes 1000 steps FWD and then 1000 steps REV
to end up in the same spot. The slave axis may go 1000 steps REV but then only 999 steps FWD. Over a period of time the slave will lag behind.

To test this you need a long stroke dial indicator, and even then you must be very particular to get the accuracy required to tell whether this is happening or not.

Craig

Ok. Both motors turn on the same side on my machine.

Offline FiveO

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Re: Slave Y axis getting behind in time.
« Reply #4 on: March 24, 2022, 10:23:24 AM »
Quote
Typically a slave motor turns in the opposite direction to the master motor. Thus if the Master is in FWD the slave will be in REV.

If you reverse one of the windings of the slave stepper it can be fed with the same polarity signals as the master. That should make the two motors behave the same.

Don't get it ???

Offline MN300

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Re: Slave Y axis getting behind in time.
« Reply #5 on: March 24, 2022, 11:14:09 AM »
My comment was based on Craig's mention that the slave motor typically turns in opposite direction as the master. He suggested if that was accomplished by changing the polarity of the direction signal to the slave motor the number of pulses received by one of the motors could be off by one when the direction reverses.
I suggested reversing the slave motor by interchanging the wires to one of the stepper windings so the polarity of the direction signals could be the same.

You mention the fault occurs over ten days. If you turn off power or disable the drives the stepper motors can align themselves to the nearest pole causing a slight position change. Are you re-zeroing every time power is restored? More explanation of what you are doing would help.