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Author Topic: Stepper motors loosing postion.  (Read 4446 times)

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Offline Len

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Stepper motors loosing postion.
« on: September 23, 2008, 03:11:34 PM »
Looking for Help

I bought a 10year old engraving machine, which I converter to run under Mack 3.
A continuing problem is that the Z axis is losing its position after cutting 30 letters, ends up being 0.5mm higher or so. The x and y are also loosing a position but not by so much.
I’ve changed the stepper motion on the z and x with the next up in the range to give more torque but this has had no effect!  If tried slowing the motor accel and vel down with no improvement.
Does anybody have suggestion as to what is wrong?
Another option would be to use the Z solenoid, this lifts the router by 1mm or so (part of the old system).  The solenoid is wired in and controllable from mach3, How could I automate this control i.e lift the router between letters.

Any suggestion would be much appreciated.

Offline Hood

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Re: Stepper motors loosing postion.
« Reply #1 on: September 23, 2008, 03:35:28 PM »
What drives do you have, maybe they are needing a wider pulse, try setting it to 6, you will see it in motor tuning.
Hood

Offline Len

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Re: Stepper motors loosing postion.
« Reply #2 on: September 23, 2008, 04:42:12 PM »
Thanks, Tried that took it upto 5, both step and direction!

Offline Hood

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Re: Stepper motors loosing postion.
« Reply #3 on: September 23, 2008, 05:36:17 PM »
What kind of drives does it have?
Hood

Offline Bodini

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Re: Stepper motors loosing postion.
« Reply #4 on: September 23, 2008, 05:50:42 PM »
I know it is said that this is not possible, but the steppers could be worn out.

Oh, I can hear it now, "YOU CANT WEAR OUT STEPPERS".

I beg to differ,  I wore out a set of Keling steppers that were 18 months old when replaced.  Slowly, it kept losing position, little by little, until it was tripping the closed loop constantly.  The CNC builder tried everything with no results.  Finally he got fed up and put new steppers on it.  Viola!... machine was like new again.

-Nick

Offline Len

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Re: Stepper motors loosing postion.
« Reply #5 on: September 24, 2008, 03:59:56 AM »
Changed the z and x motors  for 2 new higher torque motors, still loosing posn.

Offline Hood

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Re: Stepper motors loosing postion.
« Reply #6 on: September 24, 2008, 04:17:49 AM »
third time lucky ;) what drives do you have?
Hood
Re: Stepper motors loosing postion.
« Reply #7 on: September 24, 2008, 01:15:03 PM »
I had a similar problem with Z axis couple of months ago. After milling some parts the Z-axis ended up higher then when started. The difference depended on the lenght of the G-code and on it's complexity. I tried everything starting from disassembling the machine (Joe's CNC), checking the HW etc. Finally I localized the problem to be in the SW, i.e. PC, not sure if it was XP or Mach. I tried to minimize the possible area of the problem. One of the last things I did was that I was making single microsteps with Z-Axis motor (jogging). I have realized that when turning 1 step right and then one step left everything was OK, but when turning 1 step left and then 1 step right, the motor actualy made the "right" step to the left and only a second right step turned the motor right. That explained why the Z axis shifted slowly up during the milling. Basically, during each change of rotation from left to right the position shifted by 1 microstep (or actually 2 microsteps, because the second microstep turned it to the previous position). It seemed to be a Mach problem. I checked the Mach setup and tried everything like you playing with an acceleration etc. Finaly, I realised (and I'm sorry I don't remember it exactly because it was couple of months ago) that in Config->Ports&Pins->Motor Output (or Output signals, not sure) I had some pins which I used for the motor control (step, dir) toggled on other positions as well. Those positions were NOT (!) enabled so I thought it doesn't matter, nevertheless removing the pin numbers from these positions fixed the problem. I can't guarantee you've got the same problem but it would be worth to check it.

Offline RICH

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Re: Stepper motors loosing postion.
« Reply #8 on: September 24, 2008, 08:03:59 PM »
I would think if it's tens years old and used a lot the screws / ball or nut could be worn some. But first give it a good carefull mechanical inspection and maybe do some adjustments if available. I don't know how it was made so can't recomend anything specific. First rule out any mechanical problems.
RICH
Re: Stepper motors loosing postion.
« Reply #9 on: September 24, 2008, 08:40:02 PM »
I had a similar problem with Z axis couple of months ago. After milling some parts the Z-axis ended up higher then when started. The difference depended on the lenght of the G-code and on it's complexity. I tried everything starting from disassembling the machine (Joe's CNC), checking the HW etc. Finally I localized the problem to be in the SW, i.e. PC, not sure if it was XP or Mach. I tried to minimize the possible area of the problem. One of the last things I did was that I was making single microsteps with Z-Axis motor (jogging). I have realized that when turning 1 step right and then one step left everything was OK, but when turning 1 step left and then 1 step right, the motor actualy made the "right" step to the left and only a second right step turned the motor right. That explained why the Z axis shifted slowly up during the milling. Basically, during each change of rotation from left to right the position shifted by 1 microstep (or actually 2 microsteps, because the second microstep turned it to the previous position). It seemed to be a Mach problem. I checked the Mach setup and tried everything like you playing with an acceleration etc. Finaly, I realised (and I'm sorry I don't remember it exactly because it was couple of months ago) that in Config->Ports&Pins->Motor Output (or Output signals, not sure) I had some pins which I used for the motor control (step, dir) toggled on other positions as well. Those positions were NOT (!) enabled so I thought it doesn't matter, nevertheless removing the pin numbers from these positions fixed the problem. I can't guarantee you've got the same problem but it would be worth to check it.

That is a classic sign of mis-configuation of the direction pin, and/or excessive delays through the BOB.  It for sure ain't a software problem....

Regards,
Ray L.
Regards,
Ray L.