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Author Topic: Y-axis "creep"  (Read 3525 times)

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Y-axis "creep"
« on: December 24, 2011, 10:59:28 PM »
I'm using Mach3 to run my X2 mini-mill. I recently replaced the wires going to the steppers with shielded cable and made sure to ground the shielding. The other evening, I took the steppers off and adjusted the backlash on both the x and y axis. I was able to reduce the backlash from .011" to .004". At the same time, I tried to take as much slop out of the saddle by tightening up the friction screws. I could still turn the feed screws by had, so I don't think I have anything too tight.

When I went to measure the backlash, I noticed that the y-axis was "creeping" at a rate of 0.001" per second. If I manually jogged the machine or entered commands manually, it seemed to go away. However, if I shut down Mach and the restart it, I get the creep again. The motor is humming when this happens.

Any ideas as to what caused this or how I can get rid of it?
-Capel

Offline rcaffin

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Re: Y-axis "creep"
« Reply #1 on: December 25, 2011, 04:50:11 AM »
If the axis is creeping and the ball screws are 'good', then the motor is turning.
If the motor is turning and it is a stepper motor, the driver must be telling it to do so.
If the driver is turning the motor, it must be getting step commands.
The step commands could be noise on the signal lines, or they could be real step commands from Mach.

Check:
Get some LEDs and some suitable resistors and hang them on the driver outputs.
Can you see the LEDS changing from on to off and back?

Kill the Mach program. Are you still getting creep? If so, noise somewhere in the cabling is to blame.
If you are only getting creep after starting Mach, but issuing a command stops the creep, then maybe your version of Mach is outputting step commands very very slowly. Hang a LED and resistor across each of the the Step and Dir lines: can you see any pulses?

Note: a few of us have seen Mach continue to issue jog pulses after we have taken our fnger off the jog key, and issuing another command stops the movement. However, such events are rare. If it is happening to you reliably ... ummmm ... problem.

Cheers
Re: Y-axis "creep"
« Reply #2 on: December 26, 2011, 04:49:57 AM »
I have had this problem in the past. Solved it by changing the active hi/lo on the affected drive.

Neptune
Re: Y-axis "creep"
« Reply #3 on: December 27, 2011, 10:10:36 AM »
I have had this problem in the past. Solved it by changing the active hi/lo on the affected drive.

Neptune

I assume you did this in Config, Ports and Pins?
Re: Y-axis "creep"
« Reply #4 on: December 29, 2011, 04:20:14 AM »
Yes, config, ports and pins, motor outputs. Make sure that all your axis motors (X, Y & Z) step and direction, are either all active high or all active low.

I have found that if you have a mixture of some active high and some active low, it results in the creep which you are seeing.

Neptune

Offline Tweakie.CNC

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Re: Y-axis "creep"
« Reply #5 on: December 30, 2011, 07:28:38 AM »
Quote
Yes, config, ports and pins, motor outputs. Make sure that all your axis motors (X, Y & Z) step and direction, are either all active high or all active low.

I have found that if you have a mixture of some active high and some active low, it results in the creep which you are seeing.

Neptune,

Whilst I do not doubt you cured your problem in the way in which you say there is really no evidence to support the above statement. Mach allows a mixture of active HI / LOW without issue.

Tweakie.
KEEP SAFE !
Re: Y-axis "creep"
« Reply #6 on: December 30, 2011, 10:31:48 AM »
After shutting everything down and rebooting my PC running Mach3, my problem appears to have gone away. It must have been noise coming from somewhere, but I don't know where. I'll pay attention to see if it recurs.

Offline rcaffin

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Re: Y-axis "creep"
« Reply #7 on: December 30, 2011, 11:14:37 PM »
Whilst I do not doubt you cured your problem in the way in which you say there is really no evidence to support the above statement. Mach allows a mixture of active HI / LOW without issue.
I agree that MACH can handle it, but perhaps the electrical configuration was more susceptible to one polarity? Which implies a problem with ground and +5 V of course. That I CAN imagine.

Cheers