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Random Loss X-Y axis
« on: May 04, 2011, 10:05:02 AM »
Need a little help please. :'(

I've had my machine running since December.  Sometimes After long runs I get a random loss of position on my xy axis.  

What are the most common problems related to this?

I'm running the DMM Tech.- Peak 7.2Nm(1015 OZ-In) high torque AC servo motors, 3 Axis CNC kit for MACH3 on a small Bridgeport mill.

I've replaced all my hardware,  to include drivers,motors and breakout board.  (bought components to retro 2 machines so it was easy to try replacements)

tuned motor velocity as slow as 35 IPM and acceleration 2.  



Seems it mostly happens after 3 or more hours of running.

Any help is greatly appreciated.




« Last Edit: May 04, 2011, 10:11:55 AM by retro-AC-Servo »

Offline Hood

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Re: Random Loss X-Y axis
« Reply #1 on: May 04, 2011, 10:27:19 AM »
Could be a few things, noise and tuning being the top of the list. Can your drives accept differential Step/Dir signals? If they can consider making or buying line drivers to make the Step/DIir differental.
Is the error within the following error set in your drives? If its outwith then your drives should trip so if they are not then that would point to noise, if it is then it cold be tuning.
Hood
Re: Random Loss X-Y axis
« Reply #2 on: May 04, 2011, 11:25:10 AM »
I'm a little slow on terminology.  And no expert at all this.

In my driver parameters setup program there are a choice of "Pulse/Dir" "CW/CCW", "Analog", "RS232".    I have the "Pulse/Dir" set

Also In the driver parameters setup program there are a choice of: "Position Servo", "Speed Servo",  "Torque Servo" I have the "Position Servo" set


Main Gain set 72 on z  (Lifting Knee0
Main Gain set 38 on x
Main Gain set 38 on Y

also there is these settings In the driver parameters setup program
Speed Gain "38" all axis
Integration Gain "38"
Torque filter Cons "128"
Max acceleration "8"
Max speed "20"


Re: Random Loss X-Y axis
« Reply #3 on: May 04, 2011, 11:50:38 AM »
Is the error within the following error set in your drives? If its outwith then your drives should trip so if they are not then that would point to noise, if it is then it cold be tuning.
Hood
Not quite clear but if you are asking " Do the drives trip?"  Sometimes they do and other times one axis will stop all together and the other two will continue to run at a reduced speed.  Sometimes it will just loose position and continue running the program.  DRO always continues no matter what the motors are doing.
Re: Random Loss X-Y axis
« Reply #4 on: May 04, 2011, 12:42:41 PM »
I just performed a little experiment.

I ran my feed up to 70 IPM and started a simple g code to simulate cutting a arc of 6" Radius 2" deep.   beforehand I checked my "Driver Test"  which it said "system excellent"  at about 5 minutes into the simulated cut I heard a small "clunk" at which time I noticed xy was off slightly( .250").   I then ( withing a 30 seconds) performed a new driver test which it said "System Pulsing to fast".

I have no Idea why I did this but maybe it will help someone besides me figure this out.

I'm going crazy trying to figure this one out.
Re: Random Loss X-Y axis
« Reply #5 on: May 04, 2011, 12:44:21 PM »
I just performed a little experiment.

I ran my feed up to 70 IPM and started a simple g code to simulate cutting a arc of 6" Radius 2" deep.   beforehand I checked my "Driver Test"  which it said "system excellent"  at about 5 minutes into the simulated cut I heard a small "clunk" at which time I noticed xy was off slightly( .250").   I then ( withing a 30 seconds) performed a new driver test which it said "System Pulsing to fast".

I have no Idea why I did this but maybe it will help someone besides me figure this out.

I'm going crazy trying to figure this one out.

Offline Hood

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Re: Random Loss X-Y axis
« Reply #6 on: May 04, 2011, 03:16:28 PM »
What kernel are you using? Do the DROs in Mach show out of position or do they show correct.

With servos you can normally set a following error, this is the max amount that a motor can be out before a drive will trip, mine are set to 20 counts out of 8000 per rev. Some of the hobby orientated drives have a fixed following error, think Geckos are that way.
Hood
Re: Random Loss X-Y axis
« Reply #7 on: May 04, 2011, 04:36:22 PM »
What kernel are you using? Do the DROs in Mach show out of position or do they show correct.

With servos you can normally set a following error, this is the max amount that a motor can be out before a drive will trip, mine are set to 20 counts out of 8000 per rev. Some of the hobby orientated drives have a fixed following error, think Geckos are that way.
Hood
To the first question.   They look as if they are correct but they're zero's dont match the the parts zero.

To the Second Question. I have what is called and it reads like this:  "On Position Range" 1-126:  The difference between the  position command set and real motor position is than the "On Positition Range" value,  the output from Pin 5 of jp3 will be low otherwise it  will be high This option is only applical to cw/ccw, or Pulse/Direction input mode.
If the value of "On Position Range is 127 the output of pin 5 of jp3 will represent the motor alarm (fault) signal, i.e. if the motor servo is normal, the pin 5 will be low, otherwise if the drive alarm is triggered it will be high.  reference driver spec sheet to see how the alarm is triggered.

Man! windy ar'nt I

Offline Hood

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Re: Random Loss X-Y axis
« Reply #8 on: May 04, 2011, 05:17:01 PM »
Ok so sounds like as far as Mach is concerned all is on track.

What kernel do you have Mach set to? (Config menu then Ports and Pins)

What does the driver test look like when running it at the kernel you are running?

Sounds like the On Position is what most call Following Eroor. Is it a fixed value? ie less than 127 counts? Or can you adjust and if so what have you set?
Hood
 
Re: Random Loss X-Y axis
« Reply #9 on: May 04, 2011, 06:31:47 PM »
I'm set @ 25000 hz
 
As for driver test when I first "system test in green and it counts down 3,2,1 zero  I get a "pulsing too fast"... then after that in green "Mach3 taking over" It goes to "System Excellent".  Theres no line at the initial test and maybe 1/16" off of straight line bumps after Mach3 takes over.

Huey @ Dmm says I need to keep the "On Possition Range" set to 127,  which I have.

He also told me to set my "dir pulse" and "step pulse" to 2 on both.  Which I had them set @ 0 for "step" and 1 for "Pulse" 

Not sure if it fixed the problem cause it is so intermittent.

Could to slow of a acceleration be a problem?  I raised my IPM to 98 and increased my accel. and it hasn't crashed yet but now I'm too fast for the kernel speed I'm running it says.

Guess if I through enough info out there some brain will help me.
Thanks again for the help!