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Author Topic: Mach lathe losing position  (Read 6501 times)

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Re: Mach lathe losing position
« Reply #10 on: March 19, 2012, 03:30:43 PM »
20,000 steps per Inch, and 200 IPM

Offline Hood

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Re: Mach lathe losing position
« Reply #11 on: March 19, 2012, 03:37:41 PM »
20,000 x 200 = 4,000,000 steps per min
4,000,000 /60 = 66666.666666666 steps per second or Hz so divide by 1000 to get KHz so 66.666666666KHz is what you need so pick next nearest above which for SS is 128KHz
Hood
Re: Mach lathe losing position
« Reply #12 on: March 19, 2012, 09:09:24 PM »
Thanks Hood.
Re: Mach lathe losing position
« Reply #13 on: April 02, 2012, 02:18:55 PM »
Tried all that and was still having issues. I switched from constant velocity to exact stop mode and the machine runs much much better. Is that normal?

Kevin

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Re: Mach lathe losing position
« Reply #14 on: April 02, 2012, 02:37:41 PM »
The only thing ES does is decelerate to a stop at the end of each line of code before accelerating again for the next line. CV blends the two lines together to try and keep the velocity constant.
Why it would help I dont know, slow acceleration can make sharp corner rounded but shouldnt affect dimensions on straight parts.
Hood
Re: Mach lathe losing position
« Reply #15 on: April 04, 2012, 08:22:43 PM »
What counts as "slow" acceleration? What would a "good" number be?
Re: Mach lathe losing position
« Reply #16 on: April 04, 2012, 10:49:09 PM »
Just spent some time playing with a dial indicator on my Z axis. Run the axis up to zero, then using the Inc jog buttons, back it up. Strange thing- back the axis up .001", but it "jumps" about .004". Jog back the other way, it jumps again, back to zero. Only does this on the first button push each way, I.E. only when changing direction. Each successive move in either direction moves .oo1" as it should.  This might say something about my drift issue. I wonder what the problem is- obviously not backlash as that would cause it not to reverse at all, especially not that small of a move. Maybe a gib too tight? "Stick-ion?"

Hmmmm, I'm making progress.

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Re: Mach lathe losing position
« Reply #17 on: April 05, 2012, 03:38:41 AM »
Sounds like you have backlash comp enabled.
Hood

Offline RICH

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Re: Mach lathe losing position
« Reply #18 on: April 05, 2012, 07:01:47 AM »
You will always have some backlash in a system just depends on how much. If the thrust bearings are not preloaded right you can have varying
backlash. Usualy it is not repeatable and varies some. Since it's part of the of the backlash it's difficult to isolate. ie; ball nut +screw+bearing play

What is slow acceleration?
Slow could be an acceleration value which low as compared to say the max acceleration one could use for their system. How much or percent
of max is relative. Acceleration is just a number which one can relate to in how fast the axis can change from current velocity to a higher or lower velocity.
The value for a system is directly related to motor torque since it is the motor which must provide the power / force to overcome the current inertia of the system. Acceleration is specific to your machine, thus you have the capability for some desired rate and it's acceptable or need to change something to get an increased acceleration. The value you use should be reliable ie; you can only have a reliable velocity which would be below it's max and likewise would set the acceleration accordingly.
RICH
  
 
Re: Mach lathe losing position
« Reply #19 on: April 05, 2012, 05:01:40 PM »
Backlash comp was enabled. Disabling did not change the drift issue. However, re-enabling it and change the value from .005" to .001" works like a charm. I wrote a test program to to run through a series of arcs and angles, rapids and slow feeds, and its been running through the program for two hours without losing position one bit.