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I'm Losing Position HELP!!!!
« on: October 03, 2008, 12:15:25 PM »
Hello, i just got my retrofitted hurco cnc mill working.  I have a package from kelling, nema 34 servo motors, breakout board, 320 gecko drivers, 500 line US digital encoders.  I wrote a program using mach3 to run +11 inches to zero 240 times and i lose about .030 from position.  I do have indicators on both positive and 0.000 positions.  US digital offers a board which keeps tract of exactly the position of the encoders. (It seems) http://www.usdigital.com/products/interfaces/pc/internal-card/
will mach3 work with this card so can be sure i wont lose posiition?  Can anyone tell me a way or something i can buy so i know i wont lose postion?  i already tried to increase the frequency width,  (doesnt work).
Can anyone tell me what the "servo Serial Link Feedback" option is in port setup and axis selection?

Re: I'm Losing Position HELP!!!!
« Reply #1 on: October 03, 2008, 02:10:05 PM »
I assume you're doing this with rapids?  If so, then the first thing to do is repeat the test at a slower speed, and slower acceleration.  If the servos are faulting anywhere along the way, you'll lose position.  Is the position loss at both ends of the travel, or just one? 

Ray L.
Santa Cruz, CA
Ray L.

Offline Hood

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Re: I'm Losing Position HELP!!!!
« Reply #2 on: October 03, 2008, 04:38:24 PM »
Is it just one axis?
Could it be backlash?
 Does it move the correct distance in one move and is just losing after repeated runs?


Offline RICH

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Re: I'm Losing Position HELP!!!!
« Reply #3 on: October 03, 2008, 11:38:18 PM »
.030/240=.000125" per move, What is your standard for the 11"? Are you picking that up on your indicators?
Re: I'm Losing Position HELP!!!!
« Reply #4 on: October 04, 2008, 01:59:35 AM »
I did put an indicator on each end and the true position moved always moves to the negative.  i tried the test with different speeds and acceleration rates, the more rapid the travel the more loss of position i have, acceleration doesn't seem to matter.  it seems to make a few correct moves then will lose .002 thousands / inch.  repeated loss the more times i move.  its a ballscrew and the backlash is minimal.  everything is keyed so i know nothing is slipping.  i only tried this test in the Y axis as the X is still tight and i want to replace the thrust barring's and adjust the Gibb.  I'm using the readout from Mach3 and have magnetic base indicators on the table to each side of the spindle.
Re: I'm Losing Position HELP!!!!
« Reply #5 on: October 05, 2008, 03:03:57 PM »
You are going faster than the geckos can push the motors so you need lower count encoders if yo need the speed.  Remember 500 in quadrature is 2000 transitions per revolution.  So if you have it a 3:1 belt and a 5tpi screw that is 30,000 steps per inch Geckos are not made for that.
I have some of these drives on a bridgeport mill they are running nice,  I have the Viper 200.  This is the best deal for servo drives.
« Last Edit: October 06, 2008, 12:00:43 AM by DennisCNC »
Re: I'm Losing Position HELP!!!!
« Reply #6 on: October 06, 2008, 12:36:04 AM »
Hey, after countless hours dismantling, changing settings, moving wires around to differnt drivers...... i finally found the problem.  A loose connector to the endcoder.  Now it goes to perfect position every time.  Thanks everyone for the support!!!!!

Offline Bodini

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Re: I'm Losing Position HELP!!!!
« Reply #7 on: October 06, 2008, 01:09:46 AM »
For any future readers of this post, contaminants (dust) on the hub disk can also give strange results and drive you crazy.  haha, hehe!