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Author Topic: Gantry Alignment Issue  (Read 2681 times)

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Gantry Alignment Issue
« on: July 12, 2010, 02:58:34 PM »
Looking for help with a gantry driven CNC Router custom build.  Equipment summary:

Dual 1288 oz steppers, Automation Direct, with 5-1 gearbox and rack and pinion.  (X with A slaved)  
A defined as linear
both drives wired to different pins on port with A's direction reversed.
When running manually, all is well, put under higher speeds, 300 ipm, i seem to be loosing steps.  
Any idea to ensure how X and A get the exact same input?  Both have been verified to have and identical motor tuning model.

Any ideas would be greatly appreached.

Offline ger21

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Re: Gantry Alignment Issue
« Reply #1 on: July 12, 2010, 10:16:18 PM »
What kind of drives, and what voltage are you running at?

What is the motors rpm at 300ipm?

If you have the axis slaved, then they're getting the same signals.

The bigger the stepper, the slower they spin. I'm thinking you're just trying to spin them too fast, especially with the 5:1 reduction.

How big is this machine? Those are some pretty big motors. I've seen 5ft wide gantries getting over 1000ipm with  380oz steppers and 3:1 reduction. With steppers, bigger is often not always better.
Gerry

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Re: Gantry Alignment Issue
« Reply #2 on: July 13, 2010, 07:45:47 AM »
Drives are Automation Direct 1288's  running at 70v DC.
Gearbox is 5:1 planitary
drive pinion is 1.5 x 20mm on a 1500mm rack

Gantry length is approx 6 feet with 49" of travel.  machine reaches 49" x 52"

Identical setup on Y axis, getting consistant speeds at 700 ipm with no loss in positioning accuracy.  I understand the concept of bigger not always being better, but acting alone, they will run at 700 ipm.  only when both side have to drive at peak speed do i have an issue.  Lower speeds products perfect results.

Offline BR549

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Re: Gantry Alignment Issue
« Reply #3 on: July 13, 2010, 09:31:20 PM »
Are both axis loosing steps or just 1?
Re: Gantry Alignment Issue
« Reply #4 on: July 13, 2010, 10:09:28 PM »
not really sure if it is one side or the other, only that the gantry gets cocked due to one side driving more than the other.  I would think that if both are being provided the EXACT same pulses, this would be impossible given a rigid frame and quality linear bearings.  Is there an accurate way to measure which side is doing what?

Offline BR549

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Re: Gantry Alignment Issue
« Reply #5 on: July 13, 2010, 11:06:05 PM »
The only way I know is to refhome the axis or shut down the drives and relax the gantry, then move to the other end slowly(;-) and setup 2 dial indicators one on each side Zero the dials.

Then move back to the far end and command a fast move(wide open) to the other end towards the dials stopping just short of the dials then finish the move slowly to the ref point and check the dials for zero. G1 moves only at max feedrate.

Just curious but in the setup of the axis and slave is the step and dir active Hi/low the same for both the slave and master? some drives are sensitive to this setting.

Also the Gantry will have the largest amount of inertia loads Far more than Y. This may effect your acelleration settings. Try slowing down the accell and retest.