Need Help!- Z axis drifting

[Absolute Steve]

I have been having problems with a new machine I picked up. I am running servos and Wincnc. After setting it up I have everything working properly other than the Z axis wants to drift up about .050 after a run time of about 30 minutes. It slowly trends upward as the program runs on, it is not just a sudden move. I have adjusted the revolution setting in the ini file for Z and it seems to be within .005 when I check the height. Is it possible that this needs to be closer than .005? Could my Z axis encoder be bad? Bad Z axis drive?
My table has been shaved down and is level to the bit. If I cut only a couple of small parts I don't see any issues. It seems as though the more Z moves it makes the higher the Z axis will go over time. Any help would be appreciated. I need somewhere to start.

Steve

[Khalid]

Seems that something is wrong. Check following:
1- Check all the cables especially the Z-axis cable where it is connected to the controller card..Make sure you have tight connections their.. Major chances if a wire is loose.

2- Check the routing of wires ..if near the power supply, interference may occur.
3- Check steps/unit setting of Z-axis

[vger]

Check that the encoder is tight to the shaft, and that the motor is tight to the screw. Any slippage can cause a cumulative error. If the problem is in the encoder feedback, it is either missing an ocassional pulse on upward movement, or picking up extra pulses on downward movement.

You might try lowering your feed rate and/or decreasing acceleration rate and see if the problem persists at a slower speed. Are the X and Y also off at all after running for a while?

Steve

[Absolute Steve]

Hi guys,

I have tried everything that was suggested by both of the previous posts. I still have the same problem. I have been testing this with the same program each time I make a change. This program has about a 20 minute run time. When the program is finished the Z has moved up .050 to .054. I did try switching the encoder from another axis with the same results. I also switched the encoder cable with no change. Along with the other suggestions. I did a check the X and Y axis and they seem to be fine.
My acceleration rate in Z is alot less than X and Y.

In case I forgot to mention in my previous post my Z is ball screew and the others are racks.

I did read something in another post about this same problem happening to another member and they changed something in the driver? I don't have Gecko drives. I can't see any name on them other than they are light green.

Any other suggestions would be appreciated.

Steve

[LZ1TWB]

What type of servo drives are you using? You could have a problem with the drive correctly reading the encoder as they said above. Check for docs about the drive, for example I am using the UHU servo and it has error count value that I can check through the terminal software. It should show always 0.

You can check for something similar on your drive.

[vger]

Steve,

You might try a dry run without any material and see if the error still creeps in. If the encoder is good, the cable is good, and everything mechanical is tight, then the next option is the driver. If the drivers are the same, you might try switching them out to see if the problem stays with the axis or follows the driver.

Steve

[Absolute Steve]

Steve,

This does happen running a dry run. I will try to switch out the drives next. Thanks for the help everyone.

[Absolute Steve]

I tried switching the driver and was unable to run the machine because the difference between the ball screw Z and the rack X parameters programed in the driver stayed with the driver as they were switched. When I jogged the x axis it went about ten times faster than normal. And the Z was very slow. Obviously there is a something that needs to be changed to make this switch. That I don't know how to do. I put the drives back to the original position. The drivers I have are Rutex. Is it possible that the pulse count needs to be adjusted? I have looked through all my files and can not find anything that mentions pulse count for each axis, there is the word pulse mentioned in my ini file at the beginning but not for each axis. Most of this is starting to get over my head at this point. If I decide to buy a new drive for the Z axis how do I program it for the proper pulse count. Thanks Steve

[Absolute Steve]

Originally Posted by LZ1TWB What type of servo drives are you using? You could have a problem with the drive correctly reading the encoder as they said above. Check for docs about the drive, for example I am using the UHU servo and it has error count value that I can check through the terminal software. It should show always 0. You can check for something similar on your drive.

Can you give me some instruction on where to check this? The servos I have don't see any type of name on them. My encoders are US Digital.
Thanks in advance

Steve

[LZ1TWB]

I'm afraid I cannot help you if you don't have any info on the drive. It seems that it is some kind of DIY drive, because there is nothing written on it. All modern devices that are sold have some marking on them.

Try to find something similar on the net, or at least send here a picture. Maybe someone will know it.

[Absolute Steve]

Originally Posted by LZ1TWB I'm afraid I cannot help you if you don't have any info on the drive. It seems that it is some kind of DIY drive, because there is nothing written on it. All modern devices that are sold have some marking on them. Try to find something similar on the net, or at least send here a picture. Maybe someone will know it.

The drivers are Rutex. I don't have a name on the servo motors.

[vger]

Steve,

Do your drives look like one of these?
http://www.rutex.com/files/R20x0.pdf

If so... then this document should give you an idea what you are up against...
http://www.rutex.com/files/R2000setup.pdf

Steve