Hello Guest it is March 03, 2021, 08:22:49 PM

Author Topic: Z Axis Drift Problem...Losing Counts on a Servo System?  (Read 9125 times)

0 Members and 1 Guest are viewing this topic.

Z Axis Drift Problem...Losing Counts on a Servo System?
« on: March 22, 2007, 12:44:02 AM »
Hello,

I posted a little while back on the Lazy Cam Forum that I am having problems with my Z-Axis drifting.  I thought the problem was mechanical but it wasn’t.  I have an old oscilloscope I am using to look at the signals but without a test plan I am just looking at pretty signals without knowing what to look for.  Does anybody have any suggestions?

Hardware & Software Specs:
Mach 3: Version R2.0.024
LazyCam: 2.00.032 Standard Edition

Computer: 2.53 GHz, 512 MB RAM
Drivers: Gecko G340 DC Servo
Motors: Brush DC Motor with US Digital Encoder
Machine: Homemade 3 axis Gantry CNC Router

Here is a copy of the Lazy Cam posting:

I have been having some problems with my Z axis.  I use LazyCam to import a JPEG and convert it to G-Code.  I load the code into the Mach 3 Controller.  About half way through the cutting process I notice that my cutter is no longer in the material.  It looks like the cutter has been slowly ramping in the positive Z direction.  If I look at the Z axis during the engraving process it is moving up and down the way I would expect, but it must be slowly incrementing itself in the positive (upward) direction.  However if I look at the Z axis DRO it is indicating a negative value which would seem to indicate that the cutter should be in the material.  Am I missing a setting? I am confused.  Any suggestions?

I am using the following software versions:
Mach 3: Version R2.0.024
LazyCam: 2.00.032 Standard Edition

Thanks.


Also here is a copy of the first  few lines of the G-Code

N45  G1 X5.4960  Z-0.0750  F60.00
N50  Y0.0160  Z-0.0671 
N55  Y0.0240  Z-0.0703 
N60  Y0.0320  Z-0.0662 
N65  Y0.0400  Z-0.0680 
N70  Y0.0480  Z-0.0703 
N75  Y0.0560  Z-0.0677 
N80  Y0.0640  Z-0.0653 
N85  Y0.0720  Z-0.0677 
N90  Y0.0800   
N95  Y0.0880  Z-0.0686 
N100  Y0.0960  Z-0.0668 
N105  Y0.1040  Z-0.0674 
N110  Y0.1120  Z-0.0653 
N115  Y0.1200  Z-0.0677 
N120  Y0.1280  Z-0.0653 
N125  Y0.1360  Z-0.0645 
N130  Y0.1440  Z-0.0688 
N135  Y0.1520  Z-0.0697 
N140  Y0.1600  Z-0.0671 
N145  Y0.1680  Z-0.0656 
N150  Y0.1760   
N155  Y0.1840  Z-0.0665 
N160  Y0.1920  Z-0.0677


Thank you.

Regards,
Bob
Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #1 on: March 22, 2007, 08:42:33 AM »
Did you get the cable drivers for the US Digital encoders? I Have had problems in the past with noise on the encoder lines if I didn't use them (They are only about 10.00USD)
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com
Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #2 on: March 22, 2007, 09:14:14 AM »
Thanks Brian, I will try that next.  Any other troubleshooting suggestions?
Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #3 on: March 23, 2007, 12:57:54 AM »
I Think i Know what the problem is
The Multiplier Board on the G340
I have a same problem
Mine is set to 1X turns out on direction changes you can lose steps
You can By Pass the Multiplier board by removing it and putting a opto in its place
I Don't remember the PN3 but there is one the mx board for reference
it is soldered in though.
I Blew one of my drive by trying to hook up encoder shielding,
Forgot to power down and my ERR\RES jumper made contact with ARM+
Poof drive was assassinated!   Hope Marris can overnight a replacement
Will post back when i get my opto installed  (UPS please come soon)
You can test this out if you put a 20ms pause before a direction change
Marris is working on a MX Replacement board upgrade to fix this problem
based on some new fancy chip released

Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #4 on: March 23, 2007, 09:40:23 PM »
Got my opto's in today
fixed the problem
i repeated the same gcode 300 times
no more drift
Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #5 on: March 27, 2007, 01:08:53 PM »
Cybertek, Wow, how were you able to pinpoint it to the mulitplier board?  The funny thing is I don't even need the multiplier, I got it because at the time I thought it was a good feature that would provide some flexibility to my design. 

I can't even begin to tell you how many different tests I have done to try and find the problem.

Does the mfg of G340 post these design bugs anywhere?  Do you think they would be willing to swap the hardware if this is a design flaw?

Anyway I had some specific questions about your post

"You can By Pass the Multiplier board by removing it and putting a opto in its place
I Don't remember the PN3 but there is one the mx board for reference
it is soldered in though."

What is a:
- opto
- PN3
- mx

How do you remove the multiplier board?
Are there any rework instructions posted anywhere?
Rather than making changes to the driver hardware would it be easier to purchase the G320?

Thank you.

Regards,
Bob
Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #6 on: March 27, 2007, 02:42:25 PM »
With lots of frustration but marris is the one that sugjested the solution
A G340 is a G320 the 340 has the extra Multiplier board added
Order HCPL2531-ND from Digi-Key or Gecko
pop the cover remove the multiplier board it 1x1 board
pop the opto in its place they cost 1.63 each
Your Problem is solved
Marris of Gecko is working on a upgrade board to solve this problem
but it is not a design flaw it is us pushing technologies to there limits
when i purchesed my drives i thought to this would give me more options
Turns out i should have used stepers insted for my application
but i thought servo drives were the Hot Items of the industry

Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #7 on: March 28, 2007, 02:28:42 AM »
Thank you very much for the info.  I have spent the last several months and several hundreds of dollars (new cables, new couplings, etc.) trying to fix this problem.  You may have saved me from pulling my hair out and several more dollars and hours of troubleshooting.

I wish this was disclosed up front!  It is not a big deal so long as you know about it.

I ordered the parts from digikey but I would still like to exchange them for the G320 just in case any new bugs are discovered I know I am working off a known design configuaration rather than having modified it myself.  I am very conservative when it comes to tracking design changes.  I have been burnt before:-)

Last question.  How do you know which way to plug in the opto or does it matter?

Thanks again for the help.  I REALLY appreciate it.

Regards,
Bob
Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #8 on: March 28, 2007, 12:39:44 PM »
Look at the opto on the Multiplier Board
Same as that one is placed

or

close to the Dir connector
look at the drive with the connection terminals facing you

                           . . . .
                           . . . .
                    pin1 '

0 0 0 0 0 0 0 0 0 0 0 0
                        dir step Com


Hope this helps
Re: Z Axis Drift Problem...Losing Counts on a Servo System?
« Reply #9 on: March 29, 2007, 01:15:11 AM »
Well I contacted sales at gecko and they basically said the same thing you suggested.  That is, pull the daughter board and insert the opto, which they offered to send me for free.

When I get this done I will come back to the post and let you know if it solves the problem.  I hope so!

Thanks again and your directions are great, thanks for the help.

Regards,
Bob