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Author Topic: Losing steps or something?  (Read 53890 times)

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Re: Losing steps or something?
« Reply #20 on: September 24, 2010, 04:39:48 AM »
Hi, guys.  Thanks for the input.  To address your concerns and questions:
The specs on the gecko drives allow them to be set for +5V or 0V common.  I've verified this and tested both ways since the PMDX breakout board and the CNC4PC breakout boards both have selector jumpers to set this.  As I posted earlier, when I recently tried running in 0V common, the machine was very jerky...  +5V ttl style signals seem to work best. 

However,  Due to my Y axis being inverted as to the Dir polarity as compared to the X axis, it doesn't surprise me that the X and Y axes are offsetting in opposite directions.  All Step pulses are set to active lo, as per the manual.

The gibs on the ways are carefully set.  Also the running of the program multiple times accumulates error.  Gibs and backlash would play within their bounds.  Also, the pulleys aren't slipping as I have checked that carefully.  The Screw pulleys are keyed as were the original dial carriers, and the motor pulleys have set screws into the flats on the shafts.  The mechanics of this machine are Very stiff and solid.  Total lost motion measures <.0003”.

I'm in the process of trying to find some suitable 4 conductor shielded cable of about 16Ga. To re-wire all the way from my Geckos, to the motors.  When I get this done and test it, I'll report back.
Don
Re: Losing steps or something?
« Reply #21 on: September 24, 2010, 10:15:17 PM »
Hi I am new in this world (CNC), few days ago, I launch my first works, after I configured Mach3, following word by word the instructions from the manual, when I ran the first job (my companies logo) just using a pencil (after I did all tests and checked de precision of movements and positions) I saw with deception, my machine after 1200 lines, goes erratic in positions, while the screen wich follows the tool path was correct.... in this way I tought, it is not troble from the software, it is probably concerned to the tuning of motors or a mechanical problem... it was both... some pieces of garbage on the leadscrews, and the values of speed and acceleration in motor tuning... well, after many changes and tests, reducing speed and increasing acceleration, finally, the machine is runing  ok.
I think your problem is similar, I Hope the solution be in the same way..
Re: Losing steps or something?
« Reply #22 on: September 29, 2010, 04:54:37 AM »
Hi, again.  I've been trying a few things...
   
I twisted the power supply wires and rerouted the Gecko outputs and got no change in the behavior of my mill.  Then I had a flash.  I disconnected the power and signal lines from the Y-axis Gecko drive.  Then I ran the diagonal program with line 5 reading G1X+.1Y+.1 and the X axis still offset +.005, as before.  I don't believe the motor drives or power supply is causing the offsetting.
   Next I swapped the X and Y signal headers on the PMDX B.O.B. And changed the Motor Outputs in the ports and pins accordingly.  Ran the above program, results: Now the Y axis offsets -.005” and X returns to zero perfectly.
   I then swapped X and Y axis headers on the B.O.B. But didn't change the motor outputs back and ran the test.  Results:  X-axis is offset +.005, and Y axis is returning to zero perfectly.
   In Motor Outputs, I changed the Dir Active Low on the X and Y axes.  They had been checked for X and “X'ed” for Y.  The X and Y axes were still swapped but directions are now reversed.  The result:  X axis is perfect but Y axis is offset -.005”.
   I put things back to their original configuration except that the directions in Motor Outputs were still swapped.  The result was X axis offsets +.005” and Y axis returns perfectly to zero.
   I put everything back to original, except I left the X-axis Direction “X'ed” (reversed).  Now when I ran the program The x axis was moving in the wrong direction, but both axes returned to zero!
   I reversed one pair of output wires from the X-axis Gecko drive.  The machine ran the program perfectly.
   I changed line 5 of the program to read G1X-.1Y+.1 and ran the test.  The result is that the X axis offset -.005” and the Y axis returned to zero!
   I changed line 5 of the program to read G1X-.1Y-.1 and ran the test.  Result:  Both axes offset -.005”.
   I changed line 5 of the program to read G1X+.1Y-.1 and ran the test.  Result was X axis returns perfectly to zero but the Y axis offsets -.005”.
   I then changed the program back to its original G1X+.1Y+.1 and both axes returned to zero.

By changing the Dir Active Low of the X axis, I've changed the direction of the offset to -.  When the machine is commanded to move an axis in the positive direction, it will return to zero when commanded correctly.  But is an axis is sent negative, and more than one axis is moving simultaneously, then the axis that is going negative will accumulate steps in the negative direction.
   Logic, anyone?  It seems that the problem is in the computer.  Either in the way the parallel port is interpreting the instructions or in the Mach signal generation or something...  Current configuration is that the ports and pins  Motor Outputs are all “ Dir Active Hi”  and when multiple axes are commanded to move and return to zero, the axis/axes that are commanded to move in the negative direction and return to zero are getting an extra step in the negative direction for each iteration of the program!!!   
   I guess my problem now is to determine the cure.  Help!
Don
« Last Edit: September 29, 2010, 05:02:07 AM by cncnovice2 »
Re: Losing steps or something?
« Reply #23 on: September 29, 2010, 05:00:44 AM »
   

I'll try to un-install the Mach program and delete the folders and reinstall when I can to see if that changes anything.  I doubt it as the problem has occurred with 2 computers and 2 versions of mach3. 
I am curious as to what Enhanced pulsing doed in General Config. It is checked in my setup, and seems to be the default setting. 
 Don
« Last Edit: September 29, 2010, 05:06:59 AM by cncnovice2 »

Offline rcaffin

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Re: Losing steps or something?
« Reply #24 on: September 29, 2010, 06:19:35 AM »
It seems that the problem is in the computer.  Either in the way the parallel port is interpreting the instructions or in the Mach signal generation or something...

Hum ... I agree with your logic (I think), but why you and apparently no-one else? But i would try to bring this to the attention of Artsoft, methinks.

Cheers

Offline Dan13

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Re: Losing steps or something?
« Reply #25 on: September 29, 2010, 07:48:34 AM »
Hi Don,

What keeps confusing me is that you're seeing the problem only when there is motion on two or more axes, but never when it's a single axis move.

Would be still interesting to eliminate the breakout board from the equation. I know you tested with two different ones, but anyway. When you tried running the Geckos directly from the PP did you do it with both computers and they both had insufficient voltage going out from the PP? Can you find another PC with a PP that would output 5VDC signals, or find a PP card with 5VDC to install in your current PC?

Dan
Re: Losing steps or something?
« Reply #26 on: September 29, 2010, 05:26:37 PM »
I have substituted a CNC4PC model C10 B.O.B.  and it had no difference in behavior.  I'm trying to cobble together a pc with an Asus A-7N8X-E delux motherboard,  It is about 6 years old.  It would be nice to bypass the P.P. completely, but I'll have to see...   I've been wondering if the SmoothStepper would work.  It is a possibility if it doesn't create another can of worms.
Don

Offline rcaffin

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Re: Losing steps or something?
« Reply #27 on: September 29, 2010, 05:51:04 PM »
You know, I can't help feeling that you are chasing a lot of dead ends. Sorry, but. Why so?

You seem to have found that the problem is highly reproducible. That argues against random noise.
You seem to have found that the problem is a function of the number of repeat cycles. That certainly is not random noise.
You seem to have found that the problem is not dependant on which motor or which servo driver is used.
I very much doubt that BoBs have anything to do with that.
I very much doubt that the actual CPU board has anything to do with that.
I very much doubt that the PP device has anything to do with that.

This seems to leave the software: Mach and the XML files.

My 2c.

Cheers

Re: Losing steps or something?
« Reply #28 on: October 01, 2010, 05:26:11 AM »
Hi, again.  I hooked up a digital volt meter to the direction pin of X axis of the parallel port on the Intel based computer.  When I powered up the computer, the pin went to 3.3V.  As soon as I start Mach3, the pin goes to zero volts.  I expected it to toggle back and forth when the program runs, but it stays reading 0V the whole time...   Pins used are pin 3 is Direction and pin 18 is common. 
   My setup is configured so that pin 2 is X-axis step, Pin 3 is X-axis Dir., pin4 is Y-axis step, pin 5 is Y-axis direction, etc.  Since I twisted the one pair of X-axis motor leads, all three axes are direction active “hi”.  All step pins are set active low.
   The old PC Chips computer has a NetMos PCI parallel port card on it that I used with an MPG.  I decided to check it out.  When firing up that computer, the NetMos reads 5.0V on pin 3 until I start Mach3.  Then it too goes to 0V.  I set all the motor outputs to port 2 and plugged it into the PMDX breakout board.  Running the diagonal program X+ Y+ resulted in both axes offsetting -.005”.  Running the program with X- and Y- yields perfect return to zero.  Yada, yada.  It seems that with this parallel port card the polarity of the direction of commanded movement under which the error occurs is reversed from the other computer.  The error is still offset to the negative direction as with the other computer, but now it only occurs when the affected axis is starting out in the positive direction.  Strange.
   I then tried to take the breakout board out of the equation.  I have a D-sub 25 male connector that I have used that has 3 separate shielded cables with 4 conductors each.  Each cable is wired for an axis so that I can hook it up to a gecko drive directly.  Shield goes to earth ground.  One wire to com., one to step, and one to direction.  As the Geckos are set to +5 volt logic, it should work.  Right?  Result is no movement at all.  I checked everything but for some reason, even the NetMos 5V card doesn't drive the Geckos.  Huh?  I'm not sure how this TTL stuff works.  And yes, I tried reversing the Step and direction settings.  No dice.
   I plan to hook up the NetMos PP card in the new computer soon, installing the drivers was a pain last time, and then see what effect that has on the symptoms...

Thanks for your help,
Don

Offline Dan13

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Re: Losing steps or something?
« Reply #29 on: October 01, 2010, 08:33:52 AM »
Don,

It is normal - when starting Mach it takes over the PP and pulls low all the pins. What is not normal is that you don't see the direction pin changing state when moving the axis in different directions. This is strange. You didn't have anything connected to that pin when doing the measuring, did you? I don't know why that would happen...

Where did the D-sub 25 connector go in? How did you plug into the PP DB25? Can you measure the voltage of say the direction pin while it is not connected to the Gecko and compare it to the voltage when it is connected to the Gecko?

Dan