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IndustryArena Forum > Machine Controllers Software and Solutions > Fanuc > Fanuc 0T-A Z axis run away on power up
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  1. #1
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    Fanuc 0T-A Z axis run away on power up

    I have a Simco HL-320 with a Fanuc 0T-A and when I press the power button a second time to power up everything the Z axis moves in the -Z direction as long as I hold the button. The hydraulic pump also comes on as long as I hold the button. It all stops when I release the button. I do not think the axis should move and the hydraulic pump should stay on. Any ideas where I should start looking?

    I've checked all my fuses. Could a bad encoder cable cause the axis to run away on power up?

  2. #2
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    Quote Originally Posted by forhire View Post
    I have a Simco HL-320 with a Fanuc 0T-A and when I press the power button a second time to power up everything the Z axis moves in the -Z direction as long as I hold the button. The hydraulic pump also comes on as long as I hold the button. It all stops when I release the button. I do not think the axis should move and the hydraulic pump should stay on. Any ideas where I should start looking?

    I've checked all my fuses. Could a bad encoder cable cause the axis to run away on power up?
    no,your solution it is easy,look for the Z+ hard limit switch that i think it is stucked,should be near the end of the Z+ direction,it is a limit switch.

  3. #3
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    Re: Fanuc 0T-A Z axis run away on power up

    Quote Originally Posted by zavateandu View Post
    no,your solution it is easy,look for the Z+ hard limit switch that i think it is stucked,should be near the end of the Z+ direction,it is a limit switch.
    Limit switches were definitely bad/intermittent. I cleaned the +Z and the axis stopped running away. I ordered new switch internals as the contacts looked pretty worn.

    It's still not latching the hydraulic pump as expected so I suspect I still have another issue. I cannot jog or home either axis. Any thoughts?

  4. #4
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    May 2016
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    526

    Re: Fanuc 0T-A Z axis run away on power up

    Is it phased correctly as may be problem if not it will be one of your limit switches

  5. #5
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    Re: Fanuc 0T-A Z axis run away on power up

    Quote Originally Posted by mbservice View Post
    Is it phased correctly as may be problem if not it will be one of your limit switches
    The phase is correct, at least for the pump I checked. The pump that isn't latching on is external so it's possible it's reversed. I'll check that.

    After I cleaned the switches I'm still not seeing one of my limits at the honda connector so I'm hunting a bad cable. Hopefully once I get the limits sorted it will start up correctly. My schematic is very hard to read so it's taking longer than expected to trace the thing out. I think I need to energize the 24V circuit and start checking with a test light.

  6. #6
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    Re: Fanuc 0T-A Z axis run away on power up

    I spoke with Danobat-Marathon in Texas, who has been very helpful in sourcing spares for this old machine, and they indicated that the DC drives have to be adjusted using a battery whenever anything changes. I've been waiting for the instructions. I did swap out the Z axis drive for a spare I had rebuilt and replaced the flaky limit switch. It no longer runs away but I'm still not able to get the drives to indicate ready. Press power button, pumps come on, and then 401 SERVO ALARM: (VRDY OFF). I did manage to find a manual in Russian for the drives. The drives are Stromag CVT 025.4. The lathe was sold in the EU as the EEN-320. At least now I know what the lights mean. Tomorrow I'll try again and see if I can catch which lights come on the drives.

    Does anyone know how to adjust DC drives using the battery method?

  7. #7
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    Re: Fanuc 0T-A Z axis run away on power up

    did u have on the operator door a double check closing limit switch?
    check that if u have

  8. #8
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    Re: Fanuc 0T-A Z axis run away on power up

    It has been a few months. I've been busy on other projects. I did get a schematic of the battery test box and built it a couple months ago but never got around using it. Today I used it to validate the drives and I was able to home the X axis. I figured I'd upload the schematic as it may help others. Now that I understand the process, I likely could have done most of the testing without building the box.

    Now I just need to sort out the limit and reference switches once and for all. I've attached the schematic. If I'm looking at this correctly XT10-017 should supply +24V from the control DC power supply through the limit and reference switches. Any suggestions for testing them? Test light at the Honda connector? What is the best place to ground the test light when probing for +24V?

    I have replaced all of the Z axis limit switches already. One of them was flakey. Unfortunately it didn't sort the issue. zavateandu, I'm certain you nailed it originally. I just need to find the bad connection.

  9. #9
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    Re: Fanuc 0T-A Z axis run away on power up

    I made a little progress but still can't get the Z axis to home. I found if I remove connection 16 on the Stromag Z axis drive the machine will latch on and allow me to jog/home the X axis, open/close the chuck, start/stop the coolant pump, and it's running the oiler. I was able to verify a lot of stuff.

    It will not work if I simply remove the axis drive entirely. Interestingly, connection 16 on both drives are daisy chained together. The manual states this is the release/deblocking connection (translated from Russian). If I touch the blue wire to 16 on the Z axis, the machine instantly delatches. When I measured the voltage on 16 and 17 on the Z axis I read 15V. I read zero volts on the X axis. I guess now I need to discover what can cause the axis drive to release. The lights indicate both are enabled. When I swap the axis drives the behavior is the same, it doesn't follow the drive.

    My guess at this point is that the controller is signaling a stop condition to the drive. I'm back to limits... again. Is there a way to look at the limit states on the controller? I've been checking everything I can with the test light but maybe I have a bad connection at one of the Honda connectors.

    The best I've been able to glean from the Russian manual with German schematics is:
    1 & 2 setpoint input 1 (translated from Russian)
    16 & 17 Release/Deblocking
    21 & 22 Ready/Operational (betriebsbereit in German on schematic)
    Attached Thumbnails Attached Thumbnails IMG_4110.jpg   IMG_4111.jpg  
    Attached Files Attached Files

  10. #10
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    Re: Fanuc 0T-A Z axis run away on power up

    Way Lube Oil Tank is low?. I've seen some machines lockout Z movement if, a low level condition triggered.

  11. #11
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    Re: Fanuc 0T-A Z axis run away on power up

    Quote Originally Posted by machinehop5 View Post
    Way Lube Oil Tank is low?. I've seen some machines lockout Z movement if, a low level condition triggered.
    Good thought. Fluids are all topped up. I'll check the float signals tomorrow. I can see way lube moving. I don't see any flags in DGNOS 0700, 0701, or 0712, but the manual clearly states that not all switches are present in the DGNOS.

    Maybe if I can find the Fanuc signal pinout for the Honda connectors M2 & M4 I might have a better idea of what the axis drives are expecting. I don't see any voltages on 1 & 2 or 21 & 22 on either axis so I'm not sure what the signal from the velocity controller might be. Maybe I'll hook up the scope tomorrow and see what I can find.

    Is it possible to swap the axis Honda connectors and test the Z axis as X?

  12. #12
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    Re: Fanuc 0T-A Z axis run away on power up

    Quote Originally Posted by machinehop5 View Post
    Way Lube Oil Tank is low?. I've seen some machines lockout Z movement if, a low level condition triggered.
    I checked all the fluids. Spindle was a little low but still above the float. Traced out a few more things but it still won't clear.

  13. #13
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    Re: Fanuc 0T-A Z axis run away on power up

    Does your machine have a Shear Ring on the Z axis Screw. There would be a Limit Switch on it. Shear Rings are the last line of defense from major crashes...

    Or maybe its a Clutch type
    Click image for larger version. 

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  14. #14
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    Re: Fanuc 0T-A Z axis run away on power up

    Quote Originally Posted by machinehop5 View Post
    Does your machine have a Shear Ring on the Z axis Screw. There would be a Limit Switch on it. Shear Rings are the last line of defense from major crashes.
    I hadn't noticed any shear rings on the Z axis screw but I may have to remove the covers to see them. Looking at the schematic more carefully I believe I need to find switches S271 and S273, they are the Ref X and Ref Z. The part list indicates they are Balluff BNS 519-99-D-11. I haven't noticed them but the hunt is on.

    Attachment 419250

  15. #15
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    Re: Fanuc 0T-A Z axis run away on power up

    Well it appears the schematic and my machine vary slightly. I do not have any single switches. The X axis has a two double switches and the Z axis has a single quad switch. It appears to be decel and limit in each extreme. The schematic only shows 6 switches not 8. I did verify all the limit switches are appearing or toggling in diagnostics. I'm confident the limit switches are working.

    I hooked connection 16 (+15V release) back up to the Z axis drive and re-attempted to power.

    I'm back to the original problem from day one. I press the power, the Z axis moves forward about 0.75", and generates an Error 420. The manual states this is Z axis position deviation amount during stop is greater than setting value. See the photo, you can see the movement in the way oil.

    When I had the #16 release wire off I attempted to use the MPG to move the Z axis very slowly. The counter would move BUT the motor would not, and would generate the same error. The axis drive works fine on the X axis when I swapped them. The X and Z motors are the same. Could I have a brush issue on the Z axis motor?

    Click image for larger version. 

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  16. #16
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    Re: Fanuc 0T-A Z axis run away on power up

    i will go for power cable between motor and servo drive,check it closely or change it

  17. #17
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    Re: Fanuc 0T-A Z axis run away on power up

    Quote Originally Posted by zavateandu View Post
    i will go for power cable between motor and servo drive,check it closely or change it
    I disconnected the drive from the Fanuc velocity controller and hooked up the battery tester set at zero volts. When I enable the drive it moves. I've adjusted pot1, which appears to be the setpoint (sollwert in German?). With some fiddling I can get it to reverse or move forward depending on the adjustment but I can't seem to prevent the movement. Maybe I need to adjust something else? I've attached a screen shot of the pots and their description in German (from the Russian manual). Anyone familiar with German terms?

    Attachment 419418

    A tech familiar with these machines sent me these details when he sent me the battery box details a few months ago.
    Typically the drive needs to be ready and the velocity loop needs to be tuned first before the full closed loop would act normally.
    this means two things to start with:
    - the offset needs to be adjusted so that the motor is not creeping with the drive enable on and analog setpoint switched to 0V.
    - next the drive step response needs to be adjusted so that it reaches the desired speed relatively quickly but no overshooting.
    - if the axis runs away uncontrolled after enabling and no adjustments would stop it, this would be a case of bad tach generator feedback.
    After the drive is acting ok using the battery box, the analog output and the drive enable from the NC control can be reconnected.
    - if you keep getting v-ready off at this point, something else is wrong in the system related to emergency stop and drive enable logic.
    - when the axis becomes active and holding position the tuning needs to be completed in closed positioning loop.
    - if the axis worked ok with the battery box but running away in closed loop the position feedback is bad, either missing or opposite direction.
    - the actual pos. loop gain must be adjusted to match the proposed loop gain (adjust the tach feedback pot to fine tune this)
    - the actual pos loop gain need to match between any two axis involved in circular interpolation otherwise the circles comes out oval.
    - after the pos loop gain shows correct on both axes, the velocity loop P-gain can be turned up slowly until the motor starts vibrating, then back down to about 80% of that. I know this does not sound very scientific but this is kind of of rule of thumb for field adjustment to achieve reasonably good drive response quickly without a lot of measurements.
    - there is a lot more to drive tuning and a lot more can be done in a lab environment but all the above is necessary for a good start in a reasonable time frame.

  18. #18
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    Re: Fanuc 0T-A Z axis run away on power up

    I hooked up the oscilloscope to the tachogenerator input on the drives today. The Z axis encoder is sending some crazy noisy signal, nothing like what I'm seeing on the X axis. I suspect the tachogenerator is bad or I have a bad wire someplace.

    Manual states the Tachogenerator is part #T2435. Now I need to see if it can be cleaned or replaced.

  19. #19
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    Re: Fanuc 0T-A Z axis run away on power up

    I tore into the tachogenerator today. I didn't look dirty but I decided take it apart and check everything. The brushes had very little wear. Commutator wasn't too tarnished. Wires all tested good. Cleaned and re-assembled. The only difficulty was re-installing the snap ring that retains the stator on the shaft. In order to install I had to compress a belleville spring washer. I ended up turning a simple tool to drive the snap ring on while compressing the spring with a bar clamp. Turning the motor by hand I measured consistent voltage.

    Attachment 419530Attachment 419532

    After hooking everything back up I could see a huge improvement. Previously the motor would jump forward about 3/4 of an inch (~19 mm), now it only moves about 1/4 inch (~6 mm). I was able to rough tune it in until the carriage only moved a little, and one time the machine actually started error free. Yeah, all I need to do is to tune the DC axis drive. Perfect job for the morning.

    Now if I could only find a manual for the Stromag CVT drives in English.

  20. #20
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    Re: Fanuc 0T-A Z axis run away on power up

    I have been able to get the drive adjusted rough enough to start the machine but when I attempt to move the axis, even slowly, it lunges about 2" (50mm) in the wrong direction. One time I was able to get the motor to move more slowly but still reversed. Anyone experienced with Stromag drive tuning?

    UPDATE: After I posted I realized I hadn't swapped the axis drives to see if the problem followed the card. Turns out the Z axis is still crazy with the known good X axis drive. It appears the issue is likely on the Z axis motor, tachogenerator, encoder, and/or wiring. At least now I can stop turning pots for a while and trace wires.

    The encoder is a Heidenhain ROD 426A. It's 5V TTL incremental with 1500 PPR. I checked all the connections from the encoder to the AMP connector. One wire was loose and I resoldered it but no change in behavior. Could a bad encoder cause this issue?

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