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  1. #1
    *Registered User*
    Join Date
    Dec 2015

    Z Axis Troubles

    Ok here goes. I posted about problems with this before I'll start at the beginning.

    The machine is a Kiwa Excel center-4 built in 1984. The control is Fanuc 3m model c. The z servo motor is Fanuc Dc 10m.

    I was running a simple program the day this started. Countersinking some parts nothing special. I went to shut the machine off after running a while and I always had to handwheel the z down on a prop board so the head doesn't drop when the machine is off. I was handwheeling the z at a slow increment and it jumped down about a half inch. It got alarms but I don't remember exactly what they were. I reset the alarm and ran the program over. It was ok running in auto. In handwheel it dropped in the z again. I think at this point the watchdog alarm led lit on the motherboard. I turned the machine off and when I went to restart later it never came back on. The fanuc manual says if you get a watchdog alarm to replace the main board. I then bought a used motherboard off of ebay. I transferred everthing in sockets to the ebay board. After putting all the boards back in I re-entered all my parameters. After that the machine started with only a servo error 34 ( z feedback cable is disconnected). I did successfully start the machine up with no error 1 time and homed it. While it was sitting with the spindle running I heard click got the servo 34 alarm again.I then took the z motor off and took it apart to clean it out and found oil from the gearbox below it inside the motor. I cleaned the whole motor with QD electronic cleaner let it dry and put it back together. After putting the motor back on I discovered if I warm the motherboard around the z encoder plug it will come up with no servo 34 error. When I try to start the servos the z tries to slam in the minus direction into my prop board before the servos shut off. The z drive then throws an OVL alarm on the front of the drive. I have tried another drive since this started happening with no change. I'm trying to figure out what to do next.

  2. #2
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013

    Re: Z Axis Troubles

    Sounds like a bad solder connection around the Z axis encoder connector. And maybe the encoder input is inverted from the original, this also could be a parameter setting. That may be why it is slamming into the prop board. Really sounds like the encoder and motor are not in agreement as to direction.

    Now what I would do is remove the entire control system and replace it with a Centroid or Dynomotion system. But I have a very low tolerance for antique controls.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
    Join Date
    Aug 2009

    Re: Z Axis Troubles

    ...check the Z axis motor Tachometer.....dirty or failing older DC Servo Tach's can cause ruff, jumpee or a Overload condition to occur during axis movement.

  4. #4
    *Registered User*
    Join Date
    Dec 2015
    Quote Originally Posted by machinehop5 View Post
    ...check the Z axis motor Tachometer.....dirty or failing older DC Servo Tach's can cause ruff, jumpee or a Overload condition to occur during axis movement.
    I removed the z axis motor from the machine and laid it over on its side. I took off the motor cap and encoder cap. With an oscilloscope I checked the voltage to the encoder it was 5 volts. The B- and B connectors both had a positive square wave that increased the faster I rotated the shaft. Z gave 1 positive pulse per rev. Z- Gave 1 negative pulse per rev. A and A- gave a positive square wave that changed with rotation speed. The encoder is model A860-0300-T001 2000p.

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