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IndustryArena Forum > MetalWorking Machines > Fadal > 1993 Fadal VMC40 with x axis runaway
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  1. #1
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    1993 Fadal VMC40 with x axis runaway

    Hi everyone.
    I have a 1993 Fadal VMC40.

    About a year ago my way cover rubber was torn. Coolant got into the X axis motor and destroyed my bearings.
    I took the motor out and put new bearings into it. I borked the tachogenerator and I didn't know what I was doing at the time so I bought another Glentek GM4050. I have been running this one ever since. Let's call the original motor, MOTORONE and this new one MOTORTWO.

    Fast forward to now. MOTORTWO has been running great ever since. No misses, no quirks, great.
    I had an order for 20 pieces, I made 18 and then I went on vacation for a week. When I came back, I turned on the machine, I was already at my CS marks, so I typed CS [enter] and the machine ran away towards X positive until it alarmed out.

    I was stunned. This is definitely not what had happened ever before.

    So... let's get into it:
    THE Y AXIS WORKS FINE.
    THE Z AXIS WORKS FINE.
    I had since ordered a new tachogenerator and swapped it onto MOTORONE. I just assumed MOTORTWO had gone bad.
    I wired up MOTORONE, now with new tachogenerator, and I had some runaway issues.
    The X axis is slowly moving in one direction. Since I changed brushes and what not I tweaked the SIG on the X axis encoder board until the motor stopped moving. I could not CS though, because the motor still ran away.
    I am drifting about .001 every 5 seconds.
    Here's what is very weird though. If I set the increments to tenths, and spin the wheel, the x moves progressively faster. Like the handwheel is a measure of velocity.
    The X drifts slowly at low values, but if I turn the value up or down the X moves faster.
    Does that make sense?
    The x drifts really slowly at .001, but the x drifts even faster at .250, as if the handwheel is controlling the velocity of the X axis. It never stops drifting. If I crank it up too far it alarms out.
    The Y and Z work fine. One rotate click, one movement.
    When it alarms out, the X still drifts as if it's seeing residual voltage, even before I hit manual and jog to reset the servos. After playing with the SIG potentiometer I can get the X axis motor to stay stationary, but if I move x one tenth to the negative it will continue to drift until I bring it back to zero, and then it stops again. If I move one tenth positive it will drift until I bring it back to zero, but unlike moving negative it will continue to drift.

    I swapped the wires (the white and black and 2, 3, 4, 5, and 6) to the amplifier between X and Y and the problem stayed on the motor side.
    Then I swapped the coax wires between the 1040 X and Y boards and the problem stayed on the motor side even though I was now controlling it through the Y selector on the front of the machine.
    Well, that means motor, right?
    So I swapped back to MOTORONE with its tachogenerator and the motor still runs away.

    So what are the constants? I'm still using the same X axis resolver through all of this. And the wiring.

    I take apart the rotary A axis and put the A axis resolver onto the X axis motor. It still runs away, and it's still a velocity generator like it's not getting a signal to stop moving.

    I then take the Fluke meter and put a probe on the motor side and one inside the case. With the help of a friend we probed the wires one by one and jiggled the harness measuring for a resistance drop. There was no resistance drop.

    So I've tested the harness as best I can.
    I've swapped the 1010-4 boards.
    I've swapped amplifiers.
    I've swapped motors.
    I've swapped resolvers.
    I've swapped tachogenerators.

    Here's where things get even more stupid.
    I was flipping through my blue binder and it says
    SLOT 9 is X axis 1010 board
    SLOT 10 is Y axis 1010 board
    SLOT 11 is Z axis 1010 board
    SLOT 12 is B axis 1010 board
    SLOT 13 is A axis 1010 board
    SLOT 14 is Spindle

    The card in slot 9 has a sticker on it that reads X AXIS and has jumpers 5-12, 7-10, 8-9, as the manual says it should.
    The card in slot 10 has a sticker on it that reads Z AXIS and has jumpers 5-12, 6-11, and 8-9.
    The card in slot 11 has a sticker on it that reads Y AXIS and has only one jumper, 8-9

    I'm at a loss.

  2. #2
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    Re: 1993 Fadal VMC40 with x axis runaway

    Quote Originally Posted by Paraquat View Post
    I wired up MOTORONE, now with new tachogenerator, and I had some runaway issues.
    The X axis is slowly moving in one direction. Since I changed brushes and what not I tweaked the SIG on the X axis encoder board until the motor stopped moving. I could not CS though, because the motor still ran away.
    I am drifting about .001 every 5 seconds.
    ...should have adjusted the BAL pot to correct drift.

    ...from Glentek GA370 manual which is about the same for all DC Servo systems
    snip
    5.3 VELOCITY LOOP PHASING:
    For proper servo operation it is necessary for the amplifier to receive negative feedback from the tachometer. If the
    tachometer leads are reversed (positive feedback), the amplifier will run away. To check the phasing of the motor and
    tachometer proceed as follows:
    1. Make sure Current Limit potentiometer, RV5, is full CCW (as shipped from factory).
    2. Make sure that nothing is connected to the Signal Input (J1-2) or the Auxiliary Signal Input (J2-1 or J2-2).
    3. Apply the main power for DC Buss and the 120 volt power for the fans.
    4. Slowly turn the Current Limit potentiometer, RV5, CW. If the motor starts to run away turn the Current
    Limit potentiometer full CCW and reverse the motor armature leads. Again, slowly turn the Current Limit
    potentiometer CW. The motor should be stopped or rotating slowly.
    5. Set Current Limit potentiometer, RV5, to the desired peak current for the remaining adjustments and
    operations.
    Typical settings for Current Limit potentiometer, RV5 (20 turn potentiometer).
    3 turns CW = 30% peak current 10 turns CW = 85% peak current
    6 turns CW = 60% peak current 14 turns CW = 95% peak current

    5.4 TACH GAIN ADJUSTMENT:
    1. At this point the motor will be rotating slowly. Adjust the Balance potentiometer, RV6, until the motor
    rotation is stopped.
    endsnip

    At this point after reading your description of all the things you have changed/tried/swapped around. I would guess the Original runaway problem was/is the Fadal 1010 X axis board, but first need to get the X Amp adjusted correctly. Which AMP's do you have ? Do you have the manual for your Modal number?

  3. #3
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    Quote Originally Posted by machinehop5 View Post
    ...should have adjusted the BAL pot to correct drift.

    ...from Glentek GA370 manual which is about the same for all DC Servo systems
    snip
    Including his GM4050 DC servos??


    Thanks

  4. #4
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    Re: 1993 Fadal VMC40 with x axis runaway

    I've been going nuts reading every forum I can. A lot of people blame the power supply.

    I measured the large capacitor and got 120 VDC.

    I have a 1220-3A power supply board.
    I have 116.4 VAC going into the transformer.
    I have 11.5 VAC coming out of the transformer into the rectifier.
    I get 19.8 VAC coming off wires 1 and 3.
    I get 9.71 VDC coming off 4 and 5.
    I get 116.9 coming out of the power supply board into the 1100-1B board.

    I probed the outputs and 1 and 2 are grounds to the 1060-0 board
    3, 4, and 5 see 5.10 VDC
    6 and 7 get 5.11 VDC
    8, 9, and 10 get 5.12 VDC
    11 and 12 are 12.02 VDC
    13 and 14 are -12.02 VDC

    Power supply looks stable.

    I found an encoder testing page.
    It says measure for 1.7VAC at the J1 bullet connector.
    Z is 1.74 VAC
    Y is 1.69 VAC
    X is 0
    The same sheet says expect 3.5 volts coming in and on the white wire and the ground I saw 3.480 VAC.

    I found a spec sheet for the resolver that says
    Wires 1 & 2 should read 70-80 ohms.
    Wires 3 and 4 should read 190 to 220 ohms
    Wires 5 & 6 should read 190 to 220 ohms

    I measured them on my first resolver and got 0 for everything.

    I found another resolver and also got 0. Turns out there was a spot of corrosion on the pins. A dusting with some scotchbrite red and I was able to get some readings.
    77.6 ohms, 206.4 ohms, and 206.4 ohms.
    I installed this resolver and I saw 1.76 VAC at the bullet connector for X

    The X still drifts. HOWEVER, now when I do a CS the motor jerks one way and then starts to creep the opposite way before it runs away. It's sortof in the right direction towards a resolution. I think it could be a difference of signal and balance now.

  5. #5
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    Re: 1993 Fadal VMC40 with x axis runaway

    Oh.
    I forgot to add

    They are Glentek DC GM4050 servo motors.
    The amp is a 4568-4201 board (stamped in the middle) and GA4568EA stamped at the bottom.
    I do not have a manual with me but a bit of searching yielded this:
    https://www.glentek.com/download/ga4...al/?wpdmdl=369

    Glentek offers nothing more than a data sheet for the GM4050 servo motor.

  6. #6
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    Re: 1993 Fadal VMC40 with x axis runaway

    good to hear you found a dirty plug. Plugs are always a weak point. Check them all...not sure if the1993 Fadal's had the Service Programs available back than because memory was expensive but, there was a program to adjust SIG and Balance using the Lag Display for each axis. At the COMMAND prompt type TA,2 enter
    https://www.fadalcnc.com/media/pdf/t...e_Programs.pdf
    thanks for the update
    enjoy

  7. #7
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    Re: 1993 Fadal VMC40 with x axis runaway

    My manual lists three programs that have survived in my brain since the last time I did this.

    The first was a 20 inch move back and forth that was supposed to take exactly 72 seconds in order to set the master clock.
    One moved all three axes 6 inches, back and forth, and I was trying to set the gain to 1.440 volts on the positive sweep.
    The other was for the balance, and I had to bring it down to 0-1 on the display.

    I'll post an update when I'm running again.

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