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IndustryArena Forum > Machine Controllers Software and Solutions > Fanuc > 434 servo alarm: Z axis detect error
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  1. #1
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    434 servo alarm: Z axis detect error

    I have this problem on my machine.
    It is Fanuc OM and machine DAH-LIH.

    Everything is fine, machine is working and sudenly at one moment, z axis goes down and tool hits into table.
    And display "434 servo alarm: Z axis detect error"

    And after that i restart machine and everything is ok, and from time to time, it happens again.

    What could that be?

    Sorry if this is wrong forum

  2. #2
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    Quote Originally Posted by padobranac
    I have this problem on my machine.
    It is Fanuc OM and machine DAH-LIH.

    Everything is fine, machine is working and sudenly at one moment, z axis goes down and tool hits into table.
    And display "434 servo alarm: Z axis detect error"

    And after that i restart machine and everything is ok, and from time to time, it happens again.

    What could that be?

    Sorry if this is wrong forum
    Look for loose cables or worn spots in the cables that may be causing a short. Then look at other items (motor, amp).

  3. #3
    Community Moderator Al_The_Man's Avatar
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    If you look a the diagnostic work for that axis it should tell you precisely the alarm type
    diag, 720~727 for up to 8 axis.
    as per the attached PDF.
    Also if the axis runs away, you should be able to set a deviation error in one of the parameters to avoid a crash, it should shut the servo's off.
    Al.
    Attached Files Attached Files
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  4. #4
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    If This Is A Vertical Machine Look To See If There Is Any Type Of Hydraulic Conterbalance It Might Need To Be Refilled. If There Is No Counterbalance Then Do What Was Suggested Above With The Cables Or The Brake On The Motor.

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    How are you switching the machine off at the end of work. On Vertical machines in particular but on all machines really you should press the E.Stop button first then power down. This allows the brake to come on and hold everthing in place. If you just power down the vertical axis will drop slightly each time, normally this will give soft overtravel alarms when you reference up on switching but it is feasable that the axis is incrementing itself down so you are out of position when you start.
    Alan B

  6. #6
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    Fanucs

    On most Fanucs any disconect error is normally caused by a break in the encoder cable. In rare case for some reason I have seen exsesive backlash throw of this error but I amnot sure why. The easy way to test this cable is to swap the ecoder cables from the X and Y axis and if the error now follows to the X axis you know it is the cable.

    Bluesman

  7. #7
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    Quote Originally Posted by Alan B
    How are you switching the machine off at the end of work. On Vertical machines in particular but on all machines really you should press the E.Stop button first then power down. This allows the brake to come on and hold everthing in place. If you just power down the vertical axis will drop slightly each time, normally this will give soft overtravel alarms when you reference up on switching but it is feasable that the axis is incrementing itself down so you are out of position when you start.
    Alan B
    Well, i think that isn't problem, because that error appears in the middle of the work, not mmediately after starting machine
    Sorry for bad english

  8. #8
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    Quote Originally Posted by diggityds
    If This Is A Vertical Machine Look To See If There Is Any Type Of Hydraulic Conterbalance It Might Need To Be Refilled. If There Is No Counterbalance Then Do What Was Suggested Above With The Cables Or The Brake On The Motor.
    Hydraulic Conterbalance???
    I don't understand what that could be?
    Sorry for bad english

  9. #9
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    Some vertical machines come with a gas or a chain type counterbalance that help support the head, this puts less load on the motor and doesn't wear on the ballscrew as much. If the pressure of the gas counterbalance is low the head will drop when the the power to the motor is off. This might not be the problem since it's happening while it's running. You can aslo check if your machine has scales or not, if the reader head is loose or if there is any debri on the scale could cause the cnc to run looking for location. Don't count out the fact that the cable might be damaged or pinched, it can short out at any spot during operation. You can swap cables between drive cards and see if the problem follow's itself.

  10. #10
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    I'm sorry but that is not correct. The [soft disconnect alarm] in the the Fanuc book will tell you it is a broken cable. However any machine using glass scales will give this alarm. If you look at the alarm logically it is saying "I (Fanuc control) have commanded the axis to xx mm and the encoder(on the motor) says the axis hasn't therefore the encoder wire is broken" If you use a glass scale it is not attached to the motor but the axis itself and the motor encoder is not read. Fanuc doesn't allow for this even though the parameters are set so if the external encoder sends the "I haven't moved signal" because, for example the axis is tight/siezing, Fanuc throws up disconnect alarms. As a service engineer of many years(too many) the first question on disconnect alarms has to be "Do you have glass scales? What is in parameter xxxx dependent on control"
    Quote Originally Posted by Bluesman
    On most Fanucs any disconect error is normally caused by a break in the encoder cable. In rare case for some reason I have seen exsesive backlash throw of this error but I amnot sure why. The easy way to test this cable is to swap the ecoder cables from the X and Y axis and if the error now follows to the X axis you know it is the cable.

    Bluesman

  11. #11
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    Quote Originally Posted by Alan B
    If you use a glass scale it is not attached to the motor but the axis itself and the motor encoder is not read.
    So when glass scales are used the encoder is completly disabled? Even in rapid etc. I thought the scales were for "fine" positioning and both scales and encoders were used???

  12. #12
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    How will i know if my machine uses glass scales?
    Sorry for bad english

  13. #13
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    If you look at the parameters you are telling the control to look at optical scales and switching off the encoders. A quick check on scale machines for disconnect alarms is to switch the encoders back on. Often the machine will then run fine, albeit with less accuracy than before. I've often had to do this for customers with OKK machines whilst waiting for a production stop to get on the machine to sort it out.
    Alan B

  14. #14
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    Assuming you have a 18 or 21 control look at parameter 1815 bit 1. A 1 is for optical scales and a 0 is for encoders.
    Alan B

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    We had the same problem with the Z axis, diggityds is right. It was a problem with the hydraulic counterbalance. We increased the pressure and its working perfectly fine.

    Thank you for solving our problems once again

  16. #16
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    I had a, 414 servo alarm: Z axis detect error, on my Mitsui Seiki HU40A.
    I got that because the ways on the Z axis were almost dry and the servo motor had to work too hard.The ways didn't get enough lubrication.
    As soon as I got the alarm the Z axis kept going until it ran out of momentum.
    And when I started it up again after ,say an hour, it worked fine again. For a while.

  17. #17
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    the signal cable from motor to Z axis board loose because moving, or broken due to oil. Sometimes pulse coder's bad (rarely)

  18. #18
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    Quote Originally Posted by Alan B View Post
    If you look at the parameters you are telling the control to look at optical scales and switching off the encoders. A quick check on scale machines for disconnect alarms is to switch the encoders back on. Often the machine will then run fine, albeit with less accuracy than before. I've often had to do this for customers with OKK machines whilst waiting for a production stop to get on the machine to sort it out.
    Alan B
    I've never seen any machine set up so that when the OPT bit is set to a 1 that it "shuts off" the encoders and looks at the scales only. Every machine I've ever set up with scales has parameters for resolution of the scale (read), and the amount of allowable Synch error between the encoder and the read of the scale.

  19. #19
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    Post scale, 434

    when using scale, the encoder is still used to monitor motor speed as a tacho.
    The cnc compares movement from the encoder to the scale, if the motor is moving, but no feedback signal comes back from the scale within a preset distance, you get a disconnect alarm, this can be caused by excessive backlash and the alarm detection level can be compensated somewhat by parameter.(or the scale may be faulty).

    As for the 434 detect error alarm , check dianostics 720-727 and see which bit is a 1 when the alarm occurs.
    If you can't clear the alarm by pressing reset or just power off /on the cnc while leaving the main machine power on, then the alarm will be displayed on the servo drive pcb for the Z axis and can be cleared by main power off/on.

    Hope this may be of help.

  20. #20
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    Glass scales

    I have several amchines that utilize both glass scales and absolute motor encoders and they perfoem exactly as stated above. This is a safety feature that if the motor is running and scale signal doesn't you get the error another type of error is a disconnect and this may refer to a popped clutch on the spindle/ball screw.

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