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Thread: 1987 Sharnoa SDC-80D Z axis Drift problem

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    Default 1987 Sharnoa SDC-80D Z axis Drift problem

    We have a 1987 Sharnoa SDC-80D with Fanuc Motors and drives. The Z axis is having an issue.

    The Z axis Drive is a A06B-6047-H003 Velocity Control Unit

    The Z axis Motor is a DC 20M Servo # A06B-0652-B005

    This machine has a proprietary control with a PC motion card that receives the encoder feedback and directs the drives to move. The motors have feedback to the drives only.

    The issue we are having is that the Z axis physical position is drifting from indicated position, and we have to re reference to bring it back into position.

    I do not understand why, if the ball-screw encoders feed back to the motion card, how this can happen. I would think that the motion card would either have a fault indicated or require the drive to continue moving till it is in position.

    Any ideas as to where to start ??

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    Default Re: 1987 Sharnoa SDC-80D Z axis Drift problem

    UPDATE

    Ok I started looking at the encoder input "chain" and here is what I have found:

    The Z axis encoder is Heidenhan ROD type. It is connected to a terminal strip at the encoder and then a 4 pair cable brings the signals down into the control cabinet.

    The cable is NOT shielded.

    The signal is then ran into a box that has a line driver (digital amp) for each axis, and also brings in the 5VDC from the Computer power supply for the encoder(s) and the digital amp circuits.

    The signal then comes out of the box and is fed into the motion card in the PC, again with unshielded cable (I believe that it is twisted pair (4) wire)

    I do not know how old this setup is but, I am wondering if the problem could be with the Digital amp on the Z axis feed ???

    I also do not like that there is no signal shielding, I would like to fix that as well.

    Anybody think I may be on the right track ??
    Last edited by eric14779; 02-15-11 at 11:27 AM.

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