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Thread: Hardinge Emag VL3 (FAnuc 18i) Scale problem

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    Default Hardinge Emag VL3 (FAnuc 18i) Scale problem

    We have 3 of these machines in our shop. One is a year older than the other 2. We were having Abnormal Z (ext) alarms on the Fanuc 18i and when I investigated found that the newer ones had their scale modules as well as the scales grounded as well as a ceramic ring mounted next to the scale card for each axis scale cable to loop around 5 times before plugging in to the card. I duplicated this in the older machine as well as swapping the scale cables and cards with one of the other machines. The problem went away for a week and did not transfer to the other machine I swapped equipment with. The Abnormal Z (ext) slowly became a problem that resufaced to happening so much that I had to shut down again to see what was going on. In this great age of doing more with less and cheaper, my boss bought a scale on ebay and while the scale was too short for direct replacement the numbers on the reader matched so, I changed the reader, set zero and ran 4 hours before coming up with the broken LED alarm on a different shift where the tech swapped out the scale with one of the other VL3s. As soon as I came back in, it errored out with the broken LED alarm again so I disassembled the scale, cleaned it thouroughly, reassembled and installed it, set zero and started jogging. I can go down to the - overtravel then back up past zero and then at a specific position get the broken LED alarm again. I took this scale and put it on one of the other VL3s and it ran fine. I took the other scale and put it on the problem machine and got the same LED alarm at the same position. Keep in mind that I have switched the cable, the card, the scale, and made the grounding modifications I found on the other machines. The axis in question has a pulse coder not an absolute encoder and it drives the Z axis with a belt which appeaes to be in good working order. Also I tinkered around with alignment of the scale and reader to no avail. Yes it's a Heidenhain scale, pretty simple really. I am totally stumped at the moment and any advice would be greatly appreciated. Thanks, hope everyone enjoys the holiday weekend. I'll be trying everything I can to get this machine running.

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    Default Re: Hardinge Emag VL3 (FAnuc 18i) Scale problem

    The Z axis moves and so does the reader head I assume. Check the cable that goes to it in the tracking and look to see that it is not damaged. Maybe even swap if its easy enough. You say it repeats at the same position every time so this would make sense. If it repeats at the same position and you changed out the scale then it can not be it. the EXT in the alarm always from what I know points as a scale alarm. If you swapped out the preamp and the scale then to me the only thing left is the cable. Make sure the cable does not run close to any three phase lines. Make sure the preamp or card looks to be grounded the same way. Also sometimes with scale cables there is a shield that must be grounded properly on one end. Many times this shield since it is soldered to one wire can break loose. Any noise in the line will cause problems.

    Also one thing you might be able to do is turn off the scale for that axis to see if the problems go away. You would have to contact the builder for the exact parameter changes. Its sometimes the best easiest way to troubleshoot down the road when you have problems as well.

    Good luck

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    Default Re: Hardinge Emag VL3 (FAnuc 18i) Scale problem

    Yes, I had turned off the scale (parameter 1815.1 OPT) because my boss was wanting me to change out the motor and or the encoder cable and that saved time because there was no issue.

    What it ended up being was the precision of the scale's mounting. The scale has to be within 100 microns from top to bottom. I got it within 20 and that machine runs without stopping now. It was out about 3 thou andI talked with a EMAG tech who pointed out that it had to be within 100 microns top to bottom. I knew that the scale had to be mounted precisly but not that close. I still can't understand why the problem went away for a week after I grounded the scale, the amp, and added the ferrite ring to drown out noise .... then came back.
    Last edited by SteveO; 09-04-10 at 08:10 AM.

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    Default Re: Hardinge Emag VL3 (FAnuc 18i) Scale problem

    Thanks for posting what you found. I agree that it is interesting that when you connected the ground wire that it went away for awhile. Can you please tell me how you were able to check the measurements or what you were going off of? I usually just make a good guess and keep adjusting it till it reads properly, but it would be good to know.

    Thanks

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    Default Re: Hardinge Emag VL3 (FAnuc 18i) Scale problem

    This machine has a vertical spindle. The vertical spindle is on the z axis. X is the horizontal axis, C is the spindle, and there is no Y axis. I put the magnetic base of the indicator mount on the front of the spindle and adjusted the arm around to the side so the indicator could read the side of the scale at about the center point of the reader, then moved Z up and down and adjusted the scale mount. The indicator reads plus and minus 50 microns with 0 at the center. i got it to within 20 microns from top to bottom which took a while to do. This machine has an A axis which is a chain that runs around the machine carrying parts in and out on 14 prisms. The spindle only has a chuck on the end for picking up parts off the prisms. There is a B axis which is a 12 position turret that the tools are mounted on, and a V axis which is a live tool drive within the turret.

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    Default Re: Hardinge Emag VL3 (FAnuc 18i) Scale problem

    Ok, so basically the reader head needed to be parallel with the scale then. There was no adjustment the other way I assume.

    Thanks

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