[Andy_mr2sc]

Hi All!

I've had an ongoing fault with my Bridgeport 720X with Heidenhain 2500 control. If I rapid move the Z axis it stops and throws up a 'Z Measuring System Defective A' error. This was getting worse so I stripped the machine and cleaned out the (rather mucky) encoder at the bottom of the Z axis lead screw and also the one on the back of the motor (motor Fanuc model 10) Being a bit heavy handed I managed to break the glass on this so have replaced it with a like model. Straight swap.
Now when I power up the machine and press the power on button on the control the Z axis drops about 3mm and it throws up a 'Gross Positioning Error Z D' message. If I hold the power on and cycle start buttons it will rapid up a few inches before giving the message 'Gross Positioning Error Z A.'
I am guessing this is a comms issue between the replaced/disturbed encoders and the control? Can I adjust a parameter to solve this or is there a set up procedure I need to follow after disturbing the encoders? The main drive board doesn't show any errors on it; just the green led stays lit.

Any suggestions or tips are welcomed because I'm on the verge of having to call an engineer down!! ££££££££!!

[4lo]

replaced it with a like model. Straight swap.

Are the encoder specs exactly the same? If the ranges/output signals vary, then the feedback will not match the commanded movement and the error will be too large. You definitely need to set axis parameters accordingly.
Is it installed correctly? The sensors usually have a very specific placement, too close or far from the axle or cue and it won't show - unexpected feedback again. They are also very sensitive so rough handling could kill even if it doesn't look broken.
Wiring and mucky connectors can cause issues aswell. I get such errors every now and then on my X-axis and spraycleaning and drying the sensor connector just under the table has solved it every time.
Hope you find your fix.
And always make sure you have a backup of the parameters if you choose to start messing around there.


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[Andy_mr2sc]

replaced it with a like model. Straight swap.

Are the encoder specs exactly the same? If the ranges/output signals vary, then the feedback will not match the commanded movement and the error will be too large. You definitely need to set axis parameters accordingly.
Is it installed correctly? The sensors usually have a very specific placement, too close or far from the axle or cue and it won't show - unexpected feedback again. They are also very sensitive so rough handling could kill even if it doesn't look broken.
Wiring and mucky connectors can cause issues aswell. I get such errors every now and then on my X-axis and spraycleaning and drying the sensor connector just under the table has solved it every time.
Hope you find your fix.
And always make sure you have a backup of the parameters if you choose to start messing around there.


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The encoder, although a slightly older serial number is the same part number. I guess even the same part numbers could have slightly different outputs that would need setting in the parameters? I have a list of parameters and their function but none are obviously connected to matching an input from an encoder.
There are no breaks in wires and I checked all of the connectors were clean. The sensor in the encoder cannot be adjusted though the encoder itself can be twisted on its three mounting holes a few degrees in each direction. I put it in the same position as the one I removed but wasn't sure if this adjustment was to aid setting up?

[4lo]

If the encoder has the same part number I would assume the pulse counts and voltages are same so parameters should not need changing. If it is in place correctly... there have to be be specifications to that written somewhere.
Axis, drive and encoder parameters should be in a separate technical or service manual, maybe there are also some set up or zeroing parameters described there.

Some controllers require the axis to be not too close to the end switches when referencing so they have some way to go before getting that signal. If that is the case, you might need to get it away a bit.
The axis dropping at power-on rather indicates unexpected motor control than measuring when I think about it, but maybe not.
Keep testing different ideas until you don't get better help.
In my experience, if nothing gives for a while, getting some rest and going away from the problem to do other things will bring up better ideas than going around it too hard too long.




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[csg67]

Conversely installed the encoder? :nono:

[Andy_mr2sc]

Conversely installed the encoder? :nono:

How do you mean conversely? I can only see one way to install it. It came pre wired (I assume the same terminations as the original as it's the same part number??) so just plugged in. There are two wires that are joined to two loose wires in the motor with crimp connections. These are both black on the motor so I had to guess which way they went and I've tried them both ways which appeared to make no difference.
I guess I could turn the drive dog on the encoder 180° but I don't see this would effect anything?
I cannot find any other info on setting these up either physically or with the parameters. I altered parameter 1110 from 0.2mm to 30mm to see if it was a tolerance issue and I was somewhere close but again this made no difference.

[Andy_mr2sc]

ALL SORTED!!!

So I tried turning the encoder round 120° on its three mounting screws and it's all systems go!!

csg67 I guess now this is what you meant?

Thanks every one for the input. I'm off to make some chips!

[4lo]

Great news! Good luck!

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