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DMG Heidenhain absolute scale issues/resolution

gustafson

Diamond
Joined
Sep 4, 2002
Location
People's Republic
SO I have a DMG linear machine, which uses an Heidenhain absolute linear encoder and has given me continual but occasional errors on startup.

It has gone on for several years, but finally it actually refused to run, so I thought I would spell out the symptoms and solutions with some details, for posterity if you will


Machine:
DMG DMC 64V linear with Heidenhain TNC 530 control. There is a similar 104v and several other linear motor machines that would have the same type of equipment.

Symptoms:
Occasionally on startup, an error message would come up as soon as the power enable button was hit saying that the X axis had moved, and to hit the soft key to accept the new value. Not accepting is a fatal error, restarting the control. The position was of course wrong, but we discovered, nearly always the same. Basically about 1192 mm which would be 20 inches off of the travel. We learned to accept this, then restart the machine and it would come up again, this time with the correct number, which you accept and all is right. This started out as once a month or less. Then it became virtually every time we started the machine, then it got increasingly quirky about accepting the value, until it finally would never give a correct value. Once it was actually dead, it is easier to troubleshoot the machine.
Heidenhain has excellent service personnel and they helped immensely in sorting out control vs scale. It was hard for me to believe it was the scale since the machine never had a positioning error, never lost a single count ever. So my thinking is it was a battery type error, where it was losing memory, it was a hard drive error, where the position stored on the hard drive was lost, or scale.
The way the control works is that it reads an absolute band on the encoder to setup on startup, then uses the incremental band the rest of the time. I think the reasoning is that on a linear motor, there are safety advantages to not having a really fast unconstrained drive moving to discover it's initial position.


So of course the encoder reader head is dead, and the scale is no longer manufactured, and the new one has to be built in Germany flown in, you get the wallet draining picture.

Install the new scale, fire up the machine, and get a new error:
8830 EnDat: No field angle X

Great, now I need a drink. Call heidenhain service, He scratches his head and tells me some parameters to look at, which I fortunately scribble down. He thinks it may be a particular DMG setup, hafta call them. I get voicemail, so I decide to look at the parameters that had written down, literally on the back of an envelope.
AS I scroll through, I see the first familiar number, 5 digits long.....why do I know that?

It is the serial number of the scale I took out!

I have that in my phone to confirm, and I grab the paperwork for the new scale and enter the new scale s/n.

Restart the machine

No error.

Why it shows that particular error is a mystery to me, and I think everyone involved.


So now the only thing left is to align the position of the new scale. I edge find the last stop we had used on the machine and found I was almost exactly .05" off. Now one could climb on top of a 8 foot tall machine and loosen 20 little M4 bolts and jimmy the scale back and forth..but that seems a crazy way to build a machine.

I call DMG, and by the next morning I have an email with the procedure.


We are back to that 1192 number. A parameter[960.0] is set that tells the machine how far it is to the reference point on the scale that it never actually runs over.
The parameter in the machine is currently set to 1192 exactly the number that we have been seeing for years on the screen. Apparently when the control gets no reading from the absolute encoder, it spits out the parameter number. I reenter the parameter to be 1190.73, restart the machine.

Perfect.

In 15 years I have lost 2 different door switches, two toolchanger fingers, one solenoid valve, and three polyurethane hoses, and now one 5000 dollar scale.

I anticipate a hard drive in my future, as well as well as an internal battery.

I posted this because it is a weird little problem, and if anyone runs into it, it is nice to know what the problem is related to, especially if you are paying someone to fly in and fix it.
 








 
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