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Universal table woes (long)

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
I went into work on Saturday to run a little job. I needed to use the "C" axis of my Universal "Tool makers" table to cut some splines using the horizontal spindle on the FP4NC (a subject for another posting)
As part of the setup i needed to indicate in the part and make it run concentric with the built in rotary table (C). Well now i have had this table for over 10 years having purchased it from FPS in Germany. They sold it to me "rebuilt" (the only way they would sell it) and they re-surfaced the top of the table with the correct planned surface and checked the rotary encoder for correct operation.

Well as i indicated in my part having to rotate the table through multi turns , i noticed that the reading on the control was changeing on every rotation. When i got to the "0" point of the table rotation as verified by the built in indicator, the angle readout was getting smaller with every full rotation...Yikes can't make splines unless i can get a real reading. Now you have to remember that the universal table has only a protractor around the base of the table that is graduated in single degrees, and since the handwheel connects to the table rotation via a 3 speed gearbox a conventional dividing plate or degree collar is out.
Well of course i suspected the electronics. Went immediately to the "NZP" board that controls the display from the "C". On the Dialog controls all the axis use the same board and you set DIP switches to configure the board to the axis it is serving. Well i checked the swithches 4 times and the board was set correctly, no problem. So i swapped the board from the "C" with the "Z" and tested the table again, but there was no change...the readout was loosing numbers with every turn.

So now what. I did a bit more checking and the result was strange! If i rotated the table in the + direction, there was no value loss as long as i did not rotate further than about 300 degrees. I could return to the mechanical zero and everything was fine. If i went further than 300 degrees the trouble appeared. If i went in the "-" direction all was fine until i got around minus 50 degrees and then the values started differing from the actual table position. The ovious answer is that something was wrong with the rotary encoder. Possibly a dirty scale and missing counts. I had to get to the bottom of this and quickly as i needed the job done.
Well having no parts drawing for the table or manual i was shooting in the dark. I looked at the bottom of the table where the cable to the control came out...the encoder must be close i reasoned.
Removing the steel ring from the base of the table through hole did nothing to disclose the encoder location. :confused:
I decided to remove the table. The top of the table has 6 allen bolt heads showing at the bottom of the "T" slots and it seemed a fair bet that removing them might give access to the parts below.


Unitable1.jpg



I removed the bolts and the 4 nuts that provide the clamping to secure the table rotation. I tried to turn the table to see if it was loose , but it did not move. I then tried to lift the table off and with a bit of coaxing it came free.

Unitable2.jpg



With the table lifted you can see the outer bering surface..part of the casting and fitted with 2 grooves to carry oil supplied from a front mounted pressure gun fitting. Also the 4 holes for the clamp bolts can be seen. The inner disc with the holes tapped into it is where the table bolts. This disc is steel and is the rotating part, connected to the worm wheel. You might also notice the peg sticking up. This peg is in effect a dowell that locates the table to the disc and is the reason that the table would not turn free even when the bolts were out.

Unitable3.jpg



You might also be able to make out the tip of the "zero" indicator sticking proud of the outer casting surface , just a bit past the front.
The green piece in the center is a steel cover ,not sheet metal, but rather a heavy steel forming.


Unitable4.jpg



Ok so i got to the encoder and the photo shown is not quite accurate. When i opened up the cover i noticed that there were two complete reading heads, along with two lamps. I carefully cleaned the encoder scale (glass disc with lines engraved on its surface) using Isopropyl Alcohol and lint free lens cleaning tissues. I turned the power on and tried the tabel rotation again...but the trouble was still there. With the power on i noticed that both lamps were on. This seemed funny to me as i sort of remembered that the extra reader and lamp were there in case one burned out. But having never seen one of these before i reasoned that perhaps two readers were used to error check or increase accuracy...
Several additional cleanings of the scale did not help with my problem.

Unitable5.jpg


I looked at the DIP switch block and by switching #3 or #4 i was able to turn off either of the lamps. With only one lit i tried the rotary again and to my surprise the readout was correct

Now the srange thing is that i can't explain why the error only happens in one sector of the table rotation , but with both lamps lit the error returns on cue.
Now this table was never apart in my ownership. The problem must have been present since i have owned it and i never noticed the trouble because i was never making full rotations. I would by luck make plus moves (less than 300 degrees) and go back the way i went to zero i suppose. But the maddening thing is it came this way from folks that should know better......

Unitable6.jpg


Showing the under side of the table, the bolts to clamp the table rotation and the holes for holding the table to the rotary plate. Can also make out the dowell hole with a steel hardened bushing pressed in. Also the ramp notch of the "zero" indicator setup.

I replaced the table and secured it to the base with the allens. I used RTV sealant on the bolt shanks to prevent coolant from getting into the base of the table.

Unitable.jpg


Additional view of the encoder. The glass scale is visible with two concentric rings of engravings for the scales.


Cheers Ross

[ 04-16-2007, 10:56 AM: Message edited by: AlfaGTA ]
 
Thanks for the great post and accompanying photos, Ross...

I guess what I'd really like to know/hear is why 2 bulbs would cause the problem in 1 quadrant too. That seems awfully wierd. Although, truthfully, the whole idea of using incandescent bulbs seems strange to me. I've never gotten used to that.

Alan
 
ross, had a similar problem with mine , i have the seperate readout unit, as my 4th axis uses the nzp board and displays on my lcd. mine would mess up at two places 45 degrees and 275 degrees. when the miscount occurred my display would flash and quit counting. probably an error detection alert.strange you didn't get the error on your display like you do when an axis scale messes up? did all the same things found that one reader head was not working right and took it off. the instructions that came with my readout say that the encoder should only have one cable for one reader head and two cables for two and the display my display has two places to plug in the cables.
mine was also set up by deckel. it works great now with one reader. i think the you are right they use two to average the error and double the accuracy
but with .001 degree resolution who needs more.
glad you are back in business.
dave
 
Ross,
congratulations for the successful sleuthing and the excellent play-by-play report with pictures.
Hope you fired off an eMail to Michael Scheuböck and ask him for a commentary.
--
Cheers,
Arno
 
Out of curiousity (because my FP3NC has the same table) I looked through my material and could find nothing on the rotary table. It seems awfully strange to find dip switches embedded in there... :( Wierd.
 
Yeah Ross, great post. Add me to the list that would love to see some further clarification on the "whys" of this.

I'm not sure if I missed it in your post, but about how far off was the additive error per turn (if you recall)?

Sean
 
Posted by Alan:
Although, truthfully, the whole idea of using incandescent bulbs seems strange to me. I've never gotten used to that.
I think if I were in there (and not under the gun to finish a job), I'd be considering the possibility of LED replacements.

I always forget those bulbs are scattered around the machine too.

Was there a thread about LED retrofitting at some point?

Sean
 
Sean:
The change in reading was not always the exact same amount. Seems to me it was about 15 degrees per turn or so. The wierd part is that i think the error subtracted going in one direction and addeded in teh other so the amount is a bit fuzzy....

A change to LEd's would present some trouble i think...the bulbs are focused and aimed as i understand it using some instrunmentation to get the output correct. Not sure you could get the desired results with an LED...but i sure would love to know for sure. Think the difficulty of alignment of the bulbs is why the factory setup has two complete systems that run independently....think they figgured that with two bulbs one might never need a replacement in the field...so in my case, i have lost some of the units redundant features as they were bothon for all the time i have owned the machine. Also, i never turn off teh main power to my machine except to work on stuff, so the lamps are burning 24/7 :eek:

The newer Heidenhain scales do have LED's . When i was getting the FP4NC re-scraped i sent off all the measuring scales to have new seals fitted and the bulbs replaced and aligned. One of the scales i had replaced and did not need the bulb service as it was fitted with an LED. I have no idea if the internals are the same to use an incandescent or LED but it was not an option to upgrade the bulb type when servicing the scales.

Cheers Ross
 
My guess is that it would not be an easy thing to replace the bulbs with LEDs. LEDs had been around for a long time when these scales were designed, so Heidenhain *must* have specifically wanted incandescent bulbs. I just don't understand why. There must be some wavelenght collilimeter (I think that is the term) thing... But it still seems screwy to me. :confused:

The other thing that bothers me here is the way Dave and Ross have "fixed" the machines. It seems as though each of their machines was specifically setup so that both bulbs were ON. This leads to the assumption that there was/is a reason... Some type of NASA polling of three computers on the space shuttle type of thing??? Who knows... But it just seems like too much coincidence to me. I'd be curious what Arno or Don Sentner have to say about this. They are probably the only two that can really say for sure about the what/where/why of this bulb thing...

Alan

P.S. Ross, having the bulb on all the time may not be a bad thing. There is a fire station in San Jose that has the oldest known working bulb, I believe. It was built a LONG time ago... It is always on and it is fairly dim. The deal here is that the bulb was probably built with a huge hunk of tungsten. If the Deckel bulbs are not being stressed, then they may well last a long time too... Turning things on and off is stress due to thermal shock, so you may be better off leaving your machine on 24/7. Of course, if you only used it infrequently, like the typical HSM, then you are probably better turning the machine off... I think... Just my 2 cents.
 
so Heidenhain *must* have specifically wanted incandescent bulbs
Maybe not Alan, LED's have come a long way in 20 years. Maybe there just weren't any with enough output at the time in that size.

I'd also love to find out, but with me...well it's going to be when my bulbs quit....which could be tomorrow or when I'm 80.

Sean
 
Alan:
The firestation is in Pleasanton i believe and you are correct that bulbe has been on continious for over 100 years i think, and i think it is a carbon filiment bulb...

As to lwaving the control on all the time, Don S is of the opinion that it is far easier on the machine... as you point out less shock from cycling up and down. Also since i switched to the LCD dispaly the control enclosure is much cooler and i can't see how that hurts.

I talked to Don Sentner about the bulb thing after i found the trouble....His response was that every one he had seen in the field only had one bulb on at a time...not sure how large a sampeling this represents but his response was one of surprise at there being both bulbs on.

It was my opinion that the unit that Dave was talking about had two cables...one for each reading head. He is using his "C" axis reading the rotation through a DRO not the normal hookup through the control using the NZP board and the EXE 610 decoder box. With two cables seems a system that would allow use of either reading head by simply plugging either into the display eliminating the need to remove the table to change the switches in the event of a bulb falure.... The fact that his display has two plugs does not guarantee that both are to be used at the same time. Perhaps there is a peramiter in the box that turns on one or the other or both that is just not correct....The use of two cables and two plugs nakes sense as well since in a machine shop environment one would not want a loose plug with exposed pins that connected to a sensitieve reading head and its electronics. It all makes perfect sense to me.

I would surly love to hear Herr Singer's response to this question.....

Cheers Ross
 
Yup, now that I think about it, Pleasanton was the firestation location. I knew it was someplace local....

Good to know that DonS hasn't seen anything what you experienced.
I guess that helps lend credence that your machine was just an anomaly.

You are correct about Dave too. Some of the nuances of what boards do what are lost on me; for instance, I don't know what an NZP board is. I also don't understand the separate DRO. I thought the NC display had the C axis displayed on it. ??

Alan
 
Alan:
The NZP board is as i understand it the interface card to the axis and display. There are 4 card slots in the Dialog 4 control that will accept an NZP'board. The first 3 being "X,Y and Z" from left to right. Slot 4 is for the 4 th axis. If you have the NCT400 or the Horizontal 4th axis such as Dave has, it needs this card to be programmable. Dave also has the universal table, and since the indexer is already using the card slot in the control there is no way to display the angular position of the universal table except to have another display..enter a seperate DRO that is used just for the rotation of the universal table....
I have a similar problem with the FP2 fitted with the aktive control. The Heidenhain DRO displays 3 machine axis..."X,Y and Z" but that machine is also fitted with the optional (rare) universal table with the electronic readout just like my FP4NC...again this machine requires a seperate DRO just to handle the angular readout from the table.

Dave could easily run the table position through the Dialog4 display, but he would then not have the program control of his horizontal 4th axis...seems that Dave has just too much of a good thing :D

Cheers Ross
 
Alan,
I'm afraid I don't have any knowledge of the innards of the table.
I also think that white LED's had not matured until a few years back when they could be installed and left alone. Think about when LED flash lights have become commodity items. In my books they haven't reached that state yet.
--
Arno
 
Thanks for piping in Arno... Too bad that you don't know more about this stuff. Seems like black magic. :(

As for the LED comment... I don't see any reason why it would have to be a white light. I totally agree with you that white LEDs were not readily available then. But most encoders use either infrared or red LEDs, I believe... Certainly not white.

But this brings up an interesting question. Is there a reason that you thought they would need a white light?

Alan
 
Alan:
Not sure if this makes any difference ,but the receptors used in the reader heads are defined in the Heidenhain material as "photo cells". And for what its worth they look like tiny photo cells. Yea i know you can't tell just by the way they look and the deffinition might be a translation so maybe none of this makes any difference....All i know is that my bulbs are on at least for now, and i have way too much going on to think about re -engineering the scales on my machines. When you guys get the conversion kit done, sign me up for about 25 units... :eek:

Cheers Ross
 
Don changed his name (or am I the last to notice)!!! Now he is Milacron, but he still has that same fiery breath of hell in his icon. :D :eek:

Yes, I was aware that you had a thread (recalled that) but didn't dig it out. After reading it again I have resurrected my original concern. First off, sending in a table like Ross' is not feasible so your really must do an in-situ repair.

There is a comment made by DonS (DeckelDoctor) that I still find telling:
-----------
The bulbs have a focal length and will not read correctly unless they are adjusted correctly.Even though you may get the scale to read it can still be inaccurate and miss count. The bulbs with age turn gray even though they still have light they do not read properly.
------------
(how do you guys do the comment clipping?)

It is the drawing that scares me. A normal phase quadrature setup works with a (theoretical) point-source slit. But they don't really show that in the drawing within the post. There are just honking big "solar cells". Well, that is just a photo-receptor. Even so, they don't show the traditional slit that you find in encoders. So I'm wondering if this scale setup is a different beast. If not, then changing to an LED may very well be possible, so long as you use something that will trigger the photoreceptor. You would still need to adjust the LED with relation to the lens though.

Too much thinking going on... Maybe you just live with it and replace the bulbs every 20 years!
 
sending in a table like Ross' is not feasible so your really must do an in-situ repair.
Alan; i asked DD about this very thing and i was told that his Heidenhain service guy had a fixture to replicate the rotary table setup. That said, the removal of the encoder looked a bit more comples as the cord to the control appears to be soldered to the reading assembly and i don't think you could remove the unit without disconnection of the cable...and removing the reading heads from the support frame. Messing with any of that makes me a bit nervous as i am not sure how all the parts are related and what might affect the accuracy if removed/replaced.
I have decided to remove the table from my home FP2 this weekend if time is avaliable. I want to see if the encoder setup is the same and if there are both lamps lit under the cover....

Cheers Ross
 








 
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