PDA

Archiv verlassen und diese Seite im Standarddesign anzeigen : Experience CNC with frequency convertor?



Mironteau
13.04.2007, 09:52
Hello to you,

I'm wondering if there is somebody over here who has experience cq knows something about the automation of a milling machine with frequency controlled gearmotors on the spindles? Of course there should be an encoder on each spindle, in order to control each frequency convertor.
I'm considering a configuration as follows: 3 micro-master 440 with Profibus DP interface, 3 absolute encoders with Profibus connection, a 315-2DP PLC and WinCC flex RT to visualise it al.
Any suggestions?
(Don't say i need to improve my English, because my German is even worse)

Thanks in advance
"schones wochenende" (sagt man es so?)

Maxl
20.04.2007, 18:42
Question: are you going to build a cnc-system or 3 single-axis-systems? cnc-system means: linear interplation of 2 or 3 axis, circular interpolation and so on and so forth. With your configuration it's only possible to make single-axis systems without interpolation.
--> this means, the expression "cnc" doesn't fit on your configuration.

If you use your configuration, you have to write all the positioning-system in S7. This means: hands-mode, referencing, automatic-movements, controlling (lag-distance-control, limits, a.s.o.a.s.f). A big problem in this configuration is correctness of the positioning. It would be usefull to know, what exactly you want to do!

Nowadays it would be better so use complete positioning-controllers (e.g. SEW Movidrive). You install an encoder on the back-side of your motor (not on the spindle!!) and connect it directly to the Positioning-controller. Possible encoders for SEW are sin/cos (inkremental) or Hiperface (absolute). The positioning-controller can be connected via Profibus-DP to der CPU. This solution would be much more precise!

If you need interpolation, you will have no chance without a real cnc-controller (FM357, B&R, Sinumerik, ....)

greetings from austria!
maxl



PS: my English isn't good too! I prefer speaking English, not writing! :rolleyes:

Mironteau
24.04.2007, 11:00
Thanks for your kind answer.
I guess measuring the exact spindle position would be the least of my problems. As this application would be merely a diy project, precison and repeatability are not that critical. Furthermore, these parameters depend also on the milling machine itself. Which is an old one, so the mechanical precision wont be very good. If i could realise an accuracy of 0.1 mm, i'd be glad!
Referencing would'nt be a problem if i would use absolute encoders?
My goal would indeed be to mill all kinds of figures or patterns, at least in 2-D, meaning that X and Y spindle need to operate in a coordinated manner. I suppose you could call this CNC?
My bottom question is then if someone has ever programmed something similar in S7? I admit that a real CNC controller would be the correct solution, but since this is a diy application, money matters. And i have a 315-2DP and 3 MM440 with DP interface on the shelf. So i would only need to buy the encoders.
Of course, if someone experienced in this matter could give me some tips & tricks, this would be very usefull for me. (Maybe warn me that i'm dreaming, that this can't be done?)
Anyway, thanks in advance for your much appreciated answer (even in German).
And maybe practicing English is usefull for both of us?;)

Maxl
25.04.2007, 20:18
Referencing would'nt be a problem if i would use absolute encoders?The value is absolute, nevertheless you need to have a possibility to set the actual position of the measuring system to zero (e.g. after chaging a motor or an encoder)

My goal would indeed be to mill all kinds of figures or patterns, at least in 2-D, meaning that X and Y spindle need to operate in a coordinated manner. I suppose you could call this CNC?this is correct!

My bottom question is then if someone has ever programmed something similar in S7? I admit that a real CNC controller would be the correct solution, but since this is a diy application, money matters. And i have a 315-2DP and 3 MM440 with DP interface on the shelf. So i would only need to buy the encoders.
With a simple S7 you have no chance to make a correct 2D-interpolation. On Siemens you only can use a combination of S7 and FM357-2. You'd need normal incremental encoders, that are connected directly to the FM357, the FM controlles the inverters by +/-10V. The cnc-programs are loaded directly to the FM, but it is also possible to modify the cnc-programs via the S7-CPU.

A different possibility would be cnc-devices from different manufacturers (e.g. B&R - PP200, CP340 or CP1484 in combination with their soft-cnc), that are able, to read encoders directly and put out analogic values.

Nevertheless, for each solution you cannot use profibus-encoders - they are too slow. Possible are incremental encoders or high-resolution SSI-enoders (it depends on the cnc-system). All this configurations would allow you linear 2D and 3D interpolation as well as 2D circular interpolation.


And maybe practicing English is usefull for both of us?;);)


greetings
Maxl

Mironteau
26.04.2007, 09:12
Thanks a lot.
So, i'll inform myself first on FM357 and try to find such a controller on an auction or ebay.
Your tip about the lack of speed of profibus encoders is very valuable.
In the long run, maybe i'll learn something about CNC.

Danke schön
Grussen aus belgien