Drip Feeding

[widgitmaster]

Do you know what "Drip Feeding" is?

Yes, I use it all the time!
No, I haven't a clue!

[gar]

060707-1620 EST USA

widgitmaster:

Yes I know what it is, and I am of the camp want DNC to be identical in meaning to "drip feed".

I think DNC should not be used for "distributed numerical control" because this creates confusion. Clear definitions are important for effective communication.

We have an RS232 Isolator product, our I232, that is ideal for "drip feed" applications as well as others.

The I232 provides High Baud Rate Capability, simultaneously Long Cable Lengths, and Electrical Isolation.

DNC to do contouring will at times require many very short mechanical moves. At low baud rates, like 9600, this may cause data starvation and the CNC machine to move in jerks. This slows you down, is hard on the machine, and degrades the surface finish.

For more information on the I232 System visit our web site:
www.beta-a2.com

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[widgitmaster]

Gar,
Can you describe precisely what "Drip Feed" is for those who are new or inexperienced!

I believe DNC means:

Direct Numerical Control – A process of controlling a number of CNC equipped machines from a mainframe computer handling the scheduling or work and downloading complete programs into the machine’s memory.


Eric

[gar]

060707-1817 EST USA

"Drip Feeding" is a method of sending a CNC program to a CNC machine a few instructions at a time, and there is a handshake process so that the sender knows when to stop sending and when to send more data to the CNC.

The general reason for using "drip feed" is that the CNC program is bigger than the amount of available memory in the CNC for storing programs.

In a general way this is how the process works.

The operator puts the CNC machine in DNC mode. Now the CNC is ready to receive and process incoming CNC instructions.

In the CNC machine is a "first-in first-out" (FIFO) buffer that can store at least a few lines of CNC code. This buffer fills from the RS232 input up to a certain maximum limit, and then the sender is told to stop via a handshake signal. Because of time delays in communicating between the sender and the CNC the maximum limit is set less than the buffer capacity.

When data is in this FIFO the CNC extracts instructions from the buffer as needed. When the FIFO drops below a certain number of characters, then the handshake signal tells the sender to send more data. This continues until the end of the CNC program. Such a program might be 10 to 100,000,000 bytes, but the CNC program memory space might be only 100,000 bytes.

Sometimes in DNC the machine may run several days on one program.

Fanuc machines tend to have a very small FIFO whereas a HAAS machine will use a very large percentage of available CNC program memory space for the FIFO.

This is a quick overview.

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[Geof]

Originally Posted by widgitmaster Gar, Can you describe precisely what "Drip Feed" is for those who are new or inexperienced! I believe DNC means: Direct Numerical Control – A process of controlling a number of CNC equipped machines from a mainframe computer handling the scheduling or work and downloading complete programs into the machine’s memory. Eric

gar;

I agree that clear definitions are important for effective communication; perhaps you can clarify, please.

widgitmaster gives the definition above and I am confused; I was under the impresssion that the (competing) meanings for DNC are:

DNC: Distributed Numerical Control - A process of controlling a number of CNC equipped machines from a mainframe computer handling the scheduling or work and downloading complete programs into the machine’s memory

and:

DNC: Direct Numerical Control - a method of sending a CNC program to a CNC machine a few instructions at a time with a handshake process so that the sender knows when to stop sending and when to send more data to the CNC; also known as "Drip Feeding".

Either I have it backwards or widgitmaster has it backwards.

[widgitmaster]

Originally Posted by Geof gar; Either I have it backwards or widgitmaster has it backwards.

Actually, I went to Google and used the define command!

define:dnc

Of the five definitions returned by Google, only one was CNC related!

Direct Numerical Control – A process of controlling a number of CNC equipped machines from a mainframe computer handling the scheduling or work and downloading complete programs into the machine’s memory.


All I intended to do was to clarify the ambiguous terms used on the zone, because like myself, there are many who just don't know exactly what they mean!

Oh well!
Eric

[gar]

060708-0639 EST USA

Geof:

You are correct, and the definition from Google is wrong.

DNC used for systems other than "drip feeding" is very uninformative if you look at the various ways people use the term. Some simply mean communication from a computer to a CNC, others means a network of one computer and many CNCs, and so on.

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[diarmaid]

lol....when I saw this thread I thought it was something to do with coolant!

[geoff p]

As one who hasn't a clue, something I read on another forum lead me to believe drip feed was along the lines of creating a part from several separate files: complete one file's worth of operations then load another etc.
I thought this thread was trying to define 'drip feed' but it seems to be more about the definitions of DNC. Where does DNC fit into 'drip feeding' ?
Geoff P

[Geof]

Originally Posted by geoff p As one who hasn't a clue, something I read on another forum lead me to believe drip feed was along the lines of creating a part from several separate files: complete one file's worth of operations then load another etc. I thought this thread was trying to define 'drip feed' but it seems to be more about the definitions of DNC. Where does DNC fit into 'drip feeding' ? Geoff P

The way I understand DNC and dripfeed this is more or less correct. Direct Numerical Control DNC is when a program too large to fit in the machine memory is 'dripped' into the machine and executed at the same time. Your description is just bigger drops of program.

Also maybe someone can comment further but my understanding is that drip feeding originated a long time ago before machine processors had enough capacity to execute complex macro calculations fast enough to run a machine at the same time. The calculations to generate compound curves were processed in real time on a big mainframe which dripped the results into the machine. Something similar to having a CAD program simultaneously feed a CAM program which is simultaneously providing code to the machine. Maybe the analogy is a bit stretched but not too far with a bit of imagination.

In this context Distributed Numerical Control DNC is a johnny-come-lately that only became possible with the advent of desk top PCs and large scale network systems. Although I guess the Sun Workstations that were used a few years ago were a bit big to describe to describe as desk top.

[gar]

060711-0756 EST USA

geoff p:

I believe I gave a fairly good description of how a typical "drip feed" operation works in post #4.

In the most extreme case you have old machines using tape readers. Here the "drip feed" occurs one character at a time. Or maybe you would like to say one block at a time. This would depend upon whether there was an internal buffer used.

As I previously said I do not like the acronym DNC used for anything except Direct Numerical Control ("drip feed") because this leads to confusion of what one is saying.

"drip feeding" is a colloquial term for Direct Numerical Control. But is very useful because it is sufficiently unique in its meaning to avoid the problems with the many definitions of DNC relative to CNC machines. Also DNC has lots of uses besides those in the CNC arena.

The Wikipedia discussion on Direct Numerical Control is a real mishmash of concepts without clear definitions.

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[Geof]

Originally Posted by gar 060711-0756 EST USA......The Wikipedia discussion on Direct Numerical Control is a real mishmash of concepts without clear definitions.... .

I will second this. I skimmed it quickly and came to the conclusion it is not even internally consistent; which is not surprising considering how Wikipedia operates.