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So what is the feature that will allow Mach2 to be successful
coutour software? I cannot find anything in the manual that even
refers to a "look Ahead" feature (G51) nor anything that resembles
it. What am I overlooking? Do you configure CV to act as a look
ahead? How?

Bill Clemens

Hi Bill:

I'm afraid I miss your point. Why would anything special be required for
contouring?? LookAhead is a CV feature and is automatic when in G64 mode, is
there some special requirement for contouring operations?


Art
www.artofcnc.ca

3-D contouring? Don't you run into problems of 'faceting' or
excessively long programs to compensate for the lack of lookahead?
My interest is in 3-D contour machining and was asking for
information not included in the manual regarding Mach2's specific
capability. G51 is the standard G code for it and an entry for
tolerance. Not included in Mach2...

Thanks much for your help,
Bill Clemens


--- In mach1mach2cnc@..., Art <fenerty@a...> wrote:

Hi Bill:

I'm afraid I miss your point. Why would anything special be

required for

contouring?? LookAhead is a CV feature and is automatic when in

G64 mode, is

there some special requirement for contouring operations?


Art
www.artofcnc.ca

----- Original Message -----
From: "Bill C." <billsand@c...>
To: <mach1mach2cnc@...>
Sent: Thursday, February 26, 2004 5:19 PM
Subject: [mach1mach2cnc] "Look Ahead" is called what in Mach2?

So what is the feature that will allow Mach2 to be successful
coutour software? I cannot find anything in the manual that even
refers to a "look Ahead" feature (G51) nor anything that

resembles

it. What am I overlooking? Do you configure CV to act as a look
ahead? How?

Bill Clemens




Yahoo! Groups Links

Art,

I believe I have confused a couple of issues with Mach2. The ability
to perform the 3-D is covered with a full understanding of the G
codes - my shortcoming.

Thanks again,
Bill Clemens

--- In mach1mach2cnc@..., Art <fenerty@a...> wrote:

Hi Bill:

I'm afraid I miss your point. Why would anything special be

required for

contouring?? LookAhead is a CV feature and is automatic when in

G64 mode, is

there some special requirement for contouring operations?


Art
www.artofcnc.ca

----- Original Message -----
From: "Bill C." <billsand@c...>
To: <mach1mach2cnc@...>
Sent: Thursday, February 26, 2004 5:19 PM
Subject: [mach1mach2cnc] "Look Ahead" is called what in Mach2?

So what is the feature that will allow Mach2 to be successful
coutour software? I cannot find anything in the manual that even
refers to a "look Ahead" feature (G51) nor anything that

resembles

it. What am I overlooking? Do you configure CV to act as a look
ahead? How?

Bill Clemens




Yahoo! Groups Links

Bill:

>>My interest is in 3-D contour machining and was asking for
information not included in the manual regarding Mach2's specific
capability. G51 is the standard G code for it and an entry for
tolerance. Not included in Mach2...

Actually G51 is kinda standard for scaleing of axis, but then theres a lot
of standards. Sometimes called mirroring, but then thats simply a scale
of -1. Perhaps your speaking of finishing capability where you specify a
tolerance to stay away from the actual toolpath by a set amount??

I still don't get your point on faceting problems or excessivly long
programs. Though if your speaking of a finishing capability, then I can see
where the files would be longer by having the CAM program generate the final
passes, but then file length is not very important these days with multi-gig
hard drives everywhere. But how would lookahead have anything to do with
file length or contouring..

Forgive me if I'm being dense Bill, I just don't understand the question,
but "lack of lookahead" ius something I hadn't come across before, Mach2 has
more than any controller I've heard of in terms of CV.. I think I'm missing
something here...

Art
www.artofcnc.ca

Ahh, sorry Bill, I kinda got the feeling we were talking of two different
things...

Thanks,
Art
www.artofcnc.ca

Bill, Art;

I might be able to expand on this somewhat.

In Mach2 jargon we often speak of look-ahead as if it were synonymous
with constant velocity contouring. Mach2 examines the forward toolpath
so as to be able to run through data points without starting and
stopping at each one (if possible).

From a control designer's point of view, however, look-ahead is often
used for other things. One technique, called adaptive look-ahead, is
used to reduce following error in servo systems. The path is analyzed
for accelerations (changes in direction) as in the previous example.

The information is fed to the profiling algorithm through a method
called velocity feed-forward - basically, another term in the PID
equation. Acceleration feed-forward, if used, adds still another term.
These combine to give the servo advance warning that a corner is
coming, allowing it to set up for the corner as they say in dirt track
racing.

Adaptive look-ahead is more or less standard fare these days in high
speed machining. The benefits are of particular importance to laser
and plasma machines. It substantially improves the value of CV
contouring.

Unfortunately, adaptive look-ahead is not possible in Mach2. The
technique requires that the position loop be closed in the computer.
Mach2 leaves this to the drive. Rutex/Gecko servo drives perform the
PID based on immediate position data.

Doug