Re: Auto tool changers

Ray,

Do as you like. Not everybody runs EMC. And the "good programmer" I
mentioned will ALSO include a comment IN THE M06 BLOCK of what tool
is loaded. And he/she will further NOT be confused by the previously
issued "T" command since he or she KNOWS that the M06 is what CHANGES
the TOOL.

I try very hard to give advice that applies to everyone, using a WIDE
variety of tools and controls. All the while knowing that I CAN NOT
succeed. If you wish to dissect EMC to "prove" that standard industry
practice is not worthwhile FOR YOU; that is fine and all of the users
of EMC will benefit from your undertaking. (including me. I enjoyed
learning more about the internals of EMC fromyou in htis post.)

UNTIL, that is, they run machines which DON'T fit your tidy
excercise. At which time those who have followed the advice given
will run circles around you (pun intended). That this issue may be in
flux is a given. Are we moving toward a time when ALL controls behave
as you have shown EMC? Maybe, BUT WE ARE NOT THERE YET...

Next, on the PLC issue: I agree that PLC's are important. And
symbiotic. But I still say the Control runs the show! It's like a CEO
with vice presidents who do IMPORTANT things. Just because the CEO is
waiting for the output from the VeePs does not elevate the VeePs to
the presidency!

Hope this helps.

Ballendo

--- In CAD_CAM_EDM_DRO@y..., rehenry <rehenry@u...> wrote:
>
> Ballendo
>
> I snipped a bunch from your interesting reply. I hope this post
gets to
> the point that I was trying to make with respect to your suggestion
that
> tool change Txx words should be coded several blocks before the
> corresponding tool change M6 is programmed.
>
> Disclaimer -- This post applies primarily to machines that use
a "next
> tool ready" type of tool changer.
>
> >    From: "ballendo" <ballendo@y...>
> <s>
> > Most good programmers will list the "T" word at least A FEW BLOCKS
> > AHEAD OF THE M06, so the toolchange turret can "get ready"(rotate;
> > talking 'bout mills here) so as to have the next tool in position
for
> > a quicker tool change WHEN THE M06 ACTUALLY INITIATES THE PHYSICAL
> > CHANGE to the new tool.
> <s>
> > Lookahead exists to allow cutter radius comp, and to prevent
crashes
> > and gouging from accel/decel issues.
> <s>
>
> I did a little testing on the EMC. Four tools is probably overkill
but
> here is the program I ran.
>
> -----tooltest.ngc-----
> n1 g0 x0 y0 z0 (Tool change test program tooltest.ngc)
> n2 t1 m6 (Preset and load tool 1)
> n3 g1 f5 z-1
> n4 x1
> n5 y1
> n6 x0
> n7 y0
> n8 g0 z0
> n9 t2 m6 (Preset and load tool 2)
> n10 g1 f5 z-1
> n11 x1
> n12 y1
> n13 x0
> n14 y0
> n15 g0 z0
> n16 t3 m6 ((Preset and load tool 3)
> n17 g1 z-1
> n18 x1
> n19 y1
> n20 x0
> n21 y0
> n22 g0 z0
> n23 t4 m6 ((Preset and load tool 4)
> n24 g1 z-1
> n25 x1
> n26 y1
> n27 x0
> n28 y0
> n29 g0 z0
> n30 m2
> -----end of tooltest.ngc-----
>
> I asked for full debugging so that all of the EMC commands would
echo to
> the terminal. Debug shows read ahead, look ahead, commands, and
task
> completion in the order that they occur.
>
> The EMC uses an internal command EMC_TOOL_PREPARE to indicate that
the
> tool in pocket #xx needs to be moved into place. It uses a command
> EMC_TOOL_LOAD to indicate that it is time to change the tool in the
> spindle.
>
> What we are looking for is the interval between the issuing of a
> EMC_TOOL_PREPARE command and the EMC_TOOL_LOAD command. I'll
ignore the
> first tool change command since it can't be programmed to make any
> difference for our discussion. The terminal output shown below is
for
> the second tool. Immediately before this quoted block there is a
series
> of motion commands as the interpreter looks ahead and begins to
execute
> lines numbered n3-n8.
>
> -----debug output-----
> ...
> Issuing EMC_TOOL_PREPARE -- (+1104,+16, +0, +2,)
> Motion id 3 took 11.980118 seconds.
> Motion id 4 took 11.979220 seconds.
> Motion id 5 took 11.969769 seconds.
> Motion id 6 took 11.959347 seconds.
> Motion id 7 took 11.969727 seconds.
> Motion id 8 took 0.949585 seconds.
> Motion id 0 took 0.000005 seconds.
> Issuing EMC_TOOL_LOAD -- (+1105,+12, +0,)
> ...
> -----end-----
>
> There it is as clear as you could want. While running this program
the
> command to prepare a tool is issued nearly a minute before the tool
> change command even though they exist in the same program block.
This
> timing depends upon feedrate but it illustrates is that as soon as
the
> interpreter loads the tool change line into it's look ahead
buffers, it
> issues the tool prepare command! This timing is typical for
subsequent
> tool changes as well.
>
> Now this brings up the question, "Okay so the command is issued
early but
> what does the machine do with the command." The answer is all PLC
and
> only PLC.
>
> > PLC's exist as a semi-
> > intelligent "servant" OF the control, which distributes
the "brain"
> > power needed to run the machine. But I've not seen them work
together
> > to "predict/discern" the next tool and get it ready, tho' they
> > could...
>
> I looked in a Meldas 50 control book that I have on hand. It says,
> "Processing and completion sequences must be incorporated on the
PLC side
> for all T commands."
>
> Your servant notion for the plc really denegrates a complex,
symbiotic
> relationship between these two systems. While there are
many "hobby"
> level machines that use little or no PLC, most CNC machines have
> extensive PLC logic that intertwine Machine and motion. For
example, in
> this tool context, once the change tool (m6) command is given by
the CNC,
> it doesn't do jack until the PLC says, "I've got this tool in
place and
> it's ready for you to use." In that case who is the servant of
whom?
>
> Unless a CNC control has no look ahead or uses look ahead in the
very
> narrow, motion only way that you describe above, I can't see any
value to
> programming the way these experts suggest. In fact my initial
thought
> when I read your suggestion was that this was an urban legend that
grew
> from programming the first ever tool hive fitted to a 60's
generation NC
> controller running from punched tape. I really hope that even the
hobby
> level CNC units have moved past that.
>
> I see your disclaimer "most good programers" but I guess that I
program
> using the exception 'cause a single line of tool change code is a
lot
> easier for a human to understand that a Txx block followed by a
bunch of
> blocks that RUN USING A TOOL OTHER THAN THE ONE indicated.
>
> At the very least we can use the result of the test described above
to
> show that this programming technique has little value for the EMC.
>
> HTH
>
> RayH -- U.P. Michigan