Tool change - was Re: HIP4081 was Re:Re:Black box/kerr

From: "Smoke" <Smoke@...>
<s>

>As for how the big boys do tool changes, the whole thing is basically
>mechanical with the travel of the various components physically limite to
>stop at various point.

Some tool changers use almost all CNC motion. The spindle moves to an
empty location and places the old tool there, releases it and raises up
to clear, moves to the next tool and grabs it.

Many recent low end tool changers use a combination of CNC motion and
auxiliary motion. The spindle will place the old tool in a location,
release it, raise off from it. Then the tool hive, drum, or chain moves
to the new tool. Then the spindle moves down onto the new tool, grabs it
and goes to work.

More expensive changers use intermediate arms to grab the old tool,
extract it from the spindle, rotate the new tool into position and insert
it. These changers will pre locate the next tool and get it ready while
the old tool is cutting. They will also start the new tool working while
putting away the old tool. When time is of the essence this is the
quickest. Many can change tools chip to chip in a second or so.

<s>

>The elecronics required for tool changes (or moving/rotating parts) does
>not require the use of any CNC components. It does require a signal to
>get the system started tho'. For a home shop or hobby environment, this
>signal could be provided by a manual pushbutton operated during a pause in
>the G-code. After tool changes are done, simply hit the "go" (or
>"continue") button for the CNC unit.

Since the type of changer makes a big difference in the electrical logic
required it is difficult to generalize on the signals that are needed. At
a minimum there are two.

From CNC - start tool change and inhibit machine motion
From Changer logic - release motion inhibit when change is complete.

These two commands would work with a tool changer that had it's own system
of logic and required that the spindle hold still during a tool change.
This logic could be supplied by a set of position switches, relays, motors,
solenoids and such. The logic could also be supplied by a pic, stamp,
tiger, the old tandy z80, a dedicated plc (programmable logic controller)
or similar programmable device. (I once saw a logic controller made out
of a small motor that turned a mailing tube with a bunch of shim stock
glued on it and tempered copper wire for contacts)

A place one tool and move to the next type of system would have a lot more
use of the motion parts of the cnc. The systems like this that I've seen
use a dedicated set of relays or logic that tell the CNC that it should
move to a different location (over-travel release) so that the tool changer
is protected from normal milling motion. After that the

-CNC moves old tool to known place.
-CNC send a release tool command
-Tool Changer sends tool released
-CNC moves to new tool location
-CNC sends a tool clamp command
-Tool Changer sends a tool clamped
-CNC moves to work envelope and removes over travel release

A system that moves the available tools (hive, drum, belt) would also
require an over travel release followed by something like this set of
commands.

-CNC moves old tool to location.
-CNC sends a release tool command
-Tool Changer sends a tool released
-CNC moves spindle to clear tool motion
-CNC sends an clear command
-Tool Changer moves new tool under spindle
-Tool Changer sends ready command
-CNC moves spindle onto new tool
-CNC sends a clamp tool command
- Tool Changer sends a tool clamped command

Without further iterations, I think that you get the idea. You would
need to study whatever CNC you have or plan to use, the mechanical system
that you have available or plan to build, and develop a similar set of
logic that will get you from the beginning to the end of a tool change.

As smoke said above, the end inhibit could be an operator press of the go
button although I've heard of people attaching wires to the keyboard s
contacts and have the changer press it at the end.

Shameless Sales Pitch or PR -- If you use the EMC as your CNC almost any of
the above combinations can be had with the use of Tcl/Tk and iosh for a
soft-like plc. (I used soft-like 'cause I got ragged on once for Soft-PLC
being copyrighted) The commands can be sent to a serial or parallel port
or a dedicated io board and it could use an extra axis to control the drum,
belt, hive. (talk about a smart black box!!!)

And if that's not enought logic for you the puffin project is talking
about a first release.

<I've used my weeks allocation of cad_cam... bandwidth so I'll quit>
Hope this helps --

Ray