Re: 3 axis controller

[Matt Shaver <mshaver-at-erols.com>]

john s finnila wrote:


> This simply requires that the PC based control has provision for
> outputting a tool (T) strobe command along with a BCD or binary tool
> number command in TTL logic.  Then the complex logic of the tool changer
> can be written in an external PLC.
<...>

> Does the emc allow
> for these features.

I'm not sure if the current Linux based version of the EMC still has the 
code in it from way back that controls a tool changer. My biggest 
question is whether the motion system can be paused by the I/O 
controller. Right now I do a tool change (on a machine without a tool 
changer) like this:

N40G53G0Z0(retract quill)
N45X0.Y0.(move X and Y to the tool change position, change as required)
N50M05M09(spindle and coolant OFF!)
(display a message for the operator)
N55(MSG,LOAD TOOL #1)
N60M00(don't move until the operator presses the S key)
N70T1M06G43H1(change to tool 1 and get its length from the tool table)

As you can see, I do the tool change explicitly in the g-code because 
all the M6 does is change the active tool number. Obviously, that would 
have to change for your application. The motion system would have to 
send a message to the I/O controller signaling the tool change, and the 
I/O controller would have to assert a "busy" flag that stopped all 
motion while the tool change was in progress. Some machines have a tool 
changer that uses a swinging arm to fetch the next tool from the 
carousel (or belt if it has a lot of tools), and insert it into the 
spindle, but others move the carousel under the spindle and raise and 
lower the whole thing to pick up and put back tools in the pockets of 
the carousel. There is a lot of variability in how tool changes are 
accomplished, but I guess the basic sequence is:

1. Turn off coolant.
2. Move Z to the tool change position.
3. Orient the spindle.
4. Traverse the carousel fully towards the spindle.
5. Raise the carousel.
6. Release the old tool.
7. Drop the carousel.
8. Index the carousel to the correct tool pocket.
9. Raise the carousel.
10. Clamp the new tool.
11. Drop the carousel.
12. Retract the carousel to its "home" position.

Of course there are a number of switches that have to be monitored by 
the software to ensure that the mechanism is actually moving correctly. 
For example, the carousel must be fully retracted at the end of the 
cycle before we move the Z axis.

Matt