Patrick Ferrick wrote:
Hi all,
After reading (and (for the most part) understanding) the integrator's
manual, I have come up with the following plan for constructing and
controlling a custom toolchanger. The changer will use three steppers,
one to spin a carousel of sorts and two to operate a scara-type arm to
place tools from the changer somewhere that they can be taken up by the
spindle.
1. obtain and set up a second pc running EMC2
No problem.
2. connect the mill's pc and the toolchanger's pc via ethernet cable
No problem.
3. determine the correct NML messages needed to carry out the steps for
a toolchange
Not simple, but not a big problem. Tool change messages have a separate
nml command/status channel (I think). I believe you can get the
messages going to the other machine by changing the NML files. This
will cause all tool messages to go there, but that's probably what you'd
want anyway.
4. add a button/code to AXIS using pyVCP to generate these messages
It's automatic - T6 causes a tool prep message to be sent to the
toolchanger (prep tool 1). M6 causes a change tool mesasge to be sent, etc.
5. figure out how to send the messages by connecting the button to the
parport with HAL
Again, automatic.
Pretty simple, right? My rationale for this somewhat convoluted
sequence of events is that I think I can get all that going with what I
already know how to do with HAL etc.
Well, the part above is simple, but it doesn't actually get the tools to
change. You still need a way of making a tool change message turn into
motion commands for the 3 motors. Either you need to change NML (I
wouldn't even consider doing that) so there's a way to send arbitrary
commands to a remote machine (while still operating the local
machine), or you still need to get some HAL-foo working to do the tool
changes. Actually, I think you'd need the HAL-foo anyway.
Based on my reading of the manual, it's going to take a good while
before I can get pull it off with straight HAL/ClassicLadder objects.
I'm going to work on that at the same time, so I'll probably get it to
work the right way at some point.
I'd strongly suggest going straight to the right way :)
HAL has all the motor limits already - stepgen won't do anything beyond
the limits you set, and you can use a limit3 block if you want to use
servos. Kinematics for an R-theta robot are trivial, and they're really
unnecessary anyway since you can just specify the positions you want in
cylindrical coordinates. You only need the motion controller and its
kinematics if you want to specify cartesian coordinates for
non-cartesian actuators. It's very easy to write a HAL component that
outputs a sequence of positions whenever it's clocked - this can be
done in comp I think. There are only a few positions anyway - you could
almost do it with mux4 blocks as was suggested before.
Comments?
If you haven't already, I think you should define what the motions and
I/Os for the toolchanger will be:
what needs to happen at start-up? (homing ...)
what needs to happen to take a tool out of the spindle?
what needs to happen to put a tool in the spindle?
what needs to happen to get the right tool in the robot pickup position?
what does the robot need to do to grab the tool from the holder?
what does the robot need to do to place a tool in the holder?
Once you know all the actions needed, you can start to think about how
they need to be sequenced:
at tool-prep:
rotate carousel to correct position (or not - can the robot hold two
tools at once? do you need to put away the old tool first?)
at tool-change:
rotate carousel to slot for tool in the spindle (closest direction or
always forward?)
stop spindle
position robot to grab tool in spindle
transfer tool from spindle to robot
move robot to carousel
drop tool in carousel
move robot clear of carousel
...
You get the idea :)
Once you know exactly what has to be done, it's a lot easier to decide
how to implement it.
Thanks,
Pat
ps - It often occurs to me when I'm generating these posts that a twenty
minute conversation with one of you EMC gurus would be worth about a
month of back-and-forth on the list. Unfortunately, the NAMES show
happens right in the middle of exam week for me, so that's a little
tough. If anybody would be willing to try a brief phone conference
please email me privately...!
http://www.cnc-workshop.com could be a good opportunity - it should be
after exams. Then you can talk to almost all of us, so you can pick
whichever person tells you what you want to hear ;)
- Steve
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