Manual tool change + tool lengh touch off

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24 Nov 2010 22:16 - 24 Nov 2010 22:17 #5596 by axel88
I'm trying to find a solution for manual tool change. In my opinion it should work so:

I've a switch at a defined position in the mill-area. If i start a milling progress my milling machine goes to the defined position and drives the tool against the switch (in Z-direction). Then Axis knows the Tool offset. After a manual tool change Axis runs the same procedure.

So far I've to less experience with emc to know how or why not this would work.

Is it possible to do it only with an instruction block in the G-code? Or do I have to Change somthing in the HAL?
Would it be possible to abuse the Z-Axis home switch and just run an "home instruction" every tool change?

Axel
Last Edit: 24 Nov 2010 22:17 by axel88.
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25 Nov 2010 01:08 #5598 by andypugh
I think there should be a way to do this, but I have not figured it out.

EMC can be instructed to go to a specific, absolute, XYZ position for tool change
EMC2 can do a Z probe from a G-code instruction and store the result in a memory location.
G-code can use the value in that memory location to set the tool length.

I am not sure how to put it all together.
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25 Nov 2010 12:59 #5605 by Mike_Eitel
Hi

Thats exactly what I'm looking for since long time.
I was wondering if such functiuonalty is connected to the probe input ?

THX Mike
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25 Nov 2010 20:37 #5617 by axel88
andypugh wrote:

EMC2 can do a Z probe from a G-code instruction and store the result in a memory location.
G-code can use the value in that memory location to set the tool length.


So if you know these things, wouldn't it be enough to write a gcode-instruction-block and for e.g.copy paste it to every tool change in my*.ngc ?
Or ist it impossible for the gcode to route to an absolute coordinate of the mill machine?

If anyone has any code exaples i would like to experiment with them.
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25 Nov 2010 21:34 #5619 by axel88
Not an very constructive post: But i found a nice Video how this could look like if it would work :-)

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26 Nov 2010 00:25 #5620 by andypugh
axel88 wrote:

So if you know these things, wouldn't it be enough to write a gcode-instruction-block and for e.g.copy paste it to every tool change in my*.ngc ?
Or ist it impossible for the gcode to route to an absolute coordinate of the mill machine?


If you are happy to do that, then it is easy, and it needn't be anything as ugly as a copy and paste.

You can move in absolute machine coordinates with G53 using a line like
G53 G0 X10 Y10.

(You need a new G53 on each line, it is non modal).

You would then use a G38 probe to the touch sensor.

The whole thing could be a subroutine, eg create a file called "toolprobe.ngc" with all the G-code in then put
O <toolprobe> CALL in your G-code program.
(some guidance on using subroutines is here: wiki.linuxcnc.org/emcinfo.pl?SubProgramFiles )

What I am not sure how to do is to make it all happen automatically when you issue an M6 command.
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26 Nov 2010 08:47 #5623 by axel88
andypugh wrote:

What I am not sure how to do is to make it all happen automatically when you issue an M6 command.


I think this should/could be a job for the postprocessor.

Has anyone experience with touch off probe hardware:
-Just a normal switch (could be unprecise)
- an induktice switch ( I could imagine that the induction is influenced by the size of the tool?)
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26 Nov 2010 11:31 #5624 by andypugh
There are quite a lot of touch-probe designs out there. The classical Renishaw type is probably as good as anything (three rods around a circle spring-loaded into the gaps between ball bearings. It is all wired in series and so any movement in any direction breaks the continuity.

www.indoor.flyer.co.uk/probe.htm is a good example of the design.
www.cnczone.com/forums/digitizing_laser_...ade_touch_probe.html is a very cheap and easy version of the design.

For a tool-length probe you would leave off the ptobe rod.

If your tools will always be conductive (not necessarily a safe assumption with some of the coated tips, though ordinary carbide conducts well) you could just land on a spring-loaded plate and let the electrical contact be the tool-to-plate contact.
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27 Nov 2010 11:19 - 27 Nov 2010 11:38 #5657 by axel88
So far I installed a touch probe and started experimenting with the gcode. But there are some errors I can't cope with:

If i follow the tool-length-probe.ngc example i touch of with

G38.2 Z0 f50 (f50 is modified)
when I try to run
G91 g0Z.2 (off the switch) I get the error:" Probe tripped during non-probe MDI command"

This could be solved by running the probe slower (f30) but if I want to have a big safety distance this could take a long time :(
Is there a better command to release the switch that ignores that the probe is pressed?

Second Error:

I touched of my tool the first time, joged a bit with the manual control, changed the tool length and run a G30. If I try to touch of again(G38.2 Z0 f30) I get "Startpoint to close to probe point"
Last Edit: 27 Nov 2010 11:38 by axel88. Reason: third error solved
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27 Nov 2010 11:51 #5658 by axel88
Ok, I found out that G38 need to be run in G90 mode. But even if I try to release the switch with G38.5

Code Target state Direction Signal Error
G38.2 Contact Toward workpiece Yes
G38.3 Contact Toward workpiece No
G38.4 No Contact Away from workpiece Yes
G38.5 No Contact Away from workpiece No


which shouldn't cause an error, I get one :(
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