5 axis kinematic

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06 May 2012 15:28 #19875 by maufissi
5 axis kinematic was created by maufissi
Hi,

This is my first post in this forum and I am kind of a newbie, so be gentle with me :)

I am building a 5 axis gantry machine and am planning to use Linuxcnc software to control it. I have a question regarding the standard 5axis ini file that is included in the release that confuses me. In the file .ini I see XYZ axis as well as BC which is fine, but there is also a 6th axis called W that is not supposed to be there. Any reason for this?

Also how do I go about setting the Tool Center Compensation required by my cam post processor.

Sorry for any dumb questions.

Maurizio

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06 May 2012 15:59 - 06 May 2012 16:03 #19877 by cncbasher
Replied by cncbasher on topic Re:5 axis kinematic
Linuxcnc is capable of 9 axis the primary axis of XYZ along with secondary axis being UVW and also Rotary axis being ABC giving you 9 axis

these being split as x axis related X U A
y axis y v b
z axis z w c
www.linuxcnc.org/docview/html/gcode/machining_center.html#_axes

tool compensation is stored in tooltbl file in your configuration folder , although if your using a decent cam processor all tool information can be stored their instead
see www.linuxcnc.org/docview/html/gcode/tool_compensation.html

which cam post processor ?
Last edit: 06 May 2012 16:03 by cncbasher.

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06 May 2012 16:11 #19878 by maufissi
Replied by maufissi on topic Re:5 axis kinematic
Hi cncbasher,

Thanks for the reply.

My machine is a 5axis gantry with XYZ linear and BC rotary. the ini file should have in Traj section coordinate parameters XYZBC only. If I use the preconfigured ini file in axis coordinate W should be removed? With this configuration should I modify anything in the kinematics file?

My cam software is Alphacam and the post processor requires TCP (tool center position) to generate G code for Linuxcnc controller. In the Tooltbl file one needs to input the tool length relative to the C axis center of rotation?

Maurizio

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06 May 2012 16:19 #19879 by cncbasher
Replied by cncbasher on topic Re:5 axis kinematic
you should not need to alter anything in the ini file excepting the parameters you mention , do not change the names or the order of the axis .

i'm not familiar with Alphacam unfortunately

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06 May 2012 16:30 #19882 by andypugh
Replied by andypugh on topic Re:5 axis kinematic
maufissi wrote:

there is also a 6th axis called W that is not supposed to be there. Any reason for this?

The 5axiskins demo allows you to drill in the W direction, automatically making compensating moves in the other axes.

Also how do I go about setting the Tool Center Compensation required by my cam post processor.

If you have 5-axis CAM then you probably don't want to be using the 5axiskins module which that demo config uses. That performs all the axis compensation inside the LinuxCNC kinematics, assuming the parameters in the INI file and the tool-lengths are correct. So for that configuration the G-code would be entirely conventional, with XYZAB describing the location in space and orientation of the tool tip.
I tink that the demo config is actually the one from this machine:

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06 May 2012 16:53 #19883 by maufissi
Replied by maufissi on topic Re:5 axis kinematic
Andypugh,

Thank You for your reply.

My machine configuration is the same as shown in this video


I understand what you say regarding rewriting the ini file for my configuration. What is important to know is, given the tool length compensation in the tool table file, do I need to modify the kinematic file to include the rotational axis tip offset with respect to the axis of rotation or is it sufficient to incorporate this info into the tool table offset. I need to pass on to the Alphacam postprocessor tool tip position and orientation in space.

Maurizio

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07 May 2012 21:34 #19914 by andypugh
Replied by andypugh on topic Re:5 axis kinematic
maufissi wrote:

What is important to know is, given the tool length compensation in the tool table file, do I need to modify the kinematic file to include the rotational axis tip offset with respect to the axis of rotation or is it sufficient to incorporate this info into the tool table offset.


I don't actually know, you might need to experiment.

Looking at the INI file we find: "TLO_IS_ALONG_W = 1" and a search of the docs shows that that has been removed, and no longer has any effect (the tool table now has a specific column for W tool offset)

In the HAL file there is (at the very end):
net tool-len motion.tooloffset.w
5axisgui.tool_length so that seems to indicate that the tool length in the tool table W column needs to be the distance from the tool tip to the axis of rotation. So, you might well want a zero-offset in the CAM.

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31 May 2012 13:20 #20529 by maufissi
Replied by maufissi on topic Re:5 axis kinematic
Ok I am still having trouble sorting out the kinematics for my 5axis machine. Given that the only rotational axis are the B and C positioned on the Z axis (tipical 5axis gantry machine), how do I implement the kinematic file to include the length of the rotation axis so that I can define the tool tip position for any given BC axis rotation position?

Thanks for the advice.

Maurizio

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01 Jun 2012 11:52 #20553 by andypugh
Replied by andypugh on topic Re:5 axis kinematic
The video you linked to was by Jepler, who also probably made the 5-axis demo config.

Looking at the kinematics file, there are two HAL pins, tool-length (which should be linked to tool-length-w, probably) and pivot-length

However, looking in 5axiskins.c only the pivot-length pin is actually used. So it looks like Chris might have decided it wasn't necessary.

I think you might need to modify that file to suit your requirements, but it should be just a case of changing the mathematics, not the code structure. You could use tool_length as a variable in the equations, and the value of the HAL pin will be used.

You would then need to re-compile the module, but that can be done using "comp" rather than recompiling the whole of linuxCNC

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02 Jun 2012 08:58 #20587 by maufissi
Replied by maufissi on topic Re:5 axis kinematic
Andy,

Thank You for your reply. I agree that it should only be a matter of changing the mathematics, and this is not a big issue. To my understanding, with the correct kinematics, I should be able to run the machine with the RTCP (rotation tool center point). This way the cam only needs to send to emc XYZ coordinate and tool tip orientation in the B and C axes with respect to the machined surface. This would be the easiest way to write a post processor for the cam software and this is how industrial controllers are normally able to do.

Please advise me if I am wrong in thinking this is the way to achieve RTCP funcion on EMC.

Maurizio

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