Kinematic model for a 5axis mill with universal (nutating) head

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13 Jan 2024 09:21 #290548 by Aciera

It would be cool if it could display custom cutters when calling for a tool in your NC file.

Certainly not impossible. The way the vismach component works it would basically need to load the geometry of all the tools when the config is started and then show only the one that matches the current tool number.
Ultimately it would be nice to integrate the vismach simulation into the preview window.
I have customized the regular preview to show the current TWP, just like the vismach simulations.
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16 Jan 2024 09:00 #290843 by Aciera
Just in case you are still working on the joint angle calculations in the remap:
While trying to get that case structure sorted out I realized that my approach, while useful for simple kinematics, was flawed for more complex ones like the generic nutating kinematic.

I have now changed to a different idea which is much more promising.

Since we are working with 'asin()' and 'acos()' functions, we get two solutions of interest to us:
For:
theta = asin(x): theta, pi-theta
and for
theta = acos(x): theta, -theta

Our problem is to determine which combination is the right one for us, which is what I was trying to do with that case structure.

The remap now calculates all four possible solutions pairs and calculates the resulting tool-z vector. This approach allows to choose the pair of angles that give the best movement of the head.
I'll also try to eliminate angles exeeding the relevant joint limits set in the ini file.

I'm still working on this so I have not updated the sim configs yet.
Please let me know if you are in need of an updated version.

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16 Jan 2024 09:41 #290846 by Paul01
That's great to hear. Currently I have a few other things to work on, like my Vismach model. So I'm all good to wait until you've come to a resolution you're happy with.

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17 Jan 2024 16:00 #290964 by stustev
If I was putting a control on the machine you pictured I would set up the post processor to put out A and B axis commands (tool tilt) and let the post processor convert those position commands to rotary axis positions.
That may be what your plan is but just thought I would add my thoughts as early as possible.
I would also implement electronic gearing. This would minimize hesitation when moving an axis that needs the second axis to move to keep the tool oriented properly. I saw this on a 5 axis BC head with a Fanuc 15MB control. When electronic gearing was turned on the BC motion was noticeably crisper and smoother.
You can also implement 5 axis tool length offsets if the kinematics is in the machine control instead of the post processor. The 5 axis Cinci (with LinuxCNC) I had was able to use post processed NC programs using any tool length/pivot length combination by putting adjustment values in the tool length register. The important value in 5 axis positioning is the pivot point of the rotary axes. The control needs to position the XYZ of the pivot point using the rotation values of the tool angle(s). By implementing tool length and pivot length into the machine control kinematics you can also have TCP (Tool Control Point) motion.
When compensating a rotary axis that can rotate several rotations you also need to make sure your position compensation adds to ZERO for one complete rotation or you will have compensation addition or subtraction error for rotations more than one complete axis rotation.

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21 Jan 2024 13:02 #291255 by Aciera
I have just updated the config folder in the opening post.

Implemented:
G68.2                  : defines twp using euler-angles, pitch-roll-yaw, 2-vectors, 3 points, optionally with offset in XYZ and rotation in XY
G68.3                  : defines twp from current tool orientation, optionally with offset in XYZ and rotation in XY
G68.4                  : same as G68.2 but as an incremental definition from an active TWP plane
G69                      : cancels the current twp (resets all parameters, moves to G54 and sets Identity kinematics)
G53.1 (P)              : spindle orientation without tcp, switches to G59 and activates tool kinematics
G53.3 (P XYZ)      : same as G53.1 but  with simultaneous move the the XYZ coords on the twp plane 
G53.6 (P)             : same as G53.1 but spindle orientation with tcp

- Spindle is  C primary, A secondary or B secondary as defined in the [TWP] section of the ini file
- All G53.x commands will respect axis limits as set in the ini file for the respective primary and secondary spindle joints.
- The P word sets the orientation strategy: 0(default)=shortest distance, 1=positive rotation only, 2= negative rotation only (this applies to the primary rotary, the secondary move the shortest distance)
 
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22 Jan 2024 07:41 #291316 by Aciera
Some more details for which I did not have time yesterday:

- The tool kinematic mode now operates with the spindle joint angles calculated by the remap instead of the actual joint position. The operator can now jog the spindle rotation without rotating the whole coordinate system as described in the documentation which makes it a lot more fool proof.

- All angles (ie primary, secondary and virtual pre-rotation) calculated to orient the tool to the requested TWP are run through the respective tool-kinematic model in the remap to verify that the values are indeed correct.
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02 Feb 2024 03:45 #292186 by xu
Sir, why does this py program take up so many cpu processes? Is there any way to optimize it?

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02 Feb 2024 05:12 #292193 by Aciera
I'm afraid, I cannot help you there but I'm sure the matrix multiplications and atan2 functions are computationally not the most lightweight.

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02 Feb 2024 14:31 #292219 by JacobRush

 The operator can now jog the spindle rotation without rotating the whole coordinate system as described in the documentation which makes it a lot more fool proof.

 

First off all of this is all very cool and I hope it makes its way into the master branch at some point.

Regarding jogging the rotation of the head, I *think* on industrial controls I've used it doesn't allow you to rotate the head if you have a tilted work plane in effect. I can do some testing on a Heidenhain machine here if that's useful at all?

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02 Feb 2024 16:48 #292228 by Aciera
Thanks for your feedback.

Inhibiting jogging is one thing but the bigger problem is that I don't see a way to keep an operator from using an MDI command with an A,B or C word because this would require the gcode interpreter to be aware of TWP modes.

However the main issue which caused large simultaneous machine movement during spindle reorientation in TWP mode has been solved. The current kinematic component does not use the actual spindle rotary position for it's calculations anymore but uses the static angles calculated by the TWP remap. This way the operator can change the orientation of the spindle (either by jogging or MDI command) while in TWP mode but no unexpected machine movement will result from it.

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