TCP 5-axis kinematics

3D-Master wrote: Basically afaiu the center of rotation is "locked" to the machine origin right?

I would have to check, but I think that the graphical preview assumes that the centre of rotation is at the origin of the current working coordinate system. (not the machine coordinate system)

The motion planner doesn't make any assumptions, it simply does not care as things stand.

Hello

Sorry I have been away for while,
I have had so much work that I have had no time to do anything else.

I will read all messages soon and I will give some input to this topic.

Mean while:

I have solution for 3+2 indexing work where zeropoint is fixed to workpiece,
and its translated along with rotated part.
This is now a subprogram that moves one zeropoint.

To make this as standard linuxcnc command will need a lot more.



Feedrate in 5-axis motion is a topic of it's own.

There are basically two different 5-axis modes.
First is fixed to table, this means that coordinate system is fixed on part.
When part or tool rotates coordinate system will rotate along with them.

This means when you command rotary axis motion, position relative to part will not change.
So this translates to no feed rate change from rotary motion.

This is one and most best feature of it.

Second one is coordinate system fixed on machine.
This means that coordinate system will not rotate along with part.
Best thing about this is that X axis is still along original X axis regardless of rotary position.
to calculate this compensation is not a easy task and you need compensate rotary feed rate as well.
And this will complicate things a lot, easiest way is to run this mode in inverse time mode.
Commercial controllers do this feed compensation automatically.

But I have only seen Fanuc based controllers to do this non-rotating mode.

I will not go in to acceleration in 5-axis motion or motion planning in 5-axis motion.
I do not have so much experience in math in this topic that I could say something...
But I will try to give my best feedback on this issue.

We could do a general kinematics module for LinuxCNC.
Where you only define what rotary axes you have and relative distances between these axes.
Then rotary center needs to defined relative to machine zero.

I think we need to push this from one man's solution to of the box example in basic linuxcnc installation.
This will need solid documentation how it works and simple explanation how to define parameters correctly to get it work.

If you know the center of rotation you can set the post processor to calculate the offsets for 3+2 work.

why using post processor as the controll also knows the offset
and can do it with only the simple postprocess 5axis

Hello

Usually I do use my zeropoint at rotary center, this is by the way more safe cause you will know exact place of your machine vice or other stuff.

But there are some situation where you need take zeropoint to known feature on part.
Example when you need to do second phase of part and run 3+2 machining to it.

If you know the center of rotation you can set the post processor to calculate the offsets for 3+2 work.

this is exactly what we want to avoid. We want to be able to position the part wherever we want and still get the same part or when you have to correct something on an existing part, which needs 5 axis work