Cinématique avec axes "redondants" (+présentation)

vincentECN wrote:

newsig zero float
net zero => sum2.1.in0
sets zero 0

This works, but "setp sum2.1.in0 0" has the same effect and is simpler.

I wanted that when i add a shift, the movement of the machine will compensate.

I have forgotten where we got to on this. Have you looked at tool offsets and the "offset" HAL component?

vincentECN wrote:

And i expected to have a final position at X10, but finally it's X9...
I don't understand...

You need to be very clear about the distinction between joint positions (in absolute machine units), the on-screen reported position (in workpiece coordinates, unaware of anything happening in HAL, and following the XYZ commands exactly), and the actual physical position of the tool.

What you are seeing _might_ be correct. I can't tell exactly how you have things set up.

You probably need to pass the command to the offset through a limit3 component to remain within machine limits.

In your example you have an offset of -1, the joint is at 9, and the commanded position is 10. That is correct for some definitions of the offset.
In this scenario, if the "extra" axis offset was 1, then the X-joint at 9 would put the tool at 10 on the workpiece. You might need to switch some signs if it doesn't make sense like this.

In the situation you describe there are two things to control. You need the tool in the correct physical position, and you need the LinuxCNC system to know that the tool is in the correct position.

The first part would be rather easy if it were not for the second part.

Imagine a system where the Y-axis command signal has the "disturbance" subtracted from it before it goes in to the PID command input. Then the tool position would be automatically compensated in the way that you describe. Unfortunately the _feedback_ to LinuxCNC would then not match the command signal, and the system would stop with a following-error.

So, one solution to this problem is to use the "offset" HAL component, which only really adds one signal to another, but is clever enough to subtract the difference on way back so that the following-error fault is not tripped.
www.linuxcnc.org/docs/html/man/man9/offset.9.html

Putting this between the LinuxCNC joint command pin and the PID input might do what you want.

There are other possibilities: Perhaps you want to have a second PID component to control the "disturbance' correction. You could add the output of the two PID components together to get a combined motor speed command. This might work better, but it it then rather more difficult to "fiddle" the feedback pin into LinuxCNC.

Of course there is a much simpler way to "fiddle" the LinuxCNC position feedback and avoid setting the following-error: You can simply short-circuit that loop in HAL:
net axis.1.motor-position-cmd => axis.1.motor-position-fb . But then you have no following-error tracking.

Or you can stretch the f-error limits in the INI to encompass the likely size of the "disturbance" so that the system only errors when the disturbance is too big.