how does re-homing in g-code work?

...an occasional re-home would prevent positioning errors from accumulating.

You can work around it 2 ways.

Either split your code into modules, allowing you to re-home between them, or just halt at a convenient point (not inside a sub!) and then re-home and 'run from line'.
The former is more manageable and reliable, because unlike other controllers, Linuxcnc does not re-start the spindle automatically etc. on a run from .. command and the next command needs to be a linear one.
As this probably meaning a retraction from the workpiece before halting, you might as well just code G28 M2, finish that module and start another after re-homing.

Obviously it is preferable to sort out why you lose steps, cuts too deep and stalling, velocity to fast or whatever.

regards

ArcEye wrote:

Obviously it is preferable to sort out why you lose steps, cuts too deep and stalling, velocity to fast or whatever.

Purely as an intellectual excercise, as I don't think this is a good idea, but I wonder if you could use the non-home end limit switches as probe inputs and periodically run a probing routine?

It is fairly unusual to just miss a couple of steps (My lathe does it when pushing too big a drill with the toolpost). If it happens during a fast rather than very slow move then the motor stalls and there is no recovery possible.

Is it possible to achieve automatic homing when machine is powered on? I am using proximity sensors at the home positions of each axis....how do I go about doing this?
I understand it cannot be done through a G-code command....however, when we load an ngc file or power on the machine....is it possible for the axes to ho me by itself detecting the position using proximity sensors (like moving in negative X till the proximity sensors detects)?

Thanks


Regards
Susam

Is it possible to achieve automatic homing when machine is powered on?

Yes it is possible, but it is not desirable or safe.

You should not have un-commanded movement when power is applied, that is just dangerous.

It takes no time at all to type Ctrl Home or click on the Home button, I don't see the problem.

The other issue is how do you differentiate between a start-up and the F2 button having been pressed to power down the system whilst at lunch say and then pressing F2 again to resume the work.
You would not want to re-home in the latter case.

regards

Yes, that makes sense. Now I have got the sensors connections set up.....just want one pyvcp button element that homes all axes at the same time. I hope it works out.

Thanks!