forum.cncdrive.com

Hello. I'm getting a strange issue with probing. There is a difference between the Var #5063 value and the Z axis dro value. Here is simple code that i used for testing.

Code: Select all

exec.Code ("G31 Z-50");                         
while(exec.IsMoving()){}

double zvar = exec.Getvar (5063);

MessageBox.Show ("Var #5063 ---> " + zvar);


and a photo with the result.



Am i missing somthing? Thanks for any suggestions.

This is not an issue, it is normal.
What happens is that when you probe and the probe input triggers then the motion controller saves the probed value and sends it to the software, but after that your axis has to stop, it has to deccelerate.
So, for example you probe and your probe sensor hits at -4.57, then the motion controller sends that value to the software and the axis deccelerates to stop and so the stop point will be e.g. -4.58

So if i'm not wrong. The difference between var#5063 and z axis dro is related to the feedrate. High feedrate needs more time to decelerate. If i use feedrate, lets say F80 this will produce less difference between var#5063 and z axis dro instead of F600.

Acceleration setting would probably have a larger effect than feedrate.

Thanks for your replies.

Yes, ofcourse. From higher feedrate you deccelerate down with the same acceleration the longer the deccleration path will be.
And the lower the acceleration setting is the decceleration path from the same feedrate to 0 speed is longer.
So, both parameters effect the length of the decceleration path.

Because stepper motors can loose steps when they are stopped without decceleration if the rotational speed is above the so called "start/stop frequency" of the motor therefor the probing just like any other motions can only work properly with acceleration and decceleration.

Thanks Balazs for the explanation.