Help please - Linear Scale only homing

Everything homing nicely. Thanks for your help.

FYI.
- My first mistake - not knowing that you need an absolute encoder to do switch-less homing
- 2nd - some settings in my ini making the encoder look like it was an absolute encoder when it wasn't

@Andy, if I can ever do anything to help the cause - please shout out. I have skills in mechanical design CAD/FEA, have imported 3 CNC machines from China and my day job is in IT. Current project is a 1.5kw laser hybrid to do wire deposition and subtractive.
Cheers Pete

whatwasIthinking wrote:

@Andy, if I can ever do anything to help the cause

How's your C / C++ / Python / Tcl

There's plenty of things to look at in the issues list. 
github.com/LinuxCNC/linuxcnc/issues
 

Non existent sorry. Pascal / LISP back in my day but that was then.

I also have linear scales with an index signal.
On the x-axis it is in the middle and on the y-axis it is at both ends.

At the moment I home with a combination of  limit/home switch. The switches are at the far end, so I know
in which direction I have to look for the home switch, but I would like to home the index signal of the scale.

What would be a good strategy to find the index mark, especially when it is in the middle, for I don't know the position
the mill was shut down.
So I might search in the wrong direction.
 

strahlensauger wrote:

What would be a good strategy to find the index mark, especially when it is in the middle, for I don't know the position
the mill was shut down.
So I might search in the wrong direction.

 

LinuxCNC will search for a home switch in one direction, then move off the home switch in the other direction looking for an index.
So, the trick is to have a secondary track (probably with a proximity sensor) that extends to just before the index mark. 
If the machine is "off" the track it moves towards it, then off to the index. If it is already on the track it goes straight to the reverse move. In either case the system will then find the index. 

For the Y I would suggest a short target and an inverted signal. 


 

Thank you for the quick answer, but how do I set up a second track?

I thought homing is controlled by the three variables
HOME_SEARCH_VEL, HOME_LATCH_VEL and HOME_USE_INDEX.
and just could search in one direction.
Can the mill change the direction by the signal of a switch or proximity sensor?
Or do I have to calculate the sign (the direction) of the variables before travel begins?
And how do I put that in the ini or hal?