Re: [Emc-users] Soft Limits

[Eric H. J. <ejo...@aa...>]

John,

> Prior to and during homing, the soft limits are set to 
> "current position 
> +/- total length of axis"  (length of axis is the difference 
> between the
> soft limits in the ini file.  That means the home sequence 
> should run into the physical ends of the axis before it hits 
> the soft limit, unless the values in the ini file are grossly wrong.
> 
> Once an axis is homed, the soft limits are absolute, based on 
> the ini file values.

You mentioned below that EMC will prevent you from getting within 0.1% of
either limit. My X axis length is 76" and Y is 120", thus 0.076" and 0.120"
respectively. Those would seem to be about the points the soft limit is
being triggered when homing.

I had played with several ways of setting the soft limits, like setting the
homes for X and Y at 0.2" off the limit switches, and setting that position
as 0.0, hence the soft limits would go from 0 - 75.6 and 0 to 119.6
respectively, but to simplify things, I set the soft limits to the hard
limits.

> In all but the latest CVS, EMC will prevent you from getting 
> closer than 0.1% of the total axis length of either limit.  
> That doesn't sound like your situation, since "nowhere near 
> the limit" seems like a lot more than 0.1%.  (0.1% of a 20" 
> long axis is only 0.020".)  Last night after a discussion on 
> IRC, I recoded the soft limits.  You can now go all the way 
> to the limits, but not beyond.  Reaching the limits is not 
> treated as a fault, it just stops moving.  Going beyond the 
> limits is a fault, but that is hard to do because jogs and 
> other motion commands are checked before they are issued.  At 
> the moment the only way I know of to get that fault is to 
> issue an arc command with both endpoints inside the limit but 
> some part of the arc outside the limit.  (Eventually we will 
> improve the checking, and even that arc command will be 
> caught before the move starts.)

That makes a lot of sense, but I thought I had figured that out, in that it
was happening with the Z axis. I would generally encounter this problem
after issuing A G92 or similar command, so it is possible I am still getting
fooled by Z, and thinking it was X or Y which was tripping the soft limit
(hence, nowhere near the soft limits).

I think I know what to look for on the second part, still not quite sure
what is going on with homing, but I will do some more testing.

Thanks,
Eric