Hi,
home switches can be anywhere on an axis. When the home switch is activated it will reset the machine coordinates,
but you can choose to reset them to zero OR some offset. Thus if you had a home switch in the middle of an axis you
could set a 'home offset' equal to half the axis travel. This would result in the machine coordinate zero being at the
end of the axis despite the home switch being in the middle.
You have identified one problem however. If for instance you set the initial homing direction to the right, and when at power up
the machine was already to the right of the home switch, the machine will travel yet further to the right hitting the end of
the axis before any home switch activation.
I solved this problem by having my home switches near (within a few millimeters) of the end of travel. Further I used
roller plunger microswitches which because of their defined and repeatable hysteresis make good home switches.
I used to have limit switches beyond the home switches but they were cheap switches and I didn't design the mounting
well and I wiped a couple out. I removed them all and rely on 'soft limits'. Because I get very reliable and accurate homing
this has proved adequate. If I were to fit limit switches I would use inductive proximity switches. They can easily be arranged
such that an over travel event does not destroy them.
The 57CNC gives you plenty of inputs. I would take advantage of that an use one input per switch and would further recommend
separate home and limit switches. For a three axis machine that would mean six limit switches and three home switches for a total
of nine inputs. Many people combine limit and home functions but with such a capable controller you don't have to.
It means also that if a switch event occurs than Mach knows
exactly what event it represents, not having to deduce whether
its a limit or a home event or even if its a X++ or an X-- event.....with one switch/one input no deduction or interpretation
is required or potential mistake be made.
Craig
https://nz.element14.com/honeywell/bzc-2rq18-a2/switch-basic-top-roller-plunger/dp/1525198Note this is the New Zealand site and is in NZD. If you search for Element14, or equivalently for Newark in the US or
Premier Farnell in the UK you will get the same product but in your local currency.