Hi,
I don't know why industrial machines use 9 (though I agree, that's also what I have seen), when the same can be accomplished with 3.
Wrong, the same thing cannot be accomplished with three. If for instance you had one switch which activated as a limit, both ++ and --
on one axis when it triggers all Mach knows is to stop. If you try to jog in the + direction by mistake because its going to make it worse then it will let you,
it doesn't know which end the machine is at. Whereas if you had two limit switches (and two inputs) it would know that you had banged into the + limit so it would
let you jog in the - direction but stop you from jogging in the + direction.
Additionally industrial machines are powerful and fast, when you hit a limit the machine powers down, no ifs or buts. It does not rely on a computer to turn it
off, the limit switches trigger the electrical contactor to drop out. Have to for safety, in most countries its probably legally required.
The reason I don't want to fit more switches is for simplicity sake.
Its a poor excuse but I understand
Less wires, less money, less things to go wrong...
Less money, less wiring but because you are trying to combine things you have in fact ensured that there are MORE things to go wrong, not less!
Three good quality home switches and 'soft limits' are good. If you have modest steppers then 'soft limits' are probably enough. If your axis motors are powerful
and/or fast, especially servos then limits are mandatory for safety as well. If you chose to combine functions you will end up with less protection and robustness than you thought.
Craig