Home limit switches

[NC Cams]

The limit switch connection scheme depends on the system design.

The servo amps in my CNC mill have internal shut downs that address overcurrent/overvoltage/overtemps. If these trip, they "tell" the interface card that the system is shut down due to a driver fault.

The limit switches go direct to the PC control card. They are "or'd" so that if you hit ANY one, the whole system shuts down.

The amps also have "inputs" for limit travel inputs to shut down the amp exclusive of the PC controller but the system was NOT wired to use the feature this way. The mill has the limits going right to the PC input terminals that the software deals with.

My CNC lathes have X+, X-, Z+ & Z- limits again or'd right to the controller. THere is a bypass button which enables you to back off the limit should you over run the travel. Again, whole shebang shuts down at overtravel fault...

Your driver cards and software should offer ways and suggested methods for overtravel limit switch incorporation. It is FOOLISH to NOT use them.

As far as cost goes for the option, the 914 Honeywell switches mentioned previously retail at about $75 EACH and they are bullet proof.

Do 4 limits (lathe) or 6 limits (mill) plus 3 "home" switches and you could be looking at as many as 7 switches which knocks the daylights out of $525.

Add time and material for to wire them and do all the logic programming and $750 really isn't that expensive for a commercial system - especially if it prevents a runaway whatever from hurting somebody.

The emergency room cost alone will probably dwarf the $750 expense as would the higher subsequent insurance premiums.