Limit switch set up and homing question

[BobS]

Hello everyone,

I have installed electromechanical limit switches on the mill's +X , -X, +Y, -Y, +Z and -Z axes.

Question: Without respect to the home position (that is set differently for each job), how do I set up the limit switches to stop all axes travel when any one of them is tripped?

Thanks!

[cncsnw]

First some vocabulary:

Machine Home (a.k.a. Machine Zero) should be where you home the machine to every day. It should be the same place every day. That is where your software travel limits are measured from.

Part Zero (a.k.a. work zero, WCS offset, fixture offset, G54-G59) is the zero point that your CNC G code program works from. You set Part Zero wherever the stock happens to land for each particular job. The control keeps track of Part Zero as an offset distance from Machine Home.

Regarding hardware limit switches:

If you wire each limit switch to a separate input (preferable, but generally not practical on an Acorn due to shortage of inputs) then you would define each of those inputs as FirstAxisMinusLimitOk, FirstAxisPlusLimitOk, SecondAxisMinusLimitOk, SecondAxisPlusLimitOk, ThirdAxisMinusLimitOk and ThirdAxisPlusLimitOk.

In that case, you might choose to use one of the switches on each axis as a homing switch, so you can automatically and repeatably set Machine Home in the same place every day. They instead of "...LimitOk" you would define those three inputs as "...HomeLimitOk" (for example, FirstAxisHomeLimitOk, SecondAxisHomeLimitOk and ThirdAxisHomeLimitOk).

If you do not have enough available inputs to put each switch on a separate input point, then you can just wire them all in series (using the normally-closed contacts, of course) to one input, and designate that input as "LimitAll".

Someone with more Acorn experience than I will have to address whether and how you can use some of your switches for homing, while having multiple other switches act as "LimitAll".

Once you have established where your Machine Home point is going to be every day, then you can also enter software travel limit distances to tell the control how far it is from Machine Home to the end of usable travel (just short of tripping the limit switch) on each axis. That will allow the control to stop motion before it actually trips the limit switch, in most cases.

Your switches will still be there as a backup, if for example the machine has not yet been homed, or was homed in the wrong place, or has lost position.

[BobS]

Hi cncsnw,
Thanks for your very helpful reply.
I’m learning how to use the Acorn controller having just finished converting my PM-30MV to CNC. All the limit switches are NC and in series. The input status indicator page show's that they are functioning correctly. Tomorrow I’ll begin working on using your guidance.
Thanks again, Bob