configering Home switches

If i put home switches on all three of my axis in a parallel configaration that is three switches hooked up to one input, (pin 11) on my Breakout board. if it hits one switch for home will it allow the machine to move to the other switches to finish homing the remaining axis. how will this work.

helpmeout wrote:

If i put home switches on all three of my axis in a parallel configaration that is three switches hooked up to one input, (pin 11) on my Breakout board. if it hits one switch for home will it allow the machine to move to the other switches to finish homing the remaining axis. how will this work.

You cannot tell the machine to home all three axes at once.

When you first load emc2 (on a three axes configuration) the "X" axis is the default selection. When you click the "Home" button, it moves the machine toward the X axis home switch, unless the switch is open. Once it finds the switch, it then backs away, and lets the switch close, then moves toward the switch at a slower rate. Now the computer knows where the machine is, in the X freedom.

Then you click on the "Y" axis (or the "Z" if you desire) and the process repeats itself.

If you're hooking all three home switches to the same pin, the computer has no way of determining which axis has hit the home switch, so it will only try to home one axis at a time.

However, in many cases, you are going to be using the same switch for home and limit. So, rather than wire your home switches in parallel, it'd be better to wire them in series. This means that a broken wire, or bad connection will always look like you have arrived at a limit switch, and stop the machine.

And if you do it right, it is sometimes possible to use the same switch for BOTH limits on any given axis. If you use a micro switch positioned under the (moving) table, for instance, you can use a tapered block near each end of the table to activate the same switch. In other words, in some cases, you could achieve all both homing and limits with only three switches.

Tom

then the input for those switches are high or five volts, and when the axis causes the input to go low or ground it backs off so the other axis can do the same thing, this must be in the emc2 program,am i thinking correct on this and should inputs be isolated on the breakout board from ground, my breakout board can be set high or low inputs. also can you set the backoff distance that the axis backs off from the switch after it finds it and if you can how is that done.thanks so much for the info so far.

Hi

I presume your query derives from wanting to use the fewest inputs possible.

Whilst in theory it sounds that you could have 3 home switches in parallel, even if you could get EMC to work with that logic, it would be a pig to use in practice.

The EASIEST way to have full home and limit switches for 3 axes, takes 4 inputs.
Each home switch has its own input and all the limits are chained together in series (NC switches)

Then you can set the homing sequence with ease to whatever you like, X, Y, Z or all of them together.

If a limit is triggered (which it should not be if you have set soft limits) a glance will tell you which axis it was.

This leaves 2 inputs on the BOB, 1 may be required for a charge pump and the other for a spindle index say.

Any more inputs required and fit a PCI parport card ($10). It is always easier to do things that end, than alter wiring on the machine.

regards

You might want to look here...

www.linuxcnc.org/docview/html/config_ini_homing.html

You can have an axis hit the home switch, then back off the switch and then the next axis do the same, etc. if they are sharing the same home pin should not be a problem.

Rick G