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Author Topic: When Homing limit switches do not work...(?)  (Read 5386 times)

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When Homing limit switches do not work...(?)
« on: January 27, 2009, 08:47:26 AM »
I can see that while homing, the limit switches do not work.
Why is that?
Is there any specific setting about that?
The homes and the limit switches are in different input in my machine.

Offline Chip

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Re: When Homing limit switches do not work...(?)
« Reply #1 on: February 01, 2009, 11:21:30 AM »
Hi, Giannis

When Mach is homing it's just looking for home SW activity, After homing it then reverts back to just looking for Limit SW activity.

Just the way it is, Unless you have some special need, It allows you to use the Limit SW's as Home SW, Saving Input pin's for better use.

Chip
Re: When Homing limit switches do not work...(?)
« Reply #2 on: February 01, 2009, 01:05:22 PM »
I understand.
But what will happen if a home switch is broken (or if for some rason won't work) ?
So, i think it is important.
Can this check be done with a brain?

Offline Hood

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Re: When Homing limit switches do not work...(?)
« Reply #3 on: February 01, 2009, 01:54:58 PM »
Normally you would use NC switches for limits and homes, that way if a wire breaks then it will fault right away. I suppose there is a slight chance a switch could weld closed on the contacts but just a very slight one.
 As for the Brain then not sure, you could possibly have a brain look at the limits inputs and call an E-Stop, never tried it, you would of course need to be using seperate limits/home.
Hood
« Last Edit: February 02, 2009, 03:02:33 AM by Hood »

Offline jimpinder

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Re: When Homing limit switches do not work...(?)
« Reply #4 on: February 01, 2009, 01:58:45 PM »
The answer is to wire all your switches up in series to one pin. Go from the pin to one switch (normally closed contacts) to the next switch and so on, and the last switch is connected either to your 0v connection or your 5 volt connection, depending on what your breakout board requires.

On the Config/Ports and Pins/Inputs all the x y and z limts and homes are shown on the same pin. These are set up so that the normallly connected switches  normally hold the limits and homes OFF. i.e. on my machine I connect directly to the computer so my switches are connected to 0v and NOT active high on the ports and pins. The internal pull up resistor is overcome by the switches and the leds are  normally off. When activated, the line is no longer connected to 0v and the internal resistor pulls the pin up and switches it on.

As soon as any switch is activated, this breaks the connection and all pins show high - or activated. This doesn't matter - with a limit switch it is obvious which switch is activated from the position of the table, with a home switch, Mach is looking for the appropriate home switch anyway, and only reacts to that.

This has the added advantage, in that, if a wire comes off, or, as you say a switch becomes faulty, then it immediately trips the limits and your table will stop. You can find out which one it is by shorting them out in turn until you find the one that is activated.

As you probably know the state of all the input leds are shown on the diagnostics page
Not me driving the engine - I'm better looking.

Offline Hood

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Re: When Homing limit switches do not work...(?)
« Reply #5 on: February 01, 2009, 02:14:14 PM »
Just tested and a Brain will indeed call an estop if a limit is hit during a homing routine.
Hood

Offline Chip

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Re: When Homing limit switches do not work...(?)
« Reply #6 on: February 01, 2009, 09:22:15 PM »
Hi, Giannis

NC SW's, The way to go,

Chip
Re: When Homing limit switches do not work...(?)
« Reply #7 on: February 02, 2009, 01:36:46 AM »
Thank you guys!
It is clear now...