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Author Topic: Z axis home/limit problem  (Read 3197 times)

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Z axis home/limit problem
« on: July 22, 2008, 08:45:34 PM »
Hi, I am setting up my Fireball v90 using Mach3 I have 5 limit switches. 1- X home- / limit x--, 2-Y home- / limit y-- 3- Z home+ /Limit Z++, The final 2 I am using the Y-,and the x- in seires as the limit switches. None on the z- Axis Yet.  The problem that I am having is with the z axis switch when I have it set as the home switch alone it all works great, but if I activate the z-limit++ then when I home all ref the z axis moves up hits the switch and activates the limit.  I check the diagnostic and the light is on for the home and the limit, when I try to restart it wont come out of e-stop unless I turn off the z limit.  I have the z axis on its own pin input as well as the X & Y home/limit. Does anyone have an idea as to what I am doing wrong?

Thanks, Tom

Offline Hood

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Re: Z axis home/limit problem
« Reply #1 on: July 23, 2008, 02:00:31 AM »
Sounds like it could be noise or bouncy switch, try setting the debounce to 2000 and see if it helps, if it does then back off the debounce until it starts again.  Do you have shielded cabes on your switches and do you have the shield grounded only at one end and all at the same point?
 Failing that if you attach your xml, maybe something can be found in there.


Offline jimpinder

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Re: Z axis home/limit problem
« Reply #2 on: July 23, 2008, 04:05:26 AM »
The way the switches work is different when it is used as a limit or as a home switch,

Whe it is a limit switch, the switch closes (or opens, depending how you have them wired) and triggers the "limit", and as you say, activates the e-stop.

On a home movement, what is supposed to happen is that the switch closes, then the axis reverses and the switch opens again - which triggers the "home" .

What is happening is that your switch is noisy - i.e. it is making a poor contact - and when the axis reverses, the switch appears (to the computer) to open - completing the move> this only takes a millisecond. In actual fact, what has happened is that your switch has opened for a fraction of a second and then closed again - and when the computer reverts to checking the ";imit" switches it finds this one still closed and triggers the limit.

As Hood says try adjusting the de-bounce on the switches (this is a "repeat" time the computer looks at the switches to make sure they are where it thought they were), and another thing to try is the speed at which the "home" movement takes place. This is set as a percentage of max speed. If you are having trouble, set it a little higher and the switch moves a little further "open" so avoiding re-triggering the "limit"

Another thing to check is - is there any spring return on your Z axis. I had a very strong one on mine, and had to "derate" it to get the movement working to the satisfaction of the computer.
« Last Edit: July 23, 2008, 04:08:44 AM by jimpinder »
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