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Author Topic: Home/Limit switches - triggering limit when homing and where is zero  (Read 4762 times)

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Hi all,

Project is making slow but sure progress. 3 axis moving table machine.

 I have fitted temporary limit/home switches- X,Y,Z have their own home switch made from optical sensors from old printers, the home switches are also configured as limit switches. The other ends of each axis have a mechanical switch, these are connected in series to one input. Wiring is a mess as you can see but will obviously be sorted once I figure everything out and get it working properly. Motor couplings etc are also temporary !

Couple of questions here, my X and Y home/limit switches seem to work fine, but the Z switch pretty much always triggers a limit before it triggers a home. I'll try to explain - I press REF ALL HOME and Z moves up as per the first photo, but then more often than not, instead of stopping and setting Z to zero as the other axis do, it triggers a limit and therefore makes me do a reset and jog away. This happens 99% of the time, on occasion it will actually set the home position without setting off the limit warning. What I did as a temporary measure to get the machine sort of zeroed was to set the switch to just a home switch rather than a limit switch.
I noticed that each time I homed, the actual position was slightly different - only fractions - Im presuming this is down to the accuracy of my machine. What I think may be happening is that when the Z axis has homed, it isnt moving back away from the switch quite enough, is there anywhere I can alter how much it moves back off the switch once home has been found? Also is there a way to home an individual axis rather than having to do all 3 at once?

My next question is also regarding switches, but more to do with positioning. I am getting very confused with setting up the home position. I have been through quite a few tutorials/giodes etc but Im still lost. I have taken a couple of pics which will hopefully explain things better than I can in words.

I have indicated on the bottom two photos where my switches are. The pic without the table top removed to show the switches is taken from the end of the Y axis, the other from the front of the machine.
Hopefully Im right in my X,Y zero position, but no matter what I try in the configuration I cant get it to move to the rigth place, for eg if I put G0X10Y20 I would expect the machine to move to roughly where it is on the pic (i.e. the table towards the front of the machine by 10, and to the left by 20 therefore "moving" the tool to 10,20 in relation to my 0,0 position). It does move, but I cant for the life of me get it to move the right way ! Im sure this has to be something simple in the settings, can anyone offer any advice?



Z axis home/limit switch Bigger Pic

Table coordinates Bigger Pic

Switch layout Bigger Pic

Re: Home/Limit switches - triggering limit when homing and where is zero
« Reply #1 on: March 12, 2011, 11:35:58 AM »
Set the Debounce interval to 500 or so, then try the homing again.

You can home individual axis on the Diagnostics page

Your home pos. look OK. When it homes, zero each axis beside the dros, then make your move
Re: Home/Limit switches - triggering limit when homing and where is zero
« Reply #2 on: March 12, 2011, 03:05:32 PM »
Thanks, the debounce interval sorted the false triggering. I also had one of the axis direction set wrong but it seems to be sort of ok now, just trying to sort the motor tuning and get it to move the right amount.