Thread: One limit switch per axis
I've not seen this mentioned but sometimes it's hard to find specific info here. I thinking about using one limit switch per axis, so take the Z axis for example, you mount a switch at the mid travel point on the Z 'fixed' backplate, then you position 2 strikers near each end of the Z 'moving' plate, these would have slotted brackets to allow adjustment. Now when the Z axis reaches either end of it's travel one of the strikers will activate the limit switch. Obviously same goes for X and Y and the switch could be mounted on the moving part instead if that was more suitable.
Any opinions about this ?
First it depends on the encoder on the axis -Absolute meaning it knows were it is at power on or the other that requires the machine to be sent to home position/reference at start up ----these have to be very accurate switches and usually are plunger type -------Home position is found using the switch but a seperate dog is used for plus and minus over travel protecting the ball screw ends from being crashed into
I won't be using encoders, absolute or incremental, I'm just talking about physically activated switches or proximity type. I will be using separate switches for homing mainly because I will have a slaved stepper that I believe needs it's own homing switch for squaring up the gantry.
Single switch per axis is fine.
Often the number of switches per axis is more to do with convenience than anything else.
We used this method on overhead cranes and other reciprocating machinery, it's just that whenever limits are mentioned in regard to cnc machines they always talk about 2 switches per axis.
Yes it works fine many milling machines use this method.
Edit: You can still wire them in series has well.
Last edited by JAZZCNC; 29-09-2013 at 08:40 PM.
That's the method I'll use then, I thought I would get the electrical drawings done, get some stuff ordered, put it together, while waiting for items from China.
I'm going for an Ethernet Smooth Stepper, probably AM882's, but still pondering the best bob for this combination.
Last edited by EddyCurrent; 29-09-2013 at 09:00 PM.
Usual CNC setup with homing required machines
Move to Zero
Plus soft limit--- where the servo is stopped or held mode is plus 5mm and comes from the axis control
Hard limit activated by a switch linked to the Estop circuit is plus 10mm
The same goes for the Minus side
Wither its two switches or two position dogs really doesn't matter but they are there to protect the machine and zones
For recovery from these usually needs an over travel release button on the operators panel and sometimes keyed so proper- questions are ask to why its there in the first place
Last edited by Ulsterman; 29-09-2013 at 10:41 PM.
The failure is usually caused by the switch never being used and then they stick down in the on position not the wire being broke ---------So when you release the machine off the switch it is stuck on the on position -so normally open would be a good idea ?
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