Home and Limit Switches

[itsme]

Hi there,

I would like to find out a bit more about home and limit switches. I just bought a 4-axis unipolar Xylotex board, which gives me access to the unused parallel port pins.

I am aware that a limit switch can just be a simple 'mechanical' switch that the table hits when it is at its limit, but I'm not sure what a home switch is like. Is it also just a 'mechanical' switch that is situated somewhere that the table hits when it reaches home?

What power supply does a limit/home switch use?

Finally, once the table has triggered the switch and stopped all motion, how does it start moving again if the switch is still triggered, or doesn't it?

Regards
Warren

[kong]

Yes, a home switch is as you described, and will usually be run off the power supply to the xylotex board (5v?).
It is upto your controller software to decide what to do once the switch has been triggered. Mach2 for instance will hit the home switch, then move in the opposite direction until the switch is released.

[sol]

Once the limit switch has been hit ....
Different solutions. One is a manual over-ride switch which bypasses/replaces the limit switch so the axis can be jogged back to position.
Another is via software that more or less ignores the switch after the axis has stopped; slow jog is automatically enabled so the axis can be moved off of the switch.

The power used by the switches depends on your set up but in DIY systems they can be powered by the PC's +5vdc with pull-up resistors.
Breakout boards frequently will supply the power instead and also add opto isolation to help protect the computer.