Can I use an IR sensor as the X and Y endstop?



  • I noticed that could probably detect the edges of the build plate with the IR probe.
    It's mounted slightly to the right and behind the nozzle, so I would have to probe the +X and +Y edges, ie the high ends.

    The Reprap configurator has options to do this, but looking at the generated g-code it does not look like it would do anything different.

    Would I have to plug the sensors output into one of the endstop pins? That way I would lose the fractional speed reduction right?


  • administrators

    The Ormerod printer uses the IR sensor not only as the Z probe but also as the X endstop. There is a tab mounted at the end of the X axis, which the sensor sees. The sensor must not be too close to the bed during homing, so that it doesn't respond to the bed, only to the tab.

    I hadn't considered the possibility of sensing the edges of the bed instead. The problem would be working out a sequence of moves that will succeed in homing regardless of the initial position. One possibility might be:

    1. With reduced motor current, move both X and Y a small amount in the negative direction, to ensure that the probe is over the bed. If X or Y is already at or close to the minimum stop, the reduced motor current will avoid damage.

    2. Home Z using the sensor.

    3. Drop the head a little, invert the trigger polarity in M558, then home X using the sensor to find the +X edge of the bed.

    4. Move back a little in X to place the sensor over the bed again, then home Y using the sensor.

    5. Move to bed centre, restore the original trigger polarity, and re-home Z.


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