Sensorless IDEX Alignment
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I am currently designing a IDEX. I have learned that the Craftbot can align the nozzles by using a round hole on the build plate and I'm assuming stall detection to find the center of each nozzle by bumping it into the hole. I know stall detection is not as accurate as an endstop switch so I have designed them into my x-axis but this would be a cool feature to implement. Does anyone have an idea how Craftbot can make this work? I have not been able to find what stepper drivers they are using on the Craftbot.
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All that is required (in the most basic sense) to make this work, is a wire electrically connected to the nozzle/heaterblock/heatbreak/heatsink, and another wire connected to the heated bed. When the circuit is completed, it is the same result as a limit switch. This is not at all related to the stepper drivers, as it is just a calculation that is done on the controller.
They touch one side in x or y, then touch the other, if the first point is a lesser coordinate value than the second, the middle of the circle is (P2 - P1)/2. Repeat this for the other axis, and you have a 'global' reference for the center of the nozzle. This is then done for the second nozzle, and the XY values are compared.
That's the gist of the the system.
Here are some references:
http://catiadoc.free.fr/online/smgug_C2/smgugrf1200.htm
https://www.youtube.com/watch?v=R_D3-Ji3Y5Q -
Oh, I see what you are saying. It would make sense that they are using a similar method. I'm thinking this would be a good application for a Piezo sensor as a alternative to completing a circuit.
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@3DPrintingWorld Eh, I think it would be hard to get a good enough piezo mounting scheme to make this work with any accuracy. You would either need one sensor to detect in 3 directions, a number of sensors. But then your mechanical assembly needs to allow for deflection in 3 directions by a small amount. Completing the circuit is probably the best method. This is similar to how lulzbot has had their bed leveling (off the 4 metal corner pucks).
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Piezo and circuit alignment are bad ideas. The nozzle which extrudes plastic should not be relied upon to complete a circuit. Piezos have a lot of noise, you would need very smooth movements for them to be accurate.
The best is user calibration with printed veneers.
