Setting tool offset using USB microscope



  • Hi this is my first port here, I hope I posted it in the right category.

    I am building a tool changer and I want to calibrate the offset of the individual tools by using a USB microscope. I found a way where I move the nozzle right over the haircross of the microskope image and then use the M585 to measure the offset. Unfortunately this method suffers from errors caused by my endstop switches.
    I am wondering now if there is a way to just move the nozzle to the hair cross position and then to tell the Duet Wifi to calculate the offset relative to the given theoretical coordinates.

    Thanks for help in advance!



  • Upward looking camera I assume.

    You can certainly do this "by hand":

    1. Align tool to camera crosshair, and then note the X/Y position of the tool in the DWC display.

    2. Subtract this from a previously determined X/Y of the camera (which, in reality, can be somewhat arbitrary, because it is now the "reference point" for all tools).

    3. Do math.

    4. Issue G10 Px (x = tool number) Xn Yn (n for each axis calculated in step 3)

    There may be a way to get the machine to do math for you...



  • The printer is supposed to do the procedure for up to 8 heads every time something has changed. I would prefer not to do it by hand 😉



  • Very nifty!

    But... what aligns the tool on the crosshairs? You? Machine Vision? If Machine, what machine?



  • I hope it can be automized somehow but for now I would do it hand using the DWC. But that would be the only manual task.



  • Got it.

    I was hoping you had a Pi (or similar) and machine vision. Then the Pi could do the math and issue the commands. (via either 5V serial TTL to the same port the PanelDue uses, or via Telnet over the local network).

    WIthout a Pi, I'd do something like this:

    1. Use precision limit switches. Either mechanical capable of 0.03 or optical or inductive.

    2. Position those limit switches at X-10,Y-10 or even larger "minus" as possible.

    3. Position the camera as near 0,0 as practical, lets say 15,15

    4. Home machine.

    For each tool:

    1. Select the tool; use a macro; have the macro select, then G0 the tool to roughly the camera position.

    2. Manual Align.

    3. Another macro containing: M585 X-25 (or similar), then same for Y. This will hit the precision switch and then do the math for you. Then move near where tools will be put away, to make the 'next' step 5 run faster.

    Repeat 5,6,7 for each tool.

    I know you don't want to change limit switches, but, the only way (at present) to get the Duet to do the math depends on limit switches... so, it is "better switches" or "external automation" (like the Pi)



  • @Danal That it how I do it at the moment. Had to trick the printer by inverting the motor direction because it hits the endstop with the Carriage and not the Nozzle (ealier hit when nozzle is further away). But basicly thats the way.

    It would be really great if there where a parameter in the M585 or G10 that allows to tell the printer: This is the position which is supposed to be X100,Y100 for the tool. Set the offset to make that right.

    Do I have to put that on the wishlist?



  • This Hackaday.io project uses an upward facing camera. I don't think he used Duet, though, but might be useful for ideas.

    Ian



  • @TC said in Setting tool offset using USB microscope:

    It would be really great if there where a parameter in the M585 or G10 that allows to tell the printer: This is the position which is supposed to be X100,Y100 for the tool. Set the offset to make that right.

    There is. Use G10 Px L20 Xnn Ynn. The L20 will use the current position as a relative "anchor". So if you e.g. use G10 P1 L20 X0 Y0 this would tell RRF that tool 1 is at X0, Y0 where it is right now. I think to tell it that it's at X100, Y100 you would simply use G10 P1 L20 X100 Y100 but it might be necessary to invert the values of X and Y. But that should be easy to test.



  • @TC said in Setting tool offset using USB microscope:

    @Danal That it how I do it at the moment. Had to trick the printer by inverting the motor direction because it hits the endstop with the Carriage and not the Nozzle (ealier hit when nozzle is further away). But basicly thats the way.

    It would be really great if there where a parameter in the M585 or G10 that allows to tell the printer: This is the position which is supposed to be X100,Y100 for the tool. Set the offset to make that right.

    Do I have to put that on the wishlist?

    1. Endstop hit by some other part than nozzle: The distance from the part that hits to the nozzle should be added/subtracted from the number in M585. Yes? No?

    2. "This is XnnnYnnnZnnn for the tool". That's accomplished by either G92 (temporary, and offsets specified in the command are calculated from current tool position) and/or work coordinate systems, G54, G55, etc. (more persistent, and offsets are from machine 0,0, generally intended for fixtures).



  • @wilriker Interesting! But does this define the normal tool offset, which is automaticly applied when the tool is selected? Or does it create a new coordinate system, which has to be activated in the tool change macros?



  • @TC said in Setting tool offset using USB microscope:

    @wilriker Interesting! But does this define the normal tool offset, which is automaticly applied when the tool is selected? Or does it create a new coordinate system, which has to be activated in the tool change macros?

    The former.



  • @wilriker has another good way. G10 offsets the tool. And, to @TC's question, G10 Ptool (with no L parameter) becomes "part of the tool" until it is changed. Auto activated when tool is selected, auto-deactivated when different tool is selected.

    G92 is not associated with a specific tool. It is temporary (persists to end of current program) and can be turned off via G92 X0Y0Z0.

    G54, 55, ... The coordinate settings are persistent across programs, and persistent across power cycles of the machine. The offsets currently in used can be turned on by specifying G54 (or 55 or...) with no arguments.

    Note that work coordinate systems CANNOT be "turned off", the machine is ALWAYS in a given work coordinate system (G54 by default). Most people do not realize this, because they are in G54 (default) and G54 has zero offset from machine coordinates. Therefore, they are totally unaware that work coordinate systems even exist.

    The one sort-of-exception is G53, which is machine coordinates. However, G53 is not modal; it applies only to the line on which it appears. So, next line, the machine is back in one of the Work Coordinate Systems, which may or may not be offset from machine.

    Summary:

    • G10 for offsetting the tool. Auto activate/deactivate as tools are changed.

    • G92, Coordinate offsets are temporary. Often used in combination with gcode subroutines for repetitive parts, like machining a complex pocket in multiple locations on the same part.

    • G54, 55, ... Coordinate offsets are permanent, and activated by G5x with no arguments. Normally for fixtures or jigs.

    All three have their uses.



  • @wilriker Maybe I have understanding problems but as far as I understood the G10 in combination with a L2 or L20 does not relate to a tool.

    "Pnnn Tool number if L=1, coordinate system number if L=2 or L=20"

    How does it know which tool is meant?


  • administrators

    @TC said in Setting tool offset using USB microscope:

    @wilriker Maybe I have understanding problems but as far as I understood the G10 in combination with a L2 or L20 does not relate to a tool.

    "Pnnn Tool number if L=1, coordinate system number if L=2 or L=20"

    How does it know which tool is meant?

    Correct, G10 with L2 or L20 is for setting workplace coordinates systems, and nothing to do with tool offsets. It's unfortunate that G10 is used for so many functions.



  • @TC I'm sorry I mixed it up. 🤦

    @dc42 Would a G10 L10 to set tool offsets relative to current position desirable (making G10 even more complex OTOH)?



  • The NIST standard defines only L2. Any other L values are "proprietary" extensions of one firmware or another. Including Duet/RepRap's use of "No L parameter at all, with Ptool" to offset a tool.

    So... L10 could certainly be used... but... would make Duet/Reprap even further from the NIST standard. Given that G92 accomplishes the exact same thing in an NIST standard way... (and can become "part of the tool" by putting G92 in the pre/post files)... well... you asked DC42 and not me... but you can tell where I'm going with this: I'd say just use G92.

    Extract from NIST standard:

    3.5.5 Set Coordinate System Data — G10

    The RS274/NGC language view of coordinate systems is described in Section 3.2.2.

    To set the coordinate values for the origin of a coordinate system, program G10 L2 P … X… Y… Z… A… B… C…, where the P number must evaluate to an integer in the range 1 to 9 (corresponding to G54 to G59.3) and all axis words are optional. The coordinates of the origin of the coordinate system specified by the P number are reset to the coordinate values given (in terms of the absolute coordinate system). Only those coordinates for which an axis word is included on the line will be reset.

    It is an error if:
    • the P number does not evaluate to an integer in the range 1 to 9.

    If origin offsets (made by G92 or G92.3) were in effect before G10 is used, they will continue to be in effect afterwards.

    The coordinate system whose origin is set by a G10 command may be active or inactive at the time the G10 is executed.

    Example: G10 L2 P1 x 3.5 y 17.2 sets the origin of the first coordinate system (the one selected by G54) to a point where X is 3.5 and Y is 17.2 (in absolute coordinates). The Z coordinate of the origin (and the coordinates for any rotational axes) are whatever those coordinates of the origin were before the line was executed.


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