JoergS5 parallel five bar scara



  • @bondus nice face LOL - take it as logo for the printer...

    I didn't mean a partially heated bed, but a small bed. For every to be printed object a separate heat bed.



  • I made the face interactive using some JS and html: https://fivebarscara.000webhostapp.com/test.html.

    It's a little web page where you can input arm lengths, actuator distance and work mode. And interactively see the work areas, and the arms moving. Move the mouse over the work area and the arms will pop up. Different colours for different work modes.

    It's quite mesmerizing.

    I might add the angle limitations to the interface. It could be a useful tool for anyone brave enough to build a five bar scara. It's still useful to understand how fire bar scaras moves.



  • @bondus The tool is nice. I have ideas for improvement 😉
    I used arms lengths 400, so a zoom in/out would be nice. Showing the coordinates of the hotend point would be nice to know the printable area.



  • I pushed my current 5 bar code to https://github.com/bondus/5barscara/tree/master/rrf, it's what I use on my printer right now.
    The main thing compared to @JoergS5's implementation is the more general angle logic. As explained above.
    And it's updated to the current RRF.
    The code needs some love to be production quality, but it works good as is.



  • I found this interesting implementation a few days ago, http://3dgems.blogspot.com/2016/01/scara-based-3d-printer-v3-details.html.
    This kinematics should handle it. It is a work mode 2 arm with a very long negative cantilever on the left arm. It should work as long as the hotend is not offset from the straight cantilever.



  • @bondus Thanks for the link, this seems to be a very stiff construction. The print area seems to be limited somehow, because the arms are in each other's way.

    I've started building my Scara now, I will have images soon. Then I will update the source in RRF3 (including your improvements and bug fixes) and make a push request to David. My current plan to implement the endstops: set proximal arms perpendicular to base line and measure them for parallelism.



  • Looking forward to those images of your machine.

    I have been struggling a bit with the calibration of the printer. It is not accurate enough to print parts for itself.

    I made some experiments with printing a calibration item, measuring it and feeding it into a program to compute the actual homing angles, and adjustment to the arm lengths. I have not not been successful. Yet.

    Your idea to move them to 90deg and measure parallelism and perpendicularity (is that a word?) is faster and easier. Adding S1 to a G1 command moves the arm to a specified angle, G1 S1 X90 Y90.

    0_1559807107154_IMG_20190606_092654520 - Copy.jpg



  • I built this little toy to play with a more agile arm. The only things that collides are the proximal arms. It happily does all work modes. With very poor precision 🙂

    I wish I had more duets, or some other lesser board that could run RRF. The little 8-bit arduino chokes up fast. It's like being back in the 80's, but with better tools.
    0_1560035261505_IMG_20190608_190940325 - Copy.jpg



  • @bondus your image reminds me of my first model to understand parallel scara. I built it from wood. Playing around with it really helped understanding the idea.

    If you want to try alternative electronics, you can try Cortex M7 based boards. The disadvantage is of course that all other things like stepper drivers are missing, compared to Duet.



  • Some of the academics have strange ideas. Found this oddity in an (unpublished) paper:
    0_1560294153548_academic.png
    I need to sign up to the university again to get access to all the pay-walled academic papers.


 

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