Robotic kinematics

T3P3Tony

@joergs5 sure, it does not have to be a commercial robot - maybe the cad of your implementation?

JoergS5

@t3p3tony => DH will be described, see my next post.

Implementing a visual method in DWC would be a nice possibility to show the configuration.

JoergS5

@t3p3tony I've found a youtube video with a reuse license: https://www.youtube.com/watch?v=nwj0xR21ldo and use the robot images from there. It's a nice typical 6 axis robot. I'll create a separate document to explain parameters to set for robots, based on this video.

The documentation will be in https://duet3d.dozuki.com/Wiki/Denavit-Hartenberg_parameter_for_Robots?revisionid=HEAD

The video above is a good video to understand part of the DH parameters, so it is useful to watch it. In the video, the last column's values are joint 5 minus pi/2, joint 6 is 0. I am using different methods to get the Jacobian, however.

JoergS5

The robot documentation is available at the new documentation site now at https://docs.duet3d.com/User_manual/Machine_configuration/Configuring_RepRapFirmware_for_a_Robot_printer and the explanation with examples of the Denavit-Hartenberg parameters are at https://docs.duet3d.com/User_manual/Machine_configuration/Configuring_Robot_DH_parameters

I wish to implement and push to David the firmware code for 3.5, so it's time to do it calmly and well tested.

droftarts

@joergs5 nice documentation! How did you find using the new wiki?

Ian

JoergS5

@droftarts said in Robotic kinematics:

How did you find using the new wiki?

I am very pleased, a few little problems at the beginning like how to plublish external links, but nothing I could not solve. It is especially nice that one can choose between different coding options (pure html, wiki etc) and change between them on-the-fly (I had to test it...).

droftarts

@joergs5 we’re generally doing pages in markdown, with occasional html tags for specific things. If you’re okay with it, I’ll go through it and check/edit it for consistency.

Ian

JoergS5

@droftarts yes that's ok, a consistend looking for all pages is a good idea. Please don't delete any information, because I deleted the old documentation.

JoergS5

@droftarts you may wish to check https://docs.duet3d.com/en/User_manual/Machine_configuration/Configuration_five_bar_parallel_scara also, the documentation I moved for the 5 bar parallel scara kinematics.

Miss Rebekah

HI i was wondering if its possible o use these kinemaics for a 3 axis arm. base rotates 360 deg, arm 1 length is 150mm hinge to hinge with 87 degrees of movement, arm 2 150 mm hinge 95 degrees of movement. kinda like a backhoe. i have it moving on a duet 2 ethernet to where xyz is in mm but really its degrees from home. i setup as5600 encoders on an arduino for testing purposes and to prove to myself it was going where i told it to and it is so far. now i jus want o be able to send regular g gcode o it so i can draw etc with it. now i jog to the points write them down and hand write a small program.

JoergS5

@miss-rebekah the kinematics which I use is independent of number of axes, so it will be possible.

However 6 axis are necessary to define all dimentsions (3 for xyz and 3 for orientation of the endpoint in xyz directions), so your 3 actuators will not be able to define all possibilities. But for 3D printing, where the endpoint is always vertical, 3 may be sufficient.

I am currently reprogramming the code and will publish next month. If you wish to test the code and be prepared, please read the two documentation pages so you can define your robot. (If you read the article, you'll see that the defintion of setup is independent of the number of arms. This was intentionally).

I'll provide you with Duet 2 binareies, so it's just a simple upload.

JoergS5

@miss-rebekah said in Robotic kinematics:

backhoe

Your backhoe will probably have non vertical endpoints. To solve this, my construction from 2020 Oct 12, https://forum.duet3d.com/topic/17421/robotic-kinematics/112 may be a solution, 5 axis robot, removing 2 axes: one by using the parallel arms which make sure the arm 4 is always vertical, and fix the last arm to 0 degrees always, which means there is no actuator needed. Remaining 3 actuators.

Miss Rebekah

@joergs5

awesome sauce!! yay!!

yes ill test it. i glanced over that article and i had a few unknowns i understand the right hand rule and coordinate systems ill read it again and get that part figured out. the business end of my robot is parallel/perpendicular(depending on what attachment) with the base via a 4 bar lever at all times. drawing, printing, and pick and place are all i want to do. i have a solid works model of it also.

once i get my robot defined ill reply here and see where your at.

one question

if i have different tools on the end i.e suction cup, claw, pen, or hot end is there a tool offset that an be applied? i only have the suction cup attachment made i may be able to set the program point on all of them in he same location but if i cant.....??

Thank you

Miss Rebekah

@joergs5

yes this is what my robot does i didn't realize the last hinged point driven from a 4 bar lever counted as an axis. from that is where i attach tools.

JoergS5

@miss-rebekah said in Robotic kinematics:

is there a tool offset that an be applied

The code will use the G10 offsets, allowing toolchangers also. Maybe I can support fixed probes for mesh compensation this way also.

droftarts

@joergs5 I've had a look at these pages:
https://docs.duet3d.com/en/User_manual/Machine_configuration/Configuration_five_bar_parallel_scara
https://docs.duet3d.com/User_manual/Machine_configuration/Configuring_RepRapFirmware_for_a_Robot_printer
https://docs.duet3d.com/en/User_manual/Machine_configuration/Configuring_Robot_DH_parameters

The only things I've changed are:

on the Five Bar Parallel Scara page, by adding a 'zero width non joiner' ie the character string &zwnj; in a couple of places to stop :100: (in some of the parameter configurations) rendering as . Seems like it's the only way of stopping emojis being rendered in markdown. Edit: Tony has turned off emojis, so it doesn't show on the final page. However, does still show on the page preview.
fixed a link on the Robot page
Edit: DH parameters page, fixed and tidied up links

The only thing that isn't clear from the pages is that this is a fork of RRF, and not part of the main RRF release. Can you add a note at the top of both pages, and link to your Github repository for them?

Ian

JoergS5

@droftarts said in Robotic kinematics:

only thing that isn't clear from the pages is that this is a fork of RRF, and not part of the main RRF release

I'll make a remark. Thanks for checking the pages.

JoergS5

@miss-rebekah I reviewed the robot documentation and changed the M669 A parameter a bit, please check whether your config preparation is current. Please tell me whether you can understand the documentation or I should clarify parts of it. https://docs.duet3d.com/User_manual/Machine_configuration/Configuring_RepRapFirmware_for_a_Robot_printer

I'll finish the first firmware version the next two weeks and provide you with a ready-to-use Duet 2 binary. I can help you with configuration of your robot then, if you provide the information about the setup.

JoergS5

@droftarts could you please be so kind and remove a comment in https://docs.duet3d.com/User_manual/Machine_configuration/Configuring_RepRapFirmware_for_a_Robot_printer , in the title I cannot edit the second line "Currently for 4 to 6 axis robots". Maybe I am simply too stupid to find how I can edit it. Please simply remove the comment, as it is no longer correct.

jay_s_uk

@joergs5 when editing, click on page at the top right between save and close, its in there. I've removed it for you