Robotic kinematics

[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 ‌ 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

[JoergS5]

@jay_s_uk thanks a lot!!

[JoergS5]

I finished the robot kinematics about two weeks ago, but I have no good method to check whether the calculations are correct. What was missing, was a visual check whether the endpoint has the intended orientation.

I've started to develop a DWC plugin for this reason and to help finding the correct robot parameters. The result is https://forum.duet3d.com/topic/28492/robotviewer-dwc-plugin , the RobotViewer plugin, which allows DH parameter changes and seeing the consequences of changes. I'll enhance this version to cooperate good with the kinematics in the firmware.

[JoergS5]

I am enhancing the robot kinematics by closed chain and multiple chain kinematics, but I have a problem: I don't know how to define configuration syntax. Maybe someone has an idea or technical paper.

(the image is not nice, but license free!)

The first case is closed chain like stewart, CoreXY, parallel scara. The second e.g. Open5 with top hotend and button the printed object, which will be rotated. The circles are the actuators.

An idea for multichain would be
(BPPPE)(BRRO) for two chains base-prismatic-prismatic-prismatic-endpoint, base-rotational-rotational-object, the base being the point which stays at it's place with unchanged orientation. The multichain should support multiple in the sense of fingers of a hand e.g.

An idea for closed chain would be
B(RR3)(RR3)E
so it's clear that R3 is common and the closing chain, numbering only when necessary.
But Stewart would be very complex.

It's also necessary to define how the chain is closed: matching the endpoints or additionally same orientation? Or specific angle?

Any ideas?

[JoergS5]

Some time since last update, so I want to give some update information. Had Covid and recovered, hope you are all well too.

Robot kinematics will be included in RRF 3.5, after talking with David and Tony. I have agreed to have a working version end of August, so the integration will start after this date.

I am currently working on

• performance optimizing and testing
• implementing additional kinematics like CNC 5 axis and 4 axis palletizing robots which are built like ABB IRB 460
• documentation. Starting point is https://docs.duet3d.com/User_manual/Machine_configuration/Configuring_RepRapFirmware_for_a_Robot_printer and I tagged the documents with robot tag, currently 4 documents. Detailed descriptions e.g. of orientation, RobotViewer, Config. Please ignore misspelling, but if you find logical errors, please tell me to correct it
• still working on a good prototype, but this takes eternal

[o_lampe]

@joergs5 said in Robotic kinematics:

still working on a good prototype, but this takes eternal

Good to hear you're well again!
I didn't read the whole thread, but I'm curious to know where to get all the stuff required to build one? Differential screws, optical encoders and lenses, all have to fit together...
I hope you'll add a BOM to your prototype

[JoergS5]

@o_lampe I'll make a BOM for sure. Nor for every screw, but for all main parts.

The main time it takes is for building harmonic drives, where I take two paths: one to 3D print the flexspline and circular spline, and one to use steel and drill the teeth. The 3D printed is meant to be that everyone can clone it, the steel one for a robot which can have higher payloads.

[o_lampe]

@joergs5 said in Robotic kinematics:

The main time it takes is for building harmonic drives,

I was pretty impressed by the cycloidal drive I made for a direct drive extruder. It would be even easier to scale it up for a robot.
Have you ever considered those?

[JoergS5]

@o_lampe that's a very nice looking one!

Yes, another user recommended using cycloidal gears in this thread somewhere above. It is an alternative. I've decided to go with harmonic drive, but there is no reason to consider cycloidal also. I love the cycloidal drives from Nabtesco like the RV500-N, which are used in Fanuc and ABB robots, but they have similar price ranges like the harmonic drives.

I standardize / modularize the components for myself, like the dimensions of the gears, so it will be possible to exchange harmonic drive, cycloidal or belt-based gears. I take dimensions of commercial ones as a guideline.