PropellerBraider - Towards a P2-Controlled CNC-Braiding Machine

Christof Eb.

Hi, this is work in progress and an experiment, as it is new. - At least I have not seen this kind of setup.

Perhaps nevertheless it might be inspiring or funny or interesting....

So what is it about?
Braiding is known for hair and also yet another textile method. Others are weaving, knitting, crochet,... (in German there are also knüpfen and wirken, I don't know the English words.)
The basic setup and movements for braiding are quite simple and yet there are many many ways of variation. And this makes this technology interesting for a CNC project, I think.

Variants can go as far as "klöppeln", doing braiding lace:
https://commons.wikimedia.org/wiki/File:Ursuline_lace_2.jpg#/media/File:Ursuline_lace_2.jpg
This picture shows some basics: You need a number of bobbins with strands on them. You will just twist these. Direction and order of the twists creates the patterns.
Here is a very nice site showing lace pattern possibilities: https://www.theedkins.co.uk/jo/lace/patbegint.htm
Well, doing flat braiding lace would be the far end, but there are far simpler but nevertheless interesting goals in between.

There are braiding machines. Simple ones for fixt patterns or even ones for lace. They are optimised for speed and do as many movements in parallel as possible. Here are two videos, where you can see the basic movements and also a machine, which is controlled by punchcards: http://das-kloeppelmuseum.de/die-kloeppeltechniken/

Such fast machine is rather big. One of the reasons for the size is, that each bobbin carrier has some means to maintain tension of the yarn while the distance from the bobbin to the braiding point varies. This is done with a weight or a spring in parallel to a break. This link shows an impressing mechanical round braiding machine and his bobbin carrier in detail: https://fraensengineering.com/3d-printed-braiding-machine/ The height of his carrier is about 165mm. I have studied patents for bobbin carriers. There are quiet a lot....

This picture shows a my very basic means to do a braided cord:

A nice German pdf about this can be found here: https://www.regensburg.de/fm/RBG_INTER1S_VM.a.253.de/r_upload/Onlineprogramm - Freundschaftsarmband.pdf I have learned, that this method is called "Kumihimo". (Actually the way of braiding used here without twists is rather special. It is funny: I have tried to vary the number of strands from 7. But this is the only number that works in this way! Some sort of miracle.)

It shows some basic principles of the way, I want to go here:

• Have some strands of yarn, maybe with different colours
• Each strand will be held on a bobbin
• The bobbins sit on positions on a round plate.
• The fabric or cord leaves downward through the middle of the plate.
• Tension is controlled while moving bobbins.
• Movement of bobbins is not radial but vertical to the plate and in circumferential direction. (I hope, this keeps the question of tension more easy)
• The plate is rotated during work.

For my design, I have decided to split the movements:
The plate with the holding places for the bobbins will rotate and therefore I will call it carousel. A pickup-spindle can grab the bobbin with an electromagnet, has the ability to rotate the bobbin to tighten the yarn and can lift the bobbin.
There will be two pickup-spindles to be able to swap two bobbins more easily.
The idea is to be able to have the possibility of a larger carousel, but to begin with a smaller one. (Have a limited disaster, if it does not work....)

So, here is a picture of the current design, only one pickup-spindle shown:

Diameter of the carousel with 16 positions is about 300mm.
There are:
3 step motors, one for rotation via belt drive and 2 for lifting
2 DC motors for the tension and
2 electromagnets.
A 4th step motor will be used to wind up the cord. (Not shown)
I think, that for this project, to have a P2 controller with 8 cores is quite helpful. The actuations are related but not like Bresenham in one movement.

As said before, at the moment this is all theory. I have begun to produce first parts. I don't know, if it will work.

One bigger question is, if the electromagnet will hold and also let go the spindle. It is D20x15mm and said to hold 2,5kg in ideal cases. For solenoid armature, fixed to the bobbin, I hope a steel washer will work. ??? I will provide means for AC voltage and PWM.

Perhaps some comments, ideas?

Have fun, Christof

Edit: Have done some testing with the solenoid. Yes, it will hold and also release the bobbin. But it tends to de-centre the bobbin.