A Mechanism which pulls a specific amount of string (yarn) mutiple times

[AlmasAj]

TL;DR Summary

I want a mechanism which can pull a specific length of thin string (let's say 1mm string) for multiple times.
I think that this mechanism will require some robotics and electronics.
So if someone can help me it would mean a lot.
Thanks!

Yarn
Grippers,
Linear motion equipments
Motors

 

[Baluncore]

Welcome to PF.

Why do you want to pull on the yarn?
Do you also want to cut the yarn?
You need to tell us what you are actually trying to do.

 

[AlmasAj]

Yes I also want to cut the yarn and i want to use this in a machine which automatically threads a needle continuously for multiple times.

 

[jrmichler]

You need to provide more information in order that we can help you:

What type of yarn - yarn for sweaters or some sort of high tech industrial yarn for composite structures?
How much pull force - are you pulling from a spool or pulling against back tension?
What is the desired minimum and maximum speed of pulling in meters per second?
What is the desired minimum and maximum length of each pull?
What is the desired accuracy of the length of each pull?
Is this for a hobby project, a one off industrial project, or for a machine that will be produced in large quantity?
What constraints exist - does it have meet a cost target, fit in a specific space, skill of operator, etc?
And anything else that we need to know.

 

[AlmasAj]

First of all thanks for showing interest in this and replying
Now, To answer your question:

1. It is a simple basic cotton yarn , I don't know what else it is called but i have attached a pic of the yarn. This type of yarns are used for sewing and generally
2. It is pulled against a back tension which is only at an extent where the thread(yarn) stays straight similar to which in sewing machine.
3. For speed it doesn't really matter but should consider around 1 m/s.
4. Length will vary according to the task and the range for that will be from 6 inches to 12 inches.
5. I don't know how to answer this because I am a newbie but slight Inaccuracy can be acceptable.
6. This is for a machine that will be produced in a large quantity.
7. I have not decided about the cost target so give me what ever you and for space consider around 2 feet × 2feet.

- I forget to mention that the thread(yarn) will have to pass from the eye of 2 needles.
So first a mechanism will pull a certain amount of yarn and then it will be pull through the both needles eye and then the yarn will be cut this process keeps getting repeated.

 

[AlmasAj]

You need to provide more information in order that we can help you:

What type of yarn - yarn for sweaters or some sort of high tech industrial yarn for composite structures?
How much pull force - are you pulling from a spool or pulling against back tension?
What is the desired minimum and maximum speed of pulling in meters per second?
What is the desired minimum and maximum length of each pull?
What is the desired accuracy of the length of each pull?
Is this for a hobby project, a one off industrial project, or for a machine that will be produced in large quantity?
What constraints exist - does it have meet a cost target, fit in a specific space, skill of operator, etc?
And anything else that we need to know.

I hope you get the information I provided .
For the above answer I forgot to tag or quote you so this.

 

[AlmasAj]

Welcome to PF.

Why do you want to pull on the yarn?
Do you also want to cut the yarn?
You need to tell us what you are actually trying to do.

Sorry I forgot to quote you but here you go.
Yes I also want to cut the yarn and i want to use this in a machine which automatically threads a needle continuously for multiple times.

 

[Baluncore]

If you make many machines, you will need to integrate or merge the “measure and cut” process with the “needle threading”.
How will the machine thread the needles?
Will you be threading the same needle repeatedly?

 

[AlmasAj]

If you make many machines, you will need to integrate or merge the “measure and cut” process with the “needle threading”.
How will the machine thread the needles?
Will you be threading the same needle repeatedly?

For the question how will the needles be threaded?
There will a hook which will be thin around 1 mm less the the needle eye. The needle eye will be around 3mm to 2.5mm.
And for the second question.
Yes I will be threading the same needles repeatedly.

 

[AlmasAj]

If you make many machines, you will need to integrate or merge the “measure and cut” process with the “needle threading”.
How will the machine thread the needles?
Will you be threading the same needle repeatedly?

The hook will go through the eye of needle and it will hook the thread which is measured and it will pull the thread back from the both the needle eyes.

 

[jrmichler]

Some more questions:

Do you want an automatic or manual process? An automatic process repeatedly feeds while the operator watches, an automatic process that feeds and cuts every time the operator pushes a button, or a manual process that feeds every time the operator pulls a lever or steps on a pedal (no motors)?

How many operations (number of pieces of yarn) do you want per minute?

Do you want to include threading the needle and whatever operation the needle does in this system, or do you only need to feed the yarn?

 

[berkeman]

The hook will go through the eye of needle and it will hook the thread which is measured and it will pull the thread back from the both the needle eyes.

Doesn't the machine need to tie a knot with the two ends of the string after it threads it through the needle eyes? What keeps the string from falling out of the needles? How is this assembly of string + 2 needles packaged for shipment to customers?

(and what in the heck are you sewing with 2 needles on the same loop of string? Must be something pretty fancy!)

 

[AlmasAj]

Doesn't the machine need to tie a knot with the two ends of the string after it threads it through the needle eyes? What keeps the string from falling out of the needles? How is this assembly of string + 2 needles packaged for shipment to customers?

(and what in the heck are you sewing with 2 needles on the same loop of string? Must be something pretty fancy!)

Ok so i didn't want to give out the whole idea but i think I should.
So basically in India we use cotton mattresses in that mattress we have to tuft using cotton yarn. If you don't know what tufting is then you can watch it on YouTube (mattress tufting).
This machine will do this mattress tufting. There is no issue of the thread falling because the needles will be 15mm apart from each other.

 

[AlmasAj]

Some more questions:

Do you want an automatic or manual process? An automatic process repeatedly feeds while the operator watches, an automatic process that feeds and cuts every time the operator pushes a button, or a manual process that feeds every time the operator pulls a lever or steps on a pedal (no motors)?

How many operations (number of pieces of yarn) do you want per minute?

Do you want to include threading the needle and whatever operation the needle does in this system, or do you only need to feed the yarn?

I want an automatic process.
Number of operation per minute can be 6 or 7.
And yes I want to include the threading process
Just so you know that after the threading process the needles will Pierce a mattress and when it comes out there will a another system where the needles reaches out which will hook the thread and both ends of the thread will be out on the other side. Similar to which in sewing machine. Then the needles will go above and again repeat the process of feeding cutting and threading

 

[Baluncore]

Reinvent the needle to something without an eye. The needles have a trap near the point, a bit like Hartmann alligator forceps, so they can be pointed needles but also grip the thread. The two needles of a module are held on one side of the mattress, pushed in parallel through a reinforcing pad, the mattress, and another pad. Then the ends of the measured and cut thread are gripped by the needle traps, and drawn back through the pads and mattress. The knot can then be tied by the two needles moving independently under program control.

That places the thread mechanism on one side of the mattress, with the needle control mechanism and knot tying on the other. The mattress would pass under a fixed bridge, like a tunnel.

A number of identical needle modules would be mounted on the bridge, so all can work in parallel. The position of the modules would result in a hexagonal pattern of tufts, which will cover the surface more efficiently, with less bunching or fold lines, than a rectangular pattern.

 

[AlmasAj]

Reinvent the needle to something without an eye. The needles have a trap near the point, a bit like Hartmann alligator forceps, so they can be pointed needles but also grip the thread. The two needles of a module are held on one side of the mattress, pushed in parallel through a reinforcing pad, the mattress, and another pad. Then the ends of the measured and cut thread are gripped by the needle traps, and drawn back through the pads and mattress. The knot can then be tied by the two needles moving independently under program control.

That places the thread mechanism on one side of the mattress, with the needle control mechanism and knot tying on the other. The mattress would pass under a fixed bridge, like a tunnel.

A number of identical needle modules would be mounted on the bridge, so all can work in parallel. The position of the modules would result in a hexagonal pattern of tufts, which will cover the surface more efficiently, with less bunching or fold lines, than a rectangular pattern.

Thanks for all the effort and information but the thing is I have worked the piercing of the needles and the knotting of the thread.
I wanted a mechanism which can measure and cut a specific amount of yarn.

 

[Tom.G]

For measuring, run the yarn between two rollers that are in contact. Like the figure 8 with the yarn running thru the center and both rollers turning.

Since you know the roller size, count the number of turns to find the length of yarn pulled thru.

You will need two "grippers" to pull the yarn. Think of standing in one place and pulling a rope. You use one hand until you can not pull any farther then you switch to the other hand, "hand-over-hand" pulling.

If electronically measuring the rollers turns, there are devices called "rotary encoders" than can measure as little as 1/1000 of a rotation. Of course mechanical measuring is also possible with a gear train closing a switch at a given number of turns.

Well, there are a few ideas, I hope they help.

Cheers,
Tom

 

[Baluncore]

I wanted a mechanism which can measure and cut a specific amount of yarn.

The problem with cutting the yarn is that you must control the ends, so they can be threaded through the needle eye. It is easiest to thread a needle with a twisted loop in the yarn before it is cut.
If you just want a bin full of yarn cut to length, you can roll the yarn onto a drum with the correct circumference, and then run a blade along the drum.
To mechanise that, the yarn needs to be held at two points until after it is cut, and the cut end of the yarn must be held between a grip and the tensioner while it is picked up.

I would arrange a bar that rotates as a diameter, with the length of the yarn to be cut. It would grip the yarn as it passes and pull out the required length before the other end of the bar engages and begins to pull the next length. The yarn would be cut, and the grip released during the second part of the cycle. The strong grip at each end of the bar would be like the weaker yarn tensioner, two discs with a compression spring. The grips would release at a particular cam angle after the cut, and before the next length.
For high speed operation, the bar would be replaced by a partial drum to maintain the speed of the yarn being removed from the spool.

An electronic system to do the same thing would be slower and less reliable as it would need to reciprocate, probably using a ball screw and a stepper motor, while operating two clamps and a knife.

 

[AlmasAj]

For measuring, run the yarn between two rollers that are in contact. Like the figure 8 with the yarn running thru the center and both rollers turning.

Since you know the roller size, count the number of turns to find the length of yarn pulled thru.

You will need two "grippers" to pull the yarn. Think of standing in one place and pulling a rope. You use one hand until you can not pull any farther then you switch to the other hand, "hand-over-hand" pulling.

If electronically measuring the rollers turns, there are devices called "rotary encoders" than can measure as little as 1/1000 of a rotation. Of course mechanical measuring is also possible with a gear train closing a switch at a given number of turns.

Well, there are a few ideas, I hope they help.

Cheers,
Tom

Thanks you very much tom.
This is a great idea.
I have made a prototype of this 2 gripper system before you suggested but i think that this will be a bit expensive because you see the motors required for the 2 gripper to open and close plus the motors to move to and fro plus the motors to tilt 1 gripper so that the other gripper can move.
I want this machine to be as affordable as possible.
I had the same idea as you gave but without the roller.
I want to make this machine as affordable as possible.
If you can make this 2 gripper system more affordable that would be very helpful.

 

[Baluncore]

I have made a prototype of this 2 gripper system before you suggested but i think that this will be a bit expensive because you see the motors required for the 2 gripper to open and close plus the motors to move to and fro plus the motors to tilt 1 gripper so that the other gripper can move.

A diameter arm is driven by only one motor. The two grippers are operated against a spring by cam followers, as is the knife.

 

[AlmasAj]

The problem with cutting the yarn is that you must control the ends, so they can be threaded through the needle eye. It is easiest to thread a needle with a twisted loop in the yarn before it is cut.
If you just want a bin full of yarn cut to length, you can roll the yarn onto a drum with the correct circumference, and then run a blade along the drum.
To mechanise that, the yarn needs to be held at two points until after it is cut, and the cut end of the yarn must be held between a grip and the tensioner while it is picked up.

I would arrange a bar that rotates as a diameter, with the length of the yarn to be cut. It would grip the yarn as it passes and pull out the required length before the other end of the bar engages and begins to pull the next length. The yarn would be cut, and the grip released during the second part of the cycle. The strong grip at each end of the bar would be like the weaker yarn tensioner, two discs with a compression spring. The grips would release at a particular cam angle after the cut, and before the next length.
For high speed operation, the bar would be replaced by a partial drum to maintain the speed of the yarn being removed from the spool.

An electronic system to do the same thing would be slower and less reliable as it would need to reciprocate, probably using a ball screw and a stepper motor, while operating two clamps and a knife.

I partially understood what you are trying to say but can you give me an example or some images or some video so that I can understand properly.
The thing you said about using electronic, I completely agree with you it would be less reliable that is why I am looking for another option and your idea looks promising.

 

[Baluncore]

I partially understood what you are trying to say but can you give me an example or some images or some video so that I can understand properly.

I have never seen one before, so you will have to wait while I sketch it.
Do you want it hand-cranked or driven by an electric motor?

 

[AlmasAj]

I have never seen one before, so you will have to wait while I sketch it.
Do you want it hand-cranked or driven by an electric motor?

Thanks you very much for doing it.
I want motor driven

 

[Baluncore]

There was a hand operated machine used to cut 75 mm long pieces of wool or torn cloth for making rugs with a latch hook. I used one in about 1960, but do not remember how it worked. Maybe it could be modified to cut yarn for tufting.
Google images: "Rug wool cutter"
Here is a description: http://messybeast.com/rugmaking/rugmaking-3-rotary-cutters.htm

 

[AlmasAj]

There was a hand operated machine used to cut 75 mm long pieces of wool or torn cloth for making rugs with a latch hook. I used one in about 1960, but do not remember how it worked. Maybe it could be modified to cut yarn for tufting.
Google images: "Rug wool cutter"
Here is a description: http://messybeast.com/rugmaking/rugmaking-3-rotary-cutters.htm

But this tool can only cut only a single length I want a mechanism which can cut multiple length. For example sometimes it cut 8 inches sometimes it cut 12 inches like that 4 to 5 variations.

 

[Tom.G]

If you can make this 2 gripper system more affordable that would be very helpful.

• Assume the yarn is being pulled horizontally
• Looking along the yarn from where a gripper is pulling it
  • there is a gripper on each side of the yarn, left side and right side
  • the gripper that is RETURNING opens its jaws wide enough to clear the pulling gripper

Another option that may be cheaper is to use air-operated movement (pneumatics), many factories already have compressed air throughout the production area. Another advantage of being air-operated is the repair people would already be comfortable working on it. Plus, if you are after high speed, air-operated devices are easier to adjust and much cheaper than motors and gear trains.

Computer control is usually done with Programmable Logic Controllers (PLCs), of which there are many manufacturers. They range in physical size from hold-it-in-your-hand to mount-in-a-4ft x 6ft-cabinet. Pricing range: about USD $50 to a few thousand $.

Cheers,
Tom

 

[Baluncore]

But this tool can only cut only a single length I want a mechanism which can cut multiple length.

The rug wool cutter would probably make the simplest motor driven system. The way it works is to wind the yarn onto a capstan with a slight taper. As the yarn winds on, it pushes the previously wound layer down the taper until that reaches a cutter, where the circumference decides the length cut. A capstan could be selected for each length required. A capstan could also be made like a cone pulley, with several steps that would cut different lengths depending on the feed point selected.