Magnetic Tensioner (heads up for the Brits)

[David King]

Hmmm. Felt discs always seem like such a wonderfully elegant solution to this problem.
Regarding metric taps for the threads I'm betting on Travers or MSC having it in stock for a few $$. They both stock thousands of taps in crazy sizes.

[Joe Gwinn]

Hmmm. Felt discs always seem like such a wonderfully elegant solution to this problem.

A number of designs for fine wire use felt as the brake shoe friction material.

Regarding metric taps for the threads I'm betting on Travers or MSC having it in stock for a few $$. They both stock thousands of taps in crazy sizes.

This will be more like 20mm diameter by 0.75 mm pitch. Unlikely to find this in a die. Best way is to turn the thread on a lathe.

[kayakerca]

Yes is a shame , too bad they dont ship outside the UK or id be on this as well ..........group buy

If you (trust quality enough to) buy from China, minimum order is 5 units at $125 - $150:

Coil Winding Magnet Tensioner (Magnetic tensioner) - China Magentic Tensioner,Coil Winding Tensioner,Wire Tensioner in Manufacturing Equipment for Electrical & Electronic Product

[Mike Sulzer]

Joe, I looked at the patent. The description of how it works (at the top of half page 4 as numbered at the top of the column) describes it as a result of the sum of attractive and repulsive forces; I found no description of hysteresis there, nor later on when skimming through the rest of it (might have missed something, though). Of course, it cannot work that way since no energy would be dissipated and hence there would be no net damping force. So the braking must be the result of hysteresis and eddy currents, presumably with the hysteresis component dominating.

[David King]

I found this short summary of magnetic hysteresis: Hysteresis in magnetic materials
I'm thinking there must inevitably be a non-constant, eddy current drag on top of this constant hysteresis drag inducing disc scenario as described in the patent and above. Would they have sliced up the steel disk like a pie to eliminate the eddy currents?

[ken]

I see what you're doing here... kinda.

Are you saying that the eddy current drag is actually nonconstant/nonlinear, so that the eddy current drag added to the hysteresis drag could possibly be too much drag in total?

Since the eddy current drag is nonconstant, this drag force cannot be reliably used here? Therefore, since the eddy current drag is indeed nonconstant, it is to be minimized as much as possible so that hysteresis being repeatable is the only actual drag force acting here?

I can see Tanac's problem here... a pickup coil probably is considered there a 'hostile environment' for a winder ternsioner based on the coil's oblong shape. Nice round coils are easy to design tensioners for. Besides, pickup winders like us are probably such a small fraction of the total winder market it makes no sense for them to design a specialized winder just for our needs.

I wish one of the members actually owned one of these units so we can see the insides

ken

[Joe Gwinn]

Joe, I looked at the patent. The description of how it works (at the top of half page 4 as numbered at the top of the column) describes it as a result of the sum of attractive and repulsive forces; I found no description of hysteresis there, nor later on when skimming through the rest of it (might have missed something, though). Of course, it cannot work that way since no energy would be dissipated and hence there would be no net damping force. So the braking must be the result of hysteresis and eddy currents, presumably with the hysteresis component dominating.

They don't use the word hysteresis, but figures 11 and 12 and the discussion about the magnetizable disk and periodic reversal of the magnetization give the game away, and knowing that this is a kind of hysteresis brake allows one to google.

[Joe Gwinn]

I found this short summary of magnetic hysteresis: Hysteresis in magnetic materials
I'm thinking there must inevitably be a non-constant, eddy current drag on top of this constant hysteresis drag inducing disc scenario as described in the patent and above. Would they have sliced up the steel disk like a pie to eliminate the eddy currents?

There will be some eddy current drag in addition to the hysteresis drag, but I would assume that the hysteresis dominates, or the disk would be slotted radially as you suggest.

[Joe Gwinn]

I see what you're doing here... kinda.

Are you saying that the eddy current drag is actually nonconstant/nonlinear, so that the eddy current drag added to the hysteresis drag could possibly be too much drag in total?

Since the eddy current drag is nonconstant, this drag force cannot be reliably used here? Therefore, since the eddy current drag is indeed nonconstant, it is to be minimized as much as possible so that hysteresis being repeatable is the only actual drag force acting here?

The problem is that eddy current drag varies with capstan rotation speed, which is exactly what tou don't want - the whole point of a tensioner is constant tension regardless of winding speed.

One can use electronics to overcome this defect, but at some expense in complexity.

I can see Tanac's problem here... a pickup coil probably is considered there a 'hostile environment' for a winder tensioner based on the coil's oblong shape. Nice round coils are easy to design tensioners for. Besides, pickup winders like us are probably such a small fraction of the total winder market it makes no sense for them to design a specialized winder just for our needs.

Tanac units, at least the MT-100, apparently have low enough inertia that they can handle pickup bobbins.

I wish one of the members actually owned one of these units so we can see the insides.

Well, I offered the guy with a MT-300 half his asking price, and he immediately accepted my offer of $85. Wish I'd offered $50, but OK. Wonder if the tension wheel thread is worn out.

[Mike Sulzer]

They don't use the word hysteresis, but figures 11 and 12 and the discussion about the magnetizable disk and periodic reversal of the magnetization give the game away, and knowing that this is a kind of hysteresis brake allows one to google.

This is a frequently misunderstood topic as a viewing of forums that deal with this stuff shows. Even the Wikipedia article on dynamometers describes the hysteresis brake as a kind of eddy current brake.

The brake in question is a hysteresis brake, but I really do not think that the inventor knew that when the patent was written. His description of the reversal of the field appears aimed only at keeping the directions of the field components such that the (fictitious) braking force is maintained at all rotation angles.

[David King]

In my mind's eye I see the hysteresis brake as equivalent to a hump in the carpeting just in front of your Big Wheel's tires. That hump keeps moving like a bow wave in front of the tire and slows you down with a friction constant regardless of your speed. (Inevitable references to The Shining deleted.)

[Mike Sulzer]

In my mind's eye I see the hysteresis brake as equivalent to a hump in the carpeting just in front of your Big Wheel's tires. That hump keeps moving like a bow wave in front of the tire and slows you down with a friction constant regardless of your speed. (Inevitable references to The Shining deleted.)

That is a really nice analogy to a region of flipping magnetic field that moves around the disk.

[ken]

In my mind's eye I see the hysteresis brake as equivalent to a hump in the carpeting just in front of your Big Wheel's tires. That hump keeps moving like a bow wave in front of the tire and slows you down with a friction constant regardless of your speed. (Inevitable references to The Shining deleted.)

I love this analogy! ROFL

Maybe Joe will be able to dissect the tensioner he bought, and is able to give us some insight here.

The problem is that eddy current drag varies with capstan rotation speed, which is exactly what tou don't want - the whole point of a tensioner is constant tension regardless of winding speed.

One can use electronics to overcome this defect, but at some expense in complexity.

I thought you should have increasing tension with increasing speed... so you achieve a constant output of wire tension (or constant amount of wire at a constant tension) at the tensioner output no matter how much pull on the wire or speed of removing wire from the bobbin.
ken

[ken]

In my mind's eye I see the hysteresis brake as equivalent to a hump in the carpeting just in front of your Big Wheel's tires. That hump keeps moving like a bow wave in front of the tire and slows you down with a friction constant regardless of your speed. (Inevitable references to The Shining deleted.)

I love this analogy! ROFL

Maybe Joe will be able to dissect the tensioner he bought, and is able to give us some insight here.

The problem is that eddy current drag varies with capstan rotation speed, which is exactly what tou don't want - the whole point of a tensioner is constant tension regardless of winding speed.

One can use electronics to overcome this defect, but at some expense in complexity.

I thought you should have increasing tension with increasing speed... so you achieve a constant output of wire tension (or constant amount of wire at a constant tension) at the tensioner output no matter how much pull on the wire or speed of removing wire from the bobbin.
ken

[Joe Gwinn]

I thought you should have increasing tension with increasing speed... so you achieve a constant output of wire tension (or constant amount of wire at a constant tension) at the tensioner output no matter how much pull on the wire or speed of removing wire from the bobbin.

The ultimate objective is that the tension in the wire in the just-wound coil be constant, regardless of winding speed, so the tensioner's job is to maintain constant tension regardless of how fast the wire is pulled through the tensioner.

And yes, the MT-300 will suffer vivisection.