Controlling wire tension in a coil winder

Thread Starter

cmartinez

Joined Jan 17, 2007
7,411
Using brushed dc motor you still need current-limiting device, some rheostat. Then you will have hot rheostat, but only warm motor.
I'll be applying PWM (8-bit resolution) to the dc motor, so I don't think I'll be needing a resistor o rheostat ... would I?
 

MaxHeadRoom

Joined Jul 18, 2013
23,634
Are you controlling the motor in the same rotation as the spool rotation, or opposing it, are you using feedback to concur with the ever increasing rpm of the spool?
Max.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,411
Are you controlling the motor in the same rotation as the spool rotation, or opposing it, are you using feedback to concur with the ever increasing rpm of the spool?
Max.
I'm opposing the rotation of the coil winder. And no, I'm not going to go into so much sophistication as using feedback on this. But what I did is make the spool's minimum radius much larger than the coil. For instance, the spool's inner diameter is about 50mm, while the coil's is 10mm. That way I expect to ease the fluctuations in tension a little bit. Also, I plan to run the winder at a low speed. This is not for a production application, but rather for prototype testing.
 

Tonyr1084

Joined Sep 24, 2015
6,267
Can you use air pressure to provide resistance and retraction when the wire slackens? Once ran an EDM (Electric Discharge Machining) unit. It had a spool of brass wire that was kept constantly tensioned against the feed using air pressure. If the wire broke the tensioner would rewind the spool. That never happened, but when threading the machine you had to turn off the tensioner and lock the brake so that it only gave resistance but allowed you to spool out the wire as needed. During threading you ALWAYS had slack at some point. During operation, because the spool was so large that momentum would tend to unwind the spool every time the EDM operation ended. Keeping a constant back pressure using air pressure is what they use to keep the spool from slackening up.

Perhaps a couple fans on your spool. One providing air flow and the other connected to your spool. As one fan spins (electrically) the other spins due to air flow. Don't know how fast that would react to a slack wire but it's one quick and dirty way of solving the problem. I think. I could be wrong.
 

Danko

Joined Nov 22, 2017
1,134
I'll be applying PWM (8-bit resolution) to the dc motor, so I don't think I'll be needing a resistor o rheostat ... would I?
For stable continuous torque you should feed motor not by voltage but by current.
Only way is to convert PWM to analog signal and send it to input of current stabilizer then to motor. Still same rheostat, if stabilizer will not works in switching mode.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,411
Can you use air pressure to provide resistance and retraction when the wire slackens? Once ran an EDM (Electric Discharge Machining) unit. It had a spool of brass wire that was kept constantly tensioned against the feed using air pressure. If the wire broke the tensioner would rewind the spool. That never happened, but when threading the machine you had to turn off the tensioner and lock the brake so that it only gave resistance but allowed you to spool out the wire as needed. During threading you ALWAYS had slack at some point. During operation, because the spool was so large that momentum would tend to unwind the spool every time the EDM operation ended. Keeping a constant back pressure using air pressure is what they use to keep the spool from slackening up.

Perhaps a couple fans on your spool. One providing air flow and the other connected to your spool. As one fan spins (electrically) the other spins due to air flow. Don't know how fast that would react to a slack wire but it's one quick and dirty way of solving the problem. I think. I could be wrong.
I had already considered using an air turbine, but unfortunately I have no access to pressured air where I am. On the other hand, air blown from a hair dryer would be too weak for my purpose, I think ... but I'll give your suggestion some more thought anyway ... thanks for sharing
 
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Thread Starter

cmartinez

Joined Jan 17, 2007
7,411
For stable continuous torque you should feed motor not by voltage but by current.
Only way is to convert PWM to analog signal and send it to input of current stabilizer then to motor. Still same rheostat, if stabilizer will not works in switching mode.
You're right ... but first I'll try it using only pwm, and if that doesn't work well enough, then I'll put a current sensor in the circuit and adjust pwm accordingly
 

Danko

Joined Nov 22, 2017
1,134
You're right ... but first I'll try it using only pwm, and if that doesn't work well enough, then I'll put a current sensor in the circuit and adjust pwm accordingly
Yes, some like this. Inductance will provide continuous motor current:
PWM.png
It was in my previous post (buried in 1 season):
"EDIT: If you will allow motor to rewind, then you may have two not good situations.
1. If wire was loosen and motor trying to rewind it, you will have chance to break wire, because of big inertia of system (motor + spool).
2. If your wire will broken, or not anchored yet, spool can take run to some thousand RPM.
It is why I used brake for reverse rotation.
"
 
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I built a tension controller that we did not need at the end. I did learn something though. In order to control at the low end, you have to be able to use slightly negative current to compensate for the magnetized components.

We could not measure the two diameters and I had not thought about that either, but we did have an equation that could equate diameter and turns count and thickness of the material because we had to expose a piece of clear Teflon like a shutter(e.g. camera film advance) every so often. It was to prevent a quartz window from getting dirty. The turning mechanism was a synchonous motor running open loop.

So, I did use a brake and the current to the brake controlled the tension.

Actual tension measurement is usually done with a spring loaded arm and you measure angle.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,411
Yes, some like this. Inductance will provide continuous motor current:
That's a very interesting circuit, Danko. Why is there a resistor in the loop, to minimize oscillations/resonance?

Actual tension measurement is usually done with a spring loaded arm and you measure angle.
yup, that's the way it's usually done.. but I consider it overkill for the machine that I'm building.

I am aware of the perils of the wire breaking and the spool turning at a wild pace, Danko. But this machine will always be under my supervision, and I'm trying to keep things as simple as possible without sacrificing the quality of the end result.
 

Danko

Joined Nov 22, 2017
1,134
:eek: ... I missed the part in which I had to imagine the differential amplifier connected to the ADC that's in turned connected to the MCU ... :rolleyes: ... :D ... thanks again!
You are welcome!
So, your design of fully automatic tension regulator is almost done.
 
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Reloadron

Joined Jan 15, 2015
6,064
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