Hello all first time poster.

I'd appreciate some advice concerning a little project I've been working on.

My university class has been assigned the task of designing a coil-winding machine.
As a part of my team I've been assigned the task of designing the tension control subsystem, which resembles this (Top down view):

For the bobbin to be properly wound up the tension in the wire must remain constant, so I've come up with the above lever-arm design. As the tension in the wire increases/decreases above/below it's optimal tension, the lever arm moves away from it's null position, and thus sends a signal to the controller. Depending upon the arm's position, the controller sends a signal to the brake, causing it to increase/decrease the reel's friction until it returns to the null position.

I'd like some advice concerning the position sensor portion of the controller. My first thought was to use a potentiometer as a voltage divider, to manage the voltage supplied to the brake (Which will be either an electromagnetic brake or a disc brake). I've also considered using a rotational encoder instead, so I could perhaps hook up a microcontroller to the system, as I've read they can send out digital outputs.

Are there any other considerations I need to account for in designing this circuit (Power dissipation etc) that I may have missed? I've never designed a circuit from scratch before, so I'm not sure where exactly to start, aside from some resistors to limit the amount of current the brake receives.

Any assistance would be appreciated.

 

Hi Juand,
My first thought is always, what is the simplest way. If you can compare electronics with a mechanical solution, try it first. Unless of course you want to 'play' with electronics as an exercise See my first thought< attached.
Camerart

 

Hi Juand,
My first thought is always, what is the simplest way. If you can compare electronics with a mechanical solution, try it first. Unless of course you want to 'play' with electronics as an exercise See my first thought< attached.

It looks like the lever arm acts as a measure of the reel's diameter - so the brake should be applied more as the reel's mass decreases? Is that what you had in mind?

 

A simple, purely mechanical system, might use the tension in the wire to operate the brake, so as the tension increases it releases the brake.

Sewing machines also need the correct tension on the cotton and they achieve this by passing the cotton between two dished washers pressed together by a spring. The pressure from the spring controls the cotton tension.

 

It looks like the lever arm acts as a measure of the reel's diameter - so the brake should be applied more as the reel's mass decreases? Is that what you had in mind?

Hi J,
Mine was a quick answer! Albert's reply is a better one. It is better to put a slight brake on the reel, to stop spinning, and add the tension brake to the wire in a similar way to my drawing or Alberts way of constant tension. The problem with constant tension may be, that as your coil gets larger, the tension needs to be lessened (I think).
C.

 

In a motor or genrator, current is directly proportional to torque. You could add a motor to the supply spool shaft and use a current sensing resistor to apply a (slight) counterclockwise torque on the motor as the spool is turned clockwise by the drawn filiment. Depending on the inertia of your system, you may need a fairly large motor even for very low tension. Note that the motor itself can (will) add to the system inertia.

I'm not saying it will work or it will be easy but a good electronics-based attempt.

 

You could add a motor to the supply spool shaft and use a current sensing resistor to apply a (slight) counterclockwise torque on the motor as the spool is turned clockwise by the drawn filiment.

You would still need a tension sensor to make this work as otherwise the wire tension will vary as the diameter of the source spool reduces.

 

You would still need a tension sensor to make this work as otherwise the wire tension will vary as the diameter of the source spool reduces.

True, so instead of putting the motor on the feed spool, wrap the filimemt one time around an idler pulley and control the tension there.

 

Diameter of the spool! Diameter of the spool!
paper tiger.

One more guide roller will cause the wire to approach the tension bar at the same angle regardless of the diameter of the spool.

 

One more guide roller will cause the wire to approach the tension bar at the same angle regardless of the diameter of the spool.

But not if, as was suggested, the tension bar has been replaced with a motor driving/back-driving the source spool with the tension controlled by keeping the motor torque (= current) constant

 

But not if, as was suggested, the tension bar has been replaced with a motor driving/back-driving the source spool with the tension controlled by keeping the motor torque (= current) constant

True. An extra guide roller is irrelevant if you don't use the method that requires one. In fact, lots of things won't work if you don't use the method that requires them.

 

Having worked for a company that made wire, all of the machines there had what is called a "dancer arm" to control the tension as the wire was either wound on a bulk reel or when going into a machine that cut it to make the final product. A coil winding machine would use the same thing. Google for dancer arm links - https://www.google.com/search?q=dancer+arm&ie=utf-8&oe=utf-8

 

In a motor or genrator, current is directly proportional to torque. You could add a motor to the supply spool shaft and use a current sensing resistor to apply a (slight) counterclockwise torque on the motor as the spool is turned clockwise by the drawn filiment. Depending on the inertia of your system, you may need a fairly large motor even for very low tension. Note that the motor itself can (will) add to the system inertia.

I like this idea, a braking resistor across the motor will offer regenerative braking, and to solve the increase in voltage with increase in rpm and turn it into a automatic damper, the voltage could be fed back to a linear transistor amp where the generated voltage is fed back to the base and the damping resistor would be in the collector, this pair would be wired across the armature.
A self regulating damper.
The value of the resistor would require some empirical testing.
The drum could be mounted over the stator and the armature pinned, turning it in to an Outrunner.
Max.