Center-driven web winder

  • Thread starter Alvaro Rodriguez
  • Start date
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Thread Starter

Alvaro Rodriguez

We have a Web Winder with ferrous metals. The winder is handled via DC motor + drive. There was an emergency stop (sudden and extreme load change), that caused the motor to flashover, and also damaged the drive, since there is nothing between drive and motor. The motor is fine. We investigated and found that in order to prevent this from happening again, we must install a dynamic braking device (output reversing contactor and power resistors).

This is all we found. Is it OK? We need help on how to size this dynamic braking option. What is required?

Since we need to warranty constant tension, we would like to know what type of meter is commonly used for this purpose.

Thanks in advance.
 
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Gerald Moore

> We need help on how to size this dynamic braking option. What is required? I have used a dynamic brake, a while ago, to E-stop a winder for a slitter. I changed the control circuit so that when the E-Stop is pressed the DC Motor Field went to full flux. Then I put the armature across a resistance. This stopped the motor instantly. When zero speed was detected, I returned the control circuit to a normal stop and applied the pneumatic tension brake to the payoff winder on full(the payoff did not have an electric motor on it). It stopped the motor in a fraction of a second and the payoff winder stopped slightly later, this lost the tension but kept the strip from breaking. I sized the resistance by: D.B.R = (Varm/(Carm * 1.25)) - Rmotor D.B.R. = the new Dynamic Brake Varm = Rated Armature Voltage Carm = Rated Armature Current Rmotor = resistance of the Armature Coil This formula doesn't take into consideration the inductance(this should be small) and also assumes the motor can take 125 to 150% armature current for a short time. Make sure the D.B.R. can handle the power. If you have a large expensive DC Motor I would contact the manufacturer before doing anything. > Since we need to warranty constant tension, we would like to know what type of meter is commonly used for this purpose. I've never done this while keeping tension under control. You may be able to do it with some work. Keep in mind the priority in an E-Stop is to Stop the machine so that no one gets hurt. The process is secondary. Hope this helps. Gerry Moore
 
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Orsini Livio S.

Dear Mr Alvaro Rodriguez, To do the emergency stop with dynamic braking is correct, but this way can not control the web tension and it is more expensive. I suppose that the motor is drived by a four quadrants converter, with automatic field reduction over some speed. If the motor flashover occurs in the speed region of reduced field, perhaps the the problem is caused by an adjustement not satisfying of the loops parameters of field converter and armature converter. For my experiences with these kinds of drives the parameters optimization is not easy, in special way if the motor has a big load inertia. Livio S. Orsini LSOEngineering Via DeAmicis, 48 21040 Vedano Olona VA ITALY [email protected]
 
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Alvaro_A_Rodriguez

Dear Gerry: Thanks for the information. It was very helpful. Let me ask something else: on this process, it is very important to keep tension constant at all times. From your experience, what variation in percentage is allowed to remain "constant" ? Thanks, Alvaro Rodriguez
 
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