Unwinds

	M.R. Snyder
	Industrial Drive and Control Systems

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Newsletter: July 10, 2005

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Driving Unwinds with AC Drives

Are you still using brakes or clutches for your unwind applications?

Brakes and Clutches burn energy and require frequent maintenance!

Reasons to drive your unwinds:

Energy Savings:

Using brakes and clutches to control your unwinds wastes energy. Brakes and clutches consume power to maintain your unwind tension and speed. This power is dissipated as heat that costs you money. The power use of your system is (pulling rolls power) + (unwind brake power).

Many applications allow us to common bus your unwind drive with a pull-nip or rewind drive. As the unwind drive re-generates (generates power because it is being pulled) the power is shared with the drives that are motoring (pulling). The power use of your system is (pulling rolls power) – (unwind regenerated power). Also, AC drives are inherently efficient. Depending on the application the savings can be significant.

Maintenance:

	Brakes and clutches require frequent maintenance to maintain the friction surfaces. This results in machine down-time and maintenance costs.
	AC drives and motors require very little maintenance. AC motors have no brushes or friction surfaces to maintain. The expected life is many years without maintenance. AC drives frequently run 10+ years without any maintenance performed. The overall result is increased productivity and reliability.

Tension and Speed Control Range and Regulation:

	Brakes and clutches are sized to run in a narrow torque and tension range. High torque brakes typically cannot control low tensions. Low torque brakes may not give you enough tension. Brakes typically are not smooth torque regulators and cause tension variations in your product. They limit the flexibility of machines.
	AC drives and motors operating in flux-vector mode can operate in a 1000:1 constant torque speed range with 0.01% speed regulation and can maintain full torque at zero speed. When implemented properly, AC drives can give you the greatest flexibility and regulation.

Application: Constant Tension Film Unwind

This system utilizes Siemens Masterdrive Series AC flux-vector drives with Centerwind software along with CMC (Cleveland Motion Control) Tension Transducers as tension feedback to the Siemens Masterdrive. The Centerwind software greatly simplifies the winder by eliminating external cards and circuitry required for similar applications thus making setup and maintenance much easier. Each unwind drive is designed to follow a line speed reference and control in flux vector mode with tension control trim. The Siemens Masterdrive receives a line speed reference and then performs a diameter calculation to give a diameter compensated spindle motor shaft speed reference. The CMC tension load cells are feedback to the drives. A tension setpoint is given and PID loop software in the drive trims the final spindle motor shaft speed reference to maintain a constant tension on the web throughout the diameter build-down. The unwind drive is common-bused to the pull nip so that the pull nip power consumption is reduced by the regenerated power from the unwind drive, thus reducing overall energy consumption. This system provides maximum flexibility for tension, speed, and diameter build-down ratio.

Call M.R. Snyder Company today for help with your application.