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2007 PLACE

ConferenceSeptember 16-20

St Louis, MO

Basics of Web Tension Control

Presented by:Darrell WhitesideDistribution Channel Manager

MAGPOWR


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Terms and Relationships Defined

Torque = A force at a distance (X) that produces or tends to produce rotation

Force = A push or pull

X

FORCE

TORQUE (TQ)= FORCE (F) x PERPENDICULAR DISTANCE (D)(from axis of rotation)Sometimes called "Lever Arm"

FORCE

X

TENSION

TQ = T RTORQUE (TQ)= TENSION (T) x RADIUS (R)


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Typical Tension Control Applications

Normal Running Conditions

Unwind

Rewind

Point - to - Point


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Center Rewind

Clutch

Motor

T =TQR

" Pull" web to create tension

Typical Applications - Rewind

R is increasingTQ must increase for constant tension

Surface Rewind

Clutch

Motor

T =TQR

TQ must be constant for constant tension

Constant

Constant


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Typical Applications

Point-to-PointNIP NIP

Drive Clutch

Motor

R

TQ =T Constant

NIP NIP

DriveBrakeRTQ

=T

Constant torque produces constant tension

Constant


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Creating Tension Zones

What is a tension zone? A section of web where a

different tension can becreated in the web

Brake

1 2 3

Gear Box

Motor

Nip points can differentiate tension zones only if the web cannot slip through them

Clutch

Motor Clutch

T

"S" WR AP

TNIP

T

What are some typical sources used tocreate tension zones?

Motor

We show high ratio gear boxes or regenerative drives on the motors

Sets Line Speed


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Methods of Control

(Speed Control)

( )1

12

1

212 V

V-VEAVV

T=T +

R

T1

T2

V1 V2

T2 = Rewind tension

V2 = Rewind velocity

Where:T1 = Tension in the previous tension zone

V1 = Nip roll velocity

E = Elasticity of the material A = Cross sectional area of the material

The larger the elasticity (E), the less likely the material is tostretch. For most values of EA, use TORQUE CONTROL

For stretchy material, where E is small, speed control canapproach being as good as torque control


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Speed Control Case

R

T1 T2

V1 V2( )T = T VV

EA V - VV2 1

2

1

2 1

1

+

= 10 lb

If we allow a 0.25% error in V 2:

lb11.275=

Therefore: 0.25% error in speed results in a

12.75% error in tension.

Example: T 1 = 0V1 = 100 fpmV2 = 102 fpmEA = 500 lb C o n t r

o l l i n g

F u n c t i o n

= 1.0025 (102 fpm)V2 = 102.255 fpmThen :

T2

( )fpm100

fpm)100fpm102lb500fpm100fpm102

lb0 +

=

( )fpm100

fpm100fpm102.255lb500fpm100

fpm102.255lb0

+

=

%75.12

10

10275.11 =Error =

T2


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Methods of Control (Torque Control)

R

TQ

=T2

T1 T2

Where:

T2 = Rewind tension

R = Radius

TQ = Torque


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Torque Case

Magnetic Particle Clutch or Brake

C o n t r o l

l i n g

F u n c t i o

n T2 = 10 lb

Allow a 0.25% error in torque (TQ):TQ = 10.025 lb-ft

Therefore: 0.25% error in torque resul ts in a 0.25%error in tension

Torque and tension are directly related !

Example: R = 1 ftTQ = 10 lb-ft

ft1ft-lb10=

= 10 lb-ft (1.0025)

T1 T2

T =TQR2

%25.10

10025.10 =Error =

= 10.025 lbThen:

T2 ft1ft-lb10.025=


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Summary

Torque vs. Speed For a 0.25% error in the controlled output,

the resultant error in tension was:

0.25% = Magnetic particle clutch or othertorque device

12.75% = Speed case


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Example: Driving a car and as you go up a hill, youtry to adjust the accelerator by visually

estimating the incline. (No speedometer)

Manual ControlOutputDesired

OutputControl

(Amplifier)TensionSystem

(Machine)

Output / tension is influenced onlyby operator adjustment.

To try to keep tension constant as the rolldiameter changes, the operator must adjustthe control output as he thinks it is necessary.

Manual Systems


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Example: Driving a car equipped with a sensor that detectschanges in incline and makes the accelerator adjustment to tryto keep speed constant. (Sensor is not measuring speed.)

Open Loop Control

Output / tension is influenced byoperator adjustment and calculationsmade from a sensor input.

TensionSystem(Machine)

DesiredOutput

OutputControl(Calculator)

Sensor

Open Loop Systems


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Example: Driving a car and controlling the speed by adjusting theaccelerator based upon the speedometer reading.

(Actual speed feedback "Cruise Control")

TensionSystem(Machine)DesiredOutput

OutputControlComparator

Load Cell

Closed Loop Systems

Provide some form of feedback

Tension Sensors

Dancer Arm

Free Loop


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Unwind Applications

Hot brakes & web breaks.

Rewind Applications

If taper tension is required.

Point - to - Point

Constant torque on a constant radiusequals constant tension.

Not good

Good

You get what you get,based on roll build

T =TQ

R

Constant

7rpmTQ

=SW

T =TQR

Constant

Good T = TQR ConstantConstant

Constant HP is constant

Manual Tension Controls


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Compensates for changes in roll diameter only

Does not compensate for or reduce tension transientsthat occur due to other parts of the systemOpen loop does not have tension measurement

Ultrasonic control is the easiest to install and set upIts easy and it works!

Open Loop Systems Summary

Does not compensate for tension errors due to non-linearity of device being controlled (i.e. brake, clutch, motor etc.No feedback


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Closed Loop Systems

Feedback

OutputControl

TensionSystem(Machine)

Sensor

DesiredOutput

Comparator

TENSION SENSOR SYSTEM

TS

B Sensor basedControl

Feedback

DANCER SYSTEM

B

DFP

Dancer Control

Dancer

BRAKE


22/23

Identify what is setting line speed

Use a torque device to control tension

Summary (dos and donts)

Make sure web does not slip through nips

Dont use manual controls on center unwinds

Beware of diameter calculator controls For indexing or out-of-round roll applications use a dancer system

Dont control tension on the device setting line speed


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Thank YouPRESENTED BY

Darrell WhitesideDistribution Channel Manager [email protected]

Please remember to turn

in your evaluation sheet...

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