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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
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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...