U.S. patent application number 09/725556 was filed with the patent office on 2002-05-30 for device and method for automatic tension transducer calibration.
Invention is credited to Cote, Kevin Lauren, Schroeder, Lothar John.
Application Number | 20020063541 09/725556 |
Document ID | / |
Family ID | 24915019 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020063541 |
Kind Code |
A1 |
Cote, Kevin Lauren ; et
al. |
May 30, 2002 |
DEVICE AND METHOD FOR AUTOMATIC TENSION TRANSDUCER CALIBRATION
Abstract
An apparatus for calibrating a tension transducer for a web
includes a pair of nip rollers and a motor for driving at least one
of the pair of nip rollers, the motor having at least one roller
output being a function of at least one of a motor torque and a
motor velocity. A web tension transducer roll is located upstream
of the nip rollers, the web tension transducer having a tension
output being a function of the actual web tension of the web. A
processor receives the at least one roller output and the tension
output, the processor calculating a tension correction value as a
function of the at least one roller output and the tension output.
Also provided is a method for calibrating a tension transducer for
a web comprising the steps of running the web over a tension
transducer and through nip rollers, the nip rollers being run by a
motor, varying a characteristic of the motor and reading actual
reference signals from the transducer as the characteristic is
varied, and calculating at least one correction value as a function
of the actual reference signals.
Inventors: |
Cote, Kevin Lauren; (Durham,
NH) ; Schroeder, Lothar John; (Portsmouth,
NH) |
Correspondence
Address: |
DAVIDSON, DAVIDSON & KAPPEL, LLC
14th Floor
485 Seventh Avenue
New York
NY
10018
US
|
Family ID: |
24915019 |
Appl. No.: |
09/725556 |
Filed: |
November 29, 2000 |
Current U.S.
Class: |
318/432 |
Current CPC
Class: |
B65H 2557/61 20130101;
B65H 2220/02 20130101; B65H 2513/11 20130101; B65H 2515/32
20130101; G01L 5/0085 20130101; B65H 2515/31 20130101; G01L 25/00
20130101; B65H 2513/11 20130101; B65H 2515/31 20130101; B65H
2515/32 20130101; B65H 23/044 20130101; B65H 2220/01 20130101; B65H
2220/02 20130101; B65H 2220/01 20130101 |
Class at
Publication: |
318/432 |
International
Class: |
H02P 007/00 |
Claims
What is claimed is:
1. An apparatus for calibrating a tension transducer for a web
comprising: a pair of nip rollers; a motor for driving at least one
of the pair of nip rollers, the motor having at least one roller
output being a function of at least one of a motor torque and a
motor velocity; a web tension transducer roll located upstream of
the nip rollers, the web tension transducer having a tension output
being a function of the actual web tension of the web; and a
processor receiving the at least one roller output and the tension
output, the processor calculating a tension correction value as a
function of the at least one roller output and the tension
output.
2. The apparatus as recited in claim 1 wherein the tension
correction value is further a function of a predicted web tension
or predicted change in web tension.
3. The apparatus as recited in claim 1 wherein the at least one
roller output includes both a motor torque output and a motor
velocity output.
4. The apparatus as recited in claim 1 wherein the processor
outputs a calibrated web tension value as a function of the tension
output and the tension correction value.
5. The apparatus as recited in claim 1 wherein the processor
calculates a breakaway torque of the motor.
6. The apparatus as recited in claim 1 wherein the processor
calculates a correction offset of the tension output.
7. The apparatus as recited in claim 2 wherein the processor
calculates a correction factor as a function of the at least one
roller output and the predicted web tension or predicted change in
web tension.
8. A method for calibrating a tension transducer for a web
comprising the steps of: running the web over a tension transducer
and through nip rollers, the nip rollers being run by a motor;
varying a characteristic of the motor and reading actual reference
signals from the transducer as the characteristic is varied; and
calculating at least one correction value as a function of the
actual reference signals.
9. The method as recited in claim 8 further comprising reading a
first signal from the tension transducer at a known web tension so
as to determine a correction offset.
10. The method as recited in claim 8 further including determining
a breakaway torque of the motor.
11. The method as recited in claim 10 wherein the characteristic is
a motor torque and the varying step occurs between the breakaway
torque and a predetermined torque.
12. The method as recited in claim 11 wherein the actual reference
signals are linearized so as to form an actual tension versus
torque line.
13. The method as recited in claim 8 wherein the characteristic is
a motor velocity and the varying step includes changing a motor
velocity with respect to a nominal velocity.
14. The method as recited in claim 13 wherein the at least one
correction value is further a function of a known paper
modulus.
15. The method as recited in claim 8 further comprising comparing
the actual reference signals to a predicted data set, the at least
one correction value including a correction factor being a function
of the actual reference signals and the predicted data set.
16. The method as recited in claim 8 further comprising calculating
a calibrated web tension output as a function of actual signals
from the tension transducer and the least one correction value.
17. The method as recited in claim 9 wherein the known tension is
zero.
18. The method as recited in claim 8 wherein the characteristic is
a motor torque value.
19. The method as recited in claim 8 wherein the characteristic is
a motor velocity value.
20. The method as recited in claim 8 wherein the calculating step
further includes calculating a ratio of a predicted data angle over
a measured data angle, so as to form a correction factor.
21. The method as recited in claim 8 further including repeating
the step of determining a breakaway torque a plurality of times, so
as to calculate an average value for the breakaway torque.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to web printing
presses and more particularly to a device and method for
calibrating a web tension transducer.
[0003] 2. Background Information
[0004] Web printing presses print a continuous web of material,
such as paper. In order to do so, tension measurements of the web
can be critical to the operation of a web press. Different paper
types produce differing amounts of tension in the web proportional
to the speed of the web and the paper modulus.
[0005] One way to measure web tension is using analog tension
transducers. However, existing tension transducers are analog
devices and require frequent calibration, so that an electrical
signal produced by the transducer can be correlated properly to
actual web tensions. The current calibration procedure is performed
when the web is not operating by a manual measurement of signals
produced by the transducer. This method is time consuming and the
accuracy is a function of human performance. Moreover, the
calibration must be conducted when the press is not in operation.
This can result in lost production due to the downtime required for
calibration of the tension transducer and poor press performance
resulting from the erroneous tension information supplied by
uncalibrated tension transducers.
BRIEF SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide a device
and method for providing a process of automatic tension transducer
calibration. An additional or alternative object of the present
invention is to provide a method for calculating the amount of
tension in a paper at a discrete speed.
[0007] The present invention provides an apparatus for calibrating
a tension transducer for a web including a pair of nip rollers and
a motor for driving at least one of the pair of nip rollers, the
motor having at least one roller output being a function of at
least one of a motor torque and a motor velocity. A web tension
transducer roll is located upstream of the nip rollers, the web
tension transducer having a tension output being a function of the
actual web tension of the web. A processor receives the at least
one roller output and the tension output and calculates a tension
correction value as a function of the at least one roller output
and the tension output.
[0008] The tension transducer thus can be calibrated without manual
interference, using the tension correction value.
[0009] The tension correction value further may be a function of a
predicted web tension, which may be determined using a radius of
the transducer roll, or a predicted change in web tension, which
may be determined using a paper modulus.
[0010] Preferably, the at least one roller output includes both a
motor torque output and a motor velocity output.
[0011] The processor then outputs a calibrated web tension value as
a function of the tension output and the tension correction value,
and may also calculates a breakaway torque of the motor as well as
a correction offset of the tension output.
[0012] The processor can calculate a correction factor, which can
be the tension correction value, as a function of the at least one
roller output and the predicted web tension or predicted change in
web tension.
[0013] The present invention also provides a method for calibrating
a tension transducer for a web comprising the steps of:
[0014] running the web over a tension transducer and through nip
rollers, the nip rollers being run by a motor;
[0015] varying a characteristic of the motor and reading actual
reference signals from the transducer as the characteristic is
varied; and
[0016] calculating at least one correction value as a function of
the actual reference signals.
[0017] The method may further comprise reading a first signal from
the tension transducer at a known web tension, preferably zero, so
as to determine a correction offset, and may further include
determining a breakaway torque of the motor. The method may include
repeating the step of determining a breakaway torque a plurality of
times, so as to calculate an average value for the breakaway
torque.
[0018] The characteristic preferably is a motor torque and the
varying step occurs between the breakaway torque and a
predetermined torque. The actual reference signals then may be
linearized so as to form an actual tension versus torque line.
[0019] Alternatively, the characteristic may be a motor velocity
and the varying step may include changing a motor velocity with
respect to a nominal velocity. The at least one correction value
preferably then is further a function of a known paper modulus.
[0020] The actual reference signals are compared to a predicted
data set, the at least one correction value preferably including a
correction factor being a function of the actual reference signals
and the predicted data set.
[0021] The method may further comprise calculating a calibrated web
tension output as a function of actual signals from the tension
transducer and the least one correction value.
[0022] The characteristic preferably is a motor torque value or a
motor velocity value.
[0023] The calculating step may further include calculating a ratio
of a predicted data angle over a measured data angle, so as to form
a correction factor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] A preferred embodiment of the present invention is described
below by reference to the following drawings, in which:
[0025] FIG. 1 shows a side view of the automatic tension
calibration system, which includes a motor and transducer;
[0026] FIG. 2 shows a graph of the angular velocity vs. motor
torque;
[0027] FIG. 3 shows a shows a graph of a web tension vs. working
torque; and
[0028] FIG. 4 shows a graph of an alternate embodiment where the
breakaway torque need not be calculated, and shows a change in web
tension vs. a change in velocity of the motor divided by a nominal
velocity.
DETAILED DESCRIPTION
[0029] FIG. 1 shows a side view of the automatic tension
calibration system, which includes a motor 10 and a tension
transducer roll 1.
[0030] A pair of nip rollers 3 drive a web 8 in a direction 7. The
motor 10 drives the nip rollers 3 via a mechanical linkage. The
motor 10 transmits a first reference signal 6, which is
proportional to a torque 4 of the motor 10, and a second reference
signal 11, which is proportional to an angular velocity 13 of the
motor 10, to a processor 1 CO by wireless, optical or electrical
connections. Upstream from the nip rollers 3, the tension
transducer roll 1 transmits an actual tension signal 2, which is
proportional to the tension in the web 8, to the processor 100 by
an electrical, optical or wireless connection. During a calibration
process, the actual tension signal 2 forms an actual web tension
reference signal. The processor 100 transmits a calibrated output
signal 110, for example to a display device 120.
[0031] FIG. 2 shows a graph of the motor angular velocity 13 vs.
the motor torque 4. While the web 8 is not in contact with the
tension transducer roll 1 or the nip rollers 3, and with the motor
10 and nip rollers 3 stopped, the torque 4 of the motor 10 is
increased. The processor 100 determines a breakaway torque 14 by
monitoring the angular velocity 13 of the motor 10 by the second
reference signal 11 sent from the motor 10. The torque 4 of the
motor 10 is increased 15 until an actual angular velocity 113, an
angular velocity 13 that causes the nip rollers 3 to rotate, is
detected. The highest torque 4 that was transmitted from the motor
10 to the processor 100 by the first reference signal 6, before the
actual angular velocity 113 was detected, is recorded as the
breakaway torque 14. This process may be repeated a plurality of
times so as to calculate an average value for the breakaway torque
14.
[0032] FIG. 3 shows a graph of a web tension 17 vs. the working
torque 104 (which is the motor torque 4 subtracted by the breakaway
torque). After the breakaway torque 14 has been calculated and
while the web 8 is still not in contact with the tension transducer
roll 1 or the nip rollers 3, the processor 100 records the actual
reference signal 2 from the tension transducer roll 1 and compares
the actual reference signal 2 to a known quantity, in this case
zero. Since the web 8 is not in contact with the tension transducer
roll 1 or the nip rollers 3, the actual reference signal 2 should
read zero. However, if the actual reference signal 2 is non-zero,
then the processor 100 determines a correction offset, which can be
a positive correction offset 21 or a negative correction offset
22.
[0033] The web 8 is then moved, so as to contact the nip rollers 3
and the tension transducer roll 1. While running the web 8 over the
web tension transducer roll 1 and through the nip rollers 3, the
torque 4 of the motor 10 is increased from the breakaway torque 14
to a predefined upper limit. While the torque 4 of the motor 10 is
increased, the tension transducer roll 1 sends at least two actual
reference signals 2 to the processor 100. The processor 100
subtracts the correction offset for each of the at least two actual
reference signals 2 to produce at least two normalized values or
data points 19 corresponding to each of the at least two actual
reference signals 2. The processor then linearizes and plots each
of the at least two normalized values 19 on the graph of web
tension 17 vs. working torque 104. The processor then forms a
measured data curve 18 by connecting each of the at least two
discrete data points 19. The measured data curve 18 may then be
compared to a predicted data curve 20 to determine a correction
factor. The predicted data curve in this embodiment is simply a
straight line in which the predicted web tension 17 equals the
working torque 104 divided by the radius of the tension transducer
roll 1, i.e. TN=TQ/R, where TN is the web tension, TQ is the
working torque and R is the radius of the roll 1. The processor 100
calculates the angle of the measured data curve 18 with respect to
the x-axis, and records the angle as a measured data angle 24. The
processor 100 then calculates the angle of a predicted data curve
20 with respect to the x-axis, so as to form a predicted data angle
23. Then, the processor 100 may calculate the ratio of the
predicted data angle 23 over the measured data angle 24, so as to
form a correction factor.
[0034] The processor 100 may then correct future actual tension
signals 2, for example during a print run, by subtracting the
correction offset from the signals 2 and multiplying the result by
the correction factor to produce the corrected actual web tension
value 110, i.e. the calibrated web tension value=(actual signal
value-correction offset)*the correction factor. The processor 100
may then transmit the calibrated web tension value 110 to the
display device 120 or to other parts of the press which may require
a web tension measurement.
[0035] FIG. 4 shows a graph of an alternate method of the present
invention in which the breakaway torque of the motor 10 need not be
calculated. The graph shows a change in web tension 117 plotted
versus a velocity of the motor 10 divided by a nominal velocity
30.
[0036] The tension transducer roll 1 can be automatically
calibrated without first determining the breakaway torque 14 as
follows. While the web 8 is not in contact with the tension
transducer roll 1 or the nip rollers 3, the processor 100 records
the actual reference signal 2 from the tension transducer roll 1
and compares the actual reference signal 2 to the known tension
quantity, in this case zero, i.e. since the web 8 is not in contact
with the tension transducer roll 1, the actual reference signal 2
should read zero. However, if the actual reference signal 2 is
non-zero, then the processor 100 determines a correction offset as
with respect to the previous method disclosed with respect to FIGS.
2 and 3.
[0037] The web 8 is then engaged so as to contact the nip rollers 3
and the web tension transducer roll 1. At a known paper modulus and
velocity, the web 8 runs over the web tension transducer roll 1 and
through the nip rollers 3. The velocity 30 of the motor 10 is
increased slightly several times and the resulting change in
tension 27 is recorded, linearized and plotted versus the change in
velocity over the nominal velocity. The processor 100 then forms a
measured speed data curve 28 by connecting each of the at least two
discrete data points 27. The processor 100 may then compare the
measured change in tension line 28 to a predicted change in tension
curve 29, which is determined by the formula change in web tension
dTN equals the known paper modulus E multiplied by the change in
velocity dV divided by the nominal velocity V, i.e. dTN=E*DV/V.
Next, the processor 100 calculates the angle of the measured speed
data curve 28 with respect to the x-axis, so as to form a measured
angle 32. The processor 100 then calculates the angle of the
predicted curve 29 with respect to the x-axis, so as to form a
predicted angle 31. The processor then calculates the ratio of the
predicted angle 31 over the measured angle 32, so as to form a
correction factor (angle 32/angle 31).
[0038] The processor 100 may then determine a calibrated web
tension signal in the same manner as the previous embodiment,
namely by subtracting the correction offset and multiplying the
actual signals 2 by the correction factor to produce the calibrated
signals 110. The processor 100 may then transmit the calibrated
signals 110, measured speed data curve 28, and predicted speed data
curve 29 to the display device 120, or to other parts of the press
which require a web tension value.
[0039] In some cases, the paper modulus may be unknown; thus, the
predicted curve 29 is also unknown. In order to obtain the
predicted curve 29, the operator may manually calibrate the web
tension transducer roll 1 and produce the resulting predicted curve
for that type of paper. The results for different types of paper
may be saved and used whenever the same paper is used.
* * * * *