U.S. patent application number 12/322855 was filed with the patent office on 2010-08-12 for system and method for utilizing a linear sensor.
Invention is credited to Michael C. Moed, William M. Silver, Robert J. Tremblay.
Application Number | 20100199475 12/322855 |
Document ID | / |
Family ID | 42124596 |
Filed Date | 2010-08-12 |
United States Patent
Application |
20100199475 |
Kind Code |
A1 |
Tremblay; Robert J. ; et
al. |
August 12, 2010 |
System and method for utilizing a linear sensor
Abstract
Systems and methods for utilizing linear optoelectronic sensors
are provided. A plurality of linear sensors may be utilized to
obtain velocity measurements of a web material at two points. The
acceleration of the web material may be determined from the
velocity measurements and a control signal issued to a servo to
maintain proper tension along the web material.
Inventors: |
Tremblay; Robert J.;
(Grafton, MA) ; Silver; William M.; (Weston,
MA) ; Moed; Michael C.; (Hopkinton, MA) |
Correspondence
Address: |
COGNEX CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
1 VISION DRIVE
NATICK
MA
01760-2077
US
|
Family ID: |
42124596 |
Appl. No.: |
12/322855 |
Filed: |
February 6, 2009 |
Current U.S.
Class: |
26/71 |
Current CPC
Class: |
B65H 2513/11 20130101;
B65H 2557/23 20130101; B65H 2301/121 20130101; B65H 23/1888
20130101; B65H 2511/11 20130101; B65H 2513/21 20130101; B65H
2513/11 20130101; B65H 2511/11 20130101; D21G 9/0045 20130101; G01S
11/12 20130101; B65H 7/14 20130101; B65H 2515/31 20130101; B65H
2513/10 20130101; B65H 2513/10 20130101; B65H 2220/02 20130101;
B65H 2553/42 20130101; B65H 2220/01 20130101; B65H 2220/03
20130101; B65H 2220/03 20130101; B65H 2220/02 20130101; B65H
2220/11 20130101; B65H 2513/21 20130101; B65H 2515/31 20130101;
D21F 7/005 20130101 |
Class at
Publication: |
26/71 |
International
Class: |
D06C 3/00 20060101
D06C003/00 |
Claims
1. A method for draw control of a web material, the method
comprising: obtaining, using a first linear sensor, a first
velocity measurement at a first point along the web material;
obtaining, using a second linear sensor, a second velocity
measurement at a second point along the web material; determining,
using the first and second velocity measurements, an acceleration
of the web material between the first and second points; and
adjusting tension on the web material based on the determined
acceleration.
2. The method of claim 1 wherein the web material comprises a woven
material.
3. The method of claim 1 wherein the web material comprises a
non-woven material.
4. The method of claim 1 wherein the first linear sensor comprises
a one dimensional sensor arranged approximately parallel to a
direction of motion of the web material.
5. The method of claim 1 wherein the second linear sensor comprises
a one dimensional sensor arranged approximately parallel to a
direction of motion of the web material.
6. The method of claim 1 wherein adjusting tension on the web
material based on the determined acceleration comprises modifying a
speed of a motor configured to move the web material.
7. The method of claim 1 wherein the first linear sensor is located
prior to a motor controlling speed of the web material and wherein
the second linear sensor is located after the motor.
8. The method of claim 1 wherein adjusting tension on the web
material based on the determined acceleration comprises sending a
control signal to a motor.
9. A system for draw control of a web material, the system
comprising: a motor configured to provide motion to the web
material; a first linear sensor configured to obtain a first
velocity at a first point along the web material; a second linear
sensor configured to obtain a second velocity at a second point
along the web material; a control unit configured to determine an
acceleration of the web material between the first and second
points using the first and second velocities and further configured
to transmit a control signal to the motor to cause a change in
acceleration of the web material thereby maintaining a tension
along the web material within a predefined range.
10. The system of claim 9 wherein the web material comprises a
woven material.
11. The system of claim 9 wherein the web material comprises
non-woven material.
12. The system of claim 9 wherein the first linear sensor comprises
a one dimensional sensor arranged approximately parallel to a
direction of motion of the web material.
13. The system of claim 9 wherein the second linear sensor
comprises a one dimensional sensor arranged approximately parallel
to a direction of motion of the web material.
14. A method for performing cut to length operation on a web
material, the method comprising: determining, using a linear
sensor, a length of the web material that has passed a predefined
point; generating a trigger signal to activate an actuator to
perform an action on the web material; and performing, by the
actuator, the action on the web material, wherein the trigger
signal is timed so that the action is performed on the web material
at predefined distances along the web material.
15. The method of claim 14 wherein the generation of the trigger
signal is performed by a control unit.
16. The method of claim 14 wherein the generation of the trigger
signal is performed by the linear sensor.
17. The method of claim 14 wherein the predefined distance
comprises substantially equal distances.
18. The method of claim 14 wherein the predefined distance
comprises a set of variable distances.
19. The method of claim 14 wherein the action comprises cutting the
web material.
20. The method of claim 14 wherein the action comprises printing on
the web material.
21. A system for performing cut to length operation on a web
material, the system comprising: a linear sensor configured to
determine a length of the web material passing a predefined point;
a control unit operative interconnected with the linear sensor, the
control unit configured to generate a trigger signal; an actuator,
responsive to the trigger signal, configured to perform an action
on the web material wherein the trigger signal is timed so that the
action is performed on the web material at a predefined location on
the web material.
22. A method for ensuring quality control of a web material, the
method comprising: obtaining a data set of statistical data from
one or more points along the web material using one or more linear
a sensors; and calculating a quality score using the set of
statistics.
23. The method of claim 22 wherein the statistical data comprises
image-based data o the web material.
24. The method of claim 22 further comprising determining whether
the calculated quality score meets a predefined minimum quality
score; and in response to determining that the quality score does
not meet the predefined minimum quality score, rejecting at least a
portion of the web material.
25. The method of claim 22 wherein the set of statistical data
comprises an average speed of the web material.
26. The method of claim 22 wherein the set of statistical data
comprises a set of changes in tension along the web material.
Description
RELATED APPLICATIONS
[0001] This patent application is related to the following United
States patent applications:
[0002] Ser. No. 11/763,752, entitled METHOD AND SYSTEM FOR
OPTOELECTRONIC DETECTION AND LOCATION OF OBJECTS, by William M.
Silver, the contents of which are hereby incorporated by
reference,
[0003] Ser. No. 11/763,785, entitled METHOD AND SYSTEM FOR
OPTOELECTRONIC DETECTION AND LOCATION OF OBJECTS, by William M.
Silver, the contents of which are hereby incorporated by reference,
and
[0004] Ser. No. 12/100,100, entitled METHOD AND SYSTEM FOR DYNAMIC
FEATURE DETECTION, by William M. Silver, the contents of which are
hereby incorporated by reference.
FIELD OF THE INVENTION
[0005] The present invention is directed to optoelectronic sensors
and, more specifically to applications of optoelectronic linear
sensors.
BACKGROUND OF THE INVENTION
[0006] In modern production line environments, for both discrete
object manufacturing and web based material manufacturing, various
control systems are typically implemented to ensure product quality
and compliance with applicable regulations. These control systems
typically require a number of measurements of the web material
and/or other objects along the production line. Exemplary
measurements include draw control measurement of a web material to
ensure that the tension on the material at various points stays
within a predetermined range to prevent tearing, enable splicing,
distance travelled measurements to enable cut to length operations
and/or the acquisition of various statistical data measurement to
ensure that the products meet a minimum set of standards, etc.
Furthermore, product detection, velocity and/or location
measurements may need to occur to enable certain operations, for
example, the printing of an expiration date on a product box.
Typically, optoelectronic sensors and/or physical measurement
devices have been utilized for performing these tasks. Noted
disadvantages of such physical monitoring sensors is that should a
new form of monitoring be required, a production line may need to
be halted and dramatic reconfigurations occur to support the new
physical monitoring systems. Furthermore, physical monitoring
systems typically lack easy configuration and/or integration with
other systems in a production line environment.
[0007] Certain web material production environments may need
accurate measurements of tension of the web material. Typically,
these measurements are obtained by monitoring encoders that are
operatively interconnected with a motor and/or roller shafts used
to transport the web material These encoders are typically utilized
to measure velocity of the web material; however, as noted above, a
noted disadvantage of such encoder based monitoring is that the
encoders may not provide accurate measurements due to, e.g., web
material slippage, variations in material thickness, etc.
Furthermore, changes in the material may cause inaccuracies when
using conventional measuring techniques. More generally,
conventional techniques introduce inaccuracies due to their
indirect measurement of the object and/or material, i.e.,
conventional techniques measure a an encoder or drive speed and not
the speed of the object or web material itself. As such, the
measurements may not be accurate, thereby resulting in incorrect
draw control information which may result in damaged and/or wasted
material.
[0008] Furthermore, certain web material production environments
may need to perform cut to length operations, i.e., operations that
occur at substantially regular intervals along the web material.
Examples of cut to length operations include, e.g., perforating
paper towels at regular intervals, cutting diaper materials at
regular intervals, etc. Typically, an encoder based measuring
system is utilized to measure the velocity of the web material,
which is then integrated over time to determine a distance that the
material has traversed before an actuator is activated to perform
the desired operation. However, as noted above, physical monitoring
systems have a number of noted disadvantages. A first noted
disadvantage is that inaccuracies may be introduced due to physical
slippage, etc. along a conveyor and/or servo motor resulting in
measurements that may not be as precise as necessary. The diameter
of the roller to which an encoder is coupled may introduce
additional inaccuracies. Furthermore, inaccurate measurements may
be compounded due to increases in slippage, etc. as a machine ages,
thereby further reducing the preciseness of system's measurement
capabilities. A further noted disadvantage is that physical
monitoring systems typically require substantial configuration and
installation to add to a production line as well as periodic
(re-)calibrations. This complicates installation and substantially
increases the total cost of ownership of such measurement systems
due to the opportunity cost of having a production line idle during
the lengthy installation and/or during annual maintenance or
(re-)calibrations. Additionally, physical limitations may prevent
encoders from being located in desired positions along the web
material. These limitations may complicate installation and/or
prevent a system from obtaining measurements at desired
locations.
[0009] As will be appreciated by one skilled in the art,
conventional servo measurement systems, e.g., shaft encoders, etc.,
have a number of noted disadvantages. Furthermore, conventional
machine vision systems and optical sensors typically do not provide
adequate solutions. Machine vision systems typically are expensive
and require substantial configuration to operate. Additionally,
many of these tasks are not well suited for conventional machine
vision systems as conventional machine vision systems cannot
operate at a speed to sense the motion of the web material with a
sufficiently high degree of accuracy. Optical sensors have noted
disadvantages including, e.g., poor accuracy, etc.
SUMMARY OF THE INVENTION
[0010] The present invention overcomes the disadvantages of the
prior art by providing a system and method for utilizing linear
sensors to perform a plurality of measurement functions.
Illustratively, one dimensional optical linear sensors are oriented
substantially parallel to a direction of movement of objects and/or
a web material to obtain measurement information. The linear
sensors are illustratively the linear sensors described in the
above-incorporated United States patent applications; however, in
alternative embodiments, any linear sensor capable of obtaining
accurate velocity and/or length measurements at a suitably high
rate of speed may be utilized. In an illustrative embodiment of the
present invention, such linear sensors may be easily added to an
existing production line without substantial reconfiguration of the
production line, thereby reducing the installation cost.
[0011] In an illustrative embodiment, a plurality of linear sensors
are arranged along a web material production line. Velocity
measurements of the material are obtained at a first location and a
second location along the web material. The acceleration between
the two points is then determined by measuring the difference
between the two velocity measurements. As force is proportional to
acceleration, the force (tension) along the web material between
the two points is determined. Control signals are then transmitted
to appropriate servo motors to adjust the tension along the web
material, i.e., to perform draw control operations. In this way,
draw control can be maintained without requiring physical
monitoring systems.
[0012] In a further illustrative embodiment of the present
invention, a linear sensor measures the length of a web material
that traverses a particular point along the production line. When a
predefined length of the material has passed the point, a control
unit, operatively interconnected with the linear sensor, activates
a trigger signal that causes an actuator to perform an action on
the material. Illustratively, such an action may comprise cutting
the material, perforating the material, printing onto the material,
etc.
[0013] In another illustrative embodiment, linear sensors collect
statistical data relating to the web material as it moves along a
production line. The linear sensors may be utilized for other
functions, e.g., cut to length operations, etc, or may be only
utilized for acquisition of statistical data. The linear sensors
acquire various statistical data that may be utilized to calculate
a quality score. The computed quality score may be compared to a
minimum quality score to determine whether material meets
appropriate quality control requirements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above and further advantages of the invention may be
better understood by referring to the following description in
conjunction with the accompanying drawings in which like reference
numerals indicate identical or functionally similar elements:
[0015] FIG. 1 shows an example application of a system for
detecting and locating discrete objects moving down a production
line in accordance with an illustrative embodiment of the present
invention;
[0016] FIG. 2 shows an example application of a system for tracking
a moving continuous web in accordance with an illustrative
embodiment of the present invention;
[0017] FIG. 3 shows a block diagram of an illustrative apparatus in
accordance with an illustrative embodiment of the present
invention;
[0018] FIG. 4 shows a portion of a capture process that obtains an
image of a field of view, where the image is oriented approximately
parallel to a direction of motion in accordance with an
illustrative embodiment of the present invention;
[0019] FIG. 5 is schematic block diagram of an exemplary web based
environment for measuring tension and providing draw control in
accordance with an illustrative embodiment of the present
invention;
[0020] FIG. 6 is a flowchart detailing the steps of a procedure for
determining tension and providing draw control in accordance with
an illustrative embodiment of the present invention;
[0021] FIG. 7 is a schematic block diagram of an exemplary web
material production line for use in cut to length applications in
accordance with an illustrative embodiment of the present
invention;
[0022] FIG. 8 is a flowchart detailing the steps of a procedure for
performing cut to length applications in accordance with an
illustrative embodiment of the present invention; and
[0023] FIG. 9 is a flowchart detailing the steps of a procedure for
obtaining statistical information using a linear sensor in
accordance with an illustrative embodiment of the present
invention.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
A. Overview
[0024] Illustratively, the linear sensors utilized in illustrative
embodiments of the present invention are those described in the
above incorporated U.S. patent applications Ser. Nos. 11/763,752,
11/763,785 and 12/100,100. However, it should be noted that the
principles of the present invention may be utilized with any
suitable linear sensor. As such, the description of linear sensors
described in the incorporated applications should be taken as
exemplary only.
[0025] Furthermore, while this description is written in terms of
linear sensors that produce one-dimensional images oriented
approximately parallel to the direction of motion, it will be
apparent to one skilled in the art that other types of optical
sensors can also be in alternative embodiments of the present
invention. For example, a two-dimensional optical sensor can be
used to capture two dimensional images, portions of which are then
converted to one-dimensional images oriented approximately parallel
to the direction of motion. The conversion can be accomplished by
any suitable form of signal processing, for example by averaging
light measurements approximately perpendicular to the direction of
motion. As another example, a two-dimensional optical sensor
capable of capturing so-called regions of interest can be used.
Many commercially available CMOS optical sensors have this
capability. A one-dimensional region of interest oriented
approximately parallel to the direction of motion would be
functionally equivalent to a linear optical sensor. The image
portion or region of interest need not be the same for each
captured image, but can be moved in any manner as long as the
systems and methods described herein function as intended.
[0026] Illustratively, the use of one-dimensional images permits a
much higher capture and analysis rate, at lower cost, than prior
art systems that use two-dimensional images for detection and
location. An illustrative vision detector described in pending U.S.
patent application Ser. No. 10/865,155, for example, operates at
500 images per second. Illustrative linear sensors utilized for the
applications described herein typically operate at over 8000 images
per second, and at far lower cost. The above-referenced vision
detector patent application does not describe or contemplate that
one-dimensional images oriented approximately parallel to the
direction of motion could be used for the purposes described
herein, or that latency could be eliminated by any means.
[0027] As used herein a process refers to systematic set of actions
directed to some purpose, carried out by any suitable apparatus,
including but not limited to a mechanism, device, component,
software, or firmware, or any combination thereof that work
together in one location or a variety of locations to carry out the
intended actions. A system according to the invention may include
suitable processes, in addition to other elements. The description
herein generally describes embodiments of systems according to the
invention, wherein such systems comprise various processes and
other elements. It will be understood by one of ordinary skill in
the art that descriptions can easily be understood to describe
methods according to the invention, where the processes and other
elements that comprise the systems would correspond to steps in the
methods.
B. Detection and Location of Objects
[0028] FIG. 1 is an exemplary environment for detecting and
locating objects using linear sensors in accordance with an
illustrative embodiment of the present invention. Conveyer 100, or
other devices to induce motion, moves boxes 110, 112, 114, 116, and
118 in direction of motion 102. Each box in this example includes a
label, such as example label 120, and a decorative marking, such as
example marking 122. A printer 130 prints characters, such as
example characters 132, on each label as it passes by. In the
example of FIG. 1, the labels are the objects to be detected and
located.
[0029] The illustrated linear sensor 150 provides signal 134 to
printer 130 at times when labels to be printed pass, or are in some
desirable position relative to, reference point 106. In an
illustrative embodiment signal 134 comprises a pulse indicating
that a label has been detected, and wherein the leading edge of the
pulse occurs at the time that a label is at reference point 106 and
thereby serves to locate the label.
[0030] Linear sensor 150 uses lens 164 to form a one-dimensional
image of field of view 170 on linear optical sensor 160 comprising
linear array of photoreceptors 162. Field of view 170 and linear
array of photoreceptors 162 are oriented so as to produce
one-dimensional images oriented approximately parallel to the
direction of motion. Each photoreceptor makes a light measurement
in the field of view. The exemplary linear sensor embodiment
described herein with reference to FIG. 1 may be utilized to detect
and track discrete objects, e.g., boxes, in a production
environment. Various embodiments of such environments are described
in the above-incorporated U.S. patent applications.
[0031] FIG. 2 illustrates an example application of an illustrative
embodiment of the invention to track a continuous web material in
accordance with an illustrative embodiment of the present
invention. The web material 210, which may comprise a woven or
non-woven material, e.g., paper, diapers, etc., moves in direction
of motion 220 relative to apparatus 230. The web material 210
contains object features in the form of surface microstructure that
gives rise to image features when illuminated by grazing
illumination 250. Images are formed using telecentric lens 240 so
that the optical magnification is constant in the presence of
fluctuations in distance between web 210 and apparatus 230. As will
be appreciated by one skilled in the art, the use of grazing
illumination and telecentric optics are well-known in the art.
[0032] Apparatus 230 operates in accordance with an illustrative
embodiment of the invention to output motion signal 235, which in
an illustrative embodiment is a quadrature signal. With the
arrangement of FIG. 2, motion signal 235 provides information about
the true motion of web 210, in contrast to the indirect and, at
times, inaccurate information that might be provided by a
conventional mechanical encoder attached to a drive shaft of the
transport mechanism. Thus, use of an exemplary linear sensor
measuring technique in accordance with an illustrative embodiment
of the present invention provides for more accurate measurements
and enables additional functions to be performed, as described
further below.
[0033] In an illustrative embodiment, linear optical sensor 240 is
calibrated to compensate for any non-uniformity of illumination,
optics, and response of the individual photoreceptors. A uniformly
white object is placed in the field of view, or moved continuously
in the field of view, and the gain for each of the three zones is
set so that the brightest pixels are just below saturation. Then a
calibration value is computed for each pixel, such that when each
gray level is multiplied by the corresponding calibration value, a
uniform image is produced for the uniformly white object. The
calibration values are illustratively stored in flash memory 322
(see FIG. 3) and applied to subsequent captured images. The
calibration values are limited such that each gray level is
multiplied by no more than 8. Each image used by the calibration
procedure is obtained by averaging 512 captured images.
[0034] Any suitable means can be employed to illuminate the field
of view of linear optical sensor 340. In an illustrative
embodiment, two 630 nm LEDs are aimed at the field of view from one
side of linear optical sensor 340, and two 516 nm LEDs are aimed at
the field of view from the other side. A light-shaping diffuser,
such as those manufactured by Luminit of Torrance, Calif., is
placed in front of the LEDs so that their beams are spread out
parallel to linear optical sensor 340. In another illustrative
embodiment, LEDs are placed to form grazing illumination suitable
for imaging surface microstructure.
[0035] Human users, such as manufacturing technicians, can control
the system by means of human-machine interface (HMI) 350. In an
illustrative embodiment, HMI 350 comprises an arrangement of
buttons and indicator lights. Processor 310 controls HMI 350 using
PIO interface 332. In other embodiments, an HMI consists of a
personal computer or like device; in still other embodiments, no
HMI is used.
C. Apparatus
[0036] FIG. 3 is a block diagram of an illustrative embodiment of a
portion of a linear detector in accordance with an illustrative
embodiment of the present invention. Microcontroller 300, such as
the AT91SAM7S64 sold by Atmel Corporation of San Jose, Calif.,
comprises ARMv4T processor 310, read/write SRAM memory 320,
read-only flash memory 322, universal synchronous/asynchronous
receiver transmitter (USART) 330, and a parallel I/O interface
(PIO) 332. ARMv4T processor 310 controls the other elements of
microcontroller 300 and executes software instructions 324 stored
in either SRAM 320 or flash 322 for a variety of purposes. SRAM 320
holds data 326 used by ARMv4T processor 310. Microcontroller 300
illustratively operates at a clock frequency of 50 MHz.
[0037] Linear optical sensor 340, such as the TSL3301-LF sold by
Texas Advanced Optoelectronic Solutions (TAOS) of Plano, Tex.,
comprises a linear array of photoreceptors. Linear optical sensor
340, under control of ARMv4T processor 310 by commands issued using
USART 330, can expose the linear array of photoreceptors to light
for an adjustable period of time called the exposure interval, and
can digitize the resulting light measurements and transmit them in
digital form to USART 330 for storage in SRAM 320. Linear optical
sensor 340, also under control of ARMv4T processor 310, can apply
an adjustable analog gain and offset to the light measurements of
each of three zones before being digitized, as described in TAOS
document TAOS0078, January 2006.
[0038] The linear sensor illustrated in FIG. 3 produces signal 362
for purposes including indicating detection and location of
objects. Signal 362 is connected to automation equipment 360 as
required by a given application. Note that automation equipment 360
is shown for illustrative purposes only; signal 362 may be used for
any purpose and need not be connected to any form of automation
equipment, and signal 362 need not be used at all.
[0039] In an illustrative embodiment, various processes are carried
out by an interacting collection of digital hardware elements,
including those shown in the block diagram of FIG. 3, suitable
software instructions residing in SRAM 320 or flash 322, and data
residing in SRAM 320. In the illustrative apparatus of FIG. 3, a
capture procedure comprises digitizing the light measurements so as
to obtain an array of numbers, called pixels, whose values, called
gray levels, correspond to the light measurements; transferring the
pixels from linear optical sensor 340 to microcontroller 300; and
storing the pixels into SRAM memory 320 for subsequent analysis.
Following the usual convention in the art, a pixel may refer either
to an element of the array of numbers, or to a unit of distance
corresponding to the distance between two adjacent elements of the
array. The array of pixels is a one-dimensional digital image.
[0040] It will be apparent to one skilled in the art that
"approximately parallel" refers to any orientation that allows the
linear detector to obtain a time-sequence of images of a slice of
an object in a plurality of positions as it enters, moves within,
and/or exits the field of view. It will further be apparent that
the range of orientations suitable for use for with the systems and
methods described herein has a limit that depends on a particular
application of the invention. For example, if the orientation of
the image is such that the angle between the image orientation and
the direction of motion is 5 degrees, the object will drift 0.09
pixels perpendicular to the direction of motion for every pixel it
moves parallel to that direction. If the range of the plurality of
positions covers 30 pixels in the direction of motion, for example,
the drift will be only 2.6 pixels. If the systems and methods
described herein function as intended with a 2.6 pixel drift in a
given application of the invention, the example 5 degree
orientation would be approximately parallel for that
application.
[0041] Similarly, it will be apparent to one skilled in the art
that the direction of motion need not be exactly uniform or
consistent, as long as the systems and methods described herein
function as intended. The use of one-dimensional images allows very
high capture and analysis rates at very low cost compared to prior
art two-dimensional systems. The high capture and analysis rate
allows many images of each object to be analyzed as it passes
through the field of view. The object motion ensures that the image
are obtained from a plurality viewing perspectives, giving far more
information about the object than can be obtained from a single
perspective. This information provides a basis for reliable
detection and accurate location.
[0042] FIG. 4 shows a portion of an illustrative capture process
that obtains one dimensional image 430 of field of view 410, where
image 430 is oriented approximately parallel to direction of motion
400. Light emitted from field of view 410 is focused onto an
optical sensor (not shown), which makes light measurements. In the
illustrative capture process of FIG. 4, 24 discrete light
measurements are made in 24 zones of field of view 410, such as
example zone 440. The zones are shown as rectangular, contiguous,
and non-overlapping for ease of illustration, but for typical
sensors the geometry is more complex, due in part to the nature of
the optics used to focus the light and the requirements of
semiconductor fabrication. In the illustrative capture process of
FIG. 4, each light measurement is digitized to produce 24 pixels,
such as example pixel 450, which corresponds to example zone 440.
The gray level of example pixel 450 is 56, which is the light
measurement for example zone 440. The zones of FIG. 4 may
correspond, for example, to individual photoreceptors in a linear
array sensor, or to a plurality of photo receptors of a
two-dimensional sensor that have been converted to a single
measurement by any suitable form of signal processing, as described
above.
[0043] The geometry of the light measurement zones of field of view
410 define image orientation 420 of image 430. Image 430 is
oriented approximately parallel to direction of motion 400 if image
orientation 420 and direction of motion 400 are such that the
capture process can obtain a time-sequence of images of a slice of
an object in a plurality of positions as it enters, moves within,
and/or exits the field of view. Note that image orientation 420 is
a direction relative to field of view 410, as defined by the
geometry of light measurements contained in image 430. The image
itself is just an array of numbers residing in a digital memory;
there is no significance to its horizontal orientation in FIG.
4.
[0044] As used herein a measurement process makes measurements in
the field of view by analyzing captured images and producing values
called image measurements. Example image measurements include
brightness, contrast, edge quality, edge position, number of edges,
peak correlation value, and peak correlation position. Many other
image measurements are known in the art that can be used within the
scope of the invention. Image measurements may be obtained by any
suitable form of analog and/or digital signal processing.
[0045] In the illustrative embodiment of FIG. 3, a measurement
process comprises a digital computation carried out by ARMv4T
processor 310, operating on a captured image stored in SRAM 320,
under the control of software instructions stored in either SRAM
320 or flash 322. For example, a brightness image measurement may
be made by computing the average of the pixels of an image or
portion thereof; a contrast image measurement may be made by
computing the standard deviation of the pixels of an image or
portion thereof.
[0046] In the illustrative embodiment of FIG. 3, a selection
process comprises a digital computation carried out by ARMv4T
processor 310, operating on image measurements stored in SRAM 320
or in the registers of ARMv4T processor 310, under the control of
software instructions stored in either SRAM 320 or flash 322.
[0047] A linear sensor according to the invention may include a
decision process whose purpose is to analyze object measurements so
as to produce object information. In the illustrative embodiment of
FIG. 3, a decision process comprises a digital computation carried
out by ARMv4T processor 310, operating on object measurements
stored in SRAM 320 or in the registers of ARMv4T processor 310,
under the control of software instructions stored in either SRAM
320 or flash 322.
[0048] A linear sensor according to some embodiments of the
invention may optionally include a signaling process whose purpose
is to produce a signal that communicates object information. A
signal can take any form known in the art, including but not
limited to an electrical pulse, an analog voltage or current, data
transmitted on a serial, USB, or Ethernet line, radio or light
transmission, and messages sent or function calls to software
routines. The signal may be produced autonomously by the linear
sensor, or may be produced in response to a request from other
equipment.
[0049] In the illustrative embodiment of FIG. 3, a signaling
process comprises a digital computation carried out by ARMv4T
processor 310, operating on object information stored in SRAM 320
or in the registers of ARMv4T processor 310, producing signal 362,
and under the control of software instructions stored in either
SRAM 320 or flash 322. Signal 362 is an electrical pulse, which the
ARMv4T processor 310 illustratively ensures that the pulse appears
at a precise time.
D. Tension Measurement and Draw Control Applications
[0050] One illustrative application for linear sensors is
maintaining draw control of a web material in a production
environment. Illustratively, web materials are maintained with a
set tension (or a predefined range of acceptable tensions) along
the length of the material as the material traverses the production
environment. At various points along the material, servo motors
work to induce movement into the web material. Appropriate tension
needs be maintained along the web material to prevent sagging
and/or prevent the material from tearing due to excess tension. By
utilizing a linear sensor in accordance with an illustrative
embodiment of the present invention, tension and draw control may
be maintained without requiring physical contact with the web based
material.
[0051] FIG. 5 is a schematic block diagram of an exemplary
web-based material production line environment 500 in accordance
with an illustrative embodiment of the present invention. A web
material 505, e.g., paper, cloth, paper towel material, etc., is
transported in a direction of motion 510 by one or more servo
motors 515. As will be appreciated by one skilled in the art, the
motors 515 may be spaced along the web material based on a variety
of factors, e.g., type of material, distance traveled, etc.
[0052] Illustratively, two linear sensors 525A, B are configured to
measure the velocity of the material 505 at a first point 530A and
a second point 530B respectively along the web material. The linear
sensors are illustratively one dimensional linear sensors that are
arranged approximately parallel to the direction of motion 510 of
the web material 505. The linear sensors 525A,B may measure
velocity using any technique for velocity measurement using linear
sensors. Illustratively, the linear sensors utilize the technique
described in the above-incorporated U.S. patent application.
However, it should be noted that in alternative embodiments, any
technique for measuring velocity may be utilized. As such, the
description of linear sensors arranged parallel to the direction of
motion of the web material should be taken as exemplary only.
[0053] The linear sensors 525A,B and the servo motor 515 are
operatively interconnected with a control unit 520. The control
unit 520 receives the velocity measurements from the linear sensors
and determines the acceleration of the web material 505 between the
first point 530A and the second point 530B by, e.g., determining
the difference between the two velocities. As acceleration is
proportional to force, the tension along the web material is
proportional to the acceleration of the web material. The control
unit 520 is further configured to output appropriate control
signals to the servo motor 515 to (de)accelerate and thereby modify
the tension along the web material.
[0054] It should be noted that while the environment 500 is shown
with a single pair of linear sensors operatively connected to a
single control unit managing one servo motor, the principles of the
present invention may be utilized in more complex environments. For
example, a factory wide control unit may manage a plurality of
pairs of linear sensors, a plurality of servo motors, etc. Such a
factory management system may utilize wireless communication
systems enabling the various components to communicate over the
production line without requiring physical cabling interconnecting
them. As such, the description of environment 500 should be taken
as exemplary only.
[0055] FIG. 6 is a flowchart detailing the steps of a procedure 600
for determining tension and controlling draw in accordance with an
illustrative embodiment of the present invention. The procedure 600
begins in step 605 and continues to step 610 where velocity
measurements are obtained at a first point and a second point along
a web material. Illustratively, the first and second points are
associated with a first and second linear sensors, shown above in
reference to environment 500 of FIG. 5. The acceleration between
the first and second points is then determined in step 615.
Illustratively, acceleration may be determined by examining the
difference between the velocities at the first and second points.
Assuming that the web material is moving in a substantially
straight line, the difference in speed between the first and second
point in conjunction with a known distance between two points
provides the information necessary to determine the acceleration of
the web material. The acceleration of the web material is
proportional to the force applied by the servo motor 515.
[0056] Depending on the amount of force being applied to the web
material, the control unit may output appropriate control signals
to the servo of the motor 515 to maintain satisfactory tension on
the web material 505 in step 620. That is, the control unit may
output control signals to maintain the tension within a predefined
range of tensions. As will be appreciated by one skilled in the
art, the predefined ranges will vary with the type of material that
is utilized. Illustratively, should insufficient force be applied
to the web material, the control signals may signify that the servo
motor should accelerate to induce additional tension. Similarly,
should a determination be made that insufficient or too much
attention is being applied, the control signals may cause the servo
motor to slow down toward the accelerate, thereby reducing the
tension on the web material. The procedure 600 then completes in
step 625.
E. Cut to Length Applications
[0057] Another illustrative application for linear sensors may
comprise cut to length applications. Cut to length applications are
those applications where a certain operation is performed after a
variable and/or predefined distance of webbing material has passed
a given point. For example, if the webbing material comprises paper
towel material, perforations may need to be made at substantially
regular intervals. Similarly, if the webbing material comprises a
child's diaper material, the material may need to be cut at regular
intervals. More generally, cut to length applications are those
applications that require some operation to be performed at
substantially regular intervals along the length of the web
material. The operations may comprise, for example, cutting the
material, marking the material, forming perforations on the
material, printing something on the material, except. As such, the
operations described herein should be taken as exemplary only. One
skilled in the art will appreciate that any operations may be
utilized at substantially regular intervals along a web
material.
[0058] FIG. 7 is a schematic block diagram of an exemplary cut to
length application environment 700 in accordance with an
illustrative embodiment of the present invention. The web material
505 moves along direction of motion 510, similar to environment 500
described above in respect to FIG. 5. A linear sensor 525 is
illustratively arranged parallel to the direction of motion 510 of
the material 505. An actuator 710is configured to perform an action
a point 705 along the web 505. Illustratively, the actuator 710 may
cut the web material 505 at point 710. However, in alternative
embodiments, the actuator may perforate the material, print on the
material, etc. As such, the description of the material being cut
should be taken as exemplary only. In the illustrative environment
700, the material 505 has been perforated at locations 715A,B at a
predefined interval.
[0059] A control unit 520 is operatively interconnected with the
linear sensor 525 and the actuator 710. The control unit 520 is
illustratively configured to receive distance measurements from the
linear sensor 525 as to the distance that the web material 505 has
traveled. Illustratively, these signals output from the linear
sensor 525 may be in a quadrature format, such as those typically
output from conventional shaft encoders. However, in alternative
embodiments of the present invention differing formats may be
utilized. As such, the description of quadrature outputs to be
taken as exemplary only. It should be noted that by configuring a
linear sensor 525 to output distance measurements, a linear sensor
525 may replace a conventional shaft encoder. Thus, the linear
sensor may be utilized in conventional servo control systems in
place of a shaft encoder unit. In accordance with an illustrative
embodiment of the present invention, the control unit 520 detects
that the web material 505 has moved a certain length. In response,
the control unit generates a trigger signal to the actuator 710.
The actuator then performs an action on the web material 505.
Illustratively, the trigger signal is timed so that the actuator
performs the desired action on the Web material at a predefined
distance from a previous point along the material.
[0060] FIG. 8 is a flowchart detailing the steps of a procedure 800
for performing cut to length applications in accordance with an
illustrative embodiment of the present invention. The procedure 800
begins in step 805 and continues to step 810 where a quantity
(length) of web material is measured as having moved past a
selected point. Illustratively, a linear sensor is utilized to
measure the web material as it moves past a selected point. The
control unit generates a trigger signal based on the distance of
material traveled in step 815. Illustratively, the trigger signal
is generated so that the delay from the generation of the trigger
signal is such that the material has moved the proper distance
before the action is performed on the material. For example, if the
material is moving at 10 m/s and the trigger delay (i.e., the time
between generation of the trigger signal and the occurrence of the
action) is 0.1 s, then the trigger signal needs to occur after the
material has moved 1 m less than the desired distance. The material
will then move the final 1 m in the time it takes for the trigger
signal to activate the action to be performed.
[0061] An actuator receives the generated trigger signal and
performs an action in step 820. The action may comprise any
actuator operation, including, e.g., cutting the web material,
perforating the web material, printing onto the web material, etc.
By utilizing linear sensor is, conventional shaft encoders and/or
other physical means of a measurement distance traveled may be
replaced. The procedure 800 then completes in step 825.
F. Statistical Data Acquisition Applications
[0062] Another application that may utilize linear sensors is the
acquisition of statistical data regarding materials and/or objects
in a production environment. Such statistical data may be utilized
in a factory management system to ensure quality control of the
materials and/or objects being produced. Furthermore, the
statistical data may also be utilized by technicians for
identification of error conditions within a production line, or may
be utilized to fine tune a production line increase output, thereby
resulting in additional units produced.
[0063] FIG. 9 is a flowchart detailing the steps of a procedure 900
for acquiring statistical data in accordance with an illustrative
embodiment of the present invention. The procedure 900 begins in
step 905 and continues to step 910 where the material moves along a
conveyor. As material moves along the conveyor, a linear sensor
scans the material. The linear sensor may be utilized in any of the
other applications described herein or in applications not
described herein. That is, the linear sensors may be utilized
solely for statistical data acquisition or may be utilized for,
e.g., cut to length applications, etc. However, in conjunction with
the acquisition for be functioning of any other application, the
linear detector acquires statistical data from one or more points
along the material in step 915. Such statistical data may comprise,
e.g., average tension along the material, average speed of the
material, etc. In alternative embodiments, the statistical data may
comprise image-based characteristics of the web material being
inspected, e.g., a histogram of texture of the web material versus
time, maximum/minimum responses to determine defects, etc. For
those web materials that should have repetitive patterns, the
regularity of the appearance of those patterns may be utilized as
statistical data that may be used in determining a quality
score.
[0064] The system then calculate statistics and a quality score in
step 925. The quality score may be calculated using a variety of
formulas. Illustratively, the quality score may be determined based
on whether a brightness peak is greater than/less than a threshold.
In an illustrative embodiment of the present invention, the
threshold may be predefined; however, in alternative embodiments,
the threshold may be variable. For those web materials that should
have a substantially constant texture, a quality score may be
calculated by determining the location of the peak of a histogram
of the material texture is between a low texture value (TL) and a
high texture value (TH). Similarly, for those web materials that
have a distance repetitive texture, the quality value may be
calculated by determining the peak histogram of the material and
comparing it to a TL/TH values that vary along the distance of the
web material.
[0065] In an illustrative embodiment of the present invention, the
procedure determines what the material meets a minimum quality
score in step 930. If so, the material is accepted in step 935 and
the procedure completes in step 940. However, if in step 930 the
material does not meet a minimum quality score, the procedure
branches to step 945 where the material is rejected. This may occur
when, e.g., a splice occurs during manufacturing. A splice occurs
when an end of a first roll of web material is spliced onto the end
of a second roll of the material. Manufacturers typically do not
desire to utilize the region where the splice occurs. By computing
appropriate quality scores, the splice regions may be detected and
rejected, thereby preventing the splice regions from being utilized
in a manufactured product. The procedure then completes in step
940.
[0066] As will be appreciated by one skilled in the art, the
principles of the present invention may be utilized in a variety of
production environments. As such, the various specific examples and
embodiments described herein should be taken as exemplary. It is
expressly contemplated that the applications of linear sensors
described herein may be centrally managed by a factory management
system. Furthermore, while the applications of linear sensors
described herein have utilized one dimensional linear sensors
arranged approximately parallel to a direction of motion, the
principles of the present invention may be utilized with additional
and/or differing linear sensors including, for example, those
arranged perpendicular to a direction of travel, multi-dimensional
sensors, etc. As such, descriptions contained herein should be
taken as exemplary only.
[0067] The foregoing has been a detailed description of various
embodiments of the invention. It is expressly contemplated that a
wide range of modifications, omissions, and additions in form and
detail can be made hereto without departing from the spirit and
scope of this invention. For example, the processors and computing
devices herein are exemplary and a variety of processors and
computers, both standalone and distributed can be employed to
perform computations herein. Likewise, the linear array sensor
described herein is exemplary and improved or differing components
can be employed within the teachings of this invention. Numerical
constants used herein pertain to illustrative embodiments; any
other suitable values or methods for carrying out the desired
operations can be used within the scope of the invention.
Accordingly, this description is meant to be taken only by way of
example, and not to otherwise limit the scope of this
invention.
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