U.S. patent application number 14/558863 was filed with the patent office on 2015-04-09 for sheet stabilizer with suction nozzle having center protrusion.
The applicant listed for this patent is ABB Ltd.. Invention is credited to Shizhong Duan.
Application Number | 20150097070 14/558863 |
Document ID | / |
Family ID | 40669009 |
Filed Date | 2015-04-09 |
United States Patent
Application |
20150097070 |
Kind Code |
A1 |
Duan; Shizhong |
April 9, 2015 |
SHEET STABILIZER WITH SUCTION NOZZLE HAVING CENTER PROTRUSION
Abstract
This invention is related to suction nozzles having a center
protrusion for stabilizing a continuous web for various web
property measurements. Suction nozzles blow air out of the nozzle,
yet produce a vacuum proximate thereto. Two nozzles are disclosed,
a single sided sheet-contact stabilizer and a non-contact sheet
stabilizer. An air-bearing may be formed between the end surface of
the center protrusion and the moving web.
Inventors: |
Duan; Shizhong; (Vancouver,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ABB Ltd. |
Tallaght |
|
IE |
|
|
Family ID: |
40669009 |
Appl. No.: |
14/558863 |
Filed: |
December 3, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12275303 |
Nov 21, 2008 |
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14558863 |
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Current U.S.
Class: |
242/615.11 |
Current CPC
Class: |
B65H 23/245 20130101;
B65H 2601/20 20130101; B65H 2511/13 20130101; B65H 2406/112
20130101; G01B 2210/62 20130101; B65H 2406/351 20130101; B65H 23/24
20130101; B65H 2801/84 20130101; B65H 2406/122 20130101; G01B 21/08
20130101; B65H 2406/113 20130101; B65H 23/18 20130101; B65H 2553/00
20130101 |
Class at
Publication: |
242/615.11 |
International
Class: |
B65H 23/24 20060101
B65H023/24; B65H 23/04 20060101 B65H023/04; B65H 23/18 20060101
B65H023/18; B65H 23/00 20060101 B65H023/00 |
Claims
1. A web stabilizer for stabilizing a moving web, the stabilizer
comprising: a nozzle body including a first surface facing the web;
a protrusion including a second surface facing the web, said second
surface being offset from said first surface and including at least
one orifice; an air chamber located within said nozzle body and
including at least one air inlet port that directs compressed air
into said air chamber; an annular opening formed between said
protrusion and said first surface and in fluid communication with
said air chamber; an insert including an insert chamber that is in
fluid communication with said at least one orifice and receiving
pressurized air therein; and wherein compressed air evacuates said
air chamber through said annular opening and wherein compressed air
evacuates said insert chamber through said at least one
orifice.
2. The stabilizer according to claim 1 wherein said at least one
air inlet port is configured to cause a vortex flow pattern within
said air chamber
3. The stabilizer according to claim 1 wherein said at least one
orifice comprises a plurality of orifices.
4. The web stabilizer according to claim 1 wherein said first
surface is substantially parallel to said second surface.
5. The web stabilizer according to claim 2 wherein said air chamber
includes a first cylindrical section, a second cylindrical section
and a frusto-conical section, second cylindrical section having a
smaller diameter than said first cylindrical section.
6. The web stabilizer according to claim 5 wherein said at least
one air inlet port is positioned at said first cylindrical section,
said frusto-conical section joining said first cylindrical section
and said second cylindrical section, and said second cylindrical
section being proximate to said annular opening.
7. The web stabilizer according to claim 1 wherein said protrusion
includes a chamfer extending circumferentially around said second
surface.
Description
FIELD OF THE INVENTION
[0001] This invention relates to contact and non-contact sheet
stabilizers intended for on-line measurement of continuous webs.
More specifically, this invention relates to contact and
non-contact sheet stabilizers for on-line measurement of a moving
web of paper on a paper-making machine.
DESCRIPTION OF THE PRIOR ART
[0002] Modern paper-making machines use quality control systems to
monitor and control the properties of paper products. Paper
properties such as caliper, color, fiber orientation and surface
finish etc. are measured using sensors, typically mounted on a
scanner, that travel along the cross-machine direction, back and
forth over the full width of the paper to be produced. In order to
measure the paper properties accurately, many sensors require sheet
stabilizers to hold the moving web in a stable and flattened state
at a measurement point.
[0003] For example, caliper sensors commonly include an optical
sensor(s) and a magnetic sensor. Single optical sensor calipers
typically require that one of the paper surfaces of the moving web
contacts a reference plane at the measurement point. The optical
sensor measures the distance between the optical sensor and the
paper surface facing the optical sensor. The optical sensor may be
calibrated against the reference plane beforehand, so that the
thickness of the sheet can be calculated based on the two optic
readings with and without the sheet. The magnetic sensor is useful
to compensate for variations in the distance between the reference
and the optic sensor during scanning or in the case when structural
deformation occurs due to temperature change or other
disturbances.
[0004] In a dual sided optical configuration, the moving sheet does
not contact any solid surface, and one optical sensor is positioned
on each side of the moving web. A magnetic sensor is also typically
used to measure relative distance between the two optical sensors.
The optical sensors measure the respective distances between the
sheet surface and the corresponding optical sensor. The magnetic
sensor measures the distance between the two optical sensors, and
the thickness of the moving web is calculated using the three
measured distances.
[0005] In both of the above disclosed caliper configurations, the
sheet stabilizer plays an important role in achieving accurate and
repeatable results. In prior art single sided calipers, accuracy
required that the sheet maintain contact with the reference plane.
In the dual sided configuration, it is important that all measured
distances are perpendicular to the sheet surface at the measurement
point. Further, it is also important that the two optic devices be
aligned coaxially. In the case that the two optic devices are
axially offset, the sheet must be perfectly flat around the
measurement area to avoid any measurement error induced by the
offset. There is therefore a need in the art for improved sheet
stabilizers.
SUMMARY OF THE INVENTION
[0006] A web stabilizer for stabilizing a moving web has:
[0007] a nozzle body that includes a first surface facing the
web;
[0008] a protrusion including a second surface facing the web, the
second surface being offset from the first surface and including at
least one orifice;
[0009] an air chamber located within the nozzle body and including
at least one air inlet port that directs compressed air into the
air chamber;
[0010] an annular opening formed between the protrusion and the
first surface and in fluid communication with the air chamber;
[0011] an insert including an insert chamber that is in fluid
communication with the at least one orifice and receiving
pressurized air therein; and
[0012] wherein compressed air evacuates the air chamber through the
annular opening and wherein compressed air evacuates the insert
chamber through the at least one orifice.
DESCRIPTION OF THE DRAWING
[0013] FIG. 1 is a section view of a first embodiment of a single
sided contact-type sheet stabilizer of the present invention.
[0014] FIG. 2 is a top view of the embodiment of FIG. 1.
[0015] FIG. 3 is an enlarged sectional view of the nozzle exit of
the sheet stabilizer of FIG. 1.
[0016] FIG. 4 is a section view of a caliper gauge device including
the sheet stabilizer of the present invention.
[0017] FIG. 5 is a top view of the caliper gauge device of FIG. 4
with the moving web removed.
[0018] FIG. 6 is a section view of an alternate, non-contact
embodiment of the sheet stabilizer of the present invention.
[0019] FIG. 7 is a section view of the lower portion of an
alternate embodiment of a caliper gauge including the sheet
stabilizer of the present invention.
[0020] FIG. 8 is a section view of the lower portion of a second
alternate embodiment of a caliper gauge including the sheet
stabilizer of the present invention.
DETAILED DESCRIPTION
[0021] Referring now to FIG. 1, a sheet stabilizer according to the
present invention is generally indicated by the numeral 10. Sheet
stabilizer 10 includes a suction nozzle 12 including a cylindrical
center protrusion part 14, a nozzle body 16, a center piece 18 and
a back cover 20. Nozzle body 16 includes a flat top surface 22 with
a circular aperture 24 in communication with an internal chamber
26. Nozzle body 16 includes a first cylindrical wall 28 extending
downwardly from aperture 24. First cylindrical wall 28 terminates
at a downwardly extending frusto-conical wall 30. Frusto-conical
wall 30 terminates at a second cylindrical wall 32 having a larger
diameter than first cylindrical wall 28. Second cylindrical wall 32
extends from frusto-conical portion 30 to a step surface 34. A
third cylindrical wall 36 extends from step surface 34 to the
bottom end of nozzle body 16.
[0022] Protrusion part 14 includes a circular top surface 40. In
one or more embodiments top surface is substantially flat. In these
or other embodiments, an annular chamfer 42 extends around the edge
of surface 40.
[0023] In one or more embodiments, top surface 40 is positioned
substantially parallel with top surface 22 of the nozzle body 16.
Protrusion part 14 extends beyond top surface 22 of nozzle body 16
such that top surface 40 is vertically offset from top surface 22
by a distance D (see FIG. 3). In one or more embodiments, distance
D may be from about 0.8 to about 2.0 mm. In these or other
embodiments, distance D may be from about 0.8 to about 1.2 mm.
[0024] The axial offset distance D is adjustable. To that end, back
cover 20 includes a threaded central bore 44 and the bottom end of
protrusion part 14 includes a threaded outer surface 46 that
engages with the threads of bore 44. By rotating protrusion part
14, the axial offset distance D is adjusted. This adjustability is
advantageous when producing paper of varying quality and thickness.
For example, variations in paper may require larger or smaller
offset distances to achieve optimal performance.
[0025] Center piece 18 aligns and supports protrusion part 14
during normal use. Further, center piece 18 guides protrusion part
14 as it moves axially during rotation. To that end, center piece
18 includes a smooth inner cylindrical bore 48 that slidably
receives protrusion part 14 therein. The outer surface of center
piece 18 includes a frusto-conical portion 50, positioned opposite
frusto-conical wall 30 of nozzle body 16. Frusto-conical portion 50
extends downwardly from the top of center piece 18 and terminates
at a first cylindrical portion 52. As shown in FIG. 1, first
cylindrical portion 52 is positioned opposite second cylindrical
wall 32. First cylindrical portion 52 terminates at a step surface
54, from which a second cylindrical portion 56 extends to the
bottom of center piece 18. In this manner, it can be seen that
second cylindrical portion 56 is captured between step surface 34
and back cover 20 to prevent axial movement. Further, the second
cylindrical portion 56 is sized to fit in a snug fashion against
third cylindrical wall 36 to prevent radial movement.
[0026] As shown in FIG. 1, an air chamber 60 is formed between
center piece 18 and the nozzle body 16. Air chamber 60 includes an
annular section 62, a frusto-conical or cone-shaped section 64 and
a second annular section 66. Annular section 62 is formed between
second cylindrical wall 32 and first cylindrical portion 52.
Frusto-conical section 64 is formed between frusto-conical wall 30
and frusto-conical portion 50. Finally, second annular section 66
is formed between protrusion part 14 and first cylindrical wall
28.
[0027] Nozzle body 16 includes one or more inlet ports 68 which are
in communication with air chamber 60 and are connected to a
pressurized air source (not shown). Any number of inlet ports 68
may be employed, though a preferred embodiment includes at least
two inlet ports 68. Inlet ports 68 are in fluid communication with
first cylindrical section 62 and are drilled at constant angular
orientation relative thereto. Inlet ports 68 are drilled in a
manner such that compressed air entering the air chamber 60 flows
in the same circumferential direction. In one or more embodiments,
inlet ports 68 are tangential to first cylindrical section 62.
[0028] In operation, pressurized air enters the first cylindrical
section 62 of air chamber 60 through the inlet ports 68. The air
travels in a swirling, circular fashion shown by arrows F. The
swirling flow next enters the frusto-conical section 64 and the
tangential velocity component of the swirling flow increases due to
conservation of the angular momentum. At the second cylindrical
section 66, the tangential velocity component is at its maximum.
Because of the swirling motion of the air, the flow inside second
cylindrical section 66 is substantially uniform, even though the
width of second cylindrical section 66 may not be the same at all
circumferential locations due to errors and tolerances associated
with mechanical fabrication.
[0029] Referring now to FIGS. 1 and 2, air exits air chamber 60 at
annular opening 70. At any point B, air exiting annular opening 70
has two velocity components: an axial velocity component which is
in the direction parallel to the longitudinal axis A of protrusion
part 14, and a tangential velocity component V which is parallel
with flat surface 22 and normal to the radius R from axis A to the
point B at annular opening 70. When the tangential velocity V is
greater than the axial velocity at annular opening 70, air flow
exiting device 10 will stay close to the surface 22. The larger the
tangential velocity component V, the closer the emitted air flow
stays to the flat surface 22. Nozzles exhibiting this generally
tangential/sideways/radial airflow at the tip are generally
referred to as suction nozzles.
[0030] The suction nozzle configuration of the present invention
creates a vacuum at the area near the center of top surface 40. In
other words, if an object is proximate to the center of the annular
opening 70, the object is sucked towards top surface 40.
[0031] Sheet stabilizer 10 can be mounted within close proximity to
a moving web W as shown in FIGS. 1 and 3. Sheet stabilizer 10 is
shown in FIG. 1 positioned under the moving web W, however, it
should be appreciated that sheet stabilizer 10 can be installed
above a moving web W without substantially affecting the operation
thereof.
[0032] When a moving web W is positioned proximate to sheet
stabilizer 10, the web W is sucked toward protrusion 14 due to the
suction effects of the suction nozzle configuration. The air
exiting annular opening 70 in turn forms an air-bearing between the
body surface 22 of the nozzle body 16 and the moving web W.
Meanwhile, the moving web W contacts top surface 40 of the center
protrusion 14 so long as the offset distance D is large enough.
[0033] The offset distance D affects the performance of the sheet
stabilizer 10 of the present invention. If the offset distance is
too small, the moving web W tends to vibrate and generate excess
noise. The smaller the offset distance D, the greater the magnitude
of the web vibrations. When web W vibrates, it tends to disengage
from protrusion 14, thereby alternating between contact and
non-contact. Such vibration adversely affects measurement accuracy.
However if the offset distance D is greater than about 0.8 mm, the
moving web W remains stable and no web vibration is observed. The
larger the offset distance D, the more stable the moving web
remains.
[0034] The moving web proximate to body surface 22 is maintained at
a predetermined distance from the body surface 22 due to
Bernoulli's principle. If the gap between web W and surface 22
increases, the speed of air passing through the gap increases due
to reduced boundary layer friction. As a result, the pressure in
the gap reduces and the moving web W is pulled back to the
predetermined distance by the out-of-balance pressure force from
the outside environment above the web W. If the gap decreases
between web W and surface 22, air speed in the gap is reduced
because the friction force of the boundary layers increases. As a
result, the pressure in the gap increases and the moving web W is
pushed back to the predetermined distance by the increased pressure
in the gap. Consequently, the portion of web W proximate to annular
body surface 22 of the nozzle body 16 is maintained at the
predetermined distance.
[0035] As discussed above, if no support is provided at the portion
of the moving web W positioned over the center of annular opening
70, the moving web W becomes subject to residual wrinkle, potential
deformation and web vibration. By creating an offset distance D
between the surface 22 and top surface 40, the protrusion part 14
contacts and provides solid support for the moving web W.
[0036] If the protrusive amount increases further, the middle
portion of the web W above top surface 40 is pushed away from the
stabilizer 10, which drags the adjoining portion of the web W above
the nozzle top surface 22, away from the predetermined position.
Consequently the gap between the web W and the body surface 22
increases, and the unbalanced pressure force between the area in
the air-bearing gap and the environmental pressure produce a force
which tends to pull back the moving web W. Thus, two forces act on
the moving web W. The first of the forces is the pushing force from
the center protrusion part 14 pushing upwardly on the middle
portion of the web W. The other force is the pulling force from the
air-bearing due to Bernoulli's effects acting on the portion of web
W which is above the surface 22 and surrounds protrusion 14. These
two counteracting forces cause the moving web W to stretch flat
against the flat top surface 40 of the center protrusion part 14.
The chamfer 42 of the protrusion part 14 promotes a smooth
transition of the moving web W over protrusion part 14.
[0037] Stretching the moving web W against the top surface 40 and
the chamfer 42 of the protrusion part 14 removes wrinkles and
prevents potential web deformation at the area that contacts the
top surface 40 of the protrusion part 14. Stretching the web W also
adds tension to the web which prevents vibration. Thus, the area of
the moving web W that contacts the top surface 40 is highly
stabilized for measurement or other purposes. The area of the
moving web W above the body surface 22 is also stabilized through
the air-bearing between the moving web W and the nozzle top surface
22.
[0038] By adjusting the offset distance D of the center protrusion
part 14 and/or the feeding air pressure at inlet ports 68, the
contacting force acting on the moving web W through the flat
surface 40 of the protrusion part 14 is adjustable. The contacting
force is reduced if the offset distance D is reduced or the feeding
air pressure is reduced. This feature may be particularly useful
for sheet stabilization applications on coated webs. If marks on
the coated surface of the web are observed due to the contact from
protrusion part 14, the contacting force may be reduced, to
eliminate marking on the moving web. The contacting or stabilizing
force may be increased by increasing the feeding air pressure or
the offset distance D of the center protrusion part 14.
[0039] It should be appreciated that the sheet stabilizer 10 of the
present invention exhibits good web edge performance. Modern paper
machines often require the scanning sensors to measure sheet
properties from edge to edge in the cross-machine direction.
Consequently the sheet stabilizer 10 may travel on and off the
moving web frequently. The suction nozzle configuration and the
chamfer 42 of the center protrusion part 14 eliminate the need for
operational condition changes when sheet stabilizer 10 moves on and
off the moving web W at the web edges.
[0040] As shown in FIG. 3, annular opening 70 includes a rounded
edge or fillet 72 that produces a Coanda effect, wherein high speed
streams of fluid releasing from a narrow slot tend to stay attached
to the curvature of a solid surface, rather than follow a straight
line in its original direction. Sheet stabilizer 10 functions with
or without the aid of Coanda effects, and as such, the rounded edge
72 may be replaced with a sharp edge. However, Coanda effects are
useful to further increase the suction force of the sheet
stabilizer 10.
[0041] Referring now to FIG. 3, an alternative center protrusion
part 14 is shown. Stabilizer 10 is substantially the same as the
embodiment disclosed above, however, the protrusion part 14
includes an additional feature. Proximate to chamfer 42 an annular
protuberance 74 extends outwardly from protrusion part 14 and into
second cylindrical section 66 of air chamber 60. Protuberance 74 is
shown in cross-section as triangle shaped, with two tapered
circular surfaces 76 and 78. It should be appreciated, however,
that other shapes may be used. Annular protuberance 74 narrows the
second cylindrical section 66 proximate to the annular opening 70.
Protuberance 74 is positioned at a recessed level beneath body
surface 22 to ensure that it catches or entangles no portion of web
W.
[0042] The relatively large radius of fillet 72 may be used in
combination with protuberance 74 to take advantage of Coanda
effects to further increase the suction force of sheet stabilizer
10. When air flow in second cylindrical section 66 enters the
narrowed gap 80 the axial velocity components are accelerated. The
fast moving air passing through the narrowed gap 80 then attach to
the curved surface of the fillet 72 and thereafter follow the body
surface 22 due to Coanda effects. By combining both vortex effects
(ie. the swirling air pattern) and Coanda effects, the suction
force of the sheet stabilizer 10 of the present invention may be
substantially increased.
[0043] It should be appreciated that sheet stabilizer 10 may work
by Coanda effects alone, without using a vortex effect. In such a
case, the air inlet ports 68 could be relocated to point directly
radially inward toward the axis A of protrusion part 14. In such a
configuration, compressed air entering the air chamber 60 would not
produce a swirling flow inside the chamber 60. However, such an
embodiment includes drawbacks, for example, it is difficult to
control the uniformity of the narrow gap 80.
[0044] If the width of the gap 80 is not the same at all
circumferential points, the suction force will not be uniform on
the front surface 22.
[0045] Referring now to FIGS. 4 and 5, a gauge measurement device,
which incorporates the sheet stabilizer of the present invention,
is shown and generally indicated by the numeral 100. Device 100 may
be installed and used in a web making process line such as a paper
making line. When installed, device 100 is positioned in close
proximity to a moving web W for measurement purposes. Device 100
includes a first sensor heads 102 and a second sensor head 104
mounted on opposite side of the moving web W. Although first head
102 is shown as positioned under the moving web W and second sensor
head 104 is shown above the moving web W, the two heads 102 and 104
can be inversely oriented, with second head on the bottom and first
head on top.
[0046] Measuring device 100 includes a sheet stabilizer 106 that
functions in a substantially similar manner to sheet stabilizer 10,
and consequently, same numbers indicate the same elements. The
sheet stabilizer 106 includes a nozzle body 108 and a center insert
110. A ferrite target 112 may be secured to the nozzle body 108 by
applying glue to a shallow circular recess 114 through a plurality
of holes 116 that may be drilled at an angle from the outside
cylindrical surface of the nozzle body 108. An optical target 118
is provided that functions in substantially the same manner as
protrusion 14. The optical target 118 may be made of hard material
such as solid ceramic, sapphire or synthetic diamond and may be
attached to center insert 110 by glue. A set screw 120 may be used
to ensure that the end surface 122 of the optic target 118 is
parallel to a body surface 124 of the ferrite target 112 when
gluing the optic target 118 to the center insert 110. A chamber 126
is open at the bottom end of the center insert 110 that allows glue
to be injected into the area that bonds optic target 118 and the
insert 110 together. The open chamber 126 also allows the
installation of set screw 120. One or more shims 128 may be placed
between the nozzle body 108 and the insert 110. By changing the
width or number of shims 128 the offset distance D of the optic
target 118 from the ferrite target 112 is adjustable. An o-ring 130
is mounted in a groove 132 on the center insert 110 to seal the air
chamber 60.
[0047] The sensor head 104 includes an optical displacement sensor
probe 134 that may employ a laser triangular method, a confocal
chromatic aberration method or any other optic method which is
capable of determining the distance from the probe 134 to the top
surface 136 of the moving web W at the measurement area. The
measurement area is defined by end surface 122, in the first sensor
head 102 at the opposite side of the web. The bottom surface 138 of
the moving web W contacts, and is drawn against the flat end
surface 122 of the optic target 118 due to the sheet stabilizer
106. Therefore, the end surface 122 functions as a reference plane
for the optic displacement measurement.
[0048] The sensor head 104 includes a second displacement
measurement sensor using a magnetic method. A magnetic displacement
sensor using ferrite based inductor systems is shown here for
illustrative purposes, though other magnetic sensors may be used.
The magnetic sensor includes an inductor 140 having a ferrite cup
core 142 and a winding 144. The core 142 is annular and coaxial
with the optic sensor 134, defining a center aperture 146 that
provides an optical path for the optic displacement measurement.
The relative distances between inductor 140 and the optic probe 134
is precisely controlled by a mounting plate 148. Inductor 140
magnetically measures distance to ferrite target plate 112 in first
sensor head 102.
[0049] Web thickness can be calculated by comparing the magnetic
sensor displacement measurement to the optical sensor measurement.
The distance from the end surface 122 to the optic sensor can be
determined by the magnetic sensor measurement (adjusted by the
known offset distance D). The distance from the top surface 136 of
the moving web W to the optical sensor 134 is determined by the
optic sensor measurement. The difference of the two distances is
the web thickness at the measurement point.
[0050] Calibration of the magnetic distance measurement versus the
optical distance measurement for the gauge device 100 is
occasionally performed because the optical sensor typically has a
much higher resolution than that of a magnetic sensor. Calibration
is generally performed when the web W is not present. A driving
mechanism (not shown) may be used to move first sensor head 102
with the optical target 118 and ferrite target plate 112 together
to a plurality of different distances from second sensor head 104.
The resulting responses from the optical and magnetic signals are
recorded and compared, and then the magnetic displacement
measurement is calibrated against the optical displacement
measurement.
[0051] The sheet stabilizer 10/106 is superior to prior art vacuum
plates, which suck air into the vacuum plate. Continuous outward
air flow from sheet stabilizer 10/106 purges the device and
prevents clogging. The air-bearing between the body surface 124 of
the ferrite target 112 and the bottom surface 138 of the moving web
W protects the ferrite target 112 from abrasion that occurs when
using a conventional vacuum plate. Moreover blowing air outwards
controls the temperature of sensitive components such as the
ferrite target plate 112 and the optic target 118, which
consequently reduces measurement error caused by the effects of
temperature change. Instead of contacting the whole vacuum plate
including both ferrite target and optic target in a conventional
vacuum plate, the moving web contacts only the end surface 122 of
the optic target 118. This contacting area is typically less than
10 millimeter in diameter, and the contacting force is controllable
by adjusting air pressure feeding the inlet ports 68 and/or the
offset distance D between surface 122 and surface 124.
[0052] Referring now to FIG. 6, an alternate embodiment of the
sheet stabilizer of the present invention is shown and indicated by
the numeral 200. The sheet stabilizer 200 is a non-contact
stabilizer, ie. no portion of the web W contacts the stabilizer
during normal operation. Sheet stabilizer 200 includes a nozzle
body 202 and a center insert 204. The nozzle body 202 has a front
flat body surface 206, preferably circular in shape. The center
insert 204 has a protrusive portion 208 which protrudes beyond the
plane defined by the body surface 206. The protrusive portion 208
includes an end flat surface 210 with a plurality of small orifices
212 extending axially inward and communicating with an insert
chamber 214. The insert 204 includes a chamfer 216 that extends
about the periphery of the body surface 206. A shim 218 is
positioned between the nozzle body 202 and the center insert 204.
The offset distance D may be changed by using shims 218 of
different thicknesses. An air chamber 220 is formed between insert
204 and nozzle body 202 that functions substantially similarly to
air chamber 60. Accordingly, a plurality of inlet orifices 222 are
drilled in the same angular direction to create swirling/vortex air
movement. The inlet orifices 222 are in communication with a first
pressurized air source 224.
[0053] The insert chamber 214 is in communication with a second
pressurized air source 226 through a port 228. As noted above,
small orifices 212 at the protrusive portion 208 of the center
insert 204 are in communication with insert chamber 214.
[0054] In operation, the non-contact sheet stabilizer 200 is placed
in close proximity of a moving web W. Pressurized air exit the
inlet orifices 222 and forms a swirling flow inside air chamber 220
at a first cylindrical section 223, moves upward through a
frusto-conical section 225, into a second cylindrical section 227
and exits at the annular opening 230. The sheet stabilizer 200 is
configured to function as a suction nozzle so that air coming out
of annular opening 230 flows sideways along the body surface 206
instead of traveling axially. As a result, the moving web W is
sucked towards the body surface 206 of the nozzle body 202. If the
offset distance D is large enough, and no air is fed to the insert
chamber 214, the moving web W will contact the flat surface 210 of
the protrusive portion 208. Thus, without pressurizing the insert
chamber 214, sheet stabilizer 200 functions substantially similarly
to sheet stabilizer 10. The moving web W is balanced by a pushing
force from the end surface 210 and a pulling force through the
air-bearing 231 formed between web W and body surface 206.
[0055] As air pressure inside insert chamber 214 increases, the
pressure force acting on the bottom surface of the web W increases,
which in turn attempts to push the web W away from the flat surface
210 of the protrusive portion 208. If the pushing force from the
air pressure inside of the air chamber 214 is larger than the
original pushing force from the end surface 210 when there is no
positive pressure in insert chamber 214, the web W disengages from
end surface 210. A second air-bearing 233 is thereafter formed
between the flat surface 210 and the moving web W. Air flow from
the center air-bearing 233 will join the air flow exiting annular
opening 230 and become part of the air traveling through the outer
air-bearing 231 formed between the surface 206 and the moving web
W. In this manner, a non-contact sheet stabilizer is provided.
[0056] By adjusting the air pressure inside the insert chamber 214,
the height of the inner air-bearing 233 is adjustable. The higher
the air pressure inside the insert chamber 214, the bigger the
height of the inner air-bearing. By setting the air pressure in
insert chamber 214 at an appropriate level, an appropriate inner
air-bearing height can be achieved. The non-contact sheet
stabilizer 200 of the present invention maintains the benefits of
the contact sheet stabilizer 10, by stretching the web W around the
area close to and above the protrusive surface 210. Meanwhile, the
non-contact sheet stabilizer 200 eliminates all the drawbacks
associated with physically contacting the moving web W.
[0057] The non-contact sheet stabilizer 200 produces two relatively
independent air-bearings at the same side of the moving web W. The
protrusive inner air-bearing 233 pushes the web away from the sheet
stabilizer and the outer air-bearing 231 functions to pull web W
back towards the sheet stabilizer 200. Balancing the pushing force
with the pulling force, the moving web W is stretched and
stabilized at a very close proximity from the sheet stabilizer 200.
The moving web W is separated from the sheet stabilizer 200 by the
two air-bearings without touching the stabilizer 200. The outer
air-bearing can be produced using Bernoulli principle, Coanda
effects, vortex effects and a combination of any two or all of the
three methods. Instead of using a plurality of orifices for
producing the pressurized air cushion as shown in FIG. 6, the inner
air-bearing could also be generated using Bernoulli principle,
Coanda effects, vortex effects and a combination of any two or all
of the three methods in a manner similar to what is employed to
generate the outer air-bearing. In this manner, a smaller annular
air-bearing is nested inside the outer annular air-bearing. It
should further be appreciated that the offset distance D of the
present embodiment may be smaller than that of the contacting
stabilizer 10. This is due to the fact that the compressed air
exiting insert chamber 214 effectively extends the effective
protrusive distance.
[0058] Referring now to FIG. 7, a caliper measurement device 300 is
shown that employs the non-contact sheet stabilizer 200. Device 300
may include pressure regulators 304 and 306 that are installed
downstream of the compressed air sources 224 and 226 respectively.
Pressure regulator 306 controls and maintains the air pressure in
air chamber 220, which in turn controls and maintains the air
pressure near the exit of the annular opening 230 or the exit of
the plurality of orifices 212.
[0059] Pressure regulator 304 controls and maintains the air
pressure in insert chamber 214. Therefore the pressure drop through
the plurality of orifices 212 is fixed by using the two pressure
regulators 304 and 306. A flow-meter 302 is mounted between the
pressure regulator 304 and air inlet 228 at the entrance of the air
chamber 214.
[0060] Flow-meter 302 measures the rate of air passing through the
plurality of orifice 212 which is the same as the flow rate passing
through a circular gap formed between the bottom surface of the
moving web W and the circular edge around the flat surface 210. The
height of the circular gap can be considered as an averaged height
of the inner air-bearing 233. Flow-rate is functionally related to
pressure drop through the plurality of orifices 212 and the inner
air-bearing height. The reading of the flow-meter 302 may be
converted to a height measurement between web W and end flat
surface 210 since the pressure drop through the plurality of the
orifices 212 is predetermined by the two pressure regulators 304
and 306. In this manner, by adding an optic sensor above the moving
web and a magnetic sensor (as shown in FIG. 4) a non-contact
caliper sensor can be achieved.
[0061] The air-bearing height of the inner air-bearing can also be
measured more precisely using an optic probe embedded inside the
sheet stabilizer of the present invention. Referring now to FIG. 8,
a caliper measurement device 400 includes an optic sensor to
measure the inner air-bearing height. Device 400 includes
stabilizer 200 which also includes an optic probe 402 which may be
smaller but functionally equivalent to optic sensor 134 (shown in
FIG. 4) and is mounted inside the insert chamber 214. A center
aperture 404 is provided through the end surface 210 of the
protrusive portion 208 to provide an optic path for the optic
distance measurement. A plurality of orifices 212, in communication
with the insert chamber 214 are located in a spaced arrangement
around center aperture 404. A ring 406 may be contained between a
flat surface 408 located at the far end of the insert chamber 214
and an end surface 410 of the optic probe 402, so that the distance
from the optic sensor 402 to the reference surface or the end flat
surface 210 is controlled precisely. Optionally, notches may be
provided in ring 406 to allow pressurized air from insert chamber
214 to pass through the ring and purge the center aperture 404.
[0062] The air inlet 412 may be relocated away from the center axis
to make way for the installation of the optic probe 402. The optic
probe 402 can measure the air-bearing height or the distance
between the bottom surface of the moving web W and the reference
surface 210.
[0063] In this manner, by adding an optic sensor above the moving
web and a magnetic sensor to measure the relative distance between
first and second opposed sensor heads (as shown in FIG. 4), a
non-contact caliper sensor can be achieved. The optic probe 402
positioned under the web W and inside the sheet stabilizer 200 of
the present invention requires a smaller measurement range than
that of the optic probe 134 mounted above the web W. Since the
height of the center air-bearing 233 is typically less than 0.2
millimeter, a measurement range of 0.3 mm or larger for optic probe
402 provides an adequate range. Considering the z-direction
fluctuation of the sensor head packages of a typical scanning frame
and the variety of paper grades with different thickness to be
measured, the measurement range of the optic probe 134 positioned
above the sheet should preferably be at least a 2-4
millimeters.
[0064] As those of ordinary skill in the art can appreciate, the
sheet stabilizers of the present invention can have other
applications where the need exists for a web stabilizing device
with or without contacting the web. The sheet stabilizers of the
present invention can also be used for measurement applications
other than caliper measurement as disclosed in this
application.
[0065] It is to be understood that the description of the foregoing
exemplary embodiment(s) is (are) intended to be only illustrative,
rather than exhaustive, of the present invention. Those of ordinary
skill will be able to make certain additions, deletions, and/or
modifications to the embodiment(s) of the disclosed subject matter
without departing from the spirit of the invention or its scope, as
defined by the appended claims.
* * * * *