CA2150021C - A sheet break detector apparatus - Google Patents
A sheet break detector apparatusInfo
- Publication number
- CA2150021C CA2150021C CA002150021A CA2150021A CA2150021C CA 2150021 C CA2150021 C CA 2150021C CA 002150021 A CA002150021 A CA 002150021A CA 2150021 A CA2150021 A CA 2150021A CA 2150021 C CA2150021 C CA 2150021C
- Authority
- CA
- Canada
- Prior art keywords
- transducer
- vacuum
- sheet
- sheet break
- vacuum level
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F7/00—Other details of machines for making continuous webs of paper
- D21F7/04—Paper-break control devices
Landscapes
- Paper (AREA)
- Controlling Rewinding, Feeding, Winding, Or Abnormalities Of Webs (AREA)
- Controlling Sheets Or Webs (AREA)
Abstract
A sheet break detector apparatus (10) is disclosed for detecting a sheet break in a dryer section (12) of a paper machine. The apparatus (10) includes a vacuum transducer (14) which is sensitive to the vacuum level within a vacuum roll (16) of a dryer section (12). The transducer (14) detects only a sudden change in vacuum level within the vacuum roll (16) resulting from a sheet break rather than a relatively gradual change in vacuum level resulting from an operator augmented vacuum level change. A guide device is connected to the transducer (14) and responsive to the transducer (14) for redirecting the sheet to a broke chute (22) upstream relative to the transducer (14) when the transducer (14) detects the sudden change in vacuum level. The arrangement is such that excessive wind-up of the broken sheet (W) around a dryer (24) of the dryer section (12) is inhibited.
Description
~NO 94112724 21~ 0 0 21 PCT/US93/09974 PATENT APPLICATION
TITLE: A SHFFT RRF~( DFTFCTOR APPARATUS
R~ rollnd Of The Inve,-~;G, Field Of The Inve..liol.
The present invention relates to a sheet break detector apparatus for detecting a sheet break in a dryer section of a paper machine. More particularly, the present invention relates to a sheet break detector for particular application to a dryer section having no open draws therein.
Illrur~ G~l niscln~llre Sti~
Particularly in the Bel-ChampTM type dryer section, it is important that in the event of a sheet break, such breakage be detected in order to avoid excessive wind-up of the sheet around a drying cylinder. Bel-Champ is a common law trademark of Beloit Corporation.
The Bel-ChampTM single tier drying section has provided a means for drying alternate sides of a web of paper without subjecting the paper to the long open draws typically incorporated into a conventional two-tier, double felted dryer section.
While the aforementioned Bel-ChampTM type dryer section has greatly lessened the occurrence of sheet breaks during movement of the web through the dryer section, such breakages do still occur occasionally.
When a break in a Bel-ChampTM dryer section occurs, the excellent runnability of the Bel-ChampTM also contributes to the increased likelihood that the web will wrap one of the dryers. The geometry of the WO 94/12724 PCT/US93/09974 ~
Bel-ChampTM dryer section makes it difficult to remove the wrapped paper from the dryer if the wound layers around the drying cylinder become excessively thick.
~ reliable sheet break detector would sense the absence of a web and would initiate a dropping of the sheet upstream relative to the dryer section, thereby preventing excessive wrapping of a dryer cylinder.
However, generally the Bel-ChampTM concept does not include any open draws. Therefore, the employment of a conventional sheet break detector is not possihle.
A prior art break detection mèthod includes an optical sensor to deter."i-.e if a web is ~,resent. A light en-iller is located on one side of theweb and a receiver on the other. When a web is running between the emitter and receiver, the passage of light is obstructed, indicating the presence of the web.
When a sheet breaks, the light passes from the emitter to the receiver, indicating the absence of a web. In order to utilize the aforementioned arrangement, it is essential that an open draw exist in the dryer section.
Accordingly, in the Bel-ChampTMtype arrangement, a modified optical break detector has in the past been employed. More particularly, an optical sensor includes an emitter and a receiver. However, the emitter and receiver are located on the same side of the web. Such configuration utilizes reflected light rather than transmitted light in order to detect the presence of a web.
~WO 94/12724 21 5 ~ 0 21 PCT/US93/09974 More specifically, the sensor is of a type that can detect a color difference. Therefore, in order for the aforementioned method to be effective, a colored felt must be used. The sensor senses the color difference between a felt and a sheet of paper so that in the event of a sheet break, such color difference is sensed by the sensor.
Nevertheless, optical sensors are sensitive to dust and the build-up of dirt on the light sensitive lenses thereof. Such build-up of dust and dirt restricts the passage of light, thus indicating the presence of a web even when the web is absent due to a web breakage. When such a false indication occurs, there can be a significant amount of paper wrapped up on a dryer before a sheet break is discovered. Cleaning the wrapped paper from the dryer cylinder leads to excessive downtime of the dryer section.
In an effort to obtain a more reliable sheet break detection method, a vacuum l,c,,~scJucer, according to the ~uresent invention, has been utilized.
Vacuum sensors are not as sensitive to dust and dirt as optical transducer type counterparts.
Conceptually, by sensing .the vacuum level in the Bel-ChampTM
vacuum roll, it is possible to determine if a web is present. Under normal running conditions, the vacuum would be high. However, during a sheet break, the vacuum would drop to a much lower level due to the absence of the web.
The problem with vacuum detection is that it becomes difficult to determine at what level the sheet break detector should trip. Machine operators during routine operation are constantly adjusting vacuum levels in the Bel-ChampTM vacuum rolls. Accordingly, if the operator raises the vacuum level above the trip point setting, a sheet break will not be 21~0021 WO 94112724 PCT/USg3/09974 ~
detected. However if the operator drops the vacuum below the trip point setting, a false break indication will be signalled.
The present invention provides a vacuum transducer for detecting a sheet break which is insensitive to operational changes in the normal adjustments in vacuum levels of the vacuum rolls, while reliably detecting a sheet break.
Therefore, it is a primary objective of the present invention to provide a vacuum transducer for detecting a sheet break in a dryer section which is sensitive to a sudden change in vacuum within the vacuum roll, rather than a relatively gradual change in vacuum level cal~erl by routine operational adjustments.
Another object of the present invention is the provision of a vacuum sheet break dete~ling apparatus which overcomes the afole",el,Lioned problems of the prior art arrange",e"ls and which makes a considerable contribution to the art of detecting a sheet break in a dryer section.
S~ r Of The ~ re.~l;G- I
The present invention relates to a sheet break detector apparatus and method for detecting a sheet break in a dryer section of a paper machine.
The apparatus includes a vacuum lr ~nsducer which is se"si li~e to the vacuum level within a vacuum roll of the dryer section. The transducer detects only a sudden change in the vacuum level within the vacuum roll resulting from a sheet break, rather than a relatively gradual change in the vacuum level resulting from an operator augmented vacuum level change.
The apparatus also includes means connected to the transducer and responsive to the transducer for redirecting the sheet to a broke chute or 2150~21 ~WO 94112724 PCTIUS93/09974 pit upstream relative to the transducer when the transducer detects the sudden change in vacuum level. The arrangement is such that excessive wind-up of the broken sheet around a dryer of the dryer section is inhibited.
In a more specific embodiment of the present invention, the transducer is a piezoelectric pressure transducer which senses the vacuum level within a center shaft of the vacuum roll.
In another embodiment of the present invention, the transducer senses the vacuum level within a duct which connects the vacuum roll to a source of partial vacuum.
The transducer is such that during normal operation of the dryer section, when the unbroken sheet extends through the dryer section, a first output from the transducer is zero, and when a sheet break occurs, an output signal is generated which is proportional to the change in vacuum level within the vacuum roll as a result of the sheet break.
Many modifications and variations of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed desc, i~lion conlai"ed hereinafter. However, such modifications and variations fall within the spirit and scope of the present invention as defined by the appe"ded claims.
Rrjef neS~ iG,~ Of The n.~
Figure 1 is a side-elevational view of a portion of a Bel-ChampTM type dryer section showing the location of the l,al~sducer;
2150 02~
Wo 94/12724 PCT/US93109974 Figure 2 is a similar view to that shown in Figure 1, but shows how the web is directed to a broke chute or pit in the event of a downstream web breakage;
Figure 3 is a schematic representation of a sheet break detector apparatus including a vacuum transducer according to the present invention;
Figure 4 is a schematic representation of the sheet detector apparatus according to a further embodiment of the present invention in which the transducer detects the vacuum level within a duct;
Figure ~ is a graph showing the lld"sd.lcer response to a steady state condition;
Figure 6 is a graph showing the ll dl ~sclucer response to a sheet break; and Figure 7 is a graph showing the transducer response to an operator augmented damper adju:.ll"e"t.
Similar reference charac~ers refer to similar parts throughout the various views of the drawings.
Detaile~l n~s~ ;on Of The n~ .JS
Figure 1 is a side-elevational view of a portion of a Bel-ChampTM type dryer section including a sheet break detector apparatus, generally designated 10 according to the present invention, for detecting a sheet break in the dryer section, generally designated 12. The apparatus 10 215~2 1 includes a vacuum transducer 14 which is sensitive to the vacuum level within a vacuum roll 16 of the dryer section 12. The transducer 14 detects only a sudden change in the vacuum within the vacuum roll 16 resulting from a sheet break rather than a relatively gradual change in vacuum resulting from an operator augmented vacuum level change.
Figure 2 is a view similar to that shown in Figure 1, but showing the operation of the apparatus 10 in the event of a web breakage. More particularly, means 18 are connected to the transducer 14 and responsive to the Lld"s~lJcer 14 for redirecting the sheet W to a broke pit 22 disposed upstream relative to the transducer 14 when the Llal~sJucer 14 detects a sudden change in vacuum level. Thè arrangement is such that excessive wind-up of the broken web W around a dryer 24 of the dryer section 12 is inhibited.
As shown in Figure 2, the broken web W is shown as wrapping around dryer cylinder 24 and the trailing end of the downstream broken web passing the vacuum roll 16 in order to extend around drying cylinder 26.
In normal operation, a high vacuum is applied within vacuum roll 16, and a breakage of the web will cause a sudden decrease in the vacuum level within vacuum roll 16. Such sudden decrease in vacuum level is sensed by the L,d"sducer 14 which is electrically or otherwise connected to the means 18 disposed upstream relative to the group of drying cylinders 24,26.
Typically, the means 18 may include a transverse web cutting device for cutting the web as it extends around a vacuum L-dr,s~er roll 28.
Additionally, the means 18 may include an arrangement for cutting off the WO 94/12724 215 ~ 0 2 ~ PCT/US93/09974 ~
vacuum to the vacuum roll 28 such that the moving web will fall to the broke pit 22 rather than extending around the vacuum roll 28 for transfer into the downstream dryer group, which includes drying cylinders 24 and 26 and vacuum roll 16.
By the aforementioned arrangement, only a short length of the web from the vacuum roll 28 to the drying cylinder 24 will become wrapped around the drying cylinder 24.
However, the present invention is directed particularly to the transducer 14, which senses the sudden change in vacuum level, and it will be understood by those skilled in the art that such L,dnsdllcer may be used for triggering a visual or a!J~Iible alarm so that an operator may manually direct the web to the broke pit.
Additionally, the aforementioned ll~"sd!~cer 14 may ge"er~Le a signal for cutting the web upstream of the entire dryer group or, for in any other manner, interrupting the movement of the web along the dryer section.
In a ~re~rled embGd;,.,ent of the present invention, the L~nsclucer 14 is a piezoelectric pressure l,~"sducer.
Figure 3 is a schematic reptese,.talion showing the l~ansducer 14 for sensing the vacuum level existing within a center shaft 30 of the vacuum roll 16.
Figure 4 is a similar view to that shown in Figure 3, but shows an alternative embodi,..e"t of the present invention in which a transducer 14A
~WO 94/12724 PCT/US93/09974 senses the vacuum level within a duct 32 which connects the vacuum roll 1 6A to a source of partial vacuum 34.
As shown in Figure 3, the transducer 14 is arranged in such a manner that during normal operation of the dryer section 12, when the unbroken web W extends through the dryer section 12, the output from the transducer is zero. When a sheet break occurs, the change in vacuum is sensed by the transducer and an output signal is generated which is proportional to the change in vacuum level within the vacuum roll 16 as a result of the sheet break.
Figure 5 is a graph 36 showing the response of the piezoelectric l-ansducer 14 to a steady state condition with the graph 36 re~ reser.li,.g the pressure ayai..sl a number of time constants.
Figure 6 shows four graphs 38,40,42 and 44 indicating the r~llsclucer output for various time constants in response to a sheet break.
Figure 7 shows graphs 46,48 and 50 indicating the response of the transducer 14 to routine damper adjusl"-enls of the vacuum roll for various ~ime constants.
More specifically, Figure 7 shows the graphs for the pressure relative to the time of adjustment.
More particularly, the output from the transducer 14 decays to zero when a new steady state cGndi lion exists, as shown particularly in the graph 44 shown in Figure 6, following the sheet break. The difference in the output signal between a fast and a relatively slow change makes it 21~002 ~
WO 941~2724 PCT/US93/09974 possible to detect the difference between a sheet break and damper movement.
More specifically, such output signal generated as a result of a sheet break occurs within a relatively small time constant.
In a ~,refer, ed embodiment of the present invention, the time constant is within the range 1 millisecond to 3 seconds.
After the break occurs, vacuurri decreases to a new steady state condition. The output from the l.~r,s.lucer 14 will then decay to zero following the function: ' Output = A*e'-"T' Where:
A = Maximum output following step change e = base of natural loga, i ll " "
t = time T = time constant The time constant is defined as the period required for the output to reach e~1, or .368, of its original value. Figure 5 shows the graph 36 of this curve.
The objective is to configure the transducer system such that it has a time constant on the order of milliseconds. In such configuration, the vacuum change occurring during a sheet break happens fast enough to be fully sensed by the transducer, as shown in the graph depicted in Figure 6.
~1~0~ ~
~WO 94/12724 PCT/US93/09974 The much siower change in vacuum that occurs when an operator adjusts a vacuum damper, however, is competing with the constantly ~ decaying output of the transducer. Given a sufficiently short time constant, the sensor will exhibit only a slight ripple in its output, as shown in Figure 7.
The dirrere,-ce in output between a fast and a relatively slow change makes it possible to discern between sheet breaks and damper movement within the vacuum roll. A comparison of Figures 6 and 7 shows that under the conditions plotted, a time constant of .05 seconds is suitable. By adjusting the peak voltage setting in the dete~;Lion circuit based on the minimum steady state vacuum level with the sheet on, vacuum levels can be manually changed by the operators without requiring a corresponding change in the detection level or without a false i"d;calion of a sheet break.
During transient operations, such as sheet threading, sensing of the l~a,.sducer break detector must be disabled, the same as with other more conventional detectors.
The means, generally designated 18, may include a cross-machine web cutter such that the web is directed to the broke chute 22.
Alternatively, the means may include an audible or visible alarm for directing an operator to the presence of a sheet break.
What is disclosed is a method and apparatus for using a piezoelectric vacuum transducer to sense sheet breaks in a Bel-ChampTM type dryer section. The arrangement is more durable than the prior art optical detectors currently used and does not require an open draw to operate.
Additionally, the break detector, according to the present invention, can be set up to operate without false break signals due to operator adjustment of vacuum levels.
The ~rese,lt invention provides a reliable means for detecting a sheet break that is particularly advantageous for detecting a sheet break within a dryer section having no open draws.
TITLE: A SHFFT RRF~( DFTFCTOR APPARATUS
R~ rollnd Of The Inve,-~;G, Field Of The Inve..liol.
The present invention relates to a sheet break detector apparatus for detecting a sheet break in a dryer section of a paper machine. More particularly, the present invention relates to a sheet break detector for particular application to a dryer section having no open draws therein.
Illrur~ G~l niscln~llre Sti~
Particularly in the Bel-ChampTM type dryer section, it is important that in the event of a sheet break, such breakage be detected in order to avoid excessive wind-up of the sheet around a drying cylinder. Bel-Champ is a common law trademark of Beloit Corporation.
The Bel-ChampTM single tier drying section has provided a means for drying alternate sides of a web of paper without subjecting the paper to the long open draws typically incorporated into a conventional two-tier, double felted dryer section.
While the aforementioned Bel-ChampTM type dryer section has greatly lessened the occurrence of sheet breaks during movement of the web through the dryer section, such breakages do still occur occasionally.
When a break in a Bel-ChampTM dryer section occurs, the excellent runnability of the Bel-ChampTM also contributes to the increased likelihood that the web will wrap one of the dryers. The geometry of the WO 94/12724 PCT/US93/09974 ~
Bel-ChampTM dryer section makes it difficult to remove the wrapped paper from the dryer if the wound layers around the drying cylinder become excessively thick.
~ reliable sheet break detector would sense the absence of a web and would initiate a dropping of the sheet upstream relative to the dryer section, thereby preventing excessive wrapping of a dryer cylinder.
However, generally the Bel-ChampTM concept does not include any open draws. Therefore, the employment of a conventional sheet break detector is not possihle.
A prior art break detection mèthod includes an optical sensor to deter."i-.e if a web is ~,resent. A light en-iller is located on one side of theweb and a receiver on the other. When a web is running between the emitter and receiver, the passage of light is obstructed, indicating the presence of the web.
When a sheet breaks, the light passes from the emitter to the receiver, indicating the absence of a web. In order to utilize the aforementioned arrangement, it is essential that an open draw exist in the dryer section.
Accordingly, in the Bel-ChampTMtype arrangement, a modified optical break detector has in the past been employed. More particularly, an optical sensor includes an emitter and a receiver. However, the emitter and receiver are located on the same side of the web. Such configuration utilizes reflected light rather than transmitted light in order to detect the presence of a web.
~WO 94/12724 21 5 ~ 0 21 PCT/US93/09974 More specifically, the sensor is of a type that can detect a color difference. Therefore, in order for the aforementioned method to be effective, a colored felt must be used. The sensor senses the color difference between a felt and a sheet of paper so that in the event of a sheet break, such color difference is sensed by the sensor.
Nevertheless, optical sensors are sensitive to dust and the build-up of dirt on the light sensitive lenses thereof. Such build-up of dust and dirt restricts the passage of light, thus indicating the presence of a web even when the web is absent due to a web breakage. When such a false indication occurs, there can be a significant amount of paper wrapped up on a dryer before a sheet break is discovered. Cleaning the wrapped paper from the dryer cylinder leads to excessive downtime of the dryer section.
In an effort to obtain a more reliable sheet break detection method, a vacuum l,c,,~scJucer, according to the ~uresent invention, has been utilized.
Vacuum sensors are not as sensitive to dust and dirt as optical transducer type counterparts.
Conceptually, by sensing .the vacuum level in the Bel-ChampTM
vacuum roll, it is possible to determine if a web is present. Under normal running conditions, the vacuum would be high. However, during a sheet break, the vacuum would drop to a much lower level due to the absence of the web.
The problem with vacuum detection is that it becomes difficult to determine at what level the sheet break detector should trip. Machine operators during routine operation are constantly adjusting vacuum levels in the Bel-ChampTM vacuum rolls. Accordingly, if the operator raises the vacuum level above the trip point setting, a sheet break will not be 21~0021 WO 94112724 PCT/USg3/09974 ~
detected. However if the operator drops the vacuum below the trip point setting, a false break indication will be signalled.
The present invention provides a vacuum transducer for detecting a sheet break which is insensitive to operational changes in the normal adjustments in vacuum levels of the vacuum rolls, while reliably detecting a sheet break.
Therefore, it is a primary objective of the present invention to provide a vacuum transducer for detecting a sheet break in a dryer section which is sensitive to a sudden change in vacuum within the vacuum roll, rather than a relatively gradual change in vacuum level cal~erl by routine operational adjustments.
Another object of the present invention is the provision of a vacuum sheet break dete~ling apparatus which overcomes the afole",el,Lioned problems of the prior art arrange",e"ls and which makes a considerable contribution to the art of detecting a sheet break in a dryer section.
S~ r Of The ~ re.~l;G- I
The present invention relates to a sheet break detector apparatus and method for detecting a sheet break in a dryer section of a paper machine.
The apparatus includes a vacuum lr ~nsducer which is se"si li~e to the vacuum level within a vacuum roll of the dryer section. The transducer detects only a sudden change in the vacuum level within the vacuum roll resulting from a sheet break, rather than a relatively gradual change in the vacuum level resulting from an operator augmented vacuum level change.
The apparatus also includes means connected to the transducer and responsive to the transducer for redirecting the sheet to a broke chute or 2150~21 ~WO 94112724 PCTIUS93/09974 pit upstream relative to the transducer when the transducer detects the sudden change in vacuum level. The arrangement is such that excessive wind-up of the broken sheet around a dryer of the dryer section is inhibited.
In a more specific embodiment of the present invention, the transducer is a piezoelectric pressure transducer which senses the vacuum level within a center shaft of the vacuum roll.
In another embodiment of the present invention, the transducer senses the vacuum level within a duct which connects the vacuum roll to a source of partial vacuum.
The transducer is such that during normal operation of the dryer section, when the unbroken sheet extends through the dryer section, a first output from the transducer is zero, and when a sheet break occurs, an output signal is generated which is proportional to the change in vacuum level within the vacuum roll as a result of the sheet break.
Many modifications and variations of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed desc, i~lion conlai"ed hereinafter. However, such modifications and variations fall within the spirit and scope of the present invention as defined by the appe"ded claims.
Rrjef neS~ iG,~ Of The n.~
Figure 1 is a side-elevational view of a portion of a Bel-ChampTM type dryer section showing the location of the l,al~sducer;
2150 02~
Wo 94/12724 PCT/US93109974 Figure 2 is a similar view to that shown in Figure 1, but shows how the web is directed to a broke chute or pit in the event of a downstream web breakage;
Figure 3 is a schematic representation of a sheet break detector apparatus including a vacuum transducer according to the present invention;
Figure 4 is a schematic representation of the sheet detector apparatus according to a further embodiment of the present invention in which the transducer detects the vacuum level within a duct;
Figure ~ is a graph showing the lld"sd.lcer response to a steady state condition;
Figure 6 is a graph showing the ll dl ~sclucer response to a sheet break; and Figure 7 is a graph showing the transducer response to an operator augmented damper adju:.ll"e"t.
Similar reference charac~ers refer to similar parts throughout the various views of the drawings.
Detaile~l n~s~ ;on Of The n~ .JS
Figure 1 is a side-elevational view of a portion of a Bel-ChampTM type dryer section including a sheet break detector apparatus, generally designated 10 according to the present invention, for detecting a sheet break in the dryer section, generally designated 12. The apparatus 10 215~2 1 includes a vacuum transducer 14 which is sensitive to the vacuum level within a vacuum roll 16 of the dryer section 12. The transducer 14 detects only a sudden change in the vacuum within the vacuum roll 16 resulting from a sheet break rather than a relatively gradual change in vacuum resulting from an operator augmented vacuum level change.
Figure 2 is a view similar to that shown in Figure 1, but showing the operation of the apparatus 10 in the event of a web breakage. More particularly, means 18 are connected to the transducer 14 and responsive to the Lld"s~lJcer 14 for redirecting the sheet W to a broke pit 22 disposed upstream relative to the transducer 14 when the Llal~sJucer 14 detects a sudden change in vacuum level. Thè arrangement is such that excessive wind-up of the broken web W around a dryer 24 of the dryer section 12 is inhibited.
As shown in Figure 2, the broken web W is shown as wrapping around dryer cylinder 24 and the trailing end of the downstream broken web passing the vacuum roll 16 in order to extend around drying cylinder 26.
In normal operation, a high vacuum is applied within vacuum roll 16, and a breakage of the web will cause a sudden decrease in the vacuum level within vacuum roll 16. Such sudden decrease in vacuum level is sensed by the L,d"sducer 14 which is electrically or otherwise connected to the means 18 disposed upstream relative to the group of drying cylinders 24,26.
Typically, the means 18 may include a transverse web cutting device for cutting the web as it extends around a vacuum L-dr,s~er roll 28.
Additionally, the means 18 may include an arrangement for cutting off the WO 94/12724 215 ~ 0 2 ~ PCT/US93/09974 ~
vacuum to the vacuum roll 28 such that the moving web will fall to the broke pit 22 rather than extending around the vacuum roll 28 for transfer into the downstream dryer group, which includes drying cylinders 24 and 26 and vacuum roll 16.
By the aforementioned arrangement, only a short length of the web from the vacuum roll 28 to the drying cylinder 24 will become wrapped around the drying cylinder 24.
However, the present invention is directed particularly to the transducer 14, which senses the sudden change in vacuum level, and it will be understood by those skilled in the art that such L,dnsdllcer may be used for triggering a visual or a!J~Iible alarm so that an operator may manually direct the web to the broke pit.
Additionally, the aforementioned ll~"sd!~cer 14 may ge"er~Le a signal for cutting the web upstream of the entire dryer group or, for in any other manner, interrupting the movement of the web along the dryer section.
In a ~re~rled embGd;,.,ent of the present invention, the L~nsclucer 14 is a piezoelectric pressure l,~"sducer.
Figure 3 is a schematic reptese,.talion showing the l~ansducer 14 for sensing the vacuum level existing within a center shaft 30 of the vacuum roll 16.
Figure 4 is a similar view to that shown in Figure 3, but shows an alternative embodi,..e"t of the present invention in which a transducer 14A
~WO 94/12724 PCT/US93/09974 senses the vacuum level within a duct 32 which connects the vacuum roll 1 6A to a source of partial vacuum 34.
As shown in Figure 3, the transducer 14 is arranged in such a manner that during normal operation of the dryer section 12, when the unbroken web W extends through the dryer section 12, the output from the transducer is zero. When a sheet break occurs, the change in vacuum is sensed by the transducer and an output signal is generated which is proportional to the change in vacuum level within the vacuum roll 16 as a result of the sheet break.
Figure 5 is a graph 36 showing the response of the piezoelectric l-ansducer 14 to a steady state condition with the graph 36 re~ reser.li,.g the pressure ayai..sl a number of time constants.
Figure 6 shows four graphs 38,40,42 and 44 indicating the r~llsclucer output for various time constants in response to a sheet break.
Figure 7 shows graphs 46,48 and 50 indicating the response of the transducer 14 to routine damper adjusl"-enls of the vacuum roll for various ~ime constants.
More specifically, Figure 7 shows the graphs for the pressure relative to the time of adjustment.
More particularly, the output from the transducer 14 decays to zero when a new steady state cGndi lion exists, as shown particularly in the graph 44 shown in Figure 6, following the sheet break. The difference in the output signal between a fast and a relatively slow change makes it 21~002 ~
WO 941~2724 PCT/US93/09974 possible to detect the difference between a sheet break and damper movement.
More specifically, such output signal generated as a result of a sheet break occurs within a relatively small time constant.
In a ~,refer, ed embodiment of the present invention, the time constant is within the range 1 millisecond to 3 seconds.
After the break occurs, vacuurri decreases to a new steady state condition. The output from the l.~r,s.lucer 14 will then decay to zero following the function: ' Output = A*e'-"T' Where:
A = Maximum output following step change e = base of natural loga, i ll " "
t = time T = time constant The time constant is defined as the period required for the output to reach e~1, or .368, of its original value. Figure 5 shows the graph 36 of this curve.
The objective is to configure the transducer system such that it has a time constant on the order of milliseconds. In such configuration, the vacuum change occurring during a sheet break happens fast enough to be fully sensed by the transducer, as shown in the graph depicted in Figure 6.
~1~0~ ~
~WO 94/12724 PCT/US93/09974 The much siower change in vacuum that occurs when an operator adjusts a vacuum damper, however, is competing with the constantly ~ decaying output of the transducer. Given a sufficiently short time constant, the sensor will exhibit only a slight ripple in its output, as shown in Figure 7.
The dirrere,-ce in output between a fast and a relatively slow change makes it possible to discern between sheet breaks and damper movement within the vacuum roll. A comparison of Figures 6 and 7 shows that under the conditions plotted, a time constant of .05 seconds is suitable. By adjusting the peak voltage setting in the dete~;Lion circuit based on the minimum steady state vacuum level with the sheet on, vacuum levels can be manually changed by the operators without requiring a corresponding change in the detection level or without a false i"d;calion of a sheet break.
During transient operations, such as sheet threading, sensing of the l~a,.sducer break detector must be disabled, the same as with other more conventional detectors.
The means, generally designated 18, may include a cross-machine web cutter such that the web is directed to the broke chute 22.
Alternatively, the means may include an audible or visible alarm for directing an operator to the presence of a sheet break.
What is disclosed is a method and apparatus for using a piezoelectric vacuum transducer to sense sheet breaks in a Bel-ChampTM type dryer section. The arrangement is more durable than the prior art optical detectors currently used and does not require an open draw to operate.
Additionally, the break detector, according to the present invention, can be set up to operate without false break signals due to operator adjustment of vacuum levels.
The ~rese,lt invention provides a reliable means for detecting a sheet break that is particularly advantageous for detecting a sheet break within a dryer section having no open draws.
Claims (9)
1. A sheet break detector apparatus (10) for detecting a sheet break in a dryer section (12) of a paper machine, said apparatus comprising:
a vacuum transducer (14) for sensing the vacuum level within a vacuum roll (16) of the dryer section (12), said transducer (14) detecting only a sudden change in said vacuum level within said vacuum roll (16) resulting from a sheet break rather than a relatively gradual change in vacuum level resulting from an operator augmented vacuum level change; and means (18) connected to said transducer (14) and responsive to said transducer (14) for redirecting the sheet to a broke chute (22) upstream relative to said transducer (14) when said transducer (14) detects said sudden change in vacuum level, the arrangement being such that excessive wind-up of the broken sheet (W) around a dryer (24) of the drying section (12) is inhibited.
a vacuum transducer (14) for sensing the vacuum level within a vacuum roll (16) of the dryer section (12), said transducer (14) detecting only a sudden change in said vacuum level within said vacuum roll (16) resulting from a sheet break rather than a relatively gradual change in vacuum level resulting from an operator augmented vacuum level change; and means (18) connected to said transducer (14) and responsive to said transducer (14) for redirecting the sheet to a broke chute (22) upstream relative to said transducer (14) when said transducer (14) detects said sudden change in vacuum level, the arrangement being such that excessive wind-up of the broken sheet (W) around a dryer (24) of the drying section (12) is inhibited.
2. A sheet break detector apparatus (10) as set forth in claim 1, wherein said transducer (14) is a piezoelectric pressure transducer.
3. A sheet break detector apparatus (10) as set forth in claim 2, wherein said transducer (14) senses the vacuum level within a center shaft (30) of said vacuum roll (16).
4. A sheet break detector apparatus (10) as set forth in claim 2, wherein said transducer (14A) senses the vacuum level within a duct (32) connecting said vacuum roll (16A) to a source of partial vacuum (34).
5. A sheet break detector apparatus (10) as set forth in claim 2, wherein said transducer (14) is adjusted such that during normal operation of the dryer section (12) when the unbroken sheet (W) extends through the dryer section (12), an output from said transducer (14) is zero, and when a sheet break occurs, a further output signal is generated which is proportional to the change in vacuum level within the vacuum roll (16) as a result of the sheet break.
6. A sheet break detector apparatus (10) as set forth in claim 5, wherein said further output signal decays to zero when a new steady state condition exists following said sheet break, said further output signal being generated only when said change in vacuum level occurs within a relatively small time constant.
7. A sheet break detector apparatus (10) as set forth in claim 6, wherein said time constant is within the range 1 millisecond to 3 seconds.
8. A sheet break detector apparatus (10) as set forth in claim 1, wherein said means (18) includes:
a cross-machine web cutter for cutting the web;
a broke chute (22) disposed beneath said cutter for collecting the cut web.
a cross-machine web cutter for cutting the web;
a broke chute (22) disposed beneath said cutter for collecting the cut web.
9. A sheet break detector apparatus (10) for detecting a sheet break in a single tier drying section (12) of a paper machine, said apparatus comprising:
a vacuum transducer (14) for sensing the vacuum level within a vacuum roll (16) of the dryer section (12), said transducer (14) detecting only a sudden change in said vacuum level within said vacuum roll (16) resulting from a sheet break rather than a relatively gradual change in volume level resulting from an operator augmented vacuum level change; and means (18) connected to said transducer (14) and responsive to said transducer (14) for generating a signal indicating that a sheet break has occurred when said transducer (14) detects said sudden change in vacuum level, the arrangement being such that excessive wind-up of the broken sheet (W) around a dryer (24) of the single tier drying section (12) is inhibited.
a vacuum transducer (14) for sensing the vacuum level within a vacuum roll (16) of the dryer section (12), said transducer (14) detecting only a sudden change in said vacuum level within said vacuum roll (16) resulting from a sheet break rather than a relatively gradual change in volume level resulting from an operator augmented vacuum level change; and means (18) connected to said transducer (14) and responsive to said transducer (14) for generating a signal indicating that a sheet break has occurred when said transducer (14) detects said sudden change in vacuum level, the arrangement being such that excessive wind-up of the broken sheet (W) around a dryer (24) of the single tier drying section (12) is inhibited.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US98157992A | 1992-11-25 | 1992-11-25 | |
| US07/981,579 | 1992-11-25 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2150021A1 CA2150021A1 (en) | 1994-06-09 |
| CA2150021C true CA2150021C (en) | 1998-09-01 |
Family
ID=25528481
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002150021A Expired - Fee Related CA2150021C (en) | 1992-11-25 | 1993-10-19 | A sheet break detector apparatus |
Country Status (13)
| Country | Link |
|---|---|
| EP (1) | EP0660898B1 (en) |
| JP (1) | JP2562799B2 (en) |
| KR (1) | KR950704569A (en) |
| CN (1) | CN1035076C (en) |
| BR (1) | BR9307486A (en) |
| CA (1) | CA2150021C (en) |
| DE (2) | DE69304545T2 (en) |
| FI (1) | FI952548A (en) |
| MX (1) | MX9307387A (en) |
| MY (1) | MY110025A (en) |
| PL (1) | PL172455B1 (en) |
| TW (1) | TW229270B (en) |
| WO (1) | WO1994012724A1 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI109235B (en) * | 1998-04-27 | 2002-06-14 | Fotocomp Oy | A method for determining a paper web release angle and / or profile |
| DE10042243A1 (en) * | 2000-08-28 | 2002-03-14 | Voith Paper Patent Gmbh | Web break monitoring method |
| DE102004046795A1 (en) | 2004-09-27 | 2006-04-06 | Voith Paper Patent Gmbh | Device and method for monitoring the transfer of a material web and especially the broadening of the width of a transfer strip on a demolition of the transfer strip or the material web |
| DE102007000679A1 (en) | 2007-11-09 | 2009-05-14 | Voith Patent Gmbh | Method and device for detecting a crack and / or a modulus of elasticity of a material web |
| ES2731276T3 (en) | 2016-08-29 | 2019-11-14 | Siemens Ag | Procedure for the operation of a machine for the manufacture and / or treatment of a band of material |
| CN107164987B (en) * | 2017-07-14 | 2019-02-19 | 河南卷烟工业烟草薄片有限公司 | A kind of large cylinder broken and collecting paper scrap device |
| JP6902270B2 (en) * | 2017-10-02 | 2021-07-14 | デュプロ精工株式会社 | Band-shaped object forming device |
| CN110877839B (en) * | 2018-09-06 | 2022-03-25 | 西门子（中国）有限公司 | Method and equipment for processing broken paper |
| EP3699356A1 (en) * | 2019-02-25 | 2020-08-26 | Siemens Aktiengesellschaft | Method and device for detecting a tear in a fibrous web, industrial equipment and computer program product |
| CN110906972B (en) * | 2019-10-28 | 2021-06-18 | 浙江大学山东工业技术研究院 | Automatic paper monitoring and breaking prevention system |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1725108A (en) * | 1926-03-10 | 1929-08-20 | Alvin W Smith | Method and apparatus for making paper |
| US1838603A (en) * | 1929-07-11 | 1931-12-29 | Sr George S Witham | Paper making machine |
| US3097993A (en) * | 1961-05-23 | 1963-07-16 | Dominion Eng Works Ltd | Apparatus for automatic knock-off shower for paper machine |
-
1993
- 1993-10-19 BR BR9307486A patent/BR9307486A/en not_active Application Discontinuation
- 1993-10-19 DE DE69304545T patent/DE69304545T2/en not_active Expired - Fee Related
- 1993-10-19 CA CA002150021A patent/CA2150021C/en not_active Expired - Fee Related
- 1993-10-19 JP JP6513120A patent/JP2562799B2/en not_active Expired - Lifetime
- 1993-10-19 PL PL93308218A patent/PL172455B1/en not_active IP Right Cessation
- 1993-10-19 DE DE0660898T patent/DE660898T1/en active Pending
- 1993-10-19 WO PCT/US1993/009974 patent/WO1994012724A1/en active IP Right Grant
- 1993-10-19 EP EP93924356A patent/EP0660898B1/en not_active Expired - Lifetime
- 1993-10-19 KR KR1019950702070A patent/KR950704569A/en active IP Right Grant
- 1993-11-16 CN CN93114519A patent/CN1035076C/en not_active Expired - Fee Related
- 1993-11-18 MY MYPI93002420A patent/MY110025A/en unknown
- 1993-11-23 TW TW082109841A patent/TW229270B/zh active
- 1993-11-24 MX MX9307387A patent/MX9307387A/en not_active IP Right Cessation
-
1995
- 1995-05-24 FI FI952548A patent/FI952548A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| TW229270B (en) | 1994-09-01 |
| CN1088647A (en) | 1994-06-29 |
| MY110025A (en) | 1997-11-29 |
| MX9307387A (en) | 1994-06-30 |
| EP0660898A1 (en) | 1995-07-05 |
| KR950704569A (en) | 1995-11-20 |
| DE660898T1 (en) | 1996-01-18 |
| FI952548A0 (en) | 1995-05-24 |
| EP0660898B1 (en) | 1996-09-04 |
| CA2150021A1 (en) | 1994-06-09 |
| DE69304545D1 (en) | 1996-10-10 |
| WO1994012724A1 (en) | 1994-06-09 |
| BR9307486A (en) | 1999-08-24 |
| JP2562799B2 (en) | 1996-12-11 |
| CN1035076C (en) | 1997-06-04 |
| PL172455B1 (en) | 1997-09-30 |
| PL308218A1 (en) | 1995-07-24 |
| FI952548A (en) | 1995-05-24 |
| DE69304545T2 (en) | 1997-02-06 |
| JPH07507604A (en) | 1995-08-24 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |