CA2213640A1

CA2213640A1 - Diaper registration control system

Info

Publication number: CA2213640A1
Application number: CA002213640A
Authority: CA
Inventors: James Michael Fleming; Mark David Whaley; Myron Lee Stuebe
Original assignee: The Procter & Gamble Company; James Michael Fleming; Mark David Whaley; Myron Lee Stuebe
Current assignee: Procter and Gamble Co
Priority date: 1995-03-27
Filing date: 1996-02-21
Publication date: 1996-10-03
Also published as: DE69616530D1; EP0817602A1; AU4991396A; ES2163007T3; WO1996029966A1; EP0817602B1; MX9707368A; US5659538A; KR19980703340A; JPH11502738A

Abstract

The automatic registration control system of the present invention is a closed loop system including a driving mechanism (10) for feeding a continuous web (12) of disposable absorbent articles, such as diaper pads, toward a cutter (14). The cutter (14) may separate completed pads from the web. A sensor (26) is positioned along the manufacturing line, and preferably preceding the cutter (14), for detecting at least one preselected feature of each diaper pad and producing a detection signal when the feature passes by the sensor (26). A
position resolver (32) determines the angular position of the cutter (14) at the moment when the preselected diaper feature is detected, and the average angular position is calculated from a predetermined number of cutter (14) positions. The average cutter (14) position is compared to and subtracted from a target cutter (14) position to produce an error signal. The error signal is then converted into a control signal and supplied to a phase variator (44) which adjusts the position of the cutter (14) in response to the control signal.

Description

W O 96/29966 PCTrUS96102385 DIAPER REGISTRATION CONTROL SYSTEM

FIELD OF THE INVENTION
This invention relates ge"erally to a registration control system and more particularly to a closed-loop regi~l, dlion control system and method for controlling the localiGn of a rotary knife cut on a web of r"at~rial. The invention will be specifically disclosed in connection with a system for varying the angular position of a rotary cutter to cl ,a"ge the phase relationship betw~on the cutter and a preselected feature on a continuous web of inler~nnected diaper pads.

BACKGROUND OF THE INVENTION
In the manufacturing of disposable absorbe, ll articles, such as diapers, adult incG"Ii"ence a. licles, and sanitary "aphins, it is a common manufacturing pra~lice to initially fabricdle a plurality of individual articlessuch as d;aper-~ that are serially sp~ced in i,-lercGnnected posiliG"s on a continuous web. Individual diapers thereafter are fGr."ed by di~e~;ti"g the web into a rotary cutter to cut the web between the sp~ced pads, usually as the final cutting operalion in the manufacturing process.
In order to produce uniform diaper:" and to eli",i"ate waste, it is dasirable to control relatively p,ecisely the loc,-lio" at which the web is severed (typically ~ere--~d to as the "final cut"). It is particularly desirable to cut the web in a cG"~~ posilion relative to features that are for"~ecl on the diaper. For example, ~ispos~le diape~s frequently use adhesive tab strips and it is desirable to control the distance between these tabs and the top of the diaper within a relatively narrow tolera"ce.
Controlling the localion of the final cut relative to other diaper features in an eco"G",ically viable way has been and continues to be problerr!atic for diaper manufacturers. Va, ialion in the placement of the knife cut is inherent in the diaper manufacturing line equi~,,nent due to a number of factor~
including equipment wear variations in raw materials etc. Such variation in the final cut results in sequential pads that alternate between long and short W 096/29966 PCTrUS96/0238S

lengths. Web tension and temperature variations also occur when the pull rolls in the manufacturing line expand or contract as the line is placed into production. The increase in temperature makes the roll softer allowing the web to co"",,ess the rolls. As the rolls are co",pressed the surface of the roll increases i"creasing the circu",re,ence of the roll. This results in an increase in the web speed through the roll. The diaper pads are advanced into the final knife with the increased effective pull roll speed, and as a result, beyi"n;"y from a cold start the final cut dislance can shift significantly.
The variation in the final knife placement may steadily trend from one side of the specificalion timit to the other in a slllo~tll llallsiliol" II,erefore making the detection of unacceptable variation difficult. Detecting un~cceplable va, idtiOI) was previously left to the operators of the production line. This has been proven to be unacceptable in many instances bec~se the variation can go un-lelecte~l Even when the va~ialiGn can be detected by the line o~,~ralor it is usually at a point in time where an unacce~.lable level of product must be scrapped. Furthe""ore, inefficiencies are created beG:~use once the u"acceptable variation is detecte-l the opardlor must manually adjust the system to cor,e~ l the final knife placement.
Aulc""dlic regisl,cllio,, control systems have been employed in web ~rocessi,)y ap,~,ardlus to overcome the problems of manual dete~;tio". For exdl "ple aulor"alic regisl. dlion control systems have been used in the manufacturing of price tags. In these systems, the tag web being fed is cut while its cut l~osil;on is Col,slanlly cc,lected by a rotary blade. The blade isadjusted so that it can cut a variety of price tag webs having dirrerent cutting,c.itches or intervals. In these systems, after a tag is dete- te- I having a new cutting dislanc3 the cutter is adjusted to correspond to the correct cutting ,uosilion. This type of system has not been used in controlling the knife placement along the diaper web hec~ ~se the systems were not designed to acco"""odale extensible webs used in diaper production but rather were desiyned as a means for adjusting the knife when a new cutting pitch or interval was nec~ss~- y.
Allelllpts also have been made to control the rate at which a diaper web is fed to the cutter. However, this type of reyislldlion control system is undesirable ber~se it requires multiple sensors lo~ted along the web increasing the complexity of the registration system. In addition adjusting W 096/29966 PCTrUS96102385 the web speed prorluces additional tensile stresses on the web by constantly cl ,angi"g the speed at which it is fed to the cutter. Considering that web tension problems are already inherent in diaper manufacturing lines, this problem is cGi"pounded by control systems which maintain the regisl,dlio" by continually adjusting the web speed.
Tl,ererore there exists a need for an automatic registration control system that controls the placement of the final cut with respect to a pre-selected feature of the diaper which eliminates the problems ~-ssori~led with previous reyi~lldliol) control methods.

SUMMARY OF THE INVENTION
The pr~senl invention provides an automatic regisl. alion control system which elin)i. ,ales the problem of excessive variation in the placement of the final cut that se~ardles an individual ~is~,os~l~le abso,L,ent article such as a diaper, from a continuous web of completed pads. The automatic regisl.dliG" control system of the present invention is a closed loop system that inclucles a driving mechanism for feeding a continuous web of diaper pads toward a rotary cutter. A sensor is positioned along the manufacturing line u,usl.ed.., or downstream of the rotary cutter for detecti"s; at least one preselscted feature of each diaper pad and producing a detection signal when the feature r,~sses by the sensor. A posilio,) resolver deter-,-i.)es the angular posili.,.. of the rotary cutter at the ~..ol.,enl when the preselected diaper feature is detected and the average angular position is ~Ic~ ed from a pre.l~tel,.,;. ,ed number of cutter posiliGns. The average cutter i,ositio" is cG,..~ared to and su6l,dclecl from a target cutter position to produce an error signal. The error signal is then converted into a control signal and supplied to a phase varialor which ~ sts the rotational position of the rotary cutter in response and propG, lionally to the control signal.
The target cutter posiliG" is present at a value dele,-"ined by an o~,erdlor who must manually advance or retard the phase of the final knife ~ until the final cut is in the proper location. Once the proper regislr~lion has been achieved, the operator switches over the line to automatic mode. A
new target position is then ~Icu~ted by using the knife positions co"esponding to the first 25 pads to be scanned by the sensor. An average knife position is continually calculated using the 25 most recent positions stored in memory as scanned by the sensor.

W O 96/29966 PCTrUS96102385 Any deviation of the average knife position from the target value results in the error signal being supplied to a proportional co",pe"salor which ye"erdles the control signal. The control signal is then supplied to a velocity controlled servo which in tum drives, through a gear box a cor,eclion shaft of the phase variator. The phase variator either advances or retards the phase of the flnal knife so as to bring the error closer to zero.The control system detects and adjusts to any cha"yes in the average placer"e"t of the final cut.
Conse~ ~ently, it is an object of the invention to reduce the variation in the placement of a knife cut with respect to a preselected diaper feature by controlling the angular position of a rotary cutter based upon the average angular position of the rotary cutter when the preselected feature is ~etected BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the invention will beco",e apparent upon reading the following detailed description and upon rererei,ce to the drawings, in which it is u"deralood to be illust,aled by a diaper control system but ~,e"erally applicable to dis,uosable absorbent article control syalen~s:
Fig. 1 is a s~;l,e",alic diagram of the final knife cutting operation of a diaper line;
Fig. 2 is a top view of a diaper web wherein the diapers include a fastening system and a core; and Fig. 3 is a flow ~Jiay,d", of the registration control system of Fig. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention has been designed to reduce the variation in the place" ,e, ll of a knife cut along the continuous diaper web using the ap~, oach of a closed loop reyisL, alio" control system. The system may also be used to control the relative posiliol)s of any two features of the diaper so that one feature may be operated on e.g. by allacl"))ent to the diaper cutting from stock, calendaring straining printing spinl,i"g, etc. in special relationship relative to the other feature.
Fig. 1 illustrates the invention as i"co",oraled in controlling the place",e"t of the knife cut in relation to the diaper fastening tabs. In Fig. 1 W 096/29966 PCT~US96/02385 the control system 5 includes two sets of pull rolls 10 for feeding a continuous web 12 of diaper pads along a path towards knife 14. Pull rolls 10 are mecl,ar,ically driven at a preselected speed by extemal means (not shown). The knife includes a blade 16 positioned along the surface of the knife which o,tdles above an anvil 18 for separaLing a completed diaper 20 from the web 12. The se,uardled diaper 20 continues through nip rolls 22 to a final foldir,y station (not shown).
The regial, dlio" control system 5 further includes an ultraviolet lu",i"esce"ce scanner 26, preferably positioned between or after pull roll sets 10a and 10b and selected to detect at least one preselected feature of each diaper 20 on the web 12 as it passes beneath the sca"ner 26. The prere"eJ scanner 26 is an optical sensor such as an Optics LUT 14 sensor manufactured by Sick Co. that emits a mo~lul~ted ultraviolet light beam 28 towards the web. The ultraviolet luminesce"ce sca""er 26 works well for a luminescing preselected feature against a nonluminescing background. When the preselected feature such as when fastening tabs 30 pass beneath the ultraviolet beam 28 the tabs emit light at the same ms~du~ '9d frequency as the scanner 26. If the preselected feature and the background have cJirrerel,l opacities an infra-red sca"ner may be selecte~l The diaper feature selected for detection may be the fasleni.,g tabs 30 as shown in Fig. 2 or may be the edge of the core or the ds~ ~ted fastening surface, etc. The scanner 26 produces a dele~;tio" signal when it cletect~ a cl~a"ge in the light e,.,illed by, reflected by absGrbed by or l,ans"~itted through the pres~l~ed feature..
The sc~n-.er 26 should be mounted as near the knife 14 as practical hsc~ ~s~ as the unit is placed closer to the final cut 33 the control system 5 will better detect chd"ges occurring upstream and hence become more accurate at predicli"g the. point of cut in relation to the fasleni"y tabs 30.
The exact posil;on of the scanner 26 must be balanced with the convenience of mounting the scanner along the line and its likelihood of conldl,lination in various locations.
The angular position of the rotary knife 14 is deter",i"ed by means of a position resolver 32 which reads the angular position of the knife at the time the fdsle"iny tabs are detected by the scanner 26. The angular position of the knife 14 is initially set at a target value determined by an operator who must initially manually advance or retard the phase of the knife until the W O 96/29966 PCTrUS96/02385 location of final cut 33 (Fig. 2) is in the proper location with respect to the fastening tabs 30. Once the proper registration has been achieved the operdlor switches over the line to automatic mode through a control panel (not shown). Once in automatic mode at least five diaper pads and particularly the first twenty-five diaper pads are scanned and the angular position of the cutter is stored and averaged. The average angular position of the cutter represents the average distance between the fasle"iny tabs and the final cut. This average angular posilion is stored as a new target value which is more accurate than the first manually set target value.
As the web is processe~i an average knife position is continually calc~ ted using the twenty-five most recent angular positions of knife 14 and stored in memory as a twenty-five point moving average. Any deviation of the twenty-five point moving average from the new target value results in the generalion of an error signal. The error signal is fed into a propG, lional cG",pe"salor 36 which ge"erales a control signal. The control signal may be supplied to a fixed velocil~ servo 38 or more prererdbly to a velocity controlled servo 38 which drives through a gear box 40 a cGr, ection shaft 42 of a phase variator 44 pfererably manufactured by Specon Co. The phase varialor 44 either advances or ~tards the rotalional phase of the final knife 14 to com~,el ,sale for the error.
Rere"i"y now to Fig. 3 the method of controlling the variation in the place" ,e, ll of a knife cut along the continuous web of diaper pads is illusl,aled. The system has been pruy,dl,,,,,ed to ~e,ro"" the following steps. The first step is establishing a target knife ~JosiliG" illual,aled as block 50. The target knife ~Jo-ciliG" 50 is arrived at by manually advancing ill~J:.ll aled as block 52 or relardi. ~9 illu~ll aled as block 54 the phase of the knife by advd"c;ny illustrated as block 57 or retar.li"y illustrated as block 59 the phase varidlor which adjusts final knife posiliGIl. Once the target knife ,~,osiliG" 50 has been esPhlished the control system is placed in the aulG" ,alic mode illusl, aled as block 60 wherein a new target value illusl,dled as block 62 is dete""i"ed. New target value 62 is the average angular posilion of the knife c~lc~ ted from the first twenty-five diaper pads sca""ed. The target knife position may be adjusted in the automatic mode as illusl,dled by bock 50 by adding or subtldciir)g counts to or from the target ~osilion 50 as illusl, aled by blocks 56 and 58 respectively.

W 096/29966 PCTrUS96/02385 The next step is detecting, illustrated as block 64, the preselected feature of an individual diaper pad along the continuous web of pads and producing a ~etection signal as the preselected feature p~ssed beneath the scanner. The angular position of the knife is read, illusl-ated by block 66, by the position resolver as the fasle,.i.,y tabs are detecl~d. The knife position at the time tabs are detecied is co..,,uared, illuslr~l~d as block 68, to see wl,~ll,er it is within an acceptable range of the new target value. If a knife posilio.. datum point is not within the acce,.lable range, the current twenty-five diaper average, illu~l,ated as block 70, is used as the next data point and the twenty-five point moving average is recalc~ tPd using the twenty-five pad average as the new data point and dropping the 26th (oldest) pad datum point as illusl,dl~.l as block 72. This is done to prevent any one er,o..eous diaper read;"g from unduly ~rt:cti"y the twenty-five diaper average and causing an i.,,,uroper c~.dnye in the position of the knife.
The twenty-five point moving average 72 is suLl-d~;tecJ, illusl.dted as block 74, from the new target value ~0 to produce an error signal, illusl.aled as block 76. The error signal is converted, illuslraled as block 80, by the p.-opo,lio.,al col"p~"salor into a control signal and supplied to the servo for ~r, e.;tio. " illustrated as block 80, of the knife ~,osilic,n. When the system is not in auto...atic mode the error is ignored 81.
By computing a twenty-five point moving average, the phase of the knife will be pro,~,erly adjusted based upon long term variations in the process, rather than any one diaper being i~."~roperly cut. Conse~ently, knife adjusl...e"ls will be more accurate bec~se they will need to be adjusted less frequently. A ~r~det~m~ ed number of diaper pads, e.g. at least 25, may be ignored after start-up of the system. Thus, this number of pads is not used in computing the predel~.."ined average. This allows the system to achieve steady state, ll,ereby ~-~ iny premature adjusl",ents in cutter posilio".
While the invention has been desc. ibed in conjunction with the aulor~ Idlic r~gi~l, dliul ~ control of the knife position with respect to the fast6..i. ~y tabs, dedicated fastening surface or edge of the core, it is to be under:,tood that all~r, .alives, modificalions and variations will be appa, ent to those skilled in the art in light of the foregoing des~ il,lion. For example, the invention can be utilized in other areas of the diaper manufacturing process to control registration of any feature of the diaper relative to another feature W 096/29966 PCTrUS96/02385 of the diaper. Accordi"gly, the invention is intended to embrace all such all~,-,dli-/es, modific~liG"s, and variations as fall within the spirit and broad scope of the appended claims.
WHAT IS CLAIMED IS:

Claims

1. A closed-loop registration control system for a disposable absorbent article manufacturing line comprising:
means for feeding a continuous web of disposable absorbent articles along a path;
a sensor for detecting at least one preselected feature of each disposable absorbent article and producing a detection signal when said feature passes by said sensor;
a rotary cutter, said cutter disposed in angular position relative to said feature;
means for determining the angular position of said cutter at the moment when said preselected feature is detected;
means for calculating the average of a predetermined number of said cutter positions corresponding to a number of consecutive disposable absorbent articles which have passed by said detection means;
means for subtracting from said average cutter position a predetermined target cutter position so as to produce an error signal; and means for converting said error signal into a control signal and supplying said control signal to a phase modifying means;
characterized in that said means for modifying the phase of said rotary cutter modifies said cutter position in response to said control signal.

2. The control system of Claim 1 characterized in that said phase modifying means modifies said cutter position proportionally to said control signal.

3. The control system of Claims 1 and 2 characterized in that said feeding means is at least one set of pull rolls and preferably comprises two sets of pull rolls wherein said scanner is positioned between said pull rolls.

4. The control system of Claims 1,2,and 3 characterized in that phase modifying means is a velocity controlled servo and a phase variator.

The registration control system of Claims 1, 2 3 and 4 characterized in that said continuous web of disposable absorbent articles moves at a predetermined speed, said cutter position being maintained relative to said preselected feature independently of said predeterminined speed and preferably said average predetermined number of said stored cutter positions corresponds to at least five consecutive disposable absorbent articles.

6. A closed-loop registration control system for controlling the placement of a knife cut with respect to a preselected feature of an individual diaper pad along a continuous web of completed diaper pads comprising:
at least one pull roll for advancing said web along a diaper line;
a rotary knife for performing said cut;
a scanner positioned along said diaper line at a location juxtaposed with said rotary knife;
said scanner simultaneously detecting and producing a detection signal as said preselected feature passes by said scanner;
a position resolver connected to said knife for determining the angular position of said knife when said preselected feature is detected;
means for calculating an average knife position based upon a preselected number of said preselected feature being detected;
means for subtracting from said average knife position a preselected target knife position,thereby producing an error signal;
a proportional compensator for converting said error signal into a control signal; and a servo, which in response to said control signal, drives a phase variator to correct the placement of said knife cut.

7. The control system of Claim 6 characterized in that said cutter position for each said diaper is determined to be inside or outside a predetermined range, and preferably if said cutter position is outside said acceptable range, said average of said predetermined number of each pads is used as the next cutter position in calculating said average.

8. The control system of Claims 6 and 7 characterized in that, immediately after start-up of said system said system does not make a change in said position of said cutter until a predetermined number of positions of said preselected features have been determined.

9. A method for controlling the angular position of a cutter in a diaper line comprising the steps of:
establishing a target knife position;
detecting at least one preselected feature of said diaper pad and producing a detection signal as said feature passes by a detection means;
determining an angular position of said knife when said preselected feature is determined;
storing said angular position;
comparing said angular position to said target position;
calculating an average knife position from a predetermined number of stored angular positions corresponding to a number of consecutive pads which have passed by said detection means;
subtracting said target position from said average position to produce an error signal;
converting said error signal into a control signal and supplying said control signal to a cutter position modifying means; and modifying said angular position of said cutter in response to said control signal.

10. The method of Claim 9 characterized in that said detecting step further comprises the steps of:
emitting a light beam by said detection means upon said web;
detecting a change in said light beam caused by said preselected feature of said diaper pad as said preselected feature moves relative to said detection means; and sensing said change in said light beam, and preferably said step of modifying said angular position of said cutter further includes the step of driving a phase variator connected to said cutter.