WO2014007704A1

WO2014007704A1 - Force measurements for evaluating presence or amount of components in a manufacturing line for hygiene products

Info

Publication number: WO2014007704A1
Application number: PCT/SE2012/050789
Authority: WO
Inventors: Per Floberg
Original assignee: Sca Hygiene Products Ab
Priority date: 2012-07-05
Filing date: 2012-07-05
Publication date: 2014-01-09

Abstract

The present invention relates to a method for evaluating components in a manufacturing line for hygiene products, particularly diapers, comprising, for each product, - arranging a first component (1 ) and a second component (2) to be assembled in a superposed relationship, Feeding said first component (1) and said second component (2) through a nip for assembly of said components, the nip being formed between a first and a second roller (R1, R2) being arranged with a predetermined distance to each other, - Measuring the force (F) in the nip between said first and second rollers (R1, R2) during the passage of the first and second components (1, 2) through the nip, - Using said measured force (F) for evaluating at least one of the two components (1, 2) passed through the nip.

Description

Force measurements for evaluating presence or amount of components in a manufacturing line for hygiene products.

TECHNICAL FIELD

The present invention relates to a method for evaluating components in manufacturing line for hygiene products, particularly diapers. Moreover, the invention relates to an apparatus for assembly of at least two components in hygiene product, particularly a diaper.

BACKGROUND OF THE INVENTION

In manufacturing lines for hygienic products, there is a need for assembling various components to each other to form the complete hygienic products.

As an example, when forming diapers, one such assembling step may comprise the fastening of a tab onto a rear wing material for a diaper. Conventionally, the tab may be fastened to the rear wing material using a fastening component sueh as an adhesive. For accomplishing the assembly of the tab to the rear wing material, the tab may be arranged in a superposed relationship to the rear wing material, with an amount of adhesive present in between the ta and the rear wing material. Thereafter, the tab and rear wing material with the adhesive in between may be fed through a nip formed between two rollers, whereby pressure is applied to the components such that the tab is assembled with the rear wing material.

To ensure that the tab will become fastened to the rear wing material in a secure manner, that is, so that the connection will be able to withstand the forces involved during normal use of the diaper, it is of importance that the amount of adhesive applied between the rear wing material and the tab is sufficient.

For applying the adhesive to the rear wing material and/or the tab, it is known to use a metering nozzle. However, the metering nozzles may sometimes become faulty or obstructed and not deliver the intended amount of adhesive. This is problematic, since, as explained in the above, an insufficient amount of adhesive might render the connection between the tab and the rear wing material so weak that it breaks during normal use of the diaper. To control the amount of adhesive applied, it may be possible to introduce a flow senso somewhere in the adhesive delivery system. However, such solutions tend to be relatively expensiv and/or cumbersome.

Accordingly, there is a need for an alternative solution enabling the evaluation of the amount of adhesive present between a tab and a rear wing material to be fastened to each other. in a more general formulation of the problem, there is a need for enabling evaluation of components to b assembled to each other in a superposed relationship, in a

manufacturing line for hygienic products,

SUMMARY OF THE INVENTION

The above-mentioned need is met by a method for evaluating components in a manufacturing line for hygiene products, particularly diapers, comprising, for each product,

- arranging a first component and a second component to be assembled in a superposed relationship,

- feeding said first component and said second component through a nip for assembly of said components, the nip being formed between a first and a second roller being arranged with a predetermined distance to each other,

- measuring the force in the ni between said first and second rollers during the passage of the first and second components through the nip,

- using said measured force for evaluating at least one of the two components passed through the nip.

In the above, the term "component" is intended to comprise components made of solid materials such as top sheet materials, back sheet matenals, tabs, wings, inlays etc. used in th art. The term is also to encompass fastening components having as primary purpose to connect other components to each other. Such fastening components could be in a viscous state, such as adhesives. Other fastening components could include a solid component, such as adhesive tape fasteners, or mechanical fasteners such as hook and loop fasteners. At least two components to be assembled in a superposed relationship are fed through a nip for assembly of said components, said nip being formed between a first and a second roller. In accordance with the method as proposed herein, the force in the nip between the first and second rollers is measured during passage of the two components. The measured force is used for evaluating at least one of the two components passed through the nip.

The force in said nip will vary depending on the components passed therethrough. For a number of identical arrangements of first and second components, the individual forces measured in the nip during passage of the individual arrangements shall be approximately the same (provided of course that the nominal force applied to the first and second rollers is constant as is conventional during a manufacturing process). However, if some irregularity would occur in one set of first and second components, this will be reflected in the force measured in the nip deviating from the force measured under perfect

circumstances.

The measurement of the force in the nip may be accomplished using relatively simple sensors, which are applied to the already existing equipment for assembling the two components. Accordingly, it may be realised in a simple and inexpensive manner, and without any substantial additions to the space required to house the equipment

Advantageously, the method may comprise;

continuously measuring the force in the nip during passage of the first and second components, so as to obtain a maximum force value in the nip created during passage of the first and second components, and a minimum force value in the ni created before and/or after passage of the first and second components;

creating a difference value between said maximum force value and said minimum force value; and

- using the difference value for evaluating at least one of the two components (1 ,

2) passed through the nip.

The use of a difference value for the evaluation is useful for enabling better precision in the measurements. Preferably, the method may comprise measuring the force in the nip for a number of passages of first and second components through the nip so as to obtain an assembly of force values;

- Evaluating at least one of the two components passed through the ni during said number of passages using said assembly of force values.

Again, using an assembly of values for the evaluation is useful for enabling better precision. This is particularly useful when desiring to evaluate the presence of relatively thin components, or small deviations in the amount of a component, which will only give rise to relatively small deviations of the force in the nip.

The assembly of values may be used in any convenient form, e.g. by forming a mean value thereof. Advantageously, the method may comprise measuring the force in the nip for a number of passages corresponding to at least one full rotation of said rollers. In this case, any deviations in the force in the nip resulting from possible irregularities in the rollers may be compensated for. The force measured in the nip during passage of the at least two components may be used for various types of evaluations.

For example, the evaluation may comprise determining the presence or absence of at least one of said two components. Absence of one of the two components would result in a relatively large deviation from the "normal" force.

Also, or alternatively, the evaluation may comprise determining the amount of at least one of said two components using said force in the nip during passage of the components. This is most relevant for components which may be present in various amounts, such as an adhesive.

Also, or alternatively, the evaluation may comprise using said measured force for evaluating the state of at least one of the first and second rollers.

Fo ail of the above-mentioned evaluations, the skilled person will understand that it is suitable to first determine the force in the nip under normal circumstances, that is with all components present in a pre-deterrrtined amount. To this end, a number of samples may be created during controlled circumstances, for example manually. The controlled samples are fed through the nip, and the force in the nip is measured during passage of the controlled samples, so as to obtain reference values reflecting norma! components. Thereafter, new controlled samples, depicting various errors, may also be created and the force through the nip measured. For example, the effect of a component missing could be measured, or the effect of a faulty amount of a component. Accordingly, a person skilled in the art may create reference values reflecting various errors. The force in the nip may then be measured for each set of components passing therethrough during manufacturing of absorbent products. Using the reference values, deviations in the force measured in the nip may be classified as being cause by the various errors previousl tested, and appropriate measures may be taken to correct the manufacturing line.

Advantageously, the method may comprise arranging a third component in a superposed relationship to said first and second components, and using the measured force in the nip for evaluating at least one of the three components passed through the nip, preferably for evaluating a component being positioned intermediate the others.

One advantage with the proposed method is precisely that it enables evaluation of a component that lies hidden between two other components during a manufacturing step.

Advantageously, at least one of said components is provided as a continuous material web being continuously fed through said nip. Such materials could be any materials used in hygienic products such as baoksheet materials, topsheet materials, etc.

Advantageously, at least one of said components is provided as a material piece, such that material pieces are intermittently fed through the nip for in-line manufacture of hygienic products. In this case, if the force in the nip is continuously measured, each intermittent material piece will be reflected by said measurements.

Advantageously, at least one of said components is a fastening component, preferably an adhesive. The present method has the advantage of enabling measurement for example of the amount of adhesive present between two other components. The method is hence particularly advantageous when the first component is a continuous material web, said second component is a material piece, and a third component being the fastening component is arranged between said first and second components. Preferably, the force measured in the nip is used to evaluate the fastening component, preferably, when the fastening component is an adhesive, to evaluate the amount of adhesive present between the first and the second component during passage through the nip. In particular, the proposed method is advantageous in the situation mentioned in the introduction, when said first material is a rear wing material for a diaper, said second material is a tab for a diaper, and said third material is an adhesive arranged between said rear wing material and said tab, Advantageously, said first and second rollers are arranged in first and second support structures, respectively, and the force between said first and second support structures is measured for calculating said force in the nip during passage of the first and second components. Measuring the force between the support structures is a convenient way of obtaining a measure for calculating the force in the nip.

Advantageously, a nominal force is applied to said first and/or second support structure, urging the first and second support structures together so as to create a pressure in said nip, and the nominal forc is measured for calculating said force in the gap during passage of the first and second components. During function of the manufacturing line, the nominal force would be approximately constant.

Advantageously, and as already outlined in th above, a reference value of the force in said nip is obtained using referenc components prior to performing the method in a manufacturing line, said reference value being used in said evaluation of the first and second components.

Preferably, if the evaluation indicates a missing or faulty component, an indication is presented to an operator of the manufacturing line. This indication could be of any suitable kind, such as a visual or audible alarm. Optionally, certain errors could cause the manufacturing line to automatioaily stop until the cause of the error is removed. In a second aspect, there is provided an apparatus for assembly of at least two components in a hygiene product, particularly a diaper, comprising

a first and a second roller being arranged with a predetermined distance to each other so as to form a nip for passage and assembly of said at least two components, and wherein 5 a sensor is arranged for providing a measure relating to the force in said nip during passage of the two components thereto, and a processor unit is arranged to which said measure is fed, and the measure is used for evaluating at least one of th two

components passed through the nip.

10 Advantageously, said apparatus comprises a first and a second support structure, for rotatab!y supporting said first and second roller, respectively, and said sensor being arranged for measuring the force between said first and second support structures during passage of the at least two components through the nip,

15 Advantageously, the apparatus comprises a pressure application device for applying a nominal force to said first and/or second support structure, urging the first and second support structures together so as to create a pressure in said nip, wherein said nominal force is fed to the processor unit for use in calculating the force in said nip. The nominal force required is depending on the present situation, e.g. the type of components to be

20 assembled, the properties of a fastening component (when present) etc, For several practical applications in the manufacture of hygiene products, it is believed that the nominal force ma be at least 5 kN, preferably at least 10 kN.

Suitably, the sensor may be is adapted to detect forces in the range 0-20 kN, preferably 5- 25 20 kN . Such forces are generally of a size being relevant for said evaluation in a ni for assembly of components in a manufacturing line for hygienic products.

The sensor may advantageously be a load cell.

30 Suitably, the rollers are metal rollers, preferably steel rollers. The flexibility of the rollers may be selected depending on the requirements of the components to be assembled.

To enable comparative measurements, the behaviour of the rollers in the nip should be relatively stable. The necessary precautions for this may be taken by the person skilled in 35 the art by avoiding such conditions that could possibly create variations diminishing the precision of the force measurements, e g. very flexible rollers, or very thin rollers. Moreover, the suspension of the rollers could preferably be substantially inflexible.

In an advantageous embodiment, the first roller is flat and the second roller is patterned.

5 Advantageously, the rollers may be heatabie for forming a thermomechanical nip.

Suitably, the apparatus comprises first and second supports structures, and

Said first and second support structure each support the first or second roller on the two lateral sides of said roller, and

0 a senso is arranged for measuring the force between said first and second support structures on both said lateral sides .of the rollers, the measured force from both sensors being fed to the processor unit.

The provision of two sensors, one on each side of the rollers, enables a convenient and5 stable measurement of the force in the nip.

Advantageously, the nominal pressure applied to the first and/or second support structure is fed to the processor unit, for forming a difference between the nominal pressure and the force measured by the sensor between the first and second support structures, saidG difference corresponding to the force between the first roller and the second roller in th nip.

In a third aspect of the invention, there is provided the use of a force measured in the nip between a first and a second roller, during the passage of at least two components5 through said nip, for evaluating said components in a manufacturing line for hygienic products. tt will be understood that the said use may be combined with ail of the features and advantages of the method and apparatus in accordance with the previous aspects of the0 invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention wili be described by means of an exemplary embodiment, and with reference to the accompanying drawings, wherein:

5 Figs 1 and 2 schematically illustrate an embodiment of an apparatus for performing a method in accordance with the invention,

Fig. 3 schematically illustrates an example of superposed components to be assembled in accordance with the invention;

Fig. 4 schematically illustrates another example of superposed components to be assembled in accordance with the invention;

Fig. 5. is an example of the force between support structures during passage of a series of superposed components through the nip; and

Fig. 6 is an example of the force in the nip as dependent on the amount of adhesive between a first and a second component being assembled in the nip.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figs 1 and 2 illustrate a embodiment of an apparatus for carrying out a method in accordance with the invention. The apparatus comprises a first roller R1 and a second rolle R2 being arranged with a predetermine distance to each other, and hence forming a nip for passage of components to be assembled.

In the illustrated embodiment, the first and second rollers R1 and R2 are ratably arranged in a first support structure S1 and a second support structure S2, respectively. A conveyor 5 is arranged to pass through said nip, and for supporting a number or superposed components 4 to be assembled in the nip.

The force F in the nip between the first and second rollers R1 and R2 is to be measured for evaluation of at least one of the components passed through the nip. To this end, in the present embodiment, the force F2 between the support structures ST and S2, and the nominal force F1 , in thi case applied to the first support structure ST, is measured. The forces F2 and F1 are fed to a processor unit, where the force F in the nip is calculated as the difference between the nominal force F1 and the force between the support structures F2 (F= F1-F2),

The force F2 between the first and second support structures 81 and S2 may suitably be measured using a sensor, in this case a force transducer, arranged betwee said support structures S1 and S2. For example, the sensor could be arranged in mechanical stops provided between the support structures. The nomina! force F1 may be selected depending on the requirements of the particular components. For example, when assembling a rear wing material to a tab using an adhesive, the nominal force F1 might be about 6 Bar. The selection of rollers R1 and R2 may likewise be made depending on the requirements of the particular situation. Good results have been obtained using combinations of a patterned roller and a smooth roller, and with various patterns of said patterned roller. Also, the rollers could advantageously be heated so as to form a thermomechanical nip. The superposed components 4 to be assembled should comprise at least a first and a second component. Fig. 3 illustrates an example where a first component 1 , a second component 2 and a third component 3 is to be assembled. In this example, the first component 1 and the second component 2 are both separate pieces of material, whereas the third component 3 is positioned in between the first and the second component 2 and comprises a viscous material, namely an adhesive.

Another example is illustrated in Fig. 4, where the second component 2 comprises a continuous piece of material, instead of a separate piece of material. The nominal force F1 and the force measured between the support structures S1 and S2 are fed to a processor unit where the force F in the nip is calculated and used for evaluation of at least the first and/or second component.

The forces could advantageously be measured with a suitable measuring frequency during passage of the components through the nip. For example, a measuring frequency could be about 100 Hz, which gives a number of measured values during the passage of the components through the nip. Th relevant forces may then be calculated as a mean valu of the sample measurements. Moreover, the method may comprise continuously measuring the force in the nip during passage of the first and second components, so as to obtain maximum force value in the nip created during passage of the first and second components, and a minimum force value in the nip created before and/or after passage of the first second components. The term "continuously" herein need not be taken literally, but could typically include performing measurements with a suitable measuring frequency as outlined in the above. The maximum and minimum force values may advantageously be used to form a differential value, which in turn may be used for evaluating at least one of the

components. Fig. 5 illustrate the force F2 measured between the support structures S1 and S2 during passage of a number of assemblies including several components, in this case a tab, a rearwing material and an adhesive in between. Each down peak in the diagram corresponds to a tab that goes through the nip. Clearly, a missing down peak will correspond to a missing tab in the manufacturing lines. Hence, the presence or absence of a peak in the force curve may be used to evaluate the presence or absence of a component in the manufacturing line.

Rather than simply studying the presence/absence of one single peak, the method may comprise measuring the force in th nip for a number of passages of first and second components through the ni so as to obtain an assembly of force values; and to evaluate at least one of the two components during said number of passages using said assembly of feree values, as mentioned in the above. For example, a mean value running over a selected number of passages may be used. The deviation of the mean value from predetermined limits may correspond to the continued absence of a component.

Moreover, due to the increased robustness of this method, it is particularly suitable when desiring to evaluate the amount of a component, e.g. in order to detect that a too small amount of adhesive is present between two other components.

Fig. 8 illustrates an example of the force in the nip F with different amounts of adhesive (measured in gsm) present between a tab and a rear wing material. A curve is formed where a certain amount of adhesive corresponds to a force measured in the nip.

Accordingly, the force measured in the nip may be used to evaluate the amount of adhesive present between the tab and the rearwing material Parameters which could influence the measurement is the speed of the rollers, the size of the gap, and the materials of the components. All these parameters should be kept constant for the measurements to turn out correctly, and if any parameter is changed, new reference values for the force measurements should be performed. Moreover, wear or other irregularities in the rollers may be reflected in the force measurements, and eouid be analysed and compensated for, if necessary. For example, all noncircular wear will caus a periodic pattern in the force curves. To this end, the method may comprise measuring the force in the nip for a number of passages corresponding to at least one full rotation of the rollers. This is particularly advantageous for eliminating any effect of irregularities in the rollers to the

measurements. As may foe gleaned from Fig. 4, there is in this case a sinusoidal variation of the values. This variation may be seen from the maximum values (the top of the peaks) but is more pronounced from the minimum values (th valleys between the peaks).

However, having established any such variations in the measurements, they may be at least partly compensated for by considering an assembly of measurements taken during a full rotation of the rollers when performing the evaluations. Also, the effect of the sinusoidal variation might be otherwise compensated for using mathematical methods, it. will be understood that several variations and alternatives of the method and apparatus as described herein are possible. For example, the method and means for achieving the necessary force vaiues may be varied, and the evaluation methods may be adapted to the circumstances with various types of components to be evaluated.

Claims

Method for evaluating components in a manufacturing line for hygiene products, particularly diapers, comprising, for each product,

- arranging a first component (1) and a second component (2) to be assembled in a superposed relationship,

- Feeding said first component (1) and said second component (2) through a nip for assembly of said components, the nip being formed between a first and a second roller (R1 , R2) being arranged with a predetermined distance to each other,

~ Measuring the force (F) in the nip between said first and second rollers (R1 , R2) during the passage of the first and second components (1 , 2) throug the nip,

Using said measured force (F) for evaluating at least one of the two components (1 , 2) passed throu h the nip.

Method in accordance with claim 1 , comprising

~ continuously measuring the force in the nip during passage of the first and second components, so as to obtain a maximum force value in the nip created during passage of the first and second components (1 , 2) and a minimum force value in the nip created before and/or after passage of the first and second components (1 ,2);

- creating a difference value between said maximum force value and said

minimum force value; and

- using the differenc value for evaluating at least one of the two components (1 , 2) passed through the nip,

Method in accordance with claim 1 or 2, comprising measuring the force in the nip for a number of passages of first and second components through the nip so as to obtain an assembly of force values;

~ Evaluating at least one of the two components (1 , 2) passed through the nip during said number of passages using said assembly of force values.

Method in accordance with claim 3, comprising measuring the force in the nip for a number of passages corresponding to at least one full rotation of said rollers.

5. Method in accordance with an one of the preceding claims, wherein said evaluation comprises determining the presence or absence of at least one of said two components (1 , 2).

6. Method in accordance with any one of the preceding claims, wherein said evaluation comprises determining the amount of at least one of said two components (1 , 2).

7. Method in accordance with any one of the preceding claims, comprising arranging a third component (3) in a superposed relationship to said first and second components (1 , 2), and using the measured force (F) in the nip for evaluating at least one of the three components (1 , 2, 3) passed through the nip, preferably for evaluating a component (3) being positioned intermediate the others (1 , 2).

8. Method in accordance with any one of the previous claims, wherein at least one of said components (1 , 2, 3) is a fastening component, preferably an adhesive.

9. Method in accordance with claim 8, wherein said first component is a continuous material web, said second component is a material piece, and a third component being the fastening component is arranged between said first and second

components.

10. Method in accordance with claim 8 or 9. wherein said force measured in the nip is used to evaluate the fastening component, preferably, when the fastening component is an adhesive, to evaluate the amount of adhesive present between the first and the second component during passage through the nip.

11. Method in accordance with any one of the previous claims, wherein said first and second rollers ( 1 , R2) are arranged in first and second support structures (S1 , S2), respectively, and the force (F2) between said first and second support structures (S1 , D2) is measured for calculating said force (F) in the nip during passage of the first and second components (1 , 2).

12. Method in accordance with any one of the previous claims, wherein a nominal force (F1 ) is applied to said first and/or second support structure (81 , S2), urging the first and second support structures together so as to create a pressure in said nip, and the nominal force (F1) is measured for calculating said force (F) in the gap during passage of the first and second components (1 , 2).

13. Method in accordance with any one of the previous claims, wherein a reference value of the forc in said nip is obtained using reference components prior to performing the method in a manufacturing line, said reference value being used in said evaluation of

5 the first and second components.

14. Apparatus for assembly of at least two components in a hygiene product, particularly a diaper, comprising

a first and a second roller (R1 , R2) being arranged with a predetermined 10 distance to each other so as to form a nip for passage and assembly of said at least two components (1 , 2),

characterised by

a sensor being arranged for providing a measure relating to the force (F) in said nip during passage of the two components thereto, and

15 a processor unit (C to which said measure is fed and wherein the measure is used for evaluating at least one of the two components (1 , 2) passed through the nip.

15. Apparatus in accordance with claim 14, comprising a first and a second support 20 structure (SI , S2), for rotatabl supporting said first and second roller (R , R2),

respectively, and said sensor being arranged for measuring the force (F2) between said first and second support structures (S1, S2) during passage of the at least two components through the nip.

25 18. Apparatus in accordance with claim 14 or 15, comprising a pressure application

device for applying a nominal force (F1) to said first and/or second support structure (SI , S2), urging the first and second support structures together so as to create a pressure in said nip, wherein said nominal force (F1) is fed to the processor unit for use in calculating the force in said nip.

30

17. Apparatus in accordance with claim 18, wherein the nominal force (F1) applied to the first and/or second support structure is fed to the processor unit (C), for forming a difference between the nominal pressure (F1) and the force (F2) measured by the sensor between the first and second support structures, said difference corresponding 35 to the force (F) between th first roller and the second roller in the nip. 18

18. Use of a force measured in the nip between a first and a second roller, during the passage of at least two components through said nip, for evaluating said components in a manufacturing line for hygienic products.