The invention relates to an apparatus and a method in connection with a headbox of a paper machine or the like.

A patent related to EMFi film technology is known from US 4, 654, 546. The ar- rangement according to the US publication is based on EMFi film technology, which is a variant developed from PVDF film. The film is a 0.05... 0.3 mm thick elastic polypropylene-based piezofilm. A change, brought about by a force, in the thickness of the EMFi film generates a voltage proportional to the force. On the other hand, a change in the thickness of the film can be brought about by means of a voltage. This film can be freely moulded into various measuring tapes, plates, etc. Today, the film is being used especially in keyboards for terminals and in loudspeakers.

This application discloses a new way of controlling the stock flow in connection with a headbox of a paper machine by affecting the stock flow by means of a so- called film matrix, whereby, by means of a voltage introduced into the film ma- trix, a change in the volume of the stock flow is provided and a force is directed at the stock flow. The frequency and/or amplitude of vibration of the film matrix is changed by changing the voltage signal introduced into the film matrix and thus, through the vibration of said film matrix, the stock flow is controlled by generat- ing, in an embodiment of the invention, turbulence in the stock flow or by generat- ing, by means of the film matrix, vibration in the stock flow, which vibration extin- guishes/damps an interfering signal, caused e. g. by a pump, in the stock flow.

In connection with the headbox of a paper machine, different sensors can be used for producing measurement data and for controlling the headbox of the paper ma- chine. It has been difficult to produce said measurement data with traditional sen- sor technology. This invention discloses a measurement based on film technology for controlling the headbox. This application further discloses the use of a film matrix also for controlling the degree of turbulence of the stock flow. Control of the degree of turbulence takes place by feeding a voltage signal into the films, the frequency/amplitude of which signal is regulated. Said control of the degree of turbulence can be done with a separate film matrix that performs turbulence con- trol and the control can be based on the use of a matrix that carries out a separate measurement or the same film matrix can serve both as a measurement matrix and as a matrix that controls the degree of turbulence.

A surface element matrix is formed out of the film in a desired area of the head- box flow surface. Areas suitable for use are, for example, the upper and lower surfaces of the slice channel and the surfaces of vanes in the slice channel. The spacing of the elements in the machine and cross directions is chosen as desired, e. g. 1 mm. A conductor for the electronics is provided from each element.

In order to create turbulence the EMFi surface elements are fed with a phased voltage signal, the frequency and amplitude of which can be changed and thus regulated. A change in the film thickness caused by voltage brings about a volume change in the space inside the film, which volume change further causes the liquid to be displaced and thus creates turbulence. The magnitude and generation of tur- bulence on each matrix element or matrix element group can be controlled by means of amplitude regulation and time phasing of successive film elements with respect to the measurement process.

The turbulence can be measured by measuring the voltage signals coming from the different elements of the film matrix and by forming a spectrum out of said

signals e. g. relative to time and/or relative to amplitude and relative to the position of the matrix element and relative to time.

In the arrangement according to the invention the turbulence of a paper stock flow or the like can be measured in the headbox and after this it can be adjusted as de- sired e. g. in the area of the slice channel of the headbox by conducting a voltage to the matrix elements of the film matrix and by generating a force by means of them, which force is directed at the stock flow.

The damping of pressure variations occurring in the short circulation of a paper machine or the like to a level at which harmful basis weight variations do not oc- cur has to be carried out passively, in most cases by means of an air cushion. Due to the lack of a suitable actuating means producing pressure variations it has not been possible to use active dampers.

The pressure variations are measured at a suitable location in the slice of the headbox with a regular pressure sensor or with a film like the one known by the trade name EMFI. The measurement signal is processed so that a voltage signal can be formed, with which voltage signal another film of the type mentioned above and located before the place of measurement in the process is controlled, which film generates pressure variation oppositely phased with respect to the ex- isting (measured) pressure variation so that the pressure variation can be optimally minimized.

The pressure-measuring film may also be located before the headbox, in which case it can be attached, for example, to an inner wall of a pipe, most advanta- geously so that the film is annular or tubular. The length of the film in the longi- tudinal direction of the pipe must be shorter than 1/2 of the wavelength correspond- ing to the highest frequency desired to be damped. In addition, to guarantee a good damping result, it is also possible to use another pressure sensor disposed in

the headbox. The measurement of the pressure variations can also be carried out by traditional pressure sensors only.

A film producing counter pressure can similarly be attached to the inner wall of a pipe, and it is advantageously annular or tubular in shape and size. The efficiency can be improved especially at low frequencies, if the counter pressure is formed by using several separate tubular film sections, in which case they are controlled so that the highest frequencies are compensated by one film element only, and, as the frequency becomes lower, more and more elements are used depending on the frequency. Several elements may also be used for damping high frequencies, when the voltage signals are appropriately phased.

By means of the arrangement according to the invention an advantageous damp- ing system can be provided compared, for example, to air cushion arrangements.

At the same time many disadvantages caused by the use of an air cushion can be avoided (overflow, surface measurement, contamination, etc.).

A surface element matrix is formed out of the film in a desired area/areas. Areas suitable for use are, for example, an equalization chamber or a slice channel of a headbox. The spacing of the elements in the machine and cross directions is cho- sen as desired, e. g. 1 mm. A conductor for the electronics is provided from each element.

One matrix produces measurement data on the changes in the amplitude of vibra- tion, the other generates a change of volume/a force component for damping the vibration.

In order to create a damping force the EMFi surface elements are fed with a phased voltage signal, the amplitude and/or frequency of which can be changed. A change in the film thickness caused by voltage brings about a volume change in the space inside the film, which volume change further causes the liquid to be

displaced, and thus provides damping. The damping by each matrix element or matrix element group can be controlled by means of amplitude regulation and time phasing of successive film elements with respect to the measurement proc- ess.

The damping can be measured by measuring the voltage signals coming from the different elements of the film matrix and by forming a spectrum out of said sig- nals e. g. relative to time and/or relative to amplitude and relative to the position of the matrix element and relative to time.

In the arrangement according to the invention the pressure variations of a stock flow or the like, caused, for example, by the pumping of stock and/or by the op- eration of a separating means such as a screen, can be measured in the headbox and/or in a pipe system and after this said pressure variations can be damped by conducting a voltage to the matrix elements of a film matrix and by generating a volume change/a force by means of them, which force is directed at the stock flow. The amplitude and phasing of the voltage provided has been provided based on the pressure amplitude measured. The direction of the force applied from the film matrix is opposite to the direction of propagation of pressure pulses. In such a case the force applied from the matrix extinguishes or damps the pressure vibra- tion.

The film matrix advantageously comprises one or more films, and the film matrix may be of the width of the headbox.

A paper machine or the like refers to a paper, board and tissue machine and a che- mical pulp dryer.

The apparatus and method according to the invention are characterized in what is presented in the claims.

The invention will now be described with reference to some preferred embodi- ments shown in the figures of the accompanying drawings, to which embodiments the invention is, however, not intended to be solely confined.

Figure 1A shows an embodiment of the invention in which a separate measure- ment matrix is arranged in a slice channel of a headbox and a separate matrix con- trolling the degree of turbulence is arranged in an intermediate chamber of the headbox.

Figure 1 B illustrates the formation of matrices according to Figure 1 A.

Figure 1C shows an embodiment of the invention in which a turbulence- generating film matrix is disposed in a slice cone of a headbox.

Figure 1D is a sectional view along the line 1-1 in Figure 1C.

Figure 1E shows the operating principle of one matrix element of a film matrix when a force is applied to the film matrix.

Figure IF shows the operation of one matrix element of a film matrix when a voltage change is introduced into the film matrix.

Figure 2 shows an embodiment of the invention in which a separate measurement matrix is arranged in a slice channel of a headbox and in a stock inlet pipe system and a separate matrix controlling the damping is arranged in the stock inlet pipe system of the headbox.

Figure 3A shows an electronics diagram of the measurement matrix related to the embodiment of Figures 1A and 1B and 2.

Figure 3B shows an electronics diagram of the matrix controlling the flow accord- ing to the embodiment of Figures 1A, 1B and 1C, 1D and of Figure 2.

Figure 1A shows a headbox 100 of a paper machine or the like according to the invention, in which headbox film technology is applied in the measurement of the degree of turbulence of a stock flow (arrow Ll) and in the regulation of the degree of turbulence of the stock flow. As shown in Figure 1A, the headbox 100 com- prises an inlet header Jl, from which the stock is passed via tubes 11 al 11 a2... of a tube bank 11 to an intermediate chamber E and further from the intermediate chamber E via turbulence tubes 12al, 12a2... of a turbulence generator 12 to a slice channel 13 and from there further onto a forming wire H,.

As shown in Figure 1A, the headbox 100 of the paper machine comprises in its connection film matrices lOa and lOb. The measuring film matrix lOa comprises matrix elements 1 Oal., lOal. 2... lOa2. 1, lOa2. 2... and the film matrix lOb controlling the degree of turbulence comprises matrix elements 10bl. l, lObl. 2... lOb2. l, lOb2. 2.... The matrix elements 10al. 1, 10al. 2... l0az, l, lOa2. 2... are disposed in the slice channel 13 of the headbox of the paper machine, on an upper wall 13al or vanes nl, nl of the slice channel 13. In the embodiment of Figure 1 A, 1 B the ma- trix elements 10al. 1, 10al. 2... 10a2,,, 10a2. 2... are located in the slice channel 13 in different width positions of the headbox and further in different length positions of the headbox seen in the machine direction. Correspondingly, the matrix ele- ments lObl.,, lObl, 2... lOb2. l, lOb2. 2... located in the intermediate chamber E are located in different width positions of the headbox and further, seen in the ma- chine direction of the paper machine or the like, in different length positions.

Measurement data is produced from the film matrix lOa via a line t, to a central processing unit 50, and the film matrix lOb located in the intermediate chamber E is controlled based on said measurement data by means of the central processing unit 50 via a line t2, which film matrix creates a force/forces for regulating the degree of turbulence of the stock flow Ll based on said measurement data. The film matrix lOa is observed so that any change in pressure/force caused by the

stock of the headbox 100 and directed at each matrix element 10al.,, l Oa1. 2... l Oa2. l, l Oa2. 2.. of the film matrix-and the resultant change in voltage-are measured. Based on said change, the stock flow in the intermediate chamber E in the width position of said measuring matrix element or matrix element group lOal, lOa2... lOal. l, lOal. 2... lOa2. l, lOa2. 2... of the headbox 100 is regulated by producing a change in the volume of the matrix element or matrix element group 10b).), 10b). 2... 10b2. j, 10b2. 2... situated in the corresponding width position of the headbox, and thereby affecting the stock flow Li in the headbox 100.

Figure 1B shows the film matrix 10a disposed on the upper wall 13a of the slice channel 13 of the headbox and the film matrix lOb used for controlling the degree of turbulence disposed in connection with the intermediate chamber E of the headbox 100. The slice channel 13 comprises on the upper wall 13au the film ma- trix 10a comprising the matrix elements 10al. 1, 10al. 2... 10a2.,, 10a2. 2... Each ma- trix element 10al. 1, 10al. 2... lOa2. l, lOa2. 2... of the film matrix 10a measures the state of turbulence of the stock flow Ll at that particular point as changes in the state of pressure of said point. Said changes in the degree of turbulence of the stock flow thus manifest themselves as pressure changes observed by the matrix elements lOal. l, lOal. 2... lOa2., lOa2. 2... of the film matrix 10a. Information on said changes in the state of each matrix element 10al. 1, 10al. 2... 10a2,,, 10a2. 2... or matrix element group of the film matrix 10a is transmitted via the data transfer line ti to the central processing unit 50. As illustrated in the figure, the voltage data is passed from the central processing unit 50 to the film matrix lOb in the intermediate chamber E of the headbox 100, the function of which film matrix is to generate the desired changes in the degree of turbulence of the stock flow based on the measured pressure differences. Thus, from the film matrix 10a shown in Figure 1B, the data on the pressure change is provided to the central processing unit 50, and, based on said data, the desired voltage is produced in the other film matrix 10b, in its different matrix elements 10b).), 10b). 2... in order to generate the desired degree of turbulence in the stock flow. Said measurement data is passed via the data transfer line t, to the central processing unit 50, from where,

after said data has been processed, instruction data is provided as a voltage for each particular matrix element 10b lOb2... lObl. l, lObl. 2... lOb2., lOb2. 2... of each force-producing film matrix 1 Ob via the data transfer lines t2.

Figure 1C shows an embodiment of the invention in which a headbox 100 com- prises an inlet header Jl, thereafter a tube bank 11, an intermediate chamber E and after this, in the flow direction of the stock, a turbulence generator 12 and a slice channel 13. The slice channel has vanes ni and n2. Turbulence-generating matrix films lOb of the invention extending across the width of the headbox are disposed in the slice channel confined by the surfaces of an upper wall 13au and a lower wall 13a2 of the slice channel 13. Matrix films lOb extending across the width of the headbox are also disposed on the surfaces of the vanes Ut and n2. Control is passed from a central processing unit 50 via data transfer lines tl to the film matri- ces lOb for regulating the degree of turbulence of the stock flow Ll in the headbox 100.

In the embodiments of Figures 1A, 1B and 1C, 1D the degree of turbulence of the stock flow can be regulated by regulating the phasing and/or amplitude of the voltage signal fed into the matrix elements of the film matrix 10b. A paper ma- chine or the like refers to a paper, board or tissue machine and a chemical pulp dryer.

Figure 1D shows the apparatus of Figure 1C taken along the sectional line 1-1. The turbulence-generating film 1 Ob extends across the entire width of the slice channel 13 of the headbox.

Figure 1E illustrates measurement taking place by means of a film matrix. The matrix element 10au of the film matrix lOa comprises a voltage line el, e2. When a force AF is directed at the film matrix, the film matrix is compressed causing a change in the electric charge AQ of the film, which can be seen as a voltage change AU across the film matrix i. e. between its upper and lower surfaces fi and

f2. The greater the force AF applied to the matrix element 10ai, the greater the force of the measurable voltage change AQ in the matrix element between the surfaces f, and 2 of the film matrix.

Figure 1F illustrates the matrix element lObl of the film matrix 1 Ob in operation in which a voltage difference AU is generated between the surfaces f, and 2 of the film matrix lOb, which voltage difference causes a change AS in the thickness of the matrix element lOb, of the film matrix lOb. The greater the voltage difference AU that is generated between the top and bottom surfaces fi and f2 of the matrix element l Obl, the greater the change AS caused in the thickness of the film matrix.

Figure 2 shows a headbox 100 of a paper machine or the like according to the invention in which film technology is used in the measurement of the pressure variations of the stock flow and in the damping of the pressure variations of the stock flow. As shown in Figure 1C, the headbox 100 comprises an inlet header Jl, from which the stock is passed via tubes 1 lal l la2... of a tube bank 11 to an in- termediate chamber E and further from the intermediate chamber E via turbulence tubes 12au, 12a2... of a turbulence generator 12 to a slice channel 13 and from there further onto a forming wire H1.

As shown in Figure 2, the headbox 100 of the paper machine comprises in its connection film matrices lOa and lOb. The film matrix lOa comprises matrix ele- ments 10al. 1, 10al. 2... 10a2.), 10a22... and the film matrix lOb comprises matrix elements lOb. l, lObl. 2... lOb2. l, lOb2. 2.... The matrix elements lOal {, lOaz. 2... lOa2. l, lOa2. 2... are disposed in the slice channel 13 of the headbox of the paper machine and in the stock inlet pipe system 30, via which the stock is passed to the headbox 100. The matrix elements 10a 1, 10al. 2... lOa2. l, lOa2. 2... may be located in the slice channel 13 in different width positions of the headbox and further in different length positions of the headbox seen in the machine direction. They may also be in the intermediate chamber E of the headbox. The matrix elements lOb).), 10bu. 2... lOb2.,, lOb2. 2... which are located in different length positions in the stock

inlet pipe system 30 on the upstream side of the measurement matrices lova, when seen in the stock flow direction Li. Measurement data is provided from the film matrices lOa via a line tl to a central processing unit 50, and the film matrix lOb located in the pipe 30 is controlled based on said measurement data by means of the central processing unit 50 via a line t2, which film matrix creates a force/forces through volume changes for damping the pressure variations of the stock flow.

The film matrix lOa is observed so that any change in pressure/force caused by the stock and directed at each matrix element lOal. l, lOal. 2... 10a2. l, l Oa2. 2... of the film matrix-and the resultant change in voltage-are measured. Based on said change, the pressure variations in the stock flow Ll are damped via the matrix ele- ment or matrix element group lOb,. l, lObl. 2... lOb2. 1, lOb2. 2...

Figure 2 shows a film matrix lOa disposed in the slice channel 13 of the headbox and in the pipe 30 and a film matrix lOb used for controlling the damping dis- posed in the tube 30. The film matrix lOa formed of the matrix elements 10al. 1, lOal. 2... lOa2., lOa2. 2... Each matrix element 10al. 1, 10al. 2... 10a2. 1, lOa2. 2... of the film matrix lOa measures the pressure state of the stock flow at that particular point as changes in said state. Said changes in the pressure of the stock flow, caused by a pump and/or a separating means such as a screen, are transmitted di- rectly to the matrix elements of the film matrix as pressure changes, which are transmitted further by the matrix elements 10al. 1, 10al. 2... 10a2.,, 10a2. 2... of the film matrix lOa as changes in their voltage. Information on said changes in the state of each matrix element lOal. l, lOal. 2... lOa2. l, lOa2. 2... or matrix element group of the film matrix lOa is transmitted via the data transfer line tl to the cen- tral processing unit 50 and from the central processing unit 50 further, as illus- trated in the figure, to the film matrix lOb in the stock inlet pipe 30 leading to the headbox 100, the function of which film matrix is to generate, based on the meas- ured pressure differences, the desired damping in the pressure variations of the stock flow. Thus, from the film matrices lOa shown in Figure 1C, the data on the pressure change is provided to the central processing unit 50, and, based on said data, the desired voltage is produced in the different matrix elements 10bl. 1,

lOb) 2... of the film matrix lOb producing a force/a volume change, in order to generate the desired pressure damping in the stock flow. Said measurement data is passed via the data transfer line tl to the central processing unit 50, from where, after said measurement data has been processed, instruction data is provided as a voltage for each particular matrix element lOb, lOb2... lOb. , lObi. 2... lOb2. l, lOb2. 2... or matrix element group of each force-producing film matrix lOb via the transfer lines t2.

As shown in Figure 2, the matrix elements 10al. 1, 10al. 2... lOa2. l, lOa2. 2... of the measurement matrix lOa are disposed in the slice channel 13 in different length positions in the machine direction and in different width positions of the headbox relative to the width of the machine. Correspondingly, the other measuring film matrix lOa is disposed in the stock inlet pipe 30 so that it is located, as to the ma- trix elements, in different length positions of the stock inlet pipe 30 and, in addi- tion, circumferentially on the outer circumference of the pipe 30 so that the sur- face of the matrix elements is delimited, directly or via an intermediate part, by the stock flow Li.

The matrix lOb damping the pressure variations is correspondingly disposed in the stock inlet pipe 30 ahead of the measuring matrices 10a, when seen in the stock flow direction LI, and as circumferential structures on the inner surface of the pipe 30.

Figure 3A illustrates the electronics diagram relating to the measuring film matrix lOa of the embodiment of Figures 1A and 1B and 2. The film matrix lOa is also arranged in different width positions of the slice channel of the headbox 100 for producing voltage data from each matrix element 10al, lOa2... 10al. 1, 10al. 2... l0az, l, lOa2. 2... of the film matrix further via pre-amplifiers 14al, 14a2... 14a6 to a multiplexer 15, which transmits the signals further via a buffer-amplifier 16 to a data collecting means, such as the central processing unit 50. This way the voltage data can be collected from each matrix element lOal. l, lOal. 2... lOa2 l, lOa2. 2... and thus an amplitude spectrum as a function of time can be obtained, which ampli-

tude spectrum correlates with the changes in the degree of turbulence or in the pressure variations occurring in the stock flow of the headbox. The measured change in the degree of turbulence or in the pressure variations correlates with the change in the pressure of the stock flow, which, in turn, corresponds to each measured change in the voltage of the matrix elements 10al. 1, lOa. 2... lOa2. l, 10a2. 2.... or matrix element groups of the film matrix. When the matrix elements 10al. 1, 10al. 2 of the film matrix lOa are located at different points in the headbox, a measuring field can be formed by means of the matrix elements 10al, lOa2...

10al. zu 10al. 2... lOa2. l, lOa2. 2... Correspondingly, the matrix elements lOb ;), lObl. 2... lOb2. 1, lOb2. 2.... of the film matrix lOb form a power input/state change field for regulating the degree of turbulence in the stock flow Ll or for evening out of the pressure variations caused by pumps and/or a separating means such as a screen, when passing the stock flow to the headbox of the paper machine or the like.

Figure 3B illustrates the electronics diagram relating to the film matrix lOb that controls the flow according to the embodiment of Figures 1A, 1B and 1 C, 1 D and 2. In Figure 1H the controlling of the stock flow Ll of the headbox 100, such as the controlling of the degree of turbulence and of the damping, is further affected by producing, based on the measurement, a certain voltage in the film matrix lOb controlling the flow and located in the intermediate chamber E or in the slice channel 13 of the headbox 50 or when evening out the pressure variations of the stock flow in the inlet pipe 30 leading to the headbox 100. This makes it possible to introduce a voltage of the desired magnitude from the central processing unit 50 into each matrix element lObl, lOb2... lObu, lObi. 2... lOb2. i, lOb2. 2... of the film matrix lOb or into a separate group formed by them and located, for example, in the intermediate chamber or in the pipe 30. A power source 17 produces energy for a pulse generator 18, which generates pulses of the desired voltage for a con- trol 19 of analog switches 19a,, 19a2... 19a6 for producing a voltage of the desired magnitude for each matrix element lObl. l, lObl 2... lOb21, lOb2. 2.... of the film ma- trix lOb via amplifiers l9al, 19al... 19a6. Thus, by means of the voltage produced

into each matrix element lObl, lOb2... lObl., lObl. 2... lOb2. 1, lOb2. 2... of the film matrix lOb, the matrix element in question can be made to expand and bring about a change of state/a force at said matrix element or group of matrix elements in the intermediate chamber E of the stock flow Ll (embodiment of Figures 1A, 1B) or in the slice channel 13 (embodiment of Figures 1C, 1D), or in which pipe 30 the pressure variations in the stock flow are damped by means of the film matrix lOb according to the embodiment of Figure 2.