FI122635B - Determination of modulus of continuous material web - Google Patents

Description

Determination of modulus of continuous material web

Background of the Invention

The invention relates to the determination of the modulus of elasticity of a continuous material web, in particular a paper web. More particularly, the invention relates to the determination of a modulus of elasticity 5 from a continuous material path as the material path passes through a production machine.

One of the commonly defined properties of paper, board or the like is the modulus of elasticity. The modulus of elasticity describes the reversible response of the material to this applied stress, and the modulus of elasticity can be defined as the ratio of the stress to the elongation it produces with the elongation in the linear range and fully recovered upon removal of the tensile stress.

The modulus of elasticity of paper, board or similar affects both the runnability of the production machine and the quality of the end product. Often the end product is given a certain value or value threshold that the elasticity factor must meet. For example, in the case of packaging materials, the odor modulus of Al-15 indicates that the material may tear too easily during packaging. Similarly, when using paper in printed matter, the runnability in printing machines is partly dependent on the modulus of elasticity.

Determination of the modulus of elasticity is conventionally performed using laboratory measurements of the finished material. For example, after a paper machine roll is completed, a sample of paper is taken and taken to a laboratory for measurement. At best, the measurement result is obtained within hours of the machine roll being completed. If the modulus of elasticity deviates significantly from the desired value, at best cm 25 whole rolls of machine roll may be wasted. In addition, it is clear that due to the long delays, it is impossible to quickly adjust my production process with basic measurements in the laboratory.

c ^ Methods for measuring the modulus of elasticity on-line are described in which

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the sensors do not touch the material path. One of these methods is a method based on measuring changes in track width of £ 30. The web width measurement and the mathematical model can be used to estimate the tensile strength ratio and to infer the properties of the paper during production.

o Another known method is to transmit high frequency acoustic

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bursts on the paper surface and observe the correlation of frequency modulation with the paper elasticity.

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The fiber orientation of the paper web can also be used to evaluate the tensile strength of the paper.

All of the above methods for determining paper elastic modulus or tensile strength require specially designed measuring devices for this purpose. The reliability of the acoustic measurement results is also affected by the demanding environment and the high track speed. In addition, acoustic measurement is spot-centered on the material path and thus does not necessarily represent the material properties in its entirety. Mathematical models based on web width measurement, in turn, require extensive research to produce a reliable model.

US 6993964 discloses a method for measuring track velocity and tension in two different track spacing, and from this measured data to determine the modulus of elasticity of the material.

BRIEF DESCRIPTION OF THE INVENTION The object of the invention is thus to provide a method, an apparatus implementing the method, an inverter and a software product so that the above problems can be solved. The object of the invention is achieved by a method, a hardware device, a frequency converter and a software product which are characterized by what is stated in the independent claims. Preferred embodiments of the invention are claimed in the dependent claims.

The invention is based on the use of information obtained from electric motor driving a material web to determine the modulus of elasticity of a material and the quantities derived therefrom. The controlled electric motor drive coupled to the roller provides information on the speed of the track passing through the roller and the applied torque (m 25) on the basis of which the modulus of elasticity is calculated.

An advantage of the method and system of the invention is to achieve simplicity in the implementation of the measuring arrangement. There is no need to place any measuring device on the material web to measure the elasticity C 1x.

30 This avoids the need for installation and maintenance of measuring instruments.

g Further, the failure of purpose-fitted sensors and the like will make it impossible to determine the modulus of elasticity, o There will be many ways to utilize the measured modulus of elasticity during the manufacturing process, after finishing and in the final product.

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BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described in connection with preferred embodiments, with reference to the accompanying drawings, in which:

Figure 1 shows a conceptual description of a material path controlled by electric motor drives, and

Figure 2 shows an example of a stress-strain curve.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates at a fundamental level a continuous material path in a device for producing such material. An example of this is the paper web 10 in a paper machine. Fig. 1 shows how the paper web 4 passes through three rollers 1,2, 3. The figure illustrates by way of example how the roll 2 is controlled by an electric motor drive consisting of an electric motor 5 and an inverter feeding it or the like 6. The shaft 5 of the motor 5 is connected to rotate the roll as desired. It should be noted that it is not necessary to use a gearbox, whereby the motor shaft is connected directly to the roller. The motor can be any type of electric motor, such as a short circuit motor or a synchronous motor. For other rolls, electric motor drives are not shown in Figure 1.

The motors driving the rollers can be controlled by modern frequency converters or similar controls in various ways. The adjustment can be effected, for example, as a speed control while keeping the track tension desired. Such adjustment is typically made such that one of the motors delivers the desired web speed and the motors communicating therewith through the paper path are adjusted in a torque controlled manner to achieve the desired tension and maintain. There is a linear relationship between torque and track tension, where the force acting on the track per track width is track tension, and the torque is the product of the radius and track force of the roll.

In the situation where the material web travels between two holding rolls in a static state, the relative elongation between rolls 1 and 2 of Figure 1 can be determined by the equation

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When the state is static, the change in velocity v2 Av2 causes a change in elongation = (2) 5 when v7 is constant and substantially equal to v2.

Since the stress-strain relationship is essentially linear with small strain and small strain changes, Hooke's law 10 σ = Εε, (3), which defines the stress σ as the product of the elasticity E and the strain ε, can be applied. On the other hand, the stress can be defined as the ratio of track force to force perpendicular to track 15 σ ~~ Ä '(4)

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Equation (4) is further obtained

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20 σ = ΓΓΤ (5) because the area A is the product of the height h of the paper web, i.e. the thickness, and the width / ^, and the line tension T is the ratio of the track force F to the track width /.

5 Equations (3) and (5) can be used to denote Λ 25

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n Εε = τ (6) c \ j h

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and so on

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λ y o 30 ΕΔε = = L m o h 'w CM n 5

Equation (7) holds because the relationship between the changes in tension and the elongation is linear with small changes.

Placing equation (2) in equation (7) gives 5 = (8) v2 h

Taking into account the radius r of the roll and the possible gear ratio i, the change AM of the motor torque M can be represented by AFr 2ATlr 10 AM2 = - = (9) i i from which the change in tension Δ7 "= ^ (10) 2lr 15

Further solving the equation (8), the modulus of elasticity E and placing in this solution equation (10) ATv2 AM2iv2 E = - = - (11) hAv2 hAv2 21 r 20 so that it is found that the value of the modulus of elasticity can be determined by torque change, line speed and line speed change, and known 5 parameters. Change in torque, line speed and line speed

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The change is obtained directly from the drive which controls the motor connected to the roller. Correspondingly, the gear ratio i and the roll radius ^ r in equation (11) may be stored in the memory of the drive or the like. Paper web pack The width h and the width l may vary, and these values may be stored either on the basis of in-use measurements or as known parameters.

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According to the method of the invention, the velocity v2 of the material web no. 30 is determined and a change in the

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^ an adjustable feature of the image's material path. These adjustable properties include material web tension, material web torque and material web speed.

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Further according to the invention, the modulus of elasticity is calculated based on the determined material web speed and velocity change, as well as the change in torque or material web tension. In the equations above, a change was made to the speed of the material web. Such a change can be accomplished directly by instructing the engine to change the track speed. This change in line speed affects the torque applied to the roll, according to the equations. It should be noted that the effective torque can be considered to be either the torque applied to the material web or the material web applied to the roll. However, the magnitudes of these differently interpreted torques 10 are the same.

As mentioned above, the induced velocity change produced a change in torque. Based on these changes, as well as track speed and operating parameters, the amount of elasticity can be calculated.

Similarly, a change in the torque or tension applied to the roll material web may be made. This change will inevitably still cause a change in speed on the corresponding roll. Equation (11) shows the modulus of elasticity as a function of both the change in tension AT and the change in torque AM. The use of a change in tension is advantageous, for example, when a change in the tension of the material web is performed to lower the elasticity of the material while the material web is tension-adjusted. In this case, according to equation (11), the original web speed, the change in web speed due to the change in tension and the change in tension can be used to calculate a value for the elastic modulus by also considering the thickness of the material web.

Above, speed refers to material web speed. There is a known linear relationship between this no-25 speed and the engine angular velocity, so that if desired, engine angular velocities can be used instead of track speeds. Modern frequency inverters are capable of determining g the torque produced by the motor or the magnitude of the torque applied to the motor internally as well as the orbital or angular velocity. As noted above, the determination of track tension is based on the determination of torque.

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so that all quantities determined in the method of the invention are directly known to the converter control unit. As such, these quantities can be transmitted to a separate unit of account and from there to a higher level control system, such as a drive control automation system. The drive may also itself be adapted to perform the calculation operation to determine the modulus of elasticity. In such a case, the drive conveys the elasticity calculated at the upper level.

As a control device for the roll, reference is made in particular to the combination of a frequency converter and a short-circuit motor or a synchronous motor. The corresponding functionality for providing the method according to the invention may also be implemented with a DC motor and control apparatus therefor.

The elastic coefficient determination according to the method can be carried out at certain regular intervals with the material web in a static state. It is also conceivable that the modulus of elasticity is continuously determined by generating, for example, a small variation of the speed reference for the roll performing the determination. For the purpose of accurately determining the elastic coefficient, it is important that the roll for which the elastic coefficient is determined is a firm roll. This means that the surface speed of the roll and the web speed must match each other as closely as possible so that the material web does not slip on the roll.

Using the method of the invention, the point of action of the material path can be estimated based on the elasticity factor. The modulus of elasticity is the slope of the stress-strain curve that can be formed on the material as shown in Figure 2. In the region of low elongation of the material, the value of the slope is relatively high. As the slope decreases, the same strain on the 20 material webs, i.e., a change in web strength, results in greater elongation. As the web force is further increased, the point at which the material web breaks, i.e. the breaking strength of the material is reached. Before this point, the slope of the curve, i.e. the modulus of elasticity, is small, so that by utilizing the method according to the invention it is possible to deduce situations where the material-web tension threatens to cut the web. This information can be utilized directly in adjusting the cm material path by lowering the tension guide or the like, with the coefficient being significantly small.

g Typically, in the manufacture of paper or similar material, a linear region of the stress-strain curve is employed, whereby the amount of elasticity calculated by the method of x 30 does not substantially vary. When

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a decrease in the modulus of elasticity is observed, so that the material tension has changed substantially while the material quality remains the same. Paper or similar

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g the runnability and diagnostics of the material production machine can thus be improved.

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35 Further, during the production of the material, the modulus of elasticity determined according to the method provides added value in determining the causes of web breaks.

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Unexpected variations in the modulus of elasticity of a material may cause problems in the runnability of the material when operating in the linear region of the stress-strain curve for normal quality material. By registering the values of the modulus of elasticity determined in accordance with the invention, it is possible to find correlations of the process to the disturbances of the production machine upstream. Particularly if cyclic changes in the modulus of elasticity occur, it is possible to locate problems in the operation of the production machine based on this cycle.

The values of the elastic coefficient determined by the method of the invention, or deviations from the elastic coefficients considered to be normal, can be marked on the finished machine reel either by marking it on the edge of the finished material or by using electronic recording media. Based on these marks, any material that may end up in the wreck can be removed in the material further processing equipment.

The apparatus of the invention comprises means for determining the velocity of the material web, and the electric motor drive of the apparatus is adapted to provide a change in the adjustable property of the continuous material web, which is either material web tension, material web torque or material web speed. The apparatus is further adapted to calculate a modulus of elasticity of 20 based on the change in velocity and velocity of the specified material web and the change in torque or change in the material web tension. These means can be implemented by an electric motor drive, wherein the electric motor drive includes the computing capacity to perform the required calculations and the readable memory to take into account the required parameters in the calculations. The computing capacity may also be located in a control system which can receive measurement data from the process and data produced by the frequency converter c3.

g The invention may be implemented on existing systems or use c / j separate elements and devices in a centralized or decentralized manner. Existing devices-

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x 30 doing like electric motor drives typically include processor and memory,

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which can be utilized to implement the functionality of the embodiments of the invention. Thus, all modifications and configurations of the cv g required to implement the embodiments of the invention can be accomplished by software routines, which in turn can be implemented as added or updated software routines. If the functionality of the invention is implemented by software, such software may be provided in the form of a computer program product comprising a computer program code which is executed by the computer program code on a computer to cause the computer or similar hardware to perform the inventive functionality as described above. Such computer program code may be stored on a computer readable medium such as a suitable storage medium 5, for example flash memory or disk memory, from where it can be read to the unit or units executing the program code. In addition, such program code may be downloaded to the unit or units that execute the program code through a suitable data network and may replace or update any existing program code.

It will be obvious to one skilled in the art that as technology advances, the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are thus not limited to the examples described above, but may vary within the scope of the claims.

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Claims (14)

A method for determining a coefficient of elasticity for an uninterrupted web of materials, in which method the uninterrupted web of material (4) runs on a roller (2) which is controlled by an electric motor operation, characterized by the method comprising steps in which the speed of the web of web material is determined by use of the electric drive frequency inverter, a change in the controllable property of the uninterrupted material path is formed with the electric motor drive, which property is either the voltage T of the material path 10, a torque M acting on the material path or the speed of the material path v2, a change in the speed of the material path is determined by , which change has been caused by the change formed in an electric motor adjustable property, a change in torque or a change in the voltage of the material path is determined by the electric motor drive, which change is caused by the change formed in an electric motor drive a controllable property, the coefficient of elasticity E is calculated on the basis of the determined velocity v2 of the material web 20 and the change of ziv2 of the velocity and the change AM of the torque or the change AT in the voltage of the material web. 2. A method according to claim 1, characterized by the electric motor operation, a change in the velocity v2 of the material web is formed, the torque of the motor is determined before the change of speed and after the change of the speed to effect a change of the torque AM, and the coefficient of elasticity E is calculated on the basis of the speed of the material v and the resulting change Av2 in the material web speed as well as the change AM in the torque of the motor caused by the change in material web speed. x 30 3. A method according to claim 1, characterized by the electric motor operation, a change in the speed of the material web T, o the change Av2 in the speed of the material web is determined from the effect of g the change AT in voltage, and the coefficient of elasticity E is calculated on the basis of the speed v2 of the web. the change AT in the material web voltage and the change Av2 in the engine speed caused by the change in the material web voltage. 4. A method as claimed in claim 1, characterized by the electric motor operation, a change in the torque M affecting the material web is formed, the change Av2 in the speed of the material web is determined from the effect of the change ΔM in the torque, formed the change AM in the torque of the material path 10 and the change of Av2 \ engine speed caused by the change in the torque of the material path. 5. A method according to any one of the preceding claims 1-4, characterized by the speed of the material web and the torque acting on the material web is determined in the electric motor operation. 15 6. A method according to any of the preceding claims 1-5, characterized in that the method further comprises steps in which sizes of elasticity coefficients determined on different measurement threads are compared, and the tension of the material web is reduced when the decrease of elasticity coefficient is observed. 20 7. A method according to any of the preceding claims 1-6, characterized in that the elasticity coefficient is determined in the electric operation. Method according to any of the preceding claims 1-6, characterized in that the electric motor operation sends necessary information for the determination of the elasticity coefficient to an upper level at which the coefficient of elasticity is determined. Method according to any of the preceding claims 1-8, characterized in that, in calculating the elasticity coefficient, the thickness of the web further, the width of the web and a radius of a controllable roller, as well as in cv, a possible gear ratio in a switch between the electric motor and roll. x 30 Method according to any of the preceding claims 1-9, CC 'characterized in that the electric motor drive motor is an alternating current motor or co a direct current motor. CV σ> Apparatus for determining a coefficient of elasticity for a continuous web of material, wherein the continuous web of web runs on a roller arranged to be controlled by an electric motor drive, characterized in that the drive of the electric motor drive is arranged to determine the speed of the material web and the electric motor drive. forming a change in the controllable property of the continuous material web, which is either the material web voltage, a torque acting on the material web or the material web speed, the electric motor drive is arranged to determine a change in the material web speed, which change has caused Due to the change formed in an electric motor drive adjustable property, the electric drive drive is arranged to determine a change in torque or material path voltage which change has been caused by the change formed in an electric motor drive adjustable characteristic ap, the device is arranged to calculate the coefficient of elasticity on the basis of the determined velocity of the material web and the change of speed, and the change of torque or the change in the tension of the material web. 12. Apparatus according to claim 11, characterized in that the electric motor drive motor is an AC motor or a DC motor. A frequency converter arranged as part of the electric motor operation in the method according to any of the preceding claims 1-10 for controlling a roller on which an uninterrupted material path runs, wherein the frequency converter is arranged to be controlled to effect a change. in a controllable property of the continuous web and calculate the coefficient of elasticity. A computer program product, comprising a computer program code, which executes a computer program code in a computer for the computer to perform the steps of the procedure according to any of claims 1-9. δ (M) M O (M (M X cn CL CD CO) M in σ> o o (M