JP6531618B2 - Low pass filter design method - Google Patents

Description

  The present invention relates to a method of designing a low pass filter, and is particularly suitable for designing a low pass filter used in detecting the height position of the surface of molten metal in a mold in a continuous casting machine.

  In order to keep the surface level of molten metal in the mold at the target level during the operation of the continuous casting machine, performing the surface level control is to stabilize the state of cooling and solidification of the molten metal in the mold. It is extremely important from the viewpoint of improving the quality of cast slabs produced. In addition, by performing such level control, the production efficiency can be improved by preventing various disadvantages that inhibit stable operation, such as overflow of molten metal from the mold and occurrence of breakout. It is also very important from the point of view.

  In this level control, a sliding nozzle or stopper is disposed as a device for adjusting the injection amount of molten metal into the mold, and a level meter for detecting the level of molten metal is provided above the level of the molten metal in the mold. Deploy. Then, the level level of molten metal in the mold is constantly detected by a level meter, and based on the level level detected by the level meter, feedback control of the opening degree of the sliding nozzle or the stopper is performed from the tundish into the mold Adjust the injection amount of molten metal to be injected. As described above, in the continuous casting machine, automatic control is performed to keep the surface level of the molten metal in the mold as constant as possible.

  There is an eddy current level meter as a level meter for detecting the level level of molten metal in a mold. The eddy current type level meter, for example, is disposed so that an alternating current power supply, a primary coil disposed so that the coil surface is substantially parallel to the molten metal surface, and a coil surface substantially parallel to the molten metal surface above and below the primary coil. And two secondary coils.

  An AC magnetic field is generated from the primary coil by supplying AC power to the primary coil. This AC magnetic field interlinks with the secondary coil and also interlinks with the molten metal in the mold. As a result, an eddy current is generated in the molten metal in the mold, and the eddy current generates an alternating magnetic field of the reverse polarity to the alternating magnetic field generated from the primary coil. The alternating magnetic field of this reverse polarity interlinks with the primary coil and the secondary coil. The alternating magnetic field reduces the alternating magnetic field generated by the primary coil. The degree to which the alternating magnetic field decreases is different because the distances between the two secondary coils and the molten metal are different. Therefore, a difference occurs in the voltage induced in each secondary coil. In the following description, this voltage difference is referred to as a differential voltage as needed.

  The differential voltage changes corresponding to the distance between the primary coil and the two secondary coils and the surface of the molten metal in the mold. Therefore, the height position of the metal plate such as SUS plate is regarded as the surface level of the molten metal in the mold, and the difference voltage at each height position of the metal plate is measured by the eddy current level meter, and the measured difference voltage The relationship between the pressure and the height position of the metal plate is previously investigated as the relationship between the differential voltage and the surface level of the molten metal in the mold, and then the differential voltage detected in the actual operation is given to this relationship. Thus, the surface level of molten metal in the mold can be measured.

  By the way, the area on the outer peripheral side (relatively close to the mold) of the molten metal in the mold of the continuous casting machine is cooled by the mold or the like to form a solidified shell (solidified shell). The thickness of the solidified shell becomes thicker the lower the mold. In order to prevent this solidified shell from sticking to the mold, a powder for lubrication is provided on the surface of the molten metal in the mold, the mold is moved up and down in a fixed cycle, and the powder is made into the mold and the solidified shell Flow up and down (this movement of the mold is called oscillation). The magnetic field detected by the secondary coil by oscillation is added as a disturbance with a sinusoidal magnetic field according to the period and amplitude of the oscillation. Therefore, as described in Patent Documents 1 and 2, reducing the disturbance is performed by using a low pass filter. The eddy current level meter can measure the surface level of molten metal in the mold without being affected by powder.

JP-A-59-166801 Japanese Patent Application Laid-Open No. 60-216959 JP, 2015-62917, A

  By the way, when deterioration or design change of the eddy current level meter occurs, it is necessary to update the eddy current level meter. If the coil structure (size, shape, arrangement, etc.) of the eddy current level meter before updating differs from the coil structure of the eddy current level meter after updating, the investigation described above using the eddy current level meter after updating To update the relationship between the differential voltage and the surface level of the molten metal in the mold.

  However, the amplitude of the disturbance due to oscillation superimposed on the secondary coil of the vortex level meter before updating and the amplitude of the disturbance due to oscillation superimposed on the secondary coil of the vortex level meter after updating are the coil structures. The change in, even though the amplitude of the oscillation is the same, will be different. Therefore, even if the amplitude of the oscillation before and after the renewal of the vortex level meter is the same, the disturbance due to the oscillation included in the surface level of the molten metal in the mold is different from that before and after the renewal of the vortex level meter. Become. Furthermore, the slope of the curve (the amount of change in the surface level of molten metal in the mold / the amount of change in the differential voltage) in the relationship between the differential voltage and the surface level of molten metal in the mold is updated by updating the eddy current level meter. If it becomes smaller, the S / N ratio of the surface level of the molten metal in the mold becomes worse, so the influence of the disturbance due to the oscillation appears notably on the surface level of the molten metal in the mold.

  Further, as a method of driving the stopper, there is a method of generating and outputting a pulse signal having a pulse width obtained by multiplying the moving speed of the rod of the hydraulic cylinder driving the stopper by an integer defining upper and lower limit values. When such a method is adopted, if the influence of the disturbance due to the above-mentioned oscillation becomes large, the pulse width is likely to exceed the upper limit value. As a result, it is not possible to suppress the fluctuation of the surface level of the molten metal in the mold that is originally intended to be suppressed, and there is a possibility that the level of the molten metal in the mold can not be practically controlled. Such a tendency is likely to appear in the case of high gain control of the surface level of the molten metal in the mold.

  The present invention has been made in view of the above problems, and it is an object of the present invention to make the influence of disturbance due to oscillation as possible as possible after updating, after updating the eddy current sensor. Do.

The low-pass filter design method of the present invention comprises a mold, an eddy current level meter for measuring the height position of the surface of molten metal in the mold, a signal output from the eddy current level meter, and the molten metal Level conversion means for converting the signal output from the eddy current level meter into a signal indicating the height position of the surface of the molten metal based on the relationship with the height position of the surface, and the surface of the molten metal The vortex flow in a continuous casting machine having a low-pass filter for reducing noise contained in a height position signal which is a signal indicating a height position or a signal based on a signal indicating the height position of the surface of the molten metal And a method of designing the low pass filter which is updated along with the update of the equation level meter and the level conversion means, wherein the height position signal does not pass through the low pass filter, and After which the molten metal is in a state where the metal plate is disposed in a state not inside a predetermined height position within said mold, and was in a state of the mold was moved up and down at a constant frequency f _osc [Hz] A first step of acquiring the height position signal using the eddy current level meter before update and the level conversion means before update; and the height position signal acquired in the first step A second step of deriving the amplitude ΔY _O [mm] of the height position signal from the time-series data, and making the height position signal not to pass through the low-pass filter, and the molten metal inside After the metal plate is placed at the predetermined height position in the mold in the absence state, and the mold is moved up and down at the constant frequency f _osc [Hz], after updating Of the eddy current level meter and after Using said level converting means, the amplitude ΔY in the third step and the third from the time-series data of the acquired height position signal by the process, the height position signal to obtain the height position signal _{It has} the 4th process of deriving _N [mm], and the 5th process of deriving the cutoff frequency f _cutN [Hz] of the above-mentioned low pass filter after the update after updating by the following (A) The eddy current level meter is disposed at a distance from the surface of the molten metal such that the coil surface substantially faces the surface of the molten metal, and a primary coil to which an alternating voltage is applied, and a coil surface At least detecting a magnetic field based on an eddy current generated in the molten metal by a magnetic field generated from the primary coil, disposed at a distance from the surface of the molten metal so as to substantially face the surface of the molten metal. One secondary And having a yl.
In the equation (A), _fcutO is the cutoff frequency [Hz] of the low pass filter before updating, and k is the amplitude ΔY _O [mm] of the height position signal derived in the second step. The ratio ΔY _N / ΔY _O [mm / mm] of the amplitude ΔY _N [mm] of the height position signal acquired in the fourth step with respect to

  According to the present invention, after updating of the eddy current sensor, the influence of disturbance due to oscillation can be made as same as before updating as much as possible.

It is a figure which shows an example of a structure of a continuous casting machine. It is a figure which shows an example of a vortex-type level meter. It is a figure which shows an example of the method of deriving a voltage-hot-water level conversion characteristic. It is a figure which shows an example of the relationship between the voltage level-melt surface level conversion characteristic, the surface level of molten steel obtained from the said voltage-melt surface level conversion characteristic, and a display level. It is a figure which shows an example of the relationship of the surface level of molten steel and display level which are obtained from the voltage-hot-water level conversion characteristic in the eddy current level meter from which coil structure differs, and those voltage-hot-water level conversion characteristics. It is a figure which shows an example of the time series data of the board level before update, and the time series data of the board level after update. It is a figure which shows notionally an example of a mode that a eddy current level meter and an amplifier board are updated. It is a figure which shows notionally an example of a mode that a vortex type level meter, an amplifier board, and a hot-water level control apparatus are updated.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First Embodiment
First, the first embodiment will be described.
FIG. 1 is a view showing an example of the configuration of a continuous casting machine. In addition, the XYZ coordinates shown in each figure show the relationship of the direction in each figure.
In FIG. 1, the continuous casting machine has a tundish 11, an immersion nozzle 12, a stopper 13, a mold 14, a pinch roll 15, and a cooling spray 16.

The tundish 11 temporarily stores molten steel (molten metal) 17 supplied from a ladle (not shown).
The mold 14 is disposed below the tundish 11 at a distance from the tundish 11. The mold 14 has, for example, a cylindrical shape. Also, the mold 14 is water cooled.
The immersion nozzle 12 injects the molten steel 17 stored in the tundish 11 into the inside of the mold 14. The immersion nozzle 12 is disposed such that the base end thereof is located on the bottom surface of the tundish 11 and the predetermined region on the tip end side is located inside the mold 14. Moreover, the inside of the immersion nozzle 12 and the inside of the tundish 11 are in communication.

  The stopper 13 is an actuator for controlling the supply amount of the molten steel 17 supplied from the tundish 11 to the immersion nozzle 12, and is disposed at the connection portion between the tundish 11 and the immersion nozzle 12. The stopper 13 moves in the height direction (the Z-axis direction in FIG. 1). When the stopper 13 is at the lowest position, the connection between the tundish 11 and the immersion nozzle 12 is fully closed. The opening area of the connection part of the tundish 11 and the immersion nozzle 12 increases so that the stopper 13 is located in a position higher than the said position. When the stopper 13 ascends to a predetermined upper limit position, the supply amount of the molten steel 17 supplied from the tundish 11 to the immersion nozzle 12 becomes maximum.

A plurality of pairs of pinch rolls 15 are disposed along the transport path of (the mutually opposite ends of) the steel drawn downward from the mold 14. A plurality of cooling sprays 16 are disposed on the outside of the pinch roll 15 for injecting cooling water to the steel for cooling the steel drawn downward from the mold 14.
Thus, the injected molten steel inside the mold 14 is cooled by the mold 14 and a solidified shell 18 is formed and solidified from the surface thereof. The steel whose surface is a solidified shell 18 but is not solidified inside is continuously drawn from the lower end of the mold 14 while being pinched by the pinch roll 15. In this way, in the process of being pulled out of the mold 14, the steel is solidified by advancing cooling of the steel by the cooling water jetted from the cooling spray 16. The steel solidified in this manner is cut to a predetermined size on the downstream side of a continuous casting machine (not shown), and slabs having different cross-sectional shapes such as slab, bloom, and bired are manufactured.

  A vortex level meter 19 is disposed above the mold 14 so as to face the surface (hot surface) of the molten steel staying inside the mold 14 of the continuous casting machine as described above. The eddy current level meter 19 detects the height position of the surface of the molten steel 17 staying inside the mold 14. The surface of the molten steel staying inside the mold 14 is covered with powder to prevent the solidified shell 18 from sticking to the mold 14. In the following description, the height position of the surface of the molten steel 17 is referred to as the level of the surface as required. In the present embodiment, the surface level is represented by a distance [mm] from the upper surface of the mold 14. However, as long as the surface level of the molten steel 17 is specified, the surface level may not necessarily be expressed in this manner. For example, the height from the ground may be used as the surface level.

FIG. 2 is a view showing an example of the eddy current level meter 19.
In FIG. 2, the eddy current level meter 19 has an oscillation circuit 19a, a primary coil 19b, secondary coils 19c and 19d, and a synchronous detection circuit 19e.

The oscillation circuit 19a applies an alternating voltage across the primary coil 19b.
The primary coil 19b is disposed at a position spaced from the surface of the molten steel (surface of the molten steel) so that the coil surface substantially faces the surface (surface of the molten steel) of the molten steel.

The secondary coil 19c is located at the lower side of the primary coil 19b at a distance from the surface of the molten steel (the surface of the molten steel) so that the coil surface substantially faces the surface (the surface of the molten steel) of the molten steel. Be placed.
The secondary coil 19d is disposed at a position above the primary coil 19b and at a distance from the surface of the molten steel (surface of the molten steel) so that the coil surface substantially faces the surface of the molten steel (hot surface). Be done.

  Here, the coil surface is a surface in a direction perpendicular to the winding axis of the coil. When an alternating voltage is applied from the oscillation circuit 19a to the primary coil 19b, an alternating magnetic field H is generated from the primary coil 19b. The secondary coils 19c and 19d are disposed at positions where alternating magnetic fields H generated from the primary coils 19b link with each other. Preferably, the primary coil 19 b and the secondary coils 19 c and 19 d are disposed such that the winding axes of the primary coil 19 b and the secondary coils 19 c and 19 d substantially coincide with each other.

As described in the background art, the alternating magnetic field H generated from the primary coil 19b interlinks with the molten steel. Then, an eddy current I is generated in the molten steel in a direction to cancel the AC magnetic field H, and an AC magnetic field H 'is generated in the direction to cancel the AC magnetic field H by the eddy current I. The AC magnetic field H 'is linked to the primary coil 19b and the secondary coils 19c and 19d, and the AC magnetic field H generated by the primary coil 19b is reduced. The reduction degree of the AC magnetic field H is different because the distance between the secondary coils 19c and 19d and the surface of the molten steel is different. Therefore, a difference (difference voltage [V]) occurs in the voltages induced in the respective secondary coils 19c, 19d.
The synchronous detection circuit 19e converts the voltage difference (difference voltage) detected by the secondary coils 19c and 19d into a direct current voltage [V] by synchronous detection. In the present embodiment, the differential voltage is output from the eddy current level meter 19 as described above.

Returning to the description of FIG. 1, the amplifier board 100 includes a level conversion unit 110 and a low pass filter (LPF) 120.
The level converter 110 converts the differential voltage output from the eddy current level meter 19 into the surface level of molten steel. The level conversion unit 110 stores in advance information indicating the relationship between the differential voltage and the surface level of the molten steel. In the following description, information indicating the relationship between the differential voltage and the surface level of the molten steel is referred to as voltage-to-surface level conversion characteristics as needed.

Hereinafter, an example of a method of deriving the voltage-melt level conversion characteristic will be described.
FIG. 3 is a diagram showing an example of a method of deriving a voltage-hot-water level conversion characteristic.
In FIG. 3, the operation of the continuous casting machine is stopped, and there is no molten steel in the mold 14. In this state, the metal plate 310 is placed in the mold 14 in order to simulate the surface level of molten steel. The metal plate 310 is made of, for example, a SUS plate (stainless steel plate) or a lead plate. The height position of the upper surface of the metal plate 310 corresponds to the surface level of molten steel. In addition, the mold 14 is moved up and down (that is, oscillation is performed) under the same conditions as in operation.

  In the state as described above, the eddy current level meter 19 is operated to measure the difference voltage. Such measurements are performed at different heights of the metal plate 310. Thereby, the relationship between the plate level which is the height position of the upper surface of the metal plate 310 and the differential voltage is obtained. The information indicating this relationship is the voltage-melt level conversion characteristic. The height position of the metal plate 310 is preferably changed, for example, at equal pitches.

FIG. 4A is a diagram showing an example of the voltage-hot-water level conversion characteristic.
In FIG. 4 (a), a point determined by the differential voltage measured as described above and the plate level when the differential voltage is measured is on a two-dimensional coordinate with the differential voltage and the surface level of molten steel as axes. Plot to Then, based on the plotted points, a function indicating the relationship between the differential voltage and the surface level of molten steel is derived as a voltage-level conversion characteristic. A function indicating the relationship between the differential voltage and the surface level of molten steel can be derived, for example, by using a known curve fitting technique. A table storing the differential voltage and the surface level of the molten steel in association with each other may be derived as a voltage-level level conversion characteristic, not as a function. The voltage-to-melt level conversion characteristic can be obtained, for example, by inputting the information on the differential voltage and the plate level into a computer and executing the program describing the above-described derivation method.

The voltage-melt surface level conversion characteristic derived as described above is set (stored) in the level conversion unit 110.
In the present embodiment, as described above, the sixth step and the seventh step for the vortex level meter before updating are realized.

  Thereafter, when molten steel is injected into the mold 14 and a differential voltage is output from the eddy current level meter 19, the level conversion unit 110 converts the molten metal level corresponding to the differential voltage into a voltage-melt level conversion characteristic. And output to the low pass filter 120, and displaying on a computer display or the like to inform the operator.

  FIG.4 (b) is a figure which shows an example of the relationship between the surface level of molten steel and display level which are obtained from a voltage-melting-surface level conversion characteristic. The display level refers to the surface level of molten steel displayed on a computer display or the like to notify the operator. As shown in FIG. 4 (b), the voltage-hot-water level conversion characteristics are stored in advance, and the hot-water level of molten steel is derived from the differential voltage output from the eddy current level meter 19. The relationship between the surface level and the display level is a linear function of 1: 1, and from the differential voltage output from the eddy current level meter 19, it is possible to obtain a display value of the surface level of molten steel.

  The level conversion unit 110 derives the surface level of the molten steel as described above each time the differential voltage is input from the eddy current level meter 19. Thus, time series data of the molten steel level (the data of the molten steel level at each time) can be obtained. In the present embodiment, the level conversion unit 110 is an example of the level conversion unit.

Returning to the explanation of FIG. 1, the low pass filter 120 amplifies the amplitude of the molten steel level signal output from the level conversion unit 110 by the gain G times at the cutoff frequency (gain G is less than 1 (Attenuates substantially) In the present embodiment, the signal at the surface level of the molten steel is an example of the height position signal (signal indicating the height position of the surface of the molten metal).
The low pass filter 120 is noise contained in the surface level of the molten steel output from the level conversion unit 110, and is for removing noise mainly caused by oscillation.
The gain G of the low pass filter 120 is expressed by the following equations (1) to (3).

In the equations (1) and (2), f _osc is the oscillation frequency [Hz]. Further, in equation (1), T is a time constant [sec], and in equations (1) and (3), f _cut is a cutoff frequency [Hz] of the low pass filter.
As shown in the equation (1), the gain G decreases as the cutoff frequency f _cut decreases. However, when the cut-off frequency f _cut is reduced, the signal delay of the molten metal level is increased. Therefore, the gain G is set in consideration of the balance between the suppression of noise caused by the oscillation and the suppression of the signal delay of the surface level of the molten steel.

  The molten metal level control device 200 receives the molten metal level signal PV output from the amplifier board 100 and outputs an open / close pulse signal which is a pulse signal representing the change in the opening degree of the stopper 13. The molten metal level control device 200 includes a subtractor 210, a low pass filter (LPF) 220, and a control unit 230.

The subtractor 210 subtracts the actual value PV of the signal of the surface level of molten steel from the set value (target value) SV of the surface level of molten steel, and outputs a signal of deviation of the surface level of molten steel. In the present embodiment, the subtractor 210 is an example of the deviation deriving means.
Low-pass filter 220 amplifies the signal amplitude of the deviation of the surface level of the molten steel output from subtractor 210 by gain G 'times at its cutoff frequency (since gain G' is less than 1, substantially To decay). The gain G ′ is derived in the same manner as the equations (1) to (3) described above. In the present embodiment, the low pass filter 220 is not updated.
As described above, in the present embodiment, the low pass filter 120 is an example of the low pass filter to be updated, and the low pass filter 220 is an example of the second low pass filter.

  The control unit 230 performs PI calculation with a signal of deviation of the surface level of the molten steel output from the low pass filter 220 as a control cycle, thereby achieving the target of the stopper 13 necessary to eliminate the deviation. Generate an opening degree. Furthermore, based on the target opening degree of the stopper 13, the control unit 230 sets a pulse signal having a pulse width obtained by multiplying the moving speed of the rod of the hydraulic cylinder 400 by an integer for which upper and lower limits are defined. It generates and outputs to ST control device 300. The method of generating the open / close pulse signal can be realized by, for example, a known technique described in Patent Document 3, and thus the detailed description thereof is omitted here. For example, PID control may be performed instead of PI control. In the present embodiment, the control unit 230 is an example of a control unit.

  The pulse width of the switching pulse signal can not be made longer than the control period. Therefore, when the above-mentioned integer derived from the target opening of the stopper 13 exceeds the upper limit, a pulse signal having a pulse width obtained by multiplying the moving speed of the rod of the hydraulic cylinder 400 by the upper limit of the integer It is generated as a switching pulse signal. This is called pulse saturation.

  The ST control device 300 includes a drive circuit of a pulse motor for operating the hydraulic cylinder 400. The ST control device 300 receives the open / close pulse signal output from the molten metal level control device 200 and outputs the open / close pulse signal after processing by the drive circuit etc. to the hydraulic cylinder 400. The level control device 200 can output an analog signal representing information included in the switching pulse signal to the ST control device 300 instead of the switching pulse signal. In this case, the ST control device 300 generates an open / close pulse signal based on the analog signal output from the surface level control device 200 and outputs it to the hydraulic cylinder 400.

  The hydraulic cylinder 400 comprises a pulse motor. The pulse motor rotates based on the open / close pulse signal transmitted from the ST control device 300, and this rotation changes the position of the rod of the hydraulic cylinder 400. The hydraulic cylinder 400 moves the stopper 13 in the vertical direction (Z-axis direction) according to a value obtained by multiplying the pulse width of the open / close pulse signal and the moving speed of the rod of the hydraulic cylinder 400. The hydraulic cylinder 400 can be realized by a known technique, and thus the detailed description thereof is omitted here.

  In the continuous casting machine as described above, the case of updating the eddy current level meter to another eddy current level meter having a coil structure different from that of the eddy current level meter will be described. The coil structure includes, for example, at least one of coil size, shape, and arrangement. For example, in order to save space and save power with the aging of the eddy current level meter, the primary coil and secondary coil of the eddy current level meter after updating are replaced with the primary coil of the eddy current level meter before updating. It can be considered to be smaller than the secondary coil. In addition, in order to save space, as shown in FIG. 2, the primary coil and the secondary coil are arranged side by side in the horizontal direction as in the technique described in Patent Document 2, as shown in FIG. It is also conceivable to change the configuration to arrange the coil.

  Fig.5 (a) is a figure which shows an example of the voltage-hot-water level conversion characteristic in the eddy type | formula level meter from which coil structure differs. In FIG. 5 (a), the voltage-melt level conversion characteristic 510 is an example of the voltage-melt level conversion characteristic in the eddy current level meter before updating, and the voltage-melt level conversion characteristic 520 is updated after the updating. It is an example of the voltage-hot-water level conversion characteristic in an eddy type level meter.

  Due to the change of the coil structure in this manner, the voltage-melt level conversion characteristics may differ. Therefore, as described above, the voltage-level data conversion characteristic is derived using the updated eddy current level meter, and the voltage-level data conversion characteristic of the level conversion unit 110 is updated. By doing this, as shown in FIG. 5 (b), even if the eddy current level meter is updated, the relationship between the surface level of molten steel and the display level can be made to a linear function of 1: 1. it can. This means that in the absence of oscillation, if the voltage-hot-water level conversion characteristics are updated, the updated eddy-current level meter measures the hot-water level of molten steel in the same manner as the eddy current level meter before updating. It means that you can do it.

  However, in the case where the coil structure is different between the vortex level meter before updating and the vortex level meter after updating, even if the metal plate 310 is disposed at the same height position and the same oscillation is performed, the vortex type The amplitude of the noise caused by the oscillation, which is included in the difference voltage output from the level meter, differs between the case where the eddy current level meter before the update is used and the case where the eddy current level meter after the update is used. The amplitude of the noise caused by the oscillation included in the difference voltage output from the eddy current level meter is higher when the eddy current level meter after update is used than when the eddy current level meter before update is used If it becomes large, it is possible that the signal of the surface level of molten steel output from the level conversion unit 110 includes noise with large amplitude as noise due to oscillation only by updating the voltage-level conversion characteristic. Become. As a result, the low-pass filter 120 can not sufficiently remove the noise caused by the oscillation, and the above-described pulse saturation is likely to occur in the surface level controller 200.

When such pulse saturation occurs, the pulse width of the switching pulse signal largely depends on the noise caused by the oscillation. As a result, it is not possible to suppress the fluctuation of the surface level of the molten metal in the mold that is originally intended to be suppressed, and there is a possibility that the level of the molten metal in the mold can not be practically controlled. Such a tendency is likely to appear in the case of high gain control of the surface level of the molten metal in the mold.
Here, if the control gain is lowered in order to avoid pulse saturation, there is a possibility that the control of the surface level of molten steel, which is the original purpose, can not be properly performed. In addition, it takes a great deal of effort to change the design of the controller that performs the PI operation described above on a trial and error basis.

  Based on the above findings, the present inventors used the eddy current level meter before updating and the eddy current level meter after updating, and the oscillation after passing through the low-pass filter. By making the amplitude of the noise caused by the same, it was conceived that the level level of molten steel can be measured in the same manner as the eddy current level meter before updating even in the situation where the oscillation is performed.

  In this embodiment, based on the above findings, after passing through the low-pass filter in the case of using the eddy current level meter before updating and in the case of using the eddy current level meter after updating as follows. The low pass filter cutoff frequency after update is changed so that the amplitude of the noise due to the oscillation of the same becomes the same.

  FIG. 7: is a figure which shows notionally an example of a mode that the eddy current level meter 19 and the amplifier board 100 are updated. As shown in FIG. 7, the eddy current level meter 19 is changed to an eddy current level meter 19 ′ having a smaller coil size than the eddy current level meter 19, and accordingly, as described below, The case where the low pass filter 120 is changed to the low pass filter 120 'having a determined cutoff frequency will be described as an example. The low pass filter 220 in the level control device 200 is not changed. Further, as shown in FIG. 7, the level conversion unit 110 is also updated to the level conversion unit 110 ′, and the amplifier board 100 is updated to the amplifier board 100 ′. The method of updating the level conversion unit 110 is as described with reference to FIG. In this embodiment, the sixth and seventh steps for the updated eddy current level meter are realized in this manner.

Below, an example of the method to change the cutoff frequency of the low-pass filter after an update is demonstrated.
First, as described with reference to FIG. 3, the operation of the continuous casting machine is stopped, and there is no molten steel in the mold 14. In this state, the metal plate 310 is placed in the mold 14 in order to simulate the surface level of molten steel. At this time, the height position of the metal plate 310 is set to a predetermined position (for example, a position 100 mm from the upper surface of the mold 140).

  Then, the mold 14 is moved up and down at a constant frequency (that is, oscillation is performed) under the same conditions as in operation. Also, the low pass filter 120 is turned off. That is, without passing through the low pass filter 120, the output (level of molten steel (display level)) from the level conversion unit 110 can be obtained. For example, the setting of the low pass filter 120 may be changed, or the low pass filter 120 may be removed. Alternatively, the low pass filter 120 may be left as it is, and the signal before it is output from the level conversion unit 110 and input to the low pass filter 120 may be extracted.

In the above state, the eddy current level meter 19 is operated to measure the difference voltage, and the level converter 110 derives the plate level (display level). The plate is derived for a predetermined period, and time-series data (plate level data at each time) in a predetermined period of the plate level is obtained. As described above, the plate level is the height position of the upper surface of the metal plate 310. The oscillation frequency [Hz] is known because the template 14 is a frequency.
In the present embodiment, the first step is realized as described above.

Next, the eddy current level meter 19 and the amplifier board 100 (the level conversion unit 110 and the low pass filter 120) are respectively a new eddy current level meter 19 'and the amplifier board 100 (the level conversion unit 110' and the low pass filter 120 ') Oscillation is performed under the same conditions as in the case of using the eddy current level meter 19 and the amplifier board 100 before updating, and time series data in a predetermined period of the plate level is obtained in the same manner as described above.
In the present embodiment, the third step is realized as described above.

As described above, when the time-series data of the board level before updating and the time-series data of the board level after updating are obtained, the amplitude (peak to peak value: maximum value and minimum value) of the time-series data of those board levels Derivate each of the difference between the values).
In the present embodiment, the second and fourth steps are realized as described above.

FIG. 6 is a diagram showing an example of plate-level time-series data 610 before update and plate-level time-series data 620 after update.
As shown in FIG. 6, the amplitude ΔY _O of the waveform of the plate level time series data 610 before update and the amplitude ΔY _N of the waveform of the plate level time series data 610 after update are derived. This amplitude can be obtained, for example, by inputting plate-level time-series data before and after updating into a computer and executing the program in which a method of deriving the amplitude of the time-series data is described. In this case, the computer outputs the amplitude ΔY _O of the waveform of the plate level time series data 610 before the update and the amplitude ΔY _N of the waveform of the plate level time series data 610 after the update (for example, Can be displayed on a computer display). In FIG. 6, the case where the amplitude ΔY _N of the waveform of the plate level time series data 610 after updating is larger than the amplitude ΔY _O of the waveform of the plate level time series data 610 before updating is shown as an example. . However, these magnitude relationships may be reversed.

As described above, due to the oscillation after passing through the low-pass filters 120 and 120 'in the case of using the eddy current level meter 19 before updating and in the case of using the eddy current level meter 19' after updating It is necessary to make the amplitude of the noise to be the same. Therefore, the following equation (4) needs to be established.
ΔY _N × G _N = ΔY _O × G _O (4)
In the equation (4), G _N and G _O are the gain G of the low pass filter 120 ′ after the update and the low pass filter 120 gain G before the update, respectively, and are represented by the equations (1) to (3) described above Be done. Therefore, the following equation (5) is obtained from the equations (1) and (4).

In the equation (5), f _cutN and f _{cut O} are the cutoff frequency of the low pass filter 120 ′ after the updating and the cutoff frequency of the low pass filter 120 before the updating, respectively. As described above, f _osc is the oscillation frequency [Hz], which is a known value (constant value).
In the equation (5), assuming that ΔY _N / ΔY _o [mm / mm] is k, the cutoff frequency f _cutN of the updated low-pass filter 120 ′ is expressed by the following equation (6).

Therefore, the cutoff frequency f _cutO of the low-pass filter 120 before updating, the frequency f _{osc of} oscillation, the amplitude ΔY _O of the waveform of the plate level time series data 610 before updating, and the plate level time series data 610 after updating The cutoff frequency f _cutN of the updated low-pass filter 120 ′ is derived from the amplitude ΔY _N of the waveform of FIG. Thus, when the cutoff frequency f _cutN of the low-pass filter 120 'after the update is derived, the case where the eddy-current level meter 19 before the update is used and the case where the eddy-current level meter 19' after the update is used Then, the amplitude of the noise resulting from the oscillation after passing through the low pass filters 120 and 120 'can be made the same.

Derivation of the cutoff frequency f _cutN of the low-pass filter 120 ′ after the update can be realized, for example, by executing a program in which the calculation of the equation (6) is described by the computer. In this case, the computer can output (for example, display on a computer display) the cut-off frequency f _cutN of the updated low-pass filter 120 ′. Then, the updated low-pass filter 120 'is configured to have the cutoff frequency _fcutN . At this time, the operator obtains the value of k from the amplitudes ΔY _o and ΔY _N output from the computer as described above, and inputs the obtained value of k to the computer using the user interface of the computer. Can.
In the present embodiment, the fifth step is realized as described above.

As described above, in the present embodiment, after the low-pass filters 120 and 120 'are used in the case of using the eddy current level meter 19 before updating and in the case of using the eddy current level meter 19' after updating. The cutoff frequency f _cutN of the updated low-pass filter 120 ′ is derived so that the amplitude of the noise caused by the oscillation is the same. Therefore, when the eddy current level meter 19 is updated, the setting of the low pass filter 120 for suppressing the noise due to the oscillation can be transferred (converted) to the updated system, and after the eddy current sensor is updated The effect of the disturbance due to the oscillation can be made as same as before the update. Therefore, it is possible to suppress as much as possible the loss of the reproducibility and the reliability of the measurement value of the eddy current level meter 19 'after the update. As a result, even if the eddy current level meter is updated, the measurement and control performance in the existing system can be maintained as much as possible. In addition, since it is not necessary to re-adjust the low pass filter 220 and the control unit (controller) 230 of the surface level control device 200, it is possible to reduce the time required for updating.

  The eddy current level meter is not limited to the one described in the present embodiment, and, for example, the eddy current level meter described in Patent Documents 1 and 2 can be used. That is, the coil surface is disposed with a gap with the surface of the molten steel so that the coil surface substantially faces the surface of the molten steel, and the coil surface substantially faces the surface of the molten steel with an alternating voltage applied thereto. And at least one secondary coil disposed spaced apart from the surface of the molten steel and detecting at least a magnetic field based on an eddy current generated in the molten steel by a magnetic field generated from the primary coil. . In the case where there is one secondary coil, in the above description, the difference voltage may be replaced with a voltage induced in the secondary coil.

  Further, in the present embodiment, the case where the actuator for adjusting the supply amount of molten steel supplied to the mold 14 is the stopper 13 has been described as an example. However, such an actuator is not limited to the stopper 13 but may be a sliding nozzle.

Second Embodiment
Next, a second embodiment will be described. In the first embodiment, the low-pass filter 120 of the amplifier board 100 is updated without updating the low-pass filter 220 of the molten metal level control device 200 as an example. On the other hand, in the present embodiment, a case where the low pass filter 220 of the molten metal level control device 200 is updated without updating the low pass filter 120 of the amplifier board 100 will be described as an example. As described above, the present embodiment and the first embodiment are mainly different in that the low pass filter to be updated is different. Accordingly, in the description of the present embodiment, the same parts as those of the first embodiment are denoted by the same reference numerals as those of the reference numerals of FIGS.

FIG. 8 is a diagram conceptually showing an example of how the eddy current level meter 19, the amplifier board 100, and the level control device 200 are updated. FIG. 8 is a diagram corresponding to FIG.
In this embodiment, the oscillation after passing through the low-pass filters 220 and 220 'is caused by the case of using the eddy current level meter 19 before updating and the case of using the eddy current level meter 19' after updating. Make the same noise amplitude. Therefore, the following equation (7) needs to be established.
ΔY _N × G _N1 × G _N2 = ΔY _O × G _O1 × G _o2 (7)

In equation (7), ΔY _O is the amplitude of the waveform of the plate level time series data before updating. ΔY _N is the amplitude of the waveform of the plate level time series data after updating. G _N1 and G _O1 are the gain G of the low pass filter 120. G _N2 and G _O2 are respectively the gain G of the updated low pass filter 220 ′ and the gain G of the updated low pass filter 220 ′.

  The control unit 230 uses the same one in the metal surface level control device 200 before the update and the metal surface level control device 200 ′ after the update. Further, as described in the first embodiment, the level conversion unit 110 is updated to the level conversion unit 110 ′ in accordance with the update to the eddy current level meter 19 ′ of the eddy current level meter 19. At this time, the amplifier board 100 is replaced with the amplifier board 100 '. However, the low pass filter 120 included in the amplifier boards 100 and 100 'has the same function. Note that only the level conversion unit 110 may be replaced without replacing the entire amplifier board 100.

In this embodiment, since the low pass filter 120 is not updated, the gains G _N1 and G _O1 have the same value. Therefore, the equation (7) has the same form as the equation (5) described in the first embodiment. Then, the cutoff frequency of the low-pass filter 220 ′ after update is also represented by the equation (6) described in the first embodiment.
However, _fcutN and _fcutO are not the low pass filters 120 'and 120, but are the cutoff frequencies of the low pass filters 220' and 220, respectively.

As described above, even if the low pass filter 220 of the molten metal level control device 200 is updated, the same operation as the equation (6) described in the first embodiment is performed, and the cutoff frequency of the updated low pass filter 220 ' By deriving f _{cut N} , it is possible to use the eddy current level meter 19 before the update and the eddy current level meter 19 ′ after the update, and then use the Oshi after passing the low pass filters 220 and 220 ′. The amplitude of the noise caused by the signal can be made the same. Therefore, the same effect as described in the first embodiment can be obtained.

  However, in the first embodiment, the eddy current level meter 19 and the amplifier board 100 (the level converter 110 and the low pass filter 120) are respectively the new eddy current level meter 19 'and the amplifier board 100' (level converter 110 'and Let it be a low pass filter 120 '). On the other hand, in the present embodiment, in addition to the eddy current level meter 19 and the amplifier board 100 (level conversion unit 110), the molten metal level control device 200 (low pass filter 220) is respectively new eddy current level meter 19 ', amplifier A panel 100 '(level conversion unit 110') and a molten metal level control device 200 '(low pass filter 220') are used.

The various modifications described in the first embodiment can be adopted also in this embodiment.
Further, in the first embodiment and the second embodiment, the relationship between the low pass filter to be updated and the second low pass filter is reversed. That is, in the first embodiment, the low pass filter 120 is an example of the low pass filter to be updated (in this case, the low pass filter 220 is an example of the second low pass filter, as described above). is there). On the other hand, in the present embodiment, the low pass filter 220 is an example of the low pass filter to be updated, and the low pass filter 120 is an example of the second low pass filter. As described above, when the low pass filter 120 is an example of a low pass filter to be updated, the low pass filter 220 is an example of a second low pass filter, and the low pass filter 220 is a low pass to be updated In the case of an example of a filter, the low pass filter 120 is an example of a second low pass filter.
The signal of the deviation of the surface level of the molten steel output from the subtractor 210 is an example of a height position signal (a signal based on a signal indicating the height position of the surface of the molten metal, a signal indicating the deviation).

Note that among the embodiments of the present invention described above, processing that can be performed by a computer can be realized by the computer executing a program. In addition, a computer readable recording medium recording the program and a computer program product such as the program can be applied as an embodiment of the present invention. As the recording medium, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a non-volatile memory card, a ROM or the like can be used.
In addition, any of the embodiments of the present invention described above is merely an example of implementation for carrying out the present invention, and the technical scope of the present invention should not be interpreted limitedly by these. It is a thing. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  11: Tundish, 12: immersion nozzle 12, 13: stopper, 14: mold (mold), 15: pinch roll, 16: cooling spray, 100 · 100 ′: amplifier board, 110 · 110 ′: level converter, 120 · 120 ': low pass filter, 200 · 200': molten metal level control device, 210: subtractor, 220 · 220 ': low pass filter, 230: control unit

Claims (5)

Mold and
An eddy current level meter for measuring the height position of the surface of molten metal in the mold;
Based on the relationship between the signal output from the eddy current level meter and the height position of the surface of the molten metal, the signal output from the eddy current level meter is the height position of the surface of the molten metal Level conversion means for converting into a signal shown by
A low pass filter for reducing noise included in a height position signal which is a signal based on the signal indicating the height position of the surface of the molten metal or the signal indicating the height position of the surface of the molten metal;
A method of designing the low pass filter, which is updated along with the updating of the eddy current level meter and the level conversion means, in a continuous casting machine having
The height position signal does not pass through the low pass filter, and the metal plate is placed at a predetermined height position in the mold without the molten metal inside, and the mold is First, the height position signal is acquired using the eddy current level meter before updating and the level converting means before updating after being moved up and down at a constant frequency f _osc [Hz]. Process,
A second step of deriving an amplitude ΔY _O [mm] of the height position signal from the time-series data of the height position signal acquired in the first step;
The height position signal does not pass through the low pass filter, and the metal plate is disposed at the predetermined height position in the mold without the molten metal inside, and the mold The height position signal is obtained by using the eddy current level meter after updating and the level converting means after updating, after vertically moving at a constant frequency _f.sub.osc [Hz]. 3 processes,
A fourth step of deriving an amplitude ΔY _N [mm] of the height position signal from the time-series data of the height position signal acquired in the third step;
And a fifth step of deriving a cutoff frequency f _cutN [Hz] of the low-pass filter after update by the following equation (A):
The eddy current level meter is disposed at a distance from the surface of the molten metal such that the coil surface substantially faces the surface of the molten metal, and a primary coil to which an alternating voltage is applied, and the coil surface At least one of a magnetic field generated from the primary coil and a magnetic field based on an eddy current generated by the magnetic field generated from the primary coil, disposed at a distance from the surface of the molten metal so as to substantially face the surface of the molten metal. Method of designing a low pass filter characterized by comprising two secondary coils.
In the equation (A), _fcutO is the cutoff frequency [Hz] of the low pass filter before updating, and k is the amplitude ΔY _O [mm] of the height position signal derived in the second step. The ratio ΔY _N / ΔY _O [mm / mm] of the amplitude ΔY _N [mm] of the height position signal acquired in the fourth step with respect to

The low pass filter reduces noise contained in a signal indicating the height position of the surface of the molten metal output from the level conversion means ,
The continuous casting machine is a deviation deriving means for deriving a signal indicating a deviation between a signal indicating the height position of the surface of the molten metal that has passed through the low pass filter and a target value of the height position of the surface of the molten metal. When,
A second low pass filter for reducing noise contained in the signal indicating the deviation derived by the deviation deriving means;
Control means for generating a signal for operating an actuator for adjusting the supply amount of the molten metal supplied to the mold based on the signal indicating the deviation that has passed through the second low pass filter; In addition,
The lowpass filter design method according to claim 1, wherein the second lowpass filter is not updated when the eddy current level meter and the level conversion means are updated. The continuous casting machine includes a second low pass filter for reducing noise included in a signal indicating the height position of the surface of the molten metal output from the level conversion means;
Deviation deriving means for deriving a signal indicating a deviation between a signal indicating the height position of the surface of the molten metal passing through the second low pass filter and a target value of the height position of the surface of the molten metal;
And control means for generating a signal for operating an actuator for adjusting the supply amount of the molten metal supplied to the mold based on the signal indicating the deviation that has passed through the low pass filter. ,
The low pass filter reduces noise included in the signal indicating the deviation derived by the deviation deriving means as a signal based on a signal indicating the height position of the surface of the molten metal,
The lowpass filter design method according to claim 1, wherein the second lowpass filter is not updated when the eddy current level meter and the level conversion means are updated. The secondary coils are disposed one by one above and below the primary coil, respectively.
The design method of the low pass filter according to any one of claims 1 to 3, wherein the eddy current level meter outputs a signal based on a difference in voltage induced in the secondary coil. When the metal plate is disposed in the mold without the molten metal inside, the signal output from the eddy current level meter is acquired by making the height position of the metal plate in the mold different. A sixth step of performing the step for each of the eddy current level meter before updating and the eddy current level meter after updating;
Relationship between the signal output from the eddy current level meter and the height position of the surface of the molten metal based on the signal output from the eddy current level meter at each of a plurality of height positions in the mold The method according to any one of claims 1 to 4, further comprising: a seventh step of performing the derivation of the eddy current level meter before updating and the eddy current level meter after updating, respectively. The low pass filter design method according to item 1.

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