JPH062290B2 - Deterioration diagnosis method for hydraulic servo system for rolling mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is intended to diagnose deterioration of the hydraulic servo system of a rolling mill that automatically controls the thickness of rolled material in a rolling process in a steel mill. Regarding the method.

[Prior Art] In general, automatic thickness control [hereinafter referred to as AGC (Automatic Gauge
Control)] is a rolling system as shown in FIG. In FIG. 7, 1
Is a work roll of a rolling mill, 2 is a material to be rolled, 3 is a rolling load detector for detecting a rolling load ΔP by the work roll 1,
4 is a hydraulic servo system for adjusting the roll gap ΔS of the work roll 1, 4a is an input end of the hydraulic servo system, 4b is an output end of the hydraulic servo system, and 5 is a rolling load ΔP from the rolling load detector 3 and a hydraulic servo system. Roll gap Δ from 4
Receiving S, calculating the operation amount and outputting to the hydraulic servo system 4 A
It is a GC calculator. A control block diagram of the hydraulic servo system 4 is shown in FIG.

Conventionally, the deterioration diagnosis of the hydraulic servo system 4 of such a rolling mill is performed as follows, for example.

Stop the rolling mill.

In the AGC system, the pressure reduction cylinder is fixed with a jack, and feedback to the hydraulic servo system 4 is applied to the input end 4
Separate with a.

A function generator or the like generates a sine wave sweep (a sine wave continuously changed from a low frequency to a high frequency) and applies it as a command value (test signal) to the hydraulic servo system 4 from the input end 4a.

Input signal to the input end 4a and the hydraulic servo system 4 at that time
And the output signal (spool change signal) from the output terminal 4b of.

An FFT (Fast Free Fourier Transform) analyzer is used to draw a board (Bode) diagram as shown in FIG. 9 from the ratio of the input / output gain of the hydraulic servo system 4.

Deterioration of the hydraulic servo system 4 is diagnosed based on the 3 decibel (dB) reduction frequency of the Bode diagram obtained in step 1, and the gain of the hydraulic servo system 4 is adjusted.

In other words, at the time of deterioration diagnosis, the rolling mill is stopped, and the open loop of the hydraulic servo system 4 alone is configured so that the feedback of the roll gap ΔS and the rolling load ΔP from the AGC calculator 5 does not return. The sine wave of is applied as a test signal, and the Bode diagram is drawn by the ratio of the input and output gains. Then, in this Bode diagram, as shown in FIG. 9, the deterioration diagnosis is performed at the value of the frequency f that is lowered by 3 dB.

[Problems to be Solved by the Invention] However, in the above-described conventional hydraulic servo system deterioration diagnosing means for rolling mills, when a Bode diagram is drawn using the data during rolling, the data fluctuates above the resonance frequency. It is necessary to stop the rolling mill before applying the test signal for deterioration diagnosis, which is very time-consuming, and the productivity of the rolling line is reduced, so that the number of times of deterioration diagnosis is limited.

There is also a problem that equipment such as a signal generator for generating a sine wave sweep is separately required.

The present invention is intended to solve such problems,
For rolling mills, the deterioration diagnosis can be performed without stopping the rolling mill by using the data during rolling, which facilitates deterioration diagnosis, speeds up, and improves accuracy, and also prevents the productivity of the rolling line from decreasing. An object of the present invention is to provide a method for diagnosing deterioration of a hydraulic servo system.

[Means for Solving the Problems] In order to achieve the above object, a deterioration diagnosis method of a hydraulic servo system for a rolling mill according to the present invention collects input data and output data of a hydraulic servo system during rolling, and collects the collected data. After performing a Fourier transform on each of the obtained data to create a Bode diagram, a quadratic transfer function approximating a predetermined frequency section of the gain curve of the Bode diagram is obtained, and the resonance frequency and attenuation of the quadratic transfer function are obtained. The deterioration state of the hydraulic servo system is diagnosed based on the coefficient.

[Operation] In the deterioration diagnosing method for the hydraulic servo system for a rolling mill according to the present invention described above, input data and output data of the hydraulic servo system during rolling are respectively collected, and Fourier transform is applied to each data to obtain a Bode diagram. Is created. In the Bode diagram obtained at this time, when the resonance frequency is exceeded, the gain varies and a smooth gain curve cannot be drawn. Therefore, a quadratic transfer function that approximates the gain curve is obtained within a predetermined frequency range, and the deterioration state of the hydraulic servo system is diagnosed based on the resonance frequency and the damping coefficient of the obtained quadratic transfer function. .

[Embodiment of the Invention] A deterioration diagnosis method for a hydraulic servo system for a rolling mill as an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an apparatus for carrying out the method of the present embodiment. 2 and FIG. 2 are graphs showing the Bode diagram and the gain curve of the second-order lag system of the approximation result created in the present embodiment,
FIG. 3 is a control block diagram for explaining the transfer function approximating the hydraulic servo system, FIG. 4 is a Bode diagram for explaining the criteria of the deterioration state determination in the present embodiment, and FIG. 5 is a servo amplifier gain. FIG. 6 is a flow chart for explaining the adjusting means, and FIG. 6 is a graph showing the Bode diagram actually obtained and the gain curve of the second-order delay system of the approximation result.

The rolling system to which the method of this embodiment is applied is the seventh rolling system.
Although the configuration is the same as that shown in the figure, when performing the deterioration diagnosis according to the present embodiment, it is not necessary to disconnect the hydraulic servo system 4 from the rolling system as in the conventional case, and the actual rolling state is kept as it is. Deterioration diagnosis is performed by loading data into the device shown in FIG.

First, an apparatus (hardware configuration) for carrying out the method of the present embodiment will be described with reference to FIG. In FIG. 1, reference numeral 6 is input data D for the servo system target value to the hydraulic servo system 4 and the spool displacement from the hydraulic servo system 4, respectively.
_IN (i) and an interface unit that receives as output data D _OUT (i), 7 is each data D _{IN of the} hydraulic servo system 4.
(i), a memory for storing D _OUT (i), 8 is this memory 7
An FFT unit for performing a fast Fourier transform (FFT) on each of the data D _IN (i) and D _OUT (i) stored in
A Bode diagram creation circuit for creating a Bode diagram based on the data converted by the unit 8 and 10 will be described later with a two-dimensional transfer function G (s) approximating a predetermined frequency section of the gain curve of the created Bode diagram. The section model fitting circuit operated by the means for
The ω, η arithmetic circuit for calculating the resonance frequency ω and the damping coefficient η based on (s), 12 is based on the resonance frequency ω and the damping coefficient η from the ω, η arithmetic circuit 11 This is a servo system diagnostic circuit for diagnosing a deterioration state and outputting an alarm signal or a signal for adjusting the gain of a shevo amplifier.

Next, the deterioration diagnosis of the hydraulic servo system 4 executed by the device configured as described above will be described.

First, input data D _IN (i) of the hydraulic servo system 4 during rolling.
And output data Dout (i) are collected and stored in the memory 7 via the interface unit 6.

Then, the FFT unit 8 collects each data D
After performing the fast Fourier transform on _IN (i) and D _OUT (i), in the Bode diagram creation circuit 9, the gain | H (jω) | is obtained by taking the ratio of input and output, and as shown in FIG. Draw a simple gain curve C ₁ .

The Bode diagram thus obtained is approximated by the transfer function G (s) of the second-order delay system as follows.

Here, the hydraulic servo system 4 can be approximated by a control block diagram of a second-order lag system as shown in FIG. 3, and from this block diagram, the transfer function from the input u _t to the output y _t G (s) can be expressed by the following equation (1).

In the above formula (1), ω ₀ is the natural vibration angular frequency (resonance frequency), η is the damping coefficient, and s is the Laplace operator.

Further, the resonance frequency ω ₀ and the damping coefficient η
Described as (2) and (3).

It is assumed that the hydraulic servo system 4 is approximated by the above equation (1), and the data sequence of the frequency, the gain of the quadratic system model, and the actual product gain in a predetermined frequency section A that is predetermined as shown in FIG. , [Ω _i , 20log | G (jω _i ) |, 20log | H (jω _i ) |], the frequency ω at which | G (jω _i ) | ² fits to | H (jω _i ) | ^2. ₀ and damping coefficient η,
Calculation is performed by the section model fitting circuit 10 and the ω, η calculation circuit 11.

First, when β = 1 / ω ₀ ² and α = ² η / ω ₀ , | G (jω _i ) | ² becomes the following expression (4) from the expression (1).

Here, the evaluation function J is defined by the following expression (5). This corresponds to the error area between the gain curve C ₁ of the actual product data shown in FIG. ₂ and the gain curve C ₂ of the second-order lag system model.

Α and β that minimize the evaluation function J are obtained by obtaining the one satisfying the condition of the following expression (6).

(∂J / ∂α) = 0, (∂J / ∂β) = 0 ... (6) When the equation (5) is applied to the equation (6) and rearranged, the following nonlinear simultaneous equations (7), (8) Is obtained.

α = pβ ² + qβ + r (7) kβ ³ + l ² + mβ + n = 0 (8) Here, p, q, r, k, l, m, and n are constants that can be calculated from the actual product values. By solving the cubic equation relating to β by the above equation (8) and substituting it into the equation (7), α can be obtained. this
After the calculations by the equations (7) and (8) are performed by the section model fitting circuit 10 to determine α and β and the transfer function G (s) is obtained, these α and β are calculated as (2) and (2). The calculation to obtain the resonance frequency ω ₀ and the damping coefficient η by substituting into the equation 3) is ω,
This is performed by the η arithmetic circuit 11.

Based on the resonance frequency ω ₀ and the damping coefficient η obtained as described above, the servo system diagnostic circuit 12 diagnoses the deteriorated state of the hydraulic servo system 4. Here, the relationship between the damping coefficient η and the Bode diagram of the transfer function G (s) is as shown in FIG. If so, the gain becomes high and the system tends to become unstable, It will make you worse. The servo system diagnostic circuit 12 diagnoses the deterioration state of the hydraulic servo system 4 according to such a standard, and outputs an alarm signal or a signal for servo amplifier gain adjustment.

When adjusting the servo amplifier gain g, It is desirable to keep it. As is clear from the equation (3), the damping coefficient η can be changed by operating the servo amplifier gain g. When the gain g is increased, the damping coefficient η is decreased, and when the gain g is decreased, the damping coefficient η is changed. growing. Therefore, as described above, the servo amplifier gain g is adjusted according to the flow shown in FIG. 5 using the calculated and estimated damping coefficient η. That is, for the estimated damping coefficient η (step S1), Is smaller than 0, equal to 0, or larger than 0 (step S2). If equal to 0, no adjustment is made. If smaller than 0, the gain g is decreased by Δg. On the other hand, when the gain g is larger than 0 (step S3), the gain g is adjusted by Δg (step S4).

It should be noted that FIG. 6 shows the gain curve C ₃ obtained from the hydraulic servo system 4 during actual rolling and the gain curve obtained from the second-order lag system transfer function G (s) obtained as a result of the approximate calculation as described above. And C ₄ .

As described above, according to the deterioration diagnosis method of the hydraulic servo system for a rolling mill of the present embodiment, the deterioration state of the hydraulic servo system 4 can be diagnosed by using the data during rolling, so that the hydraulic servo system 4 is disconnected from the rolling system. It is not necessary to input a test signal using a function generator, and deterioration diagnosis can be omitted.
In addition to facilitating the process, deterioration diagnosis can be performed without stopping the rolling mill, which not only speeds up the deterioration diagnosis but also prevents deterioration of the productivity of the rolling line. Also, since model fitting is performed with the frequency axis section determined,
There is also an advantage that it is possible to eliminate variations in data at high frequencies exceeding the resonance frequency and to perform highly accurate diagnosis.

It should be noted that the present invention uses the resonance frequency ω ₀ and the damping coefficient η obtained by the method of the above-described embodiment to measure the gauge meter AG.
It can also be applied to an STR (self-tuning regulator) that appropriately changes the C-system AGC gain online.

[Effects of the Invention] As described in detail above, according to the deterioration diagnosis method for a hydraulic servo system for a rolling mill of the present invention, a quadratic transfer function approximating a predetermined frequency section of a gain curve of a Bode diagram is obtained, Since the deterioration state of the hydraulic servo system is diagnosed based on the resonance frequency and the damping coefficient of the secondary transfer function, the deterioration diagnosis can be performed by using the data during rolling without stopping the rolling mill. It has the effects of facilitating, speeding up, and improving accuracy, and preventing the productivity of the rolling line from decreasing.

[Brief description of drawings]

1 to 6 show a method of diagnosing deterioration of a hydraulic servo system for a rolling mill as one embodiment of the present invention, and FIG. 1 is a block diagram showing the configuration of an apparatus for carrying out the method of this embodiment. FIG. 2 is a Bode diagram created in the present embodiment and a graph showing a gain curve of a second-order lag system as an approximation result. FIG. 3 is a control block diagram explaining a transfer function approximating a hydraulic servo system. FIG. 5 is a Bode diagram for explaining the criteria of deterioration state determination in this embodiment, FIG. 5 is a flowchart for explaining servo amplifier gain adjusting means,
FIG. 6 is a graph showing an actually obtained Bode diagram and a gain curve of a second-order lag system of its approximation result, FIG. 7 is a block diagram showing a general rolling system for performing AGC, and FIG. 8 is FIG. 9 is a control block diagram of the hydraulic servo system, and FIG. 9 is a Bode diagram for explaining the deterioration diagnosing means of the conventional hydraulic servo system. In the figure, 1 ... Work roll, 2 ... Rolled material, 3 ... Rolling load detector, 4 ... Hydraulic servo system, 5 ... AGC calculator,
6 ... Interface part, 7 ... Memory, 8 ... FFT part,
9 ... Bode diagram creation circuit, 10 ... Section model fitting circuit, 11 ... ω, η arithmetic circuit, 12 ... Servo system diagnostic circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G05B 23/02 302 Z 7208-3H (56) Reference JP-A-61-111709 (JP, A)

Claims (1)

[Claims] 1. A rolling mill in which a hydraulic servo system adjusts a roll gap between work rolls to control a plate thickness of a material to be rolled, and input data and output data of the hydraulic servo system during rolling are respectively collected, After performing Fourier transform on each of the collected data to create a Bode diagram,
A quadratic transfer function approximating a predetermined frequency section of the gain curve of the Bode diagram is obtained, and the deterioration state of the hydraulic servo system is diagnosed based on the resonance frequency and the damping coefficient of the quadratic transfer function. Deterioration diagnosis method for hydraulic servo system for rolling mill.