DE102015002094B3 - Method for determining the thickness of a rolled strip - Google Patents

Abstract

The invention relates to a method for determining the thickness of a rolled strip with an upper and a lower laser distance sensor, each having a device for exposure control, and an evaluation. The problem of currently known methods is that the measuring frequency is relatively low, which results in disadvantages with regard to the accuracy of the measuring process. The solution of the problem results from the following method steps according to the characterizing features of claim 1: each laser distance sensor reports its individually calculated exposure time for the next measured value recording to the evaluation electronics; - The transmitter calculates for each laser distance sensor the optimal starting point of the next exposure, wherein the calculation is performed so that the most symmetrical temporal overlap of the measurements is achieved; - The transmitter transmits an individual pulse to start the measurement to each laser distance sensor.

Description

The invention relates to a method for determining the thickness of a rolled strip with an upper and a lower laser distance sensor, each having a device for exposure control, and an evaluation.

Such a method is generally known from the prior art document which can not be assigned by reference. In this case, the upper as well as the lower laser distance sensor each performs a distance measurement, that is, it measures the distance from the sensor to the belt surface or lower belt surface. From the sum of the two distance measured values (upper and lower sensor) and a constant (distance of the two sensors to each other), a thickness measured value is calculated. The thickness readings are then filtered before being assigned to the corresponding band section. From a large number of thickness measured values, the thickness profile for a so-called roll pass arises. In this known method, the maximum possible exposure time is first calculated by the evaluation electronics for both laser distance sensors together before the start of the distance measurements. This results on the one hand from the technical possibilities of the two measuring devices and the downstream data processing and the loss of laser power due to aging and the reduction of the transparency of the sensor window. On the other hand, in the calculation of the maximum exposure time, the surface texture and the appearance of the rolled strip, such. As color, roughness, gloss, wetting, a meaning.

Thus, in the prior art, regardless of the actual exposure time of each individual laser distance sensor, the transmitter determines the maximum exposure time, which is chosen so large that before the next distance measurements with certainty, the previous distance measurements are completed.

Specifically, this means that before the start of a rolling pass - ie before a reduction in the thickness of the rolled strip within a roller assembly - the evaluation unit statically sets the maximum exposure time for both laser distance sensors. This definition includes, for example, the expected surface condition of the strip and the maximum laser power of the two distance sensors. Since the specification applies to the entire rolling pass, a worst-case assumption must be made, the achievable measuring frequency is correspondingly low. In addition, there is the danger that, if the measurement frequency is set too high, no thickness values can be determined on a longer contiguous band section due to underexposure. This can eventually lead to failure of the roller control.

In summary, this method according to the prior art thus has the disadvantage that the measuring frequency is relatively low, resulting in disadvantages with regard to the accuracy of the measuring process. In this context, it should be noted that the measurement accuracy required today is in the range of a few μm (1 μm = 10 ^-6 m).

Furthermore, from the WO 1996 003 616 A1 a strip thickness measuring device is known, which discloses the optics for measuring the strip thickness by means of two laser distance sensors.

Based on the prior art described above, the object of the invention is therefore to provide a new method for determining the thickness of a rolled strip with an upper and a lower laser distance sensor, which on the one hand has a higher measuring frequency and on the other hand automatically compensates the aging process of the measuring devices.

• – Jeder Laserabstandssensor meldet seine individuell berechnete Belichtungszeit für die nächste Messwertaufnahme an die Auswerteelektronik;
• – Die Auswerteelektronik berechnet für jeden Laserabstandssensor den optimalen Startpunkt der nächsten Belichtung, wobei die Berechnung so durchgeführt wird, dass eine möglichst symmetrische zeitliche Überlappung der Messungen erreicht wird;
• – Die Auswerteelektronik übermittelt einen individuellen Impuls zum Start der Messung an jeden Laserabstandssensor.

The solution of the problem results from the features of claim 1, which is characterized by the following method steps:

• - Each laser distance sensor reports its individually calculated exposure time for the next measurement acquisition to the transmitter;
• - The transmitter calculates for each laser distance sensor the optimal starting point of the next exposure, wherein the calculation is performed so that the most symmetrical temporal overlap of the measurements is achieved;
• - The transmitter transmits an individual pulse to start the measurement to each laser distance sensor.

The inventive method has the significant advantage that the measurement frequency is increased on the one hand and on the other hand, the accuracy of the measurement process increases.

In this case, it is essential for the method according to the invention that the evaluation electronics do not assume a "long" static exposure time in the control and regulation of the thickness measurements, but take into account the "shorter" individual exposure time of the individual laser distance sensors. These are depending on the surface texture and appearance of the rolled strip, such. As color, roughness, gloss, wetting, etc. and on the other hand, taking into account the resulting on the time axis determined age-related changes of the individual components of the laser distance sensor.

As a result, according to the invention, the difference between the largest individually calculated exposure time of the laser distance sensors and the maximum exposure time (according to the prior art) is saved with each thickness measurement, so that significantly more measurements per unit of time can be carried out.

In addition, it is advantageous that the measurements of the upper and lower distance sensor are synchronized in an optimal way and also band vibrations due to the higher measurement frequency can be compensated much better.

Furthermore, it should be noted that it is possible to respond flexibly to unexpectedly high light requirements. Instead of a complete failure due to underexposure, there is only a temporary deterioration of the measurement accuracy. The nip control can continue to operate.

In an advantageous embodiment of the method according to the invention, the frequency of the thickness measurement is between> 30 kHz and <100 kHz.

In summary, the inventive method allows a much higher accuracy of the thickness measurements due to a larger number of measurements per unit time.

Further advantages of the invention will become apparent from the following description of an embodiment. Show it:

1 a partial schematic representation of a rolling mill,

2 a partial representation of the area II in 1 .

3 a representation of the "measurement frequency" according to the prior art and

4 a representation of the "measurement frequency" according to the inventive method.

In the 1 partially a rolling mill W is shown schematically. It can be seen that during the rolling process, a band 11 is transported in the direction of movement x. The ribbon 11 is due to numerous role arrangements 12 supported and moved in the x-direction, taking between the role arrangements 12 each rolling stands 13 are arranged, which in the direction of movement x each have a decreasing roll gap 14 exhibit.

In the direction of movement x before and after each roll stand 13 each is a device 15 arranged to determine the thickness of moving, band-shaped and plate-shaped materials, with which thickness irregularities in the band 11 in front of the rolling stand 13 or the thickness of the band 11 after a rolling process in a rolling stand 13 is measured. In the present case, it is a three-stage rolling process, wherein the thin end product 11 ultimately to a coil 16 being rolled up.

In the 2 is the one with II in the 1 marked area shown enlarged. You can see the mill stand 13 with two outer support rollers 17 and two inner work rolls 18 that the nip 14 define.

The device for thickness measurement 15 becomes an upper laser distance sensor 19 and a lower laser distance sensor 20 educated. In the area of the upper laser distance sensor 19 is also an evaluation electronics 21 exist whose function is described below.

In the 3 is on a time axis y the method for determining the thickness of a rolled strip 11 by means of the upper laser distance sensor 19 and the lower laser distance sensor 20 represented according to the prior art.

It can be seen that the distance measurements of the two laser distance sensors 19 and 20 at a common starting point 22 to be started. On this basis, it is further shown that the exposure times 23 and 24 of the upper laser distance sensor 19 and the lower laser distance sensor 20 are different. These different exposure times 23 and 24 On the one hand, this is due to the fact that the components in the measuring device change as a result of an aging process. This concerns, for example, the loss of laser power due to aging, the change in the transparency of the sensor windows or the aging of the detector. On the other hand, factors are added that relate to the surface condition of the rolled strip at the time of measurement, such. As color, roughness, gloss, wetting of the rolled strip.

Time closes to the longest exposure time 23 or 24 a laser distance sensor 19 . 20 a calculation time 25 in, from the results of the two distance measurements of the laser distance sensors 19 and 20 a thickness measurement is calculated.

In addition, there is a so-called static safety margin 26 , which is the longest exposure time 23 . 24 one of the two laser distance sensors 19 and 20 as well as the computing time 25 is pitched. In total, then corresponds to the longest exposure time 23 . 24 the laser distance sensors 19 . 20 plus the computing time 25 and the safety margin 26 the maximum possible exposure time. Only after the maximum exposure time has passed, can thus at the common starting point 22 new distance measurements of the laser distance sensors 19 and 20 be set in motion.

The maximum possible exposure time (exposure time 23 / 24 + Computing time 25 + Safety margin 26 ) is made before the start of distance measurements from the transmitter 21 established. This maximum exposure time or, in other words, the resulting measurement frequency, on the one hand determined by the technical data of the laser distance sensors 19 and 20 and the downstream data processing system and on the other hand - as already explained above - by the aging process of the components of the measuring device as well as the surface properties of the rolled strip.

Due to this static determination of the maximum exposure time, the frequency of the distance measurement is at a maximum of 30 kHz, which is because a distance measurement due to the static safety margin 26 a total of about 28 μs takes.

In the 4 Finally, the inventive method is shown on a time axis y. Again you can see the upper laser distance sensor 19 and the lower laser distance sensor 20 ,

Prerequisite for the time course of the distance measurements shown there is the essential feature of the invention method that each laser distance sensor 19 . 20 before the distance measurement its individual exposure time 23 . 24 the transmitter 21 reports and this the optimal starting point for each laser distance sensor 19 . 20 calculated and an individual pulse to start the measurement to each laser distance sensor 19 . 20 sends.

In principle, there is also the possibility that the evaluation electronics 21 the exposure times 23 . 24 for both distance sensors 19 . 20 based on the exposure times used in the last measurements 23 . 24 estimates. She then gives for both distance sensors 19 . 20 a common exposure window. The distance sensors 19 . 20 Illuminate each in the middle of this window with the time you want.

This results - as in 4 shown - individual starting points 27.1 and 27.2 the distance measurements of the laser distance sensors 19 and 20 and the fact that the exposure times 23 and 24 the laser distance sensors 19 and 20 with regard to a centering axis 28 the measurements are centered.

According to the invention then only the computing time closes 25 at which then immediately again at the individual starting points 27.1 and 27.2 of the upper laser distance sensor 19 and the lower laser distance sensor 20 a distance measurement can begin.

As a result, this means that through the actual, dynamic acquisition, calculation and consideration of the longest exposure times 23 . 24 the two laser distance sensors 19 and 20 on the necessary safety margin in the prior art 26 can be omitted and the result is a significantly higher frequency of up to 100 kHz can be achieved.

Ultimately, this is a much more accurate and faster thickness measurement of the rolled strip 11 achieved, whereby at the same time the nip 14 can be regulated more accurately and faster. This leads to end products, which - as required by the customer - have lower thickness deviations.

LIST OF REFERENCE NUMBERS

10

contraption

11

rolled strip

12

roller assemblies

13

rolling mill

14

nip

15

Device for measuring thickness

16

coil

17

outer support roller

18

inner stripper

19

Upper laser distance sensor

20

lower laser distance sensor

21

evaluation

22

common starting points of the measurement in the prior art ( 3 )

23

exposure time 23 from 19

24

exposure time 24 from 20

25

computing time

26

static safety margin for maximum exposure time

27.1

individual starting points of the measurement of 19 and 20

27.2

individual starting points of the measurement of 19 and 20

28

"Centering axis" of the measurements

x

Direction of movement of the rolled strip 11

y

Time

Claims (2)

Method for determining the thickness of a rolled strip ( 11 ) with an upper and a lower laser distance sensor ( 19 . 20 ), each having a device for exposure control, and an evaluation ( 21 ), characterized by the following method steps: each laser distance sensor ( 19 . 20 ) reports its individually calculated exposure time ( 23 . 24 ) for the next measurement acquisition to the evaluation electronics ( 21 ); - The transmitter ( 21 ) calculated for each laser distance sensor ( 19 . 20 ) individually the optimal starting point of the next exposure ( 27.1 . 27.2 ), wherein the calculation is performed in such a way that the most symmetrical temporal overlapping of the measurements is achieved; - The transmitter ( 21 ) transmits an individual impulse to start the measurement to each laser distance sensor ( 19 . 20 ). A method according to claim 1, characterized in that the frequency of the thickness measurement is between> 30 kHz and <100 kHz.

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