JPS63277910A - Detection signal processing method for infrared thickness gauge - Google Patents

Abstract

PURPOSE:To calibrate an instrument simply and easily with high accuracy by setting the decrease rate of a transmitted light quantity signal with the thickness of a body to be measured based upon the extinction coefficient of the body to be measured as a function of the level of the transmitted light quantity signal, and processing this function and setting a calibration curve. CONSTITUTION:Samples Ta, Tb,... are set on an optical path in order and detection signals Ia, Ib,... are obtained respectively to display the calibration curve. If the calibration curve deviates from a segment L, arithmetic processing based upon equations I and II (when n=1) is carried out in a linearizing process. In this case, the power number (n) in the equations is so set that the correlation coefficient between calculated values (ta', tb',...) and real values ta, tb,... of thickness is maximum. When the linearizing process is finished, the thickness values ta' and tb' of the respective samples Ta and Tb are recalculated again to set a calibration curve. Then the quantity Ii of transmitted light of the body Ti to be measured is measured and its thickness ti is measured automatically by using said calibration curve.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for calibrating an instrument in an infrared thickness needle in advance according to the ei class of the object to be measured, and in particular, to Regarding processing method.

[Conventional technology]

In general, infrared thickness gauges place the object to be measured between a light source and a photodetector, and when the light from the light source passes through the object, it is attenuated by absorption and scattering. This method measures the thickness of an object by utilizing the fact that it is a function of the object's thickness.

In this case, since the amount of attenuation of the transmitted light described above varies depending on the characteristics of the object to be measured, the instrument is calibrated prior to measurement. This calibration is performed by setting a reference line, that is, a calibration curve, determined by the characteristics of the object to be measured.

This calibration curve L (see FIG. 3) is based on the sample T of the object to be measured having known thicknesses ta and tb, which will be explained in detail later.
It is set by measuring the amount of transmitted light (a, (graph shown) is displayed as a straight line. Then, when this calibration curve is set, the amount of transmitted light of the object to be measured 1
By measuring i, the thickness ta' of the object to be measured Ti is automatically measured. This thickness ta' is usually displayed on a CRT included in the thickness gauge or recorded and output from a printer.

By the way, the function related to the attenuation of the amount of transmitted light and the thickness of the object to be measured, that is, the physical side, has conventionally been calculated using the following (5
) formula % formula % (5) where,! − Transmitted light amount detection signal value of the object to be measured■. - the light intensity detection signal value μ when the optical path is open; the extinction coefficient of the object to be measured; and the thickness of the object to be measured. That is, the amount of attenuation of the amount of transmitted light has been determined only by the extinction coefficient μ of the object to be measured.

However, in the measurement method based on equation (5), errors occur in the measured thickness of the object to be measured, for example, for objects that reflect a considerable amount of light, such as plastic sheets or films. Therefore, the applicants adopted the following equation (2) II. is the same as equation (2) shown in claim (2)], and based on this, a measurement method (hereinafter referred to as the first measurement method) for measuring the thickness of the object to be measured was developed. , filed a patent application (Japanese Unexamined Patent Publication No. 58-176508)
Publication No.).

According to this, the influence of reflected light, which conventionally causes errors, is removed, so accurate measurement can be performed even on objects to be measured with high reflectance.

Here, in connection with the instrument calibration method in this first measurement method, setting of the above-mentioned calibration curve will be explained. The calibration curve is: - Two samples Ta.

It is set by measuring Tb, that is, by calculating the physical opening formula (2). That is, the measured value Ia-16(1r) e'ne Ib-I. (1-r) e-)"b, the detection signals 1a, Ib, I. are values obtained by measurement, and the thickness ta.

Since tb is a known value and the two unknown values are the extinction coefficient μ and the reflectance r, the extinction coefficient μ and the reflectance r are calculated from the two measured values. That is, a calibration curve is set. This calibration curve is obtained by logarithmically converting the above equation (2) using the following equation: n0g61s=Ilog6I. (1-r)'', since the extinction coefficient μ and the reflectance r were conventionally assumed to be constant, everything except the thickness t is a constant, so the logarithm of the detection signal I and the thickness t are It becomes a linear equation, and the graph (
(Fig. 3) is displayed as a straight line on the top. The measured thickness tbi of the object to be measured Ti measured using such a calibration curve is based on the reflected light, since the calibration curve includes the factor of the reflectance r. Measurement errors are removed.

However, even in the first measurement method, an error occurs in the measured thickness of the object to be measured, especially when the measured thickness range of the object to be measured d is large. As a result of extensive research, the present applicants found that this error is due to the fact that the extinction coefficient of the object to be measured is not constant with respect to the thickness of the object.

A measurement method that eliminates measurement errors based on this by setting multiple calibration curves (
We developed a new measurement method (hereinafter referred to as the second measurement method) and filed a patent application (Japanese Patent Application No. 65766/1982).

Next, this second measurement method will be briefly explained below.

Note that, as in the first measurement method, the physical law defined by equation (2) is used as the physical law in this measurement method.

In this measurement method, an appropriate number of samples Ta, Tb, and TcwTg whose thicknesses are known are selected according to the thickness range of the object to be measured when calibrating the instrument, that is, when setting a calibration curve. Then, each of these samples is measured and calculated using a scale meter, and then graphically displayed on a CRT provided in the thickness needle, as shown in FIG. In this case, if the sample thickness range is large, the samples TcxTg are generally not located on the calibration curve, and they define a downwardly convex curve M with respect to the calibration curve. Note that this means that in the physical equation (2), the reflectance r does not change, so the extinction coefficient μ changes with respect to the thickness t,
This variation means that it gradually decreases as the thickness t increases. Therefore, in this measurement method, the calibration curve is replaced with line segments and the samples Ta and Td H
Te, TL; multiple line segments Na, Nb passing through Tg, Tb
, Nc.

When setting the calibration curves Na, Nb, and Nc, samples that define each of the calibration curves Na, Nb, and Nc are selected so as to be close to the curve M by observing the graphic display. -' Therefore, according to this measurement method, the thickness ti'' of the object to be measured Ti, which is measured via the calibration curve Ma by measuring the amount of transmitted light Il of the object to be measured Ti, is Even if an error occurs with respect to the true thickness ti to be measured, the error Δtt' is suppressed to a very small value.
10 is significantly improved compared to the error Δti' generated in the first measurement method shown in FIG. It goes without saying that errors based on reflected light are removed. In this way, according to the present measurement method, even if the object to be measured has a wide thickness range, its thickness can be measured with high accuracy.

[Problem that the invention seeks to solve]

In this way, according to the second measurement method described above, even objects to be measured with a wide thickness range can be measured with high accuracy. However, such a measurement method has the drawback that calibration of the instrument requires relatively complicated labor and judgment.

That is, when setting the calibration curves Na and Nb*N', a large number of samples were each measured.

This requires operations such as performing calculations, displaying them graphically, observing this graph, setting a required number of calibration curves, and determining the boundary values of each of these calibration curves. Furthermore, judgment is required to set each calibration curve. For example, as shown in FIG. 4, instead of the calibration curve Na, sample Ta,
If the calibration curve Na' determined by '['c' is set, the measurement error increases from Δ[i'' to Δti9.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an infrared ray thickness needle detection signal processing method that can easily and accurately calibrate an instrument, especially for objects having a wide thickness range. be.

[Means for solving problems]

In order to achieve the above object, the infrared thickness needle detection signal processing method according to the present invention is based on the extinction coefficient of the object to be measured.
The method is characterized in that the rate of decrease of the transmitted light amount detection signal with respect to the thickness of the object to be measured is set as a function of the magnitude of the transmitted light amount detection signal, and the calibration curve is set by arithmetic processing of this function.

In this case, the following formula (1) % formula % (1) - Thickness of the object to be measured α - Parameter n = power number is used as the function, and the transmitted light amount detection signal value in formula +11! teeth,
The following formula (2) % formula % (2) Here, ■. =Light amount detection signal value when the thickness t of the object to be measured is 0, that is, when the optical path is an oven.Reflectance μ of the object to be measured (μ) is defined by the absorption coefficient of the object to be measured.

Also, during calculation processing, the thicknesses ta and tb.

...The following equation (3) t w obtained by integrating the above equation (1) using known samples Ta, Tb, ...
a-0((1-a)-Xo(1-?L month(1-n)α ・ ・ ・ ・ ・(3) Here, when xo − thickness of the object to be measured t is 0, that is, the optical path is Calculate the thickness ta' of each sample based on the logarithm value of the light intensity detection signal in the case of open (nml) and the following formula (4) applied in the case of nml.

It is preferable to measure tb', . be.

[Effect]

The setting of a calibration curve in instrument calibration is achieved by sequentially processing a predetermined function using a combinator, and is therefore easily and quickly performed. Moreover, since the function includes the variation of the extinction coefficient with respect to the thickness of the object to be measured and the respective factors of the reflectance,
Accurate measurements can be made even for objects with a wide thickness range and high reflectance.

〔Example〕

Next, an embodiment of the infrared thick needle detection signal processing method according to the present invention will be described in detail with reference to the accompanying drawings.

First, prior to explaining the processing method, the structure of the infrared thickness needle according to the present invention will be briefly explained.

In FIG. 2, the infrared thickness gage consists of a measuring section 1O and an operator console 12, and the measuring section 10 includes an infrared light source 14 and an object to be measured or a sample whose thickness is known.
6 and a transmitted light detector 20 having a photoelectric conversion element, and the operator console 12 is equipped with an A/D converter 22 . CPU24. Internal storage device 26, operation keyboard 2B, CRT 30. A printer 32 and an external storage device 34 are provided, and the measurement unit 10 and operator console 12 are connected via a conversion amplifier circuit 36, and the CPU 24 is provided with a remote controller 22. When measuring, projection light La is projected from the infrared light source 14, transmitted light Lc transmitted through the object to be measured '16 is detected by the transmitted light detector 20, and a detection signal! Next, this detection signal I is logarithmically converted into a detection signal V in a conversion amplifier circuit 36, and the obtained detection signal V is converted into a signal indicating the thickness of the object to be measured 16 by an A/D converter 22. The image data is converted into W and displayed on the CRT 30 or stored and output from the printer 32 as appropriate. in this case,
The thickness needle is operated via the keyboard 28 or remotely via the operating device 38.

Next, we will discuss the first method for calibrating an infrared thickness gauge according to the present invention.
In the zero calibration explained with reference to the figure, first, the optical path is opened, and the detection signal IO is set in step Sl.
is detected and inputted and stored in the internal storage device 26.
Next, samples Ta, Tb, . . . are sequentially set on the optical path, and the detection signals Ii
are detected and input and stored in the internal storage device 26.Next, in step S3, a calibration curve as shown in FIG. 4 is graphically displayed on the CRT 30 using the stored data.

In this case, if the calibration curve approximates the line segment, the process immediately proceeds to step S8 as shown by the broken line, and if it deviates from the line segment, the process proceeds to a correction, ie, linearizing step.

° In the linearization process, the above equation (3) and t
= -n)α] {x(1-713-Xo(+-fL)
)(1-n)α ・ ・ ・ ・ ・(3) The calculation process is performed based on the formula (4) applied when n-1. The calculated thickness ta' is calculated during the calculation process.

tb', ... and true thickness ta, tb, ...
The value that maximizes the correlation coefficient m is selected.

In this linearization process, the number of powers n is calculated sequentially such that n=o, 1, 2, etc. The first step is to input integer values sequentially starting from 0 and select the value of n' that maximizes the m, and the selected value n' is set to ± in 0.1 increments. The process is divided into a second step of inputting numerical values in the range of 0.5 and selecting the value of n'±Δn' at which the m is the maximum value. That is, in the first step of linearization, the values of n are sequentially set to 0, 1°2, . . . in step S4.
are input and their corresponding values of m are calculated and compared. Table 1 shows the calculation results in this step for a certain sample, where m has a maximum value of 0 at n-w4.
．． 99992. Then, in step S6 in the second step of linearization, n
'' values 3.6, 3.7, ... are input, and the corresponding values of m are calculated and compared. Table 2 shows the results of the calculation. This shows that the maximum value is 0.99997.
The value of the correlation coefficient m does not exceed 1 due to its nature. Furthermore, these linearization steps are automatically performed by a combiator and are usually completed in about 10 seconds.

Table 1 Table 2 When the linearization process is completed in this way, in step S8, the thicknesses ta', tb' of each sample Ta, Tb, . . . are calculated again based on the calculation results, and in step S9 The calibration curve thus set is displayed graphically and confirmed, and finally, these data are registered in the external storage device 34 in step 310. In addition, for this registration, the above-mentioned formula (1)
Since it is organized in the form t-Ax"" +B, it is preferable to register it as parameters A, B, and n.

As a result, the calibration of the instrument is completed, that is, the setting of the calibration curve is completed, and the thickness ti' of the object to be measured Ti is automatically measured via the calibration curve by measuring the amount of transmitted light 1i. , the numerical value is displayed on a CRT or recorded and output from a printer. The thickness of the measured object measured in this way is - For example, in the sample used in the linearization process, the variation (2σ)
° was 0.34%. This value represents a significant improvement over the 8.4% variation in the conventional measurement method, ie, the measurement method without linearization, for the same sample.

As described above, the calibration method according to the present invention can be performed easily and without any judgment work, and furthermore, the calibration error can be suppressed to a small level.

Although the preferred embodiments of the present invention have been described above, various design changes can be made to the present invention without departing from the spirit thereof.

For example, the graphic display in steps S8 and S9, that is, the calibration curve confirmation operation may be omitted;
It goes without saying that the present invention is applicable not only to infrared thickness gauges but also to other optical thickness gauges that use ultraviolet light or the like.

〔Effect of the invention〕

As explained above, the infrared thickness needle detection signal processing method according to the present invention is based on fluctuations in the extinction coefficient of the object to be measured.
The reduction rate of the transmitted light amount detection signal with respect to the thickness of the object to be measured is set as a function of the magnitude of the transmitted light amount detection signal, and the calibration curve can be set by calculating this function. By performing the calibration using a computer, the calibration of the meter can be easily accomplished without requiring any judgment work. Moreover, the calibration error can be suppressed to a small level. Therefore, the thickness of an object to be measured whose thickness range is wide and whose extinction coefficient fluctuates can be easily and accurately measured. Furthermore, since the function includes a factor related to the reflectance of the object to be measured, the thickness of the object can be accurately measured even if the object has a relatively high reflectance.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing an embodiment of the instrument calibration method in the detection signal processing method for the infrared thickness needle according to the present invention, and FIG. 2 is a block diagram showing the configuration of the infrared thickness needle according to the present invention. Fig. 3 is a graph explaining a calibration curve set during instrument calibration of a conventional infrared thickness gauge, and Fig. 4 is a graph explaining a calibration curve set during instrument calibration of an infrared thickness gauge, which is the basis of the present invention. It is a graph explaining a line. 10. Measurement part 12. ,,Operator console 14, ,Infrared light source 16, ,Object to be measured or its sample 1B, ,Holder 20. ,, transmitted light detector 22. ,, A/
D converter 24. ,, CPU U26, , Internal storage device 28. ,,operation keyboard 30,...CRT
32. ,,Printer 34,,,External storage device 36. ,,conversion amplifier circuit 38, ,remote controller Tol, sample or object to be measured ■60. Transmitted light transmitted light detector o, true thickness of the sample or object to be measured Δt01.
Measurement error t', t"60. Calculated thickness or measured thickness of sample or object to be measured. FIG. 1

Claims (3)

[Claims] (1) Set the reduction rate of the transmitted light amount detection signal with respect to the thickness of the measured object based on the extinction coefficient of the measured object as a function of the magnitude of the transmitted light amount detection signal, and calculate the calibration curve by processing this function. A detection signal processing method for an infrared thickness gauge, characterized in that: (2) In the detection signal processing method according to claim 1, the function is expressed by the following formula (1) dx/dt=-αx^n (1) where x=lnI I=transmission Light amount detection signal value t = object thickness α = parameter n = power number, and the transmitted light amount detection signal value I in equation (1) is expressed by the following equation (2) I = I_o(1-r)e^- ^μ^t...(2) Here, I_o = light amount detection signal value r when the thickness of the object to be measured t is 0, that is, when the optical path is open = reflectance μ of the object to be measured = A detection signal processing method for an infrared thickness gauge that is defined by the extinction coefficient of the object to be measured. (3) In the detection signal processing method according to claim 2, the arithmetic processing is performed by integrating the equation (1) using the known samples Ta, Tb, ... with thicknesses ta, tb, ... The following formula (3) is obtained: t=-[1/(1-n)α]{x^(^1^-^n^)
-x_o^(^1^-^n^)}...(3) Here, x_o=pair of light intensity detection signals when the measured object thickness t is 0, that is, when the optical path is open. Numerical value, where n≠1, and the following formula (4), which is valid when n=1, t=-1
/α(ln x−ln x_o) (4) Calculated thickness ta′, tb′ of each sample based on
,... and selects the value of the power number n that maximizes the value of the correlation coefficient m between the calculated thickness and the true thickness by successive least squares calculations.