JP2021162526A - Highly precise temperature measurement method of heating element traveling continuously - Google Patents

Abstract

To establish a highly precise temperature measurement method of a heating element traveling continuously by suppressing a decrease in measurement precision in noncontact measurement of temperature distribution of a heating element moved continuously and a decrease in precision because of discontinuity of a measurement image caused by a temperature change in a measurement line.SOLUTION: A camera in which a 2-wavelength filter is installed in a mosaic pattern in each pixel of a CCD or a C-MOS sensor is prepared. A shield is installed in an upper part of a measurement object part of a fluid heating element such that a heating element is exposed in a rectangular strip form with a direction perpendicular to a flow as a long side. The positions of respective strip-shaped images obtained by continuously photographing the exposed part by the camera are recognized from the shape of an unheated material, a plurality of strip images are processed so as to obtain a composited image as a continuous image or a single image, and the image is processed by a two-color temperature method so as to obtain a temperature distribution, thus establishing a precise measurement method.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method of measuring the temperature distribution of a heating element that is continuously moved in a manufacturing process with high accuracy without contact.

In the conventional measurement method for a continuously moving heating element, a radiation thermometer or thermography for point measurement is installed above a non-heated material and data is acquired at a fixed time. (Fig. 1)

As another method, a thermography was devised in which a large number of line sensor cameras in which a large number of photodiodes were arranged at right angles to the moving direction were installed, and the speed of the belt conveyor was also acquired to obtain the radiation temperature as a distribution.

JP-A-2020-38107 JP 2001-157214 Japanese Patent Application Laid-Open No. 2003-344166 Patent Gazette 4378003

With conventional measurement methods,
(1) The measurement accuracy is reduced due to the influence of synchrotron radiation from the measurement point of the point / sensor or the measurement line of the line sensor.
(2) In the line sensor method, the accuracy was low because the two-color method using the mosaic type sensor could not be adopted. Even if filters with different wavelengths are attached to each pixel, accuracy cannot be expected.
(3) In the line sensor method, the condition is that the moving speed of the material to be heated on the measurement line is stable. Therefore, even a slight change in speed is easily affected by stable temperature measurement image acquisition, and as a result, accurate image construction is not easy.
There was a problem.

The outline of the invention of the present application will be described as follows. That is, the present invention has a camera in which filters of two wavelengths are installed in a mosaic pattern on each pixel of a CCD or C-MOS sensor, and has a long side in a direction perpendicular to the flow above the measurement target portion of the flow heating element. A light-shielding object is provided so that the heating element is exposed in a rectangular strip shape, and each strip-shaped image in which the exposed portion is continuously photographed by the camera recognizes the position from the shape of the non-heated material or the added position marker, and a plurality of strips are recognized. A strip image is processed and combined to obtain a continuous or single image, and the image is processed by the two-color temperature method to obtain a temperature distribution, so that the temperature distribution of the heating element that is continuously moved is non-contact. Achieves high-precision measurement. Further, the flowing heating element in the present invention can cope with both continuous flow and intermittent flow.

According to the present invention, a rectangle having a long side perpendicular to the flow is placed above a measurement target portion of a flow heating element and a camera or the like in which a filter having two wavelengths is installed in a mosaic pattern on each pixel of a CCD or C-MOS sensor. A highly accurate temperature distribution can be obtained by processing with a two-color temperature method using a light-shielding object that exposes the heating element in a strip shape.

Conventional measurement method for continuously moving heating elements Conceptual diagram of a method for measuring the temperature distribution of a continuously moving heating element with high accuracy without contact Mosaic filter example Conceptual diagram of 2-branch optical system 2-sensor optical system example A photographed image in which a light-shielding object is installed and images at two wavelengths are taken at the same time and intermittently on the same optical axis. A composite image from the strip-shaped image of FIG. Example of a method of synthesizing by matching the coincidence points of image features An example of recording a marker in an image and synthesizing it based on that marker

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention can be implemented in many different embodiments and should not be construed as limited to the description of the embodiments. The same elements shall be numbered the same throughout the embodiment.

In the following embodiments, the method will be mainly described, but as will be apparent to those skilled in the art, the present invention includes a camera in which a two-wavelength filter is arranged in a mosaic pattern on each pixel of a CCD or C-MOS sensor. The embodiment of the combination can be taken by a rectangular strip shape in which the direction perpendicular to the flow is installed or a light-shielding object having a shape other than that. Further, the method of synthesizing one image from a plurality of images can be an embodiment by adopting any method in addition to the method of creating the image based on the feature points of the images.

FIG. 2 is a conceptual diagram of the present invention. Prepare a camera in which a two-wavelength filter is installed in a mosaic pattern on each pixel of the CCD or C-MOS sensor. A light-shielding object is installed above the measurement target portion of the flow heating element so that the heating element is exposed in the shape of a rectangular strip whose long side is perpendicular to the flow. Each strip-shaped image of this exposed portion continuously photographed by the camera is recognized as its position from the shape features and markers of the material to be heated, and a plurality of strip images are processed and combined to form a continuous or single image. Obtained and processed by the two-color temperature method to obtain a temperature distribution. The flowing heating element can handle both continuous flow and intermittent flow.

In order to measure the temperature of a high-temperature workpiece of 300 ° C. or higher in a non-contact manner, the electromagnetic radiation emitted from the measurement target is measured, and the temperature is calculated from the intensity. As a commercial product, there is a radiation thermometer that obtains the temperature from visible light or infrared light, and there is thermography that measures the temperature distribution.
A general measurement target is a non-blackbody, and in order to know the true temperature from a radiation thermometer and the true temperature from thermography, it is necessary to correct it with the emissivity, which is the ratio of the amount of radiation to the blackbody. However, since the emissivity of a non-blackbody generally differs depending on its material, shape, and temperature, it is difficult to obtain an accurate temperature.

Therefore, the two-color temperature method is used.
The two-color temperature method pays attention to the fact that the emissivity of the radiation of two adjacent wavelengths is the same, and since the ratio of the radiation amount of the two wavelengths has a functional relationship with the true temperature, the radiation amount at the two wavelengths is measured and true. Calculate the temperature.
Radiation utilization at wavelength λ is obtained by Planck's radiation equation.

When the emissivity of the object is ε and the transmittance from the object to the measurement system is τ, it is shown below.

Applying Woon's approximation formula, assuming that the radiant energy at the lengths of two waves λ1 and λ2 is M1, M2, the emissivity ε1, ε2, the transmittance is τ1, τ2, and the conversion efficiency β1 and β2 of the sensor, etc., the wavelengths λ1 and λ2 Then the 2 wavelength ratio R is

By bringing the two wavelengths of radiation acquisition close to each other, the emissivity ε1 = ε2, τ1 = τ2, β1 = β2, the emissivity ε, transmittance τ, and conversion efficiency β are canceled, and the ratio of radiation amount is functionally related to temperature. It is known to be in.

Even if the emissivity and transmittance of inclusions at two wavelengths are different, if the ratio does not change with temperature, the true temperature of the object whose temperature changes can be known by correcting the ratio with the blackbody. be able to.

The advantages of performing two-color temperature measurements on images are:
Conventionally, two sets of light receiving sensors that receive different specific wavelengths are prepared by attaching a bandpass filter to the photodiode, and the output of the light receiving sensor is measured by the calculation of the number 1 to the number 5 to measure the two-color temperature. .. However, in order to obtain the temperature distribution of a product or the like, a plurality of sets of sensors are required, which is complicated to control and at the same time causes an increase in cost. Focusing on the fact that camera sensors such as CCD and C-MOS have photodiodes arranged in a compound eye, it was devised to apply this to two-color temperature measurement (Patent Publication No. 4378003). A general camera intentionally makes the electric output with respect to light incident non-linear, but here it is necessary to use a camera that emphasizes the linearity.

Regarding the camera for acquiring the amount of radiation used in the two-color temperature method, if we explain a camera using a sensor with a mosaic filter,
As a method of obtaining a distribution image of the amount of radiation at two wavelengths, a method of preparing two cameras equipped with a bandpass filter on the front surface of the sensor or the front surface of the objective lens, and a mosaic of λ1 and λ2 filters alternately for each pixel on the front surface of the sensor. There is a method of using a camera pasted in a shape. Single-plate color cameras with red, green, and blue pasted on the sensor in a mosaic pattern are widely used for consumer and industrial purposes, and a two-color temperature measuring device using this has been published as Patent No. 4378003. There is. A sensor has also been devised, in which a near-infrared two-wavelength filter is attached in a mosaic pattern for relatively low temperature measurement. (Special application 2018-165055)
FIG. 3 shows an example of a sensor with a mosaic filter as a structure of the sensor with a mosaic filter. Each pixel receives light passing through only the first wavelength or the second wavelength. For signals of other wavelengths that cannot be received by a certain pixel, the values of signals of other wavelengths in the vicinity are calculated and output. In the example of FIG. 3, since the second pixel from the top to the second from the left cannot receive the signal of the second wavelength, the value of the four signals of the second wavelength on the left, right, top and bottom of the self is added and divided by 4. Is the value of its own second signal. As a result, the amount of radiation of two wavelengths is acquired. As a result, only one piece of hardware related to radiation reception is required, and the color (wavelength) resolution is halved, but a significant cost reduction is possible. It is widely used in consumer color cameras because of this advantage.

To show the advantages of the mosaic filter method in the two-color temperature method,
Image sensors such as CCD and C-MOS are configured by arranging photodiodes in a matrix on a base material of silicon or injume, galium, and arsenic. These photodiodes are affected by the ambient temperature and drift significantly. When trying to receive radiation of two wavelengths with two cameras in two-color temperature measurement, complicated control is required to control the ratio of the two cameras so that they do not drift due to changes in ambient temperature, which is complicated. The configuration is as follows. On the other hand, when a mosaic filter type camera is used, the temperature drift of the radiation output at both wavelengths becomes the same value, and when the ratio is calculated, the drift value is erased, eliminating the need for a complicated drift control configuration. There is a big merit.

A two-branch optical system camera in the two-color temperature method and a two-sensor camera in the two-color temperature method will be described.

Two-branch optical system camera in the two-color temperature method Fig. 4 shows a conceptual diagram of the two-branch optical system. It is a camera having an optical system that divides the area of a single sensor and receives the first wavelength and the second wavelength. An additional structure such as a relay lens is required to actually configure this optical system.
In this optical system, an image of two wavelengths is received on a single sensor, and the output ratio of radiation at both wavelengths is not affected by changes in the environment such as ambient temperature. The cost is low because it consists of a sensor and one incidental electric circuit. In addition, since the sensor surface is divided into two wavelengths to receive light, the image becomes strip-shaped, but this is not inconvenient for this application. However, there is a demerit that it is not suitable for low temperature measurement because the optical system becomes complicated and the optical loss increases.

Two-sensor camera in two-color temperature method
After incorporating two sensors in one housing, splitting the optical path of incident light into two with a semi-transmissive reflector (beam splitter) or a wavelength selective reflector (dichroic mirror), and placing a wavelength selection filter in each optical path. , Input to each image sensor. The true temperature is obtained by the two-color temperature method from the ratio of the output values of both sensors, but the cost increases because it is necessary to control the temperature of the sensors so that both sensors are not affected by changes in the environmental temperature. However, since no optical loss occurs, the sensitivity is higher than that of a sensor using a sensor with a mosaic filter or a two-branch optical system camera, and it is suitable for lower temperature measurement.
Although an example of the basic two-sensor system is shown in FIG. 5, a semitransmissive mirror may be placed in front of the objective lens, and a relay lens may be placed after the semitransmissive mirror and between the sensors.

The problems of the conventional method are (1) the measurement accuracy is lowered due to the influence of the synchrotron radiation from the measurement point or the periphery of the measurement line (2) the line sensor method cannot adopt the two-color method using the mosaic type sensor. Even if filters with different wavelengths are attached to each pixel, the accuracy is low. (3) With the line sensor method, it is difficult to construct an image due to subtle speed changes in the line. The conventional problem can be solved by installing a light-shielding object so that the long side is perpendicular to the flow direction and taking images at two wavelengths simultaneously and intermittently on the same optical axis.

Taking the captured image as an example, taking the composition method as an example,
FIG. 6 shows a continuous image or FIG. 7 by extracting a feature portion in the strip image obtained by intermittent photography, which is an example of the captured image acquired in the shape of a rectangular strip, and connecting and synthesizing a plurality of images. Combine the individual images as shown and calculate the two-color temperature from the emission ratio of the two wavelengths.

Here, there are two methods for creating one image from a plurality of strip-shaped images. One is a method of matching points where the features in the image match (FIG. 8), and the other is a method of recording a mark in the image and synthesizing the image based on the mark. (Fig. 9) The latter method is easier. With either method, it is possible to correct the truncation of the overlapping portion and the displacement of the position such as rotation by software processing.

The advantage of the present invention is
(1) A two-dimensional temperature distribution instead of a point can be carried out by the two-color temperature method.
(2) Two-color temperature processing using a mosaic-type two-wavelength sensor camera or a two-branch optical system camera is possible, and the influence of ambient temperature can be avoided.
(3) Not affected by speed changes on the belt conveyor.
(4) Additive averaging and image recognition can be processed at high speed.
(5) The influence of stray light from the surroundings can be avoided by installing a light-shielding object.
Can be given.

Claims (6)

A temperature measuring device that has a device that covers the heat-generating workpiece to be flow-processed in a rectangular shape with a long side in the direction perpendicular to the flow direction, and captures this as an image. The device according to claim 1, which recognizes feature points in an image and reconstructs one image or a continuous image from a plurality of images by image composition processing. The device of claim 2, which calculates the temperature distribution from the reconstructed image by the two-color temperature method. The device of claim 3 which has a mosaic sensor. In the apparatus of claim 3, the same-axis image is separated into two wavelengths via a two-branch optical system, this is received in a divided area of a single sensor, and the temperature is measured from the output by the two-color temperature method. Equipment to The device according to claim 3, wherein a camera having two time-synchronized sensors or two cameras receives radiation of two wavelengths and measures the temperature from the output by the two-color temperature method.

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