JP2007139653A - Non-contact type flaw detection device and non-contact type flaw detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-contact type flaw detection device capable of rapidly performing non-destructive inspection due to a shearography method with high precision, and a non-contact type flaw detection method. <P>SOLUTION: The non-contact type flaw detection device is equipped with an induction heater 101 for applying heat strain to an inspection target A, a laser oscillator 102 for irradiating the inspection target A with a laser beam, an image measuring means 104 for shifting the reflected image from the inspection target A in a specific direction to perform double exposure measurement, an image analyzing means 204 for forming an inspection image from the differential image obtained by the image measuring means 104 and a cooling air sending means 106 for cooling the inspection target A. During double exposure measurement, the driving of the cooling air sending means 106 is stopped or the flow direction of cooling air 106a sent from the cooling air sending means 106 and the shift direction of a reflected image are allowed to coincide or approximate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-contact type defect inspection method called a shearography method and an apparatus for executing the defect inspection method, and more particularly to a defect inspection apparatus and method of this type in the case where thermal distortion is applied to an inspection object. The present invention relates to a means for improving inspection efficiency.

  Conventionally, in nondestructive inspections for various structural materials, VT (visual inspection method), PT (penetration flaw detection method), and the like are widely used to inspect the presence or absence of defects in an inspection object. VT is a very simple and quick non-destructive inspection method, but because judgment is left to the human eye, there are individual differences in judgment results and it is difficult to say that it is a highly reliable non-destructive inspection method. . In recent years, a VT using a photographing means such as a digital camera has been used to deal with such a drawback, but it has been pointed out that a defect is easily overlooked depending on the surface state of the inspection object. In addition, this method has a problem that, in principle, internal defects below the surface cannot be detected, so that practically sufficient defect data cannot be obtained.

  On the other hand, PT is a technology that applies a penetrating liquid to an inspection object to infiltrate the defect, wipes off the excess penetrating liquid, and then applies it with a developer to make the defect easy to see. Although it has an advantage of being very high, there is a problem in that it requires a lot of labor to apply and wipe the penetrating solution and the developer, and takes a long time for the inspection. Also, this method cannot detect internal defects under the surface in principle as in the case of VT.

  For these reasons, in recent years, optical nondestructive inspection techniques have been developed in order to realize quick and reliable nondestructive inspection.

  As an optical nondestructive inspection technique, a shearography method has been conventionally known. The inspection principle of the shearography method is as follows. First, the measurement target region is enlarged and irradiated with laser light. The reflected light from the measurement target region becomes a speckle pattern because the light being used is highly coherent laser light and the surface of the measurement target is diffusive. The reflected image from the measurement target region is divided into two by a spectroscopic element installed in front of the image sensor, and the two reflected images are slightly shifted in the direction of the surface of the measurement object and photographed by an image sensor such as a CCD. Due to the double exposure of the image sensor, the captured reflected image becomes a differential image. Further, since the laser light has high coherence, the two images that are double-exposed interfere with each other, and the double-exposed pattern becomes an interference pattern. By performing this operation twice in the course of changes in external stress, the temporal change in the differential value of strain due to external stress can be obtained as a phase change in the interference pattern, and a minute surface distortion at the wavelength level of the laser beam used can be obtained. It is measured. Since the local distortion that differs from the surroundings occurs in the part where the defect exists, by removing the low-frequency distortion due to external stress by making it a differential image, only the local distortion at the defect part is imaged, A defect can be extracted (for example, refer nonpatent literature 1).

In addition, as a means for imparting strain to the inspection object when performing the shearography method, in addition to methods such as placing the inspection object in a decompression chamber or mechanically pressing the inspection object, A method of heating has also been proposed (see, for example, Patent Document 1).
Mineyuki Hayakawa, “Non-destructive internal defect inspection by shearography”, inspection technology, Nihon Kogyo Publishing, published on June 1, 2004, Vol. 9, NO. 6, pages 21 to 26 JP 7-218449 A

  When heating means is used as means for imparting strain to the inspection object, the inspection equipment can be made smaller, simpler, and cheaper than when a decompression chamber or a mechanical pressing device is provided. In this defect inspection device, there is no cooling means for the inspection object, and the inspection object is cooled by natural heat dissipation. There is an inconvenience that it cannot be done.

  In addition, according to the study by the inventors of the present application, when the defect inspection apparatus is provided with a cooling air blowing device as a forced cooling device, the direction of cooling air from the cooling air blowing device and the speckle pattern when performing double exposure measurement If the relationship with the shift direction is inappropriate, the S / N of the detected image is lowered, and high-accuracy defect inspection cannot be performed quickly.

  The present invention has been made on the basis of such research results, and an object thereof is to provide a non-contact type defect inspection apparatus and method capable of performing non-destructive inspection by a shearography method quickly and with high accuracy. is there.

  In order to solve the above-mentioned problem, the present invention relates to a non-contact type defect inspection apparatus. First, the present invention is directed to heating means for heating an inspection object and applying thermal strain to the inspection object, and laser light to the inspection object. A laser beam irradiating means for irradiating, an image measuring means for performing double exposure measurement by shifting a reflected image from the inspection object toward the surface of the inspection object, and a differential image obtained by the image measuring means In a non-contact type defect inspection apparatus including an image analysis unit that analyzes a temporal change in distortion and generates an inspection image, and a control unit that controls the units, the inspection object heated by the heating unit Cooling air blowing means for cooling is provided, and the driving of the cooling air blowing means is controlled by the control means.

  Secondly, in the non-contact type defect inspection apparatus of the first configuration, when the double exposure measurement by the image measuring unit is performed, the driving of the cooling air blowing unit is stopped.

  Thirdly, in the non-contact type defect inspection apparatus of the first configuration, when the double exposure measurement is performed by the image measuring unit in a state where the cooling air blowing unit is driven, the cooling air blowing unit blows air. The flow direction of the cooling air and the shift direction of the reflected image measured by double exposure measurement by the image measuring means are matched or approximated.

  Fourthly, in the non-contact type defect inspection apparatus of the third configuration, the flow direction of the cooling air and the shift direction of the reflection image can be switched to at least two directions. And

  Fifth, in the non-contact type defect inspection apparatus having the first to fourth configurations, an induction heater is provided as the heating means.

  Sixth, in the non-contact type defect inspection apparatus having the first to fifth configurations, the control means includes a heating time of the inspection object by the heating means, and an inspection object by the cooling air blowing means. There is provided a database in which the relationship between the cooling rate and the time timing of double exposure measurement by the image measuring means is stored in advance.

  On the other hand, regarding the non-contact type defect inspection method, the present invention includes, firstly, a process of heating the inspection object and applying thermal strain to the inspection object, and a process of irradiating the inspection object with laser light. , A process of performing a double exposure measurement by shifting the reflected image from the inspection object in the direction of the surface of the inspection object, and a plurality of differential images obtained in a state where the thermal strain is different in a plurality of times In the non-contact type defect inspection method including a process of analyzing a time change of thermal distortion from the inspection and generating an inspection image, the inspection object is heated and then cooled air is blown to the inspection object. It has the process of cooling.

  Second, in the non-contact type defect inspection method of the first configuration, when the reflection image is subjected to double exposure measurement, the blowing of the cooling air to the inspection object is stopped.

  Third, in the non-contact type defect inspection method of the first configuration, when the reflected image is subjected to double exposure measurement, the cooling air is blown to the inspection object, and the flow direction of the cooling air is The shift direction of each reflection image measured by the double exposure is matched or approximated.

  Fourth, in the non-contact type defect inspection method of the third configuration, with respect to one inspection target region on the inspection target, the flow direction of the cooling air and the shift direction of the reflection image are at least two directions or more. Switching to multiple directions, the double exposure measurement is performed for each switching direction.

  Fifth, in the non-contact type defect inspection method of the first to fourth configurations, the heating time of the inspection object, the cooling rate of the inspection object by the cooling air blowing means, and the double exposure measurement Is determined based on data stored in advance in a database.

  In the present invention, since the non-contact type defect inspection apparatus provided with a heater as a means for imparting distortion to the inspection object is provided with cooling air blowing means for cooling the inspection object, the inspection object after heating can be quickly It can cool and can improve the speed of defect inspection.

  A first embodiment of the present invention will be described below with reference to FIGS. 1 is a configuration diagram of a non-contact type defect inspection apparatus according to the first embodiment, FIG. 2 is a side view of a flaw detection unit and an inspection object according to the first embodiment, and FIG. 3 is an image measuring unit according to the first embodiment. FIG. 4 is a diagram illustrating a heating time determination method and a measurement timing determination method performed by the analysis / control unit according to the first embodiment, and FIG. 5 is a non-contact type defect inspection apparatus according to the first embodiment. FIG. 6 is a diagram showing the operation of the flaw detector according to the first embodiment during the defect inspection.

  As shown in FIGS. 1 and 2, the non-contact type defect inspection apparatus of this example mainly includes a flaw detection unit 100, an analysis / control unit 200, and a display unit 300.

  The flaw detection unit 100 is movably installed on the inspection object A, and includes an induction heater 101 that heats the inspection object A and applies thermal distortion to a desired inspection object region B, and an illumination laser. A laser oscillator 102 that oscillates the light 102a, an enlarged irradiation optical system 103 that expands the laser light 102a oscillated from the laser oscillator 102 and irradiates the inspection target region B, and reflected light (reflected image) from the inspection target region B Cooling air blowing means such as an image measuring means 104 that double-exposes 102b, a reflecting mirror 105 that guides the reflected image 102b from the inspection target area B to the image measuring means 104, and a fan that supplies cooling air 106a to the inspection target area 106 and a wheel 107 as a moving mechanism are provided.

  As shown in FIG. 3A, the image measuring unit 104 condenses the reflected image (speckle pattern) 102b from the inspection target region B, and is collected by the condensing lens 111. A spectroscopic element 112 that branches the reflected image 102b into two reflected images 112a and 112b, and a first reflecting mirror 113 that reflects one of the reflected images 112a out of the two reflected images branched by the spectroscopic element 112, A second reflecting mirror 114 that reflects the other reflected image 112b, and an image measuring element such as a CCD that receives the two reflected images 112a and 112b reflected by the first and second reflecting mirrors 113 and 114. 115. The first reflecting mirror 113 is set substantially perpendicular to the optical axis so that one of the reflected images 112a is incident on a substantially central region of the image measuring element 115, and the second reflecting mirror 114 is an image. It is set in a slightly inclined state with respect to the optical axis so that the other reflected image 112b is incident on the light receiving surface of the measuring element 115 at a position slightly away from the incident position of the one reflected image 112a. Therefore, as schematically shown in FIG. 3B, the differential image 116 obtained by the interference of the two reflected images 112a and 112b is incident on the light receiving surface of the image measuring element 115. The differential width of the differential image is determined by the shift amount ΔX of the reflected lights 112a and 112b.

  The shifting direction of the two reflected images 112a and 112b is set to match or approximate the flow direction of the cooling air 106a blown from the cooling air blowing means 106. That is, the cooling air 106a from the cooling air blowing means 106 flowing along the inspection target region B has a non-uniform flow rate and temperature distribution, and therefore has a non-uniform refractive index of light. It is small in the flow direction of the cooling air 106a and large in the direction orthogonal to the flow direction of the cooling air 106a. Therefore, if the two reflected images 112a and 112b are shifted in the direction orthogonal to the flow direction of the cooling air 106a, the differential effect emphasizes the non-uniformity of the refractive index of the light and the noise increases. This is because if the two reflected lights 112a and 112b are shifted in the flow direction of 106a, the non-uniformity of the refractive index of light is reduced by the differential effect, and almost no noise is generated.

  As shown in FIG. 1, the analysis / control unit 200 includes an induction heating unit 201 that controls the induction heater 101, an image capturing unit 202 that captures an image acquired by the image measurement unit 104, and a cooling that controls the cooling air blowing unit 106. A control unit 203, an analysis / control unit 204 for transmitting a control start timing signal to the control unit 203 and analyzing the measured differential image, and a database 205 for determining the time timing of the image measurement are provided. The database 205 stores data on the amount of local strain of the defect portion corresponding to the material, thickness, and temperature of the inspection object A, and the analysis / control means 204 determines the heating time based on these data. And measurement timing are determined. When a computer is used as the analysis / control unit 204, the database 205 can be provided inside the computer.

  Determination of the heating time and measurement timing in the analysis / control means 204 is performed as follows based on the data stored in the database 205 and the heating / cooling characteristics of the inspection object A shown in FIG. That is, first, after the induction heater 101 is positioned in a desired inspection target region B, it is activated, and the inspection target region B is heated by induction heating. This is the heating process of FIG. 4, and the heating time is determined based on the data of the amount of local distortion of the defect portion C corresponding to the material, thickness, and temperature of the inspection object A stored in the database 205. Thereafter, the heating is stopped, the cooling process is started, and shearography measurement is performed. Also at this time, the measurement timing is determined based on the data of the amount of local distortion of the defect portion C according to the material, thickness, and temperature. As described above, in shearography measurement, since it is necessary to perform measurement twice before and after applying distortion, or in the middle of applying distortion, in the example of FIG. 4, first, image measurement of a reference image (1 After that, the second image measurement (2) is performed in a low temperature state. The time interval S between the image measurements (1) and (2) is set to a sufficiently high local distortion amount of the minimum defect size that must be detected from the distortion amount data stored in the database 205 with respect to the temperature change amount T. Set the time interval to be measurable with / N.

  The display unit 300 displays the reflected image 301 measured by the image measuring unit 104 and the inspection image 302 such as a differential image obtained by shearography measurement and a differential image after image analysis as necessary. . If there is a defect in the inspection target area B, a defect signal 303 is displayed in the inspection image 302. The presence / absence, size, shape, orientation, and type of a defect in the inspection target region B are determined based on the presence / absence, size, shape, and orientation of the defect signal.

  Next, the defect inspection method using the non-contact type defect inspection apparatus of the present invention and the operation of the flaw detection unit at the time of inspection will be described with reference to FIGS.

  First, the flaw detection unit 100 is moved on the inspection object A using the wheels 107, and the induction heater 101 provided in the flaw detection unit 100 is positioned in a desired inspection object region B as shown in FIG. (Procedure S401). Next, the desired inspection target region B is induction-heated by the induction heater 101 (step S402). Next, as shown in FIG. 6B, the flaw detection unit 100 is moved so that the inductively heated inspection target region B is within the field of view of the enlarged irradiation optical system 103 provided in the flaw detection unit 100 (step S403). ). At this time, the laser oscillator 102 and the cooling air blowing means 106 provided in the flaw detection unit 100 may be operated, or may be started in accordance with the movement of the flaw detection unit. Next, the inspection target area B is cooled by the cooling air 106a blown from the cooling air blowing means 106 provided in the flaw detection unit 100 (step S404). Then, shearography measurement is performed at a high temperature and a low temperature in the cooling process of the inspection target region B (step S405). The measurement conditions at this time are determined using the database 205 as described above. Next, the differential image obtained in this way is analyzed to obtain an inspection image corresponding to the temporal change in distortion, and a required image is displayed on the display unit 300 (step S406). The image obtained in each of the above steps may be stored in the analysis / control unit 200 as necessary. Next, it is determined whether or not the inspection of the entire range of the inspection object A has been completed (procedure S407). If it has been completed, the system is terminated (procedure S408). The flaw detection unit 100 is moved to the next inspection target area B (procedure S409), and each procedure after step S402 is repeated.

  Since the non-contact type defect inspection apparatus of this example uses the induction heater 101 as the heating means of the inspection object A, compared with the case where other heating means, for example, a warm air machine, an infrared lamp, or a laser oscillator is used, A wide range can be heated quickly, and the speed of defect inspection can be improved. Moreover, since the non-contact type defect inspection apparatus of this example includes the cooling air blowing means 106, the inspection object A after heating can be quickly cooled, and also from this point, the speed of defect inspection is improved. Can do. Furthermore, the non-contact type defect inspection apparatus of this example matches or approximates the shifting direction of the two reflected images 112a and 112b and the flow direction of the cooling air 106a when performing double exposure measurement. Even if the cooling air 106a is caused to flow through the inspection target region B, noise caused by a local temperature village of the cooling air 106a is suppressed, and a highly accurate inspection result can be obtained.

  In the first embodiment, the image measuring unit 104 is installed above the induction heater 101. However, if there is no restriction on the size of the apparatus, other arrangements may be used. For example, the laser oscillator 102, the enlarged irradiation optical system 103, and the image measuring unit 104 may be provided immediately above the inspection target region B. In this case, the reflecting mirror 105 can be omitted.

  In the first embodiment, the flaw detection unit 100 includes the wheel 107 and the flaw detection unit 100 itself can be moved. However, an automatic scanning mechanism such as a scanner may be provided to automate the inspection.

  Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 7 is a configuration diagram of the non-contact type defect inspection apparatus according to the second embodiment, and FIG. 8 is a diagram illustrating a procedure of defect inspection executed by the non-contact type defect inspection apparatus according to the second embodiment.

  As shown in FIG. 7, the non-contact type defect inspection apparatus of the present example includes a first cooling air blowing means 106 that blows cooling air 106 a from the first direction to the inspection target region B to the flaw detection unit 100. The first cooling air blowing means 108 that blows the cooling air 108a from the second direction with respect to the inspection target region B is provided. Other parts are the same as those of the non-contact type defect inspection apparatus according to the first embodiment shown in FIGS. 1 and 2, and therefore, the corresponding parts are denoted by the same reference numerals and description thereof is omitted.

  The first and second cooling air blowing means 106 and 108 are arranged so as to blow the cooling air 106a and 108a in directions substantially orthogonal to each other, and the cooling air blown from the respective cooling air blowing means 106 and 108. By appropriately adjusting the strengths of 106a and 108a, it is possible to blow synthetic cooling air in an arbitrary direction with respect to the inspection target region B. Accordingly, the image measuring unit 104 is configured to match or approximate the cooling air blowing direction with respect to the inspection target region B and the shifting directions of the two reflected images 112a and 112b (see FIG. 3) when performing the double exposure measurement. By switching the configuration, defect inspection from a plurality of directions can be executed for one inspection target region B, and the accuracy of defect inspection can be significantly improved.

  That is, as described above, the differential image of distortion measured by the shearography method becomes a differential image of distortion in the shifting direction of the two reflected images 112a and 112b when performing double exposure measurement. Depending on the shape and orientation of the defect C existing inside, the defect may be difficult to detect by inspection from one direction. On the other hand, when inspection is performed from a plurality of directions by switching between the cooling air blowing direction and the shifting direction of the two reflected images 112a and 112b when performing double exposure measurement, the shape and direction of the defect C are changed. However, since the defect C existing in the inspection target area B can be reliably detected, the accuracy of the defect inspection can be remarkably improved. In the example of FIG. 7, the double exposure measurement is performed twice by changing the differential direction of the image and the blowing direction of the cooling air 106 a and 108 a by 90 degrees, and the respective inspection images 304 and 305 are displayed on the display unit 300. .

  In the non-contact type defect inspection apparatus of this example, the inspector is notified of the cooling air blowing direction with respect to the inspection target region B and the shifting direction of the two reflection images 112a and 112b when performing double exposure measurement. Therefore, it is particularly desirable to display these notification contents on the display unit 300 so that an accurate inspection can be performed.

  Hereinafter, a defect inspection method using the non-contact type defect inspection apparatus according to the second embodiment will be described with reference to FIG. Basically, it is the same as the procedure of the defect inspection method using the non-contact type defect inspection apparatus according to the first embodiment shown in FIG. 5, but after the shearography measurement is performed (step S705), It is determined whether or not there has been a change instruction regarding the direction of cooling air blowing and the shift direction of the two reflected images 112a and 112b when performing double exposure measurement (step S706). The blowing direction and the shifting direction of the reflected images 112a and 112b are changed (step S707), and the operations after step S702 are repeated. In this case, in the first measurement, since the inspection target area B has already been cooled and the temperature has decreased, a reference image is acquired with this temperature decrease as an initial temperature condition, and then the inspection target area The temperature of B is raised and the second measurement is performed. When there is no change instruction in step S706, the process proceeds to step S708, and the measured image is stored in the analysis / control unit 200.

  In the second embodiment, a plurality of cooling air blowing means 106, 108 having different cooling air blowing directions are provided. However, instead of such a configuration, only one cooling air blowing means 106 is provided, and a duct is provided. It is also possible to switch the blowing direction of the cooling air by switching.

  Moreover, in each said embodiment, although double exposure measurement of the reflected image was performed in the state which sent the cooling air to the test object area | region B, it replaced with this structure and the reflected image in the state which stopped ventilation of the cooling air. It is also possible to perform double exposure measurement. By doing so, it is possible to prevent the occurrence of noise due to local temperature non-uniformity of the cooling air, and thus it is possible to carry out highly accurate defect inspection as in the above embodiments.

  Furthermore, in each said embodiment, although the induction heater 101 was used as a heating means of the test object A, the summary of this invention is not limited to this, A warm air heater, an infrared lamp, a laser beam, etc. Other heating means can also be used.

It is a block diagram of the non-contact-type defect inspection apparatus which concerns on 1st Embodiment. It is a side view of a flaw detection part and an inspection object concerning a 1st embodiment. It is a block diagram of the image measurement means which concerns on 1st Embodiment. It is a figure which shows the determination method of the heating time performed by the analysis and control means which concerns on 1st Embodiment, and the determination method of measurement timing. FIG. 5 is a diagram showing a procedure of defect inspection executed by the non-contact type defect inspection apparatus according to the first embodiment. It is a figure which shows operation | movement of the flaw detection part which concerns on 1st Embodiment at the time of a defect inspection. It is a block diagram of the non-contact-type defect inspection apparatus which concerns on 2nd Embodiment. It is a figure which shows the procedure of the defect inspection performed with the non-contact-type defect inspection apparatus which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Flaw detection part 101 Induction heater 102 Laser oscillator 104 Image measurement means 106 Cooling air ventilation means 200 Analysis / control part 201 Induction heating means 202 Image capture means 203 Cooling control means 204 Analysis / control means 205 Database 300 Display part

Claims (11)

A heating unit that heats the inspection object and applies thermal strain to the inspection object, a laser light irradiation unit that irradiates the inspection object with laser light, and a reflection image from the inspection object. An image measuring unit that performs double exposure measurement by shifting in the surface direction, an image analyzing unit that analyzes a temporal change of thermal strain from a differential image obtained by the image measuring unit and generates an inspection image, and controls each of the units In a non-contact type defect inspection apparatus provided with a control means,
A non-contact type defect inspection apparatus comprising cooling air blowing means for cooling the inspection object heated by the heating means, and controlling the driving of the cooling air blowing means by the control means.   The non-contact type defect inspection apparatus according to claim 1, wherein when the double exposure measurement is performed by the image measurement unit, the driving of the cooling air blowing unit is stopped.   When double exposure measurement is performed by the image measurement unit while the cooling air blowing unit is driven, the double exposure measurement is performed by the flow direction of the cooling air blown from the cooling air blowing unit and the image measurement unit. The non-contact type defect inspection apparatus according to claim 1, wherein the shift direction of the reflected image is matched or approximated.   The non-contact type defect inspection apparatus according to claim 3, wherein the flow direction of the cooling air and the shift direction of the reflected image can be switched to at least two directions.   The non-contact type defect inspection apparatus according to claim 1, further comprising an induction heater as the heating unit.   In the control means, the relationship between the heating time of the inspection object by the heating means, the cooling speed of the inspection object by the cooling air blowing means, and the time timing of the double exposure measurement by the image measurement means is previously set. The non-contact type defect inspection apparatus according to any one of claims 1 to 5, further comprising a stored database. A process of heating the inspection object to impart thermal strain to the inspection object, a process of irradiating the inspection object with laser light, and a reflection image from the inspection object in the surface direction of the inspection object A process of performing a double exposure measurement by shifting a plurality of times in a state where the magnitude of the thermal strain is different, and a process of generating a test image by analyzing temporal changes of the thermal strain from the obtained differential images In the non-contact type defect inspection method,
A non-contact type defect inspection method comprising a step of cooling the inspection object by blowing cooling air to the inspection object after heating the inspection object.   The non-contact type defect inspection method according to claim 7, wherein when the reflected image is subjected to double exposure measurement, blowing of the cooling air to the inspection object is stopped.   When the double-exposure measurement is performed on the reflected image, the cooling air is blown to the inspection object, and the flow direction of the cooling air and the shift direction of each reflection image measured by the double exposure measurement are matched or approximated. The non-contact type defect inspection method according to claim 7, wherein:   For one inspection object area on the inspection object, the flow direction of the cooling air and the shift direction of the reflected image are switched to at least two or more directions, and the double exposure measurement is performed for each switching direction. The non-contact type defect inspection method according to claim 9.   The heating time of the inspection object, the cooling rate of the inspection object by the cooling air blowing means, and the time timing of the double exposure measurement are determined based on data stored in advance in a database. The non-contact type defect inspection method according to any one of claims 7 to 10.

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