JP6894280B2 - Inspection method and inspection equipment - Google Patents

Description

The present invention relates to an inspection method for inspecting the appearance of an object to be inspected, and an inspection device using this inspection method.

In recent years, electronic circuit boards have been mounted on various devices, but in devices on which this type of electronic circuit board is mounted, miniaturization, thinning, etc. have always been issues. From this point of view, it is required to increase the density of mounting of electronic circuit boards. In such an inspection device for inspecting the soldered state of the electronic circuit board, the mounted state of electronic components, and the like, the phase shift method is used because of its precision. The phase shift method is configured to measure the height using a long-period fringe pattern and a short-period fringe pattern (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2012-053015

However, in the method of obtaining the height from the projected images of the long-period fringe pattern and the short-period fringe pattern as described above, the number of times the image is captured (the number of images for calculating the height) increases, and the inspection is performed. There was a problem that the throughput of In addition, when the object to be inspected is a bright object, if a long-period fringe pattern is projected and imaged, saturation is likely to occur. If saturation occurs, it is necessary to perform imaging again. In that case, the number of times the image is captured. There was also the issue of increasing by that amount. A method for obtaining highly accurate height information with a smaller number of imagings has also been devised, but further reduction in the number of imagings is required in order to improve the inspection throughput.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an inspection method capable of acquiring highly accurate height information with a small number of imaging times, and an inspection device using this inspection method. And.

In order to solve the above problems, the inspection method according to the present invention synchronizes the step of acquiring a short-period measurement image which is an image of the object to be inspected on which the short-period stripe pattern is projected with the step of acquiring the short-period measurement image and the long-period stripe pattern. A step of acquiring a fixed measurement image which is an image of an object to be inspected on which a fixed pattern is projected, a step of detecting the position of an image of the fixed pattern from the fixed measurement image, and a step of detecting the long-period fringe pattern are projected. An image of the reference plane, the step of determining the long-period phase, which is the phase of the position of the image, and the reference on which the short-period fringe pattern is projected, based on the long-period reference image acquired in advance. A step of determining the short-period phase, which is the phase of the position of the image, based on a short-period reference image acquired in advance in a plane image, and the long-period phase for each position of the image. It is characterized by having a step of calculating the height of the object to be inspected from the short period phase.

In such an inspection method according to the present invention, the fixed pattern is a dot .

Further, in such an inspection method according to the present invention, in the step of detecting the position of the image of the fixed pattern, the fixed measurement image is divided into a plurality of regions, and the image included in the region is divided into a plurality of regions. It is preferable to detect the position.

Further, such an inspection method according to the present invention preferably includes a step of binarizing the fixed measurement image before the step of detecting the position of the image of the fixed pattern.

Further, in such an inspection method according to the present invention, it is preferable that the step of binarizing the fixed measurement image determines the threshold value for binarization based on the luminance information of the short-period measurement image.

Further, the inspection device according to the present invention includes a projection unit that projects a pattern on the object to be inspected, a camera unit that acquires an image of the object to be inspected on which the pattern is projected, and a storage unit that stores the image. It is characterized by having a control unit for calculating the height of the object to be inspected by the above-mentioned inspection method.

According to the present invention, highly accurate height information can be acquired with a small number of imaging times.

It is explanatory drawing for demonstrating the structure of an inspection apparatus. It is explanatory drawing explaining the relationship between the phase of a reference plane and the measured phase. It is explanatory drawing explaining the relationship between a fringe pattern and a fixed pattern. It is a flowchart of an inspection method. It is explanatory drawing explaining the method of detecting the position of the image of a fixed pattern.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the configuration of the inspection device 10 according to the present embodiment will be described with reference to FIG. The inspection device 10 is a device that inspects the inspected body 12 by using an image of the inspected body obtained by imaging the inspected body 12. The object 12 to be inspected is, for example, an electronic circuit board coated with solder. The inspection device 10 determines whether the solder is applied or not based on the image of the object to be inspected.

The inspection device 10 includes an inspection table 14 for holding the inspected object 12, an imaging unit 20 that illuminates and images the inspected object 12, an XY stage 16 that moves the imaging unit 20 with respect to the inspection table 14, and an image pickup. It is configured to include a control unit 30 for controlling the operation of the unit 20 and the XY stage 16 and performing an inspection of the inspected body 12. For convenience of explanation, as shown in FIG. 1, the object to be arranged surface of the inspection table 14 is an XY plane, and the direction perpendicular to the arrangement surface (that is, the image pickup direction by the camera unit 21 constituting the image pickup unit 20 (camera unit). The optical axis direction)) of the optical system of 21 is defined as the Z direction.

The image pickup unit 20 is attached to a moving table (not shown) of the XY stage 16 and can be moved in the X direction and the Y direction by the XY stage 16. The XY stage 16 is, for example, a so-called H-shaped XY stage. Therefore, the XY stage 16 has a Y drive unit that moves the moving table in the Y direction along the Y direction guide extending in the Y direction, supports the Y direction guide at both ends thereof, and supports the moving table and the Y direction guide in the X direction. It includes two movable X-direction guides and an X drive unit. The XY stage 16 may further include a Z movement mechanism that moves the image pickup unit 20 in the Z direction, or may further include a rotation mechanism that rotates the image pickup unit 20. The inspection device 10 may further include an XY stage that allows the inspection table 14 to be moved, and in this case, the XY stage 16 that moves the imaging unit 20 may be omitted. Further, a linear motor or a ball screw can be used for the X drive unit and the Y drive unit.

The imaging unit 20 includes a camera unit 21, a lighting unit 22, and a projection unit 23 that capture images from a direction (Z-axis direction) perpendicular to the inspection surface (board surface) of the object 12 to be inspected. .. In the inspection device 10 according to the present embodiment, the camera unit 21, the lighting unit 22, and the projection unit 23 may be configured as an integrated imaging unit 20. In the integrated imaging unit 20, the relative positions of the camera unit 21, the lighting unit 22, and the projection unit 23 may be fixed, or each unit may be configured to be relatively movable. Further, the camera unit 21, the lighting unit 22, and the projection unit 23 may be separated and may be configured to be movable separately.

The camera unit 21 includes an image pickup element that generates a two-dimensional image of an object, and an optical system (for example, a lens) for forming an image on the image pickup element. The camera unit 21 is, for example, a CCD camera. The maximum field of view of the camera unit 21 may be smaller than the inspected body mounting area of the inspection table 14. In this case, the camera unit 21 divides the image into a plurality of partial images and images the entire body 12 to be inspected. The control unit 30 controls the XY stage 16 so that the camera unit 21 is moved to the next imaging position each time the camera unit 21 captures a partial image. The control unit 30 synthesizes partial images to generate an entire image of the inspected body 12.

The camera unit 21 may include an image sensor that generates a one-dimensional image instead of the two-dimensional image sensor. In this case, the entire image of the inspected body 12 can be acquired by scanning the inspected body 12 with the camera unit 21.

The illumination unit 22 is configured to project illumination light for imaging by the camera unit 21 onto the surface of the object to be inspected 12. The illumination unit 22 includes one or more light sources that emit light in a wavelength or wavelength range selected from the wavelength range that can be detected by the image sensor of the camera unit 21. The illumination light is not limited to visible light, and ultraviolet light, X-rays, or the like may be used. When a plurality of light sources are provided, each light source is configured to project light having a different wavelength (for example, red, blue, and green) onto the surface of the object 12 to be inspected at different projection angles.

In the inspection device 10 according to the present embodiment, the lighting unit 22 is a side illumination source that projects illumination light from an oblique direction with respect to the inspection surface of the object to be inspected 12, and in the present embodiment, the upper light source 22a, middle It includes a position light source 22b and a lower light source 22c. In the inspection device 10 according to the present embodiment, the upper light source 22a, the middle light source 22b, and the lower light source 22c, which are the side illumination sources, are ring illumination sources, respectively, and surround the optical axis of the camera unit 21 to be inspected. It is configured to project the illumination light diagonally to the inspection surface of the body 12. Each of the upper light source 22a, the middle light source 22b, and the lower light source 22c, which are the side illumination sources, may be configured by arranging a plurality of light sources in an annular shape. Further, the upper light source 22a, the middle light source 22b, and the lower light source 22c, which are the side illumination sources, are configured to project the illumination light at different angles with respect to the inspection surface, respectively.

The projection unit 23 projects a pattern on the inspection surface of the inspected body 12. The inspected object 12 on which the pattern is projected is imaged by the camera unit 21. The inspection device 10 creates a height map of the inspection surface of the inspected object 12 based on the captured pattern image of the inspected object 12. The control unit 30 detects a local mismatch of the pattern image with respect to the projection pattern, and obtains the height of the portion based on the local mismatch. That is, the change in the imaging pattern with respect to the projection pattern corresponds to the change in height on the inspection surface.

The projection pattern is preferably a one-dimensional fringe pattern in which bright lines and dark lines are alternately and periodically repeated. The projection unit 23 is arranged so as to project a striped pattern from an oblique direction on the inspection surface of the object to be inspected 12. The discontinuity of height on the inspection surface of the object 12 to be inspected appears as a pattern shift in the striped pattern image. Therefore, the height difference can be obtained from the amount of deviation of the pattern. For example, the control unit 30 creates a height map by the PMP (Phase Measurement Professional) method using a fringe pattern in which the brightness changes according to a sine curve. In the PMP method, the amount of deviation of the fringe pattern corresponds to the phase difference of the sine curve.

The projection unit 23 includes a pattern forming apparatus, a light source for illuminating the pattern forming apparatus, and an optical system for projecting a pattern onto the inspection surface of the object to be inspected 12. The pattern forming apparatus may be, for example, a variable patterning apparatus capable of dynamically generating a desired pattern such as a liquid crystal display, or a fixed patterning in which a pattern is fixedly formed on a substrate such as a glass plate. It may be a device. When the pattern forming apparatus is a fixed patterning apparatus, the projection position of the pattern can be made variable by providing a moving mechanism for moving the fixed patterning apparatus or by providing an adjusting mechanism in the optical system for pattern projection. preferable. Further, the projection unit 23 may be configured so that a plurality of fixed patterning devices having different patterns can be switched.

A plurality of projection units 23 may be provided around the camera unit 21. The plurality of projection units 23 are arranged so as to project a pattern onto the inspected object 12 from different projection directions. In this way, it is possible to reduce the area where the pattern is not projected due to the shadow due to the height difference on the inspection surface.

The control unit 30 shown in FIG. 1 controls the entire apparatus in an integrated manner. The hardware is realized by the CPU, memory, or other LSI of an arbitrary computer, and the software is loaded into the memory. It is realized by programs, etc., but here we draw the functional blocks realized by their cooperation. Therefore, it will be understood by those skilled in the art that these functional blocks can be realized in various ways by hardware only, software only, or a combination thereof.

FIG. 1 shows an example of the configuration of the control unit 30. The control unit 30 includes an inspection control unit 31 and a memory 35 which is a storage unit. The inspection control unit 31 includes a height measuring unit 32, an inspection data processing unit 33, and an inspection unit 34. Further, the inspection device 10 includes an input unit 36 for receiving an input from a user or another device, and an output unit 37 for outputting information related to the inspection, and the input unit 36 and the output unit 37. Are each connected to the control unit 30. The input unit 36 includes, for example, an input means such as a mouse or a keyboard for receiving an input from a user, and a communication means for communicating with another device. The output unit 37 includes known output means such as a display and a printer.

The inspection control unit 31 is configured to execute various control processes for inspection based on the input from the input unit 36 and the inspection-related information stored in the memory 35. The inspection-related information includes a two-dimensional image of the object to be inspected 12, a height map of the object to be inspected 12, and substrate inspection data. Prior to the inspection, the inspection data processing unit 33 creates the substrate inspection data using the two-dimensional image and the height map of the inspected object 12 which is guaranteed to pass all the inspection items. The inspection unit 34 executes the inspection based on the created substrate inspection data, the two-dimensional image of the object 12 to be inspected, and the height map.

The board inspection data is inspection data created for each type of board. The board inspection data is, so to speak, a collection of inspection data for each solder applied to the board. The inspection data of each solder includes the inspection items required for the solder, the inspection window which is the inspection area on the image for each inspection item, and the inspection criteria which are the criteria for quality judgment for each inspection item. One or more inspection windows are set for each inspection item. For example, in the inspection item for determining the quality of the solder coating state, the same number of inspection windows as the number of solder coating regions of the component are usually set in an arrangement corresponding to the arrangement of the solder coating regions. In addition, for inspection items that use an image that has undergone predetermined image processing on the image to be inspected, the content of the image processing is also included in the inspection data.

The inspection data processing unit 33 sets each item of inspection data according to the substrate as a substrate inspection data creation process. For example, the inspection data processing unit 33 automatically sets the position and size of each inspection window for each inspection item so as to match the solder layout of the substrate. The inspection data processing unit 33 may accept input by the user for some items of the inspection data. For example, the inspection data processing unit 33 may accept the tuning of the inspection standard by the user. Inspection criteria may be set using height information.

The inspection control unit 31 executes an imaging process of the inspected object 12 as a preprocessing for creating substrate inspection data. As the inspected body 12, one that has passed all the inspection items is used. As described above, the imaging process is performed by illuminating the object 12 to be inspected by the lighting unit 22 and controlling the relative movement between the image pickup unit 20 and the inspection table 14 to sequentially image a partial image of the object 12 to be inspected. .. A plurality of partial images are taken so as to cover the entire body 12 to be inspected. The inspection control unit 31 synthesizes these plurality of partial images to generate an image of the entire surface of the substrate including the entire inspection surface of the object 12 to be inspected. The inspection control unit 31 stores an image of the entire surface of the substrate in the memory 35.

Further, as a preprocessing for creating a height map, the inspection control unit 31 controls the relative movement between the image pickup unit 20 and the inspection table 14 while projecting a pattern on the inspected body 12 by the projection unit 23, and is inspected. The pattern image of the body 12 is divided and sequentially imaged. The projected pattern is preferably a fringe pattern whose brightness changes according to a sine curve based on the PMP method. The inspection control unit 31 synthesizes the captured divided images and generates a pattern image of the entire inspection surface of the inspected body 12. The inspection control unit 31 stores the pattern image in the memory 35. It should be noted that the pattern image may be generated not for the whole but for a part of the inspection surface.

The height measuring unit 32 creates a height map of the entire inspection surface of the inspected body 12 based on the pattern on the image pickup pattern image. First, the height measuring unit 32 obtains a phase difference map of the inspection surface of the object 12 to be inspected by obtaining a local phase difference between the image pickup pattern image and the reference pattern image for the entire image. The reference pattern image is a pattern image projected by the projection unit 23 (that is, an image generated by a pattern forming device built in the projection unit 23). The height measuring unit 32 creates a height map of the inspected object 12 based on a reference plane and a phase difference map which are reference points for height measurement. The reference plane is, for example, the substrate surface of the electronic circuit board to be inspected. The reference surface does not necessarily have to be a flat surface, and may be a curved surface that reflects deformation such as warpage of the substrate.

Specifically, the height measuring unit 32 obtains the phase difference of the fringe pattern between each pixel of the image pickup pattern image and the pixel of the reference pattern image corresponding to the pixel. The height measuring unit 32 converts the phase difference into a height. The conversion to height is performed using the local stripe width in the vicinity of the pixel. This is to compensate for the difference in the stripe width on the imaging pattern image depending on the location. Since the distance from the projection unit 23 differs depending on the position on the inspection surface, even if the stripe width of the reference pattern is constant, the stripe width changes linearly from one end to the other end of the pattern projection area on the inspection surface. Because it ends up. The height measuring unit 32 obtains the height from the reference plane based on the converted height and the reference plane, and creates a height map of the object 12 to be inspected.

The inspection control unit 31 creates an image of the object to be inspected having a height distribution by associating the height information of the height map of the object to be inspected 12 with each pixel of the two-dimensional image of the object to be inspected 12. May be good. The inspection control unit 31 may perform a three-dimensional modeling display of the inspected body 12 based on the inspected body image with a height distribution. Further, the inspection control unit 31 may superimpose the height distribution on the two-dimensional image of the object to be inspected and display it on the output unit 37. For example, the image of the object to be inspected may be color-coded according to the height distribution.

Hereinafter, a method of projecting a pattern by the projection unit 23 and measuring the height in such an inspection device 10 will be described.

First, a conventional height measurement method by the PMP method using a striped pattern will be described. Focusing on one measurement point in the fringe pattern projection area, when the fringe pattern is projected while spatially shifting the phase (in other words, when the fringe pattern is scanned in the direction in which the fringe repeats), the measurement point of the measurement point The brightness fluctuates periodically. Although the average brightness differs for each measurement point depending on the surface characteristics of the measurement points such as color and reflectance, periodic brightness fluctuations corresponding to the fringe pattern occur at each measurement point. Therefore, for example, the phase of the fringe pattern when the measurement point is brightest represents the height information of the measurement point. Generally speaking, it can be said that the initial phase of the periodic brightness fluctuation gives the height information of each measurement point.

Using the characteristics of such a striped pattern, the conventional height measuring method determines the height by using at least two patterns having different periods. The first pattern with a long period (that is, thick stripes) is used to obtain a rough height, and the second pattern with a short period (thin stripes) is used to obtain a precise height. As described above, since the height is obtained based on the phase in the PMP method, the height cannot be uniquely specified if the height difference is large and the fringes are deviated by one cycle or more. By obtaining the height in combination with the first fringe pattern, it is possible to uniquely specify the height even when the fringes are deviated by one cycle or more when the second fringe pattern is projected.

However, when the height is measured for each of a plurality of different patterns and the results are integrated to obtain a height map, it is generally considered that each pattern is individually projected and imaged. In principle, the PMP method requires imaging of one type of fringe pattern at least three times, typically four times, out of phase. The brightness fluctuation of each measurement point also becomes a sine wave corresponding to the fringe pattern being a sine wave. Since the pitch of the fringes is known, a sine wave representing the variation in brightness can be identified if the average value, amplitude, and initial phase of the brightness are known.

By obtaining the brightness measurement value of the measurement point from at least three captured images, three variables of the average value of brightness, the amplitude, and the initial phase can be determined. Further, assuming that the brightness of a pixel when one fringe pattern is imaged four times with the phase shifted by 90 degrees is l0 to l3, the initial phase φ of the measurement point corresponding to the pixel is tan (φ) = (l3-). It is known to be represented by l1) / (l2-l0). Assuming that the pitch of the fringe pattern is P, the amount of deviation of the fringe pattern is obtained by P × (φ / 2π). The height of the position can be obtained from the amount of pattern deviation using the projection angle of the pattern.

If two patterns are used, at least 6 or 8 images will be taken. In order to inspect one inspected body 12, a plurality of partial regions are imaged to obtain an entire image. Further, one partial region is imaged by each of the plurality of projection units 23. For example, if 10 subregions are imaged by 3 projection units, 10 × 3 × 6 (or 8) = 180 (or 240) times of imaging will be required. In this way, the number of imagings required for one inspection tends to be large, and the number of imagings has a large effect on the inspection required time.

Therefore, in the present embodiment, a rough height is obtained by a triangulation method using a fixed pattern synchronized with a long-period pattern (the first pattern having thick stripes) in the PMP method, and a short-period pattern in the PMP method is used. The number of imagings is reduced by obtaining a precise height from the striped pattern (second pattern, which is a thin striped pattern). Here, in the triangulation method, a fixed pattern is projected from the projection unit 23 onto the object to be inspected 12, and the height is based on the amount of deviation from the image of the fixed pattern in the reference plane from the image captured by the camera unit 21. Is a method of finding. A checker, a square wave, a dot, or the like can be used as the fixed pattern, but it will be described as a dot in the following description.

In FIG. 2, as shown in (a), the phase obtained from the image obtained by projecting the striped pattern by the projection unit 23 on the reference plane S and captured by the camera unit 21 is shown in (b). As shown, when the phase obtained from the image obtained by projecting the same fringe pattern with the object O placed on the reference plane S is shown in (d), the height of the object O is the phase of these phases. It can be calculated from the amount of deviation (phase difference = measured phase-phase of reference plane). This phase difference can be calculated for each pixel of the image captured by the camera unit 21, and the height of the position corresponding to that pixel is calculated by multiplying the phase difference obtained for each pixel by a coefficient. .. This coefficient is obtained by, for example, tan (projection angle) × stripe pitch / 2π.

Here, as shown in FIG. 3, instead of using the striped pattern Pt, consider the case where the dot pattern Pd, which is a fixed pattern synchronized with the striped pattern Pt, is used. “Synchronization” means that dots (fixed patterns) of the dot pattern Pd are arranged at positions of predetermined phases in the stripe pattern Pt. As described with reference to FIG. 2, when the reference plane S and the object O placed on the reference plane S are imaged using the striped pattern Pt, the phase difference Δφ is the measured phase φ and the phase of the reference plane. It is obtained from φ0 by the following equation (1).

Δφ = φ − φ0 (1)

On the other hand, when the dots of the dot pattern Pd are formed at the position of the phase 0 of the striped pattern Pt, the phase (measured phase) φ of the image of the dots projected on the reference plane S or the surface of the object O becomes 0. The phase difference Δφ ′ at the position of the dot image captured by the camera unit 21 is given by the following equation (2).

Δφ ′ = 0 − φ0 = −φ0 (2)

When the striped pattern Pt is used, the phase difference can be obtained for each pixel of the image captured by the camera unit 21, and the height thereof can be calculated. Compared to the case where the dot pattern Pd is used, dots are formed. Although only the phase difference and height of the vertical position can be obtained, it is not necessary to calculate the amount of movement of the dots (difference between the dot position in the image of the reference plane S and the dot position in the measured image), and the reference. Using the image of the striped pattern Pt with respect to the plane S, the phase difference can be directly obtained from the position of the dot image in the captured image by using the equation (2). That is, the fringe pattern Pt is used as the above-mentioned long-period fringe pattern, and the dot pattern Pd is synchronized with the long-period fringe pattern (for example, dots are formed at the position where the phase of the fringe pattern is 0) to form dots. The image obtained by projecting the pattern Pd onto the object 12 to be inspected can be treated in the same manner as the image acquired by projecting the long-period pattern in the PMP method. Moreover, as described above, in the PMP method, it is necessary to shift the phase of the long-period pattern and perform imaging at least three times in order to obtain the phase difference. However, when this dot pattern Pd is used, one imaging is required. Therefore, the phase difference of the dot image at a certain position can be obtained. Therefore, even if it is necessary to take three images for one visual field area to measure with a short-period pattern, it is possible to perform high-precision measurement equivalent to that of the PMP method with a total of four images. ..

Here, let Δφw be the phase difference obtained from the dot pattern at a predetermined position (the position where the dot image is detected) and the image of the reference plane on which the long-period fringe pattern is projected, and set the short-period fringe pattern. Let φf be the phase difference obtained from the image (the phase difference obtained from the image on the reference plane and the measured image), and let N be the ratio of the fringe pitch of the long-period fringe pattern to the short-period fringe pattern. The height h of the position where the image of is detected is calculated by the following equation (3). However, Round () is a function that rounds down after the decimal point.

h = Round ((N × Δφw−Δφf) / 2π) × 2π + Δφf (3)

As with the PMP method, if the measurement result by the dot pattern (long-period fringe pattern) deviates by more than half the pitch of the short-period fringe pattern (when the phase shifts by π), the correct result can be obtained. It disappears. However, in the inspection of the solder coating state of the electronic circuit board, there is no large height difference between the surface of the board and the soldered portion (that is, an object having a shape in which a fine object exists on a flat surface having a gentle curve). On the other hand, by this method, it is possible to measure a high degree of sufficient accuracy.

Then, a specific measurement method will be described with reference to FIG. The patterns projected by the projection unit 23 are a long-period fringe pattern, a dot pattern (fixed pattern) synchronized with the long-period fringe pattern, and a short-period fringe pattern. Further, in the following description, the measurement process for one visual field region will be described, but when the object 12 to be inspected spans a plurality of visual field regions, the following processing is executed for each visual field region.

First, preparations before measurement are performed. For example, when an execution command for preparatory processing is input from the input unit 36, the control unit 30 projects a short-period fringe pattern onto the reference plane by the projection unit 23, and the image (short-period reference image) is captured by the camera. An image is taken by the unit 21 and stored in the memory 35 (step S100). Next, the control unit 30 projects a long-period fringe pattern onto the reference plane by the projection unit 23, captures the image (long-period reference image) with the camera unit 21, and stores it in the memory 35 (step S110). , End the preparatory process. As the reference plane, a substrate on which no component is mounted may be set on the inspection table 14, or a dedicated member serving as the reference plane may be set on the inspection table 14.

Next, the inspected body 12 is placed on the inspection table 14 and inspected (measured). For example, when an execution command for inspection processing is input from the input unit 36, the control unit 30 projects a short-cycle fringe pattern onto the inspected object 12 by the projection unit 23, and the camera unit 21 projects the image (short cycle). The measurement image) is acquired and stored in the memory 35 (step S200). In this step S200, as described above, at least three images in which the fringe pattern is shifted with respect to one visual field region are acquired. Next, the control unit 30 projects the dot pattern onto the inspected body 12 by the projection unit 23, acquires the image (fixed measurement image) by the camera unit 21, and stores it in the memory 35 (step S210). As described above, the dot pattern image may be imaged once for one visual field area.

The control unit 30 reads a short-period measurement image from the memory 35 and performs phase calculation from the short-period measurement image (step S220). As described above, when the short-period fringe pattern is projected onto the object 12 to be inspected, the phase is shifted and the imaging is performed at least three times. The relationship between the phase shift in these imaging and the brightness when the low-period fringe pattern projected on the object 12 to be inspected is a sine wave is expressed by the following equation (4). In this equation (4), v indicates the brightness, A indicates the amplitude depending on the brightness of the object 12 to be inspected, C indicates the brightness offset depending on the camera unit 21 and the environmental brightness, and B. Indicates the desired phase, λ indicates the amount of phase shift, and x indicates the number of shifts.

v = A × sin (λ × x + B) + C (4)

The control unit 30 reads a fixed measurement image from the memory 35, and based on the luminance information of the short-period fringe pattern, that is, the threshold value determined by the amplitude A and the offset C of the above equation (4), the fixed measurement image. Is binarized (step S230). Here, the threshold value can be, for example, C or CA / 2. By binarizing the fixed image based on the brightness information of the low-frequency measurement image (the brightness information of the low-frequency stripe pattern projected to capture the low-frequency measurement image), the brightness and color of the inspected object 12 Regardless, a stable dot image can be detected. Further, the control unit 30 executes a noise reduction filter on the binarized fixed measurement image to remove noise (step S240).

Further, the control unit 30 detects the position of the dot image in the fixed measurement image that has been binarized and noise has been removed (step S250). As a method of detecting a dot image from this fixed measurement image, a template matching or labeling algorithm can be used, but since it is a sequential process, it is difficult to implement with GPU (Graphics Processing Unit) or the like, and it is realistic. In some cases, the detection time may be longer than the time required for imaging or moving the camera unit 21 (changing the visual field area).

Therefore, in the present embodiment, as shown in FIG. 5A, the fixed measurement image is divided into a plurality of grids (areas), and a dot image is detected in each grid to obtain the position thereof. ing. With such a configuration, each grid can be scanned independently, so that the number of grids can be parallelized, and high-speed processing can be performed using a GPU or the like. The grid can be detected accurately by overlapping the adjacent grids by the size of the dot image. Further, as shown in FIG. 5B, the positions of the dot images are the maximum value (xmax) and the minimum value (xmin) in the x direction and the maximum value (ymax) and the minimum value in the y direction of the position having brightness. (Ymin) can be obtained, and the center coordinates (x', y') of the dot image can be obtained from these values by the following equations (5) and (6).

x'= (xmin + xmax) / 2 (5)
y'= (ymin + ymax) / 2 (6)

Then, when the position (center coordinates) of the dot image in the fixed measurement image is obtained, the control unit 30 reads out the long-period reference image from the memory 35, and from this position and the long-period reference image, the position of the position is Acquire the phase (step S260). The acquisition method is as described above. The rough height (rough height) for each grid can be calculated from the phase obtained from this long-period reference image.

Here, as shown in FIG. 5A, there are a grid in which a dot image can be detected and a rough height can be found, and a grid in which a dot image cannot be detected and a rough height cannot be found. Exists. Therefore, for a grid whose height is unknown, the rough height is propagated by determining the height of the grid from the rough height of the surrounding grid (step S270). Finally, the control unit 30 calculates the detailed height of the position of the dot image by combining the rough height and the phase obtained from the short-period image based on the above equation (3) (step S280). ). As is clear from the above equation (3), in the calculation of the rough height, the phase difference obtained from the long-period pattern is rounded by rounding down the decimal point by the Round function, so that the dot image is somewhat distorted. Even if it is deformed, it does not affect the accuracy of the final height required.

As described above, when the inspection method according to the present embodiment is used, one imaging in which a fixed pattern is projected and an imaging in which a short-period pattern is projected while shifting the phase are performed for one visual field region. Since high-precision height information can be acquired by a total of four imagings of three times, it is possible to improve the inspection throughput while maintaining the accuracy. Further, by using the fixed pattern as a dot pattern, the fixed measurement image can be divided into grids and parallel processing using a GPU or the like can be performed, so that the throughput can be further improved. The number of times of imaging (number of shifts) in which a short-cycle fringe pattern is projected may be four or more.

10 Inspection device 21 Camera unit 23 Projection unit 30 Control unit

Claims (5)

The step of acquiring a short-period measurement image, which is an image of the object to be inspected on which a short-period fringe pattern is projected, and
A step of acquiring a fixed measurement image, which is an image of an inspected object on which a fixed pattern synchronized with a long-period fringe pattern is projected, and
A step of detecting the position of the image of the fixed pattern from the fixed measurement image, and
An image of a reference plane on which the long-period fringe pattern is projected, and a step of determining a long-period phase, which is the phase of the position of the image, based on a long-period reference image acquired in advance.
An image of a reference plane on which the short-period fringe pattern is projected, and a step of determining a short-period phase, which is the phase of the position of the image, based on a previously acquired short-period reference image.
For each position of the image, and chromatic said long period phase, wherein from the short cycle phase, and calculating the height of the object to be inspected, and
An inspection method in which the fixed pattern is a dot. Detecting the position of the image of the fixed pattern, the fixed measurement image is divided into a plurality of regions, to claim 1, characterized in that to detect the position of the image included in the area for each of the regions The described inspection method. The inspection method according to claim 1 or 2 , further comprising a step of binarizing the fixed measurement image before the step of detecting the position of the image of the fixed pattern. The inspection method according to claim 3 , wherein the step of binarizing the fixed measurement image determines a threshold value for binarization based on the luminance information of the short-period measurement image. A projection unit that projects a pattern on the object to be inspected,
A camera unit that acquires an image of the object to be inspected on which the pattern is projected, and
A storage unit that stores the image and
An inspection apparatus comprising: a control unit for calculating the height of the object to be inspected by the inspection method according to any one of claims 1 to 4.

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