JPH0674902A - Method and apparatus for detecting minute defects in curved material to be detected - Google Patents

Abstract

(57) [Abstract] [Purpose] A microdefect that is about the same size as the surface roughness of the material to be detected can be detected by clearly revealing it without any individual difference and by correcting the reference curved surface. Accurately determine the magnitude of the detected value. A surface height amount detecting device using a focus method at each position while moving a stage 11 on which a material to be detected 12 is mounted by a moving mechanism in the horizontal direction in the horizontal direction of the material to be detected 12 by a predetermined distance. 15 to be detected material 12
By repeatedly performing the operation of detecting the surface height of the target material 12, the fine shape of the surface of the material 12 to be detected is detected three-dimensionally, and the minute defect 1
In the method of detecting 2b, the surface height amount detecting device 15
The focus range of the curved detection target material 12 is made larger than the surface roughness 12a and smaller than the minute defect 12b to detect the fine shape of the detection target material 12 surface, and the detected value of the detected detection target material 12 is detected. The correction is performed based on the center coordinates of the reference curved surface of the detected material 12 calculated by the signal processing device 14 based on the surface height.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a detection device for detecting minute surface defects on the surface of a steel sheet used as an outer panel for automobiles and home electric appliances.

[0002]

2. Description of the Related Art For example, an exterior steel plate used for the body of an automobile is subjected to processing such as press molding. Therefore, as shown in FIG. Foreign matter adhering to the surface of the object to be detected 1 or microscopic surface defects 2 or foreign matter 4 adhering to the press die 3
As a result, minute defects occur in the press-molded product. Even if the minute defect has a height of about 2 to 3 μm, after coating,
Since it appears in appearance, it cannot be used as an exterior steel plate. Therefore, detecting the minute surface defects before and after press molding is one of the important items in quality control.

As a method for detecting this minute surface defect,
A stylus method that traces the detected object with a stylus and detects surface defects from the horizontal and vertical movements of the stylus,
There is a light cutting method, etc. that traces the surface of the object with the light beam and detects surface defects from the horizontal movement of the light beam and the surface height fluctuation determined by the arrival time of the light beam to the surface of the object to be detected. .

[0004]

However, in the case of a minute surface defect having a height of 2 to 3 μm, the height of the surface roughness of the object to be detected such as the molding plate or the molding plate is substantially the same as the minute defect. Since they are the same, it is difficult to distinguish them. That is, FIG.
In the case where there is a minute surface defect 1b having substantially the same height on the detected object 1 having a surface roughness 1a with a pitch of 10 μm and a height of 2 to 3 μm as shown in FIG. However, in practice, it is not possible to manufacture a stylus having a diameter of 10 μm or less.
Therefore, it cannot be distinguished from the other, and therefore, it is detected as a smooth surface as shown in FIG.

On the other hand, in the case of detection by the light section method,
The surface of the object to be detected 1 can be clearly traced and can be detected in the same manner as the surface state of the object to be detected 1 as shown in FIG. 8, but when quantifying this, it is judged which is a micro defect. Is difficult. Further, the surface roughness varies depending on the material (component) of the object to be detected 1, but in the light section method, since the focus range is fixed, it is necessary to prepare a device having a different focus range for each different surface roughness. .

Therefore, at present, it is the actual situation that the operator detects the minute defects by visual inspection, but this tends to involve the skill of the operator and there is a problem in the uniformity of the inspection. . In addition, the labor and time required for the inspection deteriorates the efficiency.

The present invention has been made in view of the above-mentioned problems of the prior art, and requires high precision and the skill level of the operator for minute defects having approximately the same height as the surface roughness described above. An object of the present invention is to provide a method and an apparatus for detecting a minute defect in a curved material to be detected, which enables highly efficient detection without doing so.

[0008]

In order to achieve the above-mentioned object, a method for detecting a minute defect of a curved material to be detected according to the present invention includes a stage on which the material to be detected is mounted in a horizontal direction of the material to be detected. By repeating the operation of detecting the surface height of the material to be detected by the focus method at each position while moving for a predetermined distance, the fine shape of the surface of the material to be detected can be detected three-dimensionally and minute defects can be detected. In the method, the fine shape of the surface of the material to be detected is detected in the focus range which is larger than the surface roughness of the curved material to be detected and smaller than the minute surface defects, and the detected value is the surface of the detected material to be detected. The correction is performed based on the center height of the reference curved surface of the detected material calculated from the surface height of the portion having no minute defect in the height and the known bending radius.

Further, the apparatus for detecting a minute defect of a curved material to be detected according to the present invention is an apparatus used in the above-described detection method of the present invention, which comprises a stage on which the curved material to be detected is mounted and a horizontal plane of this stage. Direction moving mechanism, a horizontal plane direction scaler that outputs the amount of movement of the stage in the horizontal plane by this moving mechanism, a surface height amount detection device for the material to be detected on the stage, and a detection amount by this surface height amount detection device The center coordinates of the reference curved surface are calculated from the height direction scaler that outputs the value and the detection height from any of three or more points in the portion having no microdefect among the detected amounts from the height direction scaler and the known bending radius. Is repeated a plurality of times, the mode of the calculated values is adopted as the center coordinate of the reference curved surface, and a three-dimensional view of the surface of the material to be detected is created based on the both output signals. The 3-dimensional view is corrected based on the center coordinates of the reference curved surface, the area of the micro surface defects to be detected from the correction value is're is provided a signal processing apparatus for calculating the volume and the like.

[0010]

The microdefect detecting apparatus for a curved material to be detected according to the present invention first measures the surface roughness of the curved material to be detected so that the surface height is 10 to 500 times the measured surface roughness. The focus range of the volume detection device is determined. This is because the surface roughness is affected unless it is 10 times or more. Then, the material to be detected is placed on the stage, and the surface height of the material to be detected is detected by the surface height amount detecting device at each position while moving the stage in the horizontal plane direction. The amount of movement of the stage in the horizontal plane direction is such that the determined focal ranges do not overlap and no gap is formed.

Then, in the signal processing device, the center coordinates of the reference curved surface are determined from the detected heights at arbitrary three or more points in the portion having no micro defects among the detected amounts from the height scaler and the known bending radius. The calculation is repeated a plurality of times, and the mode of the calculated values is adopted as the center coordinate of the reference curved surface, and the three-dimensional view of the surface of the detected material is obtained from the amount of movement of the stage in the horizontal direction and the amount of surface height. After creating, the created three-dimensional diagram is corrected based on the center coordinates of the reference curved surface, and the area, volume, etc. of the minute surface defect to be detected are calculated from this correction value.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method and an apparatus for detecting minute defects in a curved material to be detected according to the present invention will be described below based on an embodiment shown in FIGS. FIG. 1 is a schematic diagram showing the overall configuration of the device of the present invention, FIG. 2 is an explanatory view of an autofocus method of a surface height amount detecting device used in the present invention, and FIG. 3 is a method of implementing the present invention using the device of the present invention. 3D view of the cross-sectional shape of the press-molded product including micro defects before correction of the reference curved surface, FIG. 4 is a 3D view of the cross-section shape after correction of the reference curved surface of FIG. 3, and FIG. Drawing which shows the actual cross-sectional shape of the press-molded article containing a defect, FIG. 6 is a flowchart which shows the outline of the method of this invention.

In FIG. 1, reference numeral 11 denotes a stage on which the material 12 to be detected is placed, which can be intermittently moved at a predetermined pitch in the horizontal direction by a well-known forward / reverse moving mechanism such as a lead screw feeding mechanism. It is configured. The movement pitch is obtained by previously measuring the surface roughness of the detected material 12 to be detected, and determining the focus range of the surface height amount detection device described later so as to be 10 to 500 times the measured surface roughness. After that, the movement amounts are set so that the determined focus ranges do not overlap and no gap is formed. That is, by making this movement pitch equal to the determined focus range, the same result as when the surface of the detected material 12 is continuously detected can be obtained.

The amount of movement of the stage 11 which moves at a predetermined pitch by the forward / reverse moving mechanism is transmitted from the horizontal scaler 13 such as a magnescale to the signal processing device 14 by, for example, digital communication. 15 is disposed vertically above the stage 11, and
1 is a surface height amount detecting device for detecting the amount of surface height of the detected material 12 on the detection target 1. The automatic detection method is almost the same as an automatic focusing device such as an autofocus camera. Find the height.

That is, as shown in FIG. 2, first, when the target 16 is projected onto the material 12 to be detected with visible light or the like, the shadow 16a of the target 16 is input to the detector 17.
In many cases, the material 12 to be detected has a single color, and when it is a single color, it is difficult to focus. Therefore, the target 16 is provided to shade the material 12 to be detected. Then, image processing of a preset area of the detector input signal is performed (focus range). The image processing performed here is the shadow 1 of the target 16.
It means that the objective lens 18 is moved to the pixel frequency distribution position for each wavelength where the boundary line of 6a is most clear, and the distance is derived from the position of the objective lens 18 at that time. Therefore,
The distance measured by the autofocus method is an average value within the focus range because it is determined by all pixel tones. In FIG. 2, 19 is an eyepiece lens, and 20 is a split prism for projecting the shadow 16a of the target 16 onto the material 12 to be detected.

The height detection amount at each measurement point by the surface height amount detection device 15 is transmitted to the signal processing device 14 by the height direction scaler 21 by, for example, digital communication. In this way, the signal processing device 14 performs the following processing based on both output signals transmitted from the horizontal scaler 13 and the height scaler 21.

That is, in the signal processing device 14, first,
Of the detected amount transmitted from the height scaler 21, a spherical equation [(x−a) ² + is obtained from the detected heights of, for example, arbitrary three points in a portion without microdefects and a known curvature radius.
(Y−b) ² + (z−c) ² = r ² ] is repeated a plurality of times to calculate the center coordinates of the reference curved surface, and the mode of these calculated values is used as the center coordinates of the reference curved surface (a , B, c). Here, as a determination of a portion having no minute defect, a portion having a constant second derivative value (a portion having no change in curvature) may be obtained. Further, a three-dimensional drawing of the surface of the material 12 to be detected is created from the amount of movement of the stage 11 in the horizontal plane direction and the amount of surface height output from the horizontal scaler 13 and the height scaler 21. After that, the created three-dimensional drawing is corrected based on the calculated center coordinates of the reference curved surface, and the area, volume, etc. of the minute surface defect to be detected are calculated from this correction value. A schematic flow chart of the above method of the present invention is shown in FIG.
3 shows an example of a three-dimensional view before correction of the reference curved surface created by the signal processing device 14, and FIG. 4 shows an example of a three-dimensional view after correction of the reference curved surface. Note that FIG. 5 shows the detected material 1
2 is the actual shape of the surface.

According to the method of the present invention using the apparatus of the present invention, as shown in FIG. 5, in the actual shape of the surface of the material 12 to be detected, it is difficult to distinguish the surface roughness 12a from the minute defects 12b.
As shown in FIG. 3, since the focus range of the surface height amount detection device 15 is set to be larger than the surface roughness (surface roughness 12a) of the detected material 12 and smaller than the minute defect 12b, the detection is performed. It is extremely easy to identify the minute defect 12b to be detected, and as shown in FIG. 4, the minute defect 12b to be detected is detected.
The size of can also be accurately determined. Reference numeral 22 in FIG. 1 denotes a display device, and reference numeral 12c in FIGS. 3 to 5 denotes a microdefect that does not need to be detected.

[0019]

As described above, according to the present invention,
Since the focus range of the surface height detection device is set to be larger than the surface roughness of the material to be detected and smaller than the minute defect to be detected, the unevenness due to the surface roughness is leveled to detect the minute defect to be detected. Can be made visible, and an accurate size can be obtained by correcting the exposed microdefects based on the reference curved surface calculated using the surface height amount detection value. Therefore, according to the present invention, it is possible to clearly detect a minute defect that cannot be detected by the stylus method or a minute defect that has a surface roughness that is almost the same as the surface roughness that is difficult to determine based on the data detected by the light-section method, and the accurate The size can be calculated. Further, there is no individual difference such as visual detection.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the overall configuration of a device of the present invention.

FIG. 2 is an explanatory diagram of an automatic focusing method of the surface height amount detection device used in the present invention.

FIG. 3 is a three-dimensional view of a cross-sectional shape of a press-molded product including micro defects before the reference curved surface is corrected when the method of the present invention is performed using the device of the present invention.

4 is a cross-sectional shape 3 after the reference curved surface correction of FIG.
It is a dimensional diagram.

FIG. 5 is a drawing showing an actual cross-sectional shape of a press-molded product containing minute defects.

FIG. 6 is a flowchart showing an outline of the method of the present invention.

FIG. 7 is an explanatory diagram of generation of minute defects during press molding.

FIG. 8 is a schematic diagram of micro defects to be detected by the present invention.

9 is a schematic diagram of data when the microdefect shown in FIG. 7 is detected by a stylus method.

[Explanation of symbols]

 11 Stage 12 Detected Material 12a Surface Roughness 12b Small Defect 13 Horizontal Plane Scaler 14 Signal Processor 15 Surface Height Detecting Device 21 Height Scaler

Claims (2)

[Claims] 1. An operation of detecting a surface height of a material to be detected by a focusing method at each position while moving a stage on which the material to be detected is moved by a predetermined distance in a horizontal plane direction of the material to be detected. By performing the three-dimensional detection of the fine shape of the surface of the material to be detected, and detecting the minute defects, in the focus range which is larger than the surface roughness of the curved material to be detected and smaller than the minute surface defects. Detecting the fine shape of the surface of the detection material, the detection value is calculated from the surface height of the surface height of the detected material without micro defects and the known radius of curvature of the detection material. A method for detecting a minute defect in a curved material to be detected, characterized in that the correction is performed based on the center coordinates of the curved surface. 2. The apparatus used in the detection method according to claim 1, wherein a stage on which the curved detection target material is placed, a moving mechanism of the stage in a horizontal plane direction, and a horizontal direction of the stage by the moving mechanism. A horizontal plane scaler that outputs the movement amount, a surface height amount detection device for the material to be detected on the stage, a height direction scaler that outputs the detection amount by the surface height amount detection device, and this height direction scaler Of the detected amount from, the calculation of the center coordinates of the reference curved surface from the detected heights of arbitrary three or more points in a portion without a minute defect and the known bending radius is repeated a plurality of times to determine the most frequent values of those calculated values. The value is adopted as the center coordinate of the reference curved surface, and a three-dimensional view of the surface of the material to be detected is created based on the both output signals, and the created three-dimensional view is based on the center coordinates of the reference curved surface. correction An apparatus for detecting a minute defect in a curved material to be detected, comprising a signal processing device for calculating the area, volume, etc. of the minute surface defect to be detected from this correction value.