JPH06221836A - Surface defect inspection device - Google Patents

Abstract

PURPOSE:To extract band-shaped defect generated continuously in a direction which is vertical to the direction of a light-reception element of a line sensor from a threshold reference signal. CONSTITUTION:An average light quantity distribution signal of the entire surface of a body to be inspected is generated by a threshold reference signal measuring device 60. The average light quantity distribution signal is subjected to differential processing for two times by an operation device 70, the light-quantity distribution according to an optical system is eliminated, only the signal component of a low-frequency defect part which is 10mm or longer in width is emphasized and left, and defect extraction according to a certain threshold is performed by the threshold method, thus obtaining a defect detection signal 80 and hence extracting a band-shaped low-frequency defect generated continuously in the direction which is vertical to the direction of the light-reception element of a line sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface defect inspection apparatus, and more particularly to a surface defect capable of accurately detecting a defect on a circumferential surface of a photoconductor used in an image output device such as a copying machine or a laser printer. Regarding inspection equipment.

[0002]

2. Description of the Related Art In recent years, many photoconductors used in image output devices such as copying machines and laser printers have a structure in which an organic photoconductor is coated as a surface layer on a base material. Defects of this type of organic photoconductor include one caused by color unevenness and contamination of foreign substances which occur when a solvent is applied, and one caused by mechanical scratches produced after being manufactured as a photoconductor.

These defects appear as deterioration in the quality of the output image. In particular, defects due to uneven coating of the solvent affect the formation of halftone images in the light lens copying machine. Further, the defects due to mechanical scratches and the defects due to coating unevenness each have a characteristic that they become strip defects continuously generated in the direction perpendicular to the light receiving element direction of the line sensor. The band-shaped defects due to mechanical scratches occur continuously in the direction perpendicular to the light receiving element direction of the line sensor, which is generated by blade cleaning when the photosensitive drum is assembled as a drum unit. The band-like defects in the coating process are caused by vibrations when the drum is pulled up from the coating liquid.

FIG. 7 is a conceptual diagram of a surface defect inspection apparatus already filed by the present applicant, in which 1 is a light projector equipped with a halogen light source and the like, 2 is slit light projected from the light projector 1, and 3 is an object to be inspected. Is a photoconductor drum 4, which is an optical system for collecting scattered light scattered by defects on the surface of the photoconductor drum 3,
Reference numeral 5 is a line sensor that receives the scattered light, and reference numeral 5a is a pixel array of the line sensor, which is formed of, for example, 5000 pixels. 6 is a light-receiving visual field of the line sensor, and its width 6a is about 70 μm.

The photosensitive drum 3 is rotated once in the direction of arrow 7 at a constant speed in order to scan the entire surface thereof.
As a result, the sub-scan is performed. On the other hand, the line sensor 5 scans the received information in the direction of the arrow 8 and outputs it. As a result, main scanning is performed. Regarding the sub-scanning and the main scanning, the existing sub-scanning is performed at a rate of rotating the photosensitive drum 3 once in 5 seconds, and the main scanning period is 1 ms. With such scanning, line scratches and point scratches such as dents in the direction parallel to the axial direction of the photosensitive drum 3 can be detected with high accuracy, but circumferential scratches have low detection accuracy.

Therefore, the speed of the main scanning is slowed down while keeping the speed of the sub scanning constant, and the period is set to, for example, 6 msec to thin out the information in the main scanning direction. Therefore, the flaw in the circumferential direction of the photoconductor drum can be accurately detected from the output signal of the line sensor 5. 8A and 8B are explanatory views of the defect detection method of the surface defect inspection apparatus described in FIG. 7, in which FIG. 8A is a line sensor and FIG. 8B is a schematic view of a photosensitive drum.

Reference numeral 11 denotes a circumferential scratch on the photosensitive drum 3, 12 is a horizontal scratch on the photosensitive drum 3 in a direction parallel to the axial direction, and the same reference numerals as those in FIG. 7 correspond to the same portions. In the figure, when the circumferential length of the photosensitive drum 3 is 250 mm, the main scanning period is 1 msec while the photosensitive drum 32 is rotated once in 5 seconds. The surface of the body drum 3 moves about 50 μm in the sub-scanning direction.

For example, start of main scanning on the photosensitive drum 3.
Let p be the point and q be the end point of one main scan. ₁Then subscan
Pq measured in the direction₁The length between them is about 50 μm. This
On the other hand, the cycle in the main scanning direction is set to about 6 msec.
And make the sampling ratio coarser to 1/6)
During the main scanning period, the surface of the photoconductor drum 3 moves in the sub scanning direction.
Move about 300 μm.

That is, if the starting point of the main scanning on the photosensitive drum 3 is p and the ending point of the main scanning is q2, p−q ₂
The length between them is about 300 μm. Here, focusing on the signal received by the pixel column 5a of the line sensor 5,
The th pixel has the visual field of the circumferential wound 11, and has the n + 3th and the n + th
When the horizontal line scratch 12 is used as a field of view for the pixels on the fourth board, the moving distance in the sub-scanning direction becomes long. Therefore, the scattered light from the circumferential scratch 11 continuously enters the (n + 1) th pixel in each main scanning cycle. However, the scattered light from the lateral ray flaw 12 does not continuously enter the n + 3th pixel and the n + 4th pixel.

Therefore, the amount of scattered light from the circumferential scratch 11 which is incident on the (n + 1) th pixel and accumulated therein is 1
The amount of scattered light from No. 2 is relatively larger than the amount of incident and accumulated in the (n + 3) th and (n + 4) th pixels. As a result, the output signal for the circumferential scratch 11 output from the line sensor 5 becomes relatively larger than the signal output for the horizontal scratch 12, and the detection accuracy increases accordingly.

As described above, the band-shaped defects (circumferential scratches) continuously generated in the direction perpendicular to the light-receiving element direction of the line sensor, which are caused by the blade cleaning when the photosensitive drum is assembled as a drum unit, are shown in FIG. By making the sampling ratio in the vertical direction rougher than the light receiving element direction of the line sensor shown in FIG. 8, accurate detection can be performed.

It should be noted that the high-pass filter is used to reliably detect the scattered light of the band-shaped defect, and the defect is not affected by the light quantity distribution of the optical system and the difference in the reflectance of each inspected object by the automatic threshold tracking. Those that perform detection are known. FIG. 9 is a conceptual diagram of another surface defect inspection insertion filed by the applicant of the present invention, in which the defect detection is performed by the automatic tracking of the threshold value without being affected by the difference in the light amount distribution of the optical system and the reflectance of each inspection object. 7 and 8, the same reference numerals correspond to the same portions, 13 is a driving device, 14 is a defect extracting device, and 15 is a defect extracting device.
Is a defect determination device, and 50 is a light receiver.

In FIG. 1, a fluorescent light is used as a light source and slit light is emitted from a projector 1 having a slit on the front surface of an inspection surface of a photosensitive drum 3 using an organic photosensitive member as an inspection object. Then, the reflected light is received by the light receiver 50 including the CCD line sensor of the reduction optical system whose main scanning direction is set to the longitudinal direction of the organic photosensitive drum. The photosensitive drum 3 is rotated by the driving device 4, and the entire surface of the photosensitive drum is inspected by the light receiver 50. The output signal of the entire surface of the drum, which is received by the light receiver 50, is used by the defect extraction device 14 for image processing.
Is taken into.

In the defect extracting device 14, the threshold automatic tracking for changing the threshold so as to keep the interval between the threshold and the measured output signal constant from the threshold reference signal which is the light amount distribution of the photosensitive drum 3 and the average light amount. Thus, defect extraction that is not affected by the light amount distribution by the optical system and the difference in reflectance of each photoconductor drum is performed. Further, geometrical feature quantities such as the area of the defect and the perimeter are calculated. For the threshold value reference signal, it is most effective to use the average light intensity distribution obtained by time-averaging the entire surface data of each photoconductor drum to achieve the automatic thresholding effect. The geometrical feature amount of the defect is sent to the defect determining device 15 such as a host computer and the defect is determined.

[0015]

However, in the prior art described with reference to FIG. 7, it is not necessary to make the sampling ratio in the vertical direction coarser than the light receiving element direction of the line sensor or to use the high pass filter. There is a problem that it is necessary to newly provide a dedicated inspection device for a strip defect continuously generated in the direction perpendicular to the light receiving element direction of the sensor.

Further, the band-shaped defect damaged by the blade has a high frequency signal number of about 0.3 mm in width, but the band-shaped defect due to coating unevenness has a low frequency signal number of 10 mm or more in width, and the same band-shaped defect is also characteristic. different. In the conventional technique described with reference to FIG. 9 above, in order to improve the effect of the threshold automatic tracking that eliminates the difference in reflectance peculiar to the object to be inspected and the influence of the light amount distribution by the optical system, the average light amount distribution is individually measured for each object. Measure the threshold reference signal of the data. For this reason, there is a drawback in that strip defects continuously generated in the direction perpendicular to the light-receiving element direction of the line sensor remain in the threshold reference signal measured by averaging the signal of the line sensor in the vertical direction and cannot be detected. It was

That is, when inspecting the photosensitive drum 3 having a defect in the circumferential direction of the drum due to uneven coating, the threshold reference signal measured by the defect extracting device 14 is as shown in FIG. As the measurement conditions, the number of pixels of the line sensor that constitutes the light receiver 50 is 5000 pixels with a pitch of 7 μm, the optical magnification is 6 times, and the F number of the lens of the optical system is F.
4. For A / D conversion, 4V was used as the resolution of 256 gradations.

As shown in FIG. 3 described later, the photosensitive drum 3
In the threshold reference signal measured by averaging the entire surface data of, the point-like and linear independent defect signals and high-frequency noise components having a size of about 1 mm or less are smoothed by integrating. Although it disappears from the signal, defects in the circumferential direction of the photoconductor drum 3 are integrated and appear as a circumferential defect signal in the figure.

When such a defect signal is added to the threshold reference signal, the threshold reference signal changes along the defect signal as shown by the dotted line in FIG. become unable. That is, FIG. 10A shows a threshold reference signal waveform diagram when there is one defect on the surface of the photoconductor drum, and FIG. 10B shows a case where there is a defect in the circumferential direction on the surface of the photoconductor drum. FIG. 3 is a threshold reference signal waveform diagram, and both threshold reference signal waveforms change due to the component due to the presence of the defect.

An object of the present invention is to provide a low-frequency signal generated continuously in the direction perpendicular to the light receiving element of the line sensor without adding new inspection man-hours to the defect inspection apparatus disclosed in the latter prior art. It is an object of the present invention to provide a surface defect inspection apparatus capable of accurately detecting band-shaped defects.

[0021]

In order to achieve the above object, the present invention provides a surface layer 32 coated on the surface of a substrate 31.
The cylindrical inspection object 30 having the axis is rotated around its axis, the band-shaped light 21 parallel to the axial direction is projected on the surface of the surface layer 32, and the scattered light 22 reflected from the surface of the surface layer 32 is emitted. In a surface defect inspection device for inspecting a surface defect of the inspected object 30 by receiving light with a light receiver 50 including a line sensor, light irradiation for irradiating the surface of the surface layer 32 of the inspected object 30 with the band-shaped light 21. The device 10 and a light receiver 50 having a line sensor in which a large number of light receiving elements for detecting the reflected light amount of the scattered light 22 of the band-shaped light 21 from the surface are arranged, and an output signal of the light receiver 50. The threshold reference signal measuring device 60 for time averaging in the vertical direction and the threshold reference signal generated by the threshold reference signal measuring device 60 are 2
Arithmetic device 7 that performs a differential differentiation to extract a defective portion with a constant threshold value
0, and a moving device 13 that relatively moves the light receiver 50 and the device under test 30 in a direction orthogonal to the direction in which the light receiving elements of the line sensor are arranged. It is characterized in that band-like defects existing continuously in the direction orthogonal to the light-receiving element arraying direction constituting the line sensor of the light-receiving device 30 are detected.

[0022]

In the surface defect inspection apparatus having the above-mentioned structure,
As shown in (1), the average light intensity distribution signal (threshold reference signal) of the entire surface of the inspected object measured by the threshold reference signal measuring device 60 is generated (S-1). The average light intensity distribution signal is subjected to the second-order differential processing by the arithmetic unit 70 (S-
2), the light amount distribution due to the optical system is eliminated, and only the signal component of the low frequency defect portion with a width of 10 mm or more is emphasized and left,
Defects are extracted by a constant threshold by the threshold method (S-
3) The defect detection signal 80 is obtained.

As a result, the threshold value automatic tracking for changing the threshold value from the light quantity distribution and the average value of the reflected light quantity of the inspection object 30 is affected by the difference in the light amount distribution by the optical system and the individual reflectance of the inspection object 30. Instead, the surface defect inspection is performed.

[0024]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the following, the inspected object is an organic photoconductor drum whose substrate is coated with an organic photoconductor, and is continuous in the circumferential direction of the drum caused by uneven coating of the organic photoconductor,
An example of detecting a low-frequency defect having a width of 10 mm or more will be described.

FIG. 1 shows a surface defect inspection apparatus 1 according to the present invention.
It is a schematic diagram explaining an Example, 10 is a light irradiation device,
13 is a driving device, 21 is band light, 22 is scattered light, 30 is a photosensitive drum, 31 is a base, 32 is a surface layer, 50 is a light receiver, 60 is a threshold reference signal measuring device, 70 is a computing device, 8
0 is a defect detection signal. In the figure, the photosensitive drum 3 generated by uneven coating on the photosensitive drum, which is the inspection body,
In the defect detection in the circumferential direction of 0, as the reflected light received by the light receiver 3, there are specularly reflected light mainly due to specular reflection of the photoconductor drum 30 and scattered light removed from the specularly reflected light receiving position.

FIG. 2 is a schematic flow chart for explaining the defect inspection procedure of the surface defect inspection apparatus shown in FIG. 1. When the inspection is started, first, the average of the entire surface of the inspected object measured by the threshold reference signal measuring apparatus 60 is measured. A light amount distribution signal (threshold reference signal) is generated (S-1). The average light intensity distribution signal is subjected to second-order differentiation processing by the arithmetic unit 70 (S
-2), the light amount distribution by the optical system is eliminated, only the signal component of the defective portion having a low frequency signal number of 10 mm or more in width is emphasized and left, and the defect extraction is performed by the constant threshold by the threshold method (S-3. ), The defect detection signal 80 is obtained.

Therefore, according to the present invention, a defect in the circumferential direction of the drum due to coating unevenness is applied using a waveform processing method from the threshold reference signal of each organic photosensitive drum measured in the inspection process of the defect inspection apparatus of FIG. To detect. FIG. 3 is a threshold reference signal waveform diagram on the photosensitive drum in which there are circumferential defects due to coating unevenness. The threshold reference signal shown by the solid line obtained by A / D converting the received light signal of the reflected scattered light is the received light to be measured. Container 50
Due to the influence of the cosine fourth law of the optical system, the distribution becomes such that the light quantity in the peripheral part is lower than the light quantity in the central part.

Defects in the circumferential direction of the drum due to uneven coating are
It appears as a low-frequency signal having a width of 10 mm or more in this light amount distribution. Therefore, the light quantity distribution is canceled by approximating the distribution of the threshold reference signal to a quadratic function capable of differentiating the second order and obtaining the second derivative. When a defect signal having a frequency different from the light intensity distribution of the cosine fourth law is placed on the threshold reference signal, the defect signal portion becomes a higher-order function component of second or higher order, and the defect signal remains in the second derivative. Only the signal can be extracted with a constant threshold.

FIG. 4 is an explanatory diagram of the distribution of the derivative when the threshold reference signal shown in FIG. 3 is approximated to a quadratic function.
FIG. 5 is an explanatory diagram of the distribution of the second-order derivative with respect to the derivative shown in FIG. Defects in the circumferential direction of the drum caused by uneven coating on the photosensitive drum, which is the object to be inspected, are about 0.3 in width of mechanical scratches by the blade described in the prior art of FIG.
10 mm to 30 m width for high frequency defects of mm
m, the pixel width of the line sensor is 300 to 600 pixels, and the output value is a low frequency defect signal of about 7% of the normal surface level.

The inventors of the present invention have made the distribution of the derivative and the second derivative the difference of about 1/2 the sampling interval of the defect width in order to express the variation of the low frequency defect signal remarkably. It was confirmed experimentally that the value calculated using the value is effective. FIG. 6 is an explanatory diagram of the method of calculating the derivative distribution, and the distribution D ′ shown in (b) of the derivative of the point D in FIG. 6A is about half the defect width centered at the point D. determined by the difference value of the gradation values y ₂ gradation values y ₁ and S ₂ points S ₁ point 1 sampling interval. For a defect having a width of, for example, about 550 pixels, the difference value is obtained by setting the sampling interval to 270 pixels, which is about one half of the defect width.

As a result, the derivative distribution has a cosine of 4
The influence of the multiplication rule remains as an element of the first-order function, and a location other than the defect that becomes a higher-order function component is extracted at a certain threshold value. However, in the distribution of the second-order derivative, the influence of the cosine fourth law becomes a constant, and only a defect of a higher-order function component can be extracted by a constant threshold. In the actual measurement, a simple moving average of 10 points was also performed to further remove high frequency noise.

To obtain the second derivative of the threshold reference signal,
Similar results can be obtained by smoothing differentiation by the quadratic polynomial fitting method. Since this method also has a smoothing function, the simple moving average for removing high frequency noise is unnecessary, but the calculation method is more complicated than obtaining the difference value, and the calculation time becomes long. The smoothing derivative is Savitzky and Gol.
Convolution is performed using the coefficient table obtained by ay.

Similar to the method of calculating the difference value at the sampling interval of 1/2 of the defect width, if the sampling interval for smoothing differentiation × the number of smoothing points is approximately 1/2 of the defect width, the smoothing effect is obtained. Is increased, and the change amount of the defect signal can be remarkably expressed. For a defect having a width of about 550 pixels, for example, when performing smoothing differentiation with 25 smoothing points, the sampling interval is set to 10 pixels so that the sampling interval × the smoothing point becomes about ½ of the defect width. Good to do.

A specific operation of the defect inspection apparatus is to copy the threshold reference signal of each photosensitive drum measured by the threshold reference signal measuring apparatus 60 to the arithmetic unit 70, and the arithmetic unit 70 calculates the second derivative of the derivative. Calculation and calculation processing of defect extraction with a fixed threshold value are performed. Therefore, by incorporating this method into the conventional defect detection algorithm in the latter defect inspection apparatus described in the above-mentioned prior art, the processing time of about 1 second is added to the inspection time, but the drum circle caused by uneven coating is generated. It is possible to detect a low frequency defect having a width of 10 mm or more in the circumferential direction.

In the above embodiments, the organic photosensitive drum is taken as an example of the object to be inspected, and the surface defect is inspected. However, the object to be inspected is not limited to the above-mentioned organic photosensitive drum, and other For example, in the case of a functional component of a copying machine, a belt-shaped organic photoconductor that applies a surface layer to a substrate similarly to an organic photoconductor drum, or a circumferential band-shaped surface defect such as a fuser roll used in a fixing device. It goes without saying that it can be applied to inspection.

[0036]

As described above, according to the present invention,
Defect extraction of a defect signal carried on a threshold reference signal, which is the average light intensity distribution data of each inspected object measured to perform surface defect extraction, by the second-order differential processing of the threshold reference signal and a fixed threshold extraction processing. In order to provide a surface defect inspection apparatus which is effective for detecting a band-shaped low frequency defect continuously generated in a direction orthogonal to a row direction of light receiving elements constituting the line sensor of the light receiver including the line sensor. You can

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating one embodiment of a surface defect inspection apparatus according to the present invention.

FIG. 2 is a schematic flow chart illustrating a defect inspection procedure of the surface defect inspection apparatus shown in FIG.

FIG. 3 is a threshold reference signal waveform diagram in a photosensitive drum in which a circumferential defect due to coating unevenness exists.

FIG. 4 is an explanatory diagram of a derivative distribution when the threshold reference signal shown in FIG. 3 is approximated to a quadratic function.

5 is an explanatory diagram of a distribution of second-order derivatives with respect to the derivatives shown in FIG.

FIG. 6 is an explanatory diagram of a method of calculating a derivative distribution.

FIG. 7 is a conceptual diagram of a surface defect inspection apparatus that the applicant has already applied for.

FIG. 8 is an explanatory diagram of a defect detection method of the surface defect inspection apparatus described in FIG. 7, in which (a) is a line sensor;
(B) is a schematic diagram of a photosensitive drum.

FIG. 9 is another concept of surface defect inspection insertion already filed by the present applicant, which detects defects without being affected by the difference in the light amount distribution of the optical system and the reflectance of each inspected object by the automatic threshold tracking. It is a figure.

FIG. 10 is a threshold reference signal waveform diagram when there is one defect on the surface of the photosensitive drum (a), and a threshold reference signal waveform diagram when there is a defect in the circumferential direction on the surface of the photosensitive drum ( b).

[Explanation of symbols]

10 light irradiation device, 13 driving device, 21 strip light, 2
2 scattered light, 30 photoconductor drum, 31 substrate, 32
Surface layer, 50 light receiver, 60 threshold reference signal measuring device,
70 arithmetic unit, 80 defect detection signal.

Claims (1)

[Claims] 1. A cylindrical test object having a surface layer coated on the surface of a substrate is rotated around its axis, and band-shaped light parallel to the axial direction is projected onto the surface of the surface layer, In a surface defect inspection device for inspecting a surface defect of the inspection object by receiving scattered light reflected from the surface of the surface layer with a light receiver equipped with a line sensor, the band-shaped light on the surface of the surface layer of the inspection object A light irradiation device for irradiating, a light receiver having a line sensor in which a large number of light receiving elements for detecting the reflected light amount of scattered light of the band-shaped light from the surface are linearly arranged, and an output signal of the light receiver The threshold reference signal measuring device for time averaging in the vertical direction and the threshold reference signal generated by the threshold reference signal measuring device
An arithmetic unit for performing a differential operation to extract a defective portion with a constant threshold value, and the light receiver and the object to be inspected are relatively moved in a direction orthogonal to a direction in which the light receiving elements of the line sensor are arranged. A surface defect inspection apparatus, which includes a moving device for detecting a strip defect continuously existing in a direction orthogonal to a light receiving element arraying direction which constitutes a line sensor of the light receiver of the inspection object. .