JPH03291552A - Surface defect inspection device - Google Patents

Abstract

PURPOSE:To prevent deterioration in accuracy due to interference by irradiating the surface of a body to be inspected with the linear polarized light of laser light almost at an angle of incidence nearly corresponding to the Brewster angle and inspecting defects on the surfaces of many kinds of OPC photosensitive body which differ in surface property. CONSTITUTION:The surface of a photosensitive drum 3 to be inspected is irradiated with the linear polarized light of the laser light 4 at the angle of incidence nearly corresponding to the Brewster angle, the polarizing direction of the laser light 4 is selected, and the defect inspection of the surface is performed with the reflected light 6. Then when the photosensitive layer L of the drum 3 is so constituted that reflected light R1 and reflected light R2 interfere with each other, a 1/2-wavelength plate 13 is put in the optical path. Consequently, the laser light 4 becomes (p) polarized light about the incidence surface, the reflected light R1 disappears, and only the reflected light R2 is made incident on a photodetector 2, so that no interference is caused. Further, when the dispersion layer L2 of the photosensitive layer L is large and the reflected light R2 becomes weak, the 1/2-wavelength plate 13 is put off the optical path. Consequently, the laser light 4 becomes (s) polarized light to the incidence surface and the reflected light R1 is reflected and made incident on the photodetector 2, so that the defect inspection of the surface of the drum 3 with the reflected light R1 becomes possible.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to applying laser light while moving an object to be inspected, which is provided with an OPC photoreceptor having a homogeneous layer with low light absorption on the surface of a flat or cylindrical substrate. The present invention relates to a surface defect inspection device that inspects surface defects by irradiating with a flying spot method.

[Conventional technology]

A method called a flying spot method is known as a method for inspecting surface defects on a flat or cylindrical object to be inspected. This uses a laser as a light source and a rotating polygon mirror or a vibrating mirror to scan the moving object with laser light, and then receives the reflected light. This is used to inspect objects to be inspected for defects.

Defect states on the surface of the object to be inspected can be roughly divided into two types:

(1) Waviness defect consisting of relatively gentle unevenness (2)
Micro-irregularity defect consisting of minute irregularities that can be called a rough surface If the inspected object surface has the above-mentioned waviness defect (1), the inspected surface is slightly inclined with respect to the normal surface, so the laser reflected light As shown by the broken line n1 in the figure, the light is reflected in a direction deviating from the normal reflection direction (reflection direction when the surface of the object to be inspected is good (see FIG. 5g)).

In addition, if there is a slight unevenness defect in (2), the reflective surface of the object to be inspected will be in a scattered state as shown by the broken line n in Figure 5, and the amount of light incident on the light receiving section will be different from that in a good case. decrease in comparison.

The defects (1) and (2) above may occur in a superimposed manner, and the defects (1) and (2) above may occur in a superimposed manner.
The defect (2) may also occur separately.

Furthermore, in an electrophotographic photoreceptor drum whose surface is an organic photoconductive photoreceptor layer (OPC photoreceptor layer), the photoreceptor layer is made up of two thin parallel plane layers, as shown in FIG. It may be provided. In the figure, 3a is a drum-shaped base made of aluminum or the like with a smooth surface, LI is a homogeneous layer that is a charge transport layer that is homogeneous to light, and L2 is a charge generation layer that has the property of dispersing light. A dispersed layer (the degree of dispersion varies depending on the type),
4 is incident light, R1 is homogeneous layer, reflected light from the surface, R
2 is reflected light that is reflected at the interface between the dispersion layer L2 and the substrate 3a and comes out into the air.

Conventionally, the reflected lights R, 'R2 are received together by a light receiver without being differentiated, and defects on the surface of the photosensitive layer are detected from changes in their intensity.

[Problem to be solved by the invention]

When inspecting the surface of an object to be inspected for defects using the flying spot method, an interference phenomenon occurs if there is little difference in intensity between the reflected light R1 and the reflected light R1 in FIG. As a result, if there is a slight change in the layer thickness of the photosensitive layer L (L l + L z) close to the wavelength of the laser beam or a fluctuation in the receiving angle due to vibration of the object to be inspected during laser beam scanning, the reflected light will change as the laser beam scans. Variations in strength occur that are independent of surface defects. This variation has interfered with defect detection, making it impossible to detect relatively small defects, and sometimes even large defects. Therefore, the output fluctuation of the light receiving section due to interference is removed by an electric circuit, but at this time, the defect signal is also removed at the same time, which poses a problem that it becomes impossible to detect small defects.

In addition, when the dispersion layer L2 of the photosensitive layer has a large dispersion,
There are many types of objects to be inspected with different surface properties, such as when the light incident on the photosensitive layer is scattered and absorbed and the reflected light R2 becomes extremely weak. Conventionally, surface defects cannot be inspected using a single surface defect inspection device. It was difficult to do so.

The present invention can detect surface defects with a simple configuration both in the case of an OPC photoreceptor layer, which is an object to be inspected, which has a surface structure that causes the above-mentioned interference, and in the case of an object to be inspected, which has a dispersed layer with large dispersion. The purpose of the present invention is to provide an excellent surface defect inspection device that makes possible the following.

[Failure to solve the problem]

The above purpose is to irradiate a laser beam using a flying spot method while transporting an OPC photoreceptor having a homogeneous layer with low light absorption on the surface of the substrate, and use the reflected light to inspect defects on the surface of the object to be inspected. In the surface defect inspection apparatus, the linearly polarized laser beam is irradiated onto the surface of the object to be inspected at an incident angle approximately corresponding to the Brewster angle, the polarization direction of the laser beam is selected, and the reflected light of the laser beam is This is achieved by a surface defect inspection apparatus characterized in that the surface of the object to be inspected is inspected for defects.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a side view showing one embodiment of the present invention, and FIG. 2 is a side view showing one embodiment of the present invention.
A sectional view taken along the line A-A of the light receiver shown in the figure, 3rgJ is a central vertical cross-sectional view of the light receiver shown in FIG.

In the figure, 1 is a laser that emits linearly polarized light, such as a semiconductor laser, a 1/2 wavelength plate, a 1-rotation polygon mirror, and an fθ
A scanner consisting of a lens, a synchronization sensor, etc., 2 a light receiver consisting of two light receiving sections 2a2b which are divided into front and back by a thin plate or an edge member for incident light, 3 a photosensitive drum which is an example of an object to be inspected, 4 is a laser beam that is a scanning light, 5 is a scanning bright line drawn on the surface of the object to be inspected by scanning and irradiation with the laser beam 4, 6 is the reflected light of the laser beam 4 from the surface of the object to be inspected, and θ1 is the surface of the object to be inspected. The incident angle is the angle between the normal line standing at the laser beam 4 incident point and the incident laser beam 4, and θr is the reflection angle that is the angle between the normal line and the reflected light 6. Since the center line of 2 coincides with this reflection angle θr, it is also called the light reception angle. The incident angle .theta.l and the acceptance angle .theta.r of the scanner 1 can be changed while always maintaining the relationship of .theta.i-.theta.r.

As shown in FIG. 4, which shows an example of the structure and optical path of the scanner 1, the laser beam 4 emitted from the laser 11 passes through a shutter 12 that is opened when necessary and a 172 wavelength plate 13 that is removably installed. Thereafter, the beam diameter is expanded to an appropriate beam diameter by the beam diameter expander 14. This laser beam 4 is transmitted by a rotating polygon mirror 16 and an fθ lens 17 to the surface of the photosensitive drum 3, which is an object to be inspected, in parallel with its rotation axis.
The scanning bright line 5 is formed by scanning and irradiating at a constant speed in the direction 4b-hC. - The force photosensitive drum 3 is connected to the control CP in the direction of the arrow.
It rotates at a uniform speed under the control of U, and the entire surface to be inspected is scanned and irradiated with laser light 4, and the reflected light 6 is received by light receiver 2. The synchronization sensor 18 is composed of a light receiver sensitive to the laser beam 4, and sends a synchronization signal to the control CPU at the start of each scan of the scanner I.

Also, the laser 11 is a laser beam 4 emitted from it.
The vibration plane is set perpendicular to the incident plane in FIG. 6, that is, so as to provide S-polarized light.

As shown in FIGS. 2 and 3, the light receiver 2 is divided into upper and lower parts by an edge member 22, and each A
The light receiving section 2a and the B light receiving section 2b are equipped with a plurality of, for example, four A photomultiplier tubes 23a and B photomultiplier tubes 23b each having a cylindrical magnetic shielding member 24 made of a magnetic material at the tip thereof. Diffusion plates 21a and 21b are provided in the light receiving window portion at the tip of the light receiver l, which are spaced apart from each other, and the light receiving portion d is regulated by a mask member 25. The tip portion 22a of the edge member 22 is formed into a cutting edge shape, but this is not particularly necessary when dividing using a thin plate with a thickness of about 0.2 mm. A.

A reflective layer 26 made of a mirror member or a white diffusing material is provided on the inner wall of the B light receiving sections 2a and 2b, and the reflected light 6 enters the diffuser plates 21a and 21b, is transmitted and diffused, and is then reflected by the inner wall to improve efficiency. The light is well received by the A photomultiplier tube 23a and the B photomultiplier tube 23b. Without the diffuser plates 21a and 21b, the relative position of the scanner 1, the light receiver 2, and the photosensitive drum 3 which is the object to be inspected, or the inclination of the light receiver 2 with respect to the direction of reflection of the reflected light 6 can be changed with extreme precision. If not well adjusted, the detection accuracy will be affected, but by providing this, the detection accuracy will drop slightly, but it can be made immune to the influence of slight changes in the above-mentioned relative position and inclination.

Since the photodetector 2 has the above-described configuration, a difference appears in the output of the photodetector 2a and photodetector 2b in the case of a gentle undulation defect, and a difference appears in the output of the photodetector 2a and the photodetector 2b in the case of a fine surface in the case of a minute unevenness defect. Since the output is reduced in comparison, any defect can be detected with high accuracy.

The radiation d of the entrance window regulated by the mask member 25 varies depending on the size and type of the surface defect to be detected with the highest sensitivity, but for example, when the diameter of the bright spot on the scanning surface of the laser beam 4 is 55 μm. Good results were obtained when d-20 mm.

In the above surface defect inspection apparatus of the present invention, prior to defect inspection on the surface of the object to be inspected, the incident angle θl of the scanner 1 and the acceptance angle θr of the light receiver 2 are determined based on the surface layer of the object to be inspected, that is, the homogeneous layer;
Let n be the refractive index of air with respect to air, it is adjusted to be equal to θb below.

tan θ b = n.

Such an angle of incidence θb is called the Brewster angle.

When light is incident at an angle θb corresponding to this Brewster's angle, it has a vibration plane parallel to the incident plane as shown in Figure 7.
The reflectance of polarized light is O.

Figure 7 shows the relationship between the incident angle θ1 and the reflectance (%) when the vibration plane of the incident light is p-polarized light (solid line) parallel to the incident plane and S-polarized light (broken line) perpendicular to the incident plane at n+-1,5. This is a diagram. Changes in reflectance before and after Brewster's angle θb are very slow within a range of about 15 degrees, and the value is small, so there is no problem even if the incident angle θl is slightly deviated during adjustment of the incident angle θl and scanning. do not have.

Furthermore, if the photosensitive layer of the photosensitive drum 3, which is the object to be inspected, is configured such that the reflected lights R and R3 interfere with each other, a 1/2 wavelength plate 13 is inserted into the optical path.

As a result, the laser beam 4 becomes p-polarized light with respect to the incident plane.

Therefore, when the laser beam 4 is incident on the surface of the photosensitive drum 3 at an angle corresponding to the Brewster angle θb, the reflected light R1 becomes 0, and only the reflected light R2 enters the light receiver 2, and no interference occurs. Moreover, since the reflected light R2 contains sufficient information on defects in the photosensitive layer, defect inspection on the surface of the photosensitive drum 3 can be performed without being hindered by interference.

In addition, the dispersion layer L2 of the photosensitive layer has a large dispersion and the reflected light R2
If the light becomes weak, the half-wave plate 13 is removed from the optical path. As a result, the laser beam 4 becomes S-polarized with respect to the incident surface, so that the reflected light R8 is reflected and enters the light receiver 2, making it possible to inspect the surface of the photoreceptor drum 3 for defects using the reflected light R□.

In this embodiment, the laser 11 is installed so that the vibration plane of the emitted laser beam 4 is perpendicular to the incident plane, but the invention is not limited to this. The insertion and removal of the /2 wavelength plate 13 from the optical path may be reversed from the above embodiment, or the laser 11 may be rotated 90 degrees to emit the linearly polarized laser beam 4 without using the 172 wavelength plate 13. It goes without saying that the light may be switched to become p-polarized light or s-polarized light with respect to the incident plane.

C Effects of the Invention According to the present invention, with the configuration described above, the laser beam is incident at an angle corresponding to the Brewster angle, and the laser beam can be simply inserted and removed by inserting and removing the 1/2 wavelength plate or rotating the laser by 90 degrees. With a simple operation, it is possible to inspect for defects on the surface of many types of OPC photoreceptors that have surface layers with different properties, which could not be detected with conventional equipment. We are now able to provide defect inspection equipment.

[Brief explanation of drawings]

Fig. 1 is a side view showing one embodiment of the present invention, M2 drawing is 81
Figure 3 is a central vertical cross-sectional view of the receiver in Figure 1, Figure 4 is a developed optical path diagram of the laser beam in Figure 1, Figure 5 is the object to be inspected. Figure 6 shows the state of reflected light from various defects on the surface. Figure 6 shows the state of reflected light when the surface layer of the object to be inspected consists of two layers. Figure 7 shows the incident angle and reflection of laser light. FIG. 3 is a diagram showing the relationship between rates. l... Scanner 2... Light receiver 2a...A
Light receiving part 2b...B light receiving part 3...Photosensitive drum (object to be inspected) 4...Laser light 5...Scanning bright line 6...Reflected light 11...Laser 13...1/2 Wave plate 16...Rotating polygon mirror 17...Fθ lens 18...Synchronization sensor 21a, 21b...Diffusion plate 22...Edge member 23d...A photomultiplier tube 23b...B photomultiplier tube

Claims (1)

[Claims] Laser light is irradiated by a flying spot method while an OPC photoreceptor having a homogeneous layer with low light absorption on the surface of the substrate is conveyed, and defects on the surface of the object to be inspected are inspected using the reflected light. In the surface defect inspection apparatus, the linearly polarized laser beam is irradiated onto the surface of the object to be inspected at an incident angle approximately corresponding to the Brewster angle, the polarization direction of the laser beam is selected, and the polarization direction of the laser beam is selected. A surface defect inspection device characterized in that the surface of the object to be inspected is inspected for defects using reflected light.