JP2002062220A - Scanning optical system inspection method and inspection apparatus - Google Patents

Abstract

Abstract: [PROBLEMS] To simultaneously measure a beam diameter in a main scanning direction and a sub-scanning direction and a focal point thereof or astigmatism of a scanning optical system. In an inspection method of a scanning optical system including a laser beam incident optical system including a laser source, a rotary polygon mirror, a laser beam emitting optical system, and the like, an area sensor is moved in an optical axis direction of an emitted beam. While calculating the beam diameters of the beam images sequentially detected by the area sensor 10 in the main scanning direction and the sub-scanning direction, the beam diameter change curves Lm and Ls at the respective measurement positions are calculated.
The in-focus position and the astigmatism are measured from the position of the minimum value of Ls.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection method and an inspection apparatus for a scanning optical system, and more particularly, to a scanning optical system including a laser beam incident optical system including a laser source, a rotary polygon mirror, and a laser beam emitting optical system. The present invention relates to an inspection method and an inspection apparatus for an emitted laser beam (hereinafter, referred to as a beam).

[0002]

2. Description of the Related Art A scanning optical system used in a laser printer, a copying machine or the like generally includes a semiconductor laser as a light source, and a laser beam incident optical system including a collimator lens and a cylindrical lens, and a rotating optical system as a polarizer. It is composed of a polygon mirror and a laser beam emitting optical system including an fθ lens, and irradiates the laser beam while scanning the laser beam on a photosensitive surface which is a scanning surface.

The function of this scanning optical system is defined by the light quantity distribution of the irradiated beam, the beam shape or the beam diameter and the focal length, and the beam shape or the focal length is adjusted to keep these values within the allowable range. Inspection to measure is performed.

In the inspection of a scanning optical system, a beam receiving means such as a CCD line sensor or an area sensor is moved in a beam optical axis direction, a main scanning direction, and a sub-scanning direction (a direction orthogonal to the main scanning direction on a scanning surface). Attached to a movable slider, the laser output of the scanning optical system to be inspected is modulated, the beam image is taken into the light receiving means at the same time, the image is processed, and the waist position of the beam at each spatial position (beam diameter) (The position where is minimized) is detected, and the in-focus position is obtained. Also, conversely,
The beam shape and the beam diameter are determined from the light quantity distribution of the beam at the designed scanning position, and the degree of convergence of the beam is inspected.

For example, Japanese Patent Application Laid-Open No. Hei 6-15869 discloses a measuring unit (composed of an image intensifier tube and an area sensor) movable in a three-dimensional direction, an image processing unit, and a pulse generating unit for controlling the measuring unit. An inspection apparatus for a laser scanning optical system, comprising a display unit for displaying the result of image processing and an arithmetic control unit, is described. Japanese Patent Application Laid-Open No. 6-34329 discloses a device for modulating a laser to be inspected and a laser beam. There is described an inspection apparatus including a light receiving element array (line sensor) to be detected and a beam diameter calculating means for calculating a beam diameter in the main scanning direction from a detection signal.

Japanese Unexamined Patent Publication No. Hei 8-262350 discloses a beam detecting section comprising an optical sensor, a moving mechanism of the beam detecting section, and an adjusting device for moving a moving mechanism or a scanning optical system according to the output of the optical sensor. And a technique for measuring a beam during scanning is disclosed in JP-A-9-2196.
No. 8 discloses a beam diameter measuring device comprising a modulation driving means for a scanning optical system, a CCD camera (area sensor, light receiving means), an exposure timing control means, a means for calculating a beam diameter from image data, and a camera moving means. An apparatus is described.

Further, Japanese Patent Application Laid-Open No. 10-104541 discloses that the imaging position of a scanning optical system is moved in order to inspect the image forming performance of a laser beam when a rotating polygon mirror is rotating.
An imaging state (beam shape) is measured by a measurement unit (two-dimensional sensor) to determine a focus position in the main scanning direction.

[0008]

In the above prior art, the measurement of the focal distance or the focal position of the beam of the scanning optical system, the detection of the beam shape at each scanning position,
Although the beam diameter can be calculated by image processing, simultaneous measurement of the beam diameter in the main scanning direction and the sub-scanning direction, the focal point thereof, and the astigmatism of the scanning optical system is not performed. In addition, in the inspection apparatus, there is a problem that the load on each moving stage, slider or moving mechanism is large and the apparatus becomes complicated, and further, there is a problem of interference due to interference fringes generated in coherent laser measurement. ing. The present invention is to provide a new inspection method and an inspection apparatus that solve such a problem.

[0009]

The first aspect of the present invention relates to a method for inspecting a scanning optical system including a laser beam incident optical system including a laser source, a rotary polygon mirror, a laser beam emitting optical system, and the like. While moving the area sensor in the axial direction, sequentially calculate the beam diameter in the main scanning direction and the sub-scanning direction of the beam image detected by the area sensor to calculate a beam diameter change curve at each measurement position. This is an inspection method characterized by measuring an in-focus position and an astigmatism from a minimum value position. Thus, the beam diameter in the main scanning direction and the beam diameter in the sub-scanning direction can be measured simultaneously, and the astigmatism of the optical system can be detected.

The area sensor is sequentially moved in the main scanning direction to measure the in-focus position of the change curve at each scanning position, and to measure the scanning line of the scanning optical system. , The degree of curvature of field can be detected. Further, upon detecting the beam image of the scanning optical system to be inspected, the focal point position at each scanning position of the scanning optical system to be inspected is stored, the area sensor is roughly positioned at the focal point position, and a predetermined position is determined from the position. The one that determines the change curve by moving the area sensor of the range can shorten the measurement time, captures a plurality of beam images in the area sensor,
An apparatus that calculates each beam diameter can perform inspection efficiently. A device that enlarges the outgoing beam and forms an image on the area sensor can increase the measurement accuracy.

The second invention is an inspection apparatus for a scanning optical system comprising a laser beam incident optical system including a laser source, a rotary polygon mirror, a laser beam emitting optical system, and the like. In a scanning optical system inspection device that detects and measures a beam image by moving in the direction, a beam detection sensor is provided at a fixed position in the optical axis direction, and infinity correction that is movable in the optical axis direction in front of the beam detection sensor. An inspection apparatus provided with a mold type objective lens. As a result, the measuring instrument to be moved during the inspection is only the objective lens, the mechanism is simplified, the movement control is easy, the mechanical load is reduced, and the accuracy can be increased.

A device in which the objective lens is detachably mounted on a support table which is movable in the optical axis direction can easily cope with inspection of a scanning optical system of various specifications. If the numerical aperture of the objective lens is set to be large enough to absorb the deviation of the optical axes of the objective lens and the beam detection sensor system, the deviation of the optical axis of the inspection optical system can be tolerated. When the objective lens and the beam detection sensor are connected by a telescopic light shielding cylinder, noise factors such as stray light can be blocked.

The third aspect of the present invention is an inspection apparatus for a scanning optical system including a laser beam incident optical system including a laser source, a rotary polygon mirror, a laser beam emitting optical system, and the like, wherein a beam image is detected by a beam detection sensor. In the inspection apparatus for a scanning optical system to be measured, a diffusion plate is provided at a focal point position of the scanning optical system, and a beam image formed on the diffusion plate is detected by the beam detection sensor. Inspection device. As a result, the beam to be inspected is diffused, and coherency is reduced, so that interference in the inspection optical system can be eliminated and inspection errors can be eliminated.

In the case where the diffusion plate is rotated in the scanning plane or the diffusion plate is moved along the scanning surface of the scanning optical system, the change in the beam diameter due to the diffusion plate is leveled. , Measurement accuracy can be ensured. Further, those provided with a displacement measuring means of the diffusion plate, those which movably support the diffusion plate in the optical axis direction, and which hold the diffusion plate at a fixed position by a signal of the displacement measuring means are provided. In addition, errors due to the movement of the diffusion plate can be eliminated.

The apparatus in which the diffuser plate and the beam detection sensor are integrally supported so as to be movable in the optical axis direction and the main scanning direction, and the change in the beam diameter in the optical axis direction at each scanning position is measured. The in-focus position of the optical system can be measured without interference in the main scanning direction. The apparatus provided with the optical length measuring device for directly measuring the position of the diffusion plate in the optical axis direction can accurately grasp the position of the diffusion plate, thereby increasing the inspection accuracy.

A diffusion plate and an infinity-correction type objective lens for guiding a beam image on the diffusion plate to the beam detection sensor are integrally movably supported in the optical axis direction, and the beam detection sensor is moved in the optical axis direction. The one that is held in a fixed position has a simpler mechanism, facilitates movement control, reduces mechanical load, and can increase accuracy.

According to a fourth aspect of the present invention, in the method of inspecting a beam image of a scanning optical system, a beam to be inspected is formed on a rotating and / or moving diffusion plate, and the beam image is detected by a beam detection sensor. In addition, a plurality of beam images are detected at the same measurement position, and an average value of the beam images is used as a measured value. This makes it possible to prevent interference noise by using the diffuser, to level the beam measurement by moving the diffuser, and to further improve the measurement accuracy by performing a plurality of measurements.

Further, when an average value of a plurality of beam images obtained by the beam detection sensor is calculated for each pixel and an image composed of the average pixels is used as a measured value, a more accurate average image can be obtained. it can.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

First, a method for inspecting a scanning optical system according to the first invention will be described. FIG. 1 is a schematic plan view of an inspection apparatus that performs this method. In FIG. 1, a scanning optical system 1 to be inspected is a synchronization detection PD (photodiode).
(Laser diode) unit 2 for light source equipped with
The beam from the (laser beam incidence optical system) is scanned by the polygon mirror 3 (rotating polygon mirror), and an image is formed on the scanning surface S by the imaging lens 4 (laser beam emission optical system). For example, in a laser printer, the scanning surface S is the peripheral surface of a cylindrical photoconductor.

Light receiving device 1 with built-in CCD area sensor
0 (hereinafter, referred to as an area sensor 10) is mounted on the moving stage 11 and provided so as to be movable in the direction of the arrow in the figure.

In the first aspect of the invention, when inspecting the output beam of the scanning optical system 1, the area sensor 10 sequentially detects a beam image while moving back and forth on the scanning surface S on the moving stage 11. As shown in FIG. 2, change curves Lm and Ls of the beam diameter in the main scanning direction and the sub-scanning direction with respect to the position in the optical axis direction are acquired.

When the beam diameter is obtained, the light emission state of the beam is determined by stopping the polygon mirror 3 at a position where the beam is incident on the light receiving surface of the area sensor 10 and obtaining the beam in a static state. With the output pulse of the PD for synchronization detection mounted on the LD unit 2 as a trigger, a blinking time is designated, and the LD emits a pulse at a light-receiving timing.
In addition, as a method of calculating the beam diameter from the beam image of the area sensor 10, an appropriate known technique can be adopted.

The focal point position of the scanning optical system is represented by a change curve Lm.
And the position P1 and P2 in the optical axis direction of the area sensor 10 indicating the minimum value of Ls and Ls, and it is determined whether or not these P1 and P2 are within the allowable range of the design focal length (scanning surface position). At the same time, the distance ΔF of the focal point of the beam diameter in the main and sub scanning directions, that is, P2−P1 is evaluated as astigmatism.

Next, a method for inspecting a scanning line or a field curvature will be described. As shown in FIG. 3, the moving stage 11 to which the area sensor 1 is attached is mounted on the moving stage 12 which moves in the main scanning direction, and the area sensor 10 is obtained by moving the area sensor 10 in the main scanning direction in addition to the optical axis direction. From the beam diameters in both the main and sub scanning directions, as shown in FIG. 4, a change curve Lm− of the beam diameter in the main scanning direction at each position in the main scanning direction.
1, Lm-2... Lm-N are obtained, and each change curve Lm-N is obtained.
The scanning line SL is obtained by connecting the minimum value of 1, Lm-2... Lm-N, that is, the beam waist position. In addition,
In FIG. 4, the A axis is a position in the main scanning direction, the B axis is a position in the optical axis direction, and the C axis is an axis representing the beam diameter.

By comparing the obtained scanning line SL with a design value, it is possible to inspect and verify the scanning optical system. The beam waist position (position in the optical axis direction) can also take the average value of the beam waist position of the diameter in the main scanning direction and the beam waist position of the diameter in the sub-scanning direction. Note that the LD light emission state at this time is such that a pulse is emitted at a light receiving surface position of the area sensor 10 using a pulse output from the PD for synchronization detection as a trigger, and a pulse is emitted at a plurality of positions in the main scanning direction at regular intervals. This is performed by controlling the amount of movement of the moving stage 12 in accordance with the light emission position.

When newly inspecting a new model or a scanning optical system to be inspected which does not store position data, the position in the main scanning direction and the beam waist position obtained from the beam diameter change curve are determined in the optical axis direction. The positions are stored in a two-dimensional array and are taken into a storage device such as a computer. In the second and subsequent measurements, a beam diameter change curve is acquired by temporarily positioning the position on the position data stored on the scanning surface and moving the moving stage 11 from the position in the optical axis direction. Next, the moving stage 12 is moved on the basis of the stored next position data, and provisional positioning is performed. By limiting the position of the temporary positioning, it is possible to detect the beam waist position in a shorter time even when performing an automatic inspection, and to prevent malfunction. As described above, when the position is changed in the main scanning direction and the beam diameter change curve is acquired, the area sensor 1 is used based on the previous position data of the same model.
By roughly positioning 0 and moving the area sensor 10 in a predetermined range based on this position to obtain a change curve, the positioning time of the area sensor 10 can be shortened.

When measuring the beam, as shown in FIG. 5, a lens barrel 13 and a finite correction type objective lens 14 are fixed to the area sensor 1, and a position separated by a working distance from the tip of the objective lens 14 is scanned optically. If the optical system is set to be the scanning surface S of the system, the beam image captured by the area sensor 10 is enlarged, and the calculation accuracy of the beam diameter is improved.

Further, in order to perform the inspection efficiently, the light source of the scanning optical system is modulated and blinked at regular time intervals, and the magnification of the objective lens is adjusted so that a plurality of beam images (called dots) enter the light receiving surface. When set, an image as shown in FIG. 6 is obtained, and by detecting labeling and fillet coordinates of each label image on the image, beam diameters x1, y1, x2, and y2 of each dot in both the main and sub scanning directions are obtained. ,... Can be detected simultaneously. The change of the beam diameter in the main and sub scanning directions in the optical axis direction is defined as a change curve, and the scanning position data can be detected from the moving distance of the moving stage and the position of the center of gravity of each label image.

The CCD area sensor has been described as the area sensor used in the present inspection method. Any area sensor can be used without being limited to the CCD as long as it can detect a beam image two-dimensionally.

Next, the inspection apparatus for a scanning optical system according to the second invention will be described. This inspection apparatus is particularly effective when used in the above-described inspection method of the first invention.
It is not necessarily limited to this method. In this inspection apparatus, as shown in FIG. 7, an imaging lens 15 is connected to an area sensor 10, and an infinity-corrected objective lens 14a is mounted on a small movable stage 11a movable in the optical axis direction. Since the distance between the objective lens 14a and the imaging lens 11 is variable, when changing the working distance of the objective lens 14a and acquiring a change curve of the beam diameter, the space of the detection region is narrow and the main body of the area sensor 10 cannot be installed close. In such a case, when the load capacity of the moving stage in the main scanning direction is small, or when the moving in the optical axis direction must be performed accurately and in a short time, the objective lens 14a which is lighter and smaller than the area sensor 10 may be used. The detection can be performed only by moving the. At this time, the magnification of the optical system is m
If the magnification of the imaging lens is M times, the magnification will be mM times.

Further, in the present apparatus, as shown in FIG.
If the working distance is different, the objective lens 14a can be moved on the small moving stage 11a without moving the light receiving device when the working distance is different. In addition, it is possible to make the inspection optical system correspond to different scanning optical systems.

Even if the scanning beam of the scanning optical system has an angle of the maximum θ with respect to the optical axis of the inspection optical system, the numerical aperture of the objective lens is not less than N. A. Is set so that the following condition is satisfied, where n is the refractive index of the medium between the objective lens and the scanning optical system.

N. A. > Nx Sinθ (n = 1 in air)

Further, as shown in FIG. 9, the imaging lens 15 attached to the area sensor 10 and the small moving stage 1
The objective lens 1a is mounted on the first objective lens 1a by connecting the objective lens 14a with a bellows-like elastic light-shielding cylinder 17.
Even when the working distance is changed by replacing the 4a, or when the objective lens 14a is moved in the optical axis direction,
Since the space between the lens a and the imaging lens 15 is covered, stray light is not received and erroneous detection can be reduced.

Next, an inspection apparatus for a scanning optical system according to the third invention will be described. This inspection apparatus is also an inspection apparatus for the emitted beam of the scanning optical system, similar to the inspection apparatus described above. The configuration of the inspection optical system 1 and the configuration of the area sensor 10 and the moving stages 11 and 12 are different from those of the previous inspection apparatus. , The same function is denoted by the same reference numeral.

Now, as shown in FIG. 10, a beam emitted from a laser diode (LD) unit 2 is reflected by a rotating polygon mirror 3 and is an imaging lens f.
The light passes through the θ lens 4 and is received by the area sensor 10 as a beam detection sensor via the objective lens 14 and the lens barrel 13. The area sensor 10 is attached to a first moving stage 11 that moves in the optical axis direction and is movable in the optical axis direction. At the same time, the first moving stage 11 moves in the main scanning direction of the scanning optical system 1. Since the area sensor 10 is attached to the second moving stage 12, the area sensor 10 can also move in the main scanning direction. An opal glass diffuser plate 20 is placed at the designed focal point of the scanning optical system 1, that is, at the designed scanning surface S (corresponding to the surface position of the photosensitive member in the actual machine) so that the back surface faces the scanning optical system 1, and similarly, the objective lens The scanning beam is completely diffused by the opal glass diffuser plate 20 for matching the focal position of the area 14, and the fully diffused image is obtained by the area sensor 10.
Is obtained by The polygon mirror 3 and the LD unit 2 are controlled by a computer CP equipped with a pulse generator. The polygon mirror 3 rotates at a predetermined rotation speed and scans a scanning beam at a constant speed. Also, the beam from the LD unit 2 can control the interval of lighting and blinking.
An image processing device that processes the image from the camera detects the light amount and the profile of the beam. In this apparatus, the measurement beam is completely diffused by the opal glass diffuser 20,
Coherence is completely removed, and the inspection optical system can be constructed ignoring the relationship between the optical path length and the coherent length of the light source.
Various filters installed between the two-dimensional light receiving surface and the light source, interference of interference caused by reflection on the surface of an optical element such as a cover glass or the like is eliminated, and the beam of the scanning optical system 1 can be obtained.

As shown in FIG. 11, when a beam from the scanning optical system 1 is received by the area sensor 1 via the objective lens 14 and the lens barrel 13, a disc-type opal glass diffuser is By rotating 20A,
It is possible to make the positional deviation of the opal crystal contained in the glass random in time. It is possible to remove the positional influence of the opal glass diffusion plate 20A on the image. The belt 22 is used to change the number of rotations by changing a pulley on the motor side.
In this way, by using this mechanism, the noise on the diffused light of the beam due to the type and arrangement of the constituent materials such as the diffuser for diffusing the beam is spatially randomized, thereby smoothing the diffused state. Noise can be reduced.

As shown in FIG. 12, an opal glass diffusion plate 20B and a motor 21 for rotating the same are integrally mounted on a support 23, and the support 23 is
4 is held movably and coarsely in the main scanning direction of the scanning optical system. By applying a slight movement in the main scanning direction to the rotating opal glass diffusion plate 20B, the positional influence of the opal glass diffusion plate 20B is further removed, and the entire scanning surface is covered with a small diffusion plate by coarse movement. It is possible to do. As described above, the diffusion state can be further randomized, and a beam free of interference jima can be obtained by following a wide scanning range.

As shown in FIG. 13, the laser from the laser length measuring device 30 is installed by using a mirror 31 and a beam splitter 32 so as to coincide with the optical axis of the inspection optical system for detecting the beam of the scanning optical system. , Opal glass diffuser 20
Opal glass diffuser 20B by capturing the reflected light on the back surface of B
Is detected, and the original beam diameter of the scanning optical system is detected from the amount of displacement due to the influence of the linear positioning accuracy of the slider and the like and the design value (depth of focus) of the scanning optical system. In this apparatus, when a beam diffusing means such as a diffusion plate is displaced in the optical axis direction, the projected image of the beam on the surface is deformed or scaled. Accordingly, it is possible to obtain a desired beam detection value by calculation or the like from the detection value.

As shown in FIG. 14, an opal glass diffusion plate 20B and a motor 21 for rotating the same are integrally mounted on a support 23a, and a moving stage 25 for holding the support 23a movably in the optical axis direction. Is provided on the moving stage 24 for moving in the main scanning direction, and the laser length measuring device 30
By correcting the positional shift of the opal glass diffuser plate 20B obtained in the above step by moving the support 23a on the stage 25, the opal glass diffuser plate 20B can be accurately positioned on the photoconductor surface.
B traces and beam measurements can be performed. As described above, by mechanically correcting the positional shift of the diffuser plate or the like, it is possible to project the beam at the original detection position and acquire the beam at the light receiving unit.

As shown in FIG. 15, the area sensor 1 on which the opal glass diffuser plate 20B and the support 23b on which the rotating mechanism is mounted, the objective lens 14 and the lens barrel 13 are mounted.
0 is attached to one support 26, and this support 2
6 is provided on the moving stage 11 so as to be movable in the optical axis direction, and the area sensor 10 can be moved in the optical axis direction and the main scanning direction. By moving the support 26 with the moving slider 11 in the optical axis direction so as to minimize the beam diameter captured by the area sensor 10 and covering the entire scanning surface by moving the slider 12, the scanning line, that is, the field curvature And the change curve of the beam diameter can be obtained. In this apparatus, by tracing the position where the system of the diffused scanning beam becomes minimum, the beam diameter change curve and the scanning line,
Enables detection of field curvature

As shown in FIG. 16, the objective lens 14a of the infinity correction type, the stage 23b on which the opal glass diffuser plate 20B and its rotating mechanism are mounted are mounted on one support 27, and the support 27 is moved to the moving stage 11b. Area sensor 10 which is movably mounted on the top and is a two-dimensional CCD camera
The imaging lens 15 is attached to the support 27, and the area sensor 10 is fixed separately from the support 27, so that when the inspection optical system needs to be moved in the optical axis direction, the adjustment can be performed without moving the area sensor 10. This makes it possible to reduce the load applied to the moving mechanism, and it is possible to install a filter such as an ND filter that changes the optical path length between the objective lens 14a and the imaging lens 15. For example, the flexibility of the inspection optical system can be increased. In this apparatus, the load on the inspection optical system moving mechanism can be reduced, and the setting of the inspection optical system can be easily performed even if the model of the scanning optical system is changed.

In the inspection apparatus shown in FIG. 14, the displacement of the beam focus in the optical axis direction is detected by using one laser-side length unit 30. For example, as shown in FIG. Laser length measuring devices 30A, 30B, 30 having the same optical path length to the opal glass diffusion plate 20B
By detecting the three positions of the opal glass diffuser plate 20B by C, a three-dimensional displacement including the tilt of the opal glass diffuser plate 20B is detected, and is mechanically corrected using a gonio stage or the like? Can be calculated and corrected by software.
The position correction of B can be performed more accurately.

In the above description of the third invention, an opal glass diffusion plate is exemplified as the diffusion plate. However, the diffusion plate used in the present invention is not limited to opal glass, but may be a frosted glass-like diffusion plate containing a diffusing agent. Any diffusion plate having sufficient rigidity and an accurate plane can be used.

As described above, the CCD area sensor has been described as the beam detection sensor in the second and third inventions.
In the device of the present invention, not limited to the CCD area sensor,
An arbitrary area sensor or a line sensor may be employed depending on the detection method. Although the moving mechanism of the area sensor has been described as including the support base and the moving stage (provided with the slider), it is needless to say that any known mechanism can be used as the linear moving mechanism.

Finally, a method for inspecting a scanning optical system according to the fourth invention and a method for inspecting a scanning optical system using a diffusion plate will be described. In order to enhance the randomness of the opal crystal contained in the glass substrate of the opal glass diffuser, a rotation and translation mechanism has been added to remove the influence of the position of the diffuser and obtain multiple images in chronological order. Then, by taking the average of those images, it is possible to avoid interference errors in the inspection optical system, and to average the effect on the image of the opal glass diffuser plate that changes on the time axis, Thus, the defect of the scanning optical system to be inspected, which remains unchanged, can be left as it is, and the reliability of defect detection of the scanning optical system can be further improved. As described above, in the method of the present invention, in addition to eliminating the interference error and reducing the spatial noise of the diffusion means such as the diffusion plate, the noise inherent in the diffusion plate on the beam is reduced due to the temporal randomness. To make things possible.

An image obtained by the two-dimensional CCD area sensor is stored in a memory in a computer, and a plurality of images obtained by executing the image plural times are added and averaged for each pixel on the memory, and Those that obtain an average image allow precise image leveling.

[0049]

The first aspect of the present invention relates to a method for inspecting a scanning optical system including a laser beam incident optical system including a laser source, a rotary polygon mirror, a laser beam emitting optical system, and the like. While moving the sensor, the beam diameter in the main scanning direction and the sub-scanning direction of the beam image sequentially detected by the area sensor is calculated to calculate a curve of the beam diameter at each measurement position, and the position of the minimum value of the curve is calculated. Since the in-focus position and the astigmatism are measured, the beam diameters in the main scanning direction and the sub-scanning direction can be measured simultaneously, and the astigmatism of the optical system can be detected.

The second aspect of the present invention is an inspection apparatus for a scanning optical system including a laser beam incident optical system including a laser source, a rotary polygon mirror, a laser beam emitting optical system, and the like. In a scanning optical system inspection device that detects and measures a beam image by moving in the direction, a beam detection sensor is provided at a fixed position in the optical axis direction, and infinity correction that is movable in the optical axis direction in front of the beam detection sensor. Since the objective lens of the mold type is provided, the measuring instrument to be moved at the time of inspection is only the objective lens, the mechanism is simplified, the movement control is easy, the mechanical load is reduced, and the accuracy can be increased.

The third aspect of the present invention is an inspection apparatus for a scanning optical system including a laser beam incidence optical system including a laser source, a rotary polygon mirror, a laser beam emission optical system, and the like, wherein a beam image is detected by a beam detection sensor. In the inspection apparatus for a scanning optical system to be measured, a diffusing plate is provided at a focal point position of the scanning optical system, and a beam image formed on the diffusing plate is detected by the beam detection sensor. Since the beam is diffused and coherency is reduced, interference in the inspection optical system can be eliminated, and inspection errors are eliminated.

According to a fourth aspect of the present invention, in the method of inspecting a beam image of a scanning optical system, a beam to be inspected is formed on a rotating and / or moving diffusion plate, and the beam image is detected by a beam detection sensor. At the same time, multiple beam images are detected at the same measurement position, and the average value of the beam images is used as the measured value, so that interference noise is prevented by using a diffusion plate, and the beam measurement is leveled by moving the diffusion plate. In addition, the measurement accuracy can be further improved by a plurality of measurements.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of an inspection apparatus that performs an inspection method according to a first invention.

FIG. 2 is a diagram showing a change curve of a beam diameter in the inspection method of the first invention.

FIG. 3 is a schematic plan view of a moving stage of the inspection apparatus that performs the inspection method of the first invention.

FIG. 4 is a schematic diagram showing scanning lines in the inspection method of the first invention.

FIG. 5 is a schematic plan view of an inspection apparatus that performs the inspection method of the first invention.

FIG. 6 is a schematic diagram showing dots in the inspection method of the first invention.

FIG. 7 is a schematic side view of an embodiment of the inspection apparatus according to the second invention.

FIG. 8 is a schematic partial side view of another embodiment of the inspection apparatus of the second invention.

FIG. 9 is a schematic side view of another embodiment of the inspection apparatus of the second invention.

FIG. 10 is a schematic plan view of an embodiment of the inspection apparatus according to the third invention.

FIG. 11 is a schematic plan view of another embodiment of the inspection apparatus of the third invention.

FIG. 12 is a schematic plan view of another embodiment of the inspection apparatus of the third invention.

FIG. 13 is a schematic plan view of another embodiment of the inspection apparatus of the third invention.

FIG. 14 is a schematic plan view of another embodiment of the inspection device of the third invention.

FIG. 15 is a schematic plan view of another embodiment of the inspection apparatus according to the third invention.

FIG. 16 is a schematic plan view of another embodiment of the inspection apparatus of the third invention.

FIG. 17 is a schematic partial plan view of another embodiment of the inspection apparatus of the third invention.

[Explanation of symbols]

 Reference Signs List 1 scanning optical system 2 laser beam incident optical system 3 rotating polygon mirror 4 laser beam emitting optical system 10 Eri sensor (CCD area sensor) 13 lens barrel 14 finite correction type objective lens 14a infinite correction type objective lens 15 imaging lens 20 diffuser plate ( Opal glass diffusion plate) 20A Diffusion plate (opal glass diffusion plate) 20B Diffusion plate (opal glass diffusion plate) 30 Laser side elongator (optical side elongator) Lm Beam diameter change curve in main scanning direction Ls Beam in sub scanning direction Diameter change curve S scanning plane SL scanning line CP computer

Claims (19)

[Claims] A laser beam incident optical system including a laser source;
In the inspection method of a scanning optical system including a rotary polygon mirror and a laser beam emitting optical system, a main scanning direction and a sub-scanning direction of a beam image sequentially detected by the area sensor while moving the area sensor in an optical axis direction of the emitted beam. A beam diameter of each measurement position, a beam diameter change curve at each measurement position is calculated, and an in-focus position and astigmatism are measured from the position of the minimum value of the change curve. . 2. The scanning optical system according to claim 1, wherein the area sensor is sequentially moved in the main scanning direction to measure a focal point of the change curve at each scanning position, and to measure a scanning line of the scanning optical system. System inspection method. 3. When detecting a beam image of a scanning optical system to be inspected, a focusing position at each scanning position of the scanning optical system to be inspected is stored, and the area sensor is roughly positioned at the focusing position. The inspection method for a scanning optical system according to claim 2, wherein the change curve is obtained by moving a predetermined range area sensor from a position. 4. The inspection method for a scanning optical system according to claim 1, wherein said outgoing beam is enlarged by an objective lens to form an image on said area sensor. 5. The scanning optical system inspection method according to claim 1, wherein a plurality of beam images are taken into the area sensor, and each beam diameter is calculated simultaneously. 6. A laser beam incident optical system including a laser source,
An inspection apparatus for a scanning optical system including a rotary polygon mirror and a laser beam emission optical system, wherein the inspection apparatus moves the beam detection sensor in the optical axis direction of the beam to detect and measure a beam image. An inspection apparatus for a scanning optical system, wherein a beam detection sensor is provided at a fixed position in an optical axis direction, and an infinity correction type objective lens movable in the optical axis direction is provided in front of the beam detection sensor. 7. An inspection apparatus for a scanning optical system according to claim 6, wherein said objective lens is detachably mounted on a support table movable in an optical axis direction. 8. The inspection apparatus for a scanning optical system according to claim 6, wherein the numerical aperture of the objective lens is set to be large enough to absorb the deviation of the optical axes of the objective lens and the beam detection sensor system. 9. The inspection apparatus for a scanning optical system according to claim 6, wherein the objective lens and the beam detection sensor are connected by an extendable light shielding cylinder. 10. A laser beam incident optical system including a laser source,
A scanning optical system inspection device including a rotary polygon mirror and a laser beam emission optical system, wherein a beam image is detected by a beam detection sensor, and the scanning optical system inspection device performs measurement at a focal point position of the scanning optical system. An inspection apparatus for a scanning optical system, further comprising a diffusion plate, wherein a beam image formed on the diffusion plate is detected by the beam detection sensor. 11. The inspection apparatus for a scanning optical system according to claim 10, wherein the diffusion plate is rotated within a scanning plane. 12. The inspection apparatus for a scanning optical system according to claim 11, wherein the diffusing plate is moved along a scanning surface of the scanning optical system. 13. The inspection apparatus for a scanning optical system according to claim 11, further comprising means for measuring a position shift of the diffusion plate. 14. The scanning optical system according to claim 13, wherein the diffusion plate is supported so as to be movable in the optical axis direction, and the diffusion plate is held at a fixed position by a signal from the displacement measuring means. Inspection equipment. 15. The apparatus according to claim 1, wherein the diffusion plate and the beam detection sensor are integrally supported so as to be movable in an optical axis direction and a main scanning direction, and a change in a beam diameter in the optical axis direction is measured at each scanning position. 13. The inspection apparatus for a scanning optical system according to claim 10, 11 or 12. 16. The inspection apparatus for a scanning optical system according to claim 15, further comprising an optical length measuring device for directly measuring a position of the diffusion plate in an optical axis direction. 17. An infinity-correction type objective lens that guides the diffusion plate and a beam image on the diffusion plate to the beam detection sensor so as to be integrally movable in an optical axis direction. 17. The scanning optical system inspection apparatus according to claim 15, wherein the inspection apparatus is held at a fixed position in an axial direction. 18. A method of inspecting a beam image of a scanning optical system, wherein a beam to be inspected is formed on a rotating and / or moving diffuser plate, and the beam image is detected by a beam detection sensor and at the same measurement position. A method for inspecting a scanning optical system, comprising: detecting a plurality of beam images; and using an average value of the beam images as a measured value. 19. The inspection of the scanning optical system according to claim 18, wherein an average value for each pixel of the plurality of beam images obtained by the beam detection sensor is calculated, and an image composed of the average pixels is used as a measured value. Method.