JPH11142289A - Method and apparatus for measuring and evaluating nonuniformity in quantity of light of scanning beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure and evaluate the variation of the quantity of light of a scanning beam quantitatively in the direction of scanning without printing. SOLUTION: In a detection plane (Y-Z plane) in parallel with a Z-axis including a target scanning line A1 on a rotating drum plane 6, a photosensor 11 with a light receiving plane narrow in a Z direction 5 and a light quantity sensor 12 are provided on a moving stage 20 movable in the direction of a Y-axis. The stage 20 is moved in the direction of the Y-axis by an instruction from a control box 21 to move the sensors 11 and 12 sequentially to predetermined measurement points. Every time the sensor 11 captures a beam at the measurement point, a plane number counter 26 counts it. At the time when the counted number reaches a predetermined number, the sensor 12 measures the quantity of light. The quantity of light at a specific plane of a rotating polygon mirror 4 is stored in memory 25 for every measurement point, and they are compared with each other by a computer 22 to evaluate the variation of the quantity of light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a scanning optical system, and more particularly to a method and apparatus for measuring and evaluating unevenness in the amount of light of a scanning beam in an image forming apparatus such as a laser beam printer or a laser facsimile. is there.

[0002]

2. Description of the Related Art In recent years, an image forming apparatus such as a laser beam printer (LBP) for recording an image by scanning a laser beam with a laser beam on a photosensitive drum surface as a recording medium, for example, has been widely used. in use.

FIG. 5 is a schematic view of a main part of a scanning optical system used in this type of image forming apparatus. In FIG. 5, a laser beam emitted from a light source means 71 composed of a semiconductor laser or the like is converted into a parallel laser beam by a collimator lens 72, and is condensed by a cylindrical lens 73 having a predetermined refractive power in the sub-scanning direction. The light is incident on a reflection surface (deflection surface) 74a of an optical deflector 74 composed of a mirror (polygon mirror). The laser beam reflected and deflected by the reflection surface 74a of the optical deflector 74 composed of a rotating polygon mirror passes through an imaging lens (Fθ lens) 75 having f-θ characteristics, for example, a photosensitive drum 76 as a surface to be scanned. Light is guided on the surface. By rotating the optical deflector 74 at a constant angular velocity in the direction of arrow A in the figure, optical scanning is performed on the surface to be scanned of the photosensitive drum 76 in the direction of arrow B at a constant speed.

In a conventional image forming apparatus using such an optical scanning optical system, the optical performance of the scanning optical system is evaluated in advance by using an evaluation device when assembling or the like.

In other words, a method for evaluating the optical performance of a scanning optical system using an evaluation device is to scan a scanning light beam from a scanning optical system at a plurality of positions different in the scanning direction, for example, a beam scanning start position, an intermediate position, and a scanning position. Light is received at an end position or the like, and a scanning position (hereinafter, simply referred to as a scanning position) in a direction orthogonal to the scanning direction, a beam diameter, a scanning start timing, and the like are measured to evaluate the performance.

[0006]

However, unevenness in the light amount in the scanning direction, which is one of the optical performance evaluations, is not performed by the above-described conventional evaluation apparatus, but the scanning optical system is incorporated in the image forming apparatus. Thereafter, a performance evaluation method is adopted in which printing is actually performed on paper, and the print density unevenness is visually inspected by a person. Therefore, since the test is a sensory test, there is a disadvantage that the evaluation criteria are not clear, and the evaluation results vary widely and are ambiguous. In the performance evaluation, the scanning optical system must be incorporated into the main body of the image forming apparatus, and printing must be performed in a state in which the product is completed. Has to be disassembled and the scanning optical system must be removed, which is disadvantageous in that the cost is increased.

An object of the present invention is to quantitatively measure the unevenness of the light amount in the scanning direction without performing an evaluation based on an ambiguous sensory evaluation, in order to solve the above-mentioned unresolved problems of the prior art. Evaluate and evaluate the performance only with the scanning optical system in the same way as other optical performance evaluations, so that the evaluation can be performed reliably and in a short time. An object of the present invention is to provide a method and an apparatus for measuring and evaluating unevenness in the amount of light of a scanning beam, which can save the trouble of assembling it in a forming apparatus main body and having to disassemble it again.

[0008]

In order to achieve the above object, a method for measuring and evaluating unevenness in the amount of light of a scanning beam according to the present invention comprises identifying a rotating polygon mirror among scanning beams scanned in a predetermined scanning direction by the rotating polygon mirror. A step of detecting the light amount of the beam by only one surface at a plurality of measurement points separated in the scanning direction by detecting means arranged on the optical path, and a step of comparing and calculating the detected light amount. And The detecting means moves in a direction parallel to the scanning direction of the scanning beam, and detects the amount of light at a plurality of measurement points set along the moving direction.

Defects on each reflecting surface of the rotary polygonal mirror can be detected by repeating the evaluation of the light amount unevenness on one specific surface of the rotary polygonal mirror for the number of surfaces of the polygonal mirror and comparing the evaluation values.

An apparatus for measuring and evaluating unevenness in the amount of light of a scanning beam according to the present invention is capable of detecting the light amount of a beam on only one specific surface of a rotating polygonal mirror among scanning beams scanned in a predetermined scanning direction by a rotating polygonal mirror. Means, a moving stage for moving the detecting means in a direction parallel to the scanning direction, means for counting the output of the detecting means, a memory for storing the count value and the detected light quantity in association with each other, and detecting the light quantity. Determining means for comparing and calculating the values.

In the above-described method for measuring and evaluating unevenness in the amount of light of a scanning beam according to the present invention, the number of times of scanning of the beam is counted at a plurality of set measurement points while moving the detecting means in a direction parallel to the scanning direction. From the value, the light amount of only one specific surface of the rotating polygon mirror in the scanning beam is detected.
The detected light amount at each measurement point is compared to evaluate the light amount unevenness.

As described above, at each measurement point, the amount of light on only one specific surface of the rotating polygon mirror is detected and the detected value is used for evaluation, so that the accuracy of each surface of the polygon mirror is not uniform.
Irrespective of variations in the amount of reflected light due to dust, fluff, etc. on the reflecting surface, it is possible to quantitatively evaluate unevenness in the amount of light in the optical system.
Therefore, there is no need to incorporate the scanning optical system into an image forming apparatus or the like for printing, and since the measurement and evaluation can be performed accurately in a short time, the reliability of the evaluation can be greatly improved.
Further, since the manufacturing cost of an image forming apparatus or the like using a scanning optical system can be reduced, it can greatly contribute to lowering the price of the image forming apparatus or the like.

[0013]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an explanatory diagram showing an embodiment and a scanning optical system of a scanning beam light amount unevenness measurement evaluation device E1 of the present invention, and FIG. 2 is an explanatory diagram of a light receiving section of the device of FIG.

The laser light generated from the semiconductor laser 1a of the scanning optical system 1 is collimated by a collimator lens 2 and condensed linearly on a mirror surface 4a of a rotary polygon mirror 4 by a cylindrical lens 3 to form a rotary polygon. The beam is deflected and scanned by the rotation of the mirror 4, and the scanning beam L1 is converted into a spherical lens 5a.
And an imaging lens system 5 having a toric lens 5b. The imaging lens system 5 is an fθ lens, which has a so-called fθ function capable of equalizing the scanning beam L1 on the drum surface 6 and correcting distortion of a point image formed on the photosensitive member. The point image on the photoreceptor forms an electrostatic latent image by main scanning in the Y-axis direction, which is the scanning direction by the rotation of the rotary polygon mirror 4, and sub-scanning in the Z-axis direction by the rotation of the rotating drum 6.

The scanning beam measurement and evaluation device E1 is elongated in the Z direction on a detection surface (YZ plane) parallel to the Z axis including the target scanning line A1 (see FIG. 2) of the scanning beam L1 on the rotating drum 6. It has a photosensor 11 which is a first detecting means having a light receiving surface 11a, and a light quantity sensor 12 which is a second detecting means having a light receiving surface 12a elongated in the Z direction in the detecting surface. Y along the target scanning line A1
It is mounted on a movable stage 20 movable in the axial direction at a predetermined interval.

The light receiving surface 11a of the photo sensor 11 and the light receiving surface 12a of the light amount sensor 12 are formed to be elongated in the Z-axis direction and have a constant width in the Y-axis direction. In particular, the width of the light receiving surface 12a of the light amount sensor 12 in the Y-axis direction is changed by setting the resolution for light amount unevenness detection. The purpose of the unevenness evaluation of the scanning optical system is particularly
In order to detect dust, dirt, scratches, distortion, etc., it is preferable to set a resolution of a fraction of the scanning beam diameter on the imaging lens system 5. For example, when the diameter of the scanning beam on the imaging lens system 5 is 1 mm, the cause of the defect on the imaging lens system 5 can be detected by setting the width of the measurement resolution to about 0.3 mm. Also, the scanning beam L1 does not always follow the target scanning line A1,
For example, scanning is performed as shown by a curve B1. In order to capture the scanning beam even in such a case, the sensor 1
Since the light receiving surfaces 1 and 12 have light receiving surfaces 11a and 12a which are elongated in the Z-axis direction, a change in the light amount of the beam can be detected.

The measurement and evaluation of the scanning beam L1 by the measurement and evaluation device E1 are performed as follows. First, in response to a command from the control box 21, the moving stage 20 is moved in the Y-axis direction, whereby the photosensor 11 and the light amount sensor 12 are sequentially moved to predetermined measurement points set on the target scanning line A1. Photo sensor 11 that was moving
Each time the light sensor 12 reaches a predetermined measurement point and the photosensor 11 captures a light beam, the number of times is counted by the surface number counter 26. When the counted number reaches a predetermined number α (α + the number of rotating polygon mirrors × n), the light quantity sensor 12 takes in the light flux and measures the light quantity. In this measurement, after the host computer 22 detects the scanning beam with the photosensor 11, the host computer 22 reads out the signal of the light amount sensor 12 with a certain delay (see FIG. 4). Then, the signal of the light amount sensor 12 is stored in the memory 25 in association with the value counted by the counter 26. As a result, the amount of light on one specific surface of the rotary polygon mirror 4 is stored in the memory 25 for each measurement point. The number α determined in advance may be any number as long as it is within the number of surfaces of the rotary polygon mirror. N is an arbitrarily determined natural number. The light amount at each measurement point set on the target scanning line of the scanning beam L1 detected in this way is calculated by the host computer 22, and the value is compared to evaluate the light amount unevenness at each measurement point.

Next, a method of measuring and evaluating unevenness in the amount of light of a scanning beam according to the present invention will be described with reference to a flowchart. FIG. 3 is a flowchart showing the procedure of measurement evaluation by the measurement evaluation apparatus E1. First, a target scanning optical system is installed at a predetermined position, a semiconductor laser (light source) is emitted, and a rotary polygon mirror is rotated. (1)
01). Next, measurement is started by the photo sensor 11 and the light amount sensor 12 while continuously moving the moving stage 20 in the Y-axis direction (102). When the stage moves and the light amount sensor 12 reaches the measurement point and the light beam reaches a predetermined surface of the rotary polygon mirror, the light sensor captures the light beam (103), and the surface number counter 26 counts the number of scans. (104), the light amount is measured by the light amount sensor 12 after a certain time delay (107). This is repeated for the number of measurement points (1
05) (106) (108), the measurement ends. Then, the obtained light amounts at the respective measurement points (for one specific surface of the rotary polygon mirror) are compared, and the light amount unevenness is evaluated (109).

Further, by repeating the evaluation of the light amount unevenness on one specific surface of the rotary polygon mirror by the number of surfaces, and comparing the evaluation values, it is possible to detect a defect such as dust on each reflection surface of the rotary polygon mirror. It is possible.

[0020]

As described above, according to the present invention, the light amount on a specific surface of the polygon mirror is detected by the detecting means provided so as to be movable in parallel with the traveling direction of the beam, and this is detected for each measurement point. Since the comparative evaluation is performed, the unevenness in the light amount of the scanning optical system can be quantitatively evaluated regardless of the variation in the reflected light amount due to the unevenness of each surface of the polygon mirror. The position of dust, fluff or the like in the scanning optical system can be specified based on the result, and the defect can be removed by cleaning or replacing on the spot. Therefore, it is possible to greatly improve the reliability of the measurement and evaluation of the unevenness of the light amount of the scanning beam, and it is not necessary to incorporate the scanning optical system into an image forming apparatus or the like to print and evaluate the measurement. Therefore, there is an effect that the manufacturing cost of an image forming apparatus or the like using a scanning optical system can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an embodiment of a scanning beam light amount unevenness measurement evaluation apparatus of the present invention.

FIG. 2 is an explanatory diagram illustrating a light receiving unit of the measurement evaluation device of FIG.

FIG. 3 is a flowchart showing a procedure for performing measurement and evaluation of a scanning beam by the apparatus of FIG. 1;

FIG. 4 is a diagram illustrating signal readout timings of the photosensor and the light amount sensor of the present invention.

FIG. 5 is a schematic diagram illustrating a main part of a scanning optical system used in the image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 scanning optical system 1a, 71 semiconductor laser / light source means 2, 72 collimator lens 3, 73 cylindrical lens 4 rotating polygon mirror 4a mirror surface 5, 75 imaging lens system 5a spherical lens 5b toric lens 6, 76 rotating drum surface / photoconductor Drum 11 Photosensor 11a, 12a Light receiving surface 12 Light amount sensor 20 Moving stage 21 Control box 22 Host computer 25 Memory 26 Surface counter 74 Optical deflector 74a Reflecting surface A1 Target scanning line B1 Scan curve E1 Measurement evaluation device

Claims (4)

[Claims] 1. A method for measuring and evaluating unevenness in the amount of light of a scanning beam in an image forming apparatus having a scanning optical system, wherein only a specific surface of a rotating polygonal mirror among scanning beams scanned in a predetermined scanning direction by a rotating polygonal mirror. Detecting a light amount at a plurality of measurement points separated in the scanning direction by detecting means disposed on an optical path, and comparing and calculating the detected light amount. Evaluation methods. 2. The method according to claim 1, wherein the detecting unit moves in a direction parallel to a scanning direction of the scanning beam, and detects an amount of light at the plurality of measurement points provided along the moving direction.
The method for measuring and evaluating unevenness in light amount of a scanning beam according to claim 1. 3. A defect of each reflection surface of the rotating polygon mirror is detected by repeating the evaluation of light amount unevenness on a specific surface of the rotating polygon mirror by the number of faces of the polygon mirror and comparing the evaluation values. The method for measuring and evaluating unevenness in the amount of light of a scanning beam according to claim 1. 4. A detecting means capable of detecting the amount of light on only one specific surface of the rotating polygonal mirror among the scanning beams scanned in a predetermined scanning direction by the rotating polygonal mirror, and the detecting means detects the light amount in a direction parallel to the scanning direction. A moving stage, a means for counting the output of the detecting means, a memory for storing the counted value and the detected value of the light amount in association with each other, and a determining means for comparing and calculating the detected value. Characteristic scanning beam light amount unevenness measurement and evaluation device.