JPH10197336A - Laser beam-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laser beam-measuring apparatus which can measure a dynamic characteristic of laser beams simply. SOLUTION: The measuring apparatus measures a laser beam characteristic by a laser optical system used in a process of forming electronic images. A measured position of laser beams deflected by a rotary mirror 3 arranged at the laser optical system is set as a position where a photosensitive body 5 is to be placed. A CCD camera 6 is arranged at the measured position. Laser beams by one pixel of the CCD camera 6 are emitted, and the emitted laser beams by one pixel are read by the CCD camera 6, whereby a dynamic characteristic of the laser beams is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a laser beam measuring apparatus for measuring characteristics of a laser beam in a laser optical system used in an electronic image forming process, particularly, a dynamic characteristic of a laser beam.

[0002]

2. Description of the Related Art Conventionally, there has been proposed a laser beam measuring apparatus for measuring characteristics of a laser beam in a laser optical system. For example, Japanese Unexamined Patent Application Publication No. Hei 5-34631 discloses that a mask pattern forming plate has two linear edges crossing the beam scanning direction, and the beam is transmitted through these two edges. Are measured, and the diameters of the beams in the beam scanning direction and in the direction perpendicular to the beam scanning are measured based on the respective moving distances.

Hereinafter, the above-mentioned measuring device will be specifically described with reference to FIGS. As shown in FIG. 9, the laser beam emitted from the laser light source 91 is reflected by the reflecting surface of the rotary polygon mirror 92. The rotating polygon mirror 9
2 is used while being rotated at a constant speed.

The laser beam reflected by the rotary polygon mirror 92 passes through the fθ lens 93 and is converged to reach the surface to be scanned. At a position where the surface to be scanned should be located, a mask pattern forming plate 94 is provided. Are located. The mask pattern forming plate 94 is provided so as to be slidable on the stage 90 in a horizontal direction indicated by an arrow 97 and also slidable in a vertical direction indicated by an arrow 96.

[0005] The mask pattern forming plate 94 is formed with four linear slits having different inclination angles, so that the laser beam is not transmitted except for the four slit portions. Therefore, the laser beam reflected by the rotating polygon mirror 92 passes only through the slit.
A photodiode 95 is in close contact with the back side of the mask pattern forming plate 94 (the side opposite to the side on which the rotating polygon mirror 92 and the fθ lens 93 are arranged).

The laser beam transmitted through the slit is photoelectrically converted by the photodiode 95,
It is amplified by an amplifier and then converted to a digital signal by an A / D converter. This digital signal is
It is stored as light amount data by the RAM. The light amount data is read out by the CPU, and the diameters in the beam scanning direction and the beam scanning direction are measured based on the light amount data.

The measurement of the diameter in the beam scanning direction and in the direction perpendicular to the beam scanning is performed as follows. First, the rotating polygon mirror 92 is rotated at a constant speed to scan the beam, and each moving distance of the beam when the scanning beam passes through two linear slits of the mask pattern forming plate 94 is measured. Since the moving distances of these beams are different depending on the beam diameter in the beam scanning direction and the beam scanning perpendicular direction,
The beam diameter in the beam scanning direction and in the direction perpendicular to the beam scanning can be measured based on each moving distance of the beam.

Contrary to the technique described in the above-mentioned publication, a laser beam is reflected in a fixed direction while the rotating polygon mirror is stopped, and a rotating slit and a photodiode are arranged behind the rotating slit on the optical path of the reflected light. There is also known a technique in which a laser beam that has passed through a rotating slit is received by a photodiode and its output signal is differentiated to measure the beam diameter. In other words, while the rotating polygon mirror is rotated in the technique described in the above publication, the same result as the technique described in the above publication is obtained by rotating the slit in the latter conventional technique.

[0009]

In the conventional laser beam measuring apparatus, a laser beam is passed through a narrow slit in any type, and the beam passing through the slit is measured by a photodiode. For this reason, a task of adjusting the laser beam to the measurement point occurs, and there is a problem that a long time is required for the measurement.
Further, in the latter conventional technique, since the laser beam is measured with the rotating polygonal mirror stationary, the spot diameter (dynamic characteristic) of the laser beam when actually scanned is different. There is also a fear that. Further, according to the conventional technique described in the above-mentioned publication, according to the measurement in a state where the rotating polygon mirror is rotated, the rotating polygon mirror includes:
The angle of each reflecting surface with respect to the axis of rotation is delicately varied, and the angle of reflection changes for each reflecting surface, and the arrival position of the beam reflected by each reflecting surface is slightly shifted. The measurement accuracy of the laser beam will be degraded.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and a laser beam measuring apparatus capable of easily measuring the dynamic characteristics of a laser beam without requiring a long time. The purpose is to provide. Another object of the present invention is to provide a laser beam measuring apparatus capable of improving the measurement accuracy by eliminating the influence of the so-called rotating polygonal mirror so that the laser beam is always received on a fixed surface. is there.

[0011]

According to the first aspect of the present invention,
In a laser beam measuring device that measures laser beam characteristics with a laser optical system used in an electronic image forming process, the measurement position of a laser beam deflected by a rotating polygon mirror disposed in the laser optical system should be a photoconductor. As a position, a CCD camera is arranged at this measurement position, a laser beam is emitted for one pixel when an image is output, and the emission characteristics of the laser beam are read by the CCD camera to measure the dynamic characteristics of the laser beam. It is characterized by.

According to a second aspect of the present invention, in the first aspect of the present invention, the measurement for one pixel at the measurement position targets only the laser beam reflected from the same reflecting surface of the rotary polygon mirror. It is characterized by.

According to a third aspect of the present invention, in accordance with the first aspect of the present invention, the light emission of one pixel of the laser beam is emitted by the CCD camera by adjusting the image pickup timing of the CCD camera to a synchronization signal obtained from the laser optical system. , The amount of light emitted from one pixel of the laser beam is measured.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the light emission for one pixel of the laser beam reflected by each reflecting surface of the rotary polygon mirror is read by a CCD camera, so that each reflecting surface is read. Measuring the size of the laser beam and the difference between the measurement positions.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a laser beam measuring apparatus according to the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes a light source that emits a laser beam. The light source 1 uses a laser diode (LD). The laser beam emitted from the light source 1 is a divergent light beam. The divergent light beam passes through a cylindrical lens 2 as a line image forming element and converges only in the sub-scanning direction. Is formed as a long line image in the main scanning corresponding direction.

The rotary polygon mirror 3 is provided to deflect a laser beam (incident light beam) at a constant angular velocity.
The laser beam reflected by the deflecting / reflecting surface of the rotary polygon mirror 3 passes through an fθ lens (imaging lens) 4 and is deflected at a constant angular velocity by the rotary polygon mirror 3 so that the photoreceptor 5 is covered. Although the scanning surface is optically scanned at a constant speed, a CCD camera 6 that reads the emission of a laser beam for one pixel when outputting an image is disposed at a position where the surface to be scanned of the photoconductor 5 should be. . That is, a CCD camera 6 is arranged in place of the photosensitive member 5, and the CCD camera 6 uses the position where the surface to be scanned of the photosensitive member 5 should be located as a measurement position to read the emission of one pixel of the laser beam.

Reference numeral 7 denotes a synchronization detecting unit. The synchronization detection unit 7 is provided for adjusting the output start of the light source unit 1 and adjusting the write start timing when performing optical scanning at a constant speed with the rotation of the rotary polygon mirror 3. It is a thing. That is, the synchronization detecting section 7 is for obtaining a synchronization signal for adjusting the position at which optical writing is started. After the beam at the scanning start end of the beam scanning range due to the rotation of the rotary polygon mirror 3 passes through the fθ lens 4, it is reflected by the synchronization detection mirror 8, enters the synchronization detection unit 7, and outputs a synchronization detection signal. ing.

As shown in FIG. 3, the spot diameter of the laser beam on the surface to be scanned of the photosensitive member 5 is defined as a main scanning beam diameter 30 in the main scanning direction and a sub scanning beam diameter in the sub scanning direction. It is defined as diameter 31. The main scanning beam diameter 30 and the sub-scanning beam diameter 31 indicate the characteristics of the optical system. In particular, the diameter of the laser beam on the surface to be scanned in the actual optical scanning state, that is, the main scanning beam diameter 30 and the sub-scanning beam diameter 31 indicate dynamic characteristics.

Next, a method of measuring the dynamic characteristics of the laser beam will be described. First, a laser beam is emitted from the light source 1 so that the surface of the photoconductor 5 is actually scanned with light, and the rotating polygon mirror 3 is rotated at a constant rotation speed, so that the surface of the photoconductor 5 to be scanned is scanned. Optical scanning is performed at a certain position, that is, at a measurement position at a constant speed.

Further, control is performed such that the laser beam from the light source 1 emits light for one pixel when an image is output based on the synchronization signal obtained by the synchronization detection 7. The light emission of one pixel of the laser beam at this measurement position is read by the CCD camera 6 arranged at the position where the surface to be scanned of the photoconductor 5 should be as described above,
The spot shape of the laser beam is maintained. Here, “one pixel at the time of image output” is one pixel of pixels constituting one whole image. For example, if an entire A4-size image is 4000 pixels, One pixel corresponds to 1/4000 of the area of the A4 size.

When outputting an image of the laser beam read by the CCD camera 6, the light emission for one pixel is:
The data is captured by a processing unit (not shown) and binarized.
From this binarized signal, it is possible to calculate how many pixels of the CCD camera 6 the laser beam is incident on, and measure the diameter of the laser beam from the previously known width of one pixel of the CCD camera 6. be able to. in this way,
By performing the measurement while rotating the rotary polygon mirror 3, the dynamic characteristics of the laser beam can be measured.

When the dynamic characteristics of the laser beam are measured on each reflecting surface of the rotary polygon mirror 3, the laser beam is affected by the tilt of the rotary polygon mirror 3 as shown in FIG. As a result, the shape of the spot of the laser beam read by the CCD camera 6 is maintained as an enlarged beam spot diameter as shown in FIG. That is, the spot shape of the laser beam cannot be accurately measured.

Therefore, as shown at the bottom of FIG.
The dynamic characteristics of the laser beam are measured only for the laser beam reflected from the same reflecting surface of the rotary polygon mirror 3. In other words, control is performed so that only one laser beam reflected from the same reflection surface emits light for one pixel when an image is output at the measurement position. In this way, C is not affected by the tilting of the rotary polygon mirror 3 and C
The laser beam can be read by the CD camera 6, and the spot diameter of the laser beam can be accurately measured as shown in FIG.

As shown in FIG. 6, the light emission of a laser beam for one pixel is read by the CCD camera 6 by adjusting the image pickup timing of the CCD camera 6 to the synchronization signal obtained by the synchronization detection section 7. To
Then, the laser beam read by the CCD camera 6 is stored in a memory.

The CCD camera 6 has a characteristic of a dark output for reading a small amount of electric charges even when the laser beam is not read. Therefore, the output value of the dark output is also added to the output value of the laser beam stored in the memory. Therefore, as shown in FIG. 7, the output value of the dark output is subtracted from the sum of the output value of the laser beam and the output value of the dark output stored in the memory, so that the CCD camera 6 reads the output value. The amount of light emission of one pixel of the laser beam, that is, the intensity of one pixel of the laser beam can be measured.

In the present invention, the laser beam reflected by the rotating polygon mirror is read and measured by a CCD camera. Therefore, unlike the conventional measurement using a photodiode, the laser beam is applied to any pixel of the CCD camera. Can be detected. Therefore, as shown by one, two, three,..., N surfaces in FIG. 5, the dynamic characteristics of the laser beam can be measured for each reflecting surface of the rotary polygon mirror 3. In this case, the rotating polygon mirror 3
The laser beam is emitted for one pixel when an image is output in synchronization with each of the reflection surfaces, and the emission of one pixel of the laser beam read by the CCD camera 6 is stored in a memory, and is binarized by a processing unit. From the binarized signal, as shown in FIGS. 8A and 8B, the difference between the dynamic characteristics of the laser beam, the size of the laser beam, and the measurement position for each reflection surface of the rotary polygon mirror 3 is shown. In addition, the center deviation of the spot diameter of the laser beam can be read. In addition, it is also possible to read how much the rotary polygon mirror 3 is tilted and its influence.

[0027]

According to the first aspect of the present invention, in a laser beam measuring apparatus for measuring a laser beam characteristic by a laser optical system used in an electronic image forming process, a rotary polygon mirror disposed in the laser optical system The measurement position of the laser beam deflected by the laser beam is set as the position where the photoconductor should be, and a CCD camera is arranged at this measurement position to emit a laser beam for one pixel when outputting an image. In this case, the dynamic characteristics of the laser beam can be easily measured. Further, since there is no need to perform an adjustment operation of aligning the laser beam with the measurement position, the measurement time can be shortened as compared with the conventional measurement, and the dynamic characteristics of the laser beam can be measured with high accuracy. .

According to the second aspect of the present invention, in the first aspect of the present invention, the measurement for one pixel at the measurement position is performed only for the laser beam reflected from the same reflecting surface of the rotary polygon mirror. The dynamic characteristics of the laser beam can be accurately measured without being affected by the tilting of the rotary polygon mirror.

According to a third aspect of the present invention, in the first aspect of the present invention, an image pickup timing of the CCD camera is adjusted to a synchronization signal obtained from the laser optical system.
Since the light emission of one pixel of the laser beam is read by the CCD camera, the light emission amount of one pixel of the laser beam is
That is, the intensity of one pixel of the laser beam can be measured.

According to the fourth aspect of the invention, in the first aspect of the invention, the light emission for one pixel of the laser beam reflected for each reflection surface of the rotary polygon mirror is read by a CCD camera. It is possible to read the dynamic characteristics of the laser beam, the size of the laser beam, the difference in the measurement position, the deviation of the center of the spot diameter of the laser beam, and the like on each reflecting surface of the rotary polygon mirror. In addition, it is possible to read how much the rotary polygon mirror is tilted and its influence.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a laser beam measuring apparatus according to the present invention.

FIG. 2 is a side view schematically showing the influence of the tilting of a rotary polygon mirror applicable to the present invention.

FIG. 3 is a front view showing a laser beam diameter characteristic applicable to the present invention.

FIG. 4 is a front view showing a deviation of a diameter of a laser beam due to a surface tilt of a rotary polygon mirror applicable to the present invention.

FIG. 5 is a timing chart showing a state of beam emission when measuring using the apparatus of the present invention.

FIG. 6 is a simplified block diagram showing still another embodiment of the present invention.

FIG. 7 is a schematic diagram showing a state of signal processing according to still another embodiment of the present invention.

FIG. 8 is a front view showing characteristics of a laser beam in the embodiment.

FIG. 9 is a perspective view showing an example of a conventional laser beam measuring device.

[Explanation of symbols]

 Reference Signs List 1 light source 2 cylindrical lens 3 rotating polygon mirror 4 fθ lens 5 photoconductor 6 CCD camera

Claims (4)

[Claims] 1. A laser beam measuring apparatus for measuring a laser beam characteristic by a laser optical system used in an electronic image forming process, wherein a measuring position of a laser beam deflected by a rotary polygon mirror arranged in the laser optical system is determined. A CCD camera is arranged at this measurement position as a position where the photoreceptor should be located, a laser beam is emitted for one pixel when an image is output, and the emission of the laser beam is read by the CCD camera, thereby dynamically changing the laser beam. A laser beam measuring device for measuring characteristics. 2. The laser beam measuring apparatus according to claim 1, wherein the measurement for one pixel at the measurement position targets only the laser beam reflected from the same reflection surface of the rotary polygon mirror. 3. The light emission amount of one pixel of the laser beam is read by reading the light emission of one pixel of the laser beam by the CCD camera by adjusting the imaging timing of the CCD camera to the synchronization signal obtained from the laser optical system. The laser beam measuring apparatus according to claim 1, wherein the laser beam is measured. 4. A one-pixel light emission of a laser beam reflected by each reflecting surface of the rotary polygon mirror is read by a CCD camera, so that the size of the laser beam at each reflecting surface is determined.
2. The laser beam measuring apparatus according to claim 1, wherein the difference between the measurement positions is measured.