JPH10117042A - Color image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To match with higher accuracy the parallelism of the light-emitting direction of each laser beam and incident positions in the scanning direction and sub-scanning direction to a beam combining prism by providing a prism and a fine adjustment means which can rotate in fine steps and then using a beam detection sensor. SOLUTION: A beam L1, emitted from a semiconductor laser beam emitting body 1A, is incident on a beam-combining prism 3 via a collimater lens 2A. The beams L3, L3, emitted from semiconductor laser beam emitting bodies 1B, 1C, are also incident on the beam combining prism 3. The prisms 14A, 14B, 14C are respectively supported by supporting plates 15A, 15B, 15C, having a sub-scanning direction moving means and rotating means for the laser beam. With adjustment in the sub-scanning direction and adjustment for parallelism in the laser beam emitting direction with respect to rotation of the laser beam using the beam detection sensors 12A, 12B which are positioning sensors, an incident angle and incident position to the beam combining prism 3 can be adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a printer using a laser beam, and more particularly to a laser beam emitted from three sets of semiconductor laser light emitters which are superposed and scanned at the same point. The present invention relates to a color image forming apparatus for forming a latent image of a color image on a color photosensitive material such as a color photographic paper or a color film.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, in order to write and record on an image carrier with a laser beam, in an optical scanning optical system of an exposure unit, a semiconductor laser light emitting body for generating a laser beam, a collimator lens, and the like are used. In the case of generating two beams, for example, as an integral single unit, two single units in which the semiconductor laser light emitter and the collimator lens and the like are integrally formed are provided in the optical scanning optical system of the exposure unit, and are adjusted and fixed. doing. FIG. 1 shows an image forming apparatus that performs image exposure on a color photosensitive material.
From FIG. 1, the semiconductor laser light emitter 1C and the collimator lens 2
The lens excluding C corresponds to the adjustment and fixing portion, but as shown in FIG. 1, the second cylindrical lens 8 is a type of lens in which the R surface of the lens gradually changes, and thus the second cylindrical lens 8 is mainly used for two-beam optical scanning. When the incident position in the scanning direction changes, the sub-scanning image forming position of the two-beam optical scanning also changes. Therefore, a fine adjustment unit 14 composed of a prism is provided, and the fine adjustment unit 14 adjusts the beam of the semiconductor laser light emitter 1B.
By changing the angle of the beam of the semiconductor laser light emitter 1A, 2
Beam alignment is performed.

[0003]

As described above, in the adjustment of only a single unit in which a semiconductor laser light emitting element for generating a laser beam and a collimator lens are integrated, the deviation of the optical axis when the writing exposure unit is mounted is reduced. In particular, in the exposure unit for writing a plurality of beams, the relative deviation of the optical axis becomes a difference in the incident position with respect to the imaging lens system, and the beam position at the writing position deviates from the product standard.

Further, when an error occurs in the arrangement of a beam combining prism for combining a plurality of beams, the beam on the reflection side of the beam combining prism is likely to shift the optical axis. Cannot be improved. Further, even if the polygon mirror is formed in a small size and the surface length is effectively used, there arises a problem that the deviation of the optical axis causes a beam to be kicked at an angle of the polygon mirror.

Further, in a color image forming apparatus which forms a color image using three laser beams of three colors, generally, blue (B), green (G) and red (R), good image quality is obtained. In order to obtain a recorded image, if the centers of the three writing beams of B, G, and R do not completely coincide with each other, a problem such as a decrease in resolution or poor color turbidity or saturation occurs (the line is completely shifted by one line in the sub-scanning direction). There is almost no problem in the case).

Further, the deflection angle differs because the transmission optical system has a different refraction angle due to the difference in the wavelength of the scanning light. Therefore, even if the projection positions of the B, G, and R laser beams coincide at the scan start point of one scan line, the position gradually shifts as the scan progresses (the scan widths differ), and the closer to the end point of the scan line. Since the B, G, and R pixels gradually shift, there is a problem in that the same problems as described above, such as a decrease in resolution and a defect such as color turbidity and poor saturation occur.

Further, laser beams emitted from laser light emitters of different colors have a small beam diameter at a short wavelength and a large beam diameter at a long wavelength due to the difference in wavelength. If the beam diameter is different, as shown in FIG. 10, there is a problem that the density characteristics of the recorded image with respect to the output of the laser beam are different and the gradation of the formed image is reduced.

The present invention proposes, in particular, an invention for solving the above problems. That is, the optical axes of the three beams generated by the three sets of semiconductor laser light emitters are precisely adjusted, the beam combining prism and the first cylindrical lens are integrally fixed to the exposure unit, and the three sets of semiconductor laser light emitters are combined. Fine adjustment of main scanning and sub-scanning is easily performed, and density characteristics due to differences in beam diameters are made uniform.
It is an object of the present invention to provide a color image forming apparatus in which three laser beams of G and R are overlapped and scanned at the same position to obtain a color image having excellent resolution and gradation and excellent color reproducibility.

[0009]

According to the present invention, there is provided an optical scanning optical system having three sets of semiconductor laser light-emitting elements having different colors of light through a collimator lens, a polygon mirror, an fθ lens, and the like. In a color image forming apparatus that optically scans a photosensitive material, the color image forming apparatus includes an alignment sensor disposed near an end of the photosensitive material, and means for changing an incident position of the semiconductor laser light emitter to a beam combining prism. Is provided. (Invention of Claim 1) According to the present invention, the beam position can be adjusted by such a configuration. However, a means for changing a γ correction value for each color is provided to make the γ characteristics of each color uniform, It is a preferred embodiment that a prism is arranged between the body and the beam combining prism to change the incident position, and that the light scanning of each color is performed by being overlapped and scanned at the same position by the adjustment.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a color image forming apparatus according to the present invention.

FIG. 1 shows a three-beam light scanning optical system unit 1.
FIG. 1 is an overall configuration diagram showing one embodiment.

In FIG. 1, reference numerals 1A, 1B, and 1C denote semiconductor laser emitters, 2A, 2B, and 2C denote collimator lenses (beam shaping optical systems), and 14A, 14B, and 14C denote incident positions on a beam combining prism 3. Prism, one of the means for performing the above, 3 is a beam combining prism, 5 is a first cylindrical lens, 6 is a polygon mirror as a deflector, 7 is an fθ lens, 8 is a second cylindrical lens,
Reference numeral 10 denotes a photosensitive material such as a color film or color photosensitive paper;
Reference numeral 1 denotes a backup member provided behind the exposure position of the photosensitive material 10, and the photosensitive material 10 includes guide rollers 15A and 15B.
And is conveyed to slide on the backup member 11 to position the exposure unit. Reference numerals 12A and 12B denote beam detection sensors, which are, for example, positioning sensors composed of area-type CCDs. Reference numeral 13 denotes a drive motor for the polygon mirror 6. Beam L ₁ emitted from the semiconductor laser emitters 1A is collimated by the collimator lens 2A, then the semi-transparent reflecting surface 3a of the two surfaces, enters the beam combining prism 3 with 3b. Similarly, the beams L ₂ and L ₃ emitted from the semiconductor laser light emitters 1B and 1C arranged orthogonally to the semiconductor laser light emitter 1A are turned into parallel light by the collimator lenses 2B and 2C.
After that, the light enters the beam combining prism 3. The laser beams emitted from the semiconductor laser light emitters 1B and 1C are applied to the semiconductor laser light emitter 1B in the sub-scanning direction.
The prisms 14A, 14B, and 14C are arranged on the mounts 15A, 15B, and 15C each having a vertical (sub-scanning direction) moving unit and a rotating unit for the laser beam. Supported, the sub-scanning direction is adjusted, and the parallelism of the emission direction of the laser beam is adjusted by rotation with respect to the laser beam, so that the angle of incidence and the position of incidence on the beam combining prism 3 are further finely adjusted by a beam compression prism described later. You.
The three laser beams enter the polygon mirror 6 via the first cylindrical lens 5 of the first imaging optical system. This reflected light is transmitted to the fθ lens 7 and the second cylindrical lens 8
And is scanned simultaneously on the surface of the photosensitive material 10 with a predetermined spot diameter and the same center position.

FIG. 2 is a plan view showing the three-beam light scanning optical system unit 1 excluding a semiconductor laser light emitter 1C, a collimator lens 2C, a prism 14C, etc., provided in the image forming apparatus 113. The semiconductor laser light emitters 1A and 1B, the collimator lens 2
A, casing 201A having a 2B, provided as illustrated 201B, beams L _1, L ₂ are in the same plane 90
Fire at an angle of °. Further, a casing (20) (not shown) provided with the semiconductor laser emitter 1C and the collimator lens 2C.
1C) and the prism 14C is positioned on the base so that firing direction of the beam L ₃ to the firing by an attachment member (not shown) as a substitute of the base 111 is in the direction shown in FIG. 6 (b), each beam L ₁ , L ₂ and L ₃ are fired at an angle of 90 ° from three directions. Thereafter, the semiconductor laser light emitters 1A and 1B
And casings 201A, 201B,
Since (201C) has the same shape, only the one related to the semiconductor laser light emitter 1A will be described. The casing 201A is mounted on an angle changing member 125A, and the angle changing member 125A is mounted on a translation member 124A that translates in the main scanning direction on the base 111. Further, the beam combining prism 3 and the first cylindrical lens 5 are fixed by a support member 123, and the beams L ₁ , L ₂ , and L ₃ are combined by the beam combining prism 3 so as to enter the polygon mirror 6. Support member 1
23 is fixed on the base 111. As shown in FIG. 2, the light scanning optical system unit 1 includes a support member 114 provided in the image forming apparatus 113, and both ends of the base 111 are placed on the support member 114, and guide members provided at both ends of the base 111. 11
6, 117, the light scanning optical system unit 1 is guided in a direction orthogonal to the beam scanning direction, and is mounted at a predetermined position. Further, at the front position where the light scanning optical system unit 1 is guided, the image forming apparatus 113 is provided with a locking stay 118 serving as a reference position in the same direction as the light beam scanning direction. Locking hook member 119
120 are provided. Then, it is fitted into the grooves 121 and 122 formed in the locking stay 118. The groove 12
Reference numerals 1 and 122 denote one of the grooves 121 by the locking claw member 119.
And the other groove portion 122 has a locking claw member 120.
The width is larger than the width of the groove to facilitate the locking operation and accurately position. Further, the positioning pins 128 and 12 are positioned so that the rear end of the base 111 is positioned at a predetermined position.
8A is fixed, and positioning members 129, 129A fitted to the positioning pins 128, 128A are provided at the rear end of the base 111.

Both ends of the backup member 11 are fitted into elongated holes of a support member 91 fixed to the image forming apparatus 113, and are supported by adjusting screws 92 and springs 93 so as to be finely adjustable.

FIGS. 3 and 4 show the structure of the parallel moving member 124A and the angle changing member 125A provided on the base 111. FIG. First, as shown in FIG. 3, first guide grooves 124b formed in a parallel moving member 124A that moves in parallel in the main scanning direction.
124c is connected to the guide member 1 provided on the base 111.
32A and 133 so that the translation member 124A is fixed to the base 111 with fixing screws 134 and 135. Then, the second eccentric cam 130 provided on the core shaft 131 which rotates about the base 111 is fitted.
A guide groove 124a is formed. Further, an angle changing member 125A is mounted on the parallel moving member 124A, and one end of the angle changing member 125A is rotatably pivoted on a shaft 138. The other end of the angle changing member 125A is formed with a third guide groove 125a for fitting an eccentric cam 136 provided on a core shaft 137 that rotates about the parallel moving member 124A. Member 125A
There is provided a fixing screw 139 for fixing to the translation member 124A at a position where the angle is changed. Furthermore the semiconductor laser emitters. 1A on the angle changing member 125A, fixes along a casing 201A in which a collimator lens 2A the beam L _1. 219 and 220 are screw rods for adjusting the prism 200 (see FIG. 8) provided in the casing 201A.

With the above configuration, when the parallel moving member 124A is to be moved in parallel, the fixing screws 134 and 135 are first released, and the core shaft 131 is rotated about the base 111. Then, by rotating the eccentric cam 130, the parallel moving member 12 is moved through the second guide groove 124a.
4A is translated in the left and right directions indicated by the arrows by the first guide grooves 124b and 124c and the guide members 132 and 133 provided on the base 111. Casing 201A provided on the angle changing member 125A by the movement can be parallel moved adjustments to the beam L _1. That beam L ₁ of a semiconductor laser light emitters. 1A can be adjusted in the main scanning direction. After the adjustment is completed, the parallel moving member 124A is fixed to the base 111 with fixing screws 134 and 135. Next, when changing the angle of the angle changing member 125A, first, the fixing of the fixing screw 139 is released, and the parallel moving member 124 is released.
The eccentric cam 136 provided on the core shaft 137 is rotated about A, and the third guide groove 125 is rotated by the rotation of the eccentric cam 136.
The angle changing member 125A is rotated and adjusted about the shaft 138 in the direction indicated by the arrow through a. Casing 201A provided on the angle changing member 125A by the pivoting adjustment angularly adjusted accordingly emission direction of the beam L ₁ is adjusted.

FIG. 4 shows the core shaft 131 shown in FIG.
7, a worm gear G ₁ is provided on the core shaft 131.
And this meshing with the worm G ₂ provided, each provided with a worm gear G ₃ this meshing with the worm G ₄ are the core shaft 137,
The rotated warm G ₂ or warm G _4, worm gear G
₁ or eccentric by rotation of the worm gear G ₃ cams 130, one
Fine adjustment is possible via 36.

[0018] Figure 5 shows a beam position detecting means for adjusting the beam L _1. First remove the optical member between the light-sensitive material 10 from the polygon mirror 6 as shown in FIG, CCD area type to start and stop position of the scanning at the position a and the main scanning direction as to detect the laser beam L ₁ reflected from the polygon mirror 6 directly
From consisting beam position detecting member S arranged (beam detection sensor 12A in FIG. 1, corresponding to 12B), placing the support S ₁ having a beam position detecting member S to the outside of the measurement position. Emits a beam L ₁ from the semiconductor laser light emitters 1A in this state, the beam position is adjusted to be within a predetermined specification standard using the adjustment method. This adjustment is also performed on the beam L ₂ emitted from the semiconductor laser emitter 1B and the beam L ₃ emitted from the semiconductor laser emitter 1C at the same time, and the detection positions of the beams L ₂ and L ₃ by the beam position detecting member S are changed to the beams. it is possible to beam adjustment in the main scanning and sub-scanning direction by adjusting to match the detected position of the L _1. Reference numeral 112 denotes a cover, and a hole 112a for measurement is formed in a part of the cover 112. 113A is an outer plate of the image forming apparatus 113 in which holes are formed.

FIG. 6A shows a support member 123 to which the beam combining prism 3 shown in FIG. 2 and the first cylindrical lens 5 are fixed. The beam combining prism 3 and the first cylindrical lens 5 are integrally fixed to the support member 123. As a fixing method, an adhesive may be used, or a fixing unit may be fitted and fixed to a holding unit formed integrally with the support member 123 as illustrated. And the support member 12
3 is fixed to the base 111 with fixing screws 126 and 127.
As shown in FIG. 6 (b), the beam combining prism 3 can be composed of the same parts if the slope portion formed by combining and joining four triangular prisms formed by dividing a cube by diagonal lines is a translucent mirror. And cost can be reduced.

The angle at which the translucent reflecting surfaces 3a, 3b of the beam combining prism 3 are installed is not limited to the direction shown in FIG. 6A, but may be any direction convenient for installing the semiconductor laser emitters 1A, 1B, 1C. Can be. For example, as shown in FIG. 6C, semi-transparent reflecting surfaces 3a and 3b are provided, and semiconductor laser light emitters 1A, 1B and 1C and collimator lenses 2A, 2B and 2 are provided.
C may be installed on one plane. Since the laser beam L ₂ is in the arrangement shown in FIG. 6 and most light loss is small only it is reflected by the semi-transparent reflecting surface 3a, preferably in the 1B most output small semiconductor laser emitters.

FIG. 7 shows a method for adjusting the beam shown in FIG. 3 and means for finely adjusting the main scanning and sub-scanning directions by the light beam compression prism 200 shown in FIG. First, FIG.
3, the first guide grooves 124b, 1b formed in the translation member 124A that translates in the main scanning direction, as in FIG.
24c is connected to the guide member 13 provided on the base 111.
2 and 133 so that the translation member 124A is fixed to the base 111 with fixing screws 134 and 135. And around the base 111, the second guide groove 124a for fitting the eccentric cam 130 provided on the core shaft 131 to rotate with the gear G ₇ in reduction gear G ₆ is formed. The angle changing member 12 is provided on the translation member 124A.
5A is mounted, and one end of the angle changing member 125A is
At 38, it is pivotally mounted. The other end of the angle changing member 125A is connected to the parallel moving member 124A.
Mainly, core shaft 137 rotates with the gear G ₉ in the reduction gear G ₈
Guide groove 125a for fitting the eccentric cam 136 provided in the
And a fixing screw 139 for fixing the angle changing member 125A to the translation member 124A at a position where the angle is changed is provided. Further, the angle changing member 1
A semiconductor laser emitting body 1A is on 25A, is fixed along the casing 201A in which a collimator lens 2A the beam L _1. 219 and 220 are the casing 201
A screw rod for adjusting the light beam compression prism 200 (see FIG. 8) provided in A.

With the above arrangement, when the parallel moving member 124A is to be moved in parallel, the fixing screws 134 and 135 are first released, and the gear G ₇ and the reduction gear the core shaft 131 rotates in the G _6, by rotating the eccentric cam 130 second guiding said the translation member 124A via the groove 124a first guide groove 124
b, 124c and the guide members 132, 133 provided on the base 111 are moved in parallel in the left and right directions indicated by arrows. Casing 201A provided on the angle changing member 125A by the movement can be parallel moved adjustments to the beam L _1. That is, the beam L of the semiconductor laser emitter 1A
₁ can be adjusted in the main scanning direction. After the adjustment is completed, the parallel moving member 124A is fixed to the base 111 with fixing screws 134 and 135. Next, the angle changing member 125A
When the angle change, first to release the fixing screws 139, rotates an eccentric cam 136 provided on the core shaft 137 and the gear G ₉ in the reduction gear G ₈ around the translation member 124A, eccentric The rotation of the cam 136 causes the third guide groove 125
The angle changing member 125A is rotated and adjusted about the shaft 138 in the direction indicated by the arrow through a. Casing 201A provided on the angle changing member 125A by the pivoting adjustment is angularly adjusted relative to the beam L _1. That is, the semiconductor laser emitter 1
Angle of beam L ₁ of A is adjusted.

FIG. 8 shows a casing 201A containing a semiconductor laser light emitter 1A, a collimator lens 2A, and a beam compression prism 200. The inside of the casing 201A beam holes 203 along the beam L ₁ is formed, the collimator lens 2A among which the fixed cylinder 202
Is installed in the casing 201, the beam L ₁
A long hole 204 is formed along. Inside the long hole 204, a female screw 205 for screwing the inner cylinder 202 is formed. On the other hand, on the outer surface of the inner cylinder 202, the female screw 20 is provided.
5 is formed with a male screw 206 for screwing into the inner cylinder 20.
2 is screwed and fixed in the elongated hole 204 as shown.
A tapered surface 207 (approximately 30 ° with respect to the horizontal) is formed on the surface of the elongated hole 204 in a direction in which the beam L ₁ is spread from the female screw 205. The tapered surface is formed on the outer surface of the inner cylinder 202. 207 with the same taper angle as 20
8 are formed. And the tapered surface 208 on the formed portion, said plurality of slit 209 through until passing hole 203 of the beam L ₁ is formed. The formation angle θ of the slit 209 is formed at about 60 °.
Numeral 210 is a rotary mounting hole formed at a plurality of locations provided between the slits 209, and the rotary mounting hole 211 formed in the casing 201A is aligned with the slot 211 at the final mounting position. A mounting hole 210 is formed. 21
Reference numeral 5 denotes a hole formed in the casing 201A for pouring the adhesive 214.

The beam compression prism 200 is mounted on the beam compression prism mounting member 216 at a predetermined angle. Further, the beam-compressing prism mounting member 216 is fixed to a cylindrical frame 217, and the cylindrical frame 217 is attached to the elongated hole 204 in the casing 201A.
Beam compression prism mounting part 218 formed along
Hand, is mounted rotatably in a direction crossing the light beam L _1. A part of the cylindrical frame 217 is screwed to the casing 201 to form a symmetrical screw rod 2.
19 and 220, the tip of the screw rod 219 is brought into direct contact with a step 221 formed on the cylindrical frame 217, and one screw rod 220 is formed on the cylindrical frame 217 via a spring member 222. And the side plate 2
24, it is fixed to the casing 201A with a screw rod 226.

The beam compression prism 200 configured as described above first loosens the fixing screw rod 226 and adjusts the rotation of the screw rod 219. At this time, the cylindrical frame 21
7 is formed with a part of the spring member 222.
The light beam compression prism 200 is always in contact with the tip of the screw rod 219, and the rotation of the screw rod 219 causes the light beam compression prism 200 to pass through the cylindrical frame 217 and the beam compression prism mounting member 216. feed direction while reducing the L ₁ to a predetermined width is pivoted adjusted. After the adjustment is completed, the cylindrical frame 217 is fixed to the casing 201 by the fixing screw rod 226. At this time, the fixing screw rod 226 is used.
Even in the clockwise rotation operation, the tip of the screw rod 219 is always blocked by the step 221 formed in the cylindrical frame 217 and does not move from the adjustment position.

[0026] The beam like beam compression prism and compression prism 200 is also provided in the casing for emitting a laser beam L ₃ is not the casing 201A and illustrated, the prism 14A, 14B, 14C
In parallel with the beam L ₁ emitted by the semiconductor laser emitter 1A, the parallelism of the emission directions of the beams L ₂ and L ₃ emitted by the semiconductor laser emitters 1B and 1C, the main scanning direction and the sub-scanning. Fine adjustment of the direction can be performed accurately.

In the color image forming apparatus of this embodiment,
As shown in FIG. 9, the B, G, and R density signals sent from the image signal generating means 200 such as a scanner or a personal computer are subjected to masking and other processing in the image signal processing circuit 300 and then to a γ correction circuit. 30
In step 1, an image signal that has been γ-corrected in accordance with a table stored in a ROM 302, which will be described later, is input to the exposure control unit 400 in order to correct a difference in gradation due to the difference in beam diameter. The exposure control unit 400 includes the beam detection sensor 12A
And γ-corrected image signals B, G, and R are transmitted to the pulse width modulation circuits 500B, 500G, and 500R. The rate of this image signal is adjusted by a transfer clock generated by clock generators 501B, G, and R in pulse width modulation circuits 500B, 500G, and 500R. Sent out. Thus, an exposure process of performing gradation recording by changing the light emission time of the semiconductor laser light emitters 1A, 1B, and 1C (hereinafter simply referred to as laser light emitter) by pulse width modulation (PWM) is employed. .

Here, the laser drivers 502B, G, R
Are connected to the laser emitters 1A, 1B, 1C, but are not limited to this. The adjustment of the emission direction of the laser beam and the adjustment of a transfer clock described later are preferably performed with reference to green (G) because green (G) is important to the naked eye.

The ROM 302 stores a PWM signal on the photosensitive material 10 based on a gradation test patch signal in advance after the apparatus is assembled.
A test patch latent image for gradation correction, which is exposed stepwise from 0 to PWM 255 (maximum exposure amount), is developed, and the developed test patch image is converted into an image density sensor by an image density sensor. Then, the gradation characteristics of B, G, and R are detected, and the gradation characteristics of the recording signal are determined based on the gradation characteristics so that the gradation characteristics of the original image and the print image match or the image characteristics are emphasized. Is written in the table for correcting. FIG. 10 shows the relationship between the laser output and the recording density when the beam diameter is changed. ROM
The B, G, and R image signals are γ-corrected in the γ-correction circuit 302 according to the respective characteristics according to the table of 302, and are controlled by the exposure control unit 400 via the pulse width modulation circuits 502 B, G, and R, and the laser driver. 502
B, G, and R are sent.

Further, the pulse width modulation circuits 500B, 500
The clock frequencies of the G, 500R clock generators 501B, G, R are set in advance by causing the semiconductor laser emitters 1A, 1B, 1C to emit light prior to image formation, rotating the polygon mirror 6, and rotating the fθ lens and the cylinder. Scanning is performed by a laser beam that has passed through a lithographic lens or the like, and the beams before and after the end of scanning are detected by the beam detection sensors 12A and 12A.
2B, and the time (scanning time) required for scanning between the center of the beam detection sensor 12A and the center of the beam detection sensor 12B is measured. Thereafter, for example, the ratio of the scanning time of another beam is calculated based on the scanning time of the green (G) beam. The frequency of the transfer clocks of the B and R pulse width modulation circuits 500B, G and R is changed to the G pulse width modulation circuit 500G.
Is set to a frequency inversely proportional to the ratio. As a result, the intervals between the other blue (B) and red (R) recording pixels are the same as the intervals between the green (G) recording pixels, and the light scanning by the beams L ₁ , L ₂ , and L ₃ is performed at the same position for each pixel. Are superimposed and scanned.

During actual image printing, B, G, and R image signals are transmitted to the drive circuit 400 by index signals output by laser beams incident on predetermined positions of the beam detection sensor 12A for each line. The scan line is started and synchronization is performed.

[0032]

As described above, according to the first aspect of the color image forming apparatus provided with the three-beam optical scanning device of the present invention, each of the lasers is provided by providing the prism and the fine adjustment means for finely rotating. By using the beam detection sensor, the parallelism of the beam emission direction and the incident positions of the main scanning direction and the sub-scanning direction on the beam combining prism can be separately and easily adjusted with high accuracy.

In addition, according to the second aspect, the difference in gradation characteristics due to the difference in beam diameter for each color can be corrected by γ correction to obtain an image with excellent gradation characteristics.
According to the third aspect, the parallelism of the emission direction of each laser beam and the incident positions of the main scanning direction and the sub-scanning direction on the beam combining prism can be easily adjusted even after assembling the apparatus. According to this method, the frequency of the transfer clock of the pulse width modulation circuit for the image signal of each color is corrected for the difference in scanning speed due to the difference in the deflection angle of the laser beam by the blue (B), green (G), and red (R) deflection means. With the setting, the three laser beams can be overlapped and scanned at the same position for each pixel.

Therefore, a remarkable effect that a color image forming apparatus which obtains a color image having excellent resolution and gradation and excellent color reproducibility can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the overall configuration of a three-beam optical scanning device according to the present invention.

FIG. 2 is a plan view showing the overall configuration of a three-beam optical scanning device according to the present invention.

FIG. 3 is a plan view showing an adjusting device of the light beam generator according to the present invention.

FIG. 4 is a perspective view showing an adjusting device of the light beam generator according to the present invention.

FIG. 5 is a configuration diagram illustrating a light beam adjustment detection device according to the present invention.

FIG. 6 is a perspective view showing a beam combining prism according to the present invention and a cylindrical lens.

FIG. 7 is a plan view showing an adjustment device of the beam generation device according to the present invention.

FIG. 8 is a longitudinal sectional view of a casing incorporating the semiconductor laser light-emitting body of the present invention and an optical system.

FIG. 9 is a block diagram illustrating a processing circuit that processes an image signal.

FIG. 10 is a diagram illustrating an example of a difference between a laser output and a recording density depending on a beam diameter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical scanning optical system unit 1A, 1B, 1C Semiconductor laser emitter 2A, 2B, 2C Collimator lens 3 Beam combining prism 5 First cylindrical lens 6 Polygon mirror (deflector) 7 fθ lens 8 Second cylindrical lens 10 Photosensitive material 12A , 12B Beam detection sensor (positioning sensor) 14A, 14B, 14C Prism 111 Base 113 Image forming apparatus 118 Locking stay 123 Supporting member 124A Parallel moving member 125A Angle changing member 128, 128A Positioning pin 201A, 201B Casing 202 Inner cylinder 207, 208 Tapered surface 216 Beam compression prism mounting member 217 Cylindrical frame 219, 220 Screw rod 300 Image signal processing circuit 301 γ correction circuit 302 ROM 500B, G, R Pulse width modulation circuit 01B, G, R clock generator

Claims (4)

[Claims] 1. A color image forming apparatus that optically scans a photosensitive material through a collimator lens, a polygon mirror, an fθ lens, and the like by an optical scanning optical system unit having three sets of semiconductor laser light emitters having different emission colors. A color image forming apparatus comprising: a positioning sensor disposed near an end of the light emitting device; and means for changing an incident position from the semiconductor laser light emitter to a beam combining prism. 2. The color image forming apparatus according to claim 1, further comprising means for changing a γ correction value for each color. 3. The color image forming apparatus according to claim 1, wherein a prism is arranged between the semiconductor laser light emitter and the beam combining prism to change an incident position. 4. The optical scanning device according to claim 1, wherein the optical scanning of each color is performed by superimposing and scanning at the same position.
Item 10. A color image forming apparatus according to item 9.