JPH0954263A - Laser scanning optics - Google Patents

Abstract

(57) [Abstract] [Purpose] To control image unevenness and maintain high-quality images. [Structure] Three laser lights Lc of the laser emitting section 22c
1 to Lc3 are reflected by the reflection mirror 23c and the polygon mirror 25, pass through the fθ lens 26c, and then the photoconductor drum 3c.
The surface is scanned in the main scanning direction A. Of the three laser beams Lc1 to Lc3, the central laser beam Lc2 is assembled so as to be aligned with the center of the collimating lens barrel portion 31c, and by driving the stepping actuator 33c, a horizontal line Q detected by the photosensor 39 is generated. The angle θ formed by the line connecting the light emitting points of the three laser beams Lc1 to Lc3 can be changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser scanning optical device used in an image forming apparatus such as a laser beam printer and an electrophotographic copying machine.

[0002]

2. Description of the Related Art Conventionally, a laser scanning optical device of this kind has been used in, for example, a laser beam printer, a digital electrophotographic copying machine, a facsimile and the like. This laser scanning optical device generally emits a laser beam from a laser chip according to image information to be printed, and scans the photosensitive member in a certain direction by a beam scanning means such as a rotating polygon mirror such as a polygon mirror or a galvano mirror. , Main scanning is performed.

Generally, a photoconductor has a photoconductive photoconductive layer on a conductive substrate such as a cylindrical metal, and main scanning is performed in parallel with the axial direction of the photoconductor. At this time, the photoconductor is rotating in the circumferential direction, and the rotation causes scanning in the circumferential direction as well to perform sub-scanning. An image is formed on the photoconductor as an electrostatic latent image by these main scanning and sub scanning.
This electrostatic latent image is developed by developing means and transferred to a transfer material such as transfer paper by a transfer means to obtain an image.

The laser chip used in the laser scanning optical device has conventionally used a single-beam laser chip that emits one laser beam, but with the recent high performance and high functionality of the image forming apparatus, The demand for higher speed is increasing.

However, in order to increase the speed of the image forming apparatus using the single beam laser chip, both the main scanning speed and the sub-scanning speed must be increased. Of these, the main scanning speed depends on the scanning speed of the beam scanning means. For example, when a polygon mirror is used, in order to double the speed, the polygon mirror must be rotated at a double speed.

However, the scanning speed of the beam scanning means is limited, and if the polygon mirror is rotated at too high a speed, problems such as seizure of the bearing, deformation of the mirror surface, and breakage occur. Therefore, there is a need for a laser scanning optical device capable of coping with high speed without increasing the main scanning speed.

In recent years, a multi-beam laser chip, which emits a plurality of laser beams from one laser chip, has been proposed as a means for coping with the increase in speed, instead of the single-beam laser chip. In this multi-beam laser chip, since a plurality of beams are scanned by one main scan of the photoconductor, the sub-scanning speed of the photoconductor is increased without changing the main scanning speed of the beam scanning means. can do.

Therefore, for example, in a laser scanning optical device using a polygon mirror, by using a multi-beam laser chip, it is possible to cope with speeding up without increasing the rotation speed of the polygon mirror. As described above, by using the laser scanning optical device using the multi-beam laser chip, it has become possible to cope with high speed.

[0009]

By the way, in recent years, image forming apparatuses have been required to have higher speed and higher image quality, and the pixel density has been increased to 400 to 600 dpi. For example, when the pixel density is 400 dpi, the pixel interval is 63.5 μm on the surface of the photoconductor. If this pixel interval is to be realized by a multi-beam laser chip, the image magnification on the laser chip emission surface and the photosensitive member surface is generally about several times, so the emission point interval on the multi-beam laser chip should be about 10 to 30 μm. There must be. However, in reality, when the distance between the light emitting points becomes smaller than several hundred μm,
Crosstalk occurs between the light emitting points, and the laser emission of each beam cannot be controlled independently.

Therefore, the interval between the light emitting points of the multi-beam laser chip is limited to about several hundred μm. For example, if the interval between the light emitting points is 200 μm, the beam spot interval on the surface of the photosensitive member is about 400 to 800 μm, and the required pixel 63. of the pixel spacing when the density is 400 dpi, for example.
It becomes significantly larger than 5 μm.

FIG. 8 is an explanatory diagram of laser light spot intervals and sub-scanning intervals on the surface of the photoconductor when a multi-beam laser chip that emits three laser beams is used. Shows. Photoconductor surface S
A line H connecting the laser light spots S1, S2, S3 lined up above
Is inclined by an angle θ with respect to the main scanning direction A in which the laser light moves, and the sub-scanning is performed in the sub-scanning direction C as the photoconductor moves in the photoconductor moving direction B.

Laser beam spot spacing on the surface S of the photoconductor
X1 and the sub-scanning interval X2 satisfy the relationship of X2 = X1 · sin θ, and the sub-scanning interval X2 matches the pixel interval. For example, X1 = 600 μm, pixel density 400 dpi, that is, X2 =
When 63.5 μm, θ = sin ⁻¹ (X2 / X1) = 6.075
Therefore, the accuracy of θ is very sensitively reflected in the image quality.

FIG. 9 is an explanatory view when the angle formed by the line H connecting the laser light spots S1 to S3 and the main scanning direction A is an ideal angle θ, and the line written in one main scanning is D1 and
When D2, D3, ..., Since θ is an ideal angle, the sub-scanning interval in the same main scanning D1, D2, D3 is X2, which corresponds to the pixel interval. The sub-scanning speed at this time is set so that the interval between the final line D1L of the main scanning D1 and the first line D2S of the main scanning D2 becomes the sub-scanning interval X2, and the sub-scanning interval is X2 over the entire image. It becomes constant at.

FIG. 10 shows an explanatory view when an angle θ ′ formed by the line H connecting the laser light spots S1 to S3 and the main scanning direction A is smaller than the ideal angle θ, and the same main scanning D1. The sub-scanning interval X2 'within D3 is X2' = X1 · sin θ '<X1 · sin θ = X2, which is smaller than the sub-scanning interval X2. Therefore, the interval between the final line D1L of the main scan D1 and the leading line D2S of the main scan D2 is larger than the sub-scan interval X2.

As described above, when the angle formed by the line H connecting the laser light spots S1 to S3 and the main scanning direction A becomes small,
There is a problem that unevenness occurs in the sub-scanning intervals at intervals of each main scanning, which appears in the image as pitch unevenness, and unevenness occurs particularly in a uniform halftone image.

FIG. 11 shows an explanatory view when an angle θ ″ formed by the line H connecting the laser beam spots S1 to S3 and the main scanning direction A is larger than the ideal angle θ, and is the same main scanning D1. The sub-scanning interval X2 ″ within D3 is X2 ″ = X1 · sin θ ″> X1 · sin θ = X2, which is larger than the sub-scanning interval X2. Therefore, the interval between the final line D1L of the main scan D1 and the leading line D2S of the main scan D2 is smaller than the sub-scan interval X2.

As described above, even if the angle formed by the line H connecting the laser light spots S1 to S3 and the main scanning direction A becomes large,
Sparseness and denseness occur in the sub-scanning intervals at intervals of each main scanning.
If the sub-scanning interval deviates from the ideal position by several tens of μm, it will appear as unevenness to the human eye, and therefore the accuracy of the angle θ is required to be extremely strict. However, in reality, the inclination of the laser chip is not determined only by the assembly accuracy of the parts, and even if the accuracy is adjusted during assembly,
It is difficult to keep the laser holding member constant over time due to thermal expansion or mechanical deformation of the laser holding member due to temperature change.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a laser scanning optical device capable of controlling image unevenness due to the density of sub-scanning intervals caused by thermal expansion or mechanical deformation, and maintaining high-quality image quality.

[0019]

A laser scanning optical device according to a first invention for achieving the above object is a multi-beam laser chip for emitting a plurality of laser beams aligned in a straight line from one chip. A laser having a photoconductor for writing an image on its surface by laser light emitted corresponding to an image signal, and a beam scanning means for scanning the laser light from the multi-beam laser chip along the photoconductor surface. In the scanning optical device, the angle formed by the direction in which the laser light scans the surface of the photoconductor and the line connecting the laser light spots aligned on the surface of the photoconductor is variable.

A laser scanning optical device according to a second aspect of the present invention includes a plurality of multi-beam laser chips for emitting a plurality of laser beams aligned from one chip,
A laser scanning optical device having a plurality of photoconductors respectively arranged corresponding to these multi-beam laser chips, and a beam scanning means for scanning laser light from the multi-beam laser chips along a predetermined photoconductor surface. In the above, the direction in which the laser beam scans the surface of each photoconductor and the angle formed by the line connecting the laser beam spots aligned on the surface of each photoconductor are variable.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a configuration diagram when applied to an electrophotographic color image forming apparatus, in which a first, a second, a third, and a third corresponding to magenta, cyan, yellow, and black are linearly provided in a housing 1. Four image forming units 2m, 2c, 2y, and 2b of 4 are sequentially arranged.

The image forming sections 2m, 2c, 2y and 2b have substantially the same structure, and the periphery of the photosensitive drums 3m, 3c, 3y and 3b which are image bearing members which are rotationally driven in the direction of the arrow M. Are the primary chargers 4m, 4 which uniformly charge them.
c, 4y, 4b, developing devices 5m, 5c, 5y, 5b for developing the electrostatic latent image formed on the photosensitive drum, and a transfer charger for transferring the developed toner image which is a visible image onto the recording material P. 6m, 6c, 6y, 6b and cleaners 7m, 7c, 7y, 7b for removing the toner remaining on the photosensitive drum are sequentially arranged in the rotation direction of arrow M. The developing units 5m, 5c, 5y, and 5b contain magenta, cyan, yellow, and black toners, respectively.

On the other hand, two paper feed cassettes 8a and 8b for accommodating recording materials P of different sizes are provided as paper feed units, and the recording material P of these paper feed cassettes 8a and 8b is 1
Paper is fed onto an endless recording material carrying belt 12 which is carried and conveyed at a predetermined timing via pickup rollers 9a and 9b for feeding sheets one by one, conveyance rollers 10a and 10b, and a pair of registration rollers 11. It is like this.

The recording material supporting belt 12 is stretched between a belt driving roller 13 and a plurality of supporting rollers 14, and the belt driving roller 13 is rotationally driven in the direction of arrow N by a driving motor (not shown). The recording material P fed through the paper feeding unit is carried by the image forming unit 2
It is configured to be sequentially conveyed to the transfer areas of m, 2c, 2y, and 2b. Further, a heat roller 16 is arranged in the fixing device 15 in the conveyance direction of the belt drive roller 13, and the recording material P is discharged to the paper discharge tray 17 via the heat roller 16.

Further, the image forming sections 2m, 2c, 2y and 2b.
The first mirrors 18m and 18m
c, 18y, 18b, second mirrors 19m, 19c, 1
9y, 19b, the third mirror 20m, 20c, 20y,
20b are arranged in sequence, and further these third mirrors 2
In the incident direction of 0 m, 20 c, 20 y, and 20 b, an image exposure apparatus as shown in FIG. 2 arranged in the optical housing 21 is arranged.

FIG. 2 is an explanatory view of the image exposure apparatus, showing laser emitting portions 22m, 22c, 22y and 22b such as semiconductor lasers for exposing magenta, cyan, yellow and black provided around the optical housing 21. Laser light Lm, L
Among the emitting directions of c, Ly, and Lb, the laser emitting section 22c,
Reflection mirrors 23c and 23y are provided in the emission direction of 22y. A polygon mirror 25 provided on the motor housing 24 is arranged in the reflecting directions of the reflecting mirrors 23c and 23y and the emitting directions of the laser emitting units 22m and 22b.
Are arranged.

Further, in the reflection directions of the laser beams Lm, Lc, Ly, and Lb on the polygon mirror 25, the fθ lens 2 is used.
6m, 26c, 26y, 26b are arranged, and further the third mirrors 20m, 20c, 20y, 20b, the second mirrors 19m, 19c, 19y, 19b and the first mirrors 18m, 18c, 18y, shown in FIG. 18b are arranged in order.

When the apparatus is operated, the motor in the motor housing 24 rotates at high speed, and the laser emitting parts 22m, 22c, 2
2y and 22b blink according to the image signal. Laser light Lc, Ly from these laser emitting parts 22c, 22y
Is reflected by the reflecting mirrors 23c and 23y and is reflected by the rotating polygon mirror 25, and the laser light emitting unit 22
The laser beams Lm and Lb from m and 22b are directly reflected by the polygon mirror 25. The laser beams Lm, Lc, Ly, and Lb reflected by these polygon mirrors 25 pass through fθ lenses 26m, 26c, 26y, and 26b, respectively, and the laser beams Lm and Lc are mainly scanned in the direction of arrow E shown in FIG. Is done
Main scanning is performed in the direction of arrow F with the laser lights Ly and Lb.

Further, laser light emitted from the optical housing 21
Lm, Lc, Ly and Lb are the third mirrors 20m and 20m, respectively.
c, 20y, 20b, second mirrors 19m, 19c, 1
9y, 19b, the first mirror 18m, 18c, 18y,
18b, the photosensitive drums 3m, 3c, 3
An image is formed on y and 3b.

When a start signal of the image forming operation is input to the housing 1, the photosensitive drum 3 of the first image forming section 2m is also provided.
m starts rotating in the direction of arrow M, and is uniformly charged by the primary charger 4m. The laser light Lm modulated by the electric digital image signal corresponding to the magenta component image of the original image by the image exposure device is written on the photoconductor drum 3m to form a latent image, and then the latent image is formed by the developing device 5m. Is developed with magenta toner, and a magenta toner image is formed on the photoconductor drum 3m. The same operation is also performed in the second, third, and fourth image forming units 2c, 2y, and 2b to form cyan, yellow, and black toner images on the photoconductor drums 3c, 3y, and 3b, respectively. It

On the other hand, the recording material P is taken out from one of the recording material cassettes 8a and 8b, for example, the recording material cassette 8a by the pickup roller 9a, and sent to the registration roller 11 via the carrying roller 10a. The recording material P stopped once by the registration roller 11 is sent to the recording material carrying belt 12 which has already started to be moved by the registration roller 11 at a timing with the toner image formed on the photosensitive drum 3m. Be done.

The recording material P, which is fed onto the recording material carrying belt 12 at a proper timing, is the recording material carrying belt 12
Of the first image forming unit 2 along with the movement of the first image forming unit 2
The toner image of magenta on the photoconductor drum 3m is transferred onto the recording material P by being transferred to the transfer area of m and being transferred and charged from the back side of the carrier belt 12 by the transfer charger 6m.

The same process is performed in the second, third and fourth image forming sections 2c, 2y and 2b, and the recording material carrying belt 12 is moved so that the recording material P is second, third and fourth. Image forming sections 2c, 2y, 2b of the photoconductor drums 3c, 3
Pass the lower parts of y and 3b sequentially. While being conveyed in the direction of the arrow N, cyan, yellow, and black toner images are sequentially superimposed and transferred onto the recording material P by the transfer chargers 6c, 6y, and 6b to form a color image.

When the transfer of all the toner images is completed, the recording material P passes through the fourth image forming portion 2b and is then discharged by the discharging means (not shown) for applying an AC voltage, and the recording material P is recorded. It is separated from the material carrying belt 12.
The recording material P separated from the recording material carrying belt 12 is sent to a fixing device 15, and the multiple composite image transferred in the fixing device 15 is heated and fixed by, for example, a pair of heat rollers 16 and then discharged. The sheet is discharged from the outlet onto the sheet discharge tray 17, and one copy cycle is completed.

FIG. 3 is an explanatory view of the vicinity of the laser emission part 22c when a three-beam laser chip for cyan is used as a multi-beam laser chip, and a laser emission part 22c for emitting three laser beams Lc1, Lc2 and Lc3. A cylindrical collimating lens barrel portion 31 c is rotatably fitted in the optical housing 21. A rod 32c is projected from the collimating lens barrel portion 31c, and a stepping actuator 33 is provided at the tip of the rod 32c.
The shaft 34c of c abuts. Further, the stepping actuator 33c is a base 35 fixed to the optical housing 21.
The tension coil spring 36c is supported between the base 35c and the rod 32c, and is urged below the rod 32c.

The stepping actuator 33c
Is capable of driving the shaft 34c in the direction of arrow G with a resolution of several μm by a signal from a control circuit (not shown), the movement of the shaft 34c is transmitted to the rod 32c, and the entire laser emitting portion 22c is collimated. It is rotatable in the direction of arrow J around the cylindrical portion 31c.

Of the three laser beams Lc1, Lc2, and Lc3, the central laser beam Lc2 is assembled so as to be aligned with the center of the collimating lens barrel 31c. Therefore, by driving the stepping actuator 33c, the horizontal line Q The angle θ formed by the line connecting the light emitting points of the three laser beams Lc1 to Lc3 can be changed.

FIG. 4 is an explanatory diagram of a cyan image exposure apparatus. The reflection mirror 23c shown in FIG. 2 is arranged in the emitting direction of the laser beam Lc from the laser emitting section 22c and is reflected by the reflection mirror 23c. The laser light Lc is reflected by the polygon mirror 25, passes through the fθ lens 26c, and is sequentially reflected by the third, second, and first mirrors 20c, 19c, and 18c, and three laser lights Lc1 on the photosensitive drum 3c. Lc
2 and scan as Lc3.

A part of the laser beam outside the image area reflected by the first mirror 18c is reflected by the mirror 37c and is incident on the photosensor 39c through the slit 38c. The detection signal from the photo sensor 39c is used for detecting the image writing timing in the main scanning direction and determining the drive amount of the stepping actuator 33C.

FIG. 5 shows a slit 38c and a photo sensor 39.
3C is an explanatory diagram showing the relationship between the three laser beams Lc1 to Lc3, and the three laser beams Lc1 to Lc3 that cross the slit 38c near the photosensor 39c are all the photosensor 3;
9c is detected.

FIG. 6 is an explanatory view showing the relative positional relationship of the laser light spots S1 to S3 on the photosensitive drum 3c. The line H connecting the laser light spots S1 to S3 is at an angle θ with respect to the main scanning direction A. Leaning.

FIG. 7 is an explanatory diagram showing an output signal from the photo sensor 39. The three beam detection timings of the photo sensor 39c have an interval of time T during which the laser light advances by the interval X3 shown in FIG. Are detected as shown in FIG. Therefore, the interval X3 can be calculated by detecting the time T of the interval between the peaks K1 to K3.

The laser beam spot interval X1 on the surface of the photosensitive drum 3c is a constant value determined by the magnification of the laser scanning optical system and the laser emission point interval. Therefore, if the interval X3 is known, the angle θ can be calculated by θ = cos ⁻¹ (X3 / X1), and further, the sub-scanning interval X2 can be calculated by X2 = X1 · sin θ.

If the angle θ between the main scanning direction A on the surface of the photosensitive drum 3c and the line H connecting the laser light spots S1 to S3 is not correct, the sub-scanning interval X2 changes.
However, this change amount can be detected by calculating the sub-scanning interval X2 from the output signal from the photo sensor 39c. When the sub-scanning interval X2 changes beyond the allowable value, a stepping actuator 33c is driven by a control circuit (not shown) to rotate the laser emitting section 22c until the sub-scanning interval X2 reaches an appropriate value.

As described above, in this embodiment, the photo sensor 3
By the output signal from 9c, the angle θ formed by the main scanning direction on the surface of the photosensitive drum 3c and the line H connecting the laser light spots S1 to S2 is detected, and the angle θ is changed if necessary. Image unevenness can be controlled to maintain high-quality images.

Although the cyan optical system has been described in the embodiment, the mechanism for changing the angle θ by the stepping actuator and the means for detecting the angle θ by the photosensor are the same for other magenta, yellow and black optical systems. It is provided in. Further, in the embodiment, the case where the invention is applied to the color image forming apparatus has been described, but it is needless to say that the invention is equally applicable to the electrophotographic system other than the embodiment.

As described above, by using the present invention in an apparatus having a plurality of image forming units, in addition to image unevenness in a single color, a color generated due to the relative density of beam sub-scanning line intervals relative to other colors. It is possible to prevent unevenness.

[0048]

As described above, the laser scanning optical device according to the present invention comprises the direction in which the laser beam scans the surface of the photoconductor and the line connecting the laser beam spots aligned on the photoconductor surface. Since the angle is variable, it is possible to eliminate image unevenness due to the unevenness of the beam sub-scanning line spacing that occurs on the photosensitive drum surface when using a multi-beam laser chip, and the unevenness occurs due to thermal expansion and mechanical deformation. Even if it is done, it is possible to automatically detect the occurrence and control so as to remove the density, and it is possible to maintain a high-quality image with no image unevenness for a long period of time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is a perspective view of an image exposure apparatus.

FIG. 3 is a perspective view of the vicinity of a laser emitting portion when a multi-beam laser chip is used.

FIG. 4 is a perspective view of an image exposure apparatus when a multi-beam laser chip is used.

FIG. 5 is an explanatory diagram of a positional relationship among a photo sensor, a slit, and laser light.

FIG. 6 is an explanatory diagram of a positional relationship of laser beam spots.

FIG. 7 is an explanatory diagram of photosensor output.

FIG. 8 is an explanatory diagram of a light spot interval and a sub-scanning interval on the surface of the photoconductor.

FIG. 9 is an explanatory diagram of a light spot interval and a sub-scanning interval on the surface of the photoconductor.

FIG. 10 is an explanatory diagram of a light spot interval and a sub-scanning interval on the surface of the photoconductor.

FIG. 11 is an explanatory diagram of a light spot interval and a sub-scanning interval on the surface of the photoconductor.

[Explanation of symbols]

 1 case 2m, 2c, 2y, 2b image forming section 3m, 3c, 3y, 3b photoconductor drum 21 optical case 22m, 22c, 22y, 22b laser emitting section 25 polygon mirror 26m, 26c, 26y, 26b fθ lens 31c Collimating lens barrel 38c Slit 39c Photo sensor

Claims (3)

[Claims] 1. A multi-beam laser chip that emits a plurality of laser beams aligned in a straight line from one chip, and a photoconductor that writes an image on its surface by the laser beam emitted corresponding to an image signal. A laser scanning optical device having a beam scanning means for scanning the laser beam from the multi-beam laser chip along the surface of the photoconductor, in the direction in which the laser beam scans the surface of the photoconductor and on the surface of the photoconductor. A laser scanning optical device characterized in that an angle formed by a line connecting laser light spots aligned on a straight line is variable. 2. The tilt angle between the direction in which the laser beam scans the surface of the photoconductor and the line connecting the laser beam spots aligned on the photoconductor surface is detected, and the tilt angle is detected based on the detection result. The laser scanning optical device according to claim 1, further comprising a changing unit that changes 3. A plurality of multi-beam laser chips which emit a plurality of laser beams arranged in a straight line from one chip, and a plurality of photoconductors respectively arranged corresponding to these multi-beam laser chips, A laser scanning optical device having a beam scanning means for scanning a laser beam from the multi-beam laser chip along a predetermined surface of the photoconductor, and a direction in which the laser beam scans the surface of each photoconductor and the photoconductor. A laser scanning optical device characterized in that an angle formed by a line connecting laser light spots aligned on a surface is variable.