JPH0391778A - Color image forming device - Google Patents

Abstract

PURPOSE:To compensate color slurring generating from positional deviation of an optical system part and to form a color image of high quality by providing an optical path length changing means which differs the optical path length from a deflecting device which deflects a laser beam emitted from a laser beam source to the photosensitive body on a scanning starting side of an exposure and a scanning finishing side of the exposure. CONSTITUTION:Shafts 14a and 14b of a photosensitive body 14 are each supported freely rotatable by shaft bearing 47a and 47b, and the shaft bearings 47a and 47b are reach retained by holders 46a and 46b. Then, these holders 46a and 46b are each abutted to the edge parts of adjusting screws 49a and 49b which are each screwed to cases 45a and 45b, and each are installed freely able to travel inside the cases 45a and 45b. When a length of the optical path is shortened at the scanning starting side of the exposure and the length of the optical path is extended on the scanning finishing side of the exposure, the adjusting screw 49a is screwed in and the holder 46a is traveled to an upper direction, an elastic body 48a is made into a state of compressed deformation, and the elastic body 48b should be expanded to move the holder 46b to a lower side by putting back the adjusting screw 49b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image forming apparatus, and more particularly to a multi-transfer type color image forming apparatus equipped with a plurality of photoreceptors.

[Prior Art] A plurality of photoreceptors are provided, each photoreceptor is irradiated with a laser beam modulated with a different image signal to expose a latent image, and after these latent images are visualized, one In a color image forming apparatus that forms a color image by multiple transfer onto a sheet of transfer paper, it is necessary to align the respective color images on each photoreceptor on the transfer paper to prevent color misregistration.

In this case, a beam scanning device that matches the start positions of exposure in the main scanning direction is disclosed in Japanese Patent Laid-Open No. 62-296660.

In the beam scanning device disclosed in the above-mentioned publication, a detection signal emitted when a beam deflected by a deflecting means arrives at a specific position,
By delaying by an arbitrary time using the delay time setting means,
The image writing position is arbitrarily set and the image recording position is adjusted within one dot.

In addition, a multi-transfer type laser printer that matches the image recording width in the main scanning direction of exposure was disclosed in Japanese Patent Laid-Open No. 62-145260.
It is disclosed in the publication No.

In the multi-transfer laser printer according to this publication, by changing the transmission frequency of the video signal sent to the multiple laser scanning systems according to the optical magnification of each laser scanning system,
The effective scanning range of each laser scanning system for each photoreceptor is set constant.

By applying the above technique, in a multi-transfer type color image forming apparatus including a plurality of photoreceptors, it is possible to match the writing start position and writing width of a transferred image.

[Problem M to be Solved by the Invention] In the above-mentioned conventional technology, even if the writing start position and the writing end position of the transferred image are made to match by matching the writing start position of the transferred image and the writing width, , If an error occurs in the mounting position of the fθ lens or the reflecting mirror, the fθ characteristics will differ, and the writing position of the laser beam will shift at the intermediate position of the transferred image, resulting in color shift.

An object of the present invention is to provide a color image forming apparatus that compensates for and reduces color shifts caused by changes in fθ characteristics caused by misalignment of fθ lenses and reflective mirrors, and forms high-quality transferred images without color shift over the entire image surface. There is a particular thing.

[Means for solving the problem] The above object is to create an optical path in which the length of the optical path from the deflector that deflects the laser beam emitted from the laser light source to the photoreceptor is made different between the scanning start side and the scanning end side of exposure. This can be achieved by providing a length changing means. [Operation] The optical path length changing means changes the optical path length from the deflector to the photoreceptor so that it is different between the scan start side and the scan end side of exposure.

This change compensates for deviations in the exposure position of the laser beam on the photoreceptor due to changes in fθ characteristics caused by misalignment of the fO lens, etc., and produces high-quality color images with no color shift over the entire image. .

[Example code] below. Embodiments of the present invention will be described with reference to the drawings.

First, a color copying machine to which the present invention is applied will be explained.

The second engineering drawing is an explanatory diagram showing the structure of a color copying machine to which the present invention is applied, in which 1 is a scanner section, 2 is an image processing section, and 3 is an explanatory diagram showing the structure of a color copying machine to which the present invention is applied.
is a printer section, 4 is an original table, 5 is a light source, 6 to 8 are mirrors, 9 is an imaging lens, 10 is a dichroic prism, 12C, 12M, 12Y, 12BK are laser light sources, 13G, 13M , 13Y, 13BK are deflectors, 14C. 14M, 14Y, and 14BK are photoreceptors.

As shown in FIG. 1, this type of color copying machine includes a scanner section 1 for reading originals, an image processing section 2 for electrically processing image signals output as digital signals from the scanner section 1, and an image processing section 2 for electrically processing image signals output as digital signals from the scanner section 1. It has a printer section 3 that forms an image on transfer paper based on the image recording information of each color from the processing section 2.

The scanner section l has a lamp 5, such as a fluorescent lamp, for scanning and illuminating the original on the original placing table 4.

The reflected light from the document when illuminated by the fluorescent lamp 5 is
The light is reflected by the mirrors 6, 7.8 and enters the imaging lens 9. The image light is imaged onto a dichroic prism 10 by the imaging lens 9, for example, red R, green G.
, blue B, and a receiver 11 for each wavelength. For example, the light is input to the red CCDIIR, the green CCD11G, and the blue CCDIIB.

Each CCDIIR, 11G, and IIB converts the incident light into a digital signal and outputs it, and the output is subjected to necessary processing in the image processing section 2 to produce recorded color information for each color, such as black (hereinafter abbreviated as BK). The signals are converted into signals for recording of each color: yellow (abbreviated as Y), magenta (abbreviated as M), and cyan (abbreviated as C).

Signals from the image processing section 2 are supplied to the printer section 3, which outputs laser light sources 12C:, 12M, 12Y, and 12Y for each color.
It is input to 12BK.

Figure 1 shows a case where a color image is formed using four colors, BK, Y, M, and C. Since the device has the same structure for each color, only the device for C will be explained below, and the device for other colors will be explained below. A description of the device will be omitted. Note that the same parts in the devices of each color are denoted by the same reference numerals, and the numerals are given a subscript indicating each color.

A laser beam modulated by the C-component image signal of the original is emitted from the laser light source 12G, and this laser beam is deflected by a deflector 13G and scanned over the surface of the photoreceptor 14C.

Photoreceptor 1 uniformly charged by charger 15C
4C, a latent cyan image is formed by exposure to the laser beam gl2c, and a developed image is formed by development by the developing device l6C. On the other hand, the transfer paper fed by the paper feed roller 18 from either of the two paper feed cassettes of the paper feed section l9 has its leading edge aligned by the registration roller 20, and is sent to the transfer belt 2 at the same timing. The transfer paper conveyed by the transfer belt 21 has a photoreceptor 14BK on which a developed image is formed.
, 14Y, 14M, and 14C, and the developed images of each photoreceptor are sequentially and multiple-transferred onto the transfer paper by transfer chargers 17BK, 17Y, 17M, and 17C.

The transfer paper on which the cassette image has been formed by transfer in this manner is fixed by the fixing roller 22 and discharged by the paper discharge roller 23. In this case, the transfer paper is electrostatically attracted to the transfer belt 21 and is conveyed at the moving speed of the transfer belt.

FIG. 2 is a perspective view of the laser light source and deflector portion of a color copying machine to which the present invention is applied, and FIG. 3 is a cross-sectional view of the laser light source and deflector portion of the color copying machine to which the present invention is applied. FIG.

With reference to FIGS. 2 and 3, the laser light source and deflector portion of the color copying machine will be described in detail, focusing on the BK portion.

In Figures 2 and 3, 14BK is a photoreceptor, 25B
K is a laser unit, 26BK is a motor, 27BK is a polygon mirror, and 298K is an fθ lens. 308K, 31
BK is a mirror.

As shown in FIG. 2, a laser beam 24BK that has been modulated with the BK component image signal of the original and collimated is emitted from the laser unit 25BK, and is focused by a cylindrical lens 28BK to form a linear beam on a polygon mirror 27BK. is irradiated. This polygon mirror 27BK is rotated by a motor 26BK. Laser beam 24 reflected by polygon mirror 27BK
8K is fθ lens 29BK, mirror 30BK, 31B
The image is formed on the photoreceptor 14BK via the polygon mirror
The photoreceptor 14BK is scanned by rotation of 278K.

A reflecting mirror 35BK is disposed outside the exposure area of the photoreceptor 14BK, and a photodiode 36BK that detects that the reflected light from the polygon mirror 27BK is reflected by this reflecting mirror 35 faces the reflecting mirror 35. It is provided.

As shown in FIG. 3, the deflector 138K portion is housed in an optical housing 33BK, a motor 26BK is attached to the optical housing 33BK, and a polygon mirror 27BK rotated by the motor 26BK is inside the optical housing 3.3BK. It is positioned and arranged. An fθ lens 29BK is fixedly provided to the optical housing 338K at the optical junction of the laser beam reflected from the polygon mirror 27BK.

A mirror 30BK is fixed to the optical housing 33BK at a position where the laser beam from the fθ lens 29BK is incident, so that the incident beam from the mirror 308K is made to be incident on the surface of the photoreceptor 14BK via the dustproof glass 32BK. Mirror 3.1B inside optical housing 33BK
K is arranged.

A cover 34BK is attached to the optical housing 33BK, and the inside of the optical housing 33BK has a sealed structure.
This optical housing 33BK is fixed to a side plate of the main body of the copying machine (not shown).

In this way, a laser beam is emitted from the laser light source 1 28K of the color copying machine to which the present invention is applied.
This laser beam scans the surface of the photoreceptor 14BK with a predetermined width from a predetermined writing start position on the photoreceptor 14BK to perform exposure.

In this case, the writing start position is set by detecting that the scanning beam has reached the reflection mirror 358K position using the output signal of the photodiode 368K, and after a predetermined time by counting a predetermined number of image clocks from this detection point, the light is exposed. body 14
I am trying to write to 8K.

For example, the already explained Japanese Patent Application Laid-Open No. 62-2966
By applying the method proposed in Publication No. 60, it is possible to match the writing start positions of the four colors C, M, Y, and BK. Furthermore, the already explained JP-A-6
By applying the method proposed in Publication No. 2-145260, it is possible to match the image recording widths of the four colors C, M, Y, and BK. Next, the relationship between the positional misalignment of a component of a deflector of a color copying machine and the exposure position will be explained.

Fig. 4 is an explanatory diagram showing the exposure position of the laser beam deflected by the deflector of the color copying machine on the photoconductor surface, and Fig. 5 is an explanatory diagram showing the position of the deflector structure and parts of the color copying machine and the exposure position. FIG. 3 is an explanatory diagram showing changes in exposure position on the body surface.

In FIGS. 4 and 5, 24 is a laser beam, 25
2 is a laser unit, 27 is a polygon mirror, and 28 is a cylindrical canole lens. 29a and 29b are fθ lenses.

FIG. 4 shows an fθ lens 29a, which is a component of the deflector. 2
9b shows an ideal state with no positional deviation, and the semiconductor laser 3
7 and a collimating lens 38.
The laser beam 24 from the cylindrical drill lens 2
The light is focused at 8 and irradiated onto the polygon mirror 27 in a linear manner.

The reflected beam from the polygon mirror 27 passes through the fO lens 2
9a and 29b form an image on the surface 43 of the photoreceptor, and the rotation of the polygon mirror 27 scans the surface 43 of the photoreceptor. A to E indicate each exposure position of the laser beam 24 on the surface 43 of the photoreceptor in this case.

As shown in FIG. 5, if the fO lens 29b is slightly tilted from the ideal position shown by the two-dot chain line to the position shown by the solid line, each exposure position on the surface 43 of the photoreceptor will be A' to E'. It shifts. In this case, even if the angle of the surface of the polygon mirror 27 is constant, the fθ characteristic changes due to the positional shift of the fθ lens 29b, causing a shift in the exposure position.

Ideal exposure position A-E and misaligned exposure position fit
The amount of deviation between A' and E' is approximately 0, and the amount of deviation γ between C and C' is approximately 0.
, the amount of deviation between A and A1 is almost equal to the amount of deviation between E and E', the amount of deviation between B and B' is almost equal to the amount of deviation between D and D', and if these are α and β, respectively, then The formula is established.

In FIG. 5, a case has been explained in which the exposure position shift occurs on the surface 43 of the photoreceptor due to the tilting of the fθ lens 29b. A deviation occurs. Figure 6 is an explanatory diagram showing the deviation of the fθ lens in the main scanning direction in a color copying machine.
The θ lens 42 is shifted in the main scanning direction and moved to a position (42') indicated by a two-dot chain line.

Fig. 7 is an explanatory diagram showing the inclination of the fθ lens in the soil color copying machine.
．． 42 are tilted together at the position shown by the two-dot chain line (41', 4
2″).

The above-mentioned shift in the exposure position of the laser beam on the surface of the photoreceptor also occurs when the fθ lens shifts as shown in FIGS. 6 and 7. It can also be caused by misalignment of the beam optical axis or mirror.

In this case, the relationship between the amount of deviation of the fθ lens and the amount of deviation of the exposure position on the photoreceptor surface varies depending on the characteristics of the fθ lens, but
For example, if the inclination amounts of the fθ lenses 41 and 42 are both 0.05 mm in FIG. 7, the deviation amount α shown in FIG.
β, γ are α″F 0.1mm, β is 0.05n+m
, γ=O.

Next, regarding the state of the transferred image when the positional shift of the optical system (deflector) components occurs as described above, the fθ lens of BK is in the ideal position, but the fθ lens of C is in the ideal position. A case in which there is a deviation will be explained below.

FIG. 8 is an explanatory diagram showing the transfer position on the transfer paper when the C fθ lens shifts in a color copying machine.
Due to the shift of the fθ lens, the transfer position of the C image on the transfer paper is shifted by a maximum shift amount of α in the main scanning direction.

FIG. 9 is an explanatory diagram showing the transfer position on the transfer paper when the image recording start position and image recording width are made to match the state shown in FIG. 8, and the state shown in FIG. On the other hand, if the image recording start position and image recording width (the image recording width hardly changes) are matched, the transfer position of the BK image and the transfer position of the C image will shift at the center position in the main scanning direction, resulting in color shift. occurs.

fθ caused by misalignment of optical system components, etc.
In order to compensate for changes in characteristics and eliminate color shift, the present invention is provided with optical path length changing means. FIG. 10 is an explanatory diagram showing the principle of color shift compensation by changing the optical path length. When the optical path length is shortened at , and the optical path length is lengthened at the end of the exposure scan (exposure position E side), the surface of the photoreceptor moves to the position (43") shown by the two-dot chain line in the same figure. do.

For this reason, the exposure positions A-E in FIG.
Move to u~E I+ and find the deviation amount of A and A71 and E and E
) The deviation amounts of l are almost equal to α″, the deviation amounts of B and B II and the deviation amounts of D and D″ are almost equal to β″, and C
The deviation amount γ'' between and C I+ is approximately O, and the following equation holds between them.

To change the optical path length shown in FIG. 10, the mirror 318K shown in FIGS. 2 and 3 (in the case of a device compatible with BK) is moved without moving the surface 43 of the photoreceptor as described above. It can also be done by

The trends of the deviation amounts α″, β″, γ″ of each exposure point caused by changing the optical path length shown in FIG. 10 are the same according to equations (1) and (2), and As is clear from the comparison with the figure, the directions of the deviations are opposite to each other.

Therefore, the amount of deviation of the exposure point A-E caused by the positional deviation of the fθ lens 29b shown in FIG. 5 can be compensated for by changing the optical path length between the exposure scan start side and the exposure scan end side shown in FIG. 10. I can do it.

FIGS. 11(a) to 11(c) are a right side view, a left side view, and a front view including a cross section, respectively, showing the structure of the main parts of the first embodiment of the present invention. , 14 is a photoreceptor. 14a, 14b are axes, 24 is a laser beam, 4
5a, 45b are cases, 47a, 47b are bearings, 48a
, 48b are elastic bodies, and 49a, 49b are adjustment screws.

As shown in the first construction drawings (a) to (C), the shafts 14a and 14b of the five photoreceptor constructions 4 are rotatably mounted on bearings 47a and 47, respectively.
b, and bearings 47a. 47b is the holder 46a, 4
6b, respectively.

The holders 46a and 46b are connected to the cases 45a and 46b.
Adjustment screws 49a and 49 are screwed into 45b, respectively.
They are movably disposed within the cases 45a and 45b, respectively, in contact with the ends of the casings 45a and 45b. Further, the ends of the holders 46a, 46b and the cases 45a, . Elastic bodies 48a and 48b are sandwiched between 45b, respectively.

With this configuration, as shown in Fig. 10, when the optical path length is shortened at the start of the exposure scan and extended at the end of the exposure scan, the adjustment screw 49a is screwed in. to move the holder 46a upward and release the elastic body 48a.
is compressed and deformed, and by returning the adjusting screw 49b, the elastic body 48b is expanded and the holder 4. It is better to move 6 b downward.

In FIG. 5, when compensating for a case where the fθ lens 29b is tilted in a direction opposite to that shown in the figure, the adjusting screw 49a is returned in FIG. 11(c) to extend the optical path length at the start side of the exposure scan. It is preferable to tighten the adjustment screw 49b to shorten the optical path length at the end of the exposure scan.

In all of the above adjustments, when the optical path length is extended at one end, the optical path length is shortened at the other end, but the optical path length may be extended or shortened only at one end.

FIGS. 12(a) to 12(c) are a right side view, a left side view, and a front view including a cross section, respectively, showing the structure of the main parts of the second embodiment of the present invention. , 24 is a laser beam, 30.31 is a mirror 51a, 5lb is an elastic body, 50a, 50b is a mirror holder, and 52a, 52b is an adjustment screw.

As shown in FIGS. 12(a) to (c), the mirror holder 5
Adjustment screws 52a and 52b are screwed into 0a and 50b, respectively, and the adjustment screws! Mirrors 31, which are in contact with the ends of the mirrors 52a and 52b, respectively, are movably arranged in the mirror holders 50a and 50b, and between the mirror 31 and the mirror holders 50a and 50b, there are elastic bodies 5, respectively.
1a and 5lb are sandwiched.

In this second embodiment, when the adjusting screw 52a is screwed in, the light length on the start side of exposure scanning is extended, and the adjusting screw 52a is screwed in.
When 2a is returned, the optical path length on the start side of exposure scanning is shortened. Similarly, when the adjustment screw 52b is screwed in, the optical path length at the end of the exposure scan is extended, and when the adjustment screw 52b is returned, the optical path length at the end of the exposure scan is shortened.

The optical path length changing means in the first embodiment or the second embodiment configured as described above is capable of controlling all colors BK, M, Y, and CL.
For example, it may be provided only for M, Y, and C, and the other colors may be made to match the BK image. As described above, according to the first embodiment and the second embodiment, it is possible to compensate for color shift due to changes in fθ characteristics caused by misalignment of optical system components, etc., and to produce a color image without color shift over the entire image plane. It can be formed. The optical path length changing means in any of the embodiments has a simple structure, and does not increase the size of the entire device or significantly increase the manufacturing cost.

[Effects of the Invention] As explained in detail above, according to the present invention, the optical path length from the deflector that deflects the laser beam to the photoreceptor can be made different between the exposure scanning side and the scanning end side by the optical path length changing means. fθ caused by misalignment of optical system components, etc.
It is possible to compensate for color shift caused by changes in characteristics and form a high-quality color image without color shift over the entire image plane.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the structure, Figure 2 is a perspective view of the laser light source and deflector, Figure 3 is a front view including a cross section of the laser light source and deflector, and Figure 4 is the deflector. An explanatory diagram showing the exposure position of the deflected laser beam on the photoconductor surface, FIG. 5 is an explanatory diagram showing the positional shift of the bridge or component of the deflector and a change in the exposure position on the photoconductor surface, and FIG. 6 is an fθ lens. Fig. 7 is an explanatory drawing showing the inclination of the fθ lens, and Fig. 8 is an explanatory drawing showing the transfer position on the transfer paper when the -@-@-fθ lens is misaligned. , Fig. 9 is an explanatory diagram showing the transfer position on the transfer paper when the image recording start position and image recording width are matched with respect to the state shown in Fig. 8, and Fig. 0 shows the color shift compensation due to changing the optical path length. Explanatory diagram showing the principle, 1st
FIG. 1 is a block diagram of a main part of a first embodiment of the present invention, and FIG. 12 is a block diagram of a main part of a second embodiment of the present invention. 1...Scanner unit, 2...Image processing unit, 3...Printer unit, 4...Document placement table, 5...Light source , 6-8...mirror,
9... Imaging lens, 10... Dichroic prism, 12C, 12M, 12Y, 1 2BK
・・・・・・Laser light source, 13C, 13M, 13Y, 1
3BK... Deflector, 14C, 14M. 14Y,
14. BK...Photoconductor, 21...Transfer belt, 24...Laser beam, 25.25B
K...Laser unit, 26BK...
Motor, 27,278K-...=Borigon mirror, 29
a, 29b, 298K... fO lens, 30B
K, 318K...Mirror, 3 5BK...
...Reflection mirror, 36BK...Photodiode. Figure 1 Figure 2 Figure 3 Figure 4 Figure 6 Figure 7 Figure 421 Figure 8 Figure 8 Paper direction Manko 2 I9 Figure 9 Paper Shufe Manan Figure 10 Scanning direction

Claims (1)

[Claims] A plurality of photoconductors and a photoconductor provided corresponding to these photoconductors,
a plurality of laser light sources modulated with different image signals, at least one deflector that deflects the laser beams emitted from these laser light sources, and a reflector that guides the laser beam deflected by the deflector to the photoreceptor. In a color image forming apparatus that scans the surface of the photoreceptor with the laser beam and performs exposure corresponding to the image signal, the optical path length from the deflector to the photoreceptor is set at the start of scanning of the exposure. 1. A color image forming apparatus comprising an optical path length changing means that changes the optical path length between the scanning end side and the scanning end side.