JP2005119313A - Color-image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a color-image formation device which has a simple structure and a less jitter or misregistration. <P>SOLUTION: The color-image formation device has two or more sets consisting of a scan optical device and an image carrier corresponding to the former. The light fluxes emitted from each scan optical device are introduced onto the image carrier surfaces corresponding to each one. The image carrier surfaces are scanned with the light fluxes. Then, the image with different color light are formed on the image carrier surfaces. Following the above steps, the color images are formed by the images formed on the two or more image carrier surfaces with the color-image formation device. In the case the wave length of the two or more light fluxes are different, each scanning commencement timing for the two or more scan optical devices makes the start-position for writing the image in the scanning range on the light-flux image carrier surfaces differ each other and is controlled so that the central positions in the scanning range on the light-flux image carrier surface are consistent each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus. Here, the color image forming apparatus is used as, for example, a laser beam printer (LBP) having a color electrophotographic process, a digital copying machine, or the like that scans an image carrier with a deflected light beam to record image information. It is done.

  2. Description of the Related Art Conventionally, in a scanning optical device used in an image forming apparatus such as a laser beam printer or a digital copying machine, a light beam modulated and emitted from a light source means according to an image signal is deflected by, for example, a rotating polygon mirror. The image is periodically deflected by a detector, focused on a photosensitive recording medium (photosensitive drum) surface by an imaging optical system having fθ characteristics, and image recording is performed by optically scanning the surface (see FIG. Patent Document 1).

  FIG. 6 is a schematic diagram of a main part of a conventional scanning optical apparatus.

  In the figure, a divergent light beam emitted from a light source means 81 is made into a substantially parallel light beam by a collimator lens 82, and the light beam is limited by a diaphragm 83 and is incident on a cylindrical lens 84 having a predetermined refractive power only in the sub-scanning direction. Out of the substantially parallel light beam incident on the cylindrical lens 84, the light beam exits as it is in the state of a substantially parallel light beam in the main scanning plane. In the sub-scanning plane, the light beam is focused and formed as a substantially linear image on the deflection surface (reflection surface) 85a1 of the optical deflector 85 formed of a rotating polygon mirror (polygon mirror).

  The light beam deflected and reflected by the deflecting surface 85a1 of the optical deflector 85 is guided to a photosensitive drum surface 88 as a surface to be scanned through a scanning optical element (fθ lens) 86 having fθ characteristics, and the optical deflector. By rotating 85 in the direction of arrow 85a, image information is recorded by optically scanning the photosensitive drum surface 88 in the direction of arrow 88a (main scanning direction).

In such a scanning optical apparatus, in order to accurately control the image writing position, for example, a part of the light beam deflected by the optical deflector 85 immediately before writing the image signal is scanned with the scanning optical element 86 and the beam detector (BD). The light is incident on a beam detector (BD) sensor 92 through a mirror 95 and a slit 91. The output signal from the BD sensor 92 is used to adjust the timing of the scanning start position for image recording on the photosensitive drum surface.
JP 2001-174732 A

  In recent years, with the increase in speed and resolution of an image forming apparatus having an electrophotographic process, a multi-beam scanning optical apparatus employing a multi-beam laser having a plurality of light emitting units in the above-described scanning optical apparatus, and a high-speed color As shown in FIG. 7, a plurality of scanning optical devices as described above are used at the same time, and scanning is used for a tandem type color image forming device that records image information for each color on different photosensitive drum surfaces. There is a demand for optical devices, and combinations thereof that further increase the speed.

  7, 111, 112, 113, and 114 are scanning optical devices, 121, 122, 123, and 124 are photosensitive drums as image carriers, 131, 132, 133, and 134 are developing units, and 141 is a conveyor belt. is there.

  In addition, productivity and cost are also important for such a scanning optical device, and the scanning optical element (fθ lens) is manufactured by plastic molding, and a scanning optical element having a low-cost and simple configuration that does not compensate for lateral chromatic aberration is used. Has become the mainstream.

However, in a multi-beam scanning optical device that forms a final image with a light beam from a multi-beam laser having a plurality of light emitting units,
(1) Initial wavelength deviation between multiple light beams emitted from a multi-beam laser
(2) Wavelength deviation due to mode hopping of multi-beam lasers accompanying environmental changes
(3) Due to the change in the refractive index of the plastic lens due to environmental changes, a magnification change occurs between a plurality of light beams, leading to image degradation. FIG. 6 shows the image region when the light source wavelength of the B laser (the wavelength of the light beam emitted from the light source) changes with respect to the A laser of the multi-beam laser, and the deviation of the image formation position of the light beam at the image writing detection position Show. In FIG. 6, only the image forming points of the light beams of the A laser and the B laser are indicated by points A and B, respectively.

  As shown in FIG. 8, in the actual image, there is almost no jitter on the left end side of the image when the magnification is changed (wavelength variation). Large jitter results in image degradation. This is because the timing of the image writing position is controlled (synchronized) on the scanning start position side as described above.

  That is, in the conventional scanning optical apparatus shown in FIG. 6, the detection light beam detected by the BD sensor 92 is incident on the fθ lens 86 obliquely with the light beam scanned on the surface to be scanned, When the wavelengths of the light beams emitted from the B laser are different, the image formation position is displaced substantially equal to the scanning start position on the surface to be scanned. For this reason, when a part of each light beam is detected by the BD sensor and the scanning timing is controlled based on this detection signal, the deviation of the imaging position due to the difference in wavelength is corrected at the scanning start position, and each light beam is corrected. The scanning start positions can be aligned. However, a large jitter is generated at the scanning end position.

  The same applies to a scanning optical device in a tandem type color image forming apparatus. When a change in magnification occurs between a plurality of scanning optical devices, registration shifts between colors from the center of the image to the right end of the image as shown in FIG. (Color misregistration) increases and causes image degradation. In FIG. 9, the color misregistration in B (black) and C (cyan) is shown, but the same applies to the color misregistration between other colors.

  An object of the present invention is to provide an initial wavelength difference (wavelength shift) between a plurality of light beams emitted from a plurality of light emitting portions even when a plastic molded lens that is not corrected for lateral chromatic aberration is used for a scanning optical element. An object of the present invention is to provide a multi-beam scanning optical apparatus capable of reducing jitter caused by a change in magnification (magnification deviation) between the plurality of light beams caused by an environmental change.

  It is a further object of the present invention to provide a resist between colors resulting from a change in magnification between a plurality of scanning optical devices caused by an initial wavelength difference of a light beam between a plurality of scanning optical devices or an environmental change in a tandem type color image forming apparatus. It is an object of the present invention to provide a color image forming apparatus that reduces misregistration (color misregistration) and has a simple configuration and little registration misalignment.

The color image forming apparatus of the invention of claim 1
There are a plurality of sets of scanning optical devices and corresponding image carriers, and light beams emitted from the respective scanning optical devices are guided onto the corresponding image carrier surfaces, and the image beams are scanned with the light beams. Then, in a color image forming apparatus that forms images of different color lights on the surface of the image carrier, and forms a color image from images formed on the surfaces of the plurality of image carriers.
Each scanning start timing in the plurality of scanning optical devices, when the wavelength of the plurality of light beams are different, the image writing position of the scanning range on the image carrier surface of the light beam is different from each other,
In addition, the center position of the scanning range on the image carrier surface of the light beam is controlled so as to coincide with each other.

The invention of claim 2 is the invention of claim 1,
The color image forming apparatus has a detection optical element that condenses the detection light flux and guides it to the synchronous detection means,
Each of the plurality of scanning optical devices includes a scanning optical system,
A plurality of light beams traveling toward the detection optical element does not pass through the scanning optical system,
The optical surface of the detection optical element faces the detection light beam,
Each of the plurality of scanning optical devices is characterized in that the principal ray of the light beam incident on the center position of the scanning width in the main scanning direction on the surface of the image carrier coincides with the optical axis of the scanning optical system.

The invention of claim 3 is the invention of claim 1 or 2, wherein
The light source means of each of the scanning optical devices has a plurality of light emitting portions that emit a plurality of light beams modulated independently of each other.

The invention of claim 4 is the invention of claim 3,
The synchronization detection means controls the scanning start timing in the main scanning direction for each of the plurality of light beams emitted from the plurality of light emitting units.

The invention of claim 5 is the invention of any one of claims 1 to 4,
The detection optical element is formed of an anamorphic lens.

The invention of claim 6 is the invention of any one of claims 1 to 5,
The scanning optical system includes a refractive optical element and a diffractive optical element.

The color image forming apparatus of the invention of claim 7
There are a plurality of sets of scanning optical devices and corresponding image carriers, and light beams emitted from the respective scanning optical devices are guided onto the corresponding image carrier surfaces, and the image beams are scanned with the light beams. Then, in a color image forming apparatus that forms images of different color lights on the surface of the image carrier, and forms a color image from images formed on the surfaces of the plurality of image carriers.
The color image forming apparatus has a detection optical element that condenses the detection light flux and guides it to the synchronous detection means,
Each of the plurality of scanning optical devices includes a scanning optical system,
A plurality of light beams traveling toward the detection optical element does not pass through the scanning optical system,
The optical surface of the detection optical element faces the detection light beam,
In each of the plurality of scanning optical devices, the principal ray of the light beam incident on the center position of the scanning width in the main scanning direction on the surface of the image carrier coincides with the optical axis of the scanning optical system,
The scanning start timings of the plurality of scanning optical devices are controlled so that the center positions of the scanning ranges on the image carrier surface of the light beams coincide with each other when the wavelengths of the light beams are different. It is characterized by being.

The invention of claim 8 is the invention of claim 7,
The light source means of each of the scanning optical devices has a plurality of light emitting portions that emit a plurality of light beams modulated independently of each other.

The invention of claim 9 is the invention of claim 8,
The synchronization detection means controls the scanning start timing in the main scanning direction for each of the plurality of light beams emitted from the plurality of light emitting units.

The invention of claim 10 is the invention of any one of claims 7 to 9,
The detection optical element is formed of an anamorphic lens.

The invention of claim 11 is the invention of any one of claims 7 to 10,
The scanning optical system includes a refractive optical element and a diffractive optical element.

  In the multi-beam scanning optical apparatus of the present invention, when the wavelengths of a plurality of light beams are different, the scanning start timing is controlled so that the center positions of the scanning ranges of the light beams on the scanned surface coincide with each other. May be configured to control the scanning start timing in the main scanning direction at a position corresponding to or near the center of the scanning width in the main scanning direction on the surface to be scanned by the photodetector (BD sensor). This means that the photodetector (BD sensor) and the center position of the scanning width in the main scanning direction on the surface to be scanned are in an optically equivalent state.

  In each scanning optical apparatus used in the color image forming apparatus of the present invention, scanning in the main scanning direction is performed at or near the center of the scanning width in the main scanning direction on the surface to be scanned by the photodetector (BD sensor). Control of the start timing is also achieved by bringing the photodetector (BD sensor) and the center position of the scanning width in the main scanning direction on the surface to be scanned into an optically equivalent state.

  In order to specifically realize the state in which the photodetector and the center position of the scanning width in the main scanning direction on the surface to be scanned are equivalently realized as described above, the light beam for detection is condensed and the photodetector (BD sensor). The detection optical element that guides the light beam may be arranged so that its optical surface faces the detection light beam. This is because, in general, the principal ray of the light beam incident on the center position of the scanning width in the main scanning direction on the surface to be scanned matches the optical axis of the scanning optical system (fθ lens). This is because the light beam incident on the (BD sensor) is optically equivalent.

  In the present invention, the fact that the optical surface of the detection optical element faces the detection light beam means that the principal ray of the light beam when detected by the photodetector (BD sensor) and the optical axis of the detection optical element. Say almost matching. Here, the expression “when detected by the photodetector” means that the luminous flux incident on the photodetector is scanned, and the principal ray of the luminous flux always coincides with the optical axis of the detection optical element. It is not because I am doing it. In other words, it can be expressed that there exists a state in which the principal ray of the scanned light beam coincides with the optical axis of the detection optical element.

  According to the present invention, even when a plastic molded lens that has not been corrected for chromatic aberration of magnification as described above is used for a scanning optical element, the initial wavelength difference (wavelength shift) between a plurality of light beams emitted from a plurality of light emitting portions. And a multi-beam scanning optical device that can reduce jitter caused by a change in magnification (magnification deviation) between the plurality of light beams caused by environmental changes.

  Further, according to the present invention, as described above, the tandem type color image forming apparatus has a difference between the colors caused by the change in magnification between the plurality of scanning optical devices caused by the initial wavelength difference between the plurality of scanning optical devices and the environmental change. Registration color shift (color shift) can be reduced, and a color image forming apparatus with a simple configuration and less registration shift can be achieved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a sectional view (main scanning sectional view) of the main part in the main scanning direction of the multi-beam scanning optical apparatus according to the first embodiment of the present invention.

  In the figure, reference numeral 1 denotes a light source means (light source), which is composed of a multi-semiconductor laser (multi-beam laser) having a plurality of light emitting portions (in this embodiment, two of an A laser and a B laser), and is individually optically modulated. A plurality of luminous fluxes are emitted.

  Reference numeral 2 denotes a collimator lens (first lens) as a first optical element, which converts a plurality of light beams emitted from the light source means 1 into substantially parallel light beams. Reference numeral 3 denotes an aperture stop, which limits a passing light beam (light quantity). Reference numeral 4 denotes a cylindrical lens (second lens) as a second optical element, which has a predetermined refractive power only in the sub-scanning direction, and allows a plurality of light beams that have passed through the aperture stop 3 to fall within the sub-scanning section. An image is formed almost as a line image on a deflection surface (reflection surface) 5a1 of an optical deflector 5 to be described later.

  Each element such as the collimator lens 2 and the cylindrical lens 4 constitutes one element of the incident optical system.

  Reference numeral 5 denotes an optical deflector composed of, for example, a polygon mirror (rotating polygonal mirror) as a deflecting element (deflecting means), and is rotated at a constant speed in the direction of arrow 5a by a driving means (not shown) such as a motor. .

  Reference numeral 6 denotes a scanning optical element (scanning optical system) as a third optical element having an fθ characteristic, and includes a refractive optical element 61 and a diffractive optical element 62. The refractive optical element 61 is composed of a single plastic toric lens having different powers in the main scanning direction and the sub-scanning direction. The diffractive optical element 62 is made of a long plastic diffractive element having different powers in the main scanning direction and the sub-scanning direction. The long diffractive element 62 is made of plastic manufactured by injection molding, but the same effect can be obtained even if a diffraction grating is manufactured as a replica on a glass substrate.

  In the present embodiment, a toric lens 61 is disposed on the polygon mirror 5 side from a midpoint between the rotation axis of the polygon mirror 5 and the surface to be scanned 8, and a diffractive optical element 62 is disposed on the surface to be scanned 8. Both of these optical elements have different powers in the main scanning direction and the sub-scanning direction as described above, and form an image of the deflected light beam from the polygon mirror 5 on the scanned surface 8 and tilt the deflection surface of the polygon mirror. Is corrected.

  The scanned surface 8 corresponds to a photosensitive drum surface when the multi-beam scanning optical apparatus is applied to an electrophotographic printer. Hereinafter, reference numeral 8 is referred to as a photosensitive drum surface.

  Reference numeral 7 denotes an optical element for synchronization detection (detection optical element), which comprises an anamorphic lens made of a plastic material having different powers in the main scanning direction and the sub-scanning direction. In the present embodiment, the lens surface (optical surface) of the anamorphic lens 7 has a plurality of light beams (synchronized) from the polygon mirror 5 for controlling the scanning start timing (scanning timing synchronization timing) in the main scanning direction on the photosensitive drum surface 8. The detection light flux 73 is arranged almost in a straight line including the front, and the synchronous detection light flux 73 is imaged in the vicinity of the slit 71 in both the main scanning section and the sub-scanning section. .

  Incidentally, the fact that the lens surface of the anamorphic lens 7 is directly opposed to the synchronous detection light beam (detection light beam) 73 means that the principal ray of the light beam when detected by the photodetector (BD sensor) 72 as described above. And the optical axis of the anamorphic lens 7 substantially coincide with each other.

  Reference numeral 75 denotes a folding mirror (hereinafter referred to as “BD mirror”), which reflects a synchronous detection light beam 73 for adjusting the scanning start timing in the main scanning direction on the photosensitive drum surface 8 toward the BD sensor 72 described later. I am letting. Reference numeral 71 denotes a slit, which is disposed at a position equivalent to the photosensitive drum surface 8. Reference numeral 74 denotes a beam detector (BD) lens as an imaging means for making the BD mirror 75 and the BD sensor 72 have a conjugate relationship, and corrects the surface tilt of the BD mirror 75. Reference numeral 72 denotes synchronization detection means (light detector), which has a BD sensor (light sensor).

  In this embodiment, the synchronization detection means 72 starts scanning in the main scanning direction with respect to a plurality of light beams emitted from a plurality of light emitting sections at or near the center of the scanning width in the main scanning direction on the photosensitive drum surface 8. The timing is controlled.

  That is, in this embodiment, the scanning start timing is controlled so that the center positions of the scanning ranges on the scanned surface 8 of the respective light beams coincide with each other when the wavelengths of the plurality of light beams are different. This is configured such that the BD sensor 72 and the center position of the scanning width in the main scanning direction on the scanned surface 8 are in an optically equivalent state.

  The wavelength of the light beam means, for example, the center wavelength of the emission spectrum or the center wavelength of the emission spectrum distribution.

  In this embodiment, two divergent light beams modulated and emitted from the multi-semiconductor laser 1 in accordance with image information (only one light beam is shown in the figure) are converted into substantially parallel light beams by the collimator lens 2, and the aperture stop The light beam is limited by 3 (the light amount of the light beam is limited) and enters the cylindrical lens 4. Of the two substantially parallel light beams incident on the cylindrical lens 4, the light exits as it is in the main scanning section. In the sub-scan section, the light beam converges to form a substantially linear image (a linear image longitudinal in the main scanning direction) on the deflecting surface 5a1 of the optical deflector (polygon mirror) 5. Then, the two light beams deflected by the deflecting surface 5a1 of the optical deflector 5 are spot-formed on the photosensitive drum surface 8 through the toric lens 61 and the diffractive optical element 62, and the optical deflector 5 is moved to the arrow. By rotating in the direction 5a, the photosensitive drum surface 8 is optically scanned in the direction of the arrow 8a (main scanning direction) at a constant speed. As a result, an image is recorded on the photosensitive drum surface 8 as a recording medium.

  At this time, in this embodiment, the two synchronous detection light beams 73 reflected and deflected by the polygon mirror 5 are guided to the BD sensor 72 through the synchronous detection optical element 7, the BD mirror 75, the slit 71, and the BD lens 74. Is shining. Then, using two BD signals (synchronization signals) in the main scanning direction obtained by detecting the output signal from the BD sensor 72, the position corresponding to the center of the scanning width in the main scanning direction on the photosensitive drum surface 8 or the vicinity thereof. , The scanning start timing (synchronization timing) in the main scanning direction is controlled.

  In the present embodiment, the anamorphic lens 7 formed of a plastic material alone as described above is arranged so that the lens surface thereof faces the synchronization detecting light beam 73 almost directly including the facing. As a result, as shown in FIG. 1, for example, even if the light source wavelength of the B laser with respect to the A laser constituting the multi-semiconductor laser 1 is changed, the timing of synchronization detection (write synchronization signal) in the main scanning direction does not change. Even if the refractive index of the optical element 7 for synchronization detection changes due to an environmental change, the timing of synchronization detection does not change as described above. In FIG. 1, only the image forming points of the light beams of the A laser and the B laser are indicated by points A and B, respectively.

  On the other hand, in the present embodiment, the scanning start timing in the main scanning direction is controlled at or near the center of the scanning width in the main scanning direction on the photosensitive drum surface 8 as described above. On the other hand, when the light source wavelength of the B laser changes, the arrival position (image formation position) of the light beam on the photosensitive drum surface 8 coincides only on the optical axis of the scanning optical element 6, and the optical axis is sandwiched at other positions. A magnification change occurs symmetrically. The same applies to the case where the refractive index of the scanning optical element 6 changes due to environmental changes.

  That is, in this embodiment, the timing of synchronous detection does not change with respect to the refractive index change due to wavelength change or environmental change, and the imaging position on the image area changes symmetrically with respect to the optical axis of the scanning optical element 6. Therefore, as shown in FIG. 2, the amount of magnification change can be distributed between the image writing side and the image writing end side. That is, the scanning start timing in this embodiment is controlled so that the image writing positions of the scanning ranges of the respective light beams on the scanned surface 8 are different when the wavelengths of the plurality of light beams are different from each other. . Thereby, the amount of jitter can be halved.

  As described above, in this embodiment, the scanning start timing in the main scanning direction is controlled by the synchronization detecting means 72 at the position corresponding to or near the center of the scanning width in the main scanning direction on the photosensitive drum surface 8 as described above, and the anamorphic lens 7 is moved. By disposing the lens surface so that it substantially faces the sync detection light beam 73 including the correct face, even when an inexpensive plastic molded lens that does not correct the lateral chromatic aberration is used for the scanning optical element, the wavelength shift. It is possible to reduce jitter of the multi-scanning optical apparatus due to (initial wavelength difference) and magnification shift (magnification change) due to environmental changes.

  In this embodiment, the scanning optical element is composed of a refractive optical element and a diffractive optical element. However, the present invention is not limited to this, and the same effect as in the first embodiment can be obtained even if it is composed of only a refractive optical element. .

  In this embodiment, the synchronization detecting optical element is constituted by an anamorphic lens. However, even if it is constituted by a cylindrical lens, the present invention can be applied in the same manner as in the first embodiment.

  FIG. 3 is a schematic view of the essential portions of a color image forming apparatus according to Embodiment 2 of the present invention.

  This embodiment differs from the first embodiment described above in that four scanning optical devices are arranged, and each of them is constituted by a tandem type color image forming apparatus that records image information on a photosensitive drum surface that is an image carrier. In addition, the light source means of each scanning optical device is composed of a single beam laser. Other configurations and optical actions are substantially the same as those in the first embodiment.

  That is, 11, 12, 13, and 14 are scanning optical devices, 21, 22, 23, and 24 are photosensitive drums as image carriers, 31, 32, 33, and 34 are developing units, and 41 is a transporter. It is a belt.

  The color image forming apparatus in this embodiment has four scanning optical devices (11, 12, 13, 14) arranged in each of C (cyan), M (magenta), Y (yellow), and B (black) colors. Correspondingly, image signals (image information) are recorded on the photosensitive drums 21, 22, 23, and 24 in parallel, and a color image is printed at high speed.

  As described above, the color image forming apparatus according to this embodiment uses the light beams based on the respective modulation signals by the four scanning optical devices 11, 12, 13, and 14, and the corresponding photosensitive drums 21, 22, 23, It is formed on the 24th surface. For example, latent images of C (cyan), M (magenta), Y (yellow), and B (black) are formed on the corresponding photosensitive drums 21, 22, 23, and 24, and then multiple-transferred onto a recording material. One full color image is formed.

  Such a color image forming apparatus can print a color image at high speed as in the case of black and white. However, since the scanning optical element is not shared for each color, the scanning line position (registration) between the colors is shifted. It is easy to cause color misregistration.

  Therefore, in this embodiment, in each scanning optical apparatus used in the tandem type color image forming apparatus, as in the first embodiment, synchronization is performed at the position corresponding to the center of the scanning width in the main scanning direction on the photosensitive drum surface or in the vicinity thereof. The detection means controls the scanning start timing in the main scanning direction.

  That is, the optical detector (BD sensor) and the center position of the scanning width in the main scanning direction on the surface to be scanned are configured to be in an optically equivalent state. For this reason, in this embodiment, the optical element for synchronization detection (anamorphic lens), which is independently molded with a plastic material, is arranged so that the lens surface thereof is almost directly opposed to the light beam for synchronization detection.

  As a result, in the present embodiment, as in the first embodiment described above, for example, the timing of synchronization detection does not change even if the light source wavelength between four scanning optical devices changes. Even if the refractive index of the optical element for synchronization detection changes due to environmental changes, the timing of synchronization detection does not change as described above.

  On the other hand, in this embodiment, since the scanning start timing in the main scanning direction is controlled at or near the position corresponding to the center of the scanning width in the main scanning direction on the photosensitive drum surface as described above, four scans are performed in the image area. When the light source wavelength between the optical devices changes, the arrival position (imaging position) of the light beam on the surface of the photosensitive drum coincides only on the optical axis of the scanning optical element, and in other positions, the magnification is symmetrical with respect to the optical axis. Change occurs. The same applies to the change in the refractive index of the scanning optical element due to environmental fluctuations.

  That is, in this embodiment, the timing of synchronization detection does not change with respect to the refractive index change due to the wavelength change or the environment change, and the imaging position on the image area changes symmetrically with respect to the optical axis of the scanning optical element. As shown in FIG. 4, the magnification change amount of each color can be distributed between the image writing side and the image writing end side. That is, the scanning start timing of each of the four scanning optical devices 11, 12, 13, and 14 in the present embodiment is different from each other in the wavelengths of the light beams emitted from the four scanning optical devices 11, 12, 13, and 14. In this case, the image writing positions in the scanning range on the surface to be scanned 8 of each light flux are controlled to be different from each other. Thereby, the amount of color misregistration can be halved. In FIG. 4, color misregistration in B (black) and C (cyan) is shown, but the same applies to color misregistration between other colors.

  As described above, in this embodiment, in the scanning optical apparatus used in the tandem type color image forming apparatus as described above, the main scanning is performed by the synchronization detection means at or near the center of the scanning width in the main scanning direction on the photosensitive drum surface. An inexpensive plastic molded lens that does not correct lateral chromatic aberration by controlling the scanning start timing in the direction and arranging the anamorphic lens so that its lens surface faces the sync detection light beam almost directly including the correct face. Even when used in a scanning optical element, it is possible to reduce color misregistration of a color image due to wavelength misalignment or magnification misalignment due to environmental changes.

  The color image forming apparatus may be configured by replacing the scanning optical apparatus used in the color image forming apparatus of this embodiment with, for example, the multi-beam scanning optical apparatus of Embodiment 1 described above. According to this, it is possible to realize a color image forming apparatus that can cope with higher speed and higher definition.

  FIG. 5 is a sectional view (main scanning sectional view) of the principal part in the main scanning direction of the multi-beam scanning optical apparatus according to the third embodiment of the present invention. In the figure, the same elements as those shown in FIG.

  In this embodiment, the difference from the first embodiment described above is that the synchronization detecting optical element is integrally formed with the refractive optical element constituting the scanning optical element by plastic injection molding. Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effects are obtained.

  That is, in the figure, reference numeral 17 denotes an integrated optical element, in which an anamorphic lens as a synchronous detection optical element and a toric lens as a refractive optical element are integrally formed by plastic injection molding. As a result, in this embodiment, since there is no spatial interference between the synchronization detecting optical element and the refractive optical element, the scanning position can be detected at a position closer to the image area, and the jitter can be further reduced. .

  In this embodiment, the synchronous detection optical element and the refractive optical element are integrally molded. However, the present invention is not limited to this. For example, the synchronous detection optical element and the cylindrical lens as the second optical element are integrally formed by plastic injection molding. Alternatively, the optical element for synchronization detection, the refractive optical element, and the cylindrical lens may be integrally formed by plastic injection molding. In addition, this embodiment may be applied to the color image forming apparatus of the second embodiment described above.

1 is a schematic view of the main part of a multi-beam scanning optical apparatus according to a first embodiment of the present invention. Explanatory drawing which is the output sample by Example 1 of this invention, and shows the mode of the jitter of a main scanning direction 1 is a schematic diagram of a main part of a color image forming apparatus according to a first embodiment of the present invention. Explanatory drawing which is the output sample by Example 2 of this invention, and shows the mode of the jitter of a main scanning direction Schematic view of essential parts of a multi-beam scanning optical apparatus according to a third embodiment of the present invention. Sectional view of the main part of the conventional scanning optical device in the main scanning direction Schematic diagram of main parts of a conventional multi-beam scanning optical device Explanatory drawing which shows an output image when a jitter arises by the magnification gap between two light beams in a multi-beam scanning optical device Explanatory drawing showing an output image when a color shift occurs due to a magnification shift between colors in the scanning optical system of the color image forming apparatus

Explanation of symbols

1 Light source means (multi-semiconductor laser)
2 First optical element (collimator lens)
3 Aperture stop 4 Second optical element (cylindrical lens)
5 Deflection element (polygon mirror)
6 Scanning optical element 7 Synchronous detection optical element 61 Refraction optical element (toric lens)
62 Diffractive optical element 8 Scanned surface (photosensitive drum surface)
DESCRIPTION OF SYMBOLS 71 Slit 72 Synchronous detection means 73 Synchronous detection light beam 74 Imaging means 75 Folding mirror 17 Integrated optical element 11, 12, 13, 14 Scanning optical device 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41 Transport belt

Claims (11)

There are a plurality of sets of scanning optical devices and corresponding image carriers, and light beams emitted from the respective scanning optical devices are guided onto the corresponding image carrier surfaces, and the image beams are scanned with the light beams. Then, in a color image forming apparatus that forms images of different color lights on the surface of the image carrier, and forms a color image from images formed on the surfaces of the plurality of image carriers.
Each scanning start timing in the plurality of scanning optical devices, when the wavelength of the plurality of light beams are different, the image writing position of the scanning range on the image carrier surface of the light beam is different from each other,
In addition, the color image forming apparatus is controlled so that the center positions of the scanning ranges of the light beams on the surface of the image carrier coincide with each other. The color image forming apparatus has a detection optical element that condenses the detection light flux and guides it to the synchronous detection means,
Each of the plurality of scanning optical devices includes a scanning optical system,
A plurality of light beams traveling toward the detection optical element does not pass through the scanning optical system,
The optical surface of the detection optical element faces the detection light beam,
In each of the plurality of scanning optical devices, a principal ray of a light beam incident on a center position of a scanning width in a main scanning direction on the surface of the image carrier coincides with an optical axis of the scanning optical system. Item 2. The color image forming apparatus according to Item 1.   3. The color image forming apparatus according to claim 1, wherein the light source unit of each of the scanning optical devices includes a plurality of light emitting units that emit a plurality of light beams modulated independently of each other.   The color image forming apparatus according to claim 3, wherein the synchronization detecting unit controls the scanning start timing in the main scanning direction for each of the plurality of light beams emitted from the plurality of light emitting units.   The color image forming apparatus according to claim 1, wherein the detection optical element includes an anamorphic lens.   6. The color image forming apparatus according to claim 1, wherein the scanning optical system includes a refractive optical element and a diffractive optical element. There are a plurality of sets of scanning optical devices and corresponding image carriers, and light beams emitted from the respective scanning optical devices are guided onto the corresponding image carrier surfaces, and the image beams are scanned with the light beams. Then, in a color image forming apparatus that forms images of different color lights on the surface of the image carrier, and forms a color image from images formed on the surfaces of the plurality of image carriers.
The color image forming apparatus has a detection optical element that condenses the detection light flux and guides it to the synchronous detection means,
Each of the plurality of scanning optical devices includes a scanning optical system,
A plurality of light beams traveling toward the detection optical element does not pass through the scanning optical system,
The optical surface of the detection optical element faces the detection light beam,
In each of the plurality of scanning optical devices, the principal ray of the light beam incident on the center position of the scanning width in the main scanning direction on the surface of the image carrier coincides with the optical axis of the scanning optical system,
The scanning start timings of the plurality of scanning optical devices are controlled so that the center positions of the scanning ranges on the image carrier surface of the light beams coincide with each other when the wavelengths of the light beams are different. A color image forming apparatus.   8. The color image forming apparatus according to claim 7, wherein the light source means of each of the scanning optical devices has a plurality of light emitting portions that emit a plurality of light beams modulated independently of each other.   9. The color image forming apparatus according to claim 8, wherein the synchronization detecting unit controls scanning start timing in the main scanning direction for each of the plurality of light beams emitted from the plurality of light emitting units.   The color image forming apparatus according to claim 7, wherein the detection optical element includes an anamorphic lens.   The color image forming apparatus according to claim 7, wherein the scanning optical system includes a refractive optical element and a diffractive optical element.