JP2014041193A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner using a plurality of light sources, configured to reduce printing misregistration in a main-scanning direction on a scanned surface by using an inexpensive deflector, and to form a high-definition image with a simple configuration, and to provide an image forming device using the same.SOLUTION: A light-scanning optical system includes: light source means in which the largest gap between light fluxes separated from each other in a sub-scanning direction on a deflection surface is 0.1 mm or larger and N light-emitting spots are provided; first optical means for imaging a focal line of the light flux from the light source means near the deflection surface; deflection means; second optical means for forming spots on a scanned surface; and write start position detection means. The light-emitting spots of the light source means are grouped into M sets (M≥2, M<N) of light-emitting spot groups according to the sub-scanning position. The write start position of each group is decided by at least one beam in the group.

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus using the same, and more particularly to an optical scanning apparatus for a laser beam printer, a digital copying machine, or a multifunction printer (multifunction printer) having an electrophotographic process.

2. Description of the Related Art Conventionally, there has been proposed an optical scanning device that spot-forms a plurality of light beams from a light source means (multi-beam light source) having a plurality of light emitting portions (light emitting points) on a photosensitive drum (photosensitive member) surface as a surface to be scanned. . The method of detecting (synchronizing detection) the writing position in the main scanning direction on the surface to be scanned in these optical scanning devices is roughly classified into the following two methods.
(A) Type that generates a synchronization detection signal for each light beam (see Patent Document 1)
(B) A type in which one synchronization detection is performed using a plurality of light sources (see Patent Document 2).
For example, Patent Document 1 discloses a technique for generating a synchronization signal for each multi-beam.

  Patent Document 2 discloses a technique for generating one synchronization signal with a plurality of beams having the same scanning position in the main scanning direction.

JP 2000-235154 A Japanese Patent No. 4081973

  However, the conventional techniques disclosed in the above-mentioned patent documents have a problem that synchronization detection cannot be performed and a problem that an expensive deflector must be used.

  In the method of type (a), if the number of beams increases, the time required for performing synchronous detection of all the beams becomes longer, and it becomes difficult to perform synchronous detection of the beams of all the light emitting units during one scan. The problem occurs. In the type (b) method, since the beam for performing synchronous detection is separated in the sub-scanning direction on the deflection surface, it is necessary to use a polygon mirror having a highly accurate reflection surface. The problem that cannot be used occurs. This is because in an optical scanning device having a plurality of light emitting points separated in the sub-scanning direction, when a conventional deflector is used, the image writing position is shifted in the main scanning direction in accordance with the sub-scanning beam position, and the image is This is because a problem of deterioration occurs.

  As described above, when a conventional deflector is used in an optical scanning device using a multi-beam light source, a printing position shift in the main scanning direction occurs on the surface to be scanned, and moiré or jitter image defects occur. Further, in a color image forming apparatus that forms an image by superposing a plurality of different images, a so-called color misregistration occurs in which a print misregistration occurs for each color.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical scanning apparatus using a plurality of light sources, which can reduce a printing position deviation in the main scanning direction on a scanned surface using an inexpensive deflector and can easily form a high-definition image. It is an object of the present invention to provide an optical scanning device having a configuration and an image forming apparatus using the same.

  In order to achieve the above object, the present invention provides light source means having N light emitting points whose distance on the deflection surface of the light beam farthest away in the sub-scanning direction is 0.1 mm or more, and the light flux from the light source means In the optical scanning optical system having a first optical means for forming a focal line in the vicinity of the deflecting surface, a second optical means for forming a spot on the deflecting means and the surface to be scanned, and a writing position detecting means, the light source The means is divided into M groups (M ≧ 2, M <N) of light emitting element groups according to the sub-scanning positions, and the writing position of each group is determined by at least one beam in the group. Features.

  According to the present invention, an optical scanning device having a simple configuration capable of reducing a printing position deviation in the main scanning direction on a surface to be scanned and forming a high-definition image even using an inexpensive deflector, and an image using the same A forming apparatus can be provided.

Main scanning sectional view of Embodiment 1 of the present invention FIG. 4 is an enlarged view of a main scanning section in the vicinity of the deflection surface of the first embodiment of the present invention. Schematic diagram showing the sub-scanning interval of multi-beams on the deflecting reflecting surface of Example 1 of the present invention Timing chart for determining the writing position according to the first embodiment of the present invention Schematic diagram showing the method for measuring the writing position of Example 1 of the present invention The figure which shows the inclination of the deflection | deviation reflective surface of Example 1 of this invention. The figure which shows the beam writing position in the to-be-scanned surface of Example 1 of this invention. Schematic diagram showing the sub-scanning interval of the multi-beam on the deflecting reflecting surface of Example 2 of the present invention Timing chart for determining write start position according to the second embodiment of the present invention Schematic diagram showing the sub-scanning interval of the multi-beam on the deflecting reflecting surface of Example 3 of the present invention Timing chart for determining write start position according to embodiment 3 of the present invention The figure which shows the BD detection beam of Example 3 of this invention. 1 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  Hereinafter, an optical scanning apparatus according to a first embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a cross-sectional view (main scanning cross-sectional view) of the main part in the main scanning direction of Embodiment 1 of the present invention.

  FIG. 2 is an enlarged cross-sectional view of the vicinity of the deflecting / reflecting surface in FIG. 1, and is a main-portion cross-sectional view (main-scanning cross-sectional view) in the main scanning direction showing the relationship between the light beam traveling toward the BD optical system and the deflecting / reflecting surface.

  The light source unit of this embodiment is composed of a semiconductor laser having 16 light emitting points arranged one-dimensionally. The light beam shown in FIG. The dotted line indicates the optical axis of the collimator lens and the fθ lens, and the broken line indicates the light flux from the light emitting point 2.

  In this specification, the surface formed by the optical axis of the scanning lens and the light beam deflected by the optical deflector is a main scanning section, and the surface including the optical axis of the scanning lens and perpendicular to the main scanning section is a sub-scanning section. Define.

  In the figure, reference numeral 1 denotes a light source means, which comprises a semiconductor laser having 16 light emitting points. A rectangular aperture stop 2 regulates the width of the light beam emitted from the light source means 1 only in the sub-scanning direction. A collimator lens 3 converts the light beam that has passed through the aperture stop 2 into a substantially parallel light beam in both main scanning and sub-scanning. A cylindrical lens 4 has a predetermined refractive power only in the sub-scanning direction. Reference numeral 5 denotes a rectangular aperture stop that regulates the beam width in the main scanning direction. The sub scanning direction has an aperture width wider than the beam width. Each element such as the aperture stops 2 and 5, the collimator lens 3, and the cylindrical lens 4 constitutes an element of the incident optical means.

  Reference numeral 6 denotes an optical deflector as a deflecting element, which is composed of, for example, a polygon mirror (rotating polygon mirror), and is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor.

  Reference numerals 11a and 11b denote scanning lenses (fθ lenses) having fθ characteristics, and the distance between the deflection surface 5a of the optical deflector 5 or the vicinity thereof and the photosensitive drum surface 12 or the vicinity thereof as a scanned surface in the sub-scan section. By having a substantially conjugate relationship, the optical deflector has a surface tilt correction function.

  Reference numeral 7 denotes a reflection mirror (hereinafter referred to as “BD mirror”), which reflects a light beam (BD light beam) for performing synchronization detection to the side of the synchronization detection element 10 described later. The BD mirror 8 is used for turning back a light beam guided to a synchronization position detecting means described later, and is arranged to reduce the size of the entire apparatus.

  Reference numeral 8 denotes an imaging lens (hereinafter referred to as “BD lens”), and a sync signal detection light beam (BD light beam) for determining the timing of the scanning start position on the photosensitive drum surface 12 is within the main scanning section. In the sub-scan section, both are imaged on the sensor surface of the synchronous detection element 9. That is, the BD lens 6 forms an image on the sensor surface of the synchronization detection element 9 in the main scanning section, and optically connects the deflection surface 5a of the optical deflector 5 and the sensor surface of the synchronization detection element 9 in the sub-scanning section. Therefore, it is substantially conjugate and has a tilt correction function (surface tilt correction system). Thereby, even if the reflection surface of the optical deflector is tilted in the sub-scanning direction, the light beam is hardly separated from the sensor surface of the synchronization detecting element 9.

  Reference numeral 9 denotes an optical sensor (hereinafter referred to as “BD sensor”) as a synchronization detection element. In this embodiment, a synchronization signal (BD signal) obtained by detecting an output signal from the BD sensor 9 is used. The timing of the scanning start position for image recording on the photosensitive drum surface 12 is adjusted.

  Each element such as the BD mirror 7, the BD lens 8, and the BD sensor 9 constitutes one element of the synchronization position detecting means (BD optical system).

  In the present embodiment, the light beam modulated and emitted from the light source means 1 according to the image information is limited in size by the aperture stops 2 and 5, converted into a substantially parallel light beam by the collimator lens 3, and the cylindrical lens 4. Is incident on. Of the light beam incident on the cylindrical lens 4, the light beam is emitted as it is in the main scanning section. In the sub-scan section, the light beam converges to form a substantially line image (line image elongated in the main scanning direction) on the deflecting surface 6a of the optical deflector 6. The light beam reflected and deflected by the deflecting surface 6a of the optical deflector 6 is imaged in a spot shape on the photosensitive drum surface 12 by the scanning lenses 11a and 11b, and the optical deflector 5 is rotated in the direction of arrow A, Optical scanning is performed on the photosensitive drum surface 12 in the direction of arrow B (main scanning direction) at a constant speed. As a result, an image is recorded on the photosensitive drum surface 12 as a recording medium.

  At this time, the timing of the scanning start position on the photosensitive drum surface 12 is determined before optical scanning on the photosensitive drum surface 12. For this purpose, the light beam reflected and deflected by the optical deflector 5 is guided to the BD sensor 9 by the BD lens 8 through the BD mirror 7. Then, using the synchronization signal (BD signal) obtained by detecting the output signal from the BD sensor 9, the scanning start position timing of image recording on the photosensitive drum surface 12 from the light emitting points 1 to 16 is determined.

  In FIG. 2, reference numeral 5 denotes a stop for restricting the light beam width in the main scanning direction, and restricts the widths of 16 light beams from the light source.

  201 indicates the optical axis of the collimator lens, and 202 indicates the principal ray of the light beam from the light emitting point 1 (light ray passing through the center of the stop 5). Reference numeral 203 denotes a light beam from the light emitting point 16.

  Reference numeral 204 denotes an intersection of the optical axis 201 of the collimator lens and the optical axes of the fθ lenses 11a and 11b, and is hereinafter referred to as an on-axis deflection point.

  Reference numeral 205 denotes an optical axis of the fθ lens, which is a straight line parallel to the optical axis of the light beam toward the center of the image.

  210 indicates the state of the deflecting surface when deflecting the light beam toward the center of the image, and 211 indicates the state of the deflecting surface when deflecting the light beam toward the center of the BD slit. In this embodiment, the angle formed between the light emitting units 1 and 16 and the optical axis 201 of the collimator lens is 1 deg. This is due to the width Wm of the light emitting point in the main scanning direction and the focal length fcol of the collimator lens 3.

It can be calculated with

  FIG. 3 shows the position of each beam on the deflection surface 6a.

  In the figure, the horizontal axis represents the main scanning direction of the reflecting surface, and the vertical axis represents the sub-scanning direction. Further, the light emitting units 1 to 16 of the light source 1 form an image in the vicinity of the deflection reflection surface as a latent image that is long in the main scanning direction. In FIG. 3, the arrival positions of the principal rays of the respective light beams are indicated by circles, and are arranged at equal intervals in the main scanning direction and the sub-scanning direction. In the present embodiment, the principal ray of the light beam from the light emitting unit 16 is reflected by 0.269 mm above in the sub-scanning direction with respect to the light beam from the light emitting unit 1 on the deflecting reflection surface 6a. Further, the incident angle (angle formed by the optical axis 201 of the collimator and the optical axis 205 of the fθ lens) is different between the beam 16 and the beam 1. Therefore, on the surface to be scanned 12, the beam 1 is the downstream side of the scanning, that is, the scanning destination, and the beam 16 is the upstream side of the scanning (backward of the scanning). As shown in FIG. 3, the beams 1 to 16 are divided into six groups according to the position in the sub-scanning direction, and the writing timing is determined by the synchronous position detection signal of at least one beam in each group. Has been.

  The light beam 200 directed to the BD mirror 7 has a scanning angle (angle formed with the optical axis 205 of the scanning lens) of 54 deg. When the deflecting surface 6a of the deflector 6 rotates in the direction of the arrow 211. The light beam is directed to the center of the BD slit. The diaphragm 5 of this embodiment is disposed at a position 22.5 mm from the on-axis deflection point 204 (intersection of the collimator lens optical axis 201 and the fθ lens optical axis 205).

  Table 1 shows design values of the optical scanning device in the present embodiment.

(Collimator lens)
The exit surface of the collimator lens of the present embodiment has a rotationally symmetric aspherical shape represented by the following formula.

By making the exit surface an aspherical shape, the focal position difference on the surface to be scanned between the multiple beams is reduced, and the occurrence of a spot diameter difference is suppressed.

(Cylindrical lens)
In this embodiment, a diffractive surface is provided on the incident surface of the cylindrical lens to suppress spot diameter fluctuation due to environmental fluctuation.

  The phase function is

Where m is the diffraction order, E ₁ to E ₁₀ , and F ₀ to F ₁₀ are phase coefficients. Here, F ₀ to F ₁₀ are terms representing the power in the sub-scanning direction.

(Scanning optical system)
The shapes of the first and second imaging lenses 6a and 6b are expressed by the following mathematical expressions.

  The intersection of the imaging lens and the optical axis is the origin, and as shown in FIG. 1, the optical axis is the X axis on the scanning start side and the scanning end side with respect to the optical axis. The direction is the Y axis, and the direction orthogonal to the optical axis in the sub-scanning plane is the Z axis.

Here, R is the radius of _{curvature, K, B 4, B 6} , B 8, B 10 are aspherical coefficients.

  In this embodiment, the shape in the main scanning direction is symmetrical with respect to the optical axis, that is, the aspheric coefficients on the scanning start side and the scanning end side are made to coincide.

  In the sub-scanning direction, the curvature in one sub-scanning surface (the surface including the optical axis and perpendicular to the main scanning surface) of the second imaging lens 6b is set on the scanning start side and the scanning end side with respect to the optical axis. It is continuously changed in the effective portion, and the shape in the main scanning and sub-scanning directions is configured symmetrically with respect to the optical axis.

The shape in the sub scanning direction is the X axis on the scanning start side and the scanning end side with respect to the optical axis, the Y axis in the direction perpendicular to the optical axis in the main scanning plane, and the optical axis in the sub scanning plane. The direction is the Z axis, and can be expressed by the following continuous function.
Sub-scan direction function of r1, r2, r4 plane

(R ′ is the radius of curvature in the sub-scanning direction, and D ₂ , D ₄ , D ₆ , D ₈ , and D ₁₀ are coefficients)
The coefficient suffix s represents the scanning start side, and e represents the scanning end side.

  The radius of curvature in the sub-scanning direction is a radius of curvature in a cross section perpendicular to the shape (bus line) in the main scanning direction.

(R ′ is the radius of curvature in the sub-scanning direction, and D ₂ , D ₄ , D ₆ , D ₈ , and D ₁₀ are coefficients)
The coefficient suffix s represents the scanning start side, and e represents the scanning end side.

  The radius of curvature in the sub-scanning direction is a radius of curvature in a cross section perpendicular to the shape (bus line) in the main scanning direction.

  In the imaging optical system 6 of the present embodiment, the imaging optical elements (imaging lenses) 6a and 6b are made of plastic lenses having light transmitting power, and the imaging optical element is reduced in weight. It is also possible to improve the degree of freedom in design by using an aspherical surface.

  The imaging optical element may be made of glass or may be an optical element having diffraction power. When configured with a glass material or a diffractive surface, an optical scanning device having excellent environmental characteristics can be provided.

  In this embodiment, the image forming optical system is composed of two image forming optical elements. However, the present invention is not limited to this, and the same effect as in the above embodiment can be obtained even if the image forming optical system is composed of one or three or more. be able to.

Table 2 shows numerical values of the optical scanning device according to the first embodiment of the present invention. Here, “E−x” indicates “10 ^−x ”.

  The R1 surface is the surface on the optical deflector 10 side of the imaging optical element 6a, the R2 surface is the surface on the scanned surface 7 side of the imaging optical element 6a, and the R3 surface is the surface on the optical deflector 10 side of the imaging optical element 6b. , R4 is a surface of the imaging optical element 6b on the scanned surface 7 side.

FIG. 4 shows the relationship between the BD signal and the scan start timing. In the figure, (a) shows the timing of group 6 and (b) shows the scanning start timing of group 2.

  In this embodiment, as described above, a beam for performing BD detection is selected in accordance with the sub-scanning position of the principal ray of the light beam reflected by the polygon deflection surface 6a, and the writing timing (writing position) is determined. . In the figure, “BD signal” indicates a signal (BD signal) generated when a beam enters the BD sensor. In the figure, in group 6, the light beam from the light emitting point 16 crosses the BD slit in the main scanning direction, and the image signal is turned on for the beam 14 T1 seconds after the BD signal changes to the Lo state. Start writing. Similarly, the image signal of the beam 15 is turned on after T2 seconds, and an image is written. The beam 16 writes an image after t3 seconds. Similarly, the image writing timing of each group is determined by the BD signal of beam 1 for group 1, beam 4 for group 2, beam 7 for group 3, beam 10 for group 4, and beam 13 for group 5. ing.

  Next, a method for determining T1 to T16 will be described.

  In the present embodiment, the times T1 to T16 until the image signal of each beam is turned on are measured and determined in advance at the time of factory shipment.

  FIG. 5 shows a schematic diagram of the measurement system in the main scanning direction. A detection system composed of a slit consisting of a knife edge and a photodetector (PD) is arranged in the vicinity of the optical axis of the scanning optical system at a position corresponding to the surface to be scanned, and the BD signals of the beams 1, 4, 7, 10, 13, and 16 are used. In contrast, the time differences T1 to T16 in which the beams 1 to 16 pass through the detection system are measured. Next, the values of T1 to T16 are written in a memory (not shown) so that the writing positions of all the beams at the center position of the image coincide. In this embodiment, since the sensor is aligned with the optical axis of the scanning lens, the influence of the chromatic aberration of magnification of the scanning optical system can be distributed between the image writing side and the writing end side, and the printing position due to the wavelength difference of the beam The configuration can reduce the deviation.

  The theoretical T1 to T16 calculated from the scanning speed and the beam interval are the component error such as the position error of the light emitting point, the wavelength difference of the light source and the surface accuracy of the deflection surface, and the assembly when attaching the component to the optical device. This is because deviation occurs due to an error. In this way, by measuring the values of T1 to T16 in advance at the time of shipment, the error is canceled, and higher-precision printing position accuracy can be ensured.

  Next, the reason why the light emitting points are grouped will be described with reference to FIGS.

  FIG. 6A is a schematic diagram of a deflection reflection surface. In the figure, the principal ray of the beam 1 is on the straight line connecting the lines AA, and the beam 16 is on the straight line connecting the lines BB. As shown in FIG. 3, the distance between the beams 1 and 16 in the sub-scanning direction is 0.269 mm.

  FIG. 6B shows the height (surface accuracy) of the reflecting surface in the AA cross section and the BB cross section. In the figure, the inclination in the main scanning direction is different between a point 602 where the principal ray of the beam 1 is reflected and a point 601 where the beam 16 is reflected. In the polygon mirror processed with high accuracy, the tilt difference at a position 0.1 mm away in the sub-scanning direction is 0.05 minutes or less and can be ignored. However, in the polygon mirror of this embodiment, 0.1 mm or more in the sub-scanning direction. When separated, the amount of inclination exceeds 0.05 minutes and is 0.08 minutes, so the influence of the inclination error cannot be ignored. This tilt error occurs when the deflecting / reflecting surface is processed. The polygon mirror of the present invention is processed in multiple times in the short direction (sub-scanning direction) of the reflecting surface using the tip of the cutting tool. The processing pitch is 10 to 20 μm. If it is attempted to reduce the error, the processing time becomes long or a high-precision processing machine is required, so that an inexpensive polygon mirror cannot be provided. In general, the error amount differs not only for each component but also for each deflecting reflection surface. Therefore, when the BD detection is performed with a group of a plurality of beams having the same position in the main scanning direction as in the prior art, the deflection angle varies depending on the sub-scanning separation amount of the plurality of beams in the group, and thus on the surface to be scanned. There arises a problem that the writing position shift occurs and the image deteriorates. For example, when BD detection is performed in two groups having different positions in the main scanning direction and the writing position is determined, the light beam reflected by the surface having a different inclination according to the sub-scanning position of the reflecting surface is reflected on the surface to be scanned. As shown in FIG.

  On the other hand, as in this embodiment shown in FIG. 7B, the beams are grouped so that the sub-scan interval of the beam is 0.1 mm or less, and the write timing is set using at least one BD signal of each group. When detected, the influence of the tilt error described above can be ignored on the image. Normally, when a periodic writing position error of 0.5 mm or more occurs in the sub-scanning direction on the surface to be scanned, image degradation becomes obvious. In this embodiment, the maximum interval in the sub-scanning direction of each group is set to 0 as will be described later. .054 mm, which makes image deterioration due to writing position error on the surface to be scanned inconspicuous. In this embodiment, the maximum value of the periodic writing position error in the sub-scanning direction (the sub-scanning interval within the deflection surface group × the number of deflection surface surfaces × the sub-scanning magnification absolute value of the scanning optical system) is 0.054 × 5. * 1.18 = 0.319 mm. Further, the maximum value of the writing position error in the main scanning direction (intra-group sub-scanning interval of deflection surfaces × main scanning direction inclination difference of deflection surface per unit length × fθ coefficient) is 0.054 (mm) × 0. It is 08 / 0.1 (min / mm) × 200 (mm / rad) × 2 = 0.005 mm.

  As described above, the scanning optical system of the present embodiment achieves high speed by using a monolithic multi-beam laser having N = 16 light emitting points as the light source means. Also, conditional expression to achieve high definition

Are grouped into 6 groups of light-emitting elements according to the sub-scanning position of the deflecting reflecting surface, and the distance between the sub-scanning end beam of each group is 0.036 mm. Here, W is the distance between the sub-scanning beams of the light source, W = 0.121 mm, β is the sub-scanning lateral magnification of the incident optical system, and β = −2.22 times in this embodiment.

  If this conditional expression is not satisfied, a deflector having a highly accurate reflecting surface is used, or a printing position accuracy defect occurs, and it becomes impossible to provide inexpensive and high-definition optical scanning.

  Although the BD lens may be provided individually as in the present embodiment, a part of the fθ lens may be used. In this embodiment, the writing position adjustment value is calculated for each beam in the assembly process. However, the same effect can be obtained by forming a patch on the scanned object and correcting the writing position in the main scanning direction in the image forming apparatus. I can get it.

  As described above, it is possible to provide a low-cost, high-definition optical scanning device that can group beams according to sub-scanning positions on the deflection surface of a plurality of light sources and reduce image quality deterioration due to surface accuracy errors of the deflection reflection surface. Further, when used in a color image forming apparatus, a high-definition color image apparatus without color misregistration can be provided.

  This embodiment differs from the first embodiment in that a two-dimensional array monolithic multi-beam laser (VCSEL) capable of increasing the number of beams as a light source is used and the number of groups is set to five. Other configurations are the same as those of the first embodiment.

  Hereinafter, the beam on the deflecting reflecting surface according to the second embodiment of the present invention will be described with reference to FIG. In the figure, the horizontal axis represents the main scanning direction of the reflecting surface, and the vertical axis represents the sub-scanning direction. Further, the light emitting units 1 to 16 of the light source 1 form an image in the vicinity of the deflection reflection surface as a latent image that is long in the main scanning direction. In FIG. 8, the arrival position of the principal ray of each light beam is indicated by a circle, and is arranged two-dimensionally at equal intervals in the sub-scanning direction. In the present embodiment, similar to the first embodiment, the principal ray of the light beam from the light emitting unit 1 is reflected by 0.269 mm above the sub scanning direction with respect to the light beam from the light emitting unit 16 on the deflecting reflection surface 6a. As shown in FIG. 8, the beams 1 to 16 are divided into five groups according to the position in the sub-scanning direction, and the writing timing is determined by the synchronous position detection signal of at least one beam in each group. Has been. In this embodiment, in order to lengthen the time for performing APC (auto power control), the number of groups is set to 4, and the number of beams for performing BD detection is reduced.

  FIG. 9 shows the relationship between the BD signal of group 1 and the scan start timing.

  In this embodiment, as described above, a beam for performing BD detection is selected in accordance with the sub-scanning position of the principal ray of the light beam reflected by the polygon deflection surface 6a, and the writing timing (writing position) is determined. . In the figure, “BD signal” indicates a signal (BD signal) generated when a beam enters the BD sensor. In the same figure, in group 1, the light beam from the light emitting point 14 crosses the BD slit in the main scanning direction, and the image signal is turned on for the beam 16 T1 seconds after the BD signal changes to the Lo state. Start writing. Similarly, the image signal of the beam 15 is turned on after T2 seconds, and an image is written. The beam 16 writes an image after t3 seconds. Similarly, at the timing of image writing for each group, BD signal detection is performed with beams having different positions in the main scanning direction so that light does not simultaneously enter the BD sensor. The write timing is determined by the beam 10 for the group 2, the beam 7 for the group 3, and the BD signal of the beam 1 for the group 4.

  The scanning optical system of this embodiment uses a two-dimensional array monolithic multi-beam laser (VCSEL) having N = 16 light emitting points as a light source means, and achieves high speed. Also, conditional expression to achieve high definition

Are grouped into four groups of light emitting elements according to the sub-scanning position of the deflecting / reflecting surface, and the maximum value of the beam distance between the sub-scanning ends of the group is 0.054 mm. Here, W is the distance between the sub-scanning beams of the light source, W = 0.121 mm, β is the sub-scanning lateral magnification of the incident optical system, and β = −2.22 times in this embodiment.
If this conditional expression is not satisfied, a deflector having a highly accurate reflecting surface is used, or a printing position accuracy defect occurs, and it becomes impossible to provide inexpensive and high-definition optical scanning.

  As described above, even when two-dimensionally arranged light sources are used, by grouping the beams according to the sub-scanning position on the deflection surface, it is possible to reduce image quality degradation due to surface accuracy error of the deflection reflection surface, at a low price. A high-definition optical scanning device can be provided. Further, when used in a color image forming apparatus, a high-definition color image apparatus without color misregistration can be provided.

  Moreover, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  This embodiment differs from the first embodiment in that a two-dimensional array monolithic 36-beam laser (VCSEL) is used as the light source and that the number of groups is 12 according to the surface accuracy of the deflection surface. Other configurations are the same as those of the second embodiment. The surface accuracy of the polygon mirror of this embodiment is such that the difference in inclination in the main scanning direction at a position 0.1 mm apart in the sub scanning direction is 0.05 minutes.

  Hereinafter, with reference to FIG. 10, the beam on the deflecting reflecting surface according to the second embodiment of the present invention will be described. In the figure, the horizontal axis represents the main scanning direction of the reflecting surface, and the vertical axis represents the sub-scanning direction. Further, the light emitting units 1 to 36 of the light source 1 form an image in the vicinity of the deflection reflection surface as a latent image that is long in the main scanning direction. In FIG. 10, the arrival position of the principal ray of each light beam is indicated by a circle and is two-dimensionally arranged at equal intervals in the sub-scanning direction. In the present embodiment, similar to the first embodiment, the principal ray of the light beam from the light emitting unit 1 is reflected on the deflecting reflection surface 6a by 0.628 mm above the sub scanning direction with respect to the light beam from the light emitting unit 16. As shown in FIG. 10, the beams 1 to 36 are divided into 12 groups according to the positions in the sub-scanning direction, and the writing timing is determined by the synchronous position detection signal of at least one beam in each group. Has been. In this embodiment, the beams are grouped so that the beam sub-scanning interval is 0.1 mm or less, and the sub-scanning beam groups are determined so that the resolution can be easily switched.

  FIG. 11 shows the relationship between the BD signal of group 12 and the scan start timing.

  In this embodiment, as described above, a beam for performing BD detection is selected in accordance with the sub-scanning position of the principal ray of the light beam reflected by the polygon deflection surface 6a, and the writing timing (writing position) is determined. . In the figure, “BD signal” indicates a signal (BD signal) generated when a beam enters the BD sensor. In the figure, in the group 12, the light beam from the light emitting point 34 crosses the BD slit in the main scanning direction, and the beam 36 turns on the image signal T32 seconds after the BD signal changes to the Lo state, and the image is turned on. Start writing. Similarly, the image signal of the beam 34 is turned ON after T34 seconds, and an image is written out. The beam 32 writes an image after t36 seconds.

  The beam which performs BD detection of each group of Drawing 12 is shown. As shown in the figure, at the image writing timing of each group, BD signal detection is performed with beams having different positions in the main scanning direction so that light does not simultaneously enter the BD sensor.

  In this embodiment, the group of light emitting points is determined so that the resolution can be easily switched between 1200 dpi and 600 dpi. Specifically, at 1200 dpi, latent images are formed using the beams of groups 1 to 12 (Gr1 to Gr12), and at 600 dpi, the odd groups (Gr1, Gr3, Gr5, Gr7, Gr9, Gr11) are formed. A latent image is formed using only the beam. Even in the configurations of the first and second embodiments, the resolution can be switched by thinning out the used beam, but it is necessary to perform BD detection with a beam that does not form a latent image, which is not good because the electric circuit becomes complicated and the cost increases.

  The scanning optical system of this embodiment uses a two-dimensional array monolithic multi-beam laser (VCSEL) having N = 36 light emitting points as the light source means, and achieves high speed. Also, conditional expression to achieve high definition

Are grouped into 12 groups of light emitting elements according to the sub-scanning position of the deflecting / reflecting surface, and the maximum value of the beam distance between the sub-scanning ends of each group is 0.084 mm. Here, W is the distance between the sub-scanning beams of the light source, W = 0.283 mm, β is the sub-scanning lateral magnification of the incident optical system, and β = −2.22 times in this embodiment. In the present embodiment, the maximum value of the writing position error in the main scanning direction (sub-scanning interval within the group of deflection surfaces × main scanning direction inclination difference of deflection surface per unit length × fθ coefficient) is 0.084 (mm). X 0.05 / 0.1 (min / mm) x 200 (mm / rad) x 2 = 0.0049 mm.

  If this conditional expression is not satisfied, a deflector having a highly accurate reflecting surface is used, or a printing position accuracy defect occurs, and it becomes impossible to provide inexpensive and high-definition optical scanning.

  As described above, by grouping the beams according to the sub-scanning position on the deflection surface, it is possible to reduce image quality deterioration due to surface accuracy error of the deflection reflection surface, and to switch the resolution using an inexpensive electric circuit. An optical scanning device can be provided. Further, when used in a color image forming apparatus, a high-definition color image apparatus without color misregistration can be provided.

  Moreover, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

[Image forming apparatus]
FIG. 13 is a cross-sectional view of the main part in the sub-scanning direction showing the embodiment of the image forming apparatus of the present invention. In FIG. 13, 60 is a color image forming apparatus, 11 is a scanning optical device having any one of the configurations shown in the first to third embodiments, 21, 22, 23, and 24 are photosensitive drums as image carriers, respectively. , 32, 33 and 34 are developing units, and 51 is a conveyor belt.

  In the figure, R (red), G (green), and B (blue) color signals are input to the color image forming apparatus 60 from an external device 52 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 53 in the apparatus. These image data are respectively input to the scanning optical device 11. From these scanning optical devices, light beams 41, 42, 43, and 44 modulated according to each image data are emitted, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are caused by these light beams. Scanned in the main scanning direction.

  The color image forming apparatus in this embodiment emits light corresponding to each color of C (cyan), M (magenta), Y (yellow), and B (black) from one scanning optical device (11). Image signals (image information) are recorded on the drums 21, 22, 23, and 24, and color images are printed at high speed.

  In the color image forming apparatus according to the present embodiment, as described above, one scanning optical device 11 uses the light beam based on each image data to convert the latent images of the respective colors onto the corresponding photosensitive drums 21, 22, 23, and 24. Is formed. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, for example, a color image reading apparatus including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

DESCRIPTION OF SYMBOLS 1 Light source means 2 Aperture stop 3 Condensing lens (collimator lens)
4 Cylindrical lens 5 Aperture stop LA First optical means (incident optical system)
6 Deflection means LB Imaging optical system 11a, 11b Imaging lens 7 Sync detection mirror 8 Sync detection lens 9 Sync signal detection means 12 Scanned surface (photosensitive drum surface)
LC second optical means (synchronous detection optical system)

Claims (6)

Light source means having N light emitting points, first optical means for converging a plurality of light beams from the light source means in the sub-scanning direction near the deflection surface of the deflection means, and a plurality of light beams deflected by the deflection means A second optical means for condensing the light on the surface to be scanned in a spot shape, and a writing position detecting means,
The interval between the light beams separated most in the sub-scanning direction on the deflection surface is 0.1 mm or more, and the light emitting points of the light source means emit M sets (M ≧ 2, M <N) according to the sub-scanning position. An optical scanning device characterized in that it is grouped into point groups, and the writing position of a plurality of light beams in each group is determined by at least one light beam in the group. The optical scanning apparatus according to claim 1, wherein the M groups satisfy the following conditions.
2. The optical scanning device according to claim 1, wherein the writing position determining beams of each group are separated in the main scanning direction.   The reflecting surface of the deflecting means has an inclination difference in the main scanning direction of not less than 0.05 minutes at a position 0.1 mm apart in the sub-scanning direction, and the number of groups M is set according to the inclination difference. The optical scanning device according to claim 2.   4. The optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and a static beam formed on the photosensitive member by a light beam scanned by the optical scanning device. 5. A developing device that develops an electrostatic latent image as a toner image, a transfer device that transfers the developed toner image onto a transfer material, and a fixing device that fixes the transferred toner image onto the transfer material. Image forming apparatus. The optical scanning device according to claim 1, and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device. An image forming apparatus.