JP5648488B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus that can reduce the cost of a light source and a control board by performing time-division scanning while reducing the size of the apparatus.

  In order to cope with the recent increase in the speed of laser printers and digital copying machines, there is an increasing demand for a multi-beam optical scanning device that scans a single photosensitive member with a plurality of beams. However, since the number of beams increases in the multi-beam method, the cost of the light source and the cost of a control board (ASIC: including an application specific integrated circuit) for driving the light source increase.

  In view of the above problems, a method has been proposed in which a plurality of different scanning surfaces are switched by scanning with a beam from a single light source.

  For example, the light from one light source is divided into q pieces, and the deflecting reflection surfaces are shifted from each other by a predetermined angle in the rotation direction, and the surface to be scanned is formed using a multi-faceted mirror type optical deflector stacked in q stages. There is an optical scanning device that sequentially switches and scans (see Patent Document 1). In addition, there is an optical scanning device that uses a pyramid mirror or a flat mirror to scan a surface to be scanned with different beams from a common light source (see Patent Document 2).

  By adopting these scanning methods, the number of light sources and the number of boards (driving ASICs) for driving the light sources can be reduced, and the cost can be reduced.

  However, the method of switching the surface to be scanned by time (hereinafter referred to as “time division method”) and the method of scanning one surface to be scanned by one conventional light source (hereinafter referred to as “conventional general method”). In comparison, there is a problem in achieving both high speed and downsizing. This problem will be described with reference to FIG.

  The conventional time division method shown in FIG. 11 (a) and the conventional general method shown in FIG. 11 (b) have the same productivity (number of output images per unit time). In the time-division method, two scanned surfaces are scanned with one light source, so that the time in the area other than the scanning region is shorter than that in the conventional method.

  In order to reduce the size of the optical scanning device, it is necessary to widen the angle of view of the scanning lens of the optical scanning device to shorten the focal length. However, if the angle of view is wide, the surface to be scanned is exposed. Since the time becomes longer, the time outside the scanning region in FIG. 11 is further shortened.

  When the time other than the scanning region is shortened, the control performed in the time other than the scanning region in order to make the light quantity of the light source constant, that is, the light source emits light and is detected by the photodetector (PD), The time required for the light amount control (APC) of the light source, which is performed so that the detection result is constant, is shortened.

  As described above, in the time division method, the time required for APC is shorter than that in the conventional general method. Therefore, in order to realize the downsizing of the optical scanning device in the time division method, the APC is effectively performed in a short time. Need to be implemented.

  The present invention has been made in view of the above problems, and adopts a time division method to reduce the light source cost and the drive board (ASIC) cost, and by effectively implementing APC in a short time, An object of the present invention is to provide an optical scanning device and an image forming apparatus capable of realizing a wide angle of view and downsizing of the apparatus.

  The present invention is an optical scanning device including a light source, a deflecting unit that deflects a light beam from the light source, and a scanning optical system that forms an image of the light beam deflected by the deflecting unit on a plurality of scanned surfaces. A plurality of scanned surfaces are scanned in a time-sharing manner with a light beam from a single light source, and the time intervals between the optical scans on the scanned surface are non-uniform, and the average value of each time interval The main feature is that light emission for light amount adjustment of the light source is performed in at least one of the sections provided with a longer time interval.

  The present invention also provides a developing unit that visualizes an electrostatic image formed on an image carrier using an optical scanning device with each color toner and each color image that is visualized on the image carrier. And a transfer unit that transfers to a transfer medium. The main feature is that the optical scanning device is an optical scanning device according to the present invention.

  According to the present invention, it is possible to provide an optical scanning apparatus and an image forming apparatus capable of reducing the size of the apparatus while reducing the cost required for the light source and the control board by performing time-division scanning.

It is the schematic which shows the Example of the optical scanning device based on this invention. It is a side view which shows a half mirror prism. It is the schematic which shows what used the light source as a 4ch-LD array in the optical scanning device of FIG. It is the timing chart which compared the scanning when the time interval between scanning is uniform, and when it is not uniform. 5 is a timing chart showing how APC and scanning are performed in the optical scanning device according to each embodiment of the present invention. It is a schematic diagram which shows a mode that a to-be-scanned surface is scanned with the light source of a 4ch-LD array. It is a graph which shows the phase difference and image area angle of view of a polygon mirror. It is a timing chart which shows a mode that APC and scanning are performed in the optical scanning device using a multi-beam light source. It is a timing chart which shows the mode of the scanning performed following the scanning shown in FIG. 1 is a schematic view showing an embodiment of a multicolor image forming apparatus according to the present invention. It is the timing chart which compared the scan by a time division system with the scan by a conventional system.

  FIG. 1 shows an embodiment of an optical scanning device according to the present invention. In the following embodiments, the main scanning direction indicates the direction scanned by the rotational movement of the deflecting means composed of a polygon mirror, or the direction corresponding thereto. The sub-scanning direction is a direction orthogonal to the main scanning direction and corresponding to the direction in which the photoconductor rotates.

  A divergent light beam emitted from a semiconductor laser (not shown) as a light source is converted into a weak convergent light beam, a parallel light beam, or a weak divergent light beam by a coupling lens (not shown). The light beam that has passed through the coupling lens passes through an aperture stop (not shown) for stabilizing the beam diameter on the surface to be scanned, and enters the half mirror prism 4. Since the light beam incident on the half mirror prism 4 is divided into two upper and lower stages, the light beam emitted from the half mirror prism 4 is two.

  FIG. 2 is a sub-scan sectional view of the half mirror prism 4. The half mirror prism 4 includes a half mirror 4a inclined at 45 ° with respect to the incident direction of the light beam, and a total reflection surface 4b arranged in parallel to the half mirror 4a. The half mirror 4a separates transmitted light and reflected light at a ratio of 1: 1. The total reflection surface 4b has a function of changing the direction of the light beam. Although the half mirror prism 4 is used in this embodiment, a similar system may be configured by combining a single half mirror and a normal mirror. However, the half mirror prism 4 is most suitable for the present invention because it has very little light loss. Further, the separation ratio of the half mirror 4a is not necessarily 1: 1, and the separation ratio may be set according to the conditions of other optical systems.

  The two light beams emitted from the half mirror prism 4 pass through the soundproof glass 6 and are guided to the deflecting means 7 while being converged only in the sub-scanning direction by the cylindrical lenses 5a and 5b respectively arranged in the upper and lower stages. In addition, a long line image is formed in the main scanning direction in the vicinity of the deflecting reflecting surface of the deflecting means 7.

  The deflecting means 7 is arranged with two polygon mirrors 7a and 7b stacked one above the other. The two polygon mirrors 7a and 7b are arranged such that the angle (phase) in the rotational direction is shifted by Δα °. In the present embodiment, the two polygon mirrors 7a and 7b each have an inscribed circle radius of 7 mm, have four reflecting surfaces, and are arranged with a shift of Δα ° = 46 °. The upper and lower polygon mirrors may be formed separately and assembled, or may be integrally formed.

  When the light beam deflected by one of the two polygon mirrors 7a and 7b scans the surface of the photoreceptor (scanned surface), the light beam deflected by the other mirror does not reach the scanned surface. It is like that. In this case, the light beam deflected by the other mirror may be shielded by the light shielding member.

  When the light source is modulated and driven, the light source is modulated and driven based on the image information of the color corresponding to each of the two polygon mirrors 7a and 7b. For example, when scanning the photoconductor corresponding to the upper polygon mirror 7a, the light source is modulated based on the image information of the corresponding color (for example, black). Further, when scanning the photoreceptor corresponding to the lower polygon mirror 7b, the light source is modulated based on the image information of the corresponding color (for example, magenta).

  The light beam deflected by the deflecting means 7 passes through the soundproof glass 6 and then is appropriately reflected by the reflecting mirror 9, and then passes through the first scanning lenses 8 a and 8 b and the second scanning lenses 10 a and 10 b, to be scanned surface 11 a, Head to 11b.

  The scanning optical system described above will be described in more detail with reference to FIG. In the embodiment shown in FIG. 4, the light beam emitted from the light source 15 is deflected by the polygon mirror 7 through the isolator 1, the coupling lens 2, the aperture 3, the half mirror prism 4, and the cylindrical lenses 5a and 5b. The light beam deflected by the polygon mirror 7 is guided to the surface to be scanned through the soundproof glass 6, the scanning lens 8a or 8b, and the dustproof glass 12. In FIG. 3, only one scanning lens (first scanning lenses 8a and 8b) is shown, and the second scanning lenses 10a and 10b are omitted.

  The light source 15 is a 4ch-LD array (having four light emitting points in one light source package and emitting four light beams). In FIG. 3, a light beam emitted from one of the four light emitting points is shown.

  An isolator 1 composed of a deflection plate and a λ / 4 plate is disposed between the light source 15 and a coupling lens 2 described later. When return light to the light source 15 is generated, laser oscillation becomes unstable, and the isolator 1 prevents this return light.

  The coupling lens 2 is a lens for making the light beam substantially parallel light.

  The aperture 3 is a plate-like member for shaping the light beam emitted from the coupling lens 2 into an arbitrary size, and an opening for allowing the light beam to pass therethrough is provided at the center.

  As described above, the half mirror prism 4 has the half mirror 4a and the total reflection surface 4b, and the light beam incident on the half mirror prism 4 is divided into two upper and lower stages (see FIG. 2).

  The light beam divided into the upper and lower stages by the half mirror prism 4 is guided to the cylindrical lenses 5a and 5b. The cylindrical lenses 5a and 5b have power in the sub-scanning direction, and the light beam that has passed through the cylindrical lenses 5a and 5b becomes a long light beam in the main scanning direction and is provided in the deflection means 7 through the soundproof glass 6. Heading to the polygon mirrors 7a and 7b.

  The soundproof glass 6 is a member that is fitted in a window hole provided in a housing (not shown) of the optical scanning device and reduces noise generated when the deflecting means 7 rotates, and the light flux can pass therethrough. It is a transparent plate-like glass. The soundproof glass 6 can be disposed at an arbitrary position between the scanning lenses 8a and 8b and the scanned surfaces 11a and 11b.

  The deflecting means 7 is a member for deflecting the incident light beam as described above, and the scanned surface is scanned by deflecting the light beam toward the scanned surfaces 11a and 11b. The light beam incident on the deflecting means 7 is elongated in the main scanning direction due to the power of the cylindrical lens.

  The light beam deflected by the deflecting means 7 travels to the scanned surfaces 11a and 11b, but passes through the soundproof glass 6 again in the middle and passes through the scanning lenses 8a and 8b.

  The scanning lenses 8a and 8b are lenses having power in the main scanning direction, and convert the luminous flux deflected at a constant angular velocity by the deflecting means 7 so that the linear velocity is constant on the scanned surfaces 11a and 11b. Therefore, the central portion in the main scanning direction has fθ characteristics.

  The light beam that has passed through the outer edge of the scanning lens passes through the synchronization lens 13 and is guided to the synchronization sensor 14 provided outside the image area on the upstream side of the scanning area. The optical scanning is started after a predetermined time with the light detection time by the synchronization sensor 14 as a reference. The outer edge portions of the scanning lenses 8a and 8b are regions where there is no power in the main scanning direction. This is because even if the scanning lenses 8a and 8b are expanded and contracted due to the influence of the environmental temperature, the change in the optical path of the light beam toward the synchronous sensor 14 can be suppressed.

  In this embodiment, the light beam traveling toward the synchronization sensor 14 passes through the outer edge portion having no power among the scanning lenses 8a and 8b. However, the present invention is not limited to this, and the scanning lenses 8a and 8b are not limited to this. It is good also as a structure which does not pass. Further, in addition to the synchronization sensor 14 on the upstream side of the scan, the synchronization sensor 14 is further arranged outside the image area on the downstream side of the scan, and the surface having power in the main scanning direction of the scanning lenses 8a and 8b is passed through the upstream side and You may comprise so that it may go to the synchronous sensor 14 of a downstream side.

  The dust-proof glass 12 is a transparent plate-like glass for preventing dust from entering the scanning optical system from the scanned surfaces 11a and 11b. The dustproof glass 12 can be disposed at an arbitrary position between the scanning lenses 8a and 8b and the scanned surfaces 11a and 11b.

  The optical scanning device described above will be described in more detail based on specific numerical values.

  In this embodiment, the light source 15 is a 4-channel LD array that emits a light beam having a wavelength of 655 nm, the interval between the light emitting points is 30 μm, the angle between the sub-scanning direction and the light emitting point arrangement direction is 86.114 °, and the light beam. The divergence angle (full width at half maximum) is 9 ° in the light emitting point arrangement direction and 18 ° in the direction orthogonal to the light emitting point arrangement direction.

  The coupling lens 2 is configured such that the focal length is 20 mm, and the light beam after passing through the coupling lens 2 becomes parallel light.

  The shape of the opening of the aperture 3 is rectangular, and the width in the main scanning direction is 3.74 mm and the width in the sub-scanning direction is 1.88 mm.

  In the deflecting means 7, polygon mirrors 7a and 7b having four deflection reflecting surfaces and an inscribed circle radius of 7 mm are stacked in two upper and lower stages, and the phase difference between the upper and lower stages is 46 ° (FIG. 1). reference). Further, the average incident angle (angle from the + direction of the X axis) of the light flux to the polygon mirrors 7a and 7b is 68 °.

  The cylindrical lenses 5a and 5b have a focal length of 47.75 mm.

  The image area of the optical scanning device is ± 163.5 mm.

Table 1 shows position data of each optical element in the optical scanning device. The position of each optical element is as shown in FIG.

Table 2 shows surface shape data of each optical element, and the surface shape of the scanning lens is as shown in Equation 1 and Equation 2. In Expressions 1 and 2, X indicates the optical axis direction, and Y indicates the main scanning direction. Cm0 represents the curvature in the main scanning direction at the center of the surface, and is the reciprocal of the curvature radius Rm0. a ₀₀ , a ₀₁ , a ₀₂ ... are aspherical coefficients of the main scanning shape. C _s (Y) is a curvature in the sub scanning direction with respect to Y, R _s0 is a curvature on the optical axis in the sub scanning direction, and b ₀₀ , b ₀₁ , b ₀₂ ... Are aspherical coefficients in the sub scanning direction. The scanning lens is made of resin.

(Formula 1)

(Formula 2)

The coupling lens 2 is formed of a glass mold, and the surface shape is a rotationally symmetric aspheric surface. The incident surface of the coupling lens 2 is a flat surface.

(Formula 3)

  The cylindrical lenses 5a and 5b are made of glass, the entrance surface has a curvature only in the sub-scanning direction, and the exit surface is a plane.

  According to the lens data in Tables 1 and 2, the angle of view corresponding to the image area ± 163.5 mm (the angle of the light beam immediately after being deflected by the deflecting means) is ± 38.57 °. The synchronous field angle is + 45 °. The reference for the angle of view is also the + direction of the X axis in FIG.

  An embodiment in which a plurality of scanned surfaces are scanned in a time division manner using one light source will be described with reference to FIG. FIG. 4 shows an example in which two scanned surfaces A1 and A2 are scanned in a time-sharing manner. (A) is an embodiment in which the time during which scanning is not performed is uniform, and (b) is a case where scanning is performed. The embodiment is shown in the case where the unoccupied time is non-uniform and the angle of view of the scanning lens is wider than (a). In the examples shown in FIGS. 4A and 4B, the same productivity, that is, the number of output sheets per time is the same.

  In the example shown in FIG. 4B, since the angle of view is wider than that in the example shown in FIG. 4A, the time for scanning the surface to be scanned is longer than in the example shown in FIG. In the example shown in FIG. 4B, the time during which scanning is not performed may be long or short. When it is long, it is the same as the time interval shown in the example of FIG. Thus, by making the time during which scanning is not performed non-uniform, it is possible to increase the angle of view of the scanning lens without shortening the time interval for scanning the surface to be scanned.

  APC is performed during the time when the surface to be scanned is not scanned. If the time during which scanning is not performed is shortened, the accuracy of APC may be reduced. When the time during which scanning is not performed is made uneven, APC is performed where the time during which scanning is not performed becomes long, so that a decrease in the accuracy of APC can be prevented.

  A timing chart of APC in the optical scanning apparatus according to the present embodiment will be described with reference to FIG. The optical system is assumed to be the optical system shown in FIG. Other conditions are as follows.

<Conditions>
Resolution: main scanning 1200 dpi × sub scanning 1200 dpi
-Image area: ± 163.5mm
-Process speed: 324 mm / s
-Number of beams: 4 (4ch-LD array)
・ 4-sided 2-step phase difference polygon: phase difference 46 °
-Synchronous angle of view: 43.5 °
-Angle of view of image area: 38.57 °

  The timing chart of FIG. 5 will be described. First, a beam is emitted immediately before the synchronization sensor (in FIG. 5, lighting is started before 3.44 μs of detection by the synchronization sensor).

  When light is detected by the synchronization sensor, the light is turned off. The light source is a 4ch-LDA, and light detection by the synchronization sensor is performed with a beam (referred to as ch1) that enters the synchronization sensor first.

  Then, after a certain time, writing of the image area starts. APC cannot be performed immediately after the image area is completed. First, as shown in FIG. 6, when a 4ch-LD array is used, optical scanning is performed with a shift in the main scanning direction. The beam pitch in the sub-scanning direction is set to have a desired resolution (21.2 μm at 1200 dpi). Therefore, even if ch1 of the 4ch-LD array ends the image area, it must wait until the image area of ch4 of the 4ch-LD array ends. In FIG. 5, this waiting time is described as “wait time until the end of the ch4 image area”.

  Furthermore, APC cannot be performed immediately after the ch4 image area is completed. This is because the photoconductor has a wider range than the image area, so that the light emitted during the APC operation reaches the photoconductor and forms an unnecessary image. In order to avoid this, APC is started after waiting for a region where light does not reach the photoconductor. In FIG. 5, this area is described as “invalid time after the end of the image area”. In the example shown in FIG. 5, APC is started after waiting for 6 mm light to travel on the image plane.

  After that, a time region from the start of light emission that can be detected by the next synchronous sensor is a time during which APC can be performed. In FIG. 6, of the times during which APC can be performed, a long time is described as “APC available time (long)”, and a short time is described as “APC available time (short)”. The APC may be performed in the section of “APC available time (long)” and not be executed in the “APC available time (short)”. By doing so, it is possible to prevent the APC accuracy from being lowered while widening the angle of view of the scanning lens. The APC is not limited to the above time, and can be performed at any time zone as long as the APC can be performed.

  A half mirror prism shown in FIGS. 1 and 2 is used as a method of scanning a plurality of scanned surfaces with a light beam from a single light source. After dividing the light into a plurality of lights, the divided light is incident on an optical deflector in which a polygon mirror having a phase difference in the rotation direction is stacked in a plurality of stages in the rotation axis direction. Can scan a plurality of scanned surfaces.

  In addition to the above, as described in Japanese Patent Application Laid-Open No. 2008-276075, it is also possible to scan different scanning surfaces in a time-division manner with a single light source using polygon mirrors having different angles. Furthermore, as described in Japanese Patent Application Laid-Open No. 2008-015210, it is possible to scan different scanning surfaces with a single light source in a time-sharing manner using a micromirror that can be displaced two-dimensionally.

  Of the methods of scanning a plurality of scanned surfaces with a light beam from a single light source, the most suitable for the present invention is an optical deflector in which polygon mirrors having a phase difference in the rotational direction are stacked in a plurality of stages in the rotational axis direction. It is a method using. Furthermore, it is preferable that the number of polygon mirrors is four and the number of polygon mirrors stacked is two.

  When the phase difference (angle difference) is 45 degrees in the two-stage polygon mirror, the distance between the scanned surface and the scanned surface becomes uniform. Therefore, it is preferable to slightly shift the phase difference in the rotation direction from 45 degrees.

  If the number of polygon mirrors is too large, it is suitable for high-speed scanning, but the angle of view that can be scanned by the polygon mirror becomes narrow, which is disadvantageous for miniaturization. For this reason, using four surfaces is slightly disadvantageous for speeding up scanning compared to six surfaces, but the angle of view that can be scanned by the polygon mirror and the angle of view of the scanning lens are improved, and time-division scanning is achieved. In this case, a wide angle of view of the scanning lens can be secured, which is advantageous for downsizing the optical scanning device.

  FIG. 7 shows the relationship between the phase difference of the polygon mirror and the image area angle of view (±). The table of FIG. 7 also shows the APC available time. The conditions at this time are as follows.

<Conditions>
Resolution: main scanning 1200 dpi × sub scanning 1200 dpi
-Image area: ± 163.5mm
-Process speed: 324 mm / s
-Number of beams: 4 (4ch-LD array)
・ Four-surface two-stage phase difference polygon ・ Synchronous angle of view is +5 degrees of image area angle of view (+ side)

  The time required for APC is about 5 μs. Therefore, in FIG. 7, the APC available time (long) needs to be at least 5 μs or longer, and the APC available time (short) needs to be at least 0 μs or longer. The image area angle of view at this time was calculated. When the APC available time (short) is shorter than 0, the system is not established.

  The horizontal axis in FIG. 7 is the phase difference of the polygon mirrors stacked in two stages in the rotation axis direction, and the vertical axis is the angle of view (±) of the image area. Here, the angle of view of the image area is an angle immediately after reflection of the polygon mirror of light traveling toward both ends of the image area (an angle from the + direction of the X axis). If the phase difference is 45 °, the distance between the scanned surface and the scanned surface becomes uniform. From FIG. 7, when the phase difference is larger than 46.7 °, the angle of view of the image area becomes smaller than when the phase difference is 45 ° (the interval between the scanned surface and the scanned surface is uniform). . Therefore, the phase difference Δα is preferably set to 45 ° <Δα <46.7 ° in order to increase the angle of view of the image area by making the distance between the scanned surface non-uniform. Further, when a four-sided polygon mirror is used, Δα = 46.7 ° and Δα = 43.3 ° are equivalent (because 90-46.7 = 43.3), so that 43.3 ° < Δα <45 ° may be set.

  When a multi-beam having a plurality of light emitting points is used as the light source, it is preferable to switch the beam for performing APC for each scan in the optical scanning device. By switching the beam for performing APC for each scan, the APC time can be shortened. As a result, the angle of view of the scanning lens can be widened, which contributes to downsizing of the optical scanning device. Of course, it is also possible to perform APC for all beams in one scan.

  When a multi-beam is used as a light source, the APC time can be set to be the shortest by making one beam for APC in one scan, and the optical scanning device is the smallest.

  When a multi-beam light source is used, APC is performed for only one beam per scan, and when switching the beam for which APC is performed for each scan, the timing for performing APC is based on the scan start position on the surface to be scanned. In view of this, it is preferable to set substantially the same timing for each scan. This is shown in FIGS.

  8 and 9, it is assumed that a 4ch-LD array is used as the light source. (A) is an explanatory diagram of a timing chart, and (b) to (e) are the first and second scans, respectively. 3 is a timing chart of the third scan and the fourth scan, and shows a timing chart of light emission of each channel. Synchronization detection is always performed using ch1.

  When the LD array is used, as shown in FIG. 6, since each ch is shifted in the scanning direction, the position of the image region is shifted for each ch. APC is performed for ch1 for the first scan of (b), ch2 for the second scan of (c), ch3 for the third scan of (d), and ch4 for the fourth scan of (d). Yes. The timing for performing APC for each channel is the same for all channel image areas. If the timing is not the same, it is necessary to take a long time to perform APC, the angle of view of the scanning lens becomes narrow, and the optical scanning device may be enlarged. As described above, by making the APC timing of each channel the same, the APC time can be set short and the angle of view of the scanning lens can be widened, so that the optical scanning device can be miniaturized.

  In a general optical scanning device, for example, as disclosed in Japanese Patent Application Laid-Open No. 2000-238315, a target value for carrying out APC is held by a capacitor. However, as described above, in an optical scanning device that uses a multi-beam light source and switches a beam for performing APC for each scan, the interval for performing APC for each beam becomes long. For this reason, the change in the voltage of the capacitor becomes large, and the APC accuracy may be lowered. In order to avoid this, it is preferable that a memory is provided and a target value for carrying out APC is held in the memory as digital data. By doing so, the time required for APC can be shortened, the optical scanning device can be miniaturized, and a decrease in the accuracy of APC can be suppressed.

  In the embodiment of the optical scanning apparatus described so far, as shown in FIG. 1, it is configured as if two scanned surfaces are scanned by two beams. A configuration in which an optical scanning device having the same design specifications as the optical scanning device described above is arranged symmetrically with respect to, for example, the deflecting means 7 and capable of forming a full-color image by scanning four scanned surfaces with four beams. It has become.

  FIG. 10 shows a basic configuration of the multicolor image forming apparatus. Reference numeral 20 in FIG. 10 indicates an optical scanning device according to the present invention as described above. In FIG. 10, photoconductors 1Y, 1M, 1C, and 1K rotate in the direction of the arrow, and around each photoconductor, chargers 2Y, 2M, 2C, and 2K, a developing device 4Y, 4M, 4C and 4K, transfer charging means 6Y, 6M, 6C and 6K, and cleaning means 5Y, 5M, 5C and 5K are provided.

  The charging members 2Y, 2M, 2C, and 2K are charging devices for uniformly charging the surface of the photoreceptor. The surface of the photoreceptors 1Y, 1M, 1C, and 1K between the chargers 2Y, 2M, 2C, and 2K and the developing units 4Y, 4M, 4C, and 4K is irradiated with a beam by the optical scanning device 20, and the photoreceptor is electrostatically charged. A latent image is formed. The electrostatic latent image is manifested as a toner image when toner as a developing member is supplied to the surface of the photoreceptor. Further, the toner images of the respective colors are sequentially transferred onto the recording paper 11 by the transfer charging units 6Y, 6M, 6C, and 6K, and finally the image is fixed on the recording test by the fixing unit 30.

  Although the multicolor image forming apparatus has been described as an example, the present invention can be applied to a single color image forming apparatus. Further, in order to obtain a multicolor image forming apparatus, the deflecting means provided in the above-described optical scanning device may be configured to have four stages of polygon mirrors.

  The APC described above is a time corresponding to a time during which no image is formed, that is, a time immediately before image formation, or between papers, that is, from the end of image formation on one recording paper to the start of image formation on the next recording paper. It is better to implement in the area. When the target value for performing APC is held in the memory as digital data, if APC is performed during image formation, the APC accuracy may be affected by noise. By performing APC in a time during which no image is formed, it is possible to avoid a decrease in APC accuracy. In addition, when APC is performed in a time during which an image is not formed, the APC interval becomes very long. However, if the target value for performing APC is held in the memory as digital data, even if the APC interval becomes long. APC accuracy is not reduced.

DESCRIPTION OF SYMBOLS 1 Isolator 2 Coupling lens 3 Aperture 4 Half mirror prism 4a Half mirror 4b Total reflection surface 5a, 5b Cylindrical lens 6 Soundproof glass 7 Deflection means 7a, 7b Polygon mirror 14 Synchronous sensor 15 Light source

Japanese Patent No. 4445234 Japanese Patent Laid-Open No. 2002-23085

Claims (12)

A light source;
Deflecting means for deflecting a light beam from the light source;
A scanning optical system that forms an image of the light beam deflected by the deflecting unit on a plurality of scanned surfaces;
An optical scanning device comprising:
A plurality of scanned surfaces are scanned in a time division manner with a light beam from a single light source,
The time interval between optical scans on the scanned surface is non-uniform,
The optical scanning device according to claim 1, wherein light emission for light amount adjustment of the light source is performed in at least one of intervals in which a time interval longer than an average value of the time intervals is provided.   The optical scanning device according to claim 1, wherein light emission for light amount adjustment of the light source is performed in a section where the longest time interval is provided among the time intervals.   The deflecting means comprises a polygon mirror having a plurality of mirror surfaces, the polygon mirrors are stacked in multiple stages in the direction of the rotation axis, and the polygon mirrors at each stage are out of phase with each other in the rotation direction. 2. The optical scanning device according to 2.   4. The optical scanning device according to claim 3, wherein the number of surfaces of the polygon mirror is four and is stacked in two stages in the rotation axis direction.   5. The optical scanning device according to claim 3, wherein the phase difference Δα of the phase is 43.3 ° <Δα <45 ° or 45 ° <Δα <46.7 °.   The optical scanning device according to claim 1, wherein the deflecting unit is a micromirror that can be displaced two-dimensionally.   8. The optical scanning device according to claim 1, wherein the light source is a multi-beam light source that emits a plurality of light beams, and emits light for adjusting the light amount for each scanning by the optical scanning device.   The optical scanning device according to claim 7, wherein the light emission for adjusting the light amount is performed by one light beam per adjustment.   The optical scanning device according to claim 7 or 8, wherein the light emission for adjusting the light amount is performed at the same timing for each light flux.   The optical scanning device according to claim 1, wherein the light intensity adjustment target value is held as digital data. Developing means for developing an electrostatic image formed on the image carrier using an optical scanning device with each color toner;
Transfer means for superimposing each color image visualized on the image carrier onto a transfer medium; and
A multicolor image forming apparatus comprising:
A multi-color image forming apparatus, wherein the optical scanning apparatus is the optical scanning apparatus according to claim 1.   The multi-color image forming apparatus according to claim 11, wherein the optical scanning device emits light for adjusting a light amount between sheets.

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