JP2006035703A - Optical scanner and imaging device using optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner incorporating a synchronous detection device which not only can minimize a scan distance required for a non-image region but also can restrain a dispersion of an image data writing position, and an imaging device using the optical scanner. <P>SOLUTION: In this optical scanner, when the APC of a plurality of beams by a light source 66a is performed at the time of every scan, no synchronous detection of the beams is made immediately before starting the writing of image data, and the APC of an optical beam to be performed with an initial scan in a main scanning direction, among "n" pieces of the optical beam subjected to the APC at the time of some scan, is allowed to take place immediately after ending the writing of the image data. Further, the APC of the optical beam in the "n"th position is performed immediately before starting the writing of the following image data. At the same time, the synchronous detection of the optical beams is carried out using the optical beam which is in the position of an integer not less than n/2 and not in the "n"th position, and then the synchronous detection means 70 and a BD reflective mirror 69 are arranged in such a position where the center of an image region coincides with the center of a scan region. In addition, when the APC of all the optical beams is not performed at the time of every scan, the APC of the reference optical beam must be performed at the time of every scan and the synchronous detection of the optical beams must be carried out using the reference optical beam. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a laser beam printer and a facsimile, and an optical scanning apparatus having a light source that emits a multi-beam laser used in the image forming apparatus.

  In recent years, multi-beam lasers that emit a plurality of laser beams are often used as light sources as image forming apparatuses increase in speed and resolution. By using a multi-beam laser, a plurality of lines of images can be formed by a single scan. Therefore, when the number of rotations of the polygon mirror is the same, a latent image can be formed at a multiple speed.

  A semiconductor multi-beam laser used in an optical scanning device has one laser light monitoring photodiode for a plurality of light emission points (a plurality of light sources if each light emission point is an individual light source). Then, in order to stabilize the beam output during image formation, automatic light control (APC: Auto Power Control) for setting the laser light amount of each laser light source to a prescribed light amount is an image area (that is, main scanning) at every scanning. This is an effective area where an image can be formed in the line, and is also called a main scanning effective area. Since there is a single photo diode for monitoring, it is necessary for APC to individually apply a current to each laser light source, and other laser light sources must be turned off during the APC operation.

  Further, the optical scanning device has a horizontal synchronization detecting means for controlling the image writing position in the main scanning direction. Normally, horizontal synchronization detection is performed for each beam scanned on each surface by rotation of a polygon.

  When a multi-beam laser is used, a scanning delay time in the main scanning direction between each beam is measured in advance, and a horizontal synchronization signal detection of only a reference beam is performed during image formation (one-beam synchronization detection method) ) And a method in which horizontal synchronization signal detection is performed for each beam (all beam synchronization detection method).

  In the one-beam synchronous detection method, as shown in FIG. 10, a plurality of light emitting portions LD1 to LDn (n is an integer of 2 or more, 4 in FIG. 10) are sequentially subjected to APC, and then a reference beam (LD1) A method is described in which synchronization detection is performed by emitting light again to detect a synchronization signal. Similarly, FIG. 9 shows a state in which the LD11A and LD11B are caused to emit light sequentially, APC is performed, and then synchronization detection (BD forced lighting) is performed (for example, see Patent Documents 1 and 2).

  In addition, as shown in FIG. 11, a method of performing synchronization detection immediately after the end of the second APC after the first APC is performed (for example, see Patent Document 3).

  In any case, the APC is completed before the detection of the synchronization signal in order to prevent a synchronization detection error due to a variation in the amount of laser light upon detection of the synchronization signal.

  In the all-beam synchronization detection method, as shown in FIG. 12, when the first beam synchronization detection modulation signal is given, the optical sensor output is the first beam synchronization signal, the second beam synchronization detection modulation signal. Has been proposed in which signal processing is performed so that the output of the optical sensor becomes a synchronization signal of the second beam (see, for example, Patent Document 4).

  Further, in many optical scanning apparatuses, synchronization detection means such as an optical sensor are arranged in the apparatus for the purpose of configuring the adjustment work so as to be performed by the apparatus alone. At this time, a reflection mirror is provided for guiding a beam that forms an image near the surface of the photosensitive drum to the synchronization detection means in the apparatus.

  A form of a conventional optical system is shown in FIG. FIG. 13 is a schematic plan view of a conventional optical scanning device, and shows a development view of an OFS (Over Filled Scan) type optical system. In FIG. 13, reference numeral 66a denotes a light source device having at least two light emitting units. 66b is a collimator lens, 66c is a spherical lens, 66d is a stop, 66e is a cylindrical lens, 67 is a reflecting mirror, 62 is an fθ lens, and 63 is an anamorphic aspherical lens having power mainly in the sub-scanning direction. These optical elements are integrally supported by a case member (not shown) together with a driving device (not shown) that rotationally drives the polygon mirror 61, a folding mirror 64, and a dustproof glass 65.

  The light beam emitted from the light source device 66a is converted into near-parallel light by the collimator lens 66b, and weakly diverged light by the spherical lens 66c. After the light beam is restricted by the stop 66d, the light beam collected by the cylindrical lens 66e only in the sub-scanning direction and reflected by the reflection mirror 67 passes through the fθ lens 62 and is collected in the vicinity of the reflection surface of the polygon mirror 61. Lighted. The polygon mirror 61 rotates at a constant speed and deflects the light beam.

  Further, the deflected light beam is incident again on the fθ lens 62 having the fθ characteristic, and the light beam is condensed in the main scanning direction. Further, the light is condensed in the sub-scanning direction by the anamorphic aspherical lens 63 having power in the sub-scanning direction to form a spot on the photosensitive drum 31. The photosensitive drum 31 is rotated at a constant speed by a rotation mechanism (not shown).

Reference numeral 70 denotes horizontal synchronization detecting means, which is provided at a position where the light beam on the scanning start side _LBD of the light beam can be detected. In order to obtain a horizontal synchronization signal for adjusting the timing of the scanning start position on the surface of the photosensitive drum 31, the detection means 70 BD reflects a part of the light beam that has been deflected and reflected by the polygon mirror 61 and then passed through the fθ lens 62. The light is reflected by the reflection mirror 68 and received by the detection means 70. The BD reflection mirror 68 is positioned and supported by the BD mirror holder 69 while being abutted against the wall members 69a to 69c, and is attached to the case member.

  Further, an output signal from the detection means 69 is used by a light emission control circuit (not shown), and the light emission timing of a reference light beam is controlled among a plurality of light beams emitted from the light source device 66a in synchronization with the output signal. ing. For other light beams, the writing timing is determined by shifting the light emission timing with respect to the reference light beam by a time corresponding to the main scanning interval on the surface of the photosensitive drum.

Here, after the synchronization signal is detected, it is necessary to exceed the wall member 69b of the BD mirror holder in order for the entire light beam having a predetermined light beam width to reach the photosensitive drum surface. If the distance between the wall member 69b and the light beam Lf that is the image data writing start position is 2 mm in consideration of the design tolerance and safety factor, the synchronization detection position (the virtual position of the synchronization detection means when there is no reflection mirror is 70 ′, light The image data can be written only after the beam is scanned at a separation distance l _sp1 = 15 mm from L _BD ′).

Since the light beam of the APC light emission in that it is not desirable to reach the photosensitive drum, is provided in the vicinity of the dust-proof glass 65 light shielding member 71a is, for example, for shielding the APC light emission of LD1 to start position L _AS. A separation distance l _sp2 = 6 mm is secured on the surface of the photosensitive drum so that the APC emission is surely shielded and the light beam during image data writing with Lr as the final position is not shielded.

  Next, the positional relationship of the spots on the surface of the photosensitive drum when a semiconductor laser is used as the light source device will be described with reference to FIG. The semiconductor laser has two light sources, LD1 and LD2, and is arranged at equal intervals. At this time, the light emitting point interval is 100 μm.

  The optical system has a main scanning lateral magnification βm = 9.36 and a sub-scanning lateral magnification βs = 4.81, and in order to realize 600 dpi (1 line pitch = 42.3 μm), the sub-scanning interval at the light source position is 8 It is necessary to adjust to .79 μm (≈42.3 μm / 4.81). Since the sub-scanning pitch can be made variable by rotating the light source device around the optical axis, the semiconductor laser is tilted about 5.04 ° from the horizontal direction (the straight line connecting the light sources is parallel to the main scanning direction). realizable. The main scanning interval at the light source position is 99.6 μm, and the interval on the surface of the photosensitive drum is 0.93 mm (≈99.6 μm × 9.36).

Next, FIG. 15 shows the spatial positional relationship between LD1 and LD2 during the APC operation. In FIG. 15, the spot is scanned from the A position to the C position during the time when the LD 1 performs APC. At this time, the spot of LD2 is scanning from the B position to the D position, but the laser is extinguished. When APC of LD1 is finished and turned off, LD2 is turned on and APC is started. Here, during the time when the LD 2 performs APC, the spot scans from the D position to the F position. At this time, the LD1 spot is scanned from the C position to the E position, but the laser is extinguished. Here, when the scanning speed of the light beam is 2.5 × 10 ³ m / s and the time required for APC is 10 μs, the distance scanned between APCs is 25 mm, and the distance between LD1 and LD2 in the main scanning direction is 0. Since the distance is 93 mm, the distance l _APC scanned during APC emission is 49.07 mm.

  FIG. 16 shows a scanning distance required as a non-image area when APC and synchronization detection are performed using the methods of FIGS. 9 and 10, the all-beam extinguishing time is provided between the APCs of the respective beams. However, in FIG. 16, the all-beam extinguishing time is not considered as the shortest distance. The extinction of the last beam due to the end of APC and the start of lighting for synchronization signal detection are performed simultaneously, and the light emission time for synchronization detection is 1 μs. In the figure, the solid line portion is a lighting section, and the broken line portion is a light extinction section.

After the writing of the image data, APC of LD1 is started with a separation distance l _ap2 . At the same time as the APC of LD2 is completed, LD1 is turned on again for synchronization detection. Here, all the beams are turned off spatially during lm. _LBD is 2.5 mm.

When the synchronization detection is completed, the next image data writing is started with a separation distance l _sp1 . Therefore, the scanning distance necessary for the non-image area is l _sp2 + l _APC + lm + l _BD + l _sp1 = 73.5 mm.

Similarly, the scanning distance required as a non-image area when APC and synchronous detection are performed using the method of FIG. 11 in FIG. 17 is l _sp2 + l _APC + l _sp1 = 70.07 mm.
JP 2001-024273 A (FIG. 3) Japanese Patent Laid-Open No. 2002-086793 (FIG. 7) Japanese Patent Laying-Open No. 2001-088344 (FIG. 20) Japanese Patent No. 2965527 (FIG. 5)

However, the above-described technique has the following problems.
(1) When the reflection mirror is provided in the optical scanning device, it is arranged at a location close to the polygon mirror, unlike the case where it is arranged outside the device. In addition, the beam is not imaged at the position of the reflecting mirror, and has a predetermined width in the main scanning direction. Immediately after the synchronization detection is performed, all of the beams do not exceed the BD reflection mirror and image data cannot be written. Therefore, time and space are required from detection of the synchronization signal to writing of the image data. Therefore, as the scanning distance as the non-image area is increased, the image area is reduced.

  (2) Although it is possible to increase the image area by increasing the distance from the deflection surface of the polygon mirror to the photosensitive drum, the optical scanning device is increased in size by increasing the optical path length, or within the apparatus. As the number of mirrors that fold the light beam increases, there is concern about image unevenness due to vibration.

  (3) Further, when synchronization detection is performed after image data writing is completed using the deflection surface of the polygon mirror used for scanning for writing image data, adjacent deflection surfaces used for scanning for writing next image data The image writing position may vary depending on the angle error.

  (4) Further, the OFS optical system has a characteristic that the intensity of the light beam applied to the photosensitive drum surface varies depending on the scanning position depending on the deflection surface angle of the polygon mirror. When the light beam is irradiated toward the polygon from the optical axis direction, the intensity of the deflected and reflected light beam is the strongest at the optical axis position and decreases toward the end.

  The present invention has been made in view of the above conventional example. (1) A large image area can be secured by shortening the scanning distance as a non-image area without increasing the size of the apparatus, and (2) variation in image writing position. It is an object of the present invention to provide an optical scanning apparatus and an image forming apparatus capable of reliably generating a synchronization signal by performing synchronous detection with a sufficiently strong light beam without causing the above.

  In order to achieve the above object, the present invention has the following configuration. APC of a plurality of laser beams is performed before and after the detection of the horizontal synchronization signal, and the order of the APCs is determined with respect to the sequence of the laser beams scanned in the main scanning direction, whereby the time between the image area and the non-image area is determined. The spatial interval can be minimized, and the necessary image area can be obtained with the minimum scanning distance in the scanning optical system. In addition, when n (n: integer greater than or equal to 2) of the plurality of light beams deflected and scanned on one surface of the polygon mirror performs APC, it is an integer number greater than or equal to n / 2, and n The synchronization detection means is arranged at a position where the synchronization detection can be performed by a light beam that is not the second, so that the same deflection surface as that for writing the image data is used, the synchronization detection is performed before the image data writing, and the center of the image area is the scanning area. The synchronization detection means and the BD reflection mirror are arranged at a position that matches the center. Further, when not all APCs of a plurality of light beams are performed at every scanning, APC of a reference light beam is always performed at every scanning and synchronous detection is performed by the light beams.

  Alternatively, the present invention has the following configuration. A light source that emits a plurality of light beams, a deflecting unit that simultaneously deflects and scans the plurality of light beams, a scanning optical system that exposes and scans an object with the plurality of light beams, and a head position of an effective area of the exposure scanning. Synchronization detection means for detecting a reference horizontal synchronization signal using one of the plurality of light beams, and before and after detection of the horizontal synchronization signal by the synchronization detection means with reference to the end position of the effective area And a light amount correction means for correcting the light emission amount of each of the plurality of light beams.

  According to the present invention, when performing APC of a plurality of beams at every scanning, the scanning distance necessary for the non-image area can be minimized by not performing the synchronization detection immediately before starting the writing of the image data.

  Of the n light beams that perform APC during a certain scan, the APC of the light beam that scans first in the main scanning direction starts writing the next image data of the APC of the nth light beam immediately after the completion of writing the image data. By performing immediately before, it is possible to minimize the scanning distance that is turned on for APC, and at the same time, the synchronization detection means can detect synchronization by a light beam that is an integer number that is n / 2 or more and that is not nth. Can be used to detect the synchronization before writing the image data, using the same deflection surface as the image data writing, and the variation in the image data writing position is caused by the angle error between the deflection surfaces of the polygon mirror. Things disappear.

  Further, by arranging the synchronization detection means and the BD reflection mirror at a position where the center of the image area coincides with the optical axis, it is possible to minimize a decrease in intensity of the light beam at both ends of the image area. The unevenness of the inner light beam can be minimized.

  When not all APCs of a plurality of light beams are performed at every scanning, the APC of the reference light beam is always performed at each scanning and synchronous detection is performed by the light beam, so that the image data is detected from the synchronous detection every scanning. Since there is no need to correct the timing until the writing, the variation in the writing position of the image data does not occur.

  In addition, among the plurality of light beams, the light beam with the most advanced phase in the main scanning direction is adjusted first, the light beam with the most delayed phase is adjusted last, and the same surface area as the image area is scanned prior to scanning the effective area. The light beam deflected by the reflecting surface of the mirror and detected synchronously using a light beam other than the light beam with the most delayed phase, so that the light amount adjustment time and the separation distance to the effective area after synchronous detection Can be shortened. For this reason, the ratio of the area other than the effective area to the effective area can be reduced, and effects such as downsizing of the apparatus, speeding up of image formation, and improvement of image quality due to reduction of errors can be achieved.

[First Embodiment]
FIG. 1 is a schematic sectional view of a digital copying machine showing an example of an embodiment of the present invention. In FIG. 1, the A side of the original P set on the original platen glass 20 is read by the reading optical system 2 by the copy start command means and converted into an image signal. The image signal is taken into a digital processing unit (not shown) and converted into digital data, and then necessary data processing is performed and output to a video conversion unit (not shown) as image data. The video conversion unit converts the image data into a video signal by, for example, pulse width modulation, and the optical scanning device 6 outputs a modulated light beam such as turning on / off the light beam based on the video signal.

  The optical scanning device 6 includes a polygon mirror 61 serving as a light beam deflecting unit, a light source device (not shown), and an optical element, and outputs a light beam for forming a scanned image by a signal from a video conversion unit (not shown). After the output light beam is reflected by the folding mirror 64, the photosensitive drum 31 is irradiated through a dust-proof glass 65 for shielding the optical scanning device 6 from external dust and the like to form a latent image. The photosensitive drum 31 rotates, and the developing device 32 develops the latent image by attaching toner to the latent image portion.

  On the other hand, the transfer material S in the paper feed cassette 10 a or 10 b is taken into the apparatus one by one by the take-in roller 12 and conveyed to the photosensitive drum 31 through the registration roller 15. The developed image on the photosensitive drum 31 is transferred to the transferred transfer material S1 by the transfer unit 33. Thereafter, the transfer material S <b> 1 is transported by the transport unit 16 and reaches the fixing device 4. The fixing device 4 fixes the image transferred onto the transfer material. Then, the paper is discharged to a paper discharge tray 19 via paper discharge rollers 17 and 18. Further, the next transfer material S2 is similarly transported with an interval of L2 with respect to the transfer material S1, and after being subjected to an image forming process, it is discharged to the discharge tray 19.

  The toner remaining on the photosensitive drum 31 is removed by the cleaner 34. Further, the photosensitive drum 31 is neutralized by the static eliminator 35, charged by the charger 36, and then a latent image is formed on the photosensitive drum 31 again by the optical scanning device 6.

  In the image process as described above, the optical scanning device 6 of the digital copying machine of the present embodiment has the following configuration. FIG. 2 shows a timing chart of APC and synchronization detection of this embodiment.

  After LD1 and LD2 write image data based on the video signal, APC is started for LD1 that first scans in the main scanning direction at predetermined time intervals. A brief description of APC is as follows. During the APC period, for example, the LD emits light at full output. The amount of light is detected by a photodiode, and a bias current value to be input to the LD is determined at the maximum luminance point of the scanning in accordance with the detected amount of light. This current value is determined in advance according to the detected light amount so that the emitted light amount of the LD becomes the desired light amount. If this bias current value is determined, APC is completed.

  Almost simultaneously with the completion of APC, the light beam emitted from the LD 1 reaches the synchronization detecting means, and a horizontal synchronization signal is generated. By performing BD detection at the timing when APC is completed, BD detection can be performed with a stable light amount for each scan, and detection errors due to light amount fluctuations can be minimized.

When the horizontal synchronizing signal is detected, LD1 is turned off and LD2 is turned on. LD2 is turned off when APC is completed. An image area instruction signal is generated based on the horizontal synchronization signal, and LD1 and LD2 are turned on again to start writing image data. Here, LD1 starts writing simultaneously with the image area instruction signal, but LD2 starts writing with a delay of Td. When the distance between light spots on the surface of the photosensitive drum in the main scanning direction is lm = 0.93 mm, and the scanning speed of the light beam is 2.5 × 10 ³ m / s, Td≈0.37 μs.

  FIG. 3 is a schematic plan view of the optical scanning device of the present embodiment, showing an OFS type optical system. The folding mirror 64 is omitted. Moreover, what uses the same code | symbol as FIG. 13 has the same effect | action, and abbreviate | omits description.

Since the light beam of the APC light emission in that it is not desirable to reach the photosensitive drum, the light shielding member 71a for shielding the APC light emission of LD1 to start position L _AS is provided in the vicinity of the dust-proof glass 65. A separation distance l _sp2 = 6 mm is secured on the surface of the photosensitive drum so that the APC emission is surely shielded and the light beam during image data writing with Lr as the final position is not shielded. Shielding member 71b for blocking the APC light emission of LD2 to similarly end position L _AE is provided in the vicinity of the dust-proof glass 65. In addition, a separation distance l _sp2 = 6 mm is ensured between the light beam and the image data being written starting from Lf.

Next, FIG. 4 shows a scanning distance required as a non-image area when APC and synchronization detection are performed according to the timing chart shown in FIG. In the figure, the solid line portion is the lighting section, and the broken line portion is the unlit section. After the image data is written, APC of LD1 is started with a separation distance _lsp2 . Since the synchronization detection is completed at the end of APC of LD1, LD2 is turned on at the same time LD1 is turned off and APC is started. When the APC of LD2 is completed, image data is written again with a separation distance _lsp2 .

At this time, the distance from the synchronization detection position to the image data writing start position is larger than the separation distance _lsp1 in FIG. 13, and the light beam Lf has a sufficient gap with respect to the wall member 69b.

The scanning distance necessary for the non-image area is 2 × l _sp2 + l _APC = 61.7 mm, and the necessary scanning area can be shortened by about 10 mm compared to the conventional example.

  As described above, according to the configuration of the present embodiment, the scanning distance necessary for the non-image area can be shortened as compared with the conventional case, and the apparatus can be downsized and the error can be reduced. In addition, since the synchronization detection can be performed with the light beam after APC, it is possible to reduce the detection error due to the fluctuation of the light amount and generate a highly accurate synchronization signal. For this reason, the formed image quality is also improved.

[Second Embodiment]
FIG. 5 shows the positional relationship of spots on the surface of the photosensitive drum when the semiconductor laser according to the second embodiment is used. Except for the light source having four light emitting units, the configuration is the same as that shown in the first embodiment, and a description thereof will be omitted. The interval of the light beam on the photosensitive drum surface in the main scanning direction is lm = 0.93 mm, and the sub-scanning interval ls is 42.3 mm.

Here, the combination in which the distance l _APC scanned during APC emission is the shortest is the first APC of the light beam LD1 scanned first in the main scanning direction as shown in FIG. 6, and the light beam scanned last. This is the case where APC of LD4 is performed last, and l _APC = 97.21 mm. This is because the first scanned light beam, ie, a plurality of light beams, has the most advanced phase light beam first as the object of APC, and the last scanned light beam, ie, the plurality of light beams having the most phase. As long as the delayed light beam is finally subject to APC, the intermediate light beam can be changed by APC in the order shown in FIG. 6A or APC in the order shown in FIG. 6B. Absent.

  Based on FIG. 6A, the scanning distance required for the non-image area when APC and synchronous detection are performed in the non-image area, and the spot when scanning on the a-1st deflection surface of the polygon mirror FIG. 7 shows intensity fluctuations and spot intensity fluctuations when scanning on the a-th deflection surface. In the case of the OFS optical system, the width of the beam incident on the polygon mirror is wider than the width of the deflection surface of the polygon mirror, so that the beams reflected by the adjacent deflection surfaces are between the effective scanning areas of the fθ lens. Head to a different position.

Here, the scanning distance required for APC and synchronization detection is 2 × l _sp2 + l _APC = 2 × 6.00 + 97.21 = 109.21 mm. The synchronization detection is performed by any of LD1 to LD3, so that the shortest state of the non-image area does not change (the LD4 is not used for synchronization detection because the separation distance to the head of the image area is shortened when the synchronization detection is performed by the LD4). . However, since the APC end position of LD1 is not within the effective scanning area of the fθ lens for scanning with the a-th deflection surface, it is necessary to perform synchronization detection after the image data is written by the (a-1) -th deflection surface. is there. With this configuration, synchronous detection is performed with the light beam obtained by reflection from the (a-1) th deflection surface (point x0 in FIG. 7), and image data is written on the ath deflection surface. For this reason, there is a concern that the image writing position varies due to the angle error between the deflection surfaces. Therefore, LD1 is not used for synchronization detection, but synchronization detection is performed using LD2 or LD3.

  When the synchronization detection is performed by the LD2, the intensity of the light beam entering the synchronization detection means is weaker than that of the LD3 by the angle of the a-th deflection surface. Referring to FIG. 7, synchronization detection using LD2 is performed at point x1, and synchronization detection using LD3 is performed at point x2. As shown, the intensity of the light beam at point x3 is higher. When synchronous detection is performed with a weak light beam, the image writing position may vary due to the problem of the S / N ratio of the detection signal. Therefore, it is more desirable to perform synchronous detection with a stronger LD 3, that is, a light beam that performs n−1th APC.

  As described above, according to the present embodiment, when APC of a plurality of beams is performed at every scanning, the synchronization detection is performed using the light beam other than the light beam with the most delayed phase, thereby the non-image region. The scanning distance required for the operation can be minimized. Further, the APC of the light beam having the most advanced phase is performed immediately after the completion of the writing of the image data, and the APC of the light beam having the most delayed phase is performed immediately before the start of the writing of the next image data. The scanning distance can be minimized. Furthermore, by performing synchronous detection with a light beam deflected on the same deflection surface as that for writing image data, there is no occurrence of variations in the image data writing position due to an angle error between the deflection surfaces of the polygon mirror.

[Third Embodiment]
FIG. 8 shows a timing chart in the case where not all APCs are performed at every scanning using the semiconductor laser according to the second embodiment. When the scanning speed is increased, the time for scanning by one deflection surface is shortened, so that the fluctuation of the laser power is also reduced, and it is not necessary to perform APC for all the light sources for each scanning. The present embodiment can be applied to an image commissioning apparatus having such a configuration.

  After the light sources LD1 to LD4 output a light beam modulated by a video signal based on image data, APC is started for LD1 that first scans in the main scanning direction at predetermined time intervals. Nearly simultaneously with the completion of APC, the light beam emitted from the LD 1 reaches the synchronization detecting means and detects the horizontal synchronization signal. By performing BD detection at the timing when APC is completed, BD detection can be performed with a stable light amount for each scan, and detection errors due to light amount fluctuations can be minimized.

When a horizontal synchronizing signal is detected, LD1 is turned off and LD2 is turned on for APC. LD2 is turned off when APC is completed. An image area instruction signal is generated based on the horizontal synchronization signal, and LD1 to LD4 again output a light beam modulated by a video signal based on the image data, and start scanning the photosensitive member. Here, LD1 is turned on simultaneously with the image area instruction signal, but LD2 is turned on with a delay of Td, LD3 is turned on by 2Td, and LD4 is turned on with a delay of 3Td, and scanning based on the image data is started. When the light spot interval in the main scanning direction on the surface of the photosensitive drum is lm = 0.93 mm, and the scanning speed of the light beam is 2.5 × 10 ³ m / s, Td≈0.37 μs.

  After scanning with each light beam (image formation), APC of LD1 and LD3 is performed. Further, APC of LD1 and LD4 is performed in the next scanning. This is repeated thereafter. That is, APC is performed for each scan for LD1, but APC is performed for every two scans in this order for LD2, 3 and 4.

  Here, the reference beam (LD1 in this embodiment) is always used for synchronization detection and APC. By making the light beam for synchronization detection constant, the time Ta from the synchronization signal detection to the generation of the image area instruction signal can be made constant. Therefore, it is possible to obtain an optical scanning device with no variation in the image data writing position with a simple algorithm.

  In addition, according to the present embodiment, when performing APC of a plurality of beams at every scanning, synchronization detection is performed using a light beam other than the light beam with the most delayed phase, which is necessary for the non-image region. The scanning distance can be minimized, the APC of the light beam having the most advanced phase is performed immediately after the completion of the writing of the image data, and the APC of the light beam having the most delayed phase is performed immediately before the start of the writing of the next image data. The scanning distance for lighting can be minimized, and by performing synchronous detection with the light beam deflected on the same deflection surface as the image data writing, the image is caused by the angle error between the deflection surfaces of the polygon mirror. The same effect as in the other embodiments that the variation in the data writing position is not generated is also achieved.

1 is a cross-sectional view of an image forming apparatus according to an embodiment. It is a figure which shows APC of the laser beam of 1st Embodiment, and the timing of a synchronous signal detection. It is a top view of the optical scanning unit of an embodiment. It is a figure which shows the positional relationship about APC of the laser beam of 1st Embodiment, and the main scanning direction of a synchronous signal detection. It is a figure which shows the positional relationship on the photoconductor of the four light beams in 2nd Embodiment. It is a figure which shows the positional relationship about the main scanning direction of APC of a laser beam and synchronous signal detection of 2nd Embodiment. It is a figure which shows the positional relationship about the main scanning direction of APC of a laser beam and synchronous signal detection of 2nd Embodiment, and the light quantity of 2 continuous scanning areas. It is a figure which shows APC of the laser beam of 3rd Embodiment, and the timing of a synchronous signal detection. It is a figure which shows the timing of APC of the conventional laser beam, and a synchronous signal detection. It is a figure which shows the timing of APC of the conventional laser beam, and a synchronous signal detection. It is a figure which shows the timing of APC of the conventional laser beam, and a synchronous signal detection. It is a figure which shows the timing of APC of the conventional laser beam, and a synchronous signal detection. It is a top view of the conventional optical scanning unit. It is a figure which shows the positional relationship on the photoconductor of two light beams. It is a figure which shows the positional relationship about APC of the conventional laser beam, and the main scanning direction of a synchronous signal detection. It is a figure which shows the positional relationship about APC of the conventional laser beam, and the main scanning direction of a synchronous signal detection. It is a figure which shows the positional relationship about APC of the conventional laser beam, and the main scanning direction of a synchronous signal detection.

Claims (7)

A light source that emits multiple light beams;
Deflection means for simultaneously deflecting and scanning the plurality of light beams;
A scanning optical system for exposing and scanning an object with the plurality of light beams;
Synchronization detecting means for detecting a horizontal synchronization signal that serves as a reference of the head position of the effective area of the exposure scan using one of the plurality of light beams;
An optical scanning device comprising: a light amount correction unit that corrects the light emission amount of each of the plurality of light beams before and after detection of a horizontal synchronization signal by the synchronization detection unit with reference to the end position of the effective region. .   The deflecting unit has a rotating polygon mirror formed by a plurality of deflecting surfaces, and the deflection surface angle of the deflecting unit at the end of light amount correction by the light amount correcting unit immediately before the head position of the effective area, and the effective surface The deflection surface angle at the start of light amount correction by the light amount correction means after the end position of the region is substantially the same with reference to the deflection surface angle when scanning the central portion of the effective region with a light beam, When there are n light beams whose light amount is to be corrected in one scan among the plurality of light beams, the light that is scanned first in the main scanning direction among the light beams that are subject to light amount correction The amount of light correction of the beam is performed immediately after the end of the effective region and the amount of light of the n-th scanned light beam is corrected immediately before the effective region, and the horizontal synchronization signal detection is an integer number equal to or greater than n / 2. nth The optical scanning device according to claim 1, characterized in that with no light beam.   Of the plurality of light beams, when the number of light beams to be subjected to light amount correction in one scan by the light amount correction means includes n light beams that are first scanned in the main scan direction, the main scan direction The light amount correction of the light beam scanned first is performed at every scanning and the horizontal synchronization signal detection by the synchronization detecting means is performed together, and the light beam scanned n-th among the light beams to be subjected to light amount correction. The optical scanning device according to claim 1, wherein the light amount correction is performed immediately before the effective area.   2. The optical scanning according to claim 1, wherein the synchronization detection unit includes an optical sensor that detects a light beam, and a reflection unit that reflects at least one of the plurality of light beams toward the optical sensor. apparatus.   The plurality of light beams are out of phase with each other in the main scanning direction, and the light amount correction means has the most advanced phase among the light beams to be subjected to light amount correction during a period not corresponding to the main scanning effective region. 2. The optical scanning device according to claim 1, wherein the light amount of the light beam is first corrected, and the light beam whose phase is most delayed is corrected last.   The deflecting means has a rotating polygon mirror, and the synchronization detecting means is emitted for correcting the light amount and deflects a light beam to scan the effective area prior to scanning the effective area. 6. The horizontal synchronizing signal is detected by using a light beam deflected by the same reflecting surface as the reflecting surface of the polygonal mirror other than the light beam having the most delayed phase. The optical scanning device according to 1. An optical scanning device according to any one of claims 1 to 6,
Modulation means for modulating a light beam emitted from the optical scanning device based on an image signal;
An image forming apparatus comprising: an image forming unit that develops a latent image formed on a photosensitive member that is an object of exposure scanning by the optical scanning device to form an image on a medium.

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