JP2011064765A - Light beam scanning optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a light beam scanning optical device that stably generates a synchronized signal in the main scanning direction even when an emitted light quantity of a light source is changed upon forming an image using multiple exposure by multibeam. <P>SOLUTION: In the light beam scanning optical device, an LD array has a plurality of light emitting points, and multiple exposure to the same position (same pixel) on the photoreceptor surface is performed by beams a and c and beams b and d emitted from the light emitting points to form an image. The light emitting points (beams a and c) and the light emitting points (beams b and d) exposing the same position are made into one set, and control to change the quantity of light to the light emitting points (beams c and d) is performed while the quantity of light to other light emitting points (beams a and b) stays constant. An SOS sensor is exposed by the beams a and b emitted from the light emitting points of which the quantity of light stays constant. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light beam scanning optical apparatus, and more particularly to a light beam scanning optical apparatus mounted on an electrophotographic image forming apparatus such as a copying machine or a printer.

  In recent years, in the field of this type of light beam scanning optical apparatus, a light source having a plurality of light emitting points that emit light at different positions in the sub-scanning direction, for example, VCSEL, in order to cope with higher speed and higher definition of image formation (Surface emitting semiconductor laser) is used. In the multi-beam method, multiple exposure of the same position on the surface to be scanned (photosensitive member) is performed with a light beam output from a plurality of light emitting points selected from a plurality of light emitting points of a light source, thereby forming an image with multiple gradations. There is known a light beam scanning optical apparatus that can perform the above-mentioned (see Patent Document 1).

  In Patent Document 2, when a synchronization signal is detected by scanning a light beam output from a plurality of light emitting elements arranged two-dimensionally, the positions along the scanning direction are arranged at substantially equal positions. The plurality of light emitting elements are grouped into a plurality of groups as light emitting element groups, and a light beam output from the plurality of light emitting elements in one light emitting element group of the plurality of groups is synchronized signal output means (light It is disclosed that each is turned on during a period across the light receiving surface of the sensor) to generate a synchronization signal.

  However, in the light beam scanning optical device described in Patent Document 2, since the synchronization signal is generated by scanning the optical sensor with a plurality of light beams, the main scanning positions of the plurality of light beams must be the same position. If the main scanning position is deviated, there is a problem that image deviation due to the deviation occurs. In addition, when the amount of emitted light is changed to cope with a change in scanning speed or a deterioration in the sensitivity of the photosensitive member, a stable synchronization signal cannot be obtained depending on the characteristics of the optical sensor, and jitter occurs in the synchronization signal. A point is generated.

JP 2002-264391 A JP 2002-131661 A

  Therefore, an object of the present invention is to stably generate a synchronization signal in the main scanning direction even when the amount of light emitted from a light source is changed when an image is formed by multiple exposure using multi-beams. It is an object of the present invention to provide a light beam scanning optical apparatus capable of avoiding the occurrence of image shift even if there is a shift in the main scanning position.

In order to achieve the above object, a light beam scanning optical apparatus according to the first aspect of the present invention is provided.
A light source having a plurality of light emitting points;
Driving means for driving the light source to emit light based on image data;
Scanning means for scanning a plurality of light beams output from the light source in one direction;
Synchronization signal output means for receiving a light beam scanned by the scanning means and outputting a synchronization signal;
With
In the light beam scanning optical device for forming an image by multiple exposure of the same position on the scanned surface with a light beam output from a plurality of light emitting points selected from a plurality of light emitting points of the light source,
A plurality of light emitting points that expose the same position are set as one set, and control is performed such that only a part of the light emitting points of the set of light emitting points has a variable light amount, and the other light emitting points have a constant light amount,
Exposing the synchronization signal output means with a light beam output from a light emitting point with a constant light amount;
It is characterized by.

  In the light beam scanning optical apparatus according to the first aspect, the synchronizing signal output means is provided by a light beam output from a light emitting point with a constant light quantity among a set of light emitting points that expose the same position on the surface to be scanned. Since the sync signal output means always receives a light beam in a constant state, a stable sync signal can be obtained even when the light quantity of the light emitting point is changed, and the main scanning direction Image shift can be accurately detected and image shift can be suppressed.

The light beam scanning optical device according to the second aspect of the present invention is
A light source having a plurality of light emitting points;
Driving means for driving the light source to emit light based on image data;
Scanning means for scanning a plurality of light beams output from the light source in one direction;
Synchronization signal output means for receiving a light beam scanned by the scanning means and outputting a synchronization signal;
With
In the light beam scanning optical device for forming an image by multiple exposure of the same position on the scanned surface with a light beam output from a plurality of light emitting points selected from a plurality of light emitting points of the light source,
The light amount variable range of the light emitting point that outputs the light beam that exposes the synchronization signal output means is limited to a range in which the light beam detection accuracy of the synchronization signal output means does not decrease below a certain value,
It is characterized by.

  In the light beam scanning optical apparatus according to the second embodiment, the light amount variable range of the light emitting point that outputs the light beam that exposes the synchronization signal output means does not lower the light beam detection accuracy of the synchronization signal output means below a certain value. Since the range is limited, the synchronization signal output means always generates a stable synchronization signal, and even when the light amount of the light emitting point is changed, a stable synchronization signal can be obtained, and the main scanning direction Image shift can be accurately detected and image shift can be suppressed.

  According to the present invention, when an image is formed by multiple exposure using multiple beams, a synchronization signal in the main scanning direction can be stably generated even when the amount of light emitted from the light source is changed. Even if the scanning position is deviated, it is possible to avoid the occurrence of image deviation.

1 is a schematic configuration diagram showing an image forming apparatus equipped with a light beam scanning optical device according to the present invention. It is a top view which shows the said light beam scanning optical apparatus. It is a block diagram which shows the control part of the said light beam scanning optical apparatus. It is explanatory drawing which shows arrangement | positioning of the light emission point in a light source, and the example of multiple exposure. It is explanatory drawing which shows the positional relationship of the light-receiving surface of a synchronizing signal detection sensor, and a light beam. It is a timing chart figure which shows the control example 1 of a light source. The light quantity in the control example 1 is shown, (A) is a graph showing the exposure amount on the photoreceptor, and (B) is a graph showing the exposure amount on the synchronization signal detection sensor. It is a timing chart figure which shows the control example 2 of a light source. It is explanatory drawing which shows the pattern for a resist correction. It is a chart figure which shows the output of a registration sensor. It is explanatory drawing which shows arrangement | positioning of the light emission point in a light source, and the multiple exposure example (control example 3). It is a chart figure which shows the output state of the synchronous signal in example 3 of control. The light quantity in the control example 4 of a light source is shown, (A) is a graph which shows the exposure amount on a photoconductor, (B) is a graph which shows the exposure amount on a synchronous signal detection sensor. The light quantity in the light source control example 5 is shown, (A) is a graph showing the exposure amount on the photoreceptor, and (B) is a graph showing the exposure amount on the synchronization signal detection sensor. It is a graph which shows the output characteristic with respect to the exposure amount of a synchronous signal detection sensor.

  Embodiments of a light beam scanning optical apparatus according to the present invention will be described below with reference to the accompanying drawings. In addition, in each figure, the code | symbol which shows the same member and part is used in common.

(Schematic configuration of image forming apparatus, see FIG. 1)
First, a schematic configuration of an image forming apparatus equipped with a light beam scanning optical apparatus according to the present invention will be described with reference to FIG. This image forming apparatus is an electrophotographic color printer and is configured to form images of four colors (Y: yellow, M: magenta, C: cyan, K: black) by a so-called tandem method. is there. An image is formed at each image forming station 101 and is combined on the intermediate transfer belt 112. In FIG. 1, the letters Y, M, C, and K attached to the reference numerals mean members for yellow, magenta, cyan, and black, respectively.

  The outline of each image forming station 101 includes a photosensitive drum 102, a light beam scanning optical apparatus 1, a developing device 104, and the like. The light beams BY, BM, BC, and BK emitted from the respective light beam scanning optical devices 1 irradiate the respective photosensitive drums 102 to form images of the respective colors. On the other hand, an intermediate transfer belt 112 is stretched endlessly by rollers 113, 114, and 115 immediately below the image forming station 101, is rotationally driven in the direction of arrow A, and is a portion where the driving roller 113 is installed. A secondary transfer roller 116 is disposed in a portion (secondary transfer portion) facing the belt 112. In addition, an automatic paper feeding unit 130 that feeds stacked sheets one by one is installed in the lower part of the image forming apparatus.

  The image data is transmitted to the storage means 31 (see FIG. 3) as image data for each YMCK from an image reading device (scanner) or a computer (not shown), and the light beam scanning optical device 1 is driven based on these image data. A toner image is formed on each photosensitive drum 102. Such an electrophotographic process is well known and will not be described.

  The toner images formed on the respective photosensitive drums 102 are sequentially primary-transferred by an electric field applied from the primary transfer charger 103 onto an intermediate transfer belt 112 that is rotationally driven in the direction of arrow A, and four-color images. Is synthesized. On the other hand, the sheets are fed one by one from the sheet feeding unit 130 and the composite image is secondarily transferred from the intermediate transfer belt 112 by an electric field applied from the transfer roller 116 in the secondary transfer unit. Thereafter, the sheet is conveyed to a fixing device (not shown), and the toner is heated and fixed, and is discharged to the upper surface of the image forming apparatus.

  A TOD sensor 106 for detecting the fed sheet is installed immediately before the secondary transfer unit, and the sheet and the image on the intermediate transfer belt 112 are synchronized. In addition, a registration sensor 105 is provided for detecting a registration correction toner pattern formed on the intermediate transfer belt 112. A toner pattern for resist correction is formed on the belt 112 for each image forming station 101, and the toner pattern is detected by the sensor 105, thereby adjusting the light emission timing of each light beam BY, BM, BC, BK. These images are accurately synthesized on the belt 112.

(Light beam scanning optical device, see FIG. 2)
Next, the light beam scanning optical apparatus 1 will be described. As shown in FIG. 2, each light beam scanning optical device 1 includes a light source unit and a scanning unit including a polygon mirror 4. The light source unit includes a semiconductor laser array 2 (hereinafter also referred to as an LD array), a collimator lens 3, and a slit plate 8. The scanning unit includes a synchronization signal detection sensor 5 (hereinafter also referred to as an SOS sensor) for outputting a main scanning synchronization signal (hereinafter also referred to as an SOS signal), scanning lenses 6a and 6b, and a folding mirror 7. ing. The polygon mirror 4 is rotationally driven at a predetermined speed based on a drive signal input to the drive unit 11 (see FIG. 3).

  As will be described below, the LD array 2 has four light emitting points that emit light at different positions in the sub-scanning direction Z. The light beam emitted from each light emitting point is converted into substantially parallel light by the collimator lens 3. Then, the light is deflected / scanned in the main scanning direction Y at a constant angular velocity on each reflecting surface of the polygon mirror 4, passes through the scanning lenses 6 a and 6 b, is reflected by the folding mirror 7, and forms an image on the photosensitive drum 102. A two-dimensional electrostatic latent image is formed on the photosensitive drum 102 by the main scanning in the Y direction and the sub scanning by the rotation of the photosensitive drum 102.

  The scanning lenses 6 a and 6 b have an fθ characteristic that corrects the light beam deflected / scanned at a constant angular velocity by the polygon mirror 4 to a constant velocity in the main scanning direction Y, and a result of focusing the light beam on the photosensitive drum 102. It has image characteristics.

  The SOS sensor 5 is disposed outside the image area, and a beam that has passed through the scanning lenses 6a and 6b and reflected by the folding mirror 7 is incident thereon. The SOS sensor 5 is used for detecting the scanning speed of the polygon mirror 4 and synchronizing the main scanning direction Y of each light beam.

(Refer to FIG. 3 for the control unit of the light beam scanning optical device)
Each light beam scanning optical apparatus 1 is controlled by the control unit shown in FIG. Image data Da to Dd corresponding to each of the four beams is supplied to the modulation circuits 35a to 35d. In the modulation circuits 35a to 35d, signals based on the image data Da to Dd and the data clocks DCKa to DCKd are generated. The signals output from the modulation circuits 35a to 35d are supplied to the light emitting points of the LD array 2 via the laser drive circuits 10a to 10d, and a light beam is output.

  The laser drive circuits 10a to 10d are individually driven by a control signal from the CPU 32 so as to be driven only in the horizontal and vertical effective periods. Further, the laser drive circuits 10a to 10d feed back the monitor detection value signal from the photodiode 12 that monitors the light amount output from each light emitting point of the LD array 2 so that the light amount emitted from each light emitting point becomes a predetermined value. The current supplied to each light emitting point of the LD array 2 is controlled.

  As described above, the light beam output from the LD array 2 is deflected by the polygon mirror 4 to scan / expose the photosensitive drum 102. Drawing with four beams by scanning one surface of the polygon mirror 4 is referred to as one scanning. The writing position of the deflected light beam in the main scanning direction Y is controlled based on the SOS signal detected by the synchronization signal detecting optical sensor (SOS sensor) 5 disposed on the leading end side of the scanning region. That is, the light beam detection signal of the SOS sensor 5 is supplied to the pixel clock generation circuit 34 via the CPU 32, and the image writing timing by each light emitting point of the LD array 2 is controlled. A crystal oscillator 33 is connected to the pixel clock generation circuit 34.

  The CPU 32 calculates the amount of misregistration in the main scanning direction and sub-scanning direction in the image of each color based on the misregistration signal of each color detected by the registration sensor 105 and the information stored in the storage unit 31. The output timing of the image data Da to Dd and the driving state of the LD array 2 are adjusted so as to correct the misalignment.

(Arrangement of luminous points, see FIGS. 4 and 5)
The LD array 2 is a multi-beam laser that simultaneously emits four light beams. As shown in FIG. 4, the light emitting points a to d are arranged obliquely so as to be in different positions with respect to the sub-scanning direction Z. Yes. The pitch z in the sub-scanning direction Z is determined by the image resolution. When the resolution is 600 dpi, the pitch z is 42.33 μm. The light emitting points a to d are arranged at a pitch y in the main scanning direction Y.

  As the polygon mirror 4 rotates, the photosensitive drum 102 is simultaneously scanned / exposed by the light beams a to d modulated based on the image data. As shown on the right side of FIG. 4, a multiple exposure method is employed in which exposure positions are overlapped for each scan. That is, the first scanning light beam c, the second scanning light beam a, the first scanning light beam d, and the second scanning light beam b expose the same position in the sub-scanning direction Z. By repeating such scanning sequentially, exposure is performed twice at the same position. The image data of the n-th scanning light beams c and d and the image data of the n + 1-th scanning light beams a and b are data relating to the same pixel.

  In this embodiment, the exposure amount is adjusted by making the light quantity of each light beam subjected to double exposure variable. When the light emitting points a and c and the light emitting points b and d that expose the same position are set as one set, control is performed so that one of the set of light emitting points can change the light amount, and the other is set to have a constant light amount. Then, the SOS sensor 5 is scanned / exposed with a light beam output from a light emitting point with a constant light amount. Specifically, the light emission points a and b are set to have a constant light amount, and the light emission points c and d are set to have a variable light amount. Further, the sum of the light amounts of the light emitting points a and c exposing the same pixel and the sum of the light amounts of the light emitting points b and d are controlled to be the same, and the light amount per pixel exposing the photosensitive drum 102 is constant. It is.

  FIG. 5 shows the positional relationship between the light receiving surface of the SOS sensor 5 and the light beams a to d. The light beams a to d that scan the light receiving surface of the sensor 5 have a pitch z in the sub-scanning direction Z and a pitch y in the main scanning direction Y, similarly to the light beams a to d shown in FIG. Yes. However, the pitches z and y of the light emitting points a to d in the LD array 2 are not necessarily the same as the pitches in the sub-scanning direction and the main scanning direction on the photosensitive drum 102.

(Refer to light emission control example 1, FIGS. 6 and 7)
When the SOS sensor 5 is scanned / exposed with the light beams a to d, the light beams a, b, c, and d are exposed in this order, and the sensor 5 outputs a main scanning direction synchronization signal. In synchronization with this synchronization signal, each light emitting point is subjected to modulation control based on image data, and image writing is performed. In the present embodiment, the light beams for outputting the synchronization signal are the light beams a and b having a constant light amount. Therefore, when the sensor 5 is exposed, the light emitting points c and d are turned off.

  The above control example 1 will be described with reference to FIG. The light emission points a to d emit light based on the forced light emission signals Ea to Ed and the image data Da to Dd, respectively. The forced light emission signals Ea to Ed cause the light emission points a to d to emit light independently outside the image area in the main scanning direction Y, and the light amounts thereof are monitored by the photodiode 12 and fed back to the laser drive circuits 10a to 10d. Stabilization is achieved. The forced light emission signals Ea and Eb for the light emission points a and b also serve as light emission signals for outputting a synchronization signal, and the light emission points a and b are caused to emit light at the timing of scanning / exposure of the SOS sensor 5.

  The synchronization signal (SOS signal) is output twice in one scan by exposure of the light beams a and b to the sensor 5. The light emitting points a and b are synchronized by the corresponding SOS signals, and image data Da and Db are output. The image data Dc and Dd are output by delaying the SOS signal by the light beam a or b for a predetermined time. As a result, an image is formed on the photosensitive drum 102.

  By the way, the exposure amount to the photosensitive drum 102 (the amount of light emitted from the LD array 2) is used to suppress changes in image density due to changes in resolution (main scanning speed), environmental changes, and changes in sensitivity of the photosensitive member over time. Variable. FIG. 7A shows the light amount at each of the light emitting points a to d when the light amount is varied in this way, and FIG. 7B shows the light amount on the light receiving surface of the SOS sensor 5.

  FIG. 7A shows the light amounts of the light beams a to d when the exposure amount of the photosensitive member is changed in increments of 20% within a range of 100 to 20%. Since the beams a and c and the beams b and d expose the same pixel, the total light amount of each of the beams a and c and the beams b and d becomes an exposure amount. In this control example 1, since the SOS sensor 5 is scanned / exposed with the beams a and b having a constant light amount, the exposure amount of the SOS sensor 5 corresponds to the light amounts of the beams a and b as shown in FIG. . Note that the photosensitive body exposure amount and the SOS exposure amount may differ depending on the transmittance and reflectance of the optical element disposed in the optical path, and the light amount of 50% in FIG. 7A and 50 in FIG. 7B. % Light quantity may not be the same value. The SOS sensor 5 is an area where the detection signal is stably output when the exposure amount is 50%.

  The combination of the light quantity of each light emission point a-d in this control example 1 is demonstrated concretely. When the photosensitive drum 102 is exposed at 100%, the light emitting points a to d are each output with a light amount of 50%. When the photosensitive drum 102 is exposed at 80%, the light emitting points a and b are output with a light amount of 50%, and the light emitting points c and d are output with a light amount of 30%. In these cases, the SOS exposure amount is a light amount of 50% by the beams a and b. When the photosensitive drum 102 is exposed at 60%, the light emitting points a and b are output with a light amount of 50%, and the light emitting points c and d are output with a light amount of 10%. In this case, the SOS exposure amount is 50% of the light amount by the beams a and b. When the photosensitive drum 102 is exposed at 40%, the light amounts of the beams a and b are set to 50%. However, the image data is turned off to turn off the light, and the light amounts of the beams c and d are set to 40%. To do. In this case, the SOS exposure amount is 50% of the light amount by the beams a and b. Further, when the photosensitive drum 102 is exposed at 20%, the light amounts of the beams a and b are set to 50%. However, the image data is turned off so that the light is not emitted, and the light amounts of the beams c and d are set to 20%. To do. In this case, the SOS exposure amount is 50% of the light amount by the beams a and b.

  As described above, in this control example 1, even when the exposure amount of the photosensitive drum 102 is varied, the SOS exposure amount is constant at 50%, and a stable synchronization signal can be obtained.

(Refer to light emission control example 2, FIG. 8)
In this control example 2, as shown in FIG. 8, the synchronization signal (SOS signal) is output only once by scanning / exposure of the light beam a in one scan. The image data Da is synchronized based on a single SOS signal, and the image data Db to Dd are output after a single SOS signal by the light beam a is delayed by a predetermined time. When the pitch y of the light emitting points a to d in the main scanning direction Y is narrow, the beams a and b can be scanned and exposed even when the light emitting points a and b are simultaneously emitted to scan / exposure the light as in Control Example 1. In some cases, the synchronization signal outputs by the two overlap, making it difficult to identify each synchronization signal. However, the synchronization signal can be output more stably by taking the synchronization signal by scanning / exposure with one beam a as in the present control example 2.

(Image registration adjustment, see FIGS. 9 and 10)
Here, the registration adjustment of an image formed on each photosensitive drum 102 will be described. FIG. 9 shows the relationship between the resist correction pattern Pa formed by multiple exposure of the same pixel on the intermediate transfer belt 112 with the light beams a to d, the resist correction pattern Pb formed by single exposure, and the registration sensor 105. Show. FIG. 10 shows the output of the registration sensor 105. The intervals L1 and L2 between the resist correction patterns Pa and Pb detected by the registration sensor 105 correspond to the output intervals t1 and t2 of the registration sensor 105. The amount of deviation between the exposed pattern Pa and the single-exposed pattern Pb can be detected.

  In this embodiment, as shown in FIG. 7A, when the exposure amount of the photosensitive drum 102 is high, an image is formed by multiple exposure, and when the exposure amount is low, the image is formed by one single exposure. Is formed. In the case of multiple exposure, in order to expose the same pixel with different beams, the SOS signal is delayed to synchronize the image writing start timing. However, in reality, variations and errors also occur in the delayed signal from the SOS signal, and it is difficult to expose the two beams completely at the same position. In order to expose the two beams completely at the same position, it is necessary to increase the accuracy of the component parts and the speed of the control signal, which greatly increases the cost.

  Therefore, a measurement unit (resist sensor 105) for detecting a relative position between the pattern Pa formed by multiple exposure and the pattern Pb formed by single exposure is provided, and multiple exposure is performed based on the numerical value detected by the measurement unit. The image writing timing is corrected when an image is formed by single exposure using the pattern Pa formed by the above as a reference. Thus, it is possible to avoid an image shift when the images of the respective colors are combined.

(Refer to light emission control example 3, FIGS. 11 and 12)
In the light emission control example 3 shown here, three or more light emission points are arranged linearly, and the light emission points arranged at both ends of the linear shape are controlled to have a constant light amount. Specifically, as shown in FIG. 11, the light emission points b and c are variable in light quantity, and the light emission points a and d disposed at both ends are controlled to be constant.

  In this control example 3, since the synchronization signal is output by scanning / exposure to the SOS sensor 5 by the light beams a and d at both ends, the interval between the two synchronization signals becomes relatively large and separation is easy. In addition, the image writing timing by the light beams b and c is generated by delaying the synchronization signal by the light beam a, but the delay amount is not constant due to variations in optical elements and displacement. Therefore, as shown in FIG. 12, the interval T1 of the synchronization signals by the light beams a and d is measured, and the intervals T2 are assigned assuming that the light emitting points a to d are arranged at equal intervals. Generate delay timing.

(Refer to Light emission control example 4, FIG. 13)
In this light emission control example 4, the light emission point that makes the exposure amount of the photosensitive drum 102 variable and the light emission point that makes the exposure variable can be changed, and the light emission point with a high light amount ratio without changing the exposure amount to the SOS sensor 5. The sync signal is obtained with a constant light quantity.

  Specifically, as shown in FIGS. 13A and 13B, when the photosensitive drum 102 is exposed at 100%, the light emitting points a to d are output with 50% of the light amount respectively, and the SOS sensor 5 is output. The beams a and b are subjected to scanning exposure. When the photosensitive drum 102 is exposed at 80%, the light emitting points a and b are output with a light amount of 50%, and the light emitting points c and d are output with a light amount of 30%. In this case, the light quantity ratio of the beams a and b is higher than the light quantity ratio of the beams c and d, and the SOS sensor 5 is subjected to the scanning exposure with the beams a and b, and the exposure amount is 50%. When the photosensitive drum 102 is exposed at 60%, the light emitting points a and b are output with a light amount of 50%, and the light emitting points c and d are output with a light amount of 10%. In this case, the light quantity ratio of the beams a and b is higher than the light quantity ratio of the beams c and d, and the SOS sensor 5 is subjected to the scanning exposure with the beams a and b, and the exposure amount is 50%. Further, when the photosensitive drum 102 is exposed at 40%, the beams a and b are output with a light amount of 40% and the beams c and d are set to 50%. To do. In this case, the light quantity ratio of the beams c and d is higher than the light quantity ratio of the beams a and b, and it is the 50% light quantity by the beams c and d that scans and exposes the SOS sensor 5. Further, when the photosensitive drum 102 is exposed at 20%, the beams a and b are output with a light amount of 20% and the beams c and d are 50%. To do. In this case, the light quantity ratio of the beams c and d is higher than the light quantity ratio of the beams a and b, and it is the 50% light quantity by the beams c and d that scans and exposes the SOS sensor 5.

  As described above, in this control example 3, even when the exposure amount of the photosensitive drum 102 is varied, the SOS exposure amount is constant at 50%, and a stable synchronization signal can be obtained. In this control example 3, the SOS sensor 5 may be exposed with any beam as long as the light amount ratio is 50%, or one beam may be used.

(Refer to Light emission control example 5, FIG. 14 and FIG. 15)
In this light emission control example 5, the light amount variable range of the light emitting point that outputs the light beam that exposes the SOS sensor 5 is limited to a range in which the light beam detection accuracy of the SOS sensor 5 does not decrease below a certain value. If the exposure amount to the SOS sensor 5 is too low or too high, the synchronization signal may not be stably output. However, if the exposure amount for the SOS sensor 5 is controlled within a range in which the detection accuracy does not decrease below a certain value, a stable synchronization signal can be obtained at all times. FIG. 15 shows temporal variations in which a synchronization signal is output with respect to the exposure amount of the SOS sensor 5. If the exposure amount of the SOS sensor 5 is 40 to 50% in terms of the light beam ratio, the variation of the synchronization signal can be suppressed to an extremely small range.

  Specifically, as shown in FIGS. 14A and 14B, when the photosensitive drum 102 is exposed at 100%, the light emitting points a to d are output with 50% of the light amount respectively, and the SOS sensor 5 is output. The scanning exposure is performed with the beams a and b with a light amount of 50%. When the photosensitive drum 102 is exposed at 80%, the light emission points a to d are output with a light amount of 40%, and the SOS sensor 5 is scanned and exposed with the beams a and b with a light amount of 40%. When the photosensitive drum 102 is exposed at 60%, the light emitting points a and b are output with a light amount of 40%, the light emitting points c and d are output with a light amount of 20%, and the SOS sensor 5 is scanned and exposed. Are beams a and b, and the amount of light is 40%. Further, when the photosensitive drum 102 is exposed at 40%, the beams a and b are output with a light amount of 40%, and the beams c and d are set to 0%, or the image data is turned off to turn off the image data. To do. In this case, the scanning exposure of the SOS sensor 5 is performed by the beams a and b with a light amount of 40%. Further, when the photosensitive drum 102 is exposed at 20%, the beams a and b are output with a light amount of 50%. However, the image data is turned off to turn off the light, and the beams c and d have a light amount of 20%. To output. In this case, the scanning exposure of the SOS sensor 5 is performed by the beams a and b with a light amount of 50%.

  As described above, in this control example 5, even if the exposure amount of the photosensitive drum 102 is varied, the SOS exposure amount is set to 40 to 50% at which a stable synchronization signal can be obtained. Also in this control example 5, as long as the light amount ratio is 40 to 50%, the SOS sensor 5 may be scanned / exposed with any beam. As shown in FIG. Also good. Further, as described with reference to FIGS. 9 and 10, image registration adjustment may be performed. Alternatively, as shown in FIG. 11, the light emitting points a and d arranged at both ends are controlled to a light amount ratio of 40 to 50% at which a stable synchronization signal can be obtained, and the light emitting points a and d are obtained. The SOS sensor 5 may be subjected to scanning exposure with the light beam output from. Furthermore, as shown in FIG. 13, the light emission point having a high light amount ratio is controlled to a light amount ratio of 40 to 50% at which a stable synchronization signal can be obtained, and the light beam output from the light emission point is changed. The SOS sensor 5 may be subjected to scanning exposure.

(Other examples)
The light beam scanning optical apparatus according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof.

  In particular, the plurality of light emitting points need not be formed in one LD array, and a single light emitting element may be assembled to serve as a light source. Further, the number of light emitting points included in the light source is not limited to four. Furthermore, the type and arrangement of optical elements for scanning / exposure the photoconductor and the synchronization detection sensor with a light beam are arbitrary.

  As described above, the present invention is useful for a light beam scanning optical apparatus, and particularly excellent in that a synchronization signal in the main scanning direction can be stably generated even when the amount of light emitted from the light source is changed. .

DESCRIPTION OF SYMBOLS 1 ... Optical beam scanning optical apparatus 2 ... LD array 4 ... Polygon mirror 5 ... Synchronous signal detection (SOS) sensor 10a-10d ... Laser drive circuit 32 ... CPU
102: Photosensitive drums a to d: Light emitting points (light beams)
Pa ... Multiple exposure image pattern Pb ... Single exposure image pattern

Claims (10)

A light source having a plurality of light emitting points;
Driving means for driving the light source to emit light based on image data;
Scanning means for scanning a plurality of light beams output from the light source in one direction;
Synchronization signal output means for receiving a light beam scanned by the scanning means and outputting a synchronization signal;
With
In the light beam scanning optical device for forming an image by multiple exposure of the same position on the scanned surface with a light beam output from a plurality of light emitting points selected from a plurality of light emitting points of the light source,
A plurality of light emitting points that expose the same position are set as one set, and control is performed such that only a part of the light emitting points of the set of light emitting points has a variable light amount, and the other light emitting points have a constant light amount,
Exposing the synchronization signal output means with a light beam output from a light emitting point with a constant light amount;
A light beam scanning optical device.   2. The light beam scanning optical apparatus according to claim 1, wherein the light beam for exposing the synchronization signal output means is output from one of a plurality of light emitting points. An image forming mode in which an image is formed by exposing the surface to be scanned only with a light beam output from a single light emitting point of the set of light emitting points;
Measuring means for detecting a relative position between an image pattern formed by multiple exposure using a light beam output from the set of light emitting points and an image pattern formed by the single exposure;
Changing the timing of writing an image for each scan from the output signal timing from the synchronization signal output means based on the numerical value detected by the measuring means;
The light beam scanning optical apparatus according to claim 1, wherein   The light source has three or more light emitting points arranged linearly, and the light emitting points arranged at both ends of the linear shape are controlled to have a constant light quantity. A light beam scanning optical apparatus according to any one of the above.   5. The light beam scanning optical apparatus according to claim 1, wherein a light emitting point having a high light amount ratio among the set of light emitting points is controlled to have a constant light amount. A light source having a plurality of light emitting points;
Driving means for driving the light source to emit light based on image data;
Scanning means for scanning a plurality of light beams output from the light source in one direction;
Synchronization signal output means for receiving a light beam scanned by the scanning means and outputting a synchronization signal;
With
In the light beam scanning optical device for forming an image by multiple exposure of the same position on the scanned surface with a light beam output from a plurality of light emitting points selected from a plurality of light emitting points of the light source,
The light amount variable range of the light emitting point that outputs the light beam that exposes the synchronization signal output means is limited to a range in which the light beam detection accuracy of the synchronization signal output means does not decrease below a certain value,
A light beam scanning optical device.   7. The light beam scanning optical apparatus according to claim 6, wherein the light beam for exposing the synchronizing signal output means is output from one of a plurality of light emitting points. It has an image forming mode in which an image is formed by exposing the surface to be scanned only with a light beam output from a single light emitting point,
A plurality of light emitting points that expose the same position as a set, and an image pattern formed by multiple exposure with a light beam output from the set of light emitting points and a relative image pattern formed by the single exposure A measuring means for detecting the position;
Changing the timing of writing an image for each scan from the output signal timing from the synchronization signal output means based on the numerical value detected by the measuring means;
The light beam scanning optical apparatus according to claim 6 or 7, characterized in that:   The light source has three or more light emitting points arranged in a straight line, and the light emitting points arranged at both ends of the linear shape have a variable light amount range, and the light beam detection accuracy of the synchronizing signal output means is less than a certain value. 9. The optical beam scanning optical apparatus according to claim 6, wherein the optical beam scanning optical apparatus is limited to a range that does not decrease.   The light emitting point having a high light amount ratio among the plurality of light emitting points is limited in a light amount variable range to a range in which the light beam detection accuracy of the synchronization signal output means does not decrease below a certain value. The light beam scanning optical apparatus according to claim 9.

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