JP2011064947A - Light beam scanning optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light beam scanning optical device restraining a synchronizing signal of the main scanning direction from shifting to generate jitter when the image is formed by multiple exposure by multiple beams. <P>SOLUTION: In this light beam scanning optical device, an LD array has a plurality of light emitting points, the same position on a photoreceptor surface (same pixel) is multiply-exposed with beams a and c, and beams b and d, outputted from the light emitting points, thereby forming an image. The light emitting points (beams a and c) and the light emitting points(beams b and d) for exposing the same position are set as one group, a synchronizing signal corresponding to each group is generated by scanning and exposing an SOS sensor 5 with the beams output from the light emitting points of each group, and the light emission timing of the plurality of light emitting points is controlled based on the synchronizing signal corresponding to each group. <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. Since the amount of light emitted from the VCSEL is small, the amount of light that exposes the photoconductor cannot be secured by only one beam, and the same position (same on the surface of the photoconductor) with light beams output from a plurality of light emitting points selected from a plurality of light emitting points Multiple exposure). In such a multi-beam method, there is a problem of how to generate a synchronization signal in the main scanning direction when modulation control of each light emitting point is performed.

  Patent Document 1 describes a configuration in which a synchronization signal in the main scanning direction is generated using one of the multiple beams. Patent Document 2 describes a configuration in which a synchronization signal is generated using all of the multi-beams. Patent Document 3 describes a configuration in which a plurality of light emitting points juxtaposed in the sub-scanning direction is set as a set, and a synchronization signal is generated using a beam output from the set of light emitting points.

  However, the configuration described in Patent Document 1 has a problem that the beam interval error of multi-beams becomes a shift of the synchronization signal and appears as jitter in the image. In the configuration described in Patent Document 2, it is necessary to control the image writing start position for each beam. The configuration described in Patent Document 3 has a problem in that when the main scanning positions of a plurality of light beams are shifted during multiple exposure, the shift appears as jitter in the image.

JP-A-63-163871 Japanese Examined Patent Publication No. 3-57453 JP 2002-131661 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a light beam scanning optical device capable of suppressing the occurrence of jitter in an image due to a shift of a synchronization signal in the main scanning direction when an image is formed by multiple exposure using multiple beams. is there.

In order to achieve the above object, a light beam scanning optical device according to an aspect of the present invention includes:
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,
Corresponding to each set by forming a plurality of sets with a plurality of light emitting points that expose the same position as one set, and by scanning exposure of the synchronization signal output means with the light beam output from each set of light emitting points Generated synchronization signal,
Controlling the light emission timing of the plurality of light emission points based on a synchronization signal corresponding to each of the sets,
It is characterized by.

  In the light beam scanning optical device, a plurality of light emitting points that expose the same position on the surface to be scanned are formed as a set, and a plurality of light beams are output from each set of light emitting points. By scanning exposure means, a synchronization signal corresponding to each set is generated, so that the position of the light beam output from each light emitting point in the main scanning direction can be detected accurately, that is, the output of the synchronization signal. Accuracy can be improved and jitter can be prevented from occurring in the image.

  According to the present invention, when an image is formed by multi-exposure by a multi-beam, it is possible to suppress the occurrence of jitter in the image due to the synchronization signal in the main scanning direction being shifted.

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 perspective view which shows the said light beam scanning optical apparatus. It is explanatory drawing which shows arrangement | positioning of each light beam output from the light source. It is explanatory drawing which shows multiple exposure. It is explanatory drawing which shows the positional relationship of the light beam in the synchronous signal output example 1, and the light-receiving surface of a synchronous signal detection sensor. It is a block diagram which shows the circuit of the synchronous signal detection sensor in the synchronous signal output example 1. It is a chart figure which shows the output of the synchronous signal detection sensor in the synchronous signal output example 1. It is explanatory drawing which shows the positional relationship of the light beam in the synchronizing signal output example 2, and the light-receiving surface of a synchronizing signal detection sensor. It is a block diagram which shows the circuit of the synchronous signal detection sensor in the synchronous signal output example 2. It is a chart figure which shows the output of the synchronous signal detection sensor in the synchronous signal output example 2. It is a block diagram which shows the control part in the synchronizing signal output examples 1 and 2. It is a timing chart figure of control in synchronous signal output examples 1 and 2. It is explanatory drawing which shows the positional relationship of the light beam in a comparative example, and the light-receiving surface of a synchronous signal detection sensor. It is a chart figure which shows the output of the synchronous signal detection sensor in a comparative example. It is a chart figure which shows the output of the synchronous signal detection sensor in the synchronous signal output example 3. It is a block diagram which shows the control part in the synchronous signal output example 3. It is a timing chart figure of control in example 3 of a synchronous signal output.

  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.

  Image data is transmitted as image data for each YMCK from an image reading device (scanner) or a computer (not shown) to the controller 501 (see FIG. 11), and the drive unit 511 is driven based on these image data, and each photoconductor. A toner image is formed on the 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, a beam separation prism 9, and a cylindrical lens 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), an fθ lens 6a, a cylindrical lens 6b, and a folding mirror (not shown). It consists of and. The polygon mirror 4 is driven to rotate at a predetermined speed.

  As will be described below, the LD array 2 has four light emitting points that emit light at different positions in the main scanning direction Y and the sub-scanning direction Z. The light beam emitted from each light emitting point is a collimator lens 3. Is made into substantially parallel light, enters the cylindrical lens 8 via the beam separation prism 9, is converged linearly in the sub-scanning direction Z, and is guided to the polygon mirror 4. These light beams are deflected / scanned in the main scanning direction Y at equal angular speeds on the respective reflecting surfaces of the polygon mirror 4, pass through the lenses 6 a and 6 b, and form 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.

  Further, a part of the light beam output from each light emitting point of the LD array 2 is incident on the photodiode 12 from the prism 9, the light amount is monitored, and the LD array is set so that the light amount emitted from each light emitting point becomes a predetermined value. The current supplied to each light emitting point 2 is controlled.

  The fθ lens 6 a and the cylindrical lens 6 b are formed on the photosensitive drum 102 with an fθ characteristic that corrects the light beam deflected / scanned at a constant angular velocity by the polygon mirror 4 at a constant velocity in the main scanning direction Y, and the light beam. It has the imaging characteristics to make.

  The SOS sensor 5 is disposed outside the image area, and a beam that has passed through the lenses 6a and 6b and reflected by the folding mirror 7 is incident thereon. The SOS sensor 5 is used to detect the scanning speed of the polygon mirror 4 and synchronize the main scanning direction Y of each light beam as will be described in detail below.

(Arrangement of light emitting points and multiple exposure, see FIGS. 3 and 4)
The LD array 2 is a multi-beam laser that simultaneously emits four light beams, and the light emission points a to d are arranged so that the light beams output from the light emitting points a to d are in the positional relationship shown in FIG. Has been placed. FIG. 3 shows the imaging positions of the light beams a to d on the photosensitive drum 102 when the polygon mirror 4 is stationary.

  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. In this embodiment, as shown in FIG. 4, a multiple exposure method in which the exposure positions are overlapped for each scan is adopted. 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.

(Refer to Sync signal output example 1, FIGS. 5 to 7)
As shown in FIG. 5, the light beams a to d output from the respective light emitting points are combined with the light beams a and c and the light beams b and d as a set, and the light receiving surface ( Scan / expose the photodiode PD). In this output example 1, on the light receiving surface of the SOS sensor 5, the intervals P1 and P2 between the light beams a and c and the light beams b and d are smaller than the width dimension WPD of the light receiving surface, and the light beams a and c The interval P3 between the light beams b and d is set larger than the width dimension WPD of the light receiving surface.

  That is, P1, P2 ≦ WPD ≦ P3.

  Specifically, as shown in FIGS. 6 and 7, the SOS sensor 5 outputs a current proportional to the amount of received light, the current is amplified by the amplifier I, and flows through a resistor R connected to the terminal Ro. Thus, current / voltage conversion is performed, and as a result of comparison with the reference voltage Vref by the comparator C, SOS signals S1 and S2 are output when Vref <Ro. As a result, all the light emitting points a to d are simultaneously forcedly emitted (based on the forced emission signal E shown in FIG. 11) to scan / expose the light receiving surface of the SOS sensor 5, thereby relating to the set of light beams a and c. The SOS signal S2 relating to the set of the SOS signal S1 and the light beams b and d can be reliably generated.

(Synchronization signal output example 2, see FIGS. 8 to 10)
In this output example 2, main scanning of the light beam output from one set of light emission points a and c and one set of light emission points b and d is performed using a two-part light receiving sensor (photodiode PD1, PD2) as the SOS sensor 5. The center of gravity position in the direction Y is detected. As in the first output example, the light emission points a and c and the light emission points b and d are subjected to forced light emission control one by one. Similarly, P1, P2 ≦ WPD ≦ P3.

  Specifically, as shown in FIGS. 9 and 10, the SOS sensor 5 outputs a current proportional to the amount of received light, and the current is amplified by amplifiers I1 and I2, and is connected to terminals Ro1 and Ro2. , R2. Thus, current / voltage conversion is performed, and the voltages Ro1 and Ro2 are compared by the comparator C. When Ro1 <Ro2, SOS signals S1 and S2 are output. As a result, all the light emitting points a to d are simultaneously forcedly emitted to scan / exposure the light receiving surface of the SOS sensor 5, thereby relating to the SOS signal S1 relating to the set of the light beams a and c and the set of the light beams b and d. The SOS signal S2 can be generated reliably.

(Example of control in sync signal output examples 1 and 2, see FIGS. 11 and 12)
Here, a control example of the light beam scanning optical apparatus 1 in the synchronization signal output examples 1 and 2 will be described. As shown in FIG. 11, the control unit (controller 501) includes an SOS division circuit 502 to which an SOS signal is input, CLK synchronization means 503 and 504, counters 505 and 506, and memories 507a to 507d. ing. The SOS signals S1 and S2 shown in FIGS. 7 and 10 are transferred to the SOS dividing circuit 502, where they are divided into SOS signals S1 and S2, which are sent to the CLK synchronizing means 503 and 504, respectively. The light emitting points a to d are forcibly emitted in order to obtain the SOS signals S1 and S2 by the forced emission signal E.

  The CLK synchronization means 503 and 504 transfer the signal CLK synchronized with the SOS signals S1 and S2 to the counters 505 and 506, respectively. As shown in FIG. 12, the counter 505 instructs the memory 507a to output the image data VIDEOa when the count value corresponding to the predetermined image writing start position in the main scanning direction of the light emitting point a is reached. Similarly, the counter 505 instructs the memory 507c to output image data VIDEOc when a count value corresponding to a predetermined image writing start position in the main scanning direction of the light emitting point c is reached. The counter 506 instructs the memory 507b to output the image data VIDEOb when the count value corresponding to the predetermined image writing start position of the light emitting point b in the main scanning direction is reached. Similarly, the counter 506 instructs the memory 507d to output the image data VIDEOd when the count value corresponding to the predetermined image writing start position in the main scanning direction of the light emitting point d is reached.

  The drive unit 511 modulates the light emission points a to d based on the image data to emit light. As described above, the SOS signal S1 related to the set of the light beams a and c and the SOS signal S2 related to the set of the light beams b and d are reliably separated and generated, so that jitter of the image in multiple exposure is suppressed.

(Comparison example of synchronization signal output, see FIGS. 13 and 14)
By the way, as shown in FIG. 13, when P1, P2, P3 ≦ WPD, when the SOS sensor 5 is scanned / exposed by forcibly emitting the light emission points a to d simultaneously, as shown in the lower part of FIG. The light quantity distributions of the light beams a to d are close to each other. Therefore, as shown in FIG. 14, the SOS signal obtained exceeding the reference voltage Vref becomes wide and cannot be separated into a set of light beams a and c and a set of light beams b and d.

(Synchronization signal output example 3, see FIGS. 15 to 17)
Therefore, in the synchronization signal output example 3, the first set, the second set in the order of the scanning order of the SOS sensor 5 by the light beams a and c and the light beams b and d output from the light emitting points for each set in order. As shown in FIG. 15, when the order is set with the group, the first group of light emission points emits light simultaneously (forced light emission signal E1) to detect the synchronization signals relating to the first group of light beams a and c. (SOS signal S1), the first set of light emission is stopped. Then, the light emission points of the second group are simultaneously emitted (forced light emission signal E2) to detect a synchronization signal related to the light beams b and d of the second group (SOS signal S2), and the light emission of the second group is performed. Stop.

  The above control is performed by the control unit (controller 501) shown in FIG. 16, and has basically the same configuration as the control unit shown in FIG. The difference is that the forced light emission signal input to the drive unit 511 is classified into a forced light emission signal E1 at the light emission points a and c and a forced light emission signal E2 at the light emission points b and d. The control timing is as shown in FIG.

(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 device, and is particularly excellent in that a synchronization signal by a light beam output from each light emitting point can be detected with high accuracy.

DESCRIPTION OF SYMBOLS 1 ... Optical beam scanning optical apparatus 2 ... LD array 4 ... Polygon mirror 5 ... Synchronization signal detection (SOS) sensor 102 ... Photoconductor drum 501 ... Control part (controller)
511: Drive units a to d: Light emitting points (light beams)

Claims (4)

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 formed as a set, and a plurality of sets are formed, and a light beam output from each light emitting point scans and exposes the synchronization signal output means, thereby corresponding to each set. Generated synchronization signal,
Controlling the light emission timing of the plurality of light emission points based on a synchronization signal corresponding to each of the sets,
A light beam scanning optical device.   On the light receiving surface of the synchronization signal output means, the interval in the main scanning direction of each light beam output from the set of light emitting points is smaller than the width dimension of the light receiving surface, and the light emission for each set. 2. The light beam scanning optical apparatus according to claim 1, wherein an interval in the main scanning direction of the light beam output from the point is larger than a width dimension of the light receiving surface. When the scanning order of the synchronization signal output means by the light beams output from the light emitting points for each set is set in the order of the first group and the second group in the early order,
The first set emits light at the same time to detect a synchronization signal related to the first set of light emission points, the first set emits light,
Simultaneously causing the second set to emit light, detecting a synchronization signal relating to the second set of light emitting points, and stopping the second set to emit light;
The light beam scanning optical apparatus according to claim 1, wherein   4. The light beam according to claim 1, wherein a center of gravity of the light beam output from the set of light emitting points is detected using a two-part light receiving sensor as the synchronization signal output means. Scanning optical device.

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