JP5169099B2 - Laser scanning optical device - Google Patents

Description

  The present invention relates to a laser scanning optical device, and more particularly to a laser scanning optical device mounted as a print head in an image forming apparatus such as an electrophotographic copying machine or printer.

  In recent years, there has been a strong demand for high-speed and high-definition in copying machines and printers, and a multi-beam method in which a photoconductor is scanned with a plurality of beams at a predetermined interval in the sub-scanning direction has become mainstream. In multi-beam drawing, multiple exposure is required to make the image quality disorder of the joint portion of each scanning line inconspicuous. In multiple exposure, the density of each pixel is the sum of the light amounts of the beams used for multiple exposure. When a difference occurs in the total light amount between pixels, density unevenness is caused. Therefore, stabilization of the light amount by the total light amount and a method for controlling the light amount are important.

  In Patent Document 1, a plurality of beams emitted from one semiconductor laser array light source are divided into sets of beams for multiple exposure of the same pixel, and the combined beams are incident on a light amount detection mechanism provided outside the light source. It is described that the total light amount of a set of beams is detected and the light amount control of each beam is performed based on the detection result. However, in this light quantity control, since the light quantity detection mechanism provided outside the light source is used, the configuration becomes complicated.

  In addition to the above, there is known a method of obtaining the detection result by the light amount detection element incorporated in each semiconductor laser array light source as a sum using an electric circuit. This method has a problem that the control with good accuracy cannot be performed due to an error in the electric circuit, and the cost is increased by providing the electric circuit. Furthermore, a method of detecting the light amount for each individual beam is also known, but since it takes time to control the light amount, it cannot cope with speeding up.

On the other hand, Patent Document 2 discloses a method of controlling the light amounts of individual light sources in a balanced manner from the sum of the light amounts of a plurality of light sources. However, Patent Document 2 does not mention light amount control in the case of multiple exposure using a plurality of semiconductor laser array light sources.
JP 2006-103248 A JP-A-8-264873

  Accordingly, an object of the present invention is to provide a laser scanning optical device capable of performing light amount control with a simple configuration and high accuracy when multiple exposure is performed by combining a plurality of semiconductor laser array light sources having a plurality of light emitting sources. There is.

In order to achieve the above object, the present invention provides:
In a laser scanning optical device that performs multiple exposure on a surface to be scanned with a plurality of beams,
A plurality of light emitting sources that can be driven independently of each other, and a plurality of semiconductor laser array light sources that incorporate a single sensor that detects the light quantity of the light emitting sources;
An optical system for combining the beams emitted from the plurality of semiconductor laser array light sources and performing multiple exposure,
A plurality of beams for exposing the same pixels on the scan surface is constituted by a beam emitted from one semiconductor laser array light source,
Detecting and controlling the total amount of light of a set of beams to be subjected to multiple exposure by the single sensor built in each semiconductor laser array light source;
It is characterized by.

  In the laser scanning optical device according to the present invention, a beam for multiple exposure of the same pixel is combined with a beam emitted from the same semiconductor laser array light source, and the total light quantity of the set of multiple exposure beams is set for each semiconductor. Detection was performed by a single sensor built in the laser array light source. Thus, it is possible to control the light amount of each light source with a simple configuration and with high accuracy without providing a light amount detection means outside the light source or using an electric circuit for obtaining the total light amount.

  Embodiments of a laser scanning optical apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus, see FIG. 1)
The image forming apparatus shown in FIG. 1 is an electrophotographic color printer, and is configured to form an image of four colors (C: cyan, M: magenta, Y: yellow, K: black) in a so-called tandem system. It is a thing. An image is formed at each image forming station 101 and is combined on the intermediate transfer belt 112. In each drawing, the letters C, M, Y, and K attached to the reference numerals mean members for cyan, magenta, yellow, and black, respectively.

  The outline of each of the image forming stations 101 (101C, 101M, 101Y, 101K) will be described. The photosensitive drum 102 (102C, 102M, 102Y, 102K) and the laser scanning optical unit 103 (103C, 103M, 103Y, 103K) are described. Developing unit 104 (104C, 104M, 104Y, 104K) and the like.

  Beams BC, BM, BY, and BK emitted from each laser scanning optical unit 103 irradiate each photosensitive drum 102 to form an image of each color. On the other hand, an intermediate transfer belt 112 is stretched endlessly on rollers 113, 114, 115 immediately below the image forming station 101, is driven to rotate in the direction of arrow A, and is a portion where the drive roller 113 is installed. A secondary transfer roller 116 is disposed at a portion (secondary transfer portion) that faces 112. In addition, an automatic paper feeding unit 130 that feeds the stacked transfer materials one by one is installed in the lower part of the image forming apparatus.

  Image data is transmitted as image data for each CMYK from an image reading device (scanner) or a computer (not shown) to the image memory 35 (see FIG. 4), and each laser scanning optical unit 103 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 onto the intermediate transfer belt 112 that is rotationally driven in the direction of arrow A, and four color images are combined. On the other hand, the transfer material is fed one sheet at a time from the sheet feeding unit 130, and the composite image is secondarily transferred from the intermediate transfer belt 112 by the electric field applied from the transfer roller 116 in the secondary transfer unit. Thereafter, the transfer material 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 transfer material is installed immediately before the secondary transfer unit, and the transfer material and the image on the intermediate transfer belt 112 are synchronized. In addition, a registration sensor 105 for detecting a registration correction image formed on the intermediate transfer belt 112 is provided. A registration correction image is formed on the belt 112 for each image forming station 101, and the correction image is detected by the sensor 105, thereby adjusting the light emission timings of the laser beams BC, BM, BY, BK, and CMYK. These images are accurately synthesized on the belt 112.

(Laser scanning optical unit, see FIGS. 2 and 3)
As shown in FIG. 2, each laser scanning optical unit 103 generally includes semiconductor laser array light sources 301 and 302 each having four light emission sources 301 a to 301 d and 302 a to 302 d, a coupling position adjusting member (parallel plate) 307, and The beam combining prism 310, the first cylindrical lens 311, the polygon mirror 312 that is rotationally driven at a predetermined speed, the scanning lens 313 having the fθ function, the second cylindrical lens 314, and the horizontal synchronization sensor 316. ing. In the present embodiment, each of the semiconductor laser array light sources 301 and 302 emits four beams, but in FIG. 2, for simplification, the two laser beams are drawn.

  Beams (diverging light) emitted from the light emitting sources 301a to 301d and 302a to 302d of the semiconductor laser array light sources 301 and 302 are collimated by the collimator units 304 and 303, and the beams from the light emitting sources 302a to 302d are combined. The light passes through the image position adjusting member (parallel flat plate) 307 and is guided to the beam combining prism 310. Here, the beams are combined in the same direction, and are condensed by the first cylindrical lens 311 substantially parallel to the sub-scanning direction Z, and guided to the polygon mirror 312. These beams are deflected at a constant angular velocity in the main scanning direction Y based on the rotation of the polygon mirror 312, and necessary aberrations are corrected by passing through the scanning lens 313, passing through the second cylindrical lens 314 and passing through the photosensitive drum. The image is formed on 102. By this horizontal scanning, an electrostatic latent image is formed on the photosensitive drum 102.

  In each laser scanning optical unit 103, in order to detect the writing position of each scanning line on the photosensitive drum 102, that is, to obtain a horizontal synchronization signal, the beam deflected by the polygon mirror 312 on the upstream side in the main scanning direction. The beam is reflected by the mirror 315 and enters the horizontal synchronization sensor 316, and a horizontal synchronization signal is generated. Note that a method for generating such a horizontal synchronizing signal is well known, and a description thereof will be omitted.

  Meanwhile, as shown in FIG. 3, the semiconductor laser array light sources 301 and 302 have four light emitting sources 301a to 301d and 302a to 302d arranged at predetermined intervals, respectively. Photodiodes PD1 and PD2 functioning as a single sensor for detection are incorporated. Each light source emits light by a light emission signal corresponding to the light source.

(Control unit, see FIG. 4)
Next, the configuration of the control unit of the image forming apparatus will be described with reference to FIG. This control unit is generally composed of a CPU (microcomputer) 30, a drive clock generation circuit 31, and an image memory 35. The CPU 30 controls a motor that drives the polygon mirror 312, and the beam incident on the horizontal synchronization sensor 316 is photoelectrically converted and input to the CPU 30. The CPU 30 digitizes this signal to generate a horizontal synchronization signal HSYNC.

  Further, the CPU 30 receives a transfer material detection signal from the TOD sensor 106 and a correction image detection signal from the registration sensor 105. Based on the detection signal of the registration sensor 105, the CPU 30 calculates registration correction values such as the main scanning position and the sub scanning position of the image, and the main scanning magnification. Further, the CPU 30 controls forced light emission for obtaining a horizontal synchronization signal, and further controls forced light emission for drawing a correction image.

  The CPU 30 outputs a horizontal synchronization signal HSYNC and an image request signal TOD to the image memory 35. The image memory 35 includes a plurality of sub-scanning counters. The horizontal synchronization signal HSYNC is counted by using the signal TOD as a trigger, and the sub-scanning resist and the main-scanning resist are combined to obtain the image data C / M. / Y / K is output to the LD drivers 33 and 34. This output is performed at a timing at which the result obtained by the CPU 30 receiving the registration correction result is included.

  The image data DATA output to the LD drivers 33 and 34 adjusts the position in the main scanning direction on the photosensitive drum 102 in accordance with the relative positions of the beams emitted from the light emission sources 301a to 301d and 302a to 302d. . The forced light emission signal is shared by the light emission sources 301a to 301d and 302a to 302d. In addition, the CPU 30 controls various devices in the image forming apparatus.

(Double exposure mode, see FIGS. 5 and 6)
Next, a mode of multiple exposure on the photosensitive drum 102 (in this embodiment, double exposure) will be described. FIG. 5 shows a beam arrangement on the photosensitive drum 102 when double exposure is performed in this embodiment. A total of eight beams emitted from the light emission sources 301a to 301d and 302a to 302d are arranged in the sub-scanning direction Z on the photosensitive drum 102 in the order of 301a, 302a, 301b, 302b, 301c, 302c, 301d, and 302d. Deploy. To perform double exposure by scanning every four beams, the same pixel is exposed at 301c and 301a, 302c and 302a, 301d and 301b, and 302d and 302b. Thereafter, the same pixel is always exposed with four sets of 301c and 301a, 302c and 302a, 301d and 301b, and 302d and 302b.

  Since a set of beams for exposing the same pixel is emitted from the same semiconductor laser array light sources 301 and 302, it can be detected as a total light amount at a time by the photodiodes PD1 and PD2 incorporated in the light sources 301 and 302, respectively.

  On the other hand, FIG. 6 shows a beam arrangement in a case where double exposure is performed with a set of beams emitted from the light sources 301 and 302 as a comparative example. In this comparative example, a total of eight beams emitted from the light emitting sources 301a to 301d and 302a to 302d are placed on the photosensitive drum 102 in the sub-scanning direction Z, 301a, 301b, 301c, 301d, 302a, 302b, They are arranged in the order of 302c and 302d. In order to perform double exposure by scanning every four beams, the same pixel is exposed in 302a and 301a, 302b and 301b, 302c and 301c, and 302d and 301d. Thereafter, the same pixel is always exposed with four sets of 302a and 301a, 302b and 301b, 302c and 301c, and 302d and 301d.

  Since a set of beams for exposing the same pixel is emitted from separate semiconductor laser array light sources 301 and 302, the total light amount is obtained by detecting the light amount detection values of the photodiodes PD1 and PD2 incorporated in the light sources 301 and 302, respectively. Will be synthesized. In this case, control with good accuracy cannot be performed due to errors in the electric circuit, and the cost is increased by providing the electric circuit.

(Double exposure light emission control, see FIG. 7)
FIG. 7 shows a timing chart in the double exposure in this embodiment. Automatic light quantity control (hereinafter referred to as APC) is performed outside the image drawing area. In FIG. 7, SOS indicates the timing at which a beam for obtaining a horizontal synchronizing signal (using only the beam of the light emission source 301a) enters the sensor 316, SOI indicates the image drawing start timing, and EOI indicates The image drawing end timing is shown.

  First, when the light emitting sources 301b and 301d are turned on simultaneously, the total amount of light is detected by the photodiode PD1. Based on this total light quantity, the light quantity control (APC) of each light emission source 301b, 301d is performed. In this light amount control, light emission characteristics with respect to the applied voltages of the light emission sources 301b and 301d are obtained in advance, the light amounts of the light emission sources 301b and 301d are estimated from the detected total light amounts, and the necessary light amounts can be obtained. Balance the drive voltage. Note that such light amount control is described in detail in the above-mentioned Patent Document 2.

  Next, when the light emitting sources 301a and 301c are turned on simultaneously, the total amount of light is detected by the photodiode PD1. Based on this total light quantity, light quantity control (APC) of each light emission source 301a, 301c is performed.

  As with the semiconductor laser array light source 302, light emission sources 302b and 302d are turned on simultaneously, and light amount control (APC) is performed based on the total light amount detected by the photodiode PD2. Further, the light emission sources 302a and 302c are turned on simultaneously, and light amount control (APC) is performed based on the total light amount detected by the photodiode PD2.

  In the present embodiment, as shown in FIG. 7, the light amount adjustment of the semiconductor laser array light sources 301 and 302 is performed at the same timing, but may be performed at different timings.

(Control procedure, see FIGS. 8 and 9)
Next, a control procedure by the CPU 30 will be described. FIG. 8 shows a main routine of control. When the power is turned on, first, a RAM and a timer built in the CPU 30 are initialized (step S1), and an internal timer is set (step S2). Thereafter, pre-print setting (step S3), image memory processing (step S4), print processing (step S5), and other processing (step S6) such as temperature control and paper jam detection are executed, and the internal timer is terminated. (YES in step S7), the process returns to step S2.

  FIG. 9 shows a pre-print setting subroutine executed in step S3. First, it is determined whether or not the double exposure mode is set (step S11). In the double exposure mode, an APC period for detecting the total light amount by emitting the beam combined for the double exposure shown in FIG. 7 is set (step S12), and each light emission source is determined from the detected total light amount. A balance for correcting the amount of light is set (step S13). Next, other settings relating to double exposure are performed (step S14), and the process returns to the main routine.

  If it is the normal exposure mode (NO in step S11), an APC period for controlling the amount of light for normal exposure is set (step S15), other settings for normal exposure are performed (step S16), and the process returns to the main routine.

  In the embodiment described above, the beams for multiple exposure of the same pixel are combined with the beams emitted from the same semiconductor laser array light sources 301 and 302, and the total light amount of the set of multiple exposure beams is set for each semiconductor. Detection is performed by single sensors PD1 and PD2 incorporated in the laser array light sources 301 and 302, respectively. Thus, the light amount of each light source can be accurately controlled with a simple configuration without providing a light amount detection means outside the light sources 301 and 302 and without using an electric circuit for obtaining the total light amount. .

(Other examples)
The laser scanning optical device 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 number of semiconductor laser array light sources installed is not limited to two, and a multi-beam format using a larger number of light sources may be used. Also, the number of light emitting sources included in one semiconductor laser array light source may be any number other than four. Two or more multiple exposures may be used. Further, it goes without saying that the configuration of the image forming station, the configuration of the control unit, and the like are arbitrary.

1 is a schematic configuration diagram showing an image forming apparatus equipped with a laser scanning optical device according to the present invention. It is a schematic perspective view which shows one Example of the laser scanning optical apparatus based on this invention. It is a circuit diagram which shows the semiconductor laser array light source integrated in the said laser scanning optical apparatus. It is a block diagram which shows a control part. It is explanatory drawing which shows the beam arrangement | sequence on the photoreceptor in double exposure (example of this invention). It is explanatory drawing which shows the beam arrangement | sequence on a photoconductor in double exposure (comparative example). It is a timing chart figure which shows the light emission control of the light emission source in double exposure. It is a flowchart figure which shows the main routine of a control procedure. FIG. 6 is a flowchart showing a pre-print setting subroutine.

Explanation of symbols

30 ... CPU
DESCRIPTION OF SYMBOLS 102 ... Photosensitive drum 103 ... Laser scanning optical unit 301, 302 ... Semiconductor laser array light source 301a-301d, 302a-302d ... Light emission source 310 ... Beam composition prism 312 ... Polygon mirror 313 ... Scanning lens PD1, PD2 ... Photodiode

Claims (3)

In a laser scanning optical device that performs multiple exposure on a surface to be scanned with a plurality of beams,
A plurality of light emitting sources that can be driven independently of each other, and a plurality of semiconductor laser array light sources that incorporate a single sensor that detects the light quantity of the light emitting sources;
An optical system for combining the beams emitted from the plurality of semiconductor laser array light sources and performing multiple exposure,
A plurality of beams for exposing the same pixels on the scan surface is constituted by a beam emitted from one semiconductor laser array light source,
Detecting and controlling the total amount of light of a set of beams to be subjected to multiple exposure by the single sensor built in each semiconductor laser array light source;
A laser scanning optical device. Two comprising a semiconductor laser array light source, a laser scanning optical apparatus according to claim 1, characterized in that each of the semiconductor laser array light source has four light emitting source.   The laser scanning optical apparatus according to claim 1, further comprising a light amount control unit that corrects a light amount of each of the light emitting sources based on a light amount detected by the single sensor. .

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