JP2004106234A - Multibeam image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multibeam image forming apparatus in which pixel shift is corrected appropriately by detecting dot shift of an image formed finally on a recording medium by means of a multibeam. <P>SOLUTION: The multibeam image forming apparatus 1 comprises a pattern generating section 82 generating a pattern image for detecting pixel shift in the main scanning direction, an image signal generating section 81 generating an image signal for each LD unit 2a, 2b based on the pattern image, a section 87 for detecting the density of the pattern image for detecting pixel shift in the main scanning direction formed on a transfer sheet 88 through a multibeam scanning optical system 80 as the dot shift among a plurality of laser beams, and a pixel shift correcting section 83 for correcting the dot shift among the plurality of laser beams by adjusting the output timing of an image signal from the image signal generating section 81 for each LD unit 2a, 2b. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-beam image forming apparatus, and more particularly, to a multi-beam image forming apparatus that detects a dot shift of an image finally formed on a recording medium with a multi-beam and appropriately corrects a pixel shift.
[0002]
[Prior art]
[Patent Document 1]
JP-A-10-239606
[Patent Document 1]
JP 2001-66526 A
In image forming apparatuses such as digital copiers, digital printers and digital facsimile machines, since high-quality images can be recorded at high speed, laser light emitted from a laser light source such as a semiconductor laser is used. 2. Description of the Related Art An electrophotographic image forming apparatus for forming an image is widely used.
[0003]
In such an image forming apparatus, there is a growing demand for higher speed and higher definition of an image. In an electrophotographic image forming apparatus, a position at which an image is written on a photoconductor as a latent image forming body, That is, the synchronization signal for determining the irradiation start position of the laser beam to the photoconductor is detected by an optical sensor such as a photosensor. This optical sensor is mounted outside the image area due to its configuration, and is installed at a position where the optical path length on the scanning optical system is equivalent to that on the photoconductor as a recording medium. In the image forming apparatus, when the laser beam irradiated to the photoconductor passes through the optical sensor, the optical sensor generates a synchronization signal indicating a writing position at a timing when the laser beam passes, and based on the synchronization signal, Image position control in the main scanning direction is performed. In order to realize high definition of an image, a portion for generating a synchronization signal serving as a writing reference position timing is very important. If the detection timing of the synchronization signal is disturbed, the writing position of each line of the image output to the recording medium is disturbed, and an image shift occurs in the main scanning direction for each line, and the vertical line fluctuates throughout the image. A large defect occurs with respect to the image quality.
[0004]
The image forming apparatus uses a multi-beam scanning optical system that uses a plurality of laser beams as emission points, instead of using a single laser beam that constitutes a scanning optical system with the increase in speed. Tend to. That is, such an image forming apparatus employs a multi-beam system in which a plurality of (n) laser beams are simultaneously scanned on a photoconductor by one scan of a scanning optical system, and a plurality of lines (n) are simultaneously written. Has adopted. Therefore, if the number of rotations of the polygon mirror is constant, the image forming speed of the image forming apparatus is simply n times faster than when one laser beam is used.
[0005]
In the case where a multi-beam optical system is used, in order to prevent pixel shift in the main scanning direction due to the above-described writing position disorder, the number of laser beams is increased, so that the synchronization signal detection timing for each laser beam is made constant. There is a need. Therefore, if a configuration in which one optical sensor for detecting a synchronization signal (synchronous detection sensor) is provided for one laser beam, as in a conventional single laser beam scanning optical system, is directly applied to a multi-beam scanning optical system. In a configuration using a plurality of laser beams, it is necessary to mount a plurality of synchronous detection sensors corresponding to each laser beam in the scanning optical system. The variation in the mounting position of the synchronization detection sensor affects the variation in the synchronization signal detection timing of each laser beam, and the variation tends to increase in the configuration of the scanning optical system.
[0006]
Therefore, conventionally, a multi-beam scanning optical system has been developed in which a sensor for detecting a synchronization signal of a plurality of laser beams is constituted by a common synchronization detection sensor. This multi-beam scanning optical system has a configuration in which the timing at which a plurality of laser beams scan in the main scanning direction is detected by the same synchronous detection sensor.
[0007]
In this case, the synchronous detection sensor has a threshold level of the incident laser beam light quantity to which the synchronous detection sensor responds, and when the laser beam light quantity exceeding this threshold level enters the synchronous detection sensor, the output of the synchronous detection sensor becomes the active output. It becomes. If the laser beams are sufficiently separated in the main scanning direction, the respective laser beams scan the threshold level of the amount of the incident laser beam responded by the synchronous detection sensor. At the timing when the light enters the synchronization detection sensor, the synchronization detection sensor output becomes active. Therefore, a synchronization signal generated by the synchronization detection sensor by scanning of each laser beam is detected at a timing completely separated for each laser beam, and a synchronization signal of each laser beam is obtained at an accurate timing.
[0008]
However, if the laser beams are not sufficiently separated in the main scanning direction, the synchronization signal of the preceding laser beam is output at an accurate timing, but the rear end of the preceding laser beam still enters the synchronization detection sensor. When the following laser beam enters the synchronous detection sensor at the same timing, the threshold level of the amount of incident laser beam that the synchronous detection sensor responds to is set so that the preceding laser beam and the following laser beam simultaneously enter the synchronous detection sensor. In some cases, the synchronization signal of the succeeding laser beam is detected earlier than the predetermined timing. As a result, the image writing positions of the preceding laser beam and the following laser beam are disturbed, and there is a problem that pixel deviation occurs in each laser beam in the main scanning direction.
[0009]
Therefore, the present applicant has previously proposed a “multi-beam laser scanning device” of Patent Document 1. This conventional technology detects and detects a plurality of laser beams with a common synchronization detection sensor, and generates a synchronization signal for each laser beam based on the detection timing of the synchronization detection sensor, thereby detecting synchronization between the plurality of laser beams. The arrival time at the sensor is ascertained, and the deviation of the writing start position is corrected based on the arrival time to prevent the image writing position from being disturbed.
[0010]
In addition, the present applicant has previously proposed a “multi-beam image forming apparatus” of Patent Document 2. In this conventional technique, a plurality of laser beams are sequentially detected by a common synchronization detection sensor, and the synchronization detection sensor receives the plurality of laser beams so that the time interval of a synchronization signal generated by the synchronization detection sensor becomes an ideal value. At this time, the intensity of at least one of the plurality of laser beams is controlled to prevent the image writing position from being disturbed.
[0011]
[Problems to be solved by the invention]
However, in the above-described conventional technique, the synchronization signal detection timing in the synchronization detection sensor unit detects the time interval of the synchronization signal corresponding to each laser beam among a plurality of laser beams, and thereby the output of the image forming apparatus and Since the pixel shift of the output image in the main scanning direction is corrected, and the synchronization detection sensor needs to detect the synchronization signal outside the image area, the optical path length on the scanning optical system is image-formed. It is mounted outside the image area equivalent to that on the photoconductor.
[0012]
However, the components constituting the scanning optical system, in particular, the variation of the detection timing with the incident laser beam due to the distortion of the optical system housing that integrates the entire scanning optical system and the angular variation of the mounting portion of the synchronous detection sensor, and the multi-beam scanning optical system. Even if the mutual positional relationship with the photoconductor is varied and the time interval of the synchronization signal corresponding to each laser beam is detected by the synchronization detection sensor unit, the laser that passes through the scanning optical system and irradiates the photoconductor. Beam timing may be different for each laser beam.
[0013]
Further, in the image forming apparatus, an electrostatic latent image is formed on the surface of the photoreceptor by the irradiated laser beam. The electrostatic latent image is visualized by attaching toner through a developing unit, and is formed by a roller. The image is transferred onto a transfer sheet as a recording medium that has been conveyed, and the transferred transfer sheet is separated from the photoreceptor and sent to a fixing unit. In the fixing unit, the toner is fixed on the transfer paper by the pressure and the temperature applied by the pressure roller. The image forming apparatus forms an image on the transfer paper through the image forming process as described above. However, due to the variation in the shape of each roller and the balance of the pressure, the electrostatic latent image formed on the photoreceptor and the transfer paper are formed on the transfer paper. There is a possibility that a difference occurs in the formed output image, and there is a need for improvement.
[0014]
Therefore, the present invention generates a specific pattern image for detecting a pixel shift due to a writing position in the main scanning direction, generates an image signal for each of a plurality of laser light sources based on the specific pattern image, and Is used to detect the density of the specific pattern image formed on the recording medium as a dot shift between a plurality of laser beams, and the respective image signals for driving a plurality of laser light sources in accordance with the detected density signal. The generation timing is controlled, and the image signal generation timing is controlled so as to match the beam interval in the main scanning direction including the beam interval in the main scanning direction between a plurality of laser beams. Not only the pixel displacement of each laser beam, but also the relationship between the multi-beam scanning optical system and the photoconductor, and the image on the recording medium that is the final output of the photoconductor. Including the mutual relationship between, and correct the pixel shift between each of the laser beams, and its object is to provide a multi-beam image forming apparatus capable of improving image quality.
[0015]
Specifically, the invention according to claim 1 generates an image signal for individually driving a plurality of laser light sources by an image signal generator, and a plurality of laser light sources based on the image signal by a multi-beam scanning optical system. A laser beam is emitted from each of them, and the laser beam is irradiated on the photoconductor to form an electrostatic latent image, and the electrostatic latent image on the photoconductor is developed to form an image on a recording medium. Generating means for generating a predetermined specific pattern image and outputting it to the image signal generating means; based on the specific pattern image, the image signal generating means generates an image signal for each laser light source and outputs the image signal with a multi-beam scanning optical system; The density of the specific pattern image formed on the recording medium is detected by a density detecting means as a dot shift between a plurality of laser beams, and a density signal is output. In addition to the pixel deviation of the laser beam, the pixel deviation between the laser beams including the mutual relationship between the multi-beam scanning optical system and the photoconductor and the correlation between the photoconductor and the image on the recording medium that is the final output. It is an object of the present invention to provide a multi-beam image forming apparatus capable of detecting an image.
[0016]
According to a second aspect of the present invention, based on the density signal indicating the dot shift detected by the density detecting means, the shift correcting means adjusts the output timing of the image signal for each laser light source generated by the image signal generating means, By correcting the dot deviation between the plurality of laser beams, not only the pixel deviation of each laser beam in the synchronous detection sensor unit but also the mutual relationship between the multi-beam scanning optical system and the photoconductor and the photoconductor and the final output are obtained. It is an object of the present invention to provide a multi-beam image forming apparatus capable of correcting a pixel deviation between respective laser beams including a mutual relationship with an image on a recording medium and having good image quality.
[0017]
According to a third aspect of the present invention, the pattern generation means is an image of one dot width unit in the main scanning direction and one line width unit in the sub-scanning direction as the specific pattern image, and the dot formation density per dot unit is constant. By generating an image of the above, it is possible to easily detect a pixel shift between a plurality of laser beams, and to appropriately correct a pixel shift from a density signal of the specific pattern image formed on the recording medium. It is another object of the present invention to provide a multi-beam image forming apparatus capable of further improving image quality.
[0018]
According to a fourth aspect of the present invention, as a specific pattern image, a dot array in the sub-scanning direction having a width of one dot formed at the same position in the main scanning direction with respect to a sub-scanning line scanned by the same laser beam. By generating an image that is formed as a reference, a specific pattern image that can easily determine which laser light source has formed a specific pattern image formed by a plurality of laser beams is formed and formed. To provide a multi-beam image forming apparatus capable of easily detecting a pixel shift between a plurality of laser beams based on the density of an image obtained, and appropriately correcting the pixel shift from the detected density signal. And
[0019]
According to a fifth aspect of the present invention, an image is formed in which dots are formed at a predetermined number of line cycles at positions before and after in the main scanning direction with respect to a reference dot array in the sub-scanning direction, as a specific pattern image. Forming a specific pattern image that can more easily determine which laser light source emitted a laser beam emitted from a specific pattern image formed by a plurality of laser beams; It is an object of the present invention to provide a multi-beam image forming apparatus which can more easily detect a pixel shift between laser beams, and can more appropriately correct a pixel shift from a detected density signal. .
[0020]
[Means for Solving the Problems]
A multi-beam image forming apparatus according to a first aspect of the present invention includes a multi-beam scanning optical system that emits a laser beam from each of a plurality of laser light sources and irradiates the laser beam onto a photosensitive member to form an electrostatic latent image. Image signal generating means for generating image signals for individually driving the plurality of laser light sources, and forming an image on a recording medium by developing an electrostatic latent image on the photoreceptor. In the apparatus, a pattern generation unit that generates a predetermined specific pattern image and outputs the generated specific pattern image to the image signal generation unit, and the image signal generation unit generates each of the laser light sources based on the specific pattern image generated by the pattern generation unit. And the density of the specific pattern image formed on the recording medium by the multi-beam scanning optical system based on the image signal. And concentration detection means for outputting a density signal by detecting a dot deviation between Zabimu, due to the provision of the, have achieved the above objects.
[0021]
According to the above configuration, an image signal for individually driving the plurality of laser light sources is generated by an image signal generator, and the multi-beam scanning optical system emits a laser beam from each of the plurality of laser light sources based on the image signal. The laser beam is irradiated on the photoreceptor to form an electrostatic latent image, and the electrostatic latent image on the photoreceptor is developed to form an image on a recording medium. A pattern image is generated and output to the image signal generating means, and the image signal generating means generates an image signal for each laser light source based on the specific pattern image and forms the image signal on the recording medium by the multi-beam scanning optical system. Since the density of the pattern image is detected by the density detecting means as a dot shift between a plurality of laser beams and a density signal is output, the pixel of each laser beam in the synchronous detection sensor unit is output. In addition to this, it is possible to detect the pixel shift between each laser beam, including the correlation between the multi-beam scanning optical system and the photoconductor, and the correlation between the photoconductor and the image on the recording medium as the final output. it can.
[0022]
In this case, for example, as described in claim 2, the multi-beam image forming apparatus is configured to generate each laser light source generated by the image signal generating unit based on a density signal indicating a dot shift detected by the density detecting unit. And a shift correcting unit that adjusts the output timing of the image signal to correct the dot shift between the plurality of laser beams.
[0023]
According to the above configuration, based on the density signal indicating the dot shift detected by the density detecting unit, the shift correcting unit adjusts the output timing of the image signal for each laser light source generated by the image signal generating unit, and outputs a plurality of signals. Since the dot deviation between laser beams is corrected, not only the pixel deviation of each laser beam in the synchronous detection sensor unit but also the mutual relationship between the multi-beam scanning optical system and the photoconductor and the photoconductor and the final output on the recording medium The pixel deviation between the laser beams including the correlation with the image can be corrected, and the image quality can be improved.
[0024]
Also, for example, as described in claim 3, the pattern generating means is an image of one dot width unit in the main scanning direction and one line width unit in the sub scanning direction as the specific pattern image. An image with a constant dot formation density may be generated.
[0025]
According to the above configuration, the pattern generating means is an image in which the specific pattern image is one dot width unit in the main scanning direction and one line width unit in the sub scanning direction, and the dot formation density per dot unit is constant. Is generated, a pixel shift between a plurality of laser beams can be easily detected, and a pixel shift can be appropriately corrected from a density signal of the specific pattern image formed on the recording medium, Image quality can be further improved.
[0026]
Further, for example, as described in claim 4, the pattern generating means is formed as the specific pattern image at the same position in the main scanning direction with respect to a sub-scanning line scanned by the same laser beam. An image formed based on the dot arrangement in the sub-scanning direction with one dot width may be generated.
[0027]
According to the above configuration, as the specific pattern image, with respect to the sub-scanning line scanned by the same laser beam, the dot arrangement in the sub-scanning direction of one dot width formed at the same position in the main scanning direction is used as a reference. Since the image to be formed is generated, it is possible to form a specific pattern image which can easily determine which laser light source is used to form the dots of the specific pattern image formed by a plurality of laser beams. Pixel deviation between a plurality of laser beams can be easily detected from the density of the image, and the pixel deviation can be appropriately corrected from the detected density signal.
[0028]
Further, for example, as set forth in claim 5, the pattern generation means determines a dot as a position of the specific pattern image at a position before and after in a main scanning direction with respect to a reference dot array in a sub-scanning direction. An image to be formed in a cycle of several lines may be generated.
[0029]
According to the above configuration, as the specific pattern image, an image is generated in which dots are formed at a position before and after in the main scanning direction with a predetermined number of line cycles with respect to a reference dot array in the sub-scanning direction. A specific pattern image that can more easily determine which laser light source emitted a dot of the specific pattern image formed by the laser beam can be formed, and a plurality of dots can be formed based on the density of the formed image. Pixel deviation between the laser beams can be more easily detected, and the pixel deviation can be more appropriately corrected from the detected density signal.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the embodiments described below are preferred embodiments of the present invention, and thus various technically preferable limitations are added. However, the scope of the present invention is not limited to the embodiments described below. The embodiments are not limited to these embodiments unless otherwise specified.
[0031]
1 to 5 are views showing an embodiment of a multi-beam image forming apparatus according to the present invention, and FIG. 1 is a diagram showing a multi-beam image forming apparatus to which an embodiment of the multi-beam image forming apparatus according to the present invention is applied. FIG. 2 is a schematic perspective view of a scanning optical system of the apparatus 1.
[0032]
In FIG. 1, a multi-beam image forming apparatus 1 includes a light source unit 2, a first mirror / lens group 3, an optical polarizer 4, a second mirror / lens group 5, a photosensitive drum 6, a synchronization detecting unit 7, and the like. It is applied to a laser beam printer or the like that records an image.
[0033]
The light source unit 2 uses a laser diode in which a semiconductor laser serving as a laser light source and one photodiode for detecting the light intensity of a laser beam emitted from the semiconductor laser are incorporated in one element. And a plurality of such laser diodes. In the light source unit 2, a collimating lens for converting a divergent laser beam emitted from each laser diode into a parallel laser beam is disposed one-to-one with respect to each laser diode. After the emitted parallel beams are combined in an emission direction by a beam splitter, a beam prism, or the like, they are emitted from the light source unit 2 to the first mirror / lens group 3.
[0034]
The first mirror / lens group 3 includes a first cylindrical lens 31, a first mirror 32, an imaging lens 33, and the like, and a laser beam emitted from the light source unit 2 is incident on the first cylindrical lens 31. The first cylindrical lens 31 has a fixed refractive index in the sub-scanning direction, and converges a parallel laser beam incident from the light source unit 2 in the sub-scanning direction and makes the parallel laser beam incident on the first mirror 32. The first mirror 32 reflects the laser beam incident from the first cylindrical lens 31 to the imaging lens 33. The imaging lens 33 converts the parallel laser beam reflected by the first mirror 32 into a convergent laser beam. The light is converted and incident on the optical deflector 4.
[0035]
The optical deflector 4 includes a flat-plate type motor 41 and a polygon mirror 42 and the like that is driven to rotate at high speed in the direction of arrow A in FIG. 1 by the flat-type motor 41, and forms an image on a reflection surface (mirror surface) 42 a of the polygon mirror 42. A laser beam enters from the lens 33. The optical deflector 4 rotates the polygon mirror 42 at a high speed by the flat-plate type motor 41 to deflect the laser beam incident on the reflection surface 42 a of the polygon mirror 42 in the main scanning direction. Reflect.
[0036]
The second mirror / lens group 5 includes a second mirror 51 and a second cylindrical lens 52. The second mirror 51 reflects the laser beam reflected and deflected by the polygon mirror 42 in the direction of the second cylindrical lens 52. I do. The second cylindrical lens 52 forms an image of the laser beam reflected by the second mirror 51 on the photosensitive drum 6.
[0037]
The synchronization detection unit 7 includes a third mirror 71, a condenser lens 72, a synchronization detection plate 73, and the like. The third mirror 71 applies the laser beam reflected and deflected by the polygon mirror 42 onto the photosensitive drum 6. It is arranged at a position outside the scanning area, where the laser beam reflected and deflected by the polygon mirror 42 is incident. The third mirror 71 reflects the laser beam reflected and deflected by the polygon mirror 42 and incident toward the synchronization sensor 73, and the condenser lens 72 detects the laser beam incident from the third mirror 71 on the synchronization detection plate 73. Focus on The synchronization detection plate 73 has a light receiving element such as a photodiode provided as a synchronization detection sensor. The synchronization detection sensor photoelectrically converts an incident laser beam and writes an image on the photosensitive drum 6. The signal is converted into an electrical synchronization detection signal for keeping the start position in the scanning direction constant.
[0038]
The multi-beam image forming apparatus 1 according to the present embodiment is configured as shown in FIG. 2, and includes the multi-beam scanning optical system 80, an image signal generation unit 81, a pattern generation unit 82, and a pixel shift correction unit. 83, a laser driving unit 84, a photosensitive drum 6, a transfer unit 85, a fixing unit 86, an image density detecting unit 87, and the like.
[0039]
In FIG. 2, for simplicity of description, the light source unit 2 includes, as two laser diodes (LD), a multi-beam scanning optical system including a leading LD unit 2a and a trailing LD unit 2b. Although the case is shown, the light source unit 2 may use a multi-beam optical system including three or more laser diodes.
[0040]
When the multi-beam image forming apparatus 1 is applied to a digital copying machine, the image signal generation unit (image signal generation unit) 81 includes an image signal read by a CCD or the like by a scanner unit serving as a document reading unit. When the multi-beam image forming apparatus 1 is applied to a laser printer, an image signal transferred from a host personal computer through a printer driver. When the multi-beam image forming apparatus 1 is connected to a digital scanner, The image signal transferred through the scanner is input, and the image signal generation unit 81 performs various image processing suitable for the type of each image signal (character, photo, etc.) on the input image signal. After that, the image signals are separated as image signals for the respective laser diodes 2a and 2b and output to the pixel shift correction unit 83. That is, the image signal generation unit 81 generates image signals for the preceding LD unit 2a and the following LD unit 2b, which are laser diodes, and outputs the generated image signals to the pixel shift correction unit 83. Now, in FIG. 2, since the two-beam multi-beam scanning optical system 80 is used, it is separated into an odd-line image signal for the preceding laser diode 2a and an even-line image signal for the succeeding laser diode 2b. A pixel clock and a control signal for operating the subsequent laser diodes 2a and 2b are output together with this image signal.
[0041]
The pixel shift correction unit (shift correction unit) 83 receives the synchronization signal DETP from the synchronization detection unit 7 having the synchronization detection sensor and the density signal from the image density detection unit 87, and the pixel shift correction unit 83 The image signal is output to the laser drive unit 84 at a timing controlled based on the synchronization signal DETP input from the detection unit 7 and the density signal input from the image density detection unit 87.
[0042]
An image signal, a pixel clock, and a control signal from the pixel shift correcting unit 83 are input to the laser driving unit 84, and various modulation processes are performed on various image signals according to the type of the image signal. In response to this, the preceding laser diode (first LD) 2a and the following laser diode (second LD) 2b, which are the respective laser diodes, are turned on and off.
[0043]
The laser beams emitted from the preceding laser diode (first LD) 2a and the following laser diode (second LD) 2b are, as shown in FIG. 1, a first cylindrical lens 31, a first mirror 32, an imaging lens 33, and the like. The light is incident on the polygon mirror 42 of the optical deflector 4 via the optical deflector 4, is reflected by the polygon mirror 42, and is deflected and scanned on the photosensitive drum 6. At this time, the laser beam reflected by the tip of each mirror surface 42a of the polygon mirror 42 is incident on the synchronization detection sensor of the synchronization detection unit 7 in order to detect a synchronization signal.
[0044]
An electrostatic latent image is formed on the photosensitive drum 6 by the laser beam deflected and scanned on the photosensitive drum 6, and toner adheres to the electrostatic latent image on the photosensitive drum 6 by a developing unit (not shown). Then, the image is visualized as a toner image. The multi-beam image forming apparatus 1 is a transfer paper 88 which is a recording medium that has been transported between the photosensitive drum 6 and the transfer unit 85 at a predetermined timing by a transport roller (not shown) from the toner image on the photosensitive drum 6. The transfer paper 88 onto which the toner image has been transferred is separated from the photosensitive drum 6 and transported to the fixing unit 86. The fixing unit 86 heats and pressurizes the transfer paper 88 onto which the toner image has been transferred, fixes the toner image attached on the transfer paper 88, and transfers the toner image to the image density detection unit 87.
[0045]
The image density detecting section 87 detects the density of the image as a dot shift between a plurality of laser beams from a toner image which is an output image on the transfer paper 88, and outputs a density signal to the pixel shift correcting section 83.
[0046]
A pattern image is input to the image signal generation unit 81 from a pattern generation unit 82 independent of a scanner unit, a printer driver, and the like. The pattern generation unit 82 creates a specific pattern image, and outputs an image signal of the pattern image and a control signal to the image signal generation unit 81. The image signal generation unit 81 performs image processing on the image signal of the pattern image in the same manner as a normal image signal input from the scanner unit or the like, and then separates the image signal into image signals for the laser diodes 2a and 2b. , To the pixel shift correction unit 83. The pattern generating unit 82 generates a main scanning direction pixel shift detection pattern image 100 for detecting a pixel shift in the main scanning direction as the specific pattern image, and generates the generated main scanning direction pixel shift detection. The control signal of the pattern image 100 is output to the image density detecting section 87. The image density detecting section 87 uses the control signal to output the main scanning direction pixel shift generated on the transfer paper 88 in accordance with the output timing of the main scanning direction pixel shift detecting pattern image 100 input from the pattern generating section 82. The density level is detected from the output image of the detection pattern image 100, and the density signal is fed back to the pixel shift correction unit 83.
[0047]
Next, the operation of the present embodiment will be described. The multi-beam image forming apparatus 1 according to the present embodiment forms the main scan direction pixel shift detection pattern image generated by the pattern generation unit 82 on the transfer paper 88, and outputs the main scan direction pixel shift on the transfer paper 88. The density of the detection pattern image 100 is detected by the image density detection section 87, and pixel deviation is corrected based on the detection result.
[0048]
That is, the pattern generation unit 82 generates the main-scanning-direction pixel shift detecting pattern image 100 as shown in FIG. 3, and the main-scanning-direction pixel shift detecting pattern image 100 as shown in FIG. In a coordinate system where the scanning direction is the x-axis and the sub-scanning direction is the −y-axis, the dotted cells indicate one dot width and one line width, respectively. In the pattern image 100 for detecting a pixel shift in the main scanning direction, a line in which black dots each having a width of one dot and a certain length in the sub-scanning direction are formed at the leading end of the main scanning direction is regularly formed in the main scanning direction. A pattern image of arranged black dots is formed.
[0049]
When an image is formed by the two laser diodes 2a and 2b based on the pattern image 100 for detecting a pixel shift in the main scanning direction, a dot array of regularly arranged black dots constitutes the two beams constituting the multi-beam scanning optical system 80. Of the laser diodes 2a and 2b, a black dot is formed at the same position in the main scanning direction with one dot width with respect to the line formed by the preceding laser diode 2a, and is formed by the preceding laser diode 2a in the sub-scanning direction. A pattern in which a vertical line of black dots is drawn only with the line. That is, when an image is formed by the multi-beam scanning optical system 80 composed of the two laser beams 2a and 2b based on the pattern image 100 for detecting pixel shift in the main scanning direction, the leading laser diode 2a The black dots of the beam are arranged at the same position in the main scanning direction. Further, an image formed based on the pattern image 100 for detecting a pixel shift in the main scanning direction includes, in the first half in the sub-scanning direction, a line formed by the succeeding laser diode 2b and a preceding laser diode. With respect to the black dot of the vertical line of only the preceding laser beam of 2a, a position shifted by one dot in the main scanning direction, that is, a black dot is formed on the right side of one dot, and conversely, the latter half in the sub-scanning direction Is shifted by one dot in the main scanning direction with respect to the black dot of the vertical line of only the preceding laser beam of the preceding laser diode 2a to the line formed by the succeeding laser beam of the succeeding laser diode 2b. A black dot is formed at the position, that is, one dot to the left. In FIG. 3, the black dot line formed with one dot width at the leading end of the main scanning corresponds to the black dot of the succeeding laser beam on the right side of the black dot of the preceding laser beam in the regularly arranged pattern. Indicates the sub-scanning range, and conversely, in the range disposed on the left side, the sub-scanning range is indicated by white dot lines. In FIG. 3, black dots are arranged at the leading end in the sub-scanning direction at positions in the main scanning direction in which a vertical line is formed only by the preceding laser beam of the preceding laser diode 2a in the regular arrangement pattern. ing.
[0050]
The pattern generation unit 82 generates the pattern image 100 for detecting a pixel shift in the main scanning direction as described above, outputs the pattern image 100 to the image signal generation unit 81, and outputs the control signal of the pattern image 100 for detecting the pixel shift in the main scanning direction to the image density. Output to the detection unit 87.
[0051]
The image signal generation unit 81 outputs the main scanning direction pixel shift detection pattern image 100 input from the pattern generation unit 82 to the pixel shift correction unit 83, and the pixel shift correction unit 83 adjusts the timing to convert the image signal. Output to the laser drive unit 84. The laser driving unit 84 performs a modulation process based on the image signal of the pattern image 100 for detecting a pixel shift in the main scanning direction from the pixel shift correcting unit 83, and controls each laser diode according to the image signal and the control signal. The laser diode (first LD) 2a and the succeeding laser diode (second LD) 2b are turned on and off to form an electrostatic latent image of the pattern image 100 for detecting a pixel shift in the main scanning direction on the photosensitive drum 6.
[0052]
The multi-beam image forming apparatus 1 develops the electrostatic latent image of the pattern image 100 for detecting a pixel shift in the main scanning direction on the photosensitive drum 6 by a developing unit, and generates the developed pattern image 100 for detecting a pixel shift in the main scanning direction. The toner image is transferred onto the transfer paper 88 by the transfer unit 85, and the transfer paper 88 on which the toner image of the pattern image 100 for detecting a pixel shift in the main scanning direction is transferred is fixed by the fixing unit 86, and then the image density detection unit 87 Transport in the direction.
[0053]
The image density detector 87 calculates the timing at which the toner image of the pattern image 100 for detecting a pixel shift in the main scanning direction is output on the transfer paper 88 based on the control signal output from the pattern generator 82, and the timing The image density of the toner image of the pattern image 100 for detecting a pixel shift in the main scanning direction on the transfer paper 88 generated in the step (1) is detected and output to the pixel shift correcting unit 83.
[0054]
Here, when there is no pixel displacement of the laser diodes 2a and 2b in the main scanning direction, that is, when the pixel displacement is ± 0.0 dots, the pixel displacement for detecting the pixel displacement in the main scanning direction shown in FIG. The pixel density of the pattern image 100 and the density signal from the generated image detected by the image density detection unit 87 to be output match.
[0055]
On the other hand, if the pixel deviation between the laser diodes 2a and 2b in the main scanning direction is such that the following laser beam is generated 0.5 dots faster than the preceding laser beam, the pixel deviation in the main scanning direction shown in FIG. In response to the input of the detection pattern image 100, an output image as shown in FIG.
[0056]
From the output image as shown in FIG. 4, the image density detection unit 87 uses the one-dot black dot pattern in the main scanning direction positioned at the leading end in the sub-scanning direction and the sub-scanning position positioned at the leading end in the main scanning direction. Attention is paid to a black-and-white pattern of one dot width in the direction. The density of a black pixel disposed at the leading end in the sub-scanning direction is recognized, and the image density of a vertical line in the sub-scanning direction in which the black pixel is detected is immediately detected. That is, this vertical line is a portion where the vertical line is drawn only by the preceding laser beam of the preceding laser diode 2a in the pattern image 100 for detecting a pixel shift in the main scanning direction to be input. Then, when detecting the density of the vertical line, the image density detection unit 87 recognizes the density of the black pixel arranged at the leading end in the main scanning direction, and determines the range between the range where the black pixel is detected and the range where the white pixel is detected. The image densities of the vertical lines are separately detected, and the detection results are fed back to the pixel shift correction unit 83 as density signals.
[0057]
The pixel shift correction unit 83 corrects the pixel shift based on the density signal detected by the image density detection unit 87. At this time, the image density detection section 87 outputs the density signal to the pixel shift correction section 83 as a numerical value proportional to the density. That is, the image density detector 87 outputs a higher value as a density signal as the density of the detected image is higher, and outputs a lower value as the density of the detected image is lower. In addition, the pixel shift correction unit 83 recognizes from the image density detection unit 87 the density signal of the vertical line: Nb in the range where the black pixel is recognized at the leading end in the main scanning direction, and recognizes the white pixel at the leading end in the main scanning direction. The density signal Nw of the vertical line in the range described above is input as a density signal. The pixel displacement correction unit 83 compares which of Nb and Nw is larger, detects which of the preceding laser beam and the subsequent laser beam is displaced and in which direction, and detects the detected displacement. A control signal to be corrected is output to the laser drive unit 84.
[0058]
For example, in the case of FIG. 4, Nb> Nw. That is, in the Nb density detection range, one dot should be originally behind the main scanning direction in the main scanning direction pixel shift detection pattern image 100 in which a vertical line is formed only by the preceding laser beam. This is because some of the black dots of the row laser beam have entered. This is because the position of the following laser beam is shifted from the position of the preceding laser beam in the main scanning direction before the position of the laser beam. Accordingly, the density signal: Nb in the range where the vertical line of only the following laser beam is formed one dot behind the vertical line of only the preceding laser beam (main scanning front end: black pixel recognition range) is If the density signal is larger than Nw in the range where the vertical line of only the succeeding laser beam is formed one dot ahead of the vertical line of only the laser beam (the leading end of the main scanning: white pixel recognition range), When the position of the laser beam is used as a reference, it can be recognized that an image is formed in which the position of the succeeding laser beam is shorter than the actual beam pitch. Accordingly, the pixel shift correction unit 83 sets the timing of outputting the image signal of the succeeding laser beam (the succeeding LD unit) 2b in response to the synchronization signal DETP from the synchronization detection for a certain time in the main scanning direction. Control to delay.
[0059]
Thus, by controlling the output timing of the laser beam, the output timing of only the image signal is corrected without changing the timing of the synchronization signal between the two beams, and the output timing of the generated image formed as the output image is corrected. Pixel shift for each laser beam can be corrected.
[0060]
In contrast to the case shown in FIG. 4, when the pixel deviation between the laser diodes 2a and 2b occurs later in the succeeding laser beam than in the preceding laser beam, Nb <Nw. That is, in the vertical line of only the preceding laser beam within the range in which the white pixel is recognized at the leading end of the main scanning, a part of the black pixel of the succeeding laser beam which should be originally one dot forward in the main scanning direction enters. Because it is. In this case, if the position of the succeeding laser beam is longer than the actual beam pitch based on the position of the preceding laser beam, the pixel deviation correction unit 83 determines whether the succeeding laser diode (the latter laser diode) responds to the synchronization signal DETP. Control is performed such that the timing of outputting the image signal of the succeeding laser beam of the row LD unit 2b is advanced by a certain time in the main scanning direction.
[0061]
Thus, by controlling the output timing of the laser beam, the output timing of only the image signal is corrected without changing the timing of the synchronization signal between the two beams, and the output timing of the generated image formed as the output image is corrected. Pixel shift for each laser beam can be corrected.
[0062]
The above-described main-scanning-direction pixel shift detection pattern detection / position shift correction processing can be illustrated as in FIG. 5. That is, in the multi-beam image forming apparatus 1, first, the pattern generation unit 82 generates the pattern image 100 for detecting a pixel shift in the main scanning direction shown in FIG. 3 and outputs it to the image signal generation unit 81 (step S101).
[0063]
Next, the multi-beam image forming apparatus 1 detects the pixel deviation in the main scanning direction on the transfer paper 88 by the multi-beam scanning optical system 80 based on the pattern image 100 for pixel deviation detection in the main scanning direction from the image signal generator 81. After forming the toner image of the pattern image 100 for use (step S102), the fixing unit 86 fixes the toner image of the pattern image 100 for detecting a pixel shift in the main scanning direction on the transfer paper 88, and then the image density detecting unit 87 performs main scanning. The image density of a specific vertical line in the toner image of the directional pixel shift detection pattern image 100 is detected, and the detected density signal is fed back to the pixel shift correcting unit 83 (step S103).
[0064]
As described above, the pixel shift correction unit 83 focuses on the density signal of the vertical line, which should have been formed only by the preceding laser beam, whether the array of the succeeding laser beam is one dot ahead or one dot behind. Then, the pixel shift direction is recognized from the difference between the preceding laser beam and the succeeding laser beam (step S104), and the pixel shift is corrected based on the recognized pixel shift direction at the image signal output timing of the subsequent laser beam (step S104). S105).
[0065]
That is, the pixel shift correction unit 83 calculates the density signal: Nb in the range where the succeeding laser beam is arranged one dot behind the preceding laser beam in the main scanning direction, and the density signal in the range where the succeeding laser beam is arranged one dot ahead. The signal is compared with Nw (step S104). If Nb> Nw, it is determined that the interval between laser beams for image formation is shorter than the actual beam pitch, and the image of the succeeding laser beam is determined. The signal output timing is delayed with respect to the synchronization signal. Conversely, when Nb <Nw, it is determined that an image is formed longer than the actual beam pitch, and the image of the succeeding laser beam is determined with respect to the synchronization signal. Control is performed so that the signal output timing is advanced (step S105).
[0066]
In this corrected state, the multi-beam image forming apparatus 1 returns to step S101, forms the pattern image 100 for detecting a pixel shift in the main scanning direction on the transfer paper 88 in the same manner as described above, and By detecting the toner image of the pattern image 100 for detecting the pixel shift in the main scanning direction formed in the main scanning direction and determining the position shift, the pattern detection and the position shift correction processing are loop-processed, so that the preceding laser which is the object of the density signal is obtained. The distance in the main scanning direction between the vertical line that is supposed to be formed only by the beam and the vertical line before and after that is composed only of the succeeding laser beam is the same in the front and rear, and the vertical line Black pixels of the preceding and succeeding laser beams are formed without entering, and are the same as the input image of the pattern 100 for detecting a pixel shift in the main scanning direction shown in FIG. Pixel shift between the laser diode in the main scanning direction of a multi-beam so that the output image is obtained can be corrected.
[0067]
Then, when Nb = Nw in step S104, it is determined that the same output image as the input image of the main-scanning-direction pixel shift detection pattern 100 has been obtained, and the process ends.
[0068]
As described above, in the multi-beam image forming apparatus 1 according to the present embodiment, the pattern generation unit 82 generates the main scanning direction pixel shift detection pattern image 100 which is the predetermined specific pattern image, and the image signal generation unit 81 Then, based on the pattern image 100 for detecting a pixel shift in the main scanning direction, the image signal generating unit 81 generates an image signal for each of the LD units 2a and 2b and forms the image signal on the transfer paper 88 by the multi-beam scanning optical system 80. The density of the pattern image 100 for detecting a pixel shift in the main scanning direction is detected by a density detector 87 as a dot shift between a plurality of laser beams, and a density signal is output.
[0069]
Therefore, not only the pixel deviation of each laser beam in the synchronization detection sensor unit 7, but also the mutual relationship between the multi-beam scanning optical system 80 and the photosensitive drum 6, and the photosensitive drum 6 and the final output on the transfer paper 88 Pixel deviation between each laser beam including the correlation with an image can be detected.
[0070]
Further, in the multi-beam image forming apparatus 1 of the present embodiment, the pixel shift correcting unit 83 uses the LD unit 2a generated by the image signal generating unit 81 based on the density signal indicating the dot shift detected by the density detecting unit 87. 2b, the output timing of the image signal is adjusted to correct the dot deviation between the plurality of laser beams.
[0071]
Therefore, not only the pixel deviation of each laser beam in the synchronization detection sensor unit 7, but also the mutual relationship between the multi-beam scanning optical system 80 and the photosensitive drum 6, and the photosensitive drum 6 and the final output on the transfer paper 88 Pixel deviation between each laser beam including the correlation with the image can be corrected, and the image quality can be improved.
[0072]
Furthermore, in the multi-beam image forming apparatus 1 according to the present embodiment, the pattern generation unit 82 uses the main scanning direction pixel shift detection pattern image 100 as a specific pattern image in units of one dot width in the main scanning direction, and in the sub-scanning direction. 1 is an image in units of one line width, and an image in which the dot formation density per dot unit is constant is generated.
[0073]
Therefore, it is possible to easily detect a pixel shift between a plurality of laser beams, and appropriately correct the pixel shift from the density signal of the main scan direction pixel shift detection pattern image 100 formed on the transfer paper 88. Image quality can be further improved.
[0074]
In addition, the multi-beam image forming apparatus 1 according to the present embodiment uses the main scanning direction pixel shift detection pattern image 100, which is a specific pattern image, with respect to a sub-scanning line scanned by the same laser beam in the main scanning direction. An image formed based on a dot arrangement in the sub-scanning direction having a width of one dot formed at the same position is generated.
[0075]
Therefore, it is possible to easily determine which LD unit 2a or 2b laser beam has formed the dot of the output image of the main-scanning-direction pixel shift detection pattern image 100 which is a specific pattern image formed by a plurality of laser beams. A pattern image 100 for detecting a pixel shift in the scanning direction can be formed, a pixel shift between a plurality of laser beams can be easily detected from the density of the formed image, and a pixel shift can be detected from the detected density signal. Can be appropriately corrected.
[0076]
Further, the multi-beam image forming apparatus 1 according to the present embodiment, as the pattern image 100 for detecting a pixel shift in the main scanning direction, which is a specific pattern image, is arranged in the main scanning direction with respect to the reference dot array in the sub scanning direction. An image is generated in which dots are formed at the preceding and succeeding positions in a predetermined number of line cycles.
[0077]
Therefore, it is possible to further determine which of the LD units 2a and 2b has formed the laser beam emitted from the laser beam emitted from the output image of the pattern image 100 for detecting a pixel shift in the main scanning direction, which is a specific pattern image formed by a plurality of laser beams. A pattern image 100 for detecting a pixel shift in the main scanning direction that can be easily determined can be formed, and a pixel shift between a plurality of laser beams can be more easily detected from the density of the formed image. Pixel deviation can be more appropriately corrected from the obtained density signal.
[0078]
As described above, the invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to the above, and can be variously modified without departing from the gist thereof. Needless to say.
[0079]
【The invention's effect】
According to the multi-beam image forming apparatus of the present invention, an image signal for individually driving a plurality of laser light sources is generated by an image signal generator, and a plurality of image signals are generated by a multi-beam scanning optical system based on the image signal. A laser beam is emitted from each of the laser light sources, and the laser beam is irradiated on the photoconductor to form an electrostatic latent image, and the electrostatic latent image on the photoconductor is developed to form an image on a recording medium. At this time, the pattern generation means generates a predetermined specific pattern image and outputs it to the image signal generation means. Based on the specific pattern image, the image signal generation means generates an image signal for each laser light source and performs multi-beam scanning. Since the density of the specific pattern image formed on the recording medium by the optical system is detected by the density detecting means as a dot shift between a plurality of laser beams and a density signal is output, synchronous detection is performed. Each laser including not only the pixel shift of each laser beam in the sensor section, but also the correlation between the multi-beam scanning optical system and the photoconductor and the correlation between the photoconductor and the image on the recording medium that is the final output Pixel deviation between beams can be detected.
[0080]
According to the multi-beam image forming apparatus of the present invention, based on the density signal indicating the dot shift detected by the density detecting means, the image signal for each laser light source generated by the image signal generating means by the shift correcting means. Since the output timing of the laser beam is adjusted to correct the dot deviation between the plurality of laser beams, not only the pixel deviation of each laser beam in the synchronous detection sensor unit, but also the mutual relationship between the multi-beam scanning optical system and the photoconductor and It is possible to correct a pixel shift between respective laser beams including a mutual relationship between the photosensitive member and an image on a recording medium that is a final output, and to improve image quality.
[0081]
According to the multi-beam image forming apparatus of the third aspect, the pattern generating means is an image of one dot width unit in the main scanning direction and one line width unit in the sub scanning direction as the specific pattern image. Since an image in which the dot formation density per unit is constant is generated, a pixel shift between a plurality of laser beams can be easily detected, and a pixel shift is performed from a density signal of the specific pattern image formed on the recording medium. The deviation can be appropriately corrected, and the image quality can be further improved.
[0082]
According to the multi-beam image forming apparatus of the present invention, as a specific pattern image, one dot width formed at the same position in the main scanning direction with respect to the sub-scanning line scanned by the same laser beam. Generates an image that is formed based on the dot arrangement in the sub-scanning direction, so that a specific pattern that can easily determine which laser light source has formed the specific pattern image dots formed by multiple laser beams An image can be formed, a pixel shift between a plurality of laser beams can be easily detected from the density of the formed image, and a pixel shift can be appropriately corrected from the detected density signal. .
[0083]
According to the multi-beam image forming apparatus of the present invention, as a specific pattern image, a dot is arranged at a position before and after the reference dot array in the sub-scanning direction in the main scanning direction at a predetermined line number cycle. Since an image to be formed is generated, it is possible to form a specific pattern image that can more easily determine which laser light source emitted a laser beam emitted from a specific pattern image formed by a plurality of laser beams. Thus, it is possible to more easily detect a pixel shift between a plurality of laser beams from the density of a formed image, and to correct the pixel shift more appropriately from the detected density signal.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of a scanning optical system of a multi-beam image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of the multi-beam image forming apparatus of FIG.
FIG. 3 is a diagram showing an example of a main-scanning-direction pixel shift detection pattern generated by the pattern generation unit of FIG. 2;
FIG. 4 shows an example of an output image formed in response to the input of a pattern for detecting a pixel shift in the main scanning direction of FIG. 3 when a succeeding laser beam is generated 0.5 dots faster than a preceding laser beam. FIG.
5 is a flowchart showing a main-scanning-direction pixel shift detection pattern detection / position shift correction process performed by the multi-beam image forming apparatus of FIG. 2;
[Explanation of symbols]
1 Multi-beam image forming apparatus
2 Light source unit
2a Leading LD unit
2b Subsequent LD unit
3 First mirror lens group
4 Optical polarizer
5 Second mirror lens group
6 Photoconductor drum
7 Synchronization detector
31 1st cylindrical lens
32 1st mirror
33 imaging lens
41 Flat plate motor
42 polygon mirror
42a reflective surface
51 Second mirror
52 Second cylindrical lens
71 Third mirror
72 Condensing lens
73 Synchronous detection plate
80 Write control unit
81 Multi-beam scanning optical system
81 Image signal generator
82 Pattern Generator
83 Pixel shift correction unit
84 Laser Driver
85 Transfer unit
86 Fixing unit
87 Image density detector
88 Transfer paper
100 Pattern image for detecting pixel shift in the main scanning direction

Claims (5)

A multi-beam scanning optical system that emits a laser beam from each of the plurality of laser light sources and irradiates the laser beam onto the photoreceptor to form an electrostatic latent image, and an image signal that individually drives the plurality of laser light sources. A multi-beam image forming apparatus for developing an electrostatic latent image on the photoreceptor to form an image on a recording medium. A pattern generation unit that outputs to a signal generation unit, and the image signal generation unit generates an image signal for each of the laser light sources based on the specific pattern image generated by the pattern generation unit, and generates the image signal based on the image signal. A density signal is detected by detecting the density of the specific pattern image formed on the recording medium by a multi-beam scanning optical system as a dot shift between the plurality of laser beams. Multibeam image forming apparatus characterized by comprising a concentration detector for force, the. The multi-beam image forming apparatus adjusts an output timing of an image signal for each laser light source generated by the image signal generation unit based on a density signal indicating a dot shift detected by the density detection unit, and 2. The multi-beam image forming apparatus according to claim 1, further comprising a shift correcting unit for correcting a dot shift between the laser beams. The pattern generating means may generate, as the specific pattern image, an image having one dot width unit in the main scanning direction and one line width unit in the sub-scanning direction, and having a constant dot formation density per dot unit. 3. The multi-beam image forming apparatus according to claim 1, wherein: The pattern generating means is based on a dot arrangement in the sub-scanning direction of one dot width formed at the same position in the main scanning direction with respect to the sub-scanning line scanned by the same laser beam as the specific pattern image. The multi-beam image forming apparatus according to claim 1, wherein the multi-beam image forming apparatus generates an image formed as a multi-color image. The pattern generation means generates an image in which dots are formed at predetermined positions in a line preceding and succeeding in a main scanning direction with respect to a reference dot array in the sub-scanning direction, as the specific pattern image. The multi-beam image forming apparatus according to any one of claims 1 to 3, wherein

Images