JP4083935B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image of a laser printer, a digital copying machine, a facsimile machine, a printing machine, etc. that writes an image on a photoreceptor using a plurality of multi-beams (forms an electrostatic latent image that is an electrostatic image). The present invention relates to a forming apparatus.
[0002]
[Prior art]
Conventionally, in an image forming apparatus such as a laser printer or a digital copying machine, an electrostatic latent image is formed by scanning a photosensitive member (a surface charged in advance) with a laser beam from a single beam scanning optical system. The latent image is developed with toner to form a toner image, and then a series of electrophotographic processes for forming (transfer / fixing) the toner image on a recording medium such as paper is performed.
[0003]
Here, the conventional single beam scanning optical system will be described in more detail. A laser beam emitted from a single laser light emitting element (semiconductor laser) is cycled using a polygon mirror (rotating polygon mirror) rotated by a polygon motor. The surface of the photosensitive member (on the photosensitive member) is scanned in the main scanning direction (axial direction of the photosensitive member) to form an electrostatic latent image.
[0004]
At this time, since the photoconductor is rotating and its surface (on the photoconductor) is moved in the sub-scanning direction, which is the rotation direction, scanning with the laser beam is also performed in the sub-scanning direction. .
In an image forming apparatus equipped with such a single beam scanning optical system, the scanning speed in the main scanning direction by the laser beam onto the photosensitive member is a parameter of the rotational speed of the polygon motor, and the limit of the scanning speed is the polygon motor. Limited by the limit of the rotation speed.
[0005]
In recent years, due to the limitation of the scanning speed in the main scanning direction, each laser beam (multi-beam) emitted from each of the plurality of laser light emitting elements is periodically deflected using a polygon mirror so that the surface of the photoreceptor is in the main scanning direction. A multi-beam scanning optical system has been proposed in which a scanning speed is controlled by 1 / (number of laser light emitting elements) to form an electrostatic latent image on a photosensitive member by performing parallel scanning at the same time. The two-beam scanning optical system used has been realized.
[0006]
However, a multi-beam scanning optical system having three or more beams has not been realized yet, and it is necessary to develop a lens optical system that stably scans the photosensitive member in parallel with three or more laser beams.
[0007]
On the other hand, for example, in a digital copying machine, a copying speed (printing speed) equivalent to that of a conventional analog copying machine is required.
In order to increase the printing speed of an image forming apparatus such as a digital copying machine or a laser printer, it is preferable to simply increase the number of 2 beams, 3 beams, and the number of laser beams that are simultaneously scanned on the photosensitive member. As described above, a multi-beam scanning optical system having three or more beams has not yet been put into practical use.
[0008]
When performing parallel scanning on the photosensitive member with two or more laser beams at the same time, the scanning interval (scanning pitch) in the sub-scanning direction of each laser beam on the photosensitive member must be sufficiently close using an optical stop. Don't be.
Currently, development of technology for manufacturing a plurality of LDs (semiconductor lasers) in close proximity is progressing, but currently, there are few LD arrays composed of three or more LDs, and the manufacturing process is very limited. This is difficult and expensive.
[0009]
Therefore, by using a plurality of two-beam scanning optical systems that are already in practical use, it is possible to increase the printing speed of an image forming apparatus such as a digital copying machine or a laser printer.
If a multi-beam scanning optical system having three or more beams is put into practical use in the future, a higher printing speed can be realized by using a plurality of the multi-beam scanning optical systems.
[0010]
[Problems to be solved by the invention]
However, when using a plurality of multi-beam scanning optical systems, it is necessary to adjust the scanning pitch in the sub-scanning direction by each laser beam on the photosensitive member to be uniform, but the adjustment work is very troublesome. is there. In other words, during the assembly process of the image forming apparatus, the operator measures the actual formed image and the scanning pitch of each laser beam on the photosensitive member in the sub-scanning direction by the number of multi-beam scanning optical systems using a special device. However, it is necessary to adjust the scanning pitch to be uniform based on the measurement result.
[0011]
  The present invention has been made in view of the above points. In an image forming apparatus using a plurality of multi-beam scanning optical systems, the sub-scanning direction of each laser beam on the photosensitive member can be used without using a special apparatus. The purpose is to obtain a high-quality image by making it possible to adjust each scanning pitch to be uniform.To do.
[0012]
[Means for Solving the Problems]
The present invention has a laser light source composed of a plurality of laser light emitting elements, a plurality of laser beams emitted from the laser light source are periodically deflected by using a polygon mirror, and moved on a photosensitive member moved in the sub-scanning direction. In order to achieve the above object, an image forming apparatus provided with a plurality of multi-beam scanning means for simultaneously scanning in the main scanning direction to form an electrostatic latent image is characterized by the following.
[0013]
  According to the first aspect of the present invention, each laser light source of each multi-beam scanning means is arranged so that a plurality of laser light emitting elements are arranged on one straight line, and each laser light source of each multi-beam scanning means is each provided with a plurality of lasers. A plurality of rotating means for independently rotating in the direction perpendicular to the laser beam emitting direction around any point on a straight line passing through each light emitting point of the light emitting element is provided, and each multi-beam scanning means is provided according to image information Laser modulation means for independently modulating and controlling a plurality of laser light emitting elements in each laser light source, and a plurality of laser beams respectively emitted from each laser light source of each multi-beam scanning means by the means Each scanning pitch in the sub-scanning direction on the photoconductorBy using each rotating means,Beam scanning pitch adjusting means for adjusting each independentlyAnd detecting each of the plurality of laser beams emitted from each laser light source of each multi-beam scanning means and scanned in the main scanning direction by the polygon mirror before reaching each of the photosensitive members. Synchronous detection means for detecting the scanning position of the laser beam, and scanning position for independently measuring the time interval of each scanning position detection edge with respect to a plurality of laser light emitting elements for each laser light source of each multi-beam scanning means by the means An interval measuring unit, and the beam scanning pitch adjusting unit compares each measurement result by the scanning position interval measuring unit, and uses a plurality of laser beams emitted from a predetermined laser beam source of the multi-beam scanning unit. The scanning pitch in the sub-scanning direction on the photoreceptor and a plurality of laser beams emitted from the laser light source of other multi-beam scanning means. After calculating the adjustment angle of the scanning pitch so that the scanning pitch in the sub-scanning direction on the photosensitive member by the beam is the same, the laser light source of one predetermined multi-beam scanning means is fixed, and the others By rotating the laser light source of the multi-beam scanning means by the adjustment angle by the corresponding rotating means, the plurality of laser beams respectively emitted from the laser light sources of the multi-beam scanning means are used on the photoreceptor. Each scanning pitch in the sub-scanning direction is automatically adjusted.Is.
[0015]
  Claim2The invention of claim1In the image forming apparatus, each rotation means is a means capable of electrically controlling a minute rotation angle such as a stepping motor or a servo motor.
[0020]
  Claim3The invention of claim1 or 2In the image forming apparatus, after turning on the power and before starting the image forming operation, when each multi-beam scanning unit starts scanning with each of the plurality of laser beams emitted from each laser light source at a predetermined speed, The beam scanning pitch adjusting means performs the adjustment process.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 2 is a schematic configuration diagram showing an example around the drum of the image forming apparatus according to the embodiment of the present invention.
[0022]
The image forming apparatus 1 includes a photosensitive drum (hereinafter simply referred to as “photosensitive member”) 2 as an image carrier, a first two-beam writing unit 3 and a second two as a plurality of multi-beam scanning units. The electrophotographic image forming apparatus includes a beam writing unit 4 and a charging unit 5, a developing unit 6, a transfer unit 7, a separation unit 8, and a cleaning unit 9 centered on the photosensitive member 2.
[0023]
Note that a position a where the first two-beam writing unit 3 scans the photosensitive member 2 with a plurality of (two in this example) laser beams and a plurality of second two-beam writing units 4 (in this example). It is assumed that the distance from the position b where the photosensitive member 2 is scanned by two laser beams is D mm.
Here, a series of electrophotographic processes in the image forming apparatus 1 will be briefly described.
[0024]
The surface of the photoreceptor 2 rotated in the direction of the arrow by a main motor (not shown) is uniformly charged by the charging unit 5.
The charged surface has two laser beams (total of four laser beams) modulated from the first two-beam writing unit 3 and the second two-beam writing unit 4 according to the image information of each line. ) At the same time, an electrostatic latent image is formed.
[0025]
The electrostatic latent image is developed with toner from the developing unit 6 to form a toner image.
The toner image is transferred by the transfer unit 7 onto paper (other recording medium) fed from a paper feed tray (not shown).
[0026]
The sheet on which the toner image has been transferred is separated from the photoreceptor 2 by the separation unit 8 and then sent to a fixing unit (not shown) where the toner image is thermally fixed and discharged outside the apparatus.
On the other hand, the toner remaining on the photoreceptor 2 is removed and collected by the cleaning unit 9.
[0027]
FIG. 3 is a perspective view showing a configuration example of a two-beam scanning optical system (multi-beam scanning optical system) constituting each of the first two-beam writing unit 3 and the second two-beam writing unit 4.
The main scanning directions (main scanning directions) on the photosensitive member 2 by the respective two-beam scanning optical systems (first and second two-beam writing units 3 and 4) are opposite to each other.
[0028]
In each of these two-beam scanning optical systems, 2LD (semiconductor laser diode) units 11 and 21 as laser light sources, and an fθ lens 13 for making the scanning speed of each of the two laser beams on the photosensitive member 2 constant. , 23 and reflecting mirrors 14, 24 are arranged.
[0029]
Further, a common rotary polygon mirror (hereinafter referred to as “polygon mirror”) 15 is disposed in each of the two-beam scanning optical systems, and the polygon mirror 15 is separated from each of the 2LD units 11 and 21 by a polygon motor (not shown). The two laser beams respectively emitted are periodically deflected, and simultaneously scanned in parallel on the photosensitive member 2 moved in the sub-scanning direction via an optical element such as a lens to form an electrostatic latent image.
[0030]
Further, a common synchronization detection sensor (synchronization detection means) 16 is disposed in each of the two-beam scanning optical systems, and the synchronization detection sensor 16 is emitted from each of the 2LD units 11 and 21, and the polygon mirror 15 By detecting (receiving) the two laser beams scanned in the main scanning direction by the reflecting mirrors 17 and 27 before reaching the photosensitive member 2, the scanning positions of the two laser beams can be determined. It detects and generates and outputs an electrical timing signal (hereinafter referred to as “synchronization detection signal”).
[0031]
Therefore, by using the synchronization detection signal output from the synchronization detection sensor 16, the emission start timing of each laser beam for electrostatic latent image formation (image writing) can be controlled for each scan (periodically). it can.
It is assumed that the synchronization detection sensor 16 is optically disposed so as to be substantially flush with the surface of the photoreceptor 2. The synchronization detection sensor 16 may be provided for each two-beam scanning optical system.
[0032]
Here, the two multi-beam scanning optical systems used in the image forming apparatus 1 of this embodiment are each a two-beam scanning optical system. The relationship between the respective parts when using the two two-beam scanning optical systems is as follows. explain. However, description of the operation of the two-beam scanning optical system is omitted.
[0033]
In general, the rotational speed (RPM) of a polygon motor directly connected to a polygon mirror is determined according to the required printing speed, the linear velocity of the photoconductor is v (mm / s), and the pixel density of the image information is dpi ( dot per inch), where n is the number of reflection surfaces (number of mirror surfaces) of the polygon mirror, it is determined by the following equation (1).
RPM = (v × dpi × 60) / (25.4 × n) (1)
[0034]
The equation shown in (1) above is the number of rotations of the polygon motor when the photosensitive member is scanned with a laser beam from a single LD, and each laser beam from a plurality of LDs as in this embodiment. When the photoconductor is simultaneously scanned in parallel, the rotational speed of the polygon motor is determined by the following equation (2).
RPM = (v × dpi × 60) / (25.4 × n × m) (2)
[0035]
Here, m is the number of LD simultaneous scans.
In this embodiment, since there are four LDs, m = 4, and the rotation speed of the polygon motor can be suppressed to ¼ compared to the case of one LD.
[0036]
FIG. 1 is a perspective view illustrating a configuration example of the 2LD units 11 and 21.
The 2LD unit 11 includes LDs (semiconductor laser diodes) 31 and 32 as laser light emitting elements, collimating lenses 33 and 34, apertures 35 and 36, a beam combining prism 37, and the like. Similarly to the above, the 2LD unit 21 includes LDs 41 and 42, collimating lenses 43 and 44, apertures 45 and 46, a beam combining prism 47, and the like.
[0037]
In the 2LD unit 11, the laser beam emitted from the LD 31 passes through the collimating lens 33 and the aperture 35, passes through the reflection surface 37 b of the beam combining prism 37, is emitted from the prism 37, and is emitted from the LD 32. Similarly, two beams emitted from the LDs 31 and 32 pass through the collimating lens 34 and the aperture 36, are reflected by the reflecting surfaces 37 a and 37 b of the beam combining prism 37, and are emitted from the prism 37. The scanning pitch in the sub-scanning direction on the photosensitive member 2 by the laser beam is made close (beam synthesis processing).
[0038]
The adjustment of the scanning pitch in the sub-scanning direction on the photosensitive member 2 by the two laser beams emitted from the LDs 31 and 32 of the 2LD unit 11 is performed by using the stepping motor 38 as a power source and the light emission point of the LD 31 (light emission of the LD 32). It can be realized by rotating the entire 2LD unit 11 in a direction perpendicular to the laser beam emission direction.
[0039]
On the other hand, also in the 2LD unit 21, the laser beam emitted from the LD 41 passes through the collimating lens 43 and the aperture 45, passes through the reflecting surface 47 b of the beam combining prism 47, and is emitted from the prism 47 and emitted from the LD 42. Similarly, the laser beam passes through the collimating lens 44 and the aperture 46, is reflected by the reflecting surfaces 47 a and 47 b of the beam synthesis prism 47, and is emitted from the prism 47, thereby being emitted from the LDs 41 and 42. The scanning pitches in the sub-scanning direction on the photosensitive member 2 by the two laser beams are made close to each other.
[0040]
The adjustment of the scanning pitch in the sub-scanning direction on the photosensitive member 2 by the two laser beams emitted from the LDs 41 and 42 of the 2LD unit 21 is performed by using the stepping motor 48 as a power source and the light emission point of the LD 41 (light emission of the LD 42). This can be realized by rotating the entire 2LD unit 21 in the direction perpendicular to the laser beam emission direction.
[0041]
Each of the stepping motors 38 and 48 is a rotating means that can be electrically controlled by changing a minute rotation angle by changing the number of rotation pulses of the stepping motor. Instead of the stepping motors 38 and 48, other rotating means such as a servo motor can be used. When one LD unit is equipped with three or more LDs, the entire LD unit is perpendicular to the laser beam emission direction around any point on a straight line passing through each light emitting point. It can also rotate in the direction.
[0042]
Here, on the photosensitive member 2 by the two laser beams respectively emitted from the 2LD units 11 and 21 of the first and second two-beam writing units 3 and 4 (each two-beam scanning optical system). Each scanning pitch in the sub-scanning direction depends on the mounting of the 2LD units 11 and 12, the variation in the optical characteristics of the optical elements of the first and second two-beam writing units 3 and 4, the mounting accuracy of each optical element, etc. From the beginning, each cannot be uniform (same).
[0043]
Therefore, in the image forming apparatus 1 of this embodiment, the 2LD units 11 and 21 are independently rotated by the stepping motors 38 and 48 constituting the beam pitch adjusting mechanism, respectively, so that the 2LD units 11 and 21 are respectively rotated. Beam scanning pitch adjustment processing for independently adjusting each scanning pitch in the sub-scanning direction on the photosensitive member 2 by each of the two emitted laser beams (each multi-beam) is performed, and each scanning pitch is set. It can be uniform (same).
[0044]
By performing the beam scanning pitch adjustment process, during the image forming operation, the two laser beams respectively emitted from the 2LD units 11 and 21 are periodically deflected using the polygon mirror 15 in the sub-scanning direction. An electrostatic latent image can be formed by performing parallel scanning on the moved photosensitive member 2 in the main scanning direction at a constant scanning pitch.
[0045]
By the way, as shown in FIG. 3, the optical path of the laser beam from the reflecting surface of the polygon mirror 15 to the reflecting surface of the reflecting mirror 17 at a certain time point (referred to as the first time point), and another time point (second time point). The angle of the laser beam optical path from the reflecting surface of the polygon mirror 15 to the reflecting surface of the reflecting mirror 14 at the time) is α, and the reflection of the reflecting mirror 27 from the reflecting surface of the polygon mirror 15 at the first time If the angle between the optical path of the laser beam to the surface and the optical path of the laser beam from the reflecting surface of the polygon mirror 15 to the reflecting surface of the reflecting mirror 24 at the second time point is β, the angles α and β are α It is assumed that each reflection mirror is arranged so as to satisfy a relation of> β.
[0046]
Thus, since the angles α and β are in a relationship of α> β, for example, as shown in FIG. 4, the output of the synchronization detection signal from the synchronization detection sensor (photodetector) 16 is a polygon. Since the time difference is caused by the scanning of each multi-beam (two laser beams) by the mirror 15, the scanning position of each multi-beam can be determined (detected).
[0047]
Further, as shown in FIGS. 1 and 5, in each of the 2LD units 11 and 21, the light emission of each LD so that the scanning of the two laser beams emitted from each LD is shifted in time. Since the dots are attached so as to be diagonally aligned on a straight line, the scanning position of the two laser beams emitted from the LDs can be detected by the synchronization detection sensor 16.
[0048]
FIG. 6 is a block diagram illustrating a configuration example of a main part of the control unit of the image forming apparatus 1 of this embodiment.
In FIG. 6, image information input to the main control unit 60 by the image input unit 50 such as a scanner is subjected to predetermined image processing by the image processing unit 62 and then transmitted to the writing control unit 70.
[0049]
The image information input to the main control unit 60 is normally input at a pixel density of 600 dpi.
The CPU 61 is a microcomputer including a central processing unit, ROM, RAM, and the like, and comprehensively controls the entire image forming apparatus 1. The CPU 61 sends the designation information of the pixel density to the write control unit 70 before the image information is sent from the image processing unit 62 to the write control unit 70.
[0050]
The write control unit 70 includes a synchronization signal separation unit 71, an image information separation unit 72, a first LD unit modulation unit 73, and a second LD unit modulation unit 74. Thus, the function as the beam scanning pitch adjusting means according to the present invention is realized.
[0051]
The synchronization signal separation unit 71 uses the synchronization detection signal from the synchronization detection sensor 16 to detect the time interval (scanning time interval) of each scanning position detection edge with respect to each LD 31 and 32 of the 2LD unit 11 and each LD 41 and 42 of the 2LD unit 21. Is provided with a measuring unit (scanning position interval measuring means) 71a that independently measures the time interval of each scanning position detection edge.
[0052]
For example, as shown in FIG. 7, the writing control unit 70 measures the time interval of each scanning position detection edge with respect to each LD 31, 32 of the 2LD unit 11 by the measuring unit 71 a of the synchronization signal separating unit 71. The scanning pitch in the sub-scanning direction on the photosensitive member 2 by the two laser beams emitted from the LDs 31 and 32 can be obtained in a correlated manner.
Moreover, the beam scanning pitch adjustment process shown in the following (1) to (3) can be performed.
[0053]
(1) During the manufacturing process (assembly process) of the image forming apparatus 1, each 2LD unit 11, by each stepping motor 38, 48 of FIG. 1 according to an operator's instruction (for example, a predetermined key operation on the operation panel). The scanning pitches in the sub-scanning direction on the photosensitive member 2 by the two laser beams respectively emitted from the 2LD units 11 and 21 are independently adjusted by rotating the 21 independently.
[0054]
(2) Before the image forming apparatus 1 starts the image forming operation after the power is turned on, the polygon mirror 15 is stably rotated at a predetermined rotational speed, and each two-beam scanning optical system (first, second 2 Each time the beam writing units 3 and 4) start scanning with the two laser beams respectively emitted from the 2LD units 11 and 21 at a predetermined speed (or other time points), the measuring unit 71a may Each of the 2LD units 11 and 21 is individually rotated by the stepping motors 38 and 48 so that the measurement results (scan position time intervals) are the same. Each scanning pitch in the sub-scanning direction on the photosensitive member 2 by the two laser beams is automatically adjusted.
[0055]
Specifically, for example, at the time point described above, each measurement result by the measurement unit 71a is compared, and one predetermined two-beam scanning optical system (of the first and second two-beam writing units 3 and 4) is compared. The scanning pitch in the sub-scanning direction on the photosensitive member 2 by the two laser beams emitted from any one of the 2LD units and the photosensitive by the two laser beams emitted from the 2LD units of the other two-beam scanning optical systems The adjustment angle (adjustment value) of the latter scanning pitch is calculated by calculation so that the scanning pitch in the sub-scanning direction on the body 2 is the same, and 2LD of one predetermined two-beam scanning optical system is calculated. The unit is fixed, and the 2LD units of the other two-beam scanning optical systems are rotated by the adjustment angle by the corresponding stepping motors, so that the 2LD units 11 and 21 are respectively The sub-scanning direction of each scanning pitch on the photosensitive member 2 by each two laser beams issued automatically adjusted.
[0056]
Alternatively, by rotating the 2LD units 11 and 21 independently by the stepping motors 38 and 48 so that each measurement result by the measurement unit 71a coincides with a preset reference value at the time point described above, The respective scanning pitches in the sub-scanning direction on the photosensitive member 2 by the two laser beams respectively emitted from the 2LD units 11 and 21 are automatically adjusted.
[0057]
In this case, during the manufacturing process of the image forming apparatus 1, the scanning pitch in the sub-scanning direction on the photosensitive member 2 by each laser beam is determined by the mounting position accuracy of the first two-beam writing unit 3. In order to scan the photosensitive member 2 with the pixel density (sub-scanning pixel density), how long is the time interval of the scanning position detection edges for the LDs 31 and 32 of the 2LD unit 11 by the synchronization detection sensor 16? And the result is stored in the image forming apparatus 1 as a reference value.
[0058]
Since each of the beam scanning pitch adjustment processes described above corresponds to a normal pixel density (600 dpi in this embodiment), the pixel density designated by the pixel density designation information from the main control unit 60 is used. When (for example, the pixel density of the image information actually input by the image input unit 50) is different from the normal pixel density, each of the beam scanning pitch adjustment processes described above is performed according to the designated pixel density. To do. As a result, the scanning pitch in the sub-scanning direction on the photosensitive member 2 by the two laser beams respectively emitted from the 2LD units 11 and 21 becomes an optimum scanning pitch corresponding to the designated pixel density. .
[0059]
As described above, by performing each beam scanning pitch adjustment process, in the image forming apparatus 1 of this embodiment, the first and second two-beam writing units 3 and 4 are connected to the 2LD units 11 and 21, respectively. The two laser beams respectively emitted are periodically deflected by using the polygon mirror 15, and are optimally adapted to the pixel density simultaneously designated in the main scanning direction on the photosensitive member 2 moved in the sub-scanning direction. An electrostatic latent image can be formed by parallel scanning at a scanning pitch.
[0060]
Here, when the pixel density is changed from 600 dpi to 400 dpi, the scanning pitch in the sub-scanning direction on the photosensitive member 2 by the two laser beams emitted from the LDs 31 and 32 of the 2LD unit 11 is shown in FIG. To change.
[0061]
On the other hand, the synchronization signal separation unit 71 in FIG. 6 uses the synchronization detection signal from the synchronization detection sensor 16 as a synchronization signal indicating the scanning position of each laser beam, and as shown in FIG. 4, four synchronization signals DETP1, DETP3, DETP2, and so on. A process of separation into DETP4 and output to the image information separation unit 72 is performed.
[0062]
The image information separation unit 72 separates image information from the main control unit 60 in units of main scanning (lines), and image information of odd lines (ODD) (odd lines of electrostatic latent images formed on the photoreceptor 2). Image information) is sent to the first LD unit modulation section 73 together with the synchronization signals DETP1 and DETP3 from the synchronization signal separation section 71, and the image information of the even-numbered line (EVEN) (the electrostatic formed on the photosensitive member 2). The image information for the even lines of the latent image is sent to the second LD unit modulator 74 together with the synchronization signals DETP2 and DETP4 from the synchronization signal separator 71.
[0063]
The first LD unit modulation unit 73 performs modulation control on the LDs 31 and 32 of the 2LD unit 11 according to the synchronization signals DETP1 and DETP3 from the image information separation unit 72 and the image information of odd lines. This first LD unit modulation section 73 is assumed to be included in the first two-beam writing unit 3 of FIG.
The second LD unit modulator 74 modulates and controls each of the LDs 41 and 42 of the 2LD unit 21 in accordance with the synchronization signals DETP2 and DETP4 from the image information separator 72 and the even line image information. This second LD unit modulator 74 is assumed to be included in the second two-beam writing unit 4 of FIG.
[0064]
FIG. 9 is a block diagram illustrating a configuration example of the first LD unit modulation unit 73 and the second LD unit modulation unit 74 of FIG.
The first LD unit modulation section 73 includes a control section 80 and LD modulation sections (laser modulation means) 81 and 82.
The control unit 80 sends the image information of odd lines (for two lines) from the image information separation unit 72 to the LD modulation unit 81 and the LD modulation unit 82 in synchronization with the synchronization signals DETP1 and DETP3, respectively.
[0065]
The LD modulation unit 81 controls the LD (laser light emitting element) 31 of the 2LD unit 11 according to the odd-numbered line image information from the control unit 80 to independently modulate (turn on / off) and emit light.
The LD modulator 82 also causes the LD 32 of the 2LD unit 11 to independently modulate and emit light according to the image information of the odd lines from the controller 80.
[0066]
The second LD unit modulation unit 74 includes a control unit 90 and LD modulation units (laser modulation means) 91 and 92.
The control unit 90 includes a line memory 101 and an image inversion unit 102.
[0067]
The line memory 101 has a time difference corresponding to the amount of deviation between the scanning positions a and b (see FIG. 2) on the photosensitive member 2 by the two-beam writing units 3 and 4 and the linear velocity of the photosensitive member 2. In order to enable each of the two-beam writing units 3 and 4 to scan the photoconductor 2 with a laser beam, the image information of even lines (for two lines) from the image information separation unit 72 is stored during the time difference (temporary storage). Temporary storage for only time).
[0068]
The image inversion unit 102 inverts the image information of even lines (for two lines) temporarily stored in the line memory 101 and sequentially sends the image information to the LD modulation units 91 and 92 from the least significant bit.
The LD modulator 91 independently modulates and controls the LD 41 of the 2LD unit 21 in accordance with the even line image information from the controller 90.
The LD modulator 92 also independently modulates and controls the LD 42 of the 2LD unit 21 according to the even line image information from the controller 90.
[0069]
Next, the first LD unit modulation unit 73 and the second LD unit modulation unit 74 will be described more specifically.
The control unit 80 of the first LD unit modulation unit 73 includes 1, 5,..., 4m + 1 (m = 0, 1, 2, 2) out of the image information of odd lines (for two lines) from the image information separation unit 72. 3,..., The image information of the line is sequentially sent to the LD modulation unit 81 in synchronization with the falling edge of the synchronization pulse of the synchronization signal DETP 1, and 3, 7,..., 4 m + 3 (m = 0, 1, 2, 3 ,..., The image information of the line is sequentially transmitted to the LD modulator 82 in synchronization with the falling edge of the synchronization pulse of the synchronization signal DETP3.
[0070]
The control unit 90 of the second LD unit modulation unit 74 temporarily stores the image information of even lines (for two lines) from the image information separation unit 72 in the line memory 101 for a time given by the following equation (3). .., 4m + 2 (m = 0, 1, 2, 3,...) Line image information of the image information is synchronized with the falling edge of the synchronization pulse of the synchronization signal DETP2. Inverted by the inversion unit 102 and sequentially sent from the least significant bit (the rear end of the main scanning) to the LD modulation unit 91, on the 4th, 8,..., 4m + 4 (m = 0, 1, 2, 3,. The image information is synchronized with the falling edge of the synchronization pulse of the synchronization signal DETP4, inverted by the image inversion unit 102, and sequentially transmitted from the least significant bit to the LD modulation unit 92.
[0071]
Temporary storage time T (s) = D (mm) / v (mm / s) (3)
In this embodiment, the control unit 90 of the second LD unit modulation unit 74 includes the line memory 101 and the image inversion unit 102. However, the line memory 101 and the image inversion unit 102 are deleted, and they are equivalent to them. A line memory and an image inverting unit having a function may be provided between the image information separating unit 72 and the second LD unit modulating unit 74 or in the image information separating unit 72.
[0072]
The LD modulation sections 81 and 82 of the first LD unit modulation section 73 correspond to the image information of odd lines sent from the control section 80 in synchronization with the synchronization signals DETP1 and DETP3 synchronized with the rotation of the polygon mirror 15, respectively. Then, the LD 31 and 32 of the 2LD unit 11 are modulated and controlled, and two laser beams modulated from the LD 31 and 32 are output.
[0073]
In addition, the two laser beams output from the LDs 31 and 32 of the 2LD unit 11 are periodically deflected using the polygon mirror 15, and the scanning pitch adjusted in advance in the main scanning direction every two lines on the photosensitive member 2. At the same time, an electrostatic latent image of odd lines is formed by parallel scanning.
[0074]
The LD modulators 91 and 92 of the second LD unit modulator 74 respectively respond to the even line image information sent from the controller 90 in synchronization with the synchronization signals DETP2 and DETP4 synchronized with the rotation of the polygon mirror 15. Then, the LDs 41 and 42 of the 2LD unit 21 are modulated and controlled, and two laser beams modulated from the LDs 41 and 42 are output.
[0075]
In addition, the two laser beams output from the LDs 41 and 42 of the 2LD unit 21 are periodically deflected by using the polygon mirror 15, and the scanning pitch adjusted in advance in the main scanning direction every two lines on the photosensitive member 2. At the same time, an electrostatic latent image of even lines is formed by parallel scanning.
[0076]
That is, of the electrostatic latent images formed on the photosensitive member 2, for example, as shown in FIG. 5, the two output from the LDs 31 and 32 of the LD unit 11 of the first two-beam writing unit 3. The laser beam is deflected by using the polygon mirror 15 and the photosensitive member 2 is simultaneously scanned in parallel at a scanning pitch adjusted in advance every two lines in the main scanning direction, thereby electrostatically discharging odd lines (2 lines of 4m + 1 and 4m + 3). A latent image is formed.
[0077]
Then, by waiting for the time T (s) to elapse, the surface of the photoconductor 2 moves by D (mm) from the scanning position of the odd lines (2 lines of 4m + 1 and 4m + 3) on the photoconductor 2, and the first The two laser beams output from the LDs 41 and 42 of the LD unit 21 of the two-beam writing unit 4 are deflected by using the polygon mirror 15 respectively, and the photosensitive member 2 is lined in the main scanning direction every two lines. An electrostatic latent image of even lines (2 lines of 4m + 2, 4m + 4) is formed by simultaneously performing parallel scanning at a scanning pitch adjusted in advance.
[0078]
The interval between the scanning positions of the even lines on the photoreceptor 2 by the LDs 41 and 42 of the LD unit 21 of the second two-beam writing unit 4 is that of the LD unit 11 of the first two-beam writing unit 3. The odd-numbered line scanning position by the LD 32 is set.
The scanning direction of each even line by the LDs 41 and 42 of the LD unit 21 of the second two-beam writing unit 4 is the same as that of each odd line by the LDs 31 and 32 of the LD unit 11 of the first two-beam writing unit 3. The direction is opposite to the scanning direction.
[0079]
Further, in order to absorb variations in the mounting position of the two-beam writing unit for each image forming apparatus and the scanning position on the photosensitive member, the scanning from the odd-numbered line to the even-numbered line is performed. The time T (s) can be adjusted for each image forming apparatus.
[0080]
Furthermore, the image information input by the image input unit 50 includes transmission image information by a personal computer or a facsimile machine, read image information by a scanner of a copying machine, or an image transmitted from a scanner connected via a personal computer. There is information.
[0081]
As described above, in the image forming apparatus 1 of this embodiment, the 2LD unit is used for each 2-beam writing unit. However, an LD array in which a plurality of LDs (light emitting points) are arranged on the same line in the same package. May be used.
A plurality of multi-beam writing units that output three or more laser beams may be provided. If a multi-beam writing unit that outputs three or more laser beams is put into practical use, the printing speed can be increased more easily by using the configuration of the above-described embodiment.
[0082]
【The invention's effect】
  As described above, according to the image forming apparatus of the invention of claim 1,The beam scanning pitch adjusting means is based on scanning position interval measuring means (means for independently measuring time intervals of each scanning position detection edge for a plurality of laser light emitting elements for each laser light source of each multi-beam scanning means by the synchronization detecting means). Each measurement result is compared, and a scanning pitch in the sub-scanning direction on the photosensitive member by a plurality of laser beams emitted from a predetermined laser beam source of the multi-beam scanning unit and lasers of the other multi-beam scanning units After calculating the adjustment angle of the scanning pitch so that the scanning pitch in the sub-scanning direction on the photosensitive member by the plurality of laser beams emitted from the light source becomes the same, one predetermined multi-beam scanning means The laser light source is fixed, and the laser light source of the other multi-beam scanning means corresponds to the rotating means (each laser light source of each multi-beam scanning means). By means of means for independently rotating the laser beam in the direction perpendicular to the laser beam emission direction around any point on a straight line passing through each light emitting point of a plurality of laser light emitting elements. Accordingly, the scanning pitch in the sub-scanning direction on the photosensitive member by each of the plurality of laser beams respectively emitted from the laser light sources of the multi-beam scanning unit is automatically adjusted, so that a special apparatus is not used. And, without performing a predetermined work (the image forming apparatus performs an image forming operation and confirming an image obtained thereby) after each scanning pitch adjustment by an operator such as a serviceman,Make the above scanning pitches uniformEasy and reliable in a short timeThe image can be adjusted and a high-quality image can be obtained.
[0084]
  Claim2According to the image forming apparatus of the invention, the beam scanning pitch adjusting means uses each means for multi-beam scanning means by using means capable of electrically controlling a minute rotation angle such as a stepping motor or servo motor as each rotating means. Since each scanning pitch in the sub-scanning direction on the photosensitive member by each of the plurality of laser beams respectively emitted from the respective laser light sources can be independently adjusted, each of the above can be obtained without using a special device. The scanning pitch can be adjusted easily and accurately so as to be uniform, and a high-quality image can be obtained.
[0089]
  Claim3According to the image forming apparatus of the invention, after the power is turned on and before the image forming operation is started, each multi-beam scanning unit starts scanning with each of the plurality of laser beams emitted from each laser light source at a predetermined speed. At that point, the beam scanning pitch adjusting means is claimed.1 or 2Because any adjustment processing of1 or 2The same effect as that of the present invention can be obtained. In addition, regardless of the installation environment and operating state of the image forming apparatus, each multi-beam scanning unit always deflects each of the plurality of laser beams emitted from each laser light source periodically using a polygon mirror, Since the electrostatic latent image can be formed by parallel scanning on the photosensitive member moved in the scanning direction at the same scanning pitch in the main scanning direction at an ideal scanning pitch, a high-quality image can always be obtained stably. be able to.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating a configuration example of 2LD units 11 and 21 in FIG. 3;
FIG. 2 is a schematic configuration diagram showing an example around a drum of an image forming apparatus according to an embodiment of the present invention.
FIG. 3 is a perspective view showing a configuration example of a two-beam scanning optical system constituting each of the first two-beam writing unit 3 and the second two-beam writing unit 4 in FIG. 2;
4 is a diagram for explaining processing for a synchronization detection signal output from the synchronization detection sensor 16 of FIG. 3; FIG.
5 shows a scanning position and a scanning direction on the photosensitive member 2 by the first two-beam writing unit 3 of FIG. 2, and a scanning position and a scanning direction on the photosensitive member 2 by the second two-beam writing unit 4. FIG. It is a figure for demonstrating the relationship.
6 is a block diagram illustrating a configuration example of a main part of a control unit of the image forming apparatus illustrated in FIG. 2;
7 is a time interval of each scanning position detection edge for each LD 31, 32 of the 2LD unit 11 of FIG. 1 measured by the measuring unit 71a of FIG. 6 and two laser beams emitted from each LD 31, 32. FIG. 6 is a diagram showing a relationship with a scanning pitch in the sub-scanning direction on the photoreceptor 2.
8 shows the scanning pitch in the sub-scanning direction on the photosensitive member by two laser beams emitted from the LDs 31 and 32 of the 2LD unit 11 of FIG. 1 when the pixel density is changed from 600 dpi to 400 dpi. FIG.
9 is a block diagram illustrating a configuration example of a first LD unit modulation unit 73 and a second LD unit modulation unit 74 in FIG. 6;
[Explanation of symbols]
1: Image forming apparatus 2: Photoconductor
3: First two-beam writing unit
4: Second two-beam writing unit
11, 21: 2LD unit
15: Polygon mirror 16: Synchronization detection sensor
50: Image input unit 60: Main control unit
61: CPU 62: Image processing unit
70: Write control unit 71: Synchronization signal separation unit
72: Image information separation unit
73: First LD unit modulator
74: Second LD unit modulation section 80, 90: Control section
81, 82, 91, 92: LD modulation section
101: Line memory 102: Image inversion unit

Claims (3)

A laser light source comprising a plurality of laser light emitting elements, a plurality of laser beams emitted from the laser light source are periodically deflected using a polygon mirror, and the photosensitive member moved in the sub-scanning direction is moved in the main scanning direction. In an image forming apparatus provided with a plurality of multi-beam scanning means for simultaneously scanning in parallel to form an electrostatic latent image,
Each of the laser light sources of each of the multi-beam scanning means is arranged so that the plurality of laser light emitting elements are arranged on a straight line,
Each laser light source of each of the multi-beam scanning means is independently rotated in a direction perpendicular to the laser beam emission direction around any point on a straight line passing through each light emitting point of the plurality of laser light emitting elements. Providing a plurality of rotating means;
Laser modulation means for independently modulating and controlling a plurality of laser light emitting elements in each laser light source of each multi-beam scanning means according to image information, and each laser of each multi-beam scanning means by the means Beam scanning pitch adjusting means for independently adjusting each scanning pitch in the sub-scanning direction on the photosensitive member by each of a plurality of laser beams respectively emitted from a light source by using the rotating means ; By detecting each laser beam emitted from each laser light source of each multi-beam scanning means and scanned in the main scanning direction by the polygon mirror before reaching each photoconductor, Synchronous detection means for detecting the scanning position of the laser beam, and each laser of each multi-beam scanning means by the means A scanning position interval measuring means for measuring independently the time interval of each scan position detecting edges provided for a plurality of laser light emitting element of each source,
The beam scanning pitch adjusting unit compares the measurement results obtained by the scanning position interval measuring unit, and the beam scanning pitch adjusting unit is arranged on the photosensitive member by a plurality of laser beams emitted from a laser light source of one predetermined multi-beam scanning unit. The scanning pitch is adjusted so that the scanning pitch in the sub-scanning direction on the photosensitive member by the plurality of laser beams emitted from the laser light source of the other multi-beam scanning means becomes the same. After calculating the angle, the laser light source of the one predetermined multi-beam scanning means is fixed, and the laser light sources of the other multi-beam scanning means are rotated by the adjustment angle using the corresponding rotating means. Thus, sub-scanning on the photosensitive member by each of a plurality of laser beams respectively emitted from the laser light sources of the multi-beam scanning means Image forming apparatus, wherein a was set to automatically adjust each of the scanning pitch direction. The image forming apparatus according to claim 1 .
Each of the rotating means is a means capable of electrically controlling a minute rotation angle such as a stepping motor or a servo motor. The image forming apparatus according to claim 1 or 2 ,
After the power is turned on and before the image forming operation is started, the multi-beam scanning means starts scanning with the plurality of laser beams respectively emitted from the laser light sources at a predetermined speed. An image forming apparatus characterized in that the adjusting means performs adjustment processing.

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