JP2008058403A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is enabled to properly print on recording paper by reducing the generation of jitter, and is lowered in manufacturing cost. <P>SOLUTION: A scan unit 5 of an image forming apparatus 1 comprises a light source 5a, a polygon mirror 5b, a lens 5c, a mirror member 5d, etc., and the light source 5a outputs two laser beams L1 and L2 to irradiate a photoreceptor drum 2 in two columns in a main scanning direction. A light receiver 5e is disposed nearby the lens 5c, and a controller performs control so that a beam for image formation which is the laser beams L1 or/and L2 begins to be output after a predetermined time after a beam detect signal from the light receiver 5 is detected. The controller computes a difference in time when each beam detect signal is detected based upon the detection time of the beam detect signal, and adjusts the time from when each beam detect signal is detected until when the beam for image formation begins to be output by the time difference. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a laser beam printer that forms a latent image by irradiating a surface of a photosensitive drum with a laser beam, and in particular, scans the surface of the photosensitive drum with two rows of laser beams. About things.

  In general, in an image forming apparatus that forms (prints) an image on a recording sheet by a laser beam method, a laser beam is scanned in a main scanning direction from a laser scanning unit (hereinafter referred to as a scanning unit) disposed inside the housing. Thus, a latent image is formed on the photosensitive drum. Conventionally, as such an electrophotographic image forming apparatus, there is a so-called two-beam type apparatus in which a laser beam is simultaneously scanned on a photosensitive drum in two rows to improve a printing speed. In a two-beam image forming apparatus, when a light source that outputs a laser beam is displaced from a predetermined posture and is disposed in a scan unit, the reference positions of the two laser beams on the surface of the photosensitive drum are the main positions. Jitter occurs in the scanning direction and cannot be printed properly on recording paper. In order to prevent the occurrence of jitter, conventionally, for example, a process of adjusting the position of the light source is sometimes provided in the manufacturing process of the image forming apparatus. However, such a light source position adjustment operation is a very time-consuming operation, and there is a problem that the manufacturing cost increases. Also, for example, even if the light source is appropriately provided in this way, the output characteristics of the laser beam of the light source change due to the influence of environmental changes such as temperature changes, or the characteristics of the lens etc. that transmit the laser beam In some cases, jitter may occur after all.

  Incidentally, for example, in Patent Document 1, for each of the two lasers, the detection timing of the beam detect sensor during one rotation of the polygon mirror is measured, the time difference between the detection timings of the two lasers is obtained, and control of one laser is started. An image forming apparatus is described in which the timing is adjusted by the time difference. In the image forming apparatus described in Patent Document 2, the laser to be driven is switched between the first and second rounds of the polygon mirror, and the timing of the beam detect signal during the rotation of the polygon mirror for each laser is changed. Detecting and adjusting the start timing of the laser based on the difference in timing between them. However, when adjusting the control start timing of the laser as described in Patent Document 1 or Patent Document 2, the beam detect signal is detected by making a round of the polygon mirror for each laser, and the timing of those timings is detected. Since the difference is measured, it may be difficult to accurately measure.

In Patent Document 3, the time difference from when the preceding laser of the two lasers passes through the center of the detector to when the second laser passes through the center of the detector is obtained, and the image writing timing is adjusted. An image forming apparatus is described. Patent Document 4 describes an image forming apparatus that measures a time difference between rising positions of two beam detect signals and adjusts a laser arrangement position based on the measurement result. However, these image forming apparatuses do not adjust the timing error between the two laser beams, and Patent Document 3 or Patent Document 4 does not disclose an effective solution to the above-described problem.
JP 2000-343747 A JP 2001-197271 A JP-A-11-170603 JP 7-281112 A

  The present invention has been made in view of the above-described problems, and can be easily manufactured at low cost, can reduce the occurrence of jitter even when affected by environmental changes, and can be printed appropriately on recording paper. An object is to provide an image forming apparatus.

In order to achieve the above object, an invention according to claim 1 is a housing, a paper feed tray attached to the housing and on which recording paper is placed, and a recording paper placed on the paper feeding tray. A recording paper transport mechanism that transports inside, an image forming unit that is arranged inside the housing and forms an image on the recording paper transported by this recording paper transport mechanism, and controls each part of the device to form an image on the recording paper The image forming unit is arranged such that a main scanning direction substantially orthogonal to a recording paper conveyance direction is a longitudinal direction, and a photosensitive drum having a photosensitive layer formed on a surface thereof; A charging unit that charges the surface of the photosensitive drum substantially uniformly; a scanning unit that forms a latent image by irradiating the surface of the photosensitive drum with a laser beam; and a latent image of the surface of the photosensitive drum. Toner adheres to the part where A developing device for forming an image; and a surface of the photosensitive drum provided to face the surface of the photosensitive drum at a predetermined transfer position downstream of the developing device in the rotational direction of the photosensitive drum. A transfer roller for transferring the toner image formed on the recording paper, and a fixing roller for fixing the toner image on the recording paper by applying predetermined heat and pressure to the recording paper on which the toner image is transferred, The scan unit is arranged on a light source that emits a laser beam, a polygon mirror that reflects the laser beam emitted from the light source so as to scan in the main scanning direction, and an optical path of the laser beam reflected by the polygon mirror. A mirror member that reflects the laser beam transmitted through the lens toward the surface of the photosensitive drum, and the polygon mirror. A light receiving unit that receives a part of the reflected laser beam and outputs a beam detect signal. The light source receives two laser beams, and each laser beam is reflected by the polygon mirror to perform main scanning. Each beam detect signal is configured such that it can be emitted simultaneously so as to be scanned in two rows in the direction, the control unit controls the light source, and the light receiving unit detects and outputs each of the two laser beams. In the image forming apparatus configured to start the output of the image forming beam of each of the two laser beams at a predetermined time after the detection of
The control unit drives the laser scan unit before performing a warm-up period after power-on of the image forming apparatus or an operation for forming an image on the recording paper, and the light receiving unit performs each of the two laser beams. Corresponding to each of the two laser beams from information on the signal width of the output beam detect signal and information on a period during which the light receiving unit outputs at least one of the two laser beams. The time difference between the start times of the beam detect signals is calculated, and the time from the detection of the beam detect signal for each laser beam to the start of the output of the image forming beam is different from each other by the calculated time difference. An image forming beam of one or both of the two laser beams. By adjusting the timing of starting the output of the image, the irradiation reference positions of the two laser beams in the main scanning direction are aligned with each other on the surface of the photosensitive drum, thereby reducing the jitter of the image formed on the recording paper. It is a thing.

  In the invention of claim 2, two laser beams emitted almost simultaneously from the light source are reflected by the same polygon mirror and scanned on the surface of the photosensitive drum in the main scanning direction to form a latent image. In the image forming apparatus for forming an image by attaching and developing toner on the surface of the formed photosensitive drum, and transferring and fixing the toner on the surface of the photosensitive drum to the surface of a recording paper, the polygon mirror The two laser beams reflected by the laser beam are received by the same light receiving unit provided at a predetermined position, and the light receiving unit outputs a predetermined beam detect signal in response to reception of the laser beam, and the two laser beams Only one of the two laser beams and the beam detect signal output from the light receiving unit when the laser beam is simultaneously emitted Kino compares the beam detect signal output from the light receiving unit, and adjusts the timing of the output initiation of the imaging beam by two beam detect two laser beams based on the time difference of the signals.

  According to the first aspect of the present invention, the control unit is configured to determine each of the two laser beams from the information on the signal width of each beam detect signal and the information on the period during which the light receiving unit outputs one of the beam detect signals. The time difference between the start times of the beam detect signals is calculated, and the timing for starting the output of the image forming beam in each laser beam is adjusted based on the calculated time difference. For example, even if the mounting position of the light source is slightly deviated from a predetermined position, the irradiation reference positions of the two laser beams in the main scanning direction are automatically aligned, so that jitter can be reduced. Therefore, it is not necessary to provide a process for adjusting the position of the light source when assembling the image forming apparatus, the assembly can be easily performed, and the manufacturing cost can be reduced. At this time, the timing adjustment of the output of the image forming beam in the two laser beams is performed by calculating the time difference from the detection of the beam detect signal for each laser beam to the start of the output of the image forming beam. Therefore, the irradiation reference positions of the two laser beams can be more precisely aligned. In addition, the control unit adjusts the output timing of the image forming beam of the two laser beams before performing the warm-up period or printing operation of the image forming apparatus. It is possible to reduce the occurrence of jitter due to the printing, and it becomes possible to print on recording paper properly.

  According to the second aspect of the present invention, the beam detect signals output from the light receiving unit when the two laser beams are emitted simultaneously and when only one of the two laser beams is emitted are compared. Since the output start timing of the image forming beam by the two laser beams is adjusted based on the time difference between the beam detect signals, the irradiation reference positions of the two laser beams are aligned with each other on the surface of the photosensitive drum, thereby reducing jitter. It becomes possible to do. Therefore, as described above, the assembly can be easily performed without adjusting the position of the light source when the image forming apparatus is assembled, and the manufacturing cost can be reduced. Since the timing adjustment of the output of the image forming beam between the two laser beams is performed automatically, it is possible to reduce the occurrence of jitter caused by environmental changes, etc. Can be printed.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an example of an image forming apparatus according to this embodiment. The image forming apparatus 1 is a so-called laser beam printer, which is connected to, for example, an external personal computer, and forms an image on the recording paper P by electrophotography based on image data sent from the personal computer. (Print). The image forming apparatus 1 includes a paper feed cassette (paper feed tray) 110 that is disposed at the bottom of the housing 100 and on which the recording paper P is placed substantially horizontally, and is ejected from the housing 100 provided at the top of the housing 100. The recording paper P loaded thereon, the recording paper transport mechanism 20 that transports the recording paper P loaded in the paper feed cassette 110 into the housing 100, and the recording paper transport mechanism 20. The image forming unit 10 forms an image on the recording paper P, and the control unit 40 controls the operation of each unit of the apparatus and prints the image on the recording paper P. The paper feed cassette 110 is provided so as to be drawable with respect to the housing 100. The image forming apparatus 1 is configured such that the recording paper P can be loaded and placed by pulling out the paper feed cassette 110 from the housing 100. Note that the paper feed tray may be fixed to the housing 100 so that the recording paper P can be loaded by being inserted from the outside.

  The control unit 40 is configured by an electronic circuit having, for example, a CPU, a ROM, a RAM, and the like, and controls the printing operation by driving the image forming unit 10, the recording paper transport mechanism 20, and the like. In the present embodiment, the control unit 40 includes a non-volatile memory (not shown). For example, when the power of the image forming apparatus 1 is turned off, the non-volatile memory includes the image forming apparatus 1. Various operation information such as the operation log is stored.

  The recording paper transport mechanism 20 includes a pickup roller 21 disposed above the paper feed cassette 110, a transport roller 22 that transports the recording paper P inside the housing 100, and a motor (not shown) that drives these rollers. Etc.). The pickup roller 21 abuts on the uppermost recording paper P placed on the paper feed cassette 110 and rotates to move the recording paper P along the recording paper guide 15 in front of the housing 100. Paper is fed toward the inside of the housing 100. The fed recording paper P is transported to the image forming unit 10 by the transport roller 22, and after the image is formed by the image forming unit 10, the recording paper P is discharged onto the paper discharge unit 120.

  The image forming unit 10 includes a photosensitive drum 2 having a photosensitive layer formed on the surface, a cleaner 3, a charger (charging means) 4, a scan unit 5, a developing brush (developing device) 6, a transfer roller 7, and a transfer roller 7. On the other hand, the fixing roller 8 is disposed on the downstream side in the conveyance direction of the recording paper P. These photosensitive drums 2, rollers, and the like are attached to a frame inside the housing 100 so that the main scanning direction substantially orthogonal to the conveyance direction of the recording paper P is the longitudinal direction.

  The cleaner 3 removes toner and paper powder before one stroke (one rotation) adhering to the surface of the photosensitive drum 2 and cleans the surface of the photosensitive drum 2. The charger 4 uniformly charges the surface of the photosensitive drum 2 cleaned by the cleaner 3. The scanning unit 5 forms a latent image on the surface of the photosensitive drum 2 by irradiating the laser beam while scanning the surface of the photosensitive drum 2 charged by the charger 4. In this embodiment, the scan unit 5 is of a so-called two-beam type, and is configured so that the photosensitive drum 2 can be irradiated with two laser beams L1 and L2 at the same time to increase the printing speed. Yes. The scan unit 5 is supplied with power by a power supply device (not shown), and a drive voltage for emitting laser beams L1 and L2 is applied by the power supply device. The developing brush 6 is mounted on a toner cartridge 6a filled with toner, and forms a toner image by attaching toner to a portion of the surface of the photosensitive drum 2 where a latent image is formed. The transfer roller 7 is provided to face the surface of the photosensitive drum 2 at a predetermined transfer position downstream of the developing brush 6 in the rotation direction of the photosensitive drum 2. The transfer roller 7 rotates while pressing the recording paper P against the surface of the photosensitive drum 2 to charge the surface of the recording paper P, and the toner image formed on the surface of the photosensitive drum 2 is transferred to the recording paper P. Transfer on top of. A transfer voltage for charging the surface of the recording paper P is applied to the transfer roller 7 from a power supply device. The recording paper P on which the image is formed on the surface by the transfer roller 7 is conveyed to the fixing roller 8. The fixing roller 8 fixes the toner by applying heat and pressure to the recording paper P while sandwiching the recording paper P between the fixing roller 8 and the pressing roller 8a disposed opposite thereto. Heat for fixing the toner is supplied from a heater (for example, a halogen lamp) built in the fixing roller 8. The heater generates heat when a fixing voltage is applied by the power supply device.

  FIG. 2 shows the scan unit 5 of the image forming apparatus 1. The scan unit 5 houses a scanning unit 51 that scans the laser beams L1 and L2 in the main scanning direction (the direction of arrow A in the figure) inside a box-shaped unit housing 50 so that dust or the like does not enter from the outside. It is configured. The recording paper P is conveyed in the sub-scanning direction indicated by an arrow B in the drawing. The scanning unit 51 includes a light source 5a that outputs two laser beams L1 and L2, a polygon mirror 5b that reflects the laser beams L1 and L2 output from the light source 5a, and laser beams L1 and L2 that are reflected by the polygon mirror 5b. The fθ lens (lens) 5c that corrects the aberration according to the reflection angle of the laser beam, and the laser beams L1 and L2 that have passed through the fθ lens 5c are reflected to irradiate the photosensitive drum 2 disposed below the scan unit 5. It is composed of a mirror member 5d and, for example, a light receiving portion 5e disposed at a position where a part of the laser beams L1 and L2 reflected by the polygon mirror 5b irradiate, near the fθ lens 5c. The unit housing 50 is sealed to prevent dust and the like from entering the inside from the outside, and is configured so that a latent image can be formed on the photosensitive drum 2 properly at all times. The scan unit 5 is housed inside the housing 100 with the unit housing 50 fixed to the frame of the housing 100 with screws or the like.

  The polygon mirror 5b is composed of, for example, a mirror with six sides, and is driven by a motor (not shown) so as to rotate substantially horizontally as indicated by an arrow M in the drawing. The light source 5a is composed of, for example, two semiconductor lasers arranged so as to be lined up substantially vertically, and the laser beams L1 and L2 emitted from the respective semiconductor lasers are both applied to the polygon mirror 5b and reflected. It is configured as follows. The mirror member 5d is disposed along the main scanning direction so that the longitudinal direction is substantially horizontal, and is scanned with the rotation of the polygon mirror 5b and transmits the laser beams L1 and L2 transmitted through the fθ lens 5c. Reflect downward. The reflected laser beams L1 and L2 are passed through an opening 50c formed in the vicinity of the portion where the mirror member 5d is disposed on the lower surface of the unit housing 50 so that the main scanning direction is the longitudinal direction. The surface of the photosensitive drum 2 is scanned in two rows in the main scanning direction.

  The light receiving unit 5e is constituted by, for example, a photodiode, and detects that the laser beams L1 and L2 reflected and scanned by the polygon mirror 5b are incident. The light receiving unit 5e outputs a predetermined beam detect signal to the control unit 40 while the laser beams L1 and L2 are respectively incident. The control unit 40 drives the light source 5a so that the output of the image forming beam in the laser beam L1 or the laser beam L2 is started after a predetermined time from the detection of the beam detect signal output by the light receiving unit 5e. That is, the image forming apparatus 1 is configured such that the irradiation reference position in the main scanning direction of the two laser beams L1 and L2 on the surface of the photosensitive drum 2 is determined with reference to the timing at which the beam detect signal is detected. ing.

  By the way, in the image forming apparatus 1, the control unit 40 has a timing adjustment function for automatically adjusting the start timing of the image forming beam output for each of the two laser beams L1 and L2. This timing adjustment function is executed after calculating a correction value, for example, during a warm-up period after power-on of the image forming apparatus 1 or when printing on the recording paper P is performed.

  The timing adjustment function executed by the control unit 40 will be described below with reference to FIGS. 3 and 4. First, the control unit 40 detects the beam detect signal for each of the two laser beams L1 and L2 output from the light receiving unit 5e, thereby causing two lasers resulting from the positional deviation of the light source 5a, temperature change, and the like. The amount of deviation between the beams L1 and L2 is detected from the detection time difference between the beam detect signals detected simultaneously at the normal time, and this time difference is used as a correction value. Assuming that the beam detect signals for the laser beams L1 and L2 are BD1 and BD2, respectively, for example, as shown in FIG. 3, BD1 is detected in a pulse form only from time T1 to time t1, and BD2 is detected at time T1. Suppose that a pulse is detected only during a period from time T2 to time t2 which is delayed by time ΔT. At this time, the control unit 40 measures the time during which BD1 and BD2 are detected, that is, the widths t1 and t2 of the detection pulses of BD1 and BD2, respectively. In this embodiment, since the laser beams L1 and L2 are scanned by the same polygon mirror 5b, the detection widths t1 and t2 of BD1 and BD2 are equal to each other. Then, after measuring the times t1 and t2, the control unit 40 outputs both the laser beams L1 and L2, and measures the time t3 (indicated as BD1 + BD2 in the drawing) at which at least one of BD1 or BD2 is detected. . Using this information, the control unit 40 calculates the time difference Δt between the start times of the beam detect signals BD1 and BD2 as a difference between the time t3 and the time t2.

  FIG. 4 shows an example of outputs V1 and V2 and beam detect signals BD1 and BD2 for the laser beams L1 and L2, respectively, during the printing operation. In the figure, shaded portions of the outputs V1 and V2 indicate periods during which the image forming beam is being output. The image forming beam is output when the control unit 40 controls the light source 5a. In this embodiment, when correction is not performed, output of an image forming beam is started after time t from detection of the beam detect signal for both of the laser beams L1 and L2 (in BD1 and V1). Show). Here, when the time difference Δt is calculated as the correction value as described above, the control unit 40 performs the software process to thereby correct the timing for starting the output of the image forming beam of the laser beam L2. The light source 5a is controlled so that the output of the image forming beams in the laser beams L1 and L2 is started simultaneously by adjusting the value. That is, as shown by BD2 and V2 in FIG. 4, with respect to the laser beam L2, at time T3 after a time t ′ shorter by Δt than time t after detecting the beam detect signal at time T2, The output of the image forming beam is started. On the other hand, for the laser beam L1, output of the image forming beam is started at time T3, which is a time t after the detection of the time T1 beam detect signal.

  As described above, in the present embodiment, the control unit 40 corrects the time from the detection of the beam detect signal to the start of the output of the image forming beam using the correction value. Is slightly deviated from the predetermined position, and even when the detection times of the beam detect signals for the laser beams L1 and L2 are deviated, two rows of image forming beams are automatically output simultaneously. . Thus, by simultaneously outputting two rows of image forming beams in the two laser beams L1 and L2, the irradiation reference positions in the main scanning direction on the surface of the photosensitive drum 2 can be aligned with each other, Generation of jitter is reduced, and printing can be properly performed on the recording paper P. Therefore, it is not necessary to provide a process for adjusting the position of the light source 5a when assembling the image forming apparatus 1, and assembling can be easily performed, and the manufacturing cost of the image forming apparatus 1 can be reduced. At this time, the timing adjustment of the output of the image forming beam between the two laser beams L1 and L2 is performed by the actually calculated time difference Δt. Therefore, the irradiation reference positions of the two laser beams L1 and L2 are more strictly set. It is possible to align. Since the control unit 40 calculates the correction value for the timing adjustment described above before performing the warm-up period or the printing operation of the image forming apparatus 1, the image forming apparatus 1 is affected by an environmental change or the like. However, it is possible to reduce the occurrence of jitter due to this, and the recording paper P can always be printed properly.

  In addition, this invention is not limited to the structure of the said embodiment, A various deformation | transformation is possible suitably in the range which does not change the meaning of invention. For example, the control unit 40 adjusts the output timing of the image forming beam in the laser beam L1 to be delayed by the calculated time difference Δt, or outputs the image forming beams of both the laser beams L1 and L2. May be adjusted so that the total difference is equal to the time difference Δt, so that the output of the image forming beams is simultaneously performed in two rows. The correction value may be calculated, for example, only during the warm-up period. Information on the calculated time difference Δt is recorded in, for example, a nonvolatile memory, and the control unit 40 performs this print operation when performing each print operation. The timing adjustment function may be executed with reference to the record in the nonvolatile memory. In any case, as described above, it is possible to reduce the occurrence of jitter and to always properly print on the recording paper P.

  Further, for example, the control unit may include a delay circuit, and may be configured to perform a timing adjustment function using the delay circuit. In such a case, a plurality of time difference sections and corresponding delay times are set in advance in the delay circuit. When the time difference Δt is calculated as a correction value as described above, the delay circuit detects the beam detect signals for the two laser beams L1 and L2, and then starts outputting the image forming beam. The output start timing of one or both of the image forming beams of the two laser beams L1 and L2 is adjusted so that the times differ from each other by a delay time corresponding to the time difference section to which the calculated time difference belongs. With such a configuration, unlike the case where the control unit 40 performs software processing and performs timing adjustment as described above, the processing amount of the control unit when performing timing adjustment is relatively small. It becomes possible to drive more stably.

1 is a side view showing an example of an image forming apparatus according to an embodiment of the present invention. The perspective view which shows the scanning unit of the said apparatus. The time chart explaining the correction value calculation process which the control part of the said apparatus performs. The time chart explaining the timing adjustment function of the said apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photosensitive drum 4 Charger (charging means)
DESCRIPTION OF SYMBOLS 5 Scan unit 5a Light source 5b Polygon mirror 6 Developing apparatus 7 Transfer roller 8 Fixing roller 10 Image formation part 20 Recording paper conveyance mechanism 50 Unit housing 50a Light source 50b Polygon mirror 50c f (theta) lens (lens)
50d Mirror member 50e Light receiving unit 100 Case 110 Paper feed cassette (paper feed tray)
A Main scanning direction B Sub scanning direction L1, L2 Laser beam P Recording paper

Claims (2)

A housing,
A paper feed tray that is attached to the housing and on which recording paper is placed;
A recording paper transport mechanism for transporting the recording paper placed on the paper feed tray into the housing;
An image forming unit disposed inside the housing and forming an image on the recording paper conveyed by the recording paper conveying mechanism;
A control unit that controls each part of the apparatus to form an image on recording paper,
The image forming unit includes:
A photoconductive drum having a main scanning direction substantially orthogonal to the recording paper conveyance direction and being a longitudinal direction, and a photoconductive layer formed on the surface;
Charging means for charging the surface of the photosensitive drum substantially uniformly;
A scanning unit that forms a latent image by irradiating the surface of the photosensitive drum with a laser beam; and
A developing device for forming a toner image by attaching toner to a portion of the surface of the photosensitive drum on which a latent image is formed;
A toner image formed on the surface of the photosensitive drum is recorded at a predetermined transfer position downstream of the developing device in the rotation direction of the photosensitive drum so as to face the surface of the photosensitive drum. A transfer roller for transfer onto the paper;
A fixing roller for fixing the toner image on the recording paper by applying predetermined heat and pressure to the recording paper on which the toner image has been transferred,
The scan unit is arranged on a light source that emits a laser beam, a polygon mirror that reflects the laser beam emitted from the light source so as to scan in the main scanning direction, and an optical path of the laser beam reflected by the polygon mirror. And a mirror member for reflecting the laser beam transmitted through the lens toward the surface of the photosensitive drum, and a part of the laser beam reflected by the polygon mirror is received and a beam detect signal is output. And a light receiver
The light source is configured to be able to emit two laser beams simultaneously so that each laser beam is reflected by the polygon mirror and scanned in two rows in the main scanning direction,
The control unit controls the light source, and the light receiving unit detects each of the two laser beams and outputs each of the two laser beams at a predetermined time after detecting each beam detect signal. In an image forming apparatus configured to start output of a forming beam,
The control unit drives the laser scan unit before performing a warm-up period after power-on of the image forming apparatus or an operation for forming an image on the recording paper, and the light receiving unit performs each of the two laser beams. Corresponding to each of the two laser beams from information on the signal width of the output beam detect signal and information on a period during which the light receiving unit outputs at least one of the two laser beams. The time difference between the start times of the beam detect signals is calculated, and the time from the detection of the beam detect signal for each laser beam to the start of the output of the image forming beam is different from each other by the calculated time difference. An image forming beam of one or both of the two laser beams. To adjust the timing to start the output of the beam,
Thereby, the irradiation reference positions in the main scanning direction of the two laser beams on the surface of the photosensitive drum are aligned with each other, and the jitter of the image formed on the recording paper is reduced. The photosensitive drum on which the two laser beams emitted from the light source are reflected by the same polygon mirror and scanned on the surface of the photosensitive drum in the main scanning direction to form a latent image. In an image forming apparatus for forming an image by attaching and developing toner on the surface of the photosensitive drum, and transferring and fixing the toner on the surface of the photosensitive drum to the surface of the recording paper,
The two laser beams reflected by the polygon mirror are received by the same light receiving unit provided at a predetermined position,
The light receiving unit outputs a predetermined beam detect signal in response to reception of a laser beam,
A beam detect signal output from the light receiving unit when the two laser beams are emitted simultaneously, and a beam detect signal output from the light receiving unit when only one of the two laser beams is emitted. And compare
An image forming apparatus comprising: adjusting an output start timing of an image forming beam by two laser beams based on a time difference between two beam detect signals.

Images