Image forming apparatus

Abstract

An image forming apparatus includes a photosensitive member, a scanning optical unit, and a control section. The scanning optical unit is provided with a light source that includes a plurality of light emitting points and emits laser light from the plurality of light emitting points, respectively, and a deflector that deflects each of the laser light emitted from the plurality of light emitting points into a scanning direction. The scanning optical unit scans the photosensitive member with the plurality of laser beams deflected by the deflector and forms an electrostatic latent image on the photosensitive member. The control unit controls the scanning optical unit. The control unit identifies a light emitting point pitch based on information relating to the light emitting point pitch, which is a space between the plurality of light emitting points.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a laser beam printer (LBP), a digital copier, etc., which forms an image on a recording material using an electrophotographic recording technique. Background Art

[0002] The scanning optical device used in imaging devices such as laser beam printers and digital copiers includes a semiconductor laser element that emits laser light corresponding to an image signal, an optical deflector such as a rotating polygon mirror that deflects the laser light, an imaging optical element having an fθ characteristic, and the like. Furthermore, the scanning optical device forms a dot-shaped laser image on a photosensitive drum. The writing time of the laser light on the photosensitive drum is determined by the incident time of the laser light on the horizontal synchronization sensor. In addition, a structure is adopted in which the distribution of the electrostatic latent image on the photosensitive drum in the main scanning direction is uniform by correcting the amount of laser light in the main scanning direction (this is called illumination distribution correction), and the uneven density of the image is reduced (see Japanese Patent Application Publication No. 2008-152091).

[0003] In order to increase the number of output sheets per minute, some imaging devices use a multi-beam laser element that has multiple light-emitting points on a laser chip inside a semiconductor laser element. By increasing the number of scanning lines that can be scanned at one time by a light deflector using a multi-beam laser element, the number of revolutions of the light deflector is kept low, thereby realizing a low-noise and high-speed imaging device. A semiconductor laser is a general-purpose electronic component that is usually purchased from a laser element manufacturer. In one type of imaging device, from the perspective of a stable supply of components to be used and cost, there is a case where the imaging device is designed so that semiconductor lasers from multiple laser element manufacturers can be mounted thereon.

[0004] For multi-beam laser elements, the light point spacing, that is, the interval between each light point on the laser chip, is one of the important characteristics. However, the light point spacing of different laser element manufacturers will be different. In the case where the same imaging device allows the use of laser elements with different light point spacings, the difference in light point spacing will affect the performance. When the semiconductor laser is pivotally moved around the laser optical axis to adjust the image position of the laser in the sub-scanning direction on the photosensitive drum (when adjusting the sub-scanning spacing of the laser), if the light point spacing is different, the pivotal movement amount is also different. If the pivotal movement amount of the semiconductor laser is different, the polarization state of the laser as the vibration direction changes, thereby changing the illumination distribution of the scanning optical device. Therefore, when the illumination distribution correction is performed as in the existing example, the laser amount correction amount used to correct the illumination distribution will change.

[0005] Furthermore, if the amount of pivotal movement of the semiconductor laser is different, the interval of the image position of each laser on the photosensitive drum in the main scanning direction also changes. Therefore, in a configuration in which the writing timing of each laser in the main scanning direction is corrected based on the timing at which one of the lasers of the multi-beam laser element enters the horizontal synchronization sensor, the correction amount of the writing timing of each laser changes. Therefore, if the information about the spacing between the light-emitting points is unknown, appropriate correction cannot be performed, and uneven density may occur, or image defects such as moiré may occur due to deviations in the writing timing of each laser. Summary of the invention

[0006] The present invention was conceived under the above circumstances, and an object of the present invention is to reduce the occurrence of image defects by performing correction suitable for the installed multi-beam laser element even when a multi-beam laser element having different light-emitting point pitches is installed in a scanning optical device.

[0007] According to one aspect of the present invention, there is provided an imaging device, comprising: a photosensitive member; a scanning optical unit provided with a light source and a deflector, the light source comprising a plurality of light-emitting points and configured to emit lasers respectively from the plurality of light-emitting points, the deflector configured to deflect each laser emitted from the plurality of light-emitting points to a scanning direction, the scanning optical unit utilizing the plurality of lasers deflected by the deflector to scan the photosensitive member and form an electrostatic latent image on the photosensitive member; and a control unit configured to control the scanning optical unit, wherein the control unit identifies the light-emitting point spacing based on information related to the light-emitting point spacing as the interval between the plurality of light-emitting points.

[0008] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic cross-sectional view of the image forming apparatus in the embodiment.

[0010] Figure 2 is a perspective view of a scanning optical device in an embodiment.

[0011] Figure 3A is a perspective view showing the appearance of a first semiconductor laser in the embodiment.

[0012] Figure 3B is a perspective view showing the internal structure of the first semiconductor laser in the embodiment.

[0013] Figure 4 1 is an enlarged view showing a first semiconductor laser mounted on a scanning optical device in the embodiment.

[0014] Figure 5Ais a perspective view showing the internal structure of the second semiconductor laser in the embodiment.

[0015] Figure 5B is an enlarged view showing a second semiconductor laser mounted on the scanning optical device in the embodiment.

[0016] Figure 6 3 is a diagram showing the difference in illuminance distribution caused by the light-emitting point pitch in the embodiment.

[0017] Fig. 7A 1 is a timing chart illustrating the writing timing of each laser in the embodiment.

[0018] Figure 7B 1 is a timing chart illustrating the writing timing of each laser in the embodiment.

[0019] Fig. 8A 1 is a timing chart illustrating the method for identifying the interval between light-emitting points in the embodiment.

[0020] Figure 8B 1 is a timing chart illustrating the method for identifying the interval between light-emitting points in the embodiment.

[0021] Fig. 9 is an explanatory diagram showing a circuit board in a scanning optical device in a modified example. DETAILED DESCRIPTION

[0022] [Example]

[0023] In the following description, the direction of laser scanning is referred to as the main scanning direction; the rotation direction of the photosensitive drum, or in other words, the direction perpendicular to the main scanning direction, is referred to as the sub-scanning direction. In addition, in a multi-beam laser element as a light source, the interval between the positions of a plurality of light-emitting points mounted on a laser chip is referred to as a light-emitting point pitch.

[0024] (Imaging equipment)

[0025] exist Figure 1, an example of a schematic configuration of an image forming apparatus is shown. A laser beam printer 1100 (hereinafter referred to as printer 1100) is provided with a photosensitive drum 12 as a photosensitive member, a charging section 1102, and a developing section 1103. The photosensitive drum 12 is an image bearing member on which a latent image (hereinafter referred to as an electrostatic latent image) is formed by a scanning optical device (scanning optical unit) 1. The charging section 1102 uniformly charges the photosensitive drum 12. The developing section 1103 forms a toner image by developing the electrostatic latent image formed on the photosensitive drum 12 with a toner. The toner image formed on the photosensitive drum 12 (on the photosensitive member) is transferred to a sheet P as a recording material fed from a box 1104 by a transfer section 1105, and the unfixed toner image transferred to the sheet P is fixed by a fixing unit 1106. The photosensitive drum 12, the charging section 1102, the developing section 1103 and the transfer section 1105 are an imaging section (imaging device). The fixed sheet P is discharged to the tray 1107. In addition, the printer 1100 is provided with a power supply device 1108, and power is supplied from the power supply device 1108 to a driving section such as a motor and to a control section 1109. The control section 1109 includes a CPU (not shown) and a memory 1109a as a storage device, and controls the operation of the scanning optical device 1, the imaging operation of the imaging section, the conveying operation of the sheet P, and the like. Incidentally, the imaging device to which the scanning optical device 1 of the present invention is applicable is not limited to Figure 1 The structure illustrated in .

[0026] (Scanning optical device (scanning optical unit))

[0027] Will use Figure 2 The scanning optical device in this embodiment is described. Figure 2BD anamorphic lens 4 is a lens formed by integrating an anamorphic lens for guiding the laser incident light L to the rotating polygon mirror 7 and a lens for guiding the laser light Lb deflected by the rotating polygon mirror 7 to the horizontal synchronization sensor 13. The laser incident light L passing through the BD anamorphic lens 4 is limited to a predetermined beam diameter by an optical aperture 6 formed in a housing 5 as a shell, and is irradiated onto the reflection surface of the rotating polygon mirror 7. The rotating polygon mirror 7 is driven to rotate by the driving circuit board 8, and deflects and scans the laser incident light L incident thereon. In the present embodiment, the rotating polygon mirror 7 includes four reflection surfaces, however, the number of reflection surfaces is not limited thereto. Here, the rotating polygon mirror 7 and the driving circuit board 8 constitute an optical deflector 9 (deflector). The deflected incident laser light L passes through the fθ lens 10 as laser scanning light Ls, is reflected by the long reflective mirror 11, and is condensed on the photosensitive drum 12. Incidentally, the plane on which the laser scanning light Ls is scanned on the rotating polygon mirror 7 is defined as a scanning plane Ps.

[0028] In addition, the laser light Lb after the incident laser light L is deflected by the rotating polygon mirror 7 passes through the BD anamorphic lens 4 and converges in the main scanning direction. The laser light Lb in the converged state in the main scanning direction is incident on the horizontal synchronization sensor 13 as a detection device mounted on the circuit board 2, and the horizontal synchronization sensor 13 determines the writing timing to the photosensitive drum 12 in the main scanning direction. Specifically, when the laser light Lb passing through the BD slit 14 formed in the housing 5 is incident on the horizontal synchronization sensor 13, the output of the horizontal synchronization sensor 13 changes, and the laser emission timing is controlled based on the timing of the output change as a reference.

[0029] With this optical system, the scanning light is guided onto the photosensitive drum 12 to perform image recording. Specifically, by the rotation of the rotating polygon mirror 7, the angle of deflection of the laser incident light Ls is changed, and each point image formed by the laser scanning light Ls is scanned on the surface of the photosensitive drum 12 in the direction of the arrow Sd, which is the axial direction of the photosensitive drum 12. In addition, as the photosensitive drum 12 rotates, each point image moves in a direction perpendicular to the axial direction of the photosensitive drum 12 (sub-scanning direction). Thus, an electrostatic latent image is formed. In addition, the opening of the housing 5 is covered by a cover not shown.

[0030] (Structure of semiconductor laser and installation on optical scanning device)

[0031] Next, the semiconductor laser 32 (first semiconductor laser) having the first light-emitting point pitch (first interval) used in the light source unit 3 will be described. Figure 3ACAN type semiconductor laser 32 is a perspective view showing a semiconductor laser 32, and components such as a built-in laser chip are included inside the semiconductor laser 32. From the viewpoint of dust prevention, the CAN type semiconductor laser 32 is sealed by a cap 34 having a cap glass 33 that allows laser light to pass therethrough.

[0032] exist Figure 3B , for the sake of explanation, a stereoscopic view of a semiconductor laser 32 in a state where a cap 34 is excluded is shown. In the semiconductor laser 32, a laser chip 35 is bonded to a metal stem 36 via a sub-seat 37 made of silicon or the like. By being electrically connected to the stem 36, the laser chip 35 emits light when current is applied. In the present embodiment, the semiconductor laser 32 is a dual-beam laser having two light-emitting points, namely, a light-emitting point Ew1 (a first light-emitting point) and a light-emitting point Ew2 (a second light-emitting point), and the laser chip 35 emits laser beams from the two light-emitting points Ew1 and Ew2 provided on the end face.

[0033] The light-emitting points Ew1 and Ew2 are arranged roughly parallel to the bonding surface between the laser chip 35 and the sub-mount 37, and the distance between the light-emitting points is represented by Ww (hereinafter referred to as the distance Ww). That is, the first light-emitting point distance is the distance Ww. Here, a plane roughly parallel to the bonding surface between the laser chip 35 and the sub-mount 37 and passing through the light-emitting points Ew1 and Ew2 is defined as a light-emitting plane Pw. In addition, in the stem 36, the laser chip 35 is mounted in such a manner that the stem reference axis S connecting the cutout 36a and the cutout 36b in the stem 36 is roughly parallel to the light-emitting plane Pw. Incidentally, more specifically, the cutout 36a and the cutout 36b have portions 36a1 and 36b1 cut into the interior of the stem 36, respectively, and the stem reference axis S is also the axis connecting the portion 36a1 and the portion 36b1.

[0034] Figure 4 An enlarged view of the vicinity of the light source unit 3 in the scanning optical device 1 is shown. Figure 4 A state in which the circuit board 2 is removed for explanation is shown. The light source unit 3 includes a semiconductor laser 32 and a holder member 31 into which the semiconductor laser 32 is press-fitted. In the case of using a dual-beam laser, since it is necessary to form point images at spaced-apart positions in the sub-scanning direction on the photosensitive drum 12, the light source unit 3 is fixed to the housing 5 after performing rotation adjustment around the exit light axis. In other words, the semiconductor laser 32 is held by the holder member 31 in a state in which the light emitting plane Pw of the semiconductor laser 32 is tilted relative to the scanning plane Ps, which is a plane scanned by the rotating polygonal mirror 7.

[0035] Incidentally, the angle θw between the light emitting plane Pw and the scanning plane Ps is obtained from θ represented by the following equation (1).

[0036] [Equation 1]

[0037] θ=tan -1 {(25.4÷dpi×1000)÷β÷W}…(1)

[0038] dpi: image resolution, β: optical sub-scanning magnification of the optical scanning device, W: light-emitting point pitch.

[0039] For example, if the resolution is 600 dpi, the laser light emitting point pitch Ww is 90 μm, and the optical sub-scanning magnification β of the optical scanning device 1 is 5 times, the semiconductor laser 32 is installed tilted so that the angle θw between the light emitting plane Pw and the scanning plane Ps is 5.4°.

[0040] (Semiconductor lasers with different light-emitting point spacing)

[0041] exist Figure 5A , a semiconductor laser 42 (second semiconductor laser) having a second light emitting point pitch (second interval) different from that of the semiconductor laser 32 is shown. Components and common definitions common to the semiconductor laser 32 are denoted by the same reference numerals. Figure 3B As shown, the description will be made in a state where the cap 34 is removed. The laser chip 45 emits laser beams from two light-emitting points, namely, a light-emitting point En1 (first light-emitting point) and a light-emitting point En2 (second light-emitting point) provided on the end surface.

[0042] The light-emitting points En1 and En2 are arranged roughly parallel to the bonding surface between the laser chip 45 and the sub-mount 37, and the light-emitting point spacing is represented by Wn (hereinafter referred to as spacing Wn). That is, the second light-emitting point spacing is spacing Wn. Here, a plane roughly parallel to the bonding surface between the laser chip 45 and the sub-mount 37 and passing through the light-emitting points En1 and En2 is defined as a light-emitting plane Pn. In addition, in the stem 36, the laser chip 45 is mounted in such a manner that the stem reference axis S connecting the cutout 36a and the cutout 36b in the stem 36 is roughly parallel to the light-emitting plane Pn. Incidentally, the stem reference axis S is also the axis connecting the portion 36a1 and the portion 36b1.

[0043] Comparing the semiconductor laser 32 having the first light-emitting point pitch and the semiconductor laser 42 having the second light-emitting point pitch, the light-emitting point pitch is Ww>Wn, and the semiconductor laser 32 has a wider light-emitting point pitch than the semiconductor laser 42. In other words, the semiconductor laser 32 is a "wide pitch laser" having a wider light-emitting point pitch, while the semiconductor laser 42 is a "narrow pitch laser" having a narrower light-emitting point pitch.

[0044] Generally speaking, narrow-pitch lasers are more efficiently manufactured because the size of the laser chip can be reduced and more laser chips can be obtained from a single silicon wafer. However, the narrower the light-point pitch, the more susceptible the laser is to the heat when the adjacent light-points emit light; and, since the degree of susceptibility depends on the structure of the laser, the degree of freedom in designing the light-point pitch interval is different for each laser element.

[0045] Next, a description will be given of a state in which the semiconductor laser 42 as a narrow pitch laser is mounted on the scanning optical device 40. Figure 5B , an enlarged view of the vicinity of the light source unit 41 in the scanning optical device 40 is shown. Figure 4 As shown, Figure 5B A state in which the circuit board 2 is removed for explanation is shown. Since the scanning optical device 40 has a configuration in which the light source unit 3 in the scanning optical device 1 is changed to the light source unit 41 and other configurations are the same, description of each configuration except the light source unit 41 will be omitted. Components common to the scanning optical device 1 and common definitions are denoted by the same reference numerals.

[0046] The light source unit 41 includes a semiconductor laser 42 and a holder member 31, and the semiconductor laser 42 is press-fitted into the holder member 31. As in the light source unit 3, the light emitting plane Pn of the semiconductor laser 42 is inclined relative to the scanning plane Ps, which is a plane scanned by the rotating polygon mirror 7. Incidentally, the angle θn between the light emitting plane Pn and the scanning plane Ps is obtained from θ represented by the above equation (1). For example, if the resolution is 600 dpi, the light emitting point pitch Wn of the laser is 30 μm, and the sub-scanning magnification of the scanning optical device 40 is 5 times, the semiconductor laser 42 is installed so that the angle θn between the light emitting plane Pn and the scanning plane Ps is 15.8°. Therefore, the angle θn at which the semiconductor laser 42 having a narrower light emitting point pitch is inclined is greater than the angle θw at which the semiconductor laser 32 having a wider light emitting point pitch is inclined (θn>θw).

[0047] As described above, when a common optical system is used, the angles θw and θn between the light emitting planes Pw and Pn and the scanning plane Ps are different for the semiconductor laser 32 as a wide-pitch laser and the semiconductor laser 42 as a narrow-pitch laser. In addition, when common control is performed in the scanning optical device 1 and the scanning optical device 40 each equipped with the semiconductor lasers 32 and 42, the performance of the scanning optical device is also affected. Specifically, these influences are on the illumination distribution of the optical scanning device and the writing timing of each laser, and will be described below.

[0048] (Influence on the Illuminance Distribution of Scanning Optics)

[0049] The light of the semiconductor laser vibrates in a direction roughly parallel to the above-mentioned light-emitting planes Pw and Pn. On the other hand, the rotating polygon mirror 7 and the reflector 11 that reflect the laser light generally have different reflectivities for P-polarized light and S-polarized light, where P-polarized light is light vibrating in the light incident plane and S-polarized light is light vibrating in a direction perpendicular to the light incident plane. Therefore, as described above, the angles θw and θn between the scanning plane Ps and the light-emitting planes Pw and Pn as the laser vibration directions are different between the scanning optical device 1 and the scanning optical device 40, and the ratios of the P-polarized component and the S-polarized component of the laser light on the rotating polygon mirror 7 and the reflector 11 are also different. As a result, the illumination distribution as the laser amount distribution (light amount distribution) in the main scanning direction in the scanning optical device is also different.

[0050] exist Figure 6 In the figure, a graph showing examples of illumination distribution of the scanning optical device 1 and the scanning optical device 40 is shown. The horizontal axis of the graph represents the main scanning position [mm] based on the center position of the sheet P, and the vertical axis represents the amount of light of the scanning optical devices 1 and 40, which is normalized by the amount of light at the center position in the main scanning direction of the sheet P, and the amount of light at the center position is defined as 1. The dotted line represents the illumination distribution of the scanning optical device 1 equipped with a semiconductor laser 32, and the solid line represents the illumination distribution of the scanning optical device 40 equipped with a semiconductor laser 42. In the graph, the target value when correcting the light amount (light amount correction target) is shown as a dotted line. As shown Figure 6 As shown, the target value is set so that the illumination distribution is uniform regardless of the main scanning position [mm]. For example, the target value is set so that the light amount at positions other than the center position is the same as the light amount at the center position.

[0051] As shown in the graph, in the case where the illumination distribution is not uniform at the main scanning position, since this causes uneven density on the image, illumination distribution correction can be performed to make the light amount distribution uniform by changing (correcting) the laser amount in the main scanning direction. Specifically, the control unit 1109 performs the following steps by using Figure 6 The differences between the target value of light amount correction (dotted line) and the illumination distributions of the scanning optical devices 1 and 40 are shown as correction values ​​to correct the light amount in the main scanning direction, respectively.

[0052] For example, at the main scanning position of -60 mm, the correction amount of the light amount is ΔI1 for the scanning optical device 1 and ΔI2 for the scanning optical device 40. Therefore, the appropriate correction amount is different (ΔI1≠ΔI2) between the case where the scanning optical device 1 is installed and the case where the scanning optical device 40 is installed. Incidentally, the control section 1109 functions as a first correction means to correct the illumination distribution in the scanning direction.

[0053] Incidentally, the illuminance distribution varies depending on the configuration of the rotating polygon mirror 7 and the configuration of the reflective film of the reflective mirror 11. Furthermore, in the case where the fθ lens 10 is made of resin, the illuminance distribution varies according to a phenomenon called birefringence in which the refractive index varies depending on the vibration direction of light due to the influence of the resin orientation. Therefore, the illuminance distribution is not limited to Figure 6 The distribution illustrated in .

[0054] (Influence on the writing timing of each laser)

[0055] In the rotation control of the optical scanning device, as described above, the control unit 1109 determines the writing time based on the moment when the laser enters the horizontal synchronization sensor 13 as a reference. Here, in the case where there are multiple light-emitting points as in the case of a dual-beam laser, there is a configuration in which the writing time of each laser is determined based on the moment when one of the lasers is incident on the horizontal synchronization sensor 13 as a reference, so as to determine the writing time of each laser during imaging. Hereinafter, the configuration in which the writing time of each laser is determined based on the moment when one of the lasers is incident on the horizontal synchronization sensor 13 as a reference is referred to as a 1BD configuration. In addition, there is also a configuration in which the writing time of each laser is determined based on the moment when each laser is incident on the horizontal synchronization sensor 13 as a reference, which is referred to as an nBD configuration hereinafter.

[0056] Fig. 7A and Figure 7B A timing chart is shown showing, when two beams of the dual-beam laser are defined as LD1 and LD2, for each of LD1 and LD2, the output timing of the horizontal synchronization sensor 13 and the laser light emission timing for forming an image at a desired position on the photosensitive drum 12. Incidentally, the two beams of the dual-beam laser are beams emitted from the light-emitting point Ew1 and the light-emitting point Ew2, respectively, in the semiconductor laser 32, and beams emitted from the light-emitting point En1 and the light-emitting point En2, respectively, in the semiconductor laser 42.

[0057] Fig. 7A shows the timing diagram of the 1BD configuration, Figure 7BThe timing diagram of the nBD configuration is shown. In both cases, (i) shows the signal (high level or low level) output from the horizontal synchronization sensor 13. (ii) shows the light-emitting timing of LD1, and (iii) shows the light-emitting timing of LD2. All horizontal axes represent time.

[0058] The time when the horizontal synchronization sensor 13 detects the light of LD1 is defined as TbA, and the time when the horizontal synchronization sensor 13 detects the light of LD2 is defined as TbB. In addition, in order to form an image at a desired position on the photosensitive drum 12, the time when LD1 emits light and the time when LD2 emits light are defined as TiA and TiB, respectively. For both the 1BD structure and the nBD structure, the light emission time of LD1 is the same, and the control section 1109 causes LD1 to emit at time TiA which is ΔTaa later than time TbA.

[0059] On the other hand, the timing TiB of emitting LD2 is different between the 1BD structure and the nBD structure. Fig. 7A In the case of the 1BD structure in FIG. 1 , the control unit 1109 causes LD2 to emit at a time TiB that is ΔTab later than the time TbA. Figure 7B In the nBD configuration, the control unit 1109 causes LD2 to emit at time TiB later than time TbB by ΔTbb to form an image at a desired position. In other words, in the nBD configuration, the same laser as that emitted for imaging is used as a reference for the timing detected by the horizontal synchronization sensor 13.

[0060] Rotation control can be performed in both the 1BD structure and the nBD structure; however, in the nBD structure, the light of each light beam is incident on the BD slit 14 at positions separated from each other in the sub-scanning direction. Therefore, it is very susceptible to the straightness of the BD slit 14, mold burrs, dust or fluff adhering to the BD slit 14, etc. Specifically, the detection timing of only one laser at the horizontal synchronization sensor 13 will deviate, and the image writing timing will deviate. In this case, image defects such as moiré may occur due to the deviation of the laser spacing in the main scanning direction. On the other hand, in the 1BD structure, even if the above-mentioned influence exists on the BD slit 14, since the degree of influence on all lasers is the same, the situation in which the laser spacing deviation in the main scanning direction is caused by the deviation of the writing timing of only one laser can be avoided. On the contrary, in the case of the 1BD structure, it will be affected by lasers with different light-emitting point spacings.

[0061] Fig. 7AThe ΔTab shown is a value that varies greatly depending on the light-emitting point spacing. For example, if the resolution is 600 dpi and the main scanning magnification of the scanning optical device is 5 times, there is a difference of 300 μm on the photosensitive drum 12 between the optimal ΔTab when the light-emitting point spacing of the laser is 30 μm and the optimal ΔTab when the light-emitting point spacing is 90 μm. In this way, the appropriate correction amount for the writing time of each laser is different when the scanning optical scanning device 1 is installed and when the scanning optical device 40 is installed. The control unit 1109 acts as a second correction device for correcting the writing time of the laser.

[0062] (Identification of the distance between luminous points)

[0063] As described above, in the case of using lasers having different light-emitting point spacings, the correction amount for correcting the illumination distribution and the correction amount for correcting each laser writing moment are different from each other. Therefore, since the optimal correction amount cannot be selected without knowing the information of the light-emitting point spacing of the laser element mounted on the scanning optical device, an identification device for identifying the light-emitting point spacing is provided in this embodiment. Specifically, the control section 1109 identifies the light-emitting point spacing based on the moment difference, i.e., the time difference, between LD1 and LD2 detected by the horizontal synchronization sensor 13. The control section 1109 serves as an identification device.

[0064] exist Fig. 8A , the detection signal (high level or low level) on the horizontal synchronization sensor 13 in the case of using the scanning optical scanning device 1 with a wide pitch laser (semiconductor laser 32) is shown. Figure 8B , the detection signal on the horizontal synchronization sensor 13 is shown in the case of using the scanning optical device 40 having a narrow pitch laser (semiconductor laser 42). The horizontal axis represents time.

[0065] In the case of using the scanning optical device 1, the time difference between the moment TbA (first moment) when the horizontal synchronization sensor 13 detects LD1 and the moment TbB (second moment) when LD2 is detected is defined as the time difference Dsw. In addition, in the case of using the scanning optical device 40, the time difference between the moment TbA when the horizontal synchronization sensor 13 detects LD1 and the moment TbB when LD2 is detected is defined as the time difference Dsn. Comparing the time difference Dsw and the time difference Dsn, Dsw>Dsn, the wider the distance between the light-emitting points, the longer the time difference. In this way, by checking the time difference between the moment TbA and the moment TbB, the control unit 1109 recognizes the distance between the light-emitting points.

[0066] In other words, the time difference corresponds to information of the light-emitting point spacing. Specifically, the time difference between time TbA and time TbB for each light-emitting point spacing is stored in the memory 1109a provided to the control section 1109, and compared with the actual measurement result to identify the light-emitting point spacing. In the memory 1109a, the information can be stored as a table, for example, associating semiconductor lasers having different light-emitting point spacings with their respective time differences.

[0067] (Moment of identifying the distance between luminous points)

[0068] As described above, in the case of the nBD configuration, since the output of each laser is detected by the horizontal synchronization sensor 13, the method of identifying the light-emitting point spacing by the control section 1109 can be used during imaging. However, in the case of the 1BD configuration, the output of only one of the lasers is detected on the horizontal synchronization sensor 13 during imaging. Therefore, in the case of the 1BD configuration, if the output of each laser is detected by the horizontal synchronization sensor 13 at a time other than during imaging, such as when the scanning optical device is started before imaging, or just after the imaging device is powered on, the light-emitting point spacing identification method in the present embodiment can be applied. Incidentally, even in the nBD configuration, the light-emitting point spacing can be identified at a time other than during imaging.

[0069] By this identification method, the light-emitting point pitch of the semiconductor laser mounted on the scanning optical device is identified by the control unit 1109 on the printer 1100. Based on the identification result, the control unit 1109 selects a correction amount suitable for the light-emitting point pitch from the correction amount for illumination distribution correction for each light-emitting point pitch and the correction amount for writing timing of each laser stored in the control unit 1109, and issues an instruction to the scanning optical scanning device.

[0070] Incidentally, in the present embodiment, description is made using a dual-beam laser as the multi-beam laser, however, not limited thereto, the foregoing matters are also common to the multi-beam laser, and a multi-beam laser having two or more beams may be used.

[0071] (Variation Example)

[0072] Next, a modification of this embodiment will be described with reference to the differences from the above-described embodiment. Fig. 9 , an enlarged view of the vicinity of a circuit board 52 of a scanning optical device 50 in a modified example is shown. Since the scanning optical device 50 has a configuration in which the circuit board 2 is changed to the circuit board 52 with respect to the scanning optical device 1 and the other configurations are the same as those in the embodiment, description of each configuration except the circuit board 52 will be omitted. Components common to the scanning optical device 1 and common definitions are denoted by the same reference numerals.

[0073] A memory (storage) member 53 is provided on the circuit board 52. The memory member 53 is a nonvolatile memory, and stores information about the light-emitting point spacing when the scanning optical device 50 is manufactured. In other words, the memory member 53 provided on the circuit board 52, rather than the above-mentioned memory 1109a, stores information about the light-emitting point spacing. The control section 1109 recognizes the light-emitting point spacing of the semiconductor laser by reading the information about the light-emitting point spacing stored in the memory member 53, and sets the correction amount for illumination distribution correction and the correction amount for writing timing to values ​​suitable for the semiconductor laser.

[0074] The information on the light-emitting point pitch is not necessarily the information on the light-emitting point pitch (information on the interval) itself, but may be any information associated with the information on the light-emitting point pitch, such as hierarchical information of a laser element manufacturer.

[0075] In addition, in the modified example, a nonvolatile memory is used as the memory device, however, the memory device is not limited thereto. For example, the memory device may be a barcode label. If the barcode label is read when the scanning optical device is assembled into the imaging device, the control section 1109 may associate the information about the light-emitting point spacing with the imaging device based on the information read from the barcode label.

[0076] As described above, according to the modification, by sending information about the light-emitting point spacing from the scanning optical device to the control section of the imaging device, the light-emitting point spacing of the semiconductor laser can be identified. Then, based on the identified information about the light-emitting point spacing, the control section sends an optimal correction amount for illumination distribution correction, writing timing correction, etc. to the scanning optical device. Thus, even in the case of using semiconductor lasers with different light-emitting point spacings, an imaging device with fewer image defects (such as uneven density, moiré, etc.) can be provided.

[0077] As described above, according to the present embodiment, even when a multi-beam laser element having different light-emitting point pitches is mounted on a scanning optical device, the occurrence of image defects can be reduced by performing correction suitable for the mounted multi-beam laser element.

[0078] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications and equivalent structures and functions.

Claims

1. An imaging device, comprising: Photosensitive member; a scanning optical unit provided with a light source including a plurality of light-emitting points and configured to emit laser light from the plurality of light-emitting points, respectively, and a deflector configured to deflect each of the laser light emitted from the plurality of light-emitting points into a scanning direction, the scanning optical unit scanning a photosensitive member with the plurality of laser light deflected by the deflector and forming an electrostatic latent image on the photosensitive member; as well as a control unit configured to control the scanning optical unit, Here, the control unit identifies the light-emitting point pitch based on information related to the light-emitting point pitch that is the interval between the plurality of light-emitting points.

2. The imaging device according to claim 1, wherein The scanning optical unit comprises a detection device configured to detect the laser light deflected by the deflector, Wherein, when the plurality of light-emitting points are defined as a first light-emitting point and a second light-emitting point, the information related to the distance between the light-emitting points is a time difference between a first moment when the detection device detects the laser emitted from the first light-emitting point and a second moment when the detection device detects the laser emitted from the second light-emitting point, and The control unit identifies the distance between the light-emitting points based on the time difference.

3. The imaging device according to claim 2, wherein: The wider the distance between the light points, the longer the time difference.

4. The imaging device according to claim 1, wherein The scanning optical unit includes a memory device configured to store the light emitting point spacing, and, The control unit identifies the light-emitting point pitch based on information related to the light-emitting point pitch stored in the memory device.

5. The imaging device according to claim 1, further comprising a first correction device configured to correct a light amount distribution of the laser light in a scanning direction, in, The first correction means acquires a correction value for correcting the light amount distribution based on the light emitting point interval recognized by the control section, and corrects the light amount distribution by the correction value.

6. The imaging device according to claim 2, further comprising a second correction device configured to correct a writing timing of the laser light emitted from each of the plurality of light-emitting points by using a time from a timing when the laser light emitted from one of the plurality of light-emitting points is detected by the detection device as a correction value, and in, The second correction device acquires a correction value based on the light-emitting point interval recognized by the control section, and corrects the writing timing by the correction value.

7. The imaging device according to claim 6, wherein: The control section recognizes the light-emitting point interval at a timing other than during imaging.

Images