Image forming device

Abstract

To provide an image forming device that even when multi beam laser elements having different luminous point pitches are loaded on a scanning optical device, executes correction suitable for the loaded multi beam laser elements to reduce occurrence of poor images.SOLUTION: The image forming device comprises: a scanning optical device that has a photosensitive drum 12, a semiconductor laser that has a plurality of luminous points and emits laser beams from the plurality of luminous points respectively and a light deflector 9 that deflects the respective laser beams emitted from the plurality of luminous points, in a scanning direction, which forms an electrostatic latent image on the photosensitive drum 12 with the laser beams deflected by the light deflector 9; and a control part 1109 that control the scanning optical device. The scanning optical device can be loaded with light sources having different luminous points pitches which are intervals of the plurality of luminous points. The control part 1109 discriminates the luminous point pitches on the basis of a time difference Dsw and a time difference Dsn.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, and more particularly to a scanning optical device that performs optical writing using a laser beam in an image forming apparatus such as a laser beam printer (LBP), a digital copying machine, or a digital facsimile (FAX). [Background technology]

[0002] Conventionally, in a scanning optical device used in an image forming apparatus such as a laser beam printer or a digital copier, a laser beam modulated and emitted from a semiconductor laser element, which is a light source, in response to an image signal is periodically deflected and scanned by an optical deflector such as a rotating polygon mirror. Then, the laser beam emitted from the optical deflector is imaged in a spot shape on an imaging surface on a photosensitive drum by an imaging optical element having an fθ characteristic or a folding mirror. The spot on the imaging surface forms an electrostatic latent image in accordance with the main scanning direction scanned by the optical deflector and the sub-scanning direction caused by the rotation of the photosensitive drum, thereby performing image recording. At that time, the writing timing of the laser beam in the main scanning direction is determined by the incidence timing of the laser beam on a horizontal synchronization sensor. In addition, a configuration is adopted in which the distribution of the electrostatic latent image on the photosensitive drum in the main scanning direction is made uniform by correcting the amount of laser beam in the main scanning direction, which is called illuminance distribution correction, thereby reducing uneven density on the image (see, for example, Patent Document 1).

[0003] In addition, in recent years, as there is a demand for faster output of pages per minute, there are image forming devices that use multi-beam laser elements with multiple light emitting points on a laser chip inside a semiconductor laser element. By using a multi-beam laser element to increase the number of scanning lines that can be scanned at once by an optical deflector, the rotation speed of the optical deflector can be kept low, resulting in a low-noise, high-speed image forming device. In addition, the semiconductor laser that serves as the light source is a general-purpose electronic component, and is often purchased from a laser element manufacturer. In one type of image forming device, it is sometimes possible to mount semiconductor lasers from multiple laser element manufacturers from the standpoint of stable supply and cost. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-152091 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when semiconductor lasers from multiple laser element manufacturers are mounted on an image forming apparatus, the light emitting point pitch, which is one of the important characteristics of a laser element and is the interval between light emitting points on a laser chip, may differ in a multi-beam laser element. The main reason why the light emitting point pitch differs for each plate-shaped laser is because the laser structure differs for each laser element manufacturer. The narrower the light emitting point pitch, the more susceptible it is to the heat effect when the neighboring light emitting point emits light. Since the way in which it is affected differs depending on the laser structure, there are restrictions on the selection of the light emitting point pitch for each laser structure, and the light emitting point pitch of each laser element is determined by balancing it with the customer's required specifications. Therefore, the light emitting point pitch may differ between laser element manufacturers with different laser structures. If there is a performance margin for the customer's required specifications, it is possible to newly develop a laser element with a matching light emitting point pitch, but there is a problem that it takes time and resources to develop and causes an increase in the cost of the laser element. In such a situation, if it is possible to use laser elements with different light emitting point pitches in the same image forming apparatus, the difference in the light emitting point pitch affects performance. When rotating the semiconductor laser around the optical axis of the laser light to align the imaging position of the laser light in the sub-scanning direction on the photosensitive drum, if the light emitting point pitch is different, the amount of rotation will be different. If the amount of rotation of the semiconductor laser is different, the state of polarization, which is the vibration direction of the laser light, will change, and the illuminance distribution of the scanning optical device will also change. Therefore, when performing illuminance distribution correction as in the conventional example, there is a risk that the correction amount of the laser light amount for correcting the illuminance distribution will change.

[0006] In addition, when the rotation amount of the semiconductor laser is different, the interval in the main scanning direction between the image forming positions of each laser light on the photosensitive drum also changes. Therefore, in a configuration in which the write timing of each laser in the main scanning direction is corrected based on the timing at which one laser of the multi-beam laser element enters the horizontal synchronization sensor, the correction amount of the write timing of each laser may change. Therefore, if the information on the light emitting point pitch is not known, appropriate correction cannot be performed, and there is a risk of uneven density occurring or image defects such as moire due to a difference in the write timing between lasers occurring.

[0007] The present invention has been made under these circumstances, and aims to reduce the occurrence of image defects by performing correction appropriate to the multi-beam laser element mounted on a scanning optical device, even when multi-beam laser elements with different light-emitting point pitches are mounted on the scanning optical device. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0009] (1) An image forming apparatus comprising: a photosensitive member; a light source having a plurality of light-emitting points, emitting laser light from each of the plurality of light-emitting points; and a deflector that deflects each of the laser lights emitted from the plurality of light-emitting points in a scanning direction, the light-emitting device forming an electrostatic latent image on the photosensitive member by the laser light deflected by the deflector; and a control unit that controls the scanning optical device, the scanning optical device being capable of mounting light sources having different light-emitting point pitches, which are the spacing between the plurality of light-emitting points, and the control unit being characterized in that the image forming apparatus identifies the light-emitting point pitch based on information relating to the light-emitting point pitch. Effect of the Invention

[0010] According to the present invention, even when multi-beam laser elements having different light emitting point pitches are 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. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view showing an image forming apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 1 is a perspective view showing a scanning optical device according to an embodiment of the present invention; [Diagram 3] FIG. 1 is a perspective view showing the external appearance and internal structure of a first semiconductor laser according to an embodiment; [Figure 4] FIG. 2 is an enlarged view showing a first semiconductor laser mounted in the scanning optical device of the embodiment; [Diagram 5] FIG. 2 is a perspective view showing an internal structure of a second semiconductor laser according to an embodiment; and FIG. 3 is an enlarged view showing the second semiconductor laser mounted in a scanning optical device. [Figure 6] FIG. 13 is a diagram showing the difference in illuminance distribution depending on the light-emitting point pitch in the embodiment. [Figure 7] 1 is a timing chart illustrating the write timing of each laser in an embodiment; [Figure 8] 1 is a timing chart illustrating a method for identifying the pitch of a light emitting point according to an embodiment of the present invention; [Figure 9] FIG. 13 is an explanatory diagram showing a circuit board in a scanning optical device according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0012] In the following description, the direction in which the laser light is scanned is called the main scanning direction, and the direction of rotation of the photosensitive drum, in other words, the direction perpendicular to the main scanning direction, is called the sub-scanning direction. In addition, in a multi-beam laser element, which is a light source, the distance between the positions of multiple light emitting points mounted on a laser chip is called the light emitting point pitch.

[0013] (Image forming device) FIG. 1 shows an example of a schematic configuration of an image forming apparatus. A laser beam printer 1100 (hereinafter referred to as printer 1100) includes a photosensitive drum 12, which is a photosensitive member, a charging unit 1102, and a developing unit 1103. The photosensitive drum 12 is an image carrier on which a latent image (hereinafter referred to as an electrostatic latent image) is formed by the scanning optical device 1. The charging unit 1102 uniformly charges the photosensitive drum 12. The developing unit 1103 develops the electrostatic latent image formed on the photosensitive drum 12 with toner to form a toner image. The toner image formed on the photosensitive drum 12 (on the photosensitive member) is transferred by a transfer unit 1105 to a sheet P as a recording material supplied from a cassette 1104, and the unfixed toner image transferred to the sheet P is fixed by a fixing device 1106. The photosensitive drum 12, the charging unit 1102, the developing unit 1103, and the transfer unit 1105 constitute an image forming unit (image forming means). The fixed sheet P is discharged onto a tray 1107. The printer 1100 also includes a power supply device 1108, which supplies power to a drive unit such as a motor and a control unit 1109. The control unit 1109 has a CPU (not shown) and a memory 1109a which is a storage means, and controls the operation of the scanning optical device 1, the image forming operation by the image forming unit, the conveying operation of the sheet P, etc. It should be noted that the image forming device to which the scanning optical device 1 of the present invention can be applied is not limited to the configuration exemplified in FIG.

[0014] (scanning optical device) The scanning optical device 1 of this embodiment will be described with reference to the drawings. FIG. 2 is a perspective view of the scanning optical device 1 of this embodiment. The laser incident light L emitted from the light source unit 3 driven and controlled by the circuit board 2 is made substantially parallel in the main scanning direction by the BD anamorphic lens 4 and substantially condensed in the sub-scanning direction. The laser incident light L passing through the BD anamorphic lens 4 is limited to a predetermined beam diameter by an optical diaphragm 6 formed in the housing 5, which is a case, and is irradiated onto the reflecting 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 incident laser incident light L. The rotating polygon mirror 7 has four reflecting surfaces, but the number of reflecting surfaces is not limited to this. Here, the rotating polygon mirror 7 and the driving circuit board 8 constitute an optical deflector 9 (deflector). The deflected laser incident light L passes through the fθ lens 10 as the laser scanning light Ls, is reflected by the elongated reflecting mirror 11, and is condensed on the photosensitive drum 12. The plane along which the rotating polygon mirror 7 scans with the laser scanning light Ls is defined as a scanning plane Ps.

[0015] Furthermore, the laser light Lb, which is the incident laser light L deflected by the rotating polygon mirror 7, passes through the BD anamorphic lens 4 and is condensed in the main scanning direction. The laser light Lb, while condensed in the main scanning direction, is incident on a horizontal synchronization sensor 13, which serves as a detection means and is mounted on the circuit board 2, and determines the timing of writing in the main scanning direction onto the photosensitive drum 12. Specifically, when the laser light Lb passes through the BD slit 14 formed in the housing 5 and is incident on the horizontal synchronization sensor 13, the output of the horizontal synchronization sensor 13 changes, and the timing of the laser emission is controlled based on the timing of the output change.

[0016] Such an optical system guides the scanning light onto the photosensitive drum 12 to record an image. Specifically, the angle at which the incident laser light L is deflected changes as the rotary polygon mirror 7 rotates, and each spot image formed by the laser scanning light Ls scans the surface of the photosensitive drum 12 in the direction of the arrow Sd, which is the axial direction of the photosensitive drum 12. As the photosensitive drum 12 rotates, each spot image moves on the photosensitive drum 12 in a direction (sub-scanning direction) perpendicular to the axial direction of the photosensitive drum 12. This forms an electrostatic latent image. The opening of the housing 5 is covered by a cover (not shown).

[0017] (Structure of semiconductor laser and its implementation on scanning optical device) Next, we will explain the semiconductor laser 32 (first semiconductor laser) having a first light emitting point pitch (first interval) used in the light source unit 3. Fig. 3(a) is a perspective view of the semiconductor laser 32, in which components such as a laser chip are contained, and from the viewpoint of dust prevention, the semiconductor laser 32 is sealed by a CAN-type cap 34 having cap glass 33 that transmits laser light.

[0018] 3(b) shows a perspective view of the semiconductor laser 32 without the cap 34 for the purpose of explanation. The semiconductor laser 32 has a laser chip 35 bonded onto a metallic stem 36 via a submount 37 made of silicon or the like. The laser chip 35 is electrically connected to the stem 36, and a current is applied to the laser chip 35, causing it to emit light. In this embodiment, the semiconductor laser 32 is a two-beam laser having two light-emitting points Ew1 (first light-emitting point) and Ew2 (second light-emitting point), and the laser chip 35 emits laser beams from the two light-emitting points Ew1 and Ew2 on its end face.

[0019] The light emitting points Ew1 and Ew2 are arranged substantially parallel to the joint surface between the laser chip 35 and the submount 37, and the light emitting point pitch is indicated by Ww (hereinafter referred to as the pitch Ww). That is, the first light emitting point pitch is the pitch Ww. Here, a plane that is substantially parallel to the joint surface between the laser chip 35 and the submount 37 and passes 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 so that the stem reference axis S connecting the notch 36a and the notch 36b of the stem 36 is substantially parallel to the light emitting plane Pw. More specifically, the notch 36a and the notch 36b have portions 36a1 and 36b1 cut into the stem 36, respectively, and the stem reference axis S is also an axis connecting the portion 36a1 and the portion 36b1.

[0020] 4 shows an enlarged view of the light source unit 3 and its vicinity in the scanning optical device 1. For the purpose of explanation, the circuit board 2 has been removed. The light source unit 3 holds the semiconductor laser 32 by press fitting it into a holder member 31. When using a two-beam laser, it is necessary to form spot images at positions spaced apart in the sub-scanning direction on the photosensitive drum 12, and therefore the light source unit 3 rotates around the emission optical axis. In other words, the semiconductor laser 32 is held by the holder member 31 with the light emitting plane Pw of the semiconductor laser 32 tilted with respect to the scanning plane Ps, which is the plane scanned by the rotating polygon mirror 7.

[0021] The angle θw between the light emitting plane Pw and the scanning plane Ps is calculated from θ expressed by the following formula (1).

number

[0022] For example, if the resolution is 600 dpi, the laser light emitting point pitch Ww is 90 μm, and the sub-scanning magnification β of the optical system of the scanning optical device 1 is 5 times, the semiconductor laser 32 is mounted tilted so that the angle θw between the light emitting plane Pw and the scanning plane Ps is 5.4°.

[0023] (Semiconductor lasers with different light emitting point pitches) Fig. 5(a) shows a semiconductor laser 42 (second semiconductor laser) having a second light-emitting point pitch (second interval) different from that of the semiconductor laser 32. Components and definitions common to the semiconductor laser 32 are indicated with the same numbers. As with Fig. 3(b), the description will be given without the cap 34. The laser chip 45 emits a laser beam from two light-emitting points En1 (first light-emitting point) and En2 (second light-emitting point) on the end face.

[0024] The light emitting points En1 and En2 are arranged approximately parallel to the joint surface between the laser chip 45 and the submount 37, and the light emitting point pitch is indicated by Wn (hereinafter referred to as pitch Wn). That is, the second light emitting point pitch is pitch Wn. Here, a plane that is approximately parallel to the joint surface between the laser chip 45 and the submount 37 and passes 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 so that the stem reference axis S connecting the notch 36a and the notch 36b of the stem 36 is approximately parallel to the light emitting plane Pn. The stem reference axis S is also an axis connecting the portion 36a1 and the portion 36b1.

[0025] Comparing the semiconductor laser 32 having the first light-emitting point pitch with 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, and the semiconductor laser 42 is a "narrow-pitch laser" having a narrower light-emitting point pitch.

[0026] In general, narrow-pitch lasers have higher manufacturing efficiency because the size of the laser chip can be reduced and more laser chips can be obtained from one silicon wafer. However, the narrower the light-emitting point pitch, the more susceptible it is to the heat generated when the neighboring light-emitting point emits light, and the extent to which this effect is felt varies depending on the laser structure, so the degree of freedom in designing the light-emitting point pitch interval varies for each laser element.

[0027] Next, a state in which the semiconductor laser 42, which is a narrow-pitch laser, is mounted on the scanning optical device 40 will be described. Fig. 5(b) shows an enlarged view of the vicinity of the light source unit 41 in the scanning optical device 40. As in Fig. 4, the circuit board 2 has been removed for the purpose of explanation. The scanning optical device 40 has a configuration in which the light source unit 3 of the scanning optical device 1 is changed to the light source unit 41, and other configurations are similar, so explanations of each configuration other than the light source unit 41 will be omitted. Parts and definitions in common with the scanning optical device 1 are indicated by the same numbers.

[0028] The light source unit 41 holds the semiconductor laser 42 by press fitting it in the holder member 31, and similarly to the light source unit 3, the light emitting plane Pn of the semiconductor laser 42 is inclined with respect to the scanning plane Ps, which is the plane scanned by the rotating polygon mirror 7. The angle θn between the light emitting plane Pn and the scanning plane Ps is calculated from θ expressed by the above-mentioned formula (1). For example, when 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 mounted tilted so that the angle θn between the light emitting plane Pn and the scanning plane Ps is 15.8°. In this way, the angle θn at which the semiconductor laser 42 with a narrow light emitting point pitch is tilted is larger than the angle θw at which the semiconductor laser 32 with a wide light emitting point pitch is tilted (θn>θw).

[0029] As explained above, when using a common optical system, the wide-pitch semiconductor laser 32 and the narrow-pitch semiconductor laser 42 have different angles θw and θn between the light-emitting planes Pw and Pn and the scanning plane Ps. In addition, when common control is performed between the scanning optical device 1 and the scanning optical device 40 equipped with the respective semiconductor lasers 32 and 42, this also affects the performance of the scanning optical device. Specifically, this affects the illuminance distribution of the scanning optical device and the write timing for each laser, which will be explained below.

[0030] (Effect on illuminance distribution of scanning optical devices) The light of the semiconductor laser vibrates in a direction approximately parallel to the light-emitting planes Pw and Pn described above. On the other hand, the rotating polygon mirror 7 and the reflecting mirror 11 that reflect the laser light generally have different reflectances for P-polarized light, which is light vibrating within the incident plane of the light beam, and S-polarized light, which is light vibrating in a direction perpendicular to the incident plane of the light beam. Therefore, as described above, the scanning optical device 1 and the scanning optical device 40 have different angles θw and θn between the scanning plane Ps and the light-emitting planes Pw and Pn, which are the vibration direction of the laser light, 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 reflecting mirror 11 are also different. As a result, the illuminance distribution, which is the distribution of the laser light amount (light amount distribution) in the main scanning direction in the scanning optical device, is also different.

[0031] FIG. 6 shows a graph of an example of the illuminance distribution of the scanning optical device 1 and the scanning optical device 40. 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 light amount of the scanning optical devices 1 and 40, which are normalized by the light amount at the center position in the main scanning direction of the sheet P, and the light amount at the center position is set to 1. The dashed line shows the illuminance distribution of the scanning optical device 1 equipped with the semiconductor laser 32, and the solid line shows the illuminance distribution of the scanning optical device 40 equipped with the semiconductor laser 42. In the graph, the target value (light amount correction target) when correcting the light amount is shown by a dashed line. The target value is set so that the illuminance distribution is constant regardless of the main scanning position [mm] as shown in FIG. 6. For example, the target value is set so that the light amount at a position other than the center position in the main scanning position is the same as that at the center position.

[0032] As shown in the graph, if the illuminance distribution is not uniform with respect to the main scanning position, this leads to uneven density on the image, so illuminance distribution correction may be performed to make the light amount distribution uniform by changing (correcting) the laser light amount in the main scanning direction. Specifically, the control unit 1109 corrects the light amount in the main scanning direction using the difference between the target value (dotted line) of the light amount correction shown in Fig. 6 and the illuminance distribution of the scanning optical devices 1 and 40 as a correction value.

[0033] For example, at a main scanning position of -60 mm, the correction amount of the light amount in the scanning optical device 1 is ΔI1, and the correction amount of the light amount in the scanning optical device 40 is ΔI2. In this way, the appropriate correction amount differs between the case where the scanning optical device 1 is installed and the case where the scanning optical device 40 is installed (ΔI1 ≠ ΔI2). Note that the control unit 1109 functions as a first correction unit that corrects the illuminance distribution in the scanning direction.

[0034] The illuminance distribution changes depending on the configuration of the reflective film of the rotating polygon mirror 7 and the reflecting mirror 11, and in addition, if the fθ lens 10 is made of resin, it also changes due to a phenomenon called birefringence, in which the refractive index differs depending on the vibration direction of light due to the influence of the orientation of the resin. For this reason, the illuminance distribution is not limited to the distribution exemplified in Figure 6.

[0035] (Effect on writing timing for each laser) During rotation control of the scanning optical device, the control unit 1109 determines the write timing based on the timing at which the laser light enters the horizontal synchronization sensor 13 as described above. Here, when there are multiple light emitting points such as a two-beam laser, in order to determine the write timing of each laser during image formation, there is a configuration in which the write timing of each laser is determined based on the timing at which one laser light enters the horizontal synchronization sensor 13. Hereinafter, a configuration in which the write timing of each laser is determined based on the timing at which one laser light enters the horizontal synchronization sensor 13 is referred to as a 1BD configuration. There is also a configuration in which the write timing of each laser is determined based on the timing at which each laser enters the horizontal synchronization sensor 13, which is hereinafter referred to as an nBD configuration.

[0036] 7 is a timing chart showing the output of the horizontal synchronization sensor 13 and the laser emission timing for forming an image at a desired position on the photosensitive drum 12 in each of LD1 and LD2 when the two beams of the two-beam laser are LD1 and LD2. Note that the two beams of the two-beam laser are the beams emitted from the light emitting points Ew1 and Ew2, respectively, in the semiconductor laser 32, and the beams emitted from the light emitting points En1 and En2, respectively, in the semiconductor laser 42.

[0037] 7(a) is a timing chart for the 1BD configuration, and FIG. 7(b) is a timing chart for the nBD configuration. In both cases, (i) shows the signal (high level, low level) output from the horizontal synchronization sensor 13. (ii) shows the light emission timing of LD1, and (iii) shows the light emission timing of LD2. The horizontal axis shows time in both cases.

[0038] The timing when the light of LD1 is detected by the horizontal synchronization sensor 13 is TbA, and the timing when the light of LD2 is detected by the horizontal synchronization sensor 13 is TbB. Also, the timing when LD1 emits light is TiA, and the timing when LD2 emits light is TiB, in order to form an image at a desired position on the photosensitive drum 12. The light emission timing of LD1 is the same in both the 1BD configuration and the nBD configuration, and the control unit 1109 causes LD1 to emit light at timing TiA after ΔTaa with reference to timing TbA.

[0039] On the other hand, the timing TiB at which LD2 emits light differs between the 1BD configuration and the nBD configuration. In the case of the 1BD configuration of Fig. 7(a), the control unit 1109 causes LD2 to emit light at timing TiB after ΔTab with timing TbA as the reference. On the other hand, in the case of the nBD configuration of Fig. 7(b), the control unit 1109 causes LD2 to emit light at timing TiB after ΔTbb with timing TbB as the reference, thereby forming an image at a desired position. In other words, in the nBD configuration, the same laser as the laser emitted for image formation is used as the reference for the timing at which the horizontal synchronization sensor 13 detects it.

[0040] Although rotation control is possible in both the 1BD configuration and the nBD configuration, in the case of the nBD configuration, the light beams of the beams are incident on the BD slit 14 at positions separated in the sub-scanning direction. Therefore, it is easily affected by the straightness of the BD slit 14, mold burrs, and adhesion of dust and fur to the BD slit 14. Specifically, there is a risk that only the detection timing of one of the lasers at the horizontal synchronization sensor 13 will shift, causing a shift in the image write timing. In that case, the laser interval in the main scanning direction will shift, and image defects such as moire may occur. On the other hand, in the case of the 1BD configuration, even if the BD slit 14 is affected as described above, the amount of influence on all the lasers is the same, so it is possible to avoid a shift in the laser interval in the main scanning direction due to a shift in the write timing of only one laser. Conversely, it is the 1BD configuration that is affected by lasers with different light-emitting point pitches.

[0041] 7(a) is a value that varies greatly depending on the light-emitting point pitch. For example, when 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 laser light-emitting point pitch is 30 μm and the optimal ΔTab when it is 90 μm. In this way, the appropriate correction amount of the writing timing for each laser differs between the case where the scanning optical device 1 is installed and the case where the scanning optical device 40 is installed. The control unit 1109 functions as a second correction unit that corrects the writing timing of the laser.

[0042] (Identification of light emitting point pitch) As explained above, when lasers with different light emitting point pitches are used, the amount of correction required for correcting the illuminance distribution and the write timing for each laser is different. For this reason, if the information on the light emitting point pitch of the laser element mounted on the scanning optical device is not known, the optimal amount of correction cannot be selected, so this embodiment is provided with an identification means for identifying the light emitting point pitch. Specifically, the control unit 1109 identifies the light emitting point pitch from the difference in timing between LD1 and LD2 detected by the horizontal synchronization sensor 13, i.e., the time difference. The control unit 1109 functions as an identification means.

[0043] Fig. 8(a) shows the detection signal (high level or low level) on the horizontal synchronization sensor 13 when using a scanning optical device 1 equipped with a wide-pitch laser (semiconductor laser 32). Fig. 8(b) shows the detection signal on the horizontal synchronization sensor 13 when using a scanning optical device 40 equipped with a narrow-pitch laser (semiconductor laser 42). The horizontal axis in both cases indicates time.

[0044] When the scanning optical device 1 is used, the time difference between the timing TbA (first timing) when the horizontal synchronization sensor 13 detects LD1 and the timing TbB (second timing) when LD2 is detected is defined as the time difference Dsw. When the scanning optical device 40 is used, the time difference between the timing TbA when the horizontal synchronization sensor 13 detects LD1 and the timing TbB when LD2 is detected is defined as the time difference Dsn. When the time difference Dsw and the time difference Dsn are compared, Dsw>Dsn, and the wider the light-emitting point pitch, the longer the time difference. In this way, the control unit 1109 identifies the light-emitting point pitch by looking at the time difference between the timing TbA and the timing TbB. That is, the time difference corresponds to information on the light-emitting point pitch. Specifically, the time difference between the timing TbA and the timing TbB for each light-emitting point pitch is stored in the memory 1109a of the control unit 1109, and the light-emitting point pitch is identified by comparing it with the actual measurement result. The memory 1109a may store information, for example as a table, associating semiconductor lasers having different light emitting point pitches with their respective time differences.

[0045] (Timing for identifying the light emitting point pitch) As described above, in the case of the nBD configuration, the horizontal synchronization sensor 13 detects the output of each laser, so the method of identifying the light-emitting point pitch by the control unit 1109 during image formation can be used as is. However, in the case of the 1BD configuration, the horizontal synchronization sensor 13 detects the output of only one laser beam during image formation. For this reason, in the case of the 1BD configuration, if the horizontal synchronization sensor 13 detects the output of each laser beam at a timing other than during image formation, such as when the scanning optical device is started up before image formation or immediately after the image forming device is powered on, the light-emitting point pitch identification method of this embodiment can be applied. Note that even in the nBD configuration, the light-emitting point pitch may be identified at a timing other than during image formation.

[0046] Using this identification method, the control unit 1109 in the printer 1100 identifies the light emitting point pitch of the semiconductor laser mounted on the scanning optical device. Depending on the result, the control unit 1109 selects a correction amount suitable for the light emitting point pitch from the correction amount of illuminance distribution correction for each light emitting point pitch held in the control unit 1109 and the correction amount of the write start timing for each laser, and instructs the scanning optical device.

[0047] In this embodiment, a two-beam laser is used as the multi-beam laser, but this is not limited to this, and the above-mentioned issues are common to all multi-beams, and a multi-beam laser with two or more beams may also be used.

[0048] (Modification) Next, a modified example of this embodiment will be described, focusing on the differences from the above-mentioned embodiment. Fig. 9 shows an enlarged view of the vicinity of a circuit board 52 of a scanning optical device 50 in the modified example. The scanning optical device 50 has a configuration in which the circuit board 2 of the scanning optical device 1 is changed to a circuit board 52, and other configurations are similar, so descriptions of each configuration other than the circuit board 52 will be omitted. Parts and definitions in common with the scanning optical device 1 are indicated by the same numbers.

[0049] A memory member 53 is provided on the circuit board 52. The memory member 53 is a non-volatile memory, and stores information related to the light-emitting point pitch when the scanning optical device 50 is manufactured. That is, the memory member 53 of the circuit board 52 stores information related to the light-emitting point pitch, not the above-mentioned memory 1109a. The control unit 1109 identifies the light-emitting point pitch of the semiconductor laser by reading the information related to the light-emitting point pitch stored in the memory member 53, and sets the correction amount of the illuminance distribution correction and the correction amount of the write timing to values ​​suitable for the semiconductor laser.

[0050] The information regarding the light-emitting point pitch does not have to be the light-emitting point pitch information (spacing information) itself, but may be any information that can be linked to the light-emitting point pitch information, such as layer information from a laser element manufacturer. In addition, in this modification, a non-volatile memory is used as the storage means, but the storage means is not limited to this. For example, a barcode label may be used. If the barcode label is read when the scanning optical device is attached to the image forming apparatus, the control unit 1109 can link the light emitting point information to the image forming apparatus based on the information read from the barcode label.

[0051] As described above, according to the modified example, the light emitting point pitch of the semiconductor laser can be identified by transmitting information on the light emitting point pitch from the scanning optical device to the control unit of the image forming device. Then, based on the identified light emitting point pitch information, the control unit instructs the scanning optical device on optimal correction amounts for illuminance distribution correction, write timing correction, and the like. This makes it possible to provide an image forming device with fewer image defects such as uneven density and moire, even when using semiconductor lasers with different light emitting point pitches.

[0052] As described above, according to this embodiment, even if multi-beam laser elements having different light emitting point pitches are mounted on a scanning optical device, correction suitable for the mounted multi-beam laser element can be performed to reduce the occurrence of image defects.

[0053] The disclosure of this embodiment includes the following configuration. (Configuration 1) A photoconductor; a scanning optical device including a light source having a plurality of light emitting points and emitting laser light from each of the plurality of light emitting points, and a deflector that deflects each of the laser light emitted from the plurality of light emitting points in a scanning direction, and forming an electrostatic latent image on the photoconductor by the laser light deflected by the deflector; A control unit for controlling the scanning optical device; Equipped with The scanning optical device is an image forming device capable of mounting a light source having a different light emitting point pitch, which is an interval between the plurality of light emitting points, The image forming apparatus according to claim 1, wherein the control unit identifies the light-emitting point pitch based on information about the light-emitting point pitch. (Configuration 2) the scanning optical device has a detection unit that detects laser light emitted from the plurality of light emitting points and deflected by the deflector, When the plurality of light emitting points are defined as first light emitting points and second light emitting points, the information about the light-emitting point pitch is a time difference between a first timing at which the laser light emitted from the first light-emitting point is detected by the detection means and a second timing at which the laser light emitted from the second light-emitting point is detected by the detection means; 2. The image forming apparatus according to claim 1, wherein the control unit identifies the light emitting point pitch based on the time difference. (Configuration 3) 3. The image forming apparatus according to claim 1, wherein the time difference is longer as the light-emitting point pitch is wider. (Configuration 4) the scanning optical device has a storage means for storing information regarding the light emitting point pitch, 4. The image forming apparatus according to claim 1, wherein the control unit identifies the light emitting point pitch based on information about the light emitting point pitch stored in the storage unit. (Configuration 5) a first correction unit that corrects a light amount distribution of the laser light in the scanning direction; The image forming apparatus according to any one of configurations 1 to 4, wherein the first correction means obtains a correction value for correcting the light quantity distribution based on the light-emitting point pitch identified by the control unit, and corrects the light quantity distribution using the correction value. (Configuration 6) a second correction means for correcting a writing timing of the laser light emitted from each of the plurality of light-emitting points by using a time from a timing at which the laser light emitted from one of the plurality of light-emitting points is detected by the detection means as a correction value; The image forming apparatus according to configuration 2 or 3, wherein the second correction means obtains the correction value based on the light-emitting point pitch identified by the control unit, and corrects the write timing using the correction value. (Configuration 7) 7. The image forming apparatus according to configuration 6, wherein the control unit identifies the light emitting point pitch at a timing other than during image formation. [Explanation of symbols]

[0054] 1. Scanning optical device 32, 42 Semiconductor laser Ew1, Ew2, En1, En2 laser emission points Ww, Wn Light emitting point pitch 1109 Control section

Claims

1. A photoconductor; a scanning optical device including a light source having a plurality of light emitting points and emitting laser light from each of the plurality of light emitting points, and a deflector that deflects each of the laser light emitted from the plurality of light emitting points in a scanning direction, and forming an electrostatic latent image on the photoconductor by the laser light deflected by the deflector; A control unit for controlling the scanning optical device; Equipped with The scanning optical device is an image forming device capable of mounting a light source having a different light emitting point pitch, which is an interval between the plurality of light emitting points, The image forming apparatus according to claim 1, wherein the control unit identifies the light-emitting point pitch based on information about the light-emitting point pitch.

2. the scanning optical device has a detection unit that detects laser light emitted from the plurality of light emitting points and deflected by the deflector, When the plurality of light emitting points are defined as first light emitting points and second light emitting points, the information about the light-emitting point pitch is a time difference between a first timing at which the laser light emitted from the first light-emitting point is detected by the detection means and a second timing at which the laser light emitted from the second light-emitting point is detected by the detection means; The image forming apparatus according to claim 1 , wherein the control unit identifies the light emitting point pitch based on the time difference.

3. 3. The image forming apparatus according to claim 2, wherein the time difference is longer as the light emitting point pitch is wider.

4. the scanning optical device has a storage means for storing information regarding the light emitting point pitch, 2. The image forming apparatus according to claim 1, wherein the control unit identifies the light emitting point pitch based on information about the light emitting point pitch stored in the storage unit.

5. a first correction unit that corrects a light amount distribution of the laser light in the scanning direction; 5. The image forming apparatus according to claim 1, wherein the first correction means obtains a correction value for correcting the light quantity distribution based on the light-emitting point pitch identified by the control unit, and corrects the light quantity distribution using the correction value.

6. a second correction means for correcting a writing timing of the laser light emitted from each of the plurality of light-emitting points by using a time from a timing at which the laser light emitted from one of the plurality of light-emitting points is detected by the detection means as a correction value, 4. The image forming apparatus according to claim 2, wherein the second correction unit obtains the correction value based on the light-emitting point pitch identified by the control unit, and corrects the write timing using the correction value.

7. The image forming apparatus according to claim 6 , wherein the control unit identifies the light emitting point pitch at a timing other than during image formation.

Images