JP6834801B2 - An optical scanning device and a color image forming apparatus provided with the optical scanning device. - Google Patents

Description

The present invention relates to an optical scanning apparatus and a color image forming apparatus including the optical scanning apparatus.

Conventionally, a tandem optical scanning device equipped with a cylinder lens unit that collects light beams emitted from a plurality of light sources corresponding to each color of yellow, magenta, cyan, and black onto the same reflecting surface of a polygon mirror. Is known (see, for example, Patent Document 1). The cylinder lens unit collects a plurality of light beams emitted from a light source by obliquely incident on the reflection surface of the polygon mirror at different angles of incidence when viewed from the sub-scanning cross section. The plurality of light beams focused on the reflecting surface are reflected at different reflection angles and separated.

In the above-mentioned tandem type optical scanning apparatus, generally, one of a plurality of light beams is detected by a synchronization detection sensor so that the writing timing of image data by each light beam is synchronized.

Japanese Unexamined Patent Publication No. 2003-295079

In the optical scanning apparatus shown in Patent Document 1, the light component of the light beam emitted from each light source is closer to the upstream side in the mirror rotation direction and the light component closer to the downstream side from the cylinder lens portion (condensing lens portion). The optical path length to the reflecting surface is different. Here, when the light beam is vertically incident on the reflection surface of the polygon mirror when viewed from the sub-scanning cross section, the optical path length is different between the light component closer to the upstream side and the light component closer to the downstream side in the mirror rotation direction. However, the incident region of the light beam incident on the mirror reflecting surface extends parallel to the mirror rotation direction (direction orthogonal to the rotation axis of the polygon mirror). However, in a tandem optical scanning device, each light beam is obliquely incident on the reflecting surface of the polygon mirror, so that the optical path length differs between the upstream optical component and the downstream optical component in the mirror rotation direction. If so, the incident region of the light beam incident on the mirror reflecting surface is tilted in the sub-scanning direction with respect to the mirror rotation direction. As a result, the optical path of the light beam reflected by the mirror reflecting surface is easily vibrated due to the influence of the surface accuracy of the mirror reflecting surface.

This also applies to the light beam used for synchronization detection. That is, when the light beam used for synchronization detection is inclined with respect to the mirror rotation direction on the mirror reflection surface as described above, the optical path of the light beam reflected by the mirror reflection surface toward the synchronization detection sensor is mirrored. It vibrates under the influence of the surface accuracy of the reflecting surface. As a result, there is a problem that the detection timing of the light beam by the synchronization detection sensor varies and the synchronization detection accuracy deteriorates.

The present invention has been made in view of this point, and an object of the present invention is to provide a condensing lens unit that collects light beams emitted from a plurality of light sources on the same reflecting surface of a polygon mirror. The purpose of the tandem type optical scanning device is to prevent a decrease in synchronization detection accuracy due to the light beam detected by the synchronization detection sensor tilting in the sub-scanning direction with respect to the mirror rotation direction on the mirror reflecting surface.

The optical scanning device according to the present invention is provided between a polygon mirror, a light source unit that emits a plurality of light beams at intervals in the sub-scanning direction, and the polygon mirror and the light source unit, and is provided from the light source unit. A condensing lens unit that obliquely incidents a plurality of emitted light beams at different angles of incidence on the same reflecting surface of the polygon mirror and condenses them, and at least one of the plurality of light beams is effective. It is equipped with a synchronization detection sensor that detects outside the scanning area.

The condensing lens unit is composed of a plurality of lens units through which each of the plurality of light beams passes, and the first lens unit through which the light beam detected by the synchronization detection sensor among the plurality of lens units passes. is the radius of curvature constant curvature line connecting position where the same lens surface in the first lens unit, viewed from the optical axis direction, of the polygon mirror at a central position in the sub-scanning direction of the condensing lens unit It is configured to have a predetermined inclination angle with respect to the center line extending in the direction perpendicular to the rotation axis, the inclination angle of the curvature constant linear of the first lens unit, synchronization detection of the reflective surface of the polygon mirror The region where the light beam incident in is set to be parallel to the mirror rotation direction, and the second lens portion through which the light beam not detected by the synchronization detection sensor passes among the plurality of lens portions is A straight line having a constant curvature connecting positions where the radius of curvature of the lens surface of the second lens portion is the same when viewed from the optical axis direction has a predetermined tilt angle with respect to the center line of the condenser lens portion. The tilt angle of the constant curvature straight line of the second lens portion is such that the light beam is incident on the reflecting surface as compared with the case where the constant curvature straight line is parallel to the center line of the condensing lens portion. The maximum tilt amount in the sub-scanning direction with respect to the mirror rotation direction of the region is set to be small, and the tilt angle of the constant curvature straight line of the second lens portion is further set to the incident region of the light beam on the reflection surface of the polygon mirror. Is divided into a plurality of regions in the mirror rotation direction, the amount of inclination in the sub-scanning direction with respect to the mirror rotation direction is obtained for each area, and the total value of the obtained inclination amounts is set to be the minimum. There is.

The image forming apparatus according to the present invention includes the above-mentioned optical scanning apparatus.

According to the present invention, it is possible to prevent a decrease in synchronization detection accuracy due to the light beam detected by the synchronization detection sensor tilting in the sub-scanning direction with respect to the mirror rotation direction on the mirror reflecting surface.

FIG. 1 is a schematic view showing an image forming apparatus including an optical scanning apparatus according to an embodiment. FIG. 2 is a side view showing a schematic configuration of the optical scanning device according to the embodiment. FIG. 3 is a schematic view linearly showing an optical path from the light source portion of the optical scanning device to the polygon mirror in the embodiment. FIG. 4 is a schematic view showing how the light beam emitted from the light source of the optical scanning device according to the embodiment is reflected by the polygon mirror. FIG. 5 is a schematic view showing an optical path of a conventional optical scanning device, and is a diagram showing how a light beam is reflected at a downstream end portion in a rotation direction on a reflecting surface of a polygon mirror. FIG. 6 is a schematic view showing an optical path of a conventional optical scanning device, and is a diagram showing how a light beam is reflected at an upstream end portion in a rotation direction on a reflecting surface of a polygon mirror. FIG. 7A is a schematic view of the incident region of the black light beam D4 incident on the reflecting surface of the polygon mirror in the conventional optical scanning device, as viewed from the rotation center side of the polygon mirror. FIG. 7B is a schematic view of the incident region of the yellow light beam D1 incident on the reflecting surface of the polygon mirror in the conventional optical scanning device, as viewed from the rotation center side of the polygon mirror. FIG. 8 is a side view showing a condenser lens portion of the optical scanning device according to the embodiment. FIG. 9 is an arrow view in the IX direction of FIG. FIG. 10 is a view corresponding to FIG. 8 in a conventional optical scanning device. FIG. 11 is an arrow view in the XI direction of FIG. FIG. 12 is a schematic view schematically showing an optical path of a light beam passing through a condensing lens portion in a conventional optical scanning device. FIG. 13 is a schematic view schematically showing the optical path of the light beam that has passed through the condensing lens portion in the optical scanning device of the present embodiment. FIG. 14A is a schematic view of the scanning device of the present embodiment as viewed from the rotation center side of the polygon mirror, showing the incident region of the black light beam D4 incident on the reflecting surface of the polygon mirror in a simplified manner. FIG. 14B is a schematic view of the scanning device of the present embodiment as viewed from the rotation center side of the polygon mirror, showing the incident region of the yellow light beam D1 incident on the reflecting surface of the polygon mirror in a simplified manner. FIG. 15 is a graph showing the screen angle of each color. FIG. 16 is an explanatory diagram for explaining a method of setting the tilt angle of the split lens portion in another embodiment. FIG. 17 is a schematic view showing a simplified incident region of a light beam incident on a reflecting surface of a polygon mirror in an optical scanning apparatus adopting the setting method according to FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments.

<< Embodiment >>
FIG. 1 shows the image forming apparatus 1 in the embodiment. This image forming apparatus 1 is a tandem type color printer, and is an intermediate transfer belt 7, a primary transfer unit 8 and a secondary transfer unit 9, a fixing unit 11, an optical scanning device 15, and four image forming devices. The units 16a to 16d and the first to fourth paper transport units 21 to 24 are provided.

A paper feed cassette 3 is arranged in the lower part of the main body 2 of the image forming apparatus 1. The paper feed cassette 3 is loaded with paper (not shown) such as cut paper before printing inside the paper cassette 3. Then, this paper is separated and sent out one by one toward the upper right side of the paper feed cassette 3 in FIG.

The first paper transport unit 21 is provided on the side of the paper feed cassette 3. The first paper transport unit 21 is arranged along the right side surface of the main body 2. Then, the first paper transport unit 21 receives the paper fed from the paper feed cassette 3 and transports the paper to the upper secondary transfer unit 9 along the right side surface of the main body 2.

A manual paper feed unit 5 is provided on the left side of the paper feed cassette 3. Paper of a size not contained in the paper feed cassette 3, thick paper, an OHP sheet, or the like is placed on the manual paper feed unit 5. A second paper transport unit 22 is provided on the right side of the manual paper feed unit 5. The second paper transport unit 22 extends substantially horizontally from the manual paper feed unit 5 to the first paper transport unit 21 and joins the first paper transport unit 21. Then, the second paper transport unit 22 receives the paper or the like sent out from the manual paper feed unit 5 and conveys it to the first paper transport unit 21.

The optical scanning device 15 is arranged above the second paper transport unit 22. Here, the image forming apparatus 1 receives the image data transmitted from the outside. This image data is stored in a temporary storage unit (not shown) and then sent to the optical scanning device 15 as needed. The optical scanning device 15 irradiates the image forming units 16a to 16d with laser light controlled based on the image data.

The image forming units 16a to 16d are provided above the optical scanning device 15. Each image forming unit 16a to 16d has a photoconductor drum 10a to 10d, respectively. Chargers 20a to 20d, developing devices 30a to 30d, and cleaning devices 35a to 35d are provided for each of the photoconductor drums 10a to 10d. The cleaning devices 35a to 35d are provided for cleaning the peripheral surfaces of the photoconductor drums 10a to 10d.

An endless intermediate transfer belt 7 is provided above each of the image forming units 16a to 16d. The intermediate transfer belt 7 is wound around a plurality of rollers and is rotationally driven by a drive device (not shown).

As shown in FIG. 1, the four image forming units 16a to 16d are arranged in a row along the intermediate transfer belt 7 and form yellow, magenta, cyan, or black toner images, respectively. That is, in each of the image forming units 16a to 16d, the peripheral surface of the photoconductor drums 10a to 10d is irradiated with laser light by the optical scanning device 15 to form an electrostatic latent image of the original image, and the developing devices 30a to 30d do this. Toner images of each color are formed by developing the electrostatic latent image.

The primary transfer units 8a to 8d are arranged above the image forming units 16a to 16d, respectively. The primary transfer units 8a to 8d have primary transfer rollers 80a to 80d that first transfer the toner image formed by the image forming units 16a to 16d to the surface of the intermediate transfer belt 7. A transfer bias is applied to the primary transfer rollers 80a to 80d from a transfer bias power supply (not shown). The toner images of the image forming units 16a to 16d are transferred to the intermediate transfer belt 7 at a predetermined timing by the transfer bias applied to the primary transfer rollers 80a to 80d. Then, on the surface of the intermediate transfer belt 7, a color toner image in which four color toner images of yellow, magenta, cyan, and black are superimposed is formed.

The secondary transfer unit 9 has a secondary transfer roller 18 arranged on the right side of the intermediate transfer belt 7. A transfer bias is applied to the secondary transfer roller 18 by a transfer bias power supply. The secondary transfer roller 18 sandwiches the paper P with the intermediate transfer belt 7. Then, the toner image on the intermediate transfer belt 7 is transferred to the paper P by the transfer bias applied to the secondary transfer roller 18.

The fixing portion 11 is provided above the secondary transfer portion 9. A third paper transport unit 23 is formed between the secondary transfer unit 9 and the fixing unit 11 to transfer the paper P on which the toner image is secondarily transferred to the fixing unit 11.

The fixing portion 11 has a rotating heating roller 111 and a pressure roller 112, respectively. Then, the fixing portion 11 sandwiches the paper P between the heating roller 111 and the pressure roller 112 to heat and pressurize the toner image transferred to the paper P and fix it on the paper P.

A branch portion 27 is provided above the fixing portion 11. When double-sided printing is not performed, the paper P discharged from the fixing unit 11 is discharged from the branch portion 27 to the paper ejection unit 28 formed on the upper portion of the image forming apparatus 1. The discharge port portion where the paper P is discharged from the branch portion 27 toward the paper discharge portion 28 functions as a switchback portion 29. When double-sided printing is performed, the switchback unit 29 switches the transport direction of the paper P discharged from the fixing unit 11.

-Details of optical scanning device-
Next, the details of the optical scanning apparatus 15 will be described with reference to FIGS. 2 to 4. FIG. 2 is a side view showing the optical scanning device, and FIG. 3 is a schematic view linearly showing an incident optical system from the light source unit 40 of the optical scanning device 15 to the reflecting surface 44a of the polygon mirror 44. FIG. 4 is a schematic view showing how the light beams D1 to D4 emitted from the light sources 40a to 40d of the optical scanning device 15 are reflected by the polygon mirror 44.

The optical scanning device 15 has a housing 43 (see FIG. 2). Inside the housing 43 are a polygon mirror 44, a light source unit 40 (see FIGS. 3 and 4) that emits light beams D1 to D4 toward the polygon mirror 44, and a synchronization detection sensor 47 (shown only in FIG. 4). Is placed.

The polygon mirror 44 has a regular hexagonal shape having six reflecting surfaces 44a on the side surface. The polygon mirror 44 is rotated at a predetermined speed by a motor (not shown). The polygon mirror 44 reflects the light beams D1 to D4 emitted from the light source unit 40 and scans them in the main scanning direction.

The light source unit 40 has light sources 40a to 40d corresponding to each color of yellow, magenta, cyan, and black. The four light sources 40a to 40d are arranged at intervals in the sub-scanning direction (the direction of the rotation axis of the polygon mirror 44 and the vertical direction in FIG. 3). Each of the light sources 40a to 40d emits light beams D1 to D4 corresponding to each color.

The synchronization detection sensor 47 detects the light beam D4 corresponding to the black reflected by the polygon mirror 44 outside the effective scanning region, and transmits the synchronization signal to a control unit (not shown). The control unit controls the writing timing of the image data by the light beams D1 to D4 with reference to the time when the synchronization detection signal is received.

On the upstream side of the optical path from the polygon mirror 44, four collimator lenses 41a to 41d provided corresponding to the respective light sources 40a to 40d and light beams D1 to D4 passing through the collimator lenses 41a to 41d have a predetermined optical path width. and aperture (not shown) to a condenser lens 42 for condensing the reflection surface 44a of the polygon mirror 44 the light beam D1~D4 passing through the aperture is disposed.

The condensing lens unit 42 has a structure divided into four one lenses in the height direction (see FIG. 8). The divided lens portions 42a to 42d (hereinafter referred to as the first to fourth divided lens portions 42a to 42d) are provided in the passing optical paths of the light beams D1 to D4 emitted from the light sources 40a to 40d, respectively. The incident side surfaces of the first to fourth divided lens portions 42a to 42d have a cylindrical surface shape, and the exit side surfaces have a flat surface shape. A first imaging lens 45a, a plurality of second imaging lenses 45b (see FIG. 2), and a plurality of folded mirrors 46a to 46h are arranged on the downstream side of the optical path of the polygon mirror 44. Each imaging lens 45a, 45b is composed of, for example, an fθ lens.

Next, the operation of the optical scanning device 15 will be described with reference to FIGS. 2 to 4. The light beams D1 to D4 emitted from the light sources 40a to 40d are made into substantially parallel luminous fluxes by the collimator lenses 41a to 41d, and then incident on the divided lens portions 42a to 42d of the condenser lens portion 42. The light beams D1 to D4 incident on the divided lens portions 42a to 42d are emitted in a parallel light beam state in the main scanning cross section (cross section perpendicular to the sub scanning direction), and are emitted along the sub scanning cross section (along the sub scanning direction). In the cross section), the light is converged and ejected, and is obliquely incident on the reflecting surface 44a of the polygon mirror 44 to form an image. The angles of incidence of the polygon mirrors 44 of the light beams D1 to D4 with respect to the reflecting surface 44a are different from each other when viewed in the sub-scanning cross section (see FIG. 3). By making the incident angles different in this way, the optical path separation of the four light beams D1 to D4 is facilitated. The width of each of the light beams D1 to D4 incident on the reflecting surface 44a of the polygon mirror 44 in the mirror rotation direction is narrower than the width of the reflecting surface 44a (see FIG. 4).

The light beams D1 to D4 incident on the reflecting surface 44a of the polygon mirror 44 are scanned at a constant angular velocity by the polygon mirror 44, and then converted into constant velocity scanning light by the first imaging lens 45a. The light beams D1 to D4 that have passed through the first imaging lens 45a are reflected by the folded mirrors 46a to 46g, respectively, and pass through the second imaging lens 45b and pass through the surface of the photoconductor drums 10a to 10d (the surface to be scanned). ) Guided to 10p-10s.

5 and 6 show how the light beams D1 to D4 emitted from the light sources 40a to 40d are incident on the reflection surface 44a of the polygon mirror 44 in the conventional light scanning apparatus. FIG. 5 shows how each of the light beams D1 to D4 is incident on the downstream end of the reflection surface 44a, and FIG. 6 shows the light beam D1 in which the polygon mirror 44 rotates clockwise from the state of FIG. Is incident on the upstream end of the reflecting surface 44a. As shown in each figure, of the light beams D1 to D4, the optical component L1 closer to the downstream side in the mirror rotation direction and the light component L2 closer to the upstream side in the rotation direction are the polygon mirror 44 from the principal point of the condenser lens unit 100. There is a difference in the distance to the reflecting surface 44a (hereinafter referred to as an optical path length difference δ). Here, as shown in FIG. 3, each of the light beams D1 to D4 is inclined with respect to the normal direction of the reflection surface 44a when viewed in the sub-scanning cross section, so that such an optical path length difference δ exists. Then, the incident regions R of the light beams D1 to D4 incident on the reflecting surface 44a are tilted in the sub-scanning direction in the mirror rotation direction (see FIGS. 7A and 7B).

FIG. 7A schematically shows an incident region R with respect to the reflecting surface 44a of the black light beam D4 emitted from the light source 40a in the conventional optical scanning device, and FIG. 7B shows the yellow light emitted from the light source. The incident region R corresponding to the reflection surface 44a of the beam D1 is schematically shown. 7A and 7B are views of the reflecting surface 44a viewed from the rotation center side of the polygon mirror 44 (in the direction of the white arrow in FIG. 4). Here, the incident region R of the black light beam D4 _{has a region r BD} for synchronization detection, whereas the incident region R of the yellow light beam D1 has _{a region r BD for synchronization detection.} Not. This is because the yellow light beam D1 is emitted from the light source 40a after the black light beam D4 has passed through the synchronization detection sensor 47. Except for this point, the incident regions R of the two light beams D1 and D4 have the same vertically symmetrical shape.
Here, only the incident region R of the black light beam D4 will be described with reference to FIG. 7A.

In Figure 7A, shows separately incident region R simply to four regions r1, r2, r3 and _{r BD.} Incident region r _BD corresponds to the case where the light beam D4 enters the downstream end of the mirror rotation direction of the reflecting surface 44a, the incident region r3, the light beam D4 is upstream end of the mirror rotation direction of the reflecting surface 44a The incident regions r1 and r2 correspond to the case where the light beam D4 is incident on the intermediate portion of the reflection surface 44a in the mirror rotation direction. The incident region r _BD is a region where the light beam D4 is reflected toward the synchronization detection sensor 47. The incident regions r1 to r3 are regions in which the light beam D4 is reflected toward the surfaces of the photoconductor drums 10a to 10d to form an electrostatic latent image. The optical path length difference [delta] (see FIGS. 5 and 6), since increases in the order of incidence region _{r BD,} r1, r2, r3, incident region _{r BD,} r1, r2, r3 inclination angle alpha _BD of, [alpha] 1, When α2 and α3 are set, the relationship of _{α3>α2>α1> α BD is satisfied.} The maximum amount of inclination in the sub-scanning direction with respect to the mirror rotation direction in the incident region R is represented by W in the figure. When the maximum inclination amount W is large, the reflected light path of the light beam D4 reflected by the reflecting surface 44a of the polygon mirror 44 is easily vibrated due to the influence of the surface accuracy of the reflecting surface 44a. As a result, there is a problem that image defects such as jitter are likely to occur. Further, as shown in FIG. 7A, the incident area r _BD for synchronous detection is inclined in the sub-scanning direction relative to the mirror rotation direction, it is reflected toward the synchronization detection sensor 47 at the entrance region r _BD The optical path of the light beam D4 is easily vibrated due to the influence of the surface accuracy of the reflecting surface 44a. As a result, there is a problem that the synchronization detection accuracy is lowered.

On the other hand, in the present embodiment, as shown in FIGS. 8 and 9, the condenser lens portion 42 is divided into four split lens portions 42a to 42d through which the four light beams D1 to D4 pass. The straight lines Sa, Sb, Sc and Sd (hereinafter referred to as constant curvature straight lines) connecting the positions where the radius of curvature of each of the divided lens portions 42a to 42d are constant have a predetermined inclination with respect to the center line So of the condenser lens portion 42. It was made to have angles θa to θd. The center line So is a straight line extending along the center position in the sub-scanning direction of the cylinder lens portion 42 and extending in a direction orthogonal to the rotation axis of the polygon mirror 44. In FIG. 8, each of the divided lens portions 42a to 4
Although a step is shown between 2d, this step is actually a minute step that cannot be visually confirmed.

According to the above configuration, the amount of inclination of the light beams D1 to D4 on the reflecting surface 44a of the polygon mirror 44 in the sub-scanning direction with respect to the mirror rotation direction can be adjusted. That is, in the conventional condensing lens unit 100, as shown in FIGS. 10 and 11, the constant curvature straight lines Sa to Sd in the region through which the light beams D1 to D4 pass are parallel to each other. Therefore, as schematically shown in the lower part of FIG. 12, the light beams D1 to D4 (only the light beam D1 is shown in the figure) are tilted on the reflecting surface 44a of the polygon mirror 44. On the other hand, in the present embodiment, the constant curvature straight lines Sa to Sd of the divided lens portions 42a to 42d have inclination angles θa to θd with respect to the center line So, which is shown in the lower part of FIG. As shown above, the amount of inclination of the light beams D1 to D4 (only the light beam D1 is shown in the figure) on the reflecting surface 44a of the polygon mirror 44 can be reduced.

Next, a method of setting the inclination angles θa to θd of the constant curvature straight lines Sa to Sd will be specifically described. Tilt angle θd of the curvature constant linear Sd split lens portion 42d of the light beam D4 passes of black, as incident region r _BD for the synchronous detection, as shown in FIG. 14A is parallel to the mirror rotation direction (i.e. α It is set (so that _{BD = 0).}

As a result, it is possible to suppress the optical path of the light beam D1 reflected in _{the incident region r BD from vibrating due to the influence of the surface accuracy of the reflecting surface 44a.} As a result, the synchronization detection accuracy of the synchronization detection sensor 47 can be improved.

On the other hand, as shown in FIG. 14B, the inclination angles θa to θc of the constant curvature straight lines Sa to Sc of the split lens portions 42a to 42c through which the light beams D1 to D3 of three colors other than black pass are the reflection surfaces of the polygon mirror 44. The incident region r3 at the upstream end of 44a is set to be parallel to the mirror rotation direction (that is, α3 = 0). As a result, the maximum inclination amount W of the incident regions R of the light beams D1 to D3 on the reflecting surface 44a of the polygon mirror 44 is reduced as compared with the conventional example (compared to the case where the constant curvature straight lines Sa to Sc are parallel to each other). Has been done.

Therefore, it is possible to suppress the reflected optical paths of the light beams D1 to D3 from vibrating due to the influence of the surface accuracy of the reflecting surface 44a. As a result, it is possible to suppress the occurrence of image defects such as jitter in the printed image.

According to method of setting the inclination angle θa~θd of the above-described curvature constant linear Sa to Sd, with respect to the black light beam D4, it is preferentially to reduce the amount of tilting of the incident region r _BD for synchronization detection. Therefore, the amount of inclination of the incident region r3 on the side opposite to the incident region r _BD side increases, and there is a possibility that jitter due to dot deviation in the main scanning direction may occur in the printed image.

In order to improve this point, for the color corresponding to the light beam D4 detected by the synchronization detection sensor 47 (black in this embodiment), the screen angle at the time of image printing is shown in the other three colors as shown in FIG. It is set smaller than the screen angle of. By reducing the screen angle in this way, the dot lines forming the image can be made as close to the main scanning direction as possible. Therefore, it is possible dot misalignment in the main scanning direction is also less noticeable occurred, to prevent an adverse effect due to the parallel incident region r _BD for detecting synchronization described above the mirror rotating direction.

Here, in the above embodiment, an underfield optical system is adopted in which the width of each of the light beams D1 to D4 incident on the reflection surface 44a of the polygon mirror 44 in the mirror rotation direction is smaller than the width of the reflection surface 44a. When the underfield optical system is adopted, the output efficiency is improved because all the light beams D1 to D4 emitted from the light source unit 40 are used for latent image formation as compared with the case where the overfield optical system is adopted. Since the incident region of the light beams D1 to D4 on the reflecting surface 44a is narrow, the influence of the surface accuracy of the reflecting surface 44a (curvature or inclination of the reflecting surface) on the occurrence of image defects such as jitter becomes large. In the present invention, even when the underfield optical system in which jitter is likely to occur is adopted, the constant curvature straight lines Sa to Sd of the divided lens portions 42a to 42d are the center lines in the sub-scanning direction of the condenser lens portion 42. Since the lenses have predetermined tilt angles θa to θd with respect to So, it is possible to reliably suppress the occurrence of image defects such as jitter.

<< Other Embodiments >>
In the above embodiment, when setting the inclination angles θa to θc of the constant curvature straight lines Sa to Sc of the split lens portions 42a to 42c through which the light beams D1 to D3 of three colors other than black pass, the reflecting surface of the polygon mirror 44. The incident region r3 at the upstream end of 44a is made parallel to the mirror rotation direction. However, in this case, it is conceivable that the inclination angles α1 and α2 of the incident region r1 and the incident region r2 increase conversely. Therefore, as shown in FIG. 16, when the amount of inclination in the sub-scanning direction with respect to the mirror rotation direction of each incident region r1 to r3 is w1 to w3, the inclination angle θa to minimize the total value σ of w1 + w2 + w3. θc may be set. FIG. 17 shows the incident regions R of the light beams D1 to D3 when the inclination angles θa to θc are set by this method. In this example, as a result, it can be seen that the region r2 is parallel to the mirror rotation direction.

Further, in the above embodiment, an underfield optical system in which the width of each light beam D1 to D4 incident on the reflecting surface 44a of the polygon mirror 44 in the mirror rotation direction is narrower than the width of the reflecting surface 44a is adopted. The width of each of the light beams D1 to D4 incident on the reflection surface 44a of the polygon mirror 44 in the mirror rotation direction may be wider than the width of the reflection surface 44a by adopting an overfield optical system. Here, when the overfield optical system is adopted, the entire width direction of the reflecting surface 44a is used as the incident region of the light beams D1 to D4, so that an image of jitter or the like is compared with the case where the underfield optical system is adopted. It is possible to reduce the influence of the surface accuracy (curvature or inclination of the reflecting surface) of the reflecting surface 44a on the occurrence of defects. Therefore, it is possible to more reliably suppress the occurrence of image defects such as jitter.

In the above embodiment, the condenser lens portion 42 is composed of one cylinder lens by the split lens portions 42a to 42d, but the present invention is not limited to this. That is, the condenser lens unit 42 may be composed of one cylinder lens (four in the above embodiment) for each light source.

As described above, the present invention is useful for an optical scanning apparatus and a color image forming apparatus including the optical scanning apparatus.

σ Total value D1 Optical beam D2 Optical beam D3 Optical beam D4 Optical beam R Incident region Sa Constant curvature straight line Sb Constant curvature straight line Sc Constant constant curvature straight line Sd Constant curvature straight line So Center line r _BD Beam incident region for synchronous detection W Incident region Maximum tilt amount in the sub-scanning direction with respect to the mirror rotation direction w1 Tilt amount in the sub-scanning direction with respect to the mirror rotation direction for each region w2 Tilt amount in the sub-scanning direction with respect to the mirror rotation direction for each region w3 With respect to the mirror rotation direction for each region Amount of tilt in the sub-scanning direction θa Tilt angle θb Tilt angle θc Tilt angle θd Tilt angle 1 Image forming device 15 Optical scanning device 40 Light source unit 42 Condensing lens unit 42a First split lens unit (second lens unit)
42b Second split lens section (second lens section)
42c Third split lens section (second lens section)
42d 4th division lens part (1st lens part)
44 Polygon mirror 44a Reflective surface 47 Synchronous detection sensor

Claims (3)

A polygon mirror, a light source unit that emits a plurality of light beams at intervals in the sub-scanning direction, and a plurality of light beams provided between the polygon mirror and the light source unit and emitted from the light source unit, respectively. , A condensing lens unit that obliquely incidents light on the same reflecting surface of the polygon mirror at different incident angles and collects light, and a synchronous detection sensor that detects at least one of a plurality of light beams outside the effective scanning region. In an optical scanning device equipped with
The condenser lens unit is composed of a plurality of lens units through which each of the plurality of light beams passes.
The first lens unit into which an optical beam is detected by the synchronization detection sensor among the plurality of lens portions passes the radius of curvature of the lens surface curvature constant straight line connecting the position to be same in the first lens unit, It is configured to have a predetermined tilt angle with respect to the center line extending in the direction orthogonal to the rotation axis of the polygon mirror at the center position in the sub-scanning direction of the condenser lens portion when viewed from the optical axis direction.
The inclination angle of the curvature constant linear of the first lens unit, the region where the light beam detected by the synchronization detection of the reflective surface of the polygon mirror is incident is set to be parallel to the mirror rotation direction ,
Of the plurality of lens portions, the second lens portion through which the light beam not detected by the synchronization detection sensor passes is connected to a position where the radius of curvature of the lens surface in the second lens portion is the same when viewed from the optical axis direction. However, a straight line having a constant curvature is configured to have a predetermined tilt angle with respect to the center line of the condenser lens portion.
The inclination angle of the constant curvature straight line of the second lens portion is a mirror of the incident region of the light beam on the reflecting surface as compared with the case where the constant curvature straight line is parallel to the center line of the condensing lens portion. The maximum tilt amount in the sub-scanning direction with respect to the rotation direction is set to be small,
The tilt angle of the straight line having a constant curvature of the second lens portion further divides the incident region of the light beam on the reflecting surface of the polygon mirror into a plurality of regions in the mirror rotation direction, and each region has a mirror rotation direction. An optical scanning device in which the amount of inclination in the sub-scanning direction with respect to the light is calculated, and the total value of the calculated amounts of inclination is set to be the minimum. In the optical scanning apparatus according to claim 1,
An optical scanning apparatus that employs an underfield optical system in which the width of each light beam incident on the reflecting surface of the polygon mirror in the mirror rotation direction is narrower than the width of the reflecting surface in the mirror rotation direction. A color image forming apparatus including the optical scanning apparatus according to claim 1 or 2.
The above multiple light beams correspond to each color,
The screen angle of the todd line that constitutes the printed image by this color image forming apparatus is different for each of the above colors.
A color image forming apparatus in which the screen angle of the color corresponding to the light beam detected by the synchronization detection sensor is smaller than the screen angle of other colors.

Images