JP4744117B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning apparatus that can be used in an image forming apparatus such as a digital copying machine, a laser printer, and a laser facsimile, and an image forming apparatus as described above using the optical scanning apparatus.

  First, a conventional optical scanning device and image forming apparatus will be described. An optical scanning device widely used in image forming apparatuses such as copying machines and laser printers generally deflects a light beam from a light source by an optical deflector, and scans a surface by a scanning imaging optical system such as an fθ lens. A light spot is formed on the surface to be scanned by focusing toward the surface, and the surface to be scanned is optically scanned (main scan) with this light spot. What constitutes the surface to be scanned is a photosensitive surface on the surface of the image carrier made of a photoconductive photosensitive member or the like.

  Also, as an example of a full-color image forming apparatus, four photoconductors are arranged in the conveyance direction of the recording paper, and each photoconductor is optically scanned by a plurality of optical scanning devices corresponding to each of these photoconductors. Are formed, and images of the respective colors are transferred onto the same transfer paper in an overlapping manner. More specifically, the light beam emitted from the light source device of each optical scanning device is deflected and scanned by one deflecting unit, and each photosensitive member is scanned by a plurality of scanning imaging optical systems corresponding to each photosensitive member. At the same time, a latent image corresponding to the image information of each color is created, and these latent images are visualized by developing devices using different color developers such as yellow, magenta, cyan, and black. These visible images are sequentially superimposed and transferred and fixed on the same recording paper so that a color image can be obtained.

As described above, an image forming apparatus that obtains a two-color image, a multicolor image, a color image, or the like by using two or more combinations of optical scanning devices and photoreceptors is known as a “tandem image forming apparatus”. Yes. As such a tandem type image forming apparatus, a system in which a plurality of photosensitive media (image carriers) share a single optical deflector is known. This method is further classified as follows.
(1) A counter scanning method in which a light beam is incident from both radial sides of the optical deflector and the light beam is distributed and scanned to both radial sides of the optical deflector (see, for example, Patent Document 1 and Patent Document 2).
(2) A system in which a plurality of light beams that are substantially parallel and separated in the sub-scanning direction are incident on a deflector, and a plurality of scanning optical elements corresponding to the plurality of light beams are aligned and scanned in the sub-scanning direction (for example, see Patent Document 3) ).
(3) A light beam is incident from one side of the deflector, the scanning optical system is constituted by three lenses, and the first and second lenses L1 and L2 are lenses through which a plurality of light beams traveling toward different scanning surfaces pass. The third lens L3 is provided for each surface to be scanned (see, for example, Patent Document 4, Patent Document 5, and Patent Document 6).

  As described above, when the optical deflectors are shared by a plurality of scanned surfaces, the number of the optical deflectors is reduced, so that the image forming apparatus can be made compact and the cost can be reduced.

  Next, an oblique incidence optical system employed in a recent optical scanning device of a color image forming apparatus will be described. In an optical scanning device of a color image forming apparatus using a single optical deflector, as a means for reducing the cost, an oblique light beam is incident on the deflection reflection surface of the optical deflector at an angle in the sub-scanning direction. An incident optical system is known (see, for example, Patent Document 7). In this oblique incidence optical system, after a plurality of light beams are deflected and reflected by the deflecting and reflecting surfaces, they are separated by a folding mirror or the like and guided to the surface to be scanned (photosensitive member surface) corresponding to each light beam. At this time, the angle of each light beam in the sub-scanning direction (the angle at which the light beam obliquely enters the change reflecting surface of the optical deflector) is set to an angle at which each light beam can be separated by the mirror. By using the oblique incidence optical system configured as described above, the adjacent light beam interval in the sub-scanning direction in which each light beam can be separated by the mirror can be reduced without increasing the size of a light polarizer such as a polygon mirror (sub-mirror). (Without increasing the number of stages or the thickness of the optical deflector in the scanning direction).

  Considering the case where a polygon mirror is used as an optical deflector, it is difficult to make the light beam from the light source side incident on the rotation axis of the polygon mirror in the normal incidence method, and the polygon mirror can be downsized. Can not. It is not impossible to make the light beam incident on the rotation axis of the polygon mirror. However, if the light beam is incident on the rotation axis, the individual deflection reflection surfaces will be in the sub-scanning direction in order to secure the necessary deflection angle. Become extremely large. Also, the occurrence of so-called “sag” is large, and the generated sag is asymmetric with respect to the image height: 0. If the polygon mirror is large, a large amount of energy is required for its high-speed rotation, the “wind noise” when rotating at high speed is large, and the soundproofing means must be enlarged.

  On the other hand, according to the oblique incidence method described above, the light beam from the light source side can be incident on the rotation axis of the polygon mirror, the diameter of the polygon mirror can be reduced, and the polygon mirror can be rotated at high speed. The “wind noise” is small, so it is suitable for high speed. Since the polygon mirror can be reduced in diameter, the occurrence of sag is small, and the generated sag can be symmetric with respect to the image height: 0, so that correction is easy.

  However, the oblique incidence method has a problem that the “scan line bending” is large. The amount of bending of the scanning line varies depending on the oblique incident angle of each light beam in the sub-scanning direction, and color misregistration occurs when the latent images drawn by the respective light beams are superimposed and visualized with the respective color toners. Appears. In addition, the oblique incident light causes the light beam to be twisted and incident on the scanning lens, thereby increasing the wavefront aberration. Particularly, the optical performance is significantly deteriorated at the peripheral image height, the beam spot diameter is increased, and the image quality is improved. It becomes a factor to prevent. In addition, in the oblique incidence method, when the light source is arranged at a position overlapping with the optical axis of the scanning lens in the main scanning direction so that the light beam from the light source side is incident on the rotation axis of the polygon mirror, it interferes with the scanning lens. In order to avoid this, the oblique incidence angle increases, which causes the above problems to increase.

  As a method of correcting the “large scanning line bending” inherent to the oblique incidence method, the scanning imaging optical system “changes the inherent inclination of the lens surface in the sub-scan section in the main scanning direction so as to correct the scanning line bending. Including a “lens having a curved lens surface” (see, for example, Patent Document 8) or “scanning imaging optical system“ main scanning so as to correct the inherent inclination of the reflecting surface in the sub-scanning section and to correct the scanning line curvature ”. A method of including a “corrected reflecting surface having a reflecting surface changed in a direction” (see, for example, Patent Document 9) has been proposed.

  In addition, a method has been proposed in which the obliquely incident light flux passes through the off-axis of the scanning lens, and the position of the scanning line is aligned using a surface that changes the aspherical amount of the child line of the scanning lens along the main scanning direction. (For example, refer to Patent Document 10). In the invention described in Patent Document 10, an example is given in which correction is performed with one scanning lens, and the scanning line bending can be corrected. However, the beam spot diameter deteriorates due to an increase in wavefront aberration described below. Is not described.

  Another problem with the oblique incidence method is that a large wavefront aberration is likely to occur at the peripheral image height (near both ends of the scanning line) due to the light beam skew. When such wavefront aberration occurs, the diameter of the light spot increases at the peripheral image height. If this problem cannot be solved, “high-density optical scanning” that has been strongly demanded in recent years cannot be realized. In the optical scanning device described in Patent Document 10, a large scanning line curve peculiar to the oblique incidence method is corrected extremely well, but the correction of the wavefront aberration is not sufficient.

  As an optical scanning device that can satisfactorily correct the above-mentioned “scan line bending and wavefront aberration degradation” which can be said to be a problem with the oblique incidence method, the scanning imaging optical system includes a plurality of rotationally asymmetric lenses, and the lens surfaces of these rotationally asymmetric lenses. There has been proposed one in which the shape of the bus connecting the child line vertices is curved in the sub-scanning direction (see, for example, Patent Document 11). However, the lens having the “lens surface curved in the sub-scanning direction of the generatrix connecting the vertices of the child lines” solves various problems by curving the generatrix, and an individual scanning lens corresponding to the incident light beam. Therefore, when applied to a tandem scanning optical system, the number of scanning lenses increases. When a plurality of light beams directed to different scanning surfaces are incident on the same lens, the problem is solved for one light beam by curving the shape of the bus, but the scanning line is bent for the other light beam. It is difficult to reduce the wavefront aberration.

  Means for correcting such deterioration in optical performance has been proposed, but as the angle of oblique incidence on the deflecting / reflecting surface increases, the deterioration in optical performance increases, making correction difficult. That is, it becomes a problem to obtain the effect by using the oblique incidence optical system while keeping the oblique incidence angle small.

  Two light beams that are parallel to and parallel to the normal line of the deflecting reflection surface of the optical deflector and have an angle so as to be separated outward in the sub-scanning direction with respect to the normal line of the deflecting reflecting surface of the optical deflector An invention in which two light beams are combined has been made (see, for example, Patent Document 12). According to the configuration described in Patent Document 12, the angle in the sub-scanning direction is set as compared with the case where all the light beams are configured with light beams having an angle in the sub-scanning direction with respect to the normal line of the deflecting reflection surface of the optical deflector. It can be set small. However, in this method, the distance between the optical deflectors in the sub-scanning direction is increased and the size is increased, and the cost of the optical deflector that is a component constituting the optical scanning device and has a high cost ratio cannot be reduced. is there.

JP-A-11-157128 JP-A-9-127443 JP-A-9-54263 JP 2001-4948 A Japanese Patent Laid-Open No. 2001-10107 JP 2001-33720 A JP 2003-5114 A Japanese Patent Laid-Open No. 11-14932 Japanese Patent Laid-Open No. 11-38348 JP 2004-70109 A Japanese Patent Laid-Open No. 10-73778 JP 2004-86186 A

The present invention has a plurality of light source devices, and light beams from the respective light source devices are deflected by a common optical deflector and then condensed on the corresponding scanned surfaces by the scanning optical system and emitted from the plurality of light source devices. The light beam directed to one scanned surface is horizontal with respect to the normal of the reflecting surface of the optical deflector, and the light beam directed to the other scanned surface has an angle with respect to the normal of the reflecting surface of the optical deflector. An object of the present invention is to provide an optical scanning device that suppresses scanning line bending and wavefront aberration deterioration in an oblique incidence type optical scanning device, is suitable for low cost, low power consumption, downsizing, and is environmentally friendly.
For the purpose.
The present invention also provides an image forming apparatus that suppresses scanning line bending and wavefront aberration deterioration by using the optical scanning device described above, is suitable for low cost, low power consumption, downsizing, and is environmentally friendly. Objective.

The present invention has a plurality of light source devices, and the first light beam , the second light beam, the third light beam, and the fourth light beam emitted from the plurality of light source devices are common optical deflectors. after being deflected by, the optical scanning device is focused on the scanned surface that correspond respectively by the scanning optical system, a first light beam deflected by the reflection surface of the polarization direction unit, a second light beam The third light beam and the fourth light beam are separated in the sub-scanning direction before the first light beam, the second light beam, the third light beam, and the fourth light beam, respectively. the are arranged in the order, position where the second light beam is separated from the first light beam, the position where the third light beam is separated from the second light beam, directed to the corresponding surface to be scanned The position close to the surface to be scanned and where the third light beam is separated from the second light beam is 4 is closer to the scanned surface and closer to the scanned surface than the position where the fourth light beam is separated from the third light beam, and the angle between the first light beam and the second light beam is The angle formed between the second light beam and the third light beam in the sub-scanning direction is smaller than the angle formed between the second light beam and the third light beam. The main feature is that the angle is smaller than the angle formed by the beam and the fourth light beam.
The present invention is also characterized in that an image forming apparatus is configured by using an optical scanning apparatus having such characteristics as means for executing an exposure process of an electrophotographic process.

  In an optical scanning device that has a plurality of light source devices and the light beam from each light source device is deflected by a common optical deflector and then condensed on the corresponding scanned surface by the scanning optical system, a plurality of light source devices The light beam toward one of the scanning surfaces is horizontal with respect to the normal line of the reflecting surface of the optical deflector, and the light beam toward the other scanning surface has an angle with respect to the normal line of the reflecting surface of the optical deflector. Therefore, it is possible to suppress deterioration of scanning line bending and wavefront aberration in an oblique incidence type optical scanning device, and to be suitable for low cost, low power consumption, downsizing, and environment-friendly optical scanning device and this optical scanning device. The image forming apparatus can be realized.

  Embodiments of an optical scanning apparatus and an image forming apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram for explaining a first embodiment of an optical scanning device. In FIG. 1A, a divergent light beam emitted from a semiconductor laser 20 as a light source is converted into a light beam form suitable for the subsequent optical system by a coupling lens 21 constituting the first optical system. The form of the light beam converted by the coupling lens 21 may be a parallel light beam, or may be a light beam with weak divergent or weak convergence. The light beam that has passed through the coupling lens 21, which is a substantially parallel light beam, is collected only in the sub-scanning direction by the cylindrical lens 22 constituting the second optical system, and is deflected by an optical deflector composed of a polygon mirror (rotating polygon mirror) 23. A line image that is incident on the reflecting surface and is long in the main scanning direction is formed near the deflecting reflecting surface. The light beam from the light source side is incident on the plane A perpendicular to the rotation axis of the deflection reflection surface of the polygon mirror 23. Therefore, as can be seen from FIG. 1B, the light beam reflected by the deflecting reflecting surface is also inclined with respect to the plane A. In order to make an angle of the light beam with respect to a plane orthogonal to the rotation axis of the polygon mirror 23, the light source device and the coupling optical system (first optical system) may be arranged to be inclined at a desired angle. As shown to (a), you may give an angle using the mirror 26 arrange | positioned between the 2nd optical system and the polygon mirror 23. FIG. Further, the optical axis of the coupling lens 21 constituting the first optical system may be shifted in the sub-scanning direction so that the angle of the light beam directed toward the deflecting / reflecting surface of the polygon mirror 23 is increased.

  Four light beams are emitted from the light source 20, and each light beam reflected by the deflection reflection surface of the polygon mirror 23 is deflected at a constant angular velocity as the polygon mirror 23 rotates at a constant speed. As shown in FIG. 1B, the deflected light beams are reflected by mirrors 17Y, 17M, 17C, and 17K, and then passed through the first scanning lens L1 and the second scanning lens L2 constituting the scanning optical system. It is designed to be transparent. In FIG. 1B, the other three light beams excluding the uppermost light beam are reflected by mirrors 18Y, 18M, and 18C, and the four light beams are drum-shaped photoreceptors 3Y, 3M, It is configured to reach the surface of 3C and 3K. The surface of each of the photoreceptors 3Y, 3M, 3C, and 3K corresponds to the scanned surface indicated by reference numeral 25 in FIG. A scanning imaging optical system including the scanning lenses L1 and L2 condenses the deflected light beam toward the surface to be scanned 25. Thereby, the deflected light beam forms a light spot on the scanned surface 25 and scans the scanned surface 25. Further, the scanning imaging optical system has an fθ function for scanning a scanning beam with a constant angular velocity deflected light beam at a constant speed.

  For example, the surface shape in the main scanning direction of the first scanning lens L1 closest to the deflecting means is a non-arc shape, or the surface shape of the other scanning lens is a non-arc shape in the main scanning direction, and within the sub-scanning cross section. The curvature radius in the sub-scan section is changed in the main scan direction so that the center line of curvature connecting the center of curvature in the main scan direction is a different curve from the non-arc shape in the main scan direction in the main scan section. By using the adjusted surfaces, it is possible to satisfactorily correct field curvature in both the main scanning direction and the sub-scanning direction. FIG. 1B shows the mutual positional relationship from the deflecting / reflecting surface of the polygon mirror 23 through the scanning lenses L1 and L2 to the surface to be scanned 25 from the sub-scanning corresponding direction.

  In the example shown in FIG. 1, among the lenses L1 and L2 constituting the scanning optical system, the scanning lens L1 closest to the polygon mirror 23 as the deflecting unit is a lens common to a plurality of light beams directed to different scanning surfaces. Thus, a plurality of light beams pass through. As a result, the number of lenses constituting the scanning imaging optical system can be reduced, and a low-cost optical scanning device can be provided.

  Further, when the polygon mirror 23 as the deflecting means is rotationally driven at a high speed, the polygon motor generates heat, and a difference occurs in the temperature of the scanning lens in the main scanning direction. That is, a temperature distribution occurs and is affected by the quality of an image formed by optical scanning. However, as described above, since one scanning lens L1 is commonly used for a plurality of light beams, the light beam toward the surface to be scanned 25 is uniformly affected by the temperature distribution. And image degradation due to color can be suppressed.

  The polygon mirror 23 as the deflecting unit generates a large amount of heat by the motor unit that drives the polygon mirror 23 to rotate at high speed and its circuit board. Regarding the circuit board, it is possible to reduce the temperature fluctuation in the optical box by taking it out of the optical box, etc., but it is difficult to release the heat of the polygon motor part to the outside. The temperature rise in the optical box cannot be avoided. The heat generated in the motor unit or the like propagates through the optical box, thereby generating a temperature distribution in the lens constituting the scanning optical system, particularly the scanning lens L1 closest to the polygon mirror 23. This temperature distribution occurs because a uniform temperature change does not occur in the scanning lens due to the flow path of the air flow in the optical box generated by the high-speed rotation of the polygon mirror 23, the shape of the scanning lens, and the like. As a result, in a counter-scanning tandem color image forming apparatus in which beams directed to each scanning surface 25 pass through different scanning optical elements, the relative main scanning direction on each scanning surface 25 during continuous printing. The position of the beam spot fluctuates and the color changes.

  Therefore, among the scanning lenses constituting the scanning imaging optical system, all the light beams traveling toward different scanning surfaces may be configured to pass through the scanning lens so as to share the scanning lens closest to the deflecting unit. desirable. With this configuration, even when the scanning lens has a temperature distribution in the main scanning direction, the temperature distribution of the scanning lens through which the light beams directed to different scanning surfaces are transmitted is substantially the same, and is generated by the temperature distribution. The change in refractive power (change in surface shape) in the main scanning direction can be made almost uniform. As a result, the beam spot position deviations in the main scanning direction on the different scanning surfaces are substantially the same, and the color change and the occurrence of color deviation during continuous printing can be suppressed.

  The generation of this temperature distribution is improved by sealing the polygon mirror 23 and allowing the light flux to enter and exit the polygon mirror 23 through the parallel plate glass. However, it is difficult to perfectly match the temperature and the temperature distribution. According to the one-side scanning method in which only one side of the polygon mirror 23 is scanned and all the light beams share the first scanning lens L1, color shift and color change can be reduced relatively well.

  In a conventional optical scanning apparatus that obliquely enters in the sub-scanning direction with respect to horizontal incidence, scanning line bending occurs due to incidence at an angle in the sub-scanning direction on a scanning lens shared by all light beams. It is known that optical performance deteriorates due to deterioration of wavefront aberration. By reducing the angle of the polygon mirror constituting the optical deflector with respect to the normal line of the deflecting reflection surface, more precisely, the angle of oblique incidence in the sub-scanning direction, it is possible to suppress deterioration in optical performance, which is favorable. Optical performance can be realized. As a result, a stable beam spot diameter can be obtained, which is advantageous for improving the image quality by reducing the beam spot diameter.

  Usually, in a one-side scanning type optical scanning device that deflects and reflects a light beam only on one side of the optical deflector, the light beam deflected in a lump by the optical deflector when the plurality of light beams travel toward the corresponding scanned surface. The groups are sequentially separated in the sub-scanning direction by the folding mirror and reach the corresponding scanned surface. At this time, as shown in FIG. 1B, the light beams traveling toward the four drum-shaped photoconductors 3Y, 3M, 3C, and 3K are sequentially moved from the side closer to the optical deflector 23 toward the scanned surface side. Reflected by the arranged mirrors 17Y, 17M, and 17C and separated from other light beams. The light beam folded back at the position farthest from the optical deflector 23 is also bent in the optical path by the mirror 17K and guided to the surface of the photosensitive drum as the corresponding scanned surface, but this light beam is before reaching the mirror 17K. Since it is separated from other light beams, the mirror 17K cannot be said to be a mirror for separating from other light beams.

  As shown in FIG. 2 and FIG. 3, if the distance between adjacent light beams in the sub-scanning direction necessary for the separation of the light beams is Δd, the light beams separated at the respective separation positions and the light beams A certain interval in the sub-scanning direction is required between adjacent light beams that pass by the separating mirror. Let this required interval be Δd. Assuming that the distance Δd is constant, the longer the distance from the optical deflector 23 to the beam separation position, the smaller the angle in the sub-scanning direction can be set.

  The angle formed by the sub-scanning direction of the light beam that is separated toward the corresponding scanned surface and close to the scanned surface is separated on the side close to the optical deflector toward the corresponding scanned surface. The absolute value of the light beam can be set smaller than the angle between the adjacent light beam and the adjacent light beam, and the amount of wavefront aberration degradation and scanning line bending can be reduced. . Needless to say, this is an advantageous condition for correction of wavefront aberration and scanning line bending.

  As shown in FIG. 2A, at least one of the light beams from the plurality of light source devices reflected by the deflecting / reflecting surface of the polygon mirror 23 serving as a deflecting unit is used as the normal line of the deflecting / reflecting surface of the polygon mirror 23. The other light beams may be light beams having an angle with respect to the normal line of the deflecting / reflecting surface of the polygon mirror 23. By doing so, it is possible to reduce the cost of the polygon mirror 23 which forms an optical deflector having a high cost ratio with the components constituting the optical scanning device. Further, since a plurality of light beams can be brought close to each other or crossed in the vicinity of the deflecting / reflecting surface of the polygon mirror 23, the thickness dimension of the polygon mirror 23 in the sub-scanning direction can be reduced, and the polygon mirror 23 can be moved at high speed. In addition, it is possible to reduce the electric power required for rotational driving, and to reduce the noise accompanying high-speed rotation, and it is possible to provide an optical scanning device that considers the environment.

  In the case of the one-side scanning method in which all the light beams are shared by the first scanning lens L1, as shown in FIG. 2B, all the light beams are horizontal with respect to the normal line of the deflecting reflecting surface of the polygon mirror 23, that is, An optical scanning device that is incident and reflected without an angle in the sub-scanning direction is known. In such an optical scanning device, although good optical performance can be obtained, the light beams from each light source device, that is, the intervals between a plurality of light beams guided to different scanning surfaces are separated for each light beam. It is necessary to have the required spacing, usually 3 mm to 5 mm. Therefore, the height (height in the sub-scanning direction) h of the polygon mirror 23 as the deflection means is increased, the contact area with the air is increased, power consumption is increased due to the influence of windage loss, noise is increased, and cost is increased. There was a problem such as. In particular, the cost ratio occupied by the deflecting means in the components of the optical scanning device is high, so that there are significant problems in terms of cost.

  In that respect, according to the embodiment of the optical scanning device according to the present invention described above, one of the light beams from the plurality of light source devices reflected by the deflecting reflecting surface of the polygon mirror 23 as the deflecting means is the polygon mirror. A light beam that is horizontal with respect to the normal line of the deflecting reflection surface of 23, and a light beam that has an angle with respect to the normal line of the deflecting reflection surface of the polygon mirror 23 (with an angle in the sub-scanning direction). 3 is configured to share the scanning lens, it is possible to significantly reduce the height h of the polygon mirror 23 as shown in FIG. Can do.

  The example shown in FIG. 3 is an example in which light beams directed to four different surfaces to be scanned are aligned in the sub-scanning direction and transmitted through the scanning lens. Actually, the light beam is refracted when passing through the lens, but in this figure, the refraction is not shown and is represented by a straight line. Although it is possible to configure the scanning lens with only one lens, the scanning lens is not limited to this, and the scanning lens that is shared by the light beams directed to different scanning surfaces and the scanning lens through which the individual light beams are individually transmitted. The structure provided with may be used. Moreover, the structure which shares all the scanning lenses with a some light beam may be sufficient.

  Of the four light beams shown in FIG. 3A, the third light beam from the top in the sub-scanning direction is horizontal to the normal line of the deflection reflection surface of the polygon mirror 23 serving as an optical deflector and extends in the sub-scanning direction. The light beams have no angle, and the other three light beams have an angle in the sub-scanning direction with respect to the normal line of the deflection reflection surface. As described above, the three light beams of the light beam 2, the light beam 3, and the light beam 4 are configured to be separated from adjacent light beams by bending the optical path by a mirror as a separation optical system. The light beam 4 has its optical path bent by a mirror arranged at a position A closest to the optical deflector (position closest to the optical deflector), and has an angle in the sub-scanning direction that is horizontal to the normal line of the deflecting reflection surface. No light beam 3 is separated in the sub-scanning direction. The light beam 3 is separated from the light beam 2 in the sub-scanning direction by the mirror at a position B farther from the polygon mirror 23 than the position A. The light beam 2 is separated from the light beam 1 in the sub-scanning direction by the mirror at a position C farther from the polygon mirror 23 than the position B. In this way, the light beams 4, 3, and 2 are separated from the position on the polygon mirror 23 side in the order of the light beams 4, 3, and 2 and close to the scanned surface. When the interval necessary for separating each light beam is Δd, the interval between adjacent light beams in the sub-scanning direction needs to be equal to or greater than Δd at each corresponding separation position (A, B, C).

  When each of the separation positions A, B, and C is the same distance from the optical deflector, the angle in the sub-scanning direction of the light beam obliquely incident on the optical deflector will be described. For example, as in the example shown in FIG. 2A, the four light beams have an angle (obliquely incident) with the horizontal light beam with respect to the normal line of the deflection reflection surface of the polygon mirror 23 that is an optical deflector. ) On the entrance surface of the scanning lens that consists of light beams and is shared by all the light beams, the two light beams on the peripheral side (outside) in the sub-scanning direction spread each other, and the two light beams in the middle part in the sub-scanning direction are parallel In addition, it is assumed that the polygon mirror 23 is parallel to the normal line of the deflection reflection surface. Compared with a configuration in which all the light beams are obliquely incident on the deflecting and reflecting surface as in the example shown in FIG. 2C, this configuration allows each light beam to be incident on the entrance surface of the scanning lens shared by all the light beams. It is possible to set a small angle in the sub-scanning direction of the obliquely incident light beam in order to ensure the interval Δd necessary for separation.

  However, in practice, the separation positions A, B, and C are rarely the same distance from the optical deflector as shown in FIG. 2, and the separation positions are different as shown in FIG. A, B, and C are in this order from the side closer to the optical deflector. When the separation positions are different in this order, in the example shown in FIG. 2A, the distance between the adjacent light beams in the sub-scanning direction at the separation position C farthest from the optical deflector is more than necessary. In other words, it spreads beyond the distance Δd, leading to an increase in the size of the optical scanning device.

  Therefore, of the four light beams, only the light beam 3 is arranged horizontally (parallel) with respect to the normal line of the deflecting reflection surface of the optical deflector, and the light beam 4 is in the sub-scanning direction so as to be Δd at the separation position A. Is defined as β1. The arrangement relationship between the light beam 3 and the light beam 4 is the same as the arrangement relationship between the light beam 3 and the light beam 4 in the example shown in FIG. The light beam 1 has an angle of β1 in the sub-scanning direction and is symmetrical with the light beam 4. On the other hand, the light beam 2 is given an angle in the sub-scanning direction so that the distance in the sub-scanning direction is Δd at the separation position C of the light beam 1 and the light beam 2, and the angle is β2. To do. In the example of FIG. 2A, the light beam 2 has no angle in the sub-scanning direction, but has an angle of β2 in the example shown in FIG. The separation position B between the light beams 2 and 3 has a sub-scanning interval of Δd or more. Therefore, in the example shown in FIG. 3A, the light beam 1 and the light beam 2 are separated from each other so that the distance in the sub-scanning direction between the light beam 2 and the light beam 3 at the separation position B is Δd. Shifted to the 3 side. By doing so, it is possible to set the light beam interval in the sub-scanning direction on the deflection reflection surface of the optical deflector to be small. That is, the light beam interval in the sub-scanning direction on the deflecting reflection surface of the optical deflector can be made smaller than the above-described interval Δd, and the miniaturization of the optical deflector can be achieved.

  In the example shown in FIG. 3A, the light beam 4 determines the maximum value of the angle β in the sub-scanning direction. By making the light beam 3 horizontal with respect to the normal line of the deflecting reflecting surface, the maximum value of the angle β can be determined by the light beam 4. In order to reduce the angle β1 of the light beam 4 in the sub-scanning direction, it is necessary to set the angle of the sub-scanning direction in a direction away from the light beam 4 instead of being horizontal to the normal line of the deflecting reflection surface. Then, the angle in the sub-scanning direction between the light beam 1 and the light beam 2 increases, and the maximum value of the angle β increases. Further, since the light beams at both ends in the sub-scanning direction, that is, the angles of the light beam 1 and the light beam 4 in the sub-scanning direction are made the same, the deterioration of the wavefront aberration and the generation amount of the scanning line bending can be made the same. It becomes possible to dispose the correction means on the mirror surface with respect to a plane parallel to the normal line of the deflecting reflection surface of the optical deflector at the center of the correction means or the light beam 1 and the light beam 4 in the sub-scanning direction. The development efficiency of the correction means is remarkably improved as compared with the case where the correction means are individually arranged according to the direction angle.

  As described above, one of the light beams from the plurality of light source devices is set to a horizontal light beam with respect to the normal line of the deflecting / reflecting surface of the polygon mirror 23, and the other light beam is set to the normal line of the deflecting / reflecting surface of the polygon mirror 23. By constructing a light beam having an angle (with an angle in the sub-scanning direction), the angle in the sub-scanning direction with respect to the normal of the deflecting reflecting surface of the optical deflector can be kept small, and the wavefront aberration is degraded. And the occurrence of scanning line bending can be reduced. In addition, as described above, since the interval between the light beams in the sub-scanning direction can be reduced on the deflecting reflection surface of the optical deflector, the components of the optical scanning device are high cost ratio optical deflectors. Since the cost can be reduced and the optical deflector can be thinned, power consumption and noise can be reduced, and an optical scanning device considering the environment can be provided.

  Further, the polyhedron forming the deflecting / reflecting surface of the polygon mirror 23 only needs to have a sufficient axial length (thickness in the sub-scanning direction) to deflect a predetermined laser beam. It is desirable that the light beams having the intervals are different reflecting surfaces. Therefore, as in the example shown in FIG. 1B, it is preferable to divide the polygon mirror 23 formed of a polyhedron that forms the deflecting reflection surface in the sub-scanning direction to have two stages. By doing so, the axial length (thickness in the sub-scanning direction) of the deflecting reflecting surface can be reduced, the inertia (inertial force) as the rotating body can be reduced, and the starting time can be shortened.

Further, among the plurality of light beams that are directed from the plurality of light source devices toward different scanned surfaces, the light beam adjacent in the sub-scanning direction separates the adjacent light beam from the base point of the deflection reflection surface of the optical deflector. X is the distance to the light beam reflection position of the system (that is, the position on the separation optical system of the light beam separated from the adjacent beam by the mirror constituting the separation optical system), and the distance of the light beam separated and deflected by the separation optical system The angle of the sub-scanning direction with respect to the normal of the reflecting surface of the optical deflector is β1, the angle of the sub-scanning direction of the light beam passing through the separating optical system with respect to the normal of the reflecting surface of the optical deflector is β2, and When the distance to the farthest end in the sub-scanning direction is Δh (see FIG. 3C),
1.5 <(tan | β2 | · X-tan | β1 | · X) / Δh <5
It is desirable to satisfy Here, Δh is the distance in the sub-scanning direction of the mirror 17 constituting the separation optical system, as shown in FIG. 3C, and the mirror 17 of the light beam reflected and separated by this mirror 17. The distance from the upper position (that is, the position where the light beam is reflected by the mirror 17 constituting the separation optical system) to the farthest end on the light beam side adjacent to the separated light beam and passing near the mirror 17 Say. The sub-scanning direction is a direction orthogonal to the scanning direction (main scanning direction) and is a direction orthogonal to the normal line of the deflection reflection surface of the optical deflector.

  When the lower limit of the conditional expression is exceeded, it becomes difficult to separate the light beams for guiding the adjacent light beams to the corresponding scanned surface. If the lower limit of the conditional expression is exceeded, there is a high possibility that the separation optical system will not only separate the separated light beam but also scatter the light beam that passes through without being separated. Each light beam is blurred in the sub-scanning direction due to assembly of optical elements, processing errors, and the like. At this time, if there is no allowance between the optical system and the separation optical system, high-precision assembly adjustment and processing accuracy are required, which greatly increases the cost. It is unlikely that there will be no blur in the scanning direction.

  If the upper limit of the above conditional expression is exceeded, the angle in the sub-scanning direction with respect to the normal line of the deflecting reflecting surface of the optical deflector becomes too large, causing deterioration of wavefront aberration and occurrence of bending of the scanning line, making correction difficult. . The correction method of wavefront aberration and scanning line bending is arbitrary and is not limited to a specific method, but it goes without saying that correction becomes more difficult as the amount of wavefront aberration deterioration and the amount of scanning line bending increase. Yes.

As described above, within the range of the conditional expression, the angle in the sub-scanning direction with respect to the normal line of the deflecting reflecting surface of the optical deflector, the separation position, and the size of the separation optical system can be varied or varied in the sub-scanning direction of each light beam. It is possible to optimize it in consideration of
Note that the mirror 17 shown in FIG. 3C is one of the three mirrors 17Y, 17M, and 17C as the separation optical system shown in FIG. In FIG. 1C, the mirror 17K is not a mirror for separating the light beam from other light beams, but is merely a mirror for guiding the light beam to the photosensitive member 3K. Therefore, the mirror 17K does not correspond to the separation optical system here. .

  Next, an embodiment of an image forming apparatus using the optical scanning device according to the present invention will be described with reference to FIG. In this embodiment, the optical scanning device according to the present invention is applied to a tandem full-color laser printer. In FIG. 4, a conveying belt 2 that conveys transfer paper (not shown) drawn from a paper feeding cassette 1 arranged in the horizontal direction is provided on the lower side in the image forming apparatus. On the upper side of the conveying belt 2, a photosensitive body 3Y for yellow Y, a photosensitive body 3M for magenta M, a photosensitive body 3C for cyan C, and a photosensitive body 3K for black K are sequentially arranged from the upstream side in the transfer paper conveying direction. They are arranged at equal intervals. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction. These photoreceptors 3Y, 3M, 3C, and 3K are all formed to have the same diameter, and process members that perform each process according to the electrophotographic process are sequentially arranged around the photoreceptors. Taking the photoconductor 3Y as an example, a charging charger 4Y, an optical scanning optical system 5Y, a developing device 6Y, a transfer charger 7Y, a cleaning device 8Y, and the like are sequentially arranged. The same applies to the other photoconductors 3M, 3C, 3K. That is, in this embodiment, the surfaces of the photoreceptors 3Y, 3M, 3C, and 3K are to be scanned or irradiated surfaces set for respective colors, and the optical scanning optical system 5Y is applied to each photoreceptor. , 5M, 5C, 5K are provided in a one-to-one correspondence. However, the scanning lens L1 is commonly used for M and Y, and is commonly used for K and C. Further, a registration roller 9 and a belt charging charger 10 are provided around the transport belt 2 so as to be positioned upstream of the photoconductor 5Y in the transport direction, and are positioned downstream of the photoconductor 5K in the rotation direction of the belt 2. Thus, a belt separation charger 11, a static elimination charger 12, a cleaning device 13 and the like are sequentially provided. Further, a fixing device 14 is provided downstream of the belt separation charger 11 in the transfer paper conveyance direction, and is connected to a paper discharge tray 15 by a paper discharge roller 16.

  In such a schematic configuration, for example, in the full color mode or the multi-color mode, each of the photoconductors 3Y, 3M, 3C, 3K is based on the image signals of the respective colors for Y, M, C, K. An electrostatic latent image corresponding to each color signal is formed on the surface of each photosensitive member by optical scanning of the light beam by the optical scanning devices 5Y, 5M, 5C, and 5K. These electrostatic latent images are developed with color toners by the corresponding developing devices to become toner images, which are superposed by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transport belt 2 and transported. As a result, a full-color image or a multicolor image is formed on the transfer paper. The image on the transfer paper is fixed on the transfer paper by the fixing device 14, and the transfer paper on which the image has been fixed is discharged onto a paper discharge tray 15 by a paper discharge roller 16.

  By using the optical scanning optical systems 5Y, 5M, 5C, and 5K of the image forming apparatus as the optical scanning apparatus according to the above-described embodiment, the scanning line bending and the wavefront aberration are effectively corrected, and there is no color shift. Thus, an image forming apparatus that can ensure high-quality image reproducibility can be realized.

  In the optical scanning device according to the present invention, the light source is, for example, a semiconductor laser array having a plurality of light emitting points, or a multi-beam light source device using a single light emitting point or a plurality of light sources having a plurality of light emitting points, and a plurality of light sources. The beam may be scanned on the surface of the photoconductor at the same time. By doing so, it is possible to configure an optical scanning device and an image forming apparatus that are increased in speed and density. Even when such an optical scanning device and an image forming apparatus are configured, the same effects as those described so far can be obtained.

  FIG. 5 shows an example of a light source unit constituting the multi-beam light source device. In FIG. 5A, the semiconductor lasers 403 and 404 are individually fitted in fitting holes formed on the back side of the base member 405, respectively. The fitting hole is slightly inclined in the main scanning direction by a predetermined angle, for example, about 1.5 °, and the semiconductor lasers 403 and 404 fitted in the fitting hole are also about 1.5 ° in the main scanning direction. Inclined. The semiconductor lasers 403 and 404 have notches formed in the cylindrical heat sink portions 403-1 and 404-1, and the protrusions 406-1 and 407-1 formed in the center round holes of the pressing members 406 and 407 are provided. The alignment direction of the light emitting sources is adjusted by matching the notch portion of the heat sink portion. The holding members 406 and 407 are fixed to the base member 405 with screws 412 from the back side thereof, so that the semiconductor lasers 403 and 404 are fixed to the base member 405. Further, the collimating lenses 408 and 409 each adjust the position in the optical axis direction along the outer circumference thereof along the semicircular mounting guide surfaces 405-4 and 405-5 of the base member 405, and divergence emitted from the light emitting point. The beam is positioned and bonded so as to be a parallel light beam.

  In the above embodiment, since the light beams from the respective semiconductor lasers are set so as to intersect within the main scanning plane, the fitting hole and the semicircular mounting guide surfaces 405-4, 405 along the light beam direction. -5 is tilted. By engaging the cylindrical engagement portion 405-3 of the base member 405 with the holder member 410 and passing the screw 413 through the through hole 410-2 and screwing into the screw holes 405-6 and 405-7, the base member Reference numeral 405 denotes a light source unit that is fixed to the holder member 410.

  The holder member 410 of the light source unit has a cylindrical portion 410-1 fitted into a reference hole 411-1 provided in the mounting wall 411 of the optical housing, and a spring 611 is inserted from the front side of the mounting wall 411 to stop the member. By engaging 612 with the cylindrical protrusion 410-3, the light source unit is held in close contact with the back side of the mounting wall 411. One end of the spring 611 is hooked on the protrusion 411-2 of the mounting wall 411, and the other end of the spring 611 is hooked on the light source unit, thereby generating a rotational force about the center of the cylindrical portion in the light source unit. An adjustment screw 613 provided to lock the rotational force of the light source unit is provided, and the adjustment screw 613 can rotate the entire unit in the θ direction around the optical axis to adjust the pitch. It is configured as follows. An aperture 415 is disposed in front of the light source unit, and the aperture 415 is provided with a slit corresponding to each semiconductor laser, and is configured to be attached to an optical housing to define an emission diameter of the light beam.

  FIG. 5B shows a second embodiment of the light source unit. In FIG. 5B, each light beam from the semiconductor laser 703 having four light emitting sources is configured to be combined using beam combining means. Reference numeral 706 denotes a pressing member, 705 denotes a base member, 708 denotes a collimating lens, and 710 denotes a holder member. This embodiment is different from the embodiment shown in FIG. 5A in that there is one semiconductor laser 703 as a light source and there is one pressing member 706 corresponding to this, and other configurations are as follows. Basically the same. FIG. 5C shows an example of a light source 801 in which four light emitting sources are arranged in the vertical direction and light beams are emitted in parallel at a constant interval ds in the vertical direction. The light beams emitted from the respective light emitting sources are crossed at a fixed point by passing through a lens, and then enter the deflecting reflection surface of the optical deflector with an inclination in the sub-scanning direction. .

Further, as shown in FIG. 6B, it is desirable that all light beams emitted from the semiconductor laser intersect in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 23 which is an optical deflector. Reference numeral D ₁ represents a reflecting surface of the polygon mirror 23 when the light beam emitted from the semiconductor laser 101 reaches a certain image height on the scanned surface 407, and D ₂ represents the light beam emitted from the semiconductor laser 102. This represents a reflection surface of the polygon mirror 403 when the image surface reaches the same image height on the scanned surface 407. Each light beam is separated by a relative angle difference Δα when entering the polygon mirror 23. Therefore, the angle difference by the time lag to the reflecting surface to reach the same image height, that is, D ₁ and time delay commensurate with the angle difference between D ₂ occurs.

  In the example shown in FIG. 6A, the two light beams are deflected and reflected at different positions on the deflecting reflecting surface through considerably different optical paths. In the example shown in FIG. 6B, the light beams cross at the same position on the deflecting reflection surface and pass through the same optical path after being deflected and reflected. When the light beam passes through different positions of each optical element, it naturally undergoes different optical action, so the optical characteristics such as aberration of the two light beams that reach the same image height in the main scanning direction on the surface to be scanned are different. In particular, the influence on the fluctuation of the scanning line pitch between the image heights is very large.

  Therefore, as shown in FIG. 6B, when the two light beams intersect in the vicinity of the reflection surface of the polygon mirror 23, the same image height in the main scanning direction on the surface to be scanned 407 is reached. In addition, since the optical elements pass through substantially the same optical path in the main scanning direction, the scanning line bending can be effectively reduced. Further, fluctuations in the main scanning direction writing position between the light beams due to variations in the parts on the image plane side from the polygon mirror 23 are substantially the same for all the light beams, and the main scanning direction writing position shift between the beams. Is suppressed. Furthermore, by allowing all the light beams formed at the same image height to pass through substantially the same position in the main scanning direction of the scanning optical system, it is possible to suppress the influence of the aberration of the lenses constituting the scanning optical system, In addition, the imaging position in the main scanning direction can be accurately matched with each beam, and even if a delay time is set in common for all the light beams after synchronous detection, the main scanning direction in the image height at the beginning of writing is set. It is possible to suppress misalignment. In addition, by configuring as in the example of FIG. 6B, the inscribed circle radius of the polygon mirror 23 can be minimized. A multi-beam light source device itself using one semiconductor laser array is not within the scope of this description. However, the effect of the present invention can be obtained even if a multi-beam light source device using one semiconductor laser array is used.

  Hereinabove, the multi-beam light source device has been described with an example. When deflecting light beams that are directed to different scanned surfaces on the reflecting surface of the same phase of the polygon mirror, each light beam intersects in the main scanning direction in the vicinity of the deflecting reflecting surface of the polygon mirror, that is, approximately in the main scanning direction. You may comprise so that the same reflective point may exist. The same reflection point may be used in the sub-scanning direction, or they may be separated from each other. By doing so, the same effect as described above can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS (a) which simplifies and shows one Example of the optical scanning device concerning this invention is a top view, (b) is a side view. It is a side view which shows the relationship between the various incident modes of the several light beam to the deflection | deviation reflection surface of a deflection | deviation means, and the thickness of the deflection | deviation reflection surface with respect to this. (A) and (b) show the relationship between various incident modes of a plurality of light beams on the deflecting reflecting surface of the deflecting means, the distance between the light beams at the light beam separation position, and the thickness of the deflecting reflecting surface with respect to this (c). FIG. 4 is a side view showing a relationship between a separation optical system, a light beam separated by the separation optical system, and a light beam passing near the separation optical system. 1 is a side view showing an embodiment of an image forming apparatus according to the present invention. It is a perspective view which shows the various specific examples of the light source part which can be applied to this invention. 2A and 2B are diagrams of an optical scanning device according to an embodiment of the present invention as viewed from a direction corresponding to a main scanning plane, in which FIG. 1A illustrates an example in which a plurality of light beams reach a scanned surface without intersecting, and FIG. It is a top view which shows the example which a some light beam cross | intersects.

Explanation of symbols

17 Separation optical system 20 Light source 21 First optical system 22 Second optical system 23 Polygon mirror 25 Scanned surface L1 First scanning lens L2 Second scanning lens 3K, 3C, 3M, 3Y

Claims (7)

The first light beam , the second light beam, the third light beam, and the fourth light beam emitted from the plurality of light source devices are deflected by a common light deflector. Thereafter, in the optical scanning device focused on the corresponding scanned surface by the scanning optical system ,
And the upper Symbol said first light beam deflected by the reflection surface of the deflector, the second optical beam, said third light beam, and the fourth light beam, before being separated respectively In the sub-scanning direction, the first light beam, the second light beam, the third light beam, and the fourth light beam are arranged in this order.
Position where the second light beam is separated from the first light beam, the the position where the third light beam is separated from the second light beam, the scanned towards the corresponding surface to be scanned The side close to the surface,
Position where the third light beam is separated from the second light beam, the the position where the fourth light beam is separated from the third light beam, the scanned towards the corresponding surface to be scanned The side close to the surface,
The angle formed between the first light beam and the second light beam is smaller than the angle formed between the second light beam and the third light beam in the sub-scanning direction.
The angle between the second light beam and the third light beam is smaller than the angle between the third light beam and the fourth light beam in the sub-scanning direction. Scanning device.   2. The optical scanning device according to claim 1, wherein a light beam directed to one scanned surface among the plurality of light beams is incident perpendicularly to a rotation axis of the optical deflector, and a light beam directed to the other scanned surface is An optical scanning device having an angle with respect to a normal line of a reflection surface of an optical deflector. 3. The optical scanning device according to claim 1, wherein a light beam adjacent in the sub-scanning direction is adjacent from a base point of a deflecting reflection surface of the optical deflector among light beams traveling from a plurality of light source devices toward different scanned surfaces. The distance to the separation optical system for separating the light beam is X, the angle of the light beam separated and deflected by the separation optical system in the sub-scanning direction with respect to the plane perpendicular to the rotation axis of the optical deflector is β1, and the light passes through the separation optical system. The angle in the sub-scanning direction with respect to the plane perpendicular to the rotation axis of the optical deflector of the light beam is β2, and the separation optical system adjacent to the separated light beam from the position on the separation optical system of the light beam separated by the separation optical system When the distance in the sub-scanning direction to the farthest end of the separation optical system on the side of the light beam passing through the system is Δh,
1.5 <(tan | β2 | · X-tan | β1 | · X) / Δh <5
An optical scanning device characterized by satisfying   4. The optical scanning device according to claim 1, wherein among the plurality of light beams deflected by the optical deflector and directed to different scanning surfaces, the light beams positioned at both ends in the sub-scanning direction are the optical deflectors. An optical scanning device characterized in that the angle in the sub-scanning direction with respect to a plane perpendicular to the rotation axis is the same.   5. The optical scanning device according to claim 1, wherein a reflection point interval of all light beams deflected by the optical deflector in the sub-scanning direction on the optical deflector reflecting surface is equal to adjacent light beams. An optical scanning device characterized by being smaller than the interval in the sub-scanning direction of adjacent light beams in the separation optical system for separating the two.   6. The optical scanning device according to claim 1, wherein a multi-beam light source device that emits a plurality of light beams is used as the light source device of the optical scanning device.   An image forming apparatus for forming an image by executing an electrophotographic process, wherein the image forming apparatus comprises the optical scanning device according to claim 1 as means for performing an exposure process of the electrophotographic process. .

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