JP4841268B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and particularly has a feature in the configuration of an optical element from a light source unit to an optical deflector in order to obtain a high-density image.

  Conventionally, optical scanning devices have been widely used in connection with image forming apparatuses such as optical printers, digital copying machines, and optical plotters. Recently, the price has been reduced and the influence of environmental fluctuations such as temperature and humidity has been reduced. There is a demand for a high-definition and high-definition image that is difficult to receive.

  Various lenses are used in the optical scanning device, and resin materials are widely used as materials for the lenses. Since the resin lens is lightweight and can be integrally molded with a mold, it can be formed at a low cost, and a special surface shape represented by an aspheric surface can be easily formed. Therefore, by adopting a special surface for the resin lens, the optical characteristics can be improved and the number of lenses constituting the optical system can be reduced. In other words, the use of a resin lens greatly contributes to the reduction in size, weight, and cost of the optical scanning device. However, on the other hand, as is well known, resin lenses change in shape and refractive index in accordance with environmental changes, particularly temperature changes, so optical characteristics, especially power, are designed. There is a problem that the “beam spot diameter”, which is the diameter of the light spot on the surface to be scanned, varies due to environmental fluctuations.

  The power fluctuation of the resin lens due to the temperature change occurs in the opposite direction between the positive lens and the negative lens. Therefore, the positive and negative resin lenses are incorporated in the optical system of the optical scanning device. A method of canceling out “changes in optical characteristics due to environmental changes” that occur in resin lenses is well known.

  Further, a general semiconductor laser as a light source of an optical scanning device has a property that an emission wavelength shifts to a longer wavelength side when a temperature rises, that is, a wavelength change due to a temperature change. Therefore, in an optical scanning device that includes a resin lens in an optical system and uses a semiconductor laser as a light source, it is necessary to perform an optical design that takes into account changes in optical characteristics accompanying temperature changes.

  An optical scanning device (laser scanning device) in which the optical characteristics are stabilized by adopting a power diffractive surface in consideration of changes in optical characteristics accompanying temperature changes is known (for example, see Patent Document 1). Patent Document 1 discloses an optical scanning device having a light source optical system that condenses laser light emitted from a laser light source into parallel light in the main scanning direction and in the vicinity of the deflection reflection surface of the optical deflector in the sub scanning direction. It is disclosed. The light source optical system is “one optical element having one or more reflecting surfaces that do not have a rotational symmetry axis and two transmissive surfaces, a power diffractive surface provided on the transmissive surface, and a resin. Element ". As a comparative example, a power diffractive surface is provided for each of a resin collimator lens that collimates a light beam from a semiconductor laser and a resin cylinder lens that focuses the collimated light beam in the sub-scanning direction. An optical scanning device "is disclosed. The “power diffractive surface” is a diffractive surface having lens power by diffraction.

JP 2002-287062 A

  Patent Document 1 discloses “one optical element having one or more reflecting surfaces not having a rotational symmetry axis and two transmitting surfaces, a power diffractive surface provided on the transmitting surface, and a resin. The light source optical system by the “element” needs to form a transmission surface and a reflection surface in one optical element, and includes a curved reflection surface. There is still room for improvement in terms of cost. Moreover, in patent document 1, the response | compatibility to multi-beam making is not mentioned.

In light of the circumstances of the prior art described above, the present invention is an optical scanning device that uses a power diffraction surface to reduce beam spot diameter fluctuations due to temperature fluctuations and perform optical scanning with a more stable beam spot diameter. The object is to realize the device.
Another object of the present invention is to obtain an image forming apparatus using an optical scanning device that achieves the above object. In particular, an object of the present invention is to provide an optical scanning device and an image forming apparatus that meet the demand for higher density of formed images by using a multi-beam light source.

The present invention provides a light source unit having a plurality of light emitting units, an optical deflector for deflecting and reflecting a light beam from the light source unit , and a first optical system for guiding the plurality of light beams from the light source unit to the optical deflector. And a second optical element that focuses a plurality of light beams deflected by an optical deflector on a surface to be scanned to form a light spot and optically scans the surface to be scanned. The first optical element is a diffractive optical element having at least one surface formed of a diffractive surface, the diffractive optical element has power in at least the sub-scanning direction, and the shape of the diffractive surface has a minor axis in the sub-scanning direction. An incident angle in the sub-scanning direction of the plurality of light beams to the diffractive optical element is a plane that includes the optical axis of the diffractive optical element and is orthogonal to the rotation axis of the optical deflector. Defined as the angle to the plane of 1 and the front to the diffractive optical element The incident angle of the main scanning direction of the plurality of light beams, the said defined as an angle with respect to said first plane and perpendicular to the second plane including the optical axis of the diffractive optical element, the incident angle of the main scanning direction and the sub The optical scanning device is characterized in that the incident angle in the scanning direction is greater than 0 degree and less than or equal to 5 degrees for any light beam.

Although not particularly limited in the present invention, if the incident angle of the light beam incident on the diffractive optical element is defined as a positive angle on one side and a negative angle on the opposite side with respect to the optical axis of the diffractive optical element, a positive angle The absolute value of the incident angle of the light beam having the maximum value of − and the light beam having the minimum value of −angle may be set to be substantially equal.
Although not particularly limited in the present invention, in the optical scanning apparatus described above, the maximum value of the + angle .theta.max, upper Symbol - when the .theta.min the minimum value of the angle, configured so as to satisfy the .theta.max + .theta.min <5 ° Good.
Although not particularly limited in the present invention, in the above-described optical scanning device, the incident angle of the light beam to the diffractive optical element is set to + angle on one side and −angle on the opposite side with respect to the optical axis of the diffractive optical element. Where the maximum value of the + angle is θmax and the minimum value of the − angle is θmin, the gradient of the backcut of the diffractive optical element on the diffractive surface is divided into two regions, the θmax region and the θmin region in the main scanning direction. It is good to have a region.

Although not particularly limited in the present invention, in the above-described optical scanning device , the diffractive surface of the diffractive optical element may be formed on the incident surface side.
Although not particularly limited in the present invention, in the above-described optical scanning device , the first optical element and the second optical element may be molded from resin.
In the present invention, although not particularly limited, in the above-described optical scanning device , the light source unit may be formed of a semiconductor laser array.
Although not particularly limited in the present invention, in the above-described optical scanning device , the light source unit may have a glassy optical element.

Although not particularly limited in the present invention, in the above-described optical scanning device , the light source unit may be configured by combining a plurality of single laser semiconductors.
Although not particularly limited in the present invention, in the above-described optical scanning device , the light source section has a resin optical element, and this optical element has a groove shape in which at least one side in the incident / exit direction is concentric. A diffractive optical element having a formed diffractive surface is preferable.

The present invention also provides an image forming apparatus having an image forming unit that forms a latent image by performing optical scanning by a light scanning unit on a photosensitive image carrier and visualizes the latent image by a developing unit to obtain an image. The optical scanning means for performing optical scanning on the image carrier is the above-described optical scanning device.

The present invention also provides a color image having a plurality of image forming units for forming a latent image by performing optical scanning by the optical scanning unit on the image bearing member of the photosensitive member and visualizing the latent image by the developing unit. An image forming apparatus that is capable of forming an optical scanning unit that performs optical scanning on an image carrier is the above-described optical scanning apparatus that performs optical scanning with a plurality of laser beams modulated by image signals for each color component. It is characterized by performing.

Monochrome image formation can be performed with one image forming unit , or two or more image forming units are provided to form two-color images, multicolor images, or even full-color images. An apparatus can also be constructed. In the case of an image forming apparatus capable of forming a full-color image, the optical scanning device that performs optical scanning in each image forming unit may be separate for each image forming unit. For example, Japanese Patent Laid-Open No. 2004-280056 As is known, a part of optical components, for example, a part of an optical deflector or a scanning optical system may be shared by a plurality of scanning optical systems. When there are two or more image forming units, it is possible to set two or more image forming units at different positions with respect to the same image carrier, or a plurality of image carriers as in a so-called tandem color image forming apparatus. It is also possible to arrange the bodies in parallel and to provide individual image forming portions around the individual image carriers.

Here, when a resin lens is included in the optical system of the optical scanning device, the positional variation of the light beam condensed toward the scanned surface, that is, the beam waist position, with respect to the environmental condition variation and wavelength variation. Let us briefly consider the fluctuations. First, the cause of beam waist position fluctuation due to temperature fluctuation is due to temperature fluctuation.
a. Changes in the refractive index of the resin lens itself,
b. Plastic lens shape change,
c. Change in refractive index of resin lens due to wavelength change of semiconductor laser (chromatic aberration)
Can be considered.
The change in the refractive index itself of the resin lens accompanying the temperature fluctuation appears as a phenomenon in which the refractive index decreases as the lens expands and decreases in density as the temperature rises.
The change in the shape of the resin lens accompanying the temperature fluctuation appears as a phenomenon in which the curvature of the lens surface decreases due to the lens expanding as the temperature rises.
The change in the refractive index of the resin lens due to the change in the emission wavelength of the semiconductor laser accompanying the temperature fluctuation generally appears as a phenomenon that shifts to the longer wavelength side as the temperature rises. When the wavelength shifts to the longer wavelength side, the refractive index of the resin lens generally shifts to the decreasing side.
As described above, regardless of whether the lens made of resin is a positive lens or a negative lens, the absolute value of the power changes as the temperature rises.

  On the other hand, since the diffraction angle of the diffractive surface of the diffractive optical element is proportional to the wavelength, the power of the diffractive part is positive or negative, It tends to increase as the wavelength increases. Therefore, for example, when the combined power of the resin lens in the optical system of the optical scanning device is positive (or negative), the power of the diffractive portion of the diffractive surface is made positive (or negative), so that the resin lens It is possible to cancel the power change due to the temperature fluctuation at the diffractive surface with the power change accompanying the temperature fluctuation at the diffractive portion of the diffractive surface.

  Here, the “diffractive part” of the diffractive surface is referred to for the following reason. A diffractive surface of a general diffractive optical element is not necessarily formed in a flat surface, but includes a surface formed on a spherical surface or a cylindrical surface, and therefore has a power also in a portion corresponding to the substrate on which the diffractive surface is formed. It will be. In the present specification, this means the power of only the diffractive surface excluding the power of the portion that hits the substrate.

In order to explain a little more concretely, let us consider a case where the environmental temperature rises when the power of the resin lens included in the optical system and the power of the “diffractive part” of the diffractive surface are both positive.
Beam waist position fluctuation amount due to change in refractive index of resin lens: A
Beam waist position variation due to resin lens shape change: B
Beam waist position fluctuation amount due to change in refractive index of resin lens due to change in emission wavelength of semiconductor laser: C
Beam waist position fluctuation amount due to power change of “diffractive part” of diffractive surface due to change in emission wavelength of semiconductor laser: D
Then, A> 0, B> 0, C> 0, and D <0 (change in the direction away from the optical deflector is positive). And the total amount of beam waist position fluctuation | variation accompanying this temperature change is A + B + C-D. A to C are determined when an optical system including a resin lens is determined. Therefore, the power of the “diffractive part” of the diffractive surface is set so as to satisfy the condition that the beam waist position fluctuation amount is 0: A + B + C−D = 0. By doing so, the beam waist position fluctuation | variation accompanying a temperature change can be correct | amended favorably.

  In the optical scanning device according to the present invention, the power of the diffractive surface is set so that the fluctuation of the beam waist position in the main scanning direction and / or the sub-scanning direction due to the temperature change in the multi-beam light source is substantially zero. The beam waist position variation is effectively corrected with respect to the temperature variation, and optical scanning can always be performed with a stable beam spot diameter. By using this optical scanning device, the image forming apparatus according to the present invention can form a stable image.

Embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described below with reference to the drawings.
FIG. 1 is an optical layout diagram showing an embodiment of an optical scanning device. In FIG. 1, reference numeral 1 is a light source unit, reference numeral 3 is an aperture, reference numeral 4 is a diffractive optical element as an optical element, reference numeral 5 is a polygon mirror of a rotating polygon mirror as an optical deflector, and reference numeral 6 is a scanning lens as an optical element. Reference numeral 8 denotes a surface to be scanned. Reference numeral G1 denotes a soundproof glass that closes a window of a soundproof housing (not shown) that houses the polygon mirror 5, and reference numeral G2 is provided at the deflected light beam emitting portion of the housing that houses the optical system of the optical scanning device. The dustproof glass is shown. An optical element that guides the light beam from the light source unit 1 to the polygon mirror 5, that is, a portion including a coupling lens, an aperture 3, and a diffractive optical element 4 described later is defined as a first optical element. On the other hand, the scanning lens 6 that condenses the light beam deflected by the polygon mirror 5 onto the surface to be scanned 8 to form a light spot and optically scans the surface to be scanned 8 is used as the second optical element.

  The light beam emitted from the light source unit 1 is shaped by the aperture 3 and enters the diffractive optical element 4. The light beam that has passed through the diffractive optical element 4 is transmitted through the soundproof glass G1 while being focused in the sub-scanning direction, and is formed as a long line image in the main scanning direction in the vicinity of the deflecting reflection surface of the polygon mirror 5 that is an optical deflector. Imaged. The polygon mirror 5 is rotationally driven at a constant speed by a motor (not shown), the light beam is deflected and reflected at a constant angular velocity by the deflection reflection surface, and the deflection beam passes through the soundproof glass G1 and enters the scanning lens 6. The scanning lens 6 is composed of a single lens, and the light beam transmitted through this lens is incident on the scanned surface 8 through the dust-proof glass G2, and a light spot is formed on the scanned surface 8 by the action of the scanning lens 6. Form.

  The scanning lens 6 has a constant velocity so that a light spot by an incident light beam while being deflected at a constant angular velocity moves at a constant velocity in the main scanning direction (vertical direction in the figure) on the surface to be scanned 8. The light spot scans the scanned surface 8 at a constant speed. The scanning lens 6 is an anamorphic optical element, and in the sub-scanning direction, the position of the deflecting reflection surface of the polygon mirror 5 and the position of the surface to be scanned have a geometric optical conjugate relationship, thereby correcting the surface tilt of the polygon mirror 5. is doing. The scanned surface 8 is actually a photosensitive surface of a photosensitive medium as an image carrier.

  Next, an example of the structure of the light source unit 1 will be described in detail. The light source unit 1 is a multi-beam light source, and a semiconductor laser array having a plurality of light emitting points in one package can be used, or a plurality of ordinary semiconductor lasers having one light emitting point in one package are combined. It can also be used. When a plurality of semiconductor lasers are used in combination, the configuration shown in FIG. 2 can be adopted. That is, the light sources 1-1 and 1-2 are semiconductor lasers, each having a single light emitting point. The beams emitted from the light sources 1-1 and 1-2 are coupled by the coupling lenses 2-1 and 2-2. The form of each coupled beam can be a weak divergent light beam, a weak convergent light beam, or a parallel light beam, depending on the optical characteristics of the subsequent optical system.

  The beams transmitted through the coupling lenses 2-1 and 2-2 are shaped by the apertures 3-1 and 3-2, and are incident on the beam combining prism 20. The beam combining prism 20 has a reflecting surface, a polarization separation film, and a half-wave plate. The beam from the light source 1-2 is reflected by the reflecting surface of the beam combining prism 20 and the polarization separation film, and is emitted from the beam combining prism 20. The beam from the light source 1-1 is rotated 90 degrees on the polarization plane by the half-wave plate, passes through the polarization separation film, and is emitted from the beam combining prism 20. In this way, the two beams are combined. By adjusting the positional relationship of the light emitting portions of the light sources 1-1 and 1-2 with respect to the optical axes of the coupling lenses 2-1 and 2-2, the two combined beams are slightly tilted in the sub-scanning direction, and the reference A small angle is formed with respect to the optical axis. The light sources 1-1 and 1-2 are fitted into individual bases 5-1 and 5-2, respectively. The light sources 1-1 and 1-2 are fitted in the respective bases 5-1 and 5-2. Coupling lenses 2-1 and 2-2 are positioned and held facing the light sources 1-1 and 1-2 from the opposite side of the mating surface. Each of the bases 5-1 and 5-2 is positioned and fixed from one surface side of one flange 40, and on the other surface side of the flange 40, one aperture constituting the apertures 3-1 and 3-2. The plate 30 is positioned and fixed. The light source unit 1 is unitized by holding the flange 40 and the beam combining prism 20 with a holder 50.

  When a combination of a plurality of ordinary semiconductor lasers is used as the light source, a configuration as shown in FIG. 3 can be used. In FIG. 3, light sources 1-1 and 1-2 are semiconductor lasers, each having a single light emitting point. The beams emitted from the light sources 1-1 and 1-2 are coupled by the coupling lenses 2-1 and 2-2. The form of each coupled beam can be a weak divergent light beam, a weak convergent light beam, or a parallel light beam, depending on the optical characteristics of the subsequent optical system. The optical axes of the coupling lenses 2-1 and 2-2 are configured to form a minute angle in the main scanning direction so as to intersect on the polygon mirror, and the light beams emitted from the light sources 1-1 and 1-2 are Propagated along this optical axis. In FIG. 3, reference numeral 3 is a light source holder, 3a is a fitting hole for light sources 1-1 and 1-2, 3b is a positioning portion for coupling lenses 2-1 and 2-2, and 7 is a light source holder 3 fixed to the light. Each of the unit holders is fixed through an appropriate wall 9 such as a housing of a scanning device. If the configuration shown in FIG. 3 is used, the beam combining prism 20 and the half-wave plate used in the example shown in FIG. 2 become unnecessary, and the light source unit can be made compact and low in cost. .

  In addition, when a semiconductor laser array that emits a plurality of laser beams is used as a light source, depending on the configuration of the optical element mounted on the optical scanning device, as shown in the example of the semiconductor laser array shown in FIG. In order to achieve a desired beam pitch, the arrangement direction of a plurality of (four in the illustrated example) light emitting points may be inclined with respect to the main scanning direction (and thus also in the sub-scanning direction).

When a light source unit as shown in FIGS. 2 to 4 is used, a plurality of light beams incident on the diffractive optical element 4 in the example of the optical scanning device of FIG. 1 are incident on the optical axis as shown in FIG. Have an angle. Here, are speaking of "angle of incidence" is a plane containing the optical axis of the diffractive optical element 4 is that of that angles against the direction of rotation parallel to the plane of the optical deflector. In general, the light beam incident on the diffractive optical element is perpendicular to the diffractive surface. However, in the case of the multi-beam light source as described above, it is inevitable that the incident light on the diffraction surface has an angle. With such a configuration, it has been experimentally confirmed that the function of correcting the variation of the beam waist position due to the temperature variation can be obtained even if the light beam is incident on the diffraction surface at a considerably large incident angle. Transmission attenuation due to a decrease in diffraction efficiency has become a major issue.

  Usually, when a glass cylindrical lens is used, the transmittance is about 98% ± 2%, and the attenuation of the transmittance hardly poses a problem. However, since a diffractive optical element employing a diffractive surface is generally molded from resin, the transmittance is attenuated to about 87% ± 2% due to the difference in material. Moreover, if there is a processing error in the shape of the groove forming the diffractive surface, unnecessary diffracted light is generated, and the light energy of the diffracted light is attenuated, making it impossible to obtain the desired light energy. Furthermore, even if there is no processing error in the groove shape, if the light does not enter perpendicularly to the diffraction surface, the diffraction efficiency similarly decreases, and as a result, transmittance attenuation occurs. Therefore, in order to expose the photosensitive member, the output of the semiconductor laser must be increased, and as a result, a large amount of heat is generated, increasing the burden on the environment.

  However, it has been found that in a combination of a multi-beam and a diffractive optical element, several systems may be used in order to satisfy the minimum transmittance of 87% ± 2% of the diffractive optical element. One method is to make the incident angle of the light beam incident on the diffractive optical element 5 degrees or less. When the light source unit as shown in FIG. 3 is used, the angle between the optical axes B1 and B2 of the coupling lenses 2-1 and 2-2 may be set to 10 degrees or less. As a result, the transmittance of the diffractive optical element can be maintained at 87% ± 2%, and the output of the semiconductor laser necessary for exposing the photoconductor is the semiconductor required when the light beam is incident vertically. It will be inferior to the laser output.

  Another method for maintaining the transmittance of 87% ± 2% of the diffractive optical element is that the surface having the diffractive shape of the diffractive optical element, that is, the cross sectional shape of the diffractive surface in the sub-scanning direction is the same regardless of the position in the main scanning direction. This is the method. In the configuration example of the light source unit shown in FIGS. 2 to 4, it is very characteristic that the light beam emitted from the light source has an angle in the main scanning direction, and when this is incident on the diffractive optical element, the diffraction efficiency decreases. This is the main cause. However, if the sub-scanning sectional shape of the diffraction shape is the same regardless of the position in the main scanning direction, the contribution to diffraction does not depend on the incident angle in the main scanning direction. FIG. 6 shows an example of a diffractive optical element according to this method. In FIG. 6, the diffractive optical element 400 has a diffractive surface 401 on one side, and the diffractive surface 401 is formed in a groove shape parallel to the main scanning direction. Therefore, this diffractive surface 401 is considered to have the simplest configuration.

  The diffractive optical element shown in FIG. 6 has a function for correcting the beam waist position variation due to temperature variation only in the sub-scanning direction. However, in the main scanning direction, the beam source is devised by devising the configuration of the light source unit. Waist position fluctuation can be corrected. Since the beam waist position fluctuation can be corrected without using the power of the diffractive optical element, a stable beam spot diameter can be obtained even in such a case.

  Further, as another example of the diffractive optical element, it is conceivable to include a diffractive surface 411 formed as an elliptical groove shape with a large flatness, as in the diffractive optical element 410 shown in FIG. In this case, a stable beam spot diameter can be obtained even when the beam waist position fluctuation due to the temperature fluctuation cannot be sufficiently corrected only by devising the configuration of the light source unit in the main scanning direction. Become. In the diffractive optical element 410 configured as described above, it is more preferable to set the light source unit so that the incident angle of the light beam is 5 degrees or less.

  When the multi-beam type light source and the diffractive optical element are combined, another technical problem to be solved is a problem in that the transmission energy of each light beam varies. Certainly, the transmittance of the diffractive optical element can be suppressed to 87% ± 2% by setting the incident angles of all the light beams to 5 degrees or less. However, if the transmission energy of each light beam varies within this range, the image obtained by developing the latent image formed on the photoconductor with these light beams will be blurred. In particular, when applied to a full-color image forming apparatus, it appears in the image as a difference in color, which is not preferable.

  Therefore, as shown in FIG. 8, when one side is defined as a + angle and the opposite side is defined as a-angle with respect to the optical axis of the diffractive optical element, a light beam having a maximum + angle and a minimum-angle By making the absolute values of the light beams having substantially the same value, the problem that the transmitted energy of each light beam varies does not occur. Alternatively, when the maximum value of the + angle is θmax and the minimum value of the − angle is θmin, when the light source unit is set so as to satisfy θmax + θmin <5 degrees, an image that causes a problem in quality was not obtained.

  Further, as shown in FIG. 9, even if the surface having the diffraction shape, that is, the gradient of the backcut on the diffraction surface is configured to have two regions of the θmax region and the θmin region in the main scanning direction, Variation in transmission energy of the beam can be suppressed. In this configuration, the diffractive surface is preferably formed on the incident surface side of the diffractive optical element. The reason for this is that, as shown in FIG. 10, when a diffractive surface satisfying the above conditions is introduced on the exit surface side, the cross section of the groove forming the diffractive surface becomes an inverse wave, and the diffractive optical element is made of resin. This is because it is difficult to take out from the mold when molding with.

  The example of the light source unit shown in FIGS. 2 and 3 will be further described. In the example of the light source section shown in FIGS. 2 and 3, the coupling lenses 2-1 and 2-2 are made resin, and the diffractive optical element is a diffractive optical element having a diffractive surface formed as a concentric groove shape. Good. However, as in the example shown in FIG. 4, when a semiconductor laser array is used as the light source, it is preferable not to use the coupling lens as a diffractive optical element. The reason for this is that, in the case of a semiconductor laser array, the wavelength of the light beam emitted from each light emitting point is not necessarily the same, and the mode hop phenomenon, that is, the phenomenon in which the oscillation wavelength changes rapidly at each light emitting point. This is because they occur completely independently, and image deterioration due to wavelength variations becomes large. In order to avoid such wavelength dependence, glass is better as the material of the coupling lens, and a stable image can be obtained by using glass as the material of the coupling lens.

  FIG. 11 shows an image forming apparatus having an image forming section that forms a latent image by performing optical scanning by a light scanning unit on a photosensitive image carrier and visualizes the latent image by a developing unit to obtain an image. An embodiment of an image forming apparatus using the optical scanning device described so far will now be described as an optical scanning means for optically scanning the image carrier. This image forming apparatus is a tandem type full-color optical printer. In FIG. 11, a transport belt 132 that transports transfer paper (not shown) fed from a paper feed cassette 130 disposed in the horizontal direction is provided at the bottom of the image forming apparatus. Above the transport belt 132, a yellow (Y) photoreceptor 17Y, a magenta (M) photoreceptor 17M, a cyan (C) photoreceptor 17C, and a black (K) photoreceptor 17K, The transfer belts 132 are arranged at equal intervals in order from the upstream side in the transfer direction of the transfer paper. In the following, yellow, magenta, cyan, and black are distinguished by Y, M, C, and K added in the reference numerals.

  The photoreceptors 17Y, 17M, 17C, and 17K are all formed to have the same diameter, and process members are sequentially disposed around the photoreceptors according to an electrophotographic process. Taking the photoconductor 13Y as an example, a charging charger 140Y, an optical scanning device 150Y, a developing device 160Y, a transfer charger 130Y, a cleaning device 180Y, and the like are sequentially arranged in the rotation direction of the photoconductor. The same applies to the other photoconductors 13M, 13C, and 13K. That is, this image forming apparatus uses the photoconductors 17Y, 17M, 17C, and 17K as scanning surfaces set for respective colors, and the optical scanning devices 150Y, 150M, 150C, and 150K are used for the respective photoconductors. Are provided in a one-to-one correspondence.

  As these optical scanning devices, those having the optical arrangement as shown in FIG. 1 can be used independently. For example, as disclosed in Japanese Patent Application Laid-Open No. 2004-280056, etc. The deflector (rotating polygon mirror) is shared, and the lens of the scanning optical system in each optical scanning device is shared for optical scanning of the photoconductors 17M and 17Y, and is shared for optical scanning of the photoconductors 17K and 17C. You can also Around the conveyance belt 132, a registration roller 19 and a belt charging charger 110 are provided upstream of the photosensitive member 17Y in the transfer paper conveyance direction, and are positioned downstream of the photosensitive member 17K. A charger 112, a cleaning device 113, and the like are provided. A fixing device 114 is provided on the downstream side of the belt separation charger 111 in the transfer paper conveyance direction, and is connected to a paper discharge tray 115 by a paper discharge roller 116.

  In such a configuration, for example, in the full color mode, Y, M, and C are applied to each of the photoreceptors 17Y, 17M, 17C, and 17K whose surfaces are uniformly charged by the chargers 140Y, 140M, 140C, and 140K. , K, and the optical scanning devices 150Y, 150M, 150C, and 150K based on the image signals of the respective colors, an electrostatic latent image is formed on each of the photoconductors. These electrostatic latent images are developed with corresponding color toners by developing devices 160Y, 160M, 160C, and 160K, respectively, and become toner images. The toner images are superimposed on each other by being sequentially transferred onto transfer paper that is electrostatically attracted and conveyed on the conveyance belt 132, fixed as a full-color image by the fixing device 114, and then on the discharge tray 115. The paper is discharged.

  By using the above-described optical scanning device as the exposure unit of such an image forming apparatus, a stable beam spot diameter can be obtained at all times, and a high-definition print or image can be obtained with a compact image forming apparatus. And can be realized at low cost.

It is a top view which shows roughly the Example of the optical scanning device concerning this invention. It is a disassembled perspective view which shows the structural example of the light source part which can be used for the said Example. The another example of a structure of the light source part which can be used for the said Example is shown, (a) is a disassembled perspective view, (b) is a longitudinal cross-sectional view. It is a perspective view which shows another structural example of the light source part which can be used for the said Example. It is sectional drawing which shows the example of the diffractive optical element applicable to this invention, and the example of the incident angle to this diffractive optical element. (A) which shows another example of the diffractive optical element applicable to this invention is a front view, (b) is a left view, (c) is a top view. (A) which shows another example of the diffractive optical element applicable to this invention is a front view, (b) is a left view, (c) is a top view. It is sectional drawing which shows the example of another diffractive optical element applicable to this invention, and the example of the incident angle to this diffractive optical element. It is sectional drawing which shows the example of another diffractive optical element applicable to this invention, and the example of the incident angle to this diffractive optical element. It is sectional drawing which shows the example of another diffractive optical element applicable to this invention, and the example of the incident angle to this diffractive optical element. 1 is a front view schematically showing an embodiment of an image forming apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source part 1-1 Light source 1-2 Light source 2-1 Coupling lens 2-2 Coupling lens 3 Aperture 4 Diffractive optical element 5 Polygon mirror as an optical deflector 6 Scan lens as a 2nd optical element 8 To be scanned surface

Claims (12)

A light source unit having a plurality of light emitting units;
An optical deflector for deflecting and reflecting a light beam from the light source unit;
A first optical element for guiding a plurality of light beams from the light source unit to the optical deflector,
A second optical element that condenses a plurality of light beams deflected by the optical deflector onto the surface to be scanned to form a light spot and optically scans the surface to be scanned;
An optical scanning device comprising:
The first optical element is a diffractive optical element having at least one side formed of a diffractive surface,
The diffractive optical element has power in at least the sub-scanning direction, and the shape of the diffractive surface is an elliptical shape having a minor axis in the sub-scanning direction,
The incident angle of the plurality of light beams to the diffractive optical element in the sub-scanning direction is an angle with respect to a first plane that includes the optical axis of the diffractive optical element and is orthogonal to the rotation axis of the optical deflector. And defining an incident angle of the plurality of light beams on the diffractive optical element in a main scanning direction as an angle with respect to a second plane including the optical axis of the diffractive optical element and perpendicular to the first plane; An optical scanning device in which an incident angle in the main scanning direction and an incident angle in the sub-scanning direction are greater than 0 degree and less than or equal to 5 degrees for any light beam.   2. The optical scanning apparatus according to claim 1, wherein the incident angle of the light beam incident on the diffractive optical element is defined as a positive angle on one side and a negative angle on the opposite side with respect to the optical axis of the diffractive optical element. An optical scanning device in which the absolute values of the incident angles of the light beam having the maximum value and the light beam having the minimum value of the angle are substantially equal. 2. The optical scanning device according to claim 1, wherein the incident angle of the light beam to the diffractive optical element is defined as a positive angle on one side and a negative angle on the opposite side with respect to the optical axis of the diffractive optical element. An optical scanning device satisfying θmax + θmin <5 degrees, where θmax is the value and θmin is the minimum value of the −angle. 4. The optical scanning device according to claim 1, wherein an incident angle of the light beam to the diffractive optical element is defined as a positive angle on one side and a negative angle on the opposite side with respect to the optical axis of the diffractive optical element. If the maximum value of the + angle is θmax and the minimum value of the −angle is θmin, the gradient of the backcut of the diffractive optical element on the diffractive surface is divided into two regions, the θmax region and the θmin region in the main scanning direction. Optical scanning device having.   5. The optical scanning device according to claim 4, wherein the diffractive surface of the diffractive optical element is on the incident surface side.   6. The optical scanning device according to claim 1, wherein the first optical element and the second optical element are molded from a resin.   7. The optical scanning device according to claim 1, wherein the light source unit is a semiconductor laser array.   8. The optical scanning device according to claim 7, wherein the light source section includes a glass optical element.   7. The optical scanning device according to claim 1, wherein the light source unit is a combination of a plurality of single laser semiconductors.   10. The optical scanning device according to claim 9, wherein the light source section has a resin optical element, and the optical element has a diffraction surface formed as a concentric groove shape on at least one side in the incident / exit direction. An optical scanning device which is a diffractive optical element. In an image forming apparatus having an image forming unit that performs light scanning by a light scanning unit on a photosensitive image carrier to form a latent image, and visualizes the latent image with a developing unit to obtain an image.
The image forming apparatus according to claim 1, wherein the optical scanning unit that performs optical scanning on the image carrier is the optical scanning device according to claim 1. Image formation capable of forming a color image having a plurality of image forming units for forming a latent image by performing optical scanning with a light scanning unit on a photosensitive image carrier and visualizing the latent image with a developing unit In the device
An optical scanning unit that performs optical scanning on an image carrier is the optical scanning device according to any one of claims 1 to 10, wherein optical scanning is performed with a plurality of laser beams modulated by an image signal for each color component. An image forming apparatus to perform.

Images