JP2007233002A - Optical scanning apparatus and image forming apparatus - Google Patents

Abstract

An optical scanning device that uses a diffractive optical element to reduce fluctuations in beam spot diameter due to temperature fluctuations and suppresses variations in the amount of light on the surface to be scanned due to processing errors of the diffractive optical element is realized. The used image forming apparatus is obtained.
A light source unit having a light emitting unit, a first optical element for guiding a light beam from the light emitting unit to a subsequent optical system, and a light beam emitted from the first optical element are converted into a line image. The second optical element 4, the optical deflector 5 that deflects the light beam emitted from the second optical element 4, and a plurality of light beams deflected by the optical deflector 5 are condensed on the scanned surface 8. And a third optical element 6 that forms a light spot and optically scans the surface to be scanned 8. At least the third optical element 6 is made of resin, and any one of the first, second, and third optical elements is a diffractive optical element, and the center line average roughness Ra of the surface of the diffractive optical element is 20 nm ≦ Ra ≦ 200 nm is satisfied.
[Selection] Figure 1

Description

  The present invention relates to an optical scanning device and an image forming apparatus, and in particular, the configuration of an optical element is devised in order to perform optical scanning with a stable beam spot diameter.

  Conventionally, optical scanning devices have been widely used in connection with image forming apparatuses such as optical printers, digital copiers, and optical plotters. There is a demand for a high-density, high-definition image that is less susceptible to fluctuations.

  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.

  In addition, 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 the temperature rises, that is, a wavelength change due to a temperature change, and a mode hop phenomenon, that is, a semiconductor laser. There is also a wavelength change due to a phenomenon in which the oscillation wavelength changes rapidly. A wavelength change in the light source causes a characteristic change due to chromatic aberration of an optical system used in the optical scanning apparatus, and this characteristic change also causes a beam spot diameter fluctuation. Therefore, in an optical scanning device that includes a resin lens in the optical system and uses a semiconductor laser as the light source, an optical design that takes into account changes in the optical characteristics accompanying changes in the wavelength of the light source as well as changes in the optical characteristics accompanying changes in temperature. There is a need to do.

  There is known an optical scanning device (laser scanning device) that employs a power diffractive surface to stabilize optical characteristics in consideration of changes in optical characteristics accompanying temperature changes and wavelength changes in a light source. One of them is an example in which a diffractive optical element is applied to a scanning optical system (see, for example, Patent Document 1). Another example is an example in which a diffractive optical element is applied to a coupling lens (see, for example, Patent Document 2). Yet another example is an example in which a diffractive optical element is applied to an optical element in which a coupling lens and a cylindrical lens are integrated (see, for example, Patent Document 3).

JP 2000-292718 A JP-A-4-328512 JP 2002-287062 A

  What should be paid most attention to when using a diffractive optical element is a variation in diffraction efficiency due to a processing error of the diffractive optical element. The variation in diffraction efficiency causes variations in the amount of light spot on the surface to be scanned when viewed as the entire optical scanning device. If the amount of light spot varies on the surface to be scanned, especially when a full-color image is formed, the overlapping of the respective colors deteriorates and the image quality deteriorates extremely. However, none of the inventions described in Patent Documents 1 to 3 make a problem of a decrease in diffraction efficiency, and nothing mentions a decrease in diffraction efficiency.

  In the light scanning device using a diffractive optical element, the present invention reduces the beam spot diameter fluctuation due to the temperature fluctuation, and in addition, on the surface to be scanned due to the processing error of the diffractive optical element. It is an object of the present invention to provide an image forming apparatus capable of forming a high-density and high-quality image by using the optical scanning apparatus by realizing an optical scanning apparatus in which variations in light amount are suppressed. To do.

  The present invention provides a light source unit having a light emitting unit, a first optical element that guides a light beam from the light emitting unit to a subsequent optical system, and a first optical element. A second optical element that converts the light beam emitted from the second optical element into a line image, an optical deflector that deflects the light beam emitted from the second optical element, and a plurality of light beams deflected by the optical deflector to be scanned And a third optical element that forms a light spot by condensing on the surface and optically scans the surface to be scanned, wherein at least the third optical element is made of resin, Either the second optical element or the third optical element is a diffractive optical element, and the surface of the diffractive optical element prevents the diffracted light of unnecessary orders generated by the steps of the diffractive optical element from being collected on the surface to be scanned. The main feature is to provide roughness.

  The present invention also provides a light source unit having a light emitting unit, a first optical element for guiding a light beam from the light emitting unit to a subsequent optical system, and a first optical device. A second optical element that converts a light beam emitted from the element into a line image; an optical deflector that deflects the light beam emitted from the second optical element; and a plurality of light beams deflected by the optical deflector. And a third optical element that condenses light on the scanning surface to form a light spot and optically scans the surface to be scanned, and at least the third optical element is made of resin. One of the second and third optical elements is a diffractive optical element, and the center line average roughness Ra of the surface of the diffractive optical element satisfies 20 nm ≦ Ra ≦ 200 nm.

According to a third aspect of the present invention, in the second aspect of the present invention, the diffractive optical element is made of resin.
The invention according to claim 4 is the invention according to claim 3, wherein the resin diffractive optical element is the second optical element.
The invention according to claim 5 is the invention according to claim 2, wherein the first optical element and the second optical element are integrally formed, and the integrated optical element is a resin-made diffractive optical element. It is characterized by.
A sixth aspect of the present invention is the diffractive optical element according to any one of the second to fifth aspects, wherein the diffractive optical element has a function of correcting a change in a beam waist position due to a temperature variation at least in the sub-scanning direction. It is characterized by that.
The invention according to claim 7 is the invention according to any one of claims 2 to 6, wherein the diffractive surface of the diffractive optical element has a multi-step shape.

The invention according to claim 8 is the invention according to any one of claims 2 to 7, wherein the light source part is a multi-beam light source part having a plurality of light emitting points, and the first light source corresponding to each light emitting point. An optical element is disposed, and the first optical element is a resin diffractive optical element.
The invention according to claim 9 is the invention according to any one of claims 2 to 7, wherein the light source unit is a multi-beam light source unit having a plurality of light emitting points, and a light beam radiated from the plurality of light emitting points passes therethrough. There is one or more first optical elements, and the first optical elements are made of glass.
The invention according to claim 10 is the invention according to claim 2, 3, 4, 6 or 7, wherein the light source section is a multi-beam light source section using a surface emitting semiconductor laser, and the first optical element is a resin. It is a diffractive optical element.

  According to an eleventh aspect of the present invention, there is provided an image forming section for forming a latent image by performing optical scanning by a light scanning unit on a photosensitive image carrier and visualizing the latent image by a developing unit to obtain an image. In the image forming apparatus, the optical scanning unit that performs optical scanning on the image carrier is the optical scanning apparatus according to any one of claims 1 to 10.

  The invention according to claim 12 is provided with a plurality of image forming units for forming a latent image by performing optical scanning by the optical scanning unit on the photosensitive image carrier and visualizing the latent image by the developing unit. 11. An image forming apparatus capable of forming a color image, wherein the optical scanning unit that performs optical scanning with respect to the image carrier is the optical scanning apparatus according to claim 1, wherein an image signal for each color component is used. Optical scanning is performed with a plurality of modulated laser beams.

  Monochrome image formation can be performed with one image forming unit, or two or more image forming units can be provided as in the invention of claim 12 to provide two-color images, multicolor images, and The image forming apparatus can be configured to form a full-color image. 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 is a positive lens or a negative lens, the absolute value of the power changes as the temperature increases.

  On the other hand, since the diffraction angle by the diffractive optical element is proportional to the wavelength, the absolute value of the diffractive surface of the diffractive surface of the diffractive surface is positive or negative, and the absolute value increases as the wavelength increases. Have a tendency. 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 diffraction portion.

  Here, the “diffractive part” of the diffractive surface is referred to for the following reason. The diffractive surface of a general diffractive optical element is not necessarily limited to a flat surface, but includes a surface formed on a spherical surface or a cylindrical surface. Will also have power. 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 of the diffractive optical element 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 is substantially 0 (zero). Therefore, the beam waist position variation due to temperature variation is effectively corrected, and optical scanning can always be performed with a stable beam spot diameter. By using this optical scanning device, it is possible to provide an image forming apparatus capable of stably forming a high-quality 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 a second optical element, reference numeral 5 is a polygon mirror of a rotating polygon mirror as an optical deflector, and reference numeral 6 is a third optical element. 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. A coupling lens described later that guides the light beam from the light source unit 1 to the polygon mirror 5 is defined as a first optical element. The scanning lens 6 as a third optical element is an optical element that condenses the light beam deflected by the polygon mirror 5 on the scanned surface 8 to form a light spot and optically scans the scanned surface 8.

  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 focused in the sub-scanning direction by the optical action of the diffractive optical element 4 and transmitted through the soundproof glass G1, and then in the vicinity of the deflecting reflection surface of the polygon mirror 5 that is an optical deflector. In addition, a line image that is long in the main scanning direction is formed. 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.

  When the polygon mirror 5 rotates at a constant speed, the light beam reflected by the deflecting reflecting surface is deflected at a constant angular velocity. The scanning lens 6 has a constant velocity characteristic in which a light spot by an incident light beam is deflected at a constant angular velocity so as to move at a constant velocity on the surface to be scanned 8 in the main scanning direction (vertical direction in the figure). Therefore, the light spot optically 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. ing. The scanned surface 8 is actually a photosensitive surface of a photosensitive medium as an image carrier.

  In the embodiment of FIG. 1, the diffractive optical element 4 is applied to an optical element that converts a light beam into a line image. However, the scanning optical element 6 that is a third optical element or the first optical element is used. Even when a certain coupling lens is a diffractive optical element, the effect of the present invention is not changed.

  As shown in FIG. 5, the diffractive optical element 4 mounted in FIG. 1 is a multi-step type in which diffractive surfaces 41 are formed stepwise. In order to achieve such a multi-step type, the power of the “diffractive part” of the diffractive surface 41 and the power of the “refractive part” may have the same absolute value and different signs. The diffractive surface thus obtained is inevitably a multi-step type. With such a structure, the relationship between the diffractive surface and the backcut is almost right at any angle, and there is an advantage that not only measurement is easy, but also processing is very easy.

  Furthermore, since the obtained diffractive surface is non-powered, even if there is a decentering between the opposite surfaces, the influence thereof is extremely small, and the required level for processing accuracy can be kept low. In the case of a multi-step type, the machining time can be shortened by adopting shaper machining. The shortening of the processing time is preferable for obtaining a high-precision power diffractive surface because secondary merits such as reduction of heat generation during processing are derived. Further, the power of the lens itself is given as a combination of the power of the entrance surface and the exit surface, but a desired lens power can be obtained by appropriately setting the power on the opposite side even if one surface is non-power.

  Now, the depth corresponding to one backcut along the depth direction of the diffractive surface 41 is referred to as a “step”. There are several parameters that degrade the diffraction efficiency, but this step and surface roughness are particularly problematic. However, these two have different properties that degrade the diffraction efficiency.

  The deterioration of diffraction efficiency when an error due to a step occurs is caused by deterioration of the diffraction efficiency of a desired diffraction order by using a light beam with strong directivity other than the desired diffraction order. On the other hand, the deterioration of the diffraction efficiency when the surface roughness occurs is caused by the deterioration of the diffraction efficiency of a desired diffraction order by generating unnecessary scattered light. Therefore, the possibility of forming an image on the surface to be scanned due to the generation of an undesired light beam is high when an error due to a step that generates a light beam with high directivity occurs. In order to reduce this directivity, the present invention proposes that the surface of the diffractive optical element is intentionally given a predetermined roughness.

The centerline average roughness Ra of the surface of the diffractive optical element necessary for that is given by
Ra ≧ 20nm
It is. However, this surface roughness cannot be increased without limit. If the surface roughness is increased, the diffraction efficiency of the diffractive optical element as a whole is greatly reduced, so a higher-power light source unit is required. It becomes a factor such as an increase in energy supply. Therefore, regarding the upper limit of the centerline average roughness Ra on the surface of the diffractive optical element, in the present invention, Ra ≦ 200 nm
This solves the above problem.

  When the diffractive optical element is molded with a resin, surface roughness occurs when the molded product is released, but if Ra ≧ 20 nm, it is a level that can be sufficiently achieved by a normal resin molding process, as in the present invention. Even if the surface roughness is specified, the molding time is not increased and the cost is not increased.

The “center line average roughness” on the surface of the diffractive optical element is, as shown in FIG. 6, extracted from the roughness curve f (x) by the reference length L in the direction of the average line, The absolute values of deviations from the average line to the measurement curve are summed and defined as an average value, which can be expressed by the following equation.

  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 coupling lenses 2-1 and 2-2 as first optical elements. 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 coupling lenses 2-1 and 2-2 as first optical elements. 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).

  Consider a case where the light source unit is configured as shown in FIGS. In this configuration, the coupling lenses 2-1 and 2-2 are made of resin, and the coupling lenses 2-1 and 2-2 have a diffractive optical surface having a diffractive surface formed as a concentric groove shape on at least one surface. It is good also as an element.

  However, as in the example shown in FIG. 4, when a semiconductor laser array is used for the light source unit, it is preferable not to use the coupling lens as a diffractive optical element. The reason 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 also occurs at each light emitting point completely independently. This is because image deterioration due to variations becomes large. In order to avoid such wavelength dependency, the material of the coupling lens is preferably glass, and an image with stable quality can be formed by using glass.

  In FIG. 4, when a surface emitting semiconductor laser (VCSEL) is used instead of the semiconductor laser array, there is almost no variation in the wavelength of the light beam emitted from each light emitting point. It can be an element.

  In the case of an optical scanning apparatus in which the coupling lens and the cylinder lens as the second optical element can be made of resin, the two lenses can be formed integrally and used as a diffractive optical element. In this way, the number of parts is substantially reduced by one, which is effective for cost reduction.

  FIG. 7 shows 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. 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. 7, a conveyance belt 132 that conveys 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. (A) which shows the example of the diffractive optical element applicable to this invention is a front view, (b) is a right immediate view. It is a graph which shows the example of the centerline average roughness curve of the surface of a 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 as 1st optical element 2-2 Coupling lens as 1st optical element 3 Aperture 4 Diffractive optical element as 2nd optical element 5 Polygon mirror as an optical deflector 6 Scan lens as a third optical element 8 Surface to be scanned

Claims (12)

A light source unit having a light emitting unit, a first optical element that guides a light beam from the light emitting unit to a subsequent optical system, and a second optical that converts the light beam emitted from the first optical element into a line image An optical deflector for deflecting a light beam emitted from the second optical element; and a plurality of light beams deflected by the optical deflector are condensed on the surface to be scanned to form a light spot to form a surface to be scanned. A third optical element for optically scanning the optical scanning device,
At least the third optical element is made of resin,
Any of the first, second, and third optical elements is a diffractive optical element,
An optical scanning device provided with a roughness on the surface of the diffractive optical element so that unnecessary orders of diffracted light generated by the steps of the diffractive optical element are not condensed on the surface to be scanned. A light source unit having a light emitting unit, a first optical element that guides a light beam from the light emitting unit to a subsequent optical system, and a second optical that converts the light beam emitted from the first optical element into a line image An optical deflector for deflecting a light beam emitted from the second optical element; and a plurality of light beams deflected by the optical deflector are condensed on the surface to be scanned to form a light spot to form a surface to be scanned. A third optical element for optically scanning the optical scanning device,
At least the third optical element is made of resin,
Any of the first, second, and third optical elements is a diffractive optical element,
The center line average roughness Ra of the surface of the diffractive optical element is
20 nm ≦ Ra ≦ 200 nm
An optical scanning device that satisfies the requirements.   3. The optical scanning device according to claim 2, wherein the diffractive optical element is made of resin.   4. The optical scanning device according to claim 3, wherein the resin diffractive optical element is a second optical element.   3. The optical scanning device according to claim 2, wherein the first optical element and the second optical element are integrally formed, and the integrated optical element is a resin diffractive optical element.   6. The optical scanning device according to claim 2, wherein the diffractive optical element has a function of correcting a change in a beam waist position accompanying a temperature variation at least in the sub-scanning direction.   7. The optical scanning device according to claim 2, wherein the diffractive surface of the diffractive optical element has a multi-step shape.   8. The optical scanning device according to claim 2, wherein the light source unit is a multi-beam light source unit having a plurality of light emission points, and a first optical element is disposed corresponding to each light emission point, An optical scanning device in which the first optical element is a resin diffractive optical element.   8. The optical scanning device according to claim 2, wherein the light source unit is a multi-beam light source unit having a plurality of light emitting points, and the first optical element through which the light beams emitted from the plurality of light emitting points pass. There is one or more, and the first optical element is made of glass.   8. The optical scanning device according to claim 2, 3, 4, 6, or 7, wherein the light source unit is a multi-beam light source unit using a surface emitting semiconductor laser, and the first optical element is a resin diffractive optical element. Optical scanning device. 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