JP4878905B2 - Optical scanning device, optical writing device, and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning device, an optical writing device, and an image forming apparatus, and can be applied to a digital copying machine, a facsimile, a laser printer, and the like.

  Optical scanning devices are widely known in connection with image forming apparatuses such as optical printers, digital copying machines, and optical plotters. In recent years, along with a demand for price reduction of an image forming apparatus, it is required to realize an image forming apparatus that is not easily affected by changes in environmental conditions, has good image quality, and has high stability and fineness. The optical scanning device and the optical writing device, which are important components of the image forming apparatus, are also required to satisfy the above requirements.

In order to satisfy the above requirements, it is effective to form various lenses used in the optical scanning device with a resin material. Forming various lenses with a resin material has the following advantages.
(1) Light weight.
(2) Molding is possible at low cost.
(3) It is easy to form a special surface shape.
Taking advantage of the fact that it is easy to form a special surface shape, 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. be able to. As one form of the special surface, there is a “diffractive surface shape” in which a refracting surface shape is folded at an appropriate pitch. Since the diffractive surface can add more power than the refractive surface to the lens, it is effective in reducing the number of lenses.

  In order to construct an image forming apparatus having high stability, various types of optical scanning devices have been conventionally devised. The main ones are a combination of a plurality of lenses having opposite powers, and a diffractive surface. In particular, the method using a diffractive surface is effective because it can realize an optical scanning device that is highly stable with respect to temperature with a small number of parts, due to the highly developed molding technology of resin materials. It is a simple method.

However, the method using a diffractive surface has the following problems as specific problems.
1. This makes the optical system sensitive to variations in the wavelength of the incident light beam.
2. Compared with a surface that does not have a diffractive surface shape, unwanted scattered light / regular reflection light and light of an unnecessary diffraction order are likely to be generated.
Above 1. This problem can be avoided to some extent by designing the diffractive surface shape, and various inventions have already been published. However, 2. The above problem is a phenomenon in which a realistic diffractive surface can potentially occur. A clear solution for such a problem has not been proposed, and is not mentioned in the following patent documents, which are publicly known materials.

  When unwanted scattering, specular reflection, or the like occurs on the diffraction surface introduced into the optical scanning device, a part of the scattered and reflected light returns toward the light source as “return light”. Since a general light source includes a device that detects the amount of light and adjusts the amount of emitted light, the “return light” as described above is mixed as noise in the light emission amount adjusting device. For this reason, a light beam whose light amount is not properly adjusted is irradiated onto the surface to be scanned and image formation is performed, which causes deterioration of the formed image quality.

  The diffractive surface functions by having a fine “diffractive surface shape”. In other words, the diffractive surface shape is a set of fine edges. Therefore, the diffraction efficiency is extremely sensitive to disturbance, and unwanted diffracted light, scattered light, and unnecessary reflected light are likely to be generated. In an optical scanning device having a light source having a plurality of light emitting points or a plurality of light source devices, a light beam emitted from one light emitting point is scattered and reflected by the diffraction surface, and its own light emitting point and also the other light emitting point It can happen to return to.

Here, known techniques related to the present invention are listed.
One is to reduce the focus position fluctuation due to temperature change by combining a diffractive surface and a refracting surface in the deflector front optical system (see, for example, Patent Document 1). However, the invention described in Patent Document 1 does not take measures against the problems of the present invention as described later. Further, Patent Document 1 does not mention multi-beam optical scanning in which the same photoconductor is scanned with a plurality of beams.

  Another known technique is to correct fluctuations due to temperature changes in the focus position caused by the scanning optical system using power changes in the diffraction section (see, for example, Patent Document 2 and Patent Document 3). However, the inventions described in Patent Documents 2 and 3 do not take into account the change in the arrangement of the optical elements constituting the first optical system. Further, Patent Documents 2 and 3 do not mention multi-beam optical scanning in which the same photoconductor is scanned with a plurality of beams.

  There has also been proposed a method of correcting a focus position variation due to a temperature change by combining at least three lenses with an optical system on the front side of a deflector without using a diffractive surface (see, for example, Patent Document 4).

  Still another known technique is to reduce a focus position variation due to a temperature change by combining a diffractive surface and a refracting surface in the optical system on the front side of the deflector (see, for example, Patent Document 5). Patent Document 5 disclosing such a technique also refers to multi-beam optical scanning, and describes a technique having two diffractive surfaces on the front side of a deflector.

JP 2004-126192 A JP 2003-337295 A Japanese Patent Application Laid-Open No. 11-223783 JP 2002-214556 A JP, 2005-258392, A As mentioned above, each patent document does not mention the subject which the present invention tends to solve, and the means for solving this.

An object of the present invention is to solve the unsolved problems of the prior art.
Specifically, by attenuating the return light from the diffractive surface, the inappropriateness of the scanning light quantity caused by the return light can be improved, and an optical scanning device, an optical writing device, and a high image quality using the same. An object of the present invention is to provide an image forming apparatus capable of forming the image.
The present invention also provides an optical scanning device, an optical writing device, and an image forming apparatus that can form high-quality images by using the optical scanning device and optical writing device that can effectively remove diffracted light and scattered light of unnecessary orders. The purpose is to do.
Another object of the present invention is to provide an optical scanning device, an optical writing device, and an image forming apparatus using the same, in which one lens having a diffractive surface can have the effect of a plurality of refractive lenses. To do.

An optical scanning device according to the present invention includes a deflector front optical system for shaping a plurality of light beams emitted from a light source unit and guiding the light beams to an optical deflector, and a plurality of light beams deflected by the light deflector as a single object. A multi-beam optical scanning device comprising a scanning lens system for guiding and forming an image on a scanning surface, wherein the deflector front optical system has a function of condensing a plurality of light beams in the sub-scanning direction. The line image forming lens has one diffractive surface, and the diffractive surface is provided on the exit surface of the line image forming lens.

When the diffractive surface is the first surface of the line image forming lens, that is, the incident surface , scattered light or the like peculiar to the diffractive surface is generated, and this scattered light reaches its own light source as return light. Alternatively, in the case of a multi-beam light source, the light beam from one light source is diffracted by the diffraction surface, and the scattered light reaches the other light source. According to the present invention, by providing the diffractive surface on the second surface, that is, the exit surface of the line-image forming lens, the surface on the light source side becomes a normal refracting surface. is there. The merits of providing this diffraction surface as the diffraction surface of the line image forming lens on the exit surface will be described in more detail. When return light is generated on the diffraction surface of the exit surface, the return light first passes through the line image forming lens and is absorbed and attenuated in the line image forming lens. Also, to receive the refraction when the returning light is emitted to the first surface of linear image forming lens, a slight loss occurs even there. For the above reasons, the idea of attenuating the return light by generating the return light on the exit surface of the diffractive optical element is a main part of the present invention.

As a secondary merit produced by providing the diffractive surface on the exit surface, the effective diameter of the diffractive surface can be reduced. The diffractive surface has a folding pitch that becomes narrower toward the off-axis and becomes difficult to mold. Therefore, it is advantageous to make the diffractive surface as small in effective diameter as possible. Since the line image forming lens has a positive power, if the diffractive surface is the exit surface, the positive power refracting surface is the first surface, that is, the incident surface . Is incident on the second surface diffractive surface of the light flux is exit surface is condensed by the first surface of the linear image forming lens from the light source side, the effective diameter of the diffractive surface will be small.

  In the optical scanning device of the present invention, it is preferable that the surface shape of the diffractive surface of the line image forming lens is set so as to cancel the power of the diffractive portion and the power of the refracting portion. The diffractive part is a shape obtained by folding the surface shape of the refracting part with an appropriate step and an appropriate pitch, and has the same power as the refracting part. As shown in FIG. 3, the shape and power of the surface are a combination of the diffraction surface 13 and the refractive surface 12. Usually, since the pitch becomes finer toward the periphery of the lens, it becomes difficult to mold the diffractive part. However, if the power of the diffractive part and the power of the refracting part are set to cancel each other, the diffraction is performed as shown in FIG. This is advantageous when the line-forming lens is molded from resin.

  The surface shape of the diffractive surface employed in the present invention is preferably a multi-step type. The multi-step type refers to a step-like shape in which the angle of the folded portion is a right angle and symmetric with respect to the optical axis. As described above, the shape is a special shape set so as to cancel the power of the diffractive portion and the power of the refracting portion, and the convenience in molding is further improved. Optically, the zero-order light and the first-order and subsequent diffracted lights are the same, which is equivalent to a non-power surface. Therefore, even though this shape is most advantageous in terms of molding, it is equivalent to a parallel plate having no power, so it can be said that it is disadvantageous with respect to return light. However, the above-described problem is avoided because the diffraction surface is a multi-step type on the premise of the above-described configuration in which a diffraction surface is provided on the second surface of the line image forming lens. That is, the multi-step type diffractive surface is resistant to return light, easy to mold, and is a preferred form. With respect to the fact that the diffractive surface is optically equivalent to a non-power surface, there is also an advantage that the insensitivity of the optical performance with respect to decentration is improved, that is, it is less susceptible to decentration.

  The diffractive surface employed in the present invention is preferably 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 of the light emitting section is substantially zero. When temperature variation occurs in the optical scanning device, the wavelength of the light source, the refractive index and curvature of the optical element, etc. change, and the imaging position deviates from the ideal imaging position. That is, a focus position shift occurs. A general semiconductor laser as a light source of an optical scanning device shifts its emission wavelength toward the longer wavelength side when the temperature rises. The change in emission wavelength due to temperature change is called “mode hop”. On the other hand, since there is a characteristic of the diffractive part that "the power of the diffractive part is remarkably dependent on the incident wavelength", the diffractive part is set so that the focus position shift is substantially zero by using a mode hop due to temperature fluctuation. Can be designed. Setting the beam waist position variation due to the temperature change of the light emitting section to be substantially zero is one example for obtaining a better effect of the diffraction surface in the optical scanning device.

  The diffractive surface employed in the present invention preferably has a linear groove shape parallel to the main scanning direction and / or the sub-scanning direction. The power of the diffraction part can be provided independently with respect to the main scanning direction and the sub-scanning direction. As described above, when the independently designed diffractive portions are provided on the same surface, when the diffractive surface is viewed from the direction along the optical axis, the folded portion of the diffractive portion has a concentric elliptical shape. However, it is difficult to mold a concentric elliptical diffraction surface. Therefore, as described above, by forming one surface into a shape (parallel linear groove shape) in which the power of the diffractive portion acts only in a certain direction (main scanning direction and / or sub-scanning direction). This is advantageous.

  The reason why the linear groove shape is advantageous for molding is as follows. Since the diffractive surface of the present invention is formed of a resin, the shape of the diffractive surface is realized by cutting a mold, but in the case of a linear groove shape, as shown in FIG. The tool can be molded simply by running in one direction, and there is no problem in letting the tool escape. If the groove shape is not a straight line, for example, a concentric circle or a concentric ellipse, it takes time to draw the axis of the circle or ellipse, and it is necessary to devise a bite escape. In addition, the effects obtained by making the diffractive surface shape a multi-step type can be achieved. That is, if the shape is stepwise symmetrical with respect to the optical axis, as shown in FIGS. 5 (a) and 5 (b), the angle to which the cutting tool is applied is substantially a right angle, which further improves the convenience of mold forming.

  The light source unit in the present invention can be composed of a plurality of semiconductor laser elements. In addition, the light source unit can be constituted by a semiconductor laser element having a plurality of light emitting points. When there are a plurality of semiconductor laser elements, adjustment corresponding to each light source is possible, and since there are a plurality of light emitting points, the number of light sources can be reduced. It can be compatible that the light source unit is composed of a plurality of semiconductor laser elements and a semiconductor laser element having a plurality of light emitting points. In other words, the light source unit can be configured by using a plurality of semiconductor laser elements having a plurality of light emitting points.

  The semiconductor laser element of the light source unit in the present invention can be a surface emitting type. The diffractive part is sensitive to wavelength variations of the incident light beam. While the effect of the diffractive part uses its characteristics, unwanted wavelength fluctuations degrade optical performance. When a semiconductor laser is used as a light source, mode hopping does not occur in principle in the surface emitting type compared to the edge emitting type. Therefore, the desired effect of the diffractive part is slightly reduced, but the problems peculiar to the diffractive part can be avoided. A typical example of the surface emitting semiconductor laser element is a VCSEL (vertical cavity surface emitting laser).

Removal of unwanted order diffracted light and scattered light is one of the problems to be solved on the diffraction surface. In particular, in the case of a multi-beam optical system, it is necessary to avoid the ghost light generated by one beam from entering the other light source, so it is important to solve the above problem. Normally, an aperture stop is provided in the deflector front optical system in order to obtain a desired beam spot diameter on the surface to be scanned regardless of variations in the divergence angle of the semiconductor laser. A part of unnecessary order diffracted light and scattered light generated on the diffractive surface can be removed by the aperture stop, but this is not sufficient. The front optical system of the first deflector includes light shielding members at a plurality of positions different in the optical axis direction, so that unnecessary orders of diffracted light and scattered light can be removed, which is necessary for obtaining a good image. An optical scanning device can be provided. Furthermore, in the main scanning direction and / or the sub-scanning direction, the beam width when passing through at least one light-shielding member other than the aperture stop is made narrower than when passing through the aperture stop, so that diffracted light of unnecessary order is obtained. And scattered light can be effectively removed.
There is also a method in which the aperture stop is disposed at a position where the light flux width is reduced. However, if the aperture stop is disposed at a position where the beam width is narrowed, the amount of change in the beam spot due to processing error of the aperture width increases, and it cannot be said that the configuration is suitable for solving the problem. FIG. 6 is a sectional view in the sub-scanning direction showing an example of the arrangement of the aperture stop and the light shielding member described above, but the same concept holds true for the main scanning direction.

  As described above, since the diffractive surface can separately add power to the refracting surface, one lens having the diffractive surface can have the effect of a plurality of refracting lenses. Further, a desired power is given to one lens on the refracting surface, and 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 light emitting unit is substantially zero. The function of a diffractive surface can be added to improve stability against temperature fluctuations. For example, the deflector front optical system can be configured such that the optical element having power is a line image forming lens and the other optical power is not provided. As a result, the optical deflector front optical system can be configured with a single lens, and thus the number of components can be reduced. When a color image forming apparatus is configured using a plurality of optical scanning devices, the effect of reducing the number of parts as described above is even greater.

  By configuring an optical writing device using a plurality of optical scanning devices of the present invention, writing can be performed on a plurality of scanned surfaces. As the optical writing device, any one of the optical scanning devices having various configurations described so far can be selected and employed, and the optical deflector can be made common to the plurality of optical scanning devices. As a result, the number of relatively expensive optical deflectors in the optical writing device can be reduced, and the cost can be reduced. Since the optical deflector is the largest heat source in the optical scanning device, it is advantageous in terms of temperature stabilization of each optical scanning device. In addition, since an undesired mode hop of the semiconductor laser due to temperature fluctuation can be reduced, the configuration is advantageous also for an optical scanning device in which a diffractive surface is introduced.

  As a configuration of the optical writing device in which the optical deflector is common to a plurality of laser beams, the light beam of each optical scanning device is incident substantially symmetrically with respect to the sub-scanning section including the rotation axis of the optical deflector ( “Opposite scanning method”) and a method in which the light beam of each optical scanning device is deflected by the same reflecting surface of the optical deflector (“one-side scanning method”). FIG. 7 schematically shows an example of a counter scanning method in the case where a two-stage optical deflector is used.

  Further, the scanning method is not limited to the form in which the light beam is incident and deflected in parallel to the normal line of the reflecting surface of the optical deflector. The present invention can also be applied to a case where a light beam is incident at an angle with respect to the normal line of the reflecting surface of the optical deflector. In this specification, this method is called an oblique incidence method. FIG. 8 schematically shows an example of an oblique scanning type optical writing device for counter scanning. As an advantage of the oblique incidence method, it is possible to write four color images with a single stage optical deflector, so that the cost for configuring the optical writing device can be reduced. When the oblique incidence method is applied, scanning line bending and wavefront aberration deterioration are unavoidable problems, so the surface shape of the scanning lens needs to correspond to the obliquely incident light beam. The effect of the present invention can be utilized as it is, and the cost can be reduced by combining with the main configuration of the present invention described above.

The image forming apparatus according to the present invention forms a latent image by optically scanning a photosensitive image carrier with an optical scanning device, and visualizes the latent image with a developing unit to obtain an image. The apparatus employs any one of the optical scanning apparatuses described so far as the optical scanning apparatus.
In addition, the image forming apparatus according to the present invention forms a latent image corresponding to each color by performing light scanning with a light scanning device on a plurality of photosensitive image carriers, and visualizes the latent images with a developing unit. An image forming apparatus that obtains a color image, and employs any one of the optical scanning apparatuses described so far as the optical scanning apparatus.
The image forming apparatus according to the present invention employs an optical writing apparatus including the optical scanning apparatus described so far as an apparatus for performing optical writing on a photosensitive image carrier. It is.

The optical scanning device according to the present invention and an image forming apparatus using the same will be supplemented with some explanation.
Various photosensitive image carriers can be used. For example, a silver salt film can be used as the image carrier. In this case, a latent image is formed by writing by optical scanning, and this latent image can be visualized by processing by a normal silver salt photographic process. Such an image forming apparatus can be used as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.
As the photosensitive image carrier, it is also possible to use a color developing medium (positive printing paper) that develops color by the thermal energy of the light spot during optical scanning. In this case, a visible image can be directly formed by optical scanning.

  As the photosensitive image bearing member, a photoconductive photosensitive member can also be used. As the photoconductive photoreceptor, a sheet-like one such as zinc oxide paper can be used, or a drum-like or belt-like one made of a selenium photoreceptor or an organic photo semiconductor is used repeatedly. Can do. When a photoconductive photoreceptor is used as an image carrier, an image can be formed by an electrophotographic process described below. That is, an electrostatic latent image is formed by uniform charging of the photoreceptor and optical scanning by the optical scanning device, and the electrostatic latent image is visualized as a toner image by development. The toner image is directly fixed on the photoconductor when the photoconductor is in the form of a sheet such as zinc oxide paper, and transfer paper or an OHP sheet when the photoconductor can be used repeatedly. It is transferred and fixed on a sheet-like recording medium such as (plastic sheet for overhead projector).

The transfer of the toner image from the photoconductive photosensitive member to the sheet-like recording medium may be performed directly from the photosensitive member to the sheet-like recording medium (direct transfer method), or from the photosensitive member to the intermediate transfer belt once. After the transfer to the intermediate transfer medium, the intermediate transfer medium may be transferred to the sheet-like recording medium (intermediate transfer method). Such an image forming apparatus can be implemented as an optical printer, an optical plotter, a digital copying apparatus, or the like.
In addition, an image forming apparatus according to the present invention includes a plurality of the photosensitive members arranged along a conveyance path of a sheet-like recording medium, and forms an electrostatic latent image for each photosensitive member using a plurality of optical scanning devices. The toner image obtained by visualizing them can be transferred and fixed to the same sheet-like recording medium, and can be implemented as a tandem type image forming apparatus that synthetically obtains a color image or a multicolor image.

According to the present invention, the deflector front optical system has a resin line image forming lens having a function of condensing a plurality of light beams in the sub-scanning direction, and the line image forming lens has one diffractive surface. However, since this diffraction surface is provided on the exit surface of the line-image forming lens, the number of parts required to configure the optical scanning device is reduced, and at the same time, it is not easily affected by environmental conditions such as temperature fluctuations. An optical scanning device capable of stably performing high-precision optical scanning can be obtained. Therefore, it is possible to reduce the amount of material used to produce the optical scanning device, which leads to a reduction in the environmental load with respect to the amount of mined resources and the amount of plastic waste discharged.

  Embodiments of an optical scanning device, an optical writing device, and an image forming apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 shows an entire embodiment of an optical scanning device according to the present invention. A plurality of light beams emitted from a light source 1 made of a semiconductor laser are coupled to a subsequent optical system by a coupling lens 2. In the description of this embodiment, for the sake of simplicity, the light source has a single light emission point. However, even in the case of a light source having a plurality of light emission points, the effects of the present invention can be obtained similarly. The light beam that has passed through the coupling lens 2 passes through the opening of the aperture 3 so that the periphery of the light beam is blocked and the cross-sectional shape is shaped, and enters the line image forming lens 4 that is a line image imaging optical system. To do. The line image forming lens 4 is arranged so as to have no power in the main scanning direction and to have a positive power in the sub scanning direction, and focuses the incident light beam only in the sub scanning direction. It is configured so as to be condensed as a long line image in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 5 which is a deflector. The line image forming lens 4 has a diffraction surface on the exit surface (second surface).

  The light beam reflected by the deflecting reflection surface is transmitted through the imaging scanning lens 6 forming the scanning optical system while being deflected at a constant angular velocity as the polygon mirror 5 rotates at a constant speed, and the light beam is guided to the surface to be scanned. The optical path is bent by the bending mirror 7 for focusing, and the light is condensed as a light spot on the photoconductive photosensitive member 8 forming the substance of the surface to be scanned, and the surface to be scanned is optically scanned. In FIG. 1, the scanning optical system has a single-lens configuration with only the imaging scanning lens 6, but the effect of the present invention can be similarly obtained even with a configuration using a plurality of imaging scanning lenses. Every time the photosensitive member 8 is optically scanned, the deflected light beam is reflected by the synchronous mirror 9 prior to the optical scanning, and this reflected light is condensed by the synchronous lens 10 on the synchronous detector 11 in the main scanning direction. The synchronization detector 11 receives the reflected light and outputs a detection signal. Based on this output, the write start timing of optical scanning is determined.

The “spot diameter of the light spot” in this specification is defined by 1 / e2 intensity in the line spread function of the light intensity distribution in the light spot on the surface to be scanned. The “line spread function” is defined as follows. When the light spot light intensity distribution: f (Y, Z) is defined by the main scanning direction and sub-scanning direction coordinates: Y, Z with reference to the center coordinates of the light spot formed on the surface to be scanned, the Z direction Line spread function: LSZ is LSZ (Z) = ∫f (Y, Z) dY (Integration is performed for the full width of the light spot in the Y direction)
The line spread function in the Y direction: LSY is defined by
LSY (Y) = ∫f (Y, Z) dZ (Integration is performed for the entire width of the light spot in the Z direction)
Defined by
These line spread functions: LSZ (Z), LSY (Y) are generally in the shape of a substantially Gaussian distribution, and the spot diameters in the Y direction and Z direction are determined by these line spread functions: LSZ (Z), LSY (Y ) Is given by the width in the Y and Z directions of a region that is 1 / e2 or more of the maximum value. The spot diameter defined above by the line spread function can be easily measured by scanning the light spot at a constant speed with a slit, receiving the light passing through the slit with a photodetector, and integrating the amount of light received. There are also commercially available devices for performing such measurements.

表１に示す材質データにおいて、「中央値」とあるのは、基準温度：２５℃における使用波長に対する屈折率、「波長飛び」とあるのは、モードホップにより波長飛びを生じたときの屈折率、「温度変動」とあるのは、温度が基準温度から２０度上昇したときの屈折率である。モードホップによる「波長飛び」は、余裕を見て０．８ｎｍの波長変化を想定している。 The data of the glass material (referred to as “glass 1”) and the resin material (referred to as “resin 2”) used in Example 1 are as shown in the material data shown in Table 1.

In the material data shown in Table 1, the “median” is the refractive index with respect to the wavelength used at the reference temperature: 25 ° C., and the “wavelength jump” is the refractive index when the wavelength jump occurs due to the mode hop. “Temperature fluctuation” is the refractive index when the temperature rises 20 degrees from the reference temperature. “Wavelength skip” due to mode hopping assumes a wavelength change of 0.8 nm with a margin.

Further, the optical system data after the optical deflector in Example 1 is given to the optical system data after the optical deflector in Table 2.

  In Table 2 above, Rm is “paraxial curvature in the main scanning direction”, Rs is “paraxial curvature in the sub-scanning direction”, and Dx and Dy are “from the origin of each optical element to the origin of the next optical element” Relative distance ". The unit is mm. For example, regarding Dx and Dy with respect to the optical deflector, the origin of the incident surface of the first scanning imaging lens 6 (the optical axis position of the incident side surface) when viewed from the rotation axis of the polygon mirror 5 that is the optical deflector is: It is 43.3 mm apart in the optical axis direction (X direction, left-right direction in FIG. 2), and 2.9 mm away in the main scanning direction (Y direction, vertical direction in FIG. 2). A dust-proof glass 14 having a thickness of 1.9 mm made of glass 1 is disposed between the second scanning imaging lens 7 and the surface to be scanned, as shown in FIG. Each surface of the first scanning imaging lens 6 and the second scanning imaging lens 7 is an aspherical surface, and the entire surface has a “non-arc shape given by Formula 1” in the main scanning direction, and a sub-scanning section (optical axis and This is a special surface in which the curvature in a virtual cross section parallel to the sub-scanning direction changes in the main scanning direction according to “Equation 2”.

"Non-arc shape"
Paraxial radius of curvature in the main scanning section: Rm, distance in the main scanning direction from the optical axis: Y, conic constant: K, higher order coefficients: A1, A2, A3, A4, A5,. Depth: X is expressed by the following “Expression 1”.

"Change of curvature in sub-scan section"
The expression representing the state in which the curvature in the sub-scanning section: Cs (Y) (Y: coordinates in the main scanning direction with the optical axis position as the origin) changes in the main scanning direction is expressed in the sub-scanning section including the optical axis. Radius of curvature: Rs (0), B1, B2, B3,...

Table 3 lists the coefficients of the incident side surface (special surface) of the first scanning imaging lens 6.

Table 4 lists the coefficients of the exit side surface (special surface) of the first scanning imaging lens 6.

Table 5 lists the coefficients of the incident side surface (special surface) of the second scanning imaging lens 7.

Table 6 lists the coefficients of the exit side surface (special surface) of the second scanning imaging lens 7.

  The specific configuration of each component of the optical system is as follows. The optical elements constituting the deflector front optical system are appropriately arranged so that the imaging positions in the main scanning / sub-scanning directions of all the optical systems are in the vicinity of the surface to be scanned.

"light source"
The semiconductor laser 1 as the light source has a design emission wavelength of 655 nm, and when the temperature rises by 1 ° C. with respect to the standard temperature of 25 ° C., the emission wavelength shifts to 0.20 nm and the longer wavelength side. The mode hop assumes a wavelength change of 0.8 nm as described above. Here, two semiconductor lasers each having one light emitting point are provided, but of course, a semiconductor laser array or a VCSEL may be used.

"Coupling lens"
The coupling lens 2 is a glass lens as described above, and has a focal length of 15 mm and is arranged to have a function of converting a light beam from a light source into a substantially parallel light beam. The coupling lens 2 is aspheric on both sides, and the aspheric coefficient is not disclosed, but the wavefront aberration of the coupled light beam is sufficiently corrected by the aspheric surface. The semiconductor laser 1 and the coupling lens 2 are fixedly held by a holding member made of a material having a linear expansion coefficient of 2.3 × 10 −5. The material of the coupling lens 2 is made of glass, and has a refractive index described in the material data in Table 1.

"aperture"
The aperture 3 has a “rectangular opening” having an opening diameter in the main scanning direction: 5.4 mm and an opening diameter in the sub-scanning direction: 2.28 mm, and shapes the light beam coupled by the coupling lens 2. At this time, as shown in FIG. 6, a light shielding member is provided between the light source 1 and the coupling lens 2, and between the anamorphic optical element 4 and the deflecting unit. These light shielding members are the apertures 3.

"Linear image forming lens"
In the line image forming lens 4, the incident side surface is a “cylindrical surface having power only in the sub-scanning direction”, and the exit side surface is a “stepped diffraction surface in which the diffraction grooves are elliptical”. The curvature radius of the incident surface in the sub-scanning direction is 63.4 mm. The exit surface is a diffractive surface, and scattered light, reflected light, and unnecessary-order diffracted light from the diffractive surface do not return to the light source. The phase function φ (y, z) of the diffractive surface is expressed by the following equation.
φ (y, z) = C1 · Y2 + C2 · Z2
C1 = −0.0006199, C2 = −0.007537
This diffractive surface is formed on a toroidal surface having a radius of curvature in the main scanning direction of 425.4 mm and a radius of curvature in the sub-scanning direction of 35 mm, and a surface that becomes a “stepped diffractive surface in which the diffraction grooves are elliptical” is formed on the second surface. Is formed. At this time, P1 = −P2 (P1: power of the refracting part, P2: power of the diffractive part) in both the main scanning and sub-scanning directions, and as shown in FIG. Step type. That is, the power of the second surface is non-power for both main scanning and sub-scanning. If this diffractive surface is on the incident surface side, the diffractive part has a surface perpendicular to the optical axis, so that strong reflection occurs at the incident light beam diffracting part, and it follows the reverse optical path. Return to the semiconductor laser and induce interference. Alternatively, it enters the other semiconductor laser and induces interference. For this reason, it is preferable to set the step-shaped diffraction surface on the exit surface side.

"Optical deflector"
The polygon mirror 5 which is an optical deflector has four reflecting surfaces and an inscribed circle radius of 7 mm.

  The soundproof glass 15 is made of “Glass 1”, has a thickness of 1.9 mm, and an inclination angle α from the y direction (vertical direction in FIG. 2): 16 degrees. Further, the angle θ between the traveling direction of the light beam incident from the light source side and the “traveling direction of the light beam reflected toward the position where the image height is 0 on the scanned surface 8” by the deflection reflecting surface: θ is 60.55 degrees. It is.

回折面の効果で、それぞれのビームウエスト位置変動が低減されていることがわかる。 Table 7 shows beam waist position fluctuations in the main scanning direction and the sub-scanning direction in the first embodiment.

It can be seen that the beam waist position variation is reduced by the effect of the diffraction surface.

The data of the glass material (referred to as “glass 2”) and the resin material (referred to as “resin 2”) used in Example 2 are as shown in the material data (wavelength 780 nm) shown in Table 8. The format conforms to that of Example 1.

＊：Ｘ，Ｚの括弧内の値は、第２走査結像レンズＴｉｌｔ前の値である。 The optical system data shown in Table 9 is given as optical system data after the optical deflector in the second embodiment. The optical system of Example 2 is an oblique incidence method in which a light beam is incident on the optical deflector at an angle of 3.3 ° in the sub-scan section. The plurality of light beams deflected by the optical deflector are incident on a common first scanning imaging lens at an angle with respect to the main scanning section, and the second scanning having the optical path of each light beam as the optical axis in the sub-scanning direction. An image is formed on the surface to be scanned by the imaging lens. That is, the second scanning imaging lens has an optical axis in the sub-scanning direction having an angle with respect to the main scanning section. As shown in FIG. 2, the scanning imaging lens is composed of a first scanning imaging lens 6 and a second scanning imaging lens 6 ′, and between the second scanning imaging lens 6 ′ and the scanned surface 8. Is provided with a dust-proof glass 14 having a thickness of 1.9 mm made of “glass 2”.

*: Values in parentheses of X and Z are values before the second scanning imaging lens Tilt.

"Special tilt eccentric surface"
The exit surface of the second scanning imaging lens 6 ′ has no curvature in the sub-scanning direction, and changes the tilt angle in the sub-scanning section along the main scanning direction, as represented by “Expression 3”. The surface shape. In this specification, the surface shape is called a “special tilt eccentric surface” as a special case of the “special surface”. One of the means for performing good image formation by the oblique incidence method is the introduction of a special tilt eccentric surface.

Table 10 lists the coefficients of the incident side surface of the first scanning imaging lens 6.

Table 11 lists the coefficients of the exit side surface of the first scanning imaging lens 6.

Table 12 lists the coefficients of the incident side surface of the second scanning imaging lens 7.

Table 13 lists the coefficients of the exit side surface of the second scanning imaging lens 6 '.

  The specific configuration of each element of the optical system is as follows. The optical elements constituting the deflector front optical system are appropriately arranged so that the imaging positions in the main scanning direction and / or sub-scanning direction of the entire optical system are in the vicinity of the surface to be scanned.

"light source"
The semiconductor laser 1 as the light source has a design emission wavelength of 780 nm, and when the temperature rises by 1 ° C. with respect to the standard temperature of 25 ° C., the emission wavelength shifts to the long wavelength side by 0.25 nm. The mode hop assumes a wavelength change of 0.8 nm as described above. Here, two semiconductor lasers each having one light emitting point are provided, but of course, a semiconductor laser array or a VCSEL may be used.

"Coupling lens"
The coupling lens 2 does not exist in the second embodiment, and its function is integrated with the line image forming lens 4.

"aperture"
The aperture 3 has a “rectangular opening” having an aperture diameter of 5.0 mm in the main scanning direction and an aperture diameter of 1.12 mm in the sub scanning direction, and shapes the divergent light beam emitted from the light source. Guide to imaging lens.

"Linear image forming lens"
In the line image forming lens 4, the incident side surface is an anamorphic convex surface, and the exit side surface is a "stepped diffractive surface whose diffraction groove is elliptical". By providing the diffractive surface on the exit surface, scattered light, reflected light, and unnecessary-order diffracted light from the diffractive surface do not return to the light source.

The radius of curvature of the incident surface is 45.8 mm in the main scanning direction and 28.2 mm in the sub-scanning direction. The phase function φ (y, z) of the diffractive surface is expressed by the following equation.
φ (y, z) = C1 · Y2 + C2 · Z2
C1 = −0.00178218, C2 = −0.0323343272
This diffractive surface is provided on an anamorphic concave surface having a main scanning radius of curvature of 147 mm and a sub-scanning radius of curvature of 8.1 mm, and forms a surface that becomes a “stepped diffractive surface in which the diffraction grooves are elliptical”. P1 = −P2 (P1: power of the refracting portion, P2: power of the diffracting portion) in both the main scanning and sub-scanning directions, and the completed diffractive surface has a stepped shape, that is, a multi-step type. That is, the power of the second surface is non-power for both main scanning and sub-scanning. If this diffractive surface is on the incident surface side, the diffractive part will have a surface perpendicular to the optical axis, so that strong reflection will occur at the incident light beam diffracting part, and it will follow the reverse optical path to the semiconductor. Return to the laser and induce interference. Alternatively, it enters the other semiconductor laser and induces interference. For this reason, it is preferable to set the step-shaped diffraction surface on the exit surface side.

"Optical deflector"
The polygon mirror 5 as an optical deflector has six reflecting surfaces and an inscribed circle radius of 13 mm.

  The soundproof glass 15 is made of “Glass 1”, has a thickness of 1.9 mm, and an inclination angle α from the y direction (vertical direction in FIG. 2) is 8 degrees. The angle θ between the traveling direction of the light beam incident from the light source side and the “traveling direction of the light beam reflected toward the position where the image height is 0 on the scanned surface 8” by the deflecting reflection surface is 60 degrees. .

光偏向器前側の単一のレンズに設けられた回折面の効果で、それぞれのビームウエスト位置変動が低減されていることがわかる。 Table 14 shows beam waist position fluctuations in the main scanning direction and the sub-scanning direction in the second embodiment.

It can be seen that each beam waist position variation is reduced by the effect of the diffractive surface provided on the single lens on the front side of the optical deflector.

  Examples of the optical writing device using the optical scanning device described above are shown in FIGS. In the example of the optical writing apparatus shown in FIG. 7, four laser beams are deflected and scanned by a polygon mirror 5 which is a common optical deflector, and four scanning imaging lenses 6 arranged corresponding to the four laser beams are used. An image is written on the scanned surface 8 by converging and scanning the laser beam on the surface of the drum-shaped photoconductor which is the scanned surface 8. The polygon mirror 5 is formed with two deflection reflection surfaces in the direction of the rotation axis, and the deflection reflection surface at each stage distributes the laser beams from the two light sources to the left and right to deflect and reflect them. A total of four scanning imaging lenses 6 are arranged on the left and right with the deflecting / reflecting surfaces of each stage interposed therebetween, and the four laser beams pass through the scanning imaging lenses 6. In FIG. 7, reference numeral 7 denotes a mirror for bending the direction of travel of each laser beam that has been deflected and transmitted through the scanning imaging lens 6 to guide it to the corresponding scanned surface 8.

  FIG. 8 shows another example of the optical writing device using the optical scanning device according to the present invention. The scanning imaging lens 6 is divided into a first scanning imaging lens and a second scanning imaging lens. One scanning imaging lens is also used for two laser beams, and two polygonal mirrors 5 as optical deflectors are sandwiched between the two scanning beams, one on each side, and the second scanning imaging lens corresponds to four laser beams. 4 are arranged. Reference numeral 7 denotes a mirror for bending the direction of travel of each laser beam transmitted through the first scanning imaging lens 6 and further transmitted through the second scanning lens to guide it to the corresponding scanned surface 8.

  Since the optical writing device shown in FIGS. 7 and 8 employs one of the optical scanning devices according to the above-described embodiments, it is possible to effectively remove unnecessary-order diffracted light and scattered light. In addition, it is difficult to be affected by temperature fluctuations, and high-precision optical writing can be performed stably.

  FIG. 9 shows an embodiment of an image forming apparatus according to the present invention. This image forming apparatus is an example of a laser printer that forms an image by executing a series of electrophotographic processes including charging, exposure, development, transfer, fixing, and cleaning around a photosensitive image carrier 1110. . The laser printer 1000 has a photoconductive photosensitive member formed in a cylindrical shape as a photosensitive image carrier 1110. Around the image carrier 1110, a charging roller 1121, a developing device 1131, a transfer roller 1141, and a cleaning device 1151 are arranged as charging means. A “corona charger” can also be used as the charging means. In the image forming apparatus 1000, an optical scanning device 1171 that performs optical scanning with the laser beam LB is provided, and exposure by optical writing is performed between the charging roller 1121 and the developing device 1131.

  In FIG. 9, reference numeral 1161 denotes a fixing device, reference numeral 1181 denotes a paper feed cassette, reference numeral 1191 denotes a registration roller pair, reference numeral 1201 denotes a paper feeding roller, reference numeral 1211 denotes a conveyance path, reference numeral 1221 denotes a paper discharge roller pair, and reference numeral 1231 denotes paper discharge. A tray and a symbol P indicate transfer sheets as sheet-like recording media, respectively.

  When performing image formation, an image carrier 1110 that is a photoconductive photosensitive member is rotated at a constant speed in the clockwise direction, the surface thereof is uniformly charged by a charging roller 1121, and a laser beam LB is used by an optical scanning device 1171. An electrostatic latent image is formed upon exposure by optical writing. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 1131, and a toner image is formed on the image carrier 1110. The cassette 1181 storing the transfer paper P is detachable from the main body of the image forming apparatus 1000. When the cassette 1181 is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper P is fed by the paper feed roller 1201. Then, the transferred transfer paper P is added to the registration roller pair 1191 at the leading end. The registration roller pair 1191 feeds the transfer paper P to the transfer unit in time with the toner image on the image carrier 1110 moving to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 1141. The transfer paper P to which the toner image has been transferred is sent to the fixing device 1161, where the toner image is fixed by the fixing device 1161, passes through the conveyance path 1211, and is discharged onto the tray 1231 by the discharge roller pair 1221. The surface of the image carrier 1110 after the toner image has been transferred is cleaned by a cleaning device 1151 to remove residual toner, paper dust, and the like.

FIG. 10 schematically shows another example of the image forming apparatus according to the present invention, and shows an embodiment of an image forming apparatus capable of forming a multicolor image or a color image. Reference numerals in FIG. 10 indicate the following meanings or members, respectively.
Y: Yellow M: Magenta C: Cyan K: Black These Y, M, C, and K mean that they correspond to the color components of yellow, magenta, cyan, and black, respectively.
1Y, 1M, 1C, 1K: photoreceptor corresponding to Y, M, C, K 2Y, 2M, 2C, 2K: charger corresponding to Y, M, C, K 20: writing unit 4Y, 4M, 4C, 4K: Developers corresponding to Y, M, C, K 5Y, 5M, 5C, 5K: Cleaning means corresponding to Y, M, C, K 6Y, 6M, 6C, 6K: Y, M, C, K Corresponding transfer charging means 80: transfer belt 30: fixing means

  In FIG. 10, four drum-shaped photoconductors 1Y, 1M, 1C, and 1K are arranged at equal intervals with the rotation center axis in parallel. The photoconductors 1Y, 1M, 1C, and 1K are rotated in the clockwise direction in FIG. 10, and the chargers 2Y, 2M are sequentially arranged around the photoconductors 1Y, 1M, 1C, and 1K in the rotation direction. , 2C, 2K, developing devices 4Y, 4M, 4C, 4K, transfer charging means 6Y, 6M, 6C, 6K, and cleaning means 5Y, 5M, 5C, 5K. The charging members 2Y, 2M, 2C, and 2K are charging members that constitute a charging device for uniformly charging the surface of the photoreceptor. The surface of the photosensitive member between the charging member and the developing members 4Y, 4M, 4C, and 4K is irradiated with a beam by the optical writing device 20 having the optical scanning device according to the present invention, and the photosensitive members 1Y, 1M, An electrostatic latent image corresponding to each color is formed on the surface of 1C and 1K. The electrostatic latent image on the surface of each photoconductor is developed with toner corresponding to each color by the developing devices 4Y, 4M, 4C, and 4K, and a toner image is formed on each photoconductor surface. A transfer belt 80 is disposed below the photoconductors 1Y, 1M, 1C, and 1K, and toner images of respective colors are sequentially transferred onto the transfer belt 80 by the transfer charging units 6Y, 6M, 6C, and 6K. As a result, a color image is formed. This color image is transferred to a transfer sheet (not shown), and finally the image is fixed on the recording test by the fixing means 30.

  According to the above-described image forming apparatus according to the present invention, the above-described optical scanning apparatus and optical writing apparatus according to the present invention are used as the optical scanning apparatus and optical writing apparatus, so that diffracted light and scattered light of unnecessary orders can be generated. It can be effectively removed, is not easily affected by temperature fluctuations, etc., can perform high-precision optical writing stably, and can form extremely good images.

1 is a perspective view showing an embodiment of an optical scanning device according to the present invention. FIG. 6 is an optical arrangement diagram showing another embodiment of the optical scanning device according to the present invention from the main scanning corresponding direction. It is a model figure for demonstrating the general shape of the refractive part and diffraction part in an optical element. It is a model figure which shows the example of a diffraction surface shape at the time of setting so that the power of the diffraction part in an optical element and the power of a refractive part may cancel. It is a perspective view which shows typically the various examples of metal mold | die shaping | molding for forming a diffraction surface. FIG. 6 is an optical arrangement diagram in a sub-scanning section schematically showing an example of arrangement of apertures in the deflector front optical system of the optical scanning device. It is an optical arrangement | positioning figure which shows the example of the horizontal scanning opposed scanning system optical writing apparatus. It is an optical arrangement | positioning figure which shows the example of the diagonally-scanning opposed scanning optical writing apparatus. 1 is a front view showing an embodiment of an image forming apparatus. 1 is a front view illustrating an embodiment of an image forming apparatus capable of multicolor image formation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Coupling lens 3 Aperture 4 Line image formation lens 5 Polygon mirror as an optical deflector 6 Scanning imaging lens 7 Mirror 8 Scanned surface 9 Synchronous mirror 10 Synchronous lens 11 Synchronous detection part 12 General shape of refractive surface 13 General diffraction surface shape 14 Dust-proof glass 15 Sound-proof glass

Claims (16)

A deflector front optical system for shaping and guiding a plurality of light beams emitted from the light source unit to the optical deflector;
A multi-beam optical scanning device having a scanning lens system for guiding a plurality of light beams deflected by the optical deflector onto a single scanned surface to form an image,
The deflector front optical system has a resin line image forming lens having a function of condensing a plurality of light beams in the sub-scanning direction,
The line image forming lens has one diffractive surface,
The diffractive surface has a multi-step shape,
An optical scanning device characterized in that the power of the diffraction surface is non-power . 2. The optical scanning device according to claim 1, wherein the diffractive surface is provided on an exit surface of the line image forming lens. 3. The optical scanning device according to claim 1, wherein the power of the diffractive surface is a combination of the power of the diffractive portion and the power of the refracting portion. 4. The optical scanning device according to claim 3, wherein the angle of the folded portion of the diffraction portion is a right angle. 5. The optical scanning device according to claim 1, wherein the diffraction surface has a linear groove shape parallel to the main scanning direction and / or the sub-scanning direction. 6. The optical scanning device according to claim 1, wherein the light source unit includes a plurality of semiconductor laser elements. 7. The optical scanning device according to claim 1, wherein the light source unit is constituted by a semiconductor laser element having a plurality of light emitting points. 8. The optical scanning device according to claim 1, wherein the light source unit is formed of a semiconductor laser element, and the semiconductor laser element is a surface emitting type. 9. The optical scanning device according to claim 1, wherein the deflector front optical system includes light shielding members at a plurality of different positions in the optical axis direction. 10. The optical scanning device according to claim 9, wherein at least one of the plurality of light blocking members is an aperture stop for setting a beam diameter on the surface to be scanned, and the aperture stop in the main scanning direction and / or the sub scanning direction. An optical scanning device in which the width of a beam when passing through at least one light shielding member other than that becomes narrower than when passing through an aperture stop. 11. The optical scanning device according to claim 1, wherein the deflector front side optical system is an optical scanning device in which the optical element having power is a line image forming lens and the other optical power is not provided. An optical writing device for writing an image on a surface to be scanned by optical scanning, comprising: a plurality of optical scanning devices according to any one of claims 1 to 11; Writing device. 13. The optical writing device according to claim 12, wherein the optical deflector included in the plurality of optical scanning devices included in the optical writing device is common. 2. An image forming apparatus for forming a latent image by performing optical scanning with a light scanning device on a photosensitive image carrier and visualizing the latent image with a developing unit to obtain an image. An image forming apparatus using the optical scanning device according to any one of 11 to 11. In an image forming apparatus that forms a latent image corresponding to each color by performing optical scanning with a light scanning device on a plurality of photosensitive image carriers, and visualizes the latent image with a developing unit to obtain a color image. An image forming apparatus using the optical scanning device according to claim 1, wherein optical scanning of the carrier is performed. 13. An image forming apparatus for forming a latent image by performing optical writing on a photosensitive image carrier with an optical writing device, and visualizing the latent image with a developing unit to obtain an image. Alternatively, an image forming apparatus using the optical writing device according to 13.

Images