JP2010128023A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner that suppresses displacement of each luminous flux passing through each of a plurality of lens parts constituting a lens, from the optical axis due to a variation in the ambient temperature as much as possible with a simple configuration. <P>SOLUTION: The optical scanner includes: a deflection member 5 which deflects a laser beam; an optical lens 6 which is formed by integrating a first lens part 6a which passes the laser beam scanned by the deflection member 5 and a second lens part 6b which passes the laser beam having passed through the first lens part 6a; and lens supporting parts S1, S2 which support the optical lens 6. Viewing from the direction perpendicular to the optical axes of the first lens part 6a and the second lens part 6b, the lens supporting parts S1, S2 are provided in a region between the optical axes of the first lens part 6a and the second lens part 6b or substantially on the optical axes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic laser beam printer (LBP), a digital copying machine, and a laser which records image information by deflecting a light beam emitted from a light source by a deflecting member and optically scanning the surface to be scanned through a lens. The present invention relates to an optical scanning device suitably used for a facsimile or the like. In particular, the present invention relates to an optical scanning device that is miniaturized using an optical lens in which two lens portions are integrated.

  Due to the rapid spread of laser beam printers (LBP), digital copying machines, laser facsimiles, etc. in recent years, the demand for miniaturization of optical scanning devices has increased, and a scanning optical system that scans the surface to be scanned with a light beam is compactly arranged. However, various means for reducing the space have been proposed.

  For example, a light beam emitted from a light source means is optically modulated in accordance with an image signal in an optical scanning device such as a laser beam printer, a digital copying machine, or a laser facsimile, which is an electrophotographic image forming apparatus. Then, the light-modulated light beam is periodically deflected by a deflecting member made of a polygon mirror, and focused on a photosensitive recording medium, that is, a photosensitive drum surface by an imaging optical system having fθ characteristics. The spot on the photosensitive drum surface forms an electrostatic latent image in accordance with main scanning by deflection of the polygon mirror and sub-scanning by rotation of the photosensitive drum, and image recording is performed.

  FIG. 14 shows a schematic configuration of a main part of an optical scanning device used in a conventionally known image forming apparatus.

  In the optical scanning device shown in FIG. 14, the light beam reflected by the rotating polygon mirror (rotating polygon mirror) 205 is imaged on the surface to be scanned such as the photosensitive drum 210 via the imaging optical system 206. The imaging optical system 206 includes imaging lenses 206a and 206b, reflection mirrors 207 and 208, etc., and forms an image of a light beam in a straight line using the two imaging lenses 206a and 206b.

  Although there is one that scans the light beam with only one imaging lens, errors such as curvature of field and deterioration of aberrations of the image plane cannot be corrected with only one imaging lens, or with one imaging lens. When trying to compensate for optical performance, the design is extremely difficult and expensive. For this reason, usually, two or more imaging lenses are often used to scan the light beam.

  However, if a plurality of imaging lenses are used, a space for arranging the lenses and a space for holding the lenses are required, which hinders downsizing of the optical scanning device.

  For example, in the optical scanning device shown in FIG. 14, since the polygon mirror 205 and the two imaging lenses 206a and 206b are in a straight line, the width in the horizontal direction becomes long, which hinders downsizing of the optical scanning device.

  Further, in the optical scanning device shown in FIG. 15, the width in the horizontal direction is shortened by using a folding mirror 307 between the two imaging lenses 306 (306a, 306b). However, on the contrary, it is necessary to provide a space for arranging the lens in the vertical direction and a space for holding the lens, which increase in the vertical direction, which hinders downsizing of the optical scanning device.

  Therefore, by integrating the two imaging lenses, a method for reducing the size of an image forming apparatus such as an optical scanning device and a laser beam printer (LBP), a digital copying machine, or a laser facsimile having the optical scanning device. Has been proposed.

For example, Patent Document 1 discloses an optical scanning device using an fθ lens in which two lens portions are integrated vertically. As shown in FIG. 13 attached to the present application, the optical scanning device shown in Patent Document 1 causes the light beam from the polygon mirror 101 to enter the fθ lens 102a, reflects the light beam that has passed through the fθ lens 102a by the reflection mirror 103, and again. The light enters the fθ lens 102b. Thereafter, the surface of the photosensitive drum 104 is irradiated. The fθ lens 102 (102a, 102b) is fixed to the lens holder 105, and the lens holder 105 and the reflection mirror 103 are fixed to the housing 106. The fθ lens 102 is formed by vertically integrating a first lens portion 102a on which the light beam reflected by the polygon mirror 101 is incident and a second lens portion 102b on which the light beam reflected by the reflection mirror 103 is incident. It consists of a plastic lens system such as acrylic.
JP-A-8-194180

  An optical element such as the imaging lens (fθ lens) is deformed by a change in ambient temperature and causes an optical path error. Further, even if the optical element is slightly deformed due to a change in ambient temperature, the optical path error caused by the deformation becomes a size that cannot be ignored on the surface to be scanned. In particular, when the deformation of the optical element occurs in the sub-scanning direction, the irradiation position changes, the scanning line is bent, the spot shape is deteriorated, and the quality of the output image is deteriorated.

  The configuration of the conventional optical scanning device shown in FIG. 13 has a configuration in which the lower portion of the lower lens portion 102a of the fθ lens 102 integrated vertically is held by a lens holder 105. However, in such a configuration, when the ambient temperature changes, the upper lens portion 102b is deformed with the lens holding portion 105a below the lower lens portion 102a as a fulcrum. Therefore, the upper lens portion 102b is affected not only by its own deformation but also by the deformation of the lower lens 102a, and the amount of deformation of the lens is increased as compared with the case of using one fθ lens. Become.

  As described above, since the fθ lens 102 holds the lower portion of the lower lens portion 102a, the upper and lower lens portions 102a and 102b are lenses below the lower lens portion 102a when the ambient temperature changes. The holding portion 105a is deformed as a fulcrum. For this reason, the deformation directions of the upper and lower lens portions 102a and 102b are the same, and the direction in which the optical path error occurs in the respective lens portions 102a and 102b is also the same direction, so that the irradiation position change may be particularly large.

  The present invention solves the above-mentioned problems.

  That is, the object of the present invention is to reduce the amount of displacement as much as possible with a simple configuration even if the light beam transmitted through each lens unit is displaced from the optical axis due to a change in ambient temperature in a lens in which a plurality of lenses are integrated. Is to provide a simple optical scanning device.

The above object is achieved by an optical scanning device according to the present invention. In summary, the present invention provides a deflection member that deflects and scans a laser, a first lens portion that transmits laser scanned by the deflection member, and a second lens that transmits laser after passing through the first lens portion. In an optical scanning device having an optical lens integrated with a part, and a lens support part that supports the optical lens,
When viewed from the direction orthogonal to the optical axes of the first lens unit and the second lens unit, within a range sandwiched between the optical axes of the first lens unit and the second lens unit or substantially on the optical axis. The optical scanning device is provided with the lens support portion.

  According to the present invention, in a lens in which a plurality of lenses are integrated, a light beam transmitted through each lens unit due to a change in ambient temperature suppresses a displacement amount from the optical axis as much as possible with a simple configuration, and prevents deterioration of image quality. It is possible to provide an optical scanning device that can perform the above operation.

  Hereinafter, the optical scanning device according to the present invention will be described in more detail with reference to the drawings.

Example 1
An embodiment of an optical scanning device according to the present invention will be described with reference to FIGS. In particular, FIGS. 4 and 5 show the overall configuration of the optical scanning device of this embodiment.

  4 and 5, the optical scanning device 20 includes an optical box 21 that houses various optical elements, and an upper lid 22 that seals the optical box 21. The upper lid 22 is provided with a transparent glass (dust-proof glass) 23 for dust-proofing the laser beam exit.

  A semiconductor laser 1 as a light source is provided in the optical box 21 and emits a light beam that is light-modulated by image information. A divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by a collimator lens 2 and shaped into a desired optimum beam shape by an aperture (aperture stop) 3.

  The optical scanning device 20 further includes a cylindrical lens 4 having a predetermined refractive power in the sub-scanning direction and a deflecting member 5. The deflecting member 5 is composed of, for example, an optical deflector (polygon mirror) that deflects a light beam emitted from the first optical system including the collimator lens 2, the cylindrical 4, and the aperture 3, and driving means (not shown) such as a motor. )) At a predetermined speed.

  Referring to FIG. 1, the optical scanning device 20 integrates two lens portions 6a and 6b in the vertical direction, and forms an image of the deflected and scanned light beam in a spot shape on the surface to be scanned (for example, the photosensitive drum 9). It has an optical lens (imaging lens) 6 as imaging means. The two lens portions 6a and 6b of the imaging lens 6 have different powers (refractive indexes), and are hereinafter referred to as “double-pass lens 6”. Here, power refers to the refractive index of the lens. The power of the lens in this embodiment is adjusted by changing the spherical shape of the lens surface without changing the material of each lens part. For example, the refractive index can be increased by reducing the radius of the lens spherical surface.

  4 and 5, the folding mirrors 7 and 8 as reflecting means provided in the optical scanning device 20 reflect the light flux based on the image information deflected and reflected by the deflecting member 5, and thereby the scanned surface 9. Leading up.

  In particular, the folding mirror 7 reflects the light beam transmitted through one lens portion 6a of the double-pass lens 6 and transmits the reflected light beam through the other lens portion 6b in the opposite direction. The folding mirror 7 and the double pass lens 6 constitute a second optical system.

  In addition to the above, the optical scanning device 20 includes, in addition to these, a synchronization detection element for determining the writing start timing of a light beam, and a folding mirror (BD mirror) for guiding the light beam to the synchronization detection element. Etc.

  In the present embodiment, the light beam modulated and emitted from the semiconductor laser 1 is made into a substantially parallel light beam by the collimator lens 2 and enters the cylindrical lens 4. Of the substantially parallel light beam incident on the cylindrical lens 4, the substantially parallel light beam is emitted as it is in the main scanning section. Further, the beam converges in the sub-scan section and forms a substantially linear image on the deflection surface of the polygon mirror 5 that is a deflection member. The light beam is adjusted to a desired beam shape by the aperture 3 provided between the cylindrical lens 4 and the polygon mirror 5. The light beam deflected and reflected by the deflecting surface is condensed on the photosensitive drum surface 9 via the double pass lens 6 and the folding mirrors 7 and 8, and the polygon mirror 5 is rotated to rotate the photosensitive drum surface 9 on the main scanning direction. Scan at a constant speed. Thus, image recording is performed on the photosensitive drum surface 9 as a recording medium.

  As described above, the first optical system including the semiconductor laser 1, the collimator lens 2, the aperture 3, and the cylindrical lens 4 is housed in the frame (optical box) 21. A deflecting member made up of a polygon mirror 5 and a second optical system made up of a double pass lens 6 and folding mirrors 7 and 8 are also housed in a frame (optical box) 21.

  Here, the double pass lens 6 is made by molding a plastic material such as acrylic or polycarbonate, and the first lens portion 6a and the second lens portion 6b can be integrally molded and realized at low cost. ing. Further, as described above, the optical scanning device 20 can be reduced in size by integrating the two imaging lens portions 6a and 6b in the vertical direction.

  The optical scanning device 20 of the present embodiment shown in FIGS. 4 and 5 includes a 2-in-1 optical scanning device 20 in which two first and second optical systems are provided for each polygon mirror 5. An example is given. However, at least one or more of the first and second optical systems may be provided for one polygon mirror 5.

  Next, a method for positioning the double pass lens 6 in the sub-scanning direction will be described.

  1 and 6 are partially enlarged views of the vicinity of the double-pass lens 6 in the optical scanning device 20 of the present embodiment shown in FIGS. Similarly, FIG. 2 is a front view of the double pass lens 6 as seen from the optical axis direction, and FIG. 3 is a perspective view of the double pass lens 6 and the double pass lens holder 11.

  In FIG. 1 and the like, the folding mirror 7 located on the left side of the double pass lens 6 reflects and reflects the light beam transmitted through one lens portion (first lens portion) 6a of the double pass lens 6. 10 is transmitted in the opposite direction to the other lens part (second lens part) 6b. The double pass lens 6 is held by a lens holder 11 fixed to the optical box 21.

  As shown in FIGS. 2 and 3, the protrusions 12 and 13 are provided on the surfaces 61 and 62 at the longitudinal ends of the double pass lens 6. As shown in FIG. 1, the protrusions 12 and 13 are sandwiched between the optical axes of the double pass lens 6 and the first and second lens portions 6a and 6b arranged in the vertical direction in this embodiment. Provided in the area.

  That is, as shown in FIG. 1, the double-pass lens 6 is provided with protrusions 12 and 13 on the surfaces 61 and 62 at the end portions in the longitudinal direction. The protrusions 12 and 13 are within the range between the optical axis B and the optical axis A when viewed from the direction orthogonal to the optical axis B and optical axis A of the upper lens portion 6b and the lower lens portion 6a (see FIG. 1 in the shaded area (including on each optical axis).

  Conventionally, since the lower part of the lens is supported, the thermal expansion of the lower lens part is added to the upper lens. For this reason, the deviation between the optical axis of the upper lens portion and the laser has increased. However, according to the configuration of the present embodiment, the lens is supported between the optical axes of the upper and lower lens portions 6a and 6b even if the lens support portion is deformed as a fulcrum. Therefore, it is possible to suppress the amount of displacement of the optical axis due to thermal deformation in one lens unit from being added to the amount of displacement of the optical axis of the other lens unit.

  Further, as in the present embodiment, in the case where each lens portion of the double pass lens is a convex lens (a convex lens having power in the sub-scanning direction), the direction in which the optical axes of the upper and lower lens portions are displaced when the lens is thermally deformed. Are in opposite directions. For this reason, as will be described later, the irradiation position shifts due to thermal deformation of the lens. However, the direction of the shift is opposite to each other in each lens unit, and as a result, the irradiation position shift cancels each other. be able to.

  The optical path error (displacement of the optical axis of the lens unit) that occurs when the ambient temperature changes in the configuration of this embodiment will be described in detail below with reference to FIG.

  The folding mirror 7 reflects the light beam transmitted through one lens unit 6a of the double pass lens 6 and transmits the reflected light beam through the other lens unit 6b in the opposite direction. In the figure, reference numeral 10 is a light beam deflected and reflected by the polygon mirror 5, and symbols A and B are light beams that pass through the upper and lower lens portions 6 a and 6 b of the double pass lens 6, respectively. It is assumed that it coincides with the optical axis. Reference numerals A ′ and B ′ denote the optical axes of the upper and lower lens portions 6 a and 6 b of the double pass lens 6 that are changed when the ambient temperature changes.

  An optical element such as an imaging lens (fθ lens) is deformed by thermal expansion or thermal contraction due to a change in ambient temperature, so that the design light of the imaging lens against the light beam reflected by the polygon mirror at that time. The axis shifts, causing an optical path error.

  7, the sub-scanning direction positioning support portion S1 (S2), that is, the positioning projection 12 (13) of the double-pass lens 6 is sandwiched between optical axes that pass through the upper and lower lens portions 6a and 6b of the double-pass lens 6. A description will be given of an optical path error that occurs when it is provided within the specified range.

  When an ambient temperature change occurs in the optical scanning device 20, the double pass lens 6 is thermally expanded or contracted to cause deformation. At that time, the sub-scanning direction is deformed in the arrow direction shown in FIG. 7 with the positioning protrusion 12 (13) as a fulcrum. At the same time, the optical axes of the upper and lower lens portions 6a and 6b of the double pass lens 6 change from A and B to A 'and B'. Therefore, an optical path error is generated for the original light fluxes A and B.

  In this case, since the upper and lower lens portions 6a and 6b of the double pass lens 6 are deformed in opposite directions, the optical axes A ′ and B ′ of the upper and lower lens portions 6a and 6b of the double pass lens 6 are the original optical axis A. , B fluctuate in the opposite direction. Therefore, even if the irradiation position or the like changes due to the deformation of the lower lens portion 6a of the double pass lens 6, the upper lens portion 6b of the double pass lens 6 is deformed in a direction in which the change of the irradiation position is canceled.

  If the positioning protrusion 12 (13), that is, the positioning support portions S1 and S2 satisfy the formula (1) described in detail in Example 2 described later, the lower lens portion of the double pass lens 6 is used. The optical path error generated in 6a is theoretically canceled by the optical path error generated in the upper lens portion 6b of the double pass lens 6.

  That is, when the amount of change in the irradiation position is ΔB shown in FIG. 7, ΔB is the sum of the irradiation position change due to the optical path error of A ′ and the irradiation position change due to the optical path error of B ′. The effect of is canceled and ΔB = 0.

  Next, an optical path error that occurs when the center Ox of the positioning support portions S1 and S2 of the double pass lens 6 is provided on the optical axis (or substantially on the optical axis) of the double pass lens 6 will be described with reference to FIG. .

  As in FIG. 7, when the ambient temperature changes in the optical scanning device 20, the double-pass lens 6 undergoes thermal expansion or thermal contraction and deformation. At that time, in the sub-scanning direction, the supporting portion S1 (S2), that is, the positioning projection 12 (13) is used as a fulcrum to deform in the arrow direction shown in FIG. The optical axis also changes from A and B to A ′ and B ′, and an optical path error is generated.

  In the case of FIG. 8, the upper lens portion 6b of the double-pass lens 6 is farther away from the positioning projection 12 (13) than in the case of FIG. Further, since the optical path error generated in the upper lens portion 6b of the double pass lens 6 is not canceled as in the case of FIG. 7, an optical path error is generated by the amount of deformation and the change of the optical axis B. However, since the positioning projection 12 (13) is provided on the optical axis of the lower lens portion 6a of the double pass lens 6, the optical axis of the lower lens portion 6a does not change even if the double pass lens 6 is deformed. can do. In other words, when the change amount of the irradiation position is ΔB shown in FIG. 8, ΔB is the sum of the irradiation position change due to the optical path error of A ′ and the irradiation position change due to the optical path error of B ′. Since there is no optical path error of A ′ (A ′ = 0), ΔB = B ′.

<Comparative example>
Next, referring to FIG. 9, the optical path generated when the positioning support portion S <b> 1 (S <b> 2) of the double pass lens 6 is provided outside the range sandwiched between the optical axes of the upper and lower lens portions 6 a and 6 b of the double pass lens 6. The error will be described. Here, as shown in FIG. 9, the lower part of the double-pass lens 6 is held directly on the optical box 21 or in contact with the lens holder 15 of the lens holder 11 attached to the optical box 21. .

  7 and 8, when the ambient temperature changes in the optical scanning device 20, the double-pass lens 6 undergoes thermal expansion or thermal contraction and deformation. At this time, the sub-scanning direction is deformed in the direction of the arrow shown in FIG. 9 with the lens holding portion 15 as a fulcrum, and the optical axes of the upper and lower lens portions 6a and 6b of the double pass lens 6 are changed from A, B to A ′, B Changes to 'and causes an optical path error.

  In the case of FIG. 9, since the upper and lower lens portions 6a and 6b of the double pass lens 6 are deformed in the same direction, the optical axes A ′ and B ′ of the upper and lower lens portions 6a and 6b of the double pass lens 6 are the original. It fluctuates in the same direction with respect to the optical axes A and B.

  Therefore, as in the case of FIG. 8, the upper lens portion 6b of the double-pass lens 6 is far away from the positioning support portion S1 (S2). It becomes larger than the case of 8. Furthermore, since the fluctuation directions of the optical axes of the upper and lower lens portions 6a and 6b of the double pass lens 6 are the same, the optical path error is greatly deteriorated. That is, when the amount of change in the irradiation position is ΔB shown in FIG. 8, ΔB is the sum of the irradiation position change due to the optical path error of A ′ and the irradiation position change due to the optical path error of B ′. By adding the influences of the optical path error of ‘ΔB’ = A ′ + B ’.

  As described above, the following configuration is preferable in an optical scanning device that achieves miniaturization using a lens in which an imaging lens is integrated vertically.

  That is, on the surface of the imaging lens in the longitudinal direction, within the range sandwiched between the optical axes that pass through the upper and lower lens parts, or on the optical axis (or substantially on the optical axis), the sub-scanning direction It is better to provide a positioning projection.

  Furthermore, as will be described in detail in Example 2 described later, by adopting a configuration that satisfies Equation (8), the influence of an optical path error caused by a change in ambient temperature can be minimized.

  As shown in FIGS. 2 and 3, the double pass lens 6 is positioned in the sub-scanning direction by fitting the projections 12 and 13 with the recesses 11a and 11b of the double pass lens holder 11, respectively. It is fixed to the lens holder 11 with an adhesive, a spring or the like.

  Thus, the protrusions 12 and 13 and the recesses 11a and 11b of the double pass lens holder 11 are fitted to form the double pass lens 6, that is, the sub scanning direction positioning support portions S1 and S2 of the imaging lens 6. To do. A plurality of sub-scanning direction positioning support portions S <b> 1 and S <b> 2 may be provided on each end face of the double pass lens 6.

  In this embodiment, the upper and lower lens portions of the double pass lens 6 are both convex lenses, but the present invention is not limited to this. In general, in both concave and convex lenses, the more the light beam deviates with respect to the optical axis, the more the spot shape on the surface to be scanned is deformed, causing image quality deterioration. Therefore, even if one or both are concave lenses, the effect of the present invention can be obtained.

(Example 2)
In this embodiment, when the lens portions of the double pass lens are mutually convex lenses (convex lenses having power in the sub-scanning direction), the configuration of the first embodiment is further improved. That is, the position of the center Ox of the positioning support portion S1 (S2) that supports the double pass lens 6 is further optimized.

  Here, the powers in the sub-scanning direction of the upper lens unit 6b and the lower lens unit 6a are n1 and n2, respectively. As seen from the longitudinal direction of the imaging lens 6 as shown in FIG. 6, from the center Ox of the positioning support portions S1 and S2 with respect to the optical axes A and B of the lower lens portion 6a and the upper lens portion 6b of the double pass lens 6, respectively. Are the distances L1 and L2, respectively.

  At this time, when the powers n1 and n2 in the sub-scanning direction of the upper lens unit 6b and the lower lens unit 6a are n1> n2, it is more preferable that L1 <L2. Conversely, when n1 <n2, it is more preferable that L1> L2. By doing so, the irradiation position change due to the temperature change of the lens can be further reduced.

  More preferably, the position at which the center Ox of the positioning support portion S1 (S2) that supports the double-pass lens 6 is disposed substantially coincides with a position that satisfies the relational expression L1 / L2 = n2 / n1. The reason will be described below.

  As shown in FIG. 6, the temperature rise amounts of the upper lens unit 6b and the lower lens unit 6a with respect to the ambient temperature are t1 and t2, respectively. As described above, the power in the sub-scanning direction of the upper lens unit 6b and the lower lens unit 6a is set to n1 and n2, respectively. As seen from the longitudinal direction of the imaging lens 6 as shown in FIG. 6, from the center Ox of the positioning support portions S1 and S2 with respect to the optical axes A and B of the lower lens portion 6a and the upper lens portion 6b of the double pass lens 6, respectively. Are the distances L1 and L2, respectively. then,

It is best to provide the center Ox of the positioning support portions S1 and S2 in the sub-scanning direction of the double pass lens 6 at a position satisfying the relational expression, and to minimize the irradiation position change when the ambient temperature change occurs. Can do.

  A method for deriving the expression (1) will be briefly described with reference to FIGS.

  In order to explain as simply as possible, FIGS. 16 and 17 show the case where one lens is used. In the figure, 101 is an imaging lens, 201 is incident light on the lens 101, 202a and 202b are emitted light from the lens 101, and 301 is a surface to be scanned.

  As shown in FIG. 16, it is assumed that the optical axis of the lens changes in the direction of the arrow from C to C ′ when the ambient temperature changes. At that time, as shown in FIG. 17, when the optical axis is shifted with respect to the incident light beam, the refractive index balance between the upper and lower sides of the incident light beam is lost, and the light beam is bent. That is, the emitted light shown in FIG. 16 changes from 202a to 202b. As a result, an error Δx in the optical axis direction (a shift amount C ′ of the optical axis) and an irradiation position change Δz occur at the image forming point on the scanned surface 301.

  When Δx increases, the aberration deteriorates and the imaging spot on the surface to be scanned 301 collapses, so that sufficient image quality cannot be obtained.

  When Δz increases, an irradiation position error occurs, which leads to image defects such as color misregistration and color unevenness.

  However, in the case of FIG. 16, since the directions of the optical axes are opposite to each other, the deviation of the irradiation position is canceled as a result. On the other hand, when the deviation of the optical axis is the same direction as shown in FIG. 19, the displacement direction of the irradiation position is the same, so that the deviation of the irradiation position is not canceled when the temperature of the lens changes.

  Here, a formula for deriving the irradiation position change amount Δz will be described.

  When an ambient temperature change occurs, the lens 101 is deformed around its positioning support portion (not shown). That is, when the linear expansion coefficient of the lens 101 is K, the temperature change around the lens is t, and the distance from the positioning support portion of the lens 101 to the optical axis center is L, the change amount of the optical axis of the lens 101 (optical axis) The deviation amount is expressed by the following function.

  Since the irradiation position change amount Δz is determined by the power (refractive index) n of the lens 101 in the sub-scanning direction and the optical axis shift amount C ′, Δz is expressed by the following function.

  In general, it can be said that n and C 'are in a substantially proportional relationship. Therefore, Expression (3) can be replaced with Expression (4).

  When Expression (4) is applied to the double-pass lens 6 of the present invention, Δz1 represents an irradiation position error generated by the lower lens portion 6a of the double-pass lens 6 when an ambient temperature change occurs.

It becomes. Similarly, when an ambient temperature change occurs, an irradiation position error Δz2 generated by the upper lens portion 6b of the double pass lens 6 is

It becomes. Description of the variables n1, n2, t1, t2, L1, and L2 is omitted because it has been described above.

  K is a linear expansion coefficient of the double-pass lens 6, and in the case of the double-pass lens 6 in which the upper and lower lens parts are integrated, the lower lens part 6a and the upper lens part 6b have the same value.

  As described above, if the irradiation position error Δz1 and the irradiation position error Δz2 are the same in opposite directions, the irradiation position error on the surface to be scanned is eventually eliminated as shown in FIG. It will be. That is, it is good to have a configuration that satisfies the following formula.

  When the equations (5), (6), and (7) are arranged, the following relational expression is derived.

  Here, the lenses are the same member and are considered to have substantially the same temperature (t1 = t2). That is,

In the case of satisfying the above, it is possible to minimize the irradiation position change due to the temperature change of the lens.

  The temperature differences t1 and t2 from the ambient temperature of each lens unit can be regarded as substantially the same. Therefore, the ratio t2 / t1 can be approximated to 1. This value can be treated as almost unchanged even if the surrounding environment changes.

  Hereinafter, specific numerical examples will be described.

  For example, the power n1 and n2 in the sub-scanning direction of the lower lens portion 6a and the upper lens portion 6b of the double pass lens 6 are respectively

In FIG. 6, the positioning support of the double pass lens 6 in the sub-scanning direction is performed from the optical axis A that transmits the lower lens portion 6a of the double pass lens 6 and the optical axis B that transmits the upper lens portion 6b. The distances L1 and L2 to the center Ox of the parts S1 and S2 are expressed by the following equation (1):

A configuration satisfying the above relationship is preferable.

  For the above reasons, in this embodiment, when the powers in the sub-scanning direction of the lower lens unit 6a and the upper lens unit 6b are n1 and n2, respectively, since n1 <n2, L1> L2.

  In the optical scanning device in which the positioning of the double-pass lens 6 in the sub-scanning direction is configured as described above, the divergent light beam emitted from the light source 1 becomes a parallel light beam by the collimator lens 2 and enters the cylinder lens 4, and the aperture The amount of light is limited by 3. Since the cylinder lens 4 has refractive power only in the sub-scanning direction, the light beam in the main scanning direction is incident on the polygon mirror 5 as it is, but the light beam in the sub-scanning direction is confined by the cylinder lens 4 near the deflecting reflection surface of the polygon mirror 5. Imaged. Accordingly, the light beam incident on the polygon mirror 5 becomes a latent image that is long in the main scanning direction, and is changed by the rotation of the polygon mirror 5 in the arrow direction. The light beam deflected by the polygon mirror 5 is incident on one lens portion 6 a of the double pass lens 6, reflected by the folding mirror 7, then incident on the other lens portion 6 b of the double pass lens 6, and further reflected by the folding mirror 8. Then, an image is formed on the surface to be scanned. At that time, the upper and lower lens portions 6a and 6b of the double-pass lens 6 distribute the deformation of the lens due to the temperature change substantially evenly between the upper and lower lenses, even if there is a change in the surrounding temperature, and are deformed in opposite directions. Let Accordingly, the irradiation position is changed in a direction in which the irradiation position change generated in the lower lens unit 6a is returned to the original position by the upper lens unit 6b. Therefore, even if ambient temperature changes occur, it is possible to perform optical scanning with high accuracy while minimizing the deterioration of the aberration on the image plane and the change of the irradiation position.

  Next, a positioning method of the double pass lens in the main scanning direction and the optical axis direction will be described.

  FIG. 10 is a partially enlarged view of the vicinity of the double pass lens 6 of the optical scanning device 20 of the present embodiment. Similarly, FIG. 11A is a front view of the double-pass lens viewed from the optical axis direction, and FIG. 11B is a bottom view. FIG. 12 is a perspective view of the double pass lens 6 and the double pass lens holder 11.

  In FIG. 10, the folding mirror 7 located on the left side of the double pass lens 6 reflects the light beam transmitted through one lens portion 6 a of the double pass lens 6, and the other lens portion in a direction opposite to the reflected light beam 10. 6b is transmitted. The double pass lens 6 is held by a lens holder 11.

  As shown in FIGS. 11 and 12, a protrusion 14 is provided at the center of the longitudinal direction on the surface of the double-pass lens 6 that does not transmit the light beam. On the other hand, the double-pass lens holder 11 is provided with a corresponding recess 11c, and the protrusion 14 is fitted with the recess 11c of the double-pass lens holder 11. As a result, the double pass lens 6 is positioned in the main scanning direction and fixed to the double pass lens holder 11 with an adhesive, a spring, or the like. That is, the protrusion 14 and the concave portion 11c of the double pass lens holding body 11 are fitted to constitute the double pass lens 6, that is, the positioning support portion S3 of the imaging lens 6 in the main scanning direction. A plurality of main scanning direction positioning support portions S3 may be provided in the central portion in the longitudinal direction.

  With the above-described configuration, the double-pass lens 6 distributes the deformation of the lens due to the temperature change substantially evenly at both ends in the longitudinal direction even when the ambient temperature changes. Therefore, even if ambient temperature changes occur, deterioration of aberrations on the image plane, changes in irradiation position, etc. are suppressed to a minimum, and optical scanning is performed with high accuracy.

  In this embodiment, as shown in FIGS. 11 and 12, the protrusions 12, 13, and 14 for positioning the double-pass lens 6 in the main scanning direction and the sub-scanning direction are fitted into the recesses 11a, 11b, and 11c. Let And it was set as the structure which can also position in the said optical axis direction by abutting on the optical axis direction.

  In order to suppress the deterioration of the aberration of the image plane and the change of the irradiation position due to the ambient temperature change, it is more preferable to have the above-described configuration in the main scanning direction as well as in the sub scanning direction. .

  As described above, the optical scanning device 20 of the present invention is an optical scanning device that achieves miniaturization using a lens in which an imaging lens is integrated in the vertical direction. Then, at the end in the longitudinal direction of the imaging lens, a projection is provided in a region sandwiched by optical axes that respectively transmit the upper and lower lens portions or substantially on the optical axis. It was decided to perform positioning in the sub-scanning direction. Thereby, even if the surrounding temperature change arises, the deterioration of the aberration of an image surface, the change of an irradiation position, etc. can be suppressed.

  Similarly, in the main scanning direction, a projection is provided at a substantially central portion in the longitudinal direction of the imaging lens, and the projection is used to position the lens holder in the main scanning direction. Thereby, even if the surrounding temperature change arises, the deterioration of the aberration of an image surface, the change of an irradiation position, etc. can be suppressed.

  With the above configuration, an optical scanning device using a lens in which the imaging lens is integrated in the vertical direction, and when the lower portion of the lens is supported as shown in the conventional example, An increase in the amount of lens deformation due to a temperature change can be avoided. In addition, a high-quality image can be output with a simple configuration.

(Example 3)
In the present embodiment, the optical scanning device 20 of the first or second embodiment is applied to an image forming apparatus.

(Overall configuration of image forming apparatus)
FIG. 20 shows a schematic cross section of an electrophotographic full color printer which is an embodiment of an image forming apparatus to which the optical device 20 according to the present invention is applied.

  In this embodiment, the image forming apparatus 100 includes four image forming units (image forming units) P (PY, PM, PC, PBk). That is, the image forming unit PY that forms a yellow image, the image forming unit PM that forms a magenta image, the image forming unit PC that forms a cyan image, and the image formation that forms a black image Part PBk. These four image forming units PY, PM, PC, and PBk are arranged in a line at regular intervals.

  Each image forming unit PY, PM, PC, PBk has an image forming unit that forms an image on a recording material. That is, the image forming means in each of the image forming units PY, PM, PC, and PBk has a drum type electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 9 (9Y, 9M, 9C, 9Bk). ing. Further, around each photosensitive drum 9Y, 9M, 9C, 9Bk, a primary charger 31 (31Y, 31M, 31C, 31Bk) and a developing device 32 (32Y, 32M, 32C, 32Bk) constituting an image forming unit. Is placed. Further, a transfer roller 33 (33Y, 33M, 33C, 33Bk) and a drum cleaner device 34 (34Y, 34M, 34C, 34Bk) are arranged around the photosensitive drum 9, respectively. Below the primary chargers 31Y, 31M, 31C, and 31Bk and the developing devices 32Y, 32M, 32C, and 32Bk, scanning optical devices, that is, laser exposure devices 20 (20A and 20B) are installed.

  Each developing device 32Y, 32M, 32C, 32Bk contains yellow toner, magenta toner, cyan toner, and black toner, respectively.

  Each of the photosensitive drums 9Y, 9M, 9C, and 9Bk is a negatively charged OPC photosensitive member having a photoconductive layer on an aluminum drum base, and is driven in a direction indicated by an arrow (clockwise in FIG. 1) by a driving device (not shown). Direction) at a predetermined process speed.

  Primary chargers 31Y, 31M, 31C, and 31Bk as primary charging means bring the surface of each photosensitive drum 9Y, 9M, 9C, and 9Bk to a predetermined negative potential by a charging bias applied from a charging bias power source (not shown). Charge uniformly.

  The developing devices 32Y, 32M, 32C, and 32Bk as developing means incorporate toner, and attach toner of each color to the electrostatic latent images formed on the photosensitive drums 9Y, 9M, 9C, and 9Bk, respectively. Develop (visualize) as an image.

  Transfer rollers 33Y, 33M, 33C, and 33Bk as primary transfer units are respectively connected to the respective photosensitive drums 9Y, 9M, 9C, and the intermediate transfer belts 35 at the respective primary transfer portions T1 (T1Y, T1M, T1C, and T1Bk). It is arranged so as to be able to contact 9Bk.

  The drum cleaners 34Y, 34M, 34C, 34Bk as drum cleaning means transfer residual toner remaining at the time of primary transfer on the photosensitive drums 9Y, 9M, 9C, 9Bk to the photosensitive drums 9Y, 9M, 9C, 9Bk. Remove from.

  The intermediate transfer belt 35 is disposed on the upper surface side of each of the photosensitive drums 9Y, 9M, 9C, and 9Bk, and is stretched between the secondary transfer counter roller 36 and the tension rollers 37 and 38. The secondary transfer counter roller 36 is disposed so as to be in contact with the secondary transfer roller 39 via the intermediate transfer belt 35 in the secondary transfer portion T2. The intermediate transfer belt 35 is made of a dielectric resin such as a polycarbonate, a polyethylene terephthalate resin film, a polyvinylidene fluoride resin film, or the like.

  Further, a fixing device 50 as an image heating unit that heats and fixes an image formed on the recording material S is installed downstream of the secondary transfer portion T2 in the conveyance direction of the recording material S.

  The exposure apparatus 20 (20A, 20B) is composed of laser light emitting means, a polygon lens, a reflection mirror, and the like that emit light corresponding to time-series electric digital pixel signals of given image information. The exposure device 20 (20A, 20B) exposes the photosensitive drums 9Y, 9M, 9C, 9Bk to expose the photosensitive drums 9Y, 9M, 9C charged by the primary chargers 31Y, 31M, 31C, 31Bk. , An electrostatic latent image of each color corresponding to the image information is formed on the surface of 9Bk.

  Next, an image forming operation by the image forming apparatus having the above configuration will be described.

  When an image formation start signal is issued, the photosensitive drums 9Y, 9M, 9C, and 9Bk of the image forming units PY, PM, PC, and PBk that are rotationally driven at a predetermined process speed are respectively connected to primary chargers 31Y, 31M, It is uniformly negatively charged by 31C and 31Bk. The exposure device 20 (20A, 20B) is a scanning optical device that emits color-separated image signals input from the outside from a laser light emitting element, and passes through a polygon mirror, an imaging lens, a folding mirror, and the like. An electrostatic latent image of each color is formed on each photosensitive drum 9Y, 9M, 9C, 9Bk.

  First, in the image forming unit PY, yellow is developed by the developing device 32Y in which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 9Y is applied to the electrostatic latent image formed on the photosensitive drum 9Y. The toner is attached to make a visible image as a toner image. This yellow toner image is driven by a transfer roller 33Y to which a primary transfer bias (a reverse polarity (positive polarity) to toner) is applied in a primary transfer portion T1Y between the photosensitive drum 9Y and the transfer roller 33Y. Primary transfer is performed on the intermediate transfer belt 35.

  The intermediate transfer belt 35 onto which the yellow toner image has been transferred is moved to the image forming unit PM side. Also in the image forming unit PM, in the same manner as described above, the magenta toner image formed on the photosensitive drum 9M is superimposed on the yellow toner image on the intermediate transfer belt 35, and then the primary transfer unit T1M. Transcribed.

  At this time, the transfer residual toner remaining on the photosensitive drums 9Y and 9M is scraped off and collected by a cleaner blade or the like provided in the drum cleaner devices 34Y and 34M.

  Similarly, cyan and black toner images formed by the photosensitive drums 9C and 9Bk of the image forming unit PC and PBk on the yellow and magenta toner images superimposed and transferred on the intermediate transfer belt 35 are transferred to the primary transfer. Overlapping is performed sequentially at portions T1C and T1Bk. As a result, a full-color toner image is formed on the intermediate transfer belt 35. The transfer residual toner remaining on the photosensitive drums 9C and 9Bk is scraped off and collected by a cleaner blade or the like provided in the drum cleaner devices 34C and 34Bk.

  On the other hand, a transfer sheet (paper) S as a recording material selected from the paper feed cassette 41 or the manual feed tray 42 is fed through a transport path.

  The transfer sheet S is secondarily transferred by a registration roller in accordance with the timing at which the front end of the full color toner image on the intermediate transfer belt 35 is moved to the secondary transfer portion T2 between the secondary transfer counter roller 36 and the secondary transfer roller 39. It is conveyed to the transfer part T2. Full-color toner images are collectively transferred to the transfer sheet S conveyed to the secondary transfer portion T2 by the secondary transfer roller 39 to which a secondary transfer bias (polarity opposite to the toner (positive polarity)) is applied. Is done.

  The transfer sheet S on which the full-color toner image is formed is conveyed to the fixing device 50, and the full-color toner image is heated and pressed at the fixing nip N between the first fixing member 51 and the second fixing member 52. Then, it is heat-fixed on the surface of the transfer paper S. Thereafter, the transfer sheet S is discharged onto the discharge tray 43 on the upper surface of the main body by the discharge roller, and a series of image forming operations is completed.

  The secondary transfer residual toner and the like remaining on the intermediate transfer belt 35 are removed and collected by a belt cleaning device (not shown).

  The above is the image forming operation at the time of single-sided image formation. The image forming apparatus according to the present embodiment can perform double-sided image formation, but is well known to those skilled in the art, and thus description of the image forming operation is omitted.

(Scanning optical device)
Next, the laser exposure apparatus, that is, the scanning optical apparatus 20 (20A, 20B) that characterizes the present invention will be described.

  The scanning optical device 20 (20A, 20B) in the present embodiment uses the configuration of the first and second embodiments. By using such an optical scanning device, an image forming apparatus that performs color printing or the like can easily obtain a good image with little color unevenness and color misregistration even when the ambient temperature changes. Therefore, both miniaturization and high performance can be promoted. There is also a method (auto registration) of detecting and adjusting the irradiation position change and color shift change with time in the main body of the image forming apparatus. However, in this case, adjustment is required every time the irradiation position change or the color shift change exceeds a specified level, thereby causing a problem of a decrease in productivity. However, according to the configuration of the present embodiment, it is possible to suppress an irradiation position change or a color shift change while suppressing a decrease in productivity.

  As understood from the above, according to the present invention, the scanning optical device having the above-described configuration, in particular, using a lens in which two imaging lenses are integrated in the vertical direction can exhibit the following operational effects. .

  That is, the optical scanning device of the present invention has a support portion at least at one end of the imaging lens in the longitudinal direction, within the range between the upper and lower lens portions, or substantially on the optical axis. And it is set as the structure which supports a support part. Therefore, the optical box that houses the optical system and the lens holder are positioned in the sub-scanning direction. Therefore, the deformation of the imaging lens due to the ambient temperature change can be distributed substantially evenly between the upper and lower lens portions, and the deterioration of the aberration of the image plane, the change of the irradiation position, etc. can be suppressed to the minimum. In addition, with the above configuration, the upper and lower lens portions of the imaging lens are deformed in opposite directions, whereby the irradiation position change is also in the opposite direction between the lens portions, resulting in deterioration of image surface aberrations and irradiation. Changes in position and the like can be minimized.

  Furthermore, an optical box or a lens holding body that accommodates the optical system by having a support portion at least at one central portion in the longitudinal direction, which is a surface through which the luminous flux of the imaging lens does not transmit, and supporting the support portion. The positioning in the main scanning direction is performed. With this configuration, similarly in the main scanning direction, the deformation of the imaging lens due to a change in ambient temperature is distributed almost evenly at both ends in the longitudinal direction to minimize the deterioration of the image plane aberration and the change of the irradiation position. It can be suppressed to the limit.

It is a schematic configuration side view for explaining the positioning of the imaging lens in the sub-scanning direction in one embodiment of the optical scanning device of the present invention. It is a front view explaining the sub scanning direction positioning of the imaging lens in one Example of the optical scanning device of this invention. It is a perspective view explaining the sub scanning direction positioning of the imaging lens in one Example of the optical scanning device of this invention. It is a schematic block diagram explaining the whole structure of one Example of the optical scanning device of this invention. It is a schematic block diagram explaining the whole structure of one Example of the optical scanning device of this invention. It is a schematic configuration side view for explaining the positioning of the imaging lens in the sub-scanning direction in one embodiment of the optical scanning device of the present invention. It is a schematic configuration side view for explaining the positioning of the imaging lens in the sub-scanning direction in one embodiment of the optical scanning device of the present invention. It is a schematic configuration side view for explaining the positioning of the imaging lens in the sub-scanning direction in one embodiment of the optical scanning device of the present invention. It is a schematic configuration side view for explaining the positioning of the imaging lens in the sub-scanning direction in one embodiment of the optical scanning device of the present invention. It is a schematic structure side view explaining the sub-scanning direction positioning of the imaging lens in another embodiment of the optical scanning device of the present invention. FIG. 11A is a front view for explaining the sub-scanning direction positioning of the imaging lens in another embodiment of the optical scanning device of the present invention, and FIG. 11B is a bottom view. It is a perspective view explaining the subscanning direction positioning of the imaging lens in the other Example of the optical scanning device of this invention. It is a block diagram of the conventional optical scanning device (patent document 1). It is a block diagram of the conventional optical scanning device. It is a block diagram of the conventional optical scanning device. It is explanatory drawing explaining the relationship between the temperature rising amount, the power of a subscanning direction, and the distance from a lens support part to an optical axis. It is explanatory drawing explaining the relationship between the temperature rising amount, the power of a subscanning direction, and the distance from a lens support part to an optical axis. It is explanatory drawing explaining the relationship between the temperature rising amount, the power of a subscanning direction, and the distance from a lens support part to an optical axis. It is explanatory drawing explaining the relationship between the temperature rising amount, the power of a subscanning direction, and the distance from a lens support part to an optical axis. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus to which an optical scanning device of the present invention is applied.

Explanation of symbols

1 Semiconductor laser (light source)
2 Collimator lens 3 Aperture 4 Cylindrical lens 5 Polygon mirror (deflection member)
6 Double pass lens (imaging lens, optical lens)
6a Lower lens part (first lens part)
6b Upper lens part (second lens part)
7 Folding mirror (reflecting means)
8 Folding mirror 9 Photosensitive drum (scanned surface)
DESCRIPTION OF SYMBOLS 10 Light beam 11 Lens holder 11a, 11b, 11c Fitting recessed part 12, 13 Sub scanning direction positioning projection part 14 Main scanning direction positioning projection part 20 (20A, 20B) Optical scanning apparatus 21 Optical box 100 Image forming apparatus S1, S2 Sub Scanning direction positioning support part S3 Main scanning direction positioning support part

Claims (3)

An optical in which a deflecting member that deflects and scans a laser, a first lens portion that transmits the laser scanned by the deflecting member, and a second lens portion that transmits the laser after passing through the first lens portion are integrated. In an optical scanning device having a lens and a lens support portion that supports the optical lens,
When viewed from the direction orthogonal to the optical axes of the first lens unit and the second lens unit, within a range sandwiched between the optical axes of the first lens unit and the second lens unit or substantially on the optical axis. An optical scanning device comprising the lens support portion.   Each of the first lens unit and the second lens unit is a convex lens, and viewed from the longitudinal direction of the optical lens, the optical axis of the first lens unit and the optical axis of the second lens unit with respect to the center of the lens support unit L1 and L2, and when the powers in the sub-scanning direction of the first lens unit and the second lens unit are n1 and n2, respectively, when n1> n2, L1 <L2. The optical scanning device according to claim 1, wherein a center of the lens support portion is provided.   3. The optical scanning device according to claim 2, wherein a position where the center of the lens support portion is arranged substantially coincides with a position satisfying a relational expression of L1 / L2 = n2 / n1.

Images