JP2006323277A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner in which the relative difference in high order elements of positional deviation in the subscanning direction of respective colors is reduced, color shift in the subscanning direction is suppressed to form a high quality picture. <P>SOLUTION: The optical scanner is provided with a plurality of light sources, a polygon mirror 5 which deflects the beams from the light sources in a main scanning direction, lenses 11 and 12 which focus the deflected beams onto faces to be scanned 50Y, 50M, 50C and 50 K, and turning back mirrors 31 to 38 for guiding the beams passing through the lenses to the faces to be scanned. The following conditions are satisfied. Condition (1): ¾[K(i,θS)+K(i,-θS)]/2-K(i,0)¾>(25.4/W), and condition (2): ¾KK(1,θ)-KK(2,θ)¾<(25.4/W)/2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device, and more particularly to an optical scanning device that scans a plurality of beams, which are modulated based on image data, on each surface to be scanned using a single deflector.

  In recent years, in an image forming apparatus such as a full-color copying machine or printer, four photoconductors are juxtaposed corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black). The tandem method in which images of the respective colors formed on the respective photoconductors are transferred to an intermediate transfer belt and synthesized is the mainstream. In this type of tandem image forming apparatus, for example, there is an optical scanning apparatus that draws an image by simultaneously scanning four beams on each photoconductor using a single deflector (polygon mirror). It is installed.

  By the way, in this type of optical scanning device, a problem arises that the drawing line on the photoconductor is curved in the sub-scanning direction (hereinafter referred to as bow). The bow is more prominent when the beam is incident on the deflector in the sub-scanning direction with an inclination angle.

  If the bow is large, the scanning line becomes bowed and the image deteriorates. Further, when an image is formed by the tandem method, if the relative difference between the bows generated for each color is large, a color shift occurs and the image is further deteriorated. Therefore, it is necessary to make the absolute value of the positional deviation amount in the sub-scanning direction small and to make the relative difference for each color small. However, if an attempt is made to reduce the positional deviation in the sub-scanning direction, the beam shape deteriorates, leading to a reduction in image quality.

  Therefore, in Patent Document 1, in order to align the bow bending direction due to the linear expansion change of the housing with temperature change, the number of folding mirrors is different evenly and oddly on the left and right of the deflector, and evenly and oddly the same number on the top and bottom. An optical scanning device constituted by the above is disclosed. This device has the problem that although the bow bending direction due to the linear expansion change of the housing can be aligned, the bow bending direction of the remaining design cannot be aligned with four colors.

Further, Patent Document 2 discloses an optical scanning device that employs a configuration in which deflection is performed only on one side of a deflector and includes a member that aligns the scanning direction shift direction with respect to the sub-scanning direction. However, this optical scanning device deflects the beam only on one side of the deflector, and is not intended to be applied to the tandem method at all. As a result, the cost increases significantly.
JP 2002-202472 A Japanese Unexamined Patent Publication No. 64-909

  Accordingly, an object of the present invention is to form a high-quality image by reducing the positional deviation high-order component relative difference in the sub-scanning direction for each color when forming an image by the tandem method, and suppressing the color shift in the sub-scanning direction. An object of the present invention is to provide an optical scanning device capable of performing the above.

In order to achieve the above object, the present invention provides a plurality of light sources, a deflector for deflecting the beam from the light source in the main scanning direction, and forming an image of the beam deflected by the deflector on the surface to be scanned. And an optical path folding mirror for guiding a beam transmitted through the lens to a surface to be scanned, the deflector is installed in common for each light source, and the lens is a deflector Are arranged on both left and right sides, have at least one different surface shape on the upper side and lower side in the sub-scanning direction, the beam deflected by the deflector transmits the upper side surface and the lower side surface, and the following conditional expression Satisfy (1) and (2),
The deflection angle is θ, the amount of positional deviation in the sub-scanning direction at the designed θ is K (i, θ), i = 1 is transmitted through the upper surface of the lens, and i = 2 is transmitted through the lower surface of the lens. Suppose that the amount of the third or higher order component included in K (i, θ) is KK (i, θ).
KK (i, θ) = K (i, θ) − [A (i) θ ² + B (i) θ + C (i)]
Here, A (i), B (i), C (i): a coefficient at which KK (i, θ) becomes 0 at θ = 0, ± θN, and N is an arbitrary value on the image.
When the effective image length in the main scanning direction is ± L and the deflection angle at that time is ± θS, at least one of i = 1 and 2,
| [K (i, θS) + K (i, −θS)] / 2−K (i, 0) |> (25.4 / W) (1)
Furthermore, at an arbitrary deflection angle θ,
| KK (1, θ) −KK (2, θ) | <(25.4 / W) / 2 (2)
W is the writing resolution (dot / inch), and the unit of 25.4 is (mm / inch).
It is characterized by.

  In the optical scanning device according to the present invention, the left and right sides of the deflector refer to both sides that are symmetrical about the rotation axis of the deflector. The lower optical path refers to an optical path in which the beam deflected by the deflector travels on the scanned surface side about the optical axis of the lens, and the upper optical path travels on the opposite side of the scanned surface. Say.

  The conditional expression (1) represents the secondary component (bow) of the positional deviation in the sub-scanning direction, and satisfying this formula (1) means that the secondary component of the positional deviation in the sub-scanning direction is large. is doing. Conditional expression (2) represents a third-order or higher-order relative difference in positional deviation in the sub-scanning direction for each optical path (each color), and satisfying this conditional expression (2) indicates that higher-order components are satisfied. This indicates that the relative difference is small.

  If the secondary component of the positional deviation in the sub-scanning direction is forcibly reduced, other aberrations are deteriorated, leading to a decrease in image quality. Therefore, in the present invention, the high-order component relative difference for each optical path is reduced by satisfying the conditional expression (2), and the color shift in the sub-scanning direction is suppressed to form a high-quality image.

  In the optical scanning device according to the present invention, it is preferable that at least one of the optical path folding mirrors is provided with means for correcting the curvature in the sub-scanning direction on the surface to be scanned by bending the mirror in the main scanning direction. . The bow remaining in the design can be corrected.

Further, the lens is composed of a first lens close to the deflector and a second lens disposed downstream of the first lens, and the surface of the second lens on the surface to be scanned is above and below in the sub-scanning direction. With respect to the number of folding mirrors having at least one different surface shape on the side and disposed between the second lens and the surface to be scanned, the number of optical paths arranged on the upper side is P, and the number of the optical paths transmitting on the lower side is When the number of arranged sheets is Q, it can be set so as to satisfy the following expression (3).
| PQ | = 2j + 1 (3)
Where j is an integer greater than or equal to 0

  As described above, since the surface of the second lens on the surface to be scanned has a surface shape that differs by at least one surface on the upper side and the lower side in the sub-scanning direction, the number of lenses can be reduced.

  The high-order component of the positional deviation in the sub-scanning direction between the beam passing through the upper side of the lens and the beam passing through the lower side has a symmetrical shape with respect to the main scanning section of the optical path. By satisfying the expression (3), the number of reflections in the upper optical path and the lower optical path is shifted by one, and the bow curve direction of the drawing line on the surface to be scanned after being folded by the mirror is changed. The color misregistration can be effectively suppressed.

  Further, at least one surface of the lens has an independent aberration correction power in the optical path region that transmits the upper side in the sub-scanning direction and the optical path region that transmits the lower side, thereby easily reducing the high-order component relative difference. Can do. A similar effect can also be achieved by making the coefficients of the equations defining the surfaces different in the optical path region transmitting the upper side in the sub-scanning direction and the optical path region transmitting the lower side in at least one surface of the scanning lens.

  Hereinafter, embodiments of an optical scanning device according to the present invention will be described with reference to the accompanying drawings.

(First and second embodiments)
As for the first embodiment of the optical scanning device according to the present invention, FIG. 1 shows a three-dimensional arrangement concept, FIG. 2 shows a light source section, and FIG. 9 shows a sub-scanning section. FIG. 10 shows a sub-scan section of the second embodiment.

  This optical scanning apparatus is configured as an exposure scanning unit of an image forming apparatus based on tandem electrophotography, and as shown in FIG. 1, each of the optical scanning apparatuses is provided on four photosensitive drums 50 (50Y, 50M, 50C, 50K). A color image is formed. The four-color image (electrostatic latent image) formed on the photosensitive drum 50 is developed with toner, and then primary-transferred / combined on an intermediate transfer belt (not shown), and secondary-imaged on a recording material. Transcribed. This type of image forming process is well known and will not be described.

  In this optical scanning device, as shown in FIG. 2, the light source section includes four laser diodes 1 (1M, 1Y, 1C, and 1K), and includes a collimator lens, a cylinder lens, and a half mirror (not shown). The beam emitted from each laser diode 1 enters the deflection surface of the polygon mirror 5. This incident beam is converted into a linear shape on the deflection surface of the polygon mirror 5 in the sub-scanning direction Z by a cylinder lens (not shown).

  With respect to the polygon mirror 5, the beam of the upper right laser diode 1C is incident on the deflection surface at an incident opening angle of 90 °, the beam of the lower right laser diode 1K is incident at an opening angle of 80 °, and the beam of the upper left laser diode 1M The beam of the lower left laser diode 1Y is incident obliquely on the deflecting surface at an incident open angle of 80 ° and an incident open angle of 90 °.

  The beam from the light source unit does not necessarily need to be incident obliquely on the polygon mirror 5, but if it is incident obliquely, the beam can be separated into the upper optical path and the lower optical path without increasing the thickness of the polygon mirror 5. Become.

  As shown in FIGS. 1 and 9, a first lens 11 and a second lens 12 for imaging each beam deflected in the main scanning direction Y by the polygon mirror 5 on each photosensitive drum 50, and the lens A plurality of optical path folding mirrors 31 to 38 for guiding the beams transmitted through 11 and 12 to each photosensitive drum 50 and dust-proof window glasses 29Y, 29M, 29C, and 29K are arranged.

  The first and second lenses 11 and 12 are arranged in front of the optical path folding mirrors 31 to 38 on the left and right sides with the rotation axis 5a (see FIGS. 9 and 10) of the single polygon mirror 5 as the center. As shown in FIG. 3, the surface shape on the emission side of the second lens 12 is a surface shape different between the upper side 12 a and the lower side 12 b in the sub-scanning direction Z. That is, the coefficients of the equations that define the surface are different between the optical path region that transmits the upper side 12a of the second lens 12 and the optical path region that transmits the lower side 12b, and each of the surfaces 12a and 12b has independent aberration correction power. ing. The surface shape data will be described later (see Tables 2 to 5).

  FIG. 4 shows a developed optical path in a state where the folding mirrors 31 to 38 in the first embodiment are not shown, FIG. 4A is a main scanning section, and FIG. 4B is a sub-scanning section. Here, as shown in FIG. 5, an angle formed by the optical axis P of the first and second lenses 11 and 12 and the beam reflected by the polygon mirror 5 is defined as a deflection angle θ.

  By the way, the drawing line on the photosensitive drum 50 by the beam deflected by the polygon mirror 5 has a characteristic of causing a positional deviation curved with respect to the sub-scanning direction Z as shown in FIG. In FIG. 6, the horizontal axis is represented as the main scanning direction Y. FIGS. 7 and 8 show the positional deviation in which the main scanning direction Y is represented by the deflection angle θ.

  In the first embodiment, the polygon mirror 5 is installed in common for the four beams, and the first and second lenses 11 and 12 are arranged on both the left and right sides of the polygon mirror 5 and are arranged in the sub-scanning direction Z. The upper and lower sides have different surface shapes. In such a configuration, the deflection angle is θ, and the positional deviation amount in the sub-scanning direction Z at the designed θ is K (i, θ). When the beam is transmitted through the upper side surfaces of the lenses 11 and 12, i = 1, and when the beam is transmitted through the lower side surface, i = 2, and the amount of the third or higher order component included in K (i, θ) is KK. Let (i, θ).

In this case, the higher-order component KK (i, θ) is expressed by the following equation.
KK (i, θ) = K (i, θ) − [A (i) θ ² + B (i) θ + C (i)]
Here, A (i), B (i), C (i): a coefficient at which KK (i, θ) becomes 0 at θ = 0, ± θN, and N is an arbitrary value on the image.

When the effective image length in the main scanning direction Y is ± L and the deflection angle at that time is ± θS, it is preferable that at least one of i = 1 and 2 satisfies the following conditional expression (1). .
| [K (i, θS) + K (i, −θS)] / 2−K (i, 0) |> (25.4 / W) (1)

Furthermore, it is preferable that the following conditional expression (2) is satisfied at an arbitrary deflection angle θ.
| KK (1, θ) −KK (2, θ) | <(25.4 / W) / 2 (2)
W is the writing resolution (dot / inch), and the unit of 25.4 is (mm / inch). Therefore, the unit of the right side of the conditional expressions (1) and (2) is (mm / dot), and represents how many mm is 1 dot.

  The conditional expression (1) represents the secondary component (positional deviation) of the positional deviation in the sub-scanning direction Z, and satisfying this formula (1) has a large secondary component of the positional deviation in the sub-scanning direction Z. It means that. Further, the conditional expression (2) represents a third-order or higher-order relative component difference in positional deviation in the sub-scanning direction Z for each optical path (each color), and satisfying this conditional expression (2) is high. It represents that the relative difference of the next component is small.

  If the secondary component of the positional deviation in the sub-scanning direction Z is forcibly reduced, other aberrations are deteriorated, leading to a reduction in image quality. Instead, by satisfying conditional expression (2), it is possible to reduce the high-order component relative difference for each optical path, and to suppress color misregistration in the sub-scanning direction, thereby forming a high-quality image.

  FIG. 7 shows the relationship between the deflection angle θ and the positional deviation amount K (i, θ) in the sub-scanning direction. In the designed state, the positional deviation amount in the sub-scanning direction of the lower beam (i = 2) is 25.4 /. W is exceeded. On the other hand, FIG. 8 shows the relationship between the deflection angle θ and the higher-order component KK (i, θ) of the positional deviation amount in the sub-scanning direction. The high-order component KK (i, θ) is obtained by removing the three-point correction (second-order curve connecting the three points) from the positional deviation amount K (i, θ) in the sub-scanning direction. In the designed state, the difference between the higher-order components of the positional deviation amount in the sub scanning direction between the upper beam (i = 1) and the lower beam (i = 2) is less than (25.4 / W) / 2. 7 and 8 show the design performance of the lenses 11 and 12 on the right side with respect to the polygon mirror 5, the incident opening angle when i = 1 is 90 °, and the incident opening angle when i = 2 is 80 °. .

(Number of folding mirrors)
As for the number of the optical path folding mirrors 31 to 38, as shown in FIG. 9, the number of arranged one upper optical path (for magenta exposure) is 3, and one lower optical path (for yellow exposure) with respect to the polygon mirror 5. The number of arrangement is 2, the number of arrangement of the other lower optical path (for black exposure) is 1, and the number of arrangement of the other upper optical path (for cyan exposure) is 2.

  In other words, the number of folding mirrors arranged in the upper and lower optical paths on the left side of the polygon mirror 5 is different even and odd in the three and two optical paths. Is different. In addition, even and odd numbers are different between three and two optical paths that pass through the upper side of the first and second lenses 11 and 12, and even and odd numbers are different between two and one optical path that passes through the lower side. .

  On the other hand, in the second embodiment, as shown in FIG. 10, with respect to the number of the optical path folding mirrors 41 to 46, the arrangement number of one upper optical path (for yellow exposure) is 1 with respect to the polygon mirror 5, The number of side optical paths (for magenta exposure) is 2, the number of the other lower optical path (for black exposure) is 1, and the number of the other upper optical path (for cyan exposure) is 2.

  In other words, the number of folding mirrors in the second embodiment is such that the even and odd numbers of the optical paths corresponding to the upper and lower sides on the left side of the polygon mirror 5 are different even and odd, and two on the right and the corresponding optical paths. Even number and odd number are different in one sheet. Further, in the optical path that transmits the upper side of the first and second lenses 11, 12, the even number and the odd number are different for one and two lenses, and in the optical path that transmits the lower side, the even number and the odd number are different for two and one lens. .

  In the second embodiment shown in FIG. 4, other configurations are the same as those of the first embodiment shown in FIGS. 1 to 3, and the same members are denoted by the same reference numerals, and redundant description is omitted.

By the way, regarding the number of folding mirrors disposed between the second lens 12 and the surface to be scanned (photosensitive drum 50), the number of optical paths disposed on the upper side is P, and the number of disposed optical paths is illustrated on the lower side. When Q is set, it is preferable to set so as to satisfy the following expression (3).
| PQ | = 2j + 1 (3)
Where j is an integer greater than or equal to 0

  The higher-order component of the positional deviation in the sub-scanning direction Z is symmetrical with respect to the main-scan section of the optical path between the beam that passes through the upper side of the first and second lenses 11 and 12 and the beam that passes through the lower side. ing. When the expression (3) is satisfied, the number of reflections is shifted by one between the upper optical path and the lower optical path, and the bow of the drawing line on the surface to be scanned after being folded by the mirror is curved. The directions can be aligned, and color misregistration can be effectively suppressed.

  When the arrangement number of the folding mirrors 31 to 38 in the first embodiment is applied to the equation (3), P = 2, Q = 3 on the left side of the polygon mirror 5, P = 2, Q = 1 on the right side, PQ | is an odd number and satisfies the expression (3). Further, when the number of the folding mirrors 41 to 46 in the second embodiment is applied to the equation (3), P = 1 and Q = 2 on the left side of the polygon mirror 5, and P = 2 and Q = 1 on the right side. , | PQ | is an odd number and satisfies Expression (3).

(Bow correction)
The positional deviation in the sub-scanning direction on the surface to be scanned 50 can be corrected by the correcting means 25 shown in FIG. The correction means 25 moves the central portion of the folding mirror 30 in the main scanning direction by moving the screw 26 provided on the folding mirror 30 forward and backward with respect to the fixed frame 27, thereby deforming the main scanning of the mirror 30. The amount of deflection in the direction Y is adjusted. Both ends of the folding mirror 30 are held by fixing portions 39 and 39, and a leaf spring 28 is disposed on the opposite side of the screw 26.

  By adjusting the amount of deflection of the folding mirror 30 with the screw 26, it is possible to correct the positional deviation on the scanned surface 50. Even when a large misalignment remains in design, the correction means 25 can correct it. When the misregistration is corrected in this way, the equation (3) relating to the number of folding mirrors arranged is to align the residual misalignment in the subscanning direction Z after correcting the secondary component of the misregistration in the subscanning direction. .

  The correcting means 25 may be installed on any folding mirror, but it is preferable to install it on one folding mirror in each of the four color optical paths. As to which of the plurality of folding mirrors to be installed in each optical path, a mirror that is easy to install may be selected in terms of optical path design, but it is preferable to select a mirror with high correction sensitivity. In other words, the amount of change in the positional deviation is greater with respect to the amount of deflection of the mirror in the mirror where the beam is incident at an obtuse angle.

(Optical element arrangement and configuration data)
Table 1 below shows the arrangement of the optical elements in the first and second examples. Tables 2 to 5 show the free-form surface coefficient data of the first and second lenses 11 and 12. These free-form surfaces are calculated by the free-form surface equation shown in Equation (4).

(Other examples)
The optical scanning device according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof.

It is a three-dimensional arrangement conceptual diagram showing a first example of an optical scanning device according to the present invention. The optical path structure of the light source part of the said 1st Example is shown, (A) is a XY top view, (B) is a XZ side view. It is a perspective view which shows a 2nd lens. The developed optical path from the deflector of the first embodiment to the surface to be scanned is shown, (A) is an XY plan view, and (B) is an XZ side view. It is an XY plan view showing a deflection angle. It is a perspective view which shows generation | occurrence | production of a bow. It is a graph which shows the relationship between a deflection angle and position shift amount K (i, (theta)). It is a graph which shows the relationship between a deflection angle and the higher-order component KK (i, (theta)) of positional offset amount. FIG. 3 is an XZ side view showing an optical path configuration from the deflector of the first embodiment to the surface to be scanned. FIG. 6 is an XZ side view showing an optical path configuration from a deflector to a scanned surface in the second embodiment of the optical scanning device according to the present invention. FIG. 3 shows a bow correcting means on the surface to be scanned, (A) is an XZ side view, and (B) is an XY plan view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser diode 5 ... Polygon mirror 11, 12 ... Lens 25 ... Correction | amendment means 29 ... Window glass 30-38 ... Folding mirror 41-46 ... Folding mirror 50 ... Photosensitive drum (scanned surface)

Claims (6)

A plurality of light sources, a deflector for deflecting the beam from the light source in the main scanning direction, a lens for forming an image of the beam deflected by the deflector on the surface to be scanned, and a beam transmitted through the lens In an optical scanning device including an optical path folding mirror for guiding to a scanning surface,
The deflector is installed in common for each light source,
The lenses are disposed on both left and right sides of the deflector, have at least one different surface shape on the upper and lower sides in the sub-scanning direction, and the beams deflected by the deflector pass through the upper and lower surfaces, And satisfying the following conditional expressions (1) and (2):
The deflection angle is θ, the amount of positional deviation in the sub-scanning direction at the designed θ is K (i, θ), i = 1 is transmitted through the upper surface of the lens, and i = 2 is transmitted through the lower surface of the lens. Suppose that the amount of the third or higher order component included in K (i, θ) is KK (i, θ).
KK (i, θ) = K (i, θ) − [A (i) θ ² + B (i) θ + C (i)]
Here, A (i), B (i), C (i): a coefficient at which KK (i, θ) becomes 0 at θ = 0, ± θN, and N is an arbitrary value on the image.
When the effective image length in the main scanning direction is ± L and the deflection angle at that time is ± θS, at least one of i = 1 and 2,
| [K (i, θS) + K (i, −θS)] / 2−K (i, 0) |> (25.4 / W) (1)
Furthermore, at an arbitrary deflection angle θ,
| KK (1, θ) −KK (2, θ) | <(25.4 / W) / 2 (2)
W is the writing resolution (dot / inch), and the unit of 25.4 is (mm / inch).
An optical scanning device characterized by the above.   2. The apparatus according to claim 1, wherein at least one of the optical path folding mirrors is provided with means for correcting curvature in the sub-scanning direction on the surface to be scanned by bending the mirror in the main scanning direction. Optical scanning device.   3. The optical scanning device according to claim 2, wherein the correcting unit is provided for a mirror on which a beam is incident at an obtuse angle. The lens includes a first lens that is close to the deflector and a second lens that is disposed after the first lens, and a surface on the scanned surface side of the second lens is above and below in the sub-scanning direction. Having at least one different surface shape on the side,
With respect to the number of folding mirrors arranged between the second lens and the surface to be scanned, when the number of optical paths arranged on the upper side is P and the number of optical paths arranged on the lower side is Q, the following formula ( Satisfy 3)
| PQ | = 2j + 1 (3)
However, j is an integer greater than or equal to 0. The optical scanning device in any one of Claim 1 thru | or 3 characterized by the above-mentioned.   5. The lens according to claim 1, wherein at least one surface of the lens has independent aberration correction power in an optical path region that transmits the upper side in the sub-scanning direction and an optical path region that transmits the lower side. The optical scanning device according to 1. 5. The coefficient of an expression defining a surface is different between at least one surface of the lens in an optical path region that transmits the upper side in the sub-scanning direction and an optical path region that transmits the lower side. An optical scanning device according to claim 1.

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