Patent Application
20130222507
This application relates to and claims priority from Japanese Patent Application No. 2012-40222, filed in the Japan Patent Office on Feb. 27, 2012, the entire disclosure of which is incorporated herein by reference.
The present disclosure relates to an optical scanning device including a scanning lens which images, on a surface to be scanned, a light beam that has been deflected and scanned, and an image forming apparatus using the foregoing optical scanning device.
For example, a general optical scanning device that is used, for example, in laser printers and copiers includes a light source which emits a laser beam, a polygon mirror which reflects and then deflects/scans the laser beam, and a scanning lens which images the deflected and scanned laser beam on a peripheral surface (surface to be scanned) of a photoreceptor drum. As the scanning lens, a lens having fθ characteristics is used. Moreover, the foregoing scanning lens is generally manufactured by molding a resin material in a metal mold.
While the scanning lens is sometimes configured from a plurality of lenses, it is also sometimes configured from one lens for the purpose of downsizing the device or reducing costs. As conventional technology, in an optical scanning device in which the scanning lens is configured from one lens, known is design technology of defining the relation of the entrance face and the exit face of the scanning lens in a main scanning direction cross section. Specifically, when a curvature radius near an optical axis of the entrance face facing the polygonal mirror is R1 and a curvature radius near an optical axis of the exit face is R2, the scanning lens is configured from a meniscus lens which is convex on the polygon mirror side and which satisfies a relationship of 0<R1<R2.
Nevertheless, upon using the scanning lens of the optical scanning device of the foregoing conventional technology, there is a problem in that the optical performance is unstable, or the productivity is inferior. In other words, when the scanning lens satisfies the relationship of 0<R1<R2, the thickness of the scanning lens in the optical axis direction will become thinner from the center part to the end part in the main scanning direction. When a scanning lens having this kind of thin part is manufactured via molding, the shape tends to vary slightly in each molding process. Thus, the optical performance among the molded scanning lenses becomes unstable. This problem can be resolved by extending the cast molding time and the cooling time in the molding process. Nevertheless, a problem regarding the deterioration in productivity will naturally arise.
An object of the present disclosure is to provide an optical scanning device and an image forming apparatus capable of stabilizing the optical performance of the scanning lens.
The optical scanning device according to one aspect of the present disclosure is an optical scanning device which includes a light source which emits a light beam, a deflector, an incident optical system and one scanning lens. The deflector reflects and then deflects/scans the light beam emitted from the light source. The incident optical system causes the light beam emitted from the light source to enter the deflector. The scanning lens includes a first face facing the deflector and a second face on an opposite side to the first face, and performs imaging of the deflected/scanned light beam on a surface to be scanned. When the curvature radius of the first face in a main scanning direction cross section is R1, the curvature radius of the second face in a main scanning direction cross section is R2, the lens thickness in an optical axis direction at the center of the scanning lens in a main scanning direction is d, and the refractive index of the scanning lens is n, following Formula (1) and Formula (2) are satisfied:
0<R2<R1 (1)
0>R2−R1>−(n−1)d/n (2).
The image forming apparatus according to another aspect of the present disclosure includes an image carrier which carries an electrostatic latent image, and an optical scanning device which irradiates a light beam with a peripheral surface of the image carrier as the surface to be scanned, wherein the optical scanning device includes the foregoing configuration.
The optical scanning device according to one embodiment of the present disclosure is now explained with reference to the appended drawings.
A right cover 111 is provided to the right side face of the case 101, and a left cover 113 is provided to the left side face of the case 101. The right cover 111 is axially supported by an axis 112 provided to the lower side end part thereof, and can be opened and closed by turning around the axis. Similarly, the left cover 113 is axially supported by an axis 114 provided to the lower side end part thereof, and can be opened and closed by turning around the axis. The user can repair jams, replace consumable supplies or perform maintenance by opening the covers 111, 113.
The image forming unit 100 performs processing of forming a toner image on a sheet, and includes a charging device 102, a photoreceptor drum 103 (image carrier), a developing device 105, a transfer roller 106, a cleaning device 107, and a fixing unit 108.
The photoreceptor drum 103 is a cylindrical member, and an electrostatic latent image and a toner image are formed on a peripheral surface thereof. The photoreceptor drum 103 receives drive force from a motor not shown, and is rotated in a clockwise direction shown with an arrow A in
The developing device 105 supplies a toner to the peripheral surface of the photoreceptor drum 103, on which an electrostatic latent image was formed, and thereby forms a toner image. The developing device 105 includes a developing roller for carrying the toner, and a screw for agitating and delivering the toner. The toner image formed on the photoreceptor drum 103 is transferred to a sheet that is fed from the paper feeding cassettes 210, 220 and delivered to a feeding path 300. The toner is supplied to the developing device 105 from a toner container not shown.
The transfer roller 106 is disposed facing a lateral side of the photoreceptor drum 103, and a transfer nip portion is formed by the transfer roller 106 and the photoreceptor drum 103. The transfer roller 106 is configured from a rubber material with conductivity and provided with a transfer bias, and transfers the toner image formed on the photoreceptor drum 103 to the sheet. The cleaning device 107 cleans the peripheral surface of the photoreceptor drum 103 after the toner image is transferred.
The fixing unit 108 includes a fixing roller with a heater build therein, and a pressure roller provided at a position facing the fixing roller. The fixing unit 108 fixes the toner image, which was transferred to a sheet, on the sheet while conveying and heating the sheet with the toner image formed thereon with the rollers.
The optical scanning device 104 forms an electrostatic latent image by irradiating a laser beam according to image data that is input from external equipment such as a personal computer to the peripheral surface (surface to be scanned) of the photoreceptor drum 103 that was substantially uniformly charged by the charging device 102. The optical scanning device 104 will be described in detail later.
The paper feeding cassettes 210, 220 house a plurality of sheets P to which images are to be formed. A feeding path 300 for delivering the sheets is disposed between the paper feeding cassettes 210, 220 and the image forming unit 100. The feeding path 300 is provided with paper feed roller pairs 213, 223, transport roller pairs 214, 224, and a resist roller pair 215. Moreover, disposed on the downstream side of the fixing unit 108 are a transport roller pair 109, and a discharge roller pair 110 for discharging the sheets to the paper discharge tray 119.
The image forming operation of the printer 1 is now briefly explained. Foremost, the peripheral surface of the photoreceptor drum 103 is substantially uniformly charged with the charging device 102. The charged peripheral surface of the photoreceptor drum 103 is exposed by a laser beam emitted from the optical scanning device 104, and an electrostatic latent image of the image to be formed on the sheet P is formed on the peripheral surface of the photoreceptor drum 103. The electrostatic latent image is developed as a toner image as a result of the toner being supplied from the developing device 105 to the peripheral surface of the photoreceptor drum 103. Meanwhile, the sheet P is fed from the paper feeding cassettes 210, 220 to the feeding path 300 by the pickup rollers 212, 222, and delivered to the transport roller pairs 214, 224. Subsequently, the sheet P is once stopped by the resist roller pair 215, and delivered to the transfer nip portion between the transfer roller 106 and the photoreceptor drum 103 at a predetermined timing. The toner image is transferred to the sheet P as a result of the sheet P passing through the transfer nip portion. After the foregoing transfer operation, the sheet P is delivered to the fixing unit 108, and the toner image is fixed to the sheet P. Subsequently, the sheet P is discharged to the paper discharge tray 119 by the transport roller pair 109 and the discharge roller pair 110.
The detailed structure of the optical scanning device 104 according to the first embodiment is now explained.
The housing 104H includes a bottom plate 141 as a base member on which various members are mounted, side plates 142 that are erected substantially vertically from the peripheral edges of the bottom plate 141, and a cover for covering the upside of the side plates 142. Note that, in
The bottom plate 141 is provided with a recess 143 at a location which is adjacent to the rear side plate 142B and which has a height that is lower than its surroundings. A polygon mirror 26 is disposed in the recess 143, and the laser unit 20, the collimator lens 23, the cylindrical lens 24 and the fθ lens 28 are disposed in a region other than the recess 143 of the bottom plate 141. The front side plate 142F is provided with a window part 144 which is formed by notching the front side plate 142F from the upper edge up to around the intermediate portion thereof. Even in a state where the cover (not shown) is mounted, the window part 144 remains an opening of the housing 104H. Moreover, a first holding member 145 and a second holding member 146 are provided on a top face of the bottom plate 141 near the left side plate 142L. A minute gap is provided between the left side plate 142L and the first holding member 145, and between the left side plate 142L and the second holding member 146, respectively.
The laser unit 20 includes a substrate 21, and a substantially cylindrically shaped semiconductor laser 22 mounted on one face of the substrate 21. The semiconductor laser 22 is a light source which emits a laser beam (light beam) of a predetermined wavelength. Mounted on the substrate 21 are a semiconductor laser 22, and a drive circuit component for driving the semiconductor laser 22. The laser unit 20 is mounted on the top face of the bottom plate 141 such that the substrate 21 is sandwiched in the gap formed between the first holding member 145 and the left side plate 142L and the gap formed between the second holding member 146 and the left side plate 142L respectively, and such that the semiconductor laser 22 is fitted between the first holding member 145 and the second holding member 146. The irradiation position of the laser beam B can be adjusted by adjusting the position that the substrate 21 is fitted into the gap.
The collimator lens 23 converts the laser beam B, which is emitted from the semiconductor laser 22 and diffused, into parallel light or light that is close to parallel. The collimator lens 23 is fixed to the bottom plate 141 with an adhesive using the base part 25.
The cylindrical lens 24 converts the parallel light into linear light that is long in a main scanning direction, and images the linear light on a reflecting surface of the polygon mirror 26. The collimator lens 23 and the cylindrical lens 24 are an incident optical system which causes the laser beam B to enter the polygon mirror 26, and in this embodiment is configured from an oblique-incident optical system.
The polygon mirror 26 is a polygonal mirror in which a reflecting surface is formed along each side of a regular hexagon. A rotating axis of the polygon motor 27 is connected to the center position of the polygon mirror 26. The polygon mirror 26 rotates around the rotating axis as a result of the polygon motor 27 being rotatively driven, and deflects and scans the laser beam B which is emitted from the semiconductor laser 22 and imaged via the collimator lens 23 and the cylindrical lens 24.
The fθ lens 28 is a lens having fθ characteristics, and is a lens that is elongated in the main scanning direction. The fθ lens 28 is disposed between the window part 144 and the polygon mirror 26, the laser beam B reflected off the polygon mirror 26 is condensed, and images on the peripheral surface 103S of the photoreceptor drum 103 through the window part 144 of the housing 104H. The fθ lens 28 is manufactured by molding a translucent resin material in a metal mold.
Referring to
The fθ lens 28 has the following lens shape. In other words, when the curvature radius of the entrance face 281 in the main scanning direction cross section near the optical axis AX is R1, and the curvature radius of the exit face 282 in the main scanning direction cross section near the optical axis AX is R2, the lens shape satisfies the condition of following Formula (1).
0<R2<R1 (1)
As a result of satisfying foregoing Formula (1), it is possible to prevent the thickness of the fθ lens 28 in the optical axis AX direction from becoming thin from the center part toward the end part in the main scanning direction. Accordingly, it is possible to improve the productivity of the fθ lens 28 based on molding, and more easily stabilize the optical performance of the fθ lens 28.
Here, the focal distance of a single lens is represented with following Formula (11) in a paraxial region. Note that the lens thickness of the single lens in the optical axis direction is d, and the refractive index is n.
Since the fθ lens 28 assumes the role of imaging the light beam of the laser beam B on the peripheral surface 103S of the photoreceptor drum 103, the focal distance f of the fθ lens 28 needs to satisfy following Formula (12).
f>0 (12)
Here, the lens thickness of the optical axis direction at the center of the fθ lens 28 in the main scanning direction is d, and the refractive index of the fθ lens 28 is n. It is evident that the values of both R1 and R2 are more of a positive value than foregoing Formula (1). Moreover, generally speaking, the refractive index of an optical lens material is n>1. In light of these points, the relation of following Formula (13) is established based on foregoing Formula (11) and Formula (12).
n(R2−R1)+(n−1)d>0 (13)
Based on foregoing Formula (11), in order to increase the focal distance f, the value of n(R2−R1)+(n−1)d needs to be decreased. Assuming that, unlike the relation of foregoing Formula (1), the relation of R1, R2 is as follows as with conventional technology,
0<R1<R2 (1)′,
the value of n(R2−R1) will take on a positive value and, as described above, since n>1, the value of (n−1)d also becomes a positive value. Thus, the value of n(R2−R1)+(n−1)d cannot be reduced.
Meanwhile, in this embodiment, since the relation of foregoing Formula (1) is realized, the value of n(R2−R1) will take on a negative value. Accordingly, it is possible to decrease the value of n(R2−R1)+(n−1)d, and the focal distance f of the fθ lens can be increased in comparison to conventionally. The fact that the focal distance f can be set to be long means that the optical power of the fθ lens 28 can be reduced. Consequently, it will not be necessary to considerably change, in the main scanning direction, the thickness of the fθ lens 28 in the optical axis AX direction. In other words, the thickness of the fθ lens 28 can be made to be substantially uniform in the main scanning direction. Accordingly, it will be possible to stably mold the fθ lens 28 and reduce the deterioration in the optical performance between lots.
Upon arranging foregoing Formula (13), following Formula (14) can be obtained.
R1−R2>−(n−1)d/n (14)
Thus, based on foregoing Formula (1) and Formula (14), it is possible to elicit following Formula (2).
0>R1−R2>−(n−1)d/n (2)
Note that the refractive index n of the optical lens material is 2 at maximum, it is possible to elicit following Formula (21).
0>R1−R2>−d/2 (21)
In addition, since the refractive index n of the optical lens material is generally near 1.5, it is possible to elicit following Formula (22) approximately.
0>R1−R2>−d/2 (22)
Meanwhile, with the fθ lens 28 lens that satisfies foregoing Formula (1), the convergence of the light beam emitted from the exit face 282 becomes relatively weak. Thus, the collimator lens 23 desirably has optical power capable of converting the outgoing light from the collimator lens 23 into convergent light. As a result of the collimator lens 23 having optical power capable of generating convergent light, the light path length can be shortened.
An example of the construction data of the imaging optical system which satisfies the requirements of the optical scanning device 104 according to the first embodiment is shown as Example 1. The imaging optical system of Example 1 is configured, as shown in
In Table 1, Fb represents the back focus of the collimator lens 23. “Polygon-fθ distance” represents the distance between the entrance face 281 of the fθ lens 28 and the reflecting surface of the polygon mirror 26, and “fθ-field distance” represents the distance between the exit face 282 of the fθ lens 28 and the peripheral surface 103S of the photoreceptor drum 103, respectively. Note that the unit of f, Fb, d, “Polygon-fθ distance”, and “fθ-field distance” in Table 1 is millimeters. Moreover, in Table 1, “R1” column represents the face shape of the entrance face 281 of the fθ lens 28, and “R2” column represents the face shape of the exit face 282 of the fθ lens 28, respectively. Note that Rm represents the main scanning curvature radius, Rs0 represents the sub scanning curvature radius, Ky represents the main scanning conic coefficient, Kx represents the sub scanning conic coefficient, and An and Bn (n is an integer) represent the high order coefficients of the face shape. By way of reference, in this Example, the main scanning curvature radius (R1) of the entrance face 281 of the fθ lens 28=29.98 mm, the main scanning curvature radius (R2) of the exit face 282 of the fθ lens 28=26.90 mm, lens thickness d=9 mm, and refractive index n=1.5, and satisfy foregoing Formula (1) and Formula (2).
The face shape of the entrance face 281 and the exit face 282 is defined based on the following formula showing the sag amount by using a local orthogonal coordinate system (x, y, z) with the face vertex as the origin and the direction of heading toward the peripheral surface 103S as the positive direction of the z axis. However, Zm (main scanning direction) and Zs (sub scanning direction) are the displacement (face vertex reference) in the z axis direction at the position of height Y, Cm=1/Rm, and Cs=1/Rs.
The optical scanning device 104A according to second embodiment is now explained.
The optical scanning device 104A has the same arrangement of optical elements as the optical scanning device 104 of the first embodiment, and includes a laser unit 20 (light source), a collimator lens 23 (part of the incident optical system), a cylindrical lens 24 (part of the incident optical system), a polygon mirror 26 (deflector), and one fθ lens 28 (scanning lens). The fθ lens 28 is a lens that satisfies foregoing Formula (1) and Formula (2).
In the first embodiment, it was explained that the collimator lens 23 desirably includes the optical power capable of generating the convergent light. In the second embodiment, an optical scanning device 104A capable of exhibiting even more favorable optical property is explained as a result of the fθ lens satisfying foregoing Formula (1) and Formula (2), the collimator lens 23 having optical power, and optimizing the relation of the back focus Cofb of the collimator lens 23 and the focal distance fm of the fθ lens 28 in the main scanning direction.
As shown in
1.0<fm/Cofb<3.2 (3)
fθ characteristics=((h−h0)/h0)×100[%]
Needless to say, fθ characteristics=0[%] is ideal, and the greater the value, the greater the difference between the target position and the irradiation position of the laser beam B. In the image forming apparatus, in order to prevent the image from being affected, fθ characteristics of approximately less than 2% is demanded.
When the back focus Cofb of the collimator lens 23 is reduced (shortened), and the level of convergence of the laser beam B that enters the fθ lens 28 is increased, the focal distance fm of the fθ lens 28 in the main scanning direction can be increased (lengthened). In other words, the optical power of the fθ lens 28 can be reduced. Nevertheless, as evident from
The foregoing point is now further explained with reference to
As evident from
Meanwhile, as the back focus Cofb of the collimator lens 23 is increased and the level of convergence of the laser beam B that enters the fθ lens 28 is reduced, the positional displacement of the imaging point at the end part of the image height is increased. In the foregoing case, when the difference in the optical power between the center part and the end part of the fθ lens 28 in the main scanning direction is increased, the optical power of the fθ lens 28 itself also needs to be increased. Consequently, the correction of aberration by the fθ lens 28 becomes favorable and the side lobe can be reduced, but the fθ characteristics tend to deteriorate.
As described above, the back focus Cofb of the collimator lens 23 and the focal distance fm of the fθ lens 28 in the main scanning direction are of a relation where adverse effect is inflicted on the optical property when one is decreased (increased) relative to the other. Accordingly, in the optical design, as a result of setting the back focus Cofb and the focal distance fm so as to satisfy the relation of foregoing Formula (3), it is possible to provide an optical scanning device 104A having a favorable imaging performance and capable of inhibiting the positional displacement of the imaging point in the main scanning direction.
Next, an example of the construction data of the imaging optical system which satisfies the requirements of the optical scanning device 104A according to the second embodiment is shown as Example 2. The imaging optical system of Example 2 is configured, as shown in
The symbols used in Table 2 are the same as those used in foregoing Table 1. By way of reference, in this Example, the main scanning curvature radius (R1) of the entrance face 281 of the fθ lens 28=24.29 mm, the main scanning curvature radius (R2) of the exit face 282 of the fθ lens 28=22.84 mm, lens thickness d=9 mm, and refractive index n=1.5, and satisfy foregoing Formula (1) and Formula (2).
The face shape of the entrance face 281 and the exit face 282 is defined based on the following formula showing the sag amount by using a local orthogonal coordinate system (x, y, z) with the face vertex as the origin and the direction of heading toward the peripheral surface 103S as the positive direction of the z axis. However, Zm (main scanning direction) and Zs (sub scanning direction) are the displacement (face vertex reference) in the z axis direction at the position of height Y, Cm=1/Rm, and Cs=1/Rs.
Moreover,
According to the optical scanning device 104 of this embodiment explained above, as a result of satisfying foregoing Formula (1) and Formula (2), the thickness of the fθ lens 28 in the optical axis direction does not have to be considerably changed in the main scanning direction, and the fθ lens 28 can be stably molded. In other words, it is possible to prevent the thickness of the scanning lens in the optical axis direction from becoming thinner from the center part toward the end part in the main scanning direction. Accordingly, it is possible to improve the productivity of the fθ lens 28, as well as stabilize the optical performance of the fθ lens 28. Moreover, as a result of satisfying foregoing Formula (3) in addition foregoing Formula (1) and Formula (2), it is possible to provide an optical scanning device 104A even more superior in the fθ characteristics and imaging performance.
As described above, according to the present disclosure, the productivity of the scanning lens is favorable, and the optical performance of the scanning lens can also be stabilized.
Although the present disclosure has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present disclosure hereinafter defined, they should be construed as being included therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-040222 | Feb 2012 | JP | national |
