JP3150839U - Two-piece fθ lens for microelectromechanical system laser beam detector - Google Patents

Abstract

A two-piece fθ lens for a microelectromechanical system laser beam scanning apparatus is provided. A first lens includes a first lens and a second lens. The first lens includes a concave surface of a meniscus on the MEMS reflection mirror side, and the second lens includes a meniscus or a biconcave lens. Among them, the first lens has a first optical surface and a second optical surface, and the scanning angle of the reflection angle and time of the MEMS reflecting mirror is changed to a scanning beam spot 2 having a relationship of distance and time having a linearity relationship. replace. The second lens has a third optical surface and a fourth optical surface, corrects the scanning light beam of the first lens, and condenses it on the target. Accordingly, both the first lens and the second lens satisfy specific optical formulas, and by providing the first lens and the second lens, a linear scanning effect and a high resolution can be realized. [Selection] Figure 3A

Description

  The present invention relates to a double fθ lens of a kind of microelectromechanical system laser beam scanning device (hereinafter abbreviated as MEMS LSU), and in particular, corrects a single vibration of a kind of MEMS reflection mirror, and an angle related to time and sine. The present invention relates to a double fθ lens that forms a change amount and realizes a linearity scanning effect required by a laser scanning device (hereinafter abbreviated as LSU).

  Currently, a laser scanning unit used in a laser beam printer (Laser Beam Printer, LBP) performs laser beam scanning using a polygon mirror that rotates at high speed. The principle is that a laser beam is emitted from a semiconductor laser, passes through a collimator, passes through an aperture device, and forms a parallel beam. The parallel beam further passes through a cylindrical lens, and the width of the Y axis in the sub-scanning direction is a line image along the parallel direction of the X-axis in the main scanning direction (main scanning direction). line image) and then projected onto a polygon mirror that rotates at high speed. The polygon mirror is composed of a plurality of uniform and continuous reflecting mirrors, and the focal position of the line image (line image) or its It is mounted near the focal position. By controlling the projection direction of the laser beam from the polygon mirror, the laser beam projected on the reflection mirror is parallel to the main scanning direction (X axis) while a plurality of reflection mirrors provided continuously rotate at high speed. Along the same angular velocity, the light is reflected obliquely onto the fθ linear scanning lens. The fθ linear scanning lens is a single-element scanning lens structure or a two-lens lens structure provided near a polygon mirror. The function of this fθ linear scanning lens is that the laser beam incident on the fθ lens is converged to an elliptical spot by reflection on a reflection mirror provided in the polygon mirror, and then on a photosensitive drum (photoreceptor drum, ie, imaging plane). To achieve the scanning linearity requirement.

US patent US6,844,951 US patent US6,956,597 US patent US7,064,876 US Patent No. 7,184,187 US Patent US 7,190,499 US Patent US2006 / 0113393 Taiwan patent TW M253133 Japanese Patent JP 2006-201350

However, the following problems remain when using a known LSU.
(B) Since it is difficult to manufacture a rotary polygon mirror and the cost is high, there is a problem that the production cost of LSU is increased.
(2) The polygon mirror is required to have a high-speed rotation function (for example, 40,000 rotations per minute) and high precision. For this reason, since the general polygon mirror is made such that the Y-axis width of the lens on the reflecting surface is extremely thin, all LSUs according to the prior art must be provided with an additional cylindrical lens. The action of this cylindrical lens is to converge the passing laser beam into a single line image (one point on the Y axis) and project it again on the reflection mirror of the polygon mirror. Due to the above circumstances, there is a problem of increasing the number of components and increasing assembly work.
C Since the prior art polygon mirror requires high-speed rotation (40,000 rotations per minute), the rotation noise is high, and it takes time for the polygon mirror to stabilize from the start-up to the operating rotation speed. There is a problem that is long.
In the assembly structure of the LSU of the prior art, the central axis of the laser beam projected on the reflection mirror of the polygon mirror is not aimed at the central axis of the polygon mirror. In designing the fθ lens to be combined, there is a problem in that it takes time and labor to design and manufacture the fθ lens, which requires consideration of off-axis deviation of the polygon mirror.

In recent years, in order to improve the problems of the LSU assembly structure of the prior art, a sort of sociological MEMS reflection mirror (MEMS mirror) has been developed in the market, and laser beam scanning control by the prior art polygon mirror Instead of The MEMS reflection mirror is composed of torsion oscillators, and has a light reflection layer on its surface layer. The light reflection layer oscillates due to oscillation, and reflects light to perform scanning. In the future, it can be applied to LSUs of imaging systems, scanners or laser printers, and its scanning efficiency is expected to be superior to conventional rotating polygon mirrors. According to U.S. Pat.Nos. 6,844,951 and 6,956,597, at least one drive signal is generated, the drive frequency is made to approach the resonance frequency of a plurality of MEMS reflection mirrors, and the MEMS reflection mirror is driven by the drive signals, A mechanism for generating a scan path is disclosed. Furthermore, according to U.S. Pat. Instead of a known rotary polygon mirror, the projection direction of the laser beam is controlled. In addition, there are Japanese patent JP2006-201350. This type of MEMS reflection mirror has the advantages of small elements, high rotational speed, and low production cost. However, the MEMS reflection mirror starts simple vibration by voltage-driven input. The simple vibration (harmonic motion) has a sinusoidal relationship between time and angular velocity. The relationship between the reflection angle θ after reflection and the time t after being reflected on the MEMS reflection mirror is as shown in Equation (1).

In Equation (1), f indicates the scanning frequency of the MEMS reflecting mirror, and θ _S indicates the maximum scanning angle on one side after the laser beam passes through the MEMS reflecting mirror. Thus, at the same time interval, the corresponding reflection angle and time of Δt form a sinusoidal change. In other words, the change in reflection angle at the same time interval Δt is nonlinear with time as Δθ (t) = θ _s · (sin (2π · f · t ₁ ) -sin (2π · f · t ₂ )). Show the relationship. When the reflected light beam is projected onto the target from various angles, the interval of the spot distances formed at the same time interval is different and increases or decreases according to time.

 As an example, when the vibration angle of the MEMS reflecting mirror is in the sine wave peak and wave trough, each angle change is increased or decreased according to time, which is different from the prior art polygon mirror equiangular rotational movement method. . When the prior art fθ lens is attached to an LSU equipped with a MEMS reflection mirror, the amount of change in angle formed by the MEMS reflection mirror cannot be corrected, and the laser beam projected on the imaging surface becomes an inconstant speed scanning phenomenon. The imaging deviation of the imaging plane is generated. Therefore, LSU composed of MEMS reflecting mirror is a micro electro mechanical laser scanning device (abbreviated as MEMS LSU), and its characteristic is that after the laser beam scans through the MEMS reflecting mirror, scanning light beams with different angles are formed at the same time interval Is done. Along with this, it is applied to an fθ lens for MEMS LSU to correct the scanning light beam and accurately form an image on the target. As an example, US Pat. No. 7,184,187 discloses a change in angle in the main scanning direction due to a polynomial surface. However, the cross section of the laser beam is not an ideal micro circle, and the cross section is a flat elliptical shape, so that only the main scanning direction is corrected, and the accuracy requirement is not yet achieved. Therefore, there is an urgent need to develop an fθ lens that can correct the scanning light beam in the main scanning direction and the sub-scanning direction.

 The two-piece fθ lens is constructed by sequentially attaching a first lens having a meniscus concave surface on the MEMS reflection mirror side and a second lens of a meniscus or biconcave lens, from a MEMS reflection mirror. Either the concave surface or the convex surface of the second lens of the meniscus may be attached to the MEMS reflecting mirror side. This two-piece fθ lens is a kind of MEMS LSU two-piece fθ lens that can accurately form the reflected scanning light beam on the target by the MEMS reflecting mirror and realize the linear scanning effect required by the LSU. It is the first object of the present invention to provide

 A second object of the present invention is to provide a two-piece fθ lens suitable for a kind of MEMS LSU, which achieves a high resolution effect by reducing the area of a spot projected on a target. .

 The deviation width between the main scanning direction and the sub-scanning direction due to the off-axis of the scanning light beam increases, and the distortion correction for the problem that the imaging spot on the target becomes an elliptical shape is processed. It is a third object of the present invention to provide a two-piece fθ lens suitable for a kind of MEMS LSU, which is made uniform and achieves an improvement in resolution quality effect.

 Therefore, the two-piece fθ lens suitable for the MEMS LSU of the present invention is a light source that emits at least a laser beam, and a MEMS reflection mirror that reflects the laser beam emitted from the light source while being swung left and right due to resonance to a scanning beam as a target. Make an image. When implemented in a laser beam printer, this target is usually a photosensitive drum (ie, a drum), that is, the spot waiting for image formation is scanned from the light source emitting the laser beam to the left and right by the MEMS reflection mirror. The laser beam is reflected to form a scanning beam. The scanning beam is corrected in angle and position by a two-piece fθ lens suitable for the MEMS LSU of the present invention, and a spot is formed on the photosensitive drum. On the other hand, since the photosensitive agent is applied to the photosensitive drum, the toner is gathered on the paper and the data is printed out.

 The two-piece fθ lens of the present invention includes a first lens and a second lens from the MEMS reflecting mirror. Among them, the first lens has a first optical surface and a second optical surface, and a single-vibration MEMS reflection mirror performs constant-speed scanning of a non-constant-speed scanning phenomenon in which the spot interval on the imaging surface gradually decreases or increases with time. The laser beam is projected onto the imaging plane to perform constant velocity scanning. The second lens has a third optical surface and a fourth optical surface, and the scanning light beam is out of the optical axis in the main scanning direction and the sub-scanning direction, and the formation of an imaging deviation on the photosensitive drum is made uniform. The scanning light beam of the first lens is corrected and condensed on the target.

 The two-piece fθ lens suitable for the MEMS LSU according to the present invention can accurately form the reflected scanning beam on the target by the MEMS reflecting mirror, thereby realizing the linear scanning effect required by the LSU.

1 is a schematic diagram of an optical path of a two-piece fθ lens of the present invention. FIG. 6 is a relationship diagram between a scanning angle θ of the MEMS reflection mirror and time t. It is the optical path figure and code | symbol explanatory drawing of the scanning light of the 1st lens which provides the concave surface of a meniscus in the MEMS reflective mirror side, and the 2nd lens which provides the concave surface of a meniscus in a MEMS reflective mirror. It is the optical path figure and code | symbol explanatory drawing of the scanning ray of the 1st lens which provides the concave surface of a meniscus in the MEMS reflective mirror side, and a biconcave second lens. It is the optical path figure and code | symbol explanatory drawing of the scanning light of the 1st lens which provides the concave surface of a meniscus in the MEMS reflective mirror side, and the 2nd lens which provides the convex surface of a meniscus in a MEMS reflective mirror. FIG. 4 is a diagram illustrating a state in which a spot area changes depending on a projection position after a scanning beam is projected onto a photosensitive drum. It is a figure which shows the relationship between the Gaussian distribution map of a laser beam, and light intensity. FIG. 6 is an optical path diagram and an explanatory diagram of scanning light beams of a first lens in which a concave surface of a meniscus according to an embodiment is provided on the MEMS reflection mirror side and a second lens in which a concave surface of the meniscus is provided on the MEMS reflection mirror side. It is the optical path figure and code | symbol explanatory drawing of the scanning light of the 2nd lens which consists of the 1st lens which provides the concave surface of the meniscus by the Example at the MEMS reflective mirror side, and a biconcave lens. It is the optical path figure and code | symbol explanatory drawing of the scanning light of the 1st lens which provides the concave surface of the meniscus by the Example on the MEMS reflective mirror side, and the 2nd lens which consists of a convex surface of a meniscus. FIG. 3 is a spot schematic diagram according to Example 1. FIG. 6 is a spot schematic diagram according to Example 2. FIG. 6 is a spot schematic diagram according to Example 3. FIG. 6 is a spot schematic diagram according to Example 4. FIG. 9 is a schematic spot view according to Example 5. 7 is a spot schematic diagram according to Example 6. FIG. FIG. 10 is a spot schematic diagram according to Example 7. FIG. 10 is a spot schematic diagram according to Example 8. FIG. 10 is a spot schematic diagram according to Example 9. FIG. 10 is a spot schematic diagram according to Example 10. FIG. 14 is a spot schematic diagram according to Example 11. FIG. 14 is a spot schematic diagram according to Example 12. FIG. 14 is a spot schematic diagram according to Example 13. FIG. 14 is a spot schematic diagram according to Example 14; FIG. 18 is a spot schematic diagram according to Example 15. 18 is a spot schematic diagram according to Example 16. FIG.

 FIG. 1 shows a schematic diagram of an optical path of a MEMS LSU two-piece fθ lens according to the present invention. The MEMS LSU two-piece fθ lens according to the present invention includes a first lens 131 having a first optical surface 131a and a second optical surface 131b, and a second lens having a third optical surface 132a and a fourth optical surface 132b. 132 and suitable for MEMS LSU. As shown in the figure, the MEMS LSU mainly includes a laser light source 11, a MEMS reflecting mirror 10, a cylindrical lens 16, two optoelectronic sensors 14a and 14b, and a target to be a photoreceptor. In this figure, the target is implemented by a photosensitive drum (drum) 15. The laser beam 111 generated from the laser light source 11 passes through the cylindrical lens 16 and is then projected onto the MEMS reflection mirror 10. The MEMS reflection mirror 10 reflects the laser beam 111 while swinging left and right due to resonance, and becomes scanning light beams 113a, 113b, 114a, 114b, 115a, and 115b. Among them, the scanning rays 113a, 113b, 114a, 114b, 115a, and 115b are referred to as the sub-scanning direction in the projection in the X direction and the main scanning direction in the Y direction, respectively. Further, the scanning angle of the MEMS reflecting mirror 10 is referred to as θc.

 The MEMS reflection mirror 10 performs simple vibration, and its movement angle is a sine change with respect to time, and the emission angle of scanning light and time shown in FIG. 2 are in a non-linear relationship. It is apparent that the wave angle a-a 'and wave valley b-b' shown in the figure are smaller than the bands a-b and a'-b '. The angular velocity imbalance phenomenon is caused by the formation of an imaging deviation on the photosensitive drum 15 by the scanning light beam. Therefore, the photoelectric sensors 14a and 14b are attached within the range of the maximum angle ± θc of the MEMS reflecting mirror 10, and the scissor angle is referred to as ± θp. The laser beam 111 is reflected from the wave peak of FIG. 2 by the MEMS reflecting mirror 10, and at this time, the scanning light beam of FIG. 1 corresponds to the position 115a. Subsequently, when the optoelectronic sensor 14a detects the scanning beam, it indicates that the MEMS reflecting mirror 10 has been swung to the + θp angle. This corresponds to the position of the scanning light beam 114a in FIG. When the change in the scanning angle of the MEMS reflecting mirror 10 is point a in FIG. 2, this corresponds to the position of the scanning light beam 113a. At this time, the laser light source 11 emits a laser beam 111 by driving. Further, when the scanning beam reaches the point b in FIG. 2, it corresponds to the position of the scanning light beam 113b. (In the ± θn angle range, this corresponds to emission of the laser beam 111 from the laser light source 11). Subsequently, when the MEMS reflection mirror 10 vibrates in reverse, the band a′-b ′ also goes through the same process as described above, and the laser light source 11 is driven to emit the laser beam 111. This completes one cycle.

With reference to FIG. 1 and FIGS. FIGS. 3A to 3C show optical paths of scanning rays that pass through the first lens 131 and the second lens 132. Of these, ± θn is an effective scanning angle, and when the rotation angle of the MEMS reflecting mirror 10 enters ± θn, the laser light source 11 emits a laser beam 111 waiting for scanning, and the scanning beam reflected by the MEMS reflecting mirror 10 is reflected. It becomes. When the scanning light beam passes through the first lens 131, the distance and time reflected by the MEMS reflecting mirror 10 by the reflection of the first optical surface 131a and the second optical surface 131b of the first lens 131 have a nonlinear relationship. Replace the ray with a scanning ray with distance and time linearity relationship. Subsequently, after passing through the first lens 131 and the second lens 132, the first optical surface 131a, the second optical surface 131b, the third optical surface 132a, and the fourth optical surface 132b of the first lens 131 and the second lens 132. In addition, the scanning light beam is condensed on the photosensitive drum 15 by the light condensing effect formed from the interval between the optical surfaces, and then a row of spots on the photosensitive drum 15.
2 is projected onto the photosensitive drum 15. The interval between the two spots at the farthest distance is referred to as an effective scanning window 3. D1 is the distance from the MEMS reflecting mirror 10 to the first optical surface 131a, d2 is the distance from the first optical surface 131a to the second optical surface 131b, and d3 is the second optical surface 131b to the third optical surface. D4 is the distance from the third optical surface 132a to the fourth optical surface 132b, d5 is the distance from the fourth optical surface 132b to the photosensitive drum 15, and R1 is the radius of curvature of the first optical surface 131a. (Curvature), R2 represents the radius of curvature of the second optical surface 131b, R3 represents the radius of curvature of the third optical surface 132a, and R4 represents the radius of curvature of the fourth optical surface 132b.

FIG. 4 shows an aspect diagram in which the spot area changes according to the projection position after the scanning beam is projected onto the photosensitive drum. When the scanning light beam 113c passes through the first lens 131 and the second lens 132 along the optical axis direction and is projected onto the photosensitive drum 15, the incident angle to the first lens 131 and the second lens 132 is zero. Therefore, the shift rate formed in the main scanning direction is also zero. Therefore, the spot 2a imaged on the photosensitive drum 15 is circular. When the scanning light beams 113a and 113b pass through the first lens 131 and the second lens 132 and are projected onto the photosensitive drum 15, the scissor angles formed from the optical axis of the first lens 131 and the second lens 132 are not zero. Since the shift rate in the scanning direction is not zero, the projection length in the main scanning direction is larger than the spot formed from the scanning light beam 111a. Such a phenomenon is the same in the sub-scanning direction, and the spot formed from the scanning light beam deviated from the scanning light beam 111a becomes larger. Therefore, the spots 2b and 2c imaged on the photosensitive drum 15 are elliptical, and the areas of the spots 2b and 2c are larger than the spot 2a. Of these, S _a0 and S _b0 are the lengths of the scanning light spot on the reflecting surface of the MEMS reflecting mirror 10 in the main scanning direction (Y direction) and the sub-scanning direction (X direction), respectively, and G _a shown in FIG. G _b indicates the beam radii in the Y direction and the X direction, respectively, when the Gaussian beam of the scanning light beam has a light intensity of 13.5%. However, FIG. 5 illustrates only the laser beam radius in the Y direction.

 As described above, the two-piece fθ lens of the present invention corrects the distortion of the scanning beam reflected from the MEMS reflecting mirror 10 and the scanning beam of the Gaussian beam, and the relationship between time and angular velocity is time-distance. Replace with the relationship. In the main scanning direction and the sub-scanning direction, the scanning beam radii in the X and Y directions have a predetermined magnification at each angle of the fθ lens, form a spot on the image plane, and achieve the required resolution. provide.

In order to achieve the above effect, the first optical surface 131a or the second second optical surface 131b of the first lens 131 of the two-piece fθ lens of the present invention, and the third optical surface 132a or the fourth optical surface of the second lens 132 are used. A spherical curved surface or an aspheric curved surface can be designed in the main scanning direction or the sub scanning direction of each of the surfaces 132b. However, when designing an aspherical curved surface, the following curved surface equation is used.
1: Anamorphic equation (Anamorphic equation)

Formulas in (2), Z is the distance from the optical axis direction of any point on the lens until the switching plane origin (SAG), _{C x} and _{C y} are respectively X and Y directions of the curvature (curvature) the, Kx and _{K y} is the conical coefficient in the X and Y directions _{(conic coefficient), a R,} B R, C R and _{D R} are 4,6 respectively rotationally symmetrical part (rotationally symmetric portion), The 8 and 10th power cone thermic deformation coefficients A _P , B _P , C _P and D _P are the 4th, 6th, 8th and 10th powers of the non-totally symmetrical components, respectively. _{C x = C y, Kx =} Ky, _and, when _{a P = B P = C P} = D P = 0 Simplifies the single aspheres.
2: Toric equation

In Equation (3), Z is the distance from the optical axis direction of any point on the lens to the origin switching plane (SAG), _{C y} and _{C x} are respectively Y and X directions of the curvature (curvature) , K _y is the conic coefficient in the Y direction, and B ₄ , B 6, B 8 and B 10 are the conical deformation coefficients of the _fourth , sixth, eighth and tenth power coefficients (4th to 10th order coefficients). the conic). When C _x = C _y and K _y = A _P = B _P = C _P = D _P = 0, it is simplified to a single spherical body.

 It is conceivable that the scanning light source is kept in constant velocity scanning on the image plane on the target, for example, the two spot intervals are kept the same at two identical time intervals. In the two-piece fθ lens according to the present invention, the scanning light beam is corrected by the first lens 131 and the second lens 132 between the scanning light beam 113a and the scanning light beam 113b, and two scanning light beams having the same time interval are used. Thus, the two spot distances formed on the imaging photosensitive drum 15 are made the same. For this reason, the two-piece fθ lens according to the present invention forms and condenses Ga and Gb smaller Gaussian beams between the reflected scanning light beam 113a and the scanning light beam 113b by the MEMS reflecting mirror 10, and collects them. A small spot can be formed on the top. In addition, the two-piece fθ lens according to the present invention makes the size of the spot imaged on the photosensitive drum 15 uniform (however, it is limited to the range required by the resolution), and an optimal resolution effect is obtained.

 As shown in FIGS. 3A to 3C, the two-piece fθ lens of the present invention includes a first lens 131 and a second lens 132 in order from the MEMS reflecting mirror 10. The first lens 131 includes a lens having a meniscus concave surface on the MEMS reflection mirror 10 side. The first lens 131 includes a first optical surface 131a and a second optical surface 131b. The scanning light spot having a non-linear relationship in time is replaced with a scanning light spot having a linear relationship in distance and time. On the other hand, the second lens 132 has a third optical surface 132a and a fourth optical surface 132b, corrects the scanning light spot of the first lens 131, and condenses it on the photosensitive drum 15. The second lens 132 is a lens in which the concave surface of the meniscus shown in FIG. 3A is provided on the MEMS reflecting mirror 10 side, and is constituted by a biconcave lens of meniscus shown in FIG. 3B, or the convex surface of the meniscus shown in FIG. Any structure provided on the side may be used. These two-piece fθ lenses image the scanning light beam reflected by the MEMS reflection mirror 10 on the photosensitive drum 15. Among them, the first optical surface 131a, the second optical surface 131b, the third optical surface 132a, and the fourth optical surface 132b have an optical surface composed of at least one aspherical body in the main scanning direction, and the first optical surface The surface 131a, the second optical surface 131b, the third optical surface 132a, and the fourth optical surface 132b have an optical surface composed of at least one aspherical body in the sub-scanning direction, or all spherical bodies in the sub-scanning direction. Attach an optical surface consisting of

もしくは、主走査方向において、数式（６）の条件を満足する。

かつ、副走査方向において、数式（７）の条件を満足する。

The two-piece fθ lens shown in FIG. 3A includes a first lens 131 and a second lens 132. In terms of optical effects, the following numerical expressions (4) and (5) are further satisfied in the main scanning direction of the two-piece fθ lens according to the present invention.

Alternatively, the condition of Formula (6) is satisfied in the main scanning direction.

In addition, the condition of Expression (7) is satisfied in the sub-scanning direction.

In equations (4) and (6), f _{(1) Y} represents the focal length of the first lens 131 in the main scanning direction, and in equations (5) and (6), f _{(2) Y} represents the first The focal length of the two lenses 132 in the main scanning direction is expressed by the following formula (4): d ₃ is the MEMS reflecting mirror 10 of the second lens 132 from the optical surface on the photosensitive drum 15 side of the first lens 131 at θ = 0 °. D ₄ is the thickness of the second lens 132 at θ = 0 °, and d ₅ is the thickness of the second lens 132 at θ = 0 ° in equations (4) and (5). the distance from the optical surface of the photosensitive drum 15 side to the photosensitive drum 15, the formula (6), in (7), fs is the decoding focal length of the two pieces type fθ lens, in equation (7), R _ix the radius of curvature in the sub-scanning direction of the i-th optical surface, in equation (6), n _d1 and n _d2 includes a first lens 131 refractive index of the second lens 132 (refraction i dex) are shown, respectively.

Since the spot formed by the two-piece fθ lens according to FIG. 3A of the present invention is made uniform, the proportional value of the maximum spot and the minimum spot satisfies the condition of Expression (8) as shown by δ.

Further, the resolution formed by the two-piece fθ lens according to FIG. 3A of the present invention is η _max is the maximum proportional value obtained by scanning the spot of the scanning beam on the reflecting surface of the MEMS reflecting mirror 10 on the photosensitive drum 15, η _min represents the minimum proportional value obtained by scanning the spot of the scanning beam on the reflecting surface of the MEMS reflecting mirror 10 onto the photosensitive drum 15, thereby satisfying the conditions of the equations (9) and (10). .

In Equations (9) and (10), S _a and S _b are the lengths in the main scanning direction and the sub scanning direction of the spot formed from the scanning light beam on the photosensitive drum 15 (see FIG. 4), and δ is Proportional values of the minimum spot and the maximum spot on the photosensitive drum 15, S _a0 and S _b0 indicate the lengths of the spot of the scanning light beam on the reflection surface of the MEMS reflection mirror 10 in the main scanning direction and the sub scanning direction, respectively.

もしくは、主走査方向において、数式（１３）の条件を満足する。

かつ、副走査方向において、数式（１４）の条件を満足する。

A two-piece fθ lens as shown in FIG. 3B includes a first lens 131 and a second lens 132. In terms of optical effects, the present invention further satisfies the conditions of equations (11) and (12) in the main scanning direction of the two-piece fθ lens.

Alternatively, the condition of Expression (13) is satisfied in the main scanning direction.

In addition, the condition of Expression (14) is satisfied in the sub-scanning direction.

この二片式fθレンズによって形成される解像度は、数式（１６），（１７）の条件をそれぞれ満足する。

Further, since the spot formed by the two-piece fθ lens according to FIG. 3B of the present invention is made uniform, the scanning beam is expressed by a proportional value δ between the maximum value and the minimum value of the laser beam size on the photosensitive drum 15. The condition (15) is satisfied.

The resolution formed by this two-piece fθ lens satisfies the conditions of equations (16) and (17), respectively.

もしくは、主走査方向において、数式（２０）の条件を満足する。

かつ、副走査方向において、数式（２１）の条件を満足する。

The two-piece fθ lens shown in FIG. 3C includes a first lens 131 and a second lens 132. In terms of optical effect, the conditions of the equations (18) and (19) are further satisfied in the main scanning direction of the two-piece fθ lens according to the present invention.

Alternatively, the condition of Expression (20) is satisfied in the main scanning direction.

In addition, the condition of Expression (21) is satisfied in the sub-scanning direction.

この二片式fθレンズによって形成される解像度は、数式（２３），（２４）の条件をそれぞれ満足する。

Further, since the spot formed by the two-piece fθ lens is made uniform, the proportional value between the maximum value and the minimum value of the laser beam size on the photosensitive drum 15 by the scanning light beam is represented by δ, so that the condition of Equation (22) is satisfied. Satisfied.

The resolution formed by this two-piece fθ lens satisfies the conditions of equations (23) and (24), respectively.

  In order to ensure the structure and technical features of the present invention, a preferred embodiment will be described in detail with reference to the following diagrams.

The embodiments disclosed below are intended to illustrate the main components of a MEMS LSU two-piece fθ lens according to the present invention. Therefore, the embodiments disclosed below of the present invention can also be applied to ordinary MEMS LSUs. However, in general MEMS LSUs, structures other than the two-piece fθ lens disclosed in the present invention are known techniques. Those skilled in the art can understand that the components of the two-piece fθ lens suitable for the MEMS LSU according to the present invention are not limited to the structures of the embodiments disclosed below. In other words, this MEMS
Each component of the LSU two-piece fθ lens can be variously modified, modified, or changed in effect. As an example, it is assumed that the radius of curvature or surface shape design, material selection, and spacing adjustment of the first lens 131 and the second lens 132 are not limited.

Both the first lens 131 and the second lens 132 of the two-piece fθ lens according to this embodiment shown in FIGS. 3A and 6A are configured by providing the concave surface of the meniscus on the MEMS reflection mirror 10 side. The first optical surface 131a of the first lens 131 and the fourth optical surface 132b of the second lens 132 are aspherical bodies, designed by the aspherical surface formula of Formula (2), and the second optical surface 131b of the first lens 131 is designed. The third optical surface 132a of the second lens 132 is an aspherical body and is designed by the aspherical surface formula of Formula (2). The optical characteristics and aspherical parameters are as shown in Tables 1 and 2.

The optical surface of the two-piece fθ lens constructed by this, f _{(1) Y} = 152.84 (mm), f _{(2) Y} = -132.768
(mm) replaces the scanning beam with a scanning beam spot having a linear relationship between distance and time, and the spot S _a0 = 154.6 (μm) and S _b0 = 3587.48 (μm) on the MEMS reflecting mirror 10 are scanned. A scanning beam is formed, converged on the photosensitive drum 15 and formed into a small spot, and the conditions of the mathematical expressions (4) to (10) shown in Table 3 are satisfied. Table 4 shows the maximum diameter (μm) of a geometrical spot (Geometric Spot) composed of a Gaussian beam of a spot up to the distance (mm) from the central axis z-axis on the photosensitive drum 15 to the central axis Y in the Y direction. Further, in the spot distribution diagram according to the present embodiment, the unit circle diameter is 0.05 mm as shown in FIG.

As shown in FIGS. 3A and 6A, the first lens 131 and the second lens 132 of the two-piece fθ lens according to this embodiment are configured by providing a concave surface of the meniscus on the MEMS reflection mirror 10 side. The first optical surface 131a of the first lens 131 is an aspherical body, designed by the aspherical surface formula of Formula (3), and the second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 are designed. Is an aspherical body, and is designed by the aspherical surface formula of Equation (2). The fourth optical surface 132b of the second lens 132 is a spherical body. The optical characteristics and the parameters of the aspherical body are as shown in Tables 5 and 6.

The optical surface of the two-piece fθ lens constructed in this way, f _{(1) Y} = 750.157 (mm), f _{(2) Y} = -12420.515 (mm) The spots S _a0 = 14.27 (μm) and S _b0 = 3027.158 (μm) on the MEMS reflecting mirror 10 after scanning are formed by scanning to form a scanning beam and converge on the photosensitive drum 15 to be small. It forms in a spot and the conditions of numerical formula (4)-(10) shown in Table 7 are satisfied. Table 8 shows the maximum diameter (μm) of the geometric spot composed of the Gaussian beam of the spot up to the distance (mm) between the central axis z-axis on the photosensitive drum 15 and the central axis Y in the Y direction. Further, as shown in the spot distribution diagram of this embodiment as shown in FIG. 8, the unit circle diameter is 0.05 mm.

As shown in FIGS. 3A and 6A, the first lens 131 and the second lens 132 of the two-piece fθ lens according to this embodiment are configured by providing a concave surface of the meniscus on the MEMS reflection mirror 10 side. The sub-scanning direction of the first optical surface 131a of the first lens 131 and the fourth optical surface 132b of the second lens 132 is a spherical body, the second optical surface 131b of the first lens 131 and the third optical surface of the second lens 132. 132a is an aspherical body and is designed by the aspherical surface formula of Formula (2). Note that the main scanning direction of the first optical surface 131a of the first lens 131 and the fourth optical surface 132b of the second lens 132 is an aspherical body, and is designed by the aspherical surface formula of Equation (3). The optical characteristics and aspherical parameters are as shown in Tables 9 and 10.

The optical surface and optical path diagram of the two-piece fθ lens constructed as described above are shown in FIG. The scanning light beam is replaced with a scanning light beam spot having a linear relationship between distance and time by f _{(1) Y} = 4831.254 (mm) and f _{(2) Y} = -559.613 (mm), and then the spot on the MEMS reflecting mirror 10 S _a0 = 14.488 (μm) and S _b0 = 2800.64 (μm) are scanned to form a scanning beam, converge on the photosensitive drum 15 to form a small spot, and the formula (4) shown in Table 11 ) To (10) are satisfied. Table 12 shows the maximum diameter (μm) of the geometric spot formed by the Gaussian beam of the spot up to the distance (mm) from the central axis z-axis on the photosensitive drum 15 to the central axis Y in the Y direction. Furthermore, as shown in the spot distribution chart of this embodiment in FIG. 9, the unit circle diameter is 0.05 mm.

As shown in FIGS. 3A and 6A, the first lens 131 and the second lens 132 of the two-piece fθ lens according to this embodiment are configured by providing a concave surface of the meniscus on the MEMS reflection mirror 10 side. The first optical surface 131a of the first lens 131 and the fourth optical surface 132b of the second lens 132 are aspherical bodies, designed by the aspherical surface formula of Formula (3), and the second optical surface 131b of the first lens 131 is designed. The third optical surface 132a of the second lens 132 is an aspherical body and is designed by the aspherical surface formula of Formula (2). The optical characteristics and aspherical parameters are as shown in Table 13 and Table 14.

FIG. 11 shows an optical surface and an optical path diagram of the two-piece type fθ lens configured as described above. By using f _{(1) Y} = 199.885 (mm) and f _{(2) Y} = -162.471 (mm), the scanning light beam is replaced with a scanning light beam spot having a linear relationship between distance and time, and then a spot on the MEMS reflecting mirror 10 S _a0 = 14.374 (μm) and S _b0 = 2917.652 (μm) are scanned to form a scanning beam, converge on the photosensitive drum 15 to form a small spot, and the formula (4) shown in Table 15 ) To (10) are satisfied. Table 16 shows the maximum diameter (μm) of the geometric spot formed by the Gaussian beam of the spot up to the distance (mm) from the central axis z-axis on the photosensitive drum 15 to the central axis Y in the Y direction. Further, as shown in the spot distribution diagram of this embodiment in FIG. 10, the unit circle diameter is 0.05 mm.

Please refer to FIG. 3B and FIG. 6B. 6B is an optical path diagram through which the scanning beam passes through the first lens 131 and the second lens 132 in the embodiment of the present invention. In the present embodiment, the first lens 131 including the first lens 131 and the second lens 132 of the two-piece fθ lens is composed of a lens having a concave surface of the meniscus on the MEMS reflecting mirror 10 side, and the second lens 132 is The first optical surface 131a and the second optical surface 131b of the first lens 131, the third optical surface 132a of the second lens 132, and the fourth optical surface 132b are aspherical bodies. The design is made based on the formula of the aspherical surface of Formula (2). Table 17 and Table 18 show the optical characteristics and parameters of the aspherical body.

Optical surface of the two-piece fθ lens constructed by this, f _{(1) Y} = 102.512 (mm), f _{(2) Y} = -64.358 (mm), f _sX = _42.255 (mm), f _sY = -600 (mm) indicates that the scanning light beam is replaced with a scanning light beam spot whose distance and time are linear, and the spots S _a0 = 18.17 (μm) and S _b0 = 3918.086 (μm) on the MEMS reflecting mirror 10 are scanned, A scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (11) to (17) shown in Table 19. Table 20 shows the maximum diameter (μm) of the geometric spot formed by the Gaussian beam of the spot up to the distance (mm) between the central axis z-axis on the photosensitive drum 15 and the central axis Y in the Y direction. Further, a spot distribution diagram according to this embodiment is shown in FIG.

As shown in FIGS. 3B and 6B, the two-piece fθ lens according to the present embodiment includes a first lens 131 and a second lens 132. The first lens 131 is composed of a lens having a concave meniscus on the side of the MEMS reflecting mirror 10, and the second lens 132 is a biconcave lens, which has a first optical surface 131a and a second optical surface 131b of the first lens 131. The third optical surface 132a of the second lens 132 is an aspherical body. It is designed based on the aspherical body formula of Equation 3. Note that the fourth optical surface 132b of the second lens 132 is an aspherical body, and is designed based on the aspherical surface formula of Formula 2. The optical characteristics and aspherical parameters are as shown in Table 21 and Table 22.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 91.725 (mm), f _{(2) Y} = -53.286 (mm), f _sX = 40.302 (mm), f _sY =- In the case of 480 (mm), the scanning beam is replaced with a scanning beam spot having a linear relationship between distance and time, and the spot S _a0 = 18.17 (μm) and S _b0 = 3918.08 (μm) on the MEMS reflecting mirror 10 are scanned. Then, a scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (11) to (17) shown in Table 23. Table 24 shows the maximum diameter (μm) of the geometric spot (Geometric Spot) composed of the Gaussian beam of the spot up to the distance (mm) from the central axis z-axis on the photosensitive drum 15 to the central axis Y in the Y direction. Further, a spot distribution diagram according to this embodiment is shown in FIG.

As shown in FIGS. 3B and 6B, the two-piece fθ lens according to the present embodiment includes a first lens 131 and a second lens 132. The first lens 131 is constituted by a lens having a concave surface of a meniscus on the MEMS reflection mirror 10 side, and the second lens 132 is constituted by a biconcave lens. The third optical surface 132a of the second lens 132 including the first optical surface 131a and the second optical surface 131b of the first lens 131 is an aspherical body, and is designed based on the aspherical surface formula of Equation (3). . The fourth optical surface 132b of the second lens 132 is an aspherical body, and is designed based on the aspherical surface formula of Expression (2). The optical characteristics and aspherical parameters are as shown in Table 25 and Table 26.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 100.396 (mm), f _{(2) Y} = -58.178 (mm), f _sX = 38.34 (mm), f _sY =- In 318.7 (mm), the scanning light beam is replaced with a scanning light beam spot having a linear relationship between distance and time, and the spot S _a0 = 23.62 (μm) and S _b0 = 3667.96 (μm) on the MEMS reflecting mirror 10 are scanned. Then, a scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (11) to (17) shown in Table 27. Table 28 shows the maximum diameter (μm) of the geometric spot formed by the Gaussian beam of the spot up to the distance (mm) from the central axis z-axis on the photosensitive drum 15 to the central axis Y in the Y direction. Further, a spot distribution diagram according to this embodiment is shown in FIG.

As shown in FIGS. 3B and 6B, the two-piece fθ lens according to the present embodiment includes a first lens 131 and a second lens 132. The first lens 131 is constituted by a lens having a concave surface of a meniscus on the MEMS reflection mirror 10 side, and the second lens 132 is constituted by a biconcave lens. The third optical surface 132a of the second lens 132 including the first optical surface 131a and the second optical surface 131b of the first lens 131 is an aspherical body. It is designed based on the aspherical body formula of Equation 3. Note that the fourth optical surface 132b of the second lens 132 is an aspherical body, and is designed based on the aspherical surface formula of Formula 2. The optical characteristics and aspherical parameters are as shown in Table 29 and Table 30.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 129.589 (mm), f _{(2) Y} = -59.303 (mm), f _sX = 40.549 (mm), f _sY =- In 157.192 (mm), the scanning beam is replaced with a scanning beam spot having a linear relationship between distance and time, and spot S _a0 = 280.62 (μm) and S _b0 = 4059.84 (μm) on the MEMS reflecting mirror 10 It scans and converges on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (11) to (17) shown in Table 31. Table 32 shows the maximum diameter (μm) of a geometrical spot (Geometric Spot) made of a Gaussian beam having a distance (mm) between the central axis z-axis of the photosensitive drum 15 and the central axis Y in the Y direction. Further, a spot distribution diagram according to this embodiment is shown in FIG.

As shown in FIGS. 3B and 6B, the two-piece fθ lens according to this embodiment includes a first lens 131 and a second lens 132. The first lens 131 is composed of a lens having a meniscus concave surface on the MEMS reflecting mirror 10 side, and the second lens 132 is composed of a biconcave lens. The third optical surface 132a of the second lens 132 including the first optical surface 131a and the second optical surface 131b of the first lens 131 is an aspherical body, and is designed based on the aspherical surface formula of Equation (3). . The fourth optical surface 132b of the second lens 132 is an aspherical body, and is designed based on the aspherical surface formula of Expression (2). The optical characteristics and parameters of the aspherical body are as shown in Table 33 and Table 34.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 92.049 (mm), f _{(2) Y} = -53.487 (mm), f _sX = 40.278 (mm), f _sY =- In the case of 480 (mm), the scanning beam is replaced with a scanning beam spot having a linear relationship between distance and time, and the spot S _a0 = 18.17 (μm) and S _b0 = 3918.08 (μm) on the MEMS reflecting mirror 10 are scanned. Then, a scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (11) to (17) shown in Table 35. Table 36 shows the maximum diameter (μm) of a geometric spot (Geometric Spot) made up of a Gaussian beam of a spot up to a distance (mm) from the central axis z-axis of the photosensitive drum 15 to the central axis Y in the Y direction. Further, a spot distribution diagram according to this embodiment is shown in FIG.

As shown in FIGS. 3B and 6B, in this embodiment, the two-piece fθ lens includes the first lens 131 and the second lens 132, and the first lens 131 is a lens in which the concave surface of the meniscus is provided on the MEMS reflecting mirror 10 side. The second lens 132 is composed of a biconcave lens. The first optical surface 131a and the second optical surface 131b of the first lens 131 and the third optical surface 132a and the fourth optical surface 132b of the second lens 132 are also aspherical bodies. The design is based on the aspherical surface formula of Equation (2). Tables 37 and 38 show the optical characteristics and parameters of the aspherical body.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 102.145 (mm), f _{(2) Y} = -59.071 (mm), f _sX = 38.621 (mm), f _sY =- In the case of 480 (mm), the scanning beam is replaced with a scanning beam spot having a linear relationship between distance and time, and the spot S _a0 = 18.17 (μm) and S _b0 = 3918.08 (μm) on the MEMS reflecting mirror 10 are scanned. Then, a scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (11) to (17) shown in Table 39. Table 40 shows the maximum diameter (μm) of a geometric spot formed by a Gaussian beam of a spot whose center axis z-axis is a distance (mm) between the Y direction and the center axis Y on the photosensitive drum 15. Further, a spot distribution diagram according to this embodiment is shown in FIG.

As shown in FIGS. 3B and 6B, the two-piece fθ lens according to the present embodiment includes a first lens 131 and a second lens 132. The first lens 131 is composed of a lens having a meniscus concave surface on the MEMS reflecting mirror 10 side, and the second lens 132 is composed of a biconcave lens. The third optical surface 132a of the second lens 132, including the first optical surface 131a and the second optical surface 131b of the first lens 131, is an aspherical body, and is designed based on the aspherical surface formula of Equation 3. The fourth optical surface 132b of the second lens 132 is an aspherical body, and is designed based on the aspherical surface formula of Expression (2). The optical characteristics and parameters of the aspherical body are as shown in Table 41 and Table 42.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 92.228 (mm), f _{(2) Y} = -53.135 (mm), f _sX = 39.746 (mm), f _sY =- In the case of 480 (mm), the scanning beam is replaced with a scanning beam spot having a linear relationship between distance and time, and the spot S _a0 = 18.17 (μm) and S _b0 = 3918.08 (μm) on the MEMS reflecting mirror 10 are scanned. Then, a scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (11) to (17) shown in Table 43. Table 44 shows the maximum diameter (μm) of the geometric spot formed by the Gaussian beam of the spot up to the distance (mm) between the central axis z-axis on the photosensitive drum 15 and the central axis Y in the Y direction. Further, a spot distribution diagram according to this embodiment is shown in FIG.

Please refer to FIG. 3C and FIG. 6C. FIG. 4 is an optical path diagram through which a scanning beam passes through a first lens and a second lens in each of the embodiments of the present invention. In this embodiment, the two-piece fθ lens includes a first lens 131 and a second lens 132. The first lens 131 is a lens having a meniscus concave surface on the MEMS reflecting mirror side 10, and the second lens 132 is a meniscus. Is formed from a lens provided on the MEMS reflecting mirror side 10. Among them, the first optical surface 131a of the first lens 131 is a spherical body, and the second optical surface 131b and the third optical surface 132a and the fourth optical surface 132b of the second lens 132 are also aspherical bodies. The design is based on the aspherical surface formula of Equation (2). The optical characteristics and aspherical parameters are as shown in Table 45 and Table 46.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 145.78 (mm), f _{(2) Y} = -368.67 (mm), f _sX = 23.655 (mm), f _sY = 215.37 (mm) replaces the scanning beam with a scanning beam spot having a linear relationship between distance and time, and spot S _a0 = 13.642 (μm) and S _b0 = 3718.32 (μm) on the MEMS reflecting mirror 10 scan the scanning beam. Then, it converges on the photosensitive drum 15 to form a small spot, which satisfies the conditions of the equations (18) to (24) shown in Table 47. Table 48 shows the maximum diameter (μm) of a geometric spot (Geometric Spot) made up of a Gaussian beam with a distance (mm) between the central axis z-axis of the photosensitive drum 15 and the central axis Y in the Y direction. Further, a spot distribution diagram according to this embodiment is shown in FIG. In the figure, the unit circle diameter is 0.05 mm.

As shown in FIGS. 3C and 6C, the two-piece fθ lens according to this embodiment includes a first lens 131 and a second lens 132. The first lens 131 is composed of a lens having a concave surface of the meniscus on the MEMS reflection mirror 10 side, and the second lens 132 is composed of a lens having a convex surface of the meniscus on the MEMS reflection mirror 10 side. Among them, the first optical surface 131a and the second optical surface 131b of the first lens 131 are spherical bodies, the third optical surface 132a of the second lens 132 is an aspheric body, and the aspheric body formula of Formula (2). Design based on. The fourth optical surface 132b of the second lens 132 is an aspherical body. The design is based on the aspherical body formula of Equation (3). The optical characteristics and parameters of the aspherical body are as shown in Table 49 and Table 50.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 133.89 (mm), f _{(2) Y} = -233.70 (mm), f _sX = 20.084 (mm), f _sY = 274.205 (mm) indicates that the scanning light beam is replaced with a scanning light beam spot whose distance and time are linearly related, and the spot S _a0 = 13.824 (μm) and S _b0 = 3512.066 (μm) on the MEMS reflecting mirror 10 are scanned, A scanning beam is formed and converges on the photosensitive drum 15 to form a small spot, which satisfies the conditions of the equations (18) to (24) shown in Table 51. Table 52 shows the maximum diameter (μm) of a geometric spot (Geometric Spot) made up of a Gaussian beam of a spot up to a distance (mm) from the central axis z-axis on the photosensitive drum 15 to the central axis Y in the Y direction. Further, in the spot distribution diagram according to this embodiment, the unit circle diameter is 0.05 mm as shown in FIG.

As shown in FIGS. 3C and 6C, the two-piece fθ lens according to this embodiment includes a first lens 131 and a second lens 132. The first lens 131 is composed of a lens having a concave surface of the meniscus on the MEMS reflection mirror 10 side, and the second lens 132 is composed of a lens having a convex surface of the meniscus on the MEMS reflection mirror 10 side. Among them, the first optical surface 131a of the first lens 131 is a spherical body, and the second optical surface 131b and the third optical surface 132a and the fourth optical surface 132b of the second lens 132 are aspherical bodies. The design is based on the aspherical surface formula of Equation (2). The optical characteristics and parameters of the aspherical body are as shown in Table 53 and Table 54.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 124.07 (mm), f _{(2) Y} = -344.01 (mm), f _sX = 23.785 (mm), f _sY = 176.355 (mm) indicates that the scanning light beam is replaced with a scanning light beam spot whose distance and time are linear, and the spot S _a0 = 13.452 (μm) and S _b0 = 3941.106 (μm) on the MEMS reflecting mirror 10 are scanned, A scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (18) to (24) shown in Table 55. Table 56 shows the maximum diameter (μm) of a geometric spot (Geometric Spot) made of a Gaussian beam having a distance (mm) between the central axis z-axis of the photosensitive drum 15 and the central axis Y in the Y direction. Further, in the spot distribution diagram according to this embodiment, the unit circle diameter is 0.05 mm as shown in FIG.

As shown in FIGS. 3C and 6C, the two-piece fθ lens according to this embodiment includes a first lens 131 and a second lens 132. The first lens 131 is composed of a lens having a concave surface of the meniscus on the MEMS reflection mirror 10 side, and the second lens 132 is composed of a lens having a convex surface of the meniscus on the MEMS reflection mirror 10 side. Among them, the first optical surface 131a of the first lens 131 is a spherical body, and both the second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 are aspherical bodies. Design based on the aspherical formula. The fourth optical surface 132b of the second lens 132 is an aspherical body, and is designed based on the aspherical surface formula of Equation 3. The optical characteristics and aspherical parameters are as shown in Tables 57 and 58.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 136.21 (mm), f _{(2) Y} = -243.44 (mm), f _sX = 19.258 (mm), f _sY = 270.784 (mm) indicates that the scanning light beam is replaced with a scanning light beam spot whose distance and time are linear, and spots S _a0 = 13.81 (μm) and S _b0 = 3522.04 (μm) on the MEMS reflecting mirror 10 are scanned, A scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (18) to (24) shown in Table 59. Table 60 shows the maximum diameter (μm) of a geometrical spot (Geometric Spot) composed of a Gaussian beam of a spot up to a distance (mm) from the central axis z-axis of the photosensitive drum 15 to the central axis Y in the Y direction. Further, in the spot distribution diagram according to this embodiment, the unit circle diameter is 0.05 mm as shown in FIG.

As shown in FIGS. 3C and 6C, the two-piece fθ lens according to this embodiment includes a first lens 131 and a second lens 132. The first lens 131 is composed of a lens having a concave surface of the meniscus on the MEMS reflection mirror 10 side, and the second lens 132 is composed of a lens having a convex surface of the meniscus on the MEMS reflection mirror 10 side. Among them, the second optical surface 131b of the first lens 131 and the third optical surface 132a of the second lens 132 are both aspherical bodies, which are designed based on the aspherical surface formula of Formula (2). The first optical surface 131a and the fourth optical surface 132b of the second lens 132 are aspherical bodies. The design is based on the aspherical body formula of Equation (3). The optical characteristics and parameters of the aspherical body are as shown in Table 61 and Table 62.

The optical surface of the two-piece fθ lens configured in this way, f _{(1) Y} = 851.41 (mm), f _{(2) Y} = -2714.78 (mm), f _sX = 26.469 (mm), f _sY = 1221.728 (mm) indicates that the scanning light beam is replaced with a scanning light beam spot whose distance and time are linearly related, and the spot S _a0 = 14.31 (μm) and S _b0 = 2983.85 (μm) on the MEMS reflecting mirror 10 are scanned, A scanning beam is formed and converged on the photosensitive drum 15 to form a small spot, which satisfies the conditions of equations (18) to (24) shown in Table 63. Table 64 shows the maximum diameter (μm) of a geometric spot (Geometric Spot) composed of a Gaussian beam of a spot up to a distance (mm) from the central axis z-axis of the photosensitive drum 15 to the central axis Y in the Y direction. Further, in the spot distribution diagram according to the present embodiment, the unit circle diameter is 0.05 mm as shown in FIG.

From the description of the above embodiments, the present invention can realize at least the following effects.
B) By providing the two-piece fθ lens according to the present invention, the non-uniform scanning phenomenon in which the single-vibration MEMS reflecting mirror increases or decreases the spot interval on the imaging surface with time is corrected to uniform scanning. By projecting the beam onto the imaging surface and performing constant velocity scanning, the distance between the two spots imaged on the target can be matched.
(B) The installation of the two-piece fθ lens according to the present invention can reduce the spot imaged on the target by the distortion correction processing of the scanning light source in the main scanning direction and the sub-scanning direction.
The installation of the two-piece fθ lens according to the present invention can make the spot size formed on the target uniform by the distortion correction processing of the scanning light source in the main scanning direction and the sub-scanning direction.
The above is a description of the preferred embodiment of the present invention. These illustrate the invention and do not impose any restrictions. It should be noted that alterations, modifications, and equivalent changes made by those skilled in the art according to the claims of the present invention are also included in the claims of the present invention.

DESCRIPTION OF SYMBOLS 10 MEMS reflective mirror 11 Laser light source 111 Laser beam 113a, 113b, 113c, 114a, 114b, 115a, 115b Scanning light beam 131 1st lens 131a 1st optical surface
131b Second optical surface 132 Second lens 132a Third optical surface 132b Fourth optical surfaces 14a, 14b Photoelectric sensor 15 Photosensitive drum 16 Cylindrical lenses 2, 2a, 2b, 2c Spot 3 Effective scanning window

Claims (15)

In a two-piece fθ lens suitable for a microelectromechanical system laser scanning device (hereinafter abbreviated as MEMS LSU),
Includes a microelectromechanical system reflection mirror (hereinafter abbreviated as a MEMS reflection mirror) that reflects the laser beam emitted from the light source while shaking the emitted laser beam left and right by resonance and becomes a scanning beam, and a target to be exposed ,
The two-piece fθ lens is composed of a first lens in which the concave surface of the meniscus is provided on the MEMS reflection mirror side, and a second lens in which the concave surface of the meniscus is provided on the MEMS reflection mirror side, in order from the MEMS reflection mirror.
The first lens has a first optical surface and a second optical surface, and the reflection angle and time of the MEMS reflecting mirror are changed to a scanning light spot having a non-linear relationship between a distance and a time. Replace,
The second lens has a third optical surface and a fourth optical surface, corrects the scanning light beam of the first lens, condenses it on the target, and the MEMS reflection mirror by the two-piece fθ lens. A two-piece fθ lens suitable for a MEMS LSU, characterized in that the reflected light beam is imaged on the target. In a two-piece fθ lens suitable for MEMS LSU,
The main scanning direction of the two-piece fθ lens further satisfies Expressions (1) and (2),

The f _{(1) Y} is a focal length in the main scanning direction of the first lens, the f _{(2) Y} is a focal length in the main scanning direction of the second lens, and the d ₃ is θ = The distance from the optical surface on the first lens target side at 0 ° to the optical surface on the MEMS reflecting mirror side of the second lens, and d ₄ is the thickness of the second lens at θ = 0 °. 2. The two-piece fθ lens according to claim 1, wherein d ₅ is a distance from the optical surface on the second lens target side to the target at θ = 0 °. In a two-piece fθ lens suitable for MEMS LSU,
The two-piece fθ lens satisfies Formulas (3) and (4),
In the main scanning direction,

In the sub-scanning direction,

The f _{(1) Y} and the f _{(1) X} are focal lengths of the first lens in the main scanning direction and the sub-scanning direction, and the f _{(2) Y} and f _{(2) X} are the second focal lengths. The focal length in the main scanning direction and the sub-scanning direction of the lens, the fs is the composite focal length of the two-piece fθ lens, and the R _ix is the radius of curvature of the i-th optical surface in the X direction. 2. The two-piece fθ lens according to claim 1, wherein n _d1 and n _d2 are refractive indexes of the first lens and the second lens. In a two-piece fθ lens suitable for MEMS LSU,
The proportional value of the maximum spot and the minimum spot of the two-piece fθ lens satisfies Expression (5),

The S _a and S _b are the lengths in the main scanning direction and the sub scanning direction of the spot formed from the scanning light beam on the target, and δ is the minimum spot and the maximum spot on the target 2. The two-piece fθ lens according to claim 1, wherein In a two-piece fθ lens suitable for MEMS LSU,
The proportional value of the maximum spot on the target and the proportional value of the minimum spot on the target satisfy Equations (6) and (7), respectively.

The S _a0 is the length in the main scanning direction of the spot of the scanning beam on the MEMS reflecting mirror reflecting surface, and the S _b0 is the length of the spot of the scanning beam in the sub-scanning direction on the reflecting surface of the MEMS reflecting mirror. S _a is a length in the main scanning direction of a spot formed from the scanning light beam on the target, and S _b is a sub-portion of the spot formed from the scanning light beam on the target. The length in the scanning direction, and η _max is a proportional value of the maximum spot in which the spot of the scanning beam on the reflection surface of the MEMS reflection mirror is scanned on the target, η _min is the MEMS 2. The MEMS LSU 2 according to claim 1, wherein the spot of the scanning beam on the reflecting surface of the reflecting mirror is a proportional value of the minimum spot scanned on the target. Formula fθ lens. In a two-piece fθ lens suitable for MEMS LSU,
The MEMS LSU is composed of at least a light source that emits a laser beam, a MEMS reflection mirror that replaces the laser beam emitted from the light source with a scanning beam while swinging left and right due to resonance, and a target to be exposed.
The two-piece fθ lens is composed of a first lens provided with a concave surface of a meniscus on the side of the MEMS reflecting mirror and a biconcave second lens in order from the MEMS reflecting mirror.
The first lens includes a first optical surface and a second optical surface, and the first optical surface and the second optical surface are composed of an aspherical body in the main scanning direction,
A scanning beam spot having a non-linear relationship between reflection angle and time of the MEMS reflecting mirror is replaced with a scanning beam spot having a linear relationship between distance and time, and the second lens has a third optical surface and a fourth optical surface. In the main scanning direction of the third optical surface and the fourth optical surface, at least one optical surface is composed of an aspherical body,
The scanning beam of the first lens is corrected and condensed on the target, and the scanning beam reflected from the MEMS reflecting mirror is imaged on the target by the two-piece fθ lens. Two-piece fθ lens suitable for MEMS LSU. In a two-piece fθ lens suitable for MEMS LSU,
The main scanning direction of the two-piece fθ lens further satisfies Expressions (8) and (9),

The f _{(1) Y} is a focal length in the main scanning direction of the first lens, the f _{(2) Y} is a focal length in the main scanning direction of the second lens, and the d ₃ is θ = 0 ° is the distance from the optical surface on the first lens target side to the optical surface on the MEMS reflecting mirror side of the second lens, and d ₄ is the thickness of the second lens at θ = 0 °. The d-piece fθ lens according to claim 6, wherein d ₅ is a distance from the optical surface on the second lens target side to the target at θ = 0 °. In a two-piece fθ lens suitable for MEMS LSU,
The two-piece fθ lens satisfies Expressions (10) and (11),
In the main scanning direction,

In the sub-scanning direction,

The f _{(1) Y} and the f _{(2) Y} are focal lengths in the main scanning direction of the first lens and the second lens, and the f _sX is in the sub-scanning direction of the two-piece fθ lens. _FsY is a compound focal length in the main scanning direction of the two-piece fθ lens, Rix is a radius of curvature of the i-th optical surface in the sub-scanning direction, and n _d1 and The two-piece fθ lens according to claim 6, wherein the n _d2 is a refractive index of the first lens and the second lens, respectively. In a two-piece fθ lens suitable for MEMS LSU,
The proportional value of the maximum spot and the minimum spot formed on the target satisfies the formula (12),

Wherein S _a is the length of the main scanning direction of the spots formed from the scanning beam on the target object, wherein S _b is the sub-scanning direction length of the spot formed from the scanning beam on the target The δ is a proportional value between the minimum spot and the maximum spot on the target, and the two-piece fθ lens according to claim 6. In a two-piece fθ lens suitable for MEMS LSU,
The proportional value between the maximum spot formed on the target and the minimum spot formed on the target satisfies Equations (13) and (14),

S _a0 is the length in the main scanning direction of the spot of the scanning beam on the reflecting surface of the MEMS reflecting mirror, and S _b0 is the sub-scanning direction of the spot of the scanning beam on the reflecting surface of the MEMS reflecting mirror. S _a is a length in the main scanning direction of a spot formed from the scanning light beam on the target, and S _b is a spot formed from the scanning light beam on the target In the sub-scanning direction, and η _max is a proportional value of the maximum spot in which a scanning beam spot on the reflecting surface of the MEMS reflecting mirror is scanned on the target, and η _min is The two-piece fθ lens according to claim 6, wherein the spot of the scanning beam on the reflecting surface of the MEMS reflecting mirror is a proportional value of the minimum spot scanned on the target. In a two-piece fθ lens suitable for MEMS LSU,
The MEMS LSU includes at least a light source that emits a laser beam;
It consists of a MEMS reflecting mirror that replaces the laser beam emitted from the light source with a scanning beam while swinging left and right due to resonance, and a target to be exposed,
The two-piece fθ lens is composed of a first lens that provides the concave surface of the meniscus on the MEMS reflection mirror side and a second lens that provides the convex surface of the meniscus on the MEMS reflection mirror side in order from the MEMS reflection mirror.
The first lens has a first optical surface and a second optical surface, and the first optical surface and the second optical surface constitute an aspherical body in the main scanning direction. The angle and time reflected from the MEMS reflecting mirror side is replaced with a scanning light spot having a non-linearity relationship with a scanning light spot having a distance and time having a linearity relationship,
The second lens has a third optical surface and a fourth optical surface, and in the main scanning direction of the third optical surface and the fourth optical surface, at least one optical surface is composed of an aspherical body, The scanning beam of one lens is corrected, condensed on the target, and the scanning beam reflected from the MEMS reflecting mirror is imaged on the target by the two-piece fθ lens. Two-piece fθ lens suitable for MEMS LSU. In a two-piece fθ lens suitable for MEMS LSU,
The main scanning direction of the two-piece fθ lens further satisfies Expressions (15) and (16), respectively.

The f _{(1) Y} is a focal length in the main scanning direction of the first lens, the f _{(2) Y} is a focal length in the main scanning direction of the second lens, and the d ₃ is θ = 0 ° is the distance from the optical surface on the first lens target side to the optical surface on the MEMS reflecting mirror side of the second lens, and d ₄ is the thickness of the second lens at θ = 0 °. 12. The two-piece fθ lens according to claim 11, wherein d ₅ is a distance from the optical surface on the second lens target side to the target at θ = 0 °. In a two-piece fθ lens suitable for MEMS LSU,
Furthermore, the expressions (17) and (18) are satisfied,
In the main scanning direction,

In the sub-scanning direction,

The f _{(1) Y} and the f _{(2) Y} are focal lengths in the main scanning direction of the first lens and the second lens, and the f _sX is in the sub-scanning direction of the two-piece fθ lens. _FsY is a compound focal length in the main scanning direction of the two-piece fθ lens, Rix is a radius of curvature of the i-th optical surface in the sub-scanning direction, and n _d1 The two-piece fθ lens suitable for MEMS LSU according to claim 11, wherein the n _d2 is a refractive index of the first lens and the second lens, respectively. In a two-piece fθ lens suitable for MEMS LSU,
The proportional value of the maximum spot and the minimum spot formed on the target satisfies the formula (18),

The _Sa is the length in the main scanning direction of the spot formed from the scanning light beam on the target, and the S _b is the length in the sub-scanning direction of the spot formed from the scanning light beam on the target. The two-piece fθ lens according to claim 11, wherein the δ is a proportional value between the minimum spot and the maximum spot on the target. In a two-piece fθ lens suitable for MEMS LSU,
The proportional value of the maximum spot on the target and the proportional value of the minimum spot on the target satisfy Equations (20) and (21), respectively.

S _a0 is the length in the main scanning direction of the spot of the scanning beam on the reflecting surface of the MEMS reflecting mirror, and S _b0 is the sub-scanning direction of the spot of the scanning beam on the reflecting surface of the MEMS reflecting mirror. S _a is a length in the main scanning direction of a spot formed from the scanning light beam on the target, and S _b is a spot formed from the scanning light beam on the target In the sub-scanning direction, and η _max is a proportional value of the maximum spot in which a scanning beam spot on the reflecting surface of the MEMS reflecting mirror is scanned on the target, and η _min is The MEMS LSU two-piece fθ lens according to claim 11, wherein the spot of the scanning beam on the reflecting surface of the MEMS reflecting mirror is a proportional value of the minimum spot scanned on the target.

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