JP5765926B2 - Optical scanning device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to an optical scanning device and an image forming apparatus using the same, and is suitable for an image forming apparatus such as a laser beam printer (LBP) having an electrophotographic process, a digital copying machine, or a multifunction printer (multifunctional printer). It is.

  Conventionally, an optical scanning device is used in a laser beam printer (LBP), a digital copying machine, a multifunction printer, or the like. In this optical scanning device, a light beam that is light-modulated and emitted from the light source means according to an image signal is periodically deflected by, for example, a rotating polygon mirror. The deflected light beam is condensed in a spot shape on the surface of a photosensitive recording medium by an imaging optical system having fθ characteristics, and the surface is optically scanned to perform image recording.

  In recent years, in order to simplify and reduce the size of an optical scanning device, a sub-scanning oblique incidence optical system that causes a light beam to enter a rotary polygon mirror from an oblique direction within a sub-scan section is used. In the sub-scanning oblique incidence optical system, degradation of imaging performance peculiar to the sub-scanning oblique incidence optical system occurs, such as a scanning line curvature in which the scanning line is curved on the surface to be scanned and a spot rotation in which the wavefront aberration is twisted. Also, in many optical scanning devices, so-called main scanning oblique incidence, in which the optical axis of the imaging optical system and the optical axis of the incident optical system are arranged at an angle in the main scanning section for convenience of arrangement. An optical system is adopted.

  When such a sub-scanning oblique incidence optical system and a main scanning oblique incidence optical system are used, in addition to the above-described problems, a phenomenon occurs in which the scanning line tilts on the surface to be scanned, called scanning line tilt. . When an optical scanning device in which such imaging performance is deteriorated is used in an image forming apparatus, it is difficult to form a good image. Conventionally, various optical scanning apparatuses and image forming apparatuses in which scanning line curvature, twist of wavefront aberration, and scanning line inclination are corrected have been proposed (Patent Documents 1 to 3).

Japanese Patent Laid-Open No. 10-73778 JP-A-7-234370 JP 2006-72288 A

  In order to simplify and miniaturize the optical scanning device, it is effective to use the sub-scanning oblique incidence optical system and the main scanning oblique incidence optical system. However, when the main scanning oblique incident angle and the sub-scanning oblique incident angle are increased, scanning line curvature, twisting of wavefront aberration, and scanning line tilt frequently occur, and it becomes difficult to obtain good optical performance.

  The present invention can satisfactorily correct the scanning line curvature, the scanning line inclination, the twist of the wavefront aberration, and the like when the sub-scanning oblique incidence optical system and the main scanning oblique incidence optical system are used, and form a good image. An object of the present invention is to provide an optical scanning device capable of performing the above and an image forming apparatus using the same.

An optical scanning device according to the present invention includes an incident optical system that causes a light beam emitted from a light source unit to enter a deflection surface of a deflection unit from an oblique direction within a sub-scan section, and guides the light beam deflected by the deflection unit to a surface to be scanned. an optical scanning apparatus having an imaging optical system for light, and the incident optical system and the imaging optical system is arranged so that the respective optical axes forms an angle in the main scanning section, the imaging optical system includes a sagittal tilt change surface sagittal line tilt amount in the main scanning direction is changed independently of the sagittal curvature, the imaging optical system of light in the sagittal line tilt change surface direction sagittal tilt with respect to the axis is characterized in that the one and the passing position of the light beam at the outermost abaxial image height, and the passing position of the light beam in the other of the outermost off-axis image height, in the opposite direction.

According to the present invention, it is possible to satisfactorily correct the scanning line curvature, the scanning line inclination, the twist of the wavefront aberration, and the like when the sub-scanning oblique incidence optical system and the main scanning oblique incidence optical system are used. Can be obtained, and an image forming apparatus using the same can be obtained.

(A) (b) (c) Main scanning sectional view of Examples 1 and 2 of the present invention, sub-scanning sectional view of the imaging optical system, and sub-scanning sectional view of the incident optical system (A) (b) (c) Main scanning sectional view of Example 3 of the present invention, sub-scanning sectional view of the imaging optical system, and sub-scanning sectional view of the incident optical system (A) (b) Explanatory drawing of the sub-scanning irradiation position performance and 45 degree ass performance of Example 1 of this invention (A) (b) Explanatory drawing of the subscanning irradiation position performance and 45 degree ass performance of Example 2 of this invention Sub-scanning irradiation position performance of the comparative example of the present invention (A) (b) Explanatory drawing of the slave line tilt angle and the change rate of the slave line tilt per unit main scanning in the first embodiment of the present invention. (A) (b) Explanatory drawing of the child wire tilt angle and the child wire tilt change rate per unit main scanning according to the second embodiment of the present invention. Explanatory drawing of the child wire tilt angle of Example 3 of the present invention (A) (b) (c) Explanatory drawing showing the twist of conventional scanning line curve, 45 ° asperity performance, wavefront aberration (A) (b) (c) Explanatory drawing showing twist of wavefront aberration in the same direction at scanning line inclination, left-right image height in the same direction at 45 ° angle, left-right image height (A) (b) Explanatory drawing showing the conventional sub-wire tilt coefficient T, explanatory drawing showing the change rate dT / dY of the sub-wire tilt (A) (b) (c) Explanatory drawing showing twist position of corrected irradiation position Z, corrected 45 ° asperity performance, and corrected wavefront aberration (A) (b) (c) Explanatory drawing showing twist position of corrected irradiation position Z, corrected 45 ° asperity performance, and corrected wavefront aberration Schematic diagram of main parts of the image forming apparatus of the present invention

  Hereinafter, embodiments of the optical scanning device of the present invention will be described with reference to the drawings. In the following description, the main scanning direction is a direction perpendicular to the rotation axis (or oscillation axis) of the deflecting means and the optical axis of the imaging optical system (the direction in which the light beam is reflected and deflected (deflected and scanned) by the rotating polygon mirror). It is. The sub-scanning direction is a direction parallel to the rotation axis (or swing axis) of the deflecting means. The main scanning section is a plane including the main scanning direction and the optical axis of the imaging optical system. The sub-scanning section (child line section) is a section perpendicular to the main traveling direction.

[Example 1]
FIG. 1A is a main part sectional view (main scanning sectional view) in the main scanning direction in Example 1 of the optical scanning device of the present invention. FIG. 1B is a cross-sectional view (sub-scanning cross-sectional view) of the main part in the sub-scanning direction of the imaging optical system in Embodiment 1 of the optical scanning device of the present invention. FIG. 1C is a main-portion cross-sectional view (sub-scanning cross-sectional view) of the incident optical system LA in the sub-scanning direction in Embodiment 1 of the optical scanning device of the present invention.

  In the figure, reference numeral 1 denotes a light source means, which is composed of a semiconductor laser having a light emitting portion (light emitting point). 2 converts the luminous flux emitted from the light source means 1 into weak convergent light in the main scanning direction, and condenses it in the sub scanning direction, with positive powers (refractive powers) different from each other independently in the main scanning direction and the sub scanning direction. ) Anamorphic lens. Reference numeral 3 denotes an aperture (aperture stop), which forms a light beam emitted from the anamorphic lens 2 into a desired optimum beam shape. Reference numeral 4 denotes a rotating polygon mirror (polygon mirror) as a deflecting means, which rotates at a constant speed in the direction of arrow A in the figure.

  LB is an imaging optical system (fθ optical system) having a condensing function and fθ characteristics, and has a positive power (refractive power) in both the main scanning section and the sub-scanning section. The incident optical system LA is composed of a light source unit 1, an anamorphic lens 2, and an aperture 3, and makes a light beam from the light source unit 1 enter a deflection reflection surface (deflection surface) 5 of the deflection unit 4.

  In the present embodiment, the imaging optical system LB is composed of one imaging lens 6. The imaging optical system LB focuses a light beam based on image information reflected and deflected by the rotary polygon mirror 4 onto a spot on a photosensitive drum surface (recording medium surface) 10 as a scanned surface in the main scanning section. Further, the imaging optical system LB compensates for surface tilt of the deflecting surface 5 by optically conjugating or substantially conjugating between the deflecting surface 5 of the rotary polygon mirror 4 and the photosensitive drum surface 10 in the sub-scan section. It is carried out.

  In FIG. 1, the light beam modulated and emitted from the semiconductor laser 1 according to the image information is incident on the anamorphic lens 2. The light beam emitted from the anamorphic lens 2 is weakly converged light in the main scanning section, passes through the aperture stop 3 and is partially shielded. In the sub-scanning section, it is incident on the deflection surface 5 of the rotary polygon mirror 4 as convergent light that is condensed at or near the deflection surface 5, and as a line image that is long in the main scanning direction on the deflection surface 5 of the rotary polygon mirror 4. Form an image.

  The light beam partially reflected and deflected by the deflection surface 5 of the rotary polygon mirror 4 is guided onto the photosensitive drum surface 10 by the imaging optical system LB. By rotating the rotary polygon mirror 4 in the direction of arrow A, image information is recorded by optically scanning the photosensitive drum surface 10 in the direction of arrow B (main scanning direction). The synchronization detection means (not shown) includes a BD optical system that collects the light reflected and deflected by the rotary polygon mirror 4 and a BD sensor that detects the light. The BD optical system is disposed at a position where the scanning light deflected and reflected by the deflecting surface 5 passes, and is configured to guide the scanning light to the BD sensor when the rotary polygon mirror 4 has a predetermined angle. ing.

  The synchronization detection means rotates the rotary polygon mirror 4 in the direction of arrow A, detects the timing at which the deflection surface 5 becomes a predetermined angle, and outputs the timing to the control means (not shown). The control unit controls the rotational speed of the rotary polygon mirror 4 to be a constant speed based on the timing output from the synchronization detection unit. The control means controls the light emission timing of the light source means 1 based on the timing.

  In the present embodiment, in order to simplify the configuration, a sub-scanning oblique incidence optical system that makes a light beam incident on the deflecting surface 5 from a slanting direction with respect to the deflection surface 5 in the sub-scanning section is adopted. As can be seen from FIG. 1C, in this embodiment, the optical axis LAO of the incident optical system LA has an angle α of +3 degrees in the sub-scanning direction. Here, the angle plus is defined when the light beam is directed from the lower side to the upper side in the sub-scanning direction, and the angle minus is defined when the light beam is directed from the upper side to the lower side in the sub-scanning direction. The light is incident on the rotary polygon mirror 4 at an angle of 3 degrees.

  In such a sub-scanning oblique incidence optical system, there are sub-scanning curves and twists of wavefront aberration in the opposite directions between the positive image height and the negative image height as shown in FIGS. 9B and 9C. Degradation of imaging performance unique to the scanning oblique incidence optical system occurs.

  FIG. 9C is a contour graph showing the wavefront aberration (deviation from the reference wavefront) of each light beam reaching each image height Y, and is a general wavefront generated in the sub-scanning oblique incidence optical system. It is explanatory drawing showing the twist of the aberration. FIG. 9B is a graph showing astigmatism in the 45 ° direction at each image height in the sub-scanning oblique optical system, and is a model diagram showing conventional general wavefront aberration.

  Here, the 45 ° asphalt in FIG. 9B will be described. The 45 ° ass is the difference value obtained by subtracting the wavefront aberration in the −45 ° direction from the wavefront aberration in the + 45 ° direction when the main scanning direction is defined as 0 ° and the sub-scanning direction is defined as 90 °. This is the amount of wavefront aberration that represents the degree of deterioration in imaging performance due to the above spot rotation. As the 45 ° asperity increases, the amount of twist of wavefront aberration increases and the imaging performance deteriorates.

  Further, the twisting direction of the wavefront aberration at each image height in FIG. 9C is symmetric with respect to the optical axis. For this reason, the sign of 45 ° as in FIG. 9B is inverted between the plus image height and the minus image height across the optical axis. In general, in the sub-scanning oblique incidence optical system, the relationship between the twist of the wavefront aberration and the image height is obtained.

  In this embodiment, the optical axis of the imaging optical system LB and the optical axis of the incident optical system LA are further arranged in the main scanning section in order to align the substrate (not shown) of the semiconductor laser 1 with the optical box (not shown). The main scanning oblique incidence optical system is arranged so as to have an angle. In the case of the sub-scanning oblique incidence optical system and the main-scanning oblique incidence optical system, in addition to the above-described problems, the scanning line inclination and the positive image height as shown in FIGS. 10 (b) and 10 (c), In addition, twisting of wavefront aberration that occurs in the same direction at a negative image height occurs.

  FIG. 10C is an explanatory diagram showing wavefront aberration at each image height Y generated in the sub-scanning oblique incidence optical system and the main-scanning oblique incidence optical system. FIG. 10B is a graph showing the astigmatism in the 45 ° direction at each image height in the sub-scanning oblique incidence optical system and in the main-scanning oblique incidence optical system, for explaining the present invention. It is a model figure.

  In this embodiment, at least one surface of the imaging lens 6, specifically the second surface (surface on the scanned surface 10 side), the tilt amount of the child line is changed along the main scanning direction. ing. Specifically, it is set to a sub-line tilt change plane in which the direction of the sub-line tilt is opposite to the lens optical axis of the imaging lens 6. As a result, the wavefront twist as shown in FIGS. 10B and 10C is corrected. Here, the principle by which the twist of the wavefront as shown in FIGS. 10B and 10C can be corrected by setting the sub-tilt tilt changing surface as in this embodiment will be described.

  FIG. 10C shows a state in which the wavefront aberration is twisted at each image height Y. In order to correct this wavefront aberration with only one lens surface, it is only necessary to cancel the phase shift from the ideal wavefront by applying an antiphase to the lens surface. At this time, if the amount d of the lens surface in and out of the light beam for giving the opposite phase is expressed by the following equation.

d = −Wa / (1-n) × λ
Here, Wa is an angle in the 45 ° direction in the light beam, and represents the twist amount of the wavefront in the light beam, n is the refractive index of the lens, and λ is the wavelength of the light beam. That is, the amount d of surface entry / exit at each position in the luminous flux necessary for correcting the wavefront is a value obtained by multiplying the amount of wavefront deviation at each position by a constant. For this reason, the surface shape necessary for correcting the twist of the wavefront is a twisted surface shape similar to the wavefront, and when correcting with only one lens surface, the direction in which the surface is twisted is also uniquely determined. In FIG. 10 (b), the 45 ° angle is positive at the plus image height and the minus image height, and the twist direction of the wave front is the same direction.

  Therefore, in this embodiment, in order to correct such wavefront aberration, the second surface of the imaging lens 6 is set to a sub-tilt tilt changing surface as shown in FIG. 6B. FIG. 6B shows the amount of change in the strand tilt per unit amount with respect to the Y coordinate on the second surface of the imaging lens 6 of the present embodiment, which is calculated by the strand tilt coefficient in this embodiment, Table 4. It is the graph which showed dT / dY.

Here, the child line tilt coefficient T on the bus (Z = 0) is an arbitrary Y on the lens surface calculated from the term of Σm _j Y ^j Z ^{1 in} the surface shape expression (B) described later. The tilt coefficient T of the child line at the position is T = Σm _j Y ^j . Further, the sub-tilt tilt change amount dT / dY per unit amount Y in the main scanning direction can be calculated from the following equation.

dT / dY = d (Σm _j Y ^j ) / dY = Σ (j × m _j Y ^j−1 ) (a)
As can be seen from FIG. 6B, in the present embodiment, the change amount of the child line tilt dT / dY = 0 on the optical axis of the imaging lens 6 (Y coordinate on the lens = 0). The sub-line tilt change plane is set so that dT / dY> 0 on the Y coordinate plus side and the minus side of the imaging lens 6. That is, by providing a sub-line tilt coefficient, the torsion of the lens surface is set in the same direction (the sub-line tilt change rate dT / dY has the same sign) on both sides of the optical axis of the imaging lens 6. doing.

  In this embodiment, by setting the sub-tilt tilt changing surface in this way, the wave front is twisted in the same direction on both sides of the optical axis of the imaging lens 6 as shown in FIG. 10B. This corrects the twist of wavefront aberration in the same direction at right and left image heights.

  Next, the optical performance of the present embodiment will be described. Here, the twist of the wavefront aberration on the surface to be scanned in this embodiment is shown in FIG. FIG. 3B is a graph showing 45 ° asperity for each image height on the scanned surface of this example. FIG. 3B shows that in this embodiment, the 45 ° asperity is 0.1λ or less at the total image height, and the wavefront twist can be corrected sufficiently satisfactorily. As shown in FIG. 6B, when the sub-line tilt change rate dT / dY> 0 at a position other than the optical axis Y = 0, the sub-line tilt coefficient T increases as the image height Y increases from the optical axis in the plus region. Will increase.

  Conversely, in the image height Y minus region in the main scanning direction, the sub-line tilt coefficient T decreases as the distance from the optical axis increases. For this reason, in order to obtain a surface shape of dT / dY as shown in FIG. 6B, the sub-line tilt coefficient T is larger than the optical axis on the Y coordinate plus side of the imaging lens 6, It is set so that it is more negative than the optical axis on the Y coordinate negative side of the image lens. That is, in order to correct the wavefront twist as shown in FIG. 10B and FIG. 10C, the sub-line tilt coefficient T is the center of the optical axis in the entire effective use region on the lens surface of the imaging lens 6. As described above, the positions must be set so that the positions are symmetric with respect to the main scanning direction.

Here, the tilt angle ξ and the sub-line tilt coefficient T with respect to the optical axis of the sub-plane normal on the generatrix (Z = 0) at the main scanning direction position Y of an arbitrary imaging lens are expressed as follows: Can express.
ξ = −ATAN (T)
In the above formula, when the tilt angle ξ is a plus sign, the sub-plane normal is upward with respect to the optical axis, and when the minus angle is minus, the sub-plane normal is downward with respect to the optical axis.

  FIG. 6A is a graph showing a child tilt angle ξ with respect to the main scanning direction position Y of the first surface (surface on the deflector 4 side) and the second surface of the imaging lens 6 of the present embodiment. As can be seen from FIG. 6 (a), the second surface of the imaging lens 6 of the present embodiment is a light beam having a normal on the generatrix surface on the generatrix when the Y coordinate on the lens in the main scanning direction is Y = 0. The tilt angle with respect to the axis ξ = 0. The sub-line tilt angle ξ is set to a plus sign in the Y-coordinate minus region on the lens, and the sub-axis tilt angle ξ is set to a minus sign in the Y-coordinate plus region on the lens.

  Further, as can be seen from FIG. 6A, in this embodiment, the tilt angle ξ with respect to the optical axis of the normal of the sub-plane surface on the generatrix is in the entire effective use region of the lens surface. The positions are symmetrical in the main scanning direction with respect to the optical axis center so as to be in opposite directions. Here, the effective area of the lens surface means the entire area through which the scanning light beam passes. In addition, in the case of the sub-scanning oblique incident optical system and the main-scanning oblique incident optical system, the scanning line inclination occurs in addition to the wavefront aberration as shown in FIG.

  In this embodiment, as shown in FIG. 6A, the sub-line tilt angle is set to be opposite to each other at positions symmetrical to the main scanning direction with respect to the optical axis center of the lens surface. It is corrected. FIG. 3A is a graph showing the irradiation position Z (the arrival position of the light beam in the sub-scanning direction at each image height) with respect to each image height on the scanned surface 10 of the present embodiment. As can be seen from FIG. 3A, the irradiation position Z is ± 20 μm or less in total image height, and the scanning line curve and the scanning line inclination are sufficiently corrected.

  As described above, in the present embodiment, as shown in FIG. 6B, the lens surface is twisted in the same direction on both sides of the optical axis of the imaging lens 6 (the child tilt change amount dT / dY has the same sign). ) Is used. Thereby, the effect of correcting the twist of the wave front as shown in FIGS. 10B and 10C is obtained. Here, the amount of the strand tilt is obtained by integrating the strand tilt change amount dT / dY related to the twist of the lens surface with Y. In the present embodiment, the tilt angle ξ of the slave line is set as shown in FIG. 6A in order to realize a surface shape in which the lens surface is twisted as shown in FIG.

  That is, the tilt angle ξ with respect to the optical axis of the sub-plane normal on the generatrix is set to be opposite between positions symmetrical with respect to the main scanning direction with respect to the optical axis center of the imaging lens 6. In this embodiment, the child axis tilt is in the reverse direction at the most off-axis image height. Further, the direction of the slave line tilt is downward on the anti-light source means side and upward on the light source means side.

  Table 6 shows the imaging lens 6 of the light beam reaching the most off-axis image height (Y = ± 110) and the on-axis image height (image center) (Y = 0) on the scanned surface 10 in this embodiment. The passing position on the second surface is shown. Furthermore, it is a table | surface which showed the sub-line tilt angle (xi) in the 2nd surface in those each position, and sub-axis tilt change amount dT / dY per unit quantity of a main scanning direction. As can be seen from Table 6, the sub-line tilt amount of the second surface is the passage position of the light beam reaching the image center image height (Y = 0 mm) on the second surface of the imaging lens 6 (light of the imaging lens 6). Is set so that the sub-plane normal at (axis) is 0 min (no sub-tilt).

  On the other hand, the light beam reaching the most off-axis image height (Y = −110 mm) on the light source means 1 passing position on the second surface of the imaging lens 6 (on the light source side in the longitudinal direction of the imaging lens 6). The normal of the child line plane is set to be +7.9 minutes. That is, it is set so as to face upward with respect to the sub-plane normal on the optical axis (Y = 0). Further, the light beam reaching the most off-axis image height (Y = + 110 mm) on the side opposite to the light source means 1 passes through the second surface of the imaging lens 6 (on the side opposite to the light source in the longitudinal direction of the imaging lens 6). The normal line of the child line is set to be −6.3 minutes. That is, it is set so as to be downward from the normal of the child line surface at the optical axis (Y = 0).

  Thus, in this embodiment, the shape of the second surface of the imaging lens 6 is set as follows. That is, the imaging lens at the passing position of the reaching light beam with respect to the optical axis of the imaging lens 6 at the passing position of the reaching light beam with one off-axis image height and at the passing position of the reaching light beam with the other off-axis image height. The direction of the slave line tilt with respect to the optical axis 6 is set in the opposite direction.

  In this embodiment, the direction of the change in the slave line tilt at the position where the off-axis light beam passes is the same direction. Further, the change amount dT / dY of the child line tilt per unit amount in the main scanning direction is 0 at the passage position of the light beam reaching the image center image height (Y = 0 mm). On the other hand, the most off-axis image height (Y = −110 mm) on the light source means 1 side is 2.32E-4 at the passing position of the reaching light beam, and the most off-axis image height on the opposite side to the light source means 1 (Y = + 110 mm). It becomes 1.97E-4 at the passing position of the reaching light beam.

  In other words, in the present embodiment, the shape of the second surface of the imaging lens 6 is changed in the sub-line tilt per unit main scanning direction with respect to the optical axis of the imaging lens 6 at the passing positions of the two most off-axis image height reaching rays. Are set to be the same direction.

  In this embodiment, the shape of the second surface of the imaging lens 6 is set to such a child-line tilt change surface, so that the wavefront aberration is favorably corrected at the entire image height. In this embodiment, the imaging lens 6 is arranged eccentrically. In this embodiment, the imaging lens 6 is 1 on the upper side in the sub-scanning direction (the upper direction on the paper in FIG. 1B is Z plus) when the deflection point of the on-axis light beam in the rotary polygon mirror is used as a reference. .50mm eccentrically arranged. Further, when the main scanning plane is used as a reference, the optical axis of the imaging lens 6 is decentered by bowing and rotating by 1.83 degrees downward in the sub-scanning direction (in FIG. 1B, the Y-axis direction is Clockwise on the paper as the center of rotation).

  By such an eccentric arrangement, the effect of changing the sub-line tilt in the same direction on the left and right along the main scanning direction in the light beam passing height on the lens surface of the imaging lens 6 is obtained. That is, the eccentric arrangement of the imaging lens 6 corrects the curvature of the scanning line and the twist of the wavefront aberration in the reverse direction at the left and right image heights as shown in FIG.

  In this embodiment, by setting in this way, the sub-surface tilt change surface of the second surface has the scan line tilt and the twist of wavefront aberration in the same direction at the left and right image heights as shown in FIG. 9B. It is sufficient to correct only this, and the amount of tilt of the slave line itself can be kept small. Therefore, in this embodiment, the optical performance such as the scanning line curve, the scanning line inclination, and the twist of the wavefront aberration is corrected satisfactorily, and the sub-tilt tilt amount is suppressed to be sufficiently small, and the lens surface is configured with less twist. Yes.

  If the lens surface is less twisted, a highly accurate lens can be obtained by suppressing phenomena such as distortion, warping, and twisting of the lens during lens molding. In addition, in this embodiment, this eccentric arrangement of the imaging lens 6 can compensate the optical performance even if the sub-line tilt amount at the lens optical axis is zero, and the surface shape of the imaging lens 6 can be changed. It has a simple surface shape that is easy to evaluate. As a result, the imaging lens 6 with high molding accuracy can be obtained.

  As described above, according to this embodiment, it is possible to obtain a compact optical scanning device in which the optical performance is well corrected in the sub-scanning oblique incidence optical system and the main-scanning oblique incidence optical system, which is used in the image forming apparatus. In this case, it becomes easy to form a good image.

  In this embodiment, only one surface of the imaging lens may be used as a sub-line tilt changing surface. Table 5 shows that in this embodiment, the light beam that reaches the most off-axis image height (Y = ± 110) and on-axis image height (image center) (Y = 0) on the scanned surface 10 is the imaging lens 6. The passing position on the first surface and the child-line tilt angle ξ on the first surface at each position are shown. Furthermore, it is the table | surface which showed the child-line tilt change rate dT / dY per unit quantity.

  In this embodiment, as shown by the sub-line tilt angle ξ of the first surface in Table 5, Table 4, and FIG. 6A, the first surface changes the sub-line tilt along the main scanning direction. Not. In other words, in the embodiment, only the second surface of the imaging lens 6 is set as the above-described child-line tilt changing surface. The first surface was set to be a toric lens surface that does not change the sub-line tilt (a plane in which the sub-line curvature radius changes but the sub-line tilt amount does not change along the main scanning direction). Thereby, when measuring and evaluating the lens surface shape of the imaging lens 6, it is possible to evaluate with reference to the optical axis of the first surface that does not have a change in the child line tilt. And since the surface shape of the lens molding die can be corrected based on the measured value, the effect of making it easier to improve the optical performance is obtained.

  In this embodiment, it is not necessary to tilt the optical axis. In the present embodiment, for the same reason, the optical axis of the first surface and the optical axis of the second surface are designed to coincide. As a result, highly accurate measurement is possible, and the surface shape of the lens molding die can be corrected based on the measured value, thereby obtaining an effect of making it easier to improve the optical performance.

  In this embodiment, the main scanning oblique incident optical system is set so that the angle formed by the optical axis of the imaging optical system LB and the optical axis of the incident optical system LA is as large as 90 degrees in the main scanning section. With this configuration, the laser scanning substrate can be disposed along the side wall of the optical box (not shown) in the optical scanning device, and the optical scanning device is configured in a compact manner. As described above, in the main scanning oblique incidence optical system in which the angle θ formed by the optical axis of the imaging optical system LB and the optical axis of the incident optical system LA is very large, the reflection point of the rotary polygon mirror is different for each image height. The position shifts greatly.

  Thus, when the left-right asymmetry of the positional deviation of the reflection point is large, the inclination of the scanning line, the scanning line curve, and the spot rotation become large, so that the effect of the present invention can be sufficiently obtained. In the present embodiment, the angle Θ between the optical axis of the imaging optical system LB and the optical axis of the incident optical system LA in the main scanning section is set to 90 degrees, but the angle θ is expressed by the following conditional expression: If satisfied, the effects of the invention can be sufficiently obtained.

70 [deg] <Θ <100 [deg]
When the angle Θ is 70 degrees or less, it becomes difficult to arrange the laser light emitting substrate along the side wall of the optical box (not shown), and as a result, it is difficult to make the optical scanning device compact. Become. In addition, when used as a counter scanning system (a system in which an incident system and an imaging optical system are arranged opposite to each other with a rotating polygon mirror interposed therebetween), it is difficult to sufficiently bring the light source means of the two sets of incident optical systems close to each other. Therefore, it becomes difficult to simplify the entire apparatus by sharing the light emitting substrate of the semiconductor laser.

  On the other hand, when the angle Θ is greater than 100 degrees, it becomes difficult to maintain various optical performances at oblique incidence. Alternatively, the left-right asymmetry of the sub-line tilt becomes too large, and a left-right asymmetric deformation occurs during lens molding, making it difficult to obtain a molded lens as designed.

  From the above, it is preferable that the angle Θ satisfies the above conditional expression in order to obtain an optical scanning device with sufficiently good optical performance. In this embodiment, the imaging lens 6 is formed of a resin molded lens, so that it is easy to manufacture and good optical performance is obtained by using a sub-tilt tilt changing surface. In the present embodiment, the second surface of the imaging lens 6 is set as a child-line tilt changing surface, and the surface shape of the second surface is a surface normal to the light source means 1 closer to the light source means 1 on the axis. It is set so that it faces upward and the side far from the light source means faces downward.

  However, even if the first surface of the imaging lens 6 is set as a sub-tilt tilt changing surface, the same effect can be obtained if the lens surface is twisted in a phase opposite to the twist of the wavefront aberration of the scanning light beam. . In that case, the surface shape of the first surface may be set so that the sub-line surface normal on the side closer to the light source means 1 with respect to the axis faces downward and the side far from the light source means 1 faces upward. These relationships are limited to the case where the incident optical system LA is incident on the deflecting means 4 in an oblique direction from the lower side to the upper side in the sub-scanning direction.

  If the incident optical system LA makes incident light incident obliquely from the upper side to the lower side in the sub-scanning direction, if the direction of the sub-plane normal is set opposite to the above-described direction, Similar effects can be obtained. Further, when the imaging optical system LB is composed of only one lens, the refractive power in the sub-scanning direction must be increased, and as a result, spherical aberration in the sub-scanning direction that occurs in the imaging lens 6 is reduced. Easy to grow. For this reason, the sensitivity of the sagittal image plane increases with respect to the eccentricity of the imaging lens 6 in the sub-scanning direction.

  Therefore, in this embodiment, spherical aberration is corrected by giving a quaternary non-arc shape to the second surface of the imaging lens 6. Specifically, as shown in Table 4, a Z-order coefficient is given. Further, in the present embodiment, the amount of the child line tilt on the bus (Z = 0) is defined only by the coefficient T (Z 1st order term) and does not depend on the Z 4th order coefficient.

  In this embodiment, the imaging optical system LB is composed of a single imaging lens 6 in order to simplify the configuration. In this case, compared with the case where a plurality of lenses are used, the degree of freedom in designing the busbar shape, the surface eccentricity, the child wire R, etc. is low. For this reason, it is difficult to sufficiently correct the twist of the wavefront aberration peculiar to the oblique incidence optical system while correcting the image plane and the magnification. Therefore, in the present embodiment, the second surface is used as a sub-line tilt changing surface, and the surface is obliquely incident by setting the sub-line tilt at the most off-axis image height in the opposite direction on the left and right with respect to the axis. Degradation of imaging performance in the optical system is reduced.

  In this embodiment, the imaging optical system LB is configured by one imaging lens. However, if the oblique incident angle in the main scanning and sub-scanning directions is large even when there are two or more imaging lenses, the oblique incident optical system is used. Deterioration of the imaging performance at is increased. For this reason, the same effect as described above can be sufficiently obtained.

  In this embodiment, the image forming lens 6 is set to be a weak convergence system (the natural convergence point in the main scanning direction is a position separated from the rotating polygon mirror by 360 mm from the surface to be scanned), compared to the normal parallel system. The power required in the main scanning direction is reduced, and the thickness of the imaging lens 6 is reduced. However, even in a parallel system (when the light beam incident on the deflecting means is parallel light in the main scanning direction), the same effect as described above can be obtained sufficiently because the same scanning line tilt and twist of wavefront aberration occur. It is done.

  Next, differences between the present invention and the optical scanning device disclosed in Patent Document 3 will be described. Patent Document 3 uses a sub-line tilt changing surface that changes the tilt amount of the sub-line along the main scanning direction, so that scanning line bending and light as shown in FIGS. 9B and 9C can be obtained. A wavefront aberration that is symmetrical with respect to the axis (a wavefront aberration in which the sign of 45 ° ass is reversed left and right across the optical axis) is corrected. In Patent Document 3, unlike Patent Documents 1 and 2, since the tilt amount of the slave line can be set independently of the curvature radius in the slave line direction, the slave line tilt amount can be changed even when the slave line curvature radius is infinite. Is possible.

  However, in Patent Document 3, the scanning line curvature is corrected by the sub-line tilt change surface. For this reason, when the main scanning oblique incident angle and the sub-scanning oblique incident angle are larger, in addition to the scanning line curvature, a sub-line tilt change amount for correcting the scanning line inclination must be further added. As a result, the symmetry of the lens in the sub-scanning direction is greatly impaired, causing lens distortion and warping during lens molding, and a high-precision lens cannot be molded, making it difficult to achieve good optical performance. turn into.

  Further, when the main scanning oblique incident angle and the sub scanning oblique incident angle are large, as shown in FIGS. 10B and 10C, the wavefront aberration (45 in the same direction on the left and right sides across the optical axis). (Wavefront aberration in which the sign of ass is the same on the left and right across the optical axis). Such wavefront aberration is not disclosed in Patent Document 3. In all of the embodiments described in Patent Document 3, the direction of the child tilt is set in the same direction at positions symmetrical with respect to the main scanning direction about the lens optical axis. (B) The wavefront aberration as shown in FIG. 10C cannot be corrected.

(There is a different value for the aspherical coefficient of the sub-line tilt on the left and right of the main scanning direction across the optical axis. However, the direction of the sub-line tilt relative to the lens optical axis calculated from this is very small on the lens optical axis. In areas other than the vicinity, positions that are symmetrical with respect to the main scanning direction about the lens optical axis are set in the same direction.)
Next, in Patent Document 3, when the direction of the sub-line tilt is set in the same direction at positions symmetrical with respect to the main scanning direction about the lens optical axis, FIG. 10 (b) and FIG. 10 (c). The reason why such a wavefront aberration cannot be corrected will be described.

FIG. 11A is an explanatory diagram showing the surface shape of the sub-tilt tilt changing surface of the conventional optical scanning device. T in FIG. 11A is calculated from the term of Σm _j Y ^j Z ¹ in the surface shape expression, and the tilt coefficient T (= Σm _j of the child line at an arbitrary Y position on the lens surface). Y ^j ). Here, when the tilt angle with respect to the optical axis of the sub-plane normal on the generatrix at any lens main scanning direction position Y is defined as ξ, it can be expressed by the following equation as described above.

ξ = −ATAN (T)
As shown in FIG. 11A, conventionally, the direction of the child tilt is set in the same direction at positions that are symmetrical with respect to the main scanning direction about the lens optical axis. In FIG. 11 (a), both the plus image height and the minus image height are set so that the child-line tilt coefficient T increases as the distance from the optical axis in the main scanning direction increases.

  Here, if the amount of change in the child tilt coefficient T per unit in the main scanning direction Y is defined as dT / dY, dT / dY can be calculated from the above-described equation (a).

dT / dY = d (Σm _j Y ^j ) / dY = Σ (j × m _j Y ^j−1 ) (a)
FIG. 11B shows the change dT / dY in the sub-line tilt per unit amount in the main scanning direction at each position Y in the main scanning direction on the lens surface corresponding to each image height in the conventional optical scanning device. It is a represented graph. As can be seen from FIG. 11B, the change amount dT / dY of the child line tilt per unit amount in the main scanning direction is set to be negative at the plus image height and plus at the minus image height.

  When the change amount dT / dY of the sub-line tilt per Y in the main scanning direction is other than zero, it indicates that the sub-line tilt angle changes with respect to the main scanning direction. That is, the surface is twisted. The sign dT / dY represents the direction of twisting of the surface, and | dT / dY | represents the amount of twisting of the surface. When a light beam having an arbitrary image height passes through this twisted surface, the wavefront aberration of the light beam is twisted. If the twist of the wavefront aberration caused by this surface can be set in the direction opposite to the twist of the wavefront aberration occurring on the surface to be scanned, the effect of canceling the twist of the wavefront aberration can be obtained.

  For this reason, as shown in FIGS. 9B and 9C, the twist of the wavefront aberration in the opposite direction between the plus image height and the minus image height is the plus image height and the minus image height as shown in FIG. Thus, it is possible to cancel and correct the wavefront aberration in the reverse direction by the sub-tilt tilt changing surface.

That is, correction can be made with a sub-tilt tilt change plane in which the direction of the sub-line tilt as shown in FIG. 11A is symmetric in the main scanning direction about the lens optical axis. At this time, FIG. 12B and FIG. 12C show the distortion of the wavefront aberration after correcting the aberration of FIG. 9B with the sub-tilt change surface of FIG. 11B. At this time, the scanning line curvature is also corrected. FIG. 12 (a) shows the irradiation position Z after correcting FIG. 9 (a) on the plane tilt change plane of FIG. 11 (b).
However, as shown in FIGS. 10B and 10C, the twist of the wavefront aberration in the same direction at the plus image height and the minus image height is as follows in the conventional line tilt change surface as shown in FIG. It cannot be corrected at the full image height.

  Here, FIG. 13B and FIG. 13B show twists of the corrected wavefront aberration when trying to correct the wavefront aberration of FIG. 10B by using the conventional child tilt surface of FIG. 11A. It is shown in 13 (c). As can be seen from FIGS. 13 (b) and 13 (c), in the sub-line tilt change surface in which the twist of the wavefront aberration in the reverse direction occurs between the plus image height and the minus image height as shown in FIG. 11 (b). Although the twist of the wavefront aberration at the image height can be canceled out, the twist of the wavefront aberration at the plus image height is further deteriorated.

  That is, in the sub-line tilt change plane in which the direction of the sub-line tilt as shown in FIG. 11A is symmetric in the main scanning direction with the lens optical axis as the center in the same direction, FIG. There is a problem that the wavefront aberration as shown in FIG. 10C cannot be corrected at the entire image height. FIG. 13A shows the corrected irradiation position Z when the scan line inclination of FIG. 10A is to be corrected using the conventional sub-tilt plane of FIG. 11A. Show.

  As shown in FIG. 13A, when the scan line inclination is corrected by the conventional sub-tilt plane shown in FIG. 11A, the inclination of the irradiation position of the plus side image height is deteriorated. Therefore, in Patent Document 3, it is difficult to sufficiently correct the distortion of the wavefront aberration and the scan line tilt in the optical scanning device having a large main scanning oblique incident angle and a large sub scanning oblique incident angle.

[Example 2]
Next, an optical scanning device according to a second embodiment of the present invention will be described. The configuration of the optical system of Example 2 is substantially the same as that shown in FIGS. 1 (a) to 1 (c). Hereinafter, this embodiment will be described focusing on differences from the first embodiment. In the present embodiment, both surfaces of the imaging lens are composed of a child tilt change surface. In the first embodiment, one lens surface is set as a child tilt change surface. On the other hand, in the present embodiment, both the first surface and the second surface of the imaging lens 6 are set as the child-line tilt changing surfaces.

In this embodiment, by using two sub-line tilt change surfaces, it is possible to better correct the undulation of the scanning line and the twist of local wavefront aberration at the intermediate image height as compared with the first embodiment. ing. Hereinafter, the correction effect obtained by using the two sub-line tilt change surfaces will be described. Table 10 shows the aspheric coefficients of the imaging lens 6. As can be seen from Equation (B), this sub-line tilt does not depend on the sub-line curvature, and is independently set by the sub-line tilt coefficient (term of Σm _j Y ^j Z ¹ ) shown in Table 10. .

At this time, let T be the tilt coefficient of the child line on the generatrix (Z = 0) at an arbitrary Y position on the lens surface. A tilt angle with respect to the optical axis of the child plane normal on the generatrix at an arbitrary position Y in the main scanning direction is defined as ξ. At this time, it can be expressed by the following equation.
ξ = −ATAN (T)
In the above equation, the tilt angle ξ is defined to be upward with respect to the optical axis when the plus sign is the same as described above, and downward with respect to the optical axis when the sign is minus. ing.

  In this embodiment, the sub-tilt tilt is in the opposite direction across the optical axis in the entire effective use area of the lens surface. Here, FIG. 7 shows a graph representing the sub-line tilt angle ξ with respect to the main scanning direction of the first surface and the second surface of the imaging lens 6 of the present embodiment, calculated by the sub-line tilt coefficient in Table 10. Shown in a).

  As can be seen from FIG. 7A, when the Y coordinate on the lens surface of both the first surface and the second surface of the imaging lens 6 of the present embodiment is Y = 0, the child surface normal on the generatrix. Is set so that the tilt angle ξ = 0 with respect to the optical axis. Further, the tilt angle ξ is set to a plus sign when the Y coordinate on the lens surface is a minus region, and the tilt angle ξ is set to a minus sign when the Y coordinate on the lens surface is a plus region.

  As shown in FIG. 7 (a), the first surface and the second surface of the imaging lens 6 of the present embodiment are tilted with respect to the optical axis of the normal of the child surface on the generatrix over the entire effective area of the lens. ξ is set to be opposite to each other at positions symmetrical with respect to the main scanning direction with respect to the optical axis center of the lens. In addition, here, a graph showing dT / dY with respect to the main scanning direction of the first surface and the second surface of the imaging lens 6 of the present embodiment, which is calculated by the sub-line tilt coefficient in Table 10, is shown in FIG. Shown in b).

  As can be seen from FIG. 7 (b), on both surfaces of the imaging lens 6, the sub-line tilt change rate dT / dY at the positive and negative coordinates of the lens is set to be positive. That is, the twist direction of the surface is set to the same direction with the Y coordinate on the lens surface corresponding to the left and right image heights, and the same twisting of the scanning line and the same image height generated by the left and right image heights. The effect of correcting the twist of the wavefront in the direction is obtained.

  In this way, in the present embodiment, both sides of the imaging lens 6 are set so that the direction of the child tilt is opposite at positions symmetrical with respect to the main scanning direction across the optical axis. . This corrects the inclination of the scanning line and the twist of the wavefront in the same direction that occurs at the left and right image heights.

  In this embodiment, both sides of the imaging lens 6 have the same direction of the child tilt. Further, in this embodiment, the sub-tilt tilt changing surface of the first surface has the sub-plane normal facing upward at the most off-axis image height on the light source means 1 side with respect to the optical axis and on the opposite side of the light source means 1. The sub-line tilt coefficient is set so that the sub-plane normal is directed downward at the most off-axis image height. Further, the sub-surface tilt changing surface of the second surface is such that the sub-plane surface normal is upward at the most off-axis image height on the light source means 1 side relative to the optical axis, and the most off-axis image height on the opposite side of the light source means 1 Then, the sub-line tilt coefficient is set so that the sub-plane normal is directed downward. That is, the direction of the slave line tilt of the first surface and the direction of the slave line tilt of the second surface are set to the same direction.

  Thus, by obtaining the effect of bending the two surfaces, the undulation of the scanning line and the local wavefront distortion at the intermediate image height are corrected more satisfactorily than in the first embodiment. Here, the optical performance of this example is shown in FIGS. 4 (a) and 4 (b). FIG. 4A is a graph showing the irradiation position Z with respect to each image height on the surface to be scanned 10 of the present embodiment. FIG. 4B is a graph showing 45 ° asperity for each image height on the scanned surface 10 of this example. In FIG. 4B, 45 ° astigmatism is a wavefront aberration amount representing the degree of deterioration in imaging performance due to spot rotation on the scanned surface 10.

  As can be seen from FIG. 4A, the irradiation position Z of this embodiment is ± 10 μm or less in terms of the total image height, and the scanning line curvature and the scanning line inclination are corrected more satisfactorily than in the first embodiment. Further, from FIG. 4B, the 45 ° asperity is ± 0.05λ or less at the total image height, and the twist of the wavefront aberration is corrected more satisfactorily than in the first embodiment. Further, in a scanning optical system having a plurality of sub-tilt tilt changing surfaces, if the surfaces are relatively decentered, the optical performance is deteriorated.

  Therefore, in this embodiment, the lens tilt change surface shape is added to both surfaces of the same lens, so that the lens mounting error is smaller than that in the case where one lens tilt change surface is formed for each of the two lenses. Performance degradation due to is reduced.

  In this embodiment, the child line tilt is directed downward on the opposite side of the light source means 1 and upward on the light source means 1 side. The direction of the slave line tilt is the same on both sides. Table 11 shows that in this embodiment, the light beam that reaches the most off-axis image height (Y = ± 110) and the on-axis image height (image center) (Y = 0) on the scanned surface 10 is the imaging lens 6. The passing position on the first surface and the child-line tilt angle ξ on the first surface at each position are shown. Furthermore, it is the table | surface which showed the child-line tilt change rate dT / dY per unit quantity.

  Table 12 shows that in this embodiment, the light beam that reaches the most off-axis image height (Y = ± 110) and on-axis image height (image center) (Y = 0) on the scanned surface 10 is the imaging lens 6. The passing position on the second surface and the child-line tilt angle ξ on the second surface at each position are shown. Furthermore, it is the table | surface which showed the strand tilt change rate dT / dY per unit amount.

  As can be seen from Table 11, the amount of sub-line tilt of the first surface is the passage position of the light beam reaching the image center image height (Y = 0 mm) on the first surface of the imaging lens 6 (the optical axis of the imaging lens 6). ) Is set to be 0 minutes (no child tilt). On the other hand, the light beam reaching the most off-axis image height (Y = + 110 mm) on the side opposite to the light source means 1 side is set to −47.1 minutes (the sub-plane normal is downward with respect to the optical axis). ing. Further, the light beam reaching the most off-axis image height (Y = −110 mm) on the light source means 1 side is set to be +82.9 minutes (the sub-plane normal is upward with respect to the optical axis).

  The sub-line tilt change rate dT / dY per unit amount is the most off-axis image height (Y on the opposite side of the light source means 1 with respect to 0 at the passage position of the rays reaching the image center image height (Y = 0 mm). = + 110 mm) It is 3.10E-3 at the passing position of the reaching light beam. Moreover, it becomes 1.58E-3 in the passage position of the most off-axis image height (Y = −110 mm) arrival light on the light source means 1 side.

  Further, as can be seen from Table 12, the sub-line tilt amount of the second surface is the passing position on the first surface of the imaging lens 6 of the light beam reaching the central image height (Y = 0 mm) (light of the imaging lens 6). Is set so that the sub-plane normal at (axis) is 0 min (no sub-tilt). On the other hand, the light beam reaching the most off-axis image height (Y = + 110 mm) opposite to the light source means 1 side is set to −58.0 minutes (the sub-plane normal is downward with respect to the optical axis). ing. Then, the light beam reaching the most off-axis image height (Y = −110 mm) on the light source means 1 side is set to be +85.5 minutes (the sub-plane normal is upward with respect to the optical axis).

  The sub-line tilt change rate dT / dY per unit amount is the most off-axis image height (Y = + 110 mm) on the side opposite to the light source with respect to 0 at the passing position of the rays reaching the image center image height (Y = 0 mm). ) It is 4.50E-3 at the passing position of the reaching beam. Moreover, it becomes 1.87E-3 in the passing position of the most off-axis image height (Y = -110 mm) arrival light on the light source means 1 side.

  As described above, in this embodiment, the shapes of the first surface and the second surface of the imaging lens 6 are set as follows. That is, the direction of the child tilt with respect to the optical axis of the imaging lens 6 at the passage position of one of the most off-axis image height reaching rays and the optical axis of the lens at the other passage position of the most off-axis image height reaching rays. The direction of the slave line tilt with respect to is set in the opposite direction.

  Further, in this embodiment, the sub-plane normal is upward at the lens surface passing position of the most off-axis light beam on the light source means 1 side, and the sub-plane normal is downward at the lens surface passing position of the opposite most off-axis light beam. Is set to a sub-tilt tilt changing surface. Further, in this embodiment, the shapes of the first surface and the second surface of the imaging lens 6 are set to the unit amounts in the main scanning direction with respect to the optical axis of the lens at the passing positions of the two most off-axis image height reaching rays. The direction of the change in the slave line tilt is set to be the same direction.

  In this embodiment, by setting both surfaces of the imaging lens 6 to such a child line tilt changing surface, the scanning line tilt and the twist of the wavefront aberration at the entire image height are corrected satisfactorily. In this embodiment, the sub-line tilt changing surface has a propeller eccentric arrangement.

  In the present embodiment, the first surface and the second surface of the imaging lens 6 are 0.9 clockwise in a direction clockwise about the optical axis (the direction in which the light source means 1 side is shifted downward and the anti-light source means 1 side is shifted upward). It is rotated eccentrically and arranged eccentrically. As a result, the effect of setting the slave line tilt amount in the opposite direction on the left and right is obtained, and the left and right asymmetry amount of the slave line tilt is kept small on both the first surface and the second surface.

  FIG. 5A is a graph showing the irradiation position performance when the imaging lens 6 of the present embodiment is not decentered with the propeller, and is a comparative example with the present embodiment. As can be seen by comparing FIG. 5A and FIG. 4A, the effect of correcting the inclination of the scanning line is obtained by performing the eccentricity of the propeller. By decentering this lens with the propeller, it is possible to obtain the same effect as that in which the slave tilt is linearly changed along the main scanning direction, and the tilt of the slave tilt necessary for correcting the scan tilt is obtained. The left-right asymmetry is reduced. As a result, the imaging lens 6 of this embodiment is combined with the propeller eccentric arrangement, so that the twist of the surface is small and the deformation at the time of lens molding can be suppressed small.

[Example 3]
FIG. 2A is a main part sectional view (main scanning sectional view) in the main scanning direction in Example 3 of the optical scanning device of the present invention. FIG. 2B is a sectional view (sub-scanning sectional view) of the principal part of the imaging optical system in the sub-scanning direction in the third embodiment of the optical scanning device of the present invention. FIG. 2C is a main-portion cross-sectional view (sub-scanning cross-sectional view) of the incident optical system in the sub-scanning direction in Embodiment 3 of the optical scanning device of the present invention. However, FIG. 2A is a developed view in which the reflection mirrors 7, 8, and 9 for bending the scanned light beam in the sub-scanning direction are omitted for easy understanding of the configuration.

  Hereinafter, this embodiment will be described focusing on differences from the first and second embodiments. The present embodiment is a modification of the first embodiment, in which the second surface of the imaging lens 6 is set as a child tilt change surface. The imaging lens 6 has a mirror surface divided into two stages in the sub-scanning direction, and the scanning light beam passing above the imaging lens 6 is guided to the photosensitive body far from the light deflecting means 4. Hereinafter, the surface shape of the upper lens surface of the imaging lens 6 will be described. In this embodiment, the area where the tilt is opposite is 10% or more with respect to the optical axis direction of the effective area of the lens surface.

  FIG. 8 is a graph showing a child line tilt of the upper surface of the second surface of the imaging lens 6 of the present embodiment. Table 16 is a table showing the aspheric coefficients of the imaging lens 6 of the present embodiment. Tables 17 and 18 are tables showing the child line tilt at each position of the imaging lens 6 of the present embodiment. In the first and second embodiments, the direction of the tilt of the child line is the tilt direction relative to the optical axis at the entire image height in terms of the entire effective area of the lens (the area through which the scanning light beam passes), that is, on the surface to be scanned. The left and right are set in the opposite direction.

  On the other hand, in the present embodiment, at the light beam passing position on the second surface of the light beam reaching an image height of 90 mm or more, the direction of the sub-line tilt with respect to the axis is opposite in the left and right direction, and the image on the axis from 90 mm In high, the direction of the slave line tilt is set to be the same on the left and right. That is, in the region of about 1.8% of the total image height on the scanned surface 10 (region from the image height of 90 mm to 110 mm with respect to the total image height of 110 mm), the direction of the axis tilt relative to the axis is Left and right are in the opposite direction. Then, at an image height closer to the axis, the direction of the child line tilt with respect to the axis is set to be the same on the left and right.

  In this embodiment, by setting the sub-tilt plane in this way, the scanning line curvature is corrected with a sub-tilt component that is symmetrical and in the same direction with respect to the optical axis. The effect of correcting the scanning line tilt by the reverse child line tilt is obtained. In the present embodiment, the direction of the sub-line tilt with respect to the axis is symmetric with respect to the lens optical axis in the main scanning direction in the reaching light passage region of about 1.8% of the total image height. The positions are set to be opposite to each other.

  However, in 10% or more of the region on the lens surface, the same effect as described above can be obtained if the direction of the axis tilt relative to the axis is opposite between the symmetrical positions with respect to the optical axis. You can get enough. If the region in which the direction of the child line tilt with respect to the axis is opposite in the main scanning direction with respect to the optical axis is less than 10% of the total image height, the scanning line tilt is corrected. For this reason, the amount of change in the slave line tilt with respect to the main scanning direction becomes large. As a result, the lens is warped and distorted during molding, and the molding accuracy is deteriorated.

  In this embodiment, as shown in FIG. 2 (c), two incident optical systems LA are arranged on the upper and lower sides, and in the sub-scan section, the light beams from the incident optical system are obliquely upward on the deflection surface, respectively. The light is incident from diagonally downward. The two light beams obliquely incident on the deflecting surface 5 are conical scanned upward and downward by the deflecting means 4, respectively, and on two different photosensitive drums by the light beam separating means 7 disposed in the imaging optical system LB. Scanned as an imaging spot.

  Further, the two sets of optical scanning optical systems facing each other perform optical scanning using different deflection reflection surfaces of the same rotary polygon mirror 4. As described above, in this embodiment, the plurality of optical scanning optical systems are arranged obliquely and opposed to each other, so that the optical components are shared, and the optical scanning device is simplified and made compact.

  This embodiment is an optical scanning device used in a color image forming apparatus that forms a color image by fixing four color toners on paper by scanning light exposed on four photosensitive drums. FIG. 2B shows four photosensitive drums for forming a four-color image. From the right side in FIG. 2B, a yellow (Y) drum, a magenta (M) drum, a cyan (C) drum, and a black (Bk) drum are arranged.

  In this embodiment, the scanning light deflected and reflected by the rotary polygon mirror 4 is scanned with a yellow (Y) scanning optical system, a magenta (M) scanning optical system, a cyan (C) scanning optical system, and a black (Bk) scanning. The light is guided to each photosensitive drum by an optical system. In this embodiment, two light beams from two light source means 1 separated in the sub-scanning direction are incident on the light deflecting means 4 at an angle of ± 3 degrees obliquely in the sub-scanning direction by the incident optical system LA. . The upper and lower scanning light beams deflected and reflected by the light deflecting means 4 are separated by the folding mirror 7 after passing through the common imaging lens 6 and guided to two different photoconductors.

Further, in this embodiment, these two optical scanning optical systems are arranged so as to oppose each other with the optical deflecting means as the center, so that the light beams from the four light sources are guided to the four photosensitive members by using one optical deflecting means. .
These four photoreceptors correspond to four colors of yellow, magenta, cyan, and black, respectively, and can form a color image. In this embodiment, a multistage toric lens (MTL) having a mirror region divided into at least two or more is used for the imaging optical system LB.

  As shown in FIG. 2B, the scanning light from the light deflecting unit 4 is shifted up and down with respect to the outer shape center of the imaging lens 7 in the sub-scanning section. The imaging lens 6 is a multi-stage toric lens (so-called MTL) in which the mirror surface is divided into two upper and lower stages in the sub-scanning direction, and the two-stage mirror surfaces are set in a toric lens surface shape. The scanning light beam that passes through the upper side of the imaging lens 6 is guided to the photosensitive member far from the light deflection unit 4. On the other hand, the scanning light beam passing under the imaging lens 6 is guided to the photoconductor on the side closer to the light deflecting unit 4.

  With this configuration, two scanning light beams can be guided to two different photoconductors by the common imaging lens 6, and simplification is achieved by reducing the number of components. The two sets of optical scanning optical systems facing each other perform optical scanning using different deflecting and reflecting surfaces of the same rotary polygon mirror 4. In the present embodiment, the imaging lens 6 has a symmetrical surface shape with respect to the sub-scanning direction (aspherical shape including surface eccentricity and child line tilt is also symmetrical). For this reason, the two pairs of imaging lenses 6 facing each other can invert the same lens up and down, share optical components, and make the optical scanning device compact.

  In this embodiment, the main scanning oblique incident optical system is set so that the angle formed by the optical axis of the imaging optical system LB and the optical axis of the incident optical system LA is as large as 90 degrees in the main scanning section. With this configuration, two sets of incident optical systems for the two sets of opposing imaging optical systems can be incident from the same direction in the main scanning section. In this embodiment, with this configuration, two sets (four in total) of light source means are arranged close to each other, and the light emitting substrate of the semiconductor laser is shared, thereby simplifying.

  As described above, in the main scanning oblique incidence optical system in which the angle between the optical axis of the imaging optical system and the optical axis of the incident optical system is very large, the inclination of the scanning line, the scanning line curvature, and the spot rotation are particularly large. Therefore, the effect of the present invention can be sufficiently obtained.

  Next, Tables 1 to 6 show various values related to each member of Example 1. Tables 7 to 12 show various numerical values related to each member of Example 2. Tables 13 to 18 show various values related to each member of Example 3. In Tables 2, 8, and 14, R is the radius of curvature of the surface, D is the spacing, and N is the refractive index of the medium. However, Upper and Lower in the table represent the aspheric coefficient at the minus coordinate (light source side) with respect to the Y axis and at the plus coordinate (opposite side of the light source) with respect to the Y axis, respectively. Has independent aspherical shapes on the left and right with the optical axis in between. The aspheric shape is defined by the following expression.

  The intersection of the curved surface of the lens and the optical axis is the origin, the optical axis direction is the X axis, the axis orthogonal to the optical axis in the main scanning plane is the Y axis, and the axis orthogonal to the optical axis in the sub scanning plane is the z axis To do. In this case, when the cutting line of the XY plane and the curved surface is a generating line, and the XZ plane and the cutting surface of the curved surface in a direction orthogonal to the generating line are child lines, the shape of the generating line is expressed by the expression (A).

(Where R is the radius of curvature, K, B ₄ , B ₆ , B ₈ , B ₁₀ , B ₁₂ , B ₁₄ , B ₁₆ are the aspheric coefficients of the bus) The shape of the child wire is expressed by the expression (B) .

  Here, the radius of curvature r ′ of the child line that changes depending on the value of Y is expressed by the equation (C).

(Where r ₀ is the radius of curvature of the sub-line on the optical axis, D ₂ , D ₄ , D ₆ , D ₈ , D ₁₀ , D ₁₂ , D ₁₄ , D ₁₆ , is a coefficient)
From equation (B), the amount of sub-wire tilt on the bus (Z = 0) does not depend on the sub-bar curvature and is defined by the term Σm _j × Y ^j × Z ¹ .

[Image forming apparatus]
FIG. 14 is a cross-sectional view of the main part in the sub-scanning direction showing an embodiment of the image forming apparatus of the present invention. In the figure, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into an image signal (dot data) Di by a printer controller 111 in the apparatus. The image data Di is input to the optical scanning unit 100 having the configuration shown in the first embodiment.

  The light scanning unit 100 emits a light beam 103 modulated according to the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction. The photosensitive drum 101 serving as an electrostatic latent image carrier (photoconductor) is rotated clockwise by a motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface.

  The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with the light beam 103 scanned by the optical scanning unit 100. As described above, the light beam 103 is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. The electrostatic latent image is developed as a toner image by a developing unit 107 disposed so as to contact the photosensitive drum 101 further downstream in the rotation direction of the photosensitive drum 101 than the irradiation position of the light beam 103.

  The toner image developed by the developing unit 107 is transferred onto a sheet 112 as a transfer material by a transfer roller 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in the paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 14), but can be fed manually. A paper feed roller 110 is provided at the end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 into the transport path.

  As described above, the sheet 112 on which the unfixed toner image is transferred is further conveyed to a fixing device behind the photosensitive drum 101 (left side in FIG. 14). The fixing device includes a fixing roller (transfer device) 113 having a fixing heater (not shown) therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113. Then, the sheet 112 conveyed from the transfer unit is heated while being pressed by the pressure contact portion between the fixing roller 113 and the pressure roller 114 to fix the unfixed toner image on the sheet 112. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and the fixed paper 112 is discharged out of the image forming apparatus.

  Although not shown in FIG. 14, the print controller 111 controls not only the data conversion described above, but also controls each part in the image forming apparatus including the motor 115 and a polygon motor in the optical scanning unit described later. I do.

  The recording density of the image forming apparatus used in the present invention is not particularly limited. However, considering that higher recording density requires higher image quality, the configuration of the present invention is more effective in an image forming apparatus of 1200 dpi or higher.

DESCRIPTION OF SYMBOLS 1 Light source means 2 Anamorphic lens 3 Aperture 4 Deflection means 5 Deflection reflective surface LA Incident optical system LB Imaging optical system 6 Imaging lens
7 Inner drum_first reflection mirror M1 8 Inner drum_second reflection mirror M2
9 Outer drum_first reflection mirror 10 Scanned surface 20 Optical box of optical scanning optical system

Claims (16)

An incident optical system for causing the light beam emitted from the light source means to enter the deflection surface of the deflection means from an oblique direction within the sub-scanning section; an imaging optical system for guiding the light beam deflected by the deflection means to the scanned surface; An optical scanning device comprising:
The incident optical system and the imaging optical system are arranged such that each optical axis forms an angle in the main scanning section,
The imaging optical system includes a sub-tilt tilt changing surface in which the sub-line tilt amount changes along the main scanning direction without depending on the sub-line curvature,
The direction of the beam tilt with respect to the optical axis of the imaging optical system of the beam tilt change plane is the light beam passing position at one of the most off-axis image heights and the light beam passing position at the other most off-axis image height. An optical scanning device characterized by being in the reverse direction. In the main scanning section, the angle Θ formed by the optical axis of the incident optical system and the optical axis of the imaging optical system is:
70 [deg] <Θ <100 [deg]
The optical scanning device according to claim 1, wherein the following conditional expression is satisfied.   The imaging optical system includes an imaging lens in which one lens surface is the sub-line tilt changing plane and the other lens plane is a plane in which the sub-line tilt amount does not change along the main scanning direction. The optical scanning device according to claim 1 or 2, characterized in that   3. The optical scanning device according to claim 1, wherein the imaging optical system includes an imaging lens in which both lens surfaces are the child-line tilt change surfaces. 4. The direction of the beam tilt with respect to the optical axis of the imaging optical system of both the beam tilt change surfaces is the same at the light passing position at the one off-axis image height , and the other most axis 5. The optical scanning device according to claim 4, wherein the light beam passing positions at the outer image height are the same as each other .   The optical scanning apparatus according to claim 1, wherein the imaging optical system includes a single imaging lens.   The direction of the slave line tilt with respect to the optical axis of the imaging optical system on the axis of change of the slave line tilt is a position that is symmetrical in the main scanning direction around the optical axis of the imaging optical system in the entire effective use region. The optical scanning device according to claim 1, wherein the directions are opposite to each other. The direction of the line tilt with respect to the optical axis of the imaging optical system of the line tilt change plane is the optical axis of the imaging optical system in a region of 10% or more from the most off-axis image height out of the total image height. The optical scanning device according to claim 1, wherein positions opposite to each other in the main scanning direction with respect to the center are opposite to each other.   The incident optical system allows a light beam to be incident on the deflection surface from below in the sub-scan section, and the imaging optical system has the lens surface on the scanned surface side that is the sub-tilt tilt changing surface. An imaging lens, and a direction of a sub-plane normal of the sub-tilt tilt change surface with respect to the optical axis of the imaging optical system is closer to the light source means than the optical axis of the imaging optical system 9. The optical scanning device according to claim 1, wherein the optical scanning device is upward in a region and downward in a region far from the light source means.   The incident optical system allows a light beam to be incident on the deflection surface from below in the sub-scan section, and the imaging optical system has a lens surface on the deflection surface that is the sub-tilt tilt changing surface. An imaging lens is provided, and the direction of the sub-plane normal of the sub-tilt tilt changing surface with respect to the optical axis of the imaging optical system is a region closer to the light source means than the optical axis of the imaging optical system 9. The optical scanning device according to claim 1, wherein the optical scanning device is downward and upward in a region far from the light source means. 11. The optical scanning device according to claim 1, wherein the sub-line tilt change surface is not sub-line tilted on an optical axis of the imaging optical system .   The imaging optical system includes an imaging lens including the sub-tilt tilt changing surface, and the imaging lens is eccentrically arranged so that an optical axis has an angle with respect to a main scanning section. The optical scanning device according to claim 1.   The image forming optical system includes an image forming lens including the sub-tilt tilt changing surface, and the image forming lens is rotated about an optical axis and arranged eccentrically. The optical scanning device according to claim 1.   14. The imaging optical system includes a multi-stage toric lens that includes the sub-tilt change surface and has a mirror surface area that is divided into two or more with respect to the sub-scanning direction. The optical scanning device according to claim 1.   15. The optical scanning device according to claim 1, and a developing unit that develops, as a toner image, an electrostatic latent image formed on a photoconductor disposed on the scanned surface by the optical scanning device. An image forming apparatus comprising: a transfer device that transfers the developed toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material.   The optical scanning device according to claim 1, and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device. Image forming apparatus.