Optical scanning device and image forming apparatus including the same

Abstract

To provide a compact optical scanner capable of suppressing a change in optical performance of an optical system due to a change in environmental temperature.SOLUTION: An optical scanning apparatus according to the present invention includes a deflector that deflects a light beam from a light source to scan a surface to be scanned in a main scanning direction, a first optical system that guides the light beam deflected by the deflector to the surface to be scanned at a first timing, and a second optical system that guides the light beam deflected by the deflector to a light receiving element at a second timing different from the first timing. The second optical system includes a first optical element including a diffractive surface and configured to condense the light flux deflected by the deflector at the second timing in the main scanning section, and in the main scanning section, a value of diffractive power of the first optical element is equal to or larger than a value of refractive power of the first optical element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical scanning device, and more particularly to an optical scanning device that is suitable for use in image forming apparatuses such as laser beam printers (LBPs), digital copying machines, and multifunction printers. [Background technology]

[0002] Conventionally, in an optical scanning device, a light beam deflected by a deflector is received by a synchronous detection unit (light receiving unit), thereby performing synchronous detection to determine the timing of writing onto a surface to be scanned. On the other hand, if the ambient temperature changes during such synchronous detection, the optical performance of the synchronous detection optical system that guides the light beam to the synchronous detection unit may change, which may result in a change in the light receiving position of the light beam in the synchronous detection unit, and thus a change in the write timing.

[0003] Patent Document 1 discloses an optical scanning device in which a diffractive surface is provided in a synchronous detection optical system to suppress changes in the optical performance of the synchronous detection optical system due to changes in the environmental temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-166232 Summary of the Invention [Problem to be solved by the invention]

[0005] In the optical scanning device disclosed in Patent Document 1, sufficient consideration has not been given to achieving both miniaturization and suppressing changes in the optical performance of the synchronous detection optical system that occur due to changes in the environmental temperature. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a small optical scanning device that can suppress changes in the optical performance of the optical system that occur due to changes in the environmental temperature. [Means for solving the problem]

[0006] The optical scanning device of the present invention comprises a deflector that deflects a light beam from a light source to scan a surface to be scanned in a main scanning direction, a first optical system that guides the light beam deflected by the deflector to the surface to be scanned at a first timing, and a second optical system that guides the light beam deflected by the deflector to a light receiving element at a second timing different from the first timing, wherein the second optical system includes a diffractive surface and has a first optical element that focuses the light beam deflected by the deflector at the second timing in a main scanning cross section, and wherein the value of the diffraction power of the first optical element in the main scanning cross section is greater than or equal to the value of the refractive power of the first optical element. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a small-sized optical scanning device that can suppress changes in the optical performance of the optical system that occur due to changes in the environmental temperature. [Brief explanation of the drawings]

[0008] [Figure 1] 1A and 1B are a main scanning sectional view and a partial sub-scanning sectional view of an optical scanning device according to a first embodiment. [Figure 2] 3A and 3B are partial main-scan cross-sectional views of the optical scanning device according to the first embodiment and a diagram showing the relationship between the rotation angle of a deflector and the amount of light received by a synchronization detection unit. [Figure 3] FIG. 2 is a partial main scanning cross-sectional view of the optical scanning device according to the first embodiment. [Figure 4] 10A and 10B are diagrams showing the position dependence of the main-scanning LSF spot diameter in the optical scanning device according to the comparative example and the optical scanning device according to the first embodiment. [Figure 5] 3A and 3B are a front view and a top view of a synchronization detection optical element provided in the optical scanning device according to the first embodiment. [Figure 6] 10A and 10B are a main scanning sectional view and a partial sub-scanning sectional view of an optical scanning device according to a second embodiment. [Figure 7] 10A and 10B are a front view and a top view of a synchronization detection optical element provided in an optical scanning device according to a second embodiment. [Figure 8]10A and 10B are diagrams showing the image height dependency of the scanning speed ratio in the optical scanning device according to the second embodiment. [Figure 9] 10A and 10B are diagrams showing the position dependency of the main-scanning LSF spot diameter in the optical scanning device according to the second embodiment. [Figure 10] 10A and 10B are a main scanning sectional view and a partial sub-scanning sectional view of an optical scanning device according to a third embodiment. [Figure 11] 10A and 10B are diagrams showing the position dependency of the main-scanning LSF spot diameter in the optical scanning device according to the third embodiment. [Figure 12] FIG. 2 is a sub-scanning cross-sectional view of a main part of the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The optical scanning device according to the present embodiment will be described in detail below with reference to the accompanying drawings. Note that the drawings may be drawn to a scale different from the actual scale in order to facilitate understanding of the present embodiment. In the following description, the main scanning direction is the direction perpendicular to both the rotation axis of the deflector and the optical axis of the optical system (the direction in which the deflector scans the surface to be scanned), and the sub-scanning direction is the direction parallel to the rotation axis of the deflector.

[0010] Furthermore, the main scanning section is a section perpendicular to the sub-scanning direction, and the sub-scanning section is a section perpendicular to the main scanning direction. That is, the direction parallel to the optical axis of the optical system is a direction perpendicular to both the rotation axis of the deflector and the main scanning direction. In the following description, the main scanning direction is defined as the Y direction, the sub-scanning direction as the Z direction, and the direction parallel to the optical axis of the imaging optical system 85 as the X direction. BD Define the direction.

[0011] [First embodiment] Conventionally, optical scanning devices are provided with a synchronous detection optical system and a synchronous detection unit that acquire a synchronous detection signal to align the writing position (irradiation start timing) when a light beam deflected by a deflector optically scans the scanned surface in the main scanning direction. In order to suppress the deterioration of synchronous detection accuracy due to changes in the temperature of the optical elements provided in the synchronous detection optical system or the environment surrounding the synchronous detection optical system, an optical scanning device has been proposed in which a diffractive optical element is provided in the synchronous detection optical system.

[0012] For example, an optical scanning device has been proposed in which a blazed diffractive surface is provided in the synchronous detection optical system to reduce the shift in the light-condensing position on the light-receiving surface of the synchronous detection unit that occurs due to temperature rise. On the other hand, in the proposed optical scanning device, the shift of the focusing position in the main scanning direction due to temperature rise is reduced, but the shift of the focusing position in the direction parallel to the optical axis of the synchronous detection optical system due to temperature rise is not taken into consideration.

[0013] For example, an optical scanning device has been proposed that provides a diffractive surface in each of the imaging optical system and the synchronous detection optical system, thereby reducing the shift in the printing position on the scanned surface due to wavelength differences between multiple light sources and the shift in the focusing position on the light receiving surface of the synchronous detection unit due to temperature rise. On the other hand, the proposed optical scanning device also takes into account the shift in the focusing position on the light receiving surface of the synchronous detection unit in a direction parallel to the optical axis of the synchronous detection optical system due to temperature rise, but the depth width is wide due to the long overall length of the synchronous detection optical system.

[0014] Therefore, it is difficult to effectively apply the proposed configuration to a small synchronous detection optical system with a short overall length, in which the focus position on the light receiving surface of the synchronous detection unit in a direction parallel to the optical axis shifts significantly due to temperature rise. Therefore, an object of this embodiment is to provide an optical scanning device that can suppress a decrease in synchronous detection accuracy due to temperature changes even in a synchronous detection optical system with a short overall length.

[0015] FIG. 1(a) shows a schematic main scanning cross-sectional view of an optical scanning device 1 according to the first embodiment. 1(b) and 1(c) are schematic cross-sectional views in the sub-scanning direction of an imaging optical system 85 and a synchronization detection optical system 95 provided in the optical scanning device 1 according to the first embodiment, respectively.

[0016] The optical scanning device 1 of this embodiment comprises a light source 10, an incident optical element 30, an aperture 40, a deflector 50, a scanning optical element 60 (imaging optical element), a synchronization detection optical element 70 (first optical element), a synchronization detection edge portion 80, and a synchronization detection portion 90 (light receiving element). The light source 10 may be, for example, a semiconductor laser, and may have one or more light emitting points.

[0017] The incident optical element 30 is an anamorphic lens having different positive powers in the main scanning cross section and the sub-scanning cross section. The incident optical element 30 converts the light beam emitted from the light source 10 into a parallel light beam in the main scanning cross section, and condenses the light in the vicinity of the deflecting surface 50a of the deflector 50 in the sub-scanning cross section. It should be noted that the parallel light beam here includes not only a strictly parallel light beam but also an approximately parallel light beam such as a weakly divergent light beam or a weakly convergent light beam.

[0018] The diaphragm 40 has an elliptical opening and regulates the diameter of the light beam that has passed through the incident optical element 30 in both the main scanning direction and the sub-scanning direction. In the optical scanning device 1 according to this embodiment, the diaphragm 40 is formed integrally with a housing (not shown).

[0019] The deflector 50 is a polygon mirror (rotating polygonal mirror) formed by mirror-finishing aluminum metal and having four flat reflecting surfaces. The deflector 50 deflects the light beam that has passed through the diaphragm 40 while rotating in the direction of arrow R in FIG. 1(a) by a driving unit such as a motor (not shown).

[0020] The scanning optical element 60 is formed by a so-called fθ lens having positive power in both the main scanning section and the sub-scanning section. The scanning optical element 60 then condenses the light beam deflected by the deflector 50 at the first timing in both the main scanning cross section and the sub-scanning cross section.

[0021] The synchronous detection optical element 70 has positive power in both the main scanning cross section and the sub-scanning cross section. The synchronous detection optical element 70 then focuses the light beam deflected by the deflector 50 at a second timing different from the first timing in the vicinity of the synchronous detection edge portion 80 in the main scanning cross section.

[0022] The synchronous detection edge portion 80 is configured to block a part of the light beam that has passed through the synchronous detection optical element 70 . The synchronization detecting section 90 is configured to receive the light beam that has passed through the synchronization detecting edge section 80 . A control unit (not shown) determines (controls) the writing position (writing timing) of the light beam that optically scans the surface 100 to be scanned, based on a signal acquired by the synchronization detection unit 90 when the light beam is received.

[0023] The incident optical element 30, the scanning optical element 60, and the synchronization detecting optical element 70 provided in the optical scanning device 1 according to this embodiment are each a plastic molded lens formed by injection molding a plastic material. Molded lenses are easy to form into aspherical shapes and are suitable for mass production, so using plastic molded lenses as the incident optical element 30, scanning optical element 60, and synchronous detection optical element 70 can improve productivity and optical performance.

[0024] The light beam emitted from the light source 10 passes through the incident optical element 30 and the diaphragm 40, and is incident (guided) on the deflector 50 so as to form a long line image in the main scanning direction on the deflecting surface 50a. The diameter of the light beam in the main scanning direction when it is incident on the deflecting surface 50a of the deflector 50 is smaller than the width of the deflecting surface 50a in the main scanning cross section.

[0025] Next, the light beam incident on the deflecting surface 50a of the deflector 50 is deflected by the deflecting surface 50a. Specifically, the light beam deflected by the deflecting surface 50a at the first timing is focused in both the main scanning section and the sub-scanning section so that a spot-shaped image is formed near the scanned surface 100 by the scanning optical element 60. As the deflector 50 rotates in the direction of the arrow R in Figure 1(a), the scanned surface 100 is optically scanned at a constant speed in the direction of the arrow A in Figure 1(a), thereby forming an electrostatic latent image on the scanned surface 100.

[0026] In addition, the light beam deflected by the deflecting surface 50a at a second timing different from the first timing passes through the synchronization detection optical element 70 and is condensed near the synchronization detection edge portion 80 in the main scanning cross section. In the optical scanning device 1 of this embodiment, the deflector 50 rotates in the direction of arrow R in Figure 1(a), so that the synchronization detection edge portion 80 is optically scanned in the direction of arrow B by the light beam that has passed through the synchronization detection optical element 70, as shown in Figure 2(a).

[0027] Therefore, the light beam that has passed through the synchronous detection optical element 70 is blocked by the synchronous detection edge portion 80 until the deflector 50 reaches a predetermined rotation angle. When the deflector 50 reaches a predetermined rotation angle, the light beam passes through the synchronous detection optical element 70 and is guided to the synchronous detection section 90 by passing through the synchronous detection edge section 80 .

[0028] In the optical scanning device 1 according to this embodiment, the incident optical element 30 and the diaphragm 40 form an incident optical system 75 . The scanning optical element 60 forms an imaging optical system 85 (first optical system), and the synchronous detection optical element 70 and the synchronous detection edge portion 80 form a synchronous detection optical system 95 (second optical system).

[0029] Therefore, in the optical scanning device 1 according to this embodiment, the synchronous detection optical system 95 does not include any optical element having a refractive surface or a diffractive surface other than the synchronous detection optical element 70. In the optical scanning device 1 according to this embodiment, the synchronization detection optical system 95 is disposed between the incident optical system 75 and the imaging optical system 85 in the main scanning cross section.

[0030] FIG. 2(a) is a schematic main scanning cross-sectional view of the optical scanning device 1 according to this embodiment in the vicinity of the synchronization detection unit 90. As shown in Figure 2(a), the synchronization detection edge portion 80 provided in the optical scanning device 1 of this embodiment corresponds to the downstream end of the light-shielding member S provided upstream in the scanning direction of the synchronization detection portion 90, i.e., the direction of arrow B in Figure 2(a). The synchronous detection edge portion 80 is disposed near the optical axis of the synchronous detection optical system 95 .

[0031] That is, the optical scanning device 1 according to this embodiment is provided with a light blocking member S that blocks part of the light beam guided by the synchronization detecting optical element 70 to each position on the light receiving surface of the synchronization detecting section 90 in the main scanning direction. The light blocking member S has a predetermined corner located at a predetermined position on the optical axis of the synchronous detection optical system 95 in the main scanning cross section, and extends in a direction not parallel to the optical axis of the synchronous detection optical system 95 .

[0032] As described above, the light beam deflected by the deflecting surface 50a at the second timing passes through the synchronization detection optical element 70 and then optically scans the light-shielding member S including the synchronization detection edge portion 80 in the direction of arrow B in Figure 2(a). Then, when the deflector 50 reaches a predetermined rotation angle, the light beam passes through the synchronization detection edge portion 80 and is guided to the synchronization detection portion 90 . In the optical scanning device 1 according to this embodiment, the light blocking member S is integrally formed with a housing (not shown).

[0033] FIG. 2(b) schematically shows the relationship between the rotation angle of the deflector 50 and the amount of light of the light beam received by the synchronization detector 90 in the optical scanning device 1 according to this embodiment. As shown in FIG. 2(b), the rotation angle of the deflector 50 is classified into one of areas A, B, and C. The rotation angle of the deflector 50 is set so as to increase as it rotates in the direction of the arrow R in FIG. 1(a).

[0034] When the deflector 50 deflects the incident light beam at a rotation angle included in the region A, the deflected light beam is blocked by the light-shielding member S, and therefore the amount of light of the light beam received by the synchronization detection unit 90 becomes 0. Next, when the deflector 50 deflects the incident light beam at a rotation angle included in the region B, only a part of the deflected light beam is blocked by the light blocking member S. Therefore, when the remaining light beam is received by the synchronous detector 90, the amount of light received by the synchronous detector 90 becomes 0 and the maximum value I max The value will be between .

[0035] When the deflector 50 deflects the incident light beam at a rotation angle included in the region C, the entire deflected light beam is received by the synchronous detector 90, and the amount of light of the light beam received by the synchronous detector 90 is a maximum value I max This becomes: Here, in the optical scanning device 1 according to this embodiment, the maximum value I max multiplied by a predetermined value K between 0 and 1, K×I max is set as the threshold (slice level). The predetermined value K is, for example, 0.4.

[0036] The amount of light of the light beam received by the synchronization detector 90 is then equal to the threshold value K×I max The rotation angle of the deflector 50 when the rotation angle reaches the synchronous detection angle θ BD Set to. That is, in the optical scanning device 1 according to this embodiment, a control unit (not shown) controls the synchronous detection angle θ BD Based on this, the writing start position of the light beam that optically scans the surface 100 to be scanned is determined.

[0037] In Figure 2(b), the light intensity in area B is 0 and the maximum value I maxHowever, the change in the amount of light in region B is not limited to this. In addition, the light intensity in area C is the maximum value I max However, the change in the amount of light in the area C is not limited to this.

[0038] As described above, in the optical scanning device 1 according to this embodiment, the light beam deflected by the deflector 50 at the second timing passes through the synchronization detection optical element 70 and is focused near the synchronization detection edge portion 80 within the main scanning cross section. In other words, when the temperature of the optical scanning device 1, i.e., the ambient temperature, is at a predetermined temperature, the light beam deflected by the deflector 50 at the second timing is focused by the synchronization detection optical element 70 at a predetermined position near the synchronization detection edge portion 80 within the main scanning cross section.

[0039] Therefore, the amount of light received by the synchronous detector 90 varies from 0 to the maximum value I max It is possible to shorten the time it takes to reach region B, i.e., to narrow region B. As a result, the slope of the change in the amount of light in area B becomes steeper, and the threshold value K×I max The synchronous detection angle θ determined from BD This makes it possible to reduce variations in the synchronization detection accuracy.

[0040] Next, the specifications of the optical scanning device 1 according to this embodiment, the refractive index and coordinates of each optical surface, and the shape of each optical surface are shown in the following Tables 1, 2, and 3, respectively.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Table 3]

[0044] The shapes (meridional shapes) of the entrance surface and exit surface of the scanning optical element 60 provided in the optical scanning device 1 according to this embodiment in the main scanning cross section are aspherical shapes expressed by polynomial functions up to the 16th degree. Specifically, at each of the entrance surface and exit surface of the scanning optical element 60, the intersection point with the optical axis (surface vertex) is set as the origin, the axis parallel to the optical axis is set as the X-axis, the axis perpendicular to the optical axis in the main scanning cross section is set as the Y-axis, and the axis perpendicular to the optical axis in the sub-scanning cross section is set as the Z-axis. In this case, the shapes of the entrance surface and exit surface of the scanning optical element 60 in the main scanning cross section are expressed by the following formula (1).

number

[0045] In equation (1), R is the radius of curvature in the main scanning section (generator radius of curvature), K is the eccentricity, B i (i=1,2,3,...,16) are aspherical coefficients. The shapes (sagittal shapes) of the incident surface and the exit surface of the scanning optical element 60 provided in the optical scanning device 1 according to this embodiment in the sub-scanning cross section are expressed by the following formula (2).

number

[0046] In formula (2), S is the sagittal shape defined in a cross section perpendicular to the main scanning cross section and including the normal to the generatrix at each position in the main scanning direction. Furthermore, the radius of curvature (sagittal radius of curvature) r′ in the sub-scanning cross section at a position spaced apart from the optical axis by Y in the main scanning direction is expressed by the following equation (3).

number

[0047] In equation (3), r is the radius of curvature (radius of curvature of the sagittal line) in the sub-scan section on the optical axis, E i (i=1,2,3,···,16) is the sagittal variation coefficient. In addition, the aspherical coefficients B2, B4, B6, B8, and B 10 , B 12 , B 14 and B 16 For each, different values ​​are set for the Y≧0 region and the Y<0 region. That is, aspherical coefficients B2, B4, B6, B8, B 10 , B 12 , B 14 and B 16 For each, a coefficient with the subscript u added corresponding to the upper region where Y≧0, and a coefficient with the subscript l added corresponding to the lower region where Y<0 are set.

[0048] Similarly, the aspherical coefficients E2, E4, E6, E8, and E 10 , E 12 , E 14 and E 16 For each of these, different values ​​are set for the Y≧0 region and the Y<0 region. That is, aspherical coefficients E2, E4, E6, E8, E 10 , E 12 , E 14 and E 16 For each of these, a coefficient with the subscript u added corresponding to the upper region where Y≧0, and a coefficient with the subscript l added corresponding to the lower region where Y<0 are set.

[0049] The exit surface of the synchronization detection optical element 70 provided in the optical scanning device 1 according to this embodiment is a diffractive surface on which a diffraction grating is formed. Specifically, the exit surface of the synchronous detection optical element 70 is formed as a diffractive surface defined by a phase function φ expressed by the following equation (4).

number

[0050] In equation (4), λ is the wavelength (design wavelength) of the light beam emitted from the light source 10, and is specifically 793 nm. Furthermore, the optical scanning device 1 according to this embodiment uses first-order diffracted light.

[0051] In the optical scanning device 1 according to this embodiment, the incident surface of the synchronization detection optical element 70 has the aspherical coefficient B i and the sagittal line change coefficient E i Although all of the values ​​are set to 0, this is not limiting, and at least one of the values ​​may be set to a value other than 0. In the optical scanning device 1 according to this embodiment, the shape of each optical surface is defined by the functions expressed by the above equations (1) to (4), but the definition of the shape of each optical surface is not limited to this.

[0052] Next, the influence of temperature rise on the optical performance of the optical scanning device 1 according to this embodiment will be described. The semiconductor laser used in the light source 10 generates heat by itself when turned on, causing the temperature to rise, which in turn causes the ambient temperature to rise.

[0053] Furthermore, a driving unit such as a motor that rotates the deflector 50 generates heat, thereby increasing the environmental temperature. Such changes in the environmental temperature have the following three main effects on the optical performance of the optical scanning device 1 according to this embodiment.

[0054] The first effect is a change in the wavelength of the semiconductor laser forming the light source 10, which is called mode hopping. Generally, the oscillation wavelength of a semiconductor laser increases with increasing temperature. The amount of change in the oscillation wavelength per unit temperature varies depending on the type of laser element used and individual differences. Specifically, the light source 10 can be a semiconductor laser having a typical characteristic value in which the wavelength λ changes by 0.26 nm when the temperature T changes by 1 degree, i.e., a change of dλ / dT = 0.26 (nm / degree).

[0055] The second effect is that the ambient temperature rises as the temperature of the semiconductor laser or motor rises, causing a change in the refractive index of the optical elements arranged in the vicinity of the semiconductor laser or motor. Specifically, in the optical scanning device 1 according to this embodiment, the refractive index of the incident optical element 30 and the synchronous detection optical element 70, which are arranged close to the light source 10 and the deflector 50 and are formed from plastic molded lenses, changes.

[0056] Generally, the refractive index of a resin material decreases when the temperature is increased, but the amount of change in the refractive index per unit temperature varies depending on the type of resin material used and individual differences. Specifically, the incident optical element 30 and the synchronous detection optical element 70 each have a general characteristic value of a refractive index n of −9.9×10 when the temperature T changes by just 1 degree. -5 That is, dn / dT=-9.9×10 -5 It can be formed from a resin material having a change amount of ( / degree).

[0057] The third effect is that the ambient temperature rises as the temperature of the semiconductor laser and motor rises, causing the shapes of the incident optical element 30 and the synchronous detection optical element 70, which are arranged close to the light source 10 and the deflector 50, to change. Generally, optical elements made of resin materials expand when heated, reducing the power of the optical surface of the optical element, while the coefficient of thermal expansion per unit temperature of the optical element varies depending on the type of resin material used and individual differences.

[0058] Specifically, the incident optical element 30 and the synchronous detection optical element 70 can each be formed from a resin material having a thermal expansion coefficient of 0.008% isotropically when the temperature rises by just 1 degree, as a general characteristic value. The above three influences on the optical performance of the optical scanning device 1 according to this embodiment are not limited to the above characteristic values ​​of the semiconductor laser forming the light source 10, the incident optical element 30, the synchronous detection optical element 70, and the like.

[0059] Due to the above three influences, the synchronization detection performance of the optical scanning device 1 according to this embodiment changes as follows. 3A and 3B are schematic main-scan cross-sectional views of the optical scanning device 1 according to this embodiment near the synchronization detection unit 90. FIG. Note that Figure 3(a) shows how the luminous flux is received by the synchronous detection unit 90 when the ambient temperature is not rising, while Figure 3(b) shows how the luminous flux is received by the synchronous detection unit 90 when the ambient temperature is rising.

[0060] As shown in FIG. 3(a), when the environmental temperature is not rising, the light beam that has passed through the synchronous detection optical element 70 is condensed near the synchronous detection edge portion 80 in the main scanning cross section. On the other hand, as shown in Figure 3(b), when the ambient temperature is rising, the light beam that passes through the synchronous detection optical element 70 is concentrated downstream of the synchronous detection edge portion 80 in the main scanning cross section. In this case, the focus shifts to the rear side, and the spot formed by the light beam at the position of the synchronization detection edge portion 80 becomes larger, so that the synchronization detection angle θ BD The increased variation in the frequency reduces the accuracy of synchronization detection.

[0061] Figure 4(a) shows the change in the main scanning LSF (Line Spread Function) spot diameter with respect to the change in position in a direction parallel to the optical axis of the synchronous detection optical system 95 in the optical scanning device of the comparative example, i.e., the defocus characteristics of the main scanning LSF spot diameter. The optical scanning device of the comparative example shown here has the same configuration as the optical scanning device 1 of this embodiment, except that a specified synchronous detection optical element is provided instead of the synchronous detection optical element 70.Therefore, the same components are given the same reference numerals and their explanations are omitted.

[0062] Specifically, the specified synchronous detection optical element does not have a diffractive surface formed on the exit surface, i.e., the entrance surface and exit surface are each formed only by a refractive surface, while having the same shape as the synchronous detection optical element 70, thereby maintaining power. The main-scanning LSF spot diameter shown in FIG. 4(a) is the main-scanning LSF spot diameter of the light beam deflected by the deflector 50 toward the synchronization detector 90 at the second timing as described above. The main scanning LSF spot diameter means the width when the light quantity profile obtained by integrating the spot profile in the sub-scanning direction at each position in the main scanning direction is sliced ​​at a position that is 50% of its maximum value.

[0063] In addition, in Figure 4(a), the change in the main scanning LSF spot diameter when the environmental temperature is 25°C and not rising is shown by a solid line, while the change in the main scanning LSF spot diameter when the environmental temperature is 50°C and has risen is shown by a dashed line. 4(a) in a direction parallel to the optical axis of the synchronous detection optical system 95, 0 mm corresponds to the position of the synchronous detection section 90, and −3.00 mm corresponds to the position of the synchronous detection edge section 80.

[0064] As shown in Figure 4(a), in the optical scanning device of the comparative example, when the ambient temperature rises from 25°C to 50°C, the focal position where the main-scanning LSF spot diameter is minimum shifts downstream. Accordingly, the main-scanning LSF spot diameter at the position of the synchronization detection edge portion 80 increases by about 1.3 times. Furthermore, when the environmental temperature rises above 50° C., the focus error becomes even larger, and the main-scanning LSF spot diameter at the position of the synchronization detection edge portion 80 becomes even larger.

[0065] Furthermore, the synchronization detection performance also changes due to manufacturing errors of the housing and each optical element provided in the optical scanning device according to the comparative example. Furthermore, in a configuration such as the optical scanning device of the comparative example, in which an edge portion or an equivalent slit portion is provided on the synchronous detection optical system and the light beam is focused in the vicinity of the edge portion within the main scanning cross section to improve the synchronous detection accuracy, the effect of the above-mentioned focus deviation also changes depending on the depth width. In other words, in a configuration in which the overall length of the synchronous detection optical system is short or the focal length of the synchronous detection optical system in the main scanning cross section is short, resulting in a narrow depth of field, fluctuations in spot diameter due to focus shift caused by temperature rise are likely to become noticeable.

[0066] Therefore, in the optical scanning device 1 according to this embodiment, the synchronous detection optical element 70 has diffraction power (power due to diffraction) in the synchronous detection optical system 95, which has a short overall length, thereby suppressing the deterioration of synchronous detection accuracy due to temperature rise. Specifically, when the environmental temperature rises, the refractive indexes of the incident optical element 30 and the synchronous detection optical element 70 decrease and the elements expand. At this time, the focus of the incident optical element 30 and the synchronous detection optical element 70 shifts so as to be farther away from the light source 10 .

[0067] On the other hand, in the optical scanning device 1 according to this embodiment, the oscillation wavelength becomes longer as the temperature of the light source 10 increases. At this time, the focus of the incident optical element 30 and the synchronous detection optical element 70 shifts closer to the light source 10 in accordance with the diffraction power of the synchronous detection optical element 70 .

[0068] That is, in the optical scanning device 1 according to this embodiment, by appropriately setting the diffraction power in the synchronization detection optical element 70, the above two shifts can be cancelled out. This makes it possible to suppress the spot from becoming thicker at the position of the synchronization detection edge portion 80.

[0069] Specifically, in the optical scanning device 1 according to this embodiment, the focal lengths in the main scanning section due to only the diffraction power and only the refractive power (power due to refraction) of the synchronization detection optical element 70 are respectively defined as f dm and f rm Then, the following conditional expression (5) is satisfied:

number

[0070] In other words, in the optical scanning device 1 according to this embodiment, the value of the diffraction power of the synchronous detection optical element 70 is equal to or greater than the value of the refractive power of the synchronous detection optical element 70 in the main scanning cross section. In the optical scanning device 1 according to this embodiment, by increasing the value of the diffraction power of the synchronous detection optical element 70 so as to satisfy conditional expression (5), it is possible to suppress the decrease in synchronous detection accuracy due to temperature changes even in a synchronous detection optical system 95 that is small and has a short overall length. In the optical scanning device 1 according to this embodiment, it is preferable that the following conditional expression (5a) be satisfied instead of the conditional expression (5).

number

[0071] In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (5b) be fulfilled instead of the conditional expression (5a).

number

[0072] In the optical scanning device 1 according to this embodiment, f dm / f rm =49.81 / 160.70=0.31, so the conditions (5), (5a) and (5b) are satisfied.

[0073] FIG. 4(b) shows the change in the main-scanning LSF spot diameter relative to the change in position in the direction parallel to the optical axis of the synchronization detection optical system 95 in the optical scanning device 1 according to this embodiment, i.e., the defocus characteristic of the main-scanning LSF spot diameter. The main-scanning LSF spot diameter shown in FIG. 4(b) is the main-scanning LSF spot diameter of the light beam deflected by the deflector 50 toward the synchronization detector 90 at the second timing as described above.

[0074] In addition, in Figure 4(b), the change in the main scanning LSF spot diameter when the environmental temperature is 25°C and not rising is shown by a solid line, while the change in the main scanning LSF spot diameter when the environmental temperature is 50°C and has risen is shown by a dashed line. 4B, 0 mm corresponds to the position of the synchronous detection portion 90, and −3.00 mm corresponds to the position of the synchronous detection edge portion 80. In FIG.

[0075] As shown in Figure 4(b), in the optical scanning device 1 of this embodiment, when the ambient temperature rises from 25°C to 50°C, the focal position where the main scanning LSF spot diameter is at its minimum value shifts downstream. On the other hand, the magnitude of the shift is relatively small compared to the optical scanning device according to the comparative example.

[0076] Therefore, even when the ambient temperature rises from 25°C to 50°C, the main-scanning LSF spot diameter at the position of the synchronization detection edge portion 80 remains almost unchanged, meaning that the increase in the main-scanning LSF spot diameter can be suppressed. That is, in the optical scanning device 1 according to this embodiment, the synchronization detection optical element 70 has diffraction power, so that it is possible to suppress a decrease in synchronization detection accuracy due to a rise in temperature.

[0077] Furthermore, in the optical scanning device 1 according to this embodiment, the light beam deflected by the deflector 50 toward the synchronization detection unit 90 at the second timing as described above may be subject to surface reflection at the incident surface of the synchronization detection optical element 70. Then, the light beam is reflected from the surface, generating ghost light (returned light) that returns to the light source 10, which may degrade the optical performance of the optical scanning device 1, including the light emission accuracy of the light source 10.

[0078] On the other hand, the incident surface of the synchronous detection optical element 70 provided in the optical scanning device 1 of this embodiment has a curved shape without a diffraction grating, i.e., it is formed as a refractive surface, and the exit surface is formed as a diffractive surface with a diffraction grating formed on a flat surface. This allows the light generated by the surface reflection of the light beam on the incident surface of the synchronous detection optical element 70 to be set as divergent light.

[0079] Therefore, by reducing the amount of ghost light returning to the light source 10, it is possible to prevent the optical performance of the optical scanning device 1 from deteriorating. In addition, the incident surface of the synchronous detection optical element 70 may be tilted to reflect the light beam from the surface so that it does not return to the light source 10, or an anti-reflection coating may be applied to the incident surface of the synchronous detection optical element 70 to reduce the amount of light generated by the surface reflection of the light beam.

[0080] As described above, in the optical scanning device 1 according to this embodiment, of the entrance surface and exit surface of the synchronization detection optical element 70, the exit surface is formed as a diffractive surface. In the optical scanning device 1 according to this embodiment, the synchronization detecting optical element 70 is a plastic molded lens formed by injection molding, as described above.

[0081] When forming a diffractive surface in a plastic molded lens having two optical surfaces, due to the configuration of the mold, the optical surface fixed to the mold is generally formed as the diffractive surface, and a gate portion 71 (Figures 5(a) and (b)) is also arranged thereon. Therefore, in the optical scanning device 1 according to this embodiment, of the entrance surface and exit surface of the synchronization detection optical element 70, only the exit surface is formed as a diffractive surface, and a gate portion 71 is formed on the exit surface.

[0082] When the synchronization detection optical element 70 is formed by a method other than injection molding, such as cutting, the formation of the diffractive surface and the arrangement of the gate portion 71 are not limited to those described above. That is, both the entrance surface and the exit surface of the synchronous detection optical element 70 may be diffractive surfaces, or in other words, at least one of the entrance surface and the exit surface of the synchronous detection optical element 70 may be a diffractive surface.

[0083] In addition, in the optical scanning device 1 according to this embodiment, it is preferable to arrange the gate portion (not shown) provided on the incident optical element 30 and the gate portion 71 provided on the synchronization detection optical element 70 so that their relative positions with respect to the optical axis do not coincide with each other. This makes it possible to suppress a sudden deterioration in optical performance due to the superposition of birefringence that is likely to occur near the gate portion provided in the incident optical element 30 and the gate portion 71 provided in the synchronous detection optical element 70.

[0084] 5(a) and 5(b) are a schematic front view and a schematic top view, respectively, of the synchronous detection optical element 70 provided in the optical scanning device 1 according to this embodiment. The synchronization detecting optical element 70 provided in the optical scanning device 1 according to this embodiment is a plastic molded lens having an entrance surface and an exit surface each having a rotationally symmetrical shape. Specifically, the synchronous detection optical element 70, excluding the gate portion 71, has a circular shape in a cross section perpendicular to the optical axis, and is a so-called round lens.

[0085] As shown in Figures 5(a) and (b), in the optical scanning device 1 of this embodiment, the synchronous detection optical element 70 is supported by support portions 2a and 2b, which are each integrally formed in a housing not shown. Specifically, the synchronous detection optical element 70 is X BD In the X direction, the support 2a and 2b are struck. BD In the direction perpendicular to the Z direction and the Z direction, it is supported by being lightly press-fitted into the space between the support portions 2a and 2b. The synchronous detection optical element 70 is supported in the Z direction by a bottom surface portion (not shown) that is integrally formed with the housing.

[0086] When the synchronous detection optical element 70 is assembled into the housing in the optical scanning device 1 according to this embodiment, the synchronous detection optical element 70 is inserted into the space between the support portion 2a and the support portion 2b from the positive side in the Z direction. Therefore, during the insertion, the synchronous detection optical element 70 is positioned so that the gate portion 71 is located on the positive side in the Z direction with respect to a cross section that includes the center of the synchronous detection optical element 70 and is perpendicular to the Z direction.

[0087] In Figure 5(a), the synchronous detection optical element 70 is supported so that the gate portion 71 and the support portion 2b do not abut each other, but this is not limited to this, and the synchronous detection optical element 70 may be supported so that the two abut each other. Furthermore, the synchronous detection optical element 70 can be supported more firmly by being adhered to the support portions 2a and 2b with an ultraviolet-curing adhesive.

[0088] In the optical scanning device 1 according to this embodiment, the height in the Z direction of the support portion 2b, which is provided downstream of the support portion 2a in the rotation direction of the deflector 50, is smaller than the height of the support portion 2a. As shown in FIG. 2(a), the light beam that has passed through the upstream side of the synchronous detection unit 90 in the scanning direction relative to the center of the synchronous detection optical element 70 is blocked by the light blocking member S.

[0089] On the other hand, the light beam that passes through the downstream side of the synchronous detection unit 90 in the scanning direction relative to the center of the synchronous detection optical element 70 is guided to the synchronous detection unit 90 without being blocked by the light blocking member S. Therefore, in the optical scanning device 1 according to this embodiment, the height of the support portion 2b in the Z direction is reduced, thereby increasing the scanning width of the synchronization detection portion 90 on the downstream side in the scanning direction.

[0090] In the optical scanning device 1 according to this embodiment, the value of the composite power of the refractive power and the diffractive power of the synchronization detecting optical element 70 in the sub-scanning cross section is set to be positive. On the other hand, in a configuration in which the light beam is focused at a position near the synchronization detection edge portion 80 in the main scanning cross section, as in the optical scanning device 1 of this embodiment, it is not preferable to focus the light beam at the same position in the sub-scanning cross section as well.

[0091] As described above, the synchronization detection edge portion 80 is integrally formed with the housing of the optical scanning device 1, and there is a risk that the surface or ridge of the synchronization detection edge portion 80 may contain manufacturing errors or that foreign matter such as dust or lint may be attached. If the light beam is focused near such a synchronization detection edge portion 80 in both the main scanning section and the sub-scanning section, there is a risk that the amount of light of the light beam when it reaches the synchronization detection portion 90 will change significantly depending on the above-mentioned error of the synchronization detection edge portion 80.

[0092] Therefore, in the optical scanning device 1 of this embodiment, the light beam deflected by the deflector 50 toward the synchronization detection unit 90 at the second timing is not focused at a position near the synchronization detection edge unit 80 within the sub-scanning cross section, but is focused at a position different from that position. This makes it possible to reduce the sensitivity of the amount of light of the light beam reaching the synchronization detection section 90 to the above-mentioned error of the synchronization detection edge section 80 . On the other hand, the above-mentioned composite power in the sub-scanning section of the synchronous detection optical element 70 provided in the optical scanning device 1 of this embodiment is set so that the synchronous detection unit 90 receives a light beam having a light beam diameter that satisfies the signal strength (i.e., synchronous detection light amount) required for operation.

[0093] In the optical scanning device 1 according to this embodiment, the synchronization detecting optical element 70 has positive diffraction power in the sub-scanning cross section. As a result, similar to the main-scanning LSF spot diameter, it is possible to suppress an increase in the sub-scanning LSF spot diameter at the position of the synchronization detection edge portion 80 due to an increase in the environmental temperature.

[0094] The sub-scanning LSF spot diameter refers to the width when the light intensity profile obtained by integrating the spot profile in the main scanning direction at each position in the sub-scanning direction is sliced ​​at a position that is 50% of its maximum value. In addition, the positive diffraction power of the synchronization detection optical element 70 in the sub-scanning cross section is set to prevent the light beam from being focused at a position near the synchronization detection edge portion 80 in the sub-scanning cross section due to focus shift caused by fluctuations in environmental temperature.

[0095] In addition, the positive diffraction power in the sub-scan section of the synchronous detection optical element 70 is set to maintain the signal strength required for operation by suppressing fluctuations in the beam diameter of the light beam when received by the synchronous detection unit 90. This allows the synchronous detection angle θ BD Furthermore, the variation in the synchronously detected light amount acquired by the synchronous detection unit 90 can also be suppressed.

[0096] In the optical scanning device 1 according to this embodiment, the synchronous detection optical element 70 is disposed so as to face the optical axis of the synchronous detection optical system 95 directly. In other words, in the optical scanning device 1 according to this embodiment, the optical axis of the synchronous detection optical system 95 passes through the vertices of the entrance surface and the exit surface of the synchronous detection optical element 70.

[0097] If the synchronous detection optical element 70 does not face the optical axis, second-order or higher diffracted light will spread in a cross section perpendicular to the optical axis. In this case, the synchronous detection angle θ to be determined BD When the deflector 50 is rotated at a rotation angle different from the above, the amount of light reaching the synchronization detection edge portion 80, and hence the synchronization detection portion 90, increases somewhat.

[0098] In other words, in the optical scanning device 1 of this embodiment, the synchronous detection optical element 70 is positioned directly opposite the optical axis of the synchronous detection optical system 95, thereby suppressing the spread of second-order or higher diffracted light in a cross section perpendicular to the optical axis. This allows the synchronous detection angle θ BD Therefore, it is possible to suppress a decrease in the accuracy in determining the synchronization, that is, the accuracy of synchronization detection.

[0099] In addition, in the optical scanning device 1 according to this embodiment, the incident optical element 30 and the synchronous detection optical element 70 are provided as separate components, and the scanning optical element 60 and the synchronous detection optical element 70 are provided as separate components. That is, in the optical scanning device 1 according to this embodiment, no optical element integrated with the synchronization detection optical element 70 is provided. In other words, in the optical scanning device 1 according to this embodiment, the incident light beam guided by the incident optical system 75 and the scanning light beam guided by the imaging optical system 85 do not pass through the synchronization detection optical element 70, respectively.

[0100] In other words, in the optical scanning device 1 according to this embodiment, the synchronization detection optical element 70 is not shared by the incident optical system 75 and the imaging optical system 85. If the incident optical element 30 or the scanning optical element 60 and the synchronous detection optical element 70 were formed as an integral part using a single plastic molded lens, the molding process would be more difficult, and the optical performance would likely deteriorate.

[0101] In particular, as described above, due to the structural constraints of the mold when forming the diffractive surface on the synchronous detection optical element 70, and the support and abutment relationship of the synchronous detection optical element 70 in the housing, it becomes difficult to directly align the synchronous detection optical element 70 with the optical axis of the synchronous detection optical system 95. Furthermore, since the synchronous detection optical element 70 has a long length and a complex shape, unexpected birefringence and temperature distribution may be formed inside the synchronous detection optical element 70, which may lead to a deterioration in optical performance that is difficult to control, such as focus deviation and spot enlargement, which is undesirable.

[0102] In the optical scanning device 1 according to this embodiment, the total length of the synchronous detection optical system 95 is set to D BDWhen the scanning width of the surface 100 to be scanned is h, it is preferable that the following conditional expression (6) be satisfied.

number

[0103] Here, the total length of the synchronous detection optical system 95 means the distance between the deflection point on the deflection surface 50a of the deflector 50 for the principal ray guided by the synchronous detection optical system 95 to the intersection point between the optical axis of the synchronous detection optical system 95 and the light receiving surface of the synchronous detection unit 90 and the intersection point. The scanning width of the scanned surface 100 means the distance between one most off-axis image height on the scanned surface 100 and the other most off-axis image height.

[0104] If the overall length of the synchronization detection optical system 95 becomes so large as to exceed the upper limit of the conditional expression (6), the optical scanning device 1 will become large, which is not preferable. On the other hand, if the lower limit of conditional expression (6) is not reached, the focal length of the synchronization detection optical element 70 in the main scanning section becomes too short, narrowing the depth of field and reducing convenience, which is undesirable. In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (6a) be fulfilled instead of the conditional expression (6).

number

[0105] In the optical scanning device 1 according to this embodiment, D BD Since / h=63.54 / 214.00=0.30, the conditional expressions (6) and (6a) are satisfied. Next, the total length of the imaging optical system 85 is T c In this case, it is preferable that the optical scanning device 1 according to this embodiment fulfills the following conditional expression (7):

number

[0106] Here, the total length of the imaging optical system 85 means the distance between the deflection point on the deflection surface 50a of the deflector 50 for the chief ray of the light beam scanning the axial image height of the scanned surface 100 and the axial image height. If the upper limit of conditional expression (7) is exceeded, the scanning field angle becomes too large, making it difficult to arrange the synchronous detection optical system 95 between the incident optical system 75 and the imaging optical system 85, which is undesirable.

[0107] On the other hand, if the overall length of the imaging optical system 85 becomes so large as to fall below the lower limit of the conditional expression (7), the optical scanning device 1 becomes large, which is not preferable. In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (7a) be fulfilled instead of the conditional expression (7).

number

[0108] In the optical scanning device 1 according to this embodiment, h / (2×T c )=214.00 / (2×141.50)=0.76, so conditional expressions (7) and (7a) are satisfied. The focal lengths of the synchronous detection optical system 95 and the imaging optical system 85 in the main scanning section are respectively f m and fθ, it is preferable that the optical scanning device 1 according to this embodiment fulfills the following conditional expression (8):

number

[0109] If the upper limit of conditional expression (8) is exceeded, the overall length of the synchronization detection optical system 95 becomes too large, which undesirably increases the size of the optical scanning device 1. On the other hand, if the focal length of the synchronization detection optical system 95 in the main scanning section becomes so small as to fall below the lower limit of conditional expression (8), the depth of field at the synchronization detection edge portion 80 becomes too narrow.

[0110] Therefore, fluctuations in the main-scanning LSF spot diameter at the synchronization detection edge portion 80 due to focus deviations caused by fluctuations in the environmental temperature become large. Furthermore, the diameter of the light beam in the main scanning direction when received by the synchronization detector 90 becomes large, which is undesirable because it becomes difficult to obtain a sufficient signal strength. In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (8a) be fulfilled instead of the conditional expression (8).

number

[0111] In the optical scanning device 1 according to this embodiment, f m Since / fθ=38.26 / 126.61=0.30, the conditions (8) and (8a) are satisfied. The focal length of the synchronous detection optical system 95 in the sub-scan section is f s In this case, it is preferable that the optical scanning device 1 according to this embodiment fulfills the following conditional expression (9):

number

[0112] If the upper limit of conditional expression (9) is exceeded, the diameter of the light beam in the sub-scanning direction when received by the synchronization detector 90 becomes large, making it difficult to obtain a sufficient signal strength, which is undesirable. On the other hand, if the overall length of the synchronization detection optical system 95 becomes so large as to fall below the lower limit of the conditional expression (9), the optical scanning device 1 becomes large, which is not preferable.

[0113] In addition, the focal length f s If this becomes small, the light beam deflected by the deflector 50 toward the synchronization detection portion 90 at the second timing will be condensed in the vicinity of the synchronization detection edge portion 80 even within the sub-scanning cross section, which is undesirable. Alternatively, if the light beam that has been once focused and then spreads reaches the synchronous detector 90, it becomes difficult to obtain a sufficient signal strength in the synchronous detector 90, which is not preferable. In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (9a) be fulfilled instead of the conditional expression (9).

number

[0114] In the optical scanning device 1 according to this embodiment, f s / D BD =28.91 / 63.54=0.46, so conditional expressions (9) and (9a) are satisfied.

[0115] As described above, in the optical scanning device 1 according to this embodiment, the diffractive surface is provided in the synchronization detecting optical element 70 so as to satisfy the conditional expression (5). This makes it possible to provide an optical scanning device that can suppress a decrease in synchronous detection accuracy due to temperature changes even when the synchronous detection optical system 95 is small and has a short overall length.

[0116] In the optical scanning device 1 according to this embodiment, instead of the incident optical element 30, a coupling lens and a cylindrical lens may be provided. Furthermore, in the optical scanning device 1 according to this embodiment, the aperture 40 and the synchronization detection edge portion 80 are integrally formed in a housing (not shown) that holds each optical element, but this is not limited to this, and they may be provided as optical elements separate from the housing.

[0117] Furthermore, in the optical scanning device 1 according to this embodiment, the diaphragm 40 is provided to restrict the diameter of the light beam that has passed through the incident optical element 30 in both the main scanning direction and the sub-scanning direction, but this is not limiting. That is, instead of the diaphragm 40, a main scanning diaphragm for restricting the light beam diameter in the main scanning direction and a sub-scanning diaphragm for restricting the light beam diameter in the sub-scanning direction may be provided.

[0118] Furthermore, in the optical scanning device 1 according to this embodiment, the deflector 50 is formed by a polygon mirror, but is not limited to this and may be formed by a vibration-type reflective element such as a MEMS (Micro Electro Mechanical Systems) mirror. The deflector 50 may have deflecting surfaces 50a that are curved, such as spherical or cylindrical surfaces, and the number of deflecting surfaces 50a is not limited to four. Furthermore, in the optical scanning device 1 according to this embodiment, the imaging optical system 85 is formed by a single scanning optical element 60, but this is not limited to this and it may be formed by a plurality of optical elements such as lenses and mirrors.

[0119] In the optical scanning device 1 according to this embodiment, the above-described configuration is applied to the synchronous detection optical system 95 to suppress a decrease in synchronous detection accuracy due to changes in the environmental temperature, but the present invention is not limited to this. That is, for example, by applying the above configuration to an APC (Auto Power Control) optical system that guides a light beam to an APC (Auto Power Control) sensor for detecting light intensity so that the light emitting point of the light source 10 emits light at a desired intensity, the deterioration of light intensity detection accuracy due to changes in the ambient temperature can be suppressed.

[0120] Furthermore, in the optical scanning device 1 according to this embodiment, the incident surface of the synchronous detection optical element 70 is formed as a refractive surface on which no diffraction grating is formed, and the exit surface is formed as a diffractive surface on which a diffraction grating is formed on a plane, but this is not limited to this. That is, a diffraction grating may be formed on a base surface having a curved shape on at least one of the entrance surface and exit surface of the synchronous detection optical element 70 . In such an optical surface, the above configuration can be considered by separating the diffractive power and the refractive power from each other.

[0121] [Second embodiment] FIG. 6(a) shows a schematic main scanning cross section of the optical scanning device 2 according to the second embodiment. 6(b) and 6(c) are schematic cross-sectional views in the sub-scanning direction of an imaging optical system 85 and a synchronization detection optical system 95 provided in the optical scanning device 2 according to the second embodiment, respectively. 7(a) and 7(b) are a schematic front view and a schematic top view, respectively, of a synchronization detection optical element 70 provided in the optical scanning device 2 according to the second embodiment.

[0122] The optical scanning device 2 according to this embodiment has the same configuration as the optical scanning device 1 according to the first embodiment, except that a sub-scanning diaphragm 20 and a main-scanning diaphragm 41 are provided instead of the diaphragm 40, and an incident optical element 31 is provided instead of the incident optical element 30. Therefore, the same components are given the same reference numerals, and descriptions thereof will be omitted.

[0123] The optical scanning device 2 of this embodiment includes a light source 10, a sub-scanning aperture 20, an incident optical element 31 (second optical element), a main-scanning aperture 41, a deflector 50, a scanning optical element 60, a synchronization detection optical element 70, a synchronization detection edge portion 80, and a synchronization detection portion 90. The sub-scanning diaphragm 20 has a rectangular opening and regulates the diameter of the light beam emitted from the light source 10 in the sub-scanning direction. In the optical scanning device 2 according to this embodiment, the sub-scanning diaphragm 20 is formed integrally with a housing (not shown).

[0124] The incident optical element 31 is an anamorphic lens having different positive powers in the main scanning cross section and the sub-scanning cross section. The incident optical element 31 converts the light beam that has passed through the sub-scanning stop 20 into a parallel light beam in the main scanning cross section, and also condenses the light in the vicinity of the deflecting surface 50a of the deflector 50 in the sub-scanning cross section. It should be noted that the parallel light beam here includes not only a strictly parallel light beam but also an approximately parallel light beam such as a weakly divergent light beam or a weakly convergent light beam.

[0125] The main scanning diaphragm 41 has a rectangular opening and regulates the diameter of the light beam that has passed through the incident optical element 31 in the main scanning direction. In the optical scanning device 2 according to this embodiment, the main scanning diaphragm 41 is formed integrally with a housing (not shown).

[0126] The deflector 50 is a polygon mirror (rotating polygonal mirror) formed by mirror-finishing aluminum metal and having four flat reflecting surfaces. The deflector 50 deflects the light beam that has passed through the main scanning diaphragm 41 while rotating in the direction of arrow R in FIG. 6(a) by a driving unit such as a motor (not shown).

[0127] The light beam emitted from the light source 10 passes through the sub-scanning diaphragm 20, the incident optical element 31, and the main-scanning diaphragm 41, and is incident on the deflector 50 so as to form a long line image in the main-scanning direction on the deflection surface 50a. In the optical scanning device 2 of this embodiment, unlike the optical scanning device 1 of the first embodiment, the light beam emitted from the light source 10 enters the deflector 50 by traveling from the negative side to the positive side in the Y direction.

[0128] Therefore, in the optical scanning device 2 according to this embodiment, the deflector 50 rotates in the opposite direction compared to the optical scanning device 1 according to the first embodiment, and thus the surface to be scanned 100 is scanned in the opposite direction. In other words, since the deflector 50 rotates in the opposite direction, in the optical scanning device 2, as shown in Figures 7(a) and (b), the relative positions of the support portions 2a and 2b that support the synchronous detection optical element 70 and the gate portion 71 are different from those of the optical scanning device 1 of the first embodiment.

[0129] In the optical scanning device 2 according to this embodiment, the sub-scanning diaphragm 20, the incident optical element 31, and the main-scanning diaphragm 41 form an incident optical system 75. Furthermore, the scanning optical element 60 forms an imaging optical system 85, and the synchronous detection optical element 70 and the synchronous detection edge portion 80 form a synchronous detection optical system 95.

[0130] Next, the specifications of the optical scanning device 2 according to this embodiment, the refractive index and coordinates of each optical surface, and the shape of each optical surface are shown in Tables 4, 5, and 6 below, respectively. As shown in Table 6, the shapes (meridian shapes) of the entrance surface and exit surface of the scanning optical element 60 provided in the optical scanning device 2 according to this embodiment in the main scanning cross section respectively have aspherical shapes expressed by polynomial functions up to the tenth order. Similarly, the radius of curvature (sagittal radius of curvature) r' in the sub-scanning section at a position Y away from the optical axis in the main scanning direction of each of the incident surface and the exit surface of the scanning optical element 60 provided in the optical scanning device 2 of this embodiment is expressed by a polynomial function of up to the tenth order.

[0131] [Table 4]

[0132] [Table 5]

[0133] [Table 6]

[0134] The incident surface of the incident optical element 31 provided in the optical scanning device 2 according to this embodiment is a diffractive surface on which a diffraction grating is formed. Specifically, the incident surface of the incident optical element 31 is formed as a diffractive surface defined by a phase function φ expressed by the following equation (9).

number

[0135] In equation (9), M is the diffraction order, and since the optical scanning device 2 according to this embodiment uses first-order diffracted light, the diffraction order M is 1. That is, the diffraction order M of the incident surface of the incident optical element 31 and the exit surface of the synchronous detection optical element 70 are the same. In addition, in equation (9), λ is the wavelength (design wavelength) of the light beam emitted from the light source 10, and specifically, is 790 nm.

[0136] FIG. 8 shows the image height dependency of the scanning speed ratio in the optical scanning device 2 according to this embodiment. The scanning speed ratio here means the ratio of the scanning speed at each image height to the scanning speed at the axial image height (Y=0 mm) on the scanned surface 100, i.e., the scanning speed ratio at the axial image height is 100%.

[0137] As shown in Figure 8, the optical scanning device 2 of this embodiment has non-uniform speed scanning characteristics that exhibit a profile expressed by a quadratic function such that the scanning speed ratio at the outermost off-axis image height (Y = ±107 mm) is approximately 133%. That is, in the optical scanning device 2 according to this embodiment, the surface to be scanned 100 is optically scanned at a non-uniform speed with a light beam deflected by the deflector 50 which rotates at a uniform speed. In other words, in the optical scanning device 2 according to this embodiment, the imaging optical system 85 is configured so that the partial magnification in the main scanning direction differs between the on-axis image height and the most off-axis image height.

[0138] Such a configuration is advantageous for shortening the optical path because it can substantially tolerate distortion compared to an optical scanning device having a general constant speed scanning characteristic using a so-called fθ lens. In particular, the optical scanning device 2 of this embodiment, which has a short overall length of the imaging optical system 85 and is formed by a single scanning optical element 60, has non-uniform speed scanning characteristics, thereby enabling miniaturization while maintaining high optical performance.

[0139] Figure 9 shows the change in the main scanning LSF spot diameter with respect to the change in position in the direction parallel to the optical axis of the synchronization detection optical system 95 in the optical scanning device 2 of this embodiment, which corresponds to Figure 4(b) above, i.e., the defocus characteristic of the main scanning LSF spot diameter. 9, 0 mm corresponds to the position of the synchronous detection portion 90, and −3.19 mm corresponds to the position of the synchronous detection edge portion 80. In FIG.

[0140] Comparing Figures 4(b) and 9, the optical scanning device 2 of this embodiment has a shorter focal length of the synchronous detection optical system 95 than the optical scanning device 1 of the first embodiment, resulting in a narrower overall depth of field. Furthermore, the amount of focus fluctuation when the environmental temperature fluctuates is reduced compared to the optical scanning device 1 according to the first embodiment.

[0141] Therefore, even when the ambient temperature rises from 25°C to 50°C, the main-scanning LSF spot diameter at the position of the synchronization detection edge portion 80 remains almost unchanged, meaning that the increase in the main-scanning LSF spot diameter can be suppressed. This is because the optical scanning device 2 according to this embodiment uses, in place of the incident optical element 30, an incident optical element 31 having a diffraction grating formed on the incident surface in addition to the synchronization detection optical element .

[0142] In the optical scanning device 2 according to this embodiment, f dm / f rm =29.07 / 54.43=0.53, so the conditions (5), (5a) and (5b) are satisfied. In addition, in the optical scanning device 2 according to this embodiment, D BD Since / h=53.38 / 214.00=0.25, the conditional expressions (6) and (6a) are satisfied. In the optical scanning device 2 according to this embodiment, h / (2×T c )=214.00 / (2×125.00)=0.86, so conditional expressions (7) and (7a) are satisfied. In the optical scanning device 2 according to this embodiment, f m Since / fθ=19.31 / 109.47=0.18, the conditions (8) and (8a) are satisfied. In the optical scanning device 2 according to this embodiment, f s / DBD =19.31 / 53.38=0.36, so conditional expressions (9) and (9a) are satisfied.

[0143] As described above, in the optical scanning device 2 according to this embodiment, the diffractive surface is provided in the synchronization detecting optical element 70 so as to satisfy the conditional expression (5). This makes it possible to provide an optical scanning device that can suppress a decrease in synchronous detection accuracy due to temperature changes even when the synchronous detection optical system 95 is small and has a short overall length.

[0144] In the optical scanning device 2 according to this embodiment, the sub-scanning aperture 20 and the main-scanning aperture 41 are integrally formed in a housing (not shown) that holds each optical element, but this is not limiting and the apertures may be provided as optical elements separate from the housing. Furthermore, in the optical scanning device 2 according to this embodiment, both the incident surface and the exit surface of the incident optical element 31 may be diffractive surfaces, in other words, at least one of the incident surface and the exit surface of the incident optical element 31 may be a diffractive surface.

[0145] [Third embodiment] FIG. 10(a) shows a schematic main scanning cross section of an optical scanning device 3 according to the third embodiment. 10(b) and 10(c) are schematic cross-sectional views in the sub-scanning direction of an imaging optical system 85 and a synchronization detection optical system 95 provided in the optical scanning device 3 according to the third embodiment, respectively.

[0146] The optical scanning device 3 of this embodiment has the same configuration as the optical scanning device 2 of the second embodiment, except for different specification values, so the same components are given the same reference numbers and their descriptions are omitted. Specifically, in the optical scanning device 3 according to this embodiment, a synchronous detection optical element 70 having a shorter focal length in the main scanning cross section is used compared to the optical scanning device 2 according to the second embodiment, thereby shortening the distance between the synchronous detection optical element 70 and the synchronous detection edge portion 80. This shortens the optical path of the synchronous detection optical system 95. Furthermore, the specifications of the optical scanning device 3 according to this embodiment, the refractive index and coordinates of each optical surface, and the shape of each optical surface are shown in Tables 7, 8, and 9 below, respectively.

[0147] [Table 7]

[0148] [Table 8]

[0149] [Table 9]

[0150] Figure 11 shows the change in the main scanning LSF spot diameter with respect to the change in position in the direction parallel to the optical axis of the synchronization detection optical system 95 in the optical scanning device 3 of this embodiment, which corresponds to Figures 4(b) and 9 described above, i.e., the defocus characteristics of the main scanning LSF spot diameter. 11, 0 mm corresponds to the position of the synchronization detector 90, and −1.45 mm corresponds to the position of the synchronization detection edge portion 80. In FIG.

[0151] Comparing Figures 9 and 11, in the optical scanning device 3 of this embodiment, the focal length of the synchronous detection optical system 95 is even shorter than in the optical scanning device 2 of the second embodiment, and therefore the depth of field is even narrower. As with the optical scanning device 2 according to the second embodiment, the amount of focus fluctuation when the environmental temperature fluctuates is reduced. Therefore, even when the ambient temperature rises from 25°C to 50°C, the main-scanning LSF spot diameter at the position of the synchronization detection edge portion 80 remains almost unchanged, meaning that the increase in the main-scanning LSF spot diameter can be suppressed.

[0152] In addition, in the optical scanning device 3 according to this embodiment, f dm / f rm=20.41 / 28.40=0.72, so the conditions (5), (5a) and (5b) are satisfied. In addition, in the optical scanning device 3 according to this embodiment, D BD Since / h=44.19 / 214.00=0.21, the conditional expressions (6) and (6a) are satisfied. In the optical scanning device 3 according to this embodiment, h / (2×T c )=214.00 / (2×125.00)=0.86, so conditional expressions (7) and (7a) are satisfied. In addition, in the optical scanning device 3 according to this embodiment, f m Since / fθ=12.27 / 109.47=0.11, the conditions (8) and (8a) are satisfied. In addition, in the optical scanning device 3 according to this embodiment, f s / D BD =12.27 / 44.19=0.28, so conditional expressions (9) and (9a) are satisfied.

[0153] As described above, in the optical scanning device 3 according to this embodiment, the diffractive surface is provided in the synchronization detecting optical element 70 so as to satisfy the conditional expression (5). This makes it possible to provide an optical scanning device that can suppress a decrease in synchronous detection accuracy due to temperature changes even when the synchronous detection optical system 95 is small and has a short overall length.

[0154] Moreover, the values ​​corresponding to the respective conditional expressions in the optical scanning devices according to the first to third embodiments are shown in Table 10 below.

[0155] [Table 1]

[0156] [Image forming device] FIG. 12 is a sub-scanning cross-sectional view of a main part of an image forming apparatus 104 including an optical scanning device 4 according to any one of the first to third embodiments.

[0157] As shown in FIG. 12, the image forming apparatus 104 receives code data Dc output from an external device 117 such as a personal computer. The input code data Dc is then converted into image data (dot data) Di by a printer controller 111 provided inside the image forming apparatus 104.

[0158] Next, the converted image data Di is input to the optical scanning device 4 according to any one of the first to third embodiments. The optical scanning device 4 emits a light beam 103 modulated in accordance with the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.

[0159] A photosensitive drum 101, which is an electrostatic latent image carrier (photosensitive member), is rotated clockwise by a motor 115 as shown in FIG. As the photosensitive drum 101 rotates, the photosensitive surface of the photosensitive drum 101 moves relative to the light beam 103 in a sub-scanning direction perpendicular to the main scanning direction.

[0160] A charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided above the photosensitive drum 101 so as to come into contact with the surface. The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with a light beam 103 scanned by the optical scanning device 4.

[0161] As described above, the light beam 103 is modulated based on the image data Di, and an electrostatic latent image is formed on the surface of the photosensitive drum 101 by irradiating the surface with the light beam 103 . The formed electrostatic latent image is developed into a toner image by a developing device 107 disposed so as to contact the photosensitive drum 101 further downstream in the rotation direction from the position on the photosensitive drum 101 where the light beam 103 is irradiated.

[0162] Next, the toner image developed by the developing device 107 is transferred onto a sheet of paper 112, which is a transfer material, by a transfer roller 108 (transfer device) disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 12), but can also be fed manually. A paper feed roller 110 is disposed at the end of the paper cassette 109, and feeds paper 112 in the paper cassette 109 into the transport path.

[0163] The paper 112 onto which the unfixed toner image has been transferred in this manner is transported to the fixing device 150 disposed behind the photosensitive drum 101 (on the left side in FIG. 12). The fixing unit 150 is composed of a fixing roller 113 having a fixing heater therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113 . Then, the paper 112 conveyed from the transfer roller 108 is heated and pressed by the pressure contact portion between the fixing roller 113 and the pressure roller 114, so that the unfixed toner image on the paper 112 is fixed.

[0164] Further, a paper discharge roller 116 is disposed behind the fixing unit 150 , and the paper 112 on which the toner image has been fixed is discharged to the outside of the image forming apparatus 104 . Although not shown in FIG. 12, the printer controller 111 controls the various components in the image forming device 104, such as the motor 115, and the polygon motor in the optical scanning device 4, in addition to the above-mentioned data conversion. Although the preferred embodiments have been described above, the present invention is not limited to these embodiments and various modifications and changes are possible within the scope of the gist thereof.

[0165] The disclosure of this embodiment includes the following configuration. (Configuration 1) An optical scanning device comprising: a deflector that deflects a light beam from a light source to scan a surface to be scanned in a main scanning direction; a first optical system that guides the light beam deflected by the deflector to the surface to be scanned at a first timing; and a second optical system that guides the light beam deflected by the deflector to a light receiving element at a second timing different from the first timing, wherein the second optical system includes a diffractive surface and has a first optical element that focuses the light beam deflected by the deflector at the second timing in a main scanning cross section, and wherein the value of the diffraction power of the first optical element is equal to or greater than the value of the refractive power of the first optical element in the main scanning cross section. (Configuration 2) The total length of the second optical system is D BD , where h is the scanning width on the surface to be scanned, 0.14≦D BD The optical scanning device according to configuration 1, wherein the condition / h≦0.33 is satisfied. (Configuration 3) The total length of the first optical system is T c , where h is the scanning width on the surface to be scanned, 0.70≦h / (2×T c 3. The optical scanning device according to claim 1, wherein the condition of 1.0≦f≦1.10 is satisfied. (Configuration 4) The focal lengths of the second optical system and the first optical system in the main scanning section are respectively f m and fθ, 0.05≦f m 4. The optical scanning device according to any one of configurations 1 to 3, wherein the condition / fθ≦0.50 is satisfied. (Configuration 5) The total length of the second optical system is D BD , the focal length of the second optical system in the sub-scan section is f s When this is the case, 0.20≦f s / D BD 5. The optical scanning device according to any one of configurations 1 to 4, wherein the condition of ≦0.50 is satisfied. (Configuration 6) The optical scanning device according to any one of configurations 1 to 5, wherein the first optical element has a positive power in the sub-scanning cross section. (Configuration 7) The optical scanning device according to any one of configurations 1 to 6, wherein the first optical element has a positive diffraction power in the sub-scanning cross section. (Configuration 8) An optical scanning device according to any one of configurations 1 to 7, characterized in that the second optical system does not include any optical element having a refractive surface or a diffractive surface other than the first optical element. (Configuration 9) An optical scanning device described in any one of configurations 1 to 8, characterized in that one of the entrance surface and exit surface of the first optical element has a shape in which a diffraction grating is formed on a flat surface, and the other has a curved shape in which no diffraction grating is formed. (Configuration 10) An optical scanning device described in any one of configurations 1 to 9, characterized in that the exit surface of the first optical element has a shape in which a diffraction grating is formed on a plane, and the entrance surface of the first optical element has a curved shape in which no diffraction grating is formed. (Configuration 11) The optical scanning device according to any one of configurations 1 to 10, wherein the first optical system does not include an imaging optical element integrated with the first optical element. (Configuration 12) An optical scanning device described in any one of configurations 1 to 11, characterized in that the second optical system includes a light-shielding member that blocks a portion of the light beam guided by the first optical element to each position in the main scanning direction on the light-receiving surface of the light-receiving element. (Configuration 13) An optical scanning device described in Configuration 12, characterized in that in the main scanning cross section, a predetermined corner of the light-shielding member is positioned at a predetermined position on the optical axis of the second optical system and extends in a direction non-parallel to the optical axis of the second optical system. (Configuration 14) An optical scanning device according to configuration 13, characterized in that when the temperature of the optical scanning device is at a predetermined temperature, the light beam deflected by the deflector at the second timing is focused at a predetermined position by the first optical element in the main scanning cross section. (Configuration 15) An optical scanning device according to any one of configurations 1 to 14, characterized in that the optical axis of the second optical system passes through the vertices of the entrance surface and exit surface of the first optical element. (Configuration 16) The optical scanning device according to any one of configurations 1 to 15, further comprising a light receiving element and a control unit that controls the timing of writing on the surface to be scanned based on a signal from the light receiving element. (Configuration 17) An optical scanning device described in any one of configurations 1 to 16, characterized in that it includes a second optical element in which at least one of the entrance surface and exit surface is a diffractive surface, and is equipped with an entrance optical system that guides a light beam from a light source to a deflector. (Configuration 18) An optical scanning device described in any one of configurations 1 to 17, characterized in that the first optical system is configured so that the partial magnification in the main scanning direction is different between the on-axis image height and the outermost off-axis image height. (Configuration 19) An image forming apparatus comprising an optical scanning device according to any one of configurations 1 to 18, a developing unit that develops an electrostatic latent image formed on a surface to be scanned by the optical scanning device into a toner image, a transfer unit that transfers the developed toner image to a transfer material, and a fixing unit that fixes the transferred toner image to the transfer material. (Configuration 20) An image forming apparatus comprising: an optical scanning device according to any one of configurations 1 to 18; and a printer controller that converts a signal output from an external device into image data and inputs the image data to the optical scanning device. [Explanation of symbols]

[0166] 1 Optical scanning device 10 light source 50 Deflector 70 Synchronous detection optical element (first optical element) 85 Imaging optical system (first optical system) 90 Synchronous detection unit (light receiving element) 95 Synchronous detection optical system (second optical system) 100 Scanned surface

Claims

1. a deflector that deflects a light beam from a light source to scan the surface to be scanned in a main scanning direction; a first optical system that guides the light beam deflected by the deflector to the surface to be scanned at a first timing; a second optical system that guides the light beam deflected by the deflector to a light receiving element at a second timing different from the first timing, the second optical system has a first optical element that includes a diffractive surface and that condenses the light beam deflected by the deflector at the second timing in a main scanning cross section; 10. An optical scanning device according to claim 9, wherein a value of the diffractive power of said first optical element is equal to or greater than a value of the refractive power of said first optical element in a main scanning cross section.

2. The total length of the second optical system is D ＢＤ , where h is the scanning width on the surface to be scanned, 0.14≦D ＢＤ / h≦0.33 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

3. The total length of the first optical system is T ｃ , where h is the scanning width on the surface to be scanned, 0.70≦h / (2×T ｃ )≦1.10 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

4. The focal lengths of the second optical system and the first optical system in the main scanning section are respectively defined as f ｍ and fθ, 0.05≦f ｍ / fθ≦0.50 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

5. The total length of the second optical system is D ＢＤ , the focal length of the second optical system in the sub-scanning section is f ｓ When 0.20≦f ｓ / D ＢＤ ≦0.50 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

6. 2. The optical scanning device according to claim 1, wherein the first optical element has a positive power in the sub-scan section.

7. 2. The optical scanning device according to claim 1, wherein the first optical element has a positive diffraction power in the sub-scan section.

8. 2. The optical scanning device according to claim 1, wherein the second optical system is not provided with any optical element having a refractive surface or a diffractive surface other than the first optical element.

9. 2. The optical scanning device according to claim 1, wherein one of the entrance surface and the exit surface of the first optical element has a shape in which a diffraction grating is formed on a flat surface, and the other has a curved shape in which no diffraction grating is formed.

10. the exit surface of the first optical element has a shape in which a diffraction grating is formed on a plane; 2. The optical scanning device according to claim 1, wherein the incident surface of the first optical element has a curved surface shape on which no diffraction grating is formed.

11. 2. The optical scanning device according to claim 1, wherein the first optical system does not include an imaging optical element integrated with the first optical element.

12. 2. The optical scanning device according to claim 1, wherein the second optical system includes a light-blocking member that blocks a portion of the light beam guided by the first optical element to each position in the main scanning direction on the light-receiving surface of the light-receiving element.

13. 13. The optical scanning device according to claim 12, wherein, in the main scanning cross section, the light-shielding member extends in a direction non-parallel to the optical axis of the second optical system, and a predetermined corner of the light-shielding member is positioned at a predetermined position on the optical axis of the second optical system.

14. The optical scanning device according to claim 13, characterized in that, when the temperature of the optical scanning device is at a predetermined temperature, the light beam deflected by the deflector at the second timing is focused at the predetermined position by the first optical element in the main scanning cross section.

15. 2. The optical scanning device according to claim 1, wherein the optical axis of the second optical system passes through the vertices of the entrance surface and the exit surface of the first optical element.

16. The light receiving element; 2. The optical scanning device according to claim 1, further comprising a control unit that controls a timing for starting writing on the surface to be scanned based on a signal from the light receiving element.

17. 2. The optical scanning device according to claim 1, further comprising an incident optical system including a second optical element having at least one of an incident surface and an exit surface that is a diffractive surface, and which guides the light beam from the light source to the deflector.

18. 2. The optical scanning device according to claim 1, wherein the first optical system is configured so that partial magnifications in the main scanning direction differ between an on-axis image height and an extreme off-axis image height.

19. 19. An image forming apparatus comprising: an optical scanning device according to claim 1; a developing unit that develops an electrostatic latent image formed on the scanned surface by the optical scanning device into a toner image; a transfer unit that transfers the developed toner image to a transfer material; and a fixing unit that fixes the transferred toner image to the transfer material.

20. 19. An image forming apparatus comprising: the optical scanning device according to claim 1; and a printer controller that converts a signal output from an external device into image data and inputs the image data to the optical scanning device.

Images