Optical scanning device and image forming apparatus including the same

Abstract

The invention relates to an optical scanning device and an image forming apparatus including the same. The optical scanning device includes: a deflector configured to deflect a luminous flux from a light source to scan a surface using the luminous flux in a main scanning direction; and an optical system configured to guide the luminous flux deflected by the deflector to a surface to be scanned, in which a scanning speed is a variable speed, and in which a predetermined invariance is satisfied.

Description

Technical Field

[0001] The embodiments relate to an optical scanning device and are applicable to image forming apparatuses such as laser beam printers (LBPs), digital copiers, and multifunction printers. Background Technology

[0002] Japanese Patent Application Publication No. 2017-016144 discusses an optical scanning device configured to perform optical scanning of a surface to be scanned in a non-uniform manner using a camera optical system that guides light flux from a deflector to a surface. Summary of the Invention

[0003] According to one aspect of this disclosure, an optical scanning apparatus is provided, the optical scanning apparatus comprising: a deflector configured to deflect luminous flux from a light source to scan a surface using the luminous flux in a main scanning direction; and an optical system configured to guide the luminous flux deflected by the deflector to the surface to be scanned, wherein the scanning speed is variable, and wherein a predetermined inequality is satisfied:

[0004] 0.70≤|Y| / |Ymax|<1.00,

[0005] Wherein, on the surface to be scanned, |Ymax| is the absolute value of the maximum off-axis image height, and |Y| is the intermediate image height at the point where the scanning speed is maximum.

[0006] Other features of this disclosure will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0007] Figure 1 This is a schematic diagram illustrating the main parts of the optical scanning device according to the first example.

[0008] Figure 2 It is a graph indicating the curvature of the camera optics according to this example.

[0009] Figure 3 This is a schematic diagram of the edge thickness shown in the illustration.

[0010] Figure 4 The illustration shows the power ratio relative to on-axis power according to this example.

[0011] Figure 5 The illustration shows the optical scan ratio relative to on-axis optical scan according to this example.

[0012] Figure 6 The curvature of the camera optics according to the second example is illustrated.

[0013] Figure 7 The illustration shows the optical power ratio relative to on-axis optical power according to this example.

[0014] Figure 8 The illustration shows the optical scan ratio relative to on-axis optical scan according to this example.

[0015] Figure 9 The curvature of the camera optics according to the third example is illustrated.

[0016] Figure 10 The illustration shows the optical power ratio relative to on-axis optical power according to this example.

[0017] Figure 11 The illustration shows the optical scan ratio relative to on-axis optical scan according to this example.

[0018] Figure 12 The diagram illustrates an image forming apparatus. Detailed Implementation

[0019] Some exemplary embodiments will be described with reference to the accompanying drawings. In each drawing, for convenience, the scale may differ from the actual scale. Furthermore, in each drawing, the same components are represented by the same reference numerals, and redundant descriptions will be omitted.

[0020] Figure 1 This is a schematic diagram illustrating the main scanning section (XY section) of an optical scanning apparatus 100 according to an exemplary embodiment. The optical scanning apparatus 100 includes a deflector 105 and a camera optical system 106. The deflector 105 deflects the light flux from the light source 102 and scans the surface 101 to be scanned using the light flux in the main scanning direction (Y direction). The camera optical system 106 guides the light flux deflected by the deflector 105 to the surface 101 to be scanned.

[0021] In the following description, it is assumed that the optical axis of the imaging optical system 106 is the X-axis, and the direction of travel of the luminous flux from the imaging optical system 106 along the optical axis is defined as the +X direction. The main scanning direction (Y direction) is the direction perpendicular to the rotation axis of the deflector 105 and the optical axis direction (X direction) of the imaging optical system 106 (the direction for scanning the surface 101 to be scanned), and the scanning start side and scanning end side of the surface 101 to be scanned relative to the optical axis direction (X-axis) are defined as the +Y side and -Y side, respectively. The sub-scanning direction (Z direction) is the direction parallel to the rotation axis of the deflector 105. The main scanning section (XY section) includes the optical axis (X-axis) and is parallel to the main scanning direction (i.e., the section perpendicular to the sub-scanning direction). The sub-scanning section (ZX section) is parallel to the optical axis (X-axis) and the sub-scanning direction (i.e., the section perpendicular to the main scanning direction).

[0022] Furthermore, the image height of the optical axis of the imaging optical system 106 at the scanning surface 101 (the intersection of the scanning surface 101 and the optical axis) is defined as the on-axis image height Y0, and image heights other than the on-axis image height are defined as off-axis image heights. Within the off-axis image heights, the image heights corresponding to the two ends of the effective area (image forming area) on the scanning surface 101 are defined as the maximum off-axis image height +Ymax and -Ymax, respectively. The image height between each of the on-axis image height Y0 and the maximum off-axis image height ±Ymax is defined as the intermediate image height. The on-axis image height Y0 (Y=0) is located at the center of the effective area on the scanning surface 101. The maximum off-axis image height relative to the on-axis image height Y0 on the scanning start side is defined as +Ymax, and the maximum off-axis image height relative to the on-axis image height Y0 on the scanning end side is defined as -Ymax.

[0023] Figure 1 The diagram illustrates the maximum off-axis luminous flux L1 and L3 reaching the maximum off-axis image height + Ymax (scan start position) and the maximum off-axis image height - Ymax (scan end position), respectively, and the on-axis luminous flux L2 reaching the on-axis image height Y0 (center position), with other luminous fluxes omitted. For each of luminous fluxes L1, L2, and L3, the principal ray and the rim ray are illustrated, with other rays omitted.

[0024] A general-purpose optical scanning device using a constant-speed scanning method has the following configuration: when light emitted from a light source at fixed intervals is deflected by a deflector rotating at a constant speed, the light reaches the surface to be scanned at fixed intervals. In other words, the camera optical system in the optical scanning device using the constant-speed scanning method has a distortion aberration (fθ characteristic) such that the rotation angle (scanning angle) of the deflector is proportional to the image height in the main scanning direction on the scanning surface, allowing the light flux passing through the camera optical system 106 to scan the surface to be scanned at a constant speed. In this case, in order to form a good image (spot) in the effective area on the scanning surface, the field curvature of the camera optical system needs to be properly corrected throughout the effective area.

[0025] However, in order to maintain a constant optical scanning speed while properly correcting field curvature, the shape of each optical surface in the imaging optical system needs to vary between the optical axis and the off-axis in the main scanning section. Furthermore, if the imaging optical elements constituting the imaging optical system are positioned near the deflector to reduce the size of the optical scanning device, the shape of each optical surface becomes steep. In this case, the thickness of each imaging optical element increases with coma, making it difficult to sufficiently reduce the size of the overall optical scanning device.

[0026] To address this issue, the imaging optical system 106 according to this exemplary embodiment is configured such that the light flux of the imaging optical system 106 does not travel at a constant speed on the surface 101 to be scanned (i.e., scanning is performed at a non-uniform speed). In other words, the imaging optical system 106 has a local magnification (local magnification in the main scanning direction) such that when scanning at a constant speed, the arrival position of the light on the surface 101 to be scanned is offset from the arrival position. Therefore, the optical scanning apparatus 100 according to this exemplary embodiment employs a variable speed scanning method in which the scanning speed using light flux varies between off-axis image heights, thereby reducing the distance between the imaging optical system 106 and the deflector 105 and the surface 101 to be scanned while maintaining imaging performance. Furthermore, since it is no longer necessary to design the optical power of the imaging optical system 106 for constant speed scanning, the increase in the thickness of the imaging optical elements constituting the imaging optical system 106 can be suppressed. This makes it possible to reduce the size of the optical scanning apparatus 100.

[0027] If a variable speed scanning method is used, the scanning position (scanning distance per unit time) at the off-axis image height will be extended according to the difference between the local magnification at the off-axis image height and the local magnification at the on-axis image height (local magnification difference). If this local magnification difference is not considered when scanning the surface 101 to be scanned, it may lead to image degradation (degraded printing performance) on the surface 101 to be scanned. Therefore, preferably, the control unit (not shown) controls the light emission from the light source 102 to prevent such degradation of printing performance. Specifically, preferably, the control unit controls at least one of the modulation timing (light emission timing) and the modulation time (light emission time) of the light source 102 based on the local magnification difference to electrically correct at least one of the scanning position and scanning time on the surface 101 to be scanned. This makes it possible to correct for the local magnification difference and image degradation, thereby providing good printing performance similar to that when the fθ characteristic is satisfied. In this case, to achieve better printing performance, preferably, the local magnification difference in the imaging optics system 106 is within 2% of all image heights.

[0028] In a constant-speed scanning method, distortion aberrations are intentionally generated by increasing the optical power (refractive power) at the edges of the imaging optics system compared to the central portion, so that light rays near the maximum off-axis image height on the scanning surface arrive at fixed intervals. Conversely, in a variable-speed scanning method, it is not necessary to increase the optical power at the edges of the imaging optics system as in a constant-speed scanning method. Therefore, the edge thickness of the imaging optics components constituting the imaging optics system can be reduced compared to a constant-speed scanning method. However, simply reducing the optical power at the edges of the imaging optics system results in a monotonically increasing scanning speed from the on-axis image height to the maximum off-axis image height, leading to an increase in the luminous flux diameter (spot diameter) near the maximum off-axis image height, potentially causing poor printing performance. Furthermore, attempting to thin the entire imaging optics element while maintaining imaging performance results in an excessively thin edge (edge ​​portion) of the effective area of ​​the imaging optics element, potentially leading to molding defects in the imaging optics element.

[0029] To address this issue, in the optical scanning apparatus 100 according to this exemplary embodiment, the imaging optical system 106 is configured such that the scanning speed is maximized at an intermediate image height between the on-axis image height and the maximum off-axis image height on the surface 101 to be scanned. Specifically, when the absolute value of the maximum off-axis image height on the surface 101 to be scanned is |Ymax| and the intermediate image height with the maximum scanning speed is |Y|, the following inequality (1) is satisfied.

[0030] 0.70 ≤ |Y| / |Ymax| < 1.00 (1)

[0031] If inequality (1) is satisfied and the scanning speed is represented by a graph relative to the image height on the surface 101 to be scanned, the graph has a local maximum at the intermediate image height ±Y. This allows for the thinning of the entire imaging optics constituting the imaging optics system 106 while maintaining sufficient edge thickness of the imaging optics. If the value is less than the lower limit of inequality (1), the optical power from the center portion of the imaging optics to the middle portion of the imaging optics needs to be increased. In this case, to achieve good printing performance throughout the effective area, the edges of the imaging optics need to be significantly thinned, making the manufacturing of the imaging optics difficult. If the value exceeds the upper limit of inequality (1), the scanning speed monotonically increases from the on-axis image height Y0 to the maximum off-axis image height Ymax, resulting in an increase in the spot diameter near the maximum off-axis image height. This makes it difficult to provide good printing performance.

[0032] Furthermore, the following inequality (1a) and the following inequality (1b) are satisfied.

[0033] 0.72≤|Y| / |Ymax|≤0.98(1a)

[0034] 0.75≤|Y| / |Ymax|≤0.95(1b)

[0035] The camera optics system 106 is preferably configured such that the scanning speed of the surface 101 to be scanned using luminous flux at the maximum off-axis image height ±Ymax is higher than the scanning speed of the surface 101 to be scanned using luminous flux at the on-axis image height Y0. If the scanning speed at the maximum off-axis image height ±Ymax is configured to be slower than the scanning speed at the on-axis image height Y0 while satisfying inequality (1), then the scanning speed at the maximum off-axis image height ±Ymax needs to be significantly reduced, or the scanning speed at the on-axis image height Y0 needs to be increased to almost the maximum scanning speed. This results in the scanning speed varying too much near the maximum off-axis image height ±Ymax, or the scanning speed varying too little over the entire area of ​​the surface 101 to be scanned, thus leading to poor printing performance.

[0036] Furthermore, the imaging optical system 106 is preferably configured such that the scanning speed of scanning the surface 101 to be scanned using light flux varies monotonically between the intermediate image height ±Y and the on-axis image height Y0 and the maximum off-axis image height ±Ymax. Here, "between the intermediate image height ±Y and the on-axis image height Y0 and the maximum off-axis image height ±Ymax" refers to the interval between the intermediate image height ±Y and the on-axis image height Y0, between the intermediate image height +Y and the maximum off-axis image height +Ymax on the scan start side, and between the intermediate image height -Y and the maximum off-axis image height -Ymax on the scan end side. Therefore, when the scanning speed is represented by a graph relative to the image height on the surface 101 to be scanned, preferably, the graph has a local minimum only at the on-axis image height Y0, and a local maximum only at the intermediate image height +Y on the scan start side and the intermediate image height -Y on the scan end side.

[0037] This configuration prevents excessive variations in scanning speed between different image heights, thus maintaining good printing performance. In this case, the camera optics system 106 is configured such that the scanning speed of scanning the surface 101 using light flux monotonically increases from the on-axis image height Y0 to the intermediate image height ±Y, and monotonically decreases from the intermediate image height ±Y to the maximum off-axis image height ±Ymax. This configuration prevents poor printing performance due to reasons similar to those described above.

[0038] When the maximum value (local maximum value) of the scanning speed of scanning the surface 101 to be scanned using light flux is Vmax and the scanning speed of scanning using light flux at the maximum off-axis image height ± Ymax is Ve, preferably, the optical scanning device 100 according to this exemplary embodiment satisfies the following inequality (2).

[0039] 0.85 ≤ Ve / Vmax < 1.00 (2)

[0040] If the value is less than the lower limit of inequality (2), the optical power at the edge of the imaging optics needs to be significantly increased. Therefore, the thickness at the edge of the effective area of ​​the imaging optics (edge ​​thickness) becomes too thin, and molding defects may occur during manufacturing. If the value exceeds the upper limit of inequality (2), the scanning speed of the surface 101 scanned using luminous flux monotonically increases from the on-axis image height Y0 to the maximum off-axis image height ±Ymax. This may lead to an increase in the spot diameter near the maximum off-axis image height, making it difficult to provide good printing performance.

[0041] Furthermore, the following inequality (2a) is preferably satisfied, and the following inequality (2b) is more preferably satisfied.

[0042] 0.88≤Ve / Vmax≤0.98(2a)

[0043] 0.90≤Ve / Vmax≤0.96(2b)

[0044] When the minimum (local minimum) value of the scanning speed of scanning the surface 101 to be scanned using light flux is Vmin, preferably, the optical scanning device 100 according to this exemplary embodiment satisfies the following inequality (3).

[0045] 1.10 ≤ Vmax / Vmin < 1.40 (3)

[0046] If the value is less than the lower limit of inequality (3), the difference between the minimum and maximum scanning speeds will become too small, approaching the constant speed scanning method. This may make it difficult to reduce the thickness of the imaging optics. If the value exceeds the upper limit of inequality (3), the maximum scanning speed will become too large, which may make it difficult to prevent the spot diameter near the maximum off-axis image height from increasing.

[0047] Furthermore, the following inequality (3a) is preferably satisfied, and the following inequality (3b) is more preferably satisfied.

[0048] 1.15≤Vmax / Vmin<1.35(3a)

[0049] 1.20≤Vmax / Vmin<1.30(3b)

[0050] When the thickness of the imaging optical element on the optical axis is Do and the thickness of the imaging optical element at the position where the maximum off-axis light passes through (edge ​​thickness) is Dc, the optical scanning device 100 according to this exemplary embodiment preferably satisfies the following inequality (4).

[0051] 0.46 ≤ Dc / Do ≤ 0.60 (4)

[0052] If the value is less than the lower limit of inequality (4), the edge thickness of the camera optics will become too thin. This may lead to molding defects in the camera optics. If the value exceeds the upper limit of inequality (4), it may be difficult to thin the entire camera optics.

[0053] Furthermore, the following inequality (4a) is preferably satisfied, and the following inequality (4b) is preferably satisfied.

[0054] 0.47≤Dc / Do≤0.58(4a)

[0055] 0.48≤Dc / Do≤0.55(4b)

[0056] Now, some examples based on the exemplary embodiments described above will be described in detail.

[0057] A first example will be described. An optical scanning device 100 according to this example is described. Since the configuration of the optical scanning device 100 according to this example is equivalent to the configuration of the optical scanning device 100 according to the exemplary embodiments described above, redundant descriptions will be omitted.

[0058] like Figure 1 As shown, the optical scanning device 100 according to this example includes a light source 102, an aperture 103 for adjusting the luminous flux from the light source 102, an incident optical system 104 for guiding the luminous flux from the light source 102 to a deflector 105, the deflector 105, and the imaging optical system 106. In the optical scanning device 100, the luminous flux emitted from the light source 102 passes through the aperture 103 and is guided by the incident optical system 104 to the deflection surface of the deflector 105. The light source 102, aperture 103, and incident optical system 104 are not necessarily included in the optical scanning device 100; for example, they may be configured as an external illumination device.

[0059] The light source 102 includes a substrate and a light-emitting element (light-emitting point) disposed on the substrate. For example, the light source 102 may be a semiconductor laser and may have one or more light-emitting points. The light source 102 according to this example is an edge-emitting laser and has a configuration with a single light-emitting point disposed on the substrate. If the light source 102 is provided with multiple light-emitting points, a vertical-cavity surface-emitting laser (VCSEL) is preferably used. Alternatively, a light-emitting diode (LED) can be used as the light source 102. In this example, it is assumed that the light source 102 emits a luminous flux with a wavelength of 780 nm, but a light source emitting a luminous flux with other wavelengths can also be used.

[0060] Aperture 103 blocks a portion of the luminous flux from light source 102 to shape and regulate the amount of light reaching deflector 105. In the luminous flux passing through the aperture in the aperture, the light rays passing through the center of the aperture are the main rays, and the light rays passing through the periphery of the aperture are the peripheral rays. In this example, a rectangular aperture with a rectangular hole is used as aperture 103, but the shape of the hole is not limited to this. For example, an elliptical aperture with an elliptical hole or a circular aperture with a circular hole can be used as aperture 103.

[0061] The incident optical system 104 according to this example includes a deformable lens as an optical element (incident optical element) that converts the convergence of the luminous flux from the light source 102. The deformable lens is a lens with different optical powers (refractive strength) in the main scanning section and the sub-scanning section. The deformable lens according to this example converts the diverging luminous flux from the light source 102 into a substantially parallel or substantially convergent luminous flux in the main scanning section, and focuses the luminous flux onto the deflection surface of the deflector 105 in the sub-scanning section.

[0062] It is desirable that the morphing lens in the incident optical system 104 is positioned closer to the deflector 105 (-Y side) than the front principal surface of the morphing lens. This arrangement ensures that the light flux emitted from the morphing lens is substantially convergent in the main scanning section, thus facilitating the thinning of the imaging optical elements constituting the imaging optical system 106. Although the incident optical system 104 according to this example consists of a single optical element (morphing lens), it may also include multiple optical elements. For example, the incident optical system 104 may consist of two optical elements, a collimating lens and a cylindrical lens, to share the conversion of convergence in the main scanning section and the focusing of light in the sub-scanning section.

[0063] The deflector 105 is driven by a drive unit (e.g., a motor) not shown along... Figure 1The direction of arrow A in the diagram rotates at a constant speed, and the light flux from the incident optical system 104 is deflected by multiple deflecting surfaces (reflective surfaces). Using the light flux from the deflector 105, the effective area of ​​the surface to be scanned 101 is scanned from the scan start side (+Y side) to the scan end side (-Y side), following the sequence of the incident surface 106a (optical surface on the deflector 105 side) of the imaging optical element and the exit surface 106b (optical surface on the scanned surface 101 side) of the imaging optical element. When the optical scanning device 100 is applied to the image forming apparatus described below, the effective area of ​​the scanned surface 101 is the image forming area (the area to be printed). In this example, a rotating faceted mirror (prism) with four deflecting surfaces is used as the deflector 105, but the number of deflecting surfaces is not limited to four. A pivoting mirror with one or two deflecting surfaces configured to pivot can be used instead of the rotating faceted mirror. For example, a microelectromechanical system (MEMS) mirror can be used as the pivoting mirror.

[0064] According to the imaging optical system 106 of this example, the luminous flux deflected by the deflector 105 in the main scanning section and the sub-scanning section is focused onto the surface 101 to be scanned, so as to form an image of the light-emitting point from the light source 102 on or near the surface 101 to be scanned. In this case, the imaging optical system 106 is configured such that the deflecting surface or the vicinity of the deflecting surface and the surface 101 to be scanned or the vicinity of the surface 101 to be scanned have a conjugate relationship in the sub-scanning section. This allows for the suppression of positional shift on the surface 101 to be scanned during scanning (deflecting surface tilt correction) when the deflecting surface is tilted due to misplacement or other reasons.

[0065] Although the imaging optical system 106 according to this example consists of a single imaging optical element, it may include multiple imaging optical elements. However, in order to reduce the overall size of the optical scanning device 100, as shown in this example, it is desirable for the imaging optical system 106 to consist of a single imaging optical element. The imaging optical element according to this example is a deformable lens (annular lens) with different optical powers in the main scanning section and the sub-scanning section.

[0066] Since the deformable lenses constituting the incident optical system 104 and the imaging optical system 106 according to this example are plastic molded lenses formed by injecting resin material, the cost can be significantly reduced compared to using glass lenses. Furthermore, using plastic molded lenses makes it easier to form diffractive or aspherical surfaces, thereby improving productivity and optical performance. However, glass lenses can be used as lenses constituting the incident optical system 104 and the imaging optical system 106 as needed. Each deformable lens according to this example is a K22R manufactured by Zeon Corporation. It is composed of resin materials, but the resin materials are not limited to this.

[0067] The shapes (generatrix shapes) of the incident surface 106a and the exit surface 106b of the imaging optical element in this example within the main scanning section including the surface vertices are expressed by the following expression (aspherical equation). Here, the intersection of each optical surface (lens surface) vertex with each optical axis is set as the origin to form a local coordinate system (with...). Figure 1 (The global coordinate system shown is different), where the axis in the optical axis direction is the X-axis, the axis orthogonal to the X-axis in the main scanning section is the Y-axis, and the axis orthogonal to both the X-axis and Y-axis is the Z-axis. Furthermore, the generatrix shapes on the scan start side (+Y side) and scan end side (-Y side) relative to the optical axis (X-axis) are represented by different aspherical equations.

[0068] [Expression 1]

[0069]

[0070] [Expression 2]

[0071]

[0072] In the expression, R is the radius of curvature (generatrix radius of curvature, sub-generatrix radius of curvature) on the optical axis in the main scanning section, and K, B3, B4, B6, B8, B 10 and B 12 These are the aspherical coefficients in the main scanning section, respectively.

[0073] The suffix 's' added to the aspheric coefficient B indicates the scan start side (+Y side), and the suffix 'e' indicates the scan end side (-Y side). This is achieved by adjusting the aspheric coefficient B4 between the scan start side (+Y side) and the scan end side (-Y side) to B. 12 Different values ​​can cause the shape of the generatrix to be asymmetrical relative to the optical axis in the main scanning direction.

[0074] Furthermore, on each optical surface of the imaging optical system 106 according to this example, the radius of curvature r' (sub-line radius of curvature) in the sub-scanning section at each position (each image height) in the main scanning direction is represented by the following expression (continuous function). The following expression is based on the assumption of the local coordinate system described above and is expressed as an aspherical expression in which the sub-line radius of curvature on the scan start side (+Y side) and the sub-line radius of curvature on the scan end side (-Y side) are different from each other with respect to the optical axis (X-axis).

[0075] [Expression 3]

[0076]

[0077] [Expression 4]

[0078]

[0079] In the above expression, r is the radius of curvature on the optical axis in the sub-scanning section, and E i This is the sub-line variation coefficient. Added to the sub-line variation coefficient E. i The suffix 's' indicates the scan start side (+Y side), and the suffix 'e' indicates the scan end side (-Y side). In other words, the sub-line curvature radius (sub-line shape) of each optical surface is the surface shape in a section perpendicular to the main scanning section, which includes the surface normal on the generatrix at each position in the main scanning direction.

[0080] Table 1 shows the specification values ​​of the optical scanning apparatus 100 according to this example. Each distance shown in Table 1 indicates a value on the optical axis of the incident optical system 104 or the imaging optical system 106. Although the distance between the deflector 105 and each component varies depending on the rotation angle of the deflector 105, Table 1 shows the distance to the intersection point (on-axis deflection point) between the principal ray of the on-axis luminous flux L2 and the deflection surface when the on-axis luminous flux L2 reaching the surface 101 to be scanned at the on-axis image height Y0 is deflected. "Angle of the incident principal ray" indicates the angle formed between the principal ray of the luminous flux emitted from the incident optical system 104 and incident on the deflection surface and the optical axis of the imaging optical system 106. "Coordinates of the rotation center of the deflector" indicates the coordinates (position) of the rotation center (rotation axis) of the deflector 105 with the on-axis deflection point as the origin. In this example, the maximum scanning angle and the maximum off-axis image height (effective scan width) are symmetrical with respect to the optical axis of the imaging optical system 106. Table 1 shows that the values ​​on one side of the optical axis are positive, while the values ​​on the other side of the optical axis are negative.

[0081] [Table 1]

[0082]

[0083]

[0084] Table 2 indicates the shape of each optical surface of the camera optics according to this example. The suffix 's' added to both "incident surface" and "exit surface" indicates the scan start side (+Y side), and the suffix 'e' added to both "incident surface" and "exit surface" indicates the scan end side (-Y side). Additionally, ".E±N" indicates "×10 ±N As shown in Table 2, the shapes of the incident and exit surfaces of the camera optical element according to this example are different from each other on the main scanning section between the scanning start side and the scanning end side; in other words, they are asymmetrical with respect to the optical axis.

[0085] [Table 2]

[0086]

[0087] Figure 2 This is a graph indicating the curvature of each optical surface of the camera optics according to this example in the main scanning section, based on various positions along the main scanning direction. Figure 2 In the graph, the vertical axis represents the local curvature of the imaging optical element in the main scanning section, and the horizontal axis represents its position in the main scanning direction (Y direction) with the optical axis (X-axis) as the reference. Solid lines represent the curvature on the incident surface, while dashed lines represent the curvature on the exiting surface. Figure 2 In the diagram, a positive curvature is indicated by taking the vertex of the optical surface as a reference, with the center of curvature of the optical surface located on the +X side (the side of the surface to be scanned, 101). Conversely, a negative curvature is indicated by taking the vertex of the optical surface as a reference, with the center of curvature of the optical surface located on the -X side (the side of the deflector, 105). The curvature at each position along the main scanning direction of each optical surface can be calculated based on the radius of curvature at local locations on the optical surface, and therefore the aforementioned aspherical equations can be used for calculation.

[0088] like Figure 2 As shown, on the optical axis of the imaging optics according to this example, both the incident surface and the exit surface have negative curvature, indicating that their respective centers of curvature are located on the deflector 105 side. Therefore, on the optical axis, the incident surface has a concave shape, the exit surface has a convex shape, and the imaging optics has a meniscus shape. This helps to thin the central portion of the imaging optics.

[0089] The curvature of the exit surface of the imaging optics changes almost zero (0) from its position on the optical axis to a midpoint approximately ±10 mm away (i.e., the absolute value decreases). In this way, by maintaining sufficient curvature near the optical axis of the exit surface and reducing the absolute value of the curvature to the midpoint image height, the central portion of the imaging optics can be thinned while maintaining sufficient edge thickness. This facilitates a reduction in the overall size of the optical scanning device 100 and in the manufacture of the imaging optics.

[0090] Figure 3 yes Figure 1 A partially enlarged view of the camera optical system 106 (camera optical element) and the maximum off-axis luminous flux L1. Figure 3 In the diagram, x1 indicates the intersection point between the edge ray (maximum off-axis ray) L1a on the +Y side of the maximum off-axis luminous flux L1 and the incident surface of the imaging optics, and x2 indicates the intersection point between the edge ray L1a on the +Y side and the exit surface of the imaging optics. The distance Dc between intersection points x1 and x2 in the X direction corresponds to the maximum off-axis thickness (edge ​​thickness) of the imaging optics. Figure 3It can be seen that the edge thickness Dc of the camera optics is about half the thickness on the optical axis, which means that sufficient edge thickness can be maintained in this example.

[0091] Figure 4 This is a graph showing the optical power (refractive power) of the camera optics in this example at various positions along the main scanning direction. Figure 4 To illustrate the change in optical power of the imaging optics along the main scanning direction, the relationship between the off-axis optical power (normalized optical power) and the image height on the scanned surface 101 is shown, where the on-axis optical power is set to 1. Therefore, the normalized optical power here represents the ratio of off-axis optical power to on-axis optical power (refractive power) (optical power ratio). Figure 4 In the diagram, the vertical axis represents the local normalized optical power of the camera optical element in the main scanning section, while the horizontal axis represents the image height relative to the optical axis (X-axis).

[0092] exist Figure 4 In the graph, the solid line, dashed line, and double-dotted line correspond to this example, Comparative Example 1, and Comparative Example 2, respectively. Comparative Example 1 and Comparative Example 2 are based on the assumption that only the imaging optical element is changed in the optical scanning device 100 according to this example. Specifically, Comparative Example 1 is based on the assumption that the imaging optical element of the optical scanning device 100 employs a constant speed scanning method, while Comparative Example 2 is based on the assumption that the scanning speed of the optical scanning device 100 monotonically increases from the on-axis image height to the maximum off-axis image height.

[0093] like Figure 4 As shown, the normalized optical power of the imaging optics according to Comparative Example 1 increases significantly from near the intermediate image height (half of the maximum off-axis image height) to the maximum off-axis image height. In contrast, in Comparative Example 2 using the variable scan speed method, the increase in normalized optical power from near the intermediate image height to the maximum off-axis image height is suppressed compared to Comparative Example 1. In this example, compared to Comparative Example 2, the normalized optical power decreases significantly near the maximum off-axis image height because the image height at the point where the normalized optical power begins to increase changes significantly toward the corresponding maximum off-axis image height. Compared to Comparative Examples 1 and 2, this configuration allows for maintaining sufficient edge thickness while thinning the central portion of the imaging optics.

[0094] Figure 5 This is a graph indicating the scanning speed at which light flux is used to scan each image height on the surface 101 to be scanned. Figure 5In the diagram, the vertical axis represents the scanning speed at the off-axis image height (normalized scanning speed) when the scanning speed at the on-axis image height is set to 1, while the horizontal axis represents the image height relative to the optical axis (X-axis). Therefore, the normalized scanning speed indicates the ratio of the scanning speed at the off-axis image height to the scanning speed at the on-axis image height (scanning speed ratio). In other words, the scanning speed ratio corresponds to the ratio of the off-axis local magnification to the on-axis local magnification of the imaging optical system 106 (local magnification ratio).

[0095] like Figure 5 As shown, the normalized scan speed in this example becomes a minimum (and a local minimum) at the on-axis image height Y0 (image height of 0 mm), and a maximum (local maximum) at the intermediate image height Y (image height of 101 mm). In other words, in this example, the normalized scan speed at the maximum off-axis image height Ymax is neither a minimum nor a maximum. In this way, the configuration in which the scan speed reaches its maximum at an image height lower than the maximum off-axis image height can suppress the increase in the spot diameter near the maximum off-axis image height. Therefore, better printing performance can be achieved compared to a configuration in which the scan speed monotonically increases from the on-axis image height to the maximum off-axis image height.

[0096] The second example will now be described. An optical scanning apparatus 100 according to this example will be described. The optical scanning apparatus 100 according to this example differs from the optical scanning apparatus 100 according to the first embodiment in the shape and arrangement of the imaging optical elements. Other than these, the configuration is the same as that in the first example, and therefore its description will be omitted.

[0097] Table 3 shows the shape of each optical surface of the camera optics according to this example.

[0098] [Table 3]

[0099]

[0100] and Figure 2 similar, Figure 6 The illustration shows the curvature variation of each optical surface of the camera optics element according to this example in the main scanning section. Additionally, with... Figure 4 similar, Figure 7 The illustration shows the variation in normalized optical power of the camera optics according to this example. Furthermore, with... Figure 5 similar, Figure 8The illustration shows the variation of the normalized scanning speed on the surface 101 to be scanned. Similar to the first example, the incident surface of the imaging optics according to this example has a concave shape, the exit surface has a convex shape, and the imaging optics have a meniscus shape. The curvature of the exit surface of the imaging optics varies almost zero (0) from its position on the optical axis to a midpoint approximately ±10 mm away. Furthermore, the image height where the normalized optical power of the imaging optics begins to increase is positioned sufficiently close to the corresponding maximum off-axis image height.

[0101] like Figure 8 As shown in the example, in this example, compared to the first example, the scan rate becomes such that the position of the intermediate image height at the maximum value Vmax is closer to the position of the on-axis image height Y0. Therefore, the scan rate Ve at the maximum off-axis image height is lower than the scan rate Ve at the maximum off-axis image height in the first example. Conversely, as... Figure 7 As shown, the camera optics according to this example are configured such that the normalized optical power at the maximum off-axis image height is greater than the normalized optical power at the maximum off-axis image height in the first example. This allows for the maintenance of sufficient edge thickness while thinning the central portion of the camera optics.

[0102] The third example will now be described. An optical scanning device 100 according to this example will be described. The optical scanning device 100 according to this example differs from the optical scanning devices 100 according to the first and second examples in the shape and arrangement of the imaging optical elements. Other than these, the configuration is the same as in the first example, and therefore its description will be omitted.

[0103] Table 4 indicates the shape of each optical surface of the camera optics according to this example. Figure 2 similar, Figure 9 The illustration shows the curvature variation of each optical surface of the camera optics element according to this example in the main scanning section.

[0104] [Table 4]

[0105]

[0106] and Figure 2 similar, Figure 9 The illustration shows the curvature variation of each optical surface of the camera optics element according to this example in the main scanning section. Additionally, with... Figure 4 similar, Figure 10 The illustration shows the variation in normalized optical power of the camera optics according to this example. Furthermore, with... Figure 5 similar, Figure 11The illustration shows the variation of the normalized scanning speed on the surface 101 to be scanned. Similar to the first and second examples, the incident surface of the imaging optics according to this example has a concave shape, the exit surface has a convex shape, and the imaging optics have a meniscus shape. The curvature of the exit surface of the imaging optics varies nearly zero (0) from its position on the optical axis to a midpoint approximately ±10 mm away. Furthermore, the image height where the normalized optical power of the imaging optics begins to increase is positioned sufficiently close to the corresponding maximum off-axis image height.

[0107] like Figure 11 As shown in the example, in this example, compared to the second example, the scan rate becomes such that the position of the intermediate image height at the maximum value Vmax is closer to the position of the on-axis image height Y0. Therefore, the scan rate Ve at the maximum off-axis image height is lower than the scan rate Ve at the maximum off-axis image height in the second example. Conversely, as... Figure 10 As shown, the camera optics according to this example are configured such that the normalized optical power at the maximum off-axis image height is greater than the normalized optical power at the maximum off-axis image height in the second example. This allows for the maintenance of sufficient edge thickness while thinning the central portion of the camera optics.

[0108] Table 5 indicates the intermediate values ​​in inequalities (1) to (3) in the above examples.

[0109] [Table 5]

[0110] Example 1 Example 2 Example 3 Y (mm) 101.30 86.90 83.50 Ymax (mm) 107.00 107.00 107.00 Ve 1.280 1.230 1.200 Vmax 1.283 1.296 1.297 Vmin 1.000 1.000 1.000 Dc (mm) 2.70 2.75 2.70 Do (mm) 5.40 5.40 5.40 Inequality (1) Y / Ymax 0.947 0.812 0.780 Inequality (2) Ve / Vmax 0.998 0.949 0.925 Inequality (3) Vmax / Vmin 1.283 1.296 1.297 Inequality (4) Dc / Do 0.50 0.51 0.50

[0111] [Image forming apparatus]

[0112] Figure 12 This is a schematic diagram (ZX cross-sectional view) of the main parts of the image forming apparatus 600 according to this exemplary embodiment. The image forming apparatus 600 is a serial full-color image forming apparatus that uses optical scanning units 500 to record image information on the photosensitive surfaces (scanning surfaces) of four photosensitive drums (photosensitive components) that are parallel to each other.

[0113] The image forming apparatus 600 includes a printer controller (control unit) 530, an optical scanning unit 500, photosensitive drums 210, 220, 230, and 240 as image-carrying components, developing units 310, 320, 330, and 340, a conveyor belt 510, and a fixing unit 540. The optical scanning unit 500 may be configured to include four optical scanning devices according to any of the first to third examples described above. In this case, the optical scanning unit 500 is configured such that the sub-scanning direction matches the Z-direction, which is the rotational direction of each of the photosensitive drums 210, 220, 230, and 240.

[0114] like Figure 12As shown, red (R), green (G), and blue (B) color signals are output from an external device 520, such as a personal computer. These color signals are converted by a printer controller 530 into corresponding image signals (image data or dot data) of yellow (Y), magenta (M), cyan (C), and black (K), and are then input to the optical scanning unit 500. The printer controller 530's performance of the aforementioned signal conversions and its control of each unit (such as a motor) of the image forming apparatus 600 will be described below.

[0115] The optical scanning unit 500 scans the photosensitive surfaces of photosensitive drums 210, 220, 230, and 240 in the main scanning direction (Y direction) using light fluxes 410, 420, 430, and 440, respectively, with all light fluxes modulated according to corresponding image data. The photosensitive drums 210, 220, 230, and 240 are rotated clockwise by a motor (not shown), and these rotations cause the photosensitive surfaces to move relative to the light fluxes 410, 420, 430, and 440 in the sub-scanning direction (Z direction). The photosensitive surfaces, charged by a charging roller (not shown), are exposed to the corresponding light fluxes 410, 420, 430, and 440, thus forming electrostatic latent images on the respective photosensitive surfaces.

[0116] Subsequently, the electrostatic latent images formed on the photosensitive surfaces of the photosensitive drums 210, 220, 230, and 240 corresponding to the respective colors are developed into toner images of the corresponding colors by the developing units 310, 320, 330, and 340. The toner images of the corresponding colors are then transferred multiple times onto the transfer material to be conveyed by the conveyor belt 510, and finally fixed by the fixing unit 540. As a result of the above process, a full-color image is formed.

[0117] The optical scanning unit 500 can be configured, for example, with two optical scanning devices simultaneously scanning two surfaces using a single deflector, or with one optical scanning device simultaneously scanning four surfaces using a single deflector. Alternatively, the full-color digital copier can be configured with a full-color image reader as an external device 520 connected to the image forming apparatus 600, the external device 520 including a line sensor such as a charge-coupled device (CCD) sensor or a complementary metal-oxide-semiconductor (CMOS) sensor. Alternatively, the monochrome image forming apparatus can be configured using an optical scanning unit 500 consisting of a single optical scanning device.

[0118] Although exemplary embodiments and examples have been described, this disclosure is not limited to these exemplary embodiments and examples, and various combinations, variations and modifications can be made within the scope of this disclosure.

[0119] For example, the optical scanning apparatus 100 according to this exemplary embodiment may include a synchronization detection unit for determining a scanning start position (the position where an image is written) on the surface 101 to be scanned. A light receiving unit (sensor) that receives the luminous flux deflected by the deflector 105 may be used as the synchronization detection unit. The control unit controls the emission timing of the light source 102 based on the output (signal) from the light receiving unit to determine the scanning start position on the surface 101 to be scanned. When a synchronization detection unit is used, the light receiving element in the light receiving unit may be disposed on the substrate on which the light-emitting element of the light source 102 is provided.

[0120] Although this disclosure has been described with reference to exemplary embodiments, it should be understood that this disclosure is not limited to the disclosed exemplary embodiments. The appended claims should be interpreted in the broadest possible sense to cover all such variations and equivalent structures and functions.

Claims

1. An optical scanning device comprising: a deflector configured to deflect a light flux from a light source to scan a surface using the light flux in a main scanning direction; and an optical system configured to guide the light flux deflected by the deflector to a surface to be scanned, wherein a scanning speed at which the surface to be scanned is scanned using the light flux is a variable speed, and wherein the following inequality is satisfied: 0.70≤|Y| / |Ymax|<1.00, wherein |Ymax| is an absolute value of a maximum marginal image height on the surface to be scanned, and |Y| is an intermediate image height at which the scanning speed is maximum. The scanning speed at the maximum marginal image height is higher than the scanning speed at an on-axis image height.

2. The optical scanning device according to claim 1, wherein, The scanning speed monotonously varies between the intermediate image height and the on-axis image height and between the intermediate image height and the maximum marginal image height.

3. The optical scanning device according to claim 1, wherein The scanning speed monotonously increases from the on-axis image height to the intermediate image height and monotonously decreases from the intermediate image height to the maximum marginal image height.

4. An optical scanning device according to claim 3, wherein An optical element included in the optical system is a single optical element.

5. The optical scanning device according to claim 1, wherein, An entrance surface of the optical element has a concave shape and an exit surface of the optical element has a convex shape on an optical axis.

6. An optical scanning device according to claim 5, wherein 7.The optical scanning device according to claim 1, further comprising an optical element configured to convert a degree of convergence of the light flux from the light source, a refractive power of the optical element is different from each other between a main scanning cross section and a sub-scanning cross section. wherein The optical element is disposed closer to the deflector than a front main surface of the optical element.

8. An optical scanning device according to claim 7, wherein The optical system includes an optical element including an optical surface that changes a curvature on a main scanning cross section in a main scanning direction.

9. The optical scanning device according to any one of claims 1 to 8, wherein, An absolute value of the curvature of the optical surface in the main scanning cross section approaches zero as a distance from an optical axis in the main scanning direction increases.

10. An optical scanning device according to claim 9, wherein, The following inequality is satisfied:

11. The optical scanning device according to any one of claims 1 to 8, wherein, 0.85≤Ve / Vmax<1.00, wherein Vmax is a maximum value of the scanning speed, and Ve is the scanning speed at the maximum marginal image height. The following inequality is satisfied:

12. The optical scanning device according to any one of claims 1 to 8, wherein, 1.10≤Vmax / Vmin<1.40, wherein Vmin is a minimum value of the scanning speed, and Vmax is a maximum value of the scanning speed. The following inequality is satisfied:

13. The optical scanning device according to any one of claims 1 to 8, wherein, 0.46≤Dc / Do≤0.60, wherein Do is a thickness of an optical element included in the optical system on an optical axis, and Dc is a thickness of the optical element at a position where a maximum marginal ray passes through. 14.An optical scanning device comprising: a deflector configured to deflect a light flux from a light source to scan in a main scanning direction; and an optical system configured to guide the light flux deflected by the deflector to a surface to be scanned, wherein a scanning speed at which the surface to be scanned is scanned using the light flux is a variable speed. 15.An image forming apparatus comprising: ​ ​ The optical scanning device according to any one of claims 1 to 8 and 14; and a developing device configured to develop an electrostatic latent image formed on a surface to be scanned using the optical scanning device into a toner image.

16. An image forming apparatus comprising: The optical scanning device according to any one of claims 1 to 8 and 14; and a controller configured to convert data output from an external device into an image signal, and input the image signal into the optical scanning device.

Images