Optical scanner and image forming apparatus

Abstract

To provide an optical scanner that can specify deflection surfaces of a deflector with a simple configuration and perform image correction according to the specified deflection surface.SOLUTION: An optical scanner comprises: a light source; a deflector having a plurality of deflection surfaces that deflect a light beam from the light source and scan a surface to be scanned in a main scanning direction; a driving unit that drives to rotate the deflector; an image forming optical system that guides the light beam deflected by the deflector to the surface to be scanned; a detector that detects the light beam deflected by the deflector; and a control unit that specifies the deflection surfaces on the basis of the detection performed by the detector, and controls emission of the light beam from the light source for every deflection surface. The plurality of deflection surfaces include two or more deflection surfaces different in the distance from the center of rotation. The deflector has, in an area including the center of rotation, a shaft fitting part to which a rotation shaft of the driving unit is fitted, and the shape of the shaft fitting part on a section perpendicular to the rotation shaft has two or more straight line parts in contact with the rotation shaft.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an optical scanning device, and more particularly to an image forming apparatus such as a laser beam printer or a copying machine.

Background Art

[0002] Conventionally, an optical scanning device has been proposed in which the optical path is shortened by using a converging light beam to achieve miniaturization. In such an optical scanning device, when a converging light beam is incident on a deflector such as a polygon mirror that includes a deviation from the position of an ideal deflection plane due to manufacturing errors or the like, and the scanned surface is optically scanned, there is a risk of jitter occurring on the scanned surface.

[0003] When image formation is performed in a state with jitter, periodic density unevenness occurs in the main scanning direction of the image, causing image degradation.

[0004] Patent Document 1 discloses an optical scanning device in which a reference position mark is formed on the upper surface of a polygon mirror as a deflecting means, and the deflection plane is specified by detecting the reference position mark. Patent Document 2 discloses an optical scanning device that uses a polygon mirror in which the divided angles are intentionally different from each other and the shape of a cross section perpendicular to the rotation axis is a non-regular polygon, and detects the scanning deflection plane by utilizing the difference in the period of a synchronization signal generated for each deflection plane.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the optical scanning device of Patent Document 1, a step of setting the surface accuracy of the upper surface of the polygon mirror as the deflection means to a predetermined level and forming a reference position mark on the upper surface is required, resulting in an increase in cost. Further, in the optical scanning device of Patent Document 2, a step of manufacturing a polygon mirror having a special shape is required, resulting in an increase in cost.

[0007] An object of the present invention is to provide an optical scanning device capable of specifying a deflection plane of a deflector with a simple configuration and performing image correction according to the specified deflection plane.

Means for Solving the Problems

[0008] The optical scanning device of the present invention includes a light source, a deflector having a plurality of deflection planes that deflect a light beam from the light source and scan a surface to be scanned in a main scanning direction, a drive unit that rotationally drives the deflector, an imaging optical system that guides the light beam deflected by the deflector to the surface to be scanned, a detector that detects the light beam deflected by the deflector, and a control unit that specifies the deflection plane based on the detection by the detector and controls the emission of the light beam from the light source for each deflection plane. The plurality of deflection planes include two or more deflection planes having different distances from the rotation center. The optical deflector has a shaft fitting portion in a region including the rotation center into which the rotation shaft of the drive unit is fitted, and the shape of a cross section perpendicular to the rotation shaft of the shaft fitting portion has two or more linear portions that contact the rotation shaft.

Effects of the Invention

[0009] According to the present invention, it is possible to provide an optical scanning device capable of specifying a deflection plane of a deflector with a simple configuration and performing image correction according to the specified deflection plane.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

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Figure 4

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Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Mode for Carrying Out the Invention

[0011] Hereinafter, the optical scanning device according to the present embodiment will be described in detail with reference to the accompanying drawings. Note that the drawings shown below may be drawn at scales different from the actual ones in order to facilitate understanding of the present embodiment. In the following description, the main scanning direction is a direction perpendicular to the rotation axis of the deflector and the optical axis of the imaging optical system, and is the direction in which the light beam is deflected and scanned by the deflector. The sub-scanning direction is a direction parallel to the rotation axis of the deflector. The main scanning cross-section is a cross-section perpendicular to the sub-scanning direction. The sub-scanning cross-section is a cross-section perpendicular to the main scanning direction. Also, a direction parallel to the optical axis of the imaging lens 11 is defined as the X direction, the main scanning direction is defined as the Y direction, and the sub-scanning direction is defined as the Z direction.

[0012] Conventionally, an optical scanning device used in an image forming apparatus such as a laser beam printer or a digital copying machine guides a light beam from a light source to a deflector by an incident optical system. The light beam deflected and scanned by the deflector is focused in a spot shape on the photosensitive drum surface, which is the surface to be scanned, by an imaging optical system, and the photosensitive drum surface is optically scanned by the light beam.

[0013] In such an optical scanning device, the light beam emitted from the light source is converted into a parallel light beam by a collimator lens, and the light beam converted into a parallel light beam is imaged as a line image on the deflection surface of the deflector, which is a deflecting means, by a cylindrical lens in order to perform tilt correction. The light beam deflected and scanned on the deflection surface of the deflector is focused in a spot shape on the photosensitive drum surface by an imaging lens system, and the photosensitive drum surface is scanned at a constant speed.

[0014] Here, each deflection surface of the deflector is machined to be a flat surface, but may include a deviation from an ideal flat surface. Therefore, when light is deflected at a portion deviated from the flat surface, a phenomenon called jitter occurs in which the irradiation position in the main scanning direction of the light deviates from the target position on the surface to be scanned. Since jitter causes a periodic shift in the irradiation position for each deflection surface of the deflector, it is known that when image formation is performed in a state with jitter, periodic density unevenness occurs in the main scanning direction of the image, causing image degradation. Jitter can be reduced by improving the processing accuracy, but in that case, the processing cost increases.

[0015] Therefore, an object of the present invention is to provide an optical scanning device capable of specifying the deflection surface of a deflector with a simple configuration and performing image correction according to the specified deflection surface.

Embodiment

[0016] FIG. 1 shows a schematic diagram of the main scanning cross-section of the optical scanning device 100 according to Embodiment 1 of the present invention. The optical scanning device 100 includes, in order from the light source 1 side, a light source 1, a sub-scanning aperture 2, an anamorphic collimator lens 3, a main scanning aperture 4, a deflector 6, and an imaging lens 11. The sub-scanning aperture 2, the anamorphic collimator lens 3, and the main scanning aperture 4 constitute the incident optical system of the optical scanning device 100. Further, the imaging lens 11 constitutes the imaging optical system of the optical scanning device 100.

[0017] In addition, the optical scanning device 100 has a BD sensor (detector) 8 that detects the light beam from the light source 1 reflected and deflected by the deflector 6 in order to determine the timing of starting the light scanning on the surface to be scanned (photosensitive drum surface) 15. Further, the optical scanning device 100 has a control unit (not shown) that controls the driving of the light source 1, the deflector 6, the BD sensor 8, etc. The light source 1 is a multi-beam light source composed of a semiconductor laser having four light emitting points LD1, LD2, LD3, and LD4, as shown in FIG. 2.

[0018] The sub-scanning aperture 2 is an aperture stop having a rectangular opening, and regulates the beam width of the light beam emitted from the light source 1 in the sub-scanning direction. The anamorphic collimator lens 3 converts the light beam emitted from the light source 1 into a substantially parallel light beam with respect to the main scanning direction, and condenses the light beam so that a focal line is formed in the vicinity of the deflection plane of the deflector 6 in the sub-scanning direction, and is composed of a plastic mold lens.

[0019] The main scanning aperture 4 is an aperture stop having a rectangular opening that regulates the beam width of the light beam emitted from the light source 1 in the main scanning direction. The deflector 6 includes, for example, a polygon mirror (rotating multi-faceted mirror), and rotates at a constant speed in the direction of arrow A in FIG. 1 by a driving means (not shown) such as a motor.

[0020] The imaging lens 11 is an fθ lens having fθ characteristics and has a refractive power for forming a spot image on the image area of the photosensitive drum surface 15. The imaging lens 11 makes the deflection surface of the deflector 6 or a position in the vicinity thereof and the scanned surface 15 or the vicinity thereof substantially conjugate in the sub-scanning cross section. Thereby, it has a tilting correction function of the deflector 6.

[0021] In the scanning device 100, the light beam is optically modulated and emitted from the light source 1 according to the image information, and the width of the light beam is limited by the aperture of the sub-scanning aperture 2 and the aperture of the main-scanning aperture 4. The light beam is converted into a substantially parallel light beam in the main-scanning direction by the anamorphic collimator lens 3 and enters the deflection surface of the deflector 6. In the sub-scanning cross section, it is emitted from the anamorphic collimator lens 3 as a converging light beam and forms an image of a focal line (a line image elongated in the main-scanning direction) on the deflection surface of the deflector 6.

[0022] The light beam reflected and deflected by the deflection surface of the deflector 6 is condensed in a spot shape on the scanned surface 15 by the imaging lens 11, and by rotating the deflector 6 in the direction of arrow A shown in FIG. 1, the scanned surface 15 is scanned at a constant speed in the direction of arrow B (main-scanning direction) by light. Thereby, image recording is performed on the scanned surface 15 which is the recording medium.

[0023] At this time, it is necessary to determine the timing (emission timing) of the start of scanning on the scanned surface 15 before optically scanning the scanned surface 15. For this purpose, the light beam from the light source 1 reflected and deflected by the deflector 6 is guided to the BD sensor (detector) 8. The synchronization signal (BD signal) obtained by detecting the output signal from the BD sensor 8 is used to determine the scanning start timing of the image recording on the scanned surface 15 of the light emitting points LD1 to LD4.

[0024] Fig. 3 shows a main scanning cross-sectional view of the BD optical system (synchronous position detection optical system). In this embodiment, the synchronous detection is configured such that the light beam emitted from the anamorphic collimator lens 3 and reflected and deflected by the deflector 6 is incident on the BD sensor 8 without passing through the imaging lens 11. Therefore, it is configured such that the deflection plane of the deflector 6 can be easily specified by the method described later. Fig. 3 shows a state in which the light beam from the light emitting point LD4 of the light source 1 is incident on the BD sensor 8. The dashed line NL in Fig. 3 indicates the normal line of the deflection plane. In the state where the light beam from the light emitting point LD4 is reflected by the deflection plane and incident on the BD sensor 8, the incident angle to the deflection plane is α.

[0025] In this embodiment, the position of the main scanning aperture 4 is set so that the interval in the main scanning direction between the light beams emitted from the light emitting points LD1 and LD4 on the deflection plane becomes small. Thereby, the dot position shift of the scanned surface 15 that occurs when the focus position of the imaging lens 11 in the main scanning direction is shifted is reduced. Further, the light emitting points LD1 to LD4 have an interval in the main scanning direction and are arranged shifted in the sub-scanning direction. The light emitting points LD1 to LD4 are arranged in a one-dimensional array at an interval of 30 μm and are arranged at equal intervals in both the main scanning direction and the sub-scanning direction.

[0026] Also, the light emitting points LD1 to LD4 can be inclined and arranged so that the angle β (Fig. 2) with respect to the main scanning cross-section around the optical axis can be changed according to the resolution in the sub-scanning direction, so that a desired sub-scanning interval is obtained on the scanned surface 15 regardless of the variations in the incident optical system and the imaging optical system.

[0027] Also, between the beam from the light emitting point LD4 and the beam from the light emitting point LD1, the incident angle in the main scanning direction with respect to the deflection plane is different. Therefore, on the scanned surface 15, the beam from the light emitting point LD4 is a beam on the downstream side of the scan, that is, the front side of the scan, and the beam from the light emitting point LD1 is a beam on the upstream side of the scan, that is, the rear side of the scan. Also, the write timing (scan start timing) is determined by the synchronous position detection signal of one beam from the light emitting point LD4, and in this embodiment, the write timing is detected only by the beam from the light emitting point LD4, which is the beam on the most front side of the scan.

[0028] Also, in this embodiment, a BD optical system is arranged on the downstream side of the light source 1, the laser substrate of the light source 1 and the substrate of the BD sensor 8 are integrated, and BD detection is performed without passing through the imaging lens 11. By adopting a configuration in which the light beam directed toward the BD sensor 8 does not pass through the end portion of the imaging lens 11 as in this embodiment, there is no need to increase the effective portion of the imaging lens 11, the lens thickness can be reduced, and the cost can be reduced. Further, since there is no need to provide a BD imaging lens, an inexpensive optical scanning device can be provided.

[0029] The anamorphic collimator lens 3 of this embodiment has a flat incident surface and a spherical exit surface. Further, a diffractive surface is provided on the incident surface to suppress spot diameter variation due to environmental changes. The phase function of the diffractive surface is represented by Equation (1).

Equation

[0030] The shape of the imaging lens (fθ lens) 11 is represented by functions shown in the following Equation (2) and Equation (3) with the intersection of the imaging lens 11 and the optical axis as the origin and divided into the scanning start side and the scanning end side with respect to the optical axis. Scanning start side:

Equation

Equation

[0031] Here, R is the radius of curvature, and K, B3, B4, B6, B8, and B10 are aspherical coefficients. In this embodiment, the shape of the imaging lens 11 in the main scanning direction is configured asymmetrically with respect to the optical axis, that is, the odd-order terms of the aspherical coefficients are utilized. Further, with respect to the sub-scanning direction, the curvature in the sub-scanning cross section of both surfaces of the imaging lens 11 is continuously changed within the effective portion of the lens on the scanning start side and the scanning end side with respect to the optical axis.

[0032] In this embodiment, the shape of the imaging lens 11 in the sub-scanning direction is represented by continuous functions shown in the following equations (4) and (5) respectively, with the origin at the intersection of the imaging lens 11 and the optical axis, and divided into the scanning start side and the scanning end side with respect to the optical axis. Scanning start side:

Equation

Equation

[0033] Here, r’ is the radius of curvature in the sub-scanning direction (in the Z-X cross section), and D1, D2, D3, D4, D5, D6, D7, D8, D9, and D10 are radius-of-curvature change coefficients. Here, the radius of curvature in the sub-scanning direction is the radius of curvature in a cross section orthogonal to the shape (generatrix) in the main scanning direction. Also, the subscript s of each coefficient represents the scanning start side, and e represents the scanning end side. The imaging lens 11 of this embodiment is composed of a plastic lens having light-transmitting power, achieving weight reduction and improving the design freedom by using an aspherical surface. Note that the imaging lens 11 may be made of glass, or may further be an optical element having diffractive power. When composed of a glass material or a diffractive surface, it is possible to provide an optical scanning device with excellent environmental characteristics.

[0034] In this embodiment, the imaging lens 11 that guides light to the scanned surface 15 is constituted by a single imaging optical element. However, the present invention is not limited to this, and even if it is constituted by two or more imaging optical elements, the same effects as those of this embodiment can be obtained.

[0035] Each numerical value of the optical scanning device 100 according to this embodiment is shown in Tables 1 to 6 below. Here, "E-x" indicates "×10 -x ". [Table 1] [Table 2] [Table 3] [Table 4] [Table 5] [Table 6]

[0036] (Regarding the method for specifying the deflection plane) In order to specify the deflection plane of the deflector 6 with a simple configuration, the present invention makes it possible to specify the deflection plane by measuring the time difference in which light beams deflected by different deflection planes of the deflector 6 pass through the BD sensor 8 when the motor is started. The time interval from when the light beam from the light emitting point LD4 of the light source 1 with a large incident angle in the main scanning direction is deflected by a certain deflection plane and enters the BD sensor 8 until it is deflected by the next deflection plane and enters the BD sensor 8 is measured for several ( = 4) times the number of deflection planes to specify the deflection plane.

[0037] Fig. 4 shows a schematic diagram of the light emission sequence of the light source 1. In Fig. 4, the horizontal axis represents time, and the vertical axis represents the output of the BD sensor. 81 represents the sensor output of the light beam deflected by the deflection surface 601. 82 represents the sensor output of the light beam deflected by the deflection surface 602, 83 represents the sensor output of the light beam deflected by the deflection surface 603, and 84 represents the sensor output of the light beam deflected by the deflection surface 604. Also, T12 represents the BD time difference between the aforementioned deflection surface 601 and the deflection surface 602.

[0038] When a printing command is input to the image forming apparatus including the optical scanning device of the present embodiment, first, a polygon motor (not shown) that holds the deflector 6 starts rotational driving at a predetermined timing. Then, during the acceleration of the polygon motor or when it reaches a steady rotation state, the laser of the light source 1 is turned on and kept on until a synchronization signal is output from the BD sensor 8.

[0039] After detecting the synchronization signal 81, synchronization signals 82, 83, 84, and 85 are obtained in the same manner. The time interval between the synchronization signals 81 and 82 is taken as the BD time difference T12, the time interval between the synchronization signals 82 and 83 is taken as the BD time difference T23, the time interval between the synchronization signals 83 and 84 is taken as the BD time difference T34, and the time interval between the synchronization signals 84 and 85 is taken as the BD time difference T41. Then, after the identification of the deflection surface described later is completed, the laser is turned off a certain time after detecting the synchronization signal, and after a further certain time, the laser is turned on again to form an image in the printing area. After the image formation is completed, the laser is turned on again a certain time after the synchronization signal 81, and the synchronization signal 82 of the next deflection surface is obtained.

[0040] Fig. 5 shows a schematic diagram in which the BD time differences T12, T23, T34, and T41 are graphed. In Fig. 5(a), the vertical axis represents the time difference (BD time difference), indicating that the BD time differences T12 to T41 may be longer or shorter than the reference time difference. In the present invention, the shape, assembly method, and optical configuration of the deflector 6 are devised so as to obtain a BD time difference with a four-surface period as shown in Fig. 5(a).

[0041] In this embodiment, when the motor is started, it is unknown which deflection plane's synchronization signal will be input. That is, it is unknown whether the signals will be detected in the order of 81, 82,... or 83, 84,... with respect to the time shown in FIG. 4. However, the deflection plane is identified by pattern matching the period of the BD time difference. Therefore, when the times of T12 to T41 are equal (FIG. 5b) or when they are the same in a two-plane period (FIG. 5c), the plane cannot be identified by pattern matching.

[0042] As described above, by pattern matching the period of the BD time difference, the deflection plane of the deflector 6 used only for printing with the BD period can be identified. Therefore, the shift of the printing area and the deviation of the printing position due to manufacturing errors of the deflection plane can be easily corrected. In this embodiment, the correction table for the printing position is associated with the deflection plane data at the time of shipment.

[0043] (Method for generating the BD time difference) FIG. 6 shows a schematic diagram of the BD optical system of this embodiment. In FIG. 6, the same optical components as those shown in FIG. 1 are denoted by the same reference numerals as in FIG. 1. While referring to FIG. 6, the relationship between the BD time difference and the position of the deflection plane and the like will be described.

[0044] The light beam emitted from the light source 1 is reflected and deflected by the deflection plane of the deflector 6 and enters the BD sensor 8. At the rotational position where the principal ray of the light beam from the light source 1 enters the center position of the BD sensor 8, the broken line NL in FIG. 6 indicates the normal line of the deflection plane, and α indicates the incident angle at that rotational position. Also, let the distance L (mm) from the deflection plane to the BD sensor 8 be 105, the amount of optical axis shift before and after eccentricity be 104, the distance in the normal direction of the two adjacent deflection planes of the deflector 6 in the eccentric state (eccentricity amount δ (mm)) be 103, and the motor rotation speed R (rpm). At this time, the BD time difference ΔBD (sec) is expressed by the following formula (6).

Equation

[0045] That is, the BD time difference ΔBD can be expressed by the eccentricity δ, the incident angle of the optical system, and the distance L from the deflection plane to the BD sensor 8. That is, by detecting the BD time difference ΔBD, since the incident angle α of the optical system and the distance L from the deflection plane to the BD sensor 8 are known, the distance (eccentricity δ) in the normal direction from the rotation center of two adjacent deflection planes of the deflector 6 can be obtained.

[0046] Fig. 7 shows the mounting position of the deflector 6 with respect to the polygon motor. Fig. 7 shows a configuration for controlling the eccentricity. The deflector 6 of this embodiment has a square shape with an outer circumscribed circle radius of 10 mm. The four deflection planes 601, 602, 603, and 604 are composed of mirror surfaces. In the vicinity of the center 6a of the outer circumscribed circle of the circle circumscribing the four deflection planes of the deflector 6, a substantially square hole (shaft fitting portion) having sides 61, 62, 63, and 64 is formed. The center of the circle circumscribing the substantially square hole of the deflector 6 is configured to be at the same position as the outer circumscribed circle center 6a.

[0047] Fig. 8 shows a cross-sectional view of the motor unit (drive unit) 501 in a state where the polygon mirror 503, which is the deflector 6, is mounted on the motor rotation shaft 504. The motor unit 501 includes a polygon mirror 503, a motor rotation shaft 504, a rotor 505, a stator 506, a bearing device 508, and a pressing spring 509. The rotor 505 is integrally coupled with the motor rotation shaft 504. The bearing device 508 is integrally configured with the substrate 507. The pressing spring 509 is an elastic member for fixing the polygon mirror 503. The rotor 505 and the stator 506 together form a polygon motor 516. When current is supplied to the stator 506, the polygon motor 516 is driven, and the polygon mirror 503 rotates together with the rotor 505.

[0048] As shown in FIG. 7, the motor rotation shaft 504 is composed of a cylindrical member, and the radius of the cylindrical portion of the motor rotation shaft 504 is configured to be smaller than the inscribed circle radius of the substantially square hole portion near the center of the deflector 6. Therefore, when fixing the deflector 6 to the motor rotation shaft 504, it can be easily inserted without hitting the shaft, and the motor rotation shaft 504 can be attached so as to contact only two sides of the hole portion of the polygon mirror. That is, the polygon mirror as the deflector 6 can be eccentrically and stably fixed with respect to the motor rotation shaft 504.

[0049] A substantially square hole portion is formed so that the diagonal line of the square shape near the center of the deflector 6 of the present embodiment coincides with the normal line of the deflection plane of the deflector 6. In other words, the angle bisector of the angle formed by two adjacent sides of the square shape of the hole portion near the center of the deflector 6 of the present embodiment is formed to coincide with the normal direction of the deflection plane of the deflector 6. Thereby, by attaching the deflector 6 to the motor rotation shaft 504 so that the motor rotation shaft 504 contacts two sides of the square shape of the hole portion of the deflector 6, the eccentricity amount of the deflection plane can be maximized in the normal direction of the deflection plane.

[0050] Consider the case (FIG. 7) where the deflector 6 is attached to the motor rotation shaft 504 such that the motor rotation shaft 504 contacts two sides (sides 62 and 63) of the square shape of the hole portion arranged on the deflection plane 604 side of the deflector 6. At this time, if the distances from the center 504a of the motor rotation shaft 504 to the deflection planes 601, 602, 603, and 604 are L1, L2, L3, and L4, respectively, then L4 < L1 = L3 < L2.

[0051] For the configuration of this embodiment, consider the case where the motor rotation shaft 504 is assembled so as to contact two sides of the square shape of the hole portion in a configuration where the diagonal line of the square shape of the hole portion of the deflector 6 coincides with the diagonal line of the square deflector 6. The eccentricity amount in the normal direction of the deflection plane becomes smaller with respect to the eccentricity amount of the center 504a of the motor rotation shaft 504 with respect to the circumscribed circle center 6a of the circle circumscribing the four deflection planes of the deflector 6. The eccentricity amount in the normal direction of the deflection plane cannot be efficiently increased with respect to the eccentricity amount of the center 504a of the motor rotation shaft 504 with respect to the circumscribed circle center 6a.

[0052] Also, in order to increase the amount of eccentricity in the normal direction of the deflection surface, it is necessary to increase the difference between the diameter of the motor rotation shaft 504 and the inscribed circle diameter inscribed in the hole portion, which is not good because the balance deteriorates when the polygon motor 516 rotates. On the other hand, in the configuration of the present embodiment shown in FIG. 7, it is possible to increase the amount of eccentricity in the normal direction of the deflection surface while suppressing a decrease in balance when the polygon motor 516 rotates.

[0053] In the illustrated embodiment, it has been described that the center of the circle circumscribing the square hole portion of the deflector 6 is the same position as the circumcenter 6a of the circle circumscribing the four deflection surfaces of the deflector 6, but the present invention is not limited to this. Also, in the present invention, although L4 < L1 = L3 < L2, the same effect can be obtained even if it is assembled so as to be in contact with the other two sides, such as L1 < L2 = L4 < L3.

[0054] In the present embodiment, a configuration in which a square hole portion is formed in the central portion of the square deflector 6 has been illustrated and described, but the present invention is not limited to this. The shape of the hole portion formed in the region including the central portion of the deflector 6 is not limited to a square, and may be formed as an N-sided polygon (N ≥ 3). Further, with respect to the hole portion formed as an N-sided polygon substantially at the center of the deflector 6, the motor rotation shaft 504 may be configured to be in contact with (N - 1) or less sides of the N-sided polygon of the hole portion. For example, the hole portion of the deflector 6 may be formed as a rectangle, and the motor rotation shaft 504 may be configured to be in contact with three sides of the rectangle.

[0055] As described above, by providing a polygonal hole portion centered near the center of the circle circumscribing the polygonal deflector 6 and making the diameter of the circle inscribed in the polygon larger than the diameter of the motor rotation shaft 504, it is possible to improve the assemblability and control the eccentricity direction and amount. The hole portion is configured as a polygon having N sides (N ≥ 3).

[0056] In addition, it is preferable that the polygon of the hole near the center of the deflector 6 is configured such that the angle bisector formed by two adjacent sides coincides (is parallel) with the normal direction of the deflection plane of the deflector 6, and the two sides are in contact with the motor rotation axis 504. With this configuration, it is possible to efficiently obtain a large eccentricity in the normal direction of the deflection plane with respect to the eccentricity of the center 504a of the motor rotation axis 504 with respect to the center 6a of the circumscribed circle. Also, in that case, the shape of the hole formed near the center of the deflector 6 is not limited to a polygon, and as long as the motor rotation axis 504 is configured to be in contact with the two adjacent sides described above, the shape of the other portion where the hole is formed is not limited. That is, the shape of the cross-section perpendicular to the rotation axis of the hole of the deflector 6 into which the motor rotation axis 504 is inserted may be a shape having two or more straight portions in contact with the motor rotation axis 504.

[0057] (Reasons for the need for an appropriate BD time difference) Fig. 5(a) shows the BD time differences T12, T23, T34, and T41 of this embodiment. In Fig. 5, T12 indicates the BD time difference between the deflection planes 601 and 602 in Fig. 7, and T23 indicates the BD time difference between the deflection planes 602 and 603. Similarly, T34 indicates the BD time difference between the deflection planes 603 and 604, and T41 indicates the BD time difference between the deflection planes 604 and 601. In this embodiment, since the distances from the center 504a of the motor rotation axis 504 to each deflection plane are configured such that L4 < L1 = L3 < L2, the BD time differences at which the light beam deflected by the continuously rotating deflector 6 enters the BD sensor are T12 = T41 < T23 = T34.

[0058] This is because BD detection is accelerated in the state where the optical path length of the light beam from the light source 1 to the deflection plane is the longest (the state reflected by the deflection plane 604), and BD detection is delayed in the state where it is the shortest (the state reflected by the deflection plane 602). This shows that the BD time differences between deflection planes with different eccentricities are different from the BD time differences between non-eccentric deflection planes. In this embodiment, by pattern-matching the four BD time differences shown in Fig. 5(a) and specifying which deflection plane T12, T23, T34, and T41 correspond to, the deflection planes 601 to 604 can be specified every time the motor is started.

[0059] Figure 5(b) shows the BD time difference when the eccentricity δ is 0. In this case, since the BD time difference does not change, the deflection surfaces 601 to 604 cannot be specified at the time of motor startup based on the BD time differences T12, T23, T34, and T41 by pattern matching.

[0060] Figure 5(c) shows the BD time difference when a rhombus polygon mirror is used. In this case, the time differences T12 and T34 and the time differences T23 and T41 cannot be distinguished, and the deflection surface cannot be specified by pattern matching. In this way, by devising the eccentricity and the optical configuration, it becomes possible to specify the surface from the four consecutive BD time differences, and it is possible to correct the printing position deviation peculiar to the deflection surface.

[0061] (BD time difference of this embodiment) In the optical scanning device 100 of this embodiment, it is configured to satisfy the conditional expression (7), and both reduction of the eccentricity and specification of the deflection surface are achieved. [Number] Here, δ is the difference in the distances from the rotation centers of the deflectors 6 of two adjacent deflection surfaces, and M is the clock frequency (Hz) indicating the detection period during which the BD sensor 8 acquires the synchronization signal.

[0062] In this embodiment, L = 60 mm, R = 40000 rpm, δ = 5 μm, α = 12°, and the value on the left side is 4.05 ns. Also, since the clock frequency of the synchronization signal in this embodiment is 300 MHz, M on the right side -1 = 3.3 ns. Therefore, the optical scanning device 100 of this embodiment is configured to satisfy the conditional expression (7).

[0063] In this embodiment, BD detection is performed using only the light beam from the light emission point LD4 of the multi-beam laser shown in FIG. 2. This is because, compared to the case of performing BD detection at the light emission point LD1 with a small incident angle (α in FIG. 6), the eccentricity of the center 504a of the motor rotation axis 504 with respect to the center 6a of the circumscribed circle of the deflector 6, which is required to obtain the same BD time difference, can be made smaller.

[0064] Also, in this embodiment, the deflection plane identification and the print position deviation correction are performed using two BD time difference tables: one immediately after the motor is started and the other after the motor has been rotating steadily for 1 minute after startup. This is to change the correction value depending on whether printing is performed immediately when the motor is started or after a predetermined time has elapsed after startup. If the same BD time difference table is continuously used regardless of the elapsed time after the start of driving, it will not be possible to cope with changes in the BD time difference due to changes in the environmental temperature or the heat generation of the motor, and there may be a deviation in the print position.

[0065] (Regarding the effect when the deflection plane is identified) In this embodiment, since it is possible to identify which deflection plane is being used for printing by the method described above, it becomes possible to store image correction data (table) corresponding to the deflection plane at the time of shipment of the optical scanning device 100 and use it for correction. In this embodiment, the writing position, partial magnification, and pitch unevenness due to skew are corrected by changing the light amount of the laser for each deflection plane. Also, the length (overall magnification) of the image in the main scanning direction is changed and corrected for each deflection plane.

[0066] In this embodiment, since the BD optical system including the imaging lens is not provided in the optical path from the deflector 6 to the BD sensor 8, the focal length of the BD optical system does not shift due to changes in the environmental temperature or the like, so the BD time difference does not change, and there is also the advantage that the identification of the deflection plane can be performed stably.

[0067] As described above, by appropriately configuring the optical configuration such as the amount of eccentricity between the center 504a of the motor rotation axis 504 and the center 6a of the circumscribed circle of the deflector 6, it is possible to calculate the BD time difference between two adjacent deflection surfaces. As a result, it becomes possible to identify the deflection surface of the polygon mirror which is the deflector 6, and it is possible to provide a high-definition optical scanning device with a simple configuration without using a deflector 6 having a special shape.

[0068] In addition, an example in which it is possible to detect the BD time difference between two adjacent deflection surfaces is shown in the case where the optical scanning device is configured to satisfy the conditional expression (7) with respect to the difference δ in the distance from the rotation center of the deflector 6 between two adjacent deflection surfaces. On the other hand, when a polygonal polygon mirror is used as the deflector 6, when the difference between the maximum value and the minimum value of the distances from the rotation center of the deflector 6 to each deflection surface is δ', the following conditional expression (8) may be satisfied.

Equation

[0069] By satisfying the conditional expression (8), it is possible to specify at least the deflection surface having the maximum distance and the deflection surface having the minimum distance from the rotation center of the deflector 6 to each deflection surface. However, in this case, when the arrangement of the deflection surface having the maximum distance and the deflection surface having the minimum distance from the rotation center of the deflector 6 to each deflection surface does not have rotational symmetry other than 360 degrees of the rotation angle around the rotation center of the deflector 6, the deflection surface can be specified. Even if the number of deflection surfaces having the maximum and minimum distances from the rotation center of the deflector 6 to each deflection surface is not one each, as long as the condition of the rotational symmetry is satisfied, the deflection surface can be specified.

[0070] By this method, it is possible to identify which deflection surface is deflecting and scanning the surface to be scanned 15, so that it becomes possible to use the image correction data (table) stored corresponding to the deflection surface at the time of shipment of the optical scanning device 100 for drawing correction.

Example

[0071] FIG. 9 is a main scanning cross-sectional view of the optical scanning device 100 according to Embodiment 2 of the present invention. In FIG. 9, reference numeral 6 denotes a deflector as a common deflection means, which is rotating at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor. Reference numeral 11a denotes a first imaging lens, and reference numeral 11b denotes a second imaging lens. In the optical scanning device 100 of the present embodiment, the first imaging lens 11a and the second imaging lens 11b constitute an imaging optical system 11.

[0072] Reference numeral 12 denotes a folding mirror, which is disposed on the deflector 6 side from the second imaging lens 11b in the optical path from the deflector 6 to the surface to be scanned (photosensitive drum surface) 15. Reference numeral 15 denotes a photosensitive drum surface as the surface to be scanned. Reference numeral 1 denotes a light source unit, which is composed of, for example, a semiconductor laser.

[0073] Reference numeral 3a denotes a light beam conversion element (collimator lens), which converts the light beam emitted from the light source 1 into a substantially parallel light beam (or a substantially divergent light beam or a substantially convergent light beam). Reference numeral 3b denotes a first cylindrical lens, which has a predetermined power (refractive power) only in the sub-scanning cross section (sub-scanning direction). The first cylindrical lens 3b condenses the light beam made substantially parallel by the collimator lens 3a in the sub-scanning cross section as a substantially linear image (a linear image elongated in the main scanning direction) on the deflection surface of the deflector 6 described later.

[0074] Reference numeral 3c denotes a second cylindrical lens, which has a predetermined power only in the main scanning cross section (main scanning direction), converts the substantially parallel light beam that has passed through the collimator lens 3a into a divergent light beam, corrects the wavefront aberration, and corrects the spot shape on the surface to be scanned 15 well. Reference numeral 5 denotes a folding mirror, which deflects the light beam that has passed through the second cylindrical lens 3c in the main scanning direction and guides it to the deflector 6. Note that each element of the collimator lens 3a, the first cylindrical lens 3b, the second cylindrical lens 3c, and the first imaging lens 11a described later constitutes one element of the incident optical system LA.

[0075] Reference numeral 6 denotes a deflector (polygon mirror) as a deflecting means having a deflecting surface (deflecting surface) 6f composed of 10 surfaces, which is rotating at a constant speed in the direction of arrow A shown in Fig. 9 by a driving means (not shown) such as a motor. Reference numeral 10 denotes a BD sensor, which performs BD detection with a light beam having an incident angle of 23° on the deflecting surface.

[0076] Reference numeral 11 denotes an imaging optical system, which includes first and second imaging lenses (anamorphic lenses) 11a and 11b having different powers in the main scanning section and the sub-scanning section. The imaging optical system 11 focuses a light beam based on image information reflected and deflected by the deflector 6 in a spot shape on the scanned surface as the scanned surface 15 in the main scanning section. In the sub-scanning section, the imaging optical system 11 has a tilt correction function by making the space between the deflecting surface 6f of the deflector 6 and the scanned surface 15 optically substantially conjugate by the first and second imaging lenses 11a and 11b. Further, the first imaging lens 11a also constitutes a part of the incident optical system LA.

[0077] In this embodiment, the optical system has a double-pass configuration in which the incident light beam incident on the deflector 6 passes through the first imaging lens 11a, and the scanned light beam deflected by the deflector 6 is incident on the first imaging lens 11a again.

[0078] Reference numeral 12 denotes a correction folding mirror, which is disposed in the optical path between the deflector 6 and the scanned surface 15, and corrects (adjusts) the curvature (scanning line curvature) in the sub-scanning direction of the scanning line on the scanned surface 15. Reference numeral 15 denotes a photosensitive drum surface as the scanned surface.

[0079] In this embodiment, the light beam emitted from the semiconductor laser serving as the light source 1 after being optically modulated is converted into a substantially parallel light beam by the collimator lens 3a, and is converted into a converging light beam in the sub-scanning direction by the first cylindrical lens 3b and enters the second cylindrical lens 3c. Among the light beams incident on the second cylindrical lens 3c, the light beam in the sub-scanning cross-section converges and passes through the first imaging lens 11a (double-pass configuration) and enters the deflection surface 6f of the deflector 6, and forms a substantially linear image (a linear image elongated in the main scanning direction) near the light deflection surface 6f. At this time, the light beam incident on the light deflection surface 6f is incident obliquely from an oblique direction with a predetermined angle with respect to the main scanning cross-section from within the sub-scanning cross-section, separating the incident light beam and the deflected light beam (oblique incidence optical system).

[0080] On the other hand, the light beam in the main scanning cross-section diverges and is converted into a substantially parallel light beam by passing through the first imaging lens 11a, and enters the deflection surface 6f from approximately the center of the deflection angle of the deflector 6 (front incidence). At this time, the light beam width of the substantially parallel light beam is set to be sufficiently wider than the facet width of the deflection surface 6f of the deflector 6 in the main scanning direction (overfield optical system).

[0081] Then, the light beam deflected and reflected by the deflection surface 6f of the deflector 6 is guided to the surface to be scanned 15 through the first imaging lens 11a, the folding mirror 12, and the second imaging lens 11b. By rotating the deflector 6 in the direction of arrow A, the light beam guided to the surface to be scanned 15 scans the surface to be scanned 15 in the direction of arrow B (main scanning direction). Thereby, image recording is performed on the surface to be scanned 15 as the recording medium.

[0082] In this embodiment, the shapes of the first and second imaging lenses 11a and 11b are represented by the formulas (2) and (3) with the intersection point with the optical axis as the origin, divided into the scanning start side and the scanning end side with respect to the optical axis, similar to Embodiment 1. In this embodiment, the shapes of the first and second imaging lenses 11a and 11b in the main scanning direction are configured symmetrically with respect to the optical axis. That is, the aspherical coefficients on the scanning start side and the scanning end side are made to coincide.

[0083] Also, in the sub-scanning direction, on the scanning start side and the scanning end side with respect to the optical axis, the curvature within the effective portion is continuously changed in the sub-scanning cross-section (the plane including the optical axis and orthogonal to the main scanning cross-section) of the exit surface of the second imaging lens 11b, and the shapes in the main scanning direction and the sub-scanning direction are configured symmetrically with respect to the optical axis. The shape in the sub-scanning direction is expressed by Expression (4) and Expression (5) with the intersection point with the optical axis as the origin and divided into the scanning start side and the scanning end side with respect to the optical axis, similar to Example 1.

[0084] Numerical values of the image forming apparatus according to Example 2 of the present invention are shown in Tables 7 to 9.

Table 7

Table 8

Table 9

[0085] FIG. 10 shows a schematic view of the polygon mirror which is the deflector 6 of this embodiment. The deflector 6 is a polygon mirror having an outer circumscribed circle diameter of 17 mm and ten deflection surfaces 801 to 810. Further, in the vicinity of the center of the deflector 6, there is a polygonal (square) hole portion formed by four sides of sides 821, 822, 823, and 824. Curvatures are provided as chamfered portions near the vertices 850, 851, 852, and 853 of the four sides of the hole portion, making it difficult for burrs to occur during manufacturing. Further, the vicinity of the vertex 853 is configured such that the distance to the deflection surface 809 is the shortest, and the configuration can reduce the eccentricity amount.

[0086] Similar to Example 1, in this embodiment as well, the diameter of the circle circumscribing the square of the hole portion near the center of the deflector 6 is configured to be smaller than the distance between the opposing surfaces of the square of the hole portion. Further, the center 820 of the outer circumscribed circle of the deflector 6 and the center 830 of the motor rotation axis 840 are not made to coincide, and the rotation axis 840 is fixed so as to be in contact with two sides 821 and 824 of the hole portion.

[0087] Fig. 11 shows the BD time differences T12, T23, T34, T45, ···, T910, T101 of this embodiment. In the figure, T12 represents the BD time difference between the deflection surfaces 801 and 802 in Fig. 10, and T23 represents the BD time difference between the deflection surfaces 802 and 803. Similarly, T34 represents the BD time difference between the deflection surfaces 803 and 804, T910 represents the BD time difference between the deflection surfaces 809 and 810, and T101 represents the BD time difference between the deflection surfaces 810 and 801.

[0088] In this embodiment, the distances from the center 830 of the rotation axis 840 to each deflection surface are configured such that L09 < L10 = L08 < L01 = L07 < L02 = L06 < L03 = L05 < L04. Here, the distances from the center 830 of the rotation axis 840 to the deflection surfaces 801, 802, 803, 804, 805, 806, 807, 808, 809, 810 are denoted as L01, L02, L03, L04, L05, L06, L07, L08, L09, L10, respectively. Therefore, the BD time difference ΔBD at which the light beam deflected by the deflection surface 6f of the continuously rotating deflector 6 enters the BD sensor 8 is as shown in Fig. 11.

[0089] This is because the BD detection speeds up until the optical path length of the light beam from the light source 1 to the deflection surface 6f becomes the longest state (the state reflected by the deflection surface 809), and the BD detection is delayed until the optical path length becomes the shortest state (the state reflected by the deflection surface 804). This indicates that the BD time differences between the deflection surfaces with different eccentric amounts are different from the BD time differences between the non-eccentric deflection surfaces. That is, when the reflected lights from the deflection surfaces 809, 810, 801, 802, 803, 804 enter the BD sensor 8 in this order, the optical path length gradually becomes shorter, and the BD detection gradually speeds up, and a short BD time difference ΔBD is detected with respect to the reference line in Fig. 11.

[0090] On the other hand, when the reflected light from the deflection surfaces 804, 805, 806, 807, 808, 809 enters the BD sensor 8 in this order, the optical path length gradually becomes longer, and the BD detection is in a state of being gradually delayed. In this case, as shown in FIG. 11, a long BD time difference ΔBD with respect to the reference line is detected. In this embodiment, the 10 BD time differences shown in FIG. 11 are pattern-matched to identify the BD time differences T12, T23, T34, T45, ···, T101. That is, the deflection surfaces 801 to 810 can be specified every time the motor is started.

[0091] Also in this embodiment, similar to Embodiment 1, the optical system is configured to satisfy the conditional expression (7), and it is possible to identify the deflection surface while suppressing the eccentricity of the center 830 of the rotation axis 840 with respect to the center 820 of the circumscribed circle of the deflector 6 to be small. In this embodiment, the optical parameters on the left side of the conditional expression (7) are set to L = 158.4 mm, R = 30000 rpm, δ = 5 μm, α = 23°, respectively, and the value on the left side of the conditional expression (7) is 3.6 ns. Also, since the clock frequency of the synchronization signal in this embodiment is 300 MHz, M on the right side of the conditional expression (7) -1 = 3.3 ns. Therefore, the optical scanning device 100 of this embodiment is configured to satisfy the conditional expression (7).

[0092] In this embodiment, BD detection is performed using only the light beam from the light-emitting element with the largest incident angle among the plurality of light-emitting elements of the multi-beam laser. This is because, compared with the case of performing BD detection with a light-emitting element having a small incident angle, the eccentricity of the center 830 of the rotation axis 840 with respect to the center 830 of the circumscribed circle of the deflector 6 required to obtain the same BD time difference can be made smaller.

[0093] In this embodiment, for the deflection surfaces 810 and 805 of the regular decagon polygon mirror that are parallel to each other, the hole portion of the polygon mirror is configured such that the two square and parallel sides 821 and 823 of the hole portion of the polygon mirror are parallel to each other. In this configuration, the deflector 6 is fixed to the rotation axis 840 in a state where the rotation axis 840 is offset toward the vicinity 853 of the vertex of the hole portion closer to the deflection surface 809 adjacent to the deflection surface 810. However, the present invention is not limited to this configuration.

[0094] It is more preferable that the normal line of one deflection surface of the regular polygon polygon mirror and the angle bisector formed by two adjacent sides of the polygon constituting the hole portion of the polygon mirror are parallel to each other. According to this configuration, it is possible to more efficiently increase the eccentricity in the normal direction of the position of the deflection surface of the polygon mirror with respect to the eccentricity between the center 820 of the circumscribed circle of the polygon mirror and the center 830 of the rotation axis 840.

[0095] Also, in this embodiment, the deflection surface identification and the print position deviation correction are performed using two BD time difference tables: one immediately after the motor is started and the other after the motor has been rotating steadily for one minute after startup. This is because the correction value is changed depending on whether printing is performed immediately after the motor is started or after a certain time has elapsed after startup. If the same BD time difference table is continuously used regardless of the elapsed time after startup, it may not be possible to cope with changes in the BD time difference due to changes in the environmental temperature or the heat generation of the motor, and there may be a deviation in the print position.

[0096] (Regarding the effect when the deflection surface is identified) In this embodiment, since it is possible to identify which deflection surface is being used for printing by the method described above, it becomes possible to use the image correction data (table) stored corresponding to the surface at the time of shipment of the optical scanning device 100 for drawing correction. In this embodiment, the pitch unevenness due to surface tilt is corrected by changing the light amount of the laser for each deflection surface. This is because the optical system of this embodiment is an overfield optical system, unlike that of the first embodiment, and thus has a configuration in which the difference in the main scanning direction position of the image between surfaces is less likely to occur.

[0097] In this embodiment, since the optical path from the deflector 6 to the BD sensor 8 is configured such that there is no BD optical system including an imaging lens, the focal length of the BD optical system does not shift due to changes in the ambient temperature or the like, so the BD time difference does not change, and there is also an advantage that the deflection plane can be specified stably.

[0098] As described above, in the optical scanning device 100 including the 10-sided polygon mirror, the optical configuration such as the eccentricity of the center 830 of the rotation axis 840 with respect to the center 820 of the circumscribed circle of the deflector 6 is devised, and the BD time difference between adjacent deflection planes can be calculated. As a result, it becomes possible to specify the deflection plane of the polygon mirror, and it is possible to provide a high-definition optical scanning device with a simple configuration without using a deflector 6 having a special shape.

Example

[0099] An optical scanning device according to Embodiment 3 of the present invention will be described. The optical scanning device according to Embodiment 3 is different from the optical scanning device of Embodiment 1 in the position of the BD sensor 8 and the clock frequency of the synchronization signal, and the other configurations are the same as those of Embodiment 1. The description of the same configuration as that of the optical scanning device of Embodiment 1 will be omitted, and the different configurations will be described.

[0100] Also in this embodiment, similar to Embodiment 1, the optical system is configured to satisfy the conditional expression (7), and while suppressing the eccentricity of the center 504a of the motor rotation axis 504 with respect to the center 6a of the circumscribed circle of the deflector 6 to be small, it is possible to realize specifying the deflection plane.

[0101] In this embodiment, the optical parameters on the left side of the conditional expression (7) are set to L = 40 mm, R = 40000 rpm, δ = 5 μm, and α = 12°, respectively, and the value on the left side of the conditional expression (7) is 6.07 ns. Also, since the clock frequency of the synchronization signal in this embodiment is 200 MHz, M on the right side of the conditional expression (7) -1 = 5.0 ns. Therefore, the optical scanning device of this embodiment is configured to satisfy the conditional expression (7).

[0102] Also in the optical scanning device of this embodiment, the same effects as those in Embodiment 1 can be obtained.

[0103] As described above, by calculating the BD time difference between adjacent deflection planes using a less expensive BD sensor circuit, it becomes possible to identify the deflection plane, and a high-definition optical scanning device can be provided with a simple configuration without using a polygon mirror with a special shape.

Embodiment

[0104] An optical scanning device according to Embodiment 4 of the present invention will be described. The optical scanning device according to Embodiment 4 is different from the optical scanning device of Embodiment 1 in that the eccentricity δ is 3 μm, and other configurations are the same as those in Embodiment 1. The description of the same configuration as that of the optical scanning device of Embodiment 1 will be omitted, and different configurations will be described.

[0105] Also in this embodiment, as in Embodiment 1, the optical system is configured to satisfy the conditional expression (7), and while suppressing the eccentricity of the center 504a of the motor rotation axis with respect to the center 6a of the circumscribed circle of the deflector 6 to be small, it is possible to identify the deflection plane.

[0106] In this embodiment, the optical parameters on the left side of the conditional expression (7) are set to L = 40 mm, R = 40000 rpm, δ = 3 μm, and α = 12° respectively, and the value on the left side of the conditional expression (7) is 3.64 ns. Also, since the clock frequency of the synchronization signal in this embodiment is 300 MHz, M on the right side of the conditional expression (7) -1 = 3.3 ns. Therefore, the optical scanning device of this embodiment is configured such that the optical system satisfies the conditional expression (7).

[0107] As a result, even in a configuration of a polygon mirror and a motor rotation axis with a smaller eccentricity of the deflection plane compared to Embodiment 1, it is possible to identify the deflection plane. Therefore, the balance deterioration when the motor rotates can be further reduced, and the image deterioration due to pitch unevenness can be reduced.

[0108] Also in the optical operation device of this embodiment, the same effects as those in the first embodiment can be obtained. As described above, even when the eccentricity is reduced, by calculating the BD time difference between adjacent deflection surfaces, it becomes possible to identify the deflection surface, and a high-definition optical scanning device can be provided with a simple configuration using a polygon motor for a high-definition optical scanning device.

[0109] As described above, the preferred embodiments have been described, but the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist.

[0110] [Image forming apparatus] FIGS. 12 and 13 are cross-sectional views of main parts in the sub-scanning direction showing an image forming apparatus equipped with an optical scanning device according to any one of the first to fourth embodiments.

[0111] FIG. 12 shows a cross-sectional view of a main part in the sub-scanning direction of a monochrome image forming apparatus (electrophotographic printer) 104 including an optical scanning device according to any one of the first to fourth embodiments.

[0112] As shown in FIG. 12, a signal output from an external device 117 such as a personal computer, specifically, code data Dc, is input to the image forming apparatus 104. Then, the input code data Dc is converted into image data (dot data) Di by a printer controller 111.

[0113] The converted image data Di is input to an optical scanning device 100 according to any one of the first to fourth embodiments. Then, from the optical scanning device 100, an optical beam (light beam) 103 modulated according to the image data Di is emitted, and the photosensitive surface of the photosensitive drum 101 is scanned in the main scanning direction by the optical beam 103.

[0114] The photosensitive drum 101, which is an electrostatic latent image carrier (photoconductor), is rotated clockwise by a motor 115. Then, along with this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction orthogonal to the main scanning direction with respect to the optical beam 103.

[0115] Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface. And, a light beam 103 scanned by the optical scanning device 100 is irradiated onto the surface of the photosensitive drum 101 charged by the charging roller 102.

[0116] 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 light beam 103. And the formed electrostatic latent image is developed as a toner image by a developing device 107 disposed so as to contact the photosensitive drum 101 on the downstream side in the rotational cross section of the photosensitive drum 101 with respect to the irradiation position of the light beam 103.

[0117] The toner image developed by the developing device 107 is transferred onto a sheet of paper 112 as a material to be transferred by a transfer roller (transfer device) 108 disposed so as to face the photosensitive drum 101 below the photosensitive drum 101.

[0118] Note that the sheet of paper 112 is stored in a paper cassette 109 in front of (the right side in FIG. 12) the photosensitive drum 101, but it is also possible to feed the paper manually. And, the sheet of paper 112 in the paper cassette 109 is fed into the conveyance path by a paper feed roller 110 disposed at the end of the paper cassette 109.

[0119] The sheet of paper 112 onto which the unfixed toner image has been transferred as described above is further conveyed to a fixing device behind (the left side in FIG. 12) the photosensitive drum 101. The fixing device is composed of a fixing roller 113 having a fixing heater (not shown) inside and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113.

[0120] Then, the paper 112 conveyed from the transfer roller 108 is heated while being pressed by the pressure contact portion of the fixing roller 113 and the pressure roller 114, whereby the unfixed toner image on the paper 112 is fixed. Also, a paper discharge roller 116 is disposed behind the fixing device, and the fixed paper 112 is discharged to the outside of the image forming apparatus 104.

[0121] Although not shown in FIG. 12, in addition to the above-described data conversion, the printer controller 111 also controls each member in the image forming apparatus 104 such as the motor 115 and members such as the polygon motor in the optical scanning unit 400.

[0122] [Color Image Forming Apparatus] FIG. 13 is a cross-sectional view of a main part in the sub-scanning direction showing a color image forming apparatus equipped with the optical scanning device according to any one of Embodiments 1 to 4.

[0123] In FIG. 13, reference numeral 60 denotes a color image forming apparatus, 100 denotes an optical scanning device having any one of the configurations shown in Embodiments 1 to 4, 21, 22, 23, and 24 denote photosensitive drums as image carriers, and 31, 32, 33, and 34 denote developing devices, respectively, and 51 denotes a conveying belt. In FIG. 13, color signals of R (red), G (green), and B (blue) are input to the color image forming apparatus 60 from an external device 52 such as a personal computer. These color signals are converted by a printer controller 53 in the apparatus into respective image data (dot data) of C (cyan), M (magenta), Y (yellow), and B (black). These image data are input to the optical scanning device 100, respectively. Then, light beams 41, 42, 43, and 44 modulated according to the respective image data are emitted from these optical scanning devices 100, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are scanned in the main scanning direction by these light beams.

[0124] The color image forming apparatus 60 in this embodiment emits light beams corresponding to each of the colors C (cyan), M (magenta), Y (yellow), and B (black) from four optical scanners 100, records image signals (image information) on the surfaces of the photosensitive drums 21, 22, 23, and 24, and prints color images at high speed.

[0125] The color image forming apparatus in this embodiment forms latent images of respective colors on the surfaces of the corresponding photosensitive drums 21, 22, 23, and 24 using light beams 41, 42, 43, and 44 based on respective image data by the four optical scanners 100 as described above. Then, it performs multiple transfers onto a recording material to form a single full-color image.

[0126] As the external device 52, for example, a color image reading device equipped with a CCD sensor may be used. In this case, a color digital copier is configured by this color image reading device and the color image forming apparatus 60.

[0127] The disclosure of this embodiment includes the following configurations. (Configuration 1) A light source, A deflector having a plurality of deflection surfaces that deflect a light beam from the light source and scan a surface to be scanned in a main scanning direction, A drive unit that rotationally drives the deflector, An imaging optical system that guides the light beam deflected by the deflector to the surface to be scanned, A detector that detects the light beam deflected by the deflector, A control unit that identifies the deflection surface based on the detection by the detector and controls the emission of the light beam from the light source for each deflection surface, Comprising, The plurality of deflection surfaces include two or more deflection surfaces having different distances from the rotation center, The deflector has a shaft fitting portion into which the rotation axis of the drive unit fits in a region including the rotation center, and the shape of a cross section perpendicular to the rotation axis of the shaft fitting portion has two or more straight portions that contact the rotation axis, which is a characteristic of the optical scanning device. (Configuration 2) Among the plurality of deflection surfaces, the difference in distance from the rotation center between two adjacent deflection surfaces is δ, the incident angle on the deflection surface when the light beam from the light source deflected by the deflection surface of the deflector enters the detector is α, the clock frequency indicating the detection period of the detector is M (Hz), the rotation speed of the drive unit is R (rpm), and the distance from the deflection surface to the detector is L. When

Equation

Equation

Explanation of Reference Numerals

[0128] 1 Light source 2 Sub-scanning aperture (incident optical system) 3 Anamorphic collimator (incident optical system) 4 Main-scanning aperture (incident optical system) 6 Deflector 8 BD sensor (detector) 11 Imaging optical system 53 Printer controller 100 Optical scanning device

Claims

1. A light source, a deflector having a plurality of deflection surfaces that deflect a light beam from the light source and scan a surface to be scanned in a main scanning direction, a driving unit that rotationally drives the deflector, an imaging optical system that guides the light beam deflected by the deflector to the surface to be scanned, a detector that detects the light beam deflected by the deflector, a control unit that identifies the deflection surface based on detection by the detector and controls emission of the light beam from the light source for each deflection surface, comprising: the plurality of deflection surfaces include two or more deflection surfaces having different distances from the rotation center, the deflector has a shaft fitting portion into which a rotation shaft of the driving unit fits in a region including the rotation center, and a shape of a cross section perpendicular to the rotation shaft of the shaft fitting portion has two or more straight portions that contact the rotation shaft, and an optical scanning device characterized by this.

2. Among the plurality of deflection surfaces, when a difference in distance from the rotation center between two adjacent deflection surfaces is δ, an incident angle to the deflection surface when the light beam from the light source deflected by the deflection surface of the deflector enters the detector is α, a clock frequency indicating a detection period of the detector is M (Hz), a rotation speed of the driving unit is R (rpm), and a distance from the deflection surface to the detector is L, 【Number 1】 the optical scanning device according to claim 1, characterized by satisfying the following conditions.

3. Among the plurality of deflection surfaces, when a difference between a maximum value and a minimum value of the distance from the rotation center to the deflection surface is δ′, an incident angle to the deflection surface when the light beam from the light source reflected by the deflection surface of the deflector enters the detector is α, a clock frequency indicating a detection period of the detector is M (Hz), a rotation speed of the driving unit is R (rpm), and a distance from the deflection surface to the detector is L, 【Number 2】 the optical scanning device according to claim 1, characterized by satisfying the following conditions.

4. the light source is a multi-beam light source capable of emitting a plurality of light beams, the control unit performs the identification using, among the plurality of light beams, the light beam having the largest incident angle to the deflection surface when the light beam enters the detector, and the optical scanning device according to claim 1, characterized by this.

5. the optical scanning device according to any one of claims 1 to 4, characterized in that the rotation shaft and the shaft fitting portion are configured to contact two sides of the polygon.

6. a bisector of an angle formed by two adjacent sides of the polygon is parallel to a normal line of one of the deflection surfaces of the deflector, The optical scanning device according to claim 1, wherein the rotating shaft is in contact with the two sides of the shaft fitting portion.

7. The optical scanning device according to claim 1, wherein the control unit specifies the deflection plane based on a time difference between detection signals continuously detected by the detector.

8. The optical scanning device according to claim 1, wherein the control unit controls the emission timing of the light beam from the light source based on at least one of temperature and information on the time after the start of driving of the driving unit.

9. The optical scanning device according to claim 1, wherein the deflector is formed such that the plurality of deflection planes form a regular polygon.

10. The optical scanning device according to claim 9, wherein the deflector and the rotating shaft are fixed to each other such that the center of the rotating shaft of the driving unit is at a position different from the center of a circle inscribed in the regular polygon.

11. The optical scanning device according to claim 1, wherein the control unit controls the emission of the light beam from the light source so as to adjust the writing position of an image in the main scanning direction for each deflection plane.

12. The optical scanning device according to claim 1, wherein the control unit controls the emission of the light beam from the light source so as to adjust a magnification according to the position in the main scanning direction for each deflection plane.

13. The optical scanning device according to claim 1, wherein the control unit controls the light quantity of the light beam from the light source for each deflection plane.

14. The optical scanning device according to claim 1, comprising an incident optical system that guides the light beam from the light source to the deflector, wherein the width of the light beam in the main scanning direction incident on the deflector from the incident optical system is wider than the width of the deflection plane in the main scanning direction.

15. The optical scanning device according to claim 1, wherein no optical element is arranged in the optical path from the deflector to the detector.

16. The optical scanning device according to claim 1, wherein the control unit specifies the deflection plane when the driving unit is started.

17. An image forming apparatus comprising: the optical scanning device according to any one of claims 1 to 16; a developing device that develops an electrostatic latent image formed on the surface to be scanned by the optical scanning device into a toner image; a transfer device that transfers the developed toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material.

18. An image forming apparatus comprising: the optical scanning device according to any one of claims 1 to 16; 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