Image forming apparatus

Abstract

To provide an image forming apparatus that can easily detect displacement of a member in a plurality of directions.SOLUTION: An image forming apparatus according to the present invention comprises: a deflector that deflects a first light beam from a first light source and scans a first surface to be scanned in a main scanning direction; a first image forming optical system that guides the first light beam deflected by the deflector to the first surface to be scanned; a first reflection optical element that reflects the first light beam deflected by the deflector and not reaching the first surface to be scanned; a first light receiving element that receives the first light beam reflected by the first reflection optical element; a first light blocking member that blocks part of the first light beam incident on the first reflection optical element; a second light blocking member that blocks part of the first light beam reflected by the first reflection optical element; a first holding member that holds one of the first and second light blocking members and the first reflection optical element; and a second holding member that holds the other of the first and second light blocking members.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a laser beam printer (LBP), a digital copying machine, or a multifunction printer (MFP).

Background Art

[0002] Conventionally, in an image forming apparatus, it has been required to detect displacement of members such as a developer storage unit. Patent Document 1 discloses an image forming apparatus having an embodiment in which a holding member that holds a light shielding member that shields a part of detection light that scans the reflection surface of a reflection member by an optical scanning device is integrally formed in a developer storage unit.

[0003] And in the said embodiment, the displacement of the said light shielding member in at least one of the main scanning direction and the sub-scanning direction, namely the displacement of the said developer storage unit, is detected from the change in the light reception timing in the light reception element of the said detection light reflected by the said reflection member. Patent Document 1 also discloses an embodiment in which displacement of the developer storage unit in a direction perpendicular to the main scanning direction and the sub-scanning direction is detected from a change in the amount of received light of the detection light in the light receiving element.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, Patent Document 1 discloses an image forming apparatus having an embodiment for detecting displacement of a developer storage unit in at least one of the main scanning direction and the sub-scanning direction, and an embodiment for detecting displacement of the developer storage unit in a direction perpendicular to the main scanning direction and the sub-scanning direction. Therefore, by providing the configurations in both embodiments in the image forming apparatus, it is possible to detect the displacement of the developer storage unit in each of the main scanning direction and the direction perpendicular to the main scanning direction and the sub-scanning direction. However, in that case, the structure becomes complicated.

[0006] Therefore, an object of the present invention is to provide an image forming apparatus capable of easily detecting the displacement of a member in each of a plurality of directions.

Means for Solving the Problems

[0007] The image forming apparatus according to the present invention includes a deflector that deflects a first light beam from a first light source and scans a first scanned surface in a main scanning direction, a first imaging optical system that guides the first light beam deflected by the deflector to the first scanned surface, a first reflection optical element that reflects the first light beam deflected by the deflector and not reaching the first scanned surface, a first light receiving element that receives the first light beam reflected by the first reflection optical element, a first light shielding member that shields a part of the first light beam incident on the first reflection optical element, a second light shielding member that shields a part of the first light beam reflected by the first reflection optical element, a first holding member that holds one of the first and second light shielding members and the first reflection optical element, and a second holding member that holds the other of the first and second light shielding members.

Effects of the Invention

[0008] According to the present invention, it is possible to provide an image forming apparatus capable of easily detecting the displacement of a member in each of a plurality of directions.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 17

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the image forming apparatus 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.

[0011] 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 optical system (the direction in which the surface to be scanned is optically scanned by the deflection plane). 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. Therefore, in the following description, it should be noted that the main scanning direction and the sub-scanning cross-section are different between the incident optical system 75 and the imaging optical system 85. In the following, a direction parallel to the optical axis of the imaging optical system 85 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] [First Embodiment] FIG. 1 shows a sub-scanning cross-sectional view of the main part of the image forming apparatus 504 according to the first embodiment.

[0013] The image forming apparatus 504 according to the present embodiment is, for example, an electrophotographic printer, and code data Dc output from an external device 517 such as a personal computer is input. Then, the input code data Dc is converted into image data (dot data) Di by a printer controller 511 in the image forming apparatus 504 according to the present embodiment.

[0014] Next, the converted image data Di is input to an optical scanning device 500, and an optical beam (light beam) 503 modulated according to the input image data Di is emitted from the optical scanning device 500. Then, the photosensitive surface of the photosensitive drum 501 is scanned in the main scanning direction by the emitted optical beam 503.

[0015] The photosensitive drum 501, which is an electrostatic latent image carrier (photosensitive member), is rotated by a motor 515. As the photosensitive drum 501 rotates, its photosensitive surface moves in a sub-scanning direction perpendicular to the main scanning direction with respect to the light beam 503.

[0016] Above the photosensitive drum 501, a charging roller 502 for uniformly charging the surface of the photosensitive drum 501 is provided so as to contact the surface. And the surface of the photosensitive drum 501 charged by the charging roller 502 is irradiated with a light beam 503 scanned by the optical scanning device 500.

[0017] As described above, the light beam 503 is modulated based on the image data Di, and an electrostatic latent image is formed on the surface of the photosensitive drum 501 by irradiating the light beam 503. And the formed electrostatic latent image is developed into a toner image by a developing device 507 disposed so as to contact the photosensitive drum 501 on the downstream side in the rotational cross section of the photosensitive drum 501 with respect to the irradiation position of the light beam 503.

[0018] Next, the toner image developed by the developing device 507 is transferred onto a sheet of paper 512, which is a material to be transferred, by a transfer roller (transfer device) 508 disposed so as to face the photosensitive drum 501 below the photosensitive drum 501. The sheet of paper 512 is stored in a paper cassette 509 in front of (right side in FIG. 1) the photosensitive drum 501, but it is also possible to feed the paper manually.

[0019] A paper feed roller 510 is disposed at the end of the paper cassette 509, and the sheet of paper 512 in the paper cassette 509 is fed into the conveyance path. And the sheet of paper 512 onto which the unfixed toner image has been transferred as described above is further conveyed to a fixing device behind (left side in FIG. 1) the photosensitive drum 501.

[0020] The fixing device is composed of a fixing roller 513 having a fixing heater (not shown) inside and a pressure roller 514 disposed so as to be in pressure contact with the fixing roller 513. Then, the sheet 512 conveyed from the transfer roller 508 is heated while being pressed at the pressure contact portion between the fixing roller 513 and the pressure roller 514, so that the unfixed toner image on the sheet 512 is fixed.

[0021] Further, a paper discharge roller 516 is disposed behind the fixing device, and the fixed sheet 512 is discharged to the outside of the image forming apparatus 504 according to the present embodiment. Although not shown in FIG. 1, the printer controller 511 controls not only the above-described data conversion but also each component in the image forming apparatus 504 including the motor 515 and components such as the polygon motor in the optical scanning device 500.

[0022] Further, in the image forming apparatus 504 according to the present embodiment, a first light shielding member 108 (FIG. 2) and a reflection optical element 109 (first reflection optical element) for detecting the displacement of the developing device 507 are provided, as will be described in detail later. Specifically, the first light shielding member 108 and the reflection optical element 109 are coupled to the housing of the developing device 507, and are specifically held by a holding member 114 (FIG. 4) that is integrally formed with the housing of the developing device 507.

[0023] FIG. 2 shows a schematic main scanning cross-sectional view of the optical scanning device 500 provided in the image forming apparatus 504 according to the present embodiment. The optical scanning device 500 includes a light source 101 (first light source), a first aperture stop 102, an anamorphic collimator lens 103, a second aperture stop 104, and a deflector 105.

[0024] The optical scanning device 500 further includes a first fθ lens 106, a second fθ lens 107, a second light shielding member 110, an imaging unit 111, and a light receiving element 112 (first light receiving element). The arrow shown in FIG. 2 indicates the traveling direction of the light beam in the optical path between the light source 101 and the light receiving element 112.

[0025] In the optical scanning device 500, an incident optical system 75 is formed by a first aperture stop 102, an anamorphic collimator lens 103, and a second aperture stop 104. Also, in the optical scanning device 500, an imaging optical system 85 (first imaging optical system) is formed by a first fθ lens 106 and a second fθ lens 107.

[0026] As the light source 101, a semiconductor laser or the like is used, and emits a light beam (first light beam) toward the deflector 105. The first aperture stop 102 regulates the light beam diameter in the sub-scanning cross-section of the light beam emitted from the light source 101.

[0027] The anamorphic collimator lens 103 converts the light beam that has passed through the first aperture stop 102 into a parallel light beam in the main scanning cross-section. Here, the parallel light beam includes not only a strictly parallel light beam but also a substantially parallel light beam such as a weakly divergent light beam or a weakly convergent light beam. Also, the anamorphic collimator lens 103 has a finite power (refractive power) in the sub-scanning cross-section, and converges the light beam that has passed through the first aperture stop 102 in the sub-scanning direction.

[0028] The second aperture stop 104 regulates the light beam diameter in the main scanning cross-section of the light beam that has passed through the anamorphic collimator lens 103. In this way, the light beam emitted from the light source 101 is converged only in the sub-scanning direction in the vicinity of the deflector 105, and a long line image is formed in the main scanning direction.

[0029] The deflector 105 scans the surface to be scanned 113 (first surface to be scanned) in the main scanning direction by deflecting the incident light beam while rotating by driving means such as a motor (not shown). Note that as the deflector 105, a rotating polygon mirror having four deflection surfaces, that is, having a regular square shape, is used.

[0030] The first fθ lens 106 and the second fθ lens 107 are anamorphic imaging optical elements having different powers in the main scanning cross-section and the sub-scanning cross-section. The first fθ lens 106 and the second fθ lens 107 guide the scanning light beam deflected by the deflector 105, that is, the light beam deflected at a scanning angle included in the first range by the deflector 105, to the surface to be scanned 113. The first fθ lens 106 and the second fθ lens 107 also guide the light beam deflected at a first angle not included in the first range by the deflector 105 to the reflection optical element 109.

[0031] The first light shielding member 108 shields a part of the light beam incident on the reflection optical element 109. The reflection optical element 109 reflects the light beam deflected at a first angle not included in the first range by the deflector 105, in other words, the light beam deflected by the deflector 105 and not reaching the surface to be scanned 113, so as to return it to the deflector 105. The second light shielding member 110 shields a part of the light beam reflected by the reflection optical element 109.

[0032] The imaging means 111 is means for condensing the light beam reflected so as to return by the reflection optical element 109 and then deflected again by the deflector 105 in the vicinity of the light receiving element 112, and is formed by, for example, a convex lens. The light receiving element 112 is means for receiving the light beam that has passed through the imaging means 111, and is formed by, for example, a photodiode.

[0033] In the optical scanning device 500, the light beam emitted from the light source 101 is guided to the deflector 105 by the incident optical system 75. The scanning light beam deflected by the deflector 105 is guided to the surface to be scanned 113 by the imaging optical system 85. When the deflector 105 rotates in the direction indicated by the arrow B in FIG. 2, the scanning light beam deflected by the deflector 105 scans on the surface to be scanned 113 in the main scanning direction in the direction indicated by the arrow S in FIG. 2.

[0034] The light beam deflected in a predetermined direction by the deflector 105 passes through the first fθ lens 106 and the second fθ lens 107, and then enters the reflection optical element 109 from a direction perpendicular to the two-dimensional plane described later of the reflection optical element 109 within the main scanning cross-section. The light beam reflected by the reflection optical element 109 passes through the second fθ lens 107 and the first fθ lens 106 again, and is deflected again by the deflector 105, so that it is guided to the light receiving element 112 by the imaging means 111.

[0035] Next, the features of the image forming apparatus 504 according to the present embodiment will be described. FIGS. 3(a), (b) and (c) show a front view of the reflection optical element 109 provided in the image forming apparatus 504 according to the present embodiment, a cross-sectional view taken along line A-A in FIG. 3(a), and a cross-sectional view taken along line B-B in FIG. 3(a), respectively. FIG. 3(d) shows an enlarged front view of the reflection portion 109p forming the reflection optical element 109 provided in the image forming apparatus 504 according to the present embodiment.

[0036] As shown in FIG. 3(a), the reflection optical element 109 provided in the image forming apparatus 504 according to the present embodiment has a plurality of reflection portions 109p arranged two-dimensionally. As shown in FIG. 3(a), two directions orthogonal to each other in a cross-section (first cross-section) parallel to the two-dimensional plane in which the reflection portions 109p are arranged are defined as the y direction (first direction) and the z direction, and the direction perpendicular to the cross-section is defined as the x direction (second direction). Also, the two-dimensional plane of the reflection optical element 109 can be defined as the broad sense reflection surface of the reflection optical element 109. In FIGS. 3(a) and (d), solid lines indicate ridges and dotted lines indicate valleys.

[0037] Specifically, as shown in FIG. 3(d), the reflection portion 109p has a first reflection surface 1091, a second reflection surface 1092, a third reflection surface 1093, a fourth reflection surface 1094, a fifth reflection surface 1095, and a sixth reflection surface 1096. As shown in FIG. 3(d), in the reflection part 109p, the first to third reflecting surfaces 1091 to 1093 and the fourth to sixth reflecting surfaces 1094 to 1096 respectively form concave spaces that reflect the incident light beam. However, when an internally reflecting element is used, the same effect can be obtained even if it has a reverse convex shape.

[0038] As shown in FIG. 3(d), the first reflecting surface 1091 and the second reflecting surface 1092 are in contact with each other so as to form a ridge line 109a (the first ridge line). Also, the second reflecting surface 1092 and the third reflecting surface 1093 are in contact with each other so as to form a ridge line 109b (the second ridge line).

[0039] Also, the third reflecting surface 1093 and the first reflecting surface 1091 are in contact with each other so as to form a ridge line 109c (the third ridge line). Furthermore, the third reflecting surface 1093 and the sixth reflecting surface 1096 are in contact with each other so as to form a ridge line 109d.

[0040] Also, the fourth reflecting surface 1094 and the fifth reflecting surface 1095 are in contact with each other so as to form a ridge line 109e (the fourth ridge line). Also, the fifth reflecting surface 1095 and the sixth reflecting surface 1096 are in contact with each other so as to form a ridge line 109f (the fifth ridge line). Also, the sixth reflecting surface 1096 and the fourth reflecting surface 1094 are in contact with each other so as to form a ridge line 109g (the sixth ridge line).

[0041] The light beam incident on the reflective optical element 109 is reflected once by each of the first to third reflecting surfaces 1091 to 1093 or each of the fourth to sixth reflecting surfaces 1094 to 1096. In this way, the traveling directions of the incident light beam to the reflective optical element 109 and the emitted light beam from the reflective optical element 109 are non-parallel to each other within the main scanning cross section as shown in FIG. 2.

[0042] Here, the unit vectors of the normal lines of the first reflecting surface 1091, the second reflecting surface 1092, and the third reflecting surface 1093 (hereinafter referred to as unit normal vectors) are n 1091 , n 1092 , and n 1093 . Also, the unit normal vectors of the fourth reflecting surface 1094, the fifth reflecting surface 1095, and the sixth reflecting surface 1096 are n 1094 , n 1095 , and n 1096 . At this time, the unit normal vectors n 1091 , n 1092 , and n 1093 , n 1094 , n 1095 , and n 1096 of the reflective optical element 109 provided in the image forming apparatus 504 according to this embodiment are each represented as shown in Table 1 below.

[0043]

Table 1

[0044] Also, the inner product of the unit normal vector n 1091 of the first reflecting surface 1091 and the unit normal vector n 1092 of the second reflecting surface 1092 is denoted as S1. The inner product of the unit normal vector n 1091 of the first reflecting surface 1091 and the unit normal vector n 1093 of the third reflecting surface 1093 is denoted as T1. The inner product of the unit normal vector n 1092 of the second reflecting surface 1092 and the unit normal vector n 1093 of the third reflecting surface 1093 is denoted as U1.

[0045] Also, the inner product of the unit normal vector n 1094 of the fourth reflecting surface 1094 and the unit normal vector n 1095 of the fifth reflecting surface 1095 is denoted as S2. The inner product of the unit normal vector n 1094 of the fourth reflecting surface 1094 and the unit normal vector n 1096The inner product with is represented as T2. Unit normal vector n of the fifth reflecting surface 1095 1095 and the unit normal vector n of the sixth reflecting surface 1096 1096 The inner product with is represented as U2. At this time, the inner products S1, T1, U1, S2, T2, and U2 in the reflective optical element 109 provided in the image forming apparatus 504 according to the present embodiment are respectively represented as in Table 2 below.

[0046]

Table 2

[0047] Also, the absolute values of the inner products S1, T1, U1, S2, T2, and U2 are represented as |S1|, |T1|, |U1|, |S2|, |T2|, and |U2|, respectively. At this time, in the image forming apparatus 504 according to the present embodiment, it is preferable that the following conditional expressions (1), (2), (3), and (4) are satisfied.

[0048]

Equation

Equation

Equation

Equation

[0049] When the value exceeds the upper limit in at least one of the conditional expressions (1), (2), (3), and (4), the light beam is emitted from the reflective optical element 109 in a direction with an angle that is too large with respect to the incident direction of the light beam to the reflective optical element 109. Therefore, it becomes difficult to efficiently make the light beam enter the light receiving element 112.

[0050] On the other hand, the values in the conditional expressions (1) and (2) do not fall below the lower limit values. Further, when the value becomes equal to or less than the lower limit value in at least one of conditional expressions (3) and (4), the light beam is emitted from the reflection optical element 109 in a direction where the angle with respect to the incident direction of the light beam on the reflection optical element 109 is too small. Therefore, it becomes difficult to efficiently make the light beam enter the light receiving element 112.

[0051] Also, the angle formed by the normal line of the first reflection surface 1091 and the normal line of the second reflection surface 1092 is represented as θ1 (°), and the angle formed by the normal line of the second reflection surface 1092 and the normal line of the third reflection surface 1093 is represented as θ2 (°). The angle formed by the normal line of the third reflection surface 1093 and the normal line of the first reflection surface 1091 is represented as θ3 (°), and the angle formed by the normal line of the fourth reflection surface 1094 and the normal line of the fifth reflection surface 1095 is represented as θ4 (°).

[0052] The angle formed by the normal line of the fifth reflection surface 1095 and the normal line of the sixth reflection surface 1096 is represented as θ5 (°), and the angle formed by the normal line of the sixth reflection surface 1096 and the normal line of the fourth reflection surface 1094 is represented as θ6 (°). At this time, the angles θ1, θ2, θ3, θ4, θ5, and θ6 in the reflection optical element 109 provided in the image forming apparatus 504 according to the present embodiment are respectively represented as shown in Table 3 below.

[0053]

Table 3

[0054] As shown in Table 3, in the reflection optical element 109 provided in the image forming apparatus 504 according to the present embodiment, the two surface normal lines are not perpendicular to each other between the first to third reflection surfaces 1091 to 1093. Similarly, between the fourth to sixth reflection surfaces 1094 to 1096, the two surface normal lines are not perpendicular to each other.

[0055] Since the reflective optical element 109 has the above configuration, light beams are emitted from the reflective optical element 109 at an angle of ±2.6° with respect to the incident light beam in the main scanning cross-section and in the opposite direction to the incident light beam in the same direction in the sub-scanning cross-section. As a result, as shown in FIG. 2, the light beam reflected by the reflective optical element 109 passes through the second fθ lens 107, the first fθ lens 106, and the deflector 105 again, and passes through the imaging means 111, so that the light can be efficiently guided to the light receiving element 112. That is, in the image forming apparatus 504 according to the present embodiment, by using the reflective optical element 109 having the above configuration, even if the posture of the reflective optical element 109 changes, the light beam can be accurately guided to the light receiving element 112.

[0056] FIG. 4 shows a partially enlarged schematic main scanning cross-sectional view of the image forming apparatus 504 according to the present embodiment. As shown in FIG. 4, in the image forming apparatus 504 according to the present embodiment, the first light shielding member 108 restricts the light beam incident on the reflective optical element 109, that is, shields a part of the light beam. Thereby, the light reception start timing (the first light reception start time) of the light beam incident on the light receiving element 112 is determined. Further, the second light shielding member 110 restricts the light beam reflected by the reflective optical element 109, that is, shields a part of the light beam, thereby determining the light reception end timing (the first light reception end time) of the light beam incident on the light receiving element 112.

[0057] As shown in FIG. 4, in the image forming apparatus 504 according to the present embodiment, the reflective optical element 109 and the first light shielding member 108 are held by a holding member 114 (the first holding member). On the other hand, the second light shielding member 110 is held by a holding member (the second holding member) not shown, which is different from the holding member 114.

[0058] In the image forming apparatus 504 according to the present embodiment, while the holding member 114 is provided outside the optical scanning device 500, the holding member not shown is provided inside the optical scanning device 500. Specifically, while the holding member 114 is integrally formed with the housing of the developing device 507, the holding member (not shown) is coupled to the housing of the optical scanning device 500, specifically, is integrally formed with the housing of the optical scanning device 500.

[0059] Further, in the optical scanning device 500, a synchronization detection means (second light receiving element) (not shown) including a light receiving element that receives a light beam deflected at a second angle not included in the first range by the deflector 105 is provided. Then, based on the synchronization detection by the synchronization detection means, the position serving as a reference for the rotation phase of the deflector 105, that is, the reference time can be determined.

[0060] FIG. 5 shows a partially enlarged schematic main scanning cross-sectional view in the vicinity of the reflection optical element 109 of the image forming apparatus 504 according to the present embodiment. Specifically, FIG. 5 illustrates a method for detecting the displacement of the holding member 114 that holds the first light shielding member 108 and the reflection optical element 109 in the y direction.

[0061] In FIG. 5, when the holding member 114 is not displaced in the y direction (hereinafter referred to as the normal state), the light beams incident on the first light shielding member 108, the reflection optical element 109, and the light beam emitted from the reflection optical element 109 are shown by solid lines. Further, when the holding member 114 is displaced on the minus side in the y direction (hereinafter referred to as the minus side displacement state), the light beams incident on the first light shielding member 108, the reflection optical element 109, and the light beam emitted from the reflection optical element 109 are shown by broken lines.

[0062] Also, when the holding member 114 is displaced on the plus side in the y direction (hereinafter referred to as the plus side displacement state), the light beams incident on the first light shielding member 108, the reflection optical element 109, and the light beam emitted from the reflection optical element 109 are shown by one-dot chain lines. Note that the minus side and the plus side in the y direction substantially correspond to the minus side and the plus side in the main scanning direction (Y direction) of the scanned surface 113 indicated by the arrow S in FIG. 2, respectively.

[0063] Figures 6(a), 6(b), and 6(c) schematically show the time variations of the monitor voltage detected by the light receiving element 112 in the normal state, the minus-side displacement state, and the plus-side displacement state in the y direction, respectively. Note that the waveforms indicated by the solid line, the broken line, and the one-dot chain line in FIGS. 6(a), 6(b), and 6(c) respectively show the time variations of the monitor voltage detected by the light receiving element 112 in the normal state, the minus-side displacement state, and the plus-side displacement state in the y direction. Also, the waveforms indicated by the dotted line in FIGS. 6(a), 6(b), and 6(c) respectively show the time variations of the monitor voltage detected by synchronous detection means (not shown).

[0064] As shown in FIGS. 6(a), 6(b), and 6(c), the monitor voltage increases when the light receiving of the light beam starts in each of the light receiving element 112 and the synchronous detection means (not shown), and returns to the original value when the light receiving ends. And in each of FIGS. 6(a), 6(b), and 6(c), the time difference between the reference time by the synchronous detection means, that is, the light receiving start timing of the light beam (the second light receiving start time), and the light receiving start timing of the light beam by the light receiving element 112 is determined as Δt1, Δt1-, and Δt1+.

[0065] Specifically, as shown in FIG. 6(b), when the holding member 114 is displaced to the minus side in the y direction, the light receiving start timing of the light beam by the light receiving element 112 becomes earlier. On the other hand, as shown in FIG. 6(c), when the holding member 114 is displaced to the plus side in the y direction, the light receiving start timing of the light beam by the light receiving element 112 becomes later.

[0066] Therefore, a relationship of Δt1+ > Δt1 > Δt1- is obtained among the time differences Δt1, Δt1-, and Δt1+. That is, the time difference changes according to the displacement of the holding member 114 that holds the first light shielding member 108 and the reflection optical element 109 in the y direction. Therefore, a control unit (not shown) can detect the displacement in the y direction of the holding member 114, that is, the reflective optical element 109, from the time difference.

[0067] FIG. 7 shows a partially enlarged schematic main scanning cross-sectional view of the image forming apparatus 504 according to the present embodiment. Specifically, FIG. 7 explains a method of detecting the displacement in the x direction of the reflective optical element 109.

[0068] In FIG. 7, the reflective optical element 109, the light beam incident on the reflective optical element 109, and the light beam emitted from the reflective optical element 109 when the holding member 114 is in the normal state in the x direction are shown by solid lines. Further, the reflective optical element 109, the light beam incident on the reflective optical element 109, and the light beam emitted from the reflective optical element 109 when the holding member 114 is in the minus-side displacement state in the x direction are shown by broken lines.

[0069] Also, the reflective optical element 109, the light beam incident on the reflective optical element 109, and the light beam emitted from the reflective optical element 109 when the holding member 114 is in the plus-side displacement state in the x direction are shown by alternate long and short dash lines. Note that the minus side and the plus side in the x direction substantially correspond to the minus side and the plus side in the X direction parallel to the optical axis of the imaging optical system 85, respectively.

[0070] FIGS. 8(a), (b), and (c) schematically show the time changes of the monitor voltage detected by the light receiving element 112 in the normal state, the minus-side displacement state, and the plus-side displacement state in the x direction, respectively. Note that the waveforms shown by solid lines, broken lines, and alternate long and short dash lines in FIGS. 8(a), (b), and (c) show the time changes of the monitor voltage detected by the light receiving element 112 in the normal state, the minus-side displacement state, and the plus-side displacement state in the x direction, respectively.

[0071] In addition, in FIGS. 8(a), 8(b), and 8(c), the waveforms indicated by the dotted lines each show the time change of the monitor voltage detected by a synchronization detection means (not shown). In each of FIGS. 8(a), 8(b), and 8(c), the time differences between the reference time by the synchronization detection means and the light reception end timing by the light receiving element 112 are determined as Δt2, Δt2−, and Δt2+.

[0072] Specifically, as shown in FIG. 8(b), when the holding member 114 is displaced to the minus side in the x direction, the light reception end timing of the light flux by the light receiving element 112 becomes slower. On the other hand, as shown in FIG. 8(c), when the holding member 114 is displaced to the plus side in the x direction, the light reception end timing of the light flux by the light receiving element 112 becomes faster.

[0073] Therefore, a relationship of Δt2−>Δt2>Δt2+ is obtained among the time differences Δt2, Δt2−, and Δt2+. That is, the time difference changes according to the displacement in the x direction of the holding member 114 that holds the first light shielding member 108 and the reflection optical element 109. Therefore, a control unit (not shown) can detect the displacement in the x direction of the holding member 114, that is, the reflection optical element 109, from the time difference.

[0074] Here, consider a conventional image forming apparatus in which the first light shielding member 108, the reflection optical element 109, and the second light shielding member 110 are all held by a single holding member. At this time, when all of the above three are displaced by the displacement of the holding member in the y direction, both the light reception start timing by the first light shielding member 108 and the light reception end timing by the second light shielding member 110 at the light receiving element 112 change. In this case, by the change of the time difference Δt1 between the reference time by the synchronization detection means and the light reception start timing by the light receiving element 112, the displacement in the y direction of the reflection optical element 109 can be detected.

[0075] On the other hand, even if all of the above three are displaced due to the displacement of the holding member in the x direction, neither the light reception start timing by the first light shielding member 108 nor the light reception end timing by the second light shielding member 110 in the light receiving element 112 changes. Therefore, in such a conventional image forming apparatus, the displacement of the reflection optical element 109 in the x direction cannot be detected.

[0076] As described above, in the image forming apparatus 504 according to the present embodiment, while the reflection optical element 109 and the first light shielding member 108 are arranged to be displaced together with the developing device 507, the second light shielding member 110 is separately arranged so as not to be displaced together with the developing device 507. Thereby, the displacement of the developing device 507 in each of the y direction corresponding to the main scanning direction and the x direction corresponding to the optical axis direction can be detected.

[0077] That is, in the image forming apparatus 504 according to the present embodiment, it is possible to accurately detect the displacement generated in the developing device 507 regardless of the direction of the displacement. Note that in the image forming apparatus 504 according to the present embodiment, not limited to the developing device 507, the displacement of a predetermined provided member can be accurately detected regardless of the direction of the displacement.

[0078] In the image forming apparatus 504 according to the present embodiment, the first light shielding member 108 and the reflection optical element 109 are held by the holding member 114, and the second light shielding member 110 is held by a holding member (not shown), but it is not limited thereto. That is, the same effect can be achieved by holding the reflection optical element 109 and the second light shielding member 110 by the holding member 114 and holding the first light shielding member 108 by a holding member (not shown). In other words, the holding member 114 may hold one of the first light shielding member 108 and the second light shielding member 110 and the reflection optical element 109, and the other of the first light shielding member 108 and the second light shielding member 110 may be held by a holding member (not shown).

[0079] [Second Embodiment] Figs. 9(a) and (b) respectively show a schematic main scanning cross-sectional view and a partial schematic sub-scanning cross-sectional inner projection view of an optical scanning device 600 provided in the image forming apparatus according to the second embodiment. In the image forming apparatus according to the present embodiment, a light source 201, a first light shielding member 208, and a reflection optical element 209 are provided instead of the light source 101, the first light shielding member 108, and the reflection optical element 109 in the image forming apparatus 504 according to the first embodiment.

[0080] In addition to the above, the image forming apparatus according to the present embodiment has the same configuration as the image forming apparatus 504 according to the first embodiment, except that the arrangement of each optical element is different. Therefore, in the image forming apparatus according to the present embodiment, the same members as those in the image forming apparatus 504 according to the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[0081] Specifically, the light source 201 provided in the optical scanning device 600 included in the image forming apparatus according to the present embodiment has two light emitting points (a first light emitting point and a second light emitting point) spaced apart from each other in the main scanning direction and the sub-scanning direction, respectively. From the two light emitting points, a light beam LA (first light beam) and a light beam LB (second light beam) are emitted toward the same deflection plane of the deflector 105. In the image forming apparatus according to the present embodiment, the light beams LA and LB deflected in a predetermined direction by the deflector 105 are made incident on the reflection optical element 209 from a direction non-perpendicular to the two-dimensional plane of the reflection optical element 209 within the main scanning cross-section.

[0082] That is, in the image forming apparatus according to the present embodiment, the light beams LA and LB are made incident on the reflection optical element 209 so as not to face the two-dimensional plane. Specifically, the incident angle is 30 degrees. As a result, as shown in Fig. 9(b), the traveling directions of the light beams LA and LB when incident on the reflection optical element 209 and the traveling directions of the light beams LA and LB when reflected by the reflection optical element 209 are non-parallel to each other within the sub-scanning cross-section. Therefore, a second light-shielding member 110 that regulates the light beams LA and LB incident on the light-receiving element 112, that is, that shields a part of the light beams LA and LB, can be arranged so as not to shield the light beams LA and LB traveling on the scanned surface 113.

[0083] Further, the reflection optical element 209 has the same configuration as that shown in Tables 1 to 3 of the reflection optical element 109 provided in the image forming apparatus 504 according to the first embodiment. That is, in the image forming apparatus according to the present embodiment, the conditional expressions (1) to (4) are satisfied.

[0084] FIGS. 10(a), (b), and (c) show a partially enlarged schematic perspective view, a partially enlarged schematic main scanning cross-sectional view, and a partially enlarged schematic front view of the image forming apparatus according to the present embodiment, respectively. As shown in FIG. 10(a), in the image forming apparatus according to the present embodiment, the first light-shielding member 208 is provided on the reflection surface of the reflection optical element 209.

[0085] That is, in the image forming apparatus according to the present embodiment, miniaturization can be achieved by integrally forming the reflection optical element 209 and the first light-shielding member 208 with each other. And as shown in FIGS. 10(a) and (c), the edge portion 2081 of the first light-shielding member 208, that is, the end portion of the first light-shielding member 208 on the second light-shielding member 110 side in the y direction, has a substantially parabolic shape along the z direction.

[0086] Also, as shown in FIG. 10(b), the first light-shielding member 208 regulates the light beams LA and LB incident on the reflection optical element 209, that is, by shielding a part of the light beams LA and LB, the light reception start timing of the light beams LA and LB incident on the light-receiving element 112 is determined. On the other hand, the second light-shielding member 110 regulates the light beams LA and LB reflected by the reflection optical element 209, that is, by shielding a part of the light beams LA and LB, the light reception end timing of the light beams LA and LB incident on the light-receiving element 112 is determined.

[0087] In the image forming apparatus according to the present embodiment, since the first light shielding member 208 is disposed on the incident surface of the reflection optical element 209, the first light shielding member 208 will be displaced following the reflection optical element 209 when the reflection optical element 209 is displaced. As shown in FIG. 10(c), light beams LA and LB emitted from two light emitting points separated from each other in the main scanning direction and the sub-scanning direction of the light source 201 are displaced from each other in the main scanning direction and the sub-scanning direction, respectively, and scan the reflection surface of the reflection optical element 209 in the y direction.

[0088] FIGS. 11(a), (b), and (c) respectively show partially enlarged schematic front views in the vicinity of the reflection optical element 209 of the image forming apparatus according to the present embodiment. Specifically, FIGS. 11(a), (b), and (c) illustrate a method of detecting the displacement of the reflection optical element 209 in the z direction.

[0089] In FIG. 11(a), the light beams LA and LB that scan the reflection optical element 209 when the reflection optical element 209 is not displaced in the z direction (hereinafter referred to as the normal state) are shown by solid lines. In this case, the light beams LA and LB scan a region substantially in the center of the reflection surface of the reflection optical element 209 in the z direction.

[0090] In FIG. 11(b), the light beams LA and LB that scan the reflection optical element 209 when the reflection optical element 209 is displaced on the minus side in the z direction (hereinafter referred to as the minus side displacement state) are shown by broken lines. In this case, the light beams LA and LB scan a region on the plus side of the reflection surface of the reflection optical element 209 in the z direction.

[0091] In FIG. 11(c), the light beams LA and LB that scan the reflection optical element 209 when the reflection optical element 209 is displaced on the plus side in the z direction (hereinafter referred to as the plus side displacement state) are shown by one-dot chain lines. In this case, the light beams LA and LB scan the minus-side region in the z direction of the reflecting surface of the reflecting optical element 209. Here, the minus side and plus side in the z direction respectively correspond to the minus side and plus side in the sub-scanning direction (Z direction).

[0092] FIGS. 12(a), (b) and (c) schematically show the time variations of the monitor voltages detected by the light-receiving element 112 in the normal state, minus-side displacement state and plus-side displacement state in the z direction, respectively. In FIGS. 12(a), (b) and (c), the waveforms indicated by the solid line, broken line and one-dot chain line respectively show the time variations of the monitor voltages detected by the light-receiving element 112 in the normal state, minus-side displacement state and plus-side displacement state in the z direction. Also, in FIGS. 12(a), (b) and (c), the waveforms indicated by the dotted line show the time variations of the monitor voltages detected by synchronous detection means (not shown).

[0093] As shown in FIGS. 12(a), (b) and (c), after the monitor voltage increases when the light-receiving of the light beam LA incident on the light-receiving element 112 starts first, the monitor voltage further increases when the light-receiving of the light beam LB also starts. Then, after the monitor voltage decreases when the light-receiving of the light beam LA ends, the monitor voltage returns to its original value when the light-receiving of the light beam LB also ends. At this time, in FIGS. 12(a), (b) and (c), the time difference between the light-receiving start timing (first light-receiving start time) of the light beam LA and the light-receiving start timing (third light-receiving start time) of the light beam LB at the light-receiving element 112 is determined as Δt3, Δt3− and Δt3+.

[0094] Specifically, as shown in FIG. 11(b), when the reflecting optical element 209 is displaced to the minus side in the z direction, the light beams LA and LB scan the plus-side region in the z direction of the reflecting surface of the reflecting optical element 209. At this time, since the edge portion 2081 of the first light shielding member 208 has a substantially parabolic shape along the z direction as described above, the time difference Δt3− between the light reception start timing of the light beam LA and the light reception start timing of the light beam LB in the light receiving element 112 increases.

[0095] On the other hand, as shown in FIG. 11(c), when the reflection optical element 209 is displaced to the plus side in the z direction, the light beams LA and LB will scan the minus side region in the z direction of the reflection surface of the reflection optical element 209. At this time, since the edge portion 2081 of the first light shielding member 208 has a substantially parabolic shape along the z direction as described above, the time difference Δt3+ between the light reception start timing of the light beam LA and the light reception start timing of the light beam LB in the light receiving element 112 decreases.

[0096] Therefore, a relationship of Δt3− > Δt3 > Δt3+ can be obtained among the time differences Δt3, Δt3−, and Δt3+. That is, the time difference changes according to the displacement of the first light shielding member 208 and the reflection optical element 209 in the z direction. Therefore, a control unit (not shown) can detect the displacement of the reflection optical element 209 in the z direction from the time difference.

[0097] As described above, in the image forming apparatus according to the present embodiment, while the reflection optical element 209 and the first light shielding member 208 are arranged to be displaced together with the developing device 507, the second light shielding member 110 is separately arranged so as not to be displaced together with the developing device 507. Thereby, the displacement of the developing device 507 in each of the y direction corresponding to the main scanning direction and the x direction corresponding to the optical axis direction can be detected.

[0098] In addition, in the optical scanning device 600 included in the image forming apparatus according to the present embodiment, a light source 201 is provided that emits the light beams LA and LB from two light emitting points separated from each other in the main scanning direction and the sub-scanning direction toward the same deflection surface of the deflector 105. By forming the edge portion 2081 of the first light-shielding member 208 to have a substantially parabolic shape along the z direction, the displacement of the developing device 507 in the z direction corresponding to the sub-scanning direction can also be detected.

[0099] That is, in the image forming apparatus according to the present embodiment, it is possible to accurately detect the displacement occurring in the developing device 507 regardless of the direction of the displacement. Further, in the image forming apparatus according to the present embodiment, miniaturization can be achieved by integrally forming the reflection optical element 209 and the first light-shielding member 208 with each other.

[0100] Note that in the image forming apparatus according to the present embodiment, the displacement of the developing device 507 in the z direction corresponding to the sub-scanning direction is detected by forming the edge portion 2081 of the first light-shielding member 208 to have a substantially parabolic shape along the z direction, but it is not limited thereto. That is, if the edge portion 2081 of the first light-shielding member 208 is formed to be non-parallel to the z direction in the cross section parallel to the two-dimensional surface of the reflection optical element 209, the displacement of the developing device 507 in the z direction can be detected.

[0101] For example, by forming the edge portion 2081 of the first light-shielding member 208 in the shape of a quadratic curve in the cross section of the reflection optical element 209, the displacement of the developing device 507 in the z direction can be detected. Also, by forming the edge portion 2081 of the first light-shielding member 208 to be maximum at the center in the z direction in the cross section, that is, to be convex, the displacement of the developing device 507 on each of the plus side and the minus side in the z direction can be detected.

[0102] [Third Embodiment] FIG. 13 shows a main part sub-scanning cross-sectional view of an image forming apparatus 90 according to the third embodiment.

[0103] The image forming apparatus 90 according to this embodiment is a color image forming apparatus in which the optical scanning device 700 records image information on the photosensitive surfaces of a plurality of photosensitive drums 23, 24, 25, and 26 that are image carriers. Specifically, the image forming apparatus 90 according to this embodiment includes an optical scanning device 700, developing devices 15, 16, 17, and 18, photosensitive drums 23 to 26, a conveyance belt 91, a printer controller 93, and a fixing device 94.

[0104] As shown in FIG. 13, in the image forming apparatus 90 according to this embodiment, R (red), G (green), and B (blue) color signals output from an external device 92 such as a personal computer are input. Then, the input color signals are converted into C (cyan), M (magenta), Y (yellow), and K (black) image data (dot data) by a printer controller 93 provided inside, and are input to the optical scanning device 700.

[0105] Next, light beams 19, 20, 21, and 22 modulated according to the respective image data are emitted from the optical scanning device 700, and the photosensitive surfaces of the photosensitive drums 23 to 26 are scanned in the main scanning direction by the light beams 19 to 22. In addition, a charging roller (not shown) for uniformly charging the photosensitive surfaces of the photosensitive drums 23 to 26 is provided so as to contact the photosensitive surfaces. And the photosensitive surfaces of the photosensitive drums 23 to 26 charged by the charging roller are irradiated with the light beams 19 to 22 by the optical scanning device 700.

[0106] As described above, the light beams 19 to 22 are modulated based on the respective color image data, and an electrostatic latent image is formed on the photosensitive surface of each of the photosensitive drums 23 to 26 by irradiating the light beams 19 to 22. Then, the formed electrostatic latent image is developed into a toner image by developing devices 15 to 18 disposed so as to contact the photosensitive drums 23 to 26.

[0107] Next, the toner images developed by the developing devices 15 to 18 are multi-transferred onto a sheet of paper (transfer material), not shown, which is conveyed on the conveyance belt 91 by a transfer roller (transfer device), not shown, disposed so as to face the photosensitive drums 23 to 26, and a single full-color image is formed. Then, the sheet of paper onto which the unfixed toner image has been transferred is conveyed to a fixing device 94 provided behind (on the left side in FIG. 13) the photosensitive drums 23 to 26.

[0108] The fixing device 94 is formed of a fixing roller having a fixing heater (not shown) inside and a pressure roller disposed so as to be in pressure contact with the fixing roller. Then, the sheet of paper conveyed from the transfer unit is heated while being pressed by the pressure contact portion between the fixing roller and the pressure roller, whereby the unfixed toner image on the sheet of paper is fixed. Also, a paper discharge roller, not shown, is disposed behind the fixing device 94, and the fixed sheet of paper is discharged to the outside of the image forming apparatus 90 according to this embodiment by the paper discharge roller.

[0109] In the image forming apparatus 90 according to this embodiment, each of the light beams 19 to 22 emitted from the optical scanning device 700 scans in parallel on the photosensitive surfaces of the photosensitive drums 23 to 26 corresponding to the respective colors of C (cyan), M (magenta), Y (yellow), and K (black). Then, by recording an image signal (image information) on the photosensitive surfaces of the photosensitive drums 23 to 26 respectively, a color image can be printed at high speed.

[0110] Note that, as the external device 92, for example, a color image reading device including a CCD sensor may be used. In this case, a color digital copying machine is formed by the color image reading device and the image forming apparatus 90 according to this embodiment.

[0111] Also, in the image forming apparatus 90 according to this embodiment, a first light shielding member 308a (FIG. 14) and a first reflection optical element 309a for detecting the displacement of the developing device 15 are provided as will be described in detail later. Also, in the image forming apparatus 90 according to the present embodiment, a third light shielding member 308b (FIG. 14) and a second reflection optical element 309b for detecting the displacement of the developing device 16 are provided. Also, in the image forming apparatus 90 according to the present embodiment, a fifth light shielding member 308c (FIG. 14) and a third reflection optical element 309c for detecting the displacement of the developing device 17 are provided. Also, in the image forming apparatus 90 according to the present embodiment, a seventh light shielding member 308d (FIG. 14) and a fourth reflection optical element 309d for detecting the displacement of the developing device 18 are provided.

[0112] Specifically, in the image forming apparatus 504 according to the present embodiment, the first light shielding member 308a and the first reflection optical element 309a are coupled to the housing of the developing device 15, and specifically, are held by a holding member (first holding member) not shown that is integrally formed with the housing of the developing device 15. On the other hand, the second light shielding member 310a is coupled to the housing of the optical scanning device 700, and specifically, is held by a holding member (second holding member) not shown that is integrally formed with the housing of the optical scanning device 700. Also, the third light shielding member 308b and the second reflection optical element 309b are coupled to the housing of the developing device 16, and specifically, are held by a holding member (third holding member) not shown that is integrally formed with the housing of the developing device 16. On the other hand, the fourth light shielding member 310b is coupled to the housing of the optical scanning device 700, and specifically, is held by a holding member (fourth holding member) not shown that is integrally formed with the housing of the optical scanning device 700.

[0113] Also, the fifth light shielding member 308c and the third reflection optical element 309c are coupled to the housing of the developing device 17, and specifically, are held by a holding member (fifth holding member) not shown that is integrally formed with the housing of the developing device 17. On the other hand, the sixth light shielding member 310c is coupled to the housing of the optical scanning device 700, and specifically, is held by a holding member (sixth holding member) not shown that is integrally formed with the housing of the optical scanning device 700. Further, the seventh light shielding member 308d and the fourth reflection optical element 309d are coupled to the housing of the developing device 18, specifically, held by a holding member (seventh holding member) not shown that is integrally formed with the housing of the developing device 18. On the other hand, the eighth light shielding member 310d is coupled to the housing of the optical scanning device 700, specifically, held by a holding member (eighth holding member) not shown that is integrally formed with the housing of the optical scanning device 700.

[0114] FIG. 14 shows a schematic main scanning cross-sectional developed view of the optical scanning device 700 provided in the image forming apparatus 90 according to the present embodiment. Further, FIG. 15 shows a partial schematic sub-scanning cross-sectional projection view of the optical scanning device 700 provided in the image forming apparatus 90 according to the present embodiment.

[0115] The optical scanning device 700 includes first, second, third, and fourth light sources 301a, 301b, 301c, and 301d, and first, second, third, and fourth aperture stops 302a, 302b, 302c, and 302d. Further, the optical scanning device 700 includes first, second, third, and fourth collimator lenses 3031a, 3031b, 3031c, and 3031d, and first, second, third, and fourth cylinder lenses 3032a, 3032b, 3032c, and 3032d.

[0116] Further, the optical scanning device 700 includes fifth, sixth, seventh, and eighth aperture stops 304a, 304b, 304c, and 304d, a deflector 305, and first, second, third, and fourth fθ lenses 306a, 306b, 306c, and 306d. Further, the optical scanning device 700 includes fifth, sixth, seventh, and eighth fθ lenses 307a, 307b, 307c, and 307d, and second, fourth, sixth, and eighth light shielding members 310a, 310b, 310c, and 310d. Further, the optical scanning device 700 includes an imaging means 311 and a light receiving element 312.

[0117] As the first and second light sources 301a and 301b, a semiconductor laser or the like is used, and the first and second light beams are emitted toward the first deflection surface 3051 of the deflector 305. Also, as the third and fourth light sources 301c and 301d, a semiconductor laser or the like is used, and the third and fourth light beams are emitted toward the second deflection surface 3052 of the deflector 305.

[0118] The first, second, third, and fourth aperture stops 302a, 302b, 302c, and 302d regulate the beam diameter of the first to fourth light beams emitted from the first to fourth light sources 301a to 301d within the sub-scanning cross section. The first, second, third, and fourth collimator lenses 3031a, 3031b, 3031c, and 3031d convert the first to fourth light beams that have passed through the first to fourth aperture stops 302a to 302d into parallel light beams. Here, the parallel light beams include not only strict parallel light beams but also approximately parallel light beams such as weakly divergent light beams and weakly convergent light beams.

[0119] The first, second, third, and fourth cylindrical lenses 3032a, 3032b, 3032c, and 3032d have a finite power (refractive power) within the sub-scanning cross section. And the first to fourth cylindrical lenses 3032a to 3032d condense the first to fourth light beams that have passed through the first to fourth collimator lenses 3031a to 3031d in the sub-scanning direction.

[0120] The fifth, sixth, seventh, and eighth aperture stops 304a, 304b, 304c, and 304d regulate the beam diameter of the first to fourth light beams that have passed through the first to fourth cylindrical lenses 3032a to 3032d within the main-scanning cross section. In this way, the first to fourth light beams emitted from the first to fourth light sources 301a to 301d are condensed only in the sub-scanning direction in the vicinity of the deflector 305, and a line image that is long in the main-scanning direction is formed.

[0121] In the optical scanning device 700, a first incident optical system is formed by a first aperture stop 302a, a first collimator lens 3031a, a first cylindrical lens 3032a, and a fifth aperture stop 304a. Also, in the optical scanning device 700, a second incident optical system is formed by a second aperture stop 302b, a second collimator lens 3031b, a second cylindrical lens 3032b, and a sixth aperture stop 304b. Also, in the optical scanning device 700, a third incident optical system is formed by a third aperture stop 302c, a third collimator lens 3031c, a third cylindrical lens 3032c, and a seventh aperture stop 304c. Also, in the optical scanning device 700, a fourth incident optical system is formed by a fourth aperture stop 302d, a fourth collimator lens 3031d, a fourth cylindrical lens 3032d, and an eighth aperture stop 304d.

[0122] Then, the first and second light beams emitted from the first and second light sources 301a and 301b are obliquely incident on the first deflection surface 3051 of the deflector 305 at an angle within the sub-scanning cross-section by the first and second incident optical systems. Also, the third and fourth light beams emitted from the third and fourth light sources 301c and 301d are obliquely incident on the second deflection surface 3052 of the deflector 305 at an angle within the sub-scanning cross-section by the third and fourth incident optical systems.

[0123] The first, second, third, and fourth fθ lenses 306a, 306b, 306c, and 306d are anamorphic imaging optical elements having different powers in the main scanning cross-section and the sub-scanning cross-section. Also, the fifth, sixth, seventh, and eighth fθ lenses 307a, 307b, 307c, and 307d are anamorphic imaging optical elements having different powers in the main scanning cross-section and the sub-scanning cross-section.

[0124] In the optical scanning device 700, a first imaging optical system is formed by the first fθ lens 306a and the fifth fθ lens 307a, and a second imaging optical system is formed by the second fθ lens 306b and the sixth fθ lens 307b. Further, a third imaging optical system is formed by the third fθ lens 306c and the seventh fθ lens 307c, and a fourth imaging optical system is formed by the fourth fθ lens 306d and the eighth fθ lens 307d.

[0125] In the optical scanning device 700, the first light beam deflected at a scanning angle included in the first range by the first deflection surface 3051 of the deflector 305 is guided onto the first scanned surface 313a by the first imaging optical system. Also, the second light beam (third light beam) deflected at a scanning angle included in the second range by the first deflection surface 3051 of the deflector 305 is guided onto the second scanned surface 313b by the second imaging optical system.

[0126] Also, the third light beam (fourth light beam) deflected at a scanning angle included in the third range by the second deflection surface 3052 of the deflector 305 is guided onto the third scanned surface 313c by the third imaging optical system. Also, the fourth light beam (fifth light beam) deflected at a scanning angle included in the fourth range by the second deflection surface 3052 of the deflector 305 is guided onto the fourth scanned surface 313d by the fourth imaging optical system. Then, as the deflector 305 rotates, the first to fourth light beams deflected by the deflector 305 scan the first to fourth scanned surfaces 313a to 313d in the main scanning direction.

[0127] The first and third light-shielding members 308a and 308b are deflected in a predetermined direction by the first deflection surface 3051 of the deflector 305, and after passing through the first and second imaging optical systems, block a part of the first and second light beams incident on the first and second reflection optical elements 309a and 309b. The fifth and seventh light-shielding members 308c and 308d are deflected in a predetermined direction by the second deflection surface 3052 of the deflector 305, and after passing through the third and fourth imaging optical systems, block a part of the third and fourth light beams incident on the third and fourth reflection optical elements 309c and 309d.

[0128] The first reflective optical element 309a reflects the first light beam deflected at a first angle not included in the first range by the first deflection surface 3051 of the deflector 305 so as to return it to the deflector 305. The second reflective optical element 309b reflects the second light beam deflected at a third angle not included in the second range by the first deflection surface 3051 of the deflector 305 so as to return it to the deflector 305.

[0129] The third reflective optical element 309c reflects the third light beam deflected at a fourth angle not included in the third range by the second deflection surface 3052 of the deflector 305 so as to return it to the deflector 305. The fourth reflective optical element 309d reflects the fourth light beam deflected at a fifth angle not included in the fourth range by the second deflection surface 3052 of the deflector 305 so as to return it to the deflector 305. The second, fourth, sixth, and eighth light-shielding members 310a, 310b, 310c, and 310d shield a part of the first to fourth light beams reflected by the first to fourth reflective optical elements 309a to 309d.

[0130] The imaging means 311 condenses the first and second light beams, which are reflected so as to return by the first and second reflective optical elements 309a and 309b, pass through the first and second imaging optical systems, and are deflected again by the first deflection surface 3051 of the deflector 305, in the vicinity of the light-receiving element 312. The imaging means 311 also condenses the third and fourth light beams, which are reflected so as to return by the third and fourth reflective optical elements 309c and 309d, pass through the third and fourth imaging optical systems, and are deflected again by the second deflection surface 3052 of the deflector 305, in the vicinity of the light-receiving element 312.

[0131] The light-receiving element 312 receives the first to fourth light beams that have passed through the imaging means 311. Therefore, in the optical scanning device 700, the first to fourth imaging optical systems have a function of guiding the first to fourth light beams deflected by the deflector 305 onto the first to fourth scanned surfaces 312a to 312d.

[0132] The first to fourth imaging optical systems also have a function of guiding the first to fourth light beams deflected in a predetermined direction by the deflector 305 to the first to fourth reflective optical elements 309a to 309d. In the optical scanning device 700, synchronization detection means (not shown) is provided, and based on the synchronization detection by the synchronization detection means, the position serving as the reference for the rotational phase of the deflector 305, that is, the reference time, can be determined.

[0133] The first to fourth reflective optical elements 309a to 309d provided in the image forming apparatus 90 according to the present embodiment each have the same configuration as the reflective optical element 109 provided in the image forming apparatus 504 according to the first embodiment. And in each of the first to fourth reflective optical elements 309a to 309d, the unit normal vectors of the first reflective surface 3091, the second reflective surface 3092, and the third reflective surface 3093 are represented as n 3091 , n 3092 and n 3093 respectively.

[0134] Also, the unit normal vectors of the fourth reflective surface 3094, the fifth reflective surface 3095, and the sixth reflective surface 3096 are represented as n 3094 , n 3095 and n 3096 respectively. At this time, the unit normal vectors n 3091 to n 3096 in the first to fourth reflective optical elements 309a to 309d provided in the image forming apparatus 90 according to the present embodiment are each represented as shown in Table 4 below.

[0135]

Table 4

[0136] Also, the inner products S1, T1, U1, S2, T2, U2 in the first to fourth reflective optical elements 309a to 309d provided in the image forming apparatus 90 according to the present embodiment are each represented as shown in Table 5 below.

[0137]

Table 5

[0138] Therefore, in any of the first to fourth reflective optical elements 309a to 309d provided in the image forming apparatus 90 according to the present embodiment, the above conditional expressions (1), (2), (3), and (4) are satisfied.

[0139] And the angles θ1, θ2, θ3, θ4, θ5, and θ6 in the first to fourth reflective optical elements 309a to 309d provided in the image forming apparatus 90 according to the present embodiment are respectively represented as in Table 6 below.

[0140]

Table 6

[0141] Since the first reflective optical element 309a has the above configuration, from the first reflective optical element 309a, the light beam forms an angle of ±2.6° with respect to the incident light beam in the main scanning cross section, and the light beam is emitted in the reverse direction in the same direction as the incident light beam in the sub-scanning cross section. Also, since the second reflective optical element 309b has the above configuration, from the second reflective optical element 309b, the light beam forms an angle of ±2.3° with respect to the incident light beam in the main scanning cross section, and the light beam is emitted in the reverse direction in the same direction as the incident light beam in the sub-scanning cross section.

[0142] Also, since the third reflective optical element 309c has the above configuration, from the third reflective optical element 309c, the light beam forms an angle of ±2.3° with respect to the incident light beam in the main scanning cross section, and the light beam is emitted in the reverse direction in the same direction as the incident light beam in the sub-scanning cross section. Also, since the fourth reflective optical element 309d has the above configuration, from the fourth reflective optical element 309d, the light beam forms an angle of ±2.6° with respect to the incident light beam in the main scanning cross section, and the light beam is emitted in the reverse direction in the same direction as the incident light beam in the sub-scanning cross section. Then, as described above, even if there are errors in the arrangements of the first to fourth reflective optical elements 309a to 309d due to the emission of the light beam, it is not necessary to make adjustments.

[0143] As a result, the first light beam reflected by the first reflective optical element 309a passes through the fifth fθ lens 307a, the first fθ lens 306a, the deflector 305 again, and passes through the imaging means 311, so that the light can be efficiently guided to the light receiving element 312. Also, the second light beam reflected by the second reflective optical element 309b passes through the sixth fθ lens 307b, the second fθ lens 306b, the deflector 305 again, and passes through the imaging means 311, so that the light can be efficiently guided to the light receiving element 312.

[0144] Also, the third light beam reflected by the third reflective optical element 309c passes through the seventh fθ lens 307c, the third fθ lens 306c, the deflector 305 again, and passes through the imaging means 311, so that the light can be efficiently guided to the light receiving element 312. Also, the fourth light beam reflected by the fourth reflective optical element 309d passes through the eighth fθ lens 307d, the fourth fθ lens 306d, the deflector 305 again, and passes through the imaging means 311, so that the light can be efficiently guided to the light receiving element 312. That is, in the image forming apparatus 90 according to the present embodiment, even if the postures of the first to fourth reflective optical elements 309a to 309d having the above configuration change, the first to fourth light beams can be guided to the light receiving element 312 with high accuracy.

[0145] FIG. 16 shows a partially enlarged schematic main scanning cross-sectional development view in the vicinity of the third reflective optical element 309c of the image forming apparatus 90 according to the present embodiment. Note that the configurations in the vicinity of the first, second, and fourth reflective optical elements 309a, 309b, and 309d are the same as the configuration in the vicinity of the third reflective optical element 309c shown below with reference to FIG. 16, and thus the description thereof is omitted.

[0146] As shown in FIG. 16, in the image forming apparatus 90 according to the present embodiment, the fifth light shielding member 308c restricts the third light beam incident on the third reflection optical element 309c, that is, shields a part of the third light beam. Thereby, the light reception start timing of the third light beam incident on the light receiving element 312 is determined.

[0147] Further, the sixth light shielding member 310c restricts the third light beam reflected by the third reflection optical element 309c, that is, shields a part of the third light beam. Thereby, the light reception end timing of the third light beam incident on the light receiving element 312 is determined.

[0148] And as shown in FIG. 16, in the image forming apparatus 90 according to the present embodiment, the fifth light shielding member 308c is provided on the reflection surface of the third reflection optical element 309c. In the image forming apparatus 90 according to the present embodiment, miniaturization can be achieved by integrally forming the third reflection optical element 309c and the fifth light shielding member 308c with each other.

[0149] FIG. 17 schematically shows the time change of the monitor voltage detected by the light receiving element 312 in the image forming apparatus 90 according to the present embodiment. In FIG. 17, the waveform indicated by the solid line shows the time change of the monitor voltage detected by the light receiving element 312, and the waveform indicated by the dotted line shows the time change of the monitor voltage detected by a synchronization detection means (not shown).

[0150] As shown in FIG. 17, in the light receiving element 312, the monitor voltage increases when the light reception of the first light beam reflected by the first reflection optical element 309a starts at time t1a, and the monitor voltage returns to the original value when the light reception ends at time t2a. Also, the monitor voltage increases when the light reception of the second light beam reflected by the second reflection optical element 309b starts at time t1b, and the monitor voltage returns to the original value when the light reception ends at time t2b.

[0151] Also, when the light reception of the third light beam reflected by the third reflecting optical element 309c starts at time t1c, the monitor voltage increases, and when the light reception ends at time t2c, the monitor voltage returns to its original value. Also, when the light reception of the fourth light beam reflected by the fourth reflecting optical element 309d starts at time t1d, the monitor voltage increases, and when the light reception ends at time t2d, the monitor voltage returns to its original value.

[0152] And similar to the image forming apparatus 504 according to the first embodiment, the displacements of the first light shielding member 308a and the first reflecting optical element 309a in the y-direction and the x-direction can be detected from the changes at times t1a and t2a. Also, the displacements of the third light shielding member 308b and the second reflecting optical element 309b in the y-direction and the x-direction can be detected from the changes at times t1b and t2b. Also, the displacements of the fifth light shielding member 308c and the third reflecting optical element 309c in the y-direction and the x-direction can be detected from the changes at times t1c and t2c. Also, the displacements of the seventh light shielding member 308d and the fourth reflecting optical element 309d in the y-direction and the x-direction can be detected from the changes at times t1d and t2d.

[0153] As described above, in the image forming apparatus 90 according to the present embodiment, the first to fourth reflecting optical elements 309a to 309d and the first, third, fifth, and seventh light shielding members 308a to 308d are arranged so as to be displaced together with the developing devices 15 to 18, respectively. On the other hand, the second, fourth, sixth, and eighth light shielding members 310a to 310d are separately arranged so as not to be displaced together with the developing devices 15 to 18, respectively.

[0154] Thereby, the displacements of the developing devices 15 to 18 in the y-direction corresponding to the main scanning direction and the x-direction corresponding to the optical axis direction can be detected. That is, in the image forming apparatus 90 according to the present embodiment, it is possible to accurately detect displacements that occur in each of the plurality of developing devices 15 to 18 regardless of the directions of the displacements.

[0155] As described above, the preferred embodiments have been explained, but the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist.

[0156] Note that in the image forming apparatus 90 according to the present embodiment, four optical scanning devices 500 or an optical scanning device 600 may be provided instead of the optical scanning device 700. Also, in the present embodiment, the above-described configuration can be similarly applied to an image forming apparatus that scans two, three, or five or more photosensitive drums.

[0157] The disclosure of the present embodiment includes the following configurations. (Configuration 1) An image forming apparatus comprising: a deflector that deflects a first light beam from a first light source and scans a first surface to be scanned in a main scanning direction; a first imaging optical system that guides the first light beam deflected by the deflector to the first surface to be scanned; a first reflection optical element that reflects the first light beam deflected by the deflector and not reaching the first surface to be scanned; a first light receiving element that receives the first light beam reflected by the first reflection optical element; a first light shielding member that shields a part of the first light beam incident on the first reflection optical element; a second light shielding member that shields a part of the first light beam reflected by the first reflection optical element; a first holding member that holds one of the first and second light shielding members and the first reflection optical element; and a second holding member that holds the other of the first and second light shielding members. (Configuration 2) The image forming apparatus according to Configuration 1, further comprising a housing that houses the deflector, the first imaging optical system, and the second holding member, wherein the first holding member is provided outside the housing. (Configuration 3) A developing device that develops an electrostatic latent image formed on a first scanned surface by a first imaging optical system 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. The first holding member is integrally formed with the developing device, while the second holding member is integrally formed with the housing. The image forming apparatus according to Configuration 2, characterized in that. (Configuration 4) A second light receiving element that receives a first light beam deflected by a deflector and not reaching the first scanned surface, at least one of a first light receiving start time and a first light receiving end time of the first light beam by the first light receiving element, and a control unit that detects a displacement of the first reflective optical element based on a second light receiving start time of the first light beam by the second light receiving element. The image forming apparatus according to any one of Configurations 1 to 3, characterized in that it comprises. (Configuration 5) The first holding member holds the first reflective optical element and the first light shielding member. The control unit detects a displacement in a first direction perpendicular to the sub-scanning direction in a first cross section parallel to the reflection surface of the first reflective optical element based on a time difference between the first light receiving start time and the second light receiving start time. The image forming apparatus according to Configuration 4, characterized in that. (Configuration 6) The control unit detects a displacement in a second direction perpendicular to the first cross section of the first reflective optical element based on a time difference between the first light receiving end time and the second light receiving start time. The image forming apparatus according to Configuration 5, characterized in that. (Configuration 7) A first light source having a first light emitting point that emits a first light beam and a second light emitting point that emits a second light beam, which are separated from each other in the main scanning direction and the sub-scanning direction. The control unit detects a displacement of the first reflective optical element in the sub-scanning direction based on a time difference between the first light receiving start time and a third light receiving start time of the second light beam by the first light receiving element. The image forming apparatus according to Configuration 5 or 6, characterized in that. (Configuration 8) An end portion of the first light shielding member on the second light shielding member side in the first direction is non-parallel to the sub-scanning direction. The image forming apparatus according to Configuration 7, characterized in that. Configuration 9: The first imaging optical system guides a first light beam that is deflected by a deflector and does not reach a first scanned surface to a first reflecting optical element, and the image forming apparatus according to any one of Configurations 1 to 8, characterized in that. Configuration 10: The first reflecting optical element has a plurality of reflecting portions each having first, second, third, fourth, fifth, and sixth reflecting surfaces, and the value of the inner product of the unit normal vector of the first reflecting surface and the unit normal vector of the second reflecting surface is S1, the value of the inner product of the unit normal vector of the first reflecting surface and the unit normal vector of the third reflecting surface is T1, the value of the inner product of the unit normal vector of the second reflecting surface and the unit normal vector of the third reflecting surface is U1, the value of the inner product of the unit normal vector of the fourth reflecting surface and the unit normal vector of the fifth reflecting surface is S2, the value of the inner product of the unit normal vector of the fourth reflecting surface and the unit normal vector of the sixth reflecting surface is T2, and the value of the inner product of the unit normal vector of the fifth reflecting surface and the unit normal vector of the sixth reflecting surface is U2.

Number

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Number

Number

Explanation of Reference Numerals

[0158] 85 Imaging optical system (first imaging optical system) 101 Light source (first light source) 105 Deflector 108 First light-shielding member 109 Reflection optical element (first reflection optical element) 110 Second light-shielding member 112 Light-receiving element (first light-receiving element) 113 Scanned surface (first scanned surface) 114 Holding member (first holding member) 504 Image forming apparatus

Claims

1. A deflector that deflects a first light beam from a first light source and scans a first scanned surface in a main scanning direction; A first imaging optical system that guides the first light beam deflected by the deflector to the first scanned surface; A first reflective optical element that reflects the first light beam deflected by the deflector and not reaching the first scanned surface; A first light receiving element that receives the first light beam reflected by the first reflective optical element; A first light shielding member that shields a part of the first light beam incident on the first reflective optical element; A second light shielding member that shields a part of the first light beam reflected by the first reflective optical element; One of the first and second light shielding members, and a first holding member that holds the first reflective optical element; An image forming apparatus comprising: a second holding member that holds the other of the first and second light shielding members.

2. Comprising a housing that houses the deflector, the first imaging optical system, and the second holding member; The image forming apparatus according to claim 1, wherein the first holding member is provided outside the housing.

3. A developing device that develops an electrostatic latent image formed on the first scanned surface by the first imaging optical system into a toner image; A transfer device that transfers the developed toner image onto a transfer material; A fixing device that fixes the transferred toner image onto the transfer material; The image forming apparatus according to claim 2, wherein the first holding member is integrally formed with the developing device, while the second holding member is integrally formed with the housing.

4. A second light receiving element that receives the first light beam deflected by the deflector and not reaching the first scanned surface; A control unit that detects displacement of the first reflective optical element based on at least one of a first light receiving start time and a first light receiving end time of the first light beam by the first light receiving element and a second light receiving start time of the first light beam by the second light receiving element. The image forming apparatus according to claim 1.

5. The first holding member holds the first reflective optical element and the first light shielding member; The control unit detects displacement in a first direction perpendicular to the sub-scanning direction in a first cross-section parallel to the reflecting surface of the first reflecting optical element based on a time difference between the first light reception start time and the second light reception start time. The image forming apparatus according to claim 4, characterized in that.

6. The control unit detects displacement in a second direction perpendicular to the first cross-section of the first reflecting optical element based on a time difference between the first light reception end time and the second light reception start time. The image forming apparatus according to claim 5, characterized in that.

7. The first light source includes a first light emitting point that emits the first light beam and a second light emitting point that emits the second light beam, which are separated from each other in the main scanning direction and the sub-scanning direction, respectively. The control unit detects displacement of the first reflecting optical element in the sub-scanning direction based on a time difference between the first light reception start time and a third light reception start time of the second light beam by the first light receiving element. The image forming apparatus according to claim 5, characterized in that.

8. An end portion of the first light shielding member on the second light shielding member side in the first direction is non-parallel to the sub-scanning direction. The image forming apparatus according to claim 7, characterized in that.

9. The first imaging optical system guides the first light beam that is deflected by the deflector and does not reach the first scanned surface to the first reflecting optical element. The image forming apparatus according to claim 1, characterized in that.

10. The first reflecting optical element has a plurality of reflecting portions each having first, second, third, fourth, fifth, and sixth reflecting surfaces. When the value of the inner product of the unit normal vector of the first reflecting surface and the unit normal vector of the second reflecting surface is S1, the value of the inner product of the unit normal vector of the first reflecting surface and the unit normal vector of the third reflecting surface is T1, the value of the inner product of the unit normal vector of the second reflecting surface and the unit normal vector of the third reflecting surface is U1, the value of the inner product of the unit normal vector of the fourth reflecting surface and the unit normal vector of the fifth reflecting surface is S2, the value of the inner product of the unit normal vector of the fourth reflecting surface and the unit normal vector of the sixth reflecting surface is T2, and the value of the inner product of the unit normal vector of the fifth reflecting surface and the unit normal vector of the sixth reflecting surface is U2. 【Number 1】 【Number 2】 【Number 3】 【Number 4】 The image forming apparatus according to claim 1, characterized in that the following conditions are satisfied.

11. The first and second reflecting surfaces are in contact with each other so as to form a first ridge line. The second and third reflecting surfaces are in contact with each other so as to form a second ridge line. The third and first reflecting surfaces are in contact with each other so as to form a third ridge line. The fourth and fifth reflecting surfaces are in contact with each other so as to form a fourth ridge line. The fifth and sixth reflecting surfaces are in contact with each other so as to form a fifth ridge line. The image forming apparatus according to claim 10, wherein the sixth and fourth reflecting surfaces are in contact with each other so as to form a sixth ridge line.

12. The first light beam deflected by the deflector and not reaching the first scanned surface is reflected once by each of the first to third reflecting surfaces, or is reflected once by each of the fourth to sixth reflecting surfaces. The image forming apparatus according to claim 10, characterized in that.

13. The image forming apparatus according to claim 1, wherein the first light beam reflected by the first reflecting optical element is incident on the first light receiving element after being deflected by the deflector.

14. A second imaging optical system that guides a third light beam deflected by the first deflection surface of the deflector to a second scanned surface; A second reflecting optical element that reflects the third light beam deflected by the first deflection surface and not reaching the second scanned surface; A third light shielding member that shields a part of the third light beam incident on the second reflecting optical element; A fourth light shielding member that shields a part of the third light beam reflected by the second reflecting optical element; One of the third and fourth light shielding members, and a third holding member that holds the second reflecting optical element; A fourth holding member that holds the other of the third and fourth light shielding members, and The first imaging optical system guides the first light beam deflected by the first deflection surface to the first scanned surface. The deflector deflects the third light beam from the second light source to scan the second scanned surface in the main scanning direction. The image forming apparatus according to claim 1, wherein the first light receiving element receives the third light beam reflected by the second reflecting optical element.

15. The image forming apparatus according to claim 14, further comprising first and second incident optical systems that obliquely incident the first and third light beams from the first and second light sources on the first deflection surface at a predetermined angle with respect to the main scanning cross section within the sub-scanning cross section.

16. Third and fourth imaging optical systems that guide the fourth and fifth light beams deflected by the second deflection surface of the deflector to the third and fourth surfaces to be scanned; Third and fourth reflection optical elements that reflect the fourth and fifth light beams that are deflected by the second deflection surface and do not reach the third and fourth surfaces to be scanned; Fifth and seventh light shielding members that shield a part of the fourth and fifth light beams incident on the third and fourth reflection optical elements; Sixth and eighth light shielding members that shield a part of the fourth and fifth light beams reflected by the third and fourth reflection optical elements; One of the fifth and sixth light shielding members, and a fifth holding member that holds the third reflection optical element; A sixth holding member that holds the other of the fifth and sixth light shielding members; One of the seventh and eighth light shielding members, and a seventh holding member that holds the fourth reflection optical element; And an eighth holding member that holds the other of the seventh and eighth light shielding members, The deflector deflects the fourth and fifth light beams from the third and fourth light sources to scan the third and fourth surfaces to be scanned in the main scanning direction, The image forming apparatus according to claim 14, wherein the first light receiving element receives the fourth and fifth light beams reflected by the third and fourth reflection optical elements.

17. The image forming apparatus according to claim 16, further comprising third and fourth incident optical systems that obliquely incident the fourth and fifth light beams from the third and fourth light sources on the second deflection surface at a predetermined angle with respect to the main scanning cross section within the sub-scanning cross section.

18. The image forming apparatus according to any one of claims 1 to 17, further comprising a printer controller that converts a signal output from an external device into image data.

Images