Optical scanning apparatus and image forming apparatus

There is a demand for an inexpensive optical scanning apparatus. An optical scanning apparatus includes a light source configured to emit a laser light flux, a deflection unit configured to deflect the laser light flux emitted from the light source, and a light reception member configured in such a manner that the laser light flux reflected by the deflection unit is incident thereon. The light source emits the laser light flux tilted by a predetermined angle with respect to a horizontal direction toward the deflection unit. The light reception member is disposed above or below the light source, and the laser light flux reflected by the deflection unit and tilted by the predetermined angle with respect to the horizontal direction is incident on the light reception member.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an optical scanning apparatus that scans a scanning target surface with a laser light flux emitted from a light source and deflected by a deflection unit, and an image forming apparatus including this optical scanning apparatus, such as a laser beam printer (hereinafter referred to as an LBP), a digital copying machine, and a digital fax machine (FAX).

Description of the Related Art

An optical scanning apparatus for use with an image forming apparatus based on the electrophotographic method optically writes an image onto a photosensitive drum or the like with use of a laser beam as discussed in Japanese Patent Application Laid-Open No. 2016-109780. The optical scanning apparatus discussed in Japanese Patent Application Laid-Open No. 2016-109780 writes the image onto the photosensitive drum in the following manner. The optical scanning apparatus emits a laser light flux from a semiconductor laser unit. The emitted laser light flux passes through a lens and is imaged as a linear image on a reflection surface of a polygon mirror. Then, the laser light flux is deflected due to a rotation of the polygon mirror, and is imaged and caused to scan on a photosensitive surface (the scanning target surface) that is a surface of the photosensitive drum via an fθ lens, by which an electrostatic latent image is formed on the scanning target surface. When the polygon mirror is located in a predetermined rotational phase, the reflected laser light flux is incident on a beam detector (BD) sensor as a signal output unit that outputs a BD signal.

However, according to the technique discussed in Japanese Patent Application Laid-Open No. 2016-109780, the semiconductor laser unit, the BD sensor, and the fθ lens are arranged on a same plane, and the laser light flux is deflected and caused to scan on the same plane. Therefore, to dispose the BD sensor, an angle of the laser light flux from the semiconductor laser unit with respect to a center of the photosensitive surface in a scanning direction (a laser incident angle) is undesirably increased to approximately a right angle.

The increase in the laser incident angle leads to an increase in a width of the linear image on the reflection surface of the polygon mirror, raising a necessity of increasing a width of the reflection surface of the polygon mirror in a longitudinal direction of the linear image (hereinafter referred to as a width in a main scanning direction). The increase in the width of the reflection surface of the polygon mirror in the main scanning direction may result in increase in processing cost and material cost of the polygon mirror.

SUMMARY OF THE INVENTION

Therefore, according to an aspect of the present invention, a representative configuration of an optical scanning apparatus includes a light source configured to emit a laser light flux, a deflection unit configured to deflect the laser light flux emitted from the light source, and a light reception member configured in such a manner that the laser light flux reflected by the deflection unit is incident thereon. The light source emits the laser light flux tilted by a predetermined angle with respect to a horizontal direction toward the deflection unit. The light reception member is disposed above or below the light source, and the laser light flux reflected by the deflection unit and tilted by the predetermined angle with respect to the horizontal direction is incident on the light reception member.

DESCRIPTION OF THE EMBODIMENTS

In the following description, an exemplary embodiment of the present invention will be described in detail with reference to the drawings by way of example. However, dimensions, materials, shapes, a relative layout, and the like of components that will be described in the following exemplary embodiment shall be changed as appropriate according to a configuration of an apparatus to which the present invention is applied and various kinds of conditions. Therefore, they are not intended to limit the scope of the present invention only thereto unless otherwise specifically indicated.

In the following description, a first exemplary embodiment will be described. First, an image forming apparatus D1will be described with reference toFIG. 10.FIG. 10is a schematic cross-sectional view of the image forming apparatus D1including an optical scanning apparatus101according to the present exemplary embodiment.

The image forming apparatus D1includes the optical scanning apparatus101, and scans a photosensitive drum as an image bearing member by the optical scanning apparatus101to form an image on a recording material P such as recording paper based on an image drawn by this scanning. As illustrated inFIG. 10, the image forming apparatus D1emits a laser light flux based on image information from the optical scanning apparatus101, and irradiates a surface of a photosensitive drum8as the image bearing member built in a process cartridge102therewith. The surface of the photosensitive drum8is irradiated with and exposed to the light flux, by which a latent image is formed on the photosensitive drum8. The latent image formed on the photosensitive drum8is visualized as a toner image with use of toner. The process cartridge102is a unit integrally including the photosensitive drum8, and a charging unit, a development unit, and the like as process units acting on the photosensitive drum8, and attachable to and detachable from the image forming apparatus D1. On the other hand, the recording material P such as a sheet contained in a sheet feeding cassette104is fed while being separated one by one by a sheet feeding roller105, and is conveyed further downstream by a conveyance roller106. The toner image formed on the photosensitive drum8is transferred onto the recording material P by a transfer roller109. The recording material P with the toner image formed thereon is conveyed further downstream, and the toner image is heated and fixed onto the recording material P by a fixing unit110including a heater therein. After that, the recording material P is discharged out of the apparatus by a discharge roller111.

Next, the optical scanning apparatus101according to the present exemplary embodiment will be described with reference toFIG. 1.FIG. 1is a perspective view of the optical scanning apparatus101and the photosensitive drum8according to the present exemplary embodiment.

As illustrated inFIG. 1, the optical scanning apparatus101includes the following optical members. The optical scanning apparatus101includes a semiconductor laser unit1and a compound anamorphic collimator lens11. The semiconductor laser unit1is a light source that emits a laser light flux L. The compound anamorphic collimator lens11is a lens integrally including an anamorphic collimator lens2having both a function as a collimator lens and a function as a cylindrical lens, and a writing start position signal detection lens (a BD lens)10. Further, the optical scanning apparatus101includes an aperture diaphragm3, a rotational polygonal mirror (a polygon mirror)4, a reflection surface12of the polygon mirror4, a light deflector (a scanning motor)5, a writing start position synchronization signal detection unit (a BD sensor)6, an fθ lens (a scanning lens)7, and a substrate20. The above-described semiconductor laser unit1and the above-described BD sensor6are mounted on the substrate20, and the substrate20includes a driving circuit (not illustrated) that drives the above-described semiconductor laser unit1. The optical scanning apparatus101contains the above-described optical members in an optical box9.

The semiconductor laser unit1, the compound anamorphic collimator lens11, the scanning motor5, and the scanning lens7, which is an imaging unit, are fixed in the optical box9by press-fitting, adhesion, fastening with a screw, or the like.

The semiconductor laser unit1emits the laser light flux L, and forms a linear image on the reflection surface12of the polygon mirror4by the anamorphic collimator lens2. The polygon mirror (a deflection unit)4is rotationally driven by the scanning motor5, and deflects the laser light flux L emitted from the semiconductor laser unit1. Then, the laser light flux L deflected by the polygon mirror4is imaged and scans on a scanning target surface (the surface of the photosensitive drum8) by passing through the scanning lens7.

In the present disclosure, a scanning direction in which the laser light flux L deflected by the polygon mirror4is caused to scan the scanning target surface (the surface of the photosensitive drum8) is defined to be a main scanning direction X, and a direction perpendicular to this scanning direction is defined to be a sub scanning direction Y.

FIGS. 2A and 2Bare each a partial cross-sectional view of the optical scanning apparatus101with the semiconductor laser unit1, the anamorphic collimator lens2, the BD lens10, and the polygon mirror4taken along a plane perpendicular to the laser light flux emitted from the semiconductor laser unit1.

The semiconductor laser unit1and the BD sensor6are arranged on a same line in the direction (the sub scanning direction Y) perpendicular to the scanning direction (the main scanning direction X) as illustrated inFIGS. 1 and 2A. Further, the semiconductor laser unit1and the BD sensor6are mounted on a same substrate. In the present example, the BD sensor6is mounted on the substrate20where the semiconductor laser unit1is mounted as illustrated inFIG. 9. Further, although the semiconductor laser unit1and the BD sensor6are arranged on the same line in the direction (the sub scanning direction Y) perpendicular to the scanning direction (the main scanning direction X), the layout thereof is not limited thereto. The semiconductor laser unit1and the BD sensor6can satisfy a layout condition just by being arranged on a substantially same line in the direction (the sub scanning direction Y) perpendicular to the scanning direction (the main scanning direction X). More specifically, because an intended result can be acquired just by allowing the reflected laser light flux L to pass through the BD lens10, the semiconductor laser unit1and the BD sensor6may be disposed out of alignment with each other as long as this misalignment falls within a range of ±10 mm in the scanning direction (the main scanning direction X).

Further, in the optical scanning apparatus101, the semiconductor laser unit1and the BD sensor6are disposed respectively on one side and the other side of the polygon mirror4in the direction (the sub scanning direction Y) perpendicular to the scanning direction (the main scanning direction X) deflected by the above-described polygon mirror4.

More specifically, as illustrated inFIG. 2A, the semiconductor laser unit1emits the laser light flux L tilted upward by a predetermined angle α degrees with respect to a horizontal direction toward the anamorphic collimator lens2. InFIG. 2A, the laser light flux L is emitted from an emission point1aof the semiconductor laser unit1. The laser light flux L is imaged as the linear image on the reflection surface12of the polygon mirror4by the anamorphic collimator lens2. The reflection surface12of the polygon mirror4extends substantially vertically, and the reflected light flux L also travels straight ahead while being tilted upward by the predetermined angle α degrees with respect to the horizontal direction. This predetermined angle α can be set within a range of 2 to 10 degrees. In the present example, the above-described predetermined angle α is set to 4 degrees. The reflected laser light flux L passes through the BD lens10molded integrally with the anamorphic collimator lens2, and is incident on the BD sensor6. InFIG. 2A, the laser light flux L is incident on an incident point6aof the BD sensor6. At this time, the BD sensor (a light reception member)6outputs a signal based on receiving the laser light flux L, and determines a timing of starting writing the image to be optically emitted from the semiconductor laser unit1based on the output signal.

The laser light flux L tilted upward is emitted from the semiconductor laser unit1toward the polygon mirror4, and the BD sensor6is disposed above the semiconductor laser unit1in a direction along a rotational shaft of the polygon mirror4(the sub scanning direction Y). More specifically, the BD sensor6is disposed in such a manner that the above-described incident point6ais located at a higher position than the emission point1aof the semiconductor laser unit1. This layout allows the semiconductor laser unit1and the scanning lens7to be located close to each other in the scanning direction as illustrated inFIG. 1. As a result, a laser incident angle can be reduced.

Further, a distance h between the semiconductor laser unit1and the BD sensor6mounted on the same substrate20can be set within a range of 6 mm to 20 mm in the direction along the rotational shaft of the polygon mirror4(the sub scanning direction Y) as illustrated inFIG. 2A.

Further, the BD sensor6is disposed on the same surface as a surface (one surface) of the substrate20where the semiconductor laser unit1is mounted as illustrated inFIG. 2A, but the position of the BD sensor6is not limited thereto. As illustrated inFIG. 2B, the optical scanning apparatus101may be configured in such a manner that the BD sensor6is disposed on the other surface (a back surface) opposite from the one surface (a front surface) of the substrate20where the semiconductor laser unit1is mounted. In this case, a through-hole20ais provided at a position of the above-described substrate20that corresponds to the above-described BD sensor6to allow the laser light flux L to be incident on the BD sensor6.

FIGS. 3A to 3Dillustrate the polygon mirror4as viewed from above a rotational shaft14, and are each a schematic view illustrating a position of a linear image S on the reflection surface12of the polygon mirror4.FIGS. 3A to 3Dillustrate states in which the polygon mirror4is rotated in a clockwise direction as viewed from above, and reflection surfaces12a,12b,and12cdeflect the laser light flux L, in order starting fromFIG. 3A. The linear image S is moved from the right to the left when the reflection surface12bis viewed from above according to the rotation of the polygon mirror4.

FIG. 3Aillustrates a rotational phase of the polygon mirror4with the linear image S located across the reflection surfaces12aand12bamong the four reflection surfaces12of the polygon mirror4. A part of the laser light flux L hits a corner13aof the polygon mirror4, and stray light (unnecessary or unintended light) is generated. The stray light may cause an image defect, so that the semiconductor laser unit1should not emit the light with the laser light flux L expected to hit the corner13a.

InFIG. 3B, the rotation of the polygon mirror4shifts from the state illustrated inFIG. 3A, and the reflection surface12bfaces the laser light flux L straight. The laser light flux L reflected in such a phase that the reflection surface12bfaces the laser light flux L straight is incident on the BD sensor6as illustrated inFIGS. 2Aand2B.

FIG. 3Cillustrates a state in which the polygon mirror4is further rotated, and the polygon mirror4deflects the laser light flux L toward the not-illustrated scanning lens7.

FIG. 3Dillustrates a state in which the polygon mirror4is further rotated, and the linear image S is located across the reflection surfaces12band12c.Similarly toFIG. 3A, a part of the laser light flux L hits a corner13band stray light is generated, so that the semiconductor laser unit1should not emit the light with the laser light flux L expected to hit the corner13b.

FIG. 4illustrates light emission states of the semiconductor laser unit1when the reflection surface12b,which is one of the reflection surfaces of the polygon mirror4, deflects the laser light flux L in chronological order.

Time periods (a) to (d) illustrated inFIG. 4correspond toFIGS. 3A to 3D, respectively. As described with reference toFIGS. 3A to 3D, the laser light flux L should not be emitted during the time periods (a) and (d) since the laser light flux L would hit the corner13aor13bof the polygon mirror4and the stray light would be generated. Therefore, the laser light flux L can be emitted only during a time period other than the time periods (a) and (d).

In the present exemplary embodiment, the laser light flux L can be incident on the BD sensor6at the time period (b) when the reflection surface12bfaces the laser light flux L straight, and a time period other than the time period (b) can be used as an image formation time period (c) during which the laser light flux L is caused to scan on the photosensitive drum8. Therefore, a large proportion of a laser light emission possible time period (T) can be used as the image formation time period (c). In other words, the present exemplary embodiment can shorten the laser light emission possible time period (T) while securing a certain time period as the image formation time period (c).

The laser light emission possible time period (T) is proportional to a width W of the reflection surface12of the polygon mirror4in the main scanning direction illustrated inFIG. 3A, and therefore the present exemplary embodiment shortens the laser light emission possible time period (T). As a result, the width W of the reflection surface12of the polygon mirror4in the main scanning direction can be reduced, which allows the polygon mirror4to have a small size.

FIGS. 5A and 5Billustrate the polygon mirror4as viewed from above the rotational shaft14, and are each a schematic view illustrating a width of the linear image S on the reflection surface12of the polygon mirror4. The laser light flux L is emitted from the not-illustrated semiconductor laser unit1toward the polygon mirror4according to an illustrated arrow. Further,FIGS. 5A and 5Billustrate states in which the laser light flux L reflected by the polygon mirror4travels straight ahead toward a center of the not-illustrated photosensitive surface in the scanning direction.FIG. 5Aillustrates the present exemplary embodiment, and an angle of the laser light flux L from the semiconductor laser unit1with respect to the center of the photosensitive surface in the scanning direction (the laser incident angle) is 65 degrees.FIG. 5Billustrates an example in which the laser incident angle is set to 90 degrees for comparison. The laser light flux L having a width B in the main scanning direction is imaged as the linear image S on the reflection surface12of the polygon mirror4. Assume that S1represents a width of the linear image S on the reflection surface12of the polygon mirror4inFIG. 5A, and S2represents a width of the linear image S on the reflection surface12of the polygon mirror4inFIG. 5B.

In rotational phases of the polygon mirror4illustrated inFIGS. 5A and 5B, assuming that θ represents the laser incident angle, the linear image width S is expressed by the following equation (1), and the linear image width S1according to the present exemplary embodiment can be narrowed by approximately 16% compared to the linear image width S2according to the comparative example.
S=A/sin(90−θ/2)   (1)

The narrow width of the linear image S allows a large portion to be allocated to the rotational phase of the polygon mirror4within a range where the laser light flux L is prevented from hitting the corners13aand13bof the polygon mirror4, thereby allowing the reflection surface12of the polygon mirror4to have a narrower width in the main scanning direction.

FIGS. 6A and 6Billustrate states of an airflow around the polygon mirror4when the polygon mirror4is rotated and dirt attached on the reflection surface12, respectively.FIG. 6Aillustrates the polygon mirror4as viewed from above the rotational shaft14, andFIG. 6Billustrates the reflection surface12bas viewed from a front side.

As illustrated inFIG. 6A, when the polygon mirror4is rotated in a direction indicated by an arrow R (the clockwise direction as viewed from above), an airflow occurs as indicated by W1around the corner13aof the reflection surface12b.As a result, dust in the air is attached to a range labeled Y1inFIG. 6B. Further, an airflow occurs as indicated by W2inFIG. 6Aaround the corner13bof the reflection surface12b, and the dust is thrown against the reflection surface12band the dust in the air is attached to a range labeled Y2inFIG. 6B.

The reduction in the width W of the reflection surface12of the polygon mirror4in the main scanning direction leads to a reduction in a distance A from a center of the rotational shaft14of the polygon mirror4to each of the corners13aand13billustrated inFIG. 6A. The distance A and a speed of a uniform circular motion at each of the corners13aand13bare proportional to each other, so that the reduction in the width W of the reflection surface12in the main scanning direction leads to a reduction in the speed of the uniform circular motion at each of the corners13aand13b.As a result, a speed of each of the airflows indicated by W1and W2reduces, which makes it difficult for the reflection surface12bto be contaminated.

Further, the airflow W1is a turbulent flow and causes fluid noise, so that the reduction in the width W of the reflection surface12in the main scanning direction also leads to a reduction in the turbulent flow indicated by W1and thus a reduction in the fluid noise. The reflection surface12bhas been described here, but the same also applies to the other three reflection surfaces.

Next, the scanning motor5in the optical scanning apparatus101will be described with reference toFIG. 7.FIG. 7is a schematic cross-sectional view of the optical scanning apparatus101.

InFIG. 7, the scanning motor5includes the rotational shaft14, a rotor frame15, a balance weight17, and an iron substrate18.

The scanning motor5is fixed to the optical box19via the iron substrate18with use of screws16aand16b.Further, the polygon mirror4, the rotational shaft (a fixed shaft)14, and the rotor frame15are rotationally driven as an integrated rotational body.

Now, a correction of balance of the rotational body will be described. The rotational body is subject to an offset of a center of gravity of the rotational body from a rotational center due to, for example, variations in a connected state of each of parts and a dimension of a part (initial unbalance). In other words, mass unbalance occurs in the rotational body, and dynamic disequilibrium occurs when the rotational body is rotationally driven. The occurrence of the dynamic disequilibrium may cause a vibration and/or noise due to a wobbling rotation of the rotational body, thereby resulting in deterioration of an image quality of the image forming apparatus D1and/or an increase in the noise. Therefore, the present exemplary embodiment attempts to adjust the balance and reduce the mass unbalance of the rotational body by applying the balance weight17on a top surface of the rotor frame15forming the rotational body.

The balance weight17is formed by mixing metallic particles, glass beads, or the like in a photo-curable adhesive such as an ultraviolet curable adhesive, and is placed at an appropriate position of the rotor frame15by an appropriate amount and cured to be attached to the rotor frame15by being irradiated with light such as ultraviolet light. Further, if the balance weight17has low specific gravity, this leads to an increase in an application amount thereof, thereby causing a variation in the application amount, a shift of the application position, and/or an increase in a time period taken to cure the balance weight17. If the balance weight17has high specific gravity, this leads to an increase in the variation in the application amount per application. Therefore, generally, a balance weight having specific gravity of approximately 1 to 3 is used.

The number of times that the balance is corrected depends on an initial unbalance amount of the rotational body. If the initial unbalance amount is large, the balance weight17should be applied by a large amount, which causes the variation in the application amount and/or the shift of the application position. Therefore, the balance may be unable to be corrected to a predetermined or smaller unbalance amount by being corrected once, and the balance may be corrected twice.

The initial unbalance amount of the rotational body can be expressed as a product of the mass of the rotational body and a distance from the rotational center of the rotational body to the center of gravity of the rotational body. Reducing the width W of the reflection surface12of the polygon mirror4in the main scanning direction leads to a reduction in the mass of the polygon mirror4and thus a reduction in the initial unbalance amount of the rotational body. As a result, the present exemplary embodiment can reduce the application amount of the balance weight17when the balance is corrected, thereby improving accuracy of the application amount of the balance weight17. In other words, the present exemplary embodiment allows the balance to be accurately corrected, thereby allowing the balance weight17to be placed at one portion in the same correction surface. Therefore, the present exemplary embodiment can reduce the fluid noise of an unpleasant frequency that occurs at the balance weight portion due to the rotation of the rotational body. Further, the present exemplary embodiment reduces a weight of the rotational body by reducing the mass of the polygon mirror4, thereby reducing an inertial moment of the rotational body and thus succeeding in shortening a time period taken until the rotational body reaches a rated number of rotations (a rise time period). In other words, the present exemplary embodiment can shorten a time period taken since the optical scanning apparatus101rises until the optical scanning apparatus101becomes ready for the exposure, thus shortening a time period taken for the image forming apparatus D1to print the first page.

Next, how a shift of an irradiation position is improved when the size of the reflection surface12of the polygon mirror4in the main scanning direction is reduced will be described with reference toFIGS. 8A and 8B.

FIG. 8Aillustrates the polygon mirror4as viewed from above the rotational shaft14, and is a schematic view illustrating a shift of a point (a deflection point) where the laser light flux L is deflected on the reflection surface12of the polygon mirror4. The polygon mirror4is rotated in the direction indicated by the arrow R around the rotational shaft14. InFIG. 8A, 4a,4b,and4crepresent three phase states of the polygon mirror4during the rotation in sequential order. The deflection point is P1when the phase of the polygon mirror4is4a,and is moved to P2when the phase of the polygon mirror4is4b.Then, the deflection point returns to P1when the phase of the polygon mirror4is4c. Assume that Sa represents a positional shift amount of the deflection point at this time. InFIG. 8A, the width B of the laser light flux L in the main scanning direction is omitted to make the description easily understandable.

FIG. 8Bis a schematic cross-sectional view of the optical scanning apparatus101in cross section that passes through the reflection surface12, the scanning lens7, and the photosensitive drum8and is taken along the direction (the sub scanning direction) perpendicular to the main scanning direction. In the sub scanning direction of the laser light flux L, the image is formed on the deflection point P1on the reflection surface12of the polygon mirror4, and the deflection point P1and an exposure point Q1on the photosensitive drum8are in a conjugate relationship with each other. Since the deflection point P1and the exposure point Q1are in the conjugate relationship with each other, a position of the exposure point Q1is not shifted even when the reflection surface12is tilted as indicated by an arrow M. However, when a position of the deflection point is shifted from the deflection point P1to the deflection point P2according to the phase of the polygon mirror4as described with reference toFIG. 8A, the exposure point is also shifted to a position Q2when the reflection surface12is tilted, because the conjugate relationship is lost at a position of the deflection point P2. The exposure point is periodically changed in the sub scanning direction due to a relative difference in the tilt of each of the reflection surfaces of the polygon mirror4(an optical face tilt). This is called pitch unevenness, and density unevenness (banding) occurs in the sub scanning direction due to the pitch unevenness.

Reducing the width W of the reflection surface12of the polygon mirror4in the main scanning direction leads to a reduction in the positional shift amount Sa of the deflection point when the polygon mirror4is rotated. The reduction in the positional shift amount Sa leads to a reduction in a shift amount of the exposure point in the sub scanning direction due to the optical face tilt, thereby improving the above-described banding.

In the present exemplary embodiment, the laser light flux L tilted upward is emitted from the semiconductor laser unit1toward the polygon mirror4, and the BD sensor6is disposed above the semiconductor laser unit1. This layout can reduce the laser incident angle, and reduce the width W of the reflection surface12of the polygon mirror4in the main scanning direction.

According to the present exemplary embodiment, processing cost and material cost of the polygon mirror are reduced due to the reduction in the width of the reflection surface of the polygon mirror in the main scanning direction. Further, the present exemplary embodiment makes it difficult to contaminate the end of the reflection surface because of the reduction in the rotational speed at the end of the reflection surface of the polygon mirror. Further, the present exemplary embodiment reduces the noise when the polygon mirror is rotated at a high speed. Further, the present exemplary embodiment shortens the time period taken until the polygon mirror reaches the rated number of rotations, thereby allowing the first page to be printed in a shorter time period. Lastly, the reduction in the size of the reflection surface of the polygon mirror leads to the reduction in the positional shift of the deflection point when the laser light flux is caused to scan on the photosensitive surface drum, thereby improving the banding.

In the above-described exemplary embodiment, the optical scanning apparatus101has been described referring to the configuration in which the BD sensor6is disposed above the semiconductor laser unit1in the direction along the rotational shaft14of the polygon mirror4by way of example, but is not limited thereto. The optical scanning apparatus101may be configured in such a manner that the BD sensor6is disposed below the semiconductor laser unit1in the direction along the rotational shaft14of the polygon mirror4. More specifically, the optical scanning apparatus101may be configured in such a manner that the BD sensor6is disposed so as to allow the above-described incident point6ato be located at a lower position than the emission point1aof the semiconductor laser unit1. In other words, the semiconductor laser unit1emits the laser light flux L tilted downward by the predetermined angle a degrees with respect to the horizontal direction toward the reflection surface12of the polygon mirror4. The BD sensor6is disposed below the semiconductor laser unit1, and the laser light flux L reflected by the polygon mirror4and tilted downward by the above-described predetermined angle α degrees with respect to the horizontal direction is incident on the BD sensor6. A similar effect to the above-described exemplary embodiment can also be acquired by employing such a configuration.

This application claims the benefit of Japanese Patent Application No. 2017-047260, filed Mar. 13, 2017, No. 2017-248612, filed Dec. 26, 2017, which are hereby incorporated by reference herein in their entirety.