OPTICAL SCANNING APPARATUS

In an optical scanning apparatus, a first positioning portion has two seating surfaces that hold a mirror and a second positioning portion has only one seating surface that holds the mirror. A force of pressure of a first urging member is greater than a force of pressure of a second urging member, thereby preventing a vibration of the mirror.

BACKGROUND

Field of the Disclosure

The present disclosure relates to an optical scanning apparatus used for an image forming apparatus using an electrophotographic method, such as a laser printer and a digital copying machine.

Description of the Related Art

In many cases, an optical scanning apparatus that scans a photosensitive member mounted in an electrophotographic image forming apparatus with a laser beam in accordance with image information is equipped with a mirror to deflect an optical path of the laser beam.

If an orientation of the mirror is displaced from a desired orientation, an irradiation position of the laser beam to the photosensitive member is shifted. Thus, in an optical scanning apparatus discussed in Japanese Patent Application Laid-Open No. 2002-182144, a structure of holding a mirror is proposed to make the orientation of the mirror in the desired orientation.

The mirror is typically positioned on a seating surface of an optical box by being urged by a spring. Accordingly, the seating surface on which the mirror is mounted requires accuracy. However, in a case where the optical box is a resin molded product, it is conceivable that the accuracy of the seating surface deteriorates due to a variation at the time of molding. The deterioration in accuracy of the seating surface may make the orientation of the mirror unstable.

FIGS. 9A and 9Bare diagrams illustrating an issue to be solved in the present exemplary embodiment, and each schematically illustrate a state in which the mirror is held by the seating surface.FIG. 9Bis a sectional view taken along a line b-b illustrated inFIG. 9A. A mirror101is positioned on seating surfaces103and203at respective ends in a longitudinal direction of the mirror101. The seating surfaces103and203at two different positions having an identical shape. The one seating surface103that holds the mirror101includes seating surfaces103aand103bthat are in contact with the mirror101, and a seating surface117in contact with a surface116of the mirror101. The other seating surface203that holds the mirror101includes seating surfaces203aand203bthat are in contact with the mirror101, and a seating surface118in contact with the surface116of the mirror101. The mirror101includes a reflection surface114.

FIGS. 10A and 10Beach illustrate an example in which accuracy of part of the seating surfaces deteriorates due to a variation at the time of molding an optical box102. The example illustrated inFIGS. 10A and 10Bis an example in which the seating surface103bis lower than the seating surface103a. In this case, a straight line B connecting the seating surfaces103aand103bof the one seating surface103, and a straight line C connecting the seating surfaces203aand203bof the other seating surface203are in a non-parallel state. If the one seating surface103and the other seating surface203fail to have a parallel relationship, a gap119is generated between the mirror101and the seating surface103b.

FIG. 11Ais a diagram illustrating a case where the gap119is generated between the mirror101and the seating surface103.FIG. 11Bis a diagram illustrating a case where a gap219is generated between the mirror101and the seating surface203. As illustrated inFIG. 11A, the mirror101is urged by a force F11of a spring, which is not illustrated, at its center in a traverse direction of the mirror101on the one seating surface103side in the longitudinal direction of the mirror101toward the seating surface103. With the presence of the gap119, the force F11generates a moment M11. In a case where the force F11is insufficient, the size of the gap119changes depending on the magnitude of the force F11.

Also on the other seating surface203side, the mirror101is urged by a force F31of a spring, which is not illustrated, toward the seating surface203. However, as illustrated inFIG. 11B, the mirror101floats from the seating surface203aby a moment M21corresponding to the moment M11generated on the one seating surface103side. Consequently, the gap219is generated between the mirror101and the seating surface203a.

The gaps119and219respectively generated by the moments of forces M11and M21are located on a diagonal line T connecting opposing corners113and213of the mirror101, as illustrated inFIG. 12A. Consequently, rotational motion of the mirror101is generated about the diagonal line T serving as an axis.

FIG. 12Bis a diagram illustrating a relationship between the mirror101and a laser beam LB with which a photosensitive member D is irradiated. Driving a motor of a deflector that deflects a laser beam transmits its vibration to the mirror101via the optical box102. In a case where the gap119is present between the mirror101and the seating surface103aand the gap219is present between the mirror101and the seating surface203a, the vibration generates rotational motion of the mirror101at an angle θ. Then, an irradiation position of the laser beam LB varies by a width A and the variation in irradiation position occurs at a vibration period of the deflector, which causes banding, and eventually leads to deterioration in image quality.

SUMMARY

Aspects of the present disclosure include an optical scanning apparatus capable of reducing shift amount of an irradiation position of a laser beam due to a vibration of a mirror by surely bringing the mirror into contact with a positioning portion.

According to an aspect of the present disclosure, an optical scanning apparatus includes a light source configured to emit a laser beam, a deflector configured to deflect the laser beam emitted from the light source and perform scanning with the laser beam, a mirror having a length greater than its width and configured to reflect the laser beam, an optical box, configured to house the deflector and the mirror, including a first positioning portion configured to hold one end of the mirror and a second positioning portion configured to hold the other end, in the longitudinal direction, of the mirror, a first urging member configured to urge the mirror toward the first positioning portion, and a second urging member configured to urge the mirror toward the second positioning portion, wherein the first positioning portion has two seating surfaces configured to hold the mirror, and the second positioning portion has one seating surface configured to hold the mirror, and wherein a force of pressure of the first urging member is greater than a force of pressure of the second urging member.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a plan view illustrating an optical scanning apparatus1according to an exemplary embodiment. A laser beam LB emitted from a light source unit (light source)2is collected by an anamorphic lens4, and a beam diameter of the laser beam LB is restricted to a predetermined beam diameter by an optical diaphragm6formed in an optical box5. Then, the laser beam LB is incident on a rotational polygon mirror7. The rotational polygon mirror7is driven by a motor mounted on a driving circuit substrate8to deflect the laser beam LB incident thereon. The rotational polygon mirror7and the driving circuit substrate8constitute a deflector9. The deflected laser beam LB, after passing through a fθ lens10, is reflected on a long-length mirror11, and scans a photosensitive member (not illustrated) mounted in an electrophotographic printer. As a result, an electrostatic latent image is formed on the photosensitive member. The mirror11is fixed to the optical box5, which is a resin molded product, by a plate spring18R (first urging member) and a plate spring18L (second urging member) urging respective ends in a longitudinal direction of the mirror11. In this manner, the optical scanning apparatus1includes the light source2that emits the laser beam LB and the deflector9that deflects the laser beam LB emitted from the light source2and that performs scanning with the laser beam LB. The optical scanning apparatus1further includes the long-length mirror11that reflects the laser beam LB and the optical box5that houses the deflector9and the mirror11. The optical box5includes a first positioning portion13that holds one end in the longitudinal direction of the mirror11and a second positioning portion53that holds the other end in the longitudinal direction of the mirror11. The first positioning portion13and the second positioning portion53will be described below. Furthermore, the optical scanning apparatus1includes the first urging member18R that urges the mirror11toward the first positioning portion13and the second urging member18L that urges the mirror11toward the second positioning portion53.

FIG. 2Ais a perspective view illustrating a case where the mirror is pressed by the plate springs18R and18L.FIG. 2Bis a sectional view of the plate spring18R.FIG. 2Cis a perspective view of the plate spring18R. The plate springs18L and18R have an identical configuration.

FIGS. 3 and 4are diagrams each illustrating a state in which the mirror11is mounted on the optical box5.FIG. 3is a sectional view illustrating the one end in the longitudinal direction of the mirror11(main scanning direction of the laser beam LB).FIG. 4is a sectional view illustrating the other end of the mirror11. As illustrated inFIGS. 1 and 3, the optical box5is provided with the positioning portion13(first positioning portion) that holds the one end of the mirror11. The positioning portion13includes a base15that supports a reflection surface14of the mirror11, and a base17that supports a surface16of the mirror11orthogonal to the reflection surface14. The base15includes seating surfaces15aand15bthat support the reflection surface14at different two positions in a sub-scanning direction of the laser beam LB (Y-direction indicated by arrow). The base17includes a projection portion17athat contacts the surface16of the mirror11.

In addition, as illustrated inFIGS. 1 and 4, the optical box5is provided with the positioning portion53(second positioning portion) that holds the other end of the mirror11. The positioning portion53includes a base55that supports the reflection surface14of the mirror11, and a base57that supports the surface16of the mirror11orthogonal to the reflection surface14. The base55includes a seating surface55athat supports the reflection surface14at one position in the sub-scanning direction of the laser beam LB (Y-direction indicated by arrow). The base57includes a projection portion57athat contacts the surface16of the mirror11.

<Mounting Mirror with Plate Spring>

The mirror11is, after being placed on the optical box5, urged by the plate springs18R and18L to be fixed to the optical box5. The plate spring18R includes a pressure application portion (first pressure application portion)18Rb that applies pressure to the mirror11, and a hole (first hole)18Rc to fix the plate spring18R to the optical box5. The plate spring18R includes a rear surface18Ra. Similarly, the plate spring18L includes a pressure application portion (second pressure application portion)18Lb that applies pressure to the mirror11and a hole18Lc (second hole) to fix the plate spring18L to the optical box5. The plate spring18L includes a rear surface18La. The plate springs18R and18L are sandwiched between the optical box5and the mirror11. A claw (first claw)64and a claw (second claw)66, which are part of the optical box5, are respectively inserted into the holes18Rc and18Lc for fixing, and the plate springs18R and18L are respectively fixed to the optical box5by the claws64and66.

As illustrated inFIG. 3, the plate spring18R at one end in the longitudinal direction of the mirror11is arranged on a rear surface21side that is the opposite side of the reflection surface14of the mirror11. Then, the pressure application portion18Rb of the plate spring18R is in contact with the rear surface21of the mirror11at a position corresponding to a substantial center between the seating surface15aand seating surface15bof the base15. The mirror11is then urged by the plate spring18R and is in contact with the seating surfaces15aand15bof the base15. In addition, the surface16of the mirror11is brought into contact with the supporting projection portion17aof the optical box5by an assembly worker pressing a surface22of the mirror11.

As illustrated inFIG. 4, the plate spring18L at the one end in the longitudinal direction of the mirror11is arranged on the rear surface21side that is on the opposite side of the reflection surface14of the mirror11. A pressure application portion18Lb of the plate spring18L is in contact with the rear surface21of the mirror11at a position corresponding to the seating surface55aof the base55. The mirror11is urged by the plate spring18L and is in contact with the seating surface55aof the base55. In addition, the surface16of the mirror11is brought into contact with the support projection portion57aof the optical box5by the assembly worker pressing the surface22of the mirror11.

While the plate springs18R and18L that urge the mirror11at the different two positions in the longitudinal direction of the mirror11have an identical configuration, positions at which the plate springs18R and18L are mounted onto the optical box5(a distance between the plate spring18R and a plate spring mounting portion5aand a distance between the plate spring18L and a plate spring mounting portion5b) are different from each other. As illustrated inFIG. 3, the plate spring18R urges the mirror11toward the first positioning portion13having the two seating surfaces15aand15bof the optical box5. In addition, the rear surface18Ra of the plate spring18R is in contact with the plate spring mounting portion5aof the optical box5. A distance between the plate spring mounting portion5aand the pressure application portion18Rb is a distance L1. In addition, as illustrated inFIG. 4, the plate spring18L urges the mirror11toward the second positioning portion53having the seating surface55aof the optical box5. In addition, the rear surface18La of the plate spring18L is in contact with the plate spring mounting portion5bof the optical box5. A distance between the plate spring mounting portion5band the pressure application portion18Lb is a distance L2. The distances L1and L2corresponding to bending amounts of the plate springs, respectively, have a relationship of L1<L2, and the bending amount of the first urging member18R is smaller than the bending amount of the second urging member18L. In this manner, despite the usage of the plate springs18R and18L having the identical configuration, a force of pressure F1of the plate spring18R is greater than a force of pressure F2of the plate spring18L (F1>F2).

As described above, the first positioning portion13has the two seating surfaces that hold the mirror11, and the second positioning portion53has only one seating surface that holds the mirror11, and the force of pressure F1of the first urging member18R is greater than the force of pressure F2of the second urging member18L.

<Influence of Accuracy of Seating Surface>

FIGS. 5A and 5Bare diagrams illustrating a case where accuracy of the seating surface deteriorates due to a variation in molding the optical box5, and illustrating a state where a gap is generated between the mirror11and the seating surface15b. As illustrated inFIG. 5A, in a case where an angle of a straight line A connecting the seating surfaces15aand15band an angle of the reflection surface14of the mirror11are different from each other, the reflection surface14of the mirror11is in contact with the seating surface15a, and a gap19is generated between the remaining seating surface15band the mirror11. As described above, the force of pressure F1of the plate spring18R is greater than the force of pressure F2of the plate spring18L, and the moment M1generated by the force of pressure F1brings the reflection surface14of the mirror11into contact with the seating surface15b, thereby enabling elimination of the gap19.

FIG. 5Bis a diagram illustrating a state in which rotation of the mirror11by the moment M1brings the mirror11into contact with the two seating surfaces15aand15b. Assuming that the force of pressure F1of the plate spring18R is about 10 N and a length in the traverse direction (Y-direction) of the mirror is 10 mm, the moment M1is 50 Nmm. The moment of this magnitude can eliminate the gap19and cause the reflection surface14to be along the seating surfaces15aand15beven in a case where the angle of the straight line A connecting the seating surfaces15aand15band the angle of the reflection surface14are different from each other.

Next, the second positioning portion53will be described with reference toFIGS. 6A and 6B. As illustrated inFIG. 6A, in the second positioning portion53, placing the mirror11on the optical box5generates the moment M2corresponding to the moment M1generated in the first positioning portion13. The moment M2rotates the mirror11, thereby making the angle of the reflection surface14the same as the angle of the straight line A connecting the seating surfaces15aand15b.

In the present exemplary embodiment, the pressure application portion18Lb of the plate spring18L is in contact with a substantial central portion of the mirror11in the Y-direction, and applies pressure to the mirror11by the force of pressure F2on a line N connecting the seating surface55aand the pressure application portion18Lb. Furthermore, each of the seating surface55ain contact with the reflection surface14of the mirror11and the support projection portion57ain contact with the surface16of the mirror11are set to have a small area of about 2 to 4 mm2. With such a configuration, the mirror11is easy to rotate by the moment M2, and the mirror11maintains a state of being in contact with the seating surface55aand is never separated from the seating surface55a. As illustrated inFIG. 7, the mirror11is in contact with the seating surfaces15aand15bat the different two positions at one end in the longitudinal direction (on the first positioning portion13side), and in contact with the seating surface55aat the one position at the other end (on the second positioning portion53side), i.e., in contact with the optical box5at a total of three positions.

Such a configuration described above can reduce a variation in irradiation position of the laser beam due to the rotation of the mirror11. The orientation of the mirror11is an important parameter that determines a position at which the photosensitive member, which is not illustrated, is irradiated with the laser beam. It is important to cause the mirror11to be along the seating surfaces15aand15bthat determine the angle (orientation) of the mirror11at the two positions. Increasing the force of pressure F1of the plate spring18R on the first positioning portion13side having the two seating surfaces15aand15bto determine the angle of the mirror11causes the mirror11to be along the seating surfaces15aand15bat the two positions even in a case where accuracy in molding the seating surface has deteriorated. In contrast, there is no element that determines the angle of the mirror11on the second positioning portion53side having only one seating surface55a. Thus, it is only required to make the force of pressure F2of the plate spring18L less than the force of pressure F1of the plate spring18R to prevent the force of pressure F2from canceling out the moment M1.

As described above, the present exemplary embodiment can infallibly bring the mirror11into contact with the three seating surfaces15a,15b, and55a, even in a case where the accuracy of the seating surface of the optical box5to mount the mirror11is not good, and can reduce displacement of irradiation position of the laser beam L due to vibration of the mirror11. While the plate springs18R and18L apply pressure to the rear surface21of the mirror11in the present exemplary embodiment, the plate springs18R and18L may be configured to apply pressure to the reflection surface14of the mirror11and bring the rear surface21in contact with the seating surface. In addition, while the description has been given of the example in which the gap is generated between the mirror11and the seating surface15b, the configuration of the present exemplary embodiment can exhibit similar effects even in a case where the gap is generated between the mirror11and the seating surface15a.

Furthermore, the force of pressure of the plate spring18R on the first positioning portion13side having the two seating surfaces is only required to be greater than the force of pressure of the plate spring18L on the second positioning portion53side having only one seating surface. A configuration of using different plate springs for the two plate springs may be employed. More specifically, forces of pressure may be differentiated by differentiating thicknesses of the two plate springs. Alternatively, forces of pressure may be differentiated by differentiating lengths of action of the two plate springs (lengths from points of support to points of action of the plate springs). Still alternatively, forces of pressure may be differentiated by differentiating bending amounts of the two plate springs (displacement amounts of points of support of the plate springs).

In addition, even in a case where the two plate springs have the identical configuration, forces of pressure may be differentiated by a configuration of inclining a plate spring mounting portion75toward the gravitational direction as illustrated inFIG. 8A, or a configuration of changing a height of the plate spring by shifting a height position of the claw64toward the gravitational direction as illustrated inFIG. 8B.

This application claims the benefit of priority from Japanese Patent Application No. 2020-063776, filed Mar. 31, 2020, which is hereby incorporated by reference herein in its entirety.