JPH0990187A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the warp of a long plastic lens constituting the optical system of a laser beam printer and to execute highly precise writing. SOLUTION: A protruding part 2 receiving external force is provided at one end part (upper/lower ends) in the auxiliary scanning direction of the center part in the longitudinal direction of the cylindrical lens 1. A control screw 8 is screwed on the base of an optical unit near the cylindrical lens 1 and the control screw 3 is advanced/receded. Appropriate external force is given to the cylindrical lens 1 and warp is corrected. Thus, warp peculiar to the long plastic lens 1 can be corrected at the time of incorporating the cylindrical lens 1 into the optical unit. Thus, the deterioration of a lens optical characteristic such as the bend of an image surface, which is generated by the warp of the lens 1 is reduced, the characteristic of the optical system can be held constant and the printing performance of the laser beam printer is stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device using a plastic long lens as an optical system, and more particularly to an optical scanning device having means for correcting (warping) deformation of a long cylindrical lens. Regarding

[0002]

2. Description of the Related Art FIGS. 10 and 11 show the structure of a conventional laser printer. The laser printer modulates and deflects the laser light emitted from the light source 101 to form an optical pattern (latent image) on the photoconductor 102, and a scanning optical system (FIG. 10) on the photoconductor 102. Image forming system for making a hard copy (visualization) of the light pattern formed on the surface using an electrophotographic process (FIG. 11)
It is composed of

In the optical scanning system, a gas laser or a semiconductor laser is generally used as the light source 101. As the modulator 103, an A / O modulator using an acousto-optic (A / O) element is generally used. A / O
The modulator allows ultrasonic waves to pass through the A / O element and diffracts the incident laser beam by the synchronous change in the refractive index generated thereby to perform intensity modulation. A beam compressor 104 that narrows the incident beam diameter is provided between the light source 101 and the modulator 103 in order to increase the modulation speed of the A / O element, and is used to obtain a small imaging spot on the photoconductor 102. A beam expander 105 is arranged between the modulator 103 and the rotary polygon mirror 106. A light source 101 is provided between the beam expander 105 and the rotary polygon mirror 106.
A collimator lens (cylindrical lens) 107 for converting a divergent beam emitted from the laser beam into a parallel beam is arranged, and the rotating polygon mirror 106 as an optical deflector scans the photoconductor 102 with laser light. The rotary polygon mirror 1
A hologram may be used instead of 06.

Since the rotary polygon mirror 106 rotates at a constant speed, the laser light reflected from the rotary polygon mirror 106 is deflected at a constant angular velocity. Therefore, an imaging lens (Fθ lens) 10 is provided between the photoconductor 102 and the rotary polygon mirror 106.
8 is provided, the deflected laser light is imaged on one plane on the surface of the photoconductor 102, and an optical distortion is given to the incident light of a constant angular velocity so that the photoconductor 102 is driven at a constant velocity.
Convert to scan over the surface. This is generally called fθ characteristic.

The photoconductor 102 has a two-layer structure in which a photoconductor layer is provided on a conductive support, and the surface of the photoconductor 102 is uniformly made in advance in a dark place by discharging a plus corona (charger) 109. If the laser light from the rotary polygon mirror 106 is applied to the surface of the photoconductor 102, the resistance of the light conductor in the light-exposed portion decreases, and the charged electric charge flows to the ground, and the surface of the photoconductor 102 is charged. There are some areas where electric charge remains and some areas where no electric charge remains. In this way, a latent image is formed. The latent image formed on the photoconductor 102 is developed with positively or negatively charged toner. As shown in FIG. 11, the surface of the insulating layer is discharged to the photoconductor 102 by corona discharge, and at the same time, laser light is irradiated through the (Fθ) imaging lens 108. In the bright portion irradiated with the laser light, the resistance of the photoconductive layer is reduced to be conductive, and the charges on the front and back surfaces of the insulating layer are rapidly attenuated. In the dark area where the laser light is not applied, the electric potential of the insulating layer surface is AC corona discharge 1
When exposed to 10, the electric potential becomes almost 0, but the electric charge formed at the interface between the insulating layer and the photoconductive layer is retained.

In this way, after the charging layer is formed at the interface between the insulating layer and the photoconductive layer by the primary charging, the surface of the insulating layer is discharged by corona discharging, and at the same time, laser light is irradiated for exposure. Next, the entire surface exposure device 111 is used to expose the photosensitive member 10.
The entire surface of 2 is uniformly exposed, thereby increasing the surface potential of the dark part. The latent image formed on the photoconductor 102 is developed by the toner of the developing device 112 which is positively or negatively charged. After the developing process, the toner image on the photoconductor 102 is electrostatically transferred to the plain paper sent from the paper feed cassette 113 via the paper feed roller 114.
5, and a stable permanent image is formed by the fixing process by the fixing device 116. The transferred plain paper is sent to the stacker 117. After the transfer step, the residual toner that could not be transferred to the photoconductor is removed by the cleaning step by the cleaner 118 and the cleaning blade 119, and the charge removal lamp 120 is irradiated to remove the charge, and the latent image forming process is prepared again. Since the electrophotographic process itself is publicly known, further description will be omitted here.

[0007]

By the way, recently, in an optical system of an apparatus such as a printer or a copying machine which uses the electrophotographic process configured as described above, a scanning optical system has recently been provided for cost reduction. Plastic lenses are often used as the constituent lenses (see, for example, JP-A-59-204001), but lenses made of plastic have a lower material cost than glass and are lightweight. There are many advantages such as excellent moldability, but there are drawbacks such that various characteristics of the material are likely to change due to changes in temperature and humidity and that the uniformity of the refractive index inside the molded product is harder to obtain than glass. .

On the other hand, the introduction of aspherical lenses has been popular in optical systems of products such as cameras and laser printers.
In the laser printer apparatus, as described above, the combination of the F.theta.
2 is deflected and scanned, but one of the problems in scanning laser light is the problem of so-called surface tilt, in which scanning pitch unevenness occurs due to the inclination of the reflecting surface of the rotary polygon mirror 106. There is.

As a method for solving this, a combination of a cylinder lens and a toric lens (Japanese Patent Laid-Open No. 48-98) is used.
No. 844), a combination of a toric lens and a cylinder lens or a spherical lens (Japanese Unexamined Patent Publication No. 48-49315), and the like are known to reduce the influence of the tilt error (surface tilt) of the rotary polygon mirror. Further, as a lens with improved optical characteristics, there is known a lens in which the radius of curvature of the Fθ lens in the plane tilt direction is changed according to the deflection direction. This is to reduce the aberration by making the shape of the Fθ lens a non-axisymmetric aspherical shape so that the radius of curvature in the plane tilt direction (sub-scanning direction) increases as the distance from the optical axis increases. .

The non-axisymmetric aspherical Fθ lens is a lens having excellent optical characteristics, but when plastic is selected as the lens material, the optical characteristics may change due to the influence of temperature / humidity and nonuniformity of the refractive index. is there. Therefore, it is effective to use a combination of a non-axisymmetric aspherical plastic Fθ lens and a long plastic cylindrical lens to reduce the optical magnification and reduce the influence of temperature and humidity and refractive index nonuniformity.

By the way, when the lens is molded by the injection molding method, since the cylindrical lens has a long lens length, FIG.
As shown in (3), warp deformation may occur at the center of the lens in the longitudinal direction. In the figure, the warp amount (strain amount) is indicated by δ. When the “warp” occurs in this way, the curvature radius in the longitudinal direction (main scanning direction) of the lens changes due to the warp deformation, so that the imaging position of the lens changes. That is, reducing the warp deformation of the cylindrical lens is a technical issue necessary for realizing a low-cost and high-performance scanning optical system.

The present invention has been made in view of the above technical problems, and an object thereof is to correct the warp deformation of a cylindrical lens formed in a long shape and to perform an optical scanning device capable of highly accurate writing. To provide.

[0013]

In order to achieve the above object, a protrusion is provided at the central portion in the longitudinal direction of a cylindrical lens, and when the lens is incorporated into an optical unit, the protrusion is pushed in the opposite direction to the warp of the lens. Reduces deformation. The simplest means for pushing the protrusion is to provide a screw near the protrusion and deform the lens by the pressing force of the screw to correct the warp. That is, when the cylindrical lens is incorporated in the optical unit, the screw is pushed in the direction to reduce the warp of the lens. At that time, the work is performed while monitoring the image forming position of the laser beam, and when the predetermined image forming position is reached in the entire area of the lens, the adjusting work is finished and the screw is fixed.

Further, the deformation in the plane tilt direction of the lens can be corrected by independently pushing the upper and lower ends of the lens in the direction orthogonal to the longitudinal direction of the lens (sub-scanning direction).

In other words, in order to achieve the above object, the present invention provides an optical scanning for scanning a medium to be scanned with light emitted from a light source through a scanning means provided with an optical system including a plastic lens. The apparatus is characterized in that it is provided with means for correcting the warp of the plastic lens by an external force.

In this case, the correcting means may apply an external force from the convex side of the warp of the plastic lens to the concave side. Further, the correcting means may be provided in the sub-scanning direction with the main body portion of the plastic lens being sandwiched between the longitudinal central portions of the plastic lens.

As the correcting means, a screw member supported by a supporting portion provided in an optical unit on which the plastic lens is mounted, or a piezo actuator can be applied. At this time, after correcting the warp of the plastic lens by the piezo actuator, a means for holding the state may be provided. As the holding means, a screw member supported by a supporting portion provided in the optical unit mounting the plastic lens can be used. Further, as the holding means, it is possible to provide a meshing portion on each of the plastic lens side and the optical unit side on which the plastic lens is mounted so that the relative positions of the both are held constant. As the meshing means, for example, a combination of triangular cross sections can be used, and in this case, it is preferable that the surface on which the force is applied is formed perpendicular to the direction in which the force acts.

Further, when the piezo actuator is used, the means for detecting the warp of the plastic lens and the energization to the piezo actuator are controlled according to the amount of the warp detected by the means for detecting the warp. It is also possible to automatically correct the warp by providing control means for correcting the warp of the plastic lens.
In this case, a strain gauge can be used as a means for detecting the warp. Further, the portion that receives the external force applied by the means for applying the external force may be formed integrally with the plastic lens body.

Here, the operation of the above configuration will be described. FIG. 6 shows a state in which a warp occurs at the center of the lens in the longitudinal direction and the lens is deformed to have a gentle curvature in the principal axis direction. This is almost equivalent to the case where a concentrated load acts on the central portion of the both-end supporting beam and maximum bending occurs in the central portion of the beam. Therefore, the lens pressing force required to correct the warp can be calculated as follows. As shown in FIG. 5, the actual lens has a curvature in the sub-scanning direction (length direction of 15 mm in the figure), but here the lens has a rectangular sectional shape for simplicity. The dimensions of the lens as shown in FIG, lens length: 300 mm Lens Width: 15 mm lens thickness: When 5 mm, the second moment ^{is, I = 1.5 × 0.5 3/} 3 = 0.063cm 4 Becomes Assuming that the bending elastic modulus of the plastic material is E = 24000 kg / cm ² , the bending rigidity EI of the lens is EI = 24000 × 0.063 = 1512 kg · cm ² . As shown in FIG. 7, when the concentrated load W acts on the center of the beam having the length L, the deflection amount y of the beam at the load point is y = WL ³ / 48EI (1). Therefore, the equation (1) can be transformed into W = 48EIy / L ³ (2).

That is, by using the equation (2), it is possible to obtain the magnitude of the lens pressing force required to correct the warp deformation having the magnitude of y at the central portion of the lens. In the case of the lens shown in FIG. 6, the bending rigidity of the lens is EI = 1512 kg · cm ^{2 according} to the above calculation, and the lens length is L =
300 mm = 30 cm, and the maximum warp amount at the lens center is 350 μm = 0.035 cm. Therefore,
The magnitude of the lens pressing force W required to correct the lens warp deformation is W = 48 × 1512 × 0.035 / 30 ³ = 0.094 kg from the above formula (2).

This indicates that by applying a pressing force of 94 g to the center of the lens, the lens deformation due to the warpage that occurs during molding can be corrected. Therefore, it is possible to sufficiently correct the lens deformation even with the pressing force of a small screw such as a screw.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, the same parts as those in the above-mentioned conventional example are designated by the same reference numerals, and the duplicated description will be appropriately omitted.

[First Embodiment] FIG. 5 shows a lens shape according to the first embodiment. As described above, this lens is a lens having a cylindrical shape having a length of 300 mm, a lens width in the sub-scanning direction of 15 mm, a radius of curvature in the sub-scanning direction of 100 mm, and a radius of curvature in the main scanning direction of ∞. Acrylic synthetic resin is used for the lens material,
It was molded using an injection molding machine. The main molding conditions are maximum injection pressure of 850 kg / cm ² , injection time of 20 seconds, injection speed of 1
The holding pressure is 0 mm / s, the holding pressure is 500 kg / cm ² , and the holding time is 10 seconds. As a result of measuring the amount of warpage of the molded lens, a warp of 0.35 mm (= δ) was found at the center of the lens. The warpage δ = 0.35 mm is the maximum value as can be seen from FIG. The occurrence of a warp of 0.35 mm in the central portion of the lens is equivalent to having a certain radius of curvature in the main scanning direction of the cylindrical lens. In this case, 0.3
The size of the warp of 5 mm is 32 in the radius of curvature in the main scanning direction.
It corresponds to 143 mm.

When a cylindrical lens having a warp of 0.35 mm is incorporated in the optical unit without correcting the warp, both ends of the lens in the sub-scanning direction are 0.
A field curvature of 2 mm was generated, and a field curvature of 0.15 mm was generated in the center of the lens in the main scanning direction. Therefore, we decided to correct the warp of the lens and reduce the field curvature.

1 and 2 show a warp deformation correcting mechanism of the cylindrical lens 1 according to this embodiment. In this embodiment, the cylindrical lens 1 is provided between the Fθ lens 108 and the photoconductor 102. The cylindrical lens 1 is integrally provided with a protrusion 2 at the lower part of the central portion,
The convex surface 2a of the protrusion 2 can be pushed by the adjusting screw 3. The adjusting screw 3 is a support portion 4 provided on the apparatus main body side (main body base side of the optical unit).
It is screwed on and installed so that it can advance and retract. Both ends of the cylindrical lens 1 are incorporated into the lens hold portions 5 installed on both sides to fix the position, and the protrusion 2 is pushed by the adjusting screw 3.

That is, as shown in FIG. 1, since the cylindrical lens 1 is slightly warped and deformed, the field curvature is generated as described above. Then, the adjusting screw 3 is turned to bring the tip into contact with the surface 2c, and further turned to push the protrusion 2 in the direction opposite to the warp until the field curvature disappears as shown in FIG. The presence or absence of the curvature of field is determined by the image forming position where the cylindrical lens 1 forms an image. That is, in the curved state of FIG. 1, the laser light is focused to check the image forming position, the image forming position is observed while turning the adjusting screw 3, and the predetermined image forming position is reached in the entire lens as described above. Judgment is made based on whether or not it is done, and when it is reached, the adjustment is finished. When the adjustment is completed, the adjusting screw 3 is fixed with an adhesive 4a so that the adjusting screw 3 does not loosen. As the fixing means, a nut may be used instead of the adhesive 4a. Note that the protrusion 2 may be a separate component instead of being integrally molded, and may be attached to the lens 1 main body after the cylindrical lens 1 main body is molded.

Also. After the warp deformation of the cylindrical lens 1 is corrected, a lock mechanism for fixing the lens 1 at the correction position may be integrally formed with the lens 1 main body. This example is shown in FIG. In this example, a projection 6 for correcting and adjusting the warp deformation of the lens is provided on the bottom of the center of the lens 1 in the longitudinal direction, and a projection 7 for fixing the lens 1 at the deformation correction position is provided on the projection 6. There is. In the present embodiment, the sectional shape of the lens fixing claw 7 is a right triangle having one side perpendicular to the lens bottom surface as shown in FIG. 3, and the claw 9 that meshes with the claw 7 is provided on the base 8 side. Are formed to prevent displacement.

Table 1 shows the state of the amount of curvature of field before and after the correction of the warp deformation of the lens.

[0029]

[Table 1]

As can be seen from the above table, since the warp deformation of the cylindrical lens 1 is corrected until the field curvature disappears, naturally the field curvature disappears after the lens deformation correction. In addition, before and after correction, numbers are shown numerically to indicate the amount of deviation from the focus position in mm, where (−) represents the near side deviation and (+) represents the far side deviation. .

Incidentally, such a cylindrical lens 1
The correction of the warp (distortion) is particularly effective in improving the image quality of a high-definition laser printer, and is also very effective in preventing color misregistration in a full-color laser printer.

[Second Embodiment] This embodiment is an example of reducing a lens tilt error that occurs when a cylindrical lens is incorporated in an optical unit.

When the surface tilt error of the cylindrical lens 1 occurs by 0.5 °, in this optical system, the image forming position is displaced by about 1.3 mm over the entire lens range in the sub-scanning direction. Since the deviation of the image forming position is substantially uniform within the light scanning range, the diameter of the laser beam focused on the photosensitive drum (photosensitive member 102) is substantially uniform. However, since the size of the focused laser beam diameter is larger than the design value due to the deviation of the image forming position, the deviation of the image forming position is reduced when a high resolution printing result is obtained as a laser beam printer. There is a need. Therefore, in this embodiment, the projections 2a are formed on the upper and lower ends (sub-scanning direction) of the cylindrical lens 1.
2b are provided, and the support bases 4a projecting from the lower and upper bases 8a and 8b are provided on the respective convex surfaces 2d and 2e.
The tips of the adjusting screws 3a and 3b screwed onto the 4b are brought into contact with each other,
The strokes of the adjusting screws 3a and 3b are changed and adjusted independently to correct the surface tilt of the cylindrical lens 1. For example, when the lens is mounted with an inclination of 0.5 ° as shown in FIG. 4, the upper end of the lens is set at 13 degrees from the original setting position.
Projection 2 on the top of the lens because it is 0 μm off
When b is pressed by 130 μm using the adjusting screw 3b, the surface tilt error is eliminated.

In addition, all other parts not specifically described are constructed in the same manner as in the above-mentioned conventional example and the first embodiment.

In this embodiment, the surface tilt error of the lens is reduced, but the surface tilt error caused by the inclination of the rotation axis of the rotary polygon mirror 106 is also corrected.
A minute error that cannot be corrected by adjusting the rotation axis of 06 can be easily adjusted only by the optical system.

[Third Embodiment] This embodiment is an example of electrically correcting the warp of the cylindrical lens.

FIG. 8 is a control block diagram for automatically correcting lens deformation, and FIG. 9 is a perspective view of a cylinder lens to be corrected. In this example, the protrusion 2 is provided below the cylinder lens 1, and the strain gauge 10 is attached to the surface of the cylindrical lens 1 on the side of the photoconductor 102 as a detector. Also, the convex surface 2 of the protrusion 2
The operating surface of the piezo actuator 11 is brought into contact with c. The detection output of the strain gauge (detector) 10 is input to the processing circuit 12 of the servo system as shown in FIG. 8, and the piezoelectric actuator 1 according to the instruction output from this processing circuit 12.
1 is operated and the operating surface of the actuator 11 is pressed against the surface 2c, whereby the cylindrical lens 1
Change the curvature of. This curvature, in other words, the deformation amount 13 of the lens is monitored in real time by the strain gauge 10, and the necessary amount is automatically corrected. If the relationship between the warp (strain amount) and the output of the strain gauge 10 is calibrated in advance and the relationship between them is stored in the processing device 12, the warp of the cylinder lens 1 is corrected at an arbitrary timing. I can do it. When the optical scanning is not performed, the power supply to the piezo actuator 11 is also cut off, and the cylinder lens 1 returns to the original deformed state by its elasticity. In addition, each part that is not particularly described is configured in the same manner as the above-described conventional example, the first embodiment, and the second embodiment.

In this embodiment, the single piezo actuator 11 is not provided, but as in the second embodiment, protrusions are provided above and below the cylindrical lens 1 in the sub-scanning direction and are provided separately. The piezo actuator 11 can also be used to correct the surface tilt. Also,
It is also possible to provide a pair of piezoelectric actuators 11 so as to sandwich the projecting portion 2 and correct the distortion of the cylindrical lens 1.

In this embodiment, a control current is passed through the piezo actuator 11 so that the piezo actuator 1
Although the deformation amount of 1 is kept constant, the cylindrical lens 1 is pressed by the adjusting screw when the warp (distortion δ) becomes 0 in combination with the adjusting screw in the first embodiment. It can also be configured to. In this case, the warp (distortion) can be automatically corrected without monitoring the image forming position as described above.

Further, in this embodiment, a strain gauge is used to detect the strain amount of the cylindrical lens 1. However, in addition, eddy current is used, electrostatic capacitance is used for detection, and a laser displacement meter is used. It is also possible to do so.

[0041]

As described above, the present invention has the following effects.

According to the first aspect of the present invention, which is provided with a means for correcting the warp of the plastic lens by an external force, the optical scanning device incorporating the plastic lens is provided with the means for correcting the warp, so the plastic lens is incorporated. The warp can be corrected later, and the inexpensive plastic lens enables accurate writing.

According to the invention of claim 2, wherein the correcting means applies an external force from the convex side of the warp of the plastic lens to the concave side, the warp is corrected by a mechanism of merely pressing the plastic lens from the convex side. can do.

According to the invention as set forth in claim 3, wherein the means for applying an external force is provided in the sub-scanning direction with the plastic lens interposed therebetween, the inclination of the plastic lens in the sub-scanning direction can be adjusted. The error correction can be easily performed, and highly accurate writing is possible.

According to the invention of claim 4, the means for applying an external force comprises a screw member supported by a supporting portion provided in an optical unit on which the plastic lens is mounted. The warp of the plastic lens can be corrected, and high-precision writing can be performed at low cost.

According to the invention of claim 5, the means for applying an external force comprises a piezo actuator supported by a support portion provided in an optical unit on which the plastic lens is mounted. The warp can be corrected.

According to the invention of claim 6, further comprising means for holding the state of the plastic lens after the warp of the plastic lens is corrected by a piezo actuator. This simplifies the adjustment work.

The invention according to claim 7, wherein the holding means comprises a screw member supported by a supporting portion provided in an optical unit on which the plastic lens is mounted, and the holding means holds the plastic lens side and the plastic lens. According to the invention of claim 8, which comprises meshing means provided on the optical unit side to be mounted,
The warped state can be maintained with a simple mechanical structure.

A means for detecting the warp of the plastic lens and a control means for correcting the warp of the plastic lens by controlling the power supply to the piezo actuator according to the amount of the warp detected by the means for detecting the warp are provided. According to the invention described in claim 9, the warp of the plastic lens can be automatically corrected, and the adjustment work can be performed extremely easily.

According to the tenth aspect of the present invention in which the means for detecting the warp is a strain gauge, the warp of the plastic lens can be reliably detected by an inexpensive detection element.

According to the invention of claim 11, the portion for receiving the external force applied by the means for applying the external force is formed integrally with the plastic lens body by the external force applied to the plastic lens side. The warp can be corrected without deteriorating the optical performance of the plastic lens.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a state before correction of an optical system having a warp correction mechanism for a cylindrical lens according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a state after correction of the optical system of FIG.

FIG. 3 is a schematic view showing a mechanism for holding the corrected state after correcting the warp of the cylindrical lens.

FIG. 4 is a schematic view showing a mechanism for correcting a surface tilt of a cylindrical lens.

FIG. 5 is a perspective view showing an outer shape and an outer dimension of a cylindrical lens.

FIG. 6 is a plan view showing a state of deformation due to the warp of the cylindrical lens.

FIG. 7 is a model diagram showing a warped deformation state of a cylindrical lens.

FIG. 8 is a control block diagram for electrically operating the correction mechanism of the cylindrical lens.

FIG. 9 is a perspective view showing an example of correcting a cylindrical lens by a piezo actuator.

FIG. 10 is a schematic configuration diagram showing an optical system of a general laser beam printer.

FIG. 11 is a schematic configuration diagram showing an image forming system of a general laser beam printer.

[Explanation of symbols]

 1 Cylindrical lens 2,2b, 2c Projection part 3,3a, 3b Adjustment screw 4 Support part 4a Adhesive 5 Hold part 6 Projection part 7,9 Claw 8,8a, 8b Base 9 Claw 10 Strain gauge 11 Piezo actuator 12 Processing device 13 lens deformation amount 101 light source 102 photoconductor 106 rotating polygon mirror 108 Fθ lens

Claims (11)

[Claims] 1. An optical scanning device for scanning light emitted from a light source onto a medium to be scanned through a scanning means having an optical system including a plastic lens, wherein the warp of the plastic lens is caused by an external force. An optical scanning device comprising a correcting means. 2. The optical scanning device according to claim 1, wherein the correcting means applies an external force from the convex side of the warp of the plastic lens to the concave side. 3. The optical scanning device according to claim 1, wherein the correction means are provided in the sub-scanning direction with the plastic lens interposed therebetween. 4. The optical scanning device according to claim 1, wherein the correcting means comprises a screw member supported by a supporting portion provided on an optical unit on which the plastic lens is mounted. 5. The optical scanning device according to claim 1, wherein the correcting means comprises a piezo actuator supported by a supporting portion provided in an optical unit on which the plastic lens is mounted. 6. The optical scanning device according to claim 5, further comprising means for correcting the warp of the plastic lens by the piezo actuator and then holding the state. 7. The optical scanning device according to claim 6, wherein the holding means is a screw member supported by a support portion provided in an optical unit on which the plastic lens is mounted. 8. The optical scanning device according to claim 6, wherein the holding means comprises engaging means provided on the plastic lens side and on the optical unit side on which the plastic lens is mounted, respectively. 9. A means for detecting the warp of the plastic lens, and a control for correcting the warp of the plastic lens by controlling energization to the piezo actuator according to the amount of the warp detected by the means for detecting the warp. The optical scanning device according to claim 5, further comprising means. 10. The optical scanning device according to claim 8, wherein the means for detecting the warp comprises a strain gauge. 11. The optical scanning device according to claim 1, wherein a portion that receives an external force applied by the correcting means is integrally formed with the plastic lens main body.