JP4051741B2 - Optical scanning device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning device, and more particularly to an optical scanning device that deflects a light beam in a predetermined main scanning direction by a rotating polygon mirror and scans a surface to be scanned with the deflected light beam.
[0002]
[Prior art]
Conventionally, as an optical scanning device used in an image forming apparatus such as a digital copying machine or a laser beam printer, a light beam modulated based on digital image data of an image to be formed is used as a reflection type such as a rotary polygon mirror. For example, an image that is reflected by a deflector and deflected and then condensed as a spot on a surface to be scanned by an imaging lens such as an fθ lens is used widely. The fθ lens is a lens that refracts a light beam deflected at a constant angular velocity by a rotating polygon mirror so as to scan the surface to be scanned at a constant velocity.
[0003]
As a conventional specific configuration, a 6 to 10 rotating polygon mirror is generally driven by a motor having a rotational speed of 8000 to 20000 rpm (= rotational speed / minute). Therefore, a high-quality and high-speed output is strongly demanded, and the above-described rotary polygon mirror and motor configuration cannot be fully supported.
[0004]
By the way, in order to achieve high image quality, writing at a high density (high resolution) is the most effective means, but in order to increase the density of a written image, a light beam scans the surface to be scanned. In the scanning direction, it is necessary to increase the modulation speed of the light beam based on the digital image data, and in the sub-scanning direction, it is necessary to increase the number of writings per unit time.
[0005]
In order to realize high-speed output, it is effective to increase the process speed of the image forming apparatus (generally, the speed at which paper is conveyed). However, as the process speed increases, the peripheral speed of the medium to be scanned (for example, a photosensitive drum) increases as viewed from the optical scanning apparatus. Therefore, it is necessary to increase the writing speed of the optical scanning apparatus almost in proportion to the process speed.
[0006]
That is, in order to satisfy the requirement of high image quality and high-speed output, the optical scanning device must rapidly increase the number of write lines per unit time. For example, when the writing density is 1.5 times (400 dpi → 600 dpi) and the output speed is 1.5 times, the writing speed (= number of writings / time) of the optical scanning device is 2.25 times (= 1.5). × 1.5) Required.
[0007]
On the other hand, methods for increasing the writing speed of the optical scanning device include methods such as increasing the number of rotations of the motor that drives the rotating polygon mirror, increasing the number of surfaces of the rotating polygon mirror, and multiplexing the light beam. Proposed.
[0008]
However, if the rotational speed of the rotary polygon mirror driving motor is excessively increased, the load on the motor increases, causing not only an increase in power consumption but also a problem (1) in that the failure rate increases.
[0009]
Further, when the number of surfaces of the rotary polygon mirror is increased, the size of the rotary polygon mirror increases, so that the load on the motor increases, causing the problem (2) of increased power consumption and failure rate as described above. The increase in the size of the rotating polygon mirror is due to the constraint that the light beam incident on the rotating polygon mirror is deflected without protruding from the reflecting surface regardless of the rotation angle of the rotating polygon mirror. Arises because is determined.
[0010]
Furthermore, the multiple light beams require a light source having a plurality of light emitting points or a complicated optical system that synthesizes light beams emitted from a plurality of light sources with high accuracy, and there is a problem (3) that the apparatus becomes expensive. is there.
[0011]
As a technique for solving the above problems (1) to (3), a technique disclosed in Japanese Patent Application Laid-Open No. Hei 8-171069 is known, and FIG. 8 is a schematic configuration diagram of an optical scanning device 74 disclosed in this publication. is there.
[0012]
The optical scanning device 74 shown in FIG. 8 employs an overfilled optical system that irradiates the reflecting surface 76A with a laser beam having a width wider than the surface width in the main scanning direction of the reflecting surface 76A of the rotary polygon mirror 76. As a result, high resolution and high speed can be realized without increasing the rotational speed of the rotary polygon mirror 76 and without increasing the diameter of the rotary polygon mirror 76.
[0013]
Further, the first optical system for making the light beam incident on the rotary polygon mirror 76 is arranged in the order of the collimator lens 78, the cylindrical lens 80, and the convex lens 82, and the light source 84 is arranged inside the focal position of the collimator lens 78. By using divergent light, the optical path length from the light source 84 to the rotary polygonal mirror 76 is shortened, and the deflection angle is made larger than ± 15 °, thereby including an overfilled optical system previously proposed. The size of the apparatus is reduced compared to the optical scanning apparatus.
[0014]
[Problems to be solved by the invention]
However, the deflection angle of the light beam by the rotating polygon mirror greatly depends on the number of surfaces of the rotating polygon mirror, and the effective scanning rate (ratio of the angle used for image writing to the maximum angle that the rotating polygon mirror can deflect) is increased. However, it is unavoidable that the focal length of the imaging optical system becomes longer as the rotary polygon mirror becomes more polyhedral.
[0015]
In addition, the second imaging optical system of the optical scanning device disclosed in Japanese Patent Laid-Open No. 8-171069 is composed of an fθ lens that combines two lenses and a cylindrical mirror, so that the optical components are expensive. In addition, the position of the cylindrical mirror on the optical path from the rotating polygon mirror to the surface to be scanned and the folding angle of the cylindrical mirror (incident angle in the sub-scan section) directly affect the imaging performance, so the optical path layout It must be said that the degree of freedom is low.
[0016]
The present invention has been made to solve the above problems, and a first object of the present invention is to provide a small-sized and low-cost optical scanning device that realizes high speed and high image quality. It is a second object of the present invention to provide an optical scanning device capable of minimizing performance degradation due to processing errors and assembly errors in an optical scanning device in which a plurality of optical paths are folded back.
[0017]
[Means for Solving the Problems]
  In order to achieve the first object, an optical scanning device according to claim 1 is characterized in that a light source and a plurality of reflecting surfaces rotating around a predetermined rotation axis at a substantially equal angular velocity and parallel to the rotation axis are arranged on the outer periphery. A rotating polygon mirror that deflects an incident light beam by the reflecting surface, and a light beam emitted from a light source is converged in a sub-scanning direction parallel to the rotation axis, and is incident on the sub-surface on the reflecting surface. A first imaging optical system that forms a line image along the main scanning direction perpendicular to the scanning direction, and a substantially conjugate imaging of the reflecting surface and the surface to be scanned in a cross section along the sub-scanning direction And a second imaging optical system that forms an image of the light beam deflected by the reflecting surface as a spot that scans the surface to be scanned at a constant speed, and the second polygonal mirror from the second polygonal mirror. Arranged on the optical path to the image optical system and along the sub-scanning direction A first mirror pair having a relative angle of 90 ° with respect to the surface, and a relative angle of 90 ° with respect to the cross section along the sub-scanning direction disposed on the optical path from the second imaging optical system to the surface to be scanned. A second pair of mirrors forming an angle, andThe second imaging optical system is composed of a single plastic aspheric lens, and a conjugate magnification relating to an imaging relationship between the reflecting surface and the scanned surface in a cross section along the sub-scanning direction. β satisfies 1.5 <β <3.5, and the light beam is incident on the reflecting surface of the rotary polygon mirror as an optical beam wider than the surface width along the main scanning direction of the reflecting surface. It is characterized by.
[0018]
On the other hand, the optical scanning device according to claim 2 is configured such that a light source and a plurality of reflecting surfaces rotating around a predetermined rotation axis at a substantially equal angular velocity and parallel to the rotation axis are formed on the outer periphery, and the incident light beam And a rotating polygon mirror for deflecting the light beam by the reflecting surface, and a light beam emitted from the light source is converged in a sub-scanning direction parallel to the rotation axis, and in the main scanning direction perpendicular to the sub-scanning direction on the reflecting surface. A first imaging optical system that forms an image along the line, and a substantially conjugate imaging relationship between the reflecting surface and the surface to be scanned in a cross section along the sub-scanning direction. A second imaging optical system that forms an image of the deflected light beam as a spot that scans the surface to be scanned at a constant speed, and an optical path from the rotary polygon mirror to the second imaging optical system. And a relative angle of 90 ° is formed in the cross section along the sub-scanning direction. A first mirror pair and a second mirror pair disposed on an optical path from the second imaging optical system to the scanned surface and having a relative angle of 90 ° in a cross section along the sub-scanning direction; HaveThe first mirror pair receives a light beam from the first imaging optical system, is folded back by the first mirror pair and reflected by a predetermined plane mirror, and the reflected light beam is again reflected by the first mirror pair. It is arranged such that it is incident on one mirror pair in the opposite direction to the first time, is folded by the first mirror pair, and is incident on the reflecting surface of the rotating polygon mirror.
[0020]
  In order to achieve the second object,3In the described optical scanning device, the claim2In the optical scanning device according to claim 1, the plane mirror is rotatable around a predetermined axis parallel to a rotation axis of the rotary polygon mirror, and a normal line between the predetermined axis and a reflection surface of the rotary polygon mirror Are provided so as to be able to rotate independently of the rotation around the predetermined axis.
[0021]
  Claims4In the described optical scanning device, claims 1 to3In the optical scanning device according to any one of the above, the light source is in a direction corresponding to the main scanning direction and a direction corresponding to the sub-scanning direction within a plane orthogonal to the optical axis of the emitted light beam. It is characterized by being independently movable.
[0022]
  Claims5In the described optical scanning device, claims 1 to4In the optical scanning device according to any one of the above, the second mirror pair is provided to be rotatable and translatable within a cross section along the sub-scanning direction.
[0023]
  Claims6In the described optical scanning device, claims 1 to5In the optical scanning device according to any one of the above, the second mirror pair is a fixed point on a straight line formed by intersecting planes obtained by extending the reflecting surfaces of the mirrors of the second mirror pair. It is fixed.
[0025]
  Claim 1 aboveAnd claim 2In the described optical scanning device, the light beam emitted from the light source is incident on the first imaging optical system, and the first imaging optical system converges the light beam in the sub-scanning direction and reflects the rotating polygon mirror. A line image along the main scanning direction perpendicular to the sub-scanning direction is formed on the surface. The rotating polygon mirror rotates around a predetermined rotation axis at a substantially equal angular velocity, and deflects the light beam by a reflecting surface formed on the outer periphery. The light beam deflected by the rotating polygon mirror is incident on the second imaging optical system. This second imaging optical system has a substantially conjugate imaging relationship between the reflecting surface of the rotary polygon mirror and the surface to be scanned in a cross section along the sub-scanning direction, and an incident light beam (= main scanning). As a line image along the direction, a light beam formed on the reflecting surface of the rotary polygon mirror and deflected by the reflecting surface is imaged on the surface to be scanned as a spot for scanning the surface to be scanned at a constant speed.
[0026]
As the optical scanning device, an optical scanning device including the overfilled scanning optical system 90 shown in FIG. 9 can be exemplified. FIG. 9 is a plan view (development view) of an overfilled scanning optical system 90 including a single fθ lens 17. Here, for example, the rotary polygon mirror 16 has 12 reflecting surfaces and has an inscribed diameter of 25 mm, and the scanning width L1 by the rotary polygon mirror 16 corresponds to the short side size (297 mm) of A3. . The distance from the reflecting surface of the rotating polygon mirror 16 to the rotating polygon mirror side lens surface 17A is 135 mm, the center thickness of the fθ lens 17 is 20 mm, and the distance from the scanned surface side lens surface 17B to the scanned surface 20A is 360 mm. Yes.
[0027]
The fθ lens 17 tends to increase in size when a single lens is used to obtain sufficient imaging performance in terms of optical design, but low cost can be realized by using a plastic lens. The angle formed between the principal ray of the first imaging optical system incident on the rotary polygon mirror 16 and the optical axis of the second imaging optical system (fθ lens 17) is 35 °, and is reflected during deflection scanning. The angle is set such that the light beam overflowing to the reflection surface adjacent to the surface and reflected by the adjacent reflection surface does not return to the light source 11.
[0028]
  In order to mount the optical system as described above in a small casing, the present invention can be applied to any one of claims 1 to 3.And claim 2In the described optical scanning device, a pair of mirrors having a relative angle of 90 ° in a section along the sub-scanning direction is arranged on the optical path from the rotary polygon mirror to the second imaging optical system and from the second imaging optical system. They are arranged on the optical path to the surface to be scanned. The mirror pair disposed on the optical path from the rotary polygon mirror to the second imaging optical system is referred to as a first mirror pair, and is disposed on the optical path from the second imaging optical system to the scanned surface. The mirror pair is referred to as a second mirror pair.
[0029]
Like the first mirror pair and the second mirror pair, the mirror pair having a relative angle of 90 ° in the cross section along the sub-scanning direction bends the light beam as shown in FIG. By arranging such a mirror pair on the optical path, the optical path length on mounting can be reduced to about half of the unfolded state.
[0030]
As a configuration for bending the light beam, a configuration in which it is bent by one mirror 99 as shown in FIG. 10B is also conceivable, but in this configuration, two mirrors (as shown in FIG. 10A) ( Compared with the case where the mirror pair is bent at 98, a larger space is required in the height direction, which may make it difficult to reduce the size of the optical scanning device.
[0031]
In the example of FIGS. 10A and 10B, when the difference in height between the center point of the first imaging optical system 106 and the light beam incident point on the rotary polygon mirror 104 is compared, the light beam is converted into a mirror pair. The difference in height when the light beam is bent at 98 is 10 mm, whereas the difference in height when the light beam is bent at the mirror 99 is 27.5 mm. That is, bending with two mirrors (mirror pair) is more effective for miniaturization of the optical scanning device than bending with one mirror. Note that the gap J1 shown in each of FIGS. 10A and 10B represents a gap necessary to prevent interference between the incident light beam and the emitted light beam, and the gap J2 is the first imaging optical system. A gap (about 25 mm) necessary for attaching 106 and the rotary polygon mirror 104 from above is shown.
[0032]
  Thus, claim 1And claim 2In the described invention, mirror pairs having a relative angle of 90 ° are arranged before and after the second imaging optical system without using an optical system having a complicated structure and an expensive structure. The optical path is folded twice in the optical path leading to, so that the optical path length on mounting can be shortened at once. That is, the optical path length on mounting can be shortened at a stretch while suppressing the height of the optical scanning device, so that the optical scanning device can be downsized while avoiding an increase in device cost.
[0033]
  here,In the first aspect of the present invention, the second imaging optical system is constituted by a single plastic aspheric lens, and the imaging relationship between the reflecting surface and the scanned surface in the cross section along the sub-scanning direction. The conjugate magnification β according to is configured to satisfy 1.5 <β <3.5.
In this way, by configuring the second imaging optical system with an inexpensive single plastic aspheric lens, the cost of the optical scanning device can be kept low.
If the conjugate magnification β related to the imaging relationship between the reflecting surface and the scanned surface in the cross section along the sub-scanning direction is 1.5 or less, sufficient imaging performance cannot be obtained with a single lens. It is difficult to secure a space for arranging the 90 ° mirror pair before and after the second imaging optical system. When the conjugate magnification β is 3.5 or more, the lens of the second imaging optical system is increased in size and the casing of the optical scanning device is increased in size.
Therefore, by setting the conjugate magnification β to be larger than 1.5 and smaller than 3.5 (that is, 1.5 <β <3.5), the 90 ° mirror pair is placed before and after the second imaging optical system. Even with a single lens, sufficient optical performance can be obtained while securing a sufficient space for arrangement, and an increase in the size of the lens of the second imaging optical system can be avoided. That is, a high-performance and small-sized optical scanning device can be provided.
  Also,Claim1As described above, in the overfilled system configured such that the light beam is incident on the reflecting surface of the rotating polygon mirror as an optical beam wider than the surface width along the main scanning direction of the reflecting surface, as described above. Even if the effective scanning rate is increased, the focal length of the imaging optical system becomes long. However, by applying the invention according to claim 1, the optical path length on mounting becomes long even if the optical path length of the imaging optical system becomes long. Therefore, it is possible to avoid an increase in the size of the optical scanning device.
  on the other hand,Claim2As in the described invention, the light beam from the first imaging optical system is incident on the first mirror pair, folded back by the first mirror pair, reflected by a predetermined plane mirror, and reflected. The first mirror pair is arranged so that the light beam is incident on the first mirror pair again in the direction opposite to the first time, and is folded by the first mirror pair and incident on the reflecting surface of the rotating polygon mirror. It is preferable to do.
[0034]
In this way, the optical path from the first imaging optical system to the rotary polygon mirror is bent and the light beam passes through the first mirror pair twice, so that the optical system in the previous stage of the rotary polygon mirror can be As for the optical path, the optical path length on mounting can be reduced to about half of the unfolded state, and the optical scanning device can be further miniaturized with a relatively simple configuration without increasing the number of components.
[0035]
As described above, the optical path of the optical system subsequent to the rotary polygon mirror (the optical path from the rotary polygon mirror to the scanned surface) is folded twice by the first mirror pair and the second mirror pair, The optical path length on mounting is shortened at a stretch.
[0036]
  Therefore, the claim2According to the described invention, in both the optical path of the optical system upstream of the rotary polygon mirror and the optical path of the optical system downstream of the rotary polygon mirror, the optical path length on mounting is shortened, and the optical scanning device can be further downsized. Can be planned.
[0038]
  Claims3In the described invention, the plane mirror is rotatable about a predetermined axis parallel to the rotation axis of the rotary polygon mirror and within a plane including the predetermined axis and the normal of the reflecting surface of the rotary polygon mirror. It is provided so as to be able to rotate independently of the rotation around the axis.
[0039]
By arranging the plane mirror that can rotate in the biaxial direction as described above in combination with the first mirror pair configured so that the light beam passes twice from the light source to the rotary polygon mirror as described above. Even if there is an error in the incident angle or the like of the light beam incident on the first mirror pair, a flat surface is used so that the light beam is guided to a desired position with respect to the reflecting surface of the rotary polygon mirror during assembly and adjustment. The position of the mirror can be adjusted by rotating it in the biaxial direction.
[0040]
  Claims4As in the described invention, the light source is a direction corresponding to the main scanning direction (hereinafter referred to as a main scanning corresponding direction) and a direction corresponding to the sub scanning direction in a plane orthogonal to the optical axis of the emitted light beam. It is desirable to provide each independently movable (hereinafter referred to as a sub-scanning corresponding direction). Thereby, at the time of assembly / adjustment, the light source is moved in the direction corresponding to the main scanning direction and the direction corresponding to the sub-scanning direction so that the error such as the incident angle of the light beam incident on the first mirror pair becomes small. The position of the light source can be adjusted by appropriately moving, and a more accurate optical path adjustment is possible.
[0041]
  Claims5As in the described invention, it is desirable to provide the second mirror pair so as to be rotatable and translatable within a cross section along the sub-scanning direction. This makes it possible to correct the position of the scanning line on the surface to be scanned, the imaging magnification, and the like during assembly / adjustment.
[0042]
  Next, the claim6In the described invention, the second mirror pair is fixed at a fixed point on a straight line formed by intersecting planes obtained by extending the reflecting surfaces of the mirrors of the second mirror pair.
[0043]
Here, the reason why the optical path deviation is minimized by fixing the second mirror pair at a fixed point on a straight line formed by extending the reflection surface of each mirror will be described.
[0044]
FIG. 11 is a sub-scan sectional view showing an optical path when the second mirror pair 19 rotates due to an error. It is assumed that the incident beam I to the second mirror pair 19 and the exit beam O from the second mirror pair 19 are both in the paper.
[0045]
A broken line ACB in FIG. 11 shows a state in which the second mirror pair 19 is ideally attached, and the light beam passes through an optical path of I → A → B → O. A solid line A′CB ′ indicates a state in which the second mirror pair 19 is rotated around a straight line C that extends by extending two reflecting surfaces while maintaining a relative angle of 90 °. It passes the optical path of I → A ′ → B ′ → O.
[0046]
When the perpendicular line standing at the point A ′ on the mirror 19A is A′E, the perpendicular line standing at the point B ′ on the mirror 19B is B′F, and the intersection of the two perpendicular lines is D, the incident light beam I is emitted. Since both of the light beams O are in the plane of the paper, the following relationship is required by the law of reflection.
[0047]
∠IA'E = ∠EA'B '(1)
∠A'B'F = ∠FB'O (2)
If the relative angle between the two mirrors is maintained,
∠A'CB '= 90 ° (3)
Since ∠EA′C and ∠CB′F are both 90 °, the quadrangle A′CB′D is a rectangle.
[0048]
When the intersection point of the diagonal line A'B 'and the diagonal line CD of the rectangle A'CB'D is an intersection point G, the triangle A'GD is an isosceles triangle,
∠CDA '= ∠EA'B' (4)
Therefore, from equations (1) and (4),
∠IA'E = ∠CDA '(5)
Is obtained,
IA '// DC (6)
It becomes. That is, the intersection point G is a point located on a straight line passing through the point C and parallel to the incident beam IA ′.
[0049]
On the other hand, since the incident light beam and the light beam reflected and emitted by the 90 ° mirror 19 are always parallel,
IA '// B'O (7)
After all,
IA '// DC // B'O (8)
It becomes.
[0050]
Here, the intersection point G is the intersection point of the diagonal lines of the rectangle A′DB′C.
A'G = GB '(9)
There is a relationship.
[0051]
From the expressions (8) and (9), the distance La from the point G to the straight line IA ′ is equal to the distance Lb from the point G to the straight line B′O.
[0052]
From the above, the light beam B′O emitted from the second mirror pair 19 is positioned at a position twice the distance from the incident light beam IA ′ to a straight line passing through the point C and parallel to IA ′ (point B ′) is emitted in parallel with the incident light beam IA ′.
[0053]
As described above, when the second mirror pair 19 having a relative angle of 90 ° rotates around a straight line extending by extending the two reflecting surfaces, the position of the incident beam on the second mirror pair 19 changes. Otherwise, the exit position of the exit beam remains unchanged.
[0054]
Thereby, the optical path deviation can be minimized by fixing the holder for holding the second mirror pair at a fixed point on a straight line formed by extending the reflection surface of each mirror.
[0055]
As described above, the second mirror pair that can be used to adjust the incident angle of the light beam on the surface to be scanned is fixed at a fixed point on a straight line that extends by extending the reflecting surfaces of the mirrors. As a result, it is possible to minimize the variation in the alignment of the light beam due to the positional deviation of the second mirror pair that may occur when the screw is tightened after the adjustment is completed, and to obtain good optical performance.
[0060]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, various embodiments according to the present invention will be described.
[0061]
  [First Embodiment]
  First,According to the present inventionA first embodiment will be described. The basic specification of the optical system of the optical scanning device 30 in each of the following embodiments is the same as the configuration of FIG. 9 described above.
[0062]
Hereinafter, the schematic configuration of the optical scanning device 30 will be described along the optical path of the light beam with reference to FIGS. 9, 1, 2 (A), and 2 (B).
[0063]
The light beam emitted from the semiconductor laser 11 as the light source is converted into a light beam that converges loosely by the convex lens 12, and then converges more strongly in the sub-scanning direction by the cylindrical lens 13. The luminous flux is folded back by the first mirror pair 14 (14A, 14B) fixed to the housing 10 at a relative angle of 90 ° and is incident on the flat mirror 15.
[0064]
The plane mirror 15 is configured so that the normal H of the plane mirror 15 is within the plane (plane shown in FIG. 1) orthogonal to the rotation axis 16A of the rotary polygon mirror 16 so that the reflected light beam is directed to the rotary polygon mirror 16. Is arranged so as to form an angle θ with the incident light beam. The light beam returned to the first mirror pair 14 by the plane mirror 15 is turned back again, and then enters the rotating polygon mirror 16 in a convergent state that forms a line image in the vicinity of the reflecting surface 16B. At this time, the incident light beam to the rotary polygon mirror 16 is configured to form an angle α with respect to the center of deflection by the rotary polygon mirror 16 so that the return light beam from the adjacent surface does not return to the light source 11.
[0065]
The rotary polygon mirror 16 is rotated clockwise as viewed from above by the drive motor 22, and the scanning light beam deflected by the reflecting surface 16 </ b> B is incident on the first mirror pair 14 again. The scanning light beam folded back by the mirror pair 14 is incident on an fθ lens 17 which is attached to the back side of the housing 10 with respect to the rotary polygon mirror 16 and is composed of a single aspheric lens. The light beam emitted from the fθ lens 17 is folded back by the second pair of mirrors 19 (19 A and 19 B) fixed to the holder 18 and reaches the photosensitive drum 20.
[0066]
Of the scanning light beam, the light beam traveling toward the scanning end passes through the second mirror pair 19 and is bent by the pickup mirror 21 and guided to a synchronization detection sensor (SOS sensor) (not shown).
[0067]
In this way, the 90 ° folding mirror pair 14 is arranged in front of the second imaging optical system (here, the fθ lens 17), and the 90 ° folding mirror pair 19 is arranged after the second imaging optical system. As a result, the optical beam reciprocates almost once and a half within the housing 10, and an optical system having a very long optical path length in the unfolded state can be folded in a high-density mounting state. As a result, the compact optical scanning device 30 in which the occupied length in the mounted state, that is, the distance from the end surface of the housing 10 to the photosensitive drum 20 is about ½ of the developed state, and the height of the housing 10 is about 80 mm. Can be realized.
[0068]
Further, the entire optical system is mounted in a small casing by configuring the light beam emitted from the first imaging optical system including the convex lens 12 and the cylindrical lens 13 to pass through the first mirror pair 14 twice. It becomes possible.
[0069]
  [Second Embodiment]
  nextThe secondA second embodiment will be described. Here, the adjustment for minimizing the influence of the processing error and the mounting error according to the second object of the present invention will be described.
[0070]
The configuration shown in FIG. 1 and FIG. 2 described in the first embodiment realizes downsizing of the optical scanning device, but the number of reflections on the optical path is larger than that of the conventional optical scanning device. As the number of reflections increases, there is a concern that optical performance deteriorates due to accumulation of errors. Therefore, in the second embodiment, the processing accuracy and mounting accuracy of the optical component are tightened to avoid a high cost, and a certain level of component processing error and mounting error are allowed, and the entire optical scanning device is sufficient. A configuration for obtaining optical performance will be described.
[0071]
Specifically, an adjustment structure in which a mirror pair 14 having a relative angle of 90 ° and a plane mirror 15 having a biaxial adjustment function are combined will be described.
[0072]
Regarding the mirror pair having a relative angle of 90 °, the advantage that the size in the height direction of the housing can be reduced has already been described, but another feature is that the parallelism between the incident light beam and the outgoing light beam is preserved.
[0073]
FIG. 3 is a sub-scan sectional view showing an optical path from the light source 11 to the flat mirror 15. If there is no error in the light beam and the reflecting mirrors 14A, 14B, 15, the light beam that has passed through the mirror pair 14 returns to the same main scanning plane as the incident beam.
[0074]
Here, consider the case where there is an error. There are two possible causes of the error: the position (height) and angle of the incident light beam, and the attitude of the optical component (attachment angle).
[0075]
FIG. 4A is a diagram showing an optical path when a light beam having an error is incident on the 90 ° mirror pair 14 and the reflection mirror 15 to which ideal parts are attached. When it passes through the 90 ° mirror pair 14 for the first time and when it passes the second time, the parallelism of the incident light beam and the emitted light beam is maintained in each process.
[0076]
However, when the two processes are regarded as one and the light beam incident on the 90 ° mirror pair 14 and the light beam emitted from the 90 ° mirror pair 14 are compared, the magnitude of the angle error is preserved, but the direction is Since the position is opposite, a large error occurs in the position. In the worst case, the position is deviated from the reflection surface 16B of the rotary polygon mirror 16, and actual use without an adjustment mechanism is difficult.
[0077]
Therefore, in the second embodiment, the above problem is solved as follows by providing the plane mirror 15 with the biaxial adjustment mechanism shown in FIGS. 5 (A) and 5 (B). That is, the flat mirror 15 is attached to the bracket 51 having the rotation shaft 52 in the same plane as the reflecting surface 15A by the fixing spring 53. The angle of the reflecting surface 15A can be adjusted within the main scanning plane by rotating the bracket 51.
[0078]
On the other hand, a set screw 54 is provided in the vicinity of the upper end portion of the reflection surface 15A, and the angle of the reflection surface 15A can be adjusted in the sub-scanning section by adding a turn with the set screw 54.
[0079]
In actual adjustment, for example, in the sub-scanning direction, a position sensor (not shown) for detecting the passing position of the light beam is provided immediately before the rotary polygon mirror 16B, and the output screw is detected while detecting the output from the position sensor. 54 can be turned to adjust the angle of the reflecting surface 15A. An example of the adjusted optical path is shown in FIG.
[0080]
Similarly, an optical path deviation from a design value (so-called nominal) also occurs in the main scanning direction. Therefore, a power sensor (not shown) for detecting the power of the light beam is provided immediately before the rotary polygon mirror 16B to reflect the light. The bracket 52 is rotated while detecting the relationship between the surface 16B and the power distribution, and the flat mirror 15 is fixed to the housing 10 at an appropriate position.
[0081]
As described above, by combining the mirror pair 14 having a relative angle of 90 ° and the flat mirror 15 having the biaxial adjustment function, the adjustment of the main scanning direction and the sub-scanning direction as described above is performed, thereby processing the parts. -It is possible to correct an optical path shift caused by an installation error.
[0082]
  [Third Embodiment]
  nextThe secondThree embodiments will be described. In general, in an optical system having a large number of reflections, it is more desirable to detect and adjust optical path deviations at a plurality of positions in the optical path. This is because it is very difficult to detect the angle error as compared with the position error detection of the light beam.
[0083]
Therefore, in the third embodiment, a method of adjusting the optical path deviation at a plurality of positions in the optical path, which can be applied to the configuration of the present invention, will be described with reference to FIGS. 6 (A) and 6 (B). The adjustment is performed by the light source 11 and the plane mirror 15, and the optical path position is detected at the position 101 before being incident on the first mirror pair 14 and the position 102 immediately before the rotary polygon mirror 16.
[0084]
First, the light source 11 is moved in the main scanning corresponding direction (the directions of arrows M1 and M2 in FIG. 6B) and in the sub-scanning corresponding direction (the directions of arrows S1 and S2 in FIG. 6A), and the first mirror pair. The positional deviation at the position 101 before the incident on the lens 14 is adjusted. As a result, the error of the light beam incident on the first mirror pair 14 is substantially only an angular component.
[0085]
Next, the position immediately before the rotary polygon mirror 16 is adjusted by adjusting the angle of the reflecting surface 15A by the set screw 54 and adjusting the position of the plane mirror 15 by rotating the bracket 52 with respect to the plane mirror 15 by the method described above. The misalignment at 102 is adjusted. As a result, on the optical path from the light source 11 to the rotary polygon mirror 16, there is no portion that deviates significantly from the designed optical path. In the above, since the positional deviation is adjusted at two points (positions 101 and 102) separated from each other, the angle error of the light beam incident on the second imaging optical system is compared with the case of adjusting at one point. From this point, the deterioration of the optical performance can be suppressed.
[0086]
Next, a method for fixing the second mirror pair 19 will be described. FIGS. 7A and 7B are diagrams for explaining the holding structure of the second mirror pair 19 and the fastening method to the housing 10.
[0087]
The second mirror pair 19 has a function of adjusting the position of the scanning line on the photosensitive drum 20, the oblique scanning, the magnification, and the like by rotation and parallel movement. The adjustment is performed on a jig, but it is necessary to fix the adjustment firmly without breaking the adjustment completion state. As a fixing method, screw fastening is generally used. However, due to the tightening torque of the screw, the screw may be fixed out of the adjusted position, and the performance may be deteriorated.
[0088]
Therefore, in the present embodiment, as shown in FIG. 7B, the holder 18 is held at a fixed point 71 on a straight line that intersects with the reflection surfaces of the mirrors 19A and 19B constituting the second mirror pair 19 extending. It is fixed to the housing 10.
[0089]
In accordance with the principle described above, the holder 18 is fixed to the housing 10 at a fixed point 71 on a straight line that extends by reflecting the reflecting surfaces of the mirrors, so that the second mirror pair 19 that can occur at the time of screw fastening after the adjustment is completed. It is possible to minimize the fluctuation of the alignment of the light beam due to the position shift and obtain good optical performance.
[0090]
Next, a desirable configuration of the second imaging optical system (fθ lens 17) will be described. FIG. 1 shows a configuration example in which a single aspherical lens is adopted for the fθ lens 17 in order to reduce the cost. The scope of application of the present invention is not limited to a single aspherical lens, but the secondary surface of the reflecting surface 16B of the rotary polygon mirror 16 and the surface to be scanned of the photosensitive drum 20 having a substantially conjugate relationship. The lateral magnification (conjugate magnification) β in the scanning section is configured to satisfy 1.5 <β <3.5.
[0091]
Therefore, good optical performance can be obtained even with a single lens while securing a sufficient space for arranging the 90 ° mirror pairs 14 and 19 before and after the fθ lens 17 for the reason described above. Larger size can be avoided. For this reason, a high-performance and small-sized optical scanning device 30 can be provided.
[0092]
In the optical scanning device 30 in each of the above embodiments, the 90 ° mirror pair is disposed before and after the fθ lens 17, but the 90 ° mirror pair is provided either before or after the fθ lens 17. The effect of reducing the size of the optical scanning device 30 can be obtained even by simply arranging it.
[0093]
【The invention's effect】
  As explained above, claim 1And claim 2According to the described invention, the mirror pair having a relative angle of 90 ° is disposed before and after the second imaging optical system without using a complicated and expensive optical system, so that While suppressing the height, the optical path length on the mounting in the optical system subsequent to the rotary polygon mirror can be shortened at a stretch, so that the optical scanning device can be reduced in size while avoiding an increase in device cost.
[0094]
According to the first aspect of the present invention, since the second imaging optical system is constituted by an inexpensive single plastic aspheric lens, the cost of the optical scanning device can be kept low. Also, since the conjugate magnification β is set to be larger than 1.5 and smaller than 3.5, a single lens while securing a sufficient space for arranging the 90 ° mirror pair before and after the second imaging optical system. However, good optical performance can be obtained, and enlargement of the lens of the second imaging optical system can be avoided.
  Claims1According to the described invention, in the overfilled system in which the focal length of the imaging optical system is increased, it is possible to avoid an increase in the optical path length on mounting even if the optical path length of the imaging optical system is increased. An increase in the size of the apparatus can be avoided.
  on the other hand,Claim2According to the described invention, the optical path from the first imaging optical system to the rotary polygon mirror is bent and the light beam passes through the first mirror pair twice, so that Since the optical path length on the mounting in the optical path of the optical system can be reduced to about half of the deployed state, in both the optical path of the optical system before the rotary polygon mirror and the optical path of the optical system after the rotary polygon mirror, The optical path length on mounting is shortened, and the optical scanning device can be further miniaturized with a relatively simple configuration without increasing the number of components.
[0096]
  Claims3According to the described invention, since the plane mirror that can rotate in the biaxial direction is arranged in combination with the first mirror pair configured so that the light beam passes twice from the light source to the rotary polygon mirror, At the time of assembly / adjustment, the plane mirror can be rotated in two axes to adjust the position so that the light beam is guided to a desired position with respect to the reflecting surface of the rotary polygon mirror.
[0097]
  Claims4According to the described invention, the light source is provided so as to be independently movable in a direction corresponding to the main scanning direction and a direction corresponding to the sub-scanning direction within a plane orthogonal to the optical axis of the emitted light beam. When assembling and adjusting, the light source is appropriately moved in the direction corresponding to the main scanning direction and the direction corresponding to the sub-scanning direction so that errors such as the incident angle of the light beam incident on the first mirror pair are reduced. Thus, the position of the light source can be adjusted, and the optical path can be adjusted with higher accuracy.
[0098]
  Claims5According to the described invention, the second mirror pair is provided so as to be rotatable and translatable within the cross section along the sub-scanning direction. The magnification can be corrected.
[0099]
  Claims6According to the described invention, since the second mirror pair is fixed at a fixed point on a straight line that intersects with the reflection surfaces of the mirrors extended, the light due to the positional deviation of the second mirror pair that may occur when the screws are fastened. It is possible to minimize the beam alignment variation and obtain good optical performance.
[Brief description of the drawings]
FIG. 1 is a plan view showing an outline of an optical scanning device according to an embodiment of the invention.
2A and 2B are side views showing an outline of an optical scanning device according to an embodiment of the invention, wherein FIG. 2A is a side view relating to part A in FIG. 1 and FIG. 2B is a side view relating to part B in FIG. is there.
FIG. 3 is a cross-sectional view along the sub-scanning direction showing an optical path from a light source to a flat mirror.
4A and 4B are diagrams showing an optical path of a 90 ° mirror pair when there is an error in the incident direction of the light beam. FIG. 4A is a diagram showing an optical path before adjusting the 90 ° mirror pair, and FIG. These are figures which show the optical path after adjusting a 90 degree mirror pair.
5A is a plan view showing a structure of a flat mirror provided with a biaxial adjustment mechanism, and FIG. 5B is a side view showing a structure of a flat mirror provided with a biaxial adjustment mechanism.
6A is a side view showing a member arrangement when the optical path from the light source to the rotating polygon mirror is developed, and FIG. 6B is a member arrangement when the optical path from the light source to the rotating polygon mirror is developed. FIG.
FIG. 7A is a schematic diagram illustrating a holding structure of a second mirror pair and a fastening method to a housing, and FIG. 7B is a cross-sectional view of the second mirror pair along the sub-scanning direction.
FIG. 8 is a schematic configuration diagram illustrating an example of a conventional optical scanning device.
FIG. 9 is a plan view showing an overfilled scanning optical system constituted by a single fθ lens.
10A is a diagram showing mounting dimensions when the optical path of the light beam is bent by a mirror pair, and FIG. 10B is a diagram showing mounting dimensions when the optical path of the light beam is bent by one mirror. .
FIG. 11 is a cross-sectional view along the sub-scanning direction showing the optical path when the second mirror pair rotates due to an error.
[Explanation of symbols]
10 body
11 Semiconductor laser (light source)
12 Convex lens
13 Cylindrical lens
14 First mirror pair
15 Flat mirror
16 Rotating polygon mirror
17 Single aspherical lens
18 Holder
19 Second mirror pair
20 Photosensitive drum
30 Optical scanning device
51 Bracket
52 Rotating shaft
54 Imemo Screw
71 fixed points

Claims (6)

A light source;
A rotary polygon mirror that rotates around a predetermined rotation axis at a substantially equal angular velocity and has a plurality of reflection surfaces parallel to the rotation axis formed on the outer periphery, and deflects an incident light beam by the reflection surface;
A first result of focusing the light beam emitted from the light source in the sub-scanning direction parallel to the rotation axis to form a line image along the main scanning direction perpendicular to the sub-scanning direction on the reflecting surface. An image optical system;
The reflection surface and the surface to be scanned have a substantially conjugate imaging relationship within the cross section along the sub-scanning direction, and the light surface deflected by the reflection surface is scanned at a constant speed. A second imaging optical system that forms an image as a spot;
A first mirror pair disposed on an optical path from the rotary polygon mirror to the second imaging optical system and having a relative angle of 90 ° in a cross section along the sub-scanning direction;
Have a, a second mirror pair constituting a relative angle of 90 ° in the second from said imaging optical system is disposed on the optical path leading to the scanned surface and along said sub-scanning cross section,
The second imaging optical system is composed of a single plastic aspherical lens, and has a conjugate magnification β related to the imaging relationship between the reflecting surface and the scanned surface in a cross section along the sub-scanning direction. ,
1.5 <β <3.5
Satisfied,
The optical beam is incident on the reflecting surface of the rotary polygon mirror as an optical beam wider than the width of the reflecting surface along the main scanning direction . A light source;
A rotary polygon mirror that rotates around a predetermined rotation axis at a substantially equal angular velocity and has a plurality of reflection surfaces parallel to the rotation axis formed on the outer periphery, and deflects an incident light beam by the reflection surface;
A first result of focusing the light beam emitted from the light source in the sub-scanning direction parallel to the rotation axis to form a line image along the main scanning direction perpendicular to the sub-scanning direction on the reflecting surface. An image optical system;
The reflection surface and the surface to be scanned have a substantially conjugate imaging relationship within the cross section along the sub-scanning direction, and the light surface deflected by the reflection surface is scanned at a constant speed. A second imaging optical system that forms an image as a spot;
A first mirror pair disposed on an optical path from the rotary polygon mirror to the second imaging optical system and having a relative angle of 90 ° in a cross section along the sub-scanning direction;
Have a, a second mirror pair constituting a relative angle of 90 ° in the second from said imaging optical system is disposed on the optical path leading to the scanned surface and along said sub-scanning cross section,
The first mirror pair is:
A light beam from the first imaging optical system is incident, folded by the first mirror pair and reflected by a predetermined plane mirror;
The reflected light beam is again incident on the first mirror pair in the direction opposite to the first time, folded back by the first mirror pair, and incident on the reflecting surface of the rotary polygon mirror.
An optical scanning device characterized by being arranged . The plane mirror is rotatable around a predetermined axis parallel to a rotation axis of the rotary polygon mirror, and the plane mirror includes a plane including the predetermined axis and a normal line of the reflection surface of the rotary polygon mirror. The optical scanning device according to claim 2 , wherein the optical scanning device is provided so as to be rotatable independently of rotation around a predetermined axis. The light source is provided to be independently movable in a direction corresponding to the main scanning direction and a direction corresponding to the sub-scanning direction within a plane orthogonal to the optical axis of the emitted light beam. the optical scanning device according to any one of claims 1 to 3,. It said second mirror pair includes an optical scanning device according to any one of claims 1 to 4, characterized in that it is provided to be rotatable and translatable in a cross section taken along the sub-scanning direction . The second mirror pair is fixed at a fixed point on a straight line formed by intersecting planes obtained by extending reflecting surfaces of the mirrors of the second mirror pair. 6. The optical scanning device according to any one of items 5 .

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