JP4183207B2 - Optical scanning device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning device that scans a light spot onto a surface to be scanned, and in particular, a light flux width in a scanning plane of a light beam incident on a rotary polygon mirror is larger than a width in a scanning plane of a light deflection reflection surface. The present invention relates to an optical scanning device set to a value.
[0002]
[Prior art]
In a laser printer, a laser plate making apparatus, or the like, an optical scanning device is used as the image forming means. This optical scanning apparatus generally includes an incident optical system including a light source, a collimator lens, and a diaphragm, a rotary polygon mirror that deflects and reflects an incident beam from the incident optical system, and a light deflection reflection surface of the rotary polygon mirror. An imaging optical system that forms an image of the deflected reflected beam as a beam spot on the surface to be scanned, and the optical axis of the imaging optical system on the surface to be scanned by rotating the rotary polygon mirror. It is comprised so that it may scan over a predetermined angle range centering | focusing on.
[0003]
[Problems to be solved by the invention]
In this optical scanning device, when the size of the rotating polygon mirror is small or the number of reflecting surfaces is large, the beam width w0 in the scanning plane of the incident beam B1 to the rotating polygon mirror 14 is shown in FIG. However, in this case, the beam width of the deflected reflected beam B2 from the light deflecting / reflecting surface 14a1 in the scanning plane is larger than that of the rotating polygon mirror 14. It differs depending on the rotation angle position.
[0004]
That is, as shown in FIG. 9A, at the rotation angle position (scanning start position) at the moment when the light deflection reflection surface 14a1 completely enters the incident beam B1, the beam width of the deflection reflection beam B2 is w1. As shown in FIG. 4B, the beam width of the deflected reflected beam B2 is w2 at the rotational angle position (scanning center position) where the deflected reflected beam B2 is deflected and reflected in the direction of the optical axis Ax2 of the imaging optical system. Further, as shown in FIG. 6C, the beam width of the deflected reflected beam B2 is the rotation angle position (scan end position) at the moment when the light deflecting / reflecting surface 14a1 starts to come off from the incident beam B1. It becomes the smallest at w3.
[0005]
As shown in FIG. 8, the light intensity of the incident beam B1 is the largest at the center on the optical axis Ax1 of the incident optical system and gradually decreases as it approaches both ends, so that each of the rotation angle positions (a), ( The light quantity of the deflected reflected beam B2 in b) and (c) is larger at the rotation angle position (c) than the rotation angle positions (a) and (b), as shown by the size of the hatched area in FIG. It will be small.
[0006]
For this reason, unevenness in the amount of light occurs on the surface to be scanned, and this causes a problem in that unevenness in the density of the image is generated and the image quality is deteriorated.
Japanese Laid-Open Patent Publication No. 9-212366 discloses an optical scanning device in which an aperture for reducing the beam width w1 is provided in an incident optical system. Since the width w2 does not change, it is not possible to eliminate the light amount difference of the deflected reflected beam between the rotation angle position (b) and the rotation angle positions (a) and (c).
[0007]
The present invention has been made in view of such circumstances, and the light beam width in the scanning plane of the light beam incident on the rotary polygon mirror is set to a value larger than the width of the light deflection reflection surface in the scanning plane. An object of the present invention is to provide an optical scanning device capable of minimizing the occurrence of unevenness in the amount of light on the surface to be scanned.
[0008]
[Means for Solving the Problems]
An optical scanning device of the present invention includes a first optical system including a light source, a collimator lens that changes a light beam emitted from the light source to a parallel light beam, and a diaphragm that limits the parallel light beam to a predetermined light beam diameter,
A rotating polygon mirror that deflects and reflects an incident light beam from the first optical system;
A second optical system that forms an image of a deflected reflected light beam from the light deflecting / reflecting surface of the rotating polygon mirror as a light spot on the scanned surface;
An optical scanning device configured to scan the optical spot over a predetermined angular range around the optical axis of the second optical system on the surface to be scanned by rotating the rotary polygon mirror,
In the optical scanning device in which the light flux width in the scanning plane of the incident light flux is set to a value larger than the width in the scanning plane of the light deflection reflection surface,
Said first optical system is configured such that a predetermined amount displaced in the optical axis side of the second optical system of the light intensity peak position with respect to the optical axis of the first optical system in the incident light beam ,And,
The displacement position of the light intensity peak position is set to a position where the light beam reflected by the reflecting surface other than the light deflecting reflecting surface in the rotary polygon mirror does not appear as a ghost beam in the optical path of the second optical system . It is characterized by this.
[0009]
The “light deflecting / reflecting surface” refers to a reflection that reflects an incident light beam to the rotating polygon mirror into the optical path of the second optical system among a plurality of reflecting surfaces constituting the rotating polygon mirror. It means a surface.
[0010]
The size of the “predetermined amount” (that is, the amount of displacement of the light intensity peak position toward the optical axis side of the second optical system) is not particularly limited.
Furthermore, the above-mentioned “width of the light deflection reflection surface in the scanning plane” means “the projection width of the first optical system in the scanning plane of the light deflection reflection surface”. .
[0011]
[Operation and effect of the invention]
As shown in the above configuration, in the optical scanning device according to the present invention, the light flux width in the scanning plane of the light beam incident on the rotary polygon mirror is set to a value larger than the width in the scanning plane of the light deflection reflection surface. However, the first optical system displaces the light intensity peak position in the light beam incident on the rotary polygon mirror by a predetermined amount with respect to the optical axis of the second optical system with respect to the optical axis of the first optical system. It is configured as follows.
[0012]
Therefore, the light beam width in the scanning plane of the deflected reflected light beam gradually decreases with the rotation of the rotary polygon mirror as before, but the rotation angle position where the light beam width is large by setting the displacement of the light intensity peak position. In this case, a portion where the light intensity of the incident light beam is smaller than that of the conventional light enters the light deflection reflection surface, while a portion where the light intensity of the incident light beam is larger than that of the conventional light enters the light deflection reflection surface at the rotation angle position where the light beam width is small. Therefore, the light quantity of the deflected reflected light beam is averaged at each rotation angle position.
[0013]
Therefore, according to the optical scanning device of the present invention, in the optical scanning device in which the luminous flux width in the scanning plane of the luminous flux incident on the rotary polygon mirror is set to a value larger than the width in the scanning plane of the light deflection reflection surface Thus, the occurrence of unevenness in the amount of light on the surface to be scanned can be minimized.
[0014]
In the above configuration, the specific configuration for displacing the light intensity peak position to the optical axis side of the second optical system with respect to the optical axis of the first optical system is not particularly limited. The optical axis of the light source and the collimator lens is translated to the optical axis side of the second optical system relative to the optical axis of the first optical system, or the optical axis of the light source is changed to the optical axis of the first optical system. It is also possible to incline toward the optical axis side of the second optical system.
[0015]
By the way, in the conventional optical scanning device, as shown in FIG. 9, the rotary polygon mirror 14 includes a reflection surface 14a2 adjacent to the rear side in the rotation direction of the light deflection reflection surface 14a1 and the optical axis of the first optical system. There is a problem that a ghost light beam is generated on the surface to be scanned when the rotation angle position is perpendicular to Ax1.
[0016]
That is, of the incident light beam B1 incident on the rotary polygon mirror 14, the light beam b1 incident on the reflecting surface 14a2 is regularly reflected in the direction of the optical axis Ax1 of the first optical system and returns to the light source. The light beam reflected and reenters the rotary polygon mirror 14, and the light beam (light beam width a in the scanning plane) incident on the light deflection reflection surface 14 a 1 becomes a ghost light beam bg that reaches the surface to be scanned. This ghost light beam bg is always reflected at a constant angle (4π / n−α) with respect to the optical axis Ax2 of the second optical system even when the rotary polygon mirror 14 rotates, and is an image stationary on the surface to be scanned. In other words, the image quality is adversely affected. Here, n is the number of reflecting surfaces of the rotary polygon mirror 14, and α is an angle formed by the optical axis Ax1 of the first optical system and the optical axis Ax2 of the second optical system.
[0017]
Therefore, it is preferable to set the displacement position of the light intensity peak position to a position where the light beam reflected by the reflecting surface other than the light deflecting reflecting surface in the rotary polygon mirror does not appear as a ghost beam in the optical path of the second optical system. .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a first embodiment of the present invention will be described.
FIG. 1 is a plan view showing an optical scanning device according to the present embodiment.
As illustrated, the optical scanning device 10 is an optical scanning device used in a laser printer, and includes an incident optical system 12, a rotary polygon mirror 14, and an imaging optical system 16.
[0019]
The incident optical system 12 includes a light source 18 composed of a semiconductor laser, a collimator lens 20 that changes a beam from the light source 18 to a parallel beam B0, a diaphragm 22 that limits the parallel beam B0 to a predetermined beam diameter, and a diaphragm 22 A cylindrical lens 24 that converts the passed parallel beam into a horizontally long elliptical beam is formed, and this horizontally long elliptical beam B1 is incident on the rotary polygon mirror 14.
[0020]
The rotating polygon mirror 14 includes a plurality of (12) reflecting surfaces 14a and rotates in the direction of the arrow in the drawing around a vertical axis. In the rotating polygon mirror 14, the reflecting surface 14a1 located on the optical axis Ax1 of the incident optical system 12 out of the plurality of reflecting surfaces 14a receives the horizontally long elliptical beam (incident beam) B1 from the incident optical system 12. An optical deflecting / reflecting surface that deflects and reflects toward the imaging optical system 16 is configured.
[0021]
The imaging optical system 16 is composed of an fθ lens composed of two lenses 26 and 28 and a concave cylindrical mirror (not shown) having power only in the sub-scanning direction. The deflected reflected beam B2 from the light deflecting / reflecting surface 14a1 is imaged as a beam spot on the surface to be scanned. The optical axis Ax2 of the imaging optical system 16 is set so as to intersect with the optical axis Ax1 of the incident optical system 12 at the light deflecting / reflecting surface 14a1 and to form an angle of 60 ° with the optical axis Ax1.
[0022]
In the optical scanning device 10, by rotating the rotary polygon mirror 14, the beam spot is scanned over a predetermined angle range around the optical axis Ax2 of the imaging optical system 16 on the surface to be scanned. . The laser printer forms an image on the scanned surface by moving the scanned surface in a direction (sub-scanning direction) substantially perpendicular to the scanning direction (main scanning direction) of the optical scanning device 10. It is supposed to be.
[0023]
As shown in the figure, the beam width w0 of the incident beam B1 to the rotary polygon mirror 14 in the scanning plane is set to a value larger than the projection width in the direction of the optical axis Ax1 in the scanning plane of the light deflection reflection surface 14a1. . Therefore, only a part of the incident beam B1 (the portion indicated by oblique lines) is incident on the light deflecting / reflecting surface 14a1.
[0024]
In the present embodiment, as shown, the optical axis Ax3 of the light source 18 and the collimator lens 20 is on the right side of the optical axis Ax1 of the incident optical system 12 (on the optical axis Ax2 side of the imaging optical system 16). ) To a / 2 (this value will be described later). As a result, of the parallel beam B0 formed by the light source 18 and the collimator lens 20, a beam in a region shifted slightly to the left from the central region is used as the incident beam B1.
[0025]
As shown in FIG. 3, the distribution of the light intensity of the parallel beam B0 in the scanning plane is a distribution according to a Gaussian curve that is the largest at the center on the optical axis Ax3 and gradually decreases toward the left and right ends. However, with the shift, the light intensity peak position in the incident beam B1 is displaced to the right by a / 2 with respect to the optical axis Ax1 of the incident optical system 12. Therefore, the scanning direction distribution of the light intensity of the deflected reflected beam B2 is also a Gaussian distribution displaced by a / 2 to the right when viewed from the scanned surface side.
[0026]
FIG. 2 is a diagram illustrating a state of light deflection by the rotation of the rotary polygon mirror 14 in the optical scanning device 10.
As shown in the figure, the beam width of the deflected reflected beam B2 in the scanning plane varies depending on the rotational angle position of the rotary polygon mirror 14.
[0027]
That is, as shown in FIG. 5A, at the rotation angle position (scanning start position) at the moment when the light deflecting / reflecting surface 14a1 completely enters the incident beam B1, the beam width of the deflecting / reflecting beam B2 is the largest at w1. As shown in FIG. 2B, at the rotation angle position (scanning center position) where the deflected reflected beam B2 is deflected and reflected in the direction of the optical axis Ax2 of the imaging optical system 16, the beam width of the deflected reflected beam B2 is At a rotational angle position (scanning end position) at the moment when the light deflection reflection surface 14a1 starts to deviate from the incident beam B1, as shown in FIG. The width becomes the smallest at w3.
[0028]
As shown in FIG. 3, the amount of light of the deflected reflected beam B2 at each of the rotational angle positions (a), (b), and (c) has the light intensity distribution in the scanning plane of the deflected reflected beam B2 as shown in FIG. Since the light intensity distribution (indicated by a two-dot chain line in the figure) of the deflected reflected beam in the scanning plane is displaced to the right, it is made more uniform than in the prior art.
[0029]
That is, at the rotation angle position (a) of the beam width w1, a portion having a relatively small light intensity is used in the deflected reflected beam B2, and at the rotation angle position (b) of the beam width w2 (w2 <w1), the rotation angle position is used. A portion having a light intensity greater than that of (a) is used, and a portion having a light intensity greater than that of the rotation angle position (b) is used at the rotation angle position (c) of the beam width w3 (w3 <w2). Therefore, as shown by the size of the hatched area in the figure, the amount of light of the deflected reflected beam B2 becomes a substantially uniform value between the rotation angle positions (a), (b), and (c).
[0030]
Incidentally, the displacement amount a / 2 of the optical axis Ax3 of the light source 18 and the collimator lens 20 with respect to the optical axis Ax1 of the incident optical system 12 is a value set as follows.
That is, as shown in FIG. 4, the rotary polygon mirror 14 is at a rotation angle position where the reflection surface 14a2 adjacent to the rear side in the rotation direction of the light deflection reflection surface 14a1 and the optical axis Ax1 of the incident optical system 12 are perpendicular to each other. Of the incident beam B1, the beam b1 incident on the reflecting surface 14a2 is regularly reflected in the direction of the optical axis Ax1 and returned to the light source 18, reflected by the light emitting end surface of the light source 18 and superimposed on the beam b2. The light enters the rotating polygon mirror 14 again.
[0031]
At this time, as in the conventional example shown in FIG. 9, if a part of the beam b2 is incident on the light deflecting / reflecting surface 14a1, the beam becomes a ghost beam bg reaching the surface to be scanned, which adversely affects the image quality. Will give. In order to prevent the ghost beam bg from appearing, the optical axis Ax3 of the light source 18 and the collimator lens 20 is translated rightward with respect to the optical axis Ax1 of the incident optical system 12, and the beam in FIG. It suffices that there is no part of b2 incident on the light deflection reflection surface 14a1. If the width of the portion of the beam b2 incident on the light deflection reflection surface 14a1 is a, the amount of displacement of the optical axis Ax3 that is sufficient to completely remove the beam b2 from the light deflection reflection surface 14a1 is a / 2. It becomes.
[0032]
When the optical axis Ax3 is displaced in this way, as shown in FIG. 4, all the beams b2 are incident on the reflection surface 14a3 adjacent to the front side in the rotation direction of the light deflection reflection surface 14a1, and the reflection surface 14a3. Thus, since the light is reflected in a direction greatly deviating from the optical path of the imaging optical system 16, the possibility of generating a ghost beam can be eliminated.
[0033]
As described above in detail, in the optical scanning device 10 according to the present embodiment, the beam width in the scanning plane of the incident beam B1 to the rotary polygon mirror 14 is larger than the width in the scanning plane of the light deflection reflection surface 14a1. Although the optical axis Ax3 of the light source 18 and the collimator lens 20 is translated to the optical axis Ax2 side of the imaging optical system 16 with respect to the optical axis Ax1 of the incident optical system 12, The light intensity peak position in the incident beam B1 to the mirror 14 is configured to be displaced by a predetermined amount with respect to the optical axis Ax1 toward the optical axis Ax2 side of the imaging optical system 16.
[0034]
Therefore, the beam width of the deflected reflected beam B2 in the scanning plane gradually decreases with the rotation of the rotary polygon mirror 14 as before, but the rotation angle with a large beam width is set by setting the displacement of the light intensity peak position. At the position, a portion where the light intensity of the incident beam B1 is smaller than that of the conventional case is incident on the light deflection reflecting surface 14a1, while at a rotation angle position where the beam width is small, a portion where the light intensity of the incident beam B1 is larger than that of the conventional light deflection. Since the light is incident on the reflecting surface 14a1, the light amount of the deflected reflected beam B2 is thereby averaged at each rotation angle position.
[0035]
Therefore, according to this embodiment, in the optical scanning device in which the beam width in the scanning plane of the incident beam to the rotary polygon mirror is set to a value larger than the width in the scanning plane of the light deflection reflection surface, Occurrence of unevenness in the amount of light on the surface can be minimized.
[0036]
Moreover, the displacement position of the light intensity peak position in the incident beam B1 is such that the beam reflected by the reflecting surface 14a other than the light deflection reflecting surface 14a1 in the rotary polygon mirror 14 does not appear as a ghost beam in the optical path of the imaging optical system 16. Therefore, it is possible to prevent the image quality formed on the scanned surface from being adversely affected.
[0037]
Here, a is the number of surfaces of the rotating polygon mirror, n is the circumscribed circle radius of the rotating polygon mirror, R is the effective scanning half angle, and the optical axis of the first optical system is the optical axis of the second optical system. If the angle is α, it can be expressed by the following equation.
a = R {sin (3π / n) −sin ((α + θ) / 2 + π / n) + sin (π / n) −sin ((α−θ) / 2−π / n)}
In this embodiment, R = 12 mm, n = 12, θ = 0.349 rad (= 20 °), α = 1.047 rad (= 60 °), and at this time a = 0.715 mm, the displacement of the optical axis Ax3 a / 2 is 0.358 or more.
[0038]
Next, a second embodiment of the present invention will be described.
FIG. 5 is a plan view showing the optical scanning device according to the present embodiment.
As shown in the figure, the optical scanning device 110 includes the same components as those of the optical scanning device according to the first embodiment, but the alignment of the incident optical system 12 is different.
[0039]
That is, in this embodiment, the collimator lens 20 is disposed on the optical axis Ax1 of the incident optical system 12, but the light source 18 changes the direction of the optical axis Ax4 with respect to the optical axis Ax1 of the incident optical system 12. The collimator lens 20 is arranged so as to be inclined by an angle δ with respect to the light source side principal point of the collimator lens 20 toward the optical axis Ax2 side of the imaging optical system 16.
[0040]
Thus, by tilting the optical axis Ax4 of the light source 18, the light intensity peak position in the incident beam B1 can be displaced to the optical axis Ax2 side of the imaging optical system 16 with respect to the optical axis Ax1.
Accordingly, also in this embodiment, the amount of light of the deflected reflected beam B2 can be averaged at each rotational angle position of the rotary polygon mirror 14, thereby minimizing the occurrence of unevenness in the amount of light on the surface to be scanned. it can.
[0041]
Further, as shown in FIG. 6, the value of the inclination angle δ of the optical axis Ax4 of the light source 18 is set so that the beam reflected by the reflecting surface 14 a other than the light deflection reflecting surface 14 a 1 in the rotary polygon mirror 14 If the size is set so that it does not appear as a ghost beam in the optical path, it is possible to prevent the image quality formed on the scanned surface from being adversely affected.
[0042]
Here, if the focal length of the collimating lens is f,
δ = sin ⁻¹ (a / 2f).
In the first embodiment, since it is necessary to increase the effective diameter of the collimator lens 20, it is necessary to increase the numerical aperture or enlarge the lens. In the present embodiment, however, This is more preferable because it is not necessary.
[Brief description of the drawings]
FIG. 1 is a plan view showing an optical scanning device according to a first embodiment of the present invention. FIG. 2 is a diagram showing a state of light deflection caused by rotation of a rotary polygon mirror in the device shown in FIG. FIG. 4 is a plan view showing a configuration for removing a ghost beam in the apparatus shown in FIG. 1. FIG. 5 is a plan view showing a configuration for removing a ghost beam in the apparatus shown in FIG. FIG. 6 is a plan view showing a configuration for removing a ghost beam in the apparatus shown in FIG. 5. FIG. 7 is a view similar to FIG. 2 showing a conventional example. Fig. 9 is a diagram similar to Fig. 3 showing a conventional example. Fig. 9 is a diagram similar to Fig. 4 showing a conventional example.
DESCRIPTION OF SYMBOLS 10, 110 Optical scanning device 12 Incident optical system 14 Rotating polygon mirror 14a Reflecting surface 14a1 Light deflection reflecting surface 14a2 Reflecting surface 14a3 adjacent to the rotation direction rear side of the light deflection reflecting surface Adjacent to the rotation direction front side of the light deflection reflecting surface Reflecting surface 16 Imaging optical system 18 Light source 20 Collimator lens 22 Aperture 24 Cylindrical lenses 26 and 28 Lens (fθ lens)
Ax1 Optical axis Ax2 of the incident optical system Optical axis Ax3 of the imaging optical system Optical axis Ax4 of the light source and collimator lens Optical axis B0 of the light source Parallel beam B1 Incident beam B2 Deflection reflected beam a / 2 Parallel displacement bg Ghost beam w0 Incident beam Beam widths w1, w2, and w3 in the scanning plane of the beam width δ in the scanning plane of the deflected reflected beam tilt angle

Claims (5)

A first optical system comprising: a light source; a collimator lens that changes a light beam emitted from the light source into a parallel light beam; and a diaphragm that limits the parallel light beam to a predetermined light beam diameter;
A rotating polygon mirror that deflects and reflects an incident light beam from the first optical system;
A second optical system that forms an image of a deflected reflected light beam from the light deflecting / reflecting surface of the rotating polygon mirror as a light spot on the scanned surface;
An optical scanning device configured to scan the optical spot over a predetermined angular range around the optical axis of the second optical system on the surface to be scanned by rotating the rotary polygon mirror,
In the optical scanning device in which the light flux width in the scanning plane of the incident light flux is set to a value larger than the width in the scanning plane of the light deflection reflection surface,
Said first optical system is configured such that a predetermined amount displaced in the optical axis side of the second optical system of the light intensity peak position with respect to the optical axis of the first optical system in the incident light beam ,And,
The displacement position of the light intensity peak position is set to a position where the light beam reflected by the reflecting surface other than the light deflecting reflecting surface in the rotary polygon mirror does not appear as a ghost beam in the optical path of the second optical system . An optical scanning device.   The displacement of the light intensity peak position is performed by translating the optical axis of the light source and the collimator lens to the optical axis side of the second optical system with respect to the optical axis of the first optical system. The optical scanning device according to claim 1, wherein:   The displacement of the light intensity peak position is performed by inclining the direction of the optical axis of the light source toward the optical axis of the second optical system with respect to the optical axis of the first optical system. 2. The optical scanning device according to claim 1, wherein: When the amount of displacement of the light intensity peak position and the amount of translation of the optical axis of the light source and the collimator lens with respect to the optical axis of the first optical system is a / 2, the value of a is 3. The optical scanning device according to claim 2, wherein the optical scanning device is obtained by the following equation (1).
a = R { sin (3π / n) − sin ((Α + θ) / 2 + π / n) + sin (Π / n) − sin ((Α−θ) / 2−π / n)} (1)
Where n is the number of surfaces of the rotating polygon mirror
R: circumscribed circle radius of the rotating polygon mirror
θ: Effective scanning half angle
α: angle formed by the optical axis of the first optical system and the optical axis of the second optical system When the displacement amount of the light intensity peak position is a / 2 and the angle of inclination of the optical axis of the light source with respect to the optical axis of the first optical system is δ, the value of δ is expressed by the following equation (2) 4. The optical scanning device according to claim 3, wherein the optical scanning device is obtained by:
δ = sin ^-1 (A / 2f) (2)
Where f: focal length of the collimator lens

Images