JP2010262244A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner in which optical performance is not deteriorated and the cost of luminous flux detection optical systems for controlling the image writing positions is reduced. <P>SOLUTION: In the optical scanner, luminous fluxes emitted from a pair of light source parts composed of light sources 1y, 1m and light sources 1c, 1k, respectively, are simultaneously deflected on different reflection faces of a single rotary polygon mirror 6, and focused on respective faces to be scanned. The luminous flux detection optical systems (21, 22, 23) for controlling the image writing positions and a light receiving sensor 24 are disposed. The angle θ between the luminous fluxes directed from the light source parts to the rotary polygon mirror 6 and the optical axis of the optical elements 11 in the scanning optical system, which are closest to the rotary polygon mirror 6, satisfies the following conditional relations (1), (2). Relation (1): 180/N×(2m+A-3/4)≤θ≤180/N×(2m+A+3/4). Relation (2): 0≤θ≤90, where N: the number of faces of the rotary polygon mirror (N≥4), m: an integer including 0, A: 1 when N is an even number or 0 when N is an odd number. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical scanning device, and more particularly to an optical scanning device that scans a plurality of scanned surfaces with a plurality of light beams modulated based on image data using a single deflector.

  In recent years, in an image forming apparatus such as a digital copying machine or a laser beam printer, four photoconductors are juxtaposed corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black). However, a tandem method in which an image of each color formed on each photoconductor is transferred to an intermediate transfer belt or the like and synthesized is the mainstream. In this type of tandem image forming apparatus, for example, there is an optical scanning device that draws an image by simultaneously scanning four light beams using a single deflector (polygon mirror) on each photoconductor. It is installed.

  An optical scanning device mounted on this type of color image forming apparatus requires four light sources. Although four optical scanning devices having one light source may be mounted, four relatively expensive deflecting means are required, which is disadvantageous in terms of cost. Therefore, various optical scanning devices have been proposed in which a plurality of light beams are scanned by a single deflecting means.

  When scanning four light beams with a single deflecting means, one-side deflection scanning type in which four light beams are simultaneously incident on one reflecting surface of the deflecting means composed of a rotating polygon mirror, and two reflecting surfaces of the rotating polygon mirror, respectively. There is a double-sided deflection scanning type in which two light beams are incident. The present invention adopts a double-sided deflection scanning type.

  In addition, in order to form a desired image on the photosensitive member, it is necessary to perform modulation control of each light source according to the image data and to control writing timing of image data for one line. This writing timing control is usually performed based on the light reception timing of a sensor that receives scanning light in the optical scanning device. Ideally, the same number of light flux detection optical systems and sensors as for guiding the light flux from the rotating polygon mirror to the sensor are installed, but the rotating polygon mirror is shared by a plurality of photosensitive members. It is possible to reduce the number to the minimum necessary for cost reduction.

  Patent Documents 1, 2, and 3 are examples in which the number of light beam detection optical systems and sensors for detecting the writing position of image data for one line in the double-sided deflection scanning type is smaller than the number of photoconductors.

  In Patent Document 1, two rotating polygonal mirrors are arranged on one rotating shaft, and two light beams are incident on both sides of one rotating polygonal mirror. In this case, when the light beam detection optical system and sensor are combined into one for the four photoconductors, all four light beams scan on different surfaces. Therefore, manufacturing errors and arrangement errors of the rotary polygon mirror and the scanning lens are detected. In addition, there is a problem that color misregistration is likely to occur due to a difference in environmental conditions such as the temperature inside the optical scanning device. In order to suppress the influence of such errors, it is considered that a light beam detection optical system corresponding to the number of surfaces simultaneously incident on the rotary polygon mirror from the light source is necessary. In order to reduce the cost among them, there are a method in which the substrates on which the sensors are mounted are combined into one for a plurality of light beam detection optical systems, and a method in which a single sensor is used in common. 3 proposes such a method.

  However, in order to use a single sensor in common with the two light beam detection optical systems, it is necessary that the timing at which the sensor receives the light beams from the two light beam detection optical systems is shifted. In this regard, Patent Document 2 has no specific description. Patent Document 3 proposes to change the timing by changing the angle (incident opening angle) formed by the optical axis of the scanning lens and the optical axis of the light source unit with four light beams. However, with this method, if the angle difference is very small, the timing cannot be shifted much. Conversely, if the angle difference becomes large, the optical performance (mainly field curvature) of the scanning optical system is adversely affected. Therefore, it is not preferable.

JP-A-4-313776 JP 2005-17680 A JP 2007-147826 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a both-side deflection type optical scanning device that does not deteriorate optical performance and can reduce the cost of a light beam detection optical system for controlling the image writing position. It is in.

In order to achieve the above object, an optical scanning device according to an aspect of the present invention includes:
Two sets of light source sections each having one or more light sources;
A single rotating polygon mirror that simultaneously deflects light beams emitted from the two sets of light source units on different surfaces;
Two sets of scanning optical systems that are arranged on both sides of the rotary polygon mirror and form images of light beams deflected by the rotary polygon mirror on a plurality of scanned surfaces;
Two light flux detection optical systems for controlling the image writing position;
At least one light receiving sensor disposed on a scanning surface of a light beam by the light beam detection optical system;
With
The two light beam detecting optical systems are arranged so as to scan at least two light beams deflected by different surfaces of the rotary polygon mirror at substantially the same position, and the deflection angles of the light beams incident on the light receiving sensor are equal,
At least two light beams deflected by different surfaces of the rotary polygon mirror with respect to the two light beam detection optical systems, one on the light source side and the other on the optical axis of the two sets of scanning optical systems Each side is reflected,
The light beam traveling from the two sets of light source units to the rotary polygon mirror and the lens closest to the rotary polygon mirror of the two sets of scanning optical systems are arranged symmetrically with respect to the plane including the rotation axis of the rotary polygon mirror.
The angle θ between the light beam traveling from the two sets of light source units toward the rotary polygon mirror and the optical axis of the optical element closest to the rotary polygon mirror of the scanning optical system satisfies the following conditional expressions (1) and (2). thing,
180 / N × (2m + A−3 / 4) ≦ θ ≦ 180 / N × (2m + A + 3/4) (1)
0 ≦ θ ≦ 90 (2)
N: Number of surfaces of the rotating polygon mirror (N ≧ 4)
m: an integer including 0 A: 1 when N is an even number, or 0 when N is an odd number
It is characterized by.

  In the optical scanning device, two light beams deflected by different surfaces of the rotary polygon mirror can be incident on one light receiving sensor at different timings. Accordingly, it is only necessary to install one sensor with respect to the two light beam detection optical systems for controlling the image writing position, so that the cost can be reduced. When controlling the writing position with four light beams, two light beams deflected by the same surface of the rotary polygon mirror and having different angles in the sub-scanning direction pass through one light beam detection optical system and are high in the sub-scanning direction. What is necessary is just to inject into two sensors arrange | positioned in the position where a height differs. Since the remaining two light beams have the same configuration, the write position control of the four light beams can be performed with the two light beam detection optical systems and the two sensors. Further, since the angles θ are all the same, optical performance such as field curvature is not deteriorated.

  In particular, in the optical scanning device, it is preferable to use a single light receiving sensor and make the optical path lengths from the reflection position of the rotary polygon mirror to the light receiving sensor substantially equal.

  The light beams guided by the two light beam detection optical systems are combined and transmitted through a single condenser lens and then incident on the light receiving sensor. The light beams guided by the light beam detection optical system are part of the lenses of the scanning optical system. Or a configuration in which a part of the lens through which the light beam guided by the light beam detection optical system is transmitted has a surface shape different from the lens surface that forms an image of the light beam on the surface to be scanned. By doing so, further cost reduction can be achieved. In addition, the configuration in which the light beam guided by the light beam detection optical system transmits a part of the lens of the scanning optical system, or the part of the lens through which the light beam guided by the light beam detection optical system passes is covered with the light beam. By adopting a configuration having a surface shape different from the lens surface to be imaged on the scanning surface, the image writing position can be controlled without being affected by the arrangement of the scanning lens, processing errors, and the like.

  Furthermore, before writing to the surface to be scanned, if only one light source of the two sets of light source units emits light and a correspondence between the light source unit and the incident light beam to the light receiving sensor is provided, the light receiving sensor When the light is received, it can be identified which light beam from the light source unit on the side, and the light source from the other light source unit receives the light beam to the sensor unit by mistake, and the other light source side writes out the image data. It can be prevented beforehand.

1 is a three-dimensional layout diagram illustrating a first embodiment of an optical scanning device according to the present invention. FIG. 3 is an XZ side view showing an optical path configuration from the rotary polygon mirror to the scanned surface in the first embodiment. It is an XY plan view showing an optical path configuration from the light source unit of the first embodiment to the scanning lens including the rotary polygon mirror. It is explanatory drawing which shows the comparative example in case the number of surfaces of a rotating polygon mirror is an even number. It is explanatory drawing which shows the example of this invention in case the number of surfaces of a rotary polygon mirror is an even number. It is explanatory drawing which shows the comparative example in case the number of surfaces of a rotary polygon mirror is an odd number. It is explanatory drawing which shows the example of this invention in case the number of surfaces of a rotary polygon mirror is an odd number. FIG. 6 is an XY plan view showing an optical path configuration from a light source unit to a scanning lens including a rotary polygon mirror in the second embodiment of the optical scanning device according to the present invention.

  Hereinafter, embodiments of an optical scanning device according to the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same member and part in each figure, and the overlapping description is abbreviate | omitted.

(Configuration of the first embodiment, see FIGS. 1 to 3)
1, 2 and 3 show a first embodiment of an optical scanning device according to the present invention. This optical scanning device is configured as an exposure unit of an image forming apparatus based on tandem electrophotography, and each color is arranged on four photosensitive drums 50 (50y, 50m, 50c, 50k) as shown in FIG. The image is formed. The four-color image (electrostatic latent image) formed on the photosensitive drum 50 is developed with toner, and then primary-transferred / combined on an intermediate transfer belt (not shown), and secondary-imaged on a recording material. Transcribed. This type of image forming process is well known and will not be described.

  As shown in FIG. 3, the light source section is composed of four laser diodes 1 (1y, 1m, 1c, 1k), a collimator lens 2, an aperture 3, and a mirror 4, and a light beam B (By, Bm, Bc, Bk) The light enters the single rotating polygonal mirror 6 through the cylindrical lens 5. That is, the light beam (diverging light) B emitted from each laser diode 1 is made into substantially parallel light by the collimator lens 2, and after passing through the aperture 3, the two cylindrical mirrors 6 are rotated in the sub-scanning direction Z by the cylindrical lens 5. The light is condensed in the sub-scanning direction Z on the reflection surface. Two sets of light beams By and Bm and light beams Bc and Bk are incident on different surfaces of the rotary polygon mirror 6, respectively. The light beams By and Bm and the light beams Bc and Bk incident on the same reflecting surface are incident at the same angle and position in the main scanning direction Y but obliquely at different angles in the sub-scanning direction Z. Therefore, the laser diodes 1y, 1m and 1c, 1k are arranged so as to be orthogonal to each other, and the optical paths of the light beams Bm, Bc are bent by the mirror 4.

  As shown in FIGS. 1 and 2, the first scanning lens 11, the second scanning lens 12, and the like for imaging each light beam deflected in the main scanning direction Y by the rotary polygon mirror 6 on each photosensitive drum 50, A plurality of optical path folding mirrors 13y, 13m, 13c, 13k, 14y, 14m, 14c, and 15m for guiding the light beams that have passed through the scanning lenses 11 and 12 to the respective photosensitive drums 50 are individually disposed in the optical paths. The third scanning lens 16 (16y, 16m, 16c, 16k) and a window glass 17 for dust prevention are arranged. The subsequent optical system of the rotary polygon mirror 6 is referred to as a scanning optical system.

  The light beams from the light source part are deflected to the left and right sides simultaneously by the reflecting surfaces of the rotary polygon mirror 6 and the light beams Bc and Bk are simultaneously reflected by the other reflecting surfaces. The upper light beams Bm and Bc and the lower light beams By and Bk are separated, transmitted through the first scanning lenses 11 and 12, folded by various folding mirrors, and transmitted through the third scanning lens 16 and each window glass 17. Then, an image is formed on each photosensitive drum 50 and scanned in the main scanning direction Y.

  Further, the light beam detection optical system for controlling the image writing position on each photosensitive drum 50 combines the optical path folding mirrors 21y and 21c and the optical path so as to guide the light beams By and Bc to the single light receiving sensor 24. It comprises a half mirror 22 and a condenser lens 23. In the first embodiment in which the rotating polygon mirror 6 has six surfaces so that the light beams By and Bc are incident on the light receiving sensor 24 in different angular states (that is, at different times) of the rotating polygon mirror 6, FIG. Thus, the incident open angle θ (angle between the light beam incident on the rotary polygon mirror 6 from the light source and the optical axis of the scanning optical system) is 80 °, and the field angle γ (rotational polygon mirror 6 of the light beam incident on the light receiving sensor 24). The angle between the reflected light beam and the optical axis of the scanning optical system is 48 °.

(Refer to FIG. 4 and FIG. 5 when the number of surfaces of the rotating polygon mirror is an even number)
Here, with reference to FIG.4 and FIG.5, the effect in case the number of surfaces of the rotary polygon mirror 6 is an even number is demonstrated. 4 shows a comparative example, FIG. 5 shows an example of the present invention, and the number of surfaces of the rotary polygon mirror is six. In any of the comparative example and the present invention example, the incident light beam from the light source and the optical axes of the first and second scanning lenses 11 and 12 are arranged symmetrically with respect to the surface including the rotation axis of the rotary polygon mirror 6. Yes. In addition, the angle of view γ on both sides of the rotary polygon mirror 6 is the same. In either case, the light beam deflected on the same surface passes through the light beam detection optical system to control the image writing position on the surface of the rotary polygon mirror 6. Therefore, one light beam is reflected on the light source side and the other light beam is reflected on the counter light source side.

  In the comparative example of FIG. 4, when the rotary polygon mirror 6 is in the rotational position indicated by a thin line, that is, the normal of the surface on which the light beam from the light source is incident and the optical axis of the scanning optical system are the same angle on both sides. This is when α and the incident opening angle θ are 2α (where α = 180 / N, N: the number of surfaces of the rotating polygon mirror 6). At this time, incident light beams from the light sources on both sides of the rotary polygon mirror 6 have a deflection angle of 0 ° on either side, and scan the center of the image range. Since the angle of view γ incident on the sensor 24 is the same on both sides, the rotating polygon mirror 6 is returned (dotted line) in the counter-rotating direction from the state of scanning the center of the image range (dotted line) at the same time. The light enters the light receiving sensor 24.

  On the other hand, in the example of the present invention shown in FIG. 5, when the rotary polygon mirror 6 is at the rotation position indicated by a thin line, that is, the incident opening angle θ is 3α (where α = 180 / N, N: surface of the rotary polygon mirror 6 Number). At this time, the angle formed by the normal of the surface on which the light beam from the light source is incident and the optical axis of the scanning optical system is 3α / 2, and the deflection angle is 0 °. However, the light beams on both sides of the rotary polygon mirror 6 do not satisfy this condition at the same time. Accordingly, the two light beams By and Bc do not enter the light receiving sensor 24 at the same time, and the light receiving timing of the sensor 24 is different.

The condition shown in FIG. 5 is a condition under which the light beam incident on both sides of the rotary polygon mirror 6 can be alternately detected by the sensor 24 at equal intervals. The incident opening angle θ that satisfies this condition is not only 3α, but is when the incident opening angle θ is an odd multiple of α, such as 5α. Universally, by introducing 2m + A (m is an integer including 0, and A is 1 when the number of faces is an even number), it can be expressed by the following formula (1).
180 / N × (2m + A−3 / 4) ≦ θ ≦ 180 / N × (2m + A + 3/4) (1)

  However, if θ exceeds 90 °, it becomes difficult to cause the light beam to enter the rotary polygon mirror 6. Further, it is not always necessary to completely match the above conditions. If the relationship between the number of surfaces of the rotary polygon mirror 6 and the incident opening angle θ is in the range shown in Table 1 below, two light beams are sufficiently transmitted to the sensor 24. The incident timing can be shifted.

(See Fig. 6 and Fig. 7 when the number of surfaces of the rotating polygon mirror is odd)
Next, with reference to FIG.6 and FIG.7, the effect in case the number of surfaces of the rotary polygon mirror 6 is an odd number is demonstrated. 6 shows a comparative example, FIG. 7 shows an example of the present invention, and the number of surfaces of the rotary polygon mirror is five.

  FIG. 6 as a comparative example shows a case where the incident opening angle θ is in the relationship of α (where α = 180 / N, N: the number of surfaces of the rotating polygon mirror 6). At this time, incident light beams from the light sources on both sides of the rotary polygon mirror 6 have a deflection angle of 0 ° on either side, and scan the center of the image range. Accordingly, the two light beams are incident on the light receiving sensor 24 at the same time.

  On the other hand, FIG. 7 which is an example of the present invention shows a case where the incident opening angle θ is 2α (where α = 180 / N, N: the number of surfaces of the rotating polygon mirror 6). At this time, the angle between the normal of the surface on which the light beam from the light source is incident and the optical axis of the scanning optical system is α, and the deflection angle is 0 °. However, the light beams on both sides of the rotary polygon mirror 6 do not satisfy this condition at the same time. Accordingly, the two light beams By and Bc do not enter the light receiving sensor 24 at the same time, and the light receiving timing of the sensor 24 is different.

  The conditions shown in FIG. 7 are conditions under which the sensor 24 can alternately detect light beams incident on both sides of the rotary polygon mirror 6 at equal intervals. Universally, by introducing 2m + A (m is an integer including 0, and A is 1 when the number of faces is an even number), it can be expressed by the formula (1) as in the case where the number of faces is an even number. .

  As in the case where the number of surfaces is an even number, it is not always necessary to completely match the above conditions. The relationship between the number of surfaces of the rotary polygon mirror 6 and the incident opening angle θ is within the range shown in Table 2 below. The timing at which two light beams are incident on the sensor 24 can be sufficiently shifted.

  If the number of faces is an odd number, the case where the incident opening angle θ is 0 ° is also included. Regarding this, as in the first embodiment, when two light beams are obliquely incident on one side of the rotary polygon mirror 6 in the sub-scanning direction Z, it is difficult to dispose the light source unit. If a single light beam is incident, the light source and the scanning optical system can be arranged if their optical axes are inclined in the sub-scanning direction Z.

(Refer to the second embodiment, FIG. 8)
Next, a second embodiment of the optical scanning device according to the present invention will be described with reference to FIG. In the second embodiment, the light beam By reflected by one reflecting surface of the rotary polygon mirror 6 is transmitted through the end of the first scanning lens 11, and then folded by the optical path folding mirrors 21y and 21y 'to be collected. The light beam Bc, which is guided to the light receiving sensor 24 through 23y and reflected by the other reflecting surface, is transmitted through the end portion of the first scanning lens 11, and then folded by the optical path folding mirrors 21c and 21c ′, so that the condenser lens 23c is In this way, the light is guided to the light receiving sensor 24. Other configurations and the operational effects thereof are the same as those of the first embodiment.

  As in the second embodiment, even if the light beam guided by the light beam detection optical system passes through a part of the scanning lens 11, the light reception timing of the sensor 24 is not affected. A part of the scanning lens 11 through which the light beam guided by the light beam detection optical system passes may have a surface shape different from a lens surface that forms an image of the light beam on the photosensitive drum 50. For example, a part of the scanning lens 11 may have a function as a condenser lens.

(Identification of light flux by light receiving sensor)
In the first and second embodiments, two light beams are incident on the single light receiving sensor 24 at different timings. Therefore, it is necessary to identify which light beam is incident. For this purpose, before writing to the photosensitive drum 50 is started, only one of the light sources emits light, and the time from the light emission timing to the incidence on the sensor 24 is detected. Can be attached.

(Other examples)
The optical scanning device according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof.

  As described above, the present invention is useful for an optical scanning device mounted on an electrophotographic copying machine or the like, and in particular, a light flux detection optical system for controlling an image writing position without deteriorating optical performance. The system is excellent in that the cost can be reduced.

DESCRIPTION OF SYMBOLS 1 ... Laser diode 6 ... Rotating polygon mirror 11, 12 ... Scanning lens 21 ... Folding mirror 23 ... Condensing lens 24 ... Light receiving sensor B ... Light beam 50 ... Photosensitive drum (surface to be scanned)

Claims (7)

Two sets of light source sections each having one or more light sources;
A single rotating polygon mirror that simultaneously deflects light beams emitted from the two sets of light source units on different surfaces;
Two sets of scanning optical systems that are arranged on both sides of the rotary polygon mirror and form images of light beams deflected by the rotary polygon mirror on a plurality of scanned surfaces;
Two light flux detection optical systems for controlling the image writing position;
At least one light receiving sensor disposed on a scanning surface of a light beam by the light beam detection optical system;
With
The two light beam detecting optical systems are arranged so as to scan at least two light beams deflected by different surfaces of the rotary polygon mirror at substantially the same position, and the deflection angles of the light beams incident on the light receiving sensor are equal,
At least two light beams deflected by different surfaces of the rotary polygon mirror with respect to the two light beam detection optical systems, one on the light source side and the other on the optical axis of the two sets of scanning optical systems Each side is reflected,
The light beam traveling from the two sets of light source units to the rotary polygon mirror and the lens closest to the rotary polygon mirror of the two sets of scanning optical systems are arranged symmetrically with respect to the plane including the rotation axis of the rotary polygon mirror.
The angle θ between the light beam traveling from the two sets of light source units toward the rotary polygon mirror and the optical axis of the optical element closest to the rotary polygon mirror of the scanning optical system satisfies the following conditional expressions (1) and (2). thing,
180 / N × (2m + A−3 / 4) ≦ θ ≦ 180 / N × (2m + A + 3/4) (1)
0 ≦ θ ≦ 90 (2)
N: Number of surfaces of the rotating polygon mirror (N ≧ 4)
m: an integer including 0 A: 1 when N is an even number, or 0 when N is an odd number
An optical scanning device characterized by the above.   2. The optical scanning device according to claim 1, wherein the light receiving sensor disposed on the scanning surface of the two light beam detection optical systems is single.   3. The optical scanning device according to claim 1, wherein optical path lengths from the reflection positions of the rotary polygon mirrors of the two light beam detection optical systems to the light receiving sensor are substantially equal. 4.   4. The light beam guided by the two light beam detection optical systems is combined and transmitted through a single condenser lens, and then enters the light receiving sensor. Optical scanning device.   4. The optical scanning device according to claim 1, wherein the light beam guided by the light beam detection optical system is transmitted through a part of a lens of the scanning optical system.   6. The light according to claim 5, wherein a part of the lens through which the light beam guided by the light beam detection optical system transmits has a surface shape different from a lens surface that forms an image of the light beam on the surface to be scanned. Scanning device.   3. Before starting writing on the surface to be scanned, only one light source of the two sets of light source units emits light, and correspondence between the light source unit and the incident light beam to the light receiving sensor is attached. The optical scanning device according to 1.

Images