JP5056492B2 - Laser beam scanning device - Google Patents

Description

  The present invention relates to a laser beam scanning device, and more particularly to a laser beam scanning device that scans a plurality of photosensitive members using a single deflector using a plurality of beams modulated based on image data.

  In recent years, in an image forming apparatus such as a full-color copying machine or printer, four photoconductors are juxtaposed corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black). The tandem method in which the images of the respective colors formed on the respective photoconductors are transferred to an intermediate transfer belt or directly onto a recording medium and synthesized is the mainstream. In this type of tandem image forming apparatus, for example, a laser beam scanning apparatus that draws an image by simultaneously scanning four beams on each photosensitive member using a single deflector (polygon mirror). Is installed.

  This type of laser beam scanning device has a plurality of light sources and a collimator lens, is arranged so that the optical axes of the light source and the collimator lens coincide with each other, and a beam transmitted through the collimator lens is synthesized by an optical path synthesis mirror. It is widely known that the light is incident parallel to the cylinder lens and condensed in the sub-scanning direction in the vicinity of the deflection surface.

  On the other hand, the laser beam scanning device described in Patent Document 1 employs a configuration in which the collimator lens is eccentrically arranged with respect to the light source and is obliquely incident on the deflection surface at different angles. However, the height of incidence of the beam on the deflection surface is set to two types, which is insufficient to maintain the synthesis margin.

  Further, in the laser beam scanning devices described in Patent Document 2 and Patent Document 3, a plurality of beams are incident on the common cylinder lens at different angles, and are also incident on the deflection surface at different heights. . However, the optical axes of the light source and the collimator lens are the same. When this configuration is adopted, the substrate holding the light source is inclined and arranged, and the light source arrangement angle error tends to increase.

By the way, in a laser beam scanning device mounted on a tandem image forming apparatus, it is necessary to combine beams emitted from a plurality of light source units in the same direction. When the combining mirror is used, beams emitted from a plurality of light sources need to be spaced apart in the sub-scanning direction. In order to secure this distance, there are methods of increasing the oblique incident angle on the deflecting surface and increasing the focal length of the cylinder lens. However, if the oblique incidence angle is increased, the optical performance is deteriorated and the scanning lens is also increased. In addition, when the focal length of the cylinder lens is increased, the magnification in the sub-scanning direction changes in the case of the multi-beam optical system, so that the interval in the sub-scanning direction on the photosensitive member changes. If the focal length of the collimator lens is increased in order to avoid this, the light use efficiency is lowered.
JP 2007-41420 A JP 2005-148284 A JP 2006-184586 A

  Accordingly, an object of the present invention is to enable reliable optical path synthesis from a light source to a deflector while maintaining good optical performance in a laser beam scanning apparatus that scans a plurality of photosensitive members simultaneously in parallel. There is to do.

In order to achieve the above object, a laser beam scanning apparatus according to one aspect of the present invention is
A plurality of light source units, a plurality of optical path combining members that make the optical paths of the respective beams emitted from the light source units in the same direction, one cylinder lens through which the plurality of beams pass, and a beam that has passed through the cylinder lens One deflector that deflects in the main scanning direction, a scanning optical element that guides the beam deflected by the deflector onto the photoconductor, and an optical path separation mirror that separates the beam toward each photoconductor In a laser beam scanning device,
Each light source unit is composed of a light source, a collimator lens, and a diaphragm.
The light source is arranged so that a first plane including a generating line and an optical axis of the cylinder lens is parallel to a second plane including a maximum intensity direction of a beam emitted from the light source,
Beams emitted from different light sources pass through different collimator lenses and diaphragms, enter the cylinder lens at different angles with respect to the first plane, and have different heights in the sub-scanning direction. Enter the deflector,
The collimator lens is arranged such that its principal point is located on the opposite side of the first plane with respect to the second plane,
At least one of the plurality of optical path combining members has a focal length of the cylinder lens as fcy, oblique incident angles of the two beams combined by the optical path combining member on the deflector are β1 and β2, respectively, and an optical path combining member Satisfying the following conditional expression (1), where W is the principal ray spacing of the two beams on the combined surface of
W> | fcy · (tan β1-tan β2) | (1)
It is characterized by.

  In the laser beam scanning device, beams emitted from a plurality of light sources and having passed through different collimator lenses and diaphragms travel in directions away from the first plane including the generatrix and optical axis of the cylinder lens at different angles. That is, the distance between adjacent beams emitted from different light sources increases as the distance from the collimator lens increases between the collimator lens and the cylinder lens. Thus, the conditional expression (1) is satisfied in at least one of the plurality of optical path combining members disposed between the stop and the cylinder lens. By satisfying conditional expression (1), the principal ray interval of the beam can be set to a necessary value. In other words, it is not necessary to increase the oblique beam incidence angle to the deflector or to increase the focal length of the cylinder lens or collimator lens, and it is possible to prevent deterioration in optical performance and reduction in light utilization efficiency.

  Embodiments of a laser beam scanning apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Overall configuration, see FIGS. 1-4)
FIG. 1 shows a three-dimensional arrangement relationship for one embodiment of a laser beam scanning apparatus according to the present invention. In each figure, y, m, c, and k attached to the symbols mean members used for forming each color of yellow, magenta, cyan, and black. These subscripts are omitted.

  This laser beam scanning device is configured as an exposure unit of an image forming apparatus based on tandem electrophotography, and images of yellow, magenta, cyan, and black are respectively formed on four photosensitive drums 40y, 40m, 40c, and 40k. It is configured to form. The four-color image (electrostatic latent image) formed on the photosensitive drum 40 is developed with toner, and then primary-transferred / combined on an intermediate transfer belt (not shown), and then secondary-recorded on a recording material. Transcribed. This type of image forming process is well known and will not be described.

  As shown in FIGS. 1 and 2, the light source unit 1 includes four light sources 11y, 11m, 11c, and 11k made of laser diodes, collimator lenses 12y, 12m, 12c, and 12k, and apertures 13y, 13m, 13c, and 13k. It consists of and. Beams (diffused light) emitted from each light source 11 are converted into parallel light by each collimator lens 12 and pass through each aperture 13. The beam By emitted from the light source 11y is reflected by the optical path combining mirror 14y and travels toward the mirror 15. The beam Bm emitted from the light source 11m is reflected by the optical path combining mirror 14m and travels toward the mirror 15. The beam Bc emitted from the light source 11c is reflected by the optical path combining mirror 14c and travels to the mirror 15. The beam Bk emitted from the light source 11k goes directly to the mirror 15. Here, the optical path combining mirror 14 is a reflection mirror arranged so that the optical paths of the respective beams are in the same direction.

  Each beam reflected by the mirror 15 passes through the cylinder lens 16 and is condensed in the sub-scanning direction Z in the vicinity of the deflection surface of the polygon mirror 17. The polygon mirror 17 is rotationally driven at a predetermined speed, and each beam is deflected and scanned in the main scanning direction Y. Each beam is incident on the cylinder lens 16 at different angles with respect to a first plane P1 (see FIG. 3) described below, and on the deflection surface of the polygon mirror 17 at different heights in the sub-scanning direction Z. Incident (this point is described in detail below with reference to FIGS. 5 and 6).

  Regarding the traveling direction X of each beam from the polygon mirror 17, the first scanning lens 21, the second scanning lens 22, the third scanning lenses 23y, 23m, 23c, 23k, the mirrors 24y, 24m, 24c, 24k, 25y, 25m, 25c, 26m, 26c, and parallel flat plates (dust window glass) 27y, 27m, 27c, 27k are arranged.

  The four beams simultaneously deflected by the same deflection surface of the polygon mirror 17 are transmitted through the first scanning lens 21 and the second scanning lens 22, respectively. The beam By is reflected by the mirror 24y, passes through the third scanning lens 23y, further reflected by the mirror 25y, passes through the parallel plate 27y, forms an image on the photosensitive drum 40y, and scans in the main scanning direction Y. To do. The beam Bm is reflected by the mirrors 24m and 25m, passes through the third scanning lens 23m, is further reflected by the mirror 26m, passes through the parallel plate 27m, and forms an image on the photosensitive drum 40m. Scan to. The beam Bc is reflected by the mirror 24c, passes through the third scanning lens 23c, is further reflected by the mirrors 25c and 26c, passes through the parallel plate 27c, and forms an image on the photosensitive drum 40c. Scan to. The beam Bk passes through the third scanning lens 23k, is reflected by the mirror 24k, passes through the parallel flat plate 27k, forms an image on the photosensitive drum 40k, and scans in the main scanning direction Y.

  Here, as shown in FIGS. 3 and 4, the plane including the generatrix and the optical axis of the cylinder lens 16 is referred to as a first plane P1, and the plane including the maximum intensity direction M of the beam emitted from the light source 11 is the first plane P1. 2 plane P2. In this case, the first plane P1 and the second plane P2 are arranged to be parallel to each other. The diaphragm 13 is arranged so as to include the maximum intensity direction M of the beam emitted from the light source 11.

(Refer to the first embodiment, FIGS. 5 and 10)
In the laser beam scanning apparatus having the above-described configuration, the first embodiment shifts the collimator lens 12 by a predetermined amount in the sub-scanning direction Z with respect to the second plane P2, and uses the main scanning direction Y as the central axis. By rotating the collimator lens 12 by a predetermined angle, the collimator lens 12 is disposed so that the principal point is located on the opposite side of the first plane P1 with respect to the second plane P2.

  Tables 1 to 4 listed below show basic data and eccentricity data of the construction of each optical element constituting the light source system of Y, M, C, and K in the first embodiment. Tables 6 and 7 listed below show basic construction data and eccentricity data of the optical elements constituting the C and K scanning systems in the first embodiment. The basic data and eccentricity data of M are symmetric with C, and the basic data and eccentricity data of Y are symmetric with K.

  Table 5 below shows numerical values of various optical elements in the first example. Incidentally, the incident height in the sub-scanning direction Z where the beam is obliquely incident on the deflecting surface of the polygon mirror 17 is 0.177 mm for the beam By, 0.002 mm for the beam Bm, -0.174 for the beam Bc, Regarding Bk, it is -0.374 mm. The principal ray interval W (see FIG. 10) of the beams whose optical paths are combined on the combining surface of each combining mirror 14 is 0.98 mm at the combining mirror 14y (beams By and Bm), and the combining mirror 14m (beams Bm and Bc). 0.91 mm.

(Refer to the second embodiment, FIGS. 6 and 10)
In the laser beam scanning apparatus having the above-described configuration, the second embodiment shifts the collimator lens 12 by a predetermined amount in the sub-scanning direction Z with respect to the second plane P2, so that the principal point of each collimator lens 12 is the first point. It arrange | positions so that it may be located on the opposite side to 1st plane P1 with respect to 2 plane P2.

  Tables 8 to 11 listed below show basic data and eccentricity data of the construction of each optical element constituting the light source system of Y, M, C, and K in the second embodiment. Tables 6 and 7 listed below show basic construction data and eccentricity data of each optical element constituting the C and K scanning systems in the second embodiment. The basic data and eccentricity data of M are symmetric with C, and the basic data and eccentricity data of Y are symmetric with K.

  Table 12 below shows numerical values of various optical elements in the second example. Incidentally, the incident height in the sub-scanning direction Z where the beam obliquely enters the deflecting surface of the polygon mirror 17 is 0.122 mm for the beam By, −0.016 mm for the beam Bm, −0.155 mm for the beam Bc, Regarding the beam Bk, it is -0.292 mm. The principal ray interval W (see FIG. 10) of the beams whose optical paths are combined on the combining surface of the combining mirror 14 is 0.96 mm at the combining mirror 14y (beams By and Bm), and the combining mirror 14m (beams Bm and Bc). 0.90 mm.

(Refer to the third and fourth embodiments, FIGS. 11 and 12)
The third embodiment uses an array laser as the light source 11 in the laser beam scanning apparatus having the above-described configuration, and the other configuration is the same as that of the first embodiment.

  The fourth embodiment uses an array laser as the light source 11 in the laser beam scanning apparatus having the above-described configuration, and the other configuration is the same as that of the second embodiment.

  FIG. 11 shows an array laser, and four beams are emitted from one light source 11. FIG. 12 shows the principal ray interval W of the beam emitted from the array laser whose optical paths are combined in the combining mirror 14.

(Condition (1), see FIG. 7)
In the first to fourth embodiments, at least one of the optical path combining mirrors 14 satisfies the following conditional expression (1) in the principal ray interval W of the beam. Here, fcy is the focal length of the cylinder lens 16, and β1 and β2 are the oblique incident angles of the two beams combined by the optical path combining mirror 14 on the polygon mirror 17 (see FIG. 7).
W> | fcy · (tan β1-tan β2) | (1)

  In the first and third examples, the right side of conditional expression (1) is 0.86 mm (see Table 5). As described above, W in the composite mirror 14y is 0.98 mm, and W in the composite mirror 14m is 0.91, which satisfies the conditional expression (1). In the second and fourth examples, the right side of conditional expression (1) is 0.86 mm (see Table 12). As described above, W in the composite mirror 14y is 0.96 mm, and W in the composite mirror 14m is 0.90, which satisfies the conditional expression (1).

(Condition (2), see FIG. 8)
In the first and second embodiments, as shown in FIG. 8, the amount of eccentricity h in the sub-scanning direction Z between the center of the light source 11 and the optical axis of the collimator lens 12 is expressed by the following conditional expression (2 ) Is satisfied. Here, fco is the focal length of the collimator lens 12, and α is the divergence angle (full width at half maximum) of the beam emitted from the light source 11 in the sub-scanning direction Z.
0 ≦ h <fco · tan (α / 2) (2)

  In the first example and the second example, the right side of the conditional expression (2) is 2 mm, respectively (see Tables 5 and 12). The eccentricity h in the first example is 0.067 mm, and the eccentricity h in the second example is 0.071 mm, which satisfies the conditional expression (2). When this conditional expression (2) is satisfied, the collimator lens 12 can be disposed within the beam divergence angle, and a reduction in the amount of light can be prevented.

(Condition (3), see FIG. 9)
In the third and fourth embodiments using an array laser as the light source 11, the following conditional expression (3) is satisfied. Here, P is the image density (dpi), Bz is the magnification in the entire optical system sub-scanning direction, N is the number of beams of the array laser, fco is the focal length of the collimator lens 12, By is the magnification in the entire optical system main scanning direction, and h is The parallel eccentric amount of the collimator lens 12 parallel to the first plane P1 and from the second plane P2, θ is the tilt eccentricity (tilt angle) with respect to the second plane P2, as shown in FIG. is there.
| √ [fco ² + (h−25.4 / P × Bz × (N−1) / 2) ² ] −√ [fco ² + (h + 25.4 / P × Bz × (N−1) / 2) ² ] | × | h−fco · tan θ | / h × By ²
<0.3 mm (3)

  In the third and fourth embodiments, as shown in Table 13 (third embodiment) and Table 14 (fourth embodiment) listed below, the image density P is 1200 dpi, and the number N of array laser beams is 4. It is. The left side of conditional expression (3) is 0.01 mm in the third embodiment and 0.18 mm in the fourth embodiment, and satisfies conditional expression (3), respectively.

  When the array laser is used, if the collimator lens 12 is decentered, a difference occurs in the optical path distance between the light emitting points 11a and 11b (see FIG. 9) at both ends of the array laser and the principal point of the collimator lens 12. This leads to a shift of the focus position for each of a plurality of beams of one array laser on the image plane. If the focus position shifts, the beam diameter becomes thick and the depth decreases. By satisfying conditional expression (3), it is possible to suppress the depth reduction to a range where no practical problem occurs.

(Summary of Examples)
In each of the embodiments described above, in each light source 11, the first plane P 1 including the generatrix and the optical axis of the cylinder lens 16 and the second plane P 2 including the maximum intensity direction of the beam emitted from each light source 11 are parallel to each other. It is arranged to be. Beams emitted from different light sources 11 pass through different collimator lenses 12 and diaphragms 13, are incident on the cylinder lens 16 at different angles with respect to the first plane P1, and are different in the sub-scanning direction Z. It enters the polygon mirror 17 at a height. Each collimator lens 12 is arranged such that its principal point is located on the opposite side of the second plane P2 from the first plane P1, and at least one of the plurality of optical path combining mirrors 14 is: The conditional expression (1) is satisfied.

  In the above configuration, the distance between adjacent beams emitted from different light sources 11 increases between the collimator lens 12 and the cylinder lens 16 as the distance from the collimator lens 12 increases. Accordingly, the conditional expression (1) is satisfied in at least one of the plurality of optical path combining mirrors 14 disposed between the diaphragm 13 and the cylinder lens 16. By satisfying conditional expression (1), the principal ray interval of the beam can be set to a necessary value, and deterioration of optical performance and reduction of light utilization efficiency can be prevented.

  In each embodiment, when the conditional expression (2) is satisfied, the collimator lens 12 can be disposed within the beam divergence angle, and a reduction in the amount of light can be prevented. In addition, each diaphragm 13 is arranged so as to include the maximum intensity direction of the beam emitted from each light source 11 and can further promote the effective use of light.

  Further, as in the third and fourth embodiments, if the plurality of light source units are configured by an array laser having a plurality of light sources, the array laser has a plurality of beams to be combined, and adjacent beams to be combined. Therefore, the present invention that the principal ray interval W between adjacent beams can be set to a large value can be used effectively. When the array laser is used, the depth reduction can be suppressed to a range that does not cause a practical problem by satisfying the conditional expression (3).

  The laser beam scanning apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

1 is a three-dimensional layout diagram showing the overall configuration of an embodiment of a laser beam scanning apparatus according to the present invention. It is a top view which shows the optical path structure of a light source part. It is a perspective view which shows the arrangement | positioning relationship of a collimator lens, an aperture stop, and a cylinder lens. It is a perspective view which shows the arrangement | positioning relationship of a light source and a cylinder lens. It is a conceptual diagram which shows the light source part of 1st Example. It is a conceptual diagram which shows the light source part of 2nd Example. It is explanatory drawing of conditional expression (1). It is explanatory drawing of conditional expression (2). It is explanatory drawing of conditional expression (3). It is explanatory drawing which shows the beam space | interval on an optical path synthetic | combination mirror. It is explanatory drawing which shows an array laser. It is explanatory drawing which shows the beam space | interval on the optical path synthetic | combination mirror at the time of using an array laser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source part 11 ... Light source 12 ... Collimator lens 13 ... Aperture 14 ... Optical path synthetic | combination mirror 16 ... Cylinder lens 17 ... Polygon mirror (deflector)
21, 22, 23 ... scanning lens 24, 25, 26 ... mirror 40 ... photosensitive drum B ... beam Y ... main scanning direction Z ... sub-scanning direction P1 ... first plane P2 ... second plane W ... principal ray spacing

Claims (5)

A plurality of light source units, a plurality of optical path combining members that make the optical paths of the respective beams emitted from the light source units in the same direction, one cylinder lens through which the plurality of beams pass, and a beam that has passed through the cylinder lens One deflector that deflects in the main scanning direction, a scanning optical element that guides the beam deflected by the deflector onto the photoconductor, and an optical path separation mirror that separates the beam toward each photoconductor In a laser beam scanning device,
Each light source unit is composed of a light source, a collimator lens, and a diaphragm.
The light source is arranged so that a first plane including a generating line and an optical axis of the cylinder lens is parallel to a second plane including a maximum intensity direction of a beam emitted from the light source,
Beams emitted from different light sources pass through different collimator lenses and diaphragms, enter the cylinder lens at different angles with respect to the first plane, and have different heights in the sub-scanning direction. Enter the deflector,
The collimator lens is arranged such that its principal point is located on the opposite side of the first plane with respect to the second plane,
At least one of the plurality of optical path combining members has a focal length of the cylinder lens as fcy, oblique incident angles of the two beams combined by the optical path combining member on the deflector are β1 and β2, respectively, and an optical path combining member Satisfying the following conditional expression (1), where W is the principal ray spacing of the two beams on the combined surface of
W> | fcy · (tan β1-tan β2) | (1)
A laser beam scanning device. The amount of eccentricity in the sub-scanning direction between the center of the light source and the optical axis of the collimator lens is h, the focal length of the collimator lens is fco, and the divergence angle (half value) of the beam emitted from the light source in the sub-scanning direction. Satisfying the following conditional expression (2) where α is a full-width)
0 ≦ h <fco · tan (α / 2) (2)
The laser beam scanning apparatus according to claim 1.   3. The laser beam scanning apparatus according to claim 1, wherein the diaphragm is disposed so as to include a maximum intensity direction of a beam emitted from the light source.   The laser beam scanning apparatus according to claim 1, wherein the plurality of light source units include an array laser having a plurality of light sources. The image density is P (dpi), the total optical system sub-scanning direction magnification is Bz, the number of beams of the array laser is N, the focal length of the collimator lens is fco, the entire optical system main scanning direction magnification is By, and the first The following conditional expression (3) is satisfied, where h is the parallel eccentricity of the collimator lens from the second plane and parallel to the plane, and θ is the tilt eccentricity with respect to the second plane. thing,
| √ [fco ² + (h−25.4 / P × Bz × (N−1) / 2) ² ] −√ [fco ² + (h + 25.4 / P × Bz × (N−1) / 2) ² ] | × | h−fco · tan θ | / h × By ²
<0.3 mm (3)
The laser beam scanning apparatus according to claim 4.

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