JP2006058523A - Optical scanner and method of adjusting optical axis - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner having an inexpensive and simple structure in which the light quantity distribution on a face to be scanned is uniformized. <P>SOLUTION: An overfilled optical system is composed in such a way that four laser beams emitted from a laser light source 10 in which four light sources are arranged in line in a subscanning direction are made incident on a polygon mirror 28 via a collimator lens 12, a slit 14, a first cylindrical lens 16, a first reflection mirror 18, a second reflection mirror 20, a second cylindrical lens 22, a filter 24, and a third cylindrical lens 26. In this optical system, the angle between an incident optical axis L and a scanning optical axis Ls is set to be 65 degrees, the incident optical axis L is moved by a predetermined distance toward an fθ 30 lens side, and the optical axis is adjusted for uniformizing light quantity. Thus, the whole laser light sources in the light source 10 is adjusted only by adjusting the light quantity at one light source. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical scanning device and an optical axis adjustment method, and more particularly to an optical scanning device and an optical axis adjustment method having a function of adjusting a light amount distribution of a light beam on a scanning medium such as a photosensitive member.

  In order to scan a light beam on a scanning surface such as a photoconductor, an optical scanning device that scans a light beam using a rotating polygon mirror having a plurality of reflecting surfaces is known. In this optical scanning device, as an optical system upstream (a light source side that emits a light beam) from the rotating polygon mirror, the light beam emitted toward the rotating polygon mirror is used to reduce the size of the device. In some cases, a light beam that is wider than the width of one reflecting surface (so-called “overfilled optical system”) is used. In this optical scanning device, various adjustments and settings are considered in order to provide a light beam having a stable light amount within the scanning range.

For example, a technique is known in which a light quantity distribution on a scanning surface such as a photosensitive member is made uniform by inserting a filter (see, for example, Patent Document 1). Another technique is known in which the light quantity distribution on the scanning plane is made uniform by shifting the optical axis incident on the rotary polygon mirror from the central optical axis (see, for example, Patent Document 2). Furthermore, a technique for balancing the amount of light within the scanning range is known (see, for example, Patent Document 3).
JP-A-8-160338 JP-A-10-206778 JP 9-96769 A

  However, in recent years, there has been a call for cost reduction and miniaturization of devices equipped with optical scanning devices, and demands for cost reduction and miniaturization of optical systems of optical scanning devices are also increasing. However, each of the above technologies is insufficient to make the light quantity distribution uniform while reducing the cost and size. For example, the complexity of the optical parts leads to an increase in cost, and taking a large adjustment range leads to an increase in the size of the apparatus. That is, in the technique of Patent Document 1, if quality is improved, a multistage filter is required, resulting in an increase in cost. In the technique of Patent Document 2, it is easy to secure a balance near the end of scanning, but uniformity within the scanning range is insufficient. The technique of Patent Document 3 allows fine adjustment, but the uniformity within the scanning range is still insufficient.

  The present invention has been made in view of the above-described facts, and an object thereof is to provide an optical scanning device and an optical axis adjustment method that can achieve uniform light amount distribution on a scanning surface with an inexpensive and simple configuration. To do.

  In order to achieve the above object, an optical scanning device of the present invention comprises a plurality of reflecting surfaces, deflecting means for deflecting an incident light beam in the main scanning direction by the reflecting surfaces, and a plurality of light beams toward the deflecting means. And a plurality of light beams are arranged so as to be emitted side by side in the sub-scanning direction intersecting the main scanning direction, and the central axis of the emitted light beam is set to the main surface of the reflecting surface. Light source means provided by moving in the direction opposite to the incident side of the reflecting surface along the scanning direction, and a light beam in a range wider than the width in the main scanning direction of one reflecting surface of the deflecting means are applied to the deflecting means. And a filter configured to enlarge the light beam emitted from the light source means, and between the light source means and the deflecting means, the transmittance distribution is set to be asymmetric with respect to the optical axis. And the plurality of light beams Any one of them is set as an optical axis adjusting light beam, and the center of the light beam emitted from the light source means so that the optical axis adjusting light beam makes the light amount variation uniform over a predetermined range in the main scanning direction. And an optical axis adjusting means for adjusting the axis.

  The light beam emitted from the light source means is deflected in the main scanning direction by the deflecting means. This light beam is expanded by an enlarging unit so as to irradiate a range wider than the width of one reflecting surface of the deflecting unit in the main scanning direction, and used for a so-called overfilled optical system. The light source means is arranged so that a plurality of light beams are emitted side by side in the sub-scanning direction intersecting the main scanning direction. Therefore, since a plurality of light beams arranged in the sub-scanning direction are simultaneously scanned in the main scanning direction, the light quantity and optical axis of one light beam are adjusted, and the result is reflected in the other light beams. The amount of light can be adjusted for a plurality of light beams. The central axis of the emitted light beam is provided to move along the main scanning direction with respect to the center of the reflecting surface of the deflecting means. Therefore, at least the light quantity at the scanning end can be balanced. The filter is set so that the transmittance distribution is asymmetric with respect to the optical axis, and the light quantity distribution can be adjusted by this filter. The optical axis adjusting means sets any one of the plurality of light beams as an optical axis adjusting light beam, and the optical axis adjusting light beam makes the light amount variation uniform over a predetermined range in the main scanning direction. The central axis of the light beam emitted from the means is adjusted. As a result, at least the amount of light at the scanning end can be balanced and the amount of light can be made uniform within the scanning range.

  The light source means is arranged so that a plurality of light beams are emitted side by side in the sub-scanning direction within an inclination range of 5 degrees with respect to a rotation direction that is normal to and opposite to the orthogonal direction to the main scanning direction. And

  From the light source means, a plurality of light beams are emitted side by side in the sub-scanning direction intersecting with the main scanning direction. However, depending on the angle, the light beam may exceed the adjustable allowable range. The present inventor has confirmed that a practically sufficient result can be obtained by setting the tilt direction within 5 degrees with respect to the rotation direction that is normal to the main scanning direction by many experiments.

  Each of the light beams of the light source means is emitted toward a different photoconductor.

  The optical scanning device of the present invention is suitable for use in a multicolor image forming apparatus. That is, when a scanning surface such as a photosensitive member is exposed with a light beam emitted from an optical scanning device, it is of course possible to use a single color device, but when forming a multicolor image, it is necessary to correspond to the light beam for each color. There is. For this reason, each of the light beams of the light source means is set so as to be emitted toward different photoconductors, so that different photoconductors can be irradiated with light beams having substantially the same uniform light amount distribution. it can. Accordingly, it is possible to suppress a difference in light amount distribution between different photoconductors, that is, between colors.

  The light source means emits four light beams.

  In the multicolor image, in many cases, four colors such as yellow, magenta, cyan, and black are controlled independently. Therefore, by making the light source unit emit four light beams, it is possible to suppress differences between colors in the case of forming a multicolor image, etc. Fluctuations can be suppressed.

  The light source means and the deflecting means are set so that an angle formed by a direction of a light beam incident on the deflecting means and a deflection center direction of the deflecting means is 60 degrees or more.

  Even if trying to reduce the size of the device, if the angle at which the light beam is incident from the light source means toward the deflecting means is an acute angle, it is installed in a place where there is no optical element such as a lens inserted in the optical path on the optical design. Increases the size of the device. Further, when the light beam is incident on the deflecting means, if the incident angle is an acute angle, a part of the light beam is eroded by an optical element such as a lens inserted in the optical path in optical design. Therefore, by setting the angle between the direction of the light beam incident on the deflecting unit and the deflection center direction of the deflecting unit to be 60 degrees or more, more preferably 65 degrees or more, the optical element erodes the optical element. It is not affected by the position of the optical element on the downstream side of the deflecting means, and the size can be reduced.

  The light source means is provided so that a light beam is incident on the deflection means from the end of the main scanning by the deflection means.

  By setting the angle formed by the direction of the light beam incident on the deflecting unit and the direction of the deflection center of the deflecting unit to be 60 degrees or more, a difference occurs in the distance of the gap of the light beam on the scanning plane. This is because, in the main scanning side incident overfilled state, the beam width varies depending on the scanning position (deflection angle), so that the gap between both light beams in unit time varies depending on the scanning position (deflection angle). That is, the gap distance of the light beam at the scanning end on the scanning end side is smaller than the gap distance of the light beam at the scanning end on the scanning start side. For this reason, when the light beam used for synchronization detection is set within the effective scanning range, it is possible to easily separate them.

  An opening is provided in the optical path of the light beam between the emitting means and the deflecting means, and an opening for transmitting the light beam is provided, and the opening is set at a position that is asymmetric with respect to the optical axis. The opening member is further provided.

  An aperture member in which the aperture through which the light beam is transmitted is set at a position that is asymmetric with respect to the optical axis is placed in the optical path of the light beam between the emission means and the deflection means, that is, the center position of the aperture is the light beam. An extra light beam can be suppressed by further providing it at a position spaced a predetermined distance from the center of the optical axis in the main scanning direction.

  The filter is provided in the vicinity of the deflecting unit, and when an optical element having power in the sub-scanning direction is provided on the incident side of the deflecting unit, the filter is provided on the incident side of the optical element.

  As described above, by providing the filter in the vicinity of the deflecting unit, the filter is not affected by the spread of the light beam or the position due to the magnification of the optical element on the downstream side of the deflecting unit (for example, the influence of the component corresponding to separation for each color). The performance of can be demonstrated as it is.

  Note that the optical scanning device can easily adjust the optical axis by the following optical axis adjustment method. Specifically, a deflecting unit that includes a plurality of reflecting surfaces and deflects an incident light beam in the main scanning direction by the reflecting surface, a light source unit that emits a plurality of light beams toward the deflecting unit, and the deflecting unit. An expanding means for expanding the light beam emitted from the light source means so that a light beam in a range wider than the width of one reflecting surface in the main scanning direction is irradiated to the deflecting means, the light source means and the deflecting means An optical axis adjustment method for an optical scanning device comprising: a filter set between the light source means and the light source means for emitting the plurality of light beams side by side in a sub-scanning direction intersecting the main scanning direction The center axis of the emitted light beam is arranged and moved in the main scanning direction in the direction opposite to the incident side of the reflecting surface with respect to the center of the reflecting surface, and the filter has a transmittance distribution. Asymmetric with respect to the optical axis The light source means sets one of the plurality of light beams as a light amount adjustment light beam, and the light amount adjustment light beam makes the light amount fluctuation uniform over a predetermined range in the main scanning direction. The center axis of the emitted light beam is adjusted.

  As described above, according to the present invention, a plurality of light beams are arranged so as to be emitted side by side in the sub-scanning direction intersecting the main scanning direction, and the center axis of the light beam is set to the center of the reflecting surface of the deflecting means. The filter is set so that the transmittance distribution is asymmetric with respect to the optical axis, and the central axis of the light beam is adjusted so as to equalize the light amount fluctuation for one light beam. As a result, at least the amount of light at the scanning end can be balanced and the amount of light can be made uniform within the scanning range.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration of an optical scanning device according to an embodiment of the present invention. 1A is a side view (cross section in the sub-scanning direction), and FIG. 1B is a plan view (cross section in the main scanning direction). The optical scanning device according to the present embodiment includes a laser light source 10 including a semiconductor laser array that includes four light sources and emits four laser beams in approximately one row. In the laser light source 10, the four light sources are arranged in the sub-scanning direction so that four laser beams are emitted in a line in the sub-scanning direction. Each of the four laser beams emitted from the laser light source 10 has four colors for forming a multicolor image, for example, Y (yellow), M (magenta), C (cyan), and K (black). Corresponding and controlled according to the image information of each color. That is, the laser light source 10 is connected to the controller 60, and the laser light source 10 is on / off controlled for each color by the controller 60 in accordance with the image signal.

  On the emission side of the laser light source 10, a collimator lens 12, a slit 14, and a first cylindrical lens 16 having power in the sub-scanning direction (sagittal direction) are arranged in order, and on the emission side of the first cylindrical lens 16, One reflection mirror 18 is installed. A second reflection mirror 20 is provided on the reflection side of the first reflection mirror 18, and the laser beam reflected by the first reflection mirror 18 is incident on the second reflection mirror 20. On the reflection side of the second reflecting mirror 20, a second cylindrical lens 22 having power in the main scanning direction (tangential direction), a filter 24, a third cylindrical lens 26 having power in the sub-scanning direction (sagittal direction), and Polygon mirrors 28 are arranged in order. The polygon mirror 28 is formed with reflecting mirrors 28A on each surface of a substantially regular dodecagonal prism shape rotating at a predetermined speed, and the laser beam reflected by the second reflecting mirror 20 is reflected by the second cylindrical lens 22, the filter 24, and The light enters through the third cylindrical lens 26.

  The laser beam toward the polygon mirror 28 (in the main scanning direction) is a light beam larger than the range of one reflecting mirror 28A of the polygon mirror 28, and constitutes a so-called overfilled optical system.

  The laser beam reflected by the polygon mirror 28 passes through the fθ lenses 30 and 32 and enters the split mirror 34.

  The split mirror 34 is formed in a square cross section, and is disposed in a direction intersecting with the rotation axis direction of the polygon mirror 28 so that the longitudinal direction (center axis direction) thereof is the main scanning direction. The vertices of the reflecting surfaces 34A and 34B of the split mirror 34 are located at positions sandwiched between two of the four laser beams, and the reflecting surfaces 34A and 34B include edges connecting these vertices, and the laser beam Is adjusted to 45 ° with respect to a plane (reference plane) substantially parallel to the plane. Then, the four laser beams are adjusted by optical elements such as the collimator lens 12 and the cylindrical lens 16 so that the two laser beams are incident at substantially equal intervals on the optical path in which two laser beams are symmetrical with respect to the reference plane. Has been.

  A first guide mirror 36, a second guide mirror 38, a third guide mirror 40, and a fourth guide mirror 42 are disposed on the reflection side of the reflecting surfaces 34A and 34B of the split mirror 34, and each guide mirror 36˜ Reference numeral 42 corresponds to each of the four laser beams. The first guide mirror 36 and the fourth guide mirror 42, and the second guide mirror 38 and the third guide mirror 40 are substantially symmetrical with respect to the split mirror 34, respectively. 42 is arranged on the outside, and the second guide mirror 38 and the third guide mirror 40 are arranged on the inside. The first guide mirror 36 and the fourth guide mirror 42 are provided closer to the polygon mirror 28 than the second guide mirror 38 and the third guide mirror 40.

  A first cylindrical mirror 44, a second cylindrical mirror 46, a third cylindrical mirror 48, and a fourth cylindrical mirror 50 are disposed on the polygon mirror 28 side of the guide mirrors 36 to 42. The laser beam reflected by the first guide mirror 36 is reflected by the first cylindrical mirror 44, the laser beam reflected by the second guide mirror 38 is reflected by the second cylindrical mirror 46, and the laser beam reflected by the third guide mirror 40 is given by the third cylindrical mirror. The laser beam reflected by the fourth guide mirror 42 enters the mirror 48 and enters the fourth cylindrical mirror 50. The laser beam incident on the cylindrical mirrors 44 to 50 is reflected by the cylindrical mirrors 44 to 50, is incident on an image carrier (not shown) such as a photosensitive drum as a scanned body, and is electrostatically applied to the surface. A latent image is formed.

  The positions of the guide mirrors 36 to 42 and the cylindrical mirrors 44 to 50 are positions where the optical path lengths from the laser light source 10 of the four laser beams to the image forming position 44 of the image carrier are substantially equal. Therefore, as shown in FIG. 1B, the second cylindrical mirror 46 is on the opposite side of the second guide mirror 38 and the third cylindrical mirror 48 is on the opposite side of the third guide mirror 40 across the split mirror 34. And the optical path between the second guide mirror 38 and the second cylindrical mirror 46 and the optical path between the third guide mirror 40 and the third cylindrical mirror 48 are formed beyond the split mirror 34. Has been. The second cylindrical mirror 46 and the third cylindrical mirror 48, and the first cylindrical mirror 44 and the fourth cylindrical mirror 50 have the same radius of curvature.

  Further, an image carrier such as a photosensitive drum rotates at an appropriate speed, and the position where an electrostatic latent image is formed is changed according to this rotation. Then, the incident position on the split mirror 34 is changed by the rotation of the polygon mirror 28, whereby the incident position on the image carrier is changed. Here, a scanning direction in which the incident position on the image carrier is changed by the rotation of the polygon mirror 28 is a main scanning direction, and a scanning direction in which the incident position is changed in accordance with the rotation of the image carrier is a sub-scanning direction. A sensor mirror for causing the laser beam reflected by the reflecting surface 34A of the split mirror 34 to enter (for detecting a synchronization signal) outside the scanning range (outside the image forming area) of the split mirror 34 in the main scanning direction. 52 is provided. A scanning position detection sensor 56 is provided on the reflection side of the sensor mirror 52 (see FIG. 9).

  The scanning position detection sensor 56 is connected to the controller 60 via the main body controller 61, and the main body controller 61 can control the light amount control of the laser light source 10 for each color.

  The polygon mirror 28 corresponds to the deflecting means of the present invention, and the laser light source 10 corresponds to the light source means of the present invention. The collimator lens 12 corresponds to a part of the magnifying means of the present invention. The filter 24 corresponds to the filter of the present invention. The adjusting element for adjusting the optical path from the laser light source 10 to the polygon mirror 28 corresponds to the optical axis adjusting means of the present invention. This adjusting element includes, for example, a member 20i that holds or fixes the second reflecting mirror 20 (see FIG. 3), and in addition, each optical element used to fix the optical path from the laser light source 10 to the polygon mirror 28. There are parts. Further, these members may be held and adjusted with a plate or the like. The procedure for adjusting the optical axis corresponds to the optical axis adjusting method of the present invention.

  In the present embodiment, in the configuration of the optical scanning device described above, the optical axis, the aperture, and the like are set as follows in order to achieve a uniform amount of light.

  First, the laser beam emitted from the laser light source 10 has different light flux states in the main scanning direction and the sub-scanning direction.

  As shown in FIGS. 2 and 3, the laser beam in the main scanning direction is shaped into loose divergent light by the collimator lens 12, and transmitted light is limited by the opening of the slit 14. The laser beam transmitted through the slit 14 is collimated in the main scanning direction by the second cylindrical lens 22. On the other hand, the laser beam in the sub-scanning direction is shaped into loose divergent light by the collimator lens 12, and transmitted light is limited by the opening of the slit 14. The laser beam transmitted through the slit 14 is set so as to be imaged (linearly) on the reflection mirror 28A of the polygon mirror 28 in the sub-scanning direction by the first cylindrical lens 16, and the third cylindrical lens 26 is set. Thus, the incident angle of the reflecting mirror 28A is set to be increased (see also FIG. 7A).

  As shown in FIG. 4, in the present embodiment, the opening of the slit 14 is set asymmetric with the optical axis. FIG. 4 is a view seen through the laser light source 10 from the first cylindrical lens 16 side, and the slit 14 shows the edge of the opening 14A. The slit 14 is disposed such that the center 14X of the opening 14A is spaced a predetermined distance from the central optical axis CL of the collimator lens 12 in the main scanning direction. Therefore, when the optical axis is used as a reference, the slit 14 has an asymmetric shape in the main scanning direction.

  This makes it possible to vary the light amount distribution by moving the central portion of the opening from the optical axis in the main scanning direction, and facilitates securing the light amount balance in the main scanning direction.

  FIG. 5 shows another example of the opening of the slit 14. Further, in order to achieve a uniform amount of light, the opening 14A of the slit 14 shown in FIG. 4 is formed in a rectangular shape so that there is no influence of the imaging beam diameter in the sub-scanning direction. On the other hand, the apertures shown in FIG. 5 have different aperture widths in the sub-scanning direction with reference to the optical axis. By restricting (or opening) the light amount fluctuation in the main scanning direction, which is expected to occur when the light is incident obliquely on the polygon mirror 28, the light amount distribution is positively changed. be able to. Accordingly, the slits shown in FIG. 5 can further ensure uniformity compared to the slits 14 shown in FIG.

  FIG. 6 shows details of the filter 24. 6A is an external perspective view of the filter 24, and FIG. 6B is a front view. The filter 24 is formed so as to have a two-stage transmittance distribution (the first region 24A and the second region 24B) in the main scanning direction. That is, in the present embodiment, the filter 24 shown in FIG. 6 is used in order to suppress the occurrence of non-uniformity in the light amount distribution such as the F number change inherent in the overfilled optical system and to achieve the light amount uniformity. It is provided between the second reflecting mirror 20 and the polygon mirror 28. By inserting the filter 24 in the optical path, the non-uniformity of the light quantity distribution can be suppressed.

  The filter 24 is preferably installed near the polygon mirror 28 on the incident side of the third cylindrical lens 26 having power in the sub-scanning direction. Since the size of the filter 24 depends on the beam width of the laser beam, it is possible to form a small filter by installing the filter 24 at a position where the beam width is smaller. This is because the arrangement is taken into consideration. That is, the function of the filter 24 can be effectively used by installing the filter 24 in the immediate vicinity of the polygon mirror 28, but each of the four laser beams is expanded in the sub-scanning direction by the third cylindrical lens 26 (the divergence angle is large). ), The luminous flux width increases in the sub-scanning direction. In order to solve this problem, the filter 24 can be adjusted before the light flux width is increased in the sub-scanning direction by installing the third cylindrical lens 26 on the incident side.

  Next, in the present embodiment, in order to further ensure the light quantity balance in the vicinity of both scanning ends in the main scanning direction, the light beam center of the laser beam is moved in the main scanning direction.

  FIG. 7 shows an optical system between the second reflecting mirror 20 and the polygon mirror 28. FIG. 7A is a side view (cross section in the sub-scanning direction), and FIG. 7B is a plan view (cross section in the main scanning direction). FIG. 8 is a plan view (cross section in the main scanning direction) showing the optical path around the polygon mirror 28.

  As shown in FIGS. 7B and 8, the incident optical axis L of the laser beam incident on the polygon mirror 28 is directed from the reference point P, which is the center point of the reflection mirror 28A of the polygon mirror 28, to the fθ lens 30. It moves by a movement amount M along the main scanning direction in the direction (counter-incident side). This optical axis adjustment can be achieved by adjusting the optical elements of the laser light source 10 to the second reflection mirror 20. In particular, this can be easily achieved by moving (translating) the position of the second reflecting mirror 20. Thus, by setting the incident optical axis L to be moved by the moving amount M, the amount of fluctuation of the light amount is suppressed.

  When the optical axis is moved as described above, it is preferable to adjust the slit 14 as described above.

  Here, the optical scanning device according to the present embodiment is miniaturized by making the incident angle at which the laser beam is incident on the polygon mirror 28 an obtuse angle. That is, as shown in FIG. 1, an angle formed by the incident optical axis L to the polygon mirror 28 and the central optical axis (hereinafter referred to as the scanning optical axis Ls) of the deflection width of the laser beam deflected to the polygon mirror 28 Hereinafter, the incident scanning angle G) is set to a predetermined angle of 60 degrees or more. In the present embodiment, the incident scanning angle G is set to 65 degrees. By setting the incident scanning angle G to an obtuse angle, the laser beam incident on the polygon mirror 28 does not interfere with the laser beam deflected by the polygon mirror 28. In addition, an area where the laser beam incident on the polygon mirror 28 is not eroded by the optical elements after the polygon mirror 28 such as the fθ lens 30 can be created outside the scanning area. As the incident scanning angle G increases, the fθ lens 30 closest to the deflection side of the polygon mirror 28 can be brought closer to the polygon mirror 28.

  Further, making the incident scanning angle G an obtuse angle also produces a favorable effect for synchronous detection.

  As shown in FIG. 9, a sensor lens 54 and a scanning position detection sensor 56 are sequentially provided on the reflection side of the sensor mirror 52. The laser beam reflected by the sensor mirror 52 is configured to be converged by a sensor lens 54 and incident on a scanning position detection sensor 56 (for detecting a synchronization signal). When a laser beam is incident on the scanning position detection sensor 56, formation of an electrostatic latent image on an image carrier such as a photosensitive drum is started at an appropriate timing.

  In the present optical scanning device, scanning including the effective scanning range J is performed on the split mirror 34 by the deflection by the polygon mirror 28. That is, as the polygon mirror 28 rotates (clockwise), the laser beam is deflected from the scanning start end (downward in FIG. 9) to the scanning end end (upward in FIG. 9). The effective scanning range J corresponds to the formation area width in the main scanning direction of the electrostatic latent image on the image carrier such as the photosensitive drum. Therefore, by detecting the laser beam outside the effective scanning range J, the timing of one main scanning can be detected.

  Here, the laser beam is incident on the polygon mirror 28 from the end of one main scan. Therefore, at the same time interval dt, the gap distance of the laser beam on the split mirror 34 is longer near the scanning start end (lower in FIG. 9) than near the scanning end (upward in FIG. 9). The gap distance is a gap distance between adjacent beams per unit time. Specifically, when the vicinity of the end of scanning is set to 1 unit gap distance, the distance is about 2 unit gap near the scanning start end (downward in FIG. 9). Thereby, separation of the laser beam for sampling the laser beam by the sensor mirror 52 is facilitated.

[Uniformity]
Next, an outline of the light quantity uniformization of the optical scanning device of the present embodiment will be described.

  FIG. 10 shows a process of making the light quantity uniform (power balance adjustment). First, in the process Pr1, only one laser beam of the laser light source 10 is turned on and main scanning is repeated. In the next process Pr2, the light quantity distribution on the image carrier such as the photosensitive drum corresponding to the main scanning range (particularly the range corresponding to the effective scanning range J) is measured. In this measurement, the scanning range may be measured continuously, or a plurality of representative locations may be measured. In the next process Pr3, the optical axis is adjusted (further finely adjusted) as described above so that the light quantity distribution becomes uniform from the measurement result of the process Pr2.

  With the above adjustment, the adjustment for one laser beam is completed. At this point, the adjustment is also completed for the other three laser beams. That is, in the present embodiment, the laser light source 10 includes four light sources and is installed so as to emit four laser beams in approximately one row in the sub-scanning direction. Therefore, when the adjustment is completed for any one of the four laser beams, the adjustment for the laser beams by other light sources arranged in the sub-scanning direction is equivalently completed. In this way, all four adjustments are completed only by adjusting any one of the laser beams, so that the number of process steps for making the light quantity uniform (power balance adjustment) can be simplified.

  The light amount distribution can be further finely adjusted by the main body controller 61. In this fine adjustment process, the laser light source 10 is turned on with a constant driving voltage, and the result of measuring the light intensity distribution after the uniformization process is performed in the above process is measured data (including the sensor value by the scanning position detection sensor 56). And the drive voltage of the laser light source 10 that makes the light quantity distribution uniform is measured in advance. And the difference of the measurement result of the drive voltage of the laser light source 10 in which the light quantity distribution with respect to the measurement data becomes uniform is stored as drive data, and the sensor value by the scanning position detection sensor 56 is stored as reference data.

  FIG. 11 shows a flow of fine adjustment processing executed by the main body controller 61. In step S1, only one laser beam of the laser light source 10 is turned on to irradiate the sensor mirror 52, and the amount of light is detected in the next step S2. In the next step S3, a difference between the measurement result in step S2 and the reference data is obtained, and a correction value is obtained so that the obtained difference value is decreased (most preferably “0”). This correction value can be applied to each of the four light sources. In the next step S4, the laser light source 10 is driven with the correction value obtained in step S3. This driving is performed by the controller 60. As a result, even when there is a change in the total amount of light emitted from the laser light source 10 due to changes over time or the like, it can be corrected.

  Next, the effectiveness of the optical scanning device according to the present embodiment will be described.

  FIG. 12 shows the relationship between the rotation angle and the incident position when the laser light source 10 is rotated about the central optical axis. FIG. 12A shows the incident position change in the sub-scanning direction on the reflection mirror 28A of the polygon mirror 28 with respect to the rotation angle. FIG. 12B shows the change in the incident position in the main scanning direction on the reflection mirror 28A of the polygon mirror 28 with respect to the rotation angle. FIG. 12C shows a change in incident position in the main scanning direction on an image carrier such as a photosensitive drum with respect to the rotation angle.

  As can be understood from each drawing, when the orthogonal direction (vertical direction) of the main scanning direction is set to 0 ° as the rotation angle of the laser light source 10, the amount of change in the incident position increases as the rotation angle increases.

  The change in the incident position of the polygon mirror 28 in the sub-scanning direction as a result of FIG. 12A greatly affects the position change in the split mirror 34. Since the split mirror 34 requires separation of the four laser beams, a color shift or the like occurs when the position change in the split mirror 34 increases. Therefore, when actually measured, it was found that the incident position fluctuation of the polygon mirror 28 in the sub-scanning direction is preferably within about 0.004 mm. This result corresponds to the laser light source 10 preferably having a rotation angle within 5 degrees within an allowable range.

  Further, the incident position variation of the polygon mirror 28 in the main scanning direction as a result of FIG. 12B varies linearly, and finally affects the scanning position and magnification. As a result of various experiments, it was found that the fluctuation of the incident position in the main scanning direction is preferably within 0.20 mm. This result corresponds to a laser beam corresponding to cyan and a laser beam corresponding to black, and the rotation angle of the laser light source 10 is preferably within 5 degrees.

  Also, the incident position variation in the main scanning direction of the image carrier according to the result of FIG. 12C varies linearly. As a result of various experiments on the image carrier, it has been obtained that the incident position fluctuation is preferably within 0.10 mm, and the rotation angle of the laser light source 10 is preferably within 5 degrees. Yes.

  From the above, it was obtained that the angle change (rotation) of the light source array in the sub-scanning direction of the laser light source 10 is preferably within 5 degrees.

  FIG. 13 shows the characteristics of the light amount variation with respect to the movement amount of the slit 14, wherein (A) shows cyan, (B) shows yellow, (C) shows black, and (D) shows each color of magenta. It is. In addition, the result of FIG. 13 is measured without inserting the filter 24. SOS indicates a scanning start end, COS scanning center end, and EOS indicates a scanning end end. As understood from the figure, fluctuations other than the scanning center end are affected by the rotation of the laser light source 10. Regarding the variation of each position of each color, the variation in the amount of light can be suppressed to a width of about 10% by suppressing the angle change (rotation) of the entire light source, that is, the arrangement of the light sources in the sub-scanning direction within 5 degrees. it can. Further, when the filter 24 was inserted and adjusted, a further improvement was obtained. As a result, it was obtained that the angle change (rotation) of the light source array in the sub-scanning direction of the laser light source 10 is preferably suppressed to within 5 degrees.

  FIG. 14 shows the result of measuring the diameter of the laser beam with respect to the scanning position when the shape of the opening of the slit 14 is changed. As the slit shape, the shape shown in FIG. 4 is a normal slit, and the shape shown in FIG. 5 is a deformation slit. In the normal slit, the beam diameter gradually decreases from the scanning start end to the scanning end end, but in the deformed slit, the beam diameter can be changed to a tendency to increase from the scanning center end. Thus, it is understood that the beam diameter can be adjusted within the scanning range by the slit shape.

  FIG. 15 shows the state of the optical scanning device with respect to the incident scanning angle G, where (A) shows the balance characteristics at both ends of the scanning range, and (B) shows the characteristics of the minimum distance between the polygon mirror 28 and the fθ lens 30. showed that. As understood from the figure, even if the incident scanning angle G is changed, there is little influence on the light quantity balance, and the degree of freedom of the setting value of the incident scanning angle G can be increased (the parameter range of the incident scanning angle G can be increased). Understandable. Further, although the interval between the polygon mirror 28 and the fθ lens 30 is desired to be as close as possible, since it is obliquely incident, the incident laser beam is eroded (kerellar) by the fθ lens 30. For this reason, although it is possible to make it approach in optical design, there is substantially no problem if 14 mm or less can be secured due to various factors such as assembly adjustment and attachment, and the result that 11 mm or less is optimal is obtained. Correspondingly, it can be understood that the incident scanning angle G is preferably about 60 degrees or more, more preferably 65 degrees or more.

  In addition, this Embodiment demonstrated above does not limit the structure of this invention. In this embodiment, the optical scanning device has been described. However, the optical scanning device to which the present invention is applied is not limited to this, and an optical device built in an image forming apparatus having a basic function for image processing. The present invention can be applied to an apparatus having an arbitrary configuration having a function of scanning a plurality of laser beams, such as a system.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic structure of the optical scanning device which concerns on embodiment of this invention is shown, (A) is a side view, (B) is a top view. It is explanatory drawing of the optical path from a laser light source to a 1st cylindrical lens. It is explanatory drawing of the optical path from a laser light source to a polygon mirror. It is explanatory drawing of a slit shape. It is explanatory drawing of the slit shape of a deformation | transformation slit. The schematic structure of a filter is shown, (A) is a perspective view, (B) is a top view. It is explanatory drawing of the optical path of a 2nd reflective mirror thru | or a polygon mirror, (A) is a side view, (B) is a top view. It is explanatory drawing of moving the incident optical axis to a polygon mirror. It is explanatory drawing about the scanning of an optical scanning device. It is a flowchart which shows the flow of the process of light quantity equalization (power balance adjustment). It is a flowchart which shows the flow of a process in a main body controller. The relationship between the rotation angle and the incident position when the laser light source 10 is rotated about the central optical axis is shown. (A) is the change in the incident position in the sub-scanning direction on the polygon mirror, and (B) is the polygon mirror. (C) shows a change in the incident position in the main scanning direction on the image carrier. The light amount fluctuation characteristics with respect to the movement amount of the slit 14 are shown, (A) is cyan, (B) is yellow, (C) is black, and (D) is magenta. It is a characteristic view which shows the relationship of the diameter of the laser beam with respect to the scanning position by the opening shape change of a slit. The state of the optical scanning device with respect to the incident scanning angle is shown, (A) shows the balance characteristic at both ends of the scanning range, and (B) shows the characteristic of the minimum distance between the polygon mirror and the fθ lens.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Laser light source 12 ... Collimator lens 14 ... Slit 14A ... Aperture 16 ... 1st cylindrical lens 18 ... 1st reflective mirror 20 ... 2nd reflective mirror 22 ... 2nd cylindrical lens 24 ... Filter 26 ... 3rd cylindrical lens 28 ... Polygon mirror 28A ... reflecting mirror 30 ... fθ lens 32 ... fθ lens 34 ... split mirror 52 ... sensor mirror 54 ... sensor lens 56 ... scanning position detection sensor 61 ... main body controller

Claims (9)

Deflecting means for deflecting an incident light beam with a plurality of reflecting surfaces in the main scanning direction by the reflecting surfaces;
A plurality of light beams are emitted toward the deflecting means, and the plurality of light beams are arranged so as to be emitted side by side in the sub-scanning direction intersecting the main scanning direction, and the central axis of the emitted light beam is Light source means provided to move in the anti-incident side direction of the reflecting surface along the main scanning direction with respect to the center of the reflecting surface;
An enlarging means for enlarging the light beam emitted from the light source means so that a light beam in a range wider than the width in the main scanning direction of one reflecting surface of the deflecting means is irradiated to the deflecting means;
A filter set between the light source means and the deflecting means so that the transmittance distribution is asymmetric with respect to the optical axis;
Any one of the plurality of light beams is set as an optical axis adjusting light beam, and the optical axis adjusting light beam is emitted from the light source means so as to equalize a light amount variation in a predetermined range in the main scanning direction. Optical axis adjusting means for adjusting the central axis of the light beam to be
An optical scanning device comprising:   The light source means is arranged so that a plurality of light beams are emitted side by side in the sub-scanning direction within an inclination range of 5 degrees with respect to a rotation direction that is normal to and opposite to the orthogonal direction to the main scanning direction. The optical scanning device according to claim 1.   3. The optical scanning device according to claim 1, wherein each of the light beams of the light source means is emitted toward a different photosensitive member.   4. The optical scanning device according to claim 3, wherein the light source means emits four light beams.   2. The light source unit and the deflecting unit are set so that an angle formed by a direction of a light beam incident on the deflecting unit and a deflection center direction of the deflecting unit is 60 degrees or more. The optical scanning device according to claim 4.   6. The optical scanning device according to claim 5, wherein the light source means is provided so that a light beam is incident on the deflection means from an end side of main scanning by the deflection means.   An opening is provided in the optical path of the light beam between the emitting means and the deflecting means, and an opening for transmitting the light beam is provided, and the opening is set at a position that is asymmetric with respect to the optical axis. The optical scanning device according to claim 1, further comprising an opening member.   The filter is provided in the vicinity of the deflecting unit, and when an optical element having power in the sub-scanning direction is provided on the incident side of the deflecting unit, the filter is provided on the incident side of the optical element. The optical scanning device according to any one of claims 1 to 7. A deflecting unit that includes a plurality of reflecting surfaces and deflects an incident light beam in the main scanning direction by the reflecting surface, a light source unit that emits a plurality of light beams toward the deflecting unit, and one reflection of the deflecting unit An enlarging means for enlarging the light beam emitted from the light source means so that a light beam in a range wider than the width of the surface in the main scanning direction is irradiated to the deflecting means; and between the light source means and the deflecting means An optical axis adjustment method for an optical scanning device comprising a set filter,
The light source means is arranged so that the plurality of light beams are emitted side by side in the sub-scanning direction intersecting the main scanning direction, and the central axis of the emitted light beam is set in the main scanning direction with respect to the center of the reflecting surface And moving along the anti-incident side direction of the reflecting surface along
The filter is provided so that the transmittance distribution is asymmetric with respect to the optical axis,
One of the plurality of light beams is set as a light amount adjusting light beam, and the light amount adjusting light beam is emitted from the light source means so as to uniformize the light amount fluctuation in a predetermined range in the main scanning direction. A method of adjusting an optical axis of an optical scanning device, comprising adjusting a central axis of a light beam.

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