JP2016224141A - Optical scanner, image formation device, and adjustment method of optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that can highly accurately scan a scanned surface.SOLUTION: An optical scanner includes: a semiconductor laser; a polygon mirror that has a plurality of deflective reflection surfaces around a rotation axis, and deflects light from a light source; and a scan optical system that guides the light deflected by the polygon mirror to a scanned surface. Light to be incident upon the polygon mirror is, with respect to a direction corresponding to a main scan direction, smaller than an arbitrary one deflective reflection surface of the plurality of deflective reflection surfaces, and a first distance serving a distance to a boundary between an intermediate area of a part between an end area (an area has a light flux vignetted) on one side of a scan range and an end area (the area has the light flux vignetted) on the other side thereof and an end part on the one side from a center of the scan range, and a second distance serving a distance to a boundary between the intermediate area and an area (the area has the light flux vignetted) on the other side from the center of the scan range are different.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an optical scanning device, an image forming apparatus, and a method for adjusting the optical scanning device, and more specifically, an optical scanning device that scans a surface to be scanned with light, an image forming apparatus including the optical scanning device, and an optical scanning device. It relates to the adjustment method.

  In recent years, development of an optical scanning device that scans a surface to be scanned with light has been actively performed.

  For example, Patent Document 1 discloses an optical scanning device that deflects light from a light source with a deflector having a plurality of deflection reflection surfaces around a rotation axis, and guides the deflected light to a surface to be scanned via a scanning optical system. Is disclosed.

  However, the conventional optical scanning device such as Patent Document 1 has room for improvement with respect to scanning the surface to be scanned with high accuracy.

  The present invention includes a light source, a deflector having a plurality of deflection reflection surfaces around a rotation axis, deflecting light from the light source, and a scanning optical system for guiding light deflected by the deflector to a surface to be scanned. The light incident on the deflector is smaller than any one of the plurality of deflection reflection surfaces in the direction corresponding to the main scanning direction, and the deflection of the one deflection reflection surface Incident across the first portion including the downstream end portion in the rotation direction of the vessel and the upstream end portion in the rotation direction of the deflection reflection surface adjacent to the downstream side in the rotation direction of the one deflection reflection surface. Of the light, the light incident on the first portion is guided to the end region on one side of the scanning range of the surface to be scanned via the scanning optical system, and is incident on the end on the upstream side in the rotation direction. Is not guided to the scanning range, and includes the end of the one deflecting / reflecting surface on the upstream side in the rotational direction. Of the light that has entered across the portion 2 and the end on the downstream side in the rotation direction of the deflection reflection surface adjacent to the upstream side in the rotation direction of the one deflection reflection surface, the light has entered the second portion. The light is guided to the other end region of the scanning range through the scanning optical system, and the light incident on the end portion on the downstream side in the rotation direction is not guided to the scanning range, and the one of the one deflecting reflection surface Light incident on a portion between the first portion and the second portion is an intermediate region that is a region between the one end region and the other end region of the scanning range via the scanning optical system. And a first distance that is a distance from the center of the scanning range to a boundary between the intermediate region and the one end region, and an end of the intermediate region and the other side from the center of the scanning range. The optical scanning device is characterized in that the second distance, which is the distance to the boundary of the region, is different.

  According to the present invention, the surface to be scanned can be scanned with high accuracy.

1 is a diagram illustrating a schematic configuration of a laser printer according to a first embodiment. FIG. 2 is a diagram (part 1) for describing the optical scanning device of FIG. 1; FIG. 3 is a second diagram for explaining the optical scanning device in FIG. 1; FIGS. 4A to 4C are diagrams (No. 1 to No. 3) for explaining the deflection operation of the polygon mirror, respectively. It is a figure for demonstrating the light quantity in the edge area | region of the one side (+ Y side) of the scanning range of a to-be-scanned surface, an intermediate | middle area | region, and an edge area | region of the other side (-Y side). FIG. 6A and FIG. 6B respectively show an end region on one side (light source side region) and an end region on the other side (region on the opposite light source side) of the comparative example and the first embodiment. It is a figure for demonstrating the fall of a light quantity. FIGS. 7A and 7B are diagrams (No. 1 and No. 2) for explaining that the inclination of the decrease in the amount of light is different between the end region on one side and the other side of the scanning range. FIG. 8A and FIG. 8B are diagrams (No. 1 and No. 2) for explaining a light amount correction method, respectively. It is FIG. (1) for demonstrating the method to reduce the light quantity difference between the edge parts of the edge area | region of the one side of a scanning range, and an other side. FIG. 10 is a diagram (No. 2) for explaining a method of reducing a light amount difference between the end portions of one end side and the other end region of the scanning range. FIG. 6 is a diagram for deriving a relationship between a difference ΔY in image height at which an end region on one side and the other side of a scanning range starts to be shifted and a light amount difference ΔI between end portions on one side and the other side. It is a figure which shows schematic structure of the color printer of 2nd Embodiment. It is a figure for demonstrating the optical scanning device of FIG.

<< First Embodiment >>
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a laser printer 500 as an image forming apparatus according to the first embodiment.

  The laser printer 500 includes an optical scanning device 900, a photosensitive drum 901, a charging charger 902, a developing roller 903, a toner cartridge 904, a cleaning blade 905, a paper feeding tray 906, a paper feeding roller 907, a registration roller pair 908, and a transfer charger 911. , A static elimination unit 914, a fixing roller 909, a paper discharge roller 912, a paper discharge tray 910, and the like.

  The charging charger 902, the developing roller 903, the transfer charger 911, the charge removal unit 914, and the cleaning blade 905 are each disposed near the surface of the photosensitive drum 901. Then, with respect to the rotation direction of the photosensitive drum 901, the charging charger 902, the developing roller 903, the transfer charger 911, the static elimination unit 914, and the cleaning blade 905 are arranged in this order.

  A photosensitive layer is formed on the surface of the photosensitive drum 901. Here, the photosensitive drum 901 rotates in the clockwise direction (arrow direction) in the plane in FIG. The charging charger 902 uniformly charges the surface of the photosensitive drum 901.

  The optical scanning device 900 irradiates the surface of the photosensitive drum 901 charged by the charging charger 902 with light modulated based on image information from a host device (for example, a personal computer). As a result, a latent image corresponding to the image information is formed on the surface of the photosensitive drum 901 on the surface of the photosensitive drum 901. The latent image formed here moves in the direction of the developing roller 903 as the photosensitive drum 901 rotates. The configuration of the optical scanning device 900 will be described later.

  The toner cartridge 904 stores toner, and the toner is supplied to the developing roller 903. The developing roller 903 causes the toner supplied from the toner cartridge 904 to adhere to the latent image formed on the surface of the photosensitive drum 901 to visualize the image information. Here, the latent image to which the toner is attached moves in the direction of the transfer charger 911 as the photosensitive drum 901 rotates.

  Recording paper 913 is stored in the paper feed tray 906. A paper feed roller 907 is disposed in the vicinity of the paper feed tray 906, and the paper feed roller 907 takes out the recording paper 913 one by one from the paper feed tray 906 and conveys it to the registration roller pair 908. The registration roller pair 908 is disposed in the vicinity of the transfer charger 911, temporarily holds the recording paper 913 taken out by the paper feed roller 907, and the photosensitive paper drum 901 is rotated in accordance with the rotation of the photosensitive drum 901. It is sent out toward the gap between 901 and the transfer charger 911.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 911 in order to electrically attract the toner on the surface of the photosensitive drum 901 to the recording paper 913. With this voltage, the latent image on the surface of the photosensitive drum 901 is transferred to the recording paper 913. The recording sheet 913 transferred here is sent to the fixing roller 909.

  In the fixing roller 909, heat and pressure are applied to the recording paper 913, whereby the toner is fixed on the recording paper 913. The recording paper 913 fixed here is sent to the paper discharge tray 910 via the paper discharge roller 912 and sequentially stacked on the paper discharge tray 910.

  The neutralization unit 914 neutralizes the surface of the photosensitive drum 901. The cleaning blade 905 removes toner remaining on the surface of the photosensitive drum 901 (residual toner). The removed residual toner is used again. The surface of the photosensitive drum 901 from which the residual toner has been removed returns to the position of the charging charger 902 again.

  Next, the configuration and operation of the optical scanning device 900 will be described with reference to FIGS. As an example, this optical scanning device 900 includes an imaging optical system including a semiconductor laser 1 (laser diode: LD) as a light source, a coupling lens 6, an aperture element 7, and a cylindrical lens 8, as shown in FIG. 2 (also referred to as a pre-deflector optical system), a polygon mirror 3 as a deflector, a scanning optical system 4 including an fθ lens 9, a toroidal lens 10 and a folding mirror 11 as a scanning lens, a reflecting mirror 14, and a synchronous lens 15 and a synchronous detection system 13 including a PD 16 (photodiode) as a light receiving element, and a light source driver 100 for driving the semiconductor laser 1. A “light source device” is configured including the semiconductor laser 1 and the imaging optical system 2. The light source driver 100 may be a component of the light source device.

  A divergent light beam (light beam) emitted from the semiconductor laser 1 is converted into a light beam form suitable for the subsequent optical system in the coupling lens 6 of the imaging optical system 2. The form of the light beam converted by the coupling lens 6 can be a parallel light beam, or a light beam with weak divergence or weak convergence.

  A part of the light beam emitted from the coupling lens 6 (for example, the central portion) passes through the aperture of the aperture element 7 and is directed by the cylindrical lens 8 in the direction corresponding to the sub-scanning direction (hereinafter also referred to as “sub-scanning corresponding direction”). ) Is focused on the deflecting / reflecting surface of the polygon mirror 3 in a state of a long line image in a direction corresponding to the main scanning direction (hereinafter also referred to as “main scanning corresponding direction”). This is because the tilting of the deflection reflection surface can be corrected by the scanning optical system 4. The “sub-scanning direction” is the rotation direction of the photosensitive drum 901, and the “main scanning direction” is the longitudinal direction of the photosensitive drum 901.

  As an example, the polygon mirror 3 is composed of a low-height regular N prismatic member (N ≧ 3), and each side surface is a deflecting reflection surface. That is, the polygon mirror 3 is an N-plane rotary polygon mirror having N deflection reflection surfaces around the rotation axis. The polygon mirror 3 is rotated at a constant angular velocity in the direction of the arrow shown in FIG. 2 by a rotation mechanism (not shown). Hereinafter, the rotation direction of the polygon mirror 3 (the direction of the arrow in FIG. 2) is also referred to as “mirror rotation direction”.

  Therefore, the light beam (incident light beam) incident on the deflection reflection surface of the polygon mirror 3 is deflected at a constant angular velocity within a predetermined deflection angle range by the rotation of the polygon mirror 3. Here, each deflection reflection surface is parallel to the rotation axis of the polygon mirror 3, and the incident light beam and its reflection light beam on the deflection reflection surface are in a plane perpendicular to the rotation axis of the polygon mirror 3. That is, the light beam from the light source device is deflected by the polygon mirror 3 in a plane perpendicular to the rotation axis of the polygon mirror 3. Here, the rotation axis of the polygon mirror 3 is parallel to the Z axis (see FIG. 3).

  The light beam deflected to a predetermined angle range within the above deflection angle range is transmitted through the fθ lens 9 and the toroidal lens 10, and the optical path is turned back by the turning mirror 11, so that the surface to be scanned 901 a (the surface of the photosensitive drum 901). Focused. Note that the light passing through the fθ lens 9 and the toroidal lens 10 may be directly condensed on the surface to be scanned 901a without providing the folding mirror 11. A configuration in which one of the fθ lens 9 and the toroidal lens 10 is not provided is also possible. Here, the optical axis of the scanning optical system 4, that is, the common optical axis of the fθ lens 9 and the toroidal lens 10 is parallel to the X axis (see FIG. 3).

  As a result, the surface to be scanned 901a is scanned in the main scanning direction by the light beam deflected in the predetermined angle range. Therefore, hereinafter, the predetermined angle range is also referred to as “scanning angle range”.

  On the other hand, the light beam deflected in a predetermined direction near the upstream side of the mirror rotation direction with respect to the scanning angle range within the deflection angle range is reflected by the reflection mirror 14 of the synchronization detection system 13 and is incident on the PD 16 via the synchronization lens 15. The Hereinafter, the upstream in the mirror rotation direction is also simply referred to as “upstream”, and the downstream in the mirror rotation direction is also simply referred to as “downstream”.

  Here, in the first embodiment, the beam diameter (beam width) of the light beam incident on the polygon mirror 3 in the main scanning corresponding direction is smaller than the width of the deflection reflection surface of the polygon mirror 3 in the main scanning corresponding direction. In the intermediate part of the deflection reflection surface in the main scanning direction, almost all of the light beam is reflected in the deflection angle range, and in the peripheral part, a part of the light beam is not reflected in the deflection angle range. Specifically, it is almost the same as a conventional underfilled optical system, but a part of a light beam used for synchronous detection, for example, reflected by the deflection reflection surface of the polygon mirror 3 near the upstream end of the deflection angle range, A part of the light beam reflected near the downstream end of the deflection angle range is deflected by the deflection reflection surface.

  Here, the underfilled optical system is an optical system that deflects and scans a deflecting reflection surface of a polygon mirror with a narrow beam incident in a direction opposite to the main scanning direction than the deflecting reflecting surface, and is most widely used in a laser scanning optical system. ing.

  On the other hand, in the overfilled optical system, a wide light beam is incident on the deflecting / reflecting surface of the polygon mirror in the direction opposite to the main scanning direction than the deflecting / reflecting surface, and the deflecting / reflecting surface is deflected as a substantial aperture (aperture) in the direction corresponding to the main scanning. An optical system for scanning.

  The overfilled optical system is advantageous in speeding up and increasing the density because the polygon mirror can be multifaceted without increasing the size as compared with the underfilled optical system.

  However, in the overfilled optical system, since it is necessary to adopt an optical arrangement with oblique incidence in the sub-scanning direction, the wavefront aberration is likely to be deteriorated, and the light amount loss at the deflecting / reflecting surface is large.

  Therefore, in the first embodiment, an underfilled optical system is adopted, and as described in detail below, the entire deflection reflective surface of the polygon mirror 3 is used as a substantial reflective surface. Has been achieved.

  A specific example of the deflection operation of the polygon mirror 3 according to the first embodiment will be described below with reference to FIGS. 4 (a) to 4 (c).

  Here, as an example, the polygon mirror 3 is a regular heptagonal prism-shaped rotating polygonal mirror having seven deflection reflection surfaces around the rotation axis, and the radius of an inscribed circle inscribed in the seven deflection reflection surfaces is 14 mm. Seven deflection reflection surfaces are located at a distance of 14 mm from the rotation center (rotation axis).

  The incident direction of the light beam to the polygon mirror 3 is an angle of −60 ° with respect to a reference axis (here, the optical axis of the scanning optical system 4) passing through the rotation axis of the polygon mirror 3 and orthogonal to the rotation axis (however, the reference The angle measured from the axis in the mirror rotation direction is +, and the angle measured in the direction opposite to the mirror rotation direction is-(hereinafter the same). That is, the incident direction of the light beam emitted from the semiconductor laser 1 and passing through the imaging optical system 2 to the polygon mirror 3 is a direction from the + Y side (light source side) to the −Y side (counter light source side). The scanning start position (position corresponding to the upstream end of the scanning angle range) and the scanning end position (position corresponding to the downstream end of the scanning angle range) in the main scanning direction on the surface to be scanned are respectively determined with respect to the reference axis. It is a position reflected at an angle of −40 ° and + 40 °. Hereinafter, the range corresponding to the scanning angle range from the scanning start position to the scanning end position on the surface to be scanned is referred to as “scanning range”.

  As can be seen from FIG. 4A, when the light beam is guided by the polygon mirror 3 and the scanning optical system 4 to the scanning start position and the region including the vicinity of the −Y side (end region on the + Y side of the scanning range), the polygon mirror The incident light beam to 3 straddles the first portion including the downstream end portion of one deflection reflection surface and the upstream end portion of another deflection reflection surface adjacent to the downstream side of the one deflection reflection surface. Incident. Then, the light beam incident on the first portion is guided to the + Y side end region of the scanning range via the scanning optical system 4. On the other hand, the light beam incident on another deflecting / reflecting surface is deflected and is not guided to the scanning range.

  As a result, when the light beam is guided to the end region on the + Y side of the scanning range, the reflected light beam width becomes smaller than the incident light beam width.

  As can be seen from FIG. 4C, when the light beam is guided by the polygon mirror 3 and the scanning optical system 4 to the scanning end position and the region including the vicinity of the + Y side (the end region on the −Y side of the scanning range), the polygon mirror The incident light beam 3 is incident on the second portion including the upstream end portion of the one deflection reflection surface and the other deflection reflection surface adjacent to the upstream side of the one deflection reflection surface. Then, the light beam incident on the second portion is guided to the end region on the −Y side of the scanning range via the scanning optical system 4. On the other hand, the light beam incident on another deflecting / reflecting surface is deflected and is not guided to the scanning range.

  As a result, when the light beam is guided to the end region on the −Y side of the scanning range, the reflected light beam width becomes smaller than the incident light beam width.

  As can be seen from FIG. 4B, the light beam includes a traveling center position (an intermediate position between the scanning start position and the scanning end position in the scanning range) by the polygon mirror 3 and the scanning optical system 4, and is on the + Y side of the scanning range. When being guided to an intermediate area that is an area between the end area and the −Y side end area, the incident light flux to the polygon mirror 3 is in a portion between the first portion and the second portion of one deflection reflection surface. Incident. Then, the light beam incident on the portion between the first portion and the second portion is guided to the intermediate region of the scanning range via the scanning optical system 4.

  As a result, when the light beam is guided to the intermediate region of the scanning range, the reflected light beam width becomes equal to the incident light beam width.

  As can be seen from the above description, in the first embodiment, when the light beam is guided to the intermediate region of the scanning range, almost all of the light beam incident on the polygon mirror 3 is guided to the scanning range, whereas the light beam is scanned. When the light is guided to the + Y side end region and the −Y side end region, a part of the light beam incident on the polygon mirror 3 is guided to the scanning range, but the remainder is removed and is not guided to the scanning range (FIG. 4). (See (A) to FIG. 4C).

  As described above, in the first embodiment, by adopting the above-described configuration, the entire area including the both end portions and the intermediate portion (portions excluding both end portions) in the main scanning corresponding direction of the deflection reflection surface is substantial. Since it becomes a reflection surface, the deflection angle range by the deflection reflection surface can be maximized. For this reason, the polygon mirror 3 can be reduced in size while ensuring a desired scanning width (also referred to as a width of the scanning range in the main scanning direction or a writing width).

  By the way, when the polygon mirror is downsized, it is necessary to reduce the deflection reflection surface in order to reduce the inscribed circle radius while keeping the number of polygon mirror surfaces constant. In this case, if a configuration in which only the intermediate portion of the deflection reflection surface in the main scanning corresponding direction is a substantial reflection surface is employed, the deflection angle range is narrowed to obtain a desired scanning width. Needs to set the focal length of the scanning lens to be long, and the apparatus (optical scanning apparatus) becomes large.

  For example, when a six-surface polygon mirror is used, the inscribed circle radius is normally set to about 16 mm to 18 mm. However, in the first embodiment, the inscribed circle radius is set to, for example, about 8 mm to 9 mm. A desired scanning width can be secured without increasing the focal length. That is, in the first embodiment, the polygon mirror 3 can be reduced in size while suppressing the increase in size of the apparatus.

  By reducing the size of the polygon mirror 3, windage loss is reduced, and by reducing the weight, the diameter of the bearing can be reduced and the frictional force can be reduced. Thus, the polygon mirror 3 can be rotated at a high speed (increase in the number of rotations). .

  As a result, in the first embodiment, high-speed and high-density scanning can be realized while suppressing an increase in size of the apparatus.

  Incidentally, high-speed and high-density scanning can be achieved by increasing the number of faces of the polygon mirror in addition to the increase in the number of rotations (increase in the rotation speed) by downsizing the polygon mirror.

  When the inscribed circle radius and the number of rotations of the polygon mirror are made constant and the number of surfaces is increased, the number of scanning lines for scanning the surface to be scanned can be increased by one rotation of the polygon mirror. Since there is a limit to the increase in the number of rotations due to the miniaturization of the polygon mirror, the effect of increasing the number of polygon mirror faces for high-speed and high-density scanning is great.

  Usually, if the inscribed circle radius of the polygon mirror 3 is kept constant and the number of surfaces is increased, the deflecting / reflecting surface becomes small. In this case, if the configuration in which the luminous flux is not lost is adopted, the deflection angle range becomes narrow, It will be forced to enlarge.

  In the first embodiment, since the above-mentioned damaged method is adopted, it is possible to realize high-speed and high-density scanning while suppressing the enlargement of the apparatus.

  However, as the number of surfaces of the polygon mirror increases, it becomes more difficult to secure the angle of view of the scanning range (also referred to as an image region or a writing region), so there is a limit to the increase in the number of surfaces (multiple surfaces). .

  In view of this, by increasing the number of polygon mirrors and reducing the size (decreasing the inscribed circle radius), it is possible to realize high-speed and high-density scanning as much as possible while suppressing an increase in the size of the apparatus.

  For example, the number of polygon mirrors is increased from six to seven, and the inscribed circle radius is changed from 16 mm to 18 mm to about 12 mm to 14 mm, thereby increasing the number of polygon mirror rotations and at one rotation. The number of scanning lines can be increased, the number of scanning lines that scan the surface to be scanned per unit time can be increased significantly, and high-speed and high-density scanning can be realized.

  By the way, before the light is deflected toward the scanning range by the polygon mirror, it is necessary to make the light incident on the light receiving element (PD) and obtain a synchronization signal for determining the scanning start timing (writing start timing).

  Therefore, in the first embodiment, as shown in FIG. 2, the light is deflected by the polygon mirror 3 and passes through the upstream end of the fθ lens 9 (the upstream end of the scanning angle range upstream). A reflection mirror 14 is disposed, and light reflected by the reflection mirror 14 is incident on the PD 16 via the synchronization lens 15.

  In the first embodiment, the light source driver 100 lights the semiconductor laser 1 for a predetermined time before the reflection direction of the incident light beam at the polygon mirror 3 coincides with the upstream end of the scanning angle range (towards the scanning start position). By synchronizing (lighting on) and making light incident on the PD 16, a synchronization signal from the PD 16 can be obtained. This synchronization signal is output to the light source driver 100. The light source driver 100 turns on (writes on) the semiconductor laser 1 for a predetermined time from the predetermined timing (scanning start timing) after the synchronization signal is input to the scanning end timing.

  That is, the light source driver 100 repeatedly performs a series of cycles of the semiconductor laser 1 that is synchronously turned on, turned off, written, and turned off.

  Further, in the first embodiment, the light source driver 100 performs a certain period of time (monitor lighting) in order to monitor how much light the semiconductor laser 1 itself outputs in addition to the synchronous lighting and writing lighting of the semiconductor laser 1. Time) must be lit (monitor lit). For example, with respect to the semiconductor laser 1 which is an edge emitting laser, if a monitoring PD for monitoring its own light amount is arranged on the opposite side to the emission direction, the light amount (light emission amount) can be obtained by turning on the semiconductor laser 1. Can be measured.

  In the first embodiment, the light-off time for avoiding that the light beam emitted from the polygon mirror 3 returns to the semiconductor laser 1 as reflected light from the polygon mirror 3 and makes the output of the semiconductor laser 1 unstable. (Hereinafter referred to as “return light extinction time”) needs to be set.

  That is, it is necessary to set the return light extinction time in addition to the monitor lighting time, the synchronous lighting time, and the writing lighting time within the time for performing one deflection by one deflecting / reflecting surface.

  Increasing the number of surfaces while keeping the inscribed circle radius of the polygon mirror constant increases the number of scanning lines per rotation of the polygon mirror, which is advantageous for high-speed and high-density scanning. The angle range becomes narrower. For this reason, it is difficult to shorten the monitor lighting time, synchronous lighting time, and return light extinguishing time in order to turn on / off other than writing lighting within the deflection angle range. In order to obtain a desired writing width, the apparatus must be enlarged.

  On the other hand, when the number of deflecting and reflecting surfaces of the polygon mirror is made constant and the number of surfaces is reduced, the number of rotations can be improved by downsizing the polygon mirror, and high-speed and high-density scanning is possible. Further, for example, by changing from 7 surfaces to 6 surfaces, the deflection angle on one surface is increased from 51.43 degrees in the 7th surface to 60 degrees, and there is a margin in the angle (time) at the time of synchronization detection, writing, etc. . However, the effect of increasing the number of polygon mirrors cannot be obtained.

  In addition, the inscribed circle radius of the polygon mirror needs to be set optimally according to the optical characteristics in order to determine the amount of writing light beam and synchronization detection light beam incident near the scanning start position and near the scanning end position. . That is, the number of polygon mirror surfaces and the inscribed circle radius are determined according to the target optical characteristics, speed-up, and density specifications.

  By the way, as described above with reference to FIGS. 4A to 4C, the light flux is applied to the + Y side and −Y side end regions of the scanning range of the surface to be scanned by the polygon mirror 3 and the scanning optical system 4. Only when it is guided, “cutting” by the polygon mirror 3 occurs, so that the + Y side end region, the −Y side end region, the + Y side end region, and the −Y side end region of the scanning range of the surface to be scanned are generated. There is a difference in the amount of light (irradiation light amount) between the end regions and the intermediate region.

  This is shown in FIG. In general, the image height is expressed by coordinates in which the central image height that is the center position of scanning (the center of the scanning range) is zero. In the first embodiment, the length of the scanning range (effective writing range) is set to 327 mm, the scanning start position is set to +163.5 mm, and the scanning end position is set to −163.5 mm. However, the present invention is not limited to this.

  In FIG. 5, the light amount ratio on the vertical axis is calculated with the light amount at the center image height as 100%.

  Here, the position at which the amount of light on the scanning start side that is the light source side (+ Y side) of the optical axis of the scanning optical system 4 starts to drop, that is, “a non-clearable region” (intermediate region of the scanning range) and “clearable region” The image height (hereinafter also referred to as “starting image height”) of the boundary of the scanning area at the + Y side end region is +147.5 mm.

  That is, on the scanning start side, the amount of light decreases with a substantially constant inclination from the image height at which scanning starts (+147.5 mm) to the image height at the scanning start position (+163.5 mm).

  In addition, the position where the amount of light on the scanning end side, which is on the side opposite to the light source (−Y side) of the optical axis of the scanning optical system 4 starts to drop, that is, “a non-clearable area” (intermediate area of the scanning range) and “clearable area” The image height (hereinafter also referred to as “starting image height”) of the boundary of (the end region on the −Y side of the scanning range) is −147.5 mm.

  That is, on the scanning end side, the light amount decreases with a substantially constant inclination from the image height at which scanning starts (−147.5 mm) to the image height at the scanning end position (−163.5 mm).

  By the way, it is possible to shorten the length of the deflecting / reflecting surface of the polygon mirror in the direction corresponding to the main scanning direction by forming the light flux range on both sides rather than only on one side of the scanning range. It goes without saying that can be made smaller.

  In addition, the polygon mirror can be further miniaturized by setting the image height at the inner side of the scanning range when the image starts to be blurred.

  However, it can be easily understood that if the area to be removed is set to be excessively large, a decrease in the amount of light in the end area of the scanning range increases, resulting in a deterioration in image quality.

  In the first embodiment, the light source side is the scanning start side and the counter light source side is the scanning end side, but the present invention is not limited to this depending on the rotation direction of the polygon mirror. That is, the light source side may be the scanning end side, and the counter light source side may be the scanning start side. Specifically, in FIGS. 4A to 4C, the rotation direction of the polygon mirror 3 may be reversed, FIG. 4A may be the scanning end side, and FIG. 4C may be the scanning start side. .

  Here, the light amount decrease on the light source side and the light amount decrease on the counter light source side are compared.

  FIG. 6A shows, as a comparative example, a reduction in the amount of light in the end areas on the + Y side and −Y side of the scanning range in FIG. 5 superimposed with the image height on the horizontal axis as an absolute value. When adopting a configuration in which both end regions of the scanning range are thus employed, in order to prevent one end region (one region) from excessively entering the inside of the scanning range, in general, scanning is performed. The image heights are configured to coincide with each other at the both end regions of the range. Note that, as can be seen from FIG. 6A, the amount of light in the region on the side opposite to the light source is less than that in the region on the side of the light source. In this case, even if the amount of light in the entire area on the light source side reaches a level that does not affect the final image, there is a possibility that the amount of light in at least a part of the area on the anti-light source side does not reach that level.

  However, in practice, since the slope of the light amount decrease differs between the two end regions of the scanning range, a light amount difference occurs between the two end regions. In FIG. 6A, the light amount of the image height at the scanning start position on the light source side is about −8%, and the light amount of the image height at the scanning end position on the counter light source side is about −9%. There is a light amount difference of about 1% between the parts.

  The fact that the slope of the light amount decrease differs between the two end regions of the scanning range will be described with reference to FIGS. 7 (a) and 7 (b).

  FIG. 7A shows a state when the light is reflected on the light source side, and FIG. 7B shows a state when the light is reflected on the opposite light source side. The inclination of the decrease in the amount of light depends on a change in the light beam width that is obtained when the polygon mirror is rotated by a minute amount, and the amount of change in the light beam width depends on a change in the position of the end of the deflecting reflection surface. The end of the deflecting reflecting surface changes so as to draw a circumscribed circle of the polygon mirror. Here, when comparing the marginal rays on the respective sides shown in FIGS. The light source side is incident at an angle with respect to the tangential direction of the circumscribed circle of the polygon mirror.

  Therefore, the change in the light flux width when the end of the deflecting reflecting surface changes on the circumscribed circle of the polygon mirror is smaller than that on the counter light source side that is downstream in the incident direction of the light flux to the polygon mirror 3. The light source side that is upstream of the incident direction becomes duller. For this reason, it can be understood that the inclination of the light amount decrease in the scanning range is larger on the counter light source side than on the light source side, and the above-described light amount difference occurs.

  That is, the inclination of the light amount decrease in the scanning range is larger on the downstream side (the end region on the −Y side) than on the upstream side (the end region on the + Y side) in the incident direction of the light flux to the polygon mirror 3.

  Incidentally, a correction method for changing the light amount is generally a method of changing the output of the light source in accordance with the scanning position in the main scanning direction (changing the output of the light source within the scanning range). Theoretically, it is possible to increase the amount of light emitted from the light source by the amount that the amount of light has decreased, and to make the amount of light within the scanning range uniform.

  Specifically, the light source driver 100 adjusts the light emission amount of the semiconductor laser 1 when scanning the + Y side and −Y side end regions of the scanning range based on the output timing of the light reception signal from the PD 16.

  For example, FIG. 8A simply shows a state where the light amount reduction is completely corrected at each correction position. Here, correction positions are arranged at intervals of, for example, about 5.1 mm with respect to the scanning range, and two correction positions are set in an area where the correction positions are set.

  As can be seen from FIG. 8A, when the light amount is corrected by 3% at each of the two correction positions with respect to the light amount reduction where the end light amount before light amount correction is −9%, the end light amount after light amount correction ( Hereinafter, it is also referred to as “correction residual”) is −3%.

  However, it has been confirmed through experiments and the like that when the light amount difference between two areas adjacent to each other with the correction position interposed therebetween is 2% or more, the image appears as shading and the image quality is deteriorated.

  For this reason, when the inclination of the light amount decrease due to the squeezing of this method is large, if the light amount decrease amount is to be completely corrected as described above, the light amount step exceeds 2% as shown in FIG. Image quality will deteriorate. Therefore, in practice, as shown in FIG. 8B, the light amount correction is performed so that the light amount step is 2% of the limit. Then, although the correction residual becomes large, it is an end portion, so that the light amount step does not appear in the image, and even 2% or more is acceptable. However, it goes without saying that if the required image quality is high, it is necessary to keep the correction residual small.

  However, when the light amount correction is performed by the method described above, the correction amount in the both end regions of the scanning range is the same (the product of the number of correction positions and 2%), so the light amount difference between the light source side and the counter light source side is not corrected. . That is, the light amount side end light amount −8% in FIG. 6A is increased to −4% and the light amount side end light amount −9% in FIG. 6A is increased to −5% by two correction positions. The 1% light amount difference remains as it is. In order to obtain the maximum effect of this method, the correction residual is set close to the allowable quality limit, so that the balance of the light quantity of several percent may affect the image quality.

  Therefore, in the present embodiment, the image height at which the opposite light source begins to be shifted is made longer than the image height at which the light source begins to shift.

  In other words, in the scanning range, the length of the non-light-source side area is made longer than the length of the non-light-side side area. In other words, in the scanning range, the length of the region on the side opposite to the light source (the end region on the −Y side) is made shorter than the length of the region on the light source side (the end region on the + Y side).

  Thus, by making the length of the region to be deliberately asymmetrical, the difference in the amount of light between the two end regions of the scanning range can be reduced.

  In order to change the image height, the incident light beam to the polygon mirror may be shifted on the main scanning section (surface orthogonal to the sub-scanning direction).

  In order to make the image height different between the light source side and the counter light source side, the lengths of the first reflection portion and the second portion in the main scanning corresponding direction may be different. Further, in order to increase the image height at which the light source side starts to be shifted from the light source side, the length of the first portion of the deflecting reflection surface is made longer than the length of the second portion. It ’s fine.

  This is shown in FIGS. 9 and 10. FIG. Reference symbols an and am denote marginal rays of the incident light beam on the polygon mirror, which are incident on the deflecting / reflecting surface 3a at an incident angle θ and reflected in the direction of the field angle ω. When the reflected light beam begins to fall toward the image height, one of the incident light beam marginal rays is reflected at the end of the deflecting reflection surface. If it rotates, the marginal ray will be reflected by the adjacent deflecting reflecting surface, and scratches will begin to occur.

  In FIG. 9 showing a light beam that starts to be scattered toward the image height on the light source side, when the light beam incident on the polygon mirror is shifted so that an and am become an ′ and am ′, it is the marginal ray that begins to be scattered. Is the timing at which the light is reflected at the end of the deflecting / reflecting surface, so that the deflecting / reflecting surface is in the state of 3a 'and is deflected in the direction of the field angle ω' smaller than ω. On the other hand, in FIG. 10 showing the luminous flux toward the image height at the opposite light source side, when the incident luminous flux of the polygon mirror is similarly shifted, the marginal ray is deflected and the reflecting surface is 3a ′. When the state is reached, it is deflected in the direction of the field angle ω ′ larger than ω. That is, by shifting the incident light beam to the polygon mirror as shown in FIGS. 9 and 10, the image height at the light source side starts to be shifted toward the inside, and the image height at the counter light source side starts to shift toward the outside. As shown in FIG. 6B, the image height can be set asymmetrically with respect to the center image height, and about −8.3% (about −4.3% after the light amount correction), the light source side and the opposite side. The decrease in the amount of light on the light source side matches. Note that if the shift direction of the incident light beam is reversed, the change in the image height will be reversed when it starts to be sunk. As can be seen from FIG. 6B, the amount of light in the region located on the side opposite to the light source is larger than that in the region located on the side of the light source. In this case, if the amount of light in the entire region on the light source side reaches a level that does not affect the final image, the amount of light in the entire region on the anti-light source side also reaches that level.

FIG. 11 is a diagram for deriving the relationship between the image height difference ΔY at which both end regions of the scanning range start to be shifted and the light amount difference ΔI between the end portions of the both end regions. FIG. 11 shows a diagram when the light amount correction is not performed for the sake of simplicity. As described above, the light amount difference is preserved before and after the light amount correction. Let Y be the distance from the image height at which the light source begins to be shifted to the edge image height on the side opposite to the light source, and I be the amount of decrease in edge light amount on the side opposite to the light source. In addition, it is assumed that the slope of the light amount decrease on the light source side is p and the slope of the light amount decrease on the counter light source side is q, both of which are expressed as negative values. That is, q = I / Y and p = (I + ΔI) / (Y + ΔY). From these, the following equation (1) can be derived.
ΔI = (p−q) Y + pΔY (1)

  For example, when the image height difference ΔY starts to be zero and the light amount deviation ΔI is 0 (in the case of FIG. 6A), ΔI = (p−q) Y by substituting 0 into ΔY in the above equation (1). It is. Further, the image height difference ΔY at the start of shifting when the light amount difference ΔI is set to 0 (in the case of FIG. 6B) is obtained by substituting 0 for ΔI in the above equation (1), and ΔY = (q / p−1). ) Y.

Further, when the image height difference ΔY starts to increase, the light amount difference ΔI is generated again. When the image height difference ΔY starts to decrease and has the same light amount difference as in the case of 0 (in the case of FIG. 11), the above (1). If (q−p) Y is substituted for ΔI in the equation, ΔY = 2 (q / p−1) Y, and if it is increased more than this, the light amount difference is increased. Therefore, the condition for reducing the light amount difference ΔI can be expressed by the following equation (2).
0 <ΔY <2Y (q / p−1) (2)

  In particular, the minimum value is taken when ΔY = (q / p−1) Y. As an example, an example in which Y = 15.5 [mm], p = −0.500 [% / mm], q = −0.569 [% / mm] is given, and the above formula (2) is satisfied. By setting ΔY = 2.3 [mm] as described above, it is possible to reduce the difference in light quantity between the end portions of the scanning region (between both ends of the scanning region) as shown in FIG. 6B.

  For example, at least the main scanning of the incident position of the light beam on the polygon mirror is able to correct the deviation from the position where the image height starts to be shifted at both ends of the scanning range due to the shape error or assembly error of each optical element. It is desirable to have incident position adjusting means that can be adjusted with respect to the corresponding direction.

  For example, by adjusting the position of the coupling lens 6 of the imaging optical system 2 in the main scanning corresponding direction by an adjusting mechanism as an incident position adjusting unit, the incident position of the light beam on the polygon mirror 3 is shifted in the main scanning corresponding direction. In addition, the balance between the light source side and the counter light source side can be corrected.

  Further, by adjusting the position in the main scanning corresponding direction of the entire imaging optical system 2 or the unit in which the semiconductor laser 1 and the imaging optical system 2 are integrated with each other, the adjustment to the polygon mirror 3 is performed. The incident position of the light beam can be shifted in the direction corresponding to the main scanning, and the balance between the light source side and the counter light source side can be corrected.

  From the first viewpoint, the optical scanning device 900 according to the first embodiment described above has a light source (semiconductor laser 1) and a polygon that has a plurality of deflection reflection surfaces around the rotation axis and deflects light from the light source. A mirror 3 (deflector) and a scanning optical system 4 for guiding the light deflected by the polygon mirror 3 to the surface to be scanned are provided, and the light incident on the polygon mirror 3 has a plurality of deflection reflections in the main scanning corresponding direction. The incident direction of the light to the polygon mirror 3 is smaller than any one of the deflecting reflecting surfaces, and the angle of the incident light with respect to the optical axis of the scanning optical system 4 is one deflection when viewed from the rotational axis direction. Incident across the first portion including the downstream end of the deflector in the rotational direction of the reflecting surface and the upstream end of the deflecting reflective surface adjacent to the downstream in the rotational direction of one deflecting reflective surface Of the light, the light incident on the first portion travels through the scanning optical system. The light that is guided to the + Y side end region of the scanning range of the surface and is incident on the upstream end of the rotational direction is not guided to the scanning range, and includes the upstream end of the deflector of the one deflection reflection surface in the rotational direction. Of the light incident across the second portion and the end portion on the downstream side in the rotation direction of the deflection reflection surface adjacent to the upstream side in the rotation direction of the one deflection reflection surface, the light incident on the second portion is scanning optics. The light that is guided to the end region on the −Y side of the scanning range through the system and is incident on the end on the downstream side in the rotation direction is not guided to the scanning range, and the first portion and the second portion of one deflection reflection surface The light that has entered the portion between is guided to an intermediate region that is a region between the + Y side end region and the −Y side end region of the scanning range via the scanning optical system, and from the center of the scanning range to the intermediate region And the first distance which is the distance to the boundary between the + Y side end region and the center of the scanning range, the intermediate region and the −Y side end region The second distance is the distance to the field is an optical scanning apparatus according to claim different.

  From the second viewpoint, the optical scanning device 900 according to the first embodiment has a light source (semiconductor laser 1) and a polygon mirror that has a plurality of deflection reflection surfaces around the rotation axis and deflects light from the light source. 3 (deflector) and a scanning optical system 4 that guides the light deflected by the polygon mirror 3 to the surface to be scanned, and the light incident on the polygon mirror 3 has a plurality of deflection reflection surfaces in the main scanning corresponding direction. The incident direction of the light to the polygon mirror 3 forms an angle with respect to the optical axis of the scanning optical system 4 when viewed from the rotation axis direction, and is one deflected reflection. Light incident across the first portion including the downstream end of the surface deflector in the rotational direction and the upstream end in the rotational direction of the deflecting / reflecting surface adjacent to the downstream in the rotational direction of the one deflecting / reflecting surface Of these, the light incident on the first portion is incident on the surface to be scanned via the scanning optical system. The light that is guided to the + Y side end region of the inspection range and is incident on the upstream end of the rotation direction is not guided to the scanning range, and includes the second end including the upstream end of the deflector on the one deflection reflection surface. Of light incident on the second portion and the end portion on the downstream side in the rotational direction of the deflecting / reflecting surface adjacent to the upstream side in the rotational direction of the first deflecting / reflecting surface is the scanning optical system. The light that is guided to the end region on the −Y side of the scanning range through the rotation direction and incident on the end portion on the downstream side in the rotation direction is not guided to the scanning range, and is between the first portion and the second portion of the one deflection reflection surface. The light incident on this portion is guided to the intermediate region that is the portion between the + Y side end region and the −Y side end region of the scanning range via the scanning optical system, and the first and second portions are The lengths in the direction corresponding to the scanning direction are different from each other.

  According to the optical scanning device 900 of the first embodiment, when the incident direction of light to the polygon mirror 3 is viewed from the rotation axis direction, the optical scanning device 900 forms an angle with respect to the optical axis of the scanning optical system 4 at both ends of the scanning range. The difference in the amount of light can be reduced by making the first and second distances different (by making the distances of the first and second portions in the main scanning facing direction different). As a result, the surface to be scanned can be scanned with high accuracy.

  The incident direction of the light from the light source on the deflection reflection surface is a direction from the + Y side to the −Y side of the scanning range when viewed from the rotation axis direction of the polygon mirror 3. Of the distances, the first distance, which is the + Y side distance of the scanning range, is shorter than the second distance, which is the −Y side distance, so that the difference in the amount of light at both ends of the scanning range can be reliably suppressed.

  Further, since the light source is disposed on the + Y side of the optical axis of the scanning optical system 4 when viewed from the rotation axis direction of the polygon mirror 3, it is not necessary to turn back the optical path of the light from the light source. As a result, the imaging optical system 2 can be reduced in size and the number of parts can be reduced. On the other hand, if the light source is disposed on the −Y side of the optical axis of the scanning optical system 4, in order to make light incident on the one deflecting reflection surface from the + Y side to the −Y side, It is necessary to fold the light back using a mirror or the like. Depending on the layout of the optical system, a configuration may be employed in which the light source is arranged on the −Y side of the optical axis of the scanning optical system 4 and folded by a folding mirror or the like.

  Further, of the first and second distances, the distance on the -Y side is Y, the inclination of the decrease in the amount of light on the scanned surface on the + Y side with respect to the main scanning direction is p, and the -Y side distance on the scanned surface on the -Y side. When the inclination of the decrease in the amount of light with respect to the main scanning direction is q and the difference between the first and second distances is ΔY, if 0 <ΔY <2Y (q / p−1) is satisfied, The difference in light quantity can be more reliably suppressed.

  Further, when the optical scanning device 900 further includes incident position adjusting means that can adjust the incident position of light on one deflecting reflection surface at least in the direction corresponding to the main scanning direction, for example, device design error, device manufacturing, and the like. Deviations from the set values of the first and second distances due to time assembly errors, changes over time after use of the apparatus, and the like can be suppressed.

  When the optical scanning device 900 further includes a light emission amount adjustment unit (light source driver 100) that adjusts the light emission amount of the light source in the scanning range, the + Y side and -Y side end regions and the central region of the scanning range are used. The light quantity difference between them can be reduced.

  In the first embodiment, when the light beam is guided to the + Y side and −Y side end regions of the scanning range, a part of the light beam incident on the polygon mirror 3 is not guided to the scanning surface (deflection of the polygon mirror 3). By kicking on the reflecting surface, the polygon mirror can be downsized and rotated at high speed. In addition, by increasing the number of scanning lines per rotation by increasing the number of polygon mirrors, it is possible to respond to high density at a low cost without increasing the number of light source units (the number of light sources) with high cost weight. In addition, it is possible to implement high-speed processing at a low cost without increasing the number of light sources.

  Conventionally, in order to prevent a part of the light beam from being scattered around the scanning range in order to make the light quantity constant while securing a desired angle of view in the writing area, in particular, the polygon mirror is enlarged or an overfilled optical system is used. Adopted.

  On the other hand, in the first embodiment, an underfill optical system is employed, and a configuration in which a part of the light beam is taken when scanning one end and the other end of the scanning range in the main scanning corresponding direction is employed. Therefore, it is possible to reduce the size and increase the number of polygon mirrors while ensuring a desired angle of view of the writing area.

  On the other hand, when the polygon mirror is reduced in size and multifaceted with a conventional optical scanning device that is not lost, the deflection angle range becomes smaller. This causes problems such as a decrease in the number of rotations of the polygon mirror and noise, and an increase in the size of the apparatus.

  Further, since the laser printer 500 includes the photosensitive drum 901 (image carrier) and the optical scanning device 900 that scans the surface of the photosensitive drum 901, a high-definition image can be formed at high speed.

  Further, the first adjustment method of the optical scanning device 900 according to the present embodiment includes a step of setting the first and second distances, and the surface to be scanned is scanned with light by using the optical scanning device 900, and the optical scanning device 900 in the scanning range. A step of measuring a light amount distribution (see FIG. 5), a step of obtaining a deviation from a set value of the first and second distances based on a measurement result in the step of measuring, and a first and second distance Adjusting the incident position of the light on the one deflecting reflection surface using the incident position adjusting means so that the deviation from the set value is suppressed.

  In this case, deviations from the set values of the first and second distances due to, for example, manufacturing errors in the parts of the device, assembly errors in the parts at the time of manufacturing the device, changes in the shape of the parts after use of the device and positional relationships between the parts, etc. Can be suppressed.

  The second adjustment method of the optical scanning device 900 of the present embodiment includes a step of scanning the surface to be scanned with light using the optical scanning device 900 and measuring a light amount distribution (see FIG. 5) in the scanning range; Based on the measurement result in the measurement step, the light emission amount adjusting means is used to reduce the light amount difference between the + Y side and − side end regions of the scanning region and the central region. The step of adjusting the amount of emitted light and the incident position of the light on one deflecting / reflecting surface so that the difference in the amount of light between the end portions of one end and the other end of the scanning range (between both ends of the scanning range) is reduced. Adjusting.

  In this case, the light amount difference between the end region on one side and the other side of the scanning range and the intermediate region can be reduced, and the light amount difference between both ends of the scanning range can be reduced.

  As a result, the scanning accuracy can be further improved.

  In the first and second adjustment methods, the light quantity distribution in the scanning range is, for example, an area sensor including a plurality of light receiving units (for example, PD, CCD, CMOS, etc.) that are two-dimensionally arranged or one-dimensionally arranged. In addition, it is possible to obtain using a line sensor including a plurality of light receiving portions (for example, PD, CCD, CMOS, etc.).

<< Second Embodiment >>
Hereinafter, the second embodiment will be described with reference to FIG.

  FIG. 12 shows a schematic configuration of a color printer 2000 as an image forming apparatus according to the second embodiment.

  As shown in FIG. 12, a transport belt 17 for transporting transfer paper (not shown) fed from a paper feed cassette 30 disposed in the horizontal direction is provided on the lower side in the apparatus. On this conveying belt 17, a photosensitive drum 7Y for yellow Y, a photosensitive drum 7M for magenta M, a photosensitive drum 7C for cyan C, and a photosensitive drum 7K for black K are upstream in the conveying direction of the transfer paper. They are arranged at equal intervals in order from the side. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction.

  These photosensitive drums 7Y, 7M, 7C, and 7K are all formed to have the same diameter, and process members that execute the respective processes according to the electrophotographic process are sequentially arranged around the photosensitive drums 7Y, 7M, 7C, and 7K. Taking the photoconductor drum 7Y as an example, a charging charger 8Y, an optical scanning system 6Y, a developing device 10Y, a transfer charger 11Y, a cleaning device 12Y, and the like are sequentially arranged. The same applies to the other photosensitive drums 7M, 7C, and 7K. In other words, in the second embodiment, the surfaces of the photoconductive drums 7Y, 7M, 7C, and 7K are set as scan surfaces (or irradiated surfaces) set for the respective colors. Optical scanning systems 6Y, 6M, 6C, and 6K are provided in a one-to-one correspondence relationship. Further, a registration roller 16 and a belt charging charger 20 are provided around the transport belt 17 so as to be positioned upstream of the photosensitive drum 7Y, and are positioned downstream of the photosensitive drum 7K in the rotation direction of the belt 17. A belt static elimination charger 21 is provided. Further, a fixing device 24 including a pair of fixing rollers 24 a and 24 b that form a fixing nip is provided downstream of the belt static elimination charger 21 in the transfer paper conveyance direction, and the discharge roller 25 faces the discharge tray 26. Tied.

  In such a schematic configuration, for example, in the full color mode (multiple color mode), the photosensitive drums 7Y, 7M, 7C, and 7K are based on the image signals of the colors Y, M, C, and K. An electrostatic latent image corresponding to each color signal is formed on the surface of each photosensitive drum by optical scanning of the light beam by each of the optical scanning systems 6Y, 6M, 6C, and 6K. These electrostatic latent images are developed with color toners by the corresponding developing devices to become toner images, which are superposed by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transport belt 17 and transported. As a result, a full-color image is formed on the transfer paper. This full-color image is fixed by the fixing device 24 and then discharged to a discharge tray 26 by a discharge roller 25.

  By using each of the four optical scanning systems 6Y, 6M, 6C, and 6K of the color printer 2000 as the optical scanning device 900 according to the first embodiment, an image forming apparatus that can form a high-definition color image at high speed. Can be realized. By using the optical scanning systems 6Y, 6M, 6C, and 6K of the color printer 2000 as the optical scanning device 900 of the first embodiment described above, high-speed and high-precision optical scanning can be performed while suppressing an increase in size, and An image forming apparatus that can ensure high-quality image reproducibility while suppressing deterioration in image quality can be realized.

  The optical scanning device 1000 of the second embodiment is configured to include optical scanning systems 6Y, 6M, 6C, and 6K.

  More specifically, the optical scanning apparatus 1000 includes, as an example, four light source devices corresponding to four colors (Y, M, C, K), one polygon mirror that deflects light from each light source device, and four Four scanning optical systems provided corresponding to the individual light source devices and two synchronization detection systems are provided.

  That is, each optical scanning system includes a specific light source device, four polygon mirrors common to the four optical scanning systems, a specific scanning optical system, and a synchronous detection system common to the two upper and lower optical scanning systems. Here, the scanning optical system of each optical scanning system includes one scanning lens and two folding mirrors. Each synchronization detection system includes a synchronization lens that is deflected by a polygon mirror and disposed on the optical path of the light passing through the upstream end of the scanning lens, and a synchronization detection light-receiving element disposed on the optical path of the light that passes through the synchronization lens ( For example, PD). A synchronization detection system may be provided for each optical scanning system. In each optical scanning system, the number of folding mirrors may be one or zero depending on the layout.

  Here, as an example, the polygon mirror is configured to include two rotating polyhedra arranged in two upper and lower stages and sharing a rotation axis. As an example, the two rotating polyhedrons have substantially the same shape and the same size, and the positions around the rotation axis are also the same.

  Since the light source devices and scanning optical systems of the optical scanning systems 6Y and 6M are disposed on the right side of the polygon mirror, the optical scanning systems 6Y and 6M are also collectively referred to as the right optical scanning system. Further, since the optical scanning system 6Y is arranged in the upper stage, it is also referred to as the upper right optical scanning system, and the optical scanning system 6M is also referred to as the lower right optical scanning system because it is arranged in the lower stage. Similarly, since the light source devices and scanning optical systems of the optical scanning systems 6C and 6K are arranged on the left side of the polygon mirror, the optical scanning systems 6C and 6K are also collectively referred to as the left optical scanning system. Furthermore, since the optical scanning system 6C is arranged in the upper stage, it is also referred to as the upper left optical scanning system, and the optical scanning system 6K is also referred to as the lower left optical scanning system, because it is arranged in the lower stage.

  Here, the optical axes of the scanning optical systems of the left upper and right upper optical scanning systems that are opposed to each other are substantially coincident, and the optical axes of the scanning optical systems of the lower left and right optical scanning systems that are opposed to each other are substantially coincident. .

  Therefore, the two lights emitted from the light source devices of the upper left and upper right optical scanning systems are incident on two different deflection reflection surfaces on the upper stage of the polygon mirror, and the corresponding two scans by the two deflection reflection surfaces. The light is deflected toward the optical system and is individually guided to the corresponding surfaces (scanned surfaces) of the two photosensitive drums 7C and 7Y by the two scanning optical systems.

  Further, two lights emitted from the light source devices of the lower left and lower right optical scanning systems are incident on two different deflecting / reflecting surfaces on the lower stage of the polygon mirror, and corresponding two scans are made by the two deflecting / reflecting surfaces. The light is deflected toward the optical system and is individually guided to the surfaces (scanned surfaces) of the two corresponding photosensitive drums 7K and 7M by the two scanning optical systems.

  As described above, the counter scanning method is employed in the optical scanning device 1000 of the second embodiment.

  Therefore, according to the color printer 2000 of the second embodiment, since the optical scanning device 1000 is provided, a high-definition color image can be formed at high speed.

  In the second embodiment, the case where the optical scanning device is integrally configured has been described. However, the present invention is not limited to this. For example, an optical scanning device may be provided for each photosensitive drum, or an optical scanning device may be provided for every two photosensitive drums.

  In the second embodiment, the color printer 2000 includes four photosensitive drums. However, the present invention is not limited to this. For example, five or more photosensitive drums may be provided.

  Further, in each of the above embodiments, the incident direction of the light from the light source device on the deflecting / reflecting surface and the reflecting direction on the deflecting / reflecting surface are in the same plane perpendicular to the rotation axis of the polygon mirror. Absent. For example, the incident angle of the light from the light source device to the deflecting / reflecting surface may be inclined with respect to the rotation axis of the polygon mirror. That is, the light from the light source device may be obliquely incident on the deflecting / reflecting surface. In this case, since the return light to the light source is not actually generated even at the return light generation timing, it is not necessary to turn off the light at the return light generation timing.

  The configuration of the synchronization detection system is not limited to that described in each of the above embodiments, and can be changed as appropriate. For example, in the first embodiment, the reflection mirror may be omitted, and the light beam deflected by the polygon mirror may be incident on the PD via the synchronous lens. In each of the above embodiments, the light beam deflected by the polygon mirror is guided to the synchronization detection system via the scanning lens (for example, the fθ lens), but may be guided to the synchronization detection system without passing the scanning lens. good. In each of the above embodiments, a PD (photodiode) is used as the light-receiving element of the synchronization detection system. However, for example, another photo detector such as a phototransistor may be used.

  In addition, the configuration of the light source device is not limited to that described in the above embodiments, and can be changed as appropriate. For example, in each of the above embodiments, an edge-emitting laser (LD) is used as a light source. However, the present invention is not limited to this, and for example, a surface-emitting laser (VCSEL), another laser, or the like may be used. In addition, the number of light source devices including the light source and the number of light sources in the light source device can be appropriately changed according to the specifications of the optical scanning device.

  Further, the configuration of the scanning optical system is not limited to that described in the above embodiments, and can be changed as appropriate. For example, the scanning optical system of the first embodiment may be configured with only an fθ lens, omitting the toroidal lens. Further, for example, each scanning optical system of the second embodiment may be composed of a plurality of scanning lenses.

  Further, for example, an image forming apparatus that directly irradiates laser light onto a medium (for example, paper) that develops color with laser light may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to photographic paper by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  Further, the image forming apparatus may be an image forming apparatus other than a printer, for example, a digital copying machine, a facsimile, or a complex machine in which these are integrated.

  Below, the thought process that led the inventor to come up with the above embodiments will be described.

  In electrophotographic image recording, an image forming apparatus using a laser is widely used. Generally, this image forming apparatus scans the surface of a photosensitive drum (hereinafter also referred to as “photosensitive drum”) with a laser beam, and forms light on the surface of the photosensitive drum. A scanning device is provided.

  The optical scanning device includes a light source, a pre-deflector optical system, a deflector, and a scanning optical system. The laser light emitted from the light source enters the deflector via the pre-deflector optical system, is deflected by the reflecting surface of the deflector, and is then guided to the photosensitive drum via the scanning optical system. The reflecting surface of the deflector is also called a “deflecting reflecting surface”.

  In recent years, there has been an increasing demand for higher speed and higher quality of image formation for image forming apparatuses, and various systems have been proposed as optical systems for optical scanning apparatuses that satisfy these requirements.

  For example, an underfilled optical system can be used. In general, the number of surfaces of a polygon mirror as a deflector used in an underfilled optical system is six or less, and in order to prevent all the light beams from being deflected by the deflecting / reflecting surface when the number is seven or more. Since it is necessary to increase the inscribed circle radius of the polygon mirror and the number of rotations of the polygon mirror is reduced, it is not adopted.

  In order to cope with this problem, Patent Document 1 adopts an underfilled optical system, and only when scanning the peripheral region of the surface to be scanned, part of the incident light to the deflector cannot be guided to the surface to be scanned. The method is disclosed.

  However, the method disclosed in Patent Document 1 has a problem in that the amount of light in the peripheral region of the scanning range is reduced due to the part of the light beam being “cleared”, and further a light amount deviation occurs in the main scanning direction.

  In order to solve such a problem, the inventor has come up with the above embodiments.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser (light source), 3 ... Polygon mirror (deflector), 4 ... Scanning optical system, 9 ... f (theta) lens (a part of scanning optical system), 10 ... Toroidal lens (a part of scanning optical system), 11 ... Folding mirror (part of scanning optical system), 7K, 7C, 7M, 7Y, 901 ... photosensitive drum (image carrier), 500 ... laser printer (image forming apparatus), 900, 1000 ... optical scanning apparatus, 901a ... surface of photosensitive drum (surface to be scanned), 2000 ... color printer (image forming apparatus).

JP 2014-029482 A

Claims (10)

A light source;
A deflector having a plurality of deflecting reflecting surfaces around the rotation axis, and deflecting light from the light source;
A scanning optical system for guiding the light deflected by the deflector to a surface to be scanned,
The light incident on the deflector is smaller than any one of the plurality of deflection reflection surfaces in the direction corresponding to the main scanning direction,
The incident direction of light to the deflector forms an angle with respect to the optical axis of the scanning optical system when viewed from the rotational axis direction,
A first portion including an end of the one deflecting / reflecting surface on the downstream side in the rotation direction of the deflector and an upstream side in the rotating direction of the deflecting / reflecting surface adjacent to the downstream side in the rotating direction of the one deflecting / reflecting surface. Of the light incident across the end of the first portion, the light incident on the first portion is guided to the end region on one side of the scanning range of the scanned surface via the scanning optical system, and the rotation direction Light incident on the upstream end is not guided to the scanning range,
A second portion including an end portion on the upstream side in the rotation direction of the one deflection reflection surface and an end portion on the downstream side in the rotation direction of the deflection reflection surface adjacent to the upstream side in the rotation direction of the one deflection reflection surface. Of the light incident on the second portion, the light incident on the second portion is guided to the other end region of the scanning range via the scanning optical system and incident on the downstream end of the rotation direction. Is not guided to the scanning range,
The light incident on the portion between the first portion and the second portion of the one deflecting reflecting surface passes through the scanning optical system and the one end region and the other end region of the scanning range. Led to the middle region, which is the region between
A first distance, which is a distance from the center of the scanning range to the boundary between the intermediate region and the one end region, and a boundary from the center of the scanning region to the boundary between the intermediate region and the other end region An optical scanning device characterized in that the second distance, which is the distance of, differs. The incident direction of the light from the light source to the one deflection reflection surface is a direction from one side of the one side and the other side toward the other side as seen from the rotation axis direction.
2. The optical scanning device according to claim 1, wherein, of the first and second distances, the distance on the one side and the other side is shorter than the distance on the other side.   The optical scanning device according to claim 2, wherein the light source is disposed on the one side of the optical axis of the scanning optical system when viewed from the rotation axis direction. Of the first and second distances, the distance on the other side is Y, the slope of the light amount reduction on the scanned surface on the one side with respect to the main scanning direction is p, and the scanned side on the other side When the slope of the light amount reduction on the surface with respect to the main scanning direction is q, and the difference between the first and second distances is ΔY,
The optical scanning device according to claim 2, wherein 0 <ΔY <2Y (q / p−1) is satisfied.   The incident position adjusting means capable of adjusting the incident position of light on the one deflecting / reflecting surface in at least a direction corresponding to the main scanning direction is further provided. Optical scanning device.   The optical scanning device according to claim 5, further comprising a light emission amount adjusting unit capable of adjusting a light emission amount of the light source in the scanning range. An image carrier;
An image forming apparatus comprising: the optical scanning device according to claim 1 that scans a surface of the image carrier. An adjustment method for an optical scanning device according to claim 5,
Setting the first and second distances;
Scanning the surface to be scanned with light using the optical scanning device, and measuring a light amount distribution in the scanning range;
Obtaining a deviation from a set value of the first and second distances based on a measurement result in the measuring step;
Adjusting the incident position of the light on the one deflecting reflecting surface using the incident position adjusting means so that the deviation from the set values of the first and second distances is suppressed. Method for adjusting a scanning device. The method of adjusting an optical scanning device according to claim 6,
Scanning the surface to be scanned with light using the optical scanning device, and measuring a light amount distribution in the scanning range;
Based on the measurement result in the measuring step, using the light emission amount adjusting means so that the light amount difference between the one end region and the other end region of the scanning range and the central region is reduced. Adjusting the amount of light emitted from the light source in the scanning range;
Adjusting the incident position of the light on the one deflecting reflecting surface using the incident position adjusting means so that the difference in the amount of light between the end portions of the one side and the other end region is reduced. A method for adjusting an optical scanning device. A light source;
A deflector having a plurality of deflecting reflecting surfaces around the rotation axis, and deflecting light from the light source;
A scanning optical system for guiding the light deflected by the deflector to a surface to be scanned,
The light incident on the deflector is smaller than any one of the plurality of deflection reflection surfaces in the direction corresponding to the main scanning direction,
The incident direction of light to the deflector forms an angle with respect to the optical axis of the scanning optical system when viewed from the rotational axis direction,
A first portion including an end of the one deflecting / reflecting surface on the downstream side in the rotation direction of the deflector and an upstream side in the rotating direction of the deflecting / reflecting surface adjacent to the downstream side in the rotating direction of the one deflecting / reflecting surface. Of the light incident across the end of the first portion, the light incident on the first portion is guided to the end region on one side of the scanning range of the scanned surface via the scanning optical system, and the rotation direction Light incident on the upstream end is not guided to the scanning range,
A second portion including an end of the one deflecting / reflecting surface on the upstream side in the rotational direction of the deflector and a downstream side in the rotational direction of the deflecting / reflecting surface adjacent to the upstream side in the rotational direction of the one deflecting / reflecting surface. Out of the light that has entered across the end of the light, the light that has entered the second portion is guided to the other end region of the scanning range via the scanning optical system, and the end on the downstream side in the rotation direction The light incident on the part is not guided to the scanning range,
The light incident on the portion between the first portion and the second portion of the one deflecting reflecting surface passes through the scanning optical system and the one end region and the other end region of the scanning range. Led to the middle region, which is the part between
The optical scanning device, wherein the first and second portions have different lengths in a direction corresponding to a main scanning direction.

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