JP6459056B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly to an optical scanning apparatus that scans a surface to be scanned with light and an image forming apparatus including the optical scanning apparatus.

  In recent years, apparatuses for scanning a surface to be scanned with light have been actively developed.

  For example, Patent Documents 1 and 2 disclose an apparatus 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 by a scanning optical system. Has been.

  However, in the conventional apparatus, it is difficult to scan the surface to be scanned at high speed and high density while suppressing the enlargement of the apparatus.

  The present invention includes a light source device including a light source, a deflector having a plurality of deflection reflection surfaces around a rotation axis for deflecting light from the light source device, and light deflected in a predetermined angle range by the deflector. A scanning optical system that leads to a scanning surface, and a light receiving device that is disposed on the opposite side to the light source with respect to the optical axis of the scanning optical system and that receives light deflected in a predetermined direction outside the predetermined angular range by the deflector A part of the light from the light source device is deflected by the deflector to an upstream end in a rotation direction of the deflector within the predetermined angle range and an angle range including the predetermined direction. From the light source device, and at least a part of the remaining portion is reflected from the other deflection reflection surface adjacent to the downstream side in the rotation direction with respect to the one deflection reflection surface. When the light is deflected to the angular range After the light from the light source device is reflected in the predetermined direction by the one deflection reflection surface, and the light from the light source device is reflected by the one deflection reflection surface to the upstream end in the predetermined angle range. Before, it is an optical scanning device in which the normal line of the other deflecting / reflecting surface is parallel to the incident direction of light from the light source device when viewed from the rotation axis direction.

  According to the present invention, it is possible to scan a surface to be scanned at high speed and high density while suppressing an increase in size of the apparatus.

1 is a diagram illustrating a schematic configuration of a laser printer according to a first embodiment. It is a figure for demonstrating the optical scanning device of FIG. FIGS. 3A to 3C are diagrams (No. 1 to No. 3) for explaining the deflection operation of the polygon mirror, respectively. FIGS. 4A to 4C are diagrams (Nos. 4 to 6) for explaining the deflection operation of the polygon mirror, respectively. FIGS. 5A to 5C are diagrams (No. 7 to No. 9) for explaining the deflection operation of the polygon mirror, respectively. It is a figure which shows schematic structure of the color printer of 2nd Embodiment. FIG. 7A is a diagram for explaining the optical scanning device of FIG. 6, and FIG. 7B is a diagram for explaining a seven-sided polygon mirror. FIGS. 8A to 8C show the synchronization detection timing, return light generation timing, write start timing, and write end timing in the left and right optical scanning systems of Examples 1 to 3 of the second embodiment, respectively. It is a table | surface which shows the angle with respect to the reference axis of the normal line of a deflection | deviation reflective surface, and the maximum swing angle (deflection angle range) in a deflection | deviation reflective surface.

<< First Embodiment >>
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 5C. 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 FIG. 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, a polygon mirror 3 as a deflector, a scanning optical system 4 including an fθ lens 9 as a scanning lens, a toroidal lens 10 and a folding mirror 11, a reflection mirror 14, a synchronous lens 15, and a PD 16 as a light receiving element (photo A synchronization detection system 13 including a diode) 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 regular hexagonal columnar member having a low height, and each side surface is a deflecting reflection surface. That is, the polygon mirror 3 is a six-sided rotary polygon mirror having six 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.

  The light beam deflected to a predetermined angle range within the deflection angle range is transmitted through the fθ lens 9 and the toroidal lens 10, is returned to the optical path by the return mirror 11, and is collected on the scanned surface 901 a (the surface of the photosensitive drum 901). To be lighted. 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.

  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 by the deflecting reflecting surface is vignetted.

  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. 3 (A) to 3 (C).

  Here, as an example, the polygon mirror 3 is a regular hexagonal rotary polygonal mirror having six deflection reflection surfaces around the rotation axis, and the diameter of an inscribed circle inscribed in the six deflection reflection surfaces is 18 mm. Six deflection reflecting surfaces are located at a distance of 9 mm from the rotation center (rotation axis).

  The incident light beam to the polygon mirror 3 is −55 ° with respect to the reference axis (however, the angle measured in the mirror rotation direction with respect to the reference axis is +, and the angle measured in the direction opposite to the mirror rotation direction is −). The same applies hereinafter. 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, an area 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 a “scanning area”.

  As can be seen from FIG. 3A, when the incident light beam is deflected by the polygon mirror 3 toward the scanning start position, a part of the incident light beam is incident on one deflection reflection surface and scanned by the one deflection reflection surface. Reflected toward the start position, at least a part of the remaining portion protrudes from one deflecting reflecting surface, enters the other deflecting reflecting surface adjacent to the downstream side of the one deflecting reflecting surface, and scans with the other deflecting reflecting surface. Reflected out of the area. That is, when the incident light beam is deflected toward the scanning start position by the polygon mirror 3, the incident light beam is incident across two adjacent deflecting reflection surfaces.

  For this reason, at the scanning start position, the reflected light flux width is 3.5 mm, which is smaller than the incident light flux width of 3.8 mm.

  As can be seen from FIG. 3B, when the incident light beam is deflected by the polygon mirror 3 toward the scanning center position (intermediate position between the scanning start position and the scanning end position in the scanning region), substantially all of the incident light beam is The light is incident on one deflection reflection surface and reflected toward the scanning region by the one deflection reflection surface.

  For this reason, at the scanning center position, the reflected light beam width is 3.8 mm, which is equal to the incident light beam width 3.8 mm.

  As can be seen from FIG. 3C, when the incident light beam is deflected by the polygon mirror 3 toward the scanning end position, a part of the incident light beam is incident on one deflection reflection surface and scanned by the one deflection reflection surface. Reflected toward the start position, at least a part of the remaining portion protrudes from one deflecting reflecting surface and is incident on another deflecting reflecting surface adjacent to the upstream side of the one deflecting reflecting surface. Reflected out of the scanning area. That is, when the incident light beam is deflected toward the scanning end position by the polygon mirror 3, the incident light beam is incident across the two deflecting reflection surfaces.

  For this reason, at the scanning end position, the reflected light flux width is 3.5 mm, which is smaller than the incident light flux width of 3.8 mm.

  As can be seen from the above description, in the first embodiment, the polygon mirror 3 emits light toward the intermediate region in the main scanning direction of the scanning region (the region excluding both the vicinity of the scanning start position and the vicinity of the scanning end position in the scanning region). When the beam is deflected, almost all of the incident light beam is reflected by the deflecting reflecting surface toward the scanning region, whereas light is deflected by the polygon mirror 3 toward the vicinity of the scanning start position and the scanning end position of the scanning region. In this case, a part of the incident light beam is reflected toward the scanning region by the deflecting reflection surface, but the remaining part is not reflected toward the vignetting and scanning region (see FIGS. 4A to 4C).

  As described above, in the first embodiment, by adopting the above-described vignetting configuration, the entire area including both end portions and the intermediate portion (portions excluding both end portions) of the deflection reflection surface in the main scanning corresponding direction is substantially reflected. Therefore, the deflection angle range of the deflecting / reflecting 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 region in the main scanning direction or a writing width).

  When downsizing the polygon mirror, 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 without the vignetting of the light beam in which only the intermediate portion of the deflection reflection surface in the main scanning corresponding direction becomes a substantial reflection surface is adopted, the deflection angle range becomes narrow, and in order to obtain a desired scanning width. It is necessary to set the focal length of the scanning lens to be long, and the device (optical scanning device) becomes large.

  Normally, when a six-surface polygon mirror is used, the inscribed circle radius is set to about 16 mm to 18 mm. However, in the first embodiment, even if the inscribed circle radius is set to about 9 mm, the focal length of the scanning lens is increased. A desired scanning width can be ensured without this. 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 made constant and the number of surfaces is increased, the deflecting / reflecting surface becomes smaller. In this case, if the configuration without the vignetting of the light beam is adopted, the deflection angle range becomes narrow and the apparatus becomes large. It is forced to become.

  In the first embodiment, since the vignetting configuration is employed, high-speed and high-density scanning can be realized while suppressing an increase in the size of the apparatus.

  However, as the number of polygon mirrors increases, it becomes more difficult to ensure the angle of view of the scanning area (also referred to as an image area or a writing area). .

  Accordingly, by performing both polygon facet reduction and downsizing (decreasing the inscribed circle radius), high-speed and high-density scanning can be realized as much as possible.

  For example, the number of polygon mirrors is increased from six to seven, and the inscribed circle radius is changed from 18 mm to about 13 to 14 mm, thereby increasing the number of polygon mirror rotations and scanning lines in one rotation. The number of scanning lines can be increased, and the number of scanning lines for scanning the surface to be scanned per unit time can be significantly increased, and high-speed and high-density scanning can be realized.

  By the way, before the light is deflected toward the scanning region 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.

  Further, in the first embodiment, the light beam vignetted by the polygon mirror 3 returns to the semiconductor laser 1 as reflected light from the polygon mirror 3 to turn off the output of the semiconductor laser 1 in order to avoid instability ( In the following, it is necessary to set “return light extinction time”).

  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, it is not as effective as increasing the number of polygon mirrors.

  In addition, the inscribed circle radius of the polygon mirror needs to be optimally set according to the optical characteristics in order to determine the amount of vignetting of the writing light beam and the synchronous detection light beam incident near the scanning start position and 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-enhancing specifications.

  Here, in the first embodiment, of the incident light beams from the light source device, a light beam vignetted on one deflection reflection surface is incident on another deflection reflection surface adjacent to the downstream side with respect to the one deflection reflection surface. Timing at which the normal line becomes parallel to the incident direction of light from the light source device (hereinafter also referred to as “returned light generation timing”), that is, in the incident direction of light on the other deflecting reflecting surface, Since the light reflected by the other deflecting reflection surface returns to the light source at the timing when the light reflection directions coincide with each other (see FIG. 5B), the light source is turned off at this timing to prevent the generation of return light. ing.

  By the way, since it is necessary to turn off the light source at the return light generation timing, the return light generation timing is set to the writing lighting time (the time from the scan start timing to the scan end timing) in one deflection scan on one deflection reflection surface. Need to set outside).

  If the return light generation timing is set after the writing lighting time in one deflection scanning on one deflection reflecting surface, the angle of view of the writing area is reduced as will be described in detail later in the second embodiment. Since it becomes difficult to lay out the light source device, polygon mirror, scanning optical system, and synchronization detection system while suppressing, the return light generation timing is set before the writing lighting time (before the scanning start timing). (See FIGS. 5B and 5C).

  Further, as will be described in detail later in the second embodiment, if the return light generation timing is set after the synchronous lighting time (synchronization detection timing), the degree of freedom of the layout is improved. It is set after the synchronous lighting time (see FIGS. 5A and 5B). Although the degree of freedom of the layout is inferior, the return light generation timing may be set before the synchronous lighting time.

  Therefore, in the first embodiment, the return light extinction time is set after the synchronous lighting time and before the writing lighting time.

  The optical scanning device 900 according to the first embodiment described above includes a light source device including the semiconductor laser 1 (light source) and the imaging optical system 2, and a plurality of deflection reflection surfaces that deflect light from the light source device as a rotation axis. Around the polygon mirror 3 (deflector), the scanning optical system 4 for guiding the light deflected to the scanning angle range (predetermined angle range) by the polygon mirror 3 to the surface to be scanned 901a, and the scanning angle range by the polygon mirror 3 PD16 (light receiving element) disposed on the optical path of light deflected in a predetermined outside direction, and the light from the light source device is angled including the upstream end of the scanning angle range and the predetermined direction by the polygon mirror 3 Is deflected to the angular range by one deflecting reflecting surface, and at least a part of the remaining part is reflected by another deflecting reflecting surface adjacent to the downstream side of the one deflecting reflecting surface. Light from the device When deflected to the above angle range, before the light is reflected by the one deflection reflection surface to the upstream end of the scanning angle range, the normal line of the other deflection reflection surface is seen from the rotation axis direction of the polygon mirror 3. This coincides with the incident direction of light from the light source device.

  In this case, the polygon mirror 3 can be downsized and multifaceted while suppressing the narrowing of the scanning angle range.

  As a result, it is possible to scan the surface to be scanned at high speed and high density while suppressing an increase in the size of the apparatus.

  In the first embodiment, a part of the light beam deflected near the upstream end and the downstream end of the scanning region is not reflected toward the surface to be scanned (kicked by the deflecting / reflecting surface of the polygon mirror). The mirror is downsized and can be 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, a polygon mirror is enlarged or an overfilled optical system in order to prevent a part of the light beam from vignetting around the scanning area in order to make the light amount constant while ensuring a desired angle of view of the writing area. Was adopted.

  In contrast, the first embodiment employs a configuration in which an underfilled optical system is employed and a part of the light beam is vignetted in the peripheral portion of the scanning region in the main scanning corresponding direction. The polygon mirror can be reduced in size and multifaceted while ensuring a desired angle of view.

  On the other hand, when the polygon mirror is reduced in size and multifaceted with a conventional optical scanning device without vignetting, the deflection angle range becomes smaller. Therefore, if the desired angle of view of the writing area is to be secured, the polygon mirror becomes larger. This causes problems such as a decrease in the number of rotations of the polygon mirror, noise, and an increase in the size of the apparatus.

  Further, when the light from the light source device is deflected in the angle range, after the light from the light source device is reflected in the predetermined direction by one deflection reflection surface, the other light is seen from the direction of the rotation axis of the polygon mirror. The normal line of the deflection reflection surface is parallel to the incident direction of light from the light source device.

  In this case, the narrowing of the scanning angle range can be further suppressed, and the enlargement of the apparatus can be further suppressed.

  Further, the PD 16 is arranged on the upstream side in the rotational direction of the polygon mirror 3 with respect to at least a part of the optical path of the remaining light from the light source device reflected by another deflecting reflection surface.

  In addition, the incident direction of light from the light source device to the deflection reflection surface and the reflection direction of the light from the deflection reflection surface are in the same plane perpendicular to the rotation axis of the polygon mirror 3.

  In this case, it is possible to suppress the deterioration of the wavefront aberration and the light quantity loss on the one deflecting / reflecting surface.

  Further, when the light from the light source device is deflected in the above-mentioned angular range, the timing at which the normal lines of the other deflection reflection surfaces are parallel to the incident direction of the light from the light source device when viewed from the rotational axis direction of the polygon mirror 3. Then, since no light is emitted from the light source device, no return light is generated, and output fluctuation of the light source is suppressed.

  Further, since the PD 16 is disposed on the side opposite to the semiconductor laser 1 with respect to the optical axis of the scanning optical system, the degree of freedom in layout of the light source device, polygon mirror, scanning optical system, synchronization detection system 13 and the like is increased. high.

  Further, when the light from the light source device is deflected by one deflection reflection surface into an angle range including the downstream end of the scanning angle range, a part of the light is reflected by the one deflection reflection surface in the angle range, and the remaining At least part of the light is incident on another deflecting / reflecting surface adjacent to the upstream side of the one deflecting / reflecting surface.

  In this case, narrowing of the scanning angle range can be further suppressed.

  In addition, since the beam diameter in the direction corresponding to the main scanning direction of the light incident on the polygon mirror 3 is smaller than the width of the deflecting / reflecting surface in the direction corresponding to the main scanning direction, the maximum wide angle in the underfilled optical system. As a result, the polygon mirror 3 can be reduced in size and multifaceted.

  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.

<< Second Embodiment >>
Hereinafter, the second embodiment will be described with reference to FIGS. 6 to 8C.

  In the second embodiment, the number of faces of the polygon mirror is 7 and the inscribed circle radius is 14 mm. The 6 faces that have been widely used in the past have an inscribed circle radius of 18 mm, and both the number of faces is increased and the size is reduced. Yes.

  FIG. 6 shows a schematic configuration of a color printer 2000 as an image forming apparatus according to the second embodiment.

  As shown in FIG. 6, a transport belt 17 that transports 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.

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

  More specifically, as shown in FIGS. 6 and 7A, the optical scanning device 1000 includes four light source devices corresponding to four colors (Y, M, C, and K), and each light source device as an example. Are provided with one polygon mirror for deflecting light from the four light sources, four scanning optical systems provided individually corresponding to the four light source devices, and two synchronization detection systems.

  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.

  In FIG. 6 and FIG. 7A, since the light source devices and scanning optical systems of the optical scanning systems 6Y and 6M are arranged 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. To do. 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.

  In addition, two lights emitted from the light source device of the light scanning system on the lower left side and the lower right side are incident on two different deflecting reflection surfaces on the lower stage of the polygon mirror, and corresponding two scans on the two deflecting reflection 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.

  In particular, in the second embodiment, as shown in FIG. 7B and FIG. 7A, the number of polygon mirrors is 7 and the inscribed circle radius is 14 mm. Further, when the normal of the surface to be scanned is the reference axis (0 degree), the field angle of the writing area is ± 38 ° (total 76 °, half field angle 38 °), and the right-side optical scanning system synchronization detection light beam Is 40.5 °, and the incident angle of the left optical scanning system synchronization detection light beam is −43.5 °. The incident angle of the light beam (incident light beam) incident on the polygon mirror is 62 °. Here, the angle measured upward from the reference axis is +, and the angle measured downward is-.

  8A to 8C show the synchronization detection timing, return light generation timing, write start timing, and write in the left and right optical scanning systems in Examples 1 to 3 of the second embodiment, respectively. The angle with respect to the reference axis of the normal line of the polygon mirror at the end timing, and the maximum swing angle (deflection angle range) on the deflection reflection surface (one surface) are shown. Unlike the angle of view, when the incident angle of the light beam incident on the polygon mirror is 62 °, the normal line of the deflecting reflecting surface when the normal line of the scanned surface and the reflected light on the deflecting reflecting surface are parallel to each other The angle is 31 °.

  In the left optical scanning system, a light-receiving element for synchronization detection (for example, PD) is disposed on the opposite side of the light source with respect to the optical axis of the scanning optical system. In the right optical scanning system, a light-receiving element for synchronization detection (for example, PD) is disposed on the same side as the light source with respect to the optical axis of the scanning optical system.

  In the first and third embodiments, as shown in FIGS. 8A and 8C, in the left optical scanning system, the incident light beam from the light source device is deflected at one deflection reflection surface of the polygon mirror. Timing when the normal line of the other deflecting / reflecting surface adjacent to the downstream side of the one deflecting / reflecting surface is parallel to the incident direction (optical path) of the incident light beam. Timing) when the light reflected by one deflecting reflecting surface is incident on the light receiving element disposed on the side opposite to the light source with respect to the optical axis of the scanning optical system, and reflected by one deflecting reflecting surface. It is laid out so that it falls between the timing when light enters the scan start position (write start position).

  Specifically, as shown in FIGS. 5A to 5C, in the second embodiment, since the incident angle of the incident light beam to the polygon mirror is 62 °, one deflection of the polygon mirror is performed. When the normal angle of another adjacent deflecting reflecting surface that reflects a part of the luminous flux vignetted by the reflecting surface is 62 °, the reflection direction (traveling direction) of the part of the vignetting luminous flux is the incident direction of the incident luminous flux. That is, the normal lines of the other deflecting and reflecting surfaces are parallel to the incident direction of the incident light beam (the broken line arrows in FIGS. 5A to 5C are vignetting light beams).

  At this time, as can be seen from the table on the left side of FIG. 8A, in the case of a 7-sided polygon mirror, the reflection direction of the vignetting light beam substantially coincides with the incident direction of the incident light beam (at the return light generation timing). ) The angle of the normal line of the deflecting reflecting surface is 10.57 ° (the inner angle of the 7-sided polygon is 128.57 °). The normal angle of the deflecting reflecting surface is 9.25 ° at the synchronization detection timing and 12 ° at the writing start timing, and is between the synchronization detection timing and the writing start timing at the return light generation timing.

  The left optical scanning system rotates the light flux clockwise (clockwise) in FIG. 7A, and therefore, as the normal angle of the deflecting reflecting surface in FIG. The sequence proceeds in the order of return light generation timing and writing start timing. As described above, it is desirable to turn off the light source at the return light generation timing. At the return light generation timing, the light source may be turned on with a minute output that does not affect the output of the light source even if the return light is actually generated. Note that in FIG. 7A, for convenience, only two of the four scanned surfaces are illustrated.

  As can be seen from the table on the left side of FIG. 8 (A), in the left optical scanning system, the angle difference between the normal lines of the deflecting reflecting surface between the synchronization detection timing and the return light generation timing is 1.32 °. The angle difference between the normal lines of the deflecting reflecting surface between the return light generation timing and the writing start timing is 1.43 °. In the optical scanning system on the right side, the angle difference of the normal line of the deflecting reflecting surface between the synchronization detection timing and the writing start timing is 1.25 °, and the deflection between the writing end timing and the return light generation timing is The angle difference between the normal lines of the reflecting surfaces is 1.43 °. Although it depends on the number of rotations of the polygon mirror, if the number of mirror surfaces is 7 even at 50000 rpm, there is a time of 3.3 μs per degree. It can be considered that it is sufficiently possible to light at the start timing.

  For example, in the second embodiment shown in FIG. 8B, the return light generation timing is set before the synchronization detection timing. When the half angle of view of the writing area is fixed at 38 ° and the angle of the synchronous detection light beam is also fixed, the incident angle of the light beam (incident light beam) emitted from the light source device and incident on the polygon mirror needs to be 56.5 °. Occurs. (In FIG. 5B, it is necessary to bring the reflected light downward in the figure from the reflected light toward the left side, and the incident angle moves in the direction of decreasing).

  As described in the first embodiment shown in FIG. 8A, the reflection angle (reflection direction) of the return light to the polygon mirror is determined by the incident angle (incident direction) of the incident light beam to the polygon mirror. (In Example 2, the incident angle of the incident light beam to the polygon mirror is set so that the minimum angle difference is the same as in Example 1. Specifically, it is set to 1 degree or more. )

  In the second embodiment, in the left optical scanning system, the angle difference between the normal lines of the deflecting reflecting surface between the return light generation timing and the synchronization detection timing is 1.43 °, and the synchronization detection timing and the write start timing are The angle difference of the normal of the deflecting reflecting surface between the two is 2.75 °. In the optical scanning system on the right side, the angle difference of the normal line of the deflection reflection surface between the synchronization detection timing and the writing start timing is 1.25 °, and the deflection between the writing end timing and the return light generation timing. The angle difference between the normals of the reflecting surfaces is 4.18 °.

  Here, in the second embodiment, the incident angle of the light beam to the polygon mirror is the same in the left and right optical scanning systems. Although the incident angle to the polygon mirror can be made different between the left and right optical scanning systems, it is advantageous in terms of cost to employ substantially the same scanning lens in the left and right optical scanning systems. If substantially the same scanning lens is used in the left and right optical scanning systems, the optical characteristics of the left and right optical scanning systems will be different if the angle of incidence on the polygon mirror differs between the left and right optical scanning systems. Therefore, it is desirable that the angle of incidence on the polygon mirror is the same in the left and right optical scanning systems.

  Although it depends on the rotation speed of the polygon mirror, even if the rotation speed is 50000 rpm as described above, if the number of polygon mirror faces is 7, it takes 3.3 μs per degree, which is sufficient for the time interval. It seems possible.

  However, in this case, in the right optical scanning system, the incident angle to the polygon mirror is changed from 62 ° to 56.5 °, so that the light beam incident on the polygon mirror (incident angle 56.5 °) and the synchronization detection light beam (40.5 °) is too close (angle A in FIG. 7A becomes too small), interference with optical elements arranged between the light source and the polygon mirror, elements of the scanning optical system, This is not preferable because it causes interference with the jig during attachment. Or, productivity is remarkably poor, leading to an increase in cost.

  That is, it is desirable that the incident light beam and the synchronization detection light beam be separated from each other by at least about 20 °. In order to realize this, it is necessary to reduce the angle of view ± 38 ° (total 76 °) of the writing area. When the angle of view is reduced, it is necessary to increase the optical path length in the scanning optical system, resulting in an increase in the size of the apparatus and a deterioration in the beam spot diameter.

  The light amount monitor of the light source may be implemented within the deflection angle range on one surface of the polygon mirror regardless of the arrangement of the optical elements. The time required for monitoring the light amount is long, unlike turning off at the return light generation timing. However, in the right optical scanning system, the time from the return light generation timing to the next synchronization detection timing is long, and in the left optical scanning system, the time from the write end timing to the next synchronization detection timing is long. It is. There is no problem if the light intensity monitor does not enter the synchronous detection system or scanning area, and the light quantity monitor does not use the light scanned by the polygon mirror. I do not receive it. As described above, the LD (laser diode) monitors the amount of light using a PD disposed on the opposite side to the emission direction.

  Also in the second embodiment, when light is deflected by the one deflecting / reflecting surface to the vicinity of the upstream end of the writing region, before the light reflected by the one deflecting / reflecting surface enters the writing start position (scanning start position). A part of the incident light beam that protrudes from one deflection reflection surface is incident so that the normal line of another deflection reflection surface adjacent to the downstream side with respect to the one deflection reflection surface is parallel to the incident direction of the incident light beam. Thus, it is possible to reduce the size of the polygon mirror and increase the number of surfaces while suppressing the increase in size of the apparatus. Furthermore, after the light reflected by one deflection reflection surface is incident on the light receiving element disposed on the opposite side of the light source with respect to the optical axis of the scanning optical system, the normal line of the other deflection reflection surface is incident on the incident light beam. By laying out so as to be parallel to the direction, it is possible to further suppress the enlargement of the apparatus.

  Further, in the first and second embodiments in which a part of the incident light beam is kicked when the incident light beam is deflected toward both ends (upstream end and downstream end) of the scanning region, the field angle of the writing region is equalized by ±. It is desirable that the amount of vignetting at both ends of the deflecting / reflecting surface in the main scanning corresponding direction is matched. Therefore, if the field angle of the writing area is substantially equal to ± when the normal of the surface to be scanned is set to 0 degree and the configuration of the second embodiment is satisfied, the wide angle of the field angle of the writing area is satisfied. Can be achieved.

  As described above, in the first and second embodiments, “a light beam that is not reflected toward the scanning surface by one deflection reflection surface (a vignetting light beam) is incident on the downstream side with respect to the one deflection reflection surface. The timing at which the normal line of another deflecting reflecting surface adjacent to the light beam is parallel to the incident direction of the incident light beam is equal to the timing at which the light receiving element disposed on the opposite side of the light source with respect to the optical axis of the scanning optical system And the beam width in the main scanning direction of the light beam incident on the polygon mirror is deflected by the polygon mirror. A configuration is adopted in which a part of the light beam is not reflected toward the scanning surface only near the upstream end and the downstream end within the deflection angle range, which is smaller than the width of the reflecting surface in the main scanning correspondence direction. In this case, the number of polygon mirror surfaces can be increased from the conventional 6 surfaces to 7 surfaces and the size can be reduced, and the angle of view of the desired writing area can be secured, so there is no need to set a long optical path length. High-speed and high-density scanning can be realized while suppressing the enlargement of the apparatus. Furthermore, since the focal length can be set short in a low-cost scanning optical system composed of a single scanning lens, the beam spot diameter on the surface to be scanned can be reduced and the optical characteristics can be reduced. It becomes possible to improve.

  The timing at which the reflection direction on the other deflecting / reflecting surface coincides with the incident direction of the incident light beam on the other deflecting / reflecting surface is such that the light beam reflected on the one deflecting / reflecting surface enters the light receiving element or the scanning region. Since it is different from the timing, it is possible to suppress an insufficient amount of light received by the light receiving element and a disturbance at the edge portion of the output image (final image).

  In general, the number of polygon mirrors used in the underfilled optical system is six or less, and in order to prevent all light beams from being vignetted on the deflecting reflection surface when the number is seven or more, the polygon mirror has Since it is necessary to increase the tangent radius and the number of rotations of the polygon mirror is reduced, it is not adopted.

  For example, a portion of the light beam used for synchronization detection that enters the vicinity of the end of the deflecting / reflecting surface of the polygon mirror is vignetted on the deflecting / reflecting surface, resulting in a decrease in light amount and deterioration (thickening) of the beam spot diameter.

  Regarding the deterioration of the beam spot diameter, the amount of change is as small as about several μm, and the influence on the final image is small. On the other hand, regarding the light amount reduction, the image quality deteriorates, such as a synchronization detection error due to insufficient light amount, and in the case of an image portion, density unevenness occurs at the end due to the light amount reduction.

  As a countermeasure against a decrease in the amount of light, a correction method that changes the output of the light source in the scanning direction is generally used. Specifically, it is possible to increase the amount of light emitted from the light source by the amount corresponding to the decrease in the amount of light and make it constant on the image plane. Further, the synchronization can also be handled by adjusting the sensitivity of the synchronization detection PD.

  Further, in the second embodiment, in order to further widen the angle of view of the writing area and reduce the size of the polygon mirror, one of the left and right optical scanning systems sharing one polygon mirror (for example, the left side of FIG. 7A). In this optical scanning system, the synchronization detection light-receiving element is disposed on the opposite side of the light source with respect to the optical axis of the scanning optical system. The synchronization detection is performed only by the light receiving element for synchronization detection. That is, the write start timing is determined on both sides of the opposing scan (left and right optical scanning systems) by synchronous detection of only one side of the opposing scan (only one of the left and right optical scanning systems).

  For example, when the angle of view of the writing area is widened in the second embodiment, the time from the return light generation timing to the write start timing is shortened, and it is difficult to turn off at the return light generation timing.

  Therefore, it is conceivable to reduce the incident angle of the light beam to the polygon mirror and to increase the time difference between the return light generation timing and the writing start timing. At this time, as described above, in the right optical scanning system (the optical scanning system that performs synchronous detection on the light source side), the angle difference between the incident light beam on the polygon mirror and the synchronous detection light beam becomes small. When the angle of the synchronization detection light beam is also reduced in order to avoid interference between the incident light beam on the polygon mirror and the synchronization detection light beam, an interval between the synchronization detection light beam and the light beam toward the writing start position (also referred to as a writing start light beam) is maintained. This makes it difficult to establish a layout.

  However, the problem of layout can be solved by eliminating the synchronization detection of the right optical scanning system (synchronous detection on the light source side) and performing only the synchronization detection of the left optical scanning system (synchronous detection on the opposite light source side). Even if the incident angle of the light beam to the polygon mirror is reduced, the right-side optical scanning system does not detect synchronization, so it is sufficient to arrange the incident light beam and the writing start light beam so that they do not interfere with each other. In addition, the angle of view of the image area (writing area) can be increased. Specific numerical values at this time are described in FIG. 8C which is a table of the third embodiment. When single-sided synchronization detection is performed, the right-side optical scanning system synchronization detection system in FIG.

  Specifically, in order to ensure the return light suppression timing and the writing start timing, the incident angle of the light beam on the polygon mirror is reduced from, for example, 62 ° to 60.5 °. Further, the image area is expanded from ± 38 ° to ± 40 °, for example. As a result, if the synchronization detection angle is left at 40.5 ° in the right optical system, the interval from the start of writing the image area becomes as narrow as 0.25 °, making it difficult to establish the layout.

  Further, since the incident angle of the light beam to the polygon mirror is also reduced, it is difficult to arrange the incident light beam, the synchronization detection light beam, and the writing light beam to the polygon mirror without interfering with the arrangement of the optical elements. . That is, in the second embodiment, it is actually difficult to use the synchronization detection system in the right optical scanning system (the optical scanning system that performs synchronization detection on the light source side).

  On the other hand, in the left optical scanning system, in order to increase the interval between the return light and the writing start light beam, the incident angle of the light beam on the polygon mirror is reduced from 62 ° to 60.5 °, for example. At this time, since the interval between the synchronization detection light beam and the return light becomes narrow, the image height of the synchronization detection light beam is set to −45 °. The angle of the synchronization detection light beam (synchronization angle) and the incident angle of the light beam on the polygon mirror can be optimally set in consideration of the amount of light necessary for synchronization. For example, the incident angle of the light beam to the polygon mirror can be appropriately set to 60.7 °, the synchronization angle to −44.5 °, and the like.

  In FIG. 8C, in the left optical scanning system, the angle difference between the return light and the writing start light beam is the smallest, 1.18 degrees. As described in the first embodiment, it is considered that the layout can be established if the angle difference can be secured by 1 ° or more (a time of 3.3 μs can be secured even when the polygon mirror rotational speed is 50000 rpm. The actual rotational speed is Often lower.

  In other words, a configuration in which only the synchronization detection system on the opposite side of the light source with respect to the optical axis of the scanning optical system is synchronized (the optical scanning system on the left side in FIG. 7A) can further widen the angle of view. It can be realized. Also in this case, “the method of another deflecting / reflecting surface adjacent to the downstream side of the one deflecting / reflecting surface on which light that is not reflected by the one deflecting / reflecting surface toward the scanning surface (vignetting light) is incident. The timing at which the line is parallel to the incident direction of the incident light beam is the timing at which the light is reflected toward the light receiving element disposed on the opposite side of the light source with respect to the optical axis of the scanning optical system on one deflection reflection surface, By setting the timing so that the light is reflected toward the scanning start position on one deflecting reflecting surface, the writing area can be maximized in view angle.

  As described in the first embodiment, when the return light generation timing is set before the synchronization detection timing (for example, in the case of the second embodiment), it is necessary to reduce the incident angle to the polygon mirror. “A light beam that is not reflected by one deflecting reflection surface toward the scanning surface (a vignetting light beam) is incident, and the normal line of another deflecting reflecting surface adjacent to the downstream side of the one deflecting reflection surface is incident on the incident light beam. The timing at which the light becomes parallel to the direction is the timing at which light is reflected toward the light receiving element disposed on the opposite side of the light source with respect to the optical axis of the scanning optical system at one deflection reflection surface, and the one deflection reflection surface. Set to be between the timing when the light is reflected toward the writing start position ”, and the synchronization detection on the light source side (synchronous detection system of the right optical scanning system) is abolished, and the light flux to the polygon mirror is eliminated. Widen by setting the incident angle small The keratinocytes can be achieved.

  Next, a description will be given of the one-side synchronization described above.

  Usually, the left and right optical scanning systems detect synchronously before starting writing. That is, the write start timing is determined by both-side synchronization. In this case, since the synchronization detection and the writing start are performed on the same polygon mirror surface as the light beam from the same light source and the time interval after the detection is short, the writing start position can be set with high accuracy.

  On the other hand, in the case of one-side synchronization, it is easy to set the writing start timing of the scanning optical system on the opposite side. However, if the deflection detection surface that deflects the synchronization detection light beam and the writing light beam is different, the shape error between the deflection reflection surfaces is reduced. Be susceptible.

  For this reason, it is desirable to set the timing so that the synchronous detection light beam and the writing start light beam on the opposite side are deflected by the same deflection reflection surface. In addition, the opposite side is prone to be affected by uneven rotation of the polygon mirror because the write start time from synchronization detection is long. Since this rotation unevenness occurs at a relatively high cycle, it is possible to stably rotate the polygon mirror by performing feedback control by measuring the time of one rotation of the polygon mirror. As a result, it is possible to set the writing start position with high accuracy even with synchronous detection on only one side.

  In addition, at the time of shipment from the factory, the writing start timing may be set by measurement so that the image areas corresponding to the left and right optical scanning systems coincide so as to cancel the fluctuation of the writing start position due to various error factors. Is possible.

  In the optical scanning device 1000 according to the second embodiment described above, there are four light source devices, and two scanning optical systems are arranged on both sides of the polygon mirror (deflector) so as to correspond to the four light source devices. There are four scanning surfaces corresponding to the four scanning optical systems, and each scanning optical system guides the light emitted from the corresponding light source device and deflected by the polygon mirror to the corresponding surface to be scanned, and PD (light receiving element) The scanning start timing of each scanned surface is determined based on the output signal.

  According to the optical scanning device 1000, a color image-compatible optical scanning device that can solve the disadvantages due to layout restrictions in the synchronization detection of one of the left and right optical scanning systems and has the same effects as the first embodiment is realized. it can.

  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.

  In each of the above embodiments, when the deflection angle range (total angle of view) by the deflection reflection surface of the polygon mirror is ω1, and the half angle of view of the scanning angle range (1/2 of the angle of view of the scanning angle range) is ω2, It is preferable that ω2 / ω1 ≧ 0.7 is satisfied.

  When ω2 / ω1 is less than 0.7, the angle of view becomes narrow, and a sufficient margin is generated in the scanning angle range of the deflecting / reflecting surface of the polygon mirror. In other words, even if the configuration of each embodiment is adopted for high-speed and high-density scanning, only the inscribed circle radius of the polygon mirror is reduced, and the number of polygon mirror faces is not optimized. For this reason, the number of faces of the polygon mirror and the inscribed circle radius cannot be balanced, and the potential for high speed and high density cannot be maximized.

  By setting ω2 / ω1 to be 0.7 or more, the number of polygon mirror faces can be set optimally for the angle of view of the required image area (writing area). By adopting the configuration described in the embodiment, it is possible to improve the high speed, high density, and wide angle of view to the limit.

  Further, in each of the above embodiments, when a multi-beam method for scanning one surface to be scanned with a plurality of light beams for high-speed and high-density scanning, the plurality of light beams for scanning the surface to be scanned is used. It is desirable to obtain a synchronization signal by making a subsequent light beam incident on a light receiving element (for example, PD).

  For example, when an LDA (laser diode array) having a plurality of light emitting points in a package is used as a multi-beam light source, it transmits through a coupling lens that converts a divergent light beam from the light source into parallel or substantially parallel light in the main scanning section. Thus, the light enters the polygon mirror at a slightly different angle. As a result, the rotation angle of the polygon mirror reflected to the light receiving element for synchronization detection differs between the beams. For example, in the case of two beams, as the light beam for scanning the surface to be scanned, the light beam scanned in advance (incident on the deflection reflection surface) and the light scanned in the subsequent direction (incident on the deflection reflection surface) Become a beam.

  In the optical scanning device of each of the embodiments described above, the vignetting of the light beam by the polygon mirror increases and the amount of light decreases toward the periphery within the deflection angle range. If the amount of light to the light receiving element for synchronous detection arranged in the vicinity of the deflection angle range is significantly reduced, there is a possibility that the light cannot be detected. Although it is possible to increase the amount of light of the light source in synchronization detection, it is needless to say that the amount of vignetting in the polygon mirror should be as small as possible because the output range of the light source is limited.

  Therefore, the influence of the light amount reduction can be reduced by using the light beam used for the synchronization detection as the light beam that performs the subsequent scanning in the multi-beam (preferably, the light beam that performs the subsequent scanning most). As the subsequent light beam, the reflection position of the light beam toward the synchronous detection on the deflecting / reflecting surface shifts toward the center of the deflecting / reflecting surface, so that the vignetting of the light beam on the deflecting / reflecting surface of the polygon mirror is reduced and the reduction in the amount of light is reduced. It will be possible.

  In short, it is preferable to use a light beam other than the most advanced light beam for synchronous detection.

  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. what. 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. Even in this case, the timing at which the normal line of the other deflecting reflecting surface coincides with the incident direction of the incident light beam (return light generation timing) when viewed from the rotational axis direction of the polygon mirror 3 is the one deflecting reflecting surface. It is preferably before the timing at which light is reflected at the upstream end of the scanning angle range. Furthermore, it is more preferable that the return light generation timing is after the timing at which the light is reflected toward the light receiving element by the one deflection reflection surface.

  In each of the above embodiments, a configuration is adopted in which when the light beam is deflected toward the vicinity of the upstream end and the downstream end of the scanning region, a part of the light beam is vignetted. It is preferable to adopt a configuration in which a part of the light beam is vignetted when the light beam is deflected toward the vicinity of the end. That is, a configuration may be adopted in which a part of the light beam is not vignetted when the light beam is deflected toward the vicinity of the downstream end of the scanning region.

  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 which the inventor came up with the said embodiment and each modification is demonstrated.

  In general, for example, an optical scanning device mounted on an image forming apparatus such as a laser printer deflects a light beam from a light source by a deflector and condenses it on a surface to be scanned by a scanning optical system including a scanning lens such as an fθ lens. Thus, a light spot is formed on the surface to be scanned, and the surface to be scanned is optically scanned (main scan) with this light spot.

  What forms the surface to be scanned is the photosensitive surface of a photosensitive medium such as a photoconductive photosensitive drum. For example, an image forming apparatus represented by a laser printer has a high need for high speed and high image quality, and an optical scanning apparatus to be mounted has a strong demand for high speed and high density. High speed and high density can be dealt with by increasing the rotational speed of the polygon mirror as a deflector, but there is a limit to increasing the rotational speed.

  As a means for solving this problem, a technique of an overfilled optical system is disclosed (for example, see Patent Document 1: Japanese Patent Laid-Open No. 10-206778).

  The overfilled optical system reduces the deflection reflection surface of the polygon mirror as a deflector, increases the number of deflection reflection surfaces without enlarging the circumscribed circle, and makes a large light beam incident in the main scanning direction from the deflection reflection surface. This is a technique for increasing speed and density by increasing the number of scans per rotation without increasing the number of rotations of the mirror.

  However, in the overfilled optical system, since the number of deflecting reflecting surfaces of the polygon mirror is increased, the angle at which deflection is possible is narrow. As a result, in order to ensure a desired writing width in the main scanning direction on the surface to be scanned, it is necessary to lengthen the optical path length from the polygon mirror to the surface to be scanned, which increases the size of the apparatus.

  In addition, since the light beam incident on the polygon mirror is cut out and scanned, the amount of light decreases from the center image height to the peripheral image height.

  On the other hand, for the underfill optical system that makes the light deflector enter the light deflector in a direction opposite to the main scanning direction from the deflecting / reflecting surface of the deflector, the multi-beam writing method that increases the number of light sources without increasing the number of rotations enables high speed. Techniques for dealing with higher density and higher density are widely known.

  However, increasing the number of light sources leads to an increase in the size of the light source driving circuit, resulting in a significant increase in cost. In the optical scanning device, the cost ratio of the light source device including the light source is high, which is a serious adverse effect in providing the optical scanning device at low cost.

  Furthermore, in the optical scanning device corresponding to the full color machine, an optical scanning device corresponding to each of different colors such as yellow, magenta, cyan, and black is necessary, and when the light source corresponding to each color is prepared, Will increase further.

  Therefore, the present applicant has proposed a method for reducing the number of light sources in an underfilled optical system compatible with a color machine in Patent Document 2 (Japanese Patent Laid-Open No. 2005-092129). Specifically, the light beam from one light source is divided into two light beams by using a half mirror or the like, and guided to the scanned surface corresponding to each different color.

  According to Patent Document 2, the number of light sources corresponding to one surface to be scanned increases. However, since this light source can be shared by a plurality of surfaces to be scanned, the number of light sources in the entire optical scanning device can be halved. .

  However, in Patent Document 2, the number of components such as an optical element that divides a light beam is increased, and the light beam from one light source is divided and written on a plurality of scanned surfaces. Compared with a conventional optical system that does not perform beam splitting, the deflectable angle becomes narrower. As a result, in order to ensure a desired writing width in the main scanning direction on the surface to be scanned, it is necessary to lengthen the optical path length from the deflector to the surface to be scanned, which increases the size of the apparatus.

  In Patent Document 2, compared with Patent Document 1 that employs an overfilled optical system, the optical path length increases little, but in addition to the need for high-speed and high-density scanning, there is a great demand for downsizing and cost reduction. For the device, it becomes a big problem. Furthermore, if the angle that can be deflected is small, the size is increased, and when a low-cost scanning lens having a single lens structure is used, the focal length becomes long and the beam spot diameter on the surface to be scanned increases.

  In order to solve the above problems, the inventors have come up with the above embodiments.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser (light source, a part of light source device), 3 ... Polygon mirror (deflector), 6 ... Coupling lens (a part of light source device), 7 ... Aperture element, 8 ... Cylindrical lens (one of light source device) 4) scanning optical system, 9 ... fθ lens (part of scanning optical system), 10 ... toroidal lens (part of scanning optical system), 11 ... folding mirror (part of scanning optical system), 7K, 7C, 7M, 7Y, 901 ... photosensitive drum, 500 ... laser printer (image forming apparatus), 900, 1000 ... optical scanning apparatus, 901a ... photosensitive drum surface (scanned surface), 2000 ... color printer (image forming) apparatus).

Japanese Patent No. 3562190 Japanese Patent No. 4445234 JP 2010-122248 A

Claims (11)

A light source device including a light source;
A deflector that deflects light from the light source device and has a plurality of deflection reflection surfaces around a rotation axis;
A scanning optical system that guides light deflected by the deflector to a predetermined angle range to a surface to be scanned;
A light receiving element that is disposed on the opposite side of the light source with respect to the optical axis of the scanning optical system and that receives light deflected in a predetermined direction outside the predetermined angular range by the deflector;
When the light from the light source device is deflected by the deflector to an upstream end in the rotation direction of the deflector within the predetermined angle range and an angle range including the predetermined direction, a part of the light is reflected on the one deflection reflection surface. Reflected by the angular range, and at least a part of the remaining portion is reflected by another deflecting reflecting surface adjacent to the one deflecting reflecting surface downstream in the rotation direction,
When the light from the light source device is deflected to the angular range, the light from the light source device is reflected in the predetermined direction by the one deflection reflection surface, and the light from the light source device is Before being reflected from the deflection reflection surface to the upstream end of the predetermined angle range, the normal line of the other deflection reflection surface is parallel to the incident direction of the light from the light source device as seen from the rotation axis direction. Optical scanning device.   The light receiving element is disposed on the upstream side in the rotation direction with respect to at least a part of the optical path of the remaining portion of the light from the light source device, which is reflected by the other deflection reflection surface. The optical scanning device according to claim 1.   The beam width in the direction corresponding to the main scanning direction of the light emitted from the light source device and incident on the one deflection reflection surface is narrower than the width of the one deflection reflection surface in the direction corresponding to the main scanning direction. The optical scanning device according to claim 1 or 2, characterized in that   When the light from the light source device is deflected by the deflector to an angle range including the downstream end in the rotation direction of the predetermined angle range, a part is reflected to the angle range by the one deflection reflection surface, The at least part of the remaining portion is incident on another deflecting / reflecting surface adjacent to the one deflecting / reflecting surface on the upstream side in the rotation direction. Optical scanning device. There are a plurality of the light source devices,
The scanning optical system is disposed at least one each on both sides of the deflector, corresponding to the plurality of light source devices,
There are a plurality of the scanned surfaces corresponding to the plurality of scanning optical systems,
Each scanning optical system guides the light emitted from the corresponding light source device and deflected by the deflector to the corresponding scanned surface,
5. The optical scanning device according to claim 1, wherein a scanning start timing of each scanned surface is determined based on an output signal of the light receiving element. When the deflection angle range of light by the one deflection reflection surface is ω1, and ½ of the predetermined angle range is ω2.
ω2 / ω1> 0.7
Is satisfied, The optical scanning device according to any one of claims 1 to 5. The light source device emits a plurality of lights,
7. The optical scanning device according to claim 1, wherein light other than the light that enters the first deflecting / reflecting surface among the plurality of lights is incident on the light receiving element.   8. The optical scanning device according to claim 7, wherein the light that enters the first deflecting / reflecting surface among the plurality of lights is incident on the light receiving element. 9.   The incident direction of the light from the light source device on the one deflection reflection surface and the reflection direction on the one deflection reflection surface are in the same plane perpendicular to the rotation axis. 9. The optical scanning device according to claim 8.   10. The light source device according to claim 9, wherein light is not emitted from the light source device when a normal line of the other deflection reflection surface is parallel to an incident direction of light from the light source device when viewed from the rotation axis direction. The optical scanning device described. An image carrier;
An image forming apparatus comprising: the optical scanning device according to claim 1 that scans a surface of the image carrier.

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