JP4923958B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic system, and more particularly to an image forming apparatus provided with a laser exposure device that scans and exposes a photosensitive member with laser light.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic method, generally, the surface of a photosensitive drum rotating at a constant speed is uniformly charged by a charger, and then based on image information by a laser exposure device. The controlled laser beam is scanned and exposed to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum is converted into a toner image by a developing device, and the toner image is conveyed to a transfer unit as the photosensitive drum rotates, and is electrostatically transferred onto a recording sheet. The recording paper onto which the toner image has been transferred is conveyed to a fixing device by a conveying system, and fixing processing for the toner image is performed by the fixing device. Then, the recording paper is conveyed outside the image forming apparatus, and a toner image is completed.

  By the way, in the latent image forming step of scanning and exposing the charged photosensitive drum, the exposure pitch of the laser light in the sub-scanning direction needs to be uniform. For this reason, the photosensitive drum is positioned at a predetermined position so that the irradiation position of the laser beam on the surface of the photosensitive drum is determined, and the laser exposure apparatus is also fixedly installed. However, the image forming apparatus is provided with a driving source such as a motor for rotating the photosensitive drum and a conveying system for conveying the recording paper, and vibrations from these driving sources are easily transmitted to the entire image forming apparatus. . For this reason, the vibration causes relative position fluctuations between the laser exposure apparatus and the photosensitive drum during the image forming operation. Such a change in relative position causes non-uniformity in the exposure pitch of laser light in the sub-scanning direction. As a result, on the image formed by the image forming apparatus, density unevenness (this is referred to as “banding”) in a striped pattern in the sub-scanning direction (recording paper conveyance direction) is generated, and image quality is deteriorated. It will be.

Therefore, conventionally, a technique for suppressing the occurrence of banding due to vibration has been developed. For example, a technology in which an optical unit chassis for mounting an optical unit on which a laser exposure apparatus is mounted to an image forming apparatus body is made of an anti-vibration material, and the optical unit chassis is attached to a chassis on the image forming apparatus body side via a vibration isolator. (See, for example, Patent Document 1). This is intended to realize a configuration in which vibration of the image forming apparatus main body is not easily transmitted to the optical unit.
In addition, there is a technique for applying a vibration to a polygon mirror that has an opposite phase to the vibration frequency and frequency of the polygon mirror and approximately the same vibration amount (see, for example, Patent Document 2). This is intended to reduce the noise originally generated from the laser exposure apparatus, but also exhibits the effect of canceling vibrations in the laser exposure apparatus.

JP 2001-194849 A (page 3-4) JP 2001-38955 A (page 4-6)

However, as in the technique described in Patent Document 1 described above, a vibration isolator is provided between the optical unit on which the laser exposure apparatus is mounted or the drum support unit that supports the photosensitive drum and the image forming apparatus main body. In the configuration in which the optical unit and the drum support unit are interposed, the positional accuracy when the optical unit and the drum support unit are installed in the image forming apparatus main body is lowered. For this reason, it is difficult to set the laser beam so as to irradiate a predetermined position on the surface of the photosensitive drum with high accuracy. Further, when the laser exposure apparatus itself becomes a vibration source, there is no effect of suppressing the occurrence of banding.
Further, as in the technique described in Patent Document 2 described above, the method of applying anti-phase vibration that cancels the vibration in the laser exposure apparatus is effective against the vibration generated in the photosensitive drum. do not do. On the other hand, it is also conceivable to apply an antiphase vibration that cancels the vibration of the photosensitive drum to the drum support unit. However, even in that case, it is generally difficult to think that the vibration amount in both the laser exposure apparatus and the drum support unit is the same, and thus it is not practical to suppress the occurrence of banding.

  Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to suppress the occurrence of density unevenness in the stripe pattern in the sub-scanning direction on the image. It is in.

  For this purpose, the image forming apparatus of the present invention includes a photoconductor, a laser exposure unit that scans and exposes the photoconductor with one or a plurality of laser beams, and an irradiation position of laser light from the laser exposure unit in the sub-scanning direction. The laser exposure unit sets the light quantity of the laser light based on the irradiation position of the laser light detected by the sensor in the sub-scanning direction.

Here, the laser exposure unit sets the light amount of the laser beam at the target position when the irradiation position in the sub-scanning direction of the laser beam detected by the sensor is upstream of the predetermined target position in the rotation direction of the photosensitive member. The amount of laser light is increased more than the amount of light set at the target position when the irradiation position is downstream of the target position in the rotation direction of the photosensitive member. Can do. In addition, the laser exposure unit can set the amount of laser light for each scanning line. In particular, the laser exposure unit is characterized in that the light amount of the laser light of the scanning line next to the scanning line is set based on the irradiation position of the scanning line in which the irradiation position in the sub-scanning direction is detected by the sensor. You can also.
Here, the “upstream side in the rotation direction of the photoconductor” means the side in which the surface of the photoconductor advances due to the rotation of the photoconductor, and the “downstream side in the rotation direction of the photoconductor” means It means the direction opposite to the direction in which the surface of the photoconductor advances by the rotation operation.

Further, the sensor can be characterized in that the sensor is integrally connected to the photoconductor. In particular, a photoconductor support member that rotatably supports the photoconductor may be further provided, and the sensor may be attached to the photoconductor support member. In addition, a positioning member for positioning the photosensitive member on the apparatus main body may be further provided, and the sensor may be attached to the positioning member.
Further, the sensor can be characterized in that it is arranged in the vicinity of the surface of the photosensitive member and in the vicinity of the scanning start point of the laser beam by the laser exposure unit. Furthermore, the sensor may be arranged in the vicinity of the surface of the photosensitive member and in the vicinity of the scanning start point and the scanning end point of the laser beam by the laser exposure unit.

Furthermore, the image forming apparatus of the present invention includes a plurality of photoconductors arranged in parallel, a plurality of laser exposure units provided corresponding to the photoconductors, and scanning exposure of the photoconductors with one or a plurality of laser beams, and a plurality of photoconductors. A photosensitive member positioning member that integrally positions the photosensitive member on the apparatus main body, and a sensor that detects an irradiation position in the sub-scanning direction of laser light from a laser exposure unit that exposes one of the plurality of photosensitive members The plurality of laser exposure units is characterized in that the light quantity of the laser light is set based on the irradiation position of the laser light detected by the sensor in the sub-scanning direction.
Here, each of the plurality of photoconductors may be disposed on a photoconductor support member that rotatably supports the photoconductor, and the sensor may be attached to the photoconductor support member. Further, the sensor can be characterized in that it is integrally attached to the photosensitive member positioning member.

Further, the present invention is regarded as a photoconductor unit, and the photoconductor unit of the present invention is a photoconductor unit that rotatably supports a photoconductor to be scanned and exposed by laser light, and the photoconductor and the photoconductor are integrated. And a housing that is integrally attached to the housing and that detects an irradiation position in the sub-scanning direction of laser light to be scanned and exposed.
Here, the sensor can be characterized in that it is disposed in the vicinity of the surface of the photosensitive member and at the end of the laser beam scanning start point side. Further, a plurality of sensors may be arranged near the surface of the photoreceptor and on a scanning line of laser light. Further, the sensor is an element that changes the output voltage according to the scanning position of the laser beam, a photodiode formed by changing the shape of the light receiving surface according to the scanning position of the laser beam, or a line in the sub-scanning direction. It can also be characterized by comprising line CCDs arranged in an array.

  The image forming apparatus of the present invention also includes a photoconductor, a laser exposure unit that scans and exposes the photoconductor with one or more laser beams, and a laser reflection that reflects laser light that is scanned and exposed from the laser exposure unit to the photoconductor. And a detection unit that receives the laser beam reflected by the laser reflecting unit and detects an irradiation position in the sub-scanning direction of the laser beam that is scanned and exposed on the photosensitive member based on the received laser beam, The exposure unit is characterized in that the light amount of the laser light is set based on the irradiation position of the laser light detected by the detection unit in the sub-scanning direction.

Here, the laser reflecting portion can be characterized in that it is integrally coupled to the photosensitive member. In this case, a photosensitive member supporting member that rotatably supports the photosensitive member may be further provided, and the laser reflecting portion may be integrally attached to the photosensitive member supporting member.
Further, the laser reflecting portion is arranged such that a reflection surface for reflecting the laser beam scanned and exposed on the photosensitive member is inclined by a predetermined angle with respect to the sub-scanning direction at a position where the laser beam exposes the photosensitive member. It can be. Furthermore, the detection unit may be characterized in that the light receiving surface that receives the laser light reflected by the laser reflection unit is arranged in parallel to the reflection surface from which the laser reflection unit reflects the laser light. . In addition, the laser reflection unit reflects laser light scanned and exposed on the photosensitive member toward the laser exposure unit, and the detection unit is provided integrally with the laser exposure unit. .

The photoreceptor unit of the present invention includes a photoreceptor, a support member that integrally supports the photoreceptor, and a laser reflector that is integrally attached to the support member and reflects laser light that is scanned and exposed to the photoreceptor. It is characterized by having.
Here, the laser reflecting portion can be characterized in that it is disposed in the vicinity of the photosensitive member surface and at the end portion on the scanning start point side of the laser beam. Further, the laser reflecting section can reflect the laser light that is scanned and exposed on the photosensitive member toward the incident direction of the laser light.

  According to the present invention, even when vibration is generated in the image forming apparatus, it is possible to effectively suppress the occurrence of density unevenness in the stripe pattern in the sub-scanning direction on the formed image. Become.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a diagram showing a color copying machine 1 as an example of an image forming apparatus to which the exemplary embodiment is applied. A color copying machine 1 shown in FIG. 1 includes an image reading unit 10 and an image forming process unit 20.
The image reading unit 10 includes a transparent platen glass 12 on which a document (not shown) is placed, a light source 14 that irradiates the document, and a first reflection mirror 15 that reflects light reflected from the document. A movable document illumination unit 13, a mirror unit 16 including a second reflection mirror 17 and a third reflection mirror 18 that reflect light from the document illumination unit 13, and an optical path of light reflected by the mirror unit 16. The imaging lens 19 and the CCD (Charge Coupled Device) 21 that receives the reflected light from the mirror unit 16, and the output signals from the CCD 21 are yellow (Y), magenta (M), cyan (C), and black (K) images. An image processing unit (IPS: Image Processing System) 22 that converts the data into data, performs data processing such as density correction and enlargement / reduction correction, and outputs the data as writing image data is provided. That.

  The image forming process unit 20 includes a photosensitive drum 31 as an image carrier that rotates in the direction of arrow A, a charging roll 32 that uniformly charges the photosensitive drum 31 around the photosensitive drum 31, and an IPS 22. As an example of a laser exposure unit (ROS: Raster Output Scanner) 25 for irradiating the photosensitive drum 31 with laser light L modulated in accordance with the writing image data, yellow (Y), magenta (M ), Cyan (C), and black (K) toner containing the developing devices 33Y, 33M, 33C, and 33K are mounted on the rotary drum 33 and the photosensitive drum 31 that rotate about the rotation shaft 33a. The drum cleaner 34 is configured to remove the toner remaining on the photosensitive drum 31 and the neutralizing lamp 35 is configured to neutralize the photosensitive drum 31 before charging by the charger 32. Moreover, it has the control part 60 which controls operation | movement of each apparatus (each part).

  Further, the image forming process unit 20 is provided with an intermediate transfer belt 41 as an example of an intermediate transfer member disposed so as to be in contact with the surface of the photosensitive drum 31. The intermediate transfer belt 41 includes a drive roll 46 for rotating the intermediate transfer belt 41, a tension roll 47 for keeping the tension applied to the intermediate transfer belt 41 constant, idler rolls 48a to 48c that are driven to rotate, and secondary to be described later. It is stretched by a backup roll 49 for transfer, and is configured to rotate in the direction of arrow B.

  At the primary transfer portion T1 where the intermediate transfer belt 41 is in contact with the photosensitive drum 31, a primary transfer roll 42 is disposed on the back side of the intermediate transfer belt 41 so as to be in pressure contact with the photosensitive drum 31 via the intermediate transfer belt 41. Has been. Further, the secondary transfer portion T2 of the intermediate transfer belt 41 facing the conveyance path of the paper P is disposed on the toner carrying surface side (outside) of the intermediate transfer belt 41 so as to be able to contact with and separate from the intermediate transfer belt 41. A secondary transfer roll 50 and a backup roll 49 which is disposed on the back surface side (inside) of the intermediate transfer belt 41 and serves as a counter electrode of the secondary transfer roll 50 are disposed. Further, on the downstream side of the secondary transfer portion T2 in the intermediate transfer belt 41, a belt cleaner 55 that can be brought into contact with and separated from the intermediate transfer belt 41 is disposed at a position facing the idler roll 48a with the intermediate transfer belt 41 interposed therebetween. It is installed.

  In the image forming apparatus according to the present embodiment, when the copy start key of the user interface is turned on, first, the document placed on the platen glass 12 is irradiated by the light source 14 of the document illumination unit 13. The document reflected light reflected from the document is reflected by the first reflecting mirror 15 of the document illumination unit 13, the second reflecting mirror 17 and the third reflecting mirror 18 of the mirror unit 16, and passes through the imaging lens 19. It is read by the CCD 21 as analog signals of R (red), G (green), and B (blue). The read image signal from the CCD 21 is input to the IPS 22. In the IPS 22, the read image signal input from the CCD 21 is AD-converted and converted into yellow (Y), magenta (M), cyan (C), and black (K) image data for density correction, enlargement / reduction correction, and the like. Data processing is performed. And it outputs to the laser exposure apparatus 25 as image data for writing (laser drive data). Thereby, the laser exposure device 25 emits the laser beam L to the photosensitive drum 31.

  The photosensitive drum 31 is rotationally driven in the direction of arrow A at a constant speed, and the surface thereof is charged to a predetermined potential by the charging roll 32. Then, an electrostatic latent image is written on the surface of the photosensitive drum 31 by emitting laser light L from the laser exposure device 25. At this time, if the electrostatic latent image written on the photosensitive drum 31 corresponds to yellow (Y) image information, the electrostatic latent image is developed by the developing device 33Y containing Y toner. A Y toner image is formed on the photosensitive drum 31. The Y toner image formed on the photosensitive drum 31 is transferred to the intermediate transfer belt by the primary transfer bias applied to the primary transfer roll 42 at the primary transfer portion T1 where the photosensitive drum 31 and the intermediate transfer belt 41 face each other. 41 is transferred. On the other hand, the toner (transfer residual toner) remaining on the photosensitive drum 31 after the primary transfer is removed by the drum cleaner 34.

  In the case of forming a monochromatic image (for example, a black and white image), the toner image primarily transferred to the intermediate transfer belt 41 is immediately secondarily transferred to the paper P. On the other hand, when forming a color image composed of a plurality of color toner images, the toner image formation on the photosensitive drum 31 and the primary transfer process of the toner image are repeated for the number of colors. For example, when a full color image is formed by superimposing four color toner images, Y, M, C, and K toner images are sequentially formed on the photosensitive drum 31, and these toner images are sequentially transferred to the intermediate transfer belt. 41 is primarily transferred. The intermediate transfer belt 41 rotates at the same peripheral speed as that of the photosensitive drum 31 while holding the primary transferred toner image, and the intermediate transfer belt 41 is sequentially Y, M, C, K on the intermediate transfer belt 41 for each rotation. The toner images are superimposed. At this time, the secondary transfer roll 50 and the belt cleaner 55 are set at positions separated from the intermediate transfer belt 41.

The toner image primarily transferred onto the intermediate transfer belt 41 in this way is conveyed to the secondary transfer portion T2 as the intermediate transfer belt 41 rotates. On the other hand, the paper P is taken out from the paper tray 71 by the pick-up roll 72 and conveyed one by one to the position of the registration roll 74 by the conveyance roll 73. In synchronization therewith, the secondary transfer roll 50 is set at a position in contact with the intermediate transfer belt 41.
Subsequently, the sheet P is supplied to the secondary transfer unit T2 so as to match the timing at which the toner image on the intermediate transfer belt 41 reaches the secondary transfer unit T2. The paper P is sandwiched between the next transfer roll 50. At this time, in the secondary transfer portion T 2, a transfer electric field formed between the secondary transfer roll 50 and the backup roll 49 by the secondary transfer bias applied to the backup roll 49 is applied to the intermediate transfer belt 41. The toner image carried on the toner image is secondarily transferred (collectively transferred) to the paper P. Thereafter, the sheet P on which the toner image is transferred is conveyed to the fixing device 80 by the conveyance guide 76 and the sheet conveyance belt 77. The fixing device 80 heats and pressurizes and fixes the toner image on the paper P, and then discharges the paper P to the paper discharge tray 90. Further, the toner (transfer residual toner) attached to the intermediate transfer belt 41 after the secondary transfer is removed by the belt cleaner 55 that is in contact with the intermediate transfer belt 41 after the completion of the secondary transfer.

Next, the laser exposure apparatus 25 will be described.
FIG. 2 is a diagram showing a configuration of the laser exposure device 25 and a state in which the laser exposure device 25 scans and exposes the photosensitive drum 31. The laser exposure device 25 includes a light source 101 made of a semiconductor laser, a collimator lens 102, a cylinder lens 103, for example, a rotary polygon mirror (polygon mirror) 104 formed of a regular octahedron, an fθ lens 105, a folding mirror 106, a reflection mirror 107, and An SOS sensor (light receiving element) 108 is included. Further, the laser exposure device 25 is disposed in the housing 100a to constitute the optical unit 100.

In the laser exposure device 25, the divergent laser light L emitted from the light source 101 is converted into parallel light by the collimator lens 102, and deflected and reflected by the polygon mirror 104 by the cylinder lens 103 having a refractive power only in the sub-scanning direction. A line image that is long in the main scanning direction is formed near the surface 104a. The laser beam L is reflected by the deflecting / reflecting surface 104a of the polygon mirror 104 that rotates at a constant speed at a high speed, and is scanned counterclockwise (in the direction of arrow C) at an equal angular velocity.
After the laser beam L passes through the fθ lens 105, the direction is changed toward the surface of the photosensitive drum 31 by the folding mirror 106, and the surface of the photosensitive drum 31 is scanned and exposed in the direction of arrow D. Here, the fθ lens 105 has a function of equalizing the scanning speed of the light spot of the laser light L.
Further, the above-described line image is formed in the vicinity of the deflecting / reflecting surface 104a of the polygon mirror 104, and the fθ lens 105 causes a light spot on the surface of the photosensitive drum 31 with the deflecting / reflecting surface 104a as an object point in the sub-scanning direction. Since the image is formed, this scanning optical system has a function of correcting the surface tilt of the deflecting / reflecting surface 104a.

  The laser beam L is incident on the SOS sensor 108 via the reflection mirror 107 prior to scanning exposure on the surface of the photosensitive drum 31. That is, every time the laser beam L scans the surface of the photosensitive drum 31, the first laser beam L of each scanning line is incident on the SOS sensor 108. The SOS sensor 108 detects the irradiation timing for each scanning line on the surface of the photosensitive drum 31, and generates a signal (SOS signal) indicating the irradiation start timing.

The light source 101 is connected to a laser driver 109 that outputs a laser drive signal corresponding to the writing image data output from the IPS 22 (see FIG. 1) of the image reading unit 10 at a predetermined timing. The laser driver 109 controls ON / OFF of the semiconductor laser of the light source 101 based on the writing image data from the IPS 22. As a result, the laser beam L corresponding to the writing image data is output from the light source 101.
At that time, the laser driver 109 is connected to the SOS sensor 108 and inputs the SOS signal generated by the SOS sensor 108. In the laser driver 109, timing for starting output of a laser drive signal to the semiconductor laser of the light source 101 is set based on the SOS signal from the SOS sensor 108.

Further, in the color copying machine 1 of the present embodiment, the sub-scanning position detection that detects the position of the laser beam L on the surface of the photosensitive drum 31 in the sub-scanning direction and generates a sub-scanning position signal corresponding to the position in the sub-scanning direction. A sensor 110 is provided. The sub-scanning position detection sensor 110 is disposed between the laser exposure device 25 and the photosensitive drum 31. For example, as shown in FIG. 3 (a diagram for explaining the arrangement position of the sub-scanning position detection sensor 110), the laser light L scans and exposes the surface of the photosensitive drum 31 so as not to affect image formation. In the region where the image is formed, the surface of the photoconductive drum 31 is disposed in the vicinity of the surface of the photoconductive drum 31 in a region closer to the end in the axial direction than the region where the image is formed on the surface of the photoconductive drum 31 (image forming region). Then, the sub-scanning position detection sensor 110 detects the position in the sub-scanning direction for each line scan of the laser beam L for image formation. The sub-scanning position signal generated by the sub-scanning position detection sensor 110 is output to the laser driver 109 in real time.
The laser driver 109 adjusts the light amount of the semiconductor laser of the light source 101 in real time based on the sub-scanning position signal input from the sub-scanning position detection sensor 110.

  By the way, the color copying machine 1 is provided with driving sources such as a motor for rotating the photosensitive drum 31 and a conveying system for conveying the paper P, and vibrations from these driving sources cause the entire color copying machine 1 to vibrate. It is easy to be transmitted to. For this purpose, as shown in FIG. 4 (a diagram for explaining a change in relative position between the laser exposure device 25 and the photosensitive drum 31), the optical unit 100 on which the laser exposure device 25 is mounted, and the photosensitive drum 31. The vibration transmitted to the drum support unit 30 or the like that supports the toner causes fluctuations in the relative position between the laser exposure device 25 and the photosensitive drum 31 during the image forming operation. Such a change in relative position between the laser exposure device 25 and the photosensitive drum 31 is caused by the exposure pitch in the sub-scanning direction (rotation direction of the photosensitive drum 31) of the laser light L emitted from the laser exposure device 25. This causes non-uniformity (so-called “pitch unevenness”) of (an interval between adjacent scanning lines). As a result, striped density unevenness (this is referred to as “banding”) occurs in the sub-scanning direction (the conveyance direction of the paper P) on the image formed by the color copying machine 1, and the image quality is degraded. It will be.

Therefore, in the color copying machine 1 of the present embodiment, the sub-scanning position detection sensor 110 detects the position of the laser light L on the surface of the photosensitive drum 31 in real time for each scanning line. When the position of the laser beam L in the sub-scanning direction is shifted to the upstream side in the rotation direction of the photosensitive drum 31 with respect to the original irradiation position, the scanning pitch in the sub-scanning direction becomes dense. The amount of light of the semiconductor laser of the light source 101 is reduced according to the amount of deviation. As a result, the light spot diameter of the scanning line is reduced, and the generation of a stripe-shaped high density portion in the sub-scanning direction caused by the dense scanning pitch between the scanning lines can be suppressed.
On the other hand, when the position of the laser beam L in the sub-scanning direction is shifted to the downstream side in the rotation direction of the photosensitive drum 31 from the original irradiation position, the scanning pitch in the sub-scanning direction becomes sparse, so the laser driver 109 The amount of light of the semiconductor laser of the light source 101 is increased according to the amount of deviation. As a result, the light spot diameter of the scanning line is increased, and therefore, it is possible to suppress the occurrence of a stripe-patterned low density portion in the sub-scanning direction caused by the sparse scanning pitch between the scanning lines.
Here, in this specification, the “upstream side in the rotation direction of the photoconductor” means a direction side in which the surface of the photoconductor advances by the rotation of the photoconductor, and the “downstream side in the rotation direction of the photoconductor” It means the direction opposite to the direction in which the surface of the photoconductor advances due to the rotation of the photoconductor.
As described above, in the color copying machine 1 according to the present embodiment, the light quantity of the semiconductor laser of the light source 101 is adjusted in real time in accordance with the exposure pitch in the sub-scanning direction of the laser light L emitted from the laser exposure device 25. It is adjusting. Therefore, even when the relative position between the laser exposure device 25 and the photosensitive drum 31 changes due to vibration in the color copying machine 1, banding generated on the image formed by the color copying machine 1 is visually observed. It becomes possible to reduce to an inconspicuous level.

  In the color copying machine 1 of the present embodiment, a semiconductor laser that emits one beam is used as the light source 101, and the sub-scanning direction detection sensor 110 outputs the laser beam L of one beam on the surface of the photosensitive drum 31. The position is detected for each scanning line. In addition to such a configuration, a laser array light source that simultaneously emits a plurality of beams is used as the light source 101 in order to cope with an increase in speed and resolution of the image forming apparatus, and a plurality of beams are detected by the sub-scanning position detection sensor 110. The position of the laser beam L on the surface of the photosensitive drum 31 in the sub-scanning direction can be detected for each scanning line. Similarly, the amount of light from the laser array light source can be adjusted in real time.

  Next, FIG. 5 is a diagram illustrating a PSD (Position Sensitive Detector) as an example of the sub-scanning position detection sensor 110. As shown in FIG. 5A, in the PSD, the longitudinal direction of the detection surface is arranged along the sub-scanning direction. Then, as shown in FIG. 5B, the PSD changes the output voltage V according to the position (a, b, c) of the laser light L that passes through the detection surface of the PSD. Therefore, the position of the laser light L in the sub-scanning direction can be detected by detecting the output voltage V of PSD.

  FIG. 6 is a diagram for explaining detection of the position in the sub-scanning direction of the laser beam L when PSD is used as the sub-scanning position detection sensor 110. As shown in FIG. 6A, when the relative position between the laser exposure device 25 and the photosensitive drum 31 changes due to vibration in the color copying machine 1, sub-scanning of the laser light L is performed. The direction position fluctuates. Then, as shown in FIG. 6B, the output voltage V from the sub-scanning position detection sensor (PSD) 110 also changes in accordance with the vibration waveform. In that case, the period of the vibration waveform is sufficiently long with respect to the exposure pitch of the laser beam L. Therefore, the output voltage V from the sub-scanning position detection sensor 110 detected for one scanning line of the laser beam L, that is, the position in the sub-scanning direction can be regarded as the position in the sub-scanning direction on the next scanning line of the scanning line. it can. Therefore, the laser driver 109 sets the detected sub-scanning direction position in the next scanning line at the time of the next scanning of the scanning line whose sub-scanning direction position is detected by the sub-scanning position detection sensor 110. And The laser driver 109 sets the amount of light of the semiconductor laser of the light source 101 based on the position in the sub-scanning direction.

  As described above, when setting the light amount of the semiconductor laser of the light source 101, the laser driver 109 reduces the light amount of the semiconductor laser by using the position in the sub-scanning direction detected in the scanning line immediately before the scanning line where the light amount is set. A time margin for calculation can be provided. Therefore, it is possible to set the light amount with high accuracy for each scanning line. Further, when the detection of the position in the sub-scanning direction and the setting of the light amount of the semiconductor laser are performed simultaneously on the same scanning line, the light amount of the semiconductor laser may change between the head and the rear end of one scanning line. On the other hand, the amount of light for each scanning line can be set constant by using the sub-scanning direction position detected in the immediately preceding scanning line. Therefore, it is possible to suppress the occurrence of density unevenness in the main scanning direction due to a change in image density within the scanning line.

Here, a processing flow for setting the light amount of the semiconductor laser of the light source 101 in the laser driver 109 is shown in FIG. As shown in FIG. 7, the sub-scanning position detection sensor 110 first detects the position in the sub-scanning direction (S1). Subsequently, the light quantity of the semiconductor laser of the light source 101 is calculated based on the sub-scanning direction position detected by the sub-scanning position detection sensor 110 (S2). In the scanning line scanned next to the scanning line whose position in the sub-scanning direction is detected in step 1, the light quantity of the semiconductor laser of the light source 101 is set with the light quantity calculated in step 2 (S3). Then, the laser driver 109 starts outputting a laser drive signal corresponding to the writing image data output from the IPS 22 (see FIG. 1) of the image reading unit 10 to the light source 101 (S4).
In this way, the sub-scanning position detection sensor 110 detects the position in the sub-scanning direction for each line scan of the laser light L for image formation, and the laser driver 109 detects the light source in real time based on the detected sub-scanning direction position. The light quantity of the semiconductor laser 101 is adjusted.

Next, the arrangement position of the sub-scanning position detection sensor 110 in the axial direction of the photosensitive drum 31 will be described. As described above, the sub-scanning position detection sensor 110 is located between the laser exposure device 25 and the photosensitive drum 31, for example, in a region where the laser beam L scans and exposes the surface of the photosensitive drum 31, and forms an image. It is disposed in the vicinity of the surface of the photosensitive drum 31 in a region closer to the axial end than the region (see FIG. 3). One of the sub-scanning position detection sensors 110 is preferably arranged in such an area and in an upstream end area of the scanning line.
As described above, every time the laser beam L scans the surface of the photosensitive drum 31, the first laser beam L of each scanning line is incident on the SOS sensor 108, and a laser drive signal is transmitted from the laser driver 109 to the light source 101. An SOS signal that is a reference for the timing of starting output is generated. Accordingly, if the sub-scanning position detection sensor 110 can detect the position of each scanning line in the sub-scanning direction at the same time as the first laser light L of each scanning line enters the SOS sensor 108, the laser driver 109 performs the next scanning. It is possible to provide a large time margin for calculating the amount of semiconductor laser light in the line.

FIG. 8 is a diagram illustrating the relationship between the timing at which the sub-scanning position detection sensor 110 detects the position of each scanning line in the sub-scanning direction and the time during which the laser driver 109 can calculate the light amount. FIG. 8A shows a case where one is arranged on the downstream end (EOS) side of the scanning line, that is, near the end point of the scanning line. In this configuration, the time from when the sub-scanning position detection sensor 110 detects the position in the sub-scanning direction until the next scan is started is t1, and the time that can be calculated by the laser driver 109 is short. Therefore, it is insufficient for setting the light amount with high accuracy for each scanning line.
On the other hand, FIG. 8B shows a case where one is arranged on the upstream end (SOS) side of the scanning line, that is, in the vicinity of the starting point of the scanning line. In this configuration, the time from when the sub-scanning position detection sensor 110 detects the position in the sub-scanning direction until the start of the next scan is t2, and the time that can be calculated by the laser driver 109 is one on the EOS side. Compared to the arrangement, the time for one line scanning is increased. For this reason, it is possible to set the light amount with high accuracy for each scanning line.

  FIG. 8C shows a case where the scanning lines are arranged on the SOS side and the EOS side, respectively. In this configuration, the sub-scanning position detection sensor 110 on the SOS side can sufficiently secure the time that can be calculated by the laser driver 109 and can also detect changes in the sub-scanning direction position within one line scan. . Therefore, it is possible to set the light amount for each scanning line with higher accuracy.

By the way, in the color copying machine 1 of the present embodiment, the case where the PSD is used as the sub-scanning position detection sensor 110 has been described. However, the sub-scanning position detection sensor 110 is not limited to this, and any detection means can be used as long as it can detect the sub-scanning direction position of each scanning line.
9 and 10 are diagrams showing another configuration example of the sub-scanning position detection sensor 110. FIG. In FIG. 9, the sub-scanning position detection sensor 110 uses a photodiode formed in a triangular shape having a length in the main scanning direction along the sub-scanning direction (FIG. 9A). With such a configuration, as shown in FIG. 9B, the output time of the signal from the sub-scanning position detection sensor 110 differs according to the position (a, b, c) of the laser light L passing through the photodiode. Thus, signals with different output waveforms can be obtained. Thereby, the sub-scanning direction position of each scanning line can be detected.
As the sub-scanning position detection sensor 110 using a photodiode, the photodiode itself has a shape having the same length in the main scanning direction along the sub-scanning direction, such as a square, and the main scanning along the sub-scanning direction. The surface of the photodiode can be covered with a mask having an opening formed in a triangular shape whose length in the scanning direction becomes longer.

  Further, in FIG. 10, a line CCD (Charge Coupled Devices) arranged in a line along the sub-scanning direction is used as the sub-scanning position detection sensor 110 (FIG. 10A). With this configuration, as shown in FIG. 10B, output signals having different output timings from the sub-scanning position detection sensor 110 are obtained according to the positions (a, b, c) of the laser light L passing through the line CCD. It is done. Thereby, the sub-scanning direction position of each scanning line can be detected.

On the other hand, the sub-scanning position detection sensor 110 may be disposed in an integrally coupled state with the photosensitive drum 31 in order to accurately detect the position in the sub-scanning direction of each scanning line on the surface of the photosensitive drum 31. Necessary. That is, the photosensitive drum 31 and the sub-scanning position detection sensor 110 need to be arranged so that both vibrate in the same manner when receiving vibration from the color copying machine 1 main body.
Therefore, in the present embodiment, as shown in FIG. 11, a drum support unit (photosensitive unit) 30 as an example of a photosensitive member supporting member that rotatably supports the photosensitive drum 31 with the sub-scanning position detection sensor 110. Are integrally installed in the housing 30a. The drum support unit 30 is integral with the photosensitive drum 31. Therefore, by installing the sub-scanning position detection sensor 110 integrally with the drum support unit 30, the sub-scanning position detection sensor 110 can be moved in the same manner as the photosensitive drum 31.

  Further, the sub-scanning position detection sensor 110 can be integrally installed on a positioning member (not shown) for positioning the photosensitive drum 31 with respect to the color copying machine 1 main body. The positioning member determines the position of the photosensitive drum 31 in the main body of the color copying machine 1 and sets a position reference with all process elements such as the laser exposure device 25 and the intermediate transfer belt 41. Therefore, the positioning member is coupled in a state of being in close contact with the photosensitive drum 31. Accordingly, the positioning member moves in the same manner as the photosensitive drum 31 with respect to the vibration of the color copying machine 1 main body. Therefore, the sub-scanning position detection sensor 110 can be moved in the same manner as the photosensitive drum 31 by installing the sub-scanning position detection sensor 110 integrally with the positioning member.

  As described above, in the color copying machine 1 according to the present embodiment, the light quantity of the semiconductor laser of the light source 101 is adjusted in real time in accordance with the exposure pitch in the sub-scanning direction of the laser light L emitted from the laser exposure device 25. It is adjusted to. For this reason, even when the relative position between the laser exposure device 25 and the photosensitive drum 31 varies due to vibration in the color copying machine 1, the banding generated on the formed image is visually inconspicuous. It becomes possible to reduce. As a result, the color copying machine 1 of the present embodiment can always provide a high-quality image.

[Embodiment 2]
In the first embodiment, a so-called rotary type color image forming apparatus that sequentially forms images of respective colors on the same photosensitive drum 31 has been described. In the second embodiment, a so-called tandem color image forming apparatus that forms an image of each color on a plurality of photosensitive drums 31 will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here. Some components are omitted.

  FIG. 12 is a diagram showing an overall configuration of a digital color printer 2 as an image forming apparatus according to the present embodiment. The digital color printer 2 shown in FIG. 12 is a so-called tandem type, and an image forming process unit 20 that forms an image corresponding to image data of each color, and a control unit 60 that controls the image forming process unit 20, such as a personal computer ( The image processing unit (IPS) 22 is connected to the PC 3 and the image reading device 4 and performs predetermined image processing on the image data received therefrom.

The image forming process unit 20 includes four image forming units 26Y, 26M, 26C, and 26K that are arranged in parallel at a predetermined interval. The image forming units 26Y, 26M, 26C, and 26K uniformly charge the surface of the photosensitive drum 31 as an image carrier that forms an electrostatic latent image and carries a toner image at a predetermined potential. A charging roll 32, a developing device 33 for developing an electrostatic latent image formed on the photosensitive drum 31, and a drum cleaner 34 for cleaning the surface of the photosensitive drum 31 after transfer are configured. Corresponding to the image forming units 26Y, 26M, 26C, and 26K, there are provided laser exposure devices 25Y, 25M, 25C, and 25K as an example of a laser exposure unit that exposes the photosensitive drum 31. The laser exposure devices 25Y, 25M, 25C, and 25K have the same configuration as that of the first embodiment (see FIG. 2).
Here, the image forming units 26Y, 26M, 26C, and 26K are configured in substantially the same manner except for the toner stored in the developing device 33. The image forming units 26Y, 26M, 26C, and 26K respectively form yellow (Y), magenta (M), cyan (C), and black (K) toner images.

  In addition, the image forming process unit 20 includes an intermediate transfer belt 41 to which the toner images of the respective colors formed on the photosensitive drums 31 of the image forming units 26Y, 26M, 26C, and 26K are transferred, and the image forming units 26Y and 26Y. A primary transfer roller 42 that sequentially transfers (primary transfer) each color toner image of 26M, 26C, and 26K to the intermediate transfer belt 41 at the primary transfer portion T1, and a superimposed toner image transferred onto the intermediate transfer belt 41 is a secondary transfer portion. A secondary transfer roll 50 that performs batch transfer (secondary transfer) onto a paper P that is a recording material (recording paper) at T2 and a fixing device 80 that fixes the secondary transferred image onto the paper P are provided.

  In the digital color printer 2 of the present embodiment, the image forming process unit 20 performs an image forming operation based on a control signal supplied from the control unit 60. At that time, image data input from the PC 3 or the image reading device 4 is subjected to image processing by the IPS 22 and supplied to the laser exposure devices 25Y, 25M, 25C, and 25K. For example, in the yellow (Y) image forming unit 26Y, the surface of the photosensitive drum 31 uniformly charged at a predetermined potential by the charging roll 32 is applied by the laser exposure device 25Y based on the image data obtained from the IPS 22. An electrostatic latent image is formed on the photosensitive drum 31 by scanning exposure. The formed electrostatic latent image is developed by the developing device 33, and a Y toner image is formed on the photosensitive drum 31. Similarly, in the image forming units 26M, 26C, and 26K, M, C, and K color toner images are formed.

The color toner images formed by the image forming units 26Y, 26M, 26C, and 26K are sequentially electrostatically attracted by the primary transfer roll 42 onto the intermediate transfer belt 41 that rotates in the direction of arrow F in FIG. A toner image superimposed on the belt 41 is formed. As the intermediate transfer belt 41 moves, the superimposed toner image is conveyed to the secondary transfer portion T2 where the secondary transfer roll 50 is disposed. When the superimposed toner image is conveyed to the secondary transfer portion T2, the paper P is supplied to the secondary transfer portion T2 in accordance with the timing at which the toner image is conveyed to the secondary transfer portion T2. Then, the superimposed toner images are collectively electrostatically transferred onto the conveyed paper P by the transfer electric field formed by the secondary transfer roll 50 in the secondary transfer portion T2.
Thereafter, the sheet P on which the superimposed toner image is electrostatically transferred is peeled off from the intermediate transfer belt 41 and conveyed to the fixing device 80 by the conveyance belt 78. The unfixed toner image on the paper P conveyed to the fixing device 80 is fixed on the paper P by being subjected to fixing processing by heat and pressure by the fixing device 80. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge mounting portion (not shown) provided in the discharge portion of the image forming apparatus.

  Here, in the digital color printer 2 of the present embodiment, each of the image forming units 26Y, 26M, 26C, and 26K has a common photoconductor positioning member for positioning the photoconductor drum 31 with respect to the main body of the digital color printer 2. It is supported by 65. The photoconductor positioning member 65 determines the position of the photoconductor drum 31 in the image forming units 26Y, 26M, 26C, and 26K in the main body of the digital color printer 2, and each laser exposure device 25Y, 25M, 25C, and 25K A position reference between all the process elements such as the transfer belt 41 is set.

In the digital color printer 2, the same sub-scanning position detection sensor 110 as that of the first embodiment is installed only in the image forming unit 26K that is one of the image forming units 26Y, 26M, 26C, and 26K. . Similar to the first embodiment, the sub-scanning position detection sensor 110 installed in the image forming unit 26K detects in real time the sub-scanning direction position of each scanning line of the laser light L that forms an image in the image forming unit 26K. Then, a sub-scanning position signal is generated. The sub-scanning position detection sensor 110 installed in the image forming unit 26K is connected to each laser exposure device 25Y, 25M, 25C, 25K, and the laser driver 109 of each laser exposure device 25Y, 25M, 25C, 25K. In contrast, the sub-scanning position signal is output in real time.
The laser drivers 109 of the laser exposure devices 25Y, 25M, 25C, and 25K adjust the light quantity of the semiconductor laser of the light source 101 based on the sub-scanning position signal input from the sub-scanning position detection sensor 110 of the image forming unit 26K. is doing.
As the light source 101, a laser array light source that emits one or a plurality of beams at the same time is used, and the sub-scanning position detection sensor 110 detects the position of the laser beam L of one or a plurality of beams on the surface of the photosensitive drum 31. Can be configured to be detected for each scanning line.

Thus, in the digital color printer 2 of the present embodiment, the sub-scanning position detection sensor 110 detects the position in the sub-scanning direction in real time in one image forming unit 26K. Based on the position in the sub-scanning direction detected by one image forming unit 26K, the light quantity of the semiconductor laser of the light source 101 of each laser exposure device 25Y, 25M, 25C, 25K is adjusted in real time.
This is because the image forming units 26Y, 26M, 26C, and 26K are supported by the common photoconductor positioning member 65, so that the photosensitive drums 31 in the image forming units 26Y, 26M, 26C, and 26K are all The movement is almost the same. Therefore, by installing the sub-scanning position detection sensor 110 integrally in one image forming unit 26K, each of the laser beams L of all the photosensitive drums 31 in each of the image forming units 26Y, 26M, 26C, and 26K. It is possible to grasp the position in the sub-scanning direction for each line scan.
The sub-scanning position detection sensor 110 may be arranged in any of the image forming units 26Y, 26M, 26C, and 26K. Further, the sub-scanning position detection sensor 110 may be integrally connected to the photosensitive member positioning member 65 that moves in the same manner as the photosensitive drum 31 in each of the image forming units 26Y, 26M, 26C, and 26K. Good.

  Therefore, the sub-scanning direction position detected by the sub-scanning position detection sensor 110 in one image forming unit 26K, or the sub-scanning position detected by the sub-scanning position detection sensor 110 arranged in combination with the photosensitive member positioning member 65. By using the direction position, the light quantity of the semiconductor laser of the light source 101 is adjusted in real time in accordance with the exposure pitch in the sub-scanning direction of the laser light L emitted from each laser exposure device 25Y, 25M, 25C, 25K. be able to. Thereby, fluctuations in relative position between the laser exposure devices 25Y, 25M, 25C, and 25K and the photosensitive drums 31 in the image forming units 26Y, 26M, 26C, and 26K are caused by vibration in the digital color printer 2. Even in such a case, it is possible to reduce the banding generated on the formed image to an inconspicuous level. As a result, the digital color printer 2 of the present embodiment can always provide a high-quality image.

[Embodiment 3]
In the first embodiment, the configuration in which the sub-scanning position detection sensor 110 is integrally installed on the housing 30a of the drum support unit 30 that rotatably supports the photosensitive drum 31 has been described. In the present embodiment, a configuration in which a reflection mirror that reflects the laser light L from the light source 101 is integrally installed in the drum support unit 30 and the sub-scanning position detection sensor 110 is installed on the main body side of the image forming apparatus will be described. To do. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

The configuration for detecting the position of the laser beam L in the sub-scanning direction for each line scan on the surface of the photosensitive drum 31 in the present embodiment will be described. In the present embodiment, for example, in the color copying machine 1 according to the first embodiment, a reflection mirror 120 as an example of a laser reflection unit that reflects the laser light L from the light source 101 is integrally installed on the drum support unit 30. Yes. Further, the sub-scanning position detection sensor 110 as an example of a detection unit that detects the position of the laser beam L on the surface of the photosensitive drum 31 in the sub-scanning direction and generates a sub-scanning position signal corresponding to the position in the sub-scanning direction is color-copied. It is installed on the machine 1 main body side.
FIG. 13 is a plan view for explaining the positional relationship among the laser exposure apparatus 25 of the present embodiment, the reflection mirror 120 that reflects the laser light L from the light source 101, and the sub-scanning position detection sensor 110. FIG. 14 is a schematic view of a section XX in FIG.
As shown in FIG. 14, the reflection mirror 120 is integrally installed in a housing 30 a of a drum support unit (photosensitive unit) 30 as an example of a photosensitive support member that rotatably supports the photosensitive drum 31. . Further, as shown in FIG. 13, the reflection mirror 120 is in the region where the laser beam L scans and exposes the surface of the photosensitive drum 31 so as not to affect image formation. 31 is disposed in the vicinity of the surface of the photosensitive drum 31 in a region closer to the end in the axial direction than the region where the image is formed on the surface (image forming region). At that time, the reflection mirror 120 is preferably arranged in the upstream end region of the scanning line, similarly to the sub-scanning position detection sensor 110 in the first embodiment.

Further, as shown in FIGS. 13 and 14, the sub-scanning position detection sensor 110 is disposed on the color copying machine 1 main body side, for example, in the vicinity of the drum support unit 30, and on the color copying machine 1 main body by a holder (not shown). It is fixed. That is, the sub-scanning position detection sensor 110 is disposed separately from the drum support unit 30 on the optical path of the reflected laser beam L1 reflected by the reflecting mirror 120.
At this time, the mirror surface of the reflection mirror 120 is disposed so as to be inclined by a predetermined angle with respect to a surface orthogonal to the optical path of the laser light L so that the reflected laser light L1 reflected does not overlap the incident laser light L. ing. Further, the sensor surface of the sub-scanning position detection sensor 110 is arranged in parallel with the mirror surface of the reflection mirror 120. Therefore, when the relative position between the laser beam L and the photosensitive drum 31 in the sub-scanning direction is shifted, the movement of the laser beam L on the mirror surface of the reflecting mirror 120 that moves integrally with the photosensitive drum 31. The amount and the amount of movement of the reflected laser light L1 detected on the sensor surface of the sub-scanning position detection sensor 110 are set to have a 1: 1 relationship regardless of the amount of movement.

Here, FIG. 15 shows the sub-scanning direction generated at the position (exposure position) where the laser light L irradiates the surface of the photosensitive drum 31 when, for example, a vibration direction shift occurs at the arrangement position of the drum support unit 30 due to vibration. It is a figure explaining the relationship between the shift | offset | difference of this, and the shift | offset | difference of the irradiation position which arises on the sensor surface of the subscanning position detection sensor 110. FIG.
As shown in FIG. 15, for example, if the drum support unit 30 is displaced in the vibration direction and the photosensitive drum 31 is moved to the position indicated by the broken line, the surface of the photosensitive drum 31 should be originally exposed. The exposure position D1 moves to the surface position D2 indicated by a broken line. In this case, the laser beam L exposes the surface position D3 indicated by the broken line. Therefore, the vibration causes a shift in the sub-scanning direction by an amount corresponding to the distance between the surface position D2 and the surface position D3.

  At that time, the reflection mirror 120 integrally installed in the housing 30 a of the drum support unit 30 similarly moves to the position indicated by the broken line with the same amount of movement as the photosensitive drum 31. Therefore, the reflected laser beam L1 reflected by the reflecting mirror 120 also moves to the reflected laser beam L2 indicated by the broken line. In this case, as described above, the amount of movement of the laser light L on the mirror surface of the reflection mirror 120 is achieved by arranging the sensor surface of the sub-scanning position detection sensor 110 and the mirror surface of the reflection mirror 120 in parallel. And the amount of movement of the reflected laser light L1 detected on the sensor surface of the sub-scanning position detection sensor 110 (the amount of movement from L1 to L2) has a 1: 1 relationship regardless of the amount of movement. Set to Thereby, the movement amount of the reflection mirror 120, that is, the movement amount of the photosensitive drum 31 is detected as the movement amount of the reflected laser light L 1 on the sensor surface of the sub-scanning position detection sensor 110.

For this reason, in the sub-scanning position detection sensor 110 of the present embodiment, generally, when the vibration of the drum support unit 30 and the vibration of the laser exposure device 25 occur simultaneously or independently, The position in the sub-scanning direction on the surface of the photosensitive drum 31 is detected by the irradiation position on the sensor surface of the reflected laser light L1 by the sub-scanning position detection sensor 110, and this is detected on the surface of the photosensitive drum 31 by a predetermined calculation process. A sub-scanning position signal is generated by converting into a scanning direction position.
The sub-scanning position signal generated by the sub-scanning position detection sensor 110 is output to the laser driver 109 in real time. The laser driver 109 adjusts the light amount of the semiconductor laser of the light source 101 in real time based on the sub-scanning position signal input from the sub-scanning position detection sensor 110.
As the sub-scanning position detection sensor 110, the PSD (see FIG. 5) described in the first embodiment, the photodiode shown in FIG. 9, the line CCD (Charge Coupled) arranged in the line shape shown in FIG. Devices) and the like can be used.

By the way, as shown in FIG. 15, the mirror surface of the reflection mirror 120 intersects the sub-scanning direction at the exposure position where the laser beam L irradiates the surface of the photosensitive drum 31 with a predetermined intersection angle θ. Has been placed. In other words, the arrangement direction of the mirror surface of the reflection mirror 120 is arranged to be different from the sub-scanning direction at the exposure position of the laser beam L. Thereby, for example, even when the vibration direction of the drum support unit 30 coincides with the sub-scanning direction, the position of the laser light L on the surface of the photosensitive drum 31 can be detected.
Here, FIG. 16 is a diagram showing a case where the vibration direction of the drum support unit 30 coincides with the sub-scanning direction at the exposure position of the laser light L. As shown in FIG. 16, since the mirror surface of the reflection mirror 120 is arranged so as to intersect with the sub-scanning direction at the exposure position with an intersection angle θ, the drum support unit 30 vibrates in the sub-scanning direction. At the same time, the mirror surface position of the reflection mirror 120 moves from the original mirror surface position (solid line) as shown by the broken line. For this reason, the reflected laser beam L1 reflected by the reflecting mirror 120 moves to the reflected laser beam L2 indicated by a broken line, so that the deviation of the position of the laser beam L in the sub-scanning direction on the surface of the photosensitive drum 31 is sub-scanning position. The amount of movement of the reflected laser light L1 on the sensor surface of the detection sensor 110 (the amount of movement from L1 to L2) can be detected.

On the other hand, FIG. 17 shows a case where the vibration direction of the drum support unit 30 coincides with the sub-scanning direction in the configuration in which the mirror surface of the reflection mirror 120 is arranged to coincide with the sub-scanning direction at the exposure position of the laser beam L. It is a figure. As shown in FIG. 17, when the mirror surface of the reflection mirror 120 is arranged so as to coincide with the sub-scanning direction, when the drum support unit 30 vibrates in the sub-scanning direction, the mirror surface position of the reflection mirror 120 is As indicated by the broken line, it moves parallel to the original mirror surface position (solid line). Therefore, even if the drum support unit 30 moves due to vibration, the reflected laser beam L1 reflected by the reflecting mirror 120 does not move, and the reflected laser beam L2 after moving and the original reflected laser beam L1 have the same optical path. Will be followed. Therefore, the deviation of the position of the laser beam L on the surface of the photosensitive drum 31 in the sub-scanning direction is detected as the amount of movement of the reflected laser beam L1 on the sensor surface of the sub-scanning position detection sensor 110 (the amount of movement from L1 to L2). I can't.
Therefore, in the color copying machine 1 of the present embodiment, the mirror surface of the reflection mirror 120 intersects the sub-scanning direction at the exposure position where the laser beam L irradiates the surface of the photosensitive drum 31 with a predetermined intersection angle θ. Arrange to do. Accordingly, even when the drum support unit 30 is vibrated in the sub-scanning direction at the exposure position that has the greatest influence on the position of the laser light L in the sub-scanning direction, the photosensitive drum 31 of the laser light L is also generated. The position in the sub-scanning direction on the surface can be accurately detected.

  As described above, in the color copying machine 1 according to the present embodiment, the reflected laser beam L1 from the reflecting mirror 120 integrally installed on the drum support unit 30 is sub-scanned installed on the color copying machine 1 main body side. Detection is performed by the position detection sensor 110. Thereby, as described in the first embodiment, the position of the laser beam L in the sub-scanning direction on the surface of the photosensitive drum 31 is detected in real time for each scanning line. When the position of the laser beam L in the sub-scanning direction is shifted to the upstream side of the rotation direction of the photosensitive drum 31 from the original irradiation position (exposure position), the scanning pitch in the sub-scanning direction becomes dense. The laser driver 109 reduces the amount of light of the semiconductor laser of the light source 101 according to the amount of deviation. As a result, the light spot diameter of the scanning line is reduced, and the generation of a stripe-patterned high density portion in the sub-scanning direction caused by the dense scanning pitch between the scanning lines is suppressed.

On the other hand, when the position of the laser beam L in the sub-scanning direction is shifted to the downstream side in the rotation direction of the photosensitive drum 31 from the original irradiation position, the scanning pitch in the sub-scanning direction becomes sparse, so the laser driver 109 The amount of light of the semiconductor laser of the light source 101 is increased according to the amount of deviation. As a result, the light spot diameter of the scanning line is increased, and therefore, the generation of the stripe-patterned low density portion in the sub-scanning direction caused by the sparse scanning pitch between the scanning lines is suppressed.
As a result, even when the relative position between the laser exposure device 25 and the photosensitive drum 31 changes due to vibration in the color copying machine 1, banding that occurs on the image formed by the color copying machine 1 is prevented. Reduced to a level that is not noticeable visually.
As described above, the “upstream side in the rotation direction of the photoconductor” here means a direction side in which the surface of the photoconductor advances due to the rotation of the photoconductor, and “downstream in the rotation direction of the photoconductor”. Means the direction opposite to the direction in which the surface of the photoconductor advances due to the rotation of the photoconductor.

  Further, in the color copying machine 1 of the present embodiment, the sub-scanning position detection sensor 110 that detects the position of the laser light L on the surface of the photosensitive drum 31 in the sub-scanning direction is installed on the main body side of the color copying machine 1 and photosensitive. On the side of the body drum 31, a reflection mirror 120 that reflects the laser light L is installed integrally with the drum support unit 30 that holds the photosensitive drum 31. As a result, even when the drum support unit 30 needs to be replaced due to the life of the photosensitive drum 31, it is not necessary to replace the sub-scanning position detection sensor 110. The maintenance cost of the copying machine 1 can be reduced. In addition, since the detection signal from the sub-scanning position detection sensor 110 can be directly received without passing through a connection portion such as a connector, the detection signal can be processed without being affected by disturbance such as noise.

[Embodiment 4]
In the third embodiment, a configuration in which a reflection mirror that reflects the laser light L from the light source 101 is integrally installed in the drum support unit 30 and the sub-scanning position detection sensor 110 is installed on the main body side of the image forming apparatus will be described. did. In the present embodiment, a reflection mirror that reflects the laser light L from the light source 101 in parallel with the incident optical path is integrally installed on the drum support unit 30, and the sub-scanning position detection sensor 110 is integrated in the laser exposure device 25. The structure installed in will be described. In addition, about the structure similar to Embodiment 3, the same code | symbol is used and the detailed description is abbreviate | omitted here.

  The configuration for detecting the position of the laser beam L in the sub-scanning direction for each line scan on the surface of the photosensitive drum 31 in the present embodiment will be described. In the present embodiment, for example, in the color copying machine 1 of the first embodiment, a reflection mirror 121 as an example of a laser reflecting section that reflects the laser light L from the light source 101 in parallel with the incident optical path is integrated with the drum support unit 30. Is installed. Further, the sub-scanning position detection sensor 110 as an example of a detection unit that detects the position of the laser light L on the surface of the photosensitive drum 31 in the sub-scanning direction and generates a sub-scanning position signal corresponding to the position in the sub-scanning direction is laser-exposed. It is integrally installed inside the device 25.

FIG. 18 is a plane for explaining the arrangement positional relationship among the laser exposure apparatus 25 of the present embodiment, the reflection mirror 121 that reflects the laser light L from the light source 101 in parallel with the incident optical path, and the sub-scanning position detection sensor 110. FIG. FIG. 19 is a schematic view of the XX cross section of FIG.
As shown in FIG. 19, the reflection mirror 121 is integrally installed on a housing 30a of a drum support unit (photosensitive unit) 30 as an example of a photosensitive support member that rotatably supports the photosensitive drum 31. . In addition, as shown in FIG. 18, the reflection mirror 121 is in the region where the laser beam L scans and exposes the surface of the photosensitive drum 31 so as not to affect image formation. 31 is disposed in the vicinity of the surface of the photosensitive drum 31 in a region closer to the end in the axial direction than the region where the image is formed on the surface (image forming region). At this time, the reflection mirror 121 is preferably arranged in the upstream end region of the scanning line, similarly to the sub-scanning position detection sensor 110 in the first embodiment.

Further, as shown in FIGS. 18 and 19, the sub-scanning position detection sensor 110 is provided inside the laser exposure device 25 and on the optical path of the reflected laser light L <b> 1 reflected by the reflection mirror 121. Are arranged in one piece. That is, the sub-scanning position detection sensor 110 is disposed separately from the drum support unit 30. With such a configuration, when the relative position between the laser beam L and the photosensitive drum 31 in the sub-scanning direction is deviated, the laser on the mirror surface of the reflecting mirror 121 that moves integrally with the photosensitive drum 31. The amount of movement of the light L and the amount of movement of the reflected laser light L1 detected on the sensor surface of the sub-scanning position detection sensor 110 are detected so as to have a 1: 1 relationship regardless of the amount of movement. .
Note that the sub-scanning position detection sensor 110 may be disposed outside the laser exposure apparatus 25 as long as it is disposed integrally with the laser exposure apparatus 25.

20A shows the optical path of the laser beam L when the exposure position of the laser beam L from the light source 101 is moved by the configuration and vibration of the reflection mirror 121, and FIG. 20B shows the reflection mirror by vibration. It is the figure which showed the optical path of the laser beam L when 121 moves.
As shown in FIG. 20, the reflection mirror 121 is disposed so as to face the first reflection surface 122 and the first reflection surface 122 that is inclined at 45 ° with respect to the laser light L from the light source 101. In addition, the second reflecting surface 123 disposed at an angle of 45 ° with respect to the laser light L from the light source 101 has a configuration disposed toward the laser exposure device 25 side. By arranging the first reflecting surface 122 and the second reflecting surface 123 in this way, the reflecting mirror 121 reflects the incident laser beam L in a direction parallel to the incident optical path.

Here, as shown in FIG. 20A, for example, when the laser exposure device 25 vibrates, the laser light L incident on the first reflecting surface 122 of the reflecting mirror 121 is converted into laser light La, laser light Lb, It is assumed that the optical path has moved like the laser beam Lc. In that case, the reflected laser beam L1a, the reflected laser beam L1b, and the reflected laser beam L1c reflected by the second reflecting surface 123 are reflected by an optical path parallel to the laser beam La, the laser beam Lb, and the laser beam Lc. .
At this time, since the first reflecting surface 122 and the second reflecting surface 123 are both opposed to the incident laser beam L at an angle of 45 °, the laser beam La is, for example, at the first reflecting surface 122. The position a1 where the light is reflected and the position a1 where the laser beam La reflected at the position a of the first reflecting surface 122 is reflected by the second reflecting surface 123 are the first reflecting surface 122 and the second reflecting surface 123. The positions are symmetrical with respect to a plane m parallel to the optical path of the laser beam L passing through the intersecting vertex T. Therefore, the distance between the laser beam La, the laser beam Lb, and the laser beam Lc, that is, the movement amount of the laser beam L is equal to the distance among the reflected laser beam L1a, the reflected laser beam L1b, and the reflected laser beam L1c. Therefore, by detecting the reflected laser beam L1a, reflected laser beam L1b, and reflected laser beam L1c by the sub-scanning position detection sensor 110, the position of the laser beam L on the surface of the photosensitive drum 31 can be detected. .

  Further, as shown in FIG. 20B, for example, when the drum support unit 30 vibrates, the incident position a of the laser light L incident on the first reflecting surface 122 of the reflecting mirror 121 changes to a ′. Suppose. Accordingly, the reflection position changes from a1 to a′1. In that case, the reflected laser beam L1a and the reflected laser beam L1b reflected by the second reflecting surface 123 are parallel to the incident laser beam La. Therefore, the distance between the reflected laser beam L1a and the reflected laser beam L1b, That is, the amount of deviation of the drum support unit 30 is a change in the distance between the reflected laser beam L1a and the reflected laser beam L1b. Therefore, by detecting the reflected laser beam L1a and the reflected laser beam L1b with the sub-scanning position detection sensor 110, the position of the laser beam L on the surface of the photosensitive drum 31 can be detected.

For this reason, in the sub-scanning position detection sensor 110 of the present embodiment, generally, when the vibration of the drum support unit 30 and the vibration of the laser exposure device 25 occur simultaneously or independently, The position in the sub-scanning direction on the surface of the photosensitive drum 31 is detected by the irradiation position on the sensor surface of the reflected laser light L1 by the sub-scanning position detection sensor 110, and this is detected on the surface of the photosensitive drum 31 by a predetermined calculation process. A sub-scanning position signal is generated by converting into a scanning direction position.
The sub-scanning position signal generated by the sub-scanning position detection sensor 110 is output to the laser driver 109 in real time. The laser driver 109 adjusts the light amount of the semiconductor laser of the light source 101 in real time based on the sub-scanning position signal input from the sub-scanning position detection sensor 110.
As the sub-scanning position detection sensor 110, the PSD (see FIG. 5) described in the first embodiment, the photodiode shown in FIG. 9, the line CCD (Charge Coupled) arranged in the line shape shown in FIG. Devices) and the like can be used.

Further, since the reflected laser beam L1 reflected by the reflecting mirror 121 is reflected in a direction parallel to the incident optical path of the incident laser beam L, the reflected laser beam L1 returns to the laser exposure device 25. Therefore, the sub-scanning position detection sensor 110 can be integrally disposed inside the laser exposure device 25.
Further, the distance between the apex T and the position a where the first reflecting surface 122 reflects the laser beam L incident on the reflecting mirror 121 is appropriately set, and the distance between the incident laser beam L and the reflected laser beam L1 reflected. Is set within a predetermined value. Thereby, since the reflected laser beam L1 can be introduced into the laser exposure device 25 from a laser emission port (not shown) of the laser exposure device 25, an opening for introducing the reflected laser beam L1 into the laser exposure device 25 is separately provided. There is no need to provide it.

  As described above, in the color copying machine 1 of the present embodiment, the reflected laser beam from the reflection mirror 121 that is integrally installed on the drum support unit 30 and reflects the laser beam L from the light source 101 parallel to the incident optical path. L1 is detected by the sub-scanning position detection sensor 110 installed in the laser exposure apparatus 25. Thereby, as described in the first embodiment, the position of the laser beam L in the sub-scanning direction on the surface of the photosensitive drum 31 is detected in real time for each scanning line. When the position of the laser beam L in the sub-scanning direction is shifted to the upstream side of the rotation direction of the photosensitive drum 31 from the original irradiation position (exposure position), the scanning pitch in the sub-scanning direction becomes dense. The laser driver 109 reduces the amount of light of the semiconductor laser of the light source 101 according to the amount of deviation. As a result, the light spot diameter of the scanning line is reduced, and the generation of a stripe-patterned high density portion in the sub-scanning direction caused by the dense scanning pitch between the scanning lines is suppressed.

On the other hand, when the position of the laser beam L in the sub-scanning direction is shifted to the downstream side in the rotation direction of the photosensitive drum 31 from the original irradiation position, the scanning pitch in the sub-scanning direction becomes sparse, so the laser driver 109 The amount of light of the semiconductor laser of the light source 101 is increased according to the amount of deviation. As a result, the light spot diameter of the scanning line is increased, and therefore, the generation of the stripe-patterned low density portion in the sub-scanning direction caused by the sparse scanning pitch between the scanning lines is suppressed.
As a result, even when the relative position between the laser exposure device 25 and the photosensitive drum 31 changes due to vibration in the color copying machine 1, banding that occurs on the image formed by the color copying machine 1 is prevented. Reduced to a level that is not noticeable visually.
As described above, the “upstream side in the rotation direction of the photoconductor” here means a direction side in which the surface of the photoconductor advances due to the rotation of the photoconductor, and “downstream in the rotation direction of the photoconductor”. Means the direction opposite to the direction in which the surface of the photoconductor advances due to the rotation of the photoconductor.

  Further, in the color copying machine 1 of the present embodiment, the sub-scanning position detection sensor 110 that detects the position of the laser light L on the surface of the photosensitive drum 31 in the sub-scanning direction is installed inside the laser exposure device 25, and the photosensitive drum. On the side 31, a reflection mirror 121 that reflects the laser beam L is installed integrally with the drum support unit 30 that holds the photosensitive drum 31. As a result, even when the drum support unit 30 needs to be replaced due to the life of the photosensitive drum 31, it is not necessary to replace the sub-scanning position detection sensor 110. The maintenance cost of the copying machine 1 can be reduced. In addition, since the detection signal from the sub-scanning position detection sensor 110 can be directly received without passing through a connection portion such as a connector, the detection signal can be processed without being affected by disturbance such as noise.

1 is a diagram showing a color copying machine as an example of an image forming apparatus to which Embodiment 1 is applied. FIG. It is the figure which showed the structure of the laser exposure apparatus, and the state in which a laser exposure apparatus scans and exposes a photosensitive drum. It is a figure explaining the arrangement position of a sub-scanning position detection sensor. It is a figure explaining the fluctuation | variation of the relative position between a laser exposure apparatus and a photosensitive drum. It is a figure explaining PSD as an example of a sub-scanning position detection sensor. It is a figure explaining the detection of the subscanning direction position of the laser beam. It is a processing flowchart which sets the light quantity of the semiconductor laser of a light source. It is the figure which showed the relationship between the timing which detects the subscanning direction position of each scanning line by a subscanning position detection sensor, and the calculation time of the light quantity in a laser driver. It is the figure which showed the other structural example of the subscanning position detection sensor. It is the figure which showed the other structural example of the subscanning position detection sensor. It is a figure which shows the structure which installed the subscanning position detection sensor integrally in the drum support unit. FIG. 5 is a diagram illustrating a digital color printer as an example of an image forming apparatus to which Embodiment 2 is applied. It is a top view explaining the arrangement positional relationship of a laser exposure apparatus, the reflective mirror which reflects the laser beam L from a light source, and a subscanning position detection sensor. It is the schematic of the XX cross section of FIG. For example, when a vibration direction deviation occurs in the arrangement position of the drum support unit due to the vibration, a deviation in the sub-scanning direction generated at a position where the laser light L irradiates the surface of the photosensitive drum and a sensor surface of the sub-scanning position detection sensor. It is a figure explaining the relationship with the shift | offset | difference of the irradiation position which arises. 6 is a diagram illustrating a case where the vibration direction of the drum support unit matches the sub-scanning direction at the exposure position of the laser beam L. FIG. 6 is a diagram showing a case where the vibration direction of the drum support unit matches the sub-scanning direction in a configuration in which the mirror surface of the reflection mirror is arranged to match the sub-scanning direction at the exposure position of the laser beam L. FIG. It is a top view explaining the arrangement positional relationship of a laser exposure apparatus, the reflective mirror which reflects the laser beam L from a light source in parallel with an incident optical path, and a sub-scanning position detection sensor. It is the schematic of the XX cross section of FIG. (A) shows the optical path of the laser beam L when the exposure position of the laser beam L from the light source moves due to the configuration and vibration of the reflection mirror, and (b) shows the laser beam L when the reflection mirror moves due to the vibration. It is the figure which showed the optical path.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Color copying machine, 2 ... Digital color printer, 10 ... Image reading part, 20 ... Image formation process part, 22 ... Image processing part (IPS), 25, 25Y, 25M, 25C, 25K ... Laser exposure apparatus, 26Y, 26M, 26C, 26K ... image forming unit, 30 ... drum support unit, 30a, 100a ... housing, 31 ... photoconductor drum, 60 ... control unit, 65 ... photoconductor positioning member, 100 ... optical unit, 101 ... light source, 102 ... collimator lens, 103 ... cylinder lens, 104 ... rotating polygon mirror (polygon mirror), 105 ... fθ lens, 106 ... folding mirror, 107, 120, 121 ... reflection mirror, 108 ... SOS sensor (light receiving element), 109 ... laser Driver, 110 ... sub-scanning position detection sensor

Claims (3)

A plurality of photoconductors arranged in parallel;
A plurality of laser exposure units corresponding to the photoconductor, and scanning exposure of the photoconductor with one or a plurality of laser beams;
A photosensitive member positioning member for integrally positioning the plurality of photosensitive members on the apparatus main body;
A sensor that detects an irradiation position in the sub-scanning direction of the laser beam from the laser exposure unit that exposes one of the plurality of photosensitive members;
The plurality of laser exposure units set the light amount of the laser light based on the irradiation position of the laser light detected by the sensor in the sub-scanning direction. 2. The image according to claim 1, wherein each of the plurality of photoconductors is disposed on a photoconductor support member that rotatably supports the photoconductor, and the sensor is attached to the photoconductor support member. Forming equipment. The sensor image forming apparatus according to claim 1, wherein the integrally attached to the photosensitive member positioning member.

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