JP2013029615A - Optical scanner and image forming device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that prevents a write start position on a scanned surface from being shifted due to temperature change, with a simple configuration without increasing costs, thereby enabling highly accurate optical scanning.SOLUTION: The optical scanner has a housing 19 that includes a laser diode (light source) 20, a polygon mirror 23 that deflects light beams L, L1 emitted from the laser diode 20, and a synchronization detection sensor 27 that detects the light beam L1 deflected by the polygon mirror 23 to output a first synchronization signal for writing. The light beam L1 deflected by the polygon mirror 23 is made incident on the synchronization detection sensor 27 in a sub-scanning direction. The synchronization detection sensor 27 is mounted on a wall 19a where the laser diode 20 in the housing 19 is mounted, so that the detection position is aligned with the height of an optical axis x.

Description

  The present invention relates to an optical scanning device that scans a surface to be scanned with a light beam condensing spot and an image forming apparatus such as a copying machine and a printer equipped with the optical scanning device.

  In an image forming apparatus such as a copying machine or a printer, an image carrier whose surface is uniformly charged by a charger is exposed and scanned by an optical scanning device, and an electrostatic latent image corresponding to image information is formed on the surface. The The electrostatic latent image is developed by a developing device using toner as a developer to be visualized as a toner image. The toner image is transferred onto a sheet by a transfer device and then heated and heated by a fixing device. A series of image forming operations is completed by discharging the sheet having the toner image fixed thereon by being pressed and fixed on the sheet.

  An example of a conventional optical scanning device is shown in FIG.

  That is, FIG. 5 is a perspective view of a conventional optical scanning device. As shown in the figure, a housing 1 19 of the optical scanning device 112 is provided with a laser diode 120 as a light source. A collimator lens (not shown), a cylindrical lens 122, and a polygon mirror 123 as a deflector are arranged in a straight line along the direction of emission of the light beam L from the light source.

  In the housing 119, two fθ lenses 124 and 125 and a folding mirror 126 are disposed along the traveling direction of the light beam L deflected by the polygon mirror 123. The effective scanning range of the light beam L is deflected by a synchronous detection sensor 127 that is a light detection element and a polygon mirror 123 to the left and right of the position outside the effective scanning range (scanning range that is actually used as a print width) R. A pre-PD mirror 128 that reflects the light beam L1 traveling along the optical path off R and guides it to the synchronization detection sensor 127 is disposed.

  Thus, in the optical scanning device 112 configured as described above, when the laser diode 120 is ON / OFF controlled according to the image signal, the light beam modulated in accordance with the image data from the laser diode 120. L is emitted, and this light beam L is converted into a parallel light beam by a collimator lens (not shown), and this parallel light beam L forms an image on the reflection surface of the polygon mirror 123 by a cylindrical lens 122 having power only in the sub-scanning direction. And deflected by the polygon mirror 123 that rotates at high speed. Then, the deflected light beam L is condensed at the same speed by the fθ lenses 124 and 125 and is folded by the folding mirror 126 to form a condensed spot on the photosensitive drum 102 which is the surface to be scanned. The drum 102 is exposed and scanned in the main scanning direction, and an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 102.

  In addition, the light beam L1 is reflected by the pre-PD mirror 128 and is incident on the synchronization detection sensor 127 arranged outside the effective scanning range R, and the synchronization detection sensor 127 detects the light beam L1. A write synchronization signal is output from the detection sensor 127, and the exposure scanning (writing) start timing of the light beam L onto the photosensitive drum 102 is determined by this synchronization signal.

  By the way, in the applied optical scanning device 112, the housing 119 expands or contracts due to a temperature change, and the position of the synchronous detection sensor 127 attached to the housing 119 is in the main scanning plane (horizontal plane) in the direction of the arrow in FIG. The timing of detecting the light beam of the synchronous detection sensor 127 is shifted and the writing position on the photosensitive drum 102 is shifted. Particularly, in a color image forming apparatus, a color shift occurs in a color image. To do.

  Therefore, Patent Document 1 proposes a configuration in which the front PD mirror is rotatably supported around one end support portion, and the write front position is controlled by rotating the front PD mirror according to a temperature change. .

JP 2006-267701 A

  However, the configuration proposed in Patent Document 1 requires a mechanism and control means for rotating the pre-PD mirror, and there is a problem that the configuration and control are complicated, resulting in an increase in cost.

  The present invention has been made in view of the above problems, and the object of the present invention is to achieve high accuracy by suppressing a shift due to a temperature change of a writing position on a surface to be scanned with a simple configuration without increasing the cost. An object of the present invention is to provide an optical scanning apparatus capable of optical scanning and an image forming apparatus capable of stably forming a high quality image.

  In order to achieve the above object, the invention described in claim 1 is directed to a housing, wherein a light source, a deflector for deflecting a light beam emitted from the light source, and a light beam deflected by the deflector are detected and written. And a synchronization detection sensor that outputs a synchronization signal of the light beam, the light beam deflected by the deflector is incident on the synchronization detection sensor in a sub-scanning direction, and the synchronization detection sensor is disposed on the housing. It is characterized in that the detection position is attached to the wall to which the light source is attached so as to coincide with the height of the optical axis.

  According to a second aspect of the present invention, in the first aspect of the present invention, there is provided a reflection mirror that reflects the light beam deflected by the deflector and enters the synchronous detection sensor in the sub-scanning direction. .

  An image forming apparatus according to a third aspect includes the optical scanning device according to the first or second aspect.

  According to the first aspect of the present invention, the light beam deflected by the deflector is incident on the synchronization detection sensor in the sub-scanning direction, and the detection position of the synchronization detection sensor is set on the wall of the housing attached with the light source. Since it is mounted so as to match the height of the optical axis, the expansion or contraction of the housing in the sub-scanning direction due to the temperature change is smaller than the expansion or contraction in the main scanning surface, and the temperature in the main scanning surface of the synchronization detection sensor. The synchronization detection sensor can detect the light beam incident in the sub-scanning direction with high accuracy and output a synchronization signal regardless of the positional shift caused by the change. In addition, the synchronization detection sensor is mounted on the wall of the housing where the light source is mounted so that its detection position coincides with the height of the optical axis. Therefore, the synchronization detection sensor can suppress a deviation in timing for detecting the light beam in the sub-scanning direction that travels along the optical axis. For this reason, complicated mechanisms and control means are not required, and high-precision optical scanning can be performed with a simple configuration and suppressing a shift due to a temperature change of the writing position on the surface to be scanned without increasing costs. .

  According to the second aspect of the present invention, the light beam deflected in the main scanning direction by changing the reflection angle of the light beam according to the angle of the reflecting mirror and the shape of the reflecting surface can be incident on the synchronous detection sensor in the sub-scanning direction. it can.

  According to the third aspect of the present invention, since high-precision optical scanning is performed by the optical scanning device, a high-quality image can be stably obtained, and a color image without color misregistration can be obtained in the color image forming apparatus. be able to.

1 is a side sectional view of an image forming apparatus (color laser printer) according to the present invention. 1 is a perspective view of an optical scanning device according to the present invention. It is a figure which shows the arrival path | route of the light beam to the synchronous detection sensor of the optical scanning device based on this invention. It is a figure which shows the arrival path | route of the light beam to the synchronous detection sensor of the optical scanning device based on this invention. It is a perspective view of the conventional optical scanning device.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[Image forming apparatus]
FIG. 1 is a side sectional view of a color laser printer as an embodiment of an image forming apparatus according to the present invention. The illustrated color laser printer is a tandem type, and a magenta image is formed at a central portion of the main body 100. The unit 1M, the cyan image forming unit 1C, the yellow image forming unit 1Y, and the black image forming unit 1K are arranged in tandem at regular intervals.

  Each of the image forming units 1M, 1C, 1Y, and 1K is provided with photosensitive drums 2a, 2b, 2c, and 2d, which are image carriers, and a charger 3a is disposed around each of the photosensitive drums 2a to 2d. , 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d and cleaning devices 6a, 6b, 6c, 6d are arranged, respectively.

Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in a direction indicated by an arrow (counterclockwise) by a driving motor (not shown). The chargers 3a to 3d uniformly charge the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source (not shown).
Further, the developing devices 4a to 4d contain magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (K) toner, respectively, and are formed on the photosensitive drums 2a to 2d. In addition, the toner of each color is attached to each electrostatic latent image to visualize each electrostatic latent image as a toner image of each color.

  The transfer rollers 5a to 5d are arranged so as to be able to contact the photosensitive drums 2a to 2d via the intermediate transfer belt 7 in the respective primary transfer portions. Here, the intermediate transfer belt 7 is stretched between a driving roller 8 and a tension roller 9 and is disposed on the upper surface side of each of the photosensitive drums 2a to 2d. The driving roller 8 is a secondary roller. The transfer unit is disposed so as to be in contact with the secondary transfer roller 10 via the intermediate transfer belt 7. Further, an optical density sensor 11 is disposed at a position facing the intermediate transfer belt 7 in the vicinity of the driving roller 8.

  Further, below the image forming units 1M, 1C, 1Y, and 1K in the printer main body 100, a total of four optical scanning devices 12 according to the present invention are provided corresponding to the image forming units 1M, 1C, 1Y, and 1K. The paper feed cassette 13 is detachably installed at the bottom of the printer main body 100 below the printer body 100. A plurality of sheets (not shown) are stacked and accommodated in the sheet feeding cassette 13. In the vicinity of the sheet feeding cassette 13, the sheets are taken out from the sheet feeding cassette 13 and transported to the transport path S one by one. A transport roller pair 14 is provided.

  Further, in the transport path S extending in the vertical direction on the side portion of the printer main body 100, the secondary which is a contact portion between the driving roller 8 and the secondary transfer roller 10 at a predetermined timing after the paper is temporarily held. A registration roller pair 15 is provided to be supplied to the transfer unit.

  By the way, the conveyance path S arranged in the vertical direction on one side portion in the printer main body 100 extends to a paper discharge tray 16 provided on the upper surface of the printer main body 100, and the fixing device 17 and the discharge path are disposed in the middle. A paper roller pair 18 is provided.

  Next, an image forming operation by the color laser printer having the above configuration will be described.

  When an image formation start signal is issued, the respective photosensitive drums 2a to 2d are driven to rotate in a direction indicated by an arrow (counterclockwise) in the image forming units 1M, 1C, 1Y, and 1K at a predetermined process speed. 2a to 2d are uniformly charged by the chargers 3a to 3d. Further, each optical scanning device 12 emits a light beam modulated by a color image signal for each color, irradiates the surface of each photosensitive drum 2a to 2d, and each color is applied to each photosensitive drum 2a to 2d. The electrostatic latent images corresponding to the color image signals are respectively formed.

  First, magenta toner is attached to the electrostatic latent image formed on the photosensitive drum 2a of the magenta image forming unit 1M by the developing device 4a to which a developing bias having the same polarity as the charged polarity of the photosensitive drum 2a is applied. The electrostatic latent image is visualized as a magenta toner image. The magenta toner image is moved in the direction indicated by the arrow in the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 5a by the action of the transfer roller 5a to which a primary transfer bias having a polarity opposite to that of the toner is applied. Primary transfer is performed on the intermediate transfer belt 7 that is rotationally driven.

  The intermediate transfer belt 7 on which the magenta toner image has been primarily transferred as described above moves to the next cyan image forming unit 1C. In the cyan image forming unit 1C as well, the cyan toner image formed on the photosensitive drum 2b is transferred to the magenta toner image on the intermediate transfer belt 7 in the primary transfer portion in the same manner as described above.

  Similarly, yellow and black toners respectively formed on the photosensitive drums 2c and 2d of the yellow and black image forming units 1Y and 1K on the magenta and cyan toner images superimposed and transferred on the intermediate transfer belt 7, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 7. The transfer residual toner that is not transferred onto the intermediate transfer belt 7 and remains on the photosensitive drums 2a to 2d is removed by the cleaning devices 6a to 6d, and the photosensitive drums 2a to 2d are prepared for the next image formation. .

  The pair of transport rollers 14 from the paper feed cassette 13 is synchronized with the timing at which the front end of the full-color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion (transfer nip portion) between the drive roller 8 and the secondary transfer roller 10. Thus, the sheet sent to the transport path S is transported to the secondary transfer portion by the registration roller pair 15. Then, a full-color toner image is collectively transferred from the intermediate transfer belt 7 onto the sheet conveyed to the secondary transfer unit by the secondary transfer roller 10 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. .

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 17, where the full-color toner image is heated and pressurized and thermally fixed on the surface of the sheet, and the sheet on which the toner image is fixed Then, the paper is discharged onto the paper discharge tray 16 by the paper discharge roller pair 18, and a series of image forming operations is completed.

[Optical scanning device]
Next, the optical scanning device 12 according to the present invention will be described with reference to FIGS. Since all the four optical scanning devices 12 have the same configuration, only one optical scanning device 13 will be described below.

  FIG. 2 is a perspective view of the optical scanning device according to the present invention, and FIGS. 3 and 4 are views showing the arrival path of the light beam to the synchronization detection sensor in the optical scanning device. As shown in FIG. A laser diode (LD) 20 that is a light source is provided on a wall 19 a that vertically stands of the housing 19 of the scanning device 12, and the light beam L from the laser diode 20 is emitted in the housing 19. A collimator lens 21, a cylindrical lens 22, and a polygon mirror 23 as a deflector are arranged on a straight line.

  In the housing 19, two fθ lenses 24 and 25 and a folding mirror 26 are disposed along the traveling direction of the light beam L deflected by the polygon mirror 23. Further, between the fθ lens 25 and the folding mirror 26, on the left and right of the position outside the effective scanning range (scanning range actually used as the print width) R of the light beam L, the synchronization detection sensor 27 and the light A pre-PD mirror 28 that reflects the beam L1 and guides it to the synchronous detection sensor 27 is disposed.

  The synchronization detection sensor 27 outputs a synchronization signal by detecting a light beam L1 that is deflected by the polygon mirror 23 and travels an optical path out of the effective scanning range R, and includes a photodiode and a phototransistor. Various optical sensors such as photo ICs are used. In the present embodiment, the pre-PD mirror 28 is mounted in a state inclined at a predetermined angle with respect to the horizontal plane (main scanning plane) as shown in FIG. 3, and is deflected by the polygon mirror 23 to be in an effective scanning range. The light beam L1 traveling along the optical path out of R is reflected by the pre-PD mirror 28 and is incident on the synchronization detection sensor 27 in the sub-scanning direction (vertically upward as indicated by arrow a in FIG. 3). On the other hand, the light beam L which is deflected by the polygon mirror 23 and travels along the optical path within the effective scanning range R advances the folding mirror 26 horizontally in the main scanning direction as shown by an arrow b in FIG. 2a (2b to 2d) is exposed and scanned in the main scanning direction. In the present embodiment, a configuration in which the PD front mirror 28 is inclined with respect to the horizontal plane (main scanning plane) in order to cause the light beam L1 to enter the synchronization detection sensor 27 in the sub-scanning direction is employed. It is also possible to adopt a configuration in which the reflection surface 28 is curved and the light beam L1 is incident on the synchronization detection sensor 27 in the sub-scanning direction.

  Thus, in the present embodiment, as shown in FIG. 4, the synchronization detection sensor 27 is located on the side of the wall 19a of the housing 19 where the laser diode 20 is attached, on the side facing the laser diode 20, and the detection position is the laser. The diode 20 is mounted so as to coincide with the height of the optical axis x.

  In the optical scanning device 12 shown in FIG. 2 configured as described above, when the laser diode 20 is ON / OFF controlled according to the image signal, the light beam modulated from the laser diode 20 in accordance with the image data. L is emitted, and the light beam L is converted into a parallel light beam by the collimator lens 21, and this parallel light beam L is imaged on the reflection surface of the polygon mirror 23 by the cylindrical lens 22 having power only in the sub-scanning direction. It is deflected by a polygon mirror 23 that rotates at high speed. The deflected light beam L is condensed at the same speed by the fθ lenses 24 and 25, and is folded by the folding mirror 26 to form a condensed spot on the photosensitive drum 2a (2b to 2d) that is the surface to be scanned. As a result, the photosensitive drums 2a (2b to 2d) are exposed and scanned in the main scanning direction, and electrostatic latent images corresponding to the color image signals of the respective colors are formed on the photosensitive drums 2a (2b to 2d). .

  Further, the light beam L1 is reflected by the pre-PD mirror 28 on the synchronization detection sensor 27 arranged outside the effective scanning range R, and this light beam L1 is directed to the synchronization detection sensor 27 in the sub-scanning direction (the direction of arrow a in FIG. 3). Is incident on. Then, the synchronization detection sensor 27 detects the light beam L1 and outputs a synchronization signal. Based on this synchronization signal, the timing for starting exposure scanning (writing) on the photosensitive drum 2a (2b to 2d) by the light beam L is determined. .

  As described above, in the optical scanning device 12 according to the present invention, the light beam L1 deflected by the polygon mirror 23 is incident on the synchronization detection sensor 27 in the sub-scanning direction by the pre-PD mirror 28 and the synchronization detection sensor. 27 is attached to the wall 19a of the housing 19 to which the laser diode 20 is attached so that its detection position coincides with the height of the optical axis x of the laser diode 20, so that the housing 19 in the sub-scanning direction (vertical direction) due to temperature change. The expansion or contraction is smaller than the expansion or contraction in the longitudinal direction in the main scanning plane, and the synchronization detecting sensor 27 is sub-regardless of the positional shift caused by the temperature change in the main scanning plane. It is possible to detect the light beam L1 incident in the scanning direction with high accuracy and output a synchronization signal.

  In addition, the synchronization detection sensor 27 is attached to the wall 19a of the housing 19 where the laser diode 20 is attached so that its detection position coincides with the height of the optical axis x of the laser diode 20. And the laser diode 20 are displaced by the same amount in conjunction with the sub-scanning direction, so that the synchronization detection sensor 27 can suppress a deviation in timing for detecting the light beam L1 in the sub-scanning direction that travels along the optical axis x. .

  Therefore, according to the optical scanning device 12 of the present invention, complicated mechanisms and control means are not required, and the temperature change of the writing position on the photosensitive drum 2a (2b to 2d) can be achieved with a simple configuration without increasing the cost. It is possible to perform high-precision optical scanning while suppressing the deviation caused by the above.

  Since the optical scanning device 12 performs high-precision optical scanning on the photosensitive drum 2a (2b to 2d) as described above, the color laser printer shown in FIG. Can be obtained.

  Here, the amount of deviation in the detection scanning direction (sub-scanning direction) of the synchronization detection sensor 27 in the optical scanning device 12 according to the present invention shown in FIG. 2 and the detection of the synchronization detection sensor 127 in the conventional optical scanning device 112 shown in FIG. A trial calculation of the amount of deviation in the scanning direction (main scanning direction) is as follows.

When the linear expansion coefficient of the material constituting the housings 19 and 119 is 1.8 × 10 ⁻⁵ / ° C. in the horizontal direction, 3.0 × 10 ⁻⁵ / ° C. in the vertical direction, and the temperature rise is 20 ° C., FIG. Since the distance between the reflection surface of the polygon mirror 123 serving as a scanning reference in the conventional optical scanning device 112 shown in FIG. 1 and the center position of the synchronization detection sensor 127 in the scanning direction is 120 mm as shown in the figure, the synchronization detection sensor 127 The amount of deviation in the detection scanning direction (main scanning direction) is obtained by the following equation.

1.8 × 10 ^{−5 /} ° C. × 20 ° C. × 120 mm = 43.2 μm
On the other hand, in the optical scanning device 12 according to the present invention shown in FIG. 2, the synchronization detection sensor 27 and the laser diode 20 are attached to the same wall 19a of the housing 19 as shown in FIG. Even if it exists, there is no change in the height positional relationship between the synchronous detection sensor 27 and the laser diode 20.

  However, since the mounting heights of the collimator lens 21, the cylindrical lens 22, and the fθ lenses 24 and 25 are different from each other, if there is a temperature rise, the height relationship between these, the synchronization detection sensor 27, and the laser diode 20 is slightly shifted. . For example, as shown in FIG. 4, when the mounting height position of the fθ lenses 24 and 25 is 10 mm from the optical axis x, the shift amount in the detection scanning direction (main scanning direction) of the synchronous detection sensor 27 is obtained by the following equation. .

3.0 × 10 ^{−5 /} ° C. × 20 ° C. × 10 mm = 6.0 μm
Therefore, according to the optical scanning device 12 of the present invention, the shift amount in the detection scanning direction of the synchronization detection sensor 27 is set to 1 of the shift amount in the detection scanning direction of the synchronization detection sensor 127 in the conventional optical scanning device 112 shown in FIG. / 7 or so.

  Although the present invention has been described with respect to a mode in which the present invention is applied to a color laser printer and an optical scanning device provided in the color laser printer, the present invention is not limited to any other image forming apparatus including a monochrome printer and a copying machine. Of course, the present invention can be similarly applied to the optical scanning device provided for this.

1M Magenta image forming unit 1C Cyan image forming unit 1Y Yellow image forming unit 1K Black image forming unit 2a to 2d Photosensitive drum 3a to 3d Charger 4a to 4d Developing device 5a to 5d Transfer roller 6a to 6d Cleaning device 7 Intermediate transfer belt 8 Driving roller 9 Tension roller 10 Secondary transfer roller 11 Optical density sensor 12 Optical scanning device 13 Paper feed cassette 14 Transport roller pair 15 Registration roller pair 16 Paper discharge tray 17 Fixing device 18 Paper discharge roller pair 19 Optical scanning device housing 19a Housing wall 20 Laser diode (light source)
21 Collimator lens 22 Cylindrical lens 23 Polygon mirror (deflector)
24, 25 fθ lens 26 Folding mirror 27 Synchronization detection sensor 28 PD front mirror (reflection mirror)
100 Printer body L, L1 Light beam R Effective scanning range S Transport path x Optical axis

Claims (3)

Light having a light source, a deflector for deflecting a light beam emitted from the light source, and a synchronization detection sensor for detecting a light beam deflected by the deflector and outputting a synchronization signal for writing. In the scanning device,
The light beam deflected by the deflector is incident on the synchronization detection sensor in the sub-scanning direction, and the detection position of the synchronization detection sensor coincides with the height of the optical axis on the wall of the housing where the light source is attached. An optical scanning device characterized by being mounted as described above.   The optical scanning device according to claim 1, further comprising a reflection mirror that reflects the light beam deflected by the deflector and causes the light to be incident on the synchronization detection sensor in a sub-scanning direction. An image forming apparatus comprising the optical scanning device according to claim 1.

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