JP2008122678A - Scanning optical device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning optical device that can control a curved amount of a laser scanning beam on a scanning object at a low cost, without causing increase in the scale of the device. <P>SOLUTION: The scanning optical device 2 is equipped with a collimating optical element 22 that collimates a laser beam emitted from a light source into a parallel flux, and a linear condensing optical element 23, that condenses the collimated laser beam to a sub-scanning direction orthogonal to the main scanning direction and focuses the beam onto a rotating polygon mirror 24. A parallel plate 4 capable of transmitting the collimated laser beam is placed, as swingable around an axis extending in the main scanning direction, between the collimating optical element 22 and the linear light-condensing optical element 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a scanning optical device and an image forming apparatus.

  2. Description of the Related Art Conventionally, as a scanning optical device, for example, a device that is incorporated in an image forming apparatus and scans a photosensitive drum as a scanning target by deflecting laser light emitted from a light source with a rotating polygon mirror is known. Yes. In such a scanning optical apparatus, the surface tilt of the rotating polygon mirror may occur due to the processing accuracy of the rotating polygon mirror, and therefore a surface tilt correcting optical system is employed (see, for example, Patent Document 1).

  The surface tilt correction optical system, as a main component, condenses laser light emitted from a light source and converted into a parallel light beam by a collimating optical element in a sub-scanning direction orthogonal to the main scanning direction that is the scanning direction. A linear condensing optical element that forms an image linearly on the rotating polygon mirror, and an fθ optical element that forms an image of the laser beam deflected by the rotating polygon mirror in a dot pattern on the photosensitive drum. .

Further, in the scanning optical device described in Patent Document 1, in order to be able to adjust the amount of bending of the laser scanning line on the photosensitive drum, the main scanning direction disposed between the fθ lens and the photosensitive drum. A configuration is also employed in which the reflecting mirror extending in the direction is forcibly bent.
JP 2006-17881 A

  However, in the above configuration, since it is necessary to bend a relatively large reflecting mirror, the mechanism becomes large, and there is a problem that the cost is increased and the size of the apparatus is increased.

  In view of such circumstances, the present invention provides a scanning optical device capable of adjusting the amount of bending of a laser scanning line on a scanned object at low cost and without causing an increase in size of the device, and the scanning optical device. An object of the present invention is to provide an image forming apparatus including the apparatus.

  The invention according to claim 1 is a scanning optical device that scans a scanned object by deflecting laser light emitted from a light source with a rotating polygon mirror, and collimates the laser light emitted from the light source into a parallel light beam. An optical element, and a linear condensing optical element that focuses the laser beam made into a parallel light beam in a sub-scanning direction orthogonal to the main scanning direction, which is the scanning direction, and forms an image on the rotary polygon mirror A parallel plate capable of transmitting a laser beam converted into a parallel light beam is disposed between the collimating optical element and the linear focusing optical element, and the parallel plate has an axis extending in the main scanning direction. It is configured to be swingable around.

  According to a second aspect of the present invention, there is provided an image forming apparatus comprising: the scanning optical device according to the first aspect; and a photosensitive drum as the scanned body.

  According to the first aspect of the present invention, the parallel plate is disposed between the collimating optical element and the linear condensing optical element, and the parallel plate is configured to be swingable about an axis extending in the main scanning direction. By swinging the flat plate, the height position in the sub-scanning direction of the laser light incident on the linear condensing optical element can be changed. And, if the height position of the laser light incident on the linear condensing optical element is changed in this way, the incident angle at which the laser light transmitted through the linear condensing optical element enters the rotary polygon mirror changes, This makes it possible to adjust the amount of bending of the laser scanning line on the object to be scanned. That is, according to the present invention, the amount of bending of the laser scanning line on the scanning object is reduced at a low cost and without increasing the size of the apparatus by a simple configuration in which a relatively small parallel plate is swingably arranged. Can be made adjustable.

  According to the second aspect of the present invention, the amount of curvature of the laser scanning line on the photosensitive drum can be adjusted.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a printer 10 incorporating a scanning optical device (also referred to as a laser scanner unit or LSU) 2 according to an embodiment of the present invention. The scanning optical device 2 can be incorporated in an image forming apparatus other than a printer (for example, a copying machine, a facsimile machine, a multifunction machine, etc.).

  The printer 10 forms an image on a sheet based on image data sent from a terminal or the like in the middle of conveying the sheet along the conveyance path L. A photoconductor is provided inside the box-shaped apparatus main body 1. An image forming unit 13 that forms a toner image on the surface of the drum 131 and then transfers the toner image to a sheet, a paper feeding unit 12 that supplies the sheet to the image forming unit 13, and a fixing unit 14 that fixes the toner image on the sheet. And.

  The conveyance path L has a horizontal portion L1 extending substantially horizontally from the front to the rear (from the right side to the left side in FIG. 1), and a vertical portion L2 rising substantially vertically from the rear end portion of the horizontal portion L1. It is substantially L-shaped.

  The paper feed unit 12 includes a paper feed cassette 121 disposed below the horizontal portion L1 of the transport path L. The paper stored in the paper feed cassette 121 is taken out by a pickup roller 12a and the paper is Are fed one by one to the horizontal portion L1 of the conveyance path L by the paper feed rollers 12b to 12e, and the sheet fed to the conveyance path L is temporarily waited by the registration rollers 12f and supplied to the image forming unit 13 at a predetermined timing. It is supposed to be.

  The paper feed unit 12 also has a manual feed unit 122 disposed in the opening 11 provided on the front surface of the apparatus main body 1. The paper placed on the manual feed unit 122 is fed to the pickup roller 12 g and the paper supply unit 12. The paper rollers 12c and 12e can be sent to the horizontal portion L1 of the transport path L. The opening 11 can be opened and closed by a lid member 11a attached to the apparatus main body 1 so as to be swingable.

  The image forming unit 13 includes a photosensitive drum 131 disposed substantially at the center in the front-rear direction of the horizontal portion L1 of the conveyance path L, a charging unit 132 disposed above the photosensitive drum 131, and a photosensitive drum. A developing unit 133 disposed in front of 131, a transfer unit 134 disposed below the photosensitive drum 131, a cleaning unit 135 disposed behind the photosensitive drum 131, a charging unit 132, and a cleaning unit. The scanning optical device 2 is disposed above the fixing unit 14 and the fixing unit 14 in a posture in which the front side is lifted.

  The photosensitive drum 131 rotates in the clockwise direction in FIG. 1, and the surface of the photosensitive drum 131 is uniformly charged by the charging unit 132 and then based on the image data by the scanning optical device 2. An electrostatic latent image is formed by irradiating laser light between the charging unit 132 and the developing unit 133, and toner is supplied from the developing unit 133 to the surface on which the electrostatic latent image is formed. A toner image is formed.

  The paper supplied from the paper supply unit 12 is conveyed while being pressed against the photoconductive drum 131 by the transfer roller 134a of the transfer unit 134, so that the surface of the photoconductive drum 131 is transferred to the surface (transfer surface). The toner image formed on the toner image is transferred and then sent to the fixing unit 14.

  The residual charge and toner remaining on the surface of the photosensitive drum 131 after the transfer are removed by the cleaning unit 135.

  The fixing unit 14 includes a heat roller 14a and a pressure roller 14b. The toner image is fixed to the sheet with heat and pressure by sandwiching the sheet onto which the toner image has been transferred by the rollers 14a and 14b. It is supposed to let you.

  The sheet on which the toner image is fixed is discharged by a discharge roller 18 to a discharge unit 19 formed on the upper surface of the apparatus main body 1.

  In the printer 10 of the present embodiment, a switchback unit 15 is provided between the horizontal portion L1 of the transport path L and the paper feed cassette 121 so that images can be formed on both sides of the paper. .

  Specifically, as shown in FIGS. 2 and 3, the scanning optical device 2 deflects laser light emitted from a semiconductor laser 21 as a light source by a rotating polygon mirror (also referred to as a polygon mirror) 24. The housing 2A is a container-like housing 2A that scans on the photosensitive drum 131, which is the object to be scanned (see arrow A in FIG. 2), opens the semiconductor laser 21 and the rotary polygon mirror 24, and this housing And a lid 2B (see FIG. 1) that closes the opening of 2A. 2 and 3, the lid 2B is omitted.

  The semiconductor laser 21 is disposed at a substantially central position on the right side in the housing 2A, and emits laser light obliquely rearward on a surface parallel to the bottom surface 20 of the housing 2A.

  The rotary polygon mirror 24 is formed in a regular hexagonal plate shape, and is disposed at a rear position in the housing 2A. The rotary polygon mirror 24 is rotated at a constant speed counterclockwise in FIG. 3 by a motor fixed to the bottom surface 20 of the housing 2A in a state where the rotation axis is orthogonal. That is, in the housing 2A, a direction parallel to the bottom surface 20 is a main scanning direction that is the direction for performing the scanning, and a direction orthogonal to the bottom surface 20 is a sub-scanning direction that is orthogonal to the main scanning direction.

  Further, in the housing 2A, in addition to the semiconductor laser 21 and the rotary polygon mirror 24, a collimating optical element 22 for converting the laser light emitted from the semiconductor laser 21 into a parallel light beam, and the laser light made into the parallel light beam in the sub scanning direction. A cylindrical linear condensing optical element 23 that focuses light on the rotating polygon mirror 24 and forms a linear image on the rotating polygon mirror 24, and a laser beam that is disposed in front of the rotating polygon mirror 24 and is deflected by the rotating polygon mirror 24. Two fθ optical elements 25, 26 that form a dot image on the photosensitive drum 131, and a reflection mirror 27 that reflects the laser light transmitted through the fθ optical elements 25, 26 toward the photosensitive drum 131. It is installed. The housing 2A has an opening at a position where the laser light reflected by the reflecting mirror 27 passes, and a dustproof glass 28 is provided so as to close the opening. The laser light passes through the dustproof glass 28. The light passes through and is radiated out of the housing 2A.

  Although not shown, an aperture is provided in the housing 2A to shape the laser beam that has been converted into a parallel light beam by the collimating optical element 22 into an elongated circle extending in the main scanning direction. The aperture, the linear condensing optical element 23, and the fθ optical elements 25 and 26 constitute a surface tilt correction optical system.

  As the linear condensing optical element 23, for example, a toroidal shape other than the cylindrical shape can be adopted.

  Further, in the housing 2A, a photoelectric element 31 mounted on the wiring board 32 is disposed at a right front position as a configuration for obtaining a horizontal synchronization signal for determining an image writing timing in an image area where scanning is performed. In addition, a reflection mirror 33 that reflects the laser beam reflected by the rotary polygon mirror 24 toward the photoelectric element 31 before entering the image area is disposed at the left front position. A condensing lens 34 that condenses the laser light reflected by the reflecting mirror 33 is disposed between the reflecting mirror 33 and the photoelectric element 31. Then, the light receiving element 31 receives the laser light reflected by the reflecting mirror 33 and collected by the condensing lens 34, whereby a horizontal synchronization signal is acquired, and the semiconductor laser 21 in the image region is referenced based on this horizontal synchronization signal. The light emission start timing and the like are controlled.

  Furthermore, between the collimating optical element 22 and the linear condensing optical element 23, a parallel plate 4 capable of transmitting a laser beam converted into a parallel light beam is disposed. The parallel plate 4 is made of glass, for example, and has a rectangular plate shape that is flat in the optical axis direction of the laser light and extends in the main scanning direction, as shown in FIGS.

  The bottom surface 20 of the housing 2A is provided with support means 5 for supporting the parallel plate 4 so as to be swingable about an axis extending in the main scanning direction. In the following, for convenience of explanation, the optical axis direction of the laser light is referred to as the X direction, the direction toward the rotary polygon mirror 24 is referred to as the + X direction, and the opposite direction is referred to as the −X direction.

  The supporting means 5 is a protrusion having a trapezoidal cross-sectional shape that protrudes upward from the bottom surface 20 and extends in the main scanning direction, and a mounting portion 55 on which the parallel plate 4 is mounted, and the parallel plate 4. And a support wall 51 rising from the bottom surface 20 so as to cover from the −X direction. Note that the upper surface 55 a of the mounting portion 55 is set larger in the X direction than the lower surface of the parallel plate 4.

  The support wall 51 is provided with a rectangular opening 51a extending in the main scanning direction for passing laser light. A set screw 53 is screwed into the upper portion of the support wall 51 in the center of the main scanning direction in a state of passing through the support wall 51, and the upper portion of the parallel plate 4 is placed in the −X direction on the upper end surface of the support wall 51. A pair of left and right leaf springs 61 to be urged are attached, and the upper part of the parallel plate 4 is pressed against the tip of the set screw 53 by the leaf spring 61.

  Further, a semi-cylindrical protrusion 52 that protrudes in the + X direction and extends in the main scanning direction is provided below the support wall 51. On the other hand, a leaf spring 62 for urging the lower portion of the parallel plate 4 in the −X direction is attached to the inclined surface on the + X direction side of the mounting portion 55, and the lower portion of the parallel plate 4 is supported by the leaf spring 62. It is pressed against 51 ridges 52.

  Therefore, from the state in which the parallel plate 4 shown in FIG. 5A is orthogonal to the optical axis of the laser beam, the set screw 53 is turned to advance the set screw 53 in the + X direction against the urging force of the leaf spring 61. Then, as shown in FIG. 5B, the parallel flat plate 4 swings in the + X direction around the axis extending in the main scanning direction, with the corner portion 4a between the lower surface and the surface on the + X direction side as a fulcrum. become.

  On the contrary, when the parallel plate 4 shown in FIG. 5A is orthogonal to the optical axis of the laser beam, when the set screw 53 is rotated to retract the set screw 53 in the −X direction, the parallel plate 4 is Although not shown by being biased by the spring 61, the corner portion 4b between the lower surface and the surface on the −X direction side is used as a fulcrum, that is, swings in the −X direction around an axis extending in the main scanning direction. Become.

  If the parallel plate 4 is swung in this way, the position of the optical axis in the sub-scanning direction is lowered from L1 to L2 due to refraction by the parallel plate 4 as shown in FIG. The height position in the sub-scanning direction of the laser light incident on the linear condensing optical element 23 can be changed.

  Even if the height position of the laser light incident on the linear condensing optical element 23 is changed, the focal position when the linear condensing optical element 23 condenses the linear light does not change. Only the incident angle at which the laser light transmitted through the element 23 enters the rotary polygon mirror 24 changes. As a result, the amount of curvature of the laser scanning line on the photosensitive drum 131 can be adjusted.

  The reason for this is that, as shown in FIG. 7, there is a reflection surface entering and exiting (position variation in the X direction) due to the rotation of the rotating polygonal mirror 24, so that by adding an angle to the incident angle incident on the rotating polygonal mirror 24, The position of the reflection point in the sub-scanning direction varies within the range of Δh. If the laser scanning line on the photoconductive drum 131 is a straight line when the optical axis is at the position L1, the laser scanning line on the photoconductive drum 131 is set by setting the optical axis to the position L2. An amount of curvature commensurate with Δh is produced. In other words, if the laser scanning line on the photosensitive drum 131 is curved for some reason, the parallel plate 4 is swung in the + X direction or the −X direction to the rotating polygon mirror 24 of the laser light. The amount of curvature can be adjusted by changing the incident angle.

  As described above, in the scanning optical device 2 of the present embodiment, a relatively small parallel plate 4 is arranged so as to be swingable between the collimating optical element 22 and the linear focusing optical element 23. In addition, the amount of bending of the laser scanning line on the photosensitive drum 131 can be adjusted at low cost and without causing an increase in the size of the apparatus.

  Here, when the parallel plate 4 is provided before the collimator optical element 23 or after the linear condensing optical element 23, when the parallel plate 4 is swung, the laser scanning lines on the photosensitive drum 131 are moved in the sub-scanning direction. Since it moves, it is necessary to further employ an optical system or the like for correcting it. On the other hand, in the scanning optical device 2 of the present embodiment, the parallel flat plate 4 is disposed between the collimating optical element 22 and the linear condensing optical element 23, and the linear condensing that condenses the laser light in a linear form. By using the function of the optical element 23, in other words, the existing surface tilt correction optical system rationally, the amount of curve of the laser scanning line is not accompanied by the movement of the laser scanning line on the photosensitive drum 131 in the sub-scanning direction. It is possible to adjust.

  In the above-described embodiment, the present invention is applied to a monochrome image forming apparatus. However, the present invention is particularly effective for a tandem color image forming apparatus.

  Further, the scanning optical device 2 may be incorporated not only in the image forming apparatus but also in a printing machine that directly scans and prints a laser beam on a sheet.

  Further, as the support means 5, the parallel plate 4 may be supported so as to be swingable using a swing shaft, and the configuration thereof can be changed as appropriate.

1 is a schematic configuration diagram of a printer in which a scanning optical device according to an embodiment of the present invention is incorporated. It is a perspective view of a scanning optical apparatus. It is a top view of a scanning optical apparatus. It is a perspective view of the part by which the parallel plate of a scanning optical apparatus is arrange | positioned. (A) is a perspective view when a parallel plate is perpendicular to the optical axis, and (b) is a perspective view when the parallel plate is swung forward. It is a schematic diagram of a laser beam when viewed from the main scanning direction. (A) (b) is explanatory drawing explaining the reason which can adjust bending amount.

Explanation of symbols

10 Printer (image forming device)
131 Photosensitive drum (scanned body)
2 Scanning Optical Device 21 Semiconductor Laser 22 Collimating Optical Element 23 Linear Condensing Optical Element 24 Rotating Polyhedral Mirror 4 Parallel Plate 5 Supporting Means

Claims (2)

A scanning optical device that scans a scanned object by deflecting laser light emitted from a light source with a rotating polygon mirror,
A collimating optical element that converts laser light emitted from a light source into a parallel light beam, and the laser light that has been converted into a parallel light beam is condensed in a sub-scanning direction orthogonal to the main scanning direction, which is the scanning direction. A linear focusing optical element that forms an image on the top,
Between the collimating optical element and the linear condensing optical element, a parallel plate capable of transmitting a laser beam converted into a parallel light beam is disposed, and the parallel plate is arranged around an axis extending in the main scanning direction. A scanning optical device configured to be swingable.   An image forming apparatus comprising: the scanning optical device according to claim 1; and a photosensitive drum as the scanned body.

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