JP2008122611A - Scanning optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning optical device in which laser light which is enough to be detected by a light quantity detection sensor without providing a beam splitting means such as a half mirror is secured, a laser output is controlled in a state the light quantity necessary for forming an image on a photoreceptor drum is not reduced, and further various troubles arising when power of the laser light, which is reduced by being split by the use of the conventional beam splitting means, is increased can be solved. <P>SOLUTION: The laser light output from a semiconductor laser is taken into a polygon mirror 6. The laser light emitted form the polygon mirror 6 is focused on a photoreceptor drum 13 through scanning lenses 7 and 8. An incident mirror 5 is disposed on the optical path of the laser beam, the back to back face of the scanning lenses 7 and 8 is a flat face or a face having a large radius of curvature, and a portion of the laser light which is emitted from the incident mirror 5 and reflected from the back to back face and which does not contribute to an image formation is taken into a light quantity detection sensor S to be detected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a scanning optical device used in an electrophotographic image forming apparatus such as a laser beam printer or a digital copying machine.

  In general, in a laser scanning optical system constituting a scanning optical device, a laser beam output from a light source such as a semiconductor laser is corrected to parallel light by a collimator lens, and is condensed into a linear shape by a cylinder lens, and is a polygon that is a deflector Output toward the mirror. The laser light deflected and scanned by the polygon mirror is sent to the scanning lens as scanning light, and the scanning light emitted from the scanning lens is irradiated onto the photosensitive drum, which is the image carrier, to form a spot-like image. It is designed to be optimally narrowed down to scan.

  FIG. 6 shows an example of a laser unit of the laser scanning optical system. In this case, an edge-emitting semiconductor laser chip 51 is held by a holder 52, and a laser drive circuit 53 is provided at the rear of the holder 52. A collimating lens 54 for correcting the laser light L into parallel light is disposed on the front side of the laser chip 51, and a light amount detection such as a photodiode for detecting the laser light L ′ from the laser chip 51 is provided on the back side of the laser chip 51. Element 55 is arranged. The laser chip 51 and the collimating lens 54 are fixed in a state where the optical axis and focus are adjusted, and the light quantity detection element 55 is built in the package.

  Accordingly, when the laser light L from the laser chip 51 is diffused and emitted from the window 56, it is corrected to parallel light by the collimator lens 54 and becomes the laser light Lc. The laser light L ′ on the back side of the laser chip 51 is detected by the light quantity detection element 55 and used for so-called APC operation for holding an appropriate quantity of light output from the laser chip 51. In this APC operation, it is used that the laser light L and the laser light L ′ change approximately equivalently with respect to the laser driving current. Usually, the amount of light is increased immediately before the start of scanning or between sheets. Adjusted.

  On the other hand, it is known that a semiconductor laser having a plurality of light sources is used so that a plurality of dots can be simultaneously recorded in parallel and the recording scan is speeded up. Even in this case, the APC operation is required to keep the output light amount at an appropriate amount.

  FIG. 7 shows an example of a laser scanning optical system using a surface emitting laser array (VCSEL) as a light source when a plurality of laser beams are generated from a semiconductor laser having a plurality of light sources. That is, a plurality of laser beams output from the light source 100 are deflected and scanned by the polygon mirror 102, and scanning exposure is performed simultaneously at a plurality of points on the photosensitive drum 104.

  Since the surface emitting laser in the example of FIG. 7 does not generate backward emission light unlike the edge emitting laser of FIG. 6, a part of the laser light directed to the scanning surface such as the photosensitive drum is separated and detected. Therefore, it is necessary to enter the light amount detecting element.

  In this regard, a configuration for monitoring the beam light amount as shown in FIG. 8 is known. That is, a beam separation optical element such as a beam splitter or a half mirror 106 is arranged in the laser scanning optical system, and a part of the laser light output from the surface emitting laser 108 is separated by the half mirror 106 and taken into the light amount detection element 110. . Thus, monitor control is performed by detecting the beam light quantity.

  As another example, an apparatus has been proposed in which a plurality of laser light beams output from a plurality of light sources are detected by a plurality of light quantity detection elements (see, for example, Patent Document 1). That is, a part of the laser light branched by the half mirror is condensed and individually detected by the light amount detection element, and the light amount of the beam is controlled based on the detection signal.

  As another example, there has also been proposed an apparatus in which a coating for correcting a change in the amount of light on the surface to be scanned is applied to a folding mirror (see, for example, Patent Document 2). In other words, when the polarization state changes, the characteristics of the beam separation element change, thereby reducing the amount of light applied to the photosensitive drum. In order to prevent this, a coating that corrects the change in the amount of light on the surface to be scanned in accordance with the change in the polarization state is applied to the folding mirror.

Japanese Patent Laid-Open No. 7-110450 JP 2003-215485 A

  However, the laser scanning optical system of FIGS. 6 to 8 and the devices of Patent Documents 1 and 2 have the following common problems.

  Typically, in the apparatus of FIG. 8, a laser beam is output from a light source such as a surface emitting laser 108 to a photosensitive drum so as to form an image, and a part of the laser beam is extracted by a separating means such as a half mirror. The output light quantity is controlled by detecting it. That is, a beam separating means such as a half mirror not related to image formation is arranged in the middle of the laser beam optical path to the photosensitive drum, and spectrally separates for light quantity detection. Therefore, the amount of light applied to the photosensitive drum is reduced by the amount of the spectrally separated light, and the power is increased in order to obtain the laser power required to expose the photosensitive drum at a predetermined potential. There is a need.

  Regarding the power enhancement of the laser beam, as in Patent Document 2, applying a coating that corrects a change in the amount of light on the photosensitive drum according to the polarization state to the folding mirror reduces the reflectance of the folding mirror by a correction amount in advance. It is necessary to keep. Therefore, the amount of light detected and corrected is reduced from the amount of light for image formation. When the laser power is increased in order to compensate for the decreased light amount, the heat generation is increased accordingly, and the temperature characteristics of the laser beam are changed, and the laser life is also affected.

  An object of the present invention is to secure a sufficient amount of laser light to be detected by a light amount detection sensor without providing a new beam spectroscopic means such as a half mirror, and in a state in which the light amount necessary for image formation is not reduced by a photosensitive drum. It is an object of the present invention to provide a scanning optical device capable of controlling laser output.

The scanning optical device of the present invention includes a rotary polygon mirror that deflects and scans laser light output from a light source,
An imaging lens for forming an image of scanning light changed and scanned from the rotary multifaceted light, a light amount detection sensor for detecting laser light output from the light source, and an output of the light source based on the output of the light amount detection sensor And a control means for controlling the output, wherein the normal spring of the incident surface on which the laser light of the imaging lens is incident is tilted with respect to the sub-scanning direction, and the light quantity detection sensor is the incident light It is characterized by detecting laser light reflected by the surface.

  According to the scanning optical device of the present invention, it is possible to provide a scanning optical device capable of securing laser light for light amount detection without providing a new beam spectroscopic means such as a half mirror for light amount detection.

  Hereinafter, a preferred embodiment of a scanning optical device according to the present invention will be described in detail with reference to the drawings.

(Laser scanning optical system: first embodiment)
As shown in FIGS. 1 and 2, the scanning optical device 1 of the present embodiment is constituted by each element of the following laser scanning optical system, and a laser beam extending from a semiconductor laser 2 as a light source to a photosensitive drum 13 as an image carrier. Form an optical path. That is, it has a collimating lens 3 that corrects laser light emitted and output from the semiconductor laser 2 to parallel light, and a cylinder lens 4 that condenses the parallel light emitted from the collimating lens 3 linearly. In addition, an incident mirror 5 is provided for guiding the laser light emitted from the collimating lens 3 and the cylinder lens 4 to a polygon mirror (optical deflector) 6. The laser light incident on the polygon mirror 6 by the incident mirror 5 is deflected and scanned, and has scanning lenses 7 and 8 as imaging lenses on which the laser light emitted as the scanning light is incident. The scanning lenses 7 and 8 emit the scanning light toward the scanning surface on the photosensitive drum 13 and form an image as a predetermined spot. Guide mirrors 9, 10, and 12 for guiding the scanning light to the photosensitive drum 13 are disposed in the laser beam optical path leading to the image formation. Further, a correction lens 11 for correcting the inclination of the reflection surface of the polygon mirror 6 is also provided.

  By the way, it does not make sense for the laser light guided by the incident mirror 5 and incident on the polygon mirror 6 to return to the incident mirror 5 from the polygon mirror 6 again as scanning light. In order to prevent this, it is necessary to make the laser beam from the incident mirror 5 incident on the polygon mirror 6 from an oblique direction.

  Further, the scanning lenses 7 and 8 are generally a combination of a concave lens and a convex lens. In the scanning lenses 7 and 8, laser light reflected by a flat surface or a surface having a large curvature radius (a surface having a small curvature) that is nearly flat reaches the photosensitive drum 13 simultaneously with regular scanning light as extra reflected light. It may end up. When excess reflected light is irradiated onto the photosensitive drum 13, there is a problem that a vertical stripe appears at the center of the image, causing an image defect.

  That is, there is no problem if the laser light emitted from the polygon mirror 6 is guided to the photosensitive drum 13 as regular scanning light through the scanning lenses 7 and 8. However, a part of the laser light emitted from the polygon mirror 6 is reflected by the flat surface of the concave / convex scanning lenses 7 and 8 or a surface having a large curvature radius, and is reflected as reflected light through the guide mirrors 9, 10 and 12 and the correction lens 11. It reaches the body drum 13 and appears as vertical stripes. Incidentally, the reflectance on the surface of a scanning lens using a glass lens or a plastic lens is said to be about 1% with an antireflection coating, and about 4% without an antireflection coating.

  Therefore, the gist of the present embodiment is to prevent re-incidence of the laser beam to the incident mirror 5 as described above and to prevent image defects due to vertical stripes embodied on the photosensitive drum 13.

  One gist of the invention is that the scanning lenses 7 and 8 formed by the concave and convex lenses are provided at an appropriate inclination angle with respect to the sub-scanning direction. By doing so, the laser light reflected by the polygon mirror 6 is reflected by the flat surface of the scanning lenses 7 and 8 or the surface having a large curvature radius so as not to reach the photosensitive drum 13 as extra reflected light. The following are specific examples.

  As apparent from FIG. 2, the lens surface of the scanning lens 7 facing the scanning lens 8 and the lens surface of the scanning lens 8 facing the scanning lens 7, that is, the back-to-back surfaces of both concave and convex lenses are flat surfaces. Or a substantially flat surface having a large radius of curvature.

  Most of the laser light guided by the incident mirror 5 is incident on the polygon mirror 6, deflected and scanned, reflected and travels toward the scanning lenses 7 and 8, and is narrowed down by the concave and convex lens surfaces to be scanned as regular scanning light. , 8 are emitted. Then, it reaches the photosensitive drum 13 through the guide mirrors 9, 10, and 12. At this time, a part of the laser light from the incident mirror 5 is reflected by the lens surface of the scanning lens 7 on the side facing the scanning lens 8, and the problem of being directed toward the photosensitive drum 13 as extra reflected light is the aforementioned problem. Just as you did.

  In order to prevent this, the scanning lenses 7 and 8 are respectively arranged in a state where they are rotated by a predetermined angle in the clockwise direction and tilted. Thereby, the laser light from the incident mirror 5 reflected by the lens surface of the scanning lens 7 on the side facing the scanning lens 8 is reflected light more than most regular laser light traveling from the incident mirror 5 to the polygon mirror 6. It passes through the scanning lens 8 without overlapping in the lower region. The extra reflected light reflected by the scanning lens 7 passes through the scanning lens 8 and then passes above the incident mirror 5, so that it does not return and reenter the incident mirror 5.

  The extra reflected light from the scanning lens 7 that has passed on the incident mirror 5 does not contribute to image formation, apart from that taken into the photosensitive drum 13 as scanning light. It will be noted that such reflected light that does not contribute to image formation is used as detection light for performing laser output control (APC operation). That is, the reflected light is captured and detected by the sensor S by the light amount detection element disposed in front of the guide mirror 9, and the laser output in a state in which the light amount necessary for image formation is secured without decreasing based on the detection signal. Control becomes possible.

  As will be understood, conventionally, there is no need to provide beam spectroscopic means for taking in detection light. Therefore, the shortage of scanning light necessary for image formation due to spectroscopy is solved.

  The present inventors obtained the following conclusion from the results of the experimental measurement. As described above, the reflectance on the glass lens or plastic lens surface is about 1% when the antireflection coating is applied, and about 4% when the antireflection coating is not applied. Therefore, if the output of the semiconductor laser is 20 to 30 mW, the laser output can be controlled with about 1% of reflected light. Even if the laser light emitted from the semiconductor laser 2 is about 5 to 10 mW, Laser output control is possible with reflected light of about 4%. When reflected light that does not contribute to image formation reflected by the scanning lens 7 passes through the incident mirror 5, the reflected light is prevented from reentering the guide mirror 9 by the light amount detection sensor S and the light shielding means (not shown). The reflected light does not reach the photosensitive drum 13.

(Laser scanning optical system: second embodiment)
FIG. 3 shows a second embodiment that should be referred to as an application example of the first embodiment shown in FIGS. 1 and 2.

  In this case, the scanning lenses 7 and 8 are different from those of the first embodiment in that the scanning lenses 7 and 8 are arranged in a state of being rotated counterclockwise at a predetermined angle. Therefore, the reflected light reflected by the flat surface of the scanning lens 7 facing the scanning lens 8 or the surface having a large radius of curvature passes through the scanning lens 8 in a region above the scanning light emitted from the polygon mirror 6. That is, the reflected light reflected by the scanning lens 7 passes through the scanning lens 8, then passes through the upper side of the incident mirror 5, passes through the upper side of the guiding mirror 9, and is disposed behind the guiding mirror 9. Is incident on. The reflected light from the scanning lens 7 is detected by the light quantity detection sensor S, and the laser output control based on the detection signal enables the laser output control without reducing the light quantity necessary for image formation.

(Laser scanning optical system: Third embodiment)
In the third embodiment shown in FIGS. 4 and 5, the scanning optical device 20 in this case is configured to include the following optical system equipment. That is, it has a semiconductor laser 21 as a light source, a collimating lens 22 that corrects laser light from the semiconductor laser 21 into parallel light, a cylinder lens 23 that condenses the laser light in a linear shape, and light deflection. A polygon mirror 24 is provided. Further, the scanning optical device 20 includes scanning lenses 25 and 26 for forming an image of a laser beam scanned by the polygon mirror 24 as a predetermined spot on a not-shown photosensitive member (drum or belt). Have. In addition, a guide mirror 27 is provided for guiding the scanning light to the photosensitive member for irradiation.

  Further, in the scanning optical device 20 of the present embodiment, since the laser light from the semiconductor laser 21 is directly incident on the polygon mirror 24 without passing through the scanning lens, there is no member corresponding to the incident mirror 5 in the above-described embodiment. The laser light incident on the polygon mirror 24 from the cylinder lens 23 and the scanning light from the polygon mirror 24 are in the same plane perpendicular to the reflection surface of the polygon mirror 24. Further, the optical box 30 with a lid 31 is provided, and the optical system equipment except the guide mirror 27 is accommodated in the optical box 30.

  Further, in order to shield wind noise generated from the polygon mirror 24 and to prevent the reflection surface of the polygon mirror 24 from being contaminated, the periphery of the polygon mirror 24 is sealed with a cover 32 as a cover portion. The cover 32 is provided with an opening 32a as a transmission port through which the laser light emitted and output from the semiconductor laser 2 and the scanning light from the polygon mirror 24 pass, and a window glass (for sealing the opening 32a) A transmission glass) 33 is attached.

  The surface of the window glass 33 is flat. When the laser light incident on the polygon mirror 24 is reflected, the reflected laser light reaches the photosensitive drum 13 as extra reflected light via the scanning lenses 25 and 26, the mirror 27, the wall surface of the optical box 30, or the like. Sometimes. As a result, vertical stripes appear at the center of the image, and image defects are likely to occur. In order to prevent this, even if the window glass 33 is tilted in the sub-scanning direction and the laser light incident on the polygon mirror 24 is reflected by the surface of the window glass 33, the reflected light does not reach the photoconductor. An appropriate tilt angle is set.

  In this case, the window glass 33 is arranged in a state of being rotated and rotated at a predetermined angle in the counterclockwise direction. Therefore, the reflected light reflected by the surface of the window glass 33 passes through the scanning lens 25 in an area above the scanning light when entering the polygon mirror 24, and is above the scanning area between the scanning lenses 25 and 26. Is incident on the light quantity detection sensor S2. Laser output control is possible without detecting the amount of light necessary for image formation by detecting the light reflected by the surface of the window glass 33 by the light amount detection sensor S2 and performing laser output control based on the detection signal. .

  Further, the light quantity detection sensor S2 is reflected on the surface so that the reflected light from the surface of the window glass 33 detected by the light quantity detection sensor S2 is reflected again on the surface of the light quantity detection sensor S2 and does not reach the photosensitive member. It is tilted at an appropriate angle. By performing processing such as shading and antireflection also around the light amount detection sensor S2, it is possible to prevent the occurrence of image defects due to the reflected light reflected.

  In the above, several examples of the embodiments of the scanning optical device of the present invention have been described. However, the present invention is not limited to these embodiments, and other embodiments, application examples, and the like are within the scope of the present invention. Variations and combinations thereof are also possible.

  For example, in the third embodiment, the periphery of the polygon mirror 24 is sealed with a cover having an opening through which laser light enters and exits. However, a wall and a cover having an opening through which the laser light provided in the optical box enters and exits. A configuration in which the periphery of the polygon mirror is sealed is also possible. In this case as well, the laser output can be controlled by detecting the reflected light from the window glass that seals the opening.

  Further, as shown in each embodiment, it is assumed that the laser output control can be performed on the surface emitting semiconductor laser that does not generate backward emission light without reducing the light amount for image formation. The present invention is not limited to such a surface-emitting type semiconductor laser, and even in an edge-emitting type semiconductor laser, if any one of the embodiments is applied and laser output control is performed, no backward emission light is required, so that it can be used for image formation. It is also possible to increase the amount of laser light.

The figure which shows 1st Embodiment of the scanning optical apparatus by this invention. The figure which shows the optical system and laser beam path of the principal part in the 1st Embodiment. The figure which shows the scanning optical apparatus by 2nd Embodiment. The figure which shows the scanning optical apparatus by 3rd Embodiment. The figure which similarly shows the optical system and laser beam path of the principal part of the same 3rd Embodiment. The figure which shows the structure of the edge-emitting semiconductor laser of a prior art example. The figure which shows the scanning optical apparatus using the surface emitting laser array of a prior art example. The figure which shows the beam separation optical element of a prior art example.

Explanation of symbols

1 Scanning Optical Device 2 Semiconductor Laser (Laser Light Source)
3 Collimator lens 4 Cylindrical lens 5 Incident mirror 6 Polygon mirror (optical deflector)
7, 8 Scanning lens 9, 10, 12 Guide mirror 11 Correction lens 13 Photosensitive drum (image carrier)
S light quantity detection sensor 30 optical box 33 window glass

Claims (3)

A rotating polygon mirror that deflects and scans the laser beam output from the light source;
An imaging lens for imaging the scanning light changed and scanned from the rotary polygonal surface;
A light amount detection sensor for detecting laser light output from the light source;
A scanning optical device having control means for controlling the output of the light source based on the output of the light quantity detection sensor,
The normal spring of the incident surface on which the laser light of the imaging lens is incident is positioned to be inclined with respect to the sub-scanning direction, and the light amount detection sensor detects the laser light reflected by the incident surface. Scanning optical device. A rotating polygon mirror that deflects and scans the laser beam output from the light source;
The cover portion is provided with a transmission port that transmits light deflected and scanned by the rotary polygon mirror, and a cover portion that surrounds the periphery of the rotary polygon mirror;
A transmission glass that closes the transmission port;
A light amount detection sensor for detecting laser light output from the light source;
In the scanning optical device that controls the output of the light source based on the output of the light amount detection sensor,
A normal line of an incident surface on which the laser light of the transmissive glass is incident is inclined with respect to a sub-scanning direction, and the light amount detection sensor detects the laser light reflected by the incident surface. Scanning optical device.   The light quantity detection sensor is provided at an angle that does not directly face the reflected light reflected by the lens or the transmission glass, and a light shielding means is provided around the light quantity detection sensor to block the reflected light from reaching the rear. The scanning optical device according to claim 1, wherein the scanning optical device is a scanning optical device.

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