JP2007225844A - Optical scanner, image forming apparatus and method of detecting laser beams in optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner in which the positions of laser beams corresponding to respective colors in a subscanning direction are detected at high accuracy with an inexpensive means, scanning beams are adjusted and corrected to predetermined positions on the basis of the detected results and the shift of the positions of the beams are suppressed when the optical scanner is built in a color image forming apparatus, and to obtain a method of detecting the laser beams in the optical scanner. <P>SOLUTION: The optical scanner includes: a light source apparatus 1; a defection scanning means 7; scanning focusing means 8a and 8b; and laser beam detecting means 101a and 101b. The laser beam detecting means includes: diffraction optical elements 103a and 103b which shape the defected and scanned laser beams into a pattern consisting of dots or lines; and a plurality of light receiving elements PD1 and PD2 for detecting the pattern, wherein the plurality of light receiving elements have a light receiving face wider than the luminous flux width in a main scanning direction of dots or lines composing the pattern. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus, an image forming apparatus, and a laser beam detecting method applicable to a copying machine, a printer, and the like, and in particular, a laser beam for detecting the position of a laser beam in the sub-scanning direction. It is about detection.

  A so-called tandem system is known as one type of color image forming apparatus. This comprises an optical scanning device in which a plurality of image carriers such as photosensitive drums are juxtaposed and the surface of each image carrier is scanned with a plurality of laser beams corresponding to each image carrier. Each laser beam is emitted from a semiconductor laser that is driven and controlled in accordance with the image information signal of each color to be read. Each laser beam is focused on each uniformly charged surface of the image carrier through optical components such as a deflection scanning unit including a polygon mirror and a scanning imaging lens. Scanning is performed in the main scanning direction on the surface of the image carrier. Along with this main scanning, each image carrier is rotated about its axis to perform sub-scanning, and the surface of the image carrier is scanned with a laser beam having a predetermined interval in the sub-scanning direction to thereby obtain each image. An electrostatic latent image corresponding to the image signal is formed on the surface of the carrier. The latent image on the surface of each image carrier is developed with toner of a color corresponding to each image signal, and a color image is obtained by superimposing each toner image and transferring it onto a transfer paper or the like.

  In the optical scanning device used in such a tandem type color image forming apparatus, since the components are arranged so that the laser beam directed to the image carrier corresponding to each color passes through different paths, color image formation The scanning imaging lens is thermally deformed due to the environmental temperature in which the apparatus is installed and the temperature rise in the apparatus, and the position of the scanning beam is likely to fluctuate. In particular, when a resin lens is used, the resin lens has a large coefficient of thermal expansion, so that the scanning beam position variation due to temperature variation becomes significant.

In a tandem color image forming apparatus, if the image writing start position by each optical scanning shifts, color misregistration occurs in the color image transferred in an overlapping manner and the image quality deteriorates. Therefore, each laser beam is individually deflected and scanned. The light receiving element is arranged so that it can be detected at the start end side, and the timing from when the detection signal is output to the start of writing is adjusted for each laser beam so that the write start positions by a plurality of laser beams are aligned. Yes. The adjustment of the writing start position is adjustment in the main scanning direction.
The above color misregistration also occurs in the sub-scanning direction that is a direction orthogonal to the main scanning direction. As a cause of color misregistration in the sub-scanning direction, there are various factors such as laser optical axis misalignment due to temperature change, and eccentricity of an image bearing member, for example, a photosensitive drum.

  In view of this, the above-described misalignment of the scanning position is periodically detected and corrected at the start-up of the apparatus or between jobs based on the resist misregistration detection pattern recorded on the transfer body. However, during continuous printing operation, the scanning position further fluctuates due to the heat generated by the fixing device and the polygon motor, so that there is a problem that the color misregistration gradually increases when the number of prints for one job is large.

The prior art aimed at eliminating color misregistration in a color image forming apparatus will be described with specific examples.
The first prior art includes a polygon mirror that deflects and reflects a plurality of laser beams emitted from a plurality of semiconductor lasers, and deflects and scans each of the laser beams, and the light deflected and scanned by the polygon mirror is perpendicular to the scanning direction. A light-receiving element that receives light from one side and emits light from the other side that is inclined with respect to the scanning direction, and a signal that is output when the light-receiving element receives laser light in response to image information from the semiconductor laser. And an optical scanning device comprising: a control means for emitting the emitted light; and an optical system for guiding image information light emitted from the plurality of semiconductor lasers and scanned by the polygon mirror to the plurality of photosensitive drums. The present invention relates to an image forming apparatus using the apparatus (see, for example, Patent Document 1). According to the optical scanning device configured as described above and an image forming apparatus using the optical scanning device, when the laser light is shifted in the sub-scanning direction, the light receiving element detects the laser light on the incident side in the scanning direction of the light receiving element. However, the timing at which the light receiving element detects the laser beam changes on the light emitting element emitting side in the scanning direction, so the amount of deviation of the scanning light in the sub-scanning direction depends on this timing deviation. Can be calculated. If a correction means for correcting the calculated shift amount is provided, the shift amount can be eliminated.

  The second prior art is an image forming apparatus capable of detecting a pitch shift in the sub-scanning direction of a plurality of light beams in an optical scanning device, and scanning a light beam detection region in order to detect a light beam position. A plurality of sensors consisting of light receiving elements whose start edges are non-parallel to each other are arranged, and the time intervals of the light beams crossing the scanning start ends of the plurality of sensors are measured by individually lighting the plurality of beams. Is converted into a sub-scanning pitch between the beams (for example, see Patent Document 2).

  However, in the method of detecting the amount of positional deviation of the scanning line in the sub-scanning direction by making the shape of the light receiving element special as described in Patent Document 1 and Patent Document 2, the light receiving element is It was necessary to set a complicated layout as well as a large and complicated shape, which increased the overall size and increased the cost.

Japanese Patent Laid-Open No. 10-235928 JP-A-7-72399

  In order to detect a shift in the scanning position due to the laser beam, a special photo IC is also provided in the optical scanning device. This photo IC has a built-in light receiving element and a comparator circuit, which are integrated into an IC, and has a drawback that the cost is high. When a general-purpose inexpensive photo IC having a light receiving surface with a simple shape is used, the scanning field angle of the optical deflector is narrow, and the laser beam misalignment must be detected outside the image area of the scanning range. For this reason, the optical characteristic (fθ characteristic) of the scanning beam in the detection region is significantly different from the characteristic of the image region, and there is a problem that detection accuracy is low. Furthermore, when a general-purpose inexpensive photo IC is used, since the change in the amount of received light also affects the detection accuracy, there is a problem that the detection accuracy is degraded due to various factors related to the change in the amount of received light. Incidentally, factors related to the change in the amount of received light include changes in the light source output (for example, due to temperature fluctuations), optical element reflectivity and transmittance deterioration with time, and rotation of the optical deflector due to changes in pixel density during image formation. There are number changes.

The present invention has been made to solve the problems of the prior art as described above. When incorporated in a tandem color image forming apparatus, the position of the laser beam corresponding to each color in the sub-scanning direction is increased. An optical scanning device capable of suppressing beam misalignment by detecting the accuracy with inexpensive means and adjusting and correcting the scanning beam to a predetermined position using the detection result, and the laser beam in the optical scanning device The object is to obtain a detection method.
Another object of the present invention is to obtain an image forming apparatus capable of obtaining a high-quality color image using the optical scanning device.

  According to the present invention, the laser beam emitted from the light source device is deflected and scanned in the main scanning direction by the deflection scanning means, and the laser beam to be deflected and scanned is collected toward the surface to be scanned. A scanning imaging means for emitting light, and a laser beam detecting means for detecting the position of the laser beam, wherein the laser beam detecting means is a diffraction for shaping the laser beam to be deflected and scanned into a pattern of predetermined dots or lines. An optical element and a plurality of light receiving elements for detecting a pattern comprising dots or lines constituting the pattern, wherein the plurality of light receiving elements are in the main scanning direction of the dots or lines constituting the pattern The most important feature is to have a light-receiving surface wider than the beam width.

According to a second aspect of the present invention, in the first aspect of the invention, the plurality of light receiving elements are arranged adjacent to each other in the main scanning direction, and the adjacent interval is larger than the light flux width in the main scanning direction of the dots or lines forming the pattern. It is characterized by being narrow.
According to a third aspect of the present invention, in the first or second aspect of the invention, the pattern includes first and second dot rows or lines, and the first and second dot rows or lines are not parallel to each other. The narrowest interval in the main scanning direction between the first and second dot rows or lines is equal to or greater than the width of the light receiving surface of the light receiving element.

According to a fourth aspect of the present invention, in the first aspect of the invention, a rectangular aperture is provided on the front side of the light receiving element, and an interval between the apertures in the main scanning direction is an interval between the patterns in the main scanning direction. It is narrower than the narrowest part.
The invention described in claim 5 is the invention described in claim 4, wherein the aperture is formed integrally with a package of the light receiving element.

The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the laser beam detector detects a sub-scanning position, and the beam position in the sub-scanning direction is a predetermined value according to the detection result. It is characterized by comprising scanning position correcting means for performing correction control so that
The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the diffractive optical element has a concavo-convex structure formed in a three-dimensional shape to spatially modulate the phase of incident light. The incident light is shaped into a desired pattern.

According to an eighth aspect of the present invention, there is provided an optical scanning device that forms a latent image on a latent image carrier by optical scanning, and the latent image is visualized to obtain a desired recorded image. The optical scanning device according to any one of claims 1 to 7 is provided.
The invention according to claim 9 comprises an optical scanning device that forms a latent image for each color component on the latent image carrier by performing optical scanning with image data for each color component, and the latent image for each color component is displayed on the latent image carrier. In an image forming apparatus that obtains a desired color recording image by visualizing colors corresponding to color components and superimposing visible images for the respective color components, the light according to any one of claims 1 to 7 as the optical scanning device. A scanning device is provided.

  The invention according to claim 10 is a method of detecting a laser beam in an optical scanning device, wherein the laser beam emitted from the light source device is deflected and scanned in the main scanning direction by the deflection scanning means, and the laser beam to be deflected and scanned is covered. Scanning image forming means for condensing toward the scanning surface; and laser beam detecting means for detecting the position of the laser beam. The laser beam detecting means is configured to cause the laser beam to be deflected and scanned from a predetermined dot or line. And a plurality of light receiving elements for detecting a pattern comprising dots or lines constituting the pattern, and a main scanning of the plurality of light receiving elements. The direction light-receiving surface width is wider than the light beam width in the main scanning direction of the dots or lines constituting the pattern, and the light-receiving surface is Or consisting line pattern and detecting a sub-scanning position of the laser beam by the time difference between the detection output mutual said plurality of light receiving elements when scanned in the main scanning direction.

According to the first aspect of the present invention, it is possible to obtain a small and inexpensive optical scanning apparatus capable of detecting the sub-scanning position of the laser beam without any layout restriction.
According to the second to third aspects of the present invention, even if the light amount variation of the light source and the intensity distribution of the laser beam pattern vary, the detection accuracy is not deteriorated and the laser beam position can be detected with high accuracy. An optical scanning device can be obtained.

According to the invention described in claim 4, a general-purpose photo IC that can use a photo IC having a wide light receiving area and that can detect a laser beam position with an inexpensive light receiving element is obtained. be able to.
According to the fifth aspect of the present invention, it is possible to obtain an optical scanning device having high positioning accuracy of the opening and capable of highly accurate laser beam detection.

According to the invention described in claim 6, it is possible to obtain an optical scanning device in which a change in the position of the scanning beam in the sub-scanning direction is corrected by a temperature variation or the like and high-precision scanning is possible.
According to the seventh aspect of the invention, it is possible to obtain a small and inexpensive optical scanning apparatus capable of detecting the sub-scanning position of the laser beam without any layout restriction.

  According to the invention described in claims 8 and 9, an image forming apparatus capable of obtaining a high-quality image by obtaining the same effect as that obtained by the invention described in claims 1 to 7, and an image corresponding to color A forming device can be obtained.

  According to the tenth aspect of the present invention, it is possible to obtain a laser beam detection method in a small and inexpensive optical scanning apparatus capable of detecting the sub-scanning position of the laser beam without any layout restriction.

Embodiments of a laser beam detection method in an optical scanning device, an image forming apparatus, and an optical scanning device according to the present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment of an optical scanning device according to the present invention. In FIG. 1, reference numerals 1 and 1 ′ denote a semiconductor laser as a light source, 2 denotes a base for holding the semiconductor lasers 1 and 1 ′, 3 and 3 ′ denote coupling lenses, and 4 denotes a half mirror prism. Reference numeral 5b denotes a cylindrical lens, and reference numeral 7 denotes an optical deflection having a polygon mirror. Each laser beam emitted from the semiconductor lasers 1 and 1 'as the light source is divided in the sub-scanning direction by the half mirror prism 4 shown in detail in FIG.

  In FIG. 2, the half mirror prism 4 has an incident surface on which the beam L1 is incident at a right angle, and has a semi-transmissive surface 4a obliquely provided at an angle of 45 degrees on the path of incident light. On the path of the beam reflected by the surface 4a, the reflection surface 4b is obliquely arranged at an angle of 45 degrees so as to be parallel to the semi-transmission surface 4a so as to reflect the beam reflected by the semi-transmission surface 4a. It has become. Therefore, the single beam L1 incident from the incident surface of the half mirror prism 4 is reflected by the semi-transmissive surface 4a and the single beam L11 that passes through the semi-transmissive surface 4a and travels straight and exits from one emitting surface. In addition, the light beam is reflected by the reflecting surface 4b and is divided into another beam L12 that is emitted in parallel with the beam L11 from the other emitting surface. The laser beam L11 transmitted through the semi-transmissive surface 4a is incident on the cylindrical lens 5a shown in FIG. 1, reflected by the semi-transparent mirror 4a, and further reflected by the reflecting surface 4b so that the laser beam L12 is incident on the cylindrical lens 5b. Has been placed.

  In FIG. 1, reference numeral 6 denotes a soundproof glass provided on a window of a soundproof housing (not shown) of an optical deflector 7 made of a polygon mirror. Two laser beams emitted from the two semiconductor lasers 1 constituting the light source device, divided by the half mirror prism 4 in the sub-scanning direction, and emitted from the semiconductor laser 1 ', and emitted in the sub-scanning direction by the half mirror prism 4 A total of four laser beams of the two divided laser beams are configured to enter the optical deflector 7 through the soundproof glass 6. The polygon mirrors 7a and 7b constituting the optical deflector 7 are rotationally driven at a constant speed by a motor (not shown), and the laser beam is deflected and reflected by the polygon mirrors 7a and 7b. The deflected laser beam is emitted to the scanning imaging optical system side through the soundproof glass 6. As shown in FIG. 1, the optical deflector 7 has an upper polygon mirror 7a and a lower polygon mirror 7b stacked in two stages in the sub-scanning direction (rotating axis direction).

  In the embodiment shown in FIG. 1, both the upper polygon mirror 7a and the lower polygon mirror 7b have the same shape having four deflecting reflection surfaces, and the lower polygon mirror 7b has the same shape as the deflection reflecting surface of the upper polygon mirror 7a. The deflecting and reflecting surface is deviated by a predetermined angle: θp (= 45 degrees) in the rotation direction. Reference numerals 8a and 8b denote first scanning lenses, reference numerals 10a and 10b denote second scanning lenses, and reference numerals 9a and 9b denote optical path bending mirrors. Reference numerals 11a and 11b denote photoconductors. The first scanning lens 8a, the second scanning lens 10a, and the optical path bending mirror 9a are formed on the photosensitive member 11a, which is a corresponding optical scanning position, by converting two laser beams deflected by the upper polygon mirror 7a of the optical deflector 7. A set of scanning imaging optical systems that form two light spots that are guided to each other and separated in the sub-scanning direction. Similarly, the first scanning lens 8b, the second scanning lens 10b, and the optical path bending mirror 9b are configured to sensitize two laser beams deflected by the lower polygon mirror 7b of the optical deflector 7 at the corresponding optical scanning positions. Another set of scanning imaging optical systems is formed which guides light onto the body 11b and forms two light spots separated in the sub-scanning direction.

  The optical arrangement of the laser beams emitted from the semiconductor lasers 1 and 1 ′ is determined so that the principal rays intersect in the vicinity of the position of the deflecting reflection surface when viewed from the rotation axis direction of the optical deflector 7. Accordingly, the two laser beams that are split into two by the half mirror prism 4 and enter the deflecting reflecting surface have two opening angles, that is, when the light source side is viewed from the deflecting reflecting surface side, It has an angle formed by projection onto a plane orthogonal to the rotation axis of the laser beam. In this way, the two laser beams deflected by the upper polygon mirror 7a of the optical deflector 7 are subjected to multi-beam scanning on the surface of the photosensitive member 11a by the two laser beams. Multi-beam scanning is performed by two laser beams on the surface of the photosensitive member 11b by two laser beams deflected by the lower polygon mirror 7b.

  Since the deflection reflection surfaces of the upper polygon mirror 7a and the lower polygon mirror 7b of the optical deflector 7 are shifted from each other by 45 degrees in the rotation direction, when the deflected laser beam from the upper polygon mirror 7a performs optical scanning of the photosensitive member 11a, The deflected laser beam from the polygon mirror 7b is not guided to the photoconductor 11b. When the deflected laser beam from the lower polygon mirror 7b scans the photoconductor 11b, the deflected laser beam from the upper polygon mirror 7a is It is not guided to 11a. That is, the optical scanning of the photoconductor 11a and the photoconductor 11b is alternately performed with a time shift.

  FIG. 3 is a diagram for explaining this situation, and is a diagram for explaining a temporal shift in optical scanning by the upper and lower polygon mirrors. Although there are actually four laser beams incident on the optical deflector 7, they are depicted as one incident light, and the laser beams deflected by the upper and lower polygon mirrors are respectively referred to as deflected light a and deflected light b. Show. FIG. 3A shows a situation when incident light enters the optical deflector 7 and the deflected light a deflected by being reflected by the upper polygon mirror 7a is guided to the optical scanning position. At this time, the deflected light b from the lower polygon mirror 7b does not go to the optical scanning position. FIG. 3B shows the situation when “deflected light b” reflected and deflected by the lower polygon mirror 7 b is guided to the optical scanning position. At this time, the deflected light a from the upper polygon mirror 7a does not go to the optical scanning position. In order to prevent the deflected light from the other polygon mirror from acting as ghost light while the deflected light from one of the polygon mirrors is guided to the optical scanning position, a light shielding means is provided at an appropriate position as shown in FIG. SD may be arranged so that the deflected light that is not guided to the optical scanning position is shielded by the light shielding means SD.

  In FIG. 1, reference numerals 101a and 101b denote laser beam detectors. The laser beam detectors 101a and 101b are located outside the axial ends of the photoconductors 11a and 11b, respectively, and so that the light-receiving surfaces are positioned on the extensions of the surfaces scanned by the laser beams of the photoconductors 11a and 11b. Has been placed. As will be described in detail later, a diffractive optical element 103a for forming a scanning beam pattern of a predetermined shape on the laser beam detectors 101a and 101b on the beam path to the laser beam detectors 101a and 101b. 103b is arranged. As the laser beams pass through the diffractive optical elements 103a and 103b, scanning beam patterns of a predetermined shape are formed on the laser beam detectors 101a and 101b. In FIG. 1, reference numeral 104a schematically shows a scanning beam pattern formed on the laser beam detector 101a after passing through the diffractive optical element 103a. In FIG. 1, the arrows attached to the photoconductors 11a and 11b indicate the scanning direction of the scanning beam pattern.

  In FIG. 1, a liquid crystal deflecting element 10 is disposed between the half mirror prism 4 and the cylindrical lenses 5a and 5b. A specific example of the liquid crystal deflection element 102 is shown in FIG. In FIG. 9, a liquid crystal layer 43 is formed by filling a liquid crystal between a pair of alignment films 45 arranged to face each other at a predetermined interval by a spacer 44. Transparent electrodes 46 are disposed on the outer surfaces of the pair of alignment films 45, and laser transmitting members 42 are disposed on the outer surfaces of the transparent electrodes 46. The liquid crystal deflection element 10 has a function of deflecting an incident laser beam in the sub-scanning direction as shown in FIG. 10 by inputting a rectangular wave or sine wave voltage from the drive circuit 41 between the pair of transparent electrodes 46. Have. The deflection directions are reversed with respect to the polarity of the input voltage. When no voltage is input from the drive circuit 41, the incident laser beam is transmitted without being deflected. Based on the detection positions detected by the laser beam detectors 101a and 101b, the liquid crystal deflection element 102 is driven and controlled so that the scanning laser beam position becomes a desired sub-scanning position. The liquid crystal deflection element 102 has four liquid crystal deflection regions that can be controlled independently so as to correspond to four laser beams, and each laser beam can be controlled independently. Therefore, it is preferable that the liquid crystal deflection element 102 is disposed on the emission side of the half mirror prism 4.

  As described above, in the embodiment shown in FIG. 1, the photoconductors 11a and 11b are alternately scanned by multi-beam optical scanning. For example, when the optical scanning of the photoconductor 11a is performed, the light intensity of the light source is set. When modulated with the image signal of the black image, and when the optical scanning of the photoconductor 11b is performed, the electrostatic latent image of the black image is exposed to the photoconductor 11a by modulating the light intensity of the light source with the image signal of the cyan image. An electrostatic latent image of a cyan image can be formed on the body 11b.

  FIG. 4 shows a common light source device, for example, in the case of the embodiment of FIG. 1, when writing a black image and a cyan image by the semiconductor lasers 1 and 1 ′ to form respective electrostatic latent images, all the effective scanning regions are used. The timing chart in the case of lighting is shown. A solid line indicates a portion corresponding to writing of a black image, and a broken line indicates a portion corresponding to writing of a cyan image. The main scanning timing for writing out the black image and the cyan image is determined by detecting the laser beam toward the optical scanning start position by a known synchronization detecting means provided outside the effective scanning area. If the light emission intensity of the light source in the time region for writing the black image and the time region for writing the cyan image are set to be the same, relative to the transmittance and reflectance of the optical element in each optical path from the light source to the photoconductors 11a and 11b. If there is a general difference, the amount of laser beam reaching each photoconductor is different. Therefore, as shown in FIG. 4, when different photoconductor surfaces are optically scanned, the amount of light reaching the different photoconductor surfaces is made equal by varying the light emission intensity (light emission amount) of the light source.

  A specific example of the laser beam detector 101a is shown in FIG. The other laser beam detector 101b has the same configuration, and here, one laser beam detector 101a is representatively shown. As shown in FIG. 1, the laser beam detector 101a is disposed at a position that is optically equivalent to a laser beam that scans the surface of the photosensitive member (particularly, fθ characteristics, the same applies hereinafter). In FIG. 5, reference numeral 401 denotes a substrate, 402 denotes a light receiving portion, 402a denotes a light receiving element constituting the light receiving portion, for example, a photodiode (hereinafter referred to as “PD”), and 402b denotes a comparator circuit. The deflected and scanned laser beam passes through the diffractive optical element 103a to form a scanning beam pattern having a specific shape, and this scanning beam pattern forms an image on the laser beam detector 101a and scans it. . In this example, the scanning beam pattern is composed of two linear patterns before and after the scanning direction, the pattern on the front side in the scanning direction is a direction orthogonal to the scanning direction, and the pattern on the rear side in the scanning direction is an angle θd with respect to the scanning direction. Inclined. When the position of the incident laser beam in the sub-scanning direction shifts, the diffractive optical element 103a acts to move the scanning beam pattern in the sub-scanning direction by the same amount as the shift amount. Assuming that the scanning beam pattern is detected by a light receiving element fixed at a predetermined position, the pair of front and rear scanning beam patterns move in the sub-scanning direction, and are output by detecting the front and rear scanning beam patterns. The time interval of the light receiving element output in the laser beam detector changes. By measuring the time interval of the light receiving element output, the sub-scanning position of the laser beam can be detected. The light receiving element 402a is composed of a left light receiving element PD1 and a right light receiving element PD2 arranged side by side in the scanning direction of the scanning beam pattern. The width of the two light receiving elements PD1 and PD2 in the scanning direction of the scanning beam pattern is C, and the distance between the light receiving elements PD1 and PD2 is D.

  FIG. 13 shows an example of a laser beam detector using a general-purpose photo IC 403 having a wide light receiving area. Compared with the laser beam detector 101a shown in FIG. 5, the configuration of the photo IC 403 and the aperture 404 constituting the light receiving unit is characteristic, so this characteristic configuration part will be described in detail, and the description of the other parts will be simplified. Turn into. In FIG. 13, a photo IC 403 constituting the light receiving unit of the laser beam detector 101a has a light receiving element 403a arranged at the scanning position of the scanning beam pattern, as in the example of FIG. The light receiving element 403a includes a left light receiving element PD1 and a right light receiving element PD2 arranged side by side in the scanning direction of the scanning beam pattern. The adjacent distance between the light receiving elements PD1 and PD2 is the same distance D as in the example of FIG. 5, and an aperture 404 is disposed in front of the light receiving elements PD1 and PD2. FIG. 14 shows a specific example of the aperture 404. As shown in FIG. 14, the aperture 404 is made of a black metal plate having a thickness of 0.5 mm or less, and has an opening 404a at the center. In FIG. 13, the aperture 404 is integrally fixed to the surface of the package of the photo IC 403 by a fixing means using an adhesive, a double-sided tape or the like. The aperture 404 is preferably fixed at a position where the area of the opening 404 is equal to the combined area of the light receiving elements PD1 and PD2. Reference numeral 403a represents a comparator circuit.

  Note that an opening substantially the same as the opening 404 a may be formed by performing a plating process, a vapor deposition process, or the like on the surface side of the package of the photo IC 403 so as to have the same function as the aperture 404. According to this configuration, since fixing by bonding or the like is not required, the positioning accuracy of the opening is high, and high-precision laser beam detection is possible. If the aperture is separated (separated) from the photo IC and fixed, it is difficult and undesirable to position and fix the aperture so that the light receiving elements PD1 and PD2 have the same area.

  Next, a method for shaping the laser beam into a desired beam pattern will be described in detail. In order to shape coherence light such as a semiconductor laser beam into a desired beam pattern, it is necessary to control diffraction, and for this purpose, an element that spatially modulates the amplitude distribution, phase distribution, or both of the laser beam. Is preferably provided. By doing so, a diffraction image of a desired beam pattern can be obtained. A technique for calculating the amplitude distribution (transmittance distribution) and / or phase distribution of such an element by calculation is known as CGH (Computer Generated Holography), and an element that realizes this is a CGH element. Since the CGH element is a kind of diffractive optical element, it is hereinafter referred to as a diffractive optical element. FIG. 6 shows an image for obtaining a desired beam pattern using a diffractive optical element. In FIG. 6, when a plane wave passes through the diffractive optical element 103, the amplitude distribution and / or the phase distribution are spatially modulated, and an image is formed by the lens 406, whereby a desired diffracted image (far field) is formed on the image plane. Pattern). Since the lens function can be superimposed on the diffractive optical element 103, the lens 406 in FIG. 6 is not necessary.

  In this embodiment, a diffractive optical element that provides a desired phase distribution is used for the following reason. When the amplitude distribution is spatially modulated, that is, the transmittance is spatially modulated, there is a problem that the amount of light is reduced and that it is difficult to manufacture an element having a desired transmittance. In this embodiment, a diffractive optical element with a small decrease in the amount of light can be obtained. In order to give a phase distribution to the laser beam, for example, it can be realized by forming a concavo-convex structure on a transparent substrate in the used wavelength range. A phase distribution may be given by transmitting a laser beam to an element having such a concavo-convex structure, or a reflective film is formed on the element having a concavo-convex structure, and incident light is transmitted by the reflective film. The phase distribution may be given by reflection. If the concavo-convex shape is a used wavelength of 400 to 800 nm, it is composed of a three-dimensional fine pattern having a pitch and depth of 0.5 μm to 5 μm (about 1 to 6 times the used wavelength), and is formed by a semiconductor process or a fine transfer process. It is formed. One cell constituting the diffractive optical element has a cell structure of 5 μm square and is formed with a 256 × 256 cell structure. As shown in FIG. 6, it is preferable to shield the region without the uneven structure with an aperture 404. The number of phase levels is 256 gradations from 0 to 2π.

  FIG. 7 shows an example of a beam pattern obtained using a diffractive optical element that gives a phase distribution (hereinafter referred to as “phase-type diffractive optical element”). FIG. 7A shows an example of a line pattern, and FIG. 7B shows an example of a dot pattern. The dot-like pattern shown in FIG. 7B has a large interval between dots and a small number of dots, but in reality, the dots are formed densely with a large number of dots. The diffractive optical element used in this example has a so-called beam branching function that shapes a pattern with a plurality of dots or shapes a plurality of lines when one beam is incident. In order to detect a sub-scanning position of a beam pattern with higher accuracy, it is preferable to use a line pattern. On the other hand, when the temperature change in the optical scanning device is large, the dot type with less deterioration of the beam pattern is preferable even if the positional relationship between the diffractive optical element and the light detection means is deviated.

  As shown in FIG. 1, the laser beam detectors 101a and 101b are preferably arranged so that their light receiving surfaces are positioned on the scanning extension of the surfaces of the photoconductors 11a and 11b. For the convenience of component layout constituting the image forming apparatus, the laser beam detector 108 may be scanned through the reflection mirror 106 and the diffractive optical element 107 as shown in FIG. In the embodiment shown in FIG. 1, optical scanning means including a light source device and scanning imaging means are arranged symmetrically on the left and right sides with the optical deflector 7 in between. In order to avoid the complexity, only one side in the left-right direction is drawn. On the other hand, FIG. 11 shows an example in which optical scanning means are arranged on both the left and right sides with the optical deflector 7 interposed therebetween. Therefore, in FIG. 11, another reflecting mirror 206, diffractive optical element 207, and laser beam detector 208 corresponding to the reflecting mirror 106, diffractive optical element 107, and laser beam detector 108 are provided for the optical deflector 7. They are arranged symmetrically.

  The laser beam detector 101a shown in FIG. 1 includes a photo IC 402 as shown in FIG. The photo IC 402 is composed of two light receiving elements PD1 and Pd2 arranged on the left and right, and the light receiving element 402a is formed into one package as an IC having a comparator circuit 402b that shapes the output signal from the light receiving elements PD1 and Pd2. ing. This package is covered with resin, and the front surfaces of the light receiving elements PD1 and Pd are covered with a laser beam transmitting member made of resin. The light receiving element 402a is shown in a rectangular shape and has a length of about 50 to 150 μm in the sub-scanning direction. The beam diameter in the main scanning direction of the dots or lines forming the scanning beam pattern (1 / e2 of the peak intensity, the same applies hereinafter) is the same as the laser beam diameter that forms an image on the scanning plane as indicated by A in FIG. Equivalent to 40 to 90 μm. When the width of the two light receiving elements PD1 and Pd2 in the main scanning direction is C, the C is wider than A. If the minimum interval in the main scanning direction between dots or lines forming the scanning beam pattern is B, B is set to 200 to 500 μm, and C is set to be narrower than B. Specifically, C is preferably 100 to 150 μm.

  The width h (see FIG. 5) in the sub-scanning direction of the scanning beam pattern is preferably 1 to 3 mm. When the sub-scanning direction is less than 1 mm, it is difficult to scan the scanning pattern within the light receiving range of the light receiving element in the initial state, that is, in the initial stage of assembly in a state where adjustment is not performed. In an unadjusted state, the initial sub-scanning position deviation of the scanning beam occurs by 1 mm or more due to the influence of the component dimension crossing of the optical element and the variation of the mounting dimension tolerance, and the light receiving element cannot receive light. On the other hand, if h exceeds 3 mm, the scanning beam pattern becomes too large and the beam branching accuracy of the diffractive optical element deteriorates, making it difficult to split the beam with high uniformity, and the pattern or dot alignment accuracy and beam intensity. Varies, and the beam spot position detection accuracy decreases.

  The photo IC 402 is arranged as shown in FIG. 5 and constitutes a laser beam detector 101a. A photo IC 402 is mounted on a substrate 401, and the photodiodes PD1 and PD2 constituting the light receiving element 402a are arranged apart by a distance D. The separation distance D between the photodiodes PD1 and PD2 is preferably 10 to 20 μm, which is narrower than the light beam diameter in the main scanning direction of the dots or lines forming the scanning beam pattern. The light beam diameter A in the main scanning direction of the dots or lines forming the scanning beam pattern is set to 40 to 90 μm as described above.

  The scanning beam pattern, which is one of the scanning beam patterns, is arranged in parallel with the photodiode PD1 in the sub-scanning direction, and the other scanning beam pattern, the pattern behind the main scanning direction, is arranged with respect to the sub-scanning direction. The pattern is inclined with an angle (θd) (see FIG. 7A).

When the scanning beam pattern as described above passes through the light receiving surfaces of the light receiving elements PD1 and PD2 constituting the light receiving element 402a, an output signal as shown in the timing chart of FIG. 8 is generated from the light receiving elements PD1 and PD2. The outputs of the light receiving elements PD1 and PD2 are compared by a comparator 402b that becomes active when PD2> PD1, and a comparator signal (CMP) as shown in FIG. 8A is output. The time interval T from the fall of the comparator output to the fall of the next output depends on the position in the sub-scanning direction where the beam pattern is scanned. When the time interval is T, the sub-scanning position P of the laser beam can be obtained from the following equation (1). FIG. 8A shows an example of the time interval T1 of the CMP output when the scanning beam pattern is substantially at the center in the sub scanning direction with respect to the light receiving element, and FIG. 8B shows the scanning beam pattern in the sub scanning direction. An example of a time interval T2 of the comparator output when moved (incident position on the diffractive optical element has moved) is shown. Based on the difference (T1-T2) between T1 and T2, the amount of movement (change) in the sub-scanning direction of the laser beam deflected and scanned can be calculated according to the following equation (1). As described above, since the cross point of the outputs of the light receiving elements PD1 and PD2 is detected, even if the light amount (intensity distribution) of the scanning beam pattern changes, the detection accuracy is not affected, and high accuracy detection is possible. . Therefore, the adjacent distance D between the light receiving elements PD1 and PD2 is set to be narrower than the width A of the scanning beam pattern that passes therethrough so that a cross point is surely generated.
P = (v × T) / tan (θd) (1)
Here, v is the speed of the beam pattern to be scanned, which is the deflection scanning speed by the polygon mirror. Although the result obtained by the equation (1) varies depending on the angle θd between the scanning beam patterns before and after, θd is 30 in order to ensure the measurement accuracy of the time interval and the sub-scanning detectable area h. ˜45 ° is preferred.

  In the case where a plurality of laser beams corresponding to each color are scanned simultaneously as in the example of the optical scanning device shown in FIG. 1, only when scanning the laser beam detector, that is, scanning the inside of the diffractive optical element. As one laser beam scans, it is desirable to dimm or extinguish only so that the other laser beam is not detected. This is because if a plurality of beam patterns scan the light receiving portion of the laser beam detector, the output signal of the light receiving element is affected and the detection position is incorrect.

  Since the laser beam detector is arranged outside the image scanning region, when the number of deflecting reflection surfaces of the optical deflector is increased to, for example, six, the scanning angle of view becomes narrow and the optical characteristics deteriorate. It was. When the deflecting and reflecting surfaces of the optical deflector are four as in the present embodiment, a wide scanning angle of view can be secured and the optical characteristics are less deteriorated, but the characteristics are not deteriorated. It is desirable to arrange the detector as close to the scanning region of the image as possible.

  On the other hand, the laser beam detector 101a (101b) is preferably movable in the sub-scanning direction. For this purpose, the laser beam detector is fixed to a holder (not shown), and this holder is configured to be movable in the sub-scanning direction by a screw mechanism or the like. This adjustment mechanism performs initial adjustment so that the scanning beam pattern is substantially at the center of the sub-scanning detection area h with respect to the light receiving element in the laser beam detector in the manufacturing (assembly) process of the optical scanning device. The reason is that the position of the scanning beam pattern in the sub-scanning direction may change to the upstream side or downstream side in the sub-scanning direction. It is to keep. Note that “substantially centered” means that it is difficult to adjust to the exact center, and therefore it is only necessary to adjust the area within about 1/10 of the sub-scanning detectable area h with respect to the center. In this range, it is preferable.

  FIG. 11 shows an example in which the optical scanning device shown in FIG. 1 is symmetrically arranged at positions facing each other with the optical deflector 7 interposed therebetween, and shows an example of a tandem type optical scanning device corresponding to four colors. Yes. FIG. 11 shows a state in which the optical system portion of the optical scanning device is viewed from the sub-scanning direction, that is, the rotation axis direction of the optical deflector 7. In order to avoid complication of the drawing, the optical path bending mirror disposed on the optical path from the optical deflector 7 to the surfaces of the photoconductors 11C, 11K and 11Y, 11M, which are the scanned surfaces, is not shown. However, the optical path is drawn to be a straight line. This optical scanning device is an example in which each of four optical scanning positions is scanned with one laser beam. Further, the photoconductors 11Y, 11M, 11C, and 11K are arranged at the respective optical scanning positions, and electrostatic latent images formed on these four photoconductors are represented by magenta (M), yellow (Y), It is configured to be visualized individually with cyan (C) and black (K) toners to form a color image.

  In FIG. 11, reference numerals 1YM and 1CK denote semiconductor lasers as light sources, respectively. Each of these semiconductor lasers 1YM and 1CK emits one laser beam. The intensity of the semiconductor laser 1YM is alternately modulated with “an image signal corresponding to a yellow image” and “an image signal corresponding to a magenta image”. The intensity of the semiconductor laser 1CK is alternately modulated with “an image signal corresponding to a cyan image” and “an image signal corresponding to a black image”. The laser beam emitted from the semiconductor laser 1YM is converted into a parallel beam by the coupling lens 3YM, and after passing through the aperture 12YM, the beam is shaped, and then incident on the half mirror prism 4YM and separated in the sub-scanning direction. The beam is split into laser beams. The half mirror prism 4YM is the same as the half mirror prism 4 shown in FIG. One of the split laser beams is used to write a yellow image and the other one is used to write a magenta image.

  The two laser beams divided in the sub-scanning direction are controlled by the liquid crystal deflecting element 102YM to correct the sub-scanning position as necessary, and cylindrical lenses 5Y, 5M (sub-scanning) arranged in the sub-scanning direction. Are arranged so as to overlap each other in the direction. The optical deflector 7 is configured in the same manner as shown in FIGS. 1 and 3, and polygon mirrors having four deflecting reflecting surfaces are stacked in two stages in the direction of the rotation axis, and the deflecting reflecting surfaces between the polygon mirrors are stacked. Are integrated in the rotational direction. Each of the laser beams is converged only in the sub-scanning direction by the cylindrical lenses 5Y and 5M, and a long line image in the main scanning direction is formed in the vicinity of the deflection reflection surface position of each polygon mirror, and the polygon mirror is rotationally driven. By this, it is configured to be deflected and reflected at a constant angular velocity. The two laser beams deflected by the optical deflector 7 pass through the first scanning lenses 8Y and 8M made of fθ lenses and the second scanning lenses 10Y and 10M made of toroidal lenses, respectively. Light spots are formed at the scanning positions 11Y and 11M, and optical scanning is performed at these optical scanning positions at a constant speed.

  Similarly to the above, the laser beam emitted from the semiconductor laser 1CK is collimated by the coupling lens 3CK, shaped through the aperture 12CK, and then shaped by the half mirror prism 4CK. The beam is split into laser beams. The half mirror prism 4CK is configured in the same manner as the half mirror prism 4YM. One of the split laser beams is used to write a cyan image and the other one is used to write a black image. The two laser beams divided in the sub-scanning direction are respectively condensed only in the sub-scanning direction by cylindrical lenses 5C and 5K (arranged so as to overlap in the sub-scanning direction) arranged in the sub-scanning direction. A latent image in the main scanning direction is formed in the vicinity of the deflecting and reflecting surface of the polygon mirror. The two laser beams incident on the deflecting / reflecting surface of the polygon mirror are deflected by the rotation of the polygon mirror, and pass through the first scanning lenses 8C and 8K and the second scanning lenses 10C and 10K, respectively. Light spots are formed at the scanning positions 11C and 11K, and the optical scanning positions 11C and 11K are optically scanned at a constant speed.

  In FIG. 11, reference numerals 106 and 206 denote mirrors for making the scanned laser beams incident on the laser beam detectors 108 and 208, 107 and 207 denote diffractive optical elements, and 108 and 208 denote laser beam detectors. . The optical path length from the light source to the photoconductor and the optical path length from the light source to the laser beam detector are set to be substantially equal. As shown in FIG. 11, the diffractive optical element is preferably provided between the imaging scanning optical system including the first scanning lens and the second scanning lens and the laser beam detector. By doing so, it becomes possible to detect the influence of the imaging scanning optical system, for example, the sub-scanning position change of the beam caused by the temperature deformation of the lens system, and the scanning beam on the surface to be scanned and the laser beam detection. Thus, the correlation between changes in the sub-scanning position detected by the detector can be increased, and the detection accuracy can be increased.

  FIG. 12 shows an example of a color-compatible image forming apparatus using the optical scanning device according to the present invention described so far. The portion indicated by reference numeral 20 in FIG. 12 is an optical scanning device, and has a scanning imaging optical system corresponding to four colors of yellow, magenta, cyan, and black for an image forming apparatus capable of forming a color image. The photosensitive member surface is scanned with a laser beam corresponding to each color. One of the laser beams deflected by the upper polygon mirror of the optical deflector 7 arranged in the optical scanning device 20 is the substance of the optical scanning position by the optical path bent by the optical path folding mirrors mM1, mM2, and mM3. The other laser beam is guided to the photoconductor 11C forming the substance of the optical scanning position by the optical path bent by the optical path bending mirrors mC1, mC2, and mC3. One of the laser beams deflected by the lower polygon mirror of the optical deflector 7 is guided to the photoconductor 11Y that forms the substance of the optical scanning position by the optical path bent by the optical path bending mirror mY, and the other laser. The beam is guided to the photoconductor 11K that forms the substance of the optical scanning position by the optical path bent by the optical path bending mirror mK.

  Accordingly, the laser beams from the two semiconductor lasers 1YM and 1CK are divided into two laser beams by the half mirror prisms 4YM and 4CK, respectively, so that four laser beams are obtained. The photoconductors 11Y, 11M, 11C, and 11K are optically scanned. The photoconductors 11Y and 11M are alternately scanned by the laser beam obtained by dividing the laser beam from the semiconductor laser 1YM into two along with the rotation of the optical deflector 7, and the photoconductors 11C and 11K are lasers from the semiconductor laser 1CK. With each laser beam obtained by dividing the beam into two, optical scanning is performed alternately as the optical deflector 7 rotates.

  Each of the photoreceptors 11Y to 11K is rotated at a constant speed in the clockwise direction in FIG. 12, and the surface is uniformly charged by the charging rollers TY, TM, TC, and TK that form the charging means, and each receives light scanning of the corresponding laser beam. Thus, each color image of yellow, magenta, cyan, and black is written, and a corresponding electrostatic latent image (negative latent image) is formed. These electrostatic latent images are reversed and developed by developing devices GY, GM, GC, and GK, respectively, and a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are formed on the photoreceptors 11Y, 11M, 11C, and 11K, respectively. Is done.

  These color toner images are transferred onto a “transfer sheet” (not shown). That is, the transfer sheet is transported by the transport belt 17, the yellow toner image is transferred from the photoreceptor 11Y by the transfer device 15Y, and the magenta toner image is transferred from the photoreceptors 11M, 11C, and 11k by the transfer devices 15M, 15C, and 15K, respectively. The cyan toner image and the black toner image are sequentially transferred. In this way, a yellow toner image to a black toner image are superimposed on the transfer sheet to compose a color image synthetically. This color image is fixed on the transfer sheet by the fixing device 19 to obtain a color image.

It is a perspective view which shows the Example of the optical scanning device concerning this invention only with an optical component. It is a side view which shows the half mirror prism in the said Example. The polygon mirror in the said Example is shown, Comprising: (a) (b) is a top view which shows a mode that a beam is deflected and reflected by the separate polygon mirror which overlapped. It is a timing chart which shows the difference in the timing and intensity | strength of the several laser beam deflected and reflected by the said polygon mirror. It is a top view which shows an example of the laser beam detector applicable to the said Example. It is side surface sectional drawing which shows the example of the phase type diffractive optical element applicable to this invention. It is a pattern diagram which shows two examples of the scanning beam pattern which is formed with a diffractive optical element and can be applied to the present invention. It is a pattern diagram and signal timing charts showing two examples in which the scanning beam pattern is detected by the laser beam detector of the optical scanning device according to the present invention. It is sectional drawing which shows typically the specific example of the liquid-crystal deflection | deviation element in the Example of the optical scanning device concerning this invention. It is a side view which shows the effect | action of the said liquid-crystal deflection | deviation element. It is a top view which shows another Example of the optical scanning device concerning this invention. 1 is a front view schematically showing an embodiment of an image forming apparatus according to the present invention. It is a top view which shows another example of the laser beam detector applicable to the said Example. It is a front view which shows the specific example of the aperture applicable to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser as light source 2 Base 3 Coupling lens 4 Half mirror prism 5a Cylindrical lens 5b Cylindrical lens 7 Optical deflector 7a Polygon mirror 7b Polygon mirror 8a First scanning lens 8b First scanning lens 10a Second scanning lens 10b Second Scanning lens 11a Photoreceptor 11b Photoreceptor 101a Laser beam detector 101b Laser beam detector 103a Diffraction optical element 103b Diffraction optical element

Claims (10)

A scanning imaging means for deflecting and scanning the laser beam emitted from the light source device in the main scanning direction by the deflection scanning means, and condensing the laser beam to be scanned toward the scanning surface, and a laser for detecting the laser beam position Beam detecting means,
The laser beam detecting means includes a diffractive optical element that shapes a laser beam to be deflected and scanned into a pattern consisting of predetermined dots or lines, and a plurality of light receiving elements for detecting a pattern consisting of dots or lines constituting the pattern And comprising
The optical scanning device, wherein the plurality of light receiving elements have a light receiving surface having a width wider than a light flux width in a main scanning direction of dots or lines constituting the pattern.   2. The optical scanning device according to claim 1, wherein the plurality of light receiving elements are arranged adjacent to each other in the main scanning direction, and an adjacent interval is narrower than a light flux width in the main scanning direction of dots or lines forming the pattern.   The pattern is composed of first and second dot rows or lines, and the first and second dot rows or lines are shaped so as to be non-parallel to each other. 3. The optical scanning device according to claim 1, wherein the narrow interval in the main scanning direction is equal to or larger than the width of the light receiving surface of the light receiving element.   The rectangular aperture is provided on the front side of the light receiving element, and the interval between the apertures in the main scanning direction is narrower than the portion where the interval between the patterns in the main scanning direction is the narrowest. Optical scanning device.   The optical scanning device according to claim 4, wherein the aperture is formed integrally with a package of the light receiving element.   5. A scanning position correcting unit that detects a sub-scanning position by the laser beam detector and performs correction control so that the beam position in the sub-scanning direction becomes a predetermined value according to the detection result. The optical scanning device according to any one of 1 to 5.   7. The diffractive optical element according to claim 1, wherein the diffractive optical element has a concavo-convex structure formed in a three-dimensional shape to spatially modulate the phase of incident light and shape the incident light into a desired pattern. The optical scanning device according to any one of the above.   8. An image forming apparatus comprising an optical scanning device that forms a latent image on a latent image carrier by optical scanning and visualizing the latent image to obtain a desired recorded image, wherein the optical scanning device is any one of claims 1 to 7. An image forming apparatus comprising the above-described optical scanning device.   An optical scanning device that forms a latent image for each color component on the latent image carrier by performing optical scanning with image data for each color component, and visualizes the latent image for each color component with a color corresponding to the color component. An image forming apparatus that obtains a desired color recording image by superimposing visible images for each color component includes the optical scanning device according to claim 1 as the optical scanning device. An image forming apparatus. A scanning imaging means for deflecting and scanning the laser beam emitted from the light source device in the main scanning direction by the deflection scanning means, and condensing the laser beam to be scanned toward the scanning surface, and a laser for detecting the laser beam position Beam detecting means,
The laser beam detecting means includes a diffractive optical element that shapes a laser beam to be deflected and scanned into a pattern consisting of predetermined dots or lines, and a plurality of light receiving elements for detecting a pattern consisting of dots or lines constituting the pattern In an optical scanning device comprising:
The main scanning direction light receiving surface width of the plurality of light receiving elements is wider than the main scanning direction light flux width of the dots or lines constituting the pattern,
In the optical scanning device, wherein a sub-scanning position of the laser beam is detected by a time difference between detection outputs of the plurality of light receiving elements when the dot or line pattern is scanned in the main scanning direction on the light receiving surface. Laser beam detection method.

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