JP4716420B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly to an optical scanning apparatus that scans a surface to be scanned with a light beam and an image forming apparatus including the optical scanning apparatus.

  In recent years, in electrophotographic image forming apparatuses used in laser printers, digital copying machines, and the like, colorization has progressed and the required quality for color images has increased. The biggest problem in improving the quality of color images is the reduction of color misregistration. At the factory shipment stage, it is possible to suppress color misregistration by various adjustments in the adjustment process, but color misregistration may occur due to changes over time.

  Causes of color misregistration in the sub-scanning direction due to changes over time include decentration of optical elements (lenses, mirrors, etc.) and deformation of the housing itself in which the light source and optical elements are arranged. Therefore, if it is possible to detect a positional deviation in the sub-scanning direction of the light spot formed on the surface of the photosensitive drum (hereinafter, also referred to as “sub-scanning direction deviation” for convenience), the correction is performed using an appropriate correction unit. (For example, refer to Patent Document 1 and Patent Document 2).

  In Patent Documents 3 and 4, a photodiode having a non-parallel edge is used, and a time interval between two signals output from the photodiode is detected to detect a sub-scanning direction deviation of the light spot. An apparatus is disclosed.

  By the way, the demand for cost reduction and downsizing of image forming apparatuses is increasing year by year. However, with the devices disclosed in Patent Document 3 and Patent Document 4, it is not easy to meet these increasing demands in the future.

JP 2003-241130 A JP 2004-109700 A JP 2005-37575 A JP 2005-62597 A

  The present invention has been made under such circumstances, and its first object is to accurately determine the position of the light spot formed on the surface to be scanned in the sub-scanning direction without increasing the cost and increasing the size. An object of the present invention is to provide an optical scanning device that can detect well.

  A second object of the present invention is to provide an image forming apparatus capable of forming a high-quality image without causing an increase in cost and size.

  According to a first aspect of the present invention, there is provided an optical scanning device for scanning a surface to be scanned with a light beam, comprising: a light source; deflecting means for deflecting the light beam from the light source; and the deflected light beam A scanning optical system for condensing on the surface to be scanned; a light beam directed from the light source toward the surface to be scanned is incident, and at least partly in a direction corresponding to the main scanning direction by a position in a direction corresponding to the sub-scanning direction. An optical scanning device comprising: a diffractive optical element that forms a diffraction image including a plurality of images having different intervals; and a photodetector that detects the diffraction image.

  According to this, the light beam from the light source is deflected by the deflecting means and is condensed on the surface to be scanned by the scanning optical system. The light beams traveling from the light source toward the scanned surface are incident on the diffractive optical element, and the diffractive optical element causes at least a part of the light beam to travel in the direction corresponding to the main scanning direction. A diffraction image including a plurality of images having different values is formed. This diffraction image is detected by a photodetector. Therefore, the detection result of the photodetector includes incident position information of a light beam incident on the diffractive optical element in a direction corresponding to the sub-scanning direction. As a result, it is possible to accurately detect the position of the light spot formed on the surface to be scanned in the sub-scanning direction without increasing cost and size.

  According to a second aspect of the present invention, at least one scanning object; and at least one light that includes image information is scanned with respect to the at least one scanning object to form an image on the scanning object. An image forming apparatus comprising: one optical scanning device according to the present invention; and a transfer device that transfers an image formed on the scanning object to the transfer object.

  According to this, since at least one optical scanning device of the present invention is provided, it is possible to form a high-quality image without incurring an increase in cost and size.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a full-color image forming apparatus 100 as an image forming apparatus according to an embodiment of the present invention.

  A full-color image forming apparatus 100 shown in FIG. 1 is an apparatus that forms a color image by superimposing four colors (yellow, magenta, cyan, and black). An optical scanning device 900, four photosensitive drums (901a, 901b, 901c, 901d), four charging chargers (902a, 902b, 902c, 902d), four developing rollers (903a, 903b, 903c, 903d), and four toner cartridges (904a, 904b, 904c, 904d). ) Four cleaning cases (905a, 905b, 905c, 905d), transfer belt 906, paper feed tray 907, paper feed roller 908, registration roller pair 909, transfer charger 913, fixing roller 910, paper discharge tray 911, and A paper discharge roller 912 and the like are provided.

  The photosensitive drum 901a, the charging charger 902a, the developing roller 903a, the toner cartridge 904a, and the cleaning case 905a are used as a set and constitute a black image forming station.

  The photosensitive drum 901b, the charging charger 902b, the developing roller 903b, the toner cartridge 904b, and the cleaning case 905b are used as a set and constitute a cyan image forming station.

  The photosensitive drum 901c, the charging charger 902c, the developing roller 903c, the toner cartridge 904c, and the cleaning case 905c are used as a set and constitute a magenta image forming station.

  The photosensitive drum 901d, the charging charger 902d, the developing roller 903d, the toner cartridge 904d, and the cleaning case 905d are used as a set and constitute a yellow image forming station.

  In other words, the full-color image forming apparatus 100 has four image forming stations.

  The photosensitive drums are arranged at equal intervals along the moving direction of the transfer belt 906 (here, the X-axis direction). A photosensitive layer is formed on the surface of each photosensitive drum. Here, each photosensitive drum rotates clockwise (in the direction of the arrow) within the plane in FIG.

  Each charging charger uniformly charges the surface of the corresponding photosensitive drum.

  The optical scanning device 900 generates a light beam modulated for each color based on color image information (yellow image information, magenta image information, cyan image information, black image information) from a host device (for example, a personal computer) 90. The surface of the corresponding charged photosensitive drum is irradiated. As a result, on the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing roller as the photosensitive drum rotates. By the way, the longitudinal direction of the photosensitive drum (the direction along the rotation axis, in this case, the Y-axis direction) is called a “main scanning direction”, and the rotation direction of the photosensitive drum is called a “sub-scanning direction”. Hereinafter, in the scanning in the main scanning direction, the direction from the scanning start position to the scanning end position is referred to as “scanning direction”. An area where a latent image is formed is also referred to as an “image forming area” in the scanning area in the main scanning direction from the scanning start position to the scanning end position on each photosensitive drum. The configuration of the optical scanning device 900 will be described later.

  The toner cartridge 904a stores black toner, and the toner is supplied to the developing roller 903a. The toner cartridge 904b stores cyan toner, and the toner is supplied to the developing roller 903b. The toner cartridge 904c stores magenta toner, and the toner is supplied to the developing roller 903c. The toner cartridge 904d stores yellow toner, and the toner is supplied to the developing roller 903d.

  As each developing roller rotates, the toner supplied from the corresponding toner cartridge is charged and thinly and uniformly adhered to the surface thereof. Further, each developing roller has an electric field in the opposite direction between a charged portion (a portion not irradiated with light) and a non-charged portion (a portion irradiated with light) on the corresponding photosensitive drum. A voltage is generated to generate. By this voltage, the toner adhering to the surface of each developing roller adheres only to the portion irradiated with the light on the surface of the corresponding photosensitive drum. That is, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum to visualize the image information. Here, the toner-attached image (hereinafter referred to as “toner image”) moves in the direction of the transfer belt 906 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 906 at the same timing, and are superimposed to form a color image.

  The paper feed tray 907 stores recording paper as a transfer object. A paper feed roller 908 is disposed in the vicinity of the paper feed tray 907, and the paper feed roller 908 takes out the recording paper one by one from the paper feed tray 907 and conveys it to the registration roller pair 909. The registration roller pair 909 sends the recording paper toward the transfer belt 906 in synchronization with the recording start timing in the sub-scanning direction. Then, the color image on the transfer belt 906 is transferred to the recording paper by the transfer charger 913. The recording sheet transferred here is sent to the fixing roller 910.

  In the fixing roller 910, heat and pressure are applied to the recording paper, whereby the toner is fixed on the recording paper. The recording paper fixed here is sent to the paper discharge tray 911 via the paper discharge roller 912 and sequentially stacked on the paper discharge tray 911.

  Each cleaning case removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The removed residual toner is used again. The surface of the photosensitive drum from which the residual toner has been removed returns to the position of the corresponding charging charger again.

<Optical scanning device>
Next, the configuration of the optical scanning device 900 will be described.

  2 to 4, the optical scanning device 900 includes four light source units (250a, 250b, 250c, 250d) and four coupling lenses (207a, 207b, 207c, 207d) not shown. ), Four apertures (not shown) (208a, 208b, 208c, 208d), four cylinder lenses (209a, 209b, 209c, 209d), polygon mirror 213, four fθ lenses (218a, 218b, 218c, 218d), eight folding mirrors (224a, 224b, 224c, 224d, 227a, 227b, 227c, 227d), four toroidal lenses (220a, 220b, 220c, 220d), four not shown Synchronization sensors (referred to as 228a, 228b, 228c, 228d), 4 Scanning position detection system comprises (400a, 400b, 400c, 400d), and a processing circuit 815 and the like (see FIG. 17). 2 to 4, only a part of the optical scanning device 900 is shown for convenience.

  The light source unit 250a emits a light beam modulated in accordance with black image information (hereinafter also referred to as “black beam” for convenience). The light source unit 250b emits a light beam modulated in accordance with cyan image information (hereinafter also referred to as “cyan beam” for convenience). The light source unit 250c emits a light beam modulated in accordance with magenta image information (hereinafter also referred to as “magenta beam” for convenience). The light source unit 250d emits a light beam modulated in accordance with yellow image information (hereinafter also referred to as “yellow beam” for convenience).

  The coupling lens 207a, the aperture 208a, the cylinder lens 209a, the fθ lens 218a, the folding mirror 224a, the toroidal lens 220a, the folding mirror 227a, the synchronization sensor 228a, and the sub-scanning position detection system 400a each correspond to a black beam.

  The coupling lens 207b, the aperture 208b, the cylinder lens 209b, the fθ lens 218b, the folding mirror 224b, the toroidal lens 220b, the folding mirror 227b, the synchronization sensor 228b, and the sub-scanning position detection system 400b each correspond to a cyan beam.

  The coupling lens 207c, aperture 208c, cylinder lens 209c, fθ lens 218c, folding mirror 224c, toroidal lens 220c, folding mirror 227c, synchronization sensor 228c, and sub-scanning position detection system 400c each correspond to a magenta beam.

  The coupling lens 207d, the aperture 208d, the cylinder lens 209d, the fθ lens 218d, the folding mirror 224d, the toroidal lens 220d, the folding mirror 227d, the synchronization sensor 228d, and the sub-scanning position detection system 400d each correspond to a yellow beam.

  The light beam emitted from each light source unit is made into substantially parallel light by a corresponding coupling lens, and after being shaped by a corresponding aperture, is converged only in a direction corresponding to the sub-scanning direction by a corresponding cylindrical lens, An image is formed on the deflection surface of the polygon mirror 213 as a long line image in a direction corresponding to the main scanning direction. As a result, the deflection point in the polygon mirror 213 and the condensing point on the surface of each photosensitive drum become conjugate in the sub-scanning direction.

  The polygon mirror 213 is configured by a six-sided mirror having a two-stage structure. The light beam from the cylinder lens 209a and the light beam from the cylinder lens 209d are respectively deflected by the first-stage six-surface mirror, and the light beam from the cylinder lens 209b and the light from the cylinder lens 209c are respectively deflected by the second-stage six-surface mirror. Each beam is deflected. That is, all the light beams are deflected by the single polygon mirror 213.

  Each fθ lens has a non-arc surface shape having such a power that the light spot moves at a constant speed in the main scanning direction on the corresponding photosensitive drum surface as the polygon mirror 213 rotates. The fθ lens 218a and the fθ lens 218b are arranged on one side (here, + X side) of the polygon mirror 213, and the fθ lens 218c and the fθ lens 218d are on the other side of the polygon mirror 213 (here, the −X side). ). The fθ lens 218a and the fθ lens 218b, and the fθ lens 218c and the fθ lens 218d are stacked in a direction corresponding to the sub-scanning direction (here, the Z-axis direction). Each cylinder lens, each fθ lens, and each toroidal lens corrects the tilt of the deflection surface of the polygon mirror 213.

  The black beam from the fθ lens 218a forms an image in a spot shape on the photosensitive drum 901a via the folding mirror 224a, the toroidal lens 220a, and the folding mirror 227a. That is, the fθ lens 218a, the folding mirror 224a, the toroidal lens 220a, and the folding mirror 227a constitute a scanning optical system (referred to as “scanning optical system A” for convenience) with respect to the photosensitive drum 901a.

  The cyan beam from the fθ lens 218b forms a spot image on the photosensitive drum 901b via the folding mirror 224b, the toroidal lens 220b, and the folding mirror 227b. That is, the fθ lens 218b, the folding mirror 224b, the toroidal lens 220b, and the folding mirror 227b constitute a scanning optical system (referred to as “scanning optical system B” for convenience) with respect to the photosensitive drum 901b.

  The magenta beam from the fθ lens 218c forms a spot image on the photosensitive drum 901c via the folding mirror 224c, the toroidal lens 220c, and the folding mirror 227c. That is, the fθ lens 218c, the folding mirror 224c, the toroidal lens 220c, and the folding mirror 227c constitute a scanning optical system (referred to as “scanning optical system C” for convenience) with respect to the photosensitive drum 901c.

  The yellow beam from the fθ lens 218d forms a spot image on the photosensitive drum 901d via the folding mirror 224d, the toroidal lens 220d, and the folding mirror 227d. That is, the fθ lens 218d, the folding mirror 224d, the toroidal lens 220d, and the folding mirror 227d constitute a scanning optical system (referred to as “scanning optical system D” for convenience) with respect to the photosensitive drum 901d.

  The folding mirrors are arranged so that the optical path lengths from the polygon mirror 213 to the photosensitive drums coincide with each other, and the incident positions and incident angles of the light beams on the photosensitive drums are equal to each other. Has been.

  Further, the optical scanning device 900 can simultaneously scan the four photosensitive drums.

  Each synchronization sensor (not shown) detects the start of scanning in the main scanning direction on the corresponding photosensitive drum. Here, each synchronization sensor is disposed at a position equivalent to the image plane, and the light beam deflected by the polygon mirror 213 is incident on each synchronization sensor before starting scanning in the main scanning direction. Each synchronization sensor outputs a signal (photoelectric conversion signal) corresponding to the amount of received light.

<Sub-scanning position detection system>
The sub scanning position detection system 400a detects the position of the light spot formed on the photosensitive drum 901a in the sub scanning direction. As shown in FIGS. 3 and 4, the sub-scanning position detection system 400a includes a reflecting mirror 401a, an aperture 402a, a diffractive optical element 403a, a lens 404a, and a light receiving element 405a. Here, the light receiving element 405a is disposed behind the light beam condensing position Pfa (see FIG. 4) by the scanning optical system A. The reflection mirror 401a scans an area outside the image forming area Ara (see FIG. 4) on the photosensitive drum 901a between the folding mirror 227a and the photosensitive drum 901a when scanning in the main scanning direction. It is arranged on the optical path of the light beam. The diffractive optical element 403a receives the light beam reflected by the reflection mirror 401a and forms a diffraction image. The lens 404a condenses the light beam from the diffractive optical element 403a so that the light beam condensing position Pfa by the scanning optical system A and the light receiving position of the light receiving element 405a are conjugate. The aperture 402a corresponds to the sub-scanning direction in the light receiving region of the light receiving element 405a in order to detect only a part of the diffraction image (far field pattern) generated by the diffractive optical element 403a and the lens 404a with the light receiving element 405a. Regulate the width of the direction. The light beam (part of the diffracted light) that has passed through the aperture 402a is received by the light receiving surface of the light receiving element 405a. In other words, at least the width of the light beam incident on the light receiving element 405a in the direction corresponding to the sub-scanning direction is regulated by the aperture 402a.

  The sub scanning position detection system 400b detects the position of the light spot formed on the photosensitive drum 901b in the sub scanning direction. As shown in FIG. 3, the sub-scanning position detection system 400b includes a reflection mirror 401b, an aperture 402b, a diffractive optical element 403b, a lens 404b, and a light receiving element 405b. Here, the light receiving element 405b is disposed behind the light beam condensing position by the scanning optical system B. The reflection mirror 401b is located between the folding mirror 227b and the photosensitive drum 901b on the optical path of a light beam that scans an area outside the image forming area on the photosensitive drum 901b when scanning in the main scanning direction. Is arranged. The diffractive optical element 403b receives the light beam reflected by the reflection mirror 401b and forms a diffraction image. The lens 404b condenses the light beam from the diffractive optical element 403b so that the condensing position of the light beam by the scanning optical system B and the light receiving position of the light receiving element 405b are conjugate. The aperture 402b corresponds to the sub-scanning direction in the light receiving region of the light receiving element 405b in order to detect only a part of the diffraction image (far field pattern) generated by the diffractive optical element 403b and the lens 404b with the light receiving element 405b. Regulate the width of the direction. Then, the light beam (a part of the diffracted light) that has passed through the aperture 402b is received by the light receiving surface of the light receiving element 405b. In other words, at least the width of the light beam incident on the light receiving element 405b in the direction corresponding to the sub-scanning direction is regulated by the aperture 402b.

  The sub-scanning position detection system 400c detects the position of the light spot formed on the photosensitive drum 901c in the sub-scanning direction. As shown in FIG. 3, the sub-scanning position detection system 400c includes a reflection mirror 401c, an aperture 402c, a diffractive optical element 403c, a lens 404c, and a light receiving element 405c. Here, the light receiving element 405c is arranged behind the condensing position of the light beam by the scanning optical system C. The reflection mirror 401c is located between the folding mirror 227c and the photosensitive drum 901c on the optical path of a light beam that scans an area outside the image forming area on the photosensitive drum 901c when scanning in the main scanning direction. Is arranged. The diffractive optical element 403c receives the light beam reflected by the reflection mirror 401c and forms a diffraction image. The lens 404c condenses the light beam from the diffractive optical element 403c so that the condensing position of the light beam by the scanning optical system C and the light receiving position of the light receiving element 405c are conjugate. The aperture 402c corresponds to the sub-scanning direction in the light receiving region of the light receiving element 405c in order to detect only a part of the diffraction image (far field pattern) generated by the diffractive optical element 403c and the lens 404c with the light receiving element 405c. Regulate the width of the direction. The light beam (a part of the diffracted light) that has passed through the aperture 402c is received by the light receiving surface of the light receiving element 405c. In other words, at least the width of the light beam incident on the light receiving element 405c in the direction corresponding to the sub-scanning direction is regulated by the aperture 402c.

  The sub-scanning position detection system 400d detects the position of the light spot formed on the photosensitive drum 901d in the sub-scanning direction. As shown in FIGS. 3 and 4, the sub-scanning position detection system 400d includes a reflection mirror 401d, an aperture 402d, a diffractive optical element 403d, a lens 404d, and a light receiving element 405d. Here, the light receiving element 405d is disposed behind the light beam condensing position Pfd (see FIG. 4) by the scanning optical system D. The reflection mirror 401d scans an area outside the image forming area Ard (see FIG. 4) on the photosensitive drum 901d between the folding mirror 227d and the photosensitive drum 901d when scanning in the main scanning direction. It is arranged on the optical path of the light beam. The diffractive optical element 403d receives the light beam reflected by the reflection mirror 401d and forms a diffraction image. The lens 404d condenses the light beam from the diffractive optical element 403d so that the condensing position Pfd of the light beam by the scanning optical system D and the light receiving position of the light receiving element 405d are conjugate. The aperture 402d corresponds to the sub-scanning direction in the light receiving region of the light receiving element 405d in order to detect only a part of the diffraction image (far field pattern) generated by the diffractive optical element 403d and the lens 404d with the light receiving element 405d. Regulate the width of the direction. The light beam (a part of the diffracted light) that has passed through the aperture 402d is received by the light receiving surface of the light receiving element 405d. That is, the aperture 402d regulates the width of the light beam incident on the light receiving element 405d in the direction corresponding to at least the sub-scanning direction.

  Each diffractive optical element has irregularities arranged two-dimensionally so as to form a diffraction image (far field pattern) by spatially modulating the phase of incident light.

  Here, each diffractive optical element has two dot row images (d1, d2) extending in a direction corresponding to the sub-scanning direction (hereinafter referred to as “dir_sub direction” for convenience), as shown in FIG. 6A as an example. ) And a dot row image d3 that is between these two dot row images and is inclined by an angle θ (0 <θ <90 °) with respect to the dir_sub direction. ing. That is, the dot row image d3 extends in a direction different from both the direction corresponding to the main scanning direction (hereinafter referred to as “dir_main direction” for convenience) and the dir_sub direction. FIG. 6B is an enlarged view of the central portion of FIG. Here, a black part shows a part with strong light intensity, and a white part shows a part with low light intensity. In FIGS. 6A and 6B, for the sake of convenience, the entire dot is drawn with the same density, but the light intensity within the dot is actually not uniform (see FIG. 9B). There is also a slight difference in light intensity between the dots (see FIG. 9B).

  Each sub-scanning position detection system will be described using the results of computer simulation. Each sub-scanning position detection system detects the position of the light spot formed on the photosensitive drum in the sub-scanning direction in substantially the same manner. Therefore, hereinafter, each diffractive optical element is collectively referred to as “diffractive optical element 403”, each lens is collectively referred to as “lens 404”, and each light receiving element is collectively referred to as “light receiving element 405”.

  In the diffractive optical element 403, the diffraction region is divided into 256 pixel × 256 pixel elements. The size of one pixel is 5 μm square. Therefore, the phase modulation area of the diffractive optical element 403 is 1.28 mm × 1.28 mm (see FIG. 5). Further, the number of phase levels when spatially modulating the phase of incident light ranges from 0 to 2π in 256 gradations. As an example, as shown in FIG. 7, an aperture AP is arranged immediately before the diffractive optical element 403 so that light is incident only on the diffractive region, and immediately after the diffractive optical element 403 (the distance is set to 0). The ideal lens 404 having a focal length of 100 mm is disposed. If a diffractive optical element sufficiently large with respect to the size of the light beam is used, the aperture AP is not necessary.

Further, at the focal position of the ideal lens 404, the interval between the dots in the dir_sub direction is set to 100 μm, and the interval between the dots in the dot row image d3 is set to 50 μm. The beam diameter (1 / e ² ) of each dot was about 70 μm. Then, as shown in FIG. 8, a rectangular area of 2.56 mm × 2.56 mm including the diffraction image at the center is set as the calculation target area, and the lower left corner of the rectangular area is set as the calculation origin (0, 0). did.

  FIG. 9B shows three lines extending in the dir_main direction in the diffracted image formed by the diffractive optical element 403 and extending in the dir_main direction (see La, Lb, Lc, FIG. 9A). The calculation result of the light intensity Pw above is shown. The interval between the lines is 300 μm. The maximum value of the light intensity Pw is 1. The light intensity Pw is increased at the dot position.

  When the diffractive optical element 403 having the optical characteristics as described above is scanned with the laser beam in the dir_main direction, the diffraction image formed by the diffractive optical element 403 also moves in the dir_main direction. As an example, as shown in FIGS. 10A to 10C, when the position of the scanning line in the dir_sub direction is different, the position of the diffraction image in the dir_sub direction is also different. In this case, as shown in FIGS. 11A to 11C as an example, signals having different detection timings of the dot row image d3 with respect to the dot row image d1 and the dot row image d2 are output from the light receiving element 405. Is output. That is, the light receiving element 405 outputs a signal that changes at a time interval corresponding to the incident position of the light beam incident on the diffractive optical element 403 in the dir_sub direction. Therefore, the incident position in the dir_sub direction of the light beam incident on the diffractive optical element 403 can be obtained based on the output signal of the light receiving element 405. In the present embodiment, as an example, the position in the dir_sub direction of the center position of the diffraction image composed of the dot row image d1, the dot row image d2, and the dot row image d3 is referred to as the “position of the diffraction image in the dir_sub direction”. And

  However, the relationship between the position in the dir_sub direction of the diffraction image and the detection timing of the dot row image d3 is not necessarily linear due to the fact that dots are arranged in a discrete manner in the diffraction image. When the relationship between the position of the diffraction image in the dir_sub direction and the detection timing of the dot row image d3 has no linearity, the incident position of the light beam in the dir_sub direction is obtained based on the output signal of the light receiving element 405. The calculation becomes complicated. Further, if there is a portion where the change in the detection timing of the dot row image d3 with respect to the change in the position of the diffraction image in the dir_sub direction is small, the detection error increases.

  Therefore, in order to know the influence of the size (referred to as ds) of the light receiving element 405 on the relationship between the position in the dir_sub direction of the diffraction image and the detection timing of the dot row image d3, the diffraction image is fixed for convenience. Then, the position of the light receiving element 405 was changed in the dir_sub direction, and the relationship between the position (Dpd) of the light receiving element 405 and the detection position (Dd3) of the dot row image d3 was obtained by computer simulation. Each position is based on the origin. FIG. 12A shows the calculation result when ds = 100 μm, FIG. 12B shows the calculation result when ds = 110 μm, FIG. 12C shows the calculation result when ds = 120 μm, and ds = FIG. 12D shows the calculation result when 130 μm, FIG. 12E shows the calculation result when ds = 140 μm, and FIG. 12F shows the calculation result when ds = 150 μm. . FIG. 13A shows the calculation result when ds = 160 μm, FIG. 13B shows the calculation result when ds = 170 μm, and FIG. 13C shows the calculation result when ds = 180 μm. FIG. 13D shows the calculation result when ds = 190 μm.

  Here, as an example, as shown in FIG. 14, the threshold value Pth of the light intensity is set to 50% of the maximum intensity, the position n1 crossing the threshold value Pth while increasing the light intensity, and the threshold value Pth while decreasing the light intensity. An intermediate position n3 with the crossing position n2 was set as a detection position of the dot row image d3.

  When ds = 150 μm, the position n1 is set as the detection position of the dot row image d3, the position n2 is set as the detection position of the dot row image d3, and the position n3 is set as the detection position of the dot row image d3. FIG. 15 shows the relationship between the position (Dpd) of the light receiving element 405 and the detection position (Dd3) of the dot row image d3 for the detection position. By setting the position n3 as the detection position of the dot row image d3, it is possible to reduce detection errors due to the influence of dot intensity unevenness. Furthermore, it is possible to reduce detection errors caused by the dots being arranged in a discrete manner. It is not always necessary to set the intermediate position between the position n1 and the position n2 as the detection position of the dot row image d3, and the position obtained from a predetermined arithmetic expression using both the position n1 and the position n2 is the dot row image d3. It is good also as a detection position. Alternatively, sampling may be performed between the position n1 and the position n2 at an appropriate time interval, and the centroid of the sampled value may be used as the detection position of the dot row image d3.

Based on the result of the computer simulation, a parameter indicating the size of the light receiving element 405 in the dir_sub direction with respect to the dot interval in the dir_sub direction in the dot row image d3 (referred to as “parameter a”), and the position (Dpd) of the light receiving element 405 And the parameter indicating the linearity of the relationship between the dot row image d3 and the detected position (Dd3). Here, as an example, as a parameter indicating the linearity of the relationship between the position (Dpd) of the light receiving element 405 and the detection position (Dd3) of the dot array image d3, a multiple determination coefficient (also referred to as a certainty factor coefficient, multiple correlation coefficient) (Hereinafter referred to as “parameter R ² ”). The R ² value ranges from 0 to 1, and the closer to 1, the closer to the straight line.

  The parameter a is 0 or the maximum in which the dot interval in the dot array image d3 is ps [mm], the size of the light receiving element 405 in the dir_sub direction is ds [mm], and (ds−ps × n) is positive. This is a value obtained by the following equation (1), where n is a positive integer.

a = (ds−ps × n) / ps (1)

  a = 0.0 means that ds matches an integer multiple of ps. Here, since ps = 100 μm, ds = 100 μm corresponds to a = 0.0, ds = 110 μm corresponds to a = 0.1, ds = 120 μm corresponds to a = 0.2, ds = 130 μm corresponds to a = 0.3, ds = 140 μm corresponds to a = 0.4, ds = 150 μm corresponds to a = 0.5, ds = 160 μm corresponds to a = 0.6 , Ds = 170 μm corresponds to a = 0.7, ds = 180 μm corresponds to a = 0.8, and ds = 190 μm corresponds to a = 0.9.

  As shown in FIG. 16, by making the size of the light receiving element 405 in the dir_sub direction different from an integral multiple of the dot interval in the dir_sub direction, the position (Dpd) of the light receiving element 405 and the detection position of the dot row image d3 ( The linearity of the relationship with Dd3) can be improved. It is optimal to set a = about 0.5. Therefore, in this embodiment, an aperture is provided in front of each light receiving element, and the size of each light receiving element in the dir_sub direction is 150 μm. The size of each light receiving element itself may be 150 μm. In this case, there may be no aperture in front of each light receiving element.

  In addition, since unevenness in the light intensity between the dots causes a decrease in the linearity, the detection of the position (Dpd) of the light receiving element 405 and the dot row image d3 is further improved by increasing the uniformity of the light intensity of each dot. It is possible to make the relationship with the position (Dd3) close to linear.

<< Light source control circuit >>
The processing circuit 815 has four light source control circuits (815a, 815b, 815c, 815d) as shown in FIG.

  The light source control circuit 815a controls the light source unit 250a based on the black image information from the host device 90, the output signal of the synchronization sensor 228a, the output signal of the light receiving element 405a, and the like. The light source control circuit 815b controls the light source unit 250b based on the cyan image information from the host device 90, the output signal of the synchronization sensor 228b, the output signal of the light receiving element 405b, and the like. The light source control circuit 815c controls the light source unit 250c based on the magenta image information from the host device 90, the output signal of the synchronization sensor 228c, the output signal of the light receiving element 405c, and the like. The light source control circuit 815d controls the light source unit 250d based on the yellow image information from the host device 90, the output signal of the synchronization sensor 228d, the output signal of the light receiving element 405d, and the like. Each light source control circuit has a substantially similar circuit configuration. Therefore, the light source control circuit 815c will be described below as a representative.

  As shown in FIG. 18 as an example, the light source control circuit 815c includes a signal adjustment circuit 28, a sub-scanning position calculation circuit 23, a write control circuit 30, an image processing circuit 40, a light source driving circuit 50, and the like. .

  The image processing circuit 40 generates magenta image data based on the magenta image information from the host device 90.

  The signal adjustment circuit 28 amplifies, inverts, and binarizes the output signal of the synchronous sensor 228c to generate a signal S228c. Accordingly, when light enters the synchronization sensor 228c, the signal S228c changes from “H (high level)” to “L (low level)”. The signal adjustment circuit 28 amplifies and binarizes the output signal of the light receiving element 405c to generate a signal S405c. As an example, as shown in FIGS. 19A to 19C, the signal S405c includes a pulse p1 corresponding to a dot in the dot row image d1, a pulse p3 corresponding to a dot in the dot row image d3, and a dot row. It has a pulse p2 corresponding to a dot of the image d2. Since the position of the diffraction image in the dir_sub direction changes depending on the scanning position of the light beam that scans the diffractive optical element 404c, the time interval t13 between the pulses p1 and p3 and the time interval t32 between the pulses p3 and p2. Are different.

  The sub-scanning position calculation circuit 23 detects the position of the light spot on the photosensitive drum 901c in the sub-scanning direction based on the signal S405c. Here, as shown in FIG. 20, as an example, an intermediate timing t3 between the rising timing t1 of the pulse p1 and the falling timing t2 of the pulse p1, a rising timing t4 of the pulse p3, and a falling timing t5 of the pulse p3. And the time difference between the timing t3 and the timing t6 is calculated as t13. Then, a difference Δt between t13 (which is a reference time difference) when there is no positional deviation and the measured t13 is calculated, and the positional deviation amount and the positional deviation direction (+ side or − side) of the light spot in the sub-scanning direction. Ask for. The relationship between the reference time difference and Δt and the positional deviation amount of the light spot in the sub-scanning direction is acquired in advance and stored in a memory (not shown). Further, a timing t3 ′ obtained by substituting the rising timing t1 of the pulse p1 and the falling timing t2 of the pulse p1 into a predetermined arithmetic expression, the rising timing t4 of the pulse p3, and the falling timing t5 of the pulse p3. The time difference from the timing t6 ′ obtained by substituting the above into a predetermined arithmetic expression may be set as the t13.

  The writing control circuit 30 assigns the image data from the image processing circuit 40 to each pixel to generate modulation data, and outputs the modulation data as a serial signal. Here, a plurality of serial signals corresponding to each semiconductor laser of the light source unit 250c are output.

  Further, the writing control circuit 30 corrects the positional deviation based on the positional deviation amount and the positional deviation direction in the sub-scanning direction of the light spot detected by the sub-scanning position calculation circuit 23. Here, the position shift is corrected by adjusting the formation start position of the image in the sub-scanning direction in units of one line according to the image resolution. As an example, as shown in FIGS. 21A and 21B, the write control circuit 30 detects the optical scanning start signal (signal SOS) when the operation start signal (signal STOUT) is detected. When the pulses are counted and the count value N reaches a preset value Cs, image formation is started (see T1). One pulse of the signal SOS is detected per scan. Therefore, if image formation is started when the count value N reaches Cs-1, image formation in the sub-scanning direction is accelerated by one line (ΔL) (see T2), and the count value N is If image formation is started when Cs + 1 is reached, image formation in the sub-scanning direction is delayed by one line (ΔL) (see T3). For example, the position in the sub-scanning direction can be shifted in units of 42.3 μm for 600 dpi and 21.2 μm for 1200 dpi. That is, the writing control circuit 30 forms an image so that the positional deviation is corrected based on the positional deviation amount and the positional deviation direction of the light spot detected by the sub-scanning direction position calculation circuit 23 in the sub-scanning direction. Sets the count value when is started. Note that a blank line may be provided at the head of the image data, and the number of blank lines may be changed. This method can also adjust the formation start position of the image in the sub-scanning direction in units of one line according to the image resolution.

  Further, the writing control circuit 30 makes the intensity of the light beam going out of the image forming area on the photosensitive drum 901c stronger than the intensity of the light beam going into the image forming area. Thereby, intensity unevenness between dots can be reduced.

  The light source driving circuit 50 generates a driving signal for the light source unit 250 c based on the serial signal from the writing control circuit 30.

  As is apparent from the above description, in the optical scanning device 900 according to the present embodiment, the writing control circuit 30 implements a shift unit and a beam intensity adjustment unit.

  Further, in the full-color image forming apparatus 100 according to the present embodiment, the object to be scanned is realized by each photosensitive drum, and the transfer device is constituted by each charging charger, each developing roller, each toner cartridge, the transfer charger 913, and the fixing roller 910. It has been realized.

  As described above, according to the optical scanning device 900 according to the present embodiment, the light beam from the light source unit toward the corresponding photosensitive drum surface (scanned surface) is incident on each image forming station, and the dir_sub direction (first order). Two dot row images d1 and d2 extending in the direction (1) and a dot row image d3 extending in a direction (second direction) inclined by an angle θ (0 <θ <90 °) with respect to the dir_sub direction. A diffractive optical element 403 that forms a diffraction image and a light receiving element 405 (photodetector) that detects the diffraction image are included. As a result, the light receiving element 405 outputs a signal including position information in the dir_sub direction of the light beam incident on the diffractive optical element 403. Therefore, as a result, it is possible to accurately detect the position of the light spot formed on the surface of the photosensitive drum in the sub-scanning direction without increasing cost and size.

  Further, according to the optical scanning device 900 according to the present embodiment, the diffraction image formed by the diffractive optical element 403 includes a dot array image. Thereby, even if a temporal change occurs in the positional relationship between the diffractive optical element 403 and the light receiving element 405, the detection error can be suppressed small.

  By the way, when the wavelength of the laser light emitted from the semiconductor laser changes due to a temperature change, or when the diffractive optical element 403 itself expands / contracts, the diffraction image also expands / contracts. However, according to the optical scanning device 900 according to the present embodiment, the diffraction image formed by the diffractive optical element 403 includes two diffraction images parallel to each other, and thus detects two diffraction images parallel to each other. Thus, the influence of temperature change can be corrected. Therefore, stable detection accuracy can be maintained even when the wavelength of the laser light emitted from the semiconductor laser changes due to temperature changes or the diffractive optical element 403 itself expands and contracts.

  In addition, according to the optical scanning device 900 according to the present embodiment, the diffractive optical element 403 has unevenness arranged in a two-dimensional manner so as to form a diffraction image by spatially modulating the phase of incident light. Have. Thereby, the fall of the light quantity in the diffractive optical element 403 can be suppressed.

  In the optical scanning device 900 according to the present embodiment, the lens 404 is interposed between the diffractive optical element 403 and the light receiving element 405 so that the surface equivalent to the surface of the photosensitive drum and the light receiving surface of the light receiving element 405 are conjugate. Therefore, the range (dynamic range) in which the position of the light spot in the sub-scanning direction can be detected can be widened. In addition, the size of the diffraction image can be adjusted according to the magnification of the lens, and there is an advantage that the range of design is widened.

  Further, according to the optical scanning device 900 according to the present embodiment, the position of the light spot formed on the surface of the photosensitive drum in the sub-scanning direction is detected using the light beam that goes out of the image forming area. As a result, the position in the sub-scanning direction can be detected in real time.

  Further, according to the optical scanning device 900 according to the present embodiment, the intensity of the light beam going out of the image forming area is made stronger than the intensity of the light beam going into the image forming area. Thereby, the beam intensity detected by the light receiving element 405 can be increased without increasing the beam intensity toward the photoconductor. Therefore, the SN ratio of the signal detected by the light receiving element 405 can be improved, and the detection accuracy can be improved. Further, since the beam intensity toward the photoconductor is not increased, it is possible to avoid adversely affecting the image quality of the output image and the photoconductor drum itself.

  Further, according to the optical scanning device 900 according to the present embodiment, in each sub-scanning position detection system, the length of the light receiving element 405 in the dir_sub direction is set to be different from an integral multiple of the dot interval in the dir_sub direction in the diffraction image. is doing. Thereby, a detection error can be made small.

  Further, according to the optical scanning device 900 according to the present embodiment, each of the sub-scanning position detection systems has an aperture that regulates at least the width of the light beam incident on the light receiving element 405 in the dir_sub direction to 150 μm. Thereby, a low-cost general-purpose light receiving element can be used.

  In addition, since the full-color image forming apparatus 100 according to the present embodiment includes the optical scanning device 900, it is possible to form a high-quality image without incurring an increase in cost and size.

  Further, according to the full-color image forming apparatus 100 according to the present embodiment, the sub-scanning direction deviation of the light spot formed on the surface of the photosensitive drum is corrected by adjusting the formation start position of the image in the sub-scanning direction. . Thereby, cost reduction and size reduction can be further achieved.

  In the above-described embodiment, the case where the positional deviation in the sub-scanning direction of the light spot formed on the surface of the photosensitive drum is corrected by adjusting the formation start position in the sub-scanning direction of the image has been described. It is not limited. For example, when it is necessary to shift more finely than one line, as shown in FIG. 22 as an example, the optical axis 504 has an entrance surface and an exit surface that are non-parallel to each other, and a rotation mechanism (not shown). A wedge-shaped prism 501 that can be rotated about the rotation axis may be disposed between each light source unit and the polygon mirror 213. The wedge-shaped prism 501 emits outgoing light 503 deflected in the direction w1 corresponding to the sub-scanning direction with respect to the incident light 502 in accordance with the rotation. Note that w2 in FIG. 22 is a direction corresponding to the main scanning direction, and w3 is an optical axis direction. In this case, the writing control circuit 30 corrects the positional deviation based on the positional deviation amount and the positional deviation direction of the light spot detected by the sub-scanning position calculation circuit 23 in the sub-scanning direction. A drive signal for rotating the wedge prism 501 is generated and output to a rotation mechanism (not shown). Here, a shift means is realized by the write control circuit 30, the wedge prism 501 and a rotation mechanism (not shown).

  Further, as an example, the sub-scanning direction deviation may be corrected using the liquid crystal deflecting element 143 shown in FIGS. 23 (A) to 23 (E). A liquid crystal deflecting element is an element that deflects light by utilizing a change in refractive index with respect to light having a certain polarization direction when a voltage is applied. The liquid crystal deflection element 143 is disposed between each light source unit and the polygon mirror 213, similarly to the wedge prism 501.

  FIG. 23A shows the outer shape of the liquid crystal deflection element 143. There is an effective area EA capable of deflecting the optical path of the light beam at the center of the liquid crystal deflecting element 143. FIG. 23B is a view of the transparent electrode plate 152-1 (see FIG. 23C) in the effective area EA as viewed from the incident side. On the transparent electrode plate 152-1, a plurality of transparent electrode patterns 156 (156-1, 156-2,..., 156-n) that are long in the vertical direction in FIG. 23 (B) in the horizontal direction of the drawing. Each transparent electrode pattern is electrically connected via a pair of resistors 155. Note that the horizontal direction in FIG. 23B is the direction in which the optical path of the light beam is deflected, and is the direction w1 corresponding to the sub-scanning direction. FIG. 23C shows the cross-sectional structure of the liquid crystal deflection element 143 and the alignment state of the liquid crystal molecules. A liquid crystal layer 154 having a thickness of about several μm to several tens of μm is formed on the two glass substrates 151-1 and 151-2 via the transparent electrode plates 152-1 and 152-2 and the alignment film 153. It is pinched. A uniform electrode pattern is formed on the entire surface of the transparent electrode plate 152-2 on the light beam exit surface side.

A terminal 1 (CH1) is attached to the striped electrode pattern 156-1, and a terminal 2 (CH2) is attached to 156-n. A drive voltage is applied to these two terminals. As shown in FIG. 23D, when different voltages (for example, 1 V and 5 V) are applied to the terminal 1 and the terminal 2, a potential having a resistance value R of the resistor 155 as a proportional constant in the liquid crystal layer 154. Vt is generated. Then, according to this potential distribution, the tilt angle φ of the liquid crystal molecules in the liquid crystal layer 154 changes. When the light beam LB polarized in the major axis direction of the liquid crystal molecules when the voltage is 0 V (left and right direction in the drawing in FIG. 23C) is incident on the liquid crystal molecules thus aligned, the light beam LB is As shown in FIG. 23E, the gradient of the refractive index Ri is felt in the same direction as the polarization direction. That is, the liquid crystal deflecting element 143 has the same function as a prism and can deflect the light beam. When the driving voltage is changed, the refractive index gradient can be changed, so that the deflection angle of the light beam can be controlled. In this case, the writing control circuit 30 corrects the positional deviation based on the positional deviation amount and the positional deviation direction of the light spot detected by the sub-scanning direction position calculation circuit 23 in the sub-scanning direction. In addition, a driving signal corresponding to the driving voltage of the liquid crystal deflecting element 143 is generated. That is, the write control circuit 30 and the liquid crystal deflecting element 143 implement shift means. Instead of the liquid crystal, another electro-optical material such as LiNbO ₃ may be used.

  In the above embodiment, when the influence of the temperature change is small, one of the two dot row images (d1, d2) may not be included in the diffraction image formed by the diffractive optical element 403 (FIG. 24).

  Moreover, although the said embodiment demonstrated the case where the said 2 dot row image (d1, d2) extended in the dir_sub direction, it is not limited to this. In short, the two dot row images (d1, d2) only need to extend in a direction different from the dir_main direction and different from the dot row image d3.

  In the above embodiment, the case where the two dot row images (d1, d2) are parallel to each other has been described. However, the present invention is not limited to this, and one of the two dot row images (d1, d2) It may be parallel to the row image d3.

  Further, the diffraction image formed by the diffractive optical element 403 may be a diffraction image partially including each dot row image.

  In the above embodiment, the case where the diffracted image formed by the diffractive optical element 403 includes a plurality of dot row images is not limited to this. For example, instead of the dot row images d3, a plurality of dot row images d3 may be used. You may use the dot group image arrange | positioned so that the dot of this may comprise a predetermined | prescribed curve.

  In place of the two dot row images (d1, d2), a dot group image in which a plurality of dots are arranged to form the same predetermined curve (A) may be used. In this case, a dot group image in which a plurality of dots are arranged so as to form a curve different from the curve A may be used in place of each dot row image d3.

  In short, it is only necessary that the diffraction image formed by the diffractive optical element 403 includes a plurality of images having different intervals in the dir_main direction depending on the position in the dir_sub direction at least partially.

  In the above embodiment, when the temporal change in the positional relationship between the diffractive optical element 403 and the light receiving element 405 is small, the diffractive optical element 403 is replaced with a dot row image, as an example, as shown in FIG. As shown in FIG. 2, two line images (L1, L2) extending in the dir_sub direction and a line image that is inclined between the two line images by an angle θ (θ <90 °) with respect to the dir_sub direction. You may design so that the diffraction image which consists of L3 may be formed. FIG. 25B is an enlarged view of the central portion of FIG. In FIGS. 25A and 25B, for the sake of convenience, the entire line is drawn with the same density, but the light intensity in the line is actually not uniform (see FIG. 26B).

  FIG. 26B shows three lines extending in the dir_main direction in the diffractive image shown in FIG. 25A and extending in the dir_main direction (see Ld, Le, Lf, FIG. 26A). The calculation result by the computer simulation of the light intensity Pw is shown. The interval between the lines is 300 μm. The same tendency as in the case of the dot row is shown. The maximum value of the light intensity Pw is 1.

  In this case, as shown in FIG. 27, even when the size of the light receiving element 405 in the dir_sub direction is 100 μm, the position (Dpd) of the light receiving element 405 and the detection position (Dl3) of the line image L3 The relationship is almost linear.

  In this case, as shown in FIG. 28A to FIG. 28C, for example, the signal S405c includes the pulse p1 corresponding to the line image L1, the pulse p3 corresponding to the line image L3, and the line image L2. Has a pulse p2 corresponding to. Since the position of the diffraction image in the dir_sub direction changes depending on the incident position of the light beam in the dir_sub direction in the diffractive optical element 404c, the time interval t13 between the pulse p1 and the pulse p3 and the time interval t32 between the pulse p3 and the pulse p2 are different. ing. That is, the positional deviation in the sub-scanning direction can be obtained in the same manner as in the above embodiment.

  Also in this case, if the influence of the temperature change is small, one of the two line images (L1, L2) may not be present (see FIG. 29).

  Also in this case, the two line images (L1, L2) only need to extend in a direction different from the dir_main direction and in a direction different from the line image L3.

  Also in this case, one of the two line images (L1, L2) may be parallel to the line image L3.

  Also in this case, the diffracted image formed by the diffractive optical element 403 may be a diffracted image partially including each line image.

  Also in this case, a predetermined curved image may be used instead of the line image L3.

  Also in this case, instead of the two line images (L1 and L2), the same predetermined curved line (a) image may be used. In this case, a curved image different from the curve a may be used instead of the line image L3.

  In short, it is only necessary that the diffraction image formed by the diffractive optical element 403 includes a plurality of images having different intervals in the dir_main direction depending on the position in the dir_sub direction at least partially.

  In the above embodiment, when a lens function is added to the diffractive optical element 403 such that the condensing position of the light beam by the corresponding scanning optical system and the position of the light receiving element 405 are conjugated, the lens 404 is not necessary.

  In the above embodiment, the diffractive optical element 403 transmits the light beam and modulates the phase. However, the diffractive optical element 403 may reflect the light beam and modulate the phase.

  In the above-described embodiment, the case where the light receiving element 405 is arranged behind the light beam condensing position by the corresponding scanning optical system is described. However, the present invention is not limited thereto, and the light receiving element 405 includes: You may arrange | position in the condensing position of the light beam by a corresponding scanning optical system (refer FIG. 30). In this case, the lens 404 is not necessary.

  In the above embodiment, the case of the full-color image forming apparatus 100 has been described as the image forming apparatus. However, the image forming apparatus is not limited to this, and may be a one-color image forming apparatus such as a monochrome laser printer.

1 is a diagram for explaining a schematic configuration of a full-color image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram (part 1) for describing the optical scanning device in FIG. 1; FIG. 3 is a schematic diagram (part 2) for describing the optical scanning device in FIG. 1; FIG. 3 is a schematic diagram (part 3) for describing the optical scanning device in FIG. 1; It is a figure for demonstrating the magnitude | size of the diffraction area in a diffractive optical element. FIG. 6A and FIG. 6B are diagrams for explaining diffraction images formed by the diffractive optical element, respectively. It is a figure for demonstrating the structure of the sub-scanning position detection system in computer simulation. It is a figure for demonstrating a calculation area | region and the origin on calculation. 9 (A) and 9 (B) are diagrams for explaining the light intensity of the diffraction image of FIG. 10A to 10C are diagrams for explaining the relationship between the position of the light beam that scans the diffractive optical element in the direction corresponding to the sub-scanning direction and the position of the formed diffraction image. It is. FIGS. 11A to 11C are diagrams for explaining output signals of the light receiving elements corresponding to FIGS. 10A to 10C, respectively. FIGS. 12A to 12F are views (No. 1) for explaining the relationship between the position (Dpd) of the light receiving element and the detection position (Dd3) of the dot row image d3, respectively. FIGS. 13A to 13D are diagrams (No. 2) for explaining the relationship between the position (Dpd) of the light receiving element and the detection position (Dd3) of the dot row image d3, respectively. FIG. 6 is a diagram (No. 1) for describing a detection position of a dot row image d3 in an output signal of a light receiving element. FIG. 6 is a diagram (No. 2) for describing a detection position of a dot row image d3 in an output signal of a light receiving element. It is a figure for demonstrating the influence which the magnitude | size of the light receiving element with respect to a dot space | interval has on the linearity of the relationship between the position (Dpd) of a light receiving element and the detection position (Dd3) of the dot row image d3. It is a figure for demonstrating the processing circuit of the optical scanning device in FIG. It is a figure for demonstrating the light source control circuit 815c in FIG. FIGS. 19A to 19C are diagrams for explaining output signals of the light receiving element 405c. It is a figure for demonstrating the signal processing in a subscanning position calculating circuit. FIGS. 21A and 21B are diagrams for explaining sub-scanning direction shift correction processing in the writing control circuit. It is a figure for demonstrating a wedge-shaped prism. FIG. 23A to FIG. 23E are diagrams for explaining the liquid crystal deflection elements. It is a figure for demonstrating the diffraction image when a dot row image is two. FIG. 25A and FIG. 25B are diagrams for explaining a diffraction image of a line image, respectively. FIG. 26A and FIG. 26B are diagrams for explaining the light intensity of the diffraction image of FIG. It is a figure for demonstrating the relationship between the position (Dpd) of a light receiving element, and the detection position (Dl3) of the line image L3. FIGS. 28A to 28C are diagrams for explaining the output signal of the light receiving element 405c when the diffraction image of FIG. 25A is formed. It is a figure for demonstrating the diffraction image when there are two line images. It is the schematic for demonstrating the modification of a subscanning position detection system.

Explanation of symbols

  30 ... writing control circuit (beam intensity adjusting means, shift means, part of shift means), 100 ... full-color image forming apparatus (image forming apparatus), 213 ... polygon mirror (deflecting means), 218a to 218d ... fθ lens ( Part of scanning optical system), 220a to 220d ... Toroidal lens (part of scanning optical system), 224a to 224d ... Folding mirror (part of scanning optical system), 227a to 227d ... Folding mirror (one of the scanning optical system) Part), 250a-250d ... light source unit, 400a-400d ... sub-scanning position detection system, 402a-402d ... aperture, 403, 403a-403d ... diffractive optical element, 404, 404a-404d ... lens, 405, 405a-405d ... Light receiving element (photodetector), 900 ... optical scanning device, 901a to 901d ... photosensitive drum (running) Object).

Claims (21)

An optical scanning device that scans a surface to be scanned with a light beam,
With a light source;
Deflecting means for deflecting a light beam from the light source;
A scanning optical system for condensing the deflected light beam on the surface to be scanned;
A light beam directed from the light source toward the surface to be scanned is incident to form a diffraction image including a plurality of images whose intervals in the direction corresponding to the main scanning direction are different at least partially depending on the position in the direction corresponding to the sub-scanning direction. A diffractive optical element;
A light detector for detecting the diffraction image.   The plurality of images includes an image including at least a part of an image extending in a first direction different from a direction corresponding to the main scanning direction, and a second different from both the direction corresponding to the main scanning direction and the first direction. The optical scanning device according to claim 1, further comprising: an image including at least a part of an image extending in a direction.   3. The image according to claim 2, wherein the plurality of images further include an image including at least a part of an image parallel to one of the image extending in the first direction and the image extending in the second direction. Optical scanning device.   The optical scanning device according to claim 2, wherein each extending image is a line-shaped image.   The optical scanning device according to claim 2, wherein each extending image is a dot row image.   6. The length of the photodetector in a direction corresponding to the sub-scanning direction is different from an integral multiple of the inter-dot distance in the direction corresponding to the sub-scanning direction in the dot row image. Optical scanning device.   The optical scanning device according to claim 1, wherein the diffractive optical element forms the diffraction image by spatially modulating the phase of incident light.   8. The optical scanning device according to claim 1, wherein the light beam incident on the diffractive optical element is a light beam that passes through the scanning optical system.   9. The light beam incident on the diffractive optical element is a light beam directed to a region outside an area where an image is formed on the surface to be scanned. Optical scanning device.   The apparatus further comprises beam intensity adjusting means for making the intensity of the light beam directed to a region outside the region where the image is formed stronger than the intensity of the light beam directed toward the region where the image is formed. Item 10. The optical scanning device according to Item 9.   The said photodetector outputs the signal which changes at the time interval according to the incident position of the direction corresponding to the subscanning direction of the light beam which injects into the said diffractive optical element. The optical scanning device according to any one of the above. The photodetector is arranged behind the light beam condensing position by the scanning optical system,
The lens according to any one of claims 1 to 11, further comprising a lens that condenses the light beam from the diffractive optical element so that the position of the photodetector and the condensing position are conjugate. The optical scanning device according to Item. The photodetector is arranged behind the light beam condensing position by the scanning optical system,
12. The optical scanning device according to claim 1, wherein the diffractive optical element further has a lens function such that a position of the photodetector and the condensing position are conjugate. .   The optical scanning device according to claim 1, further comprising an aperture that regulates a width of a light beam incident on the photodetector in a direction corresponding to at least a sub-scanning direction.   15. The apparatus according to claim 1, further comprising a shift unit that shifts a light beam condensing position on the surface to be scanned in a sub-scanning direction based on an output signal of the photodetector. The optical scanning device according to 1.   The optical scanning device according to claim 15, wherein the shift unit obtains a shift amount and a shift direction by using a rising timing and a falling timing of an output signal of the photodetector.   The shift means includes a liquid crystal deflecting element that deflects a light beam from the light source in a direction corresponding to a sub-scanning direction according to a driving voltage, and a driving signal that generates the driving signal based on an output signal of the photodetector. The optical scanning device according to claim 15, further comprising a generation circuit.   The shift means includes an attitude adjustment means for adjusting an attitude of an optical element disposed between the light source and the deflection means based on an output signal of the photodetector. 16. An optical scanning device according to 16.   17. The shift unit includes a start position adjustment circuit that adjusts an image formation start position in the sub-scanning direction on the surface to be scanned based on an output signal of the photodetector. The optical scanning device described. At least one scan object;
The optical scanning device according to any one of claims 1 to 19, wherein the at least one scanning object is scanned with light including image information, and an image is formed on the scanning object. ;
An image forming apparatus comprising: a transfer device that transfers an image formed on the scanning object to the transfer object.   The image forming apparatus according to claim 20, wherein the image information is color image information.

Images