JP2007156366A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which the position of a light beam on a face to be scanned in a subscanning direction is accurately detected. <P>SOLUTION: The optical scanner is provided with: light source units (250a to 250d) each of which has thirty-six light emitting parts arranged two-dimensionally; and light detecting sensors (302a to 302d, 303a to 303d) which detect a plurality of light beams emitted from six light emitting parts arranged in dir_sub direction and five light emitting parts arranged in a direction which is different from both of the dir_sub direction and dir_main direction, among the thirty-six light emitting parts, and deflected with a polygon mirror 213. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 light and an image forming apparatus including the optical scanning apparatus.

  As one of color image forming apparatuses, a plurality of image carriers such as photosensitive drums are juxtaposed, and a plurality of optical scanning devices are provided corresponding to the respective image carriers, and each optical scanning device uses an image signal corresponding to a color. The surface of the image carrier is scanned with a laser beam to form a latent image. The latent image on the surface of each image carrier is developed with toner of a color corresponding to each image signal, and each toner image is superimposed on transfer paper or the like. A so-called tandem type color image forming apparatus is known in which a color image is obtained by transfer.

  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 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. Whatever the cause, if the laser beam deviation in the sub-scanning direction can be detected, the detected deviation can be corrected by an appropriate correction means.

  Therefore, for example, Patent Document 1 discloses a polygon mirror that deflects and reflects a plurality of laser beams emitted from a plurality of semiconductor lasers, and deflects and scans the light that is deflected and scanned by the polygon mirror in the scanning direction. A light receiving element that receives light from one vertical side and receives 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. And an optical system for guiding image information light emitted from the plurality of semiconductor lasers and scanned by the polygon mirror to a plurality of photosensitive drums, An image forming apparatus using an optical scanning device is disclosed.

  However, in the image forming apparatus disclosed in Patent Document 1 described above, the light receiving element is disposed only at one end of the image area of one scanning imaging optical system. If the scan line tilts or bends locally when the temperature distribution is in the sub-scanning direction, the laser beam cannot be detected for the local tilt or bend. Therefore, there is an inconvenience that it is difficult to correct image deterioration such as color misregistration caused by local inclination or bending of the laser beam.

Japanese Patent Laid-Open No. 10-235928

  The present invention has been made under such circumstances, and a first object thereof is to provide an optical scanning device capable of accurately detecting the position of the light beam in the sub-scanning direction on the surface to be scanned. is there.

  A second object of the present invention is to provide an image forming apparatus capable of forming a high quality image.

  From a first aspect, the present invention is an optical scanning device that scans a surface to be scanned with light, the light source unit having a plurality of light sources arranged two-dimensionally; a plurality of light sources from the light source unit; Deflection means for deflecting a light beam; light sources arranged in a first direction different from the direction corresponding to the main scanning direction among the plurality of light sources; both the direction corresponding to the main scanning direction and the first direction And a light beam detecting means for detecting a plurality of light beams emitted from a plurality of light sources including light sources arranged in different second directions and deflected by the deflecting means.

  According to this, among the plurality of light sources, the light sources arranged in the first direction different from the direction corresponding to the main scanning direction and the second direction different from both the direction corresponding to the main scanning direction and the first direction. A plurality of light beams emitted from a plurality of light sources including the aligned light sources and deflected by the deflecting unit are detected by the light beam detecting unit. In this case, based on the detection result of the light beam from the light source aligned in the first direction and the detection result of the light beam from the light source aligned in the second direction, the sub-scanning direction of the light beam on the surface to be scanned Can be detected with high accuracy.

  According to a second aspect of the present invention, at least one scanning object; the at least one scanning object is scanned with light containing image information, and an image is formed on the scanning object. And a transfer device that transfers the image formed on the scanning object to the transfer object.

  According to this, since the optical scanning device of the present invention capable of accurately detecting the position of the light beam in the sub-scanning direction on the surface to be scanned is provided, the surface to be scanned can be scanned with high accuracy. As a result, a high-quality image can be formed.

  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, discharge A paper roller 912 and a position detection device 913 are provided.

  The photosensitive drum 901a, the charging charger 902a, the developing roller 903a, the toner cartridge 904a, and the cleaning case 905a constitute an image forming station that forms a yellow toner image.

  The photosensitive drum 901b, the charging charger 902b, the developing roller 903b, the toner cartridge 904b, and the cleaning case 905b constitute an image forming station that forms a magenta toner image.

  The photosensitive drum 901c, the charging charger 902c, the developing roller 903c, the toner cartridge 904c, and the cleaning case 905c constitute an image forming station that forms a cyan toner image.

  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 an image forming station that forms a black toner image.

  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 uses 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 yellow toner, and the toner is supplied to the developing roller 903a. The toner cartridge 904b stores magenta toner, and the toner is supplied to the developing roller 903b. The toner cartridge 904c stores cyan toner, and the toner is supplied to the developing roller 903c. The toner cartridge 904d stores black 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 recording sheets one by one from the paper feed tray 907 and conveys them to a pair of registration rollers 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.

  The position detection device 913 is disposed near the + X side of the photosensitive drum 901a at a position facing the transfer belt 906, and performs light based on a toner patch (see Japanese Patent No. 3644923) formed on the transfer belt 906. A signal including spot position information is output.

  The position detection device 913 includes three position detection sensors (913a, 913b, 913c) as shown in FIG. 2 as an example. Each position detection sensor includes an LED element that irradiates illumination light toward the transfer belt 906, a condensing lens that condenses light from the LED element on the surface of the transfer belt 906, and a transfer belt 906. A condensing lens that collects reflected light (reflected light) and a photosensor that receives reflected light collected by the condensing lens are included. Each photosensor outputs a photoelectric conversion signal corresponding to the amount of received light.

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

  As shown in FIG. 3, the optical scanning device 900 includes four light source units (250a, 250b, 250c, 250d), a polygon mirror 213, a lens 218, and four folding mirrors (224a, 224b, 224c, 224d). ) 4 lenses (220a, 220b, 220c, 220d), 4 half mirrors (227a, 227b, 227c, 227d), 8 light detection sensors (302a, 302b, 302c, 302d, 303a, 303b, 303c, 303d), a liquid crystal deflection element 305, a beam deflection circuit 350 (not shown in FIG. 3), a processing circuit 815, and the like.

  The light source unit 250a has a semiconductor laser, a coupling lens, and a cylindrical lens, and emits a light beam modulated according to yellow image information. The light source unit 250b includes a semiconductor laser, a coupling lens, and a cylindrical lens, and emits a light beam modulated according to magenta image information. The light source unit 250c has a semiconductor laser, a coupling lens, and a cylindrical lens, and emits a light beam modulated according to cyan image information. The light source unit 250d includes a semiconductor laser, a coupling lens, and a cylindrical lens, and emits a light beam modulated according to black image information.

  The light beam emitted from each semiconductor laser is converted into a light beam form suitable for the subsequent optical system by a corresponding coupling lens, for example, a parallel light beam or a weakly divergent or converging light beam, and by a corresponding cylindrical lens. The light is focused in a direction corresponding to the sub-scanning direction, and is formed as a long line image in the direction corresponding to the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 213.

  As shown in FIG. 4 as an example, each semiconductor laser is a so-called surface emitting laser having 36 light emitting portions each having substantially the same light emission characteristics.

  The 36 light emitting units have a direction corresponding to the sub-scanning direction (hereinafter also referred to as “dir_sub direction” for convenience) and a direction different from the dir_sub direction and corresponding to the main scanning direction (hereinafter referred to as “for convenience”. and a direction (hereinafter also referred to as “α direction” for convenience) inclined by an angle θ (0 ° <θ <90 °) with respect to the “dir_main direction”). Here, as an example, the number of light emitting unit rows arranged in the α direction is six (referred to as “A column to F column” in order from the top to the bottom in FIG. 4), and the number of light emitting unit rows arranged in the dir_sub direction. Are six columns (referred to as “first to sixth columns” in order from the left to the right in FIG. 4). Therefore, in the following, for example, the light emitting unit in the third row in the B row is referred to as a B3 light emitting unit, and the light emitting unit in the sixth column in the F row is referred to as an F6 light emitting unit. For the dir_sub direction, the direction from the upper side to the lower side in FIG. 4 is referred to as the + direction, and for the α direction, the direction from the left side to the right side in FIG. In addition, the 36 light emitting units are arranged at equal intervals in both the dir_main direction and the dir_sub direction. Accordingly, the light emitting units are also arranged at equal intervals in the α direction.

  Note that if the pixel density in the sub-scanning direction of the latent image formed on the surface of the photosensitive drum is 4800 dpi, the interval between the light emitting portions in the dir_sub direction is about 5 μm. Further, it is assumed that the beam diameter of the light beam from one light emitting unit is 60 μm in both the dir_sub direction and the dir_main direction.

  The polygon mirror 213 is configured by a six-sided mirror having a four-stage structure. The light from the light source unit 250d is deflected by the first-stage six-sided mirror, the light from the light source unit 250c is deflected by the second-stage six-sided mirror, and the light from the light source unit 250b is deflected by the third-stage six-sided mirror. The light from the light source unit 250a is deflected by the fourth-stage six-sided mirror. The polygon mirror 213 is substantially sealed in a housing (not shown) so that noise due to high-speed rotation does not leak to the outside. This housing is provided with a window glass 215, and the light from each light source unit is incident through the window glass 215, and the light deflected by the polygon mirror 213 is emitted through the window glass 215. ing.

  The lens 218 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. Here, the lens 218 has power in the main scanning direction and non-power in the sub-scanning direction. In this lens 218, in the + Z direction, an incident position of a light beam corresponding to yellow, an incident position of a light beam corresponding to magenta, an incident position of a light beam corresponding to cyan, and an incident position of a light beam corresponding to black. It is in order.

  Each light detection sensor is mounted and fixed on a fixing substrate. Each light detection sensor outputs a signal including information on the position in the sub-scanning direction of the light beam that scans the corresponding photosensitive drum surface, and a synchronization signal in the main scanning direction.

  The light beam emitted from the light source unit 250a enters the half mirror 227a through the polygon mirror 213, the lens 218, the folding mirror 224a, and the lens 220a. The light beam that has passed through the half mirror 227a forms a spot image on the photosensitive drum 901a. Here, the light beam scans on the photosensitive drum 901a in the + Y direction. Then, when the photosensitive drum 901a rotates around its rotation center axis, scanning in the direction orthogonal to the main scanning direction, that is, sub-scanning is performed. The light beam reflected by the half mirror 227a before scanning the image forming area scans the light detection sensor 302a. Further, the light beam reflected by the half mirror 227a after scanning the image forming area scans the light detection sensor 303a. That is, the light detection sensor 302a and the light detection sensor 303a are light detection sensors used as a set.

  The light beam emitted from the light source unit 250b enters the half mirror 227b via the polygon mirror 213, the lens 218, the folding mirror 224b, and the lens 220b. The light beam transmitted through the half mirror 227b forms a spot image on the photosensitive drum 901b. Here, the light beam scans on the photosensitive drum 901b in the + Y direction. Then, the photoconductor drum 901b rotates about its rotation center axis, whereby sub-scanning is performed. The light beam reflected by the half mirror 227b before scanning the image forming area scans the light detection sensor 302b. In addition, the light beam reflected by the half mirror 227b after scanning the image forming area scans the light detection sensor 303b. That is, the light detection sensor 302b and the light detection sensor 303b are light detection sensors used as a set.

  The light beam emitted from the light source unit 250c is incident on the half mirror 227c via the polygon mirror 213, the lens 218, the folding mirror 224c, and the lens 220c. The light beam that has passed through the half mirror 227c forms a spot image on the photosensitive drum 901c. Here, the light beam scans on the photosensitive drum 901c in the + Y direction. Then, the photoconductor drum 901c rotates about its rotation center axis, whereby sub-scanning is performed. The light beam reflected by the half mirror 227c before scanning the image forming area scans on the light detection sensor 302c. Further, the light beam reflected by the half mirror 227c after scanning the image forming area scans the light detection sensor 303c. That is, the light detection sensor 302c and the light detection sensor 303c are light detection sensors used as a set.

  The light beam emitted from the light source unit 250d enters the half mirror 227d through the polygon mirror 213, the lens 218, the folding mirror 224d, and the lens 220d. The light beam transmitted through the half mirror 227d forms a spot image on the photosensitive drum 901d. Here, the light beam scans on the photosensitive drum 901d in the + Y direction. Then, the photoconductor drum 901d rotates about its rotation center axis, thereby performing sub-scanning. The light beam reflected by the half mirror 227d before scanning the image forming area scans on the light detection sensor 302d. Further, the light beam reflected by the half mirror 227d after scanning the image forming area scans the light detection sensor 303d. That is, the light detection sensor 302d and the light detection sensor 303d are light detection sensors used as a set.

  The four lenses (220a, 220b, 220c, 220d) have a smaller power than the lens 218 in the main scanning direction and have a power in the sub scanning direction.

  As the material of the lens 218 and the four lenses (220a, 220b, 220c, 220d), a plastic that is easy to form an aspherical surface and is inexpensive is used. Specifically, a polycarbonate having a low water absorption, a high transparency, and an excellent moldability is preferable.

  The misregistration here means the misregistration of the latent image formed on the surface of the photosensitive drum, the scanning unevenness due to the characteristics of the lens 218, the so-called surface tilt of the deflection reflection surface in the polygon mirror 213, This is caused by variations in the distance of the deflecting / reflecting surface from the rotation axis, uneven rotation of the polygon mirror 213, fluctuations in the wavelength of the laser light emitted from the semiconductor laser, and the like. In the following, for the sake of convenience, the positional deviation in the main scanning direction is also referred to as “main scanning direction deviation”, and the positional deviation in the sub scanning direction is also referred to as “sub scanning direction deviation”.

<Liquid crystal deflection element>
The liquid crystal deflection element 305 is disposed immediately after the lens 218. In this case, the closer the position of the liquid crystal deflecting element 305 is to the lens 218, the farther from the lens having power in the sub-scanning direction, the larger the maximum correction amount of the sub-scanning direction deviation can be made. Further, as the position of the liquid crystal deflecting element 305 is closer to the lens 218, the total length of the liquid crystal deflecting element 305 in the main scanning direction can be shortened.

  As shown in FIG. 5 as an example, the liquid crystal deflecting element 305 includes a partial region 305K into which a light beam corresponding to black (hereinafter also referred to as “black beam” for convenience) is incident, and a light beam corresponding to cyan (hereinafter referred to as “black beam”). For convenience, a partial region 305C where a “cyan beam” is incident, a light region corresponding to magenta (hereinafter, also referred to as “magenta beam” for convenience) 305M, and a light beam corresponding to yellow (hereinafter, “magenta beam”). For convenience, it is also referred to as “yellow beam”).

  Each partial region is formed such that the main scanning direction is the longitudinal direction, the length in the main scanning direction is set so as to cover at least the image forming region, and the length in the sub scanning direction is at least the sub scanning of the light beam. It is set to cover the width of the direction. In particular, the length in the sub-scanning direction is larger than the width of the incident light beam in the sub-scanning direction in consideration of the displacement of the light beam due to the position and dimensional variation (error) of each element constituting the optical scanning device. It is set to be at least 2 mm larger.

  As an example, the partial area 305C, the partial area 305M, and the partial area 305Y are divided into approximately 10 sections (section 1 to section 10) in the main scanning direction (divided width: W). Here, as an example, one section is further divided into five partial sections approximately equally. The number of sections is set according to the characteristics of the lens. An enlarged view of the frame 311 in FIG. 6A is shown in FIG. In this way, by dividing the section, it is possible to make the deterioration of the profile of the light beam at the boundary of the section inconspicuous.

  Reference numeral 312 in FIG. 6A indicates a cross section of the light beam incident on the liquid crystal deflecting element 305. The cross section 312 has a long line shape in the main scanning direction due to the action of the cylindrical lens of the light source unit. Therefore, the width of one section is set to be wider than the width L of the incident light beam in the main scanning direction (hereinafter referred to as “beam width L” for convenience). If the division width W of one section is narrower than the beam width L, the light beam deflected by the liquid crystal deflecting element 305 is separated in the sub-scanning direction, and the light beam is deteriorated.

  The light beam is incident on a region composed of a plurality of partial sections. The width of the boundary between adjacent partial sections is set to be 1/50 or less of the beam width L, and the total width of all the boundary lines is set to be 1/10 or less of the beam width L. Yes. Note that the incident light beam is not deflected at the boundary between the partial sections.

  Here, L = 10 mm, the boundary width is 0.2 mm, and the light beam is designed to straddle four boundary widths in the main scanning direction. In this case, the boundary width of the partial section is 1/50 (= 0.2 mm / 10 mm) of the beam width L, and the total width of all the boundary lines is 1 / 12.5 (= 0) of the beam width L. .2 mm × 4/10 mm). When the width of the boundary is larger than this, the profile of the light beam deflected by the liquid crystal deflecting element 305 deteriorates, and inconveniences such as an increase in the diameter of the light spot that forms an image on the photosensitive drum occur.

Further, as shown in FIG. 6B, the boundary of the partial section in the partial area 305C, the boundary of the partial section in the partial area 305M, and the boundary of the partial section in the partial area 305Y are different from each other in the main scanning direction. Are arranged as follows. If the boundary positions of the partial sections in each partial area are the same in the main scanning direction, the scanning lines of the light beams incident on the partial areas are respectively scanned in the main scanning direction when the light beam deflection angle by correction is large. The image is divided at the same position in the direction, and streaks occur at the same position in the main scanning direction in the formed image. The shift amount of the boundary position of the partial section needs to be at least equal to or larger than the diameter (1 / e ² ) of the light spot imaged on the photosensitive drum. Specifically, the thickness is preferably 50 μm or more in consideration of variation. On the other hand, the upper limit of the shift amount is ½ of the division width W. If it is the same as the division width W, the boundary positions will coincide. As a method of shifting the boundary position of the partial section in each partial area, it is preferable to use a wiring pattern. In the case of a wiring pattern, a stable deviation amount is ensured even in mass production, and quality variation is small.

  As shown in FIG. 7, each partial section has a laser transmitting member (for example, a resin having a high transmittance, glass, etc.) 403 arranged opposite to each other in parallel with each other, and a surface side of the laser transmitting member 403 facing each other. A pair of transparent electrodes 405 disposed integrally with each other, a pair of alignment films 407 disposed integrally on opposite surfaces of the pair of transparent electrodes 405, and a spacer that forms a predetermined gap between the pair of alignment films 407 408, and a liquid crystal layer 409 formed by filling a liquid crystal material in a space formed by the alignment film 407 and the spacer 408.

  The laser transmitting member 403 in each partial section is integrated, and one of the transparent electrodes 405 is shared as a ground electrode. A voltage is applied from the drive circuit 401 between the pair of transparent electrodes 405. By controlling this applied voltage, as shown in FIG. 8 as an example, the emission angle of the emitted light can be changed with respect to the incident angle of the incident light.

  On the other hand, the partial region 305K transmits incident light as it is. That is, the partial area 305K is a so-called “through area”. Therefore, here, the scanning line bending of the yellow beam, the magenta beam, and the cyan beam is corrected based on the scanning line bending of the black beam. Note that a liquid crystal layer can be formed in the partial region 305K in the same manner as the other partial regions, and the scanning line curve of the black beam can be corrected. However, for that purpose, an electrode and a driving circuit are further required. Increases power consumption and manufacturing cost.

  The deflection angle of the light beam in each partial region can be controlled by at least one of the waveform of the drive voltage, the peak value, and the duty of the pulse width.

<Processing circuit>
As shown in FIG. 9, the processing circuit 815 has four light source control circuits (815a, 815b, 815c, 815d).

  The light source control circuit 815a controls the light source unit 250a based on the yellow image information, the output signal of the light detection sensor 302a, the output signal of the light detection sensor 303a, the output signal of the position detection device 913, and the like.

  The light source control circuit 815b controls the light source unit 250b based on the magenta image information, the output signal of the light detection sensor 302b, the output signal of the light detection sensor 303b, the output signal of the position detection device 913, and the like.

  The light source control circuit 815c controls the light source unit 250c based on the cyan image information, the output signal of the light detection sensor 302c, the output signal of the light detection sensor 303c, the output signal of the position detection device 913, and the like.

  The light source control circuit 815d controls the light source unit 250d based on the black image information, the output signal of the light detection sensor 302d, the output signal of the light detection sensor 303d, the output signal of the position detection device 913, 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 shown in FIG. 10 as an example, the light source control circuit 815c includes a signal adjustment circuit 28, a writing 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 and binarizes the output signal of the light detection sensor 302c to generate a signal S302c. The signal adjustment circuit 28 also amplifies and binarizes the output signal of the light detection sensor 303c to generate a signal S303c. Further, the signal adjustment circuit 28 amplifies and binarizes the output signal of each position detection sensor of the position detection device 913 to generate signals S913a to S913c.

  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. At this time, the writing control circuit 30 synchronizes in the main scanning direction based on at least one of the signal S302c and the signal S303c. The write control circuit 30 also adjusts the pixel clock based on the signals S913a to S913c.

  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. Here, a plurality of drive signals corresponding to the respective semiconductor lasers of the light source unit 250c are generated.

<Beam deflection circuit>
The beam deflection circuit 350 is a circuit that corrects the sub-scanning direction deviation of each light beam via the liquid crystal deflection element 305. As shown in FIG. 11, as an example, the signal deflection circuit 352, the sub-scanning direction deviation detection circuit. 354 and a drive signal generation circuit 356.

  The signal adjustment circuit 28 amplifies and binarizes the output signals of the light detection sensors 302a to 302d to generate signals S302a to S302d. The signal adjustment circuit 28 also amplifies and binarizes the output signals of the light detection sensors 303a to 303d to generate signals S303a to S303d.

  Based on the signals S302a, S303a, S302d, and S303d, the sub-scanning direction deviation detection circuit 354 detects a deviation in the sub-scanning direction of the yellow beam with respect to the black beam, and outputs a signal Smy including the detection result. . The sub-scanning direction deviation detection circuit 354 detects a sub-scanning direction deviation of the magenta beam with respect to the black beam based on the signal S302b, the signal S303b, the signal S302d, and the signal S303d, and generates a signal Smm including the detection result. Output. Further, the sub-scanning direction deviation detection circuit 354 detects a sub-scanning direction deviation of the cyan beam with respect to the black beam based on the signal S302c, the signal S303c, the signal S302d, and the signal S303d, and outputs a signal Smc including the detection result. Output.

  The drive signal generation circuit 356 generates a drive signal Sdy corresponding to the voltage applied to the partial region 305Y of the liquid crystal deflection element 305 based on the signal Smy. The drive signal generation circuit 356 generates a drive signal Sdm corresponding to the voltage applied to the partial region 305M of the liquid crystal deflection element 305 based on the signal Smm. Furthermore, the drive signal generation circuit 356 generates a drive signal Sdc corresponding to the voltage applied to the partial region 305C of the liquid crystal deflection element 305 based on the signal Smc. The drive signals generated here are output to the liquid crystal deflection element 305, respectively.

  In this embodiment, when detecting the sub-scanning direction deviation of each light beam, as shown in FIG. 12 as an example, the A6 light emitting unit, B1 light emitting unit, B6 light emitting unit, C2 light emitting unit, C6 in each light source unit. The light emitting unit, D3 light emitting unit, D6 light emitting unit, E4 light emitting unit, E6 light emitting unit, F5 light emitting unit, and F6 light emitting unit emit light almost simultaneously. That is, six light emitting units (A6 light emitting unit, B6 light emitting unit, C6 light emitting unit, D6 light emitting unit, E6 light emitting unit, F6 light emitting unit) arranged in the dir_sub direction are arranged in a direction different from both the dir_sub direction and the dir_main direction. Five light emitting units (B1 light emitting unit, C2 light emitting unit, D3 light emitting unit, E4 light emitting unit, and F5 light emitting unit) emit light almost simultaneously. Thereby, as shown in FIG. 13 as an example, a substantially V-shaped light emission pattern moves on each light detection sensor.

  As an example, the sub-scanning direction deviation detection circuit 354 measures the time between two pulses and obtains the position of the light beam in the sub-scanning direction, as shown in FIGS. 14A and 14B. . Then, the sub-scanning direction shift of the yellow beam with respect to the black beam is detected from the difference between the position of the yellow beam and the black beam, and the difference of the magenta beam with respect to the black beam is determined from the difference between the position of the magenta beam and the position of the black beam. A sub-scanning direction deviation is detected, and a sub-scanning direction deviation of the cyan beam with respect to the black beam is detected from a difference between the cyan beam position and the black beam position. At this time, only one detection result of two light detection sensors used as a set may be used, or both detection results may be used.

  As described above, since the substantially V-shaped light emission pattern moves on the light detection sensor, one inexpensive light receiving element can be used as the light receiving element used for the light detection sensor. As a result, an inexpensive and high-quality image forming apparatus with little color misregistration can be realized.

  As is clear from the above description, in the optical scanning device 900 according to the present embodiment, a deflecting unit is realized by the polygon mirror 213, and eight light detection sensors (302a, 302b, 302c, 302d, 303a, 303b, 303c) are realized. 303d) realizes the light beam detecting means. Further, the position detection means is realized by the sub-scanning direction deviation detection circuit 354 of the beam deflection circuit 350, and the drive signal generation means for supplying an electric signal corresponding to the shift amount to the liquid crystal deflection element 305 is realized by the drive signal generation circuit 356. ing.

  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 36 light emission elements arranged two-dimensionally along the dir_sub direction and the α direction that is different from both the dir_sub direction and the dir_main direction. Four light source units (250a, 250b, 250c, 250d) each having a portion, a polygon mirror 213 for deflecting a plurality of light beams from each light source unit, and the il_sub direction (first of the 36 light emitting units) 1) and six light emitting units arranged in a direction (second direction) different from both the dir_sub direction and the dir_main direction, and deflected by the polygon mirror 213. Eight light detection sensors (302a, 302b, 302c, 302d, 303a, 303b, 303c, 303d) for detecting a light beam are provided. Thus, based on the detection result of the light beam from the light emitting unit arranged in the dir_sub direction and the detection result of the light beam from the light emitting unit arranged in a direction different from both the dir_sub direction and the dir_main direction, the surface of each photosensitive drum It is possible to accurately detect the position of the light beam in the sub-scanning direction above (on the surface to be scanned).

  In addition, since the light beam that scans the light detection sensor is a light beam before the start of scanning of the image formation region or a light beam after the end of scanning of the image formation region, the beam diameter of the light beam that scans the light detection sensor is The beam diameter of the light beam traveling toward the image forming area does not necessarily need to coincide with the beam diameter, and may be constant as long as it is constant in the main scanning direction and the sub-scanning direction, that is, it does not change due to a temperature change or the like. Therefore, since the desired beam diameter only needs to be ensured by only the light beam directed to the image region, the accuracy at the end of the optical element in the main scanning direction can be relaxed, and the size and cost can be reduced. It is possible.

  Further, the full-color image forming apparatus 100 according to this embodiment includes the optical scanning device 900 that can accurately detect the position of the light beam in the sub-scanning direction on the surface of each photosensitive drum. It is possible to scan the surface of the photosensitive drum (on the surface to be scanned) with high accuracy, and as a result, it is possible to form a high-quality image.

In the above embodiment, when the temperature difference between the two light detection sensors used as the set, for example, the temperature difference between the light detection sensor 302a and the light detection sensor 303a is 5 ° C. or more, the light detection sensor 302a is fixed. The substrate for fixing and the substrate for fixing the light detection sensor 303a may be a common substrate. In this case, the common substrate is preferably made of a material having a coefficient of thermal expansion of 1.0 × 10 ⁻⁵ / ° C. or less. Thereby, for example, it is possible to suppress an adverse effect due to temperature fluctuation that the detection accuracy of the position of the light beam is lowered due to the fluctuation of the position of the light detection sensor and the fluctuation of the relative positional relationship between the two light detection sensors.

Further, in the case where the light detection sensor is constituted by a photodiode, when the electric noise is generated between the plurality of light detection sensors, the fixing substrate is preferably made non-conductive. Specifically, glass (thermal expansion coefficient: 0.5 × 10 ⁻⁵ / ° C.), alumina (thermal expansion coefficient: 0.7 × 10 ⁻⁵ / ° C.), silicon carbide (thermal expansion coefficient: 0.4 × 10 ⁻⁵ ° C.) is preferred. Aluminum alloy (thermal expansion coefficient: 2.4 × 10 ⁻⁵ / ° C.) may reduce detection accuracy due to temperature fluctuation.

  In the above embodiment, instead of the light detection sensor, as shown in FIG. 15 as an example, the first light receiving unit having the dir_sub direction as the longitudinal direction and the direction different from both the dir_sub direction and the dir_main direction as the longitudinal direction. A light receiving element PD1 having a direction, a light receiving element parallel to the first light receiving part and adjacent to the first light receiving part, and parallel to the second light receiving part and adjacent to the second light receiving part. You may use the photodetector (it is set as PDa) provided with light receiving element PD2 which has a light-receiving part. In this case, the photodetector PDa performs an amplifier (AMP1) that performs current-voltage conversion and voltage amplification on the output signal of the light-receiving element PD1, and performs current-voltage conversion and voltage amplification on the output signal of the light-receiving element PD2. An amplifier (AMP2) and a comparator (CMP) that outputs a comparison result between the output signal of AMP1 and the output signal of AMP2 are further provided.

  The angle θ in FIG. 15 can exhibit a desired function by setting so as to satisfy the condition of 0 <θ <90, but a range of 30 ° to 60 ° is preferable. In FIG. 15, the most suitable angle is set to 45 °. When the angle θ is smaller than 30 °, a difference between times T1 and T2 described later with respect to the scanned light beam is reduced, and detection sensitivity is deteriorated (see FIG. 17). On the other hand, when the angle θ exceeds 60 °, the detection height H in the dir_sub direction with respect to the total width D of the light receiving surface in the dir_main direction decreases, and if the required detection height H is secured, the total width D of the light receiving surface increases. There is a problem that the light receiving surface enters the image forming area, or that an effective area of the scanning optical system needs to be set wide, and the scanning lens becomes long. If the detection height H and the total width D of the light receiving surface are set to H = 1 to 3 mm and D = 5 mm or less, respectively, the above problem does not occur, which is preferable. It should be noted that θ = 45 ° is most preferable because the above problems are distributed in a well-balanced manner and any problem can be allowed.

  In this case, as shown in FIG. 16A as an example, when a light beam L1 and a light beam L2 delayed by a time T3 with respect to the light beam L1 are incident on the light receiving element PD1 and the light receiving element PD2, As an example, a signal (CMP comparison signal) as indicated by A in FIG. 17 is output from the comparator. Since each light receiving element has two light receiving portions that are traversed by the light beam, each light receiving element outputs a signal including two pulses per light beam. The time interval (T1 or T2) between the two pulses is proportional to the position in the sub-scanning direction where the light beam is scanned. In FIG. 16A, the time interval between the two pulses is short if the position above each light receiving element is crossed, and the time interval between the two pulses is long if the position below each light receiving element is crossed. T3 is the time from when the light beam L1 is scanned to the next time when the light beam L2 is scanned. At least after the light beam L1 is not detected by the light receiving element PD1, the light beam L2 is scanned. Is set to be. This is because if a plurality of light beams are simultaneously received by the light receiving portion of the light receiving element PD1 or PD2, it may cause a false detection.

  Therefore, the sub-scanning direction deviation detection circuit 354 of the beam deflection circuit 350 obtains the position of the light beam L1 in the sub-scanning direction based on the time T1, and obtains the position of the light beam L2 in the sub-scanning direction based on the time T2. . Further, the sub-scanning direction deviation detection circuit 354 obtains an interval ΔP between the light beam L1 and the light beam L2 based on the following equation (1). Note that v is the scanning speed of the light beam.

ΔP = v × (T2−T1) / tan θ (1)

  The drive signal generation circuit 356 then determines the position of the light beam L1 in the sub-scanning direction, the position of the light beam L2 in the sub-scanning direction, the light beam L1 and the light based on the detection result of the sub-scanning direction deviation detection circuit 354. A drive signal for correcting at least one of the distance to the beam L2 is generated. Since v and θ in the above equation (1) are substantially constants, a drive signal for correcting the interval between the light beam L1 and the light beam L2 is generated using the calculation result of (T2-T1). May be. Here, drive signal generation means for supplying an electric signal corresponding to the interval adjustment amount to the liquid crystal deflection element 305 by the drive signal generation circuit 356 is realized. By the way, for example, when the recording density is 1200 dpi, the beam interval in the sub-scanning direction is about 21 μm.

  Further, as an example, as shown in FIG. 16B, the light beam is from the same light emitting portion (for convenience sake, the light emitting portion X) as the light beam L1, and is different from the light beam L1 by the deflected reflection at the polygon mirror 213. The light beam L3 deflected by the surface and the light beam from the same light emitting part (referred to as the light emitting part Y for convenience) as the light beam L2, and the light beam L2 is deflected by a different deflecting reflection surface in the polygon mirror 213 The light beam L4 may be used. Here, it is assumed that the light beam L3 is delayed by a time T4 with respect to the light beam L2, and the light beam L4 is delayed by a time T3 ′ with respect to the light beam L3. When the light beam L3 and the light beam L4 enter the light receiving element PD1 and the light receiving element PD2, for example, a signal (CMP comparison signal) as shown by B in FIG. 17 is output from the comparator. In this case, the sub-scanning direction deviation detection circuit 354 obtains the position of the light beam from the light emitting unit X in the sub-scanning direction based on the time T1 and the time T1 ′, and emits light based on the time T2 and the time T2 ′. You may obtain | require the position in the subscanning direction of the light beam from the part Y. FIG. Then, the sub-scanning direction deviation detection circuit 354 may obtain the interval ΔPxy between the light beam from the light emitting unit X and the light beam from the light emitting unit Y based on the following equation (2), for example.

ΔPxy = v × {(T2−T2 ′) / 2− (T1−T1 ′) / 2} / tan θ (2)

  Thereby, it is possible to reduce the influence of the scanning error component due to the surface tilt or jitter of the polygon mirror 213. Note that T4 is substantially longer than T3, and during this time, data processing is performed.

  In this case, the output signal of the comparator may be supplied to each light source control circuit and used as a synchronization signal in the main scanning direction. Specifically, image writing may be started after a predetermined time from detecting T1 or T1 ′ in FIG.

  In this case, three or more light beams may be incident on the light receiving element PD1 and the light receiving element PD2. Here, two light beams are combined, and the interval is calculated based on the above equation (1) for each combination. For example, the calculation based on the above equation (1) is performed three times when there are three light beams and six times when there are four light beams.

  In the above embodiment, instead of the light detection sensor, as shown in FIG. 18 as an example, the first light receiving unit having the dir_sub direction as the longitudinal direction and the direction different from both the dir_sub direction and the dir_main direction as the longitudinal direction. A light-receiving element PD1 having a second light-receiving portion in a direction, and disposed between the first light-receiving portion and the second light-receiving portion, and a side parallel to the first light-receiving portion and the second light-receiving portion. You may use the photodetector (it is set as PDb) provided with light receiving element PD2 which has a triangle-shaped light-receiving part which makes a parallel edge | side each one side. In this case, the photodetector PDb, like the photodetector PDa, an amplifier (AMP1) that performs current-voltage conversion and voltage amplification on the output signal of the light receiving element PD1, and the output signal of the light receiving element PD2. And an amplifier (AMP2) that performs current-voltage conversion and voltage amplification, and a comparator (CMP) that outputs a comparison result between the output signal of AMP1 and the output signal of AMP2.

  In this case, as shown in FIG. 19A as an example, when the light beam L1 and the light beam L2 enter the light receiving element PD1 and the light receiving element PD2, as shown in FIG. CMP comparison signal) is output from the comparator. As an example, as shown in FIG. 19B, when the light beam L3 and the light beam L4 are incident on the light receiving element PD1 and the light receiving element PD2, as shown in FIG. Signal) is output from the comparator. Then, in the sub-scanning direction deviation detection circuit 354, the position and interval of each light beam in the sub-scanning direction are obtained in the same manner as in the photodetector PDa.

  In the above embodiment, when the amount of light in the image forming region and the amount of light necessary for the light detection sensor are different, each light source control circuit goes to the light amount of the light beam toward the image forming region and the light detection sensor. You may adjust so that all the light quantity of a light beam may turn into a desired light quantity. Thereby, the detection accuracy of the position of the light beam in the sub-scanning direction can be improved.

  Moreover, in the said embodiment, it may replace with the said half mirror and may provide the total reflection mirror which reflects this light beam in the direction which goes to a light detection sensor on the optical path of the light beam which scans the said light detection sensor. Thereby, the light quantity loss of the light beam detected by the light detection sensor can be reduced.

  Further, in the above-described embodiment, when a complicated scan line curve occurs or when the scan line curve is relatively different for each color, the scan line goes not only to both ends of the image formation area but also to the image formation area. A light detection sensor that detects a part of the light beam may be further provided.

  In the above embodiment, instead of the liquid crystal changing element 305, the attitude of at least one optical element (for example, a scanning lens or a mirror) disposed on the optical path from the light source unit to the corresponding photosensitive drum is adjusted. An attitude adjustment mechanism may be used. In this case, the drive signal generation circuit 356 generates a drive signal for driving the posture adjustment mechanism based on the detection result of the sub-scanning direction deviation detection circuit 354. As a result, it is possible to correct the position of the light beam in the sub-scanning direction and the interval between the two light beams in the sub-scanning direction.

  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. It is a figure for demonstrating the position detection apparatus in FIG. It is a figure for demonstrating schematic structure of the optical scanning device in FIG. It is a figure for demonstrating the light emission part of the light source unit in FIG. FIG. 4 is a first diagram for explaining a liquid crystal deflecting element in FIG. 3; 6A and 6B are diagrams (part 2) for explaining the liquid crystal deflecting element in FIG. 3, respectively. FIG. 4 is a third diagram for explaining the liquid crystal deflecting element in FIG. 3; FIG. 4 is a (fourth) diagram for explaining the liquid crystal deflecting element in FIG. 3; It is a figure for demonstrating the processing circuit in FIG. It is a figure for demonstrating the light source control circuit in FIG. It is a figure for demonstrating a beam deflection circuit. FIG. 6 is a diagram (No. 1) for explaining a light emission pattern when detecting a position of a light beam in a sub-scanning direction. FIG. 6 is a diagram (No. 2) for explaining a light emission pattern when detecting the position of the light beam in the sub-scanning direction. FIG. 14A and FIG. 14B are diagrams for explaining the output signals of the light detection sensors, respectively. It is a figure for demonstrating the modification 1 of the optical detection sensor in FIG. FIG. 16A and FIG. 16B are diagrams for explaining the operation of the light detection sensor of FIG. It is a timing chart for demonstrating the output signal of the comparator of FIG. It is a figure for demonstrating the modification 2 of the optical detection sensor in FIG. FIG. 19A and FIG. 19B are diagrams for explaining the operation of the light detection sensor of FIG. It is a timing chart for demonstrating the output signal of the comparator of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Full color image forming apparatus (multicolor image forming apparatus), 213 ... Polygon mirror (deflection means), 250a-250d ... Light source unit, 302a-302d ... Light detection sensor (light beam detection means), 303a-303d ... Light detection Sensor (light beam detection means), 354... Sub-scanning direction deviation detection circuit (position detection means), 356... Drive signal generation circuit (drive signal generation means), 900... Optical scanning device, 901 a to 901 d. Object), 902a to 902d ... Charging charger (part of transfer device), 903a to 903d ... Developing roller (part of transfer device), 904a to 904d ... Toner cartridge (part of transfer device), 910 ... Fixing roller (Part of transfer device), 913... Transfer charger (part of transfer device).

Claims (13)

An optical scanning device that scans a surface to be scanned with light,
A light source unit having a plurality of light sources arranged two-dimensionally;
Deflecting means for deflecting a plurality of light beams from the light source unit;
A light source arranged in a first direction different from a direction corresponding to the main scanning direction, and a light source arranged in a second direction different from both the direction corresponding to the main scanning direction and the first direction, among the plurality of light sources. And a light beam detecting means for detecting a plurality of light beams emitted from a plurality of light sources and deflected by the deflecting means.   2. The optical scanning according to claim 1, further comprising position detecting means for detecting a position of the light beam in the sub-scanning direction on the surface to be scanned based on an output signal of the light beam detecting means. apparatus.   The optical scanning device according to claim 2, further comprising a shift unit that shifts a position of the light beam in the sub-scanning direction on the surface to be scanned based on a detection result of the position detection unit. .   The light according to claim 3, wherein the shift unit includes an attitude adjustment mechanism that adjusts an attitude of at least one optical element disposed on an optical path between the light source unit and the surface to be scanned. Scanning device.   The shift means is disposed on an optical path between the light source unit and the surface to be scanned, a liquid crystal deflecting element whose deflection angle changes according to an electric signal, and an electric signal corresponding to the shift amount of the liquid crystal deflecting element. The optical scanning device according to claim 3, further comprising: a drive signal generating unit that supplies the signal.   6. The position detection unit further detects intervals in the sub-scanning direction of the plurality of light beams on the scanned surface based on an output signal of the light beam detection unit. The optical scanning device according to any one of claims.   7. The apparatus according to claim 6, further comprising an interval adjusting unit that adjusts an interval in the sub-scanning direction of the plurality of light beams on the surface to be scanned based on a detection result of the position detecting unit. Optical scanning device.   The said space | interval adjustment means contains the attitude | position adjustment mechanism which adjusts the attitude | position of the at least 1 optical element arrange | positioned on the optical path between the said light source unit and the said to-be-scanned surface. Optical scanning device.   The interval adjusting means is disposed on an optical path between the light source unit and the surface to be scanned, a liquid crystal deflecting element whose deflection angle changes according to an electric signal, and the liquid crystal deflecting element according to an interval adjusting amount. The optical scanning device according to claim 7, further comprising drive signal generation means for supplying an electric signal.   10. The optical scanning device according to claim 2, wherein the position detection unit further generates a synchronization signal in a main scanning direction based on an output signal of the light beam detection unit.   The optical scanning device according to claim 1, wherein each of the plurality of light sources is formed on the same chip. At least one scan object;
The optical scanning device according to any one of claims 1 to 11, 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 scan target to the transfer target.   The image forming apparatus according to claim 12, wherein the image information is color image information.

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