JP2011123085A - Detecting device and image-forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detecting device for detecting movement information, which has excellent versatility without incurring high cost. <P>SOLUTION: A light source 11 is arranged on a +z side to a transfer belt 2040, and an illumination lens 12 converts light from the light source 11 to converging light, which has a converging point on a -z side to the transfer belt 2040, to guide it to the surface of the transfer belt 2040. Further, a light-receiving lens 14 is arranged on an optical path of light which is reflected by the surface of the transfer belt 2040, and has optically positive power. An image sensor 15 receives light, which passes through the light-receiving lens 14, and outputs image data. By this, the translation of a speckle pattern can be improved. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a detection apparatus and an image forming apparatus, and more particularly to a detection apparatus that detects movement information of a moving body, and an image forming apparatus including the detection apparatus.

  In recent years, an image forming apparatus that forms a multicolor image has a plurality of photosensitive colors corresponding to a plurality of colors (typically four colors of black, cyan, magenta, and yellow) in order to meet the demand for high speed. The so-called tandem system, in which the bodies are arranged in parallel, has become the mainstream.

  In this tandem system, it is necessary to finally superimpose toner images for each color developed on each photoconductor on a recording medium (for example, paper, plastic sheet, etc.). In addition, as a system, a direct transfer system that directly superimposes on a recording medium and an intermediate transfer belt system that uses an intermediate transfer belt to superimpose toner images on the intermediate transfer belt and collectively transfer them to the recording medium. There are two methods.

  If the conveyance belt for conveying the recording medium in the direct transfer method and the intermediate transfer belt in the intermediate transfer belt method are not driven with high accuracy, color deviation may occur in the output image.

  For example, Patent Document 1 discloses an endless moving member in which a plurality of marks are continuously provided, first mark detection means for detecting a mark and outputting a first pulse signal, and detecting a mark and a second pulse. The second mark detecting means for outputting the signal, the common fixing member for fixing the first mark detecting means and the second mark detecting means, and the influence on the phase difference between the pulse signals due to the temperature change of the fixing member are canceled out. Discloses an endless moving member drive control device including temperature compensation means for performing temperature compensation.

  Patent Document 2 discloses an image forming apparatus that conveys a print medium for image formation. The image forming apparatus includes a conveying unit that conveys a printing medium, a driving unit that drives the conveying unit, an observation object that is directly or indirectly moved by the conveying unit, and a coherency with the observation object. A surface state signal generating means for irradiating the surface of the object to be observed and receiving reflected light reflected by the surface of the observation object, and generating a signal relating to the surface state of the object to be observed according to the received reflected light; By comparing the surface state signals generated by the state signal generation means in time series, the movement amount detection means for obtaining the movement amount of the observation object, and the observation object moving when the transport means is driven by the drive means Control means for controlling the drive means based on the detection result of the movement amount detection means.

  Further, Patent Document 3 discloses a light source that emits a beam of highly coherent light that is projected on the surface and generates a plurality of scattered light, and an incident angle of the scattered light is limited so that the plurality of diffracted lights interfere with each other. A speckle image forming apparatus is disclosed that includes a light limiting element that generates a plurality of diffracted lights so as to generate a plurality of speckles, and an image sensor that receives the speckles and generates a first speckle image. . In this speckle image forming apparatus, after the light limiting element and the image sensor are moved with respect to the surface, a second speckle image is generated, and the direction and distance of this movement is the same as the first speckle image and the second speckle image. It is determined by comparing with a speckle image.

  However, for example, if an endless moving member drive control device disclosed in Patent Document 1 is applied as a drive control device for an intermediate transfer belt, it is necessary to form a mark directly on the intermediate transfer belt, resulting in poor mass productivity. There was a disadvantage that it caused a large cost increase.

  Further, in the image forming apparatus disclosed in Patent Document 2, there is no specific description about the optical system, and there is no description about the correction method of the detection error, so that it is difficult to apply to an actual image forming apparatus. there were.

  Further, the speckle image forming apparatus disclosed in Patent Document 3 has difficulty in satisfying the required detection accuracy when applied to an actual image forming apparatus. Furthermore, since the light control element that generates the diffracted light is provided, there is a disadvantage that the light utilization efficiency for guiding the scattered light from the surface to the image sensor is poor.

  The present invention has been made under such circumstances, and a first object of the present invention is to provide a detection device having excellent versatility without causing an increase in cost.

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

  From a first viewpoint, the present invention is a detection device that detects movement information of a moving body, and is disposed on one side of the moving body, and a light source that emits light that illuminates the moving body; A first optical system that converts light from the light source into convergent light having a condensing point on the other side with respect to the moving body and guides it to the surface of the moving body; and light reflected by the surface of the moving body A second optical system that is disposed on the optical path of the optical system and has an optical positive power; an image sensor that receives light through the second optical system and outputs image data; and is output from the image sensor A calculation device that calculates movement information of the moving body based on image data.

  In this specification, “movement information” includes a movement distance, a relative movement amount, a movement speed, and a change amount of the movement speed.

  According to this, versatility can be improved without increasing the cost.

  According to a second aspect of the present invention, a plurality of image carriers corresponding to different colors; and a light beam modulated according to image information of a corresponding color for each of the plurality of image carriers. An optical scanning device that scans to form a latent image; a developing device that generates a plurality of toner images by attaching toners of corresponding colors to the latent images formed on the plurality of image carriers; and a belt member. An image forming apparatus comprising: a transfer device that superimposes and transfers the plurality of toner images to a medium; and a detection device of the present invention that detects movement information of the belt member.

  According to this, since the detection device of the present invention is provided, a high-quality image can be formed as a result.

  According to a third aspect of the present invention, in an image forming apparatus that forms an image on a sheet surface of a medium while moving the sheet-like medium, the detection apparatus of the present invention detects the movement information of the medium. An image forming apparatus characterized by the above.

  According to this, since the detection device of the present invention is provided, a high-quality image can be formed as a result.

1 is a diagram illustrating a schematic configuration of a color printer according to an embodiment of the present invention. It is FIG. (1) for demonstrating the structure of an optical scanning device. It is FIG. (2) for demonstrating the structure of an optical scanning device. FIG. 6 is a third diagram for explaining the configuration of the optical scanning device; FIG. 4 is a diagram (part 4) for explaining the configuration of the optical scanning device; 6A and 6B are diagrams for describing a liquid crystal element. It is a block diagram for demonstrating the structure of a scanning control apparatus. It is a figure for demonstrating the structure of a movement information detector. It is a figure which shows an example of a speckle pattern. FIG. 10A to FIG. 10D are diagrams for explaining correlation peaks, respectively. It is a figure for demonstrating wa and ws. It is a figure for demonstrating the experimental apparatus used in order to investigate the influence which the characteristic (convergence degree) of a laser beam has on translation. It is a figure for demonstrating the convergence degree A. FIG. It is a figure for demonstrating the convergence E. FIG. It is a figure for demonstrating the convergence degree B. FIG. It is a figure for demonstrating the convergence degree C. FIG. It is a figure for demonstrating the convergence degree D. FIG. It is a figure which shows an example of the speckle pattern before a movement (movement amount 0). It is a figure for demonstrating the correlation peak value (relative value) at the time of the convergence degree A. FIG. It is a figure for demonstrating the correlation peak value (relative value) at the time of the convergence degree B. FIG. It is a figure for demonstrating the correlation peak value (relative value) at the time of the convergence degree C. FIG. It is a figure for demonstrating the correlation peak value (relative value) at the time of the convergence degree D. FIG. It is a figure for demonstrating the correlation peak value (relative value) at the time of the convergence degree E. FIG. It is a figure for demonstrating the correlation peak value (normalization value) at the time of the convergence degree A. FIG. It is a figure for demonstrating the correlation peak value (normalization value) in the case of the convergence degree B. FIG. It is a figure for demonstrating the correlation peak value (normalization value) in the case of the convergence degree C. FIG. It is a figure for demonstrating the correlation peak value (normalization value) at the time of the convergence degree D. FIG. It is a figure for demonstrating the correlation peak value (normalization value) at the time of the convergence degree E. FIG. It is a figure for demonstrating the relationship between Db and (rho). It is the figure which expanded a part of FIG. It is an example of the movement amount calculated | required from two speckle patterns adjacent in time. It is a figure for demonstrating the modification of a color printer. It is a figure for demonstrating the detection method of two-dimensional movement information. 1 is a diagram illustrating a schematic configuration of an image forming apparatus that directly forms an image on a surface of a recording sheet.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a color printer 2000 as an image forming apparatus according to an embodiment.

  The color printer 2000 is a tandem multi-color printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes an optical scanning device 2010, four photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), 4 Toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing roller 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 060, paper ejection tray 2070, a communication control device 2080, and a like movement information detector 2245 and the printer controller 2090 for totally controlling the above elements.

  In the following description, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is defined as the Y-axis direction, and the direction along the arrangement direction of the four photosensitive drums is defined as the X-axis direction.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

  A charging device 2032a, a developing roller 2033a, and a cleaning unit 2031a are disposed in the vicinity of the surface of the photosensitive drum 2030a along the rotation direction of the photosensitive drum 2030a.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a are used as a set and form an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image. Constitute.

  A charging device 2032b, a developing roller 2033b, and a cleaning unit 2031b are arranged in the vicinity of the surface of the photosensitive drum 2030b along the rotation direction of the photosensitive drum 2030b.

  The photosensitive drum 2030b, the charging device 2032b, the developing roller 2033b, the toner cartridge 2034b, and the cleaning unit 2031b are used as a set and form an image forming station (hereinafter also referred to as “C station” for convenience) that forms a cyan image. Constitute.

  A charging device 2032c, a developing roller 2033c, and a cleaning unit 2031c are arranged in the vicinity of the surface of the photosensitive drum 2030c along the rotation direction of the photosensitive drum 2030c.

  The photosensitive drum 2030c, the charging device 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c are used as a set, and form an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image. Constitute.

  A charging device 2032d, a developing roller 2033d, and a cleaning unit 2031d are arranged in the vicinity of the surface of the photosensitive drum 2030d along the rotation direction of the photosensitive drum 2030d.

  The photosensitive drum 2030d, the charging device 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d are used as a set, and form an image forming station (hereinafter also referred to as “Y station” for convenience) that forms a yellow image. Constitute.

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

  Based on the multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the higher-level device, the optical scanning device 2010 charges the light flux modulated for each color correspondingly. Irradiate each surface of the photosensitive drum. 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. The configuration of the optical scanning device 2010 will be described later.

  The toner cartridge 2034a stores black toner, and the toner is supplied to the developing roller 2033a. The toner cartridge 2034b stores cyan toner, and the toner is supplied to the developing roller 2033b. The toner cartridge 2034c stores magenta toner, and the toner is supplied to the developing roller 2033c. The toner cartridge 2034d stores yellow toner, and the toner is supplied to the developing roller 2033d.

  As each developing roller rotates, the toner from the corresponding toner cartridge is thinly and uniformly applied to the surface thereof. Then, when the toner on the surface of each developing roller comes into contact with the surface of the corresponding photosensitive drum, the toner moves only to a portion irradiated with light on the surface and adheres to the surface. In other words, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum so as to be visualized. Here, the toner-attached image (toner image) moves in the direction of the transfer belt 2040 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a color image.

  The transfer belt 2040 includes a belt main body and a light transmissive member covering the surface of the belt main body. The surface of the belt body has a fine uneven structure. On the other hand, the surface of the light transmissive member is flat. The light-transmitting member does not need to be optically completely transparent, and may have a slight light absorption.

  The transfer belt 2040 is moved by a drive motor (not shown).

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out recording sheets one by one from the paper feed tray 2060 and conveys them to a pair of registration rollers 2056. The registration roller pair 2056 feeds the recording paper toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording sheet transferred here is sent to the fixing roller 2050.

  In the fixing roller 2050, 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 a paper discharge tray 2070 via a paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

  Each cleaning unit removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The surface of the photosensitive drum from which the residual toner has been removed returns to the position facing the corresponding charging device again.

  The movement information detector 2245 is disposed on the −X side of the transfer belt 2040 and is provided to detect movement information (here, movement amount and movement speed) of the transfer belt 2040. The detection result is notified to the printer control device 2090. Details of the movement information detector 2245 will be described later.

  For example, the printer control device 2090 performs a movement information detection process of the transfer belt 2040 using the movement information detector 2245 in real time during a job. Based on the detection result, the drive motor of the transfer belt 2040 is feedback-controlled in real time.

  Next, the configuration of the optical scanning device 2010 will be described.

  2 to 5 as an example, the optical scanning device 2010 includes two light sources (2200a, 2200b), two coupling lenses (2201a, 2201b), two aperture plates (2202a, 2202b), 2 Two beam splitting prisms (2203a, 2203b), four liquid crystal elements (2211a, 2211b, 2211c, 2211d), four cylindrical lenses (2204a, 2204b, 2204c, 2204d), polygon mirror 2104, four fθ lenses (2105a, 2105b) 2105c, 2105d), 8 folding mirrors (2106a, 2106b, 2106c, 2106d, 2108a, 2108b, 2108c, 2108d), 4 toroidal lenses (2107a, 2107b, 2107c, 2107d) , Four light detection sensor (2205a, 2205b, 2205c, 2205d), and includes four light detection mirror (2207a, 2207b, 2207c, 2207d), and the scanning controller 30 and the like (see FIG. 7). These are assembled at predetermined positions of the optical housing 2300 (not shown in FIGS. 2 to 4, see FIG. 5).

  Also, the direction along the optical axis of the coupling lens 2201a is referred to as “w1 direction”, and the direction along the optical axis of the coupling lens 2201b is referred to as “w2 direction”. Furthermore, a direction orthogonal to both the Z-axis direction and the w1 direction is referred to as “m1 direction”, and a direction orthogonal to both the Z-axis direction and the w2 direction is referred to as “m2 direction”.

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The main scanning corresponding direction in the light source 2200a is the “m1 direction”, and the sub-scanning corresponding direction is the same direction as the Z-axis direction. Further, the main scanning corresponding direction in the light source 2200b is the “m2 direction”, and the sub-scanning corresponding direction is the same direction as the Z-axis direction.

  The light source 2200a and the light source 2200b are arranged at positions separated from each other in the X-axis direction.

  The coupling lens 2201a is disposed on the optical path of the light beam emitted from the light source 2200a, and makes the light beam a substantially parallel light beam.

  The coupling lens 2201b is disposed on the optical path of the light beam emitted from the light source 2200b, and makes the light beam a substantially parallel light beam.

  The aperture plate 2202a has an aperture and shapes the light beam that has passed through the coupling lens 2201a.

  The aperture plate 2202b has an aperture and shapes the light beam that has passed through the coupling lens 2201b.

  Each light beam splitting prism has a half mirror surface that transmits half of the incident light beam and reflects the remaining light beam, and a mirror surface that is arranged in parallel with the half mirror surface on the optical path of the light beam reflected by the half mirror surface. is doing. That is, each light beam splitting prism splits an incident light beam into two parallel light beams. Here, the light beam from the light source 2200a enters the light beam splitting prism 2203a, and the light beam from the light source 2200b enters the light beam splitting prism 2203b.

  Each liquid crystal element is used to suppress color misregistration in the output image.

  Each liquid crystal element can deflect incident light with respect to the Z-axis direction in accordance with an applied voltage. Each liquid crystal element has a configuration in which liquid crystal is sealed between two transparent glass plates. As an example, as shown in FIG. 6A, electrodes are formed above and below the surface of one glass plate. . When a potential difference is applied between the electrodes, as shown in FIG. 6B as an example, a potential gradient occurs in the Z-axis direction, and the orientation of the liquid crystal changes accordingly. As a result, the Z-axis direction is changed. A refractive index gradient occurs. Thereby, like the prism, the light emission axis can be slightly tilted with respect to the Z-axis direction. As the liquid crystal, nematic liquid crystal having dielectric anisotropy is used.

  Returning to FIG. 2, the liquid crystal element 2211 a is arranged on the optical path of the −Z side light beam of the two light beams from the light beam splitting prism 2203 a, and the light beam is in a plane parallel to both the Z-axis direction and the w1 direction. Can be deflected.

  The liquid crystal element 2211b is disposed on the optical path of the + Z side light beam out of the two light beams from the light beam splitting prism 2203a, and can deflect the light beam in a plane parallel to both the Z-axis direction and the w1 direction. .

  The liquid crystal element 2211c is disposed on the optical path of the + Z side light beam out of the two light beams from the light beam splitting prism 2203b, and can deflect the light beam in a plane parallel to both the Z-axis direction and the w2 direction. .

  The liquid crystal element 2211d is disposed on the optical path of the −Z side light beam out of the two light beams from the light beam splitting prism 2203b, and can deflect the light beam in a plane parallel to both the Z-axis direction and the w2 direction. it can.

  The cylindrical lens 2204a is disposed on the optical path of the light beam from the liquid crystal element 2211a, and forms an image of the light beam in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204b is disposed on the optical path of the light beam from the liquid crystal element 2211b, and forms an image of the light beam in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204c is disposed on the optical path of the light beam from the liquid crystal element 2211c, and forms an image of the light beam in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204d is disposed on the optical path of the light beam from the liquid crystal element 2211d, and forms an image of the light beam in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The polygon mirror 2104 has a four-stage mirror having a two-stage structure that rotates about an axis parallel to the Z axis, and each mirror serves as a deflecting reflection surface. The light beam from the cylindrical lens 2204a and the light beam from the cylindrical lens 2204d are deflected by the first-stage (lower) tetrahedral mirror, respectively, and the light beam from the cylindrical lens 2204b and the cylindrical light are deflected by the second-stage (upper) tetrahedral mirror. It arrange | positions so that the light beam from the lens 2204c may be deflected, respectively. Note that the first-stage tetrahedral mirror and the second-stage tetrahedral mirror rotate with a phase shift of 45 °, and writing scanning is alternately performed in the first and second stages.

  Here, the light beams from the cylindrical lens 2204 a and the cylindrical lens 2204 b are deflected to the −X side of the polygon mirror 2104, and the light beams from the cylindrical lens 2204 c and the cylindrical lens 2204 d are deflected to the + X side of the polygon mirror 2104.

  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 2104 rotates.

  The fθ lens 2105a and the fθ lens 2105b are disposed on the −X side of the polygon mirror 2104, and the fθ lens 2105c and the fθ lens 2105d are disposed on the + X side of the polygon mirror 2104.

  The fθ lens 2105a and the fθ lens 2105b are stacked in the Z-axis direction, the fθ lens 2105a is opposed to the first-stage tetrahedral mirror, and the fθ lens 2105b is opposed to the second-stage tetrahedral mirror. Further, the fθ lens 2105c and the fθ lens 2105d are stacked in the Z-axis direction, the fθ lens 2105c is opposed to the second-stage tetrahedral mirror, and the fθ lens 2105d is opposed to the first-stage tetrahedral mirror.

  Therefore, the light beam from the cylindrical lens 2204a deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum 2030a through the fθ lens 2105a, the folding mirror 2106a, the toroidal lens 2107a, and the folding mirror 2108a, thereby forming a light spot. The This light spot moves in the longitudinal direction of the photosensitive drum 2030a as the polygon mirror 2104 rotates. That is, the photosensitive drum 2030a is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030a, and the rotational direction of the photosensitive drum 2030a is the “sub-scanning direction” on the photosensitive drum 2030a.

  The light beam from the cylindrical lens 2204b deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum 2030b through the fθ lens 2105b, the folding mirror 2106b, the toroidal lens 2107b, and the folding mirror 2108b, and a light spot is formed. The This light spot moves in the longitudinal direction of the photosensitive drum 2030b as the polygon mirror 2104 rotates. That is, the photosensitive drum 2030b is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030b, and the rotational direction of the photosensitive drum 2030b is the “sub-scanning direction” on the photosensitive drum 2030b.

  The light beam from the cylindrical lens 2204c deflected by the polygon mirror 2104 is irradiated to the photosensitive drum 2030c through the fθ lens 2105c, the folding mirror 2106c, the toroidal lens 2107c, and the folding mirror 2108c, and a light spot is formed. The This light spot moves in the longitudinal direction of the photosensitive drum 2030c as the polygon mirror 2104 rotates. That is, the photosensitive drum 2030c is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030c, and the rotational direction of the photosensitive drum 2030c is the “sub-scanning direction” on the photosensitive drum 2030c.

  The light beam from the cylindrical lens 2204d deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum 2030d through the fθ lens 2105d, the folding mirror 2106d, the toroidal lens 2107d, and the folding mirror 2108d, thereby forming a light spot. The This light spot moves in the longitudinal direction of the photosensitive drum 2030d as the polygon mirror 2104 rotates. That is, the photosensitive drum 2030d is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030d, and the rotational direction of the photosensitive drum 2030d is the “sub-scanning direction” on the photosensitive drum 2030d.

  Each folding mirror is arranged so that the optical path lengths from the polygon mirror 2104 to each photosensitive drum coincide with each other, and the incident position and the incident angle of the light flux on each photosensitive drum are equal to each other. ing. Each folding mirror is held by a mirror holding member (not shown) and fixed to the optical housing 2300.

  Further, the cylindrical lens and the corresponding toroidal lens constitute a surface tilt correction optical system in which the deflection point and the corresponding photosensitive drum surface are conjugated in the sub-scanning direction.

  An optical system disposed on the optical path between the polygon mirror 2104 and each photosensitive drum is also called a scanning optical system. In this embodiment, a scanning optical system of the K station is configured by the fθ lens 2105a, the toroidal lens 2107a, and the folding mirrors (2106a and 2108a). Further, the scanning optical system of the C station is composed of the fθ lens 2105b, the toroidal lens 2107b, and the folding mirrors (2106b, 2108b). The f-theta lens 2105c, the toroidal lens 2107c, and the folding mirrors (2106c, 2108c) constitute an M station scanning optical system. Further, a scanning optical system of the Y station is configured by the fθ lens 2105d, the toroidal lens 2107d, and the folding mirrors (2106d and 2108d).

  In the light detection sensor 2205a, a part of the light beam before the start of writing in one light scanning out of the light beam deflected by the polygon mirror 2104 and passed through the scanning optical system of the K station passes through the light detection mirror 2207a. Incident.

  In the light detection sensor 2205b, a part of the light beam which is deflected by the polygon mirror 2104 and before the start of writing in one light scan out of the light beam which passes through the scanning optical system of the C station passes through the light detection mirror 2207b. Incident.

  In the light detection sensor 2205c, a part of the light beam which is deflected by the polygon mirror 2104 and passes through the scanning optical system of the M station and before the start of writing in one light scanning is transmitted through the light detection mirror 2207c. Incident.

  The light detection sensor 2205d receives a part of the light beam before the start of writing in one light scanning out of the light beam deflected by the polygon mirror 2104 and passed through the scanning optical system of the Y station via the light detection mirror 2207d. Incident.

  Each of the light detection sensors outputs a signal (photoelectric conversion signal) corresponding to the amount of received light.

  As shown in FIG. 7 as an example, the scanning control device 30 includes a CPU 210, a flash memory 211, a RAM 212, a liquid crystal element driving circuit 213, an IF (interface) 214, a pixel clock generation circuit 215, an image processing circuit 216, a writing control. A circuit 219, a light source driving circuit 221, and the like. Note that the arrows in FIG. 7 indicate the flow of typical signals and information, and do not represent all the connection relationships of the blocks.

  An IF (interface) 214 is a communication interface that controls bidirectional communication with the printer control apparatus 2090. Image data from the host device is supplied via an IF (interface) 214.

  The pixel clock generation circuit 215 generates a pixel clock signal for each station.

  The image processing circuit 216 raster-develops each piece of image information received from the host device via the printer control device 2090, and after performing predetermined halftone processing, creates image data representing the gradation of each pixel. .

  When the writing control circuit 219 detects the scanning start timing from the output signal of each photodetection sensor, the writing control circuit 219 detects the timing of each station based on the image data from the image processing circuit 216 and the pixel clock signal from the pixel clock generation circuit 215. A pulse modulation signal is generated.

  The light source driving circuit 221 drives each light source based on each pulse modulation signal from the writing control circuit 219.

  The liquid crystal element driving circuit 213 applies a voltage to the designated liquid crystal element in accordance with an instruction from the CPU 210.

  The flash memory 211 stores various programs described in codes readable by the CPU 210, various data used for executing the programs, and the like.

  The RAM 212 is a working memory.

  The CPU 210 operates according to a program stored in the flash memory 211 and controls the entire optical scanning device 2010.

  For example, the CPU 210 determines a voltage applied to the liquid crystal element in response to a spot position correction request from the printer control apparatus 2090 and notifies the liquid crystal element drive circuit 213 of the applied voltage.

  Next, the movement information detector 2245 will be described.

  As shown in FIG. 8 as an example, the movement information detector 2245 includes a light source 11, an illumination lens 12, an aperture member 13, a light receiving lens 14, an image sensor 15, a processing circuit 16, and the like.

  Here, for convenience, the direction orthogonal to the surface of the transfer belt 2040 is described as the z-axis direction, and the movement direction of the transfer belt 2040 is described as the x-axis direction, and the direction orthogonal to any of the z-axis direction and the x-axis direction is described as the y-axis direction. To do.

  In FIG. 8, the surface on the + z side of the transfer belt 2040 is the surface.

  The light source 11 is disposed on the + z side of the transfer belt 2040, and from the direction inclined to the −y side with respect to the z-axis direction (hereinafter, abbreviated as “belt surface” for convenience). A laser beam is emitted toward

  The illumination lens 12 is disposed on the optical path of the light beam emitted from the light source 11 and converts the light beam into a convergent light beam that converges at a position p on the −z side of the transfer belt 2040. . Therefore, the belt surface is illuminated obliquely.

  The opening member 13 has an opening and is disposed on the + z side of the belt surface.

  The light receiving lens 14 is disposed on the + z side of the aperture member 13 on the optical path of the light beam that has passed through the aperture of the aperture member 13 and has a positive optical power.

  The image sensor 15 is disposed on the + z side of the light receiving lens 14 and receives the light beam that has passed through the light receiving lens 14. The image sensor 15 is disposed so that the light receiving surface is parallel to the belt surface.

  The image sensor 15 is a one-dimensional image sensor and is arranged so that the longitudinal direction coincides with the x-axis direction. The image sensor 15 may be a CCD (charge coupled device), a CMOS (complementary metal-oxide semiconductor) sensor, a photodiode (PD) array, or the like.

  Here, the light receiving lens 14 and the image sensor 15 are located on the + z side of the illumination area on the belt surface. That is, the light receiving surface of the image sensor 15 faces the illumination area on the belt surface.

  Here, in the transfer belt 2040, since the surface of the belt main body having a minute uneven structure is covered with a light transmissive member, most of the light incident on the belt surface is transmitted through the light transmissive member. And scattered on the surface of the belt body. The scattered light interferes with each other, and a speckle pattern corresponding to the unevenness of the belt body surface is formed (see FIG. 9). The image sensor 15 receives this speckle pattern and outputs it as an image pattern.

  Note that the light receiving surface of the image sensor 15 and the belt surface are substantially conjugate. Further, the light receiving lens 14 projects the speckle pattern on the image sensor 15 after being reduced. That is, the light receiving lens 14 is a so-called reduction optical system.

  When receiving the movement information detection instruction from the printer control device 2090, the processing circuit 16 turns on the light source 11 and acquires image data (speckle pattern) from the image sensor 15 at regular time intervals. Then, a cross-correlation function between two speckle patterns that are close in time is calculated, and a moving amount of the belt surface is calculated based on the peak position of the cross-correlation function (for example, Japanese Patent Laid-Open No. 4-50708, JP-A-5-306908).

  Further, the processing circuit 16 calculates the moving speed of the belt surface from the moving amount of the belt surface. The calculation result here is notified to the printer control apparatus 2090.

Here, the calculation for calculating the movement amount from the two speckle patterns will be briefly described. Note that the two speckle patterns are f1, f2, the Fourier transform is F [], and the inverse Fourier transform is F ^-1 []. Further, the symbol ★ means an operation for obtaining a cross-correlation function (hereinafter abbreviated as “cross-correlation operation”), and ^* means a phase conjugate.

f1 * f2 ^* = F− ¹ [F [f1] · F [f2] ^* ] (1)

In the above equation (1), f1 * f2 ^* is image data obtained by cross-correlation calculation. If f1 and f2 are two-dimensional images, they are two-dimensional data, and if f1 and f2 are one-dimensional images. One-dimensional data.

In the image data of f1 * f2 ^* , the steepest correlation peak position (the center of the image is 0) represents the positional deviation amount between the two speckle patterns.

  Since a method using such a cross-correlation calculation can use a fast Fourier transform, it is possible to detect the amount of misalignment between two speckle patterns with a relatively small calculation amount and high accuracy.

  10A and 10B are images in which a laser beam is applied to an object having a light scattering property and photographed with a CMOS camera. FIG. 10A is before the object moves, and FIG. 10B is after the object is moved to the right by 100 μm. A lens is disposed in front of the CMOS camera so that the object surface and the CMOS surface are substantially conjugated. Further, since the photographing magnification is set to 1, the amount of displacement between the two speckle patterns calculated from the position of the correlation peak matches the amount of movement of the object.

  FIG. 10C shows an image pattern after the cross-correlation calculation, and a steep correlation peak exists in the broad intensity distribution. Although this correlation peak is not buried in the broad intensity distribution, the peak of the broad intensity distribution may be higher, so it is important to search for the steepest peak position.

  In this case, if a broad intensity distribution has an adverse effect, phase-only correlation may be used. This phase-only correlation is expressed by the following equation (2). Here, P [] means that only the phase is extracted from the complex amplitude (the amplitude is all set to 1).

f1 * f2 ^* = F− ¹ [P [F [f1]] · P [F [f2] ^* ]] (2)

  An example calculated by phase-only correlation is shown in FIG. In this case, there is no broad intensity distribution as shown in FIG. 10C, and a correlation peak is clearly seen. When the phase-only correlation is used as described above, it is possible to obtain the amount of positional deviation between the two speckle patterns with higher accuracy.

  Here, if the displacement amount between the two speckle patterns is Δ, and the time interval between the two speckle patterns is τ, the moving speed v of the belt surface can be calculated using the following equation (3). . Note that k is a proportionality constant and is determined by optical conditions such as the position of the light source 11 and each lens. Here, k is obtained in advance and stored in a memory (not shown) of the processing circuit 16.

  v = kΔ / τ (3)

  By the way, if the speckle size is too smaller than the pixel pitch of the image sensor, the detection error may increase. Further, if the speckle size is too larger than the pixel pitch of the image sensor, the speckle existing on the image sensor is reduced and the detection error may be increased. As described above, the size of the speckle needs to be appropriately determined according to the pixel pitch of the image sensor.

  The size of the speckle on the image sensor depends on the numerical aperture (NA) on the image side. If the size of the aperture (aperture) of the aperture member is reduced, the speckle becomes larger (rough). Increasing the size of the opening reduces the speckle.

  Here, the size of the opening of the opening member 13 is set so that the size of the speckle on the image sensor 15 is approximately equal to the pixel pitch.

  The position where the opening member 13 is provided is most preferably in the vicinity of the light-receiving lens 14, but may be a location other than that.

Further, here, ws and τ are set so that the following expression (4) is satisfied, where ws is the width of the illumination light on the belt surface in the x-axis direction. Note that ws is defined as a width in which the light intensity in the illumination light is 1 / e ² of the peak intensity.

  2vτ <ws <10vτ (4)

  If ws is 2 vτ or less, the capture interval becomes longer than the size of the light spot, and the amount of movement of the belt surface becomes too large. As a result, the speckle pattern is deformed and the detection error is increased.

  Also, if ws is 10 vτ or more, the size of the light spot becomes too large, the light utilization efficiency is lowered, and the speed cannot be detected when the belt surface is moving at high speed. In addition, since the capture interval is short, high speed is required for the arithmetic processing, resulting in inconveniences such as an increase in power consumption, an increase in cost, and an inability to catch up with the arithmetic operation.

  Furthermore, here, as shown in FIG. 11 as an example, when the length (width) in the x-axis direction of the observation region of the image sensor 15 on the belt surface is wa, the following expression (5) is satisfied. As described above, the magnification of the light receiving lens 14 and the size of the illumination light are set.

  wa <ws <5wa ...... (5)

  If ws is equal to or less than wa, the difference in light intensity depending on the position of the image sensor 15 in the observation region increases, and detection errors are likely to occur. If ws is 5 wa or more, the amount of light entering the image sensor 15 is reduced, and detection errors are likely to occur.

  When moving information of a moving object is detected using a speckle pattern, the speckle pattern after moving is changed to the moving direction of the moving object according to the moving amount of the moving object. It is important that it is shifted. Here, such a shift is referred to as “translation”.

  And high translation means that the translation of the speckle pattern is secured even if the moving amount of the moving body is large.

  The inventors have conducted various experiments and studies, and have newly found that the translational property varies depending on the characteristics of the laser light irradiated on the belt surface. This will be described below.

  FIG. 12 shows a schematic configuration of the experimental apparatus. This experimental apparatus includes a light source 111, an illumination lens 112, a light receiving optical system 114, a two-dimensional image sensor 115, an image processing apparatus 116, and the like.

  The light source 111 emits laser light having a wavelength of 830 nm.

  The light receiving optical system 114 includes a plurality of lenses, has a focal length of 12.5 mm, and a lateral magnification of 0.4. The light receiving optical system 114 includes an aperture inside and is set to have an F value of 8.

  The image sensor 115 is a C-MOS image sensor having a rectangular light receiving surface whose long side is in the x-axis direction. And the area | region whose pixel number is 40x20 was used. The pixel pitch is 9.9 μm.

  The image processing device 116 is a personal computer including an image processing board, monitor, keyboard, and the like on which an A / D converter, a DSP (digital signal processor), and the like are mounted, and a predetermined image processing program is installed. Yes. The output signal of the image sensor 115 is taken into the image processing device 116 via the interface.

  In this experiment, as the characteristics of the laser light irradiated to the moving body, the convergence of the light emitted from the illumination lens 112 is defined as convergence A, convergence B, convergence C, convergence D, and convergence E. The translation of each was examined. Here, the degree of convergence of the light emitted from the illumination lens 112 is changed by changing the distance between the light source 111 and the illumination lens 112.

  The light of convergence degree A is parallel light as shown in FIG.

  As shown in FIG. 14, the light with the convergence degree E is light that is collected near the belt surface.

  Three types of convergence are set between the convergence A and the convergence E, and these are designated as convergence B, convergence C, and convergence D in order from the smallest (see FIGS. 15 to 17). In other words, the lights having the convergence degrees B to D are all collected on the −z side of the moving body.

1. For each convergence, the moving body is irradiated with a light beam emitted from the light source 111 and passes through the illumination lens 112, and before the moving body moves (moving amount 0) and whenever the moving amount of the moving body increases by 50 μm, A speckle pattern was acquired via the image sensor 115.

  In the following, for convenience, the speckle pattern before movement (movement amount 0) is SP1, the speckle pattern when the movement amount is 50 μm, SP2, the speckle pattern when the movement amount is 100 μm, SP3,.・ Speckle pattern when the movement amount is 500 μm is SP11. As an example, FIG. 18 shows SP1.

2. For each speckle pattern, a cross-correlation function was calculated for each speckle pattern using SP1 as a reference pattern, and a sharp peak value in the cross-correlation function (hereinafter abbreviated as “correlation peak value”) was obtained.

  The correlation peak value obtained from the reference pattern and SP1 is a so-called autocorrelation peak value.

  FIG. 19 shows correlation peak values (relative values) in SP1 to SP11 when light having a convergence degree A is irradiated to the moving body. Even if the correlation peak value decreases, it can be considered that the translational state is maintained when it gradually decreases substantially linearly.

  FIG. 20 shows correlation peak values (relative values) in SP1 to SP11 when the moving body is irradiated with light having a convergence degree B.

  At this time, the correlation peak value gradually decreased almost linearly even when the moving body moved 500 μm.

  FIG. 21 shows correlation peak values (relative values) in SP1 to SP10 when the moving object is irradiated with light having a convergence degree C. In SP11, a correlation peak did not occur due to deformation of the speckle pattern, and the calculated correlation peak value was an abnormal value.

  At this time, the correlation peak value gradually decreases almost linearly up to SP10. After SP11, the speckle pattern was greatly deformed.

  FIG. 22 shows correlation peak values (relative values) in SP1 to SP11 when the moving object is irradiated with light having a convergence degree D.

  At this time, the correlation peak value gradually decreased almost linearly until SP3, and the speckle pattern was greatly deformed after SP4.

  FIG. 23 shows correlation peak values (relative values) in SP1 to SP11 when the moving object is irradiated with light having a convergence degree E.

  At this time, the speckle pattern was greatly deformed.

3. For each degree of convergence, each correlation peak value is normalized by setting the autocorrelation peak value to 1 and the end point when it decreases almost linearly to 0. Then, the moving amount T of the moving body until the correlation peak value became 1 / e (= 0.368) was obtained. This movement amount T is a numerical value that serves as an index when evaluating the translation, and can also be referred to as a translation amount.

  FIG. 24 shows correlation peak values (standard values) in SP1 to SP11 when the belt surface is irradiated with light of convergence degree A. At this time, the movement amount T was about 200 μm.

  FIG. 25 shows correlation peak values (standard values) in SP1 to SP11 when light having a convergence degree B is irradiated on the belt surface. At this time, the movement amount T was about 275 μm or more. Therefore, it can be said that the degree of translation is higher when the degree of convergence is B than when the degree of convergence is A.

  FIG. 26 shows correlation peak values (standard values) in SP1 to SP11 when light having a convergence degree C is irradiated on the belt surface. At this time, the movement amount T was about 275 μm. Therefore, it can be said that the degree of translation is higher when the degree of convergence is C than when the degree of convergence is A.

  FIG. 27 shows correlation peak values (standard values) in SP1 to SP11 when the belt surface is irradiated with light having a convergence degree D. At this time, the movement amount T was about 70 μm.

  FIG. 28 shows correlation peak values (standard values) in SP1 to SP11 when the belt surface is irradiated with light of convergence E. At this time, the movement amount T was about 30 μm.

  That is, in the convergence degree B and the convergence degree C, the translation is higher than when the laser light is substantially parallel light, and in the convergence degree D, the translation is lower than when the laser light is substantially parallel light. The degree of translation is higher than degree E.

  In this way, when a light beam emitted from a light source is converted into a light beam having a slight convergence by a lens having optical positive power and irradiated to a moving body, a substantially parallel light beam is irradiated. As a result, the translational property can be improved.

  By improving the translation, the detection accuracy is improved because the speckle pattern is hardly deformed before and after the movement.

  In addition, when images are acquired at the same time intervals as in the past, the speckle pattern change is small even if the moving body moves greatly, so that it is possible to measure the moving body at a higher speed.

  In addition, when a moving body having the same speed as that of a conventional object is to be detected, it is possible to increase the time interval for acquiring images, and to reduce the load on calculation.

  However, as shown in the experimental results, when the convergence is too close to the moving body, the translation is lower than the case of being almost parallel, so the convergence should be in accordance with the required translation. is required.

  Here, a value indicating the degree of convergence of the light applied to the moving body is α. As this α, it is possible to take the distance between the moving body and the condensing position geometrically, or to take the absolute value of the radius of curvature of the wavefront of the convergent light. In the case of convergence on the moving body, α = 0.

  In the convergence degree α, the moving amount of the moving body until the correlation peak value becomes 1 / e (= 0.368) is defined as T (α). Further, when the beam irradiated to the moving body is substantially parallel, the moving amount of the moving body until the correlation peak value becomes 1 / e (= 0.368) is defined as T (∞).

  Therefore, the convergence degree α is preferably a convergence degree that satisfies T (α)> T (∞). Since T (0) <T (∞), α = 0 is not included as a matter of course. Thereby, the appropriate convergence degree of illumination light can be clarified more.

  By the way, it is known that the speckle pattern performs a translational motion and a boiling motion (Laser Research, Vol. 8, No. 2, “Dynamic Laser Speckle Characteristics and Speed Measurement” Application (I) "). By moving the position (boiling surface) where the boiling motion is generated from the image plane position where the translational motion is observed, the influence of the boiling motion on the image plane position can be eliminated, and the translational property can be improved.

  When the light source, the illumination lens, the light receiving lens, and the image sensor are arranged on one optical axis, the position Db (where the boiling motion occurs when the image plane position (Gauss image plane position) is used as a reference. ρ) can be obtained from the following equation (6).

Db (ρ) = − ρf ² / {(L0−f) (L0−f + ρ)} (6)

  Here, ρ is the radius of curvature of the wavefront of the convergent light, L0 is the distance between the moving body and the light receiving lens (strictly, the front principal point position of the light receiving lens), and f is the focal length of the light receiving lens.

  When the light irradiated to the moving body is substantially parallel, the position Db (∞) where the boiling motion occurs can be obtained from the following equation (7). Here, m is the optical magnification (lateral magnification).

  Db (∞) = − f × m (7)

  As for the optical magnification (lateral magnification) m, when the distance between the rear principal point of the light receiving lens and the image surface (light receiving surface of the image sensor) is L1, the following equation (8) is established.

  m = L1 / L0 (8)

  For the focal length f, the following equation (9) is established.

  1 / f = 1 / L0 + 1 / L1 (9)

  In order to make the translation higher than when the light illuminating the moving body is substantially parallel, the boiling surface in the case of convergent light can be made sufficiently larger than Db (∞).

  In the actual movement information detector 2245, the illumination lens and the light receiving lens cannot be arranged on one optical axis unless the beam combining prism or the like is used as a coaxial system. Strictly speaking, the above (6) The equal sign in the formula does not hold. Based on this, by making Db (ρ) in the case of convergent light at least twice the absolute value of Db (∞), that is, by satisfying the following expression (10), It is possible to improve the translational performance more than the case.

  Db (ρ)> 2 | Db (∞) | (10)

  Since the focal length f of the light receiving lens is positive and the optical magnification m is positive, Db (∞) is negative. Therefore, the above equation (10) can be written as the following equations (11) and (12).

  Db (ρ)> − 2 × Db (∞) (11)

  Db (ρ) <2 × Db (∞) (12)

  When the above expression (11) is expanded using the above expressions (6) and (7), the following expression (13) is obtained.

  ρ> −2 × f / m (13)

  Similarly, when the above expression (12) is expanded using the above expressions (6) and (7), the following expression (14) is obtained.

  ρ <− (2/3) × f / m (14)

  When the above formula (13) and the above formula (14) are put together, the following (15) is obtained.

  -2 (f / m) <ρ <-2/3 (f / m) (15)

  Therefore, by setting the focal length f and the optical magnification m of the light receiving lens so that the above expression (15) is satisfied, the boiling surface when the illumination light is converged light is set so that the illumination light is substantially parallel light. It is possible to move farther away from the image plane position than the boiling surface of the case, and the translational property of the speckle pattern can be improved as compared with the case of substantially parallel light.

  FIG. 29 shows the relationship between Db (ρ) and ρ obtained from the above equation (6). FIG. 30 is an enlarged view of a part of FIG. Here, f = 12.5 mm, L0 = 43.75 m, and m = 0.4. Since L0> f, the light diverges at L0−f + ρ = 0, that is, ρ = f−L0 = −31.25 mm.

  When the illumination light is substantially parallel light, Db (∞) = − 5.0 mm. Therefore, ρ satisfying Db (ρ)> 2 | Db (∞) | is −62.5 mm from FIG. <Ρ <−20.8 mm.

  As described above, an appropriate approach according to the layout of the movement information detector can be obtained by an analytical approach without performing an experiment. In this case, it is possible to reduce time and effort for obtaining an appropriate degree of convergence by attaching a star to the values of f and m.

  In place of the above (10), the following equation (16) is used, and by narrowing the allowable range of ρ, it is also possible to derive a favorable condition for the identification of ρ and further for translation.

  Db (ρ)> 5 | Db (∞) | (16)

  In this case, −34.7 mm <ρ <−28.4 mm.

  FIG. 31 shows an example of a measurement result of the moving amount of the moving body calculated based on two speckle patterns that are temporally adjacent.

  By the way, when the moving body is belt-like like the transfer belt 2040, it is preferable to set a home position for the belt. This makes it possible to correct detection errors caused by belt thickness unevenness and rotation unevenness.

  Here, the home position is detected by comparing the speckle pattern acquired in advance at the position corresponding to the home position with the speckle pattern acquired when the movement information is detected.

  As a specific method for detecting the home position, (A) a method for obtaining a positional deviation amount from the home position, and (B) a method for obtaining a time difference from the home position are conceivable. Each method will be briefly described below. The speckle pattern at the home position is assumed to be acquired in advance and stored in a memory (not shown). Further, by continuously obtaining the belt surface moving speed v calculated from the two speckle patterns acquired at the time interval τ, the position expected to be the home position is determined.

(A) Method for determining the amount of displacement from the home position:

(A-1) A speckle pattern is acquired at a position expected to be a home position. This acquisition position is assumed to be x0 '.

(A-2) The speckle pattern at the home position is read from the memory.

(A-3) A cross-correlation function between the read speckle pattern and the acquired speckle pattern is calculated, and a positional deviation amount Δx0 of the acquired speckle pattern with respect to the read speckle pattern is obtained.

(A-4) The position x0 of the home position is obtained using the following equation (17).

  x0 = x0 ′ + Δx0 (17)

(B) Method for obtaining the time difference from the home position:

(B-1) A speckle pattern is acquired at a position expected to be a home position. The time when this speckle pattern is acquired is assumed to be t0 '.

(B-2) The speckle pattern at the home position is read from the memory.

(B-3) A cross-correlation function between the read speckle pattern and the acquired speckle pattern is calculated, and a positional deviation amount Δx0 of the acquired speckle pattern with respect to the read speckle pattern is obtained.

(B-4) The moving speed v of the belt surface between t0 'and t0 "is obtained using the speckle pattern at time t0" that is continuous in time or close to t0'.

(B-5) The home position time t0 is obtained using the following equation (18).

  t0 = t0 '+ Δx0 / v (18)

  By the way, if one turn of the transfer belt 2040 is long, the amount of deviation Δx0 between the home position and the expected position may increase, which may reduce the detection accuracy of the movement amount. In this case, the shift amount Δx0 in one round is proportionally converted, and the movement amount of the belt surface calculated from two speckle patterns acquired at the time interval τ is corrected, thereby increasing the detection accuracy of the movement amount. be able to.

  The speckle pattern at the home position is best stored in the memory at the time of shipment from the factory, but may be acquired and stored in the memory at the time of calibration performed at power-on and maintenance. .

  Moreover, if the reference positions are set at a plurality of locations other than the home position, the detection accuracy of the movement amount can be further increased.

  When the printer control device 2090 receives information on the moving speed of the belt surface from the processing circuit 16, the printer control apparatus 2090 obtains a difference from the desired moving speed, and if the difference exceeds the allowable range, the difference falls within the allowable range. Thus, the drive motor of the transfer belt 2040 is controlled.

  Further, when the difference between the moving speed of the belt surface and a desired moving speed is small, the printer control device 2090 deflects the optical path from the light source by the liquid crystal element of the optical scanning device 2010 according to the difference, and the photosensitive member The light spot position on the drum may be adjusted.

  At this time, the printer control device 2090 transmits the adjustment amount of the light spot position to the scanning control device 30 of the optical scanning device 2010, and the CPU 210 of the scanning control device 30 determines an applied voltage corresponding to the adjustment amount.

  As a result, a high-quality color image in which the expansion and contraction of the image and the color shift are suppressed to be small is formed.

  In this embodiment, as an example, the distance between the light source 11 and the illumination lens 12 is about 8 mm, the distance between the illumination lens 12 and the belt surface is about 50 mm, and the incident angle of the illumination light on the belt surface is about 45 °. Yes. As an example, the distance between the light receiving lens 14 and the belt surface is 43.75 mm, and the magnification of the light receiving lens 14 is 0.4. Further, the size (ws) of the illumination area is set to about 2 mm, and the size (wa) of the observation area is set to about 1 mm.

  Further, as an example, the transfer belt 2040 has a circumference of about 1000 to 1200 mm and a width of about 340 mm, and moves at a speed of several hundred mm / s during operation.

  Furthermore, the image pattern capture interval in the processing circuit 16 is 1000 fps (frame per sec), for example.

  As is clear from the above description, in the movement information detector 2245 according to this embodiment, the illumination lens 12 constitutes the first optical system in the detection apparatus of the present invention, and the light receiving lens 14 constitutes the second optical system. It is configured. The aperture member 13 constitutes an aperture member, and the processing circuit 16 constitutes an arithmetic device, a reference position detection device, and a correction device.

  Further, the printer control device 2090 constitutes a speed adjustment device, and the scanning control device 30 constitutes a position adjustment device.

  As described above, the movement information detector 2245 according to this embodiment includes the light source 11, the illumination lens 12, the aperture member 13, the light receiving lens 14, the image sensor 15, and the processing circuit 16.

  The light source 11 is disposed on the + z side with respect to the transfer belt 2040, and the illumination lens 12 converts light from the light source 11 into convergent light having a condensing point on the −z side with respect to the transfer belt 2040. To the surface of the transfer belt 2040. The light receiving lens 14 is disposed on the optical path of the light reflected by the surface of the transfer belt 2040 and has an optical positive power. The image sensor 15 receives light via the light receiving lens 14. , Output image data.

  Thereby, it becomes possible to improve the translation of a speckle pattern. In other words, it is possible to widen the range of movement conditions of the transfer belt 2040 that can be detected with high accuracy than before. As a result, it is possible to accurately detect the movement amount, the moving speed, and the movement speed of the transfer belt 2040.

  Therefore, versatility can be improved without increasing the cost.

  Further, when the speckle pattern is acquired at the same time interval as in the past, the movement information can be detected with high accuracy even if the movement speed of the transfer belt 2040 is faster than in the past.

  In addition, when the moving speed of the transfer belt 2040 is the same as the conventional one, the time interval for acquiring the speckle pattern can be made longer than the conventional one.

  Further, when both the moving speed of the transfer belt 2040 and the time interval for acquiring the speckle pattern are the same as the conventional one, the load on the image sensor can be reduced, and an inexpensive image sensor can be used. Further, an image sensor having a large number of pixels can be applied.

  Further, since the light receiving lens 14 is a reduction optical system, the image sensor 15 can be reduced in size. Further, when the moving speed of the transfer belt 2040 is high, the moving speed of the speckle pattern on the image sensor 15 can be reduced. Further, when the moving speed of the transfer belt 2040 is slow, the time interval for acquiring the speckle pattern can be lengthened, and time for arithmetic processing or the like can be increased. The speed can be reduced, and the cost and power consumption can be reduced.

  Further, since the light receiving lens 14 is a reduction optical system (0 <m <1), the range of ρ satisfying the above expression (10) is enlarged as compared with the case of the enlargement optical system (m> 1). can do. As a result, conditions (such as the positional accuracy of the light source 11 and the illumination lens 12) that define the degree of convergence can be relaxed.

  Further, since the light receiving surface of the image sensor 15 is disposed on the + z side of the illumination area on the belt surface, even if the belt surface is shifted in the z-axis direction, the speckle pattern on the light receiving surface is within the xy plane. There is almost no deviation. That is, an error hardly occurs in speed detection. Therefore, it is resistant to disturbance and stable detection is possible.

  The processing circuit 16 acquires speckle patterns at regular time intervals, and calculates the movement amount of the speckle pattern based on two speckle patterns that are close in time. If the amount of movement of the speckle pattern is calculated based on two speckle patterns that are separated in time, the amount of movement of the belt surface increases, the speckle pattern may be deformed, and the detection error may increase. . In the present embodiment, since the movement amount of the speckle pattern is calculated based on two speckle patterns that are close in time, the detection error can be reduced.

  Since ws and τ are set so that 2vτ <ws <10vτ is satisfied, the amount of movement of the belt surface can be obtained with high accuracy.

  Further, since the image sensor 15 is a one-dimensional image sensor, the amount of data is small, and the time required for calculation can be shortened. And power consumption can also be suppressed low.

  Further, since the magnification of the light receiving lens 14 and the size of the illumination light are set so that wa <ws <5wa is satisfied, highly accurate detection is possible.

  Moreover, since the home position is detected using the speckle pattern, the home position can be detected very easily and at low cost.

  Further, in the transfer belt 2040, since the surface of the belt main body having a minute uneven structure is covered with a light transmissive member, it is possible to prevent the minute uneven structure from being worn. Thereby, it can suppress that detection accuracy falls over time. Further, since the surface of the light transmissive member is flat, the surface can be easily cleaned, and unnecessary toner can be prevented from remaining. Therefore, strong scattered light can be obtained without degrading the image quality.

  In addition, since the light receiving lens 14 having positive optical power is disposed between the belt surface and the image sensor 15, even if the belt surface is inclined with respect to the xy plane due to some disturbance, the image The change in speckle pattern on the light receiving surface of the sensor 15 can be reduced. As a result, the detection error due to the inclination of the belt surface can be reduced.

  According to the color printer 2000 according to the present embodiment, since the movement information detector 2245 is provided, the movement speed of the transfer belt 2040 can be maintained at a desired speed, and as a result, high quality with little color misregistration can be achieved. An image can be formed.

  In the above embodiment, a light receiving lens system composed of a plurality of lenses may be used instead of the light receiving lens 14. Also in this case, a reduction system is preferable.

  In the above-described embodiment, the case where the light receiving surface of the image sensor 15 and the belt surface are substantially in a conjugate relationship has been described. However, the inclination of the belt surface is not so large and it is ensured that the detection error is within an allowable range. Thus, it is not always necessary to have a conjugate relationship.

  In the above embodiment, the case where the image sensor 15 is a one-dimensional image sensor has been described. However, the present invention is not limited to this, and a two-dimensional image sensor, a so-called area sensor may be used.

  Further, the movement information detector 2245 can be used to detect movement information of a moving body other than the transfer belt 2040. For example, it may be used to detect movement information of the fixing roller 2050. Further, it can be used to detect movement information of the drum surface in the drum-like rotating member.

  In the above-described embodiment, the case where the home position is detected using the speckle pattern has been described. Instead of this, or in addition to this, a mark is applied to the belt surface to detect it. Also good.

  In the above embodiment, the image forming apparatus is a so-called intermediate transfer belt type color printer. However, the present invention is not limited to this, and a so-called direct transfer belt as shown in FIG. 32 as an example. The color printer 3000 may be used.

  The color printer 3000 is a tandem multicolor printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and is a black station (photosensitive drum K1, charging device K2). , Developing device K4, cleaning unit K5, and transfer device K6), cyan station (photosensitive drum C1, charging device C2, developing device C4, cleaning unit C5, and transfer device C6), magenta station (photosensitive member). Drum M1, charging device M2, developing device M4, cleaning unit M5, and transfer device M6), yellow station (photosensitive drum Y1, charging device Y2, developing device Y4, cleaning unit Y5, and transfer device Y6), light Scanning device 3010, conveyor belt 3080, transfer Information detector 2245, a fixing unit 3030, and a printer controller (not shown) that collectively controls the above respective units and a like.

  Each photosensitive drum rotates in the direction of the arrow in FIG. 32, and a charging device, a developing device, a transfer device, and a cleaning unit are arranged around each photosensitive drum along the rotational direction.

  Each charging device uniformly charges the surface of the corresponding photosensitive drum. An optical scanning device 3010 performs optical scanning on the surface of each photosensitive drum charged by the charging device, and a latent image is formed on each photosensitive drum.

  Then, a toner image is formed on the surface of each photosensitive drum by a corresponding developing device. Further, the toner image of each color is sequentially transferred onto the recording paper on the conveyance belt 3080 by the corresponding transfer device, and finally the image is fixed on the recording paper by the fixing unit 3030.

  The optical scanning device 3010 is the same optical scanning device as the optical scanning device 2010 described above.

  The movement information detector 2245 detects the moving speed of the conveyor belt 3080 and notifies the printer control device.

  The printer control device controls the moving speed of the conveyor belt 3080 so that a desired moving speed is maintained in the same manner as the printer control device 2090. Further, the printer control device adjusts the light spot position on the photosensitive drum in the same manner as the printer control device 2090.

In the above-described embodiment, the case where the movement information detector detects one-dimensional movement information has been described. However, two-dimensional movement information is obtained using a two-dimensional image sensor (for example, an area sensor) as an image sensor. May be detected. For example, when there is a correlation peak at a position as shown in FIG. 33, L can be obtained from (Lx ² + Ly ² ) ^1/2 . In this case, meandering and skewing of the transfer belt can be detected.

  In addition, the movement information detector 2245 may be provided in the image forming apparatus 4000 that forms an image directly on the surface of the recording paper by ejecting ink onto the recording paper, as schematically shown in FIG. 34 as an example.

  The image forming apparatus 4000 includes a head 4010 that ejects ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K), and the head 4010, and is slidable in the main scanning direction. Are provided with a carriage 4020 held in a casing, a conveyance belt 4030 for conveying recording paper, and the like.

  The conveyor belt 4030 is an endless belt, and is configured to wrap around the conveyor roller 4031 and the tension roller 4032 and circulate in the belt conveyance direction (sub-scanning direction).

  In the vicinity of the conveyance belt 4030, a charging roller 4035 for charging the surface of the conveyance belt 4030 is provided. The charging roller 4035 is charged so that strip-like plus portions and minus portions having a predetermined width exist alternately in the sub-scanning direction.

  The recording paper taken out from the paper feed tray (not shown) by the paper feed roller 4041 and the separation pad 4042 is guided by the guide toward the charged conveyance belt 4030.

  When the recording paper is fed onto the charged conveying belt 4030, the recording paper is attracted to the conveying belt 4030 and conveyed in the sub scanning direction by the circular movement of the conveying belt 4030.

  When the recording paper reaches a predetermined position, the recording paper is stopped, the head 4010 is driven according to the image signal while moving the carriage 4020, and ink droplets are ejected onto the recording paper to record one line. Then, after the recording sheet is conveyed by a predetermined amount, the next line is recorded.

  When the recording ends or when the trailing edge of the recording paper reaches the recording area, the recording operation is finished and the recording paper is discharged to a discharge tray (not shown).

  In this case, the movement information detector 2245 is used to detect the movement information of the recording paper in real time, and based on the detection result, a control device (not shown) feedback-controls the conveying roller 4031 to obtain high quality. An image can be formed.

  In this case, the movement information of the conveyor belt 4030 may be detected using the movement information detector 2245.

  As described above, the detection device of the present invention is suitable for improving versatility without incurring an increase in cost. The image forming apparatus of the present invention is suitable for forming a high quality image.

  DESCRIPTION OF SYMBOLS 11 ... Light source, 12 ... Illumination lens (1st optical system), 13 ... Aperture member (aperture member), 14 ... Light receiving lens (2nd optical system), 15 ... Image sensor, 16 ... Processing circuit (arithmetic unit, Reference position detection device, correction device), 30 ... Scanning control device (position adjustment device), 2000 ... Color printer (image forming device), 2010 ... Optical scanning device, 2030a to 2030d ... Photosensitive drum (image carrier), 2040 ... transfer belt (moving body), 2245 ... moving information detector (detecting device), 2090 ... printer control device (speed adjusting device), 3000 ... color printer (image forming apparatus), 3080 ... conveying belt (moving body), 3010 ... optical scanning device, 4000 ... image forming apparatus, K1, C1, M1, Y1 ... photosensitive drum (image carrier).

JP 2008-65743 A JP 2003-266828 A JP 2007-198979 A

Claims (20)

A detection device for detecting movement information of a moving object,
A light source disposed on one side with respect to the moving body and emitting light for illuminating the moving body;
A first optical system that converts light from the light source into convergent light having a condensing point on the other side with respect to the moving body, and guides it to the surface of the moving body;
A second optical system disposed on an optical path of light reflected by the surface of the moving body and having an optical positive power;
An image sensor that receives light via the second optical system and outputs image data;
An arithmetic device that calculates movement information of the moving body based on image data output from the image sensor. When determining the relationship between the peak value of the cross-correlation function in the image data before and after the movement of the moving body and the amount of movement of the moving body, the peak value decreases as the amount of movement of the moving body increases,
The movement amount at which the peak value is 1 / e of the peak value of the autocorrelation function is larger than the movement amount when the light illuminating the moving body is parallel light. Detection device. Using the radius of curvature ρ (<0) of the wavefront of the light that has passed through the first optical system, the focal length f of the second optical system, and the magnification m of the second optical system,
The detection apparatus according to claim 1, wherein a relationship of −2 (f / m) <ρ <−2/3 (f / m) is satisfied.   4. The detection apparatus according to claim 1, wherein the magnification of the second optical system is smaller than 1. 5.   5. The image sensor according to claim 1, wherein a light receiving surface is disposed to face an illumination area in the moving body in a direction orthogonal to a moving direction of the moving body. The detection device described.   The detection apparatus according to claim 1, wherein an aperture member is further provided between the moving body and the second optical system. Using the moving speed v of the moving object, the time interval τ for acquiring image data, and the width ws of the illumination area in the moving object relating to the moving direction of the moving object,
The detection apparatus according to claim 1, wherein a relationship of 2vτ <ws <10vτ is satisfied. Regarding the moving direction of the moving body, using the width ws of the illumination area in the moving body and the width wa of the observation area of the image sensor in the moving body,
8. The detection apparatus according to claim 1, wherein a relationship of wa <ws <5wa is satisfied.   The detection device according to claim 1, wherein the arithmetic device calculates movement information of the moving body based on two pieces of image data that are temporally adjacent to each other.   The detection device according to claim 9, wherein the arithmetic device obtains movement information of the moving body from a peak value of a cross-correlation function between the two image data.   The detection device according to claim 10, wherein the arithmetic device obtains movement information of the moving body from a peak value of the steepest peak when a plurality of peak values of the cross-correlation function exist.   12. The detection apparatus according to claim 10, wherein the cross-correlation function is a cross-correlation function obtained using only phase information. The moving body is an endless moving body, and at least one reference position is set for the moving body,
The detection apparatus according to any one of claims 1 to 12, further comprising a reference position detection device that detects the at least one reference position. The reference position detection device has a memory storing image data at the at least one reference position,
The reference position detection device detects the at least one reference position based on image data output from the image sensor and image data stored in the memory. Detection device.   The detection device according to claim 13, further comprising a correction device that corrects movement information of the movable body calculated by the arithmetic device based on a detection result of the reference position detection device.   The detection apparatus according to claim 13, wherein the at least one reference position is a plurality of reference positions. A plurality of image carriers corresponding to different colors;
An optical scanning device that scans each of the plurality of image carriers with a light beam modulated according to image information of a corresponding color to form a latent image;
A developing device for generating a plurality of toner images by attaching toners of corresponding colors to the latent images formed on the plurality of image carriers;
A transfer device that includes a belt member and superimposes and transfers the plurality of toner images to a medium;
An image forming apparatus comprising: the detection device according to claim 1 that detects movement information of the belt member.   The image forming apparatus according to claim 17, further comprising a speed adjusting device that adjusts a moving speed of the belt member based on a detection result of the detecting device. The optical scanning device includes a position adjusting device that individually adjusts incident positions of light in the plurality of image carriers in the sub-scanning direction,
19. The image forming apparatus according to claim 17, wherein the position adjusting device individually adjusts an incident position of light in the plurality of image carriers based on a detection result of the detection device. In an image forming apparatus for forming an image on a sheet surface of a medium while moving the sheet-like medium,
An image forming apparatus comprising the detection device according to claim 1 that detects movement information of the medium.