JP2012063604A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device capable of improving work efficiency without deteriorating image quality.SOLUTION: In an image formation device, a reflection type optical sensor comprises an irradiation system including eleven light emission parts arranged in a principal direction with equal intervals therebetween and a light receiving system including eleven light receiving parts. In the reflection type optical sensor, an interval Le between light emission parts regarding the principal direction; a number m of detection light spots for irradiating one rectangular pattern; a dimension D of the detection light spot; a number N of the light emission parts; a number T of the rectangular patterns arranged in the principal direction; a gap PI of the two rectangular patterns neighboring in the principal direction; and a length Lt of the rectangular pattern in the principal direction are used to satisfy a relation T×(m+1)≤N, m×Le+D≤Lt≤((N-1)×Le+D)/T, and PI<((N-1)×Le+D-T×(m×Le+D))/(T-1)+Le/(T-1).

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image on a moving body using toner.

  2. Description of the Related Art Image forming apparatuses such as copying machines, printers, facsimile machines, plotters, and multifunction machines equipped with at least one of them are widely known. In these image forming apparatuses, generally, an electrostatic latent image is formed on the surface of a photosensitive drum (hereinafter also referred to as “photosensitive drum”), and toner is attached to the electrostatic latent image. Thus, so-called development is performed to obtain a “toner image”.

  In the image forming process in the image forming apparatus, the following image density control is performed in order to always obtain a stable image density.

(1) A test pattern composed of a plurality of patches for detecting toner density formed under different image forming conditions (exposure power, charging bias, developing bias, etc.) is formed on the photosensitive drum so that the toner density differs. To do.

(2) The toner density of each patch is calculated using the detection amount detected by the reflective optical sensor as an optical detection means and a predetermined calculation algorithm.

(3) From the relationship between the toner density of each patch and the development potential obtained from the image forming conditions, development γ (the slope when the development potential is on the horizontal axis and the toner density is on the vertical axis) and the development start voltage Vk (The x-intercept when the development potential is on the horizontal axis (x-axis) and the toner density is on the vertical axis (y-axis)) is obtained.

(4) Based on the obtained development γ, image forming conditions such as exposure power, charging bias, and developing bias are adjusted so as to obtain a developing potential at which an appropriate toner density is obtained.

  By the way, in the image forming process in the color image forming apparatus, for example, a plurality of toner images corresponding to each color such as black, magenta, cyan, yellow, etc. are transferred onto the recording paper by superimposing them directly (b) ) It is configured to form a multi-color image by superimposing the image on the intermediate transfer belt and performing primary transfer, and then performing secondary transfer on the recording paper and fixing the image on the recording paper.

  In this image forming process, variations in optical characteristics among a plurality of optical systems corresponding to each color, adjustment deviations in a plurality of photosensitive drums corresponding to each color, fluctuations of a driving mechanism for driving the plurality of photosensitive drums and the intermediate transfer belt However, since color misregistration appears on the recording sheet as it is, color misregistration control is indispensable.

  As a specific method of color misregistration control, generally, (1) a test pattern for detecting misregistration of each color such as black, magenta, cyan, and yellow is formed on an intermediate transfer belt, and (2) each color. The position of the test pattern is read by a reflection type optical sensor, (3) the amount of misregistration is calculated from the result, and (4) the color misregistration on the recording paper is corrected by feeding back to the writing timing of the image information. . Note that the direction in which the toner image moves on the intermediate transfer belt is referred to as a “sub-direction”, and the direction orthogonal to the sub-direction is referred to as a “main direction”.

  Various types of reflective optical sensors are known (see, for example, Patent Documents 1 to 5). For example, as a conventional reflective optical sensor, a 1LED-2PD type reflective optical sensor composed of one light emitting portion and two light receiving portions, or 2LED-1PD composed of two light emitting portions and one light receiving portion. Types of reflective optical sensors.

  In the 1LED-2PD type reflective optical sensor, the light emitted to the test pattern from one light emitting unit forms one light spot on the moving body (photosensitive drum, intermediate transfer belt). On the other hand, in the 2LED-1PD type reflective optical sensor, the light emitted to the test pattern from the two light emitting units forms two light spots at almost the same location on the moving body with a time difference. To do.

  The test pattern for detecting misalignment is formed on the moving body so as to overlap the formation position of the light spot in the main direction, and moves in the sub direction along with the movement of the moving body. At this time, the size of the light spot (spot diameter) was usually about 2 to 3 mm. The test pattern for detecting misalignment generally includes a plurality of line-shaped patterns that are parallel or inclined with respect to the main direction. The length of each line-shaped pattern in the longitudinal direction is about 8.0 mm, and the length in the short direction. The thickness was about 1.0 mm.

  By the way, in Patent Document 6, an irradiation unit in which M (≧ 3) light emitting units that can be flashed independently or simultaneously are arranged in one direction, and N (≧ 3) light receiving units are used as the irradiation unit. A reflection type optical sensor having light receiving means arranged in one direction in correspondence is disclosed.

  In recent years, there has been an increasing demand for stabilization of image quality in image forming apparatuses, and it has become necessary to always detect toner density, positional deviation, and the like in real time. However, in order to detect toner density and displacement in real time during image formation, it is necessary to form a test pattern on the intermediate transfer belt with high positional accuracy with respect to the reflective optical sensor. There was the inconvenience of reducing efficiency.

  The present invention has been made under such circumstances, and an object thereof is to provide an image forming apparatus capable of improving work efficiency without deteriorating image quality.

  The present invention provides an image forming apparatus that forms an image on a moving body that moves in a first direction, and a plurality of patches whose positions are different from each other with respect to a second direction orthogonal to the first direction on the moving body. A test pattern creating apparatus for creating a test pattern including: an irradiation system including at least three light emitting units arranged at equal intervals Le with respect to the second direction; and an emission system emitted from the irradiation system and reflected by the test pattern A reflection-type optical sensor including a light-receiving system including at least three light-receiving units that receive the received light; and at least a toner density and a positional deviation of the plurality of patches based on an output signal of the light-receiving system of the reflection-type optical sensor. A processing device for obtaining one of the plurality of patches, a number m of light spots that illuminate one of the plurality of patches, a size D of the light spots in the second direction, The number T of the plurality of patches arranged at different positions with respect to the two directions, the gap PI between two adjacent patches with respect to the second direction, the length Lt of one patch with respect to the second direction, and the irradiation T × (m + 1) ≦ N, m × Le + D ≦ Lt ≦ ((N−1) × Le + D) / T, PI <((N−1) × Le + D−T) The image forming apparatus is characterized in that a relationship of × (m × Le + D)) / (T−1) + Le / (T−1) is satisfied.

  According to this, the tolerance regarding the position error of the test pattern with respect to the reflective optical sensor becomes larger than before, and as a result, it is possible to improve the work efficiency without degrading the image quality.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. It is FIG. (1) for demonstrating schematic structure of an optical scanning device. FIG. 3 is a second diagram for explaining a schematic configuration of the optical scanning device; FIG. 3 is a third diagram for explaining a schematic configuration of the optical scanning device; FIG. 4 is a diagram (part 4) for explaining a schematic configuration of the optical scanning device; It is a figure for demonstrating a toner pattern detector. It is a figure for demonstrating the arrangement position of a reflection type optical sensor. It is FIG. (1) for demonstrating a reflection type optical sensor. It is FIG. (2) for demonstrating a reflection type optical sensor. It is FIG. (3) for demonstrating a reflection type optical sensor. It is FIG. (4) for demonstrating a reflection type optical sensor. It is a figure for demonstrating the light for a detection. It is FIG. (5) for demonstrating a reflection type optical sensor. FIG. 6 is a diagram for explaining a toner pattern. It is a figure for demonstrating the four rectangular patterns in each density | concentration detection pattern. It is a figure for demonstrating arrangement | positioning of each density | concentration detection pattern. It is a figure for demonstrating the positional relationship of the pattern for density | concentration detection, and a light emission part. It is a figure for demonstrating the pattern for position shift detection. 6 is a flowchart for explaining image process control performed by the printer control apparatus. 5 is a flowchart for explaining density detection processing performed by a printer control apparatus. FIG. 21A and FIG. 21B are diagrams for explaining reflected light, respectively. 22A to 22C are diagrams for explaining examples of ΔD5 to ΔD7, respectively. It is a figure for demonstrating the position of the rectangular pattern corresponding to FIG.22 (A)-FIG.22 (C). FIGS. 24A to 24D are diagrams for explaining examples of ΔD5 to ΔD8, respectively. It is a figure for demonstrating the position of the rectangular pattern corresponding to FIG. 24 (A)-FIG.24 (D). It is a figure for demonstrating the modification of a rectangular pattern. 27A and 27B, the rectangular pattern is at the position of FIG. 23, the light emitting unit E6 is turned on, and the output distribution of each light receiving unit when the illumination target is a transfer belt, and the illumination It is a figure for demonstrating the output distribution of each light-receiving part when a target object is the rectangular pattern p5. It is a figure for demonstrating the example 1 of sampling timing. It is a figure for demonstrating the example 2 of a sampling timing. It is a figure for demonstrating the example 3 of a sampling timing. It is a figure for demonstrating the example 4 of a sampling timing. It is a figure for demonstrating the example 5 of a sampling timing. It is a figure for demonstrating the example 6 of a sampling timing. It is a figure for demonstrating the example 7 of a sampling timing. It is a figure for demonstrating the example 8 of a sampling timing. It is a figure for demonstrating the example 9 of a sampling timing. It is a figure for demonstrating the output distribution of each light-receiving part when the light emission part to light is only the light emission part E3, and when this light emission part E3 is turned on, an illumination target object is a transfer belt. In FIGS. 38A and 38B, the light-emitting part that is turned on is only the light-emitting part E3. When the light-emitting part E3 is turned on, the illumination object is a rectangular pattern of the density detection pattern DP1. It is a figure for demonstrating the light reception amount distribution of each light-receiving part in the case of p1 and the rectangular pattern p2. In FIGS. 39A and 39B, only the light emitting part E3 is turned on, and when the light emitting part E3 is turned on, the illumination object is a rectangular pattern of the density detection pattern DP1. It is a figure for demonstrating the received light amount distribution of each light-receiving part in the case of p3 and the rectangular pattern p4. FIG. 40A is a diagram for explaining a specularly reflected light component in the amount of light received by each light receiving unit when the detection light S3 is reflected by the rectangular pattern p1, and FIG. 40B is a diagram for detection. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part when light S3 is reflected by the rectangular pattern p1. FIG. 41A is a diagram for explaining the specularly reflected light component in the amount of light received by each light receiving unit when the detection light S3 is reflected by the rectangular pattern p2, and FIG. 41B is a diagram for detection. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part when light S3 is reflected by the rectangular pattern p2. FIG. 42A is a diagram for explaining the specularly reflected light component in the amount of light received by each light receiving unit when the detection light S3 is reflected by the rectangular pattern p3, and FIG. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part when light S3 is reflected by the rectangular pattern p3. FIG. 43A is a diagram for explaining the specularly reflected light component in the amount of light received by each light receiving portion when the detection light S3 is reflected by the rectangular pattern p4, and FIG. 43B is a diagram for detection. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part when light S3 is reflected by the rectangular pattern p4. It is a figure for demonstrating the total value D1 of the regular reflection light component in each illumination target object. It is a figure for demonstrating the total value D2 of the diffuse reflected light component in each illumination object. It is a figure for demonstrating D2 / D1 of each illumination object. It is a figure for demonstrating the relative value of the total value D1 of the regular reflection light component in each illumination object. It is a figure for demonstrating the relative value of the total value D2 / total value D1 of the diffuse reflected light component in each illumination target object. FIG. 6 is a diagram (part 1) for describing a positional deviation detection process; FIG. 6 is a diagram (part 2) for describing a positional deviation detection process; FIG. 51A and FIG. 51B are diagrams for explaining detection of displacement in the sub direction and the main direction, respectively. FIG. 10 is a diagram (No. 1) for explaining the relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction when there are four detection lights for illuminating the toner patch. FIG. 11 is a diagram (No. 2) for explaining the relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction when there are four detection lights for illuminating the toner patch. FIG. 10 is a diagram (No. 1) for explaining the relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction when there is one detection light for illuminating the toner patch. FIG. 10 is a diagram (No. 2) for explaining the relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction when there is one detection light for illuminating the toner patch. FIG. 6 is a diagram for explaining a relative positional deviation allowable amount between a detection light spot and a toner patch in the main direction when there are five detection lights that illuminate a toner patch. 57 (A) to 57 (C) respectively show Lt = 4. FIG. 6 is a diagram for explaining a case of Le + D and five detection lights for illuminating a toner patch. 58 (A) to 58 (C) show Lt <4. FIG. 6 is a diagram for explaining a case of Le + D and five detection lights for illuminating a toner patch. Lt = 4. Le + D, and the length B in the main direction of the four light spot rows for detection is 3. It is a figure for demonstrating the case of Le + D. FIG. 60 is a diagram for explaining a relative positional shift allowable amount between the detection light spot and the toner patch in the main direction in FIG. 59. Lt = 4. Le + D, and the length B in the main direction of one detection light spot is 3. It is a figure for demonstrating the case of Le + D. FIG. 61 is a diagram for explaining a relative positional deviation allowable amount between a detection light spot and a toner patch in the main direction in FIG. 60. Two toner patches are arranged in the main direction, and Lt = 4. Le + D, and the length B in the main direction of one detection light spot is 3. It is a figure for demonstrating the case of Le + D. FIG. 64 is a diagram for describing a relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction in FIG. 63. Two toner patches are arranged in the main direction, and Lt = 4. FIG. 6 is a diagram for explaining a case of Le + D, where twelve detection lights illuminate two toner patches and a gap between two toner patches is P + 2δ. FIG. 66 is a diagram for describing a relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction in FIG. 65. Two toner patches are arranged in the main direction, and Lt = 4. FIG. 10 is a diagram for explaining a case of Le + D, where twelve detection lights illuminate two toner patches and the gap between the two toner patches is P. FIG. 68 is a diagram for describing a relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction in FIG. 67; Two toner patches are arranged in the main direction, and Lt = 4. FIG. 10 is a diagram for explaining a case of Le + D, where twelve detection lights illuminate two toner patches and a gap between the two toner patches is P−2δ. FIG. 70 is a diagram for explaining a relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction in FIG. 69. Two toner patches are arranged in the main direction, and Lt = 4. FIG. 6 is a diagram for explaining a case where Le + D, 12 detection lights for illuminating two toner patches, and a gap between two toner patches is P + Le. FIG. 72 is a diagram for describing a relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction in FIG. 71. Two toner patches are arranged in the main direction, and Lt = 5. FIG. 6 is a diagram for explaining a case of Le + D, in which twelve detection lights for illuminating two toner patches are used, and the gap between the two toner patches is zero. FIG. 74 is a diagram for explaining a relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction in FIG. 73. Two toner patches are arranged in the main direction, and Lt> 5. FIG. 6 is a diagram for explaining a case of Le + D, in which twelve detection lights for illuminating two toner patches are used, and the gap between the two toner patches is zero. FIG. 76 is a diagram for explaining a relative positional deviation allowable amount between the detection light spot and the toner patch in the main direction in FIG. 75. It is a figure for demonstrating the pattern GP for position recognition. It is a figure for demonstrating the determination method of the position of pattern GP for position recognition. FIG. 79 is a diagram for explaining the position of a position recognition pattern GP determined from FIG. 78. It is a figure for demonstrating the determination method of the position of the top rectangular pattern. It is a figure for demonstrating the position of the top rectangular pattern determined from FIG. 82 (A) and 82 (B) are diagrams for explaining the case where Lt is 1.2 mm. 83A to 83C are diagrams for explaining the case where each of the five detection lights illuminates one rectangular pattern. It is a figure for demonstrating the modification 1 of the arrangement | sequence of 16 rectangular patterns. It is a figure for demonstrating the modification 2 of the arrangement | sequence of 16 rectangular patterns.

  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 unit 2080, a toner pattern detector 2245, temperature and humidity sensor (not shown) and a printer control unit 2090 for centrally controlling the above units.

  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 and an information device (for example, a facsimile device) via a public line. Then, the communication control device 2080 notifies the received information to the printer control device 2090.

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An AD converter for converting the signal into digital data. The printer control device 2090 controls each unit in response to requests from the host device and the information device, and sends image information from the host device and the information device to the optical scanning device 2010.

  The temperature / humidity sensor detects the temperature and humidity in the color printer 2000 and notifies the printer controller 2090 of it.

  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.

  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.

  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.

  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 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).

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

  The optical scanning device 2010 uses the multi-color image information (black image information, cyan image information, magenta image information, yellow image information) from the printer control device 2090 to charge the light flux modulated for each color to the corresponding charging. Irradiate each of the surfaces of the photosensitive drums. 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. By the way, on the transfer belt 2040, the moving direction of the toner image (here, the X-axis direction) is referred to as “sub-direction”, and the direction orthogonal to the sub-direction (here, the Y-axis direction) is referred to as “main direction”. "is called.

  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 the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 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 toner pattern detector 2245 is disposed on the + Z side of the transfer belt 2040 and in the vicinity of the + X side end of the transfer belt 2040. The toner pattern detector 2245 will be described later.

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

  2 to 5 as an example, the optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four coupling lenses (2201a, 2201b, 2201c, 2201d), four openings. Plate (2202a, 2202b, 2202c, 2202d), 4 cylindrical lenses (2204a, 2204b, 2204c, 2204d), polygon mirror 2104, 4 deflector side scanning lenses (2105a, 2105b, 2105c, 2105d), 8 turns Mirrors (2106a, 2106b, 2106c, 2106d, 2108a, 2108b, 2108c, 2108d), 4 image plane side scanning lenses (2107a, 2107b, 2107c, 2107d), 4 light detection sensors (2205a, 2108d) 05b, 2205c, 2205d), 4 sheets of light detection mirror (2207a, includes 2207b, 2207c, 2207d), and the like scanning control device (not shown). These are assembled at predetermined positions of the optical housing 2300 (not shown in FIGS. 2 to 4, see FIG. 5).

  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 light source 2200b and the light source 2200c are disposed at positions separated from each other in the X-axis direction. The light source 2200a is disposed on the −Z side of the light source 2200b. The light source 2200d is arranged on the −Z side of the light source 2200c.

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

  The coupling lens 2201d is disposed on the optical path of the light beam emitted from the light source 2200d, 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.

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

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

  The cylindrical lens 2204 a forms an image of the light beam that has passed through the opening of the aperture plate 2202 a in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204b forms an image of the light beam that has passed through the opening of the aperture plate 2202b in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204 c forms an image of the light beam that has passed through the opening of the aperture plate 2202 c in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204d forms an image of the light flux that has passed through the opening of the aperture plate 2202d 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, and each mirror serves as a deflection 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.

  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 deflector-side scanning lens has a non-circular 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. ing.

  The deflector side scanning lens 2105a and the deflector side scanning lens 2105b are arranged on the −X side of the polygon mirror 2104, and the deflector side scanning lens 2105c and the deflector side scanning lens 2105d are arranged on the + X side of the polygon mirror 2104. ing.

  The deflector-side scanning lens 2105a and the deflector-side scanning lens 2105b are stacked in the Z-axis direction, the deflector-side scanning lens 2105a is opposed to the first-stage four-sided mirror, and the deflector-side scanning lens 2105b is two-stage. It faces the four-sided mirror of the eye. The deflector-side scanning lens 2105c and the deflector-side scanning lens 2105d are stacked in the Z-axis direction, the deflector-side scanning lens 2105c is opposed to the second-stage four-sided mirror, and the deflector-side scanning lens 2105d is one stage. It faces the four-sided mirror of the eye.

  Therefore, the light beam from the cylindrical lens 2204a deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum 2030a via the deflector side scanning lens 2105a, the folding mirror 2106a, the image plane side scanning lens 2107a, and the folding mirror 2108a. A light spot is formed. 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 via the deflector-side scanning lens 2105b, the folding mirror 2106b, the image plane-side scanning lens 2107b, and the folding mirror 2108b. A light spot is formed. 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 onto the photosensitive drum 2030c via the deflector-side scanning lens 2105c, the folding mirror 2106c, the image plane-side scanning lens 2107c, and the folding mirror 2108c. A light spot is formed. 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 via the deflector-side scanning lens 2105d, the folding mirror 2106d, the image plane-side scanning lens 2107d, and the folding mirror 2108d. A light spot is formed. 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.

  Incidentally, a scanning area in the main scanning direction in which image information is written on each photosensitive drum is called an “effective scanning area”, an “image forming area”, or an “effective image area”.

  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, the K station scanning optical system is composed of the deflector side scanning lens 2105a, the image plane side scanning lens 2107a, and the folding mirrors (2106a, 2108a). Further, the scanning optical system of the C station is composed of the deflector side scanning lens 2105b, the image plane side scanning lens 2107b, and the folding mirrors (2106b, 2108b). The deflector side scanning lens 2105c, the image plane side scanning lens 2107c, and the folding mirrors (2106c, 2108c) constitute the M station scanning optical system. Further, the Y station scanning optical system is composed of the deflector side scanning lens 2105d, the image plane side scanning lens 2107d, and the folding mirrors (2106d, 2108d).

  A part of the light beam before the start of writing out of the light beam deflected by the polygon mirror 2104 and passed through the scanning optical system of the K station enters the light detection sensor 2205a via the light detection mirror 2207a.

  The light detection sensor 2205b is deflected by the polygon mirror 2104, and a part of the light beam before starting writing out of the light beam via the scanning optical system of the C station enters through the light detection mirror 2207b.

  The light detection sensor 2205c is deflected by the polygon mirror 2104, and a part of the light beam before starting writing out of the light beam via the scanning optical system of the M station enters through the light detection mirror 2207c.

  A part of the light beam before the start of writing out of the light beam deflected by the polygon mirror 2104 and passed through the scanning optical system of the Y station enters the light detection sensor 2205d via the light detection mirror 2207d.

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

  The scanning control device detects the scanning start timing on the corresponding photosensitive drum based on the output signal of each light detection sensor.

  Next, the toner pattern detector 2245 will be described.

  The toner pattern detector 2245 has three reflective optical sensors (2245a, 2245b, 2245c) as shown in FIG. 6 as an example.

  As an example, as shown in FIG. 7, the reflective optical sensor 2245a is disposed at a position facing the vicinity of the −Y side end portion in the effective image area of the transfer belt 2040, and the reflective optical sensor 2245c is transferred. The belt 2040 is disposed at a position facing the vicinity of the + Y side end in the effective image area of the belt 2040, and the reflective optical sensor 2245b is disposed at a substantially central position between the reflective optical sensor 2245a and the reflective optical sensor 2245c with respect to the main direction. ing.

  Here, regarding the main direction (Y-axis direction), the center position of the reflective optical sensor 2245a is Y1, the center position of the reflective optical sensor 2245b is Y2, and the center position of the reflective optical sensor 2245c is Y3.

  The three reflective optical sensors (2245a, 2245b, 2245c) all have the same configuration and the same structure. Therefore, hereinafter, the configuration and structure of the reflective optical sensor will be described using the reflective optical sensor 2245a as a representative.

  As shown in FIGS. 8 to 11, the reflective optical sensor 2245a is an illumination system including 11 light emitting units (E1 to E11) and illumination including 11 illumination microlenses (LE1 to LE11). An optical system, a light receiving optical system including 11 light receiving microlenses (LD1 to LD11), a light receiving system including 11 light receiving portions (D1 to D11), and the like are provided.

  The eleven light emitting units (E1 to E11) are arranged at equal intervals Le along the main direction, that is, the light emitting unit intervals Le. For each light emitting unit, an LED (Light Emitting Diode) can be used. Here, as an example, Le = 0.4 mm. In this case, with respect to the main direction, the distance between E1 and E11 is 4 mm (Le × 10). The size of each light emitting portion in the main direction is about 0.04 mm. Furthermore, the wavelength of the light beam emitted from each light emitting unit is 850 nm. In the following, for convenience, the lit light emitting unit is abbreviated as “lit light emitting unit”.

  The eleven illumination microlenses (LE1 to LE11) individually correspond to the eleven light emitting units (E1 to E11), respectively.

  Each illumination microlens condenses and guides the light beam emitted from the corresponding light emitting unit toward the surface of the transfer belt 2040. In each illumination microlens, the lens diameter, the radius of curvature of the lens, and the lens thickness are the same. The optical axis of each illumination microlens is parallel to the direction orthogonal to the light emitting surface of the corresponding light emitting unit.

  Here, for easy understanding, it is assumed that only the light beam emitted from each light emitting unit and passing through the corresponding illumination microlens illuminates the transfer belt 2040 as detection light (S1 to S11) (FIG. 12). reference). Then, the center of the light spot (hereinafter abbreviated as “detection light spot” for convenience) formed on the surface of the transfer belt 2040 by each detection light is the center of the corresponding light emitting unit and light receiving unit with respect to the sub-direction. Near the middle.

  As an example, the diameter D of each detection light spot is 0.4 mm. This value is equal to the light emitting section interval Le of the eleven light emitting sections. Further, with respect to the main direction, the center-to-center distance between two adjacent detection light spots is 0.4 mm, which is equal to the light-emitting portion interval Le. The diameter of the conventional detection light spot was usually about 2 to 3 mm.

  Here, the surface of the transfer belt 2040 is smooth, and most of the detection light irradiated on the surface of the transfer belt 2040 is regularly reflected.

  The eleven light receiving parts (D1 to D11) individually correspond to the light emitting parts (E1 to E11), respectively.

  Each light receiving portion is disposed on the optical path of a light beam emitted from the corresponding light emitting portion and regularly reflected by the surface of the transfer belt 2040. The interval between two adjacent light receiving parts (light receiving part interval) is equal to the light emitting part interval Le. Each light receiving portion has a square shape with a side length of 0.35 mm, and the peak wavelength of the light receiving sensitivity is in the vicinity of 850 nm.

  A PD (photodiode) can be used for each light receiving portion. Each light receiving unit outputs a signal corresponding to the amount of received light.

  The eleven light receiving microlenses (LD1 to LD11) are individually provided for the eleven light receiving portions (D1 to D11), respectively, and collect the detection light reflected by the transfer belt 2040 or the toner pattern. In this case, the amount of light received by each light receiving unit can be increased. That is, detection sensitivity can be improved. In each light receiving microlens, the lens diameter, the radius of curvature of the lens, and the lens thickness are the same.

  For each microlens, a spherical lens having a condensing function in the main direction and the sub direction, a cylindrical lens having a positive power in the sub direction, an anamorphic lens in which the power in the main direction and the power in the sub direction are different from each other are used. be able to.

  Here, as an example, each microlens is a spherical lens. In each illumination microlens, the incident-side optical surface has condensing power, and the exit-side optical surface does not have condensing power. In each light receiving microlens, the exit-side optical surface has a condensing power, and the incident-side optical surface does not have a condensing power.

  Specifically, in each illumination microlens, the lens diameter is 0.613 mm, the radius of curvature of the lens is 0.430 mm, and the lens thickness is 0.129 mm.

  Each light-receiving microlens has a lens diameter of 0.750 mm, a lens curvature radius of 0.380 mm, and a lens thickness of 0.319 mm.

  In the present embodiment, 11 illumination microlenses (LE1 to LE11) and 11 light receiving microlenses (LD1 to LD11) are integrated into a microlens array. Thereby, workability | operativity at the time of assembling each micro lens in a predetermined position can be improved. Moreover, the positional accuracy between the lens surfaces in a plurality of microlenses can be increased. Each lens surface can be formed on a glass substrate or a resin substrate by using a processing method such as photolithography or molding.

  Hereinafter, when it is not necessary to specify the light emitting unit, the light emitting unit Ei is displayed. And the illumination microlens corresponding to the light emission part Ei is displayed as the illumination microlens LEi. The light beam emitted from the light emitting unit Ei and passing through the illumination microlens LEi is displayed as detection light Si. The light receiving unit corresponding to the light emitting unit Ei is displayed as the light receiving unit Di. Further, the light receiving microlens corresponding to the light receiving portion Di is displayed as a light receiving microlens LDi.

  As an example, as shown in FIG. 13, the optical axis of each illumination microlens is Δd (here, the light receiving system side with respect to an axis that passes through the center of each corresponding light emitting unit and is perpendicular to the light emitting unit). 0.035 mm). The optical axis of each light receiving microlens is shifted by Δd ′ (here, 0.020 mm) toward the irradiation system with respect to an axis that passes through the center of each corresponding light receiving portion and is perpendicular to the light receiving portion. Thereby, each light-receiving part can receive more reflected light.

  In the sub-direction, the distance between the illumination microlens LEi and the light receiving microlens LDi is 0.445 mm, and the distance between the light emitting portion Ei and the light receiving portion Di is 0.500 mm. Further, with respect to the sub direction, the distance from the light emitting portion Ei to the illumination microlens LEi is 0.800 mm, and the distance from the −Z side surface of each microlens to the surface of the transfer belt 2040 is 5 mm.

  Next, a toner pattern as a test pattern will be described.

  Here, as an example, as shown in FIG. 14, the pattern PP is formed at the Y1 position, the pattern PP and the patterns DP1 to DP4 are formed at the Y2 position, and the pattern PP is formed at the Y3 position. Yes.

  DP1 to DP4 are all density detection patterns, and PP is a positional deviation detection pattern.

  The density detection pattern DP1 is formed of black toner, and the density detection pattern DP2 is formed of magenta toner. The density detection pattern DP3 is formed of cyan toner, and the density detection pattern DP4 is formed of yellow toner. Hereinafter, when it is not necessary to distinguish between the density detection patterns DP1 to DP4, they are also collectively referred to as “density detection patterns DP”.

  As shown in FIG. 15 as an example, the density detection pattern DP has four rectangular patterns (p1 to p4, hereinafter referred to as “rectangular pattern” for convenience). The rectangular patterns are arranged in a line along the traveling direction of the transfer belt 2040, and the gradation of toner density differs when viewed as a whole. Here, p1, p2, p3, and p4 are set from a rectangular pattern having a low toner density. That is, the rectangular pattern p1 has the lowest toner density, and the rectangular pattern p4 has the highest toner density.

  Here, as an example, the length Lt in the main direction of each rectangular pattern is 1 mm, and the length Lm in the sub direction is 2 mm. In this case, the amount of toner required to create the density detection pattern DP can be reduced to about 1/100 of the conventional amount.

  Further, with respect to the sub direction, the center interval Ln between two adjacent rectangular patterns is 3 mm.

  The gradation of the toner density can be changed by adjusting the power of the light beam emitted from the light source, adjusting the duty in the drive pulse supplied to the light source, and adjusting the charging bias and the developing bias. In addition, the gradation of the toner density can be changed by changing the area ratio of the halftone dots.

  The density detection pattern DP2 is disposed on the −Y side of the density detection pattern DP1, and the density detection pattern DP4 is disposed on the −Y side of the density detection pattern DP3. Further, the density detection pattern DP1 and the density detection pattern DP3, and the density detection pattern DP2 and the density detection pattern DP4 are arranged along the sub-direction, respectively.

  Here, with respect to the main direction, the distance between the centers of two adjacent rectangular patterns is 2.4 mm. Therefore, with respect to the main direction, the size PI (see FIG. 16) of the gap between the density detection pattern DP1 and the density detection pattern DP2 and between the density detection pattern DP3 and the density detection pattern DP4 is 1.4 mm.

  Here, one rectangular pattern is illuminated, the number of detection light spots used for density detection is m, the number of rectangular patterns arranged at different positions in the main direction is T, and the number of light emitting units in the irradiation system is N.

  In the present embodiment, m = 1, T = 2, and N = 11, and the relationship of the following expression (1) is satisfied.

T × (m + 1) ≦ N (1)

  Further, Le = 0.4 mm, D = 0.4 mm, and Lt = 1 mm, and the relationship of the following expression (2) is also satisfied.

m × Le + D ≦ Lt ≦ ((N−1) × Le + D) / T (2)

  Further, the relationship of the following expression (3) is also satisfied. Note that P in the expression (3) is a value represented by the following expression (4).

PI <P + Le / (T-1) (3)

P = ((N−1) × Le + DT × (m × Le + D)) / (T−1) (4)

  In the present embodiment, as shown in FIG. 17 as an example, the density detection pattern DP1 is formed at a position illuminated by the detection light S9 from the light emitting unit E9 of the reflective optical sensor 2245b, and the light from the light emitting unit E3 is emitted. The density detection pattern DP2 is set to be formed at the position illuminated by the detection light S3.

  As shown in FIG. 18 as an example, the misregistration detection pattern PP is a first pattern group composed of four linear patterns (LPY1, LPM1, LPC1, LPK1) parallel to the main direction (Y-axis direction). And a second pattern group composed of four linear patterns (LPY2, LPM2, LPC2, LPK2) inclined with respect to the main direction.

  The line patterns LPY1 and LPY2 are paired and formed with yellow toner, and the line patterns LPM1 and LPM2 are paired and formed with magenta toner. The line patterns LPC1 and LPC2 are paired and formed with cyan toner, and the line patterns LPK1 and LPK2 are paired and formed with black toner.

  In the first pattern group, the length w1 in the main direction of each line pattern is 1.0 mm, the length in the sub direction is 0.5 mm, and the interval in the sub direction is 1 mm.

  In the second pattern group, the inclination angle of each linear pattern is 45 °. Each line pattern has a distance between two corners located on the inner side in the main direction of 1.0 mm and a line width of 0.5 mm.

  Next, density detection processing and positional deviation detection processing performed using the toner pattern detector 2245 for image process control will be described with reference to FIG. In the present embodiment, the density detection process and the positional deviation detection process are performed by the printer control device 2090. The flowchart in FIG. 19 corresponds to a series of processing algorithms executed by the printer control device 2090 during the density detection process and the positional deviation detection process.

  In the first step S301, it is determined whether there is a request for image process control. Here, if the image process control flag is set, the determination here is affirmed, and if the image process control flag is not set, the determination here is denied.

  When the image process control flag is turned on, (1) when the photosensitive drum stop time is 6 hours or more, (2) when the temperature in the apparatus changes by 10 ° C. or more, and (3) relative in the apparatus When humidity changes by 50% or more, during printing, (4) when the number of printed sheets reaches a predetermined number, (5) when the number of rotations of the developing roller reaches a predetermined number of times, (6) transfer belt This is set when the travel distance of the vehicle reaches a predetermined distance.

  If the determination in step S301 is negative, none of the detection processes are performed. On the other hand, if the determination in step S301 is affirmative, the image process control flag is reset, and the process proceeds to step S303.

  In step S303, the scanning control apparatus is instructed to create a toner pattern.

  As a result, the scanning control device has the line patterns LPY1, LPY2, the position Y2 at the position Y1 on the photosensitive drum 2030d, the density detection pattern DP4, the line patterns LPY1, LPY2, and the line pattern LPY1, at the position Y3. The Y station is controlled so that LPY2 is formed.

  Further, the scanning control device has the line patterns LPM1, LPM2 at the position Y1 on the photosensitive drum 2030c, the pattern DP2 for density detection at the position Y2, the line patterns LPM1, LPM2, and the line patterns LPM1, LPM2 at the position Y3. , M station is controlled to form.

  Further, the scanning control device has the line patterns LPC1 and LPC2 at the position Y1 on the photosensitive drum 2030b, the density detection pattern DP3 at the position Y2, the line patterns LPC1 and LPC2, and the line patterns LPC1 and LPC2 at the position Y3. , C station is controlled to form.

  Further, the scanning control device has the line patterns LPK1, LPK2 and the position Y2 at the position Y1 on the photosensitive drum 2030a, the density detection pattern DP1, the line patterns LPK1, LPK2, and the line pattern LPK1, LPK2 at the position Y3. , K station is controlled to form.

  The density detection pattern and the positional deviation detection pattern formed by each station are transferred to the transfer belt 2040 at a predetermined timing.

  As a result, the position deviation detection pattern PP is formed at the position Y1 on the transfer belt 2040, the density detection patterns DP1 to DP4 and the position deviation detection pattern PP are formed at the position Y2, and the position deviation detection pattern at the position Y3. PP will be formed.

  In the next step S305, toner density detection processing is performed. The toner density detection process will be described with reference to the flowchart of FIG. In the following, for the sake of clarity, it is assumed that the density detection pattern is only DP1.

  In the first step S401, the position of the rectangular pattern with respect to the main direction is recognized.

  The position of the rectangular pattern with respect to the main direction is preferably a position where the intended detection light illuminates the center of the rectangular pattern. However, an error may occur in the position of the rectangular pattern in the main direction due to a shift in the formation position of the rectangular pattern, meandering in the main direction of the transfer belt, or the like.

  Therefore, it is necessary to recognize in advance the position of the rectangular pattern in the main direction. It should be noted that the position of the rectangular pattern can be estimated based on the information that has been previously subjected to the density detection process, that is, the information when the rectangular pattern is detected.

  For example, it is possible to estimate at which position the rectangular pattern will be next from the output information of each light receiving unit stored in the RAM when the rectangular pattern is detected.

  Specifically, the light emitting unit Ei is turned on, and the output of the light receiving unit Di when the detection light Si illuminates the transfer belt and the output of the light receiving unit Di when the detection light Si illuminates the rectangular pattern When the value of the difference ΔDi has a maximum value, it can be determined that the rectangular pattern is positioned at the illumination position of the detection light Si corresponding to the maximum value.

  Note that most of the detection light that illuminates the transfer belt is regularly reflected (see FIG. 21A). On the other hand, the detection light that illuminates the rectangular pattern is diffusely reflected when irradiated on the toner (see FIG. 21B).

  For example, when ΔD1 to ΔD4 and ΔD8 to ΔD11 are 0 and the value of ΔD6 becomes the maximum value as shown in FIGS. 22A to 22C, as shown in FIG. In addition, it is determined that the center of the rectangular pattern is located at the illumination position of the detection light S6.

  Further, as shown in FIGS. 24A to 24D, when there is a relationship of ΔD5 <ΔD6≈ΔD7> ΔD8, as shown in FIG. 25, the illumination position of the detection light S6 and It is determined that the center of the rectangular pattern is located at an intermediate position of the illumination position of the detection light S7.

  Even if the output information of each light receiving unit is not viewed, the position of the rectangular pattern generally changes greatly if changes in the elapsed time or environmental conditions (temperature, humidity) since the previous detection of the rectangular pattern were small. Therefore, it can be estimated that the position is the same as the previous time.

  In the next step S403, the light emitting unit to be lit is determined.

  Here, a case where a part of the light emitting units is turned on and a case where all the light emitting units are turned on are considered.

(A-1) When lighting a part of the light emitting units.

  When some of the light emitting units are turned on, the light emitting units to be turned on can be determined based on the position of the rectangular pattern in the main direction recognized in step S401.

  For example, the case where it is recognized that the center of the rectangular pattern is located at the illumination position of the detection light S6 will be described.

  At this time, even if the light emitting units E5 and E7 are caused to emit light, a part of the detection lights S5 and S7 do not illuminate the rectangular pattern, so that the use efficiency of the detection light in density detection is small and the density detection accuracy is low.

  Therefore, at this time, only the light emitting unit E6 can be determined as the light emitting unit to be turned on.

  By the way, when the rectangular pattern is moving in the sub-direction, the position of the rectangular pattern is changed with respect to the main direction, and there is a possibility that the rectangular pattern may deviate from the illumination position of the detection light S6. Then, the light emitting units E5 and E7 adjacent to the light emitting unit E6 may be added to determine the three light emitting units E5 to E7 as the light emitting units to be lit. The margin can be determined based on the performance of the image forming apparatus (rectangular pattern formation position deviation performance, transfer belt meandering performance, etc.).

  Next, for example, a case where it is determined that the center of the rectangular pattern is located at an intermediate position between the illumination position of the detection light S6 and the illumination position of the detection light S7 will be described.

  At this time, even if the light emitting units E5 and E8 are caused to emit light, a part of the detection lights S5 and S8 do not illuminate the rectangular pattern, so that the use efficiency of the detection light in density detection is small and the density detection accuracy is low.

  Therefore, at this time, it is possible to determine two light emitting units E6 and E7 as the light emitting units to be turned on. In this case, since the calculation result of the toner density is obtained for each light emitting unit, the calculation result obtained when the light emitting unit E6 is turned on and the calculation result obtained when the light emitting unit E7 is turned on are averaged. Therefore, the accuracy of density detection can be increased.

  At this time, one of the light emitting unit E6 and the light emitting unit E7 may be determined as the light emitting unit to be lit.

  Further, at this time, when there is a possibility that the rectangular pattern may be deviated from the illumination position of the detection light, the light emitting unit E5 adjacent to the light emitting unit E6 and the light emitting unit E8 adjacent to the light emitting unit E7 are taken into account. In addition, four light emitting units E5 to E8 may be determined as the light emitting units to be turned on.

(A-2) When all the light emitting units are turned on.

  In this case, 11 light emitting units E1 to E11 are determined as the light emitting units to be lit. In this case, even if the position of the rectangular pattern changes slightly (4 mm or less) in the main direction, there is no possibility that the rectangular pattern will be out of the detection light.

  In the next step S405, a lighting pattern is determined.

  As a lighting pattern, when there are a plurality of light emitting units to be turned on, there are a case where they are turned on / off simultaneously and a case where they are turned on / off sequentially.

  For example, when the light emitting unit En and the light emitting unit Em (n ≠ m) are turned on at the same time to illuminate one rectangular pattern with the detection light Sn and the detection light Sm, the reflected light from the detection light Sn and the detection light When the reflected light by the light Sm is received by the same light receiving unit, they cannot be separated. However, when the light emitting unit En and the light emitting unit Em are sequentially turned on / off to illuminate one rectangular pattern with the detection light Sn and the detection light Sm, reflected light from the detection light Sn and detection light Even if the reflected light due to Sm is received by the same light receiving unit, it can be separated by the difference in the light receiving timing.

  On the other hand, if the reflected light by the detection light Sn and the reflected light by the detection light Sm are not received by the same light receiving unit, the light emitting unit En and the light emitting unit Em can be turned on simultaneously. Of course, the light emitting section En and the light emitting section Em may be sequentially turned on / off.

  Here, the time required to turn on / off all of the light emitting units to be turned on once is called a “line cycle”.

  When the plurality of light emitting units are turned on at the same time, there is an advantage that the line cycle can be shortened as compared with the case where the plurality of light emitting units are sequentially turned on / off.

  Whether or not reflected light from a plurality of detection lights is received by the same light receiving unit depends on the positional relationship of the plurality of light emitting units to be lit, the diffuse reflection characteristic (angle distribution of reflected light) in the rectangular pattern, and the like. .

  For example, when the light emitting unit E6 and the light emitting unit E7 are determined as the light emitting units to be lit, the reflected light by the detection light S6 can be received by the light receiving unit D6 and the light receiving unit D7, and the reflected light by the detection light S7 is also The layout allows light reception by the light receiving part D6 and the light receiving part D7. Therefore, when the light emitting unit E6 and the light emitting unit E7 are turned on simultaneously, the reflected light received by the light receiving unit D6 and the light receiving unit D7 is separated into reflected light by the detection light S6 and reflected light by the detection light S7. Can not do it. In this case, it is necessary to turn on / off the light emitting unit E6 and the light emitting unit E7 sequentially (in this case, alternately).

  For example, when four light emitting units E5 to E8 are determined as the light emitting units to be turned on, the light emitting unit E5, the light emitting unit E6, the light emitting unit E7, the light emitting unit E8, the light emitting unit E5, the light emitting unit E6,. Turn on and off in order.

  The light reflected by the detection light S3 can be received by the light receiving parts D1 to D5, but cannot be received by the light receiving parts D6 to D11. In addition, the reflected light by the detection light S9 can be received by the light receiving portions D7 to D11, but cannot be received by the light receiving portions D1 to D6. Therefore, for example, as shown in FIG. 26, when the length of the rectangular pattern in the main direction is increased, the light emitting portions E3 and E9 can be turned on simultaneously.

  In the next step S407, the lighting mode is determined.

  As the lighting mode, there are a case where the light emitting unit is always lit and a case where pulse lighting is performed.

  For example, when only one of the light emitting units E6 is determined as the light emitting unit to be lit, the light emitting unit may be constantly lit or pulsed.

  On the other hand, for example, when the light emitting unit E6 and the light emitting unit E7 are determined as the light emitting units to be turned on, the light emitting unit E6 and the light emitting unit E7 need to be turned on and off sequentially (in this case, alternately). Yes, each light emitting unit is pulsed.

  For example, when two light emitting units E3 and E9 are determined as light emitting units to be lit, each light emitting unit may be constantly lit or pulse lit.

  As described above, when there are a plurality of light emitting units to be turned on, and sequentially turning them on and off, each light emitting unit is pulse-lit. On the other hand, in other cases, each light-emitting unit can select one of always-on and pulse-on.

  The constant lighting is advantageous in that the number of times the light emitting unit is turned on / off can be reduced and the driving circuit can be simplified. Pulse lighting can shorten the time during which light is emitted, suppress deterioration of the light emitting part, and extend the life. Moreover, there is an advantage that the temperature rise of the light emitting part can be suppressed.

  Note that all of the light emitting units to be lit, the lighting pattern, and the lighting mode may be selectable, or at least one of them may be determined in advance. In the former case, the drive circuit becomes complicated, but various operations can be performed on various image forming apparatuses. On the other hand, in the latter case, for example, if the lighting pattern and the lighting mode are determined in advance, the drive circuit becomes easy and the cost can be reduced. In this case, the light emitting section to be lit is practical because it can be appropriately selected according to the length of the rectangular pattern in the main direction and the performance of the image forming apparatus.

  In the next step S409, the light receiving unit from which the output is acquired is determined.

  As light receiving units for acquiring outputs, there are a case of acquiring outputs of some light receiving units and a case of acquiring outputs of all light receiving units.

  When acquiring the outputs of some of the light receiving units, it is possible to determine the light receiving unit from which the output is acquired based on the determination result of the light emitting units to be lit.

  For example, the case where only one of the light emitting units E6 is determined as the light emitting unit to be turned on will be described.

  FIG. 27A shows the output of each light receiving unit when the detection light S6 illuminates the transfer belt, and FIG. 27B shows when the detection light S6 illuminates the rectangular pattern p4. The output of each light receiving part is shown. In this case, since the outputs of the light receiving units D1 to D3 and D9 to D11 are 0, five light receiving units D4 to D8 are necessary.

  In addition, when the light emitting unit E6 and the light emitting unit E7 are determined as the light emitting units to be turned on, and these are sequentially turned on / off, the light receiving units required for the light emitting unit E6 are D4 to D8. The required light receiving parts for the light emitting part E7 are D5 to D9, and the required light receiving parts are D4 to D9 in total.

  In addition, when the light emitting unit E3 and the light emitting unit E9 are determined as the light emitting units to be turned on, and these are simultaneously turned on / off, or sequentially turned on / off, the light receiving unit required for the light emitting unit E3. Are D1 to D5, and the required light receiving parts for the light emitting part E9 are D7 to D11, and the required light receiving parts are 10 in addition to D6.

  In this way, by not obtaining unnecessary output of the light receiving unit, it is possible to reduce the amount of data and the amount of calculation at the time of density calculation.

  Of course, when all the light emitting units are determined as the light emitting units to be turned on, the outputs of all the light receiving units are acquired.

  In addition, you may acquire the output of all the light-receiving parts irrespective of the light emission part to light.

  In the next step S411, the timing for acquiring the output of the light receiving unit is determined.

  For example, a case will be described in which only one of the light emitting units E6 is determined as the light emitting unit to be lit and is always lit. In this case, there are five light receiving units D4 to D8 for acquiring outputs.

  FIG. 28 shows the lighting / extinguishing timing of the light emitting unit E6 and the sampling timing of the outputs of the light receiving units D4 to D8.

  Here, the light emitting unit E6 is turned on before the rectangular pattern p1 enters the illumination area of the detection light S6. In addition, this lighting timing can be prescribed | regulated, for example by the elapsed time after the rectangular pattern p1 was formed. And the output of each light-receiving part is sampled at the timing t0 when there is no rectangular pattern in the illumination area of the detection light S6. Next, after detecting that there is a rectangular pattern p1 in the illumination area of the detection light S6, the output of each light receiving unit is sampled at timing t1 when the output of each light receiving unit is stabilized. Subsequently, after detecting that there is a rectangular pattern p2 in the illumination area of the detection light S6, it is detected that the output of each light receiving unit is stable at timing t2, and that there is a rectangular pattern p3 in the illumination area of the detection light S6. Thereafter, at the timing t3 when the output of each light receiving unit is stabilized, and after detecting that the rectangular pattern p4 exists in the illumination area of the detection light S6, the output of each light receiving unit is output at the timing t4 when the output of each light receiving unit is stabilized Is sampled. Then, after the rectangular pattern p4 passes through the illumination area of the detection light S6, the light emitting unit E6 is turned off.

  At this time, as shown in FIG. 29 as an example, one rectangular pattern may be sampled a plurality of times. In this case, since a plurality of calculation results are obtained for each rectangular pattern, the density detection accuracy can be increased by averaging them.

  As an example, as illustrated in FIG. 30, the light emitting unit E <b> 6 may be pulse-lit in accordance with the timing at which each rectangular pattern passes through the illumination region of the detection light S <b> 6. In this case, as shown in FIG. 31 as an example, the lighting time may be shorter than the time during which the rectangular pattern passes through the illumination area of the detection light S6. Thereby, the temperature rise of a light emission part can further be suppressed. In this case, as shown in FIG. 32 as an example, sampling may be performed a plurality of times for one rectangular pattern.

  As an example, as shown in FIGS. 33 and 34, the light emitting unit may be turned on / off a plurality of times for one rectangular pattern. The sampling may be performed every time the light emitting unit is turned on / off.

  Note that the timing for acquiring the output of the light receiving unit can be set in various timings according to the determination content regarding the light emitting unit as long as the number of times of sampling for each rectangular pattern required by the image forming apparatus is set.

  Next, a case where two light emitting units E6 and E7 are determined as the light emitting units to be turned on will be described. In this case, there are six light receiving units D4 to D9 for acquiring outputs.

  FIG. 35 shows lighting / extinguishing timing of the light emitting unit E6, lighting / extinguishing timing of the light emitting unit E7, and sampling timing of outputs of the light receiving units D4 to D9.

  In this case, since four calculation results are obtained for each rectangular pattern, the density detection accuracy can be increased by averaging them.

  As an example, the line cycle may be shortened as shown in FIG. In this case, the number of times of sampling can be increased, and the accuracy of density detection can be further increased.

  By the way, for the sake of convenience, it is assumed here that it is determined that the rectangular pattern is located at the illumination position of the detection light S3. It is assumed that the light emitting unit to be lit is determined to be E3 only, the light emission mode is pulsed light emission, the light receiving units for obtaining outputs are D1 to D5, and the sampling is determined once per rectangular pattern.

  In the next step S413, the amount of light received by each light receiving unit (here, the light receiving units D1 to D5) when the detection light S3 illuminates the transfer belt is acquired. Note that the amount of light received by each light receiving unit can be relatively obtained from the signal level of the signal output from each light receiving unit.

  FIG. 37 shows received light amounts of the light receiving portions D1 to D5 when the detection light S3 illuminates the transfer belt. Here, the amount of light received by the light receiving unit D3 is “1”. D_ALL is the sum of the amounts of light received by the five light receiving portions D1 to D5.

  In the next step S415, the amount of light received by each light receiving unit (here, the light receiving units D1 to D5) when the detection light S3 illuminates the rectangular pattern is acquired.

  FIG. 38A shows the amounts of light received by the light receiving portions D1 to D5 when the detection light S3 illuminates the rectangular pattern p1 of the density detection pattern DP1.

  In FIG. 38A, the amount of light received by the light receiving unit D3 and D_ALL are reduced compared to FIG.

  FIG. 38B shows the amounts of light received by the light receiving portions D1 to D5 when the detection light S3 illuminates the rectangular pattern p2 of the density detection pattern DP1.

  In FIG. 38B, the amount of light received by the light receiving unit D3 and D_ALL are further reduced as compared to FIG.

  FIG. 39A shows the amounts of light received by the light receiving portions D1 to D5 when the detection light S3 illuminates the rectangular pattern p3 of the density detection pattern DP1.

  In FIG. 39A, the amount of light received by the light receiving unit D3 and D_ALL are further reduced compared to FIG. 38B.

  FIG. 39B shows the amount of light received by the light receiving portions D1 to D5 when the detection light S3 illuminates the rectangular pattern p4 of the density detection pattern DP1.

  In FIG. 39B, the amount of light received by the light receiving unit D3 and D_ALL are further reduced as compared to FIG.

  In the next step S417, it is determined whether or not the rectangular pattern position is correct.

  Here, it is determined whether or not the rectangular pattern position is correct from the result of obtaining the received light amount. This determination is not necessary when the rectangular pattern position is directly detected in advance, but it is desirable to perform this determination when the rectangular pattern position is an estimated position.

  If the received light amount distribution of the light receiving parts D1 to D5 when the illumination object is a rectangular pattern is the same as the received light amount distribution of the light receiving parts D1 to D5 when the illumination object is a transfer belt, it may be due to some sudden event. It is determined that there is no rectangular pattern at the estimated position.

  When the received light amount distribution of the light receiving parts D1 to D5 when the illumination object is a rectangular pattern is different from the previous received light amount distribution, the rectangular pattern is greatly shifted in the main direction from the estimated position, and the rectangular shape It is determined that only a part of the pattern is illuminated by the detection light.

  If it is determined that the rectangular pattern position is significantly different from the estimated position, the pattern position is directly detected, and the process returns to step S303. On the other hand, when it is determined that the rectangular pattern position is substantially the same as the estimated position, the process proceeds to step S425.

  In step S425, the toner density is calculated. In the following, the received light amount of each light receiving unit when the illumination target is the transfer belt 2040 is also referred to as “reference received light amount”, and the received light amount of each light receiving unit when the illumination target is a rectangular pattern is “detected”. It is also referred to as “light reception amount”.

  First, for each rectangular pattern, the detected received light amount of each light receiving unit is separated into a received light amount by diffuse reflected light and a received light amount by regular reflected light.

(1) Regarding the amount of light received by the light receiving unit D3 Since the light receiving unit D3 is a light receiving unit corresponding to the lighting light emitting unit E3, it is assumed that all the detected light received by this light receiving unit D3 is the amount of received light by regular reflection light. Generally, since the reflectance of the toner pattern is lower than the reflectance of the transfer belt 2040, the detected light reception amount of the light receiving portion D3 is smaller than 1 (reference light reception amount).

(2) About the light-receiving amount of the light-receiving part D1 and the light-receiving part D5 In both the light-receiving part D1 and the light-receiving part D5, the reference light-receiving amount was zero. Therefore, all of the detected light reception amounts of the light receiving part D1 and the light receiving part D5 are light reception amounts due to diffusely reflected light.

(3) Regarding the amount of light received by the light receiving portion D2 In the light receiving portion D2, the reference amount of received light is not zero. Therefore, the amount of received light detected by the light receiving unit D2 is the amount of light received by light in which regular reflection light and diffuse reflection light are mixed.

  Considering the specularly reflected light, the ratio of the detected amount of light received by the light receiving unit D2 and the detected amount of received light of the light receiving unit D3 should match the ratio of the reference received light amount of the light receiving unit D2 and the reference received light amount of the light receiving unit D3. is there.

  Accordingly, a value (ratio A) obtained by dividing the reference light reception amount of the light receiving unit D2 by the reference light reception amount of the light receiving unit D3 is obtained.

  Then, the ratio A is multiplied by the detected amount of light received by the light receiving unit D3. The value obtained here is the amount of light received by the specularly reflected light contained in the detected amount of light received by the light receiving unit D2 (referred to as the amount of received light a).

  Next, the received light amount a is subtracted from the detected received light amount of the light receiving unit D2. The value obtained here is the amount of light received by the diffusely reflected light included in the detected amount of light received by the light receiving unit D2.

(4) Regarding the amount of light received by the light receiving portion D4 In this light receiving portion, the reference amount of received light was not zero. Therefore, the detected amount of light received by the light receiving unit D4 is the amount of light received by light in which regular reflection light and diffuse reflection light are mixed.

  Considering the specularly reflected light, the ratio of the detected amount of light received by the light receiver D4 and the detected amount of light received by the light receiver D3 should match the ratio of the reference received light amount of the light receiver D4 and the reference received light amount of the light receiver D3. is there.

  Therefore, a value obtained by dividing the reference light reception amount of the light receiving unit D4 by the reference light reception amount of the light receiving unit D3 (determined as a ratio B) is obtained.

  Then, the ratio B is multiplied by the detected amount of light received by the light receiving unit D3. The value obtained here is the amount of light received by the specularly reflected light included in the detected amount of light received by the light receiving portion D4 (referred to as the amount of received light b).

  Next, the received light amount b is subtracted from the detected received light amount of the light receiving unit D4. The value obtained here is the amount of light received by the diffusely reflected light included in the detected amount of light received by the light receiving unit D4.

  In this way, the amount of received light detected by each light receiving unit can be separated into the amount of light received by specularly reflected light and the amount of light received by diffusely reflected light.

  When the illumination target of the light emitting unit E3 is the rectangular pattern p1 of the density detection pattern DP1, FIG. 40A shows the amount of light received by the specularly reflected light, and FIG. 40B shows the amount of light received by the diffusely reflected light. It is shown.

  When the illumination target of the light emitting unit E3 is the rectangular pattern p2 of the density detection pattern DP1, the received light amount by the regular reflection light is shown in FIG. 41A, and the received light amount by the diffuse reflection light is shown in FIG. It is shown.

  When the illumination target of the light emitting unit E3 is the rectangular pattern p3 of the density detection pattern DP1, the amount of light received by the specularly reflected light is shown in FIG. 42A, and the amount of light received by the diffusely reflected light is shown in FIG. It is shown.

  When the illumination target of the light emitting unit E3 is the rectangular pattern p4 of the density detection pattern DP1, the amount of light received by the specularly reflected light is shown in FIG. 43A, and the amount of light received by the diffusely reflected light is shown in FIG. It is shown.

  Next, for each rectangular pattern, the total amount of light received by regular reflected light (denoted as D1) and the total amount of light received by diffusely reflected light (denoted as D2) are obtained.

  The total value D1 of the amount of light received by the regular reflection light of each illumination object is shown in FIG. According to this, the total value D1 monotonously decreases as the toner density increases. This is because the higher the toner concentration, the more toner is adhered, and the regular reflection light is reduced. The toner concentration and the total value D1 are in a one-to-one correspondence. Therefore, the toner density of the illumination object can be known from the measured value of the total value D1.

  A total value D2 of the amount of light received by the diffusely reflected light of each illumination object is shown in FIG. According to this, the total value D2 is not a monotonous function with respect to the toner density. Intuitively, as the toner concentration is higher, more toner is attached, so that the light that is diffusely reflected increases, and the total value D2 tends to increase monotonously as the toner concentration increases. The amount of light received by diffuse reflected light is determined by subtracting the amount of light received by specularly reflected light from the amount of detected light received, and is therefore considered not to increase monotonously. Therefore, it is not impossible but not always easy to know the toner density of the illumination object from the measured value of the total value D2.

  The total value D2 / total value D1 of each illumination object is shown in FIG. According to this, the total value D2 / total value D1 monotonously increases as the toner density increases. Therefore, the toner density of the illumination object can be known from the total value D2 / total value D1.

  47 shows the relative value of the total value D1 when the value on the transfer belt 2040 is 1, and FIG. 48 shows the relative value of the total value D2 / total value D1 when the maximum value is 1. Has been.

  Next, the toner density is obtained for each rectangular pattern.

  Note that the relationship between the total value D1 and the toner density, or the relationship between (total value D2 / total value D1) and the toner density is obtained in advance and stored in the ROM as a density table.

  Therefore, the printer control device 2090 refers to the density table, and obtains the toner density based on the total value D1 or (total value D2 / total value D1) for each rectangular pattern. As a result, the density detection process ends, and the process proceeds to step S307.

  In this step 307, misalignment detection processing is performed. Here, the corresponding light emitting units in each reflective optical sensor are continuously lit. The detection light from the light emitting unit sequentially illuminates the line patterns LPK1 to LPY2 as the transfer belt 2040 rotates, that is, as time elapses (see FIG. 49).

  Then, the output signal of each light receiving unit is traced in time, and the time Tkm1 from when the line pattern LPK1 is detected until the line pattern LPM1 is detected, the line pattern LPK1 is detected, and then the line pattern LPC1 is detected. Time Tkc1 until detection and time Tky1 from detection of the line pattern LPK1 to detection of the line pattern LPY1 are obtained (see FIG. 50). Here, for the sake of clarity, it is assumed that the output signal of each light receiving unit is amplified and passes through a comparison circuit that compares with a predetermined reference value.

  Further, the time Tkm2 from the detection of the line pattern LPK2 to the detection of the line pattern LPM2, the time Tkc2 from the detection of the line pattern LPK2 to the detection of the line pattern LPC2, and the detection of the line pattern LPK2 Then, a time Tky2 from when the line pattern LPY2 is detected is obtained (see FIG. 50).

  Then, the time Tkc1, the time Tkm1, and the time Tky1 are respectively compared with a reference time obtained in advance, and the misregistration amounts of the cyan, magenta, and yellow toner images in the sub-direction with respect to the black toner image based on the time difference. ΔS1 is obtained (see FIG. 51A).

  Further, the time Tkc2, the time Tkm2, and the time Tky2 are respectively compared with a reference time obtained in advance, and from the time difference ΔT, using the following equation (5), cyan in the main direction for the black toner image, A positional deviation amount ΔS2 of each of the magenta and yellow toner images is obtained (see FIG. 51B). Here, V is a moving speed of the transfer belt 2040 in the sub-direction, and θ is an inclination angle (here, 45 °) with respect to the main direction of the line pattern.

  ΔS2 = V · ΔT · cot θ (5)

  In the next step S309, image process control is performed.

  First, a toner density deviation amount is obtained for each toner color from the toner density obtained by the density detection process. When the deviation amount of the toner density exceeds the allowable limit, control is performed so that the toner density becomes the target toner density or the deviation amount of the toner density falls within the allowable limit.

  For example, depending on the toner density shift amount, the power of the light beam emitted from the light source, the duty in the driving pulse supplied to the light source, the charging bias, and the developing bias (for example, JP 2009-216930 A) Adjust at least one of the above).

  Incidentally, image density control for maintaining image density includes development potential control and gradation control.

  In the development potential control, the development potential (development bias-solid exposure potential) is controlled in order to secure a desired image density (for example, solid density). That is, from the relationship between the toner density obtained from the density detection pattern and the development potential, development γ (the slope when the development potential is on the horizontal axis and the toner density is on the vertical axis) and the development start voltage Vk (the development potential is The x-intercept when the axis (x-axis) and the toner density are the ordinate (y-axis) are obtained. Then, using the following equation (6), the development potential necessary to ensure a desired image density is determined, and based on this, the image forming conditions (exposure power, charging bias, development bias) are determined. ing.

Necessary development potential [−kV] = desired image density (toner density) [mg / cm ² ] / development γ [(mg / cm ² ) / (− kV)] + development start voltage Vk [−kV] (6)

  If the toner charge amount and the development potential are constant, the development γ is almost maintained, but the change in the toner charge amount is unavoidable in an environment where there is a change in temperature and humidity, and the gradation of the halftone region Will change. Gradation control is performed to correct this. For gradation control, a density detection pattern equivalent to development potential control can be used.

  When the light source of the optical scanning device is a semiconductor laser (LD), it is possible to change the toner density for each rectangular pattern of the density detection pattern by fixing the LD power and changing the light emission duty.

  In the gradation control, the gradation correction LUT (look-up table) is appropriately changed so as to eliminate the deviation between the obtained gradation characteristics and the target gradation characteristics. Specifically, there are a method of rewriting to a new gradation correction LUT each time, and a method of selecting an optimum one from a plurality of gradation correction LUTs prepared in advance.

  Next, in the above-described misregistration detection process, if there is a misalignment in the sub-direction positional relationship with the black toner image, for example, the change of the image writing timing in the corresponding image forming station is set so that the misalignment amount becomes zero. To the scanning control device.

  Further, in the positional deviation detection process, if there is a deviation in the positional relationship in the main direction with respect to the black toner image, for example, the phase adjustment of the pixel clock in the corresponding image forming station is scanned so that the deviation amount becomes zero. Instruct the controller.

  Next, a description will be given of a relative positional error tolerance (hereinafter, abbreviated as “positional error tolerance” for convenience) with respect to the main direction of the toner pattern and the detection light spot.

  FIG. 52 shows a case where the number of detection light spots for detecting one toner patch is four. The length Lt in the main direction of the toner patch is 4 · Le + D, and the length B in the main direction of the light spot array including the four detection light spots is 3 · Le + D.

  In this case, when only the four light emitting units are turned on, as shown in FIG. 53, the allowable position error is ± Le / 2.

  FIG. 54 shows a case where the number of detection light spots for detecting one toner patch is one. The length Lt in the main direction of the toner patch is 4 · Le + D, and the length B in the main direction of the detection light spot is 3 · Le + D. In this case, as shown in FIG. 55, the positional error tolerance is ± Le / 2.

  That is, when the length Lt in the main direction of the toner patch is “4 · Le + D” and the length B in the main direction of the illumination area of the detection light is “3 · Le + D”, detection for detecting one toner patch is performed. Even if the number of working light spots is different, the positional error tolerance is the same.

  In FIG. 56, for the toner patch (Lt = 4 · Le + D), the number of detection light spots for detecting one toner patch is four, but the number of light emitting sections to be lit is five. The case is shown. In this case, the allowable position error is ± Le.

  Thus, by having more light emitting portions than the number of detection light spots for detecting one toner patch, the positional error tolerance is larger than that of a conventional reflective optical sensor using one detection light spot. can do. That is, it is understood that the condition of m + 1 ≦ N must be satisfied.

  Next, the length Lt in the main direction of the toner patch will be described.

  Here, it is assumed that the number m of detection light spots for detecting one toner patch is four and the number N of light emitting portions is five. That is, N = m + 1.

  In the case of m × Le + D <Lt, even if there is an error in the illumination position in the main direction of the detection light spot or a position error in the main direction of the toner patch, all the illumination areas of the four adjacent detection light spots are The toner patch contained in the toner patch can be detected by four detection light spots.

  In the case of m × Le + D = Lt, even if there is an error in the illumination position in the main direction of the detection light spot or a position error in the main direction of the toner patch, all illumination areas of the four adjacent detection light spots are The toner patch included in the toner patch can be detected by four detection light spots (see FIGS. 57A to 57C).

  In the case of Lt <m × Le + D, if the center of the toner patch is positioned in the center of the light spot row in the main direction, only the entire illumination area of the three detection light spots is included in the toner patch, and four detections are made. The toner patch cannot be detected by the light spot for use (see FIGS. 58A to 58C).

  Thus, in order to detect a toner patch using m detection light spots, the size Lt of the toner patch in the main direction needs to be “m × Le + D” or more.

  Further, as shown in FIG. 59, the number N of light emitting sections is 5, the number of detection lights is 5, the number of detection light spots used for detection is 4, and the size Lt of the toner patch in the main direction is When “4 × Le + D”, as shown in FIG. 60, the position error tolerance is ± Le.

  When a similar toner patch is detected using one detection light spot having the same illumination area in the main direction as shown in FIG. 61, the positional error tolerance is as shown in FIG. ± Ls / 2.

  That is, the conventional reflective optical system that detects with one detection light spot having the same illumination area in the main direction when the reflective optical sensor satisfying m + 1 ≦ N and m × Ls + D ≦ Lt is used. The position error tolerance is larger than that using a sensor.

  Next, a case where two or more toner patches arranged in the main direction are detected simultaneously will be described with reference to FIGS.

  Light emission necessary for detecting each of T toner patches arranged in the main direction using m detection light spots from a reflective optical sensor having at least three light emitting portions and light receiving portions. Since the number N of light-receiving portions or light-receiving portions is T times that when one toner patch is detected, it can be seen that T × (m + 1) ≦ N.

  The length Lt in the main direction of the toner patch is not different from that in the case where there is one toner patch in the main direction, and may be m × Ls + D ≦ Lt.

  Here, the number T of toner patches arranged in the main direction is 2, and the length Lt in the main direction of the toner patches is “4Le + D”.

  In FIGS. 64 to 72, T × (m + 1) = 10 and N = 12. That is, T × (m + 1) <N.

  As shown in FIG. 65, when the gap between the two toner patches in the main direction is “P + 2δ”, the allowable position error is ± (Le−δ) as shown in FIG.

  As shown in FIG. 67, when the gap between the two toner patches in the main direction is “P = ((N−1) × Le + DT × (m × Le + D)) / (T−1)” The allowable error amount is ± Ls as shown in FIG.

  As shown in FIG. 69, when the gap between the two toner patches in the main direction is “P-2δ”, the allowable position error is ± (Le + δ) as shown in FIG.

  As shown in FIG. 71, when the gap between the two toner patches in the main direction is “P + Le / (T−1)”, the positional error tolerance is ± Ls / 2 as shown in FIG. Become. In this case, a conventional reflective optical sensor that detects each toner patch with a single detection light spot having the same illumination area in the main direction is used, and each detection light spot is in the center of the toner patch in the main direction. The positional error tolerance is equal to the case where they are arranged so as to be positioned (see FIG. 64).

  Therefore, when the gaps PI of the T toner patches arranged in the main direction satisfy the relationship PI <P + Ls / (T−1), each toner patch is independently detected by one detection light spot. Rather than using T conventional reflective optical sensors to detect, it is better to use one reflective optical sensor in which the number N of light emitting units and light receiving units satisfies the relationship of T × (m + 1) ≦ N. The allowable amount can be increased.

  When two or more toner patches arranged in the main direction are detected at the same time, as shown in FIGS. 73 to 76, the length Lt in the main direction of the toner patch is expressed as “((N−1) × Even if it is larger than “Le + D) / T”, the allowable position error does not increase. Therefore, the length Lt in the main direction of the toner patch only needs to satisfy the relationship of “m × Le + D ≦ Lt ≦ ((N−1) × Le + D) / T”.

  Further, when T conventional reflective optical sensors that individually illuminate one detection light spot are used for each toner patch, the T reflective optical sensors are detected in the main direction. The toner patch must be set at a position facing the center of the toner patch, and adjustment is difficult. Moreover, it is difficult to install many reflective optical sensors in a narrow area. However, when one reflection type optical sensor of the present embodiment in which the number N of light emitting units and light receiving units is T × (m + 1) ≦ N is used, adjustment is performed only for the one reflection type optical sensor. It is good, easy to adjust, and can be installed in a small area.

  As is clear from the above description, in the color printer 2000 according to the present embodiment, the reflective optical sensor 2245b constitutes the reflective optical sensor in the image forming apparatus of the present invention.

  Further, the printer control device 2090 constitutes a processing device in the image forming apparatus of the present invention.

  As described above, according to the color printer 2000 according to the present embodiment, the four photosensitive drums (2030a, 2030b, 2030c, 2030d) and the luminous flux modulated according to the image information with respect to each photosensitive drum. From the optical scanning device 2010 that scans in the main scanning direction and forms a latent image, four developing rollers (2033a, 2033b, 2033c, and 2033d) that attach toner to the latent image to generate a toner image, and each photosensitive drum A transfer belt 2040 to which the toner image is transferred, a toner pattern detector 2245 for detecting the toner pattern transferred to the transfer belt 2040, a printer control device 2090 for overall control, and the like are provided.

  The toner pattern as the test pattern includes four density detection patterns (DP1 to DP4). The density detection pattern DP1 and the density detection pattern DP2 are formed at different positions with respect to the main direction. The density detection pattern DP3 and the density detection pattern DP4 are also formed at different positions with respect to the main direction.

  The toner pattern detector 2245 has a reflective optical sensor 2245b facing the four density detection patterns.

  The reflective optical sensor 2245b includes an illumination system including 11 light emitting units (E1 to E11) arranged at equal intervals Le along the main direction, and illumination optics including 11 illumination microlenses (LE1 to LE11). A light receiving optical system including 11 light receiving microlenses (LD1 to LD11), a light receiving system including 11 light receiving portions (D1 to D11), and the like.

  The number m of detection light spots that illuminate one rectangular pattern, the size D of the detection light spot in the main direction, the number T of rectangular patterns arranged at different positions with respect to the main direction, and adjacent in the main direction T × (m + 1) ≦ N, m × Le + D ≦ Lt ≦ ((), using the gap PI between the two rectangular patterns to be performed, the length Lt of one rectangular pattern in the main direction, and the number N of light emitting portions in the irradiation system. N-1) * Le + D) / T, PI <((N-1) * Le + DT- (m * Le + D)) / (T-1) + Le / (T-1) are satisfied. .

  In this case, the allowable position error is larger than in the conventional case, and as a result, the color printer 2000 can improve the work efficiency without degrading the image quality.

  In the above embodiment, the case where eleven illumination microlenses (LE1 to LE11) and eleven light receiving microlenses (LD1 to LD11) are integrated has been described. However, the present invention is not limited to this. is not.

  Moreover, although the said embodiment demonstrated the case where one reflective optical sensor had 11 light emission parts, it is not limited to this.

  Moreover, although the case where all the reflective optical sensors have the same number of light emitting units has been described in the above embodiment, the present invention is not limited to this.

  In the above embodiment, the case where the surface of the transfer belt is smooth has been described. However, the present invention is not limited to this, and the surface of the transfer belt may not be smooth. Even in this case, the positional deviation can be detected in the same manner as in the above embodiment. Further, a part of the surface of the transfer belt may be smooth.

  In the above-described embodiment, a processing device may be provided in the reflective optical sensor, and the processing device may perform at least a part of the processing in the printer control device 2090.

  In the above embodiment, the scanning control device may perform at least a part of the processing in the printer control device 2090.

  Moreover, although the said embodiment demonstrated the case where eight linear patterns were arrange | positioned in a line along a subdirection in the pattern PP for position shift detection, it is not limited to this. For example, in the positional deviation detection pattern PP, a plurality of pattern rows arranged along the sub direction may be arranged in the main direction.

  Further, in the above embodiment, as shown in FIG. 77 as an example, a position recognition pattern GP may be formed in front of the density detection pattern. As the position recognition pattern GP, for example, a solid magenta patch having a rectangular shape with a length of 0.5 mm in the main direction and a length of 1.0 mm in the sub direction can be used. This is smaller than the length in the main direction of the density detection pattern.

  Prior to the density detection pattern, the position recognition pattern GP is formed on the surface of the transfer belt, moves in the sub-direction, and approaches the illumination area of the detection light from the reflective optical sensor 2245b.

  Since the timing at which the position recognition pattern GP is formed is known, the printer control device 2090 starts turning on and off all the light emitting units Ei (i = 1 to 11) sequentially at a predetermined timing. In this case, one line or several lines are sufficient for the sequential lighting and extinguishing. The output signal of the light receiving unit may be acquired only for the light receiving unit Di in accordance with the lighting timing of the light emitting unit Ei. Since the light emitting portion Ei is turned on and the detection light Si illuminates the transfer belt, the presence or absence of the position recognition pattern GP at the detection light spot position can be determined from the output signal of the light receiving portion Di. This is because if the position recognition pattern GP is present, the light receiving unit output is reduced as compared with the case where there is no pattern GP.

  Accordingly, at least one line is turned on / off with respect to the position recognition pattern GP, and the position recognition pattern GP is present at the position corresponding to which light emitting section from the obtained output signal of each light receiving section. .

  FIG. 78 shows an output signal of each light receiving unit when the position recognition pattern GP reaches the detection light illumination region and all the light emitting units are turned on / off for one line. The light receiving part D1 and the light receiving parts D5 to D11 receive regular reflection light from the transfer belt, and the output level is high. On the other hand, in the light receiving parts D2 and D4, the output level is slightly lower, and in the light receiving part D3, the output level is greatly reduced. From this, it can be seen that the position recognition pattern GP is just at the position facing the light emitting portion E3 (see FIG. 79).

  Further, the light emitting part pitch is 0.4 mm, the length in the main direction of the position recognition pattern GP is 0.5 mm, and the both ends of the position recognition pattern GP are slightly different from the output levels of the light receiving parts D2 and D4. It can be seen that the detection lights S2 and S4 are illuminated. Thus, it can be seen that the position recognition pattern GP is present at a position corresponding to the light receiving unit having the lowest output level of the light receiving unit.

  If the density detection pattern is arranged at the same center position in the main direction behind the position recognition pattern GP, the position of the density detection pattern in the main direction can be estimated with high accuracy.

  The color of the position recognition pattern GP is not limited and may be black, cyan, or yellow. Further, the position recognition pattern GP need not be a solid patch, and may be a halftone. However, from the viewpoint of increasing the decrease in the output level of the light emitting section, it is preferable that the density is high for black or color.

  Further, the size of the position recognition pattern GP is not limited to the above-described size, and it is only necessary to know the position in the main direction. Therefore, in order to reduce toner consumption, the size in the main direction of the density detection pattern can be reduced. Desirably smaller than size.

  Furthermore, if a decrease in the output level of the light receiving portion can be recognized only by illuminating a part of the position recognition pattern GP, the size of the position recognition pattern GP in the main direction can be made smaller than the light emitting portion pitch. good.

  In the above embodiment, when the position of the rectangular pattern in the main direction is recognized (step S401), the position of the rectangular pattern in the main direction may be directly detected.

  Since the timing at which the density detection pattern is formed is known, the printer control device 2090 starts turning on and off all the light emitting units Ei (i = 1 to 11) sequentially at a predetermined timing. In this case, one line or several lines are sufficient for the sequential lighting and extinguishing. The output signal of the light receiving unit may be acquired only for the light receiving unit Di in accordance with the lighting timing of the light emitting unit Ei. Since the light emitting portion Ei is turned on and the detection light Si illuminates the transfer belt, the presence or absence of a rectangular pattern at the detection light spot position can be determined from the output signal of the light receiving portion Di. This is because, if there is a rectangular pattern, the light receiving unit output is lower than when there is no rectangular pattern.

  As an example, FIG. 80 shows an output signal of each light receiving unit when the leading rectangular pattern reaches the illumination region of the detection light and all the light emitting units are turned on / off for one line. The light receiving part D1 and the light receiving parts D5 to D11 receive regular reflection light from the transfer belt, and the output level is high. On the other hand, the light receiving parts D2 and D4 have lower output levels, and the light receiving part D3 has a greatly reduced output level. From this, it can be seen that the rectangular pattern is just at the position facing the light emitting portion E3.

  Moreover, the light beams for detection S2 and S4 are irradiated to most of the rectangular pattern from the fact that the pitch of the light emitting portions is 0.4 mm, the size of the rectangular pattern in the main direction is 1 mm and the output levels of the light receiving portions D2 and D4 (See FIG. 81). Thus, it can be seen that there is a rectangular pattern at a position facing the light receiving unit having the lowest output level.

  This rectangular pattern is a test pattern itself, and a plurality of rectangular patterns are connected to the rectangular pattern. That is, it can be determined without estimating the position in the main direction of the density detection pattern.

  If there is a possibility of affecting the subsequent processing in terms of time, the time for detecting the position in the main direction of the rectangular pattern by increasing the length in the sub direction of only the leading rectangular pattern is increased. May be newly secured.

  Moreover, although the said embodiment demonstrated the case where the length Lt of the main direction of a rectangular pattern was 1.0 mm, it is not limited to this. For example, Lt may be 1.2 mm. In this case, Lt is equal to (D + 2 × Le). As shown in FIG. 82A, when the center position of the rectangular pattern is equal to the position of the light emitting unit E6 in the main direction, the rectangular pattern is illuminated with the three detection lights S5 to S7 without excess or deficiency. Therefore, the toner density can be calculated for each detection light. As shown in FIG. 82B, when the center position of the rectangular pattern is equal to the center position of the light emitting units E6 and E7 with respect to the main direction, the rectangular pattern is illuminated with two detection lights S6 and S7. Therefore, the toner density can be calculated for each detection light.

  In this way, the size of the rectangular pattern in the main direction is equal to or greater than the sum of the size D of the detection light spot in the main direction and twice the light-emitting portion pitch Le in the main direction, thereby at least two detections. It is possible to illuminate with the use light, and by performing the averaging process using a plurality of toner concentrations calculated for each detection light, the toner concentration averaged in the main direction can be obtained. Thereby, detection accuracy can be improved. If three toner densities can be calculated, an intermediate value that excludes the maximum and minimum values is used, and if four or more, the remaining average value excluding the maximum and minimum values is used. Thus, the detection accuracy can be improved by removing abnormal values and the like.

  Further, as shown in FIGS. 83A to 83C, the five detection lights may illuminate one rectangular pattern. In this case, the average value of the five toner densities calculated for each detection light may be employed, or the remaining average value excluding the maximum and minimum values may be employed. Thereby, detection accuracy can be improved.

  At this time, the light emitting units E4 and E11 are turned on / off at the same time, and then the light emitting units E5 and E12, the light emitting units E6 and E13, the light emitting units E7 and E14, and the light emitting units E8 and E15 are turned on and off at the same time. Also good.

  Further, the light emitting units E4, E5, E6, E7, E8 and the light emitting units E11, E12, E13, E14, E15 may be turned on / off simultaneously.

  Further, the light emitting units E4, E5, E6, E7, E8 and the light emitting units E11, E12, E13, E14, E15 may be sequentially turned on / off one by one.

  Further, the light emitting units E1 to E18 may be turned on / off at the same time.

  Further, the light emitting units E1 to E18 may be sequentially turned on / off one by one.

  Further, the arrangement of the 16 rectangular patterns in the above embodiment is an example, and the present invention is not limited to this (see FIGS. 84 and 85).

  Moreover, although the said embodiment demonstrated the case where 16 rectangular patterns were arranged in 2 rows in a subdirection, it is not limited to this. For example, 16 rectangular patterns may be arranged in four rows in the sub direction.

  In the above-described embodiment, the case where four rectangular patterns having different toner densities for one color are formed as the density detection patterns has been described. However, the present invention is not limited to this. For example, five rectangular patterns having different toner concentrations for one color may be formed.

  Moreover, although the said embodiment demonstrated the case where the density | concentration detection pattern was formed in the position Y2, it is not limited to this. For example, the density detection pattern may be formed at the position Y1 or the position Y3.

  Moreover, although the said embodiment demonstrated the case where the density | concentration detection pattern was formed only in position Y2, it is not limited to this. For example, the density detection pattern may be further formed at the position Y1 or the position Y3.

  In the above embodiment, the case where four color toners are used has been described. However, the present invention is not limited to this. For example, a case where toner of 5 colors or 6 colors is used may be used.

  In the above embodiment, the toner pattern detector 2245 detects the toner pattern on the transfer belt 2040. However, the present invention is not limited to this, and the toner pattern on the surface of the photosensitive drum is detected. Also good. Note that the surface of the photosensitive drum is close to a regular reflector like the transfer belt 2040.

  In the above embodiment, the toner pattern may be transferred to a recording sheet, and the toner pattern on the recording sheet may be detected by the toner pattern detector 2245.

  In the above embodiment, the case of the color printer 2000 has been described as the image forming apparatus. However, the present invention is not limited to this. It may be.

  As described above, according to the image forming apparatus of the present invention, it is suitable for improving the working efficiency without deteriorating the image quality.

  2000 ... Color printer (image forming apparatus), 2010 ... Optical scanning apparatus (test pattern creation apparatus), 2030a to 2030d ... Photosensitive drum, 2040 ... Transfer belt (moving body), 2090 ... Printer control apparatus (processing apparatus), 2245 ... Toner pattern detectors (positional deviation detection sensors), 2245a, 2245b, 2245c ... Reflective optical sensors, D1 to D11 ... Light receiving parts, E1 to E11 ... Light emitting parts, LD1 to LD11 ... Light receiving microlenses, LE1 to LE11 ... Micro lens for illumination, LPK1, LPK2, LPY1, LPY2, LPC1, LPC2, LPM1, LPM2,... Linear pattern.

JP-A-1-35466 JP 2004-21164 A JP 2002-72612 A Japanese Patent No. 4154272 Japanese Patent No.4110027 JP 2009-258601 A

Claims (11)

In an image forming apparatus that forms an image on a moving body that moves in a first direction,
A test pattern creation device that creates a test pattern including a plurality of patches whose positions are different from each other with respect to a second direction orthogonal to the first direction on the moving body;
A light receiving system including an irradiation system including at least three light emitting units arranged at equal intervals Le with respect to the second direction, and at least three light receiving units configured to receive light emitted from the irradiation system and reflected by the test pattern. A reflective optical sensor comprising a system;
A processing device for determining at least one of toner density and positional deviation of the plurality of patches based on an output signal of a light receiving system of the reflective optical sensor;
The number m of light spots that illuminate one of the plurality of patches, the size D of the light spot in the second direction, and the number T of the plurality of patches arranged at different positions with respect to the second direction. , Using a gap PI between two patches adjacent to each other in the second direction, a length Lt of one patch in the second direction, and the number N of light emitting units in the irradiation system,
T × (m + 1) ≦ N,
m × Le + D ≦ Lt ≦ ((N−1) × Le + D) / T,
PI <((N−1) × Le + DT × (m × Le + D)) / (T−1) + Le / (T−1),
An image forming apparatus characterized in that: The number of light spots that illuminate one of the plurality of patches is plural,
The image forming apparatus according to claim 1, wherein the processing device uses an average value of a plurality of calculation results obtained for each light spot as a detection result. The number of light spots that illuminate one of the plurality of patches is plural,
The image forming apparatus according to claim 1, wherein the processing apparatus uses a median value of a plurality of calculation results obtained for each light spot as a detection result.   4. The image forming apparatus according to claim 1, wherein the plurality of patches whose positions are different from each other in the second direction are different from each other in at least one of color, density, and shape. .   The image forming apparatus according to claim 1, wherein the plurality of patches whose positions are different from each other in the second direction have the same color, density, and shape. The number of light spots that illuminate one of the plurality of patches is plural,
6. The processing device according to claim 1, wherein the plurality of light emitting units corresponding to the plurality of light spots that illuminate the one patch are sequentially turned on and off one by one. Image forming apparatus. The number of light spots that illuminate one of the plurality of patches is plural,
6. The image forming apparatus according to claim 1, wherein the processing device simultaneously turns on / off a plurality of light emitting units corresponding to a plurality of light spots that illuminate the one patch. .   The processing device is characterized by simultaneously turning on / off a light emitting unit that illuminates one patch and a light emitting unit that illuminates another patch for a plurality of patches whose positions are different from each other with respect to the second direction. The image forming apparatus according to claim 6 or 7.   The image forming apparatus according to claim 1, wherein the processing apparatus turns on and off all the light emitting units in the irradiation system simultaneously.   The image forming apparatus according to claim 1, wherein the processing device turns on and off all the light emitting units in the irradiation system one by one in order.   The image forming apparatus according to claim 1, wherein the moving body is an intermediate transfer belt.