JP2014013343A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably forming high-quality images.SOLUTION: An image forming apparatus comprises a reflective optical sensor having an illumination system including 11 light-emitting parts, an illumination optical system including 11 microlenses for illumination, a light-receiving optical system including 11 microlenses for receiving light, and a light-receiving system including 11 light-receiving parts. A printer control device, in detecting toner density of a plurality of rectangular patterns, for a rectangular pattern with toner density predicted to be lower than 0.25(mg/cm), calculates the toner density from M1 (relative value), and for a rectangular pattern with toner density predicted to be higher than 0.25(mg/cm), calculates the toner density from M2/M1 (relative value).

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” for convenience), and toner is attached to the electrostatic latent image. Thus, so-called development is performed to obtain a “toner image”.

  In the image forming apparatus, the following image density control is performed so that a stable image density is always obtained.

  (1) A test pattern including a plurality of toner patches for toner density detection that are formed under different image forming conditions (exposure power, charging bias, developing bias, etc.) so that the toner density is different on the photosensitive drum. Form. This test pattern is developed into a toner image and is primarily transferred onto the intermediate transfer belt.

  (2) The reflected light from each toner patch in the test pattern on the intermediate transfer belt is received by a reflective optical sensor that is an optical detection means, and the output of the reflective optical sensor and a predetermined calculation algorithm are obtained. And calculate the toner density of each toner patch.

  (3) From the relationship between the toner density of each toner 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 (x intercept when developing potential is on the horizontal axis (x axis) and toner density is on the vertical axis) is obtained.

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

  Various reflective optical sensors have been proposed (see, for example, Patent Documents 1 to 5). 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 a 2LED-1PD type composed of two light emitting portions and one light receiving portion. There is a reflection type optical sensor.

  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 intermediate transfer belt. On the other hand, in the reflection type optical sensor of 2LED-1PD type, the light emitted to the test pattern from the two light emitting portions is divided into two light spots at almost the same place on the intermediate transfer belt with a time difference. Form. In any of the reflective optical sensors, the size of the light spot (spot diameter) was about 2 to 3 mm. 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”.

  The test pattern is formed on the intermediate transfer belt so as to overlap the light spot formation position with respect to the main direction, and moves in the sub direction along with the movement of the intermediate transfer belt.

  At this time, the formation position error in the main direction of the light spot, the test pattern formation position error, and the intermediate transfer belt Even if there is a position error in the main direction of the test pattern due to meandering or the like, the light spot and the test pattern must be overlapped.

  For example, the test pattern includes a plurality of toner patches arranged in a line along the sub direction, and each toner patch has a length in the main direction of about 10 mm and a length in the sub direction of about 15 mm.

  The toner used to form the test pattern is a so-called “non-contributing toner” that does not contribute to the original image formation.

  Japanese Patent Laid-Open No. 2004-260688 has an object of reducing non-contributing toner, and 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) A reflective optical sensor having a light receiving means in which one light receiving portion is arranged in one direction corresponding to an irradiation means is disclosed.

  The demand for image quality in image forming apparatuses is increasing year by year. However, in the image forming apparatus including the reflective optical sensor disclosed in Patent Document 6, it is difficult to obtain a required level of image quality.

  The present invention relates to an image forming apparatus that forms an image on a moving body using toner, a pattern creating apparatus that creates a pattern for toner density detection on the moving body, and the pattern created on the moving body. A reflection type optical sensor that irradiates light and receives the light reflected by the pattern, and the light reflected by the pattern based on the output signal of the reflection type optical sensor and the specular reflection light component and the diffuse reflection light A processing unit that calculates the toner density of the pattern based on a predetermined one of the light amount of the regular reflection light component and the light amount of the diffuse reflection light component according to an expected toner concentration of the pattern And an image forming apparatus.

  According to the image forming apparatus of the present invention, a high quality image can be stably formed.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. It is a figure for demonstrating a printer control apparatus. It is a figure for demonstrating an image forming unit. It is FIG. (1) for demonstrating the structure of an optical scanning device. It is FIG. (2) for demonstrating the structure of an optical scanning device. FIG. 6 is a third diagram for explaining the configuration of the optical scanning device; FIG. 4 is a diagram (part 4) for explaining the configuration of the optical scanning device; It is FIG. (1) for demonstrating the arrangement position of a reflection type optical sensor. It is FIG. (2) 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. 4 is a diagram for explaining a toner pattern formed on an intermediate transfer belt. It is a figure for demonstrating the five rectangular patterns in each density | concentration detection pattern. FIG. 10 is a diagram for explaining a case where the gradation of toner density is varied in an analog manner. FIG. 19A and FIG. 19B are diagrams for explaining a case where the gradation of the toner density is digitally changed. FIGS. 20A to 20C are diagrams for explaining toner adhesion states in the rectangular patterns p1, p3, and p5 when the toner density gradations are digitally different from each other. It is a figure for demonstrating the positional relationship of DP pattern row | line | column and a light emission part. It is the figure which expanded a part of FIG. It is a figure for demonstrating the pattern for position shift detection. It is a figure for demonstrating the positional relationship of the pattern for position shift detection, and DP pattern row | line | column. It is a figure for demonstrating the positional relationship of the pattern for position shift detection, and a light emission part. 6 is a flowchart for explaining image process control performed by the printer control apparatus. It is a figure for demonstrating a dummy pattern. It is a figure for demonstrating the locus | trajectory of the detection light S6. It is FIG. (1) for demonstrating the method to obtain | require the center position regarding the main direction of a dummy pattern. It is FIG. (2) for demonstrating the method of calculating | requiring the center position regarding the main direction of a dummy pattern. It is FIG. (3) for demonstrating the method to obtain | require the center position regarding the main direction of a dummy pattern. FIG. 32 is a diagram for explaining the center position of the dummy pattern DKDP in the main direction determined from FIGS. 29 to 31. It is FIG. (4) for demonstrating the method to obtain | require the center position regarding the main direction of a dummy pattern. It is FIG. (5) for demonstrating the method of calculating | requiring the center position regarding the main direction of a dummy pattern. It is FIG. (6) for demonstrating the method to obtain | require the center position regarding the main direction of a dummy pattern. It is FIG. (7) for demonstrating the method of calculating | requiring the center position regarding the main direction of a dummy pattern. It is a figure for demonstrating the center position regarding the main direction of the dummy pattern judged from FIGS. FIG. 38A is a diagram for explaining the output distribution of the light receiving system when the light emitting unit E6 is turned on and the irradiation target is the intermediate transfer belt, and FIG. 38B shows the dummy pattern in FIG. It is a figure for demonstrating the output distribution of the light-receiving system when the light emission part E6 is lighted and an irradiation target object is a dummy pattern. It is a figure for demonstrating the example 1 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 2 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 3 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 4 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 5 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 6 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 7 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 8 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 9 of the sampling timing with respect to DP pattern row | line | column. It is a figure for demonstrating the example 1 of the sampling timing with respect to the pattern for position shift detection. It is a figure for demonstrating the example 2 of the sampling timing with respect to the pattern for position shift detection. FIG. 6 is a diagram for describing toner pattern formation timing. It is a figure for demonstrating the output distribution of each light-receiving part when the light emission part E6 is turned on and an irradiation target object is an intermediate transfer belt. It is a figure for demonstrating the light reception amount distribution of each light-receiving part when the light emission part E6 is turned on and an irradiation target object is the rectangular pattern p1 of density detection pattern DP1. It is a figure for demonstrating the light reception amount distribution of each light-receiving part when the light emission part E6 is turned on and an irradiation target object is the rectangular pattern p2 of density detection pattern DP1. It is a figure for demonstrating the light-receiving amount distribution of each light-receiving part when the light emission part E6 is turned on and an irradiation target object is the rectangular pattern p3 of density detection pattern DP1. It is a figure for demonstrating the light reception amount distribution of each light-receiving part when the light emission part E6 is turned on and an irradiation target object is the rectangular pattern p4 of density detection pattern DP1. It is a figure for demonstrating the light reception amount distribution of each light-receiving part when the light emission part E6 is turned on and an irradiation target object is the rectangular pattern p5 of density detection pattern DP1. FIG. 57 (A) and FIG. 57 (B) are diagrams for explaining reflected light, respectively. It is a figure for demonstrating the regular reflection light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p1 of density detection pattern DP1. It is a figure for demonstrating the diffuse reflected light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p1 of density detection pattern DP1. It is a figure for demonstrating the regular reflection light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p2 of density detection pattern DP1. It is a figure for demonstrating the diffuse reflected light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p2 of density detection pattern DP1. It is a figure for demonstrating the regular reflection light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p3 of density detection pattern DP1. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p3 of density detection pattern DP1. It is a figure for demonstrating the regular reflection light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p4 of density detection pattern DP1. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p4 of density detection pattern DP1. It is a figure for demonstrating the regular reflection light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p5 of density detection pattern DP1. It is a figure for demonstrating the diffuse reflected light component in the light reception amount of each light-receiving part (D1-D5) when an irradiation target object is the rectangular pattern p5 of density detection pattern DP1. It is a figure for demonstrating the relationship between M1 and an irradiation target object. It is a figure for demonstrating the relationship between M1 (relative value) and an irradiation target object. It is a figure for demonstrating the relationship between M2 and an irradiation target object. It is a figure for demonstrating the relationship between M2 / M1 and an irradiation target object. It is a figure for demonstrating the relationship between M2 / M1 (relative value) and an irradiation target object. It is a figure for demonstrating the relationship between M1 (relative value) and a toner density. FIG. 6 is a diagram for explaining a relationship between M2 / M1 (relative value) and toner density. FIG. 6 is a diagram for explaining a relationship between a change rate of M1 (relative value) and a toner density. FIG. 6 is a diagram for explaining a relationship between a change rate of M2 / M1 (relative value) and a toner density. FIG. 6 is a diagram in which the relationship between the change rate of M1 (relative value) and toner density and the relationship between the change rate of M2 / M1 (relative value) and toner concentration are superimposed. It is a figure for demonstrating calculation of the amount of position shift. FIG. 79A and FIG. 79B are diagrams for explaining the amount of misalignment of the magenta line pattern, respectively. FIG. 10 is a diagram for explaining a toner pattern modification example 1; FIG. 10 is a diagram for explaining a second modification of the toner pattern. FIG. 10 is a diagram for explaining a positional relationship between a toner pattern and a light emitting unit according to Modification 2. FIG. 10 is a diagram for explaining a third modification of the toner pattern. It is a figure for demonstrating the modification of a reflection type optical sensor. It is a figure for demonstrating two reflection type optical sensors arrange | positioned outside an effective image area | region. FIG. 6 is a diagram for explaining a toner pattern formed outside an effective image area.

  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 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 image forming units (2034a, 2034b, 2034c, 2034d), an intermediate transfer belt 2040, a transfer roller 2042, a fixing roller 2050, a paper feed roller 2054, a paper discharge roller 2058, a paper feed tray 2060, A paper discharge tray 2070, a communication control device 2080, a reflection-type optical sensor 2245, a temperature / humidity sensor (not shown), a printer control device 2090 that controls the above-described units collectively, and the like are provided.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer (PC)) via a network or the like and an information device (for example, a facsimile device (FAX)) 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 And an A / D conversion circuit for converting the data into digital data (see FIG. 2). 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 and the image forming unit 2034a are used as a set, and constitute an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image.

  The photosensitive drum 2030b and the image forming unit 2034b are used as a set, and constitute an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image.

  The photosensitive drum 2030c and the image forming unit 2034c are used as a set, and constitute an image forming station (hereinafter also referred to as “C station” for convenience) for forming a cyan image.

  The photosensitive drum 2030d and the image forming unit 2034d are used as a set, and constitute an image forming station (hereinafter also referred to as “Y station” for convenience) that forms a yellow image.

  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).

  As shown in FIG. 3 as an example, each image forming unit includes a charging unit, a developing unit, a primary transfer unit, and a photoconductor cleaning unit provided around the corresponding photoconductor drum.

  Here, a contact charging type charging roller is used as the charging unit. The charging roller uniformly charges the surface of the photosensitive drum by applying a voltage in contact with the photosensitive drum. As the charging unit, a non-contact charging type such as a non-contact scorotron charger can also be used.

  In the developing unit, a two-component developer composed of a magnetic carrier and a nonmagnetic toner is used. The developing unit can be roughly divided into a stirring unit and a developing unit provided in the developing case.

  In the agitation unit, the two-component developer is conveyed while being agitated and supplied onto a developing sleeve as a developer carrying member. The stirring unit has two parallel screws, and a partition plate is provided between the two screws to partition the two screws so as to communicate with each other. Further, a TC sensor for detecting the toner concentration of the developer in the developing unit is attached to the developing case. Since the carrier of the two-component developer is a magnetic material, and the toner is a non-magnetic material, a TC sensor of the magnetic permeability type is used, and the toner concentration in the developing unit is the magnetic permeability of the developer, that is, the unit. Appears in the magnetic resistance of the developer per volume. Note that a one-component developer can also be used as the developer.

  In the developing unit, toner in the developer adhering to the developing sleeve is transferred to the photosensitive drum. The developing unit includes a developing sleeve that faces the photosensitive drum through the opening of the developing case, and a doctor blade that is disposed so that the tip approaches the developing sleeve. A magnet (not shown) is fixedly arranged in the developing sleeve.

  Therefore, in the developing unit, the developer is conveyed and circulated while being stirred by two screws, and is supplied to the developing sleeve. The developer supplied to the developing sleeve is pumped up and held by a magnet. The developer pumped up by the developing sleeve is conveyed along with the rotation of the developing sleeve and is regulated to an appropriate amount by the doctor blade. Excess developer is returned to the stirring section.

  The developer transported to the developing area facing the photosensitive drum in this manner is brought into a spiked state by the magnet and forms a magnetic brush. In the development region, a development electric field that moves the toner in the developer to the electrostatic latent image portion on the photosensitive drum is formed by the development bias applied to the development sleeve. As a result, the toner in the developer is transferred to the electrostatic latent image portion on the photosensitive drum, and the electrostatic latent image on the photosensitive drum is visualized.

  The developer that has passed through the development region is transported to a portion where the magnetic force of the magnet is weak, so that it is separated from the development sleeve and returned to the agitation unit. When the toner concentration in the stirring unit becomes light by repeating such operations, the TC sensor detects this, and toner is supplied to the stirring unit from a toner cartridge (not shown) based on the detection result.

  Further, the primary transfer unit is provided at a position facing the corresponding photosensitive drum via the intermediate transfer belt 2040.

  Here, a primary transfer roller is used as the primary transfer unit. The primary transfer roller is installed so as to be pressed against the photosensitive drum with the intermediate transfer belt 2040 interposed therebetween. As the primary transfer unit, in addition to the roller-shaped unit, a conductive brush-shaped unit, a non-contact corona charger, or the like may be used.

  The photoconductor cleaning unit has a cleaning blade (for example, made of polyurethane rubber) arranged so that the tip is pressed against the photoconductor drum, and a conductive fur brush arranged in contact with the photoconductor drum. ing. A bias voltage is applied to the fur brush from a metal electric field roller (not shown), and a tip of a scraper (not shown) is pressed against the electric field roller. The toner removed from the photosensitive drum by the cleaning blade and the fur brush is accommodated in the photosensitive member cleaning unit and collected by a waste toner collecting unit (not shown).

  Returning to FIG. 1, the optical scanning device 2010 uses light modulated for each color based on multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the printer control device 2090. The surface of the corresponding charged photosensitive drum is scanned. Thereby, an electrostatic latent image corresponding to the image information is formed on the surface of each photosensitive drum. The electrostatic latent image formed here moves in the direction of the corresponding developing unit as the photosensitive drum rotates, and is visualized by the developing unit. Here, the toner-attached image (toner image) moves in the direction of the intermediate transfer belt 2040 as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

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

  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. The paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060. The recording paper is sent out toward the gap between the intermediate transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the toner image on the intermediate transfer belt 2040 is transferred to the recording paper. Here, the recording sheet on which the toner image is transferred 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. Here, the recording paper on which the toner is fixed is sent to a paper discharge tray 2070 via a paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

  The reflective optical sensor 2245 is disposed in the vicinity of the intermediate transfer belt 2040. The reflective optical sensor 2245 will be described later.

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

  As shown in FIGS. 4 to 7 as an example, the optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four coupling lenses (2201a, 2201b, 2201c, 2201d), and four apertures. Plate (2202a, 2202b, 2202c, 2202d), four cylindrical lenses (2204a, 2204b, 2204c, 2204d), optical deflector 2104, four scanning lenses (2105a, 2105b, 2105c, 2105d), six folding mirrors ( 2106a, 2106b, 2106c, 2106d, 2108b, 2108c) and a scanning control device (not shown).

  Here, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is described as the X-axis direction, and the rotation axis direction of the optical deflector 2104 is described as the Z-axis direction.

  In the following, for convenience, in each optical member, a direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and a direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The light source 2200a, the coupling lens 2201a, the aperture plate 2202a, the cylindrical lens 2204a, the scanning lens 2105a, and the folding mirror 2106a are optical members for forming an electrostatic latent image on the photosensitive drum 2030a.

  The light source 2200b, the coupling lens 2201b, the aperture plate 2202b, the cylindrical lens 2204b, the scanning lens 2105b, the folding mirror 2106b, and the folding mirror 2108b are optical members for forming an electrostatic latent image on the photosensitive drum 2030b.

  The light source 2200c, the coupling lens 2201c, the aperture plate 2202c, the cylindrical lens 2204c, the scanning lens 2105c, the folding mirror 2106c, and the folding mirror 2108c are optical members for forming an electrostatic latent image on the photosensitive drum 2030c.

  The light source 2200d, the coupling lens 2201d, the aperture plate 2202d, the cylindrical lens 2204d, the scanning lens 2105d, and the folding mirror 2106d are optical members for forming an electrostatic latent image on the photosensitive drum 2030d.

  Each coupling lens is disposed on the optical path of light emitted from the corresponding light source, and makes the light substantially parallel light.

  Each aperture plate has an aperture and shapes the light through the corresponding coupling lens.

  Each cylindrical lens forms an image of light that has passed through the opening of the corresponding aperture plate in the vicinity of the deflection reflection surface of the optical deflector 2104 in the sub-scanning corresponding direction (here, the same as the Z-axis direction).

  The optical deflector 2104 has a two-stage polygon mirror. Each polygon mirror has four deflecting reflecting surfaces. The first-stage (lower) polygon mirror deflects the light from the cylindrical lens 2204a and the light from the cylindrical lens 2204d. The second-stage (upper) polygon mirror reflects the light from the cylindrical lens 2204b and the cylindrical lens 2204c. Are arranged such that the light from each is deflected. Note that the first-stage polygon mirror and the second-stage polygon mirror rotate with a phase shift of approximately 45 ° from each other, and writing scanning is alternately performed in the first and second stages.

  The light from the cylindrical lens 2204a deflected by the optical deflector 2104 is irradiated onto the photosensitive drum 2030a through the scanning lens 2105a and the folding mirror 2106a to form a light spot.

  The light from the cylindrical lens 2204b deflected by the optical deflector 2104 is irradiated to the photosensitive drum 2030b through the scanning lens 2105b and the two folding mirrors (2106b and 2108b), and a light spot is formed. The

  The light from the cylindrical lens 2204c deflected by the optical deflector 2104 is irradiated to the photosensitive drum 2030c through the scanning lens 2105c and the two folding mirrors (2106c and 2108c), and a light spot is formed. The

  The light from the cylindrical lens 2204d deflected by the optical deflector 2104 is applied to the photosensitive drum 2030d through the scanning lens 2105d and the folding mirror 2106d, thereby forming a light spot.

  The light spot on each photosensitive drum moves in the longitudinal direction of the photosensitive drum as the optical deflector 2104 rotates. The moving direction of the light spot on each photosensitive drum is the “main scanning direction”, and the rotating direction of the photosensitive drum is the “sub-scanning direction”. An area in which image information is written on each photosensitive drum is called an “effective scanning area”, an “image forming area”, an “effective image area”, or the like.

  An optical system disposed on the optical path between the optical deflector 2104 and each photosensitive drum is also called a scanning optical system.

  Next, the reflective optical sensor 2245 will be described. Here, as shown in FIG. 8 as an example, in the xyz three-dimensional orthogonal coordinate system, the direction orthogonal to the belt surface of the intermediate transfer belt 2040 is defined as the z-axis direction, and the main direction is defined as the y-axis direction. Further, the moving direction of the intermediate transfer belt 2040, that is, the sub direction is defined as the + x direction. The reflective optical sensor 2245 is assumed to be disposed on the + z side of the intermediate transfer belt 2040. Further, it is assumed that the reflective optical sensor 2245 is disposed at a position facing the central position y0 of the intermediate transfer belt 2040 in the y-axis direction (see FIG. 9). That is, the reflective optical sensor 2245 is disposed at a position corresponding to the effective image area.

  As shown in FIGS. 10 to 13 as an example, the reflective optical sensor 2245 includes 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 (inter-center distance) Le along the y-axis direction. 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 center-to-center distance between the light emitting part E1 and the light emitting part E11 is 4 mm (Le × 10). Moreover, each light emission part is square shape whose length of one side is about 0.04 mm. Furthermore, the wavelength of light emitted from each light emitting unit (center emission wavelength) is 850 nm. Hereinafter, for convenience, the light emitting unit that is turned on is also referred to as a “lighting 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 light emitted from the corresponding light emitting unit toward the surface of the intermediate 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 exit surface of the corresponding light emitting unit.

  Here, for easy understanding, it is assumed that only the light emitted from each light emitting unit and passing through the corresponding illumination microlens illuminates the intermediate transfer belt 2040 as detection light (S1 to S11) (FIG. 14). The center of the light spot (hereinafter also referred to as “detection light spot” for convenience) formed on the surface of the intermediate transfer belt 2040 by each detection light is the center of the corresponding light emitting unit and light receiving unit in the x-axis direction. Near the middle.

  As an example, the size (diameter) of each detection light spot is 0.40 mm. This value is equal to the interval Le. The distance between the centers of two detection light spots adjacent to each other is 0.40 mm. In addition, the size (diameter) of the detection light spot in the conventional reflective optical sensor is usually about 2 to 3 mm.

  Here, the surface of the intermediate transfer belt 2040 is smooth, and most of the detection light irradiated on the surface of the intermediate 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 light emitted from the corresponding light emitting portion and regularly reflected by the surface of the intermediate transfer belt 2040. The distance between the centers of the two adjacent light receiving parts in the y-axis direction is equal to the distance Le. The shape of each light receiving portion is a square having a side length of 0.35 mm. In each light receiving unit, the light wavelength at which the light receiving sensitivity reaches a peak is in the vicinity of 850 nm in the relationship between the light receiving sensitivity and the light wavelength. 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) individually correspond to the eleven light receiving portions (D1 to D11), and are used for detection reflected by the toner pattern on the intermediate transfer belt 2040 or the intermediate transfer belt 2040. Collect the light. 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.

  Each microlens includes a spherical lens having a condensing function in the y-axis direction and the x-axis direction, a cylindrical lens having a positive power in the x-axis direction, and power in the y-axis direction and power in the x-axis direction are different from each other. An anamorphic lens or the like can be used.

  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 injection molding.

  In the following, when it is not necessary to specify the light emitting unit, it is referred to as “light emitting unit Ei”. The illumination microlens corresponding to the light emitting unit Ei is denoted as “illumination microlens LEi”. The light emitted from the light emitting unit Ei and passing through the illumination microlens LEi is referred to as “detection light Si”. The light receiving unit corresponding to the light emitting unit Ei is referred to as “light receiving unit Di”. Further, the light receiving microlens corresponding to the light receiving portion Di is referred to as “light receiving microlens LDi”.

  As an example, as shown in FIG. 15, the optical axis of each illumination microlens is Δd on the light receiving system side with respect to an axis passing through the center of each corresponding light emitting unit and orthogonal to the light emission surface of the light emitting unit. (Here, it is 0.035 mm). Further, 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 passing through the center of each corresponding light receiving portion and orthogonal to the light receiving surface of the light receiving portion. Yes. Thereby, more reflected light can be guide | induced to the corresponding light-receiving part.

  With respect to the x-axis direction, the center-to-center distance between the illumination microlens LEi and the light-receiving microlens LDi is 0.445 mm, and the center-to-center distance between the light emitting unit Ei and the light receiving unit Di is 0.500 mm. Further, with respect to the x-axis 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 intermediate transfer belt 2040 is 5 mm. .

  Next, a toner pattern as a test pattern that is a detection target of the reflective optical sensor 2245 will be described.

  As an example, this toner pattern has five patterns (DP1, DP2, DP3, DP4, PP) as shown in FIG.

  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. When there is no need to distinguish between the density detection patterns DP1 to DP4, they are collectively referred to as “density detection patterns DP”.

  As shown in FIG. 17 as an example, the density detection pattern DP has five rectangular patterns (p1 to p5, hereinafter referred to as “rectangular pattern” for convenience). The five rectangular patterns are arranged in a line at equal intervals along the x-axis direction, and the toner density gradations are different from each other when viewed as a whole. Here, p1, p2, p3, p4, and p5 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 p5 has the highest toner density. The rectangular pattern p5 is a so-called solid pattern created with the maximum toner adhesion amount.

  By the way, as a method of changing the gradation of the toner density, there are a method of changing it in an analog manner and a method of changing it in a digital manner.

  A method for changing the gradation of the toner density in an analog manner will be briefly described below. For example, the emission intensity and development bias of a semiconductor laser used for forming an electrostatic latent image are fixed, and different density patterns (hereinafter also referred to as “analog patterns”) by changing the emission duty (Duty) of the semiconductor laser. Consider the case of forming.

  In FIG. 18, an area of 4 dots × 4 dots is extracted from the electrostatic latent image on the photosensitive drum for the analog pattern of intermediate color 1, the analog pattern of intermediate color 2, the analog pattern of intermediate color 3, and the solid analog pattern. The light emission duty (Duty) of the semiconductor laser at each dot is shown. Here, the toner density increases in the order of intermediate color 1 <intermediate color 2 <intermediate color 3 <solid. The numerical value “0” indicates a light emission duty (Duty) of 0 (%), the numerical value “1” indicates a light emission duty (Duty) of 25 (%), a numerical value “2” indicates a light emission duty (Duty) of 50 (%), The numerical value “3” means that the light emission duty (Duty) is 75 (%), and the numerical value “4” means that the light emission duty (Duty) is 100 (%). At the time of development, an amount of toner adhering to the emission intensity of the semiconductor laser, the development bias, and the emission duty (Duty) is attached. That is, the toner adhesion amount has a relationship of intermediate color 1 <intermediate color 2 <intermediate color 3 <solid.

  Therefore, in the analog pattern, toner adheres to the entire region at any density. However, the toner may not adhere to the one-dot region depending on the case where the light emission duty (Duty) is extremely small or depending on the light emission intensity of the semiconductor laser and the value of the developing bias.

  On the other hand, in the digitally different method, the gradation of the toner density is changed depending on the ratio of the area of the portion where the toner is attached and the area of the base (here, the surface of the intermediate transfer belt 2040) where the toner is not attached. It is different. That is, a so-called dither pattern is obtained. When the intermediate color based on the dither pattern is enlarged and observed with a magnifying glass or the like, as shown in FIG. 19A, it is possible to clearly distinguish an area where toner is present and an area where toner is not present in an arbitrary area. A solid pattern in this case is shown in FIG. 20A shows the toner adhesion state in the rectangular pattern p1, FIG. 20B shows the toner adhesion state in the rectangular pattern p3, and the toner adhesion state in the rectangular pattern p5. It is shown in FIG.

  In this embodiment, as an example, a method of digitally changing the gradation of the toner density is adopted.

  As an example, the length w1 in the main direction of each rectangular pattern is 1 mm, and the length w2 in the sub direction is 2 mm. That is, the length w1 (= 1 mm) in the y-axis direction of each rectangular pattern is larger than the sum of the interval Le (= 0.4 mm) and the size of the detection light spot (= 0.4 mm). Further, with respect to the x-axis direction, the center interval w3 between two adjacent rectangular patterns is 3 mm. Therefore, the size (4 × w3 + w2) of the density detection pattern DP in the x-axis direction is 14 mm.

  The conventional test pattern for density detection includes a plurality of toner patches arranged in a line along the sub direction, and each toner patch has a length in the main direction of about 10 mm and a length in the sub direction of about 15 mm. Met.

  In other words, in the present embodiment, the size of the density detection pattern can be made significantly smaller than in the conventional case in both the main direction and the sub direction. The amount of toner required to create the density detection pattern can be reduced to about 1/100 of the conventional amount. Therefore, the amount of non-contributing toner can be greatly reduced, and the replacement timing of the toner cartridge can be extended.

  As shown in FIG. 21, as an example, the four density detection patterns DP1 to DP4 are arranged in a line along the x-axis direction and are formed at positions illuminated by the detection light S6 from the light emitting unit E6. Is set to FIG. 22 is an enlarged view of a part of FIG. Hereinafter, for convenience, the row of the four density detection patterns DP1 to DP4 is also referred to as a “DP pattern row”.

  As shown in FIG. 23 as an example, the misregistration detection pattern PP has eight line patterns (LPK1, LPK2, LPM1, LPM2, LPC1, LPC2, LPY1, LPY2) arranged in a line along the x-axis direction. have.

  The line patterns LPK1 and LPK2 are formed of black toner, and the line patterns LPM1 and LPM2 are formed of magenta toner. The line patterns LPC1 and LPC2 are formed of cyan toner, and the line patterns LPY1 and LPY2 are formed of yellow toner. Here, each line pattern is formed with a so-called solid density as a toner density.

  The linear patterns LPK1, LPM1, LPC1, and LPY1 have a longitudinal direction parallel to the y-axis direction, and the linear patterns LPK2, LPM2, LPC2, and LPY2 are inclined in the longitudinal direction with respect to the y-axis direction. Here, the inclination angle is 45 °.

  In the following, a line pattern whose longitudinal direction is parallel to the y-axis direction is also referred to as a “parallel line pattern”, and a line pattern whose longitudinal direction is inclined with respect to the y-axis direction is referred to as an “inclined line pattern”. Also called.

  Each parallel line pattern has a longitudinal length w4 of 1.0 mm and a lateral length w5 of 0.5 mm. In addition, the center-to-center distance w6 between two parallel line patterns adjacent in the x-axis direction is 1.0 mm.

  In addition, in each of the inclined line patterns, the distance w7 between two corners located inside among the four corners in the y-axis direction is 1.0 mm, and the length in the short direction is 0.5 mm. The center-to-center distance w8 between two inclined line patterns adjacent in the x-axis direction is 1.0 mm.

  A conventional test pattern for detecting misalignment includes a plurality of line patterns parallel and inclined with respect to the main direction. Each line pattern has a length in the main direction of about 8 mm and a length in the sub direction. Was about 1 mm. The distance between the centers of two line patterns adjacent in the sub direction was about 3.5 mm.

  In this embodiment, as shown in FIG. 24 as an example, the misregistration detection pattern PP is set to be formed on the −x side of the DP pattern row. Therefore, as shown in FIG. 25 as an example, the misregistration detection pattern PP is set to be formed at a position illuminated by the detection light S6 from the light emitting unit E6.

  Next, density detection processing and positional deviation detection processing performed using the reflective optical sensor 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 of FIG. 26 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. Hereinafter, the density detection process and the positional deviation detection process are also collectively referred to as “detection process”.

  (1) 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.

  Immediately after the power is turned on, the image process control flag is (a) when the photosensitive drum stop time is 6 hours or more, (b) when the temperature in the apparatus is changed by 10 ° C. or more, (c) in the apparatus It is set when the relative humidity has changed by 50% or more. During printing, (d) When the number of printed sheets reaches a predetermined number, (e) When the number of rotations of the developing sleeve reaches a predetermined number (F) Set when the traveling distance of the intermediate transfer belt reaches a predetermined distance.

  If the determination in step S301 is negative, neither the density detection process nor the positional deviation detection process is 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. Here, the image process is performed at a timing after the mth image in the plurality of images is formed and the (m + 1) th image is formed after the user requests formation of a plurality of continuous images. Assume that the control flag is set.

  (2) In step S303, in order to estimate the position in the y-axis direction where the toner pattern is formed, the scan control apparatus is instructed to create a dummy pattern DKDP.

  The dummy pattern DKDP is a rectangular pattern formed of solid density black toner. The length of the dummy pattern DKDP in the y-axis direction is 1.0 mm, and the length in the x-axis direction is 0.5 mm. The color, toner density, and shape of the dummy pattern are not limited to this.

  Here, the dummy pattern DKDP is formed so that the center position thereof coincides with the center position of the toner pattern in the y-axis direction.

  Therefore, the scanning control device controls the light source 2200a so that the electrostatic latent image of the dummy pattern DKDP is formed in the center of the effective image area on the photosensitive drum 2030a in the Y-axis direction.

  The electrostatic latent image is visualized by the corresponding developing unit and transferred to the intermediate transfer belt 2040 at a predetermined timing. As a result, a dummy pattern DKDP is formed on the intermediate transfer belt 2040 (see FIG. 27). Note that image forming conditions necessary for forming the dummy pattern DKDP are stored in advance in the ROM of the printer control device 2090.

  (3) In the next step S305, the position of the dummy pattern DKDP in the y-axis direction (main direction) is obtained.

  By the way, the position of the toner pattern with respect to the reflection type optical sensor 2245 in the y-axis direction may be different from the planned position due to deviation of the toner pattern formation position, meandering of the intermediate transfer belt, and the like. Therefore, it is necessary to estimate the position of the toner pattern in the y-axis direction in advance.

  Here, the dummy pattern DKDP is set to be formed at a position illuminated by the detection light S6. FIG. 28 shows the locus of the detection light S6 when the dummy pattern DKDP is formed as set.

  FIGS. 29 to 31 show an example of the output of the light receiving unit when the dummy pattern DKDP has moved to a position facing the reflective optical sensor 2245. FIG. 29 shows the output (D6 (dp)) of the light receiving unit D6 when only the light emitting unit E6 is turned on, and FIG. 30 shows the light reception when only the light emitting unit E7 is turned on. The output of the part D7 (referred to as D7 (dp)) is shown, and FIG. 31 shows the output of the light receiving part D5 (referred to as D5 (dp)) when only the light emitting part E5 is turned on. .

  29, D6 (belt) is the output of the light receiving unit D6 when the detection light S6 illuminates only the intermediate transfer belt, and D7 (belt) in FIG. 30 is the detection light S7 is the intermediate transfer belt. 31 is an output of the light receiving unit D7 when only the intermediate transfer belt is illuminated with the detection light S5.

In FIG. 29, ΔD6 is the difference between D6 (belt) and D6 (dp), ΔD7 in FIG. 30 is the difference between D7 (belt) and D7 (dp), and ΔD5 in FIG. belt) and D5 (dp).
Here, there is a relationship of ΔD6> ΔD7 and ΔD6> ΔD5.

  In this case, since all of the detection light S6 is irradiated on the dummy pattern DKDP and scattered or absorbed by the dummy pattern DKDP, D6 (dp) has a very small value compared to D6 (belt). It is thought that there is. On the other hand, since the detection light S7 is applied to both the intermediate transfer belt and the dummy pattern DKDP, it is considered that there is little light scattered or absorbed by the dummy pattern DKDP, and ΔD6> ΔD7. Similarly, since the detection light S5 is applied to both the intermediate transfer belt and the dummy pattern DKDP, it is considered that there is little light scattered or absorbed by the dummy pattern DKDP, and ΔD6> ΔD5.

  Therefore, in this case, as shown in FIG. 32 as an example, it can be estimated that the center of the dummy pattern DKDP is substantially at the same position as the light emitting unit E6 in the y-axis direction. Here, since D5 (belt) ≈D6 (belt) ≈D7 (belt), D6 (dp) is the smallest among D5 (dp), D6 (dp), and D7 (dp). The above estimation may be performed. Here, since the center of the dummy pattern DKDP and the center of the toner pattern are set to coincide with each other in the y-axis direction, the center of the toner pattern is formed at substantially the same position as the light emitting unit E6 in the y-axis direction. Can be estimated.

  33 to 36 show another example of the output of the light receiving unit when the dummy pattern DKDP has moved to a position facing the reflective optical sensor 2245. 33 shows D6 (dp) when only the light emitting unit E6 is turned on, and FIG. 34 shows D7 (dp) when only the light emitting unit E7 is turned on. Shows D5 (dp) when only the light emitting unit E5 is turned on, and FIG. 36 shows the output (D8 (dp) of the light receiving unit D8 when only the light emitting unit E8 is turned on. )It is shown.

  36, D8 (belt) is the output of the light receiving unit D8 when the detection light S8 illuminates only the intermediate transfer belt, and ΔD8 is the difference between D8 (belt) and D8 (dp).

  Here, there is a relationship of ΔD6≈ΔD7> ΔD5≈ΔD8. In this case, as shown in FIG. 37 as an example, it can be estimated that the center of the dummy pattern DKDP is at an intermediate position between the light emitting part E6 and the light emitting part E7 in the y-axis direction. Accordingly, it can be estimated that the center of the toner pattern is formed at an intermediate position between the light emitting portion E6 and the light emitting portion E7 with respect to the y-axis direction.

  Further, even if the light emitting unit E6 is turned on at the timing of illuminating the dummy pattern DKDP, if the light receiving system output distribution is the same as the light receiving system output distribution when only the intermediate transfer belt 2040 is illuminated, some sudden occurrence occurs. For this reason, it is determined that the dummy pattern DKDP does not exist within an allowable range.

  (4) In the next step S307, it is determined whether or not the position of the dummy pattern DKDP in the y-axis direction (main direction) is within an allowable range.

  Here, if it is determined that the dummy pattern DKDP does not exist within an allowable range, the determination here is denied and the process proceeds to step S309.

  (5) In step S309, the formation position of the dummy pattern DKDP is corrected, and the process returns to step S303.

  On the other hand, if the dummy pattern DKDP exists within an allowable range in step S307, the determination in step S307 is affirmed, and the process proceeds to step S311.

(6) In step S311, a lighting light emitting unit is determined.
(6-1) A lighting light emitting unit when the irradiation target is a DP pattern array 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.

  When some of the light emitting units are lit, the lighting light emitting unit can be determined based on the position of the toner pattern estimated in step S305 in the y-axis direction.

  For example, when it is estimated that the center of the toner pattern is substantially at the same position as the light emitting unit E6 in the y-axis direction, only the light emitting unit E6 can be determined as the lighting light emitting unit. This is because even if the light emitting portions E5 and E7 are turned on, a part of the detection light S5 and S7 does not illuminate the toner pattern, so that the light use efficiency is small and the detection accuracy is hardly affected.

  When the toner pattern is moving in the sub-direction, if there is a possibility that the detection light S6 may deviate from the toner pattern, the light-emitting portions E5 and E7 on both sides of the light-emitting portion E6 are added to allow for a margin. The lighting light emitting units may be determined as three light emitting units E5 to E7. The margin can be determined according to the characteristics of the color printer 2000 (toner pattern formation position deviation state, photoconductor drum and intermediate transfer belt meandering state, etc.).

  For example, when it is estimated that the center of the toner pattern is at an intermediate position between the light emitting unit E6 and the light emitting unit E7 with respect to the y-axis direction, the light emitting unit E6 and the light emitting unit E7 are determined as the lighting light emitting unit. can do. This is because even if the light emitting portions E5 and E8 are turned on, a part of the detection light S5 and S8 does not illuminate the toner pattern, so that the light use efficiency is small and the detection accuracy is hardly affected. In this case, since the calculation result is obtained for each light emitting unit, the calculation accuracy obtained for each of the light emitting unit E6 and the light emitting unit E7 can be averaged to improve the detection accuracy.

  When there is a possibility that the detection lights S6 and S7 may deviate from the toner pattern when the toner pattern is moving in the sub-direction, the light-emitting parts E5 and E7 on both sides of the light-emitting parts E6 and E7 are checked. In addition to the light emitting unit E8, the number of lighting light emitting units may be four, E5 to E8.

  Alternatively, one of the light emitting unit E6 and the light emitting unit E7 may be selected and only the selected light emitting unit may be turned on.

  On the other hand, when all the light emitting units are turned on, all the light emitting units included in the reflective optical sensor 2245 are used.

  (6-2) A lighting light emitting unit when the irradiation object is the position shift detection pattern PP is determined. Here, the lighting light emitting unit can be determined based on the position of the toner pattern in the y-axis direction estimated in step S305.

  For example, when it is estimated that the center of the toner pattern is substantially at the same position as the light emitting unit E6 in the y-axis direction, only the light emitting unit E6 can be determined as the lighting light emitting unit.

  For example, when it is estimated that the center of the toner pattern is at an intermediate position between the light emitting unit E6 and the light emitting unit E7 with respect to the y-axis direction, two light emitting units E6 and E7 are used as lighting light emitting units. Or it can be determined as either the light emission part E6 or the light emission part E7.

(7) In the next step S313, a lighting pattern is determined.
(7-1) A lighting pattern when the irradiation object is a DP pattern array is determined. As this lighting pattern, when there are a plurality of lighting light emitting units, 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 and off, and one rectangular pattern is individually illuminated with the detection light Sn and the detection light Sm, the reflected light from the detection light Sn and the detection Even if the reflected light by the working light Sm is received by the same light receiving unit, they 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, at this time, 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 / off simultaneously, 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 lighting light emitting unit, 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 at the same time, 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 lighting light emitting units, 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 / off.

  (7-2) A lighting pattern is determined when the irradiation object is the misregistration detection pattern PP. When there are a plurality of lighting light emitting units, they are sequentially turned on and off.

  (8) In the next step S315, 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 lighting light emitting unit, 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 lighting light emitting units, the light emitting unit E6 and the light emitting unit E7 need to be turned on and off sequentially (in this case, alternately). Each light emitting unit is 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 lighting light emitting unit, 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. In the latter case, for example, if the lighting pattern and the lighting mode are determined in advance, the drive circuit can be simplified and the cost can be reduced. In this case, the lighting light emitting unit is practical because it can be appropriately selected according to the length of the target pattern in the main direction and the performance of the image forming apparatus.

(9) In the next step S317, the light receiving unit from which the output is acquired is determined.
(9-1) A light receiving unit that acquires an output when the irradiation target is a DP pattern array is determined. Here, there are a case where the outputs of some of the light receiving units are acquired and a case where the outputs of all the light receiving units are acquired as the light receiving units for acquiring the outputs.

  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 lighting light emitting unit.

For example, a case where only one of the light emitting units E6 is determined as the lighting light emitting unit will be described.
FIG. 38A shows the output of each light receiving unit when the detection light S6 illuminates the intermediate transfer belt, and FIG. 38B shows the detection light S6 illuminating the dummy pattern DKDP. 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 lighting light emitting units, and these are sequentially turned on / off, the light receiving units required for the light emitting unit E6 are D4 to D8, and light emission The light receiving parts required for the part E7 are D5 to D9, and the required light receiving parts are D4 to D9 in total.

  By the way, when unnecessary output of the light receiving unit is not acquired, it is possible to reduce the amount of data and the amount of calculation.

  Of course, when all the light emitting units are determined as the lighting light emitting units, the outputs of all the light receiving units are acquired. Moreover, you may acquire the output of all the light-receiving parts irrespective of a lighting light emission part.

  (9-2) A light receiving unit that acquires an output when the irradiation target is the positional deviation detection pattern PP is determined. Here, the light receiving unit corresponding to the lighting light emitting unit is assumed to be a light receiving unit that acquires an output.

(10) In the next step S319, the timing for acquiring the output of the light receiving unit is determined.
(10-1) The timing for acquiring the output of the light receiving unit when the irradiation object is a DP pattern array is determined.

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

  FIG. 39 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 when the irradiation target is a DP pattern array.

  As an example, as shown in FIG. 40, sampling may be performed a plurality of times for each rectangular pattern. In this case, since a plurality of calculation results are obtained for each rectangular pattern, the detection accuracy can be improved by averaging them.

  As an example, as shown in FIG. 41, the light emitting unit E6 may be pulse-lit in accordance with the timing when each rectangular pattern passes through the illumination area of the detection light S6. In this case, as shown in FIG. 42 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. 43 as an example, sampling may be performed a plurality of times for one rectangular pattern.

  As an example, as shown in FIGS. 44 and 45, 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.

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

  FIG. 46 shows the lighting / extinguishing timing of the light emitting unit E6, the lighting / extinguishing timing of the light emitting unit E7, and the sampling timing of the outputs of the light receiving units D4 to D9 when the irradiation object is a DP pattern row. . In this case, since four calculation results are obtained for each rectangular pattern, the 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 detection accuracy can be further increased.

  By the way, 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 if the number of times of sampling for each rectangular pattern required by the image forming apparatus is set.

  (10-2) The timing for acquiring the output of the light receiving unit when the irradiation target is the positional deviation detection pattern PP is determined.

  For example, FIG. 48 shows the sampling timing of the output of the light receiving unit D6 when only one of the light emitting units E6 is determined as the lighting light emitting unit and is always lit.

  Further, FIG. 49 shows the sampling timing of the output of the light receiving part D6 when the light emitting part E6 is pulse-lit.

(11) In the next step S321, the intermediate transfer belt is illuminated with detection light, and the output of each light receiving unit is acquired.
For example, the intermediate transfer belt is illuminated with the detection light S6, and the outputs of the light receiving units D4 to D8 are acquired.

(12) In the next step S323, the scanning control apparatus is instructed to create a toner pattern.
Accordingly, the scanning control device, based on the estimated position of the toner pattern, causes the electrostatic latent image of the density detection pattern DP1 on the photosensitive drum 2030a and the electrostatic latent image of the density detection pattern DP2 on the photosensitive drum 2030b. Then, an electrostatic latent image of the density detection pattern DP3 is formed on the photosensitive drum 2030c, and an electrostatic latent image of the density detection pattern DP4 is formed on the photosensitive drum 2030d.

  Further, based on the estimated toner pattern position, the scanning control device shifts the photosensitive drum 2030a to each of the electrostatic latent images of the line-shaped patterns LPK1 and LPK2 of the positional shift detection pattern PP and the photosensitive drum 2030b. Each of the electrostatic latent images of the line-shaped patterns LPM1 and LPM2 of the detection pattern PP and the positional displacement of the electrostatic latent images of the line-shaped patterns LPC1 and LPC2 of the detection pattern PP of the photosensitive drum 2030c and of the photosensitive drum 2030d. The electrostatic latent images of the line patterns LPY1 and LPY2 of the detection pattern PP are formed.

  Each electrostatic latent image is visualized by a corresponding developing unit and transferred to the intermediate transfer belt 2040 at a predetermined timing. As a result, a toner pattern is formed following the m-th image on the intermediate transfer belt 2040 (see FIG. 50).

  The image forming conditions necessary for forming the toner pattern are stored in advance in the ROM of the printer control device 2090. The ROM also stores in advance a density conversion LUT (look-up table) for converting the output of the reflective optical sensor into toner density.

  (13) In the next step S325, the toner pattern is illuminated with detection light, and the output of each light receiving unit is acquired.

  Here, the determined lighting light emitting unit is turned on / off according to the determined lighting pattern and lighting mode, and the output of the determined light receiving unit is acquired at the determined timing.

  Since the output of each light receiving unit corresponds to the amount of light received by each light receiving unit, the output of the light receiving unit is also referred to as “light receiving amount” for convenience.

  (14) In the next step S327, the toner density of each rectangular pattern in the DP pattern row is calculated. Here, a case where only one of the light emitting units E6 is determined as the lighting light emitting unit will be described.

  An example of the received light amount distribution acquired in step S321 is shown in FIG. 51, and an example of the received light amount distribution obtained in step S325 when the irradiation target is the density detection pattern DP1 is shown in FIGS. Is shown in Each received light amount distribution is standardized with the received light amount of the light receiving unit D6 when the detection light S6 illuminates the intermediate transfer belt 2040 as “1”. D_ALL is the sum of the amounts of light received by the five light receiving portions D4 to D8.

  FIG. 51 shows the received light amount distributions of the light receiving portions D4 to D8 when the detection light S6 illuminates only the intermediate transfer belt 2040.

  FIG. 52 shows received light amount distributions of the light receiving portions D4 to D8 when the detection light S6 illuminates the rectangular pattern p1 of the density detection pattern DP1.

  FIG. 53 shows the received light amount distribution of the light receiving portions D4 to D8 when the detection light S6 illuminates the rectangular pattern p2 of the density detection pattern DP1.

  FIG. 54 shows the received light amount distributions of the light receiving portions D4 to D8 when the detection light S6 illuminates the rectangular pattern p3 of the density detection pattern DP1.

  FIG. 55 shows received light amount distributions of the light receiving portions D4 to D8 when the detection light S6 illuminates the rectangular pattern p4 of the density detection pattern DP1.

  FIG. 56 shows received light amount distributions of the light receiving portions D4 to D8 when the detection light S6 illuminates the rectangular pattern p5 of the density detection pattern DP1.

  Incidentally, most of the reflected light when the detection light illuminates only the intermediate transfer belt is light that is regularly reflected on the surface of the intermediate transfer belt (see FIG. 57A). On the other hand, when the detection light illuminates the rectangular pattern, the detection light reaches not only the toner but also the surface of the underlying intermediate transfer belt (see FIG. 57B). Therefore, the reflected light when the rectangular pattern is illuminated is roughly classified into light that is regularly reflected on the surface of the intermediate transfer belt and light that is scattered by being reflected and refracted at least once by the toner. Note that the latter scattered light includes light scattered in the same direction as the regular reflection from the surface of the intermediate transfer belt, but the amount of light is small, and the light is regularly reflected from the surface of the intermediate transfer belt. Ignore it because it cannot be distinguished from light. That is, the light attributed to the former intermediate transfer belt is defined as the regular reflection contribution, and the light attributed to the latter toner is defined as the diffuse reflection contribution. In this way, the detection light that illuminates the rectangular pattern is regularly reflected and diffusely reflected. Hereinafter, for the sake of convenience, the specularly reflected light is also referred to as “regularly reflected light” and the diffusely reflected light is also referred to as “diffuse reflected light”.

  Hereinafter, the received light amount of each light receiving unit when the irradiation target is the intermediate transfer belt 2040 is also referred to as “reference received light amount”, and the received light amount of each light receiving unit when the irradiation target is a rectangular pattern is “detected light reception”. Also referred to as “amount”.

  (14-1) For each rectangular pattern, the received light amount of each light receiving unit is separated into a received light amount by diffusely reflected light and a received light amount by regular reflected light. Hereinafter, the case where the irradiation object is the rectangular pattern p1 of the density detection pattern DP1 will be described as an example.

(1) Regarding the amount of light received by the light receiving unit D6 Since the light receiving unit D6 is a light receiving unit corresponding to the lighting light emitting unit E6, it is assumed that all the detected light received by this light receiving unit D6 is the amount of received light by regular reflection light. In general, since the reflectance of the toner pattern is lower than that of the intermediate transfer belt 2040, the detected light reception amount of the light receiving portion D6 is smaller than 1 (reference light reception amount).

(2) About the light-receiving amount of the light-receiving part D4 and the light-receiving part D8 In the light-receiving part D4 and the light-receiving part D8, the reference light-receiving amount was all zero. Therefore, all of the detected light reception amounts of the light receiving part D4 and the light receiving part D8 are light reception amounts due to diffusely reflected light.

(3) Regarding the amount of light received by the light receiving portion D5 In the light receiving portion D5, the reference amount of received light was not zero. Therefore, the detected amount of light received by the light receiving unit D5 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 D5 and the detected amount of received light of the light receiving unit D6 should match the ratio of the reference received light amount of the light receiving unit D5 and the reference received light amount of the light receiving unit D6. is there.

  Accordingly, a value (ratio A) obtained by dividing the reference light reception amount of the light receiving unit D5 by the reference light reception amount of the light receiving unit D6 is obtained.

  Then, the ratio A is multiplied by the amount of light received by the light receiving unit D6. 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 D5 (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 D5. The value obtained here is the amount of light received by the diffusely reflected light included in the amount of received light detected by the light receiving unit D5.

(4) Regarding the amount of light received by the light receiving portion D7 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 D7 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 D7 and the detected amount of received light of the light receiving unit D6 should match the ratio of the reference received light amount of the light receiving unit D7 and the reference received light amount of the light receiving unit D6. is there.

  Accordingly, a value (ratio B) obtained by dividing the reference light reception amount of the light receiving unit D7 by the reference light reception amount of the light receiving unit D6 is obtained.

  Then, the ratio B is multiplied by the amount of light received by the light receiving unit D6. 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 D7 (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 D7. 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 D7.

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

  The received light amount by regular reflection light and the received light amount by diffuse reflection light in the rectangular patterns p1 to p5 of the density detection pattern DP1 are shown in FIGS.

  Next, for each rectangular pattern, the total amount of light received by specularly reflected light (denoted as M1) and the total amount of received light by diffusely reflected light (denoted by M2) are obtained.

  A total value M1 of the amount of light received by the regular reflection light of each illumination object is shown in FIG. Further, FIG. 69 shows a total value M1 of the amount of light received by the regular reflection light of each rectangular pattern when the total value M1 when the illumination target is the intermediate transfer belt 2040 is 1. According to these, the total value M1 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.

  A total value M2 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 M2 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.

  FIG. 71 shows the total value M2 / total value M1 of each illumination object. 72 shows the total value M2 / total value M1 of each illumination object when the maximum value of the total value M2 / total value M1 is 1. As shown in FIG. According to these, the total value M2 / total value M1 monotonously increases as the toner density increases.

(14-2) The toner density is calculated.
FIG. 73 shows the relationship between the toner density and M1 (relative value). M1 (relative value) decreases as the toner density increases. FIG. 74 shows the relationship between the toner density and M2 / M1 (relative value). M2 / M1 (relative value) increases as the toner density increases.

An approximate curve representing the relationship between the toner density and M1 (relative value) in FIG. 73 was obtained, the differential value at each toner density of the approximate curve was calculated, and the change rate of M1 (relative value) was obtained. FIG. 75 shows the relationship between the absolute value of the change rate of M1 (relative value) and the toner density. In the region where the toner concentration is higher than about 0.3 (mg / cm ² ), the absolute value of the change rate of M1 (relative value) is smaller than 1.

74, an approximate curve representing the relationship between the toner density and M2 / M1 (relative value) is obtained, a differential value at each toner density of the approximate curve is calculated, and a change rate of M2 / M1 (relative value) is obtained. It was. FIG. 76 shows the relationship between the absolute value of the change rate of M2 / M1 (relative value) and the toner density. In the region where the toner concentration is lower than about 0.15 (mg / cm ² ), the absolute value of the change rate of M2 / M1 (relative value) is smaller than 1.

FIG. 77 is a diagram in which FIGS. 75 and 76 are overlapped. The curve representing the relationship between the absolute value of the change rate of M1 (relative value) and the toner density, and the curve representing the relationship between the absolute value of the change rate of M2 / M1 (relative value) and the toner concentration have a toner density of about Crossing occurs at 0.25 (mg / cm ² ). That is, when the toner concentration is about 0.25 (mg / cm ² ), the absolute value of the change rate of M1 (relative value) is almost equal to the absolute value of the change rate of M2 / M1 (relative value).

In the region where the toner density is lower than about 0.25 (mg / cm ² ), the absolute value of the change rate of M1 (relative value) is larger than the absolute value of the change rate of M2 / M1 (relative value). In the region where the toner density is higher than about 0.25 (mg / cm ² ), the absolute value of the change rate of M2 / M1 (relative value) is larger than the absolute value of the change rate of M1 (relative value).

  When obtaining the toner density from M1 (relative value), the toner density can be obtained with higher accuracy as the absolute value of the change rate of M1 (relative value) is larger. Further, when obtaining the toner density from M2 / M1 (relative value), the toner density can be obtained with higher accuracy as the absolute value of the change rate of M2 / M1 (relative value) is larger.

Therefore, in this embodiment, the printer control device 2090 refers to the density conversion LUT (look up table) stored in the ROM, and the expected toner density is 0.25 (mg / cm ² ). For the lower rectangular pattern, the toner density is calculated from M1 (relative value). For the rectangular pattern whose expected toner density is higher than 0.25 (mg / cm ² ), the toner density is calculated from M2 / M1 (relative value). Toner density is calculated.

  (15) In the next step S329, the amount of positional deviation of each line pattern in the positional deviation detection pattern PP is calculated. Here, it is assumed that the light emitting unit is only the light emitting unit E6. As an example, FIG. 78 schematically shows a change in the output of the light receiving unit D6.

  (15-1) Based on the falling timing in the output waveform of the light receiving unit D6, the time Tkm1 from the detection time of the line pattern LPK1 to the detection time of the line pattern LPM1, and the detection time of the line pattern LPK1 to the line pattern A time Tkc1 until the detection time of LPC1 and a time Tky1 from the detection time of the line pattern LPK1 to the detection time of the line pattern LPY1 are obtained.

  (15-2) Based on the falling timing in the output waveform of the light receiving unit D6, the time Tkm2 from the detection time of the line pattern LPK2 to the detection time of the line pattern LPM2, and the detection time of the line pattern LPK2 to the line pattern The time Tkc2 until the detection time of LPC2 and the time Tky2 from the detection time of the line pattern LPK2 to the detection time of the line pattern LPY2 are obtained.

  (15-3) The differences (referred to as time differences ΔTm1, ΔTc1, and ΔTy1) between the obtained time Tkm1, time Tkc1, and time Tky1 and their preset reference times are obtained. If the time difference is within the allowable range, it is determined that the positional relationship of the color toner image with respect to the black toner image in the x-axis direction is appropriate. On the other hand, if the time difference is not within the allowable range, it is determined that there is a deviation in the positional relationship of the color toner image with respect to the black toner image in the x-axis direction. In this case, the printer control device 2090 obtains the positional relationship deviation amount (denoted by the deviation amount ΔS1) from the time difference, and notifies the scanning control device of the deviation amount ΔS1.

  (15-4) The differences (denoted as time differences ΔTm2, ΔTc2, and ΔTy2) between the obtained time Tkm2, time Tkc2, and time Tky2 and their preset reference times are obtained. If the time difference is within an allowable range, it is determined that the positional relationship of the color toner image with respect to the black toner image in the y-axis direction is appropriate. On the other hand, if the time difference is not within the allowable range, it is determined that the positional relationship of the color toner image with respect to the black toner image in the y-axis direction is shifted. In this case, the printer control device 2090 obtains the positional relationship deviation amount (denoted as deviation amount ΔS2) from the time difference, and notifies the scanning control device of the deviation amount ΔS2.

  As an example, FIG. 79A schematically shows a case where the time difference ΔTm1 is not within the allowable range.

FIG. 79B schematically shows a case where the time difference ΔTm2 is not within the allowable range. In this case, the printer control apparatus 2090 obtains a positional deviation amount ΔS2 in the y-axis direction of the magenta toner image with respect to the black toner image using the following equation (1). Here, V is the moving speed of the intermediate transfer belt 2040 in the sub direction.
ΔS2 = V · ΔTm2 · cot45 ° (1)

  In addition, when there are a plurality of lighting light emitting units, the above processing may be performed on the output waveform of the corresponding light receiving unit for each lighting light emitting unit, and the obtained shift amount for each lighting light emitting unit may be averaged.

(16) In the next step S331, image process control is performed.
Here, the toner density deviation amount is obtained for each toner color from the toner density obtained in the toner density calculating step. 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, development potential control and gradation control are performed in the corresponding image forming station in accordance with the toner density shift amount.

  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 An axis (x-axis) and an x-intercept with the toner density as the vertical axis are obtained. Then, using the following equation (2), 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] (2)

  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.

  In the gradation control, the gradation correction LUT (look-up table) is appropriately changed so that the deviation between the obtained gradation and the target gradation is eliminated. 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.

  In addition, in the positional deviation amount calculation step, if there is a deviation in the positional relationship in the x-axis direction with respect to the black toner image, for example, the image is written on the corresponding photosensitive drum so that the deviation amount becomes almost zero. Change the timing.

  In addition, in the above-described misregistration amount calculation step, if there is a misalignment in the positional relationship in the y-axis direction with respect to the black toner image, for example, an image is written on the corresponding photosensitive drum so that the misalignment amount becomes almost zero The phase of the pixel clock is adjusted.

  As is clear from the above description, in the color printer 2000 according to the present embodiment, the reflective optical sensor 2245 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, the color printer 2000 according to the present embodiment includes the four photosensitive drums (2030a, 2030b, 2030c, 2030d), the four image forming units (2034a, 2034b, 2034c, 2034d), and the optical scanning device 2010. An intermediate transfer belt 2040, a reflective optical sensor 2245, a printer control device 2090, and the like.

  The reflective optical sensor 2245 includes an illumination system including 11 light emitting units (E1 to E11), an illumination optical system including 11 illumination microlenses (LE1 to LE11), and 11 light receiving microlenses (LD1 to LD1). A light receiving optical system including the LD 11), a light receiving system including 11 light receiving portions (D1 to D11), and the like.

  The printer control device 2090 receives a plurality of rectangular patterns for detecting toner density and a plurality of line patterns for detecting misregistration on the intermediate transfer belt 2040 via the optical scanning device 2010 and four image forming stations. Form.

When the printer control device 2090 detects the toner density, among the plurality of rectangular patterns, a rectangular pattern whose expected toner density is lower than 0.25 (mg / cm ² ) is determined from M1 (relative value). The density is calculated, and for the rectangular pattern whose expected toner density is higher than 0.25 (mg / cm ² ), the toner density is calculated from M2 / M1 (relative value).

  In this case, the overall accuracy can be improved as compared with the case where the toner density of a plurality of rectangular patterns is calculated using only one of M1 (relative value) and M2 / M1 (relative value).

  In the reflective optical sensor 2245, the distance between the light emitting part Ei and the light receiving part Di is 0.5 mm, and the distance between the light emitting parts and the distance between the light receiving parts in the y-axis direction are both 0.4 mm. Accordingly, the size of the reflective optical sensor 2245 in the y-axis direction is about 5 mm. Therefore, it is possible to suppress an increase in the size of the image forming apparatus as compared with the case where a conventional reflective optical sensor is used.

  Further, since the size of the toner pattern can be made smaller than before, the time required for density detection and positional deviation detection can be shortened compared to the conventional case. Furthermore, the consumption of non-contributing toner can be significantly reduced compared to the conventional case.

  The toner pattern is formed in a so-called inter-paper area where no image is formed between the m-th image and the (m + 1) -th image on the intermediate transfer belt 2040, so that the print job is not stopped. Density detection and position shift detection can be performed. Therefore, the number of image outputs per unit time can be increased more than before, and the time that the user can wait can be made shorter than before. That is, it is possible to suppress a decrease in the work efficiency of image formation.

  Furthermore, in the reflective optical sensor according to the present embodiment, since the light emitting unit and the light receiving unit are close to each other, the incident angle and the reflection angle of the detection light to the irradiation object can be reduced. As a result, it is possible to reduce a detection error due to a fado factor that causes the intermediate transfer belt to become a shadow of toner, and fluttering of the intermediate transfer belt (a variation in the distance between the reflective optical sensor and the intermediate transfer belt).

  Prior to forming the toner pattern, the position of the toner pattern in the y-axis direction is estimated in advance using a dummy pattern. In this case, it is possible to suppress a decrease in detection accuracy in density detection and position shift detection, and an increase in time required for density detection and position shift detection.

  By the way, the size (spot diameter) of the light spot for detection is related to how small the toner pattern can be read. If the spot diameter is larger than the interval Le (here, 0.40 mm), only a toner pattern larger than the interval Le can be accurately detected in the x-axis direction. Further, in this case, the light spots generated by the light emitted from the two adjacent light emitting units are partially overlapped with each other because the center interval is equal to the interval Le. As described above, when a part of the light spots overlaps, if a plurality of adjacent light emitting units are turned on at the same time, the detection accuracy may be lowered.

  If the spot diameter is smaller than the interval Le, a toner pattern smaller than the interval Le in the x-axis direction can be accurately detected if the size is equivalent to the spot diameter. However, since the distance between the centers of two adjacent light spots is equal to the distance Le, an area that is not illuminated by the detection light is generated between the edges of the light spots by the light emitted from the adjacent light emitting units. When a toner pattern having a size corresponding to an area not illuminated by the detection light or a toner pattern smaller than the area passes through the area, the position of the toner pattern cannot be detected. In addition, since the toner density in the toner pattern is not always uniform, the smaller the spot diameter, the more the output of the light receiving unit varies.

  In this embodiment, since the spot diameter is equal to the interval Le, adjacent detection light spots do not overlap each other, and even when a plurality of adjacent light emitting units are turned on at the time of density detection and positional deviation detection, detection is performed. A decrease in accuracy can be suppressed. In addition, an increase in the dimension of the toner pattern in the sub direction due to the large spot diameter can be prevented. Furthermore, since an area that is not illuminated by the detection light does not occur, even a toner pattern having a size corresponding to the area or a toner pattern smaller than the area can be accurately detected.

  Therefore, according to the color printer 2000, it is possible to stably form a high-quality image without causing an increase in size and without causing a decrease in workability.

  In the above-described embodiment, the case where the gradation of the toner density in the density detection pattern is digitally different has been described. However, the present invention is not limited to this and may be different in an analog manner.

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

  Moreover, although the said embodiment demonstrated the case where the 11 illumination microlenses (LE1-LE11) and the 11 light reception microlenses (LD1-LD11) were integrated, it is limited to this is not.

  In the above-described embodiment, a processing device may be provided in the reflective optical sensor 2245, and the processing device may perform at least a part of the processing in the printer control device 2090 in the density detection processing and the positional deviation detection processing.

  In the above-described embodiment, the scanning control device may perform at least a part of the processing in the printer control device 2090 in the density detection processing and the positional deviation detection processing.

  In the embodiment, the dummy pattern DKDP does not need to be formed every time the detection process is performed. For example, the dummy pattern DKDP is formed only in the first detection process performed when the power of the color printer 2000 is turned on, and the detection process performed until the power of the color printer 2000 is turned off (OFF) The position of the toner pattern in the y-axis direction may be estimated based on the information obtained in the detection process.

  For example, it is possible to estimate the current position from the output information of each light receiving unit when the previous toner pattern stored in the RAM of the printer control device 2090 is illuminated. Specifically, when the light emitting unit Ei (i = 1 to 11) emits light, the output of the light receiving unit Di when the regular reflection light from the intermediate transfer belt 2040 is received, and the toner on the intermediate transfer belt 2040 It may be estimated that the toner pattern is present at a position substantially opposite to the light emitting portion where the difference (output difference ΔDi) from the output of the light receiving portion Di when the regular reflection light from the pattern is received.

  Even if the output information of the light receiving unit is not referred to and the change in the elapsed time from the previous detection process and the environmental conditions (temperature, humidity) are small, the position of the toner pattern generally does not change greatly. It can be estimated that the position is the same as when.

  If the dummy pattern DKDP is not formed, the processes in steps S303 to S309 are not performed.

  In addition, the toner pattern in the above embodiment is an example, and the size (dimension), shape, number, and the like are not limited thereto. For example, each density detection pattern (DP1 to DP4) may be composed of four rectangular patterns (p1 to p4), respectively (see FIG. 80). In this case, the rectangular pattern p4 may be a solid pattern. In this case, the time required for the density detection process can be further shortened.

  As an example, as shown in FIG. 81, the DP pattern row is divided into a first partial DP pattern row made up of a density detection pattern DP1 and a density detection pattern DP3, a density detection pattern DP2, and a density detection pattern. The first partial DP pattern row and the second partial DP pattern row may be formed separately from the second partial DP pattern row composed of DP4 and separated in the main direction. In this case, the time required for concentration detection can be shortened.

  In FIG. 82, a first partial DP pattern row is formed at a position illuminated by the detection light S2 from the light emitting unit E2 and the detection light S3 from the light emitting unit E3, and the detection light from the light emitting unit E9. The case where the 2nd partial DP pattern row | line | column is formed in the position illuminated by S9 and the detection light S10 from the light emission part E10 is shown. In this case, since the light receiving parts D4, D5, D7, and D8 receive the reflected light of the detection light from the different light emitting parts, the light emitting part E2, the light emitting part E3, the light emitting part E6, and the light emitting part E6 It is preferable that the light emitting part E9 and the light emitting part E10 have different lighting timings. However, if the output distribution (light reception amount profile) of the light receiving system when each light emitting unit is individually turned on is obtained in advance, the plurality of light emitting units may be turned on simultaneously. In this case, the received light amount profile can be separated for each light emitting unit by referring to the received light amount profile.

  Further, with respect to a plurality of rectangular patterns constituting one density detection pattern, a part of the rectangular patterns belong to the first partial DP pattern column and the remaining rectangular patterns belong to the second partial DP pattern column. May be. In FIG. 83, one density detection pattern is composed of four rectangular patterns, the rectangular pattern p2 and the rectangular pattern p4 belong to the first partial DP pattern row, and the rectangular pattern p1 and the rectangular pattern p3 are the second part. An example belonging to the DP pattern sequence is shown.

  By the way, since many of the conventional reflective optical sensors have only one light emitting portion, in order to detect a plurality of toner patterns arranged in the main direction, the number of toner patterns corresponding to the number of toner patterns in the main direction can be detected. Type optical sensors had to be arranged in the main direction. Some of the conventional reflective optical sensors have two light emitting portions. Even if the two light emitting portions are turned on at the same time, the distance between the reflective optical sensor and the toner pattern can be determined. When the distance is set to be detected, the light spots from the two light emitting units overlap on one toner pattern. Therefore, even with a conventional reflective optical sensor having two light emitting portions, the conventional reflective optical sensors must be arranged in the main direction by the number of toner patterns in the main direction. The conventional reflective optical sensor has a dimension in the main direction of about 3 cm.

  On the other hand, in the reflective optical sensor 2245 of the present embodiment, since a plurality of toner patterns arranged in the main direction (y-axis direction) can be detected by one reflective optical sensor, the cost can be reduced. It becomes possible.

  In the above embodiment, the case where the reflective optical sensor 2245 has eleven light emitting units has been described, but the present invention is not limited to this. For example, as shown in FIG. 84, the reflective optical sensor 2245 has an irradiation system including 19 light emitting units (E1 to E19) and a light receiving system including 19 light receiving units (D1 to D19). May be. In this case, the illumination optical system includes 19 illumination microlenses, and the light reception optical system includes 19 light reception microlenses.

  In the above embodiment, a calculation algorithm different from that in the above embodiment may be used when separating the detected light reception amount of each light receiving unit into the light reception amount by diffuse reflection light and the light reception amount by regular reflection light. At this time, if M2 is a monotonous function with respect to the toner density in the relationship between M2 and the toner density, M2 may be used instead of M2 / M1.

  In the above embodiment, the case where the reflective optical sensor 2245 is provided at a position corresponding to the central portion of the effective image region in the y-axis direction has been described, but the present invention is not limited to this. For example, the reflective optical sensor 2245 may be provided at a position corresponding to the outside of the effective image area in the y-axis direction. In this case, image process control can be performed in real time.

  In the above embodiment, the case where one reflective optical sensor 2245 is provided has been described. However, the present invention is not limited to this, and a plurality of reflective optical sensors 2245 may be provided. In this case, the detection accuracy in the density detection process and the positional deviation detection process can be further enhanced by, for example, averaging the detection results of the respective reflective optical sensors 2245.

  As an example, FIG. 85 shows a case where two reflective optical sensors (2245a, 2245b) equivalent to the reflective optical sensor 2245 are provided at positions corresponding to outside the effective image region in the y-axis direction. Yes. An example of the toner pattern formed in this case is shown in FIG.

  Further, in the above-described embodiment, not all of the four density detection patterns DP1 to DP4 need be formed in a portion between one sheet.

  For example, the density detection pattern DP1 is formed in a portion between the m-th image and the (m + 1) -th image on the intermediate transfer belt 2040, and the (m + 1) -th image on the intermediate transfer belt 2040. A density detection pattern DP2 is formed in a portion between the sheet and the (m + 2) th image, and a sheet between the (m + 2) th image and the (m + 3) th image on the intermediate transfer belt 2040. A density detection pattern DP3 is formed in the intermediate portion, and the density detection pattern DP4 and the position are located in the intermediate space between the (m + 3) -th image and the (m + 4) -th image on the intermediate transfer belt 2040. A deviation detection pattern PP may be formed.

  Further, for example, a part of the density detection pattern DP1 is formed in a portion between the m-th image and the (m + 1) -th image on the intermediate transfer belt 2040, and ( The remainder of the density detection pattern DP1 may be formed in a portion between the m + 1) th image and the (m + 2) th image.

  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-described embodiment, the case where the reflective optical sensor 2245 uses the toner pattern on the intermediate transfer belt 2040 as a detection target has been described. However, the present invention is not limited to this. It is good also as a detection object. Note that the surface of the photosensitive drum is close to a regular reflector like the intermediate 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 reflective optical sensor 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, and the image forming apparatus other than the printer, for example, a copier, a facsimile, or a multifunction machine in which these are integrated. It may be.

  2000 ... color printer (image forming apparatus), 2010 ... optical scanning apparatus (part of pattern creating apparatus), 2030a to 2030d ... photosensitive drum, 2034a to 2034d ... image forming unit (part of pattern creating apparatus), 2040 ... Intermediate transfer belt (moving body), 2090... Printer control device (processing device), 2245... Reflection type optical sensor, D1 to D11... Light receiving unit, DP1 to DP4 ... density detection pattern (toner density detection pattern), E1 ˜E11... Light emitting part, LD1 to LD11... Light receiving microlens, LE1 to LE11 .. Illuminating microlens, PP... Misregistration detection pattern, DKDP.

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 (7)

In an image forming apparatus that forms an image on a moving body using toner,
A pattern creating device for creating a pattern for toner density detection on the moving body;
A reflective optical sensor that irradiates the pattern created on the movable body with light and receives the light reflected by the pattern;
Based on the output signal of the reflective optical sensor, the light reflected by the pattern is separated into a specular reflected light component and a diffuse reflected light component, and the specular reflected light component according to the expected toner concentration of the pattern And a processing device that calculates a toner density of the pattern based on a predetermined one of the light amount of the diffuse reflected light component and the light amount of the diffuse reflected light component. The first light quantity change rate, which is the rate of change of the light quantity of the regular reflection light component in the relation between the light quantity of the regular reflection light component and the toner density, and the diffusion in the relation between the light quantity of the diffuse reflection light component and the toner density. Using the second light amount change rate that is the change rate of the light amount of the reflected light component,
When the first light amount change rate is larger than the second light amount change rate in the expected toner density of the pattern, the processing device determines the toner of the pattern based on the light amount of the regular reflection light component. The density is calculated, and when the first light quantity change rate is smaller than the second light quantity change rate, the toner density of the pattern is calculated based on the light quantity of the diffuse reflected light component. Item 2. The image forming apparatus according to Item 1. The first light quantity change rate and the second light quantity change rate are equal when the toner density is the density a,
When the expected toner density of the pattern is lower than the density a, the processing device calculates the toner density of the pattern based on the amount of the regular reflection light component, and the expected toner density of the pattern 3. The image forming apparatus according to claim 2, wherein when the density is higher than the density a, the toner density of the pattern is calculated based on the light amount of the diffuse reflected light component.   The image forming apparatus according to claim 1, wherein instead of the light amount of the diffuse reflected light component, the light amount of the diffuse reflected light component ÷ the light amount of the regular reflected light component is used.   The reflection type optical sensor includes an irradiation system including at least three light emitting units different from each other in a second direction orthogonal to the first direction in which the moving body moves, and the pattern emitted from the irradiation system and having the pattern The image forming apparatus according to claim 1, further comprising: a light receiving system including at least three light receiving portions that receive the reflected light.   The image forming apparatus according to claim 1, wherein the moving body is an intermediate transfer belt.   The image forming apparatus according to claim 1, wherein the processing device determines an image process condition based on the calculated toner density of the pattern.