JP2012133065A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of forming a high quality image without causing high cost, an increase in size and reduction of working efficiency.SOLUTION: Patterns for detecting concentration have four rectangular patterns having different toner concentration from one another and are adjacent to one another in a principal direction and in a sub direction. A reflective optical sensor comprises: an irradiation system including eleven light emitting sections disposed along the principal direction; a light receiving system including eleven light receivers; and the like. After an m th image of a plurality of images has been formed, a printer controller performs image process control at a timing before an (m+1) th image is formed. During this time period, the printer controller simultaneously causes two light emitting sections of the reflective optical sensor to emit light and simultaneously obtains toner concentration of two rectangular patterns formed at different positions from each other with respect to the principal direction based on an output signal of the light receiving system.

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 applied to the electrostatic latent image. A so-called development is performed by adhering to obtain a “toner image”.

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

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

(2) The plurality of patches are detected by a reflective optical sensor that is an optical detection means, and the toner density of each patch is calculated using the output of the reflective optical sensor and a predetermined calculation algorithm.

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

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

  For example, in Patent Document 1, a plurality of reference toner images arranged in the process direction are formed in an inter image region sandwiched between two image regions on an image carrier that carries a toner image, and reflection from the reference toner image is performed. An image forming apparatus that receives light with a light receiving sensor is disclosed.

  By the way, in the conventional test pattern, a plurality of patches having the same color and different toner densities are arranged in one row along the sub-direction (moving direction of the image carrier) with respect to one reflective optical sensor.

  In this case, in the image forming process, if the relative distance from the developing device changes due to the rotation axis of the image carrier being inclined or the cross-sectional shape of the image carrier being deviated from a perfect circle, the density unevenness in the output image is changed. Will occur. In particular, unevenness in density in the sub direction is likely to occur due to fluctuations in the image forming process caused by the rotating member.

  When a test pattern is formed under such circumstances, density unevenness is superimposed on a patch that should have a reference toner density, and the toner density is shifted. When the toner density of this test pattern is detected and image density control is performed, density unevenness may be further promoted.

  Therefore, for example, Patent Document 2 discloses image formation in which a plurality of patch images having different gradation levels are formed at a plurality of positions on the transfer carrier in the main scanning direction according to the gradation level of each patch image. An apparatus is disclosed.

  However, the image forming apparatus disclosed in Patent Document 2 requires a plurality of reflective optical sensors in accordance with the positions of a plurality of patch images, resulting in an inconvenience that the cost is increased. In addition, a space for installing a plurality of reflective optical sensors is required, leading to an increase in the size of the image forming apparatus.

  The present invention has been made under such circumstances, and an object thereof is to provide an image forming apparatus capable of forming a high-quality image without causing an increase in cost, an increase in size, and a reduction in work efficiency. There is.

  In the image forming apparatus for forming an image on a moving body that moves in a first direction, a plurality of images are continuously formed on the moving body, and the plurality of images are formed on the moving body. After the m-th image in the image is formed, before the m + 1-th image is formed, a test pattern including a plurality of patches whose positions are different from each other in the second direction orthogonal to the first direction is created. A test pattern creation device; an irradiation system comprising at least three light emitting portions arranged at equal intervals Le with respect to the second direction; and at least three for receiving light emitted from the irradiation system and reflected by the test pattern A reflection-type optical sensor including a light-receiving system including two light-receiving units; based on an output signal of the light-receiving system when at least two light-emitting units in the reflection-type optical sensor are turned on; An image forming apparatus comprising: a; simultaneously obtaining a processor toner concentration of at least two patches are created at different positions with respect to the second direction.

  According to this, it is possible to form a high-quality image without causing an increase in cost, an increase in size, and a reduction in work efficiency.

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 block diagram for demonstrating a printer control apparatus. It is a figure for demonstrating a general image forming unit. It is FIG. (1) for demonstrating schematic structure of an optical scanning device. FIG. 3 is a second diagram for explaining a schematic configuration of the optical scanning device; FIG. 3 is a third diagram for explaining a schematic configuration of the optical scanning device; FIG. 4 is a diagram (part 4) for explaining a schematic configuration of the optical scanning device; It is a figure for demonstrating a toner pattern detector. It is a figure for demonstrating the arrangement position of a reflection type optical sensor. It is FIG. (1) for demonstrating a reflection type optical sensor. It is FIG. (2) for demonstrating a reflection type optical sensor. It is FIG. (3) for demonstrating a reflection type optical sensor. It is FIG. (4) for demonstrating a reflection type optical sensor. It is a figure for demonstrating the light for a detection. It is FIG. (5) for demonstrating a reflection type optical sensor. FIG. 6 is a diagram for explaining a toner pattern. It is a figure for demonstrating the four rectangular patterns in each density | concentration detection pattern. It is a figure for demonstrating arrangement | positioning of each density | concentration detection pattern. It is a figure for demonstrating the positional relationship of the pattern for density | concentration detection, and a light emission part. It is a figure for demonstrating the pattern for position shift detection. 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. FIG. 6 is a diagram for explaining a toner pattern on a transfer belt. It is a figure for demonstrating the output distribution of each light-receiving part when an illumination target object is a transfer belt when the light emission part E3 is lighted. It is a figure for demonstrating the light reception amount distribution of each light-receiving part when the light emission part E3 is turned on and an illumination 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 E9 is turned on and an illumination target object is the rectangular pattern p2 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 E3 is turned on and an illumination 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 E9 is turned on and an illumination 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 when the detection light S3 is reflected by the rectangular pattern p1. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part when the detection light S3 is reflected by the rectangular pattern p1. It is a figure for demonstrating the regular reflection light component in the light reception amount of each light-receiving part when the detection light S9 is reflected by the rectangular pattern p2. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part when the detection light S9 is reflected by the rectangular pattern p2. It is a figure for demonstrating the regular reflection light component in the light reception amount of each light-receiving part when the detection light S3 is reflected by the rectangular pattern p3. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part when the detection light S3 is reflected by the rectangular pattern p3. It is a figure for demonstrating the regular reflection light component in the light reception amount of each light-receiving part when the detection light S9 is reflected by the rectangular pattern p4. It is a figure for demonstrating the diffuse reflection light component in the light reception amount of each light-receiving part when the detection light S9 is reflected by the rectangular pattern p4. It is a figure for demonstrating the total value D1 of the regular reflection light component in each illumination target object. It is a figure for demonstrating the relative value of the total value D1 of the regular reflection light component in each illumination object. It is a figure for demonstrating the total value D2 of the diffuse reflected light component in each illumination object. It is a figure for demonstrating the total value D2 / total value D1 of each illumination target object. It is a figure for demonstrating the relative value of total value D2 / total value D1 in each illumination object. FIG. 6 is a diagram (part 1) for describing a positional deviation detection process; FIG. 6 is a diagram (part 2) for describing a positional deviation detection process; 44A and 44B are diagrams for explaining detection of displacement in the sub-direction and the main direction, respectively. It is a figure for demonstrating the case where two light emission parts are lighted with respect to one rectangular pattern. It is a figure for demonstrating the modification 1 of the arrangement | sequence of 16 rectangular patterns. It is a figure for demonstrating the modification 2 of the arrangement | sequence of 16 rectangular patterns. It is a figure for demonstrating the modification 3 of the arrangement | sequence of 16 rectangular patterns. It is a figure for demonstrating the modification 4 of the arrangement | sequence of 16 rectangular patterns. It is a figure for demonstrating the case where each density | concentration detection pattern consists of six rectangular patterns.

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

  The color printer 2000 is a tandem multi-color printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes an optical scanning device 2010, four photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), 4 Toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing roller 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 060, paper ejection tray 2070, a communication control unit 2080, a toner pattern detector 2245, temperature and humidity sensor (not shown) and a printer control unit 2090 for centrally controlling the above units.

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

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like and an information device (for example, a facsimile device) via a public line. Then, the communication control device 2080 notifies the received information to the printer control device 2090.

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data And an AD converter for converting the digital 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, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a are used as a set and form an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image. Constitute.

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

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

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

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

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

  The optical scanning device 2010 uses the multi-color image information (black image information, cyan image information, magenta image information, yellow image information) from the printer control device 2090 to charge the light flux modulated for each color to the corresponding charging. Irradiate each of the surfaces of the photosensitive drums. As a result, on the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing roller as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

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

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

  Here, a configuration of a general image forming unit will be described with reference to FIG. In the image forming unit, a charging unit, a developing unit, and a photoconductor cleaning unit are provided around the photoconductor drum. Further, a primary transfer unit is provided at a position facing the photosensitive drum via the intermediate transfer belt.

  The charging unit is of a contact charging type employing a charging roller, and 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 using a non-contact scorotron charger or the like can also be used.

  The developing unit uses a two-component developer composed of a magnetic carrier and a nonmagnetic toner. As the developer, a one-component developer can also be used. The developing unit can be roughly divided into a stirring unit and a developing unit provided in the developing case. In the agitation section, the two-component developer is conveyed while being agitated and supplied onto a developing sleeve as a developer carrying member. This agitating part is provided with two parallel screws, and a partition plate is provided between the two screws in order 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, the TC sensor adopts a magnetic permeability method, and the toner concentration in the developing unit is the magnetic permeability of the developer, that is, per unit volume. Appears in the magnetic resistance of the developer.

  On the other hand, in the developing unit, the toner in the developer attached to the developing sleeve is transferred to the photosensitive drum. The developing portion is provided with a developing sleeve facing the photosensitive drum through the opening of the developing case, and a magnet (not shown) is fixedly disposed in the developing sleeve. A doctor blade is provided so that the tip approaches the developing sleeve.

  In this developing unit, the developer is conveyed and circulated while being stirred by two screws and 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 as the developing sleeve rotates, and is regulated to an appropriate amount by the doctor blade. The regulated developer is returned to the stirring unit. 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 to form a toner image. 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 an operation, this is detected by the TC sensor, and toner is supplied to the stirring unit based on the detection result.

  A primary transfer roller is employed as the primary transfer unit, and is installed so as to be pressed against the photosensitive drum with the intermediate transfer belt interposed therebetween. Of course, the primary transfer unit is not limited to a roller shape but may be a conductive brush shape or a non-contact corona charger.

  The photoconductor cleaning unit is arranged so that the tip is pressed against the photoconductor drum. For example, a cleaning blade made of polyurethane rubber is provided. In order to improve the cleaning performance, a conductive fur brush that contacts the photosensitive drum is also used. A bias is applied to the fur brush from a metal electric field roller (not shown), and a scraper tip (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).

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a multicolor image. By the way, the direction in which the toner image moves on the transfer belt 2040 is called a “sub direction”, and the direction orthogonal to the sub direction (here, the Y-axis direction) is called a “main direction”.

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

  In the fixing roller 2050, heat and pressure are applied to the recording paper, whereby the toner is fixed on the recording paper. The recording paper fixed here is sent to a paper discharge tray 2070 via a paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

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

  The toner pattern detector 2245 is disposed on the + Z side of the transfer belt 2040 and in the vicinity of the + X side end of the transfer belt 2040. The toner pattern detector 2245 will be described later.

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

  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), 4 cylindrical lenses (2204a, 2204b, 2204c, 2204d), polygon mirror 2104, 4 deflector side scanning lenses (2105a, 2105b, 2105c, 2105d), 8 foldings Mirrors (2106a, 2106b, 2106c, 2106d, 2108a, 2108b, 2108c, 2108d), four image plane side scanning lenses (2107a, 2107b, 2107c, 2107d), four light detection sensors (2205a, 205b, 2205c, 2205d), 4 sheets of light detection mirror (2207a, includes 2207b, 2207c, 2207d), and the like scanning control device (not shown). And these are assembled | attached to the predetermined position of the optical housing 2300 (illustration omitted in FIGS. 4-6, refer FIG. 7).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  The polygon mirror 2104 has a four-stage mirror having a two-stage structure, and each mirror serves as a deflection reflection surface. The light beam from the cylindrical lens 2204a and the light beam from the cylindrical lens 2204d are deflected by the first-stage (lower) tetrahedral mirror, respectively, and the light beam from the cylindrical lens 2204b and the cylindrical light are deflected by the second-stage (upper) tetrahedral mirror. It arrange | positions so that the light beam from the lens 2204c may be deflected, respectively.

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

  Each deflector-side scanning lens has a non-circular surface shape having such a power that the light spot moves at a constant speed in the main scanning direction on the corresponding photosensitive drum surface as the polygon mirror 2104 rotates. ing.

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

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

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

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

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

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

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

  An optical system disposed on the optical path between the polygon mirror 2104 and each photosensitive drum is also called a scanning optical system. In this embodiment, the K station scanning optical system is composed of the deflector side scanning lens 2105a, the image plane side scanning lens 2107a, and the folding mirrors (2106a, 2108a). Further, the scanning optical system of the C station is composed of the deflector side scanning lens 2105b, the image plane side scanning lens 2107b, and the folding mirrors (2106b, 2108b). The deflector side scanning lens 2105c, the image plane side scanning lens 2107c, and the folding mirrors (2106c, 2108c) constitute the M station scanning optical system. Further, the Y station scanning optical system is composed of the deflector side scanning lens 2105d, the image plane side scanning lens 2107d, and the folding mirrors (2106d, 2108d).

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

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

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

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

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

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

  Next, the toner pattern detector 2245 will be described.

  The toner pattern detector 2245 has three reflective optical sensors (2245a, 2245b, 2245c) as shown in FIG. 8 as an example.

  As an example, as shown in FIG. 9, the reflective optical sensor 2245a is disposed in the vicinity of the −Y side end of the transfer belt 2040, and the reflective optical sensor 2245c is the + Y side end of the transfer belt 2040. It is arranged in the vicinity. The reflective optical sensor 2245b is arranged at an intermediate position between the reflective optical sensor 2245a and the reflective optical sensor 2245c with respect to the main direction.

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

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

  As shown in FIGS. 10 to 13 as an example, the reflective optical sensor 2245a is an illumination system including 11 light emitting units (E1 to E11) and illumination including 11 illumination microlenses (LE1 to LE11). An optical system, a light receiving optical system including 11 light receiving microlenses (LD1 to LD11), a light receiving system including 11 light receiving portions (D1 to D11), and the like are provided.

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

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

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

  Here, for easy understanding, it is assumed that only the light beam emitted from each light emitting unit and passing through the corresponding illumination microlens illuminates the transfer belt 2040 as detection light (S1 to S11) (FIG. 14). reference). Then, the center of the light spot (hereinafter abbreviated as “detection light spot” for convenience) formed on the surface of the transfer belt 2040 by each detection light is the center of the corresponding light emitting unit and light receiving unit with respect to the sub-direction. Near the middle.

  As an example, the size (diameter) of each detection light spot is 0.4 mm. This value is equal to the interval Le between the eleven light emitting units. Note that the size (diameter) of a conventional detection light spot is usually about 2 to 3 mm.

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

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

  Each light receiving portion is disposed on the optical path of a light beam emitted from the corresponding light emitting portion and regularly reflected by the surface of the transfer belt 2040. The interval (arrangement pitch) between the 11 light receiving portions is equal to the interval Le between the 11 light emitting portions. The size of each light receiving portion in the main direction is about 0.35 mm. Further, the peak wavelength of the light receiving sensitivity in each light receiving portion is in the vicinity of 850 nm.

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

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

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

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

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

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

  Here, the lens diameter of each light receiving microlens is made larger than that of each illumination microlens so that more reflected light can be received. In addition, by making the radius of curvature of each light receiving microlens smaller than that of each illumination microlens, total reflection inside the lens increases, so the amount of specularly reflected light received can be reduced. . In addition, by reducing the radius of curvature of each light receiving microlens, it is possible to greatly refract the light beam that has passed through the light receiving microlens placed in front of the light receiving unit adjacent to the light receiving unit corresponding to the light emitting unit to be lit. Thus, it can be expected that the diffuse reflected light from the test pattern can reach the light receiving portion and the amount of the diffuse reflected light received can be increased.

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

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

  As an example, as shown in FIG. 15, the optical axis of each illumination microlens is Δd (here, the light receiving system side with respect to an axis that passes through the center of each corresponding light emitting unit and is perpendicular to the light emitting unit). 0.035 mm). The optical axis of each light receiving microlens is shifted by Δd ′ (here, 0.020 mm) toward the irradiation system with respect to an axis that passes through the center of each corresponding light receiving portion and is perpendicular to the light receiving portion. Thereby, more reflected light can be guide | induced to the corresponding light-receiving part.

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

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

  Here, as an example, as shown in FIG. 16, the pattern PP is formed at the Y1 position, the pattern PP and the patterns DP1 to DP4 are formed at the Y2 position, and the pattern PP is formed at the Y3 position.

  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.

  The density detection pattern DP1 and the density detection pattern DP2, the density detection pattern DP2 and the density detection pattern DP3, and the density detection pattern DP3 and the density detection pattern DP4 are all formed adjacent to each other in the sub direction.

  Hereinafter, when it is not necessary to distinguish between the density detection patterns DP1 to DP4, they are also collectively referred to as “density detection patterns DP”.

  As shown in FIG. 17 as an example, the density detection pattern DP has four rectangular patterns (p1 to p4, hereinafter referred to as “rectangular pattern” for convenience). Each rectangular pattern has a different toner density gradation when viewed as a whole. Here, p1, p2, p3, and p4 are set from a rectangular pattern having a low toner density. That is, the rectangular pattern p1 has the lowest toner density, and the rectangular pattern p4 has the highest toner density.

  The rectangular pattern p1 and the rectangular pattern p3 are formed adjacent to each other in the sub direction, and the rectangular pattern p2 and the rectangular pattern p4 are formed adjacent to each other in the sub direction. The rectangular pattern p1 and the rectangular pattern p2 are formed adjacent to each other in the main direction, and the rectangular pattern p3 and the rectangular pattern p4 are formed adjacent to each other in the main direction.

  Here, 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. Further, the center interval w4 between two adjacent rectangular patterns in the main direction is 2.4 mm. Therefore, the size of the entire density detection pattern DP in the main direction is 3.4 mm. This is smaller than the distance (4 mm) between the light emitting part E1 and the light emitting part E11.

  In addition, with respect to the sub direction, the center interval w3 between two adjacent rectangular patterns is 3 mm. Therefore, the size (4 · w3 + w2) of the entire density detection pattern DP in the sub direction is 14 mm.

  In this way, the size of the density detection pattern DP can be made much smaller than in the conventional case in both the main direction and the sub direction.

  In this case, the amount of toner required to create the toner pattern can be reduced to about 1/100 of the conventional amount. That is, the amount of non-contributing toner can be greatly reduced. As a result, the toner cartridge replacement time can be extended.

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

  Here, as an example, as shown in FIG. 18, the four rectangular patterns p1 and the four rectangular patterns p3 are formed in a line along the sub-direction. Hereinafter, this column is referred to as a “first pattern column”. Also, the four rectangular patterns p2 and the four rectangular patterns p4 are formed in a line along the sub direction. Hereinafter, this column is referred to as a “second pattern column”. The first pattern row and the second pattern row are adjacent to each other in the main direction.

  In the present embodiment, as shown in FIG. 19 as an example, the first pattern row is formed at the position illuminated by the detection light S3 from the light emitting unit E3 of the reflective optical sensor 2245b, and the reflective optical sensor 2245b It is set so that the second pattern row is formed at a position illuminated by the detection light S9 from the light emitting unit E9.

  As shown in FIG. 20 as an example, the misregistration detection pattern PP is a first pattern group composed of four linear patterns (LPY1, LPM1, LPC1, LPK1) parallel to the main direction (Y-axis direction). And a second pattern group composed of four linear patterns (LPY2, LPM2, LPC2, LPK2) inclined with respect to the main direction.

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

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

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

  In this embodiment, as shown in FIG. 21 as an example, the center in the main direction of the misregistration detection pattern PP is formed at the position illuminated by the detection light S6 from the light emitting unit E6 of each reflective optical sensor. Is set to

  Next, density detection processing and positional deviation detection processing performed using the toner pattern detector 2245 for image process control will be described with reference to FIG. In the present embodiment, the density detection process and the positional deviation detection process are performed by the printer control device 2090. The flowchart of FIG. 22 corresponds to a series of processing algorithms executed by the printer control apparatus 2090 during the density detection process and the positional deviation detection process.

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

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

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

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

  As a result, the scanning control device controls the Y station so that the density detection pattern DP4 and the line patterns LPY1 and LPY2 are formed at predetermined positions on the photosensitive drum 2030d. The M station is controlled so that the density detection pattern DP2 and the line patterns LPM1, LPM2 are formed.

  Further, the scanning control device controls the C station so that the density detection pattern DP3 and the line-shaped patterns LPC1 and LPC2 are formed at predetermined positions on the photosensitive drum 2030b, and at the predetermined positions on the photosensitive drum 2030a. The K station is controlled so that the density detection pattern DP1 and the line patterns LPK1, LPK2 are formed.

  It should be noted that the pattern formation position information, density information, bias conditions corresponding to each gradation of the density detection pattern necessary for forming each pattern, and the density conversion LUT of the output of the reflective optical sensor for estimating the toner density The (look-up table) is stored in advance in the ROM of the printer control apparatus 2090. Each misregistration detection pattern is formed under the same image forming conditions (exposure power, charging bias, developing bias, etc.).

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

  As a result, the toner pattern is formed at positions Y1, Y2, and Y3 on the transfer belt 2040 (see FIG. 23).

  In the next step S305, toner density detection processing is performed. Here, only the reflective optical sensor 2245b is used.

  Prior to the density detection pattern reaching the front (−Z side) of the reflective optical sensor 2245b, the light emitting part E3 and the light emitting part E9 are turned on, and the detection light S3 and the detection light S9 cause the transfer belt 2040 to move. The amount of light received by each light receiving unit when illuminated is acquired. Note that the amount of light received by each light receiving unit can be relatively obtained from the signal level of the signal output from each light receiving unit.

  The amount of light received by the light receiving portions D1 to D5 when the detection light S3 illuminates the transfer belt 2040 is shown in FIG. Here, the amount of light received by the light receiving unit D3 is “1”. D_ALL is the sum of the amounts of light received by the five light receiving portions D1 to D5.

  The amount of light received by each light receiving unit when the detection light S3 and the detection light S9 illuminate the density detection pattern is acquired.

  FIG. 25 shows received light amounts of the light receiving portions D1 to D5 when the detection light S3 illuminates the rectangular pattern p1 of the density detection pattern DP1.

  FIG. 26 shows received light amounts of the light receiving portions D1 to D5 when the detection light S9 illuminates the rectangular pattern p2 of the density detection pattern DP1.

  FIG. 27 shows the amounts of light received by the light receiving portions D1 to D5 when the detection light S3 illuminates the rectangular pattern p3 of the density detection pattern DP1.

  FIG. 28 shows received light amounts of the light receiving portions D1 to D5 when the detection light S9 illuminates the rectangular pattern p4 of the density detection pattern DP1.

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

  For each rectangular pattern, the detected light reception amount of each light receiving unit is separated into a light reception amount by diffuse reflection light and a light reception amount by regular reflection light. Hereinafter, the rectangular pattern p1 will be described as an example.

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

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

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

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

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

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

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

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

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

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

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

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

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

  When the illumination target of the light emitting unit E3 is the rectangular pattern p1 of the density detection pattern DP1, FIG. 29 shows the amount of light received by the specularly reflected light, and FIG. 30 shows the amount of light received by the diffusely reflected light.

  When the illumination target of the light emitting unit E9 is the rectangular pattern p2 of the density detection pattern DP1, FIG. 31 shows the amount of light received by the specularly reflected light, and FIG. 32 shows the amount of light received by the diffusely reflected light.

  When the illumination target of the light emitting unit E3 is the rectangular pattern p3 of the density detection pattern DP1, FIG. 33 shows the amount of light received by the specularly reflected light, and FIG. 34 shows the amount of light received by the diffusely reflected light.

  When the illumination object of the light emitting unit E9 is the rectangular pattern p4 of the density detection pattern DP1, FIG. 35 shows the amount of light received by the specularly reflected light, and FIG. 36 shows the amount of light received by the diffusely reflected light.

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

  A total value D1 of the amount of light received by the regular reflection light of each illumination object is shown in FIG. FIG. 38 shows the total amount D1 of the amount of light received by the regular reflection light of each rectangular pattern when the total value D1 when the illumination object is the transfer belt 2040 is 1. According to this, the total value D1 monotonously decreases as the toner density increases. This is because the higher the toner concentration, the more toner is adhered, and the regular reflection light is reduced. The toner concentration and the total value D1 are in a one-to-one correspondence. Therefore, the toner density of the illumination object can be known from the measured value of the total value D1.

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

  The total value D2 / total value D1 of each illumination object is shown in FIG. FIG. 41 shows the total value D2 / total value D1 of each illumination object when the maximum value of the total value D2 / total value D1 is 1. According to this, the total value D2 / total value D1 monotonously increases as the toner density increases. Therefore, the toner density of the illumination object can be known from the total value D2 / total value D1.

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

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

  In this step 307, misalignment detection processing is performed. Here, the light emitting part E6 in each reflective optical sensor is continuously lit. The detection light S6 from the light emitting unit E6 illuminates the line patterns LPK1 to LPY2 sequentially as the transfer belt 2040 rotates, that is, as time elapses (see FIG. 42).

  Then, the output signal of each light receiving unit is traced in time, and the time Tkm1 from when the line pattern LPK1 is detected until the line pattern LPM1 is detected, the line pattern LPK1 is detected, and then the line pattern LPC1 is detected. Time Tkc1 until detection and time Tky1 from detection of the line pattern LPK1 to detection of the line pattern LPY1 are obtained (see FIG. 43). Here, for the sake of clarity, it is assumed that the output signal of each light receiving unit is amplified and passes through a comparison circuit that compares with a predetermined reference value.

  Further, the time Tkm2 from the detection of the line pattern LPK2 to the detection of the line pattern LPM2, the time Tkc2 from the detection of the line pattern LPK2 to the detection of the line pattern LPC2, and the detection of the line pattern LPK2 Then, a time Tky2 from when the line pattern LPY2 is detected is obtained (see FIG. 43).

  Then, the time Tkc1, the time Tkm1, and the time Tky1 are respectively compared with a reference time obtained in advance, and the misregistration amounts of the cyan, magenta, and yellow toner images in the sub-direction with respect to the black toner image based on the time difference. ΔS1 is obtained (see FIG. 44A).

  Further, the time Tkc2, the time Tkm2, and the time Tky2 are respectively compared with a reference time obtained in advance, and from the time difference ΔT, using the following equation (1), cyan for the main direction for the black toner image, A positional deviation amount ΔS2 of each of the magenta and yellow toner images is obtained (see FIG. 44B). Here, V is a moving speed of the transfer belt 2040 in the sub-direction, and θ is an inclination angle (here, 45 °) with respect to the main direction of the line pattern.

  ΔS2 = V · ΔT · cot θ (1)

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

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

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

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

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

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

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

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

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

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

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

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

  The toner pattern as the test pattern includes four density detection patterns (DP1 to DP4). Each density detection pattern has four rectangular patterns having different toner densities, and is adjacent to each other in the main direction and the sub direction. That is, the 16 rectangular patterns are formed as two pattern rows (first pattern row and second pattern row) arranged along the sub-direction, and the pattern rows are adjacent to each other in the main direction.

  The toner pattern detector 2245 has a reflective optical sensor 2245b provided at a position facing the four density detection patterns (DP1 to DP4).

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

  The printer control device 2090 performs image process control at a timing after the m-th image in the plurality of images is formed and before the (m + 1) -th image is formed. Then, the printer control device 2090 turns on the light emitting unit E3 and the light emitting unit E9 of the reflective optical sensor 2245b at the same time, and based on the output signal of the light receiving system, two rectangular patterns created at different positions with respect to the main direction ( The toner density of p1 and p2 and p3 and p4) is obtained simultaneously. In this case, the toner density can be detected in a short time.

  In addition, since the toner density can be detected with one reflective optical sensor, it is not necessary to secure a large space for installing the reflective optical sensor.

  Further, since the size of the toner pattern can be made smaller than before, the consumption of non-contributing toner can be made smaller than before.

  Therefore, the color printer 2000 can form a high-quality image without causing an increase in cost, an increase in size, and a reduction in work efficiency.

  In the above embodiment, the case where the light emitting unit E3 and the light emitting unit E9 are turned on at the same time when detecting the toner density has been described. However, the present invention is not limited to this, and the light emitting unit E3 and the light emitting unit E9 are alternately arranged. It may be turned on / off.

  In the above embodiment, the printer control device 2090 may acquire the output signal of the light receiving system only once or a plurality of times for one rectangular pattern. Then, when the toner density is acquired a plurality of times, the toner density may be detected based on the average value thereof or the average value obtained by removing the maximum value and the minimum value therefrom. Moreover, when acquiring several times, you may light the corresponding light emission part continuously, and you may light-pulse according to the frequency | count of acquisition.

  Moreover, although the case where only one light emission part was lit with respect to one pattern row | line was demonstrated in the said embodiment, it is not limited to this, A several light emission part is sequentially added with respect to one pattern row | line | column. It may be turned on / off. For example, the light emitting unit E2 and the light emitting unit E3 may be alternately turned on / off for the first pattern row. Then, for example, an average value of the toner density obtained when the light emitting unit E2 is turned on and the toner density obtained when the light emitting unit E3 is turned on may be used as the toner density detection result. In this case, it is preferable that the intermediate position between the light emitting portion E2 and the light emitting portion E3 and the center of the first pattern row substantially coincide with each other in the main direction (see FIG. 45).

  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.

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

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

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

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

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

  Further, the arrangement of the 16 rectangular patterns in the above embodiment is an example, and the present invention is not limited to this (see FIGS. 46 to 49).

  By the way, when there is a possibility that the toner pattern forming position may be shifted with respect to the main direction, in the above-described embodiment, in the vicinity of the position where the rectangular pattern p1 of the density detection pattern DP1 faces the reflective optical sensor 2245b prior to density detection. The light emitting units E1 to E11 are turned on / off in order, and the position of the density detection pattern in the main direction is obtained based on the output signals of the light receiving units D1 to D11 at that time. You may determine the light emission part lighted at the time. For example, when the output level of the light receiving part D2 is higher than the output level of the light receiving part D3, the light emitting part E2 is a light emitting part that is turned on when the density is detected.

  In the above embodiment, the case where four rectangular patterns having different toner densities for one color are formed as the density detection patterns has been described. However, the present invention is not limited to this. For example, six rectangular patterns having different toner concentrations for one color may be formed (see FIG. 50).

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

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

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

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

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

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

  As described above, the image forming apparatus according to the present invention is suitable for forming a high-quality image without causing an increase in cost, an increase in size, and a reduction in work efficiency.

  2000 ... Color printer (image forming apparatus), 2010 ... Optical scanning apparatus (test pattern creation apparatus), 2030a to 2030d ... Photosensitive drum, 2040 ... Transfer belt (moving body), 2090 ... Printer control apparatus (processing apparatus), 2245 ... toner pattern detectors, 2245a, 2245b, 2245c ... reflective optical sensors, D1 to D11 ... light receiving parts, E1 to E11 ... light emitting parts, LD1 to LD11 ... light receiving microlenses, LE1 to LE11 ... illumination microlenses, p1 ~ P4 ... rectangular pattern (patch).

Japanese Patent No. 4254101 Japanese Patent No. 4265950

Claims (7)

In an image forming apparatus that forms an image on a moving body that moves in a first direction,
A plurality of images are continuously formed on the moving body,
After the m-th image in the plurality of images is formed on the moving body, and before the m + 1-th image is formed, a plurality of positions different from each other in the second direction orthogonal to the first direction. A test pattern creation device for creating a test pattern including a patch of
A light receiving system including an irradiation system including at least three light emitting units arranged at equal intervals Le with respect to the second direction, and at least three light receiving units configured to receive light emitted from the irradiation system and reflected by the test pattern. A reflective optical sensor comprising a system;
Based on output signals of the light receiving system when at least two light emitting units in the reflective optical sensor are turned on, toner concentrations of at least two patches created at different positions with respect to the second direction are simultaneously obtained. An image forming apparatus comprising: a processing apparatus;   The image forming apparatus according to claim 1, wherein at least two light emitting units in the reflective optical sensor are sequentially turned on and off.   The image forming apparatus according to claim 1, wherein at least two light emitting units are individually turned on / off for one patch.   The image forming apparatus according to claim 1, wherein the processing device acquires an output signal of the light receiving system a plurality of times for one patch.   5. The image forming apparatus according to claim 1, wherein a size of a light spot with which the test pattern is illuminated with respect to the second direction is substantially equal to the interval Le. 6.   The distance between two light emitting units located at both ends of the at least three light emitting units with respect to the second direction is larger than the overall size of the test pattern. The image forming apparatus according to one item.   The image forming apparatus according to claim 1, wherein the moving body is an intermediate transfer belt.