JP2014164163A - Reflective optical sensor and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective optical sensor capable of improving detection accuracy in a main direction.SOLUTION: A reflective optical sensor includes a light emitting unit, a lens for illumination, two lenses for light reception, two light receiving units, an opening member, and a substrate. The reflective optical sensor emits detection light onto an intermediate transfer belt to form an optical spot having an elliptical shape, and a long axis direction of the ellipse is inclined by an angle θ with respect to an X-axis direction. With the use of a distance of travel of the intermediate transfer belt Ls from when a light spot for detection is brought into contact with a parallel line-like pattern until when the light spot is out of the contact with the pattern, and a distance of travel of the intermediate transfer belt Lm from when the light spot for detection is brought into contact with an inclined line-like pattern until when the light spot is out of the contact with the pattern, the angle θ is set to be a value when |Lm-Ls| is the minimum.

Description

  The present invention relates to a reflective optical sensor and an image forming apparatus, and more particularly to a reflective optical sensor that receives light reflected by an object, and an image forming apparatus including the reflective optical sensor.

  Image forming apparatuses such as printers, copiers, facsimiles, and plotters 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”) by an optical scanning device (exposure device), and the electrostatic latent image is formed. So-called development is performed by attaching toner to the latent image to obtain a “toner image”.

  In an image forming process in a multicolor image forming apparatus, for example, a plurality of toner images corresponding to respective colors such as black, magenta, cyan, and yellow are superimposed on an intermediate transfer belt and primarily transferred, and then recording paper Secondary transfer is performed collectively.

  In this image forming process, adjustment deviations of the optical scanning device (exposure device) and the plurality of photosensitive drums corresponding to the respective colors, and fluctuations in the driving mechanisms for driving the photosensitive drums and the intermediate transfer belt are directly applied to the color image. Since color shift appears, color shift control is indispensable.

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

  Various reflective optical sensors have been proposed (see, for example, Patent Document 1 to Patent Document 7). For example, as a conventional reflective optical sensor, a 1LED-2PD type reflective optical sensor composed of one light emitting portion and two light receiving portions, or 2LED-1PD composed of two light emitting portions and one light receiving portion. Types of reflective optical sensors.

  Further, Patent Document 8 discloses that the density of a test pattern is obtained by irradiating light from a light emitting element onto an image carrier and a test pattern formed on the image carrier, and detecting the reflected light by two light receiving elements. An image forming apparatus having a density detection apparatus that acquires information and an image formation condition control apparatus that controls image formation conditions based on information obtained from the density detection apparatus is disclosed.

  The demand for image quality in image forming apparatuses is increasing year by year. However, the conventional reflective optical sensor does not have sufficient position detection accuracy in the main direction, and it is difficult for an image forming apparatus including the reflective optical sensor to obtain a required level of image quality.

  The present invention includes a light emitting unit that emits light toward a moving body, and a light receiving unit that receives light emitted from the light emitting unit and reflected by a detection pattern formed on the moving body, and the detection The pattern for use includes a first pattern orthogonal to the moving direction of the moving body and a second pattern inclined with respect to the first pattern, and the pattern on the moving body by the light emitted from the light emitting unit The light spot has a shape with different lengths in two axial directions orthogonal to each other, the long axis direction of the light spot is inclined by an angle θ with respect to the direction orthogonal to the moving direction, and the light spot is Using the moving distance Ls of the moving body from contact with the pattern 1 until it comes off, and the moving distance Lm of the moving body from the time the light spot touches the second pattern until it comes off, the angle θ is | Lm-Ls It is a reflection type optical sensor which is a value when |

  According to the reflective optical sensor of the present invention, it is possible to improve the position detection accuracy in the main direction.

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 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 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 reflection type optical sensor. It is a figure for demonstrating the optical path of the light inject | emitted from the light emission part. It is a figure for demonstrating an opening member. It is a figure for demonstrating the arrangement position of the lens 12 for light reception, and the light-receiving part 14. FIG. It is a figure for demonstrating the arrangement position of the lens 13 for light reception, and the light-receiving part 15. FIG. FIG. 4 is a diagram for explaining a toner pattern formed on an intermediate transfer belt. It is a figure for demonstrating the four rectangular patterns in each density | concentration detection pattern. It is a figure for demonstrating the pattern for position shift detection. 6 is a flowchart for explaining image process control performed by the printer control apparatus. FIG. 6 is a diagram for describing toner pattern formation timing. It is a figure for demonstrating the positional relationship of the light spot for a detection, and each rectangular pattern. It is a figure for demonstrating the output waveform of the light-receiving part 14 when a density | concentration detection pattern is an irradiation target object. It is a figure for demonstrating the relationship between the output waveform of the light-receiving part 14 in FIG. 21, and an irradiation target object. It is a figure for demonstrating the output waveform of the light-receiving part 15 when a density | concentration detection pattern is an irradiation target object. It is a figure for demonstrating the relationship between the output waveform of the light-receiving part 15 in FIG. 23, and an irradiation target object. It is a figure for demonstrating the positional relationship of the light spot for a detection, and each linear pattern. It is a figure for demonstrating the output waveform of the light-receiving part 14 when the pattern for position shift detection is an irradiation target object. It is a figure for demonstrating the relationship between the output waveform of the light-receiving part 14 in FIG. 26, and an irradiation target object. FIG. 6 is a diagram (part 1) for explaining a density conversion LUT (look up table); FIG. 6 is a diagram (part 2) for explaining a density conversion LUT (look-up table); It is a figure for demonstrating the detection time of each linear pattern when the pattern for position shift detection is an irradiation target object. It is a figure for demonstrating calculation of the amount of position shift. FIGS. 32A and 32B are diagrams for explaining the amount of misalignment of the magenta line pattern. FIG. 33A and FIG. 33B are diagrams for explaining an ellipse, respectively. FIG. 34A and FIG. 34B are diagrams for explaining the relationship between the parallel line pattern and the ellipse, respectively. FIGS. 35A and 35B are diagrams for explaining the relationship between the inclined line pattern and the ellipse, respectively. It is the figure which modeled the relationship between a parallel line pattern and an ellipse. It is the figure which modeled the relationship between an inclination line pattern and an ellipse. It is a figure for demonstrating Ls. It is a figure for demonstrating Lm. It is a figure for demonstrating an elliptical light spot and an elliptical light spot. It is FIG. (1) for demonstrating intensity distribution of an elliptical light spot and an elliptical light spot. It is FIG. (2) for demonstrating intensity distribution of an elliptical light spot and an elliptical light spot. It is a figure for demonstrating the relationship between a parallel line pattern and an elliptical light spot. It is a figure for demonstrating the relationship between an inclination line pattern and an elliptical light spot. 45A and 45B are diagrams for explaining the relationship between a circular detection light spot, a parallel line pattern, and an inclined line pattern (α = 45 °), respectively. 46A to 46C are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 45 °) are detected by a circular detection light spot, respectively. It is. 47A and 47B are diagrams for explaining the relationship between the detection light spot having the elliptical shape 1, the parallel line-shaped pattern, and the inclined line-shaped pattern (α = 45 °), respectively. 48 (A) to 48 (C) are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 45 °) are detected by a detection light spot having an elliptical shape 1, respectively. FIG. 49A and 49B are diagrams for explaining the relationship between the detection light spot having the elliptical shape 2, the parallel line pattern, and the inclined line pattern (α = 45 °), respectively. 50A to 50C are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 45 °) are detected by the detection light spot having an elliptical shape 2, respectively. FIG. 51A and 51B are diagrams for explaining the relationship between the detection light spot having the elliptical shape 3, the parallel line-shaped pattern, and the inclined line-shaped pattern (α = 45 °), respectively. 52A to 52C are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 45 °) are detected by the detection light spot having the elliptical shape 3, respectively. FIG. FIG. 53A is a diagram for explaining the relationship between the circular detection light spot and the inclined line pattern (α = 30 °). FIGS. 53B and 53C are It is a figure for demonstrating an output waveform when a parallel line pattern and an inclination line pattern ((alpha) = 30 degrees) are detected with the circular detection light spot, respectively. FIGS. 54A and 54B are diagrams for explaining the relationship between the detection light spot having the elliptical shape 4 and the parallel line pattern and the inclined line pattern (α = 30 °), respectively. 55 (A) to 55 (C) are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 30 °) are detected by the detection light spot having an elliptical shape 4, respectively. FIG. 56 (A) and 56 (B) are diagrams for explaining the relationship between the ellipse-shaped detection light spot 5 and the parallel line-shaped pattern and the inclined line-shaped pattern (α = 30 °), respectively. FIGS. 57A to 57C are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 30 °) are detected by the detection light spot having an elliptical shape 5, respectively. FIG. 58 (A) and 58 (B) are diagrams for explaining the relationship between the detection light spot having an elliptical shape 6 and a parallel line pattern and an inclined line pattern (α = 30 °), respectively. FIGS. 59A to 59C are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 30 °) are detected by the detection light spot having an elliptical shape 6, respectively. FIG. FIG. 60A is a diagram for explaining the relationship between a circular detection light spot and an inclined line pattern (α = 60 °). FIG. 60B and FIG. It is a figure for demonstrating an output waveform when a parallel line pattern and an inclination line pattern ((alpha) = 60 degrees) are detected with the circular detection light spot, respectively. FIGS. 61A and 61B are diagrams for explaining the relationship between the detection light spot having the elliptical shape 7 and the parallel line-shaped pattern and the inclined line-shaped pattern (α = 60 °), respectively. 62 (A) to 62 (C) are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 60 °) are detected by a detection light spot having an elliptical shape 7, respectively. FIG. FIG. 63A and FIG. 63B are diagrams for explaining the relationship between the detection light spot having an elliptical shape 8, a parallel line pattern, and an inclined line pattern (α = 60 °), respectively. FIGS. 64A to 64C are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 60 °) are detected by the detection light spot having an elliptical shape 8, respectively. FIG. FIGS. 65A and 65B are diagrams for explaining the relationship between the detection light spot having an elliptical shape 9, a parallel line pattern, and an inclined line pattern (α = 60 °), respectively. 66 (A) to 66 (C) are diagrams for explaining output waveforms when a parallel line pattern and an inclined line pattern (α = 60 °) are detected by an ellipse-shaped detection light spot, respectively. FIG. It is a figure for demonstrating Example 1 of the lens for illumination. It is a figure for demonstrating Example 2 of the lens for illumination. It is a figure for demonstrating the modification 1 of a reflection type optical sensor. It is a figure for demonstrating the modification 2 of a reflection type optical sensor. It is a figure for demonstrating the example 1 of the opening member in the reflection type optical sensor of the modification 2. FIG. It is a figure for demonstrating the example 2 of the opening member in the reflection type optical sensor of the modification 2. FIG. It is FIG. (1) for demonstrating reflection type optical sensor 2245A. It is FIG. (2) for demonstrating reflection type optical sensor 2245A. It is FIG. (3) for demonstrating reflection type optical sensor 2245A. It is FIG. (4) for demonstrating reflection type optical sensor 2245A. It is a figure for demonstrating two reflection type optical sensors arrange | positioned outside an effective image area | region.

  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 reflective optical sensor 2245, a temperature / humidity sensor (not shown), a printer control device 2090, 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 program written in a code decipherable by the CPU, a ROM storing various data used when executing the program, a RAM as a working memory, an analog signal A / D conversion circuit for converting the signal into a digital signal (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. The surface of each photosensitive 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.

  An area where 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.

  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 color image on the intermediate transfer belt 2040 is transferred to the recording paper. Here, the recording sheet on which the color 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. Here, as shown in FIG. 4 as an example, in the XYZ three-dimensional orthogonal coordinate system, the moving direction of the intermediate transfer belt 2040 with respect to the reflective optical sensor 2245, that is, the sub direction is the + Y direction, and the main direction is the X axis direction. To do. 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 X0 of the intermediate transfer belt 2040 in the X-axis direction (see FIG. 5). That is, the reflective optical sensor 2245 is disposed at a position corresponding to the effective image area. Details of the reflective optical sensor 2245 will be described later.

  Next, the configuration of the optical scanning device 2010 will be described. The optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four coupling lenses (2201a, 2201b, 2201c, 2201d), four openings, as shown in FIGS. 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).

  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 the 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.

  The optical system disposed on the optical path between each light source and the optical deflector 2104 is also called a pre-deflector optical system.

  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 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. As shown in FIG. 10 as an example, the reflective optical sensor 2245 includes a light emitting unit 10, an illumination lens 11, two light receiving lenses (12, 13), two light receiving units (14, 15), an aperture member. 16 and a substrate 17. The distance from the reflective optical sensor 2245 to the surface of the intermediate transfer belt 2040 is 5 mm.

  The light emitting unit 10 and each light receiving unit are mounted on the substrate 17. The illumination lens 11 and the two light receiving lenses (12, 13) are integrally molded.

  As the light emitting unit 10, an LED or an LD (laser diode) can be used. The light emitting unit 10 has a square shape with a length of 100 μm in the X-axis direction and a length of 100 μm in the Y-axis direction. As shown in FIG. 11 as an example, the light from the light emitting unit 10 is emitted in a direction inclined with respect to the Z axis when orthogonally projected onto the XZ plane.

  The opening member 16 is disposed on the −Z side of the light emitting unit 10, has an outer length of 1.1 mm in the X-axis direction, 6.0 mm in the Y-axis direction, and 2.0 mm in the Z-axis direction. A square opening having a side length of 0.7 mm is formed (see FIG. 12). With respect to the X-axis direction, the distance between the center of the opening and the center of the light emitting unit 10 is 0.1 mm. The gap between the opening member 16 and the substrate 17 is 0.2 mm.

  The illumination lens 11 is disposed on the −Z side of the opening member 16 and condenses the light emitted from the light emitting unit 10 toward the surface of the intermediate transfer belt 2040. Here, the incident-side optical surface has condensing power, and the exit-side optical surface does not have condensing power.

  Hereinafter, for the sake of convenience, the light that has passed through the illumination lens 11 is also referred to as “detection light”. A light spot formed on the surface position of the intermediate transfer belt 2040 by the detection light is also referred to as a “detection light spot”.

  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.

  As shown in FIG. 13 and FIG. 14 as an example, the light receiving lens 12 is light emitted from the light emitting unit 10 and regularly reflected by the surface of the intermediate transfer belt 2040 or the toner pattern on the intermediate transfer belt 2040. Located on the street. Hereinafter, the regularly reflected light is abbreviated as “regularly reflected light”. That is, the light receiving lens 12 condenses regular reflection light.

  As shown in FIG. 14 as an example, the light receiving lens 13 is disposed on the optical path of light emitted from the light emitting unit 10 and diffusely reflected by the toner pattern on the intermediate transfer belt 2040. Hereinafter, the diffusely reflected light is abbreviated as “diffuse reflected light”. That is, the light receiving lens 13 collects the diffuse reflected light.

  In each light receiving lens, the exit-side optical surface has a condensing power, and the incident-side optical surface does not have a condensing power.

  Here, an anamorphic lens that is rotationally asymmetric with respect to the optical axis is used as each light receiving lens. The lens surface of each light receiving lens has a radius of curvature of 1.0 mm with respect to the first direction and a conic constant of −1.65, and a radius of curvature of 1.0 mm with respect to the second direction orthogonal to the first direction. The conic constant is -1.9. By providing the light receiving lens, the output of each light receiving part was about 3.8 times.

  The light receiving unit 14 receives the specularly reflected light collected by the light receiving lens 12. The light receiving unit 15 receives the diffuse reflected light collected by the light receiving lens 13. PTr (phototransistor) or PD (photodiode) can be used for each light receiving portion. Each light receiving unit outputs a signal (photoelectric conversion signal) corresponding to the amount of received light to the printer control device 2090.

  Each light receiving portion has a square shape with a length of 1 mm in the X-axis direction and a length of 1 mm in the Y-axis direction. Further, with respect to the X-axis direction, the distance between the light emitting unit 10 and the light receiving unit 14 is 1.36 mm.

  In the following description, 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.

  Next, a toner pattern as a detection 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. 16 as an example, the density detection pattern DP has four square patterns (p1 to p4, hereinafter referred to as “rectangular pattern” for convenience). The four rectangular patterns are arranged in a line at equal intervals along the Y-axis direction, and the toner density gradations are different from each other 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 p4 is a so-called solid pattern created with the maximum toner adhesion amount.

  As an example, the length w1 in the X-axis direction of each rectangular pattern is about 15 mm, and the length w2 in the Y-axis direction is about 25 mm. Further, with respect to the Y-axis direction, the center distance w3 between two adjacent rectangular patterns is about 30 mm.

  The four density detection patterns DP1 to DP4 are arranged in a line along the Y-axis direction, and are set to be formed at positions illuminated by the detection light. Hereinafter, for convenience, the row of the four density detection patterns DP1 to DP4 is also referred to as a “DP pattern row”.

  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 Y-axis direction as shown in FIG. 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 X-axis direction, and the linear patterns LPK2, LPM2, LPC2, and LPY2 are inclined in the longitudinal direction with respect to the X-axis direction. Here, the inclination angle is 45 °.

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

  Each parallel line pattern has a length w4 in the longitudinal direction of 8.0 mm and a length w5 in the lateral direction of 1.0 mm. Further, the center-to-center distance w6 between two parallel line patterns adjacent in the Y-axis direction is set to 3.5 mm.

  Each inclined line pattern is obtained by inclining each parallel line pattern by 45 °.

  In the present embodiment, the misregistration detection pattern PP is set to be formed on the −Y side of the density detection pattern (see FIG. 15).

  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 in FIG. 18 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. 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 2040 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 S321. 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 S321, the intermediate transfer belt 2040 is illuminated with detection light, and the output of each light receiving unit is acquired.

  Here, in order to avoid the influence of reflection unevenness in the intermediate transfer belt 2040, sampling is performed a predetermined number of times (for example, 10 times) in a predetermined sampling time (for example, 2 ms), and the outputs of the respective light receiving units are acquired.

  (3) In the next step S323, the scanning control apparatus is instructed to create a toner pattern.

  As a result, the scanning control apparatus has the electrostatic latent image of the density detection pattern DP1 on the photosensitive drum 2030a, the electrostatic latent image of the density detection pattern DP2 on the photosensitive drum 2030b, and the density detection pattern DP3 on the photosensitive drum 2030c. The electrostatic latent image of the density detection pattern DP4 is formed on the photosensitive drum 2030d.

  Further, the scanning control device detects the electrostatic latent images of the line-shaped patterns LPK1 and LPK2 of the positional deviation detection pattern PP on the photosensitive drum 2030a, and the line-shaped patterns LPM1 and LPM2 of the positional deviation detection pattern PP on the photosensitive drum 2030b. Each of the electrostatic latent images, and each of the electrostatic latent images LPC1 and LPC2 of the positional deviation detection pattern PP on the photosensitive drum 2030c and the linear patterns LPY1 and LPY2 of the positional deviation detection pattern PP on the photosensitive drum 2030d. Each electrostatic latent image is 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. 19).

  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.

  (4) In the next step S325, the toner pattern is illuminated with detection light, and the outputs of the light receiving unit 14 and the light receiving unit 15 are acquired.

  Here, the printer control device 2090 turns on the light emitting unit 10 at a timing just before the toner pattern reaches the position facing the reflective optical sensor 2245. The detection light spot sequentially illuminates the rectangular pattern of each gradation of each color as the intermediate transfer belt 2040 moves in the sub direction, that is, as time elapses (see FIG. 20). Then, the printer control device 2090 tracks the output signal of the light receiving unit 14 and the output signal of the light receiving unit 15 in time.

  At this time, in order to avoid the influence of density unevenness in the rectangular pattern, the rectangular pattern is divided into a predetermined number (for example, 40) of regions having the same length in the x-axis direction, and data sampling is performed in each of the divided regions. A sampling time (for example, 2 ms) is set, and the predetermined number (for example, 40) of data is acquired for each rectangular pattern.

  FIG. 21 shows the time change of the output signal of the light receiving unit 14. FIG. 22 shows the irradiation object in FIG. The object to be irradiated at a timing other than the rectangular pattern is the intermediate transfer belt 2040. As shown in FIG. 22, the output signal of the light receiving unit 14 has a high output level when the irradiation target is the intermediate transfer belt 2040, and has a low output level when the irradiation target is a rectangular pattern.

  FIG. 23 shows the time change of the output signal of the light receiving unit 15. FIG. 24 shows the irradiation object in FIG. The object to be irradiated at a timing other than the rectangular pattern is the intermediate transfer belt 2040. As shown in FIG. 24, the output signal of the light receiving unit 15 has a low output level when the irradiation object is the intermediate transfer belt 2040, and when the rectangular pattern formed of the color toner other than the black toner is the irradiation object. Has a high output level.

  When the illumination of all rectangular patterns in the DP pattern row is completed, the detection light spot subsequently illuminates the misregistration detection pattern PP (see FIG. 25).

  FIG. 26 shows the time change of the output signal of the light receiving unit 14. FIG. 27 shows the irradiation object in FIG. Note that the object to be irradiated at a timing other than the line pattern is the intermediate transfer belt 2040. As shown in FIG. 26, the output signal of the light receiving unit 14 has a high output level when the irradiation target is the intermediate transfer belt 2040, and a low output level when the irradiation target is a line pattern.

  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. Further, the time change of the output of each light receiving unit is also referred to as “output waveform”.

  (5) In the next step S327, the toner density of each rectangular pattern in the DP pattern row is calculated.

  (5-1) The average value of the outputs of the respective light receiving units acquired in step S321 is obtained. Hereinafter, the average value of the output of the light receiving unit 14 obtained here is expressed as “Vsg_spe”, and the average value of the output of the light receiving unit 15 is expressed as “Vsg_dif”.

  (5-2) For each rectangular pattern, the average value of the outputs of the respective light receiving units acquired in step S325 is obtained. When the variation of sampled data is large, for example, 10 from the largest value and 10 from the smallest value may be removed, and the average value of the remaining data may be obtained.

  In the following, for convenience, the average of the outputs of the light receiving unit 14 when the irradiation target is a rectangular pattern pm (m = 1, 2, 3, 4) of the density detection pattern DPn (n = 1, 2, 3, 4). The value is expressed as “Vsp [DPn_pm] _spe”.

  Similarly, the average value of the output of the light receiving unit 15 when the irradiation target is a rectangular pattern pm (m = 1, 2, 3, 4) of the density detection pattern DPn (n = 1, 2, 3, 4) is obtained. , “Vsp [DPn_pm] _dif”.

  (5-3) The sensitivity correction coefficient K2 of the light receiving unit 14 when the irradiation target is the density detection patterns DP2, DP3, DP4 is obtained.

  Here, first, the coefficient B [DPn_pm] is calculated for each rectangular pattern using the following equation (1).

  B [DPn_pm] = Vsp [DPn_pm] _spe / Vsp [DPn_pm] _dif (1)

  The smallest value among the calculated coefficients B [DPn_pm] is set as the sensitivity correction coefficient K2 of the light receiving unit 14.

  (5-4) The amount of regular reflection light received when the irradiation object is the density detection patterns DP2, DP3, DP4 is obtained.

  Here, the received light amount K [DPn_pm] of regular reflection light is calculated for each rectangular pattern using the following equation (2).

  K [DPn_pm] = (Vsp [DPn_pm] _spe−K2 × Vsp [DPn_pm] _dif) / (K2 × Vsp [DPn_pm] _dif) (2)

  (5-5) The amount of diffusely reflected light received when the irradiation target is the density detection patterns DP2, DP3, DP4 is obtained.

  Here, for each rectangular pattern, the received light amount Vsp [DPn_pm] _dif ′ of diffuse reflected light is calculated using the following equation (3).

  Vsp [DPn_pm] _dif ′ = Vsp [DPn_pm] _dif−Vsg_dif × K [DPn_pm] (3)

  (5-6) The gain adjustment coefficient K5 of the light receiving unit 15 is obtained.

  Here, first, a quadratic approximation representing the relationship between K [DPn_pm] and Vsp [DPn_pm] _dif ′, where the horizontal axis is K [DPn_pm] and the vertical axis (Y axis) is Vsp [DPn_pm] _dif ′. Find the equation using the least squares method.

  The coefficient of the square term in the second-order approximation is α, the coefficient of the first term is β, and the Y intercept is γ.

  Next, the gain adjustment coefficient K5 is calculated using the following equation (4).

K5 = 1.63 / (α × 0.15 ² + β × 0.15 + γ) (4)

  Note that the constants (here, 1.63 and 0.15) in the above equation (4) are values unique to the apparatus, and are determined in advance through experiments or the like.

  (5-7) Normalization is performed.

  Here, the normalized value R [DPn_pm] is calculated using the following equation (5).

  R [DPn_pm] = K5 × Vsp [DPn_pm] _dif ′ (5)

  At this time, the characteristic error of the reflective optical sensor 2245, the error of the mounting position, and the variation of the reflection characteristic in the intermediate transfer belt 2040 are almost canceled.

  (5-8) Using the density conversion LUT (look-up table) stored in advance in the ROM of the printer controller 2090, the toner adhesion amount MA [DPn_pm] from the normalized value R [DPn_pm] for each rectangular pattern. ]. FIG. 28 shows a magenta toner density conversion LUT.

  (5-9) A normalized value when the irradiation object is the density detection pattern DP1 is obtained.

  The normalized value in the case of black toner is determined only by the amount of regular reflection light received from the underlying intermediate transfer belt 2040 and the light absorption characteristics of the black toner. Here, the following equation (6) is used. Then, the normalized value R [DP1_pm] is calculated.

  R [DP1_pm] = Vsp [DP1_pm] _spe / Vsg_spe (6)

  (5-10) Toner from normalized value R [DP1_pm] for each rectangular pattern using density conversion LUT (look-up table) (see FIG. 29) stored in advance in ROM of printer controller 2090 The adhesion amount MA [DP1_pm] is obtained.

  (6) In the next step S329, the amount of positional deviation of the line pattern in the positional deviation detection pattern PP is calculated.

  (6-1) A threshold voltage is obtained.

  Here, the threshold voltage Vth is calculated for each toner color using the following equation (7). The unit here is a bolt. The output of the light receiving unit 14 when the irradiation target is a line pattern is Vp, and the output of the light receiving unit 14 when the irradiation target is only the intermediate transfer belt 2040 is Vb.

  Vth = Vp + (Vb−Vp) × 0.5 (7)

  (6-2) The calculation detection time of each line pattern is obtained.

  Here, as shown in FIG. 30, for each line pattern, the timing at which the output of the light receiving unit 14 coincides with the threshold voltage Vth when the output waveform of the light receiving unit 14 falls and rises (in FIG. 30, × (Indicated by a mark) and the middle of the two timings is set as a detection time. The method for obtaining the detection time is not limited to this.

  (6-3) As schematically shown in FIG. 31 as an example, the time Tkm1 from the detection time of the line pattern LPK1 to the detection time of the line pattern LPM1 in the output waveform of the light receiving unit 14, the line pattern A time Tkc1 from the detection time of LPK1 to the detection time of the line pattern 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.

  Further, in the output waveform of the light receiving unit 14, the time Tkm2 from the detection time of the line pattern LPK2 to the detection time of the line pattern LPM2, the time Tkc2 from the detection time of the line pattern LPK2 to the detection time of the line pattern LPC2, A time Tky2 from the detection time of the line pattern LPK2 to the detection time of the line pattern LPY2 is obtained.

  (6-4) The differences (referred to as time differences ΔTm1, ΔTc1, and ΔTy1) between the time Tkm1, the time Tkc1, and the time Tky1 and their previously obtained 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.

  (6-5) The differences (time differences ΔTm2, ΔTc2, and ΔTy2) between the time Tkm2, the time Tkc2, and the time Tky2 and their previously obtained 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, a case where the time difference ΔTm1 is not within the allowable range is schematically shown in FIG. FIG. 32B 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 (8). Here, V is the moving speed of the intermediate transfer belt 2040 in the sub direction.

  ΔS2 = V · ΔTm2 · cot45 ° (8)

  (7) 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 (9), 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] (9)

  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. Then, the detection process ends.

  By the way, when the conventional reflective optical sensor is used, the position detection accuracy in the main direction is lower than the position detection accuracy in the sub-direction in the positional deviation detection process. The cause of this difference is considered to be because the shape of the output waveform when the parallel line pattern is detected is different from the shape of the output waveform when the inclined line pattern is detected in the positional deviation detection process. Therefore, if the shapes of the two output waveforms can be made the same or similar, the difference in detection accuracy can be made smaller than in the prior art. Hereinafter, for convenience, an output waveform when a parallel line pattern is detected is also referred to as a “sub-direction detection waveform”, and an output waveform when an inclined line pattern is detected is also referred to as a “main direction detection waveform”.

  In order to make the shape of the sub direction detection waveform and the shape of the main direction detection waveform the same or similar, the time required for the detection light spot to come off after making contact with one parallel line pattern, and the detection light spot It suffices if the difference from the time required to come out of contact with one inclined line pattern becomes small.

  In order to reduce the time difference, it is conceivable to reduce the size of the detection light spot. In this case, however, the detection accuracy of the toner density may be lowered. Therefore, in this embodiment, the shape of the detection light spot is an elliptical shape without changing the area with respect to the conventional detection light spot (diameter is about 1.5 mm) when detecting the toner density.

FIG. 33A shows an ellipse whose major axis direction is parallel to the X axis direction and whose minor axis direction is parallel to the Y axis direction. If the length of the major axis is 2a, the length of the minor axis is 2b, and the center of the ellipse is the origin, the shape of the ellipse is expressed by the following equation (10).
(X / a) ² + (Y / b) ² = 1 (10)

  FIG. 33 (B) shows a case where the ellipse of FIG. 33 (A) is rotated around the origin by an angle θ. In this case, the shape of the ellipse is expressed by the following equations (11) to (16). Hereinafter, the detection light spot having a shape as shown in FIG. 33B is also referred to as a “detection elliptical light spot” for convenience.

AX ′ ² + B (X ′ × Y ′) + CY ′ ² = 1 (11)
X ′ = X cos θ + Y sin θ (12)
Y ′ = − X sin θ + Y cos θ (13)
A = (a ² sin ² θ + b ² cos ² θ) / a ² b ² (14)
B = ² cos θ · sin θ (a ² −b ² ) / a ² b ² (15)
C = (a ² cos ² θ + b ² sin ² θ) / a ² b ² (16)

  34A shows the timing when the parallel line pattern touches the detection elliptical light spot, and FIG. 34B shows the timing when the parallel line pattern deviates from the detection elliptical light spot. Yes. Let Ls be the distance that the parallel line-shaped pattern has moved from the time when the parallel line-shaped pattern touches the detection elliptical light spot to the time when it deviates.

  FIG. 35A shows the timing at which the inclined line pattern touches the detection elliptical light spot, and FIG. 35B shows the timing at which the inclined line pattern deviates from the detection elliptical light spot. Yes. Let Lm be the distance that the inclined line-shaped pattern has moved from the time when the inclined line-shaped pattern contacts the detection elliptical light spot to the time when it deviates.

  Symbol c in FIG. 36 is represented by the following equation (17) from the above equations (11) to (13).

  Symbol c ′ in FIG. 37 is represented by the following equation (18) from the above equations (11) to (13).

  Therefore, as shown in FIG. 38, the distance Ls that the parallel line pattern has moved from the time when the parallel line pattern contacts the detection elliptical light spot to the time when it deviates is expressed by the following equation (19).

  Further, as shown in FIG. 39, the distance Lm that the inclined line-shaped pattern has moved from the time when the inclined line-shaped pattern touches the detection elliptical light spot to the time when it deviates is expressed by the following equations (20) and (21). Indicated. Here, α is the inclination angle of the inclined line pattern.

  Therefore, by setting the angle θ to a value at which | Lm−Ls | becomes minimum, the shape of the sub direction detection waveform and the shape of the main direction detection waveform can be made the same or similar. That is, the position detection accuracy in the main direction can be improved, and the difference from the position detection accuracy in the sub direction can be reduced.

  By the way, it is difficult to form an ideal elliptical detection light spot on the intermediate transfer belt 2040. Hereinafter, for the sake of convenience, an ideal elliptical light spot is referred to as an “elliptical light spot”, and an actual elliptical light spot is referred to as an “elliptical light spot” (see FIG. 40).

  41 and 42 show the light intensity distribution in the elliptical light spot and the elliptical light spot. Here, the elliptical light spot is set to a = 1.5 mm and b = 0.5 mm, and the light intensity is the highest at the center of gravity of the spot, and becomes weaker as it goes away from the center of gravity. 41 and 42, the vertical axis is a relative value, and is normalized so that the maximum value of the light intensity is 1.0. While the light intensity is 0 at the skirt of the elliptical light spot, the skirt spreads at the elliptical light spot, and the light intensity is not 0 at the position corresponding to the skirt of the elliptical light spot.

  Therefore, in this embodiment, as an example, the position where the relative intensity is 0.03 is defined as the edge of the light spot, and the length of the region where the relative intensity is 0.03 or greater is defined as the beam width. Therefore, the pattern being in contact with the light spot means that the end of the pattern is located at a position where the relative intensity at the light spot is 0.03 (see FIGS. 43 and 44).

  Next, regarding the parallel line pattern and the inclined line pattern, the relationship between the shape of the light spot for detection and the output waveform of the light receiving unit that receives the regular reflection light when each pattern is detected will be described. It is assumed that each pattern is detected under an ideal detection state in which there is no fluctuation that affects the position shift detection. The output of the light receiving unit is a relative value (au), and is standardized so that the maximum value of the output is 1.0.

  First, the case where the inclination angle α of the inclined line pattern was 45 ° was examined.

(1) When the detection light spot is circular (radius 0.75 mm) The relationship between the parallel line pattern and the detection light spot is shown in FIG. This relationship is shown in FIG. FIG. 46A shows an output waveform when a parallel line pattern is detected, and FIG. 46B shows an output waveform when an inclined line pattern is detected.

  Further, FIG. 46C is a diagram in which FIG. 46A and FIG. 46B are combined. Here, the slopes of the output waveforms at positions where the relative output values are within the range of 0.4 to 0.8 (au) and the same relative output values in each line pattern do not match.

(2) When the detection light spot is elliptical (a = 2.25 mm, b = 0.25 mm, θ = 26.92 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. FIG. 47B shows the relationship between the inclined line pattern and the detection light spot. FIG. 48A shows an output waveform when a parallel line pattern is detected, and FIG. 48B shows an output waveform when an inclined line pattern is detected.

  Further, FIG. 48C is a combined view of FIG. 48A and FIG. 48B. The region where the difference in the slope of the output waveform at the position where the same relative output value is obtained in each line pattern is approximately 0, the relative output value is in the range of 0.6 to 0.8 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

(3) When the detection light spot is elliptical (a = 1.5 mm, b = 0.375 mm, θ = 28.15 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. FIG. 49B shows the relationship between the inclined line pattern and the detection light spot. An output waveform when the parallel line pattern is detected is shown in FIG. 50A, and an output waveform when the inclined line pattern is detected is shown in FIG.

  FIG. 50C is a diagram in which FIG. 50A and FIG. 50B are combined. The region where the difference in the slope of the output waveform at the position where the same relative output value is obtained in each line pattern is substantially 0 is within the range of the relative output value of 0.4 to 0.8 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

  Further, comparing FIG. 50C and FIG. 48C, FIG. 50C has a wider region where the difference in inclination is almost zero.

(4) When the detection light spot is elliptical (a = 1.125 mm, b = 0.5 mm, θ = 34.22 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. The relationship between the inclined line pattern and the detection light spot is shown in FIG. An output waveform when a parallel line pattern is detected is shown in FIG. 52 (A), and an output waveform when an inclined line pattern is detected is shown in FIG. 52 (B).

  FIG. 52C is a diagram in which FIGS. 52A and 52B are combined. The region where the difference in the slope of the output waveform at the position where the same relative output value is obtained in each line pattern is approximately 0, the relative output value is within the range of 0.3 to 0.8 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

  Further, comparing FIG. 52C and FIG. 50C, FIG. 52C has a wider region where the difference in inclination is almost zero.

  Next, the case where the inclination angle α of the inclined line pattern was 30 ° was examined.

(5) When the detection light spot is circular (radius 0.75 mm) FIG. 53A shows the relationship between the inclined line pattern and the detection light spot. The output waveform when the inclined line pattern is detected is shown in FIG.

  FIG. 53C is a diagram in which FIG. 46A and FIG. 53B are combined. Here, the slopes of the output waveforms at positions where the relative output values are within the range of 0.4 to 0.8 (au) and the same relative output values in each line pattern do not match.

(6) When the detection light spot is elliptical (a = 2.25 mm, b = 0.25 mm, θ = 16.31 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. FIG. 54B shows the relationship between the inclined line pattern and the detection light spot. An output waveform when a parallel line pattern is detected is shown in FIG. 55A, and an output waveform when an inclined line pattern is detected is shown in FIG. 55B.

  FIG. 55C shows a diagram in which FIG. 55A and FIG. 55B are combined. The region where the difference in the slope of the output waveform at the position where the same relative output value is obtained in each line pattern is approximately 0, the relative output value is within the range of 0.3 to 0.8 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

(7) When the detection light spot is elliptical (a = 1.5 mm, b = 0.375 mm, θ = 17.21 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. FIG. 56B shows the relationship between the inclined line pattern and the detection light spot. An output waveform when a parallel line pattern is detected is shown in FIG. 57 (A), and an output waveform when an inclined line pattern is detected is shown in FIG. 57 (B).

  FIG. 57C is a diagram in which FIGS. 57A and 57B are combined. The region where the difference in the slope of the output waveform at the position where the same relative output value is obtained in each line pattern is substantially 0 is within the range of the relative output value of 0.2 to 0.8 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

  In addition, comparing FIG. 57C with FIG. 55C, FIG. 57C has a wider region where the difference in inclination is almost zero.

(8) When the detection light spot is elliptical (a = 1.125 mm, b = 0.5 mm, θ = 2.28 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. The relationship between the inclined line pattern and the detection light spot is shown in FIG. An output waveform when a parallel line pattern is detected is shown in FIG. 59 (A), and an output waveform when an inclined line pattern is detected is shown in FIG. 59 (B).

  FIG. 59C is a diagram in which FIG. 59A and FIG. 59B are combined. The region where the slope difference of the output waveform at the position where the same relative output value is taken in each line pattern is almost 0 is within the range of the relative output value of 0.15 to 0.8 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

  Further, comparing FIG. 59C and FIG. 57C, FIG. 59C has a wider region where the difference in inclination is almost zero.

  Next, the case where the inclination angle α of the inclined line pattern was 60 ° was examined.

(9) When the detection light spot is circular (radius 0.75 mm) FIG. 60A shows the relationship between the inclined line pattern and the detection light spot. The output waveform when the inclined line pattern is detected is shown in FIG.

  Further, FIG. 60C is a diagram in which FIG. 46A and FIG. 60B are combined. Here, the slopes of the output waveforms at positions where the relative output values are within the range of 0.4 to 0.8 (au) and the same relative output values in each line pattern do not match.

(10) When the detection light spot is elliptical (a = 2.25 mm, b = 0.25 mm, θ = 41.52 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. FIG. 61B shows the relationship between the inclined line pattern and the detection light spot. FIG. 62A shows an output waveform when a parallel line pattern is detected, and FIG. 62B shows an output waveform when an inclined line pattern is detected.

  FIG. 62C is a diagram in which FIGS. 62A and 62B are combined. The region where the difference in slope of the output waveform at the position where the same relative output value is obtained in each line pattern is substantially 0, the relative output value is within the range of 0.75 to 0.85 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

(11) When the detection light spot is elliptical (a = 1.5 mm, b = 0.375 mm, θ = 44.40 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. FIG. 63B shows the relationship between the inclined line pattern and the detection light spot. An output waveform when a parallel line pattern is detected is shown in FIG. 64A, and an output waveform when an inclined line pattern is detected is shown in FIG. 64B.

  FIG. 64C is a diagram in which FIGS. 64A and 64B are combined. The region where the slope difference of the output waveform at the position where the same relative output value is obtained in each line pattern is substantially 0 is within the range of the relative output value of 0.6 to 0.85 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

  Further, comparing FIG. 64C with FIG. 62C, FIG. 64C has a wider region where the difference in inclination is almost zero.

(12) When the detection light spot is elliptical (a = 1.125 mm, b = 0.5 mm, θ = 71.61 °) The relationship between the parallel line pattern and the detection light spot is shown in FIG. FIG. 65B shows the relationship between the inclined line pattern and the detection light spot. An output waveform when a parallel line pattern is detected is shown in FIG. 66 (A), and an output waveform when an inclined line pattern is detected is shown in FIG. 66 (B).

  FIG. 66 (C) shows a diagram combining FIG. 66 (A) and FIG. 66 (B). The region where the slope difference of the output waveform at the position where the same relative output value is obtained in each line pattern is substantially 0 is within the range of the relative output value of 0.6 to 0.85 (au). . In this case, when calculating the positional deviation amount, the position detection accuracy of the parallel line pattern and the inclined line pattern can be made substantially equal by setting an arbitrary relative output value within the range to the threshold voltage. .

  In addition, when FIG. 66C and FIG. 64C are compared, the regions where the inclination difference is almost zero are almost the same.

  As described above, without changing the area of the detection light irradiation region on the intermediate transfer belt 2040, the detection light spot is made to have an appropriate elliptical shape and an appropriate angle according to the inclination angle of the inclined line pattern. By tilting at, the position detection accuracy of the parallel line pattern and the tilt line pattern can be made substantially equal.

  Next, a specific example will be described.

(A) The case where the inclination angle α of the inclined line pattern is 45 ° and the shape of the detection light pattern is an ellipse with a = 1.125 and b = 0.5 will be described. In this case, if θ = 34.22 °, the difference in position detection accuracy between the parallel line-shaped pattern and the inclined line-shaped pattern can be reduced. Note that θ = 34.22 ° is one of appropriate solutions, and is not limited to this.

  A method for setting the detection light pattern to θ = 34.22 ° will be described.

(Method 1) As the illumination lens 11, an anamorphic lens having a rotationally asymmetric shape with respect to the optical axis and having different power in the first axial direction and power in the second axial direction is used. Then, the axial direction is set so that one of the first axis and the second axis is inclined by 34.22 ° with respect to the X-axis direction (see FIG. 67). Here, with respect to the first axial direction, the radius of curvature is 1.58 mm and the conic constant is −1.1. Further, with respect to the second axial direction, the radius of curvature is 1.19 mm and the conic constant is −1.5.

(Method 2) The entire illumination lens 11 is rotated around the optical axis so that one of the first axis and the second axis is inclined by 34.22 ° with respect to the X-axis direction (see FIG. 68). ).

(Method 3) The reflective optical sensor 2245 is rotated and arranged so that one of the first axis and the second axis of the illumination lens 11 is inclined by 34.22 ° with respect to the X-axis direction.

(Method 4) The lens surface of the illumination lens 11 is a free surface. This free surface is a lens at each coordinate on the lens surface when the coordinate on the optical axis of the lens surface is (x, y) = (0, 0) and the lens height on the optical axis is z = 0. The height is expressed by the following equation (22) (XY polynomial polynomial).

It is.

In the above formula (22), l can be up to 66, but here, l = 6. Also, C ₂ = 0, C ₃ = 0, C ₄ = 0.06, C ₅ = 0.08, and C ₆ = 0.02.

  As described above, according to the reflective optical sensor 2245 according to this embodiment, the light emitting unit 10, the illumination lens 11, the two light receiving lenses (12, 13), the two light receiving units (14, 15), and the aperture. The member 16 and the substrate 17 are provided.

  The light spot on the intermediate transfer belt 2040 by the detection light emitted from the reflective optical sensor 2245 has an elliptical shape, and the major axis direction of the ellipse is inclined by an angle θ with respect to the X-axis direction. Then, the movement distance Ls of the intermediate transfer belt 2040 from when the detection light spot comes into contact with the parallel line pattern until it comes off, and the movement distance of the intermediate transfer belt 2040 from when the detection light spot comes into contact with the inclined line pattern until it comes off. Using Lm, the angle θ is set to be a value when | Lm−Ls | is minimum.

  In this case, the detection accuracy related to the main direction of the misregistration detection pattern can be improved, and the difference from the detection accuracy related to the sub direction can be reduced.

  In addition, since the light receiving lens is provided, the reflected light can be efficiently guided to the light receiving unit. In this case, the power consumption can be kept low by reducing the injection current to the light emitting portion. Further, instead of lowering the injection current to the light emitting part, the amplification factor of the light receiving part may be suppressed. If the amplification factor can be suppressed, noise in the output signal of the light receiving unit can be reduced.

  The color printer 2000 includes an optical scanning device 2010, four image forming stations, an intermediate transfer belt 2040, a reflective optical sensor 2245, a printer control device 2090, and the like.

  The printer control device 2090 forms a density detection pattern and a positional deviation detection pattern on the intermediate transfer belt 2040 via the optical scanning device 2010 and the image forming station, and the reflection type optical sensor 2245 detects each pattern. Based on the output signal, the toner density and the amount of positional deviation of the pattern in the sub direction and the main direction are obtained. The printer control device 2090 performs image process control based on the obtained toner density and positional deviation amount.

  In this case, the displacement amount in the main direction can be obtained with higher accuracy than in the past. Therefore, the printer control device 2090 can stably form a higher quality image than the conventional one.

  In the above embodiment, when it is not necessary to detect the toner density, the light receiving lens 13 and the light receiving unit 15 are not required (see FIG. 69).

  Moreover, in the said embodiment, you may use a surface mount-type element for each light-receiving part which covers the light emission part 10 (refer FIG. 70). As an example, the distance from the reflective optical sensor 2245 to the surface of the intermediate transfer belt 2040 is 1.6 mm. The opening of the opening member 16 has an elliptical shape (see FIG. 71) having a major axis of 0.845 mm and a minor axis of 0.375 mm, and a height of 5.0 mm. The major axis of the elliptical shape of the opening is inclined by 34.22 ° with respect to the X-axis direction. As a result, the detection light beam has an elliptical shape whose major axis is inclined by 34.22 ° with respect to the X-axis direction.

  Further, in this case, the reflective optical system is such that the major axis of the elliptical shape of the opening is parallel to the X-axis direction and the major axis of the detection light beam is inclined by 34.22 ° with respect to the X-axis direction. The sensor 2245 itself may be tilted.

  Moreover, although the said embodiment demonstrated the case where the shape of the light spot for a detection was elliptical shape, it is not limited to this. For example, the shape of the detection light spot may be rectangular. In short, it is only necessary that the lengths in two directions orthogonal to each other are different.

  In the above embodiment, the light receiving lens may not be provided as long as the amount of reflected light is large.

  In the above embodiment, the case where the reflective optical sensor has one light emitting unit has been described. However, the present invention is not limited to this, and the reflective optical sensor may have a plurality of light emitting units. In this case, a plurality of light receiving portions may be provided. For example, the reflective optical sensor 2245A shown in FIGS. 72 to 75 includes 11 light emitting units (E1 to E11), 11 light receiving units (D1 to D11), and 11 irradiation microlenses (LE1 to LE11). ), 11 light receiving microlenses (LD1 to LD11). Also in this case, the light spot on the intermediate transfer belt 2040 by the detection light emitted from each light emitting portion is elliptical, and the major axis direction of the ellipse is inclined by an angle θ with respect to the X-axis direction. By setting, the detection accuracy regarding the main direction of the misregistration detection pattern can be improved, and the difference from the detection accuracy regarding the sub direction can be reduced.

  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.

  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 above embodiment, a dummy pattern may be added before the toner pattern.

  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.

  In the above embodiment, the case where each density detection pattern is composed of four rectangular patterns has been described. However, the present invention is not limited to this, and may be composed of, for example, five rectangular patterns. .

  In the above-described embodiment, the case where the reflective optical sensor 2245 is provided at a position corresponding to the center of the effective image area in the X-axis direction has been described. However, 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 with respect to the X-axis direction. In this case, it is possible to suppress a reduction in image forming work efficiency and to perform a real-time detection process.

  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 increased.

  As an example, FIG. 76 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 area in the X-axis direction. Yes.

  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, and the toner pattern on the surface of the photosensitive drum is used. 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.

  DESCRIPTION OF SYMBOLS 10 ... Light emitting part, 11 ... Illuminating lens, 12 ... Light receiving lens, 13 ... Light receiving lens, 14 ... Light receiving part, 15 ... Light receiving part, 16 ... Opening member, 17 ... Substrate, 2000 ... Color printer (image forming apparatus) ), 2010... Optical scanning device (part of pattern forming device), 2030a to 2030d... Photosensitive drum, 2040... Intermediate transfer belt (moving body), 2090. 2245A ... Reflective optical sensor, D1 to D11 ... Light receiving part, DP1 to DP4 ... Pattern for density detection, E1 to E11 ... Light emitting part, LD1 to LD11 ... Light receiving microlens, LE1 to LE11 ... Lighting microlens, PP1 ... PP4 Position misalignment detection pattern (detection pattern).

JP-A-1-35466 JP 2004-21164 A JP 2002-72612 A Japanese Patent No. 4154272 Japanese Patent No.4110027 JP-A-2005-91252 Japanese Patent No. 4689292 JP 2008-40454 A

Claims (10)

A light emitting unit that emits light toward the moving body;
A light receiving unit that receives light emitted from the light emitting unit and reflected by a detection pattern formed on the moving body;
The detection pattern includes a first pattern orthogonal to the moving direction of the moving body, and a second pattern inclined with respect to the first pattern,
The light spots on the moving body due to the light emitted from the light emitting part have different shapes in the biaxial directions perpendicular to each other, and the major axis direction of the light spots is relative to the direction perpendicular to the moving direction. Inclined by an angle θ
Using the moving distance Ls of the moving body from when the light spot comes into contact with the first pattern until it comes off, and the moving distance Lm of the moving body from when the light spot comes into contact with the second pattern to come off ,
The angle θ is a reflective optical sensor having a value when | Lm−Ls | is minimum. An inclination angle α of the second pattern with respect to the first pattern, a major axis length 2a, a minor axis length 2b of the light spot, a length W5 of the first pattern in the moving direction, the first pattern Length lm of the two patterns in the moving direction, A = (a ² sin ² θ + b ² cos ² θ) / a ² b ² , B = ² cos θ · sin θ (a ² −b ² ) / a ² b ² , C = (A ² cos ² θ + b ² sin ² θ) / a ² b ² ,
The reflective optical sensor according to claim 1, wherein   The reflection type optical sensor according to claim 1, wherein the angle θ is a value when | Lm−Ls | becomes zero. An illumination lens for condensing the light emitted from the light emitting unit;
4. The reflective optical system according to claim 1, wherein the illumination lens is an anamorphic lens, and is inclined by the angle θ around an optical axis with respect to the moving direction. 5. Sensor. An illumination lens for condensing the light emitted from the light emitting unit;
The reflective optical sensor according to any one of claims 1 to 3, wherein the lens surface of the illumination lens is a free-form surface lens.   6. The apparatus according to claim 1, further comprising an opening member disposed on an optical path of light emitted from the light emitting unit and having an opening having a shape similar to the shape of the light spot. Reflective optical sensor. A pattern creation device for creating a detection pattern on a moving object;
The reflective optical sensor according to any one of claims 1 to 6,
An image forming apparatus comprising: a processing device that obtains a position of the detection pattern in two directions orthogonal to each other on the moving body based on an output signal of the reflective optical sensor. A pattern creating apparatus for creating a detection pattern including a first pattern orthogonal to the moving direction of the moving body on the moving body and a second pattern inclined with respect to the first pattern;
A reflective optical sensor having a light emitting unit that emits light toward the moving body, and a light receiving unit that receives light emitted from the light emitting unit and reflected by the detection pattern;
A processing device for obtaining a position of the detection pattern in two directions orthogonal to each other on the moving body based on an output signal of the reflective optical sensor, on the moving body by the light emitted from the light emitting unit The light spot has a shape in which the lengths in the biaxial directions orthogonal to each other are different, and the reflective optical sensor is arranged such that the major axis direction of the light spot is inclined by an angle θ with respect to the direction perpendicular to the moving direction Arranged,
Using the moving distance Ls of the moving body from when the light spot comes into contact with the first pattern until it comes off, and the moving distance Lm of the moving body from when the light spot comes into contact with the second pattern to come off The angle θ is an image forming apparatus having a value when | Lm−Ls | is minimum. An inclination angle α of the second pattern with respect to the first pattern, a major axis length 2a, a minor axis length 2b of the light spot, a length W5 of the first pattern in the moving direction, the first pattern Length lm of the two patterns in the moving direction, A = (a ² sin ² θ + b ² cos ² θ) / a ² b ² , B = ² cos θ · sin θ (a ² −b ² ) / a ² b ² , C = (A ² cos ² θ + b ² sin ² θ) / a ² b ² ,
The image forming apparatus according to claim 8, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 7, wherein the moving body is an intermediate transfer belt or a photosensitive image carrier.