JP2010197641A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of maintaining high image quality without lowering workability. <P>SOLUTION: Respective detection sensors include: five light sources (E1 to E5) arranged in a line at equal intervals in a Y-axis direction, and emitting luminous flux toward a transfer belt 2040; five condenser lenses for illumination (LE1 to LE5) condensing the luminous flux emitted from the respective light sources; and five photodetectors for receiving the luminous flux reflected by the transfer belt 2040. When performing toner concentration detecting processing, a printer controller designates size and position of a toner pattern so as to illuminate the toner pattern with at least one of light spots by flare light and a light spot by detecting light. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image with toner.

  As an image forming apparatus that forms an image with toner, a copying machine, a printer, a plotter, a facsimile machine, a multifunction printer (MFP), and the like are widely known. In such an image forming apparatus, generally, an electrostatic latent image is formed on the surface of a photosensitive drum, and a so-called development is performed by attaching toner to the electrostatic latent image. Have gained.

  By the way, in order to obtain a good toner image, the amount of toner used for developing the electrostatic latent image must be appropriate. Various development methods are known, such as a method using a “two-component developer containing toner and carrier” and a mono-toner development method using a developer composed only of toner. The amount of toner supplied to the developing unit where the electrostatic latent image is developed is also called “toner density”.

  If the toner density is too low, a sufficient amount of toner is not supplied to the electrostatic latent image, and the image (output image) output from the image forming apparatus is an image with insufficient density. On the other hand, if the toner density is too high, the density distribution in the output image is biased toward the “high density side”, resulting in an image that is difficult to see. Thus, in order to obtain a good output image, the toner density must be within an appropriate range.

  Therefore, in order to control the toner density within an appropriate range, a toner density detection pattern (toner pattern) is formed, and the toner pattern is irradiated with light (detection light) to detect a change in the amount of reflected light. The method is widely performed (for example, refer to Patent Documents 1 to 6).

  The present invention relates to an image carrier; an optical scanning device that forms a latent image by scanning a light beam modulated in accordance with image information on the image carrier in a main scanning direction; and attaches toner to the latent image A developing device that generates a toner image; a transfer device that transfers the toner image to a medium; at least three light sources that are arranged at equal intervals in the main scanning direction and emit a light beam toward the medium; An emission optical system that collects the emitted light beam, and at least three light receivers that are arranged at equal intervals in the main scanning direction and that receive the light beam emitted from each light source and reflected by the medium, and formed on the medium A density detection sensor for detecting a density of the detected detection pattern; and a control device for controlling each light source of the density detection sensor and instructing the optical scanning device to create the detection pattern. When one of the at least three light sources is caused to emit light, one detection light spot and at least one flare light spot are formed on the medium, and the control device includes the flare light. An image forming apparatus characterized by instructing at least one of the size and the number of the detection patterns so that at least one of the light spots and the detection light spot are positioned on the detection pattern. .

  According to this, high image quality can be maintained without reducing workability.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. It is FIG. (1) for demonstrating schematic structure of an optical scanning device. FIG. 3 is a second diagram for explaining a schematic configuration of the optical scanning device; FIG. 3 is a third diagram for explaining a schematic configuration of the optical scanning device; FIG. 4 is a diagram (part 4) for explaining a schematic configuration of the optical scanning device; FIG. 2 is a diagram for explaining a toner concentration detector in FIG. 1. It is a figure for demonstrating arrangement | positioning of a detection sensor. It is a figure for demonstrating the irradiation system of a detection sensor. FIG. 9A to FIG. 9E are diagrams for explaining the light receiving system of the detection sensor, respectively. It is a figure for demonstrating the light for a detection. It is a figure for demonstrating the optical path of the light beam inject | emitted from the light emission part E3. It is a figure for demonstrating the detection light and flare light which illuminate a transfer belt when the light emission part E3 is lighted. It is a figure for demonstrating the light intensity of the light for a detection in FIG. 12, and each flare light. FIG. 6 is a diagram for explaining a toner pattern. It is a figure for demonstrating the relationship between the light beam inject | emitted from the light emission part E3, and a toner pattern. It is a figure for demonstrating the effect of illuminating a toner pattern with flare light. FIG. 10 is a diagram for explaining a toner pattern modification example 1; FIG. 10 is a diagram for explaining a second modification of the toner pattern. FIG. 10 is a diagram for explaining a relationship between a light beam emitted from a light emitting unit E3 and a toner pattern of Modification Example 2. 11 is a diagram for explaining signal levels of output signals of five light receiving units for each toner pattern according to Modification 2. FIG. FIG. 10 is a diagram for explaining a third modification of the toner pattern. FIG. 10 is a diagram for explaining a relationship between a light beam emitted from a light emitting unit E3 and a toner pattern of Modification Example 3. It is a figure for demonstrating integration of five condensing lenses for illumination. FIG. 24A to FIG. 24E are diagrams for explaining modifications of the light receiving system, respectively. It is a figure for demonstrating integration of five condensing lenses for light reception. It is a figure for demonstrating the pattern for position detection. FIG. 10 is a diagram for explaining a toner pattern modification example 4; It is a figure for demonstrating the modification 1 of a detection sensor. It is a figure for demonstrating the modification 2 of a detection sensor. It is a figure for demonstrating the modification 3 of a detection sensor. It is a figure for demonstrating the modification 4 of a detection sensor. It is a figure for demonstrating the modification 5 of a detection sensor. It is a figure for demonstrating the modification 6 of a detection sensor.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  The toner density detector 2245 is disposed on the −X side of the transfer belt 2040. The toner concentration detector 2245 will be described later.

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

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

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

  For convenience, the direction along the optical axis of the coupling lens 2201a and the coupling lens 2201b is referred to as “w1 direction”, and the main scanning corresponding direction in the light source 2200a and the light source 2200b is referred to as “m1 direction”. Furthermore, a direction along the optical axis of the coupling lens 2201c and the coupling lens 2201d is referred to as “w2 direction”, and a main scanning corresponding direction in the light source 2200c and the light source 2200d is referred to as “m2 direction”. Note that the sub-scanning corresponding direction in the light source 2200a and the light source 2200b and the sub-scanning corresponding direction in the light source 2200c and the light source 2200d are both the same direction as the Z-axis direction.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  Each folding mirror is arranged so that the optical path lengths from the polygon mirror 2104 to each photosensitive drum coincide with each other, and the incident position and the incident angle of the light flux on each photosensitive drum are equal to each other. ing.

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

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

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

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

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

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

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

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

  Next, the toner concentration detector 2245 will be described.

  The toner density detector 2245 has four detection sensors (2245a, 2245b, 2245c, 2245d) as shown in FIG. 6 as an example.

  The detection sensor 2245a is disposed at a position facing the vicinity of the + Y side end of the transfer belt 2040, and the detection sensor 2245d is disposed at a position facing the vicinity of the −Y side end of the transfer belt 2040. The detection sensor 2245b is arranged on the −Y side of the detection sensor 2245a, and the detection sensor 2245c is arranged on the + Y side of the detection sensor 2245d. Note that the detection sensor 2245b and the detection sensor 2245c are arranged so that the intervals between the detection sensors are substantially equal in the Y-axis direction.

  Here, as shown in FIG. 7 as an example, with respect to the Y-axis direction, the center position of the detection sensor 2245a is Y1, the center position of the detection sensor 2245b is Y2, the center position of the detection sensor 2245c is Y3, and the center of the detection sensor 2245d The position is Y4. The toner pattern facing the detection sensor 2245a is TP1, the toner pattern facing the detection sensor 2245b is TP2, the toner pattern facing the detection sensor 2245c is TP3, and the toner pattern facing the detection sensor 2245d is TP4.

  TP1 is a yellow toner pattern, TP2 is a magenta toner pattern, TP3 is a cyan toner pattern, and TP4 is a black toner pattern.

  When toner density detection processing using the toner density detector 2245 is performed, the printer control device 2090 instructs the scan control device to form a toner pattern.

  Then, the scanning control device controls the Y station so that the yellow toner pattern TP1 is formed at the position Y1 on the photosensitive drum 2030d, and the magenta toner pattern TP2 is formed at the position Y2 on the photosensitive drum 2030c. To control the M station. Further, the scanning control device controls the C station so that the cyan toner pattern TP3 is formed at the position Y3 on the photosensitive drum 2030b, and the black toner pattern TP4 is formed at the position Y4 on the photosensitive drum 2030a. To control the K station.

  The yellow toner pattern TP1 formed by the Y station is transferred to the position Y1 on the transfer belt 2040, and the magenta toner pattern TP2 formed by the M station is transferred to the position Y2 on the transfer belt 2040 and formed by the C station. The cyan toner pattern TP3 thus transferred is transferred to the position Y3 on the transfer belt 2040, and the black toner pattern TP4 formed by the K station is transferred to the position Y4 on the transfer belt 2040. In addition, when it is not necessary to distinguish the toner patterns, they are collectively referred to as “toner patterns TP”.

  As an example, the detection sensor 2245a includes five light emitting units (E1 to E5), five illumination condensing lenses (LE1 to LE5), and five light receiving units (see FIG. 8 to FIG. 9E). D1-D5).

  The five light emitting units (E1 to E5) are arranged at equal intervals Le along the Y-axis direction. An LED can be used for each light emitting portion. Here, as an example, Le = 0.4 mm. Each light emitting portion emits a light beam toward a −X side end portion of the transfer belt 2040 in a direction parallel to the XZ plane and inclined with respect to the X axis.

  The illumination condensing lens LE1 is disposed on the + X side of the light emitting unit E1, and condenses the light emitted from the light emitting unit E1 toward the surface of the transfer belt 2040.

  The illumination condensing lens LE2 is disposed on the + X side of the light emitting unit E2, and condenses the light emitted from the light emitting unit E2 toward the surface of the transfer belt 2040.

  The illumination condensing lens LE3 is disposed on the + X side of the light emitting unit E3 and condenses the light emitted from the light emitting unit E3 toward the surface of the transfer belt 2040.

  The illumination condensing lens LE4 is disposed on the + X side of the light emitting unit E4 and condenses the light emitted from the light emitting unit E4 toward the surface of the transfer belt 2040.

  The illumination condenser lens LE5 is disposed on the + X side of the light emitting unit E5, and condenses and guides the light beam emitted from the light emitting unit E5 toward the surface of the transfer belt 2040.

  For each illumination condenser lens, a spherical lens or an anamorphic lens having a condenser function in the Y-axis direction and the Z-axis direction can be used.

  The light receiving unit D1 is on the −Z side of the light emitting unit E1, and is disposed on the optical path of the light beam emitted from the light emitting unit E1, condensed by the illumination condenser lens LE1, and regularly reflected by the surface of the transfer belt 2040. Has been.

  The light receiving part D2 is on the −Z side of the light emitting part E2, and is arranged on the optical path of the light beam emitted from the light emitting part E2, condensed by the illumination condenser lens LE2, and regularly reflected by the surface of the transfer belt 2040. Has been.

  The light receiving unit D3 is on the −Z side of the light emitting unit E3, and is disposed on the optical path of the light beam emitted from the light emitting unit E3, condensed by the illumination condenser lens LE3, and regularly reflected by the surface of the transfer belt 2040. Has been.

  The light receiving part D4 is on the −Z side of the light emitting part E4, and is disposed on the optical path of the light beam emitted from the light emitting part E4, condensed by the illumination condenser lens LE4, and regularly reflected by the surface of the transfer belt 2040. Has been.

  The light receiving unit D5 is located on the −Z side of the light emitting unit E5, is disposed on the optical path of the light beam emitted from the light emitting unit E5, collected by the illumination condenser lens LE5, and regularly reflected by the surface of the transfer belt 2040. Has been.

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

  The other detection sensors (2245b, 2245c, 2245d) have the same configuration and structure as the detection sensor 2245a.

  The light beam emitted from the light emitting unit E1 and collected by the illumination condenser lens LE1 illuminates the transfer belt 2040 as detection light S1, as shown in FIG. 10 as an example. The light beam emitted from the light emitting unit E2 and collected by the illumination condenser lens LE2 illuminates the transfer belt 2040 as detection light S2. The light beam emitted from the light emitting unit E3 and collected by the illumination condenser lens LE3 illuminates the transfer belt 2040 as detection light S3. The light beam emitted from the light emitting unit E4 and collected by the illumination condenser lens LE4 illuminates the transfer belt 2040 as detection light S4. The light beam emitted from the light emitting unit E5 and collected by the illumination condenser lens LE5 illuminates the transfer belt 2040 as detection light S5. Here, as an example, the size of the light spot that each detection light forms on the surface of the transfer belt 2040 is 0.2 mm in diameter. The size of the light spot by the conventional detection light is usually about 2 to 3 mm in diameter.

  Note that the surface of the transfer belt 2040 is smooth, and most of the light irradiated on the surface of the transfer belt 2040 is regularly reflected. Therefore, the detection light S1 irradiated on the surface of the transfer belt 2040 is regularly reflected on the surface of the transfer belt 2040 and enters the light receiving part D1 and the light receiving part D2.

  Similarly, the detection light S2 irradiated on the surface of the transfer belt 2040 is regularly reflected on the surface of the transfer belt 2040 and enters the light receiving unit D1, the light receiving unit D2, and the light receiving unit D3.

  The detection light S3 irradiated on the surface of the transfer belt 2040 is specularly reflected on the surface of the transfer belt 2040 and enters the light receiving part D2, the light receiving part D3, and the light receiving part D4.

  The detection light S4 irradiated on the surface of the transfer belt 2040 is specularly reflected on the surface of the transfer belt 2040 and enters the light receiving unit D3, the light receiving unit D4, and the light receiving unit D5.

  The detection light S5 irradiated on the surface of the transfer belt 2040 is regularly reflected by the surface of the transfer belt 2040 and enters the light receiving part D4 and the light receiving part D5.

  By the way, the light beam emitted from the light emitting unit E1 is incident on an illumination condenser lens other than the illumination condenser lens LE1. Therefore, the flare light F2 emitted from the light emitting part E1 and coupled by the illumination condenser lens LE2, the flare light F3 emitted from the light emission part E1 and coupled by the illumination condenser lens LE3, and emitted from the light emission part E1. The flare light F4 coupled by the illumination condenser lens LE4 also illuminates the transfer belt 2040. In the illumination condenser lens LE5 located far from the illumination condenser lens LE1, the light beam emitted from the light emitting unit E1 undergoes total reflection or the like and does not pass through and does not become flare light. At this time, only the regular reflection light of the detection light S1 is received by the light receiving unit D1. Further, the flare light regularly reflected by the surface of the transfer belt 2040 is not received by any light receiving unit.

  The light beam emitted from the light emitting unit E2 also enters an illumination condenser lens other than the illumination condenser lens LE2. Therefore, the flare light F1 emitted from the light emitting part E2 and coupled by the illumination condenser lens LE1, the flare light F3 emitted from the light emission part E2 and coupled by the illumination condenser lens LE3, and emitted from the light emission part E2. The flare light F4 coupled by the illumination condenser lens LE4 and the flare light F5 emitted from the light emitting portion E2 and coupled by the illumination condenser lens LE5 also illuminate the transfer belt 2040. At this time, only the regular reflection light of the detection light S2 is received by the light receiving unit D2. Further, the flare light regularly reflected by the surface of the transfer belt 2040 is not received by any light receiving unit.

  As shown in FIG. 11 as an example, the light beam emitted from the light emitting unit E3 also enters an illumination condenser lens other than the illumination condenser lens LE3. Therefore, as shown in FIGS. 11 and 12, the flare light F1 emitted from the light emitting unit E3 and coupled by the illumination condenser lens LE1 is coupled to the flare light F1 emitted from the light emitting unit E3 and the illumination condenser lens LE2. The flare light F2, the flare light F4 emitted from the light emitting part E3 and coupled by the illumination condenser lens LE4, and the flare light F5 emitted from the light emission part E3 and coupled by the illumination condenser lens LE5 are also transferred belt 2040. Illuminate. At this time, only the regular reflection light of the detection light S3 is received by the light receiving unit D3. Further, the flare light regularly reflected by the surface of the transfer belt 2040 is not received by any light receiving unit.

  FIG. 13 shows the light intensities of the detection light S3, the flare light F1, the flare light F2, the flare light F4, and the flare light F5 in this case.

  The light beam emitted from the light emitting unit E4 also enters an illumination condenser lens other than the illumination condenser lens LE4. Therefore, the flare light F1 emitted from the light emitting part E4 and coupled by the illumination condenser lens LE1, the flare light F2 emitted from the light emission part E4 and coupled by the illumination condenser lens LE2, and emitted from the light emission part E4. The flare light F3 coupled by the illumination condenser lens LE3 and the flare light F5 emitted from the light emitting portion E4 and coupled by the illumination condenser lens LE5 also illuminate the transfer belt 2040. At this time, only the regular reflection light of the detection light S4 is received by the light receiving unit D4. Further, the flare light regularly reflected by the surface of the transfer belt 2040 is not received by any light receiving unit.

  The light beam emitted from the light emitting unit E5 also enters an illumination condenser lens other than the illumination condenser lens LE5. Therefore, the flare light F2 emitted from the light emitting part E5 and coupled by the illumination condenser lens LE2, the flare light F3 emitted from the light emission part E5 and coupled by the illumination condenser lens LE3, and emitted from the light emission part E5. The flare light F4 coupled by the illumination condenser lens LE4 also illuminates the transfer belt 2040. In the illumination condenser lens LE1 located far from the illumination condenser lens LE5, the light beam emitted from the light emitting unit E5 undergoes total reflection and the like and does not pass through and does not become flare light. At this time, only the regular reflection light of the detection light S5 is received by the light receiving unit D5. Further, the flare light regularly reflected by the surface of the transfer belt 2040 is not received by any light receiving unit.

  Therefore, when the detection light and all the flare lights illuminate the surface of the transfer belt 2040, the distribution of received light amounts in the five light receiving portions does not depend on the flare light, but only on the detection light. ing. In this case, the light received by the light receiving unit is specularly reflected light for detection. Hereinafter, for convenience, the distribution state of the received light amount in the five light receiving units at this time is also referred to as a “first distribution state”. Then, the printer control apparatus 2090 appropriately obtains the “first distribution state” and stores the information in a memory (not shown).

  As an example, the toner pattern TP has five rectangular patterns (p1 to p5, hereinafter referred to as “rectangular pattern” for convenience), as shown in FIG. The rectangular patterns are arranged in a line along the traveling direction of the transfer belt 2040, and the gradations of the toner densities are different. The gradation of the toner density can be changed by adjusting the power of the light beam emitted from the light source, adjusting the duty in the drive pulse supplied to the light source, and adjusting the developing bias. The center of each rectangular pattern in the Y-axis direction is set to face the light emitting portion E3.

  Here, a toner density detection process performed in the printer control apparatus 2090 will be described. However, only the light emitting part E3 is used among the five light emitting parts.

(1) The scanning control device is instructed to form a toner pattern having a size and a position that are not irradiated with the flare light but only the detection light S3.

(2) The light emitting unit E3 is blinked, and the distribution state of the received light amount in the five light receiving units is obtained based on the output signal of each light receiving unit. Hereinafter, for the sake of convenience, the distribution state of the received light amount in the five light receiving units at this time is also referred to as a “second distribution state”.

  At this time, the light received by the light receiving part D1 and the light receiving part D5 is diffusely reflected light of the detection light S3. Further, the light received by the light receiving part D2 and the light receiving part D4 is a mixture of the diffuse reflection light and the regular reflection light of the detection light S3.

  Therefore, next, the output signals of the light receiving unit D2 and the light receiving unit D4 are separated into a signal by the diffuse reflection light and a signal by the regular reflection light of the detection light S3.

(3) The ratio (denoted as R2) between the signal level of the output signal of the light receiving unit D3 and the signal level of the output signal of the light receiving unit D2 in the “first distribution state” is obtained.

(4) The ratio (referred to as R4) of the signal level of the output signal of the light receiving unit D3 and the signal level of the output signal of the light receiving unit D4 in the “first distribution state” is obtained.

(5) The signal level of the output signal of the light receiving unit D2 in the “second distribution state” is multiplied by R2. This value is the signal level (referred to as L2) of the regular reflection light of the detection light S3 in the output signal of the light receiving unit D2.

(6) The signal level of the output signal of the light receiving unit D4 in the “second distribution state” is multiplied by R4. This value is the signal level (referred to as L4) of the specularly reflected light of the detection light S3 in the output signal of the light receiving unit D4.

(7) The L2 is subtracted from the signal level of the output signal of the light receiving unit D2 in the “second distribution state”. This value is the signal level of the diffuse reflected light of the detection light S3 in the output signal of the light receiving unit D2.

(8) The L4 is subtracted from the signal level of the output signal of the light receiving unit D4 in the “second distribution state”. This value is the signal level of the diffuse reflected light of the detection light S3 in the output signal of the light receiving unit D4.

  Thereby, when only the detection light S3 illuminates the toner pattern, it is possible to know the distribution state of the received light amount by the regular reflection light and the distribution state of the received light amount by the diffuse reflection light in the five light receiving portions.

(9) The scanning control device is instructed to form a toner pattern having a size and a position to which the detection light S3 and the flare light F4 are irradiated (see FIG. 15). Here, Lp = 1.5 mm.

(10) The light emitting unit E3 is blinked, and the distribution state of the received light amount in the five light receiving units is obtained based on the output signal of each light receiving unit. Hereinafter, for convenience, the distribution state of the received light amount in the five light receiving units at this time is also referred to as a “third distribution state”.

  At this time, the specularly reflected light of the flare light F4 does not affect the amount of light received by the five light receiving units, but the diffusely reflected light of the flare light F4 is 5 as compared with when only the detection light S3 illuminates the toner pattern. Increasing the amount of light received at one light receiving unit

(11) Refer to the distribution state of the light reception amount by the regular reflection light and the distribution state of the light reception amount by the diffuse reflection light in the five light receiving units in the “second distribution state”, and the 5 in the “third distribution state”. The distribution state of the received light amount by the regular reflection light and the distribution state of the received light amount by the diffuse reflection light in the two light receiving units are obtained. Then, a total value of signal levels caused by diffusely reflected light in each light receiving unit is obtained, and it is determined whether the toner density is appropriate based on the total value.

  Incidentally, as shown in FIG. 16 as an example, when the detection light S3 and the flare light F4 illuminate the toner pattern as compared with the case where only the detection light S3 illuminates the toner pattern, the diffused reflected light is received. The total amount has increased. As described above, an increase in the total amount of diffuse reflection light received means that the difference in reflection characteristics between the transfer belt 2040 and the toner pattern is enlarged. When the difference between the reflection characteristics of the transfer belt 2040 and the toner pattern becomes large, it is possible to accurately determine the toner pattern in which the toner density is changed. That is, the toner density detection accuracy is improved.

  Note that the timing at which the toner pattern is formed is determined, and the time to reach the front (detection region) of the detection sensor after the toner pattern is formed is also approximately determined. Therefore, the printer control device 2090 controls the light emitting unit to blink at an appropriate timing when it is determined that the toner pattern has approached the detection area.

  When the toner density in the rectangular pattern changes, the output of the light receiving unit that receives the diffusely reflected light also changes. Specifically, when the toner concentration is high (the toner adhesion amount is increased), the specular reflection light is decreased and the diffuse reflection light is increased. Therefore, the printer control device 2090 determines whether or not the yellow toner density is appropriate from the output signal of each light receiving unit of the detection sensor 2245a, and determines the magenta toner from the output signal of each light receiving unit of the detection sensor 2245b. It is determined whether the density is appropriate, and from the output signal of each light receiving unit of the detection sensor 2245c, it is determined whether the cyan toner density is appropriate, and from the output signal of each light receiving unit of the detection sensor 2245d. Then, it is determined whether or not the black toner density is appropriate. When the printer control device 2090 determines that the toner density is not appropriate, the printer control device 2090 controls the development processing system of the corresponding station so as to be appropriate.

  As is clear from the above description, in the image forming apparatus 2000 according to the present embodiment, the toner density detector 2245 constitutes a density detection sensor. And the light source is comprised by the light emission part (E1-E5), the condensing optical system is comprised by the condensing lens for illumination (LE1-LE5), and the light receiver is comprised by the light-receiving part (D1-D5).

  As described above, according to the image forming apparatus 2000 according to the present embodiment, the four photosensitive drums (2030a, 2030b, 2030c, 2030d) and the light flux modulated in accordance with the image information with respect to each photosensitive drum. An optical scanning device for forming a latent image, four developing rollers (2033a, 2033b, 2033c, 2033d) for generating toner images by attaching toner to the latent images, and a transfer belt for transferring the toner images to the transfer belt. A transfer roller 2042 for transferring to 2040, a toner density detector 2245 for detecting the density of the toner pattern transferred to the transfer belt 2040, a printer control device 2090 for overall control, and the like are provided.

  The toner density detector 2245 has four detection sensors (2245a, 2245b, 2245c, 2245d) corresponding to the respective colors.

  Each detection sensor is arranged in a line at equal intervals Le along the Y-axis direction, and collects the five light sources (E1 to E5) that emit light beams toward the transfer belt 2040 and the light beams emitted from the respective light sources. There are five illumination condenser lenses (LE1 to LE5) and five light receiving sections (D1 to D5) that receive the light beam reflected by the transfer belt 2040.

  When the printer control device 2090 performs the toner density detection process, the size of the toner pattern is set so that at least one of the light spots by the flare light and the light spot by the detection light illuminate the scanning control device. Indicates the position and position.

  In this case, even if the toner pattern is small, the toner density can be detected with high accuracy.

  By the way, the conventional density detection sensor for detecting the toner density includes one or two light emitting units, or three light emitting units having different wavelength characteristics, and one or two light receiving units for receiving reflected light. Consisted of. Then, even if the position of the toner pattern relative to the density detection sensor is shifted, the length of the toner pattern in the main direction (here, the Y-axis direction) is set so that the entire light spot by the detection light can illuminate the toner pattern. Then, Lp) was set to 15 mm to 25 mm. Since the original image formation cannot be performed while the toner density detection process is being performed, if it takes a long time to form the toner pattern, the working efficiency for the original image formation is reduced. The toner of the toner pattern is a so-called “non-contributing toner” that does not contribute to the original image formation and affects the replacement timing of the toner cartridge.

  In this embodiment, the length of the toner pattern in the Y-axis direction can be reduced to 1/10 or less of the conventional length, so that the time required to form the toner pattern can be significantly shortened compared to the conventional case. It is. Therefore, in image formation, high image quality can be maintained without reducing workability. Further, since the size (area) of the toner pattern can be reduced to 1/100 or less of the conventional one, the amount of non-contributing toner can be significantly reduced as compared with the conventional one. Therefore, the replacement time of the toner cartridge can be delayed.

  In the above-described embodiment, as illustrated in FIG. 17 as an example, the size and position of the toner pattern may be instructed so that the detection light S3 and the flare lights F1, F2, F4, and F5 are illuminated. In this case, the difference in reflection characteristics between the transfer belt 2040 and the toner pattern is further increased, and the toner density detection accuracy can be further improved. Here, Lp = 6.0 mm. Even in this case, the length of the toner pattern in the Y-axis direction is smaller than the conventional one.

  In the above embodiment, as shown in FIGS. 18 and 19 as an example, each of the rectangular patterns is individually illuminated by the detection light S3 and the flare lights F1, F2, F4, and F5. You may divide into five rectangular patterns (DP1-DP5). In this case, the toner density detection accuracy can be further improved and the toner consumption can be reduced. The length of each rectangular pattern in the Y-axis direction may be about 1 mm.

  In this case, an example of the output distribution of each light receiving unit by reflected light from five rectangular patterns (DP1 to DP5) that are individually illuminated with the detection light S3 and the flare lights F1, F2, F4, and F5 is illustrated. 20. Normally, the output signals of all the light receiving units are used for toner density detection, but the signal level of the output signal of each light receiving unit by DP1 and the signal level of the output signal of each light receiving unit by DP5 are different from each other by DP2. When the signal level of the output signal of the light receiving unit, the signal level of the output signal of each light receiving unit by DP3, and the signal level of the output signal of each light receiving unit by DP4 are significantly smaller than those shown in FIGS. In addition, three rectangular patterns (DP2 to DP4) may be formed. As a result, the toner consumption can be reduced while maintaining the toner density detection accuracy.

  Moreover, although the said embodiment demonstrated the case where each light-receiving part was arrange | positioned at the -Z side of a corresponding light emission part, it is not limited to this. In short, it is only necessary that each light receiving unit is arranged at a position corresponding to the emission direction of the light beam from the corresponding light emitting unit.

  Moreover, although the said embodiment demonstrated the case where four detection sensors (2245a, 2245b, 2245c, 2245d) are arrange | positioned at equal intervals regarding the Y-axis direction, it is not limited to this.

  In the above-described embodiment, a part of the processing performed by the printer control device 2090 may be performed by another device.

  Moreover, in the said embodiment, as FIG. 23 shows as an example, you may integrate the said 5 condensing lenses for illumination (LE1-LE5).

  Moreover, in the said embodiment, as shown in FIG. 24 (A)-FIG.24 (E) as an example, even if each detection sensor has each five light-receiving condensing lenses (LD1-LD5). good.

  The light receiving condensing lens LD1 is on the −Z side of the illuminating condensing lens LE1, emitted from the light emitting portion E1, condensed by the illuminating condensing lens LE1, and specularly reflected on the surface of the transfer belt 2040. It is arranged on the optical path of the luminous flux.

  The light receiving condensing lens LD2 is on the −Z side of the illumination condensing lens LE2, emitted from the light emitting portion E2, condensed by the illumination condensing lens LE2, and specularly reflected on the surface of the transfer belt 2040. It is arranged on the optical path of the luminous flux.

  The light receiving condensing lens LD3 is on the −Z side of the illumination condensing lens LE3, emitted from the light emitting portion E3, condensed by the illumination condensing lens LE3, and specularly reflected on the surface of the transfer belt 2040. It is arranged on the optical path of the luminous flux.

  The light receiving condensing lens LD4 is on the −Z side of the illumination condensing lens LE4, emitted from the light emitting portion E4, condensed by the illumination condensing lens LE4, and specularly reflected on the surface of the transfer belt 2040. It is arranged on the optical path of the luminous flux.

  The light receiving condensing lens LD5 is on the −Z side of the illuminating condensing lens LE5, emitted from the light emitting portion E5, condensed by the illuminating condensing lens LE5, and specularly reflected on the surface of the transfer belt 2040. It is arranged on the optical path of the luminous flux.

  For each light receiving condensing lens, a cylindrical lens having a condensing function in the Z-axis direction, a spherical lens having a condensing function in the Y-axis direction and the Z-axis direction, or an anamorphic lens can be used.

  In this case, as shown in FIG. 25 as an example, five light receiving condensing lenses (LD1 to LD5) may be integrated.

  Further, in the above-described embodiment, as shown in FIG. 26 as an example, a position detection pattern for detecting the displacement of the light spot on the surface of the photosensitive drum may be formed in front of each toner pattern. In this case, the position of the toner pattern in the Y-axis direction can be obtained from the position detection pattern. Note that the detection of positional deviation of a light spot using a position detection pattern is known (see, for example, Japanese Patent Application Laid-Open Nos. 2008-276010 and 2005-238484).

  In the above embodiment, as an example, as illustrated in FIG. 27, TP <b> 1 to TP <b> 4 may be arranged in a line along the traveling direction of the transfer belt 2040. In this case, the toner concentration detector 2245 only needs to have one detection sensor.

  Moreover, although the said embodiment demonstrated the case where a detection sensor had five light emission parts, it is not limited to this (refer FIG. 28). In short, what is necessary is just to have three or more light emission parts.

  Moreover, although the said embodiment demonstrated the case where five light emission parts (E1-E5) were arrange | positioned in a line along the Y-axis direction, it is not limited to this (refer FIG. 29). Moreover, you may arrange | position along the direction inclined with respect to the Y-axis direction (refer FIG. 30). Further, a plurality of rows in a so-called staggered arrangement along the Y-axis direction may be provided. In short, it suffices if they are arranged at equal intervals in the Y-axis direction.

  Moreover, although the said embodiment demonstrated the case where the number of light emission parts and the number of light receiving parts were the same, it is not limited to this (refer FIGS. 31-33).

  In the above-described embodiment, the case of the color printer 2000 including a plurality of photosensitive drums has been described as the image forming apparatus. However, the present invention is not limited to this, and for example, a single photosensitive drum is provided to form a single color image. It can also be applied to a printer.

  Further, it may be an image forming apparatus other than a printer, for example, a copier, a facsimile, or a multifunction machine in which these are integrated.

  As described above, the image forming apparatus of the present invention is suitable for maintaining high image quality without deteriorating workability.

  2000 ... color printer (image forming apparatus), 2010 ... optical scanning device, 2030a to 2030d ... photosensitive drum (image carrier), 2033a to 2033d ... developing roller (part of developing device), 2034a to 2034d ... toner cartridge ( Part of developing device), 2040 ... Transfer belt (medium), 2042 ... Transfer roller (part of transfer device), 2090 ... Printer control device (control device), 2245 ... Toner density detector (density detection sensor), D1 ... D5... Light receiving unit (light receiver), E1 to E5. Light emitting unit (light source), LD1 to LD5... Light receiving condensing lens (pre-light receiving optical system), LE1 to LE5. ), TP1 to TP4... Toner pattern (detection pattern).

JP-A-1-35466 JP 2004-21164 A JP 2002-72612 A Japanese Patent No. 4154272 Japanese Patent No.4110027 Japanese Patent Laid-Open No. 2005-76885

Claims (7)

An image carrier;
An optical scanning device that scans the image carrier with a light beam modulated in accordance with image information in a main scanning direction to form a latent image;
A developing device that attaches toner to the latent image to generate a toner image;
A transfer device for transferring the toner image to a medium;
Arranged at equal intervals in the main scanning direction, at least three light sources that emit light beams toward the medium, an emission optical system that collects light beams emitted from each light source, and arranged at equal intervals in the main scanning direction, A density detection sensor for detecting the density of a detection pattern formed on the medium, including at least three light receivers that receive light beams emitted from the respective light sources and reflected by the medium;
A control device that controls each light source of the density detection sensor and instructs the optical scanning device to create the detection pattern;
When any one of the at least three light sources emits light, one detection light spot and at least one light spot by flare light are formed on the medium,
The control device instructs at least one of the size and number of the detection patterns so that at least one of the light spots by the flare light and the detection light spot are positioned on the detection pattern. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the density detection sensor further includes a pre-light-receiving optical system that collects the light beam reflected by the medium. When any one of the at least three light sources emits light, one detection light spot and a plurality of flare light spots are formed on the medium,
The control device instructs at least one of a size and a number of the detection patterns so that two light spots by the flare light and the detection light spots are included at the same time. Or the image forming apparatus according to 2;   The said control apparatus instruct | indicates at least any one of the magnitude | size and the number of the said pattern for a detection so that all the light spots by the said flare light and the said light spot for a detection may be included simultaneously. The image forming apparatus described in 1.   The control device is configured to configure the detection pattern as a plurality of patterns so that at least one of the light spots by the flare light and the detection light spot are individually positioned on the detection pattern. The image forming apparatus according to any one of claims 1 to 4.   6. The image according to claim 1, wherein the control device further controls a toner adhesion amount in the developing device based on an output signal of each light receiver of the density detection sensor. Forming equipment. The image information is multicolor image information,
The image forming apparatus according to claim 1, wherein the control device instructs creation of the detection pattern for each color.