JP5354349B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus maintaining high image quality without deteriorating work efficiency. <P>SOLUTION: In the image forming apparatus, 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 density detecting processing, a printer controller designates to make length Lp of a rectangular pattern in the Y-axis direction attain Lp&lt;2L by using an interval L between a light spot by detecting light and a light spot by flare light nearest to the light spot. <P>COPYRIGHT: (C)2010,JPO&amp;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” and the image 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 4).

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 Le in the main scanning direction and emit light beams toward the medium; A condensing optical system that condenses the emitted light beam, and at least three light receivers that are arranged at equal intervals in the main scanning direction and receive the light beam emitted from each light source and reflected by the medium. A density detection sensor for detecting the density of the detection pattern transferred to the control unit; 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; Wherein said when caused to emit light one of the at least three light sources, the light spot according to at least one flare light and one detection light spot on said medium is formed, the control device, The length Lp in the main scanning direction of the detection pattern is instructed to satisfy Lp <2L using the interval L between the detection light spot and the light spot by the flare light closest to the detection light spot. An image forming apparatus characterized by the above.

  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. FIG. 6 is a diagram for explaining a toner pattern. 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 E1. It is a figure for demonstrating the light for a detection and flare light which illuminate a transfer belt when the light emission part E1 is lighted. It is a figure for demonstrating the optical path of the light beam inject | emitted from the light emission part E2. It is a figure for demonstrating the light for a detection and flare light which illuminate a transfer belt when the light emission part E2 is lighted. 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 optical path of the light beam inject | emitted from the light emission part E4. It is a figure for demonstrating the detection light and flare light which illuminate a transfer belt when the light emission part E4 is lighted. It is a figure for demonstrating the optical path of the light beam inject | emitted from the light emission part E5. It is a figure for demonstrating the detection light and flare light which illuminate a transfer belt when the light emission part E5 is lighted. FIG. 6 is a diagram for explaining a positional shift of a toner pattern. FIG. 6 is a diagram for explaining a relationship between a light beam emitted from a light emitting unit E1 and a toner pattern when Lp = Le. FIG. 10 is a diagram for explaining a relationship between a light beam emitted from a light emitting unit E2 and a toner pattern when Lp = Le. FIG. 6 is a diagram for explaining a relationship between a light beam emitted from a light emitting unit E3 and a toner pattern when Lp = Le. It is a figure for demonstrating the relationship between the light beam inject | emitted from the light emission part E4, and a toner pattern when Lp = Le. FIG. 10 is a diagram for explaining a relationship between a light beam emitted from a light emitting unit E5 and a toner pattern when Lp = Le. It is a figure for demonstrating the relationship between the light beam inject | emitted from the light emission part E2, and a toner pattern when Lp = 2xLe. It is a figure for demonstrating the relationship between the light beam inject | emitted from the light emission part E4, and a toner pattern when Lp = 2xLe. FIG. 6 is a diagram for explaining a modified example of a toner pattern. It is a figure for demonstrating an auxiliary pattern. It is a figure for demonstrating the pattern for position detection. 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. Configure.

  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. Configure.

  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. Configure.

  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. Configure.

  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 respectively deflected by the first-stage (lower) tetrahedral mirror, 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. Here, the detection sensor 2245b and the detection sensor 2245c are arranged so that the intervals between the detection sensors are substantially equal with respect to 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.

  The scanning control apparatus 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 shown in FIGS. 8 to 9E 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 condensings. It has a lens (LD1 to LD5) and five light receiving parts (D1 to 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 part. Here, as an example, Le = 0.4 mm. Each light emitting portion emits a light beam toward the −X side end 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 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.

  The light receiving unit D1 is disposed on the −Z side of the light emitting unit E1, and receives the light beam collected by the light receiving condensing lens LD1.

  The light receiving unit D2 is disposed on the −Z side of the light emitting unit E2, and receives the light beam collected by the light receiving condensing lens LD2.

  The light receiving unit D3 is disposed on the −Z side of the light emitting unit E3, and receives the light beam collected by the light receiving condensing lens LD3.

  The light receiving unit D4 is disposed on the −Z side of the light emitting unit E4, and receives the light beam collected by the light receiving condensing lens LD4.

  The light receiving unit D5 is disposed on the −Z side of the light emitting unit E5, and receives the light beam collected by the light receiving condensing lens LD5.

  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.

  As an example, the toner pattern TP has five square 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 length Lp of each rectangular pattern in the Y-axis direction is set to be 2.5 times (here, 1.0 mm) of Le. The center of each rectangular pattern in the Y-axis direction is set to face the light emitting portion E3. Information about the size and position of each rectangular pattern is sent from the printer control device 2090 to the scanning control device.

  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. 11 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.

  Further, 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 portion D1 through the light receiving condensing lens LD1. 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 portion D2 through the light receiving condensing lens LD2. 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 unit D4 via the light receiving condensing lens LD3. 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 D4 through the light receiving condensing lens LD4. The detection light S5 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 D5 through the light receiving condensing lens LD5.

  By the way, as shown in FIG. 12 as an example, the light beam emitted from the light emitting unit E1 also enters an illumination condenser lens other than the illumination condenser lens LE1. Therefore, as shown in FIGS. 12 and 13, the flare light F2 emitted from the light emitting unit E1 and coupled by the illumination condenser lens LE2, and the light emitted from the light emitting unit E1 and coupled by the illumination condenser lens LE3. The flare light F3 and the flare light F4 (not shown in FIG. 13) emitted from the light emitting portion E1 and coupled by the illumination condenser lens LE4 also illuminate 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.

  The length Lp in the Y-axis direction of each rectangular pattern is smaller than twice the distance L between the light spot by the detection light and the light spot by the flare light closest to the light spot. Here, L = 2 mm.

  In this case, when the rectangular pattern is positioned in front of the detection sensor, the detection light S1 illuminates the surface of the transfer belt 2040, and the regular reflection light is received by the light receiving unit D1. The flare light F2 illuminates the rectangular pattern, and the diffuse reflected light by the rectangular pattern is received by all the light receiving units. The flare lights F3 and F4 illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any of the light receiving portions. Therefore, the light receiving unit D1 receives both the regular reflection light by the transfer belt 2040 and the diffuse reflection light by the rectangular pattern. Therefore, it is not appropriate to cause the light emitting unit E1 to emit light.

  As shown in FIG. 14 as an example, the light beam emitted from the light emitting unit E2 also enters an illumination condenser lens other than the illumination condenser lens LE2. Therefore, as shown in FIGS. 14 and 15, the flare light F1 emitted from the light emitting unit E2 and coupled by the illumination condenser lens LE1, and the light emitted from the light emitting unit E2 and coupled by the illumination condenser lens LE3. Flare light F3 emitted from the light emitting portion E2 and coupled with the illumination condenser lens LE4, and flare light F5 emitted from the light emission portion E2 and coupled with the illumination condenser lens LE5 (in FIG. 15) (Not shown) also illuminates the transfer belt 2040.

  In this case, when the rectangular pattern is positioned in front of the detection sensor, the detection light S2 illuminates the rectangular pattern, and the diffuse reflected light is received by all the light receiving units. The flare lights F1, F3, F4, and F5 all illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any light receiving unit. Therefore, diffuse reflection light of a rectangular pattern is received by all the light receiving portions. Therefore, a signal having a rectangular pattern of reflection characteristics can be obtained by causing the light emitting portion E2 to emit light.

  As shown in FIG. 16 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. 16 and 17, flare light F1 emitted from the light emitting unit E3 and coupled by the illumination condenser lens LE1, and emitted from the light emitting unit E3 and coupled by 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.

  In this case, when the rectangular pattern is positioned in front of the detection sensor, the detection light S3 illuminates the rectangular pattern, and the diffuse reflected light is received by all the light receiving units. The flare lights F1, F2, F4, and F5 all illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any light receiving unit. Therefore, diffuse reflection light of a rectangular pattern is received by all the light receiving portions. Therefore, a signal having a rectangular pattern of reflection characteristics can be obtained by causing the light emitting portion E3 to emit light.

  As shown in FIG. 18 as an example, the light beam emitted from the light emitting unit E4 also enters an illumination condenser lens other than the illumination condenser lens LE4. Therefore, as shown in FIGS. 18 and 19, flare light F1 (not shown in FIG. 19) emitted from the light emitting unit E4 and coupled by the illumination condenser lens LE1, and emitted from the light emitting unit E4 and collected for illumination. The flare light F2 coupled by the light lens LE2, the flare light F3 emitted from the light emitting portion E4 and coupled by the light collecting lens LE3, and the light emitted from the light emitting portion E4 and coupled by the light collecting lens LE5. The flare light F5 also illuminates the transfer belt 2040.

  In this case, when the rectangular pattern is positioned in front of the detection sensor, the detection light S4 illuminates the rectangular pattern, and the diffuse reflected light is received by all the light receiving units. The flare lights F1, F2, F3, and F5 all illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any light receiving unit. Therefore, diffuse reflection light of a rectangular pattern is received by all the light receiving portions. Therefore, a signal having a rectangular pattern of reflection characteristics can be obtained by causing the light emitting portion E4 to emit light.

  As shown in FIG. 20 as an example, the light beam emitted from the light emitting unit E5 also enters an illumination condenser lens other than the illumination condenser lens LE5. Therefore, as shown in FIGS. 20 and 21, flare light F2 (not shown in FIG. 21) emitted from the light emitting unit E5 and coupled by the illumination condenser lens LE2, and emitted from the light emitting unit E5 and collected for illumination. The flare light F3 coupled by the optical lens LE3 and the flare light F4 emitted from the light emitting unit E5 and coupled by the illumination condenser lens LE4 also illuminate 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 or the like, does not pass through, and does not become flare light.

  In this case, when the rectangular pattern is positioned in front of the detection sensor, the detection light S5 illuminates the surface of the transfer belt 2040, and the regular reflection light is received by the light receiving unit D5. The flare light F4 illuminates the rectangular pattern, and the diffuse reflected light by the rectangular pattern is received by all the light receiving units. The flare lights F3 and F2 illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any of the light receiving portions. Therefore, the light receiving unit D5 receives both the regular reflection light by the transfer belt 2040 and the diffuse reflection light by the rectangular pattern. Therefore, it is not appropriate to cause the light emitting unit E5 to emit light.

  In the present embodiment, the printer control device 2090 repeatedly turns on the light emitting unit E2 to the light emitting unit E4 sequentially in each detection sensor when performing the toner density detection process. That is, (1) the light emitting unit E2 is turned on, (2) the light emitting unit E2 is turned off, (3) the light emitting unit E3 is turned on, (4) the light emitting unit E3 is turned off, (5) the light emitting unit E4 is turned on, (6) The light emitting unit E4 is repeatedly turned off at high speed. That is, the surface of the transfer belt 2040 is scanned in the Y-axis direction with the light spots of the detection lights S2, S3, and S4. 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.

  By the way, when the toner density in the rectangular pattern changes, the output of the light receiving unit that receives the diffuse 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 obtains a total value of signal levels caused by diffusely reflected light in each light receiving unit, and determines whether the toner density is appropriate based on the total value. That is, 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. In this case, since the toner density can be accurately detected for each color without being affected by flare light, the toner adhesion amount on each developing roller can always be an appropriate adhesion amount. As a result, high image quality can be maintained.

  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 luminous flux modulated according to 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 each light source. Five illumination condenser lenses (LE1 to LE5), five light receiving condenser lenses (LD1 to LD5) for condensing the light beam reflected by the transfer belt 2040, and a light flux reflected by the transfer belt 2040 are received. It has five light receiving parts (D1 to D5).

  When performing the toner density detection process, the printer control device 2090 sets the length Lp of the rectangular pattern in the Y-axis direction to the interval L between the light spot by the detection light and the light spot by the flare light closest to the light spot. And set so that Lp <2L.

  In this case, the toner density can be detected with high accuracy without being affected by flare light.

  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 the present embodiment, the length Lp in the Y-axis direction of the toner pattern is 1.0 mm and can be reduced to 1/10 or less of the conventional one. Therefore, the time required for forming the toner pattern is significantly longer than before. It is possible to shorten it. 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. 22 as an example, when the position of the toner pattern is shifted with respect to the Y-axis direction, and the detection light S2 illuminates the end portion of the toner pattern, the detection light One half of the light spot illuminates the toner pattern, while the other half illuminates the transfer belt 2040. At this time, light in which diffuse reflection light from the toner pattern and regular reflection light from the transfer belt 2040 are mixed enters the light receiving portion D2, and they cannot be separated. In this case, the printer control device 2090 repeatedly turns on the light emitting unit E3 and the light emitting unit E4 sequentially when the toner density detection process is performed. Thus, it is important that the entire light spot by the detection light properly illuminates the toner pattern.

  Moreover, although the said embodiment demonstrated the case where Lp was 2.5 times Le, it is not limited to this. For example, as shown in FIGS. 23 to 27, Lp may be the same as Le.

  In this case, when the rectangular pattern is positioned in front of the detection sensor, when the light emitting unit E1 is turned on, the detection light S1 illuminates the surface of the transfer belt 2040, and the regular reflection light is received by the light receiving unit D1. The flare light F2 illuminates the rectangular pattern, and the diffuse reflected light by the rectangular pattern is received by all the light receiving units. The flare lights F3 and F4 illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any of the light receiving portions. Therefore, the light receiving unit D1 receives both the regular reflection light by the transfer belt 2040 and the diffuse reflection light by the rectangular pattern. Therefore, it is not appropriate to cause the light emitting unit E1 to emit light.

  When the light emitting unit E2 is turned on, the detection light S2 illuminates the surface of the transfer belt 2040, and the regular reflection light is received by the light receiving unit D2. The flare lights F1, F3, F4, and F5 all illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any light receiving unit. Therefore, only the regular reflection light from the transfer belt 2040 is received by the light receiving unit D2. Therefore, it is not appropriate to cause the light emitting unit E2 to emit light.

  When the light emitting unit E3 is turned on, the detection light S3 illuminates a rectangular pattern, and the diffuse reflected light is received by all the light receiving units. The flare lights F1, F2, F4, and F5 all illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any light receiving unit. Therefore, diffuse reflection light of a rectangular pattern is received by all the light receiving portions. Therefore, a signal having a rectangular pattern of reflection characteristics can be obtained by causing the light emitting portion E3 to emit light.

  When the light emitting unit E4 is turned on, the detection light S4 illuminates the surface of the transfer belt 2040, and the regular reflection light is received by the light receiving unit D4. The flare lights F1, F2, F3, and F5 all illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any light receiving unit. Therefore, only the regular reflection light from the transfer belt 2040 is received by the light receiving unit D4. Accordingly, it is not appropriate to cause the light emitting unit E4 to emit light.

  When the light emitting unit E5 is turned on, the detection light S5 illuminates the surface of the transfer belt 2040, and the regular reflection light is received by the light receiving unit D5. The flare light F4 illuminates the rectangular pattern, and the diffuse reflected light by the rectangular pattern is received by all the light receiving units. The flare lights F3 and F2 illuminate the surface of the transfer belt 2040, and the regular reflection light is not received by any of the light receiving portions. Therefore, the light receiving unit D5 receives both the regular reflection light by the transfer belt 2040 and the diffuse reflection light by the rectangular pattern. Therefore, it is not appropriate to cause the light emitting unit E5 to emit light.

  Therefore, in this case, the printer control device 2090 repeatedly blinks only the light emitting unit E3 in each detection sensor when performing the toner density detection process.

  In this case, it is good if the center of the toner pattern is located on the + X side of one of the light emitting parts, but when the center is between the light emitting parts, both ends of the toner pattern are located exactly on the + X side of the light emitting part. However, there is no light emitting part suitable for light emission.

  Therefore, when the center of the toner pattern is positioned at the center between the light emitting portions, the light emitting portion suitable for light emission can be obtained by setting Lp = Le + the spot size of the detection light (in the above embodiment, 0.2 mm). There can be two.

  Further, Lp may be twice that of Le. However, in this case, as shown in FIG. 28 and FIG. 29 as an example, the detection light S2 and S4 illuminate the edge of the toner pattern, so the printer control device 2090 performs toner density detection processing. At this time, in each detection sensor, only the light emitting portion E3 is repeatedly blinked.

  In the above embodiment, as an example, as shown in FIG. 30, 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.

  In the above embodiment, the case where the toner pattern transferred onto the transfer belt 2040 is detected has been described. However, the present invention is not limited to this. Depending on the form of the image forming apparatus, a toner pattern formed on a photosensitive member as an image carrier or an intermediate transfer belt (or intermediate transfer member) may be detected.

  In the above embodiment, the case where the detection light S3 illuminates the center of the toner pattern in the Y-axis direction has been described. However, the displacement of the effective scanning area and the change in the length of the photosensitive drum, the meandering of the transfer belt 2040 In some cases, the detection light S3 illuminates a position shifted from the center of the toner pattern in the Y-axis direction due to a shift in the mounting position of the detection sensor or a change in the mounting position with time.

  When there is such a possibility, the printer control device 2090 sequentially turns on and off all the light emitting units, and from the output signal of each light receiving unit when any detection light illuminates the toner pattern, the Y axis of the toner pattern Find the position in the direction. In this case, for example, the position of the toner pattern in the Y-axis direction is reduced from a fraction of Le to 1 based on the ratio 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 D4. / 10 accuracy can be obtained. Then, the printer control device 2090 determines a light emitting unit to be turned on when performing the toner density detection process according to the position of the obtained toner pattern in the Y-axis direction.

  In the above embodiment, as an example, as shown in FIG. 31, an auxiliary pattern for determining the position of the toner pattern in the Y-axis direction may be formed in front of each toner pattern. In this case, the length of the auxiliary pattern in the Y-axis direction is preferably the same as Lp.

  Further, in the above embodiment, as shown in FIG. 32 as an example, a position detection pattern for detecting the positional deviation 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 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).

  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. 33). 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. 34). Moreover, you may arrange | position along the direction inclined with respect to the Y-axis direction (refer FIG. 35). 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. 36-38).

  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.

  Moreover, although the said embodiment demonstrated the case where a detection sensor had a condensing lens for light reception, it is not limited to this, There may not be a condensing lens for light reception.

  Moreover, although the said embodiment demonstrated the case where Le was 0.4 mm, 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.

  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 part (light receiver), E1 to E5 .. light emitting part (light source), LE1 to LE5... Condensing lens for illumination (condensing optical system), TP1 to TP4.

JP-A 64-35466 JP 2004-309292 A JP 2004-21164 A JP 2002-72612 A

Claims (6)

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 Le with respect to the main scanning direction, at least three light sources for emitting light beams toward the medium, a condensing optical system for collecting the light beams emitted from the respective light sources, and at equal intervals with respect to the main scanning direction And a density detection sensor for detecting the density of the detection pattern transferred onto 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;
Wherein when light is emitted to any one of the at least three light sources, the light spot is formed by at least one flare light and one detection light spot on said medium,
The control device uses the distance L between the detection light spot and the light spot by the flare light closest to the detection light spot, so that the length Lp in the main scanning direction of the detection pattern is Lp <2L. An image forming apparatus characterized by instructing to become. Before SL control device, the one of the at least three light sources, the image forming apparatus according to claim 1, characterized in that lighting a single light source opposed to the detection pattern. The image forming apparatus according to claim 1, wherein the Lp is approximately twice the Le. The image forming apparatus according to claim 1, wherein the control device sequentially turns on at least a part of the at least three light sources one by one. Wherein the controller is further based on said output signal of each photodetector of the density detection sensor, an image according to any one of claims 1-4, characterized by controlling the amount of adhered toner in the developing device Forming equipment. The image information is multicolor image information,
Wherein the control device, an image forming apparatus according to any one of claims 1 to 5, characterized in that instructs the creation of the detection pattern for each color.