JP6675344B2 - Optical sensor and image forming apparatus - Google Patents

Description

  The present invention relates to an optical sensor for detecting specularly reflected light and irregularly reflected light of light emitted from a light emitting element with a plurality of light receiving elements to detect a detection target, and an image forming apparatus including the optical sensor. .

  2. Description of the Related Art In recent years, in order to increase the printing speed, an electrophotographic image forming apparatus is mainly of a tandem type in which a photoconductor is provided for each color. In a tandem-type image forming apparatus, for example, a detection image (toner image), which is a test pattern for detecting a color shift amount, is formed on an intermediate transfer belt, and the detection image is irradiated with light to reflect reflected light. The color misregistration amount is determined by detecting with the optical sensor. The determination of the toner density (image density) is also performed using such an optical sensor. Patent Literature 1 discloses a technique in which specularly reflected light and irregularly reflected light of light applied to a toner image are received by individual light receiving units (sensors), and the toner density is detected based on the amount of received light. . According to such a technique, it is possible to improve the detection accuracy of the toner by the optical sensor even when the multi-color toner used in the image forming apparatus has different reflection characteristics with respect to the light used by the optical sensor. It is possible.

  In an optical sensor of the type described above, a stop for restricting (stopping) light emitted from a light emitting element is generally provided, and specular reflected light and diffuse reflected light are separated in order to separate specular reflected light and diffuse reflected light. Such a stop is also provided for the light receiving element that receives light. As such an optical sensor, Patent Documents 2 and 3 disclose a surface mount type optical sensor in which an optical element is directly mounted on a surface of a circuit board.

  In Patent Document 2, an optical unit holder is attached to a circuit board on which a light emitting element and two light receiving elements are directly mounted, and the light emitting element and the two light receiving elements are respectively provided on the outer surface of the optical unit holder. Are arranged. However, using a plurality of polarizing filters in this way can lead to an increase in the cost of the apparatus and a decrease in productivity. On the other hand, in Patent Document 3, a housing having an opening (light guide path) functioning as a stop corresponding to each optical element (light emitting element and two light receiving elements) is provided. It is configured to be inserted into the provided slit hole. Thereby, the light-shielding property of the optical sensor in which each optical element is mounted on the surface of the circuit board is improved.

JP-A-10-221902 JP-A-2006-208266 JP 2013-191835 A

  However, in the optical sensor disclosed in Patent Literature 3, it is necessary to arrange the light emitting element and the two light receiving elements at a certain distance from each other in order to realize a housing with improved light shielding properties. According to such a configuration of the optical sensor, the size of the optical sensor in the direction in which the light-emitting element and the two light-receiving elements are arranged increases even though the light-shielding property can be improved. For this reason, further miniaturization of the optical sensor is desired.

  The present invention has been made in view of the above problems. An object of the present invention is to provide a technology that enables downsizing of an optical sensor for detecting a detection target by receiving specularly reflected light and irregularly reflected light of light emitted from a light emitting element with different light receiving elements. I do.

The present invention can be realized, for example, as an optical sensor. An optical sensor according to one embodiment of the present invention includes a light-emitting element that irradiates irradiation light toward an irradiation target, and a first light-emitting element that receives diffused reflection light in which the irradiation light is irregularly reflected in an irradiation region of the irradiation target. A light receiving element, and a second light receiving element for receiving the specularly reflected light in which the irradiation light is regularly reflected in the irradiation area of the irradiation object, wherein the first light receiving element is included in the irradiation area. Receiving the irregularly reflected light irregularly reflected in the first area, and the second light receiving element receives the regular reflected light at least partially reflected in the second area not including the first area in the main scanning direction. It is characterized by the following.

An optical sensor according to another embodiment of the present invention is a light-emitting element that irradiates irradiation light toward an irradiation target, and receives light that is irregularly reflected by the irradiation light in an irradiation region of the irradiation target. A first light receiving element, a second light receiving element for receiving regular reflection light in which the irradiation light is regularly reflected in the irradiation area of the irradiation object, and light emitted from the light emitting element to the irradiation object. And a second opening for guiding the diffusely reflected light irregularly reflected in the first region to the first light receiving element in the irradiation area, and at least a part in the main scanning direction. And a third opening for guiding the specularly reflected light that is specularly reflected by the second region that does not include the first region to the second light receiving element .

  Advantageous Effects of Invention According to the present invention, it is possible to reduce the size of an optical sensor for detecting a detection target by receiving specularly reflected light and irregularly reflected light of light emitted from a light emitting element with different light receiving elements.

FIG. 2 is a cross-sectional view illustrating a hardware configuration example of the image forming apparatus. FIG. 2 is a block diagram illustrating a configuration example of a control system of the image forming apparatus. FIG. 4 is a perspective view illustrating an example of the arrangement of a toner detection unit with respect to an intermediate transfer belt. FIG. 3 is a perspective view illustrating a configuration example of a toner detection unit. FIG. 3 is a cross-sectional view illustrating a configuration example of a toner detection unit. FIG. 4 is a perspective view illustrating a configuration of a toner detection unit according to a first comparative example. FIG. 6 is a diagram illustrating an example of the reflection directivity characteristics of the intermediate transfer belt. FIG. 9 is a perspective view illustrating a configuration of a toner detection unit according to a second comparative example. FIG. 9 is a cross-sectional view illustrating a configuration of a toner detection unit according to a second comparative example. FIG. 6 is a diagram illustrating an example of output from two light receiving elements of the toner detection unit. FIG. 10 is a diagram illustrating an example of a test pattern formed on an intermediate transfer belt (second to fifth embodiments). FIG. 9 is a diagram illustrating an example of a test pattern formed on an intermediate transfer belt (second embodiment). FIG. 10 is a diagram illustrating an example of a test pattern formed on an intermediate transfer belt (third embodiment). FIG. 14 is a diagram illustrating an example of a test pattern formed on an intermediate transfer belt (fourth embodiment). FIG. 13 is a diagram illustrating an example of a test pattern formed on an intermediate transfer belt and an output waveform of a light receiving element (a fifth embodiment).

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. It should be noted that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are necessarily essential to the means for solving the invention.

[First Embodiment]
<Overview of Image Forming Apparatus>
FIG. 1 is a cross-sectional view illustrating a hardware configuration example of the image forming apparatus 100 according to the first embodiment. The image forming apparatus 100 of the present embodiment is a color laser printer that forms a multicolor image using yellow (Y), magenta (M), cyan (C), and black (K) developers (toners). The image forming apparatus 100 may be, for example, any of a printing apparatus, a printer, a copying machine, a multifunction peripheral (MFP), and a facsimile machine. It should be noted that the reference characters Y, M, C, and K indicate that the colors of the developer (toner) targeted by the corresponding members are yellow, magenta, cyan, and black, respectively. In the following description, when it is not necessary to distinguish the colors, reference numerals excluding Y, M, C, and K at the end are used.

  The image forming apparatus 100 includes four process cartridges 7 (process cartridges 7Y, 7M, 7C, 7K) corresponding to image forming stations for forming Y, M, C, and K images, respectively. In FIG. 1, although reference numbers are given only to the components of the process cartridge 7Y corresponding to Y, the four process cartridges 7Y, 7M, 7C, and 7K have the same configuration. However, the four process cartridges 7Y, 7M, 7C, 7K are different in that images are formed using toners of different colors (Y, M, C, K).

  Around the photosensitive drum 1, a charging roller 2, an exposure unit 3, a developing unit 4, a primary transfer roller 26, and a cleaning blade 8 are arranged in this order along the rotation direction. In the present embodiment, the photosensitive drum 1, the charging roller 2, the developing unit 4, and the cleaning blade 8 are integrated as a process cartridge 7 that can be attached to and detached from the image forming apparatus 100. The exposure unit 3 is arranged vertically below the process cartridge 7.

  The process cartridge 7 includes a developing unit 4 and a cleaner unit 5. The developing unit 4 includes a developing roller 24, a developer applying roller 25, and a toner container. The toner container stores the toner of the corresponding color. The developing roller 24 is driven to rotate by a drive motor (not shown), and a developing bias voltage is applied from a high-voltage power supply 44 (FIG. 2), so that the electrostatic latent image is developed by the toner stored in the toner container. Do. The cleaner unit 5 has a photosensitive drum 1, a charging roller 2, a cleaning blade 8, and a waste toner container.

  The photosensitive drum 1 is formed by applying an organic photoconductor layer (OPC) to an outer peripheral surface of an aluminum cylinder. The photosensitive drum 1 is rotatably supported at both ends by flanges. When a driving force is transmitted from one end to a driving motor (not shown), the photosensitive drum 1 rotates in the direction of the arrow shown in FIG. Driven. The charging roller 2 uniformly charges the surface of the photosensitive drum 1 to a predetermined potential. The exposure unit 3 forms an electrostatic latent image on the photosensitive drum 1 by irradiating the photosensitive drum 1 with a laser beam based on image information (image signal) to expose the photosensitive drum 1. The developing unit 4 forms a toner image (toner image) on the photosensitive drum 1 by attaching toner to the electrostatic latent image on the photosensitive drum 1 and developing the electrostatic latent image.

  The intermediate transfer belt 12a, the driving roller 12b, and the tension roller 12c constitute the intermediate transfer unit 12. The intermediate transfer belt 12a is stretched between a driving roller 12b and a tension roller 12c, and is moved (rotated) in the direction of the arrow shown in FIG. 1 by being rotationally driven by the driving roller 12b. In the present embodiment, the intermediate transfer belt 12a is an example of an image carrier that is driven to rotate. A primary transfer roller 26 is disposed inside the intermediate transfer belt 12a at a position facing the photosensitive drum 1. The primary transfer roller 26 transfers the toner image on the photosensitive drum 1 to the intermediate transfer belt 12a (intermediate transfer body) when a transfer bias voltage is applied from the high voltage power supply 44 (FIG. 2). The four color toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially transferred (primary transfer) onto the intermediate transfer belt 12a. As a result, a multicolor toner image composed of Y, M, C, and K is formed on the intermediate transfer belt 12a. The multicolor toner image formed on the intermediate transfer belt 12a is transported to the secondary transfer nip 15 between the intermediate transfer belt 12a and the secondary transfer roller 16 with the rotation of the intermediate transfer belt 12a. .

  The paper feed unit 13 has a paper feed roller 9, a transport roller pair 10, a paper feed cassette 11, and a separation pad 23. Sheets S set by the user are stored in the sheet cassette 11. The sheet S may be referred to as recording paper, recording material, recording medium, paper, transfer material, transfer paper, and the like. The paper feed roller 9 feeds the sheet S from the paper feed cassette 11 to the transport path. The sheets S stored in the sheet cassette 11 are fed one by one to the transport path by the separation pad 23. The transport roller pair 10 transports the sheet S fed on the transport path toward the registration roller pair 17. When the sheet S is conveyed to the registration roller pair 17, the sheet S is conveyed to the secondary transfer nip 15 by the registration roller pair 17 at the timing when the toner image on the intermediate transfer belt 12 a reaches the secondary transfer nip 15. Is done. As a result, the toner image on the intermediate transfer belt 12a is transferred (secondarily transferred) to the sheet S in the secondary transfer nip portion 15.

  The sheet S to which the toner image has been transferred is conveyed to the fixing unit 14. The fixing unit 14 has a fixing belt 14a, a pressure roller 14b, and a belt guide member 14c, and the fixing belt 14a is guided by a belt guide member 14c to which a heating device such as a heater is adhered. A fixing nip portion is formed between the fixing belt 14a and the pressure roller 14b. The fixing unit 14 fixes the toner image on the sheet S by applying heat and pressure to the toner image formed on the sheet S in the fixing nip portion. After the fixing process by the fixing unit 14, the sheet S is discharged to a discharge tray 21 by a discharge roller pair 20.

  The toner remaining on the photosensitive drum 1 after the primary transfer of the toner image to the intermediate transfer belt 12a is removed from the photosensitive drum 1 by the cleaning blade 8, and is collected in a waste toner container in the cleaner unit 5. Further, the toner remaining on the intermediate transfer belt 12a after the secondary transfer of the toner image to the sheet S is removed from the intermediate transfer belt 12a by the cleaner unit 22, and is transferred to a waste toner container (not shown) through a waste toner conveying path. Collected.

  A toner detection unit 31 (optical sensor) is disposed at a position facing the drive roller 12b in the image forming apparatus 100. The toner detection unit 31 can optically detect the toner on the intermediate transfer belt 12a as described later. The image forming apparatus 100 of the present embodiment forms a test pattern composed of a toner image on the intermediate transfer belt 12a, and detects the test pattern formed on the intermediate transfer belt 12a by the toner detection unit 31. Further, the image forming apparatus 100 performs a calibration described later based on the detection result of the test pattern by the toner detection unit 31.

<Control Configuration of Image Forming Apparatus>
FIG. 2 is a block diagram illustrating a configuration example of a control system of the image forming apparatus 100 according to the present embodiment. FIG. 2 shows only devices necessary for the description of the present embodiment. The image forming apparatus 100 includes a control unit 41 equipped with a microcomputer as an engine control unit. The image forming apparatus 100 further includes an interface (I / F) board 42, a low-voltage power supply 43, a high-voltage power supply 44, various drive motors 45, various sensors 46, and an exposure unit 3 as devices communicably connected to the control unit 41. , A paper supply unit 13, a fixing unit 14, and a toner detection unit 31.

  The I / F board 42 can communicate with a host computer 40 outside the image forming apparatus 100 via a network such as a LAN. The low-voltage power supply 43 supplies a voltage for operating the control unit 41 to the control unit 41. The high-voltage power supply 44 supplies a bias voltage to the charging roller 2, the developing roller 24, the primary transfer roller 26, and the secondary transfer roller 16 at the time of performing image formation under the control of the control unit 41. The various drive motors 45 include a drive motor for rotating the photosensitive drum 1 and a drive motor for rotating the developing roller 24. The various sensors 46 include sensors other than the toner detection unit 31, such as a sensor for detecting the sheet S conveyed on the conveyance path. The control unit 41 controls each device shown in FIG. 2 based on various signals such as the output signal of the toner detection unit 31 and the output signals of various sensors 46, so that the calibration of the image forming apparatus 100 and the image formation are performed. Various controls, such as sequence control, are performed.

<Calibration of image forming apparatus>
Next, the calibration (automatic correction control) of the image forming apparatus 100 will be described with reference to FIG. FIG. 3 is a perspective view illustrating an example of the arrangement of the toner detection unit 31 with respect to the intermediate transfer belt 12a, and illustrates an example of a state of the intermediate transfer belt 12a when performing calibration. The calibration of the image forming apparatus 100 roughly includes two types of control, “color misregistration correction control” and “image density control”. In each of these two types of control, a test pattern 30 is formed on the intermediate transfer belt 12a while the image forming apparatus 100 is not performing image formation on the sheet S, and the formed test pattern 30 is used as a toner detection unit. This is done by optical detection by 31.

  When the test pattern 30 is detected by the toner detection unit 31 in the flat portion of the intermediate transfer belt 12a, it is difficult to obtain a good sensor output due to vibration during the movement of the belt. For this reason, the toner detection unit 31 is arranged not at a position facing the flat portion of the intermediate transfer belt 12a but at a position facing the drive roller 12b via the intermediate transfer belt 12a as shown in FIG. The test pattern 30 formed on the surface (outer peripheral surface) of the intermediate transfer belt 12a is detected by the toner detection unit 31 located at a position facing the drive roller 12b when passing the position of the drive roller 12b. Further, at least two toner detection units 31 are arranged in the orthogonal direction so that the test pattern 30 can be detected in at least two positions in the direction orthogonal to the moving direction of the surface of the intermediate transfer belt 12a. Hereinafter, each of the color misregistration correction control and the image density control will be described more specifically.

(Color shift correction control)
The color misregistration correction control measures the amount of relative misregistration (color misregistration) of the toner image formed by each image forming station between the image forming stations, and corrects the color misregistration based on the measurement result. This corresponds to shift correction control. The control unit 41 controls the exposure unit 3 so that the scanning speed and the exposure light amount of the laser beam on the photosensitive drum 1 become a predetermined speed and a predetermined light amount, respectively, and adjusts a writing start timing of each line. The color shift correction control is performed.

  For example, when the exposure unit 3 is a polygon mirror type, the control unit 41 generates an image front end signal by counting a writing reference pulse from the exposure unit 3 and forms the image front end signal when forming an image. Output to the I / F board 42. The I / F board 42 outputs the exposure data to the exposure unit 3 via the control unit 41 for each line (one side of the polygon mirror) in synchronization with the image leading end signal. By changing the output timing of the image leading edge signal from the control unit 41 for a time period of about several dots for each image forming station, the writing start timing of each line can be changed by several dots. This makes it possible to adjust the image writing position of the photosensitive drum 1 in the main scanning direction. In addition, by changing the writing start timing for each line, the entire image can be shifted in the transport direction (sub-scanning direction) of the toner image on the photosensitive drum 1. This makes it possible to adjust the writing position of the image on the photosensitive drum 1 in the sub-scanning direction. Further, by controlling the rotational phase difference of the polygon mirror of the exposure unit 3 between the image forming stations, it is possible to perform the alignment of the images of each color in the sub-scanning direction with a resolution of one line or less. . Furthermore, it is also possible to correct the main scanning magnification by changing a clock frequency that is a reference for ON / OFF of the exposure data.

  As described above, the correction of the color shift between the image forming stations in the color shift correction control can be realized by adjusting the image forming timing and the reference clock. In order to realize the color misregistration correction control, it is necessary to measure the relative color misregistration between the image forming stations as described above. In the color misregistration correction control, at least two rows of test patterns for color misregistration measurement are formed for each color on the intermediate transfer belt 12a, and at least two optical sensors (toner detection units 31) are used to determine the positions of the test patterns (optical components). (The transit time at the position facing the sensor). The control unit 41 calculates a relative color shift amount between the image forming stations in the main scanning direction and the sub scanning direction, a magnification in the main scanning direction, and a relative inclination based on the detection result. Further, the control unit 41 performs the above-described color misregistration correction so that the color misregistration amount between the image forming stations is reduced.

(Image density control)
The image density control is control for correcting image forming conditions such that the density characteristics of an image formed by the image forming apparatus 100 have desired density characteristics. In the image forming apparatus 100, the density characteristics of the formed image (toner image) change depending on the temperature and humidity conditions and the degree of use of the image forming station for each color. Image density control is performed to correct such a change. Specifically, a test pattern 30 is formed on the intermediate transfer belt 12a, and based on the detection result of the test pattern 30 by the toner detection unit 31, the image forming conditions are adjusted so as to obtain a desired density characteristic. Note that the test pattern 30 may be generated by the control unit 41 or may be generated by an external device (for example, the host computer 40).

  The control unit 41 (CPU) calculates a value corresponding to the density of the toner image as the test pattern 30 from the received light amount signal after the A / D (analog / digital) conversion output from the toner detection unit 31 (toner Image density). Further, the control unit 41 sets image forming conditions used when forming an image based on the detection result of the density of the toner image. The set image forming conditions include, for example, a charging bias voltage, a developing bias voltage, an exposure light amount (laser power of the exposure unit 3), and the like. By repeating such setting, it is possible to optimize the image forming conditions related to the density characteristics of the image. The control unit 41 stores the set image forming conditions in a memory in the control unit 41 so that the set image forming conditions can be used at the time of image formation and at the time of next image density control.

  By performing such image density control, the maximum density of each color can be adjusted to a desired value, and the occurrence of an image defect called “fog” in which unnecessary toner adheres to a white background portion of an image can be prevented. In addition, by performing image density control, it is possible to prevent image defects and fixing defects due to excessive toner loading while maintaining a constant color balance of each color.

<Configuration of Toner Detection Unit>
Next, the configuration of the toner detection unit 31 for detecting the test pattern 30 will be described. 4 and 5 are a perspective view and a schematic cross-sectional view, respectively, showing a configuration example of the toner detection unit 31. As shown in FIG. 4, the toner detection unit 31 has a configuration in which the housing 37 is fixed to the circuit board 36 by inserting a protrusion of the housing 37 into a hole provided in the circuit board 36. ing. FIG. 5 shows a state where the housing 37 is fixed to the circuit board 36.

  The toner detection unit 31 has an LED 33 (light emitting element) and two light receiving elements 34 and 35 as optical elements. The LED 33 irradiates light toward the intermediate transfer belt 12a, which is an irradiation target. That is, the LED 33 emits light toward the intermediate transfer belt 12a to which the toner to be detected (measurement target) has adhered. The light receiving elements 34 and 35 are used to receive specularly reflected light and irregularly reflected light of light emitted from the LED 33 toward the intermediate transfer belt 12a. In the toner detecting unit 31, the housing 37 is configured to guide the regular reflection light and the irregular reflection light of the light emitted from the LED 33 toward the intermediate transfer belt 12a to the light receiving elements 34 and 35, respectively.

  The LED 33 and the two light receiving elements 34 and 35 are directly mounted on the surface (mounting surface) of the same circuit board 36, and are mounted in a row on the circuit board 36. The light receiving elements 34 and 35 for receiving the regular reflection light and the irregular reflection light of the light emitted from the LED 33 toward the intermediate transfer belt 12a are arranged adjacent to each other on the circuit board 36. In the present embodiment, the light receiving element 34 is arranged at a position farther from the LED 33 than the light receiving element 35, and the light receiving element 35 is arranged at a position closer to the LED 33 than the light receiving element 34. As shown in FIG. 5, a light-shielding wall 39 is provided between the LED 33 and the light receiving element 35 so as to prevent light emitted from the LED 33 from being directly received by the light receiving element 35.

  The light receiving elements 34 and 35 of the present embodiment are each configured by an integrated circuit (IC) in which a phototransistor (semiconductor) having sensitivity to the wavelength of light emitted from the LED 33 is integrated and COB-mounted on a substrate. The phototransistor mounted on the substrate is covered with a transparent resin material. A board on which the light receiving elements 34 and 35 are mounted is arranged on a circuit board 36. The LED 33 (light emitting element) and the light receiving elements 34 and 35 of the present embodiment use infrared rays. However, as long as the light has a wavelength at which the light receiving element has sensitivity depending on the combination of the light emitting element and the light receiving element, a light emitting element and a light receiving element using light of other wavelengths may be employed in the toner detection unit 31. . Further, photodiodes may be used as the light receiving elements 34 and 35 instead of the phototransistors.

  As shown in FIG. 5A, the housing 37 of the toner detection unit 31 is provided with a light guide path 60 for guiding the light emitted from the LED 33 toward the intermediate transfer belt 12a. The housing 37 is further provided with light guide paths 61 and 62 for guiding the reflected light of the light emitted from the LED 33 to the light receiving elements 34 and 35, respectively. The light guide paths 60 and 61 are constituted by openings provided in the housing 37 and are separated by the light shielding wall 38. The light guide path 62 includes a light shielding wall 38 and a light shielding wall 39, and is separated from the light guiding path 61 by the light shielding wall 38. The light guide path 62 partially overlaps the light guide path 60 that guides the light emitted from the LED 33 toward the intermediate transfer belt 12a, which is an object to be irradiated, inside the housing 37. This contributes to the downsizing of the 31.

  The light-shielding wall 38 is provided to prevent irregularly reflected light from the light-receiving area 55 to be described later from being received by the light-receiving element 35 (not to enter the light-receiving element 35 through the light guide path 62). The light-shielding wall 38 is formed integrally with the housing 37, and the position of the light receiving element 35 on the mounting surface of the circuit board 36 is vertically above the mounting surface (that is, right above the light receiving element 35). And is formed up to the vicinity of the opening of the housing 37.

(Emission area 54 of light by LED 33)
Here, the light irradiation area 54 by the LED 33 shown in FIG. 5A corresponds to the area on the outer peripheral surface (on the irradiation target) of the intermediate transfer belt 12a where the light is irradiated from the LED 33. The irradiation area 54 is defined by a straight line connecting the left corner 60L of the light guide path 60 and one end of the LED 33, and a straight line connecting the right corner 60R of the light guide path 60 and the other end of the LED 33.

(Receivable areas 55 and 56 of light receiving elements 34 and 35)
The light-receiving area 55 (first area) of the light-receiving element 34 shown in FIG. 5A corresponds to an area (range) of the irradiation area 54 where the light receivable by the light-receiving element 34 is irradiated by the LED 33. It is a part of the irradiation area 54. The light receivable area 55 is a straight line connecting the left corner 61L of the light guide path 61 and one end of the first light receiving element 34, and a straight line connecting the right corner 61R of the light guide path 61 and the other end of the first light receiving element 34. And defined by
The light-receiving area 56 (second area) of the light-receiving element 35 shown in FIG. 5A corresponds to an area (range) of the irradiation area 54 where light that can be received by the light-receiving element 35 is irradiated by the LED 33. It is a part of the irradiation area 54. The light receivable area 56 is formed by a straight line connecting the left corner 62L of the light guide path 62 and one end of the light receiving element 35, and a straight line connecting the right corner 62R of the light guide path 62 and the other end of the light receiving element 35. Stipulated.

  In this embodiment, as shown in FIG. 5A, the housing 37 guides the regular reflection light from the light-receiving area 55 to the light-receiving element 34 in the irradiation area 54 of the LED 33, and It is configured to guide the irregularly reflected light to the light receiving element 35. The housing 37 is configured such that the light-receiving area 55 and the light-receiving area 56 are different from each other. The light-receiving area 55 and the light-receiving area 56 are areas that do not overlap each other in the present embodiment, but may partially overlap (for example, the end of each area).

  In the toner detection unit 31, the regular reflection light received by the light receiving element 34 out of the light emitted from the LED 33 travels in the light guide path 60 in the direction along the optical axis 50 as shown in FIG. , Light emitted to the outer peripheral surface of the intermediate transfer belt 12a. The specularly reflected light from the outer peripheral surface of the intermediate transfer belt 12a travels substantially along the optical axis 51, is guided into the light guide path 61 of the housing 37, reaches the light receiving element 34 and is received. More specifically, the light receiving element 34 receives the light (specular reflection light) that is incident on the area 57 within the light receiving area 55 at the incident angle θ and is reflected at the reflection angle θ, of the light emitted from the LED 33. At the same time, the irregularly reflected light of the light incident on the light-receiving area 55 is received.

  On the other hand, when the test pattern 30 that is a toner image is present in the irradiation area 54 on the outer peripheral surface of the intermediate transfer belt 12a, the light emitted from the LED 33 is specularly reflected on the outer peripheral surface of the intermediate transfer belt 12a and the test pattern 30 Diffuse reflection at 30. Some of such reflected light is reflected in the direction along the optical axis 51 to reach the light receiving element 34 and received, and the other is reflected in the direction along the optical axis 53. The light reaches the light receiving element 35 through the light guide path 62 and is received.

  In the present embodiment, as shown in FIGS. 4 and 5, by mounting the two light receiving elements 34 and 35 as ICs on the circuit board 36, the size of the toner detection unit 31 can be reduced as compared with the related art. I have. Here, FIG. 6 is a cross-sectional view illustrating a configuration of a toner detection unit 131 shown as a comparative example (first comparative example) with respect to the present embodiment. In the toner detection unit 131 shown in FIG. 6, the two light receiving elements 34 and 35 for respectively receiving the specularly reflected light and the irregularly reflected light of the light emitted from the LED 33 (light emitting element) are provided on the circuit board 136 as independent circuit elements. Has been implemented. In accordance with such mounting, the housing 137 is provided with individual openings corresponding to the LED 33 and the two light receiving elements 34 and 35. In the toner detection unit 31 of the present embodiment, the size in the direction in which the LED 33 and the two light receiving elements 34 and 35 are arranged (the horizontal direction in FIG. 6) is smaller than the toner detection unit 131 shown as a comparative example. Is possible.

  Further, when the toner detection unit 31 of the present embodiment is used, it is possible to simultaneously detect the toner image (test pattern 30) in two different areas (light-receiving areas 55 and 56) on the intermediate transfer belt 12a. For example, the toner detection unit 31 is arranged so that the two light receiving elements 34 and 35 are arranged along a direction orthogonal to the moving direction of the surface of the intermediate transfer belt 12a. In this case, the light-receiving areas 55 and 56 of the light-receiving elements 34 and 35 are also arranged along a direction orthogonal to the moving direction of the surface of the intermediate transfer belt 12a. As a result, when the toner detection unit 31 is used, the toner images (test patterns 30) passing through the light-receiving area 55 and the light-receiving area 56, respectively, are detected at the timing when the rotational phase of the intermediate transfer belt 12a is the same. Can be. In the second to fifth embodiments, examples of detection of the test pattern 30 using such features of the toner detection unit 31 and control based on the detection result are shown.

  Note that the toner detection unit 31 of the present embodiment may employ a light receiving element having different toner detection accuracy between the low density side and the high density side. For example, the light receiving element 34 that receives specularly reflected light may have high detection accuracy on the low density side, while the light receiving element 35 that receives irregularly reflected light may have high detection accuracy on the high density side. Even in such a case, the toner detection unit 31 of the present embodiment can improve the detection accuracy of the toner by using both the result of receiving the regular reflection light by the light receiving element 34 and the result of receiving the irregular reflection light by the light receiving element 35. It is possible to increase.

<Characteristics of toner detection unit>
Hereinafter, the detection characteristics of the toner by the toner detection unit 31 of the present embodiment will be described. First, the amount of light received and the optical path length of the light receiving elements 34 and 35, the reflection characteristics of the intermediate transfer belt 12a, and a comparative example, which are necessary for describing the toner detection characteristics, will be described.

(Received light amount and optical path length of light receiving element)
The received light amount, which is the intensity (light amount) of light received by the light receiving elements 34 and 35, is generally proportional to the light receiving area and inversely proportional to the square of the length of the optical path through which the light passes (optical path length). Therefore, in the present embodiment, the amount of light received by the light receiving elements 34 and 35 is proportional to the area of the light receiving areas 55 and 56 of the respective light receiving elements and inversely proportional to the square of the optical path length.

As shown in FIG. 5B, the optical path length of the light emitted from the LED 33 and received by the light receiving element 34 is a distance L _S1 from the center of the light emitting point of the LED 33 to the center of the light receiving area 55, and the light receiving area. It can be expressed as the sum of the distance L _S2 from the center of 55 to the center of the light receiving surface of the light receiving element 34. On the other hand, the optical path length of the light emitted from the LED 33 and received by the light receiving element 35 is the distance L _D1 from the center of the light emitting point of the LED 33 to the center of the light receiving area 56 and the distance of the light receiving element 35 from the center of the light receiving area 56. It can be expressed as the sum with the distance L _D2 to the center of the light receiving surface. That is,
Optical path length of light received by light receiving element 34 = L _S1 + L _S2
Optical path length of light received by light receiving element 35 = L _D1 + L _D2
It is.

(Reflection characteristics of the intermediate transfer belt)
FIG. 7 is a diagram illustrating an example of the reflection directivity characteristics of the intermediate transfer belt 12a. FIG. 7A shows a measurement result of the reflection directivity, and FIG. 7B shows a concept of a method of measuring the reflection directivity. In this measurement, as shown in FIG. 7B, the vertical direction with respect to the outer peripheral surface of the intermediate transfer belt 12a is 0 °, and the LED 33 (light emitting element) arranged as a point light source at a position rotated -15 ° from the vertical direction. Irradiates the intermediate transfer belt 12a with light. Further, while maintaining the distance from the irradiation point (point on the irradiated surface) 32 irradiated with the light emitted from the LED 33 to the light receiving element 34 at substantially the same distance, the light receiving element 34 is moved 90 degrees from the position of -90 °. The output value of the light receiving element 34 when rotated and moved to the position of ° is measured.
FIG. 7A shows the reflection directivity obtained by such a measurement. As shown in FIG. 7A, the reflection characteristic of the intermediate transfer belt 12a is mainly a regular reflection component, but also has a diffuse reflection component having an angular width 72 centered on the regular reflection direction. That is, the intermediate transfer belt 12a has a diffuse reflection characteristic in which a diffuse reflection component having a high intensity exists in the regular reflection direction.

(Comparative example)
FIGS. 8 and 9 are a perspective view and a schematic cross-sectional view, respectively, showing the configuration of a toner detection unit 231 shown as a comparative example (second comparative example) with respect to the present embodiment. In the toner detection unit 231 shown in FIGS. 8 and 9, the LED 33 (light emitting element) and the two light receiving elements 34 and 35 are directly mounted on the surface of the same circuit board 236, and are arranged in a line on the circuit board 236. ing. The light receiving elements 34 and 35 of the toner detecting unit 231 respectively transmit the regular reflection light and the irregular reflection light of the light emitted from the LED 33 toward the intermediate transfer belt 12a, similarly to the light receiving elements 34 and 35 of the toner detection unit 31 of the present embodiment. It is configured to receive light.

  However, the configuration of the toner detection unit 231 of the present embodiment is different from the configuration of the toner detection unit 31 of the present embodiment in that the arrangement of the light receiving elements 34 and 35 is opposite to the arrangement shown in FIGS. Is different. That is, in the toner detection unit 231, the light receiving element 34 is disposed at a position closer to the LED 33 than the light receiving element 35, and the light receiving element 35 is disposed at a position farther from the LED 33 than the light receiving element 34. The housing 237 of the toner detection unit 231 depends on the arrangement of the LED 33 and the light receiving elements 34 and 35 so that the light receiving elements 34 and 35 can receive the regular reflection light and the irregular reflection light of the light emitted from the LED 33, respectively. An opening is formed.

(Toner detection characteristics)
Next, the toner detection characteristics of the toner detection unit 31 of the present embodiment will be described with the toner detection characteristics of the toner detection unit 231 shown in FIGS. FIG. 10 shows an example of outputs of the light receiving elements 34 and 35 when toner images having different densities are sequentially formed as test patterns 30 on the intermediate transfer belt 12a, and the formed test patterns 30 are detected by the toner detection unit 31. FIG. FIGS. 10A and 10B show outputs of the light receiving elements 34 and 35 of the toner detection unit 31 of the present embodiment, respectively. FIGS. 10C and 10D show the outputs of the light receiving elements 34 and 35 of the toner detection unit 231 of the comparative example, which are obtained when the same measurement as that of the toner detection unit 31 of the present embodiment is performed. Each is shown.

  Here, the toner detection unit 31 is positioned in the image forming apparatus 100 such that the light receiving elements 34 and 35 are arranged along a direction orthogonal to the moving direction of the surface of the opposed intermediate transfer belt 12a. In this case, the light-receiving areas 55 and 56 of the light-receiving elements 34 and 35 are also arranged along a direction orthogonal to the moving direction of the surface of the intermediate transfer belt 12a. The light receiving elements 34 and 35 receive the reflected light from the light receivable areas 55 and 56, and generate and output a detection signal having a value corresponding to the received light amount. The moving direction of the surface of the intermediate transfer belt 12a and the direction orthogonal to the moving direction correspond to the sub-scanning direction and the main scanning direction in the scanning of the photosensitive drum 1 by the laser beam, respectively. FIG. 10 shows the measurement results of the outputs of the light receiving elements 34 and 35 obtained by forming the test pattern 30 in the same or wider range as the irradiation area 54 in the main scanning direction. That is, when the test pattern 30 passes through the light-receiving areas 55 and 56, the same test pattern is detected by the light-receiving elements 34 and 35.

  FIG. 10 shows the light receiving elements 34 and 35 when the test pattern 30 in which the toner density is increased stepwise from 0% to 100% by 20% on the intermediate transfer belt 12a and detected by the toner detection unit 31. Shows the change in the output. Each graph of FIG. 10 shows the density [%] of the toner passing through the light-receiving areas 55 and 56 of the light-receiving elements 34 and 35 (that is, the detection target). The output values 101 and 102 corresponding to the density of 0% indicate that no toner image is formed in the light receivable areas 55 and 56, and the light receiving elements 34 and 35 receive reflected light from the surface (outer peripheral surface) of the intermediate transfer belt 12a. Each corresponds to an output value when light is received.

  First, FIG. 10A shows the output of the light receiving element 34 for receiving the regular reflection light of the light emitted from the LED 33 in the toner detection unit 31 of the present embodiment. The output value of the light receiving element 34 has a maximum value (output value 101) when light reflected from the surface of the intermediate transfer belt 12a on which the test pattern 30 is not formed is received. This is because, as described with reference to FIG. 7, although the intermediate transfer belt 12a has some irregular reflection characteristics as optical characteristics, the regular reflection characteristics are dominant. Further, the output value of the light receiving element 34 becomes lower as the density of the toner increases when the reflected light from the test pattern 30 (toner image) is received. This is because the amount of regular reflection light from the toner decreases as the toner concentration increases due to the irregular reflection characteristics of the toner.

The output of the light receiving element 34 shown in FIG. 10A shows the same tendency as the output of the light receiving element 34 of the comparative example shown in FIG. Is slightly smaller. Such a difference between the output values depends on the optical path length (L _S1 + L _S2 ) of the light received by the light receiving element. Specifically, comparing the configuration of the toner detection unit 31 shown in FIG. 5B with the configuration of the comparative example shown in FIG. 9B, the configuration of the present embodiment has a higher LED 33 than the configuration of the comparative example. The distance from the light receiving element 34 is long, and the incident angle (reflection angle) θ is large. Therefore, in the configuration of the present embodiment, the optical path length (L _S1 + L _S2 ) is longer than that of the configuration of the comparative example, and as a result, a difference occurs in the output of the light receiving element 34.

  However, as shown in FIGS. 10A and 10C, the difference between the outputs of the light receiving elements 34 is small. This is because the regular reflection light received by the light receiving element 34 has relatively high directivity, and the difference in the amount of received regular reflection light caused by the difference in optical path length is small. As described above, the toner detection unit 31 of the present embodiment has a characteristic that the output of the light receiving element 34 is slightly smaller than the toner detection unit 231 of the comparative example, but has sufficient toner detection performance. doing. Specifically, as shown in FIG. 10A, the output value 101 (maximum value) when the light receiving element 34 receives the reflected light from the surface of the intermediate transfer belt 12a and the output value 101 from the toner image of each density. There is a sufficient difference between the output value when the light receiving element 34 receives the reflected light. For this reason, when the toner detection unit 31 of the present embodiment is used, the presence / absence of toner (in the light-receiving area 55) and the toner density on the intermediate transfer belt 12a are determined by comparing the output value of the light receiving element 34 with the threshold value. Can be determined with sufficient accuracy.

  Next, FIG. 10B shows the output of the light receiving element 35 that receives the irregular reflection light of the light emitted from the LED 33 in the toner detection unit 31 of the present embodiment. The output of the light receiving element 35 shows a change in a tendency opposite to the output of the light receiving element 34 (FIG. 10A) with respect to the change in the toner density. Specifically, the output value of the light receiving element 35 is a minimum value (output value 102) when light reflected from the surface of the intermediate transfer belt 12a on which the test pattern 30 is not formed is received. This is because the irregular reflection characteristic of the intermediate transfer belt 12a is weak. Further, when the reflected light from the test pattern 30 (toner image) is received, the output value of the light receiving element 35 increases as the density of the toner increases. This is because the amount of irregularly reflected light from the toner increases as the density of the toner increases, due to the irregular reflection characteristics of the toner.

  The output of the light receiving element 35 shown in FIG. 10B is larger than the output of the light receiving element 35 of the comparative example shown in FIG. It can be seen that the difference 103 between the minimum value and the maximum value is smaller than that of the comparative example. In this embodiment, the output value 102 (minimum value) when the light receiving element 35 receives the reflected light from the surface of the intermediate transfer belt 12a, and the light receiving element 35 receives the reflected light from the toner image of each density. There is a large difference between the output value in this case and the output value in the comparative example. Therefore, when the toner detection unit 31 of the present embodiment is used, the presence / absence of toner (in the light-receiving area 56) and the toner density on the intermediate transfer belt 12a are determined by comparing the output value of the light receiving element 35 with the threshold value. Can be determined with higher accuracy than the comparative example.

  Next, the toner detection unit 31 of the present embodiment and the toner detection unit 231 of the comparative example have a difference in the output of the light receiving element 35 that receives the irregularly reflected light of the light emitted from the LED 33 (that is, the toner detection performance is reduced). The reason for the difference will be described.

First, the difference between the output value 102 shown in FIG. 10B and the output value 102 shown in FIG. 10D when the test pattern 30 is not formed in the irradiation area 54 (light-receiving area 56) of the LED 33. explain. In the configuration of the comparative example illustrated in FIG. 9B, the light receiving element 35 receives both diffusely reflected light traveling in the regular reflection direction along the optical axis 51 and diffusely reflected light traveling in the direction along the optical axis 53. It is configured to be. The irregularly reflected light traveling along the optical axis 53 has a relatively long optical path length ( _LD1 + _LD2 ) and is received by the light receiving element 35 with low intensity. On the other hand, the irregularly reflected light traveling in the regular reflection direction has not only a relatively short optical path length (L _S1 + L _S2 ) but also a relatively high intensity light receiving element due to the above-mentioned irregular reflection characteristics of the intermediate transfer belt 12a. The light is received by 35. For this reason, as shown in FIG. 10D, the output value 102 of the light receiving element 35 in the toner detection unit 231 of the comparative example increases by an amount corresponding to the amount of light received from the surface of the intermediate transfer belt 12a. I have. This means that the amplitude component effective for toner detection in the output of the light receiving element 35 decreases.

  On the other hand, in the configuration of the present embodiment illustrated in FIG. 5B, the light receiving element 35 receives irregularly reflected light traveling in the direction along the optical axis 53 and travels in the regular reflection direction generally along the optical axis 51. It is configured not to receive diffusely reflected light. Specifically, the irregular reflection component of the light traveling from the LED 33 along the optical axis 50 and reflected in the direction along the optical axis 51 on the surface of the intermediate transfer belt 12a is blocked by the light shielding wall 38 and enters the light receiving element 35. I will not do it. The relatively high-intensity irregularly reflected component of the reflected light that has traveled along the optical axis 52 from the LED 33 travels in the direction of the optical axis 53 'from the intermediate transfer belt 12a. It does not enter 35. For this reason, as shown in FIG. 10B, in the toner detection unit 31 of the present embodiment, the output value 102 when the light receiving element 35 receives the reflected light from the surface of the intermediate transfer belt 12a is the comparative example ( 10 (d)). This means that an amplitude component effective for toner detection in the output of the light receiving element 35 increases.

Next, the difference between the output value shown in FIG. 10B and the output value shown in FIG. 10D when the test pattern 30 is formed in the irradiation area 54 (light-receiving area 56) of the LED 33 will be described. I do. Here, focusing on the output value of the light receiving element 35 when the reflected light from the toner image (solid image) having the density of 100% is received, the output value shown in FIG. 10B is shown in FIG. It is larger than the output value (comparative example). This is because the toner detection unit 231 of the comparative example has a configuration in which the distance between the LED 33 and the light receiving element 35 is relatively long, whereas the toner detection unit 31 of the present embodiment has the LED 33 and the light receiving element This is because the distance from the lens 35 is relatively short. That is, the toner detection unit 31 of the present embodiment receives irregularly reflected light with higher intensity because the optical path length ( _LD1 + _LD2 ) of the light received by the light receiving element 35 is shorter than the toner detection unit 231 of the comparative example. it can.

  As described above, in the toner detection unit 31 of the present embodiment, the housing attached to the circuit board 36 is such that the light-receiving area 55 of the light-receiving element 34 and the light-receiving area 56 of the light-receiving element 35 do not overlap each other. 37 are configured. Thereby, while the light receiving element 35 relatively increases the amount of light received when receiving irregularly reflected light from the toner image, the light receiving element 35 increases the amount of light received when irregularly reflected light from the surface of the intermediate transfer belt 12a is received. It is possible to reduce the number. In the toner detection unit 31 of the present embodiment, the light receiving element 35 that receives the irregularly reflected light of the light emitted by the LED 33 (light emitting element) is more than the light receiving element 34 that receives the regular reflected light of the light emitted by the LED 33. It is arranged at a position close to. This makes it possible to relatively increase the amount of received light when the light receiving element 35 receives diffusely reflected light from the toner image. Note that the toner detection unit 31 is configured so that the common LED 33 (light emitting element) can sufficiently irradiate both the light-receiving areas 55 and 56 (that is, both the light-receiving areas 55 and 56 have the irradiation area). 54 to be included).

  According to the configuration of the toner detection unit 31 of the present embodiment, the output value 102 of the light receiving element 35 when receiving the reflected light from the surface of the intermediate transfer belt 12a is smaller than the output value of the toner detection unit 231 of the comparative example. Become smaller. The output value of the light receiving element 35 when the reflected light from the toner image having the maximum density (100%) is received is larger than the output value of the toner detection unit 231 of the comparative example. That is, according to the configuration of the toner detection unit 31 of the present embodiment, the difference between the output value of the light receiving element 35 when the reflected light from the toner image of each density is received and the output value 102 (minimum value) (for example, The difference 103) can be made larger.

  Therefore, in the toner detection unit 31 of the present embodiment, the presence or absence of toner and the toner concentration in the light-receivable area 56 are compared with those of the comparative example based on the result of light reception by the light-receiving element 35 of the irregularly reflected light emitted from the LED 33. It is possible to determine with high accuracy. That is, the toner detection unit 31 of the present embodiment is superior to the toner detection unit 231 of the comparative example in the performance of toner detection (determination of presence / absence and density of toner) based on the result of receiving irregularly reflected light emitted from the LED 33. Performance.

<Other Features of Toner Detection Unit 31>
As shown in FIG. 5, in the toner detection unit 31 of the present embodiment, the light receiving area 56 of the light receiving element 35 that receives diffusely reflected light is more than the light receiving area 55 of the light receiving element 34 that receives regular reflected light. It is configured to be wide. As described above with reference to FIG. 10, the specular reflection light of the light emitted from the LED 33 is strong light having relatively high directivity. On the other hand, the diffusely reflected light emitted from the LED 33 is diffused in various directions and is weak light having low directivity. For this reason, in the present embodiment, the light-receiving area 56 for receiving diffusely reflected light is made wider than the light-receiving area 55 for receiving specularly reflected light so that the light receiving amount of diffusely reflected light by the light receiving element 35 is increased. ing. That is, as shown in FIG. 5, the light-receiving area 56 has a larger size in the direction in which the light-receiving elements 34 and 35 are arranged than the light-receiving area 55.

In the toner detection unit 31 of the present embodiment, light emitted from the LED 33 (light emitting element) is emitted from the housing 37 through a light guide path 60 provided in the housing 37. The diffusely reflected light emitted from the LED 33 enters the light receiving element 35 through the light guide path 62. The toner detection unit 31 is configured so that the exit of the light emitted from the LED 33 from the housing 37 and the entrance of the diffusely reflected light received by the light receiving element 35 into the housing 37 are common. That is, the housing 37 has a common opening for reducing the light emitted from the LED 33 and the light incident on the light receiving elements 34 and 35. This makes it possible to reduce the distance between the LED 33 and the light receiving element 35 as compared with the case where the exit of the light emitted from the LED 33 and the entrance of the irregularly reflected light are different. As a result, it is possible to further shorten the optical path length (L _D1 + LD ₂ ) of the light received by the light receiving element 35 and to further shorten the optical path length (L _S1 + L _S2 ) of the light received by the light receiving element 34. . Therefore, it is possible to further increase the amount of light received by each of the light receiving elements 34 and 35, and to increase the output value from each light receiving element indicating the light receiving result.

  In the present embodiment, the two light receiving elements 34 and 35 are integrated to reduce the size of the toner detection unit 31. However, as independent circuit elements, the two light receiving elements 34 and 35 are close to the same positions as in the present embodiment. May be arranged. Also in that case, it is possible to realize the toner detection unit 31 that can obtain the same effect as the present embodiment.

  As described above, the toner detection unit 31 of the present embodiment includes the LED 33 that irradiates the light toward the intermediate transfer belt 12a, and the light receiving unit that receives the regular reflection light and the irregular reflection light of the light emitted from the LED 33, respectively. And elements 34 and 35. These LEDs 33 and light receiving elements 34 and 35 are mounted on a circuit board 36 in a line. The circuit board 36 is provided with a light guide path for guiding the light emitted from the LED 33 toward the intermediate transfer belt 12a, and a light guide path for guiding the regular reflection light and the irregular reflection light to the light receiving elements 34 and 35, respectively. Specifically, the housing 37 guides the regular reflection light from the light-receiving area 55 to the light-receiving element 34 in the irradiation area 54 of the LED 33 and receives the irregular reflection light from the light-receiving area 56 different from the light-receiving area 55. It is configured to guide to the element 35. According to the present embodiment, the size of the toner detection unit 31 in the arrangement direction of the LED 33 and the light receiving elements 34 and 35 is reduced, and the performance of toner detection based on the result of receiving diffusely reflected light is compared with that of the comparative example. Excellent performance (compared to the toner detection unit 231) can be realized.

[Second embodiment]
In the second to fifth embodiments, as an example of use of the toner detection unit 31 described in the first embodiment, an example in which color misregistration correction control is performed using a test pattern advantageous for detection by the toner detection unit 31 will be described.

  Generally, color misregistration includes color misregistration due to static factors (static color misregistration) and color misregistration due to dynamic factors (dynamic color misregistration) in which the color misregistration amount fluctuates periodically. Static factors include errors in the image writing start position. The dynamic factor is a speed fluctuation of a transport belt (a recording material transport belt, an intermediate transfer belt, or the like) due to drive unevenness of a drive roller such as a transport belt or rotation unevenness of a photosensitive drum. When the (static) color misregistration amount is measured by detecting the test pattern formed on the intermediate transfer belt with an optical sensor, the measurement result includes a dynamic color misregistration having a size dependent on the test pattern detection timing. The components cause errors. (For example, refer to Japanese Patent Application Laid-Open No. 2002-14507.) Such a dynamic color misregistration component is a timing (dynamic color misregistration component) for detecting a patch image of a reference color and a target color for measuring a color misregistration amount. The phase of the fluctuation of

  In order to reduce the above measurement error, for example, as described in JP-A-2002-14507, a plurality of patterns corresponding to a plurality of phases of a dynamic color misregistration component are formed along the moving direction of the transport belt. It must be formed so that dynamic color shift components can be canceled. However, when a plurality of patterns are formed along the moving direction (sub-scanning direction) of the transport belt, the total length of the plurality of patterns in the sub-scanning direction increases, and the time required for color misregistration correction control (calibration) also increases. There is a problem.

  On the other hand, when the toner detection unit 31 shown in FIGS. 4 and 5 is used, as described above, it is necessary to simultaneously detect toner images in two different areas (light-receiving areas 55 and 56) on the intermediate transfer belt 12a. Is possible. Therefore, in the present embodiment, by utilizing such characteristics of the toner detection unit 31, a test pattern in which a patch image of a reference color and a patch image of a target color are arranged at the same position in the sub-scanning direction (that is, in the same phase). Form. Thus, the patch images can be simultaneously detected by the light receiving elements 34 and 35. As described above, when the patch images of the reference color and the target color can be detected at the timing when the phase of the variation of the dynamic color shift component is the same, the dynamic color shift component is not affected by the dynamic color shift component (static Na) The color shift amount can be measured. In this case, it is advantageous in that it is not necessary to form a plurality of test patterns corresponding to a plurality of phases as described above for canceling a dynamic color shift component. Hereinafter, the present embodiment will be described focusing on the differences from the first embodiment.

<Example of test pattern>
In the present embodiment, the reflectance of the intermediate transfer belt 12a at the light source wavelength of the toner detection unit 31 (optical sensor) is higher for specular reflection light than for any color toner image, and for irregular reflection light for any color toner. The case where the height is lower than the image will be described. In this case, both the regular reflection light and the irregular reflection light from the intermediate transfer belt 12a can be favorably detected by the toner detection unit 31.

  FIG. 11 is a diagram illustrating an example of the test pattern 30 at a distance Ld1 corresponding to one rotation cycle of the photosensitive drum 1. In FIG. 11, an area 155 on the intermediate transfer belt 12a is an area where the toner image passes through the light-receiving area 55 of the light receiving element 34 during conveyance by the intermediate transfer belt 12a when a toner image is formed in the area. Equivalent to. Further, an area 156 on the intermediate transfer belt 12a corresponds to an area in which, when a toner image is formed in the area, the toner image passes through the light-receiving area 56 of the light receiving element 35 during conveyance by the intermediate transfer belt 12a. . Hereinafter, the region 155 is referred to as a “specular reflection light receiving region”, and the region 156 is referred to as a “diffuse reflection light receiving region”.

  As shown in FIG. 11, independent test patterns (toner images) are formed in parallel in the regular reflection light receiving area 155 and the irregular reflection light receiving area 156, respectively. A test pattern 30v for detecting the amount of color misregistration in the sub-scanning direction and a test pattern for detecting the amount of color misregistration in the main scanning direction along the moving direction of the surface of the intermediate transfer belt 12a (the conveying direction of the toner image). 30 m are alternately arranged. Each of the test patterns 30v and 30m is composed of a patch image group including a plurality of patch images that are a plurality of toner images (toner patches). As described above, the test pattern 30 of the present embodiment includes the test pattern 30v and the test pattern 30m. The moving direction of the surface of the intermediate transfer belt 12a and the direction orthogonal to the moving direction correspond to the sub-scanning direction and the main scanning direction in the scanning of the photosensitive drum 1 by the laser beam, respectively.

  The test pattern 30v includes patch images Pstd1a, Pstd2a, Pstd3a, and Pstd4a of reference colors that are arranged along the sub-scanning direction in the regular reflection light receiving area 155 on the intermediate transfer belt 12a and serve as a reference for detecting a color shift amount. The test pattern 30v further includes patch images Ptgt1a and Ptgt2a of target colors, which are arranged along the sub-scanning direction in the irregular reflection light receiving area 156 on the intermediate transfer belt 12a and are to be subjected to the color shift amount detection based on the reference color. , Ptgt3a, and Ptgt4a. The patch images Ptgt1a, Ptgt2a, Ptgt3a, and Ptgt4a of the target color are arranged so as to have substantially the same phase in the sub-scanning direction as the patch images Pstd1a, Pstd2a, Pstd3a, and Pstd4a of the reference color, respectively. The target color patch images Ptgt1a, Ptgt2a, Ptgt3a, and Ptgt4a are formed using different color toners.

  The test pattern 30m includes reference color patch images Pstd1b, Pstd2b, Pstd3b, Pstd4b and reference color patches Pstd1c, Pstd2c, Pstd3c arranged in the regular reflection light receiving area 155 on the intermediate transfer belt 12a along the sub-scanning direction. , Pstd4c. The test pattern 30m further includes patch images Ptgt1b, Ptgt2b, Ptgt3b, Ptgt4b of target colors and patch images Ptgt1c, Ptgt2c of target colors, which are arranged along the sub-scanning direction in the irregular reflection light receiving area 156 on the intermediate transfer belt 12a. , Ptgt3c, and Ptgt4c. The patch images Ptgt1b, Ptgt2b, Ptgt3b, and Ptgt4b of the target color are arranged so as to have substantially the same phase in the sub-scanning direction as the patch images Pstd1b, Pstd2b, Pstd3b, and Pstd4b of the reference color, respectively. The target color patch images Ptgt1c, Ptgt2c, Ptgt3c, and Ptgt4c are arranged so as to be substantially in phase in the sub-scanning direction with the reference color patch images Pstd1c, Pstd2c, Pstd3c, and Pstd4c, respectively. The target color patch images Ptgt1b, Ptgt2b, Ptgt3b, and Ptgt4b are formed using different color toners, respectively, and the target color patch images Ptgt1c, Ptgt2c, Ptgt3c, and Ptgt4c are formed using different color toners, respectively. Is done.

  In the example of FIG. 11, the test patterns 30v are repeatedly formed in the sub-scanning direction at intervals of a distance Ld2 having an opposite phase corresponding to a half rotation period of the photosensitive drum 1. Thus, by repeating the pattern, it is possible to cancel the detection error component of the color misregistration amount due to the uneven rotation of the photosensitive drum 1. Note that a test pattern corresponding to a 1/3 rotation period, a 1/4 rotation period, or the like of the photosensitive drum 1 may be further formed depending on a region where a test pattern can be formed on the intermediate transfer belt 12a. This makes it possible to cancel the detection error component of the color misregistration amount due to the uneven rotation of the photosensitive drum 1 with higher accuracy.

<Detection of color shift amount in sub-scanning direction>
Next, a method of detecting (measuring) the color shift amount of the target color in the sub-scanning direction with respect to the reference color using the test pattern 30v shown in FIG. 11 will be described with reference to FIG. Here, detection of a color shift amount of the target color with respect to the reference color when the reference color is black (K) and the target color is yellow (Y) will be described as an example.

  FIG. 12A shows, as a part of the test pattern 30v shown in FIG. 11, a K patch image Pstd1a of the reference color and a Y patch image Ptgt1a of the target color in an enlarged manner. As described above, the patch image Pstd1a of the reference color (K) and the patch image Ptgt1a of the target color (Y) have sizes corresponding to the sizes of the light-receiving areas 55 and 56, respectively. As described in the first embodiment, since the light-receiving area 56 is wider than the light-receiving area 55, the patch image Ptgt1a of the target color (Y) is scanned in the main scan more than the patch image Pstd1a of the reference color (K). The size in the direction and the sub-scanning direction is increased.

  The patch image Pstd1a formed in the regular reflection light receiving area 155 passes through the light receivable area 55 of the light receiving element 34 included in the toner detection unit 31 while being transported along with the movement of the surface of the intermediate transfer belt 12a. The control unit 41 (CPU) detects the leading end and the trailing end of the patch image Pstd1a in the sub-scanning direction based on the result of the light receiving element 34 receiving the regular reflection light from the intermediate transfer belt 12a and the patch image Pstd1a. The control unit 41 detects the leading edge detection timing Tstd1ap and the trailing edge detection timing Tstd1as of the patch image Pstd1a as the leading and trailing edge positions of the patch image, respectively.

  On the other hand, the patch image Ptgt1a formed in the irregular reflection light receiving area 156 passes through the light receivable area 56 of the light receiving element 35 included in the toner detection unit 31 while being transported along with the movement of the surface of the intermediate transfer belt 12a. . The control unit 41 detects the leading end and the trailing end of the patch image Ptgt1a in the sub-scanning direction based on the result of receiving the irregularly reflected light from the intermediate transfer belt 12a and the patch image Ptgt1a by the light receiving element 35. The control unit 41 detects the leading edge detection timing Ttgt1ap and the trailing edge detection timing Ttgt1as of the patch image Ptgt1a as the leading and trailing edge positions of the patch image, respectively.

  The control unit 41 obtains the center position Tstd1a between the leading end Tstd1ap and the trailing end Tstd1as of the patch image Pstd1a of the reference color (K) and the patch image Ptgt1a of the target color (Y) from the data thus obtained. A center position Ttgt1a between the front end Ttgt1ap and the rear end Ttgt1as is calculated. Furthermore, the control unit 41 determines the difference Dtgt1a (= Ttgt1a-Tstd1a) between the center position Tstd1a of the patch image Pstd1a of the reference color (K) and the center position Ttgt1a of the patch image Ptgt1a of the target color (Y) by using the reference color (K ) Is calculated as the amount of color misregistration of the target color (Y) in the sub-scanning direction. The control unit 41 can perform the above-described color misregistration correction control (for example, color misregistration correction in the sub-scanning direction by adjusting the writing start timing) by using the calculation result of the color misregistration amount.

<Detection of color shift amount in main scanning direction>
Next, a method of detecting (measuring) the color shift amount of the target color in the main scanning direction with respect to the reference color using the test pattern 30m shown in FIG. 11 will be described with reference to FIG. Here, as in FIG. 12A, the detection of the color shift amount of the target color with respect to the reference color when the reference color is black (K) and the target color is yellow (Y) will be described as an example.

  FIG. 12B shows, as a part of the test pattern 30m shown in FIG. 11, a K patch image Pstd1b of the reference color and a Y patch image Ptgt1b of the target color in an enlarged manner. As shown in FIG. 12B, each patch image has an inclination angle with respect to the moving direction (sub-scanning direction) of the surface of the intermediate transfer belt 12a in order to enable detection of the amount of color shift in the main scanning direction. It has 45 °. Further, as described above, the patch image Pstd1b and the patch image Ptgt1b are arranged so as to have substantially the same phase in the sub-scanning direction.

  The patch image Pstd1b formed in the regular reflection light receiving area 155 passes through the light receivable area 55 of the light receiving element 34 while being transported along with the movement of the surface of the intermediate transfer belt 12a. The control unit 41 detects the leading edge and the trailing edge of the patch image Pstd1b in the sub-scanning direction based on the result of receiving the regular reflection light by the light receiving element. The control unit 41 detects the leading edge detection timing Tstd1bp and the trailing edge detection timing Tstd1bs of the patch image Pstd1b as the leading and trailing edge positions of the patch image, respectively.

  On the other hand, the patch image Ptgt1b formed in the irregular reflection light receiving area 156 passes through the light receiving area 56 of the light receiving element 35 while being transported along with the movement of the surface of the intermediate transfer belt 12a. The control unit 41 detects the leading end and the trailing end of the patch image Ptgt1b in the sub-scanning direction based on the result of receiving the irregularly reflected light by the light receiving element 35. The control unit 41 detects the leading edge detection timing Ttgt1bp and the trailing edge detection timing Ttgt1bs of the patch image Ptgt1b as the leading and trailing edge positions of the patch image, respectively.

  The control unit 41 obtains the center position Tstd1b between the leading end Tstd1bp and the trailing end Tstd1bs of the patch image Pstd1b of the reference color (K) and the patch image Ptgt1b of the target color (Y) from the data thus obtained. A center position Ttgt1b between the leading end Ttgt1bp and the trailing end Ttgt1bs is calculated. Further, the control unit 41 calculates a difference Dtgt1b (= Ttgt1b−Tstd1b) between the center position Tstd1b of the patch image Pstd1b of the reference color (K) and the center position Ttgt1b of the patch image Ptgt1b of the target color (Y). Here, the inclination angle of each patch image included in the test pattern 30m is 45 °. Therefore, under the condition that there is no color shift in the sub-scanning direction, the calculated Dtgt1b can be treated as the color shift amount of the target color (Y) with respect to the reference color (K) in the main scanning direction. The control unit 41 can perform the above-described color misregistration correction control (for example, color misregistration in the main scanning direction by adjusting the writing start timing) by using the calculation result of the color misregistration amount.

  As described above, in the present embodiment, the patch images of the reference color and the target color are arranged in substantially the same phase in the sub-scanning direction by utilizing the fact that the light-receiving areas 55 and 56 of the toner detection unit 31 do not overlap. A test pattern 30 is formed on the intermediate transfer belt 12a. Further, the color misregistration amount is detected (measured) by detecting the test pattern 30 using the light receiving elements 34 and 35.

  As described above, by using the toner detection unit 31 described in the first embodiment, it is possible to detect the color shift amount using the patch images of the reference color and the target color formed in substantially the same phase in the sub-scanning direction. is there. As a result, it is possible to detect the amount of color misregistration while removing the dynamic color misregistration component of the intermediate transfer belt 12a (excluding the dynamic color misregistration component caused by the displacement of the distance between the photosensitive drums). . That is, since a canceling process corresponding to, for example, a １ ／ rotation cycle of the intermediate transfer belt 12a is not required, a plurality of phases of the dynamic color shift component for canceling the dynamic color shift component are supported. There is no need to form a plurality of test patterns. For this reason, it is possible to improve the detection accuracy of the color shift amount per unit length of the test pattern, and it is possible to shorten the entire length of the test pattern 30 in the sub-scanning direction. As a result, the amount of toner consumption for forming the test pattern 30 can be reduced, and the time required for detecting the color shift amount and the time required for the color shift correction control can be shortened.

  In the present embodiment, the detection of the color misregistration amount in the sub-scanning direction and the main scanning direction is described with the reference color being black (K) and the target color being yellow (Y), but the same applies to other color combinations. It is possible to detect the amount of color misregistration. The test patterns 30v and 30m (FIG. 11) used in the present embodiment are merely examples, and test patterns having different characteristics such as pattern shapes, pattern intervals, and color combinations may be used. Further, the arrangement order of the patch images of the target color in the sub-scanning direction may be different from the order shown in FIG. In the present embodiment, an example is shown in which a patch image of the reference color is formed in the regular reflection light receiving area 155 on the light receiving element 34 side, and a patch image of the target color is formed in the irregular reflection light receiving area 156 on the light receiving element 35 side. However, a patch image of the reference color may be formed in the irregular reflection light receiving area 156 on the light receiving element 35 side, and a target color patch image may be formed in the regular reflection light receiving area 155 on the light receiving element 34 side.

[Third embodiment]
In the third embodiment, in the toner detection unit 31 described in the above-described embodiment, the relative displacement between the light receiving elements 34 and 35 mounted on the same circuit board 36 in the sub scanning direction and the main scanning direction is corrected. An example will be described. Hereinafter, the present embodiment will be described focusing on the differences from the first and second embodiments.

  In the second embodiment, the color difference between the reference color and the target color is detected by setting the reference color and the target color to be different colors. On the other hand, when the same processing as the detection of the amount of color misregistration in the second embodiment is performed by setting the reference color and the target color to be the same color, the light receiving elements 34, It is possible to detect 35 relative displacement amounts. In the present embodiment, as an example, the reference color and the target color are set to black (K) of the same color, and the relative displacement amount of the light receiving element 35 with respect to the position of the light receiving element 34 is detected.

<Detection of displacement in sub-scanning direction>
FIG. 13A shows, as a part of the test pattern 30v shown in FIG. 11, a patch image Pstd4a of a reference color and a patch image Ptgt4a of a target color having the same color as the reference color. As described in the second embodiment, the reference color patch image Pstd4a is formed in the regular reflection light receiving area 155, and the target color patch image Ptgt4a is formed in the irregular reflection light receiving area 156.

  The control unit 41 detects a leading end Tstd4ap and a trailing end Tstd4as of the patch image Pstd4a of the reference color formed in the regular reflection light receiving area 155 in the sub-scanning direction, based on the result of receiving the regular reflection light by the light receiving element 34. Further, the control unit 41 detects the leading end Ttgt4ap and the trailing end Ttgt4as of the patch image Ptgt4a of the target color formed in the irregular reflection light receiving area 156 in the sub-scanning direction based on the result of receiving the irregular reflection light by the light receiving element 35. The control unit 41 calculates the center position Tstd4a of the patch image Pstd4a of the reference color (K) and the center position Ttgt4a of the patch image Ptgt4a of the target color (K) from the data thus obtained. Further, the control unit 41 calculates a difference Dsns4a (Dsns4a = Ttgt4a-Tstd4a) between the center positions as a positional shift amount in the sub-scanning direction between the light receiving elements 34 and 35.

  The control unit 41 performs color misregistration correction control using the calculated misregistration amount Dsns4a as a correction value for the detected value Dtgt1a of the misregistration amount in the second embodiment. That is, the control unit 41 uses the value (= Dtgt1a + Dsns4a) obtained by correcting the detected value Dtgt1a of the color shift amount by the position shift amount Dsns4a, and performs the above-described color shift correction control (for example, in the sub-scanning direction by adjusting the writing start timing or the like). Color misregistration). This makes it possible to improve the correction accuracy in the color misregistration correction control.

<Detection of displacement in main scanning direction>
FIG. 13B shows a patch image Pstd4b of a reference color and a patch image Ptgt4b of a target color identical to the reference color as a part of the test pattern 30m shown in FIG. As described in the second embodiment, the reference color patch image Pstd4b is formed in the regular reflection light receiving area 155, and the target color patch image Ptgt4b is formed in the irregular reflection light receiving area 156. As in the second embodiment, each patch image is moved with respect to the moving direction (sub-scanning direction) of the surface of the intermediate transfer belt 12a in order to detect the amount of displacement of the light receiving elements 34 and 35 in the main scanning direction. And has an inclination angle of 45 °.

  The control unit 41 detects the leading end Tstd4bp and the trailing end Tstd4bs in the sub-scanning direction of the patch image Pstd4b of the reference color formed in the regular reflection light receiving area 155 based on the result of receiving the regular reflection light by the light receiving element 34. Further, the control unit 41 detects the leading end Ttgt4bp and the trailing end Ttgt4bs of the patch image Ptgt4b of the target color formed in the irregular reflection light receiving area 156 in the sub-scanning direction, based on the result of receiving the irregular reflection light by the light receiving element 35. The control unit 41 calculates the center position Tstd4b of the patch image Pstd4b of the reference color (K) and the center position Ttgt4b of the patch image Ptgt4b of the target color (K) from the data thus obtained. Further, the control unit 41 calculates a difference Dsns4b (Dsns4b = Ttgt4b−Tstd4b) between the center positions as a positional deviation amount between the light receiving elements 34 and 35 in the main scanning direction.

  The control unit 41 performs color misregistration correction control using the calculated misregistration amount Dsns4b as a correction value for the detected value Dtgt1b of the misregistration amount in the second embodiment. That is, the control unit 41 uses the value (= Dtgt1b + Dsns4b) obtained by correcting the detected value Dtgt1b of the color shift amount by the position shift amount Dsns4b, and performs the above-described color shift correction control (for example, in the main scanning direction by adjusting the writing start timing or the like). Color misregistration). This makes it possible to improve the correction accuracy in the color misregistration correction control.

  As described above, in the present embodiment, the reference color and the target color are set to the same color, and the same processing as the detection of the color misregistration amount in the second embodiment is performed. The relative displacement between the light receiving element 34 and the light receiving element 35 can be detected. Further, by applying the detected positional shift amount to the color shift correction control in the second embodiment, it is possible to improve the accuracy of the color shift correction. In the present embodiment, the detection of the displacement amount of the light receiving elements 34 and 35 has been described with the reference color and the target color set to black (K), but the detection of the displacement amount is similarly performed using other colors. It is possible.

[Fourth embodiment]
In the fourth embodiment, detection of the amount of color misregistration when the reflectance of the intermediate transfer belt 12a at the light source wavelength of the toner detection unit 31 (optical sensor) is different from the reflectance in the second and third embodiments will be described. . Specifically, the reflectance of the intermediate transfer belt 12a is higher for regular reflection light than for any color toner image, and for irregular reflection light for colors (Y, M, C) other than black (K). A case where the toner image is lower than the toner image and substantially equal to the K toner image will be described. In this case, a toner image of a color (Y, M, C) other than black (K) can be accurately detected by the toner detection unit 31 using either regular reflection light or irregular reflection light. However, with respect to the K toner image, the amount of light received by the light receiving element 35 is based on the irregularly reflected light from the area where the toner image is formed on the intermediate transfer belt 12a and the irregularly reflected light from the area where the toner image is not formed. Have the same light amount, and it is difficult to detect the toner image.

  Therefore, in the present embodiment, when a black (K) toner image is formed in the irregular reflection light receiving area 156 on the intermediate transfer belt 12a, a toner image of a color other than K and having a different (high) reflectance is used as a K (color) image. It is characterized in that it is formed as a base image of a toner image. That is, it is possible to increase the detection accuracy of the boundary of the K toner image by forming the K toner image so as to overlap the toner image of a color other than K having a high reflectance. In the following, this embodiment will be described focusing on the differences from the first to third embodiments.

  In the present embodiment, detection of the amount of color shift in the sub-scanning direction of the target color with respect to the reference color when the reference color is magenta (M) and the target color is black (K) will be described as an example. FIG. 14 shows a patch image Pstd2a of the reference color (M) and a patch image Ptgt2a of the target color (K) in an enlarged manner as a part of the test pattern 30v shown in FIG. The patch image Pstd2a of the reference color is formed in the regular reflection light receiving area 155, and the patch image Ptgt2a of the target color is formed in the irregular reflection light receiving area 156. In the present embodiment, a yellow (Y) patch image Ppri2a having a larger size than the target color patch image is formed in the diffuse reflection light receiving area 156 as a base image of the target color (K) patch image Ptgt2a. That is, the K patch image Ptgt2a is formed so as to overlap the Y patch image Ppri2a.

  As in the second and third embodiments, the control unit 41 determines the sub-image of the reference color (M) patch image Pstd2a formed in the specular reflection light receiving area 155 based on the result of the specular reflection light reception by the light receiving element 34. The leading end Tstd2ap and the trailing end Tstd2as in the scanning direction are detected. Further, the control unit 41 detects the leading end Ttgt2ap and the trailing end Ttgt2as of the patch image Ptgt2a of the target color formed in the irregular reflection light receiving area 156 in the sub-scanning direction, based on the result of receiving the irregular reflection light by the light receiving element 35. At this time, the control unit 41 detects the patch image Ptgt2a as the leading end and the trailing end from the boundary between the target color patch image Ptgt2a and the Y patch image Ppri2a formed as the base image.

  The control unit 41 calculates the center position Tstd2a of the patch image Pstd2a of the reference color (M) and the center position Ttgt2a of the patch image Ptgt2a of the target color (K) from the data thus obtained. Further, the control unit 41 determines the difference Dtgt2a (= Ttgt2a−Tstd2a) between the center position Tstd2a of the patch image Pstd2a of the reference color (M) and the center position Ttgt2a of the patch image Ptgt2a of the target color (K) by using the reference color (M ) Is calculated as the color shift amount of the target color (K) in the sub-scanning direction. The control unit 41 uses the calculation result of the color misregistration amount to perform color misregistration correction control (for example, color misregistration correction in the sub-scanning direction by adjusting writing start timing or the like) as in the second and third embodiments. ) Is possible.

  As described above, in the present embodiment, for diffusely reflected light, the difference in reflectance between the base image and the target color patch image is caused by the reflection between the surface of the intermediate transfer belt 12a and the target color patch image. The base image is formed so as to be larger than the difference in the rates. According to the present embodiment, even when a patch image of a color such as black (K) having a small percentage of the irregular reflection component in the reflected light is formed as the test pattern 30 in the irregular reflection light receiving area 156, the color misregistration amount is detected. Accuracy can be prevented from deteriorating.

  In the present embodiment, detection of the amount of color misregistration in the sub-scanning direction will be described with the reference color being magenta (M), the target color being black (K), and the color of the patch image to be formed as the base image being yellow (Y). However, the color shift amount can be similarly detected for other color combinations. The detection of the color misregistration amount in the main scanning direction can be realized by the same processing as that of the second embodiment by forming a patch image serving as a base image similarly to the test pattern 30v shown in FIG. . Further, the reflectance of the intermediate transfer belt 12a in the present embodiment is merely an example. For example, when a toner image having a reflectance substantially equal to the reflectance of the intermediate transfer belt 12a is formed in the regular reflection light receiving region 155 or the irregular reflection light receiving region 156 on the intermediate transfer belt 12a, a toner image having a high reflectance is used. By using the base image, the same effect as in the present embodiment can be expected.

[Fifth Embodiment]
In the fifth embodiment, a modified example of the fourth embodiment will be described. Generally, an optical element used as the light receiving elements 34 and 35 of the toner detection unit 31 has a characteristic that the response speed decreases as the amount of received light decreases. In the present embodiment, a method for more accurately detecting the color misregistration amount and controlling the color misregistration correction using the toner detection unit 31 in consideration of such a difference in the response speed of the optical element depending on the amount of received light is described. explain. In the following, this embodiment will be described focusing on the differences from the first to fourth embodiments.

  In FIG. 15, similarly to FIG. 14, a patch image Pstd4a of the reference color (M) is formed in the regular reflection light receiving area 155, and a Y patch image Ppri4a is formed in the irregular reflection light receiving area 156 as a target. This figure shows a state in which patch images Ptgt4a of color (K) are formed in an overlapping manner. FIG. 15 further shows changes in outputs of the light receiving elements 34 and 35 when patch images formed in the regular reflection light receiving area 155 and the irregular reflection light receiving area 156 are detected using the light receiving elements 34 and 35.

  In FIG. 15, a waveform M is an output waveform of the light receiving element 34, and a waveform N is an output waveform of the light receiving element 35. As shown in FIG. 15, the output waveforms M and N have a dull shape in accordance with the amount of light received by the light receiving elements 34 and 35. The control unit 41 determines the center position between two points where the output waveforms M and N intersect with the threshold voltage A based on the output waveforms M and N of such shapes output from the light receiving elements 34 and 35. It is calculated as the center position of the image in the sub-scanning direction. Therefore, there is an error ΔTstd4a between the center position Tstd4a of the patch image Pstd4a formed in the regular reflection light receiving area 155 in the sub-scanning direction and the center position Tstd4a ′ calculated based on the output waveform M of the light receiving element 34. Occurs. Similarly, there is an error between the center position Ttgt4a in the sub-scanning direction of the patch image Ptgt4a formed in the irregular reflection light receiving area 156 and the center position Ttgt4a ′ calculated based on the output waveform N of the light receiving element 35. ΔTtgt4a occurs.

  As shown in FIG. 15, the degree of bluntness of the output waveforms of the light receiving elements 34 and 35 increases as the amount of light received by the light receiving elements 34 and 35 decreases, and as a result, the above-described error increases. In particular, the irregularly reflected light received by the light receiving element 35 is diffused in various directions and is weak light having low directivity. For this reason, a larger error tends to occur in the result of receiving the irregularly reflected light by the light receiving element 35 than in the result of receiving the regular reflected light by the light receiving element 34.

  In the present embodiment, the amount of color misregistration of each color in the sub-scanning direction is detected so that the above-described error is reduced. Specifically, separately from the calibration in the image forming apparatus 100, the output waveforms of the light receiving elements 34 and 35 for each color as shown in FIG. 15 are acquired in advance, and the above-described error is calculated. Further, the calculated error is stored in advance in a storage device such as a non-volatile memory (not shown) included in the image forming apparatus 100 as a correction value. That is, a correction value for correcting an error generated in the detection value of the color shift amount due to a change in the response speed according to the amount of light received by the light receiving elements 34 and 35 is stored in the storage device. The control unit 41 corrects (offsets) the color shift amount acquired by the method described in the second to fourth embodiments using the correction value. As a result, it is possible to reduce the detection error of the color misregistration amount caused by the response speed of the light receiving elements 34 and 35.

  In the present embodiment, the detection of the color shift amount in the sub-scanning direction has been described. However, the detection of the color shift amount in the main scanning direction can be similarly realized. In the present embodiment, detection of the amount of color misregistration in the sub-scanning direction has been described, with the reference color being magenta (M), the target color being black (K), and the color of the patch image to be formed as the base being yellow (Y). However, the color misregistration amount can be similarly detected for other color combinations.

100: image forming apparatus, 1: photosensitive drum, 31: toner detection unit, 12a: intermediate transfer belt, 30: test pattern, 33: LED, 34, 35: light receiving element, 36: circuit board, 37: housing, 38, 39: light shielding wall, 41: control unit

Claims (27)

A light-emitting element that irradiates irradiation light toward an irradiation target;
A first light receiving element for receiving irregularly reflected light in which the irradiation light is irregularly reflected in an irradiation area of the irradiation target;
A second light-receiving element for receiving the regular reflection light in which the irradiation light is regularly reflected in the irradiation region of the irradiation object,
The first light receiving element receives the irregularly reflected light that is irregularly reflected in a first area of the irradiation area, and the second light receiving element includes a second light receiving element that at least partially does not include the first area in a main scanning direction. An optical sensor, which receives the specularly reflected light regularly reflected in a region. A first opening that is an opening for determining an irradiation area of the irradiation light with respect to the irradiation target, the first opening through which the irradiation light passes, and through which the irregularly reflected light received by the first light receiving element passes. 2. The optical sensor according to claim 1, further comprising: a housing forming an opening and a second opening through which the specularly reflected light received by the second light receiving element passes. 3. The housing forms a third opening in a region between the first opening and the first light receiving element, through which the irregularly reflected light passing through the first opening passes before being received by the first light receiving element. The optical sensor according to claim 2, wherein: The optical sensor according to claim 2, wherein the housing covers the light emitting element, the first light receiving element, and the second light receiving element. In a region until the irradiation light passes through the first opening, a part of a first optical path through which the irradiation light passes and a second optical path through which the irregularly reflected light received by the first light receiving element passes The optical sensor according to any one of claims 2 to 4, wherein? The optical sensor according to any one of claims 1 to 5, wherein a distance between the first light receiving element and the light emitting element is shorter than a distance between the second light receiving element and the light emitting element. The optical sensor according to any one of claims 1 to 6, wherein the first light receiving element and the second light receiving element are arranged adjacently on a circuit board. The optical device according to any one of claims 2 to 5, wherein the housing has a first light blocking wall for blocking light other than the irregularly reflected light from being received by the first light receiving element. Sensor. The first light-shielding wall is provided above a position of the first light-receiving element on a mounting surface of a circuit board on which the first light-receiving element and the second light-receiving element are mounted, in a direction perpendicular to the mounting surface. The optical sensor according to claim 8, wherein: The housing is provided between the light emitting element and the first light receiving element, and is for blocking light emitted from the light emitting element so as not to be directly received by the first light receiving element and the second light receiving element. The optical sensor according to claim 2, further comprising a second light-shielding wall. The direction in which the first light receiving element and the second light receiving element are arranged is such that the first area has a larger area irradiated with the irradiation light than the second area. The optical sensor according to any of the preceding claims. The optical sensor according to claim 1, wherein the first region and the second region are regions that are part of the irradiation region and do not overlap with each other. The optical sensor according to any one of claims 1 to 12, wherein the first light receiving element and the second light receiving element are mounted on a circuit board as one integrated circuit. The optical sensor according to claim 2, wherein the first opening is an opening for regulating the irradiation light and regulating the irregularly reflected light and the regular reflected light. The second opening is configured such that, in a region between the first opening and the first light receiving element and the second light receiving element, the irregularly reflected light received by the first light receiving element passes therethrough, and the second light receiving element The optical sensor according to claim 2, wherein the optical sensor is an opening through which the specularly reflected light received by the optical sensor passes. A first optical path through which the irradiation light passes, a second optical path through which the irregularly reflected light received by the first light receiving element passes, and a second light path through which the irradiation light passes through the first opening. The optical sensor according to claim 2 or 15, wherein a part of each of the third optical path through which the regular reflection light received by the two light receiving elements passes overlaps. A light-emitting element that irradiates irradiation light toward an irradiation target;
A first light receiving element for receiving irregularly reflected light in which the irradiation light is irregularly reflected in an irradiation area of the irradiation target;
A second light receiving element for receiving the regular reflection light in which the irradiation light is regularly reflected in the irradiation region of the irradiation target;
A first opening for guiding the light emitted from the light emitting element toward the irradiation target; and a first opening for guiding the irregularly reflected light diffusely reflected in the first region to the first light receiving element in the irradiation region. A housing that forms two openings, and a third opening that guides the specularly reflected light that is at least partially reflected in the second region not including the first region in the main scanning direction to the second light receiving element;
An optical sensor comprising: An image carrier;
The optical sensor according to any one of claims 1 to 17 , wherein the optical sensor is provided at a position facing a surface of the image carrier, and is directed from the light emitting element to the image carrier, which is the object to be irradiated. Irradiating light, the optical sensor,
The first light receiving element or the second light receiving element when an image formed on the image carrier passes through a first area or a second area in an irradiation area of the image carrier irradiated with the irradiation light; Control means for detecting the position or density of the image based on a signal output from the element, wherein the color shift correction control is executed based on the detected position of the image, or the density of the detected image is Control means for performing image density control based on
An image forming apparatus comprising: An image carrier;
The optical sensor according to any one of claims 1 to 17 , wherein a first region is provided at a position facing the surface of the image carrier along a direction orthogonal to a moving direction of the surface of the image carrier. And an optical sensor that is provided so that the second region is arranged, and irradiates light from the light emitting element toward the image carrier that is the object to be irradiated,
On the surface of the image carrier, a first patch image passing through the first area and a second patch image different in color from the first patch image passing through the second area are the same in the moving direction. Image forming means for forming the image so as to be positioned
A signal output from the first light receiving element when the first patch image passes through the first area, and a signal output from the second light receiving element when the second patch image passes through the second area. Control means for detecting a color misregistration amount based on the detected color misregistration amount, based on the detected color misregistration amount,
An image forming apparatus comprising: 20. The image forming apparatus according to claim 19 , wherein a length of the first patch image in a direction orthogonal to the moving direction is longer than a length of the second patch image in a direction orthogonal to the moving direction. The control unit detects a position of the first patch image based on a signal output from the first light receiving element when the first patch image passes through the first region, and detects the position of the second patch image. Detecting the position of the second patch image based on a signal output from the second light receiving element when the light passes through the second region, thereby detecting the color shift amount. Item 20. The image forming apparatus according to Item 19 . The image forming means further includes, on the surface of the image carrier, a third patch image passing through the first area, and a fourth patch image having the same color as the third patch image passing through the second area. , Are formed at the same position in the moving direction,
The control unit is further output from the first light receiving element and the second light receiving element when the third patch image and the fourth patch image pass through the first area and the second area, respectively. Detecting a difference between the position of the third patch image and the position of the fourth patch image as a positional shift amount between the first light receiving element and the second light receiving element based on the signal. The image forming apparatus according to any one of claims 19 to 21 . 23. The image forming apparatus according to claim 22 , wherein the control unit performs the color shift correction control based on the detected color shift amount and the detected position shift amount. When forming the first patch image, the image forming unit may use, as a base of the first patch image, a base image having a size larger than that of the first patch image and a reflectance different from that of the first patch image. the image forming apparatus according to any one of claims 19, characterized in that the formation 23. For the irregularly reflected light, a difference in reflectance between the base image and the first patch image is larger than a difference in reflectance between the surface of the image carrier and the first patch image. The image forming apparatus according to claim 24 , wherein A storage unit storing a correction value for correcting an error generated in the detection value of the color shift amount due to a change in a response speed according to a light receiving amount of the first light receiving element and the second light receiving element,
It said control means, the image forming apparatus according to any one of claims 19 to 25, characterized in that to correct the detection value of the color shift amount by the correction value stored in the storage means. The optical sensor according to any one of claims 1 to 17 , wherein the optical sensor irradiates light from the light emitting element toward the irradiation target on which an image is formed, and
Control means for controlling image forming conditions based on a signal from the optical sensor,
An image forming apparatus comprising:

Images