JP2015075619A - Toner concentration sensor and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact toner concentration sensor 605, 606 configured to improve detection accuracy thereof.SOLUTION: A toner detection sensor 605, 606 includes: a light-emitting element 610 which emits light; a first polarization element 611 which reflects the light from the light-emitting element 610 and makes the reflected light incident on a toner image; a second polarization element 612 which splits the light reflected from the toner image into transmission light and reflection light; a first light-receiving element 613 which receives the transmission light having transmitted through the second polarization element 612; a second light-receiving element 614 which receives the light reflected from the second polarization element; and a detection unit 615 which detects toner concentration, on the basis of signals of the first and second light-receiving elements 613, 614. The second polarization element is the same as the first polarization element.

Description

  The present invention relates to a toner density sensor and an image forming apparatus, and more particularly to a toner density sensor and an image forming apparatus that can improve the detection accuracy of the toner density sensor and can be downsized.

  In image forming apparatuses such as printers, copiers, facsimiles, and complex machines that form images by an electrophotographic process, a toner image is developed on a photosensitive drum, and the toner image is transferred to an intermediate transfer belt. The toner image is transferred from the intermediate transfer belt to the printing paper, and the toner image is fixed on the printing paper.

  In such an image forming apparatus, toner density correction and color misregistration correction are performed as necessary or periodically.

  In general, in the density correction process, a reference toner pattern (patch image) is developed and transferred to an intermediate transfer belt, and the toner density of the toner pattern on the intermediate transfer belt is specified using an optical sensor. Density correction is performed based on the toner density. Further, in the case of a color image forming apparatus, the position of the toner pattern on the intermediate transfer belt is specified using an optical sensor, and color misregistration correction is performed based on the position. Another method is to specify the toner density on the photosensitive drum or intermediate transfer belt.

  In a toner density sensor for measuring toner density, a specific polarized component (P-polarized light or S-polarized light) is separated from light from a light emitting diode by a beam splitter, and the specific polarized component is incident on a toner pattern on an intermediate transfer belt. . Then, the reflected light from the toner pattern is separated into a regular reflection component and a diffuse reflection component by a beam splitter and detected by a light receiving element. The toner density is specified from the intensities of the regular reflection component and the diffuse reflection component. For example, when the incident light to the toner pattern is P-polarized light, the regular reflection component is P-polarized light.

  Here, when a light emitting diode (hereinafter referred to as LED) is used as the light source of the sensor, a temperature rise that occurs with time due to heat generation of the LED main body or heat generation of the internal device of the image forming apparatus due to the LED drive current. This shifts the wavelength of light from the LED.

  Further, the polarization characteristics of the polarization separation element used to separate the specific polarization component in the toner density sensor greatly depend on the wavelength of the incident light. Therefore, there is a possibility that the transmittance of the specific polarization component in the beam splitter varies greatly due to the wavelength shift of the light from the LED, and the toner concentration may not be detected accurately.

  Therefore, Japanese Patent Laid-Open No. 2012-93655 (Patent Document 1) discloses a toner density sensor that detects light density based on reflected light by making detection light incident on a toner image. The sensor includes a light source that generates the detection light, a first polarization element that transmits a specific polarization component of the detection light, and a second polarization element that transmits a specific polarization component of the reflected light, The first polarizing element and the second polarizing element have a transmission wavelength band including at least a wavelength before the wavelength shift of the detection light to a wavelength after the wavelength shift of the detection light by continuous use. As a result, even if a wavelength shift occurs in the light from the light source, the toner density is detected accurately.

JP 2012-93655 A

  As in the technique described in Patent Document 1, in the toner density sensor, the measurement object on which the toner image is formed is transmitted light from the beam splitter of the first polarizing element among the light emitted from the light emitting element of the LED. The reflected light from the measurement object is polarized and separated by a beam splitter of a second polarizing element different from the beam splitter, and detected by two different light receiving elements. Thereby, the toner amount of the toner image formed on the measurement object can be measured.

  Here, the toner density sensor is usually mounted on an image forming apparatus such as a color printer or a color multifunction peripheral, and the image forming apparatus uses the toner density sensor to form a toner image formed on the intermediate transfer belt. The toner density is measured and the toner amount is measured, so that the toner amount is corrected to parameters (development table, exposure table, LUT, etc.) and the toner amount is controlled.

  Since this toner density sensor is mounted on the main body side facing the intermediate transfer belt, the distance between the intermediate transfer belt and the toner density sensor is due to assembly tolerances and dimensional variations of the intermediate transfer unit. There is a problem that some errors are included and accuracy is lacking.

  Further, it has been found that the distance between the intermediate transfer belt and the toner density sensor varies due to the rotation of the intermediate transfer belt, and there is a problem that the detection accuracy of the toner density deteriorates due to the variation in the distance. .

  In order to suppress this variation in distance, it is preferable that light from the light emitting element of the toner density sensor is incident at a substantially right angle to the toner image and the reflected light is detected.

  However, in the configuration of the conventional toner density sensor 500 described above, as shown in FIG. 5, in order to make the light from the light emitting element 501 substantially perpendicular to the toner image and reduce the incident angle α to the toner image. The incident angle to the first beam splitter 502 needs to be increased, in other words, the distance between the first beam splitter 502 and the light emitting element 501 needs to be increased. Further, the transmitted light from the first beam splitter 501 is reflected through the toner image, and the reflected light is separated into the transmitted light of the P-polarized component and the reflected light of the S-polarized component through the second beam splitter 503. However, the first light-receiving element 504 that receives the transmitted light of the P-polarized component and the second light-receiving element 505 that receives the reflected light of the S-polarized component are the same as the light-emitting element 501. It is necessary to greatly increase the distance between the beam splitter 503 and the beam splitter 503. Therefore, there arises a problem that the toner density sensor is increased in size.

  As shown in FIG. 5, the toner density sensor 500 is disposed at a position facing the intermediate transfer belt B1, and generally there is a space in the surface direction of the intermediate transfer belt B1 in terms of layout. However, there is no space in the direction perpendicular to the surface direction of the intermediate transfer belt B1 (the arrangement direction of the intermediate transfer belt B1 and the toner density sensor 500). Therefore, when the incident angle α of the light from the light emitting element 501 is reduced as described above, the distance between the first beam splitter 502 and the light emitting element 501, the second beam splitter 503, and the first light receiving element 504. And the distance between the second beam splitter 503 and the second light receiving element 505 are increased. As a result, there is a problem that the entire toner density sensor 500 is increased in size and cost. Such a problem cannot be solved by the technique described in Patent Document 1.

  Accordingly, the present invention has been made to solve the above problems, and an object thereof is to provide a toner concentration sensor and an image forming apparatus capable of improving the detection accuracy of the toner concentration sensor and reducing the size. And

  In order to solve the above-described problems and achieve the object, the toner density sensor according to the present invention is a toner density sensor that detects the toner density based on light incident on the toner image and reflected from the toner image. Therefore, the following configuration is adopted.

  That is, the present invention provides a light emitting element that emits light, a first polarizing element that reflects light from the light emitting element and enters the reflected light on a toner image, and transmits light reflected from the toner image. A second polarizing element that separates light into reflected light, a first light receiving element that receives transmitted light that has passed through the second polarizing element, and a first light receiving element that receives reflected light from the second polarizing element. A second light receiving element, and a detection unit that detects a toner density based on signals from the first light receiving element and the second light receiving element, wherein the second polarizing element is the first polarizing element. It is characterized by being the same.

  An image forming apparatus including a toner density sensor that detects light density based on light incident on a toner image and reflected from the toner image, the light emitting element emitting light, and the light from the light emitting element A first polarizing element that reflects the reflected light into the toner image, a second polarizing element that separates the light reflected from the toner image into transmitted light and reflected light, and the second A first light receiving element that receives transmitted light that has passed through the polarizing element; a second light receiving element that receives reflected light from the second polarizing element; the first light receiving element; and the second light receiving element. And a detection unit that detects a toner density based on the signal, and the second polarizing element is the same as the first polarizing element.

  According to the toner density sensor and the image forming apparatus of the present invention, it is possible to improve the detection accuracy of the toner density sensor and reduce the size.

1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a detailed view of one image forming unit. 2 is a schematic configuration diagram relating to control of the image forming apparatus 1 in the present embodiment. FIG. FIG. 3 is a schematic diagram of a toner concentration sensor of the present invention. It is a schematic diagram of a conventional toner concentration sensor.

  Hereinafter, an embodiment of an image forming apparatus provided with a toner concentration sensor of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not. Moreover, the alphabet S added before the number in a flowchart means a step.

<Image forming apparatus>
Hereinafter, an image forming apparatus 1 including a toner concentration sensor according to the present invention will be described. FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 of the present embodiment.

  The image forming apparatus 1 transfers a toner image formed by the tandem-type image forming unit A1 that forms a toner image based on image data, a paper storage unit 2 that stores paper, and the image forming unit A1 onto the paper. A next transfer unit 3 is provided. The image forming apparatus further includes a fixing unit 4 that fixes the transferred toner image on the paper, a paper discharge device 5 that discharges the fixed paper, and a paper discharge tray 7 that receives the discharged paper. Further, the image forming apparatus 1 includes a paper transport unit 6 that transports paper from the paper storage unit 2 to the paper discharge device 5.

  The image forming unit A1 includes an intermediate transfer belt B1 (intermediate transfer member), a cleaning unit B2 for cleaning the intermediate transfer belt B1, and each color of yellow (Y), magenta (M), cyan (C), and black (B). Are provided with image forming units FY, FM, FC, and FB, respectively.

  The intermediate transfer belt B1 is a belt-like member having an endless shape, that is, a loop shape, which is wider than a sheet having the maximum length in the direction perpendicular to the usable sheet conveying direction and having conductivity. Circulated around.

  The image forming units FY, FM, FC, and FB are arranged in this order along the intermediate transfer belt B1 in the moving direction of the intermediate transfer belt B1, downstream from the cleaning unit B2 and upstream from the secondary transfer unit 3. . Note that the order of arrangement of the image forming units FY, FM, FC, and FB is not limited to this, but this arrangement is preferable in consideration of the influence of the color mixture on the completed image. The image forming units FY, FM, FC, and FB are arranged so that the intervals between the image forming units are equal.

  Next, an image forming operation of the image forming apparatus 1 will be described. FIG. 2 is a detailed view of one of the image forming units FY, FM, FC, and FB. The image forming units FY, FM, FC, and FB have almost the same configuration.

  The image forming unit FY includes a photosensitive drum (image carrier) 10, a charger 11, an exposure device 12, a yellow developing device HY, a primary transfer roller (voltage application unit) 20, a cleaning blade 35 for the photosensitive drum 10, A static eliminator 13 and a carrier removal roller (carrier removal member) 30 are provided.

  The other image forming units FM, FC, and FB include developing devices HM, HC, and HB corresponding to the respective colors. Of the image forming units, the image forming unit FB located on the most downstream side in the moving direction of the intermediate transfer belt B1 is not provided with the carrier removing roller 30 because the image forming unit is not located downstream thereof. Other configurations are the same.

  The photoreceptor drum 10 only needs to be able to carry a toner image including toner charged on its surface (charged positively in this embodiment).

  In the present embodiment, the photosensitive drum 10 is a substantially cylindrical member that is arranged to be rotatable about a rotation axis that is perpendicular to the moving direction of the intermediate transfer belt B1 and parallel to the surface direction of the intermediate transfer belt B1. The photosensitive drum 10 is in contact with the surface of the intermediate transfer belt B1 at a predetermined primary transfer position 10S. The photosensitive drum 10 can rotate so that the moving direction at the primary transfer position 10S is the same as the moving direction of the intermediate transfer belt B1, that is, in FIG.

  The cleaning blade 35, the charge eliminating device 13, the charger 11, the exposure device 12, and the yellow developing device HY are arranged around the photosensitive drum 10 in this order as seen from the primary transfer position along the rotation direction described above. The

  The charger 11 can uniformly charge the surface of the photosensitive drum 10. The exposure device 12 has a light source such as a laser scanner unit (LSU), and irradiates the surface of the charged photosensitive drum 10 with light according to the image data in accordance with the image data from the above-described host device. An electrostatic latent image can be formed on the surface of the drum 10.

  The yellow developing device HY holds a developer containing yellow toner and a carrier so as to face the electrostatic latent image, thereby applying toner to the electrostatic latent image, and converting the electrostatic latent image into a toner image. Can be developed. This toner image is primarily transferred by the primary transfer roller 20 to the intermediate transfer belt B1. Details of the primary transfer roller 20 will be described later.

  The cleaning blade 35 is a blade-like member disposed so as to be in contact with the photosensitive drum 10. The cleaning blade 35 removes the developer remaining on the surface of the photosensitive drum 10 after the primary transfer.

  The neutralization device 13 includes a light source. After the developer is removed by the cleaning blade 35, the surface of the photosensitive drum 10 is neutralized by light from the light source to prepare for the next image formation.

  The primary transfer roller 20 is disposed so as to contact the back surface of the intermediate transfer belt B1 at a voltage application position 20S downstream from the primary transfer position 10S in the moving direction of the intermediate transfer belt B1. A voltage having a polarity opposite to that of the toner in the toner image (minus in this embodiment) is applied to the primary transfer roller 20 from a power source (not shown). That is, the primary transfer roller 20 can apply a voltage having a polarity opposite to that of the toner to the intermediate transfer belt B1 at the voltage application position 20S. Since the intermediate transfer belt B1 has conductivity, the applied voltage attracts toner to the surface side of the intermediate transfer belt B1 at the voltage application position 20S and the periphery thereof.

  Therefore, in the present embodiment, the primary transfer position 10S is disposed within a range in which toner is attracted to the intermediate transfer belt B1 side by the applied voltage. As a result, the toner moves from the photosensitive drum 10 to the surface of the intermediate transfer belt B1, and primary transfer is performed.

  As long as primary transfer is possible in this way, the specific configuration of the primary transfer roller 20 is not particularly limited, and the specific configuration can be changed as appropriate. In the present embodiment, the primary transfer roller 20 can rotate in the opposite direction to the photosensitive drum 10 around a rotation axis parallel to the rotation axis of the photosensitive drum 10, that is, the movement direction at the charge application position 20S is intermediate. It is a substantially cylindrical member that can be rotated in the same direction as the transfer belt B1.

  In this embodiment, the carrier removal roller 30 is a substantially cylindrical member that can rotate in the same direction as the photosensitive drum 10 around a rotational axis parallel to the rotational axis of the photosensitive drum 10. The carrier is not limited, and it is sufficient that the carrier can be removed from the surface of the intermediate transfer belt B1 downstream of the charge application position 20S and upstream of the secondary transfer position in the moving direction of the intermediate transfer belt B1. Specifically, the carrier removing roller 30 only needs to be able to move the carrier on the surface of the intermediate transfer belt B1 to its own surface by contacting the surface of the intermediate transfer belt B1.

  During primary transfer, a small amount of carrier may be transferred from the photosensitive drum 10 to the intermediate transfer belt B1 together with the toner. This carrier transfer may interfere with primary transfer in the downstream image forming unit and cause image defects such as image blurring and blurring. Providing the carrier removal roller 30 can prevent such an image defect.

  In the present embodiment, the carrier removal roller 30 is disposed so as to contact the surface of the intermediate transfer belt B1 downstream of the charge application position 20S in the moving direction of the intermediate transfer belt B1. The carrier removal roller 30 is incorporated in the cleaning unit 31 together with the cleaning blade 35 described above. The cleaning unit 31 is provided in the image forming unit FY. In addition to the cleaning blade 35 and the carrier removing roller 30, the cleaning unit 31 is in contact with the surface of the carrier removing roller 30 to remove the carrier attached to the surface of the carrier removing roller 30. The carrier removal blade 31b, the carrier removed from the carrier removal roller 30, and the developer (including toner and carrier) removed from the surface of the photosensitive drum 10 by the cleaning blade 35 are conveyed to the outside of the cleaning unit 31. A transport member 31c is provided. The image forming unit FY may further include a separation unit that separates the carrier and the toner in order to reuse the carrier and the toner conveyed by the conveyance member 31c.

  Next, the configuration of the developing device HY will be described. The configurations of the developing devices HY, HM, HC, and HB for the respective colors are the same.

  The developing device HY includes a developing container 40, a developing roller 40a, a magnetic roller (mag roller) 40b, a drawing roller 40c, stirring spirals 40d and 40e, and a magnetic roller doctor blade 40g.

  The developing container 40 stores therein a developer composed of yellow toner (toner particles) and a carrier. The stirring spirals 40d and 40e are provided so as to be entirely immersed in the developer in the developing container 40, and stir the developer. The toner is uniformly dispersed in the carrier by the rotation of the stirring spirals 40d and 40e.

  The drawing-up roller 40c is arranged so that a part of the drawing-up roller 40c is immersed in the developer in the developing container, and the developer is pumped up by adhering to the surface. A magnetic roller 40b is arranged in contact with the pumping roller 40c, and a developer is supplied from the pumping roller 40c. The magnetic roller 40b rotates in the counter direction of the developing roller 40a, and in the vicinity of the nip, a magnetic roller doctor blade 40g is provided that simultaneously peels off the developer and places the developer. The magnetic roller doctor blade 40g regulates the developer layer thickness on the surface of the magnetic roller 40b to a predetermined amount. A developing roller 40a (also referred to as a developing device) is disposed so as to be in contact with the magnetic roller 40b, and a developer is applied to the surface thereof from the magnetic roller 40b. Since the developer layer thickness of the magnetic roller 40b is regulated to a predetermined value, the developer layer thickness formed on the surface of the developing roller 40a is also kept at the predetermined value. The developing roller 40a is in contact with the photosensitive drum 10, and responds to an image instructed to be formed from the host apparatus by the potential difference between the electrostatic latent image potential on the surface of the photosensitive drum 10 and the developing bias value applied to the developing roller 40a. A toner image is formed on the surface of the photosensitive drum 10 (development operation).

  The image forming apparatus of the present invention is characterized in that image density correction of a toner image is performed by adjusting a developing bias value (voltage value, simply referred to as a bias value) applied to the developing roller 40a.

  Further, the developer on the surface of the magnetic roller 40b after the developing operation on the photosensitive drum 10 is removed by the magnetic roller doctor blade 40g, flows down along the surface of the magnetic roller doctor blade 40g, and passes through a flow path (not shown). The developer stored in the developer container 40 is mixed.

  A toner concentration sensor 40h is disposed in the developing container, and detects the toner concentration of the developer in the developing container 40. When it is detected that the toner concentration is lower than a predetermined value, toner (a developer having a toner concentration higher than the predetermined value) is supplied from a toner cartridge (not shown) to the developing container 40, and the toner concentration is higher than the predetermined value. The carrier is supplied to the toner container 40 from a carrier cartridge (not shown).

  Under such a configuration, the image forming apparatus 1 that has received an instruction for image formation from a host device such as a personal computer (PC) or the like forms toner images of each color corresponding to the received image data in the image forming units FY, FM. , FC, and FB. The toner image formed in each image forming unit is transferred to the intermediate transfer belt B1, and is superimposed on the intermediate transfer belt B1 to form a color toner image.

  In synchronism with the formation of the color toner image, the paper stored in the paper storage unit 2 is taken out from the paper storage unit 2 one by one by a paper feeding device (not shown) and transported on the paper transport unit 6. Then, the sheet is fed to the secondary transfer unit 3 in synchronization with the primary transfer to the intermediate transfer belt B1, and the color toner image on the intermediate transfer belt B1 is secondarily transferred to the sheet by the secondary transfer unit 3. The sheet on which the color toner image has been transferred is further conveyed to the fixing unit 4 where the color toner image is fixed on the sheet by heat and pressure. Further, the paper is discharged by a paper discharge device 5 to a paper discharge tray section 7 provided on the outer periphery of the image forming apparatus 1. The toner remaining on the intermediate transfer belt B1 after the secondary transfer is removed from the intermediate transfer belt B1 by the cleaning unit B2.

  Further, two toner density sensors 605 and 606 for detecting the patch density of the patch formed on the intermediate transfer belt B1 at the predetermined timing and the background density of the intermediate transfer belt B1 include a black image forming unit FB and a secondary image sensor. It is provided at a predetermined position between the transfer unit 3. The black image forming unit FB is located on the most downstream side with respect to the rotation direction of the intermediate transfer belt B1 as compared with the other image forming units FY, FM, and FC. Therefore, the toner density sensors 605 and 606 detect the patch density of any of the plurality of image forming units FY, FM, FC, and FB even if the patch is formed on the intermediate transfer belt B1. It is configured to be able to.

  The toner density sensors 605 and 606 are provided in advance in positions corresponding to the positions of the intermediate transfer belt B1 where the patch is formed. In the embodiment of the present invention, two toner density sensors 605 and 606 are provided near both ends of the intermediate transfer belt B1. Provided. The toner density sensors 605 and 606 may have any form as long as they can detect the patch density or background density of the patch for each color. For example, the background on the patch or the intermediate transfer belt B1 is used as a light source. Reflective toner density sensors 605 and 606 that irradiate with light from the light source, detect reflected light intensity with a light receiving sensor, and convert light intensity information into density.

  The toner density sensors 605 and 606 are also used for detecting the toner density of a solid band image to be described later.

  FIG. 3 is a schematic configuration diagram relating to control of the image forming apparatus 1 in the present embodiment.

  The image forming apparatus 1 includes a CPU (Central Processing Unit) 301, a RAM (Random Access Memory) 302, a ROM (Read Only Memory) 303, a HDD (Hard Disk Drive) 304, and a driver 305 corresponding to each driving unit in the printing. They are connected via an internal bus 306. The CPU 301 uses, for example, the RAM 302 as a work area, executes a program stored in the ROM 303, the HDD 304, or the like, and exchanges data and commands with the driver 305 based on the execution result, as shown in FIG. The operation of each driving unit is controlled. Further, control of toner density sensors 605 and 606, which will be described later, other than the drive unit also operates as each unit when the CPU 301 executes a program.

<Embodiment of the present invention>
Next, the configuration and execution procedure according to the embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic diagram of the toner density sensor of the present invention.

  In the toner density sensor according to the present invention, the toner density sensors 605 and 606 detect the toner density based on the light incident on the toner image and reflected from the toner image. As shown in FIG. A light emitting element 610 that emits light, a first polarizing element 611 that reflects light from the light emitting element 610 and makes the reflected light incident on a toner image, and light reflected from the toner image as transmitted light and reflected light. A second polarizing element 612 that separates the first polarizing element, a first light receiving element 613 that receives the transmitted light that has passed through the second polarizing element 612, and a second light that receives the reflected light from the second polarizing element. And a detector 615 that detects toner density based on signals from the first light receiving element 613 and the second light receiving element 614.

  As a result, the detection accuracy of the toner density sensors 605 and 606 can be increased and the size can be reduced.

  That is, in the conventional toner density sensor, the light incident on the toner image is transmitted light that has passed through the first polarizing element, so that the incident angle of the light incident on the toner image is increased in order to improve the toner density detection accuracy. In order to reduce α, the incident angle of light of the light emitting element that irradiates the first polarizing element had to be increased, and the distance between the light emitting element and the first polarizing element had to be increased. . The same applies to the first and second light receiving elements that receive light reflected from the toner image.

  In the toner density sensors 605 and 606 of the present invention, the light incident on the toner image is reflected light reflected by the first polarizing element 611. Therefore, if the incident angle β of the light incident on the toner image is to be reduced. The light of the light emitting element 610 that irradiates the first polarizing element 611 may be incident on the first polarizing element 611 at approximately 45 degrees. Therefore, the distance between the light emitting element 610 and the first polarizing element 611 does not become unnecessarily large, and does not spread in the direction perpendicular to the surface on which the toner image is present but spreads in the surface direction on which the toner image is present. It is possible to plan.

  Further, in the toner density sensors 605 and 606 of the present invention, the arrangement of the light emitting element 610 and the first polarizing element 611 is such that the reflected light reflected from the first polarizing element 611 is the surface on which the toner image is present (for example, an intermediate The light can enter the transfer belt B1) at a substantially right angle. As shown in FIG. 4, the incident angle β of light incident on the toner image in the toner density sensors 605 and 606 of the present invention is compared with the incident angle α of light incident on the toner image in the conventional toner density sensor 500. It is understood that it is small. Therefore, even if there are various assembly tolerances and dimensional variations, the toner concentration can be detected with high accuracy without being affected by these, and a new toner concentration sensor that is robust to distance fluctuation is provided. It becomes possible.

  Here, the light emitting element 610 may employ, for example, a light emitting diode (LED) that emits light having a predetermined wavelength spectrum. The light emitting element 610 is configured to emit light in response to an instruction from the image forming apparatus 1 (control circuit). Note that a diaphragm portion that restricts light from the light emitting element 610 may be provided between the light emitting element 610 and the first polarizing element 611. The aperture portion has, for example, a circular aperture, and is arranged so that the center of the aperture is located on the optical axis of the light emitting element 610.

  The first polarizing element 611 and the second polarizing element 612 are beam splitters that separate incident light into specific polarization components. For example, among the incident light, the P polarization component is transmitted as transmitted light. The S-polarized component is reflected as reflected light. The light incident on the toner image is reflected light of the S-polarized component of the first polarizing element 611.

  The first polarizing element 611 and the second polarizing element 612 may have any configuration. For example, a light transmissive plate and a dielectric multilayer provided on the light incident surface side of the light transmissive plate. A film and an antireflection film provided on the light emitting surface side of the light transmissive plate. By adjusting the thickness of these films, etc., the polarization transmission characteristics of each polarizing element can be changed to desired characteristics. Be changed. A polarizing plate may be used instead of the beam splitter.

  Further, the second polarizing element 612 can be the same as the first polarizing element 611 as shown in FIG. As a result, the second polarizing element 612 is also used as the first polarizing element 611, so that the required number of polarizing elements can be reduced by one, reducing the member cost and the number of assembly steps, and the overall cost. It is possible to go down.

  The first light receiving element 613 and the second light receiving element 614 may have any configuration. For example, the first light receiving element 613 and the second light receiving element 614 may be photodiodes, detect incident light, and output an electric signal having a voltage corresponding to the intensity. Output. The first light receiving element 613 outputs the light of the P-polarized component transmitted through the second polarizing element 612 as an electrical signal, and the second light receiving element 614 has the S-polarized component reflected by the second polarizing element 612. Outputs light as an electrical signal.

  The light of the S polarization component of the first polarizing element 611 incident on the toner image or the surface on which the toner image is present (the surface of the intermediate transfer belt B1) is reflected from the toner image or the surface (base, background). A regular reflection component and a diffuse reflection component are provided. The regular reflection component becomes P-polarized light through the second polarizing element 612, and the diffuse reflection component becomes S-polarized light through the second polarizing element 612.

  The detection unit 615 may be provided in the toner density sensors 605 and 606 or in the image forming apparatus 1 having the toner density sensors 605 and 606. The detection unit 615 calculates a measured value of the toner density based on the signal from the first light receiving element 613 and the signal from the second light receiving element 614. For example, the image forming apparatus 1 corrects the toner density based on the measured value. Specifically, the toner density is calculated based on the following equation.

Toner density (%) = {1− (PS) / (Po−So)} × 100
P is a signal (voltage) (sensor output value) of the first light receiving element 613 of the P-polarized component of the reflected light of the toner image, and S is the first of the S-polarized component of the reflected light of the toner image. The signal (voltage) (sensor output value) of the second light receiving element 614, Po is the first received light of the P-polarized component of the reflected light from the surface without the toner image (for example, the ground of the intermediate transfer belt B1). This is a signal of the element 613, and So is a signal of the second light receiving element 614 of the S polarization component in the reflected light of the surface without the toner image.

  For example, an amplifier or the like may be provided between the first light receiving element 613, the second light receiving element 614, and the detection unit 615 so as to amplify a signal from the light receiving element.

  In the toner density sensors 605 and 606 of the present invention, the light incident on the toner image is reflected light reflected from the first polarizing element 611. Therefore, the arrangement of the light emitting element 610 and the first polarizing element 611 is as follows. It is necessary to increase the accuracy. This is because the deviation of the incident angle of the incident light of the light emitting element 610 is reflected as a deviation of the double reflection angle in the reflected light. Therefore, the arrangement of the light emitting element 610 and the first polarizing element 611 is preferably fixed by a member having excellent dimensional stability.

  As described above, the present invention includes the light-emitting element 610, the first polarizing element 611 that reflects the light from the light-emitting element 610, and enters the reflected light into the toner image, the second polarizing element 612, and the like. The first light receiving element 613, the second light receiving element 614, and a detection unit 615 are provided. As a result, the detection accuracy of the toner density sensors 605 and 606 can be increased, and the cost and size can be reduced.

  In the present invention, a color image forming apparatus is assumed, but a monochrome image forming apparatus may be used. In the present invention, the toner image on the intermediate transfer belt B1 is assumed, but the toner image on the photosensitive drum may be used.

  In the present invention, the touch-down development method is assumed, but any image forming apparatus may be used. In the touchdown development method, a toner thin layer is formed on the developing sleeve by transferring only toner from a magnetic roller carrying a two-component developer containing toner and carrier, and an electrostatic latent image is formed. In other words, the electrostatic latent image is developed as a toner image by flying toner from the thin toner layer onto the surface of the photoreceptor.

  In the present invention, the image forming apparatus 1 is assumed. However, the image forming apparatus 1 is not particularly limited as long as it is an apparatus for measuring toner density and an apparatus equipped with a toner density sensor.

  As described above, the toner density sensor and the image forming apparatus according to the present invention are useful not only for a multifunction machine but also for a copying machine, a printer, and the like, and can improve the detection accuracy of the toner density sensor and can be downsized. It is effective as a toner density sensor and an image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 605,606 toner density sensor 610 light emitting element 611 1st polarizing element 612 2nd polarizing element 613 1st light receiving element 614 2nd light receiving element 615 detection part

Claims (2)

A toner density sensor that detects light density based on light incident on a toner image and reflected from the toner image,
A light emitting element that emits light;
A first polarizing element that reflects light from the light emitting element and makes the reflected light incident on a toner image;
A second polarizing element that separates light reflected from the toner image into transmitted light and reflected light;
A first light receiving element that receives the transmitted light that has passed through the second polarizing element;
A second light receiving element for receiving reflected light from the second polarizing element;
A detection unit that detects a toner concentration based on signals from the first light receiving element and the second light receiving element;
The toner concentration sensor, wherein the second polarizing element is the same as the first polarizing element. An image forming apparatus including a toner concentration sensor that detects a toner concentration based on light incident on a toner image and reflected from the toner image,
A light emitting element that emits light;
A first polarizing element that reflects light from the light emitting element and makes the reflected light incident on a toner image;
A second polarizing element that separates light reflected from the toner image into transmitted light and reflected light;
A first light receiving element that receives the transmitted light that has passed through the second polarizing element;
A second light receiving element for receiving reflected light from the second polarizing element;
A detector that detects a toner density based on signals from the first light receiving element and the second light receiving element, wherein the second polarizing element is the same as the first polarizing element. An image forming apparatus.

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