JP6107363B2 - Optical sensor, image forming apparatus, and object specifying method - Google Patents

Description

  The present invention relates to an optical sensor and an image forming apparatus, and more specifically, an optical sensor suitable for specifying a sheet-like object, an image forming apparatus including the optical sensor, and an object for specifying the object. It relates to an object identification method.

  Conventionally, a technique for automatically specifying the type of a sheet-like object (for example, a recording medium) is known (see, for example, Patent Documents 1 and 2).

  However, in the techniques disclosed in Patent Documents 1 and 2, it has been desired to specify an object more finely.

  In the present invention, when at least the one surface and the first region are in contact with the reflecting member including the first and second regions having different reflectivities that can contact one surface of the sheet-like object. Irradiating a portion corresponding to the first region on the other surface of the object with the first linearly polarized light in a state inclined with respect to the normal direction of the other surface, and at least the one surface and the second surface. Irradiating means for irradiating the portion corresponding to the second region on the other surface when the region is in contact with the second region in a state inclined with respect to the normal direction; Of the light reflected by the portion corresponding to the first region and the light transmitted through the portion and reflected by the first region, the polarization direction of the first linearly polarized light is perpendicular to the first linearly polarized light. 2 linearly polarized light and detecting the object An optical system comprising: light that is reflected by a portion corresponding to the second region and light detecting means that detects the second linearly polarized light out of the light that is transmitted through the portion and reflected by the second region. It is a sensor.

  According to the present invention, an object can be specified more finely.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. It is a figure for demonstrating the structure of the optical sensor in FIG. It is a figure for demonstrating a surface emitting laser array. FIG. 4A is a diagram illustrating the optical sensor when the dark box is located at the first position, and FIG. 4B is a diagram illustrating the optical sensor when the dark box is located at the second position. is there. It is a block diagram for demonstrating the structure of control of an optical sensor. It is a figure for demonstrating regular reflection light, diffuse reflection light, internal diffuse reflection light, and multiple diffuse reflection light. FIG. 7A is a diagram for explaining reflected light on a white background, and FIG. 7B is a diagram for explaining reflected light on a black background. FIG. 8A is a diagram for explaining a method of detecting light whose polarization direction has changed among the reflected light in FIG. 7A, and FIG. 8B is a reflection in FIG. 7B. It is a figure for demonstrating the method to detect the light from which the polarization direction changed among light. It is a flowchart for demonstrating the method (paper brand specification process) of specifying the brand of a paper using an optical sensor. FIGS. 10A and 10B are diagrams (No. 1 and No. 2) for explaining a method of specifying a brand of paper using an optical sensor, respectively. It is a figure for demonstrating the relationship between S01wb and S01b, and the brand of a paper. It is a figure for demonstrating the relationship between S01wb and the basic weight of each brand. It is a figure for demonstrating the influence of the number of light emission parts which acts on the contrast ratio of a speckle pattern. It is a figure for demonstrating the relationship between the contrast ratio of a speckle pattern, and a total light quantity when changing the number of light emission parts and changing the light quantity of each light emission part. It is a figure for demonstrating the light intensity distribution of a speckle pattern when the drive current of a light source is changed. It is a figure for demonstrating the effective light intensity distribution of a speckle pattern when the drive current of a light source is changed at high speed. It is a figure for demonstrating the surface emitting laser array from which the light emission part space | interval is not equal intervals. It is a figure for demonstrating the optical sensor of the modification 1. It is a figure for demonstrating the optical sensor of the modification 2. It is a figure for demonstrating the optical sensor of the modification 3. It is a figure for demonstrating the optical sensor of the modification 4. It is a figure for demonstrating the optical sensor of the modification 5.

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

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

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

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An AD conversion circuit for converting the signal into digital data. The printer control device 2090 controls each unit in response to a request from the host device, and sends image information from the host device to the optical scanning device 2010.

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

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

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

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

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

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

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

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

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

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a multicolor image.

  The paper feed tray 2060 stores print paper (hereinafter, also simply referred to as “paper”) as a sheet-like recording medium (object). A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out the paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 2056. The registration roller pair 2056 sends the sheet toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the paper. The sheet transferred here is sent to the fixing device 2050.

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

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

  By the way, in an image forming apparatus such as a digital copying machine or a laser printer, a toner image is transferred onto the surface of a sheet-like recording medium represented by printing paper, and the image is fixed by heating and pressing under predetermined conditions. Image. Conditions that must be taken into consideration in image formation are conditions such as the heating amount and pressure during fixing, and in particular, in order to perform high-quality image formation, it is necessary to individually set printing conditions according to the recording medium.

  This is because the image quality on the recording medium is greatly influenced by the material, thickness, humidity, smoothness, coating state, and the like. For example, with regard to smoothness, depending on the fixing conditions, the toner fixing rate for the concave portions in the unevenness on the surface of the printing paper is lowered. Therefore, color unevenness occurs unless fixing is performed under the correct conditions according to the recording medium.

  Furthermore, with recent advances in image forming devices and diversification of expression methods, there are hundreds of types of recording media, even on printing paper alone, and there are differences in specifications such as basis weight and thickness for each type. There are a wide variety of brands. In the following description, the most detailed classification of paper including differences in specifications such as basis weight and thickness is also referred to as brand and discrimination for identifying brand is also referred to as discrimination at the brand level. In order to form a high quality image, it is necessary to set fine printing conditions according to each of these brands.

  In recent years, the brands of plain paper, gloss coated paper, mat coated paper, coated paper typified by art coated paper, plastic sheets, and special paper with an embossed surface are increasing.

  In the conventional image forming apparatus, when the paper is filled in the paper feed tray, the user himself / herself has to set the paper brand for each tray in the control unit. For this reason, there are problems such as inconvenience that must be set by the user and setting mistakes because the user is required to have knowledge for identifying the brand of the paper. In addition, when the brand of the paper to be printed is unknown, there is a problem that it is not known which brand is suitable for setting.

  Therefore, the color printer 2000 includes the optical sensor 2245 as described above.

  The optical sensor 2245 is used to specify the brand of the paper stored in the paper feed tray 2060.

  As shown in FIG. 1 as an example, the optical sensor 2245 is disposed in the vicinity of the paper conveyance path between the paper feed roller 2054 and the registration roller pair 2056. Therefore, in the following, the paper conveyance direction between the paper feed roller 2054 and the registration roller pair 2056 is defined as the X-axis direction, and the horizontal direction orthogonal to the X-axis direction (the axial direction of the paper feed roller 2054) is defined as the Y-axis direction. A description will be given using an XYZ three-dimensional orthogonal coordinate system (see FIG. 2) in which the direction orthogonal to both the X-axis direction and the Y-axis direction is the Z-axis direction.

  As shown in FIG. 2 as an example, the optical sensor 2245 includes a light source 11, a collimating lens 12, a light receiving element 13, a polarizing filter 14, a dark box 16 in which these are housed, a reflecting member 15, an actuator 19 (see FIG. 5), A sheet specifying unit 20 (see FIG. 5) is included.

  The dark box 16 is a metal box member, for example, an aluminum box member, and has a black alumite treatment on the surface in order to reduce the influence of ambient light and stray light.

  The light source 11 has a plurality of light emitting units. Each light emitting unit is a vertical cavity surface emitting laser (VCSEL) formed on the same substrate. That is, the light source 11 includes a surface emitting laser array (VCSEL array). Here, as shown in FIG. 3 as an example, nine light emitting units (ch1 to ch9) are two-dimensionally arranged.

  For example, the light source 11 emits S-polarized light in the directions of + X side and −Z side. Here, the angle θ (see FIG. 4A) formed by the light flux from the light source 11 and the YZ plane is set to 80 °. The light source 11 is driven and controlled by the printer control device 2090 (see FIG. 5).

  The collimating lens 12 is disposed on the optical path of the light beam emitted from the light source 11, and makes the light beam substantially parallel light. The light beam that has passed through the collimating lens 12 passes through an opening provided in the dark box 16 and illuminates the paper positioned on the −Z side of the dark box 16 (see FIGS. 4A and 4B). ). In the following, the center of the illumination area on the surface of the paper is abbreviated as “illumination center”. Further, the light beam that has passed through the collimating lens 12 is also referred to as “irradiation light”.

  By the way, when light is incident on the boundary surface of the medium, a surface including the incident light ray and the normal of the boundary surface set at the incident point is called an “incident surface”. Therefore, when the incident light is composed of a plurality of light beams, there is an incident surface for each light beam. Here, for convenience, the light incident surface that is incident on the illumination center is referred to as an incident surface on the paper. . That is, the plane that includes the illumination center and is parallel to the XZ plane is the incident plane on the paper.

  The polarizing filter 14 is disposed on the + Z side of the illumination center. The polarizing filter 14 is a polarizing filter that transmits P-polarized light and shields S-polarized light. Instead of the polarizing filter 14, a polarizing filter that reflects one polarization component such as a polarizing beam splitter or a wire grid type polarizing filter having an equivalent function may be used. Note that the direction of polarization to be transmitted is not limited to P-polarized light, and may be S-polarized light when the light source 11 is arranged so as to be irradiated with P-polarized light.

  The light receiving element 13 is disposed on the + Z side of the polarizing filter 14. More specifically, the light receiving element 13 is disposed on an extension of a line connecting the illumination center and the center of the polarizing filter 14. Here, as shown in FIG. 4A, an angle ψ1 formed by a line L1 connecting the illumination center and the centers of the polarizing filter 14 and the light receiving element 13 and the surface of the sheet is 90 °.

  The light receiving element 13 outputs an electrical signal (photoelectric conversion signal) corresponding to the amount of received light to the paper specifying means 20 (see FIG. 5). In the following, the signal level in the output signal of the light receiving element 13 when the light beam from the light source 11 is irradiated onto the paper is referred to as “S01”.

  The center of the light source 11, the center of illumination, the center of the polarizing filter 14, and the center of the light receiving element 13 exist on substantially the same plane.

  The reflecting member 15 is disposed on the −Z side of the dark box 16 in parallel to the XY plane with a predetermined clearance. The reflecting member 15 has two regions with different reflectivities that are separated in the X-axis direction. Here, as the reflecting member 15, one of the two regions is a white region (hereinafter referred to as a white region 15a) and the other is a black region (hereinafter referred to as a black region 15b). A flat plate member is used. The reflecting member 15 may be, for example, one in which two areas of gloss coated paper are printed in white and black, and in either case, it is preferable that the difference in reflectance between the two areas is large.

  The actuator 19 is an actuator that moves the dark box 16 with respect to the reflecting member 15 in the X-axis direction. Specifically, the actuator 19 includes the dark box 16, a first position where the polarizing filter 14 is located on the + Z side of the white region 15a of the reflecting member 15 (see FIG. 4A), and the polarizing filter 14 is the reflecting member. It can be moved in the X-axis direction between the 15 black regions 15b and the second position located on the + Z side (see FIG. 4B). The actuator 19 is controlled by the printer control device 2090 (see FIG. 5). The light source 11, the collimating lens 12, the polarizing filter 14, and the light receiving element 13 are fixed to the dark box 16 and move together with the dark box 16.

  The actuator 19 may be any actuator that can reciprocate the dark box 16 with respect to the reflecting member 15 in the X-axis direction, such as a linear motor, a solenoid mechanism, a feed screw mechanism, and a rack and pinion mechanism.

  The actuator 19 may be a member that moves the reflecting member 15 in the X-axis direction with respect to the dark box 16 or a member that moves both the reflecting member 15 and the dark box 16 in the X-axis direction. Any member that relatively moves the member 15 and the dark box 16 in the X-axis direction may be used.

  The sheet specifying means 20 includes an output signal of the light receiving element 13 when the light beam from the light source 11 is applied to the sheet when the dark box 16 is positioned at the first position, and the dark box 16 is positioned at the second position. In doing so, the brand of the paper is estimated (specified) based on the output signal of the light receiving element 13 when the light beam from the light source 11 is irradiated onto the paper (see FIG. 5).

  By the way, the reflected light from the paper when the paper is illuminated can be divided into reflected light reflected on the surface of the paper and reflected light reflected on the inside of the paper.

  The reflected light reflected on the surface of the paper is further reflected regularly, reflected light reflected in the diffusion direction by a single reflection, and reflected multiple times by the irregularities on the paper surface and reflected in the diffusion direction. It can be classified into light (see FIG. 6). Hereinafter, for convenience, each reflected light is also referred to as “regular reflected light”, “diffuse reflected light”, and “multiple diffuse reflected light”.

  On the other hand, the reflected light reflected inside the paper (hereinafter also referred to as “internal diffuse reflected light”) is reflected many times at the interface between the fibers and pores inside the paper when the paper is general printing paper. Since it is repeated once, the reflection direction can be regarded as isotropic, and the intensity distribution can be approximated to a Lambertian distribution.

  As a result, the reflected light from the paper can be classified into regular reflected light, diffuse reflected light, multiple diffuse reflected light, and internal diffuse reflected light (see FIG. 6).

  In the techniques disclosed in Patent Documents 1 to 3, the reflected light from the paper cannot be subdivided into the above classified light and detected, and the brand of the paper cannot be specified.

  By the way, in Patent Document 2, the amount of reflected light (hereinafter, the amount of reflected light) when a white reflector is installed on the back side of the paper, that is, when the background of the paper is white (hereinafter also referred to as “white background”). ) And when the black reflector is installed on the back side of the paper, that is, when the background of the paper is black (hereinafter also referred to as “black background”), the amount of reflected light is detected and based on these detection results The paper type is determined.

  Specifically, by calculating the difference between the amount of reflected light on a white background and the amount of reflected light on a black background, the amount of light reflected by the background of the internal diffuse reflected light is calculated, and the paper is based on the calculated amount of light. The type is determined. Hereinafter, for the sake of convenience, the light reflected by the base is also referred to as “base reflected light” (see FIGS. 7A and 7B).

  More specifically, the background reflected light is considered to depend on the specific thickness of the paper because it is diffused or attenuated in the path when passing through the inside of the paper. Since the reflectance differs between the white background and the black background, a difference occurs in the amount of background reflected light detected on the paper surface. Reflected light detected on the surface of the paper includes reflected light other than the ground reflected light (see FIGS. 7A and 7B), but by taking the difference in the amount of reflected light from paper with different ground. The amount of reflected light other than the ground reflected light is subtracted, and the amount of ground reflected light can be extracted. As a result, the thickness of the paper can be detected, and the type of the paper can be determined based on the detected thickness.

  However, the reflected light detected on the paper surface includes light reflected on the paper surface such as diffuse reflected light as well as background reflected light on both white and black backgrounds. In particular, the diffuse reflected light has a larger amount of light than the ground reflected light, so the calculated value of the ground reflected light fluctuates due to the detection error of the diffuse reflected light amount between the white background and the black background, and the thickness of the paper The detection accuracy was reduced. For this reason, in patent document 2, the brand of the paper could not be specified.

  Further, as disclosed in Patent Document 3, in an image forming apparatus using an optical sensor having a polarizing filter and a single base, reflected light having a polarization component orthogonal to the polarization direction of light to be irradiated is Although internal diffuse reflection light and ground reflection are included, multiple diffuse reflection light reflected on the surface of the paper is also included, so it is difficult to distinguish between brands having very similar thicknesses. For this reason, in patent document 3, the brand of the paper could not be specified.

  By the way, the polarization directions of regular reflection light and diffuse reflection light are the same as the polarization direction of irradiation light. On the other hand, the multiple diffuse reflection light and the internal diffuse reflection light include a polarization component orthogonal to the polarization direction of the irradiation light (see FIG. 6).

  Here, the polarization direction is rotated by reflection on the paper when the irradiation light is reflected by a surface inclined in the direction of rotation with respect to the traveling direction. In the present embodiment, since the center of the light source 11, the center of illumination, and the center of the light receiving element 13 are substantially on the same plane, diffuse reflected light that has been reflected once on the paper surface and whose polarization direction has been rotated is not detected by the light receiving element 13. . On the other hand, multi-diffuse reflected light that has been reflected several times on the paper surface and whose polarization direction has been rotated, and internal diffuse reflected light that has been reflected several times inside the paper and whose polarization direction has been rotated, are separated from the plane by the reflection path and then Since it includes light reflected again on this plane by reflection, it is also detected by the light receiving element 13 on the same plane as the center of the light source 11 and the illumination center.

  Diffuse reflected light, multiple diffuse reflected light, internal diffuse reflected light, and ground reflected light are incident on the polarizing filter 14. Here, since the polarization direction of the diffuse reflected light is S-polarized light that is the same as the polarization direction of the irradiation light, the diffuse reflected light is shielded (shielded) by the polarizing filter 14. On the other hand, the polarization directions of the multiple diffuse reflected light, the internal diffuse reflected light, and the ground reflected light are rotated with respect to the polarization direction of the irradiation light, and thus are included in the multiple diffuse reflected light, the internal diffuse reflected light, and the ground reflected light. The P-polarized component is transmitted through the polarizing filter 14. That is, the light receiving element 13 receives only the P-polarized light component contained in the multiple diffuse reflection light, the internal diffuse reflection, and the base reflection light.

  The printer control device 2090 performs a paper brand identification process when the color printer 2000 is turned on or when paper is supplied to the paper feed tray 2060.

  Hereinafter, the paper brand specifying process will be described with reference to FIG. The flowchart of FIG. 9 corresponds to the processing algorithm of the CPU of the printer control apparatus 2090. The dark box 16 is initially positioned at the first position where the polarizing filter 14 is positioned on the white region 15a of the reflecting member 15 (see FIG. 4A).

  In the first step S1, the uppermost sheet (uppermost sheet) in the sheet feeding tray 2060 is positioned so as to straddle the white area 15a and the black area 15b between the dark box 16 and the reflecting member 15 (see FIG. 2).

  Specifically, the paper feed roller 2054 is driven by the printer control device 2090 and the uppermost paper (uppermost paper) is sent out from the paper feed tray 2060. At this time, the uppermost paper is guided by the reflecting member 15 and enters the gap between the dark box 16 and the reflecting member 15. Then, when the uppermost paper is straddling the white area 15a and the black area 15b of the reflecting member 15, the driving of the paper feed roller 2054 is stopped. As a result, the −Z side surface of the uppermost paper contacts both the white region 15a and the black region 15b. Note that the paper may contact the dark box 16. In this case, the paper is held between the dark box 16 and the reflection member 15, and the positional deviation in the Z-axis direction and the undulation of the paper are suppressed, and the reflected light is more accurately detected. Can be detected.

  In the next step S3, the uppermost paper is irradiated with S-polarized light. Specifically, the light source 11 is driven by the printer control device 2090, and the S-polarized light is irradiated on the part on the white area 15a on the + Z side surface of the uppermost paper (the part corresponding to the white area 15a) (see FIG. 4 (A)). At this time, the reflected light from the white area 15a and the portion on the white area 15a of the uppermost paper (corresponding to the white area 15a) enters the polarizing filter 14. Of the reflected light incident on the polarizing filter 14, S-polarized light is shielded by the polarizing filter 14. Of the reflected light incident on the polarizing filter 14, P-polarized light passes through the polarizing filter 14 and is received by the light receiving element 13, and an electrical signal corresponding to the received light amount is output to the paper specifying means 20.

  In the next step S5, the actuator 19 is driven by the printer controller 2090, and the dark box 16 is moved from the first position to the second position (see FIG. 4B).

  In the next step S7, the uppermost paper is irradiated with S-polarized light. Specifically, the light source 11 is driven by the printer control device 2090, and the S-polarized light is irradiated on the portion of the uppermost paper on the + Z side surface on the black region 15b (the portion corresponding to the black region 15b) (see FIG. 4 (B)). At this time, the reflected light from the black region 15b and a portion on the black region 15b of the uppermost paper (a portion corresponding to the black region) enters the polarizing filter 14. Of the reflected light incident on the polarizing filter 14, S-polarized light is shielded by the polarizing filter 14. Of the reflected light incident on the polarizing filter 14, P-polarized light passes through the polarizing filter 14 and is received by the light receiving element 13, and an electrical signal corresponding to the received light amount is output to the paper specifying means 20.

  In the next step S9, the top sheet is based on the output signal of the light receiving element 13 when the dark box 16 is located at the first position and the output signal of the light receiving element 13 when the dark box 16 is located at the second position. Estimate the brand name.

  Here, the signal level in the output signal of the light receiving element 13 when the reflected light from the white area and the part on the white area of the paper is received by the light receiving element 13 is “S01w”, and the signal level on the black area and the black area of the paper The signal level in the output signal of the light receiving element 13 when the light receiving element 13 receives the reflected light from the portion is referred to as “S01b”.

  Here, as S01w and S01b, the average value of S01 within the movement range between the first position and the second position of the dark box 16 is used (see FIGS. 10A and 10B). ). This is because S01 varies depending on the position of the paper. In addition to the texture of the paper, the factors of variation include external factors such as paper waviness, scratches and dirt. By using a value obtained by averaging S01, it is possible to reduce the influence of variation due to texture and the influence of scratches and dirt, although it is not measurement that changes only the ground condition for the same position on the same sheet.

  Note that S01w and S01b may be values other than the average value of S01.

  Here, for a plurality of brand papers that can be used for the color printer 2000, the value of S01 is measured in advance for each of two brands having different reflectivities in the pre-shipment process such as the adjustment process, and for each paper brand. It is stored in the ROM 20a (see FIG. 5) of the paper specifying means 20 as a “paper brand discrimination table”.

  Therefore, as an example, the sheet specifying unit 20 collates the calculated values such as the value of S01w, the value of S01b, and the difference between the two areas having different reflectivities with the data stored in the ROM 20a to determine the sheet. Estimate (specify) stocks of Hereinafter, for the sake of convenience, the difference from S01w and S01b is also referred to as “S01wb”.

  FIG. 11 shows measured values of S01b and S01wb for 30 brand papers sold in the country. In addition, the frame in FIG. 11 shows the variation range of the same brand. For example, if the measured values of S01b and S01wb are “◇”, it is identified as the brand D. Further, if the measured values of S01b and S01wb are “■”, the closest brand C is identified. If the measured values of S01b and S01wb are “♦”, it is either the brand A or the brand B. At this time, for example, the difference between the average value and the measured value of the brand A and the difference between the average value and the measured value of the brand B are calculated, and the calculation result is specified as the smaller brand. In addition, the variation including the measurement value is recalculated on the assumption that it is the brand A, and the variation including the measurement value is recalculated on the assumption that it is the brand B, and the recalculated variation is small. You may choose the other brand.

  In the next step S11, the estimated (specified) paper brand is stored in, for example, the RAM of the printer control device 2090. If the paper specifying unit 20 has a RAM, the estimated paper brand may be stored in the RAM.

  In the next step S13, the actuator 19 is driven by the printer control device 2090, and the dark box 16 is moved from the second position to the first position. When step S13 is executed, the flow ends. Note that steps S11 and S13 may be performed in reverse order or in parallel.

  Here, regarding multiple brands of paper that the color printer 2000 can handle, the optimum development conditions and transfer conditions at each station are determined for each brand of the paper in a pre-shipment process such as an adjustment process in advance. A “transfer table” is stored in the ROM of the printer controller 2090.

  Upon receiving a print job request from the user, the printer control device 2090 reads the paper brand stored in the RAM, and obtains the development conditions and transfer conditions optimal for the paper brand from the development / transfer table.

  Then, the printer control device 2090 adjusts (controls) the developing device and the transfer device of each station according to the optimum development condition and transfer condition. For example, the transfer voltage and the toner amount are controlled. As a result, a high quality image is formed on the paper.

  It has been confirmed by verification by the present inventors that S01wb has a high correlation with the basis weight (weight per unit area of the paper), which is a characteristic similar to the thickness of the paper. FIG. 12 shows the relationship between the measured value of S01wb and the basis weight of the paper for 30 brands sold in the country. The legend (plot) in FIG. 12 represents a paper brand specified by each paper manufacturer. In this verification, a plurality of brands having different basis weights were measured.

  Here, S01Wb is a signal level corresponding to the ground reflected light, which is reflected light from the inside of the paper, and is a value that accurately reflects the thickness (or basis weight) of the paper. Can be identified.

  The optical sensor 2245 of the present embodiment described above includes a white member 15a and a black member 15b having different reflectances that can contact one surface (surface on the −Z side) of a sheet (sheet-like object). 15 and at least one surface of the paper and the white region 15a are in contact with each other, the S-polarized light is applied to the portion corresponding to the white region 15a on the other surface of the paper (the surface on the + Z side) with respect to the normal direction of the other surface. The S-polarized light is tilted with respect to the normal direction at a portion corresponding to the black region 15b on the other surface when at least the one surface is in contact with the black region 15b. Irradiating means including the light source 11 and the collimating lens 12 irradiating in the state, the light reflected by the portion corresponding to the white region 15a on the paper, and transmitting the portion and reflecting by the white region 15a Among the received light, the P-polarized light whose polarization direction is orthogonal to the S-polarized light is detected, and the light reflected by the portion corresponding to the black region 15b and the light transmitted through the portion and reflected by the black region 15b. And a detecting means including a polarizing filter 14 and a light receiving element 13 for detecting P-polarized light.

  In this case, it is possible to accurately detect the P-polarized light reflected from the paper surface, the paper inside, and the white area 15a. Further, it is possible to accurately detect the P-polarized light reflected from the paper surface, the paper inside, and the black area 15b. Note that the amount of reflected light in the black region 15b is substantially zero.

  As a result, for example, by obtaining the difference between the two detection results, the amount of P-polarized light reflected by the white region 15a and passing through the inside of the paper can be obtained with high accuracy.

  As a result, the optical sensor 2245 can specify the paper more finely.

  The optical sensor 2245 further includes an actuator 19 that relatively moves the irradiating unit and the reflecting member 15 in a direction along the sheet (X-axis direction).

  In this case, by using one irradiation system including the light source 11 and the collimating lens 12 of the irradiation unit and one detection system including the polarization filter 14 and the light receiving element 13 of the detection unit, the reflected light on each of the white background and the black background is detected. Detection can be performed in time series.

  The detection means includes a polarizing filter 14 that separates light reflected by the paper and the reflecting member 15 into S-polarized light and P-polarized light, and a light receiving element 13 that receives P-polarized light from the polarizing filter 14. Contains. In this case, only the P-polarized light can be received by the light receiving element 13.

  Since the polarizing filter 14 is disposed on the optical path of the light diffusely reflected by the paper in the direction orthogonal to the paper, it can block the S-polarized light from the diffusely reflected light.

  In addition, since the color printer 2000 includes the optical sensor 2245, it is possible to refer to the brand of the paper when forming an image on the paper.

  Since the color printer 2000 includes a printer control device 2090 (adjustment unit) that adjusts image forming conditions according to the brand of the sheet specified by the sheet specifying unit 20 of the optical sensor 2245, the color printer 2000 is formed on the sheet. The image quality can be improved.

  Here, a method for suppressing the speckle pattern will be described. If a semiconductor laser is used as the light source of the sensor that detects the surface state of the paper from the amount of reflected light, the coherent light emitted from the semiconductor laser is irregularly reflected at each point on the rough surface such as the paper surface and interferes with the spec. Pattern occurs.

  The inventors used a vertical cavity surface emitting laser array (VCSEL array) in which a plurality of light emitting portions are two-dimensionally arranged as a light source, and obtained a relationship between the number of light emitting portions and the contrast ratio of the speckle pattern (see FIG. 13). Here, the contrast ratio of the speckle pattern is defined as a value obtained by standardizing the difference between the maximum value and the minimum value in the observation intensity of the speckle pattern.

  The speckle pattern was observed using a beam profiler in the Z-axis direction (diffusion direction), and the contrast ratio of the speckle pattern was calculated from the observation results obtained by the beam profiler. As the sample, three types of plain paper (plain paper A, plain paper B, plain paper C) and glossy paper having different smoothness were used. Plain paper A is plain paper with Oken-type smoothness of 33 seconds, plain paper B is plain paper with Oken-style smoothness of 50 seconds, and plain paper C has Oken-style smoothness of 100. It is plain paper for seconds.

  FIG. 13 shows that the contrast ratio of the speckle pattern tends to decrease as the number of light emitting portions increases. It can also be seen that this tendency does not depend on the paper type.

  The inventors also conducted an experiment to confirm that the effect of reducing the contrast ratio of the speckle pattern was not due to an increase in the total light amount, but due to an increase in the number of light emitting portions (FIG. 14). reference).

  FIG. 14 shows a case where the light amount of each light emitting unit is constant (1.66 mW) and the number of light emitting units is changed, and a case where the number of light emitting units is fixed to 30 and the light amount of each light emitting unit is changed. The change of the contrast ratio with respect to the total light quantity is shown.

  When the light quantity of each light emitting part is changed with the number of light emitting parts fixed, the contrast ratio is constant regardless of the light quantity, whereas when the number of light emitting parts is changed, the contrast is reduced when the light quantity is low, that is, when the number of light emitting parts is small. The ratio is large, and the contrast ratio decreases as the number of light emitting portions increases. From this, it can be confirmed that the effect of reducing the contrast ratio of the speckle pattern is not due to an increase in the amount of light but due to an increase in the number of light emitting portions.

  In addition, the inventors examined whether or not the speckle pattern can be suppressed by temporally changing the wavelength of light emitted from the light source.

  In a surface emitting laser (VCSEL), the wavelength of emitted light can be controlled by a drive current. This is because when the drive current changes, the refractive index changes due to heat generation in the surface emitting laser, and the effective resonator length changes.

  FIG. 15 shows a light intensity distribution obtained by observing a speckle pattern with a beam profiler when the emitted light quantity is changed from 1.4 mW to 1.6 mW by changing the driving current of the light source. From FIG. 15, it can be confirmed that the wavelength of light emitted from the light source changes and the light intensity distribution changes as the drive current changes.

  FIG. 16 shows an effective light intensity distribution when the drive current is changed at high speed. This light intensity distribution is equivalent to the average value of the light intensity distributions at a plurality of drive currents shown in FIG. 15, and fluctuations in the light intensity are suppressed. In this way, the contrast ratio of the speckle pattern when the driving current is changed is 0.72, which is lower than the contrast ratio of 0.96 when the driving current is constant.

  Therefore, if the drive current of the surface emitting laser is set to a drive current whose current value changes with time, for example, like a triangular wave shape, the contrast ratio can be reduced. In the present embodiment, as shown in FIG. 3, the light source 11 of the optical sensor 2245 includes a surface emitting laser array in which nine light emitting units are two-dimensionally arranged, and the CPU of the printer control device 2090 has a triangular wave shape. Is supplied to the surface emitting laser array. As a result, the speckle pattern is suppressed, and an accurate amount of reflected light can be detected. And the identification accuracy of a paper can be improved. That is, it was found that the speckle pattern is suppressed by changing the wavelength of the emitted light with time.

  Moreover, in the said embodiment, as for the some light emission part in a surface emitting laser array, at least one light emission part space | interval may differ from other light emission part space | intervals (refer FIG. 17). In this case, the regularity of the speckle pattern is disturbed, and the contrast ratio of the speckle pattern can be further reduced. That is, it is preferable that the intervals between adjacent light emitting portions are different.

  Furthermore, by using the surface emitting laser array, the adjustment for making the irradiation light parallel light becomes easy, and it becomes possible to reduce the size and cost of the optical sensor.

  Further, as in Modification 1 shown in FIG. 18, the light receiving element 130 may be added to the above embodiment. The light receiving element 130 is arranged in a regular reflection direction (a direction in which regular reflected light is incident). Here, the angle ψ2 formed by the line L2 connecting the illumination center and the center of the light receiving element 130 and the surface of the sheet is set to 170 °.

  The light receiving element 130 receives regular reflection light, multiple diffuse reflection light, internal diffuse reflection light, and ground reflection light. The light receiving element 130 outputs an electric signal (photoelectric conversion signal) corresponding to the amount of received light to the paper specifying unit 20. Here, the signal level for each background of the signal level S02 in the output signal of the light receiving element 130 when the light beam from the light source 11 is irradiated onto the paper (the signal level in the white region 15a, the signal level in the black region 15b). , And a calculated value such as a difference between them is stored in advance in the ROM of the paper specifying means 20 as a paper brand discriminating table and used for specifying the brand of the paper.

  According to the first modification, since the brand of the paper can be specified based on the signal levels S01 and S02, the brand of the paper can be specified more accurately.

  Further, as in the second modification shown in FIG. 19, the light receiving element 230 may be added to the first modification. The light receiving element 230 is arranged in the diffusing direction (the direction in which the regular reflection light is not incident). Here, the angle ψ3 formed between the line L3 connecting the illumination center and the center of the light receiving element 230 and the surface of the sheet is 120 °.

  The light receiving element 230 receives diffuse reflected light, multiple diffuse reflected light, internal diffuse reflected light, and ground reflected light. The light receiving element 230 outputs an electrical signal (photoelectric conversion signal) corresponding to the amount of received light to the paper specifying unit 20. Here, the signal level for each background of the signal level S03 in the output signal of the light receiving element 230 when the light beam from the light source 11 is irradiated onto the paper (the signal level in the white region 15a, the signal level in the black region 15b). , And a calculated value such as a difference between them is stored in advance in the ROM of the paper specifying means 20 as a paper brand discriminating table, and is used for specifying the brand of the paper.

  According to the second modification, since the brand of the paper can be specified based on the signal levels S01, S02, and S03 (for example, based on S1 and S3 / S2), the brand of the paper can be specified more accurately.

  Further, as in the third modification shown in FIG. 20, the polarizing filter 140 and the light receiving element 330 may be added to the second modification. The polarizing filter 140 is disposed in the diffusing direction (the direction in which regular reflection light is not incident). The light receiving element 330 is disposed on the optical path of the light beam through the polarizing filter 140. Similar to the polarizing filter 14, the polarizing filter 140 is a polarizing filter that transmits P-polarized light and shields S-polarized light.

  The light receiving element 330 is arranged on an extension of a line connecting the illumination center and the center of the polarizing filter 140. Here, an angle ψ4 formed by the line L4 connecting the illumination center and the centers of the polarizing filter 140 and the light receiving element 330 and the surface of the sheet is set to 150 °.

  Multiple diffuse reflected light, internal diffuse reflected light, and ground reflected light are incident on the light receiving element 330. The light receiving element 330 outputs an electrical signal (photoelectric conversion signal) corresponding to the amount of received light to the paper specifying unit 20. Hereinafter, the signal level in the output signal of the light receiving element 330 when the light beam from the light source 11 is irradiated onto the paper is referred to as “S04”.

  In addition, the internal diffuse reflection light and the ground reflection light are isotropic reflection light and can be approximated to a Lambertian distribution, so that the reflected light of the polarization component orthogonal to the polarization direction of the irradiation light as the light receiving direction becomes parallel to the paper surface. Of these, the ratio of the internal diffuse reflected light and the ground reflected light is considered to be relatively reduced. That is, S04 in Modification 3 has a larger component occupied by multiple diffused reflected light than S01 detected in the direction perpendicular to the paper surface.

  In S04, the signal level for each background (the signal level in the white area 15a, the signal level in the black area 15b) and the calculated values such as the difference between them are stored in advance in the ROM of the sheet specifying means 20 as a sheet brand discrimination table. Used to specify the brand of paper.

  According to the third modification, the brand of the paper can be identified based on the signal levels S01, S02, S03, and S04 (for example, based on S4 / S1, S3 / S2), so that the brand of the paper can be identified even more accurately. it can.

  Further, at least one detection system including at least a light receiving element may be added to Modification 3.

  In this case, the cost increases as the number of detection systems increases, but the accuracy of identifying the brand of the paper can be improved. For this reason, for example, it is preferable to increase or decrease the number of detection systems in accordance with the number of classified paper brands. Specifically, it is preferable to increase the number of detection systems as the number of paper brands increases.

  Further, the brand of the paper may be specified while the paper is being conveyed. Specifically, for example, instead of the optical sensor, the reflective member may be moved in the X-axis direction to detect reflected light on a white background and reflected light on a black background.

  Further, for example, as in Modification 4 shown in FIG. 21, a roller 150a having two regions with different reflectivities arranged along the circumferential direction may be used as the reflecting member. As an example, one side of the roller 150a in the direction orthogonal to the axial direction (Y-axis direction) is the white region 150a, and the other side is the black region 150b. In this case, the white background and the black background are switched by the rotation of the roller 150 as the paper is conveyed.

  Further, for example, as in Modification 5 illustrated in FIG. 22, the optical sensor may include two systems including the light source 11, the collimating lens 12, the polarization filter 14, and the light receiving element 13. The two systems may be individually fixed at positions corresponding to the white area 15 a and the black area 15 b of the reflecting member 15, and the paper may be positioned between each system and the reflecting member 15. In this case, the irradiation means including two irradiation systems can irradiate the S-polarized light in parallel or in time series on the portion of the paper that contacts the white region 15a and the black region 15b, and includes two detection systems. The detection means can detect the P-polarized light reflected by the paper and the white region 15a and the P-polarized light reflected by the paper in parallel or in time series. In this case, irradiation and detection may be performed while the sheet is being conveyed, or irradiation and detection may be performed while the sheet is stopped.

  In Modification 5, the optical sensor has two light sources, but the present invention is not limited to this. For example, the optical sensor has one light source, splits the light from the light source into two lights, and splits the split light into a portion on the white area 15a of the paper and a black area 15b of the paper. You may make it irradiate a part.

  In the above embodiment and each modified example, the optical sensor is disposed in the vicinity of the paper conveyance path, but is not limited thereto. For example, it may be arranged at a position facing the paper stored in the paper feed tray 2060. However, in this case, a mechanism for inserting the uppermost paper between the dark box and the reflecting plate is required. The optical sensor may be externally attached to the housing of the color printer 2000. In this case, after the paper brand is specified by the optical sensor, the paper may be conveyed to the paper feed tray 2060.

  In the above-described embodiment and each modified example, the optical sensor is disposed in the vicinity of the sheet conveyance path between the paper feed tray 2060 and the registration roller pair 2056, but between the paper feed tray 2060 and the registration roller pair 2056. It may be arranged in the vicinity of the paper conveyance path other than the interval.

  Moreover, although the said embodiment and each modification demonstrated the case where the light source 11 had a some light emission part, it is not limited to this, The light source 11 may have one light emission part.

  In the above embodiment, a conventional LD (Laser Diode) may be used instead of the surface emitting laser array. However, in this case, a polarizing filter is required to change the irradiation light to S-polarized light or P-polarized light.

  Moreover, in the said embodiment and each modification, you may arrange | position a condensing lens in the front | former stage of each light receiving element. In this case, variations in signal level detection can be reduced. The reproducibility of detection is important for an optical sensor that discriminates a sheet based on the amount of reflected light. In the optical sensor, a detection system is installed on the assumption that the light receiving surface of the light receiving element and the surface of the paper are parallel during detection. However, the paper surface may be tilted or lifted with respect to the light receiving surface due to deflection or vibration, and the paper surface may not be parallel to the light receiving surface. In this case, the amount of reflected light changes and it is difficult to make a stable and detailed determination. Therefore, by arranging the condensing lens in front of the light receiving element so that the light receiving element can reliably detect the reflected light, the light can be reliably collected even when the reflected light intensity distribution changes.

  In addition, by using a photodiode (PD) having a sufficiently large light receiving area for the light receiving element, or by narrowing the beam diameter of the irradiation light, it is possible to eliminate the inconvenience when the paper surface is not parallel to the light receiving surface. . Further, a PD having an array of light receiving elements may be used to have a light receiving region that is sufficiently large with respect to the amount of movement of the reflected light intensity distribution. In this case, even if the reflected light intensity distribution is moved, the maximum signal among the signals detected by the PDs may be set as a regular reflected light signal. In addition, when PDs are arrayed, by reducing the light receiving area of each PD, output fluctuations due to misalignment between the center of the regular reflected light and the light receiving area can be reduced, so that more accurate detection can be performed. it can.

  Moreover, although the said embodiment and each modification demonstrated the case where incident angle (theta) of irradiation light was 80 degrees, it is not limited to this. However, the incident angle θ is preferably as large as possible. This is because S-polarized light and P-polarized light have a high reflectance at a large incident angle according to the Fresnel coefficient, and it is easy to obtain each signal level at the time of detection, which is advantageous from the viewpoint of the S / N ratio.

  In the above-described embodiment and each modification, the case where there is one paper feed tray has been described. However, the present invention is not limited to this, and a plurality of paper feed trays may be provided. In this case, an optical sensor may be provided for each paper feed tray.

  Moreover, in the said embodiment and each modification, although the reflection member has two area | regions where reflectances mutually differ, it is not restricted to this. For example, the reflecting member may have three or more regions having different reflectivities. In short, the reflecting member only needs to have a plurality of regions having different reflectivities. And it is preferable to irradiate the part on each area | region of a paper, and to detect reflected light.

  Moreover, in the said embodiment and each modification, although the paper specific | specification means 20 specifies the brand of this paper based on the basic weight or thickness of a paper, the important thing is to at least one of the basic weight and thickness of a paper. It is preferable to specify the brand of the paper based on the basis.

  In the embodiment and each modification, the light receiving element may output an electric signal (photoelectric conversion signal) corresponding to the amount of received light to, for example, a printer control device. Then, the printer control device may specify the brand of the paper. The paper brand discrimination table may be stored in the ROM of the printer control device 2090. In this case, the optical sensor may not have the sheet specifying means.

  Further, in the above-described embodiment and each modification, for example, a guide member for guiding the leading edge of the sheet to the gap between the dark box and the reflecting member may be provided at the corners on the −X side and the −Z side of the dark box.

  In addition, the object specified using the optical sensor is not limited to paper, and in short, it may be a sheet-like object.

  Further, in the above embodiment and each modification, the case of the color printer 2000 has been described as the image forming apparatus. However, the present invention is not limited to this, and may be, for example, an optical plotter or a digital copying apparatus.

  In the above-described embodiment and each modified example, the case where the image forming apparatus has four photosensitive drums has been described. However, the present invention is not limited to this. Specifically, the image forming apparatus may be a color printer having, for example, five or more photosensitive drums, or may be a monochrome printer having one photosensitive drum, for example.

  In addition, the optical sensors of the above-described embodiments and modifications can be applied to an image forming apparatus that forms an image by spraying ink on paper.

  Moreover, the optical sensor of the said embodiment and each modification is applicable also to the technical field which measures the thickness of a sheet-like target object, for example.

  DESCRIPTION OF SYMBOLS 11 ... Light source (a part of irradiation means), 12 ... Collimating lens (a part of irradiation means), 13 ... Light receiving element (a part of detection means, 1st photodetector), 14 ... Polarizing filter (of a detection means) 15 ... reflecting member, 15a ... white region (first region), 15b ... black region (second region), 19 ... actuator (moving means), 140 ... polarizing filter (separate) , 130... Light receiving element (second light detector), 230... Light receiving element (third light detector), 330... Light receiving element (fourth light detector), 2000. Image forming apparatus), 2090... Printer control apparatus (adjustment apparatus), 2245.

JP 2005-156380 A Japanese Patent No. 4067671 JP 2012-127937 A

Claims (20)

A reflective member including first and second regions having different reflectivities with which one surface of a sheet-like object can contact;
When at least the one surface is in contact with the first region, the first linearly polarized light is applied to a portion corresponding to the first region on the other surface of the object with respect to the normal direction of the other surface. Irradiating in an inclined state, and at least the one surface and the second region are in contact with each other, the first linearly polarized light is applied to the portion corresponding to the second region on the other surface. Irradiating means for irradiating in a state inclined with respect to the direction;
Of the light reflected by the portion corresponding to the first region of the object and the light transmitted through the portion and reflected by the first region, the polarization direction is orthogonal to the first linearly polarized light. While detecting the second linearly polarized light, out of the light reflected by the portion corresponding to the second region of the object and the light transmitted through the portion and reflected by the second region, the second Detecting means for detecting the linearly polarized light.   The detecting means separates the light reflected by the object and the reflecting member into the first linearly polarized light and the second linearly polarized light, and the second from the separated optical element. The optical sensor according to claim 1, further comprising: a first photodetector that receives the linearly polarized light.   The optical sensor according to claim 2, further comprising a means for relatively moving the irradiating means and at least a part of the reflecting member in a direction along at least the one surface or the other surface.   When the one surface and both the first and second regions are in contact with each other, the irradiation means corresponds to the first region on the other surface and the second region on the other surface. 3. The optical sensor according to claim 2, wherein the first linearly polarized light can be irradiated in parallel to a portion corresponding to.   5. The optical sensor according to claim 2, wherein the separation optical element is disposed on an optical path of light diffusely reflected by the object in the normal direction.   The optical sensor according to any one of claims 2 to 5, further comprising a target specifying unit that specifies the target based on at least a detection result of the first photodetector.   The optical sensor according to claim 6, wherein the object specifying unit specifies a brand of the object from a plurality of brands classified according to at least one of basis weight and thickness. The detection means further includes a second photodetector that receives light specularly reflected by the object,
8. The optical sensor according to claim 6, wherein the object specifying unit specifies the object based on detection results of the first and second photodetectors. The detection means further includes a third photodetector that receives light diffusely reflected by the object in a direction inclined with respect to the normal direction.
The optical sensor according to claim 8, wherein the object specifying unit specifies the object based on detection results of the first to third photodetectors. The detection means is disposed on an optical path of light diffusely reflected by the object in a direction inclined with respect to the normal direction, and the light is converted into the first linearly polarized light and the second linearly polarized light. Another separating optical element for separating;
A fourth photodetector for detecting the second linearly polarized light from the another separating optical element;
The optical sensor according to claim 9, wherein the object specifying unit specifies the object based on detection results of the first to fourth photodetectors.   The optical sensor according to claim 6, wherein the irradiation unit includes a surface emitting laser array having a plurality of light emitting units arranged two-dimensionally.   The optical sensor according to claim 11, wherein the plurality of light emitting units have at least some light emitting unit intervals different from other light emitting unit intervals in one direction.   The optical sensor according to claim 11, further comprising a mechanism that temporally changes a wavelength of light emitted from the surface emitting laser array.   The mechanism is characterized by temporally changing the wavelength of light emitted from the surface emitting laser array by temporally changing the magnitude of a drive current supplied to the surface emitting laser array. 14. The optical sensor according to 13. In an image forming apparatus for forming an image on a recording medium,
An image forming apparatus comprising the optical sensor according to claim 6, wherein the recording medium is an object.   The image forming apparatus according to claim 15, further comprising an adjusting device that adjusts an image forming condition in accordance with an object specified by the object specifying unit of the optical sensor. An object specifying method for specifying a sheet-like object,
One surface of the object is brought into contact with the first region of the reflecting member, and the first linearly polarized light is applied to a portion corresponding to the first region on the other surface of the object with respect to the normal direction of the other surface. And the second surface on the other surface of the object is brought into contact with the second surface of the reflecting member that is different in reflectance from the first region. Irradiating a portion corresponding to a region with the first linearly polarized light in a state inclined with respect to the normal direction;
Of the light reflected by the portion corresponding to the first region of the object and the light transmitted through the portion and reflected by the first region, the polarization direction is orthogonal to the first linearly polarized light. Detecting the second linearly polarized light, and out of the light reflected by the portion corresponding to the second region of the object and the light transmitted through the portion and reflected by the second region. Detecting the two linearly polarized light. The detecting step includes a sub-step of separating light reflected by the object and the reflecting member into the first linearly polarized light and the second linearly polarized light;
The object specifying method according to claim 17, further comprising a sub-step of receiving the second linearly polarized light.   19. The object specifying method according to claim 18, further comprising a step of specifying the object based on a received light amount in the light receiving sub-step.   The object identification according to claim 19, wherein in the step of identifying the object, a brand of the object is identified from a plurality of brands classified according to at least one of basis weight and thickness. Method.

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