JP2016042102A - Optical sensor and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sensor that can specify an object in more detail than a conventional one without causing an increase in cost and size.SOLUTION: An optical sensor includes a light source 11, collimating lens 12, photodetector 13, polarization filter 14, photodetector 17, and a black box that accommodates these components. The photodetector 13 receives a p-polarization component included in internal diffused reflection light, the photodetector 17 is arranged to receive diffused reflection light. In this case, the brand of a recording sheet can be specified from an output signal of the photodetector 13 and an output signal of the photodetector 17.SELECTED DRAWING: Figure 17

Description

  The present invention relates to an optical sensor and an image forming apparatus, and more particularly to an optical sensor suitable for specifying an object and an image forming apparatus including the optical sensor.

  An image forming apparatus such as a digital copying machine or a laser printer transfers a toner image onto the surface of a recording medium represented by printing paper and heats and presses it under predetermined conditions to fix the image and form an image. Yes. It is the heating amount and pressure conditions during fixing that must be taken into consideration in image formation. In particular, in order to perform high-quality image formation, it is necessary to individually set the fixing 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 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 order to form a high-quality image, it is necessary to set fine fixing 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 current image forming apparatuses, the user himself / herself has to set fixing conditions at the time of printing. For this reason, the user is required to have knowledge for identifying the paper type, and the user has to input the setting contents corresponding to the paper type by himself / herself. If the setting contents are incorrect, an optimum image cannot be obtained.

  By the way, Patent Document 1 discloses a surface property identification device provided with a sensor that identifies the surface property of the surface of the recording material by contacting and scanning the surface of the recording material.

  Patent Document 2 discloses a printing apparatus that determines a paper type from a pressure value detected by a pressure sensor contacting a paper.

  Patent Document 3 discloses a recording material discriminating apparatus that discriminates the type of recording material using reflected light and transmitted light.

  Patent Document 4 discloses a sheet material material discriminating apparatus that discriminates the material of a moving sheet material on the basis of a reflected light amount reflected from the surface of the sheet material and a transmitted light amount transmitted through the sheet material.

  Patent Document 5 discloses an image forming apparatus having a determining unit that determines the presence / absence of a recording material accommodated in a paper feeding unit and the presence / absence of a paper feeding unit based on a detection output from a reflective optical sensor. Yes.

  Patent Document 6 discloses an image forming apparatus that irradiates a recording medium with light and detects the amounts of two polarization components of the reflected light to discriminate the surface property of the recording medium.

  However, the recording material discriminating apparatus disclosed in Patent Document 3 can discriminate only recording materials having different smoothness, and cannot distinguish recording materials having the same smoothness but different thicknesses.

  Further, in the sheet material material discrimination device disclosed in Patent Literature 4 and the image forming devices disclosed in Patent Literature 5 and Patent Literature 6, it is possible to distinguish (discriminate) from uncoated paper, coated paper, and OHP. The only difference was the sheet, and it was not possible to identify the brands necessary for high-quality image formation.

  From the first viewpoint, the present invention irradiates the surface of the sheet-like object with linearly polarized light in the first polarization direction from an incident direction inclined with respect to the normal direction of the surface; A first photodetector arranged on an optical path of light diffusely reflected in the first direction by the object; and an optical path of light diffusely reflected by the object in a second direction. A linearly polarized light component having a second polarization direction orthogonal to the first polarization direction on at least an optical path between the first photodetector and the object. It is an optical sensor in which an optical element leading to the first photodetector is arranged.

  According to a second aspect of the present invention, there is provided an image forming apparatus for forming an image on a recording medium, comprising the optical sensor of the present invention having the recording medium as an object.

  According to the optical sensor of the present invention, an object can be specified more finely than before without causing an increase in cost and size.

  According to the image forming apparatus of the present invention, it is possible to form a high-quality image without increasing the cost and size.

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. It is a figure for demonstrating the incident angle of the incident light to a recording paper. It is a figure for demonstrating the arrangement position of two light receivers. 6A is a diagram for explaining surface regular reflection light, FIG. 6B is a diagram for explaining surface diffuse reflection light, and FIG. 6C is a diagram explaining internal diffuse reflection light. It is a figure for doing. It is a figure for demonstrating the light received with each light receiver. It is a figure for demonstrating the relationship between S1 and S2 and the brand of a recording paper. 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 modification of an optical sensor. 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 light intensity distribution of a speckle pattern when a light emission part space | interval is equal intervals. It is a figure for demonstrating the light intensity distribution of a speckle pattern when the light emission part space | interval is not equal intervals. It is FIG. (1) for demonstrating the modification 1 of an optical sensor. It is FIG. (2) for demonstrating the modification 1 of an optical sensor. It is FIG. (1) for demonstrating the modification 2 of an optical sensor. It is FIG. (2) for demonstrating the modification 2 of an optical sensor. It is FIG. (1) for demonstrating the modification 3 of an optical sensor. It is FIG. (2) for demonstrating the modification 3 of an optical sensor. It is a figure for demonstrating the relationship between S4 / S1 and S3 / S2, and the brand of a recording paper. FIG. 24A and FIG. 24B are diagrams for explaining the influence of disturbance light, respectively. It is a figure for demonstrating the modification 4 of an optical sensor. It is a figure for demonstrating the modification 5 of an optical sensor. FIGS. 27A to 27C are diagrams for explaining the change in the detected light amount due to the deviation between the measurement surface and the recording paper surface. It is a figure for demonstrating the relationship between thickness and S1. It is a figure for demonstrating the relationship between a density and S1.

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

  The color printer 2000 is a tandem multi-color printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes an optical scanning device 2010, four photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), 4 Toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing device 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 2 60, the discharge 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.

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

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

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

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

  As shown in FIG. 2 as an example, the optical sensor 2245 includes a light source 11, a collimating lens 12, two light receivers (13, 15), a polarizing filter 14, and a dark box 16 in which these are stored. Yes.

  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.

  Here, in the XYZ three-dimensional orthogonal coordinate system, the direction orthogonal to the surface of the recording paper is described as the Z-axis direction, and the plane parallel to the surface of the recording paper is described as the XY plane. The optical sensor 2245 is assumed to be disposed on the + Z side of the recording paper.

  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.

  The light source 11 is disposed so that the recording paper is irradiated with S-polarized light. Further, the incident angle θ (see FIG. 4) of the light beam from the light source 11 to the recording paper is 80 °. In FIG. 4, the dark box 16 is not shown for easy understanding.

  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 passing through the collimating lens 12 passes through an opening provided in the dark box 16 and illuminates the recording paper. In the following, the center of the illumination area on the surface of the recording 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 incident surface of the light beam incident on the illumination center is referred to as an incident surface on the recording paper. To do. That is, the plane including the illumination center and parallel to the XZ plane is the incident plane on the recording 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 beam splitter having an equivalent function may be used.

  The light receiver 13 is disposed on the + Z side of the polarizing filter 14. Here, as shown in FIG. 5, the angle ψ1 formed by the line L1 connecting the illumination center and the centers of the polarizing filter 14 and the light receiver 13 and the surface of the recording paper is 90 °.

  The light receiver 15 is disposed on the + X side of the illumination center with respect to the X-axis direction. The angle ψ2 formed by the line L2 connecting the illumination center and the center of the light receiver 15 and the surface of the recording paper is 170 °.

  The center of the light source 11, the center of illumination, the center of the polarizing filter 14, the center of the light receiver 13, and the center of the light receiver 15 exist on substantially the same plane.

  By the way, the reflected light from the recording paper when the recording paper is illuminated can be divided into reflected light reflected on the surface of the recording paper and reflected light reflected inside the recording paper. Further, the reflected light reflected on the surface of the recording paper can be divided into specularly reflected light and diffusely reflected light. Hereinafter, for convenience, the reflected light that is regularly reflected on the surface of the recording paper is also referred to as “surface regular reflected light”, and the reflected light that is diffusely reflected is also referred to as “surface diffuse reflected light” (FIGS. 6A and 6B). )reference).

  The surface of the recording paper is composed of a flat surface portion and an inclined surface portion, and the smoothness of the recording paper surface is determined by the ratio. The light reflected by the plane portion becomes surface regular reflection light, and the light reflected by the slope portion becomes surface diffuse reflection light. The surface diffuse reflection light is reflected light that is completely scattered and reflected, and the reflection direction can be considered to be isotropic. And the light quantity of surface regular reflection light increases, so that smoothness becomes high.

  On the other hand, when the recording paper is a general printing paper, the reflected light from the inside of the recording paper is scattered only in the fibers inside the recording paper and thus becomes only the diffuse reflected light. Hereinafter, for convenience, reflected light from the inside of the recording paper is also referred to as “internal diffuse reflected light” (see FIG. 6C). Similar to the surface diffuse reflection light, the internal diffuse reflection light is also a reflection light that has been completely scattered and reflected, and the reflection direction can be considered to be isotropic.

  The polarization direction of the surface regular reflection light and the surface diffuse reflection light is the same as the polarization direction of the incident light. By the way, in order for the polarization direction to rotate on the surface of the recording paper, incident light must be reflected by a surface inclined in the direction of rotation with respect to the optical axis. Here, since the center of the light source, the center of illumination, and the center of each light receiver are on the same plane, the reflected light whose polarization direction is rotated on the surface of the recording paper is not reflected in the direction of any light receiver.

  On the other hand, the polarization direction of the internally diffuse reflected light is rotated with respect to the polarization direction of the incident light. This is presumably because the light passes through the fiber and rotates during multiple scattering, and the polarization direction rotates.

  Therefore, the surface diffuse reflection light and the internal diffuse reflection light are incident on the polarizing filter 14. Since the polarization direction of the surface diffuse reflection light is the same S polarization as the polarization direction of the incident light, the surface diffuse reflection light is shielded by the polarization filter 14. On the other hand, since the polarization direction of the internal diffuse reflection light is rotated with respect to the polarization direction of the incident light, the P-polarized component included in the internal diffuse reflection light is transmitted through the polarization filter 14. That is, the P polarization component contained in the internally diffuse reflected light is received by the light receiver 13 (see FIG. 7).

  The inventors have confirmed that the amount of P-polarized light component contained in the internally diffuse reflected light has a correlation with the thickness and density of the recording paper. This is because the light amount of the P-polarized component depends on the path length when passing through the fibers of the recording paper.

  Only a part of the surface regular reflection light, the surface diffuse reflection light and the internal diffuse reflection light is incident on the light receiver 15. That is, the surface regular reflection light is mainly incident on the light receiver 15.

  The light receiver 13 and the light receiver 15 each output an electrical signal (photoelectric conversion signal) corresponding to the amount of received light to the printer control device 2090. In the following description, the signal level in the output signal of the light receiver 13 and the signal level in the output signal of the light receiver 15 when the light beam from the light source 11 is irradiated onto the recording paper are referred to as “S2”.

  Here, for a plurality of brands of recording paper that can be handled by the color printer 2000, the values of S1 and S2 are measured in advance for each brand of the recording paper in a pre-shipment process such as an adjustment process, and the measurement result is recorded as a “recording paper discrimination table. Is stored in the ROM of the printer control device 2090. FIG. 8 shows the measured values of S1 and S2 for 30 brands of recording paper sold in the country. The frame in FIG. 8 shows the range of variation of the same brand. For example, if the measured values of S1 and S2 are “◇”, it is identified as a brand D. Further, if the measured values of S1 and S2 are “■”, the closest brand C is identified. Further, if the measured values of S1 and S2 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.

  Conventionally, the recording paper surface glossiness is detected from the amount of specularly reflected light, and the recording paper surface smoothness is detected from the ratio of the amount of specularly reflected light and the amount of diffusely reflected light to identify the recording paper. . In contrast, in the present embodiment, not only the glossiness and smoothness of the surface of the recording paper but also information including the thickness and density, which are other characteristics of the recording paper, is detected from the reflected light and can be identified. The type of is expanded more than before.

  For example, it is difficult to distinguish between plain paper and mat-coated paper only by the information on the surface of the recording paper used in the conventional identification method. In this embodiment, by adding information inside the recording paper to the information on the surface of the recording paper, not only distinction between plain paper and matte coated paper, but also distinction between plural brands of plain paper and plural brands of matte coated paper, respectively. It became possible to do.

  That is, in the present embodiment, it is possible to specify the brand of the object from a plurality of recording papers having at least one of glossiness, smoothness, thickness, and density.

  In addition, regarding multiple brands of recording paper that can be handled by the color printer 2000, the optimum development conditions and transfer conditions at each station are determined for each brand of recording paper in the pre-shipment process such as the adjustment process, and the results of the determination are determined. It is stored in the ROM of the printer controller 2090 as a “development / transfer table”.

  The printer control device 2090 performs a paper type discrimination process for the recording paper when the color printer 2000 is turned on and when the recording paper is supplied to the paper feed tray 2060. The paper type discrimination process performed by the printer controller 2090 will be described below.

(1) The plurality of light emitting units of the optical sensor 2245 are turned on simultaneously.
(2) The values of S1 and S2 are obtained from the output signals of the light receiver 13 and the light receiver 15.
(3) With reference to the recording paper discrimination table, the brand of the recording paper is specified from the obtained values of S1 and S2.
(4) The brand of the specified recording paper is stored in the RAM, and the paper type discrimination process is terminated.

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

  Then, the printer control device 2090 controls the developing device and the transfer device at each station in accordance with the optimum development conditions and transfer conditions. For example, the transfer voltage and the toner amount are controlled. Thereby, a high quality image is formed on the recording paper.

  Here, a method for suppressing the speckle pattern will be described.

  When a semiconductor laser is used as the light source of the sensor that detects the surface state of the recording paper from the amount of reflected light, the coherent light emitted from the semiconductor laser is diffusely reflected and interfered at each point on the rough surface such as the surface of the recording paper. As a result, a speckle pattern is generated.

  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 determined the relationship between the number of light emitting portions and the contrast ratio of the speckle pattern (see FIG. 9). 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 Y-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. 9 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. 10). reference).

  FIG. 10 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. 11 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 drive current of the light source 11. . From FIG. 11, it can be confirmed that the wavelength of the light emitted from the light source 11 changes and the light intensity distribution changes with the change of the drive current.

  FIG. 12 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. 11, and the fluctuation of the light intensity is 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, 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 outputs a triangular wave driving current to the surface-emitting laser array. To supply. As a result, the speckle pattern is suppressed, and an accurate amount of reflected light can be detected. Further, the recording paper identification accuracy can be increased. That is, it was found that the speckle pattern is suppressed by changing the wavelength of the emitted light with time.

  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.

  By the way, it has been confirmed that the light amount of the P-polarized component contained in the internally diffuse reflected light is very small with respect to the light amount (irradiation light amount) of the light irradiated on the recording paper. For example, when the incident angle θ is 80 °, the light amount of the diffuse reflected light is about four orders of magnitude smaller than the irradiation light amount, and the light amount of the P-polarized component contained in the internal diffuse reflected light is further less than half thereof.

  Therefore, in order to accurately detect the P-polarized light component contained in the internally diffuse reflected light, the output of the light source is increased and the P-polarized light component contained in the internally diffuse reflected light is accurately received under the light receiving condition that maximizes the detection amount. It is desirable to receive light.

  In order to receive the P-polarized component contained in the internally diffuse reflected light accurately and with the maximum detection amount, the following is important.

(1) The detection of the P-polarized component contained in the internally diffuse reflected light is not performed at least in the direction in which the surface regular reflected light is included.

  This is because, in practice, it is difficult to completely irradiate the irradiation light with only the S-polarized light, and the reflected light on the surface also includes the P-polarized light component. For this reason, in the direction in which the surface regular reflection light is included, the P polarization component originally included in the irradiation light and reflected by the surface is larger than the P polarization component included in the internal diffuse reflection light. Therefore, if the polarizing filter 14 and the light receiver 13 are arranged in a direction in which the surface regular reflection light is included, the amount of reflected light including information inside the recording paper cannot be accurately detected.

  By the way, it is conceivable to use a polarizing filter with a high extinction ratio in order to completely irradiate the irradiating light with only S-polarized light, but this leads to an increase in cost.

(2) The P-polarized component contained in the internally diffuse reflected light is detected in the normal direction of the illumination center of the recording paper.

  This is because the internal diffuse reflection light can be regarded as complete diffuse reflection, so that the reflected light amount with respect to the detection direction can be approximated by a Lambertian distribution, and the reflected light amount is the largest in the normal direction of the illumination center. When the polarizing filter 14 and the light receiver 13 are arranged in the normal direction of the illumination center, the S / N is high and the accuracy is the highest.

  From the above, the conventional technology is reviewed as follows.

  In the sheet material material discrimination device disclosed in Patent Document 4, the discrimination is performed based on the amount of regularly reflected light. That is, the material of the sheet material is determined only from the absolute light quantity of the regular reflection light without considering the inside of the object.

  In the image forming apparatus disclosed in Patent Document 5, the amount of reflected light from the object is detected in a plurality of directions. Also in this case, the glossiness is detected from the ratio of the regular reflection light and the diffuse reflection light without considering the inside of the object, and the paper type is determined.

  In the image forming apparatus disclosed in Patent Document 6, specularly reflected light is detected by being divided into two polarization components, the smoothness of the surface of the paper is obtained from the difference between the light amounts, and the paper type is determined. In this case, although polarized light is used, it is detected in a direction including specularly reflected light, and this also does not consider the inside of the object.

  As described above, conventionally, the non-coated paper, the coated paper, and the OHP sheet are discriminated, and the discrimination at the brand level is impossible.

  The discriminating method for recording paper in the present embodiment is a new discriminating method based on the amount of internal diffused light including information inside the recording paper, which has not been considered so far, in addition to the conventional discriminating method.

  In this case, by increasing the output of the light source and receiving the reflected light at an appropriate position, in addition to the conventional glossiness (smoothness) of the recording paper surface, information on the thickness and density of the recording paper can be obtained. The identification level can be subdivided.

  As is clear from the above description, in the optical sensor 2245 according to this embodiment, the light source 11 and the collimating lens 12 constitute the irradiation system of the present invention, and the light receiver 15 constitutes the first light detection system of the present invention. Thus, the polarizing filter 14 and the light receiver 13 constitute a second light detection system of the present invention.

  The surface property identification device disclosed in Patent Document 1 and the printing device disclosed in Patent Document 2 may damage the surface of the recording material and change the surface characteristics themselves.

  For example, in addition to the reflective optical sensor, various sensors such as a sensor that detects the thickness of the recording material using transmitted light, ultrasonic waves, and the like, a sensor that detects the resistance value of the recording material, and a temperature sensor are included. Although it is possible to further subdivide the identification level by attaching separately, there is a disadvantage that the number of parts increases, resulting in an increase in cost and size.

  By the way, in a sensor that detects the surface state of the printing paper from the amount of reflected light, it is preferable to use a semiconductor laser as a light source in order to improve the S / N. In this case, the light flux is applied to a rough surface such as the surface of the printing paper. Speckle pattern occurs when irradiated. Since the speckle pattern differs depending on the part irradiated with the light beam, it causes variations in the detection light in the light receiving unit, resulting in a decrease in identification accuracy. Therefore, conventionally, an LED or the like has been generally used as a light source.

  As described above, the optical sensor 2245 according to this embodiment includes the light source 11, the collimating lens 12, the light receiver 13, the polarizing filter 14, the light receiver 15, and the dark box 16 in which these are stored. .

  The light receiver 13 receives the P-polarized light component contained in the internally diffuse reflected light, and the light receiver 15 is disposed so as to mainly receive the surface regular reflection light.

  In this case, the brand of the recording paper can be specified from the output signal of the light receiver 13 and the output signal of the light receiver 15.

  As described above, by detecting the light quantity of the P-polarized component contained in the internally diffuse reflected light, it is possible to separate the reflected light from the inside of the recording paper with high accuracy, which was conventionally weak and difficult to separate. It became so. Reflected light from the inside of the recording paper contains information about the internal state of the recording paper, and by taking this into account, the discriminating level of the paper type could be improved to a brand level that was difficult in the past. .

  Moreover, since it is a simple component structure without combining a plurality of types of sensors, a small optical sensor can be realized at low cost.

  Therefore, the brand of the recording paper can be specified more finely than before without causing an increase in cost and size.

  Further, since the surface emitting laser array is used as the light source, a polarizing filter for making the irradiation light linearly polarized light is unnecessary. In addition, since the irradiation light can be easily converted into parallel light, and a light source having a plurality of light emitting units can be realized by downsizing, the downsizing and cost reduction of the optical sensor can be achieved.

  In addition, since the light source has a plurality of light emitting units, the light amount of the P-polarized component contained in the internal diffuse reflected light can be increased by lighting all the light emitting units simultaneously.

  The diffusely reflected light includes A: “S-polarized light reflected by the surface”, B: “S-polarized light reflected internally”, and C: “P-polarized light reflected internally”. Among these, “P-polarized light reflected inside” is separated by a polarizing filter and the amount of light is detected, whereby paper discrimination can be subdivided. However, irradiation with a high amount of light is necessary for the following reasons.

  When the irradiation light is S-polarized light, the ratio of “P-polarized light reflected internally” in the diffuse reflected light (A + B + C) is about 40% at the maximum. By the way, an inexpensive polarizing filter mounted on a general sensor has low transmittance, and is attenuated to about 80% by the polarizing filter. Therefore, “P-polarized light reflected inside” attenuates when separated by the polarization filter, and is substantially about 30%.

  In the conventional sensor, the type of recording paper is specified from about two to three types of recording paper (for example, coated paper, plastic sheet) according to the amount of diffuse reflected light (A + B + C).

  In this embodiment, the type of recording paper is specified from at least 10 types of recording paper only by “P-polarized light reflected internally”. That is, detailed paper discrimination more than five times compared with the conventional two types of recording paper is specified. Therefore, high resolution is required with a smaller amount of light than before. However, if a PD with high resolution is used, it is possible to discriminate even with a low amount of light, but this leads to an increase in cost.

  Therefore, in the present embodiment, high resolution is obtained by increasing the amount of irradiation light. Specifically, as described above, the amount of internal diffuse reflected light is attenuated to about 30% of the diffuse reflected light (A + B + C), and therefore, the irradiation light amount is required to be 3.3 times the conventional light amount. . Furthermore, in order to perform detailed paper discrimination five times that of the prior art, it is necessary to irradiate a light amount of about 3.3 × 5 times that of the prior art. Thus, it is necessary to increase the amount of irradiation light in proportion to specifying many types of recording paper. In this embodiment, in order to irradiate S polarized light, when using a non-polarized light source like LED, it is necessary to make it linearly polarized light (S polarized light) through a polarizing filter before irradiation. At this time, since an inexpensive polarizing filter similar to the above is used, the amount of light applied to the recording paper is about 40% (= 50% (the amount of cut of P-polarized light) × 80% of the amount of light emitted from the LED. (Attenuation by polarizing filter)). Therefore, in the case of an LED light source, an irradiation light amount of 40 times (= 3.3 × 5 ÷ 0.4) or more than before is required. However, the irradiation light quantity of an inexpensive LED is about several mW (typically 1 mW), and it is difficult to secure the irradiation light quantity of at least 40 mW or 50 mW or more. On the other hand, in the surface emitting laser array, it is easy to secure a desired amount of irradiation light by simultaneously lighting a plurality of light emitting units. Therefore, in the surface emitting laser array, it is possible to secure the irradiation light amount necessary for specifying the type of paper more than before.

  In addition, since the light source has a plurality of light emitting units, the contrast ratio of the speckle pattern of the reflected light is higher than when only one light emitting unit is turned on by simultaneously lighting the plurality of light emitting units. It is possible to reduce and improve the discrimination accuracy.

  Furthermore, since a surface emitting laser array is used, more stable linearly polarized light can be irradiated. Thereby, the light quantity of the P-polarized component contained in the internally diffuse reflected light can be detected with high accuracy.

  In addition, since the current whose time value varies with time is the driving current of the surface emitting laser, the contrast ratio of the speckle pattern can be further reduced.

  Further, since the surface emitting laser array is used as the light source, a polarizing filter for making the irradiation light linearly polarized light is unnecessary. In addition, since the irradiation light can be easily converted into parallel light, and a light source having a plurality of light emitting units can be realized by downsizing, the downsizing and cost reduction of the optical sensor can be achieved.

  Since the color printer 2000 according to this embodiment includes the optical sensor 2245, as a result, a high-quality image can be formed without increasing the cost and size. Furthermore, the troublesome printing that has to be manually set and the printing failure due to setting mistakes are eliminated.

  In the above embodiment, the case where the light applied to the recording paper is S-polarized light has been described. However, the present invention is not limited to this, and the light applied to the recording paper may be P-polarized light. However, in this case, a polarizing filter that transmits S-polarized light is used instead of the polarizing filter 14.

  In the above embodiment, when the identification level of the optical sensor 2245 is sufficient to specify the non-coated paper / coated paper / OHP sheet, the polarizing filter 14 is not provided as shown in FIG. May be. By using the surface emitting laser array, it is possible to irradiate the recording paper with a light amount higher than that in the case of a single light emitting unit, so that the S / N in the reflected light amount can be improved and the identification accuracy can be increased.

  Further, by turning on the plurality of light emitting units simultaneously, the contrast ratio of the speckle pattern can be reduced, and the reflected light quantity can be detected more accurately, so that the identification accuracy can be increased.

  Furthermore, when a surface emitting laser array is used, high-density integration, which has been difficult with conventional LEDs or the like, becomes possible. Therefore, since all the laser beams can be concentrated near the optical axis of the collimating lens, it becomes possible to make the plurality of light beams substantially parallel with a constant incident angle, and to easily realize a collimating optical system.

  Moreover, in the said embodiment, as for the some light emission part in a surface emitting laser array, at least one part light emission part space | interval may differ from other light emission part space | intervals (refer FIG. 14). 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.

  FIG. 15 shows a light intensity distribution obtained by observing a speckle pattern with a beam profiler in a light source including a surface emitting laser array in which five light emitting portions are arranged one-dimensionally, with the intervals between the light emitting portions being equal. Has been. In this case, periodic light intensity vibration corresponding to the regularity of the light emitting portion arrangement was confirmed, and the contrast ratio was 0.64.

  Further, in a light source including a surface emitting laser array in which five light emitting portions are arranged one-dimensionally, the specification when the ratio of the intervals between the light emitting portions is irregularly set to 1.0: 1.9: 1.3: 0.7 FIG. 16 shows the light intensity distribution obtained by observing the laser pattern with a beam profiler. In this case, the periodic light intensity vibration is suppressed, and the contrast ratio is 0.56, which is lower than the case of equal intervals.

  Therefore, the speckle pattern can be further suppressed by arranging the light emitting portions in the plurality of light emitting portions at non-equal intervals.

  By the way, when there is a risk of erroneous paper type discrimination due to disturbance light or stray light, the number of light detection systems may be increased.

  For example, as shown in FIG. 17, a light receiver 17 may be further provided. The light receiver 17 is disposed at a position for receiving the surface diffuse reflection light and the internal diffuse reflection light.

  Further, the center of the light source 11, the center of illumination, the center of the polarizing filter 14, the center of the light receiver 13, the center of the light receiver 15 and the center of the light receiver 17 exist on substantially the same plane.

  The angle ψ3 formed by the line L3 connecting the illumination center and the center of the light receiver 17 and the surface of the recording paper is 120 ° (see FIG. 18).

  In this case, a paper type determination process performed by the printer control apparatus 2090 will be described below. In the following, the signal level in the output signal of the light receiver 17 when the light beam from the light source 11 is irradiated onto the recording paper is referred to as “S3”.

(1) The plurality of light emitting units of the optical sensor 2245 are turned on simultaneously.
(2) The values of S1, S2 and S3 are obtained from the output signals of the respective light receivers.
(3) The value of S3 / S2 is obtained.
(4) With reference to the recording sheet discrimination table, the brand of the recording sheet is specified from the obtained values of S1 and S3 / S2.
(5) The brand of the specified recording paper is stored in the RAM, and the paper type discrimination process is terminated.

  In this case, for a plurality of brands of recording paper that can be handled by the color printer 2000, the values of S1 and S3 / S2 are measured in advance for each brand of the recording paper in a pre-shipment process such as an adjustment process, and the measurement result It is stored in the ROM of the printer control device 2090 as a “recording paper discrimination table”.

  Further, for example, as shown in FIG. 19, a polarizing filter 18 and a light receiver 19 may be further provided.

  The polarizing filter 18 is disposed on the optical path of the surface diffuse reflection light and the internal diffuse reflection light. The polarizing filter 18 is a polarizing filter that transmits P-polarized light and shields S-polarized light.

  The light receiver 19 is disposed on the optical path of the light beam that has passed through the polarizing filter 18. Therefore, the light receiver 19 receives the P-polarized component contained in the internally diffuse reflected light.

  The center of the light source 11, the center of illumination, the center of the polarizing filter 14, the center of the light receiver 13, the center of the light receiver 15, the center of the polarizing filter 18, and the center of the light receiver 19 are substantially the same plane. Exists on.

  The angle ψ4 formed by the line L4 connecting the illumination center and the centers of the polarizing filter 18 and the light receiver 19 and the surface of the recording paper is 150 ° (see FIG. 20).

  In this case, a paper type determination process performed by the printer control apparatus 2090 will be described below. In the following, the signal level in the output signal of the light receiver 19 when the light beam from the light source 11 is irradiated onto the recording paper is referred to as “S4”.

(1) The plurality of light emitting units of the optical sensor 2245 are turned on simultaneously.
(2) The values of S1, S2, and S4 are obtained from the output signals of the respective light receivers.
(3) The value of S4 / S1 is obtained.
(4) With reference to the recording paper discrimination table, the brand of the recording paper is specified from the obtained values of S4 / S1 and S2.
(5) The brand of the specified recording paper is stored in the RAM, and the paper type discrimination process is terminated.

  In this case, with respect to a plurality of brands of recording paper that can be handled by the color printer 2000, the values of S4 / S1 and S2 are measured in advance for each brand of the recording paper in a pre-shipment process such as an adjustment process. It is stored in the ROM of the printer control device 2090 as a “recording paper discrimination table”.

  For example, as shown in FIGS. 21 and 22, the light receiver 17, the polarizing filter 18, and the light receiver 19 may be further included. That is, a third light detection system constituted by the light receiver 19 and a fourth light detection system constituted by the polarizing filter 18 and the light receiver 19 may be further provided.

  In this case, a paper type determination process performed by the printer control apparatus 2090 will be described below.

(1) The plurality of light emitting units of the optical sensor 2245 are turned on simultaneously.
(2) The values of S1, S2, S3 and S4 are obtained from the output signals of the respective light receivers.
(3) The values of S4 / S1 and S3 / S2 are obtained.
(4) With reference to the recording sheet discrimination table, the brand of the recording sheet is specified from the obtained values of S4 / S1 and S3 / S2 (see FIG. 23).
(5) The brand of the specified recording paper is stored in the RAM, and the paper type discrimination process is terminated.

  In this case, with respect to a plurality of brands of recording paper that can be handled by the color printer 2000, the S4 / S1 and S3 / S2 values are measured in advance for each brand of the recording paper in a pre-shipment process such as an adjustment process. The result is stored in the ROM of the printer control device 2090 as a “recording paper discrimination table”.

  In this way, a plurality of light receiving systems for detecting diffused light reflected in different directions are provided, and the recording paper is discriminated using a calculated value such as a ratio of detected values in each light receiving system, thereby providing a disturbance. Accurate discrimination is possible even in the presence of light or stray light.

  In this case, the printer control device 2090 may narrow down the paper type roughly using S1 and S2, and specify the brand of the recording paper using S4 / S1 and S3 / S2.

  Here, S4 / S1 is used as the calculation method using S1 and S4, but the present invention is not limited to this. Similarly, the calculation method using S2 and S3 is not limited to S3 / S2.

  FIG. 24 shows the results of examining the influence of ambient light in the case of paper type discrimination using only S1 and S2 and the case of paper type discrimination using S4 / S1 and S3 / S2. . As apparent from FIG. 24, when there is disturbance light, the detection value in each light receiving system becomes large, and there is a risk of wrong paper type discrimination when using only S1 and S2 for paper type discrimination. On the other hand, when discriminating paper types using S4 / S1 and S3 / S2, S4 / S1 and S3 / S2 hardly change even when there is ambient light, so that correct paper type discrimination is possible. can do.

  In this case, the third light detection system may have a plurality of light receivers. The fourth light detection system may include a plurality of polarizing filters and a light receiver.

  For example, when the third light detection system has two light receivers and the fourth light detection system has two sets of polarizing filters and light receivers, each of the third light detection systems Assuming that the output level of the photoreceiver is “S3” and “S5”, and the output level of each photoreceiver of the fourth photodetection system is “S4” and “S6”, the value of (S4 / S1 + S6 / S1) and ( The paper type may be determined using the value of (S3 / S2 + S5 / S2). Further, the paper type determination may be performed using the value of S4 / S1, the value of S6 / S1, the value of S3 / S2, and the value of S5 / S2.

  Needless to say, a “recording paper discrimination table” corresponding to the calculation method used for paper type discrimination is created in advance in a pre-shipment process such as an adjustment process and stored in the ROM of the printer control device 2090.

  In the above embodiment, the optical sensor 2245 may further include two mirrors (21, 22) as shown in FIG. 25 as an example.

  Here, the light source 11 emits a light beam in a direction parallel to the Z axis, and the collimating lens 12 is disposed so that the optical axis is parallel to the Z axis.

  The mirror 21 bends the optical path of the light beam that has passed through the collimator lens 12 so that the incident angle on the recording paper is 80 °.

  The mirror 22 is a mirror equivalent to the mirror 21, and is disposed at a position facing the mirror 21 with the opening in the X-axis direction. Therefore, the optical path of the specularly reflected light from the recording paper is bent so that its traveling direction is parallel to the Z axis.

  The light receiver 15 is arranged on the + Z side of the mirror 22, and receives the surface regular reflection light whose optical path is bent by the mirror 22.

  In this case, a member for supporting the light source and the light receiver in an inclined state is unnecessary, and the electric circuit can be simplified. Thereby, an optical sensor that can be miniaturized at low cost can be realized.

  Even in the case where three or more light receivers are provided, miniaturization of the optical sensor is promoted by using a mirror so that the traveling direction of the light beam toward each light receiver is a direction parallel to the Z axis. be able to.

  Moreover, although the said embodiment demonstrated the case where the light source 11 had a several 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, as shown in FIG. 26 as an example, a polarizing filter 23 for making the irradiation light S-polarized light is necessary.

  Moreover, in the said embodiment, it is more preferable that the condensing lens is arrange | positioned ahead of each light receiver. In this case, the change in the detected light amount can be reduced.

  Measurement reproducibility is important for an optical sensor that discriminates recording paper based on the amount of reflected light. In an optical sensor that discriminates a recording paper based on the amount of reflected light, a measurement system is installed on the assumption that the measurement surface and the surface of the recording paper are in the same plane at the time of measurement. However, the recording paper surface may be inclined or lifted with respect to the measurement surface for reasons such as deflection and vibration, and the recording paper surface may not be flush with the measurement surface. In this case, the amount of reflected light changes and it is difficult to make a stable and detailed determination. Here, specular reflection will be described as an example.

  FIG. 27A shows a case where the measurement surface and the surface of the recording paper are the same plane. At this time, the light detection system can receive regular reflection.

  FIG. 27B shows a case where the surface of the recording paper is inclined by an angle α with respect to the measurement surface. At this time, if the positional relationship between the light irradiation system and the light detection system is the same as in FIG. 27A, the light detection system receives light in a direction shifted by 2α from the regular reflection direction. Since the reflected light intensity distribution moves with the shift, if the distance between the center position of the irradiation region and the light detection system is L, the light detection system receives light at a position shifted by L × tan 2α from the regular reflection light receiving position. It will be. Further, the actual incident angle is deviated by α from the prescribed incident angle θ, and the reflectance from the recording paper changes. For this reason, a change occurs in the detected light quantity, and as a result, detailed discrimination becomes difficult.

  FIG. 27C shows a case where the surface of the recording paper is displaced by d in the height direction, that is, in the Z-axis direction with respect to the measurement surface. At this time, if the positional relationship between the light irradiation system and the light detection system is the same as in the case of FIG. 27A, the reflected light intensity distribution is moved with the shift, so the light detection system is moved from the regular reflection light receiving position. Light is received at a position shifted by 2d × sin θ. For this reason, a change in the detected light amount occurs, and as a result, detailed discrimination becomes difficult.

  In the case of FIGS. 27B and 27C, a condensing lens is arranged in front of the light detection system with respect to the movement amount so that the light detection system reliably detects the specular reflection light, and the reflected light. Even if the intensity distribution moves, it can be dealt with by collecting light.

  Or, by using a photodiode (PD) with a sufficiently large light receiving area for the light receiver or by narrowing the beam diameter of the irradiated light, the inconvenience when the surface of the recording paper is not flush with the measurement surface can be solved. Can do.

  Further, it is possible to use a PD arrayed in a light receiver and 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.

  For the sake of convenience, specular reflection has been described here, but surface diffuse reflection and internal diffuse reflection also vary in the amount of detected light due to the deviation between the measurement surface and the recording paper surface, but should be handled in the same way as regular reflection. Can do.

  In the above embodiment, 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 2245 may be provided for each paper feed tray.

  In the above embodiment, the brand of the recording paper may be specified during conveyance. In this case, the optical sensor 2245 is disposed in the vicinity of the conveyance path. For example, the optical sensor 2245 may be disposed in the vicinity of the conveyance path between the paper feed roller 2504 and the registration roller pair 2056.

  The object identified by the optical sensor 2245 is not limited to recording paper.

  In the above embodiment, the color printer 2000 is 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 embodiment, the case where the image forming apparatus has four photosensitive drums has been described. However, the present invention is not limited to this.

  The optical sensor 2245 can also be applied to an image forming apparatus that forms an image by spraying ink on recording paper.

  Note that the optical sensor 2245 can be applied to the thickness detection of an object (see FIG. 28). The conventional thickness sensor has a transmissive configuration, and the optical systems must always be arranged in both directions with the object sandwiched therebetween. Therefore, a support member etc. were required. On the other hand, in the optical sensor 2245, since the thickness is detected only by the reflected light, the optical system may be disposed only on one side of the object. Therefore, the number of parts can be reduced, and the cost and size can be reduced. It is optimal for installation in an image forming apparatus that needs to detect the thickness of an object.

  Further, the optical sensor 2245 can be applied to density detection of an object (see FIG. 29). Conventional density sensors have a transmissive configuration, and the optical systems must always be arranged in both directions with the object sandwiched therebetween. Therefore, a support member etc. were required. On the other hand, since the optical sensor 2245 detects the density only with the reflected light, the optical system may be disposed only on one side of the object. Therefore, the number of parts can be reduced, and the cost and size can be reduced. It is optimal for installation in an image forming apparatus that requires detection of the density of an object.

  DESCRIPTION OF SYMBOLS 11 ... Light source, 12 ... Collimating lens, 13 ... Light receiver (2nd photodetector), 14 ... Polarizing filter (optical element), 15 ... Light receiver (1st photodetector), 16 ... Dark box, 17 ... Light receiver, 18 ... Polarizing filter, 19 ... Light receiver, 21, 22 ... Mirror (optical path changing element), 2000 ... Color printer (image forming device), 2010 ... Optical scanning device, 2030a, 2030b, 2030c, 2030d ... Photoconductor Drum (image carrier), 2032a, 2032b, 2032c, 2032d ... charging device, 2033a, 2033b, 2033c, 2033d ... developing roller, 2040 ... transfer belt, 2042 ... transfer roller, 2050 ... fixing device, 2090 ... printer control device ( Adjusting device), 2245... Optical sensor.

JP 2002-340518 A JP 2003-292170 A JP 2005-156380 A JP-A-10-160687 JP 2006-062842 A JP 11-249353 A

Claims (14)

An irradiation system for irradiating the surface of a sheet-like object with linearly polarized light in a first polarization direction from an incident direction inclined with respect to the normal direction of the surface;
A first photodetector arranged on an optical path of light diffusely reflected in the first direction by the object;
A second photodetector arranged on the optical path of the light diffusely reflected in the second direction by the object,
An optical element that guides a linearly polarized light component having a second polarization direction orthogonal to the first polarization direction to the first photodetector at least on an optical path between the first photodetector and the object. Is an optical sensor.   The optical sensor according to claim 1, wherein the optical element is not disposed on an optical path between the second photodetector and the object.   The optical sensor according to claim 1, wherein the optical element is also disposed on an optical path between the second photodetector and the object. The plurality of photodetectors further includes a third photodetector disposed on an optical path of light diffusely reflected in a third direction sandwiched between the first and second directions,
The optical element is disposed on an optical path between the second photodetector and the object;
The optical sensor according to claim 1, wherein the optical element is not disposed on an optical path between the third photodetector and the object.   The said 1st photodetector is arrange | positioned on the optical path of the light diffusely reflected in the normal line direction of the surface of the said target object, The Claim 1 characterized by the above-mentioned. Optical sensor.   The processing unit for specifying the object based on the output of the first photodetector and the output of the second photodetector is provided. The optical sensor according to item.   The angle formed between the incident direction and the reflection direction of the light reflected toward the second photodetector by the object is defined as the incident direction, where the direction regularly reflected by the object is a regular reflection direction. It is smaller than an angle formed by the regular reflection direction and larger than an angle formed by the incident direction and a reflection direction of light reflected toward the first photodetector by the object. The optical sensor as described in any one of Claims 1-6.   The direction of regular reflection by the object is a regular reflection direction, and the angle formed by the incident direction and the reflection direction of light reflected by the object toward the second photodetector, and the incident direction and An angle formed by a reflection direction of light reflected toward the third photodetector by the object is smaller than an angle formed by the incident direction and the regular reflection direction by the object, and the incident direction. 5. The optical sensor according to claim 4, wherein the angle is greater than an angle formed by a reflection direction of light reflected by the object toward the first photodetector.   The angle formed by the incident direction and the reflection direction of the light reflected by the object toward the third photodetector is defined as the incident direction, where the direction of regular reflection by the object is a regular reflection direction. It is smaller than an angle formed by the regular reflection direction and smaller than an angle formed by the incident direction and a reflection direction of light reflected toward the second photodetector by the object. The optical sensor according to claim 4.   The optical sensor according to claim 1, wherein the irradiation system includes a light source and an optical path changing element that bends an optical path of a light beam from the light source in the incident direction.   The optical sensor according to claim 1, further comprising an optical path changing element that bends an optical path of light reflected by the object in a direction toward at least one of the photodetectors.   The optical sensor according to claim 1, wherein the irradiation system includes a surface emitting laser. In an image forming apparatus for forming an image on a recording medium,
An image forming apparatus comprising the optical sensor according to claim 1, wherein the recording medium is an object.   The image forming apparatus according to claim 13, further comprising: an adjusting device that specifies a brand of the recording medium based on an output of the optical sensor and adjusts an image forming condition according to the specified brand.

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