JP5991775B2 - Measuring apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a measuring apparatus having a function of measuring a color and an image forming apparatus.

  Image quality (hereinafter referred to as image quality) of image forming apparatuses (hereinafter referred to as printers) that have been widely used in recent years includes graininess, in-plane uniformity, character quality, and color reproducibility (including color stability). ) Etc. Among them, the most important factor is color reproducibility.

  Regarding color reproducibility, color differences between not only the same model but also between different models and image forming apparatuses or image display apparatuses according to other methods are also a problem. Software and a measuring instrument for creating a multidimensional LUT (Look Up Table) called an (International Color Consortium) profile are commercially available.

  As shown in FIG. 5, the contents of each ICC profile are calibrated in association with a color space that does not depend on the device, based on the color measurement of a measurement image (patch) using a measuring instrument. Examples of the color space include a CIE L * a * b * color space (CIE is an International Illumination Committee; abbreviation for Commission Internationale de l'Eclairage). This makes it possible to match the colors to be printed between different devices. A CMM (Color Management Module) provided in the image forming apparatus or the like can create print data by performing color conversion using these profiles.

・・・（式１） Japanese Patent Laid-Open No. 2004-86013 proposes an in-line measuring instrument configuration in which a patch image formed on a sheet is detected by a color sensor including a light source, a diffraction grating, and a position detection sensor, and detection accuracy is improved. ing. The detection value from the color sensor can be converted into spectral reflectance, and converted into CIE Lab in consideration of tristimulus values and the like. In the color sensor disclosed in Japanese Patent Application Laid-Open No. 2004-86013, the color detection accuracy deteriorates due to a variation factor such as a variation in the output of the light source due to a change in environmental temperature. Therefore, there is a method in which calibration is performed using a white reference plate arranged at a position facing the color sensor, and the detection value of the color sensor is corrected. As a calibration method, the reflected light of the white reference plate is measured before or after the color measurement of the patch image is performed, and the calculation is performed based on the measured value. When calculating with the white reference plate, the spectral reflectance is calculated by (Equation 1) when the reflected light amount W (λ) of the white reference plate and the reflected light amount P (λ) of the patch are used.

... (Formula 1)

  Since the white reference plate reflects light in the measurement wavelength region with substantially the same reflectance without depending on the wavelength, the reflected light amount W (λ) from the white reference plate can be regarded as equivalent to the incident light amount on the patch image. Therefore, by measuring both the amount of light incident on the patch image (that is, W (λ)) and the amount of reflected light P (λ), the spectral reflectance R (λ) of the patch is affected by the output fluctuation of the light source. Can be derived.

  As described above, in the derivation of the spectral reflectance, it is calculated from the reflected light P (λ) of the patch and the reflected light W (λ) of the white reference plate. The output signal value of the position detection sensor that reads the reflected light includes a dark current value in addition to the reflected light. For this reason, there is a concern that the accuracy of color detection at the time of measurement is affected by the fluctuation of the dark current value due to temperature.

  Further, since the dark current value cannot be read when the position detection sensor is receiving light, conventionally, a method of reading the dark current value by providing a light-shielding light receiving element has been used. However, this method requires a light-receiving element dedicated to correction that is shielded from light. As a result, there is a need for a space for a light receiving element dedicated to correction, and further, there is a problem that the light receiving element dedicated to correction cannot be used as an effective pixel because light is shielded.

As one form of this invention, a measuring device is equipped with the light emission means which emits light, and several light receiving elements, light-receiving means which light-receives the reflected light from a measuring object and outputs spectral reflection information, and the said light emission means light-emits The first signal output by a predetermined light receiving element among the plurality of light receiving elements in the first state, and the predetermined signal among the plurality of light receiving elements in the second state where the light emitting means emits light. Based on the second signal output by the light receiving element, a determination unit that determines correction information, and on the basis of the correction information determined by the determination unit, the spectral reflection information output by the light receiving unit have a correction correcting means, said predetermined light receiving element, characterized in that said one of the plurality of light receiving elements, a light receiving element located outside the area for receiving light reflected from the measurement object

As another aspect of the present invention, a measuring apparatus includes a light emitting unit that emits light, a plurality of light receiving elements, a light receiving unit that receives reflected light from a measurement target, and outputs spectral reflection information; and Detecting means for detecting temperature; and determining a target light receiving element among the plurality of light receiving elements based on the temperature detected by the detecting means; and in the first state where the light emitting means does not emit light, the plurality of light receiving elements The first signal output by the target light receiving element of the light receiving elements and the second signal output by the target light receiving element of the plurality of light receiving elements in the second state where the light emitting means emits light. And a correction means for correcting the spectral reflection information output by the light receiving means based on the correction information determined by the determination means. Possess the door, the light receiving element of the object, wherein the one of the plurality of light receiving elements, a light receiving element located outside the area for receiving light reflected from the measurement target.

As another embodiment of the present invention, the image forming apparatus includes a measuring device, and the measuring device includes a light emitting unit that emits light and a plurality of light receiving elements, receives reflected light from the measurement object, and spectral reflection information. , A first signal output by a predetermined light receiving element among the plurality of light receiving elements in a first state in which the light emitting means does not emit light, and a second state in which the light emitting means emits light And determining means for determining correction information based on the second signal output by the predetermined light receiving element among the plurality of light receiving elements, and based on the correction information determined by the determining means, have a correction means for correcting the spectral reflectance information outputted by said light receiving means, said predetermined light receiving element, among the plurality of light receiving elements, outside the area for receiving light reflected from the measurement object Characterized in that it is a light receiving element that location.

As another embodiment of the present invention, an image forming apparatus includes a measuring device, and includes a light emitting unit that emits light and a plurality of light receiving elements, and receives light reflected from a measurement target and outputs spectral reflection information. And a detecting means for detecting the temperature of the light emitting means, a target light receiving element among the plurality of light receiving elements is determined based on the temperature detected by the detecting means, and the light emitting means does not emit light. The first light signal output by the target light receiving element among the plurality of light receiving elements in the state, and the target light receiving element among the plurality of light receiving elements in the second state where the light emitting means emits light. Determining means for determining correction information on the basis of the second signal output by, and the spectral reflection output by the light receiving means on the basis of the correction information determined by the determining means. Have a correction means for correcting the distribution, the light receiving element of said subject, and wherein among the plurality of light receiving elements, a light receiving element located outside the area for receiving light reflected from the measurement object To do.

  According to the present invention, it is possible to perform highly accurate color measurement by detecting a change in dark current value in real time without providing a light receiving element dedicated for correction.

  Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the accompanying drawings).

1 is a diagram illustrating a configuration example of an image forming apparatus. The figure which shows the structural example of a color sensor. Control block diagram. The figure for demonstrating an ICC profile. Schematic diagram of color management environment. , The block diagram containing the sensor and control part which concern on an Example. The flowchart at the time of the measurement of a white reference board. The flowchart at the time of the measurement (calculation) of a patch image. The flowchart at the time of the measurement (temperature detection) of a patch image. The flowchart of the color measurement in this invention. , The figure for demonstrating the mode of the line sensor output fluctuation | variation before and behind light irradiation. , The figure for demonstrating the mode of the line sensor output fluctuation | variation before and behind light irradiation. , The figure for demonstrating the position shift of the line sensor by the box distortion at the time of a temperature change.

<Example 1>
Embodiments according to the present invention will be described in detail with reference to the drawings.

(Image forming device)
In this embodiment, an explanation is given using an electrophotographic laser beam printer. The description will be made by an electrophotographic method, but it can also be applied to an image forming apparatus that performs image fixing by a thermal drying method such as an ink jet printer or a sublimation printer. The structure and operation of the image forming apparatus of the present invention will be described.

  FIG. 1 is a cross-sectional view showing the structure of an image forming apparatus (hereinafter referred to as a printer) 100 in this embodiment. The printer 100 includes a housing 101. The housing 101 houses a control board that houses each mechanism for configuring the engine unit, an engine control unit 312 that controls each printing process (for example, paper feed processing) by the mechanism, and the printer controller 103. Part (not shown).

  As a mechanism for configuring the engine unit, an optical processing mechanism, a fixing processing mechanism, a paper feed processing mechanism, a transport processing mechanism, and the like are provided. The optical processing mechanism forms an electrostatic latent image on the photosensitive drum 105 by scanning with a laser beam, visualizes the electrostatic latent image, multiplex transfers the image to the intermediate transfer member 106, and multiplex-transferred colors. The image is transferred to the sheet 110. The fixing processing mechanism fixes the toner image transferred to the sheet 110. The paper feed processing mechanism performs a paper feed process for the sheet 110. The conveyance processing mechanism performs conveyance processing of the sheet 110.

  The optical processing mechanism includes a laser driver that drives on and off a laser beam emitted from a semiconductor laser (not shown) in accordance with image data supplied from the printer controller 103 in the laser scanner unit 107. Laser light emitted from the semiconductor laser is swung in the scanning direction by a rotating polygon mirror. Here, the laser beam swayed in the main scanning direction is guided to the photosensitive drum 105 via the reflection mirror 109 and exposes the photosensitive drum 105 in the main scanning direction.

  On the other hand, the electrostatic latent image charged on the primary charger 111 and formed on the photosensitive drum 105 by scanning exposure with a laser beam is visualized as a toner image by the toner supplied by the developing device 112. The developed toner image on the photosensitive drum 105 is transferred (primary transfer) onto the intermediate transfer body 106 to which a voltage having a reverse characteristic to that of the toner image is applied. At the time of color image formation, the respective colors are sequentially formed on the intermediate transfer member 106 from the Y (yellow) station 120, the M (magenta) station 121, the C (cyan) station 122, and the K (black) station 123. As a result, a full color visible image is formed on the intermediate transfer member 106.

  Next, the sheet 110 fed from the storage 113 is conveyed, and the transfer roller 114 presses the sheet 110 against the intermediate transfer member 106, and at the same time, a bias having a reverse characteristic to the toner is applied to the transfer roller 114. As a result, the visible image formed on the intermediate transfer body 106 is transferred to the sheet 110 fed in synchronization with the sub-scanning direction by the paper feed processing mechanism (secondary transfer). The photosensitive drum 105 and the developing device 112 are detachable.

  Further, around the intermediate transfer member 106, an image formation start position detection sensor 115, a paper feed timing sensor 116, and a density sensor 117 are arranged. The image formation start position detection sensor 115 determines a print start position when image formation is performed. The sheet feeding timing sensor 116 is configured to timing the sheet 110 to be fed. The density sensor 117 measures the density of the measurement image (patch) during density control. When density control is performed, the density sensor 117 measures the density of each patch.

  The fixing processing mechanism includes a first fixing device 150 and a second fixing device 160 for fixing the toner image transferred to the sheet 110 by heat pressure. The first fixing device 150 includes a fixing roller 151 for applying heat to the sheet 110, a pressure belt 152 for pressing the sheet 110 against the fixing roller 151, and a post-fixing sensor 153 for detecting completion of fixing. The fixing roller 151 is hollow, has a heater (not shown) therein, and is configured to convey the sheet 110 at the same time as being rotationally driven. The second fixing device 160 is located on the downstream side of the conveyance path of the sheet 110 relative to the first fixing device 150, and adds gloss to the toner image on the sheet 110 fixed by the first fixing device 150. It is arranged for the purpose of securing the fixing property. Similar to the first fixing device 150, the second fixing device 160 also has a fixing roller 161, a pressure roller 162, and a post-fixing sensor 163.

  Depending on the type of the sheet 110, there is a sheet that does not need to pass through the second fixing device 160. In this case, a conveyance path 130 for discharging the sheet 110 without passing through the second fixing device 160 is provided for the purpose of reducing energy consumption. The sheet 110 can be guided to the conveyance path 130 by the conveyance path switching flapper 131.

  The sheet 110 is guided to the conveyance path 135 by the conveyance path switching flapper 132. Then, after the position of the sheet 110 is detected by the reversing sensor 137, the reversing unit 136 performs a switchback operation to replace the leading end of the sheet 110.

  Further, a color sensor 200 that detects a patch image on the sheet 110 is disposed downstream of the second fixing device 160 in the conveyance direction. An instruction for a color detection operation is issued in accordance with an instruction from the operation unit 180, and density adjustment, gradation adjustment, and multi-order color adjustment are executed in the engine control unit 312 based on the detection result.

(Color sensor)
The structure and measurement operation of the color sensor 200 will be described. FIG. 2 is a diagram showing the structure of the color sensor 200 in this embodiment. The color sensor 200 includes an LED light source 201, a diffraction grating 202, a line sensor 203 (203-1 to 203-s), a calculation unit 204, and a memory 205. The LED light source 201 irradiates a toner patch (hereinafter referred to as a patch) 207 on the sheet 208 with white light. The diffraction grating 202 separates the light reflected from the patch 207 and passing through the window 206 for each wavelength. The line sensor 203 (203-1 to 203-s) is composed of n pixels that are light receiving elements that detect light separated by the diffraction grating 202 for each wavelength. The calculation unit 204 performs spectral calculation from the light intensity value of each pixel detected by the line sensor 203. The memory 205 stores various data.

  Further, in the configuration of the color sensor 200, a configuration is provided in which a lens that collects the light emitted from the LED light source 201 on the patch 207 on the sheet 208 and collects the light reflected from the patch 207 on the diffraction grating 202 is built in. It may be. The color sensor 200 measures the reflected light of the white reference plate 210. The white reference plate 210 has an attachment / detachment mechanism, and moves the white reference plate 210 to the vicinity of the position of the sheet 208, or moves the white reference plate 210 to a position where the white reference plate 210 abuts from the back surface of the sheet 208 even during patch image measurement. May be.

  FIG. 6A is a block diagram including a sensor and a control unit according to the present embodiment. A CPU 3001 serving as a control unit performs light amount setting of the LED light source 201 and data reading from the memory 205. Further, the CPU 3001 issues a paper transport timing instruction to the paper transport unit 3002. Further, the CPU 3001 controls the attachment / detachment motor 3003 so as to perform an operation of attaching the white reference plate 210 to a predetermined position and an operation of attaching the white reference plate 210 to the back side of the paper at the time of patch image measurement.

(White reference plate)
The white reference plate 210 is used for adjusting the light amount of the LED light source 201 and calculating the correction coefficient h (λ). The white reference plate 210 is desired to have high light resistance in order to suppress deterioration over time and to be strong for attaching and detaching operations. For this reason, for example, a ceramic processed aluminum oxide is used.

The correction coefficient h (λ) is calculated from the difference between the spectral reflectance when the same white reference plate is measured with a standard measuring instrument (not shown) as a reference and the spectral reflectance when measured with the color sensor 200. To do. For example, it is assumed that the spectral reflectance hs (500) corresponding to a wavelength of 500 [nm] obtained when a white reference plate is measured with a standard measuring instrument is 91%. Similarly, it is assumed that the spectral reflectance hu (500) corresponding to the wavelength of 500 [nm] obtained when the white reference plate is measured by the color sensor 200 is 85%. In this case, a correction coefficient h (500) for correcting from 85% to 91% is calculated.

  The value of the correction coefficient h (λ) of the white reference plate 210 is written in the memory 205 of the color sensor 200 at the time of assembly or when the color sensor is replaced on the market. One white reference plate is prepared for one color sensor. For example, when four color sensors are arranged in the image forming apparatus main body, four white reference plates are also arranged so as to be paired with the respective color sensors.

[basic action]
Next, a configuration for feeding back the result detected by the color sensor 200 in the printer 100 will be described.

(Explanation of basic adjustment flow)
In the printer 100 according to the present embodiment, a basic flow for creating a profile and outputting using the profile will be described. In the present embodiment, an ICC (International Color Consortium) profile is used as a profile for realizing excellent color reproducibility. However, the present invention is not limited to this. For example, CRD (Color Rendering Dictionary) adopted from PostScript Level 2 proposed by Adobe, Color separation table in Photoshop (registered trademark), CMYK simulation in ColorWise of EFI that maintains black plate information, etc. are also used. be able to.

(Spectral reflectance measurement and color value calculation)
As shown in FIG. 1, the printer 100 according to the present exemplary embodiment includes a color sensor 200 as a reading unit on the upstream side in the transport direction of a post-fixing discharge tray (not shown). The printer 100 can measure the spectral reflectance by the color sensor 200, converts the measurement result into a color value, and creates a color conversion profile by itself. Then, the printer 100 performs color conversion processing using the created color conversion profile.

  A color value calculation method will be described. A signal whose color is measured and input by the color sensor 200 is obtained by reflecting the light emitted from the LED light source 201 on the object to be measured, and the reflected light is spectrally divided by the diffraction grating 202 to be in each wavelength region of 380 nm to 720 nm. It is detected on the arranged CMOS sensor (line sensor 203). Then, the spectral reflectance is measured for the input signal. In the present invention, in order to improve detection calculation accuracy, the spectral reflectance is converted into L * a * b * via a color matching function or the like as defined by CIE.

  Based on the measurement result of the patch image, the color value (L * a * b *) of the patch image is determined. The CPU 3001 sets an ICC profile based on the color value of the patch image and the signal value used by the engine unit to form the patch image.

(L * a * b * operation)
The following is a method (step) for calculating the color value (L * a * b *) from the spectral reflectance. The method shown here is defined in ISO 13655.

    a. The spectral reflectance R (λ) of the sample is obtained (380 nm to 780 nm).

    b. Color matching functions x (λ), y (λ), z (λ) and standard light spectral distribution SD50 (λ) are prepared. The color matching function is defined in JIS Z8701. SD50 (λ) is defined in JIS Z8720 and is also called auxiliary standard illuminant D50.

c. The wavelength is obtained using the prepared function.

d. Integration of each wavelength is performed.

e. The product of the color matching function y (λ) and the standard light spectral distribution SD50 (λ) is integrated for each wavelength.

f. XYZ is calculated.

    g. The value of L * a * b * is calculated. In the case of Y / Yn> 0.008856, it is obtained by the following calculation formula. Here, Xn, Yn, and Zn indicate standard light tristimulus values.

なお、

は、

とも記載する。

In addition,

Is

Also described.

(Profile creation process)
The user operates the operation unit 180 at the time of parts replacement by a customer engineer, before a job (print processing) requiring color matching accuracy, or when the user wants to know the color of the final output product at the design concept stage, Color profile creation processing is performed.

  The profile creation process is performed in the printer controller 103 shown in the control block diagram of FIG. First, a profile creation instruction is input to the profile creation unit 301 via the operation unit 180. The profile creation unit 301 sends a signal to the engine unit (engine control unit 312) to output the CMYK color chart of the ISO12642 test form (patch image) without using the profile. At the same time, the profile creation unit 301 sends a measurement instruction to the color sensor control unit 302. In the printer 100, ISO 12642 test form (patch image) is transferred and fixed on the sheet 110 through processes such as charging, exposure, development, transfer, and fixing, and the color sensor 200 measures the color. The measured spectral reflectance data of the patch is input to the printer controller 103 and converted into L * a * b * data by the Lab calculation unit 303. The L * a * b * data is converted by the profile stored in the color sensor input ICC profile storage unit 304 and input to the profile creation unit 301.

  Note that the conversion format is not limited to L * a * b *, and the spectral reflectance data may be converted into the CIE 1931XYZ color system, which is a color space signal independent of the device.

  Further, the profile creation unit 301 creates an output ICC profile based on the relationship between the output CMYK patch signal and the input L * a * b * data (converted data), and stores the output ICC profile in the output ICC profile storage unit 305. This is replaced with the output ICC profile that has been set.

  The ISO12642 test form includes CMYK color signal patches covering a color reproduction range that can be output by a general copying machine, and color conversion is performed based on the relationship between each color signal value and the measured L * a * b * value. Create a table. That is, a conversion table (A2Bx tag) of CMYK → Lab is created. Based on this conversion table, an inverse conversion table (B2Ax tag) is created.

  The ICC profile has a structure as shown in FIG. 4 and includes a header, a tag, and data thereof. In addition to the color conversion table, the tag indicates whether a certain color expressed by the white point (Wtpt) or the Lab value defined in the profile is inside or outside the hard copy reproducible range (gamt) ) Tags are also described.

  When a profile creation command is received from an externally connected device (such as a PC) via the external I / F 308, the output ICC profile created on the external device is uploaded and color conversion is performed by an application corresponding to the ICC profile. It may be possible to perform.

(Color conversion processing)
In normal color output color conversion, RGB signal values input via an external I / F 308 such as a scanner unit and image signals input assuming standard print CMYK signal values such as JapanColor are stored in an input ICC profile. Part 307. The input ICC profile storage unit 307 performs RGB → L * a * b * conversion or CMYK → L * a * b * conversion in accordance with the image signal input from the external I / F 308. The input ICC profile includes a one-dimensional LUT that controls an input signal, a multi-order color LUT called direct mapping, and a one-dimensional LUT that controls generated conversion data. The input image signal is converted from device-dependent color space to device-independent L * a * b * data using these tables.

  The image signal converted into a value in the L * a * b * color space coordinate system is input to a CMM (Color Management Module) 306. Then, GAMUT conversion, color conversion, black character determination, and the like are performed on the image signal. In GAMUT conversion, a mismatch in the output color reproduction range between the reading color space of the external I / F 308 such as a scanner unit as an input device and the printer 100 as an output device is mapped. In color conversion, a light source type mismatch at the time of input and a light source type mismatch when observing an output (also referred to as a color temperature setting mismatch) are adjusted. As a result, the L * a * b * data is converted into L * ′ a * ′ b * ′ data and input to the output ICC profile storage unit 305. The profile created as described above is stored in the output ICC profile storage unit 305, color-converted by the newly created ICC profile, converted into a CMYK signal depending on the output device, and output.

  In FIG. 3, the CMM 306 is divided into the input ICC profile storage unit 307 and the output ICC profile storage unit 305 in the block configuration. However, as shown in FIG. 5, the CMM 306 is a module that manages color management, and performs color conversion using an input profile and an output profile.

[Contents of this example]
The basic operation from the measurement of the spectral reflectance by the color sensor, the color value calculation, the Lab calculation, the ICC profile creation, and the color conversion processing has been described above. Hereinafter, details of a method for correcting the fluctuation of the dark current value of the line sensor 203 according to the present invention will be described.

  FIG. 7A shows a flow of the CPU 3001 in the measurement operation of the white reference plate 210. The measurement operation of the white reference plate 210 is started before the patch image measurement and at the timing when the previous job is finished and there is no sheet between the white reference plate 210 and the color sensor 200. In step S301, the CPU 3001 instructs the attachment / detachment mechanism of the white reference plate 210 to start the wearing operation. In step S302, the CPU 3001 determines whether or not the white reference plate 210 has finished wearing operation. Here, as a method for determining the end of the wearing operation, for example, there are a method of waiting for the time required for the wearing operation, and a method of separately providing a detecting means for detecting whether or not the arrival position has been reached and checking the wearing operation. Any method may be used. After the landing operation is completed (YES in S302), the process proceeds to S303. In step S <b> 303, the CPU 3001 instructs to turn on the LED light source 201. In step S <b> 304, the CPU 3001 instructs the color sensor 200 to start measuring the reflected light amount W (λ) for each wavelength of the white reference plate 210. In step S305, after the measurement of the reflected light amount W (λ) is completed, the CPU 3001 instructs the start of the detachment operation of the white reference plate 210. Thereafter, this measurement operation is terminated.

[Device configuration]
FIG. 6A shows a block diagram including the sensor and the control unit in the first embodiment. The CPU 3001 performs light amount setting of the LED light source 201, measurement start instruction, measurement data writing and reading to the memory 205, and dark current correction for the color sensor 200. In addition, the CPU 3001 instructs the paper transport unit 3002 of the paper transport timing at the time of patch image measurement. Further, the CPU 3001 controls the attachment / detachment motor 3003 so as to perform the attaching operation to the predetermined position of the white reference plate 210 at the time of calibration and the attaching operation to the back surface of the paper at the time of measuring the patch image. In the above-described wearing operation, the white reference plate 210 is moved to a position away from the paper back surface by a certain distance.

[Measurement of patch image]
The measurement operation for measuring the fluctuation of the dark current value of the line sensor 203 and deriving the measurement value P ′ (λ) of the reflected light of the patch image will be described with reference to FIGS. 7B and 8.

  FIG. 8 shows an image diagram of the color measurement chart according to the present embodiment. In the color measurement chart, a plurality (M) of color patch images are arranged in the paper conveyance direction on the position facing the color sensor 200. For each color patch image, P (λ) is measured at the timing when it passes over the position facing the color sensor 200. A high density patch is printed on the patch 207-1 to be measured first. The timing at which the value of P (λ) when passing over the measurement area of the color sensor 200 changes from the value of the white paper background is detected as a trigger, and the timing of the subsequent patch image measurement is determined.

  FIG. 7B shows a flow of the CPU 3001 in the measurement operation of P (λ). After the measurement of the white reference plate 210 described with reference to FIG. 7A, the measurement operation of P (λ) is started. In step S401, the CPU 3001 instructs the paper conveyance unit to pass the color measurement chart. In S402, the CPU 3001 measures the dark current value D (λ) of the line sensor 203. In step S <b> 403, the CPU 3001 stores the dark current measurement result in the memory 205. D (λ) is stored in association with a plurality of light receiving elements. In step S <b> 404, the CPU 3001 instructs to turn on the LED light source 201. In S405, the CPU 3001 performs a wait operation for a predetermined time. The wait operation here is performed in order to wait for the line sensor 203 to be in a thermal equilibrium state by the reflected light. In step S <b> 406, the CPU 3001 detects a non-light-receiving region of 1 to n (n is an arbitrary natural number) pixels in the line sensor 203. The detection method will be described later. Here, the light receiving region means a pixel that receives reflected light from a measurement target (here, a patch or the like) among a plurality of pixels (detection regions) included in the line sensor 203. On the other hand, the non-light receiving region means a pixel that does not receive reflected light.

  If the 1-n pixel area is determined to be a non-light-receiving area (YES in S406), CPU 3001 calculates dark current fluctuation in S407. On the other hand, when it is determined that there is no non-light-receiving region (NO in S406), in S408, the CPU 3001 calculates dark current fluctuations of s to sn pixels (s is the total number of pixels of the line sensor 203). In step S409, the CPU 3001 stores the calculation result for the calculated dark current fluctuation in the memory 205. In step S <b> 410, the CPU 3001 detects the timing at which the leading patch 207-1 passes through the measurement area of the color sensor 200. In step S411, the CPU 3001 sets an initial value 1 to a variable m indicating the number of measured patches. In step S413, the CPU 3001 instructs measurement of P (λ) for the patch.

  In step S413, the CPU 3001 determines whether the number of measurements has reached a predetermined number of patches M (m ≧ M). The predetermined number of patches M corresponds to the number of patches printed on the sheet, as shown in FIG. If predetermined number of patches M has not been reached (NO in S413), CPU 3001 increments patch measurement number m (S414). In step S415, the CPU 3001 waits for the measurement operation for a time based on a predetermined patch interval. Here, the time based on the predetermined patch interval is determined by the interval between the patches shown in FIG. 8 and the sheet conveyance speed. Thereafter, the process proceeds to S412, and P (λ) of unmeasured patches is sequentially measured.

  If the predetermined number of patches M has been reached (YES in S413), the CPU 3001 performs dark current correction on the measurement value obtained by the line sensor 203 in S416. The dark current correction method will be described later. In step S417, the CPU 3001 outputs a patch measurement result obtained by a calculation method described later. Thereafter, the color measurement operation of the patch image is finished.

  In the flowchart shown in FIG. 7B, the dark current value before irradiation of the LED light source 201 is measured in S402, and the dark current value after irradiation of the LED light source 201 in S407 or S408 (that is, the dark current value in the thermal equilibrium state). ) Is measured. And based on the value before and after irradiation of this LED light source 201, the measured value is correct | amended.

(Judgment method of non-light-receiving area)
Details of the determination method of the non-light-receiving area of the line sensor 203 after LED emission in S406 to S408 of FIG. 7B and the calculation method of dark current fluctuation will be described.

・・・（式２） 9A and 9B are diagrams showing output fluctuations of the line sensor 203 at the time of patch image measurement. 9A and 9B, the vertical axis represents the output value of the line sensor 203, and the horizontal axis represents each pixel constituting the line sensor 203. 9A and 9B, the dark current value indicated by a broken line is the dark current value of the line sensor 203 measured in S402 of FIG. 7B, and the measurement output indicated by the solid line is the line sensor 203 after the LED light source 201 emits light. Output. FIG. 9B shows an enlarged view of the line sensor output portions 0 to 15 in the line sensor output shown in FIG. 9A. As shown in FIG. 9B, the end portion of the line sensor 203 has a non-light-receiving region that is not exposed to light. Thus, it is possible to extract the dark current output fluctuation α from the n pixels at the end. The calculation of α is expressed by (Equation 2). In Equation 2, P (i) represents the output value of the line sensor at the i-th pixel, and D (i) represents the dark current value at the i-th pixel. D (i) is D (λ) corresponding to the i-th light receiving element.

... (Formula 2)

  The non-light-receiving region is specified by comparing α calculated as described above with a preset threshold value β. At this time, if α <β (that is, less than the threshold), α is regarded as dark current output fluctuation, and α is stored in the memory 205 as a dark current correction value.

  If α ≧ β, the position of the line sensor 203 is shifted as shown in FIG. 11B, and it is determined that the line sensor 203 of the leftmost 1 to n pixels is receiving light. FIG. 11A shows a state where a plurality of pixels located at the left end of the line sensor 203 are non-light-receiving regions. On the other hand, FIG. 11B shows a state in which a plurality of pixels located at the right end of the line sensor 203 are non-light-receiving regions. The state of FIG. 11A corresponds to the output state shown in FIGS. 9A and 9B, and the state of FIG. 11B corresponds to the output state shown in FIGS. 10A and 10B. FIG. 10B is an enlarged view of a part of FIG. 10A.

・・・（式３） When it is determined that the line sensor 203 of the leftmost 1 to n pixels receives reflected light (NO in S406), the dark current output fluctuation α ′ of the rightmost s to sn pixels is determined in S408 of FIG. 7B. Is calculated. The calculation of α ′ is expressed by (Equation 3). S is the number of pixels included in the line sensor 203, and S−n means the nth pixel from the right end of the line sensor 203.

... (Formula 3)

  After α ′ is obtained by the above method, it is compared with the threshold value β as in S407. If α ′ <β, α ′ is regarded as an output fluctuation, and α ′ is stored in the memory 205 as a dark current correction value. .

(Dark current correction method)
Details of the dark current correction calculation in S416 of FIG. 7B will be described. Here, the corrected measured value P ′ (λ) of the patch image reflected light is calculated by the following (Equation 4).

P ′ (λ) = P (λ) −D (λ) −α (or α ′) (Formula 4)
α or α ′ is the same value for all the light receiving elements.

  Based on P (λ) ′ obtained by Expression 4 and W (λ) measured in advance, the calculation unit 204 in the color sensor 200 performs spectral reflectance R (λ of the patch image by the following (Expression 5). ) Is calculated.

・・・（式５）
これにより、暗電流補正を行った値に基づいて、分光反射率が求められる。

... (Formula 5)
Thereby, the spectral reflectance is obtained based on the value subjected to the dark current correction.

(effect)
As described above, according to the present invention, the dark current value is detected in real time without providing a light receiving element dedicated to correction that shields the fluctuation of the dark current value of the line sensor 203. Accordingly, it is possible to provide an image forming apparatus that performs high-precision color measurement by correcting dark current in a timely manner and performs color adjustment according to the detection result.

  In the present embodiment, the configuration in which the dark current fluctuation is calculated only once has been described. However, in order to improve the accuracy, the fluctuation of the dark current may be measured between patches, and the measurement result for each patch may be corrected. Further, the CPU 3001 outputs the output fluctuation α based on the output value (dark current value) of the non-light-receiving pixels corresponding to the non-light-receiving area of the line sensor 203 while the color sensor 200 receives the reflected light from the patch image. (Or α ′) may be calculated. With this configuration, the apparatus can detect the dark current value in real time, and can measure the color with higher accuracy. In addition, the configuration for measuring the color of the patch image arranged in a line on the sheet with one color sensor has been described. However, even when performing color measurement of a plurality of rows of patch images using a plurality of color sensors, correction can be performed by the same correction.

<Example 2>
As another embodiment of the present invention, a configuration for estimating the fluctuation of the non-light-receiving region based on the temperature change and correcting the output value will be described.

[Device configuration]
FIG. 6B is a block diagram including the sensor and the control unit according to the second embodiment. In addition to the configuration of FIG. 6A shown in the first embodiment, the color sensor 200 further includes a thermistor 211 that is a temperature detection unit. The CPU 3001 further instructs the color sensor 200 to detect the temperature of the thermistor 211.

[Measurement of patch image]
A measurement operation for measuring the fluctuation of the dark current value of the line sensor 203 based on the temperature detection result and deriving the measurement value P ′ (λ) of the reflected light of the patch image will be described with reference to FIGS. 7C and 8. The color measurement chart is assumed to be the same as the configuration of FIG. 8 described in the first embodiment.

  FIG. 7C shows a flow of the CPU 3001 in the measurement operation of P (λ). After the measurement of the white reference plate 210 described with reference to FIG. 7A, the measurement operation of P (λ) is started. In step S501, the CPU 3001 instructs the paper transport unit to pass the color measurement chart. In step S <b> 502, the CPU 3001 measures the dark current value of the line sensor 203. In step S <b> 503, the CPU 3001 stores the dark current measurement result in the memory 205. In step S504, the CPU 3001 instructs the LED light source 201 to be turned on. In S505, the CPU 3001 performs a wait operation for a predetermined time. The wait operation here is performed in order to wait for the line sensor 203 to be in a thermal equilibrium state by the reflected light.

  In step S506, the CPU 3001 instructs the thermistor 211 to detect temperature. Based on the result of the temperature detected in S507, the CPU 3001 compares it with a threshold value T (a preset threshold value for estimating the non-light-receiving area) by a method described later. Here, when the detected temperature value is lower than the threshold value T, it is estimated that 1 to n pixels of the pixels included in the line sensor 203 are non-light-receiving regions. A table indicating the relationship between the detected temperature and the pixels in the non-light-receiving area, in advance, which pixel is the non-light-receiving area or the variation amount of the non-light-receiving area is previously defined in a table or the like according to the detected temperature. You may judge using.

  If the detected temperature is lower than threshold value T (YES in S507), CPU 3001 calculates dark current fluctuation from 1 to n pixels of line sensor 203 (S508). On the other hand, if it is equal to or greater than threshold value T (NO in S507), CPU 3001 calculates dark current fluctuation from s to sn pixels of line sensor 203 (S509). After that, in S510, the CPU 3001 stores the calculation result for the dark current fluctuation in the memory 205. In step S <b> 511, the CPU 3001 detects the timing at which the leading patch 207-1 passes through the measurement area of the color sensor 200. In S512, the CPU 3001 sets an initial value 1 to a variable m indicating the number of measured patches. In step S513, the CPU 3001 instructs measurement of P (λ) for the patch.

  In S514, the CPU 3001 determines whether or not the number of measurements has reached a predetermined number of patches M (m ≧ M). If the predetermined number of patches M has not been reached (NO in S514), CPU 3001 increments patch measurement number m (S515). In step S516, the CPU 3001 waits for the measurement operation for a time based on a predetermined patch interval. Here, the time based on the predetermined patch interval is determined by the interval between the patches shown in FIG. 8 and the sheet conveyance speed. Thereafter, the process proceeds to S513, and P (λ) of unmeasured patches is sequentially measured. If the predetermined number of patches M has been reached (YES in S514), CPU 3001 performs dark current correction on the measured value obtained by line sensor 203 in S517. In step S518, the CPU 3001 outputs a patch measurement result obtained by a calculation method described later. Thereafter, the color measurement operation of the patch image is finished.

(Judgment method of non-light-receiving area)
Details of the dark current fluctuation calculation method from the determination method of the non-light-receiving area of the line sensor 203 after LED emission based on the temperature detection result in S507 of FIG. 7C will be described.

  In this embodiment, FIGS. 9A and 9B show output fluctuations of the line sensor 203 during patch image measurement when the temperature detection result is less than T. FIG. 9A and 9B, the dark current value indicated by the broken line is the dark current value of the line sensor 203 measured in S502 of FIG. 7C, and the measurement output indicated by the solid line is that of the line sensor 203 after the light emission of the LED light source 201. Is the output. Other configurations are the same as those in the first embodiment, and thus the description thereof is omitted here.

  On the other hand, when the temperature detection result is T or more, as shown in FIG. 11B, it is estimated that the position of the line sensor 203 is shifted by the temperature change and the line sensor 203 of the leftmost 1 to n pixels receives light. As a result, the dark current output fluctuation α ′ of the right end side s to sn pixels is calculated (S509). Since the calculation method is the same as that of the first embodiment, it is omitted here. Further, the dark current correction method in S517 is also the same as that in the first embodiment, and is therefore omitted.

(effect)
As described above, according to the present embodiment, it is possible to obtain the same effects as those of the first embodiment.

  Embodiments of the present invention read and execute computer-executable instructions recorded on a recording medium (eg, a non-transitory computer-readable medium) to perform the functions of one or more of the above-described embodiments of the present invention. A method performed by a computer of a system or apparatus or by a computer of a system or apparatus, for example by reading and executing a computer-executable instruction from a recording medium to perform the functions of one or more of the above embodiments Can be realized. The computer may include one or more central processing units (CPUs), a micro processing unit (MPU), or other device, and may include a separate computer or a network of separate computer processors. The computer executable instruction may be provided to the computer from a network or a storage medium, for example. The storage medium can be, for example, one or more hard disks, random access memory (RAM), read only memory (ROM), distributed computing system storage, optical disk (compact disk (CD), digital multipurpose disk (DVD), or A Blu-ray Disc (BD) (registered trademark), a flash memory device, a memory card, and the like.

  Although the present invention has been described as exemplary embodiments, it is understood that the present invention is not limited to the disclosed exemplary embodiments. The scope of the following claims allows a wide interpretation to encompass all modifications and equivalent configurations and functions.

  This application claims priority based on Japanese Patent Application No. 2013-031424 filed on Feb. 20, 2013, the entire contents of which are incorporated herein by reference.

Claims (10)

A light emitting means for emitting light;
A light receiving means comprising a plurality of light receiving elements, receiving reflected light from a measurement object, and outputting spectral reflection information;
The first signal output by a predetermined light receiving element among the plurality of light receiving elements in the first state where the light emitting means does not emit light, and the plurality of light receiving elements in the second state where the light emitting means emits light. Determining means for determining correction information based on the second signal output by the predetermined light receiving element;
On the basis of the correction information determined by the determining means, have a correction means for correcting the spectral reflectance information outputted by said light receiving means,
The measuring apparatus according to claim 1, wherein the predetermined light receiving element is a light receiving element that is located outside a region that receives reflected light from the measurement target among the plurality of light receiving elements . The plurality of light receiving elements include a first light receiving element located outside the region, and a second light receiving element located outside the region and different from the first light receiving element,
The determination means should set the first light receiving element as the predetermined light receiving element or set the second light receiving element based on the output result of the first light receiving element in the second state. The measuring device according to claim 1 , wherein it is determined whether or not to perform. The determining means determines the first light receiving element as the predetermined light receiving element if the output result of the first light receiving element is smaller than a predetermined value in the second state, and in the second state 3. The measuring apparatus according to claim 2 , wherein if the output result from the first light receiving element is not smaller than the predetermined value, the second light receiving element is determined as the predetermined light receiving element. The plurality of light receiving elements include other light receiving elements included in a region that receives reflected light from the measurement target,
It said determining means, said first signal, said second signal, and, based on other signals output by the other light receiving element in said second state, characterized in that to determine the correction information The measuring apparatus according to any one of claims 1 to 3 . The light receiving means is a line sensor in which the plurality of light receiving elements are arranged in a line,
It said light receiving means, measuring device according to any one of claims 1 to 4, further comprising a diffraction grating for diffracting the reflected light from the measurement target. Said light receiving means, based on the amount of each wavelength of the reflected light from the measurement object, the measurement device according to any one of claims 1 to 5, characterized in that outputs the spectral reflectance information. The spectral reflectance information, measurement device according to any one of claims 1 to 6, characterized in that the information indicating the spectral reflectance of the measurement target. A light emitting means for emitting light;
A light receiving means comprising a plurality of light receiving elements, receiving reflected light from a measurement object, and outputting spectral reflection information;
Detecting means for detecting the temperature of the light emitting means;
A target light receiving element among the plurality of light receiving elements is determined based on the temperature detected by the detecting means, and the target of the plurality of light receiving elements in the first state where the light emitting means does not emit light. Correction based on the first signal output by the light receiving element and the second signal output by the target light receiving element among the plurality of light receiving elements in the second state where the light emitting means emits light A determination means for determining information;
On the basis of the correction information determined by the determining means, have a correction means for correcting the spectral reflectance information outputted by said light receiving means,
The measurement device according to claim 1, wherein the target light receiving element is a light receiving element that is located outside a region that receives reflected light from the measurement target among the plurality of light receiving elements . An image forming apparatus including a measuring device,
The measuring device is
A light emitting means for emitting light;
A light receiving means comprising a plurality of light receiving elements, receiving reflected light from a measurement object, and outputting spectral reflection information;
The first signal output by a predetermined light receiving element among the plurality of light receiving elements in the first state where the light emitting means does not emit light, and the plurality of light receiving elements in the second state where the light emitting means emits light. Determining means for determining correction information based on the second signal output by the predetermined light receiving element;
On the basis of the correction information determined by the determining means, have a correction means for correcting the spectral reflectance information outputted by said light receiving means,
The image forming apparatus according to claim 1, wherein the predetermined light receiving element is a light receiving element that is located outside a region that receives reflected light from the measurement target among the plurality of light receiving elements . An image forming apparatus including a measuring device,
A light emitting means for emitting light;
A light receiving means comprising a plurality of light receiving elements, receiving reflected light from a measurement object, and outputting spectral reflection information;
Detecting means for detecting the temperature of the light emitting means;
A target light receiving element among the plurality of light receiving elements is determined based on the temperature detected by the detecting means, and the target of the plurality of light receiving elements in the first state where the light emitting means does not emit light. Correction based on the first signal output by the light receiving element and the second signal output by the target light receiving element among the plurality of light receiving elements in the second state where the light emitting means emits light A determination means for determining information;
On the basis of the correction information determined by the determining means, have a correction means for correcting the spectral reflectance information outputted by said light receiving means,
The image forming apparatus according to claim 1, wherein the target light receiving element is a light receiving element that is located outside a region that receives reflected light from the measurement target among the plurality of light receiving elements .

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