JP5473411B2 - Recording medium imaging device and image forming apparatus - Google Patents

Description

  The present invention relates to a recording medium imaging apparatus that images a recording medium, and an image forming apparatus.

  In a conventional image forming apparatus, for example, the type (size, thickness, etc.) of a recording medium is set by a user by setting with a computer or the like as an external apparatus, or an operation panel provided on the image forming apparatus main body. It was. In accordance with the setting, for example, transfer conditions (transfer voltage and recording medium conveyance speed during transfer) and fixing conditions (fixing temperature and recording medium conveyance speed during fixing) in the transfer unit are controlled.

  In order to reduce the user's burden of setting the type of the recording medium from such a computer or operation panel, a sensor for determining the recording medium is provided inside the image forming apparatus, and the type of the recording medium is automatically set. A device for automatically determining is provided. An image forming apparatus equipped with a sensor or the like is controlled so that a transfer condition, a fixing condition, and the like are set according to the determination result after automatically determining the type of the recording medium.

  Specifically, as proposed in Patent Document 1 and Patent Document 2, the surface of the recording medium is imaged by a CMOS sensor, and the surface smoothness is detected from the captured image to determine the type of the recording medium. There is something. As described above, when the image is taken by the CMOS sensor, the shading caused by the unevenness of the surface is directly taken, so that the recording medium can be discriminated with high accuracy. In particular, when distinguishing between coated paper and non-coated paper, excellent accuracy is obtained in discriminating the type of recording medium in which the presence or absence of irregularities or the size and depth thereof can be clearly distinguished visually.

JP 2002-182518 A JP 2004-038879 A

  In the prior art as described above, the discrimination accuracy of the recording medium can be improved as the imaging area of the recording medium used for discrimination is increased. As a method of enlarging the imaging area of the recording medium, for example, there is a method of acquiring a surface image of the recording medium by transporting the recording medium by a line sensor in which CMOS sensors as imaging elements are arranged in a line.

  When such a method is performed, since the imaging area becomes larger with respect to the light source, when the surface image of the recording medium is captured due to variations in the amount of light emitted from the light source, an image with insufficient light amount is captured. An area is created. If the type of the recording medium is discriminated using the image area with insufficient light quantity, the discrimination accuracy may be lowered.

  The invention according to the present application has been made in view of the above situation, and when determining the type of the recording medium using the surface image of the imaged recording medium, the variation in the amount of light emitted from the light source It is an object to reduce the deterioration of the discrimination accuracy of the recording medium due to the influence.

To achieve the above object, an irradiation means for irradiating light to record medium, on the basis of the light through the recording medium irradiated by the irradiation unit, an imaging for imaging an image made of the surface of the recording medium from a plurality of pixels And an imaging range of the imaging unit corresponding to a plurality of pixels showing an output value equal to or greater than a threshold is selected as an effective image range for determining the surface state of the recording medium , based on the image captured by the imaging unit Control means and storage means for storing the imaging range of the imaging means selected as the effective image range, and after the control means has stored the effective image range in the storage means, A range to be used for determining a surface state of the recording medium is selected from an image captured by the imaging unit based on an effective image range .

  According to the configuration of the present invention, when the type of the recording medium is determined using the surface image of the recorded recording medium, the decrease in the accuracy of determining the type of the recording medium due to the influence of the variation in the amount of light emitted from the light source is reduced. It becomes possible to make it.

Schematic showing the configuration of a color image forming apparatus in the present invention An oblique view and a cross-sectional view showing a configuration of a recording medium imaging apparatus according to the first and second embodiments. Upper cross-sectional view showing the configuration of the recording medium imaging device in the first and second embodiments The block diagram which shows control of the recording medium imaging device in this invention An image obtained by extracting an effective image area from a surface image having no optical axis shift, a surface image having an optical axis shift, and an image captured by the recording medium imaging apparatus according to the first embodiment. Lightness distribution diagram when there is no optical axis deviation by the recording medium imaging apparatus according to the first embodiment, and lightness distribution diagram when there is an optical axis deviation An image obtained by shading correction of the image obtained by extracting the effective image area in FIG. 5 and a histogram of the image Flowchart for performing light amount correction in the recording medium imaging apparatus according to the first embodiment. 6 is a flowchart for correcting an effective image range in the recording medium imaging apparatus according to the first embodiment. The lightness distribution diagram in which the effective image range is corrected based on the lightness distribution diagram in FIG. 6 and the corrected surface image 6 is a flowchart for determining the type of a recording medium in the recording medium imaging apparatus according to the first embodiment. The figure which shows the result of having calculated the feature-value with respect to each image which carried out the shading correction | amendment with the recording medium imaging device in 1st Embodiment. Lightness distribution diagram with reduced threshold for selecting an effective image range in the recording medium imaging apparatus according to the first embodiment Lightness distribution diagram when illuminated by the recording medium imaging apparatus according to the second embodiment The surface image in which the effective image range is corrected based on the brightness distribution in FIG. 14 and the surface image in which the number of pixels in the transport direction is corrected The figure which shows the result of having calculated the feature-value with respect to each image which carried out the shading correction | amendment with the recording medium imaging device in 2nd Embodiment. An oblique view and a cross-sectional view showing a configuration of a recording medium imaging apparatus according to a third embodiment Upper sectional view showing a configuration of a recording medium imaging apparatus according to a third embodiment 10 is a flowchart for determining the type of a recording medium in the recording medium imaging apparatus according to the third embodiment. The surface image imaged with the recording-medium imaging device in 3rd Embodiment An image obtained by extracting an effective image area from the surface image of FIG. Image obtained by shading correction of the image of FIG. The figure which shows the result of having calculated the feature-value with respect to each image which carried out the shading correction | amendment with the recording medium imaging device in 3rd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

(First embodiment)
The recording medium imaging apparatus of this embodiment can be used in, for example, a copying machine or an image forming apparatus. FIG. 1 is a configuration diagram showing a color image forming apparatus in which an intermediate transfer belt is employed and a plurality of image forming units are arranged in parallel as an image forming apparatus equipped with a recording medium imaging device as an example.

Each configuration of the color image forming apparatus 1 in FIG. 1 is as follows. Reference numeral 2 denotes a paper feed cassette for storing the recording medium P. Reference numeral 3 denotes a paper feed tray for storing the recording medium P. 4 is a paper feed roller for feeding the sheet feeding cassette 2 or et recording medium P. Reference numeral 4 ′ denotes a paper feed roller that feeds the recording medium P from the paper feed tray 3. Reference numeral 5 denotes a conveyance roller that conveys the fed recording medium P, and reference numeral 6 denotes a conveyance counter roller that faces the conveyance roller 5. Reference numerals 11Y, 11M, 11C, and 11K denote photosensitive drums that carry developers of yellow, magenta, cyan, and black, respectively. Reference numerals 12Y, 12M, 12C, and 12K denote charging rollers as primary charging units for the respective colors for uniformly charging the photosensitive drums 11Y, 11M, 11C, and 11K to a predetermined potential. 13Y, 13M, 13C, and 13K irradiate laser beams corresponding to the image data of the respective colors onto the photosensitive drums 11Y, 11M, 11C, and 11K charged by the primary charging unit to form an electrostatic latent image. Is a unit.

  Reference numerals 14Y, 14M, 14C, and 14K denote developing devices for visualizing the electrostatic latent images formed on the photosensitive drums 11Y, 11M, 11C, and 11K. Reference numerals 15Y, 15M, 15C, and 15K denote developer conveying rollers for sending the developer in the developing units 14Y, 14M, 14C, and 14K to the photosensitive drums 11Y, 11M, 11C, and 11K. Reference numerals 16Y, 16M, 16C, and 16K denote primary transfer rollers for respective colors that primarily transfer images formed on the photosensitive drums 11Y, 11M, 11C, and 11K. Reference numeral 17 denotes an intermediate transfer belt that carries the primary transferred image. A drive roller 18 drives the intermediate transfer belt 17. Reference numeral 19 denotes a secondary transfer roller for transferring an image formed on the intermediate transfer belt 17 to the recording medium P, and reference numeral 20 denotes a secondary transfer counter roller facing the secondary transfer roller 19. A fixing unit 21 melts and fixes the developer image transferred to the recording medium P while conveying the recording medium P. A discharge roller 22 discharges the recording medium P that has been fixed by the fixing unit 21.

  The photosensitive drums 11Y, 11M, 11C, and 11K, the charging rollers 12Y, 12M, 12C, and 12K, the developing devices 14Y, 14M, 14C, and 14K, and the developer transport rollers 15Y, 15M, 15C, and 15K are respectively provided for each color. Is integrated. As described above, a cartridge in which the photosensitive drum, the charging roller, and the developing device are integrated is referred to as a cartridge, and each color cartridge is configured to be easily removable from the color image forming apparatus 1.

  First, the paper transport operation in the image forming operation of the color image forming apparatus 1 will be described. Print data including a print command and image information is input to the color image forming apparatus 1 from a host computer (not shown) or the like. Then, the color image forming apparatus starts a printing operation, and the recording medium P is fed from the sheet feeding cassette 2 or the sheet feeding tray 3 by the sheet feeding roller 4 or the sheet feeding roller 4 ′ and sent out to the conveyance path. In order to synchronize the operation of forming the image formed on the intermediate transfer belt 17 and the conveyance timing, the recording medium P temporarily stops at the conveyance roller 5 and the conveyance counter roller 6 and waits until image formation is performed. Thereafter, in synchronization with the image forming operation, the recording medium P is conveyed to the secondary transfer unit. The developer image formed on the intermediate transfer belt 17 is transferred onto the recording medium P by the secondary transfer roller 19 and the secondary transfer counter roller 20. The developer image transferred to the recording medium P is fixed by a fixing unit 21 including a fixing roller. The fixed recording medium P is discharged to a discharge tray (not shown) by a discharge roller 22 and the image forming operation is completed.

  Next, an electrophotographic image forming method will be described. First, when print data is input from the host computer or the like to the color image forming apparatus 1, the photosensitive drums 11Y, 11M, 11C, and 11K are charged with the charging rollers 12Y, 12M, and 12C. , 12K to be charged to a constant potential. In accordance with the input print data, the optical units 13Y, 13M, 13C, and 13K expose and scan the surfaces of the charged photosensitive drums 11Y, 11M, 11C, and 11K with a laser beam to form an electrostatic latent image. In order to visualize the formed electrostatic latent image, development is performed by the developing devices 14Y, 14M, 14C, and 14K and the developer transport rollers 15Y, 15M, 15C, and 15K. The electrostatic latent images formed on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K are developed as developer images in respective colors by the developing devices 14Y, 14M, 14C, and 14K. The photosensitive drums 11Y, 11M, 11C, and 11K are in contact with the intermediate transfer belt 17, and rotate in synchronization with the rotation of the intermediate transfer belt 17. The developed developer images are sequentially multiplex-transferred onto the intermediate transfer belt 17 by the primary transfer rollers 16Y, 16M, 16C, and 16K to form a multicolor developer image. This multicolor developer image is secondarily transferred onto the recording medium P by the secondary transfer roller 19 and the secondary transfer counter roller 20.

  In the image forming apparatus of FIG. 1, the recording medium imaging device 40 is installed on the upstream side of the transport roller 5 and the transport counter roller 6 (in the image forming apparatus of this embodiment, on the paper feed cassette 2 or the paper feed tray 3 side). Information on the surface image of the recording medium P conveyed from the paper feed cassette 2 or the like is detected. The determination by the recording medium imaging device 40 is performed while the recording medium P is sent out from the paper feed cassette 2 or the like into the image forming apparatus and is held between the conveyance roller 5 and the conveyance counter roller 6 and stopped. Alternatively, it is performed until the sheet is conveyed to the secondary transfer nip portion composed of the secondary transfer roller 19 and the secondary transfer counter roller 20. Note that the recording medium imaging device 40 can be installed at any location upstream of the conveying roller 5 and the conveying counter roller 6 as long as the type of the recording medium P can be determined. Further, it may be installed between the conveyance roller 5 and the conveyance counter roller 6 and the secondary transfer nip portion.

  Next, the recording medium imaging device 40 according to the present embodiment will be described with reference to FIGS. FIG. 2A shows a configuration of a recording medium imaging device 40 for capturing a surface image reflecting the surface smoothness. 2B is a cross-sectional view of FIG. 2A, and FIG. 3 is an upper cross-sectional view of FIG.

  The recording medium imaging device 40 illustrated in FIG. 2A includes the following. Reference numeral 41 denotes an irradiating LED which is an irradiating means for irradiating the surface of the recording medium P with light. An imaging lens 42 is an imaging unit that receives reflected light reflected from the surface of the recording medium P by light irradiated from the irradiation unit and forms an image. Reference numeral 43 denotes a CMOS line sensor which is an image pickup means for picking up the light imaged by the image forming means. Reference numeral 44 denotes a slit structure member that guides light emitted from the irradiation LED 41 in an arbitrary direction. The arbitrary direction here will be described later with reference to FIG.

  Further, as a mechanism for transporting the recording medium P, a transport roller 5 that transports the recording medium P and a transport counter roller 6 and a transport guide (not shown) that forms a transport path for the recording medium P are provided. The irradiation LED 41 used in this embodiment is a bullet-type white LED. The irradiation LED 41 is not limited to the bullet-type white LED as long as it can irradiate the recording medium P. Further, as shown in FIG. 2B, the imaging lens 42 is disposed so as to be orthogonal to the conveyance direction of the recording medium P, and the surface of the recording medium P is irradiated by the light emitted from the irradiation LED 41. The reflected light reflected from the light is imaged. The reflected light imaged by the imaging lens 42 is imaged by the CMOS line sensor 43. In the present embodiment, the light emitted from the irradiation LED 41 is emitted at an angle of 10 degrees with respect to the surface of the recording medium P. Note that this angle is an example, and the angle is not necessarily limited to 10 degrees as long as an image sufficient for determining the recording medium P can be obtained.

  As shown in FIG. 3, the irradiation LED 41 is arranged so that the optical axis of the irradiated light is 45 degrees (+45 degrees) counterclockwise with respect to the conveyance direction of the recording medium P. This angle is an arbitrary direction of the slit structure member described with reference to FIG. The irradiation angle range is a range in which the light irradiated from the irradiation LED 41 irradiates the recording medium P. The irradiation angle range represents the pixel range of the CMOS line sensor 43 to which light is irradiated from the irradiation LED 41 with respect to the conveyance direction of the recording medium P. The irradiation angle range is an area where the surface image of the recording medium P can be taken. The effective image range is a range used for determining the type of the recording medium P within the irradiation angle range. The optical axis here is defined as light on the central axis of the LED 41 for irradiation. Installing the irradiation LED 41 so that the optical axis is at the center of the previous irradiation angle range is an ideal desired position in the design. However, in actuality, it may not be installed so as to be at the center of the irradiation angle range due to problems in mounting accuracy.

  In the present embodiment, as an example, the spread angle of light emitted from the irradiation LED 41 from the light source is defined as 14 degrees, and the irradiation angle of the irradiation LED 41 is set from +38 degrees to +52 degrees. The effective image range represents an image region used for discriminating the type of the recording medium P. Here, the spread angle of light emitted from the irradiation LED 41 is defined as 10 degrees narrower than the irradiation angle range, and the irradiation of the irradiation LED 41 is performed. The angle is +40 degrees to +50 degrees. As long as the effective image range is narrower than the irradiation angle range, the effective image range may be determined based on another reference instead of using the spread angle from the light source as in the present embodiment.

  The slit structure member 44 is arranged so that light having the irradiation LED 41 as a light source is irradiated to the recording medium P at the angle described above. By arranging the slit structure member 44, the light irradiation direction in each pixel of the CMOS line sensor 43 can be uniquely specified, and the above-described optical axis can be calculated. In this embodiment, the slit structure member 44 is used as a member for guiding light, but a light guide member or the like may be used as another means.

  FIG. 4 is an example of an operation control block diagram of the recording medium imaging device 40. First, the irradiation LED 41 irradiates the surface of the recording medium P with light, and the reflected light including the surface image reflecting the surface smoothness of the recording medium P is coupled to the CMOS line sensor 43 through the imaging lens 42. Let me image. After the formed image is captured by the CMOS line sensor 43, the surface image of the recording medium P corresponding to the amount of reflected light in each area is output to the discrimination processing means 45. Thereafter, the discrimination processing unit 45 performs A / D conversion on the received surface image of the recording medium P in an A / D conversion 451 to obtain an image on the same straight line perpendicular to the conveyance direction of the recording medium P. In this embodiment, the A / D conversion 451 uses an 8-bit A / D conversion IC and outputs a value from 0 to 255.

  In the image extraction 452 and the storage area 455, the received surface image of the recording medium P is connected in the transport direction to acquire two-dimensional image information. In the present embodiment, the conveyance speed of the recording medium P is 80 mm / second, and the resolution of the CMOS line sensor 43 is 600 dpi for one line (about 42 μm per dot). The image size is 118 dots × 118 dots, which corresponds to 5 mm × 5 mm of the recording medium P. Note that the image size can be changed as appropriate depending on constraints such as the size and cost of the CMOS line sensor, the light amount unevenness of the light source, and the distance that the recording medium P can be conveyed in the image forming apparatus. The imaging timing of the CMOS line sensor 43 is calculated as 42 μm / (80 mm / second), and imaging is performed with an interval of about 530 μsec or more. Thereby, it is possible to capture images without overlapping the imaging areas on the surface of the recording medium P.

  From the obtained two-dimensional image information, a surface image used for discrimination of the type of the recording medium P is extracted based on information such as the optical axis stored in the storage area 455 and the above-described effective image range. At this time, correction (shading correction) of the light amount distribution of the irradiation LED 41 is also performed. Thereafter, in the feature amount calculation 453, the feature amount is calculated based on the extracted surface image. Finally, in the paper type discrimination 454, the type of the recording medium P is discriminated based on the result calculated in the feature amount calculation 453.

  The result of the paper type determination 454 is output to the image forming condition control unit 101 of the control unit 10, and the image forming conditions of the image forming apparatus are controlled based on the determined result. The image forming conditions are conditions such as a transfer voltage, a conveyance speed of the recording medium P, and a fixing device temperature. For example, when the paper type is determined to be rough paper, the developer fixing property is not good as compared with the image forming conditions for plain paper. Controls such as increasing the residence time of the medium P and increasing the fixing temperature are performed.

  The storage area 455 stores a current value for controlling the light emission of the irradiation LED 41 performed at the time of factory shipment, a light amount target value necessary for adjusting a light amount, which will be described later, and the like. Furthermore, when the type of the recording medium P is actually discriminated, dark current data when the irradiation LED 41 used for correcting a light amount difference, which will be described later, and light amount unevenness data when turned on are stored. ing. Further, in the light amount unevenness data when the illumination LED 41 is ON, the pixel range of the data corresponding to the output of the inner surface reference plate and the light amount value thereof, and the pixel range of the data corresponding to the optical axis of the irradiation LED 41 and the light amount value thereof are also stored. doing.

  In addition, when performing light amount correction of the irradiation LED 41, surface information orthogonal to the conveyance direction acquired in the image extraction 452 is output to the light amount correction amount calculation 456, and the light amount correction amount of the irradiation LED 41 is calculated based on the output information. . The calculated light amount correction amount is output to the irradiation control unit 102, and light emission control is performed based on the light amount correction amount. The reason for performing the light amount correction is to prevent excessive light amount or insufficient light amount. When the amount of light is excessive, the amount of reflected light from the surface of the recording medium P increases, the entire acquired surface image becomes bright, and the irregularities on the surface of the recording medium P are crushed. In addition, when the amount of light is insufficient, the entire surface image of the recording medium P becomes dark and the irregularities on the surface of the recording medium P are crushed. For this reason, it is necessary to correct | amend so that LED41 for irradiation may be light-emitted with the light quantity suitable for imaging of a surface image.

  In extracting the surface image and correcting the light amount, the position of the optical axis of the irradiation LED 41 is important. As described above, the optical axis of the irradiation LED 41 when it is arranged in the image forming apparatus may not be arranged at a desired position in the design due to manufacturing variation factors. For this reason, the angle or light amount distribution applied to the recording medium P deviates from the design calculation, and the image area extracted by the predetermined effective image range may include an area where the irradiation light is insufficient. is there. The relationship between the optical axis and light irradiation will be described below.

  FIG. 5A is a surface image in the case where the optical axis of the irradiation LED 41 is arranged at a desired position in the design without deviation. The output of each pixel of one line of the CMOS line sensor 43 representing the light amount distribution of the irradiation LED 41 at this time is shown in FIG. In the present embodiment, the design desired position is the pixel position 81, but can be set as appropriate depending on conditions such as the installation location of the slit structure member 44. As can be seen from the light amount distribution in FIG. 6A, the light amount within the effective image range is higher than the threshold value with which a highly accurate image can be obtained. Become. In the present embodiment, the threshold value for obtaining a highly accurate image is 180, but the threshold value is not limited to this, and may be set as appropriate as long as the type of the recording medium P can be normally determined. Is possible.

  FIG. 5B is a surface image in a case where the optical axis of the irradiation LED 41 is not arranged at a desired design position. FIG. 6B shows output values of a plurality of pixels in one line of the CMOS line sensor 43 representing the light amount distribution of the irradiation LED 41 at this time. As can be seen from the light quantity distribution in FIG. 6B, the optical axis is deviated from the desired position in the design, so that there is a dark image area where the light quantity is insufficient within the effective image range. Yes. For this reason, the surface image of the recording medium P shown in FIG. Note that the light amount distributions in FIGS. 6A and 6B are correction data used for shading correction for correcting a light amount difference of a surface image, which will be described later. The surface image obtained by extracting the surface image based on the effective image range necessary for determining the type of the recording medium P from the surface image obtained in FIGS. 5A and 5B is shown in FIG. Shown in (d). FIGS. 7A and 7B show the results of performing shading correction for correcting the light amount difference on the surface images of FIGS. 5C and 5D. Details of specific shading correction will be described later.

  It can be seen that the surface image with no optical axis deviation from the desired design position in FIG. 7A is a highly accurate surface image in which the surface irregularities are firmly represented. However, since the surface image with the optical axis deviation from the desired design position in FIG. 7B has selected the area where the light is not sufficiently irradiated as the effective image range, the surface unevenness is The surface image is difficult to read and has low accuracy. When the brightness information is converted into a histogram for the surface images in FIGS. 7A and 7B, distributions as shown in FIGS. 7C and 7D are obtained.

  The distribution of the histogram of the surface image with no optical axis deviation from the desired design position in FIG. 7C shows a normal distribution without singularity. However, the distribution of the histogram of the surface image having the optical axis deviation from the desired design position in FIG. 7D is the right part of the image region in FIG. 7B (the dark part in FIG. 5D). As a result, the distribution of brightness varies greatly. If such a distribution is obtained, it can be considered that a recording medium P having a large surface irregularity is erroneously identified as a recording medium P having a small surface irregularity. In addition, it is conceivable that a recording medium P having a small surface irregularity is erroneously identified as a recording medium P having a large surface irregularity. As described above, if the surface image obtained by capturing the recording medium P has a low-lightness portion as described above, it may cause erroneous determination. Therefore, by selecting a pixel having a lightness that is equal to or greater than the threshold value within the effective image range. An accurate surface image can be obtained.

  Hereinafter, a light amount correction control method and an effective image range selection method will be described. The light quantity correction control method and the effective image range selection method described below are performed at the time of factory shipment, and the obtained data is stored in the storage area 455. The light amount correction is performed based on the surface information of the imaged reference plate or the reference recording medium P within the irradiation angle range. Further, not only at the time of factory shipment, but also when the recording medium P serving as a reference is conveyed by the user, the light amount correction and the effective image range may be selected. The light amount correction and the effective image range are basically selected at the time of shipment from the factory, and the result is stored in the storage area 455 and used when the recording medium P is actually discriminated. Basically, it is based on the data stored in this storage area 455 after shipment, but the appropriate light quantity and effective image range differ from those at the time of shipment from the factory due to conditions such as deterioration of the illumination LED 41 and changes in the situation. It can also be considered. In such a case, the light amount correction and the effective image range can be selected again by using the reference plate or the reference paper.

  The reason for performing the light amount correction is that when the amount of light is excessive, the amount of reflected light from the surface of the recording medium P increases, the entire acquired surface image becomes too bright, and surface irregularities are difficult to read. . In addition, when the amount of light is insufficient, reflected light from the surface of the recording medium P is reduced, the entire acquired surface image becomes too dark, and surface irregularities are difficult to read. For this reason, it is necessary to correct | amend so that LED41 for irradiation may be light-emitted with the light quantity suitable for imaging of a surface image. Further, as described above, it is necessary to appropriately select an effective image range in order to obtain a highly accurate surface image. The reason why the effective image range is appropriately selected is to reduce the influence of the surface image due to the mounting accuracy of the irradiation LED 41.

  Based on the flowchart shown in FIG. 8, the light quantity correction control method will be described. In sequence 101, an image is acquired using the CMOS line sensor 43 with the irradiation LED 41 turned off, and is output as dark current data to the arrays B [0] to B [i_max] in the storage area 455. This dark current data is lightness information for removing noise such as ambient light, and is used as a black (dark part) reference in shading correction described later. The dark current data is obtained by performing imaging a plurality of times with the CMOS line sensor 43 and calculating an average value for each pixel with respect to a plurality of brightness information obtained in each pixel. In the present embodiment, since the CMOS line sensor 43 uses 468 pixels at 600 dpi, i_max = 468-1, the number of measurements is 5, the black reference is B, and the output in each measurement is expressed as B1 to B5, B = (B1 + B2 + B3 + B4 + B5) / 5.

  In the sequence 102, a light emission current value (hereinafter referred to as I_led) of the irradiation LED 41 is set to emit light. The value LED_current stored in the storage area 455 is used as the value of I_led. When the light amount correction is performed once or more, since the value of LED_current is already set, it is possible to reduce the number of control times of the loops of the sequences 103 to 105 shown below. Further, when light amount correction is started in the initial state, LED_current uses 0 or a predetermined default value set in advance.

  In sequence 103, the irradiation LED 41 is caused to emit light, and a surface image is acquired using the CMOS line sensor 43. Here, a reference plate is arranged in the irradiation angle range of the irradiation LED 41, and the reference plate is irradiated with light. Reflected light from the reference plate is picked up by the CMOS line sensor 43, brightness information of the reference plate is acquired, and output to the arrays W [0] to W [i_max] in the storage area 455. i_max is set to i_max = 468-1 described above. Thereby, the brightness distribution for one line of the CMOS line sensor 43 is obtained. Although the case where the reference plate is used is described here as an example, it may be performed using reference paper.

  In the sequence 104, a pixel range for performing light amount correction is detected from the obtained reference plate surface information. In the present embodiment, the pixel T having the largest lightness output value is detected in the lightness information distribution for one line. With the pixel T as the center, 30 pixels on the left and right are set as a light amount correction range. Note that the lightness information distribution is not limited to one line, and multiple line imaging may be performed and detected from an average value.

  In the sequence 105, the lightness average value is calculated from the lightness distribution of the calculated light amount correction range. In the present embodiment, the average value is W [T-30] to W [T + 30]. The value of I_led of the irradiation LED 41 is adjusted so that the calculated value becomes a desired light amount correction value. If it is determined that the brightness values are not sufficient, adjustment is performed by increasing the value of I_led of the irradiation LED 41. As a result of the adjustment, the light amount correction is terminated when the desired value is reached. If the calculated brightness value does not change, it is determined that the light amount of the irradiation LED has become maximum, and the light amount correction is terminated. In the present embodiment, as an example, the light amount correction value on the reference plate takes into account the shortest time for capturing the image of the CMOS line sensor 43 and the diffuse reflectance, and the desired light amount correction value is 192 (the lightness intensity is 256 gradations (0 (Dark) to 255 (bright)) The light amount correction value is not limited to this value, and any value can be set as long as it is a value that can accurately capture the surface image of the recording medium P.

  In the sequence 106, the value of I_led of the irradiation LED 41 is stored as LED_current. If there is no reference plate for correcting the amount of light, the irradiation LED 41 is irradiated with light to the recording medium P so that the value is stored in the storage area 455 based on the surface information of the recording medium P. Controls the light emission. The above is the light amount correction control method, which is the operation at the preparation stage before the surface image of the recording medium P is captured.

  Based on the flowchart shown in FIG. 9, a method for calculating an effective image range will be described. In the sequence 201, pixels that are equal to or greater than a predetermined threshold are calculated from the brightness distribution obtained from the light emission of the irradiation LED 41. In this embodiment, as an example, the lightness value is 180 (when the lightness intensity is 256 gradations (0 (dark) to 255 (light)), taking into account the shortest time for capturing the image of the CMOS line sensor 43 and the diffuse reflectance. In sequence 202, the number of pixels equal to or greater than the previously calculated threshold value is obtained to calculate an image range, which is an effective image range that is an adjacent continuous pixel range and within an irradiation angle range. This is necessary.

  In the sequence 203, it is determined whether or not the calculated number of pixels in the image range satisfies the value of the required number of pixels dot_w in the direction orthogonal to the transport direction used for determination (hereinafter referred to as sensor direction). . If satisfied, the process proceeds to sequence 204, and if not satisfied, the process proceeds to sequence 206. Here, when the above conditions are satisfied, the number of pixels in the image range is the same as the required number of pixels dot_w. The limiting method will be described below in sequences 204 and 205. In the present embodiment, the required number of pixels in the sensor direction dot_w is 118 pixels, but is not limited to this as long as the number of pixels for which the recording medium P can be accurately determined. In the sequence 204, the pixel having the highest brightness within the previously calculated image range is calculated.

  In sequence 205, the image range is calculated again so that the calculated pixel with the highest brightness is in the center. At this time, as described in the previous sequence 203, the calculation is performed so that the image range is the same as the required pixel number dot_w in the sensor direction. In the sequence 206, the calculated number of pixels in the image range is stored as the required number of pixels in the sensor direction dot_w. This image range is set as an effective image range used for discrimination. In the sequence 207, the calculated image range is stored as an effective image range (W [Rdot] to W [Rdot + dot_w−1]).

  FIG. 10A shows an output value of each pixel of one line of the CMOS line sensor 43 in which the effective image range is corrected. Further, FIG. 10B shows a surface image of the recording medium P in which the effective image range is corrected. The light quantity distribution in FIG. 10A is the same as that shown in FIG. In FIG. 6B, since the effective image range includes a portion whose brightness is lower than the threshold value, the accuracy of the surface image has been lowered. On the other hand, in the light quantity distribution of FIG. 10A, the effective image range is determined to be equal to or greater than the threshold value, and therefore the output value of the effective image range is high. The surface image shown in FIG. 10B is also accurate. Thereby, it turns out that the influence on the surface image by the attachment accuracy of LED41 for irradiation can be decreased.

  Next, a determination sequence of the type of the recording medium P will be described based on the flowchart of FIG. In the sequence 301, the irradiation LED 41 irradiates the recording medium P with light based on the LED light emission current value I_led stored in advance.

  In sequence 302, the reflected light from the recording medium P is imaged by the CMOS line sensor 43, and a surface image within the effective image range of the recording medium P is output to the discrimination processing unit 45. Then, the brightness information of the surface image of the recording medium P is stored in the arrays POj [0] to POj [dot_w−1]. The discrimination processing unit 45 acquires the two-dimensional image information by stitching the received surface images of the recording medium P in the transport direction. J in the sequence represents the pixel position in the transport direction.

  In the sequence 303, the sequence 302 is repeated until the necessary number of pixels “dot_h” in the transport direction stored in advance is acquired. In the present embodiment, the required number of pixels dot_h is 118 pixels and is stored in the storage area 455. The necessary number of pixels dot_h is not limited to 118 pixels, and may be any number of pixels with which the recording medium P can be accurately identified.

In sequence 304, shading correction is performed on the obtained surface image. This is because it is difficult to uniformly irradiate the effective image range even if the amount of light of the irradiation LED 41 is corrected. Therefore, a light amount difference is generated in the effective image range, and the surface image for each portion in the effective image range is changed by the light amount difference. Shading correction is performed to reduce this effect. The shading correction is performed based on the dark current data DB and the reference plate data DW when the irradiation LED 41 is turned off. The light amount distribution of the irradiation LED 41 is the light amount distribution represented by the curve of FIG. 10A described above, and the reference plate data DW is the light amount distribution within the effective image range in FIG. 10A . The data after the compensation and Dj [0] ~Dj [dot_w] . Here shows how to shading correction of j-th line i picture element as an example of a description.

  First, POj [i] -DB [i] is performed to remove the influence of dark current noise. Next, in order to remove the influence of the light amount unevenness, the light amount is adjusted to a predetermined light amount correction value (here, 192) with respect to the obtained result, and Dj [i] = (POj [i]) -Shading correction can be performed by performing [DB [i]) × 192 / DW [i]. The surface image subjected to the shading correction is shown in FIG.

  In sequence 305, surface irregularities are extracted from a plurality of images of the recording medium P subjected to shading correction, and a surface roughness feature amount is calculated. As a calculation method, the brightness information of the image area is converted into a histogram to obtain a standard deviation of the brightness distribution. When the average value of all data (i = 0 to dot_w, j = 0 to dot_h) of the correction data Dj [i] is DA, the standard deviation is (((Dj [i] −DA) squared) Of the sum of ÷ the number).

  FIG. 12 shows the result of calculating the surface roughness feature amount with respect to the surface image shown in FIG. Similarly, FIG. 5C, which is a surface image when the optical axis is arranged at a desired position in the design without deviation, and a surface image when the optical axis is not arranged at the desired position in the design. FIG. 12 shows the result of calculating the feature amount for an image in FIG. The recording medium P used for discrimination at this time is the same.

  It can be seen that the feature value obtained from the surface image in FIG. 5D with the optical axis deviation is smaller in output value than the feature quantity obtained from the surface image in FIG. 5C without the optical axis deviation. . This is because, as described above, an image region that is not sufficiently irradiated with light is selected, so that the surface image cannot be captured with high accuracy, and the output value has decreased.

  On the other hand, the feature quantity obtained from the surface image of FIG. 10B in which the effective image range is corrected from the state of FIG. 5D having the optical axis deviation is obtained from the surface image of FIG. 5C having no optical axis deviation. Compared with the obtained feature quantity, it shows almost the same value. Therefore, it can be determined that they are the same recording medium P. This is because by correcting the effective image range, it is possible to select an image area that is sufficiently irradiated with light, and to determine the unevenness of the recording medium P firmly.

  Finally, in the sequence 206, the type of the recording medium P is determined based on the obtained feature amount, and the determination result is output to the image forming condition control unit 101 in the control unit 10 of FIG. The obtained feature amount is compared with the output value for determining the type of the recording medium P stored in advance, and the type of the recording medium P is determined. The image forming condition control unit 101 controls the image forming conditions of the image forming apparatus based on the obtained discrimination result of the type of the recording medium P.

  As described above, by appropriately correcting the effective image range according to the light amount distribution, it is possible to select the area where the light is sufficiently irradiated and determine the recording medium P. The influence of accuracy can be reduced. Since the effective image range can be corrected appropriately, the determination accuracy can be improved as compared with the case where the effective image range is not corrected.

  Up to this point, the case where the light quantity distribution shows a relatively smooth output waveform has been described as an example. However, as shown in FIG. 13, the light quantity distribution is smooth due to the characteristics of the CMOS line sensor and the imaging lens. It may not be a curve. Here, how to determine the effective image range in such a case will be described with reference to FIG.

  In the light quantity distribution as shown in FIG. 13, if a pixel position having a brightness value larger than a predetermined threshold (the first threshold in FIG. 13) is an effective image range, a continuous effective image range that satisfies the required number of pixels is not calculated. There is a case. In such a case, the effective image range is widened by lowering the threshold value (second threshold value in FIG. 13) within the range where the surface image can be obtained with high accuracy. In such a range that does not affect the surface image, it is possible to cope with variations in the lightness distribution by providing a certain range of the threshold value. In addition, when a plurality of ranges can be selected as the effective image range, a range having the largest number of pixels in the range indicating the lightness equal to or higher than the threshold is selected as the effective image range.

(Second Embodiment)
Since the configuration of this embodiment can be implemented in FIGS. 1 to 4 described in the first embodiment, description thereof is omitted here. In the present embodiment, as described in the first embodiment, a case will be described in which, if the effective image range is corrected, a predetermined number of pixels in the sensor direction that can be satisfied cannot be satisfied.

FIG. 14 shows a result of correcting the effective image range based on a certain light amount distribution by the method described in the first embodiment. As a result of correcting the effective image range, pixel positions 10 to 79 became the effective image range. FIG. 15A shows the result of image extraction performed by correcting the effective image range. Size of the image is 70 × 118 (3mm × 5mm equivalent at 600 dpi). From FIG. 15A, it can be seen that a region where light is sufficiently irradiated can be selected. Therefore, by changing the required number of pixels in the sensor direction based on the light amount distribution, it is possible to capture a surface image without a region where light is not sufficiently irradiated, and to improve the deterioration of the discrimination accuracy of the recording medium be able to.

  From FIG. 14 and FIG. 15A, it was found that an accurate surface image can be obtained by correcting the effective image range. However, since the necessary number of pixels in the sensor direction has decreased, the captured surface image may be smaller than the number of pixels necessary for discrimination of the recording medium P. Hereinafter, control when the number of pixels necessary for discrimination of the recording medium P has decreased will be described.

  If the required number of pixels in the sensor direction is reduced, the type of the recording medium P must be determined based on the feature amount obtained in a small image area. With the feature of this small image area, a feature different from the entire recording medium P is calculated, and there is a possibility that the type of the recording medium P is erroneously determined. In order to prevent such erroneous determination, in order to ensure a certain number of pixels in the image area, the number of lines to be imaged is increased by enlarging the necessary number of pixels in the transport direction, thereby increasing the image area. The required number of pixels in the transport direction is obtained by dividing the required number of pixels in the sensor direction obtained by the above-described method and the required number of pixels for the entire image area specified separately. However, the required number of pixels in the transport direction depends on the moving distance of the recording medium P at the time of measurement, and is a length within the range of the length from the position where the measurement is started to the rear end of the recording medium P.

  Hereinafter, a method for changing the required number of pixels in the transport direction will be described while showing specific numerical values as an example in the present embodiment. When the total required number of pixels is 13924 pixels (118 × 118), the required number of pixels in the transport direction when the required number of pixels in the sensor direction is 70 pixels is 199 pixels. Since the number of pixels is a natural number, the result of division needs to be rounded off, and the necessary number of pixels in the transport direction is preferably as close as possible to the total necessary number of pixels.

  A surface image extracted from the corrected image region is shown in FIG. The size of the surface image at this time is 70 × 199 (equivalent to 3 mm × 8.3 mm at 600 dpi). Thus, by increasing the number of necessary pixels in the transport direction, the number of pixels in the entire image area can also be increased, and the accuracy of the image serving as a basis for determining the type of the recording medium P is improved. The type discrimination accuracy can also be improved.

In each of three cases of 118 × 118 (equivalent to 5 mm square at 600 dpi), 70 × 118 (equivalent to 3 mm × 5 mm at 600 dpi), and 70 × 199 (equivalent to 3 mm × 8.3 mm at 600 dpi), each is 6 degrees. Measurements were made. FIG. 16 shows the result of calculating the feature amount at that time. It can be seen from FIG. 16 that the output variation is large in the image region 70 × 118 in which the necessary pixels in the transport direction are not changed. On the other hand , in 118 × 118 and 70 × 199, the output variation is small, and the degree is almost equal.

  Therefore, it can be seen that as the size of the image area is reduced, the output variation is increased and the discrimination accuracy of the recording medium P is lowered. In such a case, the number of pixels necessary for discrimination of the recording medium P is secured by increasing the number of necessary pixels in the transport direction. By correcting the image area, it is possible to improve the discrimination accuracy of the recording medium P as compared to the case where the image area is not corrected.

(Third embodiment)
Since the configuration of the third embodiment can be implemented in FIGS. 1 and 4 described in the first embodiment, the description thereof is omitted here. As a configuration different from the first embodiment, a recording medium imaging device 40 according to the present embodiment will be described. As shown in FIG. 17A, the recording medium imaging apparatus 40 of the present embodiment is characterized in that a plurality of light sources are installed. Hereinafter, a case where two LEDs are provided as a light source will be described as an example. However, the number of LEDs is not limited to two, and a plurality of LEDs may be provided.

  The recording medium imaging device 40 includes the following. Reference numeral 41a denotes an irradiating LED which is an irradiating unit for irradiating the surface of the recording medium P with light. Reference numeral 41b denotes an irradiation LED which is an irradiation unit for irradiating the surface of the recording medium P with light. An imaging lens 42 is an imaging unit that forms an image of reflected light reflected from the surface of the recording medium P by light irradiated from the irradiation unit. Reference numeral 43 denotes a CMOS line sensor which is an image pickup means for picking up the light imaged by the image forming means. Reference numeral 44 denotes a slit structure member that guides light emitted from the irradiation LEDs 41a and 41b in an arbitrary direction. The arbitrary direction here will be described later with reference to FIG.

  The mechanism for transporting the recording medium P includes a transport roller 5 for transporting the recording medium P, a transport counter roller 6 provided opposite to the transport roller 5, and a transport guide (not shown) that forms a transport path for the recording medium P. ing. In FIG. 17A, bullet-type white LEDs are used as the irradiation LEDs 41a and 41b used in the present embodiment. The irradiation LED 41 is not limited to the bullet-type white LED as long as it can capture the surface image of the recording medium P.

  As shown in FIG. 17B, the imaging lens 42 is arranged so as to be orthogonal to the conveyance direction of the recording medium P, and the recording medium P is irradiated by the light emitted from the irradiation LEDs 41a and 41b. The reflected light reflected from the surface is imaged. The reflected light imaged by the imaging lens 42 is imaged by the CMOS line sensor 43.

  In the present embodiment, the light emitted from the irradiation LEDs 41a and 41b is emitted at an angle of 10 degrees with respect to the surface of the recording medium P. Note that this angle is an example, and the angle is not necessarily limited to 10 degrees as long as an image sufficient for determining the recording medium P can be obtained.

  As shown in FIG. 18, the irradiation LED 41 a is arranged so that the optical axis of the irradiated light is 45 degrees (+45 degrees) counterclockwise with respect to the conveyance direction of the recording medium P ( First direction). The LED 41b for irradiation is arranged so that the optical axis of the irradiated light is 45 degrees (−45 degrees) clockwise with respect to the conveyance direction of the recording medium P (second direction). This angle is an arbitrary direction of the slit structure member described with reference to FIG.

  The irradiation angle range a is a range in which the light irradiated from the irradiation LED 41a irradiates the recording medium P, and the irradiation angle range b is a range in which the light irradiated from the irradiation LED 41b irradiates the recording medium P. is there. The irradiation angle range a and the irradiation angle range b are areas where a surface image of the recording medium P can be captured. The effective image range a is a range used for determining the type of the recording medium P within the irradiation angle range a, and the effective image range b is used for determining the type of the recording medium P within the irradiation angle range b. It is a range. The optical axis here is defined as the light on the central axis of the irradiation LEDs 41a and 41b. Installation of the irradiation LEDs 41a and 41b so that the optical axis is at the center of the previous irradiation angle range is an ideal desired position in the design. However, in actuality, it may not be installed so as to be at the center of the irradiation angle range due to problems in mounting accuracy.

  In the present embodiment, as an example, the spread angle of light emitted from the irradiation LEDs 41a and 41b from the light source is defined as 14 degrees, the irradiation angle of the irradiation LED 41a is set from +38 degrees to +52 degrees, and the irradiation of the irradiation LED 41b is performed. The angle is -38 degrees to -52 degrees. The effective image ranges a and b represent image regions used for determining the type of the recording medium P, and here, the spread angle of the light emitted from the irradiation LED 41 is defined as 10 degrees narrower than the irradiation angle range. The irradiation angle of the irradiation LED 41a is defined as +40 degrees to +50 degrees, and the irradiation angle of the irradiation LED 41b is defined as -40 degrees to -50 degrees. As long as the effective image ranges a and b are narrower than the irradiation angle range, the effective image range may be determined based on another reference instead of using the spread angle from the light source as in the present embodiment. .

  The slit structure member 44 is disposed so that light having the irradiation LED 41a or 41b as a light source irradiates the recording medium P with light at the angle described above. By arranging the slit structure member 44, the light irradiation direction in each pixel of the CMOS line sensor 43 can be uniquely specified, and the above-described optical axis can be calculated.

The slit structure member 44 prevents light having the irradiation LED 41a as a light source from irradiating a region on the surface of the recording medium P irradiated by the irradiation LED 41b. On the contrary, it is possible to prevent the light having the irradiation LED 41b as a light source from irradiating the area on the surface of the recording medium P irradiated by the irradiation LED 41a. Thus, in order to irradiate the surface of the recording medium P with high accuracy, the irradiation direction of the irradiation LEDs 41a and 41b is limited. By restricting the irradiation direction by the slit structure member 44, the light irradiation direction in each pixel of the CMOS line sensor 43 can be uniquely specified. In this embodiment, the slit structure member 44 is used as a member for guiding light. However, a light guide member or the like may be used as a method for specifying the irradiation direction. It is also possible to acquire a plurality of images by irradiating light at different light irradiation timings for each light irradiation direction.

  Next, light quantity correction will be described. The irradiation control unit 102 in FIG. 4 performs light amount correction in order to perform light emission control with a predetermined light amount for the irradiation LED 41a or 41b. At this time, the illumination LEDs 41a and 41b perform light amount correction independently of each other. Since the light quantity correction of the irradiation LEDs 41a and 41b is performed by the control shown in FIG. 8 of the first embodiment, the description thereof is omitted here. As a result of the light amount correction, when the light amounts in the respective irradiation directions are different, the measurement timing is shifted and the surface information is obtained for each irradiation direction. If there is no reference plate, the recording medium P is irradiated with light, and each light emission is controlled so as to have a value stored in the storage area 455 based on the surface information of the recording medium P.

  Next, the determination sequence of the recording medium P will be described with reference to FIG. In the sequence 401, the irradiation LED 41a irradiates the recording medium P with light based on each LED light emission current value LED_currenta and LED_currentb stored in advance. Similarly, the irradiation LED 41b also irradiates the recording medium P with light.

  In sequence 402, the reflected light from the recording medium P is imaged by the CMOS line sensor 43, and the surface information image of the recording medium P is output to the discrimination processing unit 45. The discrimination processing means 45 acquires two-dimensional image information by stitching the received surface information images of the recording medium P in the transport direction. J in the sequence represents the pixel position in the transport direction.

In a sequence 403, until it acquires the required number of pixels in the conveying direction stored in advance, it repeats the sequence 4 02. In the present embodiment, the required number of pixels in the transport direction is (118 pixels) and is stored in the storage area 455. The necessary number of pixels dot_h is not limited to 118 pixels, and may be any number of pixels with which the recording medium P can be accurately identified.

Here, the surface images obtained by the sequence described above are shown in FIGS. FIG. 20A is a rough paper surface image, and FIG. 20B is a plain paper surface image. FIG. 20 shows a surface image of the recording medium P captured more than the required number of pixels in the transport direction. The sequence 4 02 and sequence 4 03 described above, images obtained by extracting only the pixel number required to determine the recording medium P is shown in FIG. 21 (a), (b) .

  FIG. 21A is an image within the dotted frame in FIG. 20A, and FIG. 21B is an image within the dotted frame in FIG. 20B. The size of the image area in FIGS. 21A and 21B is 118 × 118 (equivalent to 5 mm × 5 mm at 600 dpi). The images in the effective image range a in FIGS. 21A and 21B are the results (first surface image) when the irradiation LED 41a emits light, and the images in the effective image range b are the irradiation LED 41b. It is the result (2nd surface image) which irradiated light.

  In sequence 404, shading correction is performed on the obtained surface image. This is because it is difficult to uniformly irradiate within the effective image range even if the amount of light of the irradiation LEDs 41a and 41b is corrected. For this reason, a light amount difference is generated in the effective image range, and the surface image for each portion in the effective image range is changed by the light amount difference. Shading correction is performed to reduce this effect. Since the shading correction method is the same as the method described in the first embodiment, description thereof is omitted here.

  Images obtained by performing shading correction on the images in FIGS. 21A and 21B are shown in FIGS. The images in the effective image range a in FIGS. 22A and 22B are the results of correcting the image captured by the light emitted from the irradiation LED 41a, and the images in the effective image range b are from the irradiation LED 41b. It is the result of having corrected the picture picturized with the irradiated light.

  In sequence 405, the feature amount of the surface image subjected to the shading correction is calculated. As a calculation method, the brightness information of the image area is converted into a histogram to obtain a standard deviation of the brightness distribution. In the sequence 406, the average value of the feature amounts calculated in the sequence 405 is calculated. FIG. 23 shows the result of calculating the feature amount for the images of FIGS. 22 (a) and 22 (b).

  FIG. 23 shows the results of measurement with the rough and plain papers conveyed vertically and horizontally, respectively. Longitudinal conveyance indicates that the recording medium P is conveyed in the longitudinal direction, and lateral conveyance indicates that the recording medium P is conveyed in the short direction.

  The irradiation LED 41a shows the feature amount of the image obtained from the light emitted from the irradiation LED 41a, and the irradiation LED 41b shows the feature amount of the image obtained from the light emitted from the irradiation LED 41b. Yes. The LED 41a for irradiation and the LED 41b for irradiation show the feature-value obtained from the average of the image obtained from two light sources. From these output values, it can be seen that the feature values calculated for the vertical conveyance and the horizontal conveyance are greatly different. The feature amounts of the irradiation LED 41a and the irradiation LED 41b using an image obtained from one irradiation direction greatly vary between the vertical conveyance and the horizontal conveyance. On the other hand, since the feature values of the irradiation LED 41a and the irradiation LED 41b using the images obtained from the two irradiation directions are averaged, it can be seen that there is little variation between the vertical conveyance and the horizontal conveyance. As described above, in the image obtained from one irradiation direction, the output value varies between the vertical conveyance and the horizontal conveyance because the fiber direction of the recording medium P influences. Even in an image obtained from one irradiation direction, if irradiation is performed with an appropriate amount of light, an accurate image can be obtained, but it happens that the irradiation direction and the fiber direction of the recording medium P happen to be nearly parallel. The accuracy of the surface image may be reduced.

  In order to suppress such variations in the accuracy of the surface image due to the irradiation direction and the fiber direction of the recording medium P, the surface irregularities are determined from the surface image captured based on the light irradiated from the two directions, as shown in FIG. As can be seen, stable accuracy can be maintained. At this time, if the contrast of the surface image obtained from one of the light sources is increased by arranging the angle difference between the two light source LEDs to be 90 degrees, the contrast of the surface image obtained from the other light source is decreased. . Therefore, even if the paper transport direction is different, a high-contrast surface image and a low-surface image can be obtained at the same time. Therefore, for one recording medium P, the type of the recording medium P based on the two obtained surface images. By discriminating, it is possible to reduce the influence of the fiber direction.

  Therefore, by determining the type of the recording medium P using the surface images picked up from different angles in the two directions, the influence of the fiber direction can be reduced, so that an accurate feature amount can be obtained. As a result, variation in the feature amount depending on the conveyance direction of the recording medium P is reduced, and the discrimination accuracy of the type of the recording medium P can be improved. Note that, as an example of the present embodiment, the feature amounts calculated from the two light sources are used as the average value for discrimination of the recording medium P, but the same result can be obtained even with a simple sum.

  Finally, in the sequence 407, the type of the recording medium P is determined based on the obtained feature amount, and the determination result is output to the image forming condition control unit 101 in the control unit 10 in FIG. The obtained feature quantity is compared with an output value for specifying the type of the recording medium stored in advance, and the type of the recording medium P is determined. The image forming condition control unit 101 controls the image forming conditions of the image forming apparatus based on the obtained discrimination result of the type of the recording medium P. In the present embodiment, two surface images captured by light from two different irradiation directions are acquired as one two-dimensional image. However, an image sensor may be arranged independently to capture a surface image. Absent.

  As described so far, when the type of the recording medium P is determined based on the two surface images, a highly accurate result can be obtained by making the number of pixels in the image area of each surface image the same. . If each surface image is corrected independently, the number of pixels in the image area may be different, and if the feature amount is calculated with the number of pixels in the image area being different, the image area having a large number of pixels The influence of the required feature amount becomes large. In this case, the result depends on one of the surface images, and there is a possibility that accurate discrimination cannot be performed.

  In order to avoid such a situation, it is possible to determine the recording medium P without depending on a specific surface image by making the number of pixels of each surface image the same. That is, when the number of pixels of the two surface images obtained is different due to the correction of the effective image range, the selection range is changed for the surface image with a large number of images so that the number of pixels is matched with the surface image with a small number of pixels. By unifying the two surface images with a small number of pixels, it is possible to reduce the fact that the influence of either one of the surface images is strongly reflected and the discrimination accuracy of the type of the recording medium P is lowered. Although two surface images have been described here as an example, the same control can be performed when two or more surface images are targeted. In addition, here, an example in which the number of pixels of the two surface images is the same has been described. However, if there is not a large difference in the number of pixels so that one of the surface images has a large dependency, the number of pixels is not necessarily the same. May be. If it can be determined that a normal surface image is not obtained due to the influence of the fiber, etc., the surface image is not used to determine the type of recording medium, but only from the other surface image. You may do it.

  In the description so far, a CMOS line sensor has been used as an example of an image sensor, but an image sensor that is two-dimensionally arranged such as an area sensor can also be used. The effective pixel range in the transport direction can be expanded by transporting the recording medium P and capturing a surface image according to the length of the effective image range in the transport direction.

  As described in the correction of the effective image range, when the result of division is larger than the maximum number of pixels in the transport direction (line sensor resolution × paper transport distance), the number of pixels in the image area to be extracted reaches the required number of pixels. Will not. In such a case, the number of pixels in the plurality of image areas is kept constant by matching the number of pixels in the other image area to the number of pixels in the image area obtained from the smallest effective image range among the plurality of surface images. Can be. As a result, the number of pixels in the plurality of image areas can be combined, and a decrease in the accuracy of determining the type of the recording medium P due to the mismatch in the number of pixels can be reduced.

DESCRIPTION OF SYMBOLS 10 Control part 40 Recording-medium imaging sensor 41a, 41b LED for irradiation
42 Imaging Lens 43 CMOS Line Sensor 44 Slit Structure Member 45 Discrimination Processing Unit 101 Image Forming Condition Control Unit 102 Irradiation Control Unit P Recording Medium

Claims (20)

Irradiating means for irradiating light to record medium,
Based on the light through the irradiated Symbol recording medium by the irradiation means, an imaging means for capturing an image comprising the surface of the recording medium from a plurality of pixels,
Control means for selecting an imaging range of the imaging means corresponding to a plurality of pixels showing an output value equal to or greater than a threshold based on an image taken by the imaging means as an effective image range for determining the surface state of the recording medium ; ,
Storage means for storing the imaging range of the imaging means selected as the effective image range,
After the effective image range is stored in the storage unit, the control unit selects a range to be used for determining the surface state of the recording medium from the image captured by the imaging unit based on the effective image range. A recording medium imaging apparatus. An irradiation means for irradiating the recording medium with light;
An imaging unit that images the surface of the recording medium as an image composed of a plurality of pixels based on the light irradiated by the irradiation unit and passing through the recording medium;
In the image picked up by the image pickup means, a plurality of pixels showing an output value equal to or higher than a threshold value are selected as an effective image range for determining the surface state of the recording medium, and there are a plurality of ranges showing the output value equal to or higher than the threshold value If, record medium imaging apparatus characterized by and a control means for selecting the largest range of the number of pixels is a range that indicates the output value of more than the threshold value as an effective image area. An irradiation means for irradiating the recording medium with light;
An imaging unit that images the surface of the recording medium as an image composed of a plurality of pixels based on the light irradiated by the irradiation unit and passing through the recording medium;
The image captured by the imaging means, a plurality of pixels showing the threshold or more output values, selects as the effective image area for determining the surface condition of the recording medium, the number of pixels the effective image range selected record If less than the number of pixels required to determine the surface state of the medium, the control means lowers the threshold so that the number of pixels increases the effective image area, characterized by having a record medium imaging apparatus . An irradiation means for irradiating the recording medium with light;
An imaging unit that images the surface of the recording medium as an image composed of a plurality of pixels based on the light irradiated by the irradiation unit and passing through the recording medium;
Necessary for discriminating the surface state of the recording medium by selecting a plurality of pixels having an output value equal to or greater than the threshold as an effective image range for discriminating the surface state of the recording medium in the image captured by the imaging unit. If the number of pixels of the effective image range in the number of pixels is less than, record medium imaging apparatus, characterized by chromatic and control means for enlarging the range of the imaging in the conveying direction of the recording medium. Irradiating means for irradiating light to record medium,
Based on said light through an irradiated Symbol recording medium by irradiation means, a recording medium imaging apparatus comprising an imaging means for capturing an image comprising the surface of the recording medium from a plurality of pixels,
The imaging means, second based on light having a first image based on the light having an optical axis in a first direction, the optical axis of the second direction of the first direction in a direction perpendicular to the optical axis capturing a and images,
In each of the first images and the second images, a plurality of pixels showing the threshold value or more output values, selects as the effective image area for determining the surface condition of the recording medium, the effective image When the number of pixels of the first image in the range is different from the number of pixels of the second image, the control unit corrects the number of pixels of the image with a large number of pixels according to the number of pixels of the image with a small number of pixels. A recording medium imaging apparatus comprising: Wherein, when the number of pixels of the first images and the second images in the effective image area is different, the number of pixels of the small images of the number of pixels the number of pixels of the image with much number of pixels recording medium imaging apparatus according to claim 5, characterized in that the same. Wherein said control means uses the each of the first images and the second images in the effective image area, according to claim 5 or 6, characterized in that the determination of the surface state of the recording medium The recording medium imaging device according to any one of the above. Wherein, said the effective image range first images or one of the second images, and performs determination of the surface state of the record medium by using at least one of images according Item 6. The recording medium imaging device according to Item 5 . The recording medium imaging apparatus according to claim 1, wherein the surface state of the recording medium is an unevenness of the recording medium or a fiber state of the recording medium. The recording medium imaging apparatus according to claim 1, wherein the output value is lightness or light amount. Forming means for forming a developer image;
Irradiating means for irradiating light to record medium,
Based on the light through the irradiated Symbol recording medium by the irradiation means, shown an imaging means for capturing an image comprising the surface of the recording medium from a plurality of pixels, the image captured by the imaging means, the threshold value or more output values Control means for selecting an imaging range of the imaging means corresponding to a plurality of pixels as an effective image range for determining the surface state of the recording medium ;
Storage means for storing the imaging range of the imaging means selected as the effective image range,
After the effective image range is stored in the storage unit, the control unit selects a range to be used for determining the surface state of the recording medium from the image captured by the imaging unit based on the effective image range. An image forming apparatus for controlling a forming condition for forming a developer image by the forming unit based on an image in a selected range so as to be suitable for a surface state of a recording medium . Forming means for forming a developer image;
An irradiation means for irradiating the recording medium with light;
An imaging unit that images the surface of the recording medium as an image composed of a plurality of pixels based on the light irradiated by the irradiation unit and passing through the recording medium;
In the image picked up by the image pickup means, a plurality of pixels showing an output value greater than or equal to a threshold value are selected as effective image ranges for determining the surface state of the recording medium, and there are a plurality of ranges showing output values equal to or more than the threshold value If, and a control means for selecting the largest range of the number of pixels is a range that indicates the output value of more than the threshold value as an effective image area,
The control unit controls a forming condition when the developer unit forms a developer image so as to be suitable for a surface state of a recording medium based on an image in a range selected as the effective image range. images forming device. Forming means for forming a developer image;
An irradiation means for irradiating the recording medium with light;
An imaging unit that images the surface of the recording medium as an image composed of a plurality of pixels based on the light irradiated by the irradiation unit and passing through the recording medium;
The image captured by the imaging means, a plurality of pixels showing the threshold or more output values, selects as the effective image area for determining the surface condition of the recording medium, the number of pixels the effective image range selected record If less than the number of pixels required to determine the surface state of the medium, and a control means for reducing said threshold value such that the number of pixels the effective image area is increased,
The control unit controls a forming condition when the developer unit forms a developer image so as to be suitable for a surface state of a recording medium based on an image in a range selected as the effective image range. images forming device. Forming means for forming a developer image;
An irradiation means for irradiating the recording medium with light;
An imaging unit that images the surface of the recording medium as an image composed of a plurality of pixels based on the light irradiated by the irradiation unit and passing through the recording medium;
Necessary for discriminating the surface state of the recording medium by selecting a plurality of pixels having an output value equal to or greater than the threshold as an effective image range for discriminating the surface state of the recording medium in the image captured by the imaging unit. Control means for expanding the imaging range in the conveyance direction of the recording medium when the number of pixels does not satisfy the number of pixels in the effective image range ;
The control unit controls a forming condition when the developer unit forms a developer image so as to be suitable for a surface state of a recording medium based on an image in a range selected as the effective image range. images forming device. Forming means for forming a developer image;
Irradiating means for irradiating light to record medium,
Based on said light through an irradiated Symbol recording medium by irradiation means, an image forming apparatus and an image pickup means for capturing an image comprising the surface of the recording medium from a plurality of pixels,
Said imaging means, first based on the light having the first images based on light having an optical axis in a first direction, the optical axis of the second direction in a direction perpendicular to the optical axis of the first direction and second images captured,
In each of the first images and the second images, a plurality of pixels showing the threshold value or more output values, selects as the effective image area for determining the surface condition of the recording medium, the effective image When the number of pixels of the first image in the range is different from the number of pixels of the second image, the control unit corrects the number of pixels of the image with a large number of pixels according to the number of pixels of the image with a small number of pixels. Have
The control means controls the forming conditions when forming the developer image by the forming means so as to be suitable for the surface state of the recording medium based on the respective images having the same number of pixels. . Wherein, when the number of pixels of the first images and the second images in the effective image area is different, the number of pixels of the small images of the number of pixels the number of pixels of the image with much number of pixels the image forming apparatus according to claim 15, characterized in that the same. Wherein said control means uses the each of the first images and the second images in the effective image area, according to claim 15 or 16, characterized in that the determination of the surface state of the recording medium The image forming apparatus according to any one of the above. Wherein, said the effective image range first images or one of the second images, and performs determination of the surface state of the record medium by using at least one of images according Item 15. The image forming apparatus according to Item 15. 19. The image forming apparatus according to claim 15, wherein the surface state of the recording medium is an unevenness of the recording medium or a fiber state of the recording medium. The image forming apparatus according to claim 15, wherein the output value is lightness or light quantity.