Paper type discrimination device, image forming device

Abstract

To provide a paper type discriminating device that suppresses a decrease in measurement accuracy due to a change in a measurement environment.SOLUTION: A paper type discriminating device includes: an optical sensor 150 for measuring a characteristic amount of paper S conveyed in a conveying direction; a paper pressing roller 260 for pressing the paper S; a media position fixing unit 1503 for forming a nip portion between the paper pressing roller 260 and the media position fixing unit 1503 and sandwiching the paper S; an information processing unit (160) that selects a measurement result to be used for determining a type of the paper S from the measurement result by the optical sensor 150; and a control unit (400) that determines the type of the paper S based on the measurement result selected by the information processing unit (160). A measurement area of the paper S by the optical sensor 150 is an effective pixel area (Xa1 to Xa2) of the paper S facing the optical sensor 150 that is not sandwiched in the nip portion. An area selected as the measurement result by the information processing unit (160) is a first distance from a center of the measurement area (Xb1 to Xb2).SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a paper type discrimination device equipped with a media sensor for discriminating the type of paper, and an image forming apparatus equipped with such a paper type discrimination device. [Background technology]

[0002] In recent years, image forming apparatuses are equipped with a media sensor for determining the type of paper, which is a recording medium. The image forming apparatus has a built-in paper type determination device that uses the media sensor to determine the type of paper while conveying the paper, for example. The media sensor measures the characteristics of the paper using an optical sensor, ultrasonic sensor, or the like. The image forming apparatus extracts the corresponding paper information from pre-registered paper information based on the measurement results of the paper characteristics by the media sensor, and determines the type of the paper. The paper information is information that includes the characteristics of each type of paper (basis weight, surface properties, etc.).

[0003] The media sensor measures the characteristic quantities from the transported paper. For this reason, the paper may fluctuate (flutter) in the vertical direction at the measurement position of the media sensor. The flutter of the paper is a factor that hinders the highly accurate measurement of the characteristic quantities by the media sensor. In particular, when the media sensor is an optical sensor, the paper may shift from the focus of the optical sensor, reducing the accuracy of the measurement results. This leads to a decrease in the accuracy of identifying the type of paper. In response to this, Patent Document 1 discloses a configuration in which a roller is placed opposite the media sensor across the paper transport path, and the roller presses the paper against the surface of the media sensor, thereby suppressing the flutter of the paper. With such a configuration, the characteristic quantities of the paper can be measured with high accuracy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-200478 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a configuration in which the paper is pressed down by a roller, the measurement results of the media sensor, particularly the optical sensor, may change due to changes in the measurement environment. Changes in the measurement environment may cause variations in the measured feature values, which may result in a decrease in measurement accuracy. In view of the above-mentioned problems, the main object of the present invention is to provide a paper type discrimination device that suppresses a decrease in measurement accuracy due to changes in the measurement environment. [Means for solving the problem]

[0006] The paper type discrimination device of the present invention comprises a measuring means for measuring characteristics of paper transported in a transport direction by a transport means, a pressing member for pressing the paper, a frame body that forms a nip portion between the pressing member and the frame body and clamps the paper, an information processing means for selecting a measurement result to be used for discriminating the type of the paper from the measurement results by the measuring means, and a control means for discriminating the type of the paper based on the measurement results selected by the information processing means, wherein the measurement area of ​​the paper by the measuring means is an area of ​​the paper facing the measuring means that is not clamped in the nip portion, and in a direction perpendicular to the transport direction, the area selected as the measurement result by the information processing means has a first distance from the center of the measurement area, and the area not selected as the measurement result has a second distance from the center of the measurement area, and the first distance is shorter than the second distance. Effect of the Invention

[0007] According to the present invention, it is possible to suppress a decrease in measurement accuracy due to a change in the measurement environment. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 2] (a) and (b) are enlarged views of the fixing unit. [Diagram 3] FIG. [Figure 4] FIG. 4 is a diagram illustrating the configuration of a media sensor. [Diagram 5] FIG. 4 is a diagram illustrating the configuration of a media sensor. [Figure 6] 13A and 13B are diagrams illustrating the results of reading by an optical sensor. [Figure 7] 1A and 1B are diagrams illustrating the relationship between the measurement environment and the measurement results. [Figure 8] FIG. 13 is a diagram showing a state in which the paper is pressed toward an optical sensor. [Figure 9] 5A and 5B are diagrams illustrating a method for determining a data calculation pixel area. [Figure 10] FIG. 4 is an explanatory diagram of the function of an information processing unit for determining a data calculation pixel region. [Figure 11] FIG. 4 is a sequence diagram showing a process of measuring a feature amount. [Figure 12] FIG. 4 is a graph showing the relationship between transmittance and basis weight. [Figure 13] 11 is a process flow diagram showing a paper type discrimination process. [Figure 14] FIG. [Figure 15] FIG. [Figure 16] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, "basis weight" refers to the mass per unit area of ​​paper and is expressed in units of [g / m^2].

[0010] (Image forming device) 1 is a configuration diagram of an image forming apparatus according to this embodiment. The image forming apparatus 201 according to this embodiment is a tandem type intermediate transfer type laser beam printer that utilizes an electrophotographic process. The image forming apparatus 201 forms and outputs a full-color or monochrome image on a recording medium, namely, paper S, based on image data acquired via a network from an external device such as a personal computer, or image data acquired from an image reading device 202 provided above.

[0011] The image forming apparatus 201 has components for forming an image inside a main body 201A, and is provided with an image reading device 202 and an operation unit 502 on the upper part of the main body 201A. Between the main body 201A and the image reading device 202 of the image forming apparatus 201, a discharge space D is provided having a stacking unit 223 onto which paper S after image formation is discharged.

[0012] The image reading device 202 is a scanner that reads an image from an original and generates image data. The image reading device 202 is used, for example, during copying of an original. The image reading device 202 of this embodiment is configured as a part of the image forming device 201. However, the image reading device 202 may be configured to be electrically connected to the image forming device 201 as a device separate from the image forming device 201.

[0013] The operation unit 502 is a user interface having an input interface and an output interface. The input interface is, for example, various key buttons, a touch panel, etc. The output interface is a display, a speaker, etc. A user can input various instructions to the image forming apparatus 201 through the operation unit 502. The image forming apparatus 201 notifies the user of various information by displaying various screens on the display of the operation unit 502. The operation unit 502 of this embodiment is configured as a part of the image forming apparatus 201. However, the operation unit 502 may be electrically connected to the image forming apparatus 201 as a device different from the image forming apparatus 201.

[0014] The image forming apparatus 201 includes, in a main body 201A, an image forming section 201B, an intermediate transfer section 201C, a secondary transfer section 201D, a fixing device 201E, and a cassette paper feed section 230. The main body 201 is also provided with a manual paper feed section 235.

[0015] The cassette paper feed section 230 feeds the paper S from a paper feed cassette 1 that stores the paper S. The cassette paper feed section 230 includes a pickup roller 2 and a separation section that includes a feed roller 3 and a retard roller 4 for separating the paper S sent out from the pickup roller 2. The paper S is fed one sheet at a time from the paper feed cassette 1 by the pickup roller 2 and the separation section. In this embodiment, a configuration in which a plurality of cassette paper feed sections 230 (four in this example) are provided will be described, but the number of cassette paper feed sections 230 may be any number. The paper S fed from the cassette paper feed section 230 is transported to the registration roller pair 240 via the transport roller pairs 280 and 290.

[0016] In addition to cassette feeding section 230, paper S can also be fed from manual feeding section 235. Manual feeding section 235 includes a manual tray 5 on which a user places paper S. Like cassette feeding section 230, manual feeding section 235 includes a pickup roller and a separator, and feeds paper S one sheet at a time from manual tray 5. Paper S fed from manual feeding section 235 is also transported to registration roller pair 240 via transport roller pairs 280 and 290.

[0017] A media sensor 100 for measuring characteristic quantities of paper S is provided on the transport path between the pair of transport rollers 280 and the pair of transport rollers 290. The media sensor 100 outputs basis weight data, surface property data, and the like as characteristic quantities of paper S transported from the cassette paper feed unit 230 or the manual paper feed unit 235. The media sensor 100 may be configured to be provided at least one or both of a position where it can detect paper S fed from the cassette paper feed unit 230 and a position where it can detect paper S fed from the manual paper feed unit 235. The configuration of the media sensor 100 will be described in detail later.

[0018] The image forming unit 201B is a four-drum full-color type, and includes a laser scanner 210 and four process cartridges 211 for forming toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K). Each process cartridge 211 includes a photosensitive drum 212, a charger 213, and a developer 214. A toner cartridge 215 is disposed above the process cartridge 211. The toner cartridge 215 supplies toner to the developer 214.

[0019] The intermediate transfer unit 201C includes an intermediate transfer belt 216 wound around a drive roller 216a and a tension roller 216b. Four primary transfer rollers 219 are provided on the inner side of the intermediate transfer belt 216, and contact the intermediate transfer belt 216 at positions facing the respective photosensitive drums 212. The intermediate transfer belt 216 is rotated in the direction of the arrow by a drive roller 216a driven by a drive unit (not shown).

[0020] The secondary transfer section 201D includes a secondary transfer roller 217 disposed opposite the drive roller 216a with the intermediate transfer belt 216 interposed therebetween. The fixing device 201E is disposed downstream of the secondary transfer roller 217 in the transport direction of the paper S, and includes a pressure roller 220a and a heating roller 220b. A first discharge roller pair 225a, a second discharge roller pair 225b, and a double-sided reversing section 201F are disposed downstream of the fixing device 201E in the transport direction of the paper S. The double-sided reversing section 201F includes a reversible roller pair 222 and a re-transport path R that transports the paper S having an image formed on one side thereof to the image forming section 201B.

[0021] The image forming apparatus 201 configured as above operates as follows. The image forming apparatus 201 acquires image data from the image reading apparatus 202 or an external device together with an instruction to start a print job, and forms an image on the paper S according to the image data. At this time, the image forming apparatus 201 performs each step of the image formation under operating conditions according to the characteristics of the paper S. Note that a print job is a series of operations from conveying the paper S and forming an image based on a print signal instructing image formation on the paper S, to discharging the paper S onto the stacking unit 223 after the image formation operation is completed. The image forming apparatus 201 acquires an instruction to start a print job from the operation unit 502 or an external device.

[0022] In the image forming unit 201B, the surface of the photosensitive drum 212 is uniformly charged to a potential of a predetermined polarity by the charger 213. The laser scanner 210 irradiates the uniformly charged surface of the photosensitive drum 212 with laser light modulated based on image data. As a result, an electrostatic latent image corresponding to the corresponding color (yellow, magenta, cyan, black) is formed on the surface of each photosensitive drum 212.

[0023] The image forming unit 201B develops the electrostatic latent image formed on the photosensitive drum 212 by the developing unit 214. On each photosensitive drum 212, the electrostatic latent image is developed with toner of the corresponding color, thereby forming a toner image of the corresponding color. The toner images are transferred in sequence from the photosensitive drum 212 to the rotating intermediate transfer belt 216 in a superimposed state by the primary transfer roller 219. As a result, a full-color toner image is formed on the intermediate transfer belt 216. The intermediate transfer belt 216 conveys the toner image to the secondary transfer unit 201D by rotating.

[0024] In parallel with such a toner image forming operation, the paper S is conveyed one by one to the pair of registration rollers 240 by the cassette paper feeder 230 or the manual paper feeder 235. The characteristic amount of the paper S is measured by the media sensor 100 before the paper S reaches the pair of registration rollers 240. The image forming apparatus 201 determines the type of the paper S based on the measured characteristic amount, and sets image forming conditions according to the determined type of the paper S. The image forming apparatus 201 performs subsequent image formation based on the set image forming conditions. The set image forming conditions are, for example, the voltage value of the secondary transfer bias applied to the secondary transfer roller 217 when the toner image is transferred to the paper S, the fixing temperature when the image is fixed by the fixing device 201E, the conveying speed of the paper S during fixing, and the like.

[0025] The pair of registration rollers 240 corrects skew of the conveyed paper S. After the skew correction, the paper S is conveyed to the secondary transfer unit 201D by the pair of registration rollers 240 in accordance with the timing at which the toner image carried by the intermediate transfer belt 216 is conveyed to the secondary transfer unit 201D. The secondary transfer unit 201D transfers the full-color toner image from the intermediate transfer belt 216 onto the paper S by a secondary transfer bias applied to the secondary transfer roller 217.

[0026] The paper S onto which the toner image has been transferred is transported to the fixing device 201E. The fixing device 201E sandwiches and transports the paper S with a roller nip formed by the pressure roller 220a and the heating roller 220b. When sandwiching and transporting the paper S, the fixing device 201E heats the paper S with the heating roller 220b, thereby melting and mixing the toners of the various colors on the paper S. The fixing device 201E also fixes the melted and mixed toners to the paper S by applying pressure to the paper S with the pressure roller 220a. At this time, the adhesive force of the melted toner causes the paper S to stick to the heating roller 220b.

[0027] 2 is an enlarged view of the fixing unit 201E. If the stiffness (rigidity) of the paper S is weak, the paper S may be taken up by the rotating heating roller 220b due to the adhesion force generated in the paper S to the heating roller 220b (FIG. 2(b)). For this reason, a separation plate 221 for separating the paper S is provided downstream of the heating roller 220b in the conveying direction of the paper S (FIG. 2(a)).

[0028] The image forming apparatus 201 may determine the state of the separation plate 221 according to the type and basis weight of the paper S determined from the measurement results of the media sensor 100. For example, when forming an image on a type of paper S with low stiffness, the separation plate 221 is arranged so that its leading edge comes into contact with the surface of the heating roller 220b as shown in FIG. 2(a), and separates the paper S from the heating roller 220b. When forming an image on a type of paper S with high stiffness, the paper S is not taken up by the heating roller 220b. For this reason, the separation plate 221 is arranged so that its leading edge does not come into contact with the surface of the heating roller 220b. This makes it possible to prevent the surface of the heating roller 220b from being worn down by the separation plate 221.

[0029] The paper S with the fixed image is discharged to the discharge space D by either the first discharge roller pair 225a or the second discharge roller pair 225b. The paper S is stacked on a stacking section 223 provided to protrude from the bottom surface of the discharge space D. When images are formed on both sides of the paper S, the paper S with the image fixed on one side is transported to a re-conveyance path R by the reversing roller pair 222 and transported again to the image forming section 201B where an image is formed on the inverted side. The re-conveyance path R is configured to transport the paper S to a transport path between the transport roller pair 290 and the registration roller pair 240.

[0030] (Control unit) 3 is an explanatory diagram of a controller that controls the operation of such an image forming apparatus 201. The controller 200 is an information processing apparatus equipped with, for example, a CPU (Central Processing Unit). Note that the controller 200 may be realized by an MPU (Micro Processor Unit) or an ASIC (Application Specific Integrated Circuit), etc. The controller 200 controls the image forming operation by the image forming apparatus 201.

[0031] The controller 200 includes a control unit 400 and a memory 401. The memory 401 stores a control program for the image forming operation, initial values ​​of various setting values, various data necessary for the image forming operation, and the like. The memory 401 also has a storage area for storing a paper type database 402. The paper type database 402 is a database in which the correspondence between paper characteristics and image forming conditions (printing modes) is set in advance. The paper characteristics are, for example, the type and basis weight of paper. The control unit 400 is connected to a host device 501, an operation unit 502, and a media sensor 100.

[0032] The host device 501 is a personal computer, an image scanner, a facsimile, etc. The operation unit 502 inputs instructions, settings, etc. received via an input interface to the control unit 400. The operation unit 502 outputs various information via an output interface under the control of the control unit 400. As described above, the operation unit 502 has a display as an output interface, and displays various information on the display.

[0033] The control unit 400 starts a print job by receiving an instruction to start the print job from the host device 501 or the operation unit 502. The control unit 400 receives image data from the host device 501 or the image reading device 202, and processes the received image data. The control unit 400 causes the image forming unit 201B to form a toner image based on the image data after the image processing, and executes the print job.

[0034] The media sensor 100 includes an information processing unit 160, an ultrasonic sensor 120, and an optical sensor 150. In this embodiment, the ultrasonic sensor 120 and the optical sensor 150 form a paper measurement unit. In addition to the ultrasonic sensor 120 and the optical sensor 150, a paper detection sensor 270 is connected to the information processing unit 160. The information processing unit 160 is an information processing device realized by, for example, a CPU, an MPU, or an ASIC.

[0035] Image formation conditions (conveyance speed during fixing, target fixing temperature, transfer voltage during secondary transfer, etc.) vary depending on the physical properties (basis weight, stiffness, surface properties, material, etc.) of the paper S on which the image is formed. Therefore, when forming an image, it is necessary to set image formation conditions in advance according to the characteristics (type, basis weight, etc.) of the paper S to be used.

[0036] Depending on the type of paper S, restrictions may be placed on the paper feed slot (paper feed cassette 1, manual feed tray 5) when it is set. For example, some types of thick paper with high stiffness can only be fed from the manual feed tray 5, where the curvature of the transport path is small. Coated paper, which has a smooth surface and strong adhesion between sheets, needs to be fed one sheet at a time from the manual feed tray 5 to prevent multiple sheets from being fed overlapping. Paper made from pulp generally has different bending stiffness depending on the length and width due to the bias in the orientation direction (grain direction) of the pulp fibers that occurs due to manufacturing reasons. Therefore, there are some types of paper that have recommended length and width directions when set in the paper feed slot so that the bending stiffness against the bending of the transport path is low. Also, compared to plain paper, one-sided coated paper, which is coated on only one side, has a specification of the top and bottom when set in order to print on the coated side.

[0037] There are some types of paper that cannot be used in the image forming apparatus 201. For example, thick paper with too high stiffness may stop being conveyed due to the resistance when conveyed along a curved conveying path. Thin paper with too low stiffness may be strongly influenced by the adhesive force between the molten toner and the heating roller 220b when passing through the fixing device 201E, and may not be able to be peeled off from the heating roller 220b by the separation plate 221 and may wind up as it is (FIG. 2(b)). Synthetic paper made of synthetic resin instead of pulp as a raw material may melt when heated by the fixing device 201E, and may contaminate the heating roller 220b.

[0038] For the above reasons, in order to properly perform image formation, it is important to identify the type of paper S from the characteristic amounts of the paper S used before image formation. For this reason, the media sensor 100 needs to measure the characteristic amounts of the paper S before the paper S is transported to the secondary transfer unit 201D. The operation of the media sensor 100 is controlled by the information processing unit 160, and the measurement results of the ultrasonic sensor 120 and the optical sensor 150 are processed by the information processing unit 160. The information processing unit 160 operates under the control of the control unit 400, and transmits the characteristic amounts of the paper S obtained from the measurement results of the ultrasonic sensor 120 and the optical sensor 150 to the control unit 400.

[0039] The control unit 400 and the information processing unit 160 start a paper measurement sequence based on the detection result of the paper detection sensor 270. The paper detection sensor 270 detects the conveyed paper S. For example, the control unit 400 and the information processing unit 160 start the paper measurement sequence when the paper detection sensor 270 detects the paper S. By starting the paper measurement sequence, the control unit 400 and the information processing unit 160 cause the ultrasonic sensor 120 and the optical sensor 150 to perform a measurement operation.

[0040] The ultrasonic sensor 120 measures the paper S with ultrasonic waves and outputs a predetermined voltage value as the measurement result. The information processing unit 160 acquires the output value of the ultrasonic sensor 120 and derives the transmittance of the paper S from the output value when the paper S is present and the output value when the paper S is not present. The information processing unit 160 detects basis weight data representing the basis weight from the transmittance of the paper S. The optical sensor 150 is, for example, a contact image sensor (CIS). The information processing unit 160 saves the luminance value of each pixel as the imaging result by the optical sensor 150. The information processing unit 160 converts the saved luminance value of each pixel into a difference integrated value obtained by integrating the difference between the luminance values ​​of adjacent pixels and surface property data such as lightness.

[0041] The information processing unit 160 transmits information corresponding to the basis weight and information corresponding to the surface property to the control unit 400. The control unit 400 judges the type of the paper S (paper type, paper type information) based on the acquired information corresponding to the basis weight and information corresponding to the surface property. The control unit 400 determines one image forming condition (printing mode) corresponding to the type of the paper S from among a plurality of printing modes stored in the paper type database 402. The control unit 400 displays information of the determined printing mode on the display of the operation unit 502. The printing mode is an operation mode for controlling image formation under predetermined image forming conditions (for example, a secondary transfer bias value, a target fixing temperature of the fixing unit 201E, a conveying speed during fixing, etc.). The printing modes are named after the types of paper, such as "thin paper 1", "thin paper 2", "plain paper 1", "coated paper 1", "coated paper 2", "coated paper 3", etc. Note that, although a method for determining image forming conditions from the type of the paper S has been described, the present invention is not limited to this. For example, the control unit 400 determines the type (paper type, paper type information) of the paper S based on the acquired information corresponding to the surface property. The control unit 400 may determine one image forming condition (printing mode) corresponding to the information corresponding to the type and basis weight of the paper S from among a plurality of printing modes stored in the paper type database 402.

[0042] (Media sensor configuration) Figures 4 and 5 are explanatory diagrams of the configuration of the media sensor 100. Figure 4 is a diagram of the media sensor 100 as viewed from a direction perpendicular to the transport direction of the paper S. Figure 5 is a diagram of the media sensor 100 as viewed from the upstream side in the transport direction of the paper S.

[0043] 4, the media sensor 100 is provided between a pair of transport rollers 280 and a pair of transport rollers 290, and acquires feature quantities such as basis weight data and surface property data of the transported paper S. The pair of transport rollers 280 is provided upstream of the media sensor 100 in the transport direction of the paper S, and the pair of transport rollers 290 is provided downstream of the media sensor 100 in the transport direction of the paper S. The paper detection sensor 270 is disposed between the media sensor 100 and the pair of transport rollers 280. It is sufficient that the paper detection sensor 270 is provided upstream of the media sensor 100 in the transport direction of the paper S.

[0044] 5, in the media sensor 100, an ultrasonic sensor 120 and an optical sensor 150 are arranged at the same position in the transport direction of the paper S, side by side in a direction perpendicular to the transport direction. The ultrasonic sensor 120 is composed of an ultrasonic transmitter 130 and an ultrasonic receiver 131. The optical sensor 150 is a CIS having a light source 1501 (e.g., an LED) which is a light emitting unit, and a line sensor 1502 which is a light receiving unit. The optical sensor 150 may be composed of a CCD image sensor or a CMOS image sensor.

[0045] The optical sensor 150 measures the brightness value of the paper S based on the received light. To do this, the paper S needs to be held at the optical focal position of the optical sensor 150. When measuring the paper S, the ultrasonic sensor 120 can improve the measurement accuracy if it is not affected by the flapping of the paper S being transported. For this reason, the paper S needs to be transported with its posture stabilized.

[0046] In this embodiment, in order to stabilize the posture of the paper S while transporting it, paper pressure roller 260 and paper pressure roller 261 are provided between transport roller pair 280 and transport roller pair 290. Paper pressure roller 260 and paper pressure roller 261 are arranged at the same position in the transport direction of paper S. Paper pressure roller 260 and paper pressure roller 261 are pressing members that can move between a first position separated from the paper S and a second position close to the paper S in the direction of media sensor 100. Paper pressure roller 260 and paper pressure roller 261 move to the second position close to the media sensor 100 when the media sensor 100 measures the paper S, and press the paper S toward the media sensor 100.

[0047] The paper pressure roller 260 is disposed opposite the optical sensor 150 across the conveyance path, and is configured to press the paper S toward the optical sensor 150 by moving to a second position close to the media sensor 100. This reduces variation in the position and posture of the paper S when the media sensor 100 measures the surface of the paper S. In addition, the paper pressure roller 260 and the paper pressure roller 261 can stabilize the position and posture of the paper S at the measurement position (measurement position) of the ultrasonic sensor 120 by moving to the second position close to the media sensor 100. Therefore, the media sensor 100 can stably measure the surface properties, basis weight, and other characteristic quantities of the paper S. The paper pressure roller 261 is provided at a position where the ultrasonic sensor 120 is sandwiched between the paper pressure roller 260 and the paper pressure roller 260. The conveyance roller pair 280, the conveyance roller pair 290, the media sensor 100, the paper detection sensor 270, the controller 200, the paper pressure roller 260, and the paper pressure roller 261 constitute a paper type discrimination device.

[0048] (Basis weight measurement) In the ultrasonic sensor 120, an ultrasonic transmitter 130 and an ultrasonic receiver 131 are disposed at positions facing each other across the transport path. The ultrasonic transmitter 130 is provided on the upper block 110 side of the media sensor 100. The ultrasonic receiver 131 is provided on the lower block 109 side of the media sensor 100. In the ultrasonic sensor 120, the ultrasonic receiver 131 receives ultrasonic waves output from the ultrasonic transmitter 130 via the transport path of the paper S. The ultrasonic receiver 131 outputs information (output value) for determining the basis weight of the paper S based on the received ultrasonic waves.

[0049] Both the ultrasonic transmitter 130 and the ultrasonic receiver 131 are composed of a piezoelectric element (also called a piezo element), which is an element for converting mechanical displacement into an electric signal, and an electrode terminal. When a pulse voltage of a predetermined frequency is input to the electrode terminal of the ultrasonic transmitter 130, the piezoelectric element oscillates and generates an ultrasonic wave. The generated ultrasonic wave propagates through the air. When the ultrasonic wave reaches the paper S, the paper S vibrates due to the ultrasonic wave. The ultrasonic wave generated by the ultrasonic transmitter 130 propagates through the paper S to the ultrasonic receiver 131. The piezoelectric element of the ultrasonic receiver 131 generates an output voltage at the electrode terminal according to the amplitude of the received ultrasonic wave. The output voltage has a voltage value according to the basis weight of the paper S. The output voltage is transmitted to the information processing unit 160 as an output value.

[0050] The transmittance is the ratio of the output voltage when there is no paper S between the ultrasonic transmitter 130 and the ultrasonic receiver 131 to the output voltage when there is paper S. The transmittance of ultrasonic waves changes depending on the basis weight (area density) of the paper S. Therefore, the basis weight of the paper S can be measured by using a conversion formula or conversion table between transmittance and basis weight.

[0051] (Surface quality measurement) The surface property of the paper S is detected by the optical sensor 150. Light emitted from a light source 1501 is irradiated onto the paper S at a certain angle by a light guide (not shown). The paper S reflects the irradiated light. The light reflected by the paper S is imaged on the line sensor 1502 via a lens (not shown). In this way, the line sensor 1502 can read the light reflected from the paper S as an image. FIG. 6 is an explanatory diagram of the reading result by the optical sensor 150.

[0052] Fig. 6(a) illustrates an example of an image read by the line sensor 1502. The line sensor 1502 has a plurality of light receiving elements 1502a. The plurality of light receiving elements 1502a are arranged in a direction perpendicular to the conveying direction of the paper S, and can read one line of an image at a time. In the example of Fig. 6(a), 400 light receiving elements 1502a are provided, and an image of 400 pixels (A1 to A400) can be read at a time.

[0053] In this embodiment, multiple light receiving elements 1502a are arranged to provide a resolution of 300 dpi. The amount of information in a one-line image read by the line sensor 1502 at one time is insufficient to determine the surface properties of the paper S. This is because the deviation in the read results for each read position is large in a one-line image. For this reason, the optical sensor 150 performs multiple read operations on the paper S being transported, and obtains the read results of the image of multiple lines of the paper S. By stitching together the read results for the multiple lines in the transport direction of the paper S, it becomes possible to determine the tendency of the surface properties of a specified area of ​​the paper S.

[0054] The information processing unit 160 performs digital processing on the image read by the optical sensor 150, and stores the results of the digital processing as an output value for each pixel (pixel output value) in a memory (not shown). The pixel output value is, for example, a luminance value. The information processing unit 160 extracts pixel output values ​​in a data calculation pixel area used to derive surface property data indicating the surface property of the paper S from the pixel output values ​​of all pixels of the optical sensor 150 stored in the memory. A method for determining the data calculation pixel area will be described later. The information processing unit 160 acquires and accumulates a difference integrated value, a brightness integrated value, and a PP integrated value of the brightness value based on the pixel output value (brightness value) of each pixel in the extracted data calculation pixel area. These values ​​(difference integrated value, brightness integrated value, and PP integrated value) become the surface property data of the paper S.

[0055] The difference accumulation value is a value obtained by accumulating the difference in brightness value for each adjacent pixel of the image read by the line sensor 1502, and adding the result for the number of lines. The difference accumulation value is an index that expresses the unevenness of the paper. In FIG. 6(b), if the brightness value of each pixel is expressed by the pixel position (1 to n) and the detection line (A to m), the difference accumulation value Y is expressed by the following formula (1) using the difference accumulation value k for each line. Note that the detection pixel data direction in FIG. 6(b) is the arrangement direction of the light receiving elements 1502a of the line sensor 1502 (the direction of the pixels in one line). Also, the detection line direction in FIG. 6(b) is the transport direction of the paper S. k1=|A2-A1|+|A3-A2|…+|An-A(n-1)| k2=|B2-B1|+|B3-B2|…+|Bn-B(n-1)| · · · km=|m2-m1|+|m3-m2|…+|mn-m(n-1)| Y = k1 + k2 + ... + km ... (1)

[0056] The brightness integrated value is obtained by adding up the integrated values ​​of the luminance values ​​of each pixel received by the line sensor 1502 for the number of detected lines, and represents the brightness of the surface of the paper S. The brightness integrated value M is expressed by the following formula (2). M=A1+A2+…+B1+B2+…+mn…(2)

[0057] The PP integrated value is the sum of the difference between the maximum and minimum brightness values ​​of one line for the number of detected lines. Transparent films made of resins such as PET reflect less light from the light source 1501, and are detected as low in brightness. Paper with intentionally created geometric unevenness on the surface, such as embossed paper, increases the brightness difference between adjacent pixels due to the unevenness, and the difference integrated value increases. Recycled paper also has an uneven grain direction, and the pulp fibers become shorter after going through several recycling processes, so the surface tends to be detected as rough. Conversely, coated paper appears to have fewer unevenness due to the coating layer on the surface, and the difference integrated value tends to be smaller. The brightness integrated value and PP integrated value are parameters used to distinguish these types of paper.

[0058] The control unit 400 acquires basis weight data and surface property data (integrated difference value, integrated brightness value, and integrated PP value) as characteristic amounts of the paper S from the information processing unit 160, and determines the paper type by referring to the paper type database 402. The control unit 400 performs image formation according to the print job under image formation conditions corresponding to the determined paper type.

[0059] The optical sensor 150 configured as above measures the feature quantities of the paper S while the paper S is pressed by the paper pressure roller 260. The measurement results (pixel output values) of the feature quantities by the optical sensor 150 may be affected by changes in the measurement environment. Fig. 7 is an explanatory diagram of the relationship between the measurement environment and the measurement results.

[0060] FIG. 7(a) shows a state in which the paper S is pressed toward the optical sensor 150 by the paper pressure roller 260. A predetermined space is created between the paper pressure roller 260 (paper S) and the light receiving surface 1504 of the optical sensor 150. Media position fixing parts 1503 are provided near both ends of the paper pressure roller 260. The media position fixing parts 1503 are frames that form a nip part between the paper pressure roller 260 and the paper pressure roller 260 when the paper pressure roller 260 moves to the second position. The paper S transported to the designated position is pressed against the media position fixing parts 1503 by the paper pressure roller 260 and is clamped, thereby suppressing positional fluctuation. In a place where there is no media position fixing part 1503, the paper S is pressed toward the light receiving surface 1504 by the paper pressure roller 260.

[0061] When the paper S is in this state, the optical sensor 150 measures the paper S. The optical sensor 150 irradiates light from a light source 1501 onto the paper S. The line sensor 1502 receives the light reflected by the paper S and transmits an output value for each pixel (pixel output value) to the information processing unit 160. At this time, the pixel output value becomes unstable near the end of the media attitude fixing unit 1503 and becomes a stable value away from the end of the media attitude fixing unit 1503. This is because the paper S curves and deforms near the end of the media attitude fixing unit 1503 and becomes parallel to the light receiving surface of the line sensor 1502 away from the end of the media attitude fixing unit 1503.

[0062] The amount of deformation of the sheet S is determined by the stiffness of the sheet S and the pressure applied to the sheet S by the sheet pressure roller 260. If the moisture absorption amount of the sheet S changes due to a change in the measurement environment (e.g., environmental temperature or humidity), the stiffness of the sheet S changes and the amount of deformation of the sheet S also changes.

[0063] FIG. 7(b) illustrates the effect of the measurement environment on pixel output values. Here, a case where the amount of moisture absorption of paper S changes due to a change in the measurement environment is explained. The vertical axis indicates pixel output values, and the horizontal axis indicates the position of each pixel (light receiving element) of line sensor 1502. The position of each pixel of line sensor 1502 (position in a direction perpendicular to the transport direction of paper S) is divided into pixel areas m1, m2, and m3. Pixel areas m1 and m3 are areas close to the end of media attitude fixing unit 1503. Pixel area m2 is an area away from the end of media attitude fixing unit 1503.

[0064] The solid lines represent the pixel output values ​​of each pixel when the moisture absorption of paper S is steady (medium moisture absorption) at room temperature and normal humidity. The dashed lines represent the pixel output values ​​of each pixel when the moisture absorption of paper S is large (large moisture absorption) at high temperature and high humidity. The dashed and dotted lines represent the pixel output values ​​of each pixel when the moisture absorption of paper S is small (small moisture absorption) at low temperature and low humidity.

[0065] The greater the amount of moisture absorbed, the lower the stiffness of the paper S and the greater the amount of deformation. In pixel areas m1 and m3, the greater the amount of deformation of the paper S, the greater the pixel output value. In other words, the pixel output value changes due to changes in the measurement environment. In this way, the measurement results of the paper S change due to changes in the measurement environment, and the accuracy of identifying the type of the paper S decreases. Therefore, in this embodiment, by setting a data calculation pixel area for selecting pixel output values ​​used to acquire feature amounts, the effect of changes in the measurement environment is suppressed and the accuracy of identifying the type of the paper S is maintained.

[0066] (Data calculation pixel area) A method for determining a data calculation pixel region for selecting the measurement results used to obtain surface property data, which is a feature amount, from the measurement results by the optical sensor 150 will be described with reference to FIGS.

[0067] 8 is a diagram showing a state in which the edge of the paper S is pressed toward the optical sensor 150 by the paper pressure roller 260. The edge of the paper S is pressed against the media attitude fixing part 1503, and the center part is pressed toward the light receiving surface 1504 of the optical sensor 150, close to it, and parallel to the light receiving surface 1504. The line sensor 1502 is composed of N light receiving elements, each light receiving element corresponding to one pixel. The position of each pixel (hereinafter referred to as "pixel address") is represented by X0, Xa1, Xb1, ... Xb2, Xa2, XN.

[0068] The area of ​​pixel addresses X0 to XN is the total pixel area that indicates the entire result of reading one line by line sensor 1502. Pixel address X0 indicates the start point of the total pixel area. Pixel address XN indicates the end point of the total pixel area. The total pixel area includes everything between two media orientation fixing portions 1503. Optical sensor 150 measures the total pixel area in one line.

[0069] The area of ​​pixel addresses Xa1 to Xa2 indicates the effective pixel area. Pixel address Xa1 indicates the start point of the effective pixel area. Pixel address Xa2 indicates the end point of the effective pixel area. The effective pixel area indicates a pixel area where a pixel output value equal to or greater than a predetermined value is obtained when light is irradiated from a light source 1501 onto an object with uniform reflectance located at a nominal position and the reflected light is received by a line sensor 1502. The starting pixel address Xa1 and the ending pixel address Xa2 of the effective pixel area are determined in advance. The nominal position corresponds to the positions of the two media orientation fixing units 1503, and in this embodiment, is the ideal position when the paper S is transported.

[0070] The area of ​​pixel addresses Xb1 to Xb2 indicates the data calculation pixel area. Pixel address Xb1 indicates the start point of the data calculation pixel area. Pixel address Xb2 indicates the end point of the data calculation pixel area. The data calculation pixel area is an area within the effective pixel area where more stable measurement results can be obtained. For example, the data calculation pixel area is an area where the paper S is parallel to the light receiving surface 1504. The area of ​​pixel addresses Xb1 to Xb2 is an area within a first distance from the center of the measurement area of ​​the optical sensor 150, and is an area where the paper S is not clamped in the nip portion between the media attitude fixing part 1503 and the paper pressing roller 260. The area of ​​pixel addresses Xa1 to Xa2 is an area within a second distance from the center of the measurement area of ​​the optical sensor 150. The first distance is shorter than the second distance.

[0071] Fig. 9 is an explanatory diagram of a method for determining a data calculation pixel area. Fig. 9(a) shows pixel output values ​​of each pixel of the line sensor 1502 when a reference paper for determining a data calculation pixel area is measured with the configuration of Fig. 8. The horizontal axis indicates the position of each pixel of the line sensor 1502, and the vertical axis indicates the pixel output value of each pixel. The reference paper is, for example, a subject with uniform reflectance.

[0072] The pixel output values ​​in the range of pixel addresses Xa1 to Xa2 are pixel output values ​​of the effective pixel region. The pixel output values ​​in the range of pixel addresses Xb1 to Xb2 are pixel output values ​​of the data calculation pixel region. The data calculation pixel region includes the pixel region in the center of the paper S in FIG. 8, where the paper S and the light receiving surface 1504 are close to each other and are parallel to each other. The pixel output values ​​of the data calculation pixel region are stable at a constant value because they are the reading results of a portion of the paper S that is close to the light receiving surface 1504 of the optical sensor 150 and parallel to the light receiving surface 1504. The pixel output values ​​are large in the vicinity of the media attitude fixing portion 1503. The pixel output values ​​in the ranges of pixel addresses Xa1 to Xb1 and pixel addresses Xb2 to Xa2, which are within the effective pixel region and outside the data calculation pixel region, vary from pixel to pixel because they are close to the media attitude fixing portion 1503.

[0073] Fig. 9(b) shows adjacent pixel difference values ​​based on the pixel output values ​​of each pixel in Fig. 9(a). The adjacent pixel difference value S is the absolute value of the difference between adjacent pixel outputs, and is expressed by the following formula (3). Formula (3) is the adjacent pixel difference value S for measurement line A (see Fig. 6(b)), where "j" indicates the position of the pixel. The adjacent pixel difference values ​​are accumulated for all pixels in the data calculation area over the measurement lines to obtain the above difference accumulation value. Adjacent pixel difference value Sj=|Aj+1-Aj| ... (3)

[0074] 9(a), the horizontal axis of Fig. 9(b) indicates the position of each pixel of the line sensor 1502, and the vertical axis indicates the adjacent pixel difference value. Like the pixel output value, the adjacent pixel difference value also becomes large near the media orientation fixing portion 1503.

[0075] A threshold value Th is set for the adjacent pixel difference value. The area excluding the area where the adjacent pixel difference value is equal to or greater than the threshold value Th (area where the adjacent pixel difference value is less than the threshold value) is the data calculation pixel area. In FIG. 9(b), the threshold value Th is set to "1550." The area from pixel addresses Xb1 to Bb2, where the adjacent pixel difference value intersects with the threshold value Th (1550) as the starting point and pixel address Xb2 as the end point, is the data calculation pixel area.

[0076] The adjacent pixel difference value of the data calculation pixel region is stable at a constant value because the pixel output value is stable at a constant value due to the proximity of the paper S to the light receiving surface 1504 of the optical sensor 150 and being parallel to the light receiving surface 1504. However, in the vicinity of pixel address Xb1, the adjacent pixel difference value fluctuates due to the influence of fluctuations in the pixel output value on the pixel address Xa1 side. The same is true for the adjacent pixel difference value in the vicinity of pixel address Xb2.

[0077] The threshold value Th is set based on the results (output pixel values) of measuring multiple types of paper to be measured in multiple different measurement environments by the optical sensor 150. The multiple different measurement environments are, for example, high temperature and high humidity (30°C, 80%), normal temperature and normal humidity (23°C, 50%), and low temperature and low humidity (15°C, 10%).

[0078] A differential integrated value Y is obtained from the output pixel values ​​from each measurement environment. At this time, the threshold value Th is varied to vary the data calculation pixel area for obtaining the differential integrated value Y. The differential integrated value obtained from the high temperature and high humidity measurement environment is designated as "YH", the differential integrated value obtained from the normal temperature and normal humidity measurement environment is designated as "YN", and the differential integrated value obtained from the low temperature and low humidity measurement environment is designated as "YL". The threshold value Th when the differential integrated values ​​YH, YN, and YL of each measurement environment satisfy the following condition becomes the threshold value Th when determining the pixel addresses Xb1 to Bb2, which are the data calculation pixel area. Note that under the following condition, the allowable value PTh is, for example, "10". |(YH / YN-1)|×100 < PTh |{(YL / YN)-1}|×100 < PTh

[0079] When the pixel output values ​​of the effective pixel area (Xa1 to Xa2) are used as in the conventional method, the difference accumulation value Y is YH=290000, YN=240000, and YL=200000. In this case, the change amount of the difference accumulation value Y due to the influence of the measurement environment is a maximum of +20%. When the threshold value Th (=1550) is set as shown in this embodiment, the pixel area of ​​the pixel output value used for the difference accumulation value is narrowed from the pixel address Xa1 to Xa2 (effective pixel area) to the pixel address Xb1 to Xb2 (data calculation pixel area). As a result, the difference accumulation value Y is YH=140000, YN=127000, and YL=116000. In this case, the change amount of the difference accumulation value Y due to the influence of the measurement environment is a maximum of 10%. By setting the data calculation pixel area based on the threshold value Th in this way, the change amount of the difference accumulation value Y is reduced from a maximum of 20% to a maximum of 10%. In other words, by setting the data calculation pixel area based on the threshold value Th, the pixel output values ​​(pixel addresses Xb1 to Xb2) used to calculate the feature amount of the paper S are selected, and the influence of changes in the measurement environment on the measurement results of the optical sensor 150 is suppressed.

[0080] In this embodiment, the threshold value Th is set to "1550" and some pixel output values ​​of pixels in the area where the deformation of the paper is large are left. This is because if the data calculation pixel area is too narrow, it becomes impossible to measure the uneven features of the paper surface. The tolerance value PTh is set so that the minimum data calculation pixel area can be secured. Note that, even if the data calculation pixel area is set even narrower, if a pixel output value sufficient for measuring the uneven features of the paper surface can be secured, the threshold value Th may be set to a value closer to "1000". The threshold value Th and the tolerance value PTh differ depending on the configuration of the image forming device 201. For this reason, the threshold value Th and the tolerance value PTh need to be set for each image forming device. The start pixel address Xb1 and the end pixel address Xb2 of the data calculation pixel area are determined in advance and stored in the memory of the information processing unit 160.

[0081] 10 is an explanatory diagram of the function of the information processing unit 160 for determining a data calculation pixel region. The information processing unit 160 functions as a region cutout unit 1601, a memory 1602, and a parameter calculation unit 1603. A start pixel address Xb1 and an end pixel address Xb2 of the data calculation pixel region are stored in advance in the memory 1602.

[0082] The pixel output values ​​of all pixels output from the line sensor 1502 are transmitted to an area cutout unit 1601 of the information processing unit 160. The area cutout unit 1601 acquires a start pixel address Xb1 and an end pixel address Xb2 of the data calculation pixel area from the memory 1602. The area cutout unit 1601 cuts out pixel output values ​​within the range of the data calculation pixel area (pixel address Xb1 to pixel address Xb2) from the pixel output values ​​of all pixels. The area cutout unit 1601 transmits the cut-out pixel output values ​​to a parameter calculation unit 1603 as pixel output values ​​of the data calculation pixel area.

[0083] The parameter calculation unit 1603 obtains the above-mentioned difference integrated value, brightness integrated value, and PP integrated value based on the pixel output values ​​of the data calculation pixel area (pixel address Xb1 to pixel address Xb2) obtained from the area extraction unit 1601. The parameter calculation unit 1603 transmits the obtained difference integrated value, brightness integrated value, and PP integrated value to the control unit 400 as the feature amount (surface property data) of the paper S.

[0084] (Paper type identification) A description will now be given of the process of determining the type of paper S. In this embodiment, the paper type is determined by a process of measuring the characteristic amounts of the paper S and a process of determining the paper type from the characteristic amounts. FIG. 11 is a sequence diagram showing the process of measuring the characteristic amounts of the paper S.

[0085] The user sets the control unit 400 to an automatic paper identification mode using the operation unit 502 (S101). By setting the automatic identification mode, the control unit 400 can measure the characteristic amounts of the paper S, distinguish the paper type based on the characteristic amounts, and set image formation conditions based on the paper type. When the automatic identification mode is set, the control unit 400 notifies the information processing unit 160 of a command to measure the characteristic amounts of the paper S (S102).

[0086] When the information processing unit 160 receives a measurement command from the control unit 400, it performs initialization processing such as calibration of the ultrasonic sensor 120 and the optical sensor 150 in order to measure the paper S (S103). In the initialization processing, measurement setting values ​​are set according to initial setting values ​​stored in the memory 1602 of the information processing unit 160.

[0087] When the initialization process is completed, the information processing unit 160 performs ultrasonic measurement using the ultrasonic sensor 120 without conveying paper (without paper) and stores the measurement result in the memory 1602 (S104). The information processing unit 160 instructs the control unit 400 to start conveying paper S (S105). The control unit 400 starts conveying paper S in response to the instruction.

[0088] The information processing unit 160 waits until the paper detection sensor 270 detects the paper S. When the paper detection sensor 270 detects the paper S (S106), the information processing unit 160 performs ultrasonic measurement by the ultrasonic sensor 120 with the paper S present after a predetermined time has elapsed, and stores the measurement result in the memory 1602 (S107). The information processing unit 160 performs measurement of the surface property of the paper S by the optical sensor 150, and stores the pixel output value, which is the measurement result, in the memory 1602 (S108). Note that the process of S107 and the process of S108 may be reversed, or may be performed simultaneously. In other words, the measurement by the ultrasonic sensor 120 and the measurement by the optical sensor 150 may be performed in any order, or may be performed simultaneously. Note that, upon detection of the paper S by the paper detection sensor 270, the paper pressing roller 260 and the paper pressing roller 261 move to the second position to press the paper S toward the media sensor 100, thereby suppressing flapping of the paper S. This allows the characteristic quantities of the paper S to be measured with high accuracy.

[0089] The information processing unit 160 acquires the characteristic quantities (basis weight data, surface property data) of the paper S based on the measurement results by the ultrasonic sensor 120 and the measurement results by the optical sensor 150 stored in the memory 1602 (S109). The information processing unit 160 transmits the characteristic quantities to the control unit 400. The information processing unit 160 acquires the basis weight data from the measurement results of the ultrasonic sensor 120, and acquires the surface property data from the measurement results of the optical sensor 150, as the characteristic quantities of the paper S. The surface property data is acquired based on the pixel output values ​​of the data calculation pixel area, as described above.

[0090] As described above, the basis weight data is obtained based on the transmittance of the paper S derived from the measurement results of ultrasonic measurement in a paper-free state and the measurement results of ultrasonic measurement of information with paper present. The information processing unit 160 obtains the basis weight data by using a conversion formula or conversion table between the transmittance and basis weight of the paper S. FIG. 12 is an explanatory diagram of the relationship between the transmittance and basis weight. The information processing unit 160 stores in advance in the memory 1602 a conversion formula or conversion table that expresses such a relationship.

[0091] The control unit 400 acquires the characteristic amounts of the paper S from the information processing unit 160 (S110). The control unit 400 determines the type of the paper S based on the acquired characteristic amounts (basis weight data, surface property data) of the paper S. Fig. 13 is a process flow diagram showing the paper type determination process.

[0092] The control unit 400 classifies the type of the paper S based on the surface property data (S201). FIG. 14 is a classification table of paper types based on the difference integrated value and the brightness integrated value included in the surface property data. FIG. 14 is a matrix in which the surface property of the paper is measured in advance and the paper types are classified by machine learning, with the difference integrated value on the vertical axis and the brightness integrated value on the horizontal axis. The thresholds for classifying the paper types are the brightness integrated value a0 to a3 and the difference integrated value b0 to b4. These thresholds are stored in advance in the paper type database 402 of the memory 401. Note that such a classification table may be a three-dimensional matrix that can classify the paper types in more detail by adding the PP integrated value as a parameter. The control unit 400 identifies the paper type by comparing the surface property information with each threshold.

[0093] The control unit 400 classifies the type of paper based on the basis weight data (S202). Fig. 15 is a classification table of paper types by basis weight. The paper type is determined based on which basis weight range the basis weight measured by the media sensor 100 falls within. The threshold values ​​indicating the basis weight ranges are indicated by c1 to c23 and are stored in advance in a paper type database 402 in the memory 401.

[0094] The control unit 400 determines the paper type based on the basis weight data acquired from the media sensor 100 and the basis weight ranges in the classification table shown in Fig. 15 of the paper type determined based on the surface property information and the classification table in Fig. 14 (S203). The control unit 400 determines image formation conditions in accordance with the determined paper type and sets them in the image forming device 201.

[0095] Fig. 16 is a paper type classification table that combines the classification tables of Fig. 14 and Fig. 15. Such a classification table may be stored in the paper type database 402 of the memory 401, and the control unit 400 may determine the image forming conditions by identifying the paper type using such a classification table. In the classification table of Fig. 16, the surface properties of the paper are classified by a0 to a3 and b0 to b3, which are thresholds for the difference integrated value and the brightness integrated value. The range of the matrix into which the paper types are classified is changed by changing the values ​​of a0 to a3 and b0 to b3. In addition, the basis weight range of each paper type is changed by changing the values ​​of c1 to c23, which are thresholds for the basis weight range.

[0096] In the present embodiment as described above, even if the measurement environment of the media sensor 100 changes, the paper type can be determined with high accuracy because the paper type is determined using only the measurement results suitable for determining the paper type. Measurement results within the range of the data calculation pixel area are selected and used to determine the paper type. Since the paper type is determined with high accuracy, image formation conditions suitable for the paper S are set, and the quality of the image printed on the paper S is maintained at a high level. Note that in this embodiment, the paper S is pressed against the media attitude fixing section 1503 by the paper pressure rollers 260 and 261 to suppress flapping, but the position and attitude of the paper S may be stabilized by other configurations.

[0097] In the above explanation, the paper type database 402 is provided in the memory 401 of the controller 200, but the storage location of the paper type database 402 is not limited to this. For example, the paper type database 402 may be stored in the media sensor 100. In this case, the information processing unit 160 determines the type and basis weight of the paper S, and also determines the print mode.

[0098] Although the configuration of the image forming apparatus 201 has been described above, the present invention is applicable to any apparatus that has a paper type discrimination device. For example, such a paper type discrimination device can be used in an apparatus that processes paper under conditions according to the paper type while conveying the paper. For example, an ADF (Auto Document Feeder) that has the paper type discrimination device of this embodiment can perform high-precision image reading by adjusting the paper conveying speed according to the paper type.

Claims

1. a measuring means for measuring a characteristic amount of the paper conveyed in the conveying direction by the conveying means; A pressing member that presses the paper; a frame that forms a nip portion between itself and the pressing member and holds the paper; an information processing means for selecting a measurement result to be used for identifying the type of paper from the measurement results by the measurement means; a control means for determining the type of the paper based on the measurement results selected by the information processing means; the measurement area of ​​the sheet by the measurement means is an area of ​​the sheet facing the measurement means that is not clamped in the nip portion, In a direction perpendicular to the conveying direction, a region selected by the information processing means as the measurement result has a first distance from a center of the measurement region, and a region not selected as the measurement result has a second distance from the center of the measurement region; The first distance is shorter than the second distance. Paper type discrimination device.

2. The information processing means performs the selection based on the measurement result by the measurement means and a predetermined threshold value.

2. The paper type discriminating device according to claim 1.

3. the measuring means is an optical sensor having a line sensor, The information processing means performs the selection according to a position of a pixel from a measurement result for each pixel acquired from the line sensor.

2. The paper type discriminating device according to claim 1.

4. the line sensor outputs a pixel output value representing a luminance value of the paper for each pixel as a measurement result of the paper; The information processing means performs the selection based on the pixel output value and a predetermined threshold value.

4. The paper type discriminating device according to claim 3.

5. the pressing member is movable between a first position away from the measuring means and a second position closer to the measuring means than the first position, and when the paper is transported, the pressing member moves to the second position and presses the paper toward the optical sensor so that a predetermined space is created between the paper and a light receiving surface of the optical sensor; The optical sensor measures the paper pressed by the pressing member.

4. The paper type discriminating device according to claim 3.

6. the frame has two fixing portions against which the paper conveyed by the conveying means is pressed by the pressing member that has moved to the second position, the central portion of the paper pressed against the two fixed portions is pressed toward the light receiving surface by the pressing member, so that the central portion of the paper approaches the light receiving surface and is parallel to the light receiving surface; The optical sensor measures the distance between the two fixed portions of the paper.

6. The paper type discriminating device according to claim 5.

7. The information processing means calculates a difference value between the measurement results of adjacent pixels, and performs the selection based on the difference value and a predetermined threshold value.

7. The paper type discriminating device according to claim 6.

8. The information processing means is characterized in that the measurement results of pixels in an area where the difference value is less than the predetermined threshold value are selected. The paper type discriminating device according to claim 7.

9. The information processing means is characterized in that the measurement results of the area including the center part of the paper are selected.

7. The paper type discriminating device according to claim 6.

10. The paper type discriminating device according to claim 1, and an image forming means for forming an image on the paper, The control means controls the image forming means to form the image under image forming conditions corresponding to the determined type of paper. Image forming device.

Images