Sheet detection device and image formation device

Abstract

To provide a sheet detection device which can inhibit deterioration of sheet detection accuracy and inhibit occurrence of failure in sheet transportation.SOLUTION: A sheet detection device includes: a media sensor 100 for measuring a feature amount of a sheet transported by a transport roller pair 280; a media sensor facing roller 260 which may move between a first position where the media sensor facing roller 260 is separated from the media sensor 100 and a second position where the media sensor facing roller 260 is located closer to the media sensor 100 than the first position; and a moving mechanism 700 which moves the media sensor facing roller 260. When the sheet is not transported to a measurement position of the media sensor 100, the moving mechanism 700 places the media sensor facing roller 260 in the first position. When the sheet is transported to the measurement position of the media sensor 100, the moving mechanism 700 moves the media sensor facing roller 260 from the first position to the second position.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] In recent years, image forming devices have been equipped with a media sensor for determining the type of paper, which is a recording medium. The media sensor measures the characteristics of the paper using an optical sensor, ultrasonic sensor, or the like. Based on the measurement results of the characteristics of the paper by the media sensor, the image forming device extracts the corresponding paper information from pre-registered paper information 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 feature values ​​from the paper being transported. In this case, the distance between the media sensor and the paper may vary due to positional fluctuations (fluttering) of the paper at the measurement position of the media sensor. The fluttering of the paper may reduce the accuracy of detection of feature values ​​by the media sensor. In particular, if the media sensor is an optical sensor, the paper may shift from the focal point of the optical sensor, reducing the accuracy of the measurement results. This may lead to a decrease in the accuracy of identifying the type of paper.

[0004] In response to this, Patent Document 1 discloses a configuration in which a roller is disposed as a pressing member facing the media sensor across the paper transport path, and the roller presses the paper onto the surface of the media sensor, thereby suppressing the flapping of the paper. Patent Document 2 discloses a configuration in which the roller is disposed so as not to come into contact with a member that faces the paper surface in the vertical direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-200478 A [Patent Document 2] JP 2019-104624 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, although the pressing member that presses the paper against the media sensor prevents a decrease in paper detection accuracy, pressing the paper may cause paper transport problems such as paper jams. In view of the above-mentioned problems, the main object of the present invention is to provide a paper detection device that prevents a decrease in paper detection accuracy and also prevents paper transport problems. [Means for solving the problem]

[0007] The paper detection device of the present invention comprises a measuring means for measuring characteristics of paper transported by a transporting means, a pressing member movable between a first position away from the measuring means and a second position closer to the measuring means than the first position, and a moving means for moving the pressing member, wherein when the paper has not been transported to the measurement position of the measuring means by the transporting means, the moving means positions the pressing member at the first position, and when the paper has been transported to the measurement position of the measuring means by the transporting means, the moving means moves the pressing member from the first position to the second position, and the measuring means measures the characteristics of the paper while the pressing member is positioned at the second position. According to another aspect, the paper detection device of the present invention comprises a measuring means for measuring a characteristic quantity of paper transported by a transporting means, a pressing member movable between a first position away from the measuring means and a second position closer to the measuring means than the first position, and a moving means for moving the pressing member, wherein when the paper has not been transported to the measurement position of the measuring means by the transporting means, the moving means positions the pressing member at the first position, and when the paper has been transported to the measurement position of the measuring means by the transporting means, the moving means moves the pressing member from the first position to the second position, and the pressing member is positioned at the second position until the paper passes the measurement position. According to another aspect, the paper detection device of the present invention comprises a measuring means for measuring a characteristic quantity of paper transported by a transporting means, a pressing member movable between a first position away from the measuring means and a second position closer to the measuring means than the first position, and a moving means for moving the pressing member, wherein when an initial adjustment of the measuring means is performed when no paper is transported to the measurement position of the measuring means, the moving means moves the pressing member from the first position to the second position, the measuring means performs the initial adjustment when the pressing member is positioned at the second position, and after performing the initial adjustment, the moving means moves the pressing member from the second position to the first position. Effect of the Invention

[0008] According to the present invention, it is possible to suppress a decrease in the accuracy of detecting the paper and also to suppress the occurrence of paper transport failure. [Brief description of the drawings]

[0009] [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] FIG. [Figure 8] 4A and 4B are explanatory diagrams of the operation of the movement mechanism. [Figure 9] FIG. 4 is a diagram showing the configuration of the media sensor facing roller. [Figure 10] 4(a) and (b) are diagrams illustrating the role of the roller facing the media sensor. [Figure 11] 13 is a process flow diagram showing a process for moving a roller facing a media sensor. [Figure 12] 6A to 6C are diagrams illustrating the operation during the movement process of the roller facing the media sensor. [Figure 13] 4 is a process flow diagram illustrating a process for cleaning the surface of an optical sensor. [Figure 14] FIG. 4 is a diagram illustrating the configuration of a media sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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].

[0011] (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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] A media sensor 100 for measuring characteristic quantities of paper S is provided on the transport path between transport roller pair 280 and transport roller pair 290. Media sensor 100 outputs information corresponding to basis weight and information corresponding to surface properties as characteristic quantities of paper S transported from cassette paper feed unit 230 or manual paper feed unit 235. Media sensor 100 may be configured to be provided at least one of a position where paper S fed from cassette paper feed unit 230 can be detected and a position where paper S fed from manual paper feed unit 235 can be detected, or both. The configuration of media sensor 100 will be described in detail later.

[0019] 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.

[0020] 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).

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] In parallel with such a toner image forming operation, the paper S is conveyed one sheet at a time to the pair of registration rollers 240 by the cassette paper feeder 230 or the manual paper feeder 235. Before the paper S reaches the pair of registration rollers 240, the media sensor 100 measures the characteristic amount of the paper S. The image forming apparatus 201 sets the image forming conditions based on the measured characteristic amount, and 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.

[0026] 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.

[0027] 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.

[0028] 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)).

[0029] 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.

[0030] 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.

[0031] (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.

[0032] 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 print mode database 402. The print mode database 402 is a database in which the correspondence between paper characteristics and image forming conditions (print modes) is set in advance. The paper characteristics are, for example, the type and basis weight of the paper. The control unit 400 is connected to an operation unit 502, an image reading device 202, an image forming unit 201B, a conveying unit 600, a sensor 601, and a media sensor 100. The control unit 400 is also connected to a host device 501, which is an external device.

[0033] 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.

[0034] The conveying section 600 includes conveying roller pairs 280, 290, a pickup roller 2, a feed roller 3, a retard roller 4, and motors that drive these rollers. The conveying section 600 also includes a registration roller pair 240, a secondary transfer roller 217, a pressure roller 220a, a heating roller 220b, and motors that drive these rollers. The conveying section 600 further includes a first discharge roller pair 225a, a second discharge roller pair 225b, a reversing roller pair 222, and other rollers that convey the paper S within the image forming apparatus 201, and motors that drive these rollers. The conveying section 600 controls the feeding of the paper S by controlling the driving of each motor under the control of the control section 400.

[0035] 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 executes the print job by causing the image forming unit 201B to form a toner image based on the image data after image processing, and causing the conveying unit 600 to feed the paper S.

[0036] 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 includes a built-in memory 1601. The information processing unit 160 is an information processing device realized by, for example, a CPU, an MPU, or an ASIC.

[0037] 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 of the paper S to be used.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The ultrasonic sensor 120 measures the paper S with ultrasonic waves and outputs a predetermined voltage value as a 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 information corresponding to 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 stores the luminance value of each pixel in the memory 1601 as the imaging result by the optical sensor 150. The information processing unit 160 converts the luminance value of each pixel stored in the memory 1601 into an integrated difference value obtained by integrating the difference between the luminance values ​​of adjacent pixels and information corresponding to surface properties such as lightness.

[0043] 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 determines 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 printing mode 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 type 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 printing mode database 402.

[0044] (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.

[0045] As shown in Fig. 4, the media sensor 100 is provided between a pair of transport rollers 280 and a pair of transport rollers 290, and acquires information corresponding to the basis weight and surface properties of the transported paper S. The paper detection sensor 270 is disposed at approximately the same position as the media sensor 100 in the transport direction of the paper S. 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. A media sensor opposing roller 260 is provided at a position facing the media sensor 100 with respect to the transport path of the paper S. The media sensor opposing roller 260 is configured to move in a direction approaching and moving away from the media sensor 100.

[0046] 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.

[0047] The optical sensor 150 measures the brightness value of 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.

[0048] In this embodiment, in order to stabilize the posture of the paper S while transporting it, the media sensor facing roller 260 and the paper pressing roller 261 are provided between the transport roller pair 280 and the transport roller pair 290. The media sensor facing roller 260 and the paper pressing roller 261 are arranged at the same position in the transport direction of the paper S. The media sensor facing roller 260 is arranged facing the optical sensor 150 across the transport path, and is configured to press the paper S toward the optical sensor 150. This reduces the variation in the position and posture of the paper S when the media sensor 100 measures the surface of the paper S. Therefore, the media sensor 100 can stably measure the characteristic quantities of the paper S, such as the surface property and basis weight. The paper pressing roller 261 is provided at a position where the ultrasonic sensor 120 is sandwiched between the media sensor facing roller 260 and the paper pressing roller 261.

[0049] (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.

[0050] 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.

[0051] 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 estimated by using a conversion formula or conversion table between transmittance and basis weight.

[0052] (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.

[0053] 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.

[0054] 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.

[0055] 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 output values ​​(luminance values) for each pixel in the memory 1601. The information processing unit 160 obtains the integrated difference value, the lightness, and the PP (Peak to Peak) value of the luminance value from the luminance values ​​for each pixel stored in the memory 1601, and accumulates them in the memory 1601.

[0056] 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 detection value of each pixel is expressed by the pixel position (1 to n) and the detection line (A to N), the difference accumulation value Y is expressed by the following formula (1) using the difference accumulation value k for each line. Note that the direction of the detected pixel data 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)| · · · kN=|n2-n1|+|n3-n2|…+|Nn-N(n-1)| Y = k1 + k2 + … + kN … (1)

[0057] The lightness 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 lightness M is expressed by the following formula (2). M=A1+A2+…+B1+B2+…+G1+G2+…+Nn…(2)

[0058] The PP 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 having low 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. Brightness and PP value are parameters used to distinguish these types of paper.

[0059] The control unit 400 acquires the basis weight, the integrated difference value, the brightness, and the PP value as the characteristic amounts of the paper S from the information processing unit 160, and determines the print mode by referring to the print mode database 402. The control unit 400 performs image formation according to the print job under the image formation conditions according to the determined print mode.

[0060] (Position control of the roller facing the media sensor) As described above, the media sensor facing roller 260 is configured to move in a direction approaching and moving away from the media sensor 100 (optical sensor 150). In other words, the media sensor facing roller 260 can move to a first position away from the optical sensor 150 and a second position closer to the optical sensor 150 than the first position. The media sensor facing roller 260 presses the paper S toward the optical sensor 150 by moving to the second position. When the media sensor facing roller 260 is in the second position, the paper S is preferably pressed against the optical sensor 150. In this way, the media sensor facing roller 260 is a rotating member that functions as a pressing member for pressing the paper S toward the optical sensor 150. The same is true for the paper pressure roller 261.

[0061] Fig. 7 is a configuration diagram of a movement mechanism that moves the media sensor facing roller 260 and the paper pressure roller 261. Fig. 7 is a diagram of the media sensor facing roller 260 and the paper pressure roller 261 as viewed from above (the upper block 110 side). The movement mechanism 700 includes a motor 300, a rotating shaft 301, a cam 302, a detection plate 303, a rotation detection sensor 304, a gear 305, and a mounting plate 306. The media sensor facing roller 260 and the paper pressure roller 261 are attached to the mounting plate 306. Note that the ultrasonic transmitter 130 of the ultrasonic sensor 120 is not attached to the mounting plate 306, but is fixed to the upper block 110 of the media sensor 100.

[0062] When the motor 300 is driven to rotate by the control unit 400, the gear 305 rotates. The rotation of the gear 305 rotates the rotating shaft 301. The rotation of the rotating shaft 301 rotates the cam 302 and the detection plate 303. The rotation of the cam 302 moves the mounting plate 306 up and down. The up and down movement of the mounting plate 306 moves the media sensor facing roller 260 and the paper pressure roller 261. As a result, the media sensor facing roller 260 and the paper pressure roller 261 move synchronously between the first position and the second position.

[0063] The positions of the media sensor opposing roller 260 and the paper pressure roller 261 are detected using a rotation detection sensor 304. The rotation detection sensor 304 is a photointerrupter, and includes a light emitting section and a light receiving section that are arranged opposite each other, and is configured to receive light output from the light emitting section at the light receiving section. The positions of the media sensor opposing roller 260 and the paper pressure roller 261 are determined depending on whether the light output from the light emitting section is blocked by a detection plate 303. For example, the rotation detection sensor 304 outputs a detection signal of a first state when the light is not blocked, and outputs a detection signal of a second state different from the first state when the light is blocked.

[0064] FIG. 8 is an explanatory diagram of the operation of the movement mechanism 700. Here, the operation of the movement mechanism 700 to move the media sensor facing roller 260 will be described, but the paper pressing roller 261 also operates in a similar manner. FIG. 8 is a view of the movement mechanism 700 as seen from the detection plate 303 side (a direction perpendicular to the conveying direction of the paper S). Note that the motor 300 and gear 305 are not shown. FIG. 8(a) shows a state in which the media sensor facing roller 260 has moved to a first position separated from the optical sensor 150. FIG. 8(b) shows a state in which the media sensor facing roller 260 has moved to a second position where it presses the paper S against the optical sensor 150.

[0065] The mounting plate 306 is configured to rotate about a rotation axis 306a. A spring 307 is connected to the mounting plate 306, and the mounting plate 306 is biased by the spring 307 in a direction away from the optical sensor 150. The rotation angle of the mounting plate 306 changes depending on the rotation position of the cam 302 and the spring 307. In response to the change in the rotation angle of the mounting plate 306, the position of the media sensor facing roller 260 changes between a first position (FIG. 8(a)) and a second position (FIG. 8(b)).

[0066] The rotational position of the cam 302 can be determined by whether or not the light of the rotation detection sensor 304 is blocked by the detection plate 303 attached to the rotating shaft 301. The detection plate 303 is in an array shape as shown in the figure. The detection signal output from the rotation detection sensor 304 changes as the detection plate 303 rotates together with the rotating shaft 301. The rotational position of the cam 302 is detected by the state of this detection signal. For example, the media sensor facing roller 260 is in the first position when the detection signal switches from the second state to the first state (FIG. 8(a)), and is in the second position when the detection signal switches from the first state to the second state (FIG. 8(b)). The rotational drive of the motor 300 is stopped at each timing, so that the media sensor facing roller 260 stops at the first position or the second position.

[0067] Fig. 9 is a configuration diagram of the media sensor facing roller 260. The media sensor facing roller 260 is dumbbell-shaped, with a sponge material 2601 that serves as a cleaning member wound around the center. The media sensor facing roller 260 has two roles. Fig. 10 is an explanatory diagram of the roles of the media sensor facing roller 260.

[0068] The first role of the media sensor facing roller 260 is to maintain the gap between the paper S and the light guide 1503 of the optical sensor 150 during paper transport (FIG. 10(a)). The media sensor facing roller 260 presses the paper S against the light guide 1503 of the optical sensor 150 to maintain the gap between the paper S and the light guide 1503 and suppresses positional fluctuation (fluttering) of the paper S. This allows the optical sensor 150 to measure the paper S in a stable state. The second role of the media sensor facing roller 260 is to rotate after the paper has passed and wipe the surface of the light guide 1503 with the sponge material 2601 to remove paper dust (cleaning) (FIG. 10(b)). As described above, the light guide 1503 is used to irradiate the light emitted from the light source 1501 to the paper S at a certain angle.

[0069] Fig. 11 is a process flow diagram showing the movement process of the media sensor facing roller 260. This process is performed when the image forming apparatus 201 is started up or returns from a sleep state and a print job is performed. When the movement of the media sensor facing roller 260 is controlled, the movement of the paper pressure roller 261 is similarly controlled. Fig. 12 is an explanatory diagram of the operation during the movement process of the media sensor facing roller 260. Here, the case where the control unit 400 performs this process will be described, but this process may also be executed by the information processing unit 160 under the control of the control unit 400.

[0070] When the image forming apparatus 201 starts up or returns from a sleep state, the control unit 400 drives the motor 300 to rotate and move the media sensor facing roller 260 to the first position so as not to interfere with the transport of the paper S (S111). This causes the media sensor facing roller 260 to move away from the optical sensor 150 (FIG. 8(a)). In an operation mode in which the characteristic amount of the paper S is not measured, the media sensor facing roller 260 is maintained at the first position. In a media sensor mode in which the characteristic amount of the paper S is measured, the media sensor facing roller 260 is movable between the first position and the second position.

[0071] When the media sensor mode is set (S112), the control unit 400 performs initial adjustments such as calibration of the optical sensor 150 (S113). The media sensor mode is instructed, for example, from the operation unit 502. At the start of the initial adjustments, the control unit 400 drives the motor 300 to rotate and move the media sensor facing roller 260 to the second position and bring it into contact with the optical sensor 150. When the initial adjustments are completed, the control unit 400 drives the motor 300 to rotate and move the media sensor facing roller 260 to the first position and separate it from the optical sensor 150.

[0072] In the initial adjustment, the media sensor 100 is activated and measurement is performed by the ultrasonic sensor 120 in a paper-free state. Measurement in a paper-free state is a process in which ultrasonic measurement is performed without transporting paper S to detect changes in output due to environmental changes such as temperature. The results of the measurement in a paper-free state are used to correct for environmental effects during ultrasonic measurement. Also, in the initial adjustment, a black measurement is performed by the optical sensor 150 to detect dark current. The light intensity of the optical sensor 150 is adjusted based on the dark current. At this time, the media sensor facing roller is in the second position, thereby suppressing the effects of light.

[0073] After the initial adjustment is completed, the control unit 400 waits until it receives an instruction to start a print job. When the control unit 400 receives an instruction to start a print job, it starts transporting the paper S by the transport unit 600. When the paper detection sensor 270 detects the paper S after the control unit 400 starts transporting the paper S, it stops the transport of the paper S by the transport unit 600 (S114). FIG. 12(a) shows a state in which the transport of the paper S has been stopped. The paper S reaches the measurement position by the media sensor 100, and its leading edge is transported to the transport roller pair 290 and stops there. The paper S is in a state in which a predetermined tension is applied by the transport roller pair 280 and the transport roller pair 290, and wrinkles on the surface are smoothed out.

[0074] The control unit 400, which has stopped the transport of the paper S, rotates and drives the motor 300 to move the media sensor opposing roller 260 to the second position, bringing the paper S into contact with the media sensor 100 (S115). In this method, when the paper S is transported to the measurement position of the media sensor 100, the media sensor opposing roller 260 is in the first position and does not interfere with the transport of the paper S. Also, when the paper S is measured by the media sensor 100, the media sensor opposing roller 260 presses the paper S against the media sensor 100 at the second position to stabilize its posture.

[0075] The control unit 400, which has brought the media sensor facing roller 260 into contact with the media sensor 100, confirms that the media sensor facing roller 260 is in contact with the media sensor 100 based on the detection result of the rotation detection sensor 304. For example, the control unit 400 confirms that the media sensor facing roller 260 (paper S) is in contact with the media sensor 100 when the detection signal output from the rotation detection sensor 304 switches from a first state to a second state. Having confirmed that the media sensor facing roller 260 (paper S) is in contact with the media sensor 100, the control unit 400 resumes transport of the paper S by the transport unit 600 (FIG. 12(b)).

[0076] The control unit 400 resumes conveyance of the paper S and simultaneously performs measurement processing of the characteristic quantities of the paper S by the media sensor 100 (S116). The media sensor 100 performs ultrasonic measurement by the ultrasonic sensor 120, and derives the transmittance based on the measurement result. The control unit 400 derives the basis weight of the paper S based on the transmittance using a table or a formula that indicates the relationship between the transmittance and the basis weight. The media sensor 100 measures the surface properties of the paper S by the optical sensor 150, and derives the difference integrated value and the brightness. The control unit 400 determines the type of the paper S based on the difference integrated value and the brightness. The control unit refers to the print mode database, determines the print mode based on the basis weight and type of the paper S, and sets the image formation conditions according to the determined print mode. The control unit 400 stops the media sensor 100 when the measurement of the characteristic quantities of the paper S is completed.

[0077] Thereafter, the control unit 400 detects that the trailing edge of the paper S has passed the measurement position of the media sensor 100 based on the detection result of the paper detection sensor 270 (S117). FIG. 12(c) shows a state in which the trailing edge of the paper S has passed the measurement position of the media sensor 100. When the trailing edge of the paper S has passed the measurement position of the media sensor 100, the control unit 400 rotates the motor 300 to move the media sensor facing roller 260 to the first position (S118). As a result, the media sensor facing roller 260 moves away from the optical sensor 150. That is, the control unit 400 moves the media sensor facing roller 260 away from the optical sensor 150 after a predetermined time has elapsed since detecting that the trailing edge of the paper S has passed. As a result, the media sensor facing roller 260 can clean the surface of the optical sensor 150 for a predetermined time with the sponge material 2601 abutting against the surface. The media sensor facing roller 260 always waits at the first position so as not to interfere with the transport of the paper S, except for the timing for measuring the characteristic amount of the paper S.

[0078] The media sensor facing roller 260 may move to the second position and abut against the optical sensor 150 at a timing other than when the characteristic quantities of the paper S are measured. This is because, in a configuration in which the cleaning of the surface of the optical sensor 150 by the media sensor facing roller 260 is performed only at the timing when the characteristic quantities of the paper S are measured, cleaning may not be performed for a long period of time. If the surface of the optical sensor 150 is not cleaned for a long period of time, the optical sensor 150 measures the characteristic quantities of the paper with paper dust adhering to the surface, and the measurement accuracy decreases. To prevent this, the media sensor facing roller 260 is moved to the second position at a predetermined interval to clean the surface of the optical sensor 150.

[0079] 13 is a process flow diagram showing the process of cleaning the surface of the optical sensor 150 at a predetermined interval. Here, an example is described in which the cleaning process is performed every time a predetermined number of sheets of paper S are transported (every time an image is formed on a predetermined number of sheets of paper). The predetermined interval is not limited to this, and the cleaning process may be performed simply when a predetermined time has elapsed since the previous cleaning process was completed. Here, a case is described in which the control unit 400 performs this process, but this process may also be executed by the information processing unit 160 under the control of the control unit 400.

[0080] The media sensor facing roller 260 waits at the first position and is separated from the optical sensor 150. The control unit 400 counts the number of sheets S that have passed through and checks whether this count value has reached a specified number. When the count value reaches the specified number (S131), the control unit 400 waits until the paper detection sensor 270 detects the paper S. When the paper detection sensor 270 detects the paper S (S132), the control unit 400 drives the motor 300 to rotate and move the media sensor facing roller 260 to the second position and bring it into contact with the media sensor 100 (S133).

[0081] The control unit 400 removes paper dust from the optical sensor 150 by keeping the media sensor facing roller 260 in contact with the media sensor 100 until after the paper sheet S has passed the measurement position of the media sensor 100. The control unit 400 detects that the paper sheet S has passed the measurement position of the media sensor 100 based on the detection result of the paper detection sensor 270 (S134). When the paper sheet S has passed the measurement position of the media sensor 100, the control unit 400 drives the motor 300 to rotate and move the media sensor facing roller 260 to the first position (S135). This causes the media sensor facing roller 260 to move away from the optical sensor 150.

[0082] The configuration including the media sensor 100, controller 200, transport unit 600, media sensor facing roller 260, and paper pressing roller 261 of the present embodiment as described above constitutes a paper detection device. The paper detection device can measure the characteristic amount of the paper S using the media sensor 100 and determine the transport conditions such as the transport speed of the paper S based on the characteristic amount. When the paper S is transported to the measurement position of the media sensor 100, the media sensor facing roller 260 is separated from the media sensor 100 so as not to interfere with the transport of the paper S. This prevents the occurrence of transport problems such as paper jams. When the media sensor 100 measures the paper S, the media sensor facing roller 260 moves to the side of the media sensor 100 and presses the paper S against the media sensor 100. This prevents the paper S from flapping during measurement, and the media sensor 100 can perform stable and highly accurate measurements.

[0083] The image forming apparatus 201 of this embodiment, which is equipped with such a paper detection device, can measure the characteristic amounts of the paper S using the media sensor 100 and determine the conditions for forming an image on the paper S based on the characteristic amounts. When the paper S is transported to the measurement position of the media sensor 100, the media sensor facing roller 260 moves away from the media sensor 100 so as not to interfere with the transport of the paper S. When the media sensor 100 measures the paper S, the media sensor facing roller 260 moves toward the media sensor 100 and presses the paper S against the media sensor 100. This suppresses flapping of the paper S during measurement, allowing the media sensor 100 to perform stable measurements.

[0084] The above describes the operation of the media sensor facing roller 260 relative to the optical sensor 150. The media sensor facing roller 260 is positioned so that the ultrasonic sensor 120 is sandwiched between it and the paper pressure roller 261 (see FIG. 5). With this configuration, when the paper S reaches the measurement position of the media sensor 100, the media sensor facing roller 260 and the paper pressure roller 261 press the paper S against the measurement position of the ultrasonic sensor 120. The ultrasonic sensor 120 measures the characteristic amounts by transmitting ultrasonic waves through the paper S. Because the state of the paper S is stabilized by the media sensor facing roller 260 and the paper pressure roller 261, the ultrasonic sensor 120 can also measure the characteristic amounts of the paper S with high accuracy.

[0085] Similarly, the media sensor facing roller 260 and the paper pressing roller 261 are useful when a transmission type optical sensor is used. FIG. 14 is a configuration explanatory diagram of a media sensor when a transmission type optical sensor 150a is used. The transmission type optical sensor 150a transmits light through the paper S to measure the feature amount. For this purpose, a light source 1501a and a line sensor 1502a are arranged opposite each other across the conveyance path. Also, the media sensor facing roller 260 is not arranged, and the paper pressing roller 262 is arranged opposite the paper pressing roller 261 across the optical sensor 150a. Since the state of the paper S is stabilized by the paper pressing roller 261 and the transfer pressing roller 262, the transmission type optical sensor 150a can also measure the feature amount of the paper S with high accuracy. In other words, in addition to the configuration in which the media sensor facing roller 260 directly presses the paper S against the optical sensor 150, the state of the paper S can also be stabilized by pressing the paper S against the optical sensor 150a with two rollers. This allows the sheet S to be stably measured even with the transmission type optical sensor 150a.

[0086] The media sensor 100 described above is one example, and is not limited to a configuration including the optical sensor 150 and the ultrasonic sensor 120, and may be equipped with another sensor capable of measuring the characteristic quantities of the paper S. Furthermore, the media sensor 100 may be configured to include either the optical sensor 150 or the ultrasonic sensor 120.

[0087] In the above description, the print mode database 402 is provided in the memory 401 of the controller 200, but the storage location of the print mode database 402 is not limited to this. For example, the print mode database 402 may be stored in the memory 1601 in the media sensor 100. In this case, the information processing unit 160 determines the type and basis weight of the paper S, and the information processing unit 160 also determines the print mode.

[0088] 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 detection device. For example, such a paper detection device can also be used in an image reading device that reads an image printed on a sheet of paper while transporting the sheet of paper. The image reading device is equipped with an automatic document feeder (ADF). By incorporating a paper detection device in the ADF, stable image reading and paper transport become possible.

Claims

1. a measuring means for measuring a characteristic amount of the paper conveyed by the conveying means; a pressing member movable between a first position spaced apart from the measuring means and a second position closer to the measuring means than the first position; a moving means for moving the pressing member, When the paper has not been transported to the measurement position of the measurement means by the transport means, the pressing member is disposed at the first position by the moving means, and when the paper has been transported to the measurement position of the measurement means by the transport means, the pressing member is moved from the first position to the second position by the moving means, and the measurement means measures the characteristic quantity of the paper with the pressing member disposed at the second position. Paper detection device.

2. the moving means moves the pressing member from the second position to the first position after the leading edge of the paper in the transport direction has passed the measurement position by the transport means, 2. The paper detection device according to claim 1.

3. a measuring means for measuring a characteristic amount of the paper conveyed by the conveying means; a pressing member movable between a first position spaced apart from the measuring means and a second position closer to the measuring means than the first position; a moving means for moving the pressing member, When the paper has not been transported to the measurement position of the measurement means by the transport means, the pressing member is disposed at the first position by the moving means, and when the paper has been transported to the measurement position of the measurement means by the transport means, the pressing member is moved from the first position to the second position by the moving means, and the pressing member is disposed at the second position until the paper passes the measurement position. Paper detection device.

4. the pressing member, when disposed at the second position, contacts the paper until the trailing end of the paper passes through the measurement position, and contacts the measuring means after the trailing end of the paper passes through the measurement position.

4. The paper detection device according to claim 3.

5. The measuring device further includes a detection unit for detecting the sheet being conveyed to the measuring position, The moving means moves the pressing member from the first position to the second position when the detection means detects the paper.

4. The paper detection device according to claim 1 or 3.

6. The detection means is provided upstream of the measurement means in the sheet transport direction.

6. The paper detection device according to claim 5.

7. The moving means moves the pressing member to the second position during initial adjustment of the measuring means.

4. The paper detection device according to claim 1 or 3.

8. a measuring means for measuring a characteristic amount of the paper conveyed by the conveying means; a pressing member movable between a first position spaced apart from the measuring means and a second position closer to the measuring means than the first position; a moving means for moving the pressing member, When performing an initial adjustment of the measuring means in a state where no paper is transported to a measurement position of the measuring means, the pressing member is moved from the first position to the second position by the moving means, the measuring means performs the initial adjustment in a state where the pressing member is disposed at the second position, and after performing the initial adjustment, the pressing member is moved from the second position to the first position by the moving means. Paper detection device.

9. after the initial adjustment is performed, if the paper is not transported by the transport means to the measurement position of the measurement means, the pressing member is disposed at the first position, and if the paper is transported by the transport means to the measurement position of the measurement means, the pressing member is moved from the first position to the second position by the moving means, and the measurement means measures the characteristic quantity of the paper with the pressing member disposed at the second position.

9. The paper detection device according to claim 8.

10. The pressing member is moved to the second position during the initial adjustment and comes into contact with the measuring means.

9. The paper detection device according to claim 8.

11. The pressing member is a rotating member.

9. The paper detection device according to claim 1, 3 or 8.

12. The pressing member is two rotating members, The two rotating members are arranged to sandwich the measurement position in a direction perpendicular to the paper transport direction.

9. The paper detection device according to claim 1, 3 or 8.

13. The moving means moves the pressing member from the first position to the second position at predetermined intervals.

9. The paper detection device according to claim 1, 3 or 8.

14. The pressing member includes a cleaning member, and the cleaning member is brought into contact with the measuring means at the second position to clean the measuring means.

13. The sheet sensing device of claim 12.

15. A paper detection device according to claim 1, 3 or 8; and an image forming unit that forms an image on the paper under image forming conditions based on the characteristic amount of the paper measured by the measuring unit. Image forming device.

Images