Sheet detection device and image forming apparatus

Abstract

The invention relates to a sheet detection device and an image forming apparatus. A sheet detecting apparatus includes a measuring unit for measuring a characteristic quantity of a sheet conveyed by a conveying unit, a pressing member movable between a first position separated from the measuring unit and a second position closer to the measuring unit than the first position, and a moving unit configured to move the pressing member, the pressing member is arranged in a first position by the moving unit in a case where the measuring unit detects that the sheet has not been conveyed to the measuring position of the measuring unit, where the moving unit is configured to move the pressing member from the first position to a second position in a case where the measuring unit detects that the sheet has been conveyed to the measuring position of the measuring unit.

Description

Technical Field

[0001] The present disclosure relates to a sheet material detection device including a media sensor for distinguishing a type of sheet material, and also to an image forming apparatus including such a sheet material detection device. Background Art

[0002] In recent years, an image forming apparatus includes a media sensor for discriminating the type of a sheet material as a recording medium. The media sensor measures a characteristic amount of a sheet material by using, for example, an optical sensor or an ultrasonic sensor. The image forming apparatus extracts relevant sheet material information from pre-recorded sheet material information based on the measurement result of the sheet material characteristic amount obtained by the media sensor, and discriminates the type of the sheet material. The sheet material information is information including characteristic amounts (for example, basis weight and surface properties) of each type of sheet material.

[0003] The media sensor measures the characteristic quantity of the conveyed sheet. In this case, the distance between the media sensor and the sheet changes due to the position fluctuation (flapping) of the sheet at the measurement position of the media sensor. The flapping of the sheet reduces the detection accuracy of the characteristic quantity by the media sensor. In particular, when the media sensor is an optical sensor, the sheet deviates from the focus of the optical sensor, thereby reducing the accuracy of the measurement result. This leads to a reduction in the accuracy of distinguishing the type of sheet.

[0004] In contrast, Japanese Patent Application Laid-Open No. 2018-200478 discloses a structure in which a roller serving as a pressing member is arranged at a position facing a media sensor across a sheet conveying path. In this structure, the sheet is pressed onto the surface of the media sensor by the roller to suppress the flapping of the sheet.

[0005] However, although the pressing member that presses the sheet against the media sensor suppresses the reduction in sheet detection accuracy, the pressing of the sheet may cause poor sheet conveying, such as paper jam. The present disclosure is made in view of the above-mentioned problems, and the main purpose of the present disclosure is to provide a sheet detection device that can suppress the reduction in sheet detection accuracy and also suppress the occurrence of poor sheet conveying. Summary of the invention

[0006] According to one embodiment of the present disclosure, a sheet material detection device includes: a measuring device for measuring a characteristic quantity of a sheet material conveyed by a conveying device; a pressing member capable of moving between a first position separated from the measuring device and a second position closer to the measuring device than the first position; and a moving device configured to move the pressing member, wherein, in a case where the measuring device detects that the sheet material has not been conveyed to the measuring position of the measuring device, the pressing member is arranged at the first position by the moving device, wherein the moving device is configured to move the pressing member from the first position to the second position in a case where the measuring device detects that the sheet material has been conveyed to the measuring position of the measuring device, and wherein the measuring device is configured to measure the characteristic quantity of the sheet material with the pressing member arranged at the second position.

[0007] According to another embodiment of the present disclosure, a sheet material detection device includes: a measuring device for measuring a characteristic quantity of a sheet material conveyed by a conveying device; a pressing member capable of moving between a first position separated from the measuring device and a second position closer to the measuring device than the first position; and a moving device configured to move the pressing member, wherein the pressing member is arranged at the first position by the moving device when the sheet material has not yet been conveyed by the conveying device to the measuring position of the measuring device, wherein the moving device is configured to move the pressing member from the first position to the second position when the sheet material has been conveyed by the conveying device to the measuring position of the measuring device, and wherein the moving device is configured to move the pressing member from the second position to the first position before the sheet material passes through the measuring position of the measuring device.

[0008] According to another embodiment of the present disclosure, a sheet material detection device includes: a measuring device for measuring a characteristic quantity of a sheet material conveyed by a conveying device; a pressing member capable of moving between a first position separated from the measuring device and a second position closer to the measuring device than the first position; and a moving device configured to move the pressing member, wherein, in a case where an initial adjustment of the measuring device is performed in a state where the sheet material has not yet been conveyed to the measuring position of the measuring device, the pressing member is arranged in the first position by the moving device, and wherein the measuring device is configured to perform the initial adjustment in a state where the pressing member is arranged in the first position.

[0009] According to another embodiment of the present disclosure, an imaging device includes: a sheet detection device; and an imaging device configured to form an image on a sheet by using an imaging condition determined based on a characteristic amount of the sheet measured by a measuring device, wherein the sheet detection device includes: a measuring device for measuring a characteristic amount of a sheet conveyed by a conveying device; a pressing member capable of moving between a first position separated from the measuring device and a second position closer to the measuring device than the first position; and a moving device configured to move the pressing member, wherein in a case where the measuring device detects that the sheet has not been conveyed to a measuring position of the measuring device, the pressing member is arranged at the first position by the moving device, wherein the moving device is configured to move the pressing member from the first position to the second position in a case where the measuring device detects that the sheet has been conveyed to the measuring position of the measuring device, and wherein the measuring device is configured to measure the characteristic amount of the sheet with the pressing member arranged at the second position.

[0010] Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a structural diagram of an imaging device.

[0012] Figure 2A and Figure 2B It is an enlarged view of the fixing unit.

[0013] Figure 3 This is a diagram illustrating the controller.

[0014] Figure 4 This is a diagram for explaining the structure of the media sensor.

[0015] Figure 5 This is a diagram for explaining the structure of the media sensor.

[0016] Fig. 6A and Figure 6B This is a diagram illustrating the reading results obtained by the optical sensor.

[0017] Figure 7 It is a structural diagram of the moving mechanism.

[0018] Fig. 8A and Figure 8B This is a diagram for explaining the operation of the moving mechanism.

[0019] Fig. 9 This is a diagram of the structure of the media sensor facing roller.

[0020] Fig. 10A and Fig. 10B Each of them is an explanatory diagram of the function of the media sensor facing the roller.

[0021] Fig.11 is a process flow chart for illustrating the movement process of the media sensor facing roller.

[0022] Fig. 12A , Fig. 12B and Fig. 12C It is an explanatory diagram of the operation during the movement process of the media sensor facing roller.

[0023] Fig.13 : is a process flowchart for illustrating the sheet detection process of step S114.

[0024] Fig.14 : is a process flowchart for illustrating the sheet passage detection process of step S117.

[0025] Fig.15 : is a process flow chart for illustrating the movement process of the media sensor facing roller in Modification 1.

[0026] Fig.16 is a diagram for illustrating a state in which the media sensor facing roller has moved to the first position.

[0027] Fig.17 : is a process flow chart for illustrating the movement process of the media sensor facing roller in Modification 2.

[0028] Fig.18 : is a process flow chart for illustrating the movement process of the media sensor facing roller in Modification 3.

[0029] Fig.19 This is a diagram for explaining the structure of the media sensor. DETAILED DESCRIPTION

[0030] At least one exemplary embodiment of the present disclosure will now be described with reference to the accompanying drawings. In the following description, "basis weight" is the mass per unit area of ​​a sheet, in g / m 2 .

[0031] <Imaging equipment>

[0032] Figure 1 201 is a block diagram of an image forming apparatus according to at least one embodiment. An image forming apparatus 201 according to at least one embodiment is, for example, a tandem intermediate transfer laser beam printer using an electrophotographic process. Based on image data acquired from an external device such as a personal computer via a network or based on image data acquired from an image reading device 202 disposed on top of the image forming apparatus 201, the image forming apparatus 201 forms a full-color image or a monochrome image on a sheet S as a recording medium, and outputs the sheet S.

[0033] The image forming apparatus 201 has various components for forming an image inside a main body 201A, and includes an image reading device 202 and an operation unit 502 on the top of the main body 201A. A discharge space D is defined between the main body 201A of the image forming apparatus 201 and the image reading device 202, and includes a placement portion 223 for receiving a sheet S discharged therein after image formation.

[0034] The image reading device 202 is a reader that reads an image from a manuscript to generate image data. The image reading device 202 is used, for example, in the process of copying a manuscript. The image reading device 202 in at least one embodiment is configured as a part of the imaging device 201. However, the image reading device 202 is not limited to this configuration, and the image reading device 202 can also be electrically connected to the imaging device 201 as a device different from the imaging device 201.

[0035] The operation unit 502 is a user interface including an input interface and an output interface. Examples of the input interface include various key buttons and a touch panel. Examples of the output interface include a display and a speaker. The user can input various instructions to the imaging device 201 via the operation unit 502. The imaging device 201 notifies the user of various types of information by displaying various screens on the display of the operation unit 502. The operation unit 502 in at least one embodiment is configured as a part of the imaging device 201. The operation unit 502 is not limited to this configuration, and the operation unit 502 can also be electrically connected to the imaging device 201 as a device different from the imaging device 201.

[0036] The image forming apparatus 201 includes an image forming unit 201B, an intermediate transfer unit 201C, a secondary transfer unit 201D, a fixing device 201E, and a cassette sheet feeding unit 230 in a main body 201A. The main body 201A includes a manual sheet feeding unit 235.

[0037] Each box sheet feeding unit 230 feeds sheets S from a corresponding sheet feeding box 1 accommodating sheets S. The box sheet feeding unit 230 includes a pickup roller 2 and a separation unit. The separation unit includes a feed roller 3 and a delay roller 4 for separating the sheets S sent out from the pickup roller 2. The sheets S are fed one by one from the sheet feeding box 1 through the pickup roller 2 and the separation unit. In at least one embodiment, a configuration is described in which a plurality of (four in this example) box sheet feeding units 230 are provided. However, any number of box sheet feeding units 230 may be provided. The sheets S fed from the box sheet feeding unit 230 are conveyed to the registration roller pair 240 via the conveying roller pair 280 and 290.

[0038] The sheet S may be fed from a unit other than the cassette sheet feeding unit 230, that is, from the manual sheet feeding unit 235. The manual sheet feeding unit 235 includes a manual feeding tray 5 for receiving the sheet S placed by the user. Similar to the cassette sheet feeding unit 230, the manual sheet feeding unit 235 includes a pickup roller and a separation unit, and the sheet S is fed one by one from the manual feeding tray 5. The sheet S fed from the manual sheet feeding unit 235 is also conveyed to the registration roller pair 240 via the conveying roller pair 280 and 290.

[0039] The media sensor 100 for measuring the characteristic amount of the sheet S is arranged on the conveying path between the conveying roller pair 280 and the conveying roller pair 290. The media sensor 100 outputs, for example, information corresponding to the basis weight and information corresponding to the surface property as the characteristic amount of the sheet S conveyed from the cassette sheet feeding unit 230 or the manual sheet feeding unit 235. The media sensor 100 may be arranged at least one or both of a position capable of detecting the sheet S fed from the cassette sheet feeding unit 230 and a position capable of detecting the sheet S fed from the manual sheet feeding unit 235. The details of the configuration of the media sensor 100 are described later.

[0040] The imaging unit 201B is a four-drum full-color type and includes a laser scanner 210 and four process boxes 211. The four process boxes 211 form toner images of four colors, specifically, yellow (Y), magenta (M), cyan (C) and black (K). Each process box 211 includes a photosensitive drum 212, a charging device 213 and a developing device 214. A toner box 215 is arranged above the process box 211. The toner box 215 supplies toner to each developing device 214.

[0041] The intermediate transfer unit 201C includes an intermediate transfer belt 216 wound around a driving roller 216a and a tension roller 216b. Four primary transfer rollers 219 are provided inside the intermediate transfer belt 216 to abut against the intermediate transfer belt 216 at positions opposing the photosensitive drum 212. The intermediate transfer belt 216 is rotated in the direction of the arrow by the driving roller 216a driven by a driving unit (not shown).

[0042] The secondary transfer unit 201D includes a secondary transfer roller 217, which is arranged to sandwich the intermediate transfer belt 216 at a position opposite to the driving roller 216a. The fixing device 201E is arranged on the downstream side of the secondary transfer roller 217 along the sheet S conveying direction, and includes a pressure roller 220a and a heating roller 220b. On the downstream side of the fixing device 201E along the sheet S conveying direction, a first discharge roller pair 225a, a second discharge roller pair 225b and a double-sided printing reversing unit 201F are arranged. The double-sided printing reversing unit 201F includes a reversing roller pair 222 and a re-transfer path R. The reversing roller pair 222 can rotate in the forward and reverse directions. The re-transfer path R allows the sheet S with an image formed on one side to be conveyed to the imaging unit 201B.

[0043] The image forming apparatus 201 having the above-described configuration operates as follows. The image forming apparatus 201 acquires image data from the image reading device 202 or from an external device together with an instruction to start a print job, and forms an image corresponding to the image data on a sheet S. At this time, the image forming apparatus 201 performs various steps of image formation based on an operation condition given according to the characteristics of the sheet S. A print job refers to a series of operations of conveying the sheet S, forming an image on the sheet, and discharging the sheet S to the placement portion 223 after the image formation operation is completed, which are performed based on a print signal instructing image formation on the sheet S. The image forming apparatus 201 acquires an instruction to start a print job from the operation unit 502 or an external device.

[0044] The imaging unit 201B uniformly charges the surface of the photosensitive drum 212 to a potential having a predetermined polarity using the charging device 213. The laser scanner 210 irradiates the uniformly charged surface of the photosensitive drum 212 with a corresponding laser beam modulated based on image data. Thus, an electrostatic latent image of a corresponding color (yellow, magenta, cyan, and black) is formed on the surface of each photosensitive drum 212.

[0045] The image forming unit 201B develops the electrostatic latent image formed on the photosensitive drum 212 using the developing device 214. The electrostatic latent image is developed on the photosensitive drum 212 with the toner of the corresponding color, so that a toner image of the corresponding color is formed on the photosensitive drum 212. The toner images are sequentially transferred from the photosensitive drum 212 to the rotating intermediate transfer belt 216 in a superimposed manner by the primary transfer roller 219. In this way, a full-color toner image is formed on the intermediate transfer belt 216. The intermediate transfer belt 216 rotates to convey the toner image to the secondary transfer unit 201D.

[0046] Simultaneously with this operation of forming a toner image, the sheets S are conveyed one by one to the registration roller pair 240 by the cassette sheet feeding unit 230 or the manual sheet feeding unit 235. Before the sheets S reach the registration roller pair 240, the characteristic amount of the sheets S is measured by the medium sensor 100. The image forming apparatus 201 sets an image forming condition based on the measured characteristic amount, and performs subsequent image forming based on the set image forming condition. The image forming condition to be set includes, for example, a voltage value of a secondary transfer bias applied to the secondary transfer roller 217 during the transfer of the toner image to the sheet S, a fixing temperature when the image is fixed by the fixing device 201E, and a conveying speed of the sheet S during the fixing.

[0047] The registration roller pair 240 corrects the skew of the sheet S conveyed to the registration roller pair 240. After the skew is corrected, the sheet S is conveyed to the secondary transfer unit 201D by the registration roller pair 240 in synchronization with the timing at which the toner image carried on 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 to the sheet S using a secondary transfer bias applied to the secondary transfer roller 217.

[0048] The sheet S to which the toner image is transferred is conveyed to the fixing device 201E. The fixing device 201E clamps and conveys the sheet S using a clamping portion defined by the pressure roller 220a and the heating roller 220b. The fixing device 201E heats the sheet S with the heating roller 220b while clamping and conveying the sheet S, thereby melting and mixing the toners of each color on the sheet S. In addition, the fixing device 201E presses the sheet S with the pressure roller 220a, thereby fixing the melted and mixed toner to the sheet S. At this time, the viscosity of the melted toner generates an adhesive force on the heating roller 220b on the sheet S.

[0049] Figure 2A and Figure 2B 201E. In the case where the rigidity (strength) of the sheet S is small, the adhesion force generated on the sheet S to the heating roller 220b may cause the sheet S to be rolled up by the rotating heating roller 220b ( Figure 2B Therefore, a separation plate 221 ( Figure 2A ).

[0050] The image forming apparatus 201 can determine the state of the separation plate 221 according to the type and basis weight of the sheet S identified from the measurement result of the media sensor 100. For example, in the case of imaging a sheet S of a small stiffness type, as shown in FIG. Figure 2AAs shown, the separation plate 221 is arranged so that the distal end of the separation plate 221 contacts the surface of the heating roller 220b, thereby separating the sheet S from the heating roller 220b. In the case of imaging a sheet S of a large rigidity type, the sheet S is not rolled up by the heating roller 220b. Therefore, the separation plate 221 is arranged so that the distal end of the separation plate 221 does not contact the surface of the heating roller 220b. In this way, the surface of the heating roller 220b can be prevented from being worn by the separation plate 221.

[0051] The sheet S on which the image is fixed is discharged to the discharge space D by any one of the first discharge roller pair 225a and the second discharge roller pair 225b. The sheet S is placed on the placement portion 223 provided on the bottom surface of the discharge space D in a protruding manner. In the case where images are formed on both sides of the sheet S, the sheet S on which the image is fixed on one side is conveyed to the re-conveying path R by the reversing roller pair 222. The sheet S is conveyed to the imaging unit 201B again, and an image is formed on the other side of the reversed sheet S. The re-conveying path R allows the sheet S to be conveyed to the conveying path between the conveying roller pair 290 and the registration roller pair 240.

[0052] <Control Unit>

[0053] Figure 3 200 is an explanatory diagram of a controller that controls the operation of such an imaging device 201. The controller 200 is, for example, an information processing device including a central processing unit (CPU). The controller 200 can be implemented by, for example, a microprocessor unit (MPU) or an application specific integrated circuit (ASIC). The controller 200 controls the above-mentioned imaging operation performed by the imaging device 201.

[0054] The controller 200 includes a control unit 400 and a memory 401. The memory 401 stores, for example, a control program for an imaging operation, initial values ​​of various setting values, and various types of data required for the imaging operation. In addition, the memory 401 has a storage area for storing a print mode database 402. The print mode database 402 is a database in which the correspondence between sheet characteristics and imaging conditions (printing modes) is pre-set. Examples of sheet characteristics include the type and basis weight of the sheet. The control unit 400 is connected to the operating unit 502, the image reading device 202, the imaging unit 201B, the conveying unit 600, the sensor 601, and the media sensor 100. The control unit 400 can communicate with a host device 501 as an external device.

[0055] The host device 501 is, for example, a personal computer, an image scanner, or a fax machine. The operation unit 502 inputs, for example, instructions and settings received via the input interface to the control unit 400. The operation unit 502 outputs various types of information via the output interface under the control of the control unit 400. As described above, the operation unit 502 includes a display as an output interface, and displays various types of information on the display.

[0056] The conveying unit 600 includes a conveying roller pair 280 and 290, a pickup roller 2, a feed roller 3, a delay roller 4, and a motor driving these rollers. The conveying unit 600 also includes a registration roller pair 240, a secondary transfer roller 217, a pressure roller 220a, a heating roller 220b, and a motor driving these rollers. In addition, the conveying unit 600 includes a first discharge roller pair 225a, a second discharge roller pair 225b, a reversing roller pair 222, other rollers that convey the sheet S in the image forming apparatus 201, and a motor driving these rollers. The conveying unit 600 controls the feeding of the sheet S by driving and controlling each motor under the control of the control unit 400.

[0057] The control unit 400 acquires an instruction to start a print job from the host device 501 or the operation unit 502, and starts the print job. The control unit 400 acquires image data from the host device 501 or the image reading device 202, and performs image processing on the acquired image data. The control unit 400 performs the print job by causing the imaging unit 201B to form a toner image based on the image data that has been image-processed and causing the conveying unit 600 to feed the sheet S.

[0058] The media sensor 100 includes an information processing unit 160, an ultrasonic sensor 120, and an optical sensor 150. In at least one embodiment, the ultrasonic sensor 120 and the optical sensor 150 are used as a sheet measuring unit. The information processing unit 160 includes a memory 1601. The information processing unit 160 is an information processing device implemented by, for example, a CPU, an MPU, or an ASIC. In at least one embodiment, the media sensor 100 has a function of detecting the leading edge and the trailing edge of the conveyed sheet S. The media sensor 100 can detect the trailing edge and the leading edge of the sheet S by using either or both of the ultrasonic sensor 120 and the optical sensor 150.

[0059] The image forming conditions (e.g., the conveying speed at the time of fixing, the target fixing temperature, and the transfer voltage at the time of secondary transfer) differ depending on the physical properties (e.g., basis weight, rigidity, surface properties, material) of the sheet S on which the image is to be formed. Therefore, the image forming conditions need to be set in advance according to the characteristic amount of the sheet S to be used at the time of image forming.

[0060] Depending on the type of sheet S, there are some restrictions when setting the sheet S to the feed port (sheet feed box 1 or manual feed tray 5). For example, some thick paper sheets with high rigidity can only be fed from the manual feed tray 5 with a small curvature of the conveying path. Coated paper sheets with smooth surface texture and strong adhesion between sheets need to be fed one by one from the manual feed tray 5 to prevent multiple sheets from being conveyed overlapping each other. Due to the deviation of the pulp fiber orientation direction (fiber orientation) caused by the manufacturing method, paper sheets made of pulp as a raw material usually have different bending rigidity in the length direction and the width direction. Therefore, when setting the sheet to the feed port, a recommended orientation of the sheet in the length direction and the width direction is given so that the bending rigidity becomes smaller relative to the bend in the conveying path. In addition, for a single-sided coated paper sheet obtained by coating only one side of a plain paper sheet, the orientation in the up and down direction is specified when setting so that printing is performed on the coated surface.

[0061] There are also some types of sheets that cannot be used in the image forming apparatus 201. For example, in the case of a thick paper sheet with excessively high rigidity, the conveyance of the sheet may be stopped due to the resistance generated when the sheet is conveyed along the curved conveying path. A thin paper sheet with excessively low rigidity is strongly affected by the adhesion generated between the molten toner and the heating roller 220b when passing through the fixing device 201E. Therefore, there is a possibility that the sheet cannot be separated from the heating roller 220b by the separation plate 221, and the sheet is directly wound around the heating roller 220b ( Figure 2B ) In addition, in the case of a synthetic paper sheet made of synthetic resin rather than pulp as a raw material, the sheet may be melted by heating in the fixing device 201E, thereby contaminating the heating roller 220b.

[0062] Therefore, in order to appropriately perform image formation, it is important to identify the type of sheet S to be used based on the feature amount of the sheet S before image formation. Therefore, before the sheet S is conveyed to the secondary transfer unit 201D, the media sensor 100 needs to measure the feature amount of the sheet S. The operation of the media sensor 100 is controlled by the information processing unit 160, and processing of the measurement result of each of the ultrasonic sensor 120 and the optical sensor 150 is performed by the information processing unit 160. The information processing unit 160 operates under the control of the control unit 400, and transmits the feature amount of the sheet S obtained from the measurement result of each of the ultrasonic sensor 120 and the optical sensor 150 to the control unit 400.

[0063] The media sensor 100 may detect the sheet S conveyed by the conveying roller pair 280. The control unit 400 and the information processing unit 160 start a sheet measurement sequence in response to the detection of the sheet S by the media sensor 100. By starting the sheet 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.

[0064] The ultrasonic sensor 120 measures the sheet S by using ultrasonic waves, and outputs an output value of 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 sheet S from the output value given when there is a sheet S and the output value given when there is no sheet S. The information processing unit 160 detects information corresponding to the basis weight according to the transmittance of the sheet S. The optical sensor 150 is, for example, a contact image sensor (CIS). The information processing unit 160 stores the brightness value of each pixel in the memory 1601 as an imaging result obtained by the optical sensor 150. The information processing unit 160 converts the brightness value of each pixel stored in the memory 1601 into information corresponding to surface properties such as a difference cumulative value obtained by adding the difference values ​​of the brightness values ​​of adjacent pixels and brightness.

[0065] The information processing unit 160 sends the information corresponding to the basic weight and the information corresponding to the surface property to the control unit 400. The control unit 400 determines the type of the sheet S (paper type, paper type information) based on the acquired information corresponding to the basic weight and the information corresponding to the surface property. The control unit 400 determines one imaging condition (printing mode) corresponding to the type of the sheet S from a plurality of printing modes stored in the printing mode database 402. The control unit 400 displays information about the determined printing mode on the display of the operation unit 502. The printing mode is an operation mode for controlling the imaging under predetermined imaging conditions (e.g., secondary transfer bias value, target fixing temperature of the fixing device 201E, conveying speed during fixing). The printing modes are named by the sheet type, such as "thin paper sheet 1", "thin paper sheet 2", "plain paper sheet 1", "coated paper sheet 1", "coated paper sheet 2", and "coated paper sheet 3". The description given here relates to a method of determining the imaging condition based on the type of the sheet S, but the method is not limited thereto. For example, the control unit 400 determines the type (paper type, paper type information) of the sheet S based on the acquired information corresponding to the surface property. The control unit 400 can determine one imaging condition (printing mode) corresponding to the type of the sheet S and the information corresponding to the basis weight from a plurality of printing modes stored in the printing mode database 402.

[0066] <Structure of Media Sensor>

[0067] Figure 4 and Figure 5 2 is an explanatory diagram of the structure of the media sensor 100 . Figure 4 1 is a view of the media sensor 100 viewed from a direction orthogonal to the conveying direction of the sheet S. FIG. Figure 5 1 is a view of the media sensor 100 viewed from the upstream side in the conveying direction of the sheet S. FIG.

[0068] like Figure 4 As shown, the media sensor 100 is disposed between the transport roller pair 280 and the transport roller pair 290, and acquires information corresponding to the basis weight of the transported sheet S and information corresponding to the surface property of the transported sheet S. The media sensor facing roller 260 is disposed at a position facing the media sensor 100 with respect to the transport path of the sheet S. The media sensor facing roller 260 is configured to move in a direction toward the media sensor 100 and in a direction away from the media sensor 100.

[0069] like Figure 5 As shown, in the media sensor 100, the ultrasonic sensor 120 and the optical sensor 150 are arranged at the same position in the conveying direction of the sheet S, and are arranged side by side in the direction orthogonal to the conveying direction. The ultrasonic sensor 120 includes an ultrasonic transmitter 130 and an ultrasonic receiver 131. The optical sensor 150 is a CIS, which includes a light source 1501 (e.g., LED) and a line sensor 1502 as a light transmitter and a light receiver, respectively. The optical sensor 150 can be constructed by using a CCD image sensor or a CMOS image sensor.

[0070] The optical sensor 150 measures the brightness value of the received light. For this purpose, the sheet S needs to be kept at the optical focus position of the optical sensor 150. When the ultrasonic sensor 120 measures the sheet S, the measurement accuracy is improved when there is no influence due to the vibration of the conveyed sheet S. Therefore, the sheet S needs to be conveyed in a stable posture.

[0071] In at least one embodiment, in order to convey the sheet S in a stable posture, the media sensor facing roller 260 and the sheet pressing roller 261 are arranged between the conveying roller pair 280 and the conveying roller pair 290. The media sensor facing roller 260 and the sheet pressing roller 261 are arranged at the same position in the conveying direction of the sheet S. The media sensor facing roller 260 is arranged to face the optical sensor 150 across the conveying path, and is configured to press the sheet S toward the optical sensor 150. As a result, in the case where the media sensor 100 measures the surface of the sheet S, the deviation of the position and posture of the sheet S is reduced. Therefore, the media sensor 100 can measure the characteristic quantity (such as surface properties and basis weight) of the sheet S in a stable state. The sheet pressing roller 261 is arranged at a position so that the ultrasonic sensor 120 is sandwiched between the sheet pressing roller 261 and the media sensor facing roller 260.

[0072] <Basis Weight Measurement>

[0073] In the ultrasonic sensor 120, an ultrasonic transmitter 130 and an ultrasonic receiver 131 are arranged at positions opposite to each other across the conveying path. The ultrasonic transmitter 130 is arranged on the upper block 110 side of the media sensor 100. The ultrasonic receiver 131 is arranged on the lower block 109 side of the media sensor 100. The ultrasonic sensor 120 receives the ultrasonic wave output from the ultrasonic transmitter 130 via the conveying path of the sheet S through the ultrasonic receiver 131. The ultrasonic receiver 131 outputs information (output value) for determining the basis weight of the sheet S based on the received ultrasonic wave.

[0074] The ultrasonic transmitter 130 and the ultrasonic receiver 131 are both formed of a piezoelectric element (also called a "piezoelectric element") and an electrode terminal. The piezoelectric element is an element for mutual conversion between mechanical displacement and electrical signals. The ultrasonic transmitter 130 generates ultrasonic waves through the oscillation of the piezoelectric element in response to the input of a pulse voltage having a predetermined frequency to the electrode terminal. The generated ultrasonic wave propagates in the air. Once the ultrasonic wave reaches the sheet S, the ultrasonic wave causes the sheet S to vibrate. The ultrasonic wave generated in the ultrasonic transmitter 130 propagates to the ultrasonic receiver 131 via the sheet S. The piezoelectric element of the ultrasonic receiver 131 causes the electrode terminal to generate an output voltage corresponding to the amplitude of the received ultrasonic wave. The output voltage has a voltage value corresponding to the basis weight of the sheet S. The output voltage is sent to the information processing unit 160 as an output value.

[0075] The ratio of the output voltage given when there is no sheet S to the output voltage given when there is a sheet S between the ultrasonic transmitter 130 and the ultrasonic receiver 131 is the transmittance. The transmittance of ultrasonic waves varies depending on the basis weight (area density) of the sheet S. Therefore, the basis weight of the sheet S can be estimated by using a conversion formula or a conversion table between the transmittance and the basis weight.

[0076] <Surface property measurement>

[0077] The surface property of the sheet S is detected by using the optical sensor 150. Light emitted from the light source 1501 irradiates the sheet S at a constant angle through a light guide (not shown). The sheet S reflects the irradiated light. The light reflected by the sheet S forms an image on the line sensor 1502 via a lens (not shown). In this way, the line sensor 1502 can read the light reflected from the sheet S as an image. Fig. 6A and Figure 6B 1 is an explanatory diagram of the reading result obtained by the optical sensor 150 .

[0078] exist Fig. 6A, an example of an image read by the line sensor 1502 is shown. The line sensor 1502 includes a plurality of light receiving elements 1502a. The plurality of light receiving elements 1502a are arranged in a direction orthogonal to the conveying direction of the sheet S, so the line sensor 1502 can read an image corresponding to one line at a time. Fig. 6A In the example of , 400 light receiving elements 1502a are arranged, so the line sensor 1502 can read an image of 400 pixels (A1 to A400) at a time.

[0079] In at least one embodiment, the plurality of light receiving elements 1502a are arranged to achieve a resolution of 300 dpi. The image corresponding to one line read by the line sensor 1502 at one time is not sufficient as the amount of information for determining the surface properties of the sheet S. This is because: in the image corresponding to one line, there is a large deviation in the reading result of each reading position. Therefore, the optical sensor 150 performs multiple reading operations on the conveyed sheet S and obtains the reading results of multiple lines of the image of the sheet S. By connecting the reading results of the multiple lines in the conveying direction of the sheet S, the trend of the surface properties of the sheet S of a predetermined size can be determined.

[0080] The information processing unit 160 performs digital processing on the image read by the optical sensor 150, and stores the result of the digital processing as an output value (luminance value) of each pixel in the memory 1601. The information processing unit 160 acquires the cumulative difference value, the brightness, and the peak-to-peak (PP) value of the luminance value from the luminance value of each pixel stored in the memory 1601, and stores these information in the memory 1601.

[0081] The cumulative difference value is a value obtained by adding the results of accumulating the difference values ​​of the brightness values ​​of each adjacent pixel of the image read by the line sensor 1502 for the number of lines. The cumulative difference value is an index indicating the concavity and convexity of the sheet. Figure 6B In , when the detection value of each pixel is represented by the pixel position (1 to n) and the detection row (A to N), the difference cumulative value Y is represented based on the following formula (1) by using the difference cumulative value "k" of each row. Figure 6B The detection pixel data direction is the arrangement direction of the light receiving elements 1502a of the line sensor 1502 (the direction of pixels of one row). Figure 6B The detection row direction is the conveying direction of the sheet S.

[0082] k1=|A2-A1|+|A3-A2|...+|An-A(n-1)|

[0083] k2=|B2-B1|+|B3-B2|...+|Bn-B(n-1)|

[0084]

[0085] kN=|n2-n1|+|n3-n2|...+|Nn-N(n-1)|

[0086] Y=k1+k2+...+kN (1)

[0087] The brightness is the sum of the integrated values ​​of the brightness values ​​of each pixel received by the line sensor 1502 for the number of detection lines, and represents the brightness of the surface of the sheet S. The brightness M is represented by the following equation (2).

[0088] M=A1+A2+...+B1+B2+...+G1+G2+...+Nn (2)

[0089] The PP value is a value obtained by adding the difference between the maximum and minimum values ​​of the brightness value of a row for the number of detection rows. A transparent film made of a resin such as PET reflects less light irradiated from the light source 1501 and is detected as having low brightness. For sheets such as embossed paper sheets whose surfaces are intentionally provided with geometrical concavities and convexities, such concavities and convexities increase the brightness difference between adjacent pixels, resulting in a larger cumulative difference. For recycled paper sheets, the brightness values ​​in the fiber orientation are uneven, and the pulp fibers become shorter after several recycling processes, so the surface properties tend to be detected as rough. In contrast, for coated paper sheets, the coating on the surface makes the paper sheet appear less concave and convex, and the cumulative difference tends to be smaller. Brightness and PP values ​​are parameters used to distinguish these sheets.

[0090] The control unit 400 acquires basis weight, cumulative difference, brightness, and PP value as feature quantities of the sheet S from the information processing unit 160, and determines the printing mode with reference to the printing mode database 402. The control unit 400 performs image formation corresponding to the print job by using image formation conditions based on the determined printing mode.

[0091] <Media Sensor Facing Roller Position Control>

[0092] As described above, the media sensor facing roller 260 is configured to move in a direction toward the media sensor 100 (optical sensor 150) and in a direction away from the media sensor 100. That is, the media sensor facing roller 260 is movable between a first position separated 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 sheet S toward the optical sensor 150 by moving to the second position. In a case where the media sensor facing roller 260 is in the second position, the sheet S is preferably pressed against the optical sensor 150. In this way, the media sensor facing roller 260 is a rotating member that serves as a pressing member that presses the sheet S toward the optical sensor 150. The same applies to the sheet pressing roller 261.

[0093] Figure 7 2 is a diagram showing a configuration of a moving mechanism for moving the media sensor facing roller 260 and the sheet pressing roller 261 . Figure 7 1 is a view viewed from above (on the upper block 110 side) the media sensor facing roller 260 and the sheet pressing roller 261. The moving 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 sheet pressing roller 261 are mounted on the mounting plate 306. The ultrasonic transmitter 130 of the ultrasonic sensor 120 is not mounted on the mounting plate 306, but is fixed to the upper block 110 of the media sensor 100.

[0094] When the motor 300 is driven to rotate by the control unit 400, the gear 305 rotates. The rotation of the gear 305 causes the rotation shaft 301 to rotate. The rotation of the rotation shaft 301 causes the cam 302 and the detection plate 303 to rotate. The rotation of the cam 302 causes the mounting plate 306 to move up and down. As the mounting plate 306 moves up and down, the media sensor facing roller 260 and the sheet pressing roller 261 move. As a result, the media sensor facing roller 260 and the sheet pressing roller 261 move between the first position and the second position in synchronization.

[0095] The positions of the media sensor facing roller 260 and the sheet pressing roller 261 are detected by using the rotation detection sensor 304. The rotation detection sensor 304 is a photo interrupter. The rotation detection sensor 304 includes a light emitter and a light receiver arranged facing each other, and is configured so that the light receiver receives light output from the light emitter. The positions of the media sensor facing roller 260 and the sheet pressing roller 261 are determined based on whether the light output from the light emitter is blocked by the 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.

[0096] Fig. 8A and Figure 8B 2 is an explanatory diagram of the operation of the moving mechanism 700. Here, the operation of the moving mechanism 700 to move the medium sensor facing roller 260 is described, but the same operation applies to the sheet pressing roller 261. Fig. 8A and Figure 8B 300 is a view of the moving mechanism 700 viewed from the detection plate 303 side (in a direction orthogonal to the conveying direction of the sheet S). The motor 300 and the gear 305 are not shown. Fig. 8A , a state in which the media sensor facing roller 260 has moved to the first position separated from the optical sensor 150 is shown. Figure 8B, a state is shown in which the media sensor facing roller 260 has moved to the second position where the media sensor facing roller 260 presses the sheet S against the optical sensor 150 .

[0097] The mounting plate 306 is configured to rotate around a rotation axis 306a. The mounting plate 306 is connected to a spring 307 and is urged by the spring 307 in a direction away from the optical sensor 150. The rotation angle of the mounting plate 306 changes according to the rotation position of the cam 302 and the spring 307. As the rotation angle of the mounting plate 306 changes, the position of the media sensor facing the roller 260 changes from the first position ( Fig. 8A ) and the second position ( Figure 8B ) varies between.

[0098] The rotation position of the cam 302 can be determined based on whether the light from the rotation detection sensor 304 is blocked by the detection plate 303 mounted on the rotating shaft 301. As shown in the figure, the detection plate 303 is in an array shape. In the case where the detection plate 303 rotates together with the rotating shaft 301, the detection signal output from the rotation detection sensor 304 changes. The rotation position of the cam 302 is detected based on the state of the detection signal. For example, in the case where the detection signal switches from the second state to the first state, the media sensor faces the roller 260 in the first position ( Fig. 8A ), and in the case where the detection signal switches from the first state to the second state, the media sensor faces the roller 260 in the second position ( Figure 8B ). By stopping the rotational driving of the motor 300 at each timing, the medium sensor facing roller 260 stops at the first position or the second position.

[0099] Fig. 9 2 is a diagram showing the structure of the media sensor facing roller 260. The media sensor facing roller 260 is dumbbell-shaped, and a sponge material 2601 serving as a cleaning member is wound around the center of the media sensor facing roller 260. The media sensor facing roller 260 has two functions. Fig. 10A and Fig. 10B Each of them is an explanatory diagram of the function of the media sensor facing roller 260 .

[0100] The first function of the media sensor facing roller 260 is to maintain the distance between the sheet S and the light guide 1503 of the optical sensor 150 during sheet transport ( Fig. 10A). The media sensor facing roller 260 maintains the distance between the sheet S and the light guide 1503 and suppresses position fluctuation (flapping) of the sheet S by pressing the sheet S against the light guide 1503 of the optical sensor 150. Therefore, the optical sensor 150 can measure the sheet S while the sheet S is stable. The second function (cleaning) of the media sensor facing roller 260 is to wipe the surface of the light guide 1503 with the sponge material 2601 by rotation after the sheet passes to remove paper dust ( Fig. 10B ). As described above, the light guide 1503 is used to cause the light emitted from the light source 1501 to illuminate the sheet S at a fixed angle.

[0101] Fig.11 2 is a process flow chart for illustrating the movement process of the media sensor facing roller 260. This process is a process performed when the image forming apparatus 201 is started or restored from a sleep state to execute a print job. Note that in the case of controlling the movement of the media sensor facing roller 260, the movement of the sheet pressing roller 261 is also controlled in the same manner. FIG. 12A to FIG. 12C 2 is an explanatory diagram of the operation of the media sensor facing roller 260 during the moving process. Here, a case where the control unit 400 performs the process is described, but the process may also be performed by the information processing unit 160 under the control of the control unit 400.

[0102] When the image forming apparatus 201 is started or restored from the sleep state, the control unit 400 drives the motor 300 to rotate to move the media sensor facing roller 260 to the first position so as not to hinder the conveyance of the sheet S (step S111). This causes the media sensor facing roller 260 to move away from the optical sensor 150 ( Fig. 8A ). In an operation mode in which the characteristic amount of the sheet S is not measured, the media sensor facing roller 260 is maintained at the first position. In a media sensor mode for measuring the characteristic amount of the sheet S, the media sensor facing roller 260 is movable between the first position and the second position.

[0103] In the case where the media sensor mode is set (step S112), the control unit 400 performs initial adjustment, such as calibration of the optical sensor 150 (step S113). For example, an instruction for the media sensor mode may be given from the operation unit 502. When the initial adjustment starts, the control unit 400 drives the motor 300 to rotate so as to move the media sensor facing roller 260 to the second position so as to abut against the optical sensor 150. After the initial adjustment ends, the control unit 400 drives the motor 300 to rotate so as to move the media sensor facing roller 260 to the first position and away from the optical sensor 150.

[0104] In the initial adjustment, the media sensor 100 is activated, and measurement is performed by the ultrasonic sensor 120 in a state without a sheet. The measurement in the state without a sheet is a process of detecting an output change due to a change in the environment (such as temperature) by performing ultrasonic measurement in a state where the sheet S is not conveyed. The measurement result in the state without a sheet is used to correct the environmental influence during the ultrasonic measurement. In addition, in the initial adjustment, black measurement of the optical sensor 150 is performed to detect a dark current. The light amount of the optical sensor 150 is adjusted based on the dark current. At this time, the media sensor is in the second position facing the roller, so the influence of external light is suppressed.

[0105] When the initial adjustment is completed, the control unit 400 waits until an instruction to start a print job is obtained. When the control unit 400 obtains an instruction to start a print job, the conveying unit 600 starts conveying the sheet S. After the sheet S starts to be conveyed, if the media sensor 100 detects the leading edge of the sheet S, the control unit 400 stops the conveying unit 600 from conveying the sheet S (step S114). Fig. 12A , a state in which the conveyance of the sheet S has stopped is shown. The sheet S reaches the measuring position of the medium sensor 100, the leading edge is conveyed to the conveying roller pair 290, and the conveyance stops. The sheet S is in a state in which a predetermined tension is applied to the sheet by the conveying roller pair 280 and the conveying roller pair 290, and wrinkles on the surface are flattened.

[0106] The control unit 400, which has stopped the conveyance of the sheet S, drives the motor 300 to rotate to move the media sensor facing roller 260 to the second position and bring the sheet S into contact with the media sensor 100 (step S115). In this method, during the conveyance of the sheet S to the measuring position of the media sensor 100, the media sensor facing roller 260 is in the first position, so as not to hinder the conveyance of the sheet S. In addition, during the measurement of the sheet S by the media sensor 100, the media sensor facing roller 260 presses the sheet S against the media sensor 100 at the second position to stabilize the posture of the sheet S.

[0107] The control unit 400, which has caused the media sensor facing roller 260 to abut against the media sensor 100, confirms that the media sensor facing roller 260 abuts against the media sensor 100 based on the detection result of the rotation detection sensor 304. For example, in a case where the detection signal output from the rotation detection sensor 304 has switched from the first state to the second state, the control unit 400 confirms that the media sensor facing roller 260 (sheet S) abuts against the media sensor 100. After confirming that the media sensor facing roller 260 (sheet S) abuts against the media sensor 100, the control unit 400 restarts the conveyance of the sheet S by the conveyance unit 600 ( Fig. 12B ).

[0108] While the conveyance of the sheet S is restarted, the control unit 400 performs a process for measuring the characteristic amount of the sheet S by the media sensor 100 (step S116). The media sensor 100 performs ultrasonic measurement by using the ultrasonic sensor 120, and derives transmittance based on the measurement result. The control unit 400 derives the basis weight of the sheet S based on the transmittance by using a table or a mathematical formula indicating the relationship between the transmittance and the basis weight. The media sensor 100 measures the surface property of the sheet S by using the optical sensor 150, and derives the cumulative difference and the brightness. The control unit 400 distinguishes the type of the sheet S based on the cumulative difference and the brightness. The control unit 400 refers to the print mode database to determine the print mode based on the basis weight and type of the sheet S, and sets the imaging condition based on the determined print mode. When the measurement of the characteristic amount of the sheet S is finished, the control unit 400 stops the media sensor 100.

[0109] Then, the control unit 400 detects whether the trailing edge of the sheet S has passed through the measuring position of the media sensor 100 by using the media sensor 100 (step S117). Fig. 12C , a state in which the sheet S has passed through the measuring position of the media sensor 100 is shown. When the trailing edge of the sheet S passes through the measuring position of the media sensor 100, the control unit 400 drives the motor 300 to rotate to move the media sensor facing roller 260 to the first position (step S118). This causes the media sensor facing roller 260 to move away from the optical sensor 150. That is, after a predetermined period of time has passed since it was detected that the trailing edge of the sheet S has passed, the control unit 400 moves the media sensor facing roller 260 away from the optical sensor 150. As a result, the media sensor facing roller 260 can abut the surface of the optical sensor 150 with the sponge material 2601 to clean the surface of the optical sensor 150 for a predetermined period of time. Except when the characteristic amount of the sheet S is measured, the media sensor facing roller 260 is always on standby at the first position so as not to hinder the conveyance of the sheet S.

[0110] In this way, the detection of the sheet S by the media sensor 100 triggers the measurement of the characteristic amount of the sheet S, and controls the position of the media sensor facing roller 260. As a result, without providing a sensor dedicated to detecting the position of the sheet S, it is possible to prevent the conveyance of the sheet S from being hindered by the media sensor facing roller 260, suppress the flapping of the sheet S, and thereby accurately measure the characteristic amount of the sheet S.

[0111] The detection of the sheet S performed in the processing step of step S114 will now be described. The sheet S can be detected by using any one of the ultrasonic sensor 120 and the optical sensor 150. Here, the case where the ultrasonic sensor 120 is used is described.

[0112] In the case of using the ultrasonic sensor 120, the ultrasonic sensor 120 detects the leading edge and the trailing edge of the sheet S by transmitting and receiving ultrasonic waves via the conveying path. The amplitude of the ultrasonic waves received by the ultrasonic receiver 131 changes according to the presence or absence of the sheet S, and a difference is generated in the output voltage output from the ultrasonic receiver 131. The presence or absence of the sheet S can be determined based on this difference in the output voltage.

[0113] When there is no sheet S between the ultrasonic transmitter 130 and the ultrasonic receiver 131, the ultrasonic wave is not attenuated by the sheet S. As a result, the output voltage is higher than when there is the sheet S. On the contrary, when there is a sheet S between the ultrasonic transmitter 130 and the ultrasonic receiver 131, the ultrasonic wave is attenuated by the sheet S. As a result, the output voltage becomes lower than when there is no sheet S.

[0114] The information processing unit 160 sets a threshold value (threshold voltage) for determining the presence or absence of the sheet S, compares the output voltage acquired from the ultrasonic receiver 131 with the threshold value (threshold voltage), and determines the presence or absence of the sheet S based on the comparison result. For example, when the output voltage is greater than the threshold value, it is determined that there is no sheet S; when the output voltage is equal to or less than the threshold value, it is determined that there is a sheet S. When the output voltage changes from a state greater than the threshold value to a state equal to or less than the threshold value, the leading edge of the sheet S is detected. When the output voltage changes from a state equal to or less than the threshold value to a state greater than the threshold value, the trailing edge of the sheet S is detected.

[0115] Fig.13 is a processing flowchart for illustrating the sheet detection processing of step S114. Detection of the sheet S is performed by detecting the leading edge of the sheet S. Here, a case where the information processing unit 160 performs this processing is described, but this processing may also be performed by the control unit 400.

[0116] At a time before the sheet S transported by the transport roller pair 280 reaches the measurement position of the ultrasonic sensor 120, the information processing unit 160 starts to transmit ultrasonic waves through the ultrasonic transmitter 130 and starts to receive ultrasonic waves through the ultrasonic receiver 131 (step S171). For example, the information processing unit 160 performs the following steps based on step S113 (see step S171). Fig.11 ) is completed, the ultrasonic transmitter 130 starts transmitting ultrasonic waves, and the ultrasonic receiver 131 starts receiving ultrasonic waves. The ultrasonic transmitter 130 transmits ultrasonic waves and the ultrasonic receiver 131 receives ultrasonic waves at predetermined intervals.

[0117] The information processing unit 160 acquires the output voltage from the ultrasonic receiver 131, and repeatedly compares the acquired output voltage with a predetermined threshold value until the output voltage becomes equal to or less than the threshold value (step S172: No). In the case where the output voltage becomes equal to or less than the threshold value (step S172: Yes), the information processing unit 160 determines whether the leading edge of the sheet S has been detected (step S173). In the case where the information processing unit 160 detects the leading edge of the sheet S, the information processing unit 160 stops the ultrasonic transmission of the ultrasonic transmitter 130 and the ultrasonic reception of the ultrasonic receiver 131 (step S174). Thereafter, the information processing unit 160 advances the processing to step S115 (see Fig.11 ).

[0118] Fig.14 1 is a processing flow chart for illustrating the sheet passing detection processing of step S117. The sheet S passing detection is performed by detecting the trailing edge of the sheet S. For example, in step S116 (see Fig.11 ) is performed after measuring the feature amount of the sheet S in the processing step of . Here, a case where the information processing unit 160 performs the processing is described, but the processing may also be performed by the control unit 400.

[0119] After the process for measuring the characteristic amount of the sheet S is finished, the information processing unit 160 starts to transmit ultrasonic waves through the ultrasonic transmitter 130 and starts to receive ultrasonic waves through the ultrasonic receiver 131 (step S181). The ultrasonic transmission by the ultrasonic transmitter 130 and the ultrasonic reception by the ultrasonic receiver 131 are performed at a prescribed interval. Note that the ultrasonic sensor 120 has already transmitted ultrasonic waves through the ultrasonic transmitter 130 and received ultrasonic waves through the ultrasonic receiver 131 due to the measurement of the characteristic amount of the sheet S. Therefore, after the processing step of step S116, the information processing unit 160 can continue the ultrasonic transmission by the ultrasonic transmitter 130 and the ultrasonic reception by the ultrasonic receiver 131.

[0120] The information processing unit 160 acquires the output voltage from the ultrasonic receiver 131, and repeatedly compares the acquired output voltage with a predetermined threshold value until the output voltage becomes greater than the threshold value (step S182: No). In the case where the output voltage becomes greater than the threshold value (step S182: Yes), the information processing unit 160 determines whether the trailing edge of the sheet S has been detected (step S183). In the case where the information processing unit 160 detects the trailing edge of the sheet S, the information processing unit 160 stops the ultrasonic transmission of the ultrasonic transmitter 130 and the ultrasonic reception of the ultrasonic receiver 131 (step S184). Thereafter, the information processing unit 160 advances the processing to step S118 (see Fig.11 ).

[0121] As described above, the image forming apparatus 201 of at least one embodiment determines the image forming condition by using, for example, the type and basis weight of the sheet S determined based on the measurement result of the characteristic amount of the sheet S obtained by the media sensor 100. Therefore, the image forming apparatus 201 can form an image on the sheet S based on the optimal image forming condition. In the case where the media sensor 100 measures the characteristic amount of the sheet S, the media sensor facing roller 260 makes the sheet S abut against the media sensor 100. As a result, the sheet S is measured in a stable posture. Therefore, the media sensor 100 can accurately measure the characteristic amount of the sheet S.

[0122] The media sensor facing roller 260 is controlled to move between the first position and the second position in response to the detection of the sheet S by the media sensor 100. In order to detect the sheet S by the media sensor 100, it is no longer necessary to separately provide a sensor dedicated to detecting the position of the sheet S as in the prior art. Therefore, the cost can be suppressed. Therefore, the image forming apparatus 201 of at least one embodiment can suppress the reduction of the detection accuracy of the sheet S, and can also suppress the occurrence of poor conveyance of the sheet.

[0123] exist Fig.13 and Fig.14 In the embodiment of the present invention, an example in which the leading edge and the trailing edge of the sheet S are detected by the ultrasonic sensor 120 has been described, but the leading edge and the trailing edge of the sheet S may be detected by the optical sensor 150. For example, the optical sensor 150 emits light from the light source 1501 to the conveying path, and the line sensor 1502 receives the reflected light. The line sensor 1502 receives the reflected light when the sheet S is present, and does not receive the reflected light when the sheet S is not present. Based on the difference, the optical receiver outputs different output values ​​when the sheet S is present and when the sheet S is not present. The output value is compared with a predetermined threshold value, and the presence or absence of the sheet S may be determined based on the comparison result.

[0124] Furthermore, the detection of the leading edge and the trailing edge of the sheet S is not limited to being performed by a reflective sensor like the optical sensor 150, and the detection may also be performed by using a transmissive optical sensor. In this case, in the optical sensor, a light source and a light receiver are arranged facing each other across the conveying path of the sheet S. When there is a sheet S, the light emitted from the light source is not received by the light receiver, but when there is no sheet S, the light receiver receives the light. Based on the difference, the light receiver outputs different output values ​​when there is a sheet S and when there is no sheet S. The output value is compared with a predetermined threshold value, and the presence or absence of the sheet S can be determined based on the comparison result.

[0125] The above-mentioned media sensor 100 is an example and is not limited to the configuration including the optical sensor 150 and the ultrasonic sensor 120. The media sensor 100 may include other sensors capable of measuring the characteristic amount of the sheet S. In addition, the media sensor 100 may also include any one of the optical sensor 150 and the ultrasonic sensor 120. In addition, in the configuration of at least one embodiment, the media sensor 100 is included in the image forming apparatus 201, but the media sensor 100 may also be arranged outside the image forming apparatus 201. For example, when a user manually inserts the sheet S into the slot, the media sensor 100 may detect the sheet S.

[0126] Furthermore, in the above description, a configuration has been described in which the print mode database 402 is included in the memory 401 of the controller 200, but the storage location of the print mode database 402 is not limited thereto. For example, the print mode database 402 may be stored in the memory 1601 included in the media sensor 100. In this case, the information processing unit 160 determines the type and basis weight of the sheet S, and the information processing unit 160 also determines the print mode.

[0127] In addition, the above-mentioned image forming apparatus 201 determines control parameters such as image forming conditions by, for example, detecting the type and basis weight of the sheet S based on the feature amount of the sheet S measured by the media sensor 100. However, the control parameters may be directly determined from the feature amount. The media sensor 100 may be a device that measures physical properties of other sheets.

[0128] <Modification 1>

[0129] By shortening the time during which the media sensor facing roller 260 abuts against the media sensor 100 after the sheet S is measured, the sheet can be smoothly conveyed. Fig.15 : is a process flow chart for illustrating the movement process of the media sensor facing roller 260 in Modification 1. Note that in the case where the movement of the media sensor facing roller 260 is controlled, the movement of the sheet pressing roller 261 is also controlled in the same manner. Here, the case where the control unit 400 executes the process is described, but the process may be executed by the information processing unit 160 under the control of the control unit 400.

[0130] and Fig.11 Similar to the processing steps of step S111 and step S112, the control unit 400 moves the media sensor facing roller 260 away from the optical sensor 150 and confirms that the media sensor mode is set (step S131, step S132). Fig.11Similar to the processing steps of step S113, the control unit 400 moves the media sensor facing roller 260 to the second position, performs initial adjustment such as calibration, and then moves the media sensor facing roller 260 to the first position (steps S133 to S135).

[0131] and Fig.11 Similarly to the processing steps from step S114 to step S116, the control unit 400 detects the sheet S by using the media sensor 100, stops the conveyance of the sheet S, moves the media sensor facing roller 260 to the second position, and performs the measurement processing by using the media sensor 100 (steps S136 to S138). In the case where the measurement of the characteristic amount of the sheet S is completed, the control unit 400 stops the media sensor 100. Then, the control unit 400 drives the motor 300 to rotate to move the media sensor facing roller 260 to the first position (step S139). This causes the media sensor facing roller 260 to move away from the optical sensor 150. Fig.16 2 is a diagram for illustrating a state in which the media sensor facing roller 260 has moved to the first position. Fig.16 In FIG. 1 , before the sheet S passes through the measuring position of the media sensor 100 , the media sensor facing roller 260 has already moved to the first position.

[0132] After that, the control unit 400 detects whether the sheet S has passed the measuring position of the media sensor 100 (step S140). When the media sensor 100 detects the trailing edge of the sheet S, the control unit 400 detects that the sheet S has passed the measuring position of the media sensor 100. Except when measuring the characteristic amount of the sheet S, the media sensor facing roller 260 is always on standby at the first position so as not to hinder the conveyance of the sheet S.

[0133] In Modification 1, the media sensor facing roller 260 moves away from the media sensor 100 before the sheet S passes the measuring position of the media sensor 100. Therefore, the length of time the media sensor facing roller 260 abuts against the sheet S is longer than Fig.11 As a result, the load on sheet conveyance due to the abutment of the media sensor facing roller 260 against the sheet S is reduced, and the sheet S is smoothly conveyed.

[0134] <Modification 2>

[0135] By reducing the number of times the media sensor facing roller 260 moves, the durability of the moving mechanism 700 can be improved. Fig.17: is a process flow chart for illustrating the movement process of the media sensor facing roller 260 in Modification 2. Note that in the case where the movement of the media sensor facing roller 260 is controlled, the movement of the sheet pressing roller 261 is also controlled in the same manner. Here, the case where the control unit 400 executes the process is described, but the process may be executed by the information processing unit 160 under the control of the control unit 400.

[0136] and Fig.11 Similar to the processing steps of step S111 and step S112, the control unit 400 moves the media sensor facing roller 260 away from the optical sensor 150 and confirms that the media sensor mode is set (step S151, step S152). While keeping the media sensor facing roller 260 separated from the media sensor 100, the control unit 400 performs an initial adjustment process on the media sensor 100 (step S153). In the initial adjustment process, the media sensor 100 is started, and measurement is performed by the ultrasonic sensor 120 in a state where there is no sheet. Thereafter, the light amount of the optical sensor 150 is adjusted. Fig.11 Unlike the process of FIG. 1 , in this initial adjustment process, the media sensor facing roller 260 does not move from the first position.

[0137] When the initial adjustment is completed, the control unit 400 is on standby until the control unit 400 obtains an instruction to start a print job. When the control unit 400 obtains an instruction to start a print job, the control unit 400 starts to convey the sheet S by the conveying unit 600. When the medium sensor 100 detects the sheet S after the conveyance of the sheet S starts, the control unit 400 stops the conveyance of the sheet S by the conveying unit 600 (step S154). After the processing step of step S151, the media sensor facing roller 260 remains separated from the media sensor 100.

[0138] and Fig.11 Similar to the processing steps of step S115 and step S116, the control unit 400 moves the media sensor facing roller 260 to the second position and measures the characteristic amount of the sheet S by using the media sensor 100 (step S155, step S156). Fig.11 Similar to the processing steps of step S117 and step S118, the control unit 400 detects that the sheet S has passed the measuring position of the media sensor 100, and moves the media sensor facing roller 260 to the first position (step S157, step 158).

[0139] The media sensor facing roller 260 is always in the first position and separated from the media sensor 100 except when measuring the sheet S. Therefore, the media sensor facing roller 260 does not hinder the conveyance of the sheet S. Therefore, the initial adjustment process can be performed on the media sensor 100 in a state where the media sensor facing roller 260 is separated from the media sensor 100. As a result, the state in which the media sensor facing roller 260 abuts against the media sensor 100 can be shortened. The movement control of the media sensor facing roller 260 is simplified, thereby improving the durability of the moving mechanism 700.

[0140] <Modification 3>

[0141] The light source 1501 of the optical sensor 150 may emit light at a timing that does not affect the movement of the media sensor facing roller 260 . Fig.18 2 is a process flow chart for illustrating another example of the movement process of the media sensor facing roller 260 in Modification 3. Note that in the case where the movement of the media sensor facing roller 260 is controlled, the movement of the sheet pressing roller 261 is also controlled in the same manner. Here, a case where the control unit 400 executes the process is described, but the process may be executed by the information processing unit 160 under the control of the control unit 400.

[0142] and Fig.11 Similar to the processing steps of step S111 and step S112, the control unit 400 moves the media sensor facing roller 260 away from the optical sensor 150 and confirms that the media sensor mode is set (step S161, step S162). Fig.11 Similar to the processing steps of step S113, the control unit 400 moves the media sensor facing roller 260 to the second position, performs initial adjustment such as calibration, and then moves the media sensor facing roller 260 to the first position (steps S163 to S165).

[0143] and Fig.11 Similar to the processing steps of step S114, the control unit 400 detects the sheet S by using the media sensor 100, and stops the conveyance of the sheet S (step S166). The control unit 400 causes the information processing unit 160 to cause the light source 1501 included in the optical sensor 150 of the media sensor 100 to emit light (step S167). The control unit 400 drives the motor 300 to rotate to move the media sensor facing roller 260 to the second position (step S168). As a result, the media sensor facing roller 260 abuts against the media sensor 100. Based on this control, the media sensor facing roller 260 can stabilize the posture of the sheet S by pressing the sheet S against the media sensor 100 during measurement without hindering the conveyance of the sheet S to the measurement position of the media sensor 100.

[0144] Afterwards, with Fig.11 Similar to the processing steps of step S138 and step S139, the control unit 400 measures the characteristic amount of the sheet S by using the media sensor 100, and then moves the media sensor facing roller 260 away from the media sensor 100 (step S169, step S170). Except when measuring the characteristic amount of the sheet S, the media sensor facing roller 260 is always on standby at the first position so as not to hinder the conveyance of the sheet S. The light source 1501 of the optical sensor 150 emits light at a time that does not affect the movement of the media sensor facing roller 260. In this process, the light source 1501 emits light after the leading edge of the sheet S is detected and before the media sensor facing roller 260 abuts against the media sensor 100. Therefore, the optical sensor 150 can immediately measure the sheet S with a stable amount of light.

[0145] The operation of the media sensor facing roller 260 relative to the optical sensor 150 has been described above. The media sensor facing roller 260 is arranged to sandwich the ultrasonic sensor 120 between the media sensor facing roller 260 and the sheet pressing roller 261 (see Figure 5 ). With this configuration, when the sheet S reaches the measuring position of the media sensor 100, the media sensor facing roller 260 and the sheet pressing roller 261 press the sheet S against the measuring position of the ultrasonic sensor 120. The ultrasonic sensor 120 emits ultrasonic waves to penetrate the sheet S and measures the characteristic amount. The state of the sheet S is stabilized by the media sensor facing roller 260 and the sheet pressing roller 261, so the characteristic amount of the sheet S can be accurately measured by the ultrasonic sensor 120.

[0146] Similarly, in the case of using a transmission optical sensor, the media sensor facing roller 260 and the sheet pressing roller 261 are also effective. Fig.19 1 is an explanatory diagram of the construction of a media sensor using a transmission optical sensor 150t. The transmission optical sensor 150t emits light through a sheet S and measures a characteristic amount. For this purpose, a light source 1501t and a line sensor 1502t are arranged to face each other across a conveying path. In addition, the media sensor facing roller 260 is not included, and a sheet pressing roller 262 is arranged to face a sheet pressing roller 261 to sandwich the optical sensor 150t. The state of the sheet S is stabilized by the sheet pressing roller 261 and the sheet pressing roller 262, so the characteristic amount of the sheet S can also be accurately measured by the transmission optical sensor 150t. In other words, in addition to the media sensor facing roller 260 directly pressing the sheet S against the optical sensor 150t, the state of the sheet S can be stabilized by pressing the sheet S against the optical sensor 150t by two rollers. As a result, the sheet S can be stably measured even by the transmission optical sensor 150t, the reduction in the detection accuracy of the sheet can be suppressed, and the occurrence of poor sheet conveyance can also be suppressed.

[0147] The above-described media sensor 100 is an example and is not limited to the configuration including the optical sensor 150t and the ultrasonic sensor 120 . The media sensor 100 may include other sensors capable of measuring characteristic quantities of the sheet S. Furthermore, the media sensor 100 may also include any one of the optical sensor 150t and the ultrasonic sensor 120 .

[0148] Furthermore, in the above description, a configuration has been described in which the print mode database 402 is included in the memory 401 of the controller 200, but the storage location of the print mode database 402 is not limited thereto. For example, the print mode database 402 may be stored in the memory 1601 included in the media sensor 100. In this case, the information processing unit 160 determines the type and basis weight of the sheet S, and the information processing unit 160 also determines the print mode.

[0149] In the above description, the construction of the imaging device 201 has been described, but the present disclosure can be applied to any device including a sheet detection device, which includes a media sensor 100, a controller 200, a conveying unit 600, a media sensor facing roller 260 and a sheet pressing roller 261. For example, such a sheet detection device can be used in an image reading device that reads an image printed on a sheet while conveying the sheet. The image reading device includes an automatic document feeder (ADF). By including a sheet detection device in the ADF, it is possible to stably read an image and convey the sheet. In addition, although it is necessary to detect the leading edge and the trailing edge of the sheet to trigger the movement of the media sensor facing roller 260, it is not necessary to set a dedicated sensor for sheet detection, so that the cost can be reduced.

[0150] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications and equivalent structures and functions.

[0151] This application claims the benefit of Japanese Patent Application No. 2023-149048, filed September 14, 2023, which is hereby incorporated by reference into this application in its entirety.

Claims

1. A sheet material detection device, comprising: a measuring device for measuring a characteristic quantity of the sheet material conveyed by the conveying device; a pressing member movable between a first position separated from the measuring device and a second position closer to the measuring device than the first position; and a moving device configured to move the pressing member, wherein, when the measuring device detects that the sheet has not been delivered to the measuring position of the measuring device, the pressing member is arranged at the first position by the moving device, wherein the moving device is configured to move the pressing member from the first position to the second position when the measuring device detects that the sheet has been conveyed to the measuring position of the measuring device, and Here, the measuring device is configured to measure the characteristic amount of the sheet in a state where the pressing member is arranged at the second position.

2. The sheet material detection device according to claim 1, wherein: The moving device is configured to move the pressing member from the second position to the first position if the measuring device detects that the sheet has passed a measuring position of the measuring device.

3. A sheet material detection device, comprising: a measuring device for measuring a characteristic quantity of the sheet material conveyed by the conveying device; a pressing member movable between a first position separated from the measuring device and a second position closer to the measuring device than the first position; and a moving device configured to move the pressing member, wherein, when the sheet has not yet been conveyed by the conveying device to the measuring position of the measuring device, the pressing member is arranged at the first position by the moving device, wherein the moving device is configured to move the pressing member from the first position to the second position when the sheet has been conveyed by the conveying device to the measuring position of the measuring device, and The moving device is configured to move the pressing member from the second position to the first position before the sheet passes through the measuring position of the measuring device.

4. The sheet material detection device according to claim 1 or 3, wherein: The mobile device is configured as: moving the pressing member from the first position to the second position to control the pressing member to abut the measuring device when performing an initial adjustment of the measuring device; and When the initial adjustment is completed, the pressing member is moved from the second position to the first position.

5. A sheet material detection device, comprising: a measuring device for measuring a characteristic quantity of the sheet material conveyed by the conveying device; a pressing member movable between a first position separated from the measuring device and a second position closer to the measuring device than the first position; and a moving device configured to move the pressing member, wherein, in the case where the initial adjustment of the measuring device is performed in a state where the sheet has not yet been conveyed to the measuring position of the measuring device, the pressing member is arranged at the first position by the moving device, and Wherein, the measuring device is configured to perform initial adjustment in a state where the pressing member is arranged in the first position.

6. The sheet material detection device according to claim 5, in, the moving device is configured to move the pressing member from the first position to the second position in a case where the sheet has been conveyed by the conveying device to the measuring position of the measuring device after the initial adjustment is performed, and Here, the measuring device is configured to measure the characteristic amount of the sheet in a state where the pressing member is arranged at the second position.

7. The sheet material detection device according to claim 1, 3 or 5, wherein: The measuring device is configured to determine the presence or absence of the sheet based on a comparison result between an output voltage representing a detection result of the sheet by the measuring device and a predetermined threshold voltage.

8. The sheet material detection device according to claim 1, 3 or 5, in, The measuring device includes an ultrasonic sensor, and Among them, the ultrasonic sensor is configured to determine the presence or absence of the sheet by transmitting and receiving ultrasonic waves through a conveyance path of the sheet.

9. The sheet material detection device according to claim 8, in, The ultrasonic sensor includes an ultrasonic transmitter configured to transmit ultrasonic waves toward a transmission path and an ultrasonic receiver configured to receive the ultrasonic waves transmitted from the ultrasonic transmitter. The ultrasonic receiver is configured to output an output voltage corresponding to the amplitude of the received ultrasonic wave, and The measuring device is configured to determine the presence or absence of the sheet based on a comparison result between an output voltage output from the ultrasonic receiver and a predetermined threshold voltage.

10. The sheet material detection device according to claim 1, 3 or 5, in, The measuring device includes an optical sensor, and Here, the optical sensor is configured to determine the presence or absence of the sheet based on reflected light of light emitted toward the sheet conveying path.

11. The sheet material detection device according to claim 10, in, The optical sensor includes a light source configured to emit light toward a transmission path and a light receiver configured to receive the light emitted from the light source. wherein the light receiver is configured to output an output value corresponding to the amount of light received by the light receiver, and Herein, the measuring device is configured to determine the presence or absence of the sheet based on a comparison result between an output value output from the light receiver and a predetermined threshold voltage.

12. The sheet material detection device according to claim 1, wherein: The pressing member is a rotating member.

13. An imaging device comprising: Sheet material detection device; and an image forming device configured to form an image on a sheet by using an image forming condition based on a feature amount of the sheet measured by the measuring device, Wherein, the sheet material detection device comprises: a measuring device for measuring a characteristic quantity of the sheet material conveyed by the conveying device; A pressing member movable between a first position separated from the measuring device and a second position closer to the measuring device than the first position; and a moving device configured to move the pressing member, wherein, when the measuring device detects that the sheet has not been delivered to the measuring position of the measuring device, the pressing member is arranged at the first position by the moving device, wherein the moving device is configured to move the pressing member from the first position to the second position when the measuring device detects that the sheet has been conveyed to the measuring position of the measuring device, and Here, the measuring device is configured to measure the characteristic amount of the sheet in a state where the pressing member is arranged at the second position.

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