Image formation device

Abstract

A measurement means according to the present invention has a first electrode in contact with a first surface of a sheet and a second electrode in contact with a second surface of the sheet, and measures the volume resistance of the sheet while conveyance of the sheet is temporarily stopped. A moving means moves the second electrode relative to the first electrode and varies the pressure applied to the sheet by the first electrode and the second electrode. A power supply means causes a current to flow through the sheet by applying a voltage between the first electrode and the second electrode. A control means controls the pressure applied to the sheet in accordance with the current flowing through the sheet or the thickness of the sheet.

Description

Image forming apparatus

[0001] This disclosure relates to an image forming apparatus.

[0002] An image forming apparatus may use image forming conditions according to the electrical resistance value of a sheet on which an image is to be formed. According to Patent Document 1, it is described that a voltage is applied between a blade-shaped electrode and a plate-shaped electrode to detect the resistance in the thickness direction of the sheet.

[0003] Japanese Patent Application Laid-Open No. 2023-074543

[0004] A resistance value sensor needs to sandwich two electrodes and a sheet, but at this time, the problem is how much pressure should be applied to sandwich the sheet. If the pressure is too high, pressing marks (scratches or dents) due to the blade-shaped electrode will occur on the sheet. If the pressure is low, the measurement accuracy of the resistance value will decrease. Therefore, an object of the present disclosure is to accurately measure the volume resistance of a sheet.

[0005] The present disclosure has, for example, conveyance means for conveying a sheet used for image formation, a first electrode that contacts the first surface of the sheet, and a second electrode that contacts the second surface of the sheet. During a period when the conveyance means temporarily stops conveying the sheet, measurement means for measuring the volume resistance of the sheet based on the voltage applied to the sheet and the current flowing through the sheet, moving means for relatively moving the second electrode with respect to the first electrode to vary the pressure applied to the sheet by the first electrode and the second electrode, power supply means for flowing a current through the sheet by applying a voltage between the first electrode and the second electrode, detection means for detecting the current flowing through the sheet, and control means for controlling the pressure applied to the sheet according to the current flowing through the sheet, and provides an image forming apparatus.

[0006] According to the present disclosure, it becomes possible to accurately measure the volume resistance of a sheet.

[0007] Other features and advantages of the technical idea derived from the present disclosure will become clear from the following description with reference to the accompanying drawings. In the accompanying drawings, the same or similar configurations are given the same reference numerals.

[0008] The attached drawings are included in the specification and constitute part thereof, illustrating embodiments in this disclosure and used to explain the technical ideas derived from this disclosure together with their descriptions. Diagram illustrating an image forming system. Diagram illustrating an image forming unit. Diagram illustrating a fuser. Diagram illustrating a controller. Diagram illustrating a resistance sensor. Diagram illustrating the arrangement of sensors. Diagram illustrating the arrangement of sensors. Diagram illustrating the arrangement of sensors. Diagram illustrating the shape of an electrode. Diagram illustrating the shape of an electrode. Diagram illustrating the shape of an electrode. Diagram illustrating the shape of an electrode. Diagram illustrating the shape of an electrode. Flowchart of a control method. Flowchart of a control method. Flowchart of a control method. Flowchart of a control method. Flowchart of a volume resistivity measurement method. Flowchart of a volume resistivity measurement method. Flowchart of a type discrimination method. Diagram illustrating an image forming system. Diagram illustrating a thickness sensor. Diagram illustrating a thickness sensor. Diagram illustrating a surface sensor. Diagram illustrating a basis weight sensor. Diagram illustrating a stiffness sensor. Diagram illustrating a stiffness sensor. Flowchart of an image forming method.

[0009] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the scope of the claims. While the embodiments describe multiple features, not all of these features are necessary, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0010] 1. Image Forming System According to Figure 1, the image forming system 100 includes an image forming apparatus 101, a sheet processing apparatus 102, and a feeding apparatus 103. The image forming apparatus 101 includes a main body 104 and a fixing apparatus 105. The main body 104 and the fixing apparatus 105 may be housed in a single housing.

[0011] 1-1. The image forming apparatus body 104 has feeding decks 9a and 9b for loading multiple recording materials (sheets). Sheets fed from the feeding decks 9a and 9b are carried along the transport path 14 while being held between transport roller pairs 8. In this way, the sheets are transported to the secondary transfer section 7.

[0012] Image forming units 10Y, 10M, 10C, and 10K form toner images using yellow toner, magenta toner, cyan toner, and black toner, respectively, and transfer them to the intermediate transfer belt 6. Y, M, C, and K are abbreviations for the toner colors. The intermediate transfer belt 6 may also be called the intermediate transfer body. As the intermediate transfer belt 6 rotates, the toner image is transported to the secondary transfer unit 7. The secondary transfer unit 7 has an outer roller and an inner roller. The outer roller and inner roller rotate while gripping the intermediate transfer belt 6. Furthermore, the outer roller and the intermediate transfer belt 6 transport the sheet while gripping it. By applying a secondary transfer voltage between the outer roller and the inner roller, the toner image is transferred from the intermediate transfer belt 6 to the sheet. The sheet with the transferred toner image is transported from the main body 104 to the fixing device 105.

[0013] The fuser unit 105 includes a first fuser 21 and a second fuser 22. In normal fuser mode, the sheet is supplied with heat and pressure in the first fuser 21. This fixes the toner image onto the sheet. The sheet is then transported along the first fuser transport path 15 and discharged to the sheet processing device 102. In duplex printing mode, the sheet with the image formed on the first side is guided to the duplex transport path 17 and transported again to the secondary transfer unit 7. The secondary transfer unit 7 transfers the toner image to the second side of the sheet. The sheet passes through the first fuser 21 again, fixing the toner image to the second side.

[0014] The second fuser 22 receives a sheet when the sheet and toner image require more heat (gloss fuser mode). That is, the sheet discharged from the first fuser 21 is guided to the second fuser transport path 16 and transported to the second fuser 22. In the second fuser 22, the sheet and toner image are again supplied with heat and pressure. After that, the sheet is discharged to the sheet processing device 102. The gloss fuser mode increases the gloss (glossiness) of the sheet.

[0015] 1-2. Sheet Processing Device The sheet processing device 102 is a post-processing device that performs post-processing on sheets discharged from the image forming apparatus 101. For example, a sheet (e.g., interleaving paper) supplied from the sorter 35 is inserted between a preceding sheet and a succeeding sheet discharged from the image forming apparatus 101. The sheet processing devices 34a and 34b include a puncher for making holes in sheets, a binding device (e.g., a stapler) for binding multiple sheets together, and an alignment device for aligning multiple sheets. Sheets that are not subjected to post-processing are discharged to the discharge tray 31. Sheets that have been subjected to post-processing in the sheet processing device 34a are discharged to the discharge tray 32. Sheets that have been subjected to post-processing in the sheet processing device 34b are discharged to the discharge tray 33.

[0016] 1-3. Feeding device Feeding device 103 is an optional feeding device. Feeding device 103 has, for example, large capacity decks 40a, 40b, 40c that can accommodate more sheets compared to feeding decks 9a, 9b. Feeding device 103 may have a manual feed tray 48.

[0017] Sheets fed from the large capacity decks 40a, 40b, 40c and the manual feed tray 48 are transported along the first transport path 11 by a plurality of transport roller pairs 47 arranged along the transport path. The first transport path 11 is a transport path that extends from the large capacity decks 40a, 40b, 40c. The first transport path 11 branches into a second transport path 12 and a third transport path 13. The flapper 49 is a guide member that guides the sheets that have been transported along the first transport path 11 to the second transport path 12 or the third transport path 13. The second transport path 12 is a transport path that connects the first transport path 11 and the escape tray 46. The escape tray 46 is a tray from which sheets that should not be transported to the image forming apparatus 101 are discharged. Sheets that should not be transported to the image forming apparatus 101 include, for example, sheets whose type is not registered, multiple sheets that have been double-feeded, and sheets that are not recommended for use with the image forming apparatus 101. The third transport path 13 is a transport path connecting the first transport path 11 and the image forming apparatus 101. Registered sheets, single sheets, and sheets recommended by the image forming apparatus 101 are guided to the third transport path 13.

[0018] Several sensors for measuring or detecting the physical properties of the sheet may be placed in the first transport path 11 and the second transport path 12. The thickness sensor 41 is a sensor that detects the thickness of the sheet. The thickness sensor 41 is composed of, for example, an ultrasonic oscillating element and an ultrasonic receiving element. The ultrasonic receiving element receives ultrasonic waves emitted from the ultrasonic oscillating element and that have passed through the sheet. The thickness sensor 41 detects the thickness of the sheet based on the attenuation of the ultrasonic waves. The thickness sensor 41 may be composed of, for example, a light-emitting element and a light-receiving element. The light-receiving element receives light output from the light-emitting element and that has passed through the sheet. The thickness sensor 41 detects the thickness of the sheet based on the attenuation of the light. The thickness sensor 41 may also mechanically detect the thickness of the sheet. For example, the thickness sensor 41 may include a contactor that is displaced by contacting the sheet and an encoder that detects the amount of displacement of the contactor. Since the amount of displacement correlates with the thickness of the sheet, the thickness of the sheet can be determined from the amount of displacement.

[0019] The basis weight sensor 42 detects the basis weight of the sheet. The basis weight sensor 42 is also composed of, for example, an ultrasonic emitting element and an ultrasonic receiving element. The ultrasonic receiving element receives ultrasonic waves emitted from the ultrasonic emitting element and that have passed through the sheet. The basis weight sensor 42 detects the basis weight or thickness of the sheet based on the attenuation of the ultrasonic waves received by the ultrasonic receiving element. The basis weight sensor 42 may include, for example, a light-emitting element that irradiates the sheet with light having a predetermined wavelength (for example, visible light or infrared light), a first light-receiving element that receives the transmitted light that has passed through the sheet on the opposite side of the transport path, and a second light-receiving element that receives the reflected light reflected by the sheet. The basis weight sensor 42 may also detect the basis weight of the sheet based on the ratio of the amount of transmitted light and reflected light to the amount of irradiated light (e.g., attenuation rate). The basis weight sensor 42 can also detect the thickness of the sheet using a similar mechanism.

[0020] The surface property sensor 43 is a sensor that detects physical property values ​​indicating the surface properties of a sheet. These physical property values ​​are, for example, glossiness and smoothness, or both. The surface property sensor 43 includes a light-emitting element that irradiates the sheet with light at a predetermined incident angle, a first light-receiving element that receives specularly reflected light, and a second light-receiving element that receives diffusely reflected light. The surface property sensor 43 can detect the surface properties of the sheet based on the ratio of the amount of specularly reflected light and diffusely reflected light to the amount of irradiated light.

[0021] The surface properties sensor 43 may include a glossiness sensor 43a and a smoothness sensor 43b. The glossiness sensor 43a detects glossiness, which is a physical property value (surface property value) indicating the surface properties of the sheet. The glossiness sensor 43a includes, for example, a light-emitting element and a light-receiving element. The light-receiving element receives light output from the light-emitting element and reflected from the upper surface of the sheet. For example, glossiness is detected by analyzing specular reflection and random reflection. The smoothness sensor 43b detects smoothness, which is a physical property value of the surface properties of the sheet. The smoothness sensor 43b includes, for example, a light-emitting element and a light-receiving element. The light-receiving element receives light output from the light-emitting element and reflected from the upper surface of the sheet. For example, surface properties are detected by analyzing specular reflection and random reflection. The thickness sensor 41, basis weight sensor 42, and surface properties sensor 43 can perform detection without stopping the sheet, that is, while the sheet is being transported.

[0022] The stiffness sensor 44 is a sensor that detects the stiffness of the sheet. The resistance sensor 45 is a sensor that detects the volumetric resistance of the sheet. The stiffness sensor 44 and the resistance sensor 45 detect physical properties by contacting the sheet. Therefore, the sheet transport is stopped at the detection positions of the stiffness sensor 44 and the resistance sensor 45. When a preceding sheet comes to a stop in the first transport path 11, subsequent sheets must also stop, reducing the throughput of the image forming system 100. Here, throughput is the number of sheets that the image forming system 100 can process per unit time. The stiffness sensor 44 and the resistance sensor 45 may perform detection during a single stop period. In other words, the stiffness sensor 44 and the resistance sensor 45 may perform detection in parallel. This may improve throughput.

[0023] 2. Image forming section Figure 2 shows the structure of image forming sections 10Y, 10M, 10C, and 10K. The structure of image forming sections 10Y, 10M, 10C, and 10K is the same except for the toner color.

[0024] The photoreceptor drum 1 is an image carrier that is rotated by a motor or the like. The charger 2 is a charging roller or charging wire that charges the surface of the photoreceptor drum 1. The charger 2 is subjected to a predetermined charging voltage, which is an example of the image formation conditions. The exposure device 3 irradiates the surface of the photoreceptor drum 1 with light corresponding to the image signal, forming an electrostatic latent image corresponding to the image signal. The amount of light from the light source of the exposure device 3 is an example of the image formation conditions. The toner container 50 is a container that holds toner T. The developing sleeve 4 is a rotating body that supplies toner supplied from the toner container 50 to the surface of the photoreceptor drum 1. The toner container 50 and the developing sleeve 4 may also be called a developer. The developing sleeve 4 is subjected to a developing voltage, which is an example of the image formation conditions. The electrostatic latent image on the surface of the photoreceptor drum 1 is developed into a toner image by the toner T. The developing voltage is a voltage that promotes the adhesion of toner T to the photoreceptor drum 1. As the photoreceptor drum 1 rotates further, the toner image is transported to the primary transfer unit. The primary transfer section is formed by a photoreceptor drum 1 and a primary transfer roller 5. A primary transfer voltage, which is an example of image formation conditions, is applied between the primary transfer roller 5 and the photoreceptor drum 1. The primary transfer roller 5 transfers the toner image from the photoreceptor drum 1 to the intermediate transfer belt 6. The primary transfer voltage promotes the primary transfer of the toner image. The drum cleaner 51 cleans the toner T remaining on the photoreceptor drum 1.

[0025] 3. Fuser Figure 3 shows the structure of the first fuser 21 and the second fuser 22. It is assumed that the structure of the first fuser 21 and the structure of the second fuser 22 are the same. In Figure 3, the sheet P is conveyed along the conveying direction X.

[0026] The heating belt 64 is a heating member or heating rotating body consisting of an endless belt. The heating belt 64 may also be called a heating film. The pressure roller 65 is a roller-shaped pressure member or heating rotating body. The heater 60 is a heating element positioned to slide against the inner circumferential surface of the heating belt 64. The pressure roller 65 has a core metal 66 and an elastic layer 67. The core metal 66 is made of, for example, iron or aluminum. The elastic layer 67 is a rubber layer made of, for example, silicone rubber. Thus, the pressure roller 65 has a rubber layer that forms a nip portion together with the heater 60 via the heating belt 64. The heater 60 is provided on the inner surface side of the heating belt 64 and is held by a holding member 61. The holding member 61 is held by a metallic stay member 63. The stay member 63 presses the heater 60 against the inner circumferential surface of the heating belt 64 via the holding member 61.

[0027] A pressure is applied between the stay member 63 and the pressure roller 65 by a pressure mechanism (e.g., a spring) not shown. The pressure roller 65 is pressed against the heater 60 via the heating belt 64, forming a fixing nip 130. As the pressure roller 65 rotates counterclockwise, the heating belt 64 also rotates clockwise in response to the pressure roller 65. The sheet P passes over the fixing nip 130, fixing the toner image onto the sheet P.

[0028] The heater 60 is, for example, a ceramic heater having a ceramic substrate and a heating element provided thereon. The thermistor 62 is a temperature sensing element positioned in contact with the heater 60. The power supplied to the heater 60 is controlled based on the detection result of the thermistor 62. This maintains the temperature of the heating belt 64 at a target temperature. Here, the target temperature is an example of an image formation condition.

[0029] 4. Control System Figure 4 shows the control system of the image forming system 100. The controller 400 is a control device that controls the image forming apparatus 101, the sheet processing apparatus 102, and the feeding apparatus 103. The controller 400 may be built into any of the image forming apparatus 101, the sheet processing apparatus 102, and the feeding apparatus 103, or it may be installed outside of them. Furthermore, the control functions of the controller 400 may be distributed among the image forming apparatus 101, the sheet processing apparatus 102, and the feeding apparatus 103.

[0030] The CPU 401 controls the image forming system 100 according to a control program stored in the ROM area of ​​the memory 402. ROM is an abbreviation for read-only memory. The ROM area may include a hard disk drive (HDD) in addition to a semiconductor memory device. The memory 402 further has a random access memory (RAM) area. The CPU 401 displays messages, images, and a user interface (UI) on the display device 403. The CPU 401 may also accept information and instructions input by the user through an input device 404 such as a touch sensor.

[0031] Figure 4 further illustrates the load on the feeding device 103. Motor M2 rotates multiple transport roller pairs 47. Motor M3 rotates a feed roller that feeds sheets P from a large-capacity deck 40a. Motor M4 rotates a feed roller that feeds sheets P from a large-capacity deck 40b. Motor M5 rotates a feed roller that feeds sheets P from a large-capacity deck 40c. Motor M6 rotates a feed roller that feeds sheets P from a manual feed tray 48. Solenoid SL1 drives a flapper 49. For example, when solenoid SL1 is turned on, the flapper 49 guides the sheets P to the second transport path 12. When solenoid SL1 is turned off, the flapper 49 guides the sheets P to the third transport path 13. The sheet sensor 406 detects (senses) whether a sheet P is present within the detectable range of the resistance value sensor 45. The detection result from the sheet sensor 406 is used to temporarily stop the transport of the sheet P.

[0032] 5. Resistance Sensor 5-1. Structure Figure 5 shows the structure of the resistance sensor. When the sheet P stops between electrode 501 and electrode 502, the CPU 401 rotates the motor M1. The drive shaft of the motor M1 is connected to the rotating shaft 504 of the cam 503. This connection may be made via multiple gears. The cam surface of the cam 503 presses against electrode 501. Electrode 502 is fixed. As the cam 503 rotates, electrode 501 gradually approaches electrode 502 and presses against sheet P. The pressing force increases as the cam 503 rotates. It is sufficient that the pressing force can be variably controlled by the relative movement of electrode 501 to electrode 502. Therefore, electrode 502 may move. The motor M1 may be a stepping motor that can freely rotate in both forward and reverse directions. This makes it possible to control the rotation angle of the cam 503 one step at a time.

[0033] By the way, a voltage is applied between electrode 501 and electrode 502 from the power supply 511. The voltage detection circuit 515 detects the voltage applied to sheet P. The current detection circuit 513 detects the current flowing through sheet P. When the resistance sensor 45 is in standby mode, electrode 501 is in standby position. That is, electrode 501 and electrode 502 are separated. When electrode 501 contacts the first surface of sheet P and electrode 502 contacts the second surface of sheet P, a voltage is applied to sheet P and current begins to flow through sheet P. The CPU 401 acquires and monitors the value of the current detected by the current detection circuit 513. As the pressing force that the cam 503 applies to sheet P via electrode 501 and electrode 502 increases, the current flowing through sheet P also gradually stabilizes. When the current flowing through sheet P stabilizes, the CPU 401 stops the motor M1 and measures the voltage applied to sheet P using the voltage detection circuit 515. As the current stabilizes, the increase in pressing force stops, making it less likely for pressure marks to be left on the sheet P. Furthermore, the CPU 401 measures the current flowing through the sheet P using the current detection circuit 513. The CPU 401 applies Ohm's law to the measured current and voltage to calculate the resistance value (volume resistance). Once the measurement of current and voltage is complete, the CPU 401 reverses the motor M1, thereby reversing the cam 503 and releasing the pressing force that was acting between the electrode 501 and the electrode 502. The CPU 401 then resumes transporting the sheet P.

[0034] 5-2. Arrangement diagram 6A of the resistance sensor and sheet sensor shows the arrangement of the sheet sensor 406 and the resistance sensor 45. The sheet P is transported on the transport guide 600 in the direction indicated by the arrow. In this example, the sheet sensor 406 is positioned upstream of the resistance sensor 45 in the transport direction of the sheet P. When the sheet sensor 406 detects the rear end of the sheet P, the CPU 401 stops transporting the sheet P. That is, the sheet P stops within the detectable range of the resistance sensor 45. The CPU 401 detects the volume resistance of the sheet P using the resistance sensor 45.

[0035] Furthermore, the transport of sheet P may be stopped after a predetermined time has elapsed since the sheet sensor 406 detected the leading edge of sheet P. The predetermined time is determined in advance so that sheet P stops within the detectable range of the resistance sensor 45.

[0036] Figure 6B shows the arrangement of the sheet sensor 406 and the resistance sensor 45. In this example, the positions of the sheet sensor 406 and the resistance sensor 45 are approximately the same in the direction of transport of the sheet P. In the direction perpendicular to the transport direction, the positions of the sheet sensor 406 and the resistance sensor 45 are different. After a predetermined time has elapsed since the sheet sensor 406 detected the rear end of the sheet P, the CPU 401 stops transporting the sheet P. The predetermined time is set in advance so that the sheet P stops within the detectable range of the resistance sensor 45. As a result, the sheet P stops within the detectable range of the resistance sensor 45. The CPU 401 detects the volume resistance of the sheet P using the resistance sensor 45.

[0037] Figure 6C shows the arrangement of the sheet sensor 406 and the resistance sensor 45. In this example, the sheet sensor 406 is positioned downstream of the resistance sensor 45 in the direction of sheet P transport. When the sheet sensor 406 detects the leading edge of sheet P, the CPU 401 stops transporting sheet P. As a result, sheet P stops within the detectable range of the resistance sensor 45. The CPU 401 detects the volume resistance of sheet P using the resistance sensor 45.

[0038] 5-3. Electrode Shapes Figure 7A shows the shapes of electrodes 501 and 502. In this example, electrodes 501 and 502 are discs. Thus, the shapes of electrode 501 and electrode 502 may be the same. Figure 7A also shows an example where the sheet P is pressed against the bottom surface of a cylinder. Thus, one of electrodes 501 and 502 may be a disc (a thin cylinder).

[0039] According to Figure 7B, electrode 501 is a disc, and electrode 502 is a flat plate. Because the area of ​​electrode 502 is larger than the area of ​​electrode 501, the sheet P is held stably. Electrode 501 is a movable electrode. Because electrode 501 is small, the cam 503 and motor M1 that move electrode 501 can be miniaturized. Also, the movement time of electrode 501 (approach time and separation time) is reduced. Thus, the shapes of electrode 501 and electrode 502 may be different. Also, one of electrodes 501 or 502 may be a flat plate (a thin rectangular parallelepiped).

[0040] According to Figure 7C, electrode 501 is a flat plate or a rectangular parallelepiped. Electrode 502 is a flat plate. Because the area of ​​electrode 502 is larger than the area of ​​electrode 501, the sheet P is held stably. Electrode 501 is a movable electrode. Because electrode 501 is small, the cam 503 and motor M1 that move electrode 501 can be miniaturized. Also, the movement time of electrode 501 (approach time and separation time) is reduced. Thus, the shapes of electrode 501 and electrode 502 may be different. One of electrodes 501 or 502 may be a rectangular parallelepiped.

[0041] According to Figure 7D, electrodes 501 and 502 are each cylindrical (rollers). Electrodes 501 and 502 may also be rotatable metal conveying rollers. This makes it possible to use electrodes 501 and 502 as both conveying rollers and conveying rollers. Figure 7D also shows an example where the sheet P is pressed against the side of a cylinder. Thus, one of electrodes 501 and 502 may be a cylinder (rotating body).

[0042] According to Figure 7E, electrode 501 is a cylinder (roller). Electrode 502 is a flat plate. Because the area of ​​electrode 502 is larger than the area of ​​electrode 501, the sheet P is held stably. Electrode 501 is a movable electrode. Because electrode 501 is small, the cam 503 and motor M1 that move electrode 501 can be miniaturized. Also, the movement time of electrode 501 (approach time and separation time) is reduced. Thus, the shapes of electrode 501 and electrode 502 may be different. Electrode 501 may also be a rotatable metal conveying roller. This makes it possible to use electrode 501 as both a conveying roller and a conveying roller.

[0043] In any case, the CPU 401 controls the relative distance between the electrode 501 and the electrode 502 through the motor M1 and the cam 503 so that the electrode 501 and the electrode 502 do not directly contact each other, that is, so that there is no electrical short circuit.

[0044] 6. Flowchart 6-1. When the sheet sensor is arranged upstream of the resistance value sensor FIG. 8 is a flowchart showing a control method executed by the CPU 401 according to a control program. As shown in FIG. 6A, it is assumed that the sheet sensor 406 is arranged upstream of the resistance value sensor 45.

[0045] When the determination process (type registration process) of the type of the sheet S is instructed through the input device 404, the CPU 401 turns on the solenoid SL1 and then executes the following processes. It is assumed that the sheet P is specified by the user to be fed from the manual feed tray 48 through the input device 404.

[0046] In S801, the CPU 401 (measurement control unit, motor control unit) starts the motor M2 and the motor M6 and starts transporting the sheet P. The motor M6 for the manual feed tray 48 is stopped when the feeding of the sheet P is completed.

[0047] In S802, the CPU 401 (measurement control unit) detects the thickness d of the sheet P using the thickness sensor 41 when the sheet P passes through the thickness sensor 41.

[0048] In S803, the CPU 401 (measurement control unit) detects the glossiness of the sheet P using the glossiness sensor 43a when the sheet P passes through the glossiness sensor 43a.

[0049] In S804, the CPU 401 (measurement control unit) detects the smoothness of the sheet P using the smoothness sensor 43b when the sheet P passes through the smoothness sensor 43b.

[0050] In S805, the CPU 401 (measurement control unit) monitors the detection result of the sheet sensor 406 and determines whether the rear end of the sheet P is detected by the sheet sensor 406. When the rear end is detected, the CPU 401 advances the process from S805 to S806.

[0051] In S806, the CPU 401 (measurement control unit, motor control unit) stops the motor M2 and stops the transport of the sheet P.

[0052] In step S807, the CPU 401 (measurement control unit) detects the stiffness of the sheet P using the stiffness sensor 44 while the sheet P is stationary.

[0053] In step S808, the CPU 401 (measurement control unit, motor control unit) detects the volume resistivity Rv of the sheet P using the resistance sensor 45 while the sheet P is stationary. Alternatively, the CPU 401 may calculate the volume resistivity by dividing the volume resistivity Rv by the thickness of the sheet P obtained by the thickness sensor 41.

[0054] In step S809, the CPU 401 (discrimination unit, registration unit) registers the type of sheet P. For example, the CPU 401 determines the image formation conditions corresponding to the measurement results (e.g., thickness (basis weight), surface properties (glossiness, smoothness), stiffness, volume resistivity Rv (or volume resistivity)) and registers the image formation conditions linked to the type (ID). For example, the image formation conditions corresponding to a combination of measurement results may be determined by referring to a table or database that links the combination of measurement results with the image formation conditions. The image formation conditions may also be calculated using a mathematical formula that uses the combination of measurement results as a variable. Alternatively, the image formation conditions corresponding to a combination of measurement results may be determined using a program module programmed to output the image formation conditions when a combination of measurement results is input.

[0055] In S810, the CPU 401 (measurement control unit, motor control unit) restarts the motor M2 and resumes transporting the sheet P. As a result, the sheet P is discharged into the escape tray 46.

[0056] 6-2. When the sheet sensor is located downstream of the resistance sensor, Figure 9 is a flowchart showing the control method executed by the CPU 401 according to the control program. As shown in Figure 6C, it is assumed that the sheet sensor 406 is located downstream of the resistance sensor 45. Here, S805 is replaced with S905, and the remaining steps are as explained with reference to Figure 8.

[0057] In S905, the CPU 401 (measurement control unit) monitors the detection result of the sheet sensor 406 and determines whether the leading edge of the sheet P has been detected by the sheet sensor 406. If the leading edge is detected, the CPU 401 proceeds from S905 to S906. By stopping the motor M2 when the leading edge of the sheet P is detected, the sheet P can be kept stationary within the detectable range of the resistance sensor 45.

[0058] 6-3. When the sheet sensor and the resistance sensor are positioned at the same location in the transport direction, Figure 10 is a flowchart showing the control method executed by the CPU 401 according to the control program. As shown in Figure 6B, it is assumed that the sheet sensor 406 and the resistance sensor 45 are positioned at approximately the same location in the transport direction of the sheet P. Here, S805 is replaced by S1001 and S1002, and the remaining steps are as explained with reference to Figure 8.

[0059] In S1001, the CPU 401 (measurement control unit) monitors the detection result of the sheet sensor 406 and determines whether the leading edge of the sheet P has been detected by the sheet sensor 406. If the leading edge is detected, the CPU 401 proceeds from S1001 to S1002.

[0060] In S1002, the CPU 401 (measurement control unit) performs a predetermined wait (standby) for a set period of time. After the predetermined time has elapsed, the CPU 401 proceeds to process from S1001 to S806. By adding this wait, the leading edge of the sheet P moves downstream of the sheet sensor 406. When the sheet P stops, the resistance sensor 45 is located near the center of the sheet P. In other words, the sheet P comes to rest within the detectable range of the resistance sensor 45.

[0061] 7. Method for obtaining volume resistivity: Volume resistivity may be used instead of volume resistance to identify the type of sheet P. Using volume resistivity improves the accuracy of identifying synthetic paper in particular.

[0062] Incidentally, the resistance sensor 45 can accurately measure volumetric resistance by sandwiching the sheet P between electrodes 501 and 502 and applying pressure. The method for controlling the pressure applied to the sheet P will be explained below.

[0063] 7-1. Method for controlling the pressing force according to the sheet thickness Figure 11 shows a method for controlling the pressing force according to the thickness of the sheet P. Since the pressing force is controlled according to the thickness of the sheet, it will be less likely to leave press marks on the sheet P.

[0064] In S1101, the CPU 401 (thickness acquisition unit) acquires the thickness of sheet P. For example, the thickness of sheet P may be read from memory 402. The thickness of sheet P stored in memory 402 may be acquired by the thickness sensor 41 in S802, or it may be input by the user through the input device 404.

[0065] In S1102, the CPU 401 (pressure setting unit) determines (sets) the pressure according to the thickness of the sheet P. Here, the pressure may be replaced by the number of rotations of the motor M1, the rotation angle of the cam 503, or the distance between electrodes 501 and 502. These are intercorrelated control parameters. A table, formula, or program module may be used to determine the pressure from the thickness.

[0066] In S1103, the CPU 401 (pressure control unit) executes pressing of the sheet P with the determined pressing force. The CPU 401 controls the motor M1 so that the determined pressing force is achieved. For example, the number of drive pulses supplied to the motor M1 may be set according to the pressing force.

[0067] In S1104, the CPU 401 (power control unit) controls the power supply 511 and applies a voltage to the sheet P through electrodes 501 and 502.

[0068] In step S1105, the CPU 401 (measurement control unit) controls the voltage detection circuit 515 and the current detection circuit 513 to detect the voltage applied to sheet P and the current flowing through sheet P.

[0069] In S1106, the CPU 401 (arithmetic unit) calculates the volume resistance value based on the detected voltage and current.

[0070] In S1107, the CPU 401 (arithmetic unit) calculates the volume resistivity based on the acquired thickness and volume resistivity.

[0071] In S1108, the CPU 401 (pressure control unit) releases the pressing force applied to the sheet P. For example, the CPU 401 may move the motor M1 in the reverse direction to move the electrode 501 away from the electrode 502. This may release the pressing force.

[0072] 7-3. Method for controlling the pressing force according to the current flowing through the sheet Figure 12 shows a method for controlling the pressing force according to the current flowing through the sheet P. This is because when the current flowing through the sheet P is stable, the pressing force applied to the sheet P is appropriate. Since the pressing force is controlled according to the current flowing through the sheet, it will be less likely for pressure marks to be left on the sheet P.

[0073] In S1201, the CPU 401 (power control unit) controls the power supply 511 and starts applying voltage to electrodes 501 and 502.

[0074] In S1202, the CPU 401 (pressure control unit) controls the motor M1 and starts pressing against the sheet P. As a result, electrode 501 starts moving from the standby position toward electrode 502.

[0075] In S1203, the CPU 401 (measurement control unit) starts detecting the current flowing through sheet P using the current detection circuit 513. When both electrode 501 and electrode 502 come into contact with sheet P, current begins to flow through sheet P.

[0076] In S1204, the CPU 401 (determination unit) determines whether the current flowing through the sheet has stabilized. For example, the CPU 401 may sample the current at regular intervals and determine whether the difference between the previously detected current and the currently detected current is below a threshold. When the current stabilizes, the difference becomes very small. The CPU 401 may also calculate the slope from the multiple detected current values ​​and determine whether the slope is below a threshold. When the current stabilizes, the slope becomes very small. If the current is not stable, the CPU 401 proceeds from S1204 to S1205.

[0077] In S1205, the CPU 401 (pressure control unit) controls the motor M1 and increases the pressing force. After that, the CPU 401 returns from S1205 to S1203. In this way, S1203, S1204, and S1205 are repeatedly executed until the current stabilizes. Finally, when the current stabilizes, the CPU 401 proceeds to process from S1205 to S1105. S1105 to S1108 are as already described.

[0078] 8. Method for Identifying Types Figure 13 shows the method for identifying types. Here, glossiness, smoothness, and volume resistivity detected from sheet P are used for identification. The thresholds Th1 to Th13 used below for identifying types are stored in the ROM area of ​​memory 402.

[0079] In S1301, the CPU 401 determines whether the gloss level is less than or equal to the threshold Th1. If the gloss level is less than or equal to the threshold Th1, the CPU 401 proceeds to process S1301 to S1302. If the gloss level exceeds the threshold Th1, the CPU 401 proceeds to process S1301 to S1311.

[0080] In S1302, the CPU 401 determines whether the gloss level is less than or equal to the threshold Th2. Here, Th2 is smaller than Th1. If the gloss level is less than or equal to the threshold Th2, the CPU 401 proceeds to process S1302 to S1303. If the gloss level exceeds the threshold Th2, the CPU 401 proceeds to process S1310 to S1302.

[0081] In S1303, the CPU 401 determines whether the volume resistivity is less than or equal to the threshold Th4. If the volume resistivity is less than or equal to the threshold Th4, the CPU 401 proceeds to process S1303 to S1304. If the volume resistivity exceeds the threshold Th4, the CPU 401 proceeds to process S1303 to S1305.

[0082] In S1304, the CPU 401 determines whether the volume resistivity is less than or equal to the threshold Th6. If the volume resistivity is less than or equal to the threshold Th6, the CPU 401 identifies the type of sheet P as matte coated paper. If the volume resistivity exceeds the threshold Th6, the CPU 401 identifies the type of sheet P as plain paper.

[0083] In S1305, the CPU 401 determines whether the smoothness is less than or equal to the threshold Th5. If the smoothness is less than or equal to the threshold Th5, the CPU 401 identifies the type of sheet P as embossed paper. If the smoothness exceeds the threshold Th5, the CPU 401 proceeds from S1305 to S1306.

[0084] In S1306, the CPU 401 determines whether the gloss level is less than or equal to the threshold Th7. If the gloss level is less than or equal to the threshold Th7, the CPU 401 proceeds to process S1306 through S1307. If the gloss level exceeds the threshold Th7, the CPU 401 proceeds to process S1306 through S1308.

[0085] In S1307, the CPU 401 determines whether the glossiness is less than or equal to the threshold Th8. If the glossiness is less than or equal to the threshold Th8, the CPU 401 identifies the type of sheet P as matte coated paper. If the glossiness exceeds the threshold Th8, the CPU 401 identifies the type of sheet P as plain paper.

[0086] In S1308, the CPU 401 determines whether the volume resistivity is less than or equal to the threshold Th9. If the volume resistivity is less than or equal to the threshold Th9, the CPU 401 identifies the type of sheet P as plain paper. If the volume resistivity exceeds the threshold Th9, the CPU 401 identifies the type of sheet P as embossed paper.

[0087] In S1310, the CPU 401 determines whether the volume resistivity is less than or equal to the threshold Th3. If the volume resistivity is less than or equal to the threshold Th3, the CPU 401 identifies the type of sheet P as matte coated paper. If the volume resistivity exceeds the threshold Th3, the CPU 401 identifies the type of sheet P as synthetic paper.

[0088] In S1311, the CPU 401 determines whether the volume resistivity is less than or equal to the threshold Th11. If the volume resistivity is less than or equal to the threshold Th11, the CPU 401 proceeds from S1311 to S1312. If the volume resistivity exceeds the threshold Th11, the CPU 401 identifies the type of sheet P as synthetic paper.

[0089] In S1312, the CPU 401 determines whether the smoothness is less than or equal to the threshold Th12. If the smoothness is less than or equal to the threshold Th12, the CPU 401 proceeds from S1312 to S1313. If the smoothness exceeds the threshold Th12, the CPU 401 identifies the type of sheet P as gloss coated paper.

[0090] In S1313, the CPU 401 determines whether the volume resistivity is less than or equal to the threshold Th13. If the volume resistivity is less than or equal to the threshold Th13, the CPU 401 identifies the type of sheet P as plain paper. If the volume resistivity exceeds the threshold Th13, the CPU 401 identifies the type of sheet P as gloss coated paper.

[0091] 9. Modified Examples 9-1. The arrangement diagram 14 of the stiffness sensor and resistance sensor shows another example of the arrangement of the stiffness sensor 44 and the resistance sensor 45. In this example, the stiffness sensor 44 and the resistance sensor 45 are arranged on the first transport path 11. In this case, the second transport path 12 and the escape tray 46 may be omitted, or the second transport path 12 and the escape tray 46 may still be provided. If the stiffness Sd detected by the stiffness sensor 44 exceeds a predetermined threshold Sth, the flapper 49 may guide the sheet P to the second transport path 12 and discharge the sheet P to the escape tray 46. This will prevent the image forming apparatus 101 and the sheet processing apparatus 102 from malfunctioning due to a sheet P with excessively high stiffness Sd.

[0092] 9-2. Structure of the Thickness Sensor Figures 15A and 15B show the structure and measurement principle of the optical thickness sensor 41. Figure 15A shows the state before the sheet P arrives at the detection position of the thickness sensor 41. Figure 15B shows the state when the sheet P has passed the detection position of the thickness sensor 41.

[0093] The thickness sensor 41 includes a light-emitting element 1500, a focusing lens 1501, a light-receiving element 1502, and an imaging lens 1503. The light-emitting element 1500 is a light-emitting diode (LED), etc. The light-receiving element 1502 includes multiple pixels (e.g., photoelectric conversion elements), like a line sensor. The light-emitting element 1500 is configured to output light towards the transport path. The focusing lens 1501 focuses the light output from the light-emitting element 1500. The focused light is directed towards the first transport path 11. The light reflected in the first transport path 11 is incident on the light-receiving element 1502 via the imaging lens 1503. Here, the distance between the light-emitting element 1500 and the light-receiving element 1502 in the transport direction of the sheet P is defined as K. The distance between the first transport path 11 and the light-receiving surface of the light-receiving element 1502 is defined as D. The distance between the imaging lens 1503 and the light-receiving surface is defined as f. x is the distance between the center of the imaging lens on the light-receiving surface and the incident position of the reflected light. Since the two triangles are similar, the following equation holds true.

[0094] D:K = f:x ...Eq1 As shown in Figure 15B, when the sheet P enters the detection position of the thickness sensor 41, the incident position of the reflected light on the light receiving element 1502 changes. D' is obtained by subtracting the thickness d from D.

[0095] D':K = f:x' ...Eq2 d = D - K(f / x') ...Eq3 D, K, and f are fixed values. Therefore, the thickness d can be obtained by measuring x'. x' is determined based on the pixel to which light is incident among the multiple pixels in the photodetector 1502.

[0096] 9-3. Structural diagram 16 of the surface sensor shows a surface sensor 43 in which a gloss sensor 43a and a smoothness sensor 43b are integrated. The surface sensor 43 includes a light-emitting element 1601, light-receiving elements 1602 and 1603, and apertures 1604, 1605, and 1606. The light-emitting element 1601 is, for example, a light-emitting diode. The light-emitting element 1601 outputs light such that the incident angle is 75 degrees. The light output from the light-emitting element 1601 is focused by passing through the aperture 1604 and heads toward the surface of the sheet P. The light reflected from the surface of the sheet P (specular reflection) is focused by the aperture 1605 and incident toward the light-receiving element 1602.

[0097] The light-receiving element 1602 is configured to receive specularly reflected light, and the angle between the optical axis of the light-receiving element 1602 and the normal direction of the sheet P is 75 degrees. The light-receiving element 1602 is, for example, a photodiode (PD). The light-receiving element 1602 outputs a detection signal corresponding to the intensity of the specularly reflected light incident on the light-receiving element 1602. This detection signal indicates the glossiness of the sheet P.

[0098] The light-receiving element 1603 receives diffused light that diffuses according to the smoothness of the surface of the sheet P. The light-receiving element 1603 is, for example, a photodiode (PD). The angle between the optical axis of the light-receiving element 1603 and the normal direction of the sheet P is 30 degrees so that the light-receiving element 1603 can receive diffused light. The diffused light from the sheet P is focused by passing through the aperture 1606 and then incident on the light-receiving element 1603.

[0099] The higher the glossiness of sheet P, the greater the amount of light received by the light-receiving element 1602; and the lower the glossiness of sheet P, the greater the amount of light received by the light-receiving element 1602. Therefore, the amount of light received by the light-receiving element 1602 indicates the glossiness.

[0100] The higher the smoothness of sheet P, the greater the amount of light received by the photodetector 1602; and the lower the smoothness of sheet P, the greater the amount of light received by the photodetector 1602. The lower the smoothness of sheet P, the greater the amount of light received by the photodetector 1603; and the higher the smoothness of sheet P, the greater the amount of light received by the photodetector 1603. Therefore, the combination of the amount of light received by the photodetector 1602 and the amount of light received by the photodetector 1603 indicates the smoothness of sheet P.

[0101] Aperture 1604 may be replaced with a collimator lens.

[0102] 9-4. Structure of the Basis Weight Sensor Diagram 17 shows the structure of the basis weight sensor 42. The basis weight sensor 42 is installed in the first transport path 11. The first transport path 11 is formed by two transport guides 1705. The light-emitting element 1701 is a light-emitting diode that emits blue light (wavelength: approximately 450 nm). The light-emitting element 1702 is a light-emitting diode that emits near-infrared light (wavelength: approximately 850-950 nm). The light-emitting element 1703 is a light-emitting diode that emits green light (wavelength: approximately 530 nm). The light-receiving element 1704 is positioned opposite the light-emitting elements 1701 and 1702. The light-emitting elements 1701 and 1702 are mounted on the first substrate 1711. The light-emitting element 1703 and the light-receiving element 1704 are mounted on the second substrate 1712. The first substrate 1711 and the second substrate 1712 are parallel to the transport direction of the sheet P. A reference plate 1706 for adjusting the light output from the light-emitting element 1703 may be placed on the first substrate 1711.

[0103] The basis weight sensor 42 measures the transmittance and reflectance of sheet P to detect the basis weight of sheet P. The transmittance of sheet P can be measured using blue light and near-infrared light, respectively. The reflectance can be measured using green light.

[0104] The light-receiving element 1704 receives green light reflected from the surface of sheet P, as well as transmitted blue and near-infrared light that has passed through sheet P, and outputs a detection signal indicating their intensity. If the surface of sheet P is smooth, the specular reflection component will be strong and the diffuse component will be weak. If the surface of sheet P is rough, the proportion of the diffuse component will increase. Note that the light-emitting elements 1701, 1702, and 1703 do not light up simultaneously, but light up selectively. This allows a single light-receiving element 1704 to selectively receive green, blue, and near-infrared light of different wavelengths.

[0105] The CPU 401 calculates the basis weight of sheet P based on the measurement results of green, blue, and near-infrared light. For example, the CPU 401 may select one conversion formula from several based on the measurement results and use the selected conversion formula to convert the amount of near-infrared light received into basis weight.

[0106] 9-5. Structure of the stiffness sensor Figures 18A and 18B show an example of a stiffness sensor 44. The probe 1804 is a contactor that contacts the surface of the sheet P. The stiffness sensor 44 determines the stiffness by measuring the force received from the sheet P by pushing up the sheet P with the probe 1804. The transport guide 1800 has two guide plates 1810 and 1820 that form the second transport path 12. The two guide plates 1810 and 1820 are metal plates that are arranged to be roughly parallel. Guide plate 1810 has a passage opening 1811 through which the probe 1804 for pushing down the sheet P passes.

[0107] The pressure detection unit 1861 is connected to the probe 1804 and detects the pressure applied to the probe 1804 by the sheet P. The holding member 1862 is connected to the pressure detection unit 1861 and is a holding member that holds the pressure detection unit 1861. The lifting member 1863 moves up and down in accordance with the rotation of the cam 1864, and is a dependent link of the cam mechanism that raises and lowers the probe 1804 via the holding member 1862 and the pressure detection unit 1861. The cam 1864 is the driving link of the cam mechanism which is rotated by the motor M11. In other words, the rotation of the motor M11 is converted into the up and down movement of the probe 1804 by the cam mechanism.

[0108] The cam mechanism is just one example; any mechanism that can raise and lower the probe 1804 can be used. For example, the mechanism for raising and lowering the probe 1804 could be a lifting mechanism consisting of a rack gear and a pinion gear, a crank mechanism including a crank arm and a crank pin, or a ball screw mechanism including a nut and a screw shaft.

[0109] The retaining member 1862 may be connected to an elastic body 1865 such as a spring or rubber. When the retaining member 1862 rises, the elastic body 1865 stretches, and elastic energy is stored. When the retaining member 1862 descends, the elastic body 1865 expands and contracts, and the elastic energy is released. In other words, the elastic body 1865 assists the retaining member 1862 in returning to its home position.

[0110] 9-6. Image Formation Diagram 19 shows the image formation operation performed by the CPU 401 according to the control program.

[0111] In S1901, the CPU 401 (condition identification unit) accepts the designation of the type (ID) through the input device 404.

[0112] In S1902, the CPU 401 (condition identification unit) identifies the image formation conditions corresponding to the type (ID) specified by the user. For example, the CPU 401 reads the image formation conditions associated with the type (ID) specified by the user from the memory 402.

[0113] In S1903, the CPU 401 controls the image forming system 100 and causes it to perform image formation on sheet P using the specified image forming conditions.

[0114] In this embodiment, the type of sheet P is more accurately identified according to the combination of surface properties (e.g., glossiness, smoothness) and volume resistivity of sheet P. The image formation conditions suitable for the identified type are then linked to the identification information indicating the type. Therefore, the image formation conditions suitable for the type of sheet P will be selected.

[0115] 10. Summary The transport roller pair 47 is an example of a transport means for transporting a sheet P used for image formation. The electrodes 501 and 502 are an example of a first electrode that contacts the first surface of the sheet P and a second electrode that contacts the second surface of the sheet P. The resistance sensor 45 is an example of a measuring means for measuring the volume resistance of the sheet P based on the voltage applied to the sheet P and the current flowing through the sheet P during a period when the transport means has temporarily stopped transporting the sheet P. The motor M1 and cam 503 are an example of a moving means for moving the second electrode relative to the first electrode and varying the pressure applied to the sheet P by the first and second electrodes. The power supply 511 is an example of a power supply means for supplying current to the sheet P by applying a voltage between the first and second electrodes. The current detection circuit 513 is an example of a detection means for detecting the current flowing through the sheet P. The controller 400 and CPU 401 are an example of a control means for controlling the pressure applied to the sheet P according to the current flowing through the sheet P. This makes it possible to accurately measure the volume resistance of the sheet. The CPU 401 may gradually increase the pressure applied to the sheet P by the moving means until the current flowing through the sheet P stabilizes. This will make it less likely for pressure marks to be left on the sheet P. The CPU 401, thickness sensor 41, and input device 404 are examples of acquisition means for acquiring the thickness of the sheet P. This makes it possible to accurately measure the volume resistance of the sheet. The CPU 401 may set the pressure applied to the sheet P according to the thickness of the sheet P. In this way, by determining the pressure applied to the sheet P while considering the thickness of the sheet P, it will be less likely for pressure marks to be left on the sheet P. For example, the pressure according to the thickness of the sheet P may be determined based on a predetermined relationship between the thickness of the sheet P and the pressure so as not to leave pressure marks on the sheet P. This relationship may be maintained by a table, formula or program module. The moving means may include a cam 503 that presses the first electrode or the second electrode, and a motor M1 that rotates the cam 503. As a result, the pressing force on the sheet P can be adjusted with a simple structure. As shown in Figures 7A, 7B, 7D, and 7E, at least one of the first electrode and the second electrode may be cylindrical.In this case, the bottom or side of the cylinder will be in contact with the sheet P. These shapes are less likely to leave indentations on the sheet P. As shown in Figures 7B, 7C, and 7E, at least one of the first electrode and the second electrode may be a rectangular parallelepiped. A flat plate is a rectangular parallelepiped in a broad sense. A rectangular parallelepiped is composed of multiple faces, and the face with a relatively large area is used as the pressing surface. This will make it less likely to leave indentations. The sheet sensor 406 and CPU 401 may function as sensing means to sense the presence of a sheet P between the first electrode and the second electrode. The power supply 511 applies a voltage to the first electrode and the second electrode when a sheet P is present between them. The power supply 511 does not apply a voltage to the first electrode and the second electrode when a sheet P is not present between them. As a result, electrical short circuits between the first electrode and the second electrode are less likely to occur. As shown in Figure 6A, the sensing means may be located upstream of the measuring means in the conveying direction of the sheet P. As shown in Figure 6C, the sensing means may be located downstream of the measuring means in the conveying direction of the sheet P. As shown in Figure 6B, the sensing means may be located at the same position as the measuring means in the conveying direction of the sheet P, and at a different position from the measuring means in a direction perpendicular to the conveying direction of the sheet P. The CPU 401, gloss sensor 43a, and smoothness sensor 43b are examples of first measuring means for measuring the surface properties of the sheet P. The CPU 401, thickness sensor 41, and resistance sensor 45 are examples of second measuring means for measuring the volume resistivity of the sheet P. As shown in Figure 13, the CPU 401 may function as a discrimination means for determining the type of sheet P based on the surface properties of the sheet P and the volume resistivity of the sheet P. This improves the accuracy of determining the type of sheet P. In particular, the gloss sensor 43a, which improves the accuracy of distinguishing synthetic paper, is an example of a first detection means for detecting the gloss of sheet P. Gloss is a useful physical property value for distinguishing the type of sheet P. The smoothness sensor 43b is an example of a second detection means for detecting the smoothness of sheet P. Smoothness is a useful physical property value for distinguishing the type of sheet P. The thickness sensor 41 is an example of a third detection means for detecting the thickness of sheet P. The resistance sensor 45 is an example of a fourth detection means for detecting the volume resistivity of sheet P.The CPU 401 is an example of a calculation means that calculates the volume resistivity of sheet P based on the volume resistivity and thickness of sheet P. The volume resistivity may also be calculated based on the measured thickness of sheet P. This allows for accurate determination of the volume resistivity. As a result, the accuracy of discriminating the type of sheet P will improve. The first measurement means may detect the surface properties of sheet P (e.g., glossiness, smoothness) while sheet P is being transported. This will shorten the detection time. The third detection means may detect the thickness of sheet P while sheet P is being transported. This will shorten the detection time. The fourth detection means may detect the volume resistivity of sheet P while sheet P is stopped. This will improve the measurement accuracy of volume resistivity and volume resistivity. As a result, the accuracy of discriminating the type of sheet P will improve. The stiffness sensor 44 is an example of a fifth detection means that detects the stiffness of sheet P while sheet P is stopped. The fourth detection means (e.g., resistance sensor 45) and the fifth detection means (e.g., stiffness sensor 44) may be configured to perform detection in parallel when the transport of the sheet P is stopped. This may reduce the number of times the transport of the sheet P is stopped. As a result, the time required to determine the type of sheet P will be shortened. The fourth detection means (e.g., resistance sensor 45) and the fifth detection means (e.g., stiffness sensor 44) may each perform detection during a single stop period when the transport of the sheet P is stopped. This may reduce the number of times the transport of the sheet P is stopped. As a result, the time required to determine the type of sheet P will be shortened. The first transport path 111 is an example of a first transport path that transports the fed sheet P. The second transport path 12 and the third transport path 13 are examples of second and third transport paths branching off from the first transport path. The image forming unit 10Y is an example of an image forming means that forms an image on the sheet P being transported along the third transport path. The escape tray 46 is an example of a loading means on which the sheet P discharged from the second transport path is loaded. A fourth detection means (e.g., a resistance sensor 45) and a fifth detection means (e.g., a stiffness sensor 44) may be arranged in the second transport path 12.As a result, the influence of the fourth detection means (e.g., resistance sensor 45) and the fifth detection means (e.g., stiffness sensor 44) on the sheet P being transported along the first transport path 11 and the third transport path 13 will be reduced. The stiffness sensor 44 is an example of a first detection means for detecting the stiffness of the sheet P. The resistance sensor 45 is an example of a second detection means for detecting the volume resistance of the sheet P. The stiffness and volume resistance are detected during the period from when the transport roller pair 47 temporarily stops transporting the sheet P until transporting the sheet P resumes. As a result, the number of times the sheet transport needs to be stopped is reduced to just once. In other words, the efficiency of the detection process is improved.

[0116] (Other Embodiments) The present disclosure can also be realized by supplying a program that implements one or more of the functions of the embodiments described above to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more functions.

[0117] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the scope of the claims. While the embodiments describe multiple features, not all of these features are necessary, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0118] This application claims priority based on Japanese Patent Application No. 2025-017910, filed on February 5, 2025, and all of its contents are incorporated herein by reference.

Claims

1. An image forming apparatus comprising: a transport means for transporting a sheet used for image forming; a first electrode in contact with a first surface of the sheet; a second electrode in contact with a second surface of the sheet; a measuring means for measuring the volume resistance of the sheet based on a voltage applied to the sheet and a current flowing through the sheet during a period when the transport means temporarily stops transporting the sheet; a moving means for moving the second electrode relative to the first electrode and varying the pressure applied to the sheet by the first electrode and the second electrode; a power supply means for supplying current to the sheet by applying a voltage between the first electrode and the second electrode; a detection means for detecting the current flowing through the sheet; and a control means for controlling the pressure applied to the sheet according to the current flowing through the sheet.

2. The image forming apparatus according to claim 1, wherein the control means gradually increases the pressure applied to the sheet by the moving means until the current flowing through the sheet stabilizes.

3. An image forming apparatus comprising: a transport means for transporting a sheet used for image forming; a first electrode in contact with a first surface of the sheet; a second electrode in contact with a second surface of the sheet; a measuring means for measuring the volume resistance of the sheet based on a voltage applied to the sheet and a current flowing through the sheet during a period when the transport means temporarily stops transporting the sheet; a moving means for moving the second electrode relative to the first electrode and varying the pressure applied to the sheet by the first electrode and the second electrode; a power supply means for supplying current to the sheet by applying a voltage between the first electrode and the second electrode; an acquisition means for acquiring the thickness of the sheet; and a control means for controlling the pressure applied to the sheet according to the thickness of the sheet.

4. The image forming apparatus according to claim 3, wherein the control means sets the pressure applied to the sheet according to the thickness of the sheet, based on a predetermined relationship between the thickness of the sheet and the pressure, such that pressure marks are less likely to remain on the sheet.

5. The image forming apparatus according to any one of claims 1 to 4, wherein the moving means includes a cam for pressing the first electrode or the second electrode, and a motor for rotationally driving the cam.

6. The image forming apparatus according to any one of claims 1 to 5, wherein at least one of the first electrode and the second electrode is cylindrical, and the bottom surface or side surface of the cylinder is in contact with the sheet.

7. The image forming apparatus according to any one of claims 1 to 5, wherein at least one of the first electrode and the second electrode is a rectangular parallelepiped.

8. An image forming apparatus according to any one of claims 1 to 7, further comprising sensing means for sensing the presence of the sheet between the first electrode and the second electrode, wherein the power supply means applies a voltage to the first electrode and the second electrode when the sheet is present between the first electrode and the second electrode, and does not apply a voltage to the first electrode and the second electrode when the sheet is not present between the first electrode and the second electrode.

9. The image forming apparatus according to claim 8, wherein the sensing means is located upstream of the measuring means in the conveying direction of the sheet.

10. The image forming apparatus according to claim 8, wherein the sensing means is located downstream of the measuring means in the conveying direction of the sheet.

11. The image forming apparatus according to claim 8, wherein the sensing means is positioned at the same location as the measuring means in the conveying direction of the sheet, and at a different location from the measuring means in a direction perpendicular to the conveying direction of the sheet.

12. An image forming apparatus comprising: a transport means for transporting a sheet used for image forming; a first measuring means for measuring the surface properties of the sheet; a second measuring means for measuring the volume resistivity of the sheet; and a discriminant means for determining the type of sheet based on the surface properties of the sheet and the volume resistivity of the sheet.

13. The image forming apparatus according to claim 12, wherein the first measuring means includes a first detection means for detecting the glossiness of the sheet.

14. The image forming apparatus according to claim 12 or 13, wherein the first measuring means includes a second detection means for detecting the smoothness of the sheet.

15. The image forming apparatus according to any one of claims 12 to 14, wherein the second measuring means comprises: a third detection means for detecting the thickness of the sheet; a fourth detection means for detecting the volume resistivity of the sheet; and a calculation means for calculating the volume resistivity of the sheet based on the volume resistivity of the sheet and the thickness of the sheet.

16. The image forming apparatus according to claim 15, wherein the first measuring means detects the surface properties of the sheet while the sheet is being transported, the third detection means detects the thickness of the sheet while the sheet is being transported, and the fourth detection means detects the volume resistivity of the sheet while the sheet is stopped.

17. The image forming apparatus according to claim 15 or 16, further comprising a fifth detection means for detecting the stiffness of the sheet while the sheet is stopped, wherein the fourth detection means and the fifth detection means are configured to perform detection in parallel when the transport of the sheet is stopped.

18. The image forming apparatus according to claim 17, wherein the fourth detection means and the fifth detection means are configured to perform detection during a single stop period in which the transport of the sheet is stopped.

19. An image forming apparatus according to claim 17 or 18, comprising: a first transport path for transporting a supplied sheet; a second transport path and a third transport path branching from the first transport path; an image forming means for forming an image on a sheet being transported along the third transport path; and a loading means for loading sheets discharged from the second transport path, wherein the fourth detection means and the fifth detection means are located in the second transport path.

20. An image forming apparatus comprising: a conveying means for conveying a sheet; a first detection means for detecting the stiffness of the sheet; and a second detection means for detecting the volume resistance of the sheet, wherein during the period from when the conveying means temporarily stops conveying the sheet until it resumes conveying the sheet, the first detection means detects the stiffness and the second detection means detects the volume resistance.

Images