Sheet determination device, image formation device, and image formation system

Abstract

To determine the type of a sheet on the basis of a parameter fluctuating according to the type of a sheet.SOLUTION: Acquisition means is configured to acquire an electric characteristic of a sheet passing through a transfer nip part to be formed by an image carrier and transfer means to which a transfer voltage is applied for transferring a toner image carried on the image carrier to the sheet. The acquisition means is configured to acquire a heat characteristic of the sheet passing through a fixation nip part to be formed by a first rotor and second rotor to be heated by a heater. Determination means is configured to determine the type of the sheet on the basis of the acquired electric characteristic and the acquired heat characteristic.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a sheet determination device, an image forming apparatus, and an image forming system.

Background Art

[0002] An electrophotographic image forming apparatus needs to use appropriate image forming conditions (e.g., transfer voltage, fixing temperature, etc.) according to the type of sheet (e.g., basis weight, thickness, presence or absence of surface coating, material, etc.). According to Patent Document 1, it has been proposed to estimate the type of sheet based on the light transmittance, the intensity of regular reflected light, or the intensity of diffused reflected light of the sheet detected by a media sensor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in an image forming apparatus, parameters that can be detected through other members different from a media sensor may also vary according to the type of sheet. An object of the present invention is to determine the type of sheet based on parameters that vary according to the type of sheet.

Means for Solving the Problems

[0005] The present invention is, for example, first acquisition means for acquiring the electrical characteristics of the sheet passing through a transfer nip portion formed by an image carrier and transfer means to which a transfer voltage is applied to transfer a toner image carried on the image carrier to the sheet; second acquisition means for acquiring the thermal characteristics of the sheet passing through a fixing nip portion formed by a first rotating body heated by a heater and a second rotating body facing the first rotating body; Determination means for determining the type of the sheet based on the acquired electrical characteristics and the acquired thermal characteristics; A sheet determination device having the above is provided.

Advantages of the Invention

[0006] According to the present invention, it becomes possible to determine the type of the sheet based on parameters that vary according to the type of the sheet.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

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Figure 14

Figure 15

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0009] <Example 1> (1) Image forming system FIG. 1 shows an electrophotographic image forming system 100. Hereinafter, the height direction of the image forming apparatus 120 is expressed as the Z direction. Also, an X direction (width direction) and a Y direction (depth direction) are defined as directions orthogonal to the Z direction.

[0010] The image forming system 100 includes a sheet determination device 110, an image forming device 120, and an information processing device 130 (optional). The sheet determination device 110 determines the type of the sheet P used in the image forming device 120. The image forming device 120 forms an image on the sheet P. The information processing device 130 is a computer that inputs a print job to the image forming device 120.

[0011] The image forming device 120 forms a toner image on the sheet P with four colors of toner: yellow "Y", magenta "M", cyan "C", and black "K". In the following description, the letters Y, M, C, and K attached to the end of the reference numerals are omitted when common matters for the four colors are described.

[0012] The image forming apparatus 120 has one or more paper feed cassettes 10. The paper feed cassette 10 is a storage that can accommodate a plurality of sheets P. The pick-up roller 11 picks up the sheet P accommodated in the paper feed cassette 10 and feeds it to the conveyance path. The first conveyance roller 12 is a separation roller that separates only the topmost one sheet P from the plurality of sheets P and conveys it further downstream. A second conveyance roller 13 is provided downstream of the first conveyance roller 12 in the conveyance direction of the sheet P. The second conveyance roller 13 conveys the sheet P further downstream. A third conveyance roller 14 is provided downstream of the second conveyance roller 13. The third conveyance roller 14 is a registration roller that corrects the skew of the sheet P and conveys it further downstream.

[0013] A sheet sensor 15 is provided downstream of the third conveyance roller 14. The sheet sensor 15 is a sensor that detects the leading edge and the trailing edge of the sheet P. For example, the sheet sensor 15 outputs a detection signal indicating that the sheet P is passing while the sheet P is passing through the sheet sensor 15. The detection result of the sheet sensor 15 is used to detect a conveyance delay or a jam of the sheet P. For example, a conveyance delay or a jam may be detected based on the conveyance time from the start of driving of the pick-up roller 11 until the leading edge of the sheet P is detected by the sheet sensor 15. Thereafter, the sheet P is conveyed to the secondary transfer nip.

[0014] On the one hand, when the image forming apparatus 120 receives a print job accompanied by image data from the information processing apparatus 130, the image forming apparatus 120 controls the charger 22 to uniformly charge the surface of the photosensitive drum 21. The charger 22 may include a charging roller or a charging wire, etc. The laser 23 irradiates the surface of the photosensitive drum 21 with laser light according to the image data to form an electrostatic latent image corresponding to the image data. The laser 23 may be a light source of an exposure apparatus having a rotating polygon mirror as a scanning optical system. The laser 23 may be realized by a plurality of light emitting diodes or a plurality of organic EL elements. The developing device 24 develops the electrostatic latent image using toner to form a toner image on the photosensitive drum 21. The developing device 24 may have a storage container for storing toner, a stirring member for stirring the toner, and a developing sleeve that carries and rotates the toner, etc. As the photosensitive drum 21 rotates, the toner image is conveyed to the primary transfer nip N1.

[0015] The primary transfer nip N1 is formed by arranging the photosensitive drum 21 and the primary transfer roller 25 so as to face each other while sandwiching the intermediate transfer belt 26 therebetween. A primary transfer voltage that promotes the transfer of the toner image is applied to the primary transfer roller 25. Thereby, the toner image is transferred from the photosensitive drum 21 to the intermediate transfer belt 26. By superimposing the toner images of YMCK, a full-color image is formed. As the primary transfer roller 25 rotates, the toner image is conveyed to the secondary transfer nip N2.

[0016] The secondary transfer nip N2 is formed by the inner roller 31, the outer roller 32, and the intermediate transfer belt 26. The inner roller 31 is arranged so as to contact the inner peripheral side of the intermediate transfer belt 26. The outer roller 32 is arranged so as to contact the outer peripheral side of the intermediate transfer belt 26. A secondary transfer voltage is applied to the inner roller 31 and the outer roller 32. Thereby, the transfer of the toner image from the intermediate transfer belt 26 to the sheet P is promoted.

[0017] In the conveyance direction of the sheet P, a fixing device 4 is disposed downstream of the secondary transfer nip N2. The fixing device 4 applies heat and pressure to the sheet P passing through the fixing nip N3 and the toner image, thereby fixing the toner image on the sheet P. Thereafter, the sheet P is discharged to the outside of the image forming apparatus 120.

[0018] The image forming apparatus 120 has an operation unit 60. The operation unit 60 includes an input device (e.g., touch sensor, switch) for receiving an instruction from a user, and a display device (e.g., liquid crystal display, organic EL display) for displaying a message to the user. The operation unit 60 may receive a setting regarding the type of the sheet P input by the user, or may display information regarding the type of the sheet P determined by the sheet determination device 110.

[0019] (2) Fixing device FIG. 2 shows a cross section of the fixing device 4. The fixing film 42 is a cylindrical film. A heater 41 is disposed on the inner peripheral side of the fixing film 42 so as to abut against the inner periphery of the fixing film 42. The pressure roller 43 faces the fixing film 42 and presses the fixing film 42 to form a fixing nip N3. Further, the fixing film 42 rotates in a driven manner by the pressure roller 43. The heater 41 heats the fixing film 42 at the fixing nip N3. Note that the fixing film 42 rotates while sliding with respect to the heater 41.

[0020] The fixing device 4 includes a first thermistor 46 and a second thermistor 47 that detect the temperature of the heater 41. In the first embodiment, the first thermistor 46 and the second thermistor 47 are disposed so as to abut against the back surface of the heater 41. Here, the back surface (non-sliding surface) of the heater 41 is the plane farther from the pressure roller 43 among the two planes of the heater 41 having a normal line generally in the X direction. The front surface (sliding surface) of the heater 41 is the plane closer to the pressure roller 43 among the two planes of the heater 41 having a normal line generally in the X direction.

[0021] FIG. 3 shows the positions where the first thermistor 46 and the second thermistor 47 are arranged in the longitudinal direction (Y direction) of the heater 41. In the Y direction, the first thermistor 46 is arranged at the center of the heater 41. The second thermistor 47 is arranged at a position about 120 [mm] away from the center of the heater 41.

[0022] As shown in FIG. 3, the sheet P is conveyed in the Z direction, but the width of the sheet P (length in the Y direction) varies. The feeding cassette 10 has a centering mechanism (position regulating member) for centering a plurality of sheets P so that the sheet P passes through the center of the conveyance path. Therefore, the center of the sheet P in the Y direction passes through the central portion in the Y direction. That is, although the length of the sheet P in the Y direction varies, sheets P of any size pass through the central portion of the heater 41. In FIG. 3, the "minimum size" indicates the minimum size among the various sizes of the sheet P on which an image can be formed in the image forming apparatus 120. The "maximum size" indicates the maximum size among the various sizes of the sheet P on which an image can be formed in the image forming apparatus 120.

[0023] As shown in FIG. 3, among the regions in the Y direction of the heater 41, the first thermistor 46 is arranged within the region (minimum size region) through which the sheet P of the minimum size passes. Therefore, the first thermistor 46 detects the temperature of the minimum size region of the heater 41. The second thermistor 47 is arranged outside the passage region through which the sheet P of the maximum size that can be conveyed passes and inside the heating region of the heater 41. Therefore, the second thermistor 47 detects the temperature of the non-passage region through which the sheet P does not pass.

[0024] The detection result of the first thermistor 46 is used for feedback control to maintain the fixing temperature of the heater 41 at the target fixing temperature Ttgt. In the first embodiment, the detection result of the second thermistor 47 is used to determine the type of the sheet P.

[0025] (3) Control system FIG. 4 shows the control system of the image forming system 100. The sheet determination device 110 includes a CPU 111, a memory 112, and a communication circuit 113. The CPU 111 executes a program stored in the ROM area of the memory 112 and executes a sheet determination process. The CPU is an abbreviation for a central processing unit. The ROM is an abbreviation for a read only memory. However, the ROM may include an EEPROM (electrically erasable ROM) or a flash memory. Further, the CPU 111 controls the communication circuit 113 and communicates with the information processing device 130 or the image forming device 120. The CPU 111 may communicate with the image forming device 120 via the information processing device 130, or may communicate with the image forming device 120 without going through the information processing device 130.

[0026] The information processing device 130 includes a CPU 131, a memory 132, and a communication circuit 133. The CPU 131 executes a program stored in the ROM area of the memory 132 and creates a print job. Further, the CPU 131 controls the communication circuit 133 and communicates with the sheet determination device 110 or the image forming device 120.

[0027] The controller 140 of the image forming device 120 includes a CPU 141, a memory 142, and a communication circuit 143. The CPU 141 executes a program stored in the ROM area of the memory 142 and controls the image forming device 120. Further, the CPU 141 controls the communication circuit 143 and communicates with the information processing device 130 or the sheet determination device 110.

[0028] The controller 140 controls the motors M1, M2, M3, and M4 via a drive circuit (not shown). The motor M1 rotationally drives the pick roller 11. The motor M2 rotationally drives the first conveying roller 12. The motor M3 rotationally drives the second conveying roller 13. The motor M4 rotationally drives the third conveying roller 14. The motors M1 to M4 are, for example, brushless DC motors. The torque sensor 16 detects the torque required for the motor M2 to drive the first conveying roller 12 when the first conveying roller 12 is conveying the sheet P. This torque changes according to the conveying characteristics of the sheet P. The torque sensor 16 may detect the torques of the motors M1, M3, and M4.

[0029] The CPU 141 monitors or measures various times using the timer 144. For example, the CPU 141 measures the conveying time from the drive start timing of the motor M1 (pick roller 11) to the timing when the sheet sensor 15 detects the leading edge of the sheet P. This conveying time can change according to the conveying characteristics of the sheet P.

[0030] The transfer power supply 33 generates the secondary transfer voltage Vtr and applies it to the outer roller 32. A voltage sensor 34 for detecting the output voltage (secondary transfer voltage Vtr) and a current sensor 35 for detecting the output current are connected to the transfer power supply 33. The secondary transfer voltage Vtr is, for example, a DC voltage. The outer roller 32 abuts on the intermediate transfer belt 26 and forms a secondary transfer nip N2 therebetween. A secondary transfer voltage Vtr having a polarity opposite to that of the toner is applied to the secondary transfer nip N2. Thereby, the outer roller 32 transfers the toner image on the intermediate transfer belt 26 to the sheet P. The core metal of the inner roller 31 is connected (grounded) to the frame ground or the like.

[0031] The CPU 141 detects the electrical characteristics of the sheet P based on the secondary transfer voltage Vtr detected by the voltage sensor 34 and the current detected by the current sensor 35. The sheet determination device 110 determines the type of the sheet P based on this electrical characteristic.

[0032] The CPU 141 adjusts the power supplied to the heater 41a through the temperature control circuit 45 so that the fixing temperature detected by the first thermistor 46 is maintained at the target fixing temperature Ttgt. The CPU 141 detects the thermal characteristics of the sheet P passing through the fixing device 4 based on the temperature detected by the second thermistor 47. The sheet determination device 110 determines the type of the sheet P based on this thermal characteristic. That is, the CPU 111 acquires the detection result of the electrical characteristics of the sheet P from the image forming apparatus 120 and the detection result of the thermal characteristics, and determines the type of the sheet P based on the combination of these. The electrical characteristics may be any of, for example, voltage, current, resistance, and capacitance. The thermal characteristics may be any of temperature, moisture content, or heat capacity.

[0033] The CPU 141 detects the ambient temperature of the sheet P using the temperature sensor 51. The CPU 141 detects the ambient humidity of the sheet P using the humidity sensor 52. The CPU 141 can calculate the moisture content contained in the sheet P from the ambient temperature and the ambient humidity.

[0034] The media sensor 53 is installed in the conveyance path of the sheet P and detects the thickness, basis weight, or surface properties (e.g., smoothness, presence or absence of coating, reflectance) of the sheet P. The media sensor 53 is constituted by, for example, a combination of an ultrasonic oscillator and an ultrasonic receiver, or a combination of a light emitting element and a plurality (e.g., three) of light receiving elements. The first of the three light receiving elements detects the amount of transmitted light. The second light receiving element detects the amount of regular reflected light. The third light receiving element detects the amount of diffused reflected light. The amount of transmitted light is correlated with the thickness and basis weight of the sheet P. The ratio of the regular reflected light to the diffused reflected light is correlated with the surface properties.

[0035] (4) Method for determining the type of sheet In the first embodiment, two or more characteristic values about the sheet P are used to determine the type of the sheet P.

[0036] (4-1) Characteristic values (electrical characteristics) obtained from the secondary transfer process In the secondary transfer process, a predetermined secondary transfer voltage Vtr is applied to the outer roller 32. The inner roller 31 is at the ground potential. An electric field is formed between the outer roller 32 and the inner roller 31, and the toner image is transferred to the sheet P by this electric field. The current sensor 35 detects the current value flowing through the sheet P when the sheet P is passing through the secondary transfer nip N2 and the secondary transfer voltage Vtr is applied to the outer roller 32. The current value when the sheet P is passing through the secondary transfer nip N2 depends on the electrical characteristics of the sheet P (mainly the electrical resistance of the sheet P). For example, the larger the electrical resistance value Rp of the sheet P, the smaller the detected current value Ip.

[0037] (4-2)Characteristic values (thermal characteristics) obtained from the fixing process In the fixing process, the CPU 141 determines the target fixing temperature Ttgt based on the type setting of the sheet P input by the user and the environmental conditions (temperature and humidity). Further, the CPU 141 controls the power supplied to the heater 41 so that the temperature of the heater 41 (fixing temperature) detected by the first thermistor 46 is maintained at the target fixing temperature Ttgt.

[0038] A part of the heat generated by the heater 41 when the sheet P passes through the fuser 4 is consumed by the sheet P. As a result, the detected temperature of the first thermistor 46 decreases. When the temperature control circuit 45 is set with the target fixing temperature Ttgt by the CPU 141, it supplies power to the heater 41 so that the temperature of the heater 41 is maintained at the target fixing temperature Ttgt. The amount of heat consumed by the sheet P when the sheet P passes through the fuser 4 depends on the thermal characteristics of the sheet P.

[0039] On the other hand, in the non-passage area of the heater 41 in the Y direction where the sheet P does not pass, heat consumption by the sheet P does not occur. That is, the temperature of the non-passage area detected by the second thermistor 47 is more likely to be higher than the temperature of the passage area detected by the first thermistor 46. In particular, when the amount of heat consumed by the sheet P is large, the difference between the detection value of the second thermistor 47 (temperature of the non-passage area) and the target fixing temperature Ttgt is likely to be large. This difference indicates the heat characteristics of the sheet P. Therefore, the CPU 111 of the sheet determination device 110 can determine the type of the sheet P based on this difference.

[0040] (5) Function of the CPU (5-1) CPU of the image forming apparatus FIG. 5 shows functions realized by the CPU 141 of the image forming apparatus 120 executing a program. The job recording unit 501 receives a print job input from the information processing apparatus 130 or a print job input from the operation unit 60, and stores the content of the print job in the RAM area of the memory 142. For example, information indicating the type of the sheet P set by the user is stored.

[0041] The environment recording unit 502 acquires the ambient temperature detected by the temperature sensor 51 and the ambient temperature detected by the humidity sensor 52, and stores them in the RAM area of the memory 142. The ambient temperature and the ambient temperature may be referred to as environment information or moisture information.

[0042] The Itgt determination unit 503 calculates the target current Itgt based on the environment information acquired by the environment recording unit 502. Here, the target current Itgt is a secondary transfer current suitable for transferring the toner image from the intermediate transfer belt 26 to the sheet P. A table, mathematical function, or program module for obtaining the target current Itgt from the environment information may be stored in the ROM area of the memory 142. These can be determined by experiments or simulations. The target current Itgt may use these to obtain the target current Itgt.

[0043] While the sheet P has not passed through the secondary transfer nip N2, the Vb determination unit 504 controls the transfer power supply 33 to cause a current to flow from the outer roller 32 through the intermediate transfer belt 26 to the inner roller 31. When the current detected by the current sensor 35 stabilizes at the target current Itgt, the Vb determination unit 504 detects the output voltage from the transfer power supply 33 by the voltage sensor 34, and stores the detection result as the base voltage Vb in the memory 142.

[0044] The Vp determination unit 505 obtains the shared voltage Vp based on environmental information (e.g., moisture content). The shared voltage Vp refers to the voltage applied to the sheet P when the secondary transfer voltage Vtr is applied to the secondary transfer nip N2 through which the sheet P is passing. Note that a table, mathematical function, or program module for obtaining the shared voltage Vp from environmental information (moisture content) may be stored in the ROM area of the memory 142. Note that since the relationship between environmental information (e.g., moisture content) and the shared voltage Vp depends on the type of the sheet P, a table, mathematical function, or program module may be provided for each type of the sheet P. Note that the type of the sheet P used is the type recorded by the job recording unit 501. The Vp determination unit 505 may refer to these to obtain the shared voltage Vp from the environmental information.

[0045] The Vtr calculation unit 506 calculates the secondary transfer voltage Vtr by adding the base voltage Vb and the shared voltage Vp. The transfer voltage control unit 507 sets the transfer power supply 33 to output the secondary transfer voltage Vtr determined by the Vtr calculation unit 506. Thereby, the transfer power supply 33 starts to output the secondary transfer voltage Vtr.

[0046] The Rp calculation unit 508 detects the current Ip flowing through the sheet P when the sheet P passes through the secondary transfer nip N2 by the current sensor 35. Further, the Rp calculation unit 508 calculates the resistance value Rp of the sheet P by dividing the shared voltage Vp stored in the memory 142 by the current Ip. The Rp calculation unit 508 may be implemented in the sheet determination device 110. The transmission unit 520 transmits the pair of the shared voltage Vp and the current Ip, or the resistance value Rp to the sheet determination device 110.

[0047] The Ttgt calculation unit 509 calculates the target fixing temperature Ttgt based on the type acquired by the job recording unit 501 and the environmental information (e.g., moisture content) acquired by the environmental recording unit 502. In the ROM area of the memory 142, a table, a mathematical function, or a program module for obtaining the target fixing temperature Ttgt from the environmental information (e.g., moisture content) may be stored. Since the relationship between the environmental information (moisture content) and the target fixing temperature Ttgt differs for each type of sheet P, the table, the mathematical function, or the program module may be provided for each type of sheet P. The Ttgt calculation unit 509 may use these to obtain the target fixing temperature Ttgt from the environmental information (moisture content). The heater control unit 510 sets the target fixing temperature Ttgt in the temperature control circuit 45.

[0048] The Tave calculation unit 511 samples the temperature using the second thermistor 47 when the sheet P is passing through the fixing nip N3, and calculates the average value (average temperature Tave) of a plurality of sample values. The Tp calculation unit 512 calculates the temperature difference (difference Tp) between the target fixing temperature Ttgt and the average temperature Tave. The Tp calculation unit 512 may be implemented in the sheet determination device 110. The transmission unit 520 transmits a pair of the target fixing temperature Ttgt and the average temperature Tave, or the difference Tp to the sheet determination device 110.

[0049] (5-2) CPU of the Sheet Determination Device FIG. 6 shows the functions realized by the CPU 111 of the sheet determination device 110 executing a program. The acquisition unit 601 controls the communication circuit 113 to acquire various information from the image forming apparatus 120. For example, information regarding the type of the sheet P input by the user, the resistance value Rp (or a pair of the shunt voltage Vp and the current Ip), and the difference Tp (or a pair of the target fixing temperature Ttgt and the average temperature Tave) are acquired.

[0050] In the ROM area of the memory 112, a database 610 that holds the relationship between the resistance value Rp and the difference Tp for each type of sheet P obtained through prior consideration is stored.

[0051] FIG. 7 shows an example of the database 610. In the database 610, the brand name, paper type classification, basis weight, resistance value Rp, difference Tp, standardized resistance value Rp_db, and standardized difference Tp_db of various sheets P are stored in an associated manner. The standardized resistance value Rp_db is a value standardized (normalized) with respect to the resistance value Rp for all brands held in the database 610. The standardized difference Tp_db is a value standardized (normalized) with respect to the difference Tp for all brands held in the database 610. Note that the resistance value Rp for each brand used to obtain the standardized resistance value Rp_db, the average value Rp_ave of the resistance values Rp of all brands, and the standard deviation Rp_sd of the resistance values Rp of all brands are also stored in the ROM area of the memory 112. Similarly, the difference Tp for each brand used to obtain the standardized difference Tp_db, the average value Tp_ave of the differences Tp of all brands, and the standard deviation Tp_sd of the differences Tp of all brands are also stored in the ROM area of the memory 112.

[0052] The electrical property detection unit 602 shown in FIG. 6 detects the electrical properties of the sheet P based on the information acquired from the image forming apparatus 120. For example, the Rp calculation unit 508 calculates the resistance value Rp based on the shared voltage Vp and the current Ip. The normalization unit 622 normalizes or standardizes the resistance value Rp to calculate the standardized resistance value Rp_norm.

[0053] Rp_norm = (Rp - Rp_ave) / Rp_sd ···Eq1 Here, Rp_ave and Rp_sd are read from the ROM area of the memory 112.

[0054] The thermal property detection unit 603 detects the thermal properties of the sheet P based on the information acquired from the image forming apparatus 120. For example, the Tp calculation unit 512 calculates the difference Tp based on the target fixing temperature Ttgt and the average temperature Tave. The normalization unit 632 normalizes or standardizes the difference Tp to calculate the standardized difference Tp_norm.

[0055] Tp_norm = (Tp - Tp_ave) / Tp_sd ··· Eq2 Here, Tp_ave and Tp_sd are read from the ROM area of the memory 112.

[0056] The type discrimination unit 604 discriminates the type of the sheet P based on the electrical characteristics and the thermal characteristics of the sheet P. The distance calculation unit 641 calculates the Euclidean distance D between the combination of the electrical characteristics and the thermal characteristics of the sheet P and the combinations of the electrical characteristics and the thermal characteristics of various sheets P held in the database 610.

[0057] Assume that media A, B, C, D, etc. are registered in the database 610. Generally, in an n-dimensional space, the Euclidean distance D between the point P(P1, P2,..., Pn) and the point Q(Q1, Q2,..., Qn) is calculated by the following formula.

[0058] D = SQRT(Σ(Qi - Pi)^2) ··· Eq3 Here, SQRT(x) is a mathematical function for obtaining the square root of x. i is an integer from 1 to n. The Euclidean distance Dp between the characteristic values of the brands recorded in the database 610 and the characteristic values detected by the image forming apparatus 120 is obtained from the following formula.

[0059] D = SQRT((Rp_norm - Rp_db)^2 + (Tp_norm - Tp_db)^2) ··· Eq4 The minimum distance specifying unit 642 specifies the brand close to the characteristic values detected in the image forming apparatus 120 among the various brands registered in the database 610. That is, the minimum distance specifying unit 642 specifies the minimum value among the Euclidean distances Dp obtained for the various brands registered in the database 610. The minimum distance specifying unit 642 outputs the brand name, paper type, basis weight, etc. that became the minimum value as the type of the sheet P.

[0060] The determination unit 606 determines whether the type of the sheet P set by the user matches the type specified by the type determination unit 604. If the two do not match, the alarm unit 607 outputs an alarm message to the display device of the operation unit 60. The alarm message indicates that the type of the sheet P set by the user does not match the type specified by the type determination unit 604. The alarm message may be a message prompting the user to review the setting of the type of the sheet P. If the two do not match, the notification unit 608 may notify the service technician of the image forming apparatus 120. For example, the notification unit 608 may send a notification email to the email address of the service technician. The notification email includes a message suggesting that the type of the sheet P set by the user does not match the type specified by the type determination unit 604.

[0061] (6) Flowchart (6-1) Flowchart of the process executed by the CPU 141 FIG. 8 shows a method for acquiring the characteristics of the sheet P executed by the CPU 141 of the image forming apparatus 120. The CPU 141 executes the following processes according to the control program stored in the ROM area of the memory 142.

[0062] (6-1-1) Acquisition of electrical characteristics In S801, the CPU 141 (job recording unit 501) acquires job information from the information processing apparatus 130 or the operation unit 60 and records the job information in the RAM area of the memory 142. The job information includes the image information to be printed and the paper type information indicating the type of the sheet P on which the image is to be formed. The paper type information includes, for example, the paper type setting (such as "plain paper", "coated paper", and basis weight classification) input by the user in advance from the operation unit 60.

[0063] In S802, the CPU 141 (environment recording unit 502) acquires environment information (a pair of temperature and humidity or moisture content) using the temperature sensor 51 and the humidity sensor 52 and records the environment information in the RAM area of the memory 142.

[0064] In S803, the CPU 141 (Itgt determination unit 503) determines the target current Itgt based on the environmental information. As described above, the Itgt determination unit 503 refers to a table stored in the memory 142 or the like, and determines the target current Itgt corresponding to the environmental information. The target current Itgt is stored in the RAM area of the memory 142.

[0065] In S804, the CPU 141 (Vb determination unit 504) obtains the base voltage Vb by controlling the output voltage of the transfer power supply 33 so that the detected value of the current sensor 35 becomes the target current Itgt. This step is executed when the sheet P has not passed through the secondary transfer nip N2 (when the outer roller 32 and the intermediate transfer belt 26 are in contact).

[0066] In S805, the CPU 141 (Vp determination unit 505) determines the shared voltage Vp based on the paper type information (basis weight) and environmental information (moisture content) stored in the memory 142. As described above, the Vp determination unit 505 may refer to a table stored in the ROM area of the memory 142 or the like, and determine the shared voltage Vp corresponding to the combination of the basis weight and the moisture content. The shared voltage Vp is stored in the RAM area of the memory 142.

[0067] In S806, the CPU 141 (Vtr calculation unit 506) calculates the secondary transfer voltage Vtr by adding the base voltage Vb and the shared voltage Vp.

[0068] In S807, the CPU 141 (transfer voltage control unit 507) applies the secondary transfer voltage Vtr to the secondary transfer nip N2 by controlling the transfer power supply 33 to output the secondary transfer voltage Vtr. For example, the CPU 141 starts the motors M1 to M4, feeds and conveys the sheet P along the conveyance path, and when the sheet sensor 15 detects the leading edge of the sheet P, causes the transfer power supply 33 to output the secondary transfer voltage Vtr.

[0069] In S808, the CPU 141 (Rp calculation unit 508) causes the current sensor 35 to detect the current Ip flowing through the sheet P at the secondary transfer nip N2, and calculates the resistance value Rp, which is the electrical characteristic of the sheet P, based on the current Ip and the sharing voltage Vp. As described above, the resistance value Rp may be calculated according to Ohm's law. The resistance value Rp is stored in the RAM area of the memory 142.

[0070] (6-1-2) Acquisition of Thermal Characteristics In S809, the CPU 141 (Ttgt calculation unit 509) determines the target fixing temperature Ttgt based on the job information (paper type, basis weight) and the environmental information (moisture content). As described above, the Ttgt calculation unit 509 may refer to the table stored in the ROM area of the memory 142 and determine the target fixing temperature Ttgt corresponding to the pair of the basis weight and the moisture content.

[0071] In S810, the CPU 141 (heater control unit 510) causes the heater 41 to generate heat by setting the target fixing temperature Ttgt in the temperature control circuit 45. The temperature control circuit 45 adjusts the power supplied to the heater 41 so that the fixing temperature detected by the first thermistor 46 is maintained at the target fixing temperature Ttgt. More specifically, the CPU 141 samples the analog voltage signal output from the first thermistor 46 at a predetermined period. The sampling period is set to be extremely short with respect to the time it takes for the sheet P to pass through the fixing unit 4. The CPU 141 controls the power supplied to the heater 41 so that the difference between the fixing temperature obtained through sampling and the target fixing temperature Ttgt becomes small.

[0072] In S811, the CPU 141 (Tave calculation unit 511) detects the temperature with the second thermistor 47. As described above, the Tave calculation unit 511 samples the output value of the second thermistor 47 while the sheet P is passing through the fixing unit 4, obtains the average value Tave of the sample values, and records it in the RAM area of the memory 142.

[0073] In S812, the CPU 141 (Tp calculation unit 512) obtains the difference Tp based on the average value Tave stored in the RAM area of the memory 142 and the target fixing temperature Ttgt. As described above, the Tp calculation unit 512 calculates the difference Tp by subtracting the target fixing temperature Ttgt from the average value Tave. The difference Tp is stored in the RAM area of the memory 142.

[0074] In S813, the CPU 141 (transmission unit 520) causes the sheet determination device 110 to execute sheet determination by transmitting the characteristic values (e.g., resistance value Rp, difference Tp) of the sheet P to the sheet determination device 110.

[0075] (6-2) Flowchart of the process executed by the CPU 111 FIG. 9 shows a sheet determination sequence. The CPU 111 of the sheet determination device 110 executes the following processes according to the sheet determination program stored in the ROM area of the memory 112. Here, the sheet P to be determined is called the medium X.

[0076] In S901, the CPU 111 (acquisition unit 601) acquires the resistance value Rp and the difference Tp for the medium X. As described above, the acquisition unit 601 may receive the resistance value Rp and the difference Tp from the image forming apparatus 120, or may calculate the resistance value Rp and the difference Tp based on the detection result received from the image forming apparatus 120.

[0077] In S902, the CPU 111 (normalization units 622, 632) acquires the normalized resistance value Rp_norm and the normalized difference Tp_norm for the medium X. The normalization unit 622 calculates the normalized resistance value Rp_norm using the resistance value Rp for the medium X and Equation Eq1. The normalization unit 632 calculates the normalized difference Tp_norm using the difference Tp for the medium X and Equation Eq2.

[0078] In S903, the CPU 111 (type discrimination unit 604) calculates the distance Dp with respect to the values registered in the database 610. The values registered in the database 610 are the standardized resistance value Rp_db and the standardized difference Tp_db for each of the plurality of media registered in the database 610. The distance calculation unit 641 calculates the Euclidean distance Dp between the pair of the standardized resistance value Rp_norm and the standardized difference Tp_norm for the medium X and the pairs of the standardized resistance value Rp_db and the standardized difference Tp_db for each of the plurality of media. Note that the distance between the medium X and the medium A is denoted as Dp_XA. The distance between the medium X and the medium B is denoted as Dp_XB. The distance between the medium X and the medium C is denoted as Dp_XC. The distance between the medium X and the medium D is denoted as Dp_XD.

[0079] FIG. 10 shows the positions of the respective media in the media space held by the database 610. The horizontal axis represents the standardized resistance value Rp_norm. The vertical axis represents the standardized difference Tp_norm. Here, since there are two (two types) characteristic values of the sheet P, the media space is a two-dimensional space. However, this is only an example. When there are n characteristic values, the media space becomes an n-dimensional space.

[0080] In S904, the CPU 111 (minimum distance identification unit 642) identifies the minimum distance among the plurality of Euclidean distances Dp obtained in S903. In the example shown in FIG. 10, the minimum distance is Dp_XB, which is the distance between the medium X and the medium B.

[0081] In S905, the CPU 111 (type discrimination unit 604) identifies the type corresponding to the minimum distance. In the example of FIG. 10, the medium B corresponding to Dp_XB identified as the minimum distance is identified as the medium X.

[0082] (7) Specific example It is assumed that the resistance Rp of the medium X is 0.15 [V / mA]. It is assumed that the differential Tp for the medium X is 22 [°C]. In this case, the following calculations are performed for the media A, B, C, and D registered in the database 610.

[0083] The normalization units 622 and 623 perform normalization for the medium X. According to the database 610, the average value Rp_ave is 0.129 [V / mA]. The standard deviation Rp_sd is 0.024 [V / mA]. The average value Tp_ave is 21.5 [°C]. The standard deviation Tp_sd is 6.4 [°C]. Substituting these values into Equation Eq1, Rp_norm is calculated to be 0.80. Substituting these values into Equation Eq2, Tp_norm is calculated to be 0.102. Similarly, for the media A, B, C, and D, Rp_db is calculated using Equation Eq1 and Tp_db is calculated using Equation Eq2, respectively.

[0084] The distance calculation unit 641 calculates the distances Dp_XA, Dp_XB, Dp_XC, and Dp_XD using Equation Eq4. As a result, Dp_XA = 2.48, Dp_XB = 1.11, Dp_XC = 1.16, and Dp_XD = 3.77 are calculated. Therefore, among the media A, B, C, and D, the medium B is the closest to the medium X.

[0085] In this way, based on the electrical characteristics and thermal characteristics of the sheet P, the type of the sheet P (e.g., brand, basis weight, paper type) is accurately discriminated. The electrical characteristics may be, for example, a resistance value Rp derived from the current value flowing through the secondary transfer nip N2 in the sheet passing during the secondary transfer process in the image forming process. The thermal characteristics may be a differential Tp derived from the temperature of the non-sheet passing portion detected by the second thermistor 47 in the fixing process.

[0086] In this way, the electrical characteristics of the sheet P may be a value derived from the current detected by the current sensor 35 while the sheet P passes through the secondary transfer nip N2. The thermal characteristics may be a value derived from the temperature of the fixing film 42 detected by the second thermistor 47 in the fixing process.

[0087] In Example 1, the discrimination of the sheet P is based on comparison with specific media recorded in the database 610. However, this is just an example. The media in the database 610 may be divided into several categories such as paper types or basis weights. For example, plain paper may be classified by a basis weight of 60 - 90 [g / m^2]. Coated paper may be classified by a basis weight of 160 - 240 [g / m^2]. Instead of outputting the brand name or paper type of the sheet P, the type discrimination unit 604 may output a basis weight classification. In this case, a media space is assumed with the average value of the standardized resistance Tp_db within each category and the average value of the standardized difference Tp_db as coordinates. The CPU 111 calculates the distance Dp between each category in this media space and the media X, and the distances Dp for each category are compared.

[0088] The type discrimination unit 604 may be realized by a pre-trained classification model. A classification model is machine-learned by applying, in advance, the k-nearest neighbor method (knn) or a decision tree model, etc., to the data group registered in the database 610. The CPU 111 may input the electrical characteristics and thermal characteristics obtained from the sheet P into the classification model, causing the classification model to output the type of the sheet P (media X).

[0089] As described above, the determination unit 606 may determine whether the type of the identified sheet P matches the type (e.g., paper type, basis weight classification) set by the user through the operation unit 60. If the two do not match, the alarm unit 607 may cause a warning message to be displayed on the display device of the operation unit 60. Similarly, the notification unit 608 may notify the service technician of this. As described above, the notification may be the sending of an email or a message.

[0090] Alternatively, the determination unit 606 may compare a plurality of types of image formation that are defined in the specification of the image forming apparatus 120 with the type of the specified sheet P. When the type of the specified sheet P is not included in the plurality of types of image formation, the alarm unit 607 may cause a warning message to be displayed on the display device of the operation unit 60. Similarly, the notification unit 608 may notify this to the service technician. As described above, the notification may be transmission of an e-mail or transmission of a message.

[0091] The CPU 141 may acquire the determination result (the type of the sheet P) from the sheet determination device 110 and correct the shared voltage Vp, the target fixing temperature Ttgt, the rotation speed of each roller, etc. according to the determination result.

[0092] In the first embodiment, the sheet determination device 110 is communicably connected to the image forming apparatus 120, but this is merely an example. The sheet determination device 110 may be provided inside the image forming apparatus 120 or may be provided inside the information processing apparatus 130. The image forming apparatus 120 and the sheet determination device 110 may be connected through a network such as a local area network (LAN) or a wide area network (WAN).

[0093] In the first embodiment, the sheet determination device 110, the image forming apparatus 120, and the information processing apparatus 130 each have an independent CPU, RAM, and ROM, but this is merely an example. The sheet determination device 110 only needs to be able to acquire the characteristic values of the sheet P required in the image forming process. Therefore, the CPUs, RAMs, and ROMs of the sheet determination device 110 and the image forming apparatus 120 may be shared.

[0094] <Second Embodiment> The first embodiment discriminates the type of the sheet P based on the combination of the electrical characteristics and the thermal characteristics of the sheet P. The second embodiment considers another characteristic in addition to the electrical characteristics and the thermal characteristics. Thereby, the discrimination accuracy of the type of the sheet P will be further improved. In the second embodiment, the description of the matters common to the first embodiment is omitted.

[0095] (1) Added characteristic values The characteristic values added in Example 2 are the rotational torque Np and the conveyance time tp. These are characteristic values that can be obtained in the process of conveying the sheet P from the feeding cassette 10 to the detection position of the sheet sensor 15. The rotational torque Np is, for example, the rotational torque (driving torque) of the first conveyance roller 12 detected by the torque sensor 16. The conveyance time tp is the time from the timing when the driving of the pick roller 11 is instructed to the timing when the sheet sensor 15 detects the leading edge of the sheet P. The conveyance time tp is measured by, for example, the timer 144.

[0096] These two characteristic values are values that depend on the stiffness, basis weight, and frictional force derived from the surface state of the sheet P. Therefore, they are added as feature quantities (characteristic values) useful for determining the sheet P. As a result, it is considered that the discrimination accuracy of the type of the sheet P is improved.

[0097] (2) Functions of the CPU (2-1) CPU of the image forming apparatus FIG. 11 shows the functions realized by the CPU 141. The Np detection unit 1101 detects the rotational torque Np of the first conveyance roller 12 that conveys the sheet P using the torque sensor 16. The tp measurement unit 1102 measures the conveyance time tp from the timing when the pick roller 11 starts feeding the sheet P to the timing when the sheet sensor 15 detects the leading edge of the sheet P using the timer 144. The transmission unit 520 transmits the conveyance time tp and the rotational torque Np to the sheet determination device 110 in addition to the resistance value Rp and the difference Tp.

[0098] (2-2) CPU of the sheet determination device FIG. 12 shows the functions realized by the CPU 111. The acquisition unit 601 acquires the conveyance time tp and the rotational torque Np from the image forming apparatus 120 in addition to the resistance value Rp and the difference Tp.

[0099] The sheet feeding characteristic detection unit 1202 detects the feeding characteristics of the sheet P based on the physical quantity acquired by the image forming apparatus 120. For example, the sheet feeding characteristic detection unit 1202 may include a normalization unit 1222 that applies a normalization operation to the rotational torque Np detected by the image forming apparatus 120. The normalization unit 1222 calculates a normalized torque Np_norm using Equation Eq5.

[0100] Np_norm=(Np-Np_ave) / Np_sd ···Eq5 Here, Np_ave and Np_sd are read from the ROM area of the memory 112. Np_ave is the average value of the rotational torque Np for all media registered in the database 610. Np_sd is the standard deviation of the rotational torque Np for all media registered in the database 610.

[0101] The conveyance characteristic detection unit 1203 detects the conveyance characteristics of the sheet P based on the physical quantity acquired by the image forming apparatus 120. For example, the conveyance characteristic detection unit 1203 may include a normalization unit 1232 that applies a normalization operation to the conveyance time tp detected by the image forming apparatus 120. The normalization unit 1232 calculates a normalized conveyance time tp_norm using Equation Eq6.

[0102] tp_norm=(tp-tp_ave) / tp_sd ···Eq6 Here, tp_ave and tp_sd are read from the ROM area of the memory 112. tp_ave is the average value of the conveyance time tp for all media registered in the database 610. tp_sd is the standard deviation of the conveyance time tp for all media registered in the database 610.

[0103] The distance calculation unit 641 calculates the Euclidean distance Dp between two data sets. The first data set is a set of the normalized resistance value Rp_norm, the normalized difference Tp_norm, the normalized torque tp_norm, and the normalized conveyance time tp_norm. The second data set is a set of the normalized resistance value Rp_db, the normalized difference Tp_db, the normalized torque tp_fb, and the normalized conveyance time tp_db. Equation Eq7 is used as the calculation method for this distance.

[0104] D = SQRT((Rp_norm - Rp_db)^2 + (Tp_norm - Tp_db)^2+(Np_norm - Np_db)^2 + (tp_norm - tp_db)^2) ···Eq7 The minimum distance determination unit 642 determines the minimum distance among the distances Dp_XA, Dp_XB, Dp_XC, and Dp_XD obtained by Equation Eq7 for media A, B, C, and D. The type determination unit 604 identifies the medium that resulted in the minimum distance as medium X.

[0105] (3) Flowchart (3-1) Flowchart of CPU141 FIG. 13 shows a method for acquiring characteristic values executed by the CPU 141 of the image forming apparatus 120. Among the steps in FIG. 13, the steps already described in FIG. 8 are given the same reference numerals. When the secondary transfer voltage Vtr is determined in S806, the CPU 141 proceeds from S806 to S1301.

[0106] In S1301, the CPU 141 starts feeding the sheet P by starting the motor M1 to start the rotation of the pickup roller 11. As a result, the pickup roller 11 picks up the sheet P accommodated in the feed cassette 10 and feeds it to the conveyance path.

[0107] In S1302, the CPU 141 (tp measurement unit 1102) starts measuring the conveyance time tp using the timer 144. Note that the sheet P fed onto the conveyance path is conveyed to the secondary transfer nip N2 by the first conveyance roller 12, the second conveyance roller 13, and the third conveyance roller 14.

[0108] In S1303, the CPU 141 (Np detection unit 1101) detects the drive torque (rotation torque Np) of the motor M2 from the torque sensor 16 while the sheet P is in contact with the first conveyance roller 12. The rotation torque Np is stored in the RAM area of the memory 142.

[0109] In S1304, the CPU 141 (tp measurement unit 1102) determines whether the sheet sensor 15 has detected the sheet P. When the sheet sensor 15 detects the leading edge of the sheet P, the CPU 141 proceeds from S1304 to S1305.

[0110] In S1305, the CPU 141 (tp measurement unit 1102) ends the measurement of the conveyance time tp by the timer 144. The conveyance time tp is stored in the RAM area of the memory 142. Thereafter, the CPU 141 executes S807 to S813.

[0111] (3-2) Flowchart of the CPU 111 FIG. 14 shows a sheet determination sequence executed by the CPU 111 of the sheet determination device 110.

[0112] In S1401, the CPU 111 (acquisition unit 601) acquires the resistance value Rp, the difference Tp, the torque Np, and the conveyance time tp from the image forming apparatus 120. The resistance value Rp, the difference Tp, the torque Np, and the conveyance time tp are stored in the RAM area of the memory 112.

[0113] In S1402, the CPU 111 (the normalization units 1222 and 1232) acquires the normalized resistance value Rp_norm, the normalized difference Tp_norm, the normalized torque Np_norm, and the normalized conveyance time tp_norm. This calculation may use expressions Eq1, Eq2, Eq6, and Eq7 based on the resistance value Rp, the difference Tp, the torque Np, and the conveyance time tp.

[0114] In S1403, the CPU 111 (the distance calculation unit 641) obtains the distance Dp with respect to the value registered in the database 610. For example, the distance calculation unit 641 calculates the distances Dp_XA, Dp_XB, Dp_XC, and Dp_XD between the media X and the media A, B, C, and D registered in the database 610. Then, the CPU 111 executes S904 and S905 to determine the type of the media X.

[0115] (4) Database FIG. 15 shows the database 610 of the second embodiment. Compared with FIG. 7, the rotational torque Np, the conveyance time tp, the normalized torque Np_norm, and the normalized conveyance time tp_norm are added to the database 610.

[0116] According to the second embodiment, in addition to the resistance value Rp and the difference Tp, the rotational torque Np and the conveyance time tp are used. Therefore, the second embodiment will be able to determine the type of the sheet P with higher accuracy than the first embodiment.

[0117] In the second embodiment, the motor torque value (rotational torque Np) of the motor M2, which is the drive source of the first conveyance roller 12, is adopted as the characteristic value used for the determination of the sheet P. However, this is only an example of the feeding characteristics. Any drive torque of the conveyance roller that rotates in contact with the sheet P in the conveyance path of the sheet P can be used as the characteristic value. However, when the toner image is transferred to the sheet P in the secondary transfer process, the surface property of the sheet P changes. Therefore, it may be sufficient to detect the drive torque of any conveyance roller arranged in the conveyance path from when the sheet P is picked up until the sheet P reaches the secondary transfer nip N2.

[0118] In Example 2, as a characteristic value, the conveyance time tp from when the drive of the pick roller 11 is instructed until the sheet sensor 15 detects the leading edge of the sheet P is adopted. However, this is only an example. As long as the measurement section of the conveyance time tp is the conveyance time of any section in the conveyance path of the sheet P, it will be sufficient. However, in order to exclude the influence of the correction process of the skew of the sheet P by the third conveyance roller 14, the conveyance time tp should be acquired in the conveyance section from when the sheet P is picked until the sheet P reaches the third conveyance roller 14.

[0119] In Example 2, in order to improve the determination accuracy of the sheet P, the characteristic value obtained in the process of conveying the sheet P is utilized. As the characteristic value added to improve the determination accuracy, any value that responds to the characteristics of the sheet P may be used. For example, the thickness, basis weight, and surface property of the sheet P acquired by the media sensor 53 may be adopted. For example, in addition to the resistance value Rp and the difference Tp, one or more of the thickness, basis weight, and surface property of the sheet P may be considered. In addition to the resistance value Rp, the difference Tp, the conveyance time tp, and the torque Np, one or more of the thickness, basis weight, and surface property of the sheet P may be considered.

[0120] For the characteristic values adopted in Examples 1 and 2, factors that cause disturbances may be considered. For example, the CPU 141 may correct the resistance value Rp according to the environmental information obtained from the temperature sensor 51 and the humidity sensor 52 in consideration of the fact that the electrical resistance of the sheet P varies depending on environmental conditions (temperature, humidity). Note that a correction formula for correcting the resistance value Rp according to the environmental information may be stored in advance in the ROM area of the memory 142. Depending on the length of the sheet P in the longitudinal direction (conveying direction), the amount of heat consumed by the sheet P in the fixing process varies. Therefore, the CPU 141 may acquire the length of the sheet P in the longitudinal direction from the job information and correct the difference Tp according to this length. A correction formula for this purpose may also be stored in the ROM area of the memory 142. Depending on the wear state of the conveying roller that conveys the sheet P, the conveying force of the conveying roller varies. Therefore, the CPU 141 holds the wear states of the first conveying roller 12, the second conveying roller 13, and the third conveying roller 14 in the ROM area (such as a flash memory) of the memory 142, and may correct at least one of the torque Np and the conveying time tp. A correction formula for this purpose may also be stored in the ROM area of the memory 142.

[0121] In Example 1, as an example of the characteristic values, the electrical characteristics (resistance value Rp) and thermal characteristics (difference Tp) of the sheet P were exemplified. In Example 2, as an example of the characteristic values, the electrical characteristics, thermal characteristics, feeding characteristics (e.g., rotational torque Np), and conveying characteristics (e.g., conveying time tp) of the sheet P were exemplified. However, these are only examples of combinations of these characteristic values. Two or more characteristic values may be selected from these four characteristic values. For example, in Example 1, instead of the electrical characteristics, at least one of the feeding characteristics and the conveying characteristics may be adopted. Alternatively, in Example 1, instead of the thermal characteristics, at least one of the feeding characteristics and the conveying characteristics may be adopted. Alternatively, in Example 1, instead of the electrical characteristics and the thermal characteristics, the feeding characteristics and the conveying characteristics may be adopted. In Example 1, 2, or a modification thereof, furthermore, one or more characteristic values of the sheet P acquired by the media sensor 53 may be considered.

[0122] <Regarding the size information of the sheet> The detection result of the electrical characteristics of sheet P and the detection result of the thermal characteristics of sheet P also change depending on the size of sheet P. For example, the larger the size of sheet P in the direction perpendicular to the conveyance direction of sheet P (Y direction), the wider the non-passage area where sheet P does not pass, that is, the area where the intermediate transfer belt 26 and the outer roller 32 are in contact. Therefore, the current value when sheet P passes through the secondary transfer nip N2 tends to increase. Also, the larger the size of sheet P in the conveyance direction (Z direction), the greater the amount of heat consumed by sheet P when passing through the fixing device 4, and the difference Tp tends to increase. To mitigate the influence of the size of sheet P, the CPU 141 or the CPU 111 may correct the detected value according to the size of sheet P.

[0123] Also, the CPU 111 may add the size information of sheet P as a characteristic value for discriminating the type of sheet P.

[0124] Other factors that affect the detection result include the operating speed (process speed) of each unit (intermediate transfer belt 26, fixing device 4, each roller, etc.) during image formation, and the environmental information (temperature, humidity) where sheet P is placed. Therefore, the CPU 111 may correct the detection result using the operating speed or the environmental information detected by the temperature sensor 51 and the humidity sensor 52. Also, the CPU 111 may add at least one of the operating speed and the environmental information as a characteristic value for discriminating the type of sheet P.

[0125] <Regarding standardization> In Examples 1 and 2, as a model for discriminating the type of sheet P, a model is used that standardizes each characteristic value and calculates and compares the Euclidean distances from each point on a pre-registered database. However, the model for discriminating the type of sheet P after obtaining each characteristic value may be another model. For example, a model that uses a decision tree such as a random forest may be adopted. For example, the CPU 111 may have a plurality of decision trees that learn a plurality of characteristic values in parallel, and a majority decision unit that executes a majority decision on a plurality of decision results (types) output from the plurality of decision trees to obtain a final determination result. In this case, in particular, the standardization operation of each characteristic value may be omitted.

[0126] <Technical idea derived from the embodiment> (Item 1) The photosensitive drum 21 and the intermediate transfer belt 26 are examples of image carriers that carry toner images. The inner roller 31 and the outer roller 32 function as transfer means for transferring the toner image carried on the image carrier to the sheet P. The secondary transfer nip N2 is an example of a transfer nip portion formed by the image carrier and the transfer means. The fixing nip N3 is an example of a fixing nip portion formed by a first rotating body (e.g., fixing film 42) heated by a heater and a second rotating body (e.g., pressure roller 43) facing the first rotating body. The CPU 111 and the acquisition unit 601 function as first acquisition means for acquiring the electrical characteristics of the sheet P. The CPU 111 and the acquisition unit 601 function as second acquisition means for acquiring the thermal characteristics of the sheet P. The CPU 111 and the type discrimination unit 604 function as discrimination means for determining the type of the sheet P based on the electrical characteristics and the thermal characteristics of the sheet P. In this way, it becomes possible to determine the type of the sheet P based on parameters that vary according to the type of the sheet P (e.g., brand name, paper type (thickness, presence or absence of coating, material), basis weight). Also, by considering the electrical characteristics and the thermal characteristics of the sheet P, the determination accuracy of the type of the sheet P may be improved. (Item 2) The transfer power supply 33 functions as a voltage application means for applying a transfer voltage (e.g., secondary transfer voltage Vtr) for promoting the transfer of the toner image to the transfer means. The current sensor 35 and the electrical characteristic detection unit 602 are an example of first detection means for detecting the electrical characteristics of the sheet P passing through the transfer means. The fixing device 4 is an example of fixing means for fixing the toner image on the sheet P by applying heat and pressure to the toner image transferred to the sheet P. The second thermistor 47 and the heat characteristic detection unit 603 function as second detection means for detecting the heat characteristics of the sheet P passing through the fixing means. (Item 3) The pick-up roller 11 and the first conveyance roller 12 function as feeding means for feeding the sheet P. The acquisition unit 601, the torque sensor 16, and the Np detection unit 1101 function as third acquisition means for acquiring the feeding characteristics of the sheet P. The second conveyance roller 13 and the third conveyance roller 14 are an example of conveyance means for conveying the sheet S to the transfer means. The acquisition unit 601, the timer 144, and the tp measurement unit 1102 are an example of fourth acquisition means for acquiring the conveyance characteristics of the sheet P. The type discrimination unit 604 may determine the type of the sheet P based on a combination of the detection result of the electrical characteristics of the sheet P, the detection result of the heat characteristics of the sheet P, the detection result of the feeding characteristics of the sheet P, and the detection result of the conveyance characteristics of the sheet P. (Item 4) The type discrimination unit 604 may determine the type of the sheet P based on a combination of the detection result of the electrical characteristics of the sheet P, the detection result of the heat characteristics of the sheet P, and the detection result of the feeding characteristics of the sheet P (e.g., Np_norm). In this way, the type of the sheet P may be discriminated based on the three characteristic values. (Item 5) The first conveyance roller 12 is an example of a separation roller for separating one sheet P from a plurality of sheets P. The motor M2 is an example of a motor for driving the separation roller. The feeding characteristics may include the rotational torque Np of the separation roller. (Item 6) The type discrimination unit 604 may determine the type of the sheet P based on a combination of the detection result of the electrical characteristics of the sheet P, the detection result of the heat characteristics of the sheet P, and the detection result of the conveyance characteristics of the sheet P (e.g., tp_norm). (Item 7) The transport characteristics of the sheet P include the transport time tp of the sheet P measured by the timer 144. The transport characteristics of the sheet P may be the rotational torque required to drive the second transport roller 13 that transports the sheet P. In this case, the torque sensor 16 is arranged to detect the rotational torque of the second transport roller 13. That is, a torque sensor for detecting the rotational torque of the motor M3 may be required. (Item 8) The memories 112 and 122 and the CPUs 111 and 121 may function as recording means for recording the degree of wear of the pick roller 11, the first transport roller 12, the second transport roller 13, or the third transport roller 14. The CPU 141 or the CPU 111 may function as correction means for correcting the transport characteristics (e.g., Np or tp) acquired by the third acquisition means according to the recorded degree of wear. (Item 9) The media sensor 53 may function as third acquisition means for acquiring the thickness of the sheet P. The type determination unit 604 may determine the type of the sheet based on a combination of the detection result of the electrical characteristics of the sheet P, the detection result of the thermal characteristics of the sheet P, and the detection result of the thickness of the sheet P. That is, the thickness of the sheet P may also be used as one of the parameters for obtaining the Euclidean distance Dp. (Item 10) The media sensor 53 may function as third acquisition means for acquiring the basis weight of the sheet P. The type determination unit 604 may determine the type of the sheet based on a combination of the detection result of the electrical characteristics of the sheet P, the detection result of the thermal characteristics of the sheet P, and the detection result of the basis weight of the sheet P. That is, the basis weight of the sheet P may also be used as one of the parameters for obtaining the Euclidean distance Dp. (Item 11) The media sensor 53 may function as third acquisition means for acquiring the surface property of the sheet P. The type determination unit 604 may determine the type of the sheet based on a combination of the detection result of the electrical characteristics of the sheet P, the detection result of the thermal characteristics of the sheet P, and the detection result of the surface property of the sheet P. That is, the surface property of the sheet P may also be used as one of the parameters for obtaining the Euclidean distance Dp. (Item 12) The electrical properties of the sheet P may include the electrical resistance of the sheet P (eg, resistance value Rp). (Item 13) The current sensor 35 is used to detect the current Ip flowing through the sheet P passing through the transfer means. The temperature sensor 51, the humidity sensor 52, and the CPU 141 (Vp determination unit 505) may function as an acquisition unit for acquiring the voltage Vp of the transfer voltage that is distributed by the sheet P. The electrical characteristic detection unit 602 may determine the electrical resistance (resistance value Rp) of the sheet P as an electrical characteristic based on the current Ip and the voltage Vp. (Item 14) The temperature sensor 51, humidity sensor 52, and CPU 141 (environment recording unit 502, Vp determination unit 505) may obtain the amount of moisture in the atmosphere in which the sheet P is placed, and may determine the divided voltage Vp based on the amount of moisture. (Item 15) 7 and 15, the database 610 is an example of a storage unit that stores combinations of electrical characteristics and thermal characteristics for a plurality of different sheet types. The type determination unit 604 may determine the type of sheet P based on the distance Dp between the first combination and the second combination. Here, the first combination is a combination of the detection results of the electrical characteristics of sheet P and the detection results of the thermal characteristics of sheet P. The second combination is a combination of the electrical characteristics and thermal characteristics for a plurality of different sheet types that are stored in the storage unit. (Item 16) The normalization unit 622 may obtain a normalized electrical characteristic (e.g., Rp_norm) by dividing the difference between the detection result of the electrical characteristic and the average value of a plurality of electrical characteristics stored in the storage means by the standard deviation of the plurality of electrical characteristics stored in the storage means. The normalization unit 632 may obtain a normalized thermal characteristic (e.g., Tp_norm) by dividing the difference between the detection result of the thermal characteristic and the average value of a plurality of thermal characteristics stored in the storage means by the standard deviation of the plurality of thermal characteristics stored in the storage means. The type discrimination unit 604 may obtain a distance Dp between the first combination and the second combination. The first combination is a combination of the normalized electrical characteristic for the detection result of the electrical characteristic and the normalized thermal characteristic for the detection result of the thermal characteristic. The second combination is a combination of the normalized electrical characteristic and the normalized thermal characteristic for each of the types of a plurality of sheets stored in the storage means. (Item 17) The first thermistor 46 detects the temperature at a first position closer to the center in the width direction (Y direction) orthogonal to the conveyance direction of the sheet P at the fixing nip N3, and the temperature at the first position used for temperature control of the fixing nip N3. The second thermistor 47 detects the temperature at a second position farther from the center than the first position at the fixing nip N3. Here, the thermal characteristic may be a characteristic based on the temperature at the second position. (Item 18) The first thermistor 46 is an example of a first temperature sensor that detects the temperature at the first position. The second thermistor 47 is an example of a second temperature sensor that detects the temperature at the second position. The heater 41 is an example of a heating means for heating the fixing means. The CPU 141 and the temperature control circuit 45 function as temperature control means for controlling the heating means so that the temperature at the first position becomes the target fixing temperature Ttgt. Here, the thermal characteristic may be a characteristic based on the difference Tp between the temperature at the second position and the target fixing temperature. (Item 19) The CPU 111 or the CPU 141 may function as correction means for correcting the thermal characteristic (e.g., the difference Tp) according to the length of the sheet P in the conveyance direction. (Item 20) The sheet P may be conveyed so that the center of the sheet P passes through the center in the width direction of the fixing nip N3. This is achieved by providing a feeding cassette 10 and regulating (centering) the position of the sheet P in the width direction (Y direction). (Item 21) The type determination unit 604 may obtain the type of the sheet P output from the learned model by inputting a combination of the detection result of the electrical characteristics of the sheet P and the detection result of the thermal characteristics of the sheet P into the learned model. (Item 22) The learned model may have a plurality of decision trees learned in parallel, and may output the type of the sheet based on the determination results output from the plurality of decision trees. For example, the learned model may have a majority decision unit that executes a majority decision on a plurality of determination results and outputs one type. That is, the type determination unit 604 may have a plurality of decision trees and a majority decision unit. (Item 23) The image forming apparatus 120 may further include a display means (operation unit 60) that displays a setting related to the type of the sheet P input by the user. There may be a case where the type of the sheet P obtained by the sheet determination apparatus 110 is different from the type of the sheet P input by the user. In this case, the sheet determination apparatus 110 may cause the display means to display warning information. Thereby, it becomes easier for the user to recognize that the setting of the type of the sheet P may be incorrect. (Item 24) The notification unit 608 functions as a notification means for notifying the service person of the determination result of the sheet P. (Item 25) The acquisition unit 601 may function as a third acquisition means for acquiring the size information of the sheet P. The type determination unit 604 may determine the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the size information. (Item 26) The acquisition unit 601, the humidity sensor 52, and the temperature sensor 51 are examples of third acquisition means for acquiring environmental information (e.g., temperature, humidity, etc.) indicating the environment where the sheet P is placed. The type determination unit 604 may determine the type of the sheet based on a combination of electrical characteristics, thermal characteristics, and environmental information. (Item 27) The acquisition unit 601 and the CPU 141 are examples of third acquisition means for acquiring the process speed (operating speed) applied to the sheet P. Since the CPU 141 controls the motors M1 to M4, it knows the rotation speeds of the motors M1 to M4 and the rotation speeds (operating speeds) of the rotating bodies rotationally driven thereby. The type determination unit 604 may determine the type of the sheet P based on a combination of electrical characteristics, thermal characteristics, and process speed. (Item 28) The acquisition unit 601 and the CPU 111 may function as third acquisition means for acquiring the degree of wear of at least one of the feeding means, the transfer means, the conveying means, the first rotating body, or the second rotating body. The CPU 141 holds the cumulative operating time or the cumulative number of rotations of the feeding means, the transfer means, the conveying means, the first rotating body, or the second rotating body in the non-volatile storage means (the non-volatile storage area of the memory 142). The cumulative operating time or the cumulative number of rotations indicates the degree of wear of the rotating body. The type determination unit 604 may determine the type of the sheet P based on a combination of electrical characteristics, thermal characteristics, and degree of wear. (Item 29) The CPU 141 can calculate the toner loading amount from image data etc. that is the source of the toner image. Therefore, the acquisition unit 601 and the CPU 111 may function as third acquisition means for acquiring the toner loading amount for the sheet P from the CPU 141. The type determination unit 604 may determine the type of the sheet P based on a combination of electrical characteristics, thermal characteristics, and toner loading amount. (Item 30, Item 31) The image forming system 100 and the image forming apparatus 120 may include a type determination unit 604 that determines the type of the sheet P based on a combination of the detection result of the electrical characteristics of the sheet P and the detection result of the thermal characteristics of the sheet P. That is, the functions described in FIG. 6 or FIG. 12 may be implemented in the CPU 141. The image forming apparatus 120 may incorporate the sheet determination apparatus 110.

[0127] The invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the claims are appended to disclose the scope of the invention.

Description of Reference Numerals

[0128] 26: Intermediate transfer belt, 32: Outer roller, 33: Transfer power supply, 41b: Current sensor, 4: Fixer, 41b: Second thermistor, 111: CPU

Claims

1. An image carrier, and transfer means to which a transfer voltage is applied to transfer a toner image carried on the image carrier onto a sheet, and first acquisition means for acquiring electrical characteristics of the sheet passing through a transfer nip portion formed by the transfer means A first rotating body heated by a heater, and a second rotating body facing the first rotating body, and second acquisition means for acquiring thermal characteristics of the sheet passing through a fixing nip portion formed by the first rotating body and the second rotating body Determination means for determining the type of the sheet based on the acquired electrical characteristics and the acquired thermal characteristics A sheet determination device having the above components

2. The image carrier, the transfer means, the heater, the first rotating body, and the second rotating body are provided in an image forming apparatus, and the image forming apparatus further includes Voltage application means for applying a transfer voltage for promoting transfer of the toner image to the transfer means First detection means for detecting electrical characteristics of the sheet passing through the transfer means Second detection means for detecting thermal characteristics of the sheet passing through the fixing nip portion The first acquisition means acquires the electrical characteristics detected by the first detection means, and the second acquisition means acquires the thermal characteristics detected by the second detection means. The sheet determination device according to claim 1

3. Third acquisition means for acquiring feeding characteristics of the sheet fed by feeding means Fourth acquisition means for acquiring conveyance characteristics of the sheet conveyed by conveyance means to the transfer means Further comprising The determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, the feeding characteristics, and the conveyance characteristics. The sheet determination device according to claim 1

4. Further comprising third acquisition means for acquiring feeding characteristics of the sheet fed by feeding means The determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the feeding characteristics. The sheet determination device according to claim 1

5. The feeding means A separation roller for separating one sheet from a plurality of sheets A motor for driving the separation roller, and having the above components The feeding characteristics include the rotational torque of the separation roller. The sheet determination device according to claim 4

6. Further comprising third acquisition means for acquiring conveyance characteristics of the sheet conveyed by conveyance means to the transfer means The sheet determination device according to claim 1, wherein the determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the conveyance characteristics.

7. The sheet determination device according to claim 6, wherein the third acquisition means acquires, as the conveyance characteristics, the conveyance time of the sheet or the torque required to drive a conveyance roller that conveys the sheet.

8. recording means for recording the degree of wear of the conveyance means; The sheet determination device according to claim 6, further comprising correction means for correcting the conveyance characteristics acquired by the third acquisition means according to the degree of wear of the conveyance means.

9. further comprising third acquisition means for acquiring the thickness of the sheet; The sheet determination device according to claim 1, wherein the determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the thickness.

10. further comprising third acquisition means for acquiring the basis weight of the sheet; The sheet determination device according to claim 1, wherein the determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the basis weight.

11. further comprising third acquisition means for acquiring the surface property of the sheet; The sheet determination device according to claim 1, wherein the determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the surface property.

12. The sheet determination device according to claim 1, wherein the electrical characteristics include the electrical resistance of the sheet.

13. The first acquisition means acquires a current flowing through the sheet passing through the transfer means and a shared voltage shared by the sheet among the transfer voltages, and obtains the electrical resistance of the sheet as the electrical characteristics based on the current and the shared voltage. The sheet determination device according to claim 12.

14. The first acquisition means acquires the moisture content of the atmosphere in which the sheet is placed and obtains the shared voltage based on the moisture content. The sheet determination device according to claim 13.

15. further comprising storage means for storing combinations of electrical characteristics and thermal characteristics for a plurality of different types of sheets; The determination means determines the type of the sheet based on the distance between the combination of the electrical characteristics and the thermal characteristics, and the combination of the electrical characteristics and the thermal characteristics for each of the plurality of different types of sheets stored in the storage means, in the sheet determination device according to claim 1.

16. The determination means obtains standardized electrical characteristics by dividing the difference between the electrical characteristics acquired by the first acquisition means and the average value of the plurality of electrical characteristics stored in the storage means by the standard deviation of the plurality of electrical characteristics stored in the storage means, obtains standardized thermal characteristics by dividing the difference between the thermal characteristics acquired by the second acquisition means and the average value of the plurality of thermal characteristics stored in the storage means by the standard deviation of the plurality of thermal characteristics stored in the storage means, obtains the distance between the combination of the standardized electrical characteristics for the electrical characteristics acquired by the first acquisition means and the standardized thermal characteristics for the thermal characteristics acquired by the second acquisition means, and the combination of the standardized electrical characteristics and the standardized thermal characteristics for each of the plurality of types of sheets stored in the storage means, and determines the type of the sheet based on the distance, in the sheet determination device according to claim 15.

17. The thermal characteristics are characteristics based on the temperature at a second position that is farther from the center than the first position at a first position closer to the center in the width direction orthogonal to the conveyance direction of the sheet in the fixing nip portion, and the temperature at the first position used for temperature control of the fixing nip portion, among the temperature at the first position and the temperature at the second position, in the sheet determination device according to claim 1.

18. a first temperature sensor that detects the temperature at the first position; a second temperature sensor that detects the temperature at the second position; and temperature control means that controls the heater so that the temperature at the first position becomes a target fixing temperature, wherein the thermal characteristics are characteristics based on the difference between the temperature at the second position and the target fixing temperature, in the sheet determination device according to claim 17.

19. The sheet determination device according to claim 18 further includes correction means for correcting the thermal characteristics according to the length in the conveyance direction of the sheet.

20. The sheet determination device according to claim 17, wherein the sheet is conveyed so that the center of the sheet passes through the center in the width direction of the fixing nip portion.

21. The sheet determination device according to claim 1, wherein the determination means obtains the type of the sheet output from the learned model by inputting the combination of the electrical characteristics and the thermal characteristics into the learned model.

22. The sheet determination device according to claim 21, wherein the learned model has a plurality of decision trees learned in parallel, and outputs the type of the sheet based on determination results output from the plurality of decision trees.

23. The image forming apparatus further includes display means for displaying a setting regarding the type of the sheet input by a user, The sheet determination device according to claim 2, wherein when the type of the sheet obtained by the sheet determination device is different from the type of the sheet input by the user, the display means displays warning information.

24. The sheet determination device according to claim 1, further comprising notification means for notifying a service person of the determination result of the sheet.

25. The sheet determination device further includes third acquisition means for acquiring size information of the sheet, The determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the size information.

26. The sheet determination device further includes third acquisition means for acquiring environment information indicating an environment in which the sheet is placed, The determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the environment information.

27. The sheet determination device further includes third acquisition means for acquiring a process speed applied to the sheet, The determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the process speed.

28. The sheet determination device further includes third acquisition means for acquiring a degree of consumption of at least one of a feeding means for feeding the sheet, a transfer means, a conveying means for conveying the sheet, the first rotating body, or the second rotating body, The determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the degree of consumption.

29. further comprising third acquisition means for acquiring the toner loading amount on the sheet, The determination means determines the type of the sheet based on a combination of the electrical characteristics, the thermal characteristics, and the toner loading amount. The sheet determination device according to claim 1.

30. an image carrier that carries a toner image; transfer means for transferring the toner image carried on the image carrier to a sheet; voltage application means for applying a transfer voltage for promoting the transfer of the toner image to the transfer means; first detection means for detecting the electrical characteristics of the sheet passing through the transfer means; fixing means for fixing the toner image on the sheet by applying heat to the toner image transferred to the sheet; second detection means for detecting the thermal characteristics of the sheet passing through the fixing means; determination means for determining the type of the sheet based on a combination of the detection result of the electrical characteristics of the sheet and the detection result of the thermal characteristics of the sheet; An image forming apparatus comprising:

31. an image carrier that carries a toner image; transfer means for transferring the toner image carried on the image carrier to a sheet; voltage application means for applying a transfer voltage for promoting the transfer of the toner image to the transfer means; first detection means for detecting the electrical characteristics of the sheet passing through the transfer means; fixing means for fixing the toner image on the sheet by applying heat to the toner image transferred to the sheet; second detection means for detecting the thermal characteristics of the sheet passing through the fixing means; determination means for determining the type of the sheet based on the detection result of the electrical characteristics of the sheet and the detection result of the thermal characteristics of the sheet; An image forming system comprising:

Images