Image forming system, and program

Abstract

To accurately detect the value of resistance of sheets, even when a bundle of sheets is exposed to an ambient environment for a long time and an imbalance in water content occurs in peripheral parts of the sheets.SOLUTION: An image forming system 1 comprises: a resistance detection sensor 37 that is provided on a conveyance path of sheets 9, and detects a value corresponding to the value of resistance of the sheets 9; and a control unit 31 that determines an image forming condition for the sheets 9 on the basis of the value corresponding to the resistance value detected by the resistance detection sensor 37. The control unit 31 determines the image forming condition for the sheets 9 without causing the resistance detection sensor 37 to detect an area within a predetermined distance range from an end of the sheet 9 and without using the value corresponding to the resistance value, but on the basis of a value detected from an area excluding the predetermined distance range from the end of the sheet 9.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming system and a program, and more particularly to a technique for detecting characteristics of paper used in image formation. [Background technology]

[0002] Image forming devices such as electrophotographic printers are widely used in the color printing industry. Image forming devices used in the production print (PP) field, which corresponds to the color printing industry, are required to be able to handle a wider variety of paper types than image forming devices used in general offices. In order to print high-quality images on such a wide variety of paper types, image forming devices used in production print detect the characteristics of the paper and print under image formation conditions that correspond to the detected characteristics.

[0003] Conventionally, an image forming apparatus has been proposed in which a resistance detector is provided in a paper transport path and detects the resistance value of the paper as the paper passes through the resistance detector (see, for example, Patent Document 1). This image forming apparatus detects the resistance value of the paper at a position immediately before an image is formed on the paper. Based on the detected resistance value, the image forming apparatus sets transfer conditions for transferring a toner image to the paper and prints the image on the paper. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-251057 Summary of the Invention [Problem to be solved by the invention]

[0005] However, after careful investigation, the inventors discovered that the resistance of the paper stored in the paper feed tray varies not only due to variations in the original composition but also due to variations in the moisture content of the paper. In other words, the more moisture the paper contains, the lower the resistance of the paper tends to be.

[0006] A paper feed tray contains stacks of multiple sheets of paper. Therefore, for example, if the ambient environment changes from low temperature and low humidity to high temperature and high humidity, moisture gradually penetrates from the outer surface of the stack, which is exposed to the ambient environment, toward the inside of the stack. For example, the first sheet at the top of the stack is exposed to the ambient environment on its entire surface. Therefore, moisture penetrates evenly across the entire surface of the first sheet. In contrast, for sheets in the center of the stack, only the edges of the four sides are exposed to the ambient environment. Therefore, moisture penetrates from the edges of the four sides of the sheet in the center of the stack. Therefore, if a stack of sheets is exposed to a high temperature and high humidity environment for a long period of time, the resistance value of the sheets in the center of the stack will differ significantly from the edges. The moisture content varies greatly, especially at the edges of the sheets, and the resistance value fluctuation range is also large.

[0007] On the other hand, image forming devices print images mainly in the center of the paper, so when setting image forming conditions, if the image forming device detects the resistance value at the periphery of the paper, the characteristics of the center of the paper where the image is printed will not be reflected, and optimal image forming conditions cannot be set.

[0008] In addition, in Patent Document 1, the resistance value is measured for each minute region from the leading edge to the trailing edge of the paper, and the transfer conditions are changed for each minute region to accommodate variations in the resistance value within the paper. However, paper is generally transported at high speed, and it is not easy to adjust the transfer conditions to match the changes in the resistance value on paper transported at high speed. Furthermore, when the transfer conditions are changed on the same paper, the changed transfer electric field may affect other toner images that have already been transferred, resulting in image defects such as scattered characters.

[0009] The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming system and a program that improve the detection accuracy when detecting the resistance value of paper and enable high-quality images to be formed on paper. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the invention of claim 1 is an image forming system comprising: a resistance detection unit provided in a paper transport path for detecting a value corresponding to the resistance value of the paper; and a control unit for determining image forming conditions based on the value detected by the resistance detection unit, wherein the control unit does not detect an area within a predetermined distance from the edge of the paper using the resistance detection unit or use the area as a value corresponding to the resistance value, and determines the image forming conditions for the paper based on the value corresponding to the resistance value detected from an area other than within the predetermined distance from the edge of the paper.

[0011] The invention according to claim 2 is the image forming system according to claim 1, characterized in that the predetermined distance is 40 mm or less.

[0012] The invention according to claim 3 is the image forming system according to claim 1, characterized in that the predetermined distance is 100 mm or less.

[0013] The invention of claim 4 is characterized in that in the image forming system of claim 1, the control unit determines the image forming conditions based on a value corresponding to the resistance value detected from the center of the paper by the resistance detection unit.

[0014] The invention of claim 5 is an image forming system of claim 1, further comprising a moisture detection unit located upstream of the resistance detection unit on the transport path, which detects the amount of moisture contained in the paper, and the control unit is configured to change the specified distance based on the detection result by the moisture detection unit.

[0015] The invention of claim 6 is an image forming system of claim 1, further comprising a transport control unit that controls the transport of paper in the transport path, and is characterized in that the transport control unit stops the transport of paper when a detection operation is performed by the resistance detection unit.

[0016] The invention of claim 7 is characterized in that, in the image forming system of claim 1, the resistance detection unit detects values ​​corresponding to resistance values ​​at multiple different locations in an area excluding the range of the specified distance from the edge of the paper, and the control unit determines the image forming conditions based on the values ​​detected at the multiple locations by the resistance detection unit.

[0017] The invention of claim 8 is an image forming system of claim 7, further comprising a transport control unit that controls the transport of paper in the transport path, and is characterized in that the transport control unit stops the transport of paper every time the resistance detection unit performs a detection operation at the multiple locations.

[0018] The invention of claim 9 is the image forming system of claim 1, wherein the transport path comprises a first transport path for guiding fed paper to a downstream image forming position, and a second transport path that branches off from the first transport path and purges and discharges paper without guiding it to the image forming position, and the resistance detection unit is configured to be provided on the second transport path.

[0019] The invention of claim 10 is the image forming system of claim 9, further comprising a transport control unit that controls the transport of paper in the transport path, wherein the transport control unit transports the first sheet of paper to the second transport path and causes the resistance detection unit to perform a detection operation, and transports the second and subsequent sheets of paper from the first transport path to the image forming position.

[0020] The invention of claim 11 is an image forming system of claim 10, further comprising a physical property detection unit that is located upstream of the branching point on the first transport path that branches off to the second transport path and detects physical property values ​​of the paper that are different from the resistance value of the paper, wherein the physical property detection unit detects the physical property values ​​of the paper each time a sheet of paper passes through, and the control unit corrects the value corresponding to the resistance value detected by the resistance detection unit from the first sheet of paper based on the physical property values ​​detected from the second sheet of paper and subsequent sheets of paper.

[0021] The invention according to claim 12 is the image forming system according to claim 11, characterized in that the physical property detection unit is a moisture detection unit that detects the amount of moisture contained in the paper.

[0022] The invention of claim 13 is characterized in that, in the image forming system of claim 1, it further comprises a discharge unit that is provided downstream of the resistance detection unit on the conveying path and that discharges residual charges on the paper.

[0023] The invention of claim 14 is characterized in that, in the image forming system of claim 1, it further comprises an image forming unit that forms an image on an area excluding the area within the range of the specified distance from the edge of the paper.

[0024] The invention of claim 15 is a program executed in an image forming system equipped with a resistance detection unit provided in a paper transport path for detecting the resistance value of the paper, which causes the image forming system to execute a resistance detection process that drives the resistance detection unit to detect a value corresponding to the resistance value of the paper, and a control process that determines image forming conditions based on the value corresponding to the resistance value detected by the resistance detection unit, wherein the control process is characterized in that it does not cause the resistance detection unit to detect an area within a predetermined distance from the edge of the paper, or does not use the area as a value corresponding to the resistance value, and determines image forming conditions for the paper based on the value corresponding to the resistance value detected from an area excluding the area within the predetermined distance from the edge of the paper. [Effects of the Invention]

[0025] According to the present invention, even if a stack of sheets has been exposed to the ambient environment for a long period of time and the moisture content is uneven at the periphery of the sheets, the resistance value of the sheets can be detected with high accuracy. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of an image forming system. [Figure 2] FIG. 2 is a block diagram showing a hardware configuration of the image forming apparatus. [Figure 3] FIG. 2 is a diagram showing sheets of paper stored in a paper feed tray. [Figure 4] 10 is a diagram showing changes in resistance value within the surface of a plurality of sheets included in a sheet stack. FIG. [Figure 5] FIG. 2 is a block diagram showing a hardware configuration of the paper characteristic detection device. [Figure 6] FIG. 2 is an enlarged view showing the internal configuration of the paper characteristic detection device. [Figure 7] FIG. 2 is a diagram illustrating a schematic configuration of a moisture detection sensor. [Figure 8] FIG. 2 is a perspective view showing a schematic configuration of a resistance detection sensor. [Figure 9] 10A and 10B are diagrams illustrating a detection operation by a resistance detection sensor. [Figure 10] 10 is a flowchart illustrating an example of a processing procedure performed by the paper property detection device. [Figure 11] 10 is a flowchart illustrating an example of a detailed procedure of a resistance value detection process. [Figure 12] 10 is a diagram illustrating an example of measurement points of resistance values ​​by a paper property detection device. FIG. [Figure 13] 10 is a diagram illustrating an example of the relationship between the amount of moisture contained in a sheet and the resistance value of the sheet. [Figure 14] FIG. 2 is a diagram showing an area on which an image is formed on a sheet by an image forming apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Elements common to the embodiments described below are designated by the same reference numerals, and redundant description thereof will be omitted.

[0028] FIG. 1 is a diagram showing a schematic configuration of an image forming system 1 according to an embodiment of the present invention. The image forming system 1 includes a paper feeder 20, a paper characteristic detection device 30, an image forming device 10, and a post-processing device 40. The paper feeder 20, the paper characteristic detection device 30, the image forming device 10, and the post-processing device 40 are arranged in this order along the X direction shown in FIG. 1 and are mechanically and electrically connected to one another. When the image forming system 1 starts executing a print job, the paper feeder 20 feeds a sheet of paper, such as printing paper, and transports the paper along a transport path 50. That is, the paper fed from the paper feeder 20 is transported sequentially through the paper characteristic detection device 30, the image forming device 10, and the post-processing device 40. The image forming system 1 forms an image on the paper as it passes through the image forming device 10. The paper on which the image has been formed undergoes post-processing, such as stapling and punching, in the post-processing device 40 and is then ejected to paper output trays 41 and 42.

[0029] The paper feed device 20 is equipped with a plurality of paper feed trays 21. A stack of multiple sheets of paper 9 is stored in the plurality of paper feed trays 21. The paper feed device 20 is equipped with a paper feed conveying section 22. The paper feed conveying section 22 picks up the paper 9 one by one from the paper feed tray 21 specified in the job among the plurality of paper feed trays 21 and sends it to the conveying path 50.

[0030] The paper characteristic detection device 30 detects the characteristics of the paper 9 fed from the paper feed device 20. For example, the paper characteristic detection device 30 measures the resistance value related to the electrical resistance of the paper 9 and detects the resistance value as the characteristic of the paper 9. When the characteristics of the paper 9 are detected, the paper characteristic detection device 30 outputs information related to the characteristics of the paper 9 to the image forming device 10. This allows the image forming device 10 to set the image formation conditions to optimal conditions according to the characteristics of the paper 9 fed from the paper feed device 20 and form an image on the paper 9. As a result, the image forming device 10 can form a high-quality image on the paper 9 according to the characteristics of the paper 9.

[0031] 2 is a block diagram showing the hardware configuration of image forming apparatus 10. Image forming apparatus 10 forms an image on paper 9 conveyed from upstream paper characteristic detection device 30. This image forming apparatus 10 includes control unit 11, storage unit 12, operation panel 13, paper conveyance unit 14, image forming unit 15, and communication unit 16.

[0032] The control unit 11 includes a hardware processor such as a CPU and a temporary storage memory such as a RAM. The hardware processor of the control unit 11 reads and executes a program 17 stored in the storage unit 12. This causes the control unit 11 to function as a job control unit 18. The job control unit 18 controls the storage unit 12, the operation panel 13, the paper transport unit 14, the image forming unit 15, and the communication unit 16. The job control unit 18 also comprehensively controls the execution of print jobs in the image forming system 1.

[0033] The storage unit 12 is a non-volatile storage device configured with a hard disk drive (HDD), a solid state drive (SSD), or the like. The storage unit 12 stores a program 17 and various data. The storage unit 12 also stores paper information about the paper 9 contained in the paper feed tray 21 of the paper feeder 20. The paper information includes information about the paper brand, size (paper width, paper length), basis weight (basis weight), and paper type (gloss coated paper, matte coated paper, plain paper, fine paper, rough paper, etc.). The storage unit 12 may also store control parameters that match image formation conditions determined according to the characteristics of the paper 9.

[0034] The operation panel 13 is a user interface when a user uses the image forming system 1. The operation panel 13 has a display unit and an operation unit, and accepts operations by the user. The display unit is composed of, for example, a color LCD display, and displays various operation screens that the user can operate. The operation unit is composed of, for example, a touch screen panel arranged on the screen of the display unit, or push button keys arranged around the screen of the display unit. For example, the operation panel 13 accepts an instruction from the user to start executing a job.

[0035] Paper transport unit 14 drives a plurality of transport rollers arranged on transport path 50 to transport paper 9 inside image forming device 10. As shown in FIG. 1, a paper inversion path 53 branching off from transport path 50 is provided inside image forming device 10. When double-sided printing of paper 9 is specified, paper transport unit 14 guides paper 9, on whose front side an image has been formed in image forming unit 15, from transport path 50 to paper inversion path 53. Paper transport unit 14 inverts paper 9 in paper inversion path 53, and then supplies paper 9 to image forming unit 15 again. In this way, double-sided printing is performed on paper 9.

[0036] The image forming unit 15 forms an image on the paper 9 as the paper 9 passes through a predetermined image forming position P while being conveyed along the conveying path 50. The image forming unit 15 forms an image on the paper 9, for example, by electrophotography. In this case, the image forming unit 15 includes an exposure unit, a photosensitive drum, and a developing unit corresponding to each color (Y (yellow), M (magenta), C (cyan), and K (black). The developing unit contains a two-component developer consisting of a toner and a carrier corresponding to each color. The image forming unit 15 also includes an intermediate transfer belt, a secondary transfer unit, and a fixing unit. The toner images of each color formed on the photosensitive drum by the developing unit are primarily transferred onto the intermediate transfer belt in a superimposed state to form a color image. The toner images primarily transferred onto the intermediate transfer belt are secondarily transferred onto the surface of the paper 9 by a secondary transfer unit provided at the image forming position P. The toner images transferred to the paper 9 are heated and pressurized in a fixing unit provided downstream of the image forming position P, and are fixed to the paper 9.

[0037] The communication unit 16 is an interface for the image forming apparatus 10 to communicate with other paper feeders 20, paper characteristic detectors 30, and post-processing apparatuses 40.

[0038] When the job control unit 18 starts executing a job, it assigns the paper feed tray 21 to the paper feed device 20 and starts the paper feed and transport operation for the paper 9. The job control unit 18 then acquires information about the characteristics of the paper 9 from the paper characteristic detection device 30 and determines the image formation conditions in the image forming unit 15 according to the characteristics of the paper 9 fed from the paper feed device 20. The job control unit 18 then determines control parameters for operating the image forming unit 15 and drives the image forming unit 15 based on the control parameters. For example, the job control unit 18 changes the transfer voltage applied to the secondary transfer unit according to the characteristics of the paper 9 so that the transfer current when the toner image is transferred to the paper 9 in the secondary transfer unit becomes a predetermined current. This ensures that the transfer current when the toner image is transferred from the intermediate transfer belt to the paper 9 is an optimal current according to the characteristics of the paper 9. As a result, the image forming unit 15 can perform the second transfer of almost 100% of the toner constituting the toner image on the intermediate transfer belt onto the paper 9.

[0039] Returning to FIG. 1 , post-processing device 40 includes sheet discharge trays 41 and 42, and a post-processing section 43. Inside post-processing device 40, conveying path 50 branches into two, and the ends of each conveying path 50 are led to sheet discharge trays 41 and 42. Post-processing section 43 is provided on one of the branched conveying paths 50, and performs post-processing on sheets 9. The post-processing performed by post-processing section 43 includes stapling and punching, as well as cutting, folding, and binding. It is sufficient for post-processing section 43 to perform at least one of these processes.

[0040] 3A and 3B are diagrams showing paper sheets 9 stored in paper feed tray 21. As shown in FIG. 3A, paper feed tray 21 stores a stack of multiple sheets 9. The example in FIG. 3A shows a stack of N sheets 9. When paper is fed by paper feeder 20, the sheets are sent out to transport path 50 in order, starting with the first sheet 9 at the top of the stack shown in FIG. 3A.

[0041] The stack of sheets stored in the sheet feed tray 21 is exposed to the ambient environment inside the sheet feeder 20. For example, if the ambient environment is a high-temperature, high-humidity environment, moisture contained in the ambient environment gradually permeates the stack of sheets over time. At this time, moisture gradually permeates from the outer periphery of the stack of sheets exposed to the ambient environment toward the inside of the stack of sheets.

[0042] FIG. 3(b) illustrates a state in which moisture has penetrated into the first sheet 9 at the top of a stack of sheets that has been exposed to a high-temperature, high-humidity environment (e.g., a temperature of 30°C and humidity of 80%) for a predetermined period of time or more (e.g., three hours or more). In FIG. 3(b), the density of the diagonal lines indicates the amount of moisture. As shown in FIG. 3(b), the first sheet 9 at the top of the stack of sheets has its entire surface exposed to the ambient environment. Therefore, as shown in FIG. 3(b), moisture has penetrated the entire surface of the first sheet 9 almost evenly. Note that this state is not limited to the first sheet 9, but also applies to sheets 9 near the top of the stack of sheets.

[0043] Figure 3(c) illustrates the state in which moisture has penetrated into the paper 9 in the center of the paper stack under the same conditions as Figure 3(b). In Figure 3(c), as in Figure 3(b), the density of the diagonal lines indicates the amount of moisture. As shown in Figure 3(c), only the four peripheral edges of the paper 9 in the center of the paper stack are exposed to the surrounding environment. Therefore, as shown in Figure 3(c), the paper 9 in the center of the paper stack contains more moisture at the peripheral edges of the four sides, and the amount of moisture in the center of the paper 9 is lower.

[0044] The moisture contained in the paper 9 changes the resistance value of the paper 9. Specifically, the greater the moisture content, the lower the resistance value of the paper 9. For example, when comparing the first sheet 9 at the top of a stack of paper with a sheet 9 in the center of the stack, the first sheet 9 will contain more moisture per unit area. Also, in the case of the first sheet 9, the change in resistance value within the surface of the paper is relatively small, whereas in the case of the sheet 9 in the center of the stack of paper, the change in resistance value within the surface of the paper is relatively large.

[0045] Fig. 4 is a diagram showing the change in resistance value within the surface of multiple sheets of paper 9 included in a stack of sheets of paper. As shown in Fig. 4, the first sheet 9 at the top of the stack of sheets of paper contains a relatively large amount of moisture across its entire surface, so the resistance value of the sheet 9 is lower than that of the other sheets of paper 9. Furthermore, since the first sheet 9 contains moisture almost evenly across its entire surface, the change in resistance value within the surface of the sheet is relatively small.

[0046] In contrast, the 10th, 30th, and 50th sheets of paper 9 in the center of the stack contain a relatively large amount of moisture at the edges and a small amount of moisture in the center of the sheet. As a result, the resistance value of the edges of the sheets is low within the surface of the sheets, while the resistance value of the center of the sheets is high. In other words, the change in resistance value within the surface of the sheets is large. Furthermore, because the moisture content of the sheets 9 in the center of the stack is less than that of the first sheet of paper 9, the resistance value of the sheets 9 in the center of the stack is higher than that of the first sheet of paper 9.

[0047] As shown in Figure 4, the resistance value of a sheet of paper 9 varies depending on the position of the sheet of paper 9 in the stack. In particular, for a sheet of paper 9 placed in the center of the stack of sheets, the resistance value varies widely in the area GA at the edge of the sheet of paper, as shown in Figure 4. Therefore, when detecting the resistance value of a sheet of paper 9, even if the resistance value is measured near the edge of the sheet of paper 9, the resistance value does not accurately represent the characteristics of the sheet of paper 9.

[0048] Therefore, the paper characteristic detection device 30 of this embodiment is configured not to detect the resistance value of the paper 9 in an area where the resistance value fluctuates widely, so that the paper characteristic detection device 30 can appropriately detect the characteristics of the paper 9. Such a paper characteristic detection device 30 will be described in detail below.

[0049] Fig. 5 is a block diagram showing the hardware configuration of paper property detection device 30. Fig. 6 is an enlarged view showing the internal configuration of paper property detection device 30. Paper property detection device 30 includes a control unit 31, a storage unit 32, a paper transport unit 33, a first physical property detection unit 34, a second physical property detection unit 36, a static elimination unit 38, and a communication unit 39. The communication unit 39 is an interface that enables paper property detection device 30 to communicate with image forming apparatus 10.

[0050] The control unit 31 includes a hardware processor such as a CPU and a temporary storage memory such as a RAM. The hardware processor of the control unit 31 reads and executes the program 17 stored in the storage unit 32. As a result, the control unit 31 functions as a transport control unit 61 and a characteristic detection unit 62. The transport control unit 61 controls the transport operation of the paper sheet 9 in the paper characteristic detection device 30. The characteristic detection unit 62 detects the characteristics of the paper sheet 9 transported to the paper characteristic detection device 30. The transport control unit 61 and the characteristic detection unit 62 will be described in detail below.

[0051] The storage unit 32 is a non-volatile storage device configured with a hard disk drive (HDD), a solid state drive (SSD), etc. The storage unit 32 stores the program 60 and various data. The storage unit 32 may also store correction data for correcting the resistance value of the paper 9 according to the amount of moisture detected from the paper 9.

[0052] The paper transport unit 33 drives a plurality of transport rollers arranged on a transport path 50 to transport the paper 9 inside the paper characteristic detection device 30. As shown in FIG. 6, the paper characteristic detection device 30 has two transport paths 50 for transporting the paper 9: a first transport path 51 and a second transport path 52. The first transport path 51 is a path that sends the paper 9 fed from the paper feeder 20 to the image forming device 10 and transports the paper 9 on which an image is formed. The first transport path 51 is formed as a path that penetrates the paper characteristic detection device 30 in the left-right direction (X direction). The second transport path 52 branches off from the first transport path 51 inside the paper characteristic detection device 30 and is a path that purges and discharges the paper 9 without sending it to the image forming device 10. The second transport path 52 is formed upward (Z direction) from a branching portion 65 provided on the first transport path 51 and discharges the paper 9 to a purge tray 67 provided at the top of the device. The branching section 65 is provided with a blade-shaped switching member 66 that switches whether the paper 9 is guided to the first transport path 51 or the second transport path 52. The paper transport section 33 transports the paper 9 to either the first transport path 51 or the second transport path 52 by swinging the blade-shaped switching member 66.

[0053] The first physical property detection unit 34 is provided on the first transport path 51. More specifically, the first physical property detection unit 34 is provided at a predetermined position upstream of the branching point 65 on the first transport path 51. The first physical property detection unit 34 detects the physical property of the paper 9 transported from the paper feeder 20. For example, the first physical property detection unit 34 detects the moisture contained in the paper 9. For this purpose, the first physical property detection unit 34 is equipped with a moisture detection sensor 35.

[0054] 7 is a diagram showing a schematic configuration of the moisture detection sensor 35. The moisture detection sensor 35 measures the moisture content of the paper 9. As shown in FIG. 7, the moisture detection sensor 35 includes a first light-emitting unit 71, a second light-emitting unit 72, a light-receiving unit 73, and lenses 75 and 76. The first light-emitting unit 71 and the second light-emitting unit 72 irradiate light toward the paper 9 being transported along the first transport path 51.

[0055] The first light emitter 71 emits first near-infrared light (reference light) in a specific wavelength band. For example, the first light emitter 71 is configured with an LED (Light Emitting Diode) or the like. The first near-infrared light that the first light emitter 71 irradiates toward the paper 9 is light whose absorption rate in the paper 9 when reflected by the paper 9 does not depend on the moisture content (moisture content) of the paper 9. The light receiver 73 receives, via a lens 76, the first near-infrared light that is irradiated from the first light emitter 71 to the paper 9 via a lens 75 and reflected by the paper 9. The light receiver 73 then outputs information about the first received light amount, which indicates the received amount of the first near-infrared light reflected by the paper 9, to the control unit 31. For example, the light receiver 73 is configured with a CCD (Charge-Coupled Device), a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor, or the like.

[0056] The second light-emitting unit 72 emits second near-infrared light in a specific wavelength band. For example, the second light-emitting unit 72 is composed of an LED or the like. The second near-infrared light that the second light-emitting unit 72 irradiates toward the paper 9 is light whose absorption rate in the paper 9 when reflected from the paper 9 varies depending on the moisture content (moisture content) of the paper 9. The light-receiving unit 73 receives, via a lens 76, the second near-infrared light that is irradiated from the second light-emitting unit 72 to the paper 9 via a lens 75 and reflected from the paper 9. The light-receiving unit 73 then outputs information regarding the second received light amount, which indicates the received light amount of the second near-infrared light reflected from the paper 9, to the control unit 31.

[0057] That is, the first light-emitting unit 71 and the second light-emitting unit 72 emit light of wavelengths that are absorbed by moisture in the paper 9 at different rates. The second near-infrared light emitted by the second light-emitting unit 72 has a wavelength that is more absorbed by moisture in the paper 9 than the first near-infrared light (reference light) emitted by the first light-emitting unit 71.

[0058] The control unit 31 calculates the moisture content of the paper 9 based on the ratio between the first amount of received light and the second amount of received light. The higher the moisture content of the paper 9, the greater the amount of second near-infrared light absorbed by the paper 9 and the smaller the amount of second received light. Therefore, the control unit 31 calculates the moisture content of the paper 9 based on a relational expression or table that shows the relationship between the ratio between the first amount of received light and the second amount of received light and the moisture content of the paper 9. The calculation of the moisture content of the paper 9 is performed by the characteristic detection unit 62 of the control unit 31.

[0059] The moisture detection sensor 35 detects the amount of moisture contained in the paper 9 each time the paper 9 is transported from the paper feeder 20. As described above, the amount of moisture contained in the paper 9 may not be uniform across the surface of the paper. In other words, due to the influence of the paper 9 being exposed to the surrounding environment, the moisture content of the peripheral portion of the paper 9 may be higher than that of the central portion. Therefore, when detecting the moisture content of the paper 9, the moisture detection sensor 35 preferably detects the moisture content of the central portion of the paper 9 rather than the peripheral portion of the paper 9.

[0060] The first physical property detection unit 34 may be configured to include a sensor other than the moisture detection sensor 35 and to detect additional physical properties of the paper sheet 9 other than the moisture content. For example, the first physical property detection unit 34 may be configured to include, in addition to the moisture detection sensor 35, a size detection sensor that detects the size of the paper sheet 9, a paper thickness detection sensor that detects the thickness of the paper sheet 9, a basis weight detection sensor that detects the basis weight of the paper sheet 9, etc. In this case, by locating the size detection sensor upstream of the moisture detection sensor 35, the moisture detection sensor 35 will be able to detect the moisture content in the center of the paper sheet 9 based on the size of the paper sheet 9 detected by the size detection sensor.

[0061] The second physical property detection unit 36 ​​is provided on the second transport path 52. That is, the second physical property detection unit 36 ​​detects the physical property of the paper 9 discharged to the purge tray 67 downstream of the first physical property detection unit 34. The second physical property detection unit 36 ​​detects a physical property of the paper 9 that is different from the physical property detected by the first physical property detection unit 34. For example, the second physical property detection unit 36 ​​detects the resistance value, which is the electrical resistance of the paper 9. For this reason, the second physical property detection unit 36 ​​is equipped with a resistance detection sensor 37.

[0062] 8 is a perspective view showing a schematic configuration of the resistance detection sensor 37. The resistance detection sensor 37 applies a high voltage between the front and back of the paper 9 while the transport of the paper 9 is stopped in the second transport path 52, and detects the electrical resistance (resistance value) of the paper 9 from the value of the current that flows. As shown in FIG. 8, the resistance detection sensor 37 includes a high-voltage power supply unit 80, a detection roller 81, and an opposing roller 82.

[0063] The detection roller 81 is arranged so as to be able to come into contact with one side of the paper 9. The detection roller 81 is configured such that a cylindrical roller member made of an elastic material such as conductive rubber is provided on the outer circumferential surface of a metal rotating shaft 81a, for example.

[0064] The opposing roller 82 is disposed opposite the detection roller 81 with the paper 9 sandwiched therebetween. The opposing roller 82 is disposed so as to be able to come into contact with the other surface of the paper 9. The opposing roller 82 is formed in a roller shape from, for example, a metal material. The opposing roller 82 is electrically grounded.

[0065] The high-voltage power supply unit 80 is a unit for applying a high voltage to the paper 9. The high-voltage power supply unit 80 is electrically connected to the detection roller 81 and the opposing roller 82. When the paper 9 is sandwiched between the detection roller 81 and the opposing roller 82, the high-voltage power supply unit 80, the detection roller 81, and the opposing roller 82 form an electrical closed circuit via the paper 9.

[0066] The high-voltage power supply unit 80 includes a high-voltage output unit 83 and a current detection unit 84. The high-voltage output unit 83 is electrically connected to the detection roller 81. The high-voltage output unit 83 applies a high voltage to the detection roller 81. For example, the high-voltage output unit 83 can apply a high voltage of 1 kV to 5 kV to the detection roller 81. When the high-voltage output unit 83 applies a high voltage to the detection roller 81, a current flows in a closed circuit via the paper 9 sandwiched between the detection roller 81 and the opposing roller 82. The current detection unit 84 detects the current flowing in the closed circuit due to the high-voltage voltage of the high-voltage output unit 83.

[0067] The current detected by the current detection unit 84 varies depending on the resistance value of the paper 9. Therefore, the resistance detection sensor 37 can detect the resistance value of the paper 9 by detecting the current flowing in the closed circuit via the paper 9. In this way, the resistance detection sensor 37 may not directly detect the resistance value of the paper 9, but may instead detect a value (e.g., a current) corresponding to the resistance value of the paper 9 as the resistance value of the paper 9.

[0068] As described above, the resistance value of the paper 9 may not be uniform across the paper surface. In other words, exposure of the paper 9 to the surrounding environment can cause unevenness in the amount of moisture across the paper surface, which in turn causes unevenness in the resistance value of the paper 9 across the paper surface. The resistance value of the paper 9 fluctuates significantly, particularly at the periphery of the paper 9. Therefore, the resistance detection sensor 37 is configured so that the detection roller 81 and the opposing roller 82 do not sandwich the entire paper width W1 of the paper 9, but only the center portion of the paper width W1. In other words, the length W2 of the detection roller 81 and the opposing roller 82 in the width direction perpendicular to the paper conveyance direction is smaller than the paper width W1 of the paper 9. The detection roller 81 and the opposing roller 82 are positioned at the center of the paper 9 in the width direction. Therefore, the resistance detection sensor 37 can detect the resistance value of the paper 9 at the center of the paper 9 in the width direction of the paper 9.

[0069] The second physical property detection unit 36 ​​may be configured to include a sensor other than the resistance detection sensor 37 and to detect additional physical properties of the paper 9 other than the resistance value. For example, the second physical property detection unit 36 ​​may be configured to include, in addition to the resistance detection sensor 37, a stiffness detection sensor that detects the stiffness of the paper 9, a surface property detection sensor that detects the surface property (surface state) of the paper 9, and the like.

[0070] The charge neutralizing unit 38 is provided downstream of the second physical property detection unit 36 ​​on the second transport path 52. A high voltage is applied to the paper 9 by the resistance detection sensor 37. As a result, residual charges remain on the paper 9 transported downstream from the second physical property detection unit 36, causing the paper 9 to become statically charged. If the paper 9 is purged and ejected as is, there is a possibility that static electricity will be discharged when the user tries to remove the purged and ejected paper 9. The charge neutralizing unit 38 is provided to prevent such discharge. In other words, the charge neutralizing unit 38 neutralizes any residual charges on the paper 9 before the paper 9 is purged and ejected.

[0071] The transport control unit 61 drives the paper transport unit 33 and controls the transport operation of the paper 9 in the paper characteristic detection device 30. When execution of a job is started in the image forming system 1, the paper feed device 20 starts feeding the paper 9. When the first sheet of paper 9 is transported into the paper characteristic detection device 30 in response to the start of job execution, the transport control unit 61 drives the switching member 66 of the branching unit 65 to transport the paper 9 to the second transport path 52. Then, when the first sheet of paper 9 reaches the detection position detected by the resistance detection sensor 37, the transport control unit 61 stops the transport operation of the paper 9.

[0072] When the paper 9 transported to the second transport path 52 is stopped at the detection position by the resistance detection sensor 37, the characteristic detection unit 62 drives the resistance detection sensor 37 to measure the resistance value of the paper 9.

[0073] Incidentally, the resistance value near the edge of the paper 9 may fluctuate widely due to the influence of the moisture content. For this reason, the characteristic detection unit 62 causes the resistance detection sensor 37 to perform a detection operation in an area other than within a predetermined distance from the edge of the paper 9 in the transport direction of the paper 9. In other words, the characteristic detection unit 62 does not cause the resistance detection sensor 37 to perform a detection operation when the detection position of the resistance detection sensor 37 is within an area within a predetermined distance from the edge of the paper 9 in the transport direction of the paper 9.

[0074] FIG. 9 is a diagram illustrating the detection operation by the resistance detection sensor 37. As shown in FIG. 9, the paper 9 is transported toward the detection roller 81 and opposing roller 82 of the resistance detection sensor 37. The resistance value of the paper 9 varies greatly in an area RA within a predetermined distance D from the leading edge 9a of the paper 9. Therefore, the characteristic detection unit 62 does not allow the resistance detection sensor 37 to detect the resistance value in the area RA. Furthermore, even if the resistance detection sensor 37 detects a resistance value in the area RA, the characteristic detection unit 62 may not use such a resistance value as a characteristic of the paper 9.

[0075] When an area RA within a predetermined distance D from the leading edge 9a of the paper 9 passes through a detection position where the detection roller 81 and the opposing roller 82 sandwich the area RA, the characteristic detection unit 62 does not stop the conveyance of the paper 9 and causes the conveyance control unit 61 to continue the conveyance of the paper 9. When the area RA within the predetermined distance D from the leading edge 9a of the paper 9 passes through the detection position, the characteristic detection unit 62 outputs a stop command to the conveyance control unit 61. The conveyance control unit 61 stops the conveyance of the paper 9 based on the stop command. At this time, an area RC in the center of the paper 9 is in the detection position where the area RC is sandwiched between the detection roller 81 and the opposing roller 82. In this state, the characteristic detection unit 62 drives the resistance detection sensor 37 to measure the resistance value of the paper 9. The area RC in the center of the paper 9 has little moisture content. Therefore, the resistance detection sensor 37 can detect the resistance value of the paper 9 with high accuracy. The characteristic detection unit 62 then detects the characteristics of the paper 9 based on the resistance value detected by the resistance detection sensor 37. When the characteristics of the paper 9 are detected, the characteristics detection unit 62 transmits information about the characteristics of the paper 9 to the control unit 11 of the image forming apparatus 10 via the communication unit 39. This allows the image forming apparatus 10 to determine image formation conditions according to the characteristics of the paper 9.

[0076] Furthermore, the resistance value of the paper 9 also fluctuates widely in an area RB within a predetermined distance D from the rear end 9b of the paper 9. Therefore, the characteristic detection unit 62 does not allow the resistance detection sensor 37 to detect the resistance value in the area RB. Furthermore, even if the resistance detection sensor 37 detects a resistance value in the area RB, the characteristic detection unit 62 may not use such a resistance value as a characteristic of the paper 9.

[0077] The predetermined distance D is set so as to include the area where the resistance value of the paper 9 varies by a predetermined value or more. For example, the predetermined distance D is set to a value of 40 mm or less. This prevents the resistance value in the area GA shown in FIG. 4 from being used to detect the characteristics of the paper 9. However, the size of the areas RA and RB near the edges of the paper 9 where the resistance value varies by a large value may vary depending on the type of paper 9. Therefore, it is preferable to set the predetermined distance D to a value of 100 mm or less. By setting the predetermined distance D to 100 mm or less, the resistance value of the paper 9 can be detected with high accuracy by excluding the area where the resistance value varies by a large value, even if the type of paper 9 varies to some extent.

[0078] The characteristic detection unit 62 can also change the predetermined distance D depending on the type of paper 9. For example, the characteristic detection unit 62 may set the predetermined distance D depending on the type of paper 9 specified in the job settings. The characteristic detection unit 62 may also determine the type of paper 9 based on the physical properties of the paper 9 detected by the first physical property detection unit 34, and set the predetermined distance D based on the determination result.

[0079] Furthermore, the characteristic detection unit 62 may drive the moisture detection sensor 35 when the first sheet of paper 9 is being transported along the first transport path 51, and set the predetermined distance D according to the moisture content of the first sheet of paper 9. This allows the predetermined distance D to be set according to the actual moisture content of the first sheet of paper 9. Therefore, the resistance value detected in the area RC, excluding the areas RA and RB within the predetermined distance D from the ends 9a and 9b of the sheet of paper 9, is not affected by uneven moisture content within the sheet of paper. Therefore, the resistance value of the sheet of paper 9 can be detected with high accuracy.

[0080] Furthermore, the characteristic detection unit 62 may perform detection operations using the resistance detection sensor 37 at multiple different locations in an area RC, excluding areas RA and RB, within a predetermined distance D from the ends 9a and 9b of the paper sheet 9. For example, the characteristic detection unit 62 may perform detection operations using the resistance detection sensor 37 in an area RC in the center of the paper sheet 9, and then cause the conveyance control unit 61 to convey the paper sheet 9 a certain distance. Then, while the conveyance of the paper sheet 9 is stopped, the characteristic detection unit 62 may perform detection operations using the resistance detection sensor 37 at a location different from the previous detection. By repeating this operation, the characteristic detection unit 62 can detect the characteristics of the paper sheet 9 based on the resistance values ​​detected at the multiple different locations. By detecting resistance values ​​at the multiple different locations, the characteristic detection unit 62 can detect the characteristics of the paper sheet 9 with high accuracy.

[0081] As described above, the resistance value of the first sheet of paper 9 at the start of job execution is detected on the second transport path 52. The first sheet of paper 9, whose resistance value has been detected, is neutralized by the neutralization unit 38 and then discharged to the purge tray 67.

[0082] The conveyance control unit 61 conveys the second and subsequent sheets of paper 9 fed from the paper feeder 20 during job execution along the first conveyance path 51 and supplies them to the image forming apparatus 10. In other words, the image forming apparatus 10 forms images on the second and subsequent sheets of paper 9 fed from the paper feeder 20. At this time, the control unit 11 of the image forming apparatus 10 determines the image formation conditions in the image forming unit 15 based on the characteristics of the paper 9 detected for the first sheet of paper 9. In particular, the job control unit 18 determines the transfer voltage to be applied to the secondary transfer unit to be a transfer voltage according to the resistance value of the paper 9. This allows the image forming apparatus 10 to form high-quality images on the paper 9.

[0083] Incidentally, the amount of moisture contained in the second and subsequent sheets of paper 9 fed from the paper feeder 20 may differ from the amount of moisture contained in the first sheet of paper 9. In particular, when images are formed continuously on multiple sheets of paper 9 during job execution, the difference between the moisture amount of the fed sheets of paper 9 and the moisture amount of the first sheet of paper 9 increases as the number of sheets of paper fed from the paper feeder 20 increases. Accordingly, the difference between the resistance value of the sheet of paper 9 being transported to the image forming device 10 and the resistance value of the first sheet of paper 9 also increases.

[0084] Therefore, when the second or subsequent sheets of paper 9 pass through the first transport path 51, the characteristic detection unit 62 activates the moisture detection sensor 35 to detect the moisture content of the sheets of paper 9. The characteristic detection unit 62 then corrects the resistance value detected from the first sheet of paper 9 based on the moisture content detected from the second or subsequent sheets of paper 9, and detects the characteristics of the second or subsequent sheets of paper 9 based on the corrected resistance value. The characteristic detection unit 62 then outputs the characteristics of the second or subsequent sheets of paper 9 to the control unit 11 of the image forming apparatus 10 via the communication unit 39. This allows the image forming apparatus 10 to determine image formation conditions according to the characteristics of the second or subsequent sheets of paper 9 when forming images on the second or subsequent sheets of paper 9 fed from the paper feed device 20.

[0085] Next, we will explain an example of a specific operation by the paper characteristic detection device 30. Figures 10 and 11 are flowcharts showing an example of a processing procedure by the paper characteristic detection device 30. This processing is performed by the hardware processor of the control unit 31 executing the program 60.

[0086] 10, when the paper characteristic detection device 30 starts this process, it waits until execution of a job is started in the image forming system 1 (step S10). When execution of the job is started (YES in step S10), the paper characteristic detection device 30 waits until a sheet of paper 9 is conveyed from the paper feed device 20 (step S11). When it detects that a sheet of paper 9 has been conveyed from the paper feed device 20 (YES in step S11), the paper characteristic detection device 30 determines whether the conveyed sheet of paper 9 is the first sheet of paper 9 since execution of the job started (step S12).

[0087] If the conveyed paper 9 is the first sheet of paper 9 (YES in step S12), paper characteristic detection device 30 detects the amount of moisture contained in the paper 9 as the first sheet of paper 9 passes the detection position of moisture detection sensor 35 (step S13). The amount of moisture detected at this time is stored in temporary storage memory of control unit 31. After detecting the amount of moisture, paper characteristic detection device 30 conveys the first sheet of paper 9 to second conveyance path 52 (step S14). Then, paper characteristic detection device 30 executes resistance value detection processing (step S15).

[0088] FIG. 11 is a flowchart showing an example of the detailed processing procedure of the resistance value detection process (step S15). When the paper characteristic detection device 30 starts the resistance value detection process, it sets a predetermined distance D that defines the size of areas RA and RB where resistance values ​​are not detected, based on the amount of moisture detected in step S13 (step S30). Then, the paper characteristic detection device 30 determines whether the leading edge 9a of the paper 9 has reached the detection position of the resistance detection sensor 37 (step S31). If the leading edge 9a of the paper 9 has reached the detection position of the resistance detection sensor 37 (YES in step S31), the paper characteristic detection device 30 continues conveying the paper 9 (step S32). As a result, the area RA near the leading edge of the paper 9 passes the detection position of the resistance detection sensor 37. At this time, the resistance detection sensor 37 does not perform a detection operation.

[0089] While continuing to transport the paper sheet 9, the paper characteristic detection device 30 determines whether the detection position of the resistance detection sensor 37 has entered an area RC outside the range of a predetermined distance D from the leading edge 9a of the paper sheet 9 (step S33). If the detection position of the resistance detection sensor 37 has entered an area RC outside the range of the predetermined distance D from the leading edge 9a of the paper sheet 9 (YES in step S33), the paper characteristic detection device 30 stops the transport operation of the paper sheet 9 (step S34). Then, the paper characteristic detection device 30 drives the resistance detection sensor 37 to measure the resistance value of the paper sheet 9 (step S35). That is, the paper characteristic detection device 30 measures the resistance value of the paper sheet 9 in an area RC at the center of the paper sheet 9, as shown in FIG. 9.

[0090] The paper characteristic detection device 30 measures the resistance value while the transport of the paper 9 is stopped, so it can measure the resistance value of the paper 9 with high accuracy. In contrast, if the resistance detection sensor 37 is driven to measure the resistance value while the paper 9 is being transported, the electrostatic capacitance component of the paper 9 will carry charge. The amount of charge carried by the transport of the paper 9 depends on the transport speed of the paper 9. Therefore, if the resistance value is measured while the paper 9 is being transported, the current value detected by the resistance detection sensor 37 will be high, and the detected resistance value will be lower than the actual resistance value of the paper 9. To prevent this, the paper characteristic detection device 30 measures the resistance value of the paper 9 while the transport of the paper 9 is stopped.

[0091] Next, the paper characteristic detection device 30 determines whether the resistance value of the paper 9 has been measured a predetermined number of times (step S36). If the number of measurements does not reach the predetermined number (NO in step S36), the paper characteristic detection device 30 transports the paper 9 a certain distance in the transport direction (step S37). For example, the transport distance of the paper 9 is several millimeters to several tens of millimeters. The processing by the paper characteristic detection device 30 then returns to step S34. That is, the paper characteristic detection device 30 stops the transport operation of the paper 9 after transporting the paper 9 a certain distance (step S34). Then, the paper characteristic detection device 30 measures the resistance value of the paper 9 again with the paper 9 stopped (step S35). If the number of measurements of the resistance value does not reach the predetermined number of times, the above operation is repeated.

[0092] FIG. 12 is a diagram illustrating locations where resistance values ​​are measured by the paper property detection device 30. The paper property detection device 30 repeatedly executes the processes of steps S34 to S37 to measure resistance values ​​at multiple locations P1 to P7, for example, as shown in FIG. 12. These multiple locations P1 to P7 are included in an area RC in the center of the paper 9, excluding areas RA and RB within a predetermined distance D from the edges 9a and 9b of the paper 9. Therefore, the resistance values ​​detected at the multiple locations P1 to P7 are all resistance values ​​that are not affected by uneven moisture content. Note that while FIG. 12 illustrates an example where resistance values ​​are measured at seven locations, the number of locations at which resistance values ​​are detected may be two or more.

[0093] Returning to the flowchart in Figure 11, when the paper characteristic detection device 30 measures the resistance value of the paper 9 a predetermined number of times (YES in step S36), it calculates the average value of the resistance values ​​obtained in the predetermined number of measurements (step S38). The paper characteristic detection device 30 detects this average value as the resistance value of the paper 9 (step S39). The paper characteristic detection device 30 then resumes the transport operation of the paper 9 (step S40). This completes the resistance value detection process.

[0094] Returning to the flowchart of Fig. 10, the paper characteristic detection device 30 detects the characteristics of the paper 9 based on the resistance value detected in the resistance value detection process (step S15) (step S16). Then, the paper characteristic detection device 30 outputs the characteristics of the paper 9 to the image forming device 10 (step S17).

[0095] Furthermore, the paper characteristic detection device 30 neutralizes the paper 9 when the paper 9 being transported on the second transport path 52 passes through the neutralization unit 38 (step S18). Then, the paper characteristic detection device 30 ejects the neutralized paper 9 onto the purge tray 67 (step S19).

[0096] The paper characteristic detection device 30 determines whether execution of the job has finished (step S20). If execution of the job has not finished (step S20), the processing by the paper characteristic detection device 30 returns to step S11. Then, when the next paper sheet 9 is conveyed from the paper feeder 20, the paper characteristic detection device 30 determines whether it is the first sheet of paper 9 (step S12). If the conveyed paper sheet 9 is the second or subsequent sheet of paper (NO in step S12), the paper characteristic detection device 30 executes the processing of steps S21 to S25.

[0097] When the second or subsequent sheets of paper 9 pass the detection position of the moisture detection sensor 35, the paper characteristic detection device 30 detects the amount of moisture in the sheets of paper 9 (step S21). Then, the paper characteristic detection device 30 corrects the resistance value detected in step S15 based on the amount of moisture detected in the second or subsequent sheets of paper 9 and the amount of moisture detected in the first sheet of paper 9 (step S22). This correction provides the resistance value of the second or subsequent sheets of paper 9.

[0098] FIG. 13 is a diagram illustrating the relationship between the amount of moisture contained in a sheet of paper 9 and the resistance value of the sheet of paper 9. As shown in FIG. 13, as the amount of moisture contained in a sheet of paper 9 increases, the resistance value of the sheet of paper 9 tends to decrease. Here, assume that the amount of moisture detected from the first sheet of paper 9 is A1, and the amount of moisture detected from the second sheet of paper 9 and subsequent sheets of paper 9 is A2. In this case, the resistance value of the first sheet of paper 9 is R1, and the resistance value of the second sheet of paper 9 and subsequent sheets of paper 9 is R2. The difference between the resistance values ​​R1 and R2 is ΔR.

[0099] When the paper characteristic detection device 30 detects the moisture content of the second or subsequent sheets of paper 9, it calculates the difference value ΔR in the resistance values ​​from the relationship shown in Fig. 13. Then, the paper characteristic detection device 30 corrects the resistance value detected in step S15 based on the difference value ΔR. This allows the paper characteristic detection device 30 to properly detect the resistance values ​​of the second or subsequent sheets of paper 9 without actually measuring the resistance values ​​of the second or subsequent sheets of paper 9.

[0100] When the paper characteristic detection device 30 detects the resistance value of the second or subsequent sheet of paper 9 (step S22), it detects the characteristics of the second or subsequent sheet of paper 9 (step S23). Then, the paper characteristic detection device 30 outputs the characteristics of the sheet of paper 9 to the image forming device 10 (step S24). This allows the image forming device 10 to determine appropriate image formation conditions according to the characteristics of the sheet of paper 9 when forming images on the second or subsequent sheet of paper 9.

[0101] Thereafter, the paper characteristic detection device 30 repeatedly executes the processes of steps S21 to S25 until the execution of the job is completed in the image forming system 1. Therefore, the image forming device 10 can perform image formation while changing the image formation conditions for each sheet of paper 9 based on the characteristics of the sheet of paper 9 detected by the upstream paper characteristic detection device 30. This allows the image forming system 1 to form high-quality images on all of the multiple sheets of paper 9 that are continuously fed during the execution of the job.

[0102] Furthermore, when forming an image on the sheet 9, the image forming device 10 preferably forms the image in a central region RC of the sheet 9, excluding regions RA and RB where the resistance value of the sheet 9 fluctuates widely. FIG. 14 is a diagram showing the region where an image is formed on the sheet 9 by the image forming device 10. As shown in FIG. 14, the image forming device 10 forms an image 90 in the region RC of the sheet 9, excluding regions RA and RB where the resistance value of the sheet 9 is not detected. The regions RA and RB where the resistance value is not detected are regions where the resistance value fluctuates widely. Therefore, if the image 90 were to be formed in these regions RA and RB, an appropriate transfer current would not be secured during the secondary transfer of the toner image, resulting in transfer omissions and degradation of image quality. To prevent such degradation of image quality, the image forming device 10 forms the image in a central region RC of the sheet 9, excluding regions RA and RB where the resistance value of the sheet 9 fluctuates widely.

[0103] For example, when the paper characteristic detection device 30 determines the predetermined distance D, it outputs information about the predetermined distance D to the image forming device 10. This allows the image forming device 10 to grasp the predetermined distance D and identify the sizes of the areas RA and RB where the resistance value fluctuation range is large near the edges 9a and 9b of the paper 9. Therefore, the image forming device 10 shifts the position where the image 90 is to be formed to the center of the paper 9 in the transport direction of the paper 9, thereby preventing the image from being formed in the areas RA and RB.

[0104] However, if an area that avoids the areas RA and RB on the paper 9 is specified as the layout position of the image to be printed in the job settings, the image forming apparatus 10 does not need to shift the image 90 as described above.

[0105] As described above, the paper characteristic detection device 30 provided in the image forming system 1 detects the resistance value of the paper 9 upstream of the image forming device 10 and detects the characteristics of the paper 9 based on the resistance value of the paper 9. This paper characteristic detection device 30 is configured to detect the characteristics of the paper 9 based on the resistance value detected from the area RC excluding the area within a predetermined distance D from the edges 9a and 9b of the paper 9. In other words, even if moisture has penetrated the peripheral edges of the paper 9 due to exposure of a stack of sheets to the ambient environment, the paper characteristic detection device 30 does not detect the resistance value from the peripheral edges of the paper 9 where moisture has penetrated, but detects the resistance value from the center of the paper 9. This allows the paper characteristic detection device 30 to detect the resistance value of the area RC in the center of the paper 9 where an image is formed in the image forming device 10. Therefore, when forming an image on the paper 9, the image forming device 10 can form a high-quality image by setting image formation conditions based on the characteristics of the paper 9 detected by the paper characteristic detection device 30.

[0106] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible.

[0107] For example, in the above embodiment, the image forming conditions are determined by the control unit 11 of the image forming apparatus 10. However, the image forming conditions for the paper 9 may be determined by the control unit 31 in the paper characteristic detection device 30.

[0108] In the above embodiment, the paper characteristic detection device 30 detects the resistance value of the paper 9, and the image forming apparatus 10 controls the transfer voltage when secondarily transferring the image to the paper 9 based on the resistance value of the paper 9. However, the control using the resistance value of the paper 9 is not necessarily limited to the control of the transfer voltage. In other words, the resistance value of the paper 9 may be used when determining image formation conditions other than the transfer voltage.

[0109] In the above embodiment, the program 60 executed by the hardware processor of the paper characteristic detection device 30 is pre-stored in the storage unit 32. However, the program 60 is not limited to being pre-stored in the storage unit 32. In other words, the program 60 can be traded independently of the paper characteristic detection device 30. In this case, the program 60 may be provided in a downloadable form via a network such as the Internet. The program 60 may also be provided in a state recorded on a computer-readable recording medium, for example. [Explanation of symbols]

[0110] 1. Image forming system 9 Paper 10 Image forming device 15 Image forming unit 30 Paper characteristic detection device 31 Control Unit 34 First physical property detection unit 35 Water detection sensor (moisture detection part) 36 Second physical property detection unit 37 Resistance detection sensor (resistance detection part) 38 Static elimination unit 50 Transport Route 51 First transport route 52 Second transport route 60 Programs 61 Transport control unit 62 Characteristics detection unit

Claims

1. a resistance detection unit provided on a paper transport path and configured to detect a value corresponding to the resistance value of the paper; a control unit that determines image forming conditions for a sheet based on the value detected by the resistance detection unit; Equipped with The control unit determines the image forming conditions based on the values ​​detected from an area excluding the area within the predetermined distance from the edge of the paper, without causing the resistance detection unit to detect the area within the predetermined distance, or without using the values ​​detected by the resistance detection unit within the predetermined distance.

2. 2. The image forming system according to claim 1, wherein the predetermined distance is 40 mm or less.

3. 2. The image forming system according to claim 1, wherein the predetermined distance is 100 mm or less.

4. 2. The image forming system according to claim 1, wherein the control unit determines the image forming conditions based on a value corresponding to a resistance value detected from the center of the paper by the resistance detection unit.

5. a moisture detection unit that is provided upstream of the resistance detection unit in the conveyance path and detects the amount of moisture contained in the paper; Further provided with 2. The image forming system according to claim 1, wherein the control unit changes the predetermined distance based on a result of detection by the moisture detection unit.

6. a transport control unit that controls transport of the paper in the transport path; Further provided with 2. The image forming system according to claim 1, wherein the transport control unit stops transport of the paper when the resistance detection unit performs a detection operation.

7. the resistance detection unit detects values ​​corresponding to resistance values ​​at a plurality of different locations in an area excluding a range of the predetermined distance from an edge of the paper; 2. The image forming system according to claim 1, wherein the control unit determines the image forming conditions based on the values ​​detected at the plurality of locations by the resistance detection unit.

8. a transport control unit that controls transport of the paper in the transport path; Further provided with 8. The image forming system according to claim 7, wherein the transport control unit stops transport of the paper every time the resistance detection unit performs a detection operation at the plurality of locations.

9. The transport path is a first transport path for guiding the fed paper to a downstream image forming position; a second transport path that branches off from the first transport path and purges and discharges the paper without guiding it to the image forming position; Equipped with 2. The image forming system according to claim 1, wherein the resistance detection unit is provided on the second transport path.

10. a transport control unit that controls transport of the paper in the transport path; Further provided with The image forming system according to claim 9, characterized in that the transport control unit transports the first sheet of paper to the second transport path to perform a detection operation using the resistance detection unit, and transports the second and subsequent sheets of paper from the first transport path to the image forming position.

11. a physical property detection unit that is provided on the first transport path upstream of a branching portion that branches into the second transport path and detects a physical property value of the paper that is different from the resistance value of the paper; Further provided with the physical property detection unit detects a physical property value of the paper every time the paper passes through; The image forming system according to claim 10, wherein the control unit corrects the value corresponding to the resistance value detected by the resistance detection unit from the first sheet of paper based on the physical property values ​​detected from the second sheet of paper and thereafter.

12. 12. The image forming system according to claim 11, wherein the physical property detection unit is a moisture detection unit that detects the amount of moisture contained in the paper.

13. a charge removal unit that is provided downstream of the resistance detection unit in the conveyance path and that removes residual charge from the paper; 2. The image forming system according to claim 1, further comprising:

14. an image forming unit that forms an image on an area excluding the area within the predetermined distance from the edge of the paper; 2. The image forming system according to claim 1, further comprising:

15. A program executed in an image forming system having a resistance detection unit that is provided in a paper transport path and detects a resistance value of paper, the program comprising: a resistance detection process for driving the resistance detection unit to detect a value corresponding to the resistance value of the paper; a control process for determining image forming conditions based on a value corresponding to the resistance value detected by the resistance detection unit; Execute The control process is a program characterized in that it is a process of determining image formation conditions for paper based on the value corresponding to the resistance value detected from an area excluding the area within the specified distance from the edge of the paper, without having the resistance detection unit detect the area within the specified distance from the edge of the paper, or not using the area as a value corresponding to the resistance value.

Images