Image forming system and non-transitory computer readable medium

Abstract

To suppress a burden on an operator and to suppress consumption of consumables.SOLUTION: The image forming system includes a first detector disposed on an upstream side of the image former in a conveyance direction of the sheet in the conveyance path and configured to detect a characteristic value corresponding to a moisture content of the conveyed sheet, and a controller configured to determine whether the characteristic value detected by the first detector is stable, and start image formation by the image former when it is determined that the characteristic value is stable.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an image forming system and a control program. [Background technology]

[0002] In order to produce printed materials of consistent quality, a trial print may be made before the actual printing to check whether the condition of the paper is appropriate and whether there are any problems with the print settings or image formation conditions of the image forming device for this paper.

[0003] For example, in the printing system disclosed in Patent Document 1, when printing on a roll of continuous paper, if a test print is instructed, a broken paper mark is added to the side of the continuous paper to distinguish the area to be printed. Then, when an instruction to switch from test print to regular print is received from the operator via a panel, the test print with the broken paper mark is terminated and regular print begins. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-12294 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the printing system disclosed in Patent Document 1, the switch from test printing to actual printing is performed by an operator who confirms print quality, such as image quality, and then issues an instruction via a panel. This presupposes operator supervision, which requires significant operator skill and workload. Furthermore, there is a risk of variations in print quality depending on the operator's skill. Furthermore, test printing consumes consumables such as paper, ink, and toner.

[0006] The present invention has been made in view of the above circumstances, and has as its object to reduce the burden on the operator and to reduce the consumption of consumables. [Means for solving the problem]

[0007] The above object of the present invention can be achieved by the following means.

[0008] (1) an image forming unit that forms an image on a sheet conveyed through a conveyance path; a first detection unit that is disposed on the conveyance path upstream of the image forming unit in the sheet conveyance direction and that detects a characteristic value corresponding to the moisture content of the conveyed sheet; a control unit that determines whether the characteristic value detected by the first detection unit is stable, and when it is determined that the characteristic value is stable, starts image formation by the image forming unit; An image forming system comprising:

[0009] (2) Equipped with a paper feed tray that can store multiple sheets of paper, The first detection unit detects the sheets continuously fed and conveyed from the sheet feed tray, The image forming system according to (1) above, wherein the control unit makes the determination based on changes in the characteristic values ​​of a plurality of sheets of paper.

[0010] (3) The image forming system according to (2), wherein the control unit makes the determination based on a change in a moving average of the characteristic value for a first predetermined number of sheets of paper that have been continuously conveyed.

[0011] (4) The image forming system described in (2) above, wherein the control unit executes a purge process in which the paper detected by the first detection unit is discharged to the discharge unit without forming an image on it until it is determined that the paper has stabilized.

[0012] (5) The conveying path includes a purge conveying path branching off from the conveying path upstream of the image forming unit and downstream of the first detection unit, In the image forming system according to (4), in the purging process, the paper is discharged via the purging transport path.

[0013] (6) The image forming system described in (2) above, wherein the control unit interrupts the detection operation by the first detection unit if it does not determine that the sheet has stabilized even after transporting a second predetermined number of sheets of paper.

[0014] (7) The image forming system according to (6) above, wherein the control unit interrupts the printing and notifies the user that the characteristics of the paper in the paper feed tray are not stable.

[0015] (8) The image forming system according to (1) above, wherein the control unit sets control parameters for the image forming unit based on the characteristic value when it is determined that the characteristic value has stabilized.

[0016] (9) A second detection unit is further provided to detect one or more characteristic values ​​of paper types other than the moisture content, The image forming system described in (8) above, wherein the control parameters of the image forming unit are set based on a plurality of characteristic values ​​obtained by detecting the paper when the first detection unit and the second detection unit determine that the paper is stable.

[0017] (10) The image forming system according to (8) or (9), wherein the control parameters include control parameters relating to at least one of transfer, fixing, and transport.

[0018] (11) After the image forming unit starts image formation, the first detection unit continues to detect the characteristic value of the paper. The image forming system described in (1) above, wherein the control unit interrupts image formation by the image forming unit when it determines that the characteristic value detected by the first detection unit is not stable during image formation.

[0019] (12) The control unit continues to detect the characteristic value of the paper using the first detection unit even after the interruption. The image forming system according to (11) above, wherein the control unit resumes image formation by the image forming unit when it determines that the characteristic value detected by the first detection unit has stabilized.

[0020] (13) a step (a) of detecting a characteristic value of the paper by a first detection unit that is disposed on the upstream side of the image forming unit in the paper conveyance direction in the conveyance path and detects a characteristic value corresponding to the moisture content of the conveyed paper; a step (b) of determining whether the characteristic value detected in the step (a) is stable, and when it is determined that the characteristic value is stable, starting image formation by the image forming unit; A control program that causes a computer to execute a process including the above. [Effects of the Invention]

[0021] The image forming system according to the present invention includes an image forming unit that forms an image on a sheet of paper transported along a transport path, a first detection unit that is located on the transport path upstream of the image forming unit in the paper transport direction and that detects a characteristic value corresponding to the moisture content of the transported sheet of paper, and a control unit that determines whether the characteristic value detected by the first detection unit is stable and, if it is determined that the characteristic value is stable, starts image formation by the image forming unit. This reduces the burden on an operator and reduces consumption of consumables. [Brief explanation of the drawings]

[0022] Advantages and features provided by one or more embodiments of the present invention will be more fully understood from the following detailed description and the accompanying drawings, which are for purposes of illustration only and are not intended to be limiting. [Figure 1] 1 is a diagram showing a schematic configuration of an image forming system according to an embodiment of the present invention; [Figure 2] FIG. 1 is a block diagram of an image forming system. [Figure 3] FIG. 2 is a block diagram of a paper characteristic detection device. [Figure 4]FIG. 2 is a diagram illustrating a schematic configuration of a paper characteristic detection device. [Figure 5] FIG. 1 is a diagram showing a schematic configuration of a moisture percentage sensor. [Figure 6] FIG. 2 is a diagram showing a schematic configuration of a basis weight sensor. [Figure 7A] FIG. 10 is a block diagram showing a process for determining control parameters from paper characteristics in the first example. [Figure 7B] FIG. 10 is a block diagram showing a process for determining control parameters from paper characteristics in a second example. [Figure 8] 4 is a flowchart showing a printing process in the first embodiment. [Figure 9] 9 is a subroutine flowchart showing the change amount calculation process in step S05 of FIG. 8. [Figure 10] 10 is a graph showing the change in moisture content of sheets continuously transported from a sheet feed tray. [Figure 11A] 10 is a flowchart showing a printing process in the second embodiment. [Figure 11B] 11B is a flowchart showing a printing process executed following FIG. 11A. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In the description of the drawings, identical elements are designated by the same reference numerals, and redundant description will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for convenience of explanation and may differ from the actual proportions. In the drawings, the up-down direction (vertical direction) is referred to as the Z direction, the front and rear directions of the image forming system or paper characteristic detection device are referred to as the Y direction, and the direction perpendicular to these Y and Z directions is referred to as the X direction. The X direction is also referred to as the paper transport direction. The Y direction is also referred to as the width direction. In this embodiment, paper includes printing paper (hereinafter simply referred to as paper) and various films. In particular, paper includes paper made from plant-derived mechanical pulp and / or chemical pulp. In addition, types of paper include coated glossy paper and matte paper, and uncoated plain paper and fine paper, etc.

[0024] Furthermore, cut paper is used as the paper, but continuous paper (roll paper) may also be used. When cut paper is used, the paper characteristic detection device performs measurement once for each sheet of paper. When continuous paper is used, the paper characteristic detection device performs measurement at a cycle equivalent to one cut sheet of paper (e.g., equivalent to A3). Furthermore, the following description will use an electrophotographic method using toner as an example of the type of image forming apparatus, but other methods such as inkjet methods may also be used.

[0025] Fig. 1 is a diagram showing a schematic configuration of an image forming system 1000 according to this embodiment. Fig. 2 is a block diagram showing a hardware configuration of the image forming system 1000. As shown in Fig. 1, the image forming system 1000 includes an image forming apparatus 10, a paper feeder 20, a paper characteristic detection device 30, and a post-processing device 40, which are mechanically and electrically connected to one another. The image forming system 1000 is also connected to a terminal device 80 such as a PC.

[0026] (Image forming apparatus 10) Image forming apparatus 10 forms an image on paper 90 sent from upstream paper characteristic detection device 30. Image forming apparatus 10 includes control unit 11, memory unit 12, image forming unit 13, paper feed conveyance unit 14, operation panel 15, printer controller 17, communication unit 19, etc. These are connected to each other via signal lines such as a bus for exchanging signals.

[0027] (Control unit 11) The control unit 11 is composed of a CPU, ROM, RAM, etc. The control unit 11 executes various processes by executing programs stored in the ROM or in the storage unit 12 (described later), and controls each unit of the device and performs various arithmetic processing according to the programs. The control unit 11 functions as an overall control unit 111, an engine control unit 112, a paper characteristic detection device control unit 113, a post-processing device control unit 114, a paper feeder control unit 115, and a conveyance / image formation control unit 116. The functions of these sub-control units 111 to 116 will be described later.

[0028] (Storage unit 12) The storage unit 12 comprises auxiliary storage units such as a ROM for storing various programs and data in advance, a RAM for temporarily storing programs and data as a working area, and a hard disk for storing various programs and data. The storage unit 12 also stores information about the paper stored in each paper feed tray. The paper information includes information about the paper brand, size (paper width, paper length), 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 paper brands, a determination model (determination model algorithm) used to determine control parameters, and a paper profile.

[0029] (Image forming unit 13) Image forming unit 13 forms an image, for example, by electrophotography. Image forming unit 13 includes writing units corresponding to the basic colors of Y (yellow), M (magenta), C (cyan), and K (black), photosensitive drums, and developing units that contain two-component developers consisting of toner and carrier for each color. Image forming unit 13 also includes an intermediate transfer belt, a secondary transfer unit, and a fixing unit. Toner images formed on the photosensitive drums by the developing units for each color are superimposed on the intermediate transfer belt and transferred to paper 90 conveyed in the secondary transfer unit. The toner images on paper 90 are fixed to paper 90 by applying heat and pressure in a fixing unit downstream.

[0030] (Paper feed conveyance section 14) The paper feed conveyance unit 14 includes conveyance paths 141 and 142, multiple paper feed trays 145, etc. The conveyance path 141 includes multiple pairs of conveyance rollers provided along the conveyance path, and a drive motor (not shown) that drives these pairs of conveyance rollers. The paper feed conveyance unit 14 includes a feed roller that feeds the uppermost sheet of multiple sheets of paper 90 stacked and placed in the paper feed tray 145, and sends (feeds) the sheets of paper 90 in the paper feed tray one by one to the downstream conveyance path. A first conveyance path 341 of the paper characteristic detection device 30 is connected to the upstream side of the conveyance path 141.

[0031] The paper feed conveyance unit 14 conveys paper 90 fed from a paper feed tray 145 or the like. After an image is formed on the paper 90 conveyed along the conveyance path 141 by the image forming unit 13, the paper 90 is discharged onto the paper output tray 41 via the subsequent post-processing device 40. When performing double-sided printing, in which an image is also formed on the back side of the paper 90, the paper 90 with an image formed on one side is conveyed to a conveyance path 142 for double-sided image formation located at the bottom of the device main body. The paper 90 conveyed to this conveyance path 142 is turned over on a switchback path, and then merges with the conveyance path 141 for single side printing, where an image is again formed on the other side of the paper 90 by the image forming unit 13.

[0032] (Operation panel 15, etc.) Operation panel 15 is equipped with a touch screen, numeric keypad, start button, stop button, etc., and displays the status of image forming apparatus 10 or image forming system 1000, and is used by the user to set the type of paper placed in paper feed tray 145, etc., and to input instructions. Furthermore, operation panel 15 displays a warning to the user if the stabilization of the paper condition, which will be described later, cannot be achieved within a predetermined number of sheets.

[0033] Printer controller 17 acquires a print job sent from a terminal device such as a PC (personal computer). The print data (image data) contained in this print job, written in PDL (Page Description Language) or PDF format, is rasterized by printer controller 17 and converted into raster-format image data for each page, which is then temporarily stored in page memory. The image data from the page memory is read out at a predetermined timing and stored in a buffer, and is output as an exposure signal to the writing unit for each main scanning line, synchronized with the write timing.

[0034] The communication unit 19 is an interface for communicating with other devices.

[0035] (Sub-control units 111 to 116) When a print job is input, the overall control unit 111 causes the engine control unit 112 to execute the print job based on the print job setting information of the input print job. The print job is input based on instructions sent from an external terminal such as the operation panel 15 or a network-connected terminal device 80 operated by a user.

[0036] The engine control unit 112 controls the post-processing device control unit 114, the paper feeder control unit 115, and the conveyance / image formation control unit 116 to perform printing processing such as that shown in FIG. 5, which will be described later. The post-processing device control unit 114 controls the post-processing device 40. Specifically, the post-processing device control unit 114 transmits, to the post-processing device 40, paper conveyance timing, setting information for post-processing of the conveyed paper, etc. The paper feeder control unit 115 controls the paper feeder 20. Specifically, the paper feeder control unit 115 communicates with the paper feeder 20 to send and receive information such as the paper feed tray to be used and the paper conveyance timing.

[0037] The conveyance / image formation control unit 116 controls the paper feed / conveyance unit 14 (including drive motors for the conveyance paths 141, 142, the fixing unit, etc.) to control the paper feed / conveyance of the paper 90. The conveyance / image formation control unit 116 also controls the image forming unit 13, and controls the image formation conditions and the image formation timing according to the paper position.

[0038] The paper characteristic detection device control unit 113 controls the paper characteristic detection device 30 in response to an execution instruction request from the engine control unit 112, and causes the various sensors included in the paper characteristic detection device 30 to measure the paper characteristics.

[0039] (Paper feeder 20) As shown in FIG. 1, the paper feeder 20 includes a paper feed conveying section 24. The paper feed conveying section 24 has the same functions as the paper feed conveying section 14 described above. In addition to the paper feed conveying section 24, the paper feeder 20 also includes a control section, a memory section, and a communication section (none of which are shown), which are interconnected via signal lines such as a bus for exchanging signals. The paper feed conveying section 24 includes multiple paper feed trays 245 and a conveying path 241. The conveying path 241 is connected to the conveying path 341. Paper 90 fed from each paper feed tray 245 and conveyed along the conveying path 241 is conveyed to the downstream paper characteristic detection device 30, where the paper characteristics are measured, and an image is formed on the paper by the image forming device 10, which is further downstream. The paper feed conveying section 24 of the paper feeder 20 feeds the topmost paper of a stack of paper sheets stored in the paper feed tray 245, one by one.

[0040] (Post-processing device 40) The post-processing device 40 performs post-processing on the paper sheets 90 sent from the image forming device 10 and ejects them in accordance with the settings of the print job. The post-processing device 40 includes paper output trays 41 and 42, a post-processing unit 43, and a conveying path 441. The post-processing device 40 also includes a control unit, a memory unit, a conveying unit, and a communication unit (none of which are shown), which are connected to each other via signal lines such as a bus for exchanging signals. The paper output trays 41 and 42 are selected in accordance with the settings of the print job. The conveying path 441 is connected to the upstream conveying path 141. The post-processing unit 43 performs at least one of post-processing processes, including stapling, punching, cutting, folding, and binding, on the paper sheets 90 on which an image has been formed.

[0041] (Paper characteristic detection device 30) Next, the paper characteristic detection device 30 will be described with reference to Figures 3 to 6. Figure 3 is a block diagram of the paper characteristic detection device 30, and Figure 4 is a diagram showing the general configuration of the paper characteristic detection device 30. The paper characteristic detection device 30 includes a control unit 31, a storage unit 32, a transport unit 34, a first detection unit 35a, a second detection unit 35b, an environmental sensor 38, and a communication unit 39. The environmental sensor 38 detects at least one of the temperature and humidity inside the device body. The communication unit 39 is an interface for communicating with other devices.

[0042] The control unit 31 has a CPU and a memory, similar to the above-described control unit 11. The control unit 31 controls the operations of the first and second detection units 35a and 35b, and causes them to detect paper characteristic information corresponding to the paper characteristics of the paper 90.

[0043] The storage unit 32 includes auxiliary storage units such as a ROM for storing various programs and data in advance, a RAM for temporarily storing programs and data as a working area, and a hard disk for storing various programs and data. The storage unit 32 also stores an environmental correction table that associates the detection values ​​of the environmental sensor 38 with correction values. The control unit 31 may correct the detection results of the first and second detection units 35a and 35b according to the detection values ​​of the environmental sensor 38 and the environmental correction table.

[0044] The transport unit 34 includes a first transport path 341, a second transport path 342, and a purge tray 349 onto which the paper sheets 90 to be purged are discharged. The first and second transport paths 341 and 342 each include a plurality of pairs of transport rollers arranged along the transport path, and a drive motor (not shown) that drives these pairs of transport rollers. The first transport path 341 is the main transport path, and its upstream side is connected to the transport path 241 of the paper feeder 20, and its downstream side is connected to the transport path 141 of the image forming apparatus 10. The second transport path 342 branches off from the first transport path 341 at a branch j1. The second transport path 342 transports the paper sheets 90 to be purged onto the purge tray 349 without passing through the image forming unit 13 (arranged on the transport path 141). The first transport path 341 extends in a substantially horizontal direction. At least a portion of the second transport path 342 extends in a substantially vertical direction. In particular, in the area where the stiffness sensor 355 (described later) is located, the second transport path 342 extends in a substantially vertical direction, with the paper transport direction being upward. Here, substantially vertical means being in the range of 90±1°. Note that the entire second transport path 342 does not have to be a straight line. As long as at least the measurement area of ​​the stiffness sensor 355 of the second transport path 342 is straight, the other paths may be partially curved. For example, the second transport path 342 may be a curved transport path that is S-shaped overall.

[0045] (Location of each sensor) See Figures 3 and 4. As shown in these figures, the first detection unit 35a includes a moisture content sensor 350 that detects the moisture content as a paper characteristic. The second detection unit 35b includes multiple sensors that detect multiple types of paper characteristics. The multiple sensors of the second detection unit 35b include a size sensor 351, a paper thickness sensor 352, a basis weight sensor 353, a stiffness sensor 355, a surface property sensor 356, and a resistance sensor 357. These sensors of the first and second detection units 35a and 35b may output, as paper characteristic information, the characteristic or physical value of the paper itself, or a value that indicates the characteristic, such as the current or voltage of a sensor corresponding to the characteristic or physical value.

[0046] 4, on the first conveying path 341, a basis weight sensor 353 and a moisture percentage sensor 350 are disposed downstream of the paper thickness sensor 352. The basis weight sensor 353 and the moisture percentage sensor 350 are disposed side by side at the same position in the conveying direction (X direction) but different positions in the width direction (Y direction) on the first conveying path 341. Furthermore, on the first conveying path 341, the size sensor 351 is disposed upstream of the moisture percentage sensor 350.

[0047] Furthermore, the paper thickness sensor 352 is positioned second from the upstream side. By detecting the thickness of the paper 90 first, the paper characteristic detection device 30 can appropriately set the measurement range (latitude), measurement conditions, etc. when detecting with the subsequent basis weight sensor 353 and moisture percentage sensor 350, for example.

[0048] The moisture percentage sensor 350 of the first detection unit 35a, the size sensor 351, the paper thickness sensor 352, and the basis weight sensor 353 of the second detection unit 35b, which are arranged on the first conveying path 341, do not affect productivity. That is, these sensors 350-353 arranged on the first conveying path 341 detect paper characteristic information corresponding to the size, paper thickness, basis weight, and moisture content (moisture percentage) of the paper 90 conveyed along the first conveying path 341 while conveying the paper 90 without stopping it. This makes it possible to detect the paper characteristic information of each of the multiple sheets of paper 90 conveyed continuously when executing a print job that involves continuous printing. That is, these sensors can detect the paper characteristic information of all sheets. Of these, the paper characteristic information of the size, paper thickness, and basis weight corresponds to the paper type (paper type), and the paper characteristic information of the moisture percentage corresponds to changes in the state of the paper 90. The stiffness sensor 355, the surface property sensor 356, and the resistance sensor 357 arranged on the second transport path 342 detect the respective paper characteristics after the paper 90 is temporarily stopped.

[0049] In this way, the moisture percentage sensor 350 of the first detection unit 35a detects paper characteristic information corresponding to changes in the paper condition of the paper 90 each time. This makes it possible to properly detect cases where the condition of the paper 90 loaded in the paper feed tray becomes unstable and changes during continuous printing, or where the paper bundle contains paper with an inconsistent paper condition (hereinafter referred to as inconsistent paper). Then, as will be described later, when the paper characteristic detection device 30 detects an inconsistent paper 90, the paper 90 is switched to the purge conveyance path (second conveyance path 342) for conveyance and ejected to the purge tray 349. This prevents changes in image quality due to unstable paper condition, and prevents conveyance problems such as jams in the image forming device 10, post-processing device 40, etc., caused by the use of paper 90 with a high moisture content. The paper condition of the bundle of paper loaded in the paper feed tray may be inconsistent due to, for example, the following two situations: The first is when the paper stack is left in a humid room and the paper at the top (or bottom) of the stack absorbs moisture faster, resulting in a difference in moisture content between the center and the top of the stack. The second is when stacks of paper with different moisture contents are stacked when refilling a paper tray with paper that is not completely used up.

[0050] (Moisture Sensor 350) 5 is a diagram showing a schematic configuration of the moisture percentage sensor 350. The moisture percentage sensor 350 measures the moisture percentage or amount of moisture in the paper 90.

[0051] 5, the moisture percentage sensor 350 includes a first light-emitting unit 541, a second light-emitting unit 542, a light-receiving unit 543, a temperature detection sensor 544, and lenses 545 and 546. The first light-emitting unit 541 and the second light-emitting unit 542 are light-emitting units that emit light toward the paper.

[0052] The first light emitter 541 emits first near-infrared light (reference light) in a specific wavelength band toward the paper P. A specific example of the first light emitter 541 is an LED (Light Emitting Diode), etc. The first near-infrared light is light whose absorption rate in the paper P when reflected by the paper P does not depend on the moisture content of the paper P. The light receiver 543 receives, via a lens 546, the first near-infrared light emitted from the first light emitter 541 and reflected by the paper P via a lens 545. The light receiver 543 then outputs first received light amount information, which is the amount of received reflected first near-infrared light, to the control unit 31. A specific example of the light receiver 543 is a CCD (Charge-Coupled Device), a CMOS (Complementary Metal-Oxide-Semiconductor), etc.

[0053] The second light emitter 542 emits second near-infrared light of a specific wavelength band toward the paper P. A specific example of the second light emitter 542 is an LED or the like. The second near-infrared light is light whose absorption rate in the paper P when reflected by the paper P varies depending on the moisture content of the paper P. The light receiver 543 receives, via a lens 546, the second near-infrared light emitted from the second light emitter 542 and reflected by the paper P via a lens 545. The light receiver 543 then outputs information on the second received light amount, which is the amount of the reflected second near-infrared light received, to the control unit 31.

[0054] That is, the first light-emitting unit 541 and the second light-emitting unit 542 emit light of wavelengths that are absorbed by moisture in paper at different rates. The second near-infrared light emitted by the second light-emitting unit 542 has a wavelength that is more absorbed by moisture in paper than the first near-infrared light (reference light) emitted by the first light-emitting unit 541.

[0055] The control unit 31 determines the moisture content of the paper based on the ratio between the first amount of received light and the second amount of received light (the ratio between the output of the light receiving unit 543 for the first near-infrared light and the second near-infrared light). The higher the moisture content of the paper, the greater the amount of second near-infrared light absorbed, and therefore the smaller the amount of second received light. Therefore, the control unit 31 can correspond the ratio between the first amount of received light and the second amount of received light to the moisture content of the paper based on a relational expression or table that indicates the relationship between the moisture content of the paper and the ratio between the first amount of received light and the second amount of received light, and calculate the moisture content of the paper from the ratio between the first amount of received light and the second amount of received light.

[0056] (Size Sensor 351) The size sensor 351 optically detects the size (shape) of the paper 90. The size sensor 351 is, for example, a line sensor whose detection area is the entire area in the paper width direction. The control unit 31 detects the edges (positions of the four sides or the outer shape) of the paper 90 and detects the size (shape) by performing image processing on the obtained scanned image data for one sheet of paper 90.

[0057] (Paper thickness sensor 352) The paper thickness sensor 352 detects the thickness of the paper 90 by mechanically measuring the amount of displacement. The paper thickness sensor 352 is composed of a pair of transport rollers and a displacement sensor. One of the transport rollers is a driven roller, and the thickness of the paper 90 transported to the nip is detected by measuring the shaft height of this driven roller with a displacement sensor. The displacement sensor is composed of an actuator (detection lever) that contacts the shaft of the upper driven roller and an encoder that measures the amount of rotation of this actuator. The paper thickness sensor 352 outputs, for example, the paper thickness (microns) as the paper thickness measurement result.

[0058] (Basis weight sensor 353) The basis weight sensor 353 is a transmissive and reflective optical sensor that detects the basis weight of paper. It has a light-emitting element and a light-receiving element, and detects the basis weight of paper 90 by measuring the attenuation (transmittance) of light passing through paper 90 and the amount of reflected light.

[0059] FIG. 6 is a diagram showing a schematic configuration of the basis weight sensor 353. As shown in FIG. 6, the basis weight sensor 353 includes multiple light-emitting elements 531 and a single light-receiving element 532. The light-emitting element 531 includes a first light-emitting element 531a, a second light-emitting element 531b, and a third light-emitting element 531c. The first, second, and third light-emitting elements irradiate an irradiation area with first, second, and third irradiation light, respectively. This irradiation area (second irradiation area) is an inner area within the opening a12 when viewed from the Z direction. The opening a12 is provided in the upper guide plate 3411. An opening a22 is also provided in the lower guide plate 3412 at a position opposite the opening a12. The openings a12 and a22 have the same shape, for example, a rectangle. Transparent sheets 534a and 534b made of PET or the like that transmit the wavelengths of each irradiated light are attached to the openings a12 and a22 to prevent foreign matter such as paper dust from the paper 90 passing through the first conveying path 341 from adhering to the openings a12 and a22.

[0060] The first light-emitting unit 531a emits first irradiation light having a first wavelength. The first wavelength is, for example, a near-infrared wavelength that is longer than the wavelength of visible light. More specifically, the first wavelength includes, for example, a wavelength between 750 nm and 900 nm. The second light-emitting unit 531b emits second irradiation light having a second wavelength. The second wavelength is, for example, a wavelength of blue light included in visible light. More specifically, the second wavelength includes, for example, a wavelength between 400 nm and 470 nm. The first light-emitting unit 531a and the second light-emitting unit 531b are both disposed on the opposite side of the first transport path 341 from the light-receiving unit 532, and the third light-emitting unit 531c is disposed on the same side as the light-receiving unit 532 and in the vicinity of the light-receiving unit 532. The third light-emitting unit 531c emits third irradiation light having a third wavelength toward the irradiation region (opening a12). The third wavelength is, for example, the wavelength of green light in visible light. More specifically, the third wavelength includes, for example, a wavelength between 495 nm and 570 nm. The third wavelength is a wavelength different from the first wavelength (for example, a wavelength between 750 nm and 900 nm) and the second wavelength (for example, 400 nm to 470 nm).

[0061] The third irradiation light is irradiated toward the first transport path 341 inside the upper and lower guide plates 3411 and 3412. A reflector 533 is provided on the inside of the lower guide plate 3412, which is provided near the first light emitter 531a and the second light emitter 531b. The reflector 533 is painted, for example, in green, the same color as the third irradiation light, and reflects the third irradiation light. Note that the reflector 533 does not reflect the first irradiation light (near-infrared rays) and the second irradiation light (blue light rays), which are not the same color.

[0062] In this embodiment, during measurement, the control unit 31 controls the first light-emitting unit 531a and the second light-emitting unit 531b to emit first and second irradiation light at different times. The light-receiving unit 532 receives the first and second irradiation light, detects the light intensity of each irradiation light, and outputs the detected light intensity of the first and second irradiation light to the control unit 31. Similarly, the control unit 31 irradiates the paper 90 transported to the position of the opening a12 with the first and second irradiation light. The light-receiving unit 532 receives the transmitted light (first transmitted light, second transmitted light) of the first and second irradiation light, detects the light intensity of each irradiation light, and outputs the detected light intensity of the first transmitted light and the second transmitted light to the control unit 31. That is, the light receiving section 532 detects the first irradiated light and the second irradiated light when the paper 90 is not present, and the first transmitted light and the second transmitted light when the paper 90 is present in the opening a12.

[0063] Similarly, with respect to the third light-emitting unit 531c, the light-receiving unit 532 detects the first reflected light reflected by the reflecting unit 533 when no paper 90 is present, and the second reflected light reflected by the surface of the paper 90 when the paper 90 is in the opening a12.

[0064] The control unit 31 calculates a first transmittance by dividing the amount of the first transmitted light by the amount of the first irradiated light. Similarly, the control unit 31 calculates a second transmittance by dividing the amount of the second transmitted light by the amount of the second irradiated light. The type of paper 90 is then determined from the first and second transmittances and the determination criteria stored in the memory unit 12.

[0065] Furthermore, in addition to the first and second transmittances, the control unit 31 may calculate the reflectance by dividing the amount of the second reflected light by the amount of the first reflected light, and may take this reflectance into consideration when determining the type of paper 90. Although the third light-emitting unit 531c and the reflecting unit 533 are provided in this embodiment, they may be omitted.

[0066] (Stiffness Sensor 355) The stiffness sensor 355 mechanically measures the amount of displacement to detect the stiffness of the paper 90. The stiffness sensor 355 is disposed on the second transport path 342, which extends vertically, vertically below a pair of rollers that hold the stopped paper 90.

[0067] The stiffness sensor 355 detects the bending stiffness of the leading (or trailing) edge of the paper 90, which is the free edge. The stiffness sensor 355 is composed of a holding member, a push-up member that lifts the paper 90 upward from below, and a pressure detection sensor that detects the pressure of the push-up member. Here, "lower" refers to the left side, and "upper" refers to the right side. This also applies to the following description of the stiffness sensor's function in this paragraph. The holding member also serves as a transport roller. The contact surface of the push-up member with the paper 90 is parallel to the axial direction of the transport roller. The transport roller holds the paper 90 slightly inside the edge (margin), and the tip of the free edge is lifted by the push-up member, measuring the stiffness of the paper 90 based on the pressure applied at this time. The up and down movement of the push-up member is controlled by a drive motor, such as a stepping motor. The stiffness sensor 355 uses a conveying roller as a holding member, and the contact surface between the holding area (roller nip) and the push-up member is both in the conveying direction of the paper 90 and in a direction perpendicular to the paper surface (conveying surface) of the paper 90, and measures the stiffness in the paper conveying direction.

[0068] (Surface Sensor 356) The surface property sensor 356 includes a housing, a light-emitting element, a collimating lens, and multiple light-receiving elements (optical sensors). As described below, it optically detects specularly reflected light and diffusely reflected light from the paper surface (irradiation surface). This detects the characteristics of the coating layer of the paper 90. An opening (measurement area) is provided in one guide plate (the lower one in FIG. 1) in the paper passage area of ​​the transport path, and this opening serves as the irradiation area of ​​the light-receiving elements. The paper 90 is inserted up to the opening and transported, and is pressed down by a pressing mechanism that descends from above the paper passage area. As a result, the paper 90 around the opening (of the guide plate) is pressed down by the lower guide plate and the pressing mechanism from above. In this state, the light-emitting element emits light that is approximately parallelized by the collimating lens at an incident angle of 75° with respect to the reference surface. The wavelength of the irradiated light is, for example, 465 nm. The multiple light-receiving elements receive specularly reflected light and diffusely reflected light. For example, the sensors may be positioned at three locations with reflection angles of 30 degrees (for diffuse reflected light), 60 degrees (for diffuse reflected light), and 75 degrees (for specular reflected light), or at two locations with angles of 60 degrees and 75 degrees. The surface property sensor 356 detects the surface property of the paper 90 based on the absolute value and ratio of the intensity of light received by each light receiving element.

[0069] (Resistance sensor 357) Resistance sensor 357 detects the paper resistance (electrical resistance) of the transported paper 90. Resistance sensor 357 includes a pair of transport rollers that sandwich the paper 90, and an HV (high voltage) unit. When measuring the paper resistance, the drive motor of the transport rollers is stopped at a predetermined detection position on the transport path, and the paper 90 is temporarily stopped. In this state, the HV unit applies a high voltage to the upper roller (also called the detection roller) of the pair of transport rollers, and measures the value of the current that flows through the paper 90 to the grounded lower roller (opposing roller).

[0070] (Control parameter determination method) The control unit 11 determines various control parameters according to either a first example or a second example described below.

[0071] 7A is a block diagram showing a process for determining control parameters from paper characteristics in a first example. In the first example, the control unit 11 determines, based on paper characteristics 1 to n, that the paper is one of a plurality of paper types and a plurality of paper weights classified by a discrimination process. Paper characteristic sensors 1 to n correspond to any of sensors 350 to 357 of the paper characteristic detection device 30 described above. Then, a process for determining control parameters is performed based on the determined paper type and basis weight. When performing this parameter determination process, a correspondence table stored in advance in the storage unit 12 is referenced, which describes the control values ​​of each parameter for the fixing, transfer, transport / feed, and post-processing processes for each combination of paper type and basis weight.

[0072] The control unit 11 controls the fixing process of the fixing unit of the image forming unit 13 and the transfer process of the transfer unit using the determined fixing and transfer control parameters. The control unit 11 also controls the paper feed conveyance unit 14 using the determined conveyance and paper feed control parameters, and the control unit of the paper feeder 20 controls the conveyance and paper feed process of the paper feeder 20. The control unit of the post-processing device 20 also controls the post-processing process using the determined post-processing control parameters.

[0073] FIG. 7B is a block diagram showing a process for determining control parameters from paper characteristics in a second example. In the first example described above, the control unit 11 first classifies the paper into paper type and basis weight and then determines the control parameters. However, in the second example, the control unit 11 determines each control parameter directly from the paper characteristics. For example, the control unit 11 determines fixing control parameters from paper characteristics 1, 2, and 3, and determines transfer control parameters from paper characteristics 1, 3, and n. The control unit 11 also determines transport and feed control parameters from paper characteristics 1 and n, and determines post-processing control parameters from paper characteristics 1 and 3. Note that a trained model trained by machine learning may be used to determine these control parameters.

[0074] (printing process) Next, the printing process executed in the image forming system 1000 will be described with reference to Figures 8 to 10. Figure 8 is a flowchart showing the printing process in the first embodiment. In the figure, steps S01 to S12 are the process for preparing to print, and step S13 and onwards are the process for executing printing.

[0075] (Steps S01 to S03) When a print job is input based on an instruction sent from the terminal device 80 or the like, the control unit 11 feeds and transports the paper used in the print job based on the print job setting information of the input print job. For example, the control unit 11 feeds paper 90 from one of the paper feed trays 245 of the paper feed device 20 and transports the paper 90 to the first transport path 341. The control unit 31 also controls a path switching unit (not shown) of the branch unit j1 to set the paper transport path to the purge transport path (second transport path 342) leading to the purge tray 349.

[0076] (Step S04) The control unit 11 initializes the error variable j (j=1).

[0077] (Step S05) Steps S05 to S06 enclosed in a dashed line frame are the paper condition stabilization process.

[0078] In step S05, the control units 11 and 31 cooperate to execute a change amount calculation process. Figure 9 is a subroutine flowchart showing this change amount calculation process.

[0079] (Step S501) The control unit 11 sets the number of intervals n of the moving average and the threshold, and also initializes the moving variable i (i = 0). The number of intervals n of the moving average corresponds to a first predetermined number of sheets. As will be explained below, the control unit 11 determines whether the paper condition has stabilized based on the change in the moving average of the number of intervals n, which is the first predetermined number of sheets. The number of intervals n and the threshold may be fixed values ​​set in advance. The number of intervals n may be set by the user via the operation panel 15, and although the number of intervals n is preferably 3 or more, it may be 1 or more. When the number of intervals n = 1, a simple comparison of the values ​​before and after is performed.

[0080] An example of the number of sections n and the threshold is n=3, and the threshold is, for example, 0.1% or 0.5%. The threshold may be set in one of the following ways. In a first example, a table correlating paper types with thresholds is stored in the memory unit 12, and the control unit 11 sets the threshold using this table. The paper type may be determined using information input by the user via the operation panel 15, or the paper type may be determined based on the paper characteristic values ​​detected by the first and second detection units 35a and 35b for the first sheet of paper. In a second example, the threshold is set based on the detection data for the moisture content of the first sheet. For example, if the moisture content of the first sheet of paper is 10%, the control unit 11 multiplies this by a predetermined coefficient (1 / 20) and sets the resulting value (0.5%) as the threshold.

[0081] (Step S502) The control unit 11 increments i (+1).

[0082] (Steps S503 and S504) The control unit 31 conveys the paper sheet 90 to the first detection unit 35, which then detects the moisture content of the i-th sheet. The control unit 11 stores the moisture content data in the detection data stack each time detection data for each paper sheet is obtained. As described above, the moisture percentage sensor 350 of the first detection unit 35a, the size sensor 351, the paper thickness sensor 352, and the basis weight sensor 353 of the second detection unit 35b can detect paper characteristic information corresponding to the size, paper thickness, basis weight, and moisture content (moisture content) of the paper sheet 90 while it is being conveyed along the first conveying path 341 without stopping it. Therefore, the sensors on the first conveying path 341 may also detect paper characteristics other than moisture content each time. In this case, the detection data for the other paper characteristics may be erased without being used, or may be stacked and averaged to set control parameters (steps S11 and S12, described below).

[0083] (Step S505) The control unit 11 calculates the moving average if the number of data i in the detection data stack is equal to or greater than the number of sections n (for example, 3). For example, if i=10, the current moving average value ma_i of the moisture content detection data is the average value of the moisture content detection data from the 8th to 10th sheets. If the value of variable i is less than the number of sections n, the moving average cannot be calculated, so this process is skipped.

[0084] (Step S506) The control unit 11 calculates the difference d between the previous moving average value ma_i-1 and the current moving average value ma_i-1. For example, when i=10, the control unit 11 calculates the difference d between the average value of the moisture content detection data from the 7th to 9th sheets and the average value of the moisture content detection data from the 8th to 10th sheets. This ends the processing in FIG. 9, and the process returns to the processing in FIG. 8, where the processing from step S06 onwards is executed.

[0085] (Step S06) The control unit 11 determines whether the paper condition is stable. If the difference d calculated in step S05 is equal to or less than the threshold, it determines that the paper condition is stable and advances the process to step S11. On the other hand, if the difference d exceeds the threshold, the process proceeds to step S07.

[0086] FIG. 10 is a graph showing the change in moisture content of sheets continuously transported from a paper feed tray in two cases with different humidity conditions. The horizontal axis represents the number of sheets fed, and the vertical axis represents the moisture content (% moisture). In both cases 1 and 2, sheets were fed and transported from a stack of sheets left in a paper feed tray in a high-humidity environment. In case 2, the sheets were left there for a longer period of time than in case 1, resulting in sheets containing more moisture. In both cases 1 and 2, the sheets in the center of the stack absorbed less moisture than the top sheets, resulting in less moisture. Therefore, as shown in FIG. 10, as sheets are continuously fed, the moisture content gradually decreases as the number of sheets increases. In FIG. 10, a YES determination was made in step S06 at the determination timing for both case 1 and case 2. It can be seen that case 2, which has a higher initial moisture content, takes longer (number of sheets) to stabilize. Sheets before the determination timing are purged, while sheets after the determination timing undergo image formation by the processing from step S13 onward, described below.

[0087] (Step S07) The control unit 11 increments the error variable j (+1). In addition, the control unit 31 controls the conveying unit 34 to purge the paper 90. In this purge, the paper 90 is discharged to the purge tray 349 via a purge conveying path (second conveying path 342) that does not pass through the image forming unit 13.

[0088] (Step S08) The control unit 11 determines whether the error variable j is equal to or greater than a predetermined number c1 (second predetermined number). The predetermined number c1 is a number that is set in advance. For example, the predetermined number c1 can take any value between 10 and 50. For example, the predetermined number c1 is 20. If the error variable j is equal to or greater than the predetermined number c1, the control unit 11 proceeds to step S09. On the other hand, if the error variable j is less than the predetermined number c1, the control unit 11 proceeds to step S05 (step S502) (indicated by the circled number 10).

[0089] (Step S09) The control unit 11 performs error processing. As error processing, the control unit 11 interrupts the paper condition stabilization determination process and stops the moisture content detection operation. The control unit 11 also displays a warning on the operation panel 15 or the like to the effect that the paper condition is not stable within a predetermined number of sheets. This warning display may include a message urging the user to replace the paper in the paper feed tray. After error processing, the process ends (END).

[0090] (Step S11) The second detection unit 35b of the paper characteristic detection device 30 detects paper characteristics other than the moisture content of the paper 90. This detection is preferably performed on the paper 90 whose moisture content was last detected, but it is also possible to newly feed another sheet of paper 90 and detect multiple paper characteristics for this sheet 90.

[0091] Furthermore, when using the paper 90 whose moisture content was last detected in step S11, this paper 90 is transported to the second transport path 342 (purge transport path), and the paper characteristics are detected by the stiffness sensor 355, the surface property sensor 356, and the resistance sensor 357. Furthermore, since the detection of paper characteristics by the size sensor 351, the paper thickness sensor 352, and the basis weight sensor 353 on the transport path 341 can be performed without stopping the paper, this detection data can be used if the detection is performed every time.

[0092] (Step S12) The control unit 11 sets control parameters for fixing, transfer, transport, and paper feed using the multiple paper characteristics detected in step S11. The control unit 11 may also set control parameters for post-processing using the multiple paper characteristics detected in step S11. The control parameter setting is performed using either the control parameter determination method shown in Figure 7A or 7B.

[0093] (Step S13) The control unit 31 controls a path switching unit (not shown) of the branch j1 to switch the paper transport path to the main transport path (transport paths 341 and 141) leading to the image forming unit 13.

[0094] (Step S14) The control unit 11 causes the paper 90 to be conveyed to the image forming unit 13. The image forming unit 13 forms an image on the paper 90. The various control parameters used in this image formation are those set in step S12.

[0095] (Step S15) If the control unit 11 determines that printing up to the set number of sheets of the print job has not been completed (NO), the control unit 11 returns the process to step S14 and repeats image formation on the paper 90 until the set number of sheets is reached. If the control unit 11 determines that printing up to the set number of sheets has been completed (YES), the control unit 11 ends the process (END).

[0096] As described above, the image forming system according to the first embodiment includes a first detection unit located upstream of the image forming unit in the paper transport direction on the transport path, which detects a characteristic value corresponding to the moisture content of the transported paper, and a control unit that determines whether the characteristic value detected by the first detection unit is stable and, if so, starts image formation by the image forming unit. Since image formation automatically starts after confirming that the paper condition has stabilized, the burden of monitoring by the operator can be reduced. Furthermore, the consumption of ink and toner that would otherwise be consumed by forming images in unstable conditions can be reduced.

[0097] Furthermore, in this embodiment, paper is purged without image formation until it is determined that the printing state has stabilized, thereby reducing paper consumption. In particular, the image forming system purges paper to a purge tray via a purge transport path, making it possible to distinguish it from paper for actual printing and to easily reuse the purged paper.

[0098] (Second embodiment) Next, an image forming system according to a second embodiment will be described with reference to Figures 11A and 11B. In the second embodiment, even after it has been confirmed that the state of the paper has stabilized, the state of the paper in terms of moisture content continues to be monitored, and printing is suspended or resumed depending on the results of this monitoring.

[0099] Fig. 11A is a flowchart showing the printing process in embodiment 2. Fig. 11B is a flowchart showing the printing process executed subsequent to Fig. 11A.

[0100] In Fig. 11A, the processing of steps S01 to S15 is the same as that in the flowchart of Fig. 8, and a description of each step will be omitted. The parts in Fig. 11A that differ from the flowchart of Fig. 8 are the parts marked with circled numbers 20, 30, and 40. If the print job is to be continued in step S15 (step S15: NO), the processing of Fig. 11B is performed (indicated by circled number 20).

[0101] (Steps S21 to S26) The processing of steps S21 to S25 in Fig. 11B is the same as steps S502 to S506 in Fig. 9, and the processing of step S26 in Fig. 11B is the same as step S06 in Fig. 8. In the processing of steps S21 to S25 in Fig. 11B, the movement variable i and the data in the sensed data stack continue to be the same as those used in Fig. 9.

[0102] (Step S26) If the control unit 11 determines in step S26 that the state of the paper related to the paper characteristic of moisture content is stable (YES), the control unit 11 proceeds to step S14 in Fig. 11A (indicated by circled number 30). Then, the control unit 11 performs the processes from step S14 onward, and continues forming an image on the paper 90.

[0103] On the other hand, if the control unit 11 determines that the state of the paper relating to the paper property of moisture content has become unstable (NO), the process proceeds to step S27.

[0104] (Steps S27 and S28) The control unit 31 switches the paper transport path to the purge transport path (second transport path 342) and purges the paper. If image formation is in progress, the control unit 11 then suspends the image formation. For example, this occurs when paper with different humidity conditions is mixed in the same paper feed tray. For example, this occurs when a new stack of paper is replenished (overlapped) on a stack of paper that has been left in a high-humidity environment for a long time in the paper feed tray. In this case, after the newly replenished stack of paper is used up by printing, paper that has been left and has a high moisture content in the high humidity environment is transported, and it is determined that the paper condition is unstable.

[0105] 11A (indicated by circled number 40), and executes the paper condition stabilization determination process from step S05 onward. If it is determined that the paper condition has stabilized, image formation of the interrupted print job is resumed.

[0106] In this way, the image forming system according to the second embodiment performs the same processing as the first embodiment, and furthermore, even after the image forming unit starts image formation, the first detection unit continues to detect the characteristic values ​​of the paper, and if it determines that the characteristic values ​​detected by the first detection unit are not stable during image formation, it suspends image formation by the image forming unit. Furthermore, even after the suspension, the control unit continues to perform detection by the first detection unit, and if it subsequently determines that the detected characteristic values ​​are stable, it resumes image formation by the image forming unit.

[0107] This provides the same effects as the first embodiment, and furthermore, in the second embodiment, it is possible to prevent changes in print quality due to unstable paper conditions during a print job.

[0108] The configuration of the paper characteristic detection device 30 and the image forming system 1000 equipped with the same described above is a description of the main configuration in explaining the features of the above embodiment, but is not limited to the above configuration and can be variously modified within the scope of the claims. Furthermore, configurations equipped in general image forming devices are not excluded.

[0109] In the above-described embodiment, the second detection unit 35b includes six sensors: a size sensor, a paper thickness sensor, a basis weight sensor, a stiffness sensor, a surface property sensor, and a resistance sensor. However, the present invention is not limited to this, and the second detection unit 35b need only include at least one of the six sensors, rather than all six.

[0110] 1 may be included in the image forming system. Some of the functions of the control unit 11 and / or the control unit 31 may be performed on the terminal device 80 side. For example, the processing shown in FIG. 8 and the like may be performed on the terminal device 80 side in cooperation with the control unit 11 and / or the control unit 31.

[0111] Furthermore, the means and methods for performing various processes in the paper characteristic detection device 30 and image forming system 1000 according to the above-described embodiment can be realized by either a dedicated hardware circuit or a programmed computer. The above-described programs may be provided by a computer-readable recording medium such as a USB memory or a DVD (Digital Versatile Disc)-ROM, or may be provided online via a network such as the Internet. In this case, the programs recorded on the computer-readable recording medium are typically transferred to and stored in a storage unit such as a hard disk. The above-described programs may also be provided as standalone application software, or may be incorporated into the software of the device as a function of the device.

[0112] While embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and are not intended to be limiting, and the scope of the present invention should be construed by the language of the appended claims. [Explanation of symbols]

[0113] 1000 Image forming system 10 Image forming device 11 Control section 13 Image forming unit 20 Paper feeder 245 paper tray 30 Paper characteristic detection device 31 Control Unit 32 Storage section 34 Conveying section 341 First Transport Path 342 Second transport route 349 Purge Tray s1 Branch 35a First detection unit 350 Moisture Sensor 35b Second detection unit 351 size sensor 352 Paper thickness sensor 353 Basis weight sensor 355 Stiffness Sensor 356 Surface Sensor 357 Resistance Sensor 38 Environmental Sensors 39 Communications Department

Claims

1. an image forming unit that forms an image on a sheet conveyed through a conveyance path; a first detection unit that is disposed on the conveyance path upstream of the image forming unit in the sheet conveyance direction and that detects a characteristic value corresponding to the moisture content of the conveyed sheet; a control unit that determines whether the characteristic value detected by the first detection unit is stable, and when it is determined that the characteristic value is stable, starts image formation by the image forming unit; An image forming system comprising:

2. Equipped with a paper feed tray that can hold multiple sheets of paper, The first detection unit detects the sheets continuously fed and conveyed from the sheet feed tray, The image forming system according to claim 1 , wherein the control unit makes the determination based on changes in the characteristic values ​​of a plurality of sheets of paper.

3. 3. The image forming system according to claim 2, wherein the control unit makes the determination based on a change in a moving average of the characteristic value for a first predetermined number of sheets of paper that have been continuously conveyed.

4. The image forming system according to claim 2 , wherein the control unit executes a purge process for discharging the paper detected by the first detection unit to a discharge unit without forming an image on the paper until it is determined that the paper has stabilized.

5. a purge conveyance path branching off from the conveyance path on the upstream side of the image forming unit and the downstream side of the first detection unit; 5. The image forming system according to claim 4, wherein in the purging process, the paper is discharged via the purging transport path.

6. 3. The image forming system according to claim 2, wherein the control unit suspends the detection operation by the first detection unit when it is not determined that the state is stable even after a second predetermined number of sheets have been conveyed.

7. 7. The image forming system according to claim 6, wherein the control unit, upon suspending the printing, notifies a user that characteristics of the paper in the paper feed tray are not stable.

8. The image forming system according to claim 1 , wherein the control unit sets control parameters for the image forming unit based on the characteristic value when it is determined that the image forming unit is stable.

9. a second detection unit that detects one or more characteristic values ​​of paper types other than the moisture content; 9. The image forming system according to claim 8, wherein control parameters of the image forming unit are set based on a plurality of characteristic values ​​obtained by detecting the paper when the first detection unit and the second detection unit determine that the paper is stable.

10. 10. The image forming system according to claim 8, wherein the control parameters include control parameters relating to at least one of transfer, fixing, and transport.

11. even after the image forming unit starts image formation, the first detection unit continues to detect the characteristic value of the paper; 2. The image forming system according to claim 1, wherein the control unit suspends image formation by the image forming unit when it determines that the characteristic value detected by the first detection unit is unstable during image formation.

12. the control unit continues to cause the first detection unit to detect the characteristic value of the paper even after the detection is interrupted; The image forming system according to claim 11 , wherein the control unit restarts image formation by the image forming unit when it determines that the characteristic value detected by the first detection unit has stabilized.

13. a step (a) of detecting a characteristic value of the paper by a first detection unit that is disposed on the conveyance path upstream of the image forming unit in the paper conveyance direction and that detects a characteristic value corresponding to the moisture content of the conveyed paper; a step (b) of determining whether the characteristic value detected in the step (a) is stable, and when it is determined that the characteristic value is stable, starting image formation by the image forming unit; A control program that causes a computer to execute a process including the above.

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