Image forming apparatus, image forming system, and control program

Abstract

To ensure that image forming conditions are properly set even on a reverse side.SOLUTION: An image forming device 20 comprises: a first media detection unit 28 provided in a double-side conveyance path 252, and acquiring paper properties information that corresponds to the paper properties of paper having been conveyed through the double-side conveyance path 252; and a control unit 21 for setting an image forming parameter for the reverse side of paper on the basis of the paper properties information on paper acquired by the first media detection unit 28.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] In recent years, in the color printing industry, image forming apparatuses such as electrophotographic printers have been widely used. In the field of PP (production print) corresponding to the color printing industry, adaptation to various papers is required compared to the case of use in an office. And in order to perform high-quality printing on these various papers, there is an image forming apparatus that sets paper characteristics stored in a paper feed tray in a plurality of items and performs printing under image forming conditions according to the set items.

[0003] For example, in the image forming apparatus of Patent Document 1, a technique is disclosed in which a paper type is detected by an optical sensor (50) disposed immediately before a resist portion (15), and image forming conditions are changed according to the detected type.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the image forming apparatus described in Patent Document 1 detects the type of paper on the transport path from the paper feeding section to the transfer section. When forming images on both sides, if the image on the back side (hereinafter also referred to as the second side) is formed after the image on the front side (hereinafter also referred to as the front side or first side), it does not take into account that the characteristics of the paper on the back side may change depending on the position of the paper due to heat treatment during fixing (the temperature distribution may become non-uniform). On the other hand, delaying the start of printing on the paper or lengthening the transport path before transfer in order to detect the characteristics of the paper on the back side over the length of the paper would lead to a decrease in the productivity and an increase in the size of the apparatus.

[0006] This invention has been made in view of the above circumstances, and aims to provide an image forming apparatus and a control program that can properly set image forming conditions even on the reverse side. [Means for solving the problem]

[0007] The above objectives of the present invention are achieved by the following means.

[0008] An image forming unit that forms a toner image on paper, A fixing unit that fixes the toner image formed by the image forming unit onto the paper, A transport unit including a main transport path and a double-sided transport path that guides paper fed from the paper feeding unit to the discharge unit via the image forming unit and the fixing unit, A first media detection unit is provided in the double-sided transport path and acquires paper characteristic information corresponding to the paper characteristics of the paper transported in the double-sided transport path. An image forming apparatus comprising: a control unit that sets image forming parameters for the back surface of the paper based on the paper characteristic information of the paper acquired by the first media detection unit; And, The image forming apparatus is characterized in that the first media detection unit performs detection at multiple locations on a single sheet of paper that are at different positions in the transport direction, and performs detection at the multiple locations by repeatedly transporting and stopping the paper to be detected.

[0009] An image forming unit that forms a toner image on paper, A fixing unit that fixes the toner image formed by the image forming unit onto the paper, A transport unit including a main transport path and a double-sided transport path that guides paper fed from the paper feeding unit to the discharge unit via the image forming unit and the fixing unit, A first media detection unit is provided in the double-sided transport path and acquires paper characteristic information corresponding to the paper characteristics of the paper transported in the double-sided transport path. An image forming apparatus comprising: a control unit that sets image forming parameters for the back surface of the paper based on the paper characteristic information of the paper acquired by the first media detection unit, The first media detection unit performs detection on a single sheet of paper at multiple locations that differ in position in the transport direction, The control unit is characterized by setting multiple image forming parameters on a single sheet of paper according to its position in the transport direction, based on the distribution of paper characteristics obtained by detection at the multiple locations. Image forming apparatus.

[0012] An image forming unit that forms a toner image on paper, A fixing unit that fixes the toner image formed by the image forming unit onto the paper, A transport unit including a main transport path and a double-sided transport path that guides paper fed from the paper feeding unit to the discharge unit via the image forming unit and the fixing unit, A first media detection unit is provided in the double-sided transport path and acquires paper characteristic information corresponding to the paper characteristics of the paper transported in the double-sided transport path. An image forming apparatus comprising: a control unit that sets image forming parameters for the back surface of the paper based on the paper characteristic information of the paper acquired by the first media detection unit, In a printing job for continuously forming images on both sides of a plurality of sheets of paper, the control unit causes the first media detection unit to ru perform detection on the sheets of paper up to a predetermined number of sheets after starting the printing job, and sets the image formation parameters for the back side of the sheets of paper after the predetermined number of sheets using the sheet characteristics obtained by the detection of the sheets of paper up to the predetermined number of sheets Characterized by, Image forming apparatus.

[0013] A control program for controlling an image forming apparatus comprising: an image forming unit that forms a toner image on paper; a fixing unit that fixes the toner image formed by the image forming unit to the paper; and a media detection unit provided on a double-sided transport path that acquires paper characteristic information corresponding to the paper characteristics of the paper transported on the double-sided transport path, The image forming unit and the fixing unit form an image on the front surface of the paper (a), Step (a) above involves transporting the paper on which the image has been formed to the double-sided transport path and acquiring paper characteristic information using the media detection unit, Step (c) is to set the image formation parameters for the back surface of the paper based on the paper characteristic information obtained in step (b), A control program for causing a computer to perform a process including step (d) of forming an image on the back of the paper with the image forming parameters set in step (c), Step (b) above is a control program characterized by performing detection at multiple locations with different positions in the transport direction for a single sheet of paper, and by repeatedly transporting and stopping the paper to be detected.

[0014] A control program for controlling an image forming apparatus comprising: an image forming unit that forms a toner image on paper; a fixing unit that fixes the toner image formed by the image forming unit to the paper; and a media detection unit provided on a double-sided transport path that acquires paper characteristic information corresponding to the paper characteristics of the paper transported on the double-sided transport path, The image forming unit and the fixing unit form an image on the front surface of the paper (a), Step (a) above involves transporting the paper on which the image has been formed to the double-sided transport path and acquiring paper characteristic information using the media detection unit, Step (c) is to set the image formation parameters for the back surface of the paper based on the paper characteristic information obtained in step (b), A control program for causing a computer to perform a process including step (d) of forming an image on the back of the paper with the image forming parameters set in step (c), In step (b) above, detection is performed on a single sheet of paper at multiple locations that are different in the transport direction, The control program, in step (c), is characterized by setting multiple image forming parameters on a single sheet of paper according to its position in the transport direction, based on the distribution of paper characteristics obtained by detection at the multiple locations.

[0017] A control program for controlling an image forming apparatus comprising: an image forming unit that forms a toner image on paper; a fixing unit that fixes the toner image formed by the image forming unit to the paper; and a media detection unit provided on a double-sided transport path that acquires paper characteristic information corresponding to the paper characteristics of the paper transported on the double-sided transport path, The image forming unit and the fixing unit form an image on the front surface of the paper (a), Step (a) above involves transporting the paper on which the image has been formed to the double-sided transport path and acquiring paper characteristic information using the media detection unit, Step (c) is to set the image formation parameters for the back surface of the paper based on the paper characteristic information obtained in step (b), A control program for causing a computer to perform a process including step (d) of forming an image on the back of the paper with the image forming parameters set in step (c), In a printing job that continuously forms images on both sides of multiple sheets of paper, The detection by the media detection unit in step (b) above is performed on paper from the start of the print job up to a predetermined number of sheets, and, A control program characterized by setting image formation parameters for the reverse side of paper beyond a predetermined number of sheets, using the paper characteristics obtained by detecting up to a predetermined number of sheets. [Effects of the Invention]

[0025] The image forming apparatus according to the present invention comprises: an image forming unit that forms a toner image on paper; a fixing unit that fixes the toner image formed by the image forming unit to the paper; a transport unit including a main transport path and a double-sided transport path that guides paper fed from a paper feeding unit to an discharge unit via the image forming unit and the fixing unit; a first media detection unit provided in the double-sided transport path that acquires paper characteristic information corresponding to the paper characteristics of the paper transported in the double-sided transport path; and a control unit that sets image forming parameters for the back side of the paper based on the paper characteristic information of the paper acquired by the first media detection unit. This enables the setting of image forming conditions to be performed appropriately even on the back side. [Brief explanation of the drawing]

[0026] [Figure 1] This figure shows a schematic configuration of an image forming system including an image forming apparatus according to this embodiment. [Figure 2] This is a block diagram of an image forming apparatus, etc. [Figure 3] This is a schematic diagram illustrating the changes and inconsistencies in paper characteristics before and after the fixing process. [Figure 4] This is a flowchart showing the image forming process performed by the image forming apparatus in the first embodiment. [Figure 5] This is a schematic diagram illustrating detection at multiple locations with different positions in the transport direction. [Figure 6] This figure shows an example of setting image formation parameters according to the paper position in the transport direction. [Figure 7] This is a flowchart showing the image forming process performed by the image forming apparatus in the second embodiment. [Figure 8]This figure shows the position of the second media detection unit for the front surface in the third embodiment. [Figure 9] This figure shows the position of the second media detection unit for the front surface in another modified example. [Figure 10] This is a flowchart showing the image forming process performed by the image forming apparatus in the third embodiment. [Figure 11] This is a schematic diagram illustrating an example of image formation parameters for the back side, which are set based on the paper characteristics of both the front and back sides. [Modes for carrying out the invention]

[0027] Embodiments of the present invention will be described below with reference to the attached drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios. In this embodiment, the paper includes printing paper (hereinafter simply referred to as "paper") and various films. In particular, the paper includes those manufactured using plant-derived mechanical pulp and / or chemical pulp. The types of paper include coated paper such as gloss paper and matte paper, and uncoated paper such as plain paper and fine paper, etc.

[0028] Figure 1 is a diagram showing the schematic configuration of the image forming system 1000, including the image forming apparatus 20 according to this embodiment. Figure 2 is a block diagram showing the hardware configuration of the image forming apparatus 20 and other components. As shown in Figure 1, the image forming system 1000 includes a paper feeder 10, an image forming apparatus 20, and a post-processing device 30, which are mechanically and electrically connected to each other. The image forming apparatus 20 will be described first, and the paper feeder 10 and post-processing device 30 will be described later.

[0029] (Image forming apparatus 20) The image forming apparatus 20 includes a control unit 21, a storage unit 22, an operation display unit 23, a paper feeding unit 24, a transport unit 25, an image forming unit 26, a fixing unit 27, a media detection unit 28, and a communication unit 29.

[0030] (Control Unit 21) The control unit 21 includes a CPU and memory. The CPU is a control circuit consisting of a multi-core processor or the like that executes control of each of the above parts and various calculation processes according to a program, and each function of the image forming apparatus 20 is performed by the CPU executing the corresponding program. The memory is a high-speed accessible main memory that temporarily stores programs and data as a work area. For example, DRAM, SDRAM, SRAM, etc. are used for the memory. Furthermore, the control unit 21 of the image forming apparatus 20 controls the entire image forming system 1000 in cooperation with the control units of the other paper feed device 10 and the post-processing device 30 (not shown).

[0031] The memory unit 22 is a large-capacity auxiliary storage device that stores various programs, including the operating system, and various data. Examples of storage devices include hard disks, solid-state drives, flash memory, and ROM.

[0032] The operation display unit 23 is equipped with a touch panel, numeric keypad, start button, stop button, etc., and is used for displaying various information and inputting various instructions. Through the operation display unit 23, the user can set paper information such as the size and type of paper stored in each paper tray. The user can also instruct the execution of a print job through the operation of this operation display unit 23.

[0033] The paper feeding unit 24 is equipped with one or more paper trays and feeds the paper 90 stored in the paper trays one sheet at a time, sending it to the transport path of the transport unit 25.

[0034] The transport unit 25 includes a main transport path 251 and a double-sided transport path 252. The transport unit 25 also includes paper detection sensors, a plurality of transport rollers, and drive motors (none of which are shown) that drive these transport rollers, all located on the transport paths 251 and 252.

[0035] The main transport path 251 guides the paper 90 fed from the paper feeding section 24 or paper feeding device 10 to the discharge section (discharge transport paths 351, 352 or paper output trays 31, 32, described later) via the image forming section 26 and the fixing section 27.

[0036] The double-sided transport path 252 is a path used during double-sided image formation. It receives the paper 90 with the image formed on the front side (first side), flips it over, and then guides it back to the image forming unit 26 on the main transport path 251. The image forming unit 26 forms the image on the back side (second side) of the paper 90. In the transport direction, the double-sided transport path 252 connects to the main transport path 251 at a branching point p1 downstream of the fixing unit 27 and at a merging point p2 upstream of the image forming unit 26. The double-sided transport path 252 flips the paper 90 over at a switchback path along the way, then passes through merging point p2 and sends the paper 90 back to the main transport path 251.

[0037] (Image forming unit 26) The image forming unit 26 forms a toner image (unfixed image) on the paper 90, for example, by an electrophotographic method. The image forming unit 26 includes a writing unit, a photosensitive drum (both not shown), a developing unit 261 containing a two-component developer consisting of toner and a carrier, a transfer unit 262, a separation unit 263, a static elimination unit 264, etc. (some are not shown). There are multiple writing units, photosensitive drums, and developing units 261, each corresponding to one of the basic colors: Y (yellow), M (magenta), C (cyan), and K (black). The toner image formed on the photosensitive drum by the developing unit 261 of each color is transferred to an intermediate transfer belt, superimposed on the intermediate transfer belt, and then transferred to the paper 90 transported along the main transport path 251 in the transfer unit 262 (also called the secondary transfer unit) (the above process is collectively called the image forming process). The separation unit 263 is located directly downstream of the transfer unit 262 and performs a separation discharge on the paper 90 from the back side of the paper 90. The static elimination unit 264 includes a discharge electrode located near the downstream transport roller of the main transport path 251 and eliminates static electricity on the surface of the paper 90 by discharge.

[0038] (Fixing section 27) The fuser unit 27 fixes the toner image formed on the paper 90 by the upstream image forming unit 26 to the paper 90 by performing a fixing process involving heating and pressurization. Figure 3 is a schematic diagram illustrating the changes and non-uniformity of paper characteristics before and after the fixing process. As shown in Figure 3, and in Figures 1 and 2, the fuser unit 27 includes a heater 271, a thermometer 272, a heating roller 273, and a pressure roller 274, which are heat sources. The control unit 21 controls the amount of power supplied to the heater 271 so that the heating roller 273 reaches a predetermined control temperature (also called the fixing temperature) based on the surface temperature of the heating roller 273 detected by the thermometer 272. In addition to the roller system shown in Figure 3, the fuser unit 27 may also use a belt-type fuser unit using a fixing belt. The toner image formed on the paper 90 by the image forming process is fixed to the paper 90 by heating and pressurizing in the fuser unit 27 (hereinafter also referred to as the fixing process).

[0039] (Media detection unit 28) The media detection unit 28 (first media detection unit) is provided on the double-sided transport path 252 and acquires paper characteristic information corresponding to the paper characteristics of the paper 90 transported on the double-sided transport path 252. The detection position p3 of the media detection unit 28 is set to a predetermined position on the double-sided transport path 252. The media detection unit 28 is composed of multiple detection units, each equipped with multiple types of different sensors, and detects (determines) the paper characteristics based on the output values ​​corresponding to the current, voltage, amount of light received, etc. of each sensor, i.e., paper characteristic information. As shown in Figure 2, the media detection unit 28 includes, for example, a basis weight detection unit 281, a paper thickness detection unit 282, a moisture content detection unit 283, a paper resistance detection unit 284, a stiffness detection unit 285, a grain direction detection unit 286, a surface quality detection unit 287, and a paper size detection unit 288. These detection units 281 to 288 include detection units that detect paper characteristics that change before and after the fixing process by the fixing unit 27. Detection units 281-288 measure paper characteristic information. This paper characteristic information includes not only information that directly corresponds to the paper characteristics, but also information that is converted from one or more measured values ​​(paper characteristic information) to paper characteristics. In the following, paper characteristics obtained directly from detection units 281-288, or measured values, will be collectively referred to as paper characteristic information or detection data. Furthermore, in order to avoid a roundabout explanation, both cases where paper characteristics are obtained directly from paper characteristic information and cases where paper characteristics are obtained through a conversion process will be described together as if the media detection unit 28 (or detection units 281-288) had acquired the paper characteristics.

[0040] (Measurement surface at each detection unit 281-288, and temporary suspension of transport) Regarding the detection surfaces for the front and back sides, the media detection unit 28 is positioned so that detection units that distinguish between the front and back sides for measurement (for example, a surface detection unit 287 that uses surface reflected light) measure the back side (second side) of the paper 90 transported along the double-sided transport path 252, that is, the side on which the image of the front side (first side) has not been formed. Furthermore, for detection units where the toner image on the back side greatly affects the measurement (for example, a basis weight detection unit 281 that uses transmitted light), the measurement point of the paper may be moved within a predetermined range (several mm to tens of mm) in the transport direction by analyzing the original image data used for printing, in order to minimize the influence. For example, the measurement point may be shifted to a position that avoids the influencing toner image (a blank area without an image). Alternatively, each detection unit 281 to 288 may be arranged so that the measurement point is near the edge in the width direction perpendicular to the transport direction (margin area), where a toner image is normally not formed.

[0041] Of these detection units 281 to 288, detection units 284 to 287 (paper resistance detection unit 284, stiffness detection unit 285, grain direction detection unit 286, and surface quality detection unit 287) temporarily suspend the paper 90 during measurement. Measurements by the other detection units 281 to 283 and 288 can be performed while the paper 90 is being transported without temporarily suspending it. By temporarily suspending the paper, for example, when the paper resistance detection unit 284 measures the paper resistance (volume electrical resistance; the same applies hereinafter) in the center of the entire surface of the paper 90 in the transport direction, the transport of the paper 90 is temporarily suspended when the center of the paper 90 reaches the detection position p3, and the measurement is performed.

[0042] (Detection position p3 of media detection unit 28) Here, detection position p3 is the detection position of the media detection unit 28 in the transport direction, and if the media detection unit 28 includes multiple detection units 281 to 288, detection position p3 has a predetermined width in the transport direction. In the following, unless otherwise specified, detection position p3 refers to the downstream detection position among the detection positions of each of the multiple detection units 281 to 288 (particularly among the detection positions of detection units 284 to 287 that involve temporary pauses).

[0043] In the transport direction, multiple locations on the surface of the paper 90 at different positions may be measured. In this case, if 5 to 6 locations are to be measured, including the front, middle, rear, and intermediate positions, the transport is paused, measured, and then resumed each time a measurement location reaches the detection position p3. Here, the front of the paper 90 is the surface area within a predetermined distance x mm from the edge (0 mm) on the front side. For example, the predetermined distance x is 5 to tens of mm, or 10% of the total length of the paper. Similarly, the rear of the paper 90 is the surface area within a predetermined distance x mm from the edge on the rear side. Note that, as will be described later, the stiffness detection unit 285 and the grain direction detection unit 286 measure the bending stiffness with the front (or rear) of the paper 90 as the free end, so only the front or rear end is the measurement location.

[0044] The media detection unit 28 in the transport direction of the double-sided transport path 252 is positioned such that, when detecting the end of the paper 90 at one of several measurement points, the leading edge of the paper 90 remains within the double-sided transport path 252. That is, the media detection unit 28 is positioned such that the distance from the detection position p3 of the media detection unit 28 to the confluence point p2 (hereinafter referred to as the path length L1 (see Figure 5 below)) is longer than the length L2 from the leading edge of the paper 90 to the last measurement point (L1 > L2). More preferably, the media detection unit 28 may be positioned such that the path length L1 is longer than the maximum paper length L3 of the paper 90 within the specification range in which the image forming apparatus 20 can form a double-sided image (L1 > L3). This eliminates the need to secure unnecessary waiting time during measurement. As a result, the image forming parameters of the paper 90 can be set by reflecting the detection result of the last measurement point of the paper 90 while maintaining maximum productivity without causing a decrease in productivity.

[0045] (Each detection unit 281-288) (Basis weight detection unit 281) The basis weight detection unit 281 is a sensor that detects the basis weight of the paper 90, and comprises a light-emitting unit and a light-receiving unit, measuring the basis weight by the amount of attenuation of light transmitted through the paper 90. For example, the basis weight sensor has a light-emitting unit on one side of the transport path through which the paper is transported (for example, a double-sided transport path 252; the same applies hereinafter) and a light-receiving unit on the other side, and detects the basis weight of the paper 90 by the intensity of the light that passes through the paper 90 and is received by the light-receiving unit.

[0046] (Paper thickness detection unit 282) The paper thickness detection unit 282 includes a pair of transport rollers, at least one of which moves according to the thickness of the paper 90 passing through the roller nip, and a measuring unit that measures the distance between the axes of this pair of transport rollers. This measuring unit is composed of, for example, an actuator, an encoder, and a light-emitting / receiving unit. The axis position of the movable driven roller is displaced according to the thickness of the paper 90 sandwiched between the pair of transport rollers. The paper thickness detection unit 282 measures the thickness of the paper 90 by measuring the height of this displaced axis.

[0047] (Moisture content detection unit 283) The moisture content detection unit 283 measures the moisture content (a physical property value related to the amount of moisture, also called water content) of the paper 90 transported along the transport path using an optical sensor. The moisture content detection unit 283 includes an light-emitting element, a light-receiving element, and optical elements such as a lens, aperture, and collimating lens. In the moisture content detection unit 283, the light-emitting element irradiates the paper 90 with light of a predetermined wavelength in the near-infrared region, and the reflected light is detected by the light-receiving element. The moisture content detection unit 283 detects the moisture content of the paper by utilizing the property that the absorption rate of light of a predetermined wavelength in the near-infrared region changes according to the moisture content of the paper 90.

[0048] (Paper resistance detection unit 284) The paper resistance detection unit 284 detects the paper resistance of the transported paper 90. The paper resistance detection unit 284 includes a pair of transport rollers that grip the paper 90, and an HV (high voltage) unit. When measuring 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 high voltage to the upper roller (also called the detection roller) of the pair of transport rollers, and measures the current value flowing through the paper 90 to the grounded lower roller (opposing roller).

[0049] (Stiffness detection unit 285) The stiffness detection unit 285 detects the bending stiffness of the paper 90, using the leading (or trailing) end as the free end. The stiffness detection unit 285 consists of a holding member, a push-up member that lifts the paper 90 from below, and a pressure detection sensor that detects the pressing force of the push-up member. 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 its edge, and the push-up member lifts the leading end of the free end, measuring the stiffness of the paper 90 by the pressing force at that time. The vertical movement of the push-up member is controlled by a drive motor, such as a stepping motor. The stiffness detection unit 285 uses a transport roller as a holding member, and the holding area (roller nip) and the contact surface of the push-up member are both perpendicular to the transport direction of the paper 90 and the paper surface (transport surface) of the paper 90, and measures the stiffness in the paper transport direction.

[0050] (Eye direction detection unit 286) The grain direction detection unit 286 has the same configuration as the stiffness detection unit 285. The stiffness detection unit 285 measures the stiffness in the paper transport direction, but the grain direction detection unit 286 is positioned such that the contact surfaces of the holding area and the push-up member are in a direction intersecting the paper transport direction, for example, in a direction tilted at a predetermined angle, for example 45 degrees or 90 degrees, with respect to the transport direction when viewed from above (from a direction perpendicular to the transport surface). In this case, a pair of narrow plate members are used as the holding members. By comparing the stiffness in the direction tilted at a predetermined angle (for example 45 degrees) detected by the grain direction detection unit 286 with the stiffness in the paper transport direction detected by the stiffness detection unit 285, the control unit 21 determines whether the grain direction (also called the gap direction) of the paper 90 is vertical or horizontal.

[0051] (Surface texture detection unit 287) The surface detection unit 287 comprises a housing, a light-emitting unit, a collimating lens, and multiple light-receiving units (optical sensors), and optically detects specularly reflected and diffusely reflected light from the paper surface (irradiated surface) as described below. This detects the characteristics of the coating layer of the paper 90. An opening (measurement area) is provided in one of the guide plates (the lower one in Figure 1) in the paper-feeding area of ​​the transport path, and this opening becomes the irradiation area of ​​the light-receiving unit. The paper 90 inserted up to the opening and transported is pressed down by a pressing mechanism that sinks down from above the paper-feeding area. As a result, the paper 90 around the opening (of the guide plate) is held down by the lower guide plate and the pressing mechanism from above. In this state, irradiation light, which is made approximately parallel by the collimating lens, is irradiated from the light-emitting unit at an incident angle of 75° with respect to the reference surface. The wavelength of the irradiation light is, for example, 465 nm. Multiple light-receiving units receive specularly reflected and diffusely reflected light. For example, the light receivers are positioned at three locations with reflection angles of 30 degrees (for diffuse reflection), 60 degrees (for diffuse reflection), and 75 degrees (for specular reflection), or at two locations with reflection angles of 60 degrees and 75 degrees. The surface properties of the paper 90 are detected by the absolute value and ratio of the light intensity received by each light receiver.

[0052] (Paper size detection unit 288) The paper size detection unit 288 detects the length of the paper 90 in the transport direction. For example, the paper size detection unit 288 is a line sensor consisting of multiple image sensors arranged in the width direction, or an optical sensor that detects the presence or absence of paper 90 at a predetermined position in the double-sided transport path 252. In the latter case, one of the multiple paper detection sensors of the transport unit 25 may be made to function as the paper size detection unit 288. Furthermore, to avoid being affected when the line sensor or optical sensor repeatedly stops and transports, the paper length is detected by the timing at which the optical sensor detects the leading and trailing edges of the paper 90, and the transport speed or transport amount (feed amount) at that time. Note that the paper size detection unit 288 may be positioned in a different location from other detection units in the double-sided transport path 252. For example, it may be positioned at least the maximum paper length upstream of the detection position (detection position p3) of the other downstream detection unit.

[0053] (Communications Section 29) The communication unit 29 is an interface for communicating with other devices, such as the image forming apparatus 20. The communication unit 29 also serves as an interface for network connection with external devices such as a PC.

[0054] (Contents of image formation parameters) As described later (Figure 4, etc.), the media detection unit 28 detects the paper characteristics, and the control unit 11 sets image formation parameters related to the image formation process and fixing process. The image formation parameters include transfer current, transfer pressure, fixing temperature, fixing speed, fixing pressure, separation current, static elimination current, etc. The "transfer current" is the current applied to the rotation axis of the secondary transfer roller that constitutes the transfer unit 262, and is set by controlling the output of the constant current power supply. The "transfer pressure" is the pressure between the secondary transfer roller of the transfer unit 262 and the opposing roller arranged on the inner circumference of the intermediate transfer belt. It is set by controlling the pressure variable mechanism connected to the rotation axis of the secondary transfer roller. The "fixing temperature" is the control temperature of the fixing unit 27, and is set by changing the control temperature value. The "fixing speed" is the transport speed of the paper 90 by the fixing unit 27, and the rotation speed of the rollers 273 and 274 of the fixing unit 27 is controlled by the control value of the drive motor. The "fixing pressure" is the nip pressure between the rollers 273 and 274 of the fixing unit 27, and the nip pressure is varied by a pressure variable mechanism provided on the rotation axis of one of the two rollers 273 and 274. The "separation current" is the current applied to the separation unit 263, and is set by controlling the output of the constant current power supply. The "static elimination current" is the current applied to the static elimination unit 264, and is set by controlling the output of the constant current power supply.

[0055] (Setting image formation parameters) The control unit 21 sets image formation parameters based on the paper characteristics obtained by the media detection unit 28. The image formation parameters to be set include at least one of the following: transfer current, transfer pressure, fixing temperature, fixing speed, fixing pressure, static elimination current, and separation current. There are two methods for setting the image formation parameters, as described below.

[0056] (First method) The control unit 21 performs discrimination processing based on multiple paper characteristics to determine the paper type and basis weight. This discrimination process determines that the paper is one of several categorized paper types and several categorized basis weights. Based on the determined paper type and basis weight, it then performs image formation parameter setting processing. When performing this setting processing, it refers to a correspondence table stored in the storage unit 22 beforehand, which describes the control values ​​for transfer, fixing, static elimination, and separation parameters (transfer current, transfer pressure, etc.) for each paper type-basis weight combination.

[0057] (Second method) In the second method, each image formation parameter is determined directly from the paper characteristics. For example, each image formation parameter is determined from one or more of the n paper characteristics. For instance, the transfer parameter is determined from the first and second paper characteristics, the fixing parameter is determined from the first and nth paper characteristics, and the static elimination and separation parameters are determined from paper characteristics 1, 3, and n. In the second method, a pre-trained model learned by machine learning may be used to determine these image formation parameters. In this case, the memory unit 22 stores a pre-trained model used to set the image formation parameters based on the paper characteristics.

[0058] (Paper feeder 10) Refer again to Figure 1. The paper feeder 10 comprises a control unit, a storage unit, a paper feed unit 14, a transport unit 15, and a communication unit. These components have the same functions as the corresponding components of the image forming apparatus 20, so a detailed explanation is omitted. The transport unit 15 includes a transport path 151. The transport unit 15 sends the paper 90 fed from the paper feed unit 14 via the transport path 151 to the downstream image forming apparatus 20.

[0059] (Post-treatment device 30) The post-processing device 30, like the other devices, includes a control unit, a storage unit, and a transport unit 35. The transport unit 35 includes discharge transport paths 351 and 352, and discharges the paper 90 to the output trays 31 and 32 via either of these paths. The post-processing device 30 also includes a post-processing unit 33. This post-processing unit 33 can perform at least one of various post-processing operations on the paper 90 transported from the upstream image forming apparatus 20, such as stapling, punching, and booklet formation. The processed paper 90 is discharged to the output tray 31. For example, as a stapling operation, the post-processing unit 33 stacks multiple sheets of paper 90, and then staples them together.

[0060] (Changes in paper characteristics before and after fixing process) Figure 3 is a schematic diagram illustrating the changes and non-uniformity of paper characteristics before and after the fixing process. Paper characteristics change before and after the fixing process by the fixing unit 27. This change can occur not only uniformly across a single sheet of paper 90, but also unevenly. For example, the heating state changes from the leading edge to the trailing edge of the paper 90, which alters the paper characteristics. Paper characteristics also change depending on the coverage area of ​​the toner image formed by the image processing on the front side. Therefore, in this practical configuration, as described below, the paper characteristics of the paper 90 after the fixing process are detected by a media detection unit 28 located in the double-sided transport path 252, and the image formation parameters for the back side are set using the paper characteristics obtained from the detection results.

[0061] (Image forming process in the first embodiment) Figure 4 is a flowchart showing the image forming process performed by the image forming apparatus 20 in the first embodiment.

[0062] (Step S101) The image forming apparatus 20 starts a print job upon receiving it. If this print job is a double-sided print job, the process proceeds to step S102.

[0063] (Step S102) The control unit 21 feeds the paper 90 from the paper feeding unit 14 or paper feeding unit 24, and the transport unit 25 transports it along the main transport path 251.

[0064] (Step S103) The image forming unit 26 forms a toner image on the transported paper 90, and then the fixing unit 27 fixes the image to the paper 90 by heating and pressurizing.

[0065] (Steps S104, S105) The control unit 21 controls the transport unit 25 and the media detection unit 28 to transport the paper 90 to the double-sided transport path 252, measures paper characteristic information through detection by the media detection unit 28, and acquires paper characteristics either directly or by converting one or more pieces of paper characteristic information. For example, detection is performed while the paper 90 is passing through the detection position p3, and / or transport is temporarily stopped and detection is performed when the center of the transport direction of the paper 90 is reached. The paper characteristics acquired through detection include at least one of basis weight, paper thickness, moisture content, paper resistance, stiffness, grain direction, surface quality, and paper size.

[0066] (Step S106) The control unit 21 sets image formation parameters based on the obtained paper characteristics using the first or second method described above. The image formation parameters to be set include at least one of the following: transfer current, transfer pressure, fixing temperature, fixing speed, fixing pressure, static elimination current, and separation current.

[0067] (Step S107) The control unit 21 causes the transport unit 25 to transport the paper 90 back to the main transport path 251, and causes the image forming unit 26 and the fixing unit 27 on the transport path to form an image on the back side of the paper 90. The image forming parameters for back side image formation are those set in step S106.

[0068] As described above, the image forming apparatus 20 according to the first embodiment includes a first media detection unit provided on a double-sided transport path and acquiring paper characteristic information corresponding to the paper characteristics of the paper transported on the double-sided transport path, and a control unit that sets image forming parameters for the back side of the paper based on the paper characteristic information of the paper acquired by the first media detection unit. This allows for the proper setting of image forming conditions for the back side by detecting the paper characteristic information during the back side process.

[0069] (modified version) In the first embodiment described above, only one measurement was performed in the transport direction for measuring the paper 90, but multiple measurements may be performed as shown in the modified example below.

[0070] Figure 5 is a schematic diagram illustrating detection at multiple locations with different positions in the transport direction. Figure 6 is a diagram showing an example of setting image formation parameters according to the paper position in the transport direction. As shown in Figure 5(a), when the leading edge of the paper 90 reaches the detection position p3, the paper 90 is stopped and detection is performed by the media detection unit 28. Then, the paper 90 is transported again, and as shown in Figure 5(b), when the center of the paper 90 reaches the detection position p3, the paper 90 is stopped and detection is performed by the media detection unit 28. In Figure 5(c), the same transport and stop process is repeated, and detection is performed by the media detection unit 28 at the rear end of the paper 90. Note that the example shown in Figure 5 shows detection at three locations: the leading edge, the center, and the rear end, but it is not limited to this, and measurements may be taken at four or more locations. For example, detection may be performed at five locations, adding the intermediate position between the leading edge and the center, and the intermediate position between the center and the rear end, in addition to the three locations mentioned above. Furthermore, the measurement point may always be the same for paper of the same size 90, or it may be moved in the transport direction within a predetermined range (a few millimeters to a dozen millimeters) based on the original image data, or detection of that point may be skipped. For example, if a solid image is formed on the front surface, the measurement point may be shifted or skipped to avoid its influence on the detection data.

[0071] Regarding the reflection of the image formation parameters, the paper characteristics obtained using the averaged values ​​of the detection data obtained from detection at multiple locations may be used, or, as shown in Figure 6, multiple image formation parameters may be set according to the paper characteristics at each position in the transport direction of the paper 90. Figure 6 shows the settings of the transfer current at the paper position, set according to the paper resistance and moisture content obtained as paper characteristics. In Figure 6, the transfer current is set linearly according to the distribution of paper characteristics at five locations (front to rear) of the paper 90 and is changed smoothly and continuously, but it is not limited to this, and output may be set in multiple stages (for example, 5 stages).

[0072] As shown in Figure 5(c), the media detection unit 28 is positioned such that when detecting the end of the paper 90 at one of the multiple measurement points in the transport direction of the paper 90, the leading edge of the paper 90 remains within the double-sided transport path 252. In other words, if the distance between the detection point p3 and the junction point p2 is the path length L1, and the length of the paper from the leading edge of the paper 90 to the last measurement point is the length L2, the media detection unit 28 is positioned such that L1 > L2.

[0073] In this modified example, the media detection unit 28 performs detection at multiple locations on a single sheet of paper that differ in position along the transport direction. This allows the unit to appropriately grasp the paper characteristics even if the paper characteristics change unevenly due to the fixing process by the fixing unit 27, and to appropriately set the image formation parameters for the reverse side. Furthermore, by setting multiple image formation parameters according to the position along the transport direction on a single sheet of paper based on the distribution of paper characteristics obtained from detection at multiple locations, the image formation parameters can be set more appropriately.

[0074] Furthermore, in the double-sided transport 252, when the media detection unit 28 temporarily suspends paper transport to detect the paper 90, the path length L1 > length L2 is set so that when detecting the last part of the paper among multiple locations (detection areas) on a single sheet of paper, the leading edge of the paper remains within the double-sided transport path 252. This arrangement eliminates the need to secure a wait time associated with the measurement by the media detection unit 28. As a result, the image formation parameters for the back side of the paper 90 can be set while maintaining maximum productivity without causing a decrease in productivity. For example, in Patent Document 1 (JP 2014-199425 A), the paper type is detected by an optical sensor placed directly in front of the register roller (resist part), so the timing of this detection is not sufficient to set the image formation parameters for the back side, and a wait time is required to temporarily suspend the paper. In this embodiment, the image formation parameters for the back side can be set and the image formation for the back side can be performed using these parameters without requiring such a wait time.

[0075] (Second embodiment) Next, with reference to Figure 7, the image forming process in the second embodiment will be described. In the second embodiment, paper characteristics are acquired only for some of the paper types, and for the other types of paper, the image forming parameters are set using the paper characteristics obtained from the partial paper types. Figure 7 is a flowchart showing the image forming process performed by the image forming apparatus in the second embodiment.

[0076] (Steps S201~S204) The processing in steps S201 to S204 is the same as steps S101 to S104 in Figure 4 of the first embodiment, and therefore the explanation is omitted.

[0077] (Step S205) Here, the control unit 21 proceeds to step S206 if the print job in progress is a double-sided print job using the same paper 90 consecutively, and if it has not reached a predetermined number of sheets since the start of the print job (NO). On the other hand, if it has reached a predetermined number of sheets (YES), it proceeds to step S208. For example, the predetermined number of sheets is 5. For the first 1 to 5 sheets of the print job, the processing from step S206 onwards is executed, and for the predetermined number of sheets and beyond (6th sheet onwards), the processing from S208 onwards is executed. Also, if the paper tray is switched due to running out of paper in the middle of the same print job, or if multiple different paper sizes are used in one print job, the same processing may be performed for the paper 90 up to the predetermined number after feeding from a new paper tray.

[0078] (Steps S206, S207) The processes in steps S206 and S207 are the same as steps S105 and S106 in Figure 4, and therefore their explanation is omitted. The detection data or paper characteristics obtained from these processes are stored in the storage unit 22.

[0079] (Step S208) Here, the control unit 21 sets the image formation parameters on the back side based on the paper characteristics using the same process as in step S207. Unlike step S207, the paper characteristics of the target paper 90 are not acquired, so the paper characteristics of other papers 90 that have already been obtained are used. For example, the paper characteristics may be determined from the average value of the detection data obtained by detecting a predetermined number of sheets (for example, the average of the 1st to 5th sheets), or the paper characteristics of the paper 90 that was last processed in step S206 (for example, the 5th sheet) may be reused.

[0080] (Step S209) The control unit 21 causes the transport unit 25 to transport the paper 90 back to the main transport path 251, and causes the image forming unit 26 and the fixing unit 27 on the transport path to form an image on the back side of the paper 90. The image forming parameters for back side image formation are those set in step S207 or step S208.

[0081] Thus, in the second embodiment, the paper characteristics obtained by detecting a predetermined number of sheets are used to set the image formation parameters for the back side of the sheets beyond that predetermined number. By doing so, the same effects as in the first embodiment or its modified form can be obtained.

[0082] (Third embodiment) Next, a third embodiment will be described with reference to Figures 8 to 11. The third embodiment uses media detection units 28b and 28c (second media detection units) for the front side (first side), in addition to the same media detection unit 28a (first media detection unit) for the back side as in the first and second embodiments.

[0083] The configurations of the media detection units 28a, 28b, and 28c are the same as those of the media detection unit 28 in the first embodiment (Figures 1, 2, etc.), and therefore no further explanation is provided. In the third embodiment, the image formation parameters for the front side of the paper 90 are set based on the paper characteristics obtained from the second media detection unit 28b (or 28c). The image formation parameters for the front side include, as with the back side, the transfer current of the transfer unit 262, transfer pressure, fixing temperature, fixing speed, fixing pressure, separation current, static elimination current, etc.

[0084] Figure 8 shows the position of the second media detection unit 28b for the front surface in the image forming system 1000x in the third embodiment. Figure 9 shows the position of the second media detection unit 28c in the image forming system 1000y in another modified example. In Figures 8 and 9, components that are the same as those in Figure 1 are denoted by the same reference numerals and their description is omitted. In the third embodiment shown in Figures 8 and 9, the first media detection unit 28a is positioned on the double-sided transport path 252, similar to the first embodiment shown in Figure 1.

[0085] In the example shown in Figure 8, the second media detection unit 28b is included in the image forming apparatus 20. The media detection unit 28b (second media detection unit) is provided on the main transport path 251 and detects the paper 90 being transported along this main transport path 251. The detection position of the media detection unit 28b is set to a predetermined position on the main transport path 251, for example, upstream of the registration roller directly upstream of the image forming unit 26, and the media detection unit 28b detects the paper 90 before it is fixed by the fixing unit 27. In the example in Figure 8, the media detection unit 28b is located further upstream of the confluence point p2, but it may also be located downstream of the confluence point p2.

[0086] In another modified example shown in Figure 9, the second media detection unit 28c is provided in the transport path 151 of the paper feed device 10 and detects the paper 90 before fixing as it is transported along this transport path 151. The control unit 21 of the image forming apparatus 20 acquires detection data or paper characteristics of the paper 90 either via the control unit of the paper feed device 10 or directly from the media detection unit 28c.

[0087] (Image forming process in the third embodiment) The third embodiment will be described below with reference to Figures 10 and 11. In the third embodiment, a media detection unit for the front side is also used, and the image formation parameters for the front side are set based on the paper characteristics obtained from this unit. In addition, the image formation parameters for the back side are set by linking the paper characteristics obtained from the two media detection sensors. Figure 10 is a flowchart showing the image formation process in the third embodiment, and Figure 11 is a schematic diagram illustrating an example of image formation parameters for the back side set by linking the paper characteristics of both the front and back sides. The image formation process in Figure 10 is applicable to either the image formation systems 1000x and 1000y in Figures 8 and 9, but the image formation system 1000x in Figure 8 will be used as an example for explanation.

[0088] (Steps S301, S302) The processes in steps S301 and S302 are the same as steps S101 and S102 in Figure 4 of the first embodiment, and therefore their explanation is omitted.

[0089] (Step S303) Here, the second media detection unit 28b acquires paper characteristics. For example, detection is performed while the paper 90 is passing through the detection position, and / or when the center of the paper 90 in the transport direction is reached, transport is temporarily stopped and detection is performed. The paper characteristics acquired by detection include at least one of the following: basis weight, paper thickness, moisture content, paper resistance, stiffness, grain direction, surface quality, and paper size.

[0090] (Step S304) The control unit 21 sets image formation parameters based on the obtained paper characteristics using the first or second method described above. The processing here is the same as the processing in step S106 for the reverse side. The image formation parameters set in step S304 include at least one of the following: transfer current, transfer pressure, fixing temperature, fixing speed, fixing pressure, static elimination current, and separation current.

[0091] (Step S305) The control unit 21 causes the image forming unit 26 and the fixing unit 27 to form an image on the front side (first side) of the paper 90. The image forming parameters for this front side image formation are those set in step S304.

[0092] (Steps S306, S307) The processes in steps S306 and S307 are the same as steps S104 and S105 in Figure 4 of the first embodiment, and their explanation is omitted. The paper 90 is transported to the double-sided transport path 252, and the paper characteristics are acquired by the first media detection unit 28a.

[0093] (Step S308) Here, the control unit 21 sets the image formation parameters for the back side based on the paper characteristics of the back side, similar to step S106 in Figure 4. Furthermore, the control unit 21 sets some of the image formation parameters for the back side of the paper based on the paper characteristics obtained from both the first and second media detection units 28a and 28b through the processing in steps S303 and S307. These some of the image formation parameters require relative values ​​for the front and back sides when setting them. The paper characteristics of both sides are linked and reflected in the setting of the image formation parameters. Figure 11 shows an example of the back side magnification as an image formation parameter to be reflected. The degree of shrinkage of the paper 90 caused by the fixing process is grasped from the paper characteristics of both sides, and a magnification is set according to the degree of shrinkage (for example, set to the reciprocal of the shrinkage rate). Specifically, the paper size is input as the paper characteristics of the front and back sides, and is reflected in the back side magnification as the output. For example, the difference or ratio between the paper size y1 on the front side and the paper size y2 on the back side is reflected in the back magnification as an image formation parameter to suppress image shrinkage. In the example shown in the figure, the front magnification is 1.00 and the back magnification is 1.05.

[0094] (Step S309) The control unit 21 causes the transport unit 25 to transport the paper 90 back to the main transport path 251, and causes the image forming unit 26 and the fixing unit 27 on the transport path to form an image on the back side of the paper 90. The image forming parameters during back side image formation are those set in step S308. For example, the exposure period and polygon rotation speed of the exposure unit of the image forming unit 26 are changed, or the spacing between pixels is changed, according to the set magnification.

[0095] Thus, the third embodiment further includes a second media detection unit, which is positioned upstream of the image forming unit in the transport direction and detects the paper before it is fixed by the fixing unit 27. This allows for setting the image forming parameters for the front side. With this configuration, the same effects as in the first and second embodiments can be obtained, and furthermore, the image forming conditions can be properly set not only for the back side but also for the front side. By linking the paper characteristics acquired by the first and second media detection units, more appropriate image forming conditions can be set.

[0096] The configuration of the image forming apparatus including the media detection unit described above, and the configuration of the image forming system equipped therewith, are described above only as the main configuration in order to explain the features of the above embodiment, and are not limited to the above configuration, and can be modified in various ways within the scope of the claims. Furthermore, this does not preclude the configurations that are generally found in image forming apparatuses.

[0097] Furthermore, each embodiment may be combined and applied to one another. For example, modified versions (Figures 5 and 6) may be applied to the second and third embodiments. That is, in the second and third embodiments, detection may be performed at multiple locations while repeatedly transporting and pausing the paper, and furthermore, multiple image formation parameters may be set according to the position of the paper in response to this detection. In particular, in the third embodiment, for the front side, detection may be performed at only one location on the paper by the second media detection unit 28b (or 28c), and for the back side, detection may be performed at multiple locations on the paper by the first media detection unit 28a.

[0098] Furthermore, the means and methods for performing various processing in the image forming apparatus 20 according to the above embodiment can be implemented by either a dedicated hardware circuit or a programmed computer. The program may be provided, for example, on a computer-readable recording medium such as a USB memory stick or a DVD (Digital Versatile Disc)-ROM, or it may be provided online via a network such as the Internet. In this case, the program recorded on the computer-readable recording medium is usually transferred to and stored in a storage unit such as a hard disk. The program may also be provided as a standalone application software, or it may be incorporated into the software of the apparatus as a function of the apparatus. [Explanation of Symbols]

[0099] 1000, 1000x, 1000y image forming system 10 Paper feeder 20 Image forming apparatus 21 Control Unit 22 Memory section 23 Operation display section 24 Paper feed section 25 Conveying section 251 Main transport path 252 Double-sided transport path 26 Image forming unit 261 Developing Department 262 Transfer section 263 Separation section 264 Static Elimination Unit 27 Fixing section 271 Heater 272 Thermometer 28, 28a, 28b, 28c Media detection unit 281 Basis weight detection unit 282 Paper thickness detection unit 283 Moisture content detection unit 284 Paper resistance detection unit 285 Stiffness detection unit 286 Eye direction detection unit 287 Surface texture detection unit 288 Paper size detection unit 29 Communications Department 30 Post-processing equipment

Claims

1. An image forming unit that forms a toner image on paper, A fixing unit that fixes the toner image formed by the image forming unit onto the paper, A transport unit including a main transport path and a double-sided transport path that guides paper fed from the paper feeding unit to the discharge unit via the image forming unit and the fixing unit, A first media detection unit is provided in the double-sided transport path and acquires paper characteristic information corresponding to the paper characteristics of the paper transported in the double-sided transport path. An image forming apparatus comprising: a control unit that sets image forming parameters for the back surface of the paper based on the paper characteristic information of the paper acquired by the first media detection unit, The first media detection unit is characterized by detecting a single sheet of paper at multiple locations that are different in the transport direction, and by repeatedly transporting and stopping the paper to be detected, thereby performing detection at the multiple locations.

2. The image forming apparatus according to claim 1, wherein the double-sided transport path is connected to the main transport path downstream of the fixing unit and upstream of the image forming unit from the main transport path, inverts the front and back sides of the paper fixed in the fixing unit, and leads it back to the image forming unit.

3. The image forming apparatus according to claim 1 or claim 2, wherein the aforementioned multiple locations include at least the positions of the leading edge of the paper and the trailing edge of the paper.

4. The image forming apparatus according to any one of claims 1 to 3, wherein the position of the first media detection unit is set such that when detecting the last end of a sheet of paper among the multiple locations on the sheet, the leading edge of the paper remains within the double-sided transport path.

5. An image forming unit that forms a toner image on paper, A fixing unit that fixes the toner image formed by the image forming unit onto the paper, A transport unit including a main transport path and a double-sided transport path that guides paper fed from the paper feeding unit to the discharge unit via the image forming unit and the fixing unit, A first media detection unit is provided in the double-sided transport path and acquires paper characteristic information corresponding to the paper characteristics of the paper transported in the double-sided transport path. An image forming apparatus comprising: a control unit that sets image forming parameters for the back surface of the paper based on the paper characteristic information of the paper acquired by the first media detection unit, The first media detection unit performs detection on a single sheet of paper at multiple locations that differ in position in the transport direction, The image forming apparatus is characterized in that the control unit sets multiple image forming parameters on a single sheet of paper according to its position in the transport direction, based on the distribution of paper characteristics obtained by detection at the multiple locations.

6. The image forming apparatus according to claim 1, characterized in that the paper characteristics include at least one of basis weight, paper thickness, moisture content, paper resistance, stiffness, surface properties, and paper size.

7. The image forming apparatus according to claim 1, characterized in that the image forming parameters include at least one of the following: transfer current, transfer pressure, fixing temperature, fixing speed, fixing pressure, static elimination current, and separation current.

8. An image forming unit that forms a toner image on paper, A fixing unit that fixes the toner image formed by the image forming unit onto the paper, A transport unit including a main transport path and a double-sided transport path that guides paper fed from the paper feeding unit to the discharge unit via the image forming unit and the fixing unit, A first media detection unit is provided in the double-sided transport path and acquires paper characteristic information corresponding to the paper characteristics of the paper transported in the double-sided transport path. An image forming apparatus comprising: a control unit that sets image forming parameters for the back surface of the paper based on the paper characteristic information of the paper acquired by the first media detection unit, In a printing job that continuously forms images on both sides of multiple sheets of paper, The control unit causes the first media detection unit to perform detection on a predetermined number of sheets of paper from the start of the print job, and An image forming apparatus characterized by setting image forming parameters for the reverse side of paper for a number of sheets beyond the predetermined number, using the paper characteristics obtained by detecting up to the predetermined number of sheets.

9. The system further includes a second media detection unit, which is positioned upstream of the image forming unit in the transport direction and detects the paper before it is fixed in the fixing unit. The image forming apparatus according to any one of claims 1 to 8, wherein the control unit sets the image forming parameters for the front surface of the paper based on paper characteristic information corresponding to the paper characteristics acquired by the second media detection unit.

10. The image forming apparatus according to claim 9, wherein the control unit sets the image forming parameters for the back surface of the paper based on both the paper characteristic information obtained by the detection of the first and second media detection units, respectively.

11. A second media detection unit is positioned upstream of the image forming unit in the transport direction, detects the paper before it is fixed in the fixing unit, and acquires paper characteristic information corresponding to the paper characteristics used to set the image forming parameters on the front surface of the paper. An image forming apparatus according to any one of claims 1 to 8, An image forming system comprising the following features.

12. A control program for controlling an image forming apparatus comprising: an image forming unit that forms a toner image on paper; a fixing unit that fixes the toner image formed by the image forming unit to the paper; and a media detection unit provided on a double-sided transport path that acquires paper characteristic information corresponding to the paper characteristics of the paper transported on the double-sided transport path, The image forming unit and the fixing unit form an image on the front surface of the paper (a), Step (b) involves transporting the paper on which the image was formed in step (a) to the double-sided transport path and acquiring paper characteristic information using the media detection unit. Step (c) is to set the image formation parameters for the back surface of the paper based on the paper characteristic information obtained in step (b), A control program for causing a computer to perform a process including step (d) of forming an image on the back of the paper using the image forming parameters set in step (c), Step (b) is a control program characterized by performing detection at multiple locations with different positions in the transport direction for a single sheet of paper, and by repeatedly transporting and stopping the paper to be detected.

13. A control program for controlling an image forming apparatus comprising: an image forming unit that forms a toner image on paper; a fixing unit that fixes the toner image formed by the image forming unit to the paper; and a media detection unit provided on a double-sided transport path that acquires paper characteristic information corresponding to the paper characteristics of the paper transported on the double-sided transport path, The image forming unit and the fixing unit form an image on the front surface of the paper (a), Step (b) involves transporting the paper on which the image was formed in step (a) to the double-sided transport path and acquiring paper characteristic information using the media detection unit. Step (c) is to set the image formation parameters for the back surface of the paper based on the paper characteristic information obtained in step (b), A control program for causing a computer to perform a process including step (d) of forming an image on the back of the paper using the image forming parameters set in step (c), In step (b) above, detection is performed on a single sheet of paper at multiple locations that are different in the transport direction, The control program, in step (c), is characterized by setting multiple image forming parameters on a single sheet of paper according to its position in the transport direction, based on the distribution of paper characteristics obtained by detection at the multiple locations.

14. The control program according to claim 12, characterized in that the paper characteristics include at least one of basis weight, paper thickness, moisture content, paper resistance, stiffness, surface properties, and paper size.

15. The control program according to claim 12, characterized in that the image forming parameters include at least one of a transfer current, a transfer pressure, a fixing temperature, a fixing speed, a fixing pressure, a static elimination current, and a separation current.

16. A control program for controlling an image forming apparatus comprising: an image forming unit that forms a toner image on paper; a fixing unit that fixes the toner image formed by the image forming unit to the paper; and a media detection unit provided on a double-sided transport path that acquires paper characteristic information corresponding to the paper characteristics of the paper transported on the double-sided transport path, wherein The image forming unit and the fixing unit form an image on the front surface of the paper (a), Step (b) involves transporting the paper on which the image was formed in step (a) to the double-sided transport path and acquiring paper characteristic information using the media detection unit. Step (c) is to set the image formation parameters for the back surface of the paper based on the paper characteristic information obtained in step (b), A control program for causing a computer to perform a process including step (d) of forming an image on the back of the paper using the image forming parameters set in step (c), In a printing job that continuously forms images on both sides of multiple sheets of paper, The detection by the media detection unit in step (b) above is performed on paper from the start of the print job up to a predetermined number of sheets, and, A control program characterized by setting image formation parameters for the reverse side of paper beyond a predetermined number of sheets, using the paper characteristics obtained by detecting up to a predetermined number of sheets.

Images