Image forming apparatus, conveying method, and program

Abstract

To provide an image forming apparatus, a conveying method, and a program that can prevent trouble such as slack in continuous form paper and appropriately convey the continuous form paper.SOLUTION: An image forming apparatus can perform printing on continuous form paper, and the image forming apparatus comprises: a fixing unit that fixes an image to an unfixed surface of the continuous form paper, while conveying the continuous form paper at a fixing nip; a downstream side conveying unit that is arranged on the downstream side in a sheet conveyance direction of the fixing unit, and conveys the continuous form paper at a downstream side conveying nip; a detection unit that detects a physical quantity related to a thermal expansion state of a fixing member that forms the fixing nip; and a control unit that controls driving modes in the fixing unit and the downstream side conveying unit on the basis of a result of detection performed by the detection unit.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, a conveying method, and a program. [Background technology]

[0002] In image forming devices (printers, copiers, facsimiles, etc.) that utilize electrophotographic process technology, a laser beam based on image data is irradiated (exposed) onto a uniformly charged photoconductor, forming an electrostatic latent image on the surface of the photoconductor. Then, toner is supplied to the photoconductor, and the electrostatic latent image is visualized as a toner image. This toner image is indirectly transferred to a recording material, for example, via an intermediate transfer body, and is then heated and pressed in a fixing section. Through the above steps, an image is formed on the recording material. In addition to sheets of paper, continuous paper such as rolled paper can also be used as the recording material.

[0003] The electrophotographic image forming apparatus described above has transport nips at multiple locations on the transport path of the recording material. The transport nips include a fixing nip in a fixing unit. The transport nip is formed by a pair of transport members. In particular, the fixing nip is formed by a pair of fixing members (e.g., a fixing roller and a pressure roller). One of the pair of transport members (fixing member in the case of a fixing nip) is composed of a drive roller that can be rotated. When the recording material is passed through the transport nip, the rotational force of the drive roller is transmitted to the recording material, and the recording material is transported.

[0004] When printing on continuous paper, the continuous paper passes through the fixing nip of the fixing unit and the transport nip of a downstream transport unit located downstream of the fixing unit in the paper transport direction (hereinafter referred to as the "downstream transport nip").

[0005] In the fixing section, during non-printing periods when printing is not being performed on the continuous paper, the pair of fixing members that form the fixing nip are normally held apart from each other and pressed against each other when printing starts so that damage such as discoloration of the continuous paper does not occur due to heat transfer from the fixing members. When printing starts, transport of the continuous paper starts when a fixing nip of a predetermined width is formed in the process of the fixing members transitioning from a separated state to a pressed state. Also, when printing ends, transport of the continuous paper stops when the nip width becomes equal to or less than the predetermined width and the fixing nip is released in the process of the fixing members transitioning from a pressed state to a separated state.

[0006] Here, if the timing at which the fixing nip starts to transport the continuous paper (the timing at which the continuous paper starts to move) is earlier than the timing at which the downstream transport nip starts to transport the continuous paper, the continuous paper may become loose and may wind around the fixing member. Also, if the timing at which the fixing nip stops transporting the continuous paper is later than the timing at which the downstream transport nip stops transporting the continuous paper, the continuous paper may also become loose and may wind around the fixing member. Hereinafter, the transport start timing and transport stop timing at the fixing section and the transport start timing and transport stop timing at the downstream transport section are referred to as the "fixing side transport start timing," "fixing side transport stop timing," "downstream side transport start timing," and "downstream side transport stop timing," respectively.

[0007] In addition, if the downstream transport start timing is earlier than the fixing transport start timing, the continuous paper cannot be transported by the downstream transport nip alone, and the continuous paper may slip at the downstream transport nip, generating abnormal noise. This problem is particularly likely to occur when using thick continuous paper that is subject to a large transport load.

[0008] Conventionally, the operation of each driving roller is controlled in the fixing section and the downstream transport section so as not to generate abnormal noise due to slack or slippage of the continuous paper. Specifically, the operation of the driving roller in the downstream transport section is controlled assuming that the fixing side transport start timing and the fixing side transport stop timing are constant. "The fixing side transport start timing is constant" means that the time required from the start of the transition operation from the separated state to the pressed state (hereinafter referred to as the "pressing operation") until the fixing nip of a predetermined width is formed is constant. Also, "the fixing side transport stop timing is constant" means that the time required from the start of the transition operation from the pressed state to the separated state (hereinafter referred to as the "separating operation") until the fixing nip is released is constant. In other words, the driving roller in the downstream transport section is controlled to start or stop driving after a certain time based on the time point when the pressing operation or the separating operation is started in the fixing section. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2010-72493 A Summary of the Invention [Problem to be solved by the invention]

[0010] However, the fixing member is usually provided with an elastic layer made of a resin material with a relatively large thermal expansion coefficient, such as silicone rubber. Therefore, the timing at which the fixing nip is formed and the timing at which the fixing nip is released change depending on the thermal expansion state of the elastic layer. In this case, in the conventional control that assumes that the fixing side conveyance start timing and the fixing side conveyance stop timing are constant, there is a risk that a deviation occurs in the conveyance start timing and the conveyance stop timing in the fixing section and the downstream conveyance section, and problems such as slack occurring in the continuous paper cannot be prevented.

[0011] Patent Document 1 discloses that the drive speeds of the fixing roller and the upstream registration roller are corrected based on the temperature change of the device body, taking into account the thermal expansion of the fixing roller. However, there is no disclosure regarding drive control in the fixing unit and the downstream transport unit.

[0012] An object of the present invention is to provide an image forming apparatus, a conveying method, and a program that can prevent problems such as slack that can occur in the continuous paper and convey the continuous paper properly. [Means for solving the problem]

[0013] The image forming apparatus according to the present invention comprises: An image forming apparatus capable of printing on continuous paper, a fixing section that fixes an image onto an unfixed surface of the continuous paper while transporting the continuous paper through a fixing nip; a downstream transport section disposed downstream of the fixing section in a paper transport direction and configured to transport the continuous paper by a downstream transport nip; a detection unit that detects a physical quantity related to a thermal expansion state of a fixing member that forms the fixing nip; and a control unit that controls a driving mode of at least one of the fixing unit and the downstream transport unit based on a detection result by the detection unit.

[0014] The conveying method according to the present invention comprises the steps of: A conveying method in an image forming apparatus capable of printing on continuous paper, comprising the steps of: conveying the continuous paper through a fixing nip where the image is fixed onto an unfixed side of the continuous paper; transporting the continuous paper through a downstream transport nip disposed downstream of the fixing nip in a paper transport direction; detecting a physical quantity related to a thermal expansion state of a fixing member that forms the fixing nip; and controlling a driving mode of at least one of a fixing section in which the fixing nip is arranged and a downstream transport section in which the downstream transport nip is arranged based on the detected physical quantity related to the thermal expansion state.

[0015] The program according to the present invention comprises: A program for causing a computer of an image forming device capable of printing on continuous paper to execute a predetermined process, The predetermined process includes: a process of conveying the continuous paper through a fixing nip in which an image is fixed to an unfixed side of the continuous paper; a process of transporting the continuous paper by a downstream transport nip disposed downstream of the fixing nip in a paper transport direction; A process of detecting a physical quantity related to a thermal expansion state of a fixing member that forms the fixing nip; and controlling a driving mode of at least one of a fixing section in which the fixing nip is arranged and a downstream transport section in which the downstream transport nip is arranged based on the detected physical quantity related to the thermal expansion state. Effect of the Invention

[0016] According to the present invention, problems such as slackness that may occur in the continuous paper can be prevented, and the continuous paper can be transported properly. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a system configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a schematic overall configuration of the main body of the image forming apparatus. [Diagram 3] FIG. 3 is a diagram showing the main components of a control system of the image forming apparatus. [Figure 4] 4A and 4B are diagrams illustrating the configuration of the fixing unit. [Diagram 5] FIG. 5 is a flowchart showing an example of a conveyance start process in the image forming apparatus. [Figure 6] FIG. 6 is a diagram showing an example of the drive start timing setting data. [Figure 7] FIG. 7 is a flowchart showing an example of a transport stop process in the image forming apparatus. [Figure 8]FIG. 8 is a diagram showing an example of drive stop timing setting data. [Figure 9] FIG. 9 is a diagram showing an example of drive start timing setting data prepared for each paper thickness. [Figure 10] FIG. 10 is a diagram showing an example of drive start timing setting data corrected in consideration of durability. [Figure 11] FIG. 11 is a diagram showing an example of drive start timing setting data for determining the durability of the fixing roller. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0019] FIG. 1 is a diagram showing a system configuration of an image forming apparatus 1 according to an embodiment.

[0020] As shown in FIG. 1, the image forming apparatus 1 includes an image forming apparatus main body 1A, an image calibration control unit (ICCU) 1B, a paper feed unit 1C, and a winding unit 1D.

[0021] In the image forming device 1, the control unit 11 (see FIG. 3) of the image forming device main body 1A functions as a printer controller and controls the image calibration control unit 1B, the paper feeding unit 1C and the winding unit 1D, together with each block of the image forming device main body 1A, based on the printing data sent from the client terminal 2.

[0022] The image forming apparatus main body 1A is connected to a client terminal 2 via a communication network 3 such as a LAN (Local Area Network) or a WAN (Wide Area Network). The image forming apparatus main body 1A performs printing on continuous paper S based on print data from the client terminal 2, for example.

[0023] The image calibration control unit 1B inspects and calibrates the image formed by the image forming apparatus main body 1A. The image calibration control unit 1B is disposed downstream of the image forming apparatus main body 1A in the paper transport direction. The image calibration control unit 1B has a downstream transport section 40 capable of transporting the continuous paper S.

[0024] The downstream transport section 40 has a downstream drive roller 41 and a driven roller 42. The downstream drive roller 41 and the driven roller 42 have a configuration in which an elastic layer (e.g., thickness: 5 mm, JIS-A hardness: 60°) made of silicone rubber or the like is formed on the outer circumferential surface of a cylindrical core metal made of iron or the like. The outer diameter of the downstream drive roller 41 and the driven roller 42 is, for example, 24 mm.

[0025] The control unit 11 of the image forming apparatus main body 1A controls the drive of the downstream drive roller 41. Specifically, the control unit 11 controls the output to a drive motor (not shown) connected to the downstream drive roller 41 to rotate the downstream drive roller 41 at a set rotation speed.

[0026] The downstream drive roller 41 and the driven roller 42 are held in a state of being pressed against each other with a predetermined pressure load (e.g., 20 N) to form the downstream transport nip N2. The downstream drive roller 41 rotates at a set rotation speed, thereby transporting the continuous paper S that has passed through the downstream transport nip N2.

[0027] The paper feed unit 1C follows instructions from the control unit 11 of the image forming apparatus main body 1A to pay out the rolled continuous paper S and feed it to the image forming apparatus main body 1A.

[0028] The winding unit 1D winds up the continuous paper S discharged from the image calibration control unit 1B in accordance with an instruction from the control unit 11 of the image forming apparatus main body 1A.

[0029] 2 is a diagram showing a schematic overall configuration of the image forming apparatus main body 1A, and FIG.

[0030] The image forming apparatus main body 1A is an intermediate transfer type color image forming apparatus that utilizes electrophotographic process technology. The image forming apparatus main body 1A primarily transfers the Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photosensitive drum 213 onto the intermediate transfer belt 221, and then superimposes the four color toner images on the intermediate transfer belt 221, and then secondarily transfers the images onto a recording material to form an image.

[0031] In this embodiment, the image forming apparatus main body 1A employs a vertical tandem system in which photosensitive drums 213 corresponding to the four colors, CMYK, are arranged in series in the running direction (vertical direction) of the intermediate transfer belt 221, and each color toner image is transferred sequentially to the intermediate transfer belt 221 in a single step.

[0032] As shown in Figures 2 and 3, the image forming apparatus main body 1A includes a control unit 11, an operation display unit 12, an image processing unit 13, a paper feed unit 14, a paper discharge unit 15, a recording material transport unit 16, an image forming unit 20, and a fixing unit 30.

[0033] The control unit 11 is a computer having a CPU (Central Processing Unit) 111 as an arithmetic / control device, a ROM (Read Only Memory) 112 as a main storage device, and a RAM (Random Access Memory) 113. Basic programs and basic setting data are stored in the ROM 112. The ROM 112 also stores programs for implementing image forming processes including a conveying process and the like. The CPU 111 reads out a program corresponding to the process content from the ROM 112, loads it in the RAM 113, and executes the loaded program to control the operation of each functional block of the image forming apparatus 1.

[0034] The control unit 11 performs overall control of the image forming apparatus main body 1A by controlling the operation display unit 12, the image processing unit 13, the paper feed unit 14, the paper discharge unit 15, the recording material transport unit 16, the image forming unit 20 and the fixing unit 30 according to their respective functions.

[0035] In this embodiment, the functions of each functional block are realized by cooperation between each piece of hardware constituting the functional block and the control unit 11. Note that the control unit 11 may execute a program to realize some or all of the functions of each functional block.

[0036] The operation display unit 12 is configured with, for example, a flat panel display with a touch panel. As the flat panel display, a liquid crystal display, an organic EL display, etc. can be used. The operation display unit 12 has a display unit 121 and an operation unit 122.

[0037] The display unit 121 displays various operation screens, image states, operation statuses of each function, and the like, in accordance with a display control signal input from the control unit 11.

[0038] The operation unit 122 includes various operation keys such as a numeric keypad and a start key, accepts various input operations by the user, and outputs operation signals to the control unit 11. The user can operate the operation display unit 12 to perform settings related to image formation, such as document settings, image quality settings, magnification settings, application settings, output settings, and recording material settings.

[0039] The image processing unit 13 includes a circuit for performing digital image processing on the input image data according to initial settings or user settings. For example, the image processing unit 13 performs gradation correction based on gradation correction data under the control of the control unit 11. The image processing unit 13 also performs various correction processes, such as color correction, shading correction, and density correction, on the input image data. The image forming unit 20 is controlled based on the image data that has been subjected to these processes.

[0040] The image forming unit 20 has an image creating unit 21, an intermediate transfer unit 22, and a fixing unit 30. The image creating unit 21 forms a toner image using color toners of Y, M, C, and K components based on input image data. The intermediate transfer unit 22 transfers the toner image formed by the image creating unit 21 onto a recording material. The fixing unit 30 fixes the transferred toner image onto the recording material.

[0041] Specifically, the imaging unit 21 is composed of four imaging units 21Y, 21M, 21C, and 21K for the Y component, the M component, the C component, and the K component. Since the imaging units 21Y, 21M, 21C, and 21K have the same configuration, for convenience of illustration and explanation, the common components are indicated by the same reference numerals, and when distinguishing between them, the reference numerals are indicated by adding Y, M, C, and K. Note that in FIG. 1, reference numerals are only assigned to the components of the imaging unit 21Y for the Y component, and reference numerals are omitted for the components of the other imaging units 21M, 21C, and 21K.

[0042] The image forming unit 21 includes an exposure device 211, a developing device 212, a photosensitive drum 213, a charging device 214, and a drum cleaning device 215. Although not shown, the image forming unit 21 may include a charge removing device for removing residual charges remaining on the surface of the photosensitive drum 213 after the primary transfer.

[0043] The photosensitive drum 213 is, for example, a negatively charged organic photoconductor (OPC) in which an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) are sequentially laminated on the circumferential surface of an aluminum conductive cylinder (aluminum bare tube). The charge generation layer is made of an organic semiconductor in which a charge generation material (e.g., phthalocyanine pigment) is dispersed in a resin binder (e.g., polycarbonate), and generates a pair of positive and negative charges when exposed to light by the exposure device 211. The charge transport layer is made of a hole transport material (electron-donating nitrogen-containing compound) dispersed in a resin binder (e.g., polycarbonate resin), and transports the positive charges generated in the charge generation layer to the surface of the charge transport layer.

[0044] The charging device 214 is formed of a corona discharge generator such as a scorotron charging device or a corotron charging device, etc. The charging device 214 uniformly charges the surface of the photosensitive drum 213 to a negative polarity by corona discharge.

[0045] The exposure device 211 is composed of, for example, an LED print head (LPH) and has an LED array in which multiple light emitting diodes (LEDs: Light Emitting Diodes) are arranged in a line, an LPH drive unit (driver IC) for driving each LED, and a lens array for forming an image of the light emitted from the LED array on the photosensitive drum 213. One LED in the LED array corresponds to one dot of an image.

[0046] The exposure device 211 irradiates the photosensitive drum 213 with light corresponding to an image of each color component. Positive charges generated in the charge generation layer of the photosensitive drum 213 upon irradiation with light are transported to the surface of the charge transport layer, thereby neutralizing the surface charge (negative charge) of the photosensitive drum 213. As a result, an electrostatic latent image of each color component is formed on the surface of the photosensitive drum 213 due to the potential difference with the surroundings.

[0047] The developing device 212 contains a developer of each color component (for example, a two-component developer containing a toner and a magnetic carrier) and adheres the toner of each color component to the surface of the photosensitive drum 213, thereby visualizing the electrostatic latent image and forming a toner image. Specifically, a development bias voltage is applied to a developer carrier (symbol omitted, for example, a developing roller), and an electric field is formed between the photosensitive drum 213 and the developer carrier. Then, due to the potential difference between the photosensitive drum 213 and the developer carrier, the charged toner on the developer carrier moves to and adheres to the exposed portion of the surface of the photosensitive drum 213. As a result, the electrostatic latent image on the photosensitive drum 213 is visualized.

[0048] The drum cleaning device 215 has a drum cleaning blade (reference number omitted) that comes into sliding contact with the surface of the photosensitive drum 213. The drum cleaning device 215 removes untransferred toner remaining on the surface of the photosensitive drum 213 after the primary transfer.

[0049] The intermediate transfer unit 22 includes an intermediate transfer belt 221, a primary transfer roller 222, a plurality of support rollers 223 and 224, a belt cleaning device 225, a secondary transfer roller 226, and the like.

[0050] The intermediate transfer belt 221 is an image carrier that carries a toner image, and is a transfer target onto which the toner image on the photosensitive drum 213 is transferred. The intermediate transfer belt 221 is an endless belt that is stretched in a loop shape around a plurality of support rollers 223. At least one of the plurality of support rollers 223 is a drive roller, and the rest are driven rollers. The intermediate transfer belt 221 runs at a constant speed as the drive roller rotates.

[0051] The primary transfer rollers 222 are disposed on the inner circumferential surface side of the intermediate transfer belt 221, facing the photosensitive drums 213 of each color component. The primary transfer rollers 222 are pressed against the photosensitive drums 213 with the intermediate transfer belt 221 sandwiched therebetween, thereby forming a transfer nip (hereinafter referred to as a "primary transfer portion") for transferring a toner image from the photosensitive drums 213 to the intermediate transfer belt 221.

[0052] Support rollers 223 include an opposing roller 224 disposed opposite secondary transfer roller 226. Secondary transfer roller 226 is disposed on the outer circumferential surface side of intermediate transfer belt 221 and is pressed against opposing roller 224 with intermediate transfer belt 221 sandwiched therebetween. This forms a transfer nip (hereinafter referred to as a "secondary transfer portion") for transferring a toner image from intermediate transfer belt 221 to a recording material.

[0053] In the primary transfer section, the toner images on the photosensitive drums 213 are primarily transferred onto the intermediate transfer belt 221 in a sequentially overlapping manner. Specifically, a primary transfer voltage is applied to the primary transfer rollers 222, and a charge of the opposite polarity to the toner is applied to the inner circumferential surface side of the intermediate transfer belt 221 (the side in contact with the primary transfer roller 222), whereby the toner images are electrostatically transferred from the photosensitive drums 213 to the intermediate transfer belt 221.

[0054] Thereafter, when the recording material passes through the secondary transfer section, the toner image on the intermediate transfer belt 221 is secondarily transferred to the recording material. Specifically, a secondary transfer voltage is applied to the secondary transfer roller 226, and a charge of the opposite polarity to the toner is applied to the back side of the recording material (the side in contact with the secondary transfer roller 226), so that the toner image is electrostatically transferred from the intermediate transfer belt 221 to the recording material. The recording material to which the toner image has been transferred is transported toward the fixing section 30.

[0055] The belt cleaning device 225 has a belt cleaning blade (reference number omitted) that comes into sliding contact with the surface of the intermediate transfer belt 221. The belt cleaning device 225 removes untransferred toner remaining on the surface of the intermediate transfer belt 221 after the secondary transfer.

[0056] The fixing section 30 has an upper fixing section 30A and a lower fixing section 30B. The upper fixing section 30A is disposed on the fixing surface (surface on which a toner image is formed) of the recording material. The lower fixing section 30B is disposed on the back surface (surface opposite to the fixing surface) of the recording material. The fixing section 30 shown in FIG. 2 employs a belt nip method in which a fixing nip N1 is formed via a fixing belt 33.

[0057] The upper fixing section 30A has a fixing roller 31, a heating roller 32, a fixing belt 33, a heat source 34, etc. An endless fixing belt 33 is stretched around the fixing roller 31 and the heating roller 32 with a predetermined belt tension (e.g., 200 N). The fixing belt 33 is a fixing surface side member that comes into contact with the fixing surface of the continuous paper S. The control unit 11 controls the drive of the fixing roller 31 (e.g., turning the rotation on / off, the number of rotations, etc.) and the output of the heat source 34.

[0058] Fixing roller 31 has a configuration in which an elastic layer (e.g., thickness: 20 mm, JIS-A hardness: 10°) made of silicone rubber or the like is formed on the outer circumferential surface of a cylindrical core metal made of iron or the like. The outer diameter of fixing roller 31 is, for example, 90 mm.

[0059] The heating roller 32 has a configuration in which a resin layer made of PTFE (polytetrafluoroethylene) or the like is formed on the outer circumferential surface of a cylindrical core metal made of aluminum or the like. The outer diameter of the heating roller 32 is, for example, 80 mm.

[0060] The fixing belt 33 has a configuration in which, for example, an elastic layer (for example, thickness: 220 μm) made of silicone rubber or the like is formed on the outer surface of a film substrate (for example, thickness: 70 μm) made of heat-resistant polyimide, and further, a surface layer made of a fluorine-based resin such as PFA (perfluoroalkoxyalkane) or PTFE is laminated.

[0061] The heat source 34 is, for example, a halogen heater. The heat source 34 is built in the heating roller 32. The heating roller 32 is heated by the heat source 34, and the heat is transferred to the fixing belt 33.

[0062] The lower fixing unit 30B has, for example, a pressure roller 35 and a pressure contact / separation unit 36. The pressure roller 35 is a back surface side support member that contacts the back surface of the continuous paper S and supports the continuous paper S. The control unit 11 controls the drive of the pressure roller 35 (for example, turning the rotation on / off, the number of rotations, etc.) and the drive of the pressure contact / separation unit 36.

[0063] The pressure roller 35 has a configuration in which an elastic layer (e.g., thickness: 6 mm, JIS-A hardness: 10°) made of silicone rubber or the like and a surface layer made of fluororesin such as PFA are laminated in this order on the outer circumferential surface of a cylindrical core metal made of iron or the like. The pressure roller 35 has an outer diameter of, for example, 80 mm.

[0064] The pressure contact / separation unit 36 ​​brings the pressure roller 35 closer to the fixing roller 31 in the separated state, and presses the fixing roller 31 and the pressure roller 35 into contact with each other via the fixing belt 33. The pressure contact / separation unit 36 ​​also moves the pressure roller 35 away from the fixing roller 31 in the pressure contact state, and separates the fixing roller 31 and the pressure roller 35 from each other.

[0065] The fixing roller 31 and the pressure roller 35 are maintained in a separated state during non-printing (see FIG. 4A and FIG. 4B). The fixing roller 31 and the pressure roller 35 are shifted from the separated state to the pressed state at the start of printing. The pressure roller 35 is pressed against the fixing roller 31 via the fixing belt 33 with a predetermined pressing load (e.g., 3000 N), thereby forming a fixing nip N1 (see FIG. 1). When the fixing nip N1 of a predetermined width is formed, the rotational force of the fixing roller 31 and the pressure roller 35 becomes a sufficient conveying force and is transmitted to the continuous paper S, and conveyance begins. In addition, the fixing roller 31 and the pressure roller 35 are shifted from the pressed state to the separated state at the end of printing. When the fixing nip N1 reaches a predetermined width, conveyance of the continuous paper S is stopped.

[0066] Typically, the fixing roller 31 is configured as a drive roller, and the pressure roller 35 is configured as a driven roller. When the fixing roller 31 rotates, the continuous paper S that has passed through the fixing nip N1 is transported.

[0067] The fixing unit 30 may adopt a roller nip system in which the fixing nip N1 is formed by direct contact between the fixing roller 31 and the pressure roller 35. In this case, it is sufficient that either the fixing roller 31 or the pressure roller 35 is configured as a drive roller, and both the fixing roller 31 and the pressure roller 35 may be configured as drive rollers.

[0068] In this embodiment, the image forming apparatus main body 1A includes a detection unit 37 that detects a physical quantity related to the thermal expansion state of the fixing roller 31. The "thermal expansion amount of the fixing roller 31" is specifically the thermal expansion amount of the elastic layer of the fixing roller 31. The "physical quantity related to the thermal expansion state" is information that is correlated with the thermal expansion amount of the elastic layer of the fixing roller 31. The physical quantity related to the thermal expansion state includes, for example, the temperature of each part of the fixing unit 30, the outer diameter R of the fixing roller 31, the separation distance L between the fixing roller 31 and the pressure roller 35, the drive torque of the fixing roller 31, and the drive torque of the pressure contact / separation unit 36. The detection unit 37 is disposed, for example, inside the housing of the fixing unit 30.

[0069] The continuous paper S, onto which the toner image has been secondarily transferred and which has been transported along the paper path, is heated and pressurized in the fixing nip N1 as it passes through the fixing unit 30. As a result, the toner image is fixed to the continuous paper S.

[0070] The paper feed section 14 is configured to be able to receive the continuous paper fed from the paper feed unit 1C. A paper feed roller (reference number omitted) is disposed in the paper feed section 14. The paper feed section 14 sends out the fed continuous paper S to a recording material transport section 16 on the downstream side.

[0071] A paper discharge roller (reference number omitted) is disposed in the paper discharge section 15. The paper discharge section 15 discharges the continuous paper S sent from the recording material transport section 16 toward the image calibration control unit 1B on the downstream side.

[0072] The recording material transport section 16 has a plurality of transport rollers as recording material transport elements that sandwich and transport the continuous paper S. The recording material transport section 16 transports the continuous paper S fed from the paper feed section 14 to pass through the image forming section 20 (intermediate transfer section 22, fixing section 30), and transports the continuous paper S sent out from the image forming section 20 (fixing section 30) toward the paper discharge section 15.

[0073] The continuous paper S fed from the paper feed section 14 is transported to the image forming section 20 by the recording material transport section 16. When the continuous paper S passes through the secondary transfer section, the toner images on the intermediate transfer belt 221 are transferred all at once to the image forming surface (front side) of the continuous paper S, and are fixed in the fixing section 30. The continuous paper S on which the image has been formed is discharged by the paper discharge section 15 to the image calibration control unit 1B.

[0074] In the image forming apparatus 1, the continuous paper S that passes through the secondary transfer section is primarily clamped between the fixing nip N1 of the fixing section 30 and the downstream transport nip N2 of the image calibration control unit 1B, and is transported by the rotation of the respective drive rollers, i.e., the fixing roller 31 and the downstream drive roller 41.

[0075] 4A and 4B are diagrams that show a schematic configuration of the fixing unit 30. Fig. 4A shows a case where the fixing roller 31 is in a reference state where it is not thermally expanded, and Fig. 4B shows a case where the fixing roller 31 is in a thermally expanded state where it is thermally expanded. Note that the fixing belt 33 is omitted in Figs. 4A and 4B.

[0076] 4A and 4B, the fixing roller 31 and the pressure roller 35 are kept apart during non-printing (cold time). As shown in Fig. 4A, in the standard state, the outer diameter of the fixing roller 31 is R1, and the distance between the fixing roller 31 and the pressure roller 35 is L1. During printing (including during warm-up operation before printing starts), the ambient temperature of the fixing unit 30 rises, and the elastic layer of the fixing roller 31 thermally expands.

[0077] 4B, in the thermally expanded state, the outer diameter of the fixing roller 31 is R2, which is larger than the outer diameter R1 in the reference state. Also, the separation distance L2 between the fixing roller 31 and the pressure roller 35 is smaller than the separation distance L1 in the reference state.

[0078] When the pressure roller 35 is moved closer to the fixing roller 31 to transition from a separated state to a pressed state, if the speed at which the pressure roller 35 is moved closer (the driving speed of the pressure-contact / separation unit 36) is the same, the time from the start of the pressing operation of the pressure-contact / separation unit 36 ​​to the formation of the fixing nip N1 of a predetermined width varies depending on the amount of thermal expansion of the elastic layer of the fixing roller 31. In other words, the fixing-side conveyance start timing varies depending on the amount of thermal expansion of the fixing roller 31.

[0079] Furthermore, when the positional relationship between the fixing roller 31 and the pressure roller 35 in the pressure-contact state (for example, the distance between the roller axes) is fixed, the nip width of the fixing nip N1 changes depending on the amount of thermal expansion of the elastic layer of the fixing roller 31. Therefore, when the pressure roller 35 is moved away from the fixing roller 31 to transition from the pressure-contact state to the separated state, if the speed at which the pressure roller 35 is moved away (the driving speed of the pressure-contact / separation unit 36) is the same, the time from the start of the separation operation of the pressure-contact / separation unit 36 ​​to the release of the fixing nip N1 changes depending on the amount of thermal expansion of the elastic layer of the fixing roller 31. In other words, the fixing-side transport stop timing changes depending on the amount of thermal expansion of the fixing roller 31.

[0080] In this embodiment, the control unit 11 controls the operation of the drive rollers in the fixing unit 30 and the downstream transport unit 40 in a drive mode according to the amount of thermal expansion of the elastic layer of the fixing roller 31 based on the detection result of the detection unit 37. Specifically, the control unit 11 controls the downstream transport start timing and the downstream transport stop timing according to the fixing side transport start timing and the fixing side transport stop timing that change due to the thermal expansion of the fixing roller 31.

[0081] The control unit 11 controls, for example, the drive start timing when starting output to the downstream drive roller 41 and the drive stop timing when stopping output to the downstream drive roller 41. In addition to the drive start timing and drive stop timing of the downstream drive roller 41, or instead of the drive start timing and drive stop timing of the downstream drive roller 41, the control unit 11 may control the rise speed of the downstream drive roller 41 at the drive start and the fall speed of the downstream drive roller 41 at the drive stop.

[0082] The detection unit 37 measures the temperature of each part in the fixing unit 30, for example. In this case, a temperature sensor is applied to the detection unit 37. The thermal expansion amount of the fixing roller 31 is correlated with temperature information such as the surface temperature of the fixing roller 31, the temperature of the core metal, and the atmospheric temperature in the fixing unit 30. By acquiring the relationship between the temperature of each part of the fixing unit 30 and the thermal expansion amount of the fixing roller 31 in advance, the thermal expansion amount of the fixing roller 31 can be evaluated based on the temperature measured by the detection unit 37 (temperature sensor) arranged in each part of the fixing unit 30. The method of evaluating the thermal expansion amount based on the temperature of each part in the fixing unit 30 can be applied to drive control at the start of conveyance when the fixing roller 31 and the pressure roller 35 are in a separated state, and to drive control at the stop of conveyance when they are in a pressed state.

[0083] The detection unit 37 may measure the outer diameter R of the fixing roller 31. The change in the outer diameter R of the fixing roller 31 between when not printing (when cold) and immediately before printing starts (when warming up) is nothing but the amount of thermal expansion of the fixing roller 31. The detection unit 37 may also measure the distance L between the fixing roller 31 and the pressure roller 35. The larger the amount of thermal expansion of the fixing roller 31, the smaller the distance L. In these cases, an optical sensor such as a laser displacement meter is applied to the detection unit 37. The method of evaluating the amount of thermal expansion based on the outer diameter R of the fixing roller 31 or the distance L between the fixing roller 31 and the pressure roller 35 is based on the premise that the fixing roller 31 and the pressure roller 35 are in a separated state, and therefore can be mainly applied to drive control at the start of conveyance.

[0084] Furthermore, the detection unit 37 may measure the drive torque of the fixing roller 31 or the drive torque of the pressure contact / separation unit 36. In this case, a torque sensor provided in the drive motor of the fixing roller 31 or the pressure contact / separation unit 36 ​​is used as the detection unit 37.

[0085] When the pressure contact operation of the pressure contact separation unit 36 ​​is started while the fixing roller 31 is rotating, the drive torque of the fixing roller 31 or the pressure contact separation unit 36 ​​fluctuates greatly at the point where the continuous paper S passed between the fixing roller 31 and the pressure roller 35 starts to contact the fixing roller 31 or the pressure roller 35. Also, when the pressure contact separation unit 36 ​​starts to separate while the fixing roller 31 is rotating, the drive torque of the fixing roller 31 or the pressure contact separation unit 36 ​​fluctuates greatly at the point where the fixing nip N1 starts to be released. In other words, the amount of thermal expansion of the fixing roller 31 is correlated with the start of the pressure contact operation and the time from the start of the separation operation until the drive torque fluctuates. The method of evaluating the amount of thermal expansion based on the fluctuation of the drive torque can be applied to the drive control at the start of conveyance when the fixing roller 31 and the pressure roller 35 are in a separated state, and to the drive control at the stop of conveyance when they are in a pressure contact state.

[0086] In addition, in the pressure contact state, the larger the amount of thermal expansion of the fixing roller 31, the larger the drive torque of the fixing roller 31 and the pressure contact / separation unit 36. In other words, it can be said that the amount of thermal expansion of the fixing roller 31 is also correlated with the measured value of the drive torque. The method of evaluating the amount of thermal expansion based on the measured value of the drive torque can be applied to drive control when the conveyance is stopped and the fixing roller 31 and the pressure roller 35 are in a pressure contact state.

[0087] The above-mentioned method for evaluating the amount of thermal expansion of the fixing roller 31 is an example, and other evaluation methods may be applied. For example, the amount of thermal expansion of the fixing roller 31 can be evaluated based on the tension of the fixing belt 33 or the positional fluctuation of the member around which the fixing belt 33 is stretched.

[0088] In this embodiment, the fixing roller 31 is taken into consideration for thermal expansion, and the fixing side transport start timing and the downstream side transport start timing are made to coincide with each other to prevent the generation of abnormal noise due to slack or slippage of the continuous paper S. Here, "same fixing side transport start timing and downstream side transport start timing" does not necessarily mean that the timings are exactly matched, but rather that they are matched to an extent that slack does not occur in the continuous paper S due to a timing discrepancy.

[0089] At the start of conveyance, if the downstream conveyance start timing is earlier than the fixing side conveyance start timing, slack will not occur in the continuous paper S. However, if the difference between the fixing side conveyance start timing and the downstream side conveyance start timing is too large, the continuous paper S may slip in the downstream conveyance section 40 and generate abnormal noise. Therefore, it is preferable that the difference between the fixing side conveyance start timing and the downstream side conveyance start timing is, for example, 500 msec or less.

[0090] 5 is a flowchart showing an example of a conveyance start process in the image forming apparatus 1. This process is realized, for example, by the CPU 111 executing a predetermined program stored in the ROM 112 in response to input of print data to the image forming apparatus main body 1A.

[0091] It is assumed that the fixing roller 31 and the pressure roller 35 are kept separated when not printing. In the separated state, the fixing nip N1 is released, so the tension generated in the continuous paper S is smaller than during printing. Normally, in the separated state, the continuous paper S is slack in the transport path, and the paper length is longer than the transport path length. Also, it is assumed that the drive speed during the pressing operation of the pressure-contact / separation unit 36, i.e., the speed at which the pressure roller 35 approaches the fixing roller 31, is constant.

[0092] 5, the control unit 11 applies a predetermined tension to the continuous paper S being passed. The control unit 11 controls the operation of the paper feed unit 1C and the winding unit 1D, for example, to apply tension to the continuous paper S that is slack in the transport path. The slack in the continuous paper S is eliminated, and the difference between the length of the continuous paper S passed between the fixing nip N1 and the downstream transport nip N2 and the transport path length becomes a predetermined amount (for example, 10 mm) or less.

[0093] If transport is started when no tension is applied to the continuous paper S, i.e., when the continuous paper S is in a slack state, there is a risk that the continuous paper S will wrap around the fixing member (fixing belt 33 in this embodiment). Also, the tension on the continuous paper S may change suddenly, causing abnormal noise when the slack is eliminated. In this embodiment, in step S101, the slack in the continuous paper S is eliminated before the transport operation of the continuous paper S is started, so that it is possible to prevent the continuous paper S from wrapping around the fixing member or generating abnormal noise due to slack that occurs in the continuous paper S before transport starts.

[0094] It should be noted that the timing at which the downstream drive roller 41 starts to be driven may be advanced so that slack in the continuous paper S is eliminated before the transport operation in the fixing unit 30 starts.

[0095] In step S102, the control unit 11 detects the thermal expansion state of the fixing roller 31. Specifically, the control unit 11 acquires from the detection unit 37 a physical quantity related to the thermal expansion state of the fixing roller 31.

[0096] In step S103, the control unit 11 sets the drive mode of the downstream drive roller 41 in the downstream transport unit 40 based on the detection result of the detection unit 37. Specifically, the control unit 11 sets the drive start timing of the downstream drive roller 41 so that the fixation side transport start timing predicted based on the thermal expansion state of the fixation roller 31 detected in step S102 coincides with the downstream side transport start timing.

[0097] The fixing-side transport start timing, the downstream-side transport start timing, and the drive start timing of the downstream-side drive roller 41 are expressed, for example, by the time from the start of the pressing operation of the pressure contact / separation section 36. The larger the amount of thermal expansion of the fixing roller 31, the shorter the time from the start of the pressing operation of the pressure contact / separation section 36 to the formation of the fixing nip N1 of a predetermined width, and the earlier the fixing-side transport start timing becomes. Therefore, the larger the amount of thermal expansion of the fixing roller 31, the earlier the downstream-side transport start timing must be, and the drive start timing of the downstream-side drive roller 41 is also set.

[0098] The control unit 11 sets the drive start timing of the downstream drive roller 41 so that the downstream transport start timing is the same as the fixing side transport start timing or slightly earlier than the fixing side transport start timing, for example. In particular, when the drive start timing of the downstream drive roller 41 is set so that the downstream transport start timing is 0 to 50 msec earlier than the fixing side transport start timing, the effect of suppressing the winding of the continuous paper S around the fixing member is high.

[0099] The control unit 11 sets the drive start timing of the downstream drive roller 41 by, for example, referring to drive start timing setting data (see FIG. 6 ) in which the drive start timing of the downstream drive roller 41 is associated with the thermal expansion state of the fixing roller 31. The drive start timing setting data is experimentally acquired in advance and is stored in, for example, the ROM 112. The drive start timing setting data may be given as a function t=f(x) with an index x indicating the thermal expansion state of the fixing roller 31 and a drive start timing t of the downstream drive roller 41 as variables.

[0100] Fig. 6 is a diagram showing an example of drive start timing setting data. In Fig. 6, the amount of change in the outer diameter R of the fixing roller 31 is used as the index x indicating the thermal expansion state of the fixing roller 31. Note that the index x indicating the thermal expansion state of the fixing roller 31 may be the temperature of each part of the fixing unit 30 described above, the separation distance L between the fixing roller 31 and the pressure roller 35, or the timing of change in the drive torque of the fixing roller 31 or the pressure contact / separation unit 36.

[0101] 6, for example, when the change in outer diameter of the fixing roller 31 (corresponding to the amount of thermal expansion) is 0 mm, the drive start timing of the downstream drive roller 41 is set to 2 seconds after the start of the pressing operation of the pressure contact / separation unit 36. Also, when the change in outer diameter of the fixing roller 31 is 3 mm, the drive start timing of the downstream drive roller 41 is set to 0.5 seconds after the start of the pressing operation of the pressure contact / separation unit 36.

[0102] The control unit 11 may control the downstream transport start timing by fixing the drive start timing of the downstream drive roller 41 and changing the rising speed of the downstream drive roller 41. In this case, for example, based on the predicted fixing side transport start timing, the downstream drive roller 41 starts driving 500 msec before the fixing side transport start timing, and the rising speed of the downstream drive roller 41 is controlled so that the set rotation speed is reached 500 msec after the fixing side transport start timing. This makes it possible to maintain an appropriate tension state without making the tensile force on the continuous paper S in the downstream transport unit 40 too strong from the beginning of driving, thereby suppressing the generation of abnormal noise due to slipping and suppressing the winding of the continuous paper S around the fixing member.

[0103] 4, control unit 11 starts driving fixing roller 31. Fixing roller 31 rotates at a constant rotation speed.

[0104] In step S105, the control unit 11 starts the pressing operation of the pressure contact / separation unit 36. The pressure roller 35 approaches the fixing roller 31 at a constant speed, and the fixing nip N1 is formed. When the fixing nip N1 of a predetermined width is formed, the transport of the continuous paper S is started. The pressing operation of the pressure contact / separation unit 36 ​​is stopped, for example, when the pressure roller 35 reaches a preset position. The fixing roller 31 and the pressure roller 35 are held in a pressed state with a predetermined pressing force.

[0105] In step S106, the control unit 11 starts driving the downstream drive roller 41 at the drive start timing set in step S103. The drive start timing of the downstream drive roller 41 is set so that the fixing side transport start timing in the fixing unit 30 and the downstream side transport start timing in the downstream transport unit 40 coincide. Therefore, transport of the continuous paper S is started simultaneously in the fixing unit 30 and the downstream transport unit 40. No slack is generated in the continuous paper S due to a mismatch between the fixing side transport start timing and the downstream side transport start timing, and no problem occurs in which the continuous paper S winds around the fixing member (fixing belt 33). In addition, no slip noise is generated due to a mismatch between the fixing side transport start timing and the downstream side transport start timing.

[0106] The processes of steps S102-S103 may be performed before the fixing nip N1 of a predetermined width is formed and the continuous paper S starts to be transported. The processes of steps S102-S103 may be performed, for example, after the fixing roller 31 starts to be driven in step S104, or after the pressing operation of the pressure contact / separation unit 36 ​​starts in step S105.

[0107] However, when the drive start timing of the downstream drive roller 41 is set by predicting the fixation side transport start timing based on the outer diameter R of the fixation roller 31 or the separation distance L between the fixation roller 31 and the pressure roller 35, the detection process of step S102 is preferably performed before the drive of the fixation roller 31 is started in step S104 in order to improve measurement accuracy. Also, when the drive start timing of the downstream drive roller 41 is set by predicting the fixation side transport start timing based on the drive torque of the fixation roller 31 or the pressure contact / separation unit 36, the processes of steps S102-S103 are performed after step S105.

[0108] Furthermore, in this embodiment, the fixing side transport stop timing and the downstream side transport stop timing are matched in consideration of the thermal expansion of the fixing roller 31, thereby preventing the generation of abnormal noise due to slack or slippage of the continuous paper S. "Matching the fixing side transport stop timing and the downstream side transport stop timing" does not necessarily mean matching the timing exactly, but at least matching to the extent that slack does not occur in the continuous paper S due to a timing discrepancy.

[0109] When the transport is stopped, if the downstream transport stop timing is later than the fixing side transport stop timing, no slack will occur in the continuous paper S. However, if the difference between the fixing side transport stop timing and the downstream side transport stop timing is too large, there is a risk that the continuous paper S will slip in the downstream transport section 40 and generate abnormal noise, so it is preferable that the difference between the fixing side transport stop timing and the downstream side transport stop timing be, for example, 500 msec or less.

[0110] 7 is a flowchart showing an example of a transport stop process in the image forming apparatus 1. This process is realized, for example, by the CPU 111 executing a predetermined program stored in the ROM 112 when the print process based on the print data is completed.

[0111] It is assumed that the driving speed of the pressure-contact / separation unit 36 ​​in the separating operation, that is, the speed at which the pressure roller 35 is moved away from the fixing roller 31, is constant.

[0112] 7, the control unit 11 detects the thermal expansion state of the fixing roller 31. Specifically, the control unit 11 acquires a physical quantity related to the thermal expansion state of the fixing roller 31 from the detection unit 37. If the thermal expansion state of the fixing roller 31 when the conveyance is stopped can be considered to be equivalent to the thermal expansion state of the fixing roller 31 when the conveyance is started, the thermal expansion state detected at the start of the conveyance may be stored and used when the conveyance is stopped.

[0113] In step S202, the control unit 11 sets the drive mode of the downstream drive roller 41 in the downstream transport unit 40 based on the detection result of the detection unit 37. Specifically, the control unit 11 sets the drive stop timing of the downstream drive roller 41 so that the fixation-side transport stop timing predicted based on the thermal expansion state of the fixation roller 31 detected in step S201 coincides with the downstream transport stop timing.

[0114] The fixing-side transport stop timing, the downstream-side transport stop timing, and the drive stop timing of the downstream-side drive roller 41 are expressed, for example, by the time from the start of the separation operation of the pressure contact / separation unit 36. The larger the amount of thermal expansion of the fixing roller 31, the larger the nip width of the formed fixing nip N1, and therefore the longer the time from the start of the separation operation of the pressure contact / separation unit 36 ​​to the release of the fixing nip N1, and the later the fixing-side transport stop timing. Therefore, the larger the amount of thermal expansion of the fixing roller 31, the later the downstream-side transport stop timing must be, and the drive stop timing of the downstream-side drive roller 41 is also set.

[0115] The control unit 11 sets the drive stop timing of the downstream drive roller 41 so that the downstream transport stop timing is the same as the fixing side transport stop timing or slightly later than the fixing side transport stop timing. In particular, when the drive start timing of the downstream drive roller 41 is set so that the downstream transport start timing is 0 to 50 msec earlier than the fixing side transport start timing, the effect of suppressing the winding of the continuous paper S around the fixing member is high.

[0116] The control unit 11 sets the drive stop timing of the downstream drive roller 41 by, for example, referring to drive stop timing setting data (see FIG. 8 ) in which the drive stop timing of the downstream drive roller 41 is associated with the thermal expansion state of the fixing roller 31. The drive stop timing setting data is experimentally acquired in advance and is stored in, for example, the ROM 112. The drive stop timing setting data may be given by a function t=f(x) with an index x indicating the thermal expansion state of the fixing roller 31 and a drive stop timing t of the downstream drive roller 41 as variables.

[0117] Fig. 8 is a diagram showing an example of drive stop timing setting data. In Fig. 8, the amount of change in the outer diameter R of the fixing roller 31 is used as the index x indicating the thermal expansion state of the fixing roller 31. Note that the index x indicating the thermal expansion state of the fixing roller 31 may be the temperature of each part of the fixing unit 30 described above, the separation distance L between the fixing roller 31 and the pressure roller 35, the timing of change in the drive torque of the fixing roller 31 or the pressure contact / separation unit 36, or the like.

[0118] 8, for example, when the change in outer diameter of the fixing roller 31 (corresponding to the amount of thermal expansion) is 0 mm, the drive stop timing of the downstream drive roller 41 is set to 0.5 seconds after the start of the separation operation of the pressure contact and separation unit 36. Also, for example, when the change in outer diameter of the fixing roller 31 is 3 mm, the drive start timing of the downstream drive roller 41 is set to 2 seconds after the start of the separation operation of the pressure contact and separation unit 36.

[0119] As in the case of the start of transport, the control unit 11 may fix the drive stop timing of the downstream drive roller 41 and control the downstream transport stop timing by changing the fall speed of the downstream drive roller 41. This makes it possible to maintain an appropriate tension state without suddenly reducing the tensile force on the continuous paper S in the downstream transport unit 40, thereby suppressing the winding of the continuous paper S around the fixing member while suppressing the generation of abnormal noise due to slippage.

[0120] 7, the control unit 11 starts the separation operation of the pressure contact / separation unit 36. The pressure roller 35 moves away from the fixing roller 31 at a constant speed, and the fixing nip N1 is released. When the nip width of the fixing nip N1 becomes equal to or smaller than a predetermined width, the transport of the continuous paper S is stopped. The separation operation of the pressure contact / separation unit 36 ​​is stopped when the pressure roller 35 returns to its initial state.

[0121] In step S204, the control unit 11 stops driving the downstream drive roller 41 at the drive stop timing set in step S202. The drive stop timing of the downstream drive roller 41 is set so that the fixing side transport stop timing in the fixing unit 30 and the downstream side transport stop timing in the downstream transport unit 40 coincide. Therefore, transport of the continuous paper S is stopped simultaneously in the fixing unit 30 and the downstream transport unit 40. Since no slack is generated in the continuous paper S due to a mismatch between the fixing side transport stop timing and the downstream side transport stop timing, the continuous paper S does not wind around the fixing belt 33. Furthermore, no slip noise is generated due to a mismatch between the fixing side transport stop timing and the downstream side transport stop timing.

[0122] In step S205, the control unit 11 stops driving the fixing roller 31. The timing of stopping the fixing roller 31 is not particularly limited as long as it is after the fixing roller 31 and the pressure roller 35 are separated from each other.

[0123] [Variations] In the above embodiment, the driving mode in the downstream conveying section is controlled according to the thermal expansion state of the fixing roller 31, but problems such as the continuous paper S wrapping around the fixing member are also affected by factors other than the thermal expansion state of the fixing roller 31.

[0124] As an example, the likelihood of the continuous paper S wrapping around the fixing member and the likelihood of abnormal noise due to slipping change depending on the media information of the continuous paper S being fed through. Therefore, it is preferable to control the drive mode of the downstream transport unit 40 based on the media information of the continuous paper S in addition to the thermal expansion state of the fixing roller 31. "Media information" is information that indicates the type of the continuous paper S, and includes, for example, at least one of the material, melting point, paper thickness, basis weight, stiffness, and friction coefficient of the continuous paper S.

[0125] For example, when the fixing surface of the continuous paper S is made of polypropylene (PP) with a low melting point, it is more likely to wrap around the fixing member than when it is made of a material with a higher melting point than PP. Therefore, it is preferable to set the drive start timing of the downstream drive roller 41 earlier than when using the continuous paper S made of a material with a higher melting point than PP, so that slack is less likely to occur in the continuous paper S. The same can be said about the control of the drive stop timing of the downstream drive roller 41 when transport is stopped.

[0126] Furthermore, for example, since the transport load changes depending on the paper thickness, basis weight, or stiffness of the continuous paper S, the fixation-side transport start timing and fixation-side transport stop timing change even if the thermal expansion state of the fixing roller 31 is the same. Taking paper thickness as an example, when the paper thickness is large, the transport load increases mainly due to bending in the transport path, so the fixation-side transport start timing is delayed and the fixation-side transport stop timing is advanced. For this reason, it is preferable to change the drive start timing of the downstream drive roller 41 for each paper thickness. The same can be said about the control of the drive stop timing of the downstream drive roller 41 when transport is stopped.

[0127] When controlling the drive start timing and drive stop timing of the downstream drive roller 41 based on media information of the continuous paper S, data for setting the drive start timing (see Figure 6) and data for setting the drive stop timing (see Figure 8) are prepared in association with the media information.

[0128] 9 is a diagram showing an example of drive start timing setting data prepared for each paper thickness. In FIG. 9, the change in the outer diameter R of the fixing roller 31 is used as an index x indicating the thermal expansion state of the fixing roller 31.

[0129] 9, when the paper thickness is 200 μm or more, the drive start timing of the downstream drive roller 41 is set 0.5 seconds later than when the paper thickness is less than 200 μm. Since the drive start timing of the downstream drive roller 41 is appropriately controlled according to the thickness of the continuous paper S, the downstream transport start timing can be matched with high precision even if the fixation side transport start timing changes depending on the paper thickness.

[0130] The media information of the continuous paper S can be acquired, for example, based on a user operation on the operation unit 122. For example, items such as material, paper thickness, and basis weight can be presented on the display unit 121 as the media information of the continuous paper S, and the user can select from multiple options for each item.

[0131] Furthermore, the media information of the continuous paper S may be acquired by a media information detection unit (not shown) provided inside or outside the image forming apparatus 1. The media information detection unit may be, for example, a basis weight detection sensor that uses a laser, or a contact-type displacement sensor that detects the paper thickness by clamping the continuous paper S between a metal pair such as a vernier caliper.

[0132] The fixing side transport start timing and the fixing side transport stop timing change depending on the durability of the fixing member (e.g., the fixing roller 31). Similarly, the downstream side transport start timing and the downstream side transport stop timing change depending on the durability of the downstream side transport member (e.g., the downstream side drive roller 41). Therefore, it is preferable to correct the drive start timing and the downstream side drive stop timing of the downstream side drive roller 41 according to the durability of the fixing member and the downstream side transport member.

[0133] In particular, since the outer diameter of the fixing member is easily changed by thermal load and repeated compression, the durability of the fixing member should be taken into consideration when implementing drive control of the fixing unit 30 and the downstream transport unit 40. When taking the durability of the fixing roller 31 into consideration, in the same way as the thermal expansion state of the fixing roller 31, the fixing-side transport start timing becomes later and the fixing-side transport stop timing becomes earlier by the amount that the outer diameter R becomes smaller compared to the initial durability period when there is no change in the outer diameter, the same idea as the thermal expansion state of the fixing roller 31.

[0134] Fig. 10 is a diagram showing an example of drive start timing setting data corrected in consideration of durability. In Fig. 10, the amount of change in the outer diameter R of the fixing roller 31 is used as an index x indicating the thermal expansion state of the fixing roller 31. Fig. 10 shows the fixing roller 31 at the beginning of durability and after durability in which the outer diameter R of the fixing roller 31 has become smaller by 0.4 mm due to durability.

[0135] Here, the correction amount for durability of the fixing roller 31 (in the example shown in FIG. 10, the correction amount is 0.2 sec for a change in outer diameter of −0.4 mm) may be experimentally obtained in advance and stored in the ROM 112, for example.

[0136] Fig. 11 is a diagram showing an example of drive start timing setting data for durability of fixing roller 31. Fig. 11 uses the durable number of sheets (durability time) as an index showing the durability of fixing roller 31. According to Fig. 11, when the durable number of sheets is 500 kp, the correction amount is 0.2 sec.

[0137] 10 and 11 show that when the number of sheets that can be used is 500 kp, the outer diameter R of the fixing roller 31 is 0.4 mm smaller, and the drive start timing should be delayed by 0.2 sec compared to the drive start timing at the beginning of the durability test. Since the drive start timing of the downstream drive roller 41 is appropriately controlled according to the durability of the fixing members, etc., the downstream transport start timing can be accurately matched even if the fixation side transport start timing changes depending on the paper thickness. The same can be said about the control of the drive stop timing of the downstream drive roller 41 when transport is stopped.

[0138] The amount of correction for durability may be set appropriately based on the difference between the fixing-side transport start timing predicted based on the thermal expansion state of the fixing roller 31 and the timing when the continuous paper S actually starts to move. For example, a mechanism capable of detecting the transport speed of the continuous paper S may be provided in the fixing unit 30 so that the timing when the continuous paper S actually starts to move can be detected. In this case, correction is performed taking into account not only the deterioration of the fixing roller 31 but also the variations in the components, so that the fixing-side transport start timing and the downstream-side transport start timing can be further optimized.

[0139] As described above, the image forming apparatus 1 according to the present embodiment has the following features either alone or in any suitable combination.

[0140] That is, the image forming device 1 is an image forming device capable of printing on continuous paper S, and includes a fixing unit 30 that fixes an image to the unfixed surface of the continuous paper S while transporting the continuous paper S through a fixing nip N1, a downstream transport unit 40 that is arranged downstream of the fixing unit 30 in the paper transport direction and transports the continuous paper S through a downstream transport nip N2, a detection unit 37 that detects a physical quantity related to the thermal expansion state of the fixing roller 31 (fixing member) that forms the fixing nip N1, and a control unit 11 that controls the driving mode of at least one of the fixing unit 30 and the downstream transport unit 40 based on the detection result by the detection unit 37.

[0141] In addition, the conveying method of the embodiment is a conveying method in an image forming apparatus 1 capable of printing on continuous paper S, and includes the steps of conveying the continuous paper S through a fixing nip N1 that fixes an image to an unfixed surface of the continuous paper S (steps S104, S105 in FIG. 5, steps S203, S205 in FIG. 7), conveying the continuous paper S through a downstream conveying nip N2 arranged downstream of the fixing nip N1 in the paper conveying direction (steps S106, S204), detecting a physical quantity related to the thermal expansion state of the fixing roller 31 (fixing member) that forms the fixing nip N1 (steps S102, S201), and controlling the driving mode of at least one of the fixing section 30 in which the fixing nip N1 is arranged and the downstream conveying section 40 in which the downstream conveying nip N2 is arranged based on the detected physical quantity related to the thermal expansion state (steps S103, S202).

[0142] In the embodiment, the image forming apparatus 1 according to the present invention is realized by the control unit 11 of the image forming apparatus 1 executing a program. That is, the program relating to the embodiment is a program that causes a control unit 11 (computer) of an image forming apparatus 1 capable of printing on continuous paper S to execute predetermined processes, and the predetermined processes include a process of transporting the continuous paper S through a fixing nip N1 that fixes an image on the unfixed surface of the continuous paper S (steps S104, S105 in FIG. 5, steps S203, S205 in FIG. 7), a process of transporting the continuous paper S through a downstream transport nip N2 arranged downstream of the fixing nip N1 in the paper transport direction (steps S106, S204), a process of detecting a physical quantity related to the thermal expansion state of the fixing roller 31 (fixing member) that forms the fixing nip N1 (steps S102, S201), and a process of controlling the drive mode of at least one of the fixing section 30 in which the fixing nip N1 is arranged and the downstream transport section 40 in which the downstream transport nip N2 is arranged based on the detected physical quantity related to the thermal expansion state (steps S103, S202).

[0143] The above-mentioned program can be provided, for example, via a computer-readable portable storage medium (including, for example, an optical disk, a magneto-optical disk, and a memory card) in which the program is stored. Also, for example, the above-mentioned program can be provided by downloading the program from a server that holds the program via a network.

[0144] According to the image forming apparatus 1, the conveying method, and the program of the embodiment, even if the fixing roller 31 thermally expands, the fixing section 30 and the downstream conveying section 40 simultaneously start and stop conveying the continuous paper S. Since the continuous paper S does not become loose due to a difference between the fixing side conveying start timing and the downstream side conveying start timing, and a difference between the fixing side conveying stop timing and the downstream side conveying stop timing, the continuous paper S does not wind around the fixing belt 33. In addition, no slip noise is generated due to a difference between the fixing side conveying stop timing and the downstream side conveying stop timing. Therefore, it is possible to prevent problems such as loosening that may occur in the continuous paper S when conveying starts and stops, and to convey the continuous paper S appropriately. In addition, it is possible to eliminate the need for a mechanism such as a tension roller that applies tension to the continuous paper S to eliminate slack in the continuous paper S.

[0145] In the image forming apparatus 1, the fixing section 30 has a pressure contact / separation section 36 that presses and separates the fixing roller 31 and the pressure roller 35 (fixing member), and the control section 11 drives the fixing roller 31 to transition from the separated state to the pressure contact state when conveyance starts, and drives the fixing roller 31 to transition from the pressed state to the separated state when conveyance stops. In this way, when the change in the fixing side conveyance start timing and the fixing side conveyance stop timing due to the thermal expansion state of the fixing roller 31 becomes significant, problems such as slack that may occur in the continuous paper S at the start and stop of conveyance can be prevented, and the continuous paper S can be conveyed properly.

[0146] In the image forming apparatus 1, the control unit 11 transitions from the separated state to the pressed state when the difference between the length of the continuous paper S passing between the fixing nip N1 and the downstream transport nip N2 and the transport path length becomes equal to or less than a predetermined amount at the start of transport. Since the slack in the continuous paper S is eliminated before the transport operation of the continuous paper S starts, it is possible to prevent the continuous paper S from wrapping around the fixing member or generating abnormal noise due to slack that occurs in the continuous paper S before the start of transport.

[0147] In the image forming apparatus 1, the control unit 11 controls the timing of starting or stopping the drive of the downstream drive roller 41 (conveying member) in the downstream transport section 40. Specifically, the control unit 11 controls the drive start timing of the downstream drive roller 41 (conveying member) in the downstream transport section 40 to be earlier and the drive stop timing to be later as the amount of thermal expansion of the fixing roller 31 (fixing member) increases. This makes it easier to control the transport timing in the fixing section 30 and the transport timing in the downstream transport section 40 to match each other.

[0148] Furthermore, in the image forming apparatus 1, the control unit 11 may control the drive speed of the downstream drive roller 41 (conveying member) in the downstream transport section 40 at the start and stop of transport. Specifically, the control unit 11 controls the rising speed of the downstream drive roller 41 (conveying member) in the downstream transport section 40 to be faster and the falling speed to be slower as the amount of thermal expansion of the fixing roller 31 (fixing member) increases. This makes it easier to control the timing of transport in the fixing section 30 and the timing of transport in the downstream transport section 40 to coincide with each other.

[0149] In the image forming apparatus 1, the detection unit 37 detects the temperature of each part of the fixing unit 30. This makes it possible to easily detect the thermal expansion state of the fixing roller 31 based on the temperature of each part of the fixing unit 30.

[0150] In the image forming apparatus 1, the detection unit 37 detects the outer diameter R of the fixing roller 31 (fixing member). In the image forming apparatus 1, the detection unit 37 may also detect the separation distance between the fixing roller 31 and the pressure roller 35 (two fixing members) that form the fixing nip N1. This makes it possible to directly detect the thermal expansion state of the fixing roller 31 with high accuracy.

[0151] In the image forming apparatus 1, the detection unit 37 detects the drive torque of the fixing roller 31 (fixing member) or the drive torque of the pressure contact / separation unit 36. This makes it possible to detect the thermal expansion state of the fixing roller 31 by utilizing a torque detection device provided in the drive motor of the fixing roller 31 or the drive motor of the pressure contact / separation unit 36, without providing a special detection device.

[0152] In the image forming apparatus 1, the control unit 11 controls the driving mode so that the timing at which the conveyance starts in the downstream conveyance unit 40 is the same as or earlier than the timing at which the conveyance starts in the fixing unit 30. This makes it possible to reliably prevent the continuous paper S from wrapping around the fixing member at the start of conveyance.

[0153] In the image forming apparatus 1, the control unit 11 controls the driving mode so that the timing of conveyance stop in the downstream conveyance unit 40 is the same as or later than the timing of conveyance stop in the fixing unit 30. This makes it possible to reliably prevent the continuous paper S from wrapping around the fixing member when conveyance is stopped.

[0154] In the image forming apparatus 1, the control unit 11 may control the driving modes of the fixing unit 30 and the downstream transport unit 40 based on the detection result as well as on media information of the continuous paper S being used. Specifically, the media information includes at least one of the material, melting point, thickness, basis weight, stiffness, and friction coefficient of the continuous paper S. The image forming apparatus 1 may include a media information detection unit that detects the physical properties of the continuous paper S as the media information. This allows the transport timing in the fixing unit 30 and the transport timing in the downstream transport unit 40 to be matched in consideration of the ease of transport of the continuous paper S, allowing the continuous paper S to be transported more appropriately.

[0155] In the image forming apparatus 1, the control unit 11 preferably applies corrections to the drive mode controlled based on the detection results in accordance with the durability of the fixing unit 30 and the downstream transport unit 40. Furthermore, the control unit 11 preferably compares the drive mode controlled based on the detection results with the actual drive mode and sets the amount of correction. This makes it possible to match the transport timing in the fixing unit 30 and the transport timing in the downstream transport unit 40 in consideration of the durability of the image forming apparatus 1, and allows the continuous paper S to be transported more appropriately.

[0156] The invention made by the inventor has been specifically described above based on an embodiment, but the present invention is not limited to the above embodiment and can be modified within the scope of the gist of the invention.

[0157] For example, in the embodiment, a case has been described in which the drive timing of the downstream drive roller 41 is controlled as a drive mode of the fixing section 30 and the downstream transport section 40. However, it is also possible to keep the drive timing of the downstream drive roller 41 constant and control the drive timing of the fixing roller 31 or control the drive speed of the pressure contact / separation section 36.

[0158] In the embodiment, the fixing roller 31 and the pressure roller 35 are pressed against and separated from each other in the fixing unit 30, but the fixing roller 31 and the pressure roller 35 may be constantly in pressure contact with each other. In this case, the timing of starting and stopping the conveyance can change depending on the thermal expansion state of the fixing roller 31, so the present invention can be applied.

[0159] In addition, in the embodiment, the case has been described where the driving modes of the fixing section 30 and the downstream transport section 40 are controlled in accordance with the thermal expansion state of the fixing roller 31. However, the driving modes of the fixing section 30 and the downstream transport section 40 may also be controlled taking into account the thermal expansion states of fixing members other than the fixing roller 31 (e.g., the heating roller 32, the fixing belt 33, and the pressure roller 35).

[0160] The present invention can also be applied to the transport control of continuous paper in a monochrome image forming apparatus.

[0161] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0162] 1. Image forming device 11 Control section 30 Fixing section 31 Fixing roller (fixing member) 35 Pressure roller (fixing member) 40 Downstream conveying section 41 Downstream drive roller

Claims

1. An image forming apparatus capable of printing on continuous paper, a fixing section that fixes an image onto an unfixed surface of the continuous paper while transporting the continuous paper through a fixing nip; a downstream transport section disposed downstream of the fixing section in a paper transport direction and configured to transport the continuous paper by a downstream transport nip; a detection unit that detects a physical quantity related to a thermal expansion state of a fixing member that forms the fixing nip; a control unit that controls a driving mode of at least one of the fixing unit and the downstream transport unit based on a detection result by the detection unit. Image forming device.

2. the fixing section has a pressure contact / separation section that presses and separates the fixing member, the control unit, when starting conveyance, drives the fixing member to transition from a separated state to a pressure-contact state, and, when stopping conveyance, drives the fixing member to transition from the pressure-contact state to the separated state. The image forming apparatus according to claim 1 .

3. the control unit, when starting the conveyance, transitions from the separated state to the pressed state after a difference between a length of the continuous paper passing between the fixing nip and the downstream conveyance nip and a conveyance path length becomes equal to or less than a predetermined amount. The image forming apparatus according to claim 2 .

4. The control unit controls a timing of starting or stopping the driving of a transport member in the downstream transport unit.

3. The image forming apparatus according to claim 1 or 2.

5. the control unit controls the drive start timing of the transport member in the downstream transport unit to be earlier and the drive stop timing to be later as the amount of thermal expansion of the fixing member is larger. The image forming apparatus according to claim 4 .

6. the control unit controls a drive speed of the transport member in the downstream transport unit at the start and stop of transport.

3. The image forming apparatus according to claim 1 or 2.

7. the control unit controls the rise speed of the transport member in the downstream transport unit to be faster and the fall speed of the transport member in the downstream transport unit to be slower as the thermal expansion amount of the fixing member is larger.

7. The image forming apparatus according to claim 6.

8. The detection unit detects the temperature of each part in the fixing unit.

3. The image forming apparatus according to claim 1 or 2.

9. The detection unit detects an outer diameter of the fixing member.

3. The image forming apparatus according to claim 1 or 2.

10. the detection unit detects a separation distance between the two fixing members that form the fixing nip; The image forming apparatus according to claim 2 .

11. the detection unit detects a driving torque of the fixing member or a driving torque of the pressure contact / separation unit. The image forming apparatus according to claim 2 .

12. the control unit controls the driving mode so that a transport start timing in the downstream transport unit is equal to or earlier than a transport start timing in the fixing unit.

3. The image forming apparatus according to claim 1 or 2.

13. the control unit controls the driving mode so that a transport stop timing in the downstream transport unit is the same as or later than a transport stop timing in the fixing unit.

3. The image forming apparatus according to claim 1 or 2.

14. the control unit controls the drive modes of the fixing unit and the downstream transport unit based on the detection result as well as on media information of the continuous paper being used.

3. The image forming apparatus according to claim 1 or 2.

15. the media information includes at least one of the material, melting point, thickness, basis weight, stiffness, and coefficient of friction of the continuous paper; The image forming apparatus according to claim 14.

16. a media information detection unit for detecting physical properties of the continuous paper as the media information; The image forming apparatus according to claim 15.

17. the control unit corrects the driving mode controlled based on the detection result in accordance with durability of the fixing unit and the downstream transport unit.

3. The image forming apparatus according to claim 1 or 2.

18. the control unit compares the driving mode controlled based on the detection result with an actual driving mode and sets a correction amount.

18. The image forming apparatus according to claim 17.

19. A conveying method in an image forming apparatus capable of printing on continuous paper, comprising the steps of: conveying the continuous paper through a fixing nip where the image is fixed onto an unfixed side of the continuous paper; transporting the continuous paper through a downstream transport nip disposed downstream of the fixing nip in a paper transport direction; detecting a physical quantity related to a thermal expansion state of a fixing member that forms the fixing nip; and controlling a driving mode of at least one of a fixing section in which the fixing nip is disposed and a downstream transport section in which the downstream transport nip is disposed based on the detected physical amount related to the thermal expansion state. Transportation method.

20. A program for causing a computer of an image forming device capable of printing on continuous paper to execute a predetermined process, The predetermined process is a process of conveying the continuous paper through a fixing nip in which an image is fixed to an unfixed side of the continuous paper; a process of transporting the continuous paper by a downstream transport nip disposed downstream of the fixing nip in a paper transport direction; A process of detecting a physical quantity related to a thermal expansion state of a fixing member that forms the fixing nip; and controlling a driving mode of at least one of a fixing unit in which the fixing nip is disposed and a downstream transport unit in which the downstream transport nip is disposed based on the detected physical amount related to the thermal expansion state. program.

Images