JP2012063479A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a desired image gloss by appropriately controlling the temperature gradient of paper.SOLUTION: The image forming apparatus includes: a paper cooling part 40 that cools paper, as a target, which has passed through a fixing device 30 and able to adjust the ability to cool paper; and a control part 60, which controls the temperature gradient of paper passed through the fixing device 30 by controlling the ability of the paper cooling part 40 to cool paper. Here, the control part 60 controls a temperature gradient according to an image gloss, which is the gloss of a toner image formed on paper.

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses are known as printers, copiers, and the like. In this image forming apparatus, when a toner image is formed on a sheet, the toner image is transferred to the sheet, and then the sheet passes through a pressure contact portion (fixing nip portion) of a pair of fixing members constituting the fixing device. The process of fixing the toner image to the image is executed. In this case, the final gloss of the toner image formed on the paper (hereinafter referred to as “image gloss”) is an important factor for the image quality of the toner image.

  For example, Patent Document 1 discloses an image forming apparatus capable of stably obtaining an image having high gloss and no gloss unevenness. Specifically, this image forming apparatus includes a fixing device that performs a heating assumption wearing process and an image gloss control device that performs an image gloss control process. Here, in the image gloss control device, the paper that has passed through the fixing device, that is, the paper on which the toner image is fixed, is formed by a pair of control rollers in a state where the toner of the toner image can be deformed by an external force. Pass through the department.

  Japanese Patent Laid-Open No. 2004-26883 discloses that the image gloss of a toner image is greatly influenced by the nip pressure of a pressure nip portion between a pair of control rollers. It is disclosed that it is set higher than the nip pressure of the fixing nip portion. Further, it is disclosed that the control roller is cooled and maintained at a predetermined upper limit temperature or less in order to suppress the temperature rise of the pair of control rollers due to the thermal energy of the toner image. Here, it is described that the predetermined upper limit temperature or lower is a temperature at which the toner in the toner image after being processed by the image gloss control device is lower than a temperature at which the toner can be deformed by an external force.

JP 2004-139040 A

  By the way, the image gloss depends on the temporal change (hereinafter referred to as “temperature gradient”) of the sheet temperature after the fixing process, that is, after passing through the fixing device. Therefore, for example, in order to obtain a desired image gloss such as low gloss, normal gloss, and high gloss, it is required to appropriately control the temperature gradient so that the temperature gradient corresponds to each image gloss. .

  Japanese Patent Application Laid-Open No. H10-228561 discloses that paper is supplied to the image gloss control device before the paper temperature (toner temperature) reaches a predetermined state. In addition, by forcibly cooling one control roller of the image gloss control device, as a result, the paper temperature (toner temperature) when discharged from the image gloss control device becomes lower than the temperature at which the toner can be deformed by an external force. It is disclosed that control is performed. That is, according to the method disclosed in Patent Document 1, the paper temperature when reaching the image gloss control device is set to a certain temperature point or more, and the paper temperature at the exit of the image gloss control device is set to a certain temperature point or less. Although it is disclosed to control the instantaneous paper temperature at a certain position, it does not disclose the point of controlling the temperature gradient that is a time-dependent (continuous) transition of the paper temperature. .

  The present invention has been made in view of such circumstances, and an object thereof is to obtain a desired image gloss by appropriately controlling the temperature gradient of the paper.

  In order to solve such a problem, an image forming apparatus of the present invention performs sheet cooling on a sheet after passing through a fixing device, and includes a sheet cooling unit capable of adjusting sheet cooling capability, and a sheet cooling unit. A control unit that controls a temperature gradient that is a temporal transition of the paper temperature after passing through the fixing device by controlling the paper cooling capacity, and the control unit is configured to control a toner image formed on the paper. The temperature gradient is controlled according to the glossy image gloss.

  Here, in the present invention, the control unit controls the temperature gradient for each sheet according to the image gloss, thereby corresponding the temperature gradient between the sheets set to the same image gloss. Is preferred.

  Further, in the present invention, when the control unit makes the temperature gradients between the sheets correspond to each other, at least the temperature at which the wax component of the toner coagulates from the temperature at which the image gloss starts to affect after passing through the fixing device. It is preferable to correspond to each temperature gradient in the range up to.

  In the present invention, the control unit may control the sheet cooling capacity of the sheet cooling unit for each sheet to be cooled based on a post-fixing sheet temperature that is a temperature after the sheet has passed through the fixing device. preferable. Alternatively, the control unit may control the sheet cooling capability of the sheet cooling unit for each sheet to be cooled based on printing conditions when a toner image is formed on the sheet. Further, for each sheet to be cooled, the control unit is configured to change the sheet cooling unit based on a post-fixing sheet temperature that is a temperature after the sheet passes through the fixing device and a printing condition when the toner image is formed on the sheet. The sheet cooling capacity may be controlled.

  Here, it is preferable that the image forming apparatus further includes a profile for designating a sheet cooling capacity of the sheet cooling unit for achieving a predetermined temperature gradient according to one or both of the post-fixing sheet temperature and the printing conditions. In this case, it is preferable that the control unit controls the sheet cooling capacity of the sheet cooling unit with reference to the profile.

  In the present invention, it is preferable that the control unit corrects the profile based on the transition of the actual sheet temperature when passing through the sheet cooling unit.

  In the present invention, it is preferable that the control unit corrects the sheet cooling capacity of the sheet cooling unit based on the transition of the actual sheet temperature when passing through the sheet cooling unit.

  In the present invention, it is preferable that the sheet cooling unit is configured by a single cooling unit capable of adjusting a cooling amount for the sheet. Alternatively, the sheet cooling unit may be configured by a plurality of cooling units that are arranged in parallel in the sheet conveyance direction and can individually adjust the cooling amount for the sheet.

  Furthermore, in the present invention, it is preferable that the sheet cooling unit further includes a transport unit capable of adjusting a transport speed of the sheet transported through the cooling unit.

  According to the present invention, since the cooling of the sheet can be freely adjusted by controlling the sheet cooling capacity of the sheet cooling unit, the temperature gradient of the sheet after passing through the fixing device can be controlled. As a result, a desired temperature gradient can be imparted to the paper, and a desired image gloss can be obtained.

Configuration diagram schematically showing image forming apparatus 1 Schematic diagram showing the main part of the image forming apparatus 1 centering on the fixing device 30 and the sheet cooling unit 40. Block diagram schematically showing a control system of the image forming apparatus 1 Explanatory diagram showing the relationship between time Time and paper temperature C 1 is a flowchart showing the operation of the image forming apparatus 1 according to the first embodiment. Explanatory drawing which shows the correction concept of paper cooling capacity and cooling control value Conceptual explanatory diagram of temperature gradient control according to the second embodiment. Conceptual explanatory diagram of temperature gradient control according to the third embodiment. Schematic diagram showing the main part of the image forming apparatus 1 as a modified example Schematic diagram showing the main part of the image forming apparatus 1 as a modified example

(First embodiment)
FIG. 1 is a configuration diagram schematically showing an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is an electrophotographic image forming apparatus such as a copying machine, for example, and forms a full-color image by arranging a plurality of photoconductors facing a single intermediate transfer belt in a vertical direction. A tandem type color image forming apparatus.

  The image forming apparatus 1 mainly includes a document reading device (not shown), exposure units 15Y, 15M, 15C, and 15K, charging / developing units 20Y, 20M, 20C, and 20K, an intermediate transfer belt 23, a fixing device 30, and a sheet cooling unit 40. These are configured and housed in one housing.

  The document reading apparatus has an automatic document feeder (not shown) provided at the upper part of the apparatus housing, reads an image of a document being conveyed, and performs image processing on the obtained image signal. Specifically, the document reading device irradiates an image of the document with a lamp and forms an image of the reflected light on the light receiving surface of the image sensor. The image sensor photoelectrically converts incident light and outputs a predetermined image signal. The document reading apparatus performs processing such as A / D conversion, shading correction, and compression on the image signal, and outputs the image data to the control unit 60 (see FIG. 3) described later. Note that the image data input to the control unit 60 is not limited to the data read by the document reading device, and is received from, for example, a personal computer connected to the image forming device 1 or another image forming device. Also good.

  Each of the exposure units 15Y to 15K includes a laser light source, a polygon mirror, a plurality of lenses, and the like. Each of the exposure units 15Y to 15K scans and exposes the surfaces of photosensitive drums 21Y, 21M, 21C, and 21K, which will be described later, with a laser beam in accordance with output information output from the control unit 60 based on the image data.

  The charging / developing unit 20Y is mainly composed of a photosensitive drum 21Y and a charging / developing unit 22Y disposed around the photosensitive drum 21Y, and forms a toner image corresponding to yellow on the photosensitive drum 21Y. The remaining charging / developing units 20M, 20C, and 20K have the same configuration as that of the charging / developing unit 20Y, and charging / developing units 22M, 22C, and 22K are provided around the photosensitive drums 21M, 21C, and 21K, respectively. The toner images corresponding to magenta, cyan, and black are formed on the photosensitive drums 21M, 21C, and 21K, respectively.

  The surface of each of the photoconductive drums 21Y to 21K is uniformly charged by the charging / developing units 22Y to 22K, and each of the photoconductive drums 21Y to 21K is scanned and exposed by the above-described exposure units 15Y to 15K. A latent image is formed. Further, the charging / developing units 22Y to 22K develop latent images on the photosensitive drums 21Y to 21K by developing with toner. As a result, toner images are formed on the photosensitive drums 21Y to 21K. The toner images formed on the individual photosensitive drums 21 </ b> Y to 21 </ b> K are sequentially transferred to predetermined positions on the intermediate transfer belt 23.

  On the other hand, as indicated by an arrow A, the paper P is fed from a paper storage tray (not shown), and is transported to the transfer roller 24 via a paper feed roller 50 and a registration roller 51 provided in the transport path. The transfer roller 24 transfers the toner image transferred onto the intermediate transfer belt 23 onto the paper P sent out by the registration roller 51 at the timing.

  Here, the above-described elements, that is, the exposure units 15Y to 15K, the charging / developing units 20Y to 20K, and the intermediate transfer belt 23 constitute an image forming unit. That is, the image forming unit (1) charges the photosensitive drums 21Y to 21K, (2) forms electrostatic latent images on the photosensitive drums 21Y to 21K by the exposure units 15Y to 15K, and (3) is formed. (4) The toner images on the photosensitive drums 21Y to 21K are primarily transferred to the intermediate transfer belt 23. (5) The toner images on the intermediate transfer belt 23 are transferred onto the paper P. The toner image is transferred onto the paper P through a series of processes of next transfer.

  The sheet P having the transferred toner image, that is, the unfixed toner image on the fixing target surface, is sent to the fixing device 30 via the conveyance belt 52. The fixing device 30 presses and heats the paper P to fix the toner image on the paper P.

  FIG. 2 is a schematic diagram illustrating a main part of the image forming apparatus 1 centering on the fixing device 30 and a sheet cooling unit 40 described later. The fixing device 30 is mainly composed of an upper fixing roller 31 and a lower fixing roller 32. The upper fixing roller 31 and the lower fixing roller 32 are arranged in pressure contact with each other, and a fixing nip portion NP is formed at the press contact portion between the upper fixing roller 31 and the lower fixing roller 32.

  The fixing upper roller 31 is formed by laminating an elastic layer such as silicone rubber and a release layer made of fluororesin on the surface of a cylindrical steel or aluminum pipe. Inside the upper fixing roller 31, a heater 33 for heating the upper fixing roller 31, that is, for thermally fixing the toner image on the paper P is incorporated. The fixing upper roller 31 is heated by the radiant heat from the heater 33. The fixing upper roller 31 is rotationally driven in accordance with the passing speed of the paper P when power is transmitted from a driving means (for example, a motor) (not shown).

  The lower fixing roller 32 is formed by laminating an elastic layer such as silicone rubber and a release layer made of fluororesin on the surface of a cylindrical steel or aluminum pipe. The lower fixing roller 32 can include a heater (not shown) in the same manner as the upper fixing roller 31, and is configured to be able to apply heat for heat fixing.

  In the fixing device 30, the paper P is conveyed in such a manner that the surface to be fixed faces the fixing upper roller 31, and passes through the fixing nip portion NP in the conveyance process of the paper P. As a result, the toner image is fixed onto the fixing target surface of the paper P through the pressure applied by the upper fixing roller 31 and the lower fixing roller 32 and the heat action of the upper fixing roller 31.

  The paper discharge unit includes a paper discharge roller, a guide member (not shown), and the like, conveys the paper P that has been fixed by the fixing device 30, and is a paper tray (not shown) attached to the outer side surface of the apparatus housing. The paper P is discharged. Further, when an image is formed on the back side of the paper P, the paper discharge unit conveys the paper P after the fixing process of the toner image on the front surface to the reversing roller 57 below by a guide member (not shown) ( (See FIG. 1). The reverse roller 57 sandwiches the rear end of the paper P, reverses the paper P by reverse feeding, and sends the paper P to the refeed conveyance path 58.

  Here, a transport unit 53 is provided in the paper transport path from the fixing device 30 to the paper tray. The transport unit 53 includes a driving roller 54 and a driven roller 55 connected to a driving source (not shown), and an air suction belt 56 that is wound around the pair of rollers 54 and 55 and rotates. The air suction belt 56 has a large number of small-diameter through holes, and a suction duct (not shown) is disposed inside the air suction belt 56. The air suction belt 56 conveys the paper P while sucking the paper P using the suction force of air by the suction duct.

  The sheet cooling unit 40 has a function of cooling the sheet P after passing through the fixing device 30 and is provided on the sheet conveyance path so as to face the conveyance surface of the air suction belt 56. The sheet cooling unit 40 includes a plurality of cooling units each capable of individually adjusting a cooling amount, for example, four cooling units 401 to 404, and the four cooling units 401 to 404 extend in the sheet conveyance direction. They are arranged in parallel. Each cooling unit 401 to 404 includes a heat sink 41 and a cooling fan 42.

  The heat sink 41 includes a plurality of heat radiating fins on the surface of a plate-like member made of a metal such as aluminum or copper having excellent heat conduction, and is in surface contact with a member constituting the paper P conveyance path. Arranged in a state. The heat sink 41 absorbs heat of the transport path and the paper P transported through the transport path and dissipates the heat, thereby cooling the paper P heated in the fixing device 30.

  The cooling fan 42 plays a role of promoting heat exchange (paper cooling) by the heat sink 46 by blowing air to the heat sink 46. The cooling fan 42 is, for example, a multi-blade fan that rotatably includes a number of forward blades, and is configured to be able to control the rotation speed through a control unit 60 described later. Therefore, the cooling amount of each of the cooling units 401 to 404 can be adjusted by controlling the number of rotations of each cooling fan 42.

  FIG. 3 is a block diagram schematically showing a control system of the image forming apparatus 1 according to the present embodiment. The control system of the image forming apparatus 1 is mainly configured by the control unit 60. As the control unit 60, for example, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used. The control unit 60 performs various calculations according to the control program stored in the ROM, and controls the operation state of the image forming apparatus 1 based on the calculation results.

The control unit 60 controls each unit of the image forming apparatus 1 to execute the following series of processes, thereby transferring the toner image onto the conveyed paper P.
(1) Charge the photosensitive members 21Y to 21K. (2) Form electrostatic latent images on the photosensitive members 21Y to 21K by the exposure units 15Y to 15K. (3) Adhere toner to the formed electrostatic latent images ( 4) Primary transfer of toner images on photoreceptors 21Y to 21K to intermediate transfer belt 23 (5) Transport of paper P (6) Secondary transfer of toner image on intermediate transfer belt 23 to paper P

  In addition, the control unit 60 controls the fixing device 30. Specifically, the control unit 60 controls the fixing temperature by adjusting the energization amount to the heater 33. Further, the control unit 60 can control the conveyance speed of the paper P passing through the fixing nip NP by adjusting the rotation speed of the upper fixing roller 31. The controller 60 can grasp the fixing temperature through a temperature sensor (not shown).

  The control unit 60 controls the sheet cooling capacity of the sheet cooling unit 40 that cools the sheet P after passing through the fixing device 30 based on a profile 61 described later. The sheet cooling capacity is controlled by controlling the cooling amount by the sheet cooling unit 40. Specifically, the control unit 60 is executed by controlling the number of rotations of the cooling fans 42 of the individual cooling units 401 to 404. For example, when the rotational speed of the cooling fan 42 is increased, the paper cooling capacity is increased (cooling amount: large), and when the rotational speed of the cooling fan 42 is decreased, the paper cooling capacity is decreased ( Cooling amount: small).

  FIG. 4 is an explanatory diagram showing the relationship between time Time and paper temperature C. FIG. FIG. 4A shows an example of a temperature gradient that is a change over time in the sheet temperature after passing through the fixing device 30. For example, the paper P with a fast printing order has a steep temperature gradient C11, but the paper P with a slow printing order has a small temperature drop due to the influence of heat accumulated in the transport path. C12 has a gentle tendency. The temperature gradients C11 and C12 regarding the individual sheets P affect the image gloss. More specifically, from a temperature (hereinafter referred to as “starting temperature”) C1 that affects the image gloss when the temperature of the paper P is lowered to a temperature (hereinafter referred to as “solidification temperature”) C2 at which the wax component of the toner coagulates. The temperature gradient in between affects the image gloss. For this reason, if there is a difference in the temperature gradient after passing through the fixing device 30, a difference in image gloss occurs between the sheets. The start temperature C1 and the coagulation temperature C2 described above are determined by the toner composition and the like.

  Thus, from the viewpoint that the image gloss is related to the temperature gradient, a profile 61 is prepared in the control unit 60. The control unit 60 refers to the profile 61 and controls the sheet cooling capacity and controls the temperature gradient of the sheet P. Then, by controlling the temperature gradient for each sheet, the difference in temperature gradient between sheets is suppressed, thereby suppressing the difference in image gloss between individual sheets. As a result, image gloss between sheets set to the same image gloss can be made to correspond.

  The profile 61 is composed of cooling control values that specify the sheet cooling capacity for achieving this temperature gradient on the premise of a temperature gradient for obtaining a certain image glossiness. A plurality are provided depending on the situation. As the cooling control value, for example, the cooling amount of each of the cooling units 401 to 404 (specifically, the rotational speed of the cooling fan 42, etc.) can be mentioned.

  The profile 61 is prepared for each different image forming parameter. The image forming parameter is a parameter that affects the temperature gradient of the paper P. Specifically, the image forming parameter is a post-fixing paper temperature and a printing condition when a toner image is formed on the paper P. Here, the printing conditions include any one of ambient temperature, type of paper P, fixing temperature, linear speed of air suction belt 56, printing order of paper P, printing rate for paper P, and the like. The combination of is mentioned.

  Such a profile 61 is created in advance through experiments and simulations, and is stored in the memory of the control unit 60. Specifically, on the premise of predetermined image forming parameters, a temperature gradient necessary for obtaining the image gloss is acquired for each of various image glosses. For example, as shown in FIG. 4B, the temperature gradients P11 to P13 corresponding to three types of image gloss (low gloss, standard gloss, and high gloss) have a gentle tendency as the image gloss increases. is there. Next, a cooling control value for realizing the temperature gradient is acquired for each temperature gradient. Then, by executing such a method with different image formation parameters, profiles 61 corresponding to various image formation parameters are created.

  Various types of information are input to the control unit 60 from the sensor unit 70 and the input unit 80. The sensor unit 70 is composed of a plurality of temperature sensors. The inlet temperature sensor 71 is provided upstream of the paper cooling unit 40 in the paper transport path, and detects the temperature of the paper P after passing through the fixing device 30 (post-fixing paper temperature). The outlet temperature sensor 72 is provided at the rear stage of the sheet cooling unit 40 in the sheet conveyance path, and detects the temperature of the sheet P after passing through the sheet cooling unit 40. The plurality of paper temperature sensors 731 to 734 are sensors for detecting the temperature of the paper P when the paper P passes through the inside of the paper cooling unit 40, and are provided in correspondence with the four cooling units 401 to 404. It has been. The individual paper temperature sensors 731 to 734 are arranged to face the cooling units 401 to 404 with the paper P interposed therebetween, and detect the temperature of the paper P cooled by the cooling units 401 to 404 positioned immediately above. . The environmental temperature sensor 75 detects the temperature of the surrounding environment of the image forming apparatus 1 (hereinafter referred to as “environment temperature”).

  The input unit 80 includes an operation unit (not shown) provided at the upper part of the main body of the image forming apparatus 1 and an interface connected to be communicable with a personal computer or another image forming apparatus. With this input unit 80, print information set by the user through the operation unit or print information received together with input image data from a personal computer or other image forming apparatus is input to the control unit 60. Through this print information, the control unit 60 acquires, for example, single-sided / double-sided printing type, paper P type (for example, paper type such as size, plain paper / thick paper, and weight), image gloss, density, magnification, and the like. can do.

  FIG. 5 is a flowchart showing the operation of the image forming apparatus 1 according to the present embodiment. The process shown in this flowchart mainly shows the process related to sheet cooling after the fixing process, and is executed by the control unit 60 with a print start command input from the input unit 80 as a trigger. Here, when the user performs printing with the image forming apparatus 1, a print start command is input to the control unit 60 through the operation of the operation unit or from a personal computer or other image forming apparatus together with print information / image data. Has been.

  First, in step 10 (S10), the control unit 60 reads print information via the input unit 80. In step 11 (S11), the control unit 60 reads the temperature and environmental temperature of the sheet P after the fixing process as temperature information (first temperature information). Specifically, the control unit 60 reads the temperatures detected by the inlet temperature sensor 71 and the environmental temperature sensor 75 in correspondence with the timing at which the reference position (for example, the leading end) of the paper P reaches the inlet temperature sensor 71.

  In step 12 (S12), the control unit 60 refers to the profile 61, and based on the print information and the first temperature information, sets the image formation parameters (post-fixing paper temperature and printing conditions) and image gloss corresponding to them. The corresponding profile 61 is searched. Hereinafter, the cooling control value corresponding to the searched profile 61 and the temperature gradient corresponding thereto are referred to as a target cooling control value and a target temperature gradient.

  In step 13 (S13), the control unit 60 sets the sheet cooling capacity, specifically, the rotational speed of each of the cooling units 401 to 404 based on the target cooling control value that is the profile 61.

  In step 14 (S14), the control unit 60 reads the second temperature information. Specifically, the control unit 60 reads the detected temperatures of the paper temperature sensors 731 to 734 and the outlet temperature sensor 72.

  In step 15 (S15), the control unit 60, based on the second temperature information, the temperature gradient that is the transition of the actual sheet temperature of the sheet P that is transported through the sheet cooling unit 40 (hereinafter referred to as "actual temperature gradient"). Is calculated. Specifically, the control unit 60 calculates the actual temperature gradient from the temperature transition related to the reference position (for example, the leading end) of the paper P. This actual temperature gradient is determined to be negative in step 19 to be described later in the process of transporting the paper P, so that the processing in step 15 is repeated for each paper sheet, so that the temperature at the reference position of the paper P can be individually set. By monitoring with the temperature sensors 731 to 734 and 72, the temperature transition is created step by step. Note that the actual temperature gradient may be calculated as an average value by setting a plurality of reference positions of the sheet P along the sheet conveyance direction and calculating the actual temperature gradient for each reference position.

  In Step 16 (S16), the control unit 60 determines whether or not the actual temperature gradient corresponds to the target temperature gradient as the profile 61. If an affirmative determination is made in step 16, that is, if the actual temperature gradient and the target temperature gradient correspond, the process proceeds to step 19 (S19) described later. On the other hand, if a negative determination is made in step 16, that is, if the actual temperature gradient does not correspond to the target temperature gradient, the process proceeds to step 17 (S17). In the process of step 16, it is not necessary to make an affirmative determination only in a state where the actual temperature gradient and the target temperature gradient are strictly coincident with each other, and both are shifted within an allowable range for obtaining the final image gloss. Even if it is, it may be considered that it corresponds.

  In step 17, the control unit 60 determines a correction value for the sheet cooling capacity. For example, as shown in FIG. 6, the actual temperature gradient Cn1 is gentler than the target temperature gradient Po at the timing T1 when the leading end of the sheet P reaches the most upstream sheet cooling unit 401 and the sheet temperature sensor 731. Assume a case that is in a state. In this case, the correction value of the sheet cooling capacity is determined so that the actual temperature gradient Cn1 corresponds to the target temperature gradient Po. For example, the correction value of the sheet cooling capacity is set such that the number of rotations of the cooling unit 402 at the next stage is set higher than the current value. On the other hand, assume that the actual temperature gradient Cn2 is steeper than the target temperature gradient Po at the timing T1. In this case, the correction value of the sheet cooling capacity is determined so that the actual temperature gradient Cn2 corresponds to the target temperature gradient Po. For example, the correction value of the sheet cooling capacity is set such that the number of rotations of the cooling unit 402 at the next stage is set to be smaller than the current value.

  In step 18 (S18), the control unit 60 corrects the cooling control value as the profile 61. For example, as shown in FIG. 6, a case is assumed where the actual temperature gradient Cn1 is gentler than the target temperature gradient Po at the timing T1. In this case, the cooling control value is corrected so that the actual temperature gradient Cn1 corresponds to the target temperature gradient Po. For example, the correction of the cooling control value is such that the number of rotations of the cooling unit 401 for which the actual temperature gradient Cn1 is calculated is set to be higher than that at present. On the other hand, assume that the actual temperature gradient Cn2 is steeper than the target temperature gradient Po at the timing T1. In this case, the cooling control value is corrected so that the actual temperature gradient Cn2 corresponds to the target temperature gradient Po. For example, the correction of the cooling control value is such that the number of rotations of the cooling unit 401 at which the actual temperature gradient Cn2 is currently set is set to be lower than that at the present time.

  In step 19 (S19), the control unit 60 determines whether or not the sheet P to be cooled has passed the sheet cooling unit 40. If an affirmative determination is made in step 19, that is, if the paper P has passed through the paper cooling unit 40, the process proceeds to step 20 (S20). On the other hand, if a negative determination is made in step 19, that is, if the paper P has not passed through the paper cooling unit 40, the processes in and after step 13 are executed again. In this case, if the correction value of the paper cooling capacity is determined in step 17, in step 13, the paper cooling capacity of each of the cooling units 401 to 404 is set in consideration of this correction value.

  In step 20, the control unit 60 determines whether the paper P that has passed through the paper cooling unit 40 is the final paper, that is, the final paper P among the one or more print target papers P included in the job. Judging. If an affirmative determination is made in step 20, that is, if the paper P is the final paper, the routine is exited. On the other hand, if a negative determination is made in step 20, that is, if the paper P is not the final paper, the processing returns to step 11.

  As described above, in the present exemplary embodiment, the image forming apparatus 1 performs sheet cooling on the sheet P after passing through the fixing device 30 and also adjusts the sheet cooling capacity and the sheet cooling unit 40. And a control unit 60 for controlling the temperature gradient of the paper P after passing through the fixing device 30 by controlling the paper cooling capacity. Here, the control unit 60 controls the temperature gradient according to the image gloss which is the gloss of the toner image formed on the paper P. According to such a configuration, by controlling the paper cooling capacity of the paper cooling unit 40, the cooling of the paper P can be freely adjusted, so that the temperature gradient can be controlled. Thereby, since a desired temperature gradient can be given to the paper P, a desired image gloss can be obtained.

  In addition, the control unit 60 controls the temperature gradient for each sheet according to the image gloss, thereby associating the temperature gradient between the sheets set to the same image gloss. According to such a configuration, it is possible to suppress a situation in which a difference in temperature gradient occurs between sheets set to the same image gloss, and thus it is possible to suppress a situation in which a difference in image gloss occurs between sheets. it can.

  Further, the control unit 60 determines, for each sheet to be cooled, the temperature after the sheet P passes through the fixing device 30 (the sheet temperature after fixing) and the printing conditions when the toner image is formed on the sheet P. The paper cooling capacity of the paper cooling unit 40 is controlled. According to this configuration, the temperature state of the paper P before passing through the paper cooling unit 40 can be accurately estimated from the post-fixing paper temperature and printing conditions. Therefore, if the sheet cooling capacity is set according to this estimate, the temperature gradient can be controlled appropriately. Thereby, a desired image gloss can be obtained.

  In the present embodiment, the image forming apparatus 1 further includes a profile 61 that specifies the sheet cooling capability of the sheet cooling unit 40 for achieving a predetermined temperature gradient according to both the post-fixing sheet temperature and the printing conditions. Have. In this case, the control unit 60 refers to the profile 61 and controls the sheet cooling capacity of the sheet cooling unit 40. According to such a configuration, it is only necessary to control the sheet cooling capacity according to the profile 61, so that the calculation load can be reduced.

  Further, the control unit 60 corrects the profile 61 based on the transition (actual temperature gradient) of the actual sheet temperature (actual sheet temperature) when passing through the sheet cooling unit 40. As a result, even if there is a difference between the target temperature gradient and the actual temperature gradient, it can be corrected. Therefore, it is possible to improve the accuracy of temperature gradient control for the paper P after the next time.

  Further, the control unit 60 corrects the sheet cooling capacity of the sheet cooling unit 40 based on the transition (actual temperature gradient) of the actual sheet temperature when passing through the sheet cooling unit 40. As a result, even if there is a difference between the target temperature gradient and the actual temperature gradient, it is possible to improve the accuracy of temperature gradient control for the paper P that is currently processed.

  In the present embodiment, the sheet cooling unit 40 is arranged in parallel in the conveyance direction of the sheet P, and a plurality of cooling units (in this embodiment, each of which can individually adjust the cooling amount for the sheet P). 4 cooling units 401-404). According to such a configuration, the paper cooling capacity for the paper P can be subdivided and controlled along the flow over time, so that the accuracy of temperature gradient control can be improved.

  Further, according to the present embodiment, the temperature sensors 71 and 72 are arranged at the front stage and the rear stage of the paper cooling unit 40, respectively. As a result, the sheet temperature when entering the sheet cooling unit 40 can be detected, so that the sheet temperature after fixing can be reliably monitored. Therefore, the accuracy of temperature gradient control can be improved. Further, since the sheet temperature at the time of discharge from the sheet cooling unit 40 can be detected, the profile 61 can be appropriately corrected.

  In the above-described embodiment, the sheet cooling capacity of the sheet cooling unit 40 is controlled for each sheet to be cooled based on the post-fixed sheet temperature and the printing conditions. However, the present embodiment is not limited to this, and the control unit 60 cools the sheet of the sheet cooling unit 40 based on only the printing conditions or only the post-fixing sheet temperature for each sheet to be cooled. Capability may be controlled. If the post-fixing paper temperature is known, at least the starting point for the target temperature gradient is determined, so that the paper P after passing through the fixing device 30 can be controlled to a desired temperature gradient. On the other hand, even if only the printing conditions are used, if the fixing temperature is determined from these factors, the post-fixing paper temperature can be estimated. Similarly, the paper P after passing through the fixing device 30 is set to a desired temperature. The gradient can be controlled. Naturally, in any case, it is preferable that the profile is provided as in the above-described embodiment, and the control unit 60 controls the temperature gradient according to the profile.

(Second Embodiment)
The image forming apparatus according to the second embodiment will be described below. In 1st Embodiment mentioned above, although the temperature gradient which comprises the profile 61 was illustrated by the linear relationship, this invention is not limited to this. For example, the temperature gradient constituting the profile 61 may be indicated by a curved relationship, or may be indicated by a relationship in which a plurality of straight lines are connected. That is, the temperature gradient constituting the profile 61 may be set as appropriate according to the required image gloss.

  As shown in FIG. 7, for example, when the sheet temperature differs between sheets when discharged from the fixing device 30, the temperature gradient of the example P also varies. In FIG. 9A, C21 indicates a temperature gradient of the sheet P when the sheet temperature is low when discharged from the fixing device 30, and C22 indicates a high sheet temperature when discharged from the fixing device 30. The temperature gradient of the paper P in a case is shown. In order to obtain the same image gloss on these two types of paper P, it is necessary to correspond the temperature gradients of both after passing through the fixing device 30.

  When setting the temperature gradient in such a situation, it is not necessary to correspond to the temperature gradient in all temperature regions, and it is sufficient to correspond to the temperature gradient in the temperature region that affects the image gloss. That is, for each sheet P, the temperature gradient may be made to correspond in the range from the start temperature C1 to the solidification temperature C2. In FIG. 7B, P22 indicates a temperature gradient related to a sheet having a temperature gradient of C22, and P21 indicates a temperature gradient related to a sheet having a temperature gradient of C21. The temperature gradient P21 corresponding to C21 is a temperature gradient that changes at a constant gradient. On the other hand, the temperature gradient P22 corresponding to C22 is set to a steep gradient up to the start temperature C1, and the subsequent temperature gradient is set to a gradient corresponding to the temperature gradient P21.

  As described above, according to the present embodiment, it is possible to cope with various temperature gradients by controlling the sheet cooling capacity, and thus it is possible to appropriately control the image gloss for the sheet P. Further, as shown in the present embodiment, when the temperature gradients between the sheets correspond to each other, the control unit 60 at least sets the temperature gradients in the range starting from the start temperature C1 and the solidification temperature C2 as the end points. What is necessary is just to make it correspond. As a result, the temperature gradient can be made to correspond between sheets within a range that affects the image gloss, and the difference in image gloss between the sheets can be suppressed.

(Third embodiment)
The image forming apparatus 1 according to the third embodiment will be described below. In the first or second embodiment described above, the paper cooling unit 40 controls the paper cooling capacity through the cooling amount of each of the cooling units 401 to 404. However, the method for controlling the sheet cooling capacity is not limited to this. For example, the sheet cooling capacity may control the conveyance speed of the sheet P, that is, the linear speed of the air suction belt 56. That is, when the linear speed of the air suction belt 56 is increased from the normal speed, the passage time of the paper P in the paper cooling unit 40 is shortened, so that the paper cooling capacity is reduced. On the other hand, when the linear speed of the air suction belt 56 is decreased from the normal speed, the passage time of the paper P in the paper cooling unit 40 becomes longer, so that the paper cooling capacity increases. That is, the transport unit 53 has a function as a paper discharge unit that discharges the paper P to the paper tray, and also functions as a paper cooling unit 40.

  Hereinafter, an example of control of the sheet cooling capacity through the linear velocity will be described with reference to FIG. FIG. 8A shows a temperature gradient C31 related to plain paper after passing through the fixing device 30, and a temperature gradient C32 related to thin paper after passing through the fixing device 30. As shown in the figure, when the paper cooling unit 40 is operated under the same conditions for each paper P, the thermal gradient of the thin paper is smaller than that of the plain paper. It is steeper than C31. Therefore, there is a possibility that a difference in temperature gradient occurs between plain paper and thin paper, resulting in a difference in image gloss. Therefore, it is conceivable to make the temperature gradient as smooth as that of plain paper by reducing the paper cooling capacity for thin paper. However, in this case, it is conceivable that the paper P passes through the paper cooling unit 40 before the temperature of the paper P reaches the solidification temperature C2 as indicated by C41 in FIG.

  Therefore, in this case, by reducing the linear velocity of the air suction belt 56, the time for passing through each of the cooling units 401 to 404 is delayed, and the temperature of the paper P is reliably lowered to the solidification temperature C2 or lower. As described above, according to the present embodiment, the paper cooling unit 40 further includes the transport unit 53 that can adjust the transport speed of the paper P transported by the cooling units 401 to 404. By controlling the conveyance speed of the sheet P, specifically, the linear speed of the air suction belt 56, the sheet cooling capacity can be flexibly controlled, so that the accuracy of temperature gradient control can be improved. it can.

(Modification (1))
FIG. 9 is a schematic diagram illustrating a main part of an image forming apparatus 1 as a modification. The image forming apparatus 1 according to each of the above-described embodiments shows an exemplary configuration, and the present invention can be variously modified in the spirit thereof. For example, in the image forming apparatus 1, it is possible to omit the temperature sensors arranged in the front and rear stages of the sheet cooling unit 40. In addition, suppose that description is abbreviate | omitted about the structure which overlaps with each embodiment mentioned above, and demonstrates below centering on difference.

  In the configuration shown in the present embodiment, since the temperature sensor is not disposed in front of the sheet cooling unit 40, the temperature of the sheet P after passing through the fixing device 30 cannot be directly detected. Therefore, in the case of such a configuration, the fixing temperature is specified from the detection temperature from the sensor for detecting the surface temperature of the upper fixing roller 31 of the fixing device 30 or the energization amount to the heater 33, and the sheet is determined from this fixing temperature. The temperature of P can be estimated.

  In addition, since the temperature sensor is not arranged at the subsequent stage of the paper cooling unit 40, the temperature of the paper P after passing through the paper cooling unit 40 cannot be directly detected. Therefore, in the case of such a configuration, the temperature of the paper P can be estimated through the temperature detected by the paper temperature sensor 734 at the most subsequent stage, the environmental temperature, and the like.

  Thus, according to the present embodiment, it is possible to simplify the apparatus configuration by reducing the number of temperature sensors.

(Modification (2))
FIG. 10 is a schematic diagram illustrating a main part of an image forming apparatus 1 as a modification. In the image forming apparatus 1 according to the present modification, the sheet cooling unit 40 can adopt various forms. In addition, suppose that description is abbreviate | omitted about the structure which overlaps with 1st Embodiment, and demonstrates below centering on difference.

  In the present embodiment, the sheet cooling unit 40 includes a single cooling unit, specifically, a heat sink 43 and a cooling fan 44 that cools the heat sink 43. In other words, the sheet cooling unit 40 of the present embodiment cannot control the sheet cooling capacity in a divided manner, and can control the cooling capacity as a single unit. The heat sink 41 is provided with a heat sink temperature sensor 74 for detecting the temperature of the heat sink 41, that is, the cooling capacity. The temperature detected by the heat sink temperature sensor 74 is read by the control unit 60 and is referred to when the cooling capacity of the paper cooling unit 40 is controlled. In addition, an inlet temperature sensor 71 is provided in the front stage of the paper cooling unit 40 in the process of transporting the paper P. The inlet temperature sensor 71 is the temperature of the paper P after passing through the fixing device 30 (paper temperature after fixing). ) Is detected.

  In the image forming apparatus 1 having such a configuration, when the control unit 60 reads the print information and the temperature detected by the inlet temperature sensor 71, the control unit 60 searches the profile 61 for a target temperature gradient and a target cooling control value corresponding to the print information. The control unit 60 controls the temperature gradient of the paper P according to the searched target temperature gradient and target cooling control value.

  As described above, the sheet cooling unit 40 includes a single cooling unit (heat sink 43 and cooling fan 44) that can adjust the cooling amount for the sheet P. According to such a configuration, although it is difficult to control the sheet cooling capacity in stages, it is possible to control the sheet cooling capacity with a simple configuration.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 15Y-15K Exposure part 20Y-20K Charging / development unit 23 Intermediate transfer belt 24 Transfer roller 30 Fixing device 31 Upper fixing roller 32 Lower fixing roller 40 Paper cooling part 401-404 Cooling unit 41, 43 Heat sink 42, 44 Cooling fan 50 Paper feed roller 51 Registration roller 52 Conveyance belt 53 Conveyance unit 54 Drive roller 55 Driven roller 56 Air suction belt 57 Reversing roller 58 Refeed paper conveyance path 60 Control unit 61 Profile 70 Sensor unit 71 Inlet temperature sensor 72 Outlet temperature sensor 731-734 Paper temperature sensor 74 Heat sink temperature sensor 75 Environmental temperature sensor 80 Input section

Claims (12)

A paper cooling unit that can adjust the paper cooling capacity as well as performing paper cooling on the paper after passing through the fixing device,
A control unit that controls a temperature gradient that is a temporal transition of the sheet temperature after passing through the fixing device by controlling the sheet cooling capacity of the sheet cooling unit;
The image forming apparatus, wherein the control unit controls the temperature gradient according to an image gloss which is a gloss of a toner image formed on a sheet.   The control unit controls the temperature gradient for each sheet according to the image gloss, so that the temperature gradients between sheets set to the same image gloss correspond to each other. The image forming apparatus according to claim 1.   When the control unit associates the temperature gradients between the sheets, at least a range from a temperature at which the image gloss starts to affect after passing through the fixing device to a temperature at which the wax component of the toner coagulates. The image forming apparatus according to claim 2, wherein each of the temperature gradients is associated with each other.   The control unit controls, for each sheet to be cooled, a sheet cooling capability of the sheet cooling unit based on a post-fixing sheet temperature that is a temperature after the sheet has passed through a fixing device. Item 4. The image forming apparatus according to any one of Items 1 to 3.   4. The control unit according to claim 1, wherein the control unit controls, for each sheet to be cooled, a sheet cooling capacity of the sheet cooling unit based on a printing condition when a toner image is formed on the sheet. An image forming apparatus described in any one of the above.   For each sheet to be cooled, the control unit cools the sheet based on a post-fixing sheet temperature that is a temperature after the sheet has passed through the fixing device and a printing condition when a toner image is formed on the sheet. 4. The image forming apparatus according to claim 1, wherein the sheet cooling capacity is controlled. A profile for designating a sheet cooling capacity of the sheet cooling unit for achieving a predetermined temperature gradient according to one or both of the post-fixing sheet temperature and printing conditions;
The image forming apparatus according to claim 4, wherein the control unit controls the sheet cooling capacity of the sheet cooling unit with reference to the profile.   The image forming apparatus according to claim 7, wherein the control unit corrects the profile based on a transition of an actual sheet temperature when passing through the sheet cooling unit.   9. The image forming apparatus according to claim 7, wherein the control unit corrects a sheet cooling capacity of the sheet cooling unit based on a transition of an actual sheet temperature when passing through the sheet cooling unit. apparatus.   The image forming apparatus according to claim 1, wherein the sheet cooling unit includes a single cooling unit capable of adjusting a cooling amount for the sheet.   10. The sheet cooling unit is configured by a plurality of cooling units, each of which is arranged in parallel in the sheet conveyance direction and can individually adjust the cooling amount for the sheet. An image forming apparatus as described above.   The image forming apparatus according to claim 1, wherein the sheet cooling unit further includes a transport unit capable of adjusting a transport speed of a sheet transported by the cooling unit.

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