JP2016164624A - Image formation apparatus and image formation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high quality-printing by preventing a deviation between front and rear images at the time of double-sided printing by correcting contraction of a sheet after fixation.SOLUTION: An image formation apparatus comprises: a fixation device 40; a sheet information database 208 which holds information on the heat characteristics of a sheet and the change characteristics of the moisture content to an environment; a humidifier control value determination part 205 which is provided with a humidification conveyance path 66 arranged on the downstream side in the conveyance direction of the fixation device; a sheet information acquisition part 214 which acquires information on the heat characteristics of the sheet and the change characteristics of the moisture content to the environment from the sheet information database 208; a moisture content calculation part 202 which calculates the temperature and moisture content of the sheet conveyed to the fixation device; a second moisture content calculation part 203 which calculates the temperature and the reduction rate of the moisture content of the sheet immediately before conveyance to the humidifier; a third moisture content calculation part 204 which calculates the increase amount of the moisture content of the sheet from the temperature and humidity in the humidification conveyance path 66; and a humidifier control value determination part 205 which controls the humidifier so that increase and reduction of the moisture content of the sheet by the second moisture content calculation part and the third moisture content calculation part match.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus and an image forming system.

  In an image forming apparatus using an electrophotographic system, a charging device uniformly holds charges on the surface of an image carrier, and laser light or LED (Light Emitting Diode) light is irradiated from a light irradiation device according to image information. Then, a latent image is formed on the image carrier. Then, the latent image is visualized with toner of the developing device, and the toner image is transferred to the transfer belt by the transfer device, and then transferred to the surface of the paper. Next, the toner image formed on the sheet is heated and fixed on the sheet by passing between the belt or roller heating unit and the belt or roller pressing unit in the fixing device.

  At this time, the paper after coming out of the fixing device shrinks due to evaporation of moisture. If an image is formed on the back side during subsequent double-sided printing, the image on the front side becomes smaller than the image on the back side due to the shrinkage of the paper, and a shift occurs between the image on the front side and the image on the back side. Further, since the sheet is conveyed and moved at a predetermined speed, a laminar boundary layer is formed on the surface thereof, and the laminar boundary layer becomes thicker from the front end to the rear end in the conveying direction. Since the evaporation rate of water becomes slower toward the trailing edge according to the change in the thickness of the laminar boundary layer, the trailing edge is less compressed than the leading edge of the sheet, and the sheet is deformed into a trapezoid. As a result, the amount of deviation of the front and back images also changes with respect to the paper transport direction.

  FIG. 7 is a schematic diagram showing a deformed state of the sheet after fixing. The sheet 10 is deformed into a trapezoid as shown in FIG. In the sheet 10, the length L1 of the leading edge in the conveyance direction is shorter than the length L2 of the trailing edge (L1 <L2), and the image is deformed in proportion to this length. Since this deformation does not return in the several to tens of seconds until the back side is printed, for example, when a rectangle of the same size is printed on the front and back, the rectangle on the front side is not only smaller than the back side, but the shape itself is also trapezoidal The difference between the front and back becomes conspicuous.

  As described above, the cause of the deformation of the paper into the trapezoid is considered to be a laminar flow boundary layer of water vapor formed by the paper being conveyed at a constant speed while emitting water vapor itself. FIG. 8 is a graph of physical properties that change from the leading edge to the trailing edge of the paper. FIG. 8A shows the thickness of the laminar boundary layer when the leading edge of the paper 10 shown in FIG. 7 is 0 and the position in the transport direction is x. The laminar boundary layer becomes thicker toward the rear edge. As the laminar boundary layer is thicker, the evaporation rate of water from the sheet is slower, so the evaporation rate of water vapor is slower toward the rear end of the sheet as shown in FIG. Since the decrease amount of the moisture content of the paper is a value obtained by integrating the evaporation rate with time, the decrease amount of the moisture content of the paper 10 at a certain time is shown in FIG. 8B as shown in FIG. Draw a curve similar to the curved line. Furthermore, since the shrinkage rate of the paper 10 is proportional to the amount of decrease in the moisture content of the paper 10, a similar curve is drawn as shown in FIG. In this way, the paper has a trapezoidal shape with the leading edge contracted from the trailing edge in the transport direction.

  The image shift between the front and back sides due to the shrinkage of the paper after fixing is desired to be as small as possible in order to reduce the image quality during double-sided printing. Further, the change in the shift between the leading edge and the trailing edge of the paper leads to a further deterioration in quality.

  Conventionally, in order to reduce such deterioration in print quality, a humidifier is provided in the image forming apparatus to increase the moisture content of the paper in advance, or the paper that has been dried by heating the fixing device absorbs moisture and shrinks. There is a technology to prevent deformation.

  In Patent Document 1, an entrance of a transfer material that covers a region including a fixing device and a recording material reversing device, and a visible image is transferred to the first surface of the recording material, is reversed by a transfer material reversing device. An airtight case having an exit through which the transferred material escapes toward an area between the image carrier and the transfer device, and a humidifier that is provided in the case and keeps the inside of the case at a certain humidity or higher. Thus, an image forming apparatus provided with a moisture applying device that applies moisture to the recording material before the transfer of the visible image to the second surface of the recording material is disclosed.

  Further, in Patent Document 2, the conveyance means that conveys the paper is opposed to each other, and the paper conveyed by the conveyance means is allowed to pass in one direction therebetween, and the front and back sides of the cut sheet are exposed. At least a pair of paper guides that are configured to be disposed on the outside of the paper guide, and by spraying water droplets toward one of the paper guides, moisture is passed to the paper passing between the paper guides. An image forming apparatus is described. This image forming apparatus controls the amount of water sprayed according to the type of paper, the fixing temperature, and the environment.

  Further, Patent Document 3 includes a humidifying roller pair that forms a nip, and a water supply unit that supplies water to the humidifying roller pair, and a paper humidifying device that humidifies the paper by passing the paper through the nip. There is a document that variably controls the moisture content of the paper by setting the linear speed of the humidifying roller variably according to the type of paper passing through the nip. In this technique, water is applied while a sheet is conveyed by a pair of rollers, and the conveyance speed is controlled according to the type and environment of the sheet.

  However, the above-described conventional technology does not consider correction for trapezoidal deformation of paper. That is, in Patent Document 1, the front and rear conveyance paths including the reverse conveyance path of the fixing device are sealed to humidify the inside. When humidifying after reversal, the trailing edge is leading, and the laminar boundary layer at the trailing edge is thin, the tip is thick, the tip contracted by evaporation after fixing becomes difficult to absorb moisture, and trapezoidal correction cannot be made . Further, in order to perform appropriate humidification for correcting the deformation of the sheet, calculation of the moisture content that decreases after the fixing device and the moisture content that increases due to humidification is not taken into consideration. Although an example of disposing an independent humidifier before and after the fixing device is also disclosed, calculation of increase / decrease in the moisture content is not described in this case, and the length of the humidifier is also compared with the length of the paper. It is clearly short and it seems difficult to correct the trapezoidal deformation.

  Further, in Patent Document 2, since water droplets are sprayed toward the paper for humidification, moisture is directly absorbed from the water droplets adhering to the paper surface after fixing, and does not absorb moisture via the laminar flow boundary. Moisture is supplied evenly until the shrinkage difference between the front end and the rear end after fixing cannot be corrected.

  Further, in Patent Document 3, since water is uniformly supplied from the front end to the rear end with a roller, the rear end becomes larger than the front end as in Patent Document 1. Furthermore, no consideration is given to calculating the moisture content that decreases after the fixing device and the moisture content that increases with humidification.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that corrects the shrinkage of a sheet after fixing in an image forming apparatus having a fixing device.

  In order to solve the above problems, an image forming apparatus according to the present invention includes a fixing device that heats and fixes an unfixed image when a sheet holding an unfixed image passes, the thermal characteristics of the sheet, and the environment An image forming apparatus comprising: a database that holds information on change characteristics of moisture content with respect to the image forming apparatus; and a humidifying unit that includes a humidifying conveyance path that humidifies the sheet while conveying the sheet on the downstream side in the conveying direction of the fixing device. Paper information acquisition means for acquiring information on the thermal characteristics of the paper and the change characteristics of the moisture content with respect to the environment from the database, and moisture content calculation means for obtaining the temperature and moisture content of the paper before being conveyed to the fixing device; A second moisture content calculating means for obtaining a reduction rate of the temperature and moisture content of the paper conveyed to the humidifying means from the heating temperature in the fixing device; and a temperature in the humidifying conveyance path. Increase / decrease in the moisture content of the paper determined by the third moisture content calculating means for obtaining an increase in the moisture content of the paper from the humidity, the second moisture content calculating means, and the third moisture content calculating means. Setting means for performing designation of humidification conditions in the humidification conveyance path so that the minutes coincide with each other.

  According to the present invention, it is possible to correct shrinkage of a sheet after fixing.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the humidification apparatus in the image forming apparatus. 1 is a diagram illustrating a hardware configuration of an image forming system including an image forming apparatus and a server apparatus according to an embodiment. 2 is a functional block diagram showing the image forming system. FIG. It is a graph which shows the relationship between the moisture content of a paper, and the relative humidity of the surface vicinity. 6 is a flowchart illustrating a procedure of correction processing for trapezoidal deformation of a sheet in the image forming apparatus. FIG. 6 is a schematic diagram illustrating trapezoidal deformation of a sheet after fixing. (A) thru | or (d) are the graphs of the physical property which changes with the position of the back end from the front-end | tip of a paper.

  Embodiments of the present invention will be described below. In addition, embodiment of this invention is not limited to the following embodiment. In the embodiments described below, a multifunction peripheral having a color printing function will be described as an example of an image forming apparatus.

  FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 110 includes, for each color of black (K), magenta (M), cyan (C), and yellow (Y), the photosensitive drums 3a, 3b, 3c, and 3d, and the photosensitive drums 3a and 3b. 3c, 3d, charging rollers 4a, 4b, 4c, 4d for charging electric charges, and light irradiation devices 6a, 6b, 6c, 6d such as laser diodes and LEDs (light emitting diodes), and a motor that rotates at high speed and constant speed. Polygon mirrors 5a, 5b, 5c, and 5d that are driven to scan the light beam in the main scanning direction of the photosensitive drums 3a, 3b, 3c, and 3d, and electrostatic latent images on the photosensitive drums that hold the developer. Developing devices 7 a, 7 b, 7 c, 7 d to be supplied to the intermediate transfer belt 2 are arranged side by side. The image forming apparatus 110 employs a so-called tandem configuration.

  In the image forming process, first, negative charges are applied to the photosensitive drums 3a, 3b, 3c, and 3d by the charging rollers 4a, 4b, 4c, and 4d, respectively, and the toner is uniformly charged. Light beams are output from the light irradiation devices 6a, 6b, 6c, and 6d in accordance with the written image signal, and charged photosensitive drums 3a, 3b, and 3c through an optical system including polygon mirrors 5a, 5b, 5c, and 5d. The surface of 3d is irradiated, and the potential distribution according to the presence or absence of light beam irradiation and the exposure amount is written. The electrostatic latent image to be written is written in black (K), magenta (M), cyan (C), and yellow (Y) which are toner primary colors generated after processing data transmitted from a scanner or a personal computer. It is formed by controlling the on / off of the light beam in accordance with the embedded signal. The formed electrostatic latent images are conveyed in the developing devices 7a, 7b, 7c, and 7d directions as the photosensitive drums 3a, 3b, 3c, and 3d rotate, and are developed with toners of respective colors. A toner image corresponding to the writing signal is formed and carried on the photosensitive drums 3a, 3b, 3c, and 3d.

  On the other hand, an intermediate transfer belt 2 stretched around rollers 21 and 22 is disposed as an intermediate transfer member below the photosensitive drums 3a, 3b, 3c, and 3d. The intermediate transfer belt 2 is rotated in the direction of the arrow shown in the drawing, the rollers 9a, 9b, 9c, and 9d are in contact with the back side thereof, and a primary bias is applied by the power supplies 31a, 31b, 31c, and 31d connected thereto, respectively. . The toner image is conveyed to the intermediate transfer belt 2 side as the photosensitive drums 3a, 3b, 3c, and 3d are rotated, and a position at which the photosensitive drums 3a, 3b, 3c, and 3d are in contact with the intermediate transfer belt 2 by the roller 9. Then, the image is transferred onto the intermediate transfer belt 2. The toner images of the respective colors are superimposed at the same position, and a toner image of a multicolor image is formed on the intermediate transfer belt 2. The portions of the photosensitive drums 3a, 3b, 3c, and 3d where the toner images have been transferred are wiped off by the photosensitive drum cleaner after the toner remaining on the outer peripheral surface is removed, and then discharged to the next image forming process. Supplied with.

  The multi-color toner image transferred onto the intermediate transfer belt 2 is conveyed toward the transfer roller 23 of the secondary transfer portion. On the other hand, a sheet (recording medium) set in the sheet feeding cassette 51 or the sheet feeding cassette 52 is fed toward the transfer roller 23 at a set timing, and is appropriately sent from the conveying roller 12 in accordance with image writing. Sent at timing. Between the transport roller 12 and the transfer roller 23, a temperature / humidity sensor 41 for measuring the temperature / humidity in the vicinity of the sheet surface is disposed. Electric charges are supplied to the transfer roller 23 from the power source 25, and the toner images on the intermediate transfer belt 2 are collectively transferred onto a sheet fed in cooperation with the roller 14.

  The sheet (recording medium) is conveyed to a position where it contacts the intermediate transfer belt 2 and receives a multicolor toner image. The sheet on which the multicolor toner image is formed is supplied to the nip portion between the heating roller 30 of the fixing device 40 and the pressure roller 37. The sheet and the multicolor toner image are heated and pressed, and the unfixed image is fixed on the sheet. A halogen heater 34 is disposed in the heating roller 30 of the fixing device 40 to heat the heating roller 30. The pressure roller 37 is pressed against the heating roller 30 by the pressure spring 35. The roller temperature sensor 36 measures the surface temperatures of the heating roller 30 and the pressure roller 37.

  As the temperature / humidity sensor 41, for example, a capacitance type or an electric resistance type can be used. In the capacitance type, a capacitor is formed using a polymer film as a dielectric, and moisture absorption and desorption is converted into an electric signal as a change in capacitance. In addition, an electric resistance type electrostatic capacity type humidity sensor or a moisture sensitive polymer material on a substrate and a stable metal constitute an electrode, and the resistance change due to moisture at the electrode Convert to electrical signal. As the temperature sensor or roller temperature sensor 36 of the temperature / humidity sensor 41, a thermistor, a band gap temperature sensor, or the like can be used. In addition, as long as it has the same performance, the thing of another principle and another structure may be sufficient.

  The sheet after fixing is humidified by a humidifying device 60 which is a humidifying means. Thereafter, in the case of printing on only one side, the paper is discharged onto the paper discharge tray 50 by the paper discharge roller 82. When performing double-sided printing in which printing is also performed on the back side of the paper, the conveyance path is switched by the flap 71, the paper is guided to the reverse conveyance path 72, the front and back of the paper is reversed, and the double-side conveyance path 73 is conveyed to feed the paper. Then, image formation on the back surface is performed.

  The intermediate transfer belt 2 after transferring the multi-color toner image is supplied to the next image forming process after the remaining toner agent is removed by a cleaning blade or the like. The fixing device 40 of the present embodiment is described as using roller-shaped members such as the heating roller 30 and the pressure roller 37, but is configured using a belt-shaped member instead of the roller-shaped member. You can also.

  The image forming apparatus 110 is controlled by the control unit 46. The control unit 46 acquires temperature and humidity information from the pre-humidification paper temperature / humidity sensor 67 and the humidification conveyance path temperature / humidity sensor 69 in addition to the temperature sensors of the heating roller 30 and the pressure roller 37. Further, the control unit 46 acquires information on the moisture content change characteristics depending on the paper environment, calculates the decrease in the moisture content of the paper after fixing, and the humidifying conditions of the humidifying device 60 necessary for correcting it. Determine the transport speed.

  Next, the humidifier 60 will be described. FIG. 2 is a diagram illustrating a configuration of a humidifier in the image forming apparatus. The humidifier 60 is a steam generation vessel 61 that is a steam generation means, a heater 62, a steam heating device 63 that is a steam heating means, a blower fan 64, a steam supply path 65, a humidification conveyance path 66, an exhaust port 661, and an exhaust means. An exhaust duct 662, a pre-humidified sheet temperature / humidity sensor 67, a humidified conveyance path temperature / humidity sensor 69, and a sheet conveyance roller 68 are provided. Water W is stored in the water vapor generating container 61, and the water W is heated by the heater 62 to generate water vapor. Further, the steam is heated by a steam heater 63 having a plurality of heated passages, and is supplied by a blower fan 64 to a humidification conveyance path 66 through a steam supply path 65 in the direction of arrow c in the figure.

  The sheet 10 is measured for surface temperature and humidity by a pre-humidified sheet temperature / humidity sensor 67 and is conveyed by the sheet conveying roller 68 in the direction of arrow e in the figure at a predetermined speed. The humidification conveyance path 66 humidifies the conveyance of the sheet 10 on the downstream side in the conveyance direction of the fixing device 40 by supplying water vapor toward the sheet. The temperature and humidity in the humidification conveyance path 66 is measured by a humidification conveyance path temperature and humidity sensor 69. The water vapor in the humidification conveyance path 66 is discharged from the exhaust port 661 in the direction of the arrow d in the figure according to the supply of water vapor from the water vapor generation container 61, and returns to the water vapor generation container 61 through the exhaust duct 662. Here, the length of the humidification conveyance path 66 is longer than the length of the paper 10 in the conveyance direction.

  Here, in order to correct the trapezoidal deformation of the sheet, it is only necessary to humidify the sheet 10 while conveying the sheet 10 in the humidification conveyance path 66 with the humidification conveyance path 66 as a constant environment. As in the case of moisture evaporation, a laminar boundary layer is formed during humidification, and the leading edge of the paper is more likely to absorb moisture from the trailing edge, and the leading edge extends from the trailing edge, so that trapezoidal deformation can be corrected. In order to predict the correction amount and perform an accurate correction, it is desirable to make the humidification condition uniform at least from the leading edge to the trailing edge of the sheet.

  The humidifying device 60 of the present embodiment humidifies using water vapor, which is a gas, so that the paper can be uniformly humidified over the entire surface, and the unevenness of the paper due to the minute water content difference generated when humidifying with water droplets or water. There is no problem of paper wrapping around the roller that supplies moisture or smearing. Further, similarly to the laminar boundary layer formed of water vapor evaporated from the paper surface after fixing, a laminar boundary layer that increases in thickness from the front end to the rear end of the paper can be formed. For this reason, the moisture supplied at the leading and trailing edges of the paper during humidification can be made to have the same distribution as the moisture lost by evaporation after fixing, and the trapezoidal deformation can be corrected. Further, since the length of the humidification conveyance path 66 is longer than the length in the conveyance direction of the paper 10, the laminar flow boundary layer on the surface of the paper in the humidification conveyance path 66 becomes an ideal state, and the humidification state of the paper is easy to predict. Thus, the deformation correction accuracy increases. Further, the water vapor in the humidification conveyance path 66 is collected in the water vapor generation container 61 by the exhaust duct 662, so that the diffusion of the water vapor into the image forming apparatus is prevented, and the paper is stuck or deformed due to condensation in the other conveyance path. Can be prevented.

  Next, an image forming system including the image forming apparatus 110 will be described. FIG. 3 is a diagram illustrating a hardware configuration of an image forming system including the image forming apparatus and the server apparatus according to the present embodiment. The image forming system 100 according to the present embodiment is configured by connecting an image forming apparatus 110 and a server apparatus 150 via a network 130. The image forming apparatus 110 includes a CPU (Central Processing Unit) 112 that constitutes the above-described control unit 46 that controls image forming operations such as image formation and paper conveyance, and the operation of the humidifier 60, and a BIOS (Basic Input / Output). ROM (Read Only Memory) 114 for storing the system), RAM (Random Access Memory) 116 for providing the execution space of the CPU 112, and paper shrinkage calculation data for calculating system setting information and a paper shrinkage amount to be described later. And an NV-RAM (Non Volatile-RAM) 118 that stores control value calculation data for adjusting the curl correction device in accordance with the sheet shrinkage amount. Further, the image forming apparatus 110 includes a display device 120 such as an operation panel, an input device 122, a plotter 124 for performing the image forming operation, a scanner 126 for performing an image reading operation, and the image forming device 110 through a network 130. And a network interface card (NIC) 128 connected to the network.

  The image forming apparatus 110 reads a program stored in a removable storage device such as the ROM 114, the NV-RAM 118, or an SD memory card, and expands it in the memory area of the RAM 116 that provides the work area of the CPU 112, which will be described later. Each functional unit and each process are realized.

  The network 130 is connected using a local area network (LAN), a virtual private network (VPN), or a dedicated line using a transaction protocol such as Ethernet (registered trademark) or TCP / IP (Transmission Control Protocol / Internet Protocol). It can be configured as a WAN (Wide Area Network) or the like. The configuration of the network 130 is not particularly limited, and may include the Internet connected via a router, and may be configured as a wired or wireless network, or a mixed network thereof.

  A server device 150 is further connected to the network 130, and the server device 150 evaporates moisture from the paper according to the type and brand of the paper (including various types of products supplied from each supply source). The paper thickness, density, thermal characteristics, paper moisture content change characteristics depending on the environment, etc. are centrally managed, and the paper characteristic value update data is appropriately updated according to the request from the multifunction device. The server function which transmits is provided.

  The server device 150 is configured as a computer device such as a personal computer, a workstation, a blade server, or a multifunction device having a server function, and includes a CPU 152, a ROM 154, a RAM 156, a display device 158 such as a display device, and an input device such as a mouse and a keyboard. 160, NIC 162, and HDD 164. This realizes a server function for providing update data for the above-described paper shrinkage amount calculation data.

  FIG. 4 is a functional block diagram showing the image forming system. This figure shows functional blocks related to the control of the humidifier in the image forming apparatus 110 and the server apparatus 150 of the present embodiment. The image forming apparatus 110 includes a humidifying device control unit 201, an input unit 216, and a paper information DB 208 that is a database. The humidifier control unit 201 includes a moisture content calculating unit 202 that is a moisture content calculating unit, a second moisture content calculating unit 203 that is a second moisture content calculating unit, and a third moisture content that is a third moisture content calculating unit. It comprises a rate calculation unit 204 and a humidifier control value determination unit 205 as setting means. The moisture content calculation unit 202 obtains the temperature and moisture content of the paper before entering the fixing device 40 from the measured value of the temperature / humidity sensor 41 and the paper information acquisition unit 214 as paper information acquisition means. Since the temperature / humidity sensor 41 measures the temperature and humidity in the vicinity of the paper surface, it does not become the temperature and moisture content of the paper itself. Therefore, conversion is performed by applying a function obtained experimentally in advance. The same applies to the paper temperature / humidity sensor 67 before humidification.

  The second moisture content calculation unit 203 obtains the measured value of the roller temperature sensor 36 of the fixing device 40 and the heating temperature and moisture content of the paper after exiting (preferably immediately after) the fixing device 40 from the paper information acquisition unit 214. Based on the result, the humidification device 60 obtains the distribution of the temperature just before the conveyance and the reduced moisture content on the paper. Thus, the reduction rate of the paper temperature and moisture content is obtained. The third moisture content calculation unit 204 is a distribution of the temperature obtained from the second moisture content calculation unit 203 and the distribution of the reduced moisture content on the paper, and the measured value in the humidification conveyance path obtained by the humidification conveyance path temperature / humidity sensor 69. From this, the moisture content distribution absorbed by the paper in the humidification conveyance path 66 is obtained. Thereby, the amount of increase in the moisture content of the sheet is obtained from the temperature and humidity in the humidification conveyance path 66. Then, the humidifier control value determination unit 205 controls the humidification condition so that the moisture content decreased until reaching the humidifier 60 matches the moisture content increased by the humidifier 60. The control of the humidification condition means that the humidifier control value determination unit 205 controls the speeds of the heater 62, the steam heater 63, the blower fan 64, and the paper transport roller 68 of the humidifier 60, for example. Note that the humidifier control value determination unit 205 is an example of a humidification condition, such as designation of temperature, humidity, and paper conveyance speed in the humidification conveyance path 66, designation of temperature and humidity in the humidification conveyance path 66, or humidification conveyance. The paper conveyance speed in the path 66 can be designated.

  Since the paper expands and contracts substantially in proportion to the moisture content, the deformation is eliminated if an equivalent amount of water lost by heating during the fixing process and subsequent evaporation during conveyance is supplied. Therefore, deformation can be suppressed by calculating the reduced moisture content as described above and supplying the corresponding moisture.

  The distribution of the moisture content that decreases until the paper reaches the humidifying device 60 after passing through the fixing device 40 is the same as the measured value of the pre-humidified paper temperature / humidity sensor 67 and the paper information obtaining unit 214 in the third moisture content calculating unit 204. Find using. Since the measured values of the temperature and humidity in the vicinity of the sheet surface are directly used immediately before, an accurate value can be obtained from the second moisture content calculation unit 203. However, it is difficult to change the atmosphere of the humidification conveyance path 66 of the humidifier 60 from the calculation result of the moisture content at that time. For this reason, it is desirable to control the humidifier 60 based on the result of the second moisture content calculator 203 and to correct the humidifier 60 while comparing the deviation from the third moisture content calculator 204.

  The input unit 216 receives designation of the type and brand of paper currently set in the paper feed cassettes 51 and 52 from the operator, and serves as a paper information acquisition unit 214 such as the paper information database 208, the RAM 116, and the NV-RAM 118. In a separate storage area. The paper information acquisition unit 214 holds the characteristic value of the paper. This characteristic value is the thermal properties of the paper set in the paper feed set, the moisture content change characteristic according to the environment, the relationship between the temperature and humidity near the surface and the moisture content, etc. Representative numerical values and functions according to the classification of paper such as fine paper, recycled paper, and coated paper.

  Table 1 shows an example of physical property values described in the paper information. First, the paper brands A to L are classified into plain paper, high-quality paper, recycled paper, and coated paper, and whether or not the paper is a standard paper. When the brand of the paper cannot be identified, the standard paper physical property value is used for calculation of moisture evaporation and absorption. The physical property values are thickness tp, density ρp, thermal conductivity γp, specific heat Cpp, and further a function of the moisture content change characteristic according to the environment. The thermal conductivity and specific heat may be set to 0.06 [W / m · K] and 1300 [J / (kg · K)], respectively, as general physical property values of paper. The moisture content change characteristic according to the environment is a function of the relative humidity in the vicinity of the paper surface with respect to the moisture content, and also changes with the paper temperature. Although different for each paper brand, a representative function may be used for each paper classification type. An example is shown in FIG. The horizontal axis represents paper moisture content (S), and the vertical axis represents relative humidity (Rp). As shown in FIG. 5, the curve changes as the paper temperature (Tp) increases. The function is obtained by experimenting at several temperatures, and the temperature in the meantime may be supplemented by proportional conversion.

  When a new paper type or brand is added, the characteristic value of the paper is input and stored in the integrated paper information database 262 of the server apparatus 150, and information is stored in the image forming apparatus 110 connected via the network 130. I will provide a. In the image forming apparatus 110, if the operator designates the type of paper, a characteristic value corresponding to the type or brand can be obtained from the server apparatus 150. Therefore, even for new paper types, it is possible to quickly obtain the characteristic value, and it is possible to calculate the increase / decrease of the moisture content accurately, and to return the contracted paper to its original shape accurately. Is possible.

  Next, a method for correcting sheet shrinkage will be described. FIG. 6 is a flowchart illustrating a procedure of correction processing for trapezoidal deformation of a sheet in the image forming apparatus. First, in response to an instruction to start printing, the control unit 46 acquires paper information used in each calculation step from the paper information database 208 or the like (step S510). Next, the control unit 46 acquires the temperature T1 and the humidity Rh1 near the sheet by the temperature / humidity sensor 41 (step S511), and uses these values to determine the function Sp1 (Equation 1) and the sheet temperature. The water content S1 and the temperature T1 of the sheet in front of the fixing device 40 are obtained by a function Tp1 (Equation 2) for obtaining (Step S512). Each function is obtained by experiment and stored as the paper information acquisition unit 214.

  Further, the control unit 46 acquires the temperatures of the heating roller 30 and the pressure roller 37 from the roller temperature sensor 36 of the fixing device 40 (step S513), and further obtains the result obtained in step S512 and the paper information acquisition unit 214. The determined amount of water evaporated from the sheet from the fixing device 40 to the humidifier 60 and the sheet temperature immediately before the humidifier 60 are determined (step S514).

  The calculation formula at this time is shown below. If the transport time to the humidification transport path 66 of the humidifier 60 is t2, the distance from the front end of the paper is x, and the moisture content ΔS2 (x) lost during this time is obtained by time integration of the evaporation rate J2 (x). (Formula 3). The evaporation rate J2 (x) is a coefficient α, a sheet conveyance speed V2, a relative humidity pp (x) and a saturated vapor pressure P {T (x)} near the sheet surface, and a relative humidity pe and a saturated vapor pressure in the conveyance path. It is calculated | required by P (Te) (Formula 4). The saturated vapor pressure P is a function of temperature, the temperature T (x) is the temperature at a distance x from the leading edge of the paper, and Te is the temperature in the transport path. pp (x) is determined from the moisture content S (x) and the temperature T (x) at that position from the function Rpn of the paper adsorption / desorption characteristics (Formula 5). Further, the moisture content S (x) is obtained from the difference between the moisture content before the fixing device 40 and the moisture amount ΔS2 (x) evaporated after fixing (Formula 6).

  In order to predict whether moisture absorption by the humidifying device 60 is appropriate, the control unit 46 first obtains the temperature and humidity of the humidifying conveyance path 66 from the humidifying conveyance path temperature and humidity sensor 69 (step S515). The amount of moisture absorption in the humidification conveyance path 66 is calculated by setting V2 in (Equation 4) to the conveyance speed of the humidifying device 60, and the relative humidity pe and saturation vapor pressure P (Te) in the conveyance path to the values in the humidification conveyance path 66. (Step S516). For example, if the pe in the humidification conveyance path 66 is made higher than the relative humidity pp (x) in the vicinity of the sheet surface, or if the temperature Te is increased and the saturated vapor pressure P (Te) is increased, J2 (x) is negative, that is, moisture is increased. Will absorb. If the temperature of the water vapor supplied to the humidification conveyance path 66 is increased by the water vapor heating device 63 of the humidification apparatus 60, when the temperature of the paper is high, the conveyance speed is increased in order to increase productivity, and the humidification conveyance path 66 is passed. Even when the time for performing the process is shortened, it is possible to absorb the necessary and sufficient moisture in the paper.

  If the moisture absorption amount in the humidification conveyance path 66 is ΔS3 (x) and the humidification conditions are appropriately controlled to satisfy (Equation 7), that is, the heater 62 of the humidifier 60, the steam heater 63, and the blower fan 64, if the paper transport roller 68 is appropriately controlled, the paper absorbs moisture equal to the evaporated water and becomes a paper having the same size and shape as before fixing, and high-quality printing is obtained (step S517). The correction ends with the above processing.

  As described above, according to the image forming apparatus 110 according to the present embodiment, it is possible to accurately correct the trapezoidal deformation in which the front end in the paper conveyance direction contracts compared to the rear end side, and high-quality printing is possible. Become. In addition, uniform humidification with water vapor enables high-quality printing without undulations and irregularities.

<Configuration, operation and effect of exemplary embodiment of the present invention>
<First aspect>
In the present embodiment, the fixing device 40 that heats and fixes the unfixed image when the sheet holding the unfixed image passes, and the sheet information that stores information on the thermal characteristics of the sheet and the moisture content change characteristics with respect to the environment. An image forming apparatus 110 including a database 208 and a humidifying device 60 including a humidification conveyance path 66 that humidifies the paper while conveying the paper on the downstream side in the conveyance direction of the fixing device 40. From the sheet information acquisition unit 214 that acquires information on the change characteristic of the rate from the sheet information database 208, the moisture content calculation unit 202 that calculates the temperature and moisture content of the sheet before being conveyed to the fixing device, and the heating temperature in the fixing device A second moisture content calculation unit 203 for obtaining a decrease rate of the temperature and moisture content of the paper conveyed to the humidifying means, and the moisture content of the paper from the temperature and humidity in the humidification conveyance path The humidification conveyance path so that the increase / decrease in the moisture content of the paper obtained by the third moisture content calculating unit 204 for obtaining the increase amount, the second moisture content calculating unit, and the third moisture content calculating unit coincide with each other. 66 is an image forming apparatus including a humidifier control value determination unit 205 that designates a humidification condition in 66.
According to this aspect, since the deformation of the paper changes in proportion to the amount of change in the moisture content, the paper contracted by the moisture content that decreases after fixing can be made to absorb moisture so as to have the moisture content before fixing. . Thus, the humidifying means sets the humidification condition of the humidification conveyance path so that the increase and decrease in the moisture content of the sheet by the second moisture content calculation unit 203 and the third moisture content calculation unit 204 coincide, and the deformation of the sheet Can be corrected or reduced. When the moisture in the transport path is transported and absorbed, a laminar flow is formed on the surface of the paper, and the moisture absorption speed at the trailing edge is slower than the moisture absorption speed at the leading edge of the paper. In order to increase more, the trapezoidal deformation after fixing can be corrected. For this reason, it is possible to realize high-quality printing by preventing image misalignment between the front and back sides during double-sided printing.
Note that the paper is not limited to a recording medium made of plant fiber, but includes a general recording medium having hygroscopicity.

<Second form>
In the image forming apparatus according to the present embodiment, the humidification condition is any one of temperature, humidity, paper conveyance speed in the humidification conveyance path, or a combination thereof.
According to this aspect, as a humidification condition, it is possible to take all possible measures while taking into consideration the temperature, humidity, or the sheet conveyance speed in the humidification conveyance path.
<Third form>
In the image forming apparatus according to this embodiment, the humidification conveyance path 66 is characterized by being at least longer than the length in the conveyance direction of the paper to be conveyed.
According to this aspect, the laminar boundary layer formed in the humidification conveyance path 66 is in an ideal state, and correction by humidification can be accurately performed.

<4th form>
In the image forming apparatus according to the present embodiment, the humidifier 60 includes a steam generation container 61, a steam heater 63 that heats the generated steam, a steam supply path 65 that guides the steam to the humidification transport path 66, and the humidification transport path 66. And an exhaust duct 662 for guiding the water vapor therein to the water vapor generating container 61.
According to this aspect, moisture can be uniformly supplied to the paper by humidifying with water vapor. In addition, the temperature of water vapor can be increased by the heating means, and the control range of temperature and humidity can be expanded. As a result, it is possible to sufficiently absorb moisture and suppress deformation even by rapidly shrinking paper by providing a high-temperature and high-humidity environment.

<5th form>
In the image forming apparatus according to this embodiment, a temperature / humidity sensor 41 that measures the temperature and humidity near the surface of the sheet is disposed between the fixing device 40 and the humidification conveyance path 66.
According to this aspect, it is possible to know the accurate temperature and moisture content of the paper before the paper reaches the humidifying means, and it is possible to correctly humidify the paper and minimize the difference between the front and back of the image.

<Sixth form>
The image forming system 100 according to the present embodiment includes any one of the image forming apparatus 110 and the sheet thickness and density necessary for calculation of evaporation and absorption of moisture from the sheet according to the type and brand of the sheet. A server device 150 that holds the characteristic value of the paper including the thermal characteristic and the moisture content change characteristic of the paper due to environmental changes, and transmits update data of the characteristic value of the paper in response to a request from the image forming apparatus. It is characterized by that.
According to this aspect, new sheet characteristics that are not stored in the sheet information database 208 of the image forming apparatus 110 can be acquired from the server apparatus 150 from the server apparatus 150. As a result, it is possible to perform optimum processing corresponding to many sheets.

40: fixing device, 41: temperature / humidity sensor, 60: humidifier (humidifier), 61: steam generator (steam generator), 62: heater, 63: steam heater (steam heater), 64: blower fan 65: Water vapor supply path, 66: Humidification conveyance path, 661: Exhaust port, 662: Exhaust duct, 67: Paper temperature / humidity sensor before humidification, 68: Paper conveyance roller, 69: Humidification conveyance path temperature / humidity sensor, 100: Image Forming system, 110: image forming apparatus, 150: server apparatus, 202: moisture content calculating section (moisture content calculating means), 203: second moisture content calculating section (second moisture content calculating means), 204: third Moisture content calculation unit (third moisture content calculation unit), 205: humidifier control value determination unit, 214: paper information acquisition unit (paper information acquisition unit), 662: exhaust duct (exhaust unit)

Japanese Patent No. 3515236 JP 2000-118849 A JP 2007-279551 A

Claims (6)

A fixing device that heats and fixes the unfixed image when a sheet holding the unfixed image passes;
A database for storing information on thermal characteristics of the paper and change characteristics of moisture content with respect to the environment;
A humidifying unit comprising a humidifying conveyance path for humidifying the sheet while conveying the sheet downstream in the conveying direction of the fixing device;
An image forming apparatus having
Paper information acquisition means for acquiring information on the thermal characteristics of the paper and the change characteristics of moisture content with respect to the environment from the database;
Moisture content calculating means for obtaining the temperature and moisture content of the paper before being conveyed to the fixing device;
Second moisture content calculating means for obtaining a reduction rate of the temperature and moisture content of the paper conveyed to the humidifying means from the heating temperature in the fixing device;
A third moisture content calculating means for obtaining an increase in the moisture content of the paper from the temperature and humidity in the humidification conveyance path;
Setting means for specifying the humidification condition in the humidification conveyance path so that the increase / decrease in the moisture content of the paper determined by the second moisture content calculation means and the third moisture content calculation means are the same. When,
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the humidification condition specifies any one of temperature, humidity, a sheet conveyance speed in the humidification conveyance path, or a combination thereof.   The image forming apparatus according to claim 1, wherein the humidification conveyance path is longer than at least a conveyance direction length of the sheet to be conveyed.   The humidifying means includes a steam generating means, a steam heating means for heating the generated steam, a steam supply path for guiding the steam to the humidifying conveyance path, and an exhaust means for guiding the steam in the humidifying conveyance path to the steam generating means. The image forming apparatus according to claim 1, further comprising:   5. The image according to claim 1, wherein a temperature / humidity sensor that measures a temperature and humidity in the vicinity of the surface of the sheet is disposed between the fixing device and the humidifying unit. Forming equipment.   The image forming apparatus according to any one of claims 1 to 5, and the thickness, density, and heat of the paper necessary for calculation of evaporation and absorption of moisture from the paper according to the type and brand of the paper. A server device that holds characteristic values of the paper including characteristics and moisture content change characteristics of the paper due to environmental changes, and transmits update data of the characteristic values of the paper in response to a request from the image forming apparatus. An image forming system comprising:

Images