JP4899480B2 - Fixing device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and a fixing device that heats and fixes an unfixed toner image formed on a recording material to create an image and an image forming apparatus using the same. .

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine adopting an electrophotographic method, a fixing device capable of heat-welding toner is generally used to fix an electrostatically formed toner image on a recording material such as paper. Are known. Various fixing devices have been proposed. From the viewpoints of thermal efficiency, safety, downsizing, etc., the fixing device includes a heatable heating fixing member and a pressure member that presses the heating fixing member. A sheet in which a sheet carrying a toner image is inserted into the pressure nip portion and the toner image is fixedly fixed to the sheet is widely used.

In such a fixing device, a good image cannot be obtained if the temperature of the heat fixing member is too high or too low. For example, a temperature sensor that appropriately detects the surface temperature of the heat fixing member is used as the heat fixing member. The surface temperature of the heat-fixing member is controlled by a control device based on this detection information, and the surface temperature of the heat-fixing member is kept constant. In addition to this, there is also known one in which the surface temperature of the heating and fixing member is kept constant by using detection information from an environmental sensor that is disposed in the image forming apparatus and detects temperature and humidity. ing.
However, only by temperature control by appropriately taking in temperature detection information of the temperature sensor and environment information by the environment sensor as described above, for example, when a job is started immediately after a sheet is newly set in a sheet feeding cassette, the apparatus Since there is a temperature difference between the ambient temperature inside and the surface of the paper, the surface temperature of the heat-fixing member changes greatly when the paper is inserted, causing a problem that the fixing property of the toner image varies.
Therefore, Patent Document 1 proposes a technique in which the surface temperature of the heating and fixing member is detected before and after the passage of the paper, and the temperature of the heating and fixing member is controlled based on the detected information. .
According to such a technique, since the temperature control of the surface temperature of the heat fixing member is performed for each sheet, a stable toner fixing property can be obtained.

JP-A-7-234606 (Example, FIG. 3)

  However, although the prior art described in Patent Document 1 can obtain a good toner fixing property, when a paper having a low basis weight such as a thin paper is used, an excessive amount of heat is applied to the paper. Further, there is a problem that the paper curls on one side due to evaporation of moisture on the paper surface. Even if such a curl has a small curvature on a single sheet, the curvature increases as the sheets are stacked at the time of printing, and becomes prominent.

  The present invention has been made to solve such a technical problem, and is caused by excessive heating of a recording material when fixing a recording material having a low basis weight such as plain paper or thin paper. The present invention provides a fixing device capable of effectively preventing curling and an image forming apparatus using the same.

That is, in the present invention, as shown in FIG. 1, heat fixing is performed by heating and fixing an unfixed image formed on a recording material 5 whose surface is heated by a heat source to come into contact with the recording material 5 and whose conveyance speed can be changed. A member 1, a temperature sensor 2 that detects a surface temperature of the heat fixing member 1, and a control device 3 that controls the heat fixing member 1 to a predetermined control temperature based on detection information of the temperature sensor 2. fixing device a 4, the controller 3 includes a determining element which determines to execute the control variable temperature adjustment process with respect to heat fixing member 1 at a predetermined prescribed number or more of the imaging process, the When the determination element determines that the variable control temperature adjustment process is to be performed on the heating and fixing member 1, the recording material 5 enters the fixing device 4 according to the conveyance speed of the recording material 5. A predetermined time has elapsed Variably setting the temperature drop amount determined time until to be shorter than for those who are slow faster per transport speed of the recording material 5, until the amount of temperature drop determination time based on the temperature information from the temperature sensor 2 A determination element 3a for determining a temperature drop amount of the heat fixing member 1, a normal control temperature of the heat fixing member 1 within a temperature range capable of fixing, and a correction control temperature lower than the normal control temperature, and the determination element 3a It is determined whether or not the temperature drop amount determined in step 1 is lower than a predetermined threshold reference temperature. If the temperature drop amount is equal to or higher than the threshold reference temperature, the normal control temperature is selected. is characterized in further comprising a control temperature variables 3b that, the.

In such technical means, the image forming method may be appropriately selected as long as the toner image is visualized, and it does not matter whether it is an electrophotographic method or an electrostatic recording method.
The fixing device 4 is only required to have a pair of heat fixing members 1 for heat fixing and nip-conveying the recording material 5, and the mode is a combination of a roll and a combination of a belt and a roll. There may be a belt pair configuration.
Further, as a heating method of the heat fixing member 1, there is a mode in which a heat source is provided inside and heating is performed by itself, or a heat source is provided in the inside and heating is performed by itself and the heat fixing member 1 is assisted by an external heating member In addition to the mode of heating, a mode in which the heat fixing member 1 is heated by an external heating member without having a heat source inside may be selected as appropriate.
Furthermore, the temperature sensor 2 may be appropriately selected as long as it can detect the surface temperature of the heat fixing member 1.

The control device 3 also includes a determination element 3a that can measure the temperature drop amount of the heat fixing member 1 after a lapse of a predetermined time after the recording material 5 enters the fixing device 4, and the temperature drop amount information is the threshold reference temperature. The control temperature variable element 3b that adjusts to the normal control temperature if it is above and the correction control temperature otherwise is provided. That is, in addition to the normal mode in which the control device 3 performs normal temperature control, at least a temperature variable mode in which the control temperature is variably adjusted is provided.
In this case, the determination element 3 a presets a predetermined time after the recording material 5 enters the heat fixing member 1 as a temperature drop amount determination time, and heats at least when the recording material 5 enters the heat fixing member 1. The temperature drop amount is determined by taking the temperature of the fixing member 1 and the temperature of the heat fixing member 1 after a predetermined time from the temperature sensor 2 and measuring the difference therebetween.

In the present invention, the determination element 3a adopts a mode in which the temperature drop amount determination time is variably set.
Thus, by setting the temperature drop amount determination time to be variable, for example, even when the process speed is different, the temperature drop amount can be accurately determined correspondingly.

Furthermore, it is preferable that the control temperature variable element 3b variably sets at least one of the threshold reference temperature, the normal control temperature, and the correction control temperature.
“At least one of the threshold reference temperature, the normal control temperature, and the correction control temperature” may be one arbitrarily selected from the three, two arbitrarily selected, or all of them. That is the purpose.
In this case, by appropriately setting the threshold reference temperature, it is possible to perform appropriate separation adjustment according to the use environment conditions.
Further, by variably setting the normal control temperature, it is possible to set an appropriate normal control temperature according to the use environment conditions.
Furthermore, by variably setting the correction control temperature, it is possible to set the correction control temperature according to the use environment condition, and it is possible to keep the heat fixing member 1 at an appropriate surface temperature.
The use environment conditions referred to here include a wide range of image types, image formation conditions such as black and white / color, double-sided / single-sided, paper type, environmental conditions, and the like.
As described above, by appropriately variably setting at least one of the threshold reference temperature, the normal control temperature, and the correction control temperature, the temperature of the heat fixing member 1 can be adjusted to an appropriate temperature.

Further, in the present invention, the control device 3 adopts a mode in which the control temperature variable adjustment processing of the heat fixing member 1 is performed at the time of image forming processing of a predetermined number or more.
That is, when the number of image forming processes is small, when the discharged recording material 5 is placed, for example, on a flat surface discharge tray, the curl can be corrected to some extent by its own weight and heat dissipation. Even if the curvature is small, poor storage may occur when a large number of sheets are stacked in the storage unit. For this reason, it is effective to perform the control temperature variable adjustment process of the heat fixing member 1 during the image forming process of a predetermined number or more. In this case, the predetermined number of sheets may be appropriately selected according to the conditions on which curling is likely to occur due to the type of paper and environmental conditions.

Furthermore, it is preferable that the determination element 3a variably sets the temperature drop amount determination time to an individual time according to the type of the recording material 5.
According to this aspect, if the type of the recording material 5 is different, for example, the conveyance speed is different, and the temperature drop amount determination time can be variably set corresponding to the conveyance speed. In this case, for example, if the temperature drop amount judgment time is set to be the same for plain paper and thick paper, the number of recording materials 5 discharged at the initial stage is larger in plain paper with a high process speed than in thick paper. Although curling is a concern during stacking, so-called stacking, in this embodiment, it is possible to set a short time for determining the temperature drop of plain paper.
Even if the process speed cannot be changed by a monochrome image forming apparatus, for example, with plain paper, fixing is performed by narrowing the span between paper compared to thick paper, and productivity (discharge amount) However, in this embodiment, it is possible to set a short time for determining the temperature drop amount of plain paper.
Therefore, according to this aspect, it is possible to set the temperature drop amount determination time to a time that allows several recording materials 5 to travel according to the type of the recording material 5.

In addition, it is preferable that the determination element 3a variably sets the temperature drop amount determination time to an individual time according to the image forming conditions of the multi-color image forming mode or the single color image forming mode.
In this case, the monochromatic image forming mode is typically a black and white image forming mode, but is not limited thereto, and other colors may be used. The multi-color image forming mode is an image forming mode in which toners of two or more colors are used, and a full color image forming mode is a typical example.
In general, in the single-color image forming mode, the process speed is increased as compared with the multi-color image forming mode, and the stack amount increases accordingly. Therefore, it is preferable to shorten the temperature drop amount determination time. However, in the single color imaging mode and the multiple color imaging mode, the same temperature drop amount determination time may be set as long as the type of the recording material 5 and the process speed are the same.

Further, it is preferable that the control temperature variable element 3b variably sets at least one of the threshold reference temperature, the normal control temperature, and the correction control temperature according to the type of the recording material 5.
In this case, the amount of heat absorption of the recording material 5 is proportional to the basis weight, so that it corresponds to the type of the recording material 5. This is because the temperature of the recording material 5 tends to increase. According to this aspect, for example, a thin paper with a low basis weight has a small temperature drop amount of the surface temperature of the heat fixing member 1, so that the threshold reference temperature can be set low, and the correction control temperature is set low because the minimum fixing temperature is low. it can. Furthermore, for thin paper, the normal control temperature can also be set low.
As described above, by adjusting at least one of the threshold reference temperature, the normal control temperature, and the correction control temperature in accordance with the type of the recording material 5, the control temperature is adjusted to an appropriate control temperature corresponding to the recording material 5. be able to.

Furthermore, it is preferable that the control temperature variable element 3b variably sets at least one of the threshold reference temperature, the normal control temperature, and the correction control temperature according to the image forming conditions.
In this case, the image forming conditions include a multi-color / single-color image forming mode, a single-sided / double-sided image forming mode, and an image density.
According to this aspect, by setting each variable setting condition to a temperature corresponding to the image forming condition, it is possible to adjust to an appropriate control temperature corresponding to the image forming condition.

In addition, the control device 3 variably sets at least one of the variable setting conditions of the determination element 3a and the control temperature variable element 3b under the condition that the change information of the recording material 5 or the image forming condition is received during the fixing process. Is preferred.
According to such an aspect, even if a paper type change or an image forming condition change is performed during the fixing process, control corresponding to the change is performed, so that an appropriate temperature can be maintained.

Further, it is preferable that the control device 3 variably sets at least one of the variable setting conditions of the determination element 3a and the control temperature variable element 3b based on the environmental information of the environmental sensor arranged around the fixing device 4.
According to this aspect, by setting each variable setting condition to a temperature according to the environmental condition, stable temperature control can be performed without being affected by the environmental condition.

  The present invention is not limited to the fixing device 4 as described above, but also targets an image forming apparatus using the same.

Next, the operation of the technical means described above will be described with reference to FIGS.
Assuming that the recording material 5 is not yet in the fixing device 4, the surface temperature of the heat fixing member 1 at this time is normally maintained at the control temperature.
When the recording material 5 enters the fixing device 4, the recording material 5 and the unfixed toner image on the recording material 5 take away the heat of the heat fixing member 1, and the surface temperature of the heat fixing member 1 decreases. At this time, the temperature sensor 2 measures at least the temperature at the time when the heat fixing member 1 of the recording material 5 enters and the temperature after the temperature drop amount determination time has passed, and sends this detection information to the control device 3.
Further, the control device 3 measures the temperature drop amount of the heat fixing member 1 within the temperature drop amount determination time based on the detection information from the temperature sensor 2.
Further, the control device 3 determines whether or not the temperature drop amount is lower than a predetermined threshold reference temperature. If the temperature drop amount is equal to or higher than the threshold reference temperature, the control device 3 sets the normal control temperature; Carry out the adjustment.
That is, the control device 3 adjusts the control temperature to the corrected control temperature when the temperature drop amount is smaller than the threshold reference temperature as indicated by the solid line in the figure. On the other hand, as shown by the dotted line in the figure, the control device 3 adjusts so as to maintain the same normal control temperature as that before the recording material 5 enters when the temperature drop amount is equal to or higher than the threshold reference temperature.

According to the fixing device of the present invention, paying attention to the temperature drop amount of the heat fixing member, the use environment condition of the recording material is determined based on whether or not the temperature drop amount reaches the threshold reference temperature, and Since the control temperature is adjusted, a fixing device that can effectively prevent curling caused by excessive heating when fixing recording materials with low basis weight such as plain paper or thin paper is provided. can do.
In particular, in the present invention, even when the curvature of a curl per sheet is small, storage failure may occur due to the stacking of a large number of sheets in the storage unit. It is effective to perform a variable control temperature adjustment process for the heat fixing member.
Furthermore, by variably setting the temperature drop amount determination time according to the conveyance speed of the recording material, for example, even when the process speed is different, the temperature drop amount can be accurately determined correspondingly.
Further, according to the image forming apparatus provided with such a fixing device, it is possible to effectively prevent curling that occurs remarkably with the stacking of recording materials when printing a plurality of sheets.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 3 shows Embodiment 1 of an image forming apparatus to which the present invention is applied. In FIG. 1, the image forming apparatus according to the present embodiment includes a printer device 10 for creating an image, an image reading unit 11 for reading a document is disposed above the printer device 10, and an image reading unit is disposed above the image reading unit 11. A document feeder 12 for feeding a document to the unit 11 is provided.
In addition, the printer apparatus 10 includes multi-stage sheet trays 51 to 53 that supply sheets such as paper at the bottom of the printer housing 13, and a color image is formed on the sheets from the sheet trays 51 to 53 above the printer apparatus 10. A possible image forming engine 20 is provided, and a sheet conveying path 60 serving as a sheet conveying path from the sheet trays 51 to 53 is provided at a facing portion of the image forming engine 20 and on the downstream side in the sheet conveying direction of the image forming engine 20. Is provided with a fixing device 40 for fixing an unfixed toner image on the sheet.

  Further, the image forming engine 20 adopts, for example, an electrophotographic system, and is an image forming unit of four colors of yellow (Y color), magenta (M color), cyan (C color) and black (K color). 21 (21a to 21d) are arranged in parallel on the intermediate transfer belt 30 and have a so-called tandem configuration, and toner images of respective colors formed by the image forming unit 21 (21a to 21d) are transferred to the intermediate transfer belt 30. The toner images are sequentially transferred onto the sheet and multiplexed, and the multiplexed toner images are collectively transferred onto the sheet conveyed from the sheet trays 51 to 53 by the secondary transfer device 35 and guided to the fixing device 40. It is. The color arrangement of the four-color image forming units 21 is not limited to this order, and may be in other orders.

  The image forming unit 21 (21a to 21d) in the present embodiment includes a photosensitive drum 22 that forms and supports each color component toner image, a charging device 23 such as a charging roll that charges the photosensitive drum 22, and a charged photosensitive member. A laser exposure device 24 that forms a latent image on the photoconductive drum 22, a developing device 25 that visualizes the electrostatic latent image on the photoconductive drum 22, and a toner image on the photoconductive drum 22 are primarily transferred onto the intermediate transfer belt 30. For example, a primary transfer device 26 including a primary transfer roll and a cleaner 27 for cleaning residual toner remaining on the photosensitive drum 22 are configured. In the present embodiment, the laser exposure unit 24 exposes the entire four-color image forming unit 21 with one laser exposure unit 24.

  Further, the intermediate transfer belt 30 is stretched around a plurality of stretching rolls 31 to 33, and is circulated and conveyed using, for example, the stretching roll 31 as a driving roll. For example, a secondary transfer device 35 including a secondary transfer roll. However, the tension roll 33 is disposed opposite to the backup roll. Further, a belt cleaner 36 for removing residual toner on the intermediate transfer belt 30 is disposed at a position facing the tension roll 32 of the intermediate transfer belt 30.

Further, the sheet conveyance path 60 is as follows. A vertical conveyance path 61 extending substantially vertically upward from each sheet tray 51 to 53, a main conveyance path 62 extending substantially horizontally on the downstream side of the vertical conveyance path 61, and approximately Y in the vicinity of the most downstream of the main conveyance path 62. A retreat conveyance path 63 extending downward in a letter shape and a reversal conveyance path 64 extending substantially horizontally from the retreat conveyance path 63 and leading to the vertical conveyance path 61 are configured.
In addition, a pickup roll 65 for feeding sheets at a predetermined timing, a nudger roll 66 and a retard roll 67 for sheet feeding are provided in the vicinity of the sheet trays 51 to 53, and only the uppermost sheet can be sent. ing.
In the main conveyance path 62, a registration roll 54 that regulates the positioning of the sheet, a secondary transfer device 35 that batch-transfers the toner images multiplexed on the intermediate transfer belt 30, and a sheet on which the toner images are batch-transferred. A conveying belt 55 that conveys the toner, a fixing device 40 that fixes the toner image on the sheet, a discharge roll 56 that discharges the sheet to a storage tray 57 that is provided on the side of the printer housing 13 and stores the sheet are provided.
In these conveyance paths 61 to 64, conveyance members such as a conveyance roll and a conveyance guide for ensuring the conveyance of the sheet are appropriately disposed.

Further, the fixing device 40 of the present embodiment is as shown in FIG. In the figure, a fixing device 40 includes a fixing roll 41 as a fixing member rotatably disposed, and an endless belt-like fixing belt 43 that is in pressure contact with the fixing roll 41 and is driven to rotate together with the fixing roll 41. I have.
In the present embodiment, the fixing roll 41 includes a cylindrical core 41a made of metal such as aluminum having excellent mechanical strength and good thermal conductivity, and elastic such as silicone rubber formed on the surface of the core 41a. A layer 41b and a release layer 41c coated on the surface of the elastic layer 41b and provided to prevent the offset of the unfixed toner image T on the sheet S, and a halogen lamp as a heating source therein. A heater 42 such as is arranged.

In this embodiment, the material of the core 41a is not particularly limited as long as it has mechanical strength and good thermal conductivity. For example, a metal or alloy such as stainless steel, steel, or brass is used.
Further, the elastic layer 41b is not limited to silicone rubber, and may be, for example, fluorine rubber as long as it has heat resistance. The molding method for the surface of the core 41a is not particularly limited, and an injection molding method, a coating method, etc. Is adopted.
Further, the release layer 41c may be any layer having heat resistance and appropriate release properties for the toner. For example, fluorine rubber or fluorine resin is used.
Furthermore, the heater 42 in the fixing roll 41 is not particularly limited as long as it has a shape and structure that can be accommodated in the core 41a, and may be appropriately selected.

  Further, a temperature sensor 49 for measuring the surface temperature of the fixing roll 41 is disposed around the fixing roll 41, and the temperature of the heater 42 is controlled based on the detection information of the temperature sensor 49, whereby the temperature of the fixing roll 41. The surface temperature is maintained at a predetermined temperature. Further, the temperature sensor 49 is not particularly limited as long as it can measure the surface temperature of the fixing roll 41. For example, a temperature sensitive element such as a thermistor or a posistor may be appropriately selected.

On the other hand, the fixing belt 43 may have a single-layer structure, but in the present embodiment, a belt having a laminated structure in which a release layer is provided on the surface of the substrate is used.
Further, as a base material of the fixing belt 43, if it has heat resistance, for example, a resin base material such as thermosetting polyimide, thermoplastic polyimide, polyamide, polyamideimide, or a metal base material such as stainless steel, nickel, copper, or the like. Used. Further, the release layer is preferably one having good releasability of toner adhering to the surface, and for example, a fluorine resin is used as the material.

Further, the fixing belt 43 does not have a tension roll or the like, and a pressure pad 46 formed of an elastic material such as heat-resistant silicone rubber is disposed inside the fixing belt 43 facing the fixing roll 41. It is intended to support. Then, by pressing the fixing belt 43 toward the fixing roll 41 with the pressure pad 46, a contact nip area is formed between them, and the sheet S on which the unfixed toner image T is transferred to the contact nip area. The unfixed toner image T is heated and pressure-fixed by passing it through.
Further, the pressure pad 46 is disposed so as to be fitted to a holding member 48 having a substantially concave cross section, while maintaining a small frictional resistance with the fixing belt 43 on the surface on the fixing belt 43 side. In order to make the rotation of the 43 smoother, a low friction sheet 46a made of, for example, a fluorine resin sheet is provided.

Furthermore, a peeling nip member 47 that forms a peeling nip region where the sheet S can be peeled is accommodated downstream of the pressure pad 46 of the holding member 48. The peeling nip member 47 is made of a highly rigid material made of a metal or an alloy such as aluminum, stainless steel, steel, copper, or brass.
The holding member 48 is supported by a support member 44 provided on the lower side thereof, and a belt traveling guide 45 having a substantially arcuate cross section is attached to the lower side of the support member 44. A spring (not shown) is attached to the holding member 48, so that the fixing belt 43 is biased toward the fixing roll 41 through the pressure pad 46 fitted to the holding member 48. It has become.

FIG. 5 shows a control system according to the present embodiment. As shown in the figure, the control device 80 is connected to the user input 150, the temperature sensor 49, the image density information 200, the environment sensor 300, and other information so as to be input. Details of various devices will be described later.
On the other hand, the control device 80 is connected so that a control signal can be sent to the fixing device 40.
Further, the control device 80 is composed of a microcomputer system, and has a CPU, ROM, RAM, etc. as a control unit, and processing programs are stored in the ROM in advance. The CPU executes each program, and each input Based on the information, the temperature drop amount determination time, the threshold reference temperature, the correction control temperature, and the normal control temperature are variably set.

In the present embodiment, examples of the user input 150 include a selection button shown on the screen of the user interface 100 as shown in FIGS.
FIG. 6A shows a normal screen of the user interface 100. As shown in the figure, the basic screen of the user interface 100 includes “basic copy (101)”, “image quality adjustment (102)”, “reading method (103)”, “output format (104)”, “job editing”. Each setting of (105) "is displayed so as to be changeable, and now a screen of" Basic copy (101) "is shown.
In this screen, buttons for the settings of “magnification selection (111)”, “paper selection (112)”, and “color mode (113)” are displayed, and “magnification selection (111)” is now “100%”. In (121), “paper selection (112)” is selected as “A4 (122)”, and “color mode (113)” is selected as “monochrome (123)”. Further, for example, “Set (107)” is selected as 50, and the number of image forming processes is set as 50.
The selected information is sent to the control device 80 as user input information.

Further, when “tray 5” (not shown) is selected from “other tray (124)” of “paper selection (112)”, the screen is switched to the screen of FIG. 6B, and “paper size (131)” and “paper type” are displayed. (132) "is displayed as a button so that selection is possible.
On this screen, “automatic size detection (141)”, “standard size (142)”, and “non-standard size (143)” are displayed as buttons for setting “paper size (131)”. Then, a predetermined paper size is selected.
Similarly, the setting of “paper type (132)” includes “plain paper (145)”, “recycled paper (146)”, “thick paper 1 (147)”, “thick paper 2 (148)”, “OHP”. “Film (149)” is displayed as a button, and when a button to be selected is pressed, a predetermined paper type is set and the input paper type information is sent to the control device 80.

Next, an image forming process of the image forming apparatus according to the present embodiment will be described. When a start button (not shown) is pressed, a toner image is formed on the surface of the photosensitive drum 22 by, for example, a K-color image forming unit 21d by a known electrophotographic process. 26, the toner image is transferred onto the intermediate transfer belt 30 that moves at substantially the same speed as the photosensitive drum 22 (see FIG. 3). When a full-color image is formed, a toner image may be formed on the surface of the photosensitive drum 22 for each color.
Further, when the sheet conveying system feeds one sheet from the sheet tray 51 and conveys the sheet to the registration roll 54 of the main conveyance path 62 via the retard roll 67 of the vertical conveyance path 61, the sheet conveyance system temporarily stops the registration roll 54. Thereafter, the sheet is conveyed to the secondary transfer device 35 in synchronization with the image writing timing on the sheet, and the monochrome toner image on the intermediate transfer belt 30 is transferred onto the sheet. Then, the sheet passes through the conveyance belt 55 and is conveyed to the fixing device 40. After the unfixed toner image on the sheet surface is fixed by the fixing device 40, the sheet is discharged to the storage tray 57.
In the double-sided image forming mode, the fixed sheet is conveyed to the retreat conveyance path 63, reversed by the reverse conveyance path 64, and then conveyed again to the registration roll 54 of the main conveyance path 62. Then, the sheet is temporarily stopped by the resist roll 54, and then the toner image on the intermediate transfer belt 30 is transferred to the other surface of the sheet by the secondary transfer device 35, and the toner is fixed by the fixing device 40. Is then discharged to the storage tray 57.

In such an image forming process, a temperature control process of the fixing device 40 will be described with reference to FIG.
In the present embodiment, the control device 80 receives, as information from the user input 150, 50 sheets for the number of image forming processes, plain paper for the paper type, monochrome image forming mode for the image forming conditions, and single-sided image formation for the image forming conditions. A mode is input (see FIG. 5). Further, when the number of image forming processes is 50 or more, for example, the control device 80 performs a variable control temperature adjustment process for the fixing roll 41, and operates based on the input information. . Note that the prescribed value of the number of image forming processes on which the control device 80 operates is 50 as an example, but is not limited to this, and may be appropriately selected according to the paper type, environmental conditions, and the like.

If it is assumed that the sheet has not yet entered the fixing device 40, the surface temperature of the fixing roll 41 at this time is kept at the normal control temperature (see FIG. 8).
Here, the control device 80 presets a predetermined time from when the sheet enters the fixing device 40 as a temperature drop amount determination time.
When the sheet enters the fixing roll 41, the sheet and the toner image on the sheet take heat of the fixing roll 41, and the surface temperature of the fixing roll 41 decreases. At this time, the temperature sensor 49 measures at least the temperature when the sheet enters the fixing roll 41 and the temperature after a predetermined time has passed, and sends this detection information to the control device 80.
Further, the control device 80 measures the temperature drop amount on the surface of the fixing roll 41 within the temperature drop amount determination time based on the detection information from the temperature sensor 49.

Further, the control device 80 determines whether or not the temperature drop amount is less than a predetermined threshold reference temperature. If the temperature drop amount is equal to or higher than the threshold reference temperature, the control device 80 sets the normal control temperature; Carry out the adjustment.
That is, as shown by the solid line in FIG. 8, the control device 80 adjusts the control temperature to the corrected control temperature when the temperature drop amount is smaller than the threshold reference temperature. On the other hand, as indicated by a dotted line in the figure, when the temperature drop amount is equal to or higher than the threshold reference temperature, the control device 80 adjusts so as to maintain the normal control temperature.
In this embodiment, the control device 80 measures the amount of temperature drop and controls whether or not the control temperature can be changed compared to the threshold reference temperature. The temperature obtained by subtracting the threshold reference temperature from the normal control temperature is set as the switching determination temperature, and the control temperature is determined and adjusted depending on whether the temperature after the temperature drop amount determination time has passed is equal to or higher than the switching determination temperature. It may be. That is, as shown by the solid line in the figure, the control temperature is adjusted to the correction control temperature when the surface temperature of the fixing roll 41 after the determination time has passed is higher than the switching determination temperature, while, as shown by the dotted line in the figure, It is also possible to adjust so that the normal control temperature is maintained when the surface temperature of the fixing roll 41 is equal to or lower than the switching determination temperature.

In such an image forming process, as the control temperature variable adjustment process, the temperature drop amount judgment time, depending on the paper type, image density, environmental conditions, black / white / color image forming conditions, double-sided / single-sided image forming conditions, If at least one of the variable setting conditions of the threshold reference temperature, the correction control temperature, and the normal control temperature is made variable, the surface temperature of the fixing roll 41 can be made more optimal (see FIG. 9).
That is, if the number of image forming processes is equal to or greater than the specified number, the temperature drop amount variably set according to the paper type, image density, environmental conditions, black / white / color image forming conditions, double-sided / single-sided image forming conditions, etc. Based on the temperature drop amount within the determination time, the adjustment control temperature is variably set or the normal control temperature is variably set. More specifically, the control device 80 determines whether or not the temperature drop amount is less than a threshold reference temperature that is variably set. When the temperature drop amount is equal to or higher than the threshold reference temperature, the control device 80 is set to the normal control temperature. It is possible to adjust the correction control temperature. In addition, although the case where all of the variable setting conditions of the temperature drop determination time, the threshold reference temperature, the correction control temperature, and the normal control temperature are variably set has been described here, the present invention is not limited to this, and the use environment condition It may be variably set appropriately according to each.
Note that details of the mode in which the variable setting condition is made variable according to each condition will be described in an embodiment described later.

Further, if the paper type is changed by changing the tray or the image forming condition is changed while the control temperature is variably set and the fixing process is being performed in this way, the control device 80 causes the paper to be changed. At least one of the temperature drop amount determination time, the threshold reference temperature, the correction control temperature, and the normal control temperature corresponding to the seed can be set again, and can be adjusted again to an appropriate control temperature.
According to the present embodiment, it is possible to provide a fixing device that can effectively prevent curling that occurs due to excessive heating when fixing a low basis weight paper such as plain paper or thin paper. it can.
Furthermore, if the variable setting condition of the control device 80 is variably set according to the individual use environment conditions for each sheet, the temperature of the fixing roll 41 can be controlled more accurately.

Example 1
In Example 1, the same image forming apparatus as that of the first embodiment is used, and the temperature drop determination time is made variable according to the paper type, and the temperature of the fixing roll 41 is controlled (FIG. 10). reference).
Main settings and conditions in the present embodiment are as follows.
Paper type: plain paper, cardboard, temperature drop amount judgment time: plain paper 4 seconds, cardboard 6 seconds In other words, “paper type (132)” of the user interface 100 is “plain paper (145)” or “ If “thick paper 1 (147)” is selected, the temperature drop amount determination time is variably set based on this input information (see FIG. 6B).

Now, as the user input 150, 50 sheets are selected as the number of image forming processes, plain paper or thick paper as the paper type, monochrome image forming mode as the image forming condition, and single-sided image forming mode as the image forming condition. At this time, the controller 80 variably sets the temperature drop amount determination time to 4 seconds for plain paper and 6 seconds for thick paper, and whether the temperature drop amount within the temperature drop amount determination time is less than the threshold reference temperature. The control temperature is divided and adjusted based on whether or not.
That is, as shown in FIG. 10, in the case of each of plain paper and cardboard, if the temperature drop amount of the fixing roll 41 after the temperature drop amount determination time has elapsed is less than the threshold reference temperature, the control temperature is switched to the corrected control temperature. It is divided and adjusted. If the temperature drop amount is equal to or higher than the threshold reference temperature, it is adjusted to the normal control temperature.
Thus, by variably setting the temperature drop amount judgment time depending on the paper type, the number of sheets discharged at the initial stage can be reduced in the mode using plain paper whose process speed is faster than that of thick paper, and the stack Curling at the time can be suppressed.

Example 2
In the second embodiment, the control device 80 is configured to variably set the threshold reference temperature and the correction control temperature in accordance with the type of paper in the first embodiment, so that more appropriate temperature control can be performed (see FIG. 2). FIG. 11).
Main settings and conditions in the present embodiment are as follows.
-Paper type: Plain paper, thick paper-Temperature drop judgment time: Plain paper 4 seconds, thick paper 6 seconds-Threshold standard temperature: Plain paper 5 ° C, thick paper 7 ° C
・ Correction control temperature: Plain paper -10 ℃, thick paper -7 ℃
In addition, the normal control temperature is set to 188 ° C. and expressed, and in the same figure, the switching determination temperature in which the threshold reference temperature is expressed as an absolute temperature is also described in addition to the threshold reference temperature.
In this embodiment, the basis weight of the paper and the heat absorbability of the paper are in a proportional relationship. Therefore, if the process speed and productivity are the same, the amount of temperature drop is larger for thick paper with a larger basis weight. . Accordingly, since the temperature drop of the fixing roll 41 is small for plain paper with a low basis weight, the threshold reference temperature may be set small. Moreover, since the minimum fixing temperature of plain paper is low, the correction control temperature may be set low. In addition, the normal control temperature may be appropriately variably set, such as being set low for plain paper.

In this embodiment, the control device 80 sets the threshold reference temperature to 5 ° C. and the correction control temperature to 10 ° C. lower than the normal control temperature in the case of plain paper, and corrects the threshold reference temperature to 7 ° C. in the case of thick paper. The temperature is set to 7 ° C. lower than the normal control temperature.
Under such a setting, as shown in FIG. 11, the control temperature of the fixing roll 41 is such that the temperature drop after the temperature drop determination time elapses is less than the threshold reference temperature in both plain paper and cardboard forms. For example, the control temperature is adjusted to the corrected control temperature. If the temperature drop amount is equal to or higher than the threshold reference temperature, it is adjusted to the normal control temperature.
In this manner, by appropriately setting the temperature drop amount determination time, the threshold reference temperature, and the correction control temperature depending on the paper type, appropriate temperature control can be performed.

Example 3
In Example 3, the same image forming apparatus as that of the first embodiment is used, the temperature drop amount determination time is made variable according to the image forming conditions in the monochrome image forming mode or the color image forming mode, and the fixing roll 41 The temperature is controlled (see FIG. 12).
Main settings and conditions in the present embodiment are as follows.
Image forming conditions: black and white image forming mode, color image forming modeTemperature drop amount determination time: black and white image forming mode 2 seconds, color image forming mode 4 seconds In other words, “color mode (113) of user interface 100 as user input information” “Monochrome (123)” or “Full Color (125)” is selected, the temperature drop amount determination time is variably set based on this input information (see FIG. 6A).

In the user input 150, 50 sheets are selected as the number of image forming processes, plain paper is selected as the paper type, monochrome image forming mode or color image forming mode is selected as the image forming condition, and single-sided image forming mode is selected as the image forming condition. At this time, the control device 80 variably sets the temperature drop amount determination time to 2 seconds in the monochrome image formation mode and 4 seconds in the color image formation mode, and the temperature drop amount within the temperature drop amount determination time is set. The control temperature is separately adjusted based on whether the temperature is lower than the threshold reference temperature.
That is, as shown in FIG. 12, in each of the monochrome image forming mode and the color image forming mode, if the temperature drop amount of the fixing roll 41 after the temperature drop amount determination time has elapsed is less than the threshold reference temperature, the control temperature is Separately adjusted to the corrected control temperature.
By variably setting the temperature drop amount judgment time according to the image forming conditions in this way, the number of sheets discharged in the initial stage can be reduced in the black and white image forming mode, which has a faster process speed than the color image forming mode. , Curling during stacking can be suppressed.

Example 4
In the fourth embodiment, in the third embodiment, the control device 80 variably sets the threshold reference temperature and the correction control temperature according to the image forming conditions in the black and white image forming mode or the color image forming mode. Control can be performed (see FIG. 13).
Main settings and conditions in the present embodiment are as follows.
・ Image creation conditions: monochrome imaging mode, color imaging mode ・ Temperature drop amount judgment time: monochrome imaging mode 2 seconds, color imaging mode 4 seconds ・ Threshold reference temperature: monochrome imaging mode 5 ° C, color imaging mode 3 ℃
-Correction control temperature: black and white image formation mode -10 ° C, color image formation mode -5 ° C
In this case, generally, in the black and white image forming mode, the process speed is faster than that in the color image forming mode, and the amount of temperature drop is correspondingly large. Therefore, the threshold reference temperature is set to be large. In the full-color image forming mode, the image density is higher than that in the black and white image forming mode, and the correction control temperature is set high in order to obtain the color development property of the toner. In addition, the normal control temperature may be appropriately variably set such as being set low in the monochrome image forming mode.

In this aspect, the control device 80 sets the threshold reference temperature to 5 ° C. and the correction control temperature to 10 ° C. lower than the normal control temperature in the monochrome image forming mode, and sets the threshold reference temperature in the color image forming mode. The correction control temperature is set to 3 ° C. and a temperature 5 ° C. lower than the normal control temperature.
Under such a setting, as shown in FIG. 13, the control temperature of the fixing roll 41 is set such that the temperature drop after the temperature drop judgment time elapses in each of the monochrome image forming mode and the color image forming mode. If the temperature is lower than the reference temperature, the control temperature is divided and adjusted to the corrected control temperature. If the temperature drop amount is equal to or higher than the threshold reference temperature, it is adjusted to the normal control temperature.
As described above, by appropriately setting the temperature drop amount determination time, the threshold reference temperature, and the correction control temperature according to the image forming conditions, appropriate temperature control can be performed.

Example 5
In the fifth embodiment, in the fourth embodiment, the control device 80 variably sets the threshold reference temperature and the correction control temperature according to the image density, so that more appropriate temperature control can be performed (see FIG. 14). . That is, if the paper type and the process speed are the same in the single-color image forming mode and the multi-color image forming mode, the temperature drop amount depends on the image density, and thus this mode is effective.
In the present embodiment, the control device 80 takes in the image density information 200 from the image reading signal converted into the digital image signal, and performs control temperature separation adjustment (see FIG. 5).
Main settings and conditions in the present embodiment are as follows.
・ Image density conditions: Low image density, high image density ・ Temperature drop amount judgment time: Low image density 2 seconds, high image density 4 seconds ・ Threshold reference temperature: low image density 5 ° C., high image density 6 ° C.
Correction control temperature: Low image density −10 ° C., High image density −8 ° C.

In this case, for example, at a low image density, the amount of temperature drop is smaller and the minimum fixing temperature is lower than at a high image density, so the threshold reference temperature is set lower and the correction control temperature is set lower than at a high image density. . In addition, the normal control temperature may be appropriately variably set, such as being set low at a low image density.
That is, as shown in FIG. 14, in each of the low image density and the high image density, if the temperature drop amount of the fixing roll 41 after the temperature drop amount determination time has elapsed is less than the threshold reference temperature, the correction control temperature is set. Carved and adjusted. If the temperature drop amount is equal to or higher than the threshold reference temperature, it is adjusted to the normal control temperature.
Thus, appropriate temperature control can be performed by variably setting the temperature drop amount determination time, the threshold reference temperature, and the correction control temperature according to the image density.

Example 6
In Example 6, the same image forming apparatus as that of the first embodiment is used, the temperature drop amount determination time is variably set according to the image forming conditions in the single-sided image forming mode or the double-sided image forming mode, and the fixing roll 41 is used. Temperature control is performed (see FIG. 15).
Main settings and conditions in the present embodiment are as follows.
-Image formation conditions: single-sided image formation mode, double-sided image formation mode-Temperature drop judgment time: single-sided image formation mode 4 seconds, double-sided image formation mode 4 seconds-threshold reference temperature: single-sided image formation mode 5 ° C, double-sided image formation mode 3 ℃
Correction control temperature: single-sided image formation mode −10 ° C., double-sided image formation mode −6 ° C.
That is, if “reading method (103)” of the user interface 100 is selected as user input information and “single-sided copy” or “double-sided copy” (not shown) is selected, the temperature drop amount is based on this input information. The determination time is variably set (see FIG. 6A).

In the user input 150, 50 sheets are selected as the number of image forming processes, plain paper is selected as the paper type, monochrome image forming mode is selected as the image forming condition, and single-sided image forming mode or double-sided image forming mode is selected as the image forming condition. At this time, the control device 80 sets the threshold reference temperature to 3 ° C. and the correction control temperature to a temperature 6 ° C. lower than the normal control temperature in the double-sided image forming mode, and sets the threshold reference temperature to 5 in the single-sided image forming mode. The correction control temperature is set to a temperature 10 ° C. lower than the normal control temperature, and the control temperature is divided and adjusted based on whether or not the temperature drop amount within the temperature drop amount judgment time is less than the threshold reference temperature.
Under such a setting, the control temperature of the fixing roll 41 is, as shown in FIG. 15, the temperature drop amount after the temperature drop amount judgment time elapses in the single-sided image formation mode and the double-sided image formation mode. If the temperature is lower than the temperature, the control temperature is adjusted to the corrected control temperature. If the temperature drop amount is equal to or higher than the threshold reference temperature, it is adjusted to the normal control temperature.
According to this aspect, in the double-sided image forming mode, even if the curling occurs in the fixing on the first side, the curling is corrected to the opposite shape by the fixing on the second side. The temperature can be set low and the correction control temperature can be set high.
As described above, by appropriately setting the threshold reference temperature and the correction control temperature according to the image forming mode, appropriate temperature control can be performed.

Example 7
In Example 7, the same image forming apparatus as that of the first embodiment is used, and an environmental sensor 300 capable of detecting at least the temperature is disposed in the image forming apparatus, and the control device 80 is based on this detection information. Is for correcting the normal control temperature, and more appropriate temperature control can be performed (see FIGS. 3 and 5).
The environmental conditions and control temperatures in this example are as follows.
-Environmental conditions: low temperature (room temperature 10 ° C), normal (room temperature 20 ° C or more and less than 25 ° C), high temperature (room temperature 30 ° C)
・ Normal control temperature: 188 ℃
・ Normal control temperature at low temperature: Normal control temperature 188 + 10 ° C = 198 ° C
-Normal control temperature at high temperature: Normal control temperature 188-5 ° C = 183 ° C
That is, as shown in FIG. 16, the room temperature during normal fixing (for example, room temperature 20 ° C. or more and lower than 25 ° C.) is α, the normal control temperature 188 ° C. at normal temperature is β, and the temperature difference is based on room temperature 20 ° C. (Room temperature, reference temperature) is (α−t ° C., β + t ° C.) if the room temperature is less than 20 ° C., and the normal control temperature is 1 ° C. lower than β as the room temperature becomes 1 ° C. lower than α. Adjusted to rise. Therefore, if it is low temperature (room temperature 10 degreeC), it will become ((alpha) -10 degreeC, (beta) +10 degreeC), and normal control temperature will be adjusted to 198 degreeC higher 10 degreeC than usual.

On the other hand, if the room temperature is 25 ° C. or higher, the above (room temperature, reference temperature) is set to (α + t ° C., β−t / 2 ° C.) based on the room temperature of 20 ° C., and the room temperature is 1 ° C. higher than α. As a result, the control temperature is usually adjusted to be lowered by 0.5 ° C. from β. Therefore, if the room temperature is 30 ° C., (α + 10 ° C., β−5 ° C.) is obtained, and the normal control temperature is adjusted to 183 ° C., which is 5 ° C. lower than normal.
As described above, if the normal control temperature is corrected according to the environment and the threshold reference temperature and the corrected control temperature are changed based on this temperature, the temperature can be adjusted according to the environmental conditions.

FIG. 2 is an explanatory diagram showing an outline of a fixing device according to the present invention. 6 is a graph showing the adjustment adjustment to the normal control temperature or the corrected control temperature by the control device in the fixing device according to the present invention. It is explanatory drawing which shows Embodiment 1 to which this invention was applied. FIG. 2 is an explanatory diagram illustrating a fixing device according to a first embodiment. 3 is a block diagram showing a control system of a fixing device used in Embodiment 1. FIG. (A), (b) is explanatory drawing which shows the user interface used in Embodiment 1. FIG. 4 is a flowchart illustrating a fixing process of the fixing device according to the first embodiment. 6 is a graph showing the adjustment adjustment to the normal control temperature or the corrected control temperature by the control device in the fixing device according to the first embodiment. 6 is a flowchart illustrating a fixing process in a mode in which variable setting conditions are variably set according to use environment conditions in the fixing process according to the first embodiment. 3 is a graph showing the results of Example 1. 10 is a graph showing the results of Example 2. 10 is a graph showing the results of Example 3. It is a graph which shows the result of Example 4. 10 is a graph showing the results of Example 5. 10 is a graph showing the results of Example 6. 10 is a graph showing the results of Example 7.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Heat fixing member, 2 ... Temperature sensor, 3 ... Control apparatus, 3a ... Judgment element, 3b ... Control temperature variable element, 4 ... Fixing apparatus, 5 ... Recording material

Claims (9)

A heating and fixing member for heating and fixing an unfixed image formed on a recording material whose surface is heated by a heat source to come into contact with the recording material and whose conveyance speed can be changed ;
A temperature sensor for detecting a surface temperature of the heat fixing member;
A fixing device including a control device that controls the heating fixing member to a predetermined control temperature based on detection information of the temperature sensor ,
The control device determines a control temperature variable adjustment process for the heat fixing member at the time of an image forming process of a predetermined number or more, and a determining element;
When it is determined by the determining element that the control temperature variable adjustment process is performed on the heat fixing member, the recording material is determined in advance after entering the fixing device according to the conveyance speed of the recording material. and variably set to be shorter than the amount of temperature drop determination time to the elapsed time towards faster slower per transport speed of the recording material, the amount of temperature drop determined based on the temperature information from said temperature sensor A judgment element for judging the amount of temperature drop of the heat fixing member up to the time ,
It has a normal control temperature of the heat-fixing member and a correction control temperature lower than the normal control temperature within the fixable temperature range, and whether or not the temperature drop determined by the determination element is less than a predetermined threshold reference temperature. A fixing device comprising: a control temperature variable element that determines and adjusts to a normal control temperature if the temperature drop amount is equal to or higher than a threshold reference temperature, and to a correction control temperature otherwise. The fixing device according to claim 1.
The fixing device according to claim 1, wherein the control temperature variable element variably sets at least one of a threshold reference temperature, a normal control temperature, and a correction control temperature. The fixing device according to claim 1 .
The fixing device is characterized in that the determination element variably sets a temperature drop amount determination time to an individual time according to the type of recording material. The fixing device according to claim 1 .
The fixing device is characterized in that the temperature drop amount determination time is variably set to an individual time according to the image forming condition of the multi-color image forming mode or the single color image forming mode. The fixing device according to claim 2 .
The fixing device according to claim 1, wherein the control temperature variable element variably sets at least one of a threshold reference temperature, a normal control temperature, and a correction control temperature according to the type of the recording material. The fixing device according to claim 2 .
The fixing device according to claim 1, wherein the control temperature variable element variably sets at least one of a threshold reference temperature, a normal control temperature, and a correction control temperature according to an image forming condition. The fixing device according to claim 1 or 2 ,
The controller, under the conditions of accepting the change information of the recording material or the image forming condition during the fixing process, and characterized in that at least one variable setting condition of the decision element and the control temperature variables variably sets Fixing device to do. The fixing device according to claim 1 or 2 ,
Wherein the control device, based on the environmental information environmental sensors arranged around the fixing device, the decision element and the fixing device, characterized by variably setting at least one variable setting condition of the control temperature variables . An image forming apparatus using the fixing device according to any one of claims 1 to 8.

Images