JP2011209597A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fixing slips from appearing and improve the image forming capability.SOLUTION: This image forming device carries out a series of steps including a pre-turning step, an image forming process, and a post-turning step, following the printing job. It has a controller to set at least either one of the pause time set between the post-turning in the previous series of steps and the pre-turning in the next series of steps, and the time to carry out the post-turning in the series of steps, to the correction value shorter than the normal setting, when there are following printing jobs to carry out before finish of the post-turning step in this series of steps, and if the total accumulated number of recording sheets held and carried by the nip section N during the pre-set period before finishing of the series of steps becomes the pre-set threshold number of sheets or more, when carrying out a next series of steps following this series of steps.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer having a function of forming an image on a recording material such as a sheet.

In a heat fixing device (hereinafter referred to as a fixing device) included in an image forming apparatus employing an electrophotographic method, an electrostatic recording method, etc., power is not supplied to the fixing device during standby, and power consumption can be kept as low as possible. A fixing device of a flexible rotating body (hereinafter referred to as film) heating method has been put into practical use. In recent years, image forming apparatuses such as copying machines and printers have been required to have various problems such as printing speed, start-up speed, energy saving, and compactness. Under such a background, film heating type fixing devices are actively used.
As a film driving method in a film heating type fixing device, a driving roller is provided on the inner peripheral surface of the film to drive the film while tension is applied, or a pressure roller is driven by loosely fitting the film to a support member. In this way, a method of rotating in a driven manner is known. In recent years, since the number of parts is small, the latter pressure roller drive type is often employed. In the film heating type fixing device, as disclosed in Patent Document 1, a heat-resistant lubricant (grease) is interposed between the fixing film and the support member, so that the gap between the fixing film and the support member is reduced. It is customary to ensure the slidability.

Here, the fixing slip described below is raised as an existing problem in the film heating type fixing device.
In a film heating type fixing device, a recording material receives a driving force by a frictional force from a pressure roller and is nipped and conveyed. The fixing film is rotated by the frictional force received from the recording material while receiving the sliding frictional resistance from the heater and the support member via the grease.
Accordingly, the recording material is conveyed by receiving a drag force from the fixing film while receiving a driving force from the pressure roller. In this conveyance process, the recording material receives heat from the heater through the fixing film, thereby fixing the toner on the recording material as a permanent image. In this process, there is a case where the recording material feeding speed is insufficient and the recording material feed speed is delayed or stagnated in this process. This phenomenon is fixing slip. As conditions for occurrence of fixing slip, the following [Condition 1], [Condition 2] and the like are generally known.

[Condition 1] When printing a thin-walled recording material having a high water content in a high-temperature and high-humidity environment A recording material left in a high-temperature and high-humidity environment has a high water content and a large amount of water vapor when heated in the fixing nip portion of the fixing device. It is easy to generate. The water vapor generated at this time is interposed between the pressure roller and the recording material, so that the frictional force is lowered, and the fixing slip is likely to occur due to the lack of the conveyance capability of the recording material.
In the case of smooth paper having a water content of 8% or more and a basis weight of 68 g / m ² or less when left in a high temperature and high humidity environment such as 32.5 ° C. and 80% RH environment, fixing slip is likely to occur.
[Condition 2] During intermittent printing A print (image forming) job wait occurs, and in intermittent printing without a pause period from the end of one job to the next job, pre-rotation in each printing process (operation process of the image forming apparatus) Etc., the pressure roller is heated and stored for a long time. Accordingly, the pressure roller surface temperature tends to be higher than in continuous printing. When the pressure roller surface temperature is high, the amount of heat given to the recording material increases, so the amount of water vapor generated from the recording material to be nipped, conveyed and heated increases, and in particular, a water vapor layer is easily formed between the pressure roller and the recording material. Therefore, the frictional force is remarkably reduced and fixing slip is likely to occur.

In an image forming apparatus using a heat fixing device, a pre-rotation temperature adjustment is performed in advance in order to give a predetermined amount of heat to a recording material at a fixing nip portion. The temperature of the fixing device is raised before the recording material reaches the fixing nip portion. In intermittent paper feeding, the proportion of the pre-rotation temperature adjustment time inevitably increases, so the surface temperature of the pressure roller tends to increase. Therefore, when intermittent paper feeding is repeatedly performed, a fixing slip may occur in the second and subsequent sheets due to the pressure roller surface temperature becoming high.
As a prior example of the fixing slip countermeasure technique, a method of changing the fixing temperature control according to the surrounding environment is widely used. Specifically, when a high temperature environment is detected, the fixing temperature control is changed to a setting lower than the normal temperature control, thereby preventing overheating of the fixing device. However, changing the fixing temperature control has a large effect on the fixing performance, and the effect of the moisture content of the recording material is large. Therefore, changing the fixing temperature control alone is not sufficient as a countermeasure to prevent the occurrence of fixing slip. There are many.

As a countermeasure technique devised in such a situation, the following technique has been proposed (see Patent Document 2). It extends the time of idling (post-rotation) without adjusting the temperature until the temperature of the pressure roller decreases at the end of printing, or does not accept the next print until the pressure roller temperature decreases (pauses after post-rotation) Time).
Practically, when it is determined that the paper is intermittently fed under a high temperature environment, an example of applying an algorithm such as pausing for a certain time after post-rotation after the end of printing is mainly used. FIG. 9 shows an example of a conventional method for providing a rest time of 5 seconds after post-rotation. The pressure roller surface temperature rises due to the heating action with the pre-rotation and the paper passing, but the heat is dissipated during the rest period after the post-rotation, and the occurrence of fixing slip is suppressed.

JP-A-5-27619 JP 2004-145205 A

The above-described conventional countermeasure method is highly effective as a countermeasure against fixing slip, but since a pause period is provided after the post-rotation after the printing is completed, there is a concern that the specs of the printing process may be greatly reduced. In practice, when it is determined that the paper is intermittently fed in a high temperature environment, an example of applying an algorithm such as pausing between print jobs for a certain period of time is mainly applied, but specification down is inevitable.
In recent years, with the widespread use of network environments, image forming apparatuses are also incorporated into networks, so that a single image forming apparatus is often used by a plurality of users. In such a situation, intermittent printing frequently occurs because a plurality of print jobs are transmitted in succession. Since the length between intermittent print jobs is equivalent to a significant reduction in practical print processing capacity, the conventional countermeasures greatly reduce the print processing capacity if intermittent paper passes frequently. There is a concern that

  The present invention has been made in view of the circumstances as described above, and an object thereof is to prevent the occurrence of fixing slip and improve the image forming processing capability.

In order to achieve the above object, the present invention provides:
A heater,
A flexible sleeve that slides on the heater via a lubricant;
A pressure roller that forms a nip portion with the heater via the flexible sleeve, the pressure roller driving the flexible sleeve by being driven to rotate;
An image heating means for sandwiching and conveying a recording material carrying a developer image between the flexible sleeve and the pressure roller in the nip portion,
A heating step of sandwiching and conveying at least one recording material carrying a developer image, and heating;
Executed immediately before the heating step, and a pre-step for preheating the nip portion;
A post-process that is performed immediately after the heating step and reduces the temperature of the nip portion;
In an image forming apparatus in which a series of steps including
When the next image forming command exists by the end of the subsequent process in the previous series of processes, and the next series of processes is performed following the previous series of processes, the previous series of processes ends. When the cumulative number of recording materials nipped and conveyed in the nip portion within a preset period until the time is equal to or greater than a preset threshold number,
The rest time provided between the subsequent step in the previous series of steps and the previous step in the next series of steps, and the subsequent step in the previous series of steps are executed. Control means capable of executing control to set at least one of the post-process times to a correction value shorter than the normal set value is provided.

  According to the present invention, it is possible to prevent the occurrence of fixing slip and improve the image forming processing capability.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. FIG. 3 is a schematic diagram illustrating a schematic configuration of the heat fixing apparatus according to the first exemplary embodiment. Schematic sectional view showing the fixing film of Example 1 FIG. 6 is a flowchart illustrating an execution procedure of intermittent sheet feeding control according to the first embodiment. The figure which shows the threshold value change of the pressure roller surface temperature leading to the occurrence of fixing slip The figure which shows the result of having compared the print processing capability in Example 1 and the conventional method FIG. 9 is a flowchart illustrating an execution procedure of intermittent sheet feeding control according to the second embodiment. FIG. 9 is a flowchart illustrating an execution procedure of intermittent sheet feeding control according to the third embodiment. Diagram for explaining a conventional example

  DETAILED DESCRIPTION Exemplary embodiments for carrying out the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

(1) Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an image forming apparatus in the first embodiment.
Reference numeral 1 denotes a photosensitive drum, and a photosensitive material such as OPC, amorphous Se, or amorphous Si is formed on a cylindrical substrate such as aluminum or nickel. The photosensitive drum 1 is rotationally driven in the direction of the arrow, and first, the surface thereof is uniformly charged by a charging roller 2 as a charging device. Next, the laser scanner 3 performs scanning exposure with a laser beam L that is ON / OFF controlled according to image information, and an electrostatic latent image is formed on the photosensitive drum 1. This electrostatic latent image is developed and visualized by the developing device 4 using toner (developer). As a developing method, a jumping developing method, a two-component developing method, an FEED developing method, or the like is used, and image exposure and reversal development are often used in combination.

The visualized toner image (developer image) is transferred from the photosensitive drum 1 onto the recording material P conveyed at a predetermined timing by a transfer roller 5 as a transfer device. Here, the top sensor 8 detects the leading edge of the recording material P so that the image forming position of the toner image on the photosensitive drum 1 matches the writing position of the leading edge of the recording material, and the timing is adjusted.
The recording material P conveyed at a predetermined timing is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressure. The recording material P to which the toner image has been transferred is conveyed to the heat fixing device 6 and fixed as a permanent image.
On the other hand, the residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7. Reference numeral 9 denotes a discharge sensor provided in the heat fixing device 6, and is a sensor for detecting when the recording material P has a paper jam or the like between the top sensor 8 and the discharge sensor 9. .

(2) Heat fixing device 6
2A and 2B are schematic views illustrating a schematic configuration of the heat fixing device 6 according to the present embodiment, in which FIG. 2A is a cross-sectional view of the heat fixing device 6, and FIG. 2B is a cross-sectional view of a heater portion of the heat fixing device 6. c) is an exploded perspective view of the heat fixing device 6.
The heat fixing device 6 is basically a film heating type heat fixing device comprising a fixing assembly 10 and a pressure roller 20 that are in pressure contact with each other to form a nip portion N. As shown in FIGS. 2A and 2C, the fixing assembly 10 mainly includes a fixing film 13, a heater 11, a supporting member 12 that holds the heater 11, and a pressing member that receives pressure from the pressing spring 15. The metal stay 14 presses the pressure 12 against the pressure roller 20. The pressure roller 20 forms the heater 11 and the nip portion N via the fixing film 13, and is driven to rotate to drive the fixing film 13. The heating and fixing device 6 corresponds to an image heating unit that sandwiches and conveys a recording material carrying a toner image between the fixing film 13 and the pressure roller 20 in the nip portion N and heats the recording material.

(2.1) Fixing film 13
FIG. 3 is a schematic sectional view showing the fixing film 13 of this embodiment.
The fixing film 13 is a heat-resistant film having a total thickness of 200 μm or less to enable quick start as shown in FIG. 3, and corresponds to a flexible sleeve that slides on the heater 11 via a lubricant. To do. The base layer 13a is formed of a heat-resistant resin such as polyimide, polyamideimide, PEEK, or a thin metal. In order to improve thermal conductivity, high thermal conductive powders such as BN, alumina, and Al may be mixed. Further, the fixing film 13 having a sufficient strength and excellent durability for constituting a long-life heat fixing apparatus needs to have a total thickness of 20 μm or more. Therefore, the total thickness of the fixing film 13 is optimally 20 μm or more and 200 μm or less. Furthermore, in order to prevent offset and ensure separation of the recording material, the surface layer is mixed with a heat-resistant resin having good releasability such as PTFE, PFA, FEP, ETFE, CTFE, PVDF, etc., and a silicone resin. The release layer 13c is formed by covering with Here, PTFE is polytetrafluoroethylene, PFA is a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, and FEP is a tetrafluoroethylene hexafluoropropylene copolymer. ETFE is an ethylene tetrafluoroethylene copolymer, CTFE is polychlorotrifluoroethylene, and PVDF is polyvinylidene fluoride. As a coating method, the outer surface of the fixing film 13 may be etched and then the release layer may be dipped or applied by powder spraying or the like. Alternatively, a method of covering the surface of the fixing film 13 with a resin formed in a tube shape may be used. Alternatively, after the outer surface of the fixing film 13 is blasted, a primer layer 13b as an adhesive may be applied to cover the release layer.

(2.2) Pressure roller 20
The pressure roller 20 is an elastic roller in which an elastic solid rubber layer made of heat-resistant rubber such as silicone rubber or fluorine rubber is formed as an elastic layer 22 on the outside of a metal core 21 made of SUS, SUM, Al or the like. It is. The elastic layer 22 may be an elastic sponge rubber layer formed by foaming silicone rubber in order to have a more heat insulating effect. The elastic layer 22 may be an elastic cellular rubber layer in which a hollow filler (such as a microballoon) is dispersed in a silicone rubber layer and a gas portion is provided in the cured product to enhance the heat insulation effect. Further, a release layer such as perfluoroalkoxy resin (PFA) or polytetrafluoroethylene resin (PTFE) may be formed on the elastic layer 22.

(2.3) Heater 11
As shown in FIG. 2B, the heater 11 as a heating member heats the nip portion N by contacting the inner surface of the fixing film 13. The heater 11 has a plate shape with a low heat capacity. Then, on the surface of the insulating ceramic substrate 11a such as alumina or aluminum nitride, along the longitudinal direction, an energization heat generating resistance layer 11b such as Ag / Pd (silver palladium), RuO ₂ , Ta ₂ N has a thickness of about 10 μm, It is formed by screen printing or the like with a width of about 1 to 5 mm. A protective layer 11c is provided on the surface of the heater 11 in contact with the fixing film 13 to protect the energized heating resistance layer within a range that does not impair the thermal efficiency. The thickness of the protective layer is preferably thin enough to improve the surface properties, and glass or a fluororesin coat may be applied. Here, in the description of the present embodiment, the longitudinal direction refers to the rotation axis direction of the pressure roller 20 (the recording material width direction orthogonal to the recording material conveyance direction).
The support member 12 that holds the heater 11 is formed of a heat resistant resin such as liquid crystal polymer, phenol resin, PPS, or PEEK. The lower the thermal conductivity of the support member 12, the better the heat conduction to the pressure roller 20. Therefore, a filler such as a glass balloon or a silica balloon may be included in the resin layer. The support member 12 also has a role of guiding the rotation of the fixing film 13. Reference numeral 14 denotes a metal stay that contacts the support member 12 and suppresses bending and twisting of the entire fixing assembly. Further, the film potential is stabilized by disposing the conductive rubber ring 16 on the core at the end of the pressure roller.

(2.4) Driving and Control Method of Heat Fixing Device 6 The fixing assembly 10 is pressed against the elasticity of the pressure roller 20 by the following configuration to form a predetermined nip portion N. That is, as shown in FIG. 2C, both ends of the metal stay 14 in the longitudinal direction protrude from the support member 12, and spring receiving portions 14a at both ends of the stay are pressed springs via the spring receiving members. 15 is pressurized. The load is transmitted uniformly over the longitudinal direction of the support member 12 via the stay foot 14b.
At the nip portion N, the fixing film 13 is bent by being sandwiched between the heater 11 and the pressure roller 20 by the applied pressure, and is in close contact with the heating surface of the heater 11.

The pressure roller 20 obtains a driving force that rotates in the direction of the arrow in FIG. 2A by a driving gear (not shown) provided at the end of the cored bar 21. The driving force is transmitted from a motor (not shown) according to a command from the CPU of the image forming apparatus that controls the control means.
As the pressure roller rotates, the fixing film 13 is driven to rotate by the frictional force with the pressure roller 20. Since a fluorine-based or silicone-based heat-resistant grease is interposed between the fixing film 13 and the heater 11 as a lubricant, the frictional resistance can be kept low, and the fixing film 13 can be rotated smoothly.

In addition, the temperature control of the heater 11 is appropriately determined by determining the duty ratio of the voltage applied by the CPU to the energization heating resistor layer according to a signal from a temperature detection element such as a thermistor (not shown) provided on the back surface of the ceramic substrate. Controlled. As a result, the temperature in the nip portion N is maintained at a desired fixing set temperature.
The recording material P holding the unfixed toner image is appropriately supplied by a supply unit (not shown) at a predetermined timing, and is conveyed into the nip portion N to be heated and fixed. The recording material P discharged from the nip portion N is guided to a discharge guide (not shown) and discharged outside the apparatus.

(3) Intermittent paper feed control in the present embodiment In the conventional example, in order to reduce the pressure roller temperature as a countermeasure against fixing slip during intermittent paper feeding, temperature control is performed until the pressure roller temperature is lowered at the end of printing. An idle period (interval time) was always provided after the post-rotation with idling off. During the pause period, the operation is stopped and the print request contents from the user are also stored in the buffer.

This embodiment is characterized in that the rest period after post-rotation is changed according to the number of sheets.
In this embodiment, as an example, a pause period of 5 seconds is provided when the number of sheets passed is less than 10, and the pause period is eliminated when the number of sheets passed is 10 or more. Conventionally, when a print job (image formation command) sent from a user is received and the number of sheets to be passed is less than a preset threshold value (threshold number), the control unit provides a pause period after post-rotation. The same operation is performed, and if it is equal to or greater than the threshold value, the rest period after the post-rotation is not performed.
In the image forming apparatus of this embodiment, a series of steps including pre-rotation → execution of image forming process (image forming operation) → post-rotation is performed according to an image forming command (print job). Here, execution of the image forming process (image forming operation) corresponds to a heating process in which at least one recording material carrying a toner image is nipped and conveyed and heated. The pre-rotation is executed immediately before the heating process and corresponds to a pre-process for preheating the nip portion N. The post-rotation is executed immediately after the heating process, and corresponds to a post-process for reducing the temperature of the nip portion N.

Further, the number of sheets passed in the present embodiment refers to the accumulated number of sheets already passed within a predetermined period (time) before the intermittent printing. That is, when the next print job exists by the end of the post-rotation in the previous series of steps, and the next series of steps is performed following the previous series of steps, The cumulative number of recording materials nipped and conveyed at the nip portion N within a preset period until the end of the process.
In this embodiment, when the number of sheets to be passed is equal to or greater than a preset threshold number, it is provided between the subsequent process in the previous series of processes and the previous process in the next series of processes. The pause time thus set is a correction value shorter than the normal set value. Here, the time for performing the post-rotation in the previous series of steps (corresponding to the post-process time) may be a correction value shorter than the normal set value. Of the rest time provided between the post-rotation of the previous series of steps and the pre-rotation of the next series of steps, and the time of executing the post-rotation of the previous series of steps At least one of them may be a correction value shorter than the normal set value.
In this embodiment, the number of passing sheets is used to determine the uniformity of the viscosity of the grease. Here, a “preset period” for deriving the number of sheets to be passed depending on the environment (temperature, humidity) in which the image forming apparatus is installed and the type of recording material to be conveyed (for example, difference in basis weight). Alternatively, the “preset threshold number” may be set as appropriate.

FIG. 4 is a flowchart showing an execution procedure of intermittent sheet feeding control executed by the control means of this embodiment. In this flowchart, it is assumed that the next print job exists by the end of the post-rotation.
After completion of post-rotation (Step 1), a print job is received (Step 2). At this time, the application process is divided depending on whether or not the number of sheets to be passed is greater than or equal to a threshold value (Step 3). If it is determined in Step 3 that the threshold is greater than or equal to the threshold value, printing is immediately started without providing a pause period (Step 4). If it is determined in Step 3 that the threshold value is less than the threshold value, a pause period is provided after post-rotation, and then printing is started. (Step 5).

(3.1) Fixing Slip Suppression Mechanism in the Present Embodiment As described in the background art section, the fixing slip in a high temperature and high humidity environment occurs due to the overheating state of the heating fixing device. In particular, in intermittent paper feeding, a rise in the surface temperature of the pressure roller becomes a problem, and in the conventional example, a heat release is promoted by suppressing a fixing slip by providing a rest period after the subsequent rotation. This results in securing the frictional force between the pressure roller and the recording material.
Since the occurrence of fixing slip depends on the lack of recording material conveying force, it can be roughly classified into “driving force” and “drag”. It can be said that the value obtained by subtracting the drag force from the driving force corresponds to the recording material conveying force. The driving force depends on the frictional force, and the conventional example pays attention to this. On the other hand, this embodiment focuses on the drag.

The following tendencies are observed when the occurrence of fixing slip is observed in detail.
[Trend 1] Fixing slip is likely to occur in the initial stage of paper passing.
[Trend 2] The pressure roller surface temperature causing the fixing slip varies depending on the sheet passing condition.
With regard to [Trend 1], it was experimentally confirmed that, specifically, when intermittent sheet passing is performed one sheet at a time, the fixing slip remarkably occurs when the number of sheet passing is less than 10. Here, for the experiment, the paper passing evaluation is performed without the rest period after the post-rotation after the end of printing.
As this factor, the height and non-uniformity of the grease viscosity at the initial stage of paper feeding are raised. In the film heating type fixing device, the fixing film is lubricated by applying grease to the support member, but for a while after the heating drive is started, the grease is sufficiently dissolved and homogenized. The sliding friction is large and unstable. Accordingly, the drag force received by the fixing film is increased, resulting in insufficient conveyance force and occurrence of fixing slip.

  With regard to [Trend 2], it has been conventionally considered that a fixing slip occurs when the pressure roller surface temperature becomes a certain threshold value or more. However, the threshold value is not a constant value but varies depending on the sheet passing condition. It is. When the experiment was performed while changing the fixing temperature control temperature and the pause time between intermittent paper passing jobs, the following could be confirmed. That is, in the situation where the number of sheets passed is less than 10, fixing slip occurs with the pressure roller surface temperature of about 130 ° C. as a threshold, whereas when the number of sheets passed is 10 or more, the pressure roller surface temperature exceeds 130 ° C. Even in this case, it was confirmed that no fixing slip occurred.

The cause of this is considered to be due to the change in sliding friction accompanying the dissolution and equalization of the grease, as well as the ease of occurrence of the fixing slip in the initial stage of paper passing. The sliding friction is reduced and stabilized with the passage of paper, and the drag received by the recording material is reduced. Therefore, it is considered that there is a surplus in the conveyance force and offsets the increase in the pressure roller surface temperature.
Conventionally, fixing slip occurs when the pressure roller surface temperature reaches a certain threshold, and the threshold is considered to be a constant value. However, as a result of detailed investigations by the inventors, the drag component changes due to the change in the state of the grease that accompanies the sheet passing, so the pressure roller temperature threshold value causing the fixing slip is not a constant value but the number of sheets passed It turned out that it changes with.

  In the present embodiment, in consideration of the change in the drag force applied to the recording material, the occurrence of fixing slip is suppressed and the printing processing performance in intermittent paper feeding is improved by considering the change in the drag force applied to the recording material. In this embodiment, a rest period of 5 seconds is provided after the post-rotation when the number of sheets with high drag is less than 10, and a rest period after the post-rotation is eliminated when the number of sheets with a drag of 10 or more is low.

(3.2) Confirmation of effect of present example In order to confirm the effect of the method of the present example (hereinafter referred to as the present method), verification by experiment was performed.
In this method, the following LBP (laser beam printer) was used. It is an LBP equipped with a print processing capacity of 26 sheets / min and a process speed of 166 mm / sec in an environment of room temperature 32.5 ° C. and humidity 80%, a high heat conductive resin film with a diameter of 18 mm and a thickness of 70 μm, and a pressure roller with a diameter of 18 mm. is there. The pressure applied by the pressure roller that presses the high thermal conductive resin film is 13.5 kgf (132.3 N). As the recording material, A4 size basis weight 68 g thin paper that was left to stand in the above environment for 48 hours to absorb moisture was used. The results are shown in Table 1 and FIG.

A comparison was made between the conventional method and the present method in which a rest period of 5 seconds was uniformly provided after the end of the post-rotation, and no fixing slip was generated in both methods. FIG. 5 is a diagram showing a change in the threshold value of the pressure roller surface temperature that leads to occurrence of a fixing slip during intermittent paper feeding control. The drag is reduced by the dissolution of the grease and the homogenization of the viscosity accompanying the passage of the paper, and the threshold value is changed. In the present embodiment, a pause period after the post-rotation is provided at the initial stage of paper passing until the time a, and the pause period after the post-rotation is eliminated after the time a.
As a result of the experiment, the time required for printing was 6 minutes 25 seconds in the conventional method, and 4 minutes 45 seconds in the present method. FIG. 6 shows a result of comparing the print processing capability when intermittent paper feeding is performed between the conventional method and the present embodiment. Even in intermittent paper feeding under high-temperature and high-humidity conditions, the printing processing performance could be improved without impairing the fixing slip inhibition property, and the effect of this method was confirmed.

  As described above, according to the present embodiment, the sheet passing control for providing the rest period after the post-rotation is limited to the initial stage of the printing process in which the drag due to the sliding friction resistance is large, thereby suppressing the occurrence of fixing slip. It becomes possible to improve the printing performance.

  Hereinafter, the intermittent sheet feeding control according to the second embodiment will be described. In the present embodiment, the different components from the first embodiment will be described, and the description of the same components as those in the first embodiment will be omitted.

In the above-described first embodiment, the pause period after the post-rotation is not provided when the number of sheets to be passed is large. However, there is a concern that when the time elapses after the printing is finished, the grease is cooled, the viscosity is changed again to a high and non-uniform state, and the drag increases. That is, there is a concern that slip may occur when the elapsed time becomes long after printing is completed.
In order to cope with this problem, the present embodiment is characterized by having the following measuring means. That is, when the next print job exists by the end of the subsequent process of the previous series of processes, and the next series of processes is performed following the previous series of processes, immediately before the previous series of processes. It is a measuring means which measures the elapsed time after the post-process of a series of processes performed in the end.
By providing such a measuring unit, even when the number of sheets to be passed is equal to or greater than a threshold value, a pause period is provided if the time measured by the measuring unit is equal to or greater than a preset threshold value. It is characterized by carrying out control (normally set value). Here, the measuring means is controlled by the CPU of the image forming apparatus.
In the present embodiment, when the elapsed time is equal to or greater than the threshold, control for initializing the count of the number of sheets to be passed is added to the control of the first embodiment. In this embodiment, the elapsed time threshold is set to 3 minutes.

FIG. 7 is a flowchart showing an execution procedure of intermittent sheet feeding control executed by the control means of this embodiment. In this flowchart, as in FIG. 4, it is assumed that the next print job exists by the end of the post-rotation.
After the post-rotation is completed (Step 1), the print job is received (Step 2), and the application process is divided depending on whether or not the elapsed time is less than the threshold value (Step 21). If it is determined in Step 21 that the number is greater than or equal to the threshold value, a sheet passing number counter as a means for measuring the sheet passing number is initialized (Step 22). In Step 3, as in the first embodiment, the application process is divided depending on whether the number of sheets to be passed is equal to or greater than a threshold value. If it is determined in Step 3 that it is equal to or greater than the threshold value, printing is immediately started without providing a pause period (Step 4). If it is determined in Step 3 that the threshold value is less than the threshold value, a pause period is provided after post-rotation, and then printing is performed. Start (Step 5).

  As described in the first embodiment, when the grease is dissolved and the viscosity becomes uniform, the drag applied to the recording material is reduced, so that the rest period after the post-rotation can be omitted. After enough paper is passed, the viscosity of the grease is uniform, and the entire fixing device is in a state where heat is stored. Become. However, there is a concern that the viscosity of the grease will increase again and become non-uniform due to cooling over time. In the present embodiment, by limiting the elapsed time, it corresponds to the state transition of the grease with the passage of time.

  The elapsed time after continuous printing of 200 sheets of A4 size paper was varied, and then a comparison was made regarding whether or not there was a rest period after post-rotation when intermittent paper feeding was performed. The results are summarized in Table 2. ○ indicates no occurrence of slip, and × indicates occurrence of slip.

According to the present embodiment, even if the number of sheets to be passed is equal to or greater than the threshold value by adding the elapsed time from the fixing device hot state after printing to the counter value of the number of sheets to be passed, If the elapsed time measured by the means is equal to or greater than the threshold, a pause period can be provided. As a result, it is possible to improve the print processing performance without impairing the fixing slip deterrence even when the passage of time is accompanied by intermittent passage under high temperature and high humidity conditions.
In this embodiment, when the elapsed time measured by the measuring means is equal to or greater than the threshold, the control for initializing the count of the number of sheets to be passed is added to the control of the first embodiment. However, the present invention is not limited to this. is not. That is, what is necessary is just to provide an idle period when the elapsed time measured by the measuring means is equal to or greater than a threshold value. That is, any value may be used as long as the value of the sheet passing number counter is changed in Step 22 so that the number of passing sheets is determined to be less than the threshold value in Step 3.
In the present embodiment, it has been described that a pause period is provided when the elapsed time measured by the measuring means is equal to or greater than a threshold value (the pause period is set as a normal set value). Even during the rotation execution time, the normal set value is used regardless of the control state. That is, when the elapsed time is equal to or greater than the threshold value, the rest period provided between the post-rotation in the previous series of steps and the pre-rotation in the next series of steps, and the previous series The time for performing the post-rotation in the step is normally set to the set value.

  Hereinafter, the intermittent sheet feeding control according to the third embodiment will be described. In the present embodiment, different components from those of the first and second embodiments will be described, and the description of the same components as those of the first and second embodiments will be omitted.

  As described in the second embodiment, when the state of the grease, that is, the magnitude of the drag is estimated based on the number of sheets passed and the elapsed time after passing, the elapsed time after passing according to the number of sheets passed is determined. The accompanying change in grease status is also different. Therefore, it may be difficult to make an optimum determination, and setting a threshold value that allows for safety may cause a pause after post-rotation more than necessary. On the other hand, since the state of grease has a correlation with the temperature state, if the output of the temperature detection element as a temperature detection means for detecting the temperature of the heater provided on the back surface of the heater is used, the viscosity of the grease is more efficiently The situation, that is, the situation of drag, can be estimated. Here, the temperature detection means is controlled by the CPU of the image forming apparatus.

  Therefore, in this embodiment, there is a temperature detection element such as a thermistor (not shown) provided on the back surface of the heater, and when the detection result by the temperature detection element is less than the threshold value, the count of the number of sheets to be passed is initialized. The control is added to the control of the first embodiment. In this embodiment, the threshold is 145 ° C.

FIG. 8 is a flowchart showing an execution procedure of the intermittent paper feed control executed by the control means of this embodiment. In this flowchart, as in FIG. 4, it is assumed that the next print job exists by the end of the post-rotation.
After the end of post-rotation (Step 1), a print job is received (Step 2), and the application process is divided depending on whether or not the detected temperature is equal to or higher than a threshold value (Step 31). If it is determined in Step 31 that the number is less than the threshold value, a sheet passing number counter as a means for measuring the sheet passing number is initialized (Step 32). In Step 3, as in the first embodiment, the application process is divided depending on whether the number of sheets to be passed is equal to or greater than a threshold value. If it is determined in Step 3 that it is equal to or greater than the threshold value, printing is immediately started without providing a pause period (Step 4). If it is determined in Step 3 that the threshold value is less than the threshold value, a pause period is provided after post-rotation, and then printing is performed. Start (Step 5).

As described in the first and second embodiments, when the grease is dissolved and uniformed, the drag applied to the recording material is reduced, so that it is possible to omit the rest period after the post-rotation. Although it is possible to grasp the tendency of grease dissolution and homogenization depending on the paper passing status, depending on only the count of the number of paper passing, the viscosity of the grease may transition to a non-uniform state again after cooling. is there. However, since the dissolved state of grease correlates with the detection result of a temperature detection element such as a thermistor, if the detection result of the temperature detection element is equal to or greater than a threshold value, it is assumed that the grease is dissolved and the viscosity is uniform. Is possible.
In this embodiment, when 200 sheets of A4 size paper are continuously printed, the image forming apparatus is left unattended, and then, when intermittent paper feeding is performed, the output result of the temperature detection element and the rest period after post-rotation in that case are set as presence or absence. The case was compared. The results are summarized in Table 3. ○ indicates no occurrence of slip, and × indicates occurrence of slip.

According to the present embodiment, the detection result by the temperature detection element is obtained even if the detection result by the temperature detection element is added to the counter value of the number of paper passage and the detection result by the temperature detection element is equal to or greater than the threshold value. If it is less than the threshold, a pause period can be provided. As a result, it is possible to improve the print processing performance without impairing the fixing slip deterrence even when the passage of time is accompanied by intermittent passage under high temperature and high humidity conditions.
Here, in this embodiment, when the detection result by the temperature detection element is less than the threshold, the control for initializing the count of the number of sheets to be passed is added to the control of the first embodiment, but the present invention is not limited to this. . That is, what is necessary is just to provide an idle period when the detection result by a temperature detection element is less than a threshold value. That is, any value may be used as long as the value of the sheet passing number counter is changed in Step 32 so that the number of passing sheets is determined to be less than the threshold value in Step 3.
In the present embodiment, it has been described that a rest period is provided when the detection result by the temperature sensing element is less than the threshold value (the rest period is set as a normal set value). Even in the execution time, the normal set value is used regardless of the control state. That is, when the detection result is less than the threshold value, a pause period provided between the post-rotation in the previous series of steps and the pre-rotation in the next series of steps, and the previous series. The time for performing the post-rotation in the step is normally set as the set value. Moreover, you may perform control which combined the control based on the detection result by the temperature detection element of a present Example, and the control based on the elapsed time measured by the measurement means of Example 2. FIG.

  Hereinafter, the intermittent sheet feeding control according to the fourth embodiment will be described. In the present embodiment, different components from those of the first to third embodiments will be described, and the description of the same components as those of the first to third embodiments will be omitted.

In this embodiment, compared to the first to third embodiments, a storage unit that accumulates and stores the usage amount of the heat fixing device 6 and a threshold value of the number of sheets to be passed when the usage amount stored in the storage unit increases. It further has a correction means capable of executing control for correcting so as to increase. The storage unit and the correction unit are controlled by the CPU of the image forming apparatus.
In this embodiment, as the amount used, the cumulative number (number of sheets passed) of recording materials that have been heat-fixed by the heat-fixing device 6 (sandwiched and conveyed at the nip portion) is used. The usage amount is not limited to the cumulative number, and may be the total number of rotations of the pressure roller 20, for example. Further, a usage history detection unit that detects a usage history of the heat fixing device 6 may be provided, and the usage amount of the heat fixing device 6 may be detected by the usage history detection unit.

  As the printing durability increases, the oil component of the grease tends to be depleted and the sliding frictional resistance tends to increase. That is, the heat fixing device tends to relatively increase the drag force applied to the recording material with use. Therefore, since there is a difference in the conveyance force between the new state when the printer is first used and the state after the printing endurance, intermittent paper feeding control is also used for the printing endurance in order to guarantee a stable operation without causing a fixing slip. It is necessary to make it correspond. In this example, settings were made as shown in Table 4 below.

Since the oil component of the grease is sufficient when the printing durability is less than 25K (25000) sheets, the rest period after post-rotation is limited to less than 10 sheets at the initial stage for the reason explained in the first embodiment. In the following, no rest period will be provided. When the printing durability is 25K or more and less than 50K (50000), the sliding friction resistance tends to increase as the oil component of the grease depletes, so the rest period after post-rotation should be extended to the initial 20 sheets. To do. In addition, when the print endurance is 50K or more, where oil component depletion of grease is significant, it is highly possible that the sliding frictional resistance of the fixing film has increased. Therefore, the rest period after post-rotation is always performed. .
As a result, it is possible to improve the printing processing capacity as a whole and suppress the occurrence of fixing slip throughout the durable life of the heat fixing device.

Here, in the present embodiment, the threshold value for the number of sheets to be passed as to whether or not to provide a pause period is corrected, but the present invention is not limited to this. Of the rest period provided between the post-rotation of the previous series of steps and the pre-rotation of the next series of steps, and the time for executing the post-rotation of the previous series of steps What is necessary is just to correct the threshold value when at least one of the correction values is shorter than the normal set value.
In addition, the image heating unit according to the present invention is not limited to the example in which the image heating unit functions as the heat fixing device in the first to fourth embodiments described above, but as a device for giving gloss to the toner image fixed on the sheet. It is also possible to apply.

  6 Heating fixing device; 11 Heater; 13 Fixing film; 20 Pressure roller; N Nip part

Claims (4)

A heater,
A flexible sleeve that slides on the heater via a lubricant;
A pressure roller that forms a nip portion with the heater via the flexible sleeve, the pressure roller driving the flexible sleeve by being driven to rotate;
An image heating means for sandwiching and conveying a recording material carrying a developer image between the flexible sleeve and the pressure roller in the nip portion,
A heating step of sandwiching and conveying at least one recording material carrying a developer image, and heating;
Executed immediately before the heating step, and a pre-step for preheating the nip portion;
A post-process that is performed immediately after the heating step and reduces the temperature of the nip portion;
In an image forming apparatus in which a series of steps including
When the next image forming command exists by the end of the subsequent process in the previous series of processes, and the next series of processes is performed following the previous series of processes, the previous series of processes ends. When the cumulative number of recording materials nipped and conveyed in the nip portion within a preset period until the time is equal to or greater than a preset threshold number,
The rest time provided between the subsequent step in the previous series of steps and the previous step in the next series of steps, and the subsequent step in the previous series of steps are executed. An image forming apparatus, comprising: a control unit capable of executing control to set at least one of the post-process times to a correction value shorter than a normal set value. Having a measuring means for measuring the elapsed time since the end of the subsequent step of the series of steps performed immediately before the previous series of steps,
Even when the integrated number is equal to or greater than the threshold number, the control unit is configured to perform the pause time and the post-process time when the time measured by the measurement unit is equal to or greater than a preset threshold. The image forming apparatus according to claim 1, wherein the normal setting value is set. Having temperature detecting means for detecting the temperature of the heater;
Even when the integrated number is equal to or greater than the threshold number, the control means may determine that the pause time and the post-process when the temperature detected by the temperature detection means is less than a preset threshold value. 3. The image forming apparatus according to claim 1, wherein time is set as the normal setting value. Storage means for accumulating and storing the amount of use of the image heating means;
A correction unit capable of executing a control for correcting the value so that the value of the threshold number increases as the usage amount stored in the storage unit increases;
The image forming apparatus according to claim 1, further comprising:

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