JP6904671B2 - Image forming device - Google Patents

Description

The present invention relates to an electrophotographic image forming apparatus.

The electrophotographic image forming apparatus includes a fixing apparatus that heats an unfixed toner image formed on a recording material. As an example of the fixing device, a configuration including a fixing belt (endless belt) having a small heat capacity is known in order to shorten the start-up time of the fixing device. In this fixing device, the fixing process (image heating process) is performed by heating and pressurizing the recording material at the nip portion between the fixing belt (endless belt) and the pressure roller (driving rotating body).

Further, in the fixing device, when a recording material having a width smaller than the maximum width of the recording material that can be used in the fixing device is continuously passed, the region of the longitudinal end of the fixing belt that does not come into contact with the recording material (non-passing paper). There is a risk that the temperature of the area) will rise. As one of the countermeasures, a configuration in which a metal roller (hereinafter referred to as a heat equalizing roller) is brought into contact with the pressure roller is known (Patent Document 1). The soaking roller suppresses the temperature rise in the end region of the fixing belt via the pressurizing roller by dispersing the heat of the pressurizing roller in the longitudinal direction.

JP 2013-64997

Patent Document 1 discloses a configuration in which a heat equalizing roller is brought into contact with a pressure roller after the number of recording materials that have continuously passed through the nip portion reaches a predetermined number. As a result, it is possible to prevent the temperature of the fixing belt from dropping too much due to the contact of the soaking rollers.

The present inventor has found that there is room for further improvement in the configuration of Patent Document 1 through examination. In a fixing device using a fixing belt having a low heat capacity, the time required to start the fixing belt is short, so even if the fixing belt reaches a temperature at which the fixing process can be started and the start-up is completed, the soaking roller is heated too much. Not done. Therefore, for example, when the temperature of the heat equalizing roller before startup is low, the water vapor generated from the recording material is cooled by the heat equalizing roller by the fixing process at the nip portion, and dew condensation is formed on the surface of the heat equalizing roller. There is.

When the dew-condensed heat equalizing roller comes into contact with the pressure roller, moisture is transferred from the heat equalizing roller to the pressure roller, so that the recording material passing through the nip portion gets wet. Here, if the wet recording material is a recording material to be printed on both sides and the recording material gets wet during the fixing process of the toner image formed on the first surface of the recording material, the recording material 2 When the toner image is transferred to the surface, it may lead to transfer failure.

In the configuration of Patent Document 1, when the number of recording materials reaches a predetermined number during execution of double-sided printing, the first surface fixing process of the recording material to be printed on both sides depends on the timing when the heat equalizing roller comes into contact with the pressure roller. There is a risk that the recording material will get wet inside. Therefore, further improvement is required for the contact timing of the heat equalizing roller.

An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of transfer defects due to dew condensation on a heat equalizing roller when performing double-sided printing in relation to further improvement of the prior art.

In order to achieve the above object, the first invention
An image forming part that forms a toner image on the recording material,
An endless belt that heats the toner image on the recording material formed by the image forming portion at the nip portion, and
A heating unit that heats the endless belt,
A drive rotating body that forms the nip portion with the endless belt and rotationally drives the endless belt.
An endothermic rotating body that comes into contact with the driving rotating body and absorbs heat from the driving rotating body,
A contact / detachment mechanism for bringing the endothermic rotating body into contact with the driving rotating body,
Control to control the operation of the contact / detachment mechanism so that the endothermic rotating body comes into contact with the driving rotating body when the first condition is satisfied during the execution of image heat treatment on a plurality of recording materials. Department and
Have,
In the image heat treatment on a plurality of recording materials, single-sided printing is performed in which all the remaining recording materials that are subjected to the image heat treatment after the first condition is satisfied form an image only on the first surface of the recording material. In the case, the control unit brings the endothermic rotating body into contact with the driving rotating body according to the condition that the first condition is satisfied.
In the image heat treatment on a plurality of recording materials, both sides of which the remaining recording materials for which the image heat treatment is executed after the first condition is satisfied form an image on the first surface and the second surface of the recording material. In the case of printing, the control unit hits the drive rotating body with the heat absorbing rotating body so as to satisfy the first condition and the second condition regardless of the size of the remaining recording material. Let me touch
The second condition is
The region of the peripheral surface of the drive rotating body that is in contact with the heat absorbing rotating body first makes the nip portion from the time when the heat absorbing rotating body comes into contact with the driving rotating body until the heat absorbing rotating body makes one rotation. When passing through, the peripheral surface region is characterized in that the nip portion is in contact with the first surface in double-sided printing.

Further, the second aspect of the present invention includes an image forming unit that forms a toner image on a recording material, and an image forming unit.
An endless belt that heats the toner image on the recording material formed by the image forming portion at the nip portion, and
A heating unit that heats the endless belt,
A drive rotating body that forms the nip portion with the endless belt and rotationally drives the endless belt.
An endothermic rotating body that comes into contact with the driving rotating body and absorbs heat from the driving rotating body,
A contact / detachment mechanism for bringing the endothermic rotating body into contact with the driving rotating body,
A control unit that controls the operation of the contact / detachment mechanism,
A reception unit that receives from an operator an instruction of a mode to be executed by the control unit from a plurality of modes including a first mode and a second mode.
Have,
The control unit
In the case where the mode instructed by the reception unit is the first mode, in a standby state in which the endothermic rotating body is separated from the driving rotating body and waits for execution of the image forming process. When the execution command of the image forming process is input, the endothermic rotating body is brought into contact with the driving rotating body as a result of satisfying a predetermined condition after the endless belt starts the image heating process on the recording material. ,
When the mode instructed by the reception unit is the second mode, the image is in a standby state in which the endothermic rotating body is separated from the driving rotating body and waits for execution of the image forming process. When the execution command of the forming process is input, the endothermic rotating body is driven by the driving rotating body until the endless belt starts the image heating process on the recording material regardless of the type of the recording material to be image-formed. It is characterized in that it is brought into contact with.

According to the present invention, it is possible to provide an image forming apparatus capable of suppressing the occurrence of transfer defects due to dew condensation on a heat equalizing roller when performing double-sided printing.

It is a figure which shows an example of an image forming apparatus. It is a figure which shows an example of the fixing device in a state where a heat equalizing roller is separated from a pressure roller. It is a figure which shows the arrangement of the core of the fixing device. It is a figure which shows the cross section of a fixing belt. It is a figure which shows an example of the shape in the longitudinal direction of a pressure roller. It is a figure which shows an example of the structure in the longitudinal direction of a fixing device. It is a figure which shows an example of the fixing device in a state where a soaking roller is in contact with a pressure roller. It is a block diagram which shows the structure which concerns on control. It is a flowchart about control. It is a flowchart about control. It is a timing chart related to control. It is a flowchart about control.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the components described in this embodiment are merely examples, and the present invention is not limited to those described in the embodiments.

[Example 1]
[Image forming device]
The schematic configuration of the image forming apparatus 10000 of this embodiment will be described with reference to FIG. In the following, as an example of the electrophotographic image forming apparatus, a full-color image forming apparatus 10000 having a plurality of photosensitive drums will be described as an example, but the present invention is not limited thereto. For example, it may be a direct transfer type device that directly transfers from the photosensitive drum 200 to the recording material without using the intermediate transfer belt 204 described later, or a device that forms a monochrome toner image (for example, a monochrome machine). There may be. Further, the image forming apparatus 10000 may be a copying machine, a printer, a facsimile apparatus, or a multifunction device having a plurality of these functions.

FIG. 1 is a diagram showing an example of an image forming apparatus. The image forming apparatus 10000 includes an image reading apparatus 300 and a printer unit 400.

The image reading device 300 reads a document placed on the platen glass 302, and the light emitted from the light source 303 is reflected by the document and imaged on the CCD sensor 305 via an optical system member 304 such as a lens. Will be done. By scanning in the direction of the arrow, such an optical system unit converts a document into an electric signal data string for each line. The image signal obtained by the CCD sensor 305 is sent to the printer unit 400, and the control unit 309 performs image processing. The control unit 309 includes a CPU (Central Processing Unit) 1000, and controls the operation of the image forming apparatus 10000.

The image forming apparatus 10000 can also be used as a printer. The control unit 309 can execute image formation based on an image signal input from a print server or the like (not shown) connected via a network.

The printer unit 400 includes a plurality of image forming units Pa, Pb, Pc, and Pd, and each image forming unit performs image formation based on the above-mentioned image signal. That is, the image signal is converted into a laser beam PWM (pulse width modulation control) by the control unit 309. The polygon scanner (exposure apparatus) 310 scans a laser beam according to an image signal. Then, the laser beams are applied to the photosensitive drums 200a to 200d as the image carriers of the image forming portions Pa to Pd.

The image forming unit Pa is an image forming unit that forms a yellow (Y) toner image, and the image forming unit Pb is an image forming unit that forms a magenta (M) toner image. The image forming unit Pc is an image forming unit that forms a cyan (C) toner image, and the image forming unit Pd is an image forming unit that forms a black (Bk) toner image. The arrangement order of the image forming portions Pa to Pd of each color is not limited.

Hereinafter, in order to prevent the description from becoming complicated, the details of the configuration of the image forming unit Pa will be described on behalf of the image forming units Pa to Pd. Since the configurations of the image forming units Pb to Pd are the same as those of the image forming units Pa, detailed description thereof will be omitted.

In the image forming unit Pa, a toner image based on the image signal is formed on the surface of the photosensitive drum (photoreceptor) 200a. The primary charger 201a charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for forming an electrostatic latent image. The laser beam from the polygon scanner 310 forms an electrostatic latent image on the surface of the photosensitive drum 200a charged to a predetermined potential. The developer 202a develops an electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back surface of the intermediate transfer belt (intermediate transfer body) 204, applies a primary transfer bias having the opposite polarity to the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. .. The surface of the photosensitive drum 200a after the primary transfer is cleaned by the cleaner 207a.

Further, the toner image on the intermediate transfer belt 204 is conveyed to the next image forming unit. Toner images of each color formed by the respective image forming portions are sequentially transferred onto the intermediate transfer belt 204 in the order of Y, M, C, and Bk, and four-color images are formed.

The toner image that has passed through the image forming unit Pd is subjected to a secondary transfer electric field having the opposite polarity to the toner image on the intermediate transfer belt 204 in the secondary transfer unit composed of the secondary transfer rollers 205 and 206. Is secondarily transferred to the recording material P.

The recording material P is a sheet-shaped recording medium (media) on which a toner image can be formed by an image forming apparatus. Examples thereof include standard or non-standard plain paper, thin paper, thick paper, high-quality paper, coated paper, envelopes, leaflets, stickers, resin sheets, transparencies, printing papers, format papers and the like. Hereinafter, the recording material may be referred to as paper, but the recording material is not limited to paper. For convenience, the handling of recording materials (sheets) will be explained using terms related to paper such as paper-passing, paper-feeding, paper-discharging, paper-passing, and non-paper-passing parts, but the recording material is not limited to paper. do not have.

The paper P that has been fed is temporarily stopped at the cash register unit 208 provided with the registration roller. The register unit 208 is a timing at which the toner image on the intermediate transfer belt 204 reaches the transfer nip portion so that the toner image on the intermediate transfer belt 204 is transferred to a predetermined position on the paper P at the secondary transfer unit. The paper P is sent out to the transfer nip portion in accordance with the above. The control unit 309 controls the timing at which the cash register unit 208 feeds out the paper P. After that, the toner image on the paper P is fixed on the paper P by the fixing device (image heating device) 500.

In the case of single-sided printing, when the transfer and fixing process (image heat treatment) of the toner image on the first side (first side) is completed, the paper P is discharged to the outside of the machine.

In the case of double-sided printing, when the transfer and fixing process (image heat treatment) of the toner image on the first side (first side) is completed, the paper P is transferred to the reversing portion 210 provided inside the image forming apparatus 10000 after fixing. The front and back of the paper P are reversed. Then, the paper P is transported to the secondary transfer unit again via the transport path 211. The paper P transferred to the secondary transfer unit and transferred with the toner image on the second surface (second surface) is transferred to the fixing device 500. When the toner image on the second surface is fixed on the paper P by the fixing device 500, it is discharged to the outside of the machine.

[Fixing device]
Next, the fixing device 500 of the present embodiment will be described with reference to FIGS. 2 and 3.

In the following description, the longitudinal direction of the fixing device 500 or the members constituting the fixing device 500 is a width direction orthogonal to the transport direction of the recording material in the transport path surface of the recording material. The lateral direction is a direction parallel to the transport direction of the recording material. Regarding the fixing device 500, the front surface is the surface of the fixing device 500 viewed from the recording material inlet side, and the back surface is the surface opposite to the recording material outlet side (recording material outlet side). Further, with respect to the fixing device 500, the left and right are left or right when the fixing device 500 is viewed from the front. The upstream side and the downstream side are the upstream side and the downstream side with respect to the transport direction of the recording material. Further, the maximum heat generation width means the maximum width that maintains the temperature at which the toner image can be fixed to the recording material in the width direction of the fixing belt 1.

First, the schematic configuration of the fixing device 500 will be described with reference to FIG. The fixing device 500 includes a fixing belt (endless belt) 1 which is a heating rotating body for heating a recording material, a pressure roller 2 which is a pressure rotating body (driving rotating body), an induction heating device 100, and a heat equalizing member. It is provided with a heat equalizing roller 9 which is a (heat absorbing rotating body).

The fixing belt 1 is formed in an endless shape, has a metal layer that generates heat when magnetic flux passes through, and heats the recording material at the nip portion N. The pressure roller 2 is arranged so as to be in contact with the outer peripheral surface of the fixing belt 1, forms a nip portion N with the fixing belt 1, and a pressure rotating body that rotates by sandwiching a recording material between the nip portions N. Is. The pressure applying member 3 forms a nip portion N by applying a pressing force between the fixing belt 1 and the pressure roller 2 by a pressure applying mechanism 30 as a pressure applying means described later. The pressure applying member 3 is held by a metal stay 4. Further, a magnetic core 5 (inner core) for concentrating the induced magnetic field on the fixing belt 1 is provided on the induction heating device 100 side of the stay 4 in order to efficiently heat the fixing belt 1.

The induction heating device 100 is a heating source (induction heating means, heating unit) that induces and heats the fixing belt 1. The induction heating device 100 includes an exciting coil 6, a plurality of magnetic cores 7a (outer cores), a power supply device 101 that applies an electric current to the exciting coil, and a control circuit unit 102 that controls the power supply device 101. The exciting coil 6, the power supply device 101, and the control circuit unit 102 constitute a magnetic flux generating means.

The exciting coil 6 is formed by using, for example, a litz wire as an electric wire, making it horizontally long and having a ship bottom shape, and winding it so as to face a part of the peripheral surface and the side surface of the fixing belt 1. As shown in FIG. 3, the plurality of magnetic cores 7a are arranged so as to cover the outside of the exciting coil 6 so that the magnetic flux generated by the exciting coil 6 does not substantially leak to other than the metal layer (conductive layer) of the fixing belt 1. Has been done. Further, the plurality of magnetic cores 7a are arranged side by side in the width direction orthogonal to the transport direction of the recording material at positions facing the fixing belt 1, and guide the magnetic flux generated by the exciting coil 6 to the fixing belt 1. The exciting coil 6 and the plurality of magnetic cores 7a are supported by a mold member 7c formed of an electrically insulating resin. The induction heating device 100 configured in this way is arranged so as to face the outer peripheral surface of the fixing belt 1 with a gap.

In the rotating state of the fixing belt 1, a high frequency current of 20 to 50 kHz is applied to the exciting coil 6 of the induction heating device 100 from the power supply device (exciting circuit) 101. The metal layer (conductive layer) of the fixing belt 1 is induced to generate heat by the magnetic flux generated by the exciting coil 6.

The temperature sensor (temperature detecting element, first temperature detecting means) TH1 is, for example, a thermistor, and is arranged so as to be in contact with the position of the inner peripheral surface of the central portion in the width direction of the fixing belt 1. The temperature sensor TH1 detects the temperature at the center of the fixing belt 1 in the width direction. That is, the temperature sensor TH1 detects the temperature of the fixing belt 1 portion that serves as the paper passing portion through which the recording material passes. The temperature sensor TH1 is attached to the pressure applying member 3 via an elastic support member, and even if the contact surface of the fixing belt 1 undulates or the like, a good contact state is maintained by following the change in position. It is configured to be. The detected temperature information detected by the temperature sensor TH1 is fed back to the control circuit unit 102.

The control circuit unit 102 controls the electric power input from the power supply device 101 to the exciting coil 6 so that the detected temperature input from the temperature sensor TH1 is maintained at a predetermined target temperature (fixing temperature). That is, when the detection temperature of the fixing belt 1 rises to the target temperature, the energization of the exciting coil 6 is cut off. In the present embodiment, the power input to the exciting coil 6 is controlled by changing the frequency of the high-frequency current based on the detection temperature of the temperature sensor TH1 so that the target temperature of the fixing belt 1 becomes constant during the startup of the power supply. The temperature is adjusted (temperature control).

On the other hand, at the widthwise end of the fixing belt 1, a temperature sensor TH2 as a second temperature detecting means is provided in the same configuration as the temperature sensor TH1. The temperature sensor TH2 is arranged at a position, for example, 160 mm from the center of the fixing belt 1 in the width direction. Such a temperature sensor TH2 is preferably near the end of the recording material having the maximum size that can be passed through the fixing device 500, and is preferably in the range of 150 to 165 mm from the center in the width direction of the fixing belt 1.

The fixing belt 1 is driven to rotate by driving the pressurizing roller 2 to rotate by a motor M1 (driving means) controlled by the control circuit unit 102, at least when image formation is executed. Then, it is rotationally driven at a peripheral speed that is substantially the same as the transport speed of the recording material carrying the unfixed toner image transported from the secondary transfer unit. In the case of this embodiment, the motor M1 drives the pressure roller 2 so that the speed on the surface of the pressure roller 2 is, for example, 330 mm / sec. As a result, the surface rotation speed of the fixing belt 1 is also driven to rotate at about 330 mm / sec. At this rotation speed, it is possible to fix 80 full-color images in A4 size and 58 images in A4R size per minute.

Further, in a state where the fixing belt 1 rises to a predetermined fixing temperature and is temperature-controlled, a recording material having an unfixed toner image is guided by a guide member and introduced into the nip portion N. The outer peripheral surface of the fixing belt 1 is in close contact with the surface of the nip portion N on the side having the unfixed toner image of the recording material. The nip portion N sandwiches and conveys the recording material. As a result, the heat of the fixing belt 1 is mainly applied to the unfixed toner image on the recording material, and the unfixed toner image is thermally and pressure-fixed on the surface of the recording material by receiving the pressing force of the nip portion N. The recording material that has passed through the nip portion N is separated from the outer peripheral surface of the fixing belt 1 and conveyed to the outside of the fixing device.

Further, the heat equalizing roller 9 as a heat equalizing member is a metal roller for preventing excessive temperature rise at the end portion of the fixing belt 1 in the longitudinal direction. Details will be described later. Further, the cleaning device 600 is a cleaning member that cleans the soaking roller 9.

Next, the configuration of each part of the fixing device 500 will be described in detail below.

[Fixing belt]
The fixing belt 1 will be described with reference to FIG. The fixing belt 1 has an inner diameter of 30 mm. The fixing belt 1 has a nickel base layer (metal layer) 1a. The thickness of the base layer 1a is 40 μm. A heat-resistant silicone rubber layer is provided as an elastic layer 1b on the outer periphery of the base layer 1a. The thickness of the silicone rubber layer is preferably set within the range of 100 to 1000 μm. In the present embodiment, the thickness of the silicone rubber layer is set to 300 μm in consideration of reducing the heat capacity of the fixing belt 1 to shorten the warm-up time and obtaining a fixing image suitable for fixing a color image. There is. This silicone rubber layer has a hardness of JIS-A of 20 degrees and a thermal conductivity of 0.8 W / mK. Further, on the outer periphery of the elastic layer 1b, a fluororesin layer (for example, PFA or PTFE) is provided as a surface release layer 1c with a thickness of 30 μm.

A resin layer (slippery layer) 1d such as fluororesin or polyimide is provided on the inner surface side of the base layer 1a by 10 to 50 μm in order to reduce sliding friction with the temperature sensor TH1 provided inside the fixing belt 1. You may. In the present embodiment, 20 μm of polyimide is provided as the slippery layer 1d.

As the base layer 1a of the fixing belt 1, iron alloy, copper, silver, or the like can be appropriately selected in addition to nickel. Further, the structure may be such that the metals are laminated on the resin base layer. The thickness of the base layer 1a may be adjusted according to the frequency of the high-frequency current flowing through the exciting coil described later and the magnetic permeability / conductivity of the metal layer, and may be set between about 5 and 200 μm.

[Pressurized roller]
The pressure roller 2 will be described with reference to FIGS. 2 and 5. The pressurizing roller 2 is rotationally driven by a motor M1 as a driving means. Further, the pressure roller 2 is detachably arranged with respect to the fixing belt 1, and is brought into contact with or separated from the fixing belt 1 by the drive of the motor M2. The motors M1 and M2 are connected to the control unit 309, and their operation is controlled by the control unit 309. The outer diameter of the pressure roller 2 is 30 mm. Further, the pressure roller 2 is provided with a silicone rubber layer as an elastic layer on the peripheral surface of an iron alloy core metal having a diameter of 20 mm at the center in the longitudinal direction and a diameter of 19 mm at both ends. Further, the surface of the pressure roller 2 is provided with a fluororesin layer (for example, PFA or PTFE) as a release layer having a thickness of 30 μm. The hardness of the pressure roller 2 at the center in the longitudinal direction is ASK-C 70 ° C. As shown exaggerated in FIG. 5, the pressure roller 2 has an inverted crown shape in which the outer diameter of the end portion is larger than the outer diameter of the center. The amount of crown is 200 μm at the center and the end (position 163.5 mm from the center) of the pressure roller. In addition to the inverted crown shape, the outer diameter shape of the pressure roller 2 may be, for example, a straight shape having substantially the same diameter at the center and the end portion.

[Pressure application mechanism]
The pressure applying mechanism 30 will be described with reference to FIG. The fixing device 500 is provided with fixing flanges 31 at both ends in the width direction of the fixing belt 1. The fixing flange 31 is a regulating member that regulates the movement of the fixing belt 1 in the longitudinal direction and the shape in the circumferential direction. The pressure applying mechanism 30 includes a stay 4, a spring receiving member 9a, and a stay pressure spring 9b. The stay pressure spring 9a includes both ends of a metal stay 4 inserted through the fixing flange 31 and a spring receiving member 9a for the stay fixed to the frame of the fixing device 500. It is provided in an elastically contracted state between the two. Then, the stay pressurizing spring 9b applies pressure to the stay 4 in a direction approaching the pressurizing roller 2.

A pressure applying member 3 is held in the stay 4, and the fixing belt 1 is urged toward the pressure roller 2 via the pressure applying member 3 by the pressure applied to the stay 4, and the stay 4 and the fixing belt 1 A nip portion N is formed between the pressure roller 2 and the pressure roller 2.

The pressure applying member 3 is made of heat-resistant resin, and the stay 4 is made of iron in this embodiment because it needs to have rigidity to apply pressure to the pressure contact portion. The pressure applying member 3 has a crown so that the center protrudes toward the pressure roller 2 side from the end portion, and the amount of the crown is at the center and the end portion (position 163.5 mm from the center) of the pressure applying member 3. It is set to 1.4 mm. Since the base layer of the rotating fixing belt 1 is made of metal, the end portion of the fixing belt 1 is simply received as a means for restricting the deviation in the width direction even in the rotating state. It is sufficient to provide the fixing flange 31 of. This has the advantage that the configuration of the fixing device can be simplified.

[Heat soaking roller and cleaning mechanism]
As shown in FIG. 2, the fixing device 500 of this embodiment is provided with a heat equalizing roller 9 that can be brought into contact with and separated from the pressure roller 2. FIG. 2 shows the fixing device 500 in a state where the heat equalizing roller 9 is separated from the pressure roller 2, and FIG. 7 shows the heat equalizing roller 9 in contact with the pressure roller 2. The state fixing device 500 is shown.

The heat equalizing roller 9 is a roller that can rotate driven by the pressure roller 2, and disperses the heat of the pressure roller 2 in the longitudinal direction by coming into contact with the pressure roller 2. In this embodiment, the heat equalizing roller 9 is driven to rotate by friction on the surface of the pressure roller 2, and is driven to rotate by the pressure roller 2.

It is provided to suppress excessive temperature rise of the fixing belt 1. For example, when image heat treatment is performed on a recording material having a width smaller than the maximum width of the recording material that can be used by the image forming apparatus 10000, the induction heating device 100 also uses the induction heating device 100 to heat the outside of the recording material to be image heat treated in the width direction. The fixing belt 1 is heated. The region at the end of the fixing belt 1 in the longitudinal direction (non-paper-passing region) that does not come into contact with the recording material may rise in temperature because heat is not taken by the recording material. The pressure roller 2 absorbs the temperature rise of the fixing belt 1 other than the paper-passing region, and the heat of the absorbed pressure roller 2 is dispersed by the heat equalizing roller 9, so that the temperature rise of the fixing belt 1 is increased. Suppress.

The soaking roller 9 is preferably made of a material having a thermal conductivity of 100 to 250 ° C. and 100 W / m · K or more and a heat capacity of 100 to 250 ° C. and 3.0 kJ / m 3 · K or less. The material is preferably aluminum, copper or the like. The shaft diameter of the heat equalizing roller 9 is 8 mm, the diameter of the heat equalizing roller is φ20 mm, the length in the longitudinal direction is 300 mm, and the inside is filled with the material. Further, for the purpose of preventing foreign matter such as offset toner and paper dust from adhering to the pressure roller 2, a fluorine coat layer of 10 to 20 μm is provided on the surface layer of the heat equalizing roller 9, or a PFA layer is provided. You may.

The heat equalizing roller 9 is brought into contact with the pressure roller 2 by the contact / detachment mechanism 103. The contact / detachment mechanism 103 has an urging member (not shown). When the heat equalizing roller 9 comes into contact with the pressure roller 2, the heat equalizing roller 9 is urged to the pressure roller 2 by an urging member with a force of 80N. The contact / detachment mechanism 103 is connected to the control unit 309, and its operation is controlled by the control unit 309.

When the heat equalizing roller 9 is in contact with the pressure roller 2 from the start of the start-up control of the fixing device 500 (particularly when the entire fixing device 500 is at room temperature), the heat equalizing roller 9 is fixed via the pressure roller 2. It takes away the heat of the belt 1 and becomes a factor that hinders the high-speed start-up of the fixing device 500. Therefore, normally, the fixing device 500 is separated from the pressurizing roller 2 until the fixing device 500 stores heat to some extent while causing the fixing device 500 to perform an image heat treatment on the recording material. In this embodiment, the control unit 309 is provided with a heat storage counter 1007 (FIG. 8). The heat storage counter 1007 counts up each time the recording material passes through the fixing device 500.

More specifically, in the paper transport direction, a sensor 40 for detecting the passage of the recording material is arranged on the downstream side of the nip portion N. The sensor 40 is connected to the control unit 309, and the control unit 309 acquires the detection result of the sensor 40. When the rear end of the paper passes through the sensor 40, the control unit 309 determines that the paper has passed through the nip unit N and counts up. When the paper size in the transport direction is larger than the A4 size, the heat storage counter 1007 increases by 2 counts per sheet, and when the paper size is A4 size or less, the heat storage counter 1007 increases by 1 count per sheet. When the heat storage counter reaches a predetermined value or more, the control unit 309 controls the contact / detachment mechanism 103 so as to bring the heat equalizing roller 9 into contact with the pressure roller 2. In this embodiment, when the heat storage counter exceeds 25, the control unit 309 controls the contact / detachment mechanism 103 so as to bring the heat equalizing roller 9 into contact with the pressure roller 2.

The heat storage counter 1007 is designed to reduce the number counted at predetermined time intervals when there is no paper passing. Specifically, in the control unit 309, a numerical value obtained by multiplying the elapsed time (seconds) from the end of the image heating process corresponding to the input execution command (for example, copy start) by 0.5 is obtained from the heat storage counter. Subtract. Therefore, when the interval of JOBs (jobs) input to the image forming apparatus 10000 is sufficiently widened, the count-up is started again from zero. Further, when the JOB charging interval is short, the image heat treatment is started while the heat storage counter maintains a certain value. Note that JOB (job) is added with printing condition information such as image data, specified paper P type, basis weight, paper size, number of sheets, number of copies, layout, post-processing, double-sided printing or single-sided printing. It is an image forming instruction (an instruction to execute an image forming process to the image forming units Pa to Pd).

Further, the fixing device 500 has a cleaning device 600 for cleaning toner and paper dust adhering to the surface of the heat equalizing roller 9. The cleaning device 600 includes a web paper 601, two aluminum pipes 602 and 603 for winding the web paper, a cleaning roller 604 of a sponge roller, and a web feeding mechanism 104. Specifically, as the web paper 601, a non-woven fabric made of methane-based aramid fiber or the like can be used. Further, the web paper 601 wound on the 602 side is fed in the direction of arrow A (FIG. 7) by the web feeding mechanism 104, and is wound on the roller on the aluminum pipe 603 side.

When the heat equalizing roller 9 is in contact with the pressure roller 2 and the cleaning device 600, a predetermined amount of web paper is sent each time the recording material passes through the nip portion N. In this embodiment, 0.02 mm of web paper is fed each time the A4 paper passes through the two nip portions N.

[Induction heating device]
The fixing belt 1 and the exciting coil 6 of the induction heating device 100 are kept in a state of electrical insulation by a mold of 0.5 mm. Further, the distance between the fixing belt 1 and the exciting coil 6 is constant at 1.5 mm (the distance between the mold surface and the fixing belt surface is 1.0 mm), and the fixing belt 1 is uniformly heated. As described above, a high frequency current of 20 to 50 kHz is applied to the exciting coil 6, and the base layer 1a of the fixing belt 1 is induced to generate heat. Then, the power input to the exciting coil 6 is controlled by changing the frequency of the high-frequency current based on the detection value of the temperature sensor TH1 so that the temperature becomes constant at 180 ° C., which is the target temperature of the fixing belt 1 at the time of startup. The temperature is adjusted.

Since the induction heating device 100 including the exciting coil 6 is arranged outside the fixing belt 1 which becomes hot, not inside, the temperature of the exciting coil 6 is unlikely to become high. In addition, it is possible to reduce the loss due to Joule heat generation even if a high-frequency current is passed without increasing the electrical resistance, and by arranging the exciting coil 6 outside, the diameter of the fixing belt 1 can be reduced (lower heat capacity). It can be said that it contributes and, by extension, is excellent in energy saving. The warm-up time of the fixing device of the present embodiment has a very low heat capacity. Therefore, for example, when 1200 W is input to the exciting coil 6, the target temperature of 180 ° C. can be reached in about 15 seconds, and the heating operation during standby is unnecessary, so that the power consumption can be suppressed to a very low level.

[Control when the power of the device is turned on or when the image formation job is started]
As shown in FIG. 8, the control unit 309 includes a CPU 1000, a memory 1001, and a heat storage counter 1007.

The operation unit 1002 is a user interface (UI: User Interface) for the operator to input an instruction to the CPU 1000 and the CPU 1000 to display information to the operator. The operation unit 1002 is connected to the control unit 309. The operation unit 1002 functions as a reception unit that receives an image formation mode setting and an input of an instruction from a user (operator, user) to the CPU 1000. In addition, the CPU 1000 notifies the user of the state of the device to the operation unit 1002. The control unit 309 comprehensively controls each mechanism of the image forming apparatus 10000 by the CPU 1000.

The operation unit 1002 includes a main switch (main power supply) M-SW, an input unit (operation panel) 1004 for the operator to input an instruction to the image forming apparatus, and a display unit (display: UI screen) 1005 for displaying information. Has. The input unit 1004 is provided with various operation keys such as a numeric keypad group for inputting numerical values, a print start button, a stop key, and a power saving button. The display unit 1005 is a touch panel type liquid crystal screen, and displays various information such as a paper display on which the paper to be used can be selected, and also displays various operation buttons. Various settings of the operation performed by the image forming apparatus are also input to the control unit 309 by the displayed operation buttons.

Various data for the CPU 1000 to send a command to each control unit are stored in the memory 1001.

The image forming apparatus 10000 starts the fixing apparatus 500 when the main switch M-SW is turned on. If the reserved JOB is input to the control unit 309 during the startup, the image forming process and the fixing process (image heat processing) corresponding to the reserved JOB are started according to the completion of the startup. Further, if the image formation instruction is not input after the main switch M-SW is turned on, the state shifts to the standby state of waiting for the input of the image formation instruction. The image forming apparatus 10000 starts the fixing apparatus 500 when the JOB is thrown in in the standby state.

Further, the start-up of the fixing device 500 means that the fixing device 500 performs the fixing process when the power of the image forming device 10000 is turned on (the main switch M-SW is turned on) or the image forming instruction in the standby state is turned on. It is a preparatory operation to shift to a startable state. Specifically, before the recording material enters the nip portion N, the control unit 309 controls the current applied to the exciting coil to heat the fixing belt 1 so as to reach the target temperature (printable temperature). At the maximum heat generation width, the length in the width direction is 330 mm. Further, the temperature difference within the maximum heat generation width is within ± 15 ° C. The maximum heat generation width indicates the maximum length of the length of the fixing belt 1 that maintains the temperature at which the toner can be fixed to the recording material.

In this embodiment, since the fixing belt 1 has a low heat capacity and an induction heating method is adopted as a heating method for the fixing belt 1, the start-up time of the fixing device 500 is short. In such a fixing device 500, even if the fixing belt 1 reaches the printable temperature and the temperature control is completed, the atmosphere around the fixing belt 1 does not warm so much, and the temperature is adjusted to the environmental temperature to which the image forming apparatus 10000 is exposed. It remains close. As described above, normally, the heat equalizing roller 9 is in a state of being separated from the pressure roller 2 at the time of starting up for the purpose of high-speed warm-up. Therefore, in the start-up operation in which the heat equalizing roller 9 is separated from the pressure roller 2, the heat equalizing roller 9 is hardly heated.

On the other hand, when the paper passing is started after the fixing belt 1 reaches the printable temperature, water vapor is generated from the paper passing through the nip portion N by the fixing process at the nip portion N. Immediately after the fixing device 500 is started up, the members around the nip portion N may cause dew condensation due to the water vapor generated from the paper passing through the nip portion N. This dew condensation becomes more remarkable when the environment in which the image forming apparatus 10000 is exposed is low temperature or when the recording material is left in a high humidity environment.

As the heat equalizing roller 9, a material having good thermal conductivity such as an aluminum alloy is selected in order to enhance the heat equalizing effect of the pressure roller 2 as described above. Therefore, among the fixing devices 500, the soaking roller 9 takes away the heat of the steam in the vicinity as compared with other members made of resin or the like, and dew condensation is more likely to occur.

When the heat storage counter exceeds 25, the control unit 309 brings the heat equalizing roller 9 into contact with the pressure roller 2. When the heat equalizing roller 9 comes into contact with the pressure roller 2 with dew condensation on the heat equalizing roller 9, the moisture adhering to the heat equalizing roller 9 is transferred to the pressurizing roller 2, and this moisture is transferred to the nip portion N. There is a risk of wetting the recording material that passes through.

When the recording material gets wet, the resistance value of the wet part changes (reduces resistance). When the toner image formed on the first surface of the recording material to be printed on both sides is fixed, if the recording material gets wet at the nip portion N, the secondary transfer is performed with a part of the recording material wet. The toner image on the second surface is transferred at the unit. At this time, a change in the resistance value of the paper due to getting wet at the nip portion N may cause a transfer defect, which may be visually recognized as an image defect in the deliverable.

On the other hand, when the recording material to be printed on one side gets wet at the nip portion N, or when the recording material to be printed on both sides gets wet during the fixing process of the toner image formed on the second surface, the nip portion. The recording material that has passed through N is discharged without being conveyed to the secondary transfer unit. Therefore, in these cases, transfer failure due to wetting at the nip portion N does not occur.

Therefore, in the present embodiment, the control unit 309 determines whether the recording material that may get wet due to the contact of the heat equalizing roller 9 with the pressure roller 2 is a recording material that is printed on one side or a recording material that is printed on both sides. to decide. The control unit 309 controls the contact timing of the heat equalizing roller 9 so that the recording material does not get wet during the fixing process of the first surface of the recording material to be printed on both sides.

For example, when the heat equalizing roller 9 is brought into contact with the pressure roller 2 during printing of a double-sided printing JOB (for example, printing on 20 sheets (multiple sheets) of A4 paper by double-sided printing), the control unit 309 is on the second side. The heat equalizing roller 9 is brought into contact with the pressurizing roller 2 at the timing of the fixing process. This avoids the occurrence of image defects.

The control in this embodiment will be described with reference to the flowcharts of FIGS. 9 to 10 and the timing chart of FIG. The control shown in the flowchart is performed by the control unit 309 functioning as the execution unit (control unit) executing the control program stored in the built-in memory 1001.

When the JOB is input in the standby state (S101), that is, when an image formation instruction is input, the control unit 309 starts starting up the fixing device 500 (S102).

The control unit 309 drives the motor M1 to start the rotation of the pressurizing roller 2 and the fixing belt 1 (S103). When the pressure roller 2 and the fixing belt 1 are separated from each other, the motor M2 for attaching and detaching the pressure roller 2 is first driven to pressurize the pressure roller 2 against the fixing belt 1 to form a nip portion N. Let me.

The control unit 309 starts energizing the heater and starts temperature control so that the temperature of the fixing belt 1 becomes 180 ° C. (printable temperature) (S104). Specifically, the control unit 309 issues a command to the control circuit unit 102 and applies a voltage to the exciting coil 6. When the fixing belt 1 reaches 180 ° C. (that is, when the fixing device 500 stands up) (S105 YES), the JOB introduced in S101 is started (S106).

In FIG. 9, although S101 was set to turn on the JOB in the standby state, the fixing device 500 started to start up when the main switch M-SW of the image forming apparatus 10000 was turned on, and the JOB was started up during the start-up. May be adapted when is input.

When the recording material to be image-formed by the input JOB is all-page single-sided printing (single-sided JOB), as shown in S108 to S114, when the value (i) of the heat storage counter 1007 exceeds 25. The control unit 309 brings the heat equalizing roller 9 into contact with the pressure roller 2. In the case of single-sided JOB, since all the remaining pages after the value (i) of the heat storage counter 1007 exceeds 25 are also single-sided printing, the fixing device 500 does not wet the recording material for double-sided printing. Specifically, the control unit 309 passes the paper one by one through the nip portion N of the fixing device 500 (S108), and counts the value (i) of the heat storage counter 1007 each time the paper passes through the nip portion N. Up (S109). When the value (i) of the heat storage counter 1007 exceeds 25 (S111 YES), the control unit 309 controls the contact / detachment mechanism 103 to bring the heat equalizing roller 9 into contact with the pressure roller 2 (S113). When the control unit 309 contacts the heat equalizing roller 9 in response to the value (i) of the heat storage counter 1007 exceeding 25, the control unit 309 contacts the heat equalizing roller 9 with the pressurizing roller 2 until the JOB is completed. Leave it to. Whether or not the JOB is a single-sided JOB is obtained from the print condition information added to the input JOB.

When the JOB is completed (S110 YES), the control unit 309 first turns off the energization of the heater (S114). Then, the rotation of the motor M1 is stopped, and the rotation of the pressure roller 2 and the fixing belt 1 is stopped (S116). When the heat equalizing roller 9 is in contact with the pressure roller 2, the control unit 309 controls the contact / disconnection mechanism 103 to separate the heat equalizing roller 9 from the pressure roller 2 (S118).

On the other hand, in S107, when the input JOB is not a single-sided JOB, that is, when double-sided printing is included, the control unit 309 shifts to S201 (FIG. 10).

The control unit 309 determines the order of the sheets to be conveyed based on the printing condition information of the loaded JOB. The control unit 309 switches the transfer route for each paper so that the toner image on the first surface passes through the nip unit N and then is transferred to the secondary transfer unit again. For example, in this embodiment, when the input JOB is full-page double-sided printing, the first side and the second side alternately pass through the fixing device 500.

The control unit 309 passes the paper one by one through the nip portion N of the fixing device 500 (S201), and counts up the value (i) of the heat storage counter 1007 each time the paper passes through the nip portion N (S202). .. In the case of double-sided printing, the count is increased each time the first side and the second side are fixed.

When the value of the heat storage counter 1007 reaches 25 (S204 YES, S205 NO), the control unit 309 determines whether the paper to be transferred (regioned) from the cash register unit 208 is the first side or the second side. (S206). As an example of the determination method, the control unit 309 counts the order of the sheets to be conveyed, which is determined based on the printing condition information of the inserted JOB, and the number of times the paper is registered from the first sheet of the JOB. From the information, it is determined whether the next sheet is the first side or the second side. The determination method is not limited to this.

When the paper that reaches the cash register next immediately after the heat storage counter value (i) reaches 25 is the second side of double-sided printing (S206), the control unit 309 is at the timing when the paper comes to the fixing device 500. At the same time, the heat equalizing roller 9 is brought into contact with the pressure roller 2 (S207). Here, FIG. 11 shows an example of the contact timing of the heat equalizing roller 9 when the paper A in the drawing is the second side of double-sided printing.

Here, an example of a method for determining the contact timing of the heat equalizing roller 9 in S207 will be shown.

In this embodiment, the speed of the peripheral surface of the pressure roller 2 is about 330 mm / s, and the transport distance from the register portion 208 to the inlet of the nip portion N of the fixing device 500 is 280 mm. Therefore, it takes 0.848 sec for the paper that has reached the register portion 208 to reach the nip portion N from the region. On the other hand, in order to move the heat equalizing roller 9 from the separated state to the contact state, the contacting / separating mechanism 103 is operated, but after the control unit 309 sends an instruction to the contacting / separating mechanism 103, the contact operation of the heat equalizing roller 9 is completed. It has a time of 1 sec. When the paper determined in S206 is the second side of double-sided printing, the control unit 309 immediately operates the contact / detachment mechanism 103 of the heat equalizing roller 9 with the region as a trigger. The contact of the heat equalizing roller 9 is completed when the paper reaches a position about 0.15 sec ahead of the tip of the nip portion N, that is, a position where the tip of the paper is conveyed downstream from the inlet of the nip portion N by about 50 mm. do. In this embodiment, the minimum value of the size of the paper that can be passed by the image forming apparatus 10000 in the transport direction is 182 mm. When the smallest size paper is passed through, when the heat equalizing roller 9 comes into contact with the paper, about 130 mm of paper remains on the upstream side of the nip portion N. When the heat equalizing roller 9 is brought into contact with the paper, the dew condensation on the heat equalizing roller 9 adheres to the paper via the pressurizing roller 2.

Therefore, when the nip portion N sandwiches the paper at the moment when the heat equalizing roller 9 comes into contact with the paper, it is desirable that the paper having a length (L1 + L2) remains at least on the upstream side of the nip portion N.

Here, L1 is the length corresponding to one rotation of the heat equalizing roller (perimeter of the heat equalizing roller 9) after the heat equalizing roller 9 comes into contact with the heat equalizing roller 9. Further, L2 is a state in which the heat equalizing roller 9 is in contact with the pressure roller 2 from the contact position between the heat equalizing roller 9 and the pressure roller 2 to the paper via the pressure roller 2. This is the shortest arc length of the pressurizing roller 2. In this embodiment, the diameter of the heat equalizing roller 9 is φ20 and the diameter of the pressure roller 2 is φ30. Therefore, the value (L1 + L2) obtained by adding the circumference of the heat equalizing roller 9 and the arc length of the pressure roller 2 is about 110 mm. Is.

If the timing at which the control unit 309 issues a contact instruction to the contact / detachment mechanism 103 is set in this way, the toner image on the second side of the double-sided printing paper is fixed regardless of the size of the paper. , The pressure roller 2 comes into contact with the first side of the paper. As a result, the water adhering to the pressure roller 2 is absorbed by the paper. Therefore, it is possible to prevent moisture from adhering to the paper when the first side of the subsequent double-sided printing paper is fixed.

In the determination of S206, when the paper reaching the cash register unit 208 is not the second side of double-sided printing, the control unit 309 brings the heat equalizing roller 9 into contact with the second side of the paper reaching the next side (S206 NO). .. The timing of contact is as described above. That is, when the double-sided JOB is full-page double-sided printing, in the determination of S206, when the paper reaching the cash register unit 208 is the first side of the double-sided printing, the control unit 309 further reaches the second side. Aim at the paper and bring the heat equalizing roller 9 into contact with it.

In this embodiment, when the double-sided JOB includes single-sided printing, the control unit 309 reaches the next even when the paper reaching the cash register unit 208 is the paper for single-sided printing in the determination of S206. The heat equalizing roller 9 is brought into contact with the second side of the paper. However, when single-sided printing is included in the double-sided JOB, if the paper reaching the register unit 208 in the determination of S206 is single-sided printing paper, single-sided printing is performed without waiting for the second side of the double-sided printing paper. The heat equalizing roller 9 may be brought into contact with the paper to be printed. That is, in the determination of S206, only when the paper reaching the register portion 208 is the first side of the double-sided printing, the configuration may be such that the heat equalizing roller 9 is not brought into contact with the paper and the paper returns to S201.

In this embodiment, when the value of the heat storage counter 1007 exceeds 25 through the above-mentioned determination flow, the back surface (the side of the second surface) of the recording material to be printed on both sides is prevented from getting wet during the fixing process of the first surface. The contact timing of the heat equalizing roller 9 is controlled. The threshold value of the heat storage counter 1007 is always set to a value at which the second side of the double-sided printing comes, and the heat equalizing roller 9 is adjusted to the second side of the double-sided printing only by determining whether or not the value of the heat storage counter 1007 exceeds the threshold value. It is difficult to bring them into contact. As described above, the heat storage counter 1007 is designed to reduce the number counted at predetermined time intervals when there is no paper passing. That is, when the JOB ends, the value of the heat storage counter 1007 gradually decreases, so that the initial value of the heat storage counter 1007 when the next JOB starts is not always zero.

In this embodiment, in determining the contact timing of the heat equalizing roller 9 in S207, the contact / separation mechanism 103 is made to start the contact operation of the heat equalizing roller 9 at the timing when the paper of the register portion is sent out (that is, the region). It was used as a trigger. However, the trigger for starting the operation of the contact / detachment mechanism 103 is not limited to this. For example, in order to match the toner image on the intermediate transfer belt 204 with the transfer timing of the paper on which the toner image is transferred, the region and the image writing signals of the image forming units Pa to Pd are synchronized. Therefore, the image writing signal (for example, the image writing signal of the most upstream image forming unit Pa) may be used as a trigger for the operation of bringing the heat equalizing roller 9 into contact.

Further, in this embodiment, the case where the nip portion N sandwiches the paper at the moment when the heat equalizing roller 9 comes into contact with the paper is described as an example, but the contact timing of the heat equalizing roller 9 in S207 is not limited to this. As described above, the dew condensation on the heat equalizing roller 9 is transferred to the paper located at the nip portion N via the pressure roller 2.

That is, it is sufficient that the tip of the paper whose timing should be adjusted rushes into the nip portion N after a time T2 from the moment when the heat equalizing roller 9 comes into contact with the heat soaking roller 9. Then, the nip portion N may sandwich the paper from the time when the time T2 elapses after the soaking roller 9 comes into contact with the heat soaking roller 9 until the time T1 elapses. Here, the paper whose timing should be adjusted is a paper on which dew condensation on the heat equalizing roller 9 should be adhered based on the determination in S206. For example, when the paper determined in S206 is the second side of double-sided printing, that paper. Point to. Further, the time T1 is the time required for the soaking roller 9 to make one rotation in a state of being in contact with the pressure roller 2. The time T2 is the time required for the pressure roller 2 to rotate by the above-mentioned arc length L2.

In other words, it looks like this: From the time when the heat equalizing roller 9 comes into contact with the pressure equalizing roller 2 until the heat equalizing roller 9 makes one rotation (time: T1), the area of the peripheral surface of the pressure equalizing roller 2 in contact with the heat equalizing roller 9 is covered. It is referred to as region X (the arc length of the corresponding pressure roller 2 is L1). When the region X first passes through the nip portion N after the soaking roller 9 comes into contact with the pressure roller 2, the pressure roller 2 passes through the nip portion N while the region X passes through the nip portion N. Contact the paper that should be timed.

It should be noted that the contact timing of the heat equalizing roller 9 in S207 is configured so that the nip portion N exists in the image area of the paper whose timing should be adjusted after time T2 from the moment when the heat equalizing roller 9 contacts. More preferred. With this configuration, it is possible to further suppress the possibility that the tip of the paper whose timing should be adjusted gets wet, resulting in poor separation from the nip portion N. Here, the image region is an region in which a toner image can be formed by the image forming apparatus 10000.

The control unit 309 controls the operation of the contact / detachment mechanism 103 as shown in the flowchart described above. As a result, for example, when the heat storage counter 1007 exceeds 25 during printing of the double-sided printing JOB and the heat equalizing roller 9 is brought into contact with the pressure roller 2, the control unit 309 has a second surface. The heat equalizing rollers 9 are brought into contact with each other at the timing of the fixing process. That is, the control unit 309 sets the contact timing of the heat equalizing roller 9 so that the dew condensation on the heat equalizing roller 9 does not wet the back surface (the side of the second side) during the fixing process of the first side of the paper on which double-sided printing is performed. Control. Since the wet paper is not conveyed to the secondary transfer portion due to the dew condensation on the heat equalizing roller 9, it is possible to suppress the occurrence of transfer defects due to the dew condensation on the heat equalizing roller 9.

[Example 2]
In the first embodiment, the soaking roller 9 is brought into contact with the pressure roller 2 during the execution of the image forming process, and the timing thereof is controlled so that the back surface of the first side of the paper to be printed on both sides is fixed during the fixing process. The (second side) is configured so as not to get wet due to dew condensation on the heat equalizing roller 9.

In the second embodiment, a configuration for suppressing dew condensation on the heat equalizing roller 9 by bringing the heat equalizing roller 9 into contact with the pressure roller 2 before executing the image forming process will be described. Since the configuration of this embodiment is the same as that of the first embodiment except for the control by the control unit 309 as described below, detailed description thereof will be omitted. The same components as those in the first embodiment are designated by the same reference numerals.

The image forming apparatus 10000 of this embodiment includes a service switch for executing a mode for preventing dew condensation. An operator (for example, a user or a serviceman performing maintenance) can operate the operation unit 1002 to set the service switch for dew condensation countermeasures to the ON state. Specifically, when the operator inputs an instruction to display the mode selection screen on the operation unit 1002, the operation unit 1002 can select whether to turn the service switch on or off. Is displayed on the display unit 1005. The operation unit 1002 functions as a reception unit that receives a mode instruction by the operator. The control unit 309 functions as an execution unit that executes the mode instructed by the operator on the display unit 1005.

Here, the mode for preventing dew condensation is a mode in which dew condensation on the heat equalizing roller 9 is suppressed by bringing the heat equalizing roller 9 into contact with the pressure roller 2 before executing the image forming process. When the service switch is set to the ON state, that is, when the dew condensation countermeasure mode is set, the control unit 309 executes this dew condensation countermeasure mode.

Specifically, when the image formation instruction is input in the standby state in which the heat equalizing roller 9 is separated from the pressurizing roller 2 and waits for the input of the image formation instruction, the fixing device 500 accompanying the input of the image formation instruction The soaking roller 9 is brought into contact with the pressure roller 2 during the start-up process. At that time, the control unit 309 nips regardless of the value of the heat storage counter and the material (coated paper, plain paper, etc.) and thickness (thin paper, thick paper, etc.) of the recording material to be image-formed. The heat equalizing roller 9 is brought into contact with the pressure roller 2 before the recording material is passed through the portion N. That is, the control unit 309 keeps the heat equalizing roller 9 in contact with the pressure roller 2 before the recording material is passed through the nip unit N. Then, the recording material is passed through the nip portion N in a state where the heat equalizing roller 9 is in contact with the pressure roller 2. By bringing the heat equalizing roller 9 into contact with the pressure equalizing roller 2 during the start-up of the fixing device 500, the heat of the fixing belt 1 is transferred to the heat equalizing roller 9 via the pressure equalizing roller 2 to heat the heat equalizing roller 9. be able to. As a result, even if water vapor is generated from the paper that has passed through the nip portion N due to the fixing process at the nip portion N, the occurrence of dew condensation on the surface of the heat equalizing roller 9 can be suppressed.

On the other hand, when the service switch is in the off state (that is, the mode for preventing dew condensation is not set), the following occurs. That is, when the image formation instruction is input in the standby state in which the heat equalizing roller 9 is separated from the pressurizing roller 2 and the input of the image formation instruction is awaited, the heat storage counter 1007 exceeds 25. The heat equalizing roller 9 is brought into contact with the pressure roller 2 accordingly.

In the mode for preventing dew condensation, the heat equalizing roller 9 is brought into contact with the pressure roller 2 during the start-up of the fixing device 500. Therefore, when the heat equalizing roller 9 is started up without being brought into contact with the pressure roller 2. There is a possibility that the time required for starting up the fixing device 500 will be longer than that of the fixing device 500. Therefore, the user can select whether or not to execute the mode for preventing dew condensation. It is possible to respond to the user's request that emphasizes the short time from the insertion of the JOB to the output of the first sheet, rather than the countermeasure against the image defect caused by the dew condensation of the heat equalizing roller 9.

FIG. 12 shows a flow chart of control. The control shown in the flowchart is performed by the control unit 309 functioning as the execution unit (control unit) executing the control program stored in the built-in memory 1001.

When the JOB is input in the standby state (S301), that is, when an image formation instruction is input, the control unit 309 starts starting up the fixing device 500 (S302).

The control unit 309 drives the motor M1 to start the rotation of the pressurizing roller 2 and the fixing belt 1 (S303). When the pressure roller 2 and the fixing belt 1 are separated from each other, the motor M2 for attaching and detaching the pressure roller 2 is first driven to pressurize the pressure roller 2 against the fixing belt 1 to form a nip portion N. Let me.

The control unit 309 starts energizing the heater and starts temperature control so that the temperature of the fixing belt 1 becomes 180 ° C. (printable temperature) (S304). Specifically, the control unit 309 issues a command to the control circuit unit 102 and applies a voltage to the exciting coil 6.

When the mode for preventing dew condensation is set (S305 YES), the control unit 309 operates the contact / disconnection mechanism 103 to bring the heat equalizing roller 9 from the separated state to the contacted state. The timing of contact may be before the heater is energized.

When the fixing belt 1 reaches 180 ° C. (that is, when the fixing device 500 stands up) (S307 YES), the JOB introduced in S301 is started (S308). When the dew condensation countermeasure mode is set, the heat of the fixing belt 1 is taken away by the heat equalizing roller 9 via the pressure roller 2, so that the dew condensation countermeasure mode is not set. Compared with the case, the time required for the fixing belt 1 to reach 180 ° C. becomes longer. Further, when the dew condensation countermeasure mode is set, the time for heating the fixing belt 1 is longer than when the dew condensation countermeasure mode is not set in order to raise the temperature of the soaking roller 9. It is more preferable to do so.

When the mode for preventing dew condensation is set, the control unit 309 brings the heat equalizing roller 9 into contact with the pressure roller 2 in S306, and then passes the recording material through the paper while maintaining the contact state. On the other hand, when the mode for preventing dew condensation is not set, the control unit 309 brings the heat equalizing roller 9 into contact with the pressure roller 2 at the timing when the value (i) of the heat storage counter 1007 exceeds 25.

The control unit 309 passes the paper one by one through the nip portion N of the fixing device 500 (S309), and counts up the value (i) of the heat storage counter 1007 each time the paper passes through the nip portion N (S310). .. When the value (i) of the heat storage counter 1007 exceeds 25 (S311 YES), the control unit 309 shifts to S313. If the heat equalizing roller 9 is not in contact with the pressure roller 2 (s313 NO), the control unit 309 controls the contact / detachment mechanism 103 to bring the heat equalizing roller 9 into contact with the pressure roller 2 (S314). When the heat equalizing roller 9 is brought into contact with the value (i) of the heat storage counter 1007 according to the value (i) exceeding 25, the heat equalizing roller 9 is kept in contact with the heat equalizing roller 9 until the JOB is completed. When the mode for preventing dew condensation is set, the heat equalizing roller 9 is already in the contact state in S313 (S313 YES), so that the control unit 309 keeps the contact state as it is.

When the JOB is completed (S311 YES), the control unit 309 shifts to S315.

Since the processes of S315 to S320 are the same as those of S114 to S119 (FIG. 9) of the first embodiment, the description thereof will be omitted.

According to this embodiment, the control unit 309 executes the mode for preventing dew condensation, so that when the JOB is thrown in, the heat equalizing roller 9 comes into contact with the pressure roller 2 before the paper is passed. By bringing the heat equalizing roller 9 into contact with the pressure roller 2 before passing the paper, the temperature of the heat equalizing roller 9 can be raised. As a result, even if water vapor is generated from the paper that has passed through the nip portion N due to the fixing process at the nip portion N, the occurrence of dew condensation on the surface of the heat equalizing roller 9 can be suppressed. Therefore, even when double-sided printing is performed, it is possible to suppress the occurrence of transfer defects due to dew condensation on the heat equalizing roller 9.

[Example 3]
In the configuration of the second embodiment, when the mode for preventing dew condensation is executed, the heat equalizing roller 9 takes away the heat of the fixing belt 1 at the time of starting up, so that the starting up time may become long. Therefore, only in an environment where dew condensation is likely to occur on the heat equalizing roller 9, the heat equalizing roller 9 may be brought into contact with the pressure roller 2 even before the recording material is passed through the nip portion N.

For example, when the mode for preventing dew condensation is set, only when the amount of moisture in the air is equal to or higher than the predetermined amount of moisture, as in the mode for preventing dew condensation in Example 2, the heat is equalized before passing the paper. The roller 9 is brought into contact with the roller 9. Specifically, when the mode for preventing dew condensation is set, when the JOB is turned on in the standby state, the control unit 309 acquires the output of the environment sensor 250 that detects the temperature and the relative humidity. Based on the output of the environment sensor 250, the control unit 309 heats up before passing the paper when the absolute moisture content (moisture content in the air) is equal to or higher than a predetermined moisture content (for example, 10 g / kg or more). The roller 9 is brought into contact with the roller 9. When the absolute water content is less than the predetermined water content, the control unit 309 passes the heat equalizing roller 9 without contacting it, as in the case where the mode for preventing dew condensation is not set in the second embodiment. Start the paper. Since other controls are the same as those in the second embodiment, the description thereof will be omitted. The environment sensor 250 is a sensor installed inside the main body of the image forming apparatus 10000, and detects temperature and relative humidity.

Here, the absolute water content is the mass of water (water vapor) contained in 1 kg of air, and is a value determined from temperature and relative humidity.

The control unit 309 is based on the output of the environment sensor 250, and when the relative humidity (moisture content in the air) is equal to or higher than a predetermined humidity (for example, 50% or higher), the heat equalizing roller 9 is before passing the paper. It may be configured to be in a state of wearing. When the relative humidity is less than the predetermined quality, the control unit 309 passes the paper without contacting the heat equalizing roller 9 as in the case where the mode for preventing dew condensation is not set in the second embodiment. To start. The environment sensor 250 and the control unit 309 function as a detection unit that detects the amount of water in the air.

When the heat equalizing roller 9 is at a low temperature, dew condensation is more likely to occur than when the heat equalizing roller 9 is at a high temperature. Therefore, for example, when the mode for dew condensation countermeasures is set, when the JOB is turned on in the standby state, the control unit 309 describes the above-mentioned when the temperature detected by the environment sensor 250 is equal to or lower than the predetermined temperature. As described above, the heat equalizing roller 9 may be brought into contact with the paper before the paper is passed. When the temperature is equal to or higher than the predetermined temperature, the control unit 309 starts passing the paper without bringing the heat equalizing roller 9 into contact with the heat equalizing roller 9, as in the case where the mode for preventing dew condensation is not set in the second embodiment. do. In this case, the environment sensor 250 functions as a detection unit that detects the temperature.

In addition to the configuration of the second embodiment, the mode of the present embodiment (that is, only in an environment where dew condensation is likely to occur on the heat equalizing roller 9 is equalized before the recording material is passed through the nip portion N. A mode in which the thermal roller 9 is brought into contact with the pressurizing roller 2) may be implemented. That is, the operation unit 1002 does not execute the dew condensation countermeasure mode of the second embodiment, the dew condensation countermeasure mode of the present embodiment 3, the dew condensation countermeasure mode of the second embodiment, or the dew condensation countermeasure mode of the third embodiment. Accepts input of a mode instruction to be executed from a plurality of modes including a mode. The control unit 309 executes the mode instructed by the operation unit 1002.

[Example 4]
In the above Examples 1 to 3, the fixing device 500 is configured to have a heat storage counter 1007 that counts up each time the recording material passes through, but the heat equalizing roller 9 is used as the pressure roller 2 during the image forming process. The trigger to be brought into contact is not limited to this.

For example, the heat storage counter 1007 may be configured to count the time when the fixing belt 1 is heated. More specifically, the heat storage counter 1007 counts the energization time of the induction heating device 100. The control unit 309 brings the heat equalizing roller 9 into contact with the pressure roller 2 during the image forming process, using the time when the fixing belt 1 is heated reaches a predetermined time as a trigger. The time during which the non-paper-passing portion region of the fixing belt 1 is heated may be counted.

Further, for example, based on the output of the temperature sensor TH2, the soaking roller 9 is brought into contact with the pressurizing roller 2 triggered by the temperature of the non-passing portion region of the fixing belt 1 becoming equal to or higher than a predetermined temperature. May be.

[Example 5]
In the above Examples 1 to 4, the fixing device 500 has a configuration in which the induction heating device 100 by the electromagnetic induction method is provided as a heating unit for heating the fixing belt 1, but the present invention is not limited to this.

For example, a heating source (heating portion) such as a halogen heater, a ceramic heater, or an infrared lamp may be provided inside the fixing belt 1. Further, the heating source of the fixing belt 1 may be provided on the outside of the fixing belt 1. Further, a heating source for heating the pressure roller 2 may be further provided.

1 Fixing belt 2 Pressurizing roller 9 Equalizing roller 100 Induction heating device 103 Contact / detachment mechanism 250 Environment sensor 309 Control unit 1002 Operation unit 10000 Image forming device Pa, Pb, Pc, Pd Image forming unit

Claims (16)

An image forming part that forms a toner image on the recording material,
An endless belt that heats the toner image on the recording material formed by the image forming portion at the nip portion, and
A heating unit that heats the endless belt,
A drive rotating body that forms the nip portion with the endless belt and rotationally drives the endless belt.
An endothermic rotating body that comes into contact with the driving rotating body and absorbs heat from the driving rotating body,
A contact / detachment mechanism for bringing the endothermic rotating body into contact with the driving rotating body,
Control to control the operation of the contact / detachment mechanism so that the endothermic rotating body comes into contact with the driving rotating body when the first condition is satisfied during the execution of image heat treatment on a plurality of recording materials. With a part,
In the image heat treatment on a plurality of recording materials, single-sided printing is performed in which all the remaining recording materials that are subjected to the image heat treatment after the first condition is satisfied form an image only on the first surface of the recording material. In the case, the control unit brings the endothermic rotating body into contact with the driving rotating body according to the condition that the first condition is satisfied.
In the image heat treatment on a plurality of recording materials, both sides of which the remaining recording materials for which the image heat treatment is executed after the first condition is satisfied form an image on the first surface and the second surface of the recording material. In the case of printing, the control unit hits the drive rotating body with the heat absorbing rotating body so as to satisfy the first condition and the second condition regardless of the size of the remaining recording material. Let me touch
The second condition is
The region of the peripheral surface of the drive rotating body that is in contact with the heat absorbing rotating body first makes the nip portion from the time when the heat absorbing rotating body comes into contact with the driving rotating body until the heat absorbing rotating body makes one rotation. An image forming apparatus characterized in that, when passing through, the region of the peripheral surface is in contact with the first surface in double-sided printing at the nip portion. The second condition is that when the position of the peripheral surface that first abuts on the drive rotating body first reaches the nip portion, the first surface in double-sided printing is performed at the nip portion. The image forming apparatus according to claim 1, wherein the image forming apparatus is in contact with the image area of the above. When all the remaining recording materials for which the image heat treatment is performed after the first condition is satisfied in the image heat treatment for the plurality of recording materials are double-sided printing, the control unit uses the remaining recording materials. The image forming apparatus according to any one of claims 1 or 2, wherein the timing at which the endothermic rotating body is brought into contact with the driving rotating body is delayed as compared with the case of single-sided printing. The image formation according to any one of claims 1 to 3, wherein the first condition is that the number of recording materials heat-treated at the nip portion reaches a predetermined number. Device. The image forming apparatus according to any one of claims 1 to 3, wherein the first condition is that the temperature of the non-paper-passing portion region of the endless belt is equal to or higher than a predetermined temperature. The image forming apparatus according to any one of claims 1 to 3, wherein the first condition is that the heating time of the endless belt reaches a predetermined time. An image forming part that forms a toner image on the recording material,
An endless belt that heats the toner image on the recording material formed by the image forming portion at the nip portion, and
A heating unit that heats the endless belt,
A drive rotating body that forms the nip portion with the endless belt and rotationally drives the endless belt.
An endothermic rotating body that comes into contact with the driving rotating body and absorbs heat from the driving rotating body,
A contact / detachment mechanism for bringing the endothermic rotating body into contact with the driving rotating body,
A control unit that controls the operation of the contact / detachment mechanism,
A reception unit that receives from an operator an instruction of a mode to be executed by the control unit from a plurality of modes including a first mode and a second mode.
Have,
The control unit
In the case where the mode instructed by the reception unit is the first mode, in a standby state in which the endothermic rotating body is separated from the driving rotating body and waits for execution of the image forming process. When the execution command of the image forming process is input, the endothermic rotating body is brought into contact with the driving rotating body as a result of satisfying a predetermined condition after the endless belt starts the image heating process on the recording material. ,
When the mode instructed by the reception unit is the second mode, the image is in a standby state in which the endothermic rotating body is separated from the driving rotating body and waits for execution of the image forming process. When the execution command of the forming process is input, the endothermic rotating body is driven by the driving rotating body until the endless belt starts the image heating process on the recording material regardless of the type of the recording material to be image-formed. An image forming apparatus characterized in that it is brought into contact with the image forming apparatus. When the mode instructed by the reception unit is the second mode, the control unit is said to be in the standby state from the time when the execution command is input until the image heating process can be started. The image forming apparatus according to claim 7, wherein the heating unit makes the time for heating the endless belt longer than that in the first mode. It has a detector that detects the temperature and relative humidity inside the image forming apparatus.
The reception unit receives from the operator an instruction of a mode to be executed by the control unit from a plurality of modes including the first mode, the second mode, and the third mode.
The control unit depends on the type of recording material to be image-formed when the mode instructed by the reception unit is the third mode and when an execution command for image formation processing is input in the standby state. Instead, it is characterized in that whether or not the endothermic rotating body is brought into contact with the driving rotating body before the endless belt starts the image heat treatment on the recording material is determined based on the result of the detection unit. The image forming apparatus according to any one of claims 7 or 8. The control unit
When the mode instructed by the reception unit is the third mode,
When an execution command for image forming processing is input in the standby state and the relative humidity detected by the detection unit is equal to or higher than a predetermined humidity, the endless image is formed regardless of the type of recording material to be formed. When the heat-absorbing rotating body is brought into contact with the driving rotating body before the belt starts the image heat treatment on the recording material, and the relative humidity detected by the detection unit is less than the predetermined humidity. The claim is characterized in that the heat absorbing rotating body is not brought into contact with the driving rotating body until the endless belt starts the image heat treatment on the recording material regardless of the type of the recording material to be image-formed. Item 9. The image forming apparatus according to Item 9. The control unit
When the mode instructed by the reception unit is the third mode,
When the execution command of the image forming process is input in the standby state, and the amount of water in the air determined based on the detection result of the detection unit is equal to or more than the predetermined amount of water, the recording material to be image-formed. Regardless of the type of air, the heat absorbing rotating body is brought into contact with the driving rotating body until the endless belt starts the image heat treatment on the recording material, and the air is determined based on the detection result of the detecting unit. When the amount of water in the film is less than the predetermined amount of water, the heat absorption rotation is performed until the endless belt starts the image heat treatment on the recording material regardless of the type of recording material to be image-formed. The image forming apparatus according to claim 9, wherein the body is not brought into contact with the drive rotating body. The control unit
When the mode instructed by the reception unit is the third mode,
When an execution command for image formation processing is input in the standby state, and if the temperature detected by the detection unit is lower than a predetermined temperature, the endless belt is used regardless of the type of recording material to be image-formed. When the heat-absorbing rotating body is brought into contact with the driving rotating body before the image heat treatment on the recording material is started, and the temperature detected by the detection unit is equal to or higher than the predetermined temperature, the image is displayed. 9. The present invention is characterized in that the heat absorbing rotating body is not brought into contact with the driving rotating body until the endless belt starts the image heat treatment on the recording material regardless of the type of the recording material to be formed. The image forming apparatus according to. The image according to any one of claims 7 to 12, wherein the predetermined condition is that the number of recording materials continuously heat-treated at the nip portion reaches a predetermined number. Forming device. The image forming apparatus according to any one of claims 7 to 12, wherein the predetermined condition is that the temperature of the non-paper-passing portion region of the endless belt is equal to or higher than the predetermined temperature. The image forming apparatus according to any one of claims 7 to 12, wherein the predetermined condition is such that the heating time of the endless belt reaches a predetermined time. The image forming apparatus according to any one of claims 1 to 15, wherein the heating portion has a coil that generates magnetic flux, and the endless belt has a conductive layer that induces heat generation by magnetic flux.

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