JPH11282296A - Image forming device, fixing device for the image forming device and fixing method for the image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a proper fixing action without executing a complicated control action. SOLUTION: At the post stage of a main fixing device constituted of a fixing roller 10 and a pressure roller 30, an auxiliary fixing device constituted of a heating roller 31 and a press-contact roller 32 is provided and an auxiliary path for fixing 35 leading to the auxiliary fixing device from the main fixing device is arranged so that it can be switched with respect to a path for ejection 33 for advancing a recording medium 12 passed through the main fixing device toward outside by path switching means 350, 36 and 401. The roller 10 is the self-detection type pressure roller constituted so that it is detected by a contact point switch SW that the surface temperature thereof becomes equal to or under the prescribed temperature. Besides, a control means 400 controlling the switching action of the path 33 and the path 35 by the path switching means according as the switch SW is turned on or off is arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, a fixing device for the image forming apparatus, and a fixing method in the image forming apparatus.

[0002]

2. Description of the Related Art An electrostatic latent image is formed on a photoconductive photoreceptor,
Image forming apparatuses that develop a toner image by developing this electrostatic latent image and transfer and fix the obtained toner image to a sheet-shaped recording medium include analog and digital copying apparatuses and laser printers. Is widely known as various optical printers. As a fixing method for fixing a toner image on a sheet-shaped recording medium, a sheet-shaped recording medium on which a toner image is formed is formed by a fixing roller having a heat source for heating therein, and a pressure roller cooperating with the fixing roller. In general, a contact fixing method of fixing a toner image to a recording medium by applying heat and pressure to the recording medium and the toner image while nipping and transporting the toner image with the fixing roller side. In such a contact fixing method, when the fixing temperature is low, the toner image is in an insufficient fixing state. In order to realize a temperature range in which the fixing is properly performed in the fixing unit, the temperature of the fixing roller or the pressure roller is detected. Temperature detection is usually performed using a thermosensitive element such as a thermistor, but there are many restrictions on the arrangement position and the like. The inventor has previously proposed a fixing device in which when the surface temperature of the pressure roller that is in pressure contact with the fixing roller decreases by a predetermined temperature, the pressure roller itself can detect the fact that the temperature has dropped (Japanese Patent Application No. 2002-214,009). Hei 9-271487
No., Japanese Patent Application No. 10-34769). The pressure roller is hereinafter referred to as a “self-detection pressure roller”. Also in this fixing device, when the surface temperature of the self-detection type pressure roller is reduced to a certain degree or more, the fixing ability is also reduced. Therefore, some measure for covering the decrease in the fixing ability is required.

[0003]

SUMMARY OF THE INVENTION The present invention compensates for a decrease in fixing ability due to a decrease in the surface temperature of a pressure roller in a fixing device using a self-detection type pressure roller, thereby enabling satisfactory fixing. That is the task.

[0004]

According to the fixing device of the image forming apparatus of the present invention, a sheet-shaped recording medium having a toner image formed thereon is fixed to a fixing roller having a heat source for heating, and a fixing device cooperating with the fixing roller. The fixing device fixes the toner image on the recording medium by applying heat and pressure to the recording medium and the toner image while nipping and conveying the toner image with the pressure roller on the side of the fixing roller. A self-detection type pressure roller is used as the roller. The heat source for heating the fixing roller in the fixing device may be provided inside the fixing roller, may be provided outside the fixing roller, or may be provided “inside and outside” of the fixing roller. The “self-detection type pressure roller” includes a core roller having at least a part of its surface being conductive, and an external member surrounding at least part of the inner peripheral surface of the deformable hollow cylinder which is made conductive. The roller has an electrically insulating spacer for forming a gap between the core roller and the external roller, and gas is sealed and sealed at a predetermined pressure in the gap, and the surface temperature of the pressure roller is reduced. The temperature lower than the predetermined temperature is detected by a contact switch having a contact point between the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the outer roller.
The phrase “the hollow cylinder in the outer roller is“ deformable ”” means that the hollow cylinder is elastically deformed with the gas sealed therein as a cushion. The fixed toner image may be a “single color toner image” or a “multicolor toner image”
Or a “color toner image”.

[0005] "When the contact switch is turned on" means that the surface temperature of the pressure roller falls below a predetermined temperature. It is possible to deal with it.

The fixing device of the image forming apparatus according to the first aspect of the present invention includes a "main fixing device" including a fixing roller and a self-detecting pressure roller, an auxiliary fixing device, an auxiliary fixing passage, and a passage switch. Means and control means.
The “auxiliary fixing device” includes a heating roller and a pressure roller, and is disposed downstream of a fixing device including a fixing roller and a (self-detecting) pressure roller. The “auxiliary fixing passage” is a passage for moving the recording medium from the main fixing device to the auxiliary fixing device, and is opposed to a regular discharge passage (for making the recording medium passing through the main fixing device to the outside). Can be switched. "Path switching means" is a means for switching the path between the normal discharge path and the auxiliary fixing path. The "control means" controls the path switching of the recording medium by the path switching means based on ON / OFF of the contact switch. When the passage is switched to the auxiliary fixing passage, the recording medium is fixed by a fixing unit (a portion where fixing is performed by a fixing roller and a pressure roller; the same applies hereinafter), and then further supplemented by a heating roller and a pressure roller. Is done.
The "heating roller" in the auxiliary fixing device may be the same as a conventionally known fixing roller, and is always temperature-controlled to "a temperature at which auxiliary fixing is possible". "Pressing roller"
May be the same as a normal pressure roller generally used in a conventionally known fixing device.

According to a second aspect of the present invention, there is provided a fixing device for an image forming apparatus, comprising an auxiliary fixing device and a heat source control means in addition to the main fixing device. The "auxiliary fixing device" is constituted by a heat roller and a pressure roller which are immediately heated. The term “immediate heat” refers to a heat roller having a small heat capacity and capable of achieving a desired heating temperature in a short time by heating. In order to achieve the desired temperature in a shorter time, the heating roller with immediate heat may be always preheated to an appropriate temperature, and may be heated to a desired heating temperature as needed. The "heat source control means" is a means for controlling the heat source of the heating roller of the immediate heating, and controls the heating of the heating roller of the immediate heating based on ON / OFF of the contact switch. In the case of the invention described in claim 1, an auxiliary fixing passage and a regular discharge passage are required, and the heating roller in the auxiliary fixing device needs to be "always" heated and controlled to a temperature necessary for auxiliary fixing. According to the second aspect of the present invention, the auxiliary fixing device can be provided on the "regular discharge passage", so that the regular discharge passage also serves as the auxiliary fixing passage, and there is no need to switch the passage, and the heating of the heating roller is also possible. Since it is sufficient to perform the fixing only when the auxiliary fixing is performed, the energy required for heating the heating roller is smaller than that of the first aspect.

According to a third aspect of the present invention, there is provided a fixing device for an image forming apparatus, comprising a transport direction switching unit and a control unit.
The “conveying direction switching unit” is a unit that switches the conveying direction of the recording medium in the recording medium conveying path including at least the fixing unit. "Control means" is based on the ON / OFF of the contact switch,
Controls the switching of the recording medium conveyance direction. When the transport direction of the recording medium is switched in the reverse direction, the recording medium passes through the fixing unit and then passes through the fixing unit in the reverse direction to perform re-fixing. In the case of the third aspect of the present invention, the recording medium whose conveyance direction has been switched and which has passed through the fixing unit again is located in front of the fixing unit when viewed from the normal conveyance direction. The recording medium in such a state may be further passed through the fixing unit and discharged to the outside, but may be switched to a regular recording medium conveyance path,
In addition to providing a second discharge conveyance path that directs the recording medium that has passed through the fixing unit in the opposite direction to the outside, a conveyance path switching unit that switches between a regular conveyance path and a second discharge conveyance path is provided, and the control unit includes: Switching the normal recording medium transport path to the second discharge transport path by transport path switching means in accordance with the switching of the transport direction of the recording medium ", the toner image-fixed recording medium is transferred to the second discharge transport path. Alternatively, it may be discharged to the outside through the device (claim 4). The fixing device of the image forming apparatus according to the fifth aspect includes:
It has a transport path switching unit and a control unit. The “return transport path” is a transport path that is provided in addition to the regular recording medium transport path that passes through the fixing unit by the fixing roller and the pressure roller, and that returns the recording medium that has passed through the fixing unit to the fixing unit again. Are formed in a loop shape including a fixing portion. "Conveyance path switching means" is means for switching the recording medium conveyance path between a regular recording medium conveyance path and a return conveyance path. The "control means" controls switching of the transport path by the transport path switching means based on ON / OFF of the contact switch. When the transport path is switched to the return transport path, the recording medium that has passed through the fixing unit returns to the fixing unit again and is fixed again.

In the fixing device for an image forming apparatus according to any one of claims 1 to 5, the core roller of the pressure roller is a "metal roller", and the external roller is an inner peripheral surface of a deformable hollow cylinder. Wherein a deformable thin metal layer is formed on at least a part of the above (claim 6). The “gas sealed and sealed in the gap between the core roller and the external roller” of the pressure roller may be air, but may be an “inert gas” such as an argon gas or a helium gas. ). When the filling gas is an inert gas, the metal constituting the conductive portion of the core roller or the external roller does not chemically change even when the temperature rises.

An image forming apparatus according to the present invention includes a photoconductive photoreceptor, a unit for forming an electrostatic latent image on the photoreceptor, and a developing unit for developing the formed electrostatic latent image to form a toner image. When,
A transfer unit that transfers the toner image formed on the photoconductor directly to a sheet-shaped recording medium or via an intermediate transfer medium; and a fixing unit that fixes the toner image transferred to the recording medium to the recording medium. An image forming apparatus, wherein the fixing device according to any one of claims 1 to 7 is used as a fixing unit (claim 8).

The fixing method in the image forming apparatus according to the present invention is directed to a photoconductive photoreceptor, a unit for forming an electrostatic latent image on the photoreceptor, and a toner image formed by developing the formed electrostatic latent image. Developing means, a transfer means for transferring the toner image formed on the photoreceptor directly to a sheet-like recording medium or via an intermediate transfer medium, and fixing the toner image transferred to the recording medium to the recording medium The fixing device according to any one of claims 1 to 7, wherein fixing is started by setting the surface temperatures of the fixing roller and the pressure roller to a predetermined fixing temperature. When the surface temperature of the pressure roller drops by a predetermined temperature, auxiliary fixing by the auxiliary fixing device or re-transfer by the transport direction switching or transport path switching means is performed based on ON / OFF of a contact switch of the pressure roller. Controlling the execution of the call "it, characterized in (Claim 9). As the "control means" or "heat source control means", a microcomputer or a dedicated CPU can be used.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of a specific embodiment, fixing by a fixing roller and a self-detection type pressure roller will be briefly described. In FIG. 1A, reference numeral 10 denotes a fixing roller, and reference numeral 30 denotes a pressure roller. The fixing roller 10 includes the heat source 1 for heating inside the hollow roller 2. The hollow roller 2 is formed by forming a thin layer of a material having good releasability, such as Teflon (registered trademark, DuPont), on the outer peripheral surface of a hollow metal roller to prevent toner adhesion. The hollow metal roller is formed of a material having high thermal conductivity so as to have “rigidity so as not to be deformed by pressing of the pressure roller 30”. That is, the metal roller is preferably as thin as possible (about 1 to 1.5 mm) so that a uniform fixing temperature is quickly achieved by the heat source 1 for heating. (A "dent" or "axial deflection") is required, and aluminum, stainless steel or the like is suitable as a material.

The heating heat source 1 is for giving a fixing temperature to the hollow roller 2, and various heaters such as a resistance heating wire, an infrared lamp and the like can be used, and a halogen lamp can be suitably used. The heating heat source 1 has substantially the same length as the hollow roller 2 so that the hollow roller 2 can be uniformly heated in the longitudinal direction (the direction perpendicular to the drawing), and the heating region extends over the entire longitudinal direction of the hollow roller 2. Will be deployed as
In addition, in order to prevent a temperature drop at the both ends of the hollow roller 2 due to heat radiation at both ends in the longitudinal direction, the calorific value of the heating heat source 1 is set to be larger at both ends in the longitudinal direction than at the center. I have. In the following description, for the sake of specificity, it is assumed that the heating heat source 1 is a “halogen lamp”.

The surface temperature of the fixing roller 10 is detected by temperature detecting means (not shown) (such as a thermistor), and the heat generation of the heating heat source 1 is controlled based on the detected temperature. This heat generation control is such control that “the surface temperature of the fixing roller 10 is controlled within a predetermined temperature range”. The pressure roller 30 includes a core roller 3, an external roller 4, and a spacer 5.
1 to 54. The core roller 3 must be “at least part of the surface is conductive”. In this example, the “conductivity condition” is satisfied by using the new roller 3 itself as a metal roller. As another example, a metal layer may be formed on (at least part of) the peripheral surface of a roller made of a hard plastic or the like by vapor deposition or the like to make “at least a part of the surface conductive”. The outer roller 4 surrounding the core roller 3 needs to be "conductive at least a part of the inner peripheral surface of the deformable hollow cylinder". In this example, the above-described condition "at least a part of the inner peripheral surface is made conductive" is satisfied by forming the metal layer 41 on the inner peripheral surface of the hollow cylinder made of an elastic material having a thickness of about 3 mm. Various rubber materials can be used as the elastic material constituting the external roller 4, but in this embodiment, silicone rubber is used as a suitable elastic material. Also,
The metal layer 41 is formed as a thin layer (about 1 to 2 μm) by sputtering or the like so as not to hinder the deformation of the external roller 4. Other methods for making at least a portion of the inner peripheral surface of the outer roller conductive include a method in which carbon particles or the like are dispersed and contained in a desired portion of the outer roller inner peripheral surface, or a method in which the inner peripheral surface is coated with metal. A method of attaching a tape or the like is conceivable.

The spacers 51 to 54 are for maintaining a gap 42 having a predetermined size (about 1 to 2 mm) between the core roller 3 and the external roller 4, and have a diameter substantially equal to that of the gap 42. It has a columnar shape. In this embodiment, the number of spacers is four. However, five or more spacers may be used, or only three spacers may be used. In this embodiment, the spacer 5
Although a material made of "soft and elastic sponge" is used as 1 to 54, the material is not limited to this and may be made of a hard plastic or the like. Gas is sealed and sealed at "predetermined pressure" in the gap 42 between the core roller 3 and the external roller 4 maintained by the spacers 51 to 54. The "gas" to be enclosed and sealed in this example is an "inert gas" such as an argon gas. The core roller 3 and the metal layer 41 constitute a "contact switch that is turned on / off by contact / separation".

The pressure of the inert gas sealed in the gap 42 between the core roller 3 and the external roller 4 of the pressure roller 30 changes depending on the temperature of the gas. Since the external roller 4 of the pressure roller 30 is deformable, when the pressure roller 30 is pressed against the fixing roller 10, the external roller 4 (elastic material in the example being described) is elastically deformed at the pressed portion. To form a "nip". The inert gas sealed and sealed in the gap 42 acts as a cushion against the pressure contact force, and the “nip width (nip width)” formed at the pressure contact portion between the fixing roller 10 and the pressure roller 30 is the inert gas. Changes depending on the pressure. That is, if the pressure of the inert gas is high, the nip width becomes small, and the nip width becomes large as the pressure decreases. The state in which the fixing roller 10 and the pressure roller 30 can start fixing is referred to as a “reference state”. In this reference state, both the fixing roller 10 and the pressure roller 30 have a surface temperature within a predetermined temperature range, and have a nip width for performing proper fixing. The pressure of the inert gas sealed in the gap 42 of the pressure roller 30 is adjusted in advance so as to realize “a nip width for performing proper fixing” in the reference state.

A sheet-shaped recording medium (normal transfer paper or an OHP sheet for an overhead projector) 12 on which a toner image TI is formed is guided by a guide 11 to a fixing roller 1.
The toner image TI is fixed by being guided by the nip portion between the pressure roller 30 and the pressure roller 30 and applied with heat and pressure while being nipped and conveyed by the fixing roller 10 and the pressure roller 30.

When the fixing is performed, the heat of the fixing roller 10 and the pressure roller 30 is taken by the recording medium and the toner image as fixing heat, so that the temperature of the pressure roller 30 decreases (the surface of the fixing roller 10). The temperature is detected by the above-mentioned temperature detecting means (not shown), and based on the detected temperature, is controlled to a predetermined temperature range by heating control by the heating heat source 1 by a temperature control circuit (not shown). Pressure roller 3
When the temperature of 0 becomes lower than a certain temperature, fixing failure occurs.
When the temperature of the pressure roller 30 decreases, the pressure of the inert gas sealed in the gap 42 decreases, and the cushion effect decreases. Since the reduction in the cushioning effect causes an increase in the nip width, even if the temperature of the pressure roller 30 decreases to some extent, the effect is compensated by the increase in the nip width. When the temperature of the pressure roller 30 further decreases, FIG.
As shown in (b), the outer roller 4 is deformed, and the metal layer 41 on the inner peripheral surface thereof comes into contact with the core roller 3 to turn on the “contact switch”. FIG. 2 is a diagram for explaining one embodiment of the invention described in claim 1.

A fixing roller denoted by reference numeral 10 and a fixing roller denoted by reference numeral 30
The pressurized roller indicated by is the same as that described with reference to FIG. 1.
Contact switch that is turned on and off by contacting with and separating from the switch.
The temperature at which the contact switch SW is turned on is set in such a state that a sufficient fixing operation of about one recording medium can be performed in this state. Reference numeral 31 denotes a heating roller, and reference numeral 32 denotes a pressing roller. These heating roller 31 and pressing roller 32
Constitutes an "auxiliary fixing device".

Reference numeral 33 denotes a discharge passage for discharging the recording medium, on which the toner image has been fixed by the “main fixing device” including the fixing roller 10 and the pressure roller 30, to the outside, and reference numeral 34 denotes a discharge passage 33. 1 shows a discharge roller provided in the printer. In a normal fixing operation, proper fixing is performed in a fixing unit of the main fixing device, and the recording medium on which the toner image is fixed is discharged to the outside through a discharge passage 33. Reference numeral 35 denotes an “auxiliary fixing passage”. The “path switching device including the spring 350 and the solenoid 36” constitutes “path switching means” together with the driver 401, and the driver 401 drives the solenoid 36 of the “path switching device” so that the discharge passage 33 and the auxiliary fixing passage 35 are driven. And can be switched. That is, in a normal state, the solenoid 36 is not driven, and in this state, the entrance B of the discharge passage 33 is located on the exit side of the fixing unit.
When the driver 401 drives the solenoid 36, the spring 350 is pulled by the solenoid, the entrance sides of the discharge passage 33 and the auxiliary fixing passage 35 move downward, and the entrance A of the auxiliary fixing passage 35 is fixed as shown in the figure. Located on the exit side of the unit. Accordingly, when the fixing is performed in this state, the recording medium fixed by the fixing unit is sent to the auxiliary fixing device through the auxiliary fixing passage 35, and after being subjected to the auxiliary fixing, to the outside through another discharge passage (not shown). Is discharged. When the contact switch SW of the pressure roller 30 is turned on, the control unit 400 receives the
1 controls the driving of the solenoid 36. Control means 4
00 is a microcomputer or the like.

FIG. 3 is a flowchart for explaining a fixing procedure in the embodiment shown in FIG. After the fixing is started, when the contact switch is turned on, the control means 400 receives this and determines whether or not "switching is possible" in step S1.
To judge. The case where “switching is not possible” is a case where the fixing by the fixing device is currently in progress and the leading end of the recording medium that has passed the fixing unit has already entered the discharge passage 33. In such a state, the passage cannot be switched. As described above, even when the contact switch is turned on, the fixing device still has enough room for fixing “one recording medium” satisfactorily. The fixing of the recording medium that has been performed is executed as it is, and the recording medium on which the toner image is fixed is discharged to the outside through the discharge passage 33. In this way, when the recording medium that has been fixed has passed through the fixing unit (this can be detected by disposing a detector such as a photocoupler at the exit side of the fixing unit), or the contact switch is turned on. If the recording medium is not present in the fixing unit at this point, the state is "switchable", and in this state, the control unit determines whether or not the path needs to be switched (step: S
2). The case of “switching unnecessary” is a case where there is no recording medium on which the toner image is to be fixed. In such a case, it is not necessary to switch the passage, so that the fixing is terminated. Conversely, when there is a recording medium that requires fixing, it is “switching required”,
In this case, the driver 36 drives the solenoid 36 to switch the passage from the discharge passage 33 to the auxiliary fixing passage 35 (step: S3). Therefore, after the recording medium is subjected to (incomplete) fixing by the fixing unit, the auxiliary fixing passage 3
5, the toner image is completely fixed by the auxiliary fixing (step: S4), and is discharged to the outside. Thereafter, it is determined whether to continue or end the fixing (whether there is a recording medium requiring fixing) (step: S5). If there is a subsequent recording medium, the fixing process of performing auxiliary fixing is repeated. If there is no recording medium on which the toner image is to be fixed, the fixing is terminated.

That is, the fixing device described in the embodiment with reference to FIGS. 2 and 3 uses the fixing roller 10 having a heat source for heating to transfer the sheet-shaped recording medium 12 on which the toner image TI is formed.
And the pressure roller 30 cooperating with the fixing roller,
A fixing device for fixing a toner image to a recording medium by applying heat and pressure to the recording medium and the toner image while nipping and conveying the toner image on the side of the fixing roller.
An auxiliary fixing device including a heating roller 31 and a pressing roller 32 is provided at a stage subsequent to the main fixing device including the pressure roller 30 and the pressure roller 30.
An auxiliary fixing passage 35 from the main fixing device to the auxiliary fixing device is provided so as to be switchable by passage switching means 350, 36, and 401 with respect to the discharge passage 33 that directs the pressure roller 2 to the outside. Is configured to detect that the surface temperature has become equal to or lower than a predetermined temperature by the contact switch SW,
Control means 400 is provided for controlling switching between the discharge path 33 and the auxiliary fixing path 35 by the path switching means 350 and 401 based on the ON / OFF of the contact switch.

FIG. 4 is a diagram for explaining an embodiment of the invention described in claim 4.

A fixing roller denoted by reference numeral 10 and a fixing roller denoted by reference numeral 30
The pressurized roller indicated by is the same as that described with reference to FIG. 1.
This is a contact switch that is turned on and off by contact and separation with the switch. Reference numeral 31A denotes a heating roller, and reference numeral 32 denotes a pressing roller.
The heating roller 31A and the pressure roller 32 constitute an "auxiliary fixing device". The passage 35A is a discharge passage, and can discharge the recording medium to the outside via the auxiliary fixing device. The fixing roller 10 and the pressure roller 30 constituting the “main fixing device” have been described with reference to FIG. The heating roller 31A is “immediately heat” and has a built-in heat source, and the heat source driver 403 causes the heat source to generate heat, thereby quickly raising the temperature to the temperature required for auxiliary fixing.
I do. The heat source driver 403 is controlled by control means 400 such as a microcomputer. The heat source driver 403 and the control means 400 constitute "heat source control means".

FIG. 5 is a flowchart for explaining the fixing procedure in the embodiment shown in FIG. When the contact switch is turned on after the fixing is started, the control means 400 receives this, and first determines in step S1A whether or not "heating is required". "No heating required" means
This is the case where the last recording medium requiring fixing is currently being fixed in the fixing device or has passed through the fixing unit. Even in the state where the contact switch is turned on, the fixing device still has a margin enough to perform the fixing of “one recording medium” satisfactorily. There is no need to perform auxiliary fixing. At the time when the contact switch SW is turned on, if there is a subsequent recording medium that needs fixing, it is “heating required”, so the control means 400 causes the heating source of the heating roller 31A to be heated by the heating driver 403. The heating roller 31A is heated (step: S2A), so that the auxiliary fixing device can perform auxiliary fixing. At this time, after the subsequent recording medium has undergone insufficient fixing by the fixing unit, it is auxiliary fixed by the auxiliary fixing device,
The toner image is completely fixed and is discharged to the outside.

Thereafter, "whether heating is necessary" is determined based on whether there is a recording medium requiring fixing (step: S).
1A) If there is a subsequent recording medium, the fixing process of performing auxiliary fixing is repeated, and if there is no recording medium on which the toner image is to be fixed, the fixing is terminated.

That is, the fixing device described in the embodiment with reference to FIGS. 4 and 5 applies a fixing roller 10 having a heat source for heating to a sheet-shaped recording medium 12 on which a toner image TI is formed.
And the pressure roller 30 cooperating with the fixing roller,
A fixing device for fixing the toner image TI to the recording medium 12 by applying heat and pressure to the recording medium and the toner image while nipping and transporting the toner image on the side of the fixing roller. Subsequent to the main fixing device with the pressure roller 30, an auxiliary fixing device with a heating roller 31 </ b> A and a pressing roller 32 are provided, and heat source control means 400 and 4 for controlling the heat source of the heating roller 31 </ b> A.
The pressure roller 30 is a “self-detection type pressure roller”, and is configured to detect that the surface temperature has become equal to or lower than a predetermined temperature by a contact switch SW. The heating control of the heat roller 31A with the immediate heat by the heat source control means 400 and 403 is performed based on ON / OFF (claim 2). In addition,
In the case of the second aspect of the invention, the temperature at which the contact switch of the pressure roller is turned on can be set to "the temperature just before the appropriate fixing can be performed". In this case, if the contact switch is turned on in the middle of fixing, fixing failure may occur after that point. The heating of the heating roller 31A is started in order to enable the auxiliary fixing by the fixing device.

In the invention described below, the temperature at which the contact switch of the pressure roller is turned on is set to "the temperature just before the appropriate fixing is possible". FIG. 6 shows a fixing device according to a third embodiment of the present invention. Fixing roller 10
, A pressure roller 30, and a transport roller 3 at a subsequent stage thereof.
4A is driven to rotate by a driving device 300. The driving device 300 can reverse the rotation direction of each roller under the control of the control means 400. In addition to the “regular” recording medium transport passage 35A for guiding the recording medium 12 to the regular entrance side of the fixing unit,
Are provided, and the transfer paths 35A,
35B includes a spring 351, a solenoid 36A, and a driver 4
01 can be switched by “transportation path switching means”. FIG. 7 is a flowchart showing a fixing procedure in the embodiment of FIG. After the fixing is started, when the contact switch SW is turned on, the microcomputer as the control means 400 receives this, and determines whether or not "switchable" in step S1B. The case where “switching is not possible” is the case where “fixing is currently being performed in the fixing unit”, and in this case, it is waited for the recording medium actually present in the fixing unit to pass through the fixing unit (fixing unit exit portion And a detector such as a photocoupler can be disposed in this state), and when the state becomes "switchable", switching is performed (step: S2B). This "switching" is performed by reversing the rotation direction of the fixing roller 10, the pressure roller 30, and the transport roller 34A by the driving device 300, and driving the solenoid 36A by the driver 401 to move the second discharge and transport to the fixing unit entrance side. This is executed by positioning the entrance a of the road 35B.

Then, the recording medium 12 having the toner image TI in an incompletely fixed state is conveyed in a direction opposite to that of the recording medium 12, and is completely fixed by passing through the fixing section again. It is discharged to the outside through the transport path 35B. During this time, the control unit 400 receives the output of a sensor (not shown) (provided in the second discharge conveyance path 35B and detects whether or not the recording medium on which the toner image has been re-fixed has passed through the fixing unit). It is determined whether or not "re-switching is possible" (step: S3B). When a state of “re-switching possible” (a state in which the recording medium that has undergone re-fixing has passed through the fixing unit) is detected, re-switching is performed (step: S4B), and the driving device 300 normalizes the conveyance direction of the recording medium. And the exit b of the regular conveyance path 35A is positioned at the entrance of the fixing unit. Thereafter, it is determined whether or not the fixing can be completed. If there is a subsequent recording medium, the above fixing process is repeated, and if the fixing can be completed, the process is terminated.

That is, the fixing device described in the embodiment with reference to FIGS. 6 and 7 applies a fixing roller 10 having a heat source for heating to a sheet-shaped recording medium 12 on which a toner image TI is formed.
And the pressure roller 30 cooperating with the fixing roller,
A fixing device for fixing a toner image TI to a recording medium 12 by applying heat and pressure to the recording medium and the toner image while nipping and conveying the toner image with the fixing roller side, the recording medium including at least a fixing unit In the conveyance path portion, conveyance direction switching means 300 for switching the conveyance direction of the recording medium 12 between normal and reverse directions is provided, and the pressure roller 30 is a “self-detection type pressure roller”, and the surface temperature has become equal to or lower than a predetermined temperature. This is detected by the contact switch SW, and the control means 400 controls switching of the transport direction of the recording medium 12 by the transport direction switching means 300 based on ON / OFF of the contact switch SW. Item 3): a second recording medium 12 that can be switched with respect to the normal recording medium conveyance path 35A and causes the recording medium 12 that has passed through the fixing unit in the reverse direction to go outside. It has a discharge conveyance path 35B, and conveyance path switching means 351, 36A, and 401 for switching between the normal conveyance path 35A and the second discharge conveyance path 35B, and the control means 400 controls the conveyance direction of the recording medium 12 according to the switching. The transport path switching means switches the normal recording medium transport path 35A to the second discharge transport path 35B (claim 4).

FIG. 8 shows an embodiment of the fixing device according to the fifth aspect. Fixing roller 10 and pressure roller 30
The exit side passage 63 of the fixing unit can be switched between a regular recording medium conveyance path (arrow) and a return conveyance path 60 by a spring 352, a solenoid 36B, and a driver 401. FIG. 9 is a flowchart showing a fixing procedure in the embodiment of FIG. After the fixing is started, when the contact switch SW is turned on, the microcomputer as the control means 400 receives this, and executes “switching” in step: S1C. This switching is performed by the driver 401 by the solenoid 36.
B is switched so that the exit of the exit side passage 63 is connected to the return conveyance path 60. When the switch is made,
The recording medium 12 that has been incompletely fixed in the fixing unit is conveyed by the conveying roller 601 along the regression conveyance path 60, returns to the fixing unit, and undergoes re-fixing while passing through the fixing unit. During this time, the control means 400 receives the output of a sensor (not shown) (provided in the regression transport path 60 and detects whether the recording medium on which the toner image has been fixed has completely entered the regression transport path). (Step: S2C), and when the state of "re-switching possible" is detected, re-switching is performed (step: S3C), and the exit-side passage 63 is set to the normal recording medium conveyance path. Connect. Thereafter, it is determined whether or not the fixing can be completed. If there is a subsequent recording medium, the above fixing process is repeated, and if the fixing can be completed, the process is terminated.

That is, the fixing device described in the embodiment with reference to FIGS. 8 and 9 applies a fixing roller 10 having a heat source for heating to a sheet-shaped recording medium 12 on which a toner image TI is formed.
And the pressure roller 30 cooperating with the fixing roller,
In a fixing device for fixing a toner image TI to a recording medium 12 by applying heat and pressure to the recording medium and the toner image while nipping and conveying the toner image with the fixing roller being on the fixing roller side, a fixing roller 10 and a pressure roller In addition to the normal recording medium conveyance path passing through the fixing unit according to FIG.
36B and 401, the recording medium 12 can be switched to the normal recording medium conveyance path, and the recording medium 12 that has passed the fixing unit is again
It has a return conveyance path 60 for returning to the fixing unit, and the pressure roller 30 is a “self-detection type pressure roller” so that the contact switch SW detects that the surface temperature has fallen below a predetermined temperature. And transport path switching means 352, 36B, 401 based on ON / OFF of the contact switch SW.
And control means 400 for controlling the switching between the normal recording medium conveyance path and the regression conveyance path 60 according to (5).

In each of the above-described embodiments, the pressure roller 30 is, as described with reference to FIG.
The core roller is a metal roller, and the external roller is formed by forming a deformable thin metal layer on at least a part of the inner peripheral surface of the deformable hollow cylinder. The gas enclosed and sealed in the gap is an "inert gas" (claim 7).

FIG. 10 conceptually shows an embodiment of the image forming apparatus according to the present invention. This image forming apparatus is a “color image forming apparatus”. The photoconductive photoreceptor 100 rotates in the direction of the arrow and is uniformly charged by the charging unit 101, and is exposed by the image exposure unit 103 with Y (yellow), M (magenta), C (cyan), and K (black) toners. The Y latent image, the M latent image, the C latent image, and the K latent image to be imaged are sequentially written. The image exposure unit is a known optical scanning device. The written and formed Y latent image is visualized with the Y toner in the developing unit 105, and the obtained Y visible image is transferred to the intermediate transfer medium 106. Similarly, M latent image is M toner,
The C latent image is visualized with C toner, the K latent image is visualized with K toner, and M
The visible image, the C visible image, and the K visible image are sequentially transferred to the intermediate transfer medium 106. Thus, the intermediate transfer medium 10
The four visible images are superimposed on 6 to form a “color visible image”. This color visible image is transferred to the transfer roller 107.
As a result, secondary transfer is performed on the sheet-like recording medium 12.
The recording medium 12 has the color toner image fixed in the fixing device 110 and is discharged out of the device. That is, the embodiment shown in FIG. 10 is described as “a photoconductive photoconductor 100, means 101 and 103 for forming an electrostatic latent image on the photoconductor, and a toner image formed by developing the formed electrostatic latent image. Developing means 10
5, transfer means 106 and 107 for transferring the toner image formed on the photoconductor 100 to the sheet-like recording medium 12 via the intermediate transfer medium 106, and transferring the toner image transferred to the recording medium 12 to the recording medium. This is an image forming apparatus having a fixing unit 110 for fixing, and “any one of the fixing devices described in the above embodiments” is used as the fixing unit 110. Therefore, in the "image forming apparatus" of the embodiment shown in FIG. 10, fixing is started with the surface temperature of the fixing roller and the pressure roller as a predetermined fixing temperature, and when the surface temperature of the pressure roller decreases by a predetermined temperature. Further, based on ON / OFF of the contact switch, the fixing for controlling the execution of the auxiliary fixing by the auxiliary fixing device (FIGS. 2 to 5) or the re-fixing by the conveyance direction switching or the conveyance path switching means (FIGS. 6 to 9). The method (claim 9) is performed.

[0035]

As described above, according to the present invention, a novel image forming apparatus, a novel fixing device of the image forming apparatus, and a fixing method in the image forming apparatus can be realized. In the fixing device according to the present invention, since the pressure roller itself has a function of detecting a temperature decrease of the pressure roller, it is possible to realize appropriate fixing without performing complicated temperature control. According to the image forming apparatus and the fixing method of the present invention, by using the fixing device, good fixing can be realized and good image formation can be realized.

[Brief description of the drawings]

FIG. 1 is a view for explaining a fixing roller and a self-detection type pressure roller used in the embodiment of the present invention.

FIG. 2 is a view for explaining one embodiment of the fixing device according to the first aspect of the present invention;

FIG. 3 is a flowchart showing a fixing process in the embodiment of FIG. 2;

FIG. 4 is a view for explaining one embodiment of a fixing device according to the second aspect of the present invention;

FIG. 5 is a flowchart showing a fixing step in the embodiment of FIG.

FIG. 6 is a first embodiment of the fixing device according to the third and fourth aspects of the present invention;
It is a figure for explaining a form.

FIG. 7 is a flowchart showing a fixing process in the embodiment of FIG.

FIG. 8 is a view for explaining an embodiment of a fixing device according to the present invention.

FIG. 9 is a flowchart showing a fixing step in the embodiment of FIG.

FIG. 10 is a diagram conceptually showing one embodiment of an image forming apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fixing roller 12 Recording medium 30 Pressure roller 3 Core roller 4 External roller 41 Metal layer 51 Spacer TI Toner image 31 Heating roller 32 Pressure contact roller 35 Auxiliary fixing passage

Claims (9)

[Claims] 1. A sheet-like recording medium having a toner image formed thereon is sandwiched between a fixing roller having a heat source for heating and a pressure roller cooperating with the fixing roller so that the toner image is on the side of the fixing roller. In a fixing device that applies heat and pressure to the recording medium and the toner image while fixing the toner image to the recording medium while conveying the recording medium under pressure, a fixing roller and a pressure roller are disposed downstream of a main fixing device.
An auxiliary fixing device including a heating roller and a pressure roller is provided, and an auxiliary fixing passage from the main fixing device to the auxiliary fixing device is provided for a discharge passage for directing the recording medium passing through the main fixing device to the outside. The pressure roller is provided so as to be switchable, and the pressure roller is configured such that at least a part of the surface is conductive and at least a part of the inner peripheral surface of the deformable hollow cylinder is conductive. An external roller surrounding the core roller, having an electrically insulating spacer for forming a gap between the core roller and the external roller, and gas is sealed and sealed at a predetermined pressure in the gap, The fact that the surface temperature of the pressure roller is equal to or lower than a predetermined temperature is applied to a contact switch in which the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the external roller are in contact. An image forming apparatus comprising: a control unit configured to control switching between a discharge passage and an auxiliary fixing passage by the passage switching unit based on ON / OFF of the contact switch. Fixing device. 2. A sheet-like recording medium having a toner image formed thereon is sandwiched between a fixing roller having a heat source for heating and a pressure roller cooperating with the fixing roller so that the toner image is on the side of the fixing roller. In a fixing device that applies heat and pressure to the recording medium and the toner image while fixing the toner image to the recording medium while conveying the recording medium under pressure, a fixing roller and a pressure roller are disposed downstream of a main fixing device.
In addition to an auxiliary fixing device including a heating roller and a pressing roller having an immediate heat, a heat source control unit for controlling a heat source of the heating roller having an immediate heating is provided. At least a part of the surface of the pressing roller is conductive. A core roller, an external roller surrounding at least a portion of the inner peripheral surface of the deformable hollow cylinder which is made conductive and surrounding the core roller, and forming a gap between the core roller and the external roller. It has an electrically insulating spacer, and gas is sealed and sealed at a predetermined pressure in the gap, and the fact that the surface temperature of the pressure roller has become equal to or lower than a predetermined temperature indicates that the conductive portion of the core roller has It is configured to be detected by a contact switch having a contact point with the conductive portion of the inner peripheral portion of the outer roller. Based on ON / OFF of the contact switch, the heat source control means controls the rapid heat transfer. Characterized by being configured to perform heating control of the heating roller, a fixing device of an image forming apparatus. 3. A sheet-like recording medium having a toner image formed thereon is sandwiched between a fixing roller having a heat source for heating and a pressure roller cooperating with the fixing roller so that the toner image is on the side of the fixing roller. A fixing device that applies heat and pressure to the recording medium and the toner image while conveying the recording medium under pressure, and fixes the toner image onto the recording medium. The pressing roller is provided with a core roller having at least a part of the surface being conductive, and at least a part of the inner peripheral surface of the deformable hollow cylinder is made conductive. An external roller surrounding the core roller, an electrically insulating spacer for forming a gap between the core roller and the external roller, and gas is supplied to the gap by a predetermined pressure. And that the surface temperature of the pressure roller becomes equal to or lower than a predetermined temperature is detected by a contact switch having the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the external roller as contacts. A fixing device for an image forming apparatus, comprising: a control unit configured to control a conveyance direction of a recording medium by the conveyance direction switching unit based on ON / OFF of the contact switch. 4. A fixing device for an image forming apparatus according to claim 3, wherein said second discharge means is capable of switching to a normal recording medium transport path and directing the recording medium passing through the fixing section in the opposite direction to the outside. A transport path, and the second
A conveyance path switching means for switching between the first conveyance path and the second conveyance medium. The control means switches the normal recording medium conveyance path to the second discharge conveyance by the conveyance path switching means in response to the conveyance direction switching of the recording medium. Characterized by switching to the road
A fixing device of an image forming apparatus. 5. A sheet-like recording medium having a toner image formed thereon is sandwiched between a fixing roller having a heat source for heating and a pressure roller cooperating with the fixing roller so that the toner image is on the side of the fixing roller. A fixing device that applies heat and pressure to the recording medium and the toner image while conveying the recording medium under pressure to fix the toner image to the recording medium; Means for switching back to the regular recording medium transport path, having a return transport path for returning the recording medium that has passed through the fixing section to the fixing section again, wherein the pressure roller is at least part of the surface A conductive core roller, an external roller surrounding at least a part of the inner peripheral surface of the deformable hollow cylinder that is conductive and surrounding the core roller, and a gap between the core roller and the external roller. form And a gap is filled with gas at a predetermined pressure and hermetically sealed, and that the surface temperature of the pressure roller has become equal to or lower than a predetermined temperature, It is configured to detect by a contact switch having a contact between the conductive portion and the conductive portion of the inner peripheral portion of the external roller. Based on ON / OFF of the contact switch, the normal conveyance of the recording medium by the conveyance path switching means. A fixing device for an image forming apparatus, comprising: control means for controlling switching between a path and a return conveyance path. 6. The fixing device for an image forming apparatus according to claim 1, wherein the core roller of the pressure roller is a metal roller, and the external roller is an inner peripheral surface of a deformable hollow cylinder. Wherein a deformable thin metal layer is formed on at least a part of the fixing device. 7. The fixing device for an image forming apparatus according to claim 1, wherein the gas sealed in the gap between the core roller and the external roller of the pressure roller is an inert gas. A fixing device for an image forming apparatus. 8. A photoconductive photoreceptor, means for forming an electrostatic latent image on the photoreceptor, developing means for developing the formed electrostatic latent image into a toner image, Image forming apparatus comprising: a transfer unit for transferring a toner image formed on a recording medium directly or via an intermediate transfer medium; and a fixing unit for fixing the toner image transferred to the recording medium to the recording medium. An image forming apparatus, wherein the fixing device according to any one of claims 1 to 7 is used as a fixing unit. 9. A photoconductive photoreceptor, means for forming an electrostatic latent image on the photoreceptor, developing means for developing the formed electrostatic latent image into a toner image, Image forming apparatus comprising: a transfer unit for transferring a toner image formed on a recording medium directly or via an intermediate transfer medium; and a fixing unit for fixing the toner image transferred to the recording medium to the recording medium. In the apparatus, using the fixing device according to any one of claims 1 to 7, fixing is started by setting the surface temperature of the fixing roller and the pressure roller to a predetermined fixing temperature, and the conductive portion of the core roller in the pressure roller is started. Based on ON / OFF of a contact switch having a contact point with a conductive portion of the inner peripheral portion of the external roller, execution of auxiliary fixing by an auxiliary fixing device or re-fixing by conveyance direction switching or conveyance path switching means is controlled. Wherein the fixing method in an image forming apparatus.