JPH1039678A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing the occurrence of an overshoot at the time of build-up. SOLUTION: This fixing device is provided with a heating roller having a heating source, the first heating source control means controlling the surface temperature of the heating roller at the presaibed target temperature T1 in the stand-by state, a pressing means pressing a recording medium to the heating roller while the recording medium passes through the fixing region of the heating roller to fix the unfixed toner image on the recording medium together with the heating roller, and the second heating source control means turning off a heating source at the heating stop temperature T2 between the judgment temperature T3 and the target temperature T1 when the surface temperature of the heating roller is measured before the heating source of the heating roller is tuned on and the pre-heating roller surface temperature does not exceed the prescribed judgment temperature T3 set for preventing the overheating of the heating roller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device, and more particularly, to a fixing device in which an unfixed toner image formed on a recording medium is sandwiched in a fixing area between a heating roll and a pressing means, and heated under pressure. The present invention relates to a fixing device for fixing the unfixed toner image on a recording medium.

[0002]

2. Description of the Related Art Conventionally, as a fixing device for fixing a toner image transferred onto the surface of a recording medium such as paper or film onto a transfer recording medium, a heating type fixing device for heating and fixing the transfer recording medium under pressure. It has been known.

An example of such a heating type fixing device is as follows.
As shown in FIG. 8, a heating roll 1 and a pressure roll 2 pressed against the heating roll 1 are provided. A heating lamp 3 is provided at the center of the heating roll 1. The heating roll 1 is heated from the inside, and is heated until the surface temperature of the heating roll reaches a predetermined target temperature (T ₁ ). Then, when a transfer recording medium 5 such as paper having a toner image transferred to the surface thereof in a transfer step (not shown) enters a fixing area 4 formed by pressing the pressure roll 2 against the heating roll 1, the recording medium 5 The toner image 6 placed on the recording medium 5 is fixed on the recording medium 5 under heat and pressure while being conveyed to the discharge side on the left side in the figure by the rotation of the heating roll 1 and the pressure roll 2. You.

In the fixing of the toner image 6 using such a heating type fixing device, in order to uniformly fix the entire recording medium 5, the recording medium 5 passes through the fixing area 4 after starting to enter. Until the end, the toner image 6 on the recording medium 5 is required to be given a certain amount of heat, and for that purpose, the surface temperature of the heating roll needs to be kept constant.

Therefore, conventionally, the surface temperature is measured by a temperature sensor such as a thermistor attached to a predetermined position on the surface of the heating roll 1, and when the temperature falls below the target temperature (T ₁ ), the power of the heating lamp is turned on. To heat the heating roll, while the surface temperature of the heating roll reaches the target temperature (T
₁ ) When the temperature exceeds the above, a method of controlling the temperature of the heating roll so that the surface temperature of the heating roll becomes constant by turning off the power of the heating lamp and performing natural cooling or forced cooling until the temperature becomes lower than the target temperature (T ₁ ). Is commonly done.

However, in the case of the fixing device that performs the above-described temperature control, the surface temperature of the heating roll exceeds the target temperature (T ₁ ), and further rises, and the upper limit temperature of the surface of the heating roll in a standby state [hereinafter, referred to as “T. (Referred to as "upper limit temperature") (T
A problem called “overshoot” that often causes excessive heating beyond x) often occurs.

More specifically, when the power supply is turned on to start the fixing device and the heating roll is heated to a standby target temperature (T ₁ ) (hereinafter referred to as “start-up”), At the time of startup, this is called "idling", when the heating roller is contacted with the pressure roll to make it idle and warms up the peripheral parts, or is determined from a group of originals called "job". Overshoot occurs after a series of operations for fixing the deposited toner image on a plurality of sheets is completed.

For example, it is considered that the overshoot on the surface of the heating roll that occurs at the time of startup occurs as follows.

When the fixing device is energized while the heating roller is cooled down to about room temperature, such as in the morning, the surface temperature of the heating roller before heating is first measured by a temperature sensor, and the measurement result is processed by a central processing unit in the fixing device. Device (hereinafter “CPU”)
To). The CPU recognizes the surface temperature of the heating roll from the signal sent from the temperature sensor, and when determining that the surface temperature of the heating roll is lower than the preset target temperature (T ₁ ), the CPU immediately disposes the inside of the heating roll. The heating lamp provided is turned on to start heating the heating roll. Then, while measuring the surface temperature with the temperature sensor, the surface temperature of the heating roll becomes the target temperature (T ₁ ).
Continue heating until. FIG. 9 shows how the surface temperature of the heating roll changes with time from the start of energization to the fixing device.

As shown in FIG. 9, when the surface temperature of the heating roll reaches the target temperature (T ₁ ), the power of the heating lamp is turned off. At this time, the heating of the heating roll is stopped. However, after that, the surface temperature of the heating roll continues to rise, and the heating is performed as the heating roll exceeds the upper limit temperature (Tx), resulting in an overshoot state.

The overshoot also occurs when an operation called "idling" is performed when the fixing device is started up. That is, in the fixing device that performs such idling, as shown in FIG. 9, in order to warm up parts around the heating roll such as a pressure roll and an oil roll at the time of startup, the surface temperature of the heating roll is once set to the target temperature. After reaching (T ₁ ), the heating roll is energized with the fuser drive motor driving the heating roll in a state in which the heating roll is brought into contact with the heating roll, and idle rotation is performed between the heating roll and the pressure roll. The heat of the surface is absorbed by peripheral parts such as a pressure roll and an oil roll. However, after the idle rotation is over, an overshoot occurs.

This is probably because an excessive amount of heat is supplied from the heating lamp during idling. That is, in the conventional fixing device, when the surface temperature of the heating roll is lower than the target temperature (T ₁ ), the heating by the heating lamp is controlled to be started. When the surface temperature becomes lower than the target temperature (T ₁ ), the power of the heating lamp is turned on as shown in FIG. 10 and heating is started. Then, due to idling, a certain amount of heat is absorbed from the surface of the heating roll by peripheral components such as the pressure roll, and the surface temperature of the heating roll suddenly decreases at first. Contrary to the rise in the temperature of the peripheral parts, the rate of decrease in the surface temperature of the heating roll decreases, and the temperature decrease stops soon.
Then, when the amount of heat accumulated in the heating roll is transmitted to the surface, the surface temperature of the heating roll starts to rise again, and the surface temperature of the heating roll is rising just before the end of the idle rotation.

Therefore, immediately before the end of the idle rotation, the amount of heat supplied by the heating during the idle rotation is transmitted to the surface of the heating roll, and the temperature can be increased at any time. Since the pressure rolls are in contact with each other and some of the heat is taken away, the temperature rise is barely suppressed. Therefore, when the pressure roll is separated from the heating roll after the idle rotation is completed, there is no longer any obstacle to the rapid rise in the surface temperature of the heating roll, so that the surface temperature rises at once. In addition, the power of the heating lamp is kept turned on even after the idling is completed, so that the amount of heat is added to cause overshoot at once.

Further, in the overshoot, in a fixing device for controlling the temperature of the heating roll so that the surface temperature of the heating roll is lower than the target temperature in the standby state during the job, the surface temperature of the heating roll is reset after the completion of the job. Also occurs when returning to the standby state.

That is, when the fixing operation is performed after the fixing device is started, the surface temperature of the heating roll is controlled to its target temperature (T ₁ ) before the fixing operation is performed. At the start, a recording medium such as a sheet comes into contact with the surface of the heating roll to take away heat, so that the surface temperature of the heating roll sharply decreases with the start of the fixing operation. Then, in order to compensate for the decrease in the surface temperature, the power of the heating lamp is turned on to supply heat to the heating roll. However, the control temperature at this time poses a problem. That is, during the job, since the recording medium continuously passes over the heating roll to take heat, the surface temperature of the heating roll is set to the same target temperature (T
Attempting to control using ₁ ) requires more heat than in the standby state, which requires that the power of the heating lamp be always on during the job.

However, the heating lamp of the heating roll generates a large amount of heat, and the surface of the heating roll is coated with a thick layer of silicon rubber, which has a low thermal conductivity. If it is performed continuously, the amount of heat accumulated in the heating roll becomes very large. as a result,
If the heat is not removed from the surface of the heating roll after the job is completed, the accumulated heat is blown out to the surface, so that the surface temperature of the heating roll sharply rises and a large overshoot occurs.

Therefore, in a recent fixing device, in order to prevent such overshoot from occurring, as shown in FIG. 11, during a job, the temperature is controlled to a set job temperature (Tj) lower than a target temperature in a standby state. However, overshoot still occurs.

That is, in such a fixing apparatus, for example, paper sensors disposed before and after the fixing area detect whether or not a sheet is pinched in the fixing area, and a job is started and the sheet enters the fixing area. When the process is started, the target temperature of the heating roll surface temperature, which is a reference for controlling on / off of the power of the heating lamp, is switched from the target temperature (T ₁ ) in the standby state to the set temperature (Tj) in the job, and FIG. Thus, the power on / off of the heating lamp is controlled.

Next, when the job is completed and the last sheet has passed through the fixing area, based on a signal from a sheet sensor provided in the sheet conveying system, the CPU determines that the last sheet has passed through the fixing area. Recognize. Then, the CPU again switches the target temperature of the surface temperature of the heating roll from the set temperature (Tj) during the job to the target temperature (T ₁ ) in the standby state, and turns on the power of the heating lamp as shown in FIG. Start heating to. At this time, the surface temperature of the heating roll continues to increase even if it exceeds the target temperature (T ₁ ) in the standby state, and exceeds the upper limit temperature (Tx), resulting in an overshoot state.

The reason why this overshoot occurs is as follows.
It is considered that excessive heat is supplied from the heating lamp in the process of returning the surface temperature of the heating roll to the standby state after the job is completed. In other words, during the job, while the heat is supplied inward from the heating lamp, the heat is deprived from the surface of the heating roll by the paper passing through the fixing area.
The amount of heat supplied and the amount of heat removed are substantially balanced, and the surface temperature of the heating roll is kept substantially constant.However, when the job is completed and the paper is removed from the fixing area, the amount of heat taken away decreases. Since the heat is supplied from the heating lamp in the same manner as during the job, the supplied heat is excessive. Also,
Since heat is accumulated in the heating roll due to heating during the job, after the job is completed, there is residual heat enough to increase to the target temperature (T ₁ ) in the standby state without further heating. Nevertheless, if heating is performed after the end of the job, the amount of heat that is heated after the end of the job becomes excessive, and as shown in FIG. 11, it is considered that the temperature exceeds the upper limit temperature (Tx) and an overshoot state occurs.

It is considered that overshoot occurs as described above. However, if the fixing operation is performed in the overshoot state, the toner constituting the unfixed toner image on the recording medium is excessively melted and peeled off from the recording medium. This causes a phenomenon called "hot offset" to adhere to the surface of the heating roll, and a problem called "high gloss" in which the toner surface of the unfixed toner image melts and becomes unnecessarily glossy. Image quality is significantly reduced.
Therefore, once overshoot occurs,
The heating roll must be cooled to a temperature below the temperature at which the above-mentioned trouble does not occur, and a waiting time for this cooling is required. As a result, there arises a problem that the working efficiency of the fixing operation is reduced.

Therefore, as a method of shortening the cooling time after the overshoot, there has been proposed an apparatus for lowering the surface temperature of the heating roll to a predetermined temperature by cooling in combination with forced cooling by idling in addition to natural cooling. Have been. For example, JP-A-7-306609 discloses that
There is disclosed a fixing device of a system in which a mode is automatically switched after a copying operation in a high-temperature mode is completed, and then natural cooling or forced cooling is performed.

However, this device is an invention in which natural cooling and forced cooling by idling are performed as a cooling method for cooling the heating roll after completion of the fixing operation in the high-temperature mode, thereby preventing the occurrence of overshoot itself. It is not something that can fundamentally solve the problem of overshoot.

[0024]

The inventors of the present invention have conducted intensive studies on a fixing device free from the above-mentioned problems, and as a result, overshoot is caused only by the conventional heating source control means. When the control of the heating source is performed, it is found that an excessive amount of heat cannot be prevented from being supplied to the heating roll. To solve this, another heating source control means is used in addition to the conventional heating source control means. The inventors have found that the above-mentioned conventional problems can be solved by providing control of turning off the power of the heating source for a predetermined time by providing a source control means, and completed the present invention.

Accordingly, an object of the present invention is to provide a fixing device capable of preventing occurrence of overshoot at the time of startup.

Another object of the present invention is to provide a fixing device capable of preventing occurrence of overshoot when performing idling operation at startup.

Still another object of the present invention is to provide a fixing device capable of preventing occurrence of overshoot in the process of returning the surface temperature of a heating roll to a standby state after a job is completed. is there.

[0028]

According to the present invention, there is provided a heating roll having a heating source, and first heating source control means for controlling a surface temperature of the heating roll to a predetermined target temperature (T ₁ ) in a standby state. Pressure means for pressing the recording medium against the heating roll while the recording medium passes through the fixing region of the heating roll, and fixing the unfixed toner image transferred onto the recording medium in cooperation with the heating roll. In the fixing device provided with, the surface temperature of the heating roll is measured before power is supplied to the heating source of the heating roll, and the surface temperature of the pre-heating roll is set to a predetermined value set to prevent overheating of the heating roll. the determination temperature when it does not exceed the determined temperature (T ₃₎ is (T ₃₎ and the target temperature (T ₁₎ heating stop temperature between (T ₂₎ at a second turning off the power of the heating source Equipped with heating source control means A fixing device.

Further, the present invention provides a heating roll having a heating source, first heating source control means for controlling the surface temperature of the heating roll to a predetermined target temperature (T ₁ ) in a standby state, and It is controlled to a lower temperature than the heating roll even if it does not have or has a heating source, and while the recording medium passes through the fixing area of the heating roll, presses this recording medium against the heating roll, and A pressure roll for fixing the unfixed toner image transferred onto the recording medium together with the pressure roll, and when the surface temperature of the heat roll reaches its target temperature (T ₁ ), the pressure roll is turned into a heat roll. A fixing device having a third heating source control unit for turning off the power of the heating source for a predetermined time during the idle rotation. Ah .

Further, the present invention provides a heating roll having a heating source, first heating source control means for controlling the surface temperature of the heating roll to a predetermined target temperature (T ₁ ) in a standby state, and An in-job temperature control means for controlling the surface temperature of the heating roll to a set temperature in the job lower than the target temperature (T ₁ ); and a heating source having no heating source or having a heating source but having a lower temperature than the heating roll. The recording medium is pressed against the heating roll while the recording medium passes through the fixing area of the heating roll, and the unfixed toner image transferred onto the recording medium in combination with the heating roll is fixed. And a fourth heating source control means for turning off the power source of the heating source of the heating roll in a process of returning to a standby state after a job is completed. It is wearing equipment.

In the fixing device of the present invention, the second heating source control means is means for preventing overheating of the heating roll at startup (hereinafter, overheating of the heating roll is referred to as "overheating"). The third heating source control means is means for preventing overheating when idling at the time of startup. The fourth heating source control means is a means for preventing overheating from occurring in the process of returning the surface temperature of the heating roll to the standby state after the end of the job.

Only one of the second to fourth heating source control means may be provided in the fixing device. Two or three of the fourth heating source control means may be provided in one fixing device. The control of these heating sources is specifically performed by the CPU.

Of the second to fourth heating source control means,
The second heating source control means for preventing overheating at the time of start-up uses the judgment temperature (T ₃ ) and the heating stop temperature (T ₂ ) as indices for controlling the heating source, and the surface temperature of the heating roll is adjusted to this value. When the temperature is lower than the judgment temperature (T ₃ ), the power source of the heating source is turned off from the time when the surface temperature of the heating roll reaches the heating stop temperature (T ₂ ) until it reaches the target temperature (T ₁ ).

This judgment temperature (T ₃ ) is a temperature for judging whether or not to operate the second heating source control means.
The heating stop temperature (T ₂ ) is a temperature used as an index of a time when the heating source is stopped when the second heating source control means is operated.

As the determination temperature (T ₃ ), the power supply of the heating source is turned on when the surface temperature of the heating roll is (T ₃ ), and the time when the surface temperature of the heating roll reaches the target temperature (T ₁ ) After the power supply of the heating source is turned off, the temperature is not particularly limited as long as the temperature at which the surface temperature of the heating roll rises does not exceed the upper limit temperature (Tx).

The judgment temperature (T ₃ ) is determined by the calorific value of the heating source of the heating roll and the time during which this heat is transmitted to the surface of the heating roll [this time depends on the base (air) inside the heating roll / the heating roll (metal shaft). / Elastic layer). ] And the heat taken by the atmosphere around the heating roll and the component temperature, the temperature rise actually occurs when the heating source of the heating roll is turned off at the heating stop temperature (T ₂ ). T ₁ ) is a temperature at which it is possible not to fall below in any case, and when the second heating source control means is not implemented, energization of the heating roll heating source is performed by:
Determine the temperature at which the overshoot that occurs when controlled at the target temperature (T ₁ ) does not exceed the upper limit temperature (T ₃ )
Select as

Since the optimum temperature as the judgment temperature differs for each fixing device, a specific value is determined for each fixing device based on actually measured data obtained by actually operating the fixing device. Is done.

On the other hand, when the surface temperature of the heating roll before the heating is the judgment temperature (T ₃ ), the heating stop temperature (T ₂ ) is determined from the time when the power source of the heating source is turned on. After the power of the heating source is turned off when the stop temperature (T ₂ ) is reached, the upper limit at which the surface temperature of the heating roll rises is equal to or lower than the upper limit temperature (Tx).

Further, the heating stop temperature (T_Two) Heating
The calorific value of the roll heating source and this heat are transferred to the heating roll surface.
Time [This time is the gas (air) inside the heating roll /
Depending on the heat transfer coefficient of the heating roll (metal shaft / elastic layer)
Change. ] And the atmosphere around the heating roll and the part temperature
In fact, heating
Stop temperature (T_Two) When the heating roll heating source is turned off
Temperature rise to the target temperature (T₁) Below in any case
The temperature at which heating can be stopped is defined as the heating stop temperature (T _Two)age
To select.

Since the optimal temperature as the heating stop temperature (T ₂ ) differs from one fixing device to another, a specific value is based on actual measurement data obtained by actually operating the fixing device. It is determined for each fixing device.

As described above, the second heating source control means controls the heating source using the judgment temperature (T ₃ ) and the heating stop temperature (T ₂ ). When the surface temperature of the heating roll is lower than the judgment temperature (T ₃ ), the second heating source control means operates. That is, when the surface temperature of the heating roll reaches a predetermined heating stop temperature (T ₂ ), the power of the heating source is turned off, and the heating of the heating roll is stopped. Thereafter, the surface temperature of the heating roll continues to rise, but the heating stop temperature (T ₂ ) is changed from the surface temperature of the heating roll before heating to the heating stop temperature (T
₂ ) When the power source of the heating source is turned off at the time of reaching, the upper limit of the increase in the surface temperature of the heating roll is set to a value that is equal to or lower than the upper limit temperature (Tx). It does not reach the temperature that causes overheating. As a result, overheating of the heating roll is prevented from occurring.

On the other hand, when the fixing device is energized,
The surface temperature of the heat roll is the judgment temperature (T _Three) If higher
Operates the first heating source control means. Therefore, the fixing device
Heating starts when power is supplied to the
The surface temperature is the target temperature (T₁Heating is continued until
However, this determination temperature (T_Three) Indicates the surface temperature of the heating roll.
Cutoff temperature (T_Three), The target temperature (T₁)
Even if heating is continued until it reaches, the surface temperature of the heating roll
Is not more than the upper limit temperature (Tx).
Because the temperature is set, the heating roll
Is prevented from occurring.

The third heating source control means is a means for preventing overheating in the case of idling at the time of start-up. For example, the heating roll is controlled to perform idling as warming-up of peripheral parts such as a pressure roll. This is a means for turning off the power of the heating source for a predetermined time while the pressure roll is brought into contact.
Specifically, for example, when performing idle rotation using a fuser drive motor to rotationally drive the heating roll,
As this idle rotation, CP
There is a case where the idle rotation time is recognized from the command signal sent from U, and the power source of the heating source is turned off during that time. Also,
The time for turning off the power of the heating source may be a time capable of preventing overheating after idling, and is not necessarily the same as the idling time. For example, the power of the heating source is turned off at the same time as the idling and the power is turned on before the end of the idling, or the power of the heating source is turned off after the start of the idling and the power is turned on at the end of the idling, Further, there is a case where the power of the heating source is turned off after the start of idling and the power is turned on before the end of idling.

As described above, the third heating source control means turns off the power of the heating source for a predetermined time during the idling operation.
When the pressurizing roll is pressed against the heating roll at the start-up of the apparatus and idle rotation is performed, even if heat is deprived to the surface of the pressurizing roll and the surface temperature of the heating roll falls below the target temperature (T ₁ ), In order to turn off the power of the heating source while the third heating source control means is operating and the fuser driving motor is operating, only the heat is taken from the surface of the heating roll to the pressure roll surface. The supply of heat from the heating source is prevented.

On the other hand, since the surface temperature of the heating roll is lower than the target temperature (T ₁ ) in the standby state due to the idle rotation, the first control means is stopped when the idle rotation is completed and the operation of the third heating source control means is ended. Operates to turn on the power of the heating source and start heating the heating roll. Therefore, the surface temperature of the heating roll increases after the idle rotation due to the remaining amount of heat accumulated at the time of startup and the amount of heat generated by the heating after the completion of the idle rotation. During the idle rotation, the heat source is not supplied with heat for a predetermined time, and the heating time after the end of the idle rotation is short, so that the temperature of the surface of the heating roll after the end of the idle rotation is reduced. The degree of the rise is kept low and does not reach a temperature exceeding the upper limit temperature (Tx). as a result,
Also in this case, occurrence of overheating of the heating roll is prevented.

The fourth heating control means is a means for preventing overheating in the process of returning the surface temperature of the heating roll to the standby state after the end of the job, and is a timing at which the last recording medium finishes passing through the fixing area after the end of the job. This is a means for turning off the power of the heating source until the surface temperature of the heating roll returns to the target temperature (T ₁ ) in the standby state.

As a specific method of recognizing when the last recording medium has passed through the fixing region, for example, a signal from a document sensor provided in a document reading device,
The CPU recognizes the last recording medium based on the signal from the paper sensor disposed in the recording medium transport system, and the last recording medium passes through the fixing area by sensors disposed before and after the fixing area. There is a method of recognizing a time when the printing operation is completed, a method of calculating a time when the last recording medium finishes passing through the fixing area based on signals from the document sensor and the paper sensor, and a method of performing so-called anticipation control.

As described above, the fourth heating source control means changes the surface temperature of the heating roll to the target temperature (T) in the standby state after the end of the job, that is, from the time when the last recording medium of the job has passed through the fixing area. _Since the power of the heating source is turned off until returning to ₁ ), overheating after the job is completed, which was caused by the amount of heat supplied from the heating source during this period, is prevented. Is done.

After the job is completed, the pressure roll can be pressed against the heat roll and idled during the process of returning the surface temperature of the heat roll to the target temperature (T ₁ ) in the standby state. When such idle rotation is performed, since the surface temperature of the heating roll is affected by the surface temperature of the pressure roll, a large amount of heat is accumulated on the heating roll due to heating during a job. Even if an attempt is made to rapidly increase the target temperature (T ₁ ) in the standby state due to the amount of heat, the surface temperature of the heating roll rises while being affected by the surface temperature of the pressure roll. As a result, when returning to the target temperature (T ₁ ) in the standby state, overheating can be more reliably prevented from occurring.

[0050]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, the present invention will be described based on a fixing device according to a first embodiment of the present invention. FIG. 1 is a schematic diagram of a fixing device according to the present embodiment, and FIGS.
FIG. 7 is a diagram showing a change in the surface temperature of the heating roll when the surface temperature of the heating roll is controlled using the fixing device of FIG. 5, where the horizontal axis represents time (t) and the vertical axis represents the surface temperature of the heating roll (T). There is.

The fixing device of the present embodiment includes a heating roll 1 having a heating lamp (heating source) 2 and a surface temperature of the heating roll 1 in a standby state which is set to a predetermined target temperature (T
₁ ) a first heating source control means for controlling the heating roll 1 and pressing the paper 8 'against the heating roll 1 while the paper (recording medium) 8' passes through the fixing area of the heating roll 1; Unfixed toner image 8 transferred on paper 8 'together
And a pressure roll (pressing means) for fixing the toner.

The heating roll 1 has a structure in which an aluminum roll core having a thickness of 8 mm is coated with a silicone rubber layer having a thickness of 3 mm, and a surface thereof is further coated with a fluorine rubber layer having a thickness of 20 μm. And the outer diameter is 50 mm.
The pressure roll 4 has a structure in which an aluminum roll core having a thickness of 7 mm is coated with a silicone rubber layer having a thickness of 1 mm, and has an outer diameter of 50 mm.

The contact pressure and contact width between the heating roll 1 and the pressure roll 4 are 7 kg / cm ² and 6 kg / cm ² , respectively.
mm, and the transport speed of the paper 8 'carrying the unfixed toner image 8 is 160 mm / sec. It is. Specifically, the first heating source control means includes a temperature sensor 3 for measuring the surface temperature of the heating roll 1 and a CPU for recognizing the surface temperature of the heating roll 1 based on a signal from the temperature sensor 3. Consists of The CPU incorporates a ROM in which a program for controlling the heating source is written.

In the fixing device of this embodiment, the surface temperature of the heating roll 1 before the power is turned on to the heating lamp 2 of the heating roll 1 is measured. If the temperature does not exceed the predetermined judgment temperature (T ₃ ) set in the above, the judgment temperature (T ₃ )
A second heating source control means for turning off the power of the heating source at a heating stop temperature (T ₂ ) between the temperature and the target temperature (T ₁ ).

In the fixing device of this embodiment, the heating stop temperature
(T_Two) Is the heating stop temperature (T _Two) In the heating roll
When the heating source is turned off, the temperature rise rises to the target temperature (T₁)
As a temperature that can be kept under any case
This is the selected value. Then, the judgment temperature (T_Three) Value is
Heating stop temperature (T_Two) Turn off the heating source of the heating roll
The temperature rises to the target temperature (T₁) In any case
It is a temperature that can be maintained so that it does not fall below
When the second heating source control means is not implemented, the heating roll
To the heating source at the target temperature (T₁) When controlled by
Temperature at which overshoot does not exceed the upper limit temperature
Determine the temperature (T_Three).

The values of these temperatures are, specifically, T ₁ = 165 ° C., T ₂ = 155 ° C., and T ₃ = 15, respectively.
It is set to 0 ° C. Further, in this fixing device, the upper limit temperature (Tx) of the heating roll surface in the standby state
Was 178 ° C.

In the fixing device of this embodiment, a CPU is actually used as the second heating source control means.
The CPU incorporates a ROM in which a program for performing the above control is written. FIG. 4 shows a flowchart of the program.

When energization of the fixing device of this embodiment is started, first, the surface temperature (T ₀ ) of the heating roll 1 before heating is measured by the temperature sensor 3, and this surface temperature (T ₀ ) is sent to the CPU in the fixing device. Sent as a signal. On the other hand, the power of the heating lamp 2 is turned on and the heating roll 1 is turned on.
Heating to is started. The CPU recognizes the pre-heating surface temperature (T ₀ ) of the heating roll 1 based on the signal sent from the temperature sensor 3, and determines the pre-heating surface temperature (T ₀ )
The temperature is compared with the judgment temperature (T ₃ ). If the pre-heating surface temperature (T ₀ ) is lower than the judgment temperature (T ₃ ), the power of the heating lamp 2 is turned on when the surface temperature of the heating roll 1 reaches the heating stop temperature (T ₂ ). Off.

Here, the judgment temperature (T ₃ ) is a value determined based on actual measurement data when the fixing device is actually operated, and the surface temperature of the heating roll 1 is determined by the judgment temperature (T ₃ ).
Is reached, the upper limit of the rise in the surface temperature of the heating roll 1 is lower than the upper limit of the allowable range, even if heating is continued until the target temperature (T ₁ ) is reached.

The heating stop temperature (T ₂ ) is also a value determined on the basis of actual measurement data when the fixing device is actually operated, and the heating roll 1 is turned on when the power of the heating lamp 2 is turned on. After the power of the heating lamp 2 is turned off when the surface temperature reaches the heating stop temperature (T ₂ ), the upper limit of the rise in the surface temperature of the heating roll 1 is lower than the allowable range upper limit temperature.

The determined temperature (T ₃ ) thus determined.
When the surface temperature (T ₀ ) of the heating roll 1 at the time of energizing the fixing device is lower than (T ₃ ) using the heating stop temperature (T ₂ ) and the heating stop temperature (T ₂ ), the second heating source control means is used. When the surface temperature of the heating roll 1 reaches the heating stop temperature (T ₂ ) by turning on the CPU, the power supply of the heating lamp 2 is turned off to stop heating the heating roll 1.

That is, when the surface temperature of the heating roll is
Stop temperature (T_Two), The heating lamp 2 is turned off.
The heating of the heating roll 1 is stopped. afterwards,
The surface temperature of the heating roll 1 continues to rise, but the heating stop temperature
Degree (T_Two) Is the surface temperature (T) of the heating roll 1 before the heating.
₀) From the surface temperature of the heating roll 1 is the heating stop temperature
(T _Two), The heating lamp 2 is turned off.
In this case, the upper limit of the rise of the heating roll surface temperature is
Because the temperature is below the upper limit temperature of the heating roll 1,
The surface temperature should not exceed the upper limit temperature (Tx)
I can't. As a result, overheating of the heating roll
Is prevented.

On the other hand, if the surface temperature (T ₀ ) of the heating roll 1 before heating when the power supply to the fixing device is started is higher than the judgment temperature (T ₃ ), the first heating source control means operates. . Therefore, the fixing device is heated from the time of starting the energization is started, the heating until the surface temperature of the heating roll 1 is the target temperature (T ₁₎ is continued, the determination temperature (T ₃₎ is a heating roll The surface temperature of 1 is the judgment temperature (T ₃ )
Even when heating is continued until the target temperature (T ₁ ) is reached from the time when the temperature reaches the upper limit, the upper limit at which the surface temperature of the heating roll 1 rises is equal to or lower than the upper limit temperature (Tx). In this case, too, the overheating of the heating roll 1 is prevented from occurring.

(Second Embodiment) In the fixing device of the present embodiment, when the surface temperature of the heating roll 1 reaches its target temperature (T ₁ ) at startup, the pressure roll 4 is moved to the heating roll 1.
Is a fixing device for warming up peripheral components such as the pressure roll 4 by causing the roller to idle for a predetermined time by contacting the heating roller, and turning off the power of the heating lamp 2 during the operation of the idle rotation. The fixing device has the same structure as the fixing device of the first embodiment except that the fixing device is provided.

The third heating source control means specifically includes C
The CPU includes a ROM in which a program for performing the above control is written.
FIG. 5 shows changes in the surface temperature of the heating roll of the fixing device of the present embodiment with respect to time. In the fixing device according to the present embodiment, the idle rotation time (t ₁ ) starts from the time when the surface temperature of the heating roll 1 once reaches the target temperature (T ₁ ). This is a value determined as the time during which the temperature shows a tendency to increase, and specifically, t ₁ = 3.
It is set to 0 seconds.

In the fixing device of the present embodiment, when the fixing device is energized, the surface temperature of the heating roll is equal to the judgment temperature (T ₃ ).
If it is lower, idle rotation takes place. That is, the power of the heating lamp 2 is turned on when the fixing device is energized, the heating of the heating roll is started, and when the surface temperature of the heating roll reaches the heating stop temperature (T ₂ ), the second heating source control means is activated. The power of the heating lamp 2 is turned off by operation, but the surface temperature of the heating roll further rises due to residual heat, and reaches the target temperature (T ₁ ). Then, the CPU, which has measured the surface temperature of the heating roll 1 based on the signal from the temperature sensor 3, brings the pressure roll into contact with the heating roll, drives the fuser driving motor for a predetermined time in this state, and causes the emptying. Rotate.

Further, the third heating source control means operates simultaneously with the start of idling. That is, when the heating source control means attached to the fixing device is only the first heating source control means,
The idle temperature reduces the surface temperature of the heating roll, and the target temperature (T
_When the temperature falls below ₁ ), the power of the heating lamp 2 is turned on by the first heating source control means. However, in the fixing device of the present embodiment, as a result of the operation of the third heating source control means,
While the idle rotation is being performed, specifically, the power of the heating lamp 2 is kept off for a predetermined time while the power of the fuser drive motor and the latch solenoid is turned on. Therefore, heating to the heating roll 1 is not performed during idle rotation,
Only heat is removed by contact with the pressure roll 4.

Therefore, supply of an excessive amount of heat to the heating roll due to heating during idle rotation is prevented. As a result, even when the idle rotation is completed, the power of the heating lamp 2 is turned on, and the heating of the heating roll 1 is started, the surface temperature of the heating roll 1 slightly exceeds the target temperature (T ₁ ). , And does not reach a temperature exceeding the upper limit temperature (Tx), so that the heating roll 1 is prevented from being overheated after idling.

(Third Embodiment) In the fixing device of this embodiment, during a job, the surface temperature of the heating roll 1 is controlled to a set temperature (Tj) lower than the target temperature (T ₁ ) during the job. A temperature control means, and a pressure roll 4 having a built-in heating lamp (heating source) 5 like the heating roll 1 and controlled to a temperature (T ₁ ′) lower than that of the heating roll 1;
Fourth heating source control means for turning off the power of the heating lamp 2 of the heating roll 1 in the process of returning to the standby state after completion of the job, and the pressing roll 4 in the process of returning to the standby state after the completion of the job. The fixing device has the same structure as that of the first fixing device except that the fixing device has a temperature rise control unit for preventing the surface temperature of the heating roll 1 from rising sharply by making the surface of the heating roll 1 drastically rotate for a predetermined period of time (t ₂ ) by contact with the fixing roller. Device.

In the fixing device of this embodiment, the target temperature
Degree (T₁) And the upper limit temperature (Tx) in the first embodiment.
Set the same value as the fixing device of
(T ₁’), The set temperature during job (Tj)
Each T₁'= 160 ° C, Tj = 150 ° C
Was. In the fixing device of the present embodiment, the idle rotation is performed.
Now time (t_Two) Indicates that the recording medium has passed through the fixing area
Is the starting point, and from this starting point the surface temperature of the heating roll
It is a value determined as a time showing a downward trend,
Is t_Two= 80 seconds.

The fourth heating source control means specifically includes C
The CPU includes a ROM in which a program for performing the above control is written.
FIG. 7 shows a flowchart of the program.

In the fixing device of this embodiment, as shown in FIG. 7, during the job, the heating roll 1 is controlled so that the surface temperature is maintained at the set temperature (Tj) during the job, while the pressure roll is controlled. For _No. 4, the target temperature (T ₁ )
'It is controlled to, job same temperature as the standby state (T ₁ more slightly lower the temperature (T _1)' is maintained).
Therefore, the power of the heating lamp 5 is kept on during the job. Then, the heating roll 1 and the pressure roll 4
When the fuser drive motor rotates in a state in which the sheet 8 is pressed, the two rolls rotate while contacting each other, sandwich the sheet 8 ′, and convey the sheet 8 ′ while fixing it by heating. Next, when the job is completed and the sheet 8 'is discharged from the fixing nip area to the discharge side, the sheet sensor 9 detects that the sheet 8' is no longer pinched in the fixing nip area. When the CPU receives the signal from the paper sensor 9, the CPU immediately turns off the power of the heating lamp 2 in the heating roll 1.

When the job is completed, the CPU changes the temperature for controlling the surface temperature of the heating roll 1 from the set temperature (Tj) in the job to the target temperature (T
_To switch to ₁ ), the surface temperature of the heating roll 1 increases due to residual heat based on the amount of heat accumulated by heating during the job. At this time, in a state where the job is completed and the sheet 8 'is no longer in the fixing nip area, the fourth heating source control means operates to turn off the power of the heating lamp 2, so that the heating roll 1 Heat is not supplied from the heating lamp 2 to the heating roll 1 until the surface temperature of the substrate returns to the target temperature (T ₁ ) in the standby state, so that no excessive heat is supplied. .

Therefore, after the end of the job, the surface temperature of the heating roll 1 rises to a level slightly above the target temperature (T ₁ ) in the standby state due to the residual heat based on the amount of heat accumulated in the heating roll 1. In the process of returning to the target temperature (T ₁ ) in the standby state, the amount of heat accumulated in the heating roll 1 is almost consumed and hardly remains, so that the temperature of the heating roll 1 no longer reaches the temperature exceeding the upper limit temperature (Tx). No heat is stored. Further, in the fixing device of the present embodiment, in the process of returning to the standby state after the end of the job, the pressure roll is brought into contact with the heating roll and is idled for a predetermined time to prevent a rapid rise in the surface temperature of the heating roll. Control means is provided. Therefore, the occurrence of overshoot of the heating roll when returning to the standby state after the end of the job is prevented.

[0075]

According to the present invention, at the time of startup, at the time of performing idle rotation operation at the time of startup, or at the time of heating the surface temperature of the heating roll to the target temperature in the standby state after the end of the job, respectively. Thus, it is possible to provide a fixing device capable of preventing the occurrence of overheating of the heating roll.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a change with time of a heating roll surface temperature of the fixing device according to the first embodiment of the present invention;

FIG. 3 is a diagram showing a change with time of a heating roll surface temperature of the fixing device according to the first embodiment of the present invention;

FIG. 4 is a flowchart showing control of a second heating source control unit according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a change over time of a heating roll surface temperature of the second fixing device of the present invention.

FIG. 6 is a diagram showing a change with time of a heating roll surface temperature in a fixing device according to a third embodiment of the present invention.

FIG. 7 is a flowchart showing control of a fourth heating source control unit according to the third embodiment of the present invention.

FIG. 8 is a schematic sectional view of a conventional fixing device.

FIG. 9 is a diagram showing a change with time of a heating roll surface temperature of a conventional fixing device.

FIG. 10 is a diagram showing a change with time of a heating roll surface temperature of a conventional fixing device.

FIG. 11 is a diagram showing a change with time of a heating roll surface temperature of a conventional fixing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating roll, 2 ... Heating lamp (heating source), 3 ... Temperature sensor (measuring device), 4 ... Pressure roll (Pressing means),
5: heating lamp (heating source), 6: temperature sensor, 8: unfixed image, 9: paper sensor.

Claims (4)

[Claims] 1. A heating roll having a heating source, first heating source control means for controlling a surface temperature of the heating roll to a predetermined target temperature (T ₁ ) in a standby state, and a fixing area of the heating roll. A pressure unit that presses the recording medium against a heating roll during the passage of the recording medium and fixes an unfixed toner image transferred onto the recording medium in cooperation with the heating roll. The surface temperature of the heating roll before power is turned on to the heating source of the heating roll is measured, and the surface temperature of the pre-heating roll is determined to be a predetermined judgment temperature (T ₃ ) set to prevent overheating of the heating roll. If not exceeded, the heating stop temperature (T) between the judgment temperature (T ₃ ) and the target temperature (T ₁ )
₂ ) A fixing device comprising a second heating source control unit for turning off the power of the heating source. 2. A heating roll having a heating source; first heating source control means for controlling a surface temperature of the heating roll to a predetermined target temperature (T ₁ ) in a standby state; Even if it has a heating source, the temperature is controlled to be lower than that of the heating roll, and the recording medium is pressed against the heating roll while the recording medium passes through the fixing region of the heating roll. A pressure roll for fixing the unfixed toner image transferred onto the recording medium; and a pressure roll contacting the heat roll when the surface temperature of the heat roll reaches its target temperature (T ₁ ). And a third heating source control unit for turning off the power of the heating source for a predetermined time during the idle rotation. Set Apparatus. 3. A heating roll having a heating source; first heating source control means for controlling a surface temperature of the heating roll to a predetermined target temperature (T ₁ ) in a standby state; An in-job temperature control means for controlling the surface temperature to a set temperature during the job lower than the target temperature (T ₁ ); and a heating source having no heating source or having a heating source but having a temperature lower than the heating roll. A pressure roll for pressing the recording medium against the heating roll while the recording medium passes through the fixing area of the heating roll, and fixing the unfixed toner image transferred onto the recording medium in cooperation with the heating roll. And a fourth heating source control unit for turning off the power of the heating source of the heating roll in the process of returning to the standby state after the end of the job. A fixing device for the butterflies. 4. A temperature rise control means for preventing a rapid rise in the surface temperature of the heating roll by bringing the pressure roll into contact with the heating roll and rotating it idle for a predetermined time in the process of returning to the standby state after the job is completed. The fixing device according to claim 3, wherein: