JP3121495B2 - Fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device applied to an electrophotographic image forming apparatus. Specifically, a heating member and a pressing member that are in pressure contact with each other, and by controlling the power supplied to the heating member, the heating member is controlled to a set temperature, and a pressing portion between the heating member and the pressing member is controlled. The present invention relates to a fixing device for fixing a toner image on a heated body by nipping and conveying a heated body carrying an unfixed toner image.

[0002]

2. Description of the Related Art Conventionally, a so-called thermal fixing device using a heat roller, a belt, or the like is generally used as a fixing device. However, in such a fixing device, when the temperature of a pressing member is low, fixing is performed. When a defect occurs and the temperature of the pressing member is high, there is a problem that wrinkles are generated on the heated member (paper) and toner adheres to the heating member (high-temperature offset).

In particular, in an image forming apparatus such as a printer or a facsimile which receives externally transferred image data and further processes the image data internally, various types of continuously transferred image data are used. In the case where a plurality of images are continuously formed according to data, the time from the previous image output (n-th sheet) to the next image output (n + 1-th sheet), that is, Since the time between papers (paper interval) that is continuously passed becomes indefinite according to the amount and type of image data, in the fixing device, the pressing member is adjusted according to the paper interval. Temperature fluctuates, causing paper wrinkles and high-temperature offset. For example, when the amount of image data is large and it takes time to transfer image data or develop data inside the device, or when image data such as graphics images is complex and takes time to process, It takes time and the time between sheets becomes longer. Since the image forming apparatus normally drives the sheet interval as the image forming operation is continuing, regardless of whether or not there is a sheet in the fixing device,
When power is supplied to the heating member, and as a result, the time between sheets increases, the temperature of the pressing member increases due to heat from the heating member, and paper wrinkles and high-temperature offset occur. On the other hand, when the inter-sheet time is short, the heat taken from the pressing member when the paper is present in the fixing device (during paper passing) is more than the heat given to the pressing member from the heating member between the sheets. Due to the increase, the temperature of the pressing member decreases, and fixing failure occurs.

[0004] In view of the above, it is required to appropriately set the temperature of the heating member according to the temperature of the pressing member.

For example, in Japanese Patent Laid-Open Publication No. 50-39554, a temperature detecting means is provided not only for the heating member but also for the pressing member, and when the temperature of the pressing member is low, the temperature of the heating member is raised. Also, it has been proposed to control the temperature of the heating member to be low when the temperature of the pressing member is high.

In recent years, even in a home or work environment, one individual is using one or more image forming apparatuses such as a printer, a facsimile, a copying machine, and the like. Therefore, there is a demand for shortening the wait time (quick start property) from turning on the power of the image forming apparatus to actually forming an image, and saving power of the image forming apparatus.

In order to perform a quick start, it is necessary to shorten the warm-up time of the fixing device (the time required until the fixing device reaches a fixing-possible temperature). Even when the main unit is turned on, while the image forming operation is not actually performed (during standby)
It is necessary to stop the power supply to the fixing device, or to control the temperature of the heating member to be lower than that during image formation. However, if the power supply to the fixing device is stopped or reduced during standby, it is necessary to warm up the fixing device every time an image forming operation is started. It is an essential requirement.

By utilizing the fact that the temperature of the pressing member is detected and the heating member is controlled in accordance with the result, it is possible to shorten the warm-up time of the fixing device and thereby improve the quick start performance. it can.

That is, the usage history of the image forming apparatus (for example, the usage time of the apparatus when it was last used, the time from when the apparatus was stopped after the last use until the start of the next use of the apparatus, The temperature of the pressing member differs depending on the time during which the image forming operation is continuously performed by continuous paper feeding or the like. Since the set temperature of the heating member is determined on the assumption that the temperature of the member is low, a substantially constant warm-up time is required without depending on the temperature of the pressing member. In the method of controlling the temperature of the heating member, for example, when the temperature of the pressing member is high, the fixing device can fix even if the temperature of the heating member is low. Shorter than Warm-up of the fixing device between can be completed. When the temperature of the pressing member is low, it is necessary to increase the temperature of the heating member. In this case, the warm-up time is equivalent to the method using only the temperature of the heating member as a criterion, but for example, when the temperature of the pressing member is low, the amount of power supplied to the heating member is lower than usual. By performing control such as increasing the temperature, it is also possible to shorten the warm-up time as compared with a method using only the temperature of the heating member as a criterion.

As a method of controlling the temperature of the fixing device in consideration of the use history of the image forming apparatus, there are methods such as each time the apparatus usage time exceeds a predetermined time or every time image formation exceeds a predetermined number of sheets. Various methods for controlling the temperature of the fixing device based on the criterion have already been proposed. However, the use histories of the image forming device are various, and from the viewpoint of private use of one person, especially indoors or outdoors. There is a wide variety of factors, such as differences in the usage environment, such as the use of an image forming device, and differences in the frequency of use, such as at home or at work.Therefore, it is not possible to control the entire use history of an image forming apparatus based on uniform criteria. It goes without saying that it is possible.

In order to accurately control the temperature of the fixing device in accordance with the usage history of the image forming apparatus, it is necessary to actually detect the temperatures of the heating member and the pressing member and control the temperature based on the results. It is essential.

In Japanese Patent Application Laid-Open No. 5-289562, when the fixing device (pressing member or the like) is cold, more power must be supplied to the heating member in order to maintain the heating member at a constant temperature. Further, it is disclosed that when the fixing device is warm, the electric power supplied to the heating member can be reduced. In the above-mentioned publication, a fixing device using a heating member (film heating method) including a film having a small heat capacity and a heating body is disclosed. In such a fixing device, in order to prevent an excessive temperature rise of the heating body, It is disclosed that the temperature of the fixing device needs to be detected. Further, as a method of detecting the temperature of the fixing device, an example of detecting the temperature rising speed of the heating member when a constant power is supplied to the heating member when the heating member is started up. An example in which the power supply to the heating element is stopped between papers (between papers) and the rate of temperature decrease when the heating element is radiated is detected. The power supply to the heating element is switched between HIGH and LOW between papers. An example is disclosed in which control is performed at two levels to detect a temperature fluctuation (temperature ripple) of the heating element, and an example of detecting electric power supplied to the heating element while paper passes through the fixing device.

[0013]

As is apparent from the above description, it is indispensable for the fixing device to appropriately set the temperature of the heating member according to the temperature of the pressing member.

However, if a temperature detecting means is provided to detect the temperature of the pressing member as disclosed in Japanese Patent Application Laid-Open No. 50-39554, the structure of the fixing device becomes complicated. In general, the temperature detecting means is a contact type, and the pressing member is a flexible elastic body. Therefore, in a portion where the pressing member and the temperature detecting means are in contact with each other, the surface of the pressing member is worn or chipped. ,
There is a problem that the pressing force cannot be obtained partially, resulting in poor fixing or paper wrinkling.

Japanese Patent Application Laid-Open No. Hei 5-289562 discloses some examples of a method for detecting the temperature of the pressing member. For example, when a constant power is supplied to the heating element, When the temperature rise rate of the heating element is detected, a constant power is supplied regardless of the set temperature that the heating member should finally reach. It takes time to detect the temperature rise rate. In such an example, when the heating element heats the object to be heated through a film having a small heat capacity as in a film heating method, the temperature of the heating member easily rises. However, in the case of a general heat fixing device such as a heat roller, the heat capacity of the heating member is large, so that it is not possible to accurately detect the temperature rise of the heating member in a short time. It is possible.

Similarly, for example, when the power supply to the heating element is stopped between the paper sheets and the rate of temperature decrease when the heating element is radiated is detected, the heating element has a heat capacity as in the film heating method. In the case where the object to be heated is heated through a small film, the temperature of the heating member is easily lowered, so that the temperature reduction speed detection time can be easily performed in a short time, and after the temperature is lowered. Further, it is easy to raise the temperature of the heating member to the set temperature. However, in the case of a general heat fixing device such as a heat roller, the heat capacity of the heating member is large, so that the temperature decrease of the heating member can be accurately detected in a short time. In addition, it is impossible to reduce the temperature of the heating member once and then further heat it to control it to the set temperature, which wastes power and time and is not desirable.

Also, for example, when the power supply to the heating element is controlled between two levels of HIGH / LOW between the paper sheets and the temperature fluctuation (temperature ripple) of the heating element is detected, as in the case of the film heating method, In the case where the heating element heats the object to be heated through a small heat capacity film,
Since the temperature of the heating member fluctuates easily, the temperature fluctuation can be detected in a short time. However, in the case of a general heat fixing device such as a heat roller, the temperature fluctuation of the heating member is large due to the large heat capacity of the heating member. Cannot be accurately detected in a short time.

Further, for example, when detecting the electric power supplied to the heating element during the paper passing through the fixing device,
During paper passing, the paper becomes a heat insulating material, and the heat of the heating member is hardly deprived by the pressing member.The amount of heat deprived from the heating member depends on the moisture of the paper and the temperature of the paper. Cannot be accurately detected.

An object of the present invention is to provide a simple structure that does not require a separate means for detecting the temperature of the pressing member, and to accurately detect the temperature of the pressing member. To provide a fixing device capable of appropriately setting the temperature of the heating member according to the temperature of the fixing member.

[0020]

A fixing device according to the present invention includes a heating member having a heating element therein, and a pressing member which presses against the heating member. In a fixing device that sandwiches and conveys a heated body that carries an image, a temperature detection unit that detects a temperature of the heating member, and based on a detection result from the temperature detection unit, controls electric power supplied to the heating body, A temperature control unit for controlling the heating member to a predetermined set temperature, an electric power supplied to the heating unit by the temperature control unit when the object to be heated is not present at a pressure contact portion between the heating member and the pressing member. The setting temperature of the heating member is changed based on the amount.

Further, the fixing device of the present invention has a state discriminating means for discriminating that the object to be heated is being conveyed to the fixing device, and the state discriminating means conveys the object to be heated to the fixing device. The temperature control means is connected to the heating element during a period from a time when a predetermined time elapses after it is determined that the heating element is pressed to a point where the heating target enters the pressure contact portion between the heating member and the pressing member. It is characterized in that the set temperature of the heating member is changed based on the supplied electric energy.

Further, according to the fixing device of the present invention, the temperature of the heating member is set based on the amount of power supplied to the heating element by the temperature control means and the set temperature of the heating member when the amount of power is being supplied. Is changed.

[0023]

The functions of claims 1 to 3 of the present invention will be described below.

According to the first aspect of the present invention, the heat radiating state of the heating member or the amount of electric power required to maintain the heating member at a constant temperature is limited when the paper is not present at the pressure contact portion between the heating member and the pressing member. However, it is difficult to accurately detect the temperature of the pressing member based on the moisture and the temperature of the paper during paper passing. However, in the present invention, by detecting the power supplied to the heating element between the sheets, the temperature of the pressing member is accurately detected without separately installing a means for detecting the temperature of the pressing member. be able to.

Further, according to the first aspect of the present invention, the electric power is supplied to the heating member so that the heating member is at a set temperature at which a good fixing can be performed (when the pressing member is in a specific temperature range). It does not raise or lower the temperature of the heating member regardless of the feasible temperature range, so it is possible to accurately detect the temperature of the pressing member even if the heat capacity of the heating member is particularly large. Also, the temperature of the heating member can be stably maintained at the set temperature.

According to a second aspect of the present invention, when the temperature of the pressure member is detected under the condition that the paper does not exist at the pressure contact portion between the heating member and the pressure member, the temperature of the pressure member is detected and then the temperature of the pressure member is detected. If the time required for the paper to enter the pressure-contact portion between the heating member and the pressure member is unnecessarily long, the paper actually enters the pressure-contact portion between the heating member and the pressure member after detecting the temperature of the pressure member. In the meantime,
In view of the fact that the temperature of the pressing member fluctuates and, when the paper actually enters between the heating member and the pressing member, the respective temperatures of the heating member and the pressing member become inappropriate. Things. (For example, in a case where the temperature of the pressing member is detected after a predetermined period of time when the previous paper has passed during continuous paper passing, when the set temperature of the heating member is increased with respect to the detected temperature of the pressing member, The pressurizing member is heated by the heat from the heating member and rises in temperature before the next paper actually enters the fixing device. In the image forming apparatus, the temperature of the pressing member when the paper actually enters the fixing device becomes considerably higher than that at the time of detection, and paper wrinkles and high-temperature offset occur. If the set temperature of the heating member is reduced with respect to the temperature of the pressure member, the temperature of the pressure member when the paper actually enters the fixing device becomes considerably lower than the detection time, Insufficient fixing occurs.) Akira aims to set the timing of detecting the temperature of the pressing member so that the temperatures of the heating member and the pressing member when the paper actually enters the fixing device are appropriate. Specifically, it is determined whether or not the paper to be heated is being conveyed to the fixing device, and when it is determined that the paper is being conveyed to the fixing device, the pressure is increased. By detecting the temperature of the member, the temperature of the pressing member can be detected as soon as possible before the paper enters the fixing device.

In the present invention, by detecting the temperature of the pressing member when it is determined that the paper is being conveyed to the fixing device, the temperature of the pressing member is detected and then the paper is actually transferred to the fixing device. The time delay until the paper enters can be kept constant for a short time and almost always, for example, irrespective of the fluctuation of the paper interval, so that the temperature of the detected pressure member and the paper actually enter the fixing device. The temperature of the pressurizing member at the time of the fixing does not largely fluctuate, and the temperatures of the heating member and the pressurizing member at the time when the paper actually enters the fixing device can be appropriately set.

According to a third aspect of the present invention, generally, the mutual heat conduction between the objects is proportional to the temperature gradient between the objects.
Therefore, the amount of heat conduction between the heating member and the pressing member (or the amount of power consumed to maintain the heating member at the set temperature) is proportional to the temperature gradient between the heating member and the pressing member, It does not depend on the absolute value of the temperature of the heating member or the pressing member, in other words, when detecting the temperature of the pressing member by the amount of power supplied to maintain the heating member at the set temperature, Unless the temperature of the heating member at the time of detecting the temperature (when the amount of power supplied to the heating element is detected) is further considered, the temperature of the pressing member cannot be detected with higher accuracy. It was made in view of this. .

That is, according to the third aspect of the present invention, since the temperature of the pressurizing member corresponding to the amount of electric power supplied to the heating member changes according to the temperature of the heating member at that time, the temperature of the heating member is changed. The temperature of the pressurizing member is detected based on both the amount of power and the set temperature of the heating member at that time, and further, by changing the set temperature of the heating member in accordance with the result, the temperature of the pressurizing member is further increased. The temperature of the heating member with respect to the temperature can be set appropriately.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments and drawings.

The first embodiment corresponds to the first aspect of the present invention, in which the temperature of the pressing member is detected from the amount of electric power supplied to the heating member when no paper is present in the fixing device, and the result is determined. This is an embodiment in which the set temperature of the heating member is changed based on the temperature.

In the second embodiment, when the set temperature of the heating member is changed, the time required for the temperature of the heating member to actually reach the set temperature is changed to change the set temperature of the heating member. is there.

Embodiment 3 corresponds to the second aspect of the present invention, in which it is determined whether or not the paper is being conveyed to the fixing device, and it is determined that the paper is being conveyed to the fixing device. When it is determined, by detecting the temperature of the pressing member,
This is an embodiment in which the temperature of the pressure member is detected as soon as possible before the paper enters the fixing device.

Embodiment 4 is an embodiment in which the time required for measuring the duty required to determine the set temperature of the heating member is changed. Embodiment 5 Embodiment 5 corresponds to the invention described in claim 2, and Embodiment 3 corresponds to Embodiment 3.
Is an embodiment in which the boundary conditions for determining the set temperature of the heating roller are different.

Embodiment 6 corresponds to the third aspect of the present invention, in which the average duty of the power supplied to the heating roller and the average duty are measured as boundary conditions for changing the set temperature of the heating roller. This is an embodiment in which the set temperature of the heating roller is determined based on both the set temperature of the heated roller at the time.

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

The fixing device shown in FIG. 1 includes a heating member including a heating roller 1 made of a metal cylinder having good heat conductivity such as aluminum and a heating member 7 such as a halogen lamp installed inside the heating roller 1. The shaft is constituted by a pressure member which is a pressure roller 2 having an elastic body such as silicone rubber formed on an outer peripheral surface of the shaft. The heating roller 1 and the pressure roller 2 are pressed against each other by a load means (not shown).

Further, a temperature detecting means 8 such as a thermistor is provided so as to be in contact with the outer peripheral surface of the heating roller 1 or in the vicinity of the outer peripheral surface of the heating roller 1.

The heating roller 1 and the pressure roller 2
Is driven to rotate by a driving device (not shown), and the paper to be heated is heated by a heating roller 1 and a pressure roller 2 in the direction of the arrow.
After being fixed in the nip of the fixing device, the toner is discharged from the fixing device.

In addition, if necessary, the fixing device may include:
Peeling claw 9 for peeling the paper after fixing from heating roller 1
A discharge roller 10 for smoothly discharging paper discharged from the nip of the fixing device from the fixing device;
A cleaner or the like such as an oil-impregnated pad for applying a release agent such as silicone oil to the surface and removing toner adhered to the surface of the heating roller 1 may be provided.

Here, a method of controlling the temperature of the heating member will be described.

The temperature of the heating member (more specifically, the heating roller 1 constituting a part of the heating member) is controlled by the amount of heat released from the heating element 7 disposed inside the heating roller 1. The amount of heat released from the heating element 7 is controlled by the amount of power supplied from the temperature control means 8.

The temperature of the heating roller 1 is detected by the temperature detecting means 8, and the temperature detecting means 8 outputs a signal corresponding to the temperature of the heating member to the temperature control means. In the temperature control means, the target temperature of the heating member in advance (the temperature that the heating member should finally reach and should be maintained after reaching)
Is set as the set temperature. The temperature controller compares the set temperature with the output from the temperature detector 8 and controls the amount of power supplied to the heater 7 according to the result.

When the temperature of the heating roller 1 detected by the temperature detecting means 8 is lower than the set temperature set in the temperature controlling means, the temperature controlling means increases the amount of electric power supplied to the heating element 7, On the other hand, when the temperature is high, the temperature control means reduces the amount of electric power supplied to the heating element 7 so that the temperature of the heating roller 1 is controlled to the set temperature.

Specifically, a thermistor is used as the temperature detecting means 8, and the output from the thermistor is A / D converted.
It is taken in by the CPU as the temperature control means. The CPU compares the set temperature of the heating member stored in the memory with the output from the thermistor, and based on the result, determines the heating element 7 based on the result.
Of the halogen lamp is controlled. The temperature control means controls the amount of electric power supplied to the halogen lamp by controlling the phase and / or the wave number of the AC voltage supplied to the halogen lamp.

As an example of a method for controlling the amount of electric power supplied to the heater 7 such as a halogen lamp, a duty (du)
ty) The control will be described.

The energization of the heating element 7 from the temperature control means is controlled at certain time intervals. The current control time from the temperature control means to the heating element 7 is called a control cycle.

The ratio of the time during which the heating element 7 is actually energized to this control cycle is called the duty. For example, when the control cycle is 1 second and the duty is 10%, 10
The heating element 7 is energized for 0 ms, and is not energized for 900 ms. When the power consumption is 400 W when the duty is 100%, the power consumption is approximately 4 if the duty is 10%.
0W.

As described above, by changing the duty, the amount of electric power supplied to the heating element 7 can be adjusted, and the temperature of the heating roller 1 can be controlled. Conversely, the amount of power supplied to the heating element 7 can be obtained from the duty.

When a halogen lamp is used as the heating element 7, it is necessary to avoid applying a large current to the halogen lamp in order to maintain its life for a long period of time. It has the characteristics that it is low and large current easily flows (rush current). Therefore, when using a halogen lamp as the heating element 7,
Generally, by performing zero-cross control, the inrush current to the halogen lamp is suppressed, and the life of the halogen lamp is maintained for a long time. Zero-cross control refers to a case where power is supplied to the heating element 7 by an AC voltage.
This is a method in which energization is not started immediately even if a signal (starter ON signal) for instructing start of power supply to the AC power supply is started, and the heater is energized after waiting for the AC voltage to cross zero. As a result, the voltage applied to the heating element 7 gradually increases, so that the inrush current can be reduced and the life of the halogen lamp can be extended.

Next, a proportional control will be described as an example of a method of controlling the amount of electric power supplied to the heater 7 such as a halogen lamp.

The proportional control outputs electric power proportional to the difference between the temperature of the heating member (the temperature detected by the temperature detecting means 8) and the set temperature. FIG. 2 shows an example of the output characteristic with respect to the temperature of the heating member in the proportional control.

When the temperature of the heating member is lower than A, the duty is set to 100%, and when the temperature is higher than C, the duty is set to 0%. Between A and C, a duty proportional to the difference between the temperature of the heating member and the set temperature B is output.

Therefore, when the temperature of the heating member is controlled to the set temperature, in the proportional control, when the heat radiation amount of the heating member is large (or the temperature of the heating member is low), a large electric power is supplied and the heating member is discharged. When the amount of heat is small (or the temperature of the heating member is high), a small electric power is supplied. As described above, in the proportional control, electric power is supplied so as to compensate for the heat radiation amount of the heating member.

In addition to proportional control (P control), a method of outputting power in proportion to the integral of the temperature deviation (I control) and a method of outputting power in proportion to the rate of change of temperature (D control) are known. Generally, PI control, PID control, PD control, and the like are used by combining P, I, and D.

Now, a method for detecting the temperature of the pressing member will be described.

Heat is radiated from the heating member around the heating member, in particular, to the pressing member that comes into contact with the heating member. At this time, the heat radiation amount of the heating member is determined by the temperature of the pressing member (temperature gradient between the heating member and the pressing member).

On the other hand, when the heating member is controlled to the set temperature, the amount of electric power supplied to the heating member is proportional to the amount of heat radiation of the heating member.

Therefore, the temperature of the pressing member can be detected from the amount of electric power supplied to the heating member.

Further, as described above, since the amount of power supplied to the heating member can be obtained from the duty supplied to the heating member, the amount of power supplied to the heating member can be obtained without using a separate power amount measuring means such as a wattmeter. By using the energized duty, the temperature of the pressing member can be detected.

However, while the paper is passing through the nip of the fixing device, the heat of the heating member is hardly deprived by the pressure member because the paper becomes a heat insulating material. Since the amounts of heat taken from the members are different, it has been difficult to accurately detect the temperature of the pressing member from the amount of electric power supplied to the heating member. Therefore, in order to detect the temperature of the pressing member from the amount of electric power supplied to the heating member, the timing of detecting the amount of electric power of the heating member is determined in such a manner that the amount of heat radiation from the heating member is substantially limited by the pressing member, That is, the paper must not exist in the nip of the fixing device, and the heating member and the pressing member must be in direct contact.

Therefore, it is necessary to determine that there is no paper in the nip of the fixing device, and to detect the temperature of the pressing member during that time.

Here, a method used in the present embodiment will be described as a method for determining that there is no paper in the nip of the fixing device.

Hereinafter, an electrophotographic printer will be described as an example of an image forming apparatus using the fixing device of the present invention. FIG. 3 is a schematic sectional view of an electrophotographic printer using the fixing device of the present invention.

As is apparent from FIG. 3, the paper to be heated is picked up by the paper feed roller 4 and starts to be conveyed toward the fixing device. The start of the paper conveyance is detected by a state determination unit that determines that the paper is being conveyed to the fixing device. In the present embodiment, the paper feed sensor 3 is used as the state determination means. The paper that has passed through the paper feed sensor 3 is conveyed to a pressure contact portion between a photoconductor 5, which is an image carrier on which a toner image is formed, and a transfer roller 6 for transferring the toner image on the photoconductor 5 to the paper. The toner image is transferred to the paper at the pressing portion. Further, the paper on which the toner image has been transferred is conveyed toward a fixing device, and the toner image is fixed on the paper by heat and pressure at a pressure contact portion between the heating roller 1 and the pressure roller 2.

In the printer of this embodiment, the paper transport distance from the paper feed sensor 3 to the nip of the fixing device is 115
mm, and the paper conveyance speed is 23 mm / s. Therefore, it takes 5.0 seconds from when the leading edge of the paper passes through the paper feed sensor 3 to when it reaches the nip of the fixing device.

Therefore, in the present embodiment, the absence of paper in the nip of the fixing device is detected using the paper feed sensor 3 as follows.

At the start of printing, no paper is present in the nip until 5 seconds have passed since the leading edge of the first paper passed the paper feed sensor.

At the time of continuous printing, the nip is maintained from 5 seconds after the trailing edge of the n-th sheet has passed the paper feed sensor to 5 seconds after the leading edge of the (n + 1) th sheet has passed the paper feed sensor. There is no paper.

For example, assuming that the A4 size paper is transported in the vertical direction with a paper interval of 3 seconds, three seconds after the trailing edge of the n-th paper has passed the paper feed sensor (at this point, the fixing Assuming that the leading edge of the (n + 1) th sheet has passed through the paper feed sensor at the nip of the apparatus (the n-th sheet is present), after a lapse of 2 seconds (the trailing edge of the n-th paper is the paper feed sensor) 5 seconds after passing through, and 2 seconds after the leading edge of the (n + 1) th sheet has passed the paper feed sensor), the trailing edge of the nth sheet is discharged from the fixing device, and The leading edge of the sheet has not yet reached the fixing device, and no paper exists in the nip of the fixing device. After a further 3 seconds (corresponding to the inter-sheet time), that is, 5 seconds after the leading edge of the (n + 1) th sheet has passed the paper feed sensor, the leading edge of the (n + 1) th sheet is at the nip of the fixing device. , And the (n + 1) th sheet is present in the nip of the fixing device.

In this embodiment, in order to determine that paper is not present in the nip of the fixing device, a paper feed sensor is used as a means for detecting that the paper to be heated is conveyed to the fixing device. Although the present invention is used, the present invention is not limited to this. For example, various control signals such as a paper feed start signal and an image formation start signal can be used in addition to the paper feed sensor. By using such a control signal, even when a heating member having a large heat capacity is used, it is possible to obtain a sufficient time for the heating member to warm up before the paper actually starts being conveyed to the fixing device. By the way, in the present embodiment, in order to maintain the life of the heating element for a long period of time, if the paper is not fed due to a paper feeding error, the temperature of the heating member is surely not increased or decreased so that the paper is not wasted. In order to detect that the paper is conveyed to the fixing device without a paper feeding error, the paper feeding sensor detects that the paper is conveyed to the fixing device. Further, the paper feed sensor can be installed at any position between the position where the paper is started to be fed and the paper entering side of the fixing device.

In this embodiment, the fixing device is driven to rotate,
Further, when the heating member is controlled to the set temperature, and when there is no paper in the nip of the fixing device, the duty outputted by the temperature control unit to the heating member is stored in the memory as needed, and the temperature control unit stored in the memory receives the duty. The average duty was determined by dividing the sum of all duties by the total number of outputs. Specifically, for example, when the control cycle is 1 second and the sheet interval is 3 seconds, the duty after 1 second (output during 1 second between 0 second and 1 second after the start of control) is 60%, Duty 55 seconds after 2 seconds (output for 1 second between 1 second and 2 seconds after start of control) and 3 seconds (3 seconds after 2 seconds after start of control
Output in 1 second after 2 seconds) is 50
%, The total number of times of output by the temperature control means between the sheets is three times, the sum of all the duties between the sheets is 165%, and the average duty is 55%. Incidentally, based on only one specific control cycle,
For example, it is possible to detect the temperature of the pressing member only based on the duty after 2 seconds. However, this is possible when the temperature variation of the heating member and the pressing member is extremely small as a fixing device, or when the fixing characteristics or the high temperature Good results can be obtained when a toner having a good offset characteristic is used. However, in a general thermal fixing device using a heating member having a particularly large heat capacity, a temperature variation of ± several degrees Celsius occurs.
It is difficult to accurately detect the temperature of the pressurizing member from the duty cycle. Therefore, it is preferable to use an average of a plurality of duties since higher accuracy can be obtained. Therefore, in the present embodiment, the temperature of the pressurizing member is detected based on the average duty obtained by averaging a plurality of duties. The feature of the present invention resides in that the temperature of the pressurizing member is detected when no paper is present in the fixing device. When the time required for measurement (duty measurement time = duty output count × control cycle) is continuous paper feeding, the time interval must not exceed the paper interval time, and the control cycle time is the minimum paper interval time. Need to be short enough.

When a CPU is used as the temperature control means, the CPU generally takes a long time to perform the division. Therefore, instead of calculating the average of the duties, the CPU calculates the sum of the duties, and determines the temperature of the heating member from the sum of the duties. For example, the load on the CPU can be reduced and the temperature of the pressing member can be detected more quickly.

Now, in order to detect the temperature of the pressing member from the amount of electric power supplied to the heating member between the sheets, and to change the set temperature of the heating member based on the result, the temperature of the pressing member must be set to any value. In this case, it is necessary to define the boundary condition for changing the set temperature of the heating member when the amount of electric power supplied to the heating member is changed.

The boundary conditions are obtained by correlating the table format, the temperature of the pressing member (and the corresponding amount of power supplied to the heating member and the duty of the power supplied to the heating member) and the set temperature of the heating member. Any of various expressions such as a mathematical expression and an analog circuit may be used.

The method for determining the boundary conditions will be specifically described in the first embodiment.

<Embodiment 1> This embodiment corresponds to the first aspect of the present invention, in which the amount of power supplied to the heating member when no paper is present in the nip of the fixing device, such as between sheets, is increased. The temperature of the member is detected, and the set temperature of the heating member is changed based on the result.

In this embodiment, an aluminum cylinder (outer diameter 18 mmφ,
(Thickness: 0.6 mm) was used as the heating roller 1, and a halogen lamp was provided therein as the heating element 7. Further, a roller (18 mm in outer diameter) in which a silicone rubber layer having a JIS-A hardness of 23 degrees was formed on the outer peripheral surface of the steel shaft by injection molding was used as the pressure roller 2. The heating roller 1 and the pressure roller are pressed against each other with a total load of 6 kgf by load means (not shown).

The amount of power supplied to the halogen lamp is controlled by the temperature control means to control the energization time as a duty cycle with a control cycle of 1 second.

Now, how to determine the boundary condition for changing the set temperature of the heating member will be described.

FIG. 4A is a view showing conditions for occurrence of fixing failure, paper wrinkles, and high-temperature offset in the printer used in this embodiment. The horizontal axis is the temperature of the pressure roller, and the vertical axis is the temperature of the heating roller. In the figure, the temperature of the pressure roller and the temperature of the heating roller are measured by a temperature detecting means separately installed in the printer only to create FIG. 4, and in the embodiment, when the image is actually formed, Has been removed.

FIG. 4A is specifically described.

At a temperature lower than the line b, a fixing failure occurs, at a temperature higher than the line c, a high-temperature offset occurs, and at a temperature higher than the line d, paper wrinkles occur. Line e indicates the temperature of the pressure roller immediately before the first sheet enters the fixing device when printing is started in a state where the pressure roller is sufficiently cooled. Further, if continuous printing is continued, the temperature of the pressure roller rises and eventually saturates. Line f shows the saturation temperature of the pressure roller.

Therefore, poor fixing, high temperature offset,
FIG. 4A shows an area where good fixing without paper wrinkles is possible.
At the inside of the polygon surrounded by the lines b to f.

FIG. 4B shows that the temperature of the heating roller is 1 unit.
It is a figure which shows the relationship between the temperature of a pressure roller at 71 degreeC, and an average duty. The average duty before the first sheet entered the fixing device was 50 to 60%. However, in the case of continuously forming an image, the average duty decreases as the temperature of the pressure roller increases. . As is apparent from the figure, if the average duty corresponding to the amount of electric power supplied to the heating roller is known, the temperature of the pressure roller can be detected. In the figure, the temperature of the heating roller is 171 ° C., and the average duty is Is 26%, the temperature of the pressure roller is 110 ° C
It turns out that it has become.

In the present embodiment, the set temperature of the heating roller is adjusted so as not to cause a fixing failure even when the temperature of the pressure roller is sufficiently cooled (see line e in FIG. 4A). First, the temperature was set to 171 ° C. However, in this embodiment, the temperature variation of the heating roller due to the temperature detection variation and control variation of the thermistor was ± 4 degrees. Therefore, when the set temperature of the heating roller is 171 ° C., the actual temperature of the heating roller is 175 ° C. at the maximum value and 167 ° C. at the minimum value.
° C.

When the set temperature of the heating roller is set to 171 ° C., and the image is continuously formed, the temperature of the pressure roller rises, causing a high-temperature offset and paper wrinkling (FIG. 4A). Set the temperature of the line c and the heating roller to 171 ° C
(See the point of intersection with the maximum value of the temperature variation of 175 ° C.) Therefore, when the temperature of the pressure roller exceeds 110 ° C., it is necessary to change the set temperature of the heating roller from 171 ° C. In this embodiment, the set temperature of the heating roller is changed to 156 ° C. in order to prevent high-temperature offset and paper wrinkles from occurring even when the temperature of the pressure roller is 110 ° C. or higher, and to prevent occurrence of fixing failure. did. FIG. 4 (a)
As is clear, the set temperature of the heating roller is 156 ° C.
The fixing can be performed satisfactorily in a state where the temperature of the pressure roller exceeds 110 ° C. even if the temperature variation is considered.

From the above, the temperature of the pressure roller is 11
The set temperature of the heating roller is switched to 171 ° C. or 156 ° C. based on whether it is 0 ° C. or less, that is, whether the average duty corresponding to the amount of electric power supplied to the heating roller is 26% or more. As a result, it is clear that good fixing is always possible. In this embodiment, the boundary conditions for changing the set temperature of the heating member are determined as shown in Table 1.

[0089]

[Table 1]

The numerical values shown in FIGS. 4A and 4B and Table 1 are all related to the fixing device of the first embodiment.
It is determined experimentally, and if the configuration of the fixing device is different, it is of course necessary to define the boundary conditions according to the configuration of each fixing device according to the procedure of the first embodiment. (Of course, even if the configuration of the fixing device is the same, the boundary condition changes if the toner or the like changes.) By the way, in the printer of this embodiment, when forming an image continuously, The time is fixed at 3 seconds. If the amount of image data is large and it takes time to transfer and develop the data, and the image cannot be formed even after 3 seconds, the power consumption of the printer is reduced. For this purpose, the image forming process was temporarily stopped (standby state), and the image formation was started again when the data development was completed. The standby state indicates a state in which the power of the printer is turned on but the image forming operation is not started.In this standby state, the power to the halogen lamp is turned on to save power. The halogen lamp is stopped, and when the image formation becomes possible (in this case, when the data development is completed), the power supply to the halogen lamp is started. It should be noted that the sheet interval time (fixed to 3 seconds in the present embodiment) for continuously forming an image is not a standby state, but a state in which the image forming operation is continued. Therefore, the halogen lamp is energized.

(Experimental Example 1) This is an experimental example at the start of the image forming operation.

When an image formation start signal is input to the printer in the standby state, first, the temperature control means sets the set temperature of the heating roller to 171 ° C., and sets the heating roller (halogen lamp as a heating element for heating the heating roller). , The fixing device is started, and the driving is started. Next, the paper is fed, and at the same time as the leading edge of the paper passes through the paper feed sensor, the duty output by the temperature control means starts to be stored in the memory. An average duty corresponding to the amount of electric power supplied to the heating roller for 5 seconds after the leading end has passed the paper feed sensor is calculated. Based on the average duty, the set temperature of the heating roller was changed according to Table 1.

FIG. 5 shows an experimental example, that is, an algorithm for determining the set temperature of the heating roller at the start of the image forming operation.

At the start of the image forming operation, when the fixing device is started, first, the set temperature set for the heating roller is temporarily referred to as a first temperature here. In this experimental example, the first temperature was 171 ° C. However, this first
The temperature is a temperature that can be selected as a set temperature of the heating roller (156 ° C. or 17 ° C. in Table 1 in this experimental example).
1 ° C.). However, in the standby state, the temperatures of the heating roller and the pressure roller are usually considerably reduced. Therefore, in order to reduce the warm-up time of the fixing device, the first temperature can be selected as the set temperature of the heating roller. It is preferable to select the highest set temperature among the various temperatures. Also,
The set temperature of the heating roller when actually performing the fixing operation is the first temperature.
At a set temperature (hereinafter, tentatively referred to as a second temperature to distinguish it from the first temperature) determined based on an average duty corresponding to the amount of electric power supplied to the heating roller controlled to the first temperature instead of the temperature. The purpose of the present invention is
It is an object of the present invention to accurately determine the temperature according to the temperature of the pressure roller. Therefore, in order to determine the temperature of the pressure roller with high accuracy, the boundary condition, that is, the average temperature of the heat roller corresponding to the temperature of the pressure roller is determined. Then 1
71 ° C. When the temperature of the pressure roller is controlled by setting the temperature of the heating roller (see FIG. 4B) as the set temperature of the heating roller (the first temperature of the present experimental example), the temperature of the pressure roller can be detected with higher accuracy. It is preferable because the set temperature (second temperature) of the heating roller at the time of performing the above can be determined more accurately. In this experimental example, the first temperature was set to 171 ° C. for the above reason.
And

In this experimental example, even when an image was formed when the pressure roller was cold, no defective fixing occurred. Even when an image was formed when the temperature of the pressure roller was high, no paper wrinkles or high-temperature offset occurred.

(Experimental Example 2) This is an experimental example during continuous paper feeding (in the case of continuously forming an image).

When the image is continuously formed, the temperature of the pressure roller rises. Therefore, in this experimental example, the control temperature of the heating roller was determined from the average duty as shown in the algorithm of FIG. (In this experimental example, the image data is adjusted so that the printer does not enter a standby state during continuous paper feeding, that is, so that paper is continuously fed one by one with a sheet interval of 3 seconds during continuous paper feeding. Then, the temperature of the pressure roller is increased as quickly as possible by continuous paper passing.) At this time, the average duty was obtained as follows.

Five seconds after the trailing edge of the n-th paper has passed the paper feed sensor, the average of the duty starts to be calculated, and n + 1
The averaging was finished 5 seconds after the leading edge of the sheet passed the paper feed sensor, and the temperature of the heating roller was set according to Table 1 from the average duty obtained as a result of the calculation.

The set temperature of the first heating roller was determined in the same manner as in Experimental Example 1.

In this experimental example, no paper wrinkling or high-temperature offset occurred even after 100 continuous paper passes.

In this experiment, the set temperature of the heating roller when the n-th sheet enters the fixing device is the set temperature of the heating roller when the (n-1) th sheet enters the fixing device. And the set temperature of the heating roller when the (n + 1) th sheet enters the fixing device is determined based on the set temperature of the heating roller when the nth sheet enters the fixing device. Become.

An object of the present invention is to set the temperature of the heating roller when the paper actually enters the fixing device in the time interval before the paper actually enters the fixing device in accordance with the temperature of the pressure roller. You have to decide well.

Therefore, in order to determine the temperature of the pressure roller with high accuracy, in determining the boundary condition, that is, the average duty of the heat roller corresponding to the temperature of the pressure roller, the temperature of the heat roller as a reference ( In this embodiment, the temperature of the pressure roller can be detected with higher accuracy by controlling the temperature of the heating roller to 171 ° C. (see FIG. 4B) as the set temperature of the heating roller, and the fixing operation is actually performed. This is preferable because the set temperature of the heating roller at the time can be determined more accurately.

Therefore, the set temperature of the heating roller when the nth sheet enters the fixing device is determined based on the set temperature of the heating roller when the (n-1) th sheet enters the fixing device. Each time, after the (n-1) th sheet is ejected from the fixing device, regardless of the set temperature of the heating roller at that time, the set temperature of the heated roller is immediately used as a reference in determining the boundary condition. (Set in accordance with this experimental example, the temperature of the heating roller is always set to 171 ° C. between the (n−1) th sheet and the nth sheet.
), The temperature of the pressure roller can be detected with higher accuracy by detecting the temperature of the pressure roller.
More optimal temperature of the heating roller can be set when the n-th sheet enters the fixing device. However, in order to more appropriately set the set temperature of the heating roller (hereinafter, described in accordance with the configuration of the present embodiment), the setting of the heating roller is always performed between the sheets after the sheet is discharged from the fixing device. Comparing the method of controlling the temperature to 171 ° C. with the present experimental example, n
When the set temperature of the heating roller when the first sheet passes through the fixing device is 156 ° C. and the set temperature of the heating roller when the nth sheet passes through the fixing device is 156 ° C.,
In this experimental example, the set temperature of the heating roller was 156 during this time.
It is enough to keep the temperature of the heating roller at 171 ° C.
Whatever the set temperature of the heating roller for the n-th sheet is, the set temperature of the heating roller is set to 1 between the sheets.
Since the temperature is controlled to 71 ° C., wasteful electric power may be consumed between sheets in some cases, and the life of the heating element is shortened.

As described above, the selection of the set temperature of the heating roller between the papers is based on various viewpoints. In this experimental example, the set temperature of the heating roller between the papers is 156 ° C. or 171 ° C. Since no problem was observed above, the set temperature of the heating roller when the n-th sheet entered the fixing device was the set temperature of the heating roller when the (n-1) th sheet entered the fixing device. And n
The set temperature of the heating roller when the + 1st sheet enters the fixing device is determined based on the set temperature of the heating roller when the nth sheet enters the fixing device.

<Embodiment 2> This embodiment is an embodiment in which the thickness of the heating roller is different from that of Embodiment 1, and when the set temperature of the heating member is changed, the temperature of the heating member is actually set to the set temperature. The set temperature of the heating member is changed in anticipation of the time required to reach the temperature.

In this embodiment, the thickness of the heating roller is set to 1.
The thickness was increased to 7 mm, and the heat capacity of the heating roller was increased.

In the second embodiment, as in the first embodiment, the boundary condition, that is, the average duty of the heating roller corresponding to the temperature of the pressure roller was experimentally obtained. The same result as in the first embodiment was obtained. Was done. Therefore, also in the present embodiment, the set temperature of the heating roller is determined based on Table 1 as in the first embodiment.

However, in the present embodiment, by increasing the thickness of the heating roller, the time required for the temperature of the heating roller to reach the set temperature when the heating roller is controlled to the set temperature is the same as in Experimental Example 1. When the set temperature of the heating roller is changed, it takes about 3 seconds until the temperature of the heating roller reaches the changed set temperature.

Therefore, in the fixing device of this embodiment, as in the first embodiment, when the set temperature of the heating roller is switched at substantially the same time as the paper enters the fixing device, the heating is performed when the paper actually enters the fixing device. The roller temperature cannot reach the set temperature sufficiently.

Therefore, in this embodiment, the set temperature of the heating roller is determined three seconds before the paper enters the fixing device, and is changed as necessary.

That is, in this embodiment, the first embodiment is used.
The difference is that the thickness of the heating roller differs from that of the heating roller, and correspondingly, the setting temperature of the heating roller is changed earlier in anticipation of the time required for the temperature of the heating roller to reach the setting temperature. Different from Example 1.

In the present embodiment, only the case where the image forming operation is started will be described. However, it goes without saying that the same effect can be obtained also between the sheets during continuous sheet feeding.

When an image formation start signal is input to the printer in the standby state, first, the temperature control unit sets the temperature of the heating roller to 171 ° C., supplies power to the heating roller, and starts up the fixing device. , Start driving. Then
At the same time as the paper is fed and the leading edge of the paper passes through the paper feed sensor, the duty output by the temperature control means starts to accumulate in the memory. An average duty corresponding to the amount of electric power supplied to the heating roller for two seconds after passing through the paper feed sensor is calculated. Based on the average duty, the set temperature of the heating roller was changed according to Table 1.

In this embodiment, no fixing failure, no paper wrinkles or high-temperature offset occurred regardless of the initial temperature of the pressure roller.

Further, since the heat capacity of the heating roller is large and the temperature of the heating roller is stable, the environmental temperature of the printer is low (when low-temperature paper is passed) or the paper having a large heat capacity (thick paper or humidity is low). Even when passing high paper, or when using long paper (for example, legal paper or continuous form paper) in the transport direction of the fixing device, the temperature of the heating roller does not drop at the rear end of the paper, and fixing failure occurs. Did not.

<Embodiment 3> This embodiment corresponds to the second aspect of the present invention, in which it is determined whether or not paper is being conveyed to a fixing device. Detecting the temperature of the pressing member when it is determined that the paper is in the fixing state, the temperature of the pressing member is detected as soon as possible before the paper enters the fixing device. In an image forming apparatus in which the interval is indefinite, a high-temperature offset or a paper wrinkle does not occur even if the temperature of the pressure roller increases when the sheet interval is long, and a good image is obtained even when the pressure roller is cold. This has the effect that the fixing property can be ensured.

The printer according to the present embodiment differs from the printer according to the first embodiment in that the inter-sheet time for continuously forming an image is indefinite. (However, the inter-sheet time is set to be at least 3 seconds.) That is, in the printer of the present embodiment, when forming images continuously, the amount of image data is large and data transfer is large. Or even if deployment takes time,
The image forming process is not temporarily stopped (the image forming process does not wait until all the image forming is completed).
Therefore, while the image is continuously formed, the image forming operation is continued even during the transfer or the development of the image data, and the sheet interval is indefinite, and
It goes without saying that the halogen lamp is energized during the sheet interval.

When the temperature of the pressurizing member is detected between sheets during continuous paper passing, the amount of power supplied to the heating member over the entire period of the sheet interval is detected as in the first embodiment. If the temperature of the pressure member is detected, if the paper interval is long, the temperature of the pressure member rises before the paper actually enters the pressure contact portion between the heating member and the pressure member. However, when the paper actually enters between the heating member and the pressing member, the temperatures of the heating member and the pressing member become inappropriate.

Therefore, in the present embodiment, as a method for obtaining an average duty corresponding to the amount of electric power supplied to the heating roller, the duty is sampled for each control cycle during the entire interval between sheets. Unlike the first embodiment, the duty is sampled only for a predetermined period of the sheet interval, and the sampling timing of the duty and the number of times of sampling are different from those in the first embodiment.

In this embodiment, of the series of duties output from the temperature control means to the heating member between the sheets, the duty output immediately before the sheet enters the nip of the fixing device and the duty output last time The temperature of the pressure roller is detected based on the average duty, and the set temperature of the heating roller is determined according to the result.

Hereinafter, the present embodiment will be specifically described based on experimental examples.

(Experimental Example 3) At the start of image formation, ie,
Before the first sheet enters the fixing device, first, the set temperature of the heating roller is determined by the algorithm of FIG.

More specifically, when an image forming signal is input to the printer in the standby state, first, the first temperature (171 ° C. in this embodiment) is set as the set temperature, the heating roller temperature is raised, and the drive is started. I do. Next, feeding of the first sheet is started. The leading edge of the paper enters the nip of the fixing device 5 seconds after passing through the paper feed sensor.

In this experimental example, the duty output at 3 seconds and 4 seconds after the leading edge of the paper passed the paper feed sensor (specifically, the control cycle of the power supplied to the heating member is 1 cycle).
Seconds, the duty output to the heating member between 2 seconds and 3 seconds after the leading edge of the paper has passed the paper feed sensor, and 3 seconds after the leading edge of the paper has passed the paper feed sensor.
The duty output to the heating member between the second and four seconds later was averaged to obtain an average duty. The set temperature of the heating roller was determined from the average duty according to Table 1.

Further, the setting temperature of the heating member for continuously forming images on the second and subsequent sheets was determined by the algorithm shown in FIG.

Duties output 3 seconds and 4 seconds after the leading edge of the n-th sheet passed the paper feed sensor were averaged to obtain an average duty. From the calculated average duty, the set temperature of the heating roller is determined according to Table 1, and n
The fixing of the sheet of paper was performed.

In this experimental example, paper wrinkles and high-temperature offset did not occur even when the amount of image data was large and the time between sheets was as long as 30 seconds. Further, even when the temperature of the pressure roller was low, occurrence of fixing failure could be suppressed.

(Experimental Example 4) This experimental example is the same as Experimental Example 3 except that the control cycle of the power supplied to the heating member is set to 0.1 second and the minimum sheet interval is set to 2 seconds. did.

Between 1.5 seconds and 0.5 seconds before the paper enters the fixing device (from 3.5 seconds to 4.5 seconds after the leading edge of the paper has passed through the paper sensor). The pressure roller temperature was detected from the average value of the output duties (that is, the duty from 0.5 seconds before the paper entered the fixing device to the time the paper entered the fixing device was not included in the calculation).

Even when the amount of image data was large and the time between sheets was as long as 30 seconds, no paper wrinkles or high-temperature offset occurred. Further, even when the temperature of the pressure roller was low, occurrence of fixing failure could be suppressed. As described above, even if the duty just before the paper enters is not added to the calculation of the average duty, the effect of the present invention is not deviated from the intended purpose.

<Embodiment 4> This embodiment is different from the embodiment 3 in that the control cycle for supplying power to the heating member and the number of times of sampling of the power supplied to the heating member to determine the set temperature of the heating member Are different, that is, the time required to measure the required duty is different.

By using an average duty obtained by averaging a plurality of duties supplied to the heating roller,
As described above, the set temperature of the heating roller can be determined with high accuracy.

However, when obtaining the average duty from a plurality of duties, a time T (duty measurement time) required to measure the duty by an amount necessary for obtaining the average duty is required.

T = (duty output frequency) × (control cycle) If this time T is set to be excessively long, the temperature of the pressure roller rises while measuring the duty a plurality of times. However, the temperature of the pressure roller when the paper enters the fixing device becomes considerably higher than the temperature of the pressure roller corresponding to the average duty, and the set temperature of the heating roller becomes inappropriate, resulting in high-temperature offset and paper wrinkling. May occur. Therefore, T needs to be sufficiently short.

Therefore, in this embodiment, the duty measurement time (that is, the time required to calculate the average duty) will be considered.

In the printer of the present embodiment, the interval between sheets for continuously forming an image is fixed to 20 seconds, and when forming images continuously, the amount of image data is small. Even if it takes time to transfer or develop data, the image forming process is not suspended (it does not enter a standby state and forcibly starts image forming if the paper interval exceeds 20 seconds) Different from Example 1.

In this embodiment, the average number of duty output times is set to 2, 4, 8, and 16 times. Thus, T is 2, 4, 8, 16 seconds.

The relationship between T and high-temperature offset and paper wrinkles will be described. Specifically, Table 2 shows the results of the fixing state (high-temperature offset and paper wrinkle) when 100 images were continuously formed.

In Table 2, ○ indicates that no high-temperature offset or paper wrinkling occurred, Δ indicates that slight high-temperature offset or paper wrinkling occurred (no problem in practical use), and severe high-temperature offset or paper wrinkling occurred. In this case, a problem occurs in practical use.

As shown in Table 2, when T was within 4 seconds, no high-temperature offset or paper wrinkle occurred.

Therefore, T is preferably within 4 seconds.

[0143]

[Table 2]

<Embodiment 5> This embodiment is an embodiment of a fixing device having a structure corresponding to the second aspect of the present invention.

However, this embodiment is different from the first and third embodiments in the boundary conditions for determining the set temperature of the heating roller.

Table 3 shows the relationship between the set temperature of the heating roller and the average duty of the power supplied to the heating roller in this embodiment.

[0147]

[Table 3]

The set temperature of the heating roller in this embodiment is of three types, and depends on the set temperature of the heating roller when detecting the temperature of the pressure roller (measuring the average duty of the power supplied to the heating roller). When the average duty of the power supplied to the heating roller is 33% or more,
° C and 160 ° C when it is 21% or more and less than 33%.
When it was less than 1%, the temperature was set to 140 ° C.

The boundary conditions relating to the set temperature of the heating roller shown in Table 3 are obtained by the same procedure as in Example 1 (see FIGS. 4A and 4B).

The other configuration was the same as that of Example 3 (Experimental Example 3).

In this embodiment, even when continuous printing is performed when the pressure roller is cold, no fixing failure occurs. Even if continuous printing is started immediately after continuous printing, paper wrinkles are not generated. No high temperature offset occurred.

<Embodiment 6> This embodiment is an embodiment of a fixing device having a structure corresponding to the third aspect of the present invention.

However, in this embodiment, the boundary conditions for determining the set temperature of the heating roller are different from those of the first and third embodiments. Specifically, in this embodiment, unlike the above embodiment, the average duty of the power supplied to the heating roller (corresponding to the temperature of the pressure roller) is used as a boundary condition for changing the set temperature of the heating roller. ), The set temperature of the heating roller when the average duty is measured is used, and the set temperature of the heating roller is determined based on both. That is, the present embodiment is characterized in that the average duty value for determining the set temperature differs for each set temperature at that time. As described above, the relationship between the average duty of the electric power supplied to the heating roller and the temperature of the pressure roller depends on the temperature of the heating roller. The temperature of the roller can be detected, and the temperature of the heating roller can be set more appropriately.

Table 4 shows the relationship between the set temperature of the heating roller, the average duty of the power supplied to the heating roller, and the set temperature of the heating roller when the average duty was measured.

[0155]

[Table 4]

A method for determining the set temperature of the heating roller will be described with reference to Table 4.

For example, when the average duty of the power supplied to the heating roller is measured, the set temperature of the heating roller is 170 ° C., and the average duty at that time is less than 26% (when the temperature of the pressure roller is 110 ° C. or more, In this case, the set temperature of the heating roller is set to 140 ° C. Further, for example, when the set temperature of the heating roller at the time of measuring the average duty is 160 ° C. and the average duty at that time is 33% or more (corresponding to the case where the temperature of the pressure roller is less than 90 ° C.), Set temperature to 170 ° C. Further, for example, the set temperature of the heating roller when measuring the average duty is 140 ° C., and the average duty at that time is 11% or more and less than 22% (corresponding to the case where the temperature of the pressure roller is 90 ° C. or more and less than 110 ° C.) In this case, the set temperature of the heating roller is set to 160 ° C.

The boundary conditions relating to the set temperature of the heating roller shown in Table 4 are obtained by the same procedure as in the first embodiment.
However, when the set temperature of the heating roller at the time of measuring the average duty is also included in the boundary condition as in the present embodiment, in order to obtain the boundary condition, the average duty of the heating roller corresponding to the temperature of the pressure roller is determined. In this case, the reference temperature of the heating roller (see FIG. 4B) needs to be determined for all temperatures (140 ° C., 160 ° C., and 171 ° C. in this embodiment) that can be selected as the setting temperature of the heating roller. is there. However, the temperature of the pressure roller can be detected with higher accuracy, and the set temperature of the heating roller at the time of actually performing the fixing operation can be more accurately determined.

An image was formed in the same manner as in Example 3 (Experimental Example 3) except that no defective fixing, paper wrinkling, or high-temperature offset was observed in this example. .

By the way, the good fixable area shown in FIG. 4 (a) is an area in which poor fixing, paper wrinkles and high-temperature offset do not occur. By setting the temperature of the heating roller and the pressure roller within this range, fixing without any practical problem is possible, but in order to further improve the quality of the fixed image, the gloss of the print surface is required. It is necessary to suppress the occurrence of unevenness (so-called gloss unevenness). In order to suppress the gloss unevenness and the gloss unevenness, it is necessary to detect the pressure roller temperature with higher accuracy, but in the present embodiment, the occurrence of the gloss unevenness was not recognized at all.

As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to these embodiments.

The heating roller 1 is preferably a cylinder made of a metal having good heat conductivity such as aluminum and having an outer diameter of 10 to 30 mm. If necessary, the outer diameter at the center in the axial direction and the outer diameter at the end may be changed. The pressure roller 2 is formed by forming an elastic body such as silicone rubber around a metal shaft such as steel or stainless steel by injection molding or the like. It is preferable to have resistance such as not to be fused, and the outer diameter should be 1
A material having a hardness of 0 to 30 mm and a hardness of 16 to 60 degrees according to JIS-A is used. Further, the outer diameter of the center in the axial direction and the outer diameter of the end portion of the pressing roller 2 may be changed as necessary.

Although not specifically exemplified, the fixing device of the present invention is capable of fixing the temperature of the heating member when the image forming apparatus is in a standby state, or fixing the temperature when starting the image forming operation. It is a matter of course that the temperature of the heating member and the pressure member at the time when the paper enters the fixing device can be set to an appropriate temperature whether or not the device is driven to rotate.

[0164]

According to the fixing device of the present invention, the temperature of the pressing member is detected by detecting the power supplied to the heating member when the paper is not present at the pressure contact portion between the heating member and the pressing member. It is possible to accurately detect the temperature of the pressing member without separately providing a means and without being affected by members other than the pressing member. Therefore, since a contact-type temperature detecting means temperature detector for detecting the temperature of the pressing member is unnecessary, wear and loss of the pressing member can be suppressed.

Further, according to the fixing device of the present invention, the temperature of the heating member can be appropriately set in accordance with the temperature of the pressure member. Even when the temperature fluctuates, poor fixing, paper wrinkles and high-temperature offset due to insufficient heating can be prevented.

In the fixing device of the present invention, even when the temperature of the pressing member is detected, the heating member is kept energized. Therefore, when the paper enters the fixing device, the temperature of the heating member is set to the desired temperature. If the temperature of the pressing member is appropriate for the set temperature of the heating member, the fixing can be performed immediately, so that a quick start can be performed. This is particularly effective in a fixing device having a large heat capacity.

Further, the temperature of the pressing member is detected based on both the amount of power supplied to the heating element and the set temperature of the heating member at that time, and further, the set temperature of the heating member is determined in accordance with the result. By changing the temperature, the temperature of the heating member with respect to the temperature of the pressing member can be set more appropriately, so that uneven gloss can be prevented.

It is particularly effective if the apparatus of the present invention is applied to an image forming apparatus such as a printer, a facsimile, a copying machine, and the like.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an example of an output characteristic with respect to a detected temperature in proportional control.

FIG. 3 is a diagram showing an embodiment of a printer using the fixing device of the present invention.

FIG. 4A is a diagram illustrating conditions for occurrence of defective fixing, paper wrinkling, and high-temperature offset in the printer used in the first embodiment. (B) A diagram showing the relationship between the pressure roller temperature and the average duty when the heating roller temperature is 171 ° C.

FIG. 5 is an algorithm showing a method for determining a set temperature of the first sheet of the present invention.

FIG. 6 is an algorithm showing a method for determining a set temperature during continuous paper feeding according to the present invention.

FIG. 7 is another algorithm illustrating the method for determining the set temperature of the first sheet of the present invention.

FIG. 8 is another algorithm illustrating the method for determining the set temperature during continuous paper feeding according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating roller 2 Pressure roller 3 Paper feed sensor 4 Paper feed roller 5 Photoconductor 6 Transfer roller 7 Heating body (halogen lamp) 8 Temperature detecting means (thermistor) 9 Peeling claw 10 Paper discharge roller

Claims (3)

(57) [Claims] A heating member having a heating element therein;
A fixing device that has a pressing member that is in pressure contact with the heating member, and a temperature detection unit that detects the temperature of the heating member in a fixing device that nips and conveys a heated body that carries an unfixed toner image in a pressure contact portion between the members A temperature control unit that controls electric power supplied to the heating body based on a detection result from the temperature detection unit and controls the heating member to a predetermined set temperature; The fixing device according to claim 1, wherein the temperature control unit changes a set temperature of the heating member based on an amount of electric power supplied to the heating element when the temperature control unit does not exist at the pressure contact portion of the pressure member. 2. The apparatus according to claim 1, further comprising a state determination unit configured to determine that the object to be heated is being conveyed to a fixing device. It said temperature control means is supplied to said heating body <br/> between from when further predetermined time has elapsed since the judgment to the object to be heated enters the pressure contact portion of the pressing member and the heating member 2. The fixing device according to claim 1, wherein the set temperature of the heating member is changed based on the amount of power. 3. A method for changing a set temperature of the heating member based on an amount of power supplied to the heating element by the temperature control unit and a set temperature of the heating member when the amount of power is supplied. The fixing device according to claim 1, wherein: