JPH07334023A - Fixing device - Google Patents

Abstract

PURPOSE:To properly set the temperature of a heating member in accordance with the temperature of a pressurizing member by changing the set temp. of the heating member based on electric energy supplied thereto with a temperature control means, when a body to be heated does not exist on the press-contacting part of the heating member with the pressurizing member. CONSTITUTION:In the fixing device provided with the heating member 1 and the pressurizing member 2 press-contacting each other and holding/carrying the body to be heated carrying an unfixed toner image in the press-contacting part of the members 1 and 2, the temperature control means controlling the electric power supplied to the heating member 1 based on the result of the detection from a temperature detecting means 8 detecting the temp. of the heating member 1, to control the member 1 to a prescribed set temp. is provided and then, the temperature control means changes the set temp. of the member 1 based on the power supplied thereto, when the body to be heated does not exist on the press-contact part of the heating and pressurizing members 1 and 2. Therefore, the temp. of the member 1 can be stable kept with respect to the set temp.

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 image forming apparatus of electrophotographic type. Specifically, it has a heating member and a pressure member that are in pressure contact with each other, and controls the electric power supplied to the heating member to control the heating member to a set temperature, and a pressure contact portion between the heating member and the pressure member. In the above, the present invention relates to a fixing device for fixing a toner image on a heated body by sandwiching and carrying a heated body carrying an unfixed toner image.

[0002]

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

Particularly, as an image forming apparatus, in an apparatus which receives image data transferred from the outside, such as a printer or a facsimile, and further processes the image data internally, various images which are transferred continuously. When a plurality of images are continuously formed according to data, the time from the previous image output (nth sheet) to the next image output (n + 1st sheet), that is, the fixing device The time between the sheets that are continuously passed (paper interval) becomes indefinite depending on the amount and type of image data. Therefore, in the fixing device, the pressure member is adjusted according to the paper interval time. There is a problem that the temperature of the paper fluctuates and paper wrinkles and high temperature offset are generated. For example, when the amount of image data is large and it takes time to transfer the image data or develop the data in the device, or when the image data such as a graphics image is complicated and requires time to process, it is necessary to output the next image. It takes time and the time between sheets becomes long. Since the image forming apparatus normally drives the space between the sheets as if the image forming operation is continuing, regardless of whether or not the sheet exists in the fixing device,
When electric power is supplied to the heating member, and as a result, the paper interval time becomes long, the temperature of the pressing member rises due to the heat from the heating member, and paper wrinkles and high temperature offset occur. On the other hand, when the paper interval time is shortened, the heat given to the paper by the pressure member when the paper is present in the fixing device (at the time of paper passing) is more than the heat given to the pressure member by the heating member between the paper. Since the size of the pressure member increases, the temperature of the pressing member lowers, and fixing failure occurs.

Therefore, 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 Unexamined Patent Publication No. 50-39554, temperature detecting means is provided not only on the heating member but also on the pressing member, and when the temperature of the pressing member is low, the temperature of the heating member is increased. 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 a plurality of image forming apparatuses such as printers, facsimiles, copiers, etc. There is a demand for a reduction in the wait time (quick start property) from power-on of the image forming apparatus until the image formation is actually possible, and power saving 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 to reach the fixable temperature), and in order to save power, the device must be shortened. Even when the main body is turned on, while the image forming operation is not actually performed (during standby)
First, it is necessary to stop the power supply to the fixing device or control the heating member to a temperature lower than that at the time of image formation. However, if the power supply to the fixing device is stopped or reduced during standby, the fixing device needs to be warmed up every time the image forming operation is started. It is an indispensable requirement.

By detecting the temperature of the pressing member and controlling the heating member according to the result, the warm-up time of the fixing device can be shortened, and the quick start property can be improved. it can.

That is, the history of use of the image forming apparatus (for example, the apparatus use time when the apparatus was used last time, the time from when the apparatus is stopped after the last use to when the apparatus is started again, the apparatus after the power is turned on is on standby. The temperature of the pressurizing member differs depending on the operating time, the time during which the image forming operation is continued due to continuous paper passing, etc.) Since the set temperature of the heating member is determined assuming that the temperature of the member is low, almost 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 by means of, 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 the method Warm-up of the fixing device between can be completed. Further, when the temperature of the pressing member is low, it is necessary to raise the temperature of the heating member. In this case, the warm-up time is the same as that of the method in which only the temperature of the heating member is used as the judgment standard. By performing control such as increasing the temperature, it is possible to shorten the warm-up time as compared with a system in which only the temperature of the heating member is used as the criterion.

As a method for controlling the temperature of the fixing device in consideration of the history of use of the image forming apparatus, there are methods such as every time the apparatus is used for a predetermined time or when the number of image formations exceeds a predetermined number. Although various methods of controlling the temperature of the fixing device based on the judgment standard have already been proposed, the usage history of the image forming device varies widely. Especially, from the viewpoint of private use by one individual, indoor or outdoor. There is a wide variety of differences such as differences in the usage environment such as usage of the image forming device, and differences in usage frequency such as at home or at work, and it is not possible to control all the usage history of the image forming apparatus based on uniform judgment criteria. It goes without saying that it is possible.

Therefore, 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 them based on the results. It is essential.

According to Japanese Patent Laid-Open No. 5-289562, when the fixing device (pressurizing member, etc.) is cold, more electric power must be supplied to the heating member in order to maintain the heating member at a constant temperature. Also, it is disclosed that when the fixing device is warm, less electric power is supplied to the heating member. The publication discloses a fixing device using a heating member (film heating method) including a film having a small heat capacity and a heating body. In such a fixing device, for the purpose of preventing an excessive temperature rise of the heating body, It is disclosed that it is necessary to detect the temperature of the fixing device. Further, as a method of detecting the temperature of the fixing device, an example of detecting the temperature rising rate of the heating body when a constant electric power is supplied to the heating body at the time of starting the heating body, for example, paper is continuously passed through the fixing device. Example of detecting the temperature decrease speed when heat is dissipated between paper sheets (paper interval) and radiating heat from the heating element, for example, HIGH / LOW There is disclosed an example in which the temperature fluctuation (temperature ripple) of the heating element is detected by controlling at two levels, and an example in which the electric power supplied to the heating element is detected while the paper passes through the fixing device.

[0013]

As is apparent from the above, it is essential for the fixing device to properly set the temperature of the heating member according to the temperature of the pressure member.

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

Further, Japanese Patent Laid-Open No. 5-289562 discloses some examples of the method for detecting the temperature of the pressing member. For example, the heating element when a constant electric power is supplied to the heating element. When detecting the temperature rise rate of the heating element, constant power is supplied regardless of the set temperature that the heating member should finally reach.Therefore, before controlling the heating element to the set temperature, be sure to 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 like the 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, it is not possible to accurately detect the temperature rise of the heating member in a short time because the heat capacity of the heating member is large. It is possible.

Similarly, for example, when the power supply to the heating element is stopped between the sheets and the rate of temperature decrease when the heating element is dissipated is detected, the heating element must have the same heat capacity as in the film heating method. In the case of heating an object to be heated through a small film, the temperature of the heating member easily drops, so the detection time of the temperature decrease rate can be easily carried out in a short time, and Furthermore, it is easy to raise the heating member to the set temperature, but in the case of a general heat fixing device such as a heat roller, the heating member has a large heat capacity, so the temperature drop of the heating member can be detected accurately in a short time. It is impossible to do so, and it is not desirable to lower the temperature of the heating member once and then heat it further to control it at the set temperature, which consumes unnecessary power and time.

Further, for example, when the power supply to the heating element is controlled at two levels of HIGH / LOW between the sheets to detect the temperature fluctuation (temperature ripple) of the heating element, as in the film heating method, When the heated body heats the heated body through a film with a small heat capacity,
Since the temperature of the heating member easily fluctuates, it is possible to detect the temperature fluctuation in a short time. It is impossible to accurately detect the above in a short time.

Further, for example, in the case of detecting the electric power supplied to the heating body during the paper passing through the fixing device,
While the paper is passing, the paper serves as a heat insulating material, and the heat of the heating member is not easily absorbed by the pressure member. Also, the amount of heat absorbed by the heating member varies depending on the water content of the paper and the temperature of the paper. It is impossible to detect with high accuracy.

An object of the present invention is to enable the temperature of the pressing member to be detected accurately with a simple structure that does not require any additional means for detecting the temperature of the pressing member. An object of the present invention is to provide a fixing device capable of appropriately setting the temperature of the heating member according to the temperature of the.

[0020]

A fixing device of the present invention has a heating member and a pressing member which are in pressure contact with each other, and a heating member carrying an unfixed toner image is nipped and conveyed at a pressure contact portion between the members. The fixing device has a temperature detection unit that detects the temperature of the heating member and a temperature control unit that controls the electric power supplied to the heating member based on the detection result from the temperature detection unit to control the heating member to the set temperature. The temperature control means changes the set temperature of the heating member based on the amount of electric power supplied to the heating member by the temperature control means when the object to be heated is not present in the pressure contact portion between the heating member and the pressure member.

Further, the fixing device of the present invention has a state discriminating means for discriminating that the heated body is conveyed to the fixing device, and the heated body is conveyed to the fixing device by the state discriminating means. Based on the amount of electric power supplied to the heating member by the temperature control unit after it is determined that the heating target has entered the pressure contact portion between the heating member and the pressure member, the set temperature of the heating member is set. It is characterized by changing.

Further, in the fixing device of the present invention, the set temperature of the heating member is changed based on the amount of electric power supplied to the heating member by the temperature control means and the temperature of the heating member when the amount of electric power is being supplied. It is characterized by doing.

[0023]

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

According to the first aspect of the present invention, under the condition that the heat radiation state of the heating member or the amount of electric power required to maintain the heating member at a constant temperature is such that the paper does not exist at the pressure contact portion between the heating member and the pressure member. It was made paying attention to the fact that it greatly depends on the temperature of the pressure member in contact with the heating member, and it is difficult to accurately detect the temperature of the pressure member due to the moisture and temperature of the paper during the paper passing. However, in the present invention, by detecting the electric power supplied to the heating member between the sheets, it is possible to accurately detect the temperature of the pressing member without separately installing a unit for detecting the temperature of the pressing member. be able to.

According to the first aspect of the present invention, the heating member is supplied with electric power so that the heating member is at a set temperature at which good fixing can be performed (when the pressing member is in a specific temperature range), and the electric power at that time is supplied. Since the temperature of the heating member is not raised or lowered regardless of the fixing temperature range, the temperature of the pressure member can be accurately detected even when the heating member has a large heat capacity. Moreover, the temperature of the heating member can be stably maintained with respect to 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 in the pressure contact portion between the heating member and the pressure member, after the temperature of the pressure member is detected, If the time it takes for the paper to enter the pressure contact part between the heating member and the pressure member is unnecessarily long, the paper actually enters the pressure contact part between the heating member and the pressure member after the temperature of the pressure member is detected. In the meantime
This was done in view of the fact that the temperature of the pressure member fluctuates, and when the paper actually enters between the heating member and the pressure member, the temperatures of the heating member and the pressure member become inappropriate. It is a thing. (For example, in the case where the temperature of the pressure member is detected after a certain period of time when the previous paper passes during continuous paper feeding, if the set temperature of the heating member is increased with respect to the detected temperature of the pressure member, , The pressure member is heated by the heat from the heating member before the next paper actually enters the fixing device, and when the paper interval time is long (especially the paper interval time becomes indefinite). In the image forming apparatus), the temperature of the pressure member at the time 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. When the set temperature of the heating member is decreased with respect to the temperature of the pressure member, the temperature of the pressure member at the time when the paper actually enters the fixing device becomes considerably lower than the detection time, Poor fixing occurs.) That is, the generation according to claim 2. Ming aims to set the timing for detecting the temperature of the pressure member so that the temperature of the heating member and the pressure member when the paper actually enters the fixing device is appropriate. Specifically, it is determined whether or not the paper, which is the object to be heated, is conveyed to the fixing device, and when it is determined that the paper is conveyed to the fixing device, the pressure is applied. By detecting the temperature of the member, it is possible to detect the temperature of the pressing member as soon as the paper enters the fixing device.

In the present invention, the temperature of the pressing member is detected when it is determined that the paper is being conveyed to the fixing device, so that the temperature of the pressing member is detected before the paper is actually transferred to the fixing device. The time delay until the sheet enters can be kept constant for a short period of time regardless of fluctuations in the paper interval time.Therefore, the detected temperature of the pressure member and the actual sheet entering the fixing device. The temperature of the pressing member does not change significantly at this time, and the temperatures of the heating member and the pressing member at the time when the paper actually enters the fixing device can be set appropriately.

According to the third aspect of the 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 pressure 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 pressure member, It does not depend on the absolute value of the temperature of the heating member or the pressing member, in other words, when the temperature of the pressing member is detected by the amount of electric power supplied to maintain the heating member at the set temperature, Unless the temperature of the heating member when the temperature is detected (when the amount of power supplied to the heating member is detected) is also taken into consideration, 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, the temperature of the pressurizing member corresponding to the amount of electric power supplied to the heating member changes depending on the temperature of the heating member at that time, so the temperature is supplied to the heating member. The temperature of the pressurizing member is detected based on both the amount of electric power generated and the temperature of the pressurizing member at that time, and the temperature of the pressurizing member is further changed by changing the set temperature of the heating member according to the result. The temperature of the heating member 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 invention described in claim 1, and detects the temperature of the pressing member from the amount of electric power supplied to the heating member when there is no paper in the fixing device. It is an example in which the set temperature of the heating member is changed based on the above.

The second embodiment is an embodiment in which the set temperature of the heating member is changed in consideration of the time required for the temperature of the heating member to actually reach the set temperature when the set temperature of the heating member is changed. is there.

The third embodiment corresponds to the invention described in claim 2, and it is determined whether or not the paper is in the state of being conveyed to the fixing device, and the paper is in the state of being conveyed to the fixing device. By detecting the temperature of the pressure member when determined,
In this embodiment, the temperature of the pressure member is detected as soon as the paper enters the fixing device.

The fourth embodiment is an embodiment in which the time required to measure the duty required to determine the set temperature of the heating member is changed. The fifth embodiment corresponds to the invention described in claim 2, and the third embodiment is the same as the third embodiment.
Is an embodiment in which the boundary conditions for determining the set temperature of the heating roller are different.

The sixth embodiment corresponds to the invention of claim 3, and the average duty of the electric power supplied to the heating roller and the average duty thereof are measured as a boundary condition for changing the set temperature of the heating roller. In this embodiment, the set temperature of the heating roller is determined based on both the set temperature of the heating roller at the time.

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

The fixing device shown in FIG. 1 comprises a heating member composed of a heating roller 1 made of a metal cylinder having good heat conductivity such as aluminum and a heating body 7 such as a halogen lamp installed inside the heating roller 1, and a metallic member. It is composed of a pressure member which is a pressure roller 2 in which an elastic body such as silicone rubber is formed on the outer peripheral surface of the shaft, and 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 installed so as to contact 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 the heating roller 1 and the pressure roller 2 in the direction of the arrow.
Of the fixing device, and after fixing at the nip of the fixing device, the sheet is discharged from the fixing device.

The fixing device may also have other necessary
A peeling claw 9 for peeling the paper after fixing from the heating roller 1.
And a paper discharge roller 10 and a heating roller 1 for smoothly discharging the paper discharged from the nip of the fixing device from the fixing device.
A cleaner such as an oil impregnated pad for removing the toner adhering to the surface of the heating roller 1 may be provided by applying a release agent such as silicone oil on the surface.

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

The temperature of the heating member (more specifically, the heating roller 1 forming a part of the heating member) is controlled by the amount of heat released from the heating element 7 arranged inside the heating roller 1. The amount of heat emitted by the heating element 7 is controlled by the amount of electric 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. Target temperature of the heating member in advance to the temperature control means (temperature that the heating member should finally reach and should be maintained after reaching)
Is set as the set temperature. The temperature control means compares the set temperature with the output from the temperature detection means 8 and controls the amount of electric power supplied to the heating body 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 control means, the temperature control means increases the amount of electric power supplied to the heating body 7, On the contrary, when the temperature is high, the temperature control means reduces the amount of electric power supplied to the heating body 7 to control the temperature of the heating roller 1 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 which is 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, the heating element 7
The electric power supplied to the halogen lamp is controlled. The temperature control means controls the amount of electric power supplied to the halogen lamp by a method such as controlling the phase and / or 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, the duty (du)
The ty) control will be described.

The energization of the heating element 7 from the temperature control means is controlled at certain fixed time intervals. The energization 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 about 4 when the duty is 10%.
It becomes 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. On the contrary, the amount of electric 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 passing a large current through the halogen lamp in order to maintain its life for a long time. On the other hand, the halogen lamp has a resistance when the power is turned on. It has a characteristic that it is low and a large current easily flows (inrush current). Therefore, when a halogen lamp is used as the heating element 7,
Generally, zero cross control is performed to suppress the inrush current to the halogen lamp and maintain the life of the halogen lamp for a long time. Zero-cross control refers to heating element 7 when the heating element 7 is supplied with electric power by AC voltage.
Even if a signal (heater ON signal) for instructing the start of power supply to the heater rises, energization is not immediately started, but 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 small and the life of the halogen lamp can be extended.

Next, proportional control will be described as an example of a method for controlling the amount of electric power supplied to the heating element 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 output characteristics 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 100%, and when it is C or higher, the duty is 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 amount of electric power is supplied. As described above, in the proportional control, the electric power is supplied so as to compensate the heat radiation amount of the heating member.

Besides proportional control (P control), a method of outputting electric power in proportion to the integration of temperature deviation (I control) and a method of outputting electric power in proportion to the rate of change of temperature (D control) are known. In general, PI control, PID control, PD control, etc. are used by combining these P, I, and D.

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

Heat is radiated from the heating member around the heating member, particularly to the pressing member with which the heating member is in contact. At that 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, the amount of electric power supplied to the heating member when controlling the heating member at the set temperature is proportional to the amount of heat radiated by 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 electric power supplied to the heating member can be obtained from the duty applied to the heating member, the heating member can be supplied to the heating member without using a power amount measuring means such as a power meter. The temperature of the pressing member can be detected by using the duty that is energized.

However, while the paper is passing through the nip of the fixing device, the heat of the heating member is hardly absorbed by the pressure member because the paper serves as a heat insulating material, and the paper is heated by the moisture of the paper and the temperature of the paper. It is difficult to accurately detect the temperature of the pressing member from the amount of electric power supplied to the heating member, because the amount of heat taken from the member is different. Therefore, in order to detect the temperature of the pressurizing member from the amount of electric power supplied to the heating member, the time when the amount of electric power of the heating member is detected is such that the amount of heat radiated from the heating member is substantially limited by the pressing member, That is, it should be when there is no paper in the nip of the fixing device and the heating member and the pressing member are in direct contact.

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

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

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

As is clear 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 transportation is detected by the status determination unit that determines that the paper is being transported to the fixing device. In this embodiment, the paper feed sensor 3 is used as the state determination means. The paper that has passed 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 onto the paper at the pressure contact portion. Further, the paper on which the toner image is transferred is conveyed toward the fixing device, and the toner image is fixed on the paper by heat and pressure at the pressure contact portion between the heating roller 1 and the pressure roller 2.

In the printer of this embodiment, the paper conveyance distance from the paper feed sensor 3 to the nip of the fixing device is 115.
mm, and the paper transport 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 until it reaches the nip of the fixing device.

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

At the start of printing, there is no paper in the nip until 5 seconds after the leading edge of the first paper passes the paper feed sensor.

During continuous printing, the nip is kept in the nip from 5 seconds after the trailing edge of the nth sheet passes the sheet feeding sensor and 5 seconds after the leading edge of the n + 1th sheet passes the sheet feeding sensor. There is no paper.

For example, assuming that the paper interval time is 3 seconds and the A4 size paper is conveyed in the vertical direction, 3 seconds after the trailing edge of the n-th paper passes through the paper feed sensor (at this time, the fixing is performed). If the leading edge of the (n + 1) th paper has passed the paper feed sensor in the nip of the device (the nth paper is present), after another 2 seconds (the trailing edge of the nth paper is the paper feed sensor). 5 seconds after the sheet has passed through the sheet, and 2 seconds after the leading edge of the n + 1th sheet has passed the paper feed sensor), the trailing edge of the nth sheet has been ejected from the fixing device, and n + 1 The leading edge of the first sheet of paper has not yet reached the fixing device, and there is no paper in the nip of the fixing device. After another 3 seconds (corresponding to the paper interval 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 the nip of the fixing device. And the (n + 1) th sheet exists in the nip of the fixing device.

In order to determine that there is no paper in the nip of the fixing device, in this embodiment, 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, and 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 gain sufficient time for the heating member to heat up before the paper actually starts to be conveyed to the fixing device. By the way, in the present embodiment, for the purpose of maintaining the life of the heating element for a long period of time, when the paper is not fed due to a feeding error, the temperature of the heating member is not increased or decreased unnecessarily. In order to detect that the paper is conveyed to the fixing device without a paper feed 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 fed and the paper entrance side of the fixing device.

In this embodiment, the fixing device is rotationally driven,
Also, when the heating member is controlled to the set temperature and there is no paper in the nip of the fixing device, the duty output by the temperature control unit to the heating member is stored in the memory at any time, and the temperature control unit stores the duty in the memory. The average duty was calculated 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 time is 3 seconds, the duty after 1 second (outputted in 1 second between 0 seconds after the start of control and 1 second after) is 60%, 2 The duty after 55 seconds (outputted in 1 second from 1 second to 2 seconds after the start of control) is 55% and 3 seconds later (3 seconds from 2 seconds after the start of control)
It is output in 1 second during 2 seconds later)
%, The total number of outputs 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%. In addition, based on only one specific control cycle,
For example, although it is possible to detect the temperature of the pressure member based only on the duty after 2 seconds, this is because the temperature fluctuation of the heating member and the pressure member of the fixing device is extremely small, the fixing characteristic and the high temperature. Although good results are obtained when a toner having a good offset characteristic is used, actually, in a general thermal fixing device using a heating member having a large heat capacity, a temperature variation of ± several ° C occurs.
It is difficult to accurately detect the temperature of the pressing member from the duty of the operation. Therefore, it is preferable to use the average of the plurality of times of duty because higher accuracy can be obtained. Therefore, also in the present embodiment, the temperature of the pressing member is detected by the average duty obtained by averaging the duty of a plurality of times. Since the feature of the present invention is to detect the temperature of the pressure member when there is no paper in the fixing device, when the average duty is obtained from multiple duty cycles, the duty is set as much as necessary to obtain the average duty. When the time required for measurement (duty measurement time = number of duty output times control cycle) is continuous paper feeding, it is of course not to exceed the paper interval time, and the control cycle is the minimum paper interval time. Needless to say, it needs to be short enough.

When a CPU is used as the temperature control means, the CPU generally takes time to perform division. Therefore, instead of calculating the average duty, the sum of the duties is calculated and the temperature of the heating member is determined from the sum of the duties. For example, the load on the CPU is reduced and the temperature of the pressure 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 change the set temperature of the heating member based on the result, what is the temperature of the pressing member? In this case, the boundary condition must be defined for changing the set temperature of the heating member when the amount of electric power supplied to the heating member is changed.

This boundary condition is in a tabular form, and the correlation between the temperature of the pressing member (and the amount of electric power supplied to the heating member and the duty of the electric power supplied to the heating member) and the set temperature of the heating member is shown. It may be configured by any of various expression formats such as a mathematical expression and an analog circuit.

A method for determining the boundary condition will be specifically described in the first embodiment.

<Embodiment 1> This embodiment corresponds to the invention described in claim 1, and pressurizes from the amount of electric power supplied to the heating member when there is no paper in the nip of the fixing device, such as between papers. The temperature of the member is detected, and the set temperature of the heating member is changed based on the result.

In this example, an aluminum cylinder (outer diameter 18 mmφ, with a coating layer formed of fluororesin,
A heating roller 1 having a wall thickness of 0.6 mm) was provided with a halogen lamp as a heating body 7. A roller (outer diameter 18 mm) having a silicone rubber layer of JIS-A hardness of 23 degrees formed by injection molding on the outer peripheral surface of the steel shaft 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 a load means (not shown).

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

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

FIG. 4A is a diagram showing the conditions under which fixing failure, paper wrinkles, and high temperature offset occur in the printer used in this embodiment. The horizontal axis represents the temperature of the pressure roller, and the vertical axis represents 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 the temperature detecting means separately installed in the printer only for producing FIG. 4, and in the embodiment, when actually forming an image. Has been removed.

A specific description will be given with reference to FIG.

At a temperature lower than the line b, fixing failure occurs, a high temperature offset occurs above the line c, and paper wrinkles occur above the line d. Line e is the temperature of the pressure roller just before the first sheet enters the fixing device when printing is started in a state where the pressure roller is sufficiently cooled. Moreover, when continuous printing is continued, the temperature of the pressure roller rises and eventually becomes saturated. Line f shows the saturation temperature of the pressure roller.

Therefore, poor fixing, high temperature offset,
The area where good fixing is possible without paper wrinkles is shown in Fig. 4 (a).
, The inside of the polygon surrounded by the lines b to f.

Further, in FIG. 4B, the temperature of the heating roller is 1
It is a figure which shows the temperature of a pressure roller at the time of 71 degreeC, and the relationship of an average duty. The average duty before the first sheet entered the fixing device was 50 to 60%, but in the case of continuously forming images, the average duty decreases as the temperature of the pressure roller rises. . As is clear from the figure, the temperature of the pressure roller can be detected by knowing the average duty corresponding to the amount of electric power supplied to the heating roller. In the figure, the temperature of the heating roller is 171 ° C. When the temperature is 26%, the pressure roller temperature is 110 ° C.
It turns out that

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

When the set temperature of the heating roller is set to 171 ° C. and the image formation is continuously continued, the temperature of the pressure roller rises, a high temperature offset occurs, and paper wrinkles occur (see FIG. 4A). Set the temperature of line c and heating roller to 171 ℃
See the intersection with the maximum 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. Even if the temperature of the pressure roller is 110 ° C. or higher, in order to prevent high-temperature offset and paper wrinkling and to prevent defective fixing, in this embodiment, the set temperature of the heating roller is changed to 156 ° C. did. Figure 4 (a)
As is clearer, the set temperature of the heating roller is 156 ° C.
Even if the temperature variation is taken into consideration, the fixing can be satisfactorily performed when the temperature of the pressure roller exceeds 110 ° C.

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 the temperature is 0 ° C. or lower, that is, whether the average duty corresponding to the amount of power supplied to the heating roller is 26% or higher. As a result, it becomes 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]

All the numerical values shown in FIGS. 4A and 4B and Table 1 relate to the fixing device having the structure of the first embodiment,
It is determined experimentally, and if the configuration of the fixing device is different, it is needless to say that the boundary condition according to the configuration of each fixing device needs to be defined according to the procedure of the first embodiment. (Of course, even if the structure of the fixing device is the same, the boundary conditions will change if the toner or the like changes.) By the way, in the printer of this embodiment, when the images are continuously formed, the paper interval is changed. When the time is fixed to 3 seconds, the amount of image data is large, it takes time to transfer and develop the data, and if the image cannot be formed even after the paper interval time of 3 seconds, the power consumption of the printer is reduced. In order to do so, the image forming process was once stopped (standby state), and the image forming was started again when the data development was completed. The standby state refers to a state in which the printer body is powered on but the image forming operation is not started.In this standby state, the halogen lamp is not energized to save power. Power supply to the halogen lamp is started at the time when the image formation is enabled (in this case, when the data development is completed). It is needless to say that the sheet interval time (fixed to 3 seconds in this embodiment) when images are continuously formed is not the standby state but the image forming operation is continued. None, 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 temperature of the heating roller to 171 ° C. and sets the heating roller (a halogen lamp as a heating body for heating the heating roller). Then, the fixing device is started up, and driving is started. Then, the paper is fed, the leading edge of the paper passes the feeding sensor, and at the same time, the duty output by the temperature control means starts to be accumulated in the memory, and 5 seconds after the leading edge of the paper passes the feeding sensor, the paper is fed. The average duty corresponding to the amount of electric power supplied to the heating roller for 5 seconds after the leading edge passes through the paper feed sensor is calculated. Based on this average duty, the set temperature of the heating roller was changed according to Table 1.

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

At the time of starting the image forming operation, when the fixing device is started up, first, the set temperature set in the heating roller is temporarily referred to as the first temperature. In this experimental example, the first temperature was 171 ° C. But this first
The temperature is a temperature that can be selected as the set temperature of the heating roller (in this experimental example, 156 ° C or 17
Any temperature may be used as long as it is 1 ° C.). However, in the standby state, the temperatures of the heating roller and the pressure roller are usually considerably low, so in order to shorten the warm-up time of the fixing device, the first temperature can be selected as the setting 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
At a set temperature (temporarily referred to as the second temperature here to be distinguished from the first temperature) determined based on the average duty corresponding to the amount of electric power supplied to the heating roller controlled at the first temperature, not the temperature. There is a second object of the present invention.
The purpose is to accurately determine the temperature according to the temperature of the pressure roller. Therefore, in order to accurately determine the temperature of the pressure roller, the boundary temperature, that is, the average duty of the heating roller corresponding to the temperature of the pressure roller is determined. Then 1
71 ° C. It is possible to detect the temperature of the pressure roller with higher accuracy by controlling (see FIG. 4B) as the set temperature of the heating roller (the first temperature of the present experimental example), and thus the actual fixing operation. This is preferable because the set temperature (second temperature) of the heating roller at the time of performing can be determined more accurately. In this experimental example, the first temperature is 171 ° C. for the above reason.
And

In the present experimental example, even if an image was formed while the pressure roller was cold, no fixing failure occurred. Even when an image was formed when the temperature of the pressure roller was high, paper wrinkles and high temperature offset did not occur.

(Experimental Example 2) This is an experimental example during continuous sheet feeding (when images are continuously formed).

When images are 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. 6 between the sheets during continuous sheet feeding, and the temperature was adjusted. (In this experimental example, the image data is adjusted so that the printer does not enter the standby state during continuous paper feeding, that is, during continuous paper feeding, paper is always fed one after another with a paper interval time of 3 seconds. Then, the temperature of the pressure roller is raised as quickly as possible by continuous sheet feeding.) The average duty at this time was obtained as follows.

Five seconds after the trailing edge of the n-th sheet passes through the sheet feed sensor, the average duty is calculated, and n + 1 is calculated.
The averaging was terminated 5 seconds after the leading edge of the first sheet of paper passed through the sheet feeding sensor, and the temperature of the heating roller was set according to Table 1 from the average duty as the calculation result.

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

In this experimental example, paper wrinkles and high temperature offset did not occur even after 100 sheets were continuously fed.

By the way, in the present experimental example, the set temperature of the heating roller when the n-th sheet of paper enters the fixing device is the set temperature of the heating roller when the (n-1) th sheet of paper enters the fixing device. The setting temperature of the heating roller when the (n + 1) th sheet enters the fixing device is determined based on the setting temperature of the heating roller when the nth sheet enters the fixing device. Become.

The object of the present invention is to accurately set the temperature of the heating roller when the paper actually enters the fixing device in accordance with the temperature of the pressure roller in the paper interval before the paper actually enters the fixing device. It's about making good decisions.

Therefore, in order to accurately determine the temperature of the pressure roller, the boundary condition, that is, the average duty of the heating roller corresponding to the temperature of the pressure roller is determined. In this embodiment, it is 171 ° C. The temperature of the pressure roller can be detected more accurately by controlling the temperature of the heating roller as shown in FIG. 4B, and the fixing operation is actually performed. This is preferable because the set temperature of the heating roller at this time can be determined more accurately.

Therefore, the set temperature of the heating roller when the n-th sheet of paper enters the fixing device is determined based on the set temperature of the heating roller when the n-1th sheet of paper enters the fixing device. However, each time, after the (n-1) th sheet is ejected from the fixing device, regardless of the setting temperature of the heating roller at that time, the setting temperature of the heating roller is immediately used as a reference in determining the boundary condition. The temperature is set to a temperature (If explained in accordance with this experimental example, the set temperature of the heating roller is always 171 ° C. between the n−1th sheet and the nth sheet.
Then, the temperature of the pressure roller can be detected with higher accuracy by detecting the temperature of the pressure roller.
The optimum temperature of the heating roller can be set more when the n-th sheet of paper enters the fixing device. However, in order to more appropriately set the set temperature of the heating roller (which will be described below according to the configuration of this embodiment), the setting of the heating roller is always performed between the sheets after the sheet is ejected from the fixing device. Comparing the method of controlling the temperature to 171 ° C. with this experimental example, n
When the set temperature of the heating roller when the first sheet of paper passes through the fixing device is 156 ° C. and the set temperature of the heating roller when the nth sheet of paper passes through the fixing device is also 156 ° C.,
In this experimental example, the set temperature of the heating roller is 156 during this period.
It is enough to keep the temperature at ℃, but in the method of constantly controlling the set temperature of the heating roller to 171 ℃ between the paper,
Regardless of the temperature set for the heating roller for the nth sheet, the set temperature for the heating roller is set to 1 between the sheets.
Since the temperature is controlled to 71 ° C., wasteful power is 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 sheets is based on various viewpoints. In this experimental example, the set temperature of the heating roller between the sheets is practically 156 ° C. or 171 ° C. Since no problem was observed above, the set temperature of the heating roller when the nth sheet of paper enters the fixing device is the set temperature of the heating roller when the n-1th sheet of paper enters the fixing device. Based on n
The set temperature of the heating roller when the + 1st sheet of paper enters the fixing device is determined based on the set temperature of the heating roller when the nth sheet of paper enters the fixing device.

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

In this embodiment, in order to improve the temperature stability of the heating roller during sheet feeding, the thickness of the heating roller is 1.
The thickness was increased to 7 mm to increase the heat capacity of the heating roller.

Also in Example 2, as in Example 1, the boundary condition, that is, the average duty of the heating roller corresponding to the temperature of the pressure roller was experimentally obtained, and the same result as in Example 1 was obtained. Was given. Therefore, also in this embodiment, the set temperature of the heating roller is determined based on Table 1 as in the first embodiment.

However, in this 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 was controlled to the set temperature was measured 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, when the set temperature of the heating roller is switched at substantially the same time as the paper enters the fixing device as in the first embodiment, the paper is heated at the time 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 3 seconds before the paper enters the fixing device, and is changed if necessary.

That is, in this embodiment, the first embodiment
The difference is that the thickness of the heating roller is different from that of, 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 start of the image forming operation will be described, but it goes without saying that the same effect can be obtained between sheets during continuous sheet passing.

When an image formation start signal is input to the printer in the standby state, first, the temperature control means sets the temperature of the heating roller to 171 ° C., supplies power to the heating roller, and starts the fixing device. , Start driving. Then
At the same time that the paper is fed and the leading edge of the paper passes the feeding sensor, the duty output by the temperature control means starts to be accumulated in the memory, and two seconds after the leading edge of the paper passes the feeding sensor, the leading edge of the paper moves. The average duty corresponding to the amount of electric power supplied to the heating roller for 2 seconds after passing the paper feed sensor is calculated. Based on this average duty, the set temperature of the heating roller was changed according to Table 1.

In the present embodiment, regardless of the initial temperature of the pressure roller, defective fixing, paper wrinkles and high temperature offset did not occur.

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 paper having a low temperature is passed) or the paper having a large heat capacity (thick paper or humidity is used). High temperature paper) or long paper (for example, legal paper or continuous form paper) that is long in the conveying direction of the fixing device does not cause the heating roller temperature to drop at the trailing edge of the paper, resulting in defective fixing. There wasn't.

<Embodiment 3> This embodiment corresponds to the invention described in claim 2, and it is judged whether or not the paper is in the state of being conveyed to the fixing device, and the paper is conveyed to the fixing device. When it is determined that the paper is in the state of being pressed, the temperature of the pressure member is detected to detect the temperature of the pressure member as soon as possible when the paper enters the fixing device. In the image forming apparatus in which the interval is indefinite, even if the temperature of the pressure roller rises when the paper interval time is long, high-temperature offset and paper wrinkles do not occur, and a good image is obtained even when the pressure roller is cold. It has the effect of ensuring the fixability.

The printer according to the present embodiment is different from the printer according to the first embodiment in that the paper interval time when images are continuously formed is indefinite. (However, the paper interval time is set to be at least 3 seconds.) That is, in the printer of this embodiment, when images are continuously formed, a large amount of image data is transferred. Or if it takes time to deploy,
The image forming process is not temporarily stopped (after starting image formation, the image forming process does not wait until all image formation is completed).
Therefore, while the images are continuously formed, the image forming operation is continued even during the transfer or the development of the image data, the paper interval time is indefinite, and
Needless to say, the halogen lamp is energized during the paper interval time.

When the temperature of the pressure member is detected between the sheets during continuous sheet passing, the amount of electric power supplied to the heating member is detected over the entire period of the sheet interval as in Example 1. When the temperature of the pressure member is detected, if the paper interval time 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. 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 this embodiment, as a method for obtaining the 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 paper interval time. Unlike the above, the duty is sampled only in a part of a predetermined period of the paper interval, and the duty sampling timing and the number of times of sampling are different from those in the first embodiment.

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

The present embodiment will be specifically described below based on experimental examples.

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

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 driving is started. To do. Then, the feeding of the first sheet of paper is started. The leading edge of the paper enters the nip of the fixing device 5 seconds after passing the paper feed sensor.

In this experimental example, the duty output 3 seconds and 4 seconds after the leading edge of the paper passed the paper feed sensor (specifically, the control cycle of the electric power supplied to the heating member is 1
Since it is 2 seconds, the duty output to the heating member from 2 seconds to 3 seconds after the leading edge of the paper passes the paper feed sensor and 3 after the leading edge of the paper passes the paper feed sensor.
The duty output to the heating member from 2 seconds to 4 seconds was averaged to obtain the average duty. From this average duty, the set temperature of the heating roller was determined according to Table 1.

Furthermore, the set temperature of the heating member in the case of continuously forming images on the second and subsequent sheets was set by the algorithm of FIG.

The average duty was obtained by averaging the duties output 3 seconds and 4 seconds after the leading edge of the n-th sheet passed the sheet feeding sensor. From the average duty which is the result of this calculation, the set temperature of the heating roller is determined according to Table 1, and n
The first piece of paper was fixed.

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

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

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

Even when the amount of image data was large and the paper interval time was as long as 30 seconds, paper wrinkles and high temperature offset did not occur. Further, even when the temperature of the pressure roller is low, the occurrence of defective fixing could be suppressed. Thus, even if the duty immediately before the paper enters is not added to the calculation of the average duty, it does not deviate from the intent of the present invention, and there is an effect.

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

By using an average duty obtained by averaging a plurality of times of energization of the heating roller,
As described above, the set temperature of the heating roller can be accurately determined.

However, when the average duty is calculated from a plurality of times of duty, the time T (duty measurement time) required to measure the duty by the amount necessary to calculate the average duty is necessary.

T = (duty output frequency) × (control cycle) If this time T is set excessively long, the temperature of the pressure roller rises while the duty is measured a plurality of times. , 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, the set temperature of the heating roller becomes inappropriate, and high temperature offset and paper wrinkles occur. It may occur. Therefore, T needs to be sufficiently short.

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

The printer according to the present embodiment has a fixed sheet interval time of 20 seconds when images are continuously formed, and the amount of image data when images are continuously formed. However, even if it takes a lot of time to transfer or develop data, the point that the image forming process is not paused (the image forming is forcibly started when the paper interval time exceeds 20 seconds without waiting) Different from Example 1.

Further, in this embodiment, the number of times of duty output to be averaged is set to 2, 4, 8 and 16 times. Therefore, T is 2, 4, 8, 16 seconds.

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

In Table 2, when high temperature offset and paper wrinkle did not occur, ○, when slight high temperature offset and paper wrinkle occurred (no practical problem), △, severe high temperature offset and paper wrinkle occurred. If it does (which causes a problem in actual use), it is indicated by x.

As shown in Table 2, when T was within 4 seconds, high temperature offset and paper wrinkles did not occur.

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 invention described in claim 2.

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.

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

[0147]

[Table 3]

There are three kinds of set temperatures of the heating roller in the present embodiment, and it depends on the set temperature of the heating roller when the temperature of the pressure roller is detected (the average duty of the electric power supplied to the heating roller is measured). 170 when the average duty of the electric power supplied to the heating roller is 33% or more.
℃, 160 ℃ when 21% or more and less than 33%, 2
When it was less than 1%, the temperature was 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 configurations were the same as those of Example 3 (Experimental Example 3).

In this embodiment, fixing failure does not occur even when continuous printing is performed while the pressure roller is cold. Even if continuous printing is restarted 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 invention of claim 3.

However, in this embodiment, the boundary conditions for determining the set temperature of the heating roller are different from those in the first and third embodiments. Specifically, in the present embodiment, unlike the above-mentioned embodiment, as a boundary condition for changing the set temperature of the heating roller, the average duty of the electric power supplied to the heating roller (corresponding to the temperature of the pressure roller is equivalent to ), The set temperature of the heating roller when the average duty is measured is also used, and the set temperature of the heating roller is determined based on both of them. That is, the present embodiment is characterized in that the average duty value that determines the set temperature is different 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 electric power supplied to the heating roller, and the set temperature of the heating roller when the average duty is measured.

[0155]

[Table 4]

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

For example, when the average duty of the electric 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% (the temperature of the pressure roller is 110 ° C. or higher). (Corresponding to the case), the set temperature of the heating roller is set to 140 ° C. Further, for example, the set temperature of the heating roller when the average duty is measured is 160 ° C., and when 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.), the heating roller Set the set temperature to 170 ° C. Further, for example, the set temperature of the heating roller when the average duty is measured 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.). At that time, 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 Example 1.
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 this embodiment, the average duty of the heating roller corresponding to the temperature of the pressure roller is determined in order to obtain the boundary condition. At this time, the temperature of the heating roller (see FIG. 4 (b)) which is the reference must be calculated for all the temperatures (140 ° C., 160 ° C., 171 ° C. in this embodiment) that can be selected as the set 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 when 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 for the above, and in this Example as well, defective fixing, paper wrinkles and high temperature offset were not observed. .

By the way, the good fixable area shown in FIG. 4 (a) is an area in which no bad fixing, paper wrinkles and high temperature offset occur. By setting the temperature of the heating roller and pressure roller within this range, fixing without any problems is possible in practice, but in order to further improve the quality of the fixed image, the gloss of the printing surface It is necessary to suppress the occurrence of unevenness (so-called gloss unevenness). Although it is necessary to detect the pressure roller temperature with higher accuracy in order to suppress the gloss unevenness, the occurrence of the gloss unevenness was not observed at all in this embodiment.

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

The heating roller 1 is preferably a cylinder having an outer diameter of 10 to 30 mm and made of a metal having good thermal conductivity such as aluminum, and the outer diameter of the center and the outer diameter of the end may be changed as required. Further, 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 that it has resistance such as not to be fused, and the outer diameter is 1
A hardness of 0 to 30 mm and a hardness of 16 to 60 degrees according to JIS-A is used. Further, the pressure roller 2 may be changed in the outer diameter of the center and the outer diameter of the end portion in the axial direction, if necessary.

Although not specifically exemplified, the fixing device of the present invention fixes the fixing member regardless of how the temperature of the heating member is set when the image forming device is in the standby state or when the image forming operation is started. It is needless to say 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 be appropriate, whether or not the device is rotationally driven.

[0164]

According to the fixing device of the present invention, the temperature of the pressing member is detected by detecting the electric power supplied to the heating member when the paper is not in the pressure contact portion between the heating member and the pressing member. It is possible to detect the temperature of the pressing member with high accuracy without separately installing a means and without being affected by members other than the pressing member. Therefore, a contact-type temperature detecting means thermometer for detecting the temperature of the pressing member is not required, so that 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 according to the temperature of the pressing member, so that the pressing member can be used (for example, according to the history of use of the device and the time between sheets). Even when the temperature fluctuates, it is possible to prevent fixing failure, paper wrinkles and high temperature offset due to insufficient heating.

In the fixing device of the present invention, since the heating member is still energized even when the temperature of the pressing member is detected, the temperature of the heating member should be set to the desired temperature when the paper enters the fixing device. If the temperature of the pressurizing member is appropriate for the set temperature of the heating member, the fixing can be carried out immediately and 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 member and the temperature of the heating member at that time, and the set temperature of the heating member is changed according to the result. By doing so, the temperature of the heating member with respect to the temperature of the pressing member can be set more appropriately, and thus uneven gloss can be prevented.

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

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of output characteristics 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 showing conditions for occurrence of defective fixing, paper wrinkles, 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 the set temperature of the first sheet of paper of the present invention.

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

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

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

[Explanation of symbols]

 1 Heating Roller 2 Pressure Roller 3 Paper Feeding Sensor 4 Paper Feeding Roller 5 Photosensitive Member 6 Transfer Roller 7 Heating Body (Halogen Lamp) 8 Temperature Detection Means (Thermistor) 9 Peeling Claw 10 Paper Ejection Roller

Claims (3)

[Claims] 1. A fixing device, comprising a heating member and a pressing member that are in pressure contact with each other, wherein a member to be heated carrying an unfixed toner image is nipped and conveyed at a pressure contact portion between the members, the temperature of the heating member is detected. And a temperature control means for controlling the electric power supplied to the heating member based on the detection result from the temperature detection means to control the heating member to a predetermined set temperature. The fixing device changes the set temperature of the heating member on the basis of the amount of electric power supplied to the heating member by the temperature control means when the temperature does not exist in the pressure contact portion between the heating member and the pressure member. 2. A state determination means for determining that the heated body is being conveyed to the fixing device, wherein the heated body is being conveyed to the fixing device by the state determining means. Based on the amount of electric power supplied to the heating member by the temperature control means from the time when a predetermined time has elapsed after the determination until the heated body enters the pressure contact portion between the heating member and the pressure member. The fixing device according to claim 1, wherein the set temperature of the heating member is changed. 3. The temperature setting means changes the set temperature of the heating member based on the amount of electric power supplied to the heating member and the temperature of the heating member when the amount of electric power is being supplied. The fixing device according to claim 1, wherein the fixing device is a fixing device.