JP3318114B2 - 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 fixing device used in a fixing section of an image forming apparatus such as a copying machine, a facsimile, an optical printer, etc. for forming an image by an electrophotographic image forming process.

[0002]

2. Description of the Related Art Conventionally, a fixing device used in a fixing unit of an image forming apparatus for forming an image by an electrophotographic image forming process has a heating roller maintained at a predetermined temperature and an elastic layer. A hot roller fixing system in which a recording material on which an unfixed toner image is formed is heated while being nipped and conveyed by a pressure roller which is in pressure contact with the roller has been used in many cases. However, in the heat roller fixing method, there is a problem of an offset phenomenon in which the toner is transferred to the heat roller, and to prevent this, it is necessary to always maintain the heat roller at an optimum temperature. Had to increase its heat capacity. However, when the heat capacity of the heating roller is increased, the time required to raise the temperature of the heating roller to a predetermined temperature becomes longer, and the standby time becomes longer when the apparatus is used, which causes another problem that power consumption is increased. . Therefore, as a new fixing method for solving the above-mentioned problem, a fixing method by local heating via a fixing film (Japanese Patent Laid-Open No. 63-313182).
Or a fixing method using a fixing film made of a conductive heat-resistant film (hereinafter, referred to as a conductive fixing film) and performing heat fixing by self-heating of the film (Japanese Patent Laid-Open No. 3-14).
No. 4676) has been proposed.

FIG. 12 shows a configuration example of an electrophotographic process fixing unit using a conductive fixing film. In FIG. 12, the fixing unit includes an electrode support 1a on which a pair of electrodes 1d are arranged, a conductive fixing film 1b conveyed in contact with the electrode surface of the electrode support 1a, and the electrode support 1a. And a pressure roller 1c for sandwiching and pressing the recording paper 1h on which the conductive fixing film 1b and the unfixed toner image 1e are formed, together with the electrode support 1a. As the conductive fixing film 1b and the transport method thereof, as shown in FIG. 13, an endless type rotating with a driving roller 1f and a tension roller 1g using a seamless belt as the conductive fixing film 1b, or not shown, A non-endless type in which a conductive fixing film is transported while being wound up by a winding roll using a feeding roll and a winding roll around which the conductive fixing film is wound has been considered. Note that various studies have been made on a fixing device using the present technology, but there is no example of commercialization yet.

[0004]

As a result of studying the fixing process using the conductive fixing film as described above, the following problems were found. That is, in the fixing process as described above, since the heating element (conductive fixing film) is in direct contact with the toner to be fixed, it is possible to perform the fixing without any preheating time. Since the temperature of the fixing film cannot be directly detected, the method of controlling the power supply so as to keep the temperature of the temperature measurement unit constant as in all the fixing processes in the past has been difficult. Not only does the temperature rise unnecessarily, resulting in wasteful power consumption, but also affects the durability of the conductive fixing film.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and solves the above-mentioned problems in a fixing system using a conductive fixing film. It is an object of the present invention to provide a fixing device which enables the fixing.

[0006]

A fixing device according to the present invention.
Is a cylindrical conductive fixing film, a pair of electrodes provided inside the conductive fixing film, a support for supporting the pair of electrodes, and the conductive fixing film sandwiched between the pair of electrodes. An elastic roller provided at a position to be rotated, and a driving unit for driving the conductive fixing film to rotate around a pair of electrodes at a predetermined linear velocity, and the unfixed toner is fixed to the elastic roller and the conductive fixing film. The recording medium on which the image is formed is conveyed at the position where it is clamped, and the recording medium is fixed.
To the conductive fixing film through a pair of electrodes
In this configuration, power is supplied , and the toner on the recording medium is heated and fixed by Joule heat generated on the conductive fixing film .

In the first aspect of the present invention, the fixing device
In location, means for sensing the temperature of at least a portion of said pair of electrodes or a support, a means for detecting a time at which the leading end of the fixing recording medium reaches the fixing unit, the elapsed time from that time until now means for calculating, fixing unit paper feed start time the relationship between the elapsed time and the power supplied from the paper feeding start
Storage means for storing control information tabulated for each temperature of the temperature measuring section at the time of fixing, and fixing recording based on the control information.
The detected temperature at the time when the leading edge of the medium reaches the fixing section is communicated with the detected temperature.
Means for determining an appropriate effective current value from the elapsed time from when the paper is started and power is supplied, and phase control of the magnitude of the effective current supplied to the conductive fixing film based on the determination result. It is characterized by having means.

According to a second aspect of the present invention, there is provided the fixing device of the first aspect, wherein the fixing process of the recording medium to be fixed is continuously performed.
In this case, there is provided a means for storing and holding the temperature detected by the temperature detecting means for a predetermined time by the storage means, and correcting the current measured temperature result based on the stored temperature data.
And correct control of the control information based on the corrected temperature.
Select the table to determine the appropriate effective current value on the basis of the control information, Turkey <br/> and to phase control the magnitude of the effective current supplied to the conductive fixing film based on the determination result It is characterized by.

[0009]

According to the fixing device of the present invention, the recording medium on which the unfixed toner image is formed is conveyed by the elastic roller and the conductive fixing film, and the recording medium passes through the fixing section.
Sometimes power is supplied to the conductive fixing film through a pair of electrodes.
Performs supply, to perform the heat-fixing of the toner on the recording medium by the Joule heat generated in the conductive fixing film on the heating body power supply is the fixation of the and conductive fixing film heat capacity can the small (film) The fixing device may be used only when the paper passes, and a fixing device with low standby time and low power consumption can be realized. Further, in the fixing device of the present invention, a means for detecting a temperature of at least a part of the pair of electrodes or its support, and a time when the leading end of the recording medium to be fixed reaches the fixing section.
Detecting means and calculating the elapsed time from that time to the present
Output means, the elapsed time from the start of paper passing, and the supply power.
The relationship is tabulated for each temperature of the temperature measurement unit at the start of paper passing through the fixing unit.
A storage means for storing the Le of control information, and the sensed temperature, elapsed time from the paper feeding start control according to claim 1, 2 based on the control information stored in the storage means Since the control is performed by the means, it is possible to supply an appropriate amount of power without excess or deficiency in the fixing by the conductive fixing film.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a schematic sectional view of an essential part of a fixing device according to an embodiment of the present invention.
b is a pair of electrodes, 2c is a conductive fixing film, 2d is a recording paper on which an unfixed toner image is formed, 2e is a pressure roller having at least a surface layer made of an elastic body (such as silicon rubber), and 2f is a temperature detection sensor. (Temperature sensor) is shown, and in the following description of the configuration and operation in the embodiment of each claim, as shown in FIG. 1, a temperature detection sensor 2f (here, a thermistor is used) in the electrode support 2a. Or a sensor is fixed to the back surface of the electrode support 2a or the like, and the endless type cylindrical conductive fixing film 2c is rotated by a driving roller and a tension roller as in FIG. The head including the electrode 2b, the electrode support 2a, and the reinforcing plate of the electrode support (not shown) is referred to as a head. As the conductive fixing film 2c, a carbon-added polyimide belt having a thickness of 20 μm, a circumference of 190 mm, a width of 270 mm, and a sheet resistance of 2000 Ω / mm ² is used. The distance between the electrodes indicated by D in FIG. 1 is 1 mm, and the electrode length in the main scanning direction (the direction perpendicular to the paper surface) is 257 mm.

FIG. 2 is a diagram showing a main portion of an image forming apparatus using the fixing device of the present invention and a conveyance path of a recording sheet. In FIG. 2, reference numeral 2 denotes a fixing device having the configuration shown in FIG. Is a photoreceptor belt, 11 is a transfer charger, 12 is a registration sensor, 13 is a paper feed cassette, 14 is a paper feed roller, 15
Denotes a transport roller, and 16 denotes a registration roller. Although not shown, a charging device, an exposure device (for example, an optical writing device using a laser beam), a developing device, and the transfer charger 1 are provided around the photoreceptor belt 10.
1. A cleaning device, a static elimination device, and the like are provided.
Then, at the time of image formation, the photoreceptor belt 10 is uniformly charged by a charging device, and then optically written by an optical writing device or the like using laser light to form an electrostatic latent image. The toner image is developed by the toner of the developing device to be visualized, and the toner image is transferred to the recording paper 2d conveyed to the transfer unit from the paper supply cassette 13 via the paper supply roller 14, the conveyance roller 15, and the registration roller 16. The image is transferred by the charger 11. The recording paper 2d on which the toner image has been transferred is sent to the fixing device 2, and is conveyed at a position where the recording paper on which the unfixed toner image is formed is sandwiched by the pressure roller 2e of the fixing device 2 and the conductive fixing film 2c. Then, after the toner on the recording paper is heated and fixed by Joule heat generated on the conductive fixing film 2c through the pair of electrodes 2b, the recording paper is discharged onto a discharge tray (not shown). On the other hand, the photoreceptor belt 10 after the transfer is cleaned by the cleaning device, and the residual charge is removed by the charge removing device.

By the way, in the image forming apparatus shown in FIG.
A registration sensor 12 for detecting paper passing is provided in front of the transfer unit. The registration sensor 12 is generally provided to synchronize the conveyance position of the recording paper 2d to be fixed with the laser writing on the photoreceptor belt 10, and detects the time when the leading end of the recording paper reaches the registration sensor position. The detection is performed, and after an appropriate time has elapsed from that time, laser writing of each page is started, thereby forming a transfer image at a predetermined position on the recording paper.
In this embodiment, the output of the registration sensor is also used as a means for detecting the arrival time of the recording sheet to be fixed at the fixing portion. That is, the control unit that detects the time when the leading end of the recording paper arrives at the registration sensor position counts a predetermined time determined by the linear velocity of the recording paper to be fixed and the length of the paper passage path from the registration sensor position to the fixing unit. The count-up time is defined as the time at which the leading end of the recording paper to be fixed reaches the fixing section. Of course, a mechanical sensor may be separately provided immediately before the fixing unit,
The time count of the control unit may be a hard timer or a software timer.

FIG. 3 shows an example of a schematic configuration of a control unit of the fixing device according to the present invention.
The output of the temperature detection sensor 2f that detects the temperature of at least part b or the support 2a thereof is converted into a digital signal via the AD converter 21 and sent to the control device 20.
The output of the registration sensor 12 is also input to the control device 20. Further, the conductive fixing film 2 of the fixing device 2
c is supplied by a power control circuit of the phase control unit 22 based on a signal from the control device 20.
The effective power of the 100 V AC is controlled by phase control as shown in FIG. The power supply to the conductive fixing film is performed only when the recording paper to be fixed passes. Further, the control device 20 has a configuration including a known microcomputer, a memory, a counter, various control circuits, and the like. The control device 20 controls each unit of the image forming apparatus in addition to the fixing device. A memory in the apparatus stores various control programs, various data tables, and the like. The control device 20 has a separate memory (I
A C card, a RAM board, or the like) 23 or a timer 24 may be connected. The memory 23 stores temperature information within a predetermined time measured by the temperature detection sensor 2f and control information for various controls described later. It is memorized. Then, control information is selected by the microcomputer of the control device 20, and an effective current value (supplied power) supplied to the conductive fixing film 2c of the fixing unit based on the control information and the detected temperature is used in each of the embodiments described later. The phase control unit 22 is controlled based on the determination result, and the power supply to the conductive fixing film 2c is appropriately controlled. Hereinafter, embodiments of the control operation of the fixing device of the present invention will be described.

Embodiment 1 In FIG. 1, in this embodiment, a ceramic substrate having a thickness of 0.6 mm was used as an electrode support 2a, and a temperature detection sensor was provided on the back surface thereof. Also,
The conveying speed of the recording paper 2d to be fixed is 30 mm / sec, and a one-component toner is used as the toner on the recording paper. The heat conduction analysis revealed that when the same power was supplied to the conductive fixing film 2c, the temperature of the film rising near the discharge-side electrode was as shown by the solid line in FIG. At the same time, calculation and measurement of the temperature near the discharge side electrode on the surface of the head (support 2a) in contact with the film and the temperature at the sensor position were performed. The result was. In this case, the temperature behavior at the surface where the head and the conductive fixing film 2c are in contact with each other and the temperature behavior at the sensor position relatively match.

Here, the temperature rise of the conductive fixing film 2c is mainly affected by the temperature of the contact surface of the film with the film on the head. It has been found that it is possible to determine the power supplied to the film. More specifically, in the fixing device using the conductive fixing film, the film generates heat only at the distance D between the electrodes shown in FIG.
At this time, the temperature rise curve of the film is substantially determined by the temperature of the surface to be fixed of the recording paper sandwiching the film and the temperature of the head surface where the head and the film are in contact with each other for a certain supply current value. The recording paper itself is conveyed to the nip portion (D part in FIG. 1) at almost room temperature, and the heat capacity of the film itself is less than a fraction of that of the recording paper. The rising curve is determined by the temperature of the head surface where the head comes in contact with the film. The amount of heat supplied to the recording paper fixing surface is uniformly determined by the temperature rise curve of the film in the nip, and the fixing property is determined. In other words, if the temperature of the surface of the head in contact with the film can be accurately detected every hour, it is possible to keep the rising temperature curve of the film constant by setting a corresponding appropriate current value. This is a particularly important point in this fixing system, in which if the temperature of the film is too high, the durability of the film is likely to cause a problem.

As described above, in FIG. 9, the temperature at the surface where the head and the conductive fixing film 2c are in contact with each other and the temperature behavior at the sensor position relatively agree with each other. And the temperature of the surface in contact with the film "are very small in a very short time from the start of energization. This means that a temperature gradient in the head hardly occurs because a ceramic having good thermal conductivity is used as the head material. The time to reach this equilibrium is about several milliseconds in terms of thermal calculation, and is a time that does not cause any problem even when considered as a warm-up time. Since the difference between the "temperature at the sensor position" and the "temperature at the surface where the head and the film come into contact" is less than 1 degree in the calculation, the measured value of the temperature sensor is regarded as "the temperature at the surface where the head and the film come into contact". To make
By setting an appropriate current value corresponding to the measured value of the temperature sensor, it is possible to keep the rising temperature of the film constant. That is, it is possible to determine the power supplied to the film from the temperature detection result of the head temperature measuring unit.

Accordingly, the relationship between the head detection temperature (support member temperature) shown in FIG. 4 and the supply current at which the film rising temperature becomes constant is tabulated and stored as control information in the memory 23 of the control unit shown in FIG. Otherwise, the control device 20
Determines an appropriate effective current value from the temperature detected by the temperature sensor 2f based on this table, and controls the phase control unit 22 based on the determined result to determine the effective current value supplied to the conductive fixing film 2c. Control the size. When a continuous fixing operation was performed by this control method, good results were obtained. As described above, when the sheet passing speed is relatively low and the temperature gradient in the head is small, the above-described control method enables the heating and fixing by the conductive fixing film to be controlled with sufficient and sufficient power supply. FIG. 4 shows the results of calculating the temperature rise between the nips of the film under the conditions of the present embodiment by varying the supply current and the temperature of the electrode support (head). It is a plot of "supply current value required for the film reaching temperature to reach an appropriate constant value".

[Embodiment 2] Next, as a second embodiment, the conveyance speed of the recording paper 2d is 60 mm / sec, which is double that of the first embodiment, and a polyimide resin molded product (2.0 mm thick) is used as the electrode support 2a. ), A temperature detection sensor 2f was buried at a depth of 1 mm from the contact surface between the conductive fixing film 2c and the head in the electrode support. Was as shown in FIG. In this case, since the electrode support 2a is made of a resin molded product having relatively poor thermal conductivity, the temperature difference between the head surface temperature and the head temperature measuring unit is larger than that when ceramic is used, and the environmental temperature (for example, the temperature near the head) is low. When the temperature of the peripheral members fluctuates, the temperature at the head temperature measuring unit fluctuates relatively largely in accordance with the environmental temperature, but it is found that the influence of the environmental temperature change of the film temperature is relatively small (the film itself generates heat). To do). For this reason, the supply power cannot be determined uniformly based on the temperature at the head temperature measuring unit as in the first embodiment. However, it is possible to perform appropriate control by storing the relationship shown in FIG. 4 in the form of a table for each environmental temperature in the memory 23 as control information or separately providing an environmental temperature detecting unit.
This leads to higher costs.

Therefore, in the present embodiment, the conveying speed of the recording paper is high, but when the interval between the recording papers passing through the fixing is relatively long, the recording paper to be fixed reaches a relatively long time when it reaches the fixing section. The temperature distribution in the head is relatively uniform because the heating has just stopped for a while, and the subsequent temperature rise due to the heating of the film is almost equal to the initial temperature (the temperature when the leading edge of the recording paper reaches the fixing section). (This means that even if the recording paper is passed at exactly the same time interval, if the temperature of the peripheral members and the like is different, the above initial temperature will fluctuate. This means that the amount of energy that can be determined at the above initial temperature is such that the amount of heat stored in the vicinity of the fixing nip of the fixing system is the same if the temperature of the temperature measuring unit is the same. No difference even if different As shown in FIG. 7, the relationship between the elapsed time from the start of sheet feeding and the supply power is determined by the temperature of the head temperature measuring unit at the start of the fixing unit sheet feeding (initial temperatures T1 to T3 in FIG. 7). 3), a table is prepared, and stored as control information in the memory 23 of the control unit shown in FIG. 3, and the control device 20 causes the leading end of the recording paper to reach the fixing unit based on the control information. Predetermined supply power (effective current value supplied to the conductive fixing film) according to the temperature detected by the temperature detection sensor 2f at the time (initial temperature) and the elapsed time from the start of paper supply and the supply of power.
And control was performed. That is, a table corresponding to the initial temperature detected at the start of paper passing is selected from the control information stored in the memory 23, and a predetermined power supply is determined based on the elapsed time from the start of paper passing with reference to the table. The magnitude of the effective current supplied to the conductive fixing film is controlled based on the result of the determination, and good results were obtained by this control method. As described above, even when the paper passing speed is relatively high, by selecting the above-described control method, it is possible to control the heating and fixing by the conductive fixing film with a sufficient supply power.

In this embodiment, as described above, the output of the registration sensor 12 is used as a means for detecting the arrival time of the recording sheet to be fixed at the fixing section, and the time when the leading end of the recording sheet arrives at the registration sensor position is detected. Detected by the control device 20,
A predetermined time determined by the linear speed of the recording paper to be fixed and the length of the paper passing path from the registration sensor position to the fixing unit is set to a timer 2.
The recording time is counted as the time when the leading edge of the recording sheet reaches the fixing section. Also,
The elapsed time from the start of sheet passing is also detected by a signal from the timer 24.

[Embodiment 3] With the same fixing unit configuration and sheet passing speed as the configuration and operation of the second embodiment, the speed of the data processing system of the image forming apparatus is high, and the recording paper is continuously fixed. In such a case, the interval at which printing is performed on the recording paper to be fixed (that is, the interval between recording papers passing through the fixing unit) is shortened, so that the fixing operation on the previous recording paper is completed, and the temperature distribution in the head becomes uniform. Before that, the situation where the next recording paper to be fixed reached the fixing section occurred. In this case, the rate of the subsequent temperature rise of the film changes depending on the temperature distribution state at the start of the fixing operation for each recording sheet to be fixed. Therefore, in the method of the second embodiment, the appropriate power supply amount is uniformly determined. Can not do. That is, the control table cannot be selected only by the initial temperature of the temperature measuring unit. As a result, insufficient fixing occurred at the beginning of the recording paper. Therefore, in the present embodiment, the current measured temperature result is corrected from the history of the temperature measurement results of the past head temperature measuring unit, and the appropriate power supply amount is determined. That is, the control device 20 shown in FIG.
f, a temperature detection value detected at a predetermined cycle is stored and held in the memory 23 via the bus for a predetermined time, and the current measured temperature result is corrected based on the stored temperature data. Then, an appropriate control table is selected from the corrected temperature to determine the effective current value, and the magnitude of the effective current supplied to the conductive fixing film is controlled based on the determined result. When the temperature detected value for a predetermined time is stored in the memory 23, the detected value after that is stored by returning to the first memory address, so that it is possible to prevent data after a predetermined time from occupying the memory. . Hereinafter, the present embodiment will be described in more detail.

In this embodiment, the determination of the effective current value is performed by the same means as in the second embodiment. However, the difference is that the detected temperature at the time when the leading end of the recording paper to be fixed reaches the fixing section is corrected and applied. Before describing this, the characteristics of the control according to the second embodiment will be described once again. Here, FIG. 10 shows the conductive fixing film layer 3a, the electrode support 3c,
And temperature distributions in various cases corresponding to the configuration of the reinforcing plate 3d made of metal. When the film layer 3a is generating heat when energized, the temperature reached is controlled so as to be substantially constant. Therefore, the temperature may be regarded as constant during power supply. The distribution curves indicate a state in which the temperature distribution in the head has almost reached a steady state, a state in which power supply has just started, and a state in which there is no time after power supply is stopped (not shown on the opposite side of the film). There is a silicone rubber layer of the pressure roller, and the heat escapes to that area), and the recording is not performed for a long time, and the temperature distribution in the head is almost constant. When the paper interval is relatively long, the temperature distribution in the head is considered to change in the order of →→→→→.

In the second embodiment, the temperature detected by the temperature sensor is not referred to until the recording paper is discharged from the fixing unit, except for the temperature at the time when the leading end of the recording paper reaches the fixing unit.
It may be referred in some cases). This is because, as shown in FIGS. 10 and 10, a temperature gradient is generated between the surface and the inside of the electrode head (electrode support) 3c in contact with the film 3a during energization (during fixing). FIG. 3b
This is because there is a large difference between the temperature at the sensor position and the temperature at the electrode head surface. FIG. 6 shows the relationship. This is different from the case of the first embodiment shown in FIG. 9. In the second embodiment, the recording paper is conveyed at a high speed, a high film temperature is required, and the amount of heat taken by the recording paper per unit time is large. As a means for obtaining a fixing system with no wait time, the use of a high heat-resistant resin (polyimide resin) having poor thermal conductivity as a material of the electrode head (electrode support) 3c is a disaster. When a ceramic such as alumina is used as this material, the ceramic has better thermal conductivity than resin, so that a large temperature difference as shown in FIG. 6 does not occur. However, the heat generated by the current-carrying film 3a in FIG. A large power supply is required to escape, making it impractical.

This temperature difference varies depending on the temperature of the head itself and the temperature of the metal support (reinforcing plate) 3d that supports it (these depend on the heat storage of the system itself and the environmental temperature). Is extremely unreliable for use as a control reference value. The temperature of the film and the temperature near the head surface where the head and the film come into contact are significantly higher than the ambient temperature, so unlike the temperature at the sensor position, they are not easily affected by the environment. Cannot be ignored because it is large. As described above, the temperature rise curve of the film in the nip is determined by the temperature of the head surface where the head contacts the film. If the supply current is constant, the temperature on the head surface is almost uniformly determined by the initial temperature and the elapsed time after the start of sheet feeding. Therefore, a curve showing the optimum supply current with respect to the elapsed time after the start of paper feeding is determined for each head temperature (initial temperature) at the start of energization as shown in FIG. In the second embodiment, at the time of fixing, the effective current value is controlled based on the initial temperature of the temperature measuring section and the lapse of time from the start of fixing. However, FIG. 7 shows only three points (for example, 10 ° C., 25 ° C., 40 ° C., etc.) as initial temperatures at the start of fixing, but if this is insufficient, whether extrapolation or interpolation processing should be performed. More tables need to be created with additional starting temperatures.

The temperature gradient in the head becomes substantially uniform through the temperature distribution shown in FIG. 10 after a lapse of time on the order of several seconds (this time depends on the design) after the energization is stopped. However, if the next recording sheet to be fixed reaches the fixing section immediately after the power supply is stopped (that is, when the previous recording sheet is discharged), the temperature gradient in the head is large, and the temperature detected at that time and the subsequent temperature are fixed. The correspondence with the temperature rise curve of the electrode head surface (the contact surface with the conductive film) is different from when there is no temperature gradient (or when the temperature gradient is about or smaller than that in FIG. 10). Therefore, if the same control is performed in the case where there is no temperature gradient and in the case where the temperature gradient is relatively large as shown in FIG. For example, in the example shown in FIG.
When the sensor is embedded inside the support 3c of the electrode head, but is in the process of cooling as shown in FIG.
Since the inside of the head is cooled more than the surface (film side) and the reinforcing plate 3d side, the temperature is higher than the actual head surface temperature. Therefore, the detected temperature at the temperature measuring point 3b is used as the initial temperature. When the control table is selected by the method of the second embodiment, a table smaller than the actually required power supply is selected, resulting in insufficient fixing. Therefore, the third embodiment corrects the detected temperature, that is, replaces the detected temperature with another temperature to prevent this problem. This replacement temperature is called a virtual temperature here.

The temperature distribution in the head is estimated from the measured temperature at the start of fixing (at the time when the leading edge of the recording sheet reaches the fixing nip) and the measured temperature history before that, and an appropriate power supply (control table) An example of a method for determining a virtual temperature for obtaining the temperature will be described. The temperature of the temperature measuring section increases almost monotonously during energization, that is, while the recording paper passes through the fixing section. Also, almost at the same time as the power supply is stopped, the temperature of the temperature measuring section monotonously decreases. That is, heating is energized when the time derivative of the temperature history of the temperature measuring section is positive, and energization is stopped at a negative time. Therefore, the elapsed time from the stop of energization to the current time is obtained from the time differential value at each time in the temperature history. Note that the temperature measurement interval is equivalent to the line sink of the control device, but the storage time interval is too short and consumes too much memory. (Integral time).

More specifically, it is assumed that the recording sheet to be fixed reaches the fixing section at time t. Here, the time t- shown in FIG. 8 and stored in the memory 23 of the control unit shown in FIG.
From the temperature table (temperature measurement data) from n to the present time t, a time gradient (time differential value) of the temperature from the time t−n + 1 to the present time is examined. Here, n is the time required until the temperature gradient in the head becomes uniform. If the temperature gradients according to the stored data are all negative, it can be considered that the fixing operation has been suspended for a sufficient time since the stop of the energization. Control is possible. Further, if the temperature gradient calculated up to the time of tm (m: elapsed time up to the present) is positive, the pause time from the stop of energization is small, and if the temperature gradient in the head is not uniform at this time. judge. Here, n> m. In this case, if the current temperature distribution in the head can be predicted, the head surface temperature in contact with the conductive fixing film can be predicted, and the power supply can be determined uniformly.

Here, if the recording paper passing interval (interval between recording paper passing through the fixing unit) is short, the temperature distribution at time t can be regarded as the state shown in FIG. The elapsed time m from the stop, the measured temperature T at the time t, and the reinforcing plate temperature that has a small variation in the range of the time m due to the large heat capacity (the reinforcing plate 3d is made of a metal having high thermal conductivity,
The internal temperature may be regarded as substantially constant), and is determined by the temperature of the pressure roller in contact with the conductive fixing film on the side opposite to the head. However, the surface layer of the pressure roller is made of silicon rubber, and its thermal conductivity is one order of magnitude smaller than that of polyimide resin.Therefore, the contribution of the heat sink on the film side in the head to the heat distribution of the entire head is small. Almost negligible. Therefore, if the temperature on the reinforcing plate 3d side can be estimated, the temperature distribution in the head can be roughly estimated.

By the way, there is a limit to the amount of heat stored in the head at the time when the current supply was stopped last time (this is the moment when the previous recording paper was discharged from the fixing unit). There is also a limit in the temperature distribution in the head at that time, and it can be expected that the temperature distribution will be substantially uniform after being left for a certain time. For example, the case where the head surface temperature on the film side is equal to the fixing temperature and the temperature of the reinforcing plate is room temperature is the case where the temperature distribution is the largest, but even in this case, it is almost impossible to leave it without heating for a certain period of time. A uniform temperature distribution (the state shown in FIG. 10) is obtained. For example, in the configuration of the head unit of the present embodiment, if approximately seven seconds have elapsed, uniform controllability is obtained by the control method of the second embodiment. Is sufficient, but in the case of the present embodiment, it is assumed that the next recording sheet to be fixed is conveyed within 7 seconds from the previous sheet ejection, and the temperature distribution is shown in FIG. →→
Since the following fixing operation starts before the state fluctuates with time and the state is settled,
The actual temperature of the temperature measuring unit is converted to the virtual temperature, and the temperature is approximately controlled.

The virtual temperature is 1) the measured temperature T at the present time (the time t when the leading edge of the recording paper reaches the fixing portion), 2) the previous recording paper discharge time tm (m: the current time from the recording paper discharge to the present time). 3) Measured temperature history from the previous recording paper discharge time to the present, 4) Reinforcement plate temperature (temperature distribution in the head), but in this embodiment, 3) Measured temperature The history is approximated by the measured temperature at the previous recording paper discharge time (see the representative). The electrode support 3 made of a polyimide resin
The thickness of c is 2.0 mm. First, the temperature of the reinforcing plate at the time of discharge of the recording paper of the previous fixing is approximately uniformly predicted from the measured temperature Tm at that time. This approximation is a result of assuming that the power supply amount is substantially constant at the time of paper ejection, and that the temperature profile in the head has almost reached equilibrium. In this case, the film-side surface temperature is predicted to be almost constant at 170 degrees (when the fixing film reaches a temperature of 180 to 190 degrees). If a temperature sensor is provided at a depth of 1 mm of the electrode support, In the temperature profile as shown in FIG. 10, 170− (170−Tm) × 2 = 2 × Tm−170 (1) is almost the reinforcing plate temperature. This temperature is about room temperature to about 50 degrees in the actually measured range. The heat capacity of the reinforcing plate 3d is larger than that of the electrode support 3c. Even when power supply is stopped, a small amount of heat flows from the electrode support, but the temperature does not rise. Therefore, the temperature gradually decreases due to thermal diffusion such as convection and radiation. However, this temperature drop
Compared to the temperature measuring unit, it is slow and changes by several degrees in about 10 seconds. On the other hand, the temperature drop of the temperature measuring section varies greatly and depends on the temperature of the reinforcing plate (acting as a heat sink).

Here, the rate of decrease in the measured temperature until the point at which the next recording paper to be fixed is conveyed after the lapse of time m from the stop of energization is approximately (T−Tm) / m = f (Tm , Tdm, Td) (2) Here, T: measured temperature at the time when the next fixed recording paper is conveyed, Tm: measured temperature at the time when the previous recording paper to be fixed was discharged (power supply was stopped), and Td: the next recording to be fixed. Reinforcement plate temperature at the time of conveyance, Tdm: Reinforcement plate temperature at the time when the previous recording paper to be fixed was discharged (power supply was stopped). If the change in the temperature of the reinforcing plate over time m is completely ignored, the temperature of the reinforcing plate can be approximated by the expression (1). Otherwise, the temperature of the reinforcing plate can be calculated from the expressions (1) and (2). Here, (T−Tm) / m = A × (T + Tm−2 × Td) (3) can be used as an approximate expression of the function f in the expression (2). In equation (3), A is a constant of proportionality and is constant, but may be a function of T to further improve the approximation. The approximate temperature Td of the reinforcing plate is obtained from the equation (3), and the current temperature distribution in the head can be estimated from T, m, Td, and Tm. In addition, if a sensor for directly measuring the temperature Td of the reinforcing plate is provided, the current temperature distribution in the head can be more reliably estimated. However, providing a plurality of sensors on the support or the reinforcing plate requires providing a plurality of AD converters and the like. Therefore, it is not practical in terms of cost and production.

In this embodiment, the detected temperature T is corrected from the temperature distribution estimated in this manner to obtain a virtual temperature T '(the virtual temperature is obtained from T, m, Td, and Tm, but (3)
When approximated by the equation, Td is determined by T, m, and Tm, and as a result, it can be obtained by replacing with T, m, and Tm.) Based on this virtual temperature T ′, control information is selected. Performed in the same manner as in Example 2. That is, the control device 20 detects the temperature T at the start of sheet feeding by the current temperature sensor, and detects the detected temperature T and the temperature data stored in the memory (temperature measurement history information: measurement at the time of the previous fixing recording sheet ejection. Temperature Tm and elapsed time from recording paper ejection to the present time m)
The virtual temperature T 'is obtained by correcting the detected temperature T on the basis of the temperature distribution estimated by using the control information in the memory 23 (elapsed time from the start of sheet feeding and power supply). (FIG. 7)), a predetermined power supply is determined based on the elapsed time from the start of sheet feeding based on the control information, and the effective current supplied to the conductive fixing film is determined based on the determination result. Control the size.
The above operations are summarized in a flowchart as shown in FIG. As described above, in the present embodiment, even when the paper passing speed is relatively high and the fixing cycle (the interval between the recording sheets passing through the fixing unit) is short, the heat fixing by the conductive fixing film is excessively or insufficiently performed by the above control method. It can be controlled with the supplied power without.

[0033]

As described above, in a fixing device of a fixing system using a conductive fixing film, means for detecting the temperature of at least a part of a pair of electrodes or its support, Storage means for storing control information such as the relationship between the current supplied to the conductive fixing film and the like, means for determining an appropriate effective current value from a temperature detected based on the control information, and a result of the determination. In the case where the apparatus has a means for controlling the magnitude of the effective current supplied to the conductive fixing film on the basis of the above, the heating and fixing by the conductive fixing film when the paper passing speed is relatively low can be supplied without excess or shortage. It can be controlled by electric power.

According to the first aspect of the present invention, in a fixing device of a fixing system using a conductive fixing film, means for detecting a temperature of at least a part of a pair of electrodes or a support thereof, and a recording medium to be fixed. means for detecting a time at which the leading end of the medium reaches the fixing unit, and means for calculating the elapsed time from that time to the present, the elapsed time and the fixing unit paper feed start time the relationship between the power supplied from the paper feeding start Temperature of the temperature measuring section at
Storage means for storing the control information tabulated in
Based on the control information, the leading end of the recording medium to be fixed
When the paper reaches the detected temperature at the time when
Means for determining a proper effective current value from the time elapsed since made paper has a configuration having a means for phase-controlling the magnitude of the effective current supplied to the conductive fixing film based on the determination result This makes it possible to control the heating and fixing by the conductive fixing film when the sheet passing speed is relatively high, with the supplied power that is sufficient and sufficient.

According to a second aspect of the present invention, in the fixing device of the first aspect , the fixing process of the recording medium to be fixed is continuously performed.
In the case where the temperature is detected by the temperature detecting means , the temperature detected by the temperature detecting means is stored and held for a predetermined time by the storage means , and the current measured temperature result is corrected based on the stored temperature data .
Means for obtaining the control information from the corrected temperature.
Select the appropriate control table to determine the appropriate effective current value on the basis of the control information to the phase <br/> control the magnitude of the effective current supplied to the conductive fixing film based on the determination result With this configuration, when the paper passing speed is relatively high and the fixing cycle (the interval between the recording sheets passing through the fixing unit) is short, the heat fixing by the conductive fixing film can be controlled with sufficient power supply. This can contribute to the realization of an image forming apparatus having a high processing speed.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a main configuration of an image forming apparatus using a fixing device of the present invention and a conveyance path of a recording sheet.

FIG. 3 is a block diagram illustrating a schematic configuration of a control unit of the fixing device according to the present invention.

FIG. 4 is a diagram showing a relationship between an electrode support temperature and a supply current.

FIG. 5 is an explanatory diagram of energization control by phase control.

FIG. 6 is a diagram illustrating a relationship among a film temperature, a head surface temperature, and a head temperature measuring unit temperature in the fixing device according to the second embodiment .

FIG. 7 is a diagram showing the relationship between the elapsed time from the start of sheet passing and the supply power for each initial temperature when the initial temperature at the start of sheet passing is different.

FIG. 8 is an explanatory diagram of a temperature table from time t-n to present time t.

FIG. 9 is a diagram illustrating a relationship among a film temperature, a head surface temperature, and a head temperature measuring unit temperature in the fixing device according to the first exemplary embodiment .

FIG. 10 is a diagram showing temperature distributions in various cases corresponding to the configuration of a conductive fixing film layer, an electrode support, and a reinforcing plate made of metal.

FIG. 11 is a flowchart illustrating a control operation in the fixing device according to the third exemplary embodiment .

FIG. 12 is a schematic cross-sectional view of a principal part showing a configuration example of an electrophotographic process fixing unit using a conductive fixing film.

FIG. 13 is an explanatory diagram of a film conveying means of an electrophotographic process fixing section using a conductive fixing film.

[Explanation of symbols]

 2: Fixing device 2a: Electrode support 2b: Pair of electrodes 2c: Conductive fixing film 2d: Recording paper 2e: Pressure roller (elastic roller) 2f: Temperature detection sensor 3a: Conductive fixing film layer 3b: Temperature measurement Point 3c: Electrode support 3d: Reinforcement plate 10: Photoreceptor belt 11: Transfer charger 12: Registration sensor 16: Registration roller 20: Control device 21: AD conversion unit 22: Phase control unit 23: Memory 24: Timer D: Electrode Distance H: electrode height

Claims (2)

(57) [Claims] 1. A cylindrical conductive fixing film, a pair of electrodes provided inside the conductive fixing film, a support for supporting the pair of electrodes, and the conductive fixing film And a driving means for rotating the conductive fixing film around a pair of electrodes at a predetermined linear speed. The elastic roller and the conductive fixing film It is conveyed at a position where the recording medium on which the unfixed toner image has been formed is pinched, the recording medium
Conductive fixing film through a pair of electrodes
In a fixing device in which electric power is supplied to the recording medium and the toner on the recording medium is heated and fixed by Joule heat generated on the conductive fixing film, the temperature of at least a part of the pair of electrodes or its support is controlled. and means for detecting, Hijo
Hand that detects the time when the leading edge of the recording medium reaches the fixing unit
Step and means for calculating the elapsed time from that time to the present
And the relationship between the elapsed time since the start of paper passing and the power supply
A storage unit for storing control information tabulated for each temperature of the temperature measuring unit at the time of start of sheet feeding, and the leading end of the recording medium to be fixed reaches the fixing unit based on the control information. Before the time
After the detected temperature and paper feeding have been started and power has been supplied,
A fixing device comprising: means for determining an appropriate effective current value from elapsed time; and means for controlling the phase of the magnitude of the effective current supplied to the conductive fixing film based on the result of the determination. 2. The fixing device according to claim 1, wherein
When the fixing process of the recording medium is performed continuously,
The temperature detected by the temperature detection means is stored in the storage means.
Hold for a certain period of time, based on the stored temperature data
Means for compensating the current measured temperature result,
Select the appropriate control table of the control information from the temperature
And determines an appropriate effective current value based on the control information.
Supply to the conductive fixing film based on the determination result
A phase control unit that controls the magnitude of the effective current to be applied .