JP2002072764A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the partiality of the axial temperature distribution of a roller while directly cooling an induction coil by providing fans for cooling the induction coils and variously controlling their number of rotations and rotating directions. SOLUTION: This apparatus is equipped with a fixing device which is equipped with an induction heating type heating roller and has cooling fans 3 and 4 for cooling the induction coil 2 in the heating roller at both the end parts in the axial direction of the heating roller respectively and a control part which controls the cooling fans, and the control part switches and controls the rotating directions of both the cooling fans so that when one cooling fan is rotated forward to blow air in, the other cooling fan is rotated forward for suction and when the other cooling fan is reversed to blow air in, one cooling fan is reversed for suction, and further performs control for making the number of rotations of the cooling fan used to blow air in and the cooling fan currently used for suction different.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
The present invention relates to an improvement of a fixing device of an electrophotographic image forming apparatus such as a facsimile machine, and more particularly to a fixing device having an induction heating type heating roller.

[0002]

2. Description of the Related Art As a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., a fixing device having an induction heating type fixing roller (heating roller) is known. Generally, in the induction heating method, an induction coil is provided inside a heating roller, and an alternating current (high-frequency current) is supplied to the induction coil to generate an induction magnetic flux. Is generated, and the heating roller is caused to generate heat by Joule heat accompanying the induced current. However, in the conventional induction heating type fixing device, since the induction coil is provided inside the hollow cylindrical heating roller (roller core), radiant heat from the heated roller core and self-heating of the coil are generated. As a result, the temperature of the induction coil increases, and in some cases, the temperature of the induction coil exceeds the allowable temperature limit of the insulating coating, and the device may be damaged. In order to solve such a problem caused by the temperature rise of the induction coil, measures such as using a high-cost heat-resistant induction coil or cooling the induction coil by using a fan are taken. However, in this method, the temperature decreases as the position is closer to the fan, and the temperature is biased in the roller axis direction, so that a satisfactory fixing property cannot be obtained.

FIGS. 6 (a) and 6 (b) are a sectional view showing a schematic configuration of a conventional induction heating fixing device and a diagram showing driving timings of two fans, wherein reference numeral 1 denotes a hollow cylindrical heating roller main body. Reference numeral 2 denotes an induction coil disposed inside the heating roller main body 1, and reference numerals 3 and 4 denote a suction fan and a suction fan disposed at both axial openings of the heating roller main body 1, respectively. Cooling fan to prevent the In this figure, both ends of the induction coil 2 are omitted, but are assumed to be connected to an inverter. The plurality of fans 3 and 4 are blown under controlled timing, for example, as shown in FIG. 6B to cool the induction coil 2. In this conventional example, the plurality of fans 3 and 4 are controlled to cool the induction coil. Therefore, compared to the case where only one fan is provided at one end in the axial direction of the heating roller main body 1 to cool the induction coil, the induction coil is cooled. Although the unbalance of the surface temperature distribution in the roller axis direction becomes small, even if two fans are used in combination, this unbalance cannot be completely eliminated. This is an unbalance in the temperature distribution that occurs because the roller temperature tends to decrease on the blowing side where the cooling air at a room temperature (low temperature for the heating roller) blows. That is, a schematic diagram of the temperature distribution of the induction coil in FIG. 3 (the horizontal axis indicates the axial position of the roller, and the vertical axis indicates the temperature).
For the ideal temperature distribution without a cooling fan,
The actual temperature distribution of the conventional example has the following tendency. Japanese Patent Application Laid-Open No. 8-202185 discloses a configuration for cooling a heating roller of a type different from the induction heating type by a single reversible fan, and by appropriately switching the rotation direction of the fan. An object of the present invention is to prevent the temperature distribution in the axial direction of the heating roller from being biased by blowing air to the surface of the heating roller. However, in this conventional example, the arrangement of the fan for cooling the induction coil,
It does not relate to control but cools the surface of the heating roller. Therefore, even if this cooling method is applied to an induction heating type heating roller, it is difficult to effectively eliminate the temperature distribution imbalance.

Next, in the prior art described in Japanese Patent Application Laid-Open No. 5-80437, when cooling by introducing outside air into a heat-generating portion arranged inside a casing of a copying machine, a cooling fan is inverted during standby. This is to rotate the dust-proof filter to eliminate clogging, and does not prevent the temperature distribution of the induction coil in the induction heating system from being biased. Further, Japanese Patent Application Laid-Open No. 2000-56598 discloses that a blowing fan is arranged at one end in the axial direction of a heating roller having a built-in induction coil so that a sufficient air volume can be secured even at a position distant from the suction fan. A technology has been disclosed that enables cooling over the entire axial direction of the roller, efficiently cools the induction coil, and maintains a constant temperature distribution in the axial direction of the heating roller. If the direction is limited, the blowing side is cooled excessively and the temperature of the roller is liable to decrease, so that it is difficult to completely avoid imbalance in the temperature distribution.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and in an image forming apparatus using a heating roller using an induction heating method, two image forming apparatuses are disposed at both ends in the axial direction of the heating roller. It is an object of the present invention to cool an induction coil using one fan and prevent the temperature distribution in the axial direction of the induction coil located in the heating roller from being biased.

[0006]

In order to solve the above-mentioned problems,
According to the first aspect of the present invention, there is provided a fixing device including an induction heating type heating roller having an induction coil therein, and cooling fans for cooling the induction coil disposed at both axial ends of the heating roller. A control unit for controlling a cooling fan, wherein the control unit rotates the other cooling fan forward for suction while the one cooling fan is normally rotated for blowing, and blows the other cooling fan. During the reversing period, the rotation direction of both cooling fans is switched and controlled so that one of the cooling fans is reversed for suction, and the other cooling fan is used for blowing and for cooling. It is characterized in that control for varying the number of rotations of the cooling fan is performed. The invention according to claim 2 is configured such that a plurality of temperature sensors are arranged along the axial direction of the induction coil, and the temperature of each part of the induction coil is measured by each of the temperature sensors. Switching of the rotation direction of each cooling fan and control of the number of rotations are performed based on a temperature detected by a sensor. The invention according to claim 3 is characterized in that the plurality of temperature sensors are respectively disposed near both ends in the axial direction of the induction coil, and the control unit is configured to determine whether a temperature difference detected by the two temperature sensors exceeds a predetermined value on a high temperature side. Indicates that the rotation direction of both cooling fans is the normal rotation direction, and when the temperature difference detected by both temperature sensors is less than a predetermined value on the low temperature side, the rotation direction of both cooling fans is the reverse rotation direction, and the temperature detected by both temperature sensors is When the difference is within the range of each of the predetermined values on the high temperature side and the low temperature side, the rotation directions of both cooling fans are kept as they are.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. FIG. 1 is a cross-sectional view of an induction heating type heating roller provided in a fixing device according to an embodiment of the present invention, FIG. 2 is a graph showing rotation directions and rotation speeds of respective cooling fans, and FIG. It is a schematic diagram of the temperature distribution of an induction coil. The heating roller shown in FIG. 1 includes a heating roller main body 1 in which a release layer and the like are laminated around a hollow cylindrical cored bar, an induction coil 2 disposed inside the heating roller main body 1, and an axial direction of the heating roller main body 1. Coil cooling fans 3 and 4 respectively disposed facing the openings at both ends.
The coil cooling runs 3 and 4 are cooling fans that can rotate in the normal and reverse directions to form an airflow for preventing the temperature of the induction coil 2 from rising. In this figure, both ends of the induction coil 2 are omitted, but are assumed to be connected to an inverter (not shown). The fans 3, 4 and the induction coil 2 are controlled by a control unit (not shown). The fixing device having the heating roller shown in FIG. 1 includes a pressure roller (not shown) that presses the outer peripheral surface of the heating roller main body 1, and when the transfer paper is passed between the two rollers, the toner image on the transfer paper is removed. The toner image is fixed by applying pressure while heating.

In the (X) region (t0 to t1) in FIG. 2, the first cooling fan 3 is used as a blower fan.
It rotates at a constant rotation speed in X (positive direction) of FIG. 1, and the second cooling fan 4 alternately repeats high-speed rotation and low-speed rotation in the X direction of FIG. 1 as a suction fan. Next, in the (Y) region (t1 to t2) in FIG. 2, the first cooling fan 3 alternately repeats high-speed rotation and low-speed rotation in Y (reverse direction) in FIG. The cooling fan 4 rotates at a constant rotational speed in the Y direction in FIG. 1 as a blowing fan. In other words, during the period in which one fan is driven to rotate at a constant rotational speed as the blowing side, the other fan is driven to rotate as the suction side by alternately repeating high-speed rotation and low-speed rotation. At this time, it is preferable to control the rotation speed of the suction-side fan to be higher than the rotation speed (constant) of the blow-side fan during high-speed rotation, and to be lower than the rotation speed (constant) of the blow-side fan during low-speed rotation. . However, here, a control method in which the fan on the blowing side rotates at a constant speed and the fan on the suction side repeats high speed and low speed is an example, and the control of the fan depends on the characteristics of the heating roller body, the induction coil, and the performance of the fan. The method shall be appropriately performed by various methods. In the present embodiment, not only one of the two ends of the induction coil 2 in the axial direction but also both ends thereof alternately change not only the rotation speed of the two fans but also the rotation direction in this manner. Since cooling is performed by the blower-side fan, it is possible to reduce imbalance in the temperature distribution in the axial direction of the heating roller. At this time, the temperature distribution in the axial direction of the heating roller (induction coil) is considered to approach the ideal temperature distribution as shown in FIG. As described above, in the present embodiment, the rotation direction of the first and second fans 3 and 4 is reversed every predetermined time to reverse the air blowing direction. That is,
Conventionally, after cooling the induction coil 2 by flowing air in one direction for a certain period of time and then cooling it by flowing air in the opposite direction for the next fixed time As compared with the example, the unbalance of the temperature distribution in the axial direction of the heating roller due to the cooling can be reduced, and the image quality of the fixed toner image can be made uniform.

Next, FIG. 4 is a sectional view showing a main part configuration (heating roller) of an induction heating type fixing device according to another embodiment of the present invention, and the same parts as those in the embodiment of FIG. The description is given with reference numerals. Reference numeral 1 denotes a hollow cylindrical heating roller main body, 2 denotes an induction coil disposed inside the heating roller main body 1, and 3 and 4 denote coil cooling fans disposed at both axial openings of the heating roller main body 1, respectively. Yes, induction coil 2
This is a cooling fan for preventing the temperature from rising. In this figure, both ends of the induction coil 2 are omitted, but are assumed to be connected to an inverter (not shown). Each fan 3,
4 and the induction coil 2 are controlled by a control unit (not shown). A characteristic configuration of this embodiment is that temperature sensors 10 and 11 for measuring the temperature of the induction coil 2 are arranged near both ends of the induction coil 2, respectively. Each of the temperature sensors 10 and 11 is installed in contact with the induction coil 2 and detects the temperature of the induction coil 2 respectively. Although the wiring from each of the temperature sensors 10 and 11 is omitted in this figure, each of the temperature sensors is assumed to be connected to a control unit of the image forming apparatus main body. The temperature sensors 10 and 11 are used to keep the balance of the surface temperature distribution in the axial direction of the heating roller.
The control unit changes the rotation direction of each cooling fan 3, 4, that is, the direction in which the cooling air flows, based on the temperature of the induction coil measured in step (1). As a method of controlling the rotation direction and the number of rotations of each cooling fan, for example, a method as shown in FIG. 2 can be exemplified.

FIG. 5 is a flowchart showing a control procedure of the cooling fan in the fixing device according to the embodiment of FIG. In FIG. 4, the temperature of the surface of the induction coil is detected by the temperature sensors 10 and 11, respectively, and these detected temperatures are Ta and Tb, respectively. When comparing and measuring the detected temperatures Ta and Tb in step 2, (Ta-Tb) is calculated in step 3. First, in step 4, the detected temperature Ta of the temperature sensor 10 is 10 deg (the predetermined value on the higher temperature side of the detected temperature difference) than the detected temperature Tb of the temperature sensor 11.
If it is higher ((Ta−Tb) ≧ 10), each cooling fan 1
The rotation directions of 0 and 11 are set to the positive direction (X direction in FIG. 4). In the case of (−10 <(Ta−Tb) <10), the rotation direction of each cooling fan is set as it is (forward rotation direction or reverse rotation direction). When the difference (Ta−Tb) is equal to or less than −10 deg which is a predetermined value on the low temperature side ((Ta−Tb) ≦ −10), each cooling fan 10
The rotation direction of 11 is the reverse direction (Y direction in FIG. 4). Note that the temperature difference between the detected temperatures Ta and Tb is 10 deg to -10 deg (|
The reason for keeping the rotation direction as it is within the range of 10 deg |) is to prevent the rotation direction from frequently changing due to a slight temperature difference. Therefore, when each cooling fan is rotating in the forward direction, the temperature difference between the detected temperatures Ta and Tb is 10
When the temperature falls within the range of deg to -10 deg, the rotation in the forward direction is continued. Conversely, when each cooling fan is rotating in the reverse direction, the temperature difference between the detected temperatures Ta and Tb is 10 deg to -10 deg. If the value falls within the range, rotation in the reverse direction is continued. Thus, the induction coil 2 is controlled by the temperature sensors 10 and 11.
By controlling the switching direction of the cooling fan by measuring the temperature of the cooling fan, it is possible to cool the induction coil while reducing the deviation of the temperature distribution in the axial direction of the heating roller as compared with the above embodiment. In addition, | 10 shown here
The value deg | is an example, and this value
An appropriate value shall be selected in consideration of the characteristics of the induction coil and the capacity of the cooling fan. It should be noted that the fans used in the above embodiments are air blowing means for directly cooling the induction coil, and are not assumed to cool the heating roller body. For this reason, a configuration is employed in which cooling air does not actually hit the heating roller body but only the induction coil using a duct or the like.

Finally, Japanese Patent Application Laid-Open No. 8-202185 discloses a "temperature sensor for monitoring the temperature of a fixing device".
Although "a fan arranged at one end of the fixing device for cooling the periphery of the fixing device" is described, in the present invention, "a sensor for measuring the temperature of the induction coil" and "a sensor for cooling the induction coil" This publication does not disclose the gist of the present invention because the configuration in which a plurality of fans are arranged is characteristic. The “temperature sensor for monitoring the temperature of the fixing device” described in the publication is, specifically, a thermistor or the like in contact with the surface of the heating roller, and a book that measures the temperature of the coil in contact with the surface of the induction coil. It differs from the "induction coil temperature sensor" of the invention. In the heating roller, the temperature of the roller surface and the temperature of the induction coil are not irrelevant, but they do not follow without a time difference. For example, power off the fuser
In this case, the cooling method of the temperature of the induction coil is slower than the cooling method of the roller surface temperature. This is because the temperature stays inside the roller. Therefore, the object to be detected by the two temperature sensors, the result of the detection, and the method of use thereof are obviously different.

[0012]

As described above, in the image forming apparatus having the fixing device according to the first aspect, a plurality of induction coil cooling fans are provided, and the number of rotations and the direction of rotation are controlled in various ways.
The bias of the axial temperature distribution of the roller can be reduced while directly cooling the induction coil. According to the second and third aspects of the present invention, a plurality of induction coil cooling fans are provided,
By controlling the number of rotations and the direction of rotation, it is possible to reduce the bias of the temperature distribution of the rollers while cooling the induction coil, and at the same time, measure the temperature of the induction coil to switch the rotation direction of the fan. By determining, the deviation of the temperature distribution in the axial direction of the induction coil can be reduced and the fixing quality can be stabilized as compared with the case where the fan is controlled without measuring the temperature of the induction coil.

[Brief description of the drawings]

FIG. 1 is a sectional view of an induction heating type heating roller provided in a fixing device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a rotation direction and a rotation speed of each cooling fan.

FIG. 3 is a schematic diagram of a temperature distribution of an induction coil.

FIG. 4 is a cross-sectional view illustrating a main part configuration (heating roller) of an induction heating type fixing device according to another embodiment of the present invention.

FIG. 5 is a flowchart illustrating a control procedure of a cooling fan in the fixing device according to the embodiment of FIG. 4;

FIG. 6 is an explanatory diagram of a conventional example.

[Explanation of symbols]

1 heating roller body, 2 induction coils, 3 and 4 coil cooling fans, 10 and 11 temperature sensors.

Claims (3)

[Claims] 1. A fixing device comprising an induction heating type heating roller having an induction coil therein, and cooling fans for cooling the induction coil disposed at both ends in the axial direction of the heating roller. And a control unit that controls the other cooling fan to rotate normally for suction while the other cooling fan is rotating normally for blowing while the other cooling fan is used for blowing. During the reverse rotation period, the rotation direction of both cooling fans is switched and controlled so that one of the cooling fans is reversely rotated for suction, and the other cooling fan is used for blowing and the cooling fan used for suction. An image forming apparatus that performs control to vary the number of rotations of the image forming apparatus. 2. A configuration in which a plurality of temperature sensors are arranged along the axial direction of the induction coil, and the temperature of each part of the induction coil is measured by each of the temperature sensors. 2. The image forming apparatus according to claim 1, wherein switching of the rotation direction of each of the cooling fans and control of the number of rotations are performed based on the detected temperature. 3. The plurality of temperature sensors are disposed near both ends in the axial direction of the induction coil, respectively. The control unit is configured to determine whether the temperature difference between the two temperature sensors exceeds a predetermined value on the high temperature side. The rotation direction of the cooling fan is set to the normal rotation direction, and when the temperature difference detected by the two temperature sensors becomes equal to or less than a predetermined value on the low temperature side, the rotation direction of the two cooling fans is set to the reverse rotation direction, and 3. The image forming apparatus according to claim 2, wherein the rotation directions of both cooling fans are kept as they are when the temperature is within the range of each of the predetermined values on the high temperature side and the low temperature side.