JP2002357977A - Fixing device, image forming device and both-side image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrences of the wrinkles of transfer paper and the nonconformity of an image such as image blurring due to a temperature difference between the center part and the end part of a fixing roller by always keeping the temperature distribution of the fixing roller constant. SOLUTION: A fixing device 22 has a fixing roller 1, a pressing roller 2, a first heater 3, a second heater 4, a first temperature detecting element 5, a second temperature detecting element 6, and a heater controlling part 9 or the like. When an unfixed toner image formed on the transfer paper P is successively thermally fixed on the several sheets of the transfer paper P and/or fixing processing speed at which the unfixed toner image formed on the transfer paper P is thermally fixed is comparatively high, the turn-on and turn-off of the first heater 3 and the second heater 4 are controlled by the heater controlling part 9 so as to always maintain the constant temperature difference between target temperature previously set in accordance with detected temperature by the first temperature detecting element 5 at which the second heater 4 is controlled and the detected temperature by the first temperature detecting element 5 while referring to the detected temperature by the temperature detecting elements 5 and 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device, an image forming device, and a double-sided image forming device, and more particularly, to a recording material (paper, sheet, OHP sheet, transfer material) carrying an unfixed monochrome image or color image. The present invention also relates to a fixing device for performing heat fixing through the same method as described above, and an image forming apparatus such as a copying machine, a printer, a facsimile, and a double-sided image forming apparatus having the fixing device.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer or a facsimile, a toner image is formed on an image carrier based on image information, and the toner image is transferred onto a recording material to carry the toner image. 2. Description of the Related Art A recording material is passed through a fixing device to fix a toner image on the recording material by heat and pressure.
As the fixing device, a heat roller system and a film system are mainly known, and an efficient heat roller system will be described below. As the heat roller system, there are known an internal heating system having a halogen heater or the like as a heating unit inside a fixing roller, and an external heating system having a heating unit outside the fixing roller. The following describes what is applied to. An internal heating type fixing device includes a fixing roller heated by a halogen heater or the like provided therein and a pressing roller (pressing member) that forms a fixing nip between the fixing roller and the fixing roller. When the recording material carrying the unfixed toner image is passed through the fixing nip, the toner is melted by the heat of the fixing roller and is fixed by pressure.

In such a fixing device of a conventional image forming apparatus, a first heater having a heat generation distribution at a center height is provided;
A second heater having a heat generation distribution at both ends high is provided inside the fixing roller, and a first temperature detecting element for detecting a temperature of a central outer surface of the fixing roller and a temperature of an end outer surface of the fixing roller are further detected. A device provided with a second temperature detecting element for detection is known (see, for example, JP-A-63-216082). In the above fixing device, the temperature of the outer surface of the center of the fixing roller is detected by the first temperature detecting element, and the temperature of the outer surface of the end of the fixing roller is detected by the second temperature detecting element. Based on the values of the temperatures detected by the elements, the heaters are independently controlled so that the respective target temperatures are set in advance, so that the temperatures of the central outer surface and the outer surface of the end of the fixing roller are adjusted. The temperature distribution on the outer surface of the fixing roller is made uniform in the axial direction so as to reach the target temperature. Hereinafter, the prefix "first" is replaced by "first"
And "second" as "second".

[0004]

As described above, in order to make the temperature distribution on the outer surface of the fixing roller uniform, the first heater and the second heater are replaced by the first temperature detecting element and the second temperature. If the target temperature is controlled in accordance with each detected temperature from the detecting element, the temperature of the outer surface of the fixing roller (hereinafter simply referred to as a temperature close to the target temperature in the standby state of the image forming apparatus and the initial state of printing). "The temperature of the fixing roller" may be maintained.

However, if the continuous printing operation is continued, the heat of the fixing roller is taken away by the transfer paper as the recording material and the pressure roller, so that the temperature of the fixing roller cannot be maintained at the target temperature, and the temperature gradually decreases. Come. In particular, at the current level of high-speed machines (image forming apparatuses such as copiers and printers, 50 PPM (Print Per Minute)
In the above models, since the number of prints per unit time is large, much heat is taken away, and the temperature drop of the fixing roller becomes large. Furthermore, in recent image forming apparatuses, the power supply to the fixing heater is also reduced to reduce the power consumption of the entire machine, that is, to reduce power consumption, thereby reducing the temperature of the fixing roller. Becomes even more noticeable.

In such an image forming apparatus in which the temperature of the fixing roller has a large temperature drop, even if it is attempted to control the central portion and the end portion of the fixing roller to the respective preset target temperatures as in the prior art, each heater is set to full. Since the temperature of the fixing roller drops in the lighting state, the control is actually impossible. In that case, the temperature distribution between the center and the end of the fixing roller often differs from the temperature difference between the target temperatures (the reason will be described later). As described above, not only the original target temperature of the fixing roller but also the temperature difference between the center and the end of the fixing roller is an important characteristic value for maintaining the performance of the fixing unit. Problems such as wrinkling of the transfer paper and image blurring occur.

As described before and after, in the above-described conventional image forming apparatus, each heater is fully turned on after a main switch for turning on / off the power supply from the power supply of the apparatus main body is turned on, that is, At the time of startup before reloading (a state in which printing or copying is enabled), heat is generated at full power, and when the temperature of the fixing roller reaches a set target temperature, pre-rotation is performed to warm the pressure roller. Usually, the pre-rotation is also performed at the target temperature. However, regarding the actual temperature of the fixing roller, during the pre-rotation from when the main switch is turned on, the central part of the fixing roller has reached the target temperature, but both ends of the fixing roller support the fixing roller. Since the heat is taken by the frame, the drive gear, and the like, the temperature at both ends of the fixing roller does not reach the target temperature even if each heater generates heat at full power. If the pre-rotation is performed at that temperature, the temperature distribution at the center and both ends of the pressure roller becomes the same as the temperature distribution of the fixing roller, so the temperature at the center of the pressure roller is high and the temperature at both ends is high. It will be lower. As a result, the outer diameter of the pressure roller becomes larger in the central portion than the target value, and when the paper is passed in this state, a problem such as wrinkles or image blurring may occur on the transfer paper (for this, This will be explained later).

As described above, not only the original target temperature of the fixing roller but also the temperature difference between the center and each end of the fixing roller and the pressure roller (especially at the time of start-up and pre-rotation before reloading). (Including not becoming too large) is also an important characteristic value for maintaining the performance of the fixing unit, and if it cannot be maintained at the target value, if the paper is passed immediately after the pre-rotation before reloading, etc. In addition, problems such as wrinkling of the transfer paper and image blur occur.

A first object of the present invention is to always maintain a constant temperature distribution of a fixing roller, and to reduce wrinkles of a transfer sheet due to a temperature difference between a center portion and an end portion of the fixing roller, and to reduce image blur such as image blur. An object of the present invention is to provide a fixing device, an image forming apparatus, and a double-sided image forming apparatus that can prevent occurrence of a problem.

A second object of the present invention is to keep the temperature distribution of the fixing roller and the pressure roller constant at the time of startup before reloading and at the time of pre-rotation, and to fix the temperature distribution of the fixing roller and the pressure roller (pressure member). When the paper is passed immediately after the pre-rotation before reloading due to the temperature difference between the center part and the end part of the paper, it is possible to prevent the occurrence of defects on the image such as wrinkles of the transfer paper and image blur. An object of the present invention is to provide an apparatus, an image forming apparatus, and a double-sided image forming apparatus.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems and to achieve the above-mentioned object, the invention described in each claim employs the following characteristic configurations and means. According to the first aspect of the present invention, there is provided a first heating unit having a heat generation distribution at a center height, a second heating unit having a heat generation distribution at both ends, a fixing roller heated by the first and second heating units, First temperature detecting means for detecting a temperature at a substantially center of the fixing roller;
The second temperature detecting means for detecting the temperature of the fixing roller at a position distant from the first temperature detecting means, and the second temperature detecting means in response to output signals (detected temperatures) from the first and second temperature detecting means. In a fixing device having control means for controlling the first and second heating means independently of each other, a target temperature for controlling the second heating means is set in accordance with the temperature detected by the first temperature detection means. In addition, the target temperature is set lower than the detected temperature.

According to a second aspect of the present invention, in the fixing device of the first aspect, the target temperature is set so as to always be a constant temperature difference from the detected temperature.

According to a third aspect of the present invention, in the fixing device according to the second aspect, the control means is configured to thermally fix an unfixed image formed on the recording material continuously over a plurality of recording materials. And / or when the fixing processing speed for thermally fixing the unfixed image formed on the recording material is relatively high, the first and second heating units are controlled so as to maintain the constant temperature difference. The control is performed. Here, “when the unfixed image formed on the recording material is thermally fixed continuously over a plurality of recording materials” means when a continuous copying operation or a continuous printing operation is continued. Has the same meaning as Further, "when the fixing processing speed when the unfixed image formed on the recording material is thermally fixed is relatively high" means that the copying operation is relatively high or the printing operation is relatively low. Synonymous with high speed.

According to a fourth aspect of the present invention, there is provided a first heating means having a heat generation distribution having a center height, a second heating means having a heat generation distribution having both end heights, and a fixing device which is heated by the first and second heating means. A roller, first temperature detecting means for detecting a temperature substantially at the center of the fixing roller, second temperature detecting means for detecting a temperature of the fixing roller at a position distant from the first temperature detecting means, Control means for controlling the first and second heating means independently according to output signals from the first and second temperature detection means, and controlling the first and second heating means. In a fixing device that sets each target temperature according to the temperature detected by the first or second temperature detecting means, during pre-rotation before reloading, the first temperature is set according to the temperature detected by the second temperature detecting means. Set target temperature to control heating means To.

According to a fifth aspect of the present invention, in the fixing device of the fourth aspect, the target temperature is set to be equal to or higher than the detected temperature. Here, "the target temperature is set to be equal to or higher than the detected temperature" means the first one.
The target temperature (the target temperature at the center of the fixing roller) for controlling the heating means is set to be equal to or higher than the detected temperature (the temperature at the end of the fixing roller) from the second temperature detecting means. More specifically, the target temperature at the center of the fixing roller and the temperature at the end of the fixing roller are adjusted so that the temperature difference between the target temperature at the center of the fixing roller and the temperature at the end does not become too large. This means that the temperature is set equal to or higher than the temperature of the end of the fixing roller. Therefore,
Even if the temperature difference between the central portion and the end portion of the fixing roller and the pressing member (for example, the pressing roller) becomes too large, the fixing roller and the pressing member (for example, the pressing Even if the temperature of the end portion of the roller becomes higher than the temperature of the central portion, it does not mean that the temperature is within the range of the above technical matters. In other words, the most appropriate range is such that the temperature at the center of the fixing roller and the pressing member is equal to or slightly higher than the temperature of the end of the fixing roller and the pressing member. Is what you do.

The invention according to claim 6 is the invention according to claim 4 or 5.
In the fixing device described above, the target temperature is set so as to always have a constant temperature difference from the detected temperature. Here, "setting the target temperature so as to always have a constant temperature difference with respect to the detected temperature" refers to a target temperature for controlling the first heating means (the central portion of the fixing roller and the pressing member). Is the same as the temperature detected by the second temperature detecting means (the temperature of the end portions of the fixing roller and the pressing member), that is, the case where the certain temperature difference is zero and equal.

According to a seventh aspect of the present invention, in the fixing device according to the sixth aspect, the control means controls the first and the second so as to maintain the constant temperature difference during the pre-rotation before the reload. It is characterized in that the heating means is controlled.

[0018] The invention according to claim 8 is the invention according to claims 1 to 7.
The fixing device according to any one of the above, further comprising a pressure member that presses against the fixing roller to form a nip width, wherein the nip width is larger at an end portion than at a central portion of the fixing roller. It is characterized by being set.

According to the ninth aspect of the present invention, there are provided the first to eighth aspects.
In the fixing device according to any one of the above, the power supply to the first and second heating units is set relatively small. Here, "the power supply is set to be relatively small" is synonymous with saving power (saving power), that is, achieving energy saving.

According to a tenth aspect of the present invention, in the fixing device according to any one of the first to ninth aspects, the heat generation temperature of the second heating means is set higher than the heat generation temperature of the first heating means. It is characterized by having been done.

According to an eleventh aspect of the present invention, there is provided an image forming apparatus having a fixing device for thermally fixing an unfixed image formed on one surface of a recording material after forming the image on one surface of the recording material. 2. The apparatus as claimed in claim 1, wherein the fixing device comprises:
0 is described.

According to a twelfth aspect of the present invention, after an image is formed on one surface of a recording material, an unfixed image formed on one surface of the recording material is heat-fixed. After turning over and performing image formation on the other surface on the recording material,
A double-sided image forming apparatus having a fixing device for thermally fixing an unfixed image formed on the other surface of a recording material, wherein the fixing device is the one according to any one of claims 1 to 10, The target temperature at the time of fixing an unfixed image on the other surface of the recording material is set lower than the target temperature at the time of fixing an unfixed image of one surface on the recording material.

As a specific example of the double-sided image forming apparatus, besides a color double-sided image forming apparatus 500 shown in FIG. 9 described later, for example, Japanese Patent Publication No. Hei 2-13786 (JP-A-57-13216)
5), a single-color double-sided image forming apparatus as disclosed in FIG. 1 and the like, and the present invention can be applied to such a double-sided image forming apparatus.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention including embodiments with reference to the drawings (hereinafter, simply referred to as "embodiments").
Will be described. In each embodiment and the like, members and components having the same function, shape, and the like will be described once, and the description will be omitted by assigning the same reference numerals.
For the sake of simplicity of the drawings and the description, even if the members and the components are to be shown in the drawings, the members and the components that do not need to be specifically described in the drawings may be omitted as appropriate. (First Embodiment) First, an outline of the overall configuration of a printer 50 as an example of an image forming apparatus according to a first embodiment of the present invention will be described with reference to FIG. The printer 50
An image forming apparatus having a fixing device for thermally fixing an unfixed image formed on one surface of a recording material after forming an image on one surface of the recording material (claim 11). As described above, the printer 50 is an image forming apparatus that can perform only the so-called single-sided image forming mode. Specifically, the printer 50 includes a paper feed unit 14, a pair of registration rollers 16, a photosensitive drum 18 as an image carrier, a transfer unit 20, a fixing device 22 of an internal heating system, and the like. . The printer 50 is a high-speed printer having a processing capability of 70 PPM when printing using transfer paper P (or paper P) as a recording material of size A4 (horizontal), for example.

The paper feeding means 14 separates and feeds the paper feeding tray 24 in which the transfer papers P are stored in a stacked state and the transfer papers P stored in the paper feeding tray 24 one by one from the topmost one. It has a paper feed roller 26 and the like. The transfer paper P sent out by the paper feed roller 26 is temporarily stopped by the pair of registration rollers 16, and after the posture deviation is corrected, the photosensitive drum 1
8 at a timing synchronized with the rotation of the transfer roller 8, that is, at a timing when the leading end of the toner image formed on the photosensitive drum 18 coincides with the predetermined position of the leading end of the transfer paper P in the conveying direction. Sent to

Around the photosensitive drum 18, in the order of rotation indicated by the arrow, a charging roller 28 as a charging unit, a mirror 30 constituting a part of an unillustrated exposure unit, and a developing unit provided with a developing roller 32a 32 and the transfer means 20
And a cleaning means 34 having a cleaning blade 34a. Between the charging roller 28 and the developing unit 32, the exposure unit 36 on the photosensitive drum 18 is irradiated with the exposure light Lb via the mirror 30 and is scanned.

The image forming operation by the printer 50 is performed in the same manner as in the prior art. That is, when the photosensitive drum 18 starts rotating, the surface of the photosensitive drum 18 is uniformly charged by the charging roller 28, and the exposure unit 36 irradiates the exposure unit 36 with the exposure light Lb based on the image information and scans the image to be formed. Is formed. The electrostatic latent image is moved to the developing unit 32 by the rotation of the photosensitive drum 18, where the toner is supplied to be visualized and a toner image is formed. The toner image formed on the photoconductor drum 18 is transferred onto the transfer paper P conveyed to the transfer portion N at a predetermined timing by applying a transfer bias by the transfer unit 20.

The transfer paper P carrying the toner image is transferred to the fixing device 2
After being conveyed to the fixing device 22 and fixed by the fixing device 22, the sheet is discharged and stacked on a discharge tray (not shown). Details of the fixing operation in the fixing device 22 will be described later. Residual toner remaining on the photosensitive drum 18 without being transferred at the transfer portion N reaches cleaning means 34 as the photosensitive drum 18 rotates, and is scraped off by a cleaning blade 34 a while passing through the cleaning means 34. Being cleaned. After that, the residual potential on the photosensitive drum 18 is removed by a not-shown charge eliminating means, and the preparation is made for the next image forming step.

Referring to FIGS. 1 to 3, fixing device 22
The surrounding configuration will be described in detail. As shown in FIG. 1, the fixing device 22 is disposed at a position where the fixing roller 1 has a cylindrical shape and is in parallel contact under the fixing roller 1 and forms a fixing nip portion NA between the fixing roller 1 and the fixing roller 1. A pressure roller 2 serving as a pressure member, and a first heating unit which is disposed inside the fixing roller 1 and supplies heat to an outer surface of a central portion of the fixing roller 1. A first heater 3 as a fixing roller 1 disposed inside the fixing roller 1
And a second heater 4 as a second heating means having a heat generation distribution as shown in FIG. The fixing device 22 includes a first heater 3
And a second heater power supply 8 for supplying power to the second heater 4. A first heater power supply 7 for supplying power to the second heater 4.
A first temperature detecting element 5 as first temperature detecting means for detecting a temperature of an outer surface of a substantially central portion (hereinafter, simply referred to as a “central portion of the fixing roller 1”), and a distance from the first temperature detecting element 5 A second position, which is located at one end of the fixing roller 1 in the longitudinal direction, and which detects the temperature of the outer surface of one end of the fixing roller 1 (hereinafter, simply referred to as “the end of the fixing roller 1”).
A second temperature detecting element 6 as a temperature detecting means, and a control means for performing a temperature control peculiar to the present invention, which will be described later, in accordance with an output signal relating to a detected temperature from each of the temperature detecting elements 5 and 6. And a heater control unit 9.

The fixing roller 1 is made of aluminum having an outer diameter of 50 mm, a cylindrical outer peripheral portion and a core metal having a thickness of 5 mm, and has a thickness of 18 μm (0.
018 mm) coated with a Teflon (registered trademark) (PTFE) coat layer. The pressure roller 2 has an outer diameter of 50 mm and an outer peripheral portion formed of an 8 mm thick silicon rubber as an elastic layer.

In FIG. 8, a fixing nip NA formed by a pressure roller 2 pressed against a fixing roller 1 is shown.
The nip width NB in the recording material conveyance direction is set to be larger at both ends than at the center of the fixing roller 1, and a normal double-sided support beam configuration is adopted.

The first heater 3 and the second heater 4 are constituted by, for example, halogen lamps. FIG. 1 shows both of these halogen lamps in a simplified manner. As shown in FIGS. 2 and 3, the first heater 3 and the second heater 4 have different heat distributions. In FIGS. 2 and 3, numerical values surrounded by squares represent the axial length of the fixing roller 1. The first heater 3 has a light-emitting portion having a length of about 185 mm and mainly heats a central portion of the fixing roller 1. On the other hand, the second heater 4 has a length of about 318 m
m, the amount of light emission at both ends is larger than that at the center, and mainly heats both ends of the fixing roller 1. Here, the light emission amount is substantially proportional to the heat generation amount, and the heat generation temperature of the second heater 4 is set higher than the heat generation temperature of the first heater 3. In FIGS. 2 and 3, hatched regions indicate design tolerances that are allowable in using the first heater 3 and the second heater 4. The first temperature detecting element 5 and the second temperature detecting element 6 are arranged in contact with the respective outer surfaces of the fixing roller 1. As these temperature detecting elements 5 and 6, for example, thermistors are preferably used.

The heater control unit 9 includes a CP (not shown).
U (central processing unit), I / O (input / output) port, R
The microcomputer includes a microcomputer having an OM (read only storage device), a RAM (read / write storage device), a timer, and the like, which are connected by a signal bus. The heater control unit 9 includes, for example, the printer 5
0 controller. An analog output voltage signal related to the detected temperature from each of the temperature detecting elements 5 and 6 is input to the CPU of the heater control unit 9 via an A / D conversion port (not shown). A command signal from the heater control unit 9 is supplied to each heater power supply 7 through the output port.
8 is sent. Examples of practical circuits around the heater power supplies 7 and 8 include, for example, trigger circuits and triacs as shown in FIG. 1 of Japanese Patent No. 2941568 (Japanese Patent Laid-Open No. 6-11999). Things.

The CPU in the heater control section 9 (hereinafter simply referred to as "heater control section 9") has the following control functions. That is, first, the heater control unit 9 is set to be equal to or higher than the detected temperature according to the detected temperature from the second temperature detecting element 6 at the time of startup and pre-rotation before reloading. Reference is made to the detected temperatures from the temperature detecting elements 5 and 6 so that the target temperature for controlling the first heater 3 always maintains a constant temperature difference from the detected temperature from the second temperature detecting element 6. Meanwhile, each heater power supply 7,
8 has a control function as a control means for performing on / off lighting control of each of the heaters 3 and 4 (see claim 7).
Here, “before reloading” means before printing is possible.

Second, the heater control unit 9 continuously heats the unfixed toner image as an unfixed image formed on the transfer paper P (recording material) over a plurality of transfer papers P during reloading. The detection from the first temperature detecting element 5 when fixing and / or when the fixing processing speed for thermally fixing the unfixed toner image formed on the transfer paper P (recording material) is relatively high. The target temperature for controlling the second heater 4 that is set in advance to be lower than the detected temperature in accordance with the temperature is:
Each of the heater power supplies 7 and 8 is referred to by referring to the detected temperature from each of the temperature detecting elements 5 and 6 so as to always maintain a constant temperature difference with respect to the detected temperature from the first temperature detecting element 5. It has a control function as control means for performing on / off lighting control of the heaters 3 and 4 (see claim 3).

Here, "when an unfixed toner image as an unfixed image formed on the transfer paper P (recording material) is continuously heat-fixed over a plurality of transfer papers P" means continuous. This has the same meaning as when the printing operation is continued or when the continuous copying operation is continued. More specifically, it refers to a time when a continuous copying operation or printing operation for one minute or more is performed as a guide (see FIGS. 6 and 7).

The phrase "when the fixing processing speed when the unfixed toner image formed on the transfer paper P (recording material) is thermally fixed is relatively high" means that the printing operation is relatively high. This is equivalent to the case where the copying operation or the like is performed at a relatively high speed, and is achieved with a relatively high-speed image forming apparatus. Although this depends on the size of the transfer paper P (recording material) to be used, a tentative standard at the current technical level is that the transfer paper P (recording material) of size A4 (horizontal) as described above is used. In the example, this is achieved by a high-speed model having a processing capacity of 50 PPM or more in the number of prints.

In the ROM in the heater control section 9, program data for executing a series of operation programs related to a fixing operation described later are stored in advance, and the following data obtained and set in advance through experiments and the like are described below. Relationship data is stored in advance. That is, the target temperature for controlling the first heater 3 in accordance with the temperature detected from the second temperature detecting element 6 at the time of rising before reloading (hereinafter referred to as “at the time of starting”) and at the time of pre-rotation. And the relational data in which the target temperature is set to be the same as or higher than the detection temperature from the second temperature detection element 6, wherein the target temperature is The relation data set so as to always have a constant temperature difference with respect to the detected temperature is stored in advance.

In the ROM, at the time of reloading, a target temperature for controlling the second heater 4 in accordance with the temperature detected from the first temperature detecting element 5 is set, and the target temperature is set to the first temperature detection value. Relationship data set lower than the temperature detected from the element 5, wherein the target temperature is set in advance so as to always have a constant temperature difference with respect to the temperature detected from the first temperature detection element 5. It is remembered.

The RAM in the heater control section 9 stores the C
Input / output of these signals is performed by temporarily storing the calculation results in the PU, or by storing output signals relating to the detected temperatures from the temperature detecting elements 5 and 6 as needed. The timer in the heater control unit 9 has a function of measuring the elapsed time shown in FIGS.

The heaters 3 and 4 are controlled by the heater control unit 9 as follows from the start-up before reloading and during the pre-rotation to during the reloading. That is, the first heater 3 is turned on / off by the heater control unit 9 in accordance with the temperature detected from the first temperature detecting element 5.
It is controlled so that it is turned off and the temperature at the center of the fixing roller 1 becomes the target temperature. The second heater 4 is turned on / off by the heater control unit 9 according to the temperature detected by the second temperature detecting element 6 so that the temperature of the end of the fixing roller 1 becomes the target temperature. Is controlled.

The control operation of the fixing device 22 at the time of start-up and pre-rotation before reloading is roughly as follows. That is, when a main switch (not shown) for turning on / off the power supply from the power supply of the main body of the printer 50 is turned on, the power of the first and second heater power supplies 7 and 8 is changed to the first and second heaters 3 and 3. 4, the first and second heaters 3 and 4 are turned on, and the temperature of the fixing roller 1 increases. At this time, the first heater 3 is controlled by the heater control unit 9 so that the temperature detected by the second temperature detecting element 6 becomes the preset target temperature. First heater 3
Is controlled to be always the same or slightly higher than the detected temperature detected by the second temperature detecting element 6. That is, the temperature at the center of the fixing roller 1 is controlled so that the temperature difference is always constant according to the temperature at the end of the fixing roller 1. After the temperature detected by the second temperature detecting element 6 reaches the target temperature, the pressure roller 2
The pre-rotation is performed for a predetermined time to warm the.
Similarly, during the pre-rotation, the target temperature for controlling the first heater 3 is set in accordance with the detected temperature detected by the second temperature detecting element 6, and the target temperature between the central portion and the end portion of the fixing roller 1 is set. On / off lighting control of the first heater 3 and the second heater 4 is performed by the heater control unit 9 so that the temperature difference is always constant.

The control operation of the fixing device 22 at the time of reloading is roughly as follows. That is, the target temperature is
The first heater 3 is turned on / off in accordance with the temperature detected by the first temperature detecting element 5, so that the central portion of the fixing roller 1 has a preset temperature.
The second heater 4 is turned on / off in accordance with the temperature detected by the second temperature detecting element 6, so that the temperature at the end of the fixing roller 1 is changed in accordance with the temperature detected by the first temperature detecting element 5. Be changed. The target temperature for controlling the second heater 4 set in this manner is set so as to always have a constant temperature difference with respect to the first temperature detecting element 5. That is, as the temperature at the center of the fixing roller 1 decreases, the target temperature at the end of the fixing roller 1 is also set to decrease accordingly, and the temperature difference between the center and the end of the fixing roller 1 is set. The first heater 3 and the second heater 4 are controlled to be turned on / off by the heater control unit 9 so that is always constant.

Next, a comparative example (similar to the conventional example) and an example will be described. In the comparative example and the example, both are performed under the following conditions. That is, the printing speed is 70 PPM for printing on transfer paper P of size A4 (horizontal), and the heater power supplies 1200 W for the first and second heaters 3 and 4 together at the time of start-up and pre-rotation. A description will be given of a comparative example and an example in which the time is about 5 minutes and the first and second heaters 3 and 4 collectively supply 750 W during paper passing and printing. The target temperatures at the center of the fixing roller 1 were both set to 185 ° C.

As described above, the fixing device 22 has the heating means for reducing power consumption by setting the power supply to the first and second heaters 3 and 4 to be relatively small. The electric power to the first and second heaters 3 and 4 is supplied to the first and second heater power sources 7 and 4 mainly at the time of startup before reloading in order to heat and heat the fixing roller 1 and the pressure roller 2 of the fixing device 22. 8, a relatively small amount of power is supplied at the time of paper passing and printing after reloading because other units and devices of the printer 50 are driven. (Comparative Example: Same as Conventional Example) FIGS. 5 and 7 show a comparative example. In FIG. 5, the horizontal axis represents the elapsed time (seconds) at the time of startup and pre-rotation before reloading, and the vertical axis represents the fixing roller 1.
(Fixed roller temperature (° C.) in FIGS. 4, 6 and 7) is shown. In FIG. 7, the horizontal axis is immediately after the start of sheet feeding (after the start of printing).
The elapsed time (seconds) is taken as the detected temperature of the fixing roller 1 on the vertical axis. FIG. 5 shows the configuration (hardware) of the fixing device 22 similar to that described in the first embodiment, except for the temperature control specific to the present invention, that is, the same configuration and conditions as those of the comparative example and the example. In the conventional temperature control, the detected temperatures T1, T at the central portion and the end portion of the fixing roller 1 when the operation is performed at the time of start-up and pre-rotation before reloading.
2 (hereinafter simply referred to as “temperature T1” and “temperature T2”). FIG. 7 shows the configuration (hardware) of the fixing device 22 similar to that described in the first embodiment except for the temperature control specific to the present invention, that is, the same configuration and conditions as those of the comparative example and the example. 3 shows transition states of the temperatures T1 and T2 at the central portion and the end portion of the fixing roller 1 when the paper is continuously fed by the conventional temperature control.

In the conventional temperature control at the time of start-up and pre-rotation before reloading, the target temperature at the center of the fixing roller 1 is 185 ° C., and the target temperature at the end is 170 ° C. In this case, when the main switch is turned on, each of the heaters 3 and 4 is turned on at full power and continues to be turned on until the respective temperature reaches the target temperature. Normally, when the temperature at the center of the fixing roller 1 reaches the target temperature, the pre-rotation is performed for a set time to warm the pressure roller 2.

In FIG. 5 of the comparative example, it takes about 120 seconds until the temperature at the center of the fixing roller 1 reaches the target temperature, and after reaching the target temperature, the pre-rotation is performed for about 160 seconds. Reload in 280 seconds. As described above, when the conventional control is started and the pre-rotation is performed, the temperature at the end of the fixing roller 1 with respect to the temperature at the center of the fixing roller 1 is changed.
Since the heat is taken away by a frame (not shown) and a driving gear supporting the fixing roller 1, the temperature does not rise as in the central portion of the fixing roller 1. For this reason, the temperature difference between the center and the end of the fixing roller 1 is large. When pre-rotation is performed in this state, the temperature distribution of the pressure roller 2 is
In the same way, the center is high and the ends are low. Since the fixing roller 1 has heat sources of the first and second heaters 3 and 4 and also performs temperature control, it is possible to make the target temperature difference immediately. However, the pressure roller 2 has no heat source, and No control is performed, and the pressure roller 2 has a large heat capacity because the surface thereof is made of the thick rubber as described above, and it takes time to reach the same temperature difference as that of the fixing roller 1. If the paper is passed immediately after this state, the balance of the amount of heat applied to the transfer paper P is lost, or the pressure roller 2
Due to the thermal expansion of the transfer paper P, the central part becomes larger than the end part, so that the transfer paper P is wrinkled. In the worst case, the toner image on the transfer paper P moves to cause a problem such as image blurring. May occur.

Next, with reference to FIG. 7, a description will be given of a conventional temperature control at the time of paper passing and printing. In the conventional temperature control, a heater control unit (not shown) responds to output signals related to the detected temperatures from the temperature detecting elements 5 and 6 according to the output signals.
On / off lighting control of each of the heaters 3 and 4 is performed so that the center and both ends of the fixing roller 1 have a preset target temperature. In the conventional temperature control at the time of paper passing / printing, the target temperature at the center of the fixing roller 1 is set to 185 ° C. and the target temperature at the end of the fixing roller 1 is set to 1
70 ° C. In this case, in the standby state before paper passing,
The temperatures T1 and T2 at the center and the end of the fixing roller 1 are maintained at the target temperatures. However, when continuous paper feeding is started, in FIG. 7, after a time of about 60 seconds elapses, power supplied to each of the heaters 3 and 4 is not sufficient due to power saving for a high printing speed (70 PPM). The temperature of the fixing roller 1 decreases at both the center (T1) and the end (T2), and the temperature T1 at the center is stabilized at about 160 ° C. At this time, the temperature T2 at the end of the fixing roller 1 is 15
It is 7 ° C. The reason why the temperature drop of the fixing roller 1 becomes remarkable is that the central portion and the end portion of the fixing roller 1 are each controlled to a preset target temperature as described in the related art example. This is because the heaters 3 and 4 are in the fully lit state, so that the control is practically impossible.

At the time of standby and immediately after the start of sheet feeding, the temperature difference (T1-T2) between the center and the end of the fixing roller 1 is 15 ° C.
On the other hand, the temperature difference (T1−T2) is as small as 3 ° C. after continuous paper passing (after about 120 seconds in FIG. 7).

Generally, the nip width formed by the fixing roller and the pressure roller is set at the central portion because both the fixing roller and the pressure roller are supported by bearings (not shown) having both ends supporting beam structures. Both ends are larger. Therefore, the temperatures at both ends of the fixing roller are set low so that the amount of heat applied to the transfer paper is substantially the same at the center and both ends of the transfer paper.

In the case of the comparative example, the temperature T2 at the end of the fixing roller 1 is set to be 15 ° C. lower than the temperature T1 at the center. The transfer paper P supplied to the transfer paper P in this setting
, The amount of heat applied to the center portion and both end portions becomes the same. However, since the temperature difference (T1-T2) between the central portion and both ends of the fixing roller 1 after continuous paper passing is small, the amount of heat applied to the transfer paper P at both ends of the fixing roller 1 is larger. Has become. As a result, the balance of the amount of heat applied to the transfer sheet P is lost, so that the transfer sheet P may be wrinkled, or in a severe case, the toner image on the transfer sheet P may move to cause a problem such as image blurring. There is.

The reason why the temperature difference (T1-T2) between the center and both ends of the fixing roller 1 during continuous paper feeding is reduced is as follows. Generally, when the power of the image forming apparatus is turned on and the temperature of the fixing roller is raised from room temperature, both ends of the fixing roller take heat from bearings, side plates, driving gears, etc., which support the fixing roller. Therefore, the temperature at both ends of the fixing roller rises more slowly than at the center. In order to avoid this, the heat distribution of the second heater at both ends of the fixing roller is set to be higher and higher than at the center.
Therefore, during paper passing, the temperature drop at both ends is smaller than at the center of the fixing roller, and the temperature difference (T1-T2) between the center and both ends is reduced. (Example) An example of the first embodiment will be described with reference to FIGS. The elapsed time (second) and the fixing roller temperature (° C.) similar to those in the comparative example shown in FIGS. 5 and 7 are plotted on the horizontal axis and the vertical axis in FIGS. FIG. 4 shows a temperature control unique to the present invention, and is similar to the fixing device 22 described in the first embodiment.
With the same configuration and conditions as those of the above comparative example and the comparative example described above, the transition state of the temperatures T1 and T2 at the central portion and the end portion of the fixing roller 1 when starting up before reloading and performing the operation at the time of pre-rotation are as follows. It is shown. FIG. 6 shows that the temperature control unique to the present invention is performed, and the paper is continuously passed under the same configuration of the fixing device 22 as described in the first embodiment and under the same configuration and conditions as the above-described example. The transition state of each temperature T1, T2 at the center and the end of the fixing roller 1 in the case is shown.

In this embodiment, the target temperature at the end of the fixing roller 1 is 170 ° C. and the target temperature at the center of the fixing roller 1 is detected at the end at the time of start-up and pre-rotation before reloading. The temperature is set at plus 15 ° C. The operation described in detail below is performed under a command from the heater control unit 9. First, when the main switch of the main body of the printer 50 is turned on to turn on the power, 1200 W of electric power is supplied to the two heaters 3 and 4 in total, and the first and second heaters 3 and 4 are turned on. Lights up
Heat is generated, and the temperature of the fixing roller 1 increases. At this time,
A power-on signal generated by pressing the main switch is transmitted to the CPU of the heater control unit 9. When this signal is used as a trigger, the heater controller 9 causes the printer 50
Is recognized, and the specific control shown in FIG. 4 is performed by the control function described above.

At this time, the temperature at the end of the fixing roller 1 (second temperature)
Until the temperature detected by the temperature detecting element 6 reaches a preset target temperature of 170 ° C., the second heater 4 is turned on and generates heat with full power by the heater control unit 9 as in the comparative example. On the other hand, the temperature at the center of the fixing roller 1 (the temperature detected by the first temperature detecting element 5) is
Accordingly, the first heater 3 is controlled to be turned on / off so that the temperature at the end of the fixing roller 1 (the temperature detected by the second temperature detecting element 6) is always plus 15 ° C. Therefore, the temperature difference between the center and the end of the fixing roller 1 is always constant, and the pre-rotation is performed in that state, so that the temperature difference between the center and the end of the pressure roller 2 is also always constant.

Next, with reference to FIG. 6, a description will be given of the temperature control of the embodiment during paper passing and printing. Here, the target temperature at the center of the fixing roller 1 at the time of paper passing and printing is set at 185 ° C., and the target temperature at the end of the fixing roller 1 is set at −10 ° C. with respect to the detected temperature detected at the center. I have.

In parallel with the execution of the temperature control of FIG. 4, necessary operations and the like, and the temperature control of FIG. 6 are performed following the temperature control of FIG. That is, the number of prints is set and input using a ten-key pad (not shown) provided on an operation panel (not shown), and before and after this, a print speed setting key (not shown) provided on the operation panel is used. When the print speed (70 PPM) is set and entered, and the print key provided on the operation panel is pressed,
The printing operation through the transfer paper P is started. At this time, a print speed setting signal generated by pressing a print speed setting key or the like, a print start signal generated by pressing the print key, and the like are transmitted to the CPU of the heater control unit 9. With these signals as triggers, the heater control unit 9 recognizes that a high-speed and continuous printing operation is performed, and performs the specific control shown in FIG. 6 by the above-described control function.

Here, a total of 750 W of electric power is supplied to each of the two heaters 3 and 4, and each of the heaters 3 and 4 is turned on and generates heat, and each of the temperature detecting elements 5 and 6 is set to a predetermined target. The supply of the electric power is continued until the temperature is detected.

As can be easily understood from FIG. 6, as in the comparative example in the conventional temperature control configuration, the high printing speed (7
0PPM), the power supplied to each of the heaters 3 and 4 is insufficient due to power saving, so that the temperature of the fixing roller 1 drops at both the center (T1) and the end (T2). Since the target temperature at the end of 1 is always set to minus 10 ° C. with respect to the center, the heaters 3 and 4 do not become uncontrollable in the full lighting state, and the temperature T1 in the center decreases. Therefore, the temperature T2 at the end also decreases while maintaining -10 ° C. Therefore, the difference between the center and both ends of the amount of heat applied to the transfer paper P is always constant, and does not change even during continuous paper passing, and the balance of the amount of heat applied to the transfer paper P is not lost. It is possible to prevent the transfer paper P from being wrinkled in the middle of passing the paper, and to prevent the occurrence of a defect on the image such as image blur.

The same effect as described above can be obtained not only in a high-speed and continuous printing operation but also in a printing / fixing operation in which only one of the operations is performed (see claim 3). Further, under the condition that the high-speed and / or continuous printing operation is not performed, there is no wrinkle on the transfer paper P or any trouble on the image such as image blur, so that the same control operation as in the comparative example is performed. Can be configured to be switchable. However, it has been confirmed that the same operation as in the comparative example does not cause a problem even if the operation of the above-described embodiment is performed under the condition that the high-speed and / or continuous printing operation is not performed. It is desirable to perform only the temperature control operation of the above embodiment. (Second Embodiment) With reference to FIG. 9, the operation will be described together with an outline of the overall configuration of a color duplex copying machine 500 as an example of a duplex image forming apparatus according to a second embodiment. The color double-sided copying machine 500 heat-fixes an unfixed image formed on one side of the transfer paper after forming an image on one side of the transfer paper as a recording material (single-sided image formation mode). After the transfer paper is turned over, an image is formed on the other surface of the transfer paper, and then a fixing device 52 for thermally fixing the unfixed image formed on the other surface of the transfer paper (double-sided image forming mode) (see FIG. 1 is shown with parentheses). The color double-sided copying machine 500 is a double-sided image forming apparatus capable of performing a so-called double-sided image forming mode in addition to the single-sided image forming mode as in the printer 50 of the first embodiment. The color double-sided copying machine 500 has a processing capability of 50 PPM or more (for example, a maximum speed of 70 PPM) in a single-color copying operation using transfer paper P (or paper P) as a recording material of size A4 (horizontal).
PPM).

The color duplex copying machine 500 includes a color scanner 200 and a writing optical unit 40 as exposure means.
0, photoconductor drum 402 as an image carrier, photoconductor cleaning unit 414, static elimination lamp 416, potential sensor 420, rotary developing device 422, development density pattern detector 424, intermediate transfer belt 426, fixing device 52, and paper feed It has a bank 456 and the like.

The writing optical unit 400 converts the color image data from the color scanner 200 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 402. The writing optical unit 400 includes a laser diode 404, a polygon mirror 406, a rotation motor 408, and an f / θ lens 410.
And a reflection mirror 412 and the like. The photoconductor drum 402 is rotated counterclockwise as indicated by an arrow, and around the photoconductor cleaning unit 41.
4, a developing device (a developing device 438 in FIG. 9) selected from the static elimination lamp 416, the potential sensor 420, and the rotary developing device 422, a developing density pattern detector 424, an intermediate transfer belt 426, and the like.

The rotary developing device 422 includes a developing device 428 for black, a developing device 430 for cyan, and a developing device 4 for magenta.
32, a yellow developing unit 434, and a rotation drive unit (not shown) for rotating each developing unit. Each developing device includes a developing sleeve that rotates by contacting the ears of the developer with the surface of the photosensitive drum 402 in order to visualize the electrostatic latent image,
It has a developing paddle and the like that rotate to pump up and agitate the developer.

In the standby state, the rotary developing device 422
When set at the position of black development and the copy operation is started, reading of black image data starts at a predetermined timing by the color scanner 200,
Based on this image data, optical writing with laser light
Formation of an electrostatic latent image (black latent image) starts.

In order to develop from the leading end of the black latent image, before the leading end of the latent image reaches the developing position of the black developing device 428, the developing sleeve is started to rotate and the black latent image is developed with black toner. I do. Thereafter, the developing operation of the black latent image area is continued, but when the rear end of the latent image passes the black developing position, the rotary developing operation is immediately performed from the black developing position to the next color developing position. The device 422 rotates. This operation is completed at least before the leading end of the latent image based on the next image data arrives.

When the image forming cycle is started, first, the photosensitive drum 402 is rotated in a counterclockwise direction as indicated by an arrow, and the intermediate transfer belt 426 is rotated in a clockwise direction by a drive motor (not shown). . Intermediate transfer belt 4
With the rotation of 26, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed, and finally black (Bk), cyan (C), magenta (M), and yellow ( The toner images are formed on the intermediate transfer belt 426 in the order of Y).

The intermediate transfer belt 426 is
4, the transfer opposing rollers 446a and 446b, the cleaning opposing roller 448, and the driven roller group are stretched, and are driven and controlled by a drive motor (not shown). The black, cyan, magenta, and yellow toner images sequentially formed on the photosensitive drum 402 are accurately and sequentially aligned on the intermediate transfer belt 426, thereby forming a four-color superimposed belt transfer image. This belt transfer image is collectively transferred to a recording material (transfer paper) by a transfer corona discharger 454.

Each recording paper cassette 4 in the paper supply bank 456
58, 460, and 462 include cassettes 464 in the apparatus main body.
The transfer papers of various sizes different from the size of the transfer paper stored in the paper cassette are stored. Among the transfer papers, the specified transfer paper is transferred from the storage cassette of the specified size paper to the registration roller by the paper feed roller 466. Paper feed in 470 direction
It is reversed and transported. In FIG. 9, reference numeral 468 denotes a manual paper feed tray for OHP transfer paper, thick paper, and the like.

At the time when the image formation is started, the transfer paper is fed from the paper feed port of any one of the above-mentioned cassettes and waits at the nip portion of the pair of registration rollers 470. When the leading end of the toner image on the intermediate transfer belt 426 approaches the corona discharger 454, the registration roller pair 470 is driven such that the leading end of the transfer paper coincides with the leading end of the image, and the registration of the transfer paper and the image is performed. Is performed.

In this way, the transfer paper is superposed on the intermediate transfer belt 426 and passes over the corona discharger 454 connected to the positive potential. At this time, the transfer paper is charged with a positive charge by the corona discharge current, and the toner image is transferred to the transfer paper. Subsequently, the transfer paper is neutralized when passing through a portion of an unillustrated neutralization brush arranged on the left side of the corona discharger 454 in the drawing, is separated from the intermediate transfer belt 426, and moves to the paper transport belt 472.

The transfer paper on which the four-color superimposed toner image is collectively transferred from the intermediate transfer belt 426 is conveyed by a paper conveyance belt 472 to a fixing device 52 of an internal heating system, and the fixing device 52 forms the toner image by heat and pressure. Be established. The transfer paper having completed the fixing passes over a path switching member 482 indicated by a solid line provided in the transfer paper discharge path between the fixing device 52 and the discharge roller pair 480, and is driven outside by the forward rotation of the discharge roller pair 480. And stacked on a tray (not shown).
Thereby, a full-color copy is obtained.

In the case of a single-color copy, only the developing unit of that color is set in the developing operation state until the predetermined number of copies is completed, and the intermediate transfer belt 426 moves forward while being in contact with the surface of the photosensitive drum 402. The copy operation is performed while driving at a constant speed in the direction. In the case of double-sided copying, the copying is performed as follows. First, as described above, one of the single-color to four-color images is formed on one surface (front surface) of the transfer paper, and the unfixed images are heat-fixed sequentially by the fixing device 52. The transfer paper having the fixed image formed on one surface thereof is configured such that when a portion near the rear end of the transfer paper passes through the discharge roller pair 480, the discharge roller pair 480 is temporarily stopped, and then the discharge roller pair 480 is immediately rotated in reverse. This time, the transfer paper is again introduced into the apparatus main body by a so-called switchback method in which the rear end side of the transfer paper is used as a front end.

At this time, the passage switching member 482 is driven by a driving means such as a solenoid (not shown) to form the pair of introduction rollers 484.
During this time, the transfer paper is displaced to a position for guiding the transfer paper. This allows
A transfer sheet Pa indicated by a two-dot chain line in which a fixed image is formed on one surface is fed to a transfer path 486 in which a transfer sheet transfer member such as a plurality of transfer rollers is arranged, and one side of the transfer sheet Pa Is turned upward and loaded in the cassette 464.
Will be accommodated. Cassettes 464 for a predetermined number of transfer papers Pa
When the transfer paper Pa is finished, the transfer paper with one surface facing upward is formed on the other surface (back surface) of the transfer paper Pa in order to perform any one of the monochromatic or four-color image formation. Is fed / reversed and conveyed in the direction of the registration roller pair 470 by the paper feed roller 466, and the other surface on which no image is formed faces upward, and one of monochromatic or four-color image formation is formed on the other surface. Image formation, and then
The toner image is fixed again by the fixing device 52 by heat and pressure. The transfer paper on which images have been formed on both sides after fixing is passed again on the path switching member 482 displaced to the position shown by the solid line, is discharged out of the machine by the forward rotation of the discharge roller pair 480, and is discharged to a tray (not shown). Stacked. This allows
A double-sided copy is obtained in which one of the single-color to four-color images is formed on both sides.

Referring to FIG. 1, the configuration and operation of the fixing device 52 will be described. The fixing device 52 shown in parentheses in FIG. 1 is different from the fixing device 22 shown in FIG.
A heater control unit 59 shown in parentheses in FIG. 1 is provided instead of the heater control unit 9, and the second heater 4 at the time of fixing the unfixed toner image on the other surface of the transfer paper (recording material) The main difference is that the target temperature is set lower than the target temperature of the second heater 4 when the unfixed toner image on one surface of the transfer paper (recording material) is fixed.

The heater control section 59 has a microcomputer having the same configuration as that of the heater control section 9. The heater control unit 59 is obtained by adding the following control function to the above-described control function of the heater control unit 9. The added control function is that the temperature (target temperature) of the second heater 4 at the time of fixing the unfixed toner image on the other surface of the transfer paper (recording material) is set to one of the transfer paper (recording material). The heaters 3 and 4 are turned on while referring to the detection temperatures from the temperature detection elements 5 and 6 so as to be lower than the temperature (target temperature) of the second heater 4 at the time of fixing the unfixed toner image on the surface. This is a control function as a control means for controlling on / off lighting. The heater control unit 59 may be incorporated in a controller of the color duplex copying machine 500, for example. The ROM (not shown) of the heater control unit 59 is different from the ROM of the heater control unit 9 in that
The temperature (target temperature) of the second heater 4 when fixing the unfixed toner image on the other surface on the transfer paper (recording material) is determined by fixing the unfixed toner image on one surface on the transfer paper (recording material). In this case, related data for lowering the temperature (target temperature) of the second heater 4 at the time is added.

In the fixing device 52 of the color double-sided copying machine 500, when an unfixed toner image is fixed on one surface (front surface) of the transfer paper P, the fixing is performed based on the above-described embodiment shown in FIGS. When the unfixed toner image is fixed on the other surface (back surface) of the transfer paper Pa, the target temperature of the end portion of the fixing roller 1 is further reduced by -10 ° C. compared to the above embodiment. (-20 ° C. with respect to the center of the fixing roller 1).

The trigger for starting the fixing operation of the unfixed toner image on the other surface on the transfer paper Pa is as follows. That is, first, the number of prints is set and input using a ten-key pad (not shown) provided on an operation panel (not shown), and before and after this, a print speed setting key (not shown) provided on the operation panel is pressed. The user sets and inputs a print speed (for example, 70 PPM), and presses a double-sided print key (not shown) provided on the operation panel to set a single-sided and double-sided image forming mode.
When a print key provided on the operation panel is pressed, a single-sided image forming mode is performed in which an image is formed on one side of the transfer paper P after passing the set number of transfer papers P. The printing operation based on the above and the fixing operation of the unfixed toner image on one surface of the transfer paper P are started and executed as described above.

Next, the CPU of the heater control unit 59
However, the number of prints is detected and counted by a double-sided print setting signal from the double-sided print key, a print number setting signal, and a jam detection sensor (not shown) disposed downstream of each paper feed roller 466 in the paper feed bank 456. A print operation based on the duplex image forming mode for forming an image on the other surface of the transfer paper Pa based on the output signal obtained from the printer, and a fixing operation of an unfixed toner image on the other surface of the transfer paper Pa. Recognize and perform the following specific control by the control function described above.

When printing on the other side of the transfer sheet during the formation of a two-sided image, the temperature of the transfer sheet is high. When the fixing operation is performed, the amount of heat applied to the transfer paper is excessive, and the curl of the transfer paper increases. In the related art, the target temperature of the fixing roller is reduced as a whole only when the unfixed toner image is fixed on the other surface of the transfer paper. However, since the temperature at the end of the fixing roller greatly contributes to the curl of the transfer sheet, it is effective to lower only the temperature at the end of the fixing roller. Therefore, curling can be reduced without deteriorating the fixability of the central portion of the fixing roller by lowering only the end portion without lowering the target temperature of the central portion of the fixing roller.

In the first and second embodiments, specific control contents of the present invention at the time of start-up and pre-rotation before reloading, that is, the target temperature for controlling the first heater 3 (the fixing roller 1 and the pressure roller 2 (The target temperature at the center of the fixing roller 1 and the temperature at both ends of the fixing roller 1 and the pressure roller 2) from the second temperature detecting element 6 has been described, but the present invention is not limited to this. The target temperature for controlling the first heater 3 (the target temperature at the center of the fixing roller 1 and the pressure roller 2) is detected by the second temperature detecting element 6 (at both ends of the fixing roller 1 and the pressure roller 2). ), That is, the case where the certain temperature difference is zero and equal, and such a setting state is also included (refer to means for solving the problem).

As described above, the present invention has been described with respect to the specific embodiments including the examples. However, the technical scope of the present invention is limited to those exemplified in each of the above embodiments and examples. However, those skilled in the art will appreciate that various embodiments and examples can be configured in accordance with the necessity and use thereof within the scope of the present invention. it is obvious. That is, although the present invention relates to the so-called central paper passing standard, it is to be noted that the present invention is not limited to this and can be immediately applied to the so-called one-side paper passing standard by analogy with the above technical matters.

[0081]

As described above, according to the present invention,
A new fixing device, an image forming apparatus, and a double-sided image forming apparatus can be provided by solving the problems of the related art. The effects of each claim are as follows. According to the first and second aspects of the present invention, the target temperature for controlling the second heating means is set according to the temperature detected by the first temperature detection means, and the target temperature at the end of the fixing roller is set. Is set lower than the detected temperature at the center of the fixing roller, and the target temperature at the end of the fixing roller is always set to a constant temperature difference from the detected temperature at the center of the fixing roller. However, since the amount of heat applied to the center and both ends of the recording material is always constant, the balance of the amount of heat does not change between the center and both ends of the recording material, and the amount of heat on the image such as wrinkles of the recording material and image blurring Can be prevented from occurring.

According to the third aspect of the present invention, the control means is configured to continuously heat-fix the unfixed image formed on the recording material over a plurality of recording materials and / or to form the unfixed image on the recording material. When the fixing processing speed when thermally fixing the unfixed image is relatively high, the temperature difference between the detected temperature at the center of the fixing roller and the target temperature at the end of the fixing roller is maintained constant. , By controlling the first and second heating means, when fixing during continuous image formation,
And / or images such as wrinkles and image blurring of a recording material, which are particularly prone to occur due to a large temperature drop at the center and both ends of the fixing roller during fixing at the time of relatively high-speed image formation. The above problems can be prevented from occurring.

According to the present invention, during the pre-rotation before reloading, the target temperature for controlling the first heating means is set in accordance with the temperature detected by the second temperature detection means. The target temperature at the center of the fixing roller is set to be equal to or higher than the temperature at the end of the fixing roller, and the target temperature at the center of the fixing roller is set to the detected temperature at the end of the fixing roller. The temperature difference between the center of the pressing member (for example, the pressing roller) and the end of the pressing member (for example, the pressing roller) is always constant by setting the temperature difference to always be constant. The amount of heat applied to the center and both ends of the recording material is always constant, and the balance of the heat does not change between the center and both ends of the recording material, and the paper passing or fixing operation is performed immediately after the pre-rotation before reloading. Wrinkles of recording material, image blur, etc. Generation of a defect on the image can be prevented.

According to the present invention, during the pre-rotation before reloading, the control means keeps the temperature difference between the target temperature at the center of the fixing roller and the detected temperature at the end of the fixing roller constant. As described above, by controlling the first and second heating means, when the paper passing or fixing operation is performed immediately after the pre-rotation before the reload, the pressing member (for example, the pressing roller)
It is possible to prevent wrinkles of the recording material, which are particularly easily caused by a temperature difference between the both ends with respect to the temperature at the center portion thereof being too large with respect to the temperature at the center portion, and the occurrence of image defects such as image blurring. it can.

According to the present invention, the nip width formed by the pressure contact between the fixing roller and the pressing member is set to be larger at the end of the fixing roller than at the center thereof. The effects of each of the above-described inventions can be obtained with a simple fixing device configuration employing a both-ends support structure in a conventional normal fixing roller.

According to the ninth aspect of the present invention, the power supply to the first and second heating means is set to be relatively small. The effects of the above inventions are exhibited.

According to the tenth aspect of the present invention, in the fixing device configuration of the conventional fixing roller, the heat generation temperature of the second heating means is set higher than the heat generation temperature of the first heating means. The effects of the above inventions are exhibited.

According to the eleventh aspect of the present invention, there is provided a fixing device for thermally fixing an unfixed image formed on one surface of a recording material after forming an image on one surface of the recording material. In the image forming apparatus, the effects of the above inventions are exhibited.

According to the twelfth aspect of the present invention, in the double-sided image forming apparatus, the target temperature of the end of the fixing roller at the time of fixing the unfixed image on the other surface of the recording material is set to one of the temperatures on the recording material. By setting the target temperature at the end of the fixing roller at the time of fixing the unfixed image on the surface of the recording material, the target temperature at the end of the fixing roller is set only when fixing the unfixed image on the other surface of the recording material. To lower further to the center,
The curl of the recording material during double-sided image formation can be suppressed to a small extent without deteriorating the fixability at the center of the fixing roller.

[Brief description of the drawings]

FIG. 1 is a control block diagram including a main configuration of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a heat generation distribution of a first heater.

FIG. 3 is a graph showing a heat generation distribution of a second heater.

FIG. 4 is a diagram illustrating an example of the present invention, and is a diagram illustrating transitions in detected temperatures at the center and the end of the fixing roller at the time of startup before reloading and during pre-rotation.

FIG. 5 is a diagram showing a conventional example as a comparative example, and is a diagram showing transitions in detected temperatures at the center and the end of the fixing roller at the time of startup before reloading and at the time of pre-rotation.

FIG. 6 is a diagram illustrating an example of the present invention, and is a diagram illustrating a transition of a detected temperature at a center portion and an end portion of the fixing roller after the start of sheet feeding.

FIG. 7 is a diagram illustrating a conventional example as a comparative example, and is a diagram illustrating a transition of the detected temperature at the center and the end of the fixing roller after the start of sheet feeding.

FIG. 8 is a front view illustrating a configuration of a main part of a printer having the fixing device of FIG. 1;

FIG. 9 is a front view showing a configuration of a main part of a color duplex image forming apparatus having a fixing device according to a second embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 fixing roller 2 pressure roller as pressure member 3 first heater as first heating means 4 second heater as second heating means 5 first temperature detection element as first temperature detection means 6 2, a second temperature detecting element as a temperature detecting means 9, 59, a heater control section 22, 52 as a control means, a fixing device 50, a printer as an example of an image forming apparatus 500, a color duplex copying machine NB as an example of a duplex image forming apparatus Nip width P Transfer paper as recording material

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 3/00 335 H05B 3/00 335 F term (Reference) 2H028 BB04 2H033 AA03 AA15 BA25 BA27 BA32 BB18 BB33 CA07 CA13 CA28 CA30 CA48 3K058 AA02 AA72 AA73 AA86 BA18 CA23 CA61 CE23 DA02

Claims (12)

[Claims] A first heating means having a heat generation distribution at a center height; a second heating means having a heat generation distribution at both ends; a fixing roller heated by the first and second heating means; A first temperature detecting means for detecting a temperature substantially at the center of the fixing roller, a second temperature detecting means for detecting a temperature of the fixing roller at a position distant from the first temperature detecting means, and a first and a second temperature detecting means. According to the output signal from the temperature detecting means, the first and second
A control unit for controlling the heating units independently of each other, wherein a target temperature for controlling the second heating unit is set in accordance with a temperature detected by the first temperature detection unit; A fixing device wherein a target temperature is set lower than the detection temperature. 2. The fixing device according to claim 1, wherein the target temperature is set so as to always have a constant temperature difference from the detected temperature. 3. The fixing device according to claim 2, wherein the control unit is configured to thermally fix an unfixed image formed on the recording material continuously over a plurality of recording materials and / or to fix the unfixed image on the recording material. The first and second heating means are controlled so as to maintain the above-mentioned constant temperature difference when the fixing processing speed when thermally fixing the unfixed image formed in the above is relatively high. Fixing device. 4. A first heating means having a heat generation distribution having a central height, a second heating means having a heat generation distribution having a height at both ends, a fixing roller heated by the first and second heating means, and the fixing roller. A first temperature detecting means for detecting a temperature substantially at the center of the fixing roller, a second temperature detecting means for detecting a temperature of the fixing roller at a position distant from the first temperature detecting means, and a first and a second temperature detecting means. According to the output signal from the temperature detecting means, the first and second
Control means for controlling the respective heating means independently of each other, and each target temperature for controlling the first and second heating means is set in accordance with the detected temperature from the first or second temperature detecting means. In the fixing device, during pre-rotation before reloading, a target temperature for controlling the first heating unit is set according to the temperature detected by the second temperature detection unit. 5. The fixing device according to claim 4, wherein the target temperature is set to be equal to or higher than the detected temperature. 6. The fixing device according to claim 4, wherein the target temperature is set so as to always have a constant temperature difference from the detected temperature. 7. A fixing device according to claim 6, wherein said control means controls said first and second heating means so as to maintain said constant temperature difference during pre-rotation before said reloading. A fixing device characterized by the above-mentioned. 8. The fixing device according to claim 1, further comprising a pressure member that presses against the fixing roller to form a nip width, wherein the nip width is equal to or smaller than the fixing roller. A fixing device characterized in that its end is set to be larger than its center. 9. The fixing device according to claim 1, wherein the power supply to the first and second heating units is set to be relatively small. . 10. The fixing device according to claim 1, wherein a heat generation temperature of the second heating means is set higher than a heat generation temperature of the first heating means. Fixing device. 11. An image forming apparatus having a fixing device for thermally fixing an unfixed image formed on one surface of a recording material after forming an image on one surface of the recording material. An image forming apparatus according to any one of claims 1 to 10. 12. After forming an image on one surface of the recording material, an unfixed image formed on one surface of the recording material is heat-fixed, and then the recording material is turned over. A double-sided image forming apparatus having a fixing device for thermally fixing an unfixed image formed on the other surface of the recording material after forming an image on the other surface on the upper side, wherein the fixing device comprises: 10. The target temperature at the time of fixing an unfixed image on the other side of the recording material when fixing the unfixed image on the other side of the recording material. A two-sided image forming apparatus, wherein the temperature is set lower than the temperature.