Patent Application
20110142468
This application is based on Japanese Patent Application No. 2009-281314 filed on Dec. 11, 2009, in Japanese Patent Office, the entire content of which is hereby incorporated by reference.
The present invention relates to image forming apparatuses which forms a toner image by the electrographic method, fixing device for fixing a toner image, and image forming systems provided with the image forming apparatus and the fixing device.
In the image forming apparatus using the electrographic method, a toner image is formed on an image carrier of a rotating photoreceptor drum or a photoreceptor belt, the formed toner image is transferred onto a recording sheet directly or indirectly, and the toner image is fixed to form an image.
In the above-mentioned image forming method, the toner image electrostatically transferred onto the recording sheet is stably fixed on the recording sheet by heat and pressure of a fixing roller. The fixing roller surface may be scratched or grooved by the edge of a recording sheet often touching the same part of the fixing roller surface. This situation will cause the problem that the service life of the fixing roller becomes short.
In order to prevent such scratching and grooving, there are measures of shifting the fixing roller in an axial direction. By this shift of the fixing roller, the position at which the edge of a recording sheet touches the fixing roller is varied, and scratches and grooves will be reduced. Whereby, the problem that the service life of the fixing roller is shortened will be resolved.
When the fixing roller is shifted in such a way, the temperature gradient gets large and the temperature distribution on the fixing roller gets uneven due to individual variations of parts and depending on the accuracy variation of assembly, thereby causing insufficient fixing and insufficient gloss of image, resulting in insufficient image quality.
An image forming apparatus employing such a reciprocal shift is proposed following Japanese Laid-Open Patent Application Publication No. 2006-133581 and the like.
In Japanese Laid-Open Patent Application Publication No. 2006-133581, it is determined based on information of temperature whether the location of the recording sheet is appropriate. Thus, the temperature is not actively controlled for the fixing device. Therefore, when the aforementioned situation such as insufficient fixing, insufficient gloss of image, and uneven gloss has occurred, it cannot be surely prevented.
In recent years, there is an image forming apparatus using two fixing devices, a first fixing device and a second fixing device, in order to realize sufficient fixing. In such an image forming apparatus as well, the reduction of the service life due to scratching and grooving on the fixing roller surface is a problem. However, even if the two fixing devices are simply shifted, the imaging quality may be reduced due to a temperature gradient.
In view of forgoing, one embodiment according to one aspect of the present invention is an image forming apparatus, comprising:
an image forming section configured to form an toner image depending on image data and transfer the toner image onto a recording sheet;
a first fixing roller configured to fix the toner image on the recording sheet by heat;
a first temperature sensor configured to detect temperatures of the first fixing roller at a plurality of positions in a longitudinal direction of the first fixing roller;
a second fixing roller configured to fix the toner image on the recording sheet by heat;
a second temperature sensor configured to detect temperatures of the second fixing roller at a plurality of positions in a longitudinal direction of the second fixing roller,
a rocking section configured to reciprocally shift at least one of the first fixing roller and the second fixing roller in a longitudinal direction of the at least one of the rollers; and
a controller configured to obtain a first temperature gradient of the first fixing roller and a second temperature gradient of the second fixing roller based on the temperatures detected by the first temperature sensor and the second temperature sensor, set a central position of the reciprocal shift of the at least one of the rollers at a predetermined position so that the first temperature gradient and the second temperature gradient cancel each other, and then control the rocking section to reciprocally shift the at least one of the rollers.
According to another aspect of the present invention, another embodiment is a fixing device which is installed in an imager forming apparatus configured to form a toner image depending on image data and transfer the toner image onto a recording sheet, the fixing device comprising:
a first fixing roller configured to fix the toner image on the recording sheet by heat;
a first temperature sensor configured to detect temperatures of the first fixing roller at a plurality of positions in a longitudinal direction of the first fixing roller,
a second fixing roller configured to fix the toner image fixed by the first fixing roller, on the recording sheet by heat;
a second temperature sensor configured to detect temperatures of the second fixing roller at a plurality of positions in a longitudinal direction of the second fixing roller; and
a rocking section configured to reciprocally shift at least one of the first fixing roller and the second fixing roller in a longitudinal direction of the at least one of the rollers,
wherein a first temperature gradient of the first fixing roller and a second temperature gradient of the second fixing roller are obtained based on the temperatures detected by the first temperature sensor and the second temperature sensor, a central position of the reciprocal shift of the at least one of the rollers is set at a predetermined position so that the first temperature gradient and the second temperature gradient cancel each other, and the rocking section then reciprocally shifts the at least one of the rollers.
According to another aspect of the present invention, another embodiment is an image forming system, comprising:
an image forming device configured to form an toner image depending on image data and transfer the toner image onto a recording sheet; and
a fixing device, the fixing device including:
a, 6b, and 6c are diagrams showing a state of the fixing device of the embodiment according to the present invention;
a, 7b, and 7c are diagrams showing a state of the fixing device of the embodiment according to the present invention;
With reference to the drawings, an embodiment according to the present invention will be described in detail below.
<Configuration of an Image Forming Apparatus 100>
Here, a configuration of the image forming apparatus 100, using the electrographic method, of the first embodiment is described in detail based on
The image forming apparatus 100 shown in
The controller 101 is provided with a CPU (Central Processing Unit), a ROM Read Only Memory), a RAM (Random Access Memory), and the like which are not illustrated. The CPU collectively controls respective portions of the image forming apparatus 100 by executing various programs stored in the ROM, using a predetermined area of the RAM as a working area The Controller 101 performs a shift-fixing control shown in the flowchart, as will be described later.
Here, operation/display section 105 is provided with input devices such as a keyboard, a mouse, and a touch panel, and transmits inputted various instruction signals to the controller 101. The operation/display section 105 is provided with a display device such as an LCD (Liquid Crystal Display) and a CRT (Cathode Ray Tube), and displays the various image data fed from the controller 101. The operation/display section may have an operation section and another indicator separately. However, in the following description the operation/display section 105 is described as a touch panel type, since a touch panel, through which icons and keys (hereinafter, both referred to as a key) are displayed to be pushed down, is widely used.
The storing section 110 is a storage device, such as a HDD (Hard Disc Drive) and a flash memory which are capable of writing, reading, and erasing data, and it can be fixedly provided or detachably provided. The storing section 110 stores job data (including processed job, job under processing, and job to be processed) including registered one or more jobs. The storing section 110 stores the date of replacement of respective parts, and information related to respective parts, for ease of adjustment when replacing parts.
The print engine 140 is an image forming section using the electrographic method or other methods, and is for forming and outputting an image on a predetermined sheet in photocopy machines and fax machines. The print engine 140 has a configuration shown in
A finisher 150 is a post-processing device for performing various post-processings such as stapling, punching, bending, binding, bookbinding, and stacking, on the sheets with images formed thereon.
In the example shown in
<Configuration of the Print Engine 140>
A configuration of the print engine 140 will be described below in detail with reference to
Although a configuration only for one color is shown in
The print control section 141 collectively controls the print engine 140 and the image forming apparatus 100 by controlling respective sections constituting the print engine 140 so as to perform various adjustments and controls, according to control programs of the controller 101 and the image forming apparatus.
The sheet feeding section 1450 is a feeding section which sends out a single or plural recording sheets stored in the sheet tray 1450T to an image formation position, with a feed roller. The sheet conveyance section 1460 is a sheet feeding means which conveys the recording sheet sent out from the sheet feeding section 1450 at a predetermined conveyance speed, and the it is provided with a registration roller, various kinds of conveying, a conveyance belt. In addition, on places of the conveyance section, there are provided in place conveyance sensors 1460s such as an edge sensor for sensing the leading edge of a recording sheet. A bypass route 1460B going around the second fixing device 1480B (to be described later) is provided near the second fixing device 1480B, as a detour conveyance route.
The image forming section 1470 is provided with charging sections 1471 (1471Y, 1471M, 1471C, 1471K) for charging photoreceptor drums at a predetermined voltage; exposure sections 1472 (1472Y, 1472M, 1472C, 1472K) for forming electrostatic images on the photo receptors by performing exposure on the charged photoreceptors, in correspondence to image data; photoreceptor drums as image carriers on which the electrostatic images formed by the aforementioned charging and exposure are turned into toner images; developing sections 1474 (1474Y, 1474M, 1474C, 1474K) for attaching toner to the electrostatic images formed on the photoreceptors 1471 (1471Y, 1471M, 1471C, 1471K) to develop them to be toner images; and a transfer section 1475 for electrostatically transferring the toner images formed on the photoreceptors 1473 onto a recording sheet.
Regarding the charging sections 1471, the exposure sections 1472, photoreceptors 1473, they may be independent with respect to each color of YMCK used for image forming as shown in
The transfer section 1475 may be provided with an intermediate transfer member 1475A which superposes the toner images of respective colors of YMCK, and a secondary transfer section 1475B which transfers the superposed toner images onto a recording sheet.
The toner image transferred on the recording sheet is fixed stably thereon by two fixing devices, a first fixing device 1480A and a second fixing device 1480B. In addition, at least one of the two fixing devices can be reciprocally shifted in the direction of an shaft of a fixing roller by a rocking section 1485A or a rocking section 1485B, as described later.
<Configuration of the Fixing Device 1480 (the First Fixing Device 1480A and the Second Fixing Device 1480B)>
In the following description, the first fixing device 1480A and the second fixing device 1480B are assumed to have the same configuration, and they are called a fixing device as a whole.
The fixing roller 1481 is heated by a fixing heater, and is rotated by a fixing drive motor (not shown in the figure). The temperature of the first fixing roller is measured by a plurality of temperature sensors including an L (left) temperature sensor 1480SL, a C (center) temperature sensor 1480SC, and an R (right) temperature sensor 1480SR to obtain a gradient of temperature distribution, and the measurement result is communicated to a print control section 141 and a controller 101.
In this application specification, this gradient of temperature distribution is called “temperature gradient”. The temperature distribution depends on the state of the fixing roller, and in some cases, the distribution may be even or flat as illustrated in the figure. Even in this case, that temperature distribution is included in a temperature gradient in the following description.
The fixing roller of at least one of the first fixing device 1480A and the second fixing device 1480B is configured to be shifted with respect to the image forming apparatus 100 in the roller shaft direction. In particular, the fixing roller 1481 or the whole fixing device is configured to be shifted in the shaft direction of the fixing roller 1481 by the rocking section 1485 (a rocking motor and a rocking gear driven by the rocking motor), one end of which is fixed to some portion of the image forming apparatus 100. In the figure, the rocking section 1485 is illustrated to have a rocking motor and a rocking gear, but it can be modified in many ways using a voice coil motor, an ultrasonic motor, or a solenoid. Alternatively, the fixing roller 1481 or the whole fixing device may be held by a sliding mechanism (not shown in the figure) for shifting.
The position of the fixing roller 1481 or the whole fixing device being shifted is detected by a swing sensor 1480SH, and the detection result is communicated to the print control section 141 and the controller 101.
In this configuration, even in the both end portions of the recording sheet, the temperature is kept within a predetermined range (for example, the temperature in the flat part −20° C.), and the stable fixing is thus performed. On the other hand, when the fixing roller 1481 is shifted toward the L side in the main scanning direction as shown in
The magnitude of this temperature gradient depends on the amplitude of the shift. In particular, when the shift is made larger toward the L side, the temperature on the L side is accordingly raised, and that on the R side is accordingly lowered, resulting in a larger temperature gradient. To the contrary, when the shift toward the L side in
a, 6b, and 6c shows the relationship between the shift and the temperature distribution of the fixing roller, in the case that the first fixing roller 1481A and the second fixing roller 1481B are both able to be shifted.
b shows the first fixing roller 1481A shifted toward the L side and the second fixing roller 1481B shifted toward the R side. In this situation, as shown in
c shows the first fixing roller 1481A shifted toward the R side and the second fixing roller 1481B shifted toward the L side. In this situation, as shown in
a, 6b, and 6c show the case where the opposite temperature gradients are the same, and thus superposing the temperature gradients of the two fixing rollers makes a flat temperature distribution. However, there may be a case where the temperature gradients are not cancelled, even if the opposite temperature gradients are actually superposed. Such a case will be described below with reference to
a shows the temperature distribution of the first fixing roller 1481A in which the L side is higher and the R side is lower, and the temperature distribution of the second fixing roller 1481B in which the L side is lower and the R side is higher. The two fixing rollers have the temperature gradients which are opposite but approximately identical. Superposing the temperature gradients of the two fixing roller makes a flat temperature distribution.
On the other hand,
Alternatively, as shown in
Alternatively, both of the manners of
<Operation>
With reference to the flow charts of
In the following, description will be made on the case that both of the first fixing roller 1481A and the second fixing roller 1481B can be shifted. When the image forming is started, the instruction to start image forming is given from the controller 101, and according to the instruction, the first fixing roller 1481A and the second fixing roller 1481B are controlled by a not-shown typical fixing control method to rotate while they are temperature-controlled to be a predetermined temperature. In addition, the print control section 141 controls the rocking section 1485A and the rocking section 1485B to start reciprocal shift of the first fixing roller 1481A and the second fixing roller 1481B with a predetermine phase difference and a predetermined amplitude at a predetermined cycle, as shown in
In the mean time, it is preferable that the print control section 141 checks whether the first fixing roller 1481A and the second fixing roller 1481B are reciprocally driven with the predetermined phase difference and the predetermined amplitude, based on the detection result of the swing sensor 1480SH. In this case, although depending on the performance of the image forming apparatus 100, the print control section 141 may control the rocking section 1485A and the rocking section 1485B to perform a reciprocal shift by millimeters to tens of millimeters, for example, every image forming of tens or hundreds of recording sheets.
At that time, the print control section 141 detects the temperatures of the first fixing roller 1481A and the second fixing roller 1481B with a plurality of temperature sensors including the L temperature sensor 1480SL, the C temperature sensor 1480SC, and the R temperature sensor 1480SR which are arranged at a predetermined positions in a vicinity of each fixing roller surface (step S102 of
The print control section 141 judges whether the difference between the detected temperature gradients of the first detected fixing roller 1481A and the second fixing roller 1481B can be cancelled to be within a predetermined range (step s104, of
If the difference between the detected temperature gradients of the first fixing roller 1481A and the second fixing roller 1481B is not expected to be cancelled to be within the predetermined range (step S104 of
When continuing the image formation, after image formation of a predetermined volume of recording sheets or image formation for a predetermined time period (steps S106 and S107 of
Due to these controls, the temperature gradients of the two fixing rollers are in different directions and have an approximately identical gradient, whereby the two temperature gradients makes a flat temperature distribution being superposed on each other.
As described above, in the case of using two fixing devices to perform thermal fixing, since the position of the roller with which the recording sheet is in contact is varied due to the shift of the two rollers, the service life of the fixing rollers are improved without causing reduction in image quality due to temperature gradient.
In addition, the print control section 141 checks whether the difference in the numbers of processed sheets between the first fixing device 1480A and the second fixing device 1480B is more than a predetermined number (step S108 of
When performing two-side image formation, a recording sheet goes through the first fixing device 1480A twice. A recording sheet goes through the second fixing device 1480B only once for any of one-side image formation and two-side image formation. Therefore, the number of processed sheets of the first fixing device 1480A may increase more than the number of processed sheets of the second fixing device 1480B.
In addition, when a thinner recording sheet is used, since appropriate fixing is done by going through only the first fixing device 1480A, the sheet goes through the bypass route 1460B instead of the second fixing device 1480B. With this arrangement, the number of processed sheets may be more in the first fixing device 1480A than in the second fixing device 1480B.
For this reason, the first fixing device 1480A may be affected, for example, being scratched by a sheet edge, more than the second fixing device 1480B.
For this reason, if the difference in the numbers of processed sheets between the first fixing device 1480A and the second fixing device 1480B is more than the predetermined number (step S108 of
As described above, a greater amplitude of shill makes a greater temperature gradient. Therefore, the print control section 141 sets the amplitude of shift for the first fixing roller 1481A to be greater than that for the second fixing roller 1481B to the extent that the difference between the temperature gradients of the first fixing roller 1481A and the second fixing roller 1481B are cancelled to be in a predetermined range (step S109 of
With this arrangement, the first fixing roller 1481A, which has the greater number of processed sheets, contacts with the recording sheet edge at a wider area than the second fixing roller 1481B, thereby reducing scratches and grooves. Thus, the issue that the difference between the service lives is caused depending on the difference in the numbers of processed sheets is reduced.
In addition, it is preferable that the print control section 141 calculates the remnant lives of the first fixing roller 1481A and the second fixing roller 1481B, referring to the last part replacement times and the numbers of processed sheets, and it controls to increase the amplitude of shift for the fixing roller having a shorter remnant life, if it can be shifted. These controls prolong the service life of the one having a shorter remnant life as much as possible.
In addition, the print control section 141 controls the center position of the reciprocal shift for each of the first fixing roller 1481A and the second fixing roller 1481B in such a manner that the surface temperature of the fixing roller is within a preferable predetermined temperature range, for example, m ° C. to n ° C., and it then performs a reciprocal shift center position control and a reciprocal shift amplitude control so as to shift with a maximum amplitude of shift within that temperature range (step S110 of
Since the control described below is equally performed on both of the first fixing device 1480A and the second fixing device 1480B, description will be made without distinguishing the first and the second. The print control section 141 detects the temperatures of the first fixing roller 1481A and the second fixing roller 1481B with a plurality of temperature sensors including the L temperature sensor 1480SL, the C temperature sensor 1480SC, and the R temperature sensor 1480SR which are arranged at predetermined positions in a vicinity of each fixing roller surface (step S201 of
First, regarding the detection temperature TR obtained by the R temperature sensor 1480SR, it is judged which of the following relationships it satisfies: TR>n, TR<m, and n≧TR≧m (step S202 of
If the detection temperature TR obtained by the R temperature sensor 1480SR is n≧R≧m (step S203 of
If the detection temperature TL obtained by the L temperature sensor 1480SL satisfies the relationship n≧TL≧m (step S203 of
Instead, the detection temperature TR obtained by the R temperature sensor 1480SR satisfies the relationship TR>n (step S202, TR>n), it means that the R side exceeds the preferable temperature range n ° C., therefore, the print control section 141 controls the rocking section 1485 so as to move the center of reciprocal shift of the fixing roller 1481 toward the L side by a small amount (step S205 of
In this case, the appropriate center of reciprocal shift only has to be gradually obtained by repeating the temperature detection and the movement of the central position, and the amount of the slight movement may be 1 mm or approximately a tenth of the current shift amount of the center of reciprocal shift.
Then, the movement of the center of reciprocal shift toward the L side is continued until the detection temperature TR obtained by the R temperature sensor 1480SR becomes n or lower (steps S205 and S206 of
Instead, the detection temperature TR obtained by the R temperature sensor 1480SR satisfies the relationship TR<m (step S202, TR<m), it means that the R side is lower than the preferable temperature range m ° C., therefore, the print control section 141 controls the rocking section 1485 so as to move the center of reciprocal shift of the fixing roller 1481 toward the R side by a small amount (step S208 of
In this case, the appropriate center of reciprocal shift only has to be gradually obtained by repeating the temperature detection and the movement of the central position, and the amount of the slight movement may be 1 mm or approximately a tenth of the current shift amount of the center of reciprocal shift.
Then, the movement of the center of reciprocal shift toward the R side is continued until the detection temperature TR obtained by the R temperature sensor 1480SR becomes m or higher (steps S208 and S209 of
Instead, the detection temperature TL obtained by the L temperature sensor 1480SL satisfies the relationship TL>n (step S203, TL>n), it means that the L side exceeds the preferable temperature range n ° C., therefore, the print control section 141 controls the rocking section 1485 so as to move the center of reciprocal shift of the fixing roller 1481 toward the R side by a small amount (step S211 of
In this case, the appropriate center of reciprocal shift only has to be gradually obtained by repeating the temperature detection and the movement of the central position, and the amount of the slight movement may be 1 mm or approximately a tenth of the current shift amount of the center of reciprocal shift.
Then, the movement of the center of reciprocal shift toward the R side is continued until the detection temperature TL obtained by the L temperature sensor 1480SL becomes nor lower (steps S211 and S212 of
Instead, the detection temperature TL obtained by the L temperature sensor 1480SL satisfies the relationship TL<m (step S203, TL<m), it means that the L side is lower than the preferable temperature range m ° C., therefore, the print control section 141 controls the rocking section 1485 so as to move the center of reciprocal shift of the fixing roller 1481 toward the L side by a small amount (step S214 of
In this case, the appropriate center of reciprocal shift only has to be gradually obtained by repeating the temperature detection and the movement of the central position, and the amount of the slight movement may be 1 mm or approximately a tenth of the current shift amount of the center of reciprocal shift.
Then, the movement of the center of reciprocal shift toward the L side is continued until the detection temperature TL obtained by the L temperature sensor 1480SL becomes m or higher (steps S214 and S215 of
With the above mentioned arrangement, the print control section 141 controls the center position of the reciprocal shift for each of the first fixing roller 1481A and the second fixing roller 1481B in such a manner that the surface temperature of the fixing roller is within a preferable predetermined temperature range, for example, m ° C. to n ° C., and it then performs a reciprocal shift center position control and a reciprocal shift amplitude control so as to shift with a maximum amplitude of shift within that temperature range, thereby obtaining the maximum amplitude of reciprocal shift without causing reduction in image quality due to temperature change and prolonging the service life of the fixing roller.
In the above description of the embodiment, it is assumed that both the first fixing roller 1481A and the second fixing roller 1481B can be shifted.
However, in some configurations of the image forming apparatus 100, only one of the fixing rollers may be shifted. In that configuration, the print control section 141 is configured to detect the temperature gradient of the fixing roller which cannot be shifted and set the central position of reciprocal shift of the fixing roller which can be shifted so as to cancel the detected temperature gradient. In addition, the print control section 141 controls the rocking section 1485 to shift the fixing roller with a certain amplitude of reciprocal shift such that the temperatures of the both sides of the temperature distribution are kept in a preferable temperature range. With this manner, in the case of using two fixing devices to perform thermal fixing, the service life of the fixing roller is improved without causing reduction in image quality due to a temperature gradient by employing reciprocal shift.
In addition, if the fixing roller having processed the greater number of recording sheets can be shifted, the print control section 141 may instruct the rocking section 1485 to shift that roller. Similarly, if the fixing roller having a shorter remnant life can be shifted, the print control section 141 may instruct the rocking section 1485 to shift that roller. In this case, the maximum amplitude of reciprocal shift can be obtained without causing reduction in image quality due to temperature change, thereby prolonging the service life of the fixing roller as much as possible.
In the above description of the embodiments, although the image forming apparatus 100 is assumed to have both the first fixing device 1480A and the second fixing device 1480B, it is not limited thereto.
For example, an image forming apparatus having no fixing device may be externally provided with a first fixing device 1480A and a second fixing device 1480B. In that case, a controller of either of the image forming apparatus or an external fixing device may perform the above-described control.
Instead, an image forming apparatus having only a first fixing device 1480A may be externally provided with a second fixing device 1480BA. In that case, the controller provided in either of the image forming apparatus or the external second fixing devices 1480B may perform the above-described control.
In addition, in an image forming system made up of the image forming apparatus, or the image forming apparatus and an external fixing device, any one of the control sections may perform the above-described control.
In the above description of the embodiments, in the case that the first fixing roller 1481A and the second fixing roller 1481B already have opposite temperature gradients, the center of reciprocal shift is further shifted so as to cancel the gradients. However, when the first fixing roller 1481A and the second fixing roller 1481B already have opposite temperature gradients, control may be conducted so as not to further shift the center of reciprocal shift, if need be.
In the above description of the embodiments, although the image forming apparatus 100 is assumed to have both the first fixing device 1480A and the second fixing device 1480B, it is not limited thereto. The control of reciprocal shift may be conducted as described above even for an image forming apparatus and a fixing device provided with three or more fixing devices such as a first fixing device 1480A, a second fixing device 1480B, and a third fixing device.
In the above description of the embodiments, although the four-color image forming apparatus of
Although the fixing device for thermally fixing toner images formed by the electrophotographic method is described as a concrete example, the embodiments are not limited thereto. For example, the above-described embodiments may be applied to image forming apparatuses, fixing devices, and image forming systems for thermally fixing images formed with other material than toner, and an excellent result can be obtained
In the above description of the embodiments, the names of “first” and “second” such as the first fixing device, the first fixing roller, the second fixing device, and the second fixing roller are used just for ease of description. Therefore, when applying the technologies of the above-described embodiments to obtain advantages, which one should be named “first” or “second” and “first” is arbitrarily determined in individual image forming apparatus, fixing device, and image forming system.
According to the above-described embodiments, the following advantages can be obtained.
(1) By reciprocally shifting a fixing roller, the service life of the fixing roller is improved without causing reduction in image quality due to a temperature gradient, where the gradient of temperature distribution (temperature gradient) of each of the first fixing roller and the second fixing roller is detected, the central position of the reciprocal shift of one fixing roller which can be shifted is set such that the temperature gradient of the other fixing roller is cancelled, and then the one fixing roller is reciprocally shifted by a rocking section.
(2) By reciprocally shifting two fixing rollers, the service life of the fixing roller is improved without causing reduction in image quality due to a difference between temperature gradients when the two fixing rollers are used for thermal fixing, where the gradient of temperature distribution (temperature gradient) of each of the first fixing roller and the second fixing roller is detected, the central positions of the reciprocal shift of the first fixing roller and the second fixing roller are set such that both of the temperature gradients are cancelled, and then the first fixing roller and the second fixing roller are reciprocally shifted by a rocking section.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2009-281314 | Dec 2009 | JP | national |
