JP5233540B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a fixing device installed therein, and more particularly, a pressure member by a heating means such as a heater. The present invention relates to a fixing device that directly heats the image forming apparatus and an image forming apparatus.

2. Description of the Related Art Conventionally, in a fixing device in an image forming apparatus such as a copying machine or a printer, a technique for heating a pressure member such as a pressure roller by a heating unit such as a heater is known in order to prevent occurrence of hot offset and gloss unevenness. (For example, refer to Patent Document 1).
Specifically, in such a fixing device, in addition to a heater (first heating means) for heating a fixing member such as a fixing belt and a fixing roller, a heater (second heating) for heating a pressure member such as a pressure roller. Means) are installed. Each heater is controlled based on the temperature detected by the temperature sensor that detects the temperature of the fixing member (fixing temperature) and the temperature of the pressure member so that the fixing member and the pressure member reach the desired temperatures. .

On the other hand, in Patent Document 2 and the like, the temperature of the fixing member is detected at a plurality of locations, the temperature of the pressure member is detected at a plurality of locations, and the fixing process is started after the temperature difference is within an appropriate range. Technology is disclosed.
Further, in Patent Document 3 and the like, temperature sensors are installed at the width direction center and the width direction end of the pressure member, and the end of the pressure member according to the temperature difference detected by those temperature sensors. Has been disclosed.

JP 2007-316544 A Japanese Patent No. 3109322 Japanese Patent No. 3398500

  In the conventional fixing device described above, when a recording medium (small size paper) having a small size in the width direction is continuously passed, a large temperature difference occurs between the non-passing area and the passing area of the pressure member. Therefore, the amount of heat applied from the pressure member to the fixing member also varies depending on the position in the width direction, causing problems such as uneven fixing on the image of a large-size paper printed thereafter, and the degree of thermal expansion of the pressure member. However, there may be a problem that a difference occurs depending on the position in the width direction and the recording medium is wrinkled due to a difference in conveyance speed, or a non-sheet passing region of the heating member is thermally deteriorated due to excessive temperature rise.

In order to solve such a problem, the temperature of the pressure member is detected at a plurality of locations by applying the techniques of Patent Document 2, Patent Document 3, and the like, and the pressure member is heated based on the detected temperature. A measure for controlling the heating means (second heating means) can be considered. However, in that case, there are restrictions on the installation of multiple temperature sensors for detecting the temperature of the pressure member, and restrictions on the positions and types of the temperature sensors, which hinder the cost reduction and downsizing of the fixing device. End up.
For example, when an inexpensive contact type thermistor is used as the temperature sensor, it is necessary to install the contact type thermistor in contact with the non-sheet passing area of the pressure member in order to avoid damage to the sheet passing area of the pressure member. Therefore, it becomes difficult to solve the above-mentioned problems without side effects. When the contact type thermistor is installed in contact with only the non-sheet passing area of the pressure member, the second heating means for heating the pressure member is based on the temperature of the non-sheet passing area of the pressure member. Therefore, the temperature of the sheet passing area of the pressure member becomes too low when small-size sheets are continuously fed, and the temperature of the sheet passing area is less likely to rise thereafter.

  The present invention has been made to solve the above-described problems. Even when the recording medium having a small size in the width direction is continuously fed without increasing the cost and size of the apparatus, the present invention is provided. An object of the present invention is to provide a fixing device and an image forming apparatus capable of appropriately controlling the temperature of the pressure member.

According to a first aspect of the present invention, the fixing device is heated by the first heating means, and a fixing member that melts and fixes the toner image onto the recording medium, and the recording medium that is in pressure contact with the fixing member. A pressure member that forms a nip portion to be conveyed and is heated by a second heating unit, a first temperature detection unit that detects a temperature at a position corresponding to a minimum sheet passing area in the fixing member, and the fixing unit a third temperature detection means for detecting a second temperature detecting means for detecting the temperature of the position corresponding to the outside of the minimum sheet passing area, the temperature of the position corresponding to the outside of the minimum sheet passing area in the pressure member in member, wherein Predicting the temperature of the position corresponding to the minimum sheet passing area in the pressure member from the temperature detection results of the first temperature detection means, the second temperature detection means, and the third temperature detection means. Provided with a first temperature controller for controlling the second heating means based on the temperature, and a second temperature controller for controlling the second heating means based on the temperature detected by said third temperature detecting means, The first temperature controller and the second temperature controller are configured to be switchable, and when the first temperature controller is selected, the driving of the fixing member and the pressure member is started, and the predicted temperature After reaching the predetermined value, the recording medium is started to pass, and after the recording medium is passed, the temperature difference between the predicted temperature and the temperature detected by the third temperature detecting means is predetermined. The driving of the fixing member and the pressure member is continued until the value is lower than the value, and then the driving of the apparatus is stopped by switching from the first temperature controller to the second temperature controller. State in enters standby mode, the third temperature temperature sensed by the sensing means is for controlling said second heating means to be constant.

According to a second aspect of the present invention, there is provided the fixing device according to the first aspect , wherein the first temperature controller uses the temperature detection result of the first temperature detecting unit and the second temperature detecting unit. is predictive basis and temperature distribution in the width direction of the fixing member obtained by the temperature detection result of the third temperature sensing means, the temperature of the position corresponding to the minimum sheet passing area in the pressure member from .

According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the first temperature controller is switched to the second temperature controller by an operation of an operation unit, and the first temperature controller is switched. The driving of the fixing member and the pressure member can be started in a state where the two-temperature controller is selected.

A fixing device according to a fourth aspect of the present invention is the fixing device according to any one of the first to third aspects, wherein the third temperature detecting means is outside the maximum sheet passing area of the pressure member. This is a contact-type temperature sensor that contacts the pressure member at a corresponding position.

According to a fifth aspect of the present invention, there is provided the fixing device according to any one of the first to fourth aspects, wherein the temperature detected by the third temperature detecting means exceeds a predetermined value. The heating of the pressure member by the second heating means is interrupted.

According to a sixth aspect of the present invention, in the fixing device according to the fifth aspect , when the temperature detected by the third temperature detecting unit exceeds a predetermined value, the first heating unit is used. The heating of the fixing member is also interrupted.

The fixing device according to a seventh aspect of the present invention is the fixing device according to any one of the first to sixth aspects, wherein the second heating means includes PID control, PI control, I-PD control, I It is controlled by either -P control or PI-D control.

According to an eighth aspect of the present invention, there is provided a fixing device according to any one of the first to seventh aspects, wherein the first heating means and the second heating means are heaters. .

An image forming apparatus according to a ninth aspect of the present invention includes the fixing device according to any one of the first to eighth aspects.

In the present application, the “minimum sheet passing area” is the width direction (the direction orthogonal to the transport direction) among a plurality of sizes of recording media that can be passed (conveyed) in the image forming apparatus (or fixing device). Is defined as a paper passing area in the width direction of a recording medium having a small size.
In the present application, the “maximum sheet passing area” is the width direction (the direction orthogonal to the conveying direction) among a plurality of sizes of recording media that can be passed (conveyed) in the image forming apparatus (or fixing device). Is defined as a sheet passing area in the width direction of the recording medium having a large size.

  The present invention detects the temperature within the minimum sheet passing area of the fixing member, the temperature outside the minimum sheet passing area of the fixing member, and the temperature outside the minimum sheet passing area of the pressure member, and the temperature detection results thereof. The second heating means for predicting the temperature in the minimum sheet passing region in the pressure member and heating the pressure member based on the predicted temperature is controlled. Accordingly, the temperature of the pressure member can be appropriately controlled even when a recording medium having a small size in the width direction is continuously passed without increasing the cost and size of the apparatus, and the fixing device, and An image forming apparatus can be provided.

Embodiment.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, reference numeral 1 denotes an apparatus main body of a tandem color copier as an image forming apparatus, 2 a writing unit that emits laser light based on input image information, and 3 an original conveying unit that conveys an original D to an original reading unit 4. 4 is a document reading unit that reads image information of the document D, 7 is a paper feeding unit that accommodates a recording medium P such as transfer paper, 9 is a registration roller that adjusts the conveyance timing of the recording medium P, and 11Y, 11M, and 11C. , 11BK are photosensitive drums on which toner images of respective colors (yellow, magenta, cyan, and black) are formed, 12 is a charging unit that charges the photosensitive drums 11Y, 11M, 11C, and 11BK, and 13 is each photosensitive drum. A developing unit that develops electrostatic latent images formed on 11Y, 11M, 11C, and 11BK, and a toner image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK Transfer bias roller for transferring superimposed on the recording medium P (1 transfer bias roller), 15 denotes the photosensitive drums 11Y, 11M, 11C, cleaning unit for collecting the untransferred toner on 11BK, a.

  Reference numeral 16 denotes an intermediate transfer belt cleaning unit that cleans the intermediate transfer belt 17, 17 an intermediate transfer belt on which toner images of a plurality of colors are transferred and superimposed, and 18 a color toner image on the intermediate transfer belt 17 on the recording medium P. A secondary transfer bias roller 20 for transferring the toner image onto the recording medium P is a fixing device for fixing the toner image (unfixed image) on the recording medium P.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport rollers of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document D placed on the contact glass 5.

  Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light (exposure light) based on the image information of each color toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated clockwise in FIG. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (this is a charging process). Thus, a charged potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.
In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser beam is applied to the surface of the fourth photosensitive drum 11BK from the left side of the paper, and an electrostatic latent image of the black component is formed.

Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing unit 13, respectively. Then, the respective color toners are supplied from the developing units 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (development process). .)
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the intermediate transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photosensitive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the intermediate transfer belt 17 at the position of the transfer bias roller 14 (in the primary transfer process). is there.).

Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (this is a cleaning process).
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a neutralization unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

On the other hand, the intermediate transfer belt 17 on which the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11BK are transferred (carrying) are run in the clockwise direction in FIG. Reach the opposite position. Then, a color toner image carried on the intermediate transfer belt 17 is transferred onto the recording medium P at a position facing the secondary transfer bias roller 18 (secondary transfer step).
Thereafter, the surface of the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning unit 16. Then, the untransferred toner adhered on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit 16, and a series of transfer processes in the intermediate transfer belt 17 is completed.

Here, the recording medium P transported between the intermediate transfer belt 17 and the secondary transfer bias roller 18 (secondary transfer nip) is transported from the paper supply unit 7 via the registration roller 9 and the like. It is a thing.
Specifically, the recording medium P fed by the paper feeding roller 8 from the paper feeding unit 7 that stores the recording medium P is guided to the registration roller 9 after passing through the conveyance guide. The recording medium P that has reached the registration roller 9 is conveyed toward the secondary transfer nip at the same timing.

Then, the recording medium P on which the full-color image is transferred is guided to the fixing device 20 by the transport belt. In the fixing device 20, the color image (toner) is fixed on the recording medium P at the nip between the fixing belt and the pressure roller.
Then, the recording medium P after the fixing step is discharged as an output image outside the apparatus main body 1 by a paper discharge roller, and a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS.
2 and 3, the fixing device 20 includes a fixing belt 21 as a fixing member, a fixing auxiliary roller 22, a heating roller 23, a first heater 25 as a first heating unit, and a first temperature detection unit. First temperature sensor 40A, second temperature sensor 40B as second temperature detection means, pressure roller 31 as pressure member, second heater 34 as second heating means, third temperature as third temperature detection means It comprises a sensor 45, a separation plate 37, a guide plate 35, and the like.

Here, the fixing belt 21 as a fixing member is an endless belt having a multilayer structure in which an elastic layer and a release layer are sequentially laminated on a base layer made of a resin material such as polyimide (a circumferential length is set to about 70 mm). Is.) The elastic layer of the fixing belt 21 is formed of an elastic material such as fluorine rubber, silicone rubber, or foamable silicone rubber. The release layer of the fixing belt 21 is made of PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin) or the like. By providing the release layer on the surface layer of the fixing belt 21, the releasability (peelability) for the toner T (toner image) is ensured. The fixing belt 21 is stretched and supported by two roller members (a fixing auxiliary roller 22 and a heating roller 23), and travels in the direction of the arrow in FIG.
By using the fixing belt 21 having a low heat capacity as the fixing member, the temperature rise characteristic of the apparatus is improved.

  The fixing auxiliary roller 22 is a roller member (an outer diameter is set to about 52 mm) in which an elastic layer 22b made of a foam material such as foamable silicone rubber is formed on a core metal 22a such as SUS304. Then, a nip portion is formed by pressing the pressure roller 31 as a pressure member through the fixing belt 21. By forming the elastic layer 22b from a foamed material, the nip width (nip amount) at the nip portion can be set relatively large, and the heat of the fixing belt 21 is difficult to transfer to the auxiliary fixing roller 22. The fixing auxiliary roller 22 rotates in the clockwise direction in FIG.

The heating roller 23 is a hollow roller member (cylindrical body) made of a metal material such as aluminum or stainless steel, and a first heater 25 (heat source) as a first heating means is fixed inside the cylindrical body. It is installed.
By setting the thickness of the heating roller 23 to 1 mm or less, the heat capacity of the heating body is reduced and the temperature rise characteristic of the apparatus is improved (rise time is shortened). Here, the heating roller 23 in the present embodiment is made of aluminum and has a wall thickness of 0.6 mm and an outer diameter of 35 mm.

The first heater 25 (first heating means) of the heating roller 23 is a halogen heater, and both ends thereof are fixed to side plates (not shown) of the fixing device 20. Then, with the main switch of the image forming apparatus main body 1 turned on, power is supplied from the commercial power supply to the first heater 25 via the control unit 50 of the image forming apparatus main body 1. Then, the heating roller 23 is heated by the radiant heat from the first heater 25 whose output is controlled by the control unit 50, and the toner image T on the recording medium P is heated from the surface of the fixing belt 21 heated by the heating roller 23. Is added.
The output control of the first heater 25 is based on the detection result of the belt surface temperature by the two temperature sensors (the first temperature sensor 40A and the second temperature sensor 40B) facing the surface of the fixing belt 21 in a non-contact manner. It is carried out. Specifically, the AC voltage is applied to the first heater 25 for the energization time determined based on the detection results of the temperature sensors 40A and 40B (thermopile). By such output control of the first heater 25, the temperature of the fixing belt 21 (fixing temperature) can be adjusted and controlled to a desired temperature (target control temperature). In the present embodiment, the output control of the first heater 25 is performed based on the temperature detection results of the two temperature sensors 40A and 40B. However, the first heater is based only on the temperature detection results of the first temperature sensor 40A. 25 output controls can also be performed.
Here, in the present embodiment, the first heater 25 having a rated wattage of 1200 watts is used. Thus, by increasing the total wattage of the first heater 25, the rise time (warming up time) of the apparatus can be shortened.
In the present embodiment, the first temperature sensor 40A (first temperature detecting means) is disposed in the minimum sheet passing area N, and the second temperature sensor 40B (second temperature detecting means) is set in the minimum sheet passing area N. It is arranged outside. This will be described in detail later.

The pressure roller 31 as a pressure member mainly includes a cored bar 32 and an elastic layer 33 formed on the outer peripheral surface of the cored bar 32 via an adhesive layer. The elastic layer 33 of the pressure roller 31 is made of a material such as foamable silicone rubber, fluorine rubber, or silicone rubber. A thin release layer made of PFA or the like can be provided on the surface layer of the elastic layer 33.
The pressure roller 31 is pressed against the fixing auxiliary roller 22 via the fixing belt 21 by a pressure mechanism (not shown). In this way, a desired nip portion is formed between the pressure roller 31 and the fixing belt 21. In addition, the above-mentioned pressurization mechanism is comprised so that pressurization cancellation | release (or pressure reduction) can be performed.
In the present embodiment, in order to improve the heating efficiency of the fixing belt 21, a second heater 34 (for example, a halogen heater) as a second heating unit is provided in the pressure roller 31. . Further, a third temperature sensor 45 (contact temperature sensor (thermistor)) serving as third temperature detecting means for detecting the surface temperature of the pressure roller 31 is provided at a position corresponding to the outside of the maximum sheet passing area W in the pressure roller 31. Is disposed so as to abut against the pressure roller 31. Then, the control unit 50 controls the output of the second heater 34 based on the detection result of the third temperature sensor 45, or each of the first temperature sensor 40A, the second temperature sensor 40B, and the third temperature sensor 45. The output control of the second heater 34 is performed based on the detection result. The control of the second heater 34 will be described in detail later.

Referring to FIG. 2, guide plates 35 for guiding the conveyance of the recording medium P are respectively provided at the entrance side and the exit side of the contact portion (nip portion) between the fixing belt 21 and the pressure roller 31. It is arranged. The guide plate 35 is fixed to the side plate of the fixing device 20.
Further, a separation plate 37 is disposed in a position facing the outer peripheral surface of the fixing belt 21 and in the vicinity of the exit side of the nip portion. By installing the separation plate 37, it is possible to reduce a problem that the recording medium P after the fixing process is wound around the fixing belt 21 along the travel of the fixing belt 21.

The fixing device 20 configured as described above operates as follows.
When the main switch of the apparatus main body 1 is turned on, an AC voltage is applied (powered) to the heaters 25 and 34. When a print command is input, rotation driving of the fixing belt 21 (fixing auxiliary roller 22 and heating roller 23) and the pressure roller 31 in the arrow direction in FIG. 2 is started.
Thereafter, the recording medium P is fed from the paper supply unit 7 and the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11BK are carried on the recording medium P as unfixed images. The recording medium P carrying the unfixed image T (toner image) is conveyed in the direction of the arrow Y10 in FIG. 2 and fed into the nip portion between the fixing belt 21 and the pressure roller 31 that are in a pressure contact state. The toner image T is fixed on the surface of the recording medium P by the heating by the fixing belt 21 and the pressing force of the fixing belt 21 (fixing auxiliary roller 22) and the pressure roller 31. Thereafter, the recording medium P sent out from the nip portion by the rotating fixing belt 21 and the pressure roller 31 is conveyed in the direction of the arrow Y11.

Hereinafter, a characteristic configuration and operation of the fixing device 20 of the present embodiment will be described in detail.
Referring to FIG. 3, the first temperature sensor 40 </ b> A as the first temperature detecting means is disposed at a distance H <b> 1 from one end in the width direction, and is within the minimum sheet passing area N of the fixing belt 21. Detect the temperature at the corresponding position. The second temperature sensor 40B as the second temperature detecting means is disposed at a distance H2 from one end in the width direction, and the temperature at a position corresponding to outside the minimum sheet passing area N in the fixing belt 21. Is detected.
Further, the third temperature sensor 45 as the third temperature detecting means is disposed at a distance H3 from one end in the width direction, and corresponds to a position (outside the minimum sheet passing area N in the pressure roller 31). Further, the temperature of the pressure roller 31 is a position corresponding to outside the maximum sheet passing area W.). Here, as the third temperature sensor 45, a relatively inexpensive contact thermistor is used.
Thus, in this embodiment, since only one inexpensive thermistor is used as the temperature sensor 45 for controlling the temperature of the pressure roller 31, the fixing device 20 is increased in cost and size. Defects can be suppressed. Further, since the third temperature sensor 45 (contact type temperature sensor) is installed in the non-sheet passing area of the pressure roller 31 (outside the maximum sheet passing area W), the sheet passing area of the pressure roller 31 is set. Problems such as poor conveyance of the recording medium P and poor fixing due to damage of the recording medium P are suppressed.

Note that in the image forming apparatus 1 according to the present embodiment, the size of the recording medium P that can be passed is A5 length (width direction 148 mm × transport direction 210 mm) to A3 length (width direction 297 mm × transport direction 420 mm) (or HLT). Vertical (5.5 inches in the width direction × 8.5 inches in the conveyance direction) to DLT vertical (11 inches in the width direction × 17 inches in the conveyance direction)). That is, in the image forming apparatus 1 according to the present embodiment, the length of the minimum sheet passing area N is set to 148 mm (or 5.5 inches), and the length of the maximum sheet passing area W is set to 297 mm (or 11 inches). Has been.
In the present embodiment, the lateral registration of the recording medium P conveyed to the nip portion of the fixing device 20 is set to be the center reference in the width direction. That is, the minimum sheet passing area N and the maximum sheet passing area W are N / 2 and W / 2 in the width direction, respectively, with the center position of the fixing device 20 (the position of M / 2 from the end) as the center reference. It is formed in the range. In the present embodiment, the fixing belt 21, the heating roller 23, the auxiliary fixing roller 22, and the pressure roller 31 are all set to have substantially the same length in the width direction (distance M).

  In the present embodiment, the temperature detection results T1, T2, and T3 of the first temperature sensor 40A, the second temperature sensor 40B, and the third temperature sensor 45 are within the minimum sheet passing area N of the pressure roller 31. The temperature T4 ′ at the corresponding position is predicted (simulated), and the second heater 34 is controlled based on the predicted temperature T4 ′ (predicted temperature, simulation temperature). Specifically, the temperature distribution (temperature deviation) in the width direction of the fixing belt 21 obtained based on the temperature detection results T1 and T2 of the first temperature sensor 40A and the second temperature sensor 40B, and the temperature detection of the third temperature sensor 45. Based on the result, a temperature T4 ′ at a position corresponding to the minimum sheet passing area N in the pressure roller 31 is predicted, and the second heater 34 is controlled and added so that the predicted temperature T4 ′ becomes a predetermined value. The pressure roller 31 is heated.

  Here, in the image forming apparatus 1 according to the present embodiment, the controller 50 that controls the second heater 34 of the pressure roller 31 includes the first temperature that controls the second heater 34 based on the predicted temperature T4 ′. A controller and a second temperature controller that controls the second heater 34 based on the temperature T3 detected by the third temperature sensor 45 are provided. The first temperature controller and the second temperature controller are configured to be switchable.

FIG. 4 is a block diagram illustrating a control unit (control circuit) 50 that controls the second heater 34 of the pressure roller 31.
As shown in FIG. 4, the control unit 50 includes a PID controller 51 and a PWM drive circuit 52 for performing PID control, and a CPU for predicting (simulating) the surface temperature of the central portion in the width direction of the pressure roller 31. (Simulation CPU) 53 and the like are provided. The controller 50 controls the duty of energizing the second heater 34 (the lighting rate of the heater that is lit per predetermined energization time (control cycle)). In addition to the detection result of the third temperature sensor 45, the detection result of the first temperature sensor 40A and the detection result of the second temperature sensor 40B are input to the simulation CPU 53.
When the switch SW1 is connected (when the first temperature controller is selected), the PID controller 51 predicts a predetermined target control temperature based on a PID control algorithm (predetermined algorithm). The duty is calculated from the deviation from the temperature T4 ′. On the other hand, when the switch SW2 is connected (when the second temperature controller is selected), the PID controller 51 uses the PID control algorithm (predetermined algorithm) and a predetermined target control temperature. The duty is calculated from the deviation from the temperature T3 detected by the third temperature sensor 45. In either case, the second heater 34 is turned on through the PWM drive circuit 52 based on the calculated duty. Specifically, the ratio of applying the rated AC voltage per control cycle to both ends of the second heater 34 (halogen heater) is controlled.

FIG. 5A is a graph showing the temperature distribution in the width direction of the fixing belt 21 when small-size paper (A5 vertical size recording medium P in this embodiment) is continuously fed. . FIG. 5B is a graph showing the temperature distribution in the width direction of the pressure roller 31 at that time.
In FIG. 5, the horizontal axis indicates the distance (position) from one end in the width direction of the fixing belt 21 (or the heating roller 23) or the pressure roller 31, and the vertical axis indicates the surface temperature of the fixing belt 21 or the pressure roller 31 ( Temperature detection result).
As shown in FIG. 5, when small-size paper is continuously fed, the temperature of the area N corresponding to the size of both the fixing belt 21 and the pressure roller 31 falls compared to the temperature outside the area. It will end up. In such a state, since the temperature T3 detected by the third temperature sensor 45 has substantially reached the target temperature, the output of the second heater 34 is based only on the temperature T3 detected by the third temperature sensor 45. When the control is performed, the power supply to the second heater 34 is hardly performed. Therefore, most of the heating in the central portion in the width direction of the pressure roller 31 is performed by heat transfer from both ends in the width direction, and the rise of the temperature in the central portion of the pressure roller 31 becomes very slow. .

In order to deal with such a problem, in the present embodiment, the temperature detection results T1, T2, and T3 of the first temperature sensor 40A, the second temperature sensor 40B, and the third temperature sensor 45 are used to determine the center of the pressure roller 31. Temperature T4 ′ of the portion (position corresponding to the minimum sheet passing area N) is predicted, and the second heater 34 is controlled based on the predicted temperature T4 ′. Is done quickly and properly.
The temperature T4 ′ at the central portion (within the minimum sheet passing area N) of the pressure roller 31 can be obtained using a linear approximation method or a logarithmic approximation method. Hereinafter, as a specific example, a calculation method using both approximation methods will be described with reference to FIGS. 5A and 5B.
The (installation position, detected temperature) of the first temperature sensor 40A is (H1, T1), the (installation position, detected temperature) of the second temperature sensor 40B is (H2, T2), and the (installation position, The detected temperature is (H3, T3). Here, the relationship between H2 and H3 may be H2 = H3 or H2 ≠ H3.
(1) In the case of linear approximation The dashed-dotted line S1 of FIG. 5 (A) is a straight line approximated. from now on,
(T2−T1) = k ₁ (H2−H1)
Because
k ₁ = (T2-T1) / (H2-H1)
It becomes. Note that k ₁ is a coefficient calculated for each temperature control cycle.
A dashed line S1 ′ in FIG. 5B is a straight line approximated by a straight line. Similarly, when a linear approximation formula is applied to the temperature distribution of the pressure roller 31, the predicted temperature T4 ′ at the center portion (the position of M / 2) of the pressure roller 31 is
_{T4' = T3-k 2 (M} / 2-H3)
It becomes. However,
k ₂ = q ₁ × k ₁
And q ₁ is a predetermined coefficient. q ₁ may be determined assuming any mode, or may be changed depending on the paper passing mode and environmental conditions.
Then, feedback control of the second heater 34 is performed so that the predicted temperature T4 ′ obtained sequentially in this way follows the target value (predetermined value).
(2) Case of Logarithmic Approximation A two-dot chain line S2 in FIG. 5A is a logarithmically approximated curve. from now on,
(T2-T1) = m ₁ exp (H2-H1)
Because
m ₁ = (T2-T1) / exp (H2-H1)
It becomes. Note that m ₁ is a coefficient calculated for each temperature control cycle.
A two-dot chain line S2 ′ in FIG. 5B is a straight line approximated by a straight line. Similarly, when a logarithmic approximate expression is applied to the temperature distribution of the pressure roller 31, the predicted temperature T 4 ′ at the central portion (the position of M / 2) of the pressure roller 31 is
T4 ′ = T3-m ₂ (M / 2−H3)
It becomes. However,
m ₂ = q ₂ × m ₁
And q ₂ is a predetermined coefficient. q ₂ may be determined assuming any mode, or may be changed depending on the paper passing mode and environmental conditions.
Then, feedback control of the second heater 34 is performed so that the predicted temperature T4 ′ obtained sequentially in this way follows the target value (predetermined value).

  In the present embodiment, the temperature T4 ′ at the central portion (in the minimum sheet passing area N) of the pressure roller 31 is calculated (predicted) using a linear approximation method or a logarithmic approximation method. May be used to calculate the temperature T4 ′ at the center of the pressure roller 31.

Referring to FIG. 4, when the fixing device 20 is operating (when the fixing belt 21 and the pressure roller 31 are rotationally driven), the switch SW1 (first temperature controller) is first selected. For the deviation between the target temperature and the actual temperature used for the feedback control of the PID controller 51, the predicted temperature T4 ′ described above is used without using the temperature detected by the third temperature sensor 45 of the pressure roller 31 as it is. The As a result, the temperature of the central portion of the pressure roller 31 can be quickly and appropriately raised.
In such a control, after the passing of the recording medium P is finished, the operation of the fixing device 20 is continued until the temperature difference between the predicted temperature T4 ′ and the temperature T3 detected by the third temperature sensor 45 becomes a predetermined value or less. This is performed while continuing (rotating drive of the fixing belt 21 and the pressure roller 31).
If the fixing belt 21 continues to be driven (running), the temperature of the pressure roller 31 rises rapidly and the temperature distribution in the width direction becomes uniform due to heat transfer from the fixing belt 21 to the pressure roller 31. Further, by performing the above-described control after the paper is passed, the fixing device 20 is in a standby state after eliminating the temperature deviation in the width direction of the pressure roller 31, so there is no temperature deviation in the pressure roller 31 at the time of the next printing. In this state, printing starts immediately. Therefore, the waiting time at the start of printing is reduced.

  When the paper feeding is started again, the driving of the fixing device 20 (rotation driving of the fixing belt 21 and the pressure roller 31) is started first, and the predicted temperature T4 ′ reaches a predetermined value (target value). After that, control is performed so as to start passing the recording medium P. As a result, since the fixing step is performed after the temperature deviation in the width direction of the pressure roller 31 is reliably eliminated, a good fixed image can be obtained.

In the case where the above-described control is performed after the recording medium P has been passed, if the temperature of the pressure roller 31 rises, it is not necessary to drive the fixing device 20 further. The driving is stopped and the standby mode is entered (the paper can be immediately passed). In this way, in the state where the fixing device 20 is stopped in the standby mode, the switch SW2 (second temperature controller) in FIG. 4 is selected, and the temperature T3 detected by the third temperature sensor 45 is constant. Thus, the output of the second heater 34 is controlled.
Moreover, it can also comprise so that a user can operate the operation part not shown and can select either the control by a 1st temperature controller and the control by a 2nd temperature controller. When the user desires high image quality when a large temperature deviation occurs as shown in FIG. 5, the user operates the operation unit (not shown) and selects control by the first temperature controller, so that the pressure roller The temperature deviation of 31 can be eliminated and a good fixed image can be provided. On the other hand, when the user gives priority to shortening the startup time of the apparatus over the high image quality, the temperature of the pressure roller 31 can be quickly raised by selecting the control by the second temperature controller. it can. Thus, usability improves by making it possible to select two temperature controllers as appropriate.

Here, in the present embodiment, when the temperature T3 detected by the third temperature sensor 45 exceeds a predetermined value, the heating of the pressure roller 31 by the second heater 34 is controlled to be interrupted. Such control is performed because in the simulation for obtaining the temperature T4 ′ at the center of the pressure roller 31, if the error of the predicted temperature T4 ′ increases due to disturbance, the amount of power supplied to the second heater 34 is reduced. This is because the pressure roller 31 may be thermally damaged or the thermostat may be broken.
Further, when the temperature T3 detected by the third temperature sensor 45 exceeds a predetermined value, the heating of the fixing belt 21 by the first heater 25 is also controlled to be interrupted. This is because the heating of the fixing belt 21 by the first heater 25 is also interrupted when the error of the predicted temperature T4 ′ increases due to disturbance and the amount of power supplied to the second heater 34 increases. This is because the temperature of the pressure roller 31 that has been overheated can be quickly reduced.

  As described above, in the present embodiment, the temperature within the minimum sheet passing area N of the fixing belt 21 (fixing member), the temperature outside the minimum sheet passing area N of the fixing belt 21, and the pressure roller 31 (additional pressure). The temperature outside the minimum sheet passing area N in the pressure member) is detected, and the temperature T4 ′ in the minimum sheet passing area N in the pressure roller 31 is predicted from those temperature detection results, and the predicted temperature T4 ′ The second heater 34 (second heating means) for heating the pressure roller 31 is controlled based on the above. As a result, the temperature control of the pressure roller 31 can be appropriately performed even when the recording medium P having a small size in the width direction is continuously fed without increasing the cost and size of the fixing device 20. it can.

In the present embodiment, PID control is used to perform output control of the second heater 34, but other controls (for example, PI control, I-PD control, IP control, PI-D control, etc.) Can also be used.
When PID control is used, it is easy to construct a control system that supplies an optimal amount of heat so as to follow the target control temperature.
When PI control is used, it is easy to construct a control system that supplies an optimal amount of heat with a steady deviation minimized with respect to the step-like target control temperature.
When I-PD control is used, it is easy to construct a control system that supplies an optimal amount of heat with suppressed characteristics of excessive response to the target temperature.
When the IP control is used, it becomes easy to construct a control system that quickly removes the influence of the input disturbance and supplies a stable and optimal amount of heat.
When PI-D control is used, it is easy to construct a control system that quickly removes the influence of input disturbance and supplies an optimum amount of heat that quickly follows the target temperature.

In the present embodiment, the first temperature sensor 40A installed in the minimum sheet passing area N, the second temperature sensor 40B installed outside the minimum sheet passing area N, and installed outside the minimum sheet passing area N. A single third temperature sensor 45 is provided, but a plurality of the third temperature sensors 45 may be provided.
In the present exemplary embodiment, the present invention is applied to the fixing device 20 in which the lateral registration of the recording medium P conveyed to the nip portion is set to be the center reference in the width direction. The present invention can also be applied to the fixing device 20 in which the lateral registration of the recording medium P to be set is set as the width direction end portion reference.

In the present embodiment, the pressure roller 31 is used as the pressure member, but a pressure belt or a pressure pad may be used as the pressure member. Even in that case, the same effect as the present embodiment can be obtained.
In the present embodiment, the present invention is applied to the fixing device 20 using the fixing belt 21 as a fixing member. However, the present invention is also applied to a fixing device using a fixing roller, a fixing film, and a fixing pad as the fixing member. Of course, the present invention can be applied. In these cases, the same effect as in the present embodiment can be obtained.

  In the present embodiment, the present invention is applied to the fixing device 20 that heats the fixing member 21 and the pressure member 31 by radiant heat using the heaters 25 and 34. However, the fixing member and the pressure are applied by electromagnetic induction heating. Naturally, the present invention can also be applied to a fixing device that heats a member. Even in that case, the same effect as the present embodiment can be obtained.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. 2 is a configuration diagram illustrating a fixing device. FIG. FIG. 3 is a schematic view of the fixing device as viewed in the width direction. FIG. 3 is a block diagram illustrating a control circuit that controls the fixing device. FIG. 4A is a graph showing the temperature distribution in the width direction of the fixing belt and FIG. 5B is a graph showing the temperature distribution in the width direction of the pressure roller when small-size paper is continuously fed.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20 fixing device,
21 fixing belt (fixing member),
22 fixing auxiliary roller,
23 Heating roller,
25 1st heater (1st heating means),
31 Pressure roller (pressure member),
34 2nd heater (2nd heating means),
40A 1st temperature sensor (1st temperature detection means),
40B 2nd temperature sensor (2nd temperature detection means),
45 third temperature sensor (third temperature detection means, contact temperature sensor),
N Minimum paper passing area, W Maximum paper passing area, P Recording medium.

Claims (9)

A fixing member that is heated by the first heating means and that melts and fixes the toner image on the recording medium;
A pressure member that is pressed against the fixing member to form a nip portion on which a recording medium is conveyed and is heated by a second heating unit;
First temperature detecting means for detecting a temperature at a position corresponding to a minimum sheet passing area in the fixing member;
A second temperature detecting means for detecting a temperature at a position corresponding to outside the minimum sheet passing area in the fixing member;
Third temperature detecting means for detecting a temperature at a position corresponding to outside the minimum sheet passing area in the pressure member;
Predicting the temperature at the position corresponding to the minimum sheet passing area in the pressure member from the temperature detection results of the first temperature detection means, the second temperature detection means, and the third temperature detection means, A first temperature controller for controlling the second heating means based on the predicted temperature;
A second temperature controller for controlling the second heating means based on the temperature detected by the third temperature detecting means;
With
The first temperature controller and the second temperature controller are configured to be switchable,
In a state where the first temperature controller is selected, the driving of the fixing member and the pressure member is started, and after the predicted temperature reaches a predetermined value, the recording medium is started to pass,
After the recording medium is passed, the fixing member and the pressure member continue to be driven until the temperature difference between the predicted temperature and the temperature detected by the third temperature detecting means becomes a predetermined value or less. And
Thereafter, the second temperature controller is switched from the first temperature controller to enter a standby mode in a state where the driving of the apparatus is stopped, and the second temperature controller is configured so that the temperature detected by the third temperature detector is constant. A fixing device that controls a heating means . The first temperature controller includes a temperature distribution in the width direction of the fixing member obtained based on a temperature detection result of the first temperature detection unit and the second temperature detection unit, and a temperature detection of the third temperature detection unit. The fixing device according to claim 1, wherein a temperature at a position corresponding to a minimum sheet passing area in the pressure member is predicted from a result. Switching from the first temperature controller to the second temperature controller by operating the operation unit, and the driving of the fixing member and the pressure member can be started in a state where the second temperature controller is selected. The fixing device according to claim 1, wherein: 4. The contact temperature sensor according to claim 1, wherein the third temperature detection unit is a contact-type temperature sensor that contacts the pressure member at a position corresponding to the outside of the maximum sheet passing area of the pressure member. A fixing device according to claim 1. The heating of the pressurizing member by the second heating unit is interrupted when the temperature detected by the third temperature detecting unit exceeds a predetermined value. The fixing device according to 1. 6. The fixing device according to claim 5, wherein when the temperature detected by the third temperature detecting unit exceeds a predetermined value, heating of the fixing member by the first heating unit is also interrupted. The second heating means is controlled by any one of PID control, PI control, I-PD control, IP control, and PI-D control. The fixing device described. The fixing device according to claim 1, wherein the first heating unit and the second heating unit are heaters. An image forming apparatus comprising the fixing device according to claim 1.

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