JP5239671B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a fixing device installed therein, and in particular, each of a fixing member and a pressure member. The present invention relates to a fixing device provided with a heater 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 is known in which a pressure member such as a pressure roller is directly heated by a heater in order to shorten a warm-up time (rise time). (For example, refer to Patent Document 1).
Specifically, in such a fixing device, in addition to a heater (first heater) for heating a fixing member such as a fixing belt and a fixing roller, a heater (second heater) for heating a pressure member such as a pressure roller. Is installed. Each heater is controlled based on a temperature detected by a temperature sensor that detects the temperature of the fixing member (fixing temperature) so that the fixing member and the pressure member have a desired temperature.

  On the other hand, conventionally, in an image forming apparatus such as a copying machine or a printer, in order to maintain the temperature of a fixing member in a fixing device at a target temperature and ensure stable fixing performance, a temperature detecting means (temperature detecting means) is used. A technique is known in which on / off control of a heater for heating a fixing member is performed based on the detected temperature of the fixing member (see, for example, Patent Document 2). Specifically, when the temperature detected by the temperature detecting means is lower than a predetermined value (target control temperature), the duty of energizing the heater is set to 100% (energization is turned on), and the temperature detected by the temperature detecting means is predetermined. When it is higher than the value, the duty of energizing the heater is set to 0% (the energization is off). Such a temperature control method is called an on / off control method.

  In such a fixing device using an on / off control method, since the temperature ripple with respect to the target control temperature becomes large as it is, detection is performed by combining the control algorithm with Proportional, Integral, and Differential. PID control that optimizes a plurality of parameters according to the deviation between the temperature and the target control temperature is performed (see, for example, Patent Document 2). In PID control, the duty of energizing the heater is varied in the range of 0 to 100%.

Further, in Patent Document 2 and the like, for the purpose of suppressing defects of other electrical devices on the same power line as the image forming apparatus (particularly, flickering phenomenon (flicker phenomenon) of lighting devices such as fluorescent lamps) A technique for supplying a specific pattern of power to a heater for heating a fixing member is disclosed.
Further, in Patent Document 3 and the like, in order to avoid an inrush current being input to the heater that heats the fixing member, the heater is turned on or off at the zero-cross point of the alternating current, and the phase angle during energization is set. There is disclosed a phase control method to be changed (such a control method is also referred to as soft start or soft stop).

JP 2007-316544 A Japanese Patent No. 3746913 Japanese Patent No. 3833392

  In the conventional fixing device described above, when the fixing member is heated by the heater and the pressure member is heated by another heater, the fixing temperature feedback control is high without slowing down the warm-up time of the device. It has been difficult to achieve both accuracy and prevention of flickering phenomenon of lighting devices such as fluorescent lamps.

  Specifically, in order to improve the feedback control of the fixing temperature with high accuracy, if the PID control is performed on the heater (second heater) of the pressure member together with the heater (first heater) of the fixing member, the control cycle is increased. As the length becomes shorter, the inrush current generated in each control cycle increases, and the flicker phenomenon of the lighting equipment connected on the same power supply line as the image forming apparatus worsens.

In order to suppress the occurrence of such an inrush current, it is possible to apply a technique disclosed in Patent Document 3 or the like and perform a soft start or a soft stop for the above-described PID control for the two heaters. However, in that case, the energization time per unit time for the two heaters is shortened by the time for which the soft start or soft stop is executed, so the heater duty and the heat generation amount per unit time The linearity cannot be maintained. When the control period of the heater is constant, the tendency becomes more prominent as the time for executing the soft start or soft stop is set longer.
In particular, in a fixing device using a fixing belt having a small heat capacity as a fixing member in order to further reduce the warm-up time of the device, soft start or If the soft stop is sufficiently performed, the ratio of the time for executing the soft start or the soft stop to the control cycle increases, and the influence on the linearity between the heater duty and the heat generation amount per unit time is large. Therefore, it becomes difficult to improve the feedback temperature feedback control with high accuracy without slowing down the warm-up time.

  The present invention has been made in order to solve the above-described problems. Even when the fixing member is heated by the first heater and the pressure member is heated by the second heater, the warm-up time of the apparatus is improved. To provide a fixing device and an image forming apparatus that can achieve both high accuracy of feedback control of the fixing temperature and prevention of flickering phenomenon of lighting equipment such as a fluorescent lamp without slowing down the shortening of the image forming apparatus. It is in.

According to a first aspect of the present invention, a fixing device is heated by a plurality of first heaters, and a fixing member that melts and fixes a toner image on a recording medium, and a recording medium that is pressed against the fixing member and pressed. power through PWM driving circuit but to form a nip portion to be conveyed, a pressure member which is heated by the second heater, wherein the plurality of first heater based on the duty defined by any PID control There is provided, the second heater is on-off control, at least one of the plurality of first heater, the rated wattage is configured to be greater than the rated wattage of the second heater, the plurality The control cycle of the first heater is the same cycle and the phases are shifted from each other .

  According to a second aspect of the present invention, there is provided a fixing device according to the first aspect of the present invention, further comprising temperature detecting means for detecting the temperature of the fixing member, wherein the first heater is based on a predetermined algorithm. PID control is performed in which the duty of energization is varied so as to obtain a value calculated from the deviation between the detection result of the temperature detection means and a predetermined target temperature, and the second heater is connected to the temperature detection means. On / off control is performed so that the duty of energization is 100% when the detection result is smaller than a predetermined value and the duty of energization is 0% when the detection result of the temperature detecting means is larger than the predetermined value. .

  The fixing device according to a third aspect of the present invention is the fixing device according to the first or second aspect, wherein the first heater and / or the second heater is soft-started or soft-stopped at each control period. Is executed.

  The 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 control cycle of the first heater is shorter than the control cycle of the second heater. It is comprised so that it may become.

A fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, wherein the first heater is a halogen heater.

The fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the first heater and the second heater are energized respectively when the recording medium is fed. It is what is done.

A 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 fixing member is a fixing belt stretched around a plurality of roller members. It is.

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

  In the present invention, the first heater that heats the fixing member is PID-controlled and the second heater that heats the pressure member is controlled to be turned on / off, so that the fixing can be performed without slowing down the warm-up time of the apparatus. It is possible to provide a fixing device and an image forming apparatus that can achieve both high accuracy of temperature feedback control and prevention of flickering phenomenon of a lighting device such as a fluorescent lamp.

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 (first heating means), and a first temperature detection means. The temperature sensor 40A, a second temperature sensor 40B as temperature detecting means, a pressure roller 31 as a pressure member, a second heater 34 (second heating means), a separation plate 37, a guide plate 35, etc. .

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 of the heating roller 23 is a halogen heater, and both ends thereof are fixed to a side plate (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). Note that the output control of the first heater 25 will be described in more detail later together with the output control of the second heater 34.

Here, in the present embodiment, the first heater 25 having a rated wattage of 1000 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 is disposed at the center in the width direction, and the second temperature sensor 40B is disposed at the end in the width direction. The average temperature and temperature deviation in the width direction on the fixing belt 21 are obtained from the temperature detection results of the two temperature sensors 40A and 40B, and output control of the first heater 25 is performed based on the average temperature and temperature deviation.
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 (temperature detection means), but one temperature sensor (for example, the first temperature sensor) is used. The output control of the first heater 25 can also be performed based only on the temperature detection result of 40A).
In the present embodiment, the two temperature sensors 40A and 40B (temperature detection means) are directly opposed to the fixing belt 21, but the two temperature sensors 40A and 40B (temperature detection means) are replaced with heat transfer plates. It is also possible to indirectly face the fixing belt 21 via the fixing belt 21.
In this embodiment, thermopile is used as the temperature sensors 40A and 40B (temperature detection means), but a thermistor can also be used as the temperature sensors 40A and 40B (temperature detection means).

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 (a halogen heater having a rated wattage of about 250 watts) is provided in the pressure roller 31. . By energizing the second heater 34 in addition to the first heater 25 when the recording medium P is passed, the heating efficiency of the fixing belt 21 is improved, and the temperature of the pressure roller 31 is increased during continuous feeding. The problem that the recording medium P is curled or a defective fixing image is generated due to the decrease is suppressed.
The output control of the second heater 34 is performed by the control unit 50 based on the detection results of the temperature sensors 40A and 40B. Note that the output control of the second heater 34 will be described in more detail later together with the output control of the first heater 25.
In the present embodiment, the output control of the second heater 34 is performed based on the detection results of the temperature sensors 40A and 40B facing the fixing belt 21, but the surface temperature of the pressure roller 31 is directly detected. A temperature sensor may be installed, and the output control of the second heater 34 may be performed based on the detection result of the temperature sensor.

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 body 1 is turned on, an AC voltage is applied (powered) to the two heaters 25 and 34. When the recording medium P is passed (in the paper passing mode), the first heater 25 and the second heater 34 are continuously energized.
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.
In the image forming apparatus according to the present embodiment, measurement is performed by the control unit (control circuit) 50 with temperature sensors 40A and 40B (thermopile) as temperature detection means during warm-up, standby, and printing (when paper is passed). Based on the temperature of the fixing belt 21, the heaters 25 and 34 are controlled to control the fixing belt 21 at an optimum temperature. At this time, the first heater 25 that heats the fixing belt 21 is PID-controlled, and the second heater 34 that heats the pressure roller 31 is ON / OFF-controlled.
Specifically, the first heater 25 has a duty ratio of energization so as to be a value calculated from a deviation between the detection results of the temperature sensors 40A and 40B and a predetermined target temperature (target control temperature) based on a predetermined algorithm. Is controlled. On the other hand, when the detection results of the temperature sensors 40A and 40B are smaller than a predetermined value, the second heater 34 has a duty ratio of 100% when the detection results of the temperature sensors 40A and 40B are larger than the predetermined value. On / off control is performed so that the duty of energization is 0%.

FIG. 4 is a block diagram showing a control unit (control circuit) 50 that controls the first heater 25 of the fixing belt 21 and the second heater 34 of the pressure roller 31.
As shown in FIG. 4, the control circuit 50 includes a PID controller 51 and a PWM drive circuit 52 for performing PID control of the first heater 25, an on / off controller 53 for performing on / off control of the second heater 34, and Is provided.

The PID controller 51 controls the duty of energization to the first heater 25 (the lighting rate of the heater that is lit per predetermined energization time (control cycle)). Specifically, the PID controller 51 is based on a temperature deviation between a predetermined target control temperature and the temperature of the fixing belt 21 detected by the temperature sensors 40A and 40B based on a PID control algorithm (predetermined algorithm). Calculate the duty. Then, the first heater 25 is turned on through the PWM drive circuit 52 based on the calculated duty. Specifically, the rate at which the rated AC voltage per control cycle is applied to both ends of the first heater 25 (halogen heater) is controlled.
In the present embodiment, the control cycle of the first heater 25 is set to 200 to 1000 [ms]. If the control period of the first heater 25 is set to about 100 [ms], the feedback control of the fixing temperature is improved, but the occurrence of inrush current is increased and the flickering phenomenon of a lighting device such as a fluorescent lamp is caused. Will get worse. Specifically, when the control cycle of the first heater 25 is set to about 100 [ms] and a commercial power source having a frequency of 50 Hz is used, the zero cross point within the control cycle of the first heater 25 is 10 times. Thus, the first heater 25 can be controlled only in increments of 10% duty.

On the other hand, the on / off controller 53 has a duty of 100% when the detection results of the temperature sensors 40A and 40B (temperature detection means) are smaller than the target control temperature (predetermined value), and the detection results of the temperature sensors 40A and 40B are the target. The energization of the second heater 34 is controlled (on / off control) so that the duty becomes 0% when the temperature is higher than the control temperature.
In the present embodiment, the control period of the second heater 34 is set to 200 to 2000 [ms]. Since the temperature controller that controls the second heater 34 is the on / off controller 53, the temperature ripple naturally increases as compared with the case where the PID control is performed (the temperature ripple is about 10 to 20 degrees). However, since the heating of the pressure roller 31 by the second heater 34 is intended to supplementarily supply heat from the pressure roller 31 to the fixing belt 21, even when fixing the color toner, Even if a temperature ripple of about 10 to 20 degrees occurs in the temperature control of the pressure roller 31, it hardly affects the quality of the fixed image. Therefore, the upper limit of the temperature ripple of the pressure roller 31 capable of obtaining a good quality of the fixed image is determined in advance, and the control period for generating the temperature ripple is selected, whereby the first of the pressure roller 31 is selected. As the temperature controller for controlling the two heaters 34, the on / off controller 53 can be used without any trouble.

  Thus, in this embodiment, since the second heater 34 for heating the pressure roller 31 is provided in addition to the first heater 25 for heating the fixing belt 21, the warm-up time of the fixing device 20 is set. Can be shortened. Further, by performing PID control on the first heater 25 that heats the fixing belt 21, high accuracy of feedback control of the fixing temperature is achieved, and a good fixed image can be provided. Furthermore, for the second heater 34 that heats the pressure roller 31, it is possible to reduce the occurrence of a large inrush current every control cycle by using on / off control that does not increase the accuracy of feedback control. The occurrence of flickering phenomenon in lighting equipment such as fluorescent lamps can be suppressed.

  In the present embodiment, one halogen heater (with a rated wattage of about 1000 watts) having a relatively large rated wattage is used as the first heater 25 for heating the fixing belt 21 (heating roller 23). Yes. When a halogen heater having a large rated wattage is used, the level of the current value of the generated inrush current tends to be large, which is disadvantageous with respect to the flicker phenomenon. As a result, the occurrence of inrush current is sufficiently suppressed, so that an upper limit value of the inrush current generated in the first heater 25 can be provided. Therefore, even when one halogen heater having a relatively large rating is used for the purpose of reducing the cost of the fixing device 20 and reducing the number of parts, the above-described effects of the present embodiment can be sufficiently achieved. become.

  Here, in the present embodiment, the first heater 25 and / or the second heater 34 may be soft-started or soft-stopped every control cycle. That is, in at least one of the PID control of the first heater 25 and the on / off control of the second heater 34, soft start or soft stop (the phase at the time of energization by turning on or off the heater at the zero cross point of the AC current). It is a phase control method that changes the angle.). In that case, soft start or soft stop will be performed to the extent that it does not affect the linearity of the transfer function between input power and output temperature in the entire temperature control system, and the occurrence of inrush current will be reduced. The flicker phenomenon is further reduced.

The control cycle of the first heater 25 is preferably set to be shorter than the control cycle of the second heater 34.
Since the on / off control cycle is longer than the PID control cycle, the occurrence of inrush current in the on / off control can be reduced regardless of whether soft start or soft stop is executed. Will be reduced. Moreover, even when soft start or soft stop is executed, generation of harmonics is reduced, and linearity between input (power supply) and output (temperature sensor detection result) can be secured. .

In the present embodiment, the rated wattage of the first heater 25 is set to be larger than the rated wattage of the second heater 34.
Accordingly, a sufficient amount of heat necessary for melting the toner is supplied to the fixing belt 21, and the energy efficient fixing device 20 can be provided. In this embodiment, even if PID control is performed on the first heater 25 having a large rated wattage in a short control cycle, the on / off control is performed on the second heater 34 side, so that the occurrence of the flicker phenomenon is sufficiently reduced. Will be.

In this embodiment, one halogen heater is used as the first heater 25 for heating the fixing belt 21 (heating roller 23). However, a plurality of halogen heaters can be used as the first heater 25.
FIG. 5 is a configuration diagram showing another type of fixing device 20 provided with two first heaters 25 (halogen heaters). Here, of the two first heaters 25, one of the first heaters 25 heats the central portion in the width direction of the fixing belt 21, and the other first heater 25 has both end portions in the width direction of the fixing belt 21. Is to heat. In this way, the first heater 25 is divided in the width direction, and the combination of the first heaters 25 that are energized according to the size of the recording medium P is varied, so that the recording medium (small size paper) having a small size in the width direction is changed. ) Is prevented from overheating at both ends in the width direction of the fixing belt 21 (non-sheet passing region).

Here, when a plurality of first heaters 25 are installed, it is preferable that the rated wattage of one of the first heaters 25 is set larger than the rated wattage of the second heater 34. Accordingly, a sufficient amount of heat necessary for melting the toner is supplied to the fixing belt 21, and the energy efficient fixing device 20 can be provided.
Specifically, in the fixing device 20 shown in FIG. 5, the rated wattage of one first heater 25 (halogen heater) is 700 watts, and the rated wattage of the other first heater 25 (halogen heater) is 500 watts. The rated wattage of the second heater 34 (halogen heater) is set to 250 watts. The two first heaters 25 are both PID controlled (the control cycle is 400 [ms]), and the second heaters 34 are both on / off controlled (the control cycle is 1000 [ms]). The deviation of the control cycle of the two first heaters 25 is set to 200 [ms] (the deviation of the control cycle of the second heater 34 is arbitrarily set). The soft start interval of all the heaters 25 and 34 is set to 120 [ms] from the start of the control cycle. The target temperature of the fixing belt 21 and the pressure roller 31 is set to about 160 ° C. The conveyance speed (process linear velocity) of the recording medium P is set to about 140 mm / second.

In the fixing device 20 shown in FIG. 5, since the lighting start timing of the two halogen heaters 25 having a relatively large rated wattage is slightly shifted (1/2 of the control period), both heaters 25 Inrush current does not occur simultaneously. Therefore, if the sum of the rated wattages of the first heater 25 is the same, increasing the number of the first heaters 25 is more advantageous with respect to the flickering phenomenon than the one having the first heater 25.
As a result of an experiment conducted by the inventor of the present application, it was confirmed that a flicker phenomenon would occur if PID control was performed on the second heater 34 in addition to the two first heaters 25. On the other hand, by providing a plurality of first heaters 25 to reduce the occurrence of inrush current and further controlling the on / off of the second heater 34, the upper limit value of the inrush current generated in the first heater 25 can be afforded. It was confirmed that the flicker phenomenon was reliably reduced.

  As described above, in the present embodiment, the first heater 25 that heats the fixing belt 21 (fixing member) is PID-controlled, and the second heater 34 that heats the pressure roller 31 (pressure member) is turned on / off. Since the control is performed, the accuracy of the feedback control of the fixing temperature and the prevention of flickering of a lighting device such as a fluorescent lamp can be achieved without slowing down the warm-up time of the fixing device 20. Can do.

In this 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 exemplary embodiment, the present invention is applied to the fixing device 20 using the fixing belt 21 as a fixing member. Of course, the present invention can be applied. In these cases, the same effect as in 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. It is a block diagram which shows the fixing device of another form.

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 first heater,
31 Pressure roller (pressure member),
34 Second heater,
40A 1st temperature sensor (temperature detection means),
40B second temperature sensor (temperature detection means),
51 PID controller,
53 On-off controller, P recording medium.

Claims (8)

A fixing member that is heated by a plurality of first heaters and that melts and fixes the toner image to a recording medium;
A pressure member heated by a second heater and formed with a nip portion for conveying a recording medium in pressure contact with the fixing member;
With
Wherein the plurality of first heater based on the duty defined by any PID control power is supplied via the PWM drive circuit, the second heater is on-off control,
At least one of the plurality of first heaters is configured such that its rated wattage is greater than the rated wattage of the second heater,
The fixing device, wherein a control cycle of the plurality of first heaters is the same cycle, and the phases are shifted from each other . A temperature detecting means for detecting the temperature of the fixing member;
The first heater is subjected to PID control in which the duty of energization is varied so as to be a value calculated from the deviation between the detection result of the temperature detection means and a predetermined target temperature based on a predetermined algorithm. ,
The second heater has an energization duty of 100% when a detection result of the temperature detection means is smaller than a predetermined value, and an energization duty of 0% when the detection result of the temperature detection means is larger than a predetermined value. The fixing device according to claim 1, wherein on / off control is performed to achieve the above.   The fixing device according to claim 1, wherein the first heater and / or the second heater is soft-started or soft-stopped at each control cycle.   The fixing device according to claim 1, wherein a control cycle of the first heater is configured to be shorter than a control cycle of the second heater. The fixing device according to claim 1, wherein the first heater is a halogen heater. The fixing device according to claim 1, wherein the first heater and the second heater are energized when a recording medium is passed. The fixing device according to claim 1, wherein the fixing member is a fixing belt stretched around a plurality of roller members. An image forming apparatus comprising the fixing device according to claim 1.

Images