JP2014085430A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a variation in voltage at the start of energization to fixing member heating means and flicker of a fluorescent light due to the variation, and minimize an influence to fixing temperature control.SOLUTION: A fixing device uses soft start control to gradually heat heating means at the start of energization to the heating means for heating a fixing member, and provides energization to the heating means so as to change a method of the soft start control according to a non-energization time from the completion of the previous energization to the start of the subsequent energization to the heating means and compensate the increment and decrement of effective power caused by the change in the control method.

Description

  The present invention relates to a fixing device for fixing an unfixed image on a recording medium and an image forming apparatus including the fixing device.

  In a conventional image forming apparatus using an electrophotographic system, a recording medium on which an unfixed toner image is transferred is conveyed while being sandwiched between a fixing member and a pressure member, and unfixed toner is applied by applying heat and pressure. A fixing device that fixes an image on a recording medium is widely used.

  As this type of fixing device, there is a belt fixing device using an endless belt as a fixing member. 6 and 7 show an example of a conventional belt fixing device. The fixing device 150 shown in this figure includes a fixing roller 151, a pressure roller 152, a heating roller 154, a fixing belt 155, and the like in the apparatus housing. The heating roller 154 includes a fixing heater 153 including a plurality of heaters, a fixing belt 155 made of a heat-resistant elastic material is stretched between the heating roller 154 and the fixing roller 151, and a pressure roller facing the fixing roller 151. 152 forms a nip. A tension roller 157 is in contact with the inner surface of the fixing belt 155, and an appropriate tension is applied to the fixing belt 155.

  Such a belt fixing device is superior in thermal efficiency as compared with the heat roll type, but in order to further reduce the startup time and power consumption, a reduction in the heat capacity of the fixing device is required.

  Accordingly, a fixing device that heats the belt while sliding the belt on a pipe containing a heating means (heater), sends the recording member to the nip with the pressure member, and fixes the paper while nipping and transporting the belt is, for example, the following patent: Proposed in the literature. JP 2007-334205 A (Patent Document 1), JP 2008-158482 A (Patent Document 2), JP 2009-003410 A (Patent Document 3).

  With such a low heat capacity fixing device, the heater heater filament is also easy to cool, especially when printing a large size immediately after printing a small size and only the central heater is lit, the end heater that has been cooled until now Because it lights up, it is easy for flicker. Furthermore, since the member to be heated (fixing belt) is thin and the lighting state of the heater tends to appear as the temperature as it is, the temperature control tends to be disturbed particularly in the local heating method. If the heater passes through the heating portion when the heater is in the lit state, the heater can be warmed. However, if the heater passes through the heating portion when the heater is in the unlit state, the heater cannot be heated and appears as temperature unevenness in the circumferential direction. Especially in the case of PWM control, since the heater is repeatedly turned on and off, this problem (circumferential temperature unevenness) becomes more prominent, and the smaller the heated member, the shorter the time required for one round. Therefore, since the number of times of control per round is reduced, temperature control becomes difficult. When feedback control is performed to determine the heater lighting rate of the next control cycle from the detected temperature information in order to keep the fixing device at a constant temperature, if the circumferential temperature unevenness is large, it is detected and the heater lighting rate is detected. The problem that is caused by the feedback loop such as temperature divergence or temperature ripple not working well is often disturbed because the function of keeping the fixing device, which is the original purpose, is significantly hindered. Occur.

  Accordingly, the present invention solves the above-described problems in a fixing device with a reduced heat capacity, reduces temperature ripples, improves fixing properties, obtains a uniform gloss, and reduces power consumption. It is an object to provide a forming apparatus.

  According to the present invention, there is provided a fixing device for fixing an unfixed toner image by pressing a fixing member and a pressure member and passing a recording material carrying an unfixed toner image between the two members. In the fixing device using soft start control that gradually heats the heating unit when the energization of the heating unit that heats the fixing member is started, the energization is not performed from the end of the previous energization to the heating unit until the next energization start. The problem is solved by changing the control method of the soft start according to the time and energizing the heating means so as to complement the increase / decrease of the effective power due to the change of the control method.

  According to the fixing device and the image forming apparatus of the present invention, it is possible to prevent voltage fluctuation at the start of energization of the fixing heating means and flickering of the fluorescent lamp and thereby minimize influence on fixing temperature control. The temperature ripple can be reduced to improve the fixability, so that uniform gloss can be obtained and the power consumption can be reduced.

1 is a cross-sectional view illustrating a schematic configuration of a color printer which is an example of an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view illustrating a main configuration of the fixing device. FIG. 3 is a schematic diagram illustrating a heat generation area of a heater provided in the fixing device. It is a schematic diagram for demonstrating the control which supplements the electric power reduced by the soft start. It is a schematic diagram shown about the length of soft start time (section). FIG. 10 is a cross-sectional configuration diagram of an example of a conventional fixing device. It is a perspective view of the principal part of the fixing device.

Hereinafter, a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic configuration of a color printer which is an example of an image forming apparatus according to the present invention. The color printer shown in this figure is a color printer that can form a full-color image by adopting a tandem method, and four image forming units 1 (a, b, c, d) are arranged at substantially the center of the apparatus main body. Has been established. Each image forming unit 1 (a, b, c, d) has the same configuration except that the color of the toner to be handled is different from yellow, cyan, magenta, and black. In the following description, a, b, c in reference numerals are used. , D will be omitted as appropriate.

  Each image forming unit 1 includes a photosensitive drum 2 as an image carrier. Around the photosensitive drum 2, a charging unit 3, a developing device 4, a cleaning unit 5, and the like are disposed. Further, a transfer as a primary transfer unit is provided inside the intermediate transfer belt 7 so as to face each photosensitive drum 2. A roller 18 is provided. In each image forming unit 1, a part including the photosensitive drum 2, the charging unit 3, and the cleaning unit 5 is detachably provided as a process cartridge in the printer main body.

  The intermediate transfer belt 7 is stretched around the support rollers 15a and 15b and is driven to run counterclockwise in the drawing. A cleaning device 70 for cleaning the intermediate transfer belt is disposed outside the left support roller 15a. In the upper space of the intermediate transfer belt 7, toner bottles 20 (a, b, c, d) that store toners of yellow, cyan, magenta, and black are arranged.

  An optical writing device 6 is disposed below the tandem image forming unit in which the four image forming units 1 are arranged. The optical writing device 6 includes appropriate components such as a light source, a polygon mirror, an f-θ lens, and a reflection mirror, and applies laser light to the surface of each photoconductor 1 based on image data of each color toner. Irradiate while scanning.

  The lowermost part of the apparatus main body is configured as a paper feed unit, and a paper feed tray 50 for storing a recording medium is disposed. On the right side of the paper feed tray 50 is a paper feed roller 51 that feeds the papers stacked on the paper feed tray, and separates the papers one by one using a separation pad or the like. A registration roller 55 is provided above the paper feed roller 51 (on the downstream side in the paper conveyance direction). Above the registration roller 55, a transfer roller 18 as a secondary transfer unit is provided to face a support roller 15 b as a transfer counter roller to form a secondary transfer portion.

  A fixing device 30 is provided above the secondary transfer unit. Although the fixing device will be described in detail later, the fixing is performed by heating and pressurizing the recording medium on which the unfixed toner image is transferred in the secondary transfer unit. A paper discharge roller 60 is provided above the fixing device 30.

An image forming operation in the color printer configured as described above will be briefly described.
The photosensitive drum 2 of the image forming unit 1 is rotated in the clockwise direction in the figure by a driving unit (not shown), and the surface of the photosensitive drum 2 is uniformly charged to a predetermined polarity by the charging unit 3. The charged photoconductor surface is irradiated with laser light from the optical writing device 6, whereby an electrostatic latent image is formed on the photoconductor drum 2 surface. At this time, the image information exposed on each photosensitive drum 2 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. Each color toner is applied from the developing device 4 to the electrostatic latent image formed in this manner, and visualized as a toner image.

  Further, the intermediate transfer belt 7 is driven to run counterclockwise in the figure, and the respective color toner images are sequentially transferred from the photosensitive drum 2 to the intermediate transfer belt 7 by the action of the primary transfer roller 8 in each image forming unit 1. In this way, the intermediate transfer belt 7 carries a full-color toner image on its surface.

  Note that any one of the image forming units 1 can be used to form a single-color image or a two-color or three-color image. In the case of monochrome printing, image formation is performed using the rightmost black unit 1d in the drawing among the four image forming units.

  The residual toner adhering to the surface of the photosensitive drum after the toner image is transferred is removed from the surface of the photosensitive drum by the cleaning unit 5, and then the surface potential is initialized by the action of the static eliminator. Prepare for the next image formation.

  On the other hand, the paper is fed from the paper feed tray 50 and is sent out toward the secondary transfer position by the registration roller 55 in timing with the toner image carried on the intermediate transfer belt 7. The toner image on the surface of the intermediate transfer belt is collectively transferred onto the sheet by the secondary transfer roller 18 to which the transfer bias is applied. When the sheet on which the toner image has been transferred passes through the fixing device 30, the toner image is fused and fixed to the sheet by heat and pressure. The fixed paper is discharged by a paper discharge roller 60 to a paper discharge tray formed on the upper surface of the apparatus main body.

FIG. 2 is a cross-sectional view showing a main configuration of the fixing device 30.
As shown in this figure, a fixing belt 31, a nip forming member 32, a pressure roller 33, a pipe-shaped heat conductor 34, a fixing heater 35, a temperature detecting means 36, and the like are provided inside the unit of the fixing device. .

  The fixing belt 31 is a flexible endless belt (or film), and the pipe-like heat conductor 34 disposed in the loop of the fixing belt 31 is a heat conductor constituted by a thin metal pipe. It is attached to the support 37 and fixedly supported. A portion of the pipe-shaped heat conductor 34 facing the pressure roller 33 is provided as a concave portion recessed inward, and the nip forming member 32 is mounted and held in the concave portion. A pressure roller 33 is pressed against the nip forming member 32 with the fixing belt 31 interposed therebetween to form a fixing nip.

  A fixing heater 35 as a heat source is disposed inside the pipe-shaped heat conductor 34. In the present embodiment, a halogen heater (halogen lamp) is used as the fixing heater 35. Further, as will be described later with reference to FIG. 3, the fixing heater 35 of the present embodiment is composed of a plurality of heaters having different heat generation regions. When the fixing heater 35 generates heat, the fixing belt 31 is heated via the pipe-shaped heat conductor 34.

  Further, the pressure roller 33 is driven to rotate clockwise in FIG. 2 by a driving unit (not shown), and the fixing belt 31 is rotated counterclockwise in FIG. When the fixing belt 31 rotates, the fixing belt 31 rotates while sliding on the pipe-shaped heat conductor 34 and the nip forming member 32.

  The fixing heater 35 is divided into a central heater 35a and an end heater 35b, which are controlled using temperature sensors 36A and 36B, respectively. FIG. 3 shows the heat generation area of each heater, and the central heater 35a has a heat generation area (heat generation electric resistance portion) 35aw corresponding to the central portion in the paper width direction. Further, the end heater 35b has two heat generation regions (heat generation electric resistance portions) 35bw and 35bw corresponding to both end portions in the paper width direction. By changing the lighting DUTY of the heater depending on the size of the transfer paper, it is possible to suppress the end temperature rise and to save useless power. In addition, it is effective as a countermeasure against flicker by dividing it into two instead of one heater.

  For large size paper, both the central heater 35a and the end heater 35b are used in the same DUTY, but for small size transfer paper, the DUTY of the end heater is remarkably lowered to suppress heating and power consumption of useless portions. be able to. In this example, heating is performed from the inside of the fixing belt 31 by the pipe-shaped heat conductor 34, but non-contact heating (radiant heat from a halogen heater or the like) may be performed from the outside of the belt. In this example, the number of heaters is two, but the number of heaters may be increased.

  As shown in FIG. 3, the temperature detecting means 36 includes two temperature sensors 36A and 36B. The temperature sensor 36A is provided at a position corresponding to the heat generation area 33aw of the central heater 35a, and the end heater 35b is provided. A temperature sensor 36B is disposed at a position corresponding to the heat generation area 33bw on one side. In this example, a thermopile is used as the temperature sensor 36A, and a non-contact thermistor is used as the temperature sensor 36B. That is, the temperature of the central heater of the fixing heater 35 is controlled by a thermopile, and the end heater is controlled by a non-contact thermistor.

  A thermopile is a sensor with good time response that generates an electromotive force according to the temperature difference from the cold junction by condensing the infrared rays radiated from the object at the hot junction where many thermocouples are connected in series. is there. It has an atmosphere sensor to compensate for changes in the temperature of the thermopile itself (especially the temperature at the cold junction).

  The non-contact thermistor is a thermistor pair whose resistance value varies with temperature, and includes a detection sensor that detects the temperature of the object and an atmosphere sensor that detects the ambient temperature of the detection sensor. The detection temperature of the detection sensor can be corrected by the detection value of the atmosphere sensor. Non-contact thermistors are less expensive than thermopiles but are less responsive.

  In this example, since two fixing heaters are used, two temperature sensors are provided. However, when the number of heaters is further increased, the number of temperature sensors may be increased. Further, if there is a temperature sensor that can maintain the fixing property without using a thermopile or a non-contact thermistor, it may be used. If the distance between the fixing member and the non-contact sensor changes due to component tolerances and the deviation from the set value of the ambient temperature is unacceptable, adjust the distance between the non-contact sensor and the fixing member so that the ambient temperature falls within the set value. A spacer or the like may be inserted when the non-contact sensor is screwed.

  The nip forming member 32 and the pressure roller 33 are made of an elastic material such as rubber or a foamed material such as sponge so as to have an appropriate surface pressure and nip width. In this embodiment, the nip forming member 32 is a rubber member having a width of 10 mm, the pressure roller 33 has a hardness of about 60 Hs using a rubber having a thickness of about 3 mm on the surface, and a diameter of about 30 mm.

  The fixing belt 31 is an endless belt (or film) using a metal belt such as nickel or SUS or a polyimide resin. In order to give releasability, the belt surface has a fluororesin layer such as PFA or PTFE.

  The pipe of the pipe-shaped heat conductor 34 is made of aluminum, or a metal such as iron or stainless steel. The pipe-shaped heat conductor 34 of the embodiment is a circular shape having a diameter of 1 mm smaller than that of the fixing belt 31, but may be a square shape or other cross-sectional shapes. In the embodiment, the heating means (heat source) 35 uses a halogen heater, but it may be a carbon heater or induction heating means.

  In the fixing device 30 having the above configuration, by controlling the lighting rate of the fixing heater 35 according to the output of the temperature detecting means 36 (controlling the amount of power per unit time or the lighting time in the heating means), The temperature control necessary for the fixing process is performed.

  By the way, in the image forming apparatus of this embodiment, in order to suppress the inrush current when the fixing heater is turned on and to suppress voltage fluctuation (flickering of a fluorescent lamp connected to the same system power supply as the image forming apparatus), the fixing heater Soft start is performed to gradually increase the heater lighting time at the start of lighting. This soft start is a method of turning on the heater by repeatedly turning on and off the heater on the order of several milliseconds before becoming fully lit, gradually warming the heater, and then bringing the heater into a full fall state. If the soft start is not performed or the soft start time is short, the inrush current is large, causing the voltage fluctuation as described above. However, if the soft start time is too long, the heater temperature control is disturbed or the start-up time is delayed.

  The magnitude of the inrush current varies depending on the heater temperature (halogen heater filament temperature). By changing the soft start time according to the time from the previous lighting, it is possible to always set the optimum soft start time. Variation can be suppressed. However, since the effective power changes due to the change of the soft start, control is performed to output the complemented increase / decrease of the effective power.

  To supplement the description with reference to FIG. 4, after calculating the lighting request duty by feedback control, additional lighting is performed so as to store the power reduced by the soft start. That is, in the soft start section (while the soft start is being performed), there is a time during which the heater is turned off. By providing this supplementary lighting section, as shown in the figure, “lighting request time by feedback control” = “lighting time in soft start section” + “full lighting time” + “complementary lighting time” The decrease due to the start can be compensated. Then, as described above, the soft start time (in FIG. 4) according to the time from the previous lighting (the time during which the heater is extinguished from the previous lighting to the next lighting = the non-energization time to the fixing heating means). Since the control for changing the soft start period) is performed, the “complementary lighting time” is changed (controlled) in accordance with the changed soft start time.

  To change the soft start time, if the time since the last lighting is short, the soft start time (soft start interval in FIG. 4) is short, and if the time since the previous lighting is long, the soft start time (soft start interval in FIG. 4) Is controlled to be longer. That is, when the fixing heater (the filament in the case of a halogen heater) is warmed, the soft start interval can be shortened.

  Such control suppresses inrush power to the fixing heater 35 to prevent voltage fluctuations and resulting flickering of fluorescent lamps, and can minimize temperature ripple by reducing the influence on fixing temperature control. As a result, fixing properties can be improved, uniform gloss can be obtained, and power consumption can be reduced.

  FIG. 5 is a schematic diagram showing the length of the soft start time (section). The upper part (a) shows the case where the soft start time (section) is increased, and the lower part (b) shows the case where the soft start time (section) is shortened. The full lighting section (full lighting time) is the same in both cases.

  In order to shorten the soft start section, the method of reducing the number of lighting with the soft start lighting pattern as it is, or preparing multiple soft start lighting patterns, when the filament is cold, when it is slightly warm, warm You may use it properly for use. For example, when the turn-off time from the previous turn-on (the time during which the heater is turned off from the previous turn-on to the next turn-off) is within 1 second, when the turn-off time is 1 to 10 seconds, 10 seconds or more have elapsed. There is a way to change the soft start pattern used when Complementing the difference between the power to be lit and the effective power for each pattern, the required power can be output.

On the other hand, when the heater is away from the target temperature and the heater is 100% lit and fully lit, it is not necessary to perform soft start, so there is no need to supplement power.
Further, when the current temperature of the fixing member is a predetermined temperature or more away from the target temperature, the power supplement may not be performed for fail-safe. As a result, it is possible to prevent the power supply to the fixing device from being excessive and to ensure safety.

  By the way, if the soft start time (section) is the same every time, the same portion of the fixing member is heated in the soft start section every time. However, since the lighting state of the fixing heater is different between the soft start section and the full lighting section, the heating method of the fixing member (the fixing belt 31 in the present embodiment) is different. Therefore, it is not preferable that the same portion of the fixing member is heated in the soft start section every time. In this regard, in the present embodiment, as described above, the soft start time (section) is changed according to the time from the previous lighting, so that the same portion of the fixing member is not heated in the soft start section every time. The adverse effect on the fixing member can be suppressed.

  In the case where the fixing heater has two configurations corresponding to the paper size (in this embodiment, the fixing heater 35 heats the central heater 35a having a heating region corresponding to a small size paper and both side portions of the central heater. When the small size paper is fixed, only one heater is lit (only the central heater 35a in this embodiment). In this case, the other heater (the end heater 35b in the present embodiment) is not warmed, and when the large-size sheet is fixed immediately from this state, the influence of the inrush current of the other heater occurs.

  Therefore, when there are a plurality of fixing heaters, the time from the previous lighting (the time during which the heater is turned off from the previous lighting) is stored for each heater, and each heater is stored. It is preferable to change the soft start time (section) according to the time from the previous lighting every time.

  As a result, in the print mode in which the fixing of the large size paper is performed after the fixing of the small size paper as described above, if the end heater 35b corresponding to the small size paper has a long turn-off time (time from the previous lighting), the end. It is determined that the part heater 35b is cold, and the soft start time (section) is controlled to be longer than usual. Therefore, it is possible to suppress the influence due to the inrush current such as the flickering of the fluorescent lamp. In addition, when the turn-off time of the end heater 35b corresponding to the small size paper (time from the previous turn-on) is short, the soft start time (section) is made shorter than usual to minimize the influence on the fixing temperature control. can do.

In addition, it is preferable to set the minimum value and the maximum value of the soft start time (section) because safety can be ensured.
It is also preferable to set the minimum value and the maximum value of the complementary power when complementing the increase / decrease of the effective power because safety can be ensured.

  Further, voltage detection means for detecting the voltage applied to the fixing heater 35 may be provided, and the soft start time (section) may be changed according to the input voltage to the heating means detected by the voltage detection means. . Thereby, appropriate electric power supplement can be performed by the soft start according to the input voltage to a heater. Further, flickering of the fluorescent lamp can be prevented.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. For example, the number of heaters and heater positions (inside and outside of the belt loop) can be set as appropriate. Arrangement of the heating area of the heater is also arbitrary. Moreover, you may have a heating means in the pressurization side.

Further, the length of the soft start time (section) and the degree of change when changing the soft start time (section) can be set as appropriate. Any appropriate soft start pattern can be used.
The configuration of the image forming unit in the image forming apparatus is also arbitrary, and the order of colors in the tandem image forming unit is arbitrary. Configurations other than the tandem method are also possible. Further, the present invention can be applied not only to a color image forming apparatus but also to a monochrome apparatus. Of course, the image forming apparatus is not limited to a printer, and any form such as a copying machine, a facsimile machine, or a multifunction machine having a plurality of functions can be adopted.

DESCRIPTION OF SYMBOLS 1 Image forming unit 2 Photosensitive drum 7 Intermediate transfer belt 30 Fixing device 31 Fixing belt (fixing member)
32 nip forming member 33 pressure roller 34, pipe-shaped heat conductor 35 fixing heater 35 a central heater 35 b end heater 36 temperature detecting means 36 A central temperature sensor 36 B end temperature sensor

JP 2007-334205 A JP 2008-154822 A JP 2009-003410 A

Claims (9)

A fixing device for fixing an unfixed toner image by pressing a fixing member and a pressure member and passing a recording material carrying an unfixed toner image between the two members, and heating the fixing member In the fixing device using soft start control that gradually heats the heating unit when energization to the heating unit is started,
The soft start control method is changed according to the non-energization time from the end of the previous energization to the heating means to the next energization start, and the heating means is supplied to the heating means so as to complement the increase / decrease in effective power due to the control method change. A fixing device that is energized. The heating means comprises a plurality of heating means having a heating region according to the size of the recording material,
The non-energization time is stored for each heating means, and the soft start control method of each heating means is changed according to the non-energization time of each heating means. Fixing device.   A voltage detection means for detecting a voltage applied to the heating means is provided, and the control method of the soft start is changed according to the input voltage to the heating means detected by the voltage detection means. Item 3. The fixing device according to Item 1 or 2. The soft start control method change is a change in the time for performing the soft start,
The time for performing the soft start is shortened when the non-energization time is short, and the time for performing the soft start is prolonged when the non-energization time is long. The fixing device according to claim 1.   The fixing device according to claim 4, wherein a minimum value and a maximum value of the time for performing the soft start are set.   The fixing device according to claim 1, wherein a minimum value and a maximum value of the effective power complement are set.   A temperature detection unit that detects a temperature of the fixing member is provided, and the effective power is not supplemented when the temperature detected by the temperature detection unit is away from a target temperature by a predetermined temperature or more. Item 7. The fixing device according to any one of Items 1 to 6.   The fixing device according to claim 1, wherein the heating unit is a halogen heater. An image forming apparatus comprising the fixing device according to claim 1.

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