JP4423342B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device provided in an image forming apparatus.

  An image forming apparatus using an electrophotographic method usually includes a heating unit that presses and rotates a recording material and a toner composed of a resin, a magnetic material, a colorant and the like electrostatically supported on the recording material. It has a fixing device that melts and fixes it by applying heat and pressure while being nipped and conveyed by the pressure contact part (nip part) of the roller, endless belt body, etc.) and pressure means (roller, endless belt body, etc.) .

  Generally, a fixing device as an image heating device is used to heat and fix a toner image formed on a recording material by an electrophotographic recording method onto the recording material.

  The fixing device includes a heating roller having a heater that generates heat, and a pressure roller that presses against the heating roller and forms a nip portion that sandwiches and conveys the recording material. The toner image on the recording material is heated and pressed. It is fixed on the recording material.

  The recording material onto which the toner image has been transferred is guided by a guide and carried between a heating roller and a pressure roller, and the recording material is heated and pressed to melt and fix the toner of the toner image on the recording material. The toner image is fixed on the recording material.

  The conditions necessary for fixing are given by the roller temperature for melting the toner layer on the recording material, the time for the toner layer to pass between the heating roller and the pressure roller, and the pressure between the heating roller and the pressure roller. The time for the recording material to pass between the heating roller and the pressure roller is determined by the peripheral speed of the heating roller and the pressure roller and the nip width between the heating roller and the pressure roller.

  Further, in order to prevent the temperature rise of the non-sheet passing portion that occurs when the small size recording material is passed through the heater, the heat generation amount distribution in the longitudinal direction of the heater A4 and the heater B5 is differentiated into two types as shown in FIG. The heat generation amount peak positions based on the heat generation amount distribution are configured so as not to overlap each other.

  That is, in the case of a small-sized recording material with a narrow width during normal image formation, the temperature control is performed by reducing the lighting ratio of the heater B. In the case of a wide recording material, the heaters are controlled by sequentially generating heat in a time division manner. The outputs of the heater A4 and the heater B5 in FIG. 5 are about 800W for the heater A and about 400 to 600W for the heater B, respectively. This value is within a range that does not exceed the allowable power of the image forming apparatus even when the heater A4 and the heater B5 are simultaneously turned on at the time of warm-up, and can be sufficiently fixed only by the heater A4 even in the case of a small size recording material. Each output is determined from these conditions.

  On the other hand, in a color image forming apparatus that forms a color image by mixing a plurality of color toners, an unfixed toner image spreads in the nip portion if the hardness of the heating roller that contacts the toner image on the recording material is high. A clear color image cannot be obtained. For this reason, an elastic layer is provided on the core of the heating roller to prevent the toner image from spreading due to the elastic layer and to obtain a clear color image.

In the start-up operation of the fixing device having such a configuration, the heater A and the heater B are each fully lit at the maximum power, so that the heating roller can reach the preset start-up temperature in a short time.

  However, when a heating roller having an elastic layer is heated, the following problems occur. Since the thermal conductivity of the elastic layer is low, it takes time to reach the surface via the elastic layer after heat is applied to the core, so the heater is energized after the surface temperature reaches the target temperature. Even if it is finished, an overshoot occurs in which the internal heat is transferred to the surface with a delay. In order to reduce the overshoot, there is a method of reducing the heat generation amount, but in this case, the startup time becomes longer.

Therefore, as described in Patent Document 1, as a method for preventing overshoot without extremely increasing the start-up time, the main heater is forcibly turned off when the surface temperature of the heating roller reaches a predetermined temperature. Then, there is a method in which only the sub-heater is operated and an overshoot is generated at the center when only the sub-heater is operated to keep the temperature distribution uniform.
JP 62-124581 A

  However, the amount of overshoot greatly depends on the amount of heat supplied to the heating roller. That is, if the heater lighting time is long, the amount of heat accumulated in the heating roller increases and the amount of overshoot also increases. Conversely, if the heater lighting time is short, the overshoot amount is small. Therefore, when the temperature of the heating roller is high, such as during the recovery operation after jam processing, it takes a short time for the surface temperature of the heating roller to reach the target temperature. Even if it is turned on, the amount of overshoot is small. Therefore, regardless of the surface temperature of the heating roller, if the main heater is forcibly turned off when the predetermined temperature is reached, the overshoot amount is small even if the main heater is turned on. Regardless, as a result of the start-up operation using only the sub-heater, a problem that requires time for recovery occurs.

  An object of the present invention is to raise the temperature to enable image formation in a short time.

  Another object of the present invention is to reduce the amount of overshoot after the start-up operation is completed.

In order to achieve the above object, the present invention provides:
A fixing member and a pressure member for fixing the toner image on the recording material at the pressure contact portion;
A first heating member having a higher ability to heat a central region than both axial end regions of the fixing member;
A second heating member having a higher ability to heat both end regions than the central region of the fixing member;
A temperature detector for detecting the temperature of the central region of the fixing member;
Control means for controlling energization to the first heating member and the second heating member in accordance with the output of the temperature detector;
In a fixing device having
When performing a start-up operation for raising the temperature of the fixing member to a fixing temperature at which fixing is possible,
When the detected temperature when starting the startup operation is lower than a predetermined temperature,
Energizing the first and second heating members until the detected temperature reaches a set temperature lower than the fixing temperature,
After the detected temperature reaches the set temperature, the energization to the first heating member is stopped and the energization to the second heating member is continued.
When the detected temperature when starting the start-up operation is higher than the predetermined temperature,
The first and second heating members are energized until the detected temperature reaches the fixing temperature.

  According to the present invention, the temperature can be raised to a value that enables image formation in a short time.

  In addition, the amount of overshoot after the start-up operation is completed can be reduced.

  DETAILED DESCRIPTION Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

(First embodiment)
FIG. 1 is a cross-sectional view illustrating a cross-sectional configuration of a fixing device 1 according to an embodiment. In FIG. 1, the fixing device 1 includes a heating roller 2 as a fixing member (heating body) and a pressure roller 3 as a pressure member (pressing body) that comes into pressure contact with the heating roller 2. The fixing device 1 is heated together with the heating roller 2 in a state where the surface of the heating roller 2 is heated to a predetermined temperature by two heaters (heater A4 and heater B5) as a plurality of heating members (heating elements) in the heating roller 2. By passing the recording material carrying the toner image between the pressure rollers 3 (nip) (clamping and transporting), the toner image side (upper surface side) of the recording material is heated and pressed to melt and fix the toner, and the sheet A toner image is fixed on the top.

  The heating roller 2 is a hollow cylindrical body, and uses a metal core with a hollow thickness of 3.0 mm or less, and a release resin layer such as PTFE is provided on the surface thereof. And heater A4 and heater B5 are arranged in the metal core. Further, a thermistor 6 as a temperature detecting means (temperature detecting body) is in contact with the vicinity of the axial center of the surface of the heating roller 2 to measure the temperature of the surface of the heating roller 2.

  The heat generation amount distribution (hereinafter referred to as heat distribution) in the axial direction of the heater A4 as the first heating member (first heating element) and the heater B5 as the second heating member (second heating element) is shown in FIG. Use the same as shown in the previous section. In the present embodiment, a halogen heater is used as the heating element.

  That is, the heater A4 has a peak position (hereinafter referred to as a heat distribution peak) of a calorific value with a high heating capability at a central portion (central area) corresponding to a small size recording material of 60 to 85% with respect to the maximum width. Hereinafter, the heat distribution of the heater A4 is referred to as a center heat distribution height. The heater B5 has a heat distribution peak at both ends in the axial direction (both ends in the axial direction) other than the heat distribution peak of the heater A4. Hereinafter, the heat distribution of the heater B5 is referred to as end heat distribution height. The heat distributions of the heaters A4 and B5 are configured so that the heat distribution peaks do not substantially overlap. The heaters A4 and B5 are controlled by energization control means that controls energization of the heaters.

  The heater A4 and the heater B5 are simultaneously heated during warm-up and recovery from the sleep mode.

  Further, when an image is formed on a small-sized recording material having a small width during normal image formation, the temperature control is performed using only the heater A4, thereby generating a temperature rise at the axial end of the surface of the heating roller 2. To prevent.

  On the other hand, when forming an image on a wide recording material during normal image formation, both the heater A4 and the heater B5 are used and controlled by sequentially generating heat in a time division manner.

  The heater output in the present embodiment is the same as the conventional one, the output of the heater A4 is 800W, and the output of the heater B5 is 400W.

  The heater sequence used during warm-up, recovery from sleep mode, and transition from standby to image formation (generically referred to as “image ready state”) in the present embodiment, and the heating roller 2 at that time FIG. 2 shows the temperature distribution and the roller shape of the heating roller 2.

  In this embodiment, four types of set temperatures are provided during warm-up, sleep mode, and recovery from the standby state.

  The fixing temperatures in which copying can be started (fixed) are the first set temperature TT, the second set temperature T1, the third set temperature T2, and the fourth set temperature T3, and the relationship of T3 <T1 <TT <T2 is satisfied. Have. For example, in the present embodiment, the first set temperature TT = 190 ° C., the second set temperature T1 = 185 ° C., the third set temperature T2 = 195 ° C., and the fourth set temperature T3 = 170 ° C. are set. In the present embodiment, the temperature is adjusted at 190 ° C. during fixing, and the temperature is adjusted at 190 ° C. during standby.

  In the present embodiment, at the time of power-on or recovery from the sleep mode, when the temperature of the heating roller 2 is sufficiently lowered (for example, the early morning when the apparatus is completely cooled at night (hereinafter referred to as “the first morning”)), jam processing The heater sequence is changed when the temperature of the heating roller 2 is hot to some extent, such as when the power is turned on immediately after the power is turned off. The heater sequence is changed depending on whether the temperature of the heating roller 2 is higher or lower than the fourth set temperature (predetermined temperature) T3.

  First, when the temperature of the heating roller 2 measured by the thermistor 6 such as turning on the power in the morning or recovering from the sleep mode is lower than the fourth set temperature T3, the following heater sequence is used.

  As shown in FIG. 2A, both the heater A4 and the heater B5 are turned on. After that, when the temperature of the heating roller 2 reaches the second set temperature T1, the heater A4 having the central heat distribution height is forcibly turned off by the power supply stop portion as the power supply stop means, and the end heat distribution height is immediately after that. Temperature control is started so as to maintain the third set temperature T2 only with the heater B5.

  At this time, since there is a relationship of T1 <TT <T2, after reaching the second set temperature T1, the temperature of the heating roller 2 is raised to the third set temperature T2 while the heater B5 remains ON. In the middle of the increase, the temperature reaches the first set temperature TT which is ready to start copying, and image formation for copying and printing can be started anytime after reaching the first set temperature TT.

  The temperature distribution of the heating roller 2 at this time changes with time as shown in FIG. That is, when the temperature reaches the second set temperature T1, as shown in the temperature distribution 1, the temperature of the heating roller 2 is uniform in the foreground or in the end temperature sag state.

  When the first set temperature TT is reached, as shown in the temperature distribution 2, the temperature at the end of the heating roller 2 in the axial direction is higher than the temperature at the center in the axial direction of the heating roller 2 due to the heat distribution at the end of the heater B 5. Is also relatively high.

The roller shape of the heating roller 2 when the first set temperature TT is reached is as shown in the roller shape 2 of FIG. 2C. The core metal at the axial end of the heating roller 2 is heated and expanded, and the heating roller 2 is heated. As a result, the inverted crown shape is moderately formed.

  The amount of increase in the reverse crown that can be achieved by this thermal expansion can be finely adjusted by the temperature difference condition between the axial end and the axial central portion as compared with the formation of the reverse crown by machining. An optimum inverted crown shape that can be applied only when the heater B5 is simultaneously turned on can be formed. In the present embodiment, a crown amount of about 50 μm can be formed by setting the temperature difference between the axial end and the axial center to about 10 ° C.

  If the reverse crown shape formed by processing is formed only for the purpose of fixing wrinkles when the two heaters A4 and B5 are turned on at the same time without using the heater sequence of this embodiment, In consideration of the decrease in the amount of reverse crown during warm-up, an excessively large reverse crown shape must be formed from the beginning. It is thought that the crown amount that prevents both the fixed wrinkles of harmful effects due to the decrease in the amount is lost.

  Therefore, by using the heater sequence of the present embodiment, when the two heaters A4 and B5 such as warm-up and recovery are simultaneously turned on, the optimal crown amount of the heating roller 2 is not increased by processing. An inverted crown shape could be formed, and fixing wrinkles could be prevented without any adverse effects such as trailing edge splashes.

  After reaching the first set temperature TT, the temperature adjustment based on the third set temperature T2 is performed only by the heater B5 until the predetermined time t1 elapses. In the control at this time, the heater B5 continues to be turned on until the third set temperature T2 is reached, and the heater B5 has a high end portion heat distribution. It becomes more gradual than when A4 is ON.

  As a result, the end temperature of the heating roller 2 remains maintained higher than the center temperature until the third set temperature T2 is reached, so that the reverse of the roller shape 3 in FIG. The crown shape can be maintained.

  Similarly, after the surface temperature of the heating roller 2 reaches the third set temperature T2, only the ON / OFF control of the heater B5 is performed, and the temperature is adjusted by the heater B5 having the high end heat distribution. The end temperature of 2 is maintained higher than the center temperature, and the inverted crown shape can be maintained.

  Therefore, the reverse crown shape can always be used as the roller shape of the heating roller 2 until the predetermined time t1 elapses after the first set temperature TT at which copying can start, and recovery from the warm-up or sleep mode in the morning. It is possible to suppress the disappearance of the crown shape due to time and the like, and the fixing wrinkles due to the formation of the regular crown shape. Here, the predetermined time t1 is 3 to 5 minutes in the present embodiment.

  Further, by using the heater sequence of the present embodiment, the heater A4 having a high center heat distribution can be turned on for a relatively long time without being thinned as in the conventional case during warm-up and recovery. While maintaining the roller shape in the inverted crown shape, the warm-up and recovery time could be greatly shortened.

Further, when the surface temperature of the heating roller 2 at the start of the start-up operation is low, the amount of heat supplied to the heat roller 2 becomes extremely large because it takes a long time to heat the heat roller 2 until the start-up end temperature. . Therefore, even if the main heater is turned off, the amount of overshoot that causes internal heat to appear outside is large, so by using such a sequence, the subsequent overshoot amount can be reduced even after the start-up operation is completed. As a result, the temperature unevenness in the longitudinal direction of the heating roller 2 can be made uniform.

  Next, when the temperature of the heating roller 2 is higher than the fourth set temperature T3 after the jam processing or when the power is turned on immediately after the power is turned off, the following sequence is used.

  Both heater A4 and heater B5 are turned ON. Thereafter, when the temperature of the heating roller 2 reaches the first set temperature TT, copying or printing can be started anytime. The sequence after the start of copying is the same as the above-described heater sequence when the temperature of the heating roller 2 is lower than the fourth set temperature T3. That is, even when the temperature T1 at which the main heater is forcibly turned off is reached, energization to the main heater is continued, and the temperature at which the main heater is forcibly turned off is changed to a temperature TT higher than T1 by the temperature changing means. Is.

  This sequence is disadvantageous in that if the heater sequence is performed when the temperature of the heating roller 2 is lower than the fourth set temperature T3 from a state where the heating roller 2 is hot to some extent, the warm-up time is delayed. Because.

  That is, even if the heater A4 and the heater B5 are simultaneously turned on from a state where the heating roller 2 is hot to some extent, the second set temperature T1 is reached immediately, so the lighting time of the main heater is short and the overshoot amount is small. Further, even when the image can be formed, the start-up operation is continued with only the heater B, so that the temperature unevenness of the heating roller due to overshoot can be prevented.

  Further, when the heating roller 2 is hot to some extent, the temperature of the heating roller 2 immediately reaches the first set temperature TT, and then the temperature is adjusted by the heater B5. Sag is unlikely to occur and the reverse crown amount of the heating roller 2 does not decrease, so that fixing wrinkles can be sufficiently suppressed.

  The heater sequence used during warm-up, recovery from sleep mode, and transition from standby to image formation will be described with reference to the flowchart of FIG.

  In FIG. 3, the detected temperature TH at the start of the starting operation is the surface temperature of the heating roller 2 detected by the thermistor 6.

  First, the detected temperature TH of the heating roller 2 is detected by the thermistor 6 in S11, and the process proceeds to S12.

  In S12, it is checked whether or not the detected temperature TH <the fourth set temperature T3, and it is determined whether or not the temperature of the heating roller 2 at the start is hot. If the detected temperature TH <the fourth set temperature T3 in S12, the process proceeds to S13 which is the first start-up mode, and both the heater A4 and the heater B5 are turned on to heat the heating roller 2, and the process proceeds to S14. If the detected temperature TH is not the fourth set temperature T3 in S12, the process proceeds to S111 in the second startup mode, but S111 and S112 will be described later.

  In S14, it is checked whether or not the temperature of the heating roller 2 has reached the second set temperature T1. If the temperature of the heating roller 2 has not reached the second set temperature T1, the process returns to S13 and both the heater A4 and the heater B5 are turned on to heat the heating roller 2. If the temperature of the heating roller 2 has reached the second set temperature T1, the process proceeds to S15, the heater A4 is turned off, and the temperature is adjusted so that the temperature of the heating roller 2 is maintained at the third set temperature T2 only by the heater B5. And proceed to S16.

In S16, the detected temperature TH ≧ first set temperature TT is checked to determine whether the temperature of the heating roller 2 has reached the first set temperature TT. If the temperature of the heating roller 2 reaches the first set temperature TT, the process proceeds to S17, the copy start enable signal is turned on, the process proceeds to S18, and the temperature is adjusted at the third set temperature T2 only by the heater B5, and the process proceeds to S19. move on. If the temperature does not reach the first set temperature TT, the process returns to S15, and the temperature is adjusted at the third set temperature T2 by the heater B5.

  In S19, it is checked whether or not a copy start signal has been input. If it has been input, the heater sequence of the present embodiment ends. If not input, the process proceeds to S110, where it is checked whether or not a predetermined time t1 has elapsed from the first set temperature TT. If not, the process returns to S18 and the temperature is adjusted again at the third set temperature T2 by the heater B5. In this case, the heater sequence according to the present embodiment ends.

  Among the above, S111, which proceeds when the detected temperature TH is not the fourth set temperature T3 in S12, is a heater sequence when the temperature of the heating roller 2 at the time of start is relatively high. If the detected temperature TH <the fourth set temperature T3 is not satisfied in S12, the process proceeds to S111, both the heater A4 and the heater B5 are turned on, and the process proceeds to S112.

  In S112, if the temperature of the heating roller 2 has reached the first set temperature TT, the process proceeds to S17, the copy start signal is turned on, and the process proceeds to S18. If the temperature of the heating roller 2 does not reach the first set temperature TT in S112, the process returns to S111, and both the heaters A4 and B5 are turned on again.

  Even when the detected temperature TH <the fourth set temperature T3 is not satisfied, the sequence after S17 is the same as the heater sequence when the temperature of the heating roller 2 at the start is relatively low.

(Outline of image forming apparatus)
The overall configuration and operation of the image forming apparatus in which the fixing device 1 of this embodiment is used will be described with reference to FIG. FIG. 4 is a schematic sectional view of the image forming apparatus.

  On the upper surface of the image forming apparatus 40, an automatic document reading unit 41 is located. The automatic document reader 41 inverts both sides of the document, automatically feeds it onto the platen glass, reads the image information of the document on the platen glass by a light receiving element such as a CCD, and outputs it as an image signal.

  Next, an image signal output from the automatic document reading unit 41 is converted into a recording signal suitable for laser recording and processed by an image processing unit (not shown).

  The laser optical system 42 emits light according to a recording signal, performs optical scanning on the rotating photosensitive drum 43, and forms a latent image on the photosensitive drum 43 charged by the primary charger 45.

  Here, a primary charger 45, a surface potential meter 50, a developing device 46, a post charger 47, a transfer charger 51, a separation charger 52, a cleaner 48, and a pre-exposure lamp 49 provided on the photosensitive drum 43 and its peripheral portion. The image forming unit 44 is configured from the above.

  The image forming unit 44 develops the latent image on the photosensitive drum 43 into a toner image. Thereafter, the toner image is transferred from the photosensitive drum 43 onto a recording material fed in synchronization with one of the paper feeding units 9a to 9d. As a result, the toner image is carried on the recording material P.

  In the single-sided image forming mode, the recording material P carrying the transferred toner image T is transported by the transport belt 53 and fixed by the fixing device 1, and then discharged from the paper discharge unit 56.

  Although not shown, the paper discharge unit 56 is provided with a finisher that enables finishing such as stapling, and a staple process is performed for each of the plurality of discharged recording materials P.

  In the double-sided image forming mode, the recording material P on which the single-sided image is formed after the fixing of the image on the one side of the recording material P by the fixing device 1 is conveyed to the reverse conveying unit 60 and reversed by the reversing unit 31. The toner image T is retransmitted to the image forming unit 44 through the reverse conveyance path for conveying the reversed recording material P, and the toner image T is transferred to the back surface of the recording material P.

  Unlike the method in which the recording material P on which the single-sided image has been formed is accumulated in the stack and discharged after the stacking, the reverse conveying unit 60 immediately conveys the recording material P on which the single-sided image is formed without providing the stack to the image forming unit 44. This is a “non-stack type” reversing conveyance unit. This type of non-stack type reversing conveyance unit has an effect of eliminating a loss in the stack portion.

  Further, in the stack type reversal conveyance unit, the recording material P is accumulated in the stack and is primarily placed. Therefore, the recording material P is not nipped by any roller, and the recording with the single-sided image formed immediately after fixing is performed. Due to the curl that always occurs in the material P, jamming or double feeding at the mounting portion such as a stack occurred very often. However, since the recording material P is always nipped between the rollers in the non-stack type reversing conveyance unit, the cause of the decrease in the feeding reliability in the stack type is greatly reduced.

  The image forming apparatus 40 employs a method of alternately performing image formation on the first surface and image formation on the second surface of the recording material P in order to improve the productivity of the non-stack type double-sided image formation. Yes.

  As described above, according to the present embodiment, the energization to the main heater is forcibly stopped in the middle of the start-up operation, and when the temperature of the heating roller 2 is high, overshooting is prevented while preventing overshoot. Can be launched in time.

(Second embodiment)
A further embodiment will be described with reference to FIG. The configuration of the fixing device of this embodiment is the same as that of the first embodiment.

  The set temperatures in the present embodiment are the first set temperature TT = 190 ° C., the second set temperature T1 = 180 ° C., the third set temperature T2 = 195 ° C., the fourth set temperature T3 = 100 ° C., and the fifth set temperature. T4 = 170.degree. C., sixth set temperature T5 = 185.degree. C., the image-forming temperature is 190.degree. C., and the temperature is adjusted to 190.degree. C. during the fixing operation. Further, the temperature is controlled at a temperature of 190 ° C. during standby.

  In FIG. 6, the detected temperature TH at the start of the starting operation is the surface temperature of the heating roller 2 detected by the thermistor 6.

  First, the detected temperature TH of the heating roller 2 is detected by the thermistor 6 in S21, and the process proceeds to S22.

In S22, it is checked whether or not the detected temperature TH <the fourth set temperature T3, and it is determined whether or not the temperature of the heating roller 2 at the start is hot. If the detected temperature TH <the fourth set temperature T3 in S22, the process proceeds to S23 in the first start-up mode, and both the heater A4 and the heater B5 are turned on to heat the heating roller 2, and the process proceeds to S24. If the detected temperature TH is not the fourth set temperature T3 in S24, the process proceeds to S23, and energization of the heaters A and B is continued until the detected temperature TH is less than the fourth set temperature T3. If this condition is satisfied, the process proceeds to S25 and the heater A is forcibly turned off. Then, S25 is continued until the condition of S26 is satisfied. When the detected temperature reaches T1, the state shifts to an image formable state. Note that the flow of S27, S28, S29, and S210 is the same as the flow of S17, S18, S19, and S110 of the first embodiment. However, in the present embodiment, the predetermined time t2 from the arrival of T1 is a time shorter than t1, for example, 1 minute.

  In S22, it is checked whether or not the temperature of the heating roller 2 has reached the fourth set temperature T3. When the temperature of the heating roller 2 has reached the fourth set temperature T3, the process proceeds to S213, and the magnitude relationship between the detected temperature and T4, which is a temperature lower than T3, is compared. When the detected temperature TH is higher than T4, the process proceeds to S211 in the second startup mode, and when the detected temperature TH becomes higher than TT in S212, the process proceeds to S27. If the detected temperature TH is lower than T4 in S213, it is determined that the heating roller 2 is slightly warmed.

  That is, if energization is continued up to S27 in both the heater A and the heater B in this state, the overshoot amount increases, and in order to make the temperature of the heating roller 2 uniform, the predetermined time after reaching TT must be lengthened. Goodbye. On the other hand, the temperature of the heating roller can be made uniform even when the predetermined time is set short by increasing the number of steps as in the present embodiment.

  In the present embodiment, a third start-up mode is further provided. In this mode, the set temperature for forcibly turning off the heater A is higher than the set temperature in the first start-up mode than in the first start-up mode. Therefore, T5 is newly provided in S215, and when T5 is reached, the main heater is forcibly turned off in S216, and the temperature is controlled only by the heater B, thereby causing an overshoot during this time. Even if the predetermined time after arrival is shortened, the temperature of the heating roller 2 can be made uniform.

  According to the present embodiment, in the configuration in which energization to the main heater is forcibly stopped during the start-up operation, when the temperature of the heating roller 2 is high, overshoot is prevented and the start-up is completed. Time can be shortened.

(Third embodiment)
A further embodiment will be described with reference to FIG. The configuration of the fixing device of this embodiment is the same as that of the first embodiment.

  In the first embodiment and the second embodiment, the temperature at which the heater A, which is the main heater, is forcibly turned off is switched based on the temperature detected by the thermistor during the start-up operation. In the embodiment, the temperature at which the heater A is forcibly turned off is switched using the temperature increase ratio.

  Here, the set temperature used in this embodiment will be described. The fixing temperature at which copying can be started is a first set temperature TT, a second set temperature T1, a third set temperature T2, and a fourth set temperature T3, and has a relationship of T3 <T1 <TT <T2. For example, in the present embodiment, the first set temperature TT = 190 ° C., the second set temperature T1 = 185 ° C., the third set temperature T2 = 195 ° C., and the fourth set temperature T3 = 170 ° C. are set. In the present embodiment, the temperature is adjusted at 190 ° C. during fixing, and the temperature is adjusted at 190 ° C. during standby.

  In FIG. 7, the detected temperature TH at the start of the starting operation is the surface temperature of the heating roller 2 detected by the thermistor 6.

  First, the detected temperature TH of the heating roller 2 is detected by the thermistor 6 in S31, and the process proceeds to S32.

In S32, it is checked whether or not the detected temperature TH <100 ° C., and it is determined whether or not the temperature of the heating roller 2 at the start is hot. When the temperature of the heating roller 2 is higher than 100 ° C., the process proceeds to S312 of the second startup mode, and the lighting of the heater A and the heater B is continued until the detected temperature reaches TT (S313). When the detected temperature TH reaches TT, the process shifts to S38, shifts to an image formable state, and then shifts to S39. In the present embodiment, S38, S39, S310, and S311 that are flows after S38 are the same as S17, S18, S19, and S110 of the first embodiment.

  On the other hand, if TH is lower than 100 ° C. in S32, this time, in S33, the time required from the start-up operation start to a predetermined temperature, that is, 20 ° C. in the present embodiment, is confirmed. That is, when the rising time is short, it is considered that the inside of the heating roller 2 is sufficiently warm even if the temperature of the surface of the heating roller 2 is lowered. Therefore, even if the heater A and the heater B are turned on for a long time, the image formation temperature is reached in a short time, so that the amount of overshoot is small and it can be started up in a short time. Thus, in the present embodiment, the temperature at which the heater A is forcibly turned off is switched according to the rate of temperature increase.

  Thus, when the temperature increase rate of the heater is large in S33, it is determined that the startup time is short, and the process proceeds to S312 in the second startup mode, and the same flow as described above passes. . On the other hand, if the rate of temperature increase that takes 30 seconds or longer in S33 is small, it is considered that the lighting time of the heater A is prolonged, and the temperature at which the heater A is forcibly turned off is lowered. , Take longer time to overshoot. As described above, the heater A and the heater B are turned on until the detected temperature TH reaches T1 in S34 of the first start-up mode, and when the detected temperature TH reaches T1, the heater A is forcibly turned off. (S36), and the process proceeds to S37. Thereafter, heating of only the heater B is continued until the detected temperature TH reaches TT. When the detected temperature TH reaches TT, the process proceeds to S38.

  In this way, even if judged not only by the detected temperature but also by the rate of temperature rise, in a configuration in which energization to the main heater is forcibly stopped during the start-up operation, when the temperature of the heating roller 2 is high, While preventing overshoot, the time to start-up can be shortened.

  Further, the predetermined times t1 and t2 from the set temperature and the arrival of TT in the embodiment are not limited to the values in the embodiment, and there is no problem even if other values are appropriately used.

  In the embodiment, the configuration using the halogen heater as the heating element has been described, but the present invention is not limited to this.

  For example, there is no problem even if the present invention is used for a configuration of an induction heating system in which a heating element itself generates heat by an eddy current generated in a conductive layer of the heating element by using a coil that generates a magnetic field. FIG. 8 is a schematic cross-sectional view of a heat fixing device 1106 using the heating device of the present invention as a heat source. The heat fixing device 1106 of this example carries an unfixed toner image t on a fixing nip portion N which is a pressure contact portion between a fixing roller 11 as a heating body to be induction-heated and a pressure roller 12 as a pressure member. This is a heat roller type apparatus that introduces a recording material P that is held and conveys it, and fixes the unfixed toner image t on the surface of the recording material P by heat and nip pressure of the fixing roller 11 at the fixing nip N. .

  The fixing roller 11 is an iron cored bar cylinder that is a magnetic metal member having an outer diameter of 40 mm and a thickness of 0.7 mm. The surface of the fixing roller 11 is made of a fluororesin such as PTFE or PFA in order to improve releasability. You may provide a 10-50 micrometers thick layer in an outer peripheral surface.

  Both ends of the fixing roller 11 are rotatably supported and attached to the fixing unit frame, and are rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed by a driving system (not shown).

  The pressure roller 12 includes a hollow metal core 12a and an elastic layer 12b which is a surface releasable heat-resistant rubber layer formed on the outer peripheral surface thereof. The pressure roller 12 is arranged in parallel to the fixing roller 11 below the fixing roller 11, and both ends of the hollow core metal 12a are rotatably supported by a fixing unit frame (not shown) and supported. Further, the biasing mechanism (not shown) using a spring or the like is pushed up and biased in the direction of the rotation axis of the fixing roller 11 to press the lower surface of the fixing roller 11 with a predetermined pressing force.

  Due to the pressure roller 12 being pressed against the fixing roller 11, the elastic layer 12 b is elastically deformed at the pressure contact portion with the fixing roller 11, and a fixing nip portion having a predetermined width as a heated material heating portion is formed between the elastic layer 12 b and the fixing roller 11. N is formed. In this example, the pressure roller 12 is loaded with a total pressure of about 304 N (about 30 kg weight), and the nip width of the fixing nip portion N in that case is about 6 mm. The pressure roller 12 is driven to rotate by the contact friction force at the fixing nip portion N as the fixing roller 11 rotates. However, the total pressure and the nip width are only examples, and other values may be used.

  Reference numeral 19 denotes an induction coil assembly as magnetic flux generation means, which includes an induction coil 13, a magnetic core 14, a coil holder 15, and the like. The induction coil 13 is covered with a covering made of a heat resistant material such as polyimide or polyamideimide. This coil holder 15 is a member having a semi-circular cross section made of heat-resistant resin such as PPS, PEEK, phenol resin, etc., and an induction coil 13 wound in a boat shape inside the coil holder 15 and a thickness of 4 mm. An induction coil assembly 19 is formed by containing a magnetic core 14 in which a flat ferrite is combined with a T type. The outer surface of the coil holder 15 is disposed so as to face the inner surface of the fixing roller 11. The induction coil 13 is in close contact with the induction coil assembly 19.

  The induction coil assembly 19 is held by the stay 16 and inserted into the hollow portion of the fixing roller 11, and the both ends of the stay 16 are fixed to a fixing unit frame (not shown) with the semicircular arc surface side of the coil holder 15 facing downward. And supported. The induction coil assembly 19 is disposed so that a gap is provided between the induction coil assembly 19 and the fixing roller 11.

  Next, the heating operation will be described. The fixing roller 11 is rotationally driven, the pressure roller 12 is driven to rotate, and an alternating current of 10 to 100 kHz is applied from the excitation circuit 111 to the induction coil 13. The magnetic field induced by the alternating current causes an eddy current to flow through the inner surface of the fixing roller 11 that is a conductive layer, and generates Joule heat. That is, the fixing roller 11 is induction-heated.

  The temperature of the fixing roller 11 is detected by a temperature sensor 17 such as a thermistor disposed so as to contact the surface of the fixing roller 11, and the detected temperature information (detection signal) is input to the control circuit 112. The control circuit 112 automatically adjusts the temperature of the fixing nip N to a predetermined fixing temperature so that the surface temperature of the fixing roller 11 becomes a predetermined constant temperature based on the detected temperature information inputted. As described above, the power supply from the excitation circuit 111 to the induction coil 13 is increased or decreased.

  Thus, the recording material P carrying the unfixed toner image t is conveyed in a state in which the fixing roller 11 and the pressure roller 12 are rotated and the fixing roller 11 is induction-heated and adjusted to a predetermined temperature. Guided by the guide 18 and introduced into the fixing nip portion N to be nipped and conveyed, the unfixed toner image t is fixed to the surface of the recording material P by heat and pressure by the heat of the fixing roller 11 and the nip pressure. The recording material P exiting the fixing nip portion N is separated from the surface of the fixing roller 11 and discharged and conveyed. Reference numeral 110 denotes a recording material separation claw disposed on the recording material outlet side of the fixing nip N so as to contact or be close to the surface of the fixing roller 11.

  In this case, the amount of heat generated at the center of the heating element is greater than the amount of heat generated at the end of the coil, and the amount of heat generated at the end of the first coil and the heating element is greater than the amount of heat generated at the center. The second coil is configured. With this configuration, the heater A in the above-described embodiment corresponds to the first coil, and the heater B corresponds to the second coil. The first coil is energized using the flowchart described above. When the temperature for forcibly turning OFF is set and the temperature of the heating body during the start-up operation increases, the temperature for forcibly turning off the energization of the first coil is further increased. With such a configuration, even in a heating device using an induction heating method, the fixing roller can be used even if the power supply to the main heater is forcibly stopped during the start-up operation by using the present invention. When the temperature of 11 is high, it can be started up in a short time while preventing overshoot.

  As described above, according to the present invention, in the configuration in which energization to the main heater is forcibly stopped during the start-up operation, when the temperature of the fixing rotator is high, overshooting is prevented in a short time. Can be launched.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made within the technical idea of the present invention.

1 is a cross-sectional view illustrating a fixing device according to a first embodiment. It is a figure showing the heater sequence, heating roller temperature distribution, and heating roller roller shape which concern on 1st embodiment. It is a flowchart explaining the heater sequence which concerns on 1st embodiment. 1 is a cross-sectional view illustrating an image forming apparatus to which a fixing device according to a first embodiment is applied. It is a figure explaining the schematic structure and calorific value distribution of the heater arrange | positioned in a heating roller. It is a flowchart explaining the heater sequence which concerns on 2nd embodiment. It is a flowchart explaining the heater sequence which concerns on 3rd embodiment. It is sectional drawing which shows the fixing device using an induction heating system.

DESCRIPTION OF SYMBOLS 1 Fixing device 2 Heating roller 3 Pressure roller 4 Heater A
5 Heater B
DESCRIPTION OF SYMBOLS 6 Thermistor 11 Fixing roller 12 Pressure roller 13 Inductive coil 14 Magnetic core 15 Coil holder 16 Stay 17 Temperature sensor 18 Conveyance guide 19 Inductive coil assembly 40 Image forming apparatus 44 Image forming part 111 Excitation circuit 112 Control circuit 1106 Heat fixing apparatus

Claims (3)

A fixing member and a pressure member for fixing the toner image on the recording material at the pressure contact portion;
A first heating member having a higher ability to heat a central region than both axial end regions of the fixing member;
A second heating member having a higher ability to heat both end regions than the central region of the fixing member;
A temperature detector for detecting the temperature of the central region of the fixing member;
Control means for controlling energization to the first heating member and the second heating member in accordance with the output of the temperature detector;
In a fixing device having
When performing a start-up operation for raising the temperature of the fixing member to a fixing temperature at which fixing is possible,
When the detected temperature when starting the startup operation is lower than a predetermined temperature,
Energizing the first and second heating members until the detected temperature reaches a set temperature lower than the fixing temperature,
After the detected temperature reaches the set temperature, the energization to the first heating member is stopped and the energization to the second heating member is continued.
When the detected temperature when starting the start-up operation is higher than the predetermined temperature,
The fixing device, wherein energization is continued to the first and second heating members until the detected temperature reaches the fixing temperature. The fixing device according to claim 1, wherein the first heating member and the second heating member include a heating element that generates heat when energized. The fixing device according to claim 1, wherein the first heating member and the second heating member include an induction coil that induction-heats the fixing member when energized.

Images