JP5164703B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device mounted on an image forming apparatus.

  A conventional image forming apparatus will be described using an electrophotographic printer as an example.

  In an electrophotographic printer, an image forming operation is performed as follows. First, the surface of the photoreceptor having the photosensitive layer is uniformly charged, and the photoreceptor is exposed according to an image signal sent from the host computer to form a latent image. Then, this is developed as a visualized image with a developer (toner), transferred to a recording material, transported to a fixing device, a recording material carrying an unfixed toner image, and the unfixed toner image is heated and fixed and fixed. Form an image. Generally, a fixing device includes a heater as a heat source, a rotating member heated by the heater, a pressure member that forms a nip portion in contact with the rotating member, and a temperature detection unit that detects the temperature of the heater. Some have control means for controlling energization to the heater.

  The fixing device needs to be warmed up before image formation is started. That is, the temperature of the rotating member is raised in order to sufficiently heat the recording material, and specifically, the fixing operation is performed after the temperature of the rotating member is raised until the temperature reaches the target temperature. Hereinafter, the operation of raising the temperature of the rotating member in advance in order to heat the recording material sufficiently and sufficiently is referred to as a preheating operation. In the fixing device that performs the preheating operation, it is desirable that the temperature of the rotating member reaches the target temperature as a condition for completing the preheating operation, that is, for starting image formation.

  When preheating operation from a low temperature state is assumed, it is desirable to set the target temperature higher assuming that heat is taken around the fixing device. However, when the temperature around the fixing device is warm, the heat supply from the rotating member to the recording material becomes excessive if the target temperature is set high. As a result, problems such as hot offset and the problem that the preheating operation time extends more than necessary occur.

  In Patent Document 1, in order to cope with fluctuations in the surrounding environment of the image forming apparatus, the target temperature is lowered when the initial temperature is high based on the temperature of the rotating member before heating (hereinafter, initial temperature). A configuration in which the target temperature is set high when the initial temperature is low is disclosed.

Patent Document 2 discloses a central region heater that heats the central region of the rotating member, an end region heater that heats the end region of the rotating member, a main thermistor that detects the temperature of the central region of the rotating member, and the rotating member. And a sub-thermistor for detecting the temperature of the end region of the fixing device. In Patent Document 2, the energization to the central area heater is controlled based on the detected temperature of the main thermistor, and the energization to the end area heater is controlled based on the detected temperature of the sub-thermistor. When heating the central area heater and the end area heater so that the main heater and the sub-thermistor reach the target temperature, if the temperature detected by the main thermistor and the sub-thermistor exceeds the specified temperature difference, the temperature The temperature of the heater heating the high region is further increased. Further, the temperature of the rotating member is made uniform in the longitudinal direction by lowering the temperature of the heater that heats the low temperature region.
JP-A-10-26901 JP 2002-174899 A

  However, the following problems have occurred despite the above improvement.

  In the configuration of Patent Document 1, when performing the fixing operation after the end of the preheating operation, the temperature of the central region of the rotating member reaches the temperature at which the recording material reaches a necessary and sufficient temperature. Since the temperature did not reach, fixing failure sometimes occurred on the end side of the recording material. Further, when the temperature of the end region of the rotating member reaches a temperature at which the recording material can be heated sufficiently and sufficiently, the temperature of the central region of the rotating member is excessively increased, which causes a hot offset. There was a case.

  In the configuration of Patent Document 2, uniformity is achieved during fixing by having a plurality of heaters and thermistors, but the main thermistor and the sub-thermistor reach the same target temperature in the preheating operation regardless of the starting temperature. I was trying to do it. Therefore, in the configuration of Patent Document 2, since the target temperature of the main thermistor and the sub thermistor is set to the same temperature until the temperature detected by the main thermistor and the sub thermistor becomes equal to or higher than the predetermined temperature difference, preheating is more than necessary. There was a case where the operation time becomes longer.

  That is, according to the present invention, when performing the fixing operation after the end of the preheating operation regardless of the initial temperature of the rotating member, the preheating operation time is longer than necessary while maintaining a temperature distribution that does not cause fixing failure or hot offset. It is an object of the present invention to provide a fixing device that does not become a problem.

In order to solve the above-described problems, the fixing device of the present invention is provided with a rotating member that contacts a recording material carrying an unfixed toner image, and an inside of the rotating member. A first heater having a larger central region in the longitudinal direction than both end regions in the direction, and a second heater disposed inside the rotating member, and having a larger amount of heat generation per unit length than the central region in the longitudinal direction. A heating member, a pressure member that forms a nip portion that sandwiches and conveys the recording material together with the rotating member, a first temperature detecting portion that detects the temperature of the central region in the longitudinal direction of the rotating member, and a predetermined maximum width A second temperature detection unit for detecting a temperature of the rotating member corresponding to a non-sheet passing region when the recording material is passed, and a control circuit for controlling energization to the first heater and the second heater; And carried on the recording material In a fixing device that heats and fixes the unfixed toner image that has been made at the nip portion,
The control circuit controls energization to the first heater so that the temperature detected by the first temperature detection unit reaches a first target temperature when starting the warm-up of the device, The energization of the second heater is controlled so that the temperature detected by the second temperature detection unit reaches the second target temperature, and the initial temperature of the rotating member when starting the warm-up is a predetermined temperature. If lower, the first target temperature is set higher than the first target temperature set when the initial temperature is equal to or higher than the predetermined temperature, and the second target temperature is set higher than the predetermined temperature. It is characterized by being set lower than the second target temperature that is sometimes set.

  According to the present invention, regardless of the initial temperature of the rotating member, the temperature distribution in the longitudinal direction of the rotating member when performing the fixing operation after the end of the preheating operation can be set to a temperature distribution that does not cause fixing failure or hot offset. is there. Furthermore, it is possible to provide a fixing device in which the preheating operation time does not become longer than necessary.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

Example 1
(1) Image forming apparatus (FIG. 1)
FIG. 1 is a schematic sectional view showing an example of an image forming apparatus. The image forming apparatus of the present embodiment is an inline electrophotographic full color printer, and can form 20 A3 size full color images per minute.

  This configuration includes photosensitive drums 11a, 11b, 11c, and 11d (hereinafter referred to as 11a to 11d) corresponding to yellow, magenta, cyan, and black color toners, respectively. The transfer belt 20 is in contact with the respective photosensitive drums 11a to 11d at respective transfer portions (transfer portions I, II, III, and IV in order).

As the resistance of the transfer belt 20, a material having a thickness of 0.1 mm, in which carbon is dispersed in polyimide resin and the volume resistivity is adjusted to 10 ⁸ Ω · cm, is used.

In each of the transfer portions I to IV, transfer rollers 15a to 15d in which a core metal is coated with an elastic material having a medium resistance (actual resistance in nip formation when 500 V is applied is 10 ⁶ to 10 ¹⁰ Ω) are photosensitive drums 11a to 11d. At the same time, the transfer belt 20 is sandwiched.

Note that 12a to 12d are primary chargers, 13a to 13d are scanners, 14a to 14d are developing devices, 16a to 16d are cleaning devices, and 17a to 17d are power supplies. Reference numeral 18 denotes a current detection circuit, and 19 denotes a control device. 20a is a driving roller, and 20b is a driven roller. t _Y , t _M , t _C , and t _K are yellow, magenta, cyan, and black toners (developers). P is a recording material. Reference numeral 10 denotes a fixing device (fixing means), and (3) the fixing device will be described.

(2) Image Forming Operation The photosensitive drum 11a rotates in the direction of the arrow shown in FIG. 1 and is uniformly charged by the primary charger 12a. Then, the image data sent from the host computer is converted into laser emission intensity and time by image data processing, and an electrostatic latent image is created on the photosensitive drum 11a with the laser light from the scanner 13a. The intensity of the laser beam and the irradiation spot diameter are appropriately set according to the resolution of the image forming apparatus and the desired image density. In the electrostatic latent image on the photosensitive drum 11a, the portion irradiated with the laser light is at a bright portion potential V _L (about −100V), and the other portion is dark portion potential V _D (about −700V) charged by the primary charger 12a. ) To be formed. The electrostatic latent image reaches a portion facing the developing device 14a by the rotation of the photosensitive drum 11a, and is supplied with toner charged with the same polarity (negative polarity in this embodiment) to be visualized. In full color image formation, toner images are similarly formed on the photosensitive drums 11a to 11d corresponding to the respective colors, and sequentially transferred onto the recording material P conveyed together with the transfer belt 20 at each transfer nip, and the toner images are synthesized. At each transfer nip formed by the transfer belt 20 and the photosensitive drums 11a to 11d, the toner image is transferred by an electric field formed in the transfer nip region by a voltage (+500 to + 4000V) having a polarity opposite to that of the toner applied to the transfer rollers 15a to 15d. Is done. When the recording material P passes through the transfer nip with the photosensitive drum 11d, the full color image is carried on the recording material P, and the transfer process is completed.

On the other hand, the surfaces of the photosensitive drums 11a to 11d after the transfer of the toner images are cleaned by the cleaning devices 16a to 16d, respectively, and then prepared for the next image forming process. The voltage (transfer voltage) supplied to the transfer rollers 15a to 15d is determined as follows. That is, before the recording material P is supplied, the current when a predetermined voltage is applied to the transfer roller 15a is measured by the current detection circuit 18, and the resistance of the transfer member (transfer roller 15a and transfer belt 20) is controlled by the control device 19. Is calculated and determined (Vo ₁ , Vo ₂ , Vo ₃ , Vo ₄ ). By this control, it is possible to absorb a change in the resistance of the recording material due to the environment where the recording material is placed, particularly moisture absorption, and supply a constant transfer charge, thereby maintaining a stable image quality.

  The recording material P that has completed the transfer process is separated from the transfer belt 20 by the curvature of the drive roller 20a. Thereafter, the recording material P is nipped and conveyed by the fixing device 10, and an unfixed toner image carried on the recording material P is heated and fixed at the nip portion.

(3) Fixing device 10
FIG. 2 is a partially cutaway side view of the fixing device 10.
Note that P is a recording material, M is a driving motor (driving means) for driving the fixing roller 1, t is toner, and N is a fixing nip portion.

  Reference numeral 1 denotes a fixing roller which is a rotating member. An elastic core 1e is formed by coating an iron core 1d having a hollow structure with a thickness of 1.5 mm with a silicone rubber having a thickness of 2.1 mm (thermal conductivity 0.6 W / m · K), and further forming a surface layer 1 f. A tube made of 50 μm PFA resin was provided and had a diameter of 50 mm. Reference numeral 3 denotes a pressure roller that is a pressure member, and is pressed against the fixing roller 1 by about 700 N to form a fixing nip portion N. The pressure roller 3 is an iron core 3a having a diameter of 24 mm, covered with a 3 mm thick silicone rubber, provided with an elastic layer 3b, and the surface layer 3c is formed of a 50 μm thick PFA tube.

  The fixing roller 1 includes two halogen heaters as heaters inside, and the main heater 2c (heater other than the auxiliary heating source) has an output of 500W having 90% of the calorific value in a 200 mm wide area in the central distribution. It is a heater. That is, the main heater 2c is a first heater that generates a larger amount of heat per unit length in the longitudinal central region than in the longitudinal end regions. The main heater 2c mainly heats the main part in the longitudinal direction of the rotating member. The other sub-heater 2d is a heater with an output of 300 W having a width of 70 mm at both ends and 90% of the calorific value. That is, the sub-heater 2d is a second heater in which the heat generation amount per unit length is larger in the longitudinal end regions than in the longitudinal central region. The sub-heater 2d mainly heats the longitudinal end of the rotating member. These heaters can be individually driven, and their outputs are adjusted by the control circuit 100 (control means).

  In the present embodiment, the main portion in the longitudinal direction of the rotating member refers to the central region in the longitudinal direction. More specifically, the main portion in the longitudinal direction means that a recording material having a predetermined minimum width (a length in a direction perpendicular to the conveyance direction of the recording material) that can pass through at least the image forming apparatus is the fixing device 10. This is an area that includes all of the area (sheet passing area) through which the recording material passes when being conveyed. The end in the longitudinal direction of the rotating member in this embodiment is an area where the recording material does not pass through when the recording material having the maximum width that can be passed by the image forming apparatus is conveyed to the fixing device 10 (non-sheet passing portion). Area). FIG. 3 shows the heat generation distribution of the heater in the longitudinal direction of the rotating member when the same voltage is applied to the main heater and the sub heater of the present embodiment by the control circuit 100.

  Reference numeral 5c denotes a thermopile for detecting the temperature of the central region in the longitudinal direction of the fixing roller 1, that is, a first temperature detecting unit, which is arranged to face the fixing roller 1 in a non-contact state. Reference numeral 5d denotes a thermistor that detects the temperature of the end region of the fixing roller 1, that is, a second temperature detecting unit, which is applied to the fixing roller 1 corresponding to a non-sheet passing region when a recording material having a predetermined maximum width is passed. It is in contact contact. FIG. 4 is a schematic diagram in the longitudinal direction of the fixing device according to the first embodiment of the present invention. The thermopile 5c and the thermistor 5d are connected to the control circuit 100 by signal lines, respectively. The thermopile 5c is basically referred to the control for the main heater 2c, and the thermistor 5d is referred to the control for the sub heater 2d. The triac 6c is a drive member that can switch the power supply to the main heater 2c between a conductive state and a non-conductive state by the control circuit 100. The triac 6d is a drive member that can switch the power supply to the sub-heater 2d between a conductive state and a non-conductive state by the control circuit 100.

(4) Image formation preparation (FIG. 5)
In this embodiment, the fixing device is configured using a roller having a large heat capacity, and it is necessary to warm up before starting image formation. That is, the fixing roller 1 is heated to sufficiently heat the recording material, and specifically, the fixing roller 1 is heated until the temperature reaches the target temperature, and then the fixing operation is performed. Yes.

  In the present embodiment, the operation of raising the temperature of the fixing roller 1 in order to heat the recording material sufficiently and sufficiently is hereinafter referred to as a preheating operation. The preheating operation of the present embodiment is finished when both the detected temperatures of the thermopile 5c and the thermistor 5d reach the target temperature. After the preheating operation is completed, standby temperature control is performed to maintain the temperature of the rotating member so that image formation can be started immediately.

  In this embodiment, since the fixing roller 1 is heated using two heaters having different heat generation distributions, the main portion in the longitudinal direction and the end portion in the longitudinal direction of the fixing roller 1 are individually heated even during the preheating operation. There is a feature that can be.

FIG. 5 shows a flow of preheating operation for image formation preparation. Detecting the temperature of the fixing roller 1 by the thermopile 5c before entering the pre-heating operation, the temperature of the fixing roller 1 is detected as the initial temperature T _0. (Step S199, hereinafter omitted "step"), to change the respective imageable temperature for thermopile 5c and the thermistor 5d (target temperature) by the initial temperature _{T 0} (S201). Specifically, when the initial temperature T ₀ is less than 120 ° C. (predetermined temperature), the control circuit 100 sets the image formable temperature T _SH-M (main part target temperature) for the thermopile 5c to 190 ° C. and the image for the thermistor 5d. Formable temperature T _SH-S (end target temperature) is set to 140 ° C. That is, the control circuit 100 sets the first target temperature to 190 ° C. and the second target temperature to 140 ° C. On the other hand, when the initial temperature T ₀ is 120 ° C. or higher, the control circuit 100 sets the image formable temperature T _SH-M (main part target temperature) for the thermopile 5a to 175 ° C. and the image formable temperature T _SH for the thermistor 5b. _-S (end target temperature) is set to 150 ° C. That is, the control circuit 100 sets the first target temperature to 175 ° C. and the second target temperature to 150 ° C.

When the detected temperature T _M of the main heater 2c by the thermopile 5c is lower than the image formable temperature T _SH-M (No in S202), the main heater 2c is turned on (S203). Then, if the detected temperature _{T M} of the thermopile 5c reaches the imageable temperature _{T SH-M} stops energization to (S202 Yes), the main heater 2c (OFF) (S204). Then, until the detected temperature _{T S} of the sub-heater 2d by the thermistor 5d reaches imageable temperature _{T SH-S (S206 No)} , the sub-heater 2d ON (ON) and (S207), continued image formation preparation operation . If the detected temperature _{T S} of the sub-heater 2d reaches the imageable temperature _{T SH-S,} and stops the power supply to the sub-heater 2d. When the detected temperatures of the thermopile 5c and the thermistor 5d reach the image formable temperatures (Yes in S206), image formation is started (S208), and standby temperature adjustment (S209) is performed after the image formation is completed. Note that the preheating operation of the present embodiment may be terminated when the thermopile 5c and the thermistor 5d reach the target temperature. That is, the flow of the preheating operation of the present embodiment is not limited to the flow disclosed in FIG. For example, the main heater 2c and the sub heater 2d may be energized at the same time, and when the respective target temperatures are reached, the energization of the respective heaters may be stopped.

  The preheating operation in this embodiment is performed not only when the power is turned on, but also during a return operation after a jam (JAM) (conveyance failure) process or after replacement of consumables such as a photosensitive drum. In the returning operation, the fixing roller 1 may already be at a high temperature. In such a case, the image formable temperature is reset in S201.

FIG. 6 shows the temperature transition of the surface layer 1f of the fixing roller 1 of the fixing device 10 used in this embodiment. Here, the temperature of the main part of the fixing roller 1 is the temperature detected by the thermopile 5c (solid line), and the temperature of the fixing roller 1 at the end is indicated by the temperature detected by the thermistor 5d (broken line). Main unit during heating operation from room temperature (corresponding to the time t _0), both ends, but the temperature is increased substantially linearly, increase gradient of the end portion has a more gradual than the main portion. This indicates that the end portion is deprived of heat from the low temperature to the ambient temperature, and the temperature does not easily rise. After the image forming operation at time t _1, the main heater until the next image formation, when stopping the power supply to the sub-heater, the temperature of both begins to fall. However, the difference between the two decreases while descending. This is considered to be because a large temperature gradient occurs in the longitudinal direction of the rotating member, heat flows from the central portion having a high temperature to the end portion having a low temperature, and uniformization is achieved throughout the longitudinal direction of the fixing roller 1. It is done. When the temperature raising operation is performed again at time t ₂ , the temperature of both rises. However, compared to the temperature raising operation from a low temperature state, the temperature rising gradient at the end is larger, and time t ₃ The difference is that the temperature difference between the two is small at the time when the temperature raising operation is performed. As for the former, in FIG. 6, the straight line l (temperature rise gradient of the temperature at the end part up to the time t _1), and a straight line m (temperature rise gradient of the temperature at the end part from time t ₂ to time t ₃₎ You can see by comparing. This is in a state already once fixing roller 1 is heated as time t _2, the heat from the surroundings and the ambient environment warm the fixing apparatus is considered to be due to hard deprived. For this reason, the temperature at the end of the fixing roller 1 is likely to rise.

  Therefore, when the fixing roller 1 is heated to some extent, the surrounding environment is also warmed, so that it is difficult for heat to be radiated from the end of the fixing roller 1. Therefore, the temperature difference between the two becomes small, and the amount of heat transfer from the main part to the end part is reduced. That is, as compared with the case where the fixing roller 1 is cold, the heat generated by the main heater is easily supplied to the main part and the heat generated by the sub heater is supplied to the end part.

In the present embodiment, when the fixing roller 1 is warmed to some extent, that is, in the preheating operation when the initial temperature is equal to or higher than a predetermined temperature (120 ° C. or higher), the control circuit controls the image formable temperature T _SH-M (mainly for the thermopile 5c). Set target temperature) to 175 ° C. Further, the image formable temperature T _SH-S (edge target temperature) for the thermistor 5d is set to 150 ° C. This setting makes it possible to heat the fixing roller 1 efficiently, so that the preheating operation time is not unnecessarily extended.

  However, when the temperature of the fixing roller 1 is low as described above, since the surrounding environment is also cold, the temperature at the end of the rotating member is less likely to rise than the temperature at the main part. When the pre-heating operation is performed with the initial temperature set to the same target temperature or higher (120 ° C or higher) when the ambient environment of the fixing device is cold, the end until the end reaches the end target temperature. The time will be longer. Therefore, although the main part has already reached the main part target temperature, the time until the end part reaches the end target temperature is long, resulting in a long preheating operation time.

Therefore, in the present embodiment, when the fixing roller 1 is cold, that is, in the preheating operation when the initial temperature is lower than a predetermined temperature (less than 120 ° C.), the control circuit 100 allows the image forming temperature T _SH− for the thermopile 5c. Set _M (main part target temperature) to 190 ° C. Further, the image formable temperature T _SH-S (edge target temperature) for the thermistor 5d is set to 140 ° C. If a temperature gradient is formed in the longitudinal direction of the fixing roller 1, the heat is dispersed from the higher temperature to the lower temperature. With this setting, the sub-heater that heats the end portion is turned off before reaching the temperature required for fixing the end portion of the fixing roller 1, but the insufficient amount of heat is turned from the main portion where the temperature easily rises. It becomes possible. As a result, the preheating operation time can be shortened.

  If the preheating operation is performed with the initial target temperature set to a predetermined temperature or higher (120 ° C or higher) with the main target temperature set to 190 ° C and the end target temperature set to 140 ° C, the main temperature is It becomes too expensive because there are few escape areas. If the temperature of the main part becomes too high because there are few escape points for heat, there is a possibility that a hot offset may occur in some cases. If the main part target temperature is set to 175 ° C. and the end target temperature for the thermistor 5d is set to 150 ° C., the main heater for heating the main part can be turned off at an early stage. Generation can be suppressed. In addition, when the initial temperature is equal to or higher than the predetermined temperature, the amount of heat transfer from the main part to the end is less than when the initial temperature is lower than the predetermined temperature, but the target temperature at the end is set from 140 ° C. to 150 ° C. It is possible to prevent a fixing failure caused by a lack of heat at.

  FIG. 7 shows the temperature distribution on the surface of the fixing roller 1 at the end of the preheating operation time when the initial temperature is less than 120 ° C. and when the initial temperature is 120 ° C. or more.

FIG. 8 shows a region where neither hot offset nor fixing failure occurs in the combination of the image formable temperature T _SH-M (main part target temperature) and the image formable temperature T _SH-S (end part target temperature). (Denoted as “appropriate fixing area” in the figure). It can be seen that when the main part temperature is high, the end part temperature can be set low, and when the main part temperature is high, the main part temperature can be set low.

(5) Comparative Example In this embodiment, the image formable temperature for the temperature detection unit that detects the temperature of a different region is changed as described above according to the initial temperature T ₀ of the main part of the fixing roller 1, and It has heaters that can be individually driven based on the detected temperatures of the respective temperature detectors.

As a comparative example for this configuration, when the end target temperature is not changed in S201 described with reference to FIG. 5, that is, the setting of the image formable temperature T _SH-S (end target temperature) is not changed regardless of the initial temperature To. The case was referred to as Comparative Example 1. Further, a fixing device using a single heater (with an output of 1200 W) having a uniform heat generation distribution was defined as Comparative Example 2. In any case, it was confirmed that when the temperature is low, that is, when the initial temperature is less than 120 ° C., the result of the image forming operation by the preheating operation from 25 ° C. (room temperature) does not cause any hot offset or fixing failure.

  The result of the image forming operation by the preheating operation from the state where the thermopile 5c is detecting 120 ° C. when the temperature is high, that is, when the initial temperature is 120 ° C. or higher was examined.

  As shown in Table 1, in this embodiment, even when the initial temperature is high, there is no occurrence of hot offset or fixing failure, and it can be seen that the heat supply to the recording material is appropriate (“◯” in Table 1). ). On the other hand, in the first comparative example, the image formation start temperature at the end portion is kept low, so that the heat supply from the main portion is not expected and heat supply at the end portion is insufficient, resulting in fixing failure (see Table 1). “×” in 1). In Comparative Example 2, when the image forming temperature at the end portion is reset to a high value, the main portion is heated by the image formation preparation operation for the end portion heating, and the heat supply to the main portion becomes excessive. A hot offset occurred ("X" in Table 1).

  Further, as Comparative Example 3, the experiment was also performed in Comparative Example 1 in which the image forming temperature at the edge was set high (150 ° C.) in advance. In Comparative Example 3, although the problem of hot offset and fixing failure is solved, it is necessary to wait for the edge temperature to rise even in preparation for image formation from a low temperature, so the preheating operation time is extended to 4 minutes or more. The result was unfavorable.

  As described above, in this embodiment, an advantage was obtained in that hot offset and fixing failure from a high temperature were prevented and a preheating operation time from a low temperature was shortened.

  Next, a comparison was made by paying attention to switching of the image formable temperature according to the initial temperature To.

In Comparative Example 4, regardless of the initial temperature T ₀ , the image formable temperature T _SH-M (main part target temperature) for the thermopile 5c is always 190 ° C., and the image formable temperature T _SH-S for the thermistor 5d (end part target). Temperature) was set to 140 ° C.

In Comparative Example 5, regardless of the initial temperature T ₀ , the image formable temperature T _SH-M (main part target temperature) for the thermopile 5c is always 175 ° C., and the image formable temperature T _SH-S (end part target for the thermistor 5d). Temperature) was set to 150 ° C.

In Comparative Example 6, when the initial temperature T ₀ is less than 120 ° C. (predetermined temperature), the image formable temperature T _SH-M (main part target temperature) for the thermopile 5c is 175 ° C., and the image formable temperature for the thermistor 5d. T _SH-S (end target temperature) is set to 160 ° C. On the other hand, when the initial temperature T ₀ is 120 ° C. or higher, the image formable temperature T _SH-M (main part target temperature) for the thermopile 5a is 175 ° C., and the image formable temperature T _SH-S (end part target for the thermistor 5b). Set the temperature to 150 ° C.

In Comparative Example 7, when the initial temperature T ₀ is less than 120 ° C. (predetermined temperature), the image formable temperature T _SH-M (main part target temperature) for the thermopile 5c is 180 ° C., and the image formable temperature for the thermistor 5d. T _SH-S (end target temperature) is set to 180 ° C. On the other hand, when the initial temperature T ₀ is 120 ° C. or higher, the image formable temperature T _SH-M (main part target temperature) for the thermopile 5a is 180 ° C., and the image formable temperature T _SH-S (end part target for the thermistor 5b is set. Temperature) is set to 180 ° C.

  The results are shown in Table 2. The case where neither hot offset nor fixing failure occurs is indicated as ◯, and the case where it occurs is indicated as x. The preliminary operation time is evaluated as “x” when it extends to 4 minutes or more.

  In Example 1, the preheating operation time was optimal while preventing hot offset and fixing failure.

  In Comparative Example 4, the preheating operation time was optimum regardless of the initial temperature, but when the initial temperature was 120 ° C. or higher, a hot offset sometimes occurred.

  In Comparative Example 5, although the occurrence of hot offset and fixing failure was suppressed, the preheating operation time was evaluated as x when the initial temperature was less than 120 ° C.

  Also in Comparative Example 6, when the initial temperature is less than 120 ° C., the evaluation of the preheating operation time is x. The preheating operation time when the initial temperature is less than 120 ° C. is longer than that of Comparative Example 5.

  In Comparative Example 7, the occurrence of hot offset and fixing failure may not be suppressed. Furthermore, the evaluation of the preheating operation time when the initial temperature was less than 120 ° C. was x.

As described above, the fixing device according to the first exemplary embodiment does not cause defective fixing or hot offset regardless of the initial temperature T ₀ of the fixing roller 1 and does not increase the preheating operation time more than necessary. It can be understood that.

  In addition, the structure which arrange | positions two or more 2nd temperature detection parts in a non-sheet passing part area | region may be sufficient. In FIG. 9, a thermistor 5 d that detects the temperature of one end area of the fixing roller 1 and a thermistor 5 e that detects the temperature of the other end area of the fixing roller 1 are arranged. The thermistor 5d and the thermistor 5e are connected to the control circuit 100 by signal lines, respectively, and are basically referred to for control of the sub heater 2c. During the preheating operation, energization of the sub-heater 2c is stopped when both the thermistor 5d and the thermistor 5e reach the target temperature. With this configuration, there is an effect that the fixing defect at both ends of the fixing roller 1 is more reliably suppressed.

(Example 2)
The apparatus of the present embodiment uses the fixing device 10 shown in FIG. 10 in comparison with the apparatus of the first embodiment, and sets an image formable temperature (target temperature) corresponding to the fixing device 10 of FIG. Is the same except that For this reason, it demonstrates using the code | symbol used until now.

(1) Fixing device 10 (FIG. 10)
Reference numeral 1 denotes a fixing roller 1 which is a rotating member. The fixing roller 1 having a hollow structure having a thickness of 1.5 mm is covered with a silicone rubber having a thickness of 2.1 mm (thermal conductivity 0.6 W / m · K). Thus, the elastic layer 1e was formed. Further, the surface layer 1 f was provided with a tube made of 50 μm PFA resin and had a diameter of 50 mm. Reference numeral 3 denotes a pressure roller 3 which is another rotating body, and is pressed against the fixing roller 1 by about 700 N to form a fixing nip portion N. The pressure roller 3 is formed by covering a hollow iron core 3a having a diameter of 50 mm with a 2.1 mm-thick silicone rubber (thermal conductivity 0.6 W / m · K) to provide an elastic layer 3b, and the surface layer 3c having a thickness of 50 μm. It is formed of a thick PFA tube.

  The fixing roller 1 and the pressure roller 3 each include a halogen heater as a heater, and the main heater 2c (heater other than the auxiliary heating source) has an output of 900 W having a uniform heat distribution over the entire area of the sheet passing portion. The fixing roller 1 is heated with a heater. In this embodiment, a roller having a large heat capacity is used, and a heater having a large output is used as the main heater 2c in order to shorten the preheating operation time. The sub-heater 2d (auxiliary heater) is a heater having an output of 400 W having a width of 70 mm at both ends and 90% of the calorific value, and mainly heats the end of the pressure roller 3. These heaters can be individually driven, and the output is adjusted by the control circuit 100.

  A thermopile (first temperature detection unit) 5c is a first temperature sensor that detects the temperature of the main part of the fixing roller 1, and is arranged to face the fixing roller 1 in a non-contact state. Reference numeral 5d denotes a thermistor (second temperature detection unit) which is a second temperature sensor for detecting the temperature of the end portion of the pressure roller 3, and is a pressure roller in a region outside the maximum width of the recording material P capable of passing paper. 3 is brought into contact with the surface. The thermopile 5c and the thermistor 5d are connected to the control circuit 100 by signal lines, respectively. The thermopile 5c is basically referred to the control for the main heater 2c, and the thermistor 5d is referred to the control for the sub heater 2d. P is a recording material, M is a driving motor (driving means) for driving the fixing roller 1, and t is toner.

(2) Image formation preparation (FIG. 11)
In this embodiment as well, as in the description of the first embodiment, standby temperature control is performed after image preparation is performed. In the standby temperature control, the fixing roller 1 is maintained at a substantially uniform temperature by the main heater 2c, whereas in the preheating operation in the image formation preparation, the subheater 2d is operated to shorten the preheating operation time and the end portion. To prevent fixing failure.

  Further, in order to reflect the end temperature of the fixing roller 1 in the temperature detected by the thermistor 5d, the fixing roller 1 is rotated at a predetermined speed during image formation preparation so as to ensure heat transfer with the pressure roller 3. To do.

FIG. 11 shows a flow of preheating operation for image formation preparation. Before entering the image formation preparation, the initial temperature T ₀ is measured by the thermopile 5c (step S299, hereinafter “step” is omitted), and the image forming temperatures for the thermopile 5c and the thermistor 5d are set by the initial temperature T ₀ . (S301). Specifically, when the initial temperature T ₀ is less than 120 ° C. (predetermined temperature), the image forming temperature T _SH-M (main part image forming temperature) for the thermopile 5c is 190 ° C., and the image forming for the thermistor 5d is possible. The temperature T _SH-S (temperature at which end image formation is possible) is set to 140 ° C. On the other hand, when the initial temperature T ₀ is 120 ° C. or higher, the image formable temperature T _SH-M for the thermopile 5a is set to 175 ° C., and the image formable temperature T _SH-S for the thermistor 5b is set to 150 ° C.

When the detected temperature T _M of the main heater 2c by the thermopile 5c is lower than the image formable temperature T _SH-M (No in S302), the main heater 2c is turned on (S303). Next, when the detected temperature T _M of the thermopile 5c has reached the image formable temperature T _SH-M (S302 Yes), the output of the main heater 2c is stopped (OFF) (S304). Then, until the detected temperature _{T S} of the sub-heater 2d by the thermistor 5d reaches imageable temperature _{T SH-S} and (S307) in (S306 No) sub-heater 2d ON (ON), continued image formation preparation operation. When the detected temperatures of the thermopile 5c and the thermistor 5d reach the image-forming temperature (S306 Yes), image formation is started (S308), and standby temperature adjustment (S309) is performed after completion. Note that the preheating operation of the present embodiment may be terminated when the thermopile 5c and the thermistor 5d reach the target temperature. That is, the flow of the preheating operation of the present embodiment is not limited to the flow disclosed in FIG.

  This image formation preparation is performed not only when the power is turned on, but also during a return operation after JAM processing or after replacement of consumables such as a photosensitive drum. In the returning operation, the heating member may already be at a high temperature. In such a case, the image formable temperature is reset in S301.

  In the present embodiment, the same effects as in the first embodiment can be obtained, and at the same time, the temperature of the pressure roller 3 can be actively managed, the amount of heat applied to the front and back of the recording material can be easily controlled, and the curled deformation can be achieved. Also good results can be obtained.

(Example 3)
In contrast to the apparatus of the first embodiment, the apparatus of the present embodiment is made of high thermal conductivity silicone rubber (thermal conductivity 0.8 W / m · K) on the elastic layer 1e of the fixing roller 1 of the fixing apparatus 10 shown in FIG. It is the same except that it is used. For this reason, what can use the same code | symbol as Example 2 is demonstrated using the same code | symbol.

In the image formation preparation of this embodiment, when the initial temperature T ₀ is less than 120 ° C. as the optimum image forming temperature in step S201 of FIG. 5, the image forming possible temperature T _{SH-M is set} to 180 ° C. The possible temperature T _SH-S is set to 120 ° C. On the other hand, when the initial temperature T ₀ is 120 ° C. or higher, the image forming temperature T _{SH-M is set} to 175 ° C., and the image forming temperature T _SH-S is set to 150 ° C. Can be prevented.

Compared with the first embodiment, this setting can lower the image-forming temperatures T _SH-M and T _SH-S when the initial temperature T ₀ is less than 120 ° C., and can further shorten the preheating operation time. There is an advantage.

  In order to investigate what caused the above setting, an experiment was conducted on the relationship between the main part temperature and the end part temperature at which fixing failure does not occur by changing the thickness and thermal conductivity of the silicone rubber, as shown in FIG. Results were obtained.

  Here, a in FIG. 12 is an elastic layer having a thickness of 2 mm made of silicone rubber having a thermal conductivity of 0.6 W / m · K, and b in FIG. 12 is a thickness having a thickness of 1 mm made of silicone rubber having a thermal conductivity of 0.4 W / m · K. It is an elastic layer. On the other hand, c in FIG. 12 is an elastic layer having a thickness of 0.3 mm made of silicone rubber having a thermal conductivity of 1.6 W / m · K, and d in FIG. 12 is a thickness of 2 mm made of silicone rubber having a thermal conductivity of 0.8 W / m · K. The elastic layer has a configuration close to that of the present embodiment.

Considering the result of FIG. 12, it is found that when the temperature of the main part is increased according to the value obtained by multiplying the thermal conductivity λ by the thickness L of the elastic layer, the end part temperature tends to be lowered. It was. Further, it was confirmed that when L · λ is 4 × 10 ⁻⁴ W / K or more, heat compensation from the main part to the end part can be obtained.

Based on the above consideration, this embodiment can obtain a larger L · λ, and therefore, it is easy to secure a large amount of heat from the main part to the end part when the initial temperature T ₀ is less than 120 ° C. There is an effect of further shortening the preheating operation time.

1 is a schematic cross-sectional view illustrating an example of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a partially cutaway side view of the fixing device according to the first exemplary embodiment of the present invention. Heat generation distribution when the same voltage is applied to the main heater and the sub heater of the fixing device according to the first exemplary embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a relationship between a heater and a temperature detection unit in the longitudinal direction of the fixing device according to the first exemplary embodiment of the present invention. 6 is a flowchart illustrating an image formation preparation flow according to the first exemplary embodiment of the present invention. The figure which shows the temperature transition of the surface layer 1f of the fixing roller 1 of the fixing device in Example 1 of this invention. When the initial temperature in Embodiment 1 of the present invention is less than 120 ° C., the temperature distribution of the fixing roller 1 at the end of the preheating operation time when the initial temperature is 120 ° C. or higher. The figure which shows the appropriate fixing area | region of the principal part temperature and edge part temperature in Example 1 of this invention. FIG. 5 is a schematic diagram illustrating a relationship between a heater in the longitudinal direction of the fixing device and a plurality of temperature detection units in Embodiment 1 of the present invention. FIG. 9 is a partially cutaway side view of the fixing device according to the second embodiment of the present invention. Flowchart for explaining an image formation preparation flow in Embodiment 2 of the present invention The figure which shows the experimental result which changed the thickness and thermal conductivity of the silicone rubber about the relationship between main part temperature and edge part temperature in which the fixing defect does not generate | occur | produce in Example 3 of this invention.

Explanation of symbols

1 Fixing roller (rotating member)
2a Heater (heating source)
2c Main heater 2d Sub heater 3 Pressure roller 5c Thermopile (first temperature detection unit)
5d thermistor (second temperature detector)
10 Fixing device (fixing means)
100 Control circuit (control means)

Claims (6)

A rotating member that contacts a recording material that carries an unfixed toner image, and a first member that is disposed inside the rotating member and that generates a larger amount of heat per unit length in the longitudinal central region than in the longitudinal end regions. A recording medium is sandwiched and conveyed together with the heater, the second heater, which is disposed inside the rotating member, and has a heat generation amount per unit length larger in the longitudinal end regions than in the longitudinal central region. Corresponds to the pressure member that forms the nip, the first temperature detection unit that detects the temperature of the central region in the longitudinal direction of the rotating member, and the non-sheet passing region when a recording material having a predetermined maximum width is passed. And a second temperature detector that detects the temperature of the rotating member, and a control circuit that controls energization of the first heater and the second heater, and is not fixed to the recording material. The toner image is heated at the nip. In the fixing apparatus,
The control circuit controls energization to the first heater so that the temperature detected by the first temperature detection unit reaches a first target temperature when starting the warm-up of the device, The energization of the second heater is controlled so that the temperature detected by the second temperature detection unit reaches the second target temperature, and the initial temperature of the rotating member when starting the warm-up is a predetermined temperature. If lower, the first target temperature is set higher than the first target temperature set when the initial temperature is equal to or higher than the predetermined temperature, and the second target temperature is set higher than the predetermined temperature. A fixing device, wherein the fixing device is set to be lower than the second target temperature that is sometimes set.   2. The fixing device according to claim 1, wherein both end regions in the longitudinal direction of the second heater heat a non-sheet passing region of the rotating member when the recording material having the predetermined maximum width is passed. .   The fixing device according to claim 1, wherein the initial temperature is a temperature detected by the first temperature detection unit.   In the control circuit, the temperature detected by the first temperature detection unit has reached the first target temperature, and the temperature detected by the second temperature detection unit has reached the second target temperature. The fixing device according to any one of claims 1 to 3, wherein the warm-up is terminated at times.   A plurality of the second temperature detection units are arranged in a non-sheet passing region of the rotating member when the recording material having the predetermined maximum width is passed, and the control circuit is configured to include the first temperature detection unit. When the temperature detected by the first temperature reaches the first target temperature and the temperatures detected by all the second temperature detection units reach the second target temperature, the warm-up is terminated. The fixing device according to any one of claims 1 to 3, wherein the fixing device is characterized in that: The rotating member has an elastic layer, wherein L · λ ≧ 4 × 10 ⁻⁴ (W / K) where L is the thickness of the elastic layer and λ is the thermal conductivity of the elastic layer. The fixing device according to any one of claims 1 to 5.

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