JP4482606B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device for fixing a toner image (image) on a member to be fixed in a color image forming apparatus such as a copying machine or a laser printer, and more particularly to a fixing device using an induction heating method.

  For example, a fixing device in a color image forming apparatus heats a color toner image such as yellow (Y), magenta (M), cyan (C), and black (K) that is visualized by being superimposed on a member to be fixed. Each toner is melted and fixed to a member to be fixed, and includes a member to be fixed, a pair of fixing rollers (heat roller and press roller) for applying a predetermined pressure to the toner, and a heat source for heating the heat roller. Yes.

  In this type of fixing device, one using an induction heating coil as a heat source is known. As an example, there has been proposed one in which induction heating coils are arranged at the center and both ends in the axial direction of the heat roller.

  This proposal is provided with a center thermistor for detecting the surface temperature of the central portion of the heat roller and a side thermistor for detecting the surface temperature of one end. The center temperature detected by the center thermistor when the power to the induction heating coil is turned on is compared with the end temperature detected by the side thermistor, and the energization time of the induction heating coil that heats the lower one is heated. It is set to be longer than the energizing time of the induction heating coil to be energized first, and the heat generation of the heat roller is made substantially uniform at the center and both ends. (For example, refer to Patent Document 1).

  Incidentally, the fixing device needs to maintain the surface temperature of the heat roller heated by the heat source within a predetermined fixing temperature region. Therefore, conventionally, the surface temperature of the center portion of the heat roller detected by the center thermistor is compared with the OFF reference temperature set near the upper limit of the fixing temperature region and the ON reference temperature set near the lower limit, and the surface temperature is Energization on / off of each induction heating coil so that energization to each induction heating coil is not permitted if the temperature rises to the OFF reference temperature, and energization to each induction heating coil is permitted if the temperature falls to the ON reference temperature. Was controlling.

  An example of the detected temperature CST of the center thermistor and the detected temperature SST of the side thermistor by conventional control is shown in FIG. In the figure, a pulse signal EPS is an energization control signal for each induction heating coil, a pulse signal CDS is an energization signal for an induction heating coil that heats the center of the heat roller, and a pulse signal SDS is It is the energization signal of the induction heating coil which heats both ends. The duty signal DUTY output in synchronization with the CPU temperature monitoring timings t1, t2, t3... Is “H” → “L” when the detected temperature CST is lower than the detected temperature SST, and the detected temperature CST is higher than the detected temperature SST. When it is high, “L” → “H”. The temperature level OFFL is the OFF reference temperature, and the temperature level ONL is the ON reference temperature.

  As shown in the figure, the induction heating coil provided at the center of the heat roller and the induction heating coil provided at both ends alternately until the time T1 when the detected temperature CST of the center thermistor rises to the OFF reference temperature OFFL. Energized. Energizing both induction heating coils simultaneously increases power consumption and is out of specification. For this reason, both coils cannot be energized simultaneously. When the detected temperature CST of the center thermistor reaches the OFF reference temperature OFFL, the energization control signal EPS is turned off. As a result, energization of the induction heating coil is not permitted, and the surface temperature of the heat roller is reduced entirely. Thereafter, when the detected temperature CST of the center thermistor decreases to the ON reference temperature ONL, the energization control signal EPS is turned on at that time T2, and energization of the induction heating coil is permitted. At this time, the temperature is higher than the detected temperature SST at the time of the temperature monitoring timing t5, and the duty signal DUTY is “H” at the time T6, so that the induction heating coil provided at the center of the heat roller is energized first.

  As described above, in this type of conventional fixing device, energization on (permitted) and off (not permitted) of the induction heating coil are controlled only by the surface temperature of the center portion of the heat roller detected by the center thermistor. So there were the following problems.

  That is, since both ends of the heat roller are usually harder to heat than the center, the surface temperature at the center of the heat roller rises to the OFF reference temperature OFFL before the surface temperature at the both ends of the heat roller rises to the OFF reference temperature OFFL. And the energization control signal EPS is turned off. For this reason, when the surface temperature of the center portion of the heat roller is lowered to the ON reference temperature ONL, the surface temperature of both ends of the heat roller is lower than the ON reference temperature ONL. It will be energized first. (Time point T4 in FIG. 7). Therefore, at the time when energization of the induction heating coil for heating the center portion of the heat roller starts, the surface temperature of the center portion of the heat roller is further lower than the ON reference temperature ONL, and the temperature ripple of the heat roller center portion, that is, the fixing portion. Had to be big.

  A fixing device used in a monochrome image forming apparatus has a large allowable range of temperature ripple, so there is no problem with conventional control. However, in a color image forming apparatus that forms a color toner image on a fixing member, When the temperature ripple is large, the superimposed color toner images may be reversely fixed on the high temperature side and unfixed on the low temperature side, which may cause a deterioration in image quality.

  The present invention has been made based on such circumstances, and an object of the present invention is to provide a fixing device capable of reducing the temperature ripple of the fixing portion.

The present invention relates to a fixing device that heats and fixes a heat roller, and is arranged in the vicinity of the heat roller in the axial direction of the heat roller so as to heat the first region of the heat roller. And a second induction heating coil for heating a second region different from the first region, and a first temperature detection means for detecting the temperature of the first region heated by the first induction heating coil, Second temperature detecting means for detecting the temperature of the second region heated by the second induction heating coil, temperature of the first region detected by the first temperature detecting means, and second temperature detecting means depending on the temperature difference between the temperature of the second region to be detected by its electrical communication with the output timing of the duty signal for switching alternately the timing of energization of the first induction heating coil and the second induction heating coil A duty signal generator means for determining the ratio of the duty width corresponding to between energization on the temperature of the first region detected by the first temperature sensing means, the first induction heating coil is set in advance The second induction heating coil in which the temperature and the temperature in the second region detected by the second temperature detecting means are compared with the first temperature comparing means for comparing the temperature and the energized off temperature higher than the energized on temperature. a second temperature comparing means for comparing the current on temperatures and high excitation-off temperatures than the current on the temperature of the, more the result of the comparison by the comparison result and the second temperature comparison means of the first temperature comparison means, the When one of the temperature of the first region and the temperature of the second region becomes lower than the energization on temperature, the first and second induction heating coils are energized, and the first region and the second region The temperature of the region It is entered with energization control signal generating means for generating a current control signal no longer allow the power supply to the higher than each of the excitation-off temperature first and second induction heating coils, and a power supply control signal and the duty signal, When energization is permitted by the energization control signal, energization of the first and second induction heating coils is alternately performed according to the duty signal, and when energization is not permitted, the first and second induction heating coils are energized. An induction heating coil that heats the lower temperature region of the first region and the second region when energization is permitted by the energization control signal. Is heated first .

  As described above in detail, according to the present invention, it is possible to reduce the temperature ripple caused by the temperature at the center of the heat roller being significantly lower than the reference temperature.

1 is a longitudinal sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention. FIG. 2 is a perspective view illustrating a state in which a fixing process is performed on a sheet by a fixing roller of the fixing device illustrated in FIG. 1. The control block diagram of an induction heating coil. The block diagram which shows the functional structure of an electricity supply control part. The flowchart which shows the specific operation | movement of an electricity supply control signal generation part. The wave form diagram which shows an example of the center thermistor detection temperature by the control of this Embodiment, a side thermistor detection temperature, and the various control signals at that time. The wave form diagram which shows an example of the center thermistor detection temperature by the conventional control, and a side thermistor detection temperature, and the various control signals at that time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In this embodiment, color toner images such as yellow (Y), magenta (M), cyan (C), and black (K), which are visualized by being superimposed on a fixing member, are heated to form each toner. Is a fixing device for a color image forming apparatus that melts and adheres to a fixing member.

  FIG. 1 is a longitudinal sectional view showing a schematic configuration of a fixing device according to the present embodiment. FIG. 2 is a perspective view showing how the fixing process is performed on the sheet by the fixing roller of the fixing device shown in FIG.

  As shown in FIGS. 1 and 2, the fixing device 1 includes a pair of fixing rollers 4 including a heat roller 2 and a press roller 3.

  The heat roller 2 is driven in the arrow direction by a drive motor (not shown). The press roller 3 rotates in the direction of the arrow following the heat roller. Further, a sheet P, which is a fixing material that supports the toner image, passes between both rollers.

  The heat roller 2 is an endless member having a metal layer composed of, for example, an iron cylinder having a thickness of 1 mm, that is, a conductor, and a release layer such as Teflon (registered trademark) is formed on the surface. In addition, stainless steel, aluminum, an alloy of stainless steel and aluminum, or the like can be used for the heat roller 2.

  The press roller 3 is formed by covering the cored bar 3a with an elastic body such as silicon rubber or fluorine rubber, and is pressed against the heat roller 2 with a predetermined pressure by a pressure mechanism (not shown). A nip N having a predetermined width (the outer peripheral surface of the press roller 3 is elastically deformed by pressure contact) N is provided at a position where both rollers contact.

  As a result, when the paper P passes through the nip N, the toner on the paper P is melted and fixed on the paper P.

  On the periphery of the heat roller 2 and on the downstream side of the nip N in the rotational direction, a peeling claw 5 for peeling the paper P from the heat roller 2, and toner or paper offset-transferred to the outer peripheral surface of the heat roller 2 The temperature of the cleaning member 6 for removing paper dust and the like, the release agent application device 8 for applying a release agent to prevent toner from adhering to the outer peripheral surface of the heat roller 2, and the temperature of the outer peripheral surface of the heat roller 2 are set. Two thermistors 9a and 9b to detect are provided.

  One thermistor 9a is provided at a substantially central portion in the axial direction of the heat roller 2, and the other thermistor 9b is provided at one end. Here, the thermistor 9a functions as a center temperature detecting means for detecting the temperature of the central portion of the heat roller 2, and is referred to as a center thermistor. The thermistor 9b functions as a side temperature detecting means for detecting the temperature of at least one end of the heat roller 2, and is referred to as a side thermistor.

  Inside the heat roller 2, an induction heating coil 10 as a heating means is provided.

  FIG. 3 is a control block diagram of the induction heating coil 10. As shown in the figure, the induction heating coil 10 provided inside the heat roller 2 includes a central coil 10C for heating the central portion of the heat roller 2, a left end coil 10L for heating the left end portion, and a right end for heating the right end portion. The coil 10R is divided into three.

  The structure for dividing the induction heating coil 10 is not particularly limited in the present invention. For example, the applicant of the present application has shown the first to fifteenth embodiments in Japanese Patent Application No. 2001-159449 as a structure in which the induction heating coil 10 is divided into a plurality of parts in the axial direction of the heat roller. Even if it is a thing, this invention is applicable.

  The drive circuit 20 including the DC power supply 21, the switching circuits 22a and 22b, and the capacitors 23a and 23b drives the central coil 10C by the switching circuit 22a and the capacitor 23a, and the left end coil 10L and the right end coil 10R by the switching circuit 22b and the capacitor 23b. To drive.

  The main CPU 30 controls the entire fixing device 1 and is connected to a ROM, a RAM, and the like through a bus (not shown). In particular, the main CPU 30 takes in analog signals output from the center thermistor 9 a and the side thermistor 9 b as digital data via the A / D converter 31. Then, the temperature of the center portion of the heat roller detected by the center thermistor 9a is compared with the temperature of the end portion of the heat roller detected by the side thermistor 9b, and the output timing and duty width of the duty signal DUTY are determined according to the temperature difference. The ratio is determined (duty signal generation means).

  The energization control unit 40 generates an energization control signal EPS for controlling energization permission / denial from the temperature of the center portion of the heat roller detected by the center thermistor 9a and the temperature of the end portion of the heat roller detected by the side thermistor 9b. , Supplied to the IH control unit 32.

  When the energization control signal EPS is on, that is, energization is permitted, the IH control unit 32 outputs the energization signal CDS to the switching circuit 22a on the central coil 10C side if the duty signal DUTY is “H”. If the duty signal DUTY is “L”, the energization signal SDS is output to the switching circuits 22b on the end coils 10L, 10R side to control the energization of the induction heating coil 10.

  FIG. 4 is a block diagram functionally showing the configuration of the energization control unit 40. The energization control unit 40 includes a center reference voltage generation unit 41, a side reference voltage generation unit 42, a center side comparison unit 43, a side side comparison unit 44, an energization control signal generation unit 45, and an energization control signal output unit 46. .

  The center reference voltage generation unit 41 generates a reference voltage to be compared with a measurement voltage corresponding to the temperature of the heat roller 2 detected by the center thermistor 9a. Control from the CPU 30 or feedback control of output from the comparison unit 43 To generate an ON reference voltage and an OFF reference voltage.

  The side reference voltage generation unit 42 generates a reference voltage to be compared with a measurement voltage corresponding to the temperature of the heat roller 2 detected by the side thermistor 9b, and controls from the CPU 30 or feedback control of the output of the comparison unit 44. To generate an ON reference voltage and an OFF reference voltage.

  Incidentally, in this embodiment, when the fixing temperature range in which each color toner image can be stably fixed on the fixing member (paper P) is, for example, 180 ° C. to 220 ° C., the OFF reference with a slight margin. The voltage is 210 ° C., and the ON reference voltage is 190 ° C. Instead of generating each reference voltage fixedly, the reference voltage may be finely adjusted as appropriate by software control of the CPU 30.

  The center side comparison unit 43 compares the measured voltage corresponding to the detected temperature of the center thermistor 9a with the reference voltage supplied from the center reference voltage generation unit 41, and outputs an output corresponding to the comparison result to the energization control signal generation unit 45. In this embodiment, when the measured temperature is lower than the reference temperature, an “L” (low) level output is given, and when the measured temperature is higher than the reference temperature, an “H” (high) level output is given ( First temperature comparison means).

  The side comparison unit 44 compares the measured voltage corresponding to the detected temperature of the side thermistor 9b with the reference voltage supplied from the side reference voltage generation unit 42, and outputs an output corresponding to the comparison result to the energization control signal generation unit 45. In this embodiment, when the measured temperature is lower than the reference temperature, an “L” level output is given, and when the measured temperature is higher than the reference temperature, an “H” level output is given (second temperature comparing means). ).

  The energization control signal generation unit 45 calculates a logical sum negation of the negative logic input A from the center side comparison unit 43 and the negative logic input B from the side side comparison unit 44, and outputs the result as an energization control signal output C Part 46 is given.

  A specific operation of the energization control signal generation unit 45 will be described with reference to the flowchart of FIG. That is, the energization control signal generation unit 45 monitors the negative logic input A and the negative logic input B. When either one of the negative logic inputs A or B becomes “L” level, the output C is set to “L” level. If both the negative logic inputs A and B are at “H” level, the output C is set to “H” level.

  The energization control signal output unit 46 outputs to the IH control unit 32 an energization control signal EPS that turns on when the input C from the energization control signal generation unit 45 becomes “L” level and turns off when the input C becomes “H” level.

  Here, the center reference voltage generation unit 41, the side reference voltage generation unit 42, the center side comparison unit 43, and the side side comparison unit 44 of the energization control unit 40 calculate the detected temperature by the center thermistor 9a and the detected temperature by the side thermistor 9b. It functions as a temperature monitoring means for monitoring.

  The energization control signal generation unit 45 and the energization control signal output unit 46 turn on energization of the induction heating coil 10 when the temperature monitoring means detects that one of the detected temperatures has decreased to a preset ON reference temperature. Functions as energization control means. The energization control signal generator 45 and the energization control signal output unit 46 turn off the energization of the induction heating coil 10 when the temperature monitoring means detects that both the detected temperatures have risen to the OFF reference temperature higher than the ON reference temperature. It also has means to do.

  In the fixing device 1 of the present embodiment configured as described above, as shown in FIG. 6, the energization control signal EPS is in the ON state during the warm-up period. The energization signals SDS for the partial coils 10L and 10R are alternately output to the drive circuit 20, and the central coil 10C and the end coils 10L and 10R are alternately energized. As a result, the heat roller 2 is heated and its surface temperature rises.

  When the temperature CST at the center of the heat roller 2 detected by the center thermistor 9a and the temperature SST at the end of the heat roller 2 detected by the side thermistor 9b both reach the OFF reference voltage OFFL (FIG. 6). At time T1), the outputs of the comparison units 43 and 44 (negative logic inputs A and B of the energization control signal generation unit 45) are both at the “H” level, and the output C of the energization control signal generation unit is at the “H” level. Therefore, the energization control signal EPS is turned off (energization is not permitted). As a result, the energization signals CDS and SDS are not output to the drive circuit 20, and neither the central coil 10C nor the end coils 10L and 10R are energized.

  After that, when one of the temperature CST at the center of the heat roller 2 detected by the center thermistor 9a and the temperature SST at the end of the heat roller 2 detected by the side thermistor 9b falls to the ON reference voltage ONL, it corresponds. Since the output A or B of the comparison section 43 or 44 on the side becomes “L” and the output C of the energization control signal generation section becomes “L” level, the energization control signal EPS is turned on (energization permitted).

  Generally, the heat roller 2 is less likely to be heated at both ends than at the center, so that the temperature CST at the center reaches the end when the temperature SST at the end reaches the OFF reference voltage OFFL (T1 in FIG. 6). The temperature is higher than SST. For this reason, the temperature SST at the end falls to the ON reference voltage ONL earlier than the temperature CST at the center (T2 in FIG. 6). At this time, the temperature SST at the end is lower than the temperature CST at the center, so that the energization signal SDS for the end coils 10L and 10R is ahead of the energization signal CDS for the center coil 10C. Given to. For this reason, while the energization signal SDS is output, the temperature CST at the center of the heat roller 2 decreases, but at the time when the energization signal SDS is turned off and the energization signal CDS is given to the drive circuit 20, It is not much lower than the reference voltage ONL (in the figure, it is at a higher level than the ON reference voltage ONL). Accordingly, it is possible to reduce the temperature ripple of the fixing unit that is the center of the heat roller 2.

  In the present embodiment, the energization control signal EPS is turned on until both the center temperature CST and the end temperature SST of the heat roller 2 reach the OFF reference voltage OFFL. Yes. Therefore, even when the control for turning on the energization permission signal EPS is introduced when either the temperature CST at the center of the heat roller 2 or the temperature SST at the end reaches the ON reference voltage ONL, On and off are not repeated frequently, and flicker can be reduced.

  In the above-described embodiment, the energization control unit 40 is configured by hardware such as a comparator or a NOR gate. However, the energization control signal EPS is converted by software processing by converting the outputs of the center thermistor 9a and the side thermistor 9B into digital data. The on / off state may be controlled.

  DESCRIPTION OF SYMBOLS 1 ... Fixing device, 2 ... Heat roller, 3 ... Press roller, 4 ... Fixing roller, 9a ... Center thermistor, 9b ... Side thermistor, 10 ... Induction heating coil, 20 ... Drive circuit, 30 ... Main CPU, 32 ... IH control , 40 ... energization control unit, 41 ... center reference voltage generation unit, 42 ... side reference voltage generation unit, 43 ... center side comparison unit, 44 ... side side comparison unit, 45 ... energization control signal generation unit, 46 ... energization control Signal output section.

JP 2002-174981 A

Claims (2)

In a fixing device for fixing by heating a heat roller,
A first induction heating coil that is arranged in the vicinity of the heat roller in the axial direction of the heat roller and that heats the first region of the heat roller, and a second region that is different from the first region. A second induction heating coil for heating;
First temperature detection means for detecting the temperature of the first region heated by the first induction heating coil;
Second temperature detecting means for detecting the temperature of the second region heated by the second induction heating coil;
The first induction according to a temperature difference between the temperature of the first area detected by the first temperature detecting means and the temperature of the second area detected by the second temperature detecting means. Duty signal generation means for determining a duty signal output timing for alternately switching the timing of energization to the heating coil and the second induction heating coil and a ratio of a duty width corresponding to the energization time ;
The first region temperature detected by the first temperature detecting means is compared with a preset energization on temperature to the first induction heating coil and an energization off temperature higher than the energization on temperature. 1 temperature comparison means;
The second region temperature detected by the second temperature detecting means is compared with a preset energization on temperature to the second induction heating coil and an energization off temperature higher than the energization on temperature. 2 temperature comparison means;
The comparison result of the first temperature comparing means more and comparison result by the second temperature comparing means, said current-on one of the respective one of the temperature of said temperature and said second region of the first region When lower than the temperature , energization of the first and second induction heating coils is permitted, and when both the temperature of the first region and the temperature of the second region are higher than the respective energization off temperatures, the first Energization control signal generating means for generating an energization control signal that does not permit energization of the first and second induction heating coils ;
The energization control signal and the duty signal are input, and when energization is permitted by the energization control signal, energization is alternately performed to the first and second induction heating coils according to the duty signal, and energization is performed. Energization control means for stopping energization of the first and second induction heating coils when the operation is not permitted ,
When energization is permitted by the energization control signal, the energization control means heats the induction heating coil that heats the lower one of the first region and the second region first. A fixing device characterized. Wherein the first region is a central portion of said heat roller, said second region, a fixing device according to claim 1, characterized in that the end portion of the heat roller.

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