JP3360521B2 - Fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fixing an image recorded on transfer paper in a copying machine, a laser printer, or the like.

[0002]

2. Description of the Related Art For example, in a copying machine, a laser printer, or the like, a toner image formed on a photosensitive drum is transferred onto transfer paper by electrostatic force generated by a charge of a transfer charger. The transferred toner image is in an unstable state where it is immediately peeled off when it is touched. Therefore, the toner component is heated and pressed at a predetermined temperature by a fixing roller having a built-in heater, whereby the toner component is transferred to the fibers of the transfer paper. It is made to penetrate the inside and fix it.

[0003] If the fixing temperature is not stable, the degree of fixing becomes uneven, which may cause image unevenness in a reproduced image. Therefore, the conventional fixing device detects the temperature of the fixing roller and compares it with a reference temperature. A constant temperature is maintained by controlling the energization / de-energization of the heater. However, since the heater is usually coil-shaped,
When the non-energization is switched, electromagnetic induction occurs and the voltage fluctuates greatly, which has a considerable effect on other electric appliances. In particular, lighting devices such as fluorescent lamps are easily affected, and if the switching between energization and non-energization is frequently performed, the flickering (flicker) of the fluorescent lamp may occur, which may cause discomfort.

Therefore, conventionally, even if the heater temperature becomes equal to or higher than a predetermined reference temperature, the energization is not stopped or started immediately, but a required time elapses from the start of the energization or the stop of the energization. If not, while managing the time so that switching between energized / deenergized is not performed,
The temperature of the fixing roller is controlled. According to such a temperature control method, the generation of flicker can be effectively prevented, the life of the heater can be extended, and a double effect can be obtained.

In general, a fixing device is rotated by pressing a transfer paper between a fixing roller having a heater as described above and a pressing roller opposed to a lower portion of the fixing roller and pressing the transfer paper. The fixing is performed (hereinafter, the above-described fixing roller is simply referred to as “upper roller”, and the pressure roller is referred to as “lower roller”). This lower roller does not have its own heat generating means, but is in direct contact with the upper roller except at the time of fixing, so it is maintained at almost the same temperature as the upper roller by heat conduction. Does not cause any particular inconvenience.

However, when a large number of transfer papers are continuously fixed, the state in which the transfer roller is not in direct contact with the upper roller continues for a long time, while the transfer paper loses heat. Drops rapidly, causing a temperature difference with the upper roller, which results in uneven fixing strength. Therefore, a fixing device that incorporates a heater also in the lower roller and performs the same temperature control as the above-described upper roller is becoming widespread. In the fixing device having such a configuration, the upper and lower rollers are controlled in time with the same cycle. The temperature is controlled.

FIG. 7 is a time chart showing a state of temperature control in the fixing device. As shown in the figure, the cycle of the ON / OFF signal of the lighting signal for both the upper heater (the upper roller heater) and the lower heater (the lower roller heater) is set to be equal to or longer than a predetermined time t1. In accordance with ON / OFF of the heater lighting signal, each heater is energized / de-energized, and the temperatures of the upper roller and the lower roller are respectively reduced from the lower limit temperature Td to the upper limit temperature Tu with respect to the fixing reference temperature Ts. The waveform changes in the temperature range.

If such a temperature change from the temperature Td to Tu (hereinafter referred to as "temperature ripple") becomes too large, fixing unevenness occurs. Therefore, an appropriate value of t1 is set in accordance with the heat generation amount of the heater. Is done. The reason that the temperature ripple of the lower roller is smaller than the temperature ripple of the upper roller is that the heat generation amount of the lower roller is usually set to be smaller.

[0009]

However, the fixing device having the heaters on the upper and lower rollers as described above has the following problem in terms of measures against flicker. That is, since the temperature control of the upper and lower rollers is basically performed independently, electromagnetic induction is generated each time the heater is energized and the energization is stopped. This causes flickering of the lighting equipment twice as often (in FIG. 7, ON / O of the lighting signal of the upper and lower heaters).
Although the timings of the FFs seem to be exactly the same, this merely shows the minimum cycle of switching between energization / non-energization, and actually the ON / OFF timing is slightly different. By the way, if the energization control of the upper and lower rollers is performed by the same relay circuit and the timing of energization / non-energization switching is made exactly the same, the temperature of the upper and lower rollers gradually shifts due to the difference of various conditions, so that accurate temperature control cannot be performed. In addition, since the start / stop of the supply of a large amount of power is performed at a time, the voltage fluctuation due to the electromagnetic induction also increases, so that the temperature of each roller must be controlled individually.

However, according to the configuration in which the heaters are provided on both the upper and lower rollers to independently control the temperature, there is an advantage that the fixing can be stably performed, but the flicker frequently occurs as described above. Problem arises. SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a fixing device that does not easily generate flicker while performing high-precision temperature control for each roller including a heat generating unit.

[0011]

To achieve the above object, a fixing device according to the present invention comprises a plurality of rollers having heat generating means, and a temperature control means for controlling each of the rollers to a predetermined reference temperature. Wherein at least one of the plurality of rollers generates a different amount of heat from the other rollers, the temperature control unit includes a temperature detection unit that detects a temperature of each roller, and the reference temperature. Comparing the temperature detected by the temperature detecting means with each other, and determining whether the heat generating means of each roller is energized / de-energized, and at least one energized / de-energized cycle based on the determination result of the determining means. However, there is provided an energization control means for controlling energization / de-energization of each of the heat generation means in a state where the heat generation amount does not fall within a predetermined time limit. It is characterized in that is.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fixing device according to the present invention will be described below by taking a fixing device in a digital copying machine as an example. (1) Overall Configuration of Digital Copier First, the overall configuration of the digital copier (hereinafter, simply referred to as "copier") will be described with reference to FIG.

As shown in FIG. 1, the copying machine is roughly divided into an image reader section 10 for reading a document image and a printer section 20 for reproducing an image read by the image reader section 10. A scanner 11 in the image reader unit 10 includes an exposure lamp 12 for irradiating a document, and a rod lens array 13 for condensing light reflected from the document.
And a close-contact CCD that converts the collected light into electrical signals
A color image sensor (hereinafter simply referred to as “CCD sensor”) 14 is provided.

When the user opens the document holder 16 upward, places the document on the document glass plate 15, and instructs the start of copying, the scanner 11 is driven by the scanner motor M2 and moves in the direction of the arrow. Then, the original is scanned. The reflected light of the original by irradiation of the exposure lamp 12 of the scanner 11 is photoelectrically converted by the CCD sensor 14,
The image data thus obtained is subjected to A / D conversion by the control unit 100 to become a digital signal, and further subjected to necessary processing such as shading correction, density conversion, and edge enhancement, and then output as a drive signal for the laser diode 21. Is done.

The laser light emitted from the laser diode 21 passes through a collimating lens 22 to become parallel light, and is reflected and deflected by a mirror surface of a polygon mirror 23 driven to rotate at a constant speed by a polygon motor 24. . The deflected laser light passes through the fθ lens 25, is reflected by the folding mirrors 26a and 26b, and performs exposure scanning on the surface of the photosensitive drum 27.

Before the photosensitive drum 27 receives the above-mentioned exposure, the residual toner on the surface of the photosensitive drum is removed by a cleaner 28,
Further, after being erased by irradiating the eraser lamp 29,
The photosensitive drum 27 is uniformly charged by the charging charger 30, and when exposed to light in such a uniformly charged state, an electrostatic latent image is formed on the photosensitive member on the surface of the photosensitive drum 27. The electrostatic latent image is developed by the developing device 31 to form a toner image on the surface of the photosensitive drum 27.

Transfer paper (not shown) placed on a paper cassette 34 in synchronization with the rotation of the photosensitive drum 27
Is fed to a transfer position below the photosensitive drum 27 by the feed roller 341, the timing roller 342, and the transport belt 33, and at this transfer position, the photosensitive drum is charged by the charge of the transfer charger 32 installed behind the transport belt 33. The toner image formed on the body drum 27 is transferred onto the transfer paper.

The toner image transferred to the copy paper is in an unstable state where it is immediately peeled off when it is touched.
The sheet is conveyed to a fixing device 36 by a reference numeral 5, where it is pressurized and fixed at a high temperature, and then discharged onto a discharge tray 38 by a discharge roller 37. An operation panel 17 is provided at a position on the front surface of the image reader unit 10 where the user can easily operate, for inputting, for example, the start of copying by the user. (2) Configuration of Fixing Device (Mechanical Portion) Next, the configuration of the mechanical portion of the fixing device 36 excluding the control system will be described.

FIG. 2 is an enlarged vertical sectional view of a mechanical portion of the fixing device 36. As shown in FIG.
Has an upper roller 42 having a heater 41 therein, and a lower roller 43 provided below the upper roller 42 and having a heater 51 therein. The outer peripheral portion of the upper roller 41 is usually formed of metal, and its surface is subjected to chemically stable Teflon processing or the like. The lower roller 4
The outer peripheral portion of 3 is formed of a heat-resistant elastic member such as silicon rubber.

As described above, the difference in the members of the outer peripheral portion between the upper roller 42 and the lower roller 43 is that the upper roller 42 needs to directly contact the toner image and quickly heat the toner image. The use of an elastic member as the outer peripheral member of the lower roller 43 ensures a sufficient contact heating time for the transfer paper at the portion (nip portion) in contact with the upper roller 42. Therefore, it is necessary to increase the contact width between the transfer paper and the roller by utilizing the elastic deformation of the elastic member.

With such a configuration (particularly, the outer peripheral portion of the lower roller 43 is covered with an elastic member having low thermal conductivity), the upper roller 42 generates a larger amount of heat than the lower roller 43. In general, the heat value of the heater 41 of the upper roller 42 is set to be larger than the heat value of the heater 51 of the lower roller 43 (for example, the heater 41
00W, heater 51 is 600W).

Around the respective rollers, separation claws 44 and 45 for separating transfer paper when the paper comes into close contact with the respective rollers, and thermistors 46 and 52 for detecting the surface temperature of the respective rollers; In order to prevent overheating of each roller, thermoswitches 47 and 53 are provided to forcibly stop energization when the temperature becomes equal to or higher than a predetermined temperature. The upper and lower rollers 42 and 43 and components around them are thermally connected to the outside. It is housed in a heat insulation case 48 for cutting off.

The separating claws 44 and 45 are connected to the heat insulating case 4.
8, supported by supporting shafts 44a, 45a fixed to
The upper roller 4 is driven by the tension springs 44b and 45b, respectively.
2. It is urged toward the lower roller 43. The thermistors 46 and 52 and the thermoswitches 47 and 53 are respectively formed by leaf springs 46a, 52a, 47a and 53a.
Each heat sensitive portion is urged to abut the surface of the respective roller.

Upper roller 42 and / or lower roller 4
3 is driven to rotate in the direction of the arrow in the figure by a rotation drive device (not shown), and when the transfer paper is conveyed along the guide plate 49, the transfer paper is nipped by the upper roller 42 and the lower roller 43 and discharged while pressing. It is sent out in the direction of the roller 37.
The temperatures of the upper and lower rollers 42 and 43 are individually controlled to be about 190 ° C. by a temperature controller 60 (FIG. 3) to be described later. The toner image adhered to the surface melts and firmly enters between the fibers of the transfer paper and is fixed.

Even if the transfer paper comes into close contact with the upper roller 42 or the lower roller 43 during pressurization, the tips of the separation claws 44 and 45 urged against the surface of each roller as described above transfer the roller surface to the roller surface. The transfer paper is peeled off from the surface of the roller by entering a gap between the papers, thereby preventing the paper from being rolled up. The transfer paper on which the toner image is fixed in this manner is
The paper is sent to the discharge roller 37 along the lines 0a and 50b, and is discharged onto the paper discharge tray 38 (FIG. 1). (3) Configuration of Temperature Control Device Next, the configuration of the temperature control device 60 for controlling the temperatures of the upper and lower rollers 42 and 43 will be described with reference to FIG.

As shown in FIG.
Are a CPU 61, a first counter section 62, a second counter section 63, a RAM 64, and A / D converters 65 and 67.
And SSRs (solid state relays) 66 and 68. One end of each of the thermistors 46 and 52 is grounded, and the resistance value changes as the surface temperature of the contacting roller changes, thereby changing the voltage value on the output side.

The A / D converters 65 and 67 convert the voltage values on the output sides of the thermistors 46 and 52 into digital signal values and output the digital signal values to the CPU 61, respectively. The RAM 64 has a set temperature Ts (more precisely, a digital signal value corresponding to the temperature) at the time of fixing and initial count values C2, C3 (corresponding to predetermined times t2, t3 for power supply / non-power supply time management). C2 <C3) is stored, and the CPU 6
1 is a digital signal value corresponding to the reference temperature Ts and an A / D converter 65 detected by the thermistors 46 and 52;
The digital signal values obtained by the conversion at 67 are compared with each other (hereinafter, in order to avoid such a roundabout expression, the comparison between the digital signal values is simply referred to as “compare the reference temperature and the detected temperature”). Expressed as.).

On the other hand, the first counter section 62 has a CPU 61
The initial counter value C2 stored in the RAM 64 is set as an initial value each time the heater ON (energization start) and heater ON (power stop) signals are output to the SSR 66, and the count is decremented by "1". I do. CP
When the count value becomes "0" while the heater 41 is energized, the reference temperature Ts and the thermistor 4
6 and the detected temperature is compared with the reference temperature Ts.
If it is determined to be higher, a signal to turn off the heater is sent to the SSR 66. The SSR 66 receives this signal, opens the internal relay contact, and stops energizing the heater 41.

If the count value becomes "0" when the heater 41 is not energized (when the heater is not energized),
The CPU 61 compares the reference temperature Ts with the detected temperature. If it is determined that the detected temperature is lower than the reference temperature, the CPU 61 sends a heater ON signal to the SSR 66, and
66 receives this signal, closes the internal relay contact,
Power supply to the heater 41 is started.

The second counter unit 63 is provided with a CPU 61
Each time the heater ON and heater OFF signals are output to the SSR 68 from, the initial counter value C3 stored in the RAM 64 is set as an initial value to "1".
The CPU 61
When the count value becomes “0”, the reference temperature Ts and the temperature detected by the thermistor 52 are compared, and the energization control to the heater 51 is performed in the same manner as in the case of the heater 41 described above.

If the count values of the first counter section 62 and the second counter section 63 are not counted down from C2 and C3 and become "0", the CPU 61
Does not issue a heater ON / OFF signal to the SSRs 66 and 68, so that the switching cycle of energization / non-energization of the heaters 41 and 51 is set to the predetermined times t2 and t, respectively.
It will not be shorter than three.

In addition, since the initial count value C2 <C3, the switching cycle of the heater 51 is set longer than the switching cycle of the upper heater, so that the upper heater and the lower heater are turned ON / OFF at substantially the same timing as in the prior art. The number of ON / OFF times per unit time is reduced as compared with the case where it has been performed, which contributes to flicker countermeasures. Note that an increase in the switching period between the energization and non-energization of the heater 51 means that the temperature ripple increases accordingly. However, as described above, the amount of heat generated by the heater 51 is Because it is set smaller than the amount
Even if the switching cycle becomes somewhat longer, the temperature ripple can be kept within an allowable range.

FIG. 4 is a common flowchart showing the operation of controlling the temperatures of the upper and lower rollers 42 and 43 by the temperature controller 60. The temperature control of the upper roller 42 will be described below with reference to this flowchart. The CPU 61 first checks whether or not the heater 41 is currently in the OFF state (step S1).
If it is F (that is, if power is not supplied), it is determined whether or not the count value Coff of the first counter unit 62 is “0” (step S2).

The count value Coff is determined by a predetermined time t2 after the energization is stopped (switching between energization / non-energization is performed within the predetermined time as described above, and is hereinafter referred to as a "switching limit time"). )), The initial count C corresponding to
s (= C2) is subtracted from the count value. If the count value Coff = 0, it means that the switching limit time t2 has elapsed since the energization was stopped. The reference temperature Ts and the temperature T detected by the thermistor 46 are compared, and if “T ≦ Ts”, the SSR 66
To turn on the heater (step S
3, S4), set in the first counter section 62 and the heater O
Count value Co, which is counted down from the point in time at which it reaches N
n is reset to the initial count value Cs (= C2) (step S5).

In step S2, the count value Cof
If f = 0, the switching limit time t2 has not yet elapsed, so the count value is decremented by "1" (step S6) and the routine returns. If it is not “T ≦ Ts” in step S3, it is not necessary to start energization, and the process returns. Returning to step S1, if the heater is not currently in the OFF state, that is, if the heater 41 is energized, the process proceeds to step S7 to determine whether or not the count value Con of the first counter unit 62 is 0. .

If the count value Con = 0, it means that the switching limit time t2 has elapsed since the start of energization, and thus the stop of energization is permitted. Then, next, the reference temperature Ts and the detected temperature T are compared, and "T> T
s ", the flow goes to S so that the power supply to the heater 41 is stopped.
A signal is output to the SR 66 to turn off the heater (steps S8 and S9), and the count value Coff set in the first counter section 62 is reset to the initial count value Cs (= C2) (step S10).

In step S7, the count value Con
If it is not = 0, it means that the switching limit time t2 has not elapsed, so the count value is decremented by "1" (step S11) and the routine returns. Step S8
In, if it is not "T>Ts", there is no need to stop energization, and the process returns. In this way, first, it is determined whether or not the switching limit time t2 has elapsed,
If it is determined that the elapsed time has elapsed, the reference temperature Ts and the detected temperature T are compared for the first time, and the ON / OFF control of the heater is performed as necessary. Within.

Similarly, in the case of controlling the temperature of the lower roller 43, the heater 4
1. First counter section 62, thermistor 46 and SSR
66 is replaced with the heater 51, the second counter 63, the thermistor 52, and the SSR 68, respectively, and the reference count Cs is changed to a count value C3 corresponding to the switching limit time t3.
Should be set to.

The temperature control of the upper and lower rollers 42 and 43 is performed by the CPU 61 in parallel. Of course, if the temperature rises or falls too much before the switching limit times t2 and t3 elapse and the temperature ripple increases, fixing unevenness will occur. Therefore, the switching limit times t2 and t3 are determined for each roller. Is determined in consideration of the amount of heat generated by the heater to be used so that the temperature ripple within the range is within an allowable range.

Next, FIG. 5A shows how the temperature of the upper and lower rollers changes according to the temperature control routine described above.
As shown in the figure, the heater 41 output from the CPU 61
The lighting signal of the (upper heater) is turned ON / OFF in a cycle longer than the switching limit time t2, and accordingly, the upper roller 4
The temperature of No. 2 changes into a waveform with the reference temperature Ts interposed therebetween.

On the other hand, the lighting signal of the heater 51 (lower heater) is longer than t3, which is considerably longer than the upper roller switching limit time t2 (for example, if t2 = 25 seconds, t2 = 25 seconds).
3 = 50 seconds), and accordingly, the temperature of the lower roller 43 changes to a waveform across the reference temperature Ts. Since t3> t2, the number of times of ON / OFF per unit time is reduced as a whole, thereby contributing to the above-described countermeasure against flicker and extending the life of the heater 51.

As described above, these switching limit times t2,
At time t3, the temperature ripple in each roller is controlled within a temperature range in which stable fixing can be obtained. By further adjusting the values of t2 and t3, the temperature ripple of both rollers can be made substantially equal. In this case, more stable fixing can be performed. (4) Modified Example of Temperature Control Device In this modified example of the temperature control device, what is set as the switching limit time is one cycle of energization / non-energization from the heater lighting to the next heater lighting. The difference from the above-described temperature control is that the control is performed only by the detected temperature of the thermistor when the transition from the heater ON to the heater OFF is performed.

FIG. 5B is a diagram showing an outline of the temperature control in the present modification, in which the switching limit time of one cycle of ON / OFF of the lighting signal of the upper heater output from the CPU 61 is t4, and the lower limit time is t4. 1 of ON / OFF of heater lighting signal
The cycle switching time limit is t5, and t5> t4 (for example, t5 = 100 seconds, t4 = 50 seconds).

Therefore, also in this modification, the configuration itself of the temperature control device 60 is the same as that of the embodiment of FIG. 3, and only the contents of the initial count value stored in the RAM 64 and the temperature control routine by the CPU 61 are different. Different as described below. FIG. 6 is a common flowchart showing a routine of temperature control of each of the upper and lower rollers 42 and 43 of the temperature control device 60 in the present modification.

Based on this flowchart, the upper roller 42
The temperature control will be described as follows. At the same time when the heater is turned on, the switching limit time t4 is supplied to the first counter section 62.
Is set, and when the count value C becomes "0" (step S21), the switching limit time t4 has elapsed, so the temperature T detected by the thermistor 46 and the reference temperature Ts Is compared with "T
≦ Ts ”, the CPU 61 turns off the heater.
Is output to the SSR 66 to start energizing the heater 41 to turn on the heater, set the count value Con to the initial count value Cs (= C4), and return (step S).
22, S23, S24).

If “T ≦ Ts” is not satisfied in step S22, that is, if “T> Ts”, the CPU
The controller 61 outputs a signal for turning off the heater to the SSR 66, stops the power supply, turns off the heater, and returns (step S28). In step S21, if the count value C has not been set to "0" yet,
The count is subtracted (step S25), and the detected temperature T is compared with the reference temperature Ts (step S26).

In this step S26, "T> T
In the case of "s", in the present modification, there is no time limit for the heater OFF, so that the heater is immediately turned off (step S27) and the process returns. If "T>Ts" is not satisfied, the process returns as it is. Further upper roller 4
Wait for the temperature of 1 to rise. As described above, in the present modified example, there is only a time restriction for one cycle of energization / non-energization, so that the temperature control routine is simplified.

Therefore, the restriction on the time from the energization to the stop of the energization is apparently eliminated, but the fact that the time of one cycle is equal to or longer than the predetermined time means that the temperature drop after the stop of the energization exceeds a certain level. Since the time corresponding to the temperature drop is required from the re-energization to the rise of the reference temperature Ts, there is no possibility that the switching from the energization to the non-energization becomes extremely short.

In the case of controlling the temperature of the lower roller 43,
In the above description, the heater 41, the first counter 62,
Thermistor 46 and SSR 66 are connected to heater 5
1, second counter section 63, thermistor 52, SSR 68
And the reference count Cs may be set to the count value C5 corresponding to the switching limit time t5. The temperature control of these upper and lower rollers 42 and 43 is performed by the CPU 61 in parallel.

Of course, also in this modified example, the switching limit times t4 and t5 are determined to be optimum values in consideration of the amount of heat generated by the heater to be used so that the temperature ripple of each roller temperature falls within the allowable range. Will be. In this modification, the count value is reset and the subtraction count is performed from when the heater lighting signal is turned on. However, when the heater lighting signal is turned off, the count value is reset and the subtraction count is performed. One cycle time until the heater lighting signal is turned off may be limited.

Although the present invention has been described based on the embodiments and the modified examples, it goes without saying that the contents of the present invention are not limited to those described above. For example, the present invention can also be applied to temperature control when there are three or more fixing rollers and each roller has a built-in heater. The smaller the amount of heat generated by each heater, the longer the switching limit time. Is set.

If the reference temperature Ts is set to the temperature at the time of preheating, the temperature of each roller in the standby state can be controlled. Further, the fixing device according to the present invention is not limited to the above-described digital copying machine, but can be applied to all image forming apparatuses having a fixing unit that performs fixing while maintaining a predetermined temperature, such as an analog copying machine and a laser printer. It is.

[0053]

As described above, according to the fixing device of the present invention, a plurality of rollers having heat generating means,
In a fixing device provided with a temperature control means for controlling the temperature of each roller to a predetermined reference temperature, if at least one energized / de-energized cycle does not exceed a predetermined time limit, each roller is The control of energization / non-energization of the heat generating means is not performed, and the time limit is set to be larger for a roller having a smaller amount of heat generation, so that the number of times of energization / de-energization per unit time is reduced, This can contribute to the prevention of flicker and can further extend the life of the heater that generates a small amount of heat.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a copying machine to which a fixing device according to the present invention is applied.

FIG. 2 is a longitudinal sectional view of a mechanical part of the fixing device according to the present invention.

FIG. 3 is a block diagram of a temperature control device in the fixing device according to the present invention.

FIG. 4 is a flowchart showing a temperature control routine in the temperature control device.

FIG. 5 is a diagram showing how the temperature of the upper and lower rollers changes under the control of the temperature control device, and how the temperature of the upper and lower rollers changes according to a modification.

FIG. 6 is a flowchart showing a temperature control routine in a modification of the temperature control device.

FIG. 7 is a diagram illustrating a state of temperature control of upper and lower rollers in a conventional fixing device.

[Explanation of symbols]

 36 Fixing device 41, 51 Heater 42 Upper roller 43 Lower roller 60 Temperature controller 61 CPU 62 First counter 63 Second counter 64 RAM 65, 67 A / D converter 66, 68 SSR

Continuation of front page (56) References JP-A-62-279380 (JP, A) JP-A-61-134775 (JP, A) JP-A-63-75775 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G03G 13/20 G03G 15/20

Claims (1)

(57) [Claims] 1. A fixing device comprising: a plurality of rollers having heat generating means; and a temperature control means for controlling each of the rollers to have a predetermined reference temperature, wherein at least one of the plurality of rollers is provided. Has a different heat value from the other rollers. The temperature control means compares the temperature detected by the temperature detection means with the temperature detection means for detecting the temperature of each roller, and generates heat of each roller. Determining means for determining whether the means is energized / de-energized, and energizing each of the heat generating means in a state where at least one cycle of energization / de-energization does not fall within a predetermined time limit based on the determination result of the determining means. A fixing device, comprising: an energization control unit configured to perform control of non-energization, wherein the time limit is set to be longer for a roller having a smaller amount of heat generation.