JPH07121051A - Temperature controller for fixing device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of high-temperature offset, wrinkles and defective fixation by calculating the temperature of a pressure roller based on the temperature change of a heat roller and correcting a control temperature based on the temperature of the pressure roller. CONSTITUTION:The temperature (tp) of the pressure roller 54b is estimated based on the temperature change of the heat roller 54a, and the control temperature Tc is corrected based on the temperature (tp). That is, an intermittent control for energizing a heater 59 is carried out by combining an on time, or an off time and the control temperature Tc, then, the temperature fluctuation is restrained. And at usual control stage, the control temperature Tc is corrected in accordance with the obtained temperature(tp) of the pressure roller, the control temperature Tc is highly corrected only when the paper passes through, and also, the correction is performed in accordance with an ambient temperature (t0). Thus, the temperature is controlled with a consideration given to the temperature (tp) of the pressure roller 54b, so that the actual fixing temperature is more stabilized even in the case of using a low calorific capacity roller 54a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device for a fixing device which is applied to a fixing device of an image forming apparatus such as an electrostatic copying machine or a facsimile and which controls on / off of a heater for heating the fixing device.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus such as a copying machine, an electrostatic latent image formed on a photosensitive drum is visualized as a toner image, the toner image is transferred onto a sheet, and then heated by a fixing device. I am trying to fix it. This fixing device includes a heat roller heated by a pressure roller and a heater, and heats and fixes the toner on a sheet passing between the rollers.

In order to perform heat fixing, it is necessary that the fixing device has reached a predetermined high temperature. Therefore, in a copying machine or the like, a predetermined waiting time is required from turning on the power until copying is possible, which is inconvenient for the user. Therefore, it is desired to shorten the waiting time and, if possible, eliminate the waiting time. For that purpose, it is necessary to heat the fixing device to a predetermined high temperature in a short time.

[0004]

On the other hand, from the viewpoint of energy saving, it is preferable to heat the fixing device only when required.
Also in this case, it is necessary to heat the fixing device to a predetermined high temperature within a very short time from the start of copying until the sheet is conveyed to the fixing device. Therefore, in order to enable rapid heating of the fixing device, the inventor of the present application increases the heating capacity of the heater and reduces the diameter of the heat roller and the pressure roller so that the heat capacity of the heater is relatively large. I tried to make it smaller.

However, the temperature fluctuations due to the turning on / off of electricity to the heater are large, and high temperature offsets, wrinkles, and fixing defects occur. In particular, in many copying from the start of copying to several times, fixing failure often occurred. The inventor of the present application has a tendency that even if the heat roller heated by the heater reaches a predetermined temperature, the pressure roller is not yet sufficiently warmed, and therefore the actual fixing temperature becomes low, which causes a fixing failure. I thought it would be the cause. It was also considered that high temperature offset and wrinkles might be generated when the temperature of the pressure roller was too high.

On the other hand, since the pressure roller is made of rubber and has poor heat conduction, it is very difficult to detect this temperature. The present invention has been made in view of the above problems,
An object of the present invention is to provide a temperature control device of a fixing device that can perform stable fixing even when a heat roller having a small heat capacity is used by performing control in consideration of the temperature of the pressure roller.

[0007]

In order to solve the above problems, a temperature control device for a fixing device according to a first aspect of the present invention includes a pressure roller and a heat roller heated by a heater, and a sheet passing between the rollers. A temperature control device for a fixing device, which is applied to an image forming apparatus having a fixing device for heating and fixing toner, and which controls on / off of energization to the heater based on the temperature detected by a heat roller temperature detecting means for detecting the temperature of the heat roller. In, the temperature of the pressure roller is calculated based on the falling gradient of the detected temperature due to the turning off of the power supply to the heater, and the control temperature is corrected by adding a required correction amount according to the calculated temperature of the pressure roller. It is characterized by including a correction unit.

According to a second aspect of the present invention, there is provided a temperature control device for a fixing device, which includes a pressure roller and a heat roller heated by a heater, and heats and fixes the toner on a sheet passing between the rollers, and an image forming device. A fixing device which is applied to an image forming apparatus provided with a blowing unit for cooling the inside of the apparatus main body, and which controls on / off of energization to the heater based on a temperature detected by a heat roller temperature detecting unit detecting the temperature of the heat roller. In the temperature control device, the temperature of the pressure roller is calculated on the basis of the falling gradient of the detected temperature due to the turning off of the power supply to the heater, and the air volume for adjusting the air volume of the blower means is calculated according to the calculated temperature of the pressure roller. It is characterized by including an adjusting unit.

Further, in the temperature control device of the fixing device according to the third aspect, the fixing device includes a pressure roller and a heat roller heated by a heater, and heats and fixes the toner on a sheet passing between the pressure roller and the pressure roller. And a heat roller temperature for detecting the temperature of the heat roller, which is applied to an image forming apparatus including a sheet conveying device having a plurality of roller groups including a heat roller and a rotation driving unit that rotationally drives the roller group of the sheet conveying device. In a temperature control device of a fixing device for controlling on / off of energization to the heater based on the temperature detected by the detection means, the temperature of the pressure roller is calculated based on the falling gradient of the detected temperature due to turning off the energization to the heater. A rotation speed adjusting unit for adjusting the rotation speed of the rotation driving means according to the calculated temperature of the pressure roller. That.

[0010]

The temperature of the heat roller rises and falls with the turning on and off of electricity to the heater. The heat of the heat roller is transferred to the pressure roller side, and it is considered that this transfer amount affects the gradient of the temperature change of the heat roller.
The heat transfer amount to the pressure roller side is considered to depend on the temperature of the pressure roller. That is, it is considered that there is a predetermined relationship between the temperature change gradient of the heat roller and the temperature of the pressure roller. Then, the inventor of the present application has found that there is a high correlation between the temperature gradient of the pressure roller and the falling gradient of the detected temperature of the heat roller due to the turning off of the power to the heater.

Therefore, according to the configuration of the invention according to claim 1, paying attention to the above relationship, the temperature of the pressure roller is estimated based on the temperature change of the heat roller, and the control temperature is corrected based on this. I chose As a result, control can be performed in consideration of the temperature of the pressure roller, so that the actual fixing temperature can be made more stable. In particular, it is effective in preventing the fixing failure that occurs in the early stage of heating, in which the pressure roller tends to be still not sufficiently warm even if the heat roller heated by the heater reaches a predetermined temperature. Demonstrate.

According to the second aspect of the invention, the air volume of the cooling ventilation means is adjusted in accordance with the calculated temperature of the pressure roller, so that control can be performed in consideration of the temperature of the pressure roller. I chose According to the configuration of the third aspect of the invention, the rotation speed of the rotation driving means is adjusted according to the calculated temperature of the pressure roller, and the speed at which the paper passes through the fixing device is adjusted. As a result, the amount of heat per unit time taken by the paper is adjusted, and the balance with the amount of heat per unit time supplied by the heater is maintained.

[0013]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is a schematic diagram showing an internal configuration of a copying machine as an image forming apparatus including a temperature control device of a fixing device according to an embodiment of the present invention. Referring to FIG. 1, this copying machine is arranged inside the copying machine main body 1 along the upper surface of the copying machine main body 1 in a state where an original placed on a transparent original placing plate is pressed by an original pressing member. An original system 2 to be moved, an original system moved by the original system 2 is illuminated, and an optical system 3 for guiding reflected light from the original system to the photoconductor drum 42, and an electrostatic latent image formed on the photoconductor drum 42 is developed. After the image is visualized by the apparatus 41, the image forming unit 4 that transfers the image onto the sheet and the fixing device 54 that heats and fixes the toner image transferred onto the sheet are provided. The paper transport unit 5 and the like for discharging the paper to the discharge tray 56 are provided.

Although not shown, on the upper surface of the copying machine main body 1, there is provided an operation section in which a copy start switch and other switches are arranged. Inside the copying machine main body 1, above the fixing device 54, a fan F is arranged as a blowing unit for discharging the hot air inside the copying machine main body 1 to the outside. The optical system 3 includes a fluorescent lamp 31 as a light source for illuminating an original moving on the original table, and a fluorescent lamp 31 arranged in a direction orthogonal to the original moving direction, and reflects light from the original on the photosensitive drum 42.
A plurality of image forming lenses 32 for forming an image on the top are provided.

As the image forming section 4, a charging charger 43, a developing device 41, a transfer charger 44 and a cleaning device 45 are arranged in this order around the photosensitive drum 42. The image forming unit 4 includes a charging charger 43.
On the outer peripheral surface of the photosensitive drum 42 that is uniformly charged by
After the original image is formed to form an electrostatic latent image, the electrostatic latent image is visualized as a toner image by the developing device 41, the toner image is transferred to a sheet by the transfer charger 44, and the residual toner is cleaned by a cleaning device. It is designed to be collected by 45.

The sheet conveying section 5 pulls out sheets one by one from the sheet feeding tray 61, and brings the sheet from the sheet feeding roller 51 having a half-moon shape in cross section and the sheet from the manual sheet feeding section 60 or the sheet feeding tray 61 into contact with each other. Registration rollers 53a and 53b for temporarily holding the sheet and a heat roller 54a included in the fixing device 54 for fixing the toner image transferred to the sheet.
And the pressure roller 54b and the pair of discharge rollers 55a, 5
5b and.

Further, the paper transport section 5 is further provided with a paper feed detection switch 57, a paper discharge detection switch 58, a heat roller temperature detection sensor SH and an ambient temperature detection sensor SA. The paper feed detection switch 57 includes a limit switch arranged upstream of the registration rollers 53a and 53b in the paper conveyance direction, and the paper ejection detection switch 58 includes a limit switch arranged upstream of the discharge rollers 55a and 55b in the paper conveyance direction. It consists of a switch. The heat roller temperature detection sensor SH includes a thermistor arranged in a predetermined portion of the heat roller 54a, and detects the temperature of the heat roller 54a.
The ambient temperature detection sensor SA is a thermistor arranged at a predetermined position inside the copying machine main body 1 where it is not affected by heat, and detects the ambient temperature around the copying machine main body 1.

The fixing device 54 heats and fixes the toner on the sheet passing between the pressure roller 54b and the heat roller 54a heated by the heater 59. Heat roller 5
4a is a small metal hollow roller (for example, the outer shape is 1
5 mm or less and a film thickness of 1 mm or less),
The above-mentioned heater 59 composed of a quartz glass tube heater (for example, the outer shape is about 6 mm, preferably 500 W or more) is housed inside, and is heated by the heater 59.
The pressure roller 54b is composed of a rubber roller having a small diameter (for example, an outer shape is 15 mm or less), is supported movably in the radial direction, and is biased toward the heat roller 54a by a predetermined biasing force by a spring member (not shown). There is.

FIG. 2 is a block diagram showing the electrical construction of this copying machine. The control unit 7 for controlling the operation of each unit of the copying machine includes a CPU 71, a ROM 72 storing a program executed by the CPU 71, and a RAM 73 used as a work area of the CPU. C
The PU 71 is provided on the upper surface of the copying machine main body 1 and includes an operation unit 10 including a copy start switch 10a, an image forming unit 4, a sheet conveying unit 5, a motor drive circuit MC, and a fan drive circuit FDC.
And the document table moving mechanism 20 is connected. The motor drive circuit MC drives a motor M as a drive source for driving the document table 2, the image forming section 4, the sheet conveying section 5, and the like. The original table moving mechanism 20, the image forming unit 4, and the sheet conveying mechanism PDM are driven in synchronization by the motor M. The fan drive circuit MDC is for driving the fan F having a built-in fan motor.

In addition to the paper feed detection switch 57, the paper ejection detection switch 58, the heat roller temperature detection sensor SH, and the ambient temperature detection sensor SR, the paper conveyance section 5 is for turning on / off the power supply to the heater 59. A relay drive circuit RDC for driving the relay R and a paper transport mechanism PDM for transporting the paper by the driving force of the motor M are included, and each is connected to the CPU 71.

The CPU 71 controls ON / OFF of the heater 59 of the fixing device 54 based on the program read from the ROM 72. The concept of the control at this time is to continuously energize the heater 59 in accordance with a copy start signal to a predetermined level. Temperature (1st OFF temperature T ₁ described later) at once, and a warm-up control unit (not shown) for intermittently energizing the heater 59 after the warm-up is completed based on the elapsed time. And a normal control unit (not shown) for maintaining a predetermined control temperature.

A heater 59 is provided in the normal control section.
The pressure roller temperature calculation for calculating the temperature of the pressure roller 54b based on the falling gradient of the heat roller detection temperature due to the turning off of electricity to the pressure roller, and adding the required correction amount to the control temperature accordingly.
A correction unit (not shown), a sheet passing correction unit (not shown) that adds the sheet passing correction amount to the control temperature only when sheet passing, and an environmental correction amount to the control temperature according to the ambient temperature. An environment correction unit (not shown) for addition is included. In the pressure roller temperature calculation / correction unit, the lower the pressure roller temperature, the higher the control temperature.

Regarding the operation in the case of performing the control as described above, the flowcharts of FIGS. 3 to 5, FIG. 6 showing the temperature changes of the heat roller 54a and the pressure roller 54b with time, and the heat accompanying the turning on / off of the heater. This will be described with reference to FIG. 7, which shows a temporal change in the temperature of the roller. Figure 7
7A shows the temperature change of the heat roller when the temperature of the pressure roller is relatively high, and FIG. 7B shows the temperature change of the heat roller when the temperature of the pressure roller is relatively low.

Steps S1 to S10 show the flow of processing by the warm-up control section. In response to the input of the copy start signal by depression of a copy start switch 10a, when the warm-up control unit starts the processing, first, the detected temperature _{t 2, t 3, t n} , t n + 1 previous data, such as The initial setting to clear is performed (step S
1), energizing the heater 59 is turned on (step S2)
After that, the timer is reset to start counting (steps S3 and S4).

Next, in step S5~ step S9, the detected temperature t ₂ of the heat roller 54a is monitored, when the detected temperature t ₂ of the heat roller 54a reaches the first round off temperature T ₂ the current supply to the heater 59 Turn off (step S9, 1
0. ), The processing by the warm-up control unit ends. On the other hand, even if a predetermined time has elapsed since the heater 59 was turned on (determined by the count value C of the timer being equal to or greater than a predetermined value C ₁ ), the detected temperature t ₂ of the heat roller is the first time. When the temperature does not reach the off temperature, it is determined to be abnormal (steps S6 and S7) and, for example, a display indicating the abnormality is displayed on the operation unit 10 of the copying machine.

The first round off temperature T ₂ above, because it is set lower than the control temperature T _c according to the normal control section after, it is possible to reduce the overshoot amount to the temperature rise side. Next, step S11 to step S39
Shows processing by the normal control unit. First, the timer is reset to start counting (step S1
1, 12). In step S13, it is determined whether or not there is a copy end signal. When the copy end signal is input, it is confirmed that the heater 59 has been de-energized, and then the process ends (steps S14 to 16). The case where the copy end signal is output includes the case where the copying of the number set in the operation unit 10 is completed and the case where the apparatus is stopped due to an abnormality of the copying machine.

When the copy end signal is not input, the processing by the normal control unit is continued. Next, the current heat roller temperature t _n is read (step S17),
In comparison with the heat roller temperature t _{n + 1} read after the elapse of a predetermined time (steps S19 to S22), if there is a downward tendency, based on the temperature gradient θ (indicated by θ ₁ and θ ₂ in FIG. 7). Te calculates the temperature t _p of the pressure roller, calculates a correction amount D _P (t _p) based on the temperature of the computed pressure roller, it adds this to the control temperature T _C (step S2
3). The calculation of the pressure roller temperature t _p and the correction amount D _P (t _p ) is performed based on a pre-programmed calculation formula. As compared with the descending gradient θ ₁ of the heat roller temperature when the temperature of the pressure roller 54b is relatively high, as shown in FIG.
The descending slope θ ₂ shown in (b) when the temperature of the pressure roller 54b is relatively low is larger. Therefore, in the above operation expression, as when a falling slope of the temperature is large, the pressure roller temperature t _p is calculated to be lower.

Next, in steps S24 and S25, the paper feed correction amount D is further constant at the control temperature Tc on condition that the paper is being fed (the paper is present in the fixing device 54).
₂ is added. It is determined that the paper is being passed through the time region from when the paper discharge detection switch 58 is turned on to when a predetermined time (for example, 3 seconds) has elapsed after the paper feed detection switch 57 was turned off. By increasing the control temperature Tc only when the paper is passed in this way, there are the following advantages. That is, when the heat capacity of the heat roller 54a is set to be small, the pressure roller 54b may be changed depending on the sheet passing therethrough.
Since the heat of the sheet is taken away, there is a possibility that fixing failure may occur at the trailing edge of the sheet. Therefore, it is conceivable to constantly increase the control temperature Tc, but in such a case, a high temperature offset occurs at the leading edge of the paper. On the other hand, since the control temperature Tc is set to be high only when the paper is passed, it is possible to prevent both the high temperature offset at the front end of the paper and the poor fixing at the rear end of the paper. That is, when the leading edge of the paper passes, the control temperature Tc is set to be low until this time, so the temperature of the heat roller 54a becomes low,
It is possible to prevent the occurrence of high temperature offset. on the other hand,
Since the temperature of the heat roller 54a becomes high during the passage of the trailing edge of the sheet, it is possible to prevent the occurrence of defective fixing.

On the other hand, the above-mentioned constant correction amount D ₂ during sheet passing is set to D
It is also possible to set the value to ₂ (x), and to set the function so that the paper feed starts (increases according to the elapsed time x from when the paper discharge detection switch is turned on). This enables more accurate temperature control during paper feed. It is possible to reliably prevent the above-mentioned high-temperature offset and poor fixing.
In steps S26 and S27, the ambient temperature t ₀ around the copying machine body 1 is read, and the environmental correction amount D ₃ (t ₀ ) corresponding to the ambient temperature t ₀ is further added to the control temperature Tc.
This has the following advantages. That is, when the ambient temperature t ₀ is low, the temperature of the paper is also low and the pressure roller 54 b
Since the amount of heat taken by the paper from the sheet is large and this is considered to hinder stable temperature control, stable temperature control is performed by correcting the control temperature Tc according to the ambient temperature t ₀ .

Next, after confirming that the energization of the heater 59 is off (step S28), steps S29 to S are performed.
32, the first time off (or previous heater 59
Has passed a predetermined time (for example, 2 seconds) or more (when the energization to the power is turned off) (the count value C by the timer is equal to or more than the predetermined value C _OFF ), and the temperature detected by the heat roller 54a. Two conditions are monitored: t ₃ is below the control temperature T _C. Only when both conditions are satisfied, the power supply to the heater 59 is turned on (step S23). The OFF state of the power supply to the heater 59 continues for at least 2 seconds. After that, the timer is reset (step S34), the process returns to step S13 and the process is repeated.

In the state where the heater 59 is energized, in steps S35 to S38, the elapsed time from the previous energization of the heater 59 is
A predetermined time (for example, 1 second) is reached (the count value C by the timer is a predetermined value C _ON or more), and the detected temperature t ₃ of the heat roller 54a becomes higher than the control temperature T _C. 2 One condition is monitored. Only when either one of the two conditions is satisfied, the power supply to the heater 59 is turned off (step S39). Therefore, the heater 5
The ON state of the energization of 9 continues for a maximum of 1 second. After that, the timer is reset (step S34),
The process returns to step S15 and the process is repeated.

In the normal control in which the steps starting from step S15 are repeated as described above, the energization of the heater 59 is intermittently controlled by combining the ON time or the OFF time with the control temperature Tc, and the temperature fluctuation is suppressed. Further, in the normal control stage, the control temperature Tc is corrected according to the obtained pressure roller temperature t _P , the control temperature Tc is corrected to be high only when the paper is passed, and the correction according to the atmospheric temperature t ₀ is also performed. Done. Thereby, more stable temperature control can be performed. When the copying is completed, if the power supply to the heater 59 is off, the current state remains as it is, and if the power supply to the heater 59 is on, the power is turned off and the process ends. As a result, the state of waiting for the start of the next copy is entered.

As described above, according to this embodiment, the temperature t of the pressure roller 54b is changed based on the temperature change of the heat roller 54a.
_P was estimated and the control temperature T _C was corrected based on this. Therefore, since control can be performed in consideration of the temperature t _P of the pressure roller 54b, the heat roller 54 having a small heat capacity can be used.
Even when a is adopted, the actual fixing temperature can be more stabilized, and as a result, it is possible to prevent the occurrence of high temperature offset and wrinkles due to the fixing temperature being too high, and to lower the fixing temperature. It is possible to prevent the occurrence of defective fixing due to the excessive passage. In particular, even if the heat roller 54a heated by the heater 59 has reached a predetermined temperature, the pressure roller 54b tends not to be sufficiently warmed yet. can do. Moreover, these effects can be achieved with a simple structure without providing a pressure roller temperature detection sensor.

FIG. 8 shows another embodiment of the present invention. Referring to the figure, the feature of this embodiment is that the temperature t of the pressure roller 54b is set in the fan drive circuit FDC based on the falling gradient θ of the temperature detected by the heat roller 54a due to the turning off of the power supply to the heater 59. Calculate _P and calculate the calculated pressure roller 54
This is because there is provided an air volume adjusting unit BC that adjusts the air volume by varying the rotation speed of the cooling fan F according to the temperature t _P of b. As the air volume adjusting unit BC, a tap changing system in which a plurality of taps having different numbers of coil turns are switched to change the current applied to the fan motor, and other known speed adjusting circuits can be adopted.

According to this embodiment, control similar to the embodiment of FIG. 1 can be performed in consideration of the temperature t _P of the pressure roller 54b, so that the actual fixing temperature can be made more stable and high temperature offset, wrinkles and It is possible to prevent the occurrence of fixing failure. FIG. 9 shows still another embodiment of the present invention. Referring to the figure, the feature of this embodiment is that the temperature t of the pressure roller 54b is set in the motor drive circuit MC based on the falling gradient θ of the detected temperature of the heat roller 54a accompanying the turning off of the power supply to the heater 59. _The pressure roller 54b is calculated by calculating _P
This is because the rotation speed adjusting unit VC for adjusting the rotation speed of the motor M is provided in accordance with the temperature t _P of. By adjusting the rotation speed, the speed of the original table moving mechanism 20, the image forming unit 4, and the paper transport mechanism PDM are all adjusted in the same manner. As the rotation speed adjusting unit VC, a tap changing method for changing a current applied to the motor M by switching a plurality of taps having different numbers of coil turns, and other known speed adjusting circuits can be adopted.

According to this embodiment, the calculated pressure roller 5
By adjusting the speed at which the paper passes through the fixing device 54 in accordance with the temperature t _P of 4b, the amount of heat taken by the paper per unit time can be adjusted. Therefore, similar to the embodiment of FIG. 1, the actual fixing temperature can be made more stable, and the occurrence of high temperature offset, wrinkles and fixing failure can be prevented.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0038]

According to the configuration of the invention of claim 1, the temperature of the pressure roller is calculated based on the temperature change of the heat roller,
The control temperature is corrected based on this. As a result, control that takes into account the temperature of the pressure roller can be performed, and as a result, the actual fixing temperature can be made more stable.As a result, high-temperature offset, wrinkles, and improper fixing occur even when a heat roller with a small heat capacity is used. Can be prevented. In particular, even when the heat roller has reached a predetermined temperature, it is possible to reliably prevent the occurrence of fixing failure in the initial stage of heating, in which the pressure roller tends not to be sufficiently warmed. Further, these effects can be realized with a simple structure without providing a pressure roller temperature detection sensor.

According to the configuration of the second aspect of the present invention, by controlling the air volume of the ventilation means for cooling according to the calculated temperature of the pressure roller, it is possible to perform control in consideration of the temperature of the pressure roller. did. As a result, the same effect as the invention according to claim 1 is obtained. According to the third aspect of the invention, the amount of heat per unit time taken by the paper is adjusted by adjusting the speed at which the paper passes through the fixing device according to the calculated temperature of the pressure roller. as a result,
The same effect as the invention according to claim 1 is obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an internal configuration of a copying machine including a temperature control device of a fixing device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of a copying machine.

FIG. 3 is a flowchart showing a warm-up operation of the temperature control operation of the fixing device.

FIG. 4 is a flow chart showing an operation during normal control of the temperature control operation of the fixing device.

5 is a flowchart showing an operation during normal control of the temperature control operation of the fixing device, which is continuous with the flowchart of FIG.

FIG. 6 is a diagram showing a temporal change in temperature of a heat roller and a pressure roller.

FIG. 7 shows a temporal change of the temperature of the heat roller with turning on / off of the heater, FIG. 7A shows a temperature change of the heat roller when the temperature of the pressure roller is relatively high, and FIG. The temperature change of the heat roller when the temperature of the pressure roller is relatively low is shown.

FIG. 8 is a block diagram showing an electrical configuration of a copying machine including a temperature control device of a fixing device according to another embodiment of the present invention.

FIG. 9 is a block diagram showing an electrical configuration of a copying machine including a temperature control device of a fixing device according to still another embodiment of the present invention.

[Explanation of symbols]

1 copier body 54 fixing device 54a heat roller 54b pressure roller 59 heater SH heat roller temperature detection sensor 7 control unit 71 CPU 72 ROM T _C control temperature D _P (t _P) correction amount t _2, t ₃ detects the temperature of the heat roller VC rotation speed adjustment unit BC air volume adjustment unit

Claims (3)

[Claims] 1. An image forming apparatus including a heat roller heated by a pressure roller and a heater and having a fixing device for heating and fixing toner on a sheet passing between the rollers, and detecting the temperature of the heat roller. In a temperature control device of a fixing device for controlling on / off of energization to the heater based on a temperature detected by a heat roller temperature detecting means, a temperature of a pressure roller is determined based on a descending gradient of the detected temperature due to turning off the energization to the heater. And a temperature correction device for the fixing device, which includes a correction unit that corrects the control temperature by adding a required correction amount according to the calculated temperature of the pressure roller. 2. A fixing device which includes a heat roller heated by a pressure roller and a heater, and which heats and fixes toner on a sheet passing between the rollers, and a blower for cooling the inside of the image forming apparatus main body. In a temperature control device for a fixing device, which is applied to an image forming apparatus and which controls on / off of energization to the heater based on a temperature detected by a heat roller temperature detecting means for detecting the temperature of the heat roller, The temperature of the fixing device is characterized by including an air volume adjusting unit that calculates the temperature of the pressure roller based on the falling gradient of the detected temperature, and adjusts the air volume of the blowing unit according to the calculated temperature of the pressure roller. Control device. 3. A fixing device that includes a heat roller heated by a pressure roller and a heater, and heats and fixes toner on a sheet passing between the rollers, and a sheet conveyance having a plurality of roller groups including the pressure roller and the heat roller. The present invention is applied to an apparatus and an image forming apparatus including a rotation driving unit that rotationally drives a roller group of the above-described sheet conveying device, and energizes the heater based on the temperature detected by a heat roller temperature detecting unit that detects the temperature of the heat roller. In the temperature control device of the fixing device for controlling the on / off of the pressure roller, the temperature of the pressure roller is calculated based on the falling gradient of the detected temperature due to the turning off of electricity to the heater, and the rotation of the pressure roller is performed according to the calculated temperature of the pressure roller. A temperature control device for a fixing device, comprising a rotation speed adjusting section for adjusting the rotation speed of a driving means.