JP2003050520A - Heater driving device, fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that temperature ripple gets large. SOLUTION: A heater driving device is provided with a means for changing the conduction ratio of a switching element 14 by supplying power from an AC power source 1 to a heater 10 through a rectifier circuit 3 and the element 14 and detecting the temperature of a heating body by the use of a temperature detection means 12, and voltage detection means 8 and 9 detecting the voltage of the power source 1. The conduction ratio of the element 14 is widened in accordance with the voltage of the power source 1 detected by the detection means 8 and 9, the temperature of the heating body detected by the detection means 12 and the image forming circumstances of the image forming apparatus before the temperature of the heating body falls.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater driving device, a fixing device and an image forming apparatus used for a fixing device in an image forming apparatus such as a copying machine or a laser printer.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus such as a copying machine or a laser printer, in order to fix toner on a transfer sheet,
A thermal fixing device having a fixing roller containing a heater is used. The heater is connected to an AC power source through a switch element such as a triac, and the fixing roller is connected to a temperature detecting means such as a thermistor for detecting the temperature of the fixing roller.

Normally, in an image forming apparatus, electric power is supplied to the heater from an AC power source through a switch element by a signal from an engine control circuit, and when the fixing roller reaches a predetermined temperature, the temperature of the fixing roller reaches a predetermined temperature. Therefore, the energization time of the switch element is adjusted by the phase control method so that the image can be formed.

When the toner on the transfer paper is fixed to the transfer paper by the fixing roller in order to form an image in the image forming apparatus, the temperature of the fixing roller becomes the speed / amount of image formation (size of transfer paper × number of sheets). Accordingly, the temperature drops below a predetermined temperature. Since the temperature of the fixing roller is constantly detected by the temperature detecting means such as a thermistor, when the temperature of the fixing roller falls below a predetermined temperature, the energizing time of the switch element is controlled to be increased, and the temperature of the fixing roller is reset again. Reach a predetermined temperature.

In addition to the above method, the method of supplying electric power to the heater supplies electric power to the heater from an AC power source through a rectifier circuit and a switch element, and switches the switch element at a speed higher than the frequency of the AC power source. There is also known a method of changing the conductivity ratio of this switching so that the temperature of the fixing roller becomes a predetermined temperature.

In Japanese Patent Laid-Open No. 11-95607, the amount of electric power supplied to the heater is increased or decreased so as to reduce the difference between the temperature of the fixing roller and the reference temperature, and the reference value is set according to the number of images formed from the start of image formation. An image forming apparatus is described in which the temperature is sequentially switched and the amount of electric power supplied to the heater at the start of image formation is selected based on the paper size.

Japanese Unexamined Patent Publication No. 9-218720 discloses an AC
Power is supplied from the power supply to the load via the rectifier circuit and the switch element, the switch element is switched at a speed higher than the frequency of the AC power source, and the conductivity ratio of this switching is controlled so that the temperature of the fixing roller becomes a predetermined value. However, there is described an AC control device that limits the above-mentioned conductivity ratio when the load current value is equal to or more than a predetermined value and sets the maximum value of the conductivity ratio at the time of switching according to the power supply voltage.

[0008]

In the former method of supplying electric power to the heater, in the former method, the temperature of the fixing roller is detected by a temperature detecting means such as a thermistor, and when the temperature changes, the switch element Since the temperature of the fixing roller is controlled to a predetermined temperature by changing the energization time, the temperature ripple of the fixing roller becomes large. Further, both the time constant from when the electric power is supplied to the heater until the temperature of the fixing roller rises and the time constant when the heat of the heater is transmitted to the fixing roller are large, and the temperature of the fixing roller is further detected by a temperature detecting means such as a thermistor. Since the time constant until the detection is large, the temperature ripple of the fixing roller is further increased.

When the temperature ripple of the fixing roller becomes large,
There is a problem that uneven fixing occurs when an image is formed when the conditions for fixing the toner on the transfer paper to the transfer paper are different and the temperature of the fixing roller is largely different from a predetermined temperature. This problem becomes more noticeable as the amount of image formation (size of transfer paper x number of sheets) increases, and in the case of continuously forming images, the faster the image formation speed becomes.

In the latter of the above-mentioned methods of supplying electric power to the heater, the temperature control of the fixing roller is the same as the former, and there is a problem similar to the former. Japanese Patent Laid-Open No. 11-956
In the image forming apparatus described in Japanese Patent Publication No. 07, the amount of electric power supplied to the heater is increased or decreased so as to reduce the difference between the temperature of the fixing roller and the reference temperature, and the reference temperature is sequentially set according to the number of images formed from the start of image formation. Switch to, and select the amount of power supplied to the heater when starting image formation based on the paper size.
The temperature ripple of the fixing roller cannot be sufficiently reduced and the fixing unevenness cannot be sufficiently reduced.

AC described in Japanese Patent Laid-Open No. 9-218720
In the control device, electric power is supplied from the AC power source to the load through the rectifier circuit and the switch element, and the switch element is switched at a speed higher than the frequency of the AC power source. When the load current value is equal to or higher than a predetermined value, the conductivity ratio is limited, and the maximum value of the conductivity ratio during switching is set according to the power supply voltage, but the temperature ripple of the load is sufficiently reduced. I can't.

The present invention has been made to solve the above problems, and can greatly reduce temperature ripples and reduce fixing unevenness regardless of the speed and amount of image formation, thus improving image quality. An object of the present invention is to provide a heater driving device, a fixing device, and an image forming apparatus that can perform the above.

[0013]

In order to achieve the above object, the invention according to claim 1 is an AC heater control device for controlling the drive of a heater for heating a heating body of a fixing device in an image forming apparatus. Power is supplied from a power source to the heater through a rectifier circuit and a switch element, the temperature of the heating element is detected by a temperature detecting means, and the conduction ratio of the switch element is changed, and the voltage of the AC power source is detected. Voltage detecting means, and the voltage of the AC power source detected by the voltage detecting means, the temperature of the heating element detected by the temperature detecting means, and the image forming state of the image forming apparatus according to the image forming state. The conduction ratio of the switching element is expanded before the temperature of the heating element is lowered.

According to a second aspect of the present invention, in the heater driving device according to the first aspect, the digital control means converts the voltage detection signal from the voltage detection means and the temperature detection signal from the temperature detection means into a digital signal. According to the image forming situation of the image forming apparatus, the conduction ratio of the switch element is expanded before the temperature of the heating element is lowered.

The invention according to claim 3 is the invention according to claim 1 or 2.
The heater driving device described above has means for stopping the power supply to the heater when the temperature of the heating element rises to a predetermined temperature.

According to a fourth aspect of the present invention, in the heater driving device according to the first, second or third aspect, means for detecting the power supply amount to the heater, and power supply amount to the heater detected by this means. Has a predetermined size, the means for stopping the power supply to the heater.

According to a fifth aspect of the present invention, there is provided the heater driving device according to any one of the first to fourth aspects.

The invention according to claim 6 has the fixing device according to claim 5.

[0019]

FIG. 1 shows a first embodiment of the present invention. The first embodiment is an example of a heater driving device used for a fixing device in an image forming apparatus. This heater driving device has a function of controlling the power supply to the heater of the fixing device and controlling the temperature of the fixing roller as a heating body to a predetermined temperature.

In FIG. 1, 1 is an external AC power source, 2 is a noise filter, and 3 is a diode bridge as a rectifying circuit. The external AC power supply 1 is connected to the diode bridge 3 via the noise filter 2, and the AC input from the external AC power supply 1 is full-wave rectified by the diode bridge 3 via the noise filter 2. A noise filter including a capacitor 4, a coil 5 and a capacitor 6 is connected to the diode bridge 3.

An inverter circuit 7 is connected to the noise filter, and resistors 8 and 9 as voltage detecting means for detecting the voltage of the AC power source 1 are connected in series.
In the inverter circuit 7, the heater 10 for heating the fixing roller of the fixing device, the temperature fuse 11, and the switch element 14 are connected in series to the output side of the noise filter including the capacitor 4, the coil 5, and the capacitor 6.

A fixing roller is connected to the outer periphery of the heater 10, and a thermistor 12 constituting a temperature detecting means is arranged near the fixing roller. This thermistor 12
Detects the temperature of the fixing roller, and the roller temperature detection circuit 13
Outputs a temperature detection signal corresponding to the temperature detected by the thermistor 12. A drive circuit 15 and a heater control circuit 16 as heater control means are connected to the switch element 14 and the roller temperature detection circuit 13 of the inverter circuit 7, and the voltage dividing points of the resistors 8 and 9 are connected to the heater control circuit 16. . An engine control circuit 17 as an engine control means of the image forming apparatus is connected to the heater control circuit 16.

Next, the operation of the first embodiment will be described separately for a case where the image forming apparatus does not form an image and a case where the image forming apparatus forms an image. First, the operation of this embodiment when the image forming apparatus does not form an image will be described. The AC input from the AC power supply 1 is full-wave rectified by the diode bridge 3 through the noise filter 2, and the noise filter including the capacitor 4, the coil 5, and the capacitor 6, the temperature fuse 11, and the switching element 14
It is supplied to the heater 10 via. The switch element 14 is driven by the drive circuit 15 to perform switching, and the resistors 8 and 9 divide the output voltage of the noise filter including the capacitor 4, the coil 5 and the capacitor 6 to generate AC.
The voltage of the power supply 1 is detected.

The temperature of the fixing roller is detected by the thermistor 12, and the roller temperature detection circuit 13 outputs a temperature detection signal according to the detection value of the thermistor 12. Heater control circuit 1
A temperature detection signal 6 is fed back from the roller temperature detection circuit 13, and the switch element 14 is controlled via the drive circuit 15 so that the temperature of the fixing roller reaches a target value.

That is, when the engine control circuit 17 controlling the overall operation of the image forming apparatus outputs a roller temperature setting signal to the heater control circuit 16, the heater control circuit 16
Causes the drive circuit 15 to start switching the switch element 14 to energize the heater 10. Switch element 1
0 performs switching that repeats ON and OFF at a frequency (for example, 20 KHz) sufficiently higher than the frequency of the AC power supply 1. Therefore, the AC input from the AC power source 1 is full-wave rectified by the diode bridge 3 via the noise filter 2 and is switched by the switch element 14 via the noise filter composed of the capacitor 4, the coil 5 and the capacitor 6, and the temperature fuse 11 A load current that is supplied to the heater 10 via the switch 10 and is synchronized with the switching frequency of the switch element 14 flows through the heater 10. The heater 10 generates heat due to the load current and heats the fixing roller.

The temperature of the fixing roller is detected by the thermistor 12, and the roller temperature detection circuit 13 outputs a temperature detection signal corresponding to the detected value of the thermistor 12 to the heater control circuit 16. The heater control circuit 16 includes the roller temperature detection circuit 1
Based on the temperature detection signal from 3, the conductivity ratio of the switch element 14 is controlled via the drive circuit 15 so that the temperature of the fixing roller becomes a predetermined value corresponding to the roller temperature setting signal.

The switching of the switch element 14 is repeated in a fixed cycle, and when the conductivity of the switch element 14 increases, the amount of electricity supplied to the heater 10 increases and the temperature of the fixing roller rises. On the contrary, when the conductivity ratio of the switch element 14 decreases, the amount of electricity supplied to the heater 10 decreases and the temperature of the fixing roller decreases. When the image forming apparatus does not form an image in this way, the heater control circuit 16 feeds back the temperature detection signal from the roller temperature detection circuit 13 to control the conductivity of the switch element 14 to control the temperature of the fixing roller. Is maintained at a predetermined value.

Next, the operation of this embodiment when the image forming apparatus forms an image will be described. After the temperature of the fixing roller reaches a predetermined value according to the signal from the heater control circuit 16, the engine control circuit 17 receives the image forming signal,
Each drive load in the image forming apparatus is operated to form an image, but after the image formation, the image formation is performed a plurality of times depending on the amount of image formation (size and number of transfer sheets as a recording medium on which an image is formed). The roller temperature setting signal is output to the heater control circuit 16.

The heater control circuit 16 determines the conductivity ratio of the switch element 14 from the roller temperature setting signal from the engine control circuit 17 and the voltage signal at the voltage dividing point of the resistors 8 and 9 for detecting the voltage of the AC power source 1. By determining and controlling, the conductivity ratio of the switch element 14 is controlled so that the amount of electricity supplied to the heater 10 becomes a predetermined value corresponding to the roller temperature setting signal. Thus, when the image forming apparatus forms an image,
The temperature of the fixing roller is deprived of heat by the transfer sheet, and therefore, in order to keep the temperature of the fixing roller at a predetermined value, it is necessary to increase the amount of electricity supplied to the heater 10 as compared with the case where an image is not formed. The heater control circuit 16 performs a feed-forward constant temperature control in which the conductivity ratio of the switch element 14 is gradually increased before the temperature of the fixing roller is lowered in accordance with the roller temperature setting signal from the engine control circuit 17. The temperature of the fixing roller can be controlled without ripples, and the temperature of the fixing roller can be maintained at a predetermined value regardless of the amount of image formation.

This will be described in more detail as follows. As described above, the engine control circuit 17 operates each drive load in the image forming apparatus to form an image by the image forming signal after the temperature of the fixing roller reaches a predetermined value. The temperature of the fixing roller when an image is formed by fixing the conductivity of the switch element 14 before formation is as shown in FIG.

FIG. 2 shows the temperature of the fixing roller from the start of image formation to the end of image formation. Before the image formation, the fixing roller temperature is controlled to a predetermined value, and the image formation at point A in FIG. When started, the heat of the fixing roller is taken by the transfer paper, so the temperature of the fixing roller gradually drops, and the heat consumption of the transfer paper is subtracted from the heat supply of the fixing roller due to the energization amount of the heater. The temperature depends on the amount of heat.

When the fixing roller temperature becomes lower than a predetermined value,
The conditions for fixing the toner on the transfer paper deviate from the optimum conditions, resulting in uneven fixing. In order to prevent this, conventionally, as described above, when the temperature of the fixing roller decreases, the feedback control is performed to increase the conductivity of the switch element and increase the amount of electricity to the heater. But in this case
The time constant from when the amount of electricity to the heater increases until the temperature of the heater rises and the time constant when the heat of the heater is transmitted to the fixing roller are both large, and moreover, the time until the temperature of the fixing roller is detected by the thermistor. Since the constant is also large, the temperature ripple of the fixing roller becomes large as shown in FIG. 3, and the fixing conditions change between the high temperature and the low temperature in the temperature ripple, and uneven fixing occurs.

In the present embodiment, when an image is formed, feedback control is not performed after the fixing roller temperature is detected, but the heater control circuit 16 causes the engine control circuit 17 to control the temperature before the fixing roller temperature decreases. Roller temperature setting signal and resistor 8 for detecting the voltage of the AC power supply 1,
The voltage signal at the voltage dividing point of 9 expands the conduction angle of the switch element 14 so that the temperature of the fixing roller is constant, and when the heat is absorbed by the transfer sheet, the energization amount to the heater 10 is increased almost at the same time. Eliminate the drop in roller temperature.

The engine control circuit 17 controls the amount of continuous image formation (size of transfer paper on which image is continuously formed x
Since the number of sheets is known, the heater control circuit 1
By changing the roller temperature setting signal to 6 and outputting the roller temperature setting signal a plurality of times, A
C Power supply 1 voltage / image formation amount (transfer paper size x number of sheets)
Regardless, as shown in FIG. 4, temperature ripple of the fixing roller is significantly reduced to reduce fixing unevenness and improve image quality.

Specifically, the roller temperature setting signal from the engine control circuit 17 to the heater control circuit 16 is a signal that raises the fixing roller temperature as the size of the transfer paper increases, and the number of transfer papers increases. A signal to raise the temperature of the fixing roller, and when images are formed on both sides of the transfer paper, it takes time to invert the transfer paper, and heat consumption per unit time is reduced. Lowers the temperature.

According to the first embodiment, electric power is supplied from the AC power source 1 to the heater 10 via the diode bridge 3 as a rectifying circuit and the switch element 14, and the temperature of the fixing roller as a heating member is used as a temperature detecting means. Has a means for changing the conduction ratio of the switch element 14 detected by the thermistor 12 and resistors 8, 9 as voltage detecting means for detecting the voltage of the AC power source 1, and the AC power source detected by this voltage detecting means. According to the voltage of 1, the temperature of the fixing roller detected by the temperature detecting unit, and the image forming state of the image forming apparatus, the conduction ratio of the switch element 14 is expanded before the temperature of the fixing roller is reduced. The temperature ripple of the fixing roller can be reduced. As a result, it is possible to fix the toner on the transfer paper at the optimum fixing roller temperature regardless of the image forming condition of the image forming apparatus, and it is possible to reduce uneven fixing and improve image quality.

Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment is an example of a heater driving device used for a fixing device in an image forming apparatus.
The same parts as those in FIG.
The second embodiment has the function of controlling the temperature of the fixing roller to a predetermined temperature by digitally controlling the power supply to the heater of the fixing device by the digital control circuit 18 as the heater control means. In the example, the heater control circuit 16
The digital control circuit 18 is used instead of The digital control circuit 18 includes a temperature detection signal from the roller temperature detection circuit 13 and a resistor 8 for detecting the voltage of the AC power supply 1.
It has an A / D converter (A / D converter) 181 for converting each of the voltage signals at the voltage dividing points of 9 into a digital signal, and an arithmetic means 182.

Next, the operation of the second embodiment will be described separately for the case where the image forming apparatus does not form an image and the case where the image forming apparatus forms an image. First, the operation of this embodiment when the image forming apparatus does not form an image will be described. The digital control circuit 18 converts the analog temperature detection signal fed back from the roller temperature detection circuit 13 into a digital signal by the A / D converter 181,
This digital signal and the roller temperature setting signal input from the engine control circuit 17 by the communication means are operated by the calculating means 18
2 is used to determine the conductivity ratio of the switch element 14, and the conductivity ratio of the switch element 14 is set via the drive circuit 15 so that the temperature of the fixing roller becomes a predetermined value corresponding to the roller temperature setting signal. Control. The other points are the same as in the first embodiment.

Next, the operation of this embodiment when the image forming apparatus forms an image will be described. The digital control circuit 18 includes resistors 8 and 9 for detecting the voltage of the AC power supply 1.
The voltage signal at the voltage dividing point is converted into a digital signal by the A / D converter 181, and this digital signal and the roller temperature setting signal input from the engine control circuit 17 by the communication means are operated by the operation means 182 to switch. The conductivity ratio of the element 14 is determined. The other points are the same as in the first embodiment.

In the second embodiment, the digital control circuit 18 controls the energization amount to the heater 10 for keeping the fixing roller temperature constant, so that the roller temperature input from the engine control circuit 17 through the communication means is controlled. It becomes possible to directly calculate the setting signal and the signal inputted from the voltage dividing points of the resistors 8 and 9 and digitized by the A / D converter 181, and inputted from the engine control circuit 17 by one communication. The conductivity ratio of the switch element 14 can be gradually changed by the roller temperature setting signal. As a result, AC power supply 1
Irrespective of the voltage and the amount of image formation (size of transfer paper × number of sheets), temperature ripple of the fixing roller can be further greatly reduced to reduce fixing unevenness and improve image quality. Further, the circuit configuration is simplified and the cost is reduced, and the rate of change of the conductivity ratio of the switch element 14 can be changed by software, and the setting can be changed easily.

Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is an example of a heater driving device used for a fixing device in an image forming apparatus, and the same parts as those in FIG. The third embodiment is the same as the second embodiment, except that
The main purpose is to protect in the event of an abnormality, and has the function of stopping the power supply to the heater 10 when the temperature of the fixing roller rises above the upper limit temperature.

In the third embodiment, instead of the digital control circuit 18 in the second embodiment, the digital control circuit 1 is used.
8a is used, and a relay 19 having a contact 19b inserted between the noise filter 2 and the diode bridge 3
Is provided. The digital control circuit 18a has an additional function of activating the relay 19 when an abnormality occurs in the digital control circuit 18.

Normally, the relay 19 is off and the contact 19b of the relay 19 is closed. The temperature of the fixing roller is detected by the thermistor 12, and the roller temperature detection circuit 13 outputs a temperature detection signal corresponding to the detection value of the thermistor 12 to the digital control circuit 18a.
The temperature detection signal from is digitized by the A / D converter 181.

The digital control circuit 18a compares the digitized temperature detection signal with a preset digital signal for the maximum usable temperature of the fixing roller, and the temperature detection signal exceeds the digital signal (fixing roller temperature is preset). When the set maximum use temperature of the fixing roller is exceeded), the relay 19 is operated to open the contact 19b to stop the power supply to the heater 10 and to send an abnormal signal to the engine control circuit 17 by the communication means. Output. As a result, damage to the fixing roller and the heater 10 can be prevented when the temperature of the fixing roller is out of control due to a component failure or the like and the fixing roller temperature rises abnormally.

In the first embodiment, the third
Similar to the embodiment, the relay 19 is provided and the heater control circuit 16 is provided.
The temperature detection signal from the roller temperature detection circuit 13 is compared with an analog signal for a preset maximum use temperature of the fixing roller, and the temperature detection signal exceeds the analog signal (the fixing roller with the preset fixing roller temperature is set. Relay 1 is activated to contact 1
By opening 9b, the power supply to the heater 10 may be stopped and an abnormal signal may be output to the engine control circuit 17 by the communication means.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The fourth embodiment is an example of a heater driving device used for a fixing device in an image forming apparatus. The same parts as those in FIG. 6 are designated by the same reference numerals and the description thereof will be omitted. The fourth embodiment is the same as the third embodiment, except that
The main purpose of protection is to protect the heater 10
It has a function of stopping the power supply to the heater 10 when the power supplied to the heater exceeds the upper limit value.

In the fourth embodiment, a digital control circuit 18b is used in place of the digital control circuit 18a in the third embodiment, and a noise filter composed of a capacitor 4, a coil 5 and a capacitor 6 and an inverter circuit 7 are provided. A current detection resistor 20 as a current detection means is connected in series with the switch element 14, and a current detection circuit 21 is connected in parallel with the current detection resistor 20.

The current of the inverter circuit 7 (current of the heater 10) is detected by the current detection resistor 20, and the current detection circuit 21 outputs a current detection signal according to the detection value of the current detection resistor 20 to the digital control circuit 18b. The digital control circuit 18b is similar to the digital control circuit 18a in that the A / D
In the converter (A / D converter) 181a, the current detection signal from the current detection circuit 21, the voltage signal at the voltage dividing point of the resistors 8 and 9 for detecting the voltage of the AC power supply 1, and the roller temperature detection circuit 13 are detected. The temperature detection signals of are converted into digital signals.

The digital control circuit 18b has a current detection signal and a voltage signal (the current detection signal from the current detection circuit 21 and the resistor 8 for detecting the voltage of the AC power supply 1) digitized by the A / D converter 181a. The voltage signal at the voltage dividing point 9 is digitized by the A / D converter 181a) to obtain the power supply amount to the heater 10, and this power supply amount is set to the preset maximum power of the heater 10. The power supply amount exceeds the digital signal as compared with the digital signal for the heater 1 (the heater 1 having a preset power supply amount to the heater 10).
When the maximum electric power of 0 is exceeded), the relay 19 is operated to open the contact 19b to stop the electric power supply to the heater 10 and to communicate with the engine control circuit 17 by the communication means.
An abnormal signal is output to. As a result, damage to the fixing roller and the heater 10 can be prevented when the temperature control of the fixing roller is lost due to a component failure or the like and the electric power supplied to the heater 10 rises abnormally.

In the first and second embodiments, the relay 19 and the relay 19 are the same as in the fourth embodiment.
The current detection resistor 20 and the current detection circuit 21 are provided, and the heater control circuit 16 and the digital control circuit 18 divide the current detection signal from the current detection circuit 21 and the voltage division of the resistors 8 and 9 for detecting the voltage of the AC power supply 1. The voltage signal at the point is calculated to obtain the power supply amount to the heater 10, and this power supply amount is compared with a preset signal for the maximum power of the heater 10 to set the power supply amount to the heater 10 in advance. When the maximum power of the heater 10 is exceeded, the relay 19 is activated to contact 1
By opening 9b, the power supply to the heater 10 may be stopped and an abnormal signal may be output to the engine control circuit 17 by the communication means.

Next, a fifth embodiment of the present invention will be described. The fifth embodiment is an example of an image forming apparatus, in which a drum-shaped photoconductor 22 as an image carrier is rotationally driven by a drive unit (not shown). The photoconductor 22 is uniformly charged by a charging roller 23 as a charging means, and is exposed to light 24 by a writing device as an exposing means (not shown) to form an electrostatic latent image.

The electrostatic latent image on the photoconductor 22 is developed by the developing device 2.
5 is developed into a toner image, and a transfer paper 26 as a recording medium is fed to a registration roller 27 from a paper feeding device (not shown). The registrar 27 is the photoconductor 22.
The transfer paper 26 is sent out in accordance with the upper toner image, and the toner image on the photoconductor 22 is transferred to the transfer paper 26 by a transfer roller 28 as a transfer unit. The transfer paper 26 on which the toner image is transferred is fixed by a fixing roller 30 as a fixing member in the fixing device 29 and a pressure roller 3 as a pressure member.
When passing through the nip portion with 1, the toner image is fixed by heating and pressurization by the fixing roller 30 and the pressure roller 31, and is discharged to the outside. Further, the toner remaining on the photoconductor 22 after the transfer is removed by the cleaning device 32. Here, the fixing roller 30 is heated by the heater 10, and the drive control of the heater 10 is performed by the first to fourth embodiments.
This is performed by any of the heater driving circuits of the embodiments. The fourth embodiment has the engine control circuit 17 described above. After the temperature of the fixing roller reaches a predetermined value by the signal from the heater control circuit 16, the engine control circuit 17 operates each drive load in the image forming apparatus to form an image by the image forming signal, After the image formation, a roller temperature setting signal is output to the heater control circuit 16 a plurality of times according to the amount of image formation (size and number of transfer sheets).

According to the fixing device 29 of the fifth embodiment,
Since the drive control of the heater is performed by any of the heater drive circuits of the first to fourth embodiments, the toner is fixed to the transfer paper at the optimum fixing roller temperature regardless of the image forming condition of the image forming apparatus. This makes it possible to reduce uneven fixing and improve image quality.

Further, according to the image forming apparatus of the fourth embodiment, the fixing device 2 in which the drive control of the heater is performed by any one of the heater drive circuits of the first to fourth embodiments.
Since it has No. 9, it is possible to fix the toner on the transfer paper at the optimum fixing roller temperature regardless of the image forming condition of the image forming apparatus, and it is possible to reduce uneven fixing and improve the image quality.

The present invention is not limited to the above embodiment, and can be applied to the case where the heater heats a heating member such as a fixing member such as a fixing belt or another roller of the fixing device. .

[0056]

As described above, according to the first aspect of the present invention, the temperature ripple of the heating element can be reduced, and the recording medium can be recorded at the optimum heating element temperature regardless of the image forming condition of the image forming apparatus. It is possible to fix the toner, and it is possible to reduce uneven fixing and improve image quality. According to the second aspect of the present invention, it is possible to further greatly reduce the temperature ripple of the heating element, reduce uneven fixing, and improve the image quality. Further, the circuit configuration is simplified and the cost is reduced, and the rate of change of the conductivity of the switch element can be changed by software, and the setting can be changed easily.

According to the third aspect of the present invention, when the temperature control of the heating element is out of order due to a component failure or the like and the temperature of the heating element rises abnormally, it is possible to prevent damage to the heating element and the heater. According to the invention of claim 4, when the temperature control of the heating element is lost due to a component failure or the like and the electric power supplied to the heater is abnormally increased, the heating element and the heater can be prevented from being damaged.

According to the fifth aspect of the invention, the temperature ripple of the heating element can be reduced, and the toner can be fixed to the recording medium at the optimum heating element temperature regardless of the image forming condition of the image forming apparatus. Therefore, it is possible to reduce uneven fixing. According to the invention of claim 6, it is possible to improve image quality by reducing fixing unevenness.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a fixing roller temperature according to an image forming state when the conductivity ratio of a switch element is constant in a heater driving device.

FIG. 3 is a characteristic diagram showing a fixing roller temperature according to an image forming state when feedback control is performed on a conductivity ratio of a switch element by a heater driving device.

FIG. 4 is a characteristic diagram showing a fixing roller temperature according to an image forming state of the first embodiment.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

FIG. 6 is a block diagram showing a third embodiment of the present invention.

FIG. 7 is a block diagram showing a fourth embodiment of the present invention.

FIG. 8 is a schematic view showing a fifth embodiment of the present invention.

[Explanation of symbols]

1 AC power supply 3 diode bridge 7 Inverter circuit 8, 9 resistance 10 heater 12 Thermistor 14 switch element 15 Drive circuit 16 Heater control circuit 17 Engine control circuit 18, 18a, 18b Digital control circuit 19 relays

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 3/00 H05B 3/00 310E 335 335 F term (reference) 2H033 AA03 BB00 CA07 CA23 CA45 3K058 AA22 AA72 BA18 CA03 CA12 CA61 CB02 DA11 5H730 AA12 AS12 BB11 BB57 CC01 DD02 FD11 FD61 FF09 FG05 FG25 FG26 ZZ11

Claims (6)

[Claims] 1. A heater driving device for controlling driving of a heater for heating a heating body of a fixing device in an image forming apparatus, wherein electric power is supplied to the heater from an AC power source through a rectifying circuit and a switch element. The temperature detecting means detects the temperature of the body to change the conduction ratio of the switch element, and the voltage detecting means detects the voltage of the AC power supply. The AC power supply detects the voltage of the AC power supply. Depending on the voltage, the temperature of the heating element detected by the temperature detecting means, and the image forming state of the image forming apparatus,
A heater driving device, wherein the conduction ratio of the switch element is expanded before the temperature of the heating element is lowered. 2. The heater driving device according to claim 1,
In the digital control means, the temperature of the heating element is lowered according to the digital signal obtained by converting the voltage detection signal from the voltage detection means and the temperature detection signal from the temperature detection means and the image forming condition of the image forming apparatus. The heater driving device is characterized in that the conduction ratio of the switch element is increased before the heating. 3. The heater driving device according to claim 1 or 2, further comprising means for stopping power supply to the heater when the temperature of the heating element rises to a predetermined temperature. 4. The heater driving device according to claim 1, 2 or 3, wherein the means for detecting the amount of electric power supplied to the heater and the amount of electric power supplied to the heater detected by the means have a predetermined magnitude. And a means for stopping the supply of electric power to the heater when the temperature of the heater becomes low. 5. A fixing device comprising the heater driving device according to claim 1. Description: 6. An image forming apparatus comprising the fixing device according to claim 5.