JP2774802B2 - Thermal fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an improvement in a heat fixing device.

(Prior Art) An electrophotographic method is one of the recording methods used for copying machines, printers, and the like. In this electrophotographic method, an electric image is formed on a charged photoconductive drum, or an electric latent image is formed on the photoconductive drum by drawing with an optical beam, and toner is adhered to the latent image. The image obtained by the development is transferred to recording paper, or the electric latent image formed directly on the recording paper is developed by attaching toner,
The hard copy is obtained by fixing the toner image thus formed on the recording paper.

By the way, there have been several fixing methods such as a heat fixing method and a pressure fixing method, which are used for electrophotography and the like and fix toner adhered to the recording paper on the recording paper.
Among them, a heat roll, that is, a heater is used,
2. Description of the Related Art A heat fixing apparatus of a heat fixing system for fixing a roller by heating the roller is widely used because of its simple structure and light weight.

In this heat fixing device, it is necessary to always maintain a constant temperature in order to ensure good image quality and maintain the stability of the heat fixing state. Therefore, temperature control constitutes a kind of automatic feedback control system.

FIG. 8 shows a conventional apparatus using this automatic control method.
That is, in FIG. 8, reference numeral 1 denotes a cylindrical heat fixing roller (heat roller), which has a built-in heater 8, and heats the heat fixing roller 1 by energizing the heater 8. I do. The heat fixing roller 1 is paired with a cylindrical pressure roller 1a. By rotating these rollers, the recording paper is sandwiched and fed, and the heat pressure roller 1a is heated and pressed with the heat fixing roller 1 at that time. The toner on the recording paper is heated and welded by force to apply heat to fix the toner. Reference numeral 2 denotes a temperature detector which is provided in sliding contact with the heat fixing roller 1 and detects the temperature of the heat fixing roller 1 and converts the temperature into an electric signal. The comparator 4 has another input terminal for providing a reference voltage for comparing the output of the temperature detector 2 with the output. The output of the reference voltage generator 3 is supplied to the input terminal. The output of the comparator 4 is input to an energization control unit 5 for performing on / off control of the heater 8, and controls on / off of the power from the heater power supply 6 to keep the temperature of the heater 1 constant. I try to keep it. Numeral 7 denotes an over-temperature preventer provided by a temperature fuse or a thermostat, which is provided in slidable contact with the heat fixing roller 1 and which is interposed between the power supply control unit 5 and the heater 8 to perform heat fixing. When the temperature of the roller 1 rises abnormally, the power from the heater power supply 6 applied to the heater 8 in the heat fixing roller 1 from the power supply control unit 5 is cut off and protected.

In such a configuration, for example, when the output of the temperature detector 2 is larger than the output of the reference voltage generator 3, the heater 8 is turned on, and conversely, when the output becomes smaller, the heater 8 is turned off to keep the heater 8 constant. However, in the case of the conventional method, when the temperature is controlled at a constant value, the temperature hardly rises and falls, which is good. However, as shown in FIG.
When the output of the temperature detector 2 is turned on after that, when the output of the temperature detector 2 exceeds the voltage of the reference voltage generator 3, that is, the temperature set value (or target value) TO, it is turned off for the first time. But,
At this time, the temperature continues to rise due to the influence of the thermal time constant of the heater 8, the heat fixing roller 1, and the like, and the temperature does not immediately become constant, but becomes too high as indicated by a symbol a in FIG. A rise always occurs. Since the temperature rise at the beginning of turning on the power is large, the temperature may exceed the allowable thermal rating, thereby shortening the life of the fixing device and preventing the temperature from rising excessively in series with the heater 8 power supply. This may cause the device 7 to malfunction. If the excessive temperature rise prevention device 7 malfunctions, if it is a temperature fuse, it is necessary to replace the blown temperature fuse and maintenance is troublesome. For this reason, a method of raising the setting of the excessive temperature rise prevention device 7 by an amount corresponding to the above-mentioned excessive temperature rise value can be considered. However, such a problem occurs that safety is impaired.

Therefore, in order to solve this problem, as shown in FIG. 10, the outputs of the second comparator 10, the second reference voltage generator 9, the first comparator 3, and the second comparator 10 are provided. A control signal switch 11 for switching the control signal and providing the control signal to the energization control unit 5 is added, and the output voltage of the second reference voltage generator 9 is set lower than the output voltage of the first reference voltage generator 3. At the time of rising, when the second set value by the second comparator 10 is reached, the heater 8 is turned off once, and the target temperature is raised by an excessive temperature rise using the thermal time constant of the heat fixing roller 1 or the like. After the temperature is raised to the first set value and the first set value is exceeded at least once, the switch 11
, The control is transferred to the first comparator 4, and thereafter, the above-described control for the target value (first set value) TO by the first comparator 4 is performed.

However, even in this method, during constant temperature control, the heater is cut off due to, for example, jamming of the recording paper or a power failure, and as shown in FIG. 11, the temperature is lowered and the power is turned on again near the second set value T1, Assuming that the control is started, the heater 8 is turned off before the heat fixing roller 1 is sufficiently heated, so that the target first set value TO cannot be reached. Since the above-described control shifts to the temperature control using the first set value TO after increasing the temperature of the first set value TO with the residual heat, it is not possible to shift to the temperature control using the first set value TO. There is a drawback that the control is fixed to the second set value T1 as it is, and the temperature becomes constant near the second set value T1, so that the function as the heat fixing device cannot be performed.

(Problems to be Solved by the Invention) As described above, the thermal fixing device for thermally fixing the toner on the recording paper sandwiches the recording paper between a thermal fixing roller having a built-in heater and a pressure roller. The pair of rollers are driven to rotate and sent out, and while monitoring the temperature of the heat fixing roller, the heater in the heat fixing roller is energized so as to be maintained at a reference temperature, thereby controlling the toner on the recording paper. Is heated and welded. However, in such a heat fixing device, since the heater of the heat fixing device is turned on / off by one or two set values (target values), the former of which follows one target value. In the system, there is a problem that a large over-temperature always occurs due to the thermal time constant of the heat fixing roller at the time of startup and shortens the life of the fixing machine. Two target values are set for start-up, and control is performed at the start-up temperature setting value at start-up. When this temperature is reached, the power is turned off once, and the temperature is raised with residual heat to reach the temperature set value for steady operation. Then, after that, in the latter method in which the temperature is set to follow the temperature set value for the steady operation, the power is turned off during the control, and the power is restarted before the temperature of the heat fixing roller sufficiently decreases. When the target temperature does not rise Cormorant problem there is.

Therefore, an object of the present invention is to suppress the excessive rise of heat as much as possible at the time of start-up, and to surely raise the temperature to the set value for the purpose even after restarting after shutting off the power supply. An object of the present invention is to provide a heat fixing device having good temperature controllability.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention is configured as follows. That is, the temperature is controlled by controlling the energization of a built-in heater, and the toner is brought into contact with the recording paper having the toner attached thereto.
And a power supply for energizing the heater to generate heat, and detecting means for detecting the temperature of the heat fixing section. In the heat fixing device, the detection unit is controlled to control the temperature of the heat fixing unit to a predetermined target temperature value by controlling on / off of energization of the heater of the power supply according to the temperature. Sampling means for sampling the detected temperature at a predetermined time interval shorter than the time constant of the temperature change of the heat fixing section, and a temperature value obtained by this sampling obtained by this sampling means and obtained by the previous sampling. A first difference from the obtained temperature value is obtained, and a second difference between the target temperature value and the temperature value obtained by the current sampling is obtained, and the first difference between the first difference and the second difference is obtained. Seki However, when the first difference is smaller than the result of multiplication of the second difference and the predetermined count, for example, the power supply to the heater of the power supply is turned on. And control means for instructing the power supply to the heater to be turned off.

(Operation) In the apparatus having the above-described configuration, the control unit determines the current temperature value and the temperature value obtained by the previous sampling based on the detected temperature value of the heat fixing unit obtained by sampling at a predetermined time interval. The first difference α and the second difference β between the target set value and the temperature value obtained by the current sampling are calculated.
And if β <k (β), according to the difference between β and β,
If α ≧ k (β), a heater-off control output is generated,
Energization control is performed. α is proportional to the rate of change of the temperature that changes every moment, and β decreases as the value approaches the target value TO.Thus, by comparing these values, the difference between the temperature target value for the heat fixing unit and the current temperature is calculated. The on / off control of the heater is performed in consideration of the temperature rise gradient. As the temperature of the heat fixing unit approaches the target value, the interval at which the heater is turned on becomes shorter, and the heater is turned on and off. Since the energization control is performed intermittently so that the interval becomes longer, the temperature is gradually controlled to reach the target value. As a result, it is possible to suppress an excessive rise in temperature of the heat fixing unit at the time of startup without being affected by the thermal characteristics of the heat fixing unit and the like. In addition to being able to raise the temperature to the target value, since the temperature rise is suppressed, the temperature rise prevention device does not malfunction.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a heat fixing device showing an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a cylindrical heat fixing roller (heater).
The heat fixing roller 1 has a built-in heater 8 and heats the heat fixing roller 1 when the heater 8 is energized. The heat fixing roller 1 is a cylindrical pressure roller.
The recording paper is sandwiched and sent by rotating these rollers, and the toner on the recording paper is heated and welded by heat and pressure with the heat fixing roller 1 at that time to thermally fix the toner. Things. Reference numeral 2 denotes a temperature detector which is provided in sliding contact with the heat fixing roller 1 and detects the temperature of the heat fixing roller 1 and converts the temperature into an electric signal. Reference numeral 12 denotes an analog / digital converter (hereinafter, referred to as an ADC) for converting the output of the temperature detector 2 into a digital signal, and reference numeral 13 denotes a control unit 13 for controlling energization based on the digital signal. The control signal from the control unit 13 is used to control a switch in the power supply control unit 5 that controls on / off of the power supply to the heater 8. A signal for controlling heater ON / OFF is generated in accordance with the difference between the previous temperature and the difference between the current temperature of the heat fixing roller 1 and the target temperature. In the present invention, the control unit 13 may be performed by software control using a microcomputer, or may be performed by hardware.

Here, software control will be described as an example. The details in the control unit 13 are as shown in FIG. That is, the CPU 14 which plays a central role in calculation and control, the ROM 15 in which the control program to be executed by the CPU 14 is stored, and the data storage RAM
A micro computer circuit comprising a bus 16 and a periodic interrupt timer 18 connected by a bus 19 is used. The signal from the temperature detector 2 is converted into a digital signal by the ADC 12 in this micro computer circuit. When the detected temperature data is input, the CPU 14 calculates a difference α between the data and the data obtained by the previous sampling, and calculates a difference β between the target value and the data obtained by the current sampling. <K
If (β) (where k is a constant), the heater-on, α ≧ k
In the case of (β), a function of generating a heater-off control output and giving it to the power supply control unit 5 is executed. α is proportional to the rate of change of the temperature which changes every moment, and β becomes smaller as it approaches the target value TO. By comparing these values, the difference between the target value of the heat fixing roller 1 and the current temperature is calculated. The on / off control of the heater 8 is determined in consideration of the temperature rise gradient, and the result can be output to the port 17. The output of the port 17 controls the energization control unit 5 for heat-on / off control. Reference numeral 7 denotes an over-temperature prevention device which is provided with a temperature fuse or a thermostat, and which is provided in sliding contact with the heat fixing roller 1 and which is interposed between the power supply control unit 5 and the heater 8 for heat fixing. When the temperature of the roller 1 rises abnormally, the power supplied from the heater power supply 6 to the heater 8 in the heat fixing roller 1 from the power supply control unit 5 is cut off and protected.

Next, the operation of the present apparatus having the above configuration will be described below. First, the control unit 13 receives an instruction to start the temperature rise of the fixing device from outside (not shown). When this instruction is received, first, the current temperature data of the heat fixing roller 1 is read from the ADC 12 and its value T
If 11 is smaller than a preset target value TO which is a target temperature value for steady operation, an ON control signal is output from port 17 to turn on heater 8. At the same time, the control unit 13 stores the value T11 in the RAM 16. In response to an ON control signal from the port 17, the energization control unit 5 turns on the switch, and supplies the output power of the heater power supply 6 to the heater 8 to generate heat. As a result, the heat fixing roller 1 is heated, and its temperature is detected by the temperature detector 2 and input to the ADC 12. The ADC 12 samples the output of the temperature detector 2 at certain intervals. The control unit 13 performs the following calculation and control using the detected temperature value acquired at the sampling interval.

That is, as shown in FIG. 7, the calculation and control by the previous sampling are completed, and the current temperature is calculated by the next sampling.
When a new temperature value T12 (corresponding to Tn) is obtained by taking in the TX (S1) (S2), the detected temperature value T12 of the heat fixing roller 1 obtained by this sampling and the temperature data T11 previously stored are obtained. Is calculated, and the difference β between the target values TO and T12 is calculated (S3, S4).
Since the sampling interval is constant, α is proportional to the temperature rise rate (slope) at that moment, and β is a value that indicates how close to the target value TO. Here, the value of α is compared with a reference value k (β) (s7). If α <k (β), it is determined that the temperature rise rate is still low, and the heater 8 is kept on. To control. However, if α ≧ k (β), it is determined that the temperature rise rate is too high, and an off-control output is output from the port 17 so as to turn off the heater 8, and is given to the energization control unit 5 (s6).

K (β) is a data of a function of β which is a difference from the target value TO.
The value decreases as it approaches TO.

Therefore, as the current temperature Tn approaches the target value TO, the gradient becomes smaller, and the target temperature TO can be stably reached.

FIG. 4 shows the relationship between β and k (β). Although the graph shows a proportional relationship in the figure, the characteristics may be changed according to the temperature characteristics of the fixing device, the structure of the housing, and the like.

FIG. 5 shows the control at the time of temperature rise in the method as described above, and FIG. 6 shows an example in which the control of the restart is performed after the power is cut off during the steady operation. Are shown below. Although not described in detail in each figure, AD
The sampling interval of C12 is sufficiently smaller than the rise time of the temperature. FIG. 7 is a flow chart summarizing these controls.

The detected temperature value is sampled at such a short time interval, and the difference between the data obtained by the immediately preceding sampling and the current detected temperature value data is used as the temperature gradient at that moment.
Control is performed so as to determine whether the heater power supply is turned on or off by comparing a value of a function determined by a difference between the target value and the present temperature with the temperature gradient data. And the current temperature value with respect to the target value, the heater power is turned on / off. At the same time, as the target value is approached, the comparison value is changed so as to decrease the slope. Even if the start of raising, the target value is not overturned,
Control can be performed reliably.

As described above, in the present apparatus, the temperature is controlled by controlling the energization of the built-in heater, and the heat fixing section that contacts the recording paper to which the toner adheres and thermally fixes the toner to the recording paper; And a detecting element for detecting the temperature of the heat fixing section. The heater is turned on / off in accordance with the temperature detected by the detecting element to control the heat generation. In a heat fixing device in which the temperature of the fixing unit is controlled to a target temperature, means for sampling the detected temperature of the detecting element at a predetermined time interval shorter than the temperature change of the heat fixing unit, and the current time obtained by the sampling. The difference α between the temperature value of the previous sampling and the temperature value of the previous sampling is obtained, and the difference β between the target value and the temperature value of the current sampling is obtained.
And control means for instructing on / off control of the heater in accordance with the difference between the two. Then, based on the detected temperature value of the heat fixing unit obtained by sampling at predetermined time intervals, the control unit determines a difference α between the current temperature value and the temperature value obtained by the previous sampling, and the target value and the current value of the current value. A difference β from the temperature value by sampling is obtained, and if α <k (β), a heater-on and α ≧
If k (β), a heater-off control output is generated to control the energization. α is proportional to the rate of change of the temperature that changes every moment, and β decreases as the value approaches the target value TO.Thus, by comparing these values, the difference between the temperature target value for the heat fixing unit and the current temperature is calculated. The on / off control of the heater can be performed in consideration of the temperature rise gradient. As the temperature of the heat fixing unit approaches the target value, the interval at which the heater is turned on becomes short and the heater turns off. Since the energization control is performed intermittently so that the interval becomes longer, the temperature is gradually controlled to reach the target value. as a result,
Excessive temperature rise of the heat fixing section can be suppressed at startup without affecting the thermal characteristics of the heat fixing section, etc. In addition to being able to raise the temperature up to this point, excessive temperature rise is suppressed, so that there is no erroneous operation of the excessive temperature rise prevention device.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to suppress an excessive rise in the temperature of the heat fixing unit at the time of startup, and to reliably set the desired setting even after restarting after the power is turned off. It is possible to provide a heat fixing device with good temperature controllability that can raise the temperature to a value.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the configuration of the control unit 13 shown in FIG. 1, and FIGS. FIG. 7 is a flow chart for explaining the operation of the present invention, FIGS. 8 and 10 are block diagrams showing a conventional example, FIGS. 9 and 11. FIG. 2 is a waveform diagram for explaining the operation of the conventional example. 1 ... heat fixing roller, 2 ... temperature detector, 5 ... energization control unit, 6 ... heater power supply, 7 ... excessive temperature rise prevention device,
8 ... heater, 12 ... analog / digital converter, 13
... Control unit.

Claims (2)

(57) [Claims] A heat-fixing unit whose temperature is controlled by energization control of a built-in heater, which is in contact with a recording sheet to which toner is adhered to thermally fix the toner on the recording sheet; and a power supply for energizing the heater to generate heat. Detecting means for detecting the temperature of the heat fixing section, and controlling on / off of energization of the heater of the power supply in accordance with the detected temperature detected by the detecting means, thereby controlling the heat fixing section. Wherein the temperature detected by the detection unit is sampled at a predetermined time interval shorter than a time constant of a temperature change of the heat fixing unit. And a first difference between a temperature value obtained by the current sampling obtained by the sampling means and a temperature value obtained by the previous sampling obtained by the sampling means. A second difference between the temperature value and the temperature value obtained by the current sampling is obtained, and when the relationship between the first difference and the second difference is in a predetermined state, the power supply to the heater is performed. And a control unit for instructing the power supply to turn off the power supply to the heater at other times. 2. The control means instructs to turn on the power supply to the heater when the first difference is smaller than the result of multiplication of the second difference and a predetermined coefficient. The heat fixing device according to claim 1.