JP2004151603A - Fixing controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing controller with which proper heater output is obtained without being affected by the power source condition (input voltage) of a place where the fixing controller is installed. <P>SOLUTION: In the fixing controller provided with a fixing unit 1 possessing a heater 3 and a temperature detecting element 2 and a controlling means 5 by which the turn-on duty of a heater within a specified control time is made variable so as to obtain proper heater output, the correction processing of the turn-on duty of the heater is performed so as to realize optimum heater energizing control under use environment by the controlling means 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing control device that controls a heater for toner fixing of a fixing unit used in an image forming apparatus such as a copying machine, a facsimile, and a printer.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an image forming apparatus having a fixing unit using a heater, an appropriate heater output is obtained by changing a lighting time (lighting duty) of a heater within a predetermined control time, that is, quickly and unnecessarily. A control method of causing a heater to reach and maintain a set temperature without causing excessive overshoot is generally used.
For example, when controlling the heater lighting so that the temperature at the position where the temperature detecting element in the fixing unit is attached becomes a predetermined set temperature, an amount obtained by multiplying a difference between the set temperature and the current temperature by a proportional constant is used. Commonly known automatic control methods such as P (proportional) control that determines the lighting time with P, PI (proportional / integral) control that also takes into account temperature transition, and PID (proportional / integral / differential) control that also takes into account time response There are many examples of application.
However, these controls do not consider the variation of each element that composes the control system, so when designing as a product, design a control system with a high margin that takes the variation tolerance into consideration or detect the variation. Either a control system to be corrected is designed. In the latter case, various studies have been made and many technologies have been announced.
In connection with the fixing heater control, Japanese Patent Application Laid-Open No. Hei 5-100755 (Japanese Patent No. 2867766) discloses that a rate of temperature rise from the start of energization to a control temperature is calculated, and a control pattern prepared in advance is selected. Techniques for correcting variations in heater resistance have been proposed. In this technique, since correction control cannot be performed when correction data is collected, the correction control does not work, for example, when the power is turned on in the morning.
Japanese Patent Application Laid-Open No. Hei 10-161466 discloses that the temperature rise gradient is measured to correct the time delay of the output of the thermistor and that the output of the thermistor is corrected. There has been proposed a technique for detecting and correcting the ON / OFF duty of the heater. This technique also cannot perform correction control during collection of correction data, so that, for example, when power is turned on in the morning, the correction control does not work.
Japanese Patent Application Laid-Open No. 2000-147942 discloses a temperature control method based on heater turn-on time and temperature rise data within a predetermined time, whereby appropriate temperature control can be performed with respect to variations in characteristics such as thermal conductivity of a heat fixing device. There has been proposed a technology that makes it possible to always realize optimum temperature control even when the heat fixing device is replaced. With this technology, the load on the microcomputer that performs control is very heavy.
[Patent Document 1] JP-A-5-100755 [Patent Document 2] JP-A-10-161466 [Patent Document 3] JP-A-2000-147942 [0003]
[Problems to be solved by the invention]
Here, the constant for determining the lighting duty is usually determined by the characteristics of the apparatus at the rated input of the image forming apparatus (100 V AC in Japan), and may be targeted depending on the power supply situation at the installation location of the apparatus. Disadvantageously that the heater output cannot be obtained.
Therefore, an object of the present invention is to provide a fixing control device that can obtain an appropriate heater output without being affected by a power supply situation (input voltage) at a place where the device is installed.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a fixing unit having a heater and a temperature detecting element and a lighting duty of the heater within a certain control time are varied to obtain an appropriate heater output. In a fixing control device including a control unit, the control unit has a fixing control unit that performs a heater lighting duty correction process as a main feature in order to realize optimal heater energization control in a use environment.
According to a second aspect of the present invention, in the fixing control device according to the first aspect, the control unit determines a temperature-time characteristic under a predetermined condition, and adjusts a heater lighting duty according to a gradient of the temperature-time characteristic. The main feature of the fixing control device is that the optimum heater output is always obtained regardless of the input voltage.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall configuration diagram of a fixing control device according to an embodiment of the present invention. The fixing control device includes a fixing unit 1, a base engine control unit (hereinafter, BCU) 4, and an AC control plate 6.
The fixing unit 1 includes a heater 3 and a temperature detecting element 2 to be controlled. The heater 3 is a bidirectional switching element 7 such as a triac included in an AC control plate 6. It is connected to a commercial AC power supply 8 via a current detection fuse or the like. The input / output insulated photocoupler or the like is often used as the drive of the switching element 7, and the ON / OFF control is performed by the CPU 5 operated by the secondary power supply. In FIG. 1, the CPU 5 is mounted on the BCU 4.
On the other hand, the temperature detecting element 2 is arranged near a roller surface (belt surface) (not shown) of the fixing unit 1, and an inexpensive thermistor is generally used. Hereinafter, the thermistor will be described as an example. The thermistor 2 has a characteristic that the resistance value changes according to the detected temperature, and converts the detected temperature into a voltage. This voltage value is taken into the A / D input of the CPU 5 mounted on the BCU 4, and the CPU 5 determines the roller surface (belt surface) temperature from this voltage value.
With the configuration of the control system as described above, the CPU 5 controls the ON / OFF of the heater 3 so that the roller (belt) surface temperature of the fixing unit 1 can be shifted to or maintained at a predetermined set temperature.
[0006]
Hereinafter, the fixing control (heater energization control) will be described. Basically, a known automatic control technique is used as described above. For example, taking P control as an example, first, the temperature is detected by the thermistor 2, the difference between the detected temperature and the set target temperature is obtained, and the lighting duty (time) of the heater 3 is calculated by multiplying the difference by a proportional constant Kp. Will decide.
Referring to FIG. 3, the thermistor temperature is detected at every control unit time t ₀ , and what percentage of the time (t ₁ , t ₂ , t ₃ ,... Calculation and ON / OFF control are performed. At this time, the lighting time increases as the difference from the set temperature increases, and the lighting time decreases as the difference from the set temperature decreases. The control unit time is determined by the CPU performance and the required resolution of the lighting time.
The above is a case where the basic control is the P control. However, if the lighting duty is determined in consideration of the temperature transition and the temperature change rate by the microcomputer without changing the control system, the PI control and the PID control are performed.
Although these are established as conventional techniques, the design of the control constants Kp, Ki, and Kd is generally performed in consideration of the tolerance (variation) of the elements constituting the control system. It is a target. However, as described above, the variation that occurs due to the consideration depends on the target of the control operation, that is, in the present control system, the heater lighting time (heater amount to be supplied) varies from device to device. is there.
In the present invention, correction is performed so that the above-described variation of the control system element does not affect the control operation amount. Specifically, the heater output (heater) is controlled by the fluctuation of the input voltage which is one of the control system elements. (The amount of heat) is corrected. Hereinafter, the control for correction will be described with reference to FIG.
[0007]
In the present invention, in order to realize optimal control in the usage environment, correction processing is performed on the heater lighting duty. However, an adjustment mode is provided for performing preliminary data collection for the correction processing. FIG. 2 shows a detected temperature-time characteristic of the thermistor 2 in the fixing unit 1 in the adjustment mode. As an operation, first, the heater 3 is turned on, the time until the thermistor detection temperature reaches a certain temperature from a certain temperature is counted, and the heater 3 is turned off.
In the example of FIG. 2, the temperature transition time from 50 ° C. to 100 ° C. is measured, and after the heater is turned on, the thermistor detection temperature is monitored by the CPU 5. After detecting 50 ° C., the timer in the CPU 5 is started. Timer detection and heater OFF at 100 ° C detection. The measured time is t = ba.
Note that the heater output in this adjustment mode needs to have a fixed duty, and the duty is selected such that the transition of the temperature detected by the thermistor 2 becomes a primary straight line as shown in FIG. Although the time between 50 ° C. and 100 ° C. is measured in FIG. 2, there is no problem as long as the thermistor 2 has a linear temperature-voltage characteristic with a small error.
The time t measured under such a setting is based on the previously measured temperature transition time t0 at the rated power supply voltage V0 (100 [V] in Japan). It is obtained from the following equation.
V = a · (t ₀ / t) · V ₀ (1)
Here, although a is an arbitrary constant, it can be obtained as a value specific to the control system by previously measuring the characteristics of the above equation due to variations in the power supply voltage.
When the power supply voltage is obtained, the heater output under the environment can be obtained. If the heater output at the rated input is W0 and the heater output under the environment is W, the following equation is established.
W = (V / V ₀ ) b · W ₀ (2)
Here, b is a value unique to the heater product (data can be obtained from the heater maker) (1) and (2), and the correction coefficient α of the heater lighting duty is given by the following equation.
α = W ₀ / W
= 1 / (a · (t ₀ / t)) b (3)
In the present invention, normal heater duty control is multiplied by α obtained by the equation (3). As a result, an output equivalent to the heater output at the rated input can be obtained without being affected by the power supply situation (input voltage) at the place where the device is installed, and the heater 3 can be quickly and unnecessarily generated without causing overshoot. Can reach and maintain the set temperature.
As for the execution timing of the adjustment mode, there is no need to make adjustments at the time of factory shipment, and it is necessary to perform the adjustments at the minimum at the time of installation of the machine, because the object of variation correction is the power supply condition (input voltage) used by the machine. . If only the machine is installed, the lighting duty is only multiplied by α obtained by equation (3) during normal control, so that the microcomputer load is small, and if the voltage situation changes every moment, the environment is more suitable. It is possible to cope by frequently collecting data for correction (every time the power is turned on or at the time of standby) and updating α.
[0008]
【The invention's effect】
As described above, according to the present invention, a temperature-time characteristic under a predetermined condition is obtained, a change in the input voltage of the apparatus is detected based on the slope, and the excess or deficiency of the heater output due to the change is corrected. As a result, proper heater output can be obtained without being affected by the power supply situation (input voltage) at the place where the device is installed, and the heater reaches and maintains the set temperature quickly and without unnecessary overshoot. It is possible to do.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a fixing control device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a detected temperature-time characteristic of a thermistor in a fixing unit in an adjustment mode.
FIG. 3 is a diagram showing a lighting duty of a heater.
[Explanation of symbols]
1 fixing unit 2 temperature detection element (thermistor)
3 heater 5 CPU (control means)

Claims (2)

A fixing unit having a heater and a temperature detecting element, and a control unit for varying a lighting duty of the heater within a certain control time in order to obtain an appropriate heater output, wherein the control unit includes: A fixing control device for performing a heater lighting duty correction process in order to realize optimum heater energization control in a use environment. 2. The fixing control device according to claim 1, wherein the control unit obtains a temperature-time characteristic under a predetermined condition, corrects a heater lighting duty in accordance with a slope of the temperature-time characteristic, and adjusts a heater lighting duty in accordance with an input voltage. A fixing control device wherein an optimum heater output is always obtained.

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