JPH01319082A - Temperature controller for fixing device - Google Patents

Abstract

PURPOSE:To prevent erroneous detection by predicting the temperature of fixing devices after prescribed time from the detected temperature changing rates of the fixing devices and the then temperature of the devices and controlling a heating element based on the comparison between the predicted temperature and a set temperature. CONSTITUTION:Temperature changing rates of fixing devices 1 and 2 are measured by means of a temperature changing measuring means 5 based on the detected temperatures of the devices 1 and 2 and the temperatures of the devices after prescribed time are predicted from the measured temperature changing rates and the then temperatures of the devices 1 and 2. Then a heating element 3 is controlled based on the comparison between the predicted temperature and a set temperature. Therefore, overshooting can be prevented at the rising time, etc., and occurrence of erroneous detection of high temperature abnormality can be prevented at the time of overshooting.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device that fixes an image on paper or the like using at least heat, such as a fixing device in an electrophotographic device such as a copying machine or a laser printer. This relates to a control device.

[Conventional technology]

A fixing device such as a copying machine fixes a toner image on a sheet of paper using heat and pressure from a fixing roller. As described above, the fixing device that performs fixing using at least heat has a temperature control device that controls the heating element to maintain the temperature used during fixing.

Such a conventional temperature control device determines a set temperature that indicates a temperature or temperature range suitable for fusing, and controls the temperature by turning on and off a heating element based on a comparison between the temperature of the fixing device and this set temperature. was going on.

For example, in Japanese Patent Publication No. 62-9907, a set temperature (appropriate temperature t2) indicating the optimum temperature for fixing is defined, and based on a comparison between the surface temperature of the heat roller detected by a thermistor and this set temperature, the heater This document describes an invention in which temperature control is performed by controlling the phase of AC power supplied to the AC power source.

Note that this phase control also turns the power on and off, but instead of switching on and off based on the comparison between the detected temperature and the set temperature as in the case of the above-mentioned ON/OFF control, it is based on the comparison between these. It adjusts the phase angle for cutting off the AC power supply based on the , and performs stepless power control.
More stable temperature control can be performed. However, the invention described in the claims of Japanese Patent Publication No. 62-9907 is aimed at detecting an abnormality when the heater temperature does not rise normally.

[Problem to be solved by the invention]

However, since the fixing device requires a certain amount of heat capacity in the part that performs fixing, there is a relatively large delay in heat conduction between the fixing device and the heating element. Since it is necessary to detect the temperature of the part where fixing is actually performed as the temperature of the fixing device, a large delay element is added to the feedback loop of the temperature control device.

For this reason, if temperature control is performed only by comparing a predetermined set temperature with the temperature of the fixing device at that time, as in conventional temperature control devices, for example, when starting up the fixing device, etc. -It is unavoidable that overshoots that exceed the set temperature from time to time will occur. This situation is similar to the case where the AC power source of the heating element is phase controlled, although there is a difference in degree compared to the case where ON/OFF control is performed.

Therefore, the conventional temperature control device has a problem in that during this overshoot, a high temperature abnormality may be erroneously detected and the device may stop. In addition, if such false detections are eliminated only by measures on the detection side, the high temperature during overshoot may deteriorate the resin roller of the fixing device, offset prevention oil, etc., and have a negative impact on the fixing function itself. A problem arose that this would happen.

[Means to solve the problem]

In order to solve the above problems, a temperature control device for a fixing device according to the present invention detects the temperature of the fixing device and controls the temperature of the fixing device based on the detected temperature. , a temperature change measuring means for measuring the rate of change in temperature based on the detected temperature of the fixing device; and a temperature change measuring means for measuring the rate of change in temperature based on the detected temperature of the fixing device; Based on a temperature prediction means for predicting the temperature of the subsequent fixing device, and a comparison between the predicted temperature predicted by this temperature prediction means and the set temperature,
It is characterized by having a heating element control means for controlling the heating element.

[For production]

First, the temperature change measuring means measures the rate of change in temperature based on the detected temperature of the fixing device. The rate of temperature change can be measured, for example, by finding the difference between the previously detected temperature and the currently detected temperature, and dividing this by the time interval between the previous time and this time. In such a case, the temperature of the fixing device is usually detected at regular intervals, and the rate of temperature change is measured each time. Furthermore, the rate of temperature change can also be measured by continuously detecting the temperature of the fixing device and differentiating it.

Next, the temperature prediction means predicts the temperature of the fixing device after a predetermined time based on the measured rate of temperature change and the temperature of the fixing device at that time. The temperature of the fixing device after this predetermined time can be predicted by, for example, multiplying the rate of temperature change by the predetermined time and adding the temperature of the fixing device at that time. Alternatively, a method may be used in which the temperature change curve of the fixing device is predicted from the temperature of the fixing device at that time and the rate of temperature change, and the temperature after a predetermined time is predicted based on this. . Note that the predetermined time is determined as an appropriate value based on actual measurements of the delay in heat conduction between the heating element and the temperature detection section of the fixing device. Further, different predetermined temperatures can be determined depending on the state at that time, such as when the temperature is rising and when the temperature is falling.

Then, the heating element control means controls the heating element based on the comparison between the predicted temperature and the set temperature. The heating element is controlled, for example, by turning off the heating element when the predicted temperature exceeds the set temperature, and turning on the heating element when the predicted temperature becomes lower than the set temperature. Furthermore, the phase of the AC power source for a heating element such as a heater may be controlled based on the difference between the predicted temperature and the set temperature. Note that the set temperature is set to a temperature at which fixing by the fixing device is optimal. However, since there may be a difference in temperature between the temperature detection part of the fixing device and the part where fixing is actually performed, it is necessary to take this difference into consideration when determining the set temperature.

As a result of controlling the temperature of the heating element as described above, when the temperature of the fixing device approaches the set temperature, the heating element can be controlled in advance to suppress the temperature change in accordance with the rate of temperature change. For this reason, if the temperature rises suddenly, such as when starting up the equipment, control is performed to suppress the heat generation of the heating element while the detected temperature is still sufficiently lower than the set temperature. Shoots can be prevented from occurring. Further, when the rate of temperature change is slow, control is performed at a correspondingly slow rate, so that a constant temperature state with little temperature change can be maintained.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 4.

The fixing device is composed of an upper fixing roller 1 and a lower fixing roller 2, as shown in FIG. The upper fixing roller l is
This is a drive roller with a heater lamp 3 installed inside.

Further, the lower fixing roller 2 is a driven roller that is pressed against the upper fixing roller 1 from below. The upper half of the upper fixing roller 1 is covered by a fixing cover 4. A thermistor 5 is arranged inside this fixing cover 4,
This is pressed against the upper end of the circumferential surface of the upper fixing roller 1.

In the fixing device configured as described above, the lower fixing roller 2 rotates as the upper fixing roller 1 rotates. Further, the upper fixing roller 1 is heated by an internal heater lamp 3. The surface temperature of the upper fixing roller 1 is determined by a thermistor 5.
detected by.

When paper A is fed into this fixing device, this paper A is sandwiched between upper fixing roller 1 and lower fixing roller 2,
It is discharged as the upper fixing roller 1 is rotated. At this time, toner B that had been transferred onto paper A is melted by heat from upper fixing roller 1 and fixed onto paper A by pressure from lower fixing roller 2.

The temperature control device of the fixing device is as shown in FIG.
It is composed of a microcomputer. Heater lamp 3 in the fixing device is connected to I10 interface 11 of this microcomputer. Further, the thermistor 5 is connected to an A/D converter 13 of this microcomputer via a resistance-voltage conversion circuit 12. These I10 interfaces 11 and A/
The D converter 13 has an address bus 14 and a data bus 15.
It is connected to the CPU 16 via. This CPU16
A ROM 17 that stores programs and constants for temperature control of this embodiment, and a RAM 18 that provides a storage area for program variables and work are connected via the same address bus 14 and data bus 15. has been done. Furthermore, this ri! AM18 has 1 backup battery
9 is connected.

In the temperature control device, the CPU 16 inputs the temperature detected by the thermistor 5 according to a program stored in the ROM 17, and controls the heater lamp 3 based on this input.

The specific operation of this temperature control device will be explained based on the flowchart of FIG.

When the power of the device is turned on, the first step (hereinafter referred to as “S”) is
1), the temperature detected by the thermistor 5 is taken in, and this value is substituted into the variable T1 set in the RAM 18. Then, the temperature indicated by this variable T1 and ROM1
7 is compared with the constant 170 stored above (S2). This constant 170 is the set temperature 17 for optimal fixing.
Indicates 0°C. Note that the case where the temperature of variable T is already higher than 170° C. will be explained later.

Here, if the temperature of the variable T1 is 170° C. or lower, the heater lamp 3 is turned on (S3) to heat the upper fixing roller 1, and the process waits for 200 ma to elapse (S4). 20
When 0 ms has elapsed, the temperature detected by the thermistor 5 is read again and another variable D'r2 set in the area on the RAM 18 is read.
(S5). And these variables T1 and T2
Based on the constant and 1, the following +112 judgment is made (S
6).

(Tz TI )XKI +TZ≧170 ...(
11 Here, the value of the variable T indicates the detected temperature at 200 hizen, and the value of the variable T2 indicates the current detected temperature. child(
Therefore, (T2-TI) indicates the rate of change in detected temperature over 200 ma. Further, the constant 1 is a constant indicating a predetermined time when the temperature rises. Specifically, it is the value obtained by dividing the delay time until the change is transmitted to the surface of the upper fixing roller l when the heater lamp 3 is switched from ON to OFF by 2°Q ma. The optimal value is determined by Therefore,
Multiplying this constant by 1 to the above (T tT+) yields the rate at which the detected temperature changes over a predetermined period of time, and adding the variable T2 indicating the current detected temperature to this yields the predicted temperature after the predetermined period of time. . Then, in S6, this predicted temperature is compared with a constant of 170°C.

If the predicted temperature is lower than 170°C, the variable T.

After assigning the value of variable T2 to (S7), the process returns to S4.

That is, the predicted temperature after a predetermined time is calculated every 200 mA, and the process from 84 to S7 is performed until the predicted temperature reaches 170°C or higher.
Repeat the process.

If the predicted temperature exceeds 70° C., the heater lamp 3 is turned off (S8) and heating of the upper fixing roller 1 is stopped. However, the surface temperature of the upper fixing roller l continues to rise for a while after that due to a delay in heat conduction. However, the more rapid the temperature rise, the more
The value of (Tz - TI ) When it slightly exceeds the limit, the temperature stops rising and begins to fall.

When the heater lamp 3 is turned off, the value of Tw is assigned to the variable T1 (39), and the process waits for 200 na to elapse again (SIO). Further, in S2, if the temperature of the variable T1 is already higher than 170°C, the process directly proceeds to this SIO process.

When 200 trillion have elapsed, the temperature detected by the thermistor 5 is taken in again and substituted into the variable T2 (S11). Then, based on the variables T1 and T2 and the constant 2, the following equation (2) is determined (S12).

(Tz −TI') XKZ +TZ < 170
(2) Here, the constant 2 is a constant indicating a predetermined time when the temperature decreases. Specifically, when the heater lamp 3 is switched from OFF to ON, it is the value obtained by dividing the delay time until the change is transmitted to the surface of the upper fixing roller 1 by 200 ms, and is a constant K.

Similarly, the optimum value is determined in advance through experiments or the like. Therefore, the left side of equation (2) indicates the predicted temperature after a predetermined time when the temperature decreases. And in S12,
This predicted temperature is compared with a constant of 170°C.

If the predicted temperature is 170°C or higher, the variable T1 is set to
After substituting the value 2 (S13), the process returns to StO. That is, the predicted temperature after a predetermined time is calculated every 200 nas, and the SIO~31
Repeat step 3.

If the predicted temperature is lower than 170°C, the value of variable T2 is assigned to variable T1 (314), and S3
Return to , turn on the heater lamp 3, and perform steps 34 to S mentioned above.
Repeat step 7.

As a result, the temperature of the fixing device, that is, the surface temperature of the upper fixing roller 1 can be maintained at a substantially constant temperature near the set temperature.

FIG. 4 shows a comparison of changes in detected temperature due to temperature control of the above-mentioned temperature control device with a conventional one.

In conventional temperature control devices, the heater lamp 3 is turned on and off after the detected temperature reaches the set temperature, so there is a large overshoot when starting up the device (
Even after that, the temperature changes significantly before and after the set temperature.

In contrast, in this embodiment, the heater lamp 3 can be turned on and off before the detected temperature reaches the set temperature, so overshoot at the time of device startup is suppressed, and even after that, the temperature can be kept within a small range around the set temperature.

It should be noted that FIG. 4 also shows the temperature of the heater lamp 3 and the temperature of the fixing section as well as the detected temperature of this embodiment. As is clear from the comparison between the temperature of the heater lamp 3 and the detected temperature, the temperature detected on the surface of the upper fixing roller 1 has a time delay due to heat conduction with respect to the temperature of the heater lamp 3, which is a heating element. are doing.

Further, in the fixing section which is the lower end of the upper fixing roller l, heat is taken away by the lower fixing roller 2 and the like, so the temperature is lower than the temperature detected at the upper end. Since the temperature that toner B actually receives during fixing is the temperature of this fixing section, the set temperature here is set to a temperature slightly higher than the optimum fixing temperature.

〔Effect of the invention〕

As described above, the temperature control device for a fixing device according to the present invention is a temperature control device that controls the temperature of the fixing device by detecting the temperature of the fixing device and controlling the heating element based on the detected temperature. a temperature change measuring means that measures the rate of change in temperature based on the temperature of the fixing device; The apparatus includes a temperature prediction means for predicting the temperature of the apparatus, and a heating element control means for controlling the heating element based on a comparison between the predicted temperature predicted by the temperature prediction means and a set temperature.

Thereby, the temperature of the fixing device after a predetermined period of time can be predicted and the heating element can be controlled in advance, so that overshoot at startup, for example, can be suppressed.

Therefore, the temperature control device of the present invention has the effect of preventing false detection of high temperature abnormality from occurring at the time of overshoot. Furthermore, since the fixing device is not exposed to unnecessarily high temperatures, it also has the effect of contributing to extending the life of the device.

[Brief explanation of the drawing]

1 to 4 show an embodiment of the present invention, in which FIG. 1 is a flowchart of a temperature control device, FIG. 2 is a schematic vertical sectional view of a fixing device, and FIG. 3 is a temperature control device. FIG. 4 is a block diagram showing the configuration of the fixing device, and FIG. 4 is a diagram showing temperature changes of the fixing device in the embodiment and the conventional example. 1 is an upper fixing roller, 2 is a lower fixing roller, 3 is a heater lamp (heating element), and 5 is a thermistor. Patent applicant Sharp Co., Ltd. Figure 2

Claims (1)

[Claims] 1. In a temperature control device that controls the temperature of the fixing device by detecting the temperature of the fixing device and controlling a heating element based on the detected temperature, the temperature control device controls the temperature of the fixing device based on the detected temperature of the fixing device. Temperature change measuring means for measuring the rate of change in temperature, and temperature predicting means for predicting the temperature of the fixing device after a predetermined time based on the rate of temperature change measured by the temperature change measuring means and the temperature of the fixing device at that time. and heating element control means for controlling a heating element based on a comparison between the predicted temperature predicted by the temperature prediction means and a set temperature.