JPH09319255A - Controlling method for fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform heat control without causing over shoot of the heating temp. or fixing defect, at any time of the temp. on a fixing device in heating-up. SOLUTION: In this device, controlling means make a fixing device heated by a heat applying heater (S1). The present temp. of the fixing device is always measured (S2). Based on the measured present temp. and the preceding present temp., the heating-up grade is calculated (S3). Based on a correction table storing the correction value of lagging of a thermistor output obtained by the previous measuring, the correction value is selected from the measured present temp. and the calculated heating up grade (S4). Based on the selected correction value, the correction of the thermistor output is performed (S5). The on/off control of the heat applying heater by the corrected thermistor output (S6). The correct and optimum heating control is performed by performing the correction of the thermistor output delay based on the heating-up grade.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device control method for controlling a heater, which is applied to a fixing device of an image forming apparatus such as a copying machine, a facsimile or a printer.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, for example, in a copying machine, toner is transferred and adhered to an electrostatic latent image formed on a photoreceptor, developed, transferred to a sheet of paper, and then heated by a fixing device. I try to fix it. In order to heat and fix the toner by passing the sheet on which the toner image has been transferred between the heat roller and the pressure roller of the fixing device, the fixing device needs to reach a predetermined fixable temperature. For this reason, when the power was turned on, the temperature of the fixing device was maintained at approximately the feasible temperature.However, due to recent energy saving situations, the number of devices that set the fusing device temperature to a much lower temperature than the feasible temperature during standby increased. doing. The heater is controlled so that the temperature can be fixed when the apparatus is used.

In temperature control of this type of fixing device used in an image forming apparatus, particularly in temperature control using a thermistor as a temperature detecting element, an overshoot occurs at the time of temperature rise due to a delay in the thermistor output. As a means for suppressing this overshoot at the time of temperature rise, there has been taken a means of allowing a delay in the thermistor output at the time of temperature rise and turning off a heat source such as a heating heater before reaching the fixable temperature.

FIG. 6 is a diagram showing a temperature change under the control of a conventional heater. Te is a fixing temperature, te is a fixing temperature, and A is a delay time from the time te. In temperature control using a thermistor as a temperature sensing element,
According to the temperature-resistance characteristic of the thermistor, there is a delay before the thermistor output having an arbitrarily determined temperature is obtained. Therefore, when the temperature is raised by the heater of the fixing device, the temperature of the fixing device rises to the point where it exceeds the fixable temperature Te. Then, an overshoot as shown by the broken line in FIG. 6 occurs. In order to suppress this, the control shown by the solid line in FIG. 6 is performed in consideration of the delay in the thermistor output, and the heater is turned off at a temperature lower than the fixable temperature Te.

Further, FIG. 7 is a diagram showing a temperature change when heating is controlled to a constant temperature (fixable temperature) using the thermistor output. Due to the thermistor output delay when this heating control is performed, the actual temperature changes, but the current temperature of the fixing device is beginning to drop, but the thermistor output detects that the temperature is rising, and the heating heater is turned off. If the temperature becomes excessive, the undershoot Td becomes large as the temperature changes. The same is true in the opposite case, and the heater is turned on too much and the overshoot To increases.

In order to perform a normal fixing operation, the heater is heated until the fixing temperature is reached, or when a predetermined time elapses due to temperature fluctuation due to paper passing, or by measuring the temperature and comparing it with a set temperature. Intermittent control for turning on / off is performed. The temperature control device of this fixing device is disclosed in Japanese Patent Application Laid-Open No. HEI 7
It is also disclosed in Japanese Patent Publication No. 114289.

[0007]

However, in the image forming apparatus having such a structure, the temperature of the fixing device is maintained at a substantially fixable temperature when the power is turned on. Although it was okay to consider it only when the power was turned on, due to energy saving circumstances, the temperature of the fixing device during standby was set to a temperature much lower than the fixing possible temperature, and the heating heater was controlled to make it the fixing possible temperature when using the device. Is performed.

Further, since the delay in the thermistor output differs depending on the temperature rise gradient, the set value of the control that allows for the delay in the thermistor output is too tight for the temperature rise gradient, that is, when the temperature of the fixing device at the start of temperature rise is low. When the temperature of the fixing device at the start of temperature rise is higher than the set value (control of the solid line shown in FIG. 6), the time until reaching the fixable temperature is delayed as shown by the one-dot chain line in FIG. It becomes longer by time A.
If the paper passes through the fixing device during this period, the fixing temperature is not reached and there is a problem that fixing failure occurs.

The present invention solves the above-mentioned problems of the prior art, and provides a method of controlling a fixing device which does not cause overshooting of heating temperature or defective fixing at any temperature of the fixing device at the time of temperature rise. The purpose is to do.

[0010]

In order to achieve this object, a method of controlling a fixing device according to the present invention includes a thermistor as a temperature detecting element, a correction table in which a correction value is obtained by measurement in advance, and a correction value. It is characterized in that the control is performed by a configuration including a control unit for selecting and controlling the heating heater and a heating heater for heating the fixing device.

Further, a thermistor as a temperature detecting element,
It is controlled by a configuration including a difference table in which a difference control value is obtained by measurement in advance, a control unit that selects the difference control value and controls the heater, and a heater that heats the fixing device.

With the above configuration, the temperature rise gradient is calculated from the current temperature measured during temperature rise, the correction value is selected from the correction table according to the current temperature and the temperature rise gradient, and the delay in the thermistor output is corrected. , The heater can be controlled.

Further, it is possible to calculate the temperature rise gradient from the current temperature measured during temperature rise, select a difference control value from the difference table according to the current temperature and the temperature rise gradient, and control the heater by the difference control value. it can.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an electrical configuration for controlling a heater of a fixing device according to Embodiment 1 of the present invention. In FIG.
Reference numeral 1 is a thermistor for controlling heating by a temperature detection element of a fixing device, and 2 is provided with a correction table in which correction values obtained by measurement in advance are collected, and control means for correcting the delay of the thermistor output by the correction value, Reference numeral 3 is a heating heater of a heating unit that heats the fixing device by the corrected output of the control unit 2. Further, FIG. 2 is a flowchart showing the control operation of the heater of the fixing device according to the first embodiment. FIG. 3 is a diagram showing temperature-resistance characteristics of the thermistor.

The heating control of the fixing device having the above-described configuration according to the first embodiment will be described with reference to the flowcharts of FIGS. 1 and 2. The heating of the fixing device is controlled by turning on the heater 3 in response to power-on, a fixing command, or the like, so that the initial setting temperature in the standby state or the fixing temperature at which the fixing operation is performed is performed. An example is taken until the temperature is raised to the temperature.

First, when a fixing command is input, the control means 2
Turns on the heater 3 to heat the fixing device.
(S1). The current temperature of the fixing device is constantly measured, and the measured value is sent to the control means 2 (S2). A temperature rise gradient is calculated from the measured current temperature and the current temperature measured immediately before (S
3). From the temperature rise gradient δ and the current temperature T, the correction value α indicating the delay in the thermistor output is selected from the correction table shown in the following (Table 1) in which the correction values for the thermistor output delay obtained by measurement in advance are tabulated (S4). ). The control means 2 corrects the thermistor output from the temperature-resistance characteristic of the thermistor with the selected correction value α. That is, the thermistor output is corrected to R + α 'as shown in FIG. 3 by the temperature rise gradient δ and the correction value α of the current temperature T (S5). The heater 3 is turned on / off by the corrected thermistor output (S6).

[0017]

[Table 1]

From the above, in order to correct the delay of the thermistor output which differs depending on the temperature rising gradient, the temperature rising gradient is calculated from the presently measured current temperature, and the correction values of the thermistor output delay correction values are tabulated. A correction value is selected from the table according to the measured current temperature and the calculated temperature rise gradient. Then, the thermistor output can be corrected from the selected correction value, and heating control by turning on / off the heater can be performed according to the corrected output.

Next, FIG. 4 is a diagram showing a temperature change due to differential control of the heater in the second embodiment of the present invention. Further, FIG. 5 is a flowchart showing the control operation of the heater of the fixing device according to the second embodiment. The heating control of the fixing device according to the second embodiment will be described with reference to the flowcharts of FIGS. 4 and 5. Here, as in the case of the first embodiment, the heating control is performed to raise the temperature to the feasible temperature and maintain the feasible temperature.

When the fixing command is input, the heater is turned on by the control means to heat the fixing device (S10). The current temperature of the fixing device is constantly measured and the measured value is sent to the control means (S11). A temperature rise gradient is calculated from the measured current temperature and the immediately preceding measured current temperature (S12). The difference control value indicated by the temperature rising gradient and the current temperature is selected from the difference table shown in the following (Table 2), which is a table of the difference control values for performing the difference control obtained by measurement in advance (S13). The control means uses the on / off ratio indicated by the selected differential control value to
ON / OFF control of the heater is performed (S14).

[0021]

[Table 2]

Further, the difference control according to the second embodiment is optimal for the current temperature of the fixing device and the calculated temperature rising gradient in the control of maintaining the fixable temperature or reaching the target fixable temperature. The heating is controlled by obtaining the on / off ratio of the heater.

The setting of the ON / OFF ratio of the heater is
It varies depending on the power consumption of the heater, the input voltage, and the amount of heat generated by the configuration of the fixing device (roller size, thickness, etc.). A difference table of difference control values as shown in FIG.

For example, using a difference table of difference control values obtained by measurement in advance, there is a difference between the present temperature and the target fixable temperature and the temperature rise gradient is small depending on the selected difference control value. For example, the heating heater is turned on at a high rate, and conversely, if the temperature rise gradient is large in the vicinity of the target fixable temperature, the heating heater is turned off at a high rate to perform heating control.

According to this control method, it is possible to more finely respond to the temperature change of the fixing device, and it is possible to reduce the ripple of the temperature change in the heating control.

[0026]

As described above, according to the present invention,
By using the correction table having the correction value obtained by the measurement in advance and the difference table having the difference control value obtained by the measurement in advance, it is possible to perform the heating control in a reliable and optimal state, and to increase the heating temperature of the fixing device. It is possible to prevent overshoot, undershoot, temperature change ripple, and fixing failure due to insufficient heating.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration for controlling a heater of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a control operation of a heater of a fixing device according to the first embodiment.

FIG. 3 is a diagram showing temperature-resistance characteristics of a thermistor.

FIG. 4 is a diagram showing a temperature change due to differential control of a heater according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing a control operation of a heater of a fixing device according to the second embodiment.

FIG. 6 is a diagram showing a temperature change under the control of a conventional heater.

FIG. 7 is a diagram showing a temperature change when heating is controlled to a constant temperature (fixable temperature) by using a thermistor output.

[Explanation of symbols]

 1 ... Thermistor, 2 ... Control means, 3 ... Heating heater.

Claims (2)

[Claims] 1. In a fixing device using a thermistor as a temperature detecting element, a temperature rise gradient is calculated from a current temperature measured at the time of temperature rise, and the current temperature and the rising temperature are calculated from a correction table having a correction value obtained by measurement in advance. Select a correction value according to the temperature gradient to correct the delay of the thermistor output,
A method for controlling a fixing device, comprising controlling a heater. 2. In a fixing device using a thermistor as a temperature detecting element, a temperature rise gradient is calculated from the current temperature measured at the time of temperature rise, and the current temperature and the current temperature are calculated from a difference table having a difference control value obtained by measurement in advance. A method for controlling a fixing device, wherein a difference control value is selected according to a temperature rise gradient, and a heater is controlled by the difference control value.