JPH05112065A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To enhance the safety of the above apparatus by controlling temp. by a plurality of temp. detection elements and detecting abnormal temp. by said elements. CONSTITUTION:An electric heating element driver 206 is controlled on the basis of the detection values of two first and second temp. detection elements 202, 207 by a temp. control circuit 203 to control the temp. of an electric heating element 201. Further, a switch circuit 205 is controlled on the basis of the detection values of two temp. detection elements 202, 207 by an abnormal temp. processing means 204 to deal with the abnormal temp. of the electric heating element 201.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a heat fixing device and forming an image, and is particularly applied to a laser beam printer, a copying machine and the like.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus for performing heat fixing using an electric heating element, one temperature detecting element 102 detects the temperature of the electric heating element 101 as shown in FIG. Input to the temperature control circuit 103 and the abnormal temperature processing means 104. The electric heating element driver 106 controlled by the output of the temperature control circuit 103 drives the electric heating element 101 via the switch circuit 105. The switch circuit 105 turns off the drive of the electric heating element 101 by the driver 106 based on the abnormal temperature processing signal from the abnormal temperature processing means 104. in this way,
Using one temperature detection element 102, temperature control is performed and abnormal temperature processing is performed.

[0003]

However, since the temperature detecting element has a high failure rate and the reliability of attachment to the electric heating element is low, the structure which relies on only one temperature detecting element as in the above-mentioned conventional example does not generate electricity. The reliability was insufficient as a means for preventing excessive heating of the heating element.

Moreover, since the temperature detecting element cannot obtain linear temperature resolution over the entire temperature range,
When the control temperature and the abnormal temperature are significantly different from each other, a detection error occurs or it is necessary to add a linearity correction circuit.

An object of the present invention is to provide an image forming apparatus which solves the above problems.

[0006]

In order to achieve the above object, the present invention provides a plurality of temperature detecting means for detecting the temperature of the electric heating element in an image forming apparatus for performing heat fixing by the electric heating element. Temperature control means for controlling the temperature of the electric heating element to a predetermined temperature based on the detection results of the plurality of temperature detecting means, and abnormal temperature processing for the electric heating element based on the detection results of the plurality of temperature detecting means And an abnormal temperature processing means for performing.

[0007]

According to the present invention, the safety of the apparatus can be improved by controlling the temperature with the plurality of temperature detecting elements and detecting the abnormal temperature with the plurality of temperature detecting elements.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIGS. 1, 2, 3 and 4 show a first embodiment of the present invention. FIG. 1 is a block diagram showing an electrical configuration of the embodiment, and FIG. 2 is an FTA showing a failure mode.
(Failure Tree Analysis). FIG. 3 is a diagram showing a change in resistance value with respect to the temperature of the temperature detecting element, and FIG. 4 is an electric circuit in the case of implementing FIG.

In this embodiment, the case where two temperature detecting elements are used is shown.

In FIG. 1, 201 is an electric heating element for performing heat fixing, 202 is a first temperature detecting element, 207 is a second temperature detecting element, 203 is a temperature control circuit, 204 is an abnormal temperature processing means and 205. Is a switch circuit, and 206 is an electric heating element driver.

From the temperatures detected by the two temperature detecting elements 202 and 207, the temperature control circuit 203 is the electric heating element 2.
The electric heating element 201 is controlled by the electric heating element driver 206 so that 01 becomes a predetermined temperature. Also, 20
The abnormal temperature processing circuit 204 constantly detects whether the temperatures detected by the two temperature detecting elements 2, 207 are abnormal temperatures, and controls the switch circuit 205. If an abnormal temperature is detected, the switch 205 is turned off. At the same time, the temperature control circuit 203 also detects an abnormality,
The electric heating element driver 6 is turned off.

FIG. 4 is a more specific version of the electric circuit block diagram of FIG.

In FIG. 4, 501 is an electric heating element and 502 is a first
Is a temperature thermistor, a second thermistor is the same, a reference numeral 503 is a temperature control circuit, a reference numeral 504 is an abnormal temperature detection processing circuit, a reference numeral 505 is a relay which is a switch circuit, and a reference numeral 506 is an electric heating element driver.

The abnormal temperature processing circuit 504 is provided with two comparators C1 and C2 having an open collector output, each of which has two comparators.
The outputs of the two thermistors 502 and 507 are set to the reference value (Vre
(based on f) for constant monitoring, and when an abnormal temperature is detected, the transistor Tr1 is turned off to turn off the relay 505 which is a switch circuit. R
1 to R9 are resistors.

The temperature control circuit 503 comprises a CPU, a port P0 is an input analog port used for detecting the second thermistor voltage, a port P1 is an input analog port used for detecting the first thermistor voltage, and a port P2 is an electric heating element. Is an output port for outputting a drive signal for driving the.

FIG. 3 shows the temperature-resistance characteristics of the thermistor used in FIG. 401 is the characteristic of the thermistor as the first temperature detecting element, 402 is the characteristic of the thermistor as the second temperature detecting element, the horizontal axis 404 is the temperature, and the vertical axis 403 is the resistance value. In this way, the first thermistor and the second thermistor are different in the range of high detection temperature resolution, and when performing temperature control, the priority of the first thermistor is increased to increase the resolution of the low temperature range. When controlling the abnormal temperature range, the resolution of the high temperature range can be increased by increasing the priority of the second thermistor, and thus the required temperature range can be entirely covered.

FIG. 2 is an FTA for analyzing the cause of failure.
(Failure Tree Analysis). 301 is the case where the control of the electric heating element is disabled, the temperature continues to rise, and the worst case is ignition and smoking.

The causes leading to 301 may be: the switch circuit of 302 does not operate normally, and the drive of the electric heating element of 308 does not stop.

The reason why the switch of 302 does not operate normally is as follows: When the abnormal temperature processing circuit of 303 fails (open due to solder deterioration, element deterioration, short circuit due to inclusion of foreign matter, etc.) If the seizure or the switch circuit fails, or if the temperature detection element of 305 fails (degradation of the temperature detection element, connector failure, mounting failure, open due to solder deterioration, short circuit due to inclusion of foreign matter, etc.).

The reasons why the drive of the electric heating element of 308 does not stop are as follows: When the temperature control circuit of 309 fails (open due to solder deterioration, element deterioration, short circuit due to inclusion of foreign matter, C
PU or runaway of PU), or failure of drive circuit of electric heating element 310 (open due to solder deterioration, element deterioration, short circuit due to inclusion of foreign matter, etc.), or temperature detection element 311 fails (temperature detection element) Deterioration, connector failure, mounting failure, open due to solder deterioration, short circuit due to foreign matter, etc.).

Since the temperature detecting element installed in contact with the electric heating element used for heating and fixing is used in a place where the temperature cycle from high temperature to low temperature is severe, the failure rate of the temperature detecting element is caused by mounting. At present, it is extremely high compared to the failure rates of other parts including those.

Therefore, according to the configuration of FIG.
At 06, the first temperature detecting element has failed, and 307,3
Only when the second temperature detecting element fails at 13
The reliability of the temperature detecting element is dramatically improved because the temperature detecting element failure of 1,305 is configured.

(Other Embodiments) FIGS. 5 and 6 show a second embodiment of the present invention.
FIG.

In the first embodiment, the case where two temperature detecting elements having different temperature-resistance characteristics are used as shown in FIG. 3 is shown, but in the second embodiment, as shown in FIG. The case where temperature detection elements having different thermal response speeds are used is shown. Second
In the second embodiment, the characteristics of the temperature detecting element are different from those in the first embodiment, but the other electrical configurations are the same.

In FIG. 5, reference numeral 601 denotes an electric heating element, 60
2 is a first temperature detecting element for temperature control, 603 is a second temperature detecting element provided for abnormal temperature processing means, 6
Reference numeral 04 is a recording material on which heat fixing is performed, and reference numerals 605 and 606 are areas showing the passage range of the recording material.

One of the temperature detecting elements 602 and 603 is installed in the pass area of the recording material so as to have a structure suitable for controlling the temperature of the print material, and the other one other than the pass area of the recording material. The temperature of the hottest part can be detected by installing the device in a position suitable for detecting an abnormal temperature.

Further, as shown in FIG. 6, the temperature detecting element 6
02 and 603 have different thermal response speeds 703 and 703, respectively.
704, the temperature detecting element 602 installed in the pass area of the recording material has a high thermal response speed, and the temperature detecting element 60 installed in the non-pass area of the recording material.
For element 3, an inexpensive element having a slow thermal response speed was used.

In the second embodiment, two temperature detecting elements are installed at different places, and one of the two temperature detecting elements is used as an electric heating element by using a relatively expensive temperature detecting element having a high thermal response speed. By increasing the priority of the temperature control of (1) and the other of the abnormal temperature processing by using a relatively inexpensive temperature detecting element, the safety of the device can be improved at low cost.

[0030]

As described above, according to the present invention,
By providing a plurality of temperature detection elements, controlling the temperature by the plurality of temperature detection elements, and detecting an abnormal temperature by the plurality of temperature detection elements, the safety of the device can be dramatically improved. .

[Brief description of drawings]

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

FIG. 2 is a diagram showing a failure mode of the present invention.

FIG. 3 is a diagram showing temperature characteristics of a temperature detection element in the first embodiment.

FIG. 4 is an electric circuit diagram of the present invention.

FIG. 5 is a diagram showing an installation location of a temperature detection element in the second embodiment.

FIG. 6 is a diagram showing temperature characteristics of a temperature detection element in the second embodiment.

FIG. 7 is a block diagram showing a conventional configuration.

[Explanation of symbols]

101, 201, 301, 501, 601 Electric heating element 102, 202, 207, 502, 507 Temperature detection element 103, 203, 503 Temperature control circuit 104, 207, 504 Abnormal temperature processing circuit 401, 402 Temperature-resistance value characteristic 703 , 704 Thermal response speed characteristics

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G05D 23/19 C 9132-3H

Claims (2)

[Claims] 1. In an image forming apparatus for performing heat fixing by an electric heating element, a plurality of temperature detecting means for detecting a temperature of the electric heating element, and the electric heating element based on detection results of the plurality of temperature detecting means. An image characterized by comprising: temperature control means for controlling the temperature of a predetermined temperature to a predetermined temperature; and abnormal temperature processing means for performing an abnormal temperature processing on the electric heating element based on the detection results of the plurality of temperature detection means. Forming equipment. 2. The image forming apparatus according to claim 1, wherein the plurality of temperature detecting units are set to have at least two different temperature characteristics or are installed at locations having different temperature distributions.