JPH02141784A - Fixing temperature control device for image forming apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fixing temperature control device for an image forming apparatus, and particularly to a fixing temperature control device that prevents a completely disconnected state when a contact failure occurs in a fixing thermistor that detects the fixing temperature. However, it is related to humidity control when a thermistor resistance value increases over time.

(Prior Art) In an image forming apparatus that has a fixing unit that uses a fixing heater to heat and pressurize toner transferred to a recording paper at an appropriate temperature, the fixing temperature control system is designed to detect warming up (fixing roller rise of set temperature), maintenance of fixing temperature (ON/OF of fixing heater, F control),
Detection of abnormally high or low temperatures.

It also detects disconnections, short circuits, etc. of the fixing thermistor.

Furthermore, even if the fixing temperature control system does not operate due to some reason and the fixing heater continues to be in the ON state, there is a protection means that turns the fixing heater OFF[' by a temperature fuse before firing.

The temperature control of the fixing heater described above, except for the final OFF operation using the temperature fuse, is entirely dependent on a detection signal based on a change in the resistance value of the fixing thermistor.

(Problems to be Solved by the Invention) However, the fusing thermistor is a very precision component and has weak mechanical strength.For this reason, failures may occur in the image forming apparatus, such as spot defects or when removing jammed fusing paper. , there was a possibility that the fixing thermistor could be damaged, resulting in disconnection or poor contact.

If the wire is broken, the fuser heater will be turned off immediately upon detection of the wire breakage.
However, if the resistance value temporarily increases due to poor contact.

Since the temperature control system determines that a low temperature has been detected, the fusing heater is left in the ON state, and after a predetermined period of time has elapsed, the fusing heater is turned OFF and a low temperature detection error is displayed. The heating roller (heating roller) continues to heat up, and if there is jammed paper or the like left in the fixing unit, it will emit smoke. In addition, the synthetic resin gears and the like in the fixing unit sometimes become deformed.

In this case, lower the operating temperature of the temperature fuse.

Although this can be dealt with, it cannot be easily lowered because it is related to the operation of other parts.

In addition, the detection output of the fixing thermistor is A/D converted and the CP
There is also a means of inputting it into U and monitoring the output of the fixing thermistor at regular intervals. This not only complicates the circuit and increases the workload of the CPU, but also causes considerable loss, as well as poor contact with the fixing thermistor.

Since the frequency of occurrence of abnormalities was low, it could not be said to be a very economical and effective means.

In the present invention, when a contact failure of the fixing thermistor occurs,
The purpose is to detect this and prevent deformation of the jammed paper smoke 1 synthetic resin gear etc. in the fixing unit.

(Structure and Function) In order to achieve the above object, the present invention uses a signal from a temperature detecting fixing thermistor of a fixing heater to fuse the toner transferred to the recording paper with heat and pressure at an appropriate humidity.
a temperature control unit that controls the ON10FF operation of the fixing heater; and a sequence control unit that performs sequence control of the entire image forming apparatus and forces the fixing heater that has detected an abnormality from the information from the temperature control unit to perform a forced OFF operation. The image forming apparatus is characterized in that a spare fixing thermistor is further provided, and when the output difference with the fixing thermistor exceeds a set value, the fixing heater is forcibly turned off.

The present invention provides a difference voltage 6. between the detection voltage e1 of the fixing thermistor and the detection voltage e2 of the preliminary thermistor. (=6°-f!,)
is calculated and compared with the set value, and when the set value is exceeded, an abnormal signal is generated for the fuser thermistor and the fuser heater is turned off.
F operation causes jammed paper to emit smoke.

This prevents deformation of the synthetic resin gear.

(Example) Before explaining the present invention in detail, the relationship between the fixing unit of a laser printer in which the present invention is implemented will be described.

Figure 2 shows a schematic configuration diagram of a small laser printer, and its operation is explained by the paper feeding device! Recording paper 2 fed in the direction of arrow A from l is timed by a pair of registration rollers 3 and conveyed to a latent image carrier consisting of a drum-shaped photoreceptor 4. The photoreceptor 4 is rotationally driven in one counterclockwise direction, the surface of which is charged by the charger 5, and irradiated with laser light from the laser optical system 6 to form an electrostatic latent image on the photoreceptor.

When this latent image passes through the developing device 7, it is made visible by toner. This visible image is transferred to the recording paper 2 that is conveyed to the photoreceptor 4.
The visible image is transferred onto the recording paper by a transfer charger 8 and fixed by a fixing unit 9. The recording paper 2 leaving the fixing unit 9 is then discharged to the paper discharge section 11 in the direction of arrow B.

On the other hand, the cleaning blade 1
The residual toner is removed by a cleaning device having 2. The toner removed from the photoreceptor is collected in a toner collection tank 13 and stored there.

Note that 10 is the printer body, 14 is the controller, and 15 is the printer body.
is the printer control unit.

The fixing unit 9 is composed of a fixing heating roller 9A having a built-in fixing heater 9H, and a fixing pressure roller 9B that presses the recording paper 2 against the fixing heating port 9A. A fixing thermistor 9 T detects the surface temperature of the fixing heating roller.
H (FIG. 3) is disposed near the surface of the fixing heating roller (approximately at the center in the longitudinal axis direction of the roller). Also, if the temperature control system goes down, the fixing heater 9H will be forcibly turned off.
The temperature fuse 9F (Fig. 3) that causes the fusing heater 9
Connected to H.

FIG. 3 is an example of a block diagram showing the configuration of the fixing temperature control system. In FIG. 0, L5A is a sequence control section;
is a temperature control section, which is included in the printer control section 15 in FIG. 16 is solid state relay (SSR)
Then, the fixing heater 9H is cut off by a control signal (heater OFT;') from the sequence control section L5A.

The fixing thermistor 9TH detects the surface humidity of the fixing heater 9A heated by the fixing heater 9H, inputs the detection signal (resistance value change) to the temperature control section 15B, and the temperature control section sets a predetermined fixing temperature. 5S to maintain
R16 is operated to control the ON/OFF operation of the fixing heater 9H.

In the state of the fixing thermistor 97H, the temperature control section 15B:
It also detects temperature abnormalities and fixing thermistor abnormalities, and provides various information (FUS RDY, I(TERR).

HTEMP) to the sequence control unit 15A, and the sequence control unit sends a fixing heater OFF signal to the temperature control unit 15B depending on each abnormal state, and forcibly turns the fixing heater OFF.
F control.

FIG. 4 shows a specific circuit diagram of the fixing temperature control section 15B in FIG.
/OFF block, (2) is the forced OFF of the fixing heater 9H.
F block (3) is an abnormality detection block of the fixing unit 9.

To describe the operation of the fixing heater ON/OFF block (1), a change in the surface temperature of the heating roller 9A of the fixing heater 9H is taken as a change in the resistance value of the fixing thermistor 9T), and this change in potential is reflected in the comparator 17 ( +) terminal and is compared with the set temperature potential set at the (-) terminal via the variable resistor 18.If the potential on the fixing thermistor QTH side is high, the 1-transistor I
Current flows through the bases of 9 and 20 and they operate simultaneously. Due to the collector current of this operating transistor 20, 5SR1
6 is turned on to turn on the fixing heater 9H. Further, the collector current of the operating transistor 19 outputs fixing reload (H) to the sequence control section 15A.

Then, by lighting the fixing heater 9H, the fixing thermistor 9
When the resistance value of TI() decreases and the potential (+) on the thermistor side of the comparator 17 gradually decreases and becomes lower than the set potential (-), the comparator 17 causes both transistors 19.
The base current to 20 is cut off and transistor 20 becomes 0
FFL/, 5SR16 is also 0FFL, fixing heater 9H is O
Becomes FF. Further, the transistor 19 is also 0FFL, and the fixing reload is turned off.

Then, when the temperature drops due to the fixing heater 9H being turned off,
The drive circuit for the fixing heater operates and lights up again. Repeat this step by step.

As shown in FIG. 3, the information sent from the transistor 19 to the sequence control unit 15A is that while the fixing heater 9H is in the ON state, the FtJS -Rr)Y (LOW) output is
During the OFF state, FtJS-RDY (HIGH) output is output. This FtJS-RDY is used to detect the start-up after the cover is opened when the power is turned on.

Next, the operation of the fixing heater forced OFF block (2) is described. When the sequence control unit 15A sends a fixing heater OFF signal based on an abnormality signal to be described later,
The transistor 21 operates and turns the fixing heater ON/OFF.
The transistor 20 of block (1) is operated, and its collector current operates the 5SR 16 to forcibly turn off the fixing heater.

Next, the operation of the abnormality detection block (3) of the fixing unit will be described. This abnormal state is as follows (a), (b), (c)
There are cases where

(rl) Disconnection of fixing thermistor 97H (b) Detection of low temperature or high humidity of fixing thermistor 9TH (C) Low temperature detection of fixing thermistor 9TH Comparator 22A is used to detect the above-mentioned abnormal state.

22B and 22G are provided, and the (-) terminal of 22A, 22B,
Output potentials indicating abnormal states (a), (b), and (c) of the fixing thermistor 9TH are input to the (+) terminal of the fixing thermistor 9TH. On the - side, a predetermined set potential is applied to the (+) terminal of 22A and the (-) terminals of 228 and 22C via resistors 23A, 23B, and 23G.

If the fixing thermistor 9TH is disconnected (a), the converter 22C is set to ONL, and the information HTERR to the sequence control unit 15A is set to LOW. Also.

Fixing thermistor 9 T H seam or high temperature detection (
In case b), the comparator 22A is set to ONL, and the information TIT ERR is set to r and ow. Further, when the fixing thermistor 9TH detects a low temperature (C), the comparator 22B is set to ONL, and the information HTMP is set to LOW (fixing reload L).

In the present invention, the fixing unit abnormality detection block shown in FIG. 4(3) is constructed as in the embodiment circuit shown in FIG. 1(1). Further, FIG. 1(2) shows detection signals and control signals between the temperature control section 15B and the sequence control section 15A.

In FIG. 1(1), 9TH(]) corresponds to the conventional solid fixing thermistor 9TH, and a precise thermistor is used. 9TH (2) is a spare thermistor, and the above 9T
Although the accuracy is lower than H(1), a material with excellent mechanical strength is used. 24 is a comparator, and fixing thermistor 9
T (1) output voltage e and pre-fixing thermistor 9
T I (differential output voltage e of output voltage e2 of (2). (=
ex e2. ). 25 is also a comparator, and the reference voltage V□F ((+) terminal) is divided by resistors R, , R,
and the differential voltage el, and outputs an abnormal state of the fixing thermistor as an error signal (TIIERR). The reference voltage (VRRF) here is the differential voltage e. (If it is in a steady state, it will be near Ov) is outputted, this is the voltage to be detected.

To explain this operation, the comparator 24 compares the output voltage e□ of the fixing thermistor 9TH(1) with the output voltage e2 of the preliminary fixing thermistor 9TH(2).

Then, there is a differential voltage e between both sets of pressures ex+e and e. When there is no comparator 25, the comparator 25 does not operate. However, for some reason, the fixing thermistor 9TH(1) is abnormal (see (a) above).
, (b), (c)), a differential voltage e0 is output, and the comparator 25 compares it with the reference voltage
R) is generated. This signal is set to LOW and interrupts the sequence control unit 1.5A, and the sequence control unit generates an OFF signal for the fixing heater 9TI and turns the temperature control unit 1.
Output to 5T3. This temperature control unit 15B operates the transistor 21 of the fixing heater forced block (FIG. 4 (2)), and operates the 0N10FI? The transistor 20 of the block (FIG. 4(1)) is operated, and the fixing heater 9H is turned off by the 5SR16.

In other words, the fixing thermistor 97H(+) is disconnected (a).

Abnormal conditions such as short circuit or high temperature detection (b), low humidity detection (C), etc. are detected by the operation of comparators 22A, 22B, and 22G of the fixing unit abnormality detection block (3) as well as the detection output from the preliminary fixing thermistor 9 TII (2). This activates the comparators 24 and 25, allowing each abnormal state to be detected with higher precision than in the conventional temperature detection using only one fixing thermistor.

(Effects of the Invention) As explained above, the present invention uses both an accurate thermistor and a thermistor with excellent mechanical strength to detect 4λ degrees of the fixing heater, and prevents contact failure in the former thermistor resulting in complete disconnection. However, if there is a temporary increase in resistance, the latter thermistor detects this, which prevents jammed paper from smoking due to an abnormality in the fixing thermistor, or deformation of synthetic resin gears due to abnormally high temperatures. It can be prevented.

[Brief explanation of the drawing]

FIG. 1 shows a fixing temperature control circuit (1) according to an embodiment of the present invention.
) and the flow (2) of the fixing temperature control information of the sequence control section and the temperature control section, FIG. 2 is a schematic configuration diagram of a laser printer as an example of an image forming apparatus in which the present invention is implemented, and FIG. 3 2 is an example of a block diagram of the fixing temperature control system shown in FIG. 2, and FIG. 4 is a diagram showing a specific circuit example of the temperature control section 15B shown in FIG. 3. 9... Fixing unit, 9A... Fixing heating roller, 9B... Fixing pressure roller, 9H... Fixing heater, 9F... Temperature fuse, 15... Printer control unit, 15A... Sequence control section, 15B
...Temperature control section, 16...Solid state relay (SSR), 17.22A, 22J 22C, 2
4, 25... Comparator, 18... Variable resistor,
19゜20, 21... 1-transistor, 9TH
(1)...Precise fixing thermistor, 9 T I ((
2)...Fixed thermistor with excellent mechanical strength.

Claims (1)

[Claims] a temperature control unit that controls ON/OFF operation of the fixing heater based on a signal from a fixing thermistor for detecting the temperature of the fixing heater in order to heat and pressure fuse the toner transferred to the recording paper at an appropriate temperature; In an image forming apparatus having a sequence control section that performs sequence control of the entire forming apparatus and forcibly turns off the fixing heater that detects an abnormality based on information from the temperature control section, a spare fixing thermistor is further provided, A fixing temperature control device for an image forming apparatus, characterized in that the fixing heater is forcibly turned off when an output difference with a fixing thermistor exceeds a set value.