JP2560338B2 - Abnormal lighting control device for heater - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device such as a copying machine.
The present invention relates to an abnormal lighting control device for a heater that is a heating source.

2. Description of the Related Art Conventionally, a so-called heat roll method has been widely used for fixing devices of electrophotographic printers and copying machines. In this method, a heater is built in at least one roller as a heating source, and a copy sheet is passed between these rollers to thermally fix the toner image.

By the way, the heater is controlled to turn on / off in association with the copy operation, but there is an optimum temperature for fixing,
Turning on / off of the heater is automatically controlled so as to maintain this temperature (or temperature range). In most cases, automatic control uses a thermistor as a temperature sensing element, detects the surface temperature of the heat roller with this thermistor, and uses a resistor bridge circuit including the thermistor and a microcomputer that processes the output signal of the comparator or thermistor. (JP-A-53-65743, JP-A-60-115977).

However, if the thermistor fails or the program that processes the thermistor output signal of the microcomputer does not work as designed for some reason (including program runaway due to noise or lightning surge), the heater may turn on abnormally. There is. When this abnormal lighting occurs, the heat roller is excessively heated, which may damage the heat roller, damage the members around the heat roller, or ignite the copy paper, causing a fire. However, a thermal breaker such as a thermal fuse is usually provided in the vicinity of the surface of the heat roller, and safety measures are taken to cut off the power supply to the heater when the temperature of the heat roller exceeds a predetermined temperature. However, in general, the responsiveness of the thermal breaker is low, and the operating temperature is set in consideration of a certain margin from the upper limit of the temperature change in the normal operation of the heat roller, so at the time the thermal breaker actually operates,
Even if the ignition can be stopped, there is a problem that the heat roller is already damaged.

Therefore, the abnormal overheating of the heat roller is prevented before the thermal breaker is activated. That is, means for preventing abnormal lighting of the heater has been considered. However,
All of the conventional ones also use the thermistor that detects the surface temperature of the heat roller for abnormality detection and operate normally (in the case of program control, the relevant program also).
Therefore, it was completely useless in the case where the thermistor fails or the control program does not operate due to runaway.

An object of the present invention is to provide a heater abnormal lighting control device capable of effectively and beforehand preventing abnormal lighting of a plurality of heaters regardless of the presence or absence of a failure of a thermistor or the like that detects the surface temperature of a heat roller. To do.

SUMMARY OF THE INVENTION In an abnormality detection control device, the present invention provides a heater, power supply means for supplying power to the heater based on an input signal, detection means for directly detecting a lighting state of the heater, and power. Immediately after the switch is turned on, in order to detect the abnormal lighting of the heater, an electric power is supplied to the heater for a predetermined time and then an abnormality detection control signal is output to the electric power supply means so as to stop for a predetermined time. The electric power supply to the heater is stopped by the signal output means and the abnormality detection control signal output from the signal output means, but the heater is turned on by the detection means. When it is detected, a prohibition unit that prohibits the operation of the power supply unit is provided.

The detection means for directly detecting the lighting state of the heater,
Those that detect the supply of electrical energy to the heater, such as galvanometers, magnetic sensors that detect changes in the magnetic field, and those that directly receive visible light and heat rays from the filament that is generating heat due to the supply of electrical energy, such as light receiving elements in general Or infrared sensor, thermistor, positive temperature coefficient thermistor, pyroelectric sensor.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples shown in the accompanying drawings.

FIG. 1 is an external view of a copying machine according to an embodiment.
(2) is a main switch as a power switch. When this switch is turned on, AC100V is supplied to the copying machine (1).
(3) is a display for displaying the number of copies. When a trouble occurs in the copying machine, the trouble code is displayed on this display (3). After the May switch (2) is turned on, the ON operation of the print key (4) cannot be accepted until the heat fixing device reaches a predetermined temperature. During this time, if there is an abnormality in the heat fixing device, the trouble code is displayed on the display section (3). If there is no abnormality, the print enable display of the print key (4) lights up after a predetermined time, and the copy operation starts when the print key (4) is pressed.

FIG. 2 shows a central sectional view of the copying machine (1). The image of the original placed on the original glass (5) is scanned by the scanning optical system (6) and is exposed on the photosensitive drum (7) to form an electrostatic latent image. After the electrostatic latent image is converted into a toner image by the developing device (8), the copy paper sent from the paper cassettes (9) and (10) detachably attached to the copying machine (1), The toner image is transferred by a transfer charger (11), and the toner image is transferred to a thermal fixing device (13) by a conveyor belt (12) to be fixed. A known electrophotographic system is used for the configuration and operation of the copying machine (1) for image formation, and the details are omitted.

FIG. 3 shows the details of the heat fixing device (13). The cylindrical heat roller (14) coated with a non-adhesive material on the surface of which the toner does not adhere has a heat lamp (15) fixed inside.
Heated from inside by (15 '). Heat lamp (1
5) is for main heating (for example, 900W), (15 ') is for sub-heater (for example, 400W), and sub-heater (1
5 ') is provided to shorten the temperature rise time of the heat roller (14) when the power is turned on or to make the surface temperature of the heat roller (14) uniform. The thermistor (16), which is in contact with or close to the surface of the heat roller (14) supported by an appropriate bracket, detects the surface temperature of the heat roller (14), and if it reaches a predetermined temperature, it is controlled by the control means described later. Rotation of the heat roller (14) and the heating roller (17) is allowed. Copy paper sent between rollers (18)
Toner image (18t) by rotating heat roller (14)
Is fixed and sent out.

The thermal fuse (19) arranged close to the surface of the heat roller (14) operates when the surface temperature of the heat roller (14) reaches or exceeds a predetermined temperature to prevent abnormal heating of the heat roller (14). . That is, the thermal fuse (19) is connected in series with the energization line (20) of the heat lamps (15), (15 ') to operate, and the heat lamp (15),
Turn off the power to (15 ').

(21) is an infrared sensor. Infrared sensor (21)
Is the filament (15) of the heat lamps (15), (15 ')
Infrared rays emitted from f) and (15'f) are detected. In addition,
The infrared sensor (21) may be provided inside the tubular shape of the heat roller (14) by a suitable bracket. As will be described later, the infrared sensor (21) is used to detect abnormal lighting of the heat lamp (15), but for the same purpose, the infrared sensor (21) is replaced by the energization line (20). A magnetic sensor (22) provided in close proximity may be used. The magnetic sensor (22) detects a magnetic field based on a current change in the energization line (20).

FIG. 4 shows the configuration of the control circuit of the heat lamps (15) and (15 ') using the infrared sensor (21) or the magnetic sensor (22).

When the main switch (2) in FIG. 1 is turned on, its contact (2p) is turned on. This turns on the relay (31)
Then, the contact (31a) in parallel with the contact (2p) is turned on to self-hold and the two contacts (31) of the energizing line (20)
By turning on b) and (31c), the heat lamps (15) and (15 ') can be energized.

The microcomputer (32) (hereinafter, referred to as MPU), which has been in a stable state for a while after the power is turned on, outputs a high level signal (hereinafter, high level as a heat lamp lighting signal from the output boats (P ₁ ) and (P ₀ ). Output as "H").
This “H” signal is passed through drivers (33) and (33 ′) to solid state relays (34) and (35) such as dryac.
(Hereinafter, referred to as SSR ₁ and SSR ₂ ), and the SSR ₁ (34) or SSR ₂ (35) becomes conductive, so that the heat lamp (15)
Or (15 ') is energized.

While the heat roller (14) (see Fig. 3) is being heated, the thermistor (16) detects its surface temperature and outputs a voltage signal corresponding to the temperature to the A / D conversion input port (P) of the MPU (32). Output to ₂ ). The MPU (32) converts the analog voltage signal into digital data based on the voltage Vcc of the reference voltage Vref port (P ₃ ). This digital data is compared with preset data corresponding to the surface temperature of the heat roller, and if the surface temperature rises, the MPU (32) outputs low level signals (P ₁ ) and (P ₀ ) to the output ports (P ₁ ) and (P ₀ ). Below, low level is described as "L") and SSR (34) and (35) are turned off.
Then turn off the heat lamps (15) and (15 '). After this,
If the surface temperature of the heat roller (14) becomes low, MPU (3
2) outputs "H" to the output port (P ₁ ) to control the lighting of the heat lamp (15). The above is the case where the control system including the heat lamps (15) and (15 ') operates normally in the conventional temperature control.

The abnormal lighting of the heat lamp (15) or (15 ') is checked in the present embodiment in the initial stage after the main switch (2) is turned on. Basically, first, the heat lamp lighting output port (P ₁ ) outputs an intermittent signal of "H", "L", "H" ..., and whether the heat lamp (15) blinks following this. Be examined. It is impossible for the thermistor (16) to check in a short time whether or not it blinks due to the heat capacity of the heat roller (14). There is also the possibility of failure. Therefore, with the infrared sensor (21), the heat lamp (1
5) Directly detect the infrared rays emitted from and check the blinking state. Then, output from the output port (P ₀ ) as above,
Check the heat lamp (15 ') for blinking.

The circuit (40) regards the heat lamp (15) or (15 ') as an abnormal lighting when the heat lamp (15) or (15') does not follow the lighting control and does not blink, and the heat lamp (15), (15 ') energization line (20). It is for shutting off. Infrared sensor (2
The bridge circuit (41) including 1) is connected to the comparator (42), and the output of the comparator (42) is flip-flop circuit (43).
Latch with. The latch output is integrated by the integrating circuit (44), and the integrated voltage is compared with a predetermined level voltage (V ₀ ) by the comparator (45).

FIG. 5 shows a specific timing chart of the circuit (40). In the case of normal lighting, the + input of the comparator (42) follows the “L”, “H”, “L”, and “H” of the heat lamp lighting control signal (P ₁ ) or (P ₀ ). "H", "L",
It becomes “H” and “L”. The signal time of the lighting control signal is determined in consideration of the response time of the sensor (21).
From this, the output of the comparator (42) is "H", "L",
Since it becomes "H" and "L", the output of the flip-flop (43) becomes "L", "H" and "L". The-input (integrated voltage) of the comparator (45) exceeds a predetermined comparison voltage (V ₀ ) if the output of the flip-flop (43) changes to "L", "H", "L". The output of the comparator (45) remains "H".

On the other hand, when the light “L” is given to the heat lamp but the lamp is abnormally lit as indicated by A, the input / output of the comparator (42) and the output of the flip-flop (43) are performed. Has the movement indicated by the broken line. Comparator (4
The-input of 5) exceeds the comparison voltage (V ₀ ), at which point the output of the comparator (45) falls to "L".

As shown in FIG. 4, the falling signal from “H” to “L” is transmitted to the relay circuit (31) via the driver (46) and turns off the relay circuit (31). When the relay circuit (31) is turned off, the contacts (31b) and (31c) of the relay circuit (31) are opened, and the power lines to the heat lamps (15) and (15 ') are cut off. Thus, it is checked whether the heat lamps (15), (15 ') follow the lighting control signals of "H", "L", "H" ... If it is turned on, it is abnormally turned on and the energizing line (20) immediately
The heat roller (1
4) Abnormal overheating and other damage to equipment can be prevented. In addition, the falling signal of the comparator (45) is
The trouble code may be input to the input port (P ₄ ) of the MPU (32) and displayed as a trouble code on the display unit (3) (FIG. 1). The initial check when the main switch is turned on is performed regardless of the overheated state of the heat roller (14). Therefore, in the prior art, after detecting an abnormality, there is a possibility that the heat roller may be damaged or fired by repeatedly turning on the main switch without repairing this failure mode. Never.

Further, in the embodiment, since the control means for preventing the heater abnormal lighting is constituted by the hardware circuit (40) which does not depend on a program, various standards (for example, TF and CS) are used.
A) has the advantage that the fixing device itself is certified as safe. However, when such restrictions on the standard are not taken into consideration, for example, as shown in FIG. 4, the output of the sensor (21) is input to the input port (P ₅ ) of the MPU (32) and this input data is input. Abnormal lighting may be prevented by processing.

Also, heat lamps (15), (15 '), SSR ₁ (34), SSR ₂
When the relay (31) is turned off when the (35), driver (33) and (33 ') operate normally without any failure, this is the heat output from the port (P ₁ ) or (P ₀ ). This means that the lamp lighting signal remains "H", and this determines that the MPU (32) is not functioning normally for some reason. For example, there is a case where a program is disturbed by noise, or in some cases, the program is out of control. The circuit (40) including the sensor (21) detects this and prevents the MPU from malfunctioning in advance.

Furthermore, each input data at the input port (P ₄ ) or (P ₅ ) of the MPU (32) and the voltage signal input port (P ₂ ) of the thermistor (16) is output to the output port (P ₁ ) or (P ₀ ). By performing a systematic check in association with the heat lamp lighting signal in (1), it is possible to determine the quality of the main element of the automatic control system for lighting the heater lamp. Defective heat lamps (15), (15 ') including disconnection,
Defective thermistor (16) including failure, SSR ₁ (34) or SSR
₂ (35) short, open, etc. In particular, according to the present embodiment, the defects of the heaters (15) and (15 ') and the defects of the thermistor (16) can be distinguished. In other words, there is no any abnormality in the initial check after the main switch is turned on (input port (P ₄₎ is kept at "H"), but also over time A /
If there is no significant signal at the D input port (P ₂ ), it can be determined that the thermistor (16) has failed. Conventionally, even if the heater is defective, it is often determined that the thermistor is defective, and it takes much time to repair it, but this can be improved.

Furthermore, the heat lamp (15) in this embodiment,
If (15 ') is replaced with the exposure lamp (L) in the scanning optical system (6) of FIG. 2, it is pointed out that the present invention can be applied to abnormal lighting of the exposure lamp. An automatic document feeder (ADF) is installed in the copying machine (1) as shown in FIG.
This is because when the is installed, the lighting of the exposure lamp may not be visible from the outside.

EFFECTS OF THE INVENTION As is apparent from the above description, according to the present invention, the heater is turned on by the detection means for directly detecting the lighting state of the heater and the signal output means for outputting the abnormality detection control signal immediately after the power switch is turned on. When an abnormality is detected and the abnormality is detected, the prohibiting means prohibits the supply of electric power to the heater. Therefore, it is possible to prevent abnormal lighting quickly and effectively and in advance prevent damage caused by abnormal lighting.

[Brief description of drawings]

FIG. 1 is an external view of a copying machine according to an embodiment of the present invention, and FIG.
FIG. 4 is a schematic central sectional view of the same, FIG. 3 is a perspective view of a main part of a heat fixing device, FIG. 4 is a circuit diagram of an embodiment of the present invention, and FIG. 5 is a timing chart for explaining the operation of the circuit (40) Is. 1 ... Copier, 2 ... Main switch, 13 ... Thermal fixing device, 14 ... Heat roller, 15, 15 '... Heat lamp, 1
6 …… thermistor, 21 …… infrared sensor, 22 …… magnetic sensor, 32 …… microcomputer or microprocessor (MPU), 20 …… energization line.

Claims (1)

(57) [Claims] 1. A heater, power supply means for supplying power to the heater based on an input signal, detection means for directly detecting a lighting state of the heater, and immediately after turning on a power switch of the heater. In order to detect abnormal lighting, power supply to the heater is performed for a predetermined time, and then a signal output unit that outputs an abnormality detection control signal to the power supply unit so as to stop for a predetermined time; When the detection means detects that the heater is turned on by the abnormality detection control signal output from the output means, even though the electric power supply to the heater is stopped, An abnormal lighting control device comprising: a prohibiting unit that prohibits the operation of the power supply unit.