JPH04251775A - Image formation device - Google Patents

Abstract

PURPOSE:To prevent fuming or catching of fire from occurring to an image formation device by a method wherein the results of temperature detection in a heating means are stored, and passing of current to said heating means is controlled, based on the result of a comparison made between the stored results of the temperature detection and the results of temperature detection made after the lapse of a specified time. CONSTITUTION:An image formation device is equipped with a fixing heater as a heating means for printing paper, a fixing device composed of a thermistor that detects the temperature of said fixing heater, and TRIAC, a circuit controlled by the detected results of said thermistor for passing and cutting off of current to the aforementioned heater. The temperature of the fixing heater is detected immediately after input of ignition signal to the TRIAC and stored by employing an A/D converter 15, a latch 16, and a digital comparator 18. The value of the temperature stored by the above-mentioned processes is compared with the value of the temperature measured after the lapse of a specified time. When there is no rise in the temperature in said comparison, it means occurrence of abnormality and such state is stored in a flip-flop and the relay in the circuit for passing the current to the heater is cut off.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an image forming apparatus.
In particular, the present invention relates to an image forming apparatus having a safety circuit for preventing smoke and ignition.

0002

2. Description of the Related Art Image forming apparatuses that visualize images stored in memory by fixing toner on printing paper are typified by laser beam printers and copying machines. Since then, it has been widely used.

[0003] A printing operation in an image forming apparatus is completed by making toner visible on print paper through known electrophotographic techniques, that is, exposure, development, and transfer processes, and finally fixing the toner on print paper. In the process of fixing the toner to the print paper, a method using heat, a method using pressure, or a method using both heat and pressure is selected. If a thermal fixing method is selected, there is a risk of a fire accident because the printing paper, which can become an ignitable substance, is heated, so ensuring safety in this case is an extremely important technology.

FIG. 5 shows a control circuit for the fuser heater and a circuit for ensuring the safety (hereinafter referred to as a safety circuit). FIG. 5 shows a fixing heater 101, which is a heating means for printing paper, and a thermistor 10, which detects the temperature of the fixing heater.
The temperature detected by the fuser 103 and the thermistor consisting of 2 components is input as a voltage value, and based on this result, instructions are given to open and close the triac 105, which is the heater energization control circuit.In addition, if any abnormality occurs, the heater energization is immediately shut off. A CPU 104 that controls a relay 106 that is a circuit, a current detection circuit that includes a current transformer 107 that detects the heater energization current, an overheating state detection circuit that includes a comparator 108 that detects the overheating state of the heater, and the CPU outputs an energization instruction. It is composed of a flip-flop 109 that stores and holds information that a current is detected or that an overheating state of the heater is detected even though the current is not being applied.

[0005] The circuits of each part will be explained in detail below.

[0006] 103 is a fixing device, and the electrical parts are AC
It consists of a heater 101 inserted into the primary circuit and a thermistor 102 that monitors the temperature of the heater. A voltage dividing circuit with a fixed resistor 110 converts the resistance value of the thermistor into a voltage value, which is input to the A/D conversion circuit. In the figure, a CPU with a built-in A/D conversion circuit is used;
The D conversion circuit may be externally attached.

[0007] The CPU knows the temperature of the heater using a thermistor, and when the temperature is high, it stops firing the triac 105 and opens the AC primary circuit, and when the temperature is low, it starts firing the triac and opens the AC primary circuit. Close the circuit. This controls the heater of the fixing device to maintain a constant temperature.

[0008] The CPU outputs a triac firing signal from the port 2 output. HI the triac firing signal
When set to GH or LOW level signal, C
If the PU goes out of control, the output may be fixed in a direction that continues to heat the fixing heater. In order to avoid this problem, the firing signal of the triac is made into a pulse.

[0009] Furthermore, an open collector output from a transistor 111 is provided from the CPU board on which the CPU is mounted. By using open collector output, CPU
This is a measure against disconnection of the harness between the board and the safety circuit. In other words, there is a pull-up resistor 11 on the safety circuit side.
2, when the harness is disconnected, it is connected to the power supply line with low impedance, so pulse-like noise is not superimposed on the signal line.

113 is a DC cut capacitor. This makes it possible to cut off the signal that has reached the DC level when the CPU runs out of control or when the harness is disconnected.

[0011] The next stage resistor 114, diode 115,
The capacitor 116 is a rectifier/smoothing circuit, and is used to obtain the envelope of the pulse waveform.

The transistor 117 drives the LED of the phototriac coupler 118 and discharges the charge of the capacitor 128 for measuring abnormal energization.

When the built-in LED of the phototriac coupler lights up, the triac 105 fires and the AC primary circuit closes. By using a phototriac coupler with a built-in zero-cross comparator, it is possible to suppress noise generation when the triac is fired.

Reference numeral 107 is a current transformer, and a current value proportional to the current of the AC primary circuit is obtained in the secondary winding. Next, the resistor 119 converts the secondary winding current value into a current/voltage.

Resistors 120, 121, 122, 123 and comparators 124, 125 constitute a window comparator. The comparator has an open collector output, and when the inverted input voltage exceeds the non-inverted input voltage, current is sucked from the output terminal. The two comparators are wired-ORed and pulled low by resistor 126.
OW level is created. The window width is determined by the ratio of the four resistors, and when the input voltage of the comparator is above or below the window width, the output becomes LOW level.

Transistor 127 is connected to capacitor 128
When the transistor is OFF, the capacitor is charged via the resistors 129 and 130. When the transistor is ON, the capacitor is discharged through the resistor 130 and the transistor.

When charging of the capacitor progresses and the potential across the capacitor exceeds the sum of the base-emitter voltage of the transistor 131 and the Zener voltage of the Zener diode 132, the transistor 131 is turned on.

Further, the overheating state of the fixing heater is detected by the overheating state detection comparator 108, and the transistor 133 is turned off.

The transistor 133 is connected to the capacitor 134.
When the transistor is OFF, the capacitor is charged via the resistors 135 and 136. When the transistor is ON, the capacitor is discharged through the resistor 136 and the transistor.

When the charging of the capacitor progresses and the potential across the capacitor exceeds the sum of the base-emitter voltage of the transistor 137 and the Zener voltage of the Zener diode 138, the transistor 137 is turned on.

The reference time for checking the duration of the overheating state is based on the capacitance value of the capacitor 134 and the resistors 135 and 136.
The resistance value of the zener diode 138 is determined by the zener voltage value of the zener diode 138. By optimizing these values, it is possible to build a system that ensures safety while improving noise resistance.

Flip-flop 109 is used only for setting, and transistor 131 is ON or transistor 1 is ON.
37 is turned ON, the memory is retained.

[0023] In other words, either the energization state continues for a certain period of time or more even though the CPU has not outputted an energization instruction to the fixing heater, or the fusing heater remains overheated for a certain period of time or more. Due to this factor, the flip-flop stores that it is in an abnormal state.

106 is a relay, and the transistor 13
When 9 is ON and transistor 140 is ON, current flows through the relay winding and the relay contacts close.

By setting the port 1 output of the CPU 104 to HIGH, the transistor 141 is turned on, and thereby the transistor 140 is turned on. After the CPU detects that some kind of failure has occurred, the CPU sets the port 1 output to LO.
By setting it to W, the fixing heater can be immediately shut off. The reason why the port 1 output is enabled HIGH is that when the port 1 output harness is disconnected, the resistor inserted in parallel between the base and emitter of the transistor 141 opens the relay contact, which is a highly safe method. This is to calm down the direction.

When the flip-flop is set, transistor 139 is turned off and the relay contact is opened.

[0027] In the above conventional example, the overheating state is memorized and retained, but the relay may be cut off every time an overheating state is detected, and the relay may be restored when the overheating state is eliminated.

[0028] In either form, the power supply to the heater is cut off when the overheating state of the fixing heater continues for a certain period of time or more, so even if the overheating state detection signal line is extended for a long time, malfunctions due to noise may occur. can be prevented.

[0029]

[Problem to be Solved by the Invention] However, in the conventional example described above, temperature adjustment of the heater, overheating detection, etc. are performed by temperature detection with a thermistor, so if a problem related to the thermistor occurs, the device will not operate properly. Not only that, but there was a risk of ignition and smoke.

In order to solve this problem, it is possible to detect defects related to the thermistor through software, but the CP which controls the temperature control of the fixing heater
It has no effect when U goes out of control.

[0031]Furthermore, the malfunctions related to the thermistor are as follows:
Temperature cannot be detected because the thermistor is disconnected or the thermistor is not installed in the specified position.

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

[0033]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a heating means, a temperature detection means for detecting the temperature of the heating means, and a memory storage for storing and holding the temperature detection result of the temperature detection means. means, and comparison means for comparing the temperature detection result of the temperature detection means and the value in the memory retention means after a certain period of time from the time of memory retention in the memory retention means;
It is characterized by comprising means for controlling energization to the heating means based on the comparison result of the comparison means.

[0034]

According to the present invention, it is determined that the temperature of the heating means cannot be detected without using software based on the comparison result of the comparison means, and it is possible to appropriately control the energization of the heating means.

[0035]

[Example] (Example 1) In this example, an A/D converter, a latch, and a digital comparator are used to store and hold the temperature detection value immediately after the triac firing signal is input, and the temperature detection value after a certain period of time is Compared to this, if the temperature does not rise, the flip-flop stores the abnormal state and shuts off the relay.

FIG. 1 shows a heater temperature comparison circuit for explaining this embodiment.

In the figure, the flip-flop 109, the relay winding drive transistor 139, the phototriac coupler drive transistor 117, and other circuits not shown are the same as those in the conventional example, and therefore their explanation will be omitted.

11 is a pull-up resistor. This resistor 11 ensures a HIGH level on the collector side of the phototriac coupler driving transistor 117. Incidentally, the LOW level is the saturated collector-emitter voltage of the transistor 117, which is already guaranteed. 12 is a sequencer that controls the circuit shown in FIG. 1
3 is a clock supply circuit. 14 is a capacitor,
This is a reset circuit using a resistor, and resets the sequencer 12 when the power is turned on.

FIG. 2 shows a state transition diagram of the sequencer 12. First, by setting the negative logic reset input *RST to LOW, the sequencer is reset, and *RST goes HIGH.
When the signal becomes H, a transition is made to state 1. state 1
All outputs of the sequencer are initialized. In other words, S
AMPLE output is LOW, LATCH output is LOW, *
COMP output is HIGH, ENT output is LOW, *CL
The R output becomes LOW, and the *LOAD output becomes HIGH. In this state, it waits for the *HEAT input to become LOW. That is, it waits until the heater drive signal is output from the CPU and the LED of the phototriac coupler lights up. When the heater drive signal is output, a transition is made to state 2.

In state 2, the SAMPLE output is set to HIG.
By setting it to H, a sampling clock is given to the A/D converter 15 in FIG. The A/D converter 15 samples and holds the input voltage VIN, which is the temperature of the fixing heater, at the rising edge of the SAMPLE signal, performs A/D conversion, and outputs 4 bits. At the next clock, it transitions to the next state and sets the SAMPLE output to LOW (state 3). At the next clock, it transitions to the next state and sets the LATCH output and *CLR output to HIGH (state 4). At the rising edge of the LATCH output, the latch 16 outputs the A signal immediately after the input of the heater drive signal from the CPU.
/D converted temperature detection value is stored and held. * Clearing the counter 17 is canceled by setting the CLR output to HIGH. Note that the counter 17 does not start counting because the ENT input remains LOW. At the next clock, transition to the next state, LATCH output, *LOA
Set the D output to LOW (state 5).

*By setting the LOAD input to LOW, the counter 17 internally loads the initial value. The initial value is
As shown in FIG. 1, by setting it to 0, the counter 17 overflows after 15 clock cycles. At the next clock, it transitions to the next state and sets the *LOAD output to HIGH (state 6). At the next clock, a transition is made to the next state and the count enable signal ENT is set to HIGH (state 7). As a result, the counter 17 starts counting from the set initial value. In state 7,
Wait for counter overflow. That is, it waits for the RCO input to become HIGH. This is because the temperature is detected again after a certain period of time has passed since the heater drive signal was input from the CPU. Also, if the heater drive signal from the CPU is canceled during standby, that is, *HEA
When the T input becomes HIGH, the state returns to state 1. After a certain period of time from state 7, transition to the next state, and S
The AMPLE output is made HIGH again (state 8). As a result, the temperature of the fixing heater is detected after a certain period of time has elapsed since the heater drive signal was input from the CPU. At the next clock, it transitions to the next state and sets the *COMP output to LOW (state 9). *COMP output LOW
By doing so, the external circuit is the digital comparator 18
You can know that the temperature comparison is complete. In state 9, the CPU waits for the heater drive signal to be released. In other words, it waits for the *HEAT input to become HIGH, and returns to state 1 when it is satisfied.

In FIG. 1, 18 is a 4-bit digital comparator. It has two systems of 4-bit inputs, A and B, and when the A input value is lower than the B input value, A<B output becomes HIGH. In other words, if the temperature has increased after a certain period of time compared to the fixing heater temperature immediately after the heater drive signal is input from the CPU, the A<B output will be HI.
It becomes GH.

19 is an OR gate with an open collector output expressed in negative logic. The output of OR gate 19 is L
The condition for OW is A<B of the digital comparator 18.
The output is LOW, and the *COMP output of the sequencer 12 is LOW. That is, compared to the temperature of the fixing heater immediately after the heater drive signal is input from the CPU, the output of the OR gate 19 becomes LOW if the temperature has not risen even after a certain period of time has elapsed. When the output of the OR gate 19 becomes LOW, the abnormal state is stored in the flip-flop 109 and the relay is cut off.

(Embodiment 2) In addition to the functions of Embodiment 1, this embodiment checks the energization state, and if the temperature does not rise even though the heater is energized, it is determined that the flip-flop is in an abnormal state. Remember something and shut off the relay. A function to report this abnormal state to the CPU is also added.

FIG. 3 shows a heater temperature comparison circuit for explaining this embodiment. In the figure, flip-flop 10
9, the relay winding drive transistor 139, the phototriac coupler drive transistor 117, and other circuits (not shown) are the same as those in the prior art example, so their explanation will be omitted. Further, the same circuits as in Example 1 are given the same numbers as in FIG.

21 is an OR gate expressed in negative logic. The condition for the output of the OR gate 21 to be LOW is that the output of either the window comparator 124 or 125 is LOW.
, and the phototriac coupler driving transistor 117 is ON. In other words, a heater drive signal is output from the CPU, and in response to this, a current transformer (not shown) detects a current, and the output of the OR gate becomes LOW.
becomes.

When the output of the OR gate 21 becomes LOW, the state transition of the sequencer 12 whose operation was explained in the first embodiment is started. The operation in Figure 3 is based on the digital comparator 1
Example 1 until it is determined that the A<B output of 8 is LOW, that is, the temperature has not increased even though a certain period of time has elapsed compared to the fixing heater temperature immediately after the heater drive signal was input from the CPU. It works the same way.

22 is a NOR gate expressed in negative logic. The conditions for the output of the NOR gate 22 to be HIGH are that the A<B output of the digital comparator 18 is LOW and the *COMP output of the sequencer 12 is LOW. That is, compared to the temperature of the fixing heater immediately after the heater drive signal is input from the CPU, the output of the NOR gate becomes HIGH if the temperature has not risen even after a certain period of time has elapsed.

23 is a thermistor abnormality detection output for the CPU port. By monitoring the thermistor abnormality detection output 23 after outputting the heater drive signal, the CPU can confirm an abnormal state in which the temperature does not rise despite outputting the heater drive signal. 24 is an inverter with open collector output, and the output is LOW.
As a result, the abnormal state is stored in the flip-flop 109 and the relay is cut off.

(Embodiment 3) In this embodiment, the same function as in Embodiment 2 is realized by an analog circuit. FIG. 4 shows a heater temperature comparison circuit for explaining this embodiment. In the figure, the flip-flop 109, the relay winding drive transistor 139, the phototriac coupler drive transistor 117, and other circuits not shown are the same as those in the conventional example, and therefore their explanation will be omitted. Further, the same circuits as in Example 1 are given the same numbers as in FIG. 1, and the same circuits as in Example 2 are given the same numbers as in FIG.

Reference numeral 31 denotes an analog switch, which is turned ON when the LATCH output of the sequencer 12 is LOW. 32 is also an analog switch, which is turned ON when the LATCH output of the sequencer 12 is HIGH. 33,
34 is an operational amplifier. 35 is a capacitor, which connects the analog switches 31, 32, operational amplifier 33,
34, an integral type sample/hold circuit is configured, and the LATCH output of the sequencer 12 is set to HIGH.
If H, the input voltage is sampled, and if the LATCH output is LOW, the sampled voltage is held. Input and output voltages are in phase.

36 is a comparator with an open collector output, and a resistor 37 guarantees a LOW level. The output of comparator 36 goes LOW when the inverting input voltage exceeds the non-inverting input voltage. In other words, the CPU
The output of the comparator 36 becomes LOW when the temperature of the fixing heater does not rise even after a certain period of time has elapsed compared to the temperature of the fixing heater immediately after the heater drive signal was input from the fixing heater. As a result, the abnormal state is stored in the flip-flop 109 and the relay is cut off.

[0053]

[Effects of the Invention] As explained above, according to the present invention,
It is possible to prohibit energization of the heating means when temperature cannot be detected without using software, for example, when the temperature detection means is disconnected or when the temperature detection means is not installed at a predetermined position.
Even when the CPU controlling the temperature of the heating means goes out of control, it is possible to prevent the device from igniting or emitting smoke.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a state transition diagram of the sequencer 12.

FIG. 3 is a circuit diagram of a second embodiment of the invention.

FIG. 4 is a circuit diagram of a third embodiment of the present invention.

FIG. 5 is a circuit diagram for explaining a conventional technique.

[Explanation of symbols]

11 Pull-up resistor 12 Sequencer 13 Clock supply circuit 14 Reset circuit 15 A/D converter 16 Latch 17 Counter 18 Digital comparator

Claims (1)

[Claims] 1. A heating means, a temperature detecting means for detecting the temperature of the heating means, a memory holding means for storing and holding the temperature detection result of the temperature detecting means, and a heating means for storing the temperature of the heating means for a certain period of time from the time when the memory is held by the memory holding means. Comparing means for later comparing the temperature detection result of the temperature detecting means with a value in the memory holding means, and means for controlling energization to the heating means based on the comparison result of the comparing means. Features of the image forming device.