JP2001042697A - Temperature controller for thermal fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a heater error before the upper limit temperature at which overheat safety device (thermostat) works and to avoid damages to peripheral parts is reached. SOLUTION: This controller is provided with a thermistor 5 detecting the temperature of a heater 2 and a timer 9a counting a prescribed time starting from the driving of the heater. Then, heater temperature at the time of starting the driving of the heater is detected, and the prescribed time counted by the timer is changed to a shorter time as the heater temperature at driving becomes higher. If the heater temperature detected when the prescribed time counted by the timer elapses does not reach target temperature, it is decided that there is a heater error, and the heater is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a printer, for example,
The present invention relates to a temperature control device of a thermal fixing device used for a copying machine, a facsimile machine, and the like.

[0002]

2. Description of the Related Art In a heat fixing apparatus, a heater is provided in a heat roller, and the heat roller is heated by the heater. When the surface temperature of the heat roller reaches a target temperature, heat fixing can be performed. In such a heat fixing device, the heater temperature is controlled to a constant temperature in order to maintain the surface temperature of the heat roller at a target temperature.

Specifically, when the heater temperature is controlled to a constant temperature, after the heater is turned on by a heater start signal (ON signal), the surface temperature of the heat roller is detected by a thermistor or the like, and this is set as the heater temperature. The power supply to the heater is controlled so as to keep the current.

Conventionally, during such energization control, if the heater temperature does not reach the target temperature within a certain time (error determination time) from when the heater is turned on, the temperature control device may have some abnormality (for example, a heater error). It has been determined that a heater error has occurred when an abnormality such as a thermistor for detecting temperature has occurred.

[0005]

However, in the conventional apparatus, since the error determination time is fixed, if there is an abnormality in the thermistor for detecting the heater temperature, the target temperature is reduced until the error determination time is reached. In some cases, the temperature greatly exceeded the temperature, resulting in an overheating state. This is because the heater temperature (initial temperature) when the heater is driven differs depending on the situation, such as when printing is started from a state where the heater is cold, immediately after printing is completed, and the target temperature increases as the initial temperature increases. Is also short.

In such a case, in order to prevent the heater temperature from becoming abnormally high, the upper limit temperature (for example, when the target temperature is about 190 ° C., 2
(About 50 ° C.), and a thermostat or the like is provided as an overheating safety device so that the power to the heater is automatically cut off when the temperature reaches the upper limit temperature.

However, at the upper limit temperature at which the thermostat works, there is a problem that components around the heater are often damaged.

Accordingly, the present invention is to provide a temperature control device of a thermal fixing device which can detect a heater error before reaching an upper limit temperature at which an overheat safety device operates and can avoid damage to peripheral components. Is what you do.

[0009]

According to a first aspect of the present invention, there is provided a temperature detecting means for detecting a temperature of a heater provided in a heat fixing device, and a timer for measuring a predetermined time from the start of driving of the heater. And an error detecting means for making an error when the heater temperature detected by the temperature detecting means has not reached the target temperature when a predetermined time by the timer elapses, and a heater temperature at the start of driving the heater is detected by the temperature detecting means. And a control means for changing the predetermined time measured by the timer to a shorter time as the driving heater temperature is higher.

[0010]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a schematic diagram showing the configuration of a heat fixing device. Reference numeral 1 denotes a heat roller in which a heater 2 is disposed, 3 denotes a control unit for controlling the temperature of the heater 2,
Denotes a power supply unit that supplies electric power to the heater 2 and the control unit 3.

The heat roller 1 is heated from the inner surface by the heat of the heater 2 and heat-fixes the toner image transferred onto the sheet conveyed between the heat roller 1 and a roller (not shown) opposed to the heat roller 1. Has become.

On the surface of the heat roller 1, a temperature sensing element as a temperature detecting means for detecting the surface temperature, for example, a thermistor 5, is disposed, and power is supplied to the heater 2 at an upper limit temperature higher than a target temperature. A thermostat 6 is provided as an overheat safety device that cuts off the power.

The control unit 3 includes a control unit C
PU (Central Processing Unit) 7, ROM (Read Only Memory) 8 storing program data and the like for the CPU 7 to control each unit, Memory area used for various data processing performed by the CPU 7, which will be described later. A RAM (random access memory) 9 provided with a timer 9 a for measuring an error detection time (a predetermined time measured by a timer) TE, and an I / O port 11 are provided.

The power supply section 4 has a power plug 12. A commercial AC power supply (10
0V) is supplied to the DC circuit unit 14 via the switch 13. The DC circuit unit 14 converts an alternating current into a direct current (5 V, 24 V).
V), the 5V voltage is supplied to the control unit 3, and the 24V voltage is supplied to a transport motor (not shown).

One terminal of the switch 13 is connected to one terminal of the heater 2, and the other terminal is connected to the other terminal of the heater via a triac 15 and a thermostat 6 which are switch elements in series. ing.

Further, the power supply unit 4 includes a photocoupler including a light emitting element 16 and a light receiving element 17. The light emitting element 16 is connected to the I / O in the control unit 3 via the resistor 18.
Connected to port 11. And the light emitting element 16
The light emitting element 16 is controlled based on a heater control signal from the CPU 7.
Is turned on and off.

The other terminal of the switch 13 has a resistor 1
9 and the light receiving element 17 in series,
5 gate. The gate of the triac 15 and one terminal are connected via a resistor 21.

The CPU 7 repeats the control as shown in FIG. First, the CPU 7 executes S
At T1, it is determined whether or not printing has started. For example, when a print start command is issued from a host device connected to a printer or the like including the apparatus, a print start signal is generated. When the print start signal is present, it is determined that the print is started.

If it is determined in ST1 that the printing is not to be started, the heater is turned off in ST2 to end this control, and if it is determined that printing is to be started, ST is started.
At 3, the detected temperature of the thermistor 5 is read via the I / O port 11.

Subsequently, in ST4, it is determined whether or not the heater 2 is operating. It is determined whether or not the heater 2 is being controlled. If it is determined in ST4 that the heater 2 is not operating, the error detection time TE calculated based on the expression (1) described later is set in the timer 9a in ST5 (control means).

TE = K1 × (CG−CX) + T1 (1) Here, TE is an error detection time (a predetermined time detected by a timer), and is a heater for judging a heater error such as a failure of the thermistor 5. This is the time measured from the start of driving. CG is a target temperature, CX is a heater temperature for driving the heater, that is, the thermistor 5 at the start of printing.
, K1 is a temperature constant (time / temperature) based on the thermal efficiency of the heater 2, and T1 is a constant (time) calculated from a delay in heat transfer and an error / margin. .

K1 is a coefficient that is proportional to the heat capacity and inversely proportional to the wattage of the heater 2. Based on experiments and experiences,
When the time required to raise the temperature from the initial temperature of 20 ° C. to the target temperature of 190 ° C. is 50 seconds, K1 is:
Substantially 50 / (190-20) can be substituted.

The time T1 needs to be set shorter than the time required to reach the upper limit temperature at which the thermostat 6 operates from the target temperature. For example, 5 to 10 seconds is appropriate as a margin including an error. .

Subsequently, in ST6, the CPU 7 sets the timer 9a.
At the same time, the heater 2 is turned on by asserting a heater control signal connected to the power supply unit 4 via the I / O port 11, and the control is terminated.

If it is determined in ST4 that the heater is operating, it is determined in ST7 whether the heater temperature C read in ST3 is lower than the target temperature CG. ST7
If it is determined that the heater temperature C is not lower than the target temperature CG, the target temperature has been reached.
7 turns off the heater 2 by negating the heater control signal via the I / O port 11. Then, S
At T9, a flag is set to indicate that printing is possible (heater ready), and this control ends. Printing is started by this flag.

If it is determined in ST7 that the heater temperature C is lower than the target temperature CG, it is determined in ST10 whether or not the counting of the timer 9a has been completed. ST10
When it is determined that the counting of the timer 9a has not ended, the control is ended. When it is determined that the counting of the timer 9a has ended, a heater error is determined in ST11 and, for example, the operation of the heater 2 is stopped. (E.g., setting an error flag) (error detection means). With this flag, the CPU 7 stops the operation of the heater 2.

In the embodiment of the present invention having such a configuration, when a print start signal is generated, the heater temperature (initial temperature) at that time is detected. The higher the initial temperature, the shorter the error detection time TE is set. For example, when the initial temperature is 80 ° C. as shown by y1 in FIG. 3, the initial temperature is 20 ° C. as shown by y2 in FIG.
, TE3 (TE1 <TE2), and TE3 (TE2 <T2) when the initial temperature is −10 ° C. as indicated by y3 in FIG.
E3) is set.

If the heater temperature does not reach the target temperature CG before the error detection time TE elapses after the heater 2 is driven, it is determined that a heater error has occurred, and the heater 2 is stopped. Is performed.

As described above, by changing the error detection time TE according to the initial temperature which is the temperature at which the heater 2 is driven, the printing operation is started again immediately before the printing is completed. If the initial temperature is high, a shorter error detection time TE is set, so that an error is detected when the heater temperature is lower than the upper limit temperature at which the thermostat 6 operates, and the heater is stopped. be able to. Thus, the heater temperature can be prevented from reaching the upper limit temperature, so that damage to peripheral components can be avoided.

Further, when the initial temperature of the heater 2 is low, such as when the apparatus is used in a low temperature environment, the temperature does not rise easily in a short time, but a longer error detection time TE
Is set, the heater 2 can be sufficiently heated.

[0031]

As described in detail above, according to the present invention, a heater error can be detected before reaching the upper limit temperature at which the overheat safety device (thermostat) operates, and damage to peripheral components can be avoided. It is possible to provide a temperature control device of the heat fixing device.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a temperature control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing control performed by a CPU shown in FIG. 1;

FIG. 3 is a diagram showing a relationship between heater temperature and time in the present embodiment.

[Explanation of symbols]

 2. Heater 3. Control unit 4. Power supply unit 5. Thermistor 6. Thermostat 7. CPU 9a. Timer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA12 DA38 EA12 ED25 EK11 HA04 2H033 BA31 CA03 CA06 CA20 CA28 CA34 5H323 AA36 BB17 CA08 CB02 DA01 FF03 KK05 LL13 QQ06 SS02 SS08 TT09 TT17

Claims (1)

[Claims] A temperature detecting means for detecting a temperature of a heater provided in the heat fixing device; a timer for measuring a predetermined time from the start of driving of the heater; and a timer for measuring a predetermined time by the timer. An error detection unit that sets an error when the heater temperature detected by the temperature detection unit does not reach the target temperature; and a heater temperature at the time of starting the driving of the heater, which is detected by the temperature detection unit. A temperature control device for changing the predetermined time measured by the timer to a shorter time as the value of the temperature is higher.