JPH01200422A - Heater temperature control device - Google Patents

Abstract

PURPOSE:To suppress the overshoot at the rise of a heater by energizing continuously the heater until the detected temperature reaches a specific level by the output of a 2nd comparator after the rise of the heater and then energizing discontinuously the heater by the output of a 1st comparator. CONSTITUTION:When the temperature of a heater 2 is sufficiently low, the outputs of both 1st and 2nd comparators 5 and 6 are kept at L levels. Under such conditions, an energization ON command is issued to a heater driving circuit 3 from a temperature control part 8 with application of a heater rise signal S3. Then a heat fixing roll 1 is heated with energization of the heater 2. When the detecting temperature of a temperature detector 4 reaches a specific level lower than the fixing temperature by several tens of degree, the output of the comparator 6 is set at an H level and a command is given to the circuit 3 from the part 8 to repeat the energization ON/OFF states according to the prescribed energizing time. Then the output of the comparator 5 is set at an H level when the detecting temperature of the detector 4 reaches the fixing level. Thus an energization OFF command is issued to the circuit from the part 8. An energization ON command is issued when the detected temperature drops, and the output of the comparator 5 is set at an L level. Such operations are repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heater temperature control device suitable for use in a heat fixing heater used in a laser printer, an electrophotographic device, or the like.

[Prior Art] For example, a printing mechanism such as a laser printer or an electrophotographic device is provided with a thermal fixing roller for thermally fixing toner attached to paper, and this thermal fixing roller is heated and maintained at a high temperature. A heater for this purpose is built into the roller.

Conventional temperature control devices for this type of heater include a thermistor that detects the surface temperature of the heat fixing roller heated by the heater by resistance change, and compares the detected temperature of this thermistor with a preset fixing temperature of the roller. and a control unit that controls energization to the heater based on the output of this comparator.After the heater starts up, the current is continuously applied until the detected temperature reaches the fixing temperature, and once the detected temperature reaches the fixing temperature, the heater is energized continuously. Generally, the heater is turned off and then turned on and off repeatedly so that the detected temperature is maintained at the fixing temperature.

However, in this case, there is a time delay (hysteresis) between the roller surface temperature change and the thermistor resistance change, so even if it is detected that the fixing temperature has been reached and the energization is turned off, the time delay will still occur. Temperature overshoot only occurs. This overshoot appears conspicuously when the temperature when the heater starts up is low (for example, room temperature) and the temperature change up to the fixing temperature is large, causing wrinkles in the paper during thermal fixing and deterioration of print quality.

Therefore, in order to reduce such a temperature overshoot, it has been considered to make the temperature rise curve gentle by discontinuously supplying electricity to the heater from when the heater starts up until the fixing temperature is reached. However, in order to sufficiently suppress the overshoot, it is necessary to make the temperature rise curve considerably gentler, and in this case, the so-called warm-up time, the time from when the heater starts up until the fixing temperature is reached, becomes long, making it difficult to use. It had become a thing.

[Problems to be Solved by the Invention] As described above, in the conventional heater temperature control device of this kind, it is difficult to suppress the temperature overshoot when the heater starts up, unless the warm-up time is lengthened and the usability is worsened. I couldn't do it.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a heater temperature control device that can reliably suppress temperature overshoot when the heater starts up without reducing usability due to a short warm-up time.

[Means for Solving the Problems] The present invention includes a temperature detector that detects the temperature of a heater, a first comparator that compares the detected temperature with a preset temperature of the heater, and a temperature detector that detects the temperature of the heater. A second comparator compares the temperature with a specific temperature lower than the set temperature, and after the heater starts up, the heater is continuously energized until the detected temperature reaches the specific temperature according to the output of the second comparator. The heater energization control means discontinuously energizes the heater from when the temperature reaches a specific temperature until the set temperature is reached based on the output of the first comparator.

[Function] If the heater temperature control device takes such measures,
After the heater starts up, the heater is continuously energized until the temperature of the heater detected by the temperature detector reaches a specific temperature, so that the specific temperature is reached in a short time. After reaching the specific temperature, the heater is energized discontinuously until the detected temperature reaches the set temperature of the heater, so the temperature rise curve becomes gentle and overshoot is suppressed. Further, since the time from the specific temperature to the set temperature is relatively short, the warm-up time is short.

[Example] Hereinafter, an example in which the present invention is applied to a heater for heating a heat fixing roller in a laser printer or an electrophotographic apparatus will be described with reference to the drawings.

FIG. 1 is a diagram showing the configuration of this embodiment. In the figure, reference numeral 1 denotes a heat fixing roller, and a heater 2 is housed within this roller. When the heater 2 is energized by a heater drive circuit 3, the heat fixing roller 1 is heated. A temperature detector 4 is attached to the heat fixing roller 1 to detect the temperature of the heater 2, that is, the temperature of the heat fixing roller 1 heated by the heater 2. This temperature detector 4 is a so-called thermistor that detects temperature change as a resistance change, and detects a change in voltage level caused by this resistance change. The second comparator 5.6 detects this as a change in the detected temperature level. The first comparator 5 inputs the output voltage of the temperature detector 4 to the non-inverting input terminal (+), and connects the resistor R2 and R
5 and the voltage Vo set by the inverting input terminal (-)
, compare both input terminals, and output the comparison result s
1 is applied to the temperature control section 8 via the input/output section 7. Note that the voltage Vo corresponds to the set temperature of the heater 2, that is, the fixing temperature of the thermal fixing roller 1 heated by the heater 2. The second comparator 6 inputs the output voltage of the temperature detector 4 to a non-inverting input terminal (+), and resistors R3 and R6
The voltage VW set by is input to the inverting input terminal (-), the two input voltages are compared, and the comparison result is output S2.
The temperature is supplied to the temperature control section 8 via the input/output section 7. Note that the voltage vw corresponds to a specific temperature set several tens of degrees lower than the set temperature of the heater 2.

The temperature control section 8 is activated by a rise signal S3 of the heater 2 given from the outside, and is activated by the first . A device that determines on/off of energization of the heater 2 based on the outputs Sl and S2 of the second comparators 5 and 6, and outputs a control signal S4 to the heater drive circuit 3 via the input/output section 7. It is. That is,
The temperature control section 8 is the first. The output Sl of the second comparator 5, 6,
When both S2 are at LOW level, when the heater rise signal S3 is given, the heater drive circuit 3 is commanded to turn on the current. In this state, when the output of the second comparator 6 becomes HIGH level, a command is given to repeat the energization on/off according to the preset energization time. When the output of the first comparator 5 also goes to HIGH level, a command is given to turn off the power, and then the output of the first comparator 5 goes to the HIGH level.
When the output of the first comparator 5 reaches the OW level, a command is issued to turn on the energization, and when the output of the first comparator 5 reaches the HIGH level, a command is issued to turn off the energization. Thereafter, by repeating this energization on/off, the heater temperature is controlled so that the heat fixing roller 1 maintains the fixing temperature.

In this embodiment having such a configuration, when the temperature of the heater 2 is sufficiently low, the first. Both outputs of the second comparator 5.6 are at the LOW level, and when the heater rise signal S3 is given in this state, the temperature control section 8 gives an energization on command to the heater drive circuit 3, which causes the heater 2 to turn on.
energization is performed, and the heat fixing roller 1 is heated. Then, the temperature detected by the temperature detector 4 is several 1 higher than the fixing temperature.
When the specified temperature 0 degrees lower is reached, the output of the second comparator 6 becomes H.
The temperature reaches the IGH level, and a command is given from the temperature control unit 8 to the heater drive circuit 3 to repeat the energization on/off according to the preset energization time. Next, when the temperature detected by the temperature detector 4 reaches the fixing temperature, the output of the first comparator 5 also becomes HIGH level, and the temperature control section 8 issues a command to turn off the power supply to the heater drive circuit 3. Thereafter, when the detected temperature falls below the fixing temperature and the output of the first comparator 5 becomes LOW level, a command is issued to turn on the current.
When the output of the first comparator 5 becomes HIGH level, a command is issued to turn off the current. In this way, the temperature of the heater 2 is controlled so that the heat fixing roller 1 maintains the fixing temperature by repeating the power supply on/off.

Figure 2 shows the energization on/off operation when the heater 2 starts up, in the case of this embodiment (A) and in the conventional example (B, C).
), and Fig. 3 is a timing diagram showing a comparison between the
FIG. 2 is a characteristic diagram showing the temperature of the heater 2 that changes over time due to each energization on/off operation shown in the figure.

In the conventional example (B), when the heater temperature is at room temperature TR, the heater 2
heater 2 until the fixing temperature T0 is reached.
In this example, the time required for the heater temperature to reach the fixing temperature To, so-called warm-up time (t2'-tO), is short. However, temperature overshoot (G in FIG. 3) occurs due to hysteresis.

In the conventional example (C), when the heater temperature is at room temperature TR, heater 2
After that, heater 2 is turned on until the fixing temperature To is reached.
For example, this is an example of discontinuous energization while gradually shortening the off interval. In this case, temperature overshoot can be suppressed to some extent, but the warm-up time (t2'-tO) becomes considerably long.

On the other hand, in the present embodiment (A), the heater 2 is turned on when the heater temperature is at room temperature TR, and then the heater 2 is continuously energized until it reaches a specific temperature Tw, and then the heater 2 is continuously energized until it reaches the fixing temperature To from the specific temperature Tw. is an example in which the heater 2 is energized discontinuously for a preset energization time; in this case, the time from the rise of the heater 2 until reaching the specific temperature Tw (tl-tO
) is a short time, and the time (t2-tl) from the specific temperature W to the fixing temperature/degree 0 is also relatively short, so the warm-up time (t2-to) is sufficient compared to the conventional example (C). It can be shortened to Also, from the specific temperature TW to the fixing temperature T
. Since the temperature rise curve up to

As described above, according to this embodiment, by setting an appropriate value as the specific temperature Tw, it is possible to reliably suppress temperature overshoot while relatively shortening the warm-up time. It is possible to prevent deterioration of print quality due to

In the above embodiment, the case where the heater 2 is applied to heat the heat fixing roller 1 of a laser printer or an electrophotographic device is shown, but the invention is not limited to this, and the heater 2 may be applied to a heater used for other purposes. Of course, it can also be applied.

Furthermore, in this embodiment, it is possible to save energy by controlling the temperature of the heater 2 so that the temperature of the heat fixing roller 1 during standby after the heater has started up becomes a specific temperature Tw.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide a heater temperature control device that can reliably suppress temperature overshoot when the heater starts up without reducing usability due to a short warm-up time. .

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a timing diagram showing heater energization on/off operations between this embodiment and a conventional example, and Fig. 3 is a diagram showing the energization timing in Fig. 2. FIG. 3 is a characteristic diagram showing a corresponding change in heater temperature over time. DESCRIPTION OF SYMBOLS 1... Heat fixing roller, 2... Heater, 3... Heater drive circuit, 4... Temperature detector, 5, 6... 1st. Second comparator, 8...temperature control section. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] a temperature detector that detects the temperature of the heater; a first comparator that compares the temperature detected by the temperature detector with a preset temperature of the heater; and the temperature detected by the temperature detector and the setting. a second comparator that compares the temperature with a specific temperature lower than the temperature, and a second comparator that compares the temperature with a specific temperature lower than the
The heater is continuously energized until the detected temperature reaches a specific temperature based on the output of the first comparator, and the heater is turned off until the detected temperature reaches the specific temperature and the set temperature is reached based on the output of the first comparator. 1. A heater temperature control device comprising a heater energization control means that continuously energizes the heater.