JPS649633B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In a heat fixing device of an electronic copying machine, the present invention issues a copy ready signal (hereinafter referred to as a ready signal) before the temperature inside the fixing device reaches a control temperature.
The present invention relates to a temperature control device that reduces so-called overshoot, in which the temperature inside a fixing device becomes higher than a control temperature.

Conventionally, known fixing devices for electronic copying machines include a heating roll system using a heating roll, a hot plate system, a radiant system, and an oven system. All of these methods use heat to melt the toner image on the paper and fix it on the paper, and the temperature inside the fixing device needs to be maintained above the melting point of the toner. For this reason, these methods require warm-up time after the copier is turned on until the toner reaches its melting temperature, and since copying cannot be performed during this time, various studies have been made to shorten this warm-up time. Therefore, methods have already been proposed to shorten the warm-up time by reducing the heat capacity of the heating roll or by applying large amounts of electric power during the warm-up time. In addition, in these methods, when the temperature inside the fixing device reaches the control temperature, a ready signal is issued to notify that copying is possible. Because the detector and its surroundings are cold, even if the temperature inside the fixing device has reached the fixing temperature, it actually detects a temperature lower than this, which causes the detector to lower the control temperature. At the time when the temperature inside the fixing device is detected, the temperature inside the fixing device is
As shown in the figure, the overshoot temperature was reached, and there was a problem that extra time and power were consumed by the temperature difference a during this time.

This invention was made with the aim of improving such a problem, and after power is applied to a heating roll equipped with a heating heater, a ready signal is issued before the surface temperature of the heating roll reaches a control temperature to make it ready for copying. Provided is a temperature control device for a fixing device in an image forming apparatus that allows the temperature of the surface of a heating roll to reach a control temperature before paper to which toner is transferred reaches the heating roll, thereby eliminating overshoot that consumes extra power and time. The aim is to reduce the

The present invention will be described in detail below with reference to an illustrated embodiment. In FIG. 2, 1 is a heating roll provided in a fixing device of an electronic copying machine (not shown), 2 is a heater provided in the heating roll 1, and an AC power source 4 is supplied via a power control element 3 such as a triax. is being applied. Reference numeral 5 denotes a temperature detection element such as a thermistor provided near the surface of the heating roll 1, which constitutes a bridge circuit with an internal resistance R _T and a plurality of resistors R ₁ , R ₂ , R ₃ and R ₄ . Potential V _A between detection element 5 and resistor R ₁ and potential V _C between resistors R ₂ and R ₃
to the ready temperature detection comparator 6, and the above potential
V _A and the potential V _B between the resistors R ₃ and R ₄ are input to the control temperature detection comparator 7, respectively. On the output side of the comparator 6, there is a ready circuit 8 that makes the copying machine ready for copying, and a ready circuit 8 that always generates an output synchronized with the power supply voltage OV when the output of the comparator 6 is at a low level. When the output of the comparator 7 is at a high level, the power control circuits 9 that generate every other two signals synchronized with the power supply voltage OV are connected to each other, and the output of the power control circuit 9 is connected to the output of the comparator 7. Power control element drive signal generator 10 connected to the output side
is input to the AND circuit 11 along with the output of the power control element 3.
is controlled as follows.

However, when the copying machine (not shown) is powered on, the AC power source 4 having the waveform shown in FIG. heating roll 1
The surface temperature of is constantly detected by the temperature detection element 5 and generates an electromotive force according to the temperature, and when the surface temperature is low, the potential between each resistor R ₁ is in the relationship V _A > V _C > V _B. The output of the comparator 7 becomes "H", and the power control element drive signal generator 10 outputs an output synchronized with the power supply voltage OV as shown in FIG. 3b, and at this time, the output of the comparator 6 becomes Since the signal is "L", the power control circuit 9 generates a signal c' shown in FIG. maintained.

When the surface temperature of the heating roll 1 rises and the potential of each part becomes V _C ≧V _A > V _B , the output of the comparator 6 becomes "H" and each part of the copying machine becomes ready for copying. As shown in FIG. 3c, the power control circuit 9 now generates two signals synchronized with the power supply voltage OV every other signal (c''), and as a result, the AND circuit 11 also generates two signals synchronized with the power supply voltage OV (c''). As shown in Figure d, two signals synchronized with the power supply voltage OV are generated every other device (d'), so the power control element 3 controlled by the output of the AND circuit 11 is in a conductive state at intervals. As a result, electric power e' is supplied to the heater 2 at intervals as shown in FIG.
After the ready signal B, the temperature rise curve becomes a gentle curve as shown by the broken line in FIG. 1, and the temperature continues to rise. Next, when the potentials of each part become in the relationship V _C > V _B > V _A , the output of the comparator 7 becomes "L", so the output from the electronic control element drive signal generator 10 disappears, and the power control element 3 is turned off, and the supply of power to the heater 2 is stopped. As a result, the heating roll 1 reaches the fixing temperature without causing a large overshoot as in the conventional case. After that, heating roll 1
The power control element 3 is turned on and off depending on the level of the surface temperature of the surface, and the surface temperature is controlled to a constant temperature A shown in FIG.

Note that the present invention is not limited to the circuit of the above embodiment; for example, the outputs of the power control circuit 9 and the comparator 7 are input to the AND circuit 11, and the power control element 3 is controlled by the output. Of course, the circuit can be adopted.

As described in detail above, this invention enables copying by emitting a ready signal before the surface temperature of the heating roll equipped with a heater reaches the control temperature.
It is possible to significantly reduce the temperature overshoot of the heating roll, which occurs when the temperature sensor and its surroundings are cold, such as immediately after power is turned on, and the temperature is not detected accurately.

In particular, since the surface temperature of the heating roll is directly controlled, overshoot during warm-up can be appropriately reduced, thereby shortening warm-up time and reducing the power used for overshoot. At the same time, before the paper with the toner image transferred to it reaches the fixing device, the temperature inside the fixing device has exceeded the control temperature that allows fixing, resulting in poor fixing and offset to the heating roller due to low fixing temperature. No such problems occur at all.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a diagram showing the relationship between controlled temperature and time, FIG. 2 is a circuit diagram of the temperature control device, and FIG. 3 is a waveform diagram of each part. 1 is a heating roll, 2 is a heater, 3 is a power control element, 5 is a temperature detector, and 6 and 7 are comparators.

Claims (1)

[Claims] 1. In a fixing device consisting of a heating roll equipped with a heating heater and a pressure roll, after power is applied to the heating roll equipped with the heating heater, a ready signal is issued before the surface of the heating roll reaches the control temperature, and the heating An image comprising means for limiting the electric power supplied to the roll, and means for detecting when the surface temperature of the heating roll reaches the control temperature and controlling the surface temperature of the heating roll to the control temperature. A temperature control device for a fixing device in a forming device.