JPH0362208A - Temperature control circuit for object to be heated - Google Patents

Abstract

PURPOSE:To detect the abnormality without using any independent protection circuit for detection of abnormality by providing plural temperature control systems with different control target levels set and switching these control systems with each other for execution of the temperature control. CONSTITUTION:A normal range of fluctuation is decided as long as the comparison values H1 and H2 are kept in a range of R+ or -alpha, where R shows the ideal count value and alpha shows a normal range of fluctuation caused by the influence of an external environment, etc. Then a trouble of a temperature control system is decided when the value H1 exceeds the range of R+ or -alpha since the automatic correction is impossible. Thus an abnormal signal is sent to a switch selection means 6, and the corresponding one of both control systems 4 and 5 is forcibly stopped via a switch means 8a or 8b. Then a fixing action is controlled without performing a switch action with one of both systems 4 and 5 only before the faulty system is repaired. As a result, the abnormality can be detected without using any independent protection circuit for detection of abnormality.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention is applicable to a heat fixing device that thermally fixes an unfixed toner image. It relates to a temperature control circuit that has at least one temperature control system that aims to shift to and maintain a control target value while performing control, and in particular automatic correction of control signals of a control circuit including temperature detection means or the presence or absence of abnormality or heating. The present invention relates to a temperature control circuit for a heated body that can perform accurate temperature control of the body.

``Prior Art'' Conventionally, temperature control of a roller-type thermal fixing device consisting of a combination of a fixing roller with a built-in heater and a pressure roller has generally been performed using an 0N-OFF control method, a proportional control method, or a control method consisting of a combination of these. However, even if such a control method is adopted, the fixing roller pair of the heat fixing device has to be made smaller in diameter and thinner in order to correspond to the miniaturization of the entire device. The accumulated heat capacity of the fixing roller is decreasing, and in recent years, in configurations that use large heaters to minimize the waiting time at startup, large overtemperatures are likely to occur due to various factors that disrupt the slight thermal equilibrium. Therefore, in conventional temperature control devices, a microprocessor is used to perform more precise temperature control.

However, if a microprocessor is used to achieve more precise control, the mechanism becomes complicated both in terms of software and hardware, and thermal runaway of the heater is likely to occur due to a failure in the control system.

For this reason, existing temperature control devices are provided with a protection circuit that forcibly cuts off the power to the heater and the device itself when thermal runaway occurs in the heater.

``Problems to be Solved by the Invention'' However, for example, in an electrophotographic device incorporating a heat fixing device, if the power to the heater or the device itself is forcibly cut off by the protection circuit during printing, the problem occurs when the fixing device is used. An image fixation failure may occur on the recording paper on which the image is fixed, or the image forming operation of the recording paper itself may become invalid, so when the image formation is resumed, the controller side may not be able to send an image signal from any of the image storage units. In some cases, it may become unclear whether the image processing is correct or not, which may cause errors in the overall image processing control system.

In order to eliminate this drawback, it is conceivable to provide a second temperature control system for backup in addition to the first temperature control system that controls the energization of the heater. (Note that a technique in which a second control circuit is provided separately from the first temperature control circuit is disclosed in JP-A-58-226911, but the second control circuit is simply connected in series in the heater circuit. The purpose is to forcibly cut off the connected relay circuit, and there is no technology that provides a backup control system that controls energization of the heater like the present invention.) ``Problem to be solved by the invention'' However, backup Providing a backup control system separate from the main control system just for the purpose of use is problematic from a cost performance standpoint, and providing multiple control systems requires multiple protection circuits, etc. Because of this, the configuration becomes complicated, and if each control system and protection circuit are arranged in parallel without being correlated with each other, the failure probability and noise signal will increase accordingly. , it has the disadvantage that malfunctions are more likely to occur.

Therefore, the present invention makes it possible to detect abnormalities without providing an independent protection circuit for abnormality detection by effectively utilizing the backup control system, and also to grasp the control status of the control system. The purpose of the present invention is to provide a temperature control circuit for a heated body that enables automatic correction of the temperature.

Another object of the present invention is to always be optimal for a heated object that is intermittently heat-absorbed due to heat load, such as a laser printer, which has variations in printing interval in response to image processing operations on the host side. An object of the present invention is to provide a temperature control circuit for a heated object that can perform temperature control.

"Means to solve the !2I problem" The present invention aims to achieve this technical problem.

■Although multiple temperature control systems are provided to control the energization of the heater built into the heated object based on the temperature detected by the temperature detection means and the control target value, the point that the control target temperature of the temperature control systems is different is that This is the first feature.

In this case, as will be clarified in the second component below, the temperature control system is not used under different types of control operations, such as fixing operation and weight control, but under one type of control operation, such as fixing operation. This is based on the premise that multiple temperature control systems are used during control operations.

(2) The second feature is that when controlling the fixing operation, for example, the plurality of control systems are alternately switched to perform predetermined temperature control.

In this case, alternately switching the control system includes both cases where the temperature control system itself is alternately switched, and control signals transmitted from the temperature control system are alternately selected and transmitted to the heater heating control means.

"Function" For example, when the present invention is applied to heating control of a fixing device, if control is performed by alternately switching temperature control systems with different control target temperatures as described above, the fixing roller heating temperature ( As shown in Fig. 2, the detected temperature) forms a rectangular wave at appropriate time intervals. By analyzing the history of detected temperatures for each rectangular wave, in other words, by performing statistical processing, abnormality detection and correction of the pulse width and pulse period of the control signal from the control system can be performed.

Note that the detected temperature is likely to have errors depending on the external environment, so changes in the control signal from the control system may be directly detected.
This allows more accurate abnormality detection and correction of control signals for the control system.

In addition, in recent electrophotographic printers, where the storage heat capacity of the fixing roller is decreasing due to the miniaturization of the device, even if the temperature is maintained accurately by one control system, the recording paper carrying the unfixed toner image is At the insertion start end side, the fixing roller surface temperature decreases and undershoot occurs, and each time the insertion ends, the fixing roller surface temperature increases and overshoot occurs, making it impossible to maintain accurate temperature control.

Therefore, before the recording paper is intermittently inserted, the second temperature control system with a higher control target value is preheated, and the first temperature control system is switched to the first temperature control system in conjunction with the insertion of the recording paper into the fixing roller. By switching to , the fixing operation is performed using the control target value controlled to be lower by the first temperature control system, thereby eliminating both of the above-mentioned drawbacks and enabling accurate temperature control.

Immediately after inserting the recording paper, residual heat from the control target value of the second temperature control system, which is set higher, eliminates undershoot, and at the end of insertion, the control target value, which is set lower by the first temperature control system, eliminates overshoot. This makes it possible to control the temperature with high accuracy.

"Embodiments" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to page v4. However, unless otherwise specified, the dimensions, materials, shapes, and relative arrangements of the components described in this example are not intended to limit the scope of this invention, but are merely illustrative examples. It's nothing more than that.

FIG. 1 shows the basic configuration of the present invention, in which 1 is a heater incorporated in a fixing device (not shown), 2 is a temperature detection means for detecting the surface temperature of the fixing device, and a pair of fixed resistors R1 and R2 are provided. A thermistor disconnection detection means 3 is attached to the ground side of the thermistor R3, and the 7th node side of the thermistor R3 is connected to a detection voltage V.
It is configured such that it can be input to the first temperature control system 4, the second temperature control system 5, and the automatic correction/abnormality detection signal generation means 7, respectively.

As is well known, the temperature control system 4.5 compares the detection voltage V with a target voltage corresponding to the control target temperature formed by a reference voltage setting circuit (not shown), and adjusts the frequency in proportion to the difference voltage between the two. Alternatively, it is configured to be able to transmit a control signal whose pulse width is modulated or a level signal formed using a target voltage as a reference (hereinafter referred to as a control signal) to the control system switching selection means 6.

Note that the target temperature of the second temperature control system 5 is set slightly higher than the control target temperature of the first temperature control system 4.

Incidentally, the temperature control system 4.5 is the first temperature control system used during the fixing operation.
and a third temperature control system necessary for weight control in addition to the second temperature control system.
Although a temperature control system is required, it is omitted in this embodiment.

The control system switching selection means a is formed by a CPU, and selects the temperature control system 4 based on a built-in timer or a switching signal generated based on a print signal from the host side as described later.
.

The switching signal is also sent to the signal generating means 7, which generates signals for abnormality detection and signal correction of the temperature control system 4.5, as described later, based on the count value etc. generated each time the signal is switched. By transmitting the signal from the signal generation means 7 to the control system switching selection means B, the control system 4.5 is selected and the signal generated from the control system is corrected.

The signal generation means 7 is formed of a CPU that has a built-in circuit and a counter that sets the reference temperature S between the control target values, a register that temporarily stores the counter value, and a plurality of comparators, etc. The counter is started by inputting a signal and stopped when the detected temperature reaches the reference temperature S. The comparator compares each count value (rising or falling) and compares it with the abnormality judgment signal described later. Generates dynamic compensation signals, etc.

FIG. 5 shows a schematic configuration of a laser printer incorporating such a temperature control circuit, and since the configuration is already known, it will be briefly explained. Paper is fed into the apparatus based on the signal Pr, and after being guided to the transfer position of the photosensitive drum 13 in synchronization with the registration rollers 12, it is transferred to the fixing device 14 while transferring the toner carried on the drum 13 onto the recording paper. After a jam is detected by a jam detection sensor 15 located on the population side, the toner image is guided to a fixing device 14, and the unfixed toner image is fixed in the fixing device 14.

Next, the operation of this embodiment will be explained based on the temperature distribution diagram of FIG. 2.

First, when a print start command Sr is inputted from the host side to the control system switching selection means 6 from the wait control state, first, the first temperature control system 4 starts up the control target value 〒1 and maintains that temperature. In this state, when the print signal Pr is input from the host side, the temperature control system 5 is switched to the second temperature control system 5 and the control target value rises to 〒2. At the same time as the start-up, the print signal Pr is also input to the signal generating means 7 to start the counter and stop when the detected temperature reaches the reference temperature S to obtain the first comparison value old.

On the other hand, since the jam detection sensor 15 is arranged at a position immediately before the recording paper on the input side of the fixing device 14 is introduced into the fixing device 14, the jam detection sensor 15 uses the jam detection signal Jc as a switching signal, and uses the jam detection signal Jc as a switching signal. At the same time as input, the temperature is switched to the first temperature control system 4, and the temperature is lowered to the control target value TI.
At the same time, a counter in the signal generating means 7 is started based on the switching signal and stopped when the detected temperature reaches the reference temperature S to obtain a second comparison value H2.

In addition, in the state where the print signal Pr is output, it is in a stable state after the fixing of the previous recording paper has been completed, and therefore there is less possibility that variation will occur in the start-up energy (count time) to reach the control target value T2. In addition, the jam detection signal Jc is generated just before the recording paper is introduced into the fixing device 14 (therefore, at the falling point, the recording paper is in the state immediately after being inserted into the fixing device 14), and therefore, the recording paper is not stolen. This converts into thermal energy, allowing stable shutdown without being affected by the external environment.

Therefore, it is possible to automatically correct the control signal of the temperature control system and determine whether the control system is abnormal or not depending on whether or not the quantity comparison value H1 is within the following range.

In order to facilitate comparative judgment, the reference voltage (temperature) is calculated based on the startup time from the first control target value TI to the reference temperature S and the second control target value in the case of normal print fixing operation. The reference temperature S is set so that the start-up time from T1 to the reference temperature S is approximately the same.

For example, if the ideal count value is R1 and the range of normal variation caused by the influence of the external environment is α, then if the comparison values H1 and H2 are within the range of R±α, it is considered to be within the normal variation range, and By sending a correction signal according to the variation to the control system switching selection means 8, each temperature control system 4.5
By making the control signal transmitted from the control signal correspond to the correction signal within the selection means 6 and performing automatic correction, a so-called learning function is activated, and optimal temperature control can be performed at all times.

If the comparison value OLD exceeds R±α, it is determined that the temperature control system that exceeded the value is at fault since it cannot be corrected even by automatic correction, and the display section 9 displays this fact. At the same time, an abnormality signal is sent to the switching selection means 6 to forcibly stop the corresponding temperature control systems 4 and 5 via the power cutoff means 8d and 8b until the temperature control systems 4 and 5 are repaired. The fixing operation is controlled only by the other fllllTk5.4 without performing any switching operation.

According to this embodiment, abnormality detection and automatic correction can be performed without providing an independent protection circuit, and 1. Before the recording paper is inserted, the second temperature control system 5 with a higher control target value T2 is always switched to the second temperature control system 5 for backup. The fixing device 14a is heated in order to keep it heated.
Even in a printer where the accumulated heat capacity of the printer is reduced, the residual heat of the control target value T2 is used to perform a soft landing to the control target value TI, thereby eliminating undershoot and enabling accurate temperature control.

In the above embodiment, the control signal itself generated by the temperature control system 4.5 is not grasped, but the temperature change state of the rising or falling of the fixing device 14a heated by the control signal is grasped and automatic correction is performed. Since it detects abnormalities, time delays are likely to occur.

FIG. 3 shows an embodiment in which such a control signal itself can be grasped directly.The differences from the previous embodiment will be mainly explained.This embodiment uses a built-in timer from the control system switching selection means 60 during the fixing operation. Based on this, the first temperature control system 4 and the second temperature control system 5 are alternately switched to perform the fixing operation while changing the surface temperature of the fixing roller 14a in a rectangular waveform with a slight temperature difference.

With this configuration, the thermal load on the fixing device is not necessarily stable depending on whether or not the recording paper is inserted.

Therefore, in this embodiment, as shown in FIG. 4, each time the control target value 1 is changed, the pulse width of the control signals IPi and 2Pi is changed by the number of clocks when the surface temperature of the fixing device 14a is stabilized at the target value. Temporary storage means 70 is provided for counting and storing the count values l5Pi, 2SPi.
is statistically processed, and if the count values l5Pi and 2SPi are in the range of Xi±36 due to normal distribution, (SL7
%) within the normal variation range, and the control signal of the control system is automatically corrected in accordance with the variation.

When the count value exceeds X±36, it is determined that the control system is malfunctioning, and the same operation as in the previous embodiment is performed.

According to this embodiment, since the control signal itself can be directly grasped, there is no time delay, and the count value is not generated by setting a reference temperature as in the previous embodiment, but based on historical data. Because it grasps pulse signals and statistically generates automatic correction signals and abnormality detection signals,
There is no need for setup work to set the reference temperature, and the -layer preference is I/%.

"Effects of the Invention" As described above, according to the present invention, the backup control system for the buffer 2 is effectively utilized to enable abnormality detection without providing an independent protection circuit for abnormality detection. In addition to this, it also makes it possible to grasp the control status of the control system and automatically correct it, making it possible to perform accurate temperature control and abnormality detection, and because it eliminates the need for an independent protection circuit, the structure is simple. become

Further, according to the present invention, even in a device to be heated which intermittently loses heat due to a heat load, such as a laser printer, the printing interval varies depending on the image processing operation of the host side. Even when the accumulated heat capacity of the heated object is reduced in response to miniaturization, optimal temperature control is always possible.

It has various effects such as

[Brief explanation of drawings]

1 and 3 are circuit block diagrams showing a temperature control device according to an embodiment of the present invention, FIG. 2 is a temperature distribution in each embodiment of FIG. 1, and FIG. 4 is a temperature distribution in each embodiment of FIG. 2. It is a diagram. FIG. 5 is a schematic diagram of a laser printer incorporating the circuit shown in FIG. 1.

Claims (1)

[Scope of Claims] 1) A plurality of temperature control systems are provided with different control target values for controlling the energization of the heater incorporated in the heated object based on the temperature detected by the temperature detection means and the control target value, Temperature control circuit for a heated object characterized by performing predetermined temperature control while alternately switching the plurality of control systems under one control operation 2) Temperature detection during or before and after the switching operation of the temperature control system 3) The temperature control system according to claim 1, wherein the temperature control circuit is configured to be able to grasp the output change from the means in time series or history, and determine the operating state of the temperature control circuit based on the amount of change. 2. The temperature control circuit according to claim 1, wherein the temperature control circuit is configured to be able to grasp signal changes from the control system in time series or history during or before and after the switching operation, and determine the operating state of the temperature control circuit based on the amount of change. Temperature control circuit 4) In a temperature control circuit that performs heating control of a heated object that is intermittently heat-absorbed by a heat load, at least a second temperature having a relatively high control target value before the heat load is intermittently heat-absorbed. The temperature control circuit according to claim 1, wherein the temperature control circuit is configured to perform preliminary heating by the control system and to be able to switch to the first temperature control system in conjunction with the heat removal operation by the heat load.