JPH11237813A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection accuracy of the abnormal output of a middle high voltage power source with respect to the image forming device of an electrophotographic system. SOLUTION: A comparator 3 compares a feed-back signal from a high voltage power source (the middle high voltage power source) 2 with a comparison voltage Vref (an upper limit value previously set), and generates an external interruption signal only when the feed-back signal exceeds the comparison voltage Vref. A CPU 1 detects the leakage (the abnormal output) of the high voltage power source 2, based on the external interruption signal generated by the competitor 3. For instance, the leakage of the high voltage power source 2 is detected by the number of generation times of the external interruption signal within a fixed time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine provided with a digital control type medium-voltage power supply.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, in order to apply a bias to loads such as a charging section, a developing section, a transfer section, a separating section, and a cleaning section, a medium-high voltage power supply (hereinafter also referred to as a "high voltage power supply") is used. Is essential).

Conventionally, such a high-voltage power supply is of an analog control type, and an output feedback circuit, a PWM (pulse width modulation) control circuit, an output short-circuit (leakage) detection circuit and the like have been constituted by analog circuits. In order to reduce the size and cost of the high-voltage power supply, a digitally controlled high-voltage power supply in which a conventional analog circuit is replaced by a digital circuit is used.

A flyback type output current feedback type digitally controlled high voltage power supply which is a digitally controlled high voltage power supply will be described with reference to FIG. FIG. 6 is a circuit diagram showing a configuration example of a flyback type output current feedback digitally controlled high-voltage power supply. This high-voltage power supply is a negative-output constant-current control high-voltage power supply, and includes a high-voltage transformer T, a switching transistor Tr (or FET), a current detection resistor r, and a diode D.

The control of the high-voltage power supply configured as described above is performed by a CPU (microcomputer) not shown.
Switching transistor Tr directly on / off
The duty of the PWM signal is calculated and controlled so that the output feedback signal matches a preset target value. Specifically, when the feedback signal is lower than the target value, the duty of the PWM signal is widened, and when the feedback signal is higher than the target value, control is performed to narrow the duty of the PWM signal.

The load of the high-voltage power supply includes a charge wire, a roller for applying a bias, and the like. However, these loads often fluctuate significantly depending on the environment, transfer paper, mechanical accuracy, and the like. Therefore, constant current or constant voltage control is performed.
The output of the high-voltage power supply may discharge abnormally (leak) due to a remarkable change or abnormality on the load side. Normally, a leak is detected based on feedback data (data obtained by converting a feedback signal by an A / D converter) or a duty of a PWM signal for driving a transformer of a high-voltage power supply.

Here, as well as control of the high voltage power supply, sampling of feedback data is also started by timer interrupt processing, and feedback data is read by an A / D conversion end interrupt or timer interrupt. Output (load) if the value of feedback data exceeds this value in control
Is set to an upper limit value for making an error. Usually, a leak detection counter is provided for judging a leak when the upper limit is exceeded only once, but not when the limit is exceeded several times. The leak detection counter turns off the output of the high-voltage power supply after a certain time has elapsed.
Cleared when it becomes.

[0008]

However, the output waveform at the time of occurrence of a leak does not become a constant level as shown in FIG. Conventionally, feedback data is sampled (read) at a predetermined sampling interval. Therefore, when the value of the feedback data exceeds the upper limit, the feedback data cannot always be sampled.

In FIG. 7, feedback data exceeding the upper limit value can be sampled only at point A. For this reason, leak (output abnormality) detection may not be performed in some cases, leading to a decrease in the reliability of leak detection. The present invention has been made in view of the above points, and has as its object to improve the accuracy of detecting an output abnormality of a high-voltage power supply in an image forming apparatus.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a digitally controlled medium-to-high voltage power supply, and a microcomputer for controlling the output of the medium and high voltage power supply by a PWM signal generated in response to a feedback signal from the medium to high voltage power supply. In order to achieve the above object, an image forming apparatus provided with:

According to a first aspect of the present invention, an external interrupt which generates an external interrupt signal only when a feedback signal from a medium-to-high voltage power supply is compared with a preset upper limit value and the feedback signal exceeds the upper limit value is provided. An interrupt signal generating circuit is provided, and the microcomputer detects an abnormality in the output of the medium-voltage power supply based on an external interrupt signal generated from the interrupt signal generating circuit. According to a second aspect of the present invention, the microcomputer detects an abnormality in the output of the medium-to-high voltage power supply based on the number of times the external interrupt signal is generated within a predetermined time.

[0012]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a circuit diagram illustrating a configuration example of a main part of an image forming apparatus according to an embodiment of the present invention.

In this image forming apparatus, reference numeral 1 denotes a microcomputer (hereinafter referred to as a "CPU"), an external interrupt processing section (IRQ) 1a, an A / D converter 1b, and a PW
It has a function as an M timer 1c. If the CPU 1 does not have these functions, those functions may be achieved by peripheral devices. The PWM timer 1c has the above-described leak detection counter and a clear counter that clears the leak detection counter within a certain time.
The high voltage power supply 2 is a digital control type high voltage power supply shown in FIG.

A first embodiment is provided between the CPU 1 and the high-voltage power supply 2.
A circuit corresponding to the external interrupt generation circuit of
The circuit includes a comparator 3 and a filter circuit including a resistor R and a capacitor C. The feedback signal from the high voltage power supply 2 is the same as the conventional
It is input to the A / D converter 1b of U1. The output of the comparator 3 is input to the external interrupt processing unit 1a of the CPU 1. The output signal (PWM) of the PWM timer 1c of the CPU 1
Signal) is input to the high-voltage power supply 2.

Next, control according to the present invention in the image forming apparatus of this embodiment will be described with reference to FIGS. 1 compares the feedback signal from the high-voltage power supply 2 with a comparison voltage (preset upper limit) Vref, and generates an external interrupt signal only when the feedback signal exceeds the comparison voltage Vref. . For example, as shown in FIG. 5, when a leak occurs, the feedback signal exceeds the comparison voltage Vref.
An external interrupt signal is generated for PU1.

The CPU 1 detects a leak (output abnormality) of the high-voltage power supply 2 based on an external interrupt signal generated from the comparator 3. For example, as shown in FIG. 2, the leak detection counter is counted up (+1) in the interrupt processing.
If the count value reaches a preset value (the number of leak detections), it is determined that a leak has occurred, and a leak occurrence process is performed. That is, it notifies that the output of the high-voltage power supply 2 has stopped or that a leak has occurred in the sequence of the machine.

On the other hand, when the first timer interrupt occurs, as shown in FIG. 3, for example, it is first determined whether or not the output timing of the high voltage power supply 2 has been reached. After the start of the / D conversion, the clear counter is counted up, and when the value reaches a preset value (clear time), the leak detection counter is cleared. The reason why the leak detection counter is cleared each time the value of the clear counter reaches a preset value (every fixed time) is to always detect a leak under the same condition.

When a second timer interrupt (or a first timer interrupt) occurs, for example, as shown in FIG. 4, it is first determined whether or not the output timing of the high voltage power supply 2 has been reached. Feedback data (A
/ D conversion data) and reads P based on the data.
An arithmetic process for determining the duty of the WM signal is performed.

When the duty of the PWM signal is determined, the PWM signal is output to the high voltage power supply 2 at the duty. If the output timing of the high-voltage power supply 2 is not the timing when the second timer interrupt occurs, the output of the PWM signal to the high-voltage power supply 2 is stopped, and the leak detection counter is cleared.

As described above, in the image forming apparatus of this embodiment, the comparator 3 compares the feedback signal from the high-voltage power supply 2 with the comparison voltage Vref (predetermined upper limit), and the feedback signal is compared with the comparison voltage Vr.
An external interrupt signal is generated only when ef is exceeded. Then, the CPU 1 detects a leak of the high voltage power supply 2 based on an external interrupt signal generated from the comparator 3. For example, the leak of the high voltage power supply 2 is detected based on the number of occurrences of the external interrupt signal within a certain time. Therefore, the leak of the high voltage power supply 2 is detected in real time, and the detection accuracy of the leak of the high voltage power supply 2 is improved.

[0021]

As described above, according to the image forming apparatus of the present invention, the detection accuracy of the output abnormality of the middle and high voltage power supply is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration example of a main part of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an example of an external interruption process by a CPU 1 of FIG. 1;

FIG. 3 is a flowchart showing an example of a first timer interrupt process.

FIG. 4 is a flowchart showing an example of a second timer interrupt process.

5 is a diagram showing an example of a relationship between an external interrupt signal by a comparator 3 in FIG. 1 and an output waveform of a high-voltage power supply 2. FIG.

FIG. 6 is a circuit diagram illustrating a configuration example of a flyback type output current feedback digitally controlled high-voltage power supply.

FIG. 7 is a diagram illustrating an example of a relationship between a sampling interval of feedback data (data after A / D conversion of a feedback signal from a high-voltage power supply) by a CPU and an output waveform of a high-voltage power supply in a conventional image forming apparatus.

[Description of Signs] 1: Microcomputer (CPU) 2: High-voltage power supply 3: Comparator

Claims (2)

[Claims] 1. An image forming apparatus comprising: a digital control type medium / high voltage power supply; and a microcomputer which controls an output of the medium / high voltage power supply by a pulse width modulation signal generated in response to a feedback signal from the medium / high voltage power supply. An external interrupt signal generating circuit that compares a feedback signal from the medium-voltage power supply with a preset upper limit value and generates an external interrupt signal only when the feedback signal exceeds the upper limit value is provided. An image forming apparatus, wherein the microcomputer detects an abnormality in the output of the medium-voltage power supply based on an external interrupt signal generated from the interrupt signal generating circuit. 2. The image forming apparatus according to claim 1, wherein the microcomputer detects an abnormality in the output of the medium-voltage power supply based on the number of times the external interrupt signal is generated within a predetermined time. .