JP2002058241A - High-voltage power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten rise time while preventing the overshoot at the start-up of drive, in a high-voltage power supply device. SOLUTION: In a high-voltage power supply device which has a high-voltage generating circuit which includes a high-voltage transformer which generates the output geared to the on-off duty, with its primary side turned on or turned off by switching means, and a control means which monitors, as a feedback signal, the signal from an A/D converter which receives the input of the high- voltage output of the above high-voltage generating circuit, and compares the output feedback value by the above feedback signal with the objective output value in every fixed cycle, and operates and updates the above on-off duty from the comparison results, the above control means makes the above on-off duty a fixed value without recourse of the feedback control by the above output feedback value at the start-up of output only.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage power supply, and more particularly to a high-voltage power supply used as a high-voltage power supply for an image forming apparatus such as a copying machine, a facsimile, and a printer using an electrophotographic process. is there.

[0002]

2. Description of the Related Art As a high-voltage power supply for a copying machine, a facsimile, a printer, or the like by an electrophotographic process, a high-voltage generator including a high-voltage transformer whose primary side is turned on and off by switching means and generates an output corresponding to the on-off duty. A high-voltage output of the high-voltage generating circuit
It is input to a D converter and monitored as a feedback signal, and a microprocessor (CPU) compares the output feedback value by the feedback signal with a target output value at regular intervals, and determines the on / off duty from the comparison result. Update the operation,
2. Description of the Related Art A high-voltage power supply device of an arithmetic control system capable of outputting a high voltage having an arbitrary target output value by duty (duty ratio) control is known. This type of high-voltage power supply is disclosed, for example, in Japanese Patent Application Laid-Open No. 9-218567.

In the electrophotographic process, the effect of applying an overcurrent or overvoltage to a photosensitive member, a developing roller, or the like as a recording medium deteriorates their characteristics over time and greatly contributes to image quality. Therefore, it is important to control the high-voltage output of a high-voltage power supply used in a copying machine, a facsimile, a printer, or the like by an electrophotographic process.

A microprocessor mounted on a copying machine, a facsimile, a printer, or the like by an electrophotographic process includes:
It is rarely installed exclusively for controlling the high-voltage power supply unit.From the viewpoint of downsizing of the apparatus and cost, control of other parts of the image forming apparatus, for example, motor control of recording paper conveyance, taking in of various sensors, and image formation. Many control optical writing. For this reason, the control of the high-voltage power supply is performed by taking into account the load of the microprocessor, performing calculations at intervals of several tens of milliseconds by means of a timer interrupt, and updating the drive pulse duty at that time interval.

[0005]

In the image forming conditions of the electrophotographic process, it is necessary to supply a minimum necessary charge to the recording medium.
The start-up characteristics such as fall time, overshoot, and undershoot must be satisfied under severe conditions. In the conventional high-voltage power supply device as described above, the image quality is reduced by the start-up characteristics such as slow start-up and large overshoot. It can be significantly impaired.

Further, in the above-mentioned conventional high-voltage power supply device, in the high-voltage drive by the arithmetic control of the microprocessor, the control interval is performed at intervals of several tens of milliseconds as described above, so that the starting characteristic has a reaction. Phenomena, such as slowing down of the image and overshoot cannot be suppressed.

A feedback value for monitoring the output of the high-voltage power supply is obtained by current-voltage conversion by a resistor in the case of constant voltage control and by a resistor in the case of constant current control. In this case, if the feedback value is to be set for the entire range of the possible output of the high voltage output, it is necessary to lower the resolution of the A / D conversion, and the control width is inevitably reduced, and the control accuracy is reduced. .

Further, in this method in which the drive duty of the next cycle is determined by calculation based on the feedback value of the A / D converter, if the feedback value greatly fluctuates due to noise when the feedback value is fetched, the output is correspondingly changed. There is a problem that the fluctuation increases and the phenomenon appears in the image.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the rise time while preventing overshoot at the start of driving, to achieve high control accuracy, and to provide a feedback value due to noise. It is an object of the present invention to provide a high-voltage power supply device that performs stable output of a high-voltage power supply without reacting to erroneous detection.

[0010]

In order to achieve the above object, a high voltage power supply according to the first aspect of the present invention has a primary side turned on / off by a switching means, and generates an output corresponding to the on / off duty. A high-voltage generating circuit including a high-voltage transformer that performs
Control means for inputting to the converter and monitoring this as a feedback signal, comparing an output feedback value by the feedback signal with a target output value at regular intervals, and calculating and updating the on / off duty from the comparison result. In the high-voltage power supply device, the control unit sets the on / off duty to a fixed value only at the time of starting output without using feedback control by the output feedback value.

According to the first aspect of the present invention, the ON / OFF duty for driving the high-voltage transformer is set to a fixed value only at the time of starting the output without relying on the feedback control based on the output feedback value.

The high-voltage power supply according to the second aspect of the present invention further includes an environmental temperature / humidity detecting means installed in the high-voltage power supply for detecting the environmental temperature / humidity.
The fixed value of the on / off duty at the start of output is set according to the environmental temperature / humidity detected by the environmental temperature / humidity detecting means.

According to the second aspect of the present invention, at the start of output, the on / off duty for driving the high voltage transformer is set according to the environmental temperature and humidity.

Further, in the high voltage power supply according to the third aspect of the present invention, the primary side is turned on / off by switching means,
A high-voltage generating circuit including a high-voltage transformer for generating an output corresponding to the on / off duty; a high-voltage output of the high-voltage generating circuit being input to an A / D converter and monitoring it as a feedback signal; Control means for comparing the output feedback value based on the feedback signal with the target output value and calculating and updating the on / off duty based on the comparison result, wherein the high-voltage output feedback signal is supplied to the A / D converter. Means for switching two or more resistance values of a detection resistor for conversion so as to be fetchable,
The resistance value of the detection resistor is switched depending on whether the output feedback value taken by the converter is within a predetermined range.

According to the third aspect of the present invention, the resistance value of the detection resistor is switched depending on whether the output feedback value received by the A / D converter is within a predetermined range.

According to a fourth aspect of the present invention, in the high-voltage power supply device, the operation update is reflected in the drive duty of the next cycle only when the predetermined value is continuously out of the predetermined range when the feedback output value is fetched. Is switched and imported.

According to the fourth aspect of the present invention, the operation update is reflected in the drive duty of the next cycle and the resistance of the detection resistor is switched and fetched only when the feedback output value is continuously deviated from the predetermined range. Is performed.

[0018]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of a high-voltage power supply according to the present invention.

The high-voltage power supply has a high-voltage generating circuit 10 including a high-voltage transformer 12 whose primary side is turned on and off by a switching transistor 11 and generates an output corresponding to the on-off duty, a CPU 20, a PWM generator 21 and , An A / D converter 22 for inputting a high-voltage output of the high-voltage generation circuit 10 as a feedback signal, and a temperature / humidity sensor 23.

In a copying machine, a facsimile, a printer, or the like, the CPU 20 controls the entire apparatus, such as taking in various sensors and controlling optical writing, and has a timer function internally. / D
The output feedback value A / D-converted by the converter 22 is compared with the target output value, and the driving condition of the high-voltage power supply is calculated and updated in a feedback control manner so as to eliminate the deviation. This calculation update is repeatedly performed by a timer interrupt until the high voltage output stop timing.

The PWM generator 21 generates an on / off duty pulse signal under necessary driving conditions, turns on / off the switching transistor 11 according to the on / off duty, and drives the high voltage transformer 12.

The temperature / humidity sensor 23 is a sensor for grasping the environmental conditions in which the high-voltage power supply device is arranged. The temperature / humidity sensor 23 detects the environmental temperature / humidity, and an output signal is input to the A / D converter 22. A / D-converted.

Next, a basic calculation update of the high-voltage power supply driving condition will be described with reference to FIG. The CPU 20
If it is determined by the flag that it is the output start timing (Yes at step S201), the current timer interrupt (here, a 10ms interrupt) is input (step S202 affirmative) to synchronize the operation update with the current timer. The high voltage output (A / D conversion value = output feedback value) is fetched from the A / D converter 22 (step S203), the difference between the target output value and the A / D conversion value is determined (step S204), and a predetermined arithmetic expression 1 is calculated (step S205), and the pwm is updated (step S205).
206). This is continuously performed every 10 ms until the output is stopped (step S207).

Equation 1 multiplies the difference between the A / D conversion value and the target output value by an operation coefficient, and increases / decreases the current pwm set value. Specifically, it is shown by equation (1). New pwm set value = current pwm set value + (difference between A / D conversion value and target output value × operation coefficient) (1)

When the output of the high-voltage transformer 12 is smaller than the target output, the ON width of the pwm duty is increased.
Calculation is performed so that the ON width of wm duty is reduced.
If the difference (deviation) between the A / D conversion value and the target output value is large, the increase / decrease of the pwm duty becomes large, and if the difference is small, the increase / decrease is updated small.

At this time, if the output is 0 when the output rises, the difference between the target value and the A / D conversion value of the current output becomes the largest. The pwm duty amplification is a value close to the maximum.

In such a case, depending on the load condition,
There is a possibility that overshoot may occur, and if an attempt is made to suppress the occurrence of overshoot, a problem arises that it takes a long time to start up.

With reference to FIG. 3, a description will be given of updating the pwm operation at the time of startup to prevent the occurrence of overshoot and to minimize the rise time with reference to FIG.

At the output start timing when the output flag is turned on (Yes at step S301), the output power exceeds the power supply condition and load condition assumed based on the use conditions in advance, based on the characteristics of the pwm duty output as shown in FIG. Pwm duty that shoots cannot occur, for example, ma in the figure
pw where overshoot between x and min cannot occur
Set m duty (type). This pwm duty is set as a fixed open duty at the time of the first setting (step S302).

This makes it possible to shorten the rise time while preventing overshoot at the start of driving, thereby eliminating the influence on the image quality.

At this time, the output for the open duty changes greatly depending on the process load. However, the process load greatly varies depending on environmental conditions, and the load is always started with a fixed open duty. Characteristics cannot be optimized. Therefore, environmental conditions are captured by the temperature / humidity sensor 23, the impedance of the load is predicted based on the values, and the open duty is determined and controlled.

This makes it possible to shorten the rise time while preventing overshoot at the start of driving in response to a change in the load impedance of the high-voltage power supply due to environmental conditions, thereby eliminating the effect on image quality.

When a 10 ms interrupt, which is the next operation update timing, occurs under the drive condition of open duty (Yes at step S303), the A / D conversion value of the current output whose output is being monitored is fetched and a certain value a If it is smaller or larger than a certain value b (Yes at step S304), the next time (after 10 ms) the feedback value is fetched, the current detection resistor 1 (using the detection resistor 1 at the start of output) is continuously used. (Step S30)
5), the entire output range is set to a resistance value that can be monitored, and the calculation is updated (step S308). The feedback characteristic of the detection resistor 1 is shown in FIG.

On the other hand, if the A / D conversion value of the current output is a ≦
If the feedback value ≤ b (Yes at step S306), the detection resistor is switched to the detection resistor 2 such that the feedback voltage change width with respect to the output becomes large in the vicinity of the set output, and the next capture is performed (step S307). ), And update the calculation (step S308). The feedback characteristic of the detection resistor 2 is shown in FIG.
Is shown in As a result, the range of change of the feedback value with respect to the output can be made large, control accuracy can be improved, and a stable high-voltage power supply output can be obtained. The above control is performed every 10 ms until the output is stopped (step S309).

Under a process condition that does not cause a sudden load change during output, a large change in the feedback voltage may be caused by a sudden noise. After entering, even if a value outside this range is detected once at the time of capturing, the resistance is not switched and the calculation result is not updated. The calculation result is reflected only when it continuously deviates from this range,
/ D capture.

As a result, a stable high-voltage power supply output can be obtained so as not to react to erroneous detection of the feedback value due to noise.

At the end of the output (Yes at Step S309), at the next 10 ms interrupt timing (Step S309).
310) In order to prevent the occurrence of undershoot when driving is stopped from the driving pwm duty, before stopping, pwm in which undershoot cannot occur under the power supply condition and load condition assumed based on use conditions in advance The duty is set as a closed duty (step S311), and the output is stopped.

[0038]

As can be understood from the above description, according to the high voltage power supply of the present invention, the on / off duty for driving the high voltage transformer is limited to the feedback control based on the output feedback value only at the start of output. The rise time is shortened while preventing overshoot at the start of driving to determine the operation coefficient that determines the driving duty of the next cycle from the output feedback value at that ON / OFF duty And the effect on image quality can be eliminated.

According to the high voltage power supply of the second aspect, the on / off duty at the start of output is set in accordance with the environmental temperature and humidity, so that the high voltage power supply is driven in response to a change in load impedance of the high voltage power supply due to environmental conditions. The rise time can be shortened while preventing the overshoot at the start, and the influence on the image quality can be removed.

According to the third aspect of the present invention, the resistance value of the detection resistor is switched depending on whether or not the output feedback value received by the A / D converter is within a predetermined range. When the feedback value is within the predetermined range, the variation range of the feedback value with respect to the output can be made large, and the control accuracy is improved and a stable high-voltage power supply output is obtained.

According to the high voltage power supply device of the present invention, when the output feedback value falls within the predetermined range and the detection resistance is switched, the operation is updated in the next cycle only when the detection feedback is continuously deviated from the predetermined range. The detection resistance can be switched to the original value and taken in by reflecting the duty, and a stable high-voltage power supply output can be obtained so as not to react to erroneous detection of the feedback value due to noise.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a high-voltage power supply device according to the present invention.

FIG. 2 is a flowchart illustrating a basic calculation update process of a high-voltage power supply driving condition.

FIG. 3 is a flowchart showing a process for updating the high-voltage power supply driving conditions in the high-voltage power supply according to the present invention.

FIG. 4 is a graph showing output-feedback characteristics for different detection resistors.

FIG. 5 is a graph showing duty output characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 High voltage generation circuit 11 Switching transistor 12 High voltage transformer 20 CPU 21 PWM generator 22 A / D converter 23 Temperature / humidity sensor

Claims (4)

[Claims] The primary side is turned on by a switching means.
A high-voltage generating circuit including a high-voltage transformer that is turned off and generates an output corresponding to the on / off duty; a high-voltage output of the high-voltage generating circuit is input to an A / D converter and monitored as a feedback signal; A high-voltage power supply device comprising: a control unit for comparing an output feedback value and a target output value by the feedback signal with each other, and calculating and updating the on / off duty from the comparison result. A high-voltage power supply device wherein the on / off duty is set to a fixed value without relying on feedback control based on the output feedback value. 2. The environment temperature and the temperature installed in the high-voltage power supply.
An environmental temperature / humidity detecting means for detecting humidity, wherein the control means sets the fixed value of the on / off duty at the start of output according to the environmental temperature / humidity detected by the environmental temperature / humidity detecting means The high-voltage power supply device according to claim 1, wherein: 3. The primary side is turned on by switching means.
A high-voltage generating circuit including a high-voltage transformer that is turned off and generates an output corresponding to the on / off duty; a high-voltage output of the high-voltage generating circuit is input to an A / D converter and monitored as a feedback signal; Control means for comparing an output feedback value by the feedback signal with a target output value every time and calculating and updating the on / off duty based on the comparison result. Means for switching two or more resistance values of a detection resistor for conversion so as to be able to be taken in by a converter, and wherein an output feedback value taken by the A / D converter is within a predetermined range. A high-voltage power supply device, wherein a resistance value of the detection resistor is switched depending on whether or not the voltage is detected. 4. The method according to claim 1, wherein when the feedback output value is fetched continuously, the calculation update is reflected in the drive duty of the next cycle and the resistance of the detection resistor is switched and fetched only when the value falls outside the predetermined range continuously. 4. The high-voltage power supply device according to 3.