JP2002281755A - High voltage power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a high voltage power source which can improve the quality of image by preventing unstable output due to the oscillation. SOLUTION: This high voltage power supply comprises a PWM generator 2 which can optionally set the ON/OFF duty and a high voltage transformer which generates an output depending on such duty. Therefore this high voltage power supply is characterized in that a feedback signal of the high voltage output is monitored with an A/D converter 3 and calculation is conducted in every constant period using the monitored output feedback signal. Thereby, a calculation coefficient for determining update width of PWM is determined with variation width of an output feedback value for the update width of PWM obtained from the update result of calculation by the predetermined calculation formula.

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 for an image forming apparatus such as a copying machine, a facsimile and a printer using an electrophotographic process.

[0002]

2. Description of the Related Art Conventionally, a microprocessor CPU, a timer, and an A / D converter have been provided as a control method of a high voltage power supply for a copying machine, a facsimile, a printer, etc. by an electrophotographic process, and each high voltage output is A / D converted. The operation of the switching transistor for controlling the high-voltage transformer is controlled by the CPU, and the switching duty of the switching transistor for driving the high-voltage transformer is controlled based on the comparison result between the current output feedback value from the A / D conversion and the target output at regular intervals. A high-voltage power supply that outputs high voltage is mounted.

[0003]

However, in the above-mentioned prior art, the load of the high-voltage power supply in the electrophotographic process is such that the impedance of the roller to be applied and the photoreceptor itself is wide and the image quality is high. In many cases, the output set value differs depending on the environment in which the apparatus is placed and the type and size of the recording paper, and the output range and load range become very wide.

As described above, if a constant control is performed for a device having a wide output range and a wide load range, the start-up characteristics vary greatly depending on the load condition, and the image may be affected. In particular, the rise time or the overshoot at the rise may affect the image or cause deterioration with time.

In order to improve the start-up characteristics and follow-up characteristics of the rise, when the load is light, the control is over-corrected, and the output oscillates. Will be. In addition, if a high-pressure leak occurs during output, the output drops, and correction is applied from that point of time, which again causes oscillation and it takes time for the output to stabilize after the leak occurs. for that reason,
The image during this period is adversely affected.

The present invention has been made in view of the above problems, and has as its object to provide a high-voltage power supply capable of improving an image by preventing unstable output due to oscillation. I have.

[0007]

According to a first aspect of the present invention, there is provided a high-voltage power supply according to the first aspect of the present invention, comprising a PWM generating means capable of arbitrarily setting an on / off duty, and a high-voltage power supply corresponding to the duty. And a high-voltage power supply having a high-voltage transformer for generating an output, wherein a feedback signal of the high-voltage output is monitored by an A / D converter, and an operation is performed using the output feedback signal monitored at regular intervals. And a calculation coefficient for determining the PWM update width is determined based on a change width of the output feedback value with respect to the PWM update width obtained from the calculation update result of the above.

Further, in the high voltage power supply according to the present invention, the output feedback value for the PWM update width and a target feedback value which the output feedback value is a target in the first aspect. In comparison, when the output feedback value repetitively oscillates at a predetermined value or more with respect to the target feedback value, an arithmetic coefficient determining the PWM update width is changed.

According to a third aspect of the present invention, in the high voltage power supply according to the first or second aspect of the present invention, when the amount of change in the output feedback value becomes a predetermined value or more, It is characterized in that periodic PWM update is not performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the high-voltage power supply according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram showing a configuration of a high-voltage control system for a high-voltage power supply according to an embodiment of the present invention.
In FIG. 1, a CPU 1 controls the entire apparatus such as motor control for recording paper conveyance, taking in of various sensors, and optical writing control, and also has an internal timer function. The operation conditions of the power supply are updated.

The CPU 1 turns on / off the switching transistor under the necessary driving conditions by the PWM generator 2 and drives the high-voltage transformer 4. As a result, the output applied to the high voltage output terminal is fed back to the A / D converter 3 for monitoring, and the CPU 1 calculates and updates the driving condition based on the result of the A / D conversion by the A / D converter 3 at the high voltage output stop timing. Repeat until

The temperature / humidity sensor 5 is a sensor for grasping the environmental conditions in which the apparatus is placed, and takes in the temperature and humidity by the A / D converter 3. With this information, it is possible to predict the impedance of the transfer roller (not shown) and to grasp the moisture absorption state of the recording paper. In addition, the recording paper size sensor 6 has several bits of S.
W is used to detect 7 to 8 types of standard paper sizes, set image areas, and determine high-voltage output values to be applied to transfer rollers.

Next, a basic operation update will be described with reference to FIG. FIG. 2 is a flowchart illustrating a calculation update process of the high-voltage power supply according to the embodiment of the present invention. In FIG. 2, if the output start timing (judgment by the flag) is used (step 201: Yes)
(Y)), in order to synchronize the operation update, the CPU 1 interrupts the internal timer (step 202).
ms interrupt) (Step 202: Y)
Then, the current output is captured by A / D conversion (step 203), the difference from the A / D value of the target output is obtained (step 204), and a PWM set value to be updated is calculated according to a predetermined arithmetic expression 1 (step 205). ), PWM update drive (step 206). This is continuously performed until the output is stopped every 10 ms (step 207: Y).

The calculation formula multiplies the difference between the A / D value obtained above and the target value by an operation coefficient, and increases or decreases the current PWM set value. Specifically, as an expression,

New PWM set value = Current PWM set value + (A / D value difference × Operation coefficient) Equation 1

When the output is smaller than the target output, the on-width of the PWM duty becomes larger, and when the output is larger than the target output, the on-width of the PWM duty becomes smaller. Is calculated. Also,
If the A / D difference is large, the increase / decrease of the PWM duty becomes large, and if the difference is small, the increase / decrease is updated small.

In the actual high voltage output, the PWM duty is set at the output start timing, the driving is started with the initial fixed PWM set value, and the fb value for the output at that time is set to A / D.
After the conversion, the PWM of the next cycle is calculated. The startup characteristics such as the rise time and overshoot are determined by the initial PWM set value, the target output value, and the load condition. For example, if the rise time is to be shortened, the initial PWM
This can be achieved by increasing the set value, but when the load is small, it becomes a factor of causing overshoot.

Similarly, the rise time varies depending on the operation coefficient. As described above, since the starting condition is dominated by the load condition, the initial P
Set the WM set value and calculation coefficient. Based on this control method, assuming that the load is heavy when viewed from the high-voltage power supply, it is necessary to set the operation coefficient so that the update width becomes large to some extent considering the rise time of the output.

For example, if the operation coefficient is set to 1/5. According to the operation formula, if the difference between the output feedback value and the target value (target value-capture feedback value) is 15, PWM is ++ from the current setting.
The value becomes 3. At this time, when the increase / decrease of PWM is ± 1 and the change of the feedback value is ± 60 or more, it is determined that the load is light, and the calculation coefficient is changed to 1/10 to calculate and change the PWM. Reduce the width. By this, 1
The output change in the cycle has a small width, so that oscillation can be prevented.

However, at this time, the difference from the target value increases by reducing the operation coefficient.
Rather than being updated by calculation, the WM is increased / decreased by 1 step, and switching to control that approaches the target output enables more accurate output control. Conversely, when the load suddenly fluctuates in the heavy direction, the width of change in one cycle can be increased by halving the operation coefficient, and the followability is improved.

In addition, if the calculation coefficient setting is not appropriate for the load, overcorrection is repeated, and the phenomenon of output oscillation tends to occur. Once the output oscillation starts, it takes time to converge, so that the effect on the image appears. Cheap. Therefore, the difference between the feedback value and the target value becomes equal to or more than a predetermined value (+ α) by the PWM update. As a result of performing the calculation update with reference to the value, the next fetched feedback value is different from the target value. Is repeatedly detected twice more than a predetermined value (−α), it is determined that the output is oscillating, the operation coefficient is changed to a small value (1/20), and the subsequent operation is performed. Do it.

If the difference between the output feedback value and the target value is twice within ± β, it is determined that the output control has entered a stable period (other than rising), and thereafter, the output feedback value becomes a predetermined value. If the above change occurs, it is determined that the output has changed due to a factor other than a load change such as a leak, and the driving is continued without performing the calculation update. If the feedback value returns to near the target value by the next acquisition, the calculation update is continued as it is, and if the feedback value is not changed (it does not return), the calculation coefficient is increased (1/2) and the update is performed. It is possible to improve the followability with respect to a large change in the output, and to perform output control without overcorrection for a phenomenon that suddenly changes at the moment of the output due to a leak or the like.

In this way, the load impedance is estimated from the change width of the output feedback value with respect to the PWM update width, which is obtained from the calculation update result by the predetermined arithmetic expression. If the change width of the output feedback value is large, the PWM impedance is increased or decreased. The operation update is performed using an operation coefficient that reduces the rate, and when the change width of the output feedback value is small, the operation update is performed using an operation coefficient that increases the PWM update increase / decrease rate, thereby improving the startup characteristics. And a rapid change in impedance can be followed, an unstable output due to oscillation can be prevented, and an image can be improved.

Further, the output feedback value with respect to the PWM update width, which is obtained from the operation update result by the predetermined operation expression, is compared with the target feedback value, and the target value + the predetermined value (α) and the target value-the predetermined value ( If α) is repeatedly detected, the output coefficient can be reduced by suppressing the PWM update width by setting the operation coefficient to a small value, thereby making it possible to prevent unstable output due to oscillation and improve the image. Can be.

If the change width of the output feedback value exceeds a certain value, it is determined that a leak may have occurred, and the calculation of the next cycle is not updated, and the feedback value returns even when the next output feedback value is fetched. Since the calculation update is restarted only when it does not occur, overcorrection for output abnormalities such as instantaneous leaks is not performed, making it possible to prevent unstable output due to oscillation and improve the image. it can.

[0027]

As described above, according to the present invention,
By preventing unstable output due to oscillation, there is an effect that a high-voltage power supply capable of improving an image can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of a high-voltage control system for a high-voltage power supply according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a high-voltage power supply calculation update process according to the embodiment of the present invention;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU 2 PWM generator 3 A / D converter 4 High voltage transformer 5 Temperature / humidity sensor 6 Recording paper size sensor

Claims (3)

[Claims] 1. A high voltage power supply comprising: a PWM generating means capable of arbitrarily setting an on / off duty of switching for driving a transformer; and a high voltage transformer generating an output according to the duty. Is monitored by an A / D converter, an arithmetic operation is performed using an output feedback signal monitored at regular intervals, and a change width of the output feedback value with respect to a PWM update width obtained from a calculation update result by a predetermined arithmetic expression is calculated as follows. A high-voltage power supply for determining an operation coefficient for determining a PWM update width. 2. An output feedback value corresponding to the PWM update width is compared with a target feedback value targeted by the output feedback value, and the output feedback value is repeatedly set to a predetermined value or more with respect to the target feedback value. 2. The high-voltage power supply according to claim 1, wherein when the amplitude is increased, an operation coefficient that determines the PWM update width is changed. 3. The high-voltage power supply according to claim 1, wherein when the amount of change in the output feedback value is equal to or greater than a predetermined value, the next cycle of PWM updating is not performed.