JPH09218567A - High voltage power unit for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance resolution of a feedback signal for constant current control, and to detect an overcurrent abnormality. SOLUTION: This device CPH is composed of a high voltage generating circuit DCC of PWM control, a resistor unit for feeding back its output current I-out, and A/D converter ADC for converting the feedback current into digital data, and constant current controlling means (CNT, PG) for adjusting duty of the PMW signal. In the device, at least tow unit of resistors for feeding back the output currant value is provided to select one of the resistors corresponding to an image forming mode to be executed, and to apply the voltage to the ADC. Then the resolution of the feedback voltage is enhanced. Moreover, a margin is set between the normal feedback voltage area and the upper limit value of A/D converting range, and the overcurrent detection is executed in this margin area.

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 device for an image forming apparatus, for example, a photosensitive member is charged and exposed to form an electrostatic latent image on the photosensitive member, and the electrostatic latent image is developed by a toner. The present invention relates to a power supply device for supplying a high voltage to a high-voltage functional member for charging a photoconductor or for transferring a toner image on the photoconductor onto a recording sheet in image formation of an electrophotographic system for transfer to a sheet.

[0002]

2. Description of the Related Art A high-voltage functional member includes a corona discharger, a charging roller, etc., which is not contacted with or comes into contact with a photoconductor (or recording paper) to apply a high voltage thereto to charge it. FIG. 4 shows an outline of the mechanism of one conventional image forming apparatus. The drum-shaped photoconductor PC is grounded (device ground connection) and rotates in the direction of the arrow. Around the photoconductor PC, a corona discharger CH for charging the photoconductor PC before exposure,
There is a phenomenon device D and a transfer belt B. The transfer roller RB applies a high voltage for transfer to the transfer belt B. Roller RA is grounded. In this example, the corona discharger CH and the transfer belt B are high-voltage functional members, the charging circuit CHP shown in FIG. 5 applies high voltage to the corona discharger CH, and the transfer belt B is transferred via the roller RB. The bias power supply PP applies high voltage.

The photoreceptor PC is charged by the corona discharger CH. Next, the exposure device EXP irradiates the photoconductor PC with image light to form an electrostatic latent image on the photoconductor PC. This electrostatic latent image is developed with toner by the developing device D and is visualized (toner).
Image). The toner image is electrostatically attracted to the recording paper sent onto the transfer belt B to which the transfer bias is applied. That is, a toner image is transferred to the recording paper by applying a bias having a polarity opposite to the electric charge of the toner from the back surface of the recording paper via the transfer belt B. The recording paper carrying the toner image is separated from the transfer belt B, and the toner image is fixed on the transfer paper by passing through a fixing device F including a fixing roller RF and a pressure roller. On the other hand, the cleaning device C removes paper dust and a small amount of untransferred toner adhering to the photoconductor PC after the transfer. Next, the photoconductor PC is photo-erased by the static eliminator QL.

In the above image forming process, electric charges are supplied to the corona discharger CH and the dielectric belt B from a high voltage power source. In order to bring this amount of charge to the required value, the high voltage power supply
Constant current control is performed so that the output current value becomes the target value. The corona discharger CH and the transfer belt B are basically the same in configuration of the high-voltage power supply that applies a high voltage. Therefore, the charging circuit CH shown in FIG.
P will be described.

Referring to FIG. 5, the charging circuit CHP has an output current Iout for uniformly charging the surface of the photoconductor PC.
Is controlled to be constant. That is, the output current Iou
The voltage Io generated by the detection resistor R provided in the current path of t
ut × R is converted into digital data by the A / D converter ADC, and the switching transistor of the DC / DC converter DCC is set so that the charging controller CNT sets this voltage data to the target value. The duty of a pulse (PWM pulse) for on / off driving of the switching driver PG for on / off driving is controlled. That is, the controller CNT controls the on / off duty of the switching transistor so that the current Iout flowing through the detection resistor R reaches the target value (PWM control).

Specifically, when the AD conversion value (Iout × R) is larger than the target value, the duty of the PWM pulse (the time width of the high level H for turning on the switching transistor for one pulse) / Pulse period) and the duty of the PWM pulse is increased when it is smaller than the target value. DC in the high level H section of this PWM pulse
The switching transistor on the primary side of the transformer T of the / DC converter DCC is turned on and turned off in the low level L section. The duty of the PWM pulse is limited to a level at which the transformer T is not magnetically saturated. That is, the upper limit is set for the duty. Normal charging current value I
Although out is controlled to a constant current value by a constant current value, the charging current may be adjusted due to environmental changes and deterioration of the charging device, the photoconductor, etc. with time. Therefore, the charging circuit CHP has a specification that allows for the control width of the current. Each part is composed of parts that can withstand the specifications.

In the case of an image forming apparatus capable of selecting or setting image forming modes having different image forming speeds (specifically, rotation speeds of the photoconductors PC), the output current value Iout is set in accordance with the image forming speed. , And the control current range differs for each image forming mode. For example, JP-A-1-82
Japanese Unexamined Patent Publication No. 076 discloses an electrostatic recording apparatus in which transfer and separation voltages are individually set in correspondence with image forming modes such as high speed recording, low speed recording, front surface recording and back surface recording.
Further, Japanese Patent Laid-Open No. 2-259668 discloses an electrophotographic apparatus in which a high-voltage power supply circuit is shared for charging a photoreceptor and a developing bias, and a target value voltage is switched to switch the output voltage of the high-voltage power supply circuit. There is. In addition, Japanese Unexamined Patent Publication No.
Japanese Patent No. 47277 discloses a leak in which a high voltage power supply circuit detects a leak as a low voltage output and an image is formed as a high voltage output.
A black detector is presented.

[0008]

The image forming apparatus shown in FIG. 1 will be described as an example. Specifically, the control range of the charging current value is 500 to 10 in the first image forming mode in which low speed recording is performed.
00 μA. If the input voltage range of the A / D conversion that is the input destination of the feedback voltage (Iout × R) is 0 to 5V, the feedback voltage must be within this voltage range, so the value of the detection resistor R is 4.7 kΩ. , The feedback voltage range is
It becomes 2.35 to 4.70V.

Next, when the image forming apparatus has the second image forming mode in which the process linear velocity (high speed recording) is faster than the first image forming mode, the adjustment range of the charging current value is 750 to 1500 μA. (The higher the process linear velocity, the higher the current value). In this way, considering both modes, the high-voltage power supply is designed with a specification of 500 to 1500 μA, but the upper limit of the feedback voltage is 4.7 V as in the former case.
If it is made to be about, the value of the detection resistor R becomes about 3.12 kΩ, and the feedback voltage width becomes 1.56 to 4.68 V (see FIG. 6). However, the feedback voltage width in the first image forming mode is 1.56 to 3.12V, and the feedback voltage width in the second image forming mode is 2.34 to 4.68V. In this case, the feedback voltage width in the first image forming mode is 4.7 kΩ.
It will be narrower than when. Therefore, the resolution of the feedback voltage to the A / D converter ADC declines even with the same control range of the charging current value. That is, in an image forming apparatus having a digital high-voltage power source that feeds back an output current, A / D-converts the feedback voltage, calculates using the A / D-converted data, and determines the duty of a PWM signal. , The image forming apparatus has a plurality of image forming modes,
When the control current range is different for each image forming mode,
If a detection resistor with a resistance value that satisfies the entire control current range of each image forming mode is selected, the feedback voltage range with respect to the output current range is narrowed in a certain specific image forming mode, and control accuracy decreases. There are cases. The first object of the present invention is to solve this problem.

Further, in the case of the digital type high voltage power supply, output short circuit, leak, etc. are judged and controlled by the software (CPU leak detection program) in the CPU of the controller CNT. Without making false detections,
It is not easy to increase the reliability of safely stopping output. A second object of the present invention is to solve this problem.

[0011]

SUMMARY OF THE INVENTION The present invention includes a switching means, a high voltage generating circuit (DCC) for generating a high voltage corresponding to an on / off duty of the switching and outputting the high voltage to a high voltage functional member of an image forming apparatus, A current detecting means (R) for generating a feedback signal whose level is proportional to the output current (Iout) of the circuit, and an A / D converter for converting the feedback signal into digital data.
(ADC) and constant current control means for determining the duty of the PWM signal for turning on / off the switching means so that the value represented by the digital data matches the target value.
(CNT, PG), high voltage power supply (CHP) of image forming apparatus
In the above, the current detecting means (R) generates at least two resistors (R1, R1) having different resistance values to generate a voltage proportional to the output current (Iout) of the high voltage generating circuit (DCC).
2), and switching means for selectively applying the voltage generated by one of the resistors to the A / D converter (ADC)
(SW, CNT) are included. In addition, in order to facilitate understanding, the reference numerals of the corresponding elements in the embodiments shown in the drawings and described later are added for reference in parentheses.

Explaining according to the above example, the first resistor R1 of 4.7 kΩ is associated with the first image forming mode,
Corresponding to the second image forming mode, the second of 3.12 kΩ
The resistor R2 is provided, and the voltage generated by the first resistor R1 is fed back by the switching means (SW, CNT) corresponding to the setting of the image forming mode when the first image forming mode is set. As the signal, when the second image forming mode is set, the voltage generated by the second resistor R2 is used as the feedback signal,
When applied to the A / D converter (ADC), the feedback voltage range in the first image forming mode is 2.35 to 4.7 V as shown in FIG. The feedback voltage range is 2.34 to 4.68V, and constant current control with higher accuracy can be performed than in the case where only one detection resistor (R in FIG. 5) is provided.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

[0014]

【Example】

-First Embodiment- FIG. 1 shows an embodiment of the present invention. The high-voltage power supply device, that is, the charging circuit CHP of this embodiment applies a high voltage for charging the photoconductor to the corona discharger CH shown in FIG. In FIG. 1, an image forming controller Mcnt for controlling the sequence of the image forming process has a first image forming mode for performing high speed image recording and a second image forming mode for performing low speed image recording. A signal (charging timing signal) that gives information indicating which has been set to the controller CNT and that instructs high-voltage output during the time period for charging the photoconductor
give.

The controller CNT is an image forming controller M while the charging timing signal (high voltage output instruction) is received.
When the mode setting signal given by cnt indicates the first image forming mode, the changeover switch SW is connected to the resistor R1 and the voltage Iout × R1 generated by the resistor R1 is digitalized by the A / D converter ADC. PWM pulse so that it is converted into data and becomes the first target value addressed to the first image forming mode)
Control the duty of. That is, the controller CNT is controlled so that the current Iout flowing through the detection resistor R becomes the target value.
Controls the on / off duty of the switching transistor (PWM control). Specifically, if the AD conversion value (Iout × R1) is larger than the first target value, P
The duty of the WM pulse is reduced, and when it is smaller than the second target value, the duty of the PWM pulse is increased.

The image forming controller Mcnt provided
When the mode setting signal indicates the second image forming mode, the controller CNT connects the changeover switch SW to the resistor R2 and digitalizes the voltage Iout × R2 generated by the resistor R2 by the A / D converter ADC. Converted to data, this voltage data
The duty of the PWM pulse) is controlled so that the data becomes the second target value addressed to the second image forming mode.

While there is no charging timing signal (high voltage output instruction), the switching transistor of the DC / DC converter DCC is held off.

In this embodiment, the resistance R1 is 4.7 kΩ,
The resistance R2 is 3.12 kΩ. Therefore, as shown in FIG. 2, the feedback voltage range in the first image forming mode is 2.3.
5 to 4.7V, the feedback voltage range in the second image forming mode is 2.34 to 4.68V, which is different in each mode than the conventional one having only one detection resistor (FIG. 5). The resolution of the feedback signal (feedback voltage) is high and constant current control of the high-voltage power supply can be performed with high accuracy. Second Embodiment The configuration of the second embodiment is substantially the same as that shown in FIG. 1, but the resistance value of the first resistor R1 is 3.9 KΩ and the resistance value of the second resistor R2 is 2. It is 6 KΩ. In order to improve the resolution of the feedback voltage (Iout × R1, Iout × R2) with respect to the output current Iout, it is desirable to maximize the input voltage range of the A / D converter ADC. However, in the case of the image forming apparatus, the output of the charging circuit CHP may be short-circuited or leak in the apparatus. In these cases, only the current is limited by the current limiting resistor RL, and an overcurrent exceeding the control current range flows, and the product of the value of this overcurrent and the resistance value of the resistor R1 or R2 becomes the feedback voltage. Therefore, the input voltage range (5 V) of the A / D converter ADC may be greatly exceeded. Actually, the overvoltage input to the A / D converter ADC is cut off by a clamp diode, a filter circuit, etc. not shown, and the A / D converter ADC is protected, but the photoconductor PC or the corona discharger is substantially protected. However, when a short circuit or a leak occurs, the charging circuit C
HP needs to be turned off.

In the second embodiment, R1 = 3.9 as described above so that an overcurrent due to a short circuit and a leak can be detected.
Since KΩ and R2 = 2.6 KΩ are set, the feedback voltage ranges are both 1.95 to 3.9 V as shown in FIG. However, there are cases where the charging current is adjusted due to environmental changes and deterioration of the charging device, the photosensitive member, etc. over time, and if the adjustment allowance is ± 0.5 V in terms of feedback voltage, the feedback voltage range is 1.45 to 4. It becomes 4V, and when the abnormal feedback voltage of 4.5V is detected, the normal output is not made. Further, as the control, the duty of the PWM signal is decreased, but even if the duty is decreased, if an abnormal feedback voltage is detected, it can be determined that the output has leaked or is short-circuited.

In the controller CNT of the second embodiment, when the feedback voltage exceeds 4.4 V, the duty of the PWM pulse is reduced, but the duty is a reference value (in this embodiment, the duty is reduced). If the feedback voltage is 4.5 V or more below the duty adjustment width of the PWM pulse), the generation of the PWM pulse is stopped and the switching transistor on the primary side of the transformer T of the DC / DC converter DCC. Is kept off and the sequence controller Mcnt is notified of a short circuit abnormality in the charging circuit. In response to the abnormality notification, the sequence controller Mcnt interrupts the image forming process, displays the abnormality notification on the operation board, and returns the image forming functional element to the standby state.

Also in this second embodiment, the first image forming mode is used.
And the feedback voltage of 500-1000 μA of the output current Iout is 1.
In the second image forming mode, the range voltage of 95 to 3.90 is 1.95 V, and the output voltage Iout of 750 to 1500 μA is also 1.95 V to 3.90 V and the range width is 1.95 V. And the range width of each of the conventional example shown in FIG.
1.56 = 1.56V, 4.68-2.34 = 2.34
In contrast to this, although the resolution of the feedback voltage in the first image forming mode is slightly improved and the resolution of the feedback voltage in the second image forming mode is lower than that of the conventional example, Second
In any of the image forming modes, the short circuit abnormality of the charging circuit can be detected. In the conventional example shown in FIG. 6, a short circuit abnormality of the charging circuit can be detected in the first image forming mode, but in the second image forming mode, environmental changes and deterioration with time of the charging device, the photoconductor, etc. The adjustment allowance for adjusting the charging current cannot be set to ± 0.5 V in terms of feedback voltage (when +0.5 V is added, 4.68 + 0.5 = 5.18: A / D converter ADC's The conversion range exceeds 5V), and short circuit abnormality detection is impossible.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

2 is a graph showing a range of a voltage fed back to the A / D converter ADC via the changeover switch SW of FIG.

FIG. 3 is a second embodiment of the present invention, an A / D converter AD.
6 is a graph showing the range of the voltage fed back to C.

FIG. 4 is a block diagram showing an outline of a mechanism of a conventionally known image forming apparatus.

5 is a block diagram showing a configuration of a conventional charging circuit CHP for applying a high voltage to the corona discharger CH shown in FIG.

FIG. 6 is a diagram showing the resistance R to the A / D converter AD shown in FIG.
6 is a graph showing the range of the voltage fed back to C.

[Explanation of symbols]

PC: Photoconductor CH: Corona discharger D: Phenomenon device B: Transfer belt RB, RA: Transfer transport device C: Cleaning device QL: Static eliminator PP: Transfer bias power supply F: Fixing device RF: Fixing roller RP: Pressure roller T: Transformer Iout: Output current R, R1, R2:
Detection resistance DCC: DC / DC converter PG: Switching driver CNT: Charging controller ADC: A / D converter Mcnt: Sequence controller

Claims (3)

[Claims] 1. A switching means, a high voltage generating circuit for generating a high voltage corresponding to an ON / OFF duty of the switching and outputting the high voltage to a high voltage functional member of an image forming apparatus, and a feedback signal whose level is proportional to an output current of the circuit. For detecting the current, the A / D converter for converting the feedback signal into digital data, and turning on / off the switching means so that the value represented by the digital data matches the target value. In the high-voltage power supply device of the image forming apparatus, which includes a constant current control unit that determines the duty of the PWM signal to be turned off, the current detection unit generates a voltage proportional to an output current of the high voltage generation circuit. , At least two resistors having different resistance values, and switching means for selectively applying the voltage generated by one of the resistors to the A / D converter. A high-voltage power supply device for an image forming apparatus, characterized in that 2. The switching means is a set image forming mode.
2. The high-voltage power supply device for an image forming apparatus according to claim 1, wherein a voltage generated by a resistance corresponding to the voltage is applied to the A / D converter. 3. The resistance value of each resistor is the maximum value at which the voltage generated by the resistor at the maximum value of the normal output current in the image forming mode with which the resistor is associated is digitally convertible by the A / D converter. 3. The value is lower than the input voltage and is a value for leaving a margin for overcurrent detection up to the maximum input voltage.
A high-voltage power supply device for the image forming apparatus described.