JPH09197769A - Electrifier image forming device and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a high-voltage leakage phenomenon between a developing sleeve and a photoreceptor caused by the overshooting of the surface potential of the photoreceptor. SOLUTION: A deviation amplifier 4 for controlling an AC output with a constant current normally keeps an electrifying current output value to a constant value independently of the fluctuation in a load capacity accompanying a change in environmental conditions. A deviation amplifier 5 for controlling the AC output with the constant current keeps an electrifying voltage output value proportional to time to the constant value independently of the fluctuation of the load capacity accompanying the change in the environmental conditions. Then, these deviation amplifiers 4 and 5 are operated as an analog AND circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging a surface to be charged to a predetermined potential by bringing a charging member to which a voltage is applied into contact with the surface to be charged, and a color laser beam printer provided with this charging device. And the like, and an image forming method using the charging process.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, there is one shown in FIG. 7, for example. FIG. 7 is a schematic configuration diagram of a color laser beam printer which is an example of a conventional image forming apparatus.

Reference numeral 31 is a drum type electrophotographic photosensitive member,
A photosensitive layer (photoconductive material layer) 37 is formed on the outer peripheral surface of the conductive drum substrate 33, and is rotated at a predetermined peripheral speed (process speed) in the clockwise direction indicated by the arrow in the figure.

Reference numeral 32 denotes a charging roller as a charging member which is brought into pressure contact with the surface of the photoconductor 31 at a predetermined pressure. As the charging roller 32, a conductive elastic material is used. The charging roller 32 is pressed against the photoconductor 31 to form a predetermined nip width, and is driven and rotated in the forward direction as the photoconductor 31 is rotationally driven.

Reference numeral 50 is a high voltage power supply for supplying a voltage to the charging roller, and FIG. 8 is an output waveform diagram thereof. That is,
The oscillating voltage as shown in FIG. 8 is applied to the charging roller 32, and the surface of the photoconductor layer 37 is charged to the potential of the average value of the applied voltage. In this charging, the photoconductor layer 37 is charged by the direct movement of the charge in the nip portion, and is charged by the air discharge before and after the nip portion.

Next, the surface of the photoconductor layer 37 directly charged by the charging roller 32 is exposed by an exposing means 49 such as a projection optical system, a laser, an LED or a liquid crystal array (a laser is shown as an example in FIG. 7). , Main scanning exposure is performed in the generatrix direction of the photoconductor 31. Due to the main scanning by the exposing means 49 and the sub-scanning movement due to the rotation of the photoconductor 31, the photoconductor layer 3
Electrostatic latent images corresponding to target image information are sequentially formed on the seven surfaces.

Reference numerals 34a, 34b, 34c and 34d denote developing devices, and 35 denotes a rotating member of a developing cartridge for sequentially rotating and switching the developing devices. Photoconductor layer 37 of photoconductor 31
The electrostatic latent image formed on the surface is sequentially developed as a toner image by the developing device. Then, the paper feeding unit 40
The transferred transfer material is brought into contact with and fixed to the transfer drum body 36 by the gripper 44, a predetermined high voltage bias is applied by the suction roller 41, and the electrostatic attraction force by the electric charge applied to the back surface of the transfer material is applied. It is sucked onto the surface of the transfer drum body 36.

This transfer material is rotationally driven together with the transfer drum body 36 until the development of each color of yellow, magenta, cyan and black is sequentially performed. When the processes of developing and transferring each color are completed, the transfer material is separated from the transfer drum body 36 by the separation claw 46 after the gripper 44 holding the transfer material front end is released.

Depending on the environmental conditions, a high voltage bias is applied to remove the electrostatic attraction force due to the charges on the transfer material, and the transfer material is separated from the transfer drum body 36. The transfer material separated from the transfer drum body 36 is conveyed between the fixing rollers 38 whose temperature is adjusted to a predetermined temperature. The unfixed toner on the transfer material conveyed to the fixing roller 38 is heated and melted, soaks into the transfer material and the fixing is completed. Printing is completed when the transfer material on which the toner is fixed is discharged to the outside.

Now, the charging process will be described in more detail.

The corona discharge charging device has 50
In order to obtain a potential of 0 to 700 V, a high voltage of 4 to 8 kV is required, charging efficiency is low, and there are problems such as generation of corona discharge products. A roller charging contact charging device has been used as a means for charging the surface of a photoconductor as a charged body such as a dielectric.

Specifically, a conductive member (conductive potential fiber member), which is a charging member such as a conductive fiber bristle brush or a conductive elastic roller, to which a voltage in which a DC voltage or an AC voltage of about 1 kV is superimposed is applied. By contacting the surface of the photoconductor, which is a charged body, charges are directly injected into the surface of the photoconductor to charge the surface of the photoconductor to a predetermined potential.

Even if the charging process is carried out by the contact charging device in which only the DC voltage is applied to the charging roller, the charging on the surface of the photosensitive member is not uniformly performed, and spot-like charging unevenness occurs. This is presumably because the charging member to which a voltage is applied and the surface of the photoconductor that is in contact with the charging member are microscopically difficult to obtain ideal adhesion due to the unevenness of both surfaces. Then, even if the following image forming process by light image exposure is applied to the photoconductor surface in the spot-like uneven charging state and the image is output, the output image becomes a spot-like black spot image corresponding to the spot-like uneven charging state. You cannot get a quality image.

FIG. 9 shows the relationship between the surface potential of the charged photosensitive drum after passing through the charging roller and the DC voltage applied to the charging roller. The measurement state of this relationship is that the photoconductor drum is driven to rotate, the surface of the photoconductor drum is brought into contact with the surface of the photoconductor drum, and then a direct current voltage is applied to the charge roller to perform contact charging of the photoconductor drum in a dark place. To do. When a voltage equal to or higher than the charging start voltage value (about 500 V) is applied to the applied DC voltage, the obtained surface potential has a linear relationship with a slope of 1 on the graph. In terms of environmental characteristics (for example, high-temperature high-humidity / low-temperature low-humidity environment), almost the same result is obtained.

That is, assuming that the value of the DC voltage applied to the conductive roller is VDC, the value of the charging potential obtained on the surface of the photosensitive drum is VC, and the value of the charging start voltage is VTH, there is a relationship of VC = VDC-VTH. .

Next, description will be made on the case where the charging process is performed by the contact charging device in which the alternating voltage as shown in FIG.

DC voltage Vp to the charging roller is Vp
FIG. 10 shows the relationship between the applied AC voltage value and the photoconductor charging potential when an AC voltage (VDC + VAC) on which an AC voltage VAC having a −p peak-to-peak voltage is applied and the photoconductor drum is contact-charged. . In the region where the Vp-p value is small, the value of the charging potential linearly increases in proportion to Vp-p, and when it exceeds a certain value, the DC component V in the pulsating voltage component is increased.
It is almost saturated with DC and takes a constant value with respect to Vp-p change.

The above-mentioned inflection point with respect to the change of the value of Vp-p of the charging potential of the photoconductor is about 1000 V, which is almost twice the charging start voltage at the time of applying the DC voltage obtained above. According to this relationship, even if the frequency of the applied voltage and the DC component VDC are changed, the saturation point of the charging potential is only shifted by the change of the VDC value, and the position of the inflection point with respect to the change of Vp-p is constant, and It does not depend on the speed of the charging roller relative to the photoreceptor (eg, stop, rotate, reverse).

When the surface of the photoreceptor obtained by applying such an AC voltage is developed, when the value of Vp-p is small, that is, linearly with a slope of 1 between Vp-p / 2 and the charging potential. In a region having such a relationship, spot-like unevenness is generated as in the case where only the direct current is applied to the charging roller, but in the region where the peak-to-peak voltage above the inflection point is applied,
When the charging potential is constant, the obtained visible image becomes uniform.

To obtain charging uniformity and uniformity,
It suffices to apply an oscillating voltage having a peak-to-peak voltage that is at least twice the charging start voltage VTH when a DC voltage is applied, which is determined by various characteristics of the photoconductor, and a charging potential that depends on the DC component of the applied voltage can be obtained. . That is, the uniformity of charging is determined by the peak-to-peak voltage Vp-p of the AC voltage and the charging start voltage value VTH.
When the relation of Vp-p> 2VTH is established between and, it is as described above.

The inflection point in the relationship between the change in Vp-p and the charging potential is the starting point of charge reversal movement from the photoconductor to the charging member under the electric field between the photoconductor and the charging member. For example,
Even if a local excess charge is applied to the photoconductor and the potential becomes high, the charge is reversed and uniformized.

In short, when a DC voltage having a certain level or more of AC voltage superposed thereon is applied to the contact charging device, the drum surface can be charged to a uniform potential as compared with the case where only the DC voltage is applied. Become.

However, since the AC voltage is superposed on the DC voltage, compared to the conventional DC voltage applying corona charger,
Since the image forming apparatus of this example has a problem that it is likely to cause toner fusion, the AC voltage is turned on / off during the sheet interval and the sheet passing period as shown in FIG. Specifically, in the image forming period, an AC voltage obtained by superimposing an AC voltage corresponding to an AC current of 1800 μArms on a DC voltage (−700 V) is applied to the charging roller to perform uniform charging processing. Then, only the DC voltage (-1200 V) is applied to the conductor roller during the paper interval (between colors).

As described above, the toner fusion is reduced by keeping the surface potential of the photoconductor constant at -700 V both in the paper interval and in the image area and turning off the AC voltage during the paper interval not in the image area.

The above-mentioned graph of FIG. 10 also shows the relationship of the surface potential uniquely determined by the correlation between the applied DC current voltage value and the applied AC voltage value. For example, the direct-current voltage and the alternating-current voltage make a transition as indicated by the broken line arrow, and by repeating on / off in the sequence shown in FIG. 11, the surface potential can be kept constant at −700V.

[0026]

However, in the above-mentioned conventional example, there is a problem that the surface potential of the photosensitive member becomes unstable in the transition process from the sheet interval to the image area. Hereinafter, a specific description will be given.

The charging potential on the surface of the photosensitive member is caused by the voltage value as described above. However, since the charging action itself by the AC voltage superposition in the contact charging device is due to the injection of charges,
The constant current circuit can be more reliably charged. Therefore, in recent years, a contact charging device having a constant current circuit has been generalized.

However, the impedance of the photoconductor, which is the load of the charging device, changes with changes in environmental conditions such as temperature and humidity. Therefore, with only the constant current circuit configuration, the output voltage value fluctuates even with the same output current value as shown in FIG. 12, and as a result, the surface potential cannot maintain a constant −700 V due to the relationship in FIG. In some cases, overshoot occurred as shown in 13. It is expected that the extent of the excessive voltage that overshoots will be remarkable, as the transient time of each DC voltage and AC voltage becomes shorter, the degree of concern about the surface potential increases. Therefore, the transition time from the transient state to the steady state is set to about 100 ms.

When the photoconductor layer is charged more than a predetermined potential (for example, -800 V), the potential difference between the developing sleeve and the developing sleeve to which a high voltage is applied increases, so that the rising of the developing bias increases in the positive voltage direction. When overshooting, a high voltage leak phenomenon may occur. Further, when a high-pressure leak phenomenon occurs on the surface of the photoconductor in the image area, the potential of the leak occurrence point on the surface of the photoconductor drops, and an electrostatic latent image is formed as when exposure is performed.
The toner transitions after the leak of the image receiving area. That is,
In the transition process from the transient state of the DC voltage and the AC voltage to the steady state, there is a high degree of concern about the surface potential, and an image of originally nonexistent data is transferred onto the transfer material depending on the instantaneous rising voltage of the developing bias. There was a possibility.

In view of the above-mentioned conventional problems, the present invention is provided with a charging device which prevents a high-pressure leak phenomenon between the developing sleeve and the photosensitive member due to overshooting of the surface potential of the photosensitive member. Another object of the present invention is to provide an image forming apparatus and an image forming method.

[0031]

In order to achieve the above object, a charging device according to a first aspect of the present invention is provided with an AC voltage generating means for generating an AC voltage and a DC voltage generating means for generating a DC voltage. And a charging member to which the voltage generated by the power supply means is applied, the power supply means generating a voltage in which the AC voltage output of the AC voltage generation means is superimposed on the DC voltage output of the DC voltage generation means, In the charging device for contacting the charging member to which a voltage is applied to the surface of the body to be charged to charge the surface of the body to be charged to a predetermined potential, the AC voltage generating means sets a predetermined AC current output.
An alternating current output setting means, an alternating current output detecting means for detecting an alternating current output, and a first comparison calculating means for comparing and calculating the output of the first alternating current output setting means and the output of the alternating current output detecting means. First control means having, second AC output setting means for setting a predetermined AC voltage output, AC voltage output detecting means for detecting AC voltage output, and output of the second AC output setting means and the AC Second control means having a second comparison operation means for performing a comparison operation with the output of the voltage output detection means, and pulse wave peak value modulation means for modulating the high value of the pulse wave by the outputs of the first and second control means. With and
The AC voltage output is generated based on the output of the pulse peak value modulation means.

In the first aspect of the invention, it is desirable that the first AC output setting means sets a voltage defined by a slew rate as the predetermined AC voltage output when the power is turned on.

In the first aspect of the present invention, the DC voltage generating means detects the DC voltage output, and the third DC output setting means for setting the voltage defined by the slew rate as a predetermined DC voltage output when the power is turned on. And a third control means having a DC voltage output detecting means and a third comparing and calculating means for comparing and calculating the output of the third DC output setting means and the output of the DC voltage output detecting means. It is desirable to switch the DC power supply by the output of the control means to generate the DC voltage output.

In order to achieve the above object, the image forming apparatus according to the second invention is provided with an AC voltage generating means for generating an AC voltage and a DC voltage generating means for generating a DC voltage. Means for generating a voltage in which the AC voltage output of the means is superimposed on the DC voltage output of the DC voltage generating means, and a charging member to which the voltage generated by the power source means is applied. In the contact charging type image forming apparatus including a charging device for contacting the charging member with the surface of the image bearing member to charge the surface of the image bearing member to a predetermined potential, the AC voltage generating means may output a predetermined AC current. First AC output setting means for setting
A first control having an alternating current output detecting means for detecting an alternating current output, and a first comparison calculating means for comparing and calculating an output of the first alternating current output setting means and an output of the alternating current output detecting means. Second means for setting a predetermined AC voltage output
AC output setting means, AC voltage output detecting means for detecting an AC voltage output, and second comparison calculating means for performing a comparison operation between the output of the second AC output setting means and the output of the AC voltage output detecting means. And a pulse crest value modulating means for modulating the peak value of the pulse wave by the outputs of the first and second controlling means, and based on the output of the pulse crest value modulating means, This is what generated the AC voltage output.

In the second aspect of the invention, it is desirable that the first AC output setting means sets a voltage defined by a slew rate as the predetermined AC voltage output when the power is turned on.

In the second invention, the DC voltage generating means detects the DC voltage output, and a third DC output setting means for setting a voltage regulated by a slew rate as a predetermined DC voltage output when the power is turned on. And a third control means having a third comparison calculation means for comparing and calculating the output of the third DC output setting means and the output of the DC voltage output detection means. Desirably, the output of the third control means is used to switch the DC power supply to generate the DC voltage output.

In order to achieve the above object, the image forming method according to the third aspect of the invention is such that the voltage is applied to the charging member by the power supply means for generating a voltage in which the AC voltage output is superimposed on the DC voltage output, and the charging member is charged. In the image forming method of bringing the surface of the image carrier into contact with the surface of the image carrier and charging the surface of the image carrier to a predetermined potential, first AC output setting means for setting a predetermined AC current output, and AC current for detecting the AC current output. A first comparison calculation process for comparing and calculating the output of the first AC output setting means and the output of the AC current output detection means by using the output detection means, and setting a predetermined AC voltage output. A second AC output setting means and an AC voltage output detecting means for detecting the AC voltage output are used to perform a comparison operation of the output of the second AC output setting means and the output of the AC voltage output detecting means. Comparison operation Perform a physical, in which so as to generate the AC voltage output by modulating the height of the pulse wave by comparing calculation results of the first and second comparison processing.

In the third aspect of the present invention, it is desirable that the first AC output setting means sets a voltage defined by a slew rate as the predetermined AC voltage output when the power is turned on.

In the third aspect of the invention, third DC output setting means for setting a voltage defined by the slew rate as a predetermined DC voltage output when the power is turned on, and DC voltage output detecting means for detecting the DC voltage output. Is used to perform a third comparison calculation process for performing a comparison calculation between the output of the third DC output setting unit and the output of the DC voltage output detection unit, and the DC power supply is obtained based on the comparison calculation result of the third comparison calculation process. It is desirable to perform the above switching to generate the DC voltage output.

[0040]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic structure of a high-voltage power supply section of a charging device mounted on an image forming apparatus according to the first embodiment of the present invention.

In the figure, 1 is a power supply, 2 and 3 are power supplies 1
Connected to the diode constituting an analog AND circuit, 4 and 5 are error amplifiers constituting an analog AND circuit and performing a comparison operation between a threshold value and a feedback voltage, 6 and 7 are threshold value setting sections for setting a reference voltage for the comparison operation, Reference numeral 8 is an output current detector of the transformer 13, and 9 is a detector of an input voltage of the transformer 13.

A sine wave generating circuit 10 for high frequency attenuation is connected to the power source 1, the diodes 2 and 3 and the switching element 15. The output side of the sine wave generation circuit 10 is connected to the inverter transformer 1 via the drive circuit 11 for current amplification and the coupling capacitor 12.
3 is connected to the input side (primary side). The output side (secondary side) of the inverter transformer 13 is connected with the input side of the current detector 8 and the DC voltage generating circuit 20,
Further, an output terminal 14 for voltage applied to the charging member is connected. Further, the switching element 15 is adapted to perform a switching operation based on a clock CK generated by a clock generation means (oscillation circuit using an operational amplifier or the like, oscillator, etc.) not shown.

Here, the diode 2, the error amplifier 4, the threshold value setting unit 6 and the current detector 8 constitute a first control means, and the diode 3, the error amplifier 5, the threshold value setting unit 7 and the voltage detector 9 constitute the first control means. Two control means are configured.

Next, the operation of this embodiment will be described.

A periodic pulse voltage is generated by turning on / off the voltage supplied from the power source 1 by the clock CK via the switching element 15. The peak value of the periodic pulse voltage (hereinafter referred to as the reference peak value) basically depends on the power supply 1, but in the control state of the booster circuit, it depends on the output voltage value of the error amplifier 4 or 5. This is because the error amplifiers 4 and 5 draw the current through the diodes 2 and 3 to lower the reference peak value. This current drawing operates on the smaller output voltage side of the error amplifiers 4, 5, and as a result, the larger output voltage side of the error amplifiers 4, 5 outputs the upper saturation voltage. That is, when one diode is conducting, the other diode is non-conducting, indicating an open state.

The periodic pulse voltage signal uniquely determined by the power supply 1, the diodes 2 and 3, the error amplifiers 4,5, the clock CK, and the switching element 15 is attenuated and filtered at high frequency by the sine wave generation circuit 10. As a result, the signal is converted into a sinusoidal periodic voltage signal containing only the fundamental periodic component. The sine wave periodic signal is current-amplified by the drive circuit 11, the DC component is removed by the coupling capacitor 12, and is input to the inverter transformer 13.

As a result, the inverter transformer 13 boosts the input voltage and outputs it. The feedback loop using the error amplifier 4 and the error amplifier 5 has the analog A as described above.
It operates as an ND circuit (minimum value circuit). Error amplifier 4
Performs constant current control and operates so as to maintain the current value in a steady state at a constant value. The error amplifier 5 performs constant voltage control, and the voltage (a rising voltage when the AC output is on, a falling voltage when the AC output is off) in the transient region until the error amplifier 4 reaches the control region has the characteristic shown in FIG. Control to be.

The current detector 8 is an inverter transformer 13.
By double-voltage rectifying the AC voltage obtained by current / voltage converting the AC current of the output, the Peak-to-Peak output current value is detected, and the voltage signal of the detected level is input to the error amplifier 4. The threshold setting unit 6 is an inverter transformer 13
The reference voltage is generated and set so that the output current value becomes a desired value.

The error amplifier 4 for performing constant current control compares the voltage signal detected by the current detector 8 with the reference voltage set by the threshold value setting unit 6 and performs a calculation process. When the output current of the inverter transformer 13 is less than a desired value, that is, the output voltage value of the current detector 8 is smaller than the reference voltage value of the threshold value setting unit 6 and the error amplifier 5 as an analog AND circuit outputs a smaller voltage. During the operation (area A in FIG. 3), the error amplifier 4 outputs the upper limit saturation voltage, so that the diode 2 is in the non-conducting state and is in the non-controlling state.

The voltage detector 9 includes an inverter transformer 13
By rectifying the input voltage of
The Peak output voltage value is detected, and the voltage signal of the detected level is input to the error amplifier 5. The threshold value setting unit 7 generates and sets a reference voltage so that a desired voltage (voltage rising or falling at a constant slew rate) is input to the inverter transformer 13.

The error amplifier 5 for performing constant voltage control compares the voltage signal detected by the voltage detector 9 with the reference voltage set by the threshold value setting section 7 to perform a calculation operation. When the input voltage of the inverter transformer 13 is less than a desired value, that is, the output voltage value of the voltage detector 9 is smaller than the reference voltage value of the threshold value setting unit 5 and the error amplifier 4 as an analog AND circuit outputs a smaller voltage. When outputting (area B in Fig. 3),
Since the error amplifier 5 outputs the upper limit saturation voltage, the diode 3 is in a non-conducting state and is in a non-controlling state.

FIG. 4 is a block diagram showing the structure of the DC voltage generating circuit 20 shown in FIG.

In this DC voltage generating circuit 20, the switching unit 21 performs high frequency switching of the DC power source, and the high voltage boosted by the converter transformer 22 is rectified by the rectifier circuit 2.
A high voltage DC output voltage is obtained by rectifying and smoothing at 3.

The error amplifier 24 compares the voltage detected by the voltage detection circuit 25 with the reference voltage which is the threshold value set by the threshold value setting unit 26 to control the voltage of the switching unit 21 to make it a constant voltage. It is carried out. Further, in the threshold value setting unit 26, a threshold value in the transient range is set so as to increase or decrease a constant voltage defined by the slew rate as in the transient range control of the AC voltage described above.

Inferring from the above-mentioned graph of FIG. 10, in this embodiment, from the state in which the DC voltage = −1200V is applied, the DC voltage = −700V and the AC current 1800 μAr.
It is said that the surface potential of the photoconductor can be kept constant if a certain relation is satisfied in a transient state in which an AC voltage equivalent to ms (which fluctuates depending on the load capacitance) is applied, regardless of environmental conditions. From the idea, that is,
If the applied AC voltage value is set and changed so as to satisfy the relationship of FIG. 5, it is possible to keep the surface potential of the photosensitive member constant in the transient state of each applied voltage. Since the forming apparatus is configured, it is possible to obtain desired characteristics shown in FIG.

That is, the first control means for performing the constant current control of the AC output keeps the charging current output value at a constant value in a steady state, without depending on the load capacity variation due to the change in environmental conditions. The second control means for performing the constant voltage control of the AC output keeps the charging voltage output value, which is proportional to time, at a constant value, without depending on the change in the load capacity due to the change in the environmental conditions. By operating the first and second control means as an analog AND circuit (minimum value circuit), the voltage with a constant slope with respect to time is obtained in the transient region when the AC output is turned on, regardless of load capacity fluctuations. The voltage rises and holds a constant current and a constant voltage according to the load capacity in the steady range when the AC output is on, and drops at a constant slope with time in the transient range when the AC output is off. A charging device can be configured.

As a result, the DC voltage is −120 between the sheets.
In the case where both the DC voltage application and the AC superimposed voltage application are used in spite of the sequence of 0 V single application, DC voltage = -700 V during the paper passing period, and AC voltage of 1800 µArms (varied depending on the load capacity). By utilizing the above characteristics, it is possible to maintain a stable surface potential irrespective of environmental changes during both the image forming period and the non-image forming period during the paper interval and the paper passing period, and high pressure leak on the surface of the photoconductor in the non-image area. It is possible to eliminate the surface potential overshoot that may cause the phenomenon.

FIG. 6 is a block diagram showing a schematic configuration of a high-voltage power supply section of a charging device mounted in an image forming apparatus according to the second embodiment of the present invention, and elements common to FIG. Is attached.

In this embodiment, the transformer 13A, which detects the voltage on the transformer output side, has a tertiary winding for voltage detection. That is, in the configuration shown in FIG. 1, the voltage detector 9 is used as the voltage detector 9A and its input side is connected to the tertiary output side of the transformer 13A.

According to this embodiment, the voltage detector 9A is
By rectifying the input voltage of the inverter transformer 13 by double voltage, the Peak-to-Peak output voltage value is detected,
The voltage signal of the detected level is input to the error amplifier 5. The error amplifier 5 that performs constant voltage control is a voltage detector 9A.
The voltage signal detected in step 3 and the reference voltage set in the threshold setting part 7 are compared and processed.

In the present embodiment, the inverter transformer 13
Since the output voltage of A is fed back, the output voltage control including the output variation of the inverter transformer 13A is possible in addition to the effect of the first embodiment.

[0063]

As described in detail above, according to the present invention,
It is possible to maintain a stable surface potential regardless of environmental changes during both the image forming period and the non-image forming period during the paper interval and the paper passing period, which may cause a high pressure leak phenomenon on the surface of the photoconductor in the non-image area. It becomes possible to remove the overshoot of the surface potential.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a high voltage power supply unit of a charging device mounted in an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an output characteristic diagram of the charging device according to the first embodiment.

FIG. 3 is a correlation diagram between an AC output voltage under current control and an AC output voltage under voltage control.

FIG. 4 is a block diagram showing a configuration of a DC voltage generation circuit 20 in FIG.

FIG. 5 is a relationship diagram of an applied AC voltage and an applied DC voltage for keeping the surface potential of the photoconductor constant.

FIG. 6 is a block diagram showing a schematic configuration of a high voltage power supply unit of a charging device mounted in an image forming apparatus according to a second embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a color laser beam printer which is an example of a conventional image forming apparatus.

FIG. 8 is an output waveform diagram of a high-voltage power supply that applies a voltage to a charging member.

FIG. 9 is a relationship diagram between an applied AC voltage value and a photoreceptor surface potential when a DC voltage is applied to the charging member.

FIG. 10 is a relationship diagram between an applied AC voltage value and a photoreceptor surface potential when a DC voltage superimposed with an AC voltage is applied to the charging member.

FIG. 11 is a diagram showing a timing of an on / off sequence of each applied voltage.

FIG. 12 is an AC output voltage diagram when only dependent on constant current control.

FIG. 13 is a diagram showing an overshooting photoreceptor surface potential.

[Explanation of symbols]

 1 Power Supply 2,3 Diodes 4,5 Error Amplifier 6,7 Threshold Setting Section 8 Output Current Detector 9,9A Voltage Detector 10 Sine Wave Generation Circuit 11 Drive Circuit 12 Coupling Capacitor 13 Inverter Transformer 14 Applied Voltage Output Terminal 15 Switching element 20 DC voltage generation circuit 21 Switching unit 22 Converter transformer 23 Rectifier circuit 24 Error amplifier 25 Voltage detection circuit 26 Threshold setting unit CK clock

Claims (9)

[Claims] 1. An AC voltage generating means for generating an AC voltage and a DC voltage generating means for generating a DC voltage are provided, and an AC voltage output of the AC voltage generating means is superimposed on a DC voltage output of the DC voltage generating means. It has a power supply unit for generating a voltage and a charging member to which the voltage generated by the power supply unit is applied. The charging member to which the voltage is applied is brought into contact with the surface of the body to be charged, and the surface of the body to be charged is predetermined. In the charging device that performs a charging process to a potential of 1, the AC voltage generation unit includes a first AC output setting unit that sets a predetermined AC current output, an AC current output detection unit that detects an AC current output, and the first AC output setting unit. First control means having a first comparison calculation means for comparing and calculating the output of the AC output setting means and the output of the AC current output detection means, and a second AC output setting for setting a predetermined AC voltage output. A second means having a constant means, an alternating voltage output detecting means for detecting an alternating voltage output, and a second comparing and calculating means for comparing and calculating the output of the second alternating output setting means and the output of the alternating voltage output detecting means. And a pulse wave peak value modulating means for modulating the high value of the pulse wave by the outputs of the first and second control means, and the AC voltage output is generated based on the output of the pulse wave peak value modulating means. A charging device characterized in that 2. The charging device according to claim 1, wherein the first AC output setting means sets a voltage defined by a slew rate as the predetermined AC voltage output when the power is turned on. 3. The DC voltage generating means is a third DC output setting means for setting a voltage defined by a slew rate as a predetermined DC voltage output when the power is turned on,
Third control means having direct current voltage output detection means for detecting direct current voltage output, and third comparison operation means for performing comparative operation on the output of the third direct current output setting means and the output of the direct current voltage output detection means. 3. A DC voltage output is generated by switching a DC power supply by the output of the third control means.
The charging device described. 4. An AC voltage generating means for generating an AC voltage and a DC voltage generating means for generating a DC voltage are provided, and the AC voltage output of the AC voltage generating means is superimposed on the DC voltage output of the DC voltage generating means. It has a power supply means for generating a voltage and a charging member to which the voltage generated by the power supply means is applied, and the charging member to which the voltage is applied is brought into contact with the surface of the image carrier to predetermined the surface of the image carrier. In the image forming apparatus of the contact charging type, which is equipped with a charging device for charging the potential of the AC voltage, the AC voltage generation unit is a first AC output setting unit that sets a predetermined AC current output, and an AC that detects the AC current output. First output means for current output and first control means for comparing and calculating the output of the first alternating current output setting means and the output of the alternating current output detecting means; and a predetermined alternating current Second AC output setting means for setting a voltage output, AC voltage output detecting means for detecting an AC voltage output, and output of the second AC output setting means and output of the AC voltage output detecting means are compared and calculated. A second control unit having a second comparison calculation unit; and a pulse peak value modulation unit that modulates the high value of the pulse wave by the outputs of the first and second control units. An image forming apparatus, wherein the AC voltage output is generated based on an output. 5. The image forming apparatus according to claim 4, wherein the first AC output setting unit sets a voltage defined by a slew rate as the predetermined AC voltage output when the power is turned on. 6. The DC voltage generating means comprises a third DC output setting means for setting a voltage regulated by a slew rate as a predetermined DC voltage output when the power is turned on, and a DC voltage output detecting means for detecting the DC voltage output. Means and
An output of the third DC output setting means and a third control means having a third comparison operation means for performing an operation of comparing the output of the DC voltage output detection means. 6. The image forming apparatus according to claim 4, wherein the DC voltage output is generated by switching a DC power supply according to. 7. A power source means for generating a voltage obtained by superimposing an AC voltage output on a DC voltage output, applies the voltage to a charging member and brings the charging member into contact with the surface of the image carrier to bring the surface of the image carrier to a predetermined potential. In the image forming method in which the charging process is performed on the first AC output setting unit, a first AC output setting unit that sets a predetermined AC current output and an AC current output detection unit that detects the AC current output are used. The first comparison calculation process for performing a comparison calculation between the output and the output of the AC current output detection means, the second AC output setting means for setting a predetermined AC voltage output, and the AC voltage for detecting the AC voltage output Output comparison means is used to perform second comparison calculation processing for comparing and calculating the output of the second AC output setting means and the output of the AC voltage output detection means, and the first and second comparison calculations are performed. Comparison operation of processing An image forming method, wherein the high value of a pulse wave is modulated according to the result to generate the AC voltage output. 8. The image forming method according to claim 7, wherein the first AC output setting unit sets a voltage defined by a slew rate as the predetermined AC voltage output when the power is turned on. 9. A third direct current output setting means for setting a voltage regulated by a slew rate as a predetermined direct current voltage output when the power is turned on, and a direct current voltage output detecting means for detecting a direct current voltage output. The third comparison calculation process for comparing and calculating the output of the DC output setting unit and the output of the DC voltage output detection unit is performed, and the DC power supply is switched according to the comparison calculation result of the third comparison calculation process. 9. The image forming method according to claim 7, wherein the DC voltage output is generated.