JP3031418B2 - Corona discharge device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corona discharge device used for forming an image on a photosensitive member in an electrophotographic copying machine or a laser printer, for example.

2. Description of the Related Art For example, in an electrophotographic copying machine, in order to form an image, a charging discharger, a transfer discharger,
Various corona dischargers, such as a discharger for separation and a discharger for static elimination, are provided. For preferable image formation, it is necessary to supply a stable current to the photoconductor in each corona discharger. However, the value of the current fluctuates under the influence of, for example, contamination of the corona discharger or environmental fluctuation.

Therefore, a technique for detecting a current flowing through a photoconductor and a technique for stabilizing a voltage applied to a corona discharger have been conventionally proposed as follows.

JP-B 1-26062, JP-A-64-59264, JP-A-53-15834, JP-B-46-25480, JP-A-51-131635 [Problems to be Solved by the Invention] JP-A-64-59264 and JP-A-53-15834 disclose that a voltage applied to a corona discharger is automatically controlled to stabilize a discharge current. However, in the former case, since a comparison circuit is provided for each corona discharger, the circuit configuration becomes complicated. In the latter case, when the discharge current is alternating current, the current cannot be directly detected. Further, in the case of detecting a current at the time of corona discharge, a large detection error occurs due to noise with respect to a single spark discharge occurring in the corona discharger, and control may become unstable.

The present invention detects a DC charging current and an AC charging current of a photoreceptor and automatically controls and stabilizes the photosensitive member. In addition, even when noise or the like occurs, the DC and AC currents are accurately detected and a stable DC or AC current is detected. It is an object to realize control of AC corona discharge.

[Means for Solving the Problems] A corona discharge device according to the present invention includes a corona discharge electrode (PQC, PTC) disposed opposite to a surface of a photoconductor (PC) for forming an image; High voltage power supply means (40 ₁ , 40n) for applying a voltage; charging current detection means (R1) for detecting a current flowing from the corona discharge electrode to the photoreceptor; electric signal output from the charging current detection means (Rl); First low-pass filter means (1) for removing a noise component; second low-pass filter means (2) for removing an AC component of an electric signal output from the first low-pass filter means (1); first low-pass filter means (1) Absolute value conversion means (5) for converting a signal obtained by removing a DC component from an electric signal output by the above into a signal of the absolute value level; a signal output by the second low-pass filter means (2) and the absolute value conversion means (5) A / D converting means for converting the level into a digital quantity (60); and, on the basis of the digital value output from the A / D converting means, for controlling the output level of the high voltage power supply means, the control means (l0
~ 30);

For easy understanding, the reference numerals of the corresponding elements of the embodiments shown in the drawings and described later are added for reference in Kakko.

[Action] For example, a single spark discharge generated by contamination of a corona discharge wire has a very short cycle (about 50 μse).
c). When the current level is detected by A / D converting a signal containing such noise, a large error occurs in the detection level depending on the sampling timing. However, this problem is solved because the first low-pass filter means (1) removes noise components.

Furthermore, the second port-pass filter means (2) removes the AC component of the electric signal output from the first low-pass filter means (1), while the absolute value conversion means (5) removes the first low-pass filter means The signal obtained by removing the DC component from the electric signal output by (1) is converted into a signal of its absolute value level, and A / A
D conversion means (60) is second port-pass filter means (2)
Also, since the level of the signal output by the absolute value conversion means (5) is converted into a digital amount, no matter what timing the sampling is executed, a noise component based on spark discharge does not appear in the A / D conversion output, The discharge current of the corona discharge and the AC corona discharge current can always be accurately obtained by digital data.

Since the control means (10 to 30) controls the output level of the high-voltage power supply means (40 ₁ , 40n) based on the digital amount output from the A / D conversion means (60), stable control of corona discharge is achieved. Realize.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[Embodiment] FIG. 2 shows a configuration of a main part of an electrophotographic copying machine embodying the present invention, that is, a mechanism of an image forming unit. Referring to FIG. 2, the cylindrical photoconductor PC rotates at a constant speed in the direction of the arrow. In the image forming process, first, a positive DC corona discharge is performed by the main corona discharger C, and
The PC is charged to a potential of about 800V. Next, the surface of the photoconductor is irradiated with light reflected from the document. Thereby, a potential distribution according to the intensity change of the irradiation light, that is, an electrostatic latent image is formed on the surface of the photoconductor PC. In the developing device B, a negatively charged toner is applied to the photoconductor PC, and the toner is attracted to the electrostatic latent image. Next, an AC corona discharge with a negative DC bias is performed by a pre-transfer charge eliminating corona discharger PTC to weaken the electrostatic attraction force between the toner and the photoconductor. The transfer paper fed from the registration roller RR in synchronization with the leading edge position of the image is
Superimposed on the toner image on the photoconductor PC. In this state,
From the back of the transfer paper, a positive DC corona discharge is performed by a transfer corona discharger T to transfer the toner image on the photoreceptor to the transfer paper. Subsequently, from the back of the transfer paper, an alternating current corona discharge with a positive direct current bias is performed by the separation corona discharger D to eliminate the charge of the transfer paper. Thereby, the transfer paper is separated from the photoreceptor by its own weight and rigidity. The transfer paper is transported by a transport belt to a fixing device (not shown), where the toner image is fixed, and then discharged outside the apparatus. After the separation of the transfer paper is completed, on the photoconductor, an AC corona discharge with a negative DC bias is performed by a pre-cleaning corona discharger PCC,
The potential between the untransferred toner and the photoconductor is made uniform. Next, untransferred toner and paper dust are removed from the photoconductor by a cleaning device. Further, a positive DC corona discharge is performed by the charge removing corona discharger PQC, and light is irradiated by the charge removing lamp QL to return the photosensitive member to the initial state. Thus, one cycle of the image forming process is completed.

Next, the electrical operation of each corona discharger will be described with reference to FIG. The corona discharger is composed of a corona discharge wire W connected to a high-voltage power supply PP and a shield electrode CL arranged so as to surround the corona discharge wire W. When a high voltage is applied to the corona discharge wire W, the output current Io
Flows. This current Io is divided into a photoreceptor charging current 1d and a shield current Ic by a corona discharger. Photoconductor charging current
Depending on Id, charging or discharging of the photoconductor and transfer paper is performed. Therefore, it is important to stably control the current Id in order to obtain a preferable image forming result. FIG. 1 shows the configuration of a circuit for performing this control.

Referring to FIG. 1, in this example, a high voltage applied to each corona discharger so that the photoconductor charging current detected by the photoconductor charging current detection circuit connected to the photoconductor PC becomes a predetermined value (target value). It controls the circuit that generates the voltage. This control is performed at a predetermined cycle (for example, once every 5000 rotations of the photoconductor).
This is performed for each discharger.

Each element constituting the control loop will be described.
Although FIG. 1 shows only the DC corona discharger PQC and the AC corona discharger PTC, in actuality, as described above, a large number of dischargers and a high-voltage power supply for generating power to be supplied thereto are provided. And they are not shown.

High voltage power supply 40 _{1 to} 40n for supplying high voltage to corona discharger
Outputs a voltage or current corresponding to the control signal (DC level) applied from the integrating circuit 30 ₁ ~30n. The control signal is
Each PWM (pulse width modulation) signal output from the timer 20 is generated by passing the signal through an integration circuit. As shown in FIG. 4, each PWM signal has a constant period t2, and its duty is changed by changing the L period (low-level period) t1.
And the analog signal level after integration changes. FIG. 5 shows the correlation between the duty of the PWM signal and the value of the current. Therefore, the output voltage or current of each high-voltage power supply changes according to the level of the input control signal, that is, the duty of the PWM signal. Each high-voltage power supply performs constant current control so as to keep its output current at a predetermined value.

In the photoconductor charging current detection circuit, the conductive substrate of the photoconductor PC is grounded via a voltage conversion circuit 51, and here, the photoconductor charging current Id is converted into a voltage. The detection signal converted into the voltage passes through the low-pass filter 52 to remove a single spark discharge in the corona discharger, an induction noise from the photoconductor heater, and the like. Lowpass filter 52
Cutoff frequency is spark discharge (cycle is about 50μsec = 20KHz)
It is set to about 2.5 KHz so that the component can be sufficiently reduced.

The signal output from the low-pass filter 52 is further applied to the low-pass filter 53. The filter 53 is for extracting a DC component, and its cutoff frequency is set to about 25 Hz so that the component of the AC frequency (about 500 to 1000 Hz) applied to the AC corona discharger can be sufficiently reduced. It has been set. The DC signal component output from the low-pass filter 53 is applied to the input terminals of the two detection circuits 54 and 55.
That is, the plus component of the DC signal is detected by the + detection circuit 54, and the minus component is detected by the − detection circuit 55. In addition,
-The detection circuit 55 inverts the polarity of the signal inside. The signals output from each detection circuit are
Is applied to an analog input terminal of an A / D (analog / digital) converter 60 via the. On the other hand, low-pass filter 52
Of the signals output from the, the AC component is detected by the AC detection circuit and applied to the A / D converter 60 via the limiter 59. The limiters 57, 58 and 59 are provided for preventing an excessive voltage from being applied to the input of the A / D converter 60.

The A / D converter 60 samples the level of the analog signal applied to each input terminal, converts the level into a digital value, and transfers the data to a microcomputer (hereinafter referred to as CPU) 10 via a bus line. I do. The CPU 10 controls the entire corona discharge device. That is, the CPU 10
For each corona discharger, the set value of the timer 20 is updated according to the magnitude of the difference between the preset target value and each detected value (data from the A / D converter), and the PWM signal Adjust the duty. By adjusting the duty, the output level of the high-voltage power supply to which the signal is applied changes, and the current value of corona discharge changes, so that the detected value (the output of the A / D converter) obtained by sampling the current value also changes. When the detected value converges to the target value, that is, when the two coincide, the CPU 10 ends the adjustment and holds data corresponding to the duty at that time in the memory. Until the next control starts,
The duty of the PWM signal is kept constant.

As shown in FIG. 1, two control signals ACPWM and DCPWM are applied to a high-voltage power supply 40n connected to an AC corona discharger PTC via an integration circuit 30n. In the corona discharger, even when an AC voltage having the same positive and negative voltages is applied, a DC-biased AC current flows as the discharge current because the corona discharge start voltage differs depending on the polarity.
Since the DC component increases and decreases in proportion to the AC voltage, in this embodiment, for the AC corona discharger, both the AC component and the DC component are detected and each is controlled to a predetermined value. For this reason, the AC voltage power supply is configured as shown in FIG.

Referring to FIG. 6, an inverter ACINV for AC output is provided.
And a DC output inverter DCINV are connected in series, and each inverter is configured so that the output can be adjusted independently. That is, when the ACPWM signal changes, the output level of the integration circuit 41 changes, the output duty of the comparator 41 changes, the output current of the driver 43 changes, and the AC voltage output by the ACINV changes. Similarly, if the DCPWM signal changes, the output duty of the integrating circuit 42 changes, the output current of the driver 44 changes, and the DC voltage output by DCINV changes.

FIG. 7 shows the output voltage waveform of this high-voltage power supply. Referring to FIG. 7, this voltage is a square wave of 500 Hz and −Vdc
Are superimposed. The bias value Vdc changes according to the DC PWM signal DCPWM, and the AC voltage Vpp changes according to the AC PWM signal ACPWM.

Next, the operation of the CPU 10 shown in FIG. 1 will be described with reference to the flowcharts shown in FIGS. When it is time to adjust the corona discharger, the CPU 10
The processing shown in the figure is executed. In the first step 1, it is determined whether or not the setting of the static elimination corona discharger PQC has been completed. If the setting has not been completed, the process proceeds to step 7, where a setting execution flag is set. If it has been completed, the process proceeds to the next step 2, where it is determined whether or not the setting of the pre-transfer charge eliminating corona discharger PTC has been completed. If not, the process proceeds to step 8, where a setting execution flag is set. Hereinafter, in the same manner, the separation corona discharger D, the pre-cleaning corona discharger PCC, the transfer corona discharger
The processing is executed in the order of T and the main corona discharger C. Here, the setting of the static elimination corona discharger is performed before the setting of the indispensable corona discharger requiring the static elimination after the setting. In particular, in the case of an inorganic photoreceptor containing selenium as a main component, negative charge cannot be removed by light, so that the charge is removed by a discharge lamp after uniformly charging the positive polarity.

Next, the processing of FIG. 9 will be described. This processing is performed in a predetermined cycle (for example, until the setting of all the corona dischargers is completed).
It is executed repeatedly at 10msec intervals). First, it is determined from which corona discharger to execute. Step S1
Then, it is determined whether or not the setting of the static elimination corona discharger PQC is to be performed. If not, the determination is made in the order shown in FIG.
Here, the charge removing corona discharger PQC and the pre-transfer charge removing corona discharger PTC will be described, and description of the other dischargers will be omitted.

When the static elimination corona discharger PQC is selected in step S1,
In step S2, the output of the high voltage power supply 1 (40 ₁ ) is turned on. Next, in step S3, a positive detection signal is sampled from the input terminal A / D1 of the A / D converter, and the digital data is read. In the next step S4, the digital data of the detected value is compared with a target value (photoconductor charging current) relating to the static elimination corona discharger PQC, and if the two are equal, the next step is performed.
It sets the setting completion flag of PQC in S5, and turns off the output of the high-voltage power supply 1 (40 ₁₎ at step S6. When the detected value is not equal to the target value, the process proceeds to step S7, and it is determined whether the detected value Id is larger than the target value. If it is larger, the duty of the PWM signal supplied to the high-voltage power supply 1 (40 ₁ ) is reduced in step S8 according to the difference between the detected value and the target value. Conversely, when the detected value is smaller than the target value, step S9
The duty of the PWM signal is increased according to the magnitude of the difference between the detected value and the target value. In the next step S10, the current P
The duty value of the WM signal is stored in the memory. This is 1
One control cycle ends. If the setting has not been completed, the setting of the static elimination corona discharger PQC is performed again in the next control cycle. When the setting is completed, the next pre-transfer charge removing corona discharger PT is performed according to the flowchart of FIG.
C is selected.

When the pre-transfer charge eliminating corona discharger PTC is selected in step S11, it is determined in next step S12 whether or not the photoconductor has rotated once since the setting of the photoconductor charging current is started. When one rotation is not made, the output of the high voltage power supply n (40n) is turned on in step S19. Further, during one rotation, the high-voltage power supply n (4
0n), the output is turned off, and in step S14, the corona discharger P
Turn on the high voltage power supply 1 of QC. Next, in step S15, the static elimination lamp QL is turned on, and in step S16, a timer is activated to determine whether static elimination is completed. When the static elimination is completed, step S17
To turn off the output of the high voltage power supply 1 (40 ₁ ), and furthermore, step S18
To turn off the neutralizing lamp QL.

In step S19, the high voltage power supply n (40n) is turned on,
At S20, the signal (AC component) applied to the input terminal A / D3 of the A / D converter is sampled and the digital data is read. In the next S21, the detected value in S20 is compared with the target value for the AC component of the PTC, and if the two are equal, the current setting end flag for the AC component of the pre-transfer neutralizing corona discharger PTC is set in the next S22, When not equal to the target value, S2
At 3, it is determined whether or not the detected value Id is larger than the target value. If it is larger, the duty of the PWM signal applied to the high-voltage power supply 1 (40 ₁ ) is reduced in step S24 according to the difference between the detected value and the target value. Conversely, when the detected value is smaller than the target value, the duty of the PWM signal is increased in S25.
In step S26, the current duty of the PWM signal is stored in the memory.

Subsequently, the process proceeds to setting of a DC component. In step S27, the flip-flop F / F is inverted, and as a result, if the state of the F / F is 1, the setting of the current related to the DC component is executed. Also, F / F
Is zero, no DC component is set. Here, the setting of the DC component is performed in a control cycle twice as large as that of the AC component. That is, the setting of the DC component is performed once while the process of setting the AC component is performed twice. This is to prevent hunting from occurring due to control interference between the AC and DC components.

The setting of the DC component will be described. In step S28, A
The signal applied to the input terminal A / D1 of the / D converter is sampled, and the digital data thereof is read as a positive detection value. In step S29, the signal applied to the input terminal A / D2 of the A / D converter is sampled. And read the digital data as a negative detection value. In step S30,
The plus detection value and the minus detection value are compared, and the larger of the two is determined as the detection value of the DC component (S31, S32). In step S33, the detected value and the target value are compared, and if they are equal, it is determined in next step S34 whether or not the setting of the AC component has been completed. If completed, the current setting end flag of the pre-transfer charge removing corona discharger PTC is set in S35, and the output of the high voltage power supply n (40n) is turned off in S36. If not completed, the process in the current control cycle is executed. When the detected value is not equal to the target value in step S33, S37 identifies whether the detected value is larger than the target value, and when it is larger, the PWM supplied to the high-voltage power supply n (40n) in S38.
The signal duty is reduced according to the magnitude of the difference between the detected value and the target value. Conversely, when the detected value is smaller than the target value, the duty of the PWM signal is increased in S39. Steps
In S40, the current duty of the PWM signal is stored.

The above processing is repeatedly executed until all the settings are completed.

FIG. 10 shows a specific configuration of the photoconductor charging current detection circuit shown in FIG. The voltage conversion circuit 51 in FIG. 1 corresponds to the input resistor R1 of the circuit 1 in FIG. Most of the circuit 1 constitutes the low-pass filter 52 of FIG. Similarly, the circuits 2, 3, 4, and 5 in FIG. 10 correspond to the low-pass filter 53, the plus detection circuit 54, the minus detection circuit 55, and the AC detection circuit 56 in FIG. 1, respectively. The circuit 5 forms an absolute value circuit. In each detection circuit, the power supply voltage of the detection circuit is set higher than the power supply voltage of the subsequent A / D converter in order to increase the dynamic range for signals. For this reason, a limiter 6 is provided to prevent an excessively high level signal outside the range from being input to the A / D converter 60 in the event of an abnormality. The limiter 6 in FIG.
It includes all of the limiters 57, 58, 59 of FIG. Note that Vs
Is a reference voltage.

[Effects] As described above, according to the present invention, a noise component is removed from the detected photoconductor charging current signal by the first low-pass filter means (1), and further, the second low-pass filter means (2)
To remove the AC component, while the absolute value conversion means (5)
A / D conversion means (60) converts the electric signal output from the first low-pass filter means (1) to a signal of its absolute value level
Converts the level of the signal output by the second low-pass filter means (2) and the absolute value conversion means (5) into a digital quantity, and the control means (10 to 30) outputs the signal from the A / D conversion means (60). High voltage power supply means (40 ₁ , 40n) based on the amount of digital
, The stable control of DC corona discharge and AC corona discharge can be performed without being affected by noise caused by a single spark discharge or the like occurring in the corona discharger.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a control system relating to a corona discharger of the apparatus shown in FIG. FIG. 2 is a front view showing an image forming unit of the electrophotographic apparatus. FIG. 3 is a block diagram showing a current flow relating to one corona discharger, FIG. 4 is a waveform diagram of a PWM signal, FIG. 5 is a graph showing a correlation between a signal duty and a current value, and FIG. And FIG. 7 is a block diagram showing a specific configuration of two high-voltage power supplies.
The figure is a waveform diagram showing the output voltage waveform of the high voltage power supply of FIG. FIG. 8 and FIG. 9 are flowcharts showing a part of the processing of the CPU 10. FIG. 10 is an electric circuit diagram showing a specific configuration of the photosensitive member charging current detection circuit of FIG. 10: microcomputer (control means) 20: timer 30 _{1 to} 30n: integration circuit 40 _{1 to} 40m: high-voltage power supply (high-voltage power supply means) 50: photoconductor charging current detection circuit 51: voltage conversion circuit (charging current detection means) 52 : Low-pass filter (low-pass filter means) 53: low-pass filter 54: plus detection circuit 55: minus detection circuit 56: AC detection circuit 57, 58, 59: limiter 60: A / D converter (A / D conversion means) PC: Photoconductor

Claims (1)

(57) [Claims] A corona discharge electrode disposed opposite to a surface of a photoreceptor for forming an image; a high voltage power supply for applying a high voltage to the corona discharge electrode; and a current flowing from the corona discharge electrode to the photoreceptor. Charging current detecting means for detecting; first low-pass filter means for removing a noise component of the electric signal output from the charging current detecting means; second low-pass for removing an AC component of the electric signal output from the first low-pass filter means Filter means; absolute value conversion means for converting a signal obtained by removing a DC component from the electric signal output from the first low-pass filter means to a signal of its absolute value level; signal of the signals output by the second low-pass filter means and the absolute value conversion means A / D conversion means for converting a level into a digital quantity; and an output level of the high-voltage power supply means based on the digital quantity output from the A / D conversion means. A corona discharge device comprising: control means for controlling