JPH0253789B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an apparatus for forming an electrostatic latent image by charging a photoreceptor and then exposing it to light, and forming an image by developing the electrostatic latent image. Conventionally, in an image forming apparatus such as a copying machine, the surface potential of a photoreceptor is detected prior to the start of an image forming cycle, and the amount of charge is determined so that the detected value becomes a target potential.
There is known a method in which process conditions such as exposure amount are controlled and an image forming cycle is executed under the process conditions obtained by the control. However, when performing surface potential detection and process means condition control, for example, if the initial current flowing through the charger etc. is set to a constant value each time and the above control is performed, the state of the equipment, for example when the equipment is not used for a short time, Even though there is little variation from the process conditions set during the image forming cycle, control must be performed again using the initial values, and the time loss until the process conditions are optimized is rather large. This resulted in a decrease in copy speed. The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus that can shorten the time required to optimize the amount of charge and prevent an increase in the time required for image formation as much as possible. It is about providing. That is, the present invention provides a charging means for charging a photoreceptor, an exposure means for forming an electrostatic latent image by exposing the charged photoreceptor, a developing means for developing the electrostatic latent image on the photoreceptor, and the photoreceptor. a detection means for detecting the surface potential of the body; prior to an image forming cycle, the charging means is operated based on initial data to charge the photoreceptor, and thereafter the surface potential of the photoreceptor detected by the detection means is detected; a control unit that executes optimization control to obtain control data for the charging unit to bring it closer to a target potential, and operates the charging unit based on the control data in a subsequent image forming cycle, the control unit comprises a storage means for storing control data for the charging means obtained by the optimization control during execution of an image forming cycle and after the end of the image forming cycle,
The present invention provides an image forming apparatus characterized in that the optimization control is executed using the control data stored in the storage means as the initial data during the next optimization control performed prior to the next image forming cycle. . In electrostatic recording devices using conventional surface electrometers, when the detection output of the detection means for detecting surface potential is held for a long time, stable images cannot be formed due to changes in the holding voltage over time. Nakatsuta. The object of the present invention is to provide an electrostatic recording device that does not have the above-mentioned drawbacks. More specifically, a high-voltage power supply for a charging corona discharge device whose output can be varied, a detection means for detecting an electrical state according to the surface potential on the recording medium, and an output of the high-voltage power supply according to the output of the detection means. In an electrostatic recording apparatus having a control means, the detection by the detection means and the output control of the high voltage power source are repeatedly performed, and the output of the high voltage power source to the recording medium is set to a predetermined value at a predetermined time. An object of the present invention is to provide an electrostatic recording device characterized by having a setting means for adjusting the settings. FIG. 1a is a sectional view of a copying apparatus to which the present invention can be applied. The surface of the drum 47 is made of a three-layer seamless photoconductor using a CdS photoconductor, is rotatably supported on a shaft, and is rotated in the direction of the arrow by a main motor 71 activated when the copy key is turned on. Start. When the drum 47 rotates by a predetermined angle, the original placed on the original platen glass 54 is moved to the first scanning mirror 44.
illuminated by an illumination lamp 46 integrally configured with
The reflected light is scanned by the first scanning mirror 44 and the second scanning mirror 53. By moving the first scanning mirror 44 and the second scanning mirror 53 at a speed ratio of 1:1/2, the original is scanned while the optical path length in front of the lens 52 is always kept constant. The above reflected light image shows the lens 52 and the third mirror 55.
After passing through, an image is formed on a drum 47 at an exposure section. The drum 47 is simultaneously neutralized by the pre-exposure lamp 50 and the pre-AC charger 51, and then the drum 47 is charged by the primary charger 5.
It is corona charged (for example, +) by 1a. Thereafter, the drum 47 is the exposure section, and the image irradiated by the illumination lamp 46 is slit-exposed. At the same time, AC or corona charge removal with a polarity opposite to the primary one (for example -) is performed by a charge remover 69, and then a high-contrast electrostatic latent image is formed on the drum 47 by uniform surface exposure using a full-surface exposure lamp 68. The electrostatic latent image on the photosensitive drum 47 is then visualized as a liquid-developed toner image by the developing roller 65 of the developing device 62, and the toner image is easily transferred by the pre-transfer charger 61. The transfer paper in the upper cassette 10 or the lower cassette 1 is fed into the machine by a paper feed roller 59, and is sent in the direction of the photosensitive drum 47 with accurate timing by a register roller 60, where the leading edge of the latent image and the leading edge of the paper are conveyed. can be matched at the transfer section. Next, while the transfer paper passes between the transfer charger 42 and the drum 47, the toner image on the drum 47 is transferred onto the transfer paper. After the transfer is completed, the transfer paper is separated from the drum 47 by the separation roller 43, sent to the conveyance roller 41, guided between the hot plate 38 and press rollers 40, 41, and fixed by pressure and heat. The paper is discharged to the tray 34 by the discharge roller 37 via the paper detection roller 36 . After the transfer, the drum 47 continues to rotate and its surface is cleaned by a cleaning device composed of a cleaning roller 48 and an elastic blade 49, and the process proceeds to the next cycle. Here, a surface electrometer 67 for measuring the surface potential is connected to the drum 47 between the entire surface exposure lamp 68 and the developing device 62.
mounted in close proximity to the surface of the As a cycle executed prior to the above-mentioned copy cycle, there is a step of pouring a developer onto the cleaning blade 49 while the drum 47 is stopped after the power switch is turned on. Hereinafter referred to as Priwetsu. This is to flush out the toner accumulated near the cleaning blade 49 and to provide lubrication to the contact surface between the blade 49 and the drum 47. Also, after the prewetting time (4 seconds), the drum 47 is rotated, residual charges and memory on the drum 47 are erased using a pre-exposure lamp 50, a pre-AC static eliminator 51a, etc., and the drum surface is cleaned using a cleaning roller 48 and a cleaning blade 49. There is. Hereinafter, this will be referred to as forward rotation. This is to make the sensitivity of the drum 47 appropriate and to form an image on a clean surface. The pre-wet time and pre-rotation time (number) are automatically changed depending on various conditions (described later). Also, as a cycle after the set number of copy cycles are completed, the drum 47 is rotated several times,
There is a step in which residual charges and memory on the drum are removed using an AC charger 69 or the like, and the drum surface is cleaned. Hereinafter referred to as post-rotation LSTR. This is to electrostatically and physically clean the drum 47 before leaving it. FIG. 1b is a plan view of the vicinity of the blank exposure lamp 70 in FIG. Blank exposure lamp 70-1
70-5 is turned on when the drum is rotating and not during exposure to erase the drum surface charge and prevent excess toner from adhering to the drum. However, the blank exposure lamp 70-1 is
Since the drum surface corresponding to 7 is irradiated, it is turned off momentarily when measuring the dark area potential with the surface electrometer 67. Also, for B size copies, the image area is A4
The blank exposure lamp 70-5 is turned on for the non-image area even when the optical system is moving forward. The lamp 70-0 is called a sharp cut lamp, and the separation guide plate 43
- Irradiate the drum part that is in contact with 1 with light,
The electric charge in that area is completely erased to prevent toner from adhering to the area and to prevent contamination of the width of the separation gap.
This sharp cut lamp is always lit while the drum is rotating. At each processing position in the copying process of such an electrophotographic copying device, how does the surface potential of the photosensitive drum correspond to the bright areas (areas that reflect more light) and dark areas (areas that reflect less light) of the document? Figure 2 shows how it changes. What is required for the final electrostatic latent image is the surface potential at point C in the figure, and the surface potentials a and b in the dark and bright areas are the surface potentials of the photosensitive drum 47.
When the ambient temperature rises, it changes as shown in Figure 3 A' and B', and as the photosensitive drum 47 ages, it changes as shown in Figure 4 A' and B', and the difference between dark and bright areas changes. Contrast cannot be obtained. A method for compensating for changes in surface potential due to temperature changes or aging will be described in detail below. First, a surface electrometer as a detection means for detecting surface potential will be explained. Figure 5 is a side sectional view of the surface electrometer, and Figure 6 is a side sectional view of the surface electrometer.
A cross-sectional view taken along the line X-X' in the figure.
FIG. 8 is a cross-sectional view taken along line Y--Y' in the figure, and a perspective view of a chopper as an intermittent interrupting means to be described later. In FIGS. 5, 6, 7, and 8, reference numeral 81 denotes an outer cylinder made of brass, and the outer cylinder has a surface charge detection window 88. 82 is a motor serving as a driving means for rotating the chopper 83; 83 is a cylindrical chopper having a light emitting diode light passage window 90 and a potential measurement window 89; 84 is a light emitting diode, 85 is a surface charge measuring electrode, 86 is a preamplifier printed board on which a detection circuit for detecting the output of the electrode 55 is formed;
87 is a phototransistor. The surface electrometer 67 is installed at a position 2 mm away from the surface of the drum, which is the fixed surface to be covered, so that the surface charge detection window 88 faces the drum surface. A preamplifier printed board 86 for amplifying voltage is built-in and integrally formed. When a sensor motor drive signal SMD is output from a control circuit (not shown), the sensor motor 82 is driven, the cylindrical chopper 83 rotates, and the charge on the drum surface is induced in the electrode 85 via the potential measurement window 89. Ru. The potential measurement windows 89 are provided at four locations on the chopper 83 at equal intervals, and the light emitting diode light passing windows 90 are provided at four locations at equal intervals exactly in the middle of each potential measurement window 89. The voltage induced at the electrode 85 becomes an alternating current voltage because the chopper 83 rotates and interrupts the drum surface and the electrode 85 at equal intervals. The light from the light emitting diode 84 is received by the phototransistor 87 when the chopper 83 intercepts the drum surface and the electrode 85, and the output of the phototransistor 87 is used as a synchronizing signal. Reference numeral 91 denotes a shielding member for preventing light from entering the phototransistor 87 from the outside, and prevents dust, toner, etc. from entering the surface electrometer and adversely affecting measurement. A variable resistor 92 that adjusts the gain of the surface potential detection output by changing the amplification factor of an amplifier mounted on the printed board 86 can be adjusted through an opening 93 with a driver or the like. The surface electrometer 67 is slightly longer than the drum 47, and is attached to side plates 96, 97 that support the drum etc. by means of a circular vertical tip 94 for positioning and a rear end 95. The side plate 97 is removable. Next, an overview of the surface potential control method will be explained. In this embodiment, in order to detect the drum surface potential in bright and dark areas, the document illumination lamp 4 shown in FIG.
A blank exposure lamp 70 is used instead of a lamp 6. The surface potential of the portion of the drum surface that is irradiated with light from the blank exposure lamp 70 is measured as the bright surface potential, and the surface potential of the portion of the drum surface that is not irradiated with the light of the blank exposure lamp is measured as the dark surface potential. First, values of the bright area potential and dark area potential that can obtain an appropriate image contrast are set as target values. In this example, the target bright area potential V _L0 is −
The target dark potential V _D0 was set to 100V and +500V.
In this embodiment, the surface potential is controlled by controlling the current flowing through the primary charger and the AC charger, so that the bright area potential and the dark area potential are the target potentials V _L0 and V _D0 respectively.
It is assumed that the positive charger reference current I _P1 and the AC charger reference current I _AC1 are as follows. In this embodiment, I _P1 =350 μA I _AC1 =200 μA. Explain the control procedure. First, the surface potentials detected at the first time are assumed to be a bright area potential V _L1 and a dark area potential V _D1 , respectively, and it is determined how much difference there is from the target bright area potential V _L0 and the target dark area potential V _D0 , respectively. If the differential voltages are △ _L1 and △V _D1 , respectively, △ _L1 = V _L0 −V _L1 (1) △ _D1 = V _D0 − V _D1 (2) The difference in bright area potential is corrected using an AC charger, and the dark area potential is Correction of the difference is performed in the primary charger, but in reality
Controlling the AC charger affects not only the bright area potential but also the dark area potential. Similarly, controlling the primary charger affects not only the dark area potential but also the light area activity, so we adopted a correction method that takes both the AC charger and the primary charger into consideration. The corrected current value △I _P1 of the primary charger is △ _P1 = α ₁ · △V _D1 + α ₂ · △V _L1 (3). Here, the setting coefficients α ₁ and α ₂ are changes in the current value of the primary charger when the surface potentials V _D and V _L are changed, respectively, and can be expressed as follows. α ₁ = △I _P (Change in primary charger current) / △V _D (Change in dark area potential) (4) α ₂ = △I _P (Change in primary charger current) / △V _L (Light area Change in potential) (5) On the other hand, the corrected current value △I _AC1 of the AC charger is I _AC1 = β ₁・△V _D1 +β ₂・△V _L1 (6) Here, the setting coefficients β ₁ and β ₂ are as follows. It can be expressed as follows. β ₁ = △I _AC (Change in AC charger current) / △V _D (Change in dark potential) (7) β ₂ = △I _AC (Change in AC charger current) / △V _L (Change in light potential) change) (8) Therefore, the positive charger current I _P2 after the first correction
and AC charger current I _AC2 is expressed as follows. From equations (4)(5)(1), similarly, I _P2 =α ₁・△V _D1 +α ₂・△V _L1 +I _P1 I _AC2 =β ₁・△V _D1 +β ₂・△V _L1 +I _AC1 (9 ) (10) Here, the setting coefficients α ₁ , α ₂ , β ₁ , and β ₂ are determined based on predetermined charging conditions, such as ambient temperature, humidity, and the state of the corona charger, so changes in the atmosphere may affect charging. Because it is not known whether the surface potential will reach the target value with one control due to deterioration of the device, etc., the surface potential was measured multiple times when the device was in a specified state, and the output of the corona discharge device was controlled the same number of times as the measurements. There is. Since the second and subsequent corrections use the same method as the first correction described above, the current values of the positive charger and AC charger after the nth correction I _Po+1 ,
I _ACo+1 can be expressed as follows. I _Po+1 = α ₁・△V _Do +α ₂・△V _Lo +I _Po I _ACo+1 = β ₁・△ _Do +β ₂・△V _Lo +I _ACo Figure 9 a and b show the primary charger control current It shows the change in dark potential when Ip is corrected three times. 9th
Figure a shows the case where the set calibration coefficient is smaller than the actual coefficient, and Figure 9 b shows the case where the set calibration coefficient is larger than the actual coefficient. In this embodiment, the number of corrections was set as shown in the table below.

[Table] By setting in this way, it is possible to further stabilize the surface potential on the photoreceptor and at the same time to minimize the decrease in copy speed. Also, in state 1, the previous control output current values of the primary charger and AC charger are memorized and the primary charger and AC charger are controlled using those values, and in state 2, the previous control output current is It detects and controls the surface potential by flowing it through the body. However, in states 3 and 4, the reference currents I _P1 and I _AC1 are applied to the photoreceptor during the first correction measurement. That is, in states 3 and 4, the control current used in the previous copy is reset and returned to the reference current, the surface potential is measured, and the output current is controlled. In addition, if a copy operation is performed continuously for 30 minutes without leaving it for more than 30 seconds, one correction is performed after 30 minutes have passed. This is due to the performance of the memory circuit that stores the control signals, and the range in which the information stored in the analog memory (integrator circuit (see Figure 14) described later) is not lost is as follows:
This is because it is desirable to do this within 30 minutes after memorizing it. 30
If more than a minute has elapsed, the stored information may change by more than 5% from the initial value, so the surface potential is reset and then remeasured. Further, the number of corrections is made different for states 2, 3, and 4 because the degree of recovery from fatigue of the photoreceptor varies depending on the standing time. That is, the shorter the standing time, the greater the degree of recovery from fatigue of the photoreceptor. Therefore, the longer the neglect time, the more times the corrections are made. In this embodiment, a timer is operated in synchronization with the copy completion rate to measure time until the next copy start key is pressed. Then, the number of corrections is set as shown in the table above according to the time measured by this timer. Further, in this embodiment, similar surface potential control is performed when the power is turned on. That is, in this embodiment, power is supplied to each load via the main switch SW and the sub-switch SSW, and when the main switch SW is turned on for the first time after the sub-switch SSW is turned on, the same correction operation as in the case of state 4 is performed. I do. Also, if the main switch SW is turned on again while the sub switch SSW is turned on, the main switch
If the time from when the SW is turned off until it is turned on is less than 5 hours, the same corrective action as in Purification State 3 is performed, and the time from when the main switch SW is turned off until it is turned on is 5 hours or less. In the above case, the same correction operation as in the case of the above-mentioned state 4 is performed. In this embodiment, the developing bias voltage is further controlled. FIG. 10a shows a schematic cross-sectional view for explanation. This is done in the following way. A standard white plate 8 attached to the side of the document table glass 54 just before exposing the document
0 with a halogen lamp 46 for exposing the original,
The scattered reflected light is irradiated onto the drum 47 via the mirrors 44, 53, 55, the lens 52, and the like. This irradiation light amount is a standard light amount, and then the exposure amount when the lamp 81 moves and the original is actually exposed is changed to the exposure amount arbitrarily set by the operator. The surface potential meter 67 measures the surface potential V _L of the portion of the drum 47 irradiated with the scattered reflected light, and sets the voltage obtained by adding +50 V to the measured value V _L as the developing bias voltage V _H. Due to the developing bias voltage V _H , the potential of the toner becomes almost the same as the bias voltage. For example, when the standard bright area potential, that is, the measured value V _L is -100V, the potential of the toner becomes -50V, and the toner and drum repel, and the toner Since it does not adhere to the surface of the document, it is possible to prevent fogging in the background area of the document and to always perform stable development, resulting in a stable image. In addition, in this embodiment, a standard white plate 80 corresponding to the white part of a general original is irradiated with a standard amount of light, and when the original is actually exposed, the exposure amount is changed to an amount arbitrarily set by the operator. Even when the drum is colored rather than white, a stable image can be obtained by changing the bright area surface potential of the drum depending on the exposure amount. A lighting control circuit for adjusting the amount of light from the document exposure lamp 46 is shown in FIG. 10b. In the figure, k301 is a relay in the normal state as shown in the figure, which turns off the power to the lamp LA1 in the event of an abnormality. When the switch Sw11 is turned on by the timing output IEXP 1 signal from the DC controller (not shown), the try-out Tr is turned on.
to turn on the lamp. Please refer to the time chart in FIG. 11 for the timing. This device adjusts the copy density by changing the amount of light emitted from the lamp LA. For this purpose, a dimming circuit is provided to change the amount of light by controlling the phase of the energization amount of the triax according to the amount of displacement of the density adjustment means VR106. Relay K103 performs dimming operation by resistor VR106 in the state shown in the figure, and performs dimming by the same amount (standard light amount) as when lever 5 is operated in the reverse state. Switch Sw1 is activated by the standard light intensity signal SEXP.
When 2 is turned on, the standard white plate is irradiated with the amount of light 5, the bright area potential (on the photoreceptor) is measured, and the bias voltage of the developing roller is determined in accordance with that value. As described above, since the developing bias voltage _VH is determined by shining light onto the standard white plate 80 using the document exposure lamp that actually uses exposure, the precision of the control of the developing bias voltage is improved, and the control is performed just before exposing the document. There is no reduction in copy speed due to the high speed. Furthermore, since the exposure amount is changed to an amount arbitrarily set by the operator when exposing the original, a stable image can be obtained without fogging even when the background of the original is not white but colored. FIG. 11 shows a time chart for performing the image formation and surface potential control described above. In FIG. 11, INTR is a pre-rotation for erasing residual charges on the drum and making the sensitivity of the drum appropriate, and is always executed before a copying operation.
CONTR-N is a drum rotation to keep the drum in a steady state depending on the standing time, and at the same time,
A surface potential meter measures the bright area potential V _L and dark area potential V _D alternately each time the drum rotates, and the potential of the drum surface is brought close to the target value by the action of a surface potential control circuit, which will be described later. Although the surface potentials V _D and V _L are detected once per rotation, it is of course possible to detect them multiple times. CR1 is the bright area potential V _L and the dark area potential at 0.6 rotations of the drum.
This is the drum rotation that detects _VD and controls the corona charger. CR2 is the rotation of the drum immediately before the start of copying, and is used to measure the bright area potential with a standard amount of light from the document illumination lamp and to determine the bias value for the developing roller. It is always executed when copying starts.
SCFW indicates that the optical system is moving forward. In other words, it shows the actual copy operation rotation. A circuit for realizing the surface potential control described above will be described below. FIG. 12 is a surface potential detection processing circuit diagram. Explain circuit operation. Sensor motor drive signal from input terminal T1
When SMD is input, sensor motor drive control circuit
The CT 1 operates to drive the sensor motor 82 and the chopper 83 to rotate. When the chopper 83 rotates, an AC voltage having an amplitude proportional to the absolute value of the surface potential of the photosensitive drum 47 is induced in the measurement electrode 85 as described above. The AC voltage is amplified by an amplifier circuit CT2 and input to an input terminal of a synchronous clamp circuit CT4. FIG. 13 shows the output waveform of the amplifier circuit CT2. In Figure 13, Figure 13a
The solid line indicates the case where the surface potential is positive, and the dotted line indicates the case where the surface potential is negative.
and the synchronizing signal SYC generated by the phototransistor 87. The synchronous signal SYC is amplified by the synchronous amplifier circuit CT3 and then sent to the synchronous clamp circuit.
Input to CT4. The other output terminal of the synchronous amplifier circuit CT3 is connected to a light emitting diode LED6, which lights up when a synchronous signal is generated and detects the rotation of the sensor motor 82. The synchronous clamp circuit CT4 converts the AC voltage from the amplifier circuit CT2 into a synchronous amplifier circuit.
This is a circuit that clamps to zero volts using the synchronization signal of the output of CT3. The clamping timing corresponds to when the chopper 83 closes the potential detection window 89, so when the drum surface potential is positive, the output of the synchronous clamp circuit CT4 is positive, and when the surface potential is negative, the output is negative. Further, the light emitting diode LED1 connected to the synchronous clamp circuit CT4 lights up when the surface potential is positive, and the light emitting diode LED2 lights up when the surface potential is negative. The output signal of the synchronous clamp circuit CT4 is input to the smoothing circuit CT5 and exchanged into a DC voltage. The output signal of the smoothing circuit CT5 is the standard bright area surface potential V _L Hold circuit CT7, the bright area surface potential V _L
It is input to the hold circuit CT8 and the dark area surface potential _VD hold circuit CT9. Said V _L hold circuit CT
7 is the V _L detection pulse signal from the DC controller
V _L CTP is inverter INV in pulse circuit CT6
1 and 2, and the signal V _L CTP
The output voltage of the smoothing circuit CT5 when is output is held. Further, the light emitting diode LED4 in the pulse circuit CT6 lights up when the signal V _L CTP is output. Similarly, the V _L hold circuit CT8 holds the output voltage of the smoothing circuit CT5 when the V _L detection signal V _L CTP is output, and the light emitting diode LED5 lights up when the signal V _L CTP is output. Similarly, the V _D hold circuit CT9 holds the output voltage of the smoothing circuit CT5 when the V _D detection signal V _D CTP is output, and the light emitting diode LED3 lights up when the signal V _D CTP is output. The output of the V _L hold circuit CT7 is output from the output terminal T.
2 is output. Also, V _L hold circuit CT8 and V _D
The output of the hold circuit CT9 is output to a display circuit CT10 and an arithmetic circuit CT11. The display circuit CT10 inputs the output of the preamplifier circuit CT2, the output of the V _L hold circuit CT8, and the output of the V _D hold circuit, and displays a surface potential contrast voltage (V _D - V _L ) below a predetermined voltage. In case light emitting diode LED7, and LED8
lights up to notify you that a stable image cannot be obtained. The light emitting diode LED7 lights up when the predetermined voltage is set to +500V, for example, and the potential contrast voltage is 500V or less, and the LED
8 sets the predetermined voltage to +450V, for example, and lights up when the potential contrast voltage is 450V or less.
These display elements make it possible to know whether the surface potential is normal even without a special measuring device. Further, the light emitting diode LED9 is a display circuit that lights up if a potential is generated on the drum surface, regardless of whether the polarity is positive or negative. The arithmetic circuit CT11 is a circuit that performs the arithmetic operations described above in the surface potential control method, and is a circuit that performs the arithmetic operations described above in the surface potential control method.
The current I _Po passed through the AC charger when detecting the surface potential,
Calculate the current values △I _Po and △ _{I ACo} that are the differences between I ACo and the control current value I _{Po +1} I _ACo+1 that should be passed next time. △I _Po , △
Each I _ACo is expressed as follows. △I _Po ＝I _Po+1 −I _Po ＝α ₁・△V _Do ＋α ₂・△V _Lo △I _ACo ＝I _ACo+1 −I _ACo ＝β ₁・△V _Do ＋β ₂・△V _Lo calculation circuit CT11 is CT11-a and CT11-b
The CT11-a amplifies the outputs of the hold circuits CT8 and CT9, shifts them to a bright potential V _Lo and a dark potential V _Do for calculation, and sends them to the circuit CT11-b. . Circuit CT1
1-b is α ₁ (V _D0 −V _Do ) ……(1) β ₁ (V _D0 −V _Do ) ……(2) α ₁ (V _L0 −V _Lo ) ……(3) β ₂ (V _L0 −V _o ) ...(4) is calculated and returned to the circuit CT11-a again, and (1)+(3), (2)+(4) are calculated and outputted to the integrating circuit CT12. The integrating circuit CT12 has two circuits having the configuration shown in FIG. 14, one for bright area potential and one for dark area potential. In Fig. 14, the terminal T11 has a set signal.
SET is input, and a reset signal RESET is input to terminal T12. Switch SW
1, SW2 is an analog switch, and when the set signal SET occurs, the switch SW1 closes, and when the reset signal RESET occurs, the switch SW2 closes.
2 closes. When the dark potential detection signal V _D CTP is generated, the set signal SET is activated by the monostable circuit CT13, which closes the switch SW1 and is input to the negative input terminal of the operational amplifier Q1.At the same time, the capacitor C1 is charged to the input voltage Vi. Also, as previously stated that initial settings are performed in states 3 and 4, the initial setting signal ISP is output at this time. The setting signal ISP is a reset signal circuit.
The signal is inputted to the integrating circuit C12 as an integrating circuit reset signal via CT14 and closes the switch SW2. When switch SW2 closes, capacitor C1
The charged charge is discharged by the resistor R1 and output to the output terminal T1.
4, a reference potential of 12V is output. In addition, since switch SW1 is closed for only 1/5 of the time required to fully charge and discharge capacitor C1, input terminal T1
The battery is charged and discharged by 1/5 of the difference between the input voltage Vi of No. 3 and the reference voltage (12 [V]). For example, if the input voltage Vi ₁ =14.5 [V] when the first set signal SET is generated, the output voltage v _p1 can be expressed as follows. v _p1 =12−v _i1 /5+12=−2.5/5+12=11.5 [V] The output voltage v _p1 is 11.5 [V]. Next, when the second set signal is generated, if the input voltage v _i2 = 9.5 [V], the output voltage v _p2 will be similarly v _p2 = v _p1 - v _i2 /5 + 12 = 11.5 - 9.5 / 5 + 12 = 12.4 [V].
] becomes. Repeat this depending on the number of corrections. In other words, the output voltage v _p before switch SW1 closes is v _po-1
Assuming that the next input voltage V _i is V _io , the next output voltage V _po will be V _po =V _po −V _io /5+12, and 1/5 of the change will be charged. Here, as mentioned above, the input voltage V _i corresponds to the current values △I _Po and △I _ACo of the difference, and the output voltage V _p corresponds to the control current value I _Po+1 or I _ACo+1 . . The output voltage V _p is output from multiplexer circuit CT15.
are input respectively. Multiplexer circuit CT15 is a pulse control circuit
It is controlled according to the signal from CT16. The pulse control circuit CT16 inputs different control signals as 2-bit parallel signals to the multiplexer circuit CT15 during a prewetting or standby period, an initial setting period, a period during controlled rotation or copying, and a period of post-rotation after copying is completed. .
The multiplexer circuit CT15 changes the contact point for each period. The multiplexer circuit CT15 receives the primary charger control voltage V _P from the terminals T3 and T4, respectively.
Outputs AC charger control voltage V _AC . In detail, the pulse control circuit CT16 is activated by the multiplexer circuit CT1 depending on the states of the initial setting signal ISP, the high voltage control pulse HVCP, and the post-rotation pulse LRP.
Control so that contact points Xc and Yc of 5 are converted. When the input side contacts are Xn and Yn (n = 0.1.2.3), the truth table for each pulse signal and the connection status of the input/output contacts is shown below.

【table】 The contents of input side contacts Xn and Yn are as follows.

[Table] FIG. 15 shows a control pulse generation timing chart. While copying is stopped, Xc and Yc are connected to X ₀ and Y ₀ , respectively. Since both X ₀ and Y ₀ are +18V, both the primary and secondary high-voltage power supplies are in a non-operational state. In the first half of the forward rotation, XcYc are X ₁ Y ₂ respectively
connected to. Since both X ₁ and X ₂ are +12V,
Both the primary and secondary high voltage power supplies are in a state of generating standard current, and at this time the surface potential of the drum is detected by the surface electrometer. Next, in the second half of the forward rotation, XcYc
are connected to X _{2 and} Y ₂ respectively, and if the surface potential of the drum measured in the first half of the previous rotation deviates from the target surface potential, the amount of correction is transmitted to X ₂ and Y ₂ ,
The high voltage power supply supplies the corrected high voltage current to the charger. This state is maintained during the next copying stage as well.
During post-rotation, XcYc is connected to X ₃ and Y ₃ respectively, so since X ₃ is +18V, the primary charger stops operating, and Y ₃ becomes the post-rotation control signal.
A predetermined corona current is applied to the AC charger to remove the charge remaining on the drum surface. Primary charger control voltage V _P outputted from the multiplexer circuit CT15, AC charger control voltage
V _AC is input to the charging voltage control circuit shown in FIG. The charging voltage control circuit will be explained. The primary charger control voltage V _P is input to the inverting input terminal of the operational amplifier Q5 via a resistor R7. The voltage difference between the voltage V _FP applied to the non-inverting input terminal of the operational amplifier Q5 from the resistor VR1 and the correction voltage V _P is multiplied by −R ₆ /R ₇ and output from the operational amplifier Q5. Primary charger drive signal
When HVT1 is “H”, the output of operational amplifier Q5 is the transistor of Darlington current amplifier AMP1.
Tr3 does not turn on. In other words, the output of the Darlington current amplifier AMP1 is 0. Said signal HVT
When 1 is "L", the transistor Tr3 is turned on and the voltage that is almost the same as the output voltage of the operational amplifier Q5 is 1.
It is then output to the high voltage transformer TC1. The oscillator Q1 in the primary transformer TC1 is a transistor Tr1,
Turn on Tr2 alternately. The transformer TS1 boosts the voltage to the secondary side according to the turns ratio and sends the secondary output to the diode D1.
The voltage is rectified and applied to the primary charger 51. The primary corona current I _P flowing through the primary charger 51 is the resistor R1.
1 and is detected by the op amp Q through resistor VR1.
The primary corona current I _P is controlled such that the voltage V _FP and the primary charger control voltage V _P coincide with each other. Similarly, the AC charger control voltage V _PC is input to the inverting input terminal of the operational amplifier Q7 via the resistor R13. Voltage applied to the non-inverting input terminal of operational amplifier Q7 from resistor VR2
The voltage difference between V _FAC and the correction voltage V _P is multiplied by -R9/R10 and output from the operational amplifier Q7. When AC charger drive signal HVT2 is “H”, operational amplifier Q7
The output of the transistor Tr5 of the Darlington current amplifier AMP2 does not turn on. In other words, the output of the Darlington current amplifier AMP2 is 0. When the signal HVT2 is "L", the transistor Tr5 is turned on and a voltage substantially the same as the output voltage of the operational amplifier Q7 is output to the AC high voltage transformer TC2. The generator Q2 in the secondary high voltage transformer TC2 is a transistor.
Turn on Tr7 and Tr8 alternately. The transformer TS2 boosts the voltage on the secondary side according to the turns ratio, rectifies the secondary side output with the diode D12, and outputs it as a DC component output. The AC voltage generator ACS outputs an AC high voltage using an AC oscillator Q3 and a transformer TS2, and outputs the same to the secondary charger 69, superimposed on the DC output.
AC corona current flowing through AC charger I _AC is resistance R1
Detected at 2. The detection output is amplified by an amplifier AMP3, and then only the difference between positive and negative components is detected by a smoothing circuit REC, and then amplified by a DC amplifier AMP4.
Further, the detection output is amplified by the amplifier AMP4, and then input to the non-inverting input terminal of the operational amplifier Q7 via the resistor VR2, so that the voltage is increased as described above.
AC is adjusted so that V _FAC and the AC correction voltage V _P match.
This controls the corona current I _AC . As described above, in this embodiment, since the corona current value is controlled to be constant by the surface potential detection output and the corona current detection output, the charger load fluctuation due to temporary environmental changes or the power supply of the corona discharge device It is possible to correct fluctuations and keep the corona current constant, and it is also possible to correct fluctuations in surface potential with respect to corona current due to changes over time such as drum deterioration. Furthermore, by switching the switches SW21 and SW22, it is also possible to set the input voltage to a predetermined voltage regardless of the control voltages V _P and V _AC . Furthermore, in this embodiment, limiter circuits LIM1 and LIM2 are provided as output limiting means to prevent accidents. The operation of the limiter circuits LIM1 and LIM2 will be explained. Operational amplifier Q14 and resistor R39 are buffer circuits, and a voltage obtained by dividing the power supply voltage by resistors R31, R38 and variable resistor VR31 is obtained as the output of Q14. The output voltage of Q14 is an AC charger control signal that adjusts VR31 to activate the limiter.
Set it to a value 0.6V higher than the maximum value of V _AC , V _{AC MAX} . The operational amplifier Q7 is an inverter, and is in a relationship such that the voltage output current increases as the AC charger control signal V _AC decreases. AC charger control signal
If V _AC tries to fall below the minimum value V _{AC MIN} ,
Diode D31 turns on and control signal V _AC becomes R1
0, and is connected to the output of Q14 through a low resistance R41. The output voltage of Q14 is almost constant, and if the resistor R41 is sufficiently smaller than R10, the high voltage output current will no longer increase.
This means that there are limits. Diode D31
When it is ON and the limiter is applied,
The comparator 15 is reversed and the LED 31 lights up to confirm the operation of the limiter. The operating mechanism of the limiter circuit LIM1 of the primary charger is also very similar to the operation of the limiter circuit LIM2 of the AC charger.
The reason for providing the limiter circuit is to prevent the corona current of each charger from becoming abnormally large. The limiter circuits LIM1 and LIM2 operate because the target surface potential has not been reached even though a predetermined current is passed through the primary charger and AC charger, and this situation is particularly likely to occur if the drum has deteriorated. Become. Therefore, the light emitting diode LED30,LED
31 displays the operation of the limiter circuit LIM1 and at the same time monitors drum deterioration. Also, the electrode of the charger may be too close to the drum surface, or there may be foreign objects such as paper between the charger and the drum surface.
Alternatively, when the charger electrode breaks and contacts the drum surface, the charger electrode changes to glow discharge instead of corona discharge. If this happens, an excessive current may flow and damage the drum surface.
By providing the limiter circuit described above, the above-mentioned drawbacks can also be prevented. Next, a control circuit for controlling the developing roller bias voltage _VH will be explained based on the circuit diagram of FIG. 17. The output of the V _L hold circuit CT7 is input to the terminal T2. Main motor drive signal DRMD indicating drum rotation is connected to terminal T6, and terminal T7 is connected to main motor drive signal DRMD indicating drum rotation.
A roller bias control signal RBTP, which is generated during development of a latent image corresponding to a document, is input to RBTP.
While the drum is rotating and the latent image is being developed, the signal DRMD,
Since both RBTP are “H”, transistor Tr1
7, Tr18 is turned on and the gates of the depletion type junction FETs Q12 and Q13 become 0V, so both the FETs Q12 and Q13 are turned off. Therefore, the signal input to the operational amplifier Q11 is the output voltage V _L via the resistors R105 and VR13. The output of the operational amplifier Q11 is applied to a fixed point of the primary coil of the transformer T12 via a current booster composed of transistors Tr15 and Tr16, and the developing bias voltage V _H is adjusted according to the output voltage V _L by inverter circuits VINV and SINV, which will be described later. It becomes variable. At this time, the developing bias voltage V _H is controlled by inverter circuits SINV and VINV so that it is +50 V with respect to the standard bright area potential on the drum. Also, when the drum is rotating and the latent image is not being developed, DRMD is "H" and RBTP is "L", so transistor Tr17 is on and Tr18 is off, so the FET Q12 is off and Q13 is off. Turn on. When FET Q13 turns on, operational amplifier Q11
A predetermined voltage determined by a variable resistor VR15 is input to the transformer T12, and a fixed voltage corresponding to the predetermined voltage is input to the transformer T12 via the current booster.
At this time, the predetermined voltage determined by the variable resistor VR15 is set to a value such that the bias voltage _VH becomes -75V. When the drum is rotating and development is not in progress, developer is prevented from getting on the drum. Furthermore, when the drum is not rotating, both DRMD and RBTP are "L". At this time, the transistor Tr17 is turned off and the transistor Tr18 is turned on via the diode D27.The FET Q12 is turned on, and the transistor Tr18 is turned on via the diode D27.
3 is off. When the FET Q12 is turned on, a predetermined voltage determined by the variable resistor VR14 is input to the operational amplifier Q11, and a fixed voltage corresponding to the predetermined voltage is input to the transformer T12 via the current booster. At this time, the predetermined voltage determined by the variable resistor VR14 is set to a value such that the developing bias voltage _VH becomes 0V. This prevents the charged liquid developer from stagnation when the drum is not rotating. As described above, since the developing roller bias voltage V _H is changed according to the control state and the bias voltage V _H is controlled by the surface potential detection output during latent image development, more stable development is possible. Next, the operations of the fixed voltage output inverter transformer circuit SINV (hereinafter referred to as fixed inverter circuit) and the output variable inverter transformer circuit VINV (hereinafter referred to as variable inverter circuit) will be explained. The circuit operation of the fixed inverter circuit SINV will be explained. When power is applied to a fixed point of the primary winding of transformer T11, either transistor Tr11 or Tr12 begins to turn on. When the transistor Tr11 is turned on, the collector current of the transistor Tr11 increases, and reverse activation occurs in the collector side coil of the transistor Tr12 in accordance with the increase in the collector current, causing the base potential of the transistor Tr11 to become positive. To go. Therefore, the collector current of the transistor Tr11 further increases. In other words, positive feedback is applied to the transistor Tr11, and the transistor Tr11 is saturated with a time constant determined by the resistors R103, R104 and the inductance of the transformer Tr11. The transistor Tr1
When the collector current of transformer T11 is saturated, the collector current of transformer T11 is saturated.
The back electromotive force of the next coil becomes 0 and the transistor
Tr11 is turned off and the collector current decreases, and a back electromotive force corresponding to the decrease in collector current is generated in the primary coil of transformer T11, and transistor Tr1
Turn on 2. Similarly, transistors Tr11,
Tr12 is alternately turned on and off. Here, diodes D21 and D22 are transistor Tr1
1. This is a diode for protecting the base of Tr12. Resistor R105 is transistor Tr11, Tr12
This resistor is used to prevent variations in the collector current due to variations in hFE, and to prevent the oscillation duty ratio from becoming 1:1. The oscillation amplitude of the voltage induced in the primary coil of transformer T11 is approximately twice the voltage applied to the midpoint of transformer T11. The voltage induced in the primary coil is transferred to the transformer T
Diode D is boosted to a voltage determined by the number of turns of 11.
25. It is rectified and smoothed by capacitor C23 and a DC high voltage is output. Similarly, the operation of the variable inverter circuit VINV is almost the same, but since the voltage supplied to the midpoint of transformer T12 changes according to the input signal, transformer T1
The output voltage of 2 varies depending on the input signal. Figure 18 shows the high output voltage. In FIG. 18, the vertical axis shows the high voltage output voltage Vout, and the horizontal axis shows the input voltage Vin input to a fixed point of the transformer T12. Output voltage from the fixed inverter circuit SINV
Vs is always constant with respect to the input voltage Vin,
The output voltage _VV of the variable inverter circuit changes linearly with respect to the input voltage Vin. Therefore, the actual developing bias voltage _VH obtained by superimposing the output voltages Vs and _VV varies linearly from positive to negative with respect to the input voltage. As described above, since it has become possible to vary the developing bias voltage V _H linearly from positive to negative, the potential of the latent image on the photoreceptor corresponding to the background of the original is positive or negative. Control is easy, and since the inverter circuit as described above is used, the device can be made smaller. As described above, according to the present invention, when the surface potential is detected prior to the image forming cycle and the charge amount is controlled to be optimized based on the detected output, the control data obtained by the previous optimization control is used as the initial data. Since the charging means is operated using the charging means to perform optimization control, the time required for optimization control can be shortened, such as when the device is not in use for a short time, and an increase in the time required for image formation can be prevented as much as possible.

[Brief explanation of drawings]

FIG. 1a is a sectional view of a copying apparatus to which the present invention can be applied, FIG. 1b is a plan view of the vicinity of the blank exposure lamp 70, FIG. 2 is a characteristic diagram showing the surface potential of each part of the photosensitive drum, and FIG. , Fig. 4 is a characteristic diagram showing changes in surface potential, Fig. 5 is a side sectional view of the surface electrometer, Fig. 6 is a sectional view taken along the line X-X' in Fig. 5,
Figure 7 is a sectional view taken along the Y-Y' line in Figure 5;
9 is a perspective view of a cylindrical chipper, FIGS. 9a and 9b are diagrams showing changes in dark area surface potential, FIG.
Figure b is a lighting control circuit diagram of the original exposure lamp, No. 11.
The figure is a time chart of image formation and surface potential control, Figure 12 is a surface potential detection processing circuit diagram, and Figure 13 is a time chart of image formation and surface potential control.
The figure shows the output waveform diagram of the amplifier circuit CT2 and the synchronization signal.
Fig. 14 is an integral circuit diagram, Fig. 15 is a control pulse generation timing chart, Fig. 16 is a charging voltage control circuit diagram, Fig. 17 is a developing bias control circuit diagram, and Fig. 18 is a waveform diagram of high voltage output voltage. . In the figure, 47 is a photosensitive drum, 71 is a main motor, 46 is an original illumination lamp, 51 is a primary charger, 69 is an AC charger, 70 is a blank exposure lamp, 65 is a developing roller, and 67 is a surface electrometer. show.

Claims (1)

[Scope of Claims] 1. Charging means for charging a photoreceptor; Exposure means for forming an electrostatic latent image by exposing the charged photoreceptor; Development means for developing the electrostatic latent image on the photoreceptor; a detection means for detecting a surface potential of the photoreceptor; prior to an image forming cycle, the charging means is operated based on initial data to charge the photoreceptor, and the surface of the photoreceptor is then detected by the detection means; a control unit that executes optimization control to obtain control data for the charging unit to bring the potential closer to a target potential, and operates the charging unit based on the control data in a subsequent image forming cycle; The control means includes a storage means for storing control data for the charging means obtained by the optimization control during execution of an image forming cycle and after the end of the image forming cycle, and the control means stores the control data for the charging means obtained by the optimization control, and the control means stores the control data for the charging means obtained by the optimization control. An image forming apparatus characterized in that the optimization control is executed using control data stored in the storage means as the initial data.