JPH024902B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to an electronic copying apparatus having an original exposure lamp. [Background of the Invention] Conventionally, in an electrophotographic copying device, the surface potential on a photoreceptor is detected, and charging conditions are adjusted according to this detected value.
Devices that determine process conditions such as exposure conditions and development conditions are known. When performing such control,
Irradiating light from an original exposure lamp onto a photoreceptor and measuring the surface potential of the portion of the photoreceptor that is irradiated with the light to control a processing means such as a corona discharge device or a developing device is actually a method of exposure. This method is effective because it uses a document exposure lamp. However, in a device that adjusts the copy density by changing the amount of light emitted from an original exposure lamp, when attempting to control the processing means using the original exposure lamp, the amount of light changes each time the surface potential is measured. Accurate and stable measurement and stable control of the processing means based on the measurement are not possible. [Objective] The present invention has been made in view of the above points, and its object is to provide an electronic copying apparatus that can set appropriate developing conditions with extremely high accuracy and that enables proper original copying without fogging. It is about providing. That is, the present invention provides a latent image forming means that has a charging means that charges a recording medium and a first exposure means that exposes an original, and forms an electrostatic latent image corresponding to an image of the original on the recording medium; A developing means for developing an electrostatic latent image formed thereon, a second exposing means for exposing a non-image area of the recording medium, and an exposure amount of the first exposing means are arbitrarily set within a predetermined range. a setting means capable of detecting the surface potential of the recording medium, a reference member having a reference density, and turning on and off the second exposure means with the first exposure means turned off. The detection means detects the bright area surface potential and the dark area surface potential formed on the recording medium, and controls the output current of the charging means according to the detected values, and the reference is determined based on the controlled charging conditions. By exposing the member by the first exposure means, the bright area surface potential formed on the recording medium is detected by the detection means, and a developing bias voltage to be applied to the developing means is determined according to the detected value. When the output current of the charging means is controlled by the control means, the first exposure means is turned off, and when the developing bias voltage is determined, the exposure amount of the first exposure means is set to the standard light amount regardless of the setting means. An electronic copying apparatus is provided, comprising: a light amount adjustment means for adjusting the exposure amount of the first exposure means to the exposure amount set by the setting means during exposure of a document. [Embodiment] (Schematic configuration of copying apparatus) 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 in an exposure path. The drum 47 is simultaneously neutralized by the pre-exposure lamp 50 and the pre-AC charger 52, and then the drum 47 is charged by the primary charger 5.
1, it is corona charged (for example, +). 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 primary corona charge removal with a polarity opposite to that of the primary (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 developed with liquid by the developing roller 65 of the developing device 62 and visualized as a toner image, and the toner image is easily transferred by the pre-transfer charger 61. Upper cassette 10 or lower cassette 11
The transfer paper inside is fed into the machine by a paper feed roller 59, and is sent toward the photosensitive drum 47 with accurate timing by a register roller 60, so that the leading edge of the latent image and the leading edge of the paper are aligned at the transfer section. Can be done. 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 39, 40, and fixed by pressure and heat. The discharge roller 37 discharges the paper to the toner 34 via the paper detection roller 36 . After the transfer, the drum 47 continues to rotate and its surface is cleaned by a cleaning device comprising 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 copy cycle, there is a step of pouring a developer into 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 by a pre-exposure lamp 50, a pre-AC static eliminator 52, etc., and the drum surface is cleaned by a cleaning roller 48 and a cleaning blade 49. There are steps. 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 leave the drum 47 electrostatically and physically clean. 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, since the image size is smaller than the A3 size. 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. (Characteristics of the photosensitive drum) At each processing position in the copying process of such an electrophotographic copying device, the photosensitive drum is adjusted to correspond to bright areas (areas that reflect more light) and dark areas (areas that reflect less light) of the document. Figure 2 shows how the surface potential changes. What is necessary for the final electrostatic latent image is the surface potential at the center point 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 of the photosensitive drum 47 rises, it will change as shown in Figure 3 A' and B', and as the photosensitive drum 47 ages, it will change as shown in Figure 4 A' and B'. 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. (Structure of surface electrometer) First, a surface electrometer as a detection means for detecting surface potential will be described. 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 85 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. (Surface potential control method) Next, an outline of the surface control method will be explained. <Charger control> In this embodiment, in order to detect the drum surface potential in bright and dark areas, the document illumination lamp 4 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, the values of the bright and dark potentials that allow obtaining 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 difference voltages are ΔV _L1 and ΔV _D1 , respectively, ΔV _L1 = V _L0 −V _L1 (1) ΔV _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 potential but also the bright potential, so we adopted a modification method that takes both the AC charger and the primary charger into consideration. The corrected current value ΔI _P1 of the primary charger is Δ _P1 = α ₁ · ΔV _D1 + α ₂ · ΔV _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 = ΔI _P (Change in primary charger current) / ΔV _D (Change in dark potential) (4) α ₂ = ΔV _P (Change in primary charger current) / ΔV _L (Change in bright potential) (5) On the other hand, the corrected current value ΔI _AC1 of the AC charger is ΔI _AC1 = β ₁ · ΔV _D1 + β ₂ · ΔV _L1 (6) Here, the setting coefficients β ₁ and β ₂ can be expressed as follows. β ₁ = ΔI _AC (Change in AC charger current) / ΔV _D (Change in dark potential) (7) β ₂ = ΔI _AC (Change in AC charger current) / ΔV _L (Change in light potential) (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・ΔV _D1 +α ₂・ΔV _L1 +I _P1 …(9) I _AC2 = β ₁・ΔV _D1 +β ₂・ΔV _L1 +I _AC1 …( 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. Since it is not known whether the surface potential will reach the target value with one control due to deterioration, etc., the surface potential is measured multiple times when the device is in a predetermined state, and the output of the corona discharge device is controlled the same number of times as the measurements.
Since the second and subsequent corrections use the same method as the first correction described above, the current values I _Po+1 and I _ACo+1 of the positive charger and AC charger after the nth correction are It can be expressed as follows. I _Po =α ₁・ΔV _Do +α ₂・ΔV _Lo +I _Po I _ACo+1 =β ₁・Δ _Do +β ₂・ΔV _Lo +I _ACoThe primary charger control current I _P is applied three times to Figure 9 a and b. It shows the change in dark potential when corrected. 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. In addition, 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 based on those values, and in state 2
In this case, the previous control output current is passed through the photoreceptor to detect and control the surface potential. 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. Also, if the device is left unused for more than 30 seconds, the
If a copy operation is performed for 30 minutes, 1
Make the necessary corrections. This is due to the performance of the memory circuit that stores the control signals, and it is desirable that the information stored in the analog memory (integrator circuit (see Figure 14) described later) is not lost within 30 minutes after being stored. . If more than 30 minutes have elapsed, the stored information may change by more than 5% from the initial value, so the surface potential is reset and then remeasured. <Developing Bias Control> 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 46 moves and the original is actually exposed is changed to an exposure amount arbitrarily set by the operator. The surface potential meter 67 measures the surface potential ν _L of the portion of the drum 47 that is irradiated with the scattered reflected light, and sets the voltage obtained by adding plus 50 V to the measured value ν _L as the developing bias voltage V _H
shall be. 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 arbitrary value set by the operator, so that the original back is not exposed. Even when the ground is not white but colored, a stable image can be obtained by changing the bright area surface potential of the drum depending on the exposure amount. <Dimming of Original Exposure Lamp> A lighting adjustment circuit for adjusting the light amount of the original exposure lamp 46 is shown in FIG. 10b. In the figure, K301 is a relay normally in the state 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 a timing output IEXP signal from a DC controller (not shown), the triac Tr is activated to light 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 SW12 by standard light intensity signal SEXP
When turned on, the standard white plate is irradiated with this amount of light, the bright area potential (on the photoreceptor) is measured, and the bias voltage of the developing roller is determined according to that value. As described above, since the developing bias voltage V _H is determined by irradiating the standard light amount onto the standard white plate 80 using the document exposure lamp actually used for exposure, the accuracy of the control of the developing bias voltage is improved, and the There is no reduction in copy speed because the copy is being performed. 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. (Surface potential control sequence) 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. (Circuit Configuration) A circuit for realizing the surface potential control described above will be described below. <Surface potential detection processing circuit> FIG. 12 is a surface potential detection processing circuit diagram. Explain circuit operation. Sensor motor drive signal from input terminal T1
When SWD 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
13b shows the synchronizing signal SYC generated by the light emitting diode 84 and the phototransistor 87. The synchronous signal SYC is amplified by the synchronous amplifier circuit CT3 and then passed through the synchronous clamp circuit CT4.
is input. 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 is a circuit that clamps the AC voltage from the amplifier circuit CT2 to zero volts using a synchronous signal output from the synchronous amplifier circuit CT3. The clamp timing corresponds to when the chopper 83 closes the potential detection window 89, so when the drum surface potential is positive, the synchronous clamp circuit CT
The output of 4 is positive, and when the surface potential is negative, the output is negative. The output signal of the synchronous clamp circuit CT4 is input to the smoothing circuit CT5 and converted into a DC voltage. The output signal of the smoothing circuit CT5 is the standard bright area surface potential ν _L hold circuit CT7, the bright area surface potential V _L hold circuit
CT8 and the dark area surface potential _VD are input to the hold circuit CT9. The ν _L detection pulse signal ν _L CTP from the DC controller is input to the ν _L hold circuit CT7 via the inverters INV1 and INV2 in the pulse circuit CT6, and smoothing is performed when the signal ν _L CTP is output. Holds the output voltage of circuit CT5. Further, the light emitting diode LED4 in the pulse circuit CT6 lights up when the signal ν _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 holds the output voltage of the smoothing circuit CT5 when the V L detection signal V _L CTP is output.
Lights up when 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 ν _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 ν _L hold circuit CT8, and the output of the V _D hold circuit, so that the surface potential contrast voltage (V _D −V _L ) is less than or equal to a predetermined voltage. In case light emitting diode LED7, and LED8
lights up to notify 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,
Current values ΔI Po and ΔI _ACo that are the differences between I ACo and the control current values I _Po+1 and I _{ACo +1} to _be applied next time are calculated. ΔI _Po ,
ΔI _ACo is expressed as follows. ΔI _Po = I _Po+1 −I _Po = α ₁・ΔV _Do +
α ₂・ΔV _Lo ΔI _ACo = I _ACo+1 −I _ACo = β ₁・ΔV _Do
+β ₂・ΔV _Lo calculation circuit CT11 is CT11-a and CT11-b
It is divided into two circuits, and CT11-a amplifies the outputs of the hold circuits CT8 and CT9 and shifts them to bright potential V _Lo and dark potential V _Do for calculation, and sends them to circuit CT11-b. Circuit CT11
−b is α ₁ (V _D0 −V _Do ) …(1) β ₁ (V _D0 −V _Do ) …(2) α ₂ (V _L0 −V _Lo ) …(3) β ₂ (V _L0 −V _o ) ...(4) are respectively calculated and returned to the circuit CT11-a, 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 PESET occurs, the switch SW2 closes.
2 closes. When the dark potential detection signal V _D CTP is generated, the monostable circuit CT13 is activated and the switch SW1 is closed, and the set signal SET 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 _V1 . 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 input to the integrating circuit CT12 as an integrating circuit reset signal via the reset signal circuit CT14, and is input to the integrating circuit CT12 as an integrating circuit reset signal.
Close. When the switch SW2 is closed, the charge in the capacitor C1 is discharged by the resistor R1, and a reference potential of 12V is outputted to the output terminal T14. In addition,
Since the switch SW1 is closed only for 1/5 of the time required to completely charge and discharge the capacitor C1, it is charged and discharged only for 1/5 of the difference between the input voltage v _i of the input terminal T13 and the reference voltage (12 [V]). be done. For example, if the input voltage vi1 is 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 described 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 the 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 is performed to convert the contact points X _c and Y _c of No. 5. When the contacts on the input side are X _o and _Yo (n=0, 1, 2, 3), the truth table of each pulse signal and the connection state of the input/output contacts is shown below.

[Table] The contents of input side contacts X _o and Y _o are as follows.

[Table] FIG. 15 shows a control pulse generation timing chart. While copying is stopped, X _c and Y _c are connected to X ₀ and Y ₀ , respectively. Both X ₀ and Y ₀ are +18V
Therefore, both the primary and secondary high-voltage power supplies become inoperable. In the first half of the forward rotation, X _c Y _c are respectively X ₁ ,
Connected to Y ₁ . Since X ₁ and Y ₁ are both +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,
X _c and Y _c are connected to X ₂ and Y ₂ respectively, and when 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 backward rotation, X _c and Y _c are respectively X ₃ ,
Since X ₃ is connected to Y ₃ , the voltage is +18V, so the primary charger stops operating, and Y ₃ becomes the post-rotation control signal, causing a predetermined corona current to flow to the AC charger and remaining on the drum surface. Remove the electric charge. Primary charger control voltage V _P outputted by the multiplexer circuit CT15, AC charger control voltage
v _AC is input to the charging voltage control circuit shown in FIG. <Charging voltage control circuit> 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 does not turn on transistor Tr3 of Darlington current amplifier AMP1. In other words, the output of the Darlington current amplifier AMP1 is 0. said signal
When HVT1 is "L", the transistor Tr3 is turned on and a voltage almost the same as the output voltage of the operational amplifier Q5 is output to the primary high voltage transformer TC1. The oscillator Q1 in the primary transformer TC1 is a transistor Tr.
1. Turn on Tr2 alternately. The transformer TS1 boosts the voltage to the secondary side according to the turns ratio, rectifies the secondary output with the diode D1, and applies it to the primary charger 51. The primary corona current I _P flowing through the primary charger 51 is detected by the resistor R11, and is inputted to the non-inverting input terminal of the operational amplifier Q5 via the resistor VR1 to provide the voltage
The primary corona current I _P is controlled so that V _FP and the primary charger control voltage V _P match. Similarly, AC charger control voltage V _AC is operational amplifier Q
The signal is input to the inverting input terminal of No. 7 via the resistor R10. The difference voltage between the voltage V _FAC applied to the non-inverting input terminal of the operational amplifier Q7 from the resistor VR2 and the correction voltage V _AC is multiplied by -R ₉ /R ₁₀ and output from the operational amplifier Q7. AC charger drive signal HVT2 is “H”
When , the output of the operational amplifier Q7 does not turn on the transistor Tr5 of the Darlington current amplifier AMP2. 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 the operational amplifier Q7 is turned on.
The voltage is almost the same as the output voltage of AC high voltage transformer TC
2 is output. The oscillator Q2 in the secondary high voltage transformer TC2 turns on transistors 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. Also, AC voltage generator
The ACS outputs an AC high voltage using an AC oscillator Q3 and a transformer TS2, superimposes it on the DC component output, and outputs it to the secondary charger 69. The AC corona current I _AC flowing through the AC charger is detected by resistor R12. The detection output is amplified by the amplifier AMP3 and then sent to the smoothing circuit.
REC detects only the difference between positive and negative components and converts it into a DC amplifier.
Amplified by 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,
As described above, the voltage V _FAC and the AC correction voltage V _AC
This is to control the AC corona current I _AC so that it matches. As described above, in this embodiment, since the corona current value is controlled to be constant using the surface potential detection output and the corona current detection output, the charger load fluctuation due to temporary environmental changes or the corona discharge device power supply 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 . <Limiter Circuit> Further, 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
is a buffer circuit, and the power supply voltage is connected to resistors R31 and R3.
8 and the voltage divided by variable resistor VR31 is Q1
We get an output of 4. The output voltage of Q14 is set by adjusting VR31 to a value 0.6V higher than the maximum value V _{AC MAX} of the AC charger control signal V _AC to activate the limiter. The operational amplifier Q7 is an inverter, and is in a relationship such that as the AC charger control signal V _AC decreases, the high voltage output current increases. When the AC charger control voltage V _AC is about to drop below the minimum value V _{AC MIN} , diode D31 turns on and the control signal V _AC
is connected to the output of Q14 through R10 and 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, and a limiter will be applied. Diode D3
1 is ON and the limiter is applied, the comparator 15 is inverted and the LED 31 lights up, allowing you 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 is not reached even when a predetermined current is passed through the primary charger and AC charger.
This situation occurs especially when the drum is deteriorated. Therefore, the light emitting diode LED30,
The LED 31 displays the operation of the limiter circuits LIM1 and LIM2 and at the same time monitors drum deterioration. Also, if the charger's electrode is too close to the drum surface, if a foreign object such as paper gets between the charger and the drum surface, or if the charger's electrode breaks and comes into contact with the drum surface. For example, the charger's 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. <Developing Bias Control Circuit> 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 ν _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.
When 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 depletion type junction FETQ12 and Q13 are 0V.
Therefore, both FETQ12 and Q13 are turned off. Therefore, the signal input to the operational amplifier Q11 is the output voltage V _L via the resistors R115 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 formed,
Since DRMD is "H" and RBTP is "L", the transistor Tr17 is turned on and Tr18 is turned off, so the FET Q12 is turned off and the FET Q13 is turned on. When FETQ13 is turned on, a predetermined voltage determined by variable resistor VR15 is input to operational amplifier Q11, and a fixed voltage corresponding to the predetermined voltage is input to 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, developing material is prevented from getting on the drum. Also, 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, so the FET Q12 is turned on and the FET Q13 is turned off. When FETQ12 turns on, operational amplifier Q11
A predetermined voltage determined by a variable resistor VR14 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 VR14 is set to a value such that the developing bias voltage _VH becomes OV. 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 is the inverter transformer circuit with fixed voltage output.
The operations of SINV (hereinafter referred to as fixed inverter circuit) and variable output 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 a back electromotive force corresponding to the increase in the collector current is generated in the collector side coil of the transistor Tr12.
The base potential of is made positive. Therefore, the collector current of the transistor Tr11 further increases. That is, 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 T11. The transistor Tr1
When the collector current of transformer T11 is saturated, the back electromotive force in the primary coil of transformer T11 becomes 0, transistor Tr11 is turned off, the collector current decreases, and the primary coil of transformer T11 receives the amount of the decreased collector current. A back electromotive force is generated according to the
Turn on 12. Similarly, transistor Tr1
1, Tr12 alternately turns on and off. Here, diodes D21 and D22 are transistors
This is a diode for protecting the bases of Tr11 and 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 boosted to a voltage determined by the number of turns of transformer T11, rectified and smoothed by diode D25 and capacitor C23, and a high DC 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 depending on the input signal, transformer T
The output voltage of 12 varies depending on the input signal. <Input/output characteristics of fixed inverter circuit and variable inverter circuit> Figure 18 shows the high voltage output voltage. In FIG. 18, the vertical axis shows the high voltage output voltage _Vput , and the horizontal axis shows the input voltage _Vio input to a fixed point of the transformer T12.
The output voltage V _s of the fixed inverter circuit SINV is always constant with respect to the input voltage V _io , and the output voltage V _v of the variable inverter circuit is equal to the input voltage V _io
changes linearly with respect to Therefore the output voltage
The actual developing bias voltage V _H obtained by superimposing V _s and V _v changes linearly from positive to negative with respect to the input voltage. As described above, it has become possible to vary the developing bias voltage V _H linearly from positive to negative, so whether the latent image potential of 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. (Effects of the Invention) As described above, according to the present invention, after the charging conditions have been optimized, the reference member is exposed to light at a standard light intensity under the optimized charging conditions and regardless of the set light intensity, thereby forming a The developing bias voltage is determined according to the surface potential to be developed, and the document is exposed at an arbitrarily set exposure amount when exposing the document, making it possible to detect the surface potential and set the developing bias voltage with extremely high accuracy. , it becomes possible to properly copy the original with the desired density.

[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;
The figure is a perspective view of a cylindrical chipper, FIGS. 9a and 9b are diagrams showing changes in dark area surface potential, and FIG. 10a is a schematic cross-sectional view of the copying device regarding developing bias control.
Figure 10b is a lighting control circuit diagram of the original exposure lamp;
Fig. 11 is a time chart of image formation and surface potential control, Fig. 12 is a surface potential detection processing circuit,
Figure 3 is an output waveform diagram of amplifier circuit CT2 and synchronization signal, Figure 14 is an integration circuit diagram, Figure 15 is a control pulse generation timing chart, Figure 16 is a charging voltage control circuit diagram, and Figure 17 is a developing bias control circuit. FIG. 18 is a waveform diagram of the 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. A latent image forming means that has a charging means for charging a recording medium and a first exposure means for exposing an original, and forms an electrostatic latent image corresponding to an image of the original on the recording medium; A developing means for developing an electrostatic latent image formed on a recording medium; a second exposing means for exposing a non-image area of the recording medium; and an exposure amount of the first exposing means can be set arbitrarily within a predetermined range. a setting means that can be set; a detection means that detects the surface potential of the recording medium; a reference member having a reference density; The detection means detects the bright area surface potential and the dark area surface potential formed on the recording medium by turning off the recording medium, and controls the output current of the charging means according to the detected values, and then adjusts the controlled charging conditions. By exposing the reference member to light by the first exposure means, the bright area surface potential formed on the recording medium is detected by the detection means, and the detected value is applied to the development means. a control means for determining a developing bias voltage; when the control means controls the output current of the charging means, the first exposing means is turned off, and when the developing bias voltage is determined, the first exposing means is exposed regardless of the setting means; An electronic copying apparatus comprising: a light amount adjustment means that sets the amount of light to be a standard light amount, and sets the exposure amount of the first exposure means to the exposure amount set by the setting means when exposing a document.