JPS6361665B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an image forming apparatus that forms an electrostatic latent image on a recording medium and then visualizes the latent image, and particularly relates to an image forming apparatus equipped with a surface electrometer that detects the potential of the latent image. Conventionally, various methods have been proposed in which a latent image potential on a recording medium is detected and an apparatus is controlled using a detection signal. One of the methods is to rotate a chopper using a motor to chop the lines of electric force from an object to be measured, such as a recording medium, toward a measurement electrode, induce an AC signal in the measurement electrode, and reproduce this DC signal to create a recording medium. A method for detecting the surface potential of is proposed. However, in such a configuration, the device becomes large due to the motor drive, and a high-precision motor is required to improve detection accuracy, leading to an increase in cost. Furthermore, a device in which the measurement electrode is vibrated in a direction perpendicular to the object to be measured has also been proposed. However, with this configuration, the signal line connected to the measurement electrode moves together with the electrode signal, which has the disadvantage that it is susceptible to noise and has poor detection accuracy. Furthermore, since the output of an electrometer is largely dependent on the distance between the recording medium and the measurement electrode, if there are variations in the mounting accuracy of the electrometer, accurate potential detection and control of image forming conditions may be impossible. It was hot. The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus capable of highly accurate potential detection and appropriate control of image forming conditions. That is, the present invention provides an image forming means for forming and developing an electrostatic latent image on a recording medium, a detecting means for detecting the surface potential of the recording medium, and an operating condition of the image forming means according to the output of the detecting means. In the image forming apparatus, the detection means includes a measurement electrode in which a voltage corresponding to the surface potential of the recording medium is induced, first and second vibrating pieces, and the first and second vibrating pieces.
a tuning fork that includes a chopper that intermittently cuts electric lines of force from the recording body toward the measurement electrode by vibrating the second vibration piece to induce an alternating current signal in the measurement electrode; by outputting a drive signal to the drive piezoelectric element attached to the drive piezoelectric element, the feedback piezoelectric element attached to the second vibrating piece, and the drive piezoelectric element, and inputting the feedback signal from the feedback piezoelectric element. a drive circuit that causes the tuning fork to self-excite vibration by oscillating at a resonant frequency of the tuning fork; a first conversion means that converts an alternating current signal induced in the measurement electrode into a low impedance signal; the first conversion means converts the alternating current signal into a low impedance signal; a second conversion means for converting the converted AC voltage into a DC voltage; a DC voltage such that the DC voltage from the second conversion means becomes zero in order to make the potential difference between the recording medium and the measurement electrode zero; configured to include voltage supply means for supplying voltage to the chopper and the first conversion means,
Furthermore, the present invention provides an image forming apparatus characterized in that the control means controls operating conditions of the image forming means in accordance with the voltage supplied from the voltage supply means. Embodiments of the present invention will be described below with reference to the drawings. 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. The first scanning mirror 44 and the second scanning mirror 53 move at a speed ratio of 1:1/2, so that 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 a pre-exposure lamp 50 and a pre-AC charger 51', and then corona-charged (+ in a row) by a primary charger 51. 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 the entire surface exposure lamp 18. 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 made easy to transfer 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. I can do it. 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 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 18 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 the current line liquid onto the cleaning blade 49 while the drum 47 is stopped after the power switch is turned on. Hereinafter, it will be referred to as Briwet. 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. After the pre-wetting 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 51', etc., and the drum surface is cleaned using 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 above-mentioned briewet 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 charge on the drum surface and prevent excess toner from adhering to the drum. However, since the blank exposure lamp 70-1 illuminates the drum surface corresponding to the surface electrometer 67, it is momentarily turned off when measuring the dark area potential with the surface electrometer 67. Also, for B size copies, the image area
Since the size is smaller than that of A4 or A3, 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 cassette lamp, and it irradiates light onto the portion of the drum that is in contact with the separation guide plate 43-1 to completely erase the charge on that portion and prevent toner from adhering to it. I try not to contaminate the width of the separation chip. This sharp cutlet lamp is rotating while the drum is rotating.
It's lit all the time. 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 the center point in the figure, and the surface potentials ○a and ○b in the dark and bright areas there are at the photosensitive drum 47.
When the ambient temperature of and contrast in bright areas 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.
Figure 7 is a cross-sectional view taken along line X-X' in the figure and viewed from the right side of the drawing, Figure 7 is a cross-sectional view taken along line X-X' in Figure 5 and viewed from the left side of the figure, and Figure 8 is an electrometer. FIG. In Figures 5, 6, 7, and 8, the entire electrometer is
It is covered with a metal shield member 81 and a metal base 95 to eliminate the influence of external electric fields. The shield member 81 has an opening for a measurement window 88, and the measurement window 88 is opposed to the portion to be measured of the drum 47 to measure the potential. The tuning fork 82 is attached to the base 95 in an electrically conductive state, and the drive circuit shown in FIG. When voltage is applied, tuning fork 8
Self-excited vibration is performed at the mechanical resonance frequency of 2. One tip of the vibrating piece of the tuning fork constitutes a chopper electrode 83, and the vibration of the tuning fork causes the measurement window 88 to open and close at regular intervals. A printed circuit board 86 is fixed to the rear side of the chopper electrode, and a measurement electrode 85 having the same shape as the window is formed at a position facing the measurement window using a copper foil pattern on the printed circuit board. The electric lines of force based on the surface charge of the photosensitive drum 47 are:
The electric force enters the measuring electrode 85 through the measuring window 88, but the chopper electrode 83 located between the measuring window 88 and the measuring electrode interlinks and cuts the lines of electric force due to the vibration of the tuning fork 82. , an AC voltage having an amplitude proportional to the voltage difference between the surface potential on the photosensitive drum 47 and the chopper electrode (same potential as the shield member potential) is induced in the measurement electrode. The alternating current signal is passed through a current amplification circuit (20
After being converted to a low impedance signal by
Externally taken out as the output of the electrometer. Reference numeral 89 in FIG. 8 is an internal shield member for preventing the drive signal from the tuning fork drive unit 84 from being guided to the measurement electrode 85. The driving of the tuning fork will be explained with reference to FIG. 19. As shown in FIG. 19, piezoelectric elements 84-1 and 84-2 are bonded to the fulcrum side of the vibrating piece of the tuning fork 82 at opposing positions in the length direction using a conductive adhesive. 84-1 and 84-2 are piezoelectric elements that generate distortion in the plane direction when an electric field is applied in the thickness direction, and are sandwiched between electrodes 99 as shown in FIG. When fixed to the vibrating piece with conductive adhesive 98, it forms a unimorph vibrator together with the vibrating piece, and since the shape of the piezoelectric element is elongated in the length direction of the vibrating piece, an electric field is applied in the thickness direction. This causes distortion in the length direction of the vibrating piece. The output of the drive circuit (collector of transistor Tr51) is connected to the piezoelectric element 84-1, and the output of the drive circuit is connected to the piezoelectric element 84-2.
When the input of the drive circuit (the base of transistor Tr52) is connected to It is converted into an electrical signal and fed back to the input of the drive circuit, so it begins to oscillate at the tuning fork's resonant frequency. The feedback signal output taken out to both ends of the piezoelectric element 84-2 is current-amplified by the transistor Tr51, and then applied to the base of the transistor Tr52 via the low resistor R52 and the capacitor C52, where it is amplified into a large-amplitude AC signal. Then, the piezoelectric element 84-1 is driven. The feedback signal 84-2 is selected to have a phase that provides positive feedback to the drive circuit shown in FIG. 19, and since the Q of the tuning fork is also high, it continues to oscillate at the resonant frequency of the tuning fork. To attach the electrometer to the copying machine body, use the support base 95.
is fixed to a printed circuit board 67, and this printed circuit board is supported on the main body by a circuit board connector 94 and a circuit board guide 87. On the connector insertion side of the printed circuit board 67, the connector contact terminal part is made of copper foil, and supplies power to the electrometer and takes out the output signal, making it possible to easily remove the electrometer. There is. As described above, driving the tuning fork with a piezoelectric element does not require a high-precision small motor, compared to the conventionally proposed method of intermittent electric lines of force driven by a motor, resulting in lower costs. It is possible to reduce the size of the tuning fork, and since the resonant frequency of the tuning fork is constant, highly accurate detection and device control based on the detection are possible. 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.
6 is not used, but a blank exposure lamp 70 is used. 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, since the surface potential is controlled by controlling the current flowing through the primary charger and the AC charger, 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 potential detected at the first time is determined as a bright area potential V _L1 and a dark area potential V _D1 , respectively, and how much difference there is between the target bright area potential V _L0 and the target dark area potential V _D0 , respectively. The difference voltages are △V _L1 and △V _D1, respectively.
Then, △V _L1 = V _L0 −V _L1 (1) △V _D1 = V _D0 −V _D1 (2) The difference in potential in the bright area is corrected by an AC charger, and the difference in potential in the dark area is corrected by a primary charger. However, in reality, when an AC charger is controlled, not only the bright area potential but also the dark area potential is affected. Similarly, when controlling the primary charger, not only the dark potential but also the light potential is affected, so a modification method was adopted that takes both the AC charger and the primary charger into consideration. The corrected current value △I _P1 of the primary charger is △I _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 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. Similarly, from equations (4)(5)(1), I _P2 =α ₁・△V _D1 +α ₂・△V _L1 +I _P1 (9) I _AC2 =β ₁・△V _D1 +β ₂・△V _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, so changes in the atmosphere,
Because it is not known whether the surface potential will reach the target value with one control due to deterioration of the charger, etc., the surface potential is measured multiple times when the device is in a specified state, and the output of the corona discharge device is controlled the same number of times as the measurements. ing. Since the second and subsequent corrections use the same method as the first correction described above, the current value of the positive charger and AC charger after the nth correction is I _po +1,
I _ACo +1 can be expressed as follows. I _P2 +1=α ₁・△V _Do +α ₂・△V _Lo +I _Po I _ACo +1=β ₁・△V _Do +β ₂・△V _Lo +I _ACo Figure 9 a and b show the primary charger control current I It shows the change in dark potential when _P is corrected three times. FIG. 9a shows the case where the set calibration coefficient is smaller than the actual coefficient, and FIG. 9b 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.
flow. 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. or,
Continuously without being left unused for 30 seconds or more
If a copy operation is performed for 30 minutes, one correction will be made after 30 minutes have passed. 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 15 A) described later) is not lost within 30 minutes after being stored. It depends. If more than 30 minutes have passed, the stored information may change by more than 5% from the initial value, so the surface potential is reset and then remeasured. 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. Immediately before exposing the original, a standard white plate 80 attached to the side of the original table glass 54 is irradiated with a halogen lamp 46 for exposing the original, and the scattered reflected light is sent to the drum 47 via mirrors 44, 53, 55, lens 52, etc. irradiate.
This irradiation light amount is the standard light amount, and then the lamp 81
The exposure amount when the scanner moves and actually exposes the document is changed to an 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, fogging of the background portion of the document can be prevented and stable development can be performed at all times, and as a result, stable images can be obtained. 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. 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 a 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 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 amount of current supplied according to the amount of displacement of the density adjusting means VR106 using a triax. 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 actually used for exposure, the precision of the control of the developing bias voltage is improved, and the control is performed immediately before exposing the document. There is no reduction in copy speed due to the slow 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 surface potential of the drum 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 the surface potentials V D and V L 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 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. 12A is a surface potential measurement circuit diagram. Explain circuit operation. When the sensor drive signal SWD is output, the tuning fork drive control circuit CT101 operates, the tuning fork 82 starts vibrating, and the chopper 83 vibrates. As described above, when the chopper 83 vibrates, an alternating voltage with an amplitude proportional to the absolute value of the difference between the surface potential of the photosensitive drum 47 and the bias voltage of the chopper is induced in the measurement electrode 85. The AC signal induced in the measurement electrode 85 is
By the measurement circuit shown in Figure A, the DC potential is regenerated and amplified to a DC potential of the same polarity as the potential to be measured.
3 and the shield member 81,
The chopper potential and shield potential are kept at the same potential as the potential to be measured. As a result, the voltage fed back to the chopper becomes the voltage to be measured itself, which does not vary depending on the measurement distance. The process until the same potential as the potential to be measured is fed back to the chopper and the shield member will be explained with reference to FIG. 12A. In FIG. 12A, CT101 is the tuning fork drive circuit in FIG. 19, CT102 is the preamplifier circuit in FIG. 20, CT103 is the isolator in FIG. 13A,
CT104 and CT105 are monostable multivibrators, CT106 is a DC regeneration circuit consisting of a synchronous clamp circuit, CT107 is an integrating circuit, and CT108
is a high voltage amplifier, CT109 is an attenuator, CT110
is a buffer amplifier, and CT111 is a power supply circuit. The power supply circuit of CT111 is composed of a switching regulator, and input terminals P102 and P103
By applying a 24V DC voltage to the
104, P105), and 30V (between terminals P106,
P107). The low voltage side of the isolated power supply is both 24V and 30V.
It is connected to the output of CT108 and has the same potential as the shield member and chopper. On the high voltage side of the isolated power supply, 30V is the tuning fork drive circuit CT.
24V is applied to the power supply of 101 (terminal P51), preamplifier CT102 (terminal P53) and isolator CT
103 (terminal P113). The weak alternating current signal induced in the measurement electrode 85 is converted into a low impedance signal by the preamplifier CT 102 so as not to be affected by external noise such as hum, and is taken out to the outside of the electrometer. The output of the preamplifier is output from the chopper 83 and the shield member 81.
is connected to the output of CT108, and the power supply of the preamplifier circuit is also biased to the output of CT108 as mentioned above, so when viewed from the ground potential reference, CT1
The output potential of 08 is superimposed. The isolator in Figure 13A is connected to the output signal of the preamplifier.
This is to remove the superimposed part of the output of CT108, and the output of the preamplifier is AC amplified by operational amplifier CA1, and the light emitting diode of photocoupler PC1 is
By changing the current of LED101 and changing the emitter current of phototransistor PTr1 by optical coupling, CT10 is applied to the emitter of phototransistor PTr1.
A signal is obtained by removing the superimposed part of the output of 8. The operation of isolator CT103 is shown in Figure 13B.
This will be explained with reference to the operation waveforms. Now, the surface potential V _P of the part to be measured, that is, the drum 47
is set to +500V as shown in Figure 13 B○A, and the feedback voltage V _F of the DC amplifier circuit CT108 (Figure 13 B○B)
Suppose that starts from 0V (ground potential). feedback voltage
V _F changes from the ground potential to 500 V, which is the same as the surface potential V _P , as shown in Figure 13 B. preamplifier
When the output voltage from the CT 102 is based on the feedback voltage V _F , it becomes an AC signal (on the order of mV) with an amplitude proportional to the absolute value of the difference between the measured potential V _P and the feedback voltage V _F , as shown in Figure 13 B○C. . However, when the ground potential is used as a reference, the voltage becomes a voltage obtained by superimposing the AC signal on the feedback voltage V _F as shown in B○D in FIG. 13. Light emitting diode LED1 of isolator CT103 in Figure 13A
On the 01 drive side, the feedback voltage V _F is connected to the terminal P115, V _F +24 [V] is connected to the terminal P113, and the output of the preamplifier CT101 is connected to the terminal 114, so the potential to be measured V _P and the bias of the chopper or shield member are connected. It becomes an AC signal with an amplitude proportional to the potential, that is, the voltage difference from the feedback voltage V _F. The AC signal changes the emitter current of the phototransistor PTr1 by optical coupling, but the phototransistor has a voltage of +24 [V].
Since it is driven at ~0 [V] (ground potential), a feedback voltage is applied to the output terminal P117 as shown in Figure 13 B○ho.
An AC signal with the superimposed component of V _F removed is obtained. The output of the isolator CT103 is regenerated as DC by the synchronous clamp circuit CT106, and then
It is smoothed in step 107. The CTs 106 and 107 are shown in FIG. 14A, and their operations will be explained according to the operating waveforms in FIG. 14B. The output of the isolator (see B○ in Figure 14) is an AC signal with an amplitude proportional to the voltage difference between the measured potential V _P and the chopper potential (feedback voltage V _F ), as described above. Tuning fork driving pulse signal
Compared to PLS1, it has a constant phase relationship. ○The solid line signal in F is the chopper potential.
When the measured potential V _P is positive with respect to V _F , the wire covered shows a case where the measured potential is negative with respect to the chopper potential. The timing of the rise of the output pulse PLS1 of the tuning fork drive circuit is delayed by the monostable circuit CT104 to the timing of the negative peak of the signal indicated by the solid line ◯ to obtain the pulse signal PLS2. The monostable circuit CT105 is driven at the timing of the fall of PLS2 to obtain a narrow negative pulse PLS3 (FIG. 14 B). the pulse
PLS3 is synchronized with the timing of the negative peak of the solid line signal to the isolator output ○ and the positive peak of the wired signal. The output of the isolator is connected to terminal P119 (14th
Added to Figure A), Emituta Foorova Tr10
After the current is amplified by step 4, it is connected to capacitor C7. The opposite terminal of capacitor C7 is Tr105
Source follower gate and Tr106 FET
Connected to the drain of the switch, Tr10
When FET switch 6 is cut off, the gate of Tr105 and the drain of Tr106 become high impedance, so there is no place for the charge charged in C207 to escape, so the terminal potential of the gate side of Tr105 of C207 is the same as that of the opposite terminal. Changes in the same way as electric potential. The output pulse PLS3 of the monostable circuit CT105 is
It is connected to the input terminal P120 and turns on the transistor Tr107 at the timing of the negative pulse. Operational amplifier OA2 has an output of 0 to ±5V using Zener diodes ZD1 and ZD2 for clamping.
Therefore, when Tr107 becomes conductive, the cathode of diode D101 is biased to +12V, D101 is cut off, and the FET switch Tr
There is zero bias between the source and gate of 106,
The drain and source of the Tr 106 are brought into conduction.
When Tr106 becomes conductive, a feedback loop of operational amplifier OA2 is formed by the route of FET switch Tr106, source follower Tr105, and resistor R221, so the potential difference between the two input terminals of OA2 becomes zero, and the input resistance of OA2 decreases. Considering that is high, the source potential of Tr105 is 0V (ground potential)
Therefore, the terminal voltage of C207 on the gate side of Tr105 is biased to a potential shifted from 0V by the gate-source voltage of Tr105. When the output pulse PLS3 of CT105 returns to a high level after the timing of the negative pulse ends, the transistor Tr107 is cut off, and the diode D10
1 becomes conductive, current flows through the resistors R226 and R230, a deep reverse bias is applied to the gate of Tr106, and Tr106 is cut off. When Tr106 is cut off, as described above, the terminal voltage on the gate side of Tr105 of capacitor C207 exhibits the same condition as the terminal potential on the opposite side. Therefore, for a source as shown by the solid line in Figure 14B, when the measured potential is positive with respect to the chopper potential, the negative peak is 0V (ground potential), and a waveform with the same shape as the output of the clamped isolator is generated. can get. Moreover, as shown by the broken line of ○, when the measured potential is negative with respect to the chopper potential, a waveform having the same shape as the output of the isolator with the positive peak clamped to 0V is obtained. The output ○nu is operational amplifier OA3
After being amplified by resistor R231 and capacitor C20
8 and current amplified by operational amplifier OA4, and then connected to high voltage amplifier CT108. The CT108 is shown in Figure 14C, and has two DC-
The inverter INV2, which is composed of a DC inverter and one operational amplifier, and is composed of an inverter transformer T102 and transistors Tr112 and Tr113, provides a fixed output of -1 KV on the anode side of the high voltage diode D103. Inverter transformer T101, transistor
Inverter fixed by Tr110 and Tr111
INV1 is a variable inverter, and 0
~2KV output with capacitor C211 and resistor R2
It is designed to be taken out at both ends of the transformer T.
The low voltage side terminal of 101 is connected to the cathode of D103, so the cathode of D102 has -
Variable output from 1KV to +1KV can be obtained. integral circuit
The output of the CT107 is connected to the operational amplifier OA5 via the terminal P122, and the polygon VR1 described later is connected to the operational amplifier OA5.
After amplifying the voltage difference with the DC potential selected in 01, buffer transistors Tr108 and Tr10
9 to the common terminal on the primary side of the inverter transformer T101, and the output of the OA5 is boosted by about 100 times by the inverter INV1.
VR101 is a volume for correcting offset voltage, and the DC potential applied to the negative input terminal of OA5 is almost 0V (ground potential). The output, that is, the feedback voltage V _F boosted by the transformer T101 is fed back to the chopper part 83 and the shield member 81 via the terminal P123, so the part to be measured and the electrometer form a negative feedback control system. so that the potential difference at the input of the operational amplifier OA5 becomes zero, that is, the chopper 8
3. The potential of the shield member 81 becomes equal to the voltage to be measured, and the input voltage of P122 becomes zero similarly to the input voltage of the negative input terminal of OA5. When the potential to be measured V _P is within the range of -1 KV to +1 KV, the output voltage of the CT 108, that is, the feedback voltage V _F is always equal to the potential to be measured V _P. The output of the amplifier circuit CT108 is sent to the attenuator CT109.
The current is attenuated to 1/100 by the CT 110, and after being amplified by the buffer of the CT 110, it is taken out to the output terminal P124.
The detection output taken out from the terminal P124 is the 12th
The signal is sent to terminal P125 shown in FIG. Since the feedback voltage V _F is applied to the chopper 83 and the shield member 81 and changes so that the potential difference with the potential to be measured V _P is always zero,
The output taken out in step 3 is from CT101 to CT108.
This provides stable output that is unaffected by the offsets and errors of each circuit up to this point. The experimental results of the characteristics of the measured potential V _P and the feedback voltage V _F when the distance between the shield member 81 and the drum 47 was changed to 2 mm, 4 mm, and 6 mm are shown in the 14th section.
Shown in Figure D. In FIG. 14D, the amplifier CT1 of this embodiment
08 output voltage range from -350 [V] to +750 [V]
It is said that As shown in FIG. 14D, it can be said that the feedback voltage V _F is almost constant with respect to the potential to be measured V _P even if the distance is changed. This is because when V _P = V _F , that is, when the surface potential of the drum and the bias potential of the tipper or shield member are equal, the measuring electrode is completely unaffected by the electric field from the drum surface, and the relationship between the electrode and the drum surface is reduced. This is probably because it is not affected by distance. Next, the detected voltage processing circuit in FIG. 12B will be explained. The detection voltage input through the terminal P125 is input to the standard bright area surface potential V _L hold circuit CT7, the bright area surface potential V _L hold circuit CT8, and the dark area surface potential V _D hold circuit CT9. The V _L detection pulse signal V _L CTP from the DC controller is connected to the V _L hold circuit CT7.
It is input via inverters INV11 and INV12 in CT6, and holds the output voltage of smoothing circuit CT5 when the signal V _L CTP is output. 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 arithmetic circuit CT11 is a circuit that performs the arithmetic operations described in the above-mentioned surface potential control method, and is a circuit that performs the arithmetic operations described in the above-mentioned surface potential control method.
The current IP _o passed through the AC charger when detecting the surface potential,
I _ACo and the control current value to be passed next time I _Po +1, I _ACo +
Calculate the current values △I _Po and △I _ACo that are different from 1. △
I _Po and △I _ACo are each 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
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 CT1
1-b is α ₁ (V _Dp −V _Do ) ……(1) β ₁ (V _Dp −V _Do ) ……(2) α ₂ (V _Lp −V _Lo ) ……(3) β ₂ ( V _Lp −V _o ) ...(4) is calculated respectively and returned to the circuit CT11-a again, and (1)+(3), (2)+(4), are calculated and outputted to the integrating circuit CT12. The integration circuit CT12 has two circuits configured as shown in FIG. 15A, one for bright area potential and one for dark area potential. In Fig. 15A, 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 the set signal is
When SET occurs, switch SW1 closes, and when the reset signal RESET occurs, switch SW2 closes.
closes. The set signal SET is the dark potential detection signal
When V _D CTP occurs, the monostable circuit CT13 operates, closing the switch SW1 and inputting it to the negative input terminal of the operational amplifier Q1, and at the same time charging the capacitor C1 to the input voltage V _i . 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. Furthermore, since the switch SW1 is closed only for 1/5 of the time required to completely charge and discharge the capacitor C1, the difference between the input voltage V _i of the input terminal T13 and the reference voltage (12 [V]) is only 1/5. Charged and discharged. For example, if the input voltage V _i1 =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 and the next input voltage V _i is set to V _io , the next output voltage V _po becomes V _po =V _po -V _io /5+12, and 1/5 of the change is charged. Here, as described above, the input voltage V _i corresponds to the difference current values ΔI _Po and ΔI _ACo , 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 to the multiplexer circuit CT15 as two-pit parallel signals during the prewetting or standby period, the initial setting period, the period during controlled rotation or copying, and the 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 T ₃ and T ₄ 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 contact points X _C and Y _C of No. 5. The truth table for each pulse signal and the connection status of the input/output contacts is shown below when the input side contacts are X _o and Y _o (n = 0.1.2.3.).

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

[Table] FIG. 15B 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 and Y _C are respectively
Connected to X ₁ and Y ₁ . Since both X ₁ and Y ₁ 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 previous rotation, X _C and Y _C are connected to X ₂ and Y ₂ respectively, and if the drum surface potential measured in the first half of the previous rotation deviates from the target surface potential, the correction amount is 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, X _C and Y _C are 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 difference voltage 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 turns on the transistor Tr2 alternately. Transformer TS1 is 2 depending on the turns ratio
The voltage is boosted to the next side, and the secondary output is rectified by the diode D1 and applied 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 input to the non-inverting input terminal of the operational amplifier Q5 via the resistor VR1 so that the voltage V _Fp and the primary charger control voltage V _P are The primary corona current V _P is controlled to match. Similarly AC charger control voltage
V _PC is the resistor R1 connected to the inverting input terminal of operational amplifier Q7.
3. The voltage difference 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 _P is multiplied by -R ₉ /R ₁₀ and output from the operational amplifier Q7. When the AC charger drive signal HVT2 is "H", 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. said signal
When 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 oscillator Q2 in the secondary high voltage transformer TC2 is a transistor Tr.
7.Turn on 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. Further, 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 component 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 the value to be 0.6V higher than the maximum value of _VAC , _VAC , _MAX . 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. AC charger control voltage
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, 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. Next, the control circuit for controlling the developing roller bias voltage _VH is installed in the 17th circuit.
The explanation will be based on the circuit diagram shown in the figure. 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 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 is applied to the fixed point of the primary coil of the transformer T12, and is connected to the inverter circuits VINV and SINV, which will be described later.
Therefore, the developing bias voltage V _H becomes variable according to the output voltage V _L. At this time, the developing bias voltage V _H
is controlled by inverter circuits SINV and VINV so that it is +50V 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 Q1
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. or,
DRMD, RBTP when the drum is not rotating
Both are "L". At this time, transistor Tr17
is off and transistor Tr18 is turned off by diode D2.
7, the FET Q12 is turned on and FET Q13 is turned 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. By changing the developing roller bias voltage V _H according to the control state as described above and controlling the bias voltage V _H based on the surface potential detection output during latent image development, more stable development has become 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, rectified and smoothed by capacitor C23 and outputs DC high voltage. 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 V _pUt and the horizontal axis shows the input voltage V _io 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 varies linearly from positive to negative with respect to the input voltage. As explained in detail above, in the present invention, since the same voltage as the latent image potential is applied to the chopper that shields the electric field between the measurement electrode and the recording medium, the detection voltage is equal to the distance between the measurement electrode and the recording medium. Not affected. Therefore, the detection voltage determines the image forming conditions of the process means for image formation, such as the developing bias voltage,
Control of charging voltage, etc. becomes extremely accurate. In other words, even if the device vibrates during image formation, stable potential detection and potential control are possible, and the accuracy of mounting the electrometer is not affected.

[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 from the right side of the line X-X' in Fig. 5, and Fig. 7 is a characteristic diagram showing changes in surface potential. Fig. 5 is a sectional view taken from the left side along line X-X', Fig. 8 is a perspective view of the electrometer, Fig. 9 a,
10b is a diagram showing changes in dark area surface potential, FIG. 10a is a schematic cross-sectional view of the copying device regarding development bias control,
Figure 10b is a lighting control circuit diagram of the original exposure lamp;
Figure 11 is a time chart for image formation and surface potential control, Figure 12A is a constant circuit diagram on the surface potential side, and
Figure 2B is a detection voltage processing circuit diagram, Figure 13A is a circuit diagram of isolator CT103, and Figure 13B is a circuit diagram of the isolator CT103.
Waveform diagram of each part in Figure 2A, Figure 14A is the integration circuit
Detailed circuit diagram of CT106 and amplifier CT107, 1st
Figure 4B is a waveform diagram of each part of Figure 14A, Figure 14C
is a detailed circuit diagram of the high voltage amplifier CT108, attenuator CT109, and buffer amplifier CT110; FIG. 14D is a diagram showing the relationship between the surface potential V _P and the feedback voltage V _F ;
FIG. 15A is a detailed circuit diagram of the integrating circuit CT12, FIG. 15B 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, Fig. 18 is a waveform diagram of high voltage output voltage, Fig. 19 is a piezoelectric tuning fork drive circuit, Fig. 20 is a potential detection circuit, The figure is a cross-sectional view of the vibrator. 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. shows.

Claims (1)

[Scope of Claims] 1. An image forming means for forming an electrostatic latent image on a recording medium and then developing it; a detecting means for detecting the surface potential of the recording medium; and an operation of the image forming means in accordance with the output of the detecting means. In an image forming apparatus, the detection means includes a measurement electrode in which a voltage corresponding to the surface potential of the recording medium is induced, first and second vibrating pieces, and the first and second vibrating pieces. a tuning fork that intermittently cuts electric lines of force from the recording body toward the measurement electrode by vibrating the second vibrating piece, and induces an alternating current signal in the measurement electrode; a driving piezoelectric element attached to the second vibrating piece; a feedback piezoelectric element attached to the second vibrating piece; by outputting a drive signal to the driving piezoelectric element and inputting a feedback signal from the feedback piezoelectric element. a drive circuit that causes the tuning fork to self-excite vibration by oscillating at a resonant frequency of the tuning fork; a first conversion means that converts an alternating current signal induced in the measurement electrode into a low impedance signal; a second converting the converted alternating current voltage into direct current voltage;
a converting means, in order to make the potential difference between the recording medium and the measuring electrode zero, a DC voltage is applied to the tipper and the first converter such that the DC voltage from the second converting means becomes zero;
An image forming apparatus comprising: a voltage supply means for supplying a voltage to a conversion means, and further characterized in that said control means controls operating conditions of said image forming means in accordance with the voltage supplied from said voltage supply means.