JPS6240710B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic apparatus that detects a surface condition on a recording medium and controls image forming conditions using the detected output. Generally, in an electrophotographic apparatus that has charging, exposure, development, and transfer processes, light is applied to a non-image area other than the area onto which image light is projected to eliminate static electricity and prevent the non-image area from being developed. A lamp for this purpose is generally called a blank exposure lamp. In an electrophotographic apparatus such as an electronic copying machine having such a blank exposure lamp, a predetermined amount of light is irradiated onto a non-image area of the photoreceptor by the blank exposure lamp,
It is conceivable to measure the surface potential of the irradiated area and control the charger, developing bias, etc. based on the measured output. However, when measuring the surface potential using the blank exposure lamp, the eighth
As shown in the figure, when the amount of light exceeds a certain value, the photoreceptor becomes saturated and the measurement becomes meaningless. Therefore, the amount of light for blank exposure for measurement should be within a so-called dynamic range, a region where the potential changes with respect to the amount of light. In other words, the light intensity of the blank exposure lamp needs to be a little weak. This amount of light is now tentatively called a weak blank. When static electricity is removed with a weak blank, a non-uniform electric field remains due to carriers (electrons, holes) generated within the photosensitive layer. If left as it is, the carrier will transition to a metastable state and generate electron traps and hole traps, resulting in the formation of a non-uniform electric field. Furthermore, in the case of a photoconductor with a three-layer structure in which an insulating layer is formed on the surface, followed by a photoconductive layer, and then a metal layer, the photoconductor layer becomes conductive by irradiating the entire surface with light after static electricity removal, making it photosensitive. Non-uniform electric fields inside the layer are eliminated. However, if it is left for a long time, the surface charge will disappear because the developing brush, cleaning blade, etc. are in contact with the photoreceptor. Furthermore, since spontaneous disappearance occurs, a non-uniform electric field is formed inside the photosensitive layer, which has a very negative effect on the next formation of a latent image. The present invention aims to eliminate the above-mentioned drawbacks, and includes an electrostatic latent image forming means for forming an electrostatic latent image on a recording medium, and a means for developing the electrostatic latent image formed on the recording medium. a developing means, a blank exposure means for exposing a non-image area on the recording body, a detection means for detecting a surface potential on the recording body exposed by the blank exposure means, and a detection means for detecting a surface potential on the recording body exposed by the blank exposure means; control means for controlling the bias voltage of the developing means, and when the surface potential is measured by the detection means, the amount of light from the blank exposure means is adjusted to a dynamic range in which the surface potential of the recording medium changes with respect to the amount of light. and at the end of image formation, the light amount of the blank exposure means is set to a light amount that is equal to or greater than the predetermined light amount and can erase the non-uniform electric field of the recording medium. It provides equipment. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a copying apparatus to which the present invention can be applied. The surface of the drum 11 is made of a three-layer photoreceptor using a CdS photoconductor, is rotatably supported on a shaft 12, and starts rotating in the direction of an arrow 13 in response to a copy command. When the drum 11 rotates to the normal position, the document placed on the document table glass 14 is illuminated by an illumination lamp 16 that is integrated with the first scanning mirror 15, and the reflected light is used for the first scanning. Mirror 15 and second
It is scanned by a scanning mirror 17. First scanning mirror 1
5 and the second scanning mirror 17 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 18 is always kept constant. The above reflected light image shows the lens 18 and the third mirror 19.
After passing through the fourth mirror 20, the exposure section 21
Then, an image is formed on the drum 11. After the drum 11 is charged (for example, +) by a primary charger 22, an image irradiated by an illumination lamp 16 is slit-exposed in the exposure section 21. At the same time, AC or primary charge removal with a polarity opposite to that of the primary charge (for example, -) is performed by a charge remover 23, and then a high-contrast electrostatic latent image is formed on the drum 11 by full-surface exposure using a full-face exposure lamp 24.
The electrostatic latent image on the photosensitive drum 11 is then transferred to a developing device 25.
It is visualized as a toner image. Although liquid development, magnetic brush development, etc. can be used as a developing method, magnetic brush development is used in this embodiment. The transfer paper 27-1 or 27-2 in the cassette 26-1 or 26-2 is transferred to the paper feed roller 28-
1 or 28-2, the rough timing is determined by the first register roller 29-1 or 29-2, and the accurate timing is determined by the second register roller 30, and then sent toward the photosensitive drum 11. . Next, while the transfer paper 27 passes between the transfer charger 31 and the drum 11, the toner image on the drum 11 is transferred onto the transfer paper. After the transfer is completed, the transfer paper is guided to the conveyor belt 32, and then to a pair of fixing rollers 33-1, 33-2, where it is fixed by pressure and heat, and then discharged onto the tray 34. After the transfer, the surface of the drum 11 is cleaned by a cleaning device 35 composed of an elastic blade, and the process proceeds to the next cycle. In addition, in order to control the above image forming cycle at each point in time, a drum clock pulse DCK is generated by a sensor 11b that optically detects the clock point of a clock board 11a that rotates with the rotation of the drum 11. Reference numeral 50 denotes a surface electrometer for detecting the surface potential on the drum 11, which is attached to the developing unit 21. The surface electrometer 50 will be explained. FIG. 2 is a cross-sectional view showing the mounting position of the surface electrometer 50 and the drum 11, FIG. 3 is a side sectional view of the electrometer 50, FIG. 4 is a surface potential detection circuit, and FIG. 5 is a surface to be measured. FIG. 5 is a perspective view of a squirrel-cage chopper 53 that shields the antenna and the measurement electrode. In FIGS. 2, 3, and 4, reference numeral 52 denotes a conductive outer cylinder made of brass or aluminum, and the outer cylinder 82 has a surface charge detection window 65. 55 is a sensor motor as a driving means for rotating the chopper 53; 53 is a cylindrical chopper having a potential measurement window 64; 54 is a surface potential measuring electrode;
6 is a preamplifier printed board on which a detection circuit for detecting the output of the electrode 54 is formed. The surface electrometer 50 is installed at a position 2 mm away from the drum surface, which is the surface to be measured, so that the potential measurement window 65 faces the drum surface. A preamplifier printed board 56 for amplifying the signal is built-in and integrally formed. CPU2 of the control circuit in Figure 6
When the sensor motor drive signal SMD is output from 01, the sensor motor 55 rotates, and the charge on the drum surface is induced in the electrode 54 through the potential measurement window 64. The potential measurement windows 64 are provided at four locations on the chopper 53 at equal intervals. Since the chopper 53 rotates and cuts off the drum surface 1 and the electrode 54 at equal intervals, an alternating current voltage is induced in the electrode 54 as shown in FIG. 7-1. The period T of this AC voltage is T=1/sensor motor rotation speed×4. Further, this voltage amplitude V _p - _p is determined by the drum potential V _p , the potential outer cylinder 52, the tipper blade 53, and the preamplifier board 56.
It is proportional to the difference in the sensor bias voltage VBIAS, which is the reference voltage of _VBIAS . Therefore, when V _p - _p = V _BIAS , the AC voltage becomes 0. The internal circuit provided in the preamplifier board 56 is driven by the sensor power supply SVcc superimposed on the aforementioned sensor bias voltage _VBIAS , and Q1 which performs impedance conversion of the AC conversion signal detected by the electrode 54 is a junction type. A minute alternating current signal induced in the electrode 54 by the FET is received by the high input resistance of the gate and converted into a low impedance signal. R3 and R4 are protective resistors. Part 7-2 shows the relationship between the drum potential V _p and the peak value of the output 62 from the preamplifier using _the sensor bias V _BIAS as a parameter _. Differences are detected faithfully. Furthermore, the drum potential V _p is V _p ≧V _BIAS or V _p ≦V _BIAS
If it changes within one of the ranges, the AC detection voltage has a monotonically increasing or decreasing characteristic depending on the drum potential _Vp , so there is no need to provide a new synchronous rectifier circuit for polarity determination. Chapter 7-2
In the figure, when V _BIAS is 150V, when the drum potential V _p is in the range of 150V, the detected voltage increases monotonically in the range of -nV to +150V, and the magnitude relationship in both the positive and negative directions can be determined. However, the positive range is +150Vmax, -nv
is limited by the saturation voltage of the circuitry included in preamplifier board 56. As described above, by applying a constant positive or negative bias to the electrometer housing and the internal circuit built in the electrometer, the bias voltage can be applied to the electrometer housing and the internal circuit built in the electrometer. It is now possible to determine the polarity of the measured surface potential. With this configuration, not only is there no need to newly provide a synchronization detection circuit, etc., but it is also possible to prevent fluctuations in the measured potential due to external noise affecting the internal circuit of the electrometer. By the way, in a type of copying machine that removes static electricity by applying light onto the photoreceptor, the output voltage of the primary charger 22 V _p1 The output voltage of the AC static eliminator 23 V _SL The amount of exposure light from the exposure lamp 16 is kept constant. If copies are made continuously while maintaining the same, the previous latent image creation will affect the photosensitive characteristics of the next latent image creation. In other words, a photosensitive plate has a memory characteristic.The memory characteristic varies depending on the manufacturing conditions of the photosensitive plate, and as shown in FIG. 8, when the sensitivity of the photosensitive plate becomes faster (2-
There are cases (2-b) where the reference light intensity is slower than c).
The surface potential of the photosensitive plate changes with respect to Eo (here, Eo is the amount of reflected light when the exposure lamp shines light on a standard white document with a light emission amount adjustment dial (not shown) set to the 5 position). In addition, the potential especially after AC static electricity removal changes due to changes in the environment such as temperature and humidity. Fluctuations in AC static elimination particularly affect bright areas of the document. Figure 9 shows the characteristics of the photosensitive plate when the AC static elimination varies. In this way, continuous copying or changes in the environment will cause changes in image conditions such as dark area density, halftone density, bright area fog, etc. of the original, but in order to make good copies, it is especially important to suppress fog in the bright areas of the original. This becomes an important element. A control method for controlling the bias voltage of the developing device in order to suppress fog in bright areas will be described in detail below. In this embodiment, the blank exposure lamp 10 is used instead of the document illumination lamp 16 to detect the drum surface potential in the bright area. The blank exposure lamp 10 illuminates the drum surface during the forward rotation and the backward movement of the optical system. The surface potential of the drum surface at this time is measured as the bright area surface potential, and the developing bias applied to the developing device 25 is controlled according to this detected voltage. At this time, the blank exposure lamp 1
The amount of light irradiated onto the drum surface at 0 is set to the same amount of light reflected from the document illumination lamp 16 when a white document is placed with the light emission adjustment dial (not shown) on the operation unit at position 5. It has been adjusted accordingly. Therefore, detecting the surface potential of the drum due to irradiation with the blank exposure lamp 10 is the same as the surface potential generated on the drum surface during copying when the white document is being copied, and a certain positive voltage is added according to the detected voltage. By applying a developing bias in this manner, it is possible to prevent the copy from being fogged even if the photosensitive characteristics of the drum 11 fluctuate and the bright area potential fluctuates. In this embodiment, the bright area surface potential measurement using the blank exposure lamp 10 measures the potential of the non-image area during the aforementioned pre-rotation and the non-image area between successive electrostatic latent images, and the measurement output is This serves as a reference voltage for applying a developing bias during development of the latent image following . In the timing charts of FIGS. 6 and 15, when a copy start signal is input from the key input means 208, a motor drive signal MD is output from the CPU 201, and the high-voltage AC static eliminator 23, high-voltage primary charger 22, and full-surface irradiation lamp 24. Blank exposure lamp 10 and sensor sensor 55 are turned on,
Perform the pre-rotation described above. At this time, sensor motor 5
5 is driven by a sensor motor drive circuit. The above-mentioned constant sensor bias V _BIAS (+150V) is applied to the potential outer cylinder 52 and the chopper 53, and the constant sensor power supply is applied to the circuit inside the preamplifier board 56.
SVcc (+175v) development bias control circuit 207
are applied through lead wires 60 and 61, respectively. The AC signal detected by the electrometer 50 is connected to the lead 62.
The signal is amplified by an AC amplifier 204, and then regenerated into DC by a rectifying and smoothing circuit 205. This DC reproduction voltage is input to a sample hold circuit 206, and the DC reproduction voltage when the STB signal output from the CPU 201 is "H" is stored in this circuit 206.
When the pre-rotation is completed, the paper feed and exposure lamp 16 is turned on, the optical system consisting of the lamp 16 and mirrors 15 and 17 scans according to the document size, and the developer motor rotates to perform development. The developing bias control circuit 207 switches between the above-mentioned DC reproduction signal and a constant value based on the developing device drive signal DVL inputted from the CPU 201 through the lead wire 74. Therefore, a developing bias corresponding to the detected bright area potential is applied to the developing device 25 only when the developing device motor is rotating and developing the latent image. In the case of multiple copying, the strobe signal STB is set to cpu20 each time during optical system backward movement (SCRV) for each copy.
1, a blank light is irradiated while the optical system is moving backward, and the bright area potential is measured and stored, and the developing bias control circuit 207 is similarly controlled. In other words, when forming latent images continuously, an electrostatic image is formed by projecting a predetermined amount of light onto a non-image area between two consecutive latent images, and the potential of the electrostatic image is measured. Since the latent image that follows the electrostatic image is controlled, the output of the charger can be changed by controlling the developing device to compensate for changes in the characteristics of the photoreceptor due to continuous image formation and changes in the output of the charger due to environmental changes as described above. This can be compensated for by controlling the developing device, and stable image formation can be performed, which is particularly effective in preventing fog in bright areas. Furthermore, by detecting each time a latent image is formed, it is possible to faithfully follow changes in bright area potential, which is effective. FIG. 10 is a detailed circuit diagram of the sensor motor drive circuit 203 in FIG. 6. When the motor drive signal MD becomes "H", the open collector inverter output becomes "L" and the voltage across capacitor C1 becomes Q3. , Q6 of the constant voltage circuit
7. Supply the voltage determined by R8 to the motor windings. FIG. 11 is a detailed circuit diagram of the AC amplifier 204, the rectifying and smoothing circuit 205, and the sample-hold circuit 206. The AC voltage waveform detected by the electrometer 50 is connected to the coupling capacitor C3 from J1.
The AC signal is input to the amplifier Q6 and is amplified by the AC amplifier Q6 to become an amplified AC signal centered on +12V. VR6 is a detection gain adjustment volume. The rectifier circuit 205 includes an operational amplifier Q7, diodes D3 and D4, and a resistor R20, and constitutes a linear detection circuit that linearly amplifies only the positive component around +12V. When the input voltage at the inverting input terminal of operational amplifier Q7 is positive with respect to the input voltage at the non-inverting input terminal, the point becomes negative, turning diode D4 off and D3 on. The negative input terminal of Q7 becomes + by turning on D3.
Since it becomes 12V, the output (point B) becomes +12V.
Also, when the input voltage of the inverting input terminal is negative with respect to the input voltage of the non-inverting input terminal, the point becomes positive and diode D4 is on, diode D3 is off, so the gain is -R ₂₀ /R ₁₉ and linear amplification and detection are performed. Ru.
Since such a linear detection circuit is used, the linearity of the DC reproduction voltage characteristic with respect to the surface potential of the drum is improved, and furthermore, temperature compensation is made sufficient. The detected signal passes through a buffer amplifier consisting of an operational amplifier Q8 and is smoothed by a smoothing capacitor C6. It is further amplified by a Q9 buffer amplifier. The signal here is outputted to the outside as a check terminal J5 for potential setting via a voltage follower Q13. As shown in FIG. 12A, the relationship between the output of J5, that is, the integral output, and the potential of the drum surface has a characteristic that is symmetrical about the sensor bias V _BIAS . The sensor bias compensation signal COMP of J2 is inputted to the inverting input terminal of the summing amplifier Q10 via the developing bias control circuits 207 to 71.
A voltage is extracted from the sensor bias V _BIAS by dividing it with a resistor, and in the example, it is +1V (+12V reference). The sensor bias compensation signal V _COMP has its polarity inverted by the operational amplifier Q14 and becomes one input of the summing amplifier Q10 at -1V (+12 reference). The output of Q10 exhibits the characteristics shown in FIG. 12B. Therefore, the sensor bias compensation signal V _COMP can be adjusted by applying the sensor bias V _BIAS to the surface potential of the drum.
Its role is to eliminate offset by level shifting the DC regenerated detection output at Ov (+12v reference). Furthermore, the variation in V _BIAS acts to offset the variation in the DC regenerated detection output described above. In other words, by adding a voltage obtained by resistance-dividing the bias voltage applied to the electrometer casing to the measured output of the electrometer that has been regenerated with direct current, the fluctuations in the bias voltage are offset, making stable measurement possible. In this case, the present invention is not limited to the squirrel cage electrometer of this embodiment, but can be applied to any type of electrometer that extracts the potential of the surface to be measured as an AC signal and reproduces the DC signal. By the way, the output of summing amplifier Q10 is a junction type.
The signal is input to a sample and hold circuit consisting of FET Q11, amplifier Q12, capacitor C7 with low leakage current, and resistor R44. At this time, when the stroke signal input from J3 is "H", transistor Q15 is turned off, and the gate and source of junction type FETQ11 are reverse biased, and FETQ11 is
Since it is OFF, the output of amplifier Q10 cannot be stored in capacitor C7. When is "L", transistor Q15 is turned on, and the voltage between the gate and source of FET Q11 becomes Ov, and the gate and source are forward biased and the output capacitor C7 of Q10 is charged. Next, when the signal becomes “H”, FETQ
11 is turned off and one terminal of the capacitor C7 becomes open, so that the charged electric charge is held. With the above operation, the sample and hold circuit can sample and hold the output of Q10 when Q10 is at L. Further, since the gain is multiplied by 1/2 by R41 and R44, the characteristic shown in FIG. 12C is shown. This signal is sent from J4 to the developing bias control circuit 207 via 72 in FIG. FIG. 13 is a detailed circuit diagram of the developing bias control circuit 207 shown in FIG. Blocks 6-1 and 6-2 are high voltage generating circuits, respectively. Block 6-2 will be explained. When +24V power is supplied to the inverter transformer T2, either transistor Q24 or Q25 starts to turn on. transistor Q
When 24 starts to turn ON, the collector current of Q24 increases, and a back electromotive force corresponding to the increase in collector current is generated in transformer T2, which is also transferred to the base of Q25.Then, the collector current of Q24 increases further. do. Due to this positive feedback, Q24 is saturated with a time constant determined by resistors R86, R88 and the inductance of transformer T2. When the collector current of Q24 is saturated, the back electromotive force of the coil T2 becomes 0 and Q24 is turned off, and a back electromotive force corresponding to the decrease in the collector current is generated in the transformer T2, and the Q
Turn on 25. Similar positive feedback causes transistors Q24 and Q25 to continue oscillating. D11,
D12 is a protection diode resistor for Q24 and Q25. R89 is a resistor to prevent the collector current from varying due to variations in hFE of transistors Q24 and Q25, and to prevent the oscillation duty from becoming 1:1. . The oscillation amplitude will be approximately twice the voltage supplied to T2. This oscillation voltage is boosted to a voltage determined by the turns ratio of T2, and D14,C
It is rectified and smoothed in step 15, and a high voltage DC is output. Block 6-1 also outputs high voltage in a similar manner, but it is a variable high voltage output in which the voltage supplied to T1 changes in accordance with the output voltage of Q17. Switch the developer drive signal input from terminal J7 to "H" or "L" to set the input of operational amplifier Q17 to the above-mentioned sample board voltage value, or change variable resistor VR1.
It is selected whether to use a voltage determined by 0.
When is “H”, transistors Q16 and Q19
It turns OFF, and the gate of FETQ18 becomes the same potential as the source via R62, and the source and gate are forward biased, so FETQ18 turns ON. Therefore, the voltage input to the operational amplifier Q17 is determined by the variable resistor VR10.
When is "L", the sample and hold voltage input from J6 becomes the input to Q17 in a completely opposite operation. The signal input to Q17 is connected to variable resistor VR8.
It is compared with the inverted input voltage determined by VR9 and amplified, and is composed of transistors Q20 and Q21. It is supplied as power to the transformer T1 via a current booster. As the voltage applied to the transformer T1 increases, the oscillation amplitude increases, and the negative high voltage on the secondary side of the transformer T2 becomes even more negative. This voltage is superimposed with the positive fixed output of block 6-2 and applied to the developer via relay K2 as developer bias D _BIAS . When the input to Q17 is the sample bold voltage at terminal J6, the characteristics of the developing bias D _BIAS with respect to the drum potential are as shown in FIG. 12D. Here, variable resistor VR8 determines the Y-axis intercept in FIG. 12D, and resistor VR9 determines the slope. Therefore, if the drum bright area potential is 150V or less, the developing bias voltage D _BIAS will be the bright area potential +75V. The signal MODE input to terminal J8 becomes "H" when setting the potential as described later, and the sample hold voltage from J6 is selected as the input to Q17. Furthermore, relay K1 is opened, and the developing bias voltage D _BIAS is applied to the developing device. It prevents it from happening. The motor drive signal of terminal J9 connects relay K2.
Turn ON and apply the developing bias voltage D _BIAS to the developing unit 25. The sensor bias switching signal is switched between "H" and "L" when setting the potential, and the sensor bias V _BIAS is set to the voltage between resistors R76 and R77.
Select 225V or 150V between R77 and R78. During normal copying, SVCH is “H” and V
+150V is supplied to _BIAS . sensor power supply
SVcc is independent winding L1 to D1 of transformer T2
The voltage rectified and smoothed by C16, R9, C17, and C18 is used as a power supply, and +24V is added to the sensor bias voltage _VBIAS , so even if _VBIAS is switched, SVcc will always be +24V. Furthermore, as shown in the time chart of FIG. 15, in this embodiment, when measuring the potential of the signal BEXP indicating the light amount of the blank exposure lamp 10, the light is adjusted to a predetermined light amount and the image is recorded on the recording medium. The light amount is changed over to the predetermined light amount or more. In other words, when measuring the surface potential, the light intensity of the blank exposure lamp is adjusted to the light intensity within the dynamic range where the surface potential changes with respect to the light intensity, and after recording is completed, the light intensity of the blank exposure lamp is adjusted to a high intensity for exposure. It has become possible to eliminate the non-uniform electric field caused by carriers within the layer. Next, the mode switch for setting the drum potential will be explained according to FIG. 6 and Table 1.

【table】

[Table] In order to set the appropriate potential on the drum when replacing the drum or adjusting the image when assembling the machine, as shown in Table 1, the dark area potential V _D , bright area saturation potential V _SL , and standard white original There is a bright area potential V _IMAGE, etc., and when the developing bias is controlled, the bright area potential V _L due to the weak blank must be set appropriately. At this time, by providing a switch that can select each setting mode, as shown in mode switch 202 in FIG. 6, it is possible to select load driving conditions that cause each set potential to be generated in the drum simply by pressing the switch. Mode switch SW1 is used to turn off the blank exposure lamp and set the dark area potential V _D corresponding to the dark area potential of the document to the target potential +450V, and adjust the primary charger wire while monitoring the output of the surface electrometer. and set it to the target potential. Mode switch SW2 is used to set the bright side saturation potential _VSL of the photosensitive drum to the target potential -150V by lighting the blank exposure lamp strongly, and outputs the AC static eliminator while detecting the output of the surface electrometer. Adjust and set to target potential. Mode switch SW3 is for lighting the blank exposure lamp weakly and setting the bright area potential V _L corresponding to the bright area of the photosensitive drum to the target potential -75V, and blank exposure is performed while detecting the output of the surface electrometer. The bright area potential V _L is set to the target potential by adjusting the variable resistor VR3 for adjusting the light amount of the lamp. The mode switch SW4 is the reflected light when a standard white original is illuminated by the halogen lamp at the bright area potential V _L due to blank dimming set by SW3 and the light emission amount adjustment dial 5 of the original exposure halogen lamp. This is a switch for adjusting the diaphragm of the halogen lamp so that the bright area potential V _IMAGE matches the bright area potential V IMAGE.
Before pressing mode switch SW4, place a standard white original on the platen 14, and set the light emission adjustment dial on the operation unit to position 5. Next, press mode switch SW5 to drive the optical system forward clutch and expose the original. An optical system consisting of a lamp and a mirror is stopped at a position where the white original is irradiated with light from the original exposure lamp. Thereafter, by pressing the mode switch SW4 and adjusting the aperture of the halogen lamp while detecting the surface electrometer output, the V _IMAGE and the bright area potential V _L are made to match. In this way, the light intensity of the blank exposure lamp for developing bias control (blank weak) is matched with the reflected light intensity when the light from the halogen lamp is applied to a standard white original at position 5 of the light emission adjustment dial, and the developing bias is controlled. is more accurate. Furthermore, the adjuster can change the sensor bias voltage V _BIAS from the CPU 201 in FIG _. In order to set
Each adjustment can be made to match a single value without having to memorize various values. When the mode switch SW1 is pressed, the pre-programmed output is output from the CPU 201, and the main motor drive signal MD,
A high-voltage primary charger on signal HV1 and a high-voltage AC static eliminator on signal HV2 are output. Further, the signal MD is also supplied to the sensor motor drive circuit 203 and the developing bias control circuit 207 via 76 and 75, respectively, so that the sensor motor rotates and the potential detection signal is sent to the AC amplifier 204 and the DC regeneration circuit 2.
05, the signal path from the sample hold circuit 206 to the developing bias control circuit 207 is closed.
At this time, the strobe signal STB also becomes H.
STB becomes L, the analog switch FET Q11 in FIG. 11 in the sample hold circuit 206 turns on, and the sensor bias switching signal SVCH becomes H.
Therefore, SVCM becomes L, and the contact of relay K3 in Fig. 12 is connected to the +150V side, and the developing bias voltage V _B
Supplied as _IAS to the sensor housing, chopper and internal circuit. When the mode switch 202 is pressed, a signal is sent to determine whether the mode switch is pressed.
MODE becomes “H”, transistor Q19 and relay K1 in Fig. 13 are turned on, and operational amplifier Q
The signal J6 is selected as the input of 17, and the developing bias D _BIAS going to the developing device is cut off. On the other hand, the 6th
In the figure, the drum 11 rotates, and the primary charger 2
2. Since the AC static eliminator 23 and the full exposure lamp 24 are both ON and no other exposure irradiation is being performed, the surface potential of the drum measured by the electrometer 50 is the dark area potential V _D corresponding to the dark area of the original. It is. At this time, the check terminal J5 exhibits the characteristics shown in Figure 12A, so when the target dark potential is 450V, the adjuster adjusts the primary charger wire VR1 to set the terminal J5 to 2V (12V reference). good. Similarly, when the potential setting mode switches SW2 to SW3 shown in Table 1 are pressed, the surface potential of the drum detected by the electrometer 50 changes to the bright area saturation potential V _SL , according to the pre-programmed load driving conditions.
The dark area potential V _L due to blank dimming, the potential V _IMAGE due to the reflected light of the halogen of the standard white original, and the sensor bias V _BIAS is switched to 225 V with mode switches SW3 and SW4. Yes, but the set target potential is the mode switch.
Even though SW1, 3, and 4 are different, set the check terminal J5 to high voltage to 2V (12V standard).
All you need to do is adjust the AC output regulator VR2, the blank exposure lamp light intensity regulator VR3, and the halogen aperture diaphragm regulator VR4. By providing this mode switch 202, the electrometer 50 not only has the role of simply controlling the developing bias and preventing fog, but also serves as a built-in electrometer for setting the potential. . Furthermore, there is an advantage that the adjuster can adjust only one value without having to memorize the value of each set potential. Further, by using a comparison circuit as shown in FIG. 14, it is possible to display the surface potential detection output by level. The DC reproduction voltage of the surface potential detection circuit is input to the non-inverting input terminals of the comparators COM1 to COM5, and the comparison voltages _V1 to _V5 are input to the inverting input terminals of the comparators COM1 to COM5. The magnitudes of the comparison voltages V ₁ to _{V 5} are V ₁ > V ₂ > V ₃ > V ₄ >
V is set to ₅ . Adjust the regulators VR1 to VR4 so that only the light emitting diode LED3 lights up.
In this way, it has become possible to adjust different surface potentials just by lighting the same light emitting diode. or,
The mode switch can selectively drive some of the plurality of processing means for image formation. By providing such a command means, when checking the operating state of an image forming apparatus such as a copying machine, it has become possible to closely examine the operating state of a part of the apparatus without driving the entire apparatus. Furthermore, when measuring the surface potential of different modes (bright area potential, dark area potential, etc.) on the drum using a surface electrometer, it is effective because the load can be selectively driven so that the surface potential of the desired mode can be easily measured.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a copying machine to which the present invention can be applied, FIG. 2 is a cross-sectional view showing the mounting positions of a surface electrometer and a drum, FIG. 3 is a side cross-sectional view of the electrometer, and FIG. Surface potential detection circuit diagram, Figure 5 is a perspective view of the squirrel-cage chipper, Figure 6 is a control circuit diagram of the copying machine shown in Figure 1, Figure 7-1 is an output waveform diagram of the electrometer, Figure 7-2
The figure shows the relationship between the drum potential V _p and the peak value of the output 62 from the preamplifier using the sensor bias V _BIAS as a parameter. 8th is a photosensitive characteristic diagram of the photosensitive plate. 9th figure is the characteristic of the photosensitive plate due to environmental changes. 10 is a rotation control circuit diagram of the sensor motor, FIG. 11 is a detailed circuit diagram of the amplifier circuit 204, rectification smoothing circuit 205, and sample hold circuit 206 in FIG. 6, and FIG. 12 is a diagram showing the surface potential V. A diagram showing the relationship between _p and the output of each part in FIG. 11, FIG. 13 is a detailed circuit diagram of the developing bias control circuit diagram 207 in FIG. 6,
FIG. 14 is a comparison display circuit diagram, and FIG. 15 is a timing chart of the copying apparatus of FIG. 1.
In the figure, 10 is a blank exposure lamp, 11 is an exposure drum, 16 is an original exposure lamp, 22 is a primary charger, 23 is a static eliminator, 24 is a full-surface exposure lamp, 2
5 is a developing device, 50 is a surface electrometer, 52 is an electrometer housing, 53 is a cage-shaped chipper, 54 is a measurement electrode, Q
1 is a junction FET, V _BIAS is an electrometer bias voltage, V _COMP is a compensation voltage, and SW1 to SW6 are mode switches.

Claims (1)

[Scope of Claims] 1. An electrostatic latent image forming means for forming an electrostatic latent image on a recording medium; a developing means for developing the electrostatic latent image formed on the recording medium; blank exposure means for exposing a non-image area; detection means for detecting a surface potential on the recording medium exposed by the blank exposure means; and controlling a bias voltage of the developing means in accordance with the output of the detection means. a control means, when the surface potential is measured by the detection means, the light amount of the blank exposure means is set to a predetermined light amount within a dynamic range in which the surface potential of the recording medium changes with respect to the light amount; An electrophotographic apparatus characterized in that upon completion of formation, the light amount of the blank exposure means is set to a light amount that is equal to or greater than the predetermined light amount and can erase a non-uniform electric field of the recording medium.