JP2532072B2 - Residual potential controller - Google Patents

Description

TECHNICAL FIELD The present invention relates to a residual potential correction method for a multicolor image forming apparatus.

(Prior Art) When a photoconductor of an electrophotographic copying machine is repeatedly subjected to a predetermined copy cycle and discharged, for example, even after being discharged by light irradiation or the like, the electric potential may remain due to its fatigue. Are known. Since the residual potential of the photoconductor rises as the number of copies (the number of copy cycles) increases, when the potential level reaches a certain value or more, the background stain of the copy is caused.

Further, in an image forming apparatus that forms an electrostatic latent image on a photoconductor, develops the electrostatic latent image by a developing device, and then transfers it to a transfer paper, an electrostatic latent image having a specific density pattern is formed on the photoconductor. Then, the electrostatic latent image is developed by a developing device, the density of the toner image is optically detected by a sensor, and an image forming condition such as a developing bias is controlled based on an output signal of the sensor. ing.

However, when the above method is adopted in a multi-color image forming apparatus that selectively uses a plurality of developing devices for developing electrostatic latent images on the photoconductor with toners of a plurality of colors, In order to correct the residual potential fluctuation, it is necessary not to be affected by the toner characteristics for each color, but the output signal level of the above sensor is affected by the toner characteristics and changes, leaving the photoreceptor pure. Since the potential cannot be detected, it becomes impossible to properly control the image forming conditions.

(Object) It is an object of the present invention to prevent background stains due to the residual potential of the photoconductor in a multicolor image forming apparatus, and to prevent the residual potential of the photoconductor from being detected purely due to the characteristics of the toner. It is to provide a residual potential correction method capable of preventing the residual potential.

(Structure) In order to achieve the above object, the invention described in claim 1 is an electrostatic latent image formed on a photoconductor by selectively setting a plurality of developing devices containing toners of different colors. A multicolor image forming apparatus that forms a toner image by developing the image with the developing device that has been set, and forms the toner image on a transfer paper to form a plurality of images using the plurality of developing devices, respectively. In the residual potential correction method, the developing bias of a developing device having a toner of a specific color among the plurality of developing devices is set to a value at which the residual potential after the charge removal of the photoconductor can be developed, To form a visible image pattern according to the residual potential by using a developing device having the toner of the specific one color, the density of the visible image pattern is detected by an optical detecting means, and based on this detection signal, It is characterized in that each image forming condition of a plurality of image formations using each of the plurality of developing devices of the multicolor image forming apparatus is corrected.

The invention according to claim 2 is the residual potential correction method according to claim 1, characterized in that the toner of the specific one color is black toner.

 Hereinafter, the present invention will be described based on an illustrated embodiment.

This embodiment is an example applied to a multicolor image forming apparatus including a multicolor copying machine. In FIG. 1, around a photoconductor 1 made of a photoconductor drum, a charger 2 made of a charger, an eraser 3, developing devices 4A and 4B, a visible image pattern detection sensor 5, a transfer device 6 made of a transfer charger, A separator 7, which is a separation charger, a cleaning device 8 and an optical static eliminator 9 are arranged at positions suitable for executing a predetermined copying process.

The visible image pattern detection sensor 5 is connected to the copying process control unit 100.

The developing device 4A supplies color toners such as red, blue and green to the photosensitive drum 1 to visualize the electrostatic latent image formed on the surface of the photosensitive drum 1 as a color image.

On the other hand, the developing device 4B supplies black toner to the photosensitive drum 1 to visualize the electrostatic latent image into a black image.

Each of these developing devices 4A and 4B has a copy mode.
Set selectively. That is, this multicolor copying machine
In the color copy mode, the developing device 4A is set, and in the normal copy mode, the developing device 4B is set, and by operating according to a predetermined copying process together with the above devices,
It is configured to obtain a color copy, or a white, black copy. FIG. 1 shows a developing device 4B that supplies black toner.
Is set, and the developing device 4A that supplies color toner is reset.

The developing sleeves 4a and 4b of the developing devices 4A and 4B.
Are respectively connected to the bias output terminals OUTB of the high voltage power supply unit 200.

These are well known and operate in a well known manner. That is, the photosensitive drum 1 is rotationally driven by a motor and is uniformly charged by the charger 2, and then an unnecessary portion is erased by the eraser 3 and image exposure is performed by an exposing device (not shown) to form an electrostatic latent image. It This electrostatic latent image is developed with color toner or black toner by a developing device 4A or 4B in a set state to form a color toner image or a black toner image, which is fed by a transfer device 6 from a paper feeding device (not shown). The toner image is transferred to the transfer sheet. The transfer paper is separated from the photosensitive drum 1 by a separator 7, the toner image is fixed by a fixing device (not shown), and the transfer paper is ejected to the outside as a copy. Further, the photosensitive drum 1 is cleaned by the cleaning device 8 after the transfer paper is separated, the residual toner is removed, and the charge is removed by the optical charge remover 9.

The electrodes of the charger 2, the transfer device 6 and the separator 7 are connected to the output terminals OUTC, OUTT and OUTD of the high voltage power supply unit 200, respectively.

This high-voltage power supply unit 200 is provided with a charger 2, developing devices 4A, 4A
B, the copying machine 6 and the separator 7 are operated to supply electric power at predetermined timings.

FIG. 2a shows the configuration of the high voltage power supply unit 200 shown in FIG. The output of the commercial AC power supply (voltage 100V) should be DC.
The circuit for converting to 24V is omitted. A description will be given with reference to FIG. 2a. It is the microcomputer CPU that controls this circuit. A single chip microcomputer (8049) is used here. Microcomputer CPU input port P24, P25, P26, P27, P20, P21, P
Photocouplers PC1 and PC for 22, P23 and T1 respectively
2, PC3, PC4, PC5, PC6, PC7, PC8 and the signal from the output end of PC9 is applied through the inverter N ₁ ~N ₉ (7404). The input terminals of the photo couplers PC1 to PC9 are the charging voltage applying trigger terminal (C trigger) and the transfer voltage applying trigger terminal (T
Trigger), development bias voltage application trigger terminal (B trigger), separation voltage application trigger terminal (D trigger), development bias voltage setting terminal (b0, b1, b2), timing pulse read control signal terminal and timing pulse The input terminals of the photocouplers PC1 to PC8 are connected to the output terminals of the copy process control unit 100, and the output terminals of the timing pulse generator TPG are connected to the input terminals of the photocoupler PC9. Has been done. The timing pulse generator TPG optically detects the rotation of a slitted disk (not shown) that rotates together with the photosensitive drum 1, and generates a timing pulse signal in synchronization with the rotation of the photosensitive drum 1.

Microcomputer CPU output port P14, P15, P10, P
An analog / digital (hereinafter abbreviated as A / D) converter ADC (4052) is connected to 11 and the input port T0.
This A / D converter ADC has four signal input terminals A0, A1, A2 and A3, and channel selection input terminals C0 and C1.
Four signal input terminals A0, A according to the signal applied to
Converts the input voltage of 1, A2 or A3 into 8-bit digital data in synchronization with the signal applied to the clock input terminal CLK, and outputs the result to the output terminal DATA one bit at a time. To do. T1, T2, T3 and T4 are pulse transformers. One ends of the primary sides of the pulse transformers T1, T2, T3 and T4 are grounded, and the other ends thereof are connected to the output terminals of a driver circuit including switching transistors Q1, Q2, Q3 and Q4, respectively. 24V DC power is supplied to the input terminals of the driver circuits, that is, the emitter terminals of the transistors Q1, Q2 and Q3.

In addition, the control input terminal (transistor
Q1, Q2, Q3, Q4 base terminals) are buffers B1, B2,
It is connected to output ports DB0, DB1, DB2 and DB3 of the microcomputer CPU via B3 and B4 (7407). In the pulse transformer T4, the winding on the primary side is divided into two,
The driver circuit connected to it has two additional switching transistors to select the windings to energize.
Has Q5 and Q6. Each transistor Q5 and Q6
The input terminal of is connected to output ports DB4 and DB5 of the microcomputer CPU via buffers B5 and B6.

One of the secondary windings of the pulse transformers T1, T2 and T3 and one of the secondary windings of the pulse transformer T4 has a rectifying and smoothing circuit REC1, REC2, REC3, RE including a diode and a capacitor.
C4 is equipped with these rectifying and smoothing circuits REC1, REC2,
Output terminals OUTC, OUTT, OUTB, OUTD on the output side of REC3, REC4
The output signals of the rectifying / smoothing circuits REC1, REC2, REC3, and REC4 are provided to the charger 2, the developing devices 4A and 4B, and the transfer device 6.
And applied to the separator 7. Rectifying and smoothing circuit REC1, REC2,
Variable resistors VR1, VR2, VR3 and VR4 are provided on the output side of REC3 and REC4 to detect the output level of each power supply. Reference numeral 5 is for optically detecting the density of the visible image pattern formed by the residual potential on the surface of the photosensitive drum 1,
It is an optical detection means composed of a visible image pattern detection sensor using a reflection type photo sensor, and a signal amplification circuit including an operational amplifier Z4 and a variable resistor VR5 is connected to this output terminal.

Output terminals (slider) of variable resistors VR1, VR2 and VR3
Are connected to the signal input terminals A0, A1 and A2 of the A / D converter ADC respectively, and the output from the variable resistor VR4 and the output from the operational amplifier Z4 are respectively connected to the analog switch Z2.
And Z3, and is connected to the signal input terminal A3 of the A / D converter ADC.

Control input terminal (CONT) for analog switches Z2 and Z3
Are the output ports P12 and P1 of the microcomputer CPU
Connected to 3. The power supply for the control circuit Vcc (5V)
Is generated by the DC voltage regulator Z1.

2b and 2C show an outline of the processing timing of the microcomputer CPU shown in FIG. 2a, and FIGS. 3a and 3b show a schematic operation of the microcomputer CPU,
Figures 4a, 4b, 4c, 4e, 4f, 4g, and 4g
Figure 4h, Figure 4i, Figure 4j, Figure 4k, Figure 4l, Figure 4m, and Figure 4n show the operation of each subroutine or interrupt routine. Note that FIG. 2c is an enlarged view of a part of FIG. 2b.

The operation will be described below with reference to the drawings. Before that, the functions assigned to each port of the microcomputer CPU, the definition of the counter / timer used in the operation description, and the definition of the arithmetic register are described in the following The results are shown in Table 1, Table 2 and Table 3.

The symbols in the drawings and the specification with () indicate the contents of a register or an input / output port, and the symbols without this indicate immediate data. The microcomputer CPU is shown in Figs. 3a, 3b,
The operation shown in FIGS. 4a to 4n is performed as follows.
That is, when a power switch (not shown) is turned on as shown in FIG. 3a, first, all output ports are initially set to the off level, and each power supply system (charger 2, developing devices 4A, 4B, transfer device 6 and separator). Output pulse duty ((TC / TP), (TT / TP), each of the internal registers TC, TT, TB and TD holding the control pulse width of
(TB / TP) and (TD / TP): TP is the pulse period) is 30 to 50
Set a predetermined value that will be about%. Then, the timer interrupt is permitted, the value of the timer is set to a predetermined value, and then the timer is started. Note that the timer here is a programmable hardware timer provided inside the microcomputer CPU, and in the operation mode of this embodiment, when the count value reaches a predetermined set value, an internal interrupt is generated. , Set the interrupt flag TF.

When the internal interrupt is enabled, the timer interrupt occurs when a predetermined time has passed since the timer was started. When a timer interrupt occurs, the microcomputer CPU interrupts the current processing and enters the timer processing routine shown in FIG. 4b. In this timer interrupt processing, the timer is once stopped, the predetermined value N is reset to it, then the timer is started, and then the content of the AC counter (ACNT) described later is incremented by one. When the content of this AC counter reaches a predetermined value I, it is cleared to 0. In the timer interrupt, the timer is reset and returned, so the timer interrupt always has a fixed cycle (first
It occurs every Tp) shown in Fig. 2c.

The microcomputer CPU reads the state of the input signal from the copying process control unit 100 after starting the timer as described above. In this read, the 4a
As shown in the figure, the input signals input from the copy process control unit 100 to the input ports P20 to P27 are read and stored in the input buffer INBUFF. Next, an instruction to turn on each power supply system from the copying process control unit 100 (C trigger, T trigger, B trigger, D to turn on the charger 2, the developing devices 4A and 4B, the transfer device 6 and the separator 7). Triggers) are all off, and if all the triggers are not off, the timer flag TF set by the timer interrupt is monitored, and one is set for each timer interrupt. Operates to execute loop processing. In addition, when the loop processing is not required, that is, when all the instructions (triggers) to turn on each power supply are off (for example, immediately after turning on the power of the copying machine), the cycle of the timing pulse from the timing pulse generator TPG is set. It is checked to measure the linear velocity of the photosensitive drum 1, and the control target value (voltage or current) of each power system output is set according to the result.

This is a process for making the same power supply unit compatible with a plurality of types of copying machines having different drum linear velocities. The linear velocity measurement is processed by the drum linear velocity measurement subroutine shown in FIG. 4c. Referring to FIG. 4c and FIG. 4d, first, the timing pulse at which the timing pulse changes from high level H to low level L is found, the timer is started from there, and then the timing pulse changes from H to L. When it does, the timer is stopped and its contents are read.
The value (v) is obtained by multiplying the reciprocal of the value obtained by multiplying (timer clock pulse period) by a constant k. This value (v) is the drum linear velocity. In this example, γ = 43.6μsec, k = 1mm
And (v) = 229 (mm / sec).

When the drum linear velocity (v) is obtained, the current / voltage set value calculation process shown in FIG. 4e is performed. In this process, the voltage or current set values (SC), (ST), and (SD) of the charger 2, the transfer device 6, and the separator 7 are obtained. These set values are values that set the charged amount of each electrode to a predetermined value regardless of the drum linear velocity. For example, in the case of the set value (SC), the constant αc related to the linear velocity of the drum is multiplied by the linear velocity of the drum (v), and a constant βc not related to the linear velocity is added to the set value. The constants αc and βc are determined according to the charging characteristics of the charger 2. The same applies to other setting values (ST) and (SD). αt, βt and αd, βd are constants determined by the characteristics of the transfer device 6 and the separator 7, respectively, and ST = αt × v + βt and SD = αd × v + βd.

When either trigger is turned on, loop processing is performed. First, the timer flag TF is checked, and when it becomes 1, the process proceeds to the next. Turn on the triggered driver output.
If the trigger inputs CTRIG, TTRIG, BTRIG and DTRIG are on,
Output of drivers B1 to B4 respectively CDRIVE, TDRIVE, BDRIVE
And DDRIVE (if DDRIVE is ON, ACNEGA is also ON). That is, if all the triggers are turned on, each drive output level is set to the low level L in synchronization with the interrupt timing, as shown in FIG. 2c.

Next, the pulse width for controlling the voltage or current of each drive output is controlled. This is performed by the pulse width counter check & trigger input check processing shown in FIG. 4f. Each time this processing is performed once, the content of the pulse width counter (PCNT) is incremented by one, and when all driver outputs become the off level H, this pulse width control is exited and the process proceeds to the next step.

Refer to FIG. 4f. The pulse width counter (PCNT) has an initial value of 0 and sequentially counts up in a predetermined cycle. The contents of the pulse width counter (PCNT) and the contents of the pulse width registers (TC), (TT), (TB), and (TD) of each output system are sequentially compared, and the value of the pulse width counter (PCNT) is compared to each pulse width. When the register value is reached or the trigger input goes to the off level (H), the driver output (CDRIV
Set the off level (H) to E), (TDRIVE), (BDRIVE) or (DDRIVE). In other words, as shown in Fig. 2c, it becomes low level L in synchronism with the occurrence of a timer interrupt, and then becomes high level H after a lapse of time according to the value of each pulse width register. Repeated pulse signals are output from each power system (CDRIVE),
Available in (TDRIVE), (BDRIVE) and (DDRIVE).

When all driver outputs are turned off, the contents of the function counter (FCNT) are checked and the corresponding processing is executed. The initial value of the function counter (FCNT) is 0, and it is incremented by 1 every time the state counter to be described later changes from 0 to 9 by performing loop processing (performing 10 times of loop processing), and is cleared to 0 when it becomes 4. To be done.
If the contents of the function counter (FCNT) are 0, 1, 2, 3 and 4, C as the input signal of the A / D converter ADC respectively.
Feedback signal from power supply output, feedback signal from T power supply output, feedback signal from B power supply output, feedback signal from D power supply output, and residual potential signal (variable resistors VR1, VR2, VR3, VR4, operational amplifier Z4 Each output signal).

Next, the contents of the state counter (SCNT) are checked and the processing corresponding to it is proceeded to. State counter (SCNT)
Has an initial value of 0, is incremented by 1 each time the loop processing is performed, and is cleared to 0 when it reaches 9. When the state counter (SCNT) is 0, the output port P14 to A / D converter ADC
Set the output signal to the chip select terminal CS of
A / D converter A / D conversion of ADC is allowed, and the start bit check shown in Fig. 4g is performed.

First, high level H is applied to the clock terminal CLK of the A / D converter ADC.
When the data terminal DATA becomes low level L, the low level L is applied to the clock terminal CLK. If the data terminal DATA is low level, it is determined that the start bit is detected.
This A / D converter ADC converts the level of the input analog signal into a digital signal bit by bit in synchronization with the level of the clock terminal CLK changing from the high level to the low level after outputting the start bit. , Set the bit data to the data terminal DATA.

After performing the state bit check, increment the state counter (SCNT) by one. When the value of the state counter (SCNT) is between 1 and 8, the 1-bit A / D conversion process shown in Fig. 4h is performed once for each loop process and the state counter (SCNT) is incremented by one. Let First, A / D converter ADC clock terminal CLK
Is set to a high level H, the carry flag (CV) is cleared to 0, and a low level L is applied to the clock terminal CLK.
At this timing, 1-bit digital data is output from the A / D converter ADC to the data terminal DATA, so the level of that terminal is checked. At high level H, the contents of the carry flag (CV) are inverted (complemented), at low level L they are left unchanged, and the contents of the accumulator (A) including this carry flag (CV) are bit-shifted. When this is repeated eight times, that is, when the start bit is detected and loop processing is performed eight times, all 8-bit A / D conversion is completed, and the 8-bit data remains in the accumulator (A).

When the A / D conversion is completed, the value of the state counter (SCNT) becomes 9. If the state counter is 9, A / D conversion is prohibited (H is applied to the terminal CS of the A / D converter ADC), and the 8-bit data remaining in the accumulator (A) is stored in a predetermined memory area. The next process is selected according to the contents of the function counter (FCNT). When the value of the function counter (FCNT) is 0, 1, 2, 3 and 4, C current proportional calculation, T current proportional calculation, B voltage proportional calculation, D voltage proportional calculation, bias voltage array calculation and photoconductor potential Perform correction calculation.

The C current proportional calculation will be described with reference to FIGS. 4i and 4m. The set value SC of the C power supply output current is loaded into the set value register (S), the reference value GC is loaded into the gap register (G), and the proportional gain (K) is loaded into the proportional gain register (K).
Load C) and proceed to the subroutine <PWM>. <PWM>
Then, the content of the detected value register (V) (which holds the A / D converted feedback data) is subtracted from the content of the set value register (S), and the result is stored in the deviation register (E).

The absolute value of the contents of the deviation register (E) is compared with the contents of the gap register (G), and if the deviation between the set value and the detected value is larger than the contents of the gap register (G), the deviation register (E) is set. Multiply the contents by the contents of proportional gain register (K) and store the result in pulse width counter operation amount register (TE).
Add the value of the pulse width counter operation amount register (TE) to the contents of M). When the deviation between the set value and the detected value is equal to or less than the content of the gap register (G), the content of the register (TM) is not changed in order to prevent the occurrence of hunting due to excessive control.

After exiting the subroutine <PWM>, the contents of the pulse width counter set value register (TM) are stored in the pulse width register (TC) of the C power supply (power supply for supplying power to the charger 2). In the T current proportional calculation, the set value ST of the T power supply output current is loaded into the set value register (S) as shown in FIG.
The gap register (G) is loaded with the reference value GT, the proportional gain register (K) is loaded with the proportional gain (KT), and the subroutine <PWM> is executed as described above. After exiting the subroutine <PWM>, the contents of the pulse width counter set value register (TM) are stored in the pulse width register TT of the T power supply (power supply for supplying power to the transfer device 6).

Moreover, in the B voltage proportional calculation, as shown in FIG. 4k, the set value register (S) is loaded with the set value SB of the T power supply output current, the gap register (G) is loaded with the reference value GB, and the proportional gain register is loaded. The proportional gain (KB) is loaded into (K) and the subroutine <PWM> is executed as described above. After exiting the subroutine <PWM>, set the content of the pulse width counter set value register (TM) to the pulse width register TB of the B power source (power source that applies the developing bias voltage to the developing devices 4A and 4B).
To be stored.

In the D voltage proportional calculation, the set value register (S) is loaded with the set value SD of the D power output current, and the gap register (G) is loaded with the reference value GD as shown in FIG. Load proportional gain (KD) into (K) and execute subroutine <PWM> as described above. After exiting the subroutine <PWM>, the contents of the pulse width counter set value register (TM) are stored in the pulse width register TD of the D power supply (power supply for supplying power to the separator 7).

However, it is important to note that the set values ST and SD are preset fixed values, but the set values SC and (SB) need to be changed in order to perform development without scumming. Is there. That is, for example, the B power supply output (bias voltage) is the bias control data (b0, b1 shown in FIG. 2a) from the copying process control unit 100.
And b2 3 bit data) and photoconductor drum 1
Need to be changed according to the residual potential of. The developing bias voltage (B power output) is generally as shown in FIG.
It is necessary to increase in proportion to the residual potential (VR) of the photoconductor (to keep the developing characteristics constant). For example, when adjusting the density from the operation panel, the voltage value should be 1
It is necessary to stepwise increase or decrease by a predetermined value for the notch.

That is, the output voltage OUTB (setting value) of the bias voltage is
The residual potential of the photosensitive drum 1 is detected by the visible image pattern detection sensor 5
When the voltage correction amount based on the detection level detected in step (Vp), the constant determined by the characteristics of the photosensitive member is D, and the voltage adjustment amount is (B), the following equation is set.

OUTB = (Vp) × D + (B) [V] In the residual potential correction calculation, as shown in FIG. 4n, first, an input buffer (INBU that holds the states of the input ports P20 to P27) is used.
The contents of (FF) are transferred to the accumulator (A) and 07H
The lower 3 bits, that is, bias control data is extracted by taking the theoretical product with (hexadecimal), and this is added to the start address TABLE of the bias voltage data table to generate a table reference address, and the table data of that address is obtained. It is read and stored in the register (B), the residual potential data read at the image timing from the visible image pattern detection sensor 5 is stored in the register (V), and (V)
Calculate × D + (B) and store the result in the set value register (SB). The bias voltage data table is an 8-byte continuous memory area starting from the address TABLE, and 8-bit data corresponding to the voltage adjustment amount (B) is stored in each address in ascending order.

C current proportional calculation, T current proportional calculation, B voltage proportional calculation,
After each execution of the D voltage proportional operation, the function counter is incremented by one to clear the state counter, and after the residual potential correction operation is executed, the function counter and the state counter are cleared. Next, the content of the AC counter (ACNT) is checked, and if it is 0, the outputs of the AC drivers B5 and B6 are inverted. That is, the output signal from the output port DB5 to the AC driver B6 (ACP
If OSI) is L and the output signal (ACNEGA) from output port DB4 to AC driver B5 is H, (ACPOSI) is set to H and (ACNEGA) is set to L. If the AC counter value is not 0, the AC driver output status is not changed. AC counter (ACNT) in timer interrupts, as shown in Figure 4b.
+1 the contents of and the contents of I (1 in this example
When it becomes 2), the AC counter is cleared to 0, so the AC counter becomes 0 at a rate of once every 12 timer interrupts. Therefore, the AC driver output is inverted once every 12 cycles of the timer timer interrupt. That is, the transformer
The polarity of the applied power on the primary winding side of T4 changes at a rate of once every 12 cycles of the timer interrupt, so the polarity of the D power supply output changes every 12 cycles and this is the AC voltage output from the D power supply. Corresponding to the frequency of.

In this example, a 1MHz crystal oscillator XT is used as the oscillation source of the microcomputer CPU, and the basic clock pulse that oscillates it is divided into 43.6μ for the internal timer.
Counting sec clock pulses. When the count value reaches 256, this internal timer also generates an interrupt and flags T
Although F is set, since 256 (N) is preset in the timer here, the timer flag TF is set every 87.2 μsec.

Therefore, since the above loop processing is executed once every 87.2 μsec, the ON / OFF cycle of the pulse power for activating the primary windings of the transformers T1, T2, T3 and T4 is 87.2 μsec.
become. Looking at the operation of the microcomputer CPU shown in FIG. 3a and FIG. 3b, the A / D conversion processing for sampling the feedback signal of one power system takes 9 cycles, including the check of the start bit, that is, 784.8 μsec. It is performed once, and the set value calculation process of one power supply system is performed in one subsequent period.

In this example, there are four power supply systems, and since the residual photoconductor potential is sampled and the bias voltage is corrected, the above process is repeated 5 times, and the entire process is performed once in 50 processing cycles, that is, 4.36 msec. It will be. In other words, if the load changes, the maximum is 4.36ms.
After ec has passed, a process for correcting it can be performed. Since the AC cycle of the D power source corresponds to 24 cycles of the timer interrupt, it is approximately 2.01 msec in this example.

In this embodiment, one microcomputer is used to control a plurality of power supply systems in a time-division manner. However, as is generally done conventionally, a sawtooth wave generator, an analog comparator, a reference voltage generator are provided. Alternatively, pulse width control may be performed in an analog manner. However, according to the embodiment, since a single control device can control a large number of power supplies, the circuit configuration is simplified, and since it is digital control, it is less susceptible to noise and the adjustment work is simplified.

In the present embodiment, the case of one type of multicolor copying machine has been described. However, for example, in a facsimile or the like that moves a recording sheet (charge carrier), a timing pulse corresponding to the movement of the recording sheet is generated. Then, the voltage and the current may be set according to the measurement result.

By the way, for example, as shown in FIG. 6, normally, even if the densities of the visible patterns of the black toner and the red toner, that is, the toner adhesion amounts are the same, the light reflectances thereof are different depending on the colors of the toners. The amount of light received by the photo sensor differs between black toner and red toner, and the detection output of the visible image pattern detection sensor 5 differs.

Therefore, in a multicolor copying machine equipped with a plurality of developing devices 4A and 4B for selectively supplying a plurality of toners of different colors, the visible pattern detecting sensor 5 is changed depending on the colors of the toners supplied by the developing devices. The detection level changes, and it becomes impossible to properly correct the bias voltage corresponding to the residual potential of the photoconductor.

Therefore, as described above, a multicolor copying machine equipped with a developing device that uses a plurality of color toners (in the illustrated example, an example in which two developing devices are installed is shown, and one developing device 4A supplies the toner. Toner color is changed as needed)
When detecting the visible image pattern, for example, this visible image pattern is formed using one predetermined developing device, and the color of the toner forming the visible image pattern is specified.

As the toner forming the visible image pattern, if the light reflectance is the same, it is not necessary to specify the color, but in the case of a color toner, the color is exchanged as necessary, It is preferable to specify a black toner that does not exist. Further, when the visible image pattern is formed of black toner, as is apparent from FIG. 6, the output range of the visible image pattern detection sensor 5 is widened, so that the above-mentioned control of the developing bias voltage becomes easy.

Next, an example of an operation of specifying the type of toner forming the visible image pattern (here, the developing device 4B that supplies black toner is set at the time of forming the visible image pattern) will be described.

The copy process control unit 200 and the microcomputer CPU operate as follows. First, it is determined whether or not it is the image timing when the above-described copying operation is performed in the image area on the photoconductor drum 1, and since the toner is not attached to the photoconductor at the image timing, it is higher than the photoconductor residual potential. Set the development bias voltage in the bias output memory (OUTB memory).

Next, the number of copies (the cumulative value of the number of copy cycles of the photosensitive drum 1 is added to the value of the copy number memory for each copying operation +
It is determined whether or not the number of copies counted by 1 has reached a predetermined number of copies. Here, since the residual potential of the photosensitive member normally increases by only one notch of the bias voltage in copying 1000 to 10,000 sheets, the timing for correcting the developing bias should be experimentally adjusted in advance in consideration of the increase in the residual potential of the photosensitive member. Then, the number of copies at this time (500 to 1000 at the above-mentioned rate of increase) is set as the above-mentioned predetermined number of copies. If the number of copies at this time does not reach the predetermined number of copies, the contents of the bias output memory (OUTB memory) is set in the output port DB2, and the developing bias voltage higher than the residual potential of the photoconductor of the developing device 4A, 4B is set. It is applied to the developing sleeves 4a and 4B. Therefore, when the image timing is not reached, the toner does not adhere to the photosensitive drum 1 during the developing operation by the developing devices 4A and 4B.

If the number of copies is equal to or larger than the predetermined number, the developing device 4B
If (black toner) is set, and if the developing device 4B is not set, the contents of the bias output memory (OUTB memory) are set in the output port DB2 and the photoconductor remains as in the above case. A developing bias voltage higher than the electric potential is applied to the developing sleeves of the developing devices 4A and 4B. Therefore, when the image timing is not reached, the toner does not adhere to the photosensitive drum 1 during the developing operation by the developing devices 4A and 4B. Whether the developing device 4A or 4B is set is determined by the operator selecting a copy mode (black and white copy or color copy) on the operation panel.

The number of copies is greater than or equal to the specified number, and the developing device 4B
If (black toner) is set, the development bias voltage (the correction amount VP of the development bias voltage as described above
XD) is set in the bias output memory (OUTB memory) and applied to the developing sleeve 4b of the developing device 4B in the set state. Therefore, the residual potential of the photoconductor drum 1 at the time of not image timing is developed with black toner by the developing device 4B in the set state to form a visible image pattern, and the density of this visible image pattern is detected by the visible image pattern detection sensor 5. It

Next, this visible image pattern is read by the visible image pattern detecting sensor 5 (FIG. 9), and the visible image pattern detecting sensor 5 is read.
Output value VP ₁ of the new development bias voltage correction amount VP ₁ ×
Calculates the D, and the correction amount VP ₁ × D correction amount VP ₀ × new correction amount D VP ₁ × D of the sense bias voltage by replacing it in the correct amount VP ₀ × D of the developing bias voltage so far to correct. The new correction amount Vp ₁ × D is set to be treated as the correction amount Vp ₀ × D immediately after that.

Next, when the image timing for performing the above-mentioned copying operation is reset by resetting the copy number memory, the voltage adjustment amount B is selected based on the notch selection data operated by the operator, and the correction amount Vp ₀ × D is added to this. A developing bias voltage is set by adding and setting in the bias output memory (OUTB memory), and this developing bias voltage is set in the output port PB2 and applied to the developing sleeve 4a or 4b of the developing device 4A or 4B.

In the above embodiment, the case where two developing devices are installed has been described, but the same control is performed when three or more developing devices are installed as in a full-color copying machine. You can By the way, in the above-mentioned embodiment, the example in which the developing bias voltage of the developing device is corrected in order to prevent the occurrence of the background stain due to the rise of the residual potential of the photoconductor is shown. It is also possible to correct any one of the exposure voltage, the exposure voltage, or a combination thereof to correct any one of the charge amount and the exposure amount of the photosensitive drum 1, or a combination thereof. Here, the charging grid voltage, the developing bias voltage, and the exposure voltage are, for example, as shown in FIG. 10, the rate of increase in the residual potential of the photosensitive member, that is, the detection level when the visible image pattern detection sensor 5 detects the visible image pattern. (VS
R) and the detection level (VSG) at the time of detection of the non-developed area of the photoconductor are increased in steps and corrected.

(Effects) As described above, according to the present invention, a plurality of developing devices containing toners of different colors are selectively set,
The electrostatic latent image formed on the photoconductor is developed by the developing device set as described above to form a toner image, and the toner image is formed on the transfer paper, thereby forming a plurality of images using the plurality of developing devices, respectively. In the residual potential correction method for a multi-color image forming apparatus for forming, a developing bias of a developing device having a toner of a specific one of the plurality of developing devices is
The residual potential after charge removal of the photoconductor is set to a value at which development is possible, and a visible image pattern corresponding to the residual potential is created on the photoconductor using the developing device having the toner of the specific one color, Since the density of the visible image pattern is detected by the optical detection means, and based on this detection signal, the respective image forming conditions of the plurality of image formings respectively using the plurality of developing devices of the multicolor image forming apparatus are corrected. In a multi-color image forming apparatus that selectively sets a plurality of developing devices that store toners of different colors to form an image, it is possible to prevent background stains due to the residual potential of the photosensitive member, and It is possible to prevent that the residual potential of the photoconductor cannot be detected purely due to the influence of the above.

[Brief description of drawings]

FIG. 1 is a block diagram showing a connection between a photosensitive drum and a power supply device in an example of a copying machine to which the present invention is applied, and FIG. 2a is an electric circuit diagram showing a circuit configuration of a high voltage power supply unit shown in FIG. 2b is a timing chart showing the operation timing of the device shown in FIG. 2a, FIG. 2c is a timing chart showing a part of FIG. 2b in an enlarged manner, and FIGS. 3a and 3b are shown in FIG.
Flow chart showing the schematic operation of the microcomputer shown in FIG. 2a, FIG. 4a, FIG. 4c, FIG. 4e, FIG. 4f, and FIG.
Figure, Figure 4h, Figure 4i, Figure 4j, Figure 4k, Figure 4l, Figure 4m, and Figure 4n are flow charts showing details of the processing shown in Figure 3a or Figure 3b, respectively. Is a flow chart showing the timer interruption process, FIG. 4d is a waveform diagram showing timing pulses, FIG. 5 is a diagram showing the relationship between the residual potential of the photoconductor and the bias voltage, and FIG. 6 is the output of the visible image pattern detection sensor and toner. FIG. 7 is a flow chart showing the operation for identifying the developing device shown in FIG. 1, and FIGS. 8 (a) and 8 (b) are graphs showing the developing bias and the residual potential and the toner adhesion amount. FIG. 9 is a diagram showing the relationship, FIG. 9 is a schematic diagram of the above-mentioned visible image pattern detection sensor, and FIG. 10 is a diagram showing the relationship between the rate of increase in the residual potential of the photoconductor and the charging grid voltage, developing bias voltage, and exposure voltage. 1 ... photosensitive drum, 2 ... charger, 3 ... eraser,
4A, 4B ... Developing device, 4a, 4b ... Developing sleeve, 5 ... Visual image pattern detector, 6 ... Transfer device, 7 ... Separator, 100 ...
… Copier process unit, 200 …… High-voltage power supply unit.

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Claims (2)

(57) [Claims] 1. A plurality of developing devices respectively containing toners of different colors are selectively set, and an electrostatic latent image formed on a photoconductor is developed by the set developing devices to form a toner image. In the residual potential correction method for a multicolor image forming apparatus, which forms a plurality of images using the plurality of developing devices by forming the toner image on transfer paper, a method for correcting a specific color of the plurality of developing devices. The developing bias of the developing device having toner is set to a value capable of developing the residual potential after the charge removal of the photoconductor to develop a visible image pattern corresponding to the residual potential on the photoconductor with the toner of the specific one color. It is created by using the developing device having the above, the density of the visible image pattern is detected by the optical detecting means, and the plurality of developing devices of the multicolor image forming apparatus are used based on the detection signal. Residual potential correction method characterized by correcting the respective image forming conditions in the number of image forming. 2. The residual potential correction method according to claim 1, wherein the toner of the specific one color is black toner.