JPS6211345B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that controls the surface potential on a recording medium by changing the output of a charging corona discharge device.

Conventionally, several methods have been proposed for constant control of the surface potential on a recording medium of an image forming apparatus. For example, there is a method of controlling the applied voltage applied to the corona discharge device by the detection output of a detection means that detects the surface potential, but in a region where the temperature and humidity change temporarily, the corona current changes due to fluctuations in the power supply voltage of the corona discharge device. Therefore, it was not possible to compensate for changes in surface potential.

There is also a method of keeping the corona current value constant using a constant current circuit, but due to deterioration of the photoreceptor or other changes in its characteristics over time, the same potential is generated on the photoreceptor even if the corona current value is constant. Therefore, it was not possible to maintain the surface potential at an appropriate value.

It is an object of the present invention to provide an image forming apparatus that eliminates the above-mentioned drawbacks, and more specifically, it is an object of the present invention to maintain the surface potential of the photoreceptor regardless of changes in the atmosphere, deterioration of the photoreceptor, dirt on the corona discharge electrode, etc. The purpose of the present invention is to provide an image forming apparatus that can be maintained stably.

That is, the present invention provides an image forming apparatus that forms an electrostatic latent image according to the image on a photoreceptor, develops it, and then transfers it to a recording material, including a charging corona discharge means whose output can be varied, and the corona discharge means. a detection means for detecting the surface potential on the photoreceptor during the pre-rotation; a potential control means for controlling the current supplied to the corona discharge means in accordance with the above, and after the end of the potential control, detecting the current supplied to the corona discharge means in order to keep the current set by the potential control means constant; and current control means for controlling the power supply means according to the detected output thereof.

An embodiment of the present invention will be described in detail 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 completes its forward rotation and rotates to its normal position, the original placed on the original platen glass 14 is
The light is irradiated by an illumination lamp 16 that is integrated with the first scanning mirror 15, and the reflected light is scanned by the first scanning mirror 15 and the second scanning mirror 17. 1st
The ratio of the scanning mirror 15 and the second scanning mirror 17 is 1:1/2.
By moving at a speed ratio of , the document 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.

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 taken by the first register roller 29-1 or 29-2, and the second register roller 30
The photosensitive drum 11 is sent out in the direction of the photosensitive drum 11 with accurate timing.

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 further 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.

Here, a surface electrometer 50 for measuring the surface potential is connected to the drum 11 between the entire surface exposure lamp 24 and the developing device 25.
mounted in close proximity to the surface of the

FIG. 2 is a control block diagram of the corona discharge device. In FIG. 2, 50 is a surface electrometer as a detection means for detecting the surface potential of the photosensitive drum 11;
53 is a potential measurement circuit; 54 is a hold circuit that holds the output of the potential measurement circuit when the hold signal HS is output; 55 is a signal that outputs a signal corresponding to the appropriate current value to be passed through the charger based on the output of the hold circuit. 56 is a multiplexer that switches input terminals in accordance with the switching signal EX, 57 is a primary charger high-voltage power supply circuit, and 58 is a secondary charger high-voltage power supply circuit.

During the pre-rotation of the drum before the copying operation starts, an initial value set voltage is inputted to the multiplexer via the terminal 59, and a corona current corresponding to the set voltage is applied to the primary and secondary charger high voltage power supply circuits 57,
58 and flows to the drum 11. Next, the surface potential of the drum is detected by a surface electrometer 50, and a potential measuring circuit 53 inputs a voltage output of 1/300 of the surface potential to a hold circuit 54. The hold circuit 54 holds a surface potential detection output when a hold signal HS is output from a control circuit (not shown). The hold signal HS is output when the surface potential detection position of the drum comes to a position opposite to the surface electrometer. The arithmetic circuit 55 outputs a signal corresponding to an appropriate current value to be applied to the chargers 22 and 23 based on the output of the hold circuit 54, that is, based on the surface potential. When the above routine is completed, the multiplexer 56 outputs the optimum value calculated by the calculation circuit 55 from the initial set voltage to the primary and secondary charger high voltage power supply circuits 57 and 58, and adjusts the surface potential of the drum. The corona current flowing through the primary charger 22 and the secondary charger 23 is controlled so that the value becomes an appropriate value.

However, during the copying operation, the high-voltage power supplies 57 and 58 are continuously controlled using the surface potential measured during the pre-rotation, so the charger control based on surface potential detection can be performed without pre-rotation for a long time, such as when copying a large number of sheets. Not done. In this case, load fluctuations between the charger and the drum due to environmental changes cannot be corrected, but can be corrected by making the current flowing through the high-voltage power supply a constant current. A known constant current circuit for achieving this purpose is shown in FIG.

The current I flowing through the resistor R ₁ is determined by I=V/R ₂ . In other words, even if the value of resistor _R1 changes, the input voltage V
If is constant, the current flowing through resistor _R1 is constant.

FIG. 4 shows a more detailed block diagram of the high voltage power supply circuits 57 and 58 using constant current circuits as shown in FIG.

The primary charger correction voltage V _p and the secondary charger correction voltage V _AC output from the multiplexer 56 are input to the inverting input terminals of operational amplifiers OP ₁ and OP ₂ , respectively. The non-reflective input terminals of operational amplifiers OP ₁ and OP ₂ are compared with voltages determined by resistors VR ₁ and VR ₂ and amplified.

When the primary charger drive signal HVT ₁ is output, the signal HVT ₁ is input to the primary high voltage control circuit HC 1 and _{the output of the operational amplifier OP 1 is} sent to the amplifier AMP ₁ .

Similarly, when the secondary charger drive signal HVT ₂ is output, the signal HVT ₂ is input to the secondary high voltage control circuit HC 2 and _{the output of the operational amplifier OP 2 is} sent to the amplifier AMP ₂ . The output of the amplifier AMP ₁ increases or decreases the output voltage of the primary charger high voltage transformer TC ₁ . Similarly amplifier
The output of AMP ₂ controls the output voltage of secondary charger transformer TC ₂ .

Primary corona current I _p flowing through the primary charger 22,
The secondary corona current I _AC flowing through the secondary charger 23 is detected by resistors R ₁₁ and R ₁₂ respectively, and the primary high voltage transformer TC ₁ detects the voltage V _FP determined by the resistors R ₁ and VR ₁ and the primary charger. The primary corona current I _P is passed until the correction voltage V _P matches, and when the voltage V _FP and the primary correction voltage V _P match, the primary corona current I _P remains constant as long as the primary correction voltage V _P does not change. controlled. Similarly, the secondary high voltage transformer TC ₂ has a resistance R ₁₂ ,
The secondary corona current I _AC is caused to flow until the voltage V _FAC determined by VR ₂ matches the secondary charger correction voltage V _AC , and when the voltage V _FAC and the secondary correction voltage V _AC match, the secondary correction voltage The secondary corona current I _AC is controlled to be constant unless V _AC changes. That is, unless the next surface potential measurement is performed, both the primary and secondary corona currents are controlled to be constant. Further, as time passes, the surface potential is detected again, and if the surface potential is not appropriate, the corona current is controlled again. The surface potential may be controlled by measuring the part of the photoreceptor where the previously corrected corona current was passed, and then controlling the corona current.
The corona current may be controlled after measuring the portion of the photoreceptor through which the initially set corona current is applied again.

By the way, since the secondary charger is an AC charger, the AC voltage V _ACS of the AC power supply ACS and the DC output voltage V _DC
A superimposed voltage is applied to the secondary charger. In other words, constant current difference control is performed in which the AC voltage V _ACS is constant and only the DC voltage V _DC is controlled by the secondary charger correction voltage V _AC . Therefore, the secondary corona current I _AC detected by the resistor R ₁₂ is amplified by the amplifier AMP ₃ , and then the difference between the positive and negative components, that is, only the DC component is detected by the smoothing circuit REC, and the secondary corona current I AC detected by the resistor R 12 is amplified by the DC amplifier AMP ₄ , and then the resistor Added to VR ₂ .

FIG. 5 shows an actual circuit diagram of the block diagram of FIG. 4. In the figure, R is a resistance, C is a capacitor, and D
is a diode, Q ₅ , Q ₇ , Q ₈ , Q ₉ are operational amplifiers,
Q ₁ , Q ₂ , Q ₃ are oscillators, Q ₄ , Q ₆ are inverters,
T ₁ , T ₂ , and T ₃ represent transformers, respectively.

The primary charger correction voltage V _P is input to the inverting input terminal of the operational amplifier Q ₅ via the resistor R ₇ . Resistance VR ₁
The difference voltage between the voltage V _FP applied to the non-inverting input terminal of the operational amplifier Q ₅ and the correction voltage voltage _VP is −R ₆ /R
It is multiplied by ₇ and output from operational amplifier _Q5 . When the primary charger drive signal HVT ₁ is “H”, the operational amplifier Q ₅
The output of Darlington current amplifier AMP ₁ 's transistor Tr ₃ does not turn on. In other words, the output of Darlington current amplifier AMP ₁ is 0. said signal
When HVT ₁ is "L", the transistor Tr ₃ is turned on and a voltage approximately equal to the output voltage of the operational amplifier Q ₅ is output to the primary high voltage transformer TC ₁ . The oscillator Q ₁ in the primary transformer TC ₁ turns on transistors Tr ₁ and Tr ₂ alternately. Transformer T ₁ is 2 depending on the turns ratio
The voltage is boosted to the next side, and the secondary output is rectified by the diode D ₁ and applied to the primary charger 22 . The primary corona current I _P flowing through the primary charger is detected by the resistor R ₁₁ ,
The primary corona current I _P is input to the non-inverting input terminal of the operational amplifier Q ₅ via the resistor VR ₁ and is controlled so that the voltage V _FP and the primary correction voltage V _P match as described above. Similarly, the secondary charger correction voltage V _AC is input to the inverting input terminal of the operational amplifier Q ₇ via the resistor R ₁₃ . The difference voltage between the voltage V _FAC applied to the non-inverting input terminal of the operational amplifier Q ₇ from the resistor VR ₂ and the correction voltage V _P is multiplied by -R ₉ /R ₁₀ and output from the operational amplifier Q ₇ . When the secondary charger drive signal HVT ₂ is "H", the output of the operational amplifier Q ₇ does not turn on the transistor Tr ₅ of the Darlington current amplifier AMP ₂ . In other words, the output of Darlington current amplifier AMP ₂ is 0. When the signal HVT ₂ is "L", the transistor Tr ₅ is turned on and a voltage substantially the same as the output voltage of the operational amplifier Q ₇ is output to the secondary high voltage transformer TC ₂ .
The oscillator Q ₂ in the secondary high voltage transformer TC ₂ turns on transistors Tr ₇ and Tr ₈ alternately. The transformer _T2 boosts the voltage to the secondary side according to the turns ratio, rectifies the secondary side output with the diode _D12 , and outputs it as a DC component output. Also, the AC voltage generator ACS consists of AC oscillator Q ₃ and transformer T ₂
This outputs an AC high voltage, superimposes it on the DC output, and outputs it to the secondary charger 23. The secondary corona current I _AC flowing through the secondary charger is detected by the resistor R ₁₂ . The detection output is amplified by an amplifier AMP ₃ , and then a smoothing circuit REC detects only the difference between positive and negative components, and the detected output is amplified by a DC amplifier AMP ₄ . Further, the detection output is amplified by the amplifier AMP ₄ and then input to the non-inverting input terminal of the operational amplifier Q ₇ via the resistor VR ₂ , and as described above, the voltage V _FAC and the primary correction voltage V _P match. The secondary corona current I _AC is controlled as follows.

Another embodiment of the invention is shown in FIG. In the figure, 101 is a fixed output DC-AC inverter, 102 is a variable output DC-AC inverter, _T2 ' and _T3 ' are transformers, 11' is a two-layer photosensitive drum, 11'a is a photoconductive layer, 11'b is a conductive layer, C11 is a capacitor for detecting a current difference, EXP is reflected light from a document (not shown), 50' is a surface electrometer, DEV is a developing unit, OP ₁₁ and OP ₁₂ are operational amplifiers, and D31 is for rectification. It is a diode.

The reflected light EXP removes the charge on the photoconductive layer 11'a formed by the charger 23', and the photoconductive layer 11'a is
A latent image corresponding to the original image is formed thereon. The latent image is developed by a developing unit DEV and transferred onto transfer paper by a transfer unit (not shown). A surface potential meter 50' measures the surface potential on the drum 11' and inputs the measured value to one input terminal of the operational amplifier _OP12 . A reference voltage corresponding to the reference surface potential is input to the other input terminal of the operational amplifier _OP12 , and the operational amplifier _OP12 amplifies and outputs the difference between the reference voltage and the surface potential detection output voltage. The output of the operational amplifier OP ₁₂ is output to one input terminal of the operational amplifier OP ₁₁ , and the output from the current difference detection capacitor, which will be described later, is input to the other input terminal of the operational amplifier OP ₁₁ .

The operational amplifier _OP11 outputs an output so that the output of the operational amplifier _OP12 and the output of the current difference detection capacitor C11 match. In other words, the operational amplifier _OP11 operates so that the current difference changes according to the output of the operational amplifier _OP12 .

The output of the operational amplifier _OP11 changes the output of the variable DC-AC inverter 102, and a DC shifted portion of the AC voltage applied to the charger 23' is outputted from the transformer _T2 '.

The fixed DC-AC-inverter 101 outputs an alternating current voltage of about 100 Hz from the transformer T ₃ '.

The superimposed voltages of transformers T ₂ ' and T ₃ ' are applied to charger 23'. Charge corresponding to the difference between the positive and negative components of the current flowing through the charger 23' is accumulated in the capacitor C11, and a voltage corresponding to the accumulated charge is fed back to the operational amplifier _OP11 .

The operational amplifier _OP11 controls the DC-AC inverter 102 so that the output of the capacitor C11 becomes the same as the output of the operational amplifier _OP12 . It is therefore possible to maintain a desired corona current corresponding to the reference value set by the surface electrometer.

As described above, since the present invention controls the corona current value to be constant using the surface potential detection output and the corona current detection output, it is possible to prevent charger load fluctuations or corona discharge device power supply fluctuations due to temporary environmental changes. The corona current can be kept constant through correction, and it is also possible to correct variations in surface potential with respect to the corona current due to changes over time such as drum deterioration. Therefore, it is not necessary to measure the surface potential every time, and it is only necessary to measure it once every several dozen or hundreds of sheets, so it is possible to prevent a decrease in the image forming processing speed due to the measurement of the surface potential. .

Further, although this embodiment has been explained based on a transfer type electrophotographic apparatus, the present invention can also be applied to an electrophotographic apparatus using photosensitive paper by measuring the surface potential of the photosensitive paper.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a copying machine to which the present invention can be applied, FIG. 2 is a control block diagram of a corona discharge device,
Fig. 3 is a known constant current circuit diagram, Fig. 4 is a block diagram of a high voltage power supply circuit, Fig. 5 is an actual circuit diagram of the block diagram in Fig. 4, and Fig. 6 is a control block diagram of another embodiment. It is. In the figure, 11 is a photosensitive drum, 22 is a primary charger, 23 is a secondary charger, 50 is a surface electrometer,
OP ₁ , OP, OP ₂ , Q ₅ , Q ₇ are operational amplifiers, R ₁₁ is 1
_R12 is a secondary corona current detection resistor, _TC1 is a primary charger high-voltage transformer, and _TC2 is a secondary charger high-voltage transformer.

Claims (1)

[Claims] 1. Forming an electrostatic latent image according to the image on a photoreceptor,
An image forming apparatus that transfers onto a recording material after development includes a charging corona discharge means whose output can be varied, a power supply means for supplying current to the corona discharge means, and a surface potential on the photoreceptor detected during pre-rotation. a detection means for controlling the current supplied to the corona discharge means in accordance with a detection potential of the detection means in order to control the surface potential of the photoreceptor during pre-rotation to a predetermined potential; After the termination, current control means detects the current supplied to the corona discharge means in order to keep the current set by the potential control means constant, and controls the power supply means according to the detected output. An image forming apparatus characterized by: