JP2999338B2 - Image quality correction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality correcting method for improving image quality in an electrophotographic copying machine.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional copy lamp control circuit. When the copy lamp is turned on, a predetermined duty ratio,
The PWM signal of the frequency is transmitted to the pulse generation circuit. In the pulse generation circuit, in order to generate the required light amount from the control circuit from the information (voltage, zero-cross pulse) obtained from the input power supply, the triac is turned on through the phototriac coupler. A pulse signal for arcing is generated.
This control is a control in which the execution power is controlled by changing each phase and the light amount is adjusted. As shown in FIG. 7 , the light amount is not constant, but has a ripple based on the current waveform.

[0003]

As described above, when the phase of the copy lamp is controlled, a light amount ripple occurs.
This light amount ripple affects the latent image formed on the photoconductor. In particular, when a halftone image is formed, the effect is remarkable. This will be described with reference to FIG. This figure shows the relationship between the effective values of the surface potential of the photosensitive member and the copy lamp voltage and the color of the original. In the case of a white document, since the reflectivity of the document is high, a predetermined amount or more of light is applied to the photoconductor regardless of the copy lamp voltage, and the potential of the photoconductor surface is substantially constant. In the case of a black original, since the reflectance of the original is low, the amount of light applied to the photoconductor is low regardless of the copy lamp voltage, and the surface potential of the photoconductor is substantially constant. However, in the case of a halftone original, if the copy lamp voltage changes, the amount of reflected light from the original changes, and the surface potential of the photosensitive member also changes greatly. Now, the effective value of the copy lamp voltage is
65V _rms When the time axis t is provided in the figure,
The copy lamp light quantity changes by the ripple due to the phase control, and the photoconductor surface potential also changes by ΔV. When the surface potential of the photosensitive member fluctuates in this manner, the amount of toner adhered by the developing device changes, resulting in uneven image density.

Although the above-mentioned variation in the surface potential of the photoreceptor is very small, with the advent of a high-quality copying machine in recent years, the variation ΔV in the surface potential of the photoreceptor due to the ripple of the light intensity of the copy lamp has been reduced. The problem has been regarded as a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image quality correcting method capable of forming a high quality image by correcting the influence of the ripple of the copy lamp light amount on the image density.

[0006]

According to the present invention, a latent image is formed based on the light of a copy lamp for adjusting the amount of light by changing the voltage, and toner is adhered to the latent image by a developing device to perform a copying process. An image quality correction method for a copying machine, comprising: generating a voltage change reference signal such as a zero-cross pulse based on a power supply to the copy lamp, and applying a copy lamp light amount to a developing bias of a developing device based on the voltage change reference signal.
Is characterized in that a ripple is generated in a direction to cancel the ripple .

[0007]

When the voltage of the power supply to the copy lamp fluctuates, ripples in the amount of light occur, and when a latent image is formed based on the light from the copy lamp, the surface potential fluctuates even within the same density region. By the way, when toner is attached to a latent image, the amount of toner attached to the latent image changes depending on the developing bias. When the difference between the photoconductor surface potential and the developing bias is large, the amount of toner adhering to the photoconductor increases, and when the difference between the photoconductor surface potential and the developing bias is small, the amount of toner adhering to the photoconductor decreases. Therefore, when the surface potential of the photoconductor is different in the same density region as described above, the developing bias has a direction in which the ripple of the light amount of the copy lamp is canceled.
By causing the ripple, development with the same density can be performed in that area. The fluctuation of the surface potential in the same density region is caused by the fluctuation of the voltage of the power supply to the copy lamp, and the developing bias is changed based on a voltage change reference signal (such as a zero cross pulse) indicating the state of the fluctuation. Then, the same density development can be performed in the same density region.

[0008]

FIG. 1 is a block diagram of a main part of a copying machine according to an embodiment of the present invention.

Power is supplied from the AC power supply to the inside of the copying machine. A transformer L is provided in the copying machine main body.
The power input from the power supply is separated from the primary side circuit by the transformer L, and the zero cross pulse signal generation circuit 1
It is connected to the DC power supply unit 2. The zero-cross pulse signal generating circuit 1 includes diodes D1 and D2, a resistor R
1, R2 and a waveform shaper IC1.
The zero cross pulse generation circuit 1 generates a zero cross pulse as a voltage change reference signal based on the input power. First, since the output voltage of the transformer L has an AC waveform, a pulsating waveform is formed by the diodes D1 and D2.
Waveform shaper IC by adjusting voltage by resistors R1 and R2
Enter 1 The waveform shaper IC1 is an inverter with hysteresis, converts an input waveform into a pulse-like square wave, and inputs the same to an interrupt port of the CPU 3.

On the other hand, the applied voltage of the copy lamp 4 is adjusted by a copy lamp voltage generating circuit 5. The copy ramp voltage generating circuit 5 sends the PWM signal P
WM1 has been input. The PWM signal PWM1 is for obtaining a copy lamp voltage so that the light amount of the copy lamp approaches a predetermined light amount, and is set based on a detected copy lamp light amount, a set image density, and the like.
In the copy ramp voltage generation circuit 5, the PWM signal P
Phototriac coupler with WM1 pulse waveform
The signal is transmitted to the primary circuit by a transformer or the like, and D /
A conversion is performed, a phase control pulse signal is generated, and a copy ramp firing control element (triac or the like) is controlled. Note that the CPU 3 may directly output a pulse signal for controlling the firing element. In this case, the pulse signal may be output with a delay of a desired time after the output of the zero cross signal.

The developing device is of a known type, in which a developing bias is applied to a developing roller, and a toner is attached to the photosensitive member by a potential difference between the developing bias and the surface potential of the photosensitive member. The developing bias is generated by a developing bias generating circuit 6. The developing bias voltage generating circuit 6 controls the voltage based on the PWM signal PWM2 from the CPU 3. The developing bias voltage generating circuit 6 generates a voltage according to the duty ratio of the PWM signal PWM2. First, the PWM signal PWM2 is D / A converted and an output corresponding to the value is generated. In addition, the D / A of the CPU 3 is determined in advance.
An analog amount according to the duty ratio may be output from the conversion port.

In the above configuration, since the CPU 3 receives the zero cross pulse, the CPU 3 can grasp the timing of the ripple generated by the copy lamp 4. Therefore, the PWM signal PWM2 is output so as to change the development bais value according to the timing, and the ripple of the development bias is intentionally created in the direction to cancel the light amount ripple. FIG. 2 shows the relationship between the effective value of the voltage of the copy lamp and the duty ratio, and FIG. 3 shows the relationship between the developing bias voltage and the duty ratio. As shown in the figure, when the duty ratio increases, the effective voltage of the copy lamp,
Both the developing bias voltages increase in direct proportion. The CPU 3 generates a PWM signal based on this relationship. FIG. 5 shows the state of the copy lamp light amount and the state of the developing bias voltage. As for the copy lamp light amount, a voltage corresponding to the duty ratio is applied by the PWM signal PWM1 output based on the zero cross pulse, and a light amount ripple 1 as shown in the drawing is generated. On the other hand, a PWM signal PWM2 is output to the developing device based on the zero-cross pulse, and a developing bias is applied based on the PWM signal. As shown in FIG.
The phase of the bias ripple is
180 ° offset, copy lamp with light ripple
Develop bias ripple in response to increase and decrease of light quantity
Increases and decreases the toner adhesion amount. The relationship between the developing bias voltage and the developing density is as shown in FIG. In this example, an OPC photoconductor is used, and the photoconductor is set to -700V.
The image density is shown when the developing bias is changed by charging the toner. If the difference between the surface potential of the photoconductor and the bias potential increases, the density of the developed toner image increases, and the toner amount ID (Image Density) on the transfer paper also increases. The copy ramp voltage generation circuit 5 uses zero input power.
Duty of PWM signal PWM1 based on cross pulse
The input power is supplied to the copy lamp 4 at a timing according to the ratio.
The period of the copy ramp voltage as shown in FIG.
Corresponds to the cycle of the input power supply, and
A light amount ripple of a half cycle of the power supply is generated. Against this
Then, the developing bias generating circuit 6 detects the zero cross of the input power.
Input to the developing device by PWM signal PWM2 based on pulse
To create the development bias ripple to be applied,
The cycle of the ear ripple is の of the cycle of the input power supply
Matches the period of the zero cross pulse, the period of the input power source 1
The light amount ripple period is also equal to / 2. Accordingly
The developing bias output from the developing bias generating circuit 6
The phase of the ripple is
Direction to cancel the light amount ripple by controlling
Can intentionally create development bias ripple
You.

[0013]

[0014]

According to the present invention, even when the surface potential of the photosensitive member fluctuates due to the ripple of the copy lamp light amount, a ripple is intentionally generated in the developing bias.
Variations in the surface potential of the photoreceptor can be canceled, and a stable amount of toner can be attached. As a result, the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a copying machine according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a duty ratio and a copy lamp voltage effective value.

FIG. 3 is a diagram showing a relationship between a duty ratio and a developing bias voltage value.

FIG. 4 is a diagram showing a relationship between a developing bias and an image density.

FIG. 5 is a diagram illustrating a relationship between a light amount ripple and a developing bias ripple.

FIG. 6 is a diagram showing a configuration of a general copy lamp lighting system;

FIG. 7 shows that the copy lamp is turned on by the copy lamp lighting system.
Figure showing the state of the light amount ripple when

FIG. 8 shows the surface potential of the photoconductor, the effective value of the copy lamp voltage and the original value.
Diagram showing the relationship with the color of the manuscript

Continuation of the front page (56) References JP-A-61-52658 (JP, A) JP-A-61-143805 (JP, A) JP-A-61-151667 (JP, A) JP-A-63-101867 (JP) JP-A-1-172852 (JP, A) JP-A-2-36402 (JP, A) JP-A-61-52660 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB G03G 15/06 101 G03G 15/00 303

Claims (1)

(57) [Claims] An image quality correcting method in a copying machine for forming a latent image based on light of a copy lamp for adjusting a light amount by changing a voltage, and applying a toner to the latent image by a developing device to perform a copying process. Generating a voltage change reference signal such as a zero-cross pulse based on the power supply to the copy lamp, and applying the copy lamp
An image quality correction method characterized by generating a ripple in a direction to cancel the amount of ripple .