JPS6240711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in reverse bias development methods for electrophotographic copying machines and the like.

As shown in FIG. 1, one of the conventional reverse bias developing methods is to apply a charge with the same polarity as the toner to the entire surface of the photoreceptor drum, including non-image areas, and to There is a method of developing by applying a bias voltage to the developing sleeve from the beginning to the end position. When using this method, toner does not adhere to the non-image area of the photoreceptor drum, but a high potential remains on the surface of the photoreceptor drum, resulting in increased charge fatigue of the photoreceptor drum.

Another method is to start the photoreceptor drum by synchronizing the potential of the photoreceptor drum surface with the image area and applying a charge of the same polarity as the toner polarity, as shown in FIG. There is a method of developing by applying a bias voltage to the developing sleeve from the position to the end position. This method has the disadvantage that more toner adheres to non-image areas.

Another method is to synchronize the potential on the surface of the photoreceptor drum with the image area to apply an electric charge of the same polarity as the toner polarity, and apply a bias voltage to the developing sleeve in synchronization with the electric charge on the photoreceptor drum. be. When this method is used, it is possible to prevent toner from adhering to the non-image area if the above-mentioned synchronization is completely achieved, but it is difficult to apply the bias voltage of the developing sleeve to the image area on the surface of the photoreceptor drum in synchronization, and the developing If the application of the bias voltage to the sleeve is delayed, there is a disadvantage that the density decreases at the beginning of the image area as shown in Figure 3a, and toner adheres to the non-image area following the end of the image area. Ta. Conversely, if the bias voltage is applied too early to the developing sleeve, toner will adhere to the non-image area preceding the starting edge of the image area, as shown in FIG. There was a drawback that it caused a decrease in concentration.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a reverse bias developing method which eliminates the above-mentioned drawbacks. In other words, charge fatigue of the photoreceptor, toner adhesion to the non-image area of the photoreceptor, density reduction in the image area of the photoreceptor, and unnecessary adhesion of toner to the non-image area near the image area are minimized. The purpose is to provide a developing method.

The present invention will be explained below with reference to Examples.

FIG. 4 is a schematic diagram of a developing section for explaining an embodiment of the present invention, and FIG. 5 is a timing diagram for explaining an embodiment of the present invention.

In FIG. 4, reference numeral 1 is a photoreceptor drum, charging charger 2 is a charger that charges the photoreceptor drum 1 with an electric charge of the same polarity as that of the toner, and 3
is a developing sleeve, 4 is a bias power source for the developing sleeve 3, 5 is a switching device for the bias power source, 6 is an AC power source, which supplies power to a motor 8 through a switch 7, and the motor 8 is a bias power source for the developing sleeve 3. The electrostatic latent image is rotated to form and develop an electrostatic latent image in a typical electrophotographic copying machine.

By operating the copy start button, the charging charger 2
is activated, the surface of the photoreceptor drum 1 is charged with charges of the same polarity as the toner charges, and the original is exposed to light, thereby forming an electrostatic latent image corresponding to the original on the surface of the photoreceptor drum 1. A portion of this electrostatic latent image is shown as an image area in FIG. 5a.

Then, the photoreceptor drum 1 is charged by the charging charger 2.
The surface of the toner includes the image area shown in FIG. 5a, and is charged to the same polarity as the toner charge over a wider area than the image area. The charged area on the surface of the photosensitive drum 1 is shown in FIG. 5b.

The developing motor 8 is operated at the fifth stage before the surface position of the photosensitive drum 1 reaches a position facing the developing sleeve 3 where charging of the surface of the photosensitive drum 1 has started.
It starts at the timing shown in Figure c.

Further, the application of the bias voltage to the developing sleeve 3 (the first developing bias voltage for applying toner from the developing sleeve 3 to the photosensitive drum 1) is performed within the charged area of the surface of the photosensitive drum 1 and within the photosensitive drum 1. This is carried out at the time when the position on the surface of the photosensitive drum 1 that does not fall within the image area on the surface of the photosensitive drum 1 reaches a position facing the developing sleeve 3, that is, at the time of the rising edge in FIG. 5d. The distance between the position of the surface of the photosensitive drum 1 facing the developing sleeve 3 and the starting edge of the image area at the rising time point in FIG. 5d is determined by the copying speed of the copying machine and the response speed of the bias voltage switching device. A prescribed developing bias voltage is applied to the developing roller 3 at least in the image area.

On the other hand, the second voltage is set such that the toner does not adhere to the photoreceptor drum 1 from the developing sleeve 3 of the developing bias voltage.
The developing bias voltage, for example, is switched to the OFF state when the surface position of the photosensitive drum 1 facing the developing roller 3 passes the end of the image area shown in FIG.
This is carried out at a point within the charging range shown in FIG. 5b, that is, at a falling edge in FIG. 5d.

The timing for stopping the developing motor 8 is determined when the surface of the photosensitive drum 1 outside the charging area of the photosensitive drum 1 reaches a position facing the developing sleeve 3, that is, at the falling edge in FIG. 5c.

As described above, in this embodiment, an area slightly wider than the image area of the photoreceptor drum 1 is charged,
Since the entire area of the photoreceptor drum 1 is not charged, charge fatigue of the photoreceptor drum 1 can be reduced.

In addition, since the bias voltage to the developing sleeve is switched to the second developing bias voltage corresponding to the area other than the image area (non-image area) of the photoreceptor drum 1, the amount of excess toner adhering to the non-image area is reduced. is reduced, and the cleaning load on the photosensitive drum 1 can be reduced.

Furthermore, when a predetermined area within the charged area of the photoreceptor and other than the image area faces the developing sleeve, the voltage applied to the developing sleeve 3 is between the first developing bias voltage and the second developing bias voltage. Since it is set to switch the applied voltage,
Even if there is a slight error in the timing of the bias voltage switching described above, the second developing bias voltage area of the developing sleeve 3 may be opposed to the image area of the photoreceptor drum 1, or the second developing bias voltage area may be opposite to the image area of the photoreceptor drum 1. The first developing bias voltage regions of the developing sleeve 3 do not face each other. This prevents the density from decreasing at the start and end portions of the electrostatic latent image, and prevents unnecessary toner from adhering to the non-image area near the image area.

Next, a developing bias voltage switching device will be explained.

FIG. 6 is a circuit diagram of an embodiment of a developing bias voltage switching device.

In FIG. 6, reference numeral 10 denotes a power transformer, which constitutes a DC power source in which the secondary voltage of the power transformer is rectified by a full-wave rectifier circuit 11 and smoothed by a capacitor 12. The voltage of the capacitor 12 is applied to the developing sleeve 3 through the resistors 13 and 16 and the diode 17, and a series circuit of symmetrical varistors 14 and 15 is connected between the common connection point of the resistors 13 and 16 and the common end of the DC power supply. The transistor 18 is connected between the common connection point of the resistor 16 and the anode of the diode 17 and the common terminal of the DC power supply.
The structure is such that a control voltage having the timing shown in FIG. 5d is applied to the base of the circuit.

In the developing bias switching circuit constructed as described above, the voltage of the DC power supply is stabilized by the varistors 14 and 15 and applied between the collector and emitter of the transistor 18. Now, when a positive signal is applied to the base of transistor 18, transistor 1
8 is turned on and no bias voltage is applied to the developing sleeve 3. Further, when a zero or negative signal is applied to the base of the transistor 18, the transistor 18 is turned off, and a DC voltage as a bias voltage is applied to the developing sleeve 3.

On the other hand, when developing an electrostatic latent image, charges on the surface of the photoreceptor drum 1 induce charges of the same polarity as the charges on the developing sleeve 3 . Therefore, when the transistor 18 is on, no developing bias voltage is applied to the developing sleeve 3, so the anode voltage of the diode is approximately zero. However, due to the charge induced in the developing sleeve 3 during the development of the electrostatic latent image immediately before, the cathode voltage of the diode becomes higher than that on the anode side, and the diode is reverse biased and turns off, so that the potential of the developing sleeve is substantially reduced. It becomes a floating state.

In addition, the peak value of the control voltage is reduced so that the transistor 18 is not completely turned on, but is brought into partial conduction for a period corresponding to the turning-on timing, and the transistor is used as a variable resistance element, so that the transistor 18 is not completely turned on, and the transistor is used as a variable resistance element. A developing bias voltage may be applied to the developing sleeve 3.

As mentioned above, by setting the potential of the developing sleeve to a float when the developing bias power supply is turned off, or by applying a predetermined voltage to the developing sleeve 3 locally instead of the float, the image area due to carrier adhesion due to ground development can be prevented. Negative effects can be avoided.

As explained above, according to the present invention, in the reverse bias developing method, the developing bias voltage to the developing sleeve is switched within the charged area of the surface of the photoreceptor drum and at a point outside the image area, and the developing bias voltage is applied to the non-image area. The application of voltage to the developing sleeve is cut off or the voltage is set lower than the developing bias voltage value in the image area to prevent toner from adhering to the photoreceptor from the developing sleeve, so toner adhesion in non-image areas is reduced. Therefore, it is possible to eliminate the decrease in density at the starting and ending portions of the electrostatic latent image, and to reduce the cleaning load.

[Brief explanation of the drawing]

Figures 1, 2, and 3 a and b are explanatory diagrams of the conventional reverse bias developing method, Figure 4 is a schematic diagram of the developing section of a copying machine, and Figure 5 is a bias bias according to the method of the present invention. FIG. 6, a timing diagram of voltage switching, is an example of a circuit diagram of a bias voltage switching device for implementing the method of the present invention. DESCRIPTION OF SYMBOLS 1... Photosensitive drum, 3... Developing sleeve, 4... Bias power supply, 5... Bias power supply switching device, 11
... Rectifier circuit, 14 and 15... Varistor, 17...
Diode, 18...Transistor.

Claims (1)

[Claims] 1. While applying a first developing bias voltage to the developing sleeve to charge the developing sleeve to the same polarity as the toner, toner is applied from the developing sleeve to an uncharged portion in the image area of the photoreceptor. , a reversal bias developing method in which a second developing bias voltage is applied to the developing sleeve so that toner does not adhere to the photoconductor from the developing sleeve when the developing sleeve faces an area other than the image area of the photoconductor; is charged slightly wider than the image area, and when the area of the photoconductor other than the image area faces the developing sleeve within the charged area of the photoreceptor, the voltage applied to the developing sleeve is set to be equal to the first developing bias voltage and the first developing bias voltage. A reversal bias developing method characterized by switching between two developing bias voltages. 2. The reversal bias developing method according to claim 1, wherein the second developing bias voltage is in a state where the potential difference is 0, and at the same time, the voltage of the developing sleeve is floated. 3. The inversion according to claim 1, wherein the second developing bias voltage has the same polarity as the first developing bias voltage, but is smaller in magnitude than the first developing bias voltage. Bias development method.