JPH04204876A - Reversal development controller - Google Patents

Abstract

PURPOSE:To prevent the scattering of toner and carrier by making a light quantity control means for an exposure means vary the quantity of exposed light applied by the use of the exposure means, from the prescribed value to 0 gradually and making a bias control means for a bias applying means vary a bias voltage applied by the use of the bias imparting means to the prescribed voltage value gradually. CONSTITUTION:A high voltage power source circuit 11 which applies a high voltage to a developing unit 4 is connected to the developing unit 4. A control circuit 12 which controls the intensity of a voltage produced by the high voltage power source circuit 11 is connected to the high voltage power source circuit 11. Further, a control circuit 14 which controls the quantity of exposed light is connected to a LED array 3. A CPU(central processing circuit) 13 which gives instructions concerning the contents of controls by the control circuits 9, 12, and 14, instructs the circuit to vary the quantity of exposed light, applied by use of the LED array 3, from the prescribed value to 0, and also instructs the circuit so as to vary a bias voltage, applied to the developing unit 4, to the prescribed voltage value gradually. Thus, scattering of toner and carrier is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a reversal developing device applied to an image forming apparatus such as an electrostatographic copying machine, and more particularly to a reversing developing control device for a reversing developing device. It is something.

(Prior Art) In general, in a reversal development type copying machine that uses a two-component developer, the surface of the photoreceptor drum is negatively charged, for example, by a charging means, and the portion (exposed area) that has a zero potential due to exposure is Among the developer, negatively charged toner is attached for development. At this time, the carrier is positively charged.

To be more specific, in this reversal development method, as shown in FIG. is rotated to the exposure position and exposed. Thereafter, the photoreceptor drum 2 further rotates and the developing roller 41
At this point, the developing roller 4 reaches the developing position opposite the developing roller 4.
A negative bias voltage of about -400 volts is applied to the photoreceptor drum 2, and the negatively charged toner flies out due to the electrostatic repulsion and adheres to the exposed portion of the photoreceptor drum 2, which has a zero potential.

(Problem to be Solved by the Invention) Incidentally, it is preferable that the bias voltage to the developing roller 41 be applied at the same time as the charged and exposed portion of the photosensitive drum 2 reaches the developing position facing the developing roller 41. However, it is not easy to control this timing, and the timing of applying the bias voltage may shift.

Therefore, for example, the timing at which a bias voltage of 400 volts is applied to the developing roller 41 is such that the portion of the photosensitive drum 2 charged to 700 volts is the timing when the developing roller 41 is charged with a voltage of 700 volts.
If the toner reaches the developing position with 1 too early, the potential on the surface of the photosensitive drum 2 will become larger than the bias voltage value of the developing roller 41, and the toner will fly to the photosensitive drum 2. That is, as shown in FIG. 5(a), the developing roller 41 is moved against the photosensitive drum 2 that has reached the developing position.
If the timing of the bias voltage applied to the voltage is off, the voltage difference will exceed the allowable relative difference, as shown in Figure 5(b) (relative difference assuming the bias voltage value is O volts). .

Conversely, the timing at which a bias voltage of 1,400 volts is applied to the developing roller 41 is 170 volts on the photosensitive drum 2.
If it is too late than the point at which the portion charged to 0 volts reaches the developing position with the developing roller 41, the photosensitive drum portion charged at -700 volts will have reached the developing position with the developing roller 41 during that time. Despite this, developing roller 4
Since no bias voltage is applied to the photoreceptor drum 1, positively charged carriers are attracted to the surface of the photoreceptor drum 2.

That is, as shown in FIG. 6(a), if the timing of the bias voltage applied to the developing roller 41 is shifted with respect to the photosensitive drum 2 reaching the developing area, the bias voltage applied to the developing roller 41 is shifted as shown in FIG. 6(b).
As shown in (relative difference assuming bias voltage value as O volts), the voltage difference exceeds the allowable relative difference.

On the other hand, although some inventions have been made in which the bias voltage is not applied suddenly, if the timing of application of both voltages is inappropriate, the voltage difference will exceed the allowable range and the toner and carrier will be scattered.

The present invention takes into consideration the problems of the conventional reversal development control device, and even if the timing of applying voltage to the photoreceptor drum or the timing of applying bias voltage to the developing means deviates from the normal timing, It is an object of the present invention to provide a reversal development control device in which toner and carrier do not scatter.

(Means for Solving the Problems) The reversal development control device of the present invention includes: a photoreceptor on which a latent image is formed; a charging means for applying a voltage to the photoreceptor to charge it to a predetermined surface potential; An exposure means for exposing a photoreceptor charged by the charging means to form a latent image, a developing means for reversing and developing the latent image, and a bias applying means for applying a predetermined bias voltage to the developing means. In the reversal developing device of the image forming apparatus, the exposure means includes a light amount control means for controlling the exposure light amount to gradually change from a predetermined value to O, and the bias applying means changes the bias voltage value to a predetermined voltage value. The present invention is characterized in that it includes a bias control means that gradually changes the bias.

(Function) In the present invention, a photoreceptor is charged by a charging means, and a latent image is formed by exposure when the charged photoreceptor reaches an exposure position by an exposure means. Then, when the photoreceptor on which the latent image is formed reaches a developing position by the developing means, a predetermined bias voltage is applied to the developing means by the bias applying means to cause the toner to adhere to the photoreceptor.

At this time, the light amount control means of the exposure means controls the exposure light amount so as to gradually change from a predetermined value to O, and the bias control means of the bias applying means gradually changes the applied voltage to a predetermined voltage value. to control.

Therefore, the difference between the surface potential of the photoreceptor at the developing position and the bias voltage value of the developing means is within the allowable range even if the timing of application is slightly off from the regular timing, so unnecessary toner and carrier scattering is prevented.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of the main parts of a copying machine to which an embodiment of the reversal development control device according to the present invention is applied.

In the figure, a charger 1, a surface potential sensor 6, and an exposure position are installed around a photoconductor drum 2, which is an example of a photoconductor on which a latent image is formed, in order counterclockwise in the drawing. An LED array 3 as an exposure means, a developing device 4 and its developing roller 41 as an example of a developing means, a cleaning means 5 for removing residual toner, and the like are arranged.

A high voltage power supply circuit 10 is connected to the charger 1 for charging the photoreceptor drum 2 to about -700 volts. Further, a control circuit 9 that controls the magnitude of the voltage generated by the high voltage power supply circuit 10 is connected to the high voltage power supply circuit 10.

On the other hand, a high voltage power supply circuit 11 for applying high voltage to the developing device 4 is connected to the developing device 4 .

In addition, this high voltage power supply circuit 11 includes the high voltage power supply circuit 1
A control circuit 12 for controlling the magnitude of the voltage generated by 1 is connected. Furthermore, the LED array 3 is connected to a control circuit 14 that controls the amount of exposure light.

A CPU (Central Processing Unit) 13 is provided for instructing the control contents of these control circuits 9, 12, and 14, and the output signal of the surface potential sensor 6 is input thereto.

This CPU 13 instructs to gradually change the exposure light amount of the LED array 3 from a predetermined value to O, and
An instruction is also given to gradually change the bias voltage applied to the developing device 4 up to a predetermined voltage value.

Next, the operation of the above embodiment will be explained.

First, I will explain the outline. Here, the photosensitive drum 2 is the first
Assume that it is rotating counterclockwise as shown in the figure. The charger 1 charges the photoreceptor drum 2 with a high voltage, the surface potential sensor 6 measures the surface potential of the charged photoreceptor drum 2, and when the charged portion reaches the exposure position 1, the LE
It is exposed by the D array 3 and a latent image is formed. When the toner rotates further and reaches the developing position of the developing device 4, the high voltage power supply circuit 11 applies a high voltage to the developing roller 41 of the developing device 4, thereby causing the toner to fly off and developing. Thereafter, the developed portion is transferred (not shown), and the remaining toner is removed by the cleaning device 5.

Next, the timing of changing the amount of exposure light and applying the bias voltage in the above operation will be explained in detail.

It takes a certain amount of time for the portion P1 of the photoreceptor drum 2 to which a voltage is applied by the charger 1 to rotate and reach the exposure position P2 of the LED array 3 and the development position P3 of the developing roller 41 of the developer 4. For example, assume that the time required from PI to P2 is 0.2 seconds, and the time required from P1 to P3 is 0.4 seconds.

First, the CPU 13 drives the control circuit 9 so that the high-voltage power supply circuit 10 charges the photosensitive drum 1 by the charger 1.
0 applied so that the volt is charged, then that 0
．． After 2 seconds, the control circuit 14 is driven to start exposing the LED array 3 such that the amount of exposure light from the LED array 3 decreases stepwise from a predetermined value toward 0. As a result, since the charged potential of the photoreceptor is constant at 1,700 volts, the surface potential of the photoreceptor drum after exposure increases stepwise. After another 0.2 seconds, the control circuit 12 is driven and the high voltage power supply circuit 11 applies a bias voltage to the developing roller 41.
The voltage is applied in steps from +100 volts to a predetermined voltage.

As shown in FIG. changes as =100 volts → -200 volts → -300 volts → -400 volts → -500 volts → -600 volts → -700 volts, and the bias voltage of the developing roller 41 changes from +100 volts → 0 volts → -
100 volts → -200 volts → -300 volts → -4
It changes to 00 volts. The timing (horizontal axis) of the graph of the surface potential of the photosensitive drum 2 in FIG. 2 is drawn 0.2 seconds later than the exposure time.

As a result, the difference between the surface potential of the photosensitive drum 2 and the bias voltage value of the developing roller 41 at the developing position is as shown in FIG. The figure shows the relative difference in surface potential of the photosensitive drum 2 with respect to the bias voltage value of zero.

That is, if the voltage is gradually changed at the timing shown in the figure, the relative difference in the surface potential of the photosensitive drum 2 with respect to the bias voltage value of the developing roller 41 will fall within an allowable range. Here, even if the timing of exposure of the LED array 3 is shifted back or forth, the relative difference between the surface potential of the photoreceptor drum 2 and the bias voltage value of the developing roller 41 will change, but the potentials of both will gradually change. Since the voltage is changing, it falls within the allowable range of about 300 volts. Therefore, inconveniences such as toner and carrier scattering do not occur.

In the above embodiment, the high-voltage power supply circuit 11 is used as a bias applying means for applying a predetermined bias voltage to the developing means, and the control circuit 12 and the CPU 13 are used as bias control means, but the present invention is not limited to this. In short, any device that can reach a predetermined voltage value by gradually changing the bias voltage value will suffice.Also, in the above embodiment, the exposure means is composed of the LED array 3, but is not limited to this. Any method may be used as long as it gradually changes the amount of exposure light applied to the photoreceptor drum to gradually change the surface potential of the photoreceptor drum. Furthermore, in the above embodiment, each voltage was applied in steps, but
The invention is not limited to this, and it may be changed continuously and gradually.Also, in the above embodiment, a reversal developing device using a two-component developer was applied, but it can be applied to a reversing developing device using a one-component developer. It is also possible to do so.

(Effects of the Invention) In the present invention, the light amount control means of the exposure means controls the exposure light amount to gradually change from a predetermined value to 0, and the bias control means of the bias applying means controls the bias voltage applied by the bias applying means. By controlling the application so that it gradually changes to a predetermined voltage value, toner and carriers will not be scattered even if the timing of applying the bias voltage or the timing of applying the surface potential is slightly shifted.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the reversal development control device according to the present invention, and FIG. 2 is a graph showing temporal changes in the surface potential and bias voltage value of the photoreceptor after exposure in the same embodiment.
FIG. 3 is a graph showing the relative difference between the surface potential of the photoreceptor and the bias voltage value after exposure in the same example, FIG. 4 is a schematic cross-sectional view showing the main parts of a conventional copying machine, and FIG. 5 is a graph showing the relationship between the surface potential and bias voltage value of a conventional photoreceptor;
The figure is a graph showing the relationship between the surface potential and bias voltage value of another conventional photoreceptor. 1... Charger, 2... Photosensitive drum, 3... LE
D array, 4...Developing device, 41...Developing roller, 1
1... High voltage power supply circuit, 12... Control circuit, 13...
・CPU

Claims (3)

[Claims] (1) A photoreceptor on which a latent image is formed, a charging means that applies a voltage to the photoreceptor to charge it to a predetermined surface potential, and a latent image is formed by exposing the photoreceptor charged by the charging means to light. In a reversal developing device of an image forming apparatus, the exposure means has an exposure means for reversing the latent image, a developing means for reversing developing the latent image, and a bias applying means for applying a predetermined bias voltage to the developing means. The invention further comprises a light amount control means for gradually changing the bias voltage value from a predetermined value to 0, and the bias applying means further comprises a bias control means for gradually changing a bias voltage value to a predetermined voltage value. Development control device. (2) The reversal development control device according to claim 1, wherein the light amount control means changes the exposure light amount in steps when gradually changing the exposure light amount from a predetermined value to 0. (3) The reversal development control device according to claim (1), wherein the bias control means applies the predetermined voltage value in steps.