JPS61281258A - Electronic photograph picture forming device - Google Patents

Abstract

PURPOSE:To prevent the damage of a photosensitive body due to the high electric field impression by stopping the rotation of the photosensitive body to hold the constant electric potential before the copying action for the prescribed time and measuring the dark attenuation of the photosensitive body from the charging part of the surface electric potential value and the time to leave in the darkness. CONSTITUTION:Before the picture forming action, a constant quantity of charging is executed in a short time to the photosensitive body, the charged part arrives at the position of a surface electric potential sensor 10, then, the rotation of the photosensitive body is stopped for the prescribed time, thus, the dark attenuating characteristic of said photosensitive body is detected. While the inside of the machine is dark, the rotation of the photosensitive body 1 is stopped and after that, the surface electric potential value is recorded by a DC controller 12 again. At such a time, the direct current part is impressed to a developing sleeve 4, at the time of the dark attenuating measuring mode, it is the conditions that the toner is not stuck and also, the output of a transferring charging device 7 is OFF. After such a time, while a front exposure lamp 14 only is turned on, the photosensitive body 1 is rotated one time, the average destaticization is executed then, the dark attenuating measuring mode is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic image forming apparatus, and particularly to an electrophotographic image forming apparatus having a function of detecting and controlling the surface potential of a photoreceptor.

When an electrophotographic photoreceptor is used as a latent image carrier in an electrophotographic image forming apparatus, there is a phenomenon in which the surface potential of the photoreceptor attenuates as a characteristic of the photoreceptor, and the surface potential due to this attenuation decreases. How to control the fluctuations in image quality is an important factor in obtaining high-quality images.

For this reason, conventional electrophotographic image forming apparatuses, in particular, are equipped with at least a primary charging device and a developing device around an electrophotographic photosensitive drum, and a surface potential sensor is disposed between the charging device and the developing device. In an electrophotographic copying apparatus in which the surface potential of the photoreceptor is detected by a mold position sensor, the surface potential of the photoreceptor is set to a potential value that provides the optimum image density in the developing section where the developing device is installed. The amount of primary charge was controlled by the value detected by a surface potential sensor.

Recently, amorphous silicon photoreceptors have been frequently used as photoreceptors in electrophotographic copying devices because of their good durability and non-polluting properties. However, since the amorphous silicon photoreceptor has particularly poor dark decay characteristics compared to other photoreceptors, the potential on the photoreceptor surface controlled by the surface potential sensor position is several tens of volts as the photoreceptor moves and reaches the developing section. There was a drawback that the potential at which the optimum density could be obtained could not be secured in the developing section due to the lowering of the potential.

For this reason, it is necessary to appropriately change the potential setting value at the surface potential sensor position while looking at the image, or to set the potential value from the beginning to be higher than the potential value at which the optimum density is obtained in the developing section.

However, in this method, primary charging of a higher electric field than necessary is applied to the photoreceptor, which accelerates the deterioration of the photoreceptor and causes phenomena such as color spots and black spots to occur in copied images.

11 Therefore, an object of the present invention is to provide an electrophotographic method that can form high-quality images without applying an excessive primary charge to the photoconductor even if a photoconductor with poor dark decay characteristics is used as the photoconductor. An object of the present invention is to provide an image forming apparatus.

1. The above objects are achieved by the present invention. To summarize, the present invention comprises at least a charging device and a developing device around an electrophotographic photoreceptor that moves endlessly, and a gap between the charging device and the developing device. In an electrophotographic image forming apparatus in which a surface potential sensor is arranged and the surface potential of a photoreceptor is detected and controlled by the surface potential sensor, the photoreceptor is charged to a certain amount in a short time before an image forming operation, Electrophotography characterized by having a dark decay characteristic detection mode that stops the rotation of the photoconductor for a predetermined period of time when the charged portion reaches the surface potential sensor position, thereby detecting the dark decay characteristic of the photoconductor. It is an image forming apparatus.

Further, in the present invention, preferably, the charging device is controlled by a signal obtained in the dark decay characteristic detection mode, and the surface potential of the photoreceptor is controlled.

Next, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

FIG. 1 shows an embodiment in which the present invention is implemented in an electrophotographic copying apparatus. In this embodiment, an amorphous silicon photosensitive drum 1 with a diameter of 60 mm is used as a photoreceptor, and the peripheral speed is 376 mm/sec in the direction of arrow a. be rotated.

Around the photosensitive drum l, there is a -order charging device 2. Image exposure section 3
and a developing device 4 are arranged, and a latent image and a toner image are formed according to a normal electrophotographic process. Next, a toner image is transferred by a transfer charger 7 to a transfer paper 6 that has passed through a transfer guide 5, and then the transfer paper 6 is separated from the photosensitive drum 1 by a separation roller 8 rotating in the direction of arrow C. On the other hand, the toner image on the photosensitive drum 1 remaining after the transfer is cleaned by the cleaner 9, and the photosensitive drum 1 is moved to the pre-exposure lamp 14.
Static electricity is removed uniformly by

In such a configuration, the dark area potential Vd in the developing section 4 is required to be 400 V or more to obtain the optimum image density. A surface potential sensor 10 that detects the surface potential of the photoreceptor 1 is located at an angle α (in this embodiment, 72 degrees, that is, 0.1 seconds in time) f relative to a developing roller 4a disposed in a developing device 4. It is arranged so as not to be affected by scattering from the developing section. In such a configuration, a standard amorphous silicon photoreceptor with a dark decay characteristic that drops Vd by 40V in 0.1 seconds
When using □, it is necessary to secure Vd at 440V at the position of the 1st surface type sensor lO.The -order charging current at this time may be about 700gA/7KV.However, in reality, the dark side of each photoreceptor The amount of potential drop due to attenuation is not uniform, and may also change depending on the environment and the number of durable sheets, so if necessary, dark attenuation must be accurately measured with the main unit and reflected in the optimal Vd setting. Must be.

According to the present invention, a mode for measuring dark decay before a copying operation is provided, and a function for automatically setting an optimum Vd value is provided.

To explain in more detail, only when the main switch of the main unit is turned on, the photosensitive drum l rotates in the dark attenuation measurement mode and the primary charger 2 receives a standard current of 700 lA before the copying operation.
/7KV is applied for about 0.1 seconds. After that, image exposure 3 is set to O.
In the FF state, the surface potential of the photoconductor is detected by the surface potential sensor lO, and the surface potential value A+ (V) is recorded by the DC controller 12 via the potential measurement circuit 11.
Then, with the pre-exposure lamp 14 also not lit and the interior of the machine in darkness, the rotation of the photoreceptor 1 is stopped for 0.5 seconds, and the subsequent surface potential value Az (V) is recorded again by the DC controller 12. At this time, the developing sled 4 has a DC component of +5
00V is applied, and the condition is such that toner does not adhere during the dark decay measurement mode, and the output of the transfer charger 7 is also turned off.

Thereafter, the photoreceptor 1 rotates once with only the pre-exposure lamp 14 turned on, and when the static electricity is uniformly removed, the dark decay measurement mode ends.

In this example, the time the photosensitive drum 1 was stopped and left in the dark was 0.5 seconds, and the potential drop during this period was A+A.
z (V), and since the time between the potential sensor io and the developing roller 4 is 0.1 seconds, using the linearity of the dark decay characteristic, we assume that the potential decreases by (A+Az)15 (V) and convert it to DC. Processed by the controller part 12. The potential value at this time (A+, Az, (A+ Az)1
5) etc. can be displayed by the potential display unit 13 as necessary. In addition, the Vd control value at the potential sensor part 10 is automatically set to 400+(A+
Az )15 (V).

Next, the dark area potential (Vd) control mode is entered, and a DC voltage of +500 V is applied to the developing roller 4, and the transfer charger 7 and pre-exposure lamp 14 are activated. And image exposure is turned off.
The position of the potential sensor 10 in the state 't'v dka 400
A primary current is applied from the high-voltage transformer 15 to the negative charger 2 via the DC controller 12 until +(A+-Az)/5 (V).

According to the present invention, by carrying out the dark decay measurement mode and the dark area potential control mode before the copying operation, the optimum potential in the developing section is always ensured.

In the above description, the photoreceptor is a cylindrical photoreceptor drum, but the present invention is not limited to this, and a belt-shaped photoreceptor that moves endlessly may also be used.

According to the image forming apparatus of the present invention, the rotation of the photoreceptor, which is maintained at a constant potential, is stopped for a predetermined period of time before the copying operation, so that the photoreceptor's rotation can be determined based on the change in surface potential value and the time it has been left in the dark. Because it is possible to accurately measure dark decay and thereby determine the optimal dark potential control value at the potential sensor position, taking into account the amount of dark decay from the potential sensor to the developing section, photosensitive There is no need to apply more than necessary primary charge to the body, and it is possible to prevent damage to the photoreceptor due to application of a high electric field and obtain high-quality images.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an embodiment of an electrophotographic image forming apparatus according to the present invention. 1: Photoreceptor 2: Charging device 4: Developing device 1O: Potential sensor 11: Potential measuring circuit 12: DC controller 15: High voltage transformer

Claims (1)

[Scope of Claims] 1) At least a charging device and a developing device are provided around the endlessly moving electrophotographic photoreceptor, a surface potential sensor is disposed between the charging device and the developing device, and the surface potential sensor In an electrophotographic image forming apparatus that detects and controls the surface potential of a photoreceptor, the photoreceptor is charged with a certain amount of electricity in a short period of time before an image forming operation, and the charged portion reaches the surface potential sensor position. 1. An electrophotographic image forming apparatus comprising a dark decay characteristic detection mode in which the rotation of a photoconductor is stopped for a predetermined period of time, and thereby the dark decay characteristic of the photoconductor is detected. 2) The device according to claim 1, wherein the charging device is controlled by the signal obtained in the dark decay characteristic detection mode, and the surface potential of the photoreceptor is controlled.