JPH0579988B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) Electronic devices such as copying machines that are designed to prevent members disposed close to the image bearing member of the present invention from being stained with toner. Concerning photographic equipment.

(Prior Art) For example, in a dry type copying machine, the surface of an image bearing member such as a photosensitive drum is charged to impart photosensitivity, and an electrostatic latent image is formed. Develop and transfer to transfer material,
A configuration is known in which residual toner is removed after transfer using a cleaner, and then the next copying process is started. Incidentally, in recent years, as there has been a demand for smaller copying machines, efforts have been made to make the machines more compact by arranging equipment or members around the image carrier as close as possible to the image carrier. . As is known, toner on an image carrier originally has some potential, and therefore, if the member near the image carrier is a grounded conductive member, the toner on the image carrier A portion of the toner on the body is transferred to and collected by such conductive member,
deface it. Moreover, in the case of a device that applies a bias in the developing process, the developing bias is, for example, 700 V when the image carrier is idling, and a DC voltage of 200 to 400 V is superimposed during copying. Because the toner is charged with the above-mentioned charges, the toner may reach a potential of several hundred volts due to these charges. With such high-potential toner, the adhesion of the toner to the conductive member is further increased.

In addition, the toner remaining on the image carrier in the above process is not completely removed by the cleaner, and therefore, a small amount of toner scattered or leaked from the cleaner or developing device may be left on the surface of the image carrier or in the air inside the machine. Toner is present and also adheres to the conductive member.

(Problems to be Solved by the Invention) Toner carried on the surface of the image carrier as described above and transported (including during copying and idling)
Since the toner remaining inside the machine has a relatively high potential, some of the toner adheres to a conductive member placed close to the image carrier, and even when the machine is idling, the toner does not adhere to the conductive member. Even slight adhesion of dirt can be seen, and these stains cause problems such as deteriorating the quality of copies.
In particular, if toner adheres to and stains the guide or transfer member of the paper feeder near the image carrier, there is a drawback that the back side of the copied paper becomes stained. In the past, attempts have been made to solve this problem by using an insulating material or varistor to electrically interrupt the member close to the image carrier, or to remove the toner by sucking polluted air near the member. However, neither was successful.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic apparatus in which a conductive member, particularly a paper feed guide, disposed close to an image carrier in the electrophotographic apparatus can be prevented from being contaminated with toner. It is.

(Means for Solving the Problems) An electrophotographic apparatus according to the present invention provides toner that is supplied to an image bearing member forming an electrostatic latent image by a developing member biased with a voltage of direct current or alternating current superimposed on direct current. form an image, and this toner image,
In an electrophotographic apparatus in which transfer material is transferred onto a transfer material supplied to an image carrier by a paper feed guide, the paper feed guide is made of a conductive member with one end close to the image carrier, and the paper feed The guide is connected to the DC voltage source of the bias, and a surface electrometer is further provided for measuring the surface potential of the image carrier at a position upstream of the developing member, and a bias voltage having a value corresponding to the value detected by the electrometer is provided. is applied to the developing member and paper feed guide.

(Function) Therefore, in the electrophotographic apparatus of the present invention, a voltage of the same potential as the developing bias potential is applied to the paper feed guide near the image carrier, so that the paper feed guide located near the image carrier always has the same potential as the developing bias potential. Since the toner is maintained at approximately the same potential as the toner, the toner is repelled by the member, and therefore, even if it comes into contact with the member, it immediately leaves the member, so that it does not adhere to the member and therefore does not cause stains.

(Example) Next, an example of the present invention will be described with reference to the drawings. FIG. 1 illustrates an electrophotographic apparatus according to the present invention, in which 1 is an image carrier having a photoreceptor on its outer circumferential surface, 2 is a developing device, 3 is a paper feeding device, and 4 is a transfer device. This is a corona discharger for use. In this example, the image carrier 1 has a drum shape that rotates in the direction of arrow A, but the present invention is also applicable to a belt or flat plate shape. The developing device 2 is a magnetic brush type developing device of known construction, and its sleeve is biased with an alternating current voltage superimposed with a direct current voltage of an appropriate polarity. Although magnetic toner is used in this example, a two-component developer may also be used. An AC power supply 11 and a transformer 5 are provided for supplying the AC voltage and DC voltage. Note that the AC power supply 11 may be omitted depending on the case. On the other hand, a surface electrometer 8 is disposed at a position upstream of the developing device 2 to measure the surface potential of the bright portion of the electrostatic latent image on the image carrier 1.
is connected to the transformer 5 by a lead wire 9. Therefore, an optimal DC voltage depending on the surface potential of the image carrier 1 detected by the electrometer 8 via the transformer 5, for example, a DC voltage of a value obtained by adding several +V to the detected potential, is superimposed on the sleeve. , it is possible to form an optimal developed image according to the electrostatic latent image. The paper feeding device 3 consists of a pair of rollers 3a and a guide 3b adjacent thereto and whose tip end is close to the image carrier 1, and the guide 3b is formed of a conductive member.

The guide 3b is connected to the transformer 5 in order to apply a voltage (bias) having approximately the same potential as the toner existing in the vicinity, especially the toner on the image carrier.
Connected to the DC output end of the A resistor 7 for shot protection is inserted into the lead wire 6 at an appropriate position.

Since it is difficult to directly measure the potential of the toner existing near the guide 3b, especially the toner on the image carrier, in the method of applying a bias to the developing sleeve as described above, the DC developing bias potential is Since it can be regarded as an approximate value of the potential of the toner, such a value is used as a substitute, and by this, it is possible to apply a voltage of almost the same potential as the potential of the toner to the paper feed guide 3b by a simple means. Become. In addition, in one example, the DC voltage is idling.
Suitable results were obtained by controlling the leading voltage applied to the sleeve to be approximately 800 to 1,500 V with a voltage of 700 V and 200 to 400 V during copying.

(Effects of the Invention) As described above, according to the present invention, the paper feed guide around the image carrier is maintained at approximately the same potential as the toner existing in the vicinity, so that toner does not adhere to the paper feed guide. Therefore, staining of the transfer material due to toner is prevented. According to the present invention, such stains can be prevented with a simple configuration. Therefore, the maintenance cycle can be lengthened, and the quality of the copies can be improved without staining the copies for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention. In the figure, 1...image carrier, 2...developing device, 3b...
...Paper feed guide, 5...DC voltage source, 8...Surface electrometer.

Claims (1)

[Claims] 1 A toner image is formed by supplying toner to an image carrier that forms an electrostatic latent image using a developing member biased with a voltage of direct current or alternating current superimposed on direct current, and this toner image is passed through a paper feed guide. In an electrophotographic apparatus in which the paper is transferred onto a transfer material that is supplied to an image carrier, the paper feed guide is made of a conductive member with one end close to the image carrier, and the paper feed guide is connected to the bias. A surface electrometer connected to a DC voltage source and measuring the surface potential of the image carrier at a position upstream of the developing member is provided, and a bias voltage corresponding to the detected value by this electrometer is applied to the developing member and the surface electrometer. An electrophotographic device characterized in that a voltage is applied to a paper feed guide.