JPS61213875A - Transfer device for electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To attain always a stable transfer efficiency independently of the density of toner images by controlling the quantity of light of a pretransfer lamp in accordance with the detected density of a target image. CONSTITUTION:A target 3 is scanned in the preceding stage of copying, and the electrostatic latent image of the target 3 is developed by a developing machine 9 and passes a PTL 10, a chute 11, a transfer corotron 12, and a density sensor 13 successively. The photoelectric conversion output of the density sensor 13 is inputted to a density detecting circuit 14 and is detected as a density signal corresponding to the input level. A control circuit 15 sets the supply voltage from a power supply circuit 16 to the PTL 10 on the basis of the detected density of the target image. Since the quantity of light of the PTL 10 is controlled in accordance with the density of the target image, namely, the density of a toner concentration by the supply voltage control of the control circuit 15, the electrostatic latent image is always eliminated in a uniform state adapted to the density.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a transfer device for an electrophotographic copying machine that also uses a pre-transfer lamp to transfer a toner image formed on a photoreceptor to paper. In particular, the present invention relates to an improvement for always obtaining stable transfer efficiency regardless of the density of the toner image.

[Prior Art] Generally, when obtaining a copy of an original image using an electrophotographic copying machine, five steps are required: charging, exposure, development, transfer, and fixing. A sheet of paper is carried onto the photoreceptor as the toner image formed on the photoreceptor passes through the development process, and the sheet is charged by a transfer corotron with a charge having a polarity opposite to that of the toner and a predetermined potential or higher, and This is carried out by moving the toner that has been electrostatically attracted to the latent image portion of the photoreceptor toward the paper.

In such a transfer process, there is not much of a problem under normal circumstances, but especially when transferring with paper containing moisture in a high-humidity environment, the latent image on the photoreceptor may cause a backlash to the interface between the paper and the photoreceptor. A charge flow is induced, which may cause a corresponding amount of toner to remain on the photoreceptor, resulting in so-called transfer failure. To deal with such transfer defects, conventional transfer devices install a pre-transfer lamp (Pre-Tr) before the transfer corotron on the circumferential surface of the photoreceptor.
Immediately before the above-described transfer process, an intense light is irradiated onto the photoreceptor through the toner image to erase the latent image that is a factor that induces the reverse charge flow. An attempt was made to eliminate toner remaining on the photoreceptor during transfer.

[Problems to be Solved by the Invention] However, in the transfer device of the conventional electrophotographic copying machine described above, the light intensity of the pre-transfer lamp is always controlled to a constant value regardless of the density of the toner image on the photoreceptor. For example, in the case of a high-density toner image, the latent image cannot be completely erased due to insufficient light intensity, resulting in a decrease in transfer efficiency and the occurrence of white spots (hollow characters) in the image. There was a problem in that printing quality was significantly impaired.

[Means for Solving the Problems] Therefore, in the present invention, before scanning a document, the density of the target image formed on the photoreceptor is detected by scanning and developing a target that corresponds to the reference density. means and
The apparatus further includes means for controlling the light intensity of the pre-transfer lamp in accordance with the density of the target image detected by the detection means.

Effect 1 According to such a configuration, the target image density detected by the density detection means matches the density of the toner image (original image) formed subsequently, and the light M of the pre-transfer lamp, however, Since the control means variably controls the density according to the density, it is possible to always erase the latent image on the photoreceptor by irradiating the toner image with an amount of light that is appropriate for the density of the toner image. ! This makes it possible to completely remove factors that induce transcription defects.

[Example] Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings. The figure conceptually shows the configuration of an electrophotographic copying machine equipped with a transfer device according to the present invention, which includes a platen glass 1, a platen support 2, a target 3, a light source lamp 4, a mirror 5.7, Lens 6, photoreceptor 8, developing machine 9, pre-transfer lamp (Pre-Trans
ferlamp: hereinafter abbreviated as PTL) 10, shoot 1
1, a transfer corotron 12, a density sensor 13, a density detection circuit 14, a 111111 circuit 15, and a power supply circuit 16. The operation will be explained below.

First, as a preliminary step for copying, when the placement of the original 17 to be copied on the platen glass 1 is completed and a command to start the operation of the copy 4J cycle is issued, the light source lamp 4 is turned on and the platen support 2 is first placed. A target 3 arranged below is scanned.

The target 3 is made of a reflector having a standard density, and the scanning light thereof is exposed onto the photoreceptor 8 through an optical system including a mirror 5, a lens 6, and a mirror 7.

The target 3 formed on the photoreceptor 8 by the exposure
The electrostatic latent image is then developed by the developing device 9 to become a target image to which toner of a predetermined density is adsorbed. pass through sequentially. Among those placed on the passing position of this target image,
The concentration sensor 13 includes, for example, an emitting element that irradiates a predetermined amount of light onto the surface of the photoreceptor 8, and a light receiving element that receives the reflected light, and directs the light received by the light receiving element to its light receiving port. Converts it into an electrical signal according to the signal and outputs it.

The photoelectric conversion output of this concentration sensor 13 is the concentration detection circuit 1
4, and detected as a density signal according to the input level. Therefore, the detection value of the density detection circuit 14 obtained when the target image passes over the irradiation position of the light emitting element indicates the density of the target image. Next, the detected density signal of the density detection circuit 14 is input to the control circuit 15, where the control circuit 15 sets the supply voltage from the power supply circuit 16 to the PTLIO based on the detected density of the target image. Do the following. On the other hand, the target image that has passed over the density sensor 13 is completely erased from the surface of the photoreceptor 8 by the surface treatment of the photoreceptor 8 performed by the cleaning section and snow removal section that the photoreceptor 8 passes through. The photoreceptor 8, which has been subjected to such processing, is then driven and enters the rotation for the next copy cycle, and the surface of the photoreceptor 8 is charged as the first operation of this copy cycle. Further, with the start of this copy cycle, the scanning optical system starts scanning the original 17 with the light source lamp 4, and the scanning light passes through the mirror 5, lens 6, and mirror 7 to the photoreceptor after the charging process. 8. The electrostatic latent image formed on the photoreceptor 8 by the exposure is then developed by a developer (1119) to form a toner image, and then sequentially passes over the PTL 10.

At this timing, the control circuit 15 starts controlling the power supply from the power supply circuit 16 to the PTLlo based on a voltage value set in advance according to the density of the target image, and lights up the PTL10. Light is irradiated onto the photoreceptor 8 passing over the PTL 10 through the toner image. Just like before, this PTLI
The photoreceptor 8 is irradiated with light by O in order to remove the electrostatic latent image on the photoreceptor 8, which is a factor that causes a decrease in transfer efficiency. In contrast to the conventional device in which υ was constant and the state of removal of the electrostatic latent image 0a varied depending on its concentration, the device of the present invention has the following features:
Since the light amount of the PTL 10 is controlled according to the density of the target image, that is, the density of the toner image, by the power supply control of the control circuit 15 described above, the electrostatic latent image can always be removed in a uniform state adapted to the density. It will be done.

The toner image after the light irradiation process by the PTL 10 is carried through the chute 11 onto the circumferential surface of the photoreceptor 8, and is then transferred onto the paper 18 where it is charged with an electric charge of opposite polarity to the toner by the transfer corotron 12. After that, the image is transferred to the paper 18 through a fixing process, and then fixed onto the paper 18 and discharged. In the transfer step, the electrostatic latent image on the photoreceptor 8 is transferred to the PTL according to the density of the toner image (copy image).
Because it is completely removed by IO's light irradiation treatment,
Good transfer efficiency can always be achieved regardless of the density of the toner image.

Note that the means for detecting the density of the target image during the dead cycle immediately after the start of the copy cycle is, for example, an SDC (SQLID DENSIT) for controlling toner density.
There are models that are already installed as components such as Y C0NTOROL, and the configuration can be simplified by using these components.

[Effects of the Invention] As explained above, according to the transfer device of the electrophotographic copying machine of the present invention, the light intensity of the pre-transfer lamp is controlled according to the density of the target image detected during the dead cycle immediately after the start of the copy cycle. As a result, latent image removal can be performed with an optimum amount of light for a toner image formed on the photoreceptor at the same density as the target image,
This provides excellent effects in that a stable transfer efficiency can be obtained at all times regardless of the temperature of the toner image, and thereby a copy image of good quality without any self-destruction can be obtained.

[Brief explanation of drawings]

The figure is a conceptual diagram showing the main part configuration of an electrophotographic copying machine equipped with a transfer device according to the present invention. 1...Platen glass, 2...Platen support,
3...Target, 4...Light source lamp, 5.7...
・Mirror, 6... Lens, 8... Photoreceptor, 9...
Developing machine, 10... Pre-transfer lamp (PTL)
), 11... Shoot, 12... Transfer corotron,
13... Temperature sensor, 14... Concentration detection circuit, 15
...Control circuit, 16...Power supply circuit.

Claims (1)

[Claims] In a transfer device of an electrophotographic copying machine that uses a pre-transfer lamp to transfer a toner image formed on a photoreceptor to a sheet of paper in response to document scanning, a target having a reference density is scanned prior to the document scanning. means for detecting the density of the target image formed on the photoreceptor, and means for controlling the light amount of the pre-transfer lamp according to the density of the target image detected by the density detecting means. Features of a transfer device for an electrophotographic copying machine.