JPS5952231A - electronic copying device - Google Patents

Abstract

PURPOSE:To obtain a picture having no density variation all the time by detecting the distance between an original platen glass and an original, and correcting optical path length and picture density on the basis of the detection signal. CONSTITUTION:A sensor 11 is scanned in the same direction with an original illumination system prior to the scanning of the original scanning system and the distance between the surface of the original 1 and the surface of the original platen glass 2, i.e. image plane of the optical system is calculated by the scan signal. A lens 4 is moved by a lens position moving device 12 to a preset position according to the calculated value to form an image on a drum surface correctly. At this time, an adjusting device 13 for the quantity of light of a light source corrects the picture density by correcting the emission quantity of light of the light source so that the intensity of illumination on the drum is corrected in order to prevent variation in the picture density with the intensity of illumination on the drum surface resulting from a shift in lens position.

Description

DETAILED DESCRIPTION OF THE INVENTION In an electrophotographic copying apparatus, an image of a document is formed on the surface of a photoreceptor, which is uniformly charged in a predetermined process, through an optical system and exposed to light. An electrostatic latent image is formed on the surface of the photoreceptor, the electrostatic latent image is developed, and a copy is obtained through a transfer process.

In a conventional electrophotographic copying apparatus, as shown in FIG. 1, an original, that is, an object to be copied, is placed on two sides of an original table glass, and the original surface is scanned by relative movement. The surface of the document is illuminated by a light source 3, and the light reflected from the document is imaged on the surface of the photoreceptor S by a lens. However, when the copying magnification is constant, the optical path length between the surface of the document glass and the lens q and the optical path length between the lens and the surface of the photoreceptor S do not change, and the depth of field of the lens is generally 7 to 3-3. Because it is shallow, there is a drawback that when copying three-dimensional objects or particularly thick books, the image at a distance from the platen glass becomes unclear. Note that ``Otsu'' indicates a developing device.

An object of the present invention is to provide an electronic copying apparatus that overcomes the above-mentioned conventional drawbacks.In the present invention, the distance between the document surface and the document table glass surface is detected while the document surface is being scanned, and this signal is used to detect the distance between the document surface and the document table glass surface. By moving the lens so that the image is correctly formed on the surface of the photoreceptor and correcting the change in image density caused by the movement of the lens, it has become possible to clearly copy even three-dimensional objects.

Next, the present invention will be described by way of examples with reference to the drawings.

Figure Ω is a schematic cross-sectional view for explanation of the first embodiment of the present invention. is,
The reflected light is imaged on the surface of the drum 3 by the lens q.

In this embodiment, a distance detection device // (hereinafter referred to as a sensor) is provided near the bottom surface of the document table glass unit, a lens position moving device 12 is provided in the lens, and a light emission amount adjustment device 13 is connected to the light source 3. Ru.

In this embodiment, in scanning the document surface, prior to the scanning of the document illumination system, the sensor l/ is scanned in the same direction as the document illumination system, and the signal is used to scan the surface of the document l and the surface of the document table glass, that is, the Calculate the distance to the image plane of the optical system. According to this calculated value, the lens q is moved to a preset position by the lens position moving device lλ, so that the image is correctly formed on the drum surface. At this time, the illuminance on the drum surface inevitably changes due to the fluctuation of the lens position, and in order to prevent a change in image density from occurring, the light emitting amount adjustment device 13 of the light source is used to correct the illuminance on the drum surface. The image density is corrected by correcting the amount of light emitted.

To explain the distance detection device (sensor) //, for example, as shown in Fig. 3, it has a light emitting element //a and a light receiving element //b.
The sensor detects changes in distance based on changes in the amount of light reflected from the object surface, and can be installed in front of the original scanning by the amount of time required for the lens movement and light amount correction to rise, or if the rise times are different for each, the sensor can be removed. The lens may be moved further forward and the output of the sensor may be delayed to move the lens and correct the amount of light. You can also set the document scanning end position to the opposite position to the document scanning start position, detect and store the distance change in advance when returning before starting document scanning, and perform lens position and light intensity correction when scanning the document. good.

In either case, as mentioned above, the sensor detects the misalignment between the document surface and the optical system image surface, and the lens position and light amount are corrected based on this signal so that the photoreceptor surface always becomes the image formation surface. Even with three-dimensional objects such as books, clear and good images were always obtained.

Next, a first embodiment of the present invention will be described with reference to FIG.

In this case, the arrangement and operation of the sensor // and lens position moving device /, 2 are the same as in the first embodiment explained using Fig. Ω, but in this first embodiment, the image density is As the light amount correction means as a correction means, there is used a means for changing the amount of exposure to the photoreceptor by driving a light amount correction Surin)/4 by a slit correction device (not shown). In other words, the amount of exposure to the photoreceptor is corrected based on the detection signal from the sensor by raising and lowering the light amount correction lens), rotating it, opening and closing the slit width, etc. In an electrophotographic copying apparatus having a mechanism, it is possible to correct the amount of light even when a light source such as a fluorescent lamp whose amount of light emission cannot be easily changed is used.

FIG. 3 shows a third embodiment of the present invention, and in this embodiment, the light emission amount adjusting device 13 (FIG. 1) of the first embodiment or the light amount correction device 13 of the first embodiment is used. )/& (Figure 1), the image density is corrected by controlling the bias value of the developing bias power supply IS of the developing device B, instead of correcting the light amount using a light amount correcting means such as shown in FIG.

As explained above, according to the present invention, the image plane and By detecting the distance to the actual image plane and controlling the lens position using this detection signal so that the surface of the photoreceptor always becomes the image plane, and by correcting changes in drum surface illuminance by adjusting the light amount and developing bias. Even for three-dimensional objects, it was possible to always obtain clear and good copied images with no density changes.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a conventional electrophotographic copying device, FIG. 2 is a schematic explanatory diagram of a first embodiment of the present invention, and FIG. 3 is a side view of an embodiment of a distance detection device used in the present invention. FIG. 7 is a schematic explanatory diagram of a second embodiment of the present invention, and FIG. S is a schematic explanatory diagram of a third embodiment of the present invention. L...Copy (original) U...Original platen glass 3...Light source lens K...Photoconductor B...Developer//...Distance detection device /2...Lens moving device 13...Light source light emission amount adjustment device/9...Light amount correction Surin + l Left...Development bias power supply Patent applicant Canon Corporation 7- Fig. 1 Fig. 2 Fig. 4 Figure 5

Claims (1)

[Claims] (1) In an electrophotographic copying apparatus that performs exposure by forming an image of an original on a glass platen surface on a photoreceptor surface via an optical system, means for detecting the distance between the glass platen plate and the original; means for correcting the optical path length according to the detected signal;
An electronic copying apparatus comprising means for correcting image density based on a detected signal.