JPH04221971A - Image density controller for image forming device - Google Patents

Abstract

PURPOSE:To make a base void and to obtain appropriate image density by providing a means for setting the surface potential of a photosensitive drum at a low potential according as original density becomes higher when the original density is equal to or above a reference. CONSTITUTION:When copying actions are instructed by a copying key 34, a CPU 30 transmits a control signal for prescanning to an optical system driving circuit 31 and a control signal instructing light emission to a light emission control circuit 32 so that an original irradiating lamp (halogen lamp) 42 may emit the light of constant emitted light quantity previously set and moving frames 41 and 51 may be moved by a specified quantity. Reflected light of the light with which the original is irradiated at the time of prescanning is received by a light receiving sensor 61, and the emitted light quantity of the lamp 42 and the surface potential of the photosensitive drum 7 are decided based on the level of the received light by the CPU 30. When the original density is equal to or above the specified reference value, the surface potential of the drum 7 is set at the low potential in accordance with the rising quantity of the original density, and then exposure is executed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density control device for controlling image density after copying (image formation) in an image forming apparatus such as a copying machine.

0002

2. Description of the Related Art Conventionally, in image forming apparatuses such as copying machines, the surface potential of a photoreceptor drum is held constant and the amount of light irradiated onto a document is varied to control the image density after copying. It has become. For example, in a copying machine equipped with a pre-scan type automatic exposure device, a pre-scan is performed while a pre-scanned document is irradiated with a predetermined amount of light from a document irradiation lamp such as a halogen lamp, and the reflected light is received by a light-receiving sensor. The density of the original is detected, and the amount of light emitted from the original irradiation lamp during actual copying is determined based on the density of the original.

FIG. 5 is a diagram showing the relationship between document density and light emission amount for determining the light emission amount of the document irradiation lamp. In the figure, A, B, and C are the reference original G1, respectively.
, G2, and G3, for example, if the detected document density is substantially the same as the reference documents G1, G2, and G3, the amounts of light emitted from the document irradiation lamps are a, b, and c, respectively.
is emitted.

0004

[Problems to be Solved by the Invention] In the conventional image density control device described above, the light emission amount of the document irradiation lamp is set to increase as the document density becomes darker. If the light emission amount is around C, the base density is darker than the reference original G3, and if you copy a dark original (original of C or higher in Figure 5), the light emission amount of the document irradiation lamp is insufficient, and the base density is darker than the reference original G3. It becomes impossible to cut out the image (forming a white image on the white background part of the original). In order to solve this problem, it may be possible to use a document illumination lamp with a large light emitting capacity, but this would not only increase the cost but also cause the temperature of the optical system to rise due to the heat generated by the document illumination lamp. Measures against heat generation are required.

The present invention has been made in view of the above-mentioned problems, and it is possible to obtain a suitable image density by adjusting the surface potential of the photoreceptor drum when the original density is higher than the standard value and is dark. An object of the present invention is to provide an image density control device for an image forming apparatus.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention irradiates light from an original irradiation lamp to an original, and emits light from the original irradiation lamp based on the density of the original obtained by receiving the reflected light. An image density control device for an image forming apparatus that adjusts image density by controlling the amount of light emitted and the surface potential of a photoreceptor drum, the document irradiation lamp setting the amount of light emitted to a predetermined value when the density of the document is equal to or higher than a reference value. and surface potential control means for setting the surface potential of the photosensitive drum to a lower potential as the density of the original increases when the density of the original is higher than the reference value. .

[0007]

According to the present invention, light is irradiated onto the original from the original irradiation lamp, and the density of the original is detected by receiving the reflected light. When this document density is equal to or higher than a predetermined reference value, the light emission amount of the document irradiation lamp is set to a predetermined value, and the surface potential of the photosensitive drum is set to a low potential corresponding to the amount of increase in the document density. Exposure is performed.

[0008]

Embodiment FIG. 2 is an overall configuration diagram showing an embodiment of an image forming apparatus equipped with an image density control device according to the present invention. A copying machine (image forming apparatus) 1 shown in the figure has a contact glass 2 and a document holder 3 on its upper surface, and an optical system L below it. The optical system L includes a first moving frame 41 that includes an original irradiation lamp 42 such as a halogen lamp, a reflector 43, and a mirror 44, a second moving frame 51 that includes mirrors 52 and 53, and detects the density of the original. Light receiving sensor 61 for
The lens 6 has a mirror 54, and serves to guide the image of the document on the contact glass 2 to the photosensitive drum 7 below. Therefore, the density of the copied image (copy density) changes depending on the amount of light emitted from the document irradiation lamp 42.

Around the photosensitive drum 7, as image forming means, there are a charging device 8 for setting the surface potential of the photosensitive drum 7, a blank lamp 9, a developing device 10, and a transfer device 11.
, a separation device 12, a cleaning device 13, etc. are provided. The copying machine 1 also includes a plurality of paper feed cassettes 14 as paper transport means in order from the upstream side in the transport direction.
, a paper feed roller 15, a pair of conveyance rollers 16 and 17, a pair of registration rollers 18, a conveyance belt 19, a fixing device 20, a pair of discharge rollers 21, a discharge tray 22, and the like.

FIG. 1 is a block diagram configuring an image density control device according to the present invention. In the figure, 30 is a central control unit (hereinafter referred to as CPU) that centrally controls the image forming operation of the copying machine 1, and 31 is the first and second
an optical system drive circuit that controls the drive of the moving frames 41 and 51;
32 is a light emission control circuit for controlling the light emission of the document irradiation lamp 42; 33 is a surface potential control circuit for controlling the surface potential of the photosensitive drum 7; and 34 is a copy key for instructing a copying operation.

When a copy operation is instructed by the copy key 34, the CPU 30 sends a control signal for pre-scanning to the optical system drive circuit 31, and also sends a control signal for instructing light emission to the light emission control circuit 32. , the first and second moving frames 41 and 51 are moved by a predetermined amount while causing the document irradiation lamp 42 to emit light at a predetermined constant amount of light. The reflected light of the light irradiated onto the document during this pre-scanning is received by the light receiving sensor 61, and based on the received light level, the CPU 3
0, the amount of light emitted from the document irradiation lamp 42 and the surface potential of the photosensitive drum 7 are determined. Note that during pre-scanning, the document irradiation lamp 42 emits light with a constant amount of light, so that the light receiving sensor 61 obtains a light receiving level corresponding to the density of the document. That is, when the document density is low (the document is white), the light reception level is high, and when the document density is high (the document is black), the light reception level is low. Therefore, the amount of light emitted from the document irradiation lamp 42 and the surface potential of the photoreceptor drum 7 are calculated based on the relationship between the density of the document, the amount of light emitted, and the surface potential, which will be described later, or determined by a conversion table provided in advance. . Then, during actual copying,
The charging device 8 sets the surface potential of the photoreceptor drum 7 to the calculated surface potential, and the document irradiation lamp 42 emits light at the calculated amount of light emission, thereby performing exposure scanning of the document.

FIG. 3 shows an example of the relationship between the density of the document, the amount of emitted light, and the surface potential for determining the amount of emitted light and the surface potential. In the figure, A, B, and C are document densities of reference documents G1, G2, and G3, respectively. The reference document G1 is, for example, a blank document having a predetermined degree of whiteness. Further, the reference original G2 is, for example, a reference original in which characters are written on the white original at a predetermined density, and a reference original G3
is a standard manuscript that has characters written at a predetermined density on a gray background of a predetermined brightness, and corresponds to a standard newspaper. The document density becomes darker toward the reference document C side, resulting in a darker document. Further, P indicates the relationship between the document density and the amount of light emitted, and Q indicates the relationship between the document density and the surface potential. As shown in the figure, the original irradiation lamp 42
Although the proportional coefficient differs between document densities AB and BC, the amount of light emitted is set to a large value according to the document density, and in the case of a dark document that is higher than the density of reference document G3 (C or higher). is fixed to the amount of light emitted c. On the other hand, the surface potential of the photosensitive drum 7 is fixed at a constant potential V2 when the original has a density lighter than that of the reference original G3 (between AC), and when the original has a density higher than that of the reference original G3 ( C or higher) is set to a low potential depending on the amount of increase in document density. That is, in the case of an original whose original density is lighter than the density of the reference original G3 (between AC), the image density is controlled by the amount of light emitted from the original irradiation lamp 42, and in the case of an original whose original density is higher than the density of the reference original G3 ( C or higher), the image density is controlled by the surface potential of the photoreceptor drum.

FIG. 4 shows the relationship between the density of the original and the image density after copying, with the amount of light emitted from the original irradiation lamp 42 kept constant and the surface potential of the photosensitive drum 7 as a parameter. The surface potential of the photosensitive drum 7 increases in the order of F1, F2, and F3. As shown in the figure, when the surface potential of the photosensitive drum 7 is lowered, the position of the saturation point on the side where the image density is higher moves toward the side where the density of the original is higher, and the sensitivity of the image density to the density of the original decreases. Therefore, it is possible to reduce the image density of a dark original after copying. That is, in FIG. 4, when the density of the original is at point D, when the surface potential of the photosensitive drum 7 is changed from F2 to F1, the image density changes from m to n, and the image density becomes lighter. Therefore, even if the density of the original is darker than the density of the reference original G3 and the amount of light irradiated to the original is fixed at a constant level regardless of the original density, the image density becomes darker than the desired density. By setting the surface potential of the drum 7 to a low potential according to the amount of increase in image density, the density of the original becomes lighter accordingly, making it possible to remove the base and form an image with a suitable image density. .

In FIG. 3, the amount of light emitted by the document irradiation lamp 42 in the range of documents having a density higher than that of the reference document G3 (above C) is not set to a constant value c, but is determined according to the document density as shown by a virtual line. The temperature may be increased gradually.

[0015]

As explained above, according to the present invention, when the density of the original is higher than the reference value, the amount of light emitted from the original irradiation lamp is set to a predetermined level, and the surface potential of the photoreceptor drum is adjusted so that the density of the original is higher than the reference value. Since the exposure is performed by setting the potential to a lower value as the potential increases, even if the original has a darker density than the standard original, which exceeds the light emitting capacity of the original irradiation lamp, the base can be whitened out. A suitable image density can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of an image density control device of an image forming apparatus according to the present invention.

FIG. 2 is an overall configuration diagram of an image forming apparatus including an image density control device according to the present invention.

FIG. 3 is a diagram showing the relationship between the document density, the amount of light emitted from the document irradiation lamp, and the surface potential of the photoreceptor drum.

FIG. 4 is a diagram showing the relationship between the density of a document and the density of an image after copying.

FIG. 5 is a diagram showing the relationship between document density and light emission amount of a document irradiation lamp in a conventional image density control device.

[Explanation of symbols]

1 Copy machine (image forming device) 6 Lens 7 Photoreceptor drum 8　Charging device 30 CPU 31 Optical system drive circuit 32 Light emission control circuit 33 Surface potential control circuit 41 First moving frame 42 Original irradiation lamp 43 Reflector 44, 52, 53, 54 Mirror 51 Second moving frame 61 Light receiving sensor

Claims (1)

[Claims] 1. Image density is determined by controlling the amount of light emitted from the document irradiation lamp and the surface potential of the photoreceptor drum based on the document density obtained by irradiating the document with light from the document irradiation lamp and receiving the reflected light. An image density control device for an image forming apparatus that adjusts the light emission amount of an original irradiation lamp, which sets the light emission amount to a predetermined value when the original density is equal to or higher than the reference value; An image density control device for an image forming apparatus, comprising: a surface potential control means for setting the surface potential of the photosensitive drum to a low potential in accordance with an increase in the density of the document.