Facsimile and static presentation processing – Facsimile – Picture signal generator
Reexamination Certificate
2001-03-29
2004-09-07
Coles, Edward (Department: 2622)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C358S462000, C358S482000, C358S486000, C348S297000, C348S298000, C250S208100
Reexamination Certificate
active
06788438
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading device used in equipment such as a scanner, a copying machine, or a facsimile, and an image forming apparatus comprising the image reading device.
2. Description of Related Art
Image forming apparatuses such as copying machines or facsimiles comprise an image reading device for reading a document image and an image recording device for recording on a paper sheet an image corresponding to the image read by the image reading device. The speed at which the image is read by the image reading device and the speed at which the image is recorded by the image recording device are generally set to approximately equal values. An image reading operation and an image recording operation are synchronously performed.
The image reading device comprises an image sensor represented by a CCD (Charge Coupled Device). The image sensor detects, when a light source is moved relative to an image surface of a document, light reflected from the image surface as incident light while illuminating the image surface by the light source. The image sensor converts the incident light into charge and stores the charge, and converts the stored charge into an electric signal and outputs the electric signal.
The electric signal is inputted to a laser scan unit in a copying machine, for example, as an image signal. The laser scan unit subjects laser beams to ON/OFF control depending on the image signal, and exposes a surface of a photoreceptor by the laser beams. The surface of the photoreceptor before the exposure is uniformly charged, so that an electrostatic latent image is formed on the surface of the photoreceptor upon exposure by the laser beams. The electrostatic latent image is thereafter developed into a toner image by a developing device, and the toner image is transferred onto the paper sheet.
Generally, the smaller the amount of light incident on the image sensor is, the smaller the amount of charge stored in the image sensor is, while the larger the amount of the incident light is, the larger the amount of the stored charge is. If the amount of incident light is insufficient, the amplitude of the image signal is decreased, so that the SN (Signal-to-Noise) ratio thereof is lowered. As a result, the image quality of the toner image is degraded. On the other hand, if the amount of the incident light is too large, an overflow of charge called blooming occurs, thereby making it impossible to perform normal image reading.
A light source for illuminating the document is degraded with an elapse of a time period during which it is used (a time period during which it is turned on) so that the amount of emitted light is decreased. Correspondingly, the S/N ratio of the image signal is reduced. A light amount adjusting function has been conventionally provided to the light source to adjust the amount of light emitted from the light source, thereby adjusting the amount of light incident on the image sensor in a suitable range.
In order to provide the light amount adjusting function to the light source, however, a light amount adjusting circuit or the like must be provided. Accordingly, the cost of the image forming apparatus is increased.
On the other hand, even when a light source having a light amount adjusting function is used, the amount of light incident on the image sensor cannot be always suitably adjusted. That is, there is a case where even if the amount of light from the light source is adjusted to a maximum, an amount of incident light required for the image sensor cannot, in some cases, be ensured. If a light amount adjusting range is narrow, it may be impossible to ensure a suitable amount of light incident on the image sensor.
An example of the image reading device provided in the image forming apparatus is one capable of setting a monochrome mode in which a document image is read in a single color and a full color mode in which a document image is read in a full color. Further, the image reading device in the image forming apparatus may, in some cases, be used as an image scanner for accepting an image in a personal computer or the like.
Since the image sensor capable of reading an image in a full color comprises a color filter, sensitivity to the amount of incident light tends to be low due to the effect. If a light source outputting a large amount of light, for example, a halogen lamp is used, the problem will be solved. However, such a high-power light source is expensive and consumes a large amount of power. Further, a rare gas lamp which has been frequently used in recent years as a light source for document illumination cannot obtain a sufficient amount of light. So long as the rare gas lamp is used, a sufficient S/N ratio at the time of reading a high-quality image in the full color mode is difficult to ensure.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide an image reading device capable of improving the image quality of a read image without requiring to adjust the amount of light from a light source.
A second object of the present invention is to provide an image reading device capable of reading an image with its quality enhanced depending on an image reading mode.
A third object of the present invention is to provide an image forming apparatus capable of reading a document image with its quality enhanced without requiring to adjust the amount of light from a light source and forming an image corresponding to the read image on a paper sheet.
A fourth object of the present invention is to provide an image forming apparatus capable of reading a document image with its quality enhanced depending on an image reading mode and forming an image corresponding to the read image on a paper sheet.
An image reading device according to the present invention comprises an image sensor for scanning a surface of a document, optically reading an image formed on the surface of the document, and outputting an electric signal corresponding to the read image; a period control circuit for controlling the period of a horizontal synchronizing signal to be fed to the image sensor in order to change a time period during which charge is stored in the image sensor; and a scanning speed control circuit for controlling the scanning speed for the surface of the document by the image sensor to be a speed conforming to the period of the horizontal synchronizing signal.
The image reading device according to an embodiment of the present invention further comprises an image reading mode setting section for setting an image reading mode. In this case, it is preferable that the period control circuit variably sets the period of the horizontal synchronizing signal depending on the image reading mode set by the image reading mode setting section. Similarly, it is preferable that the scanning speed control circuit variably sets the scanning speed depending on the image reading mode set by the image reading mode setting section.
The scanning of the surface of the document by the image sensor may be attained by causing the document to stand still on a transparent platen, for example, while moving a light source for illuminating the document relative to the document as well as causing light reflected from the document to be incident on the image sensor. Further, the scanning of the surface of the document may be attained by causing the light source for illuminating the document to stand still, while conveying the document such that the document passes through a position illuminated by the light source and causing the light reflected from the document to be incident on the image sensor in the course of conveying the document. Consequently, the adjustment of the scanning speed for the surface of the document by the image sensor is attained by adjusting the speed of a motor for moving the light source or a motor for conveying the document (hereinafter generically referred to as a scan motor), for example.
It is preferable that the image reading mode which can be set by the image reading mode setting se
Fujihara Kensuke
Satonaka Shinobu
Takahashi Masayoshi
Coles Edward
Kyocera Mita Corporation
Safaipour Houshang
Smith , Gambrell & Russell, LLP
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