Installation for increasing usable range along axial direction of light source

An installation for increasing the usable range along the axial direction of a light source. The installation has a light source and an optical sensor. The light source generates a sense image. The optical sensor further has a sensor and a transparent panel. The sensor is responsible for detecting the image generated by the light source so that a sense image is created. The transparent panel is positioned between the sensor and the light source. A coating on the transparent panel modifies the light transparency along the axial direction of the light source such that light transparency is lower in the middle compared with the ends.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 88222561, filed Dec. 18, 1999.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an installation capable of increasing the usable range of a light source. More particularly, the present invention relates to an installation capable of increasing the usable range along the axial direction of a light source.

2. Description of Related Art

The operating principles of most image-extraction instruments, such as scanners and digital cameras, are very similar. Common features of image-extraction instruments include the use of a light source to produce an optical image and the passing of an optical image through an optical transmission system to an optical sensor. In general, the optical sensor is a charge couple device (CCD).

However, the longitudinal light source of a scanner has one major drawback, namely, brightness level along the central portion of the light axis is usually higher than along the adjacent sides. Hence, an image produced by the light source is brighter in the middle while dimmer along the edges. Since a scanner depends on brightness contrast to operate, a conventional scanner has poorer contrast near the two edges of the light axis. To preserve quality of the scan image, a section near the edge regions is often unused.

Hence, reducing brightness level variation along the axial direction of a light source has become one of the major improvement targets. For example, in Taiwan patent publication no. 244013 entitled ‘Improved lamp shade compensation of an optical scanner’, brightness variation along the light axis is improved by modifying the lamp shade structure. However, the invention requires specially made components, and hence may lead to an increase in production cost.

In Taiwan patent publication no. 352886 entitled ‘A lens structure and its integration with an image-reading device’, another method of improving brightness level along the axial direction of a light source is proposed. By changing the degree of reflectivity of a coated film on the reflecting lens inside the scanner, brightness level variation is reduced. However, the reflectivity of more than one reflecting lens needs to be modified, thereby increasing the production cost necessary for achieving the results. In addition, the method is not suitable for other optical sensing devices besides a scanner.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide an installation for increasing the scanning range along the axial direction of a light source by changing the light transparency of the transparent panel leading, to an optical sensor. In addition, the installation can be applied to other optical devices besides a scanner,such as a digital camera.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an installation for increasing the scanning range of a light source. The installation includes a light source and an optical sensor. The light source is used as a source for generating the image to be detected. The optical sensor includes a sensor and a transparent panel. The transparent panel is positioned between the sensor and the light source. Furthermore, the transparent panel also has a long axis that runs from edge to edge passing through the panel. The sensor receives an optical image formed by projecting light from the light source through the transparent panel. There is a coating over the transparent panel such that light transparency in the middle section of the long axis is higher than either side.

The coating can be deposited over the entire transparent panel. The coating can be deposited over the imaging section on the transparent panel only. In addition, the coating can be made by forming a plurality of coating materials of the same thickness over surface regions of the transparent panel so that a range of light transparencies are obtained across the panel. Conversely, a coating made from a single material but having a variable thickness is formed across the transparent panel to obtain a range of light transparencies across the panel.

In this invention, a coating is added onto the transparent panel of an optical sensor so that light transparency varies across the panel. Hence, there is no need to produce or modify components. Therefore, this invention is able to improve brightness variation of a light source with only minimum modification of the components. In addition, the installation can be applied to other optical devices besides a scanner, such as a digital camera.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a schematic structural diagram of an optical sensor system according to one preferred embodiment of this invention. The system includes, a light source10, a coating15, a transparent panel20and a sensor25. The light source10is able to generate an image for sensing. The sensor25, the transparent panel20and the coating15together constitute the optical sensor. The transparent panel20is positioned between the sensor25and the light source10. When the image produced by the light source is projected onto the transparent panel20, a long axis is created. The coating15is formed over one glass surface of the transparent panel20.

The sensor25detects the light image after light from the light source10has passed through the coating15and the transparent panel20. The coating15on the transparent panel20modifies the light transparency along the long axis such that the light transparency is lower in the middle compared with either end.

The coating15, as shown inFIG. 1, is formed only over the region within the transparent panel20where the projected image produced by the light source10is covered. In practice, the coating15may cover the entire glass surface of the transparent panel20.

FIG. 2ais a cross-sectional side view of the structure along line2—2′ ofFIG. 1according to a first embodiment of this invention. As shown inFIG. 2a, the coating15on the transparent panel20is formed using a single material having a variable thickness along the long axis. In other words, the thickness of the coating15near the middle is greater than the thickness along the two sides. Light transparency of the coating15has a characteristic curve shown in FIG.3a. In fact,FIG. 3ais a graph showing the variation of light transparency along the long axis of the transparent panel due to the presence of the coating.

FIG. 3bis a graph showing the variation of brightness level along the light axis of the light source. After light from the light source10is passed through the transparent panel20with a single-layered coating15, variation of brightness level along the long axis is shown in FIG.3c. As shown inFIGS. 3b and 3c, brightness level after passing through the transparent panel20is much flatter and wider than the brightness level along the light axis of the original light source10. Since the optical sensor relies heavily on brightness contrast to carry out detection, the brightness curve shown inFIG. 3cis more suitable for image detection than the curve shown in FIG.3b.

FIG. 2bis a cross-sectional side view of the structure along line2—2′ ofFIG. 1according to a second embodiment of this invention. As shown inFIG. 2b, the coating15on the transparent panel20is actually comprised of three different coatings15a,15b and15c, each having a different light transparency but identical thickness. All the coatings15a,15b and15c together produce a light transparency curve shown in FIG.3a. In other words, light transparency in the middle is lower relative to the sides.

FIG. 3bis a graph showing the variation of brightness level along the light axis of the light source. After light from the light source10is passed through the transparent panel20with multiple coatings15a,15b and15c, variation of brightness level along the long axis is shown in FIG.3c. As shown inFIGS. 3b and 3c, brightness level after passing through the transparent panel20is much flatter and wider than the brightness level along the light axis of the original light source10. Since the optical sensor relies heavily on brightness contrast to carry out detection, the brightness curve shown inFIG. 3cis more suitable for image detection than the curve shown in FIG.3b.

Note that the number of coatings on the transparent panel20is not limited to three. To fit a particular design, the number of coatings can increase and the type of material forming the coatings can vary.

In summary, the greatest benefit of this invention is the reduction of brightness variation of a light source without the need to produce new components. In fact, only minor modifications of a single component are needed.