Image reading apparatus
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image reading apparatus applicable to, say, a facsimile, OCR, etc. 
     2. Description of Prior Art 
     An image reading apparatus reads information such as characters and figures on a document and converts it to an electric signal. The typical construction of a conventional image reading apparatus is shown in FIG. 1. Referring to FIG. 1, 31 is a document, 32 and 33 are transport rollers connected to a driving source for conveying the document 31, 34 is a fluorescent lamp (light source) for illuminating the document 31 when transmitted to the reading position, and 35 is a back plate facing to the fluorescent lamp 34 with the document 31 therebetween. 361, 362 and 363 are reflection mirrors which lead light reflected from the document 31 to a CCD (charge coupled device) image sensor 38 described later. 37 is a condenser lens through which the light reflected by the mirror 363 passes. 38 is a CCD image sensor which is mounted on a base 39 to receive light reflected from the document 31 and transmitted through the condenser lens 37 for conversion to an electric signal. 
     According to the prior art as mentioned above, the optical system (comprising the fluorescent lamp 34, the reflection mirrors 361, 362 and 363 and the condenser lens 37) is inevitably complicated in construction and large in size, resulting in a large image reading apparatus. In addition, the set of mirrors 361, 362 and 363 and the condenser lens 37 in the optical system tend to become displaced, affecting the reading performance adversely. 
     OBJECT OF THE INVENTION 
     In view of the above problems of the conventional image reading apparatus, an object of the present invention is to provide an image reading apparatus which contains a compact optical system to make the entire apparatus small. 
     Another object of the present invention is to provide an image reading apparatus in which an entire optical system is formed into an integral unit so as to prevent displacement of a lens system and to effect better reading performance. 
     Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     SUMMARY OF THE INVENTION 
     To achieve the above objects, an image reading apparatus of the present invention includes an optical unit comprising a light source base, a lens and a sensor base all mounted on a common optical system mounting member. An array of light emitting elements is mounted as a light source on the light source base. The lens is mounted in such a manner that an end of the lens is positioned adjacent the document surface, to be irradiated the other end being adjacent an image sensor mounted on the sensor base, thereby leading light reflected from the document to the image sensor. According to the present invention, a small image reading apparatus can be realized due to the compact unit construction of the optical system. Besides, the unit construction of the optical system makes it easy to mount the light emitting element array, the lens and the image sensor in the apparatus and prevents the displacement of these components, thus facilitating assembling operation and effecting better reading performance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: 
     FIG. 1 is a schematic sectional view of the conventional image reading apparatus; 
     FIG. 2 is a sectional view of the reading section of the image reading apparatus of the present invention; and 
     FIG. 3 is an exploded view of the optical unit of the image reading apparatus of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 is a sectional view of the reading section of the image reading apparatus of the present invention. 1 is a document on which information such as characters and figures is printed. 2 and 3 are transport rollers for transmitting the document 1 to the reading position. The transport rollers 2 and 3 are connected to a driving source. 4 is an optical unit mounted at the reading position between the transport rollers 2 and 3. The optical unit 4 contains a LED array 5 as a light source, a self focus lens 6 and an image sensor 7 which receives light reflected from the document 1 and led through the self focus lens 6 and converts the light to an electric signal. The optical unit 4 is housed in a unit case 8 mounted in the apparatus. The optical unit 4 is fixed to the bottom of the unit case 8 via leaf springs 9 (See FIG. 3.) provided on both ends of the optical unit 4, so that the optical unit 4 is allowed to move slightly in the vertical direction (along the arrow &#34;A&#34;). 10 is a back roller facing to the optical unit 4 with the document 1 therebetween. The optical unit 4 is forced toward the back roller 10 by the leaf springs 9. 
     The construction of the optical unit 4 is described in further detail referring to FIG. 3. The optical unit body 4 comprises a rectangular block whose length covers at least the width of the document 1. The optical unit block contains steps 4A formed in the top of the block for mounting a cover glass 11 horizontally, a groove 4B for mounting a light source base 12 on which the LED array 5 is set, and a slot 4C formed vertically through the optical unit block for mounting the self focus lens 6 lead the reflected light from the document 1 to the image sensor 7. One side 12a of the light source base 12 is linear. The LED array 5 is mounted in parallel to the linear side 12a of the light source base 12. A radiation plate 13 is mounted on the back of the base 12. The light source base 12 is inserted in the groove 4B of the unit body 4 with the LED array 5 faced upwardly. Since the groove 4B has a slant, the light source base 12 is inclined when set in the groove 4B, permitting the LED array 5 to illuminate a document obliquely from the lower side. The self focus lens 6 is of a rectangular shape and converges the light reflected from the document 1 onto the image sensor 7. The self focus lens 6 is set virtually perpendicular in the optical unit body 4 when inserted into the mounting hole 4C. The cover glass 11 is set in the upper mounting steps 4A of the optical unit body 4, protecting the LED array 5 and the self focus lens 6. A filter 11A is formed by evaporation on the surface of the cover glass 11. 
     The image sensor 7 comprising a CCD is mounted on a sensor base 14. The sensor base 14 is mounted on the bottom wall of the optical unit body 4, allowing the image sensor 7 to be kept in contact with an end of the self focus lens 6. Therefore, the upper end of the self focus lens 6 is made in contact with the document 1 via the cover glass 11, and the lower end in contact with the image sensor 7 on the sensor base 14. 
     Thus the cover glass 11, the light source base 12, the self focus lens 6 and the sensor base 14 are mounted integrally in the optical unit 4 which is fixed to the inner bottom wall of the unit case 8 by the leaf springs 9. In this embodiment of the present invention, the light source base 12 of the optical unit 4 is provided with a radiation plate 13. The radiation plate may be omitted if the optical unit itself is made of radiating material. 
     In the image reading apparatus of the present invention shown in FIG. 2, the document 1 to be read is transmitted by the transport rollers 2 to the reading position between the optical unit 4 and the back roller 10. Since the optical unit 4 is movable vertically due to the leaf springs 9, the document 1 is easily sent into the reading position between the optical unit 4 and the back roller 10 by the transport roller 2. Due to the compression force of the leaf springs 9, the cover glass 11 on top of the optical unit 4 depresses the document 1 against the back roller 10, making the read area of the document 1 flat. The light from the LED array 5 scans the flat surface of the document 1 optically through the cover glass 11. The light reflected from the document 1 passes through the cover glass 11 into the self focus lens 6 which condenses and leads the reflected light to the image sensor 7 made in contact with the lower end of the self focus lens 6. The image sensor 7 converts the incident light to an electric signal and outputs it. Thus, information on the document 1 is read sequentially as the document 1 is moved. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.