Apparatus for Reading an Original Surface by Illuminating It With a Slit-Like Beam

1. Field of the Invention

This invention relates to a compact reading apparatus for use for the reading of a facsimile apparatus or the like.

2. Description of the Prior Art

As one of the reading systems for a facsimile apparatus or the like, there is a system in which an original is intermittently moved in a secondary scanning direction, namely, in the direction of the shorter side of a slit, and a reading scanning head having a solid state image pick-up element such as CCD having the array direction thereof set in parallelism to the secondary scanning direction is reciprocated in a primary scanning direction, namely, in the lengthwise direction of the slit orthogonal to the secondary scanning direction, whereby an original image is read for each of a plurality of lines corresponding to the number of arrays of the solid state image pick-up element.

The illuminating system in such reading apparatus must effect, for example, illumination of 1/8 mm at GIII of CCITT standard and 1/6 mm at GII in the primary scanning direction and illumination of a length corresponding to the number of arrays of the solid state image pick-up element in the secondary scanning direction, namely, linear illumination elongated in the secondary scanning direction.

An apparatus disclosed in Japanese Laid-open Patent Application No. 74621/1979 is known as such reading apparatus, and this reading apparatus is shown in FIG. 1 of the accompanying drawings. In FIG. 1, reference numeral 1 designates an original which is intermittently fed in the direction of arrow 2 (secondary scanning direction). Reference characters 3a and 3b denote rod-like illuminating light sources which illuminate the slit width areas 6a-6b of the original 1, and an image element of the slit width areas 6a-6b is projected upon a solid state image pick-up element 5 arranged in the secondary scanning direction by an imaging lens 4.

The illuminating light sources 3a, 3b, the imaging lens 4 and the solid state image pick-up element 5 together constitute a reading head 7 which is reciprocated in the direction of arrow 8 (primary scanning direction). Thus, by one reciprocal movement of the reading head 7, reading-scanning of a plurality of lines is accomplished at the same time.

However, this apparatus has suffered from a problem that movement of the light sources 3a and 3b reduces the life thereof and unless the light sources are firmly fixed to the reading head, the positions of the light sources become deviated during movement of the reading head, thus resulting in irregular illumination.

To overcome such disadvantage, a reading apparatus in which the light source is fixed as shown in FIG. 2 of the accompanying drawings has heretofore been proposed. In FIG. 2, the original 1 is intermittently fed in the direction of arrow 2 (secondary scanning direction). Reference numeral 9 designates an illuminating light source such as a fluorescent lamp fixedly provided to effectively illuminate the entire lengthwise area of the slit, and reference numeral 10 denotes a fixed reflecting mirror for illuminating the entire area of the slit width areas 6a-6b of the original 1 in the primary scanning direction. An image element of the slit width areas 6a-6b of the original 1 in the primary scanning direction is projected upon a solid state image pick-up element 5 set in the secondary scanning direction, by an imaging lens 4. The imaging lens 4 and the solid state image pick-up element 5 together constitute a reading head 11 which is reciprocated in the direction of arrow 8 (primary scanning direction). However in the reading apparatus shown in FIGS. 1 and 2, the illuminating light source always illuminates the entire area of the slit width areas 6a-6b in the primary scanning direction and therefore, the light of the light source is not efficientl utilized and irregular illumination occurs in the array direction of the solid state image pick-up element.

Further, U.S. Pat. No. Re 29,017 discloses an optical system in which a point source of light is fixed an illuminating light beam is made into a substantially rectangular parralel light beam in a cross-section perpendicular to the optical axis and finally linear illumination is effected.

In this system, the light source is fixed to thereby prevent reduced life thereof, but in order to obtain an illuminating light source having a substantially rectangular cross-section, it has been necessary to use a mirror of complicated configuration called a parabolic mirror having a refractive power in two directions in a cross-section perpendicular to the optical axis.

It is an object of the present invention to provide a reading apparatus provided with an illuminating optical system which can illuminate an original surface efficiently and without irregularity of illumination with a light for illuminating the original being fixed and which can structurally be readily realized. This illuminating optical system is particularly suitable for a reading apparatus of the type in which a line sensor such as a solid state image pick-up element having the array direction thereof provided in parallelism to a secondary scanning direction in which an original is intermittently moved is moved in a primary scanning direction orthogonal to the secondary scanning direction to thereby read the image of the original.

In the reading apparatus according to the present invention, the above object is achieved by forming the illuminating system by a linear light source secured in parallelism to the secondary scanning direction, a fixed cylindrical parabolic mirror having the center of the linear light source as its focal line position and having a generating line in the secondary scanning direction, and a cylindrical scanning mirror movable in the primary scanning direction to scan the original surface and having the generating line direction thereof in the secondary scanning direction. That is, the light beam emitted from the linear light source is made into a light beam collimated in one direction by the cylindrical parabolic mirror and is directed toward the cylindrical scanning mirror. This cylindrical scanning mirror is moved in the primary scanning direction along the original surface and, of the components of the light beam from the cylindrical parabolic mirror, the parallel component is imaged on the original surface by the cylindrical scanning mirror while, at the same time, the original surface is scanned by a slit-like light beam with movement of the cylindrical scanning mirror.

In the above-described illuminating system applied to the reading apparatus of the present invention, of the light beam components which arrive at the original surface, the light beam component in the generating line direction of the cylindrical parabolic mirror and cylindrical scanning mirror is not subjected to any refracting action and therefore, of the light beam which arrives at the original surface, the light beam of the component in the secondary scanning direction is a divergent light beam. Accordingly, where the original surface is long in the primary scanning direction, it sometimes happens that the quantity of light reaching from the light source is varied by the position of the original surface in the primary scanning direction. In such cases, a reflecting plate is provided near the cylindrical scanning mirror and means for detecting the light beam from this reflecting plate is provided to detect a signal, and an electric circuit is provided for causing the detection signal to be fed back to a light source input power source to render the illumination on the original surface constant, whereby there is provided a reading apparatus capable of effecting more reading.

The invention will become more fully apparent from the following detailed description thereof taken in conjunction with the accompanying drawings.

FIGS. 1 and 2 show the reading apparatus according to the prior art.

FIG. 3 shows a first embodiment of the reading apparatus according to the present invention.

FIG. 4 is a cross-sectional view of the FIG. 3 apparatus taken in the primary scanning direction.

FIG. 5 is a cross-sectional view of a second embodiment of the reading apparatus according to the present invention taken in the primary scanning direction.

FIG. 6 shows a third embodiment of the reading apparatus according to the present invention.

FIG. 3 shows a first embodiment of the present invention.

A linear light source 12 having a sufficient length to illuminate slit width areas 6a-6b and secured in parallelism to the direction of arrow 2 (secondary scanning direction) is partly surrounded by a parabolic mirror 13 which is cylindrical with the position thereof as the focal line position, namely, which has no refractive power in the secondary scanning direction or, in other words, has a generating line in the secondary scanning direction. The light emitted from the linear light source 12 is reflected by the parabolic mirror 13, and is reflected by an in-mirror lens 14 which is moved with an imaging lens 4 and a solid state image pick-up element 5 and which is cylindrical, namely, which has no refractive power in the secondary scanning direction, and travels on the slit width areas 6a-6b while being imaged substantially linearly. A cylindrical parabolic mirror may be used instead of the cylindrical in-mirror lens 14.

FIG. 4 shows the cross-section of the FIG. 3 apparatus in the primary scanning direction. The light from the linear light source 12 secured at the focal line position of the fixed cylindrical parabolic mirror 13 is reflected by the parabolic mirror 13 and made into a parallel light beam in this cross-section, and is reflected by the cylindrical in-mirror lens 14 moved in the direction of arrow 8 (primary scanning direction) and projected in a slit-like form upon an original surface 1 which is the focal line position thereof. The illuminated slit area on the original surface 1 is projected upon the solid state image pick-up element 5 by the imaging lens 4.

FIG. 5 shows a second embodiment of the reading apparatus according to the present invention, and like FIG. 4, it is a cross-sectional view in the primary scanning direction. In the apparatus shown in FIG. 5, the cylindrical in-mirror lens 14 is replaced by the cylindrical parabolic mirror. As shown in FIG. 5, the parallel light beam reflected by the fixed cylindrical parabolic mirror 13 is reflected by the cylindrical parabolic mirror 15 moved in the direction of arrow 8 (primary scanning direction) and is projected in a slit-like form upon the original surface 1 which is the focal line position thereof.

The light beam spreads in a plane perpendicular to the cross-section of FIGS. 4 and 5, namely, in the direction of the shorter side of the slit (secondary scanning direction, but since the slit width is slight, any reduction in illumination offers not so great a problem depending on the length of the scanning area. However, where the length of the scanning area in the primary scanning direction is great, namely, for an original of a large size, any reduction in illumination may lead to a problem.

FIG. 6 shows an embodiment of the reading apparatus which has overcome the difficulty of reduced illumination. As shown in FIG. 6, during the scanning in the direction of arrow 8, namely, in the primary scanning direction, a reference reflection plate 16 is provided near a cylindrical in-mirror lens 14, and a light-receiving element 17 for detecting the light reflected by the reference reflection plate through the imaging lens 4 is further provided near the solid state image pick-up element 5, and these are constructed as a part of the reading head and moved in the direction of arrow 8 (primary scanning direction) with the imaging lens 4, the solid state image pick-up element 5 and the cylindrical in-mirror lens 14. During the scanning, part of the illuminating light beam reflected by the reference reflection plate 16 is projected upon a light-receiving element 17 adjacent to the solid state image pick-up element 5 through the imaging lens 4, and the output from the light-receiving element 17 is amplified by an amplifier 18 and compared with a reference voltage 19, and fed back to the base of a transistor 22 as a control signal passed through an error amplifier 20, and the input of an applying power source 21 to the linear light source 12, namely, the applied voltage or current is controlled, whereby the illumination on the original surface can always be maintained constant during the movement in the primary scanning direction.

The reference reflection plate 16 may be a fixed reflection plate which is long in the primary scanning direction.

The light-receiving element 17 may be embedded onto the solid state image pick-up element 5.

Thus, according to the present invention, there can be provided a compact reading apparatus for use the reading of a facsimile apparatus or the like .