DOCUMENT ILLUMINATING APPARATUS

Abstract: A document illuminating apparatus (10) is used to illuminate a portion of a document (14) at a scanning line (20) as the document is moved in a scanning plane (18). First and second light arrays (30,32) are positioned symmetrically with respect to a line (24) extending perpendicularly to the scanning line (20). Each of the first and second arrays (30,32) in­ cludes light sources (A, B, and C) each having different optical radiation and arranged in a periodic, repeating sequence ABCA to provide a superposition of light in both spatial and spectral domains at the scanning line. Light emtting diodes, for example, may be used as the light sources.

Description: This invention relates to a document illumination apparatus in general, and in particular, it relates to an illumination apparatus which is especially useful for evenly illuminating a narrow scanning line used, for example, in document imaging and photocopying apparatuses. Currently, arrays of green light emitting diodes (LEDs) are used for illuminating documents in some facsimile machines. These LEDs typically emit light at a peak wavelength of 565 nanometers with a spectral width of 60 nanometers. For black and white documents with a sufficiently high contrast, using such green LEDs produces good document images. However, for coloured documents, the narrow-spectrum light source from the green LEDs mentioned may not be suitable. For example, with the LEDs mentioned, a light colour background on a document may appear darker than expected on an image of the document whereas a dark character printed in a certain colour on the document may turn out lighter than expected on the image. As a consequence, the contrast between the character and its background will be significantly reduced. In an extreme case, this reduction of contrast can lead to a loss of information in the final electronic image. The arrangements of Patents JP-A-6189764 and JP-A-5843656, go some way to alleviate this problem. They describe two parallel linear light arrays positioned to illuminate a scanning line. One array consists of green light emitting diodes and the other array consists of light emitting diodes of a different colour, viz. red in the first Japanese abstract and yellow in the second Japanese abstract. A disadvantage of the arrangements described in the above Japanese abstracts is that they are limited in the manner in which they can be adapted for different purposes, because of their use of only two colours. It is an object of the present invention to provide a document illuminating apparatus which is improved as regards to adaptability for use with different types of documents. Thus, according to the invention, there is provided an apparatus for illuminating a line, including light sources of different spectral characteristics arranged in first and second linear light source arrays, and positioning means for positioning said first and second linear light source arrays so as to direct the associated optical radiations of said light sources at said line to be illuminated, characterized in that each of said linear light source arrays comprises light sources of three different spectral characteristics, said light sources being arranged in a periodic, repetitive sequence in which the three spectral chacarcteristics follow each other always in the same order. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a general diagrammatic view, in perspective, of a document illuminating apparatus according to this invention; Fig. 2 is a diagrammatic view, showing how light sources A, B, and C in a light array are arranged in a periodic, repeating sequence ABCA; Fig. 3 is a view similar to Fig. 2, showing how first and second light arrays are offset relative to each other in a direction along the scanning line of the apparatus; Fig. 4 is a plan view, in diagrammatic form, of a second embodiment of this invention which uses light concentrators for directing light at the associated scanning line; Fig. 5 is a side view, in perspective, of the embodiment shown in Fig. 4; Fig. 6 is a cross-sectional view, in diagrammatic form, of the light concentrators shown in Figs. 4 and 5; and Fig. 7 is a diagrammatic view, in perspective, of another embodiment of the document illuminating apparatus of this invention. Fig. 1 is a general diagrammatic view, in perspective, of an apparatus 10, according to this invention, for illuminating a scanning line in a scanning plane. While the apparatus 10 may be used for many applications in which a narrow strip of uniform illumination is required, as in facsimile, photocopying, machine vision, robotics, and industrial inspection applications, the particular apparatus 10 shown relates to an apparatus for imaging documents, like checks, in a financial institution, like a bank. The apparatus 10 includes a document track 12 having upstanding side walls 12-1 and 12-2 which are spaced apart as shown in Fig. 1 to receive a document 14 therebetween. The document track 12 and the document transport 16 provide the means for moving the document 14 in a scanning plane (shown by the dashed rectangle 18) which includes a scanning line 20 i.e. the line to be illuminated. In the embodiment described, the scanning line 20 is vertically oriented and is perpendicular to the movement of the document 14 in the document track 12, as indicated by arrow 22. The apparatus 10 also includes an optical axis 24 which is positioned perpendicularly to the scanning line 20. A lens system 26 is used to direct light reflected from the document 14 at the scanning line through the lens system 26 to the imaging sensor 28. Two light arrays 30 and 32 (Fig. 1) are used to illuminate the scanning line 20, and they are part of the apparatus 10. In the embodiment described, the light arrays 30 and 32 are positioned symmetrically with respect to the optical axis by conventional positioning means such as brackets 30-1 and 32-1. The light arrays 30 and 32 are also positioned at an angle theta (ϑ) with respect to the optical axis 24, which angle is about 30 degrees. The function of the light arrays 30 and 32 is to provide light at the scanning line 20 which results from both spatial and spectral superposition. Each light array 30 and 32 has light sources A, B, and C which are arranged in a periodic, repeating sequence ABCA as shown best in Fig. 2. Each of the light sources A, B, and C has a different spectral characteristic so that the outputs of the light arrays 30 and 32, when directed at the scanning line 20, will produce a resultant spectral distribution of optical radiation which is the sum of the spectral distribution of the optical radiations from the light sources A, B, and C. In other words, the resultant spectral distribution will be the same for all points along the scanning line 20. In this regard the light arrays 30 and 32 are offset relative to each other in a direction which is along the scanning line 20 so that if placed in side by side relationship, they would have the relationship shown in Fig. 3. Notice that any one light source in one array would be positioned between two different light sources in the opposed array. For example, the topmost light source A (as viewed in Fig. 3) in light array 32 is positioned between the light sources B and C in light array 30. Correspondingly, the bottommost light source B in light array 30 is positioned between the light sources C and A in light array 32. As a consequence, the light intensity and the spectral content at any given point along the scanning line 20 are due to the complementary light sources A, B, and C. As a result, the illumination pattern for a document 14 (Fig. 1) which is illuminated at the scanning line 20 will have the following characteristics: 1. There will be a uniform light intensity over the entire scanning line 20; and 2. For each point along the scanning line 20, the resultant spectral distribution of the optical radiation thereat will be the sum of the spectral distributions of the light sources A, B, and C. Another feature of this invention is that the light sources A, B, and C are selected to have the appropriate spectral distributions for the particular application in which the apparatus 10 is used. For example, when processing financial documents 14, like checks, the light sources A, B, and C may be green, yellow, and red LEDs, respectively. These are conventional LEDs, with each LED having its own associated focusing lens, like lens 34, shown only schematically for light source B in Fig. 1. The optical radiations from the LEDs have the following approximate ranges of wavelengths: Green = 525 - 610 nm; Yellow = 540 - 640 nm; and Red = 575 - 705 nm. Based on the commercial availability of colored LEDs, the principles of this invention could be expanded to include other colors of LEDs, such as blue, green, and red, for example. With regard to the discussion of the light arrays 30 and 32, it was previously stated that each of the light sources A, B, and C had its own associated focusing lens 34 to direct light at the scanning line 20. Naturally, in this type of system, the lens system 26 directs the light reflected from a document 14 along the scanning line 20 to a small conventional imaging sensor 28 which itself includes an array of light sensors with each sensor representing a "pixel" or picture area or element at the scanning line 20. The principles of this invention can also be extended to include an apparatus in which the light sources A, B, and C have no integral focusing lenses. In this regard, Figs. 4, 5, and 6 show a second embodiment of the invention in which the apparatus utilizes an external light concentrator to direct light from the light arrays to the scanning line. The apparatus 36 shown in Figs. 4, 5, and 6 is generally similar to the apparatus 10 (Fig. 1) already described; consequently, the same reference numerals used in Fig. 1 will be used to describe identical parts in Figs. 4, 5, and 6. Figs. 4, 5 and 6 are also schematically presented so as to further simplify these figures. The principal difference between the apparatus 36 and the apparatus 10 is that the first and second light arrays 38 and 40 do not have a focusing lens 34 (Fig. 1) associated with each of the light sources A, B, and C in the light arrays 30 and 32. In addition, the apparatus 36 includes a light concentrator 38-1 for the light array 38, and similarly, a light concentrator 40-1 is included for the light array 40. The light sources in the light arrays 38 and 40 are arranged in the same periodic, repeating sequence ABCA as discussed in relation to apparatus 10, and they may be comprised of the various LEDs mentioned with regard to apparatus 10. The light concentrators 38-1 and 40-1 are identical; consequently, only a description of light concentrator 38-1 will be given. The light concentrator 38-1 is a cylindrical reflector whose cross section is a portion of an ellipse. For example, Fig. 6 shows a cross-sectional view of the light concentrators 38-1 and 40-1. Notice that the cross section of the light concentrator 38-1 is a portion of an ellipse 42 shown in dashed outline. The major axis 44 of the ellipse 42 is positioned at the angle theta (ϑ) to the optical axis 24. The light array 38 is positioned at one of the focal points F1 of the ellipse 42 while the scanning line 20 is positioned at the other focal point F2. The light array 38 is positioned so that it extends in a direction along the scanning line 20 and is parallel thereto. The individual light sources A, B, and C of the light array are arranged in a periodic, repeating sequence like that shown in Fig. 2, and the light sources A, B, and C are positioned to direct their outputs at the light concentrator 38-1. Light from the light concentrator 38-1 is then directed at the scanning line 20 (as represented by focal point F2) as shown by light directing arrows 46 and 48, for example. The light concentrators 38-1 and 40-1 have conventional, highly reflective surfaces to direct the light as described, and they are adjustably positioned in a frame 50 of the apparatus 36 by a bracket 52 (Fig. 5). The focal point F2 (Fig. 6) is a common focal point for ellipses 42 and 54. Notice also from Fig. 6 that the light concentrators 38-1 and 40-1 have cross sections which are not symmetrical with respect to their associated major axes 44 and 56, respectively. Theis is an important feature of the light concentrators 38-1 and 40-1 and is due to a constraint which is dictated by the characteristics of LEDs when they are used as the light sources A, B, and C. Fig. 7 shows another embodiment of the imaging apparatus which is designated generally as 58. The apparatus 58 is identical to the apparatus 10 already described in relation to Fig. 1 except as will be described hereinafter; consequently, the same reference numerals will be used to describe similar parts of apparatus 58. The light arrays 30 and 32 direct light at the scanning line 20 located in the scanning plane 18 as previously described in relation to apparatus 10 (Fig. 1). The principal differences between the apparatus 58 and the apparatus 10 are that the apparatus 58 uses a self-focusing lens array 60 and a larger imaging sensor 62 instead of the conventional photographic lens system 26 and the smaller imaging sensor 28. The self-focusing lens array 60 is commercially available as part number SLA09 from NSG America, Inc., for example. An advantage of the apparatus 58 is that the size of the image formed by the lens array 60 is the same as the size of the scanning line 20.

Claims: An apparatus for illuminating a line (20), including light sources of different spectral chacacteristics arranged in first and second linear light source arrays (30,32), and positioning means (30-1,32-1) for positioning said first and second linear light source arrays (30,32) so as to direct the associated optical radiations of said light sources at said line to be illuminated (20), characterized in that each of said linear light source arrays comprises light sources of three different spectral characteristics, said light sources being arranged in a periodic, repetitive sequence in which the three spectral characteristics follow each other always in the same order. Apparatus according to claim 1, characterized in that said light sources are light emitting diodes. Apparatus according to claim 2, characterized in that said light sources are green, yellow, and red light emitting diodes respectively. Apparatus according to either claim 2 or 3, characterized in that each of said emitting diodes has an integral focusing lens (34) associated therewith. Apparatus according to any one of the preceding claims, characterized in that each of said first and second linear light source arrays (30,32) has the associated light sources arranged to form a linear array extending in parallel to said line to be illuminated (20). Apparatus according to claim 5, characterized in that said first and second linear light source arrays (30,32) are offset relative to each other in a direction along said line to be illuminated (20) such that, if said arrays were placed in side by side relationship, any one light source in one of said linear arrays would be positioned between light sources of the other two spectral characteristics in the other array. Apparatus according to either claim 5 or 6, characterized in that said first and second linear light source arrays (30,32) are positioned symmetrically on opposite sides of, and at a predetermined angle to, a line (24) extending perpendicularly to said line (20) to be illuminated Apparatus according to claim 7, characterized by a cylindrically-shaped reflector (38-1, 40-1) for each of said first and second linear light source arrays (38,40) for directing light from the associated first and second linear light source arrays (38,40) on to said line (20) to be illuminated Apparatus according to claim 1, characterized by a light sensitive array (28) positioned parallel to said line to be illuminated (20), and a lens system (26) for directing light reflected from a document (14) at said line to be illuminated (20) to said light sensitive array (28). Apparatus according to claim 9, characterized in that said lens system (26) includes a self-focusing lens array (60) whose length as measured along said line to be illuminated (20) is sufficient to produce an image at said light sensitive array (28) which is the same as the associated object present at said line (20) to be illuminated.

Inventors: LIM, TUAN-KAY
Applicants: NCR INTERNATIONAL INC.
Application year: 1988
Main classification: G02B26
IPC codes: H04N1, G03G15, G03B27