Camera-based scanners are well established tools for bar code and symbol data entry in retailing and other industries. For example, a camera-based scanner may be used to read universal product code (“UPC”) bar codes and reduced space symbology (“RSS”) bar codes. Camera-based scanners may also be used to read non-UPC bar codes such as Code 3, Code 128, and two-dimensional bar codes.
Conventional camera-based scanners generally have a limited depth-of-field capable of acquiring a focused image at a single fixed distance. An image scanner capable of focusing at more than one distance would be advantageous to improve the ease of reading data symbols and decrease the time required to read each data symbol.
The present invention relates to a scanner system and method for imaging an object (e.g., a data symbol, a bar code) which includes an illumination system, a chromatically aberrant lens system and an imaging sensor. The illumination system generates light of first and second wavelengths. The lens system has a first focal distance for the first wavelength light and a second focal distance for the second wavelength light. The sensor receives, via the lens system, light reflected from an object to be imaged. The sensor generates an image of the object by assembling first wavelength light focused thereon when a distance of the object from the lens system is the first focal distance and second wavelength light focused thereon when the distance of the object from the lens system is the second focal distance.
The present invention is directed to a camera-based scanner (e.g., imager-chip-based scanner) which is capable of reading symbols or encoded data and, in particular, a imaging scanner capable of focusing at two or more distances simultaneously. The present invention may be useful for reading one-dimensional and two-dimensional bar codes.
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The lenses of the lens system 302 may be manufactured of a material with a low Abbe number. As one of ordinary skill in the art will understand, the Abbe number (V) of a material (e.g., an optical medium) is a measure of the material's dispersion or variation of refractive index with wavelength. Low dispersion materials generally have high values of V. The Abbe number is also directly proportional to the chromatic quality of a lens. In the exemplary embodiment, the lens system 302 may be manufactured of an extra dense flint glass (e.g., SF5 glass) with an Abbe number of less than thirty-five (35), e.g., twenty (20).
The system 300 includes an imaging sensor 310. The imaging sensor may be, for example, a solid-state imaging array. In the exemplary embodiment, the imaging sensor 310 is positioned approximately 5.3096 mm from the lens system 302. The imaging sensor 310 may be a color sensor capable of acquiring images in multiple object planes simultaneously. In the exemplary embodiment, the imaging sensor 310 is a KAC-1310 RGB CMOS Imaging sensor available from Kodak Corporation. However, any similarly capable imaging sensor 310 may be used.
The imaging sensor 310 may include a color filter 312. The color filter 312 may be, for example, a Bayer RGB color filter including an array of red (R), green (G), and blue (B) filters (e.g., 314, 316) covering individual pixels. An exemplary embodiment of a color filter 312 (e.g., a Bayer RGB color filter) is shown schematically in
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The illumination system 320 preferably includes at least two light sources. As one of ordinary skill in the art will understand, any number of light sources may be used depending on the number of focal lengths desired. In the exemplary embodiment, the illumination system includes three light sources, e.g., 322, 324, and 326. Each light source 322/324/326 and may provide light at a different wavelength than the other light sources. For example, the light source 322 may provide red light with a wavelength of approximately 635 nm, the light source 324 may provide green light with a wavelength of approximately 530 nm, and the light source 326 may provide blue light with a wavelength of approximately 470 nm.
The system 300 may be designed to acquire images (e.g., read a data symbol) at any distance or distances from lens system 302. For example, the lens system 302 may have three different focal lengths corresponding to the different wavelengths of light provided by each light source 322/324/326. Light from each light source 322/324/326 may be reflected off object planes (e.g., 350, 352, 354) situated at distances corresponding approximately to the designed focal lengths. The reflected light may then be received by the imaging sensor 310 via the lens system 302.
In the exemplary embodiment, the system 300 is optimized to acquire sharp images at 155 mm (e.g., object plane 350) using the 470 nm blue light, at 257 mm (e.g., object plane 352) with the 530 nm green light, and at 829 mm (e.g., object plane 354) with the 635 nm red light. Therefore, as a data symbol is moved between three different distances from the lens system 302, its image may be focused in the different object planes 350/352/354 (i.e., at the predetermined distances). Likewise, the lens system 302 may be moved (i.e., rather than the data symbol) between three different distances from the data symbol and the image of the data symbol focused in the different object planes 350/352/354. The different colors (i.e., wavelengths) of the light received by the imaging sensor 310 may be separated by the color filter 312 of the imaging sensor 310 to generate an image of the data symbol.
The imaging scanner 600 may be used to read or decode a data symbol, e.g. a bar code 660. For example, the illumination system 620 may direct a portion of light at a first distance, a portion of light at a second distance, and a portion of light at a third distance. In the present example, the distances correspond to a first object plane 650, a second object plane 652, and third object plane 654 respectively. The bar code 660, or any other data symbol known to those in the art, may lie in one or more of the object planes 650/652/654. The imaging sensor 610 of the imaging scanner 600 may acquire a focused image of the bar code 660 when it is approximately within any one of the object planes 650/652/654. The imaging sensor 610 may then separate the acquired images, preferably with minimal superposition. The processor (not shown) of the imaging scanner 600 may then decode or read the image(s) of the bar code 660.
As one of ordinary skill in the art will understand, a conventional imaging scanner may have only one focal length, i.e. only one optimal distance at which a sharp image of a data symbol may be acquired. The present invention includes at least two, and preferably three, focal lengths at which focused images may be acquired simultaneously. Therefore, the imaging scanner 600 according the present invention need not be positioned at a single optimal distance to scan a data symbol. The imaging scanner 600 according to the present invention may provide for quick and accurate scanning.
In step 701, the imaging scanner 600 is arranged to project light towards and receive light from a plurality of object planes (e.g., object planes 650/652/654). For example, the imaging scanner 600 may be directed towards one or more data symbols (e.g., bar code 660). The imaging scanner 600 may be approximately situated at one of any number of known distances (e.g., focal lengths) from the bar code(s) 660. However, as discussed above the imaging scanner 600 according to the present invention may have multiple design focal lengths corresponding to distances for optimal image scanner performance. Therefore, precise situation of the imaging scanner 600 with reference to the data symbol(s) may not be necessary.
In step 703, light is projected on at least one of the object planes 650/62/654 using the illumination system 620. As described above, the illumination system 620 preferably includes at least two light sources. However, the illumination system 620 may include additional light sources if additional focal lengths are desired. For example, the illumination system 620 may project multiple wavelengths of light from a first light source 622, a second light source 624, and a third light source 626. Each light source may provide light at a color that corresponds to a peak response wavelength of the imaging sensor 610. Illumination with sharp bands at these wavelengths is preferable to produce the most distinct image separation. For example, the light source 622 may provide red light with a wavelength of approximately 635 nm, the light source 624 may provide green light with a wavelength of approximately 530 nm, and the light source 626 may provide blue light with a wavelength of approximately 470 nm.
In step 705, light reflected from at least one object plane is received by the imaging sensor 610 via the lens system 602. For example, light originating from the light sources 622, 624, and 626 may be reflected off one or more of the object planes 650,652, and 654, respectively. A bar code 660 may lie in one or more of the object planes 650/652/654. The reflected light at differing wavelengths may be received by the imaging sensor 610 via the lens system 602.
In a step 707, a color filter (e.g., color filter 312) of the imaging sensor 610 separates the reflected light having originated from one or more of the light sources 622/624/626. The imaging sensor 610 then generates an image of the data symbol (e.g., bar code 660). For example, the imaging sensor 610 may generate a digital and/or analog output representing each pixel in the imaging sensor 610.
In step 709, a processor of the imaging scanner 600 may decode or read the image(s) of the date symbol. For example, the processor may decode data in the bar code 660 using the images obtained from the object planes 650/652/654.
While specific embodiments of the invention have been illustrated and described herein, it is realized that numerous modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.