Patent Application
20100078483
Solid-state imaging systems or imaging readers, as well as moving laser beam readers or laser scanners, have both been used to electro-optically read targets, such as one-dimensional bar code symbols, particularly of the Universal Product Code (UPC) type, each having a row of bars and spaces spaced apart along one direction, as well as two-dimensional symbols, such as Code 49, which introduced the concept of vertically stacking a plurality of rows of bar and space patterns in a single symbol. The structure of Code 49 is described in U.S. Pat. No. 4,794,239. Another two-dimensional code structure for increasing the amount of data that can be represented or stored on a given amount of surface area is known as PDF417 and is described in U.S. Pat. No. 5,304,786.
The imaging reader includes an imaging module having a solid-state imager with a sensor array of cells or photosensors, which correspond to image elements or pixels in a field of view of the imager, and an imaging lens assembly for capturing return light scattered and/or reflected from the symbol being imaged, and for projecting the return light onto the sensor array to initiate capture of an image of the symbol. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electronic signals corresponding to a one- or two-dimensional array of pixel information over the field of view.
It is therefore known to use the imager for capturing a monochrome image of the symbol as, for example, disclosed in U.S. Pat. No. 5,703,349. It is also known to use the imager with multiple buried channels for capturing a full color image of the symbol as, for example, disclosed in U.S. Pat. No. 4,613,895. It is common to provide a two-dimensional CCD with a 640×480 resolution commonly found in VGA monitors, although other resolution sizes are possible.
In order to increase the amount of the return light captured by the imager, especially in dimly lit environments and/or at far range reading, the imaging module generally also includes an illuminating light assembly for illuminating the symbol with illumination light for reflection and scattering therefrom. When the imager is one-dimensional, i.e., linear, or is two-dimensional with an anamorphic field of view, the illumination light preferably is distributed along a short height, distributed pattern, also termed an illuminating or scan line, that extends lengthwise along the symbol. The distributed line pattern is typically generated by using a single, large light source, e.g., a light emitting diode (LED) sized in the millimeter range, and a single cylindrical lens.
Although generally satisfactory for its intended purpose, the use of the single large LED and the single cylindrical lens has been problematic, because the distributed line pattern typically has a height taller than that desired, does not have sharp edges, is dominated by optical aberrations, and is nonuniform in intensity since the light intensity is brightest along an optical axis on which the LED is centered, and then falls off away from the axis, especially at opposite end regions of the distributed line pattern. Also, the coupling efficiency between the LED and the cylindrical lens has been poor. Adding an aperture stop between the LED and the cylindrical lens will improve the sharpness (i.e., shorten the height) of the distributed line pattern, but at the cost of a poorer coupling efficiency and a dimmer distributed line pattern that, of Course, degrades reading performance.
In addition, the use of an imaging reader has been frustrated, because an operator cannot tell whether the imager, or the reader in which the imager is mounted, is aimed directly at the target symbol, which can be located anywhere within a range of working distances from the reader. The imager is a passive unit and provides no visual feedback to the operator to advise where the imager is aimed. To alleviate such problems, the prior art has proposed an aiming light assembly for an imaging reader. The known aiming light assembly utilizes an aiming light source for generating an aiming beam and an aiming lens for focusing the aiming beam as a visible aiming light line or pattern on the symbol prior to reading. The above-described illuminating light assembly can also serve as the aiming light assembly, in which case, the aiming pattern will suffer the same disadvantages described above for the distributed line pattern.
One feature of the present invention resides, briefly stated, in a module or an arrangement for generating a generally uniform distributed line pattern of light on a symbol to be read by image capture. The module or arrangement includes a light source for generating light along an optical axis in a light distribution having different extents along intersecting directions, e.g., the horizontal and vertical directions, generally perpendicular to the axis.
In one embodiment, the light source is an aiming light source for generating an aiming light pattern on the symbol. In another embodiment, the light source is an illumination light source for illuminating the symbol with an illumination light pattern. In either or both embodiments, the light source is a plurality of light emitting diode (LED) chips, each sized in the micron range and serving essentially as point sources, spaced apart from one another along the horizontal direction. Alternatively, the light source is a single, horizontally elongated, linear LED chip in a casing having a narrow vertical slit or opening. In either alternative, the light distribution is wide or long along the horizontal direction and extends lengthwise across and past the symbol, and is short and narrow along the vertical direction and extends for a small limited distance heightwise of the symbol.
The module or arrangement further includes a linear lens array having a plurality of compound curvature lenses spaced apart from one another along one of said directions, e.g., the horizontal direction, for receiving the light from the light source, and for optically modifying the light from the light source to generate the generally uniform distributed line pattern of light on the symbol. Each lens has a concave curvature, preferably an aspheric toroid, for diverging the light along said one horizontal direction that extends lengthwise along the symbol, and a convex curvature, again preferably an aspheric toroid, for collimating the light along the other of said directions, e.g., the vertical direction, that extends for a short, narrow, limited distance along a height of the symbol. The lenses are commonly molded of a one-piece construction, preferably of a light-transmissive plastic material. The one-piece construction advantageously has tapered end and side walls diverging apart from each other in a direction away from the light source to resist internal reflections within the linear lens array.
The module or arrangement still further includes a solid-state imager, such as a CCD or a CMOS, having an array of image sensors for capturing return light from the symbol over a field of view having different extents along the intersecting horizontal and vertical directions. The array is one-dimensional, i.e., linear, or is two-dimensional with an anamorphic field of view. The field of view of the imager generally matches the distributed line pattern of light on the symbol.
Each LED chip emits light, typically with a Lambertian intensity profile in which the intensity falls off along the horizontal direction as a function of the cosine angle. Hence, the LED chips are preferably spaced apart such that their intensity profiles overlap, thereby creating a more uniform intensity distribution along the horizontal direction. Since light emitted by one chip could interfere with light emitted by an adjacent chip, a baffle is preferably located between adjacent LED chips for resisting optical crosstalk that would otherwise corrupt the uniformity of the distributed line pattern. The baffles could also serve as an alignment aid when positioning the linear lens array relative to the light source.
One additional feature of the present invention resides in first coupling the LED chips to dome-shaped field lenses to reduce the conical angle of the emitted light prior to reaching the linear lens array. This feature will increase the light throughput. The LED chips could also be coupled to an array of parabolic reflective concentrators, again to constrain the conical angle and to increase the light throughput. The concentrators could also serve as the aforementioned baffles.
Yet another feature of the present invention resides in configuring the LED chips to emit light of different colors. For example, one group of the chips could emit green light which is more visible to a human eye, and thus is especially useful when the distributed line pattern is used as an aiming pattern; and another group of the chips could emit red light which is more visible to the imager due to increased sensitivity to red light, and thus is especially useful when the distributed line pattern is used as an illuminating pattern.
For a more integrated construction, a centrally located LED chip could be replaced with the imager, in which case, the associated lens on the linear lens array would either be replaced by an aperture, or with an imaging lens operative to project captured light onto the imager.
In accordance with this invention, the compound curvature lenses form the distributed line pattern as wide and short with sharp edges and as not dominated by optical aberrations. The intensity of the distributed line pattern is uniform with much less fall off away from the axis at opposite end regions of the distributed line pattern. Also, the coupling efficiency between the elongated light source and the elongated linear lens array is much improved, thereby increasing light throughput and enhancing reading performance.
The method of generating a generally uniform distributed line pattern of light on a symbol to be read by image capture is performed by generating light emitted from a light source along an optical axis in a distribution having different extents along intersecting directions generally perpendicular to the axis, spacing a plurality of compound curvature lenses apart from one another along one of said directions to form a linear lens array for receiving the light from the light source, and for optically modifying the light from the light source to generate the generally uniform distributed line pattern of light on the symbol, configuring each lens with a concave curvature for diverging the light along said one direction, configuring each lens with a convex curvature for collimating the light along the other of said directions, and capturing return light from the symbol with an array of image sensors of a solid-state imager over a field of view having different extents along the intersecting directions.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Reference numeral 30 in
As schematically shown in
An illuminating assembly is also mounted in the imaging reader and preferably includes an illuminator or illuminating light source 12, e.g., a light emitting diode (LED), and an illuminating lens assembly 10 to uniformly illuminate the symbol 38 with an illuminating light pattern. Details of the illuminating assembly, as best seen in
An aiming assembly is also mounted in the imaging reader and preferably includes an aiming light source 18, e.g., an LED, and an aiming lens assembly 16 for generating an aiming light pattern on the symbol 38. Details of the aiming assembly, as also best seen in
As shown in
In operation, the microprocessor 36 sends a command signal to energize the aiming light source 18 prior to reading, and also pulses the illuminating light source 12 for a short exposure time period, say 500 microseconds or less, and energizes and exposes the imager 24 to collect light, e.g., illumination light and/or ambient light, from a target symbol only during said exposure time period. A typical array needs about 33 milliseconds to acquire the entire target image and operates at a frame rate of about 30 frames per second.
One feature of the present invention resides, briefly stated, in a module or an arrangement for, and a method of, generating a generally uniform distributed line pattern of light on the symbol 38 to be read by image capture. The module or arrangement includes a light source 50, as shown in
In one embodiment, the light source 50 is the aiming light source 18 for generating the aforementioned aiming light pattern on the symbol 38. In another embodiment, the light source 50 is the illumination light source 12 for illuminating the symbol 38 with the aforementioned illumination light pattern. In either or both embodiments, the light source 50, as shown in
The module or arrangement further includes a linear lens array 52, as shown in
As previously noted, the imager 24 captures the return light front the symbol 38 over a field of view having different extents along the intersecting horizontal and vertical directions. The field of view of the imager 24 generally matches the distributed line pattern of light on the symbol 38.
Each LED chip 50a, 50b, 50c, 50d, 50e emits light, typically with a Lambertian intensity profile in which the intensity falls off along the horizontal direction as a function of the cosine angle. Hence, the LED chips are preferably spaced apart such that their intensity profiles overlap, thereby creating a more uniform intensity distribution along the horizontal direction. Since light emitted by one chip could interfere with light emitted by an adjacent chip, a light-obstructing baffle 62 has blocking portions preferably located between adjacent LED chips for resisting optical crosstalk that would otherwise corrupt the uniformity of the distributed line pattern. The baffle has a plurality of tapered openings each sized to match the numerical aperture of the linear lens array 52. The baffle 62 could also serve as an alignment aid when positioning the linear lens array relative to the light source. End baffles could also be employed.
One additional feature of the present invention resides in first coupling the LED chips to a microlens array 54, as shown in
Yet another feature of the present invention resides in configuring the LED chips to emit light of different colors. For example, one group of the chips, e.g., 50a and 50e, could emit green light which is more visible to a human eye, and thus is especially useful when the distributed line pattern is used as an aiming pattern; and another group of the chips, e.g., 50b and 50d, could emit red light which is more visible to the imager 24 due to increased sensitivity to red light, and thus is especially useful when the distributed line pattern is used as an illuminating pattern.
For a more integrated construction, a centrally located LED chip, e.g., 50c, could be replaced with the imager 24, in which case, the associated lens 52c on the linear lens array 52 would either be replaced by an aperture, or with the imaging lens 20 operative to project captured light onto the imager 24. The chips, the baffles and the imager are preferably commonly mounted on the board 22.
In accordance with this invention, the compound curvature lenses 52a, 52b, 52c, 52d, 52e form the distributed line pattern as wide and short with sharp edges and as not dominated by optical aberrations. The intensity of the distributed line pattern is uniform with much less fall off away from the axis 46 at opposite end regions of the distributed line pattern. Also, the coupling efficiency between the elongated light source 50 and the elongated linear lens array 52 is much improved, thereby increasing light throughput and enhancing reading performance.
It will be understood that each of the elements described above, or two or more together, also may find a useful application in other types of constructions differing from the types described above. For example, higher order aspherical terms could be provided in the concave curvatures 54 at the ends of the linear lens array 52 in order to send more light to the opposite end regions of the distributed line pattern.
While the invention has been illustrated and described as an arrangement or module for, and a method of, generating a generally uniform distributed line pattern of light on a symbol to be read by image capture by an imaging reader, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.
