Patent Application
20100276490
This invention relates generally to the field of optical scanning systems, and more particularly to a system and method for decoding images that increases performance of the system.
Various optical scanning apparatus have been developed to read and decode optical indicia, such bar as code symbols on a target such as a label. While early bar code scanners were designed to read symbols at a relatively close distance, there exists a need to read symbols at greater and greater distances, for example in warehousing environments. Conventional optical scanning systems, such as hand-held bar code laser scanners, typically have a limited working range due to the constraints imposed on the optical assembly. Motorized systems with additional lenses or mirrors have been developed to re-position the laser beam waist relative to the fixed lens assembly, thereby increasing the working range of the scanning apparatus, but such improvements are complicated and add cost.
Decoding images has always proved challenging, in part because decoding systems work best with a sharp representation of the bar code symbol, and a sharp representation is not always possible. Due to optical, environmental or physical factors, the representation may be out of focus, too close to the reader, or too far away from the reader. One solution to this problem is to manually move the symbol to a range within the capability of the reader, either by moving the scanning apparatus or by moving the target. This solution can be cumbersome, frustrating, or may not even be possible. Various systems have been developed to aide in focusing the laser on the target, such as ranging systems to determine the distance from the reader to the target, but these systems add complexity and cost.
In view of the background, it is therefore an object of the present invention to provide a scanning apparatus that includes a laser source operable to emit a beam along an axis and illuminate a target. The target includes an encoded symbol character. A variable focus distance lens assembly in optical communication with the laser source focuses the beam on the target at an object distance, and a detector receives light of varying intensities scattered from the encoded symbol character and converts the light into a first signal. A digitizer converts the first signal to a digital bit stream. The scanning apparatus further includes pre-stored information correlating a non-standard symbol pattern to a valid symbol character according to a standard definition of the symbology. The non-standard symbol pattern comprises a first number of elements that deviates from a second number of elements associated with the valid symbol character. A decoder receives the digital bit stream and utilizes the pre-stored information for decoding the signal.
It is another object of the present invention is to utilize the pre-stored information to provide a scanning apparatus with an enhanced depth of field, thereby allowing a user of the apparatus to decipher symbol characters more quickly.
It is another object of the present invention is to utilize the pre-stored information to provide a scanning apparatus with an extended working range, thereby allowing a user of the apparatus to decipher symbol characters such as bar codes at a greater range of distances than previous scanning apparatuses.
The novel features that are characteristic of the preferred embodiment of the invention are set forth with particularity in the claims. The invention itself may be best be understood, with respect to its organization and method of operation, with reference to the following description taken in connection with the accompanying drawings in which:
Referring to
The fixed-lens reader 1 operates with the beam 3 focused at a fixed point D0 from the housing. The depth of field (DOF) of the fixed-lens assembly 2 is the linear range about the focused point in which the reader 1 is able to decode the symbol 8. As used herein, depth of field is defined as the distance between the maximum and minimum plane in which a code reader is capable of reading symbols of a specified X dimension (nominal width dimension of the narrow bars and spaces in a bar code symbol). When the target 7 is brought into the depth of field of the reader at an object distance D0, the bar code symbol 8 is decoded. A typical depth of field value for a 13 mil UPC bar code is approximately 13 inches (33 centimeters).
Variable focus lens assemblies have been developed to aide in extending the object distance of a laser bar code reader, for example in warehousing environments where the location of the target may be difficult to access. One example is an electro-wetting focusing apparatus that changes the object distance of the reader by varying the curvature of the lens according to an applied voltage. The electro-wetting lens assembly has the advantage of not only being able to decode symbols at long distances, twenty feet for example, but also at shorter distances. Although the electro-wetting lens assembly increases the range of working distances of the reader, they can be improved.
Typically, a reader employing a variable focus lens assembly will cycle through a pre-set range of object distances until a valid decode is achieved. The change in object distance between each scan cannot exceed the depth of field distance, or else there will be gaps in the working range of the reader. Thus, because the depth of field is limited by the ability of the reader to decode slightly out-of-focus images, as the working range of the reader increases more iterations are required to find a successful decode. As an example, a bar code reader with a working range from 12 inches to 24 inches (30.5 to 61 centimeters) will find a proper decode much faster than a scanner with a working range of 12 inches to 20 feet (30.5 centimeters to 6.1 meters), if the depth of focus is approximately the same. As the working range is increased by technological advancements to the lens assembly, additional pre-selected iterations must be evaluated before a proper decode is achieved.
Referring to
As used herein, “encoded symbol character” is intended to denote a representation of a unit of information in a message, such as the representation in a bar code symbology of a single alphanumeric character. One or more encoded symbol characters can be used to convey information, such as the identification of the source and the model of a product, for example in a UPC bar code that comprises twelve encoded symbol characters representing numerical digits. Also, an encoded symbol character may be a non-alphanumeric character that has an agreed upon conventional meaning, such as the elements comprising bars and spaces that are used to denote the start (left hand guard pattern), the end (right hand guard pattern), and the center (center guard bar pattern) of a UPC bar code. The bars and spaces used to encode a character as an encoded symbol are referred to generally as “elements.” For example an encoded character in a UPC symbol consists of four elements, two bars and two spaces. Similarly, encoded symbol characters can be defined for other bar code symbologies, such as other one-dimensional (“1-D”) bar code systems including Code 39 and Code 128, or for stacked two-dimensional (“2-D”) bar code systems including PDF417.
The scanning apparatus 10 includes a laser source 26 mounted securely to the housing 16 and aligned so as to emit the laser beam 14 along an optical path, or axis 28, to illuminate a target 30. The laser source 26 may be a laser diode, for example. The scanning apparatus 10 further includes a scanning mirror 32 disposed within the optical path. In the disclosed embodiment, the scanning mirror 32 is positioned within the housing 16 after the variable focus distance lens assembly 112. The scanning mirror 32 reflects the emitted beam 14 incident thereon and aligns it to the target 30. Further, the scanning mirror 32 oscillates at a pre-determined frequency to sweep the beam 14 over the target 30 according to a pre-described scan pattern. The scan pattern may be along a line transverse to the plane of the target, e.g. a side-to-side motion. In some instances, an orthogonal scanning mechanism is added to allow raster scanning. The oscillation motion of the scanning mirror 32 may be driven by a motor 34.
A collimating lens 36 may be disposed along the axis 28 between the laser source 26 and the variable focus distance lens assembly 112 to produce a focused beam of light. In the disclosed example, the collimating lens 36 is disposed between the laser source 26 and the scanning mirror 32, but the lens may be placed at any advantageous location along the axis 28. In one embodiment, the collimating lens 36 is included as part of the assembly of the laser source 26. The collimating lens 36 is chosen by the manufacturer of the scanning apparatus 10 according to the particular requirements of the design.
As mentioned above, the scanning apparatus 10 includes the variable focus distance lens assembly 112 for focusing a beam on the target 30. As shown in
Referring to
In another embodiment, a focusing apparatus 12 for use in scanning apparatus 10 may also be provided in accordance with focusing technologies described in U.S. patent application Ser. No. ______ [attorney docket no. H0019748], entitled “FLUID LENS ELEMENT FOR USE IN CHANGING THERMAL OPERATING ENVIRONMENT” filed concurrently herewith, which is incorporated herein by reference in its entirety.
In yet another embodiment, a focusing apparatus 12 for use in scanning apparatus 10 may also be provided in accordance with focusing technologies described in U.S. patent application Ser. No. ______ [attorney docket no. H0021206], entitled “LASER SCANNER WITH DEFORMABLE LENS” filed concurrently herewith, which is incorporated herein by reference in its entirety.
Various actuators can be utilized with the present invention. The actuator 50 illustrated in
The focusing apparatus 12 operates within a range bounded by two extreme states. One extreme state is a “power off” state depicted in
In another embodiment, the tab-like elements 56 could be biased in an opposite manner to provide a convex (bulged) deformable surface 42 only when voltage is applied. At a “power off” state, the deformable surface 42 assumes a generally flat and less convex configuration. In some embodiments surface 42 may even assume a concave configuration.
In yet another embodiment, a focusing apparatus 12 including the actuator for use in scanning apparatus 10 may also be provided in accordance with focusing technologies described in U.S. patent application Ser. No. ______ [attorney docket no. H0023171], entitled “FOCUSING APPARATUS AND TERMINAL COMPRISING VARIABLE FOCUS LENS ASSEMBLY” filed concurrently herewith, which is incorporated herein by reference in its entirety.
Referring to
Turning now to
In operation, an appropriate electric current is passed through the coil 78 and generates an electrical field. The electric field interacts with the magnetic field induced by the permanent magnet 74 according to the Lorentz law, creating a driving force F at right angles to both the direction of current and magnetic flux, shown by the arrow in
Referring to
A first electrode 86 extends into the liquid 82, and a second electrode 88 is located below the wall 84. The electrodes are connected to a voltage source V, which may be thought of as the actuator 50. The electrodes, especially electrode 88, are preferably light-transmissive. When a voltage is applied across the electrodes, an electrical force field is created which alters the wetting characteristic of the drop 80 with respect to the wall 84. The wetting increases substantially in the presence of an electrical field. With no voltage applied, the drop 80 takes the generally hemispherical shape shown in solid lines in
Referring now back to
The decoder 99 measures and quantizes the width of each element (light or dark) and compares the quantized element widths to valid symbol characters of the symbology contained in pre-stored information 100. In one example, the pre-stored information 100 is a lookup table residing within the controller 96. When the signal 102 is successfully decoded, the output may be passed to a display device, for example.
In one example, the scanning apparatus 10 operates in an open-loop cycle, meaning the controller 96 receives no feedback as to the location of the beam waist W0 relative to the target 30. When the scanning apparatus 10 is activated, such as when an operator depresses the trigger, the scanning apparatus 10 captures a first signal 94 with the variable focus distance lens assembly 112 set to a first focus distance. If the signal 102 cannot be decoded using the conventional techniques described above, the controller 96 may alternately attempt to decode the signal by correlating it to non-standard symbol patterns that are not associated with valid symbol characters, as will be explained in detail below. If the signal 102 still cannot be decoded after attempting to correlate it to non-standard symbol patterns, the controller 96 may command the focusing apparatus 12 to change the focus distance of the beam 28 and capture a second signal 94 with the lens assembly 112 set to a second focus distance. The sequence of attempting to decode by comparing the signal 102 to valid symbol characters and non-standard symbol patterns prior to adjusting the focus distance continues until one of either a successful decode, trigger release or a time limit is achieved.
In a bar code scan, information is available as to what the particular bar code is expected to look like and how it is expected to appear in coded form. For example, a UPC bar code is comprised of encoded symbol characters represented by sequences of 4 alternating bars and spaces (or spaces and bars) having a total width of 7 width units. The bars are generally black rectangular marks having low reflectivity. The spaces are generally regions free of ink such that a white or light color of a substrate is visible, and are generally highly reflective by comparison to bars. An image of a valid symbol character in bar code comprises one or more bars and spaces typically represented by a step function. When imaged and processed by a digitizer 97 with the bar code reader, the bar code is represented as a codeword having a sequence of binary values, for example. Typically, a decode table defines the exact step function of each codeword that is available, and the decoder 99 decodes the signal 102 according to at least one algorithm.
As mentioned above, not all encoded symbol characters 90 read by the scanning apparatus 10 can be decoded, however. In some situations, optical, environmental or physical factors may distort the signal 94 such that conventional decode algorithms are of little use. The target 30 may be at an object distance significantly different from the beam waist (out of focus), the bar code may be poorly illuminated so the contrast between black and white is not distinct, or the symbol characters 90 may be degraded.
As defined herein, “degraded encoded symbol character” is intended to denote an encoded symbol character that has been modified, whether deliberately or by happenstance, so that the degraded encoded symbol character is no longer in conformance with accepted standards for that type of encoded symbol character, no matter what orientation is used for viewing or scanning the encoded symbol character.
A degraded UPC encoded symbol character could be any of an encoded symbol character in which ink or other dark material is applied so that one or more bars are expanded in width over their entire length, for example by covering a white space intervening between two black bars with black ink, so that a bar-space-bar sequence is converted into a single wide bar. Conversely, the application of a white (or highly reflective) substance over some width of a bar (and over its entire length) can create a situation where the width of a space is increased and the width of an adjacent bar is decreased (in the extreme converting a space-bar-space sequence into a single wider space), or a wide bar is made to appear as a thinner bar followed by a space followed by another bar, such that the total width of the original bar is used to represent not one bar, but two bars separated by a space.
In some examples, the symbol characters 90 may appear to be degraded in the signal 94, but are in fact within the printing specification. Such an example may exist when the laser beam waist is not aligned with the target 30. Referring to
Referring to
The curve identified by the letter “A” is an illustrated signal recorded as the output signal of the detector 92 (
In reading the sequence of fluctuations or changes of state in the actual data of curve “A,” or in the step function “B” derived from curve “A,” there is a mathematical sequence that can be defined. The sequence of widths of the elements (the bars and spaces) that appear in the encoded symbol characters is termed the “e-sequence” or “eseq” for convenience. An element width sequence (“eseq”) can be derived from measuring the width of edge to edge transitions of the step function “B”. For example, the step function “B” eseq is: (left hand guard bar pattern) 3211-1114-1411-1132-1411-1231 (center guard bar pattern) 1213-1231-2221-1114-3211-3112-(right hand guard bar pattern). Curve “A” and step function “B” represent an undistorted, unmodified, and undamaged UPC bar code which is being read under proper conditions of illumination and within the depth of field of the bar code reader. Applying conventional decoding techniques using decoding values such as that found in columns one and two of Table I, the signal 94 would decode as the alphanumeric string of numbers 0-6-3-4-3-5-8-5-1-6-0-9.
Curve “C” of
In curve “E”, further degradation is evident due to reading a bar code that is well beyond beam waist of the laser beam, or a bar code that is hand motion smeared while capturing the image, or both, for example. The measured data has lost much of its detail, and some elements appear as large undifferentiated signals. As is seen from step function “F,” conventional decoding algorithms are not able to identify a significant number of zero crossings, and the digitized step function “F” is not meaningful when viewed with a conventional bar code reader or imager.
The system and method of the present invention alleviates decoding problems encountered when the signal 102 (
Table I illustrates one example of deviated symbol patterns. Column one lists the numeric value encoded in the symbology, and column two lists the corresponding valid symbol characters, e.g., the 4-element width sequence of each numeral. Column three lists possible distorted symbol elements that deviate from the valid symbol characters of column two. In the illustrated example, the distorted symbol elements arise if bars and spaces having one-element widths are distorted, smeared, blurred, or damaged as compared to bars and spaces having widths of two-, three-, or four-element widths. Note that the distorted symbol elements of column three form a 3-element sequence width and do not correspond to any numeral in column one, so a conventional bar code reader would not be able to decode the pattern. One example of such a distorted symbol element can be found in curve “F” in
Similarly, column four of Table I lists additional possible distorted symbol elements that deviate from the valid symbol characters of column two. In column four, the distorted symbol elements form a 2-element sequence width and do not correspond to any numeral in column one. An example of such a distorted symbol element can be found in curve “F” in
Referring now to
In another embodiment of the invention, the scanning apparatus 10 is utilized to decode a bar code symbol that has been intentionally distorted. In one example, two 1-element sequences in a bar space pattern are joined together to form one 2-element sequence. The sequences may be joined together by filling in the space of the bar space pattern with a pen, for example. The resulting distorted pattern may still be decoded by the scanning apparatus 10 because the distorted pattern is stored in a reference table, e.g., Table I.
Two advantages can readily be discerned by utilizing the scanning apparatus 10. First, the depth of field is increased, thereby requiring less iterations by the controller 96 to achieve a proper decode. Second, if the object distance of the target 30 is beyond the maximum range capability of the scanning apparatus 10, for example at the “power off” state, the scanning apparatus 10 may still be operable to decode the symbol pattern if the target 30 is within the extended depth of field. In this manner, the overall working range of the scanning apparatus 10 is increased beyond its physical capabilities.
Referring to
At a step 230, the laser source 26 is activated and at a step 240 the laser source passes the laser beam 14 through the focusing apparatus 12 (
At a step 300, the signal 94 is compared to valid, e.g., known, symbol patterns for a symbology. If the observed symbol pattern does not match any known patterns, as shown at a step 305, the controller accesses the pre-stored information and, at a step 310, correlates the observed deviations to the deviations stored in the pre-stored information. If the observed symbol pattern matches any of the deviations stored in the pre-stored information, as shown at a step 315, the decode is successful and the controller proceeds to a step 320 and the result is indicated by a display or a beep, for example. If the symbol pattern cannot be decoded, the method 200 iterates until a valid symbol pattern is correlated and the controller 96 can successfully decode the signal 94 or time out and initiate the process anew with new data.
A small sample of systems methods and apparatus that are described herein is as follows:
a laser source operable to emit a beam along an axis and illuminate a target, the target comprising the encoded symbol character;
a scanning mirror disposed intermediate the laser source and the target, the scanning mirror operable to deflect the beam emitted from the laser source so that the beam scans across the target according to a scan pattern;
a focusing apparatus in optical communication with the laser source for focusing the beam on the target at an object distance;
a detector operable to receive light of varying intensities scattered from the encoded symbol character and convert the light into a first signal;
a digitizer operable to convert the first signal to a digital bit stream;
pre-stored information correlating a non-standard symbol pattern to a valid symbol character according to a standard definition of the symbology, the non-standard symbol pattern comprising a first number of elements that deviates from a second number of elements associated with the valid symbol character; and
a decoder operable to receive the digital bit stream and utilize the pre-stored information for decoding the signal.
providing a laser light source, a focusing apparatus, a detector, a digitizer, and a decoder;
providing pre-stored information correlating a non-standard symbol pattern to a valid symbol character according to a standard definition of the symbology, the non-standard symbol pattern comprising a first number of elements that deviates from a second number of elements associated with the valid symbol character;
activating the laser light source;
passing a laser beam through the focusing apparatus along an axis to illuminate a target, the target comprising an encoded symbol character;
scanning the encoded symbol character;
receiving scattered light from the target and converting it to a first signal;
converting the first signal to a second signal comprising a digital bit stream;
generating a non-standard symbol pattern from the digital bit stream; and
decoding the non-standard symbol pattern utilizing the pre-stored information.
While the present invention has been described with reference to a number of specific embodiments, it will be understood that the true spirit and scope of the invention should be determined only with respect to claims that can be supported by the present specification. Further, while in numerous cases herein wherein systems and apparatuses and methods are described as having a certain number of elements it will be understood that such systems, apparatuses and methods can be practiced with fewer than the mentioned certain number of elements. Also, while a number of particular embodiments have been described, it will be understood that features and aspects that have been described with reference to each particular embodiment can be used with each remaining particularly described embodiment.
