Long-distance barcode scanning via coherent light conversion

Abstract

The present disclosure relates to long-range barcode scanning by coherent light conversion. A method for optically scanning a mark on an object includes providing a coherent light source for illuminating the object with coherent light. The object is marked with a mark including a first feature and a second feature, wherein the first feature includes reflection of coherent light and the second feature includes emission of incoherent light when illuminated. An imaging device is capable of distinguishing coherent light from incoherent light. The mark is illuminated with coherent light generated by the coherent light source, causing the mark to reflect coherent light and emit incoherent light. The coherent light is distinguished from the incoherent light emitted from the mark by a controller for identifying a pattern of one of the first feature and the second feature.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 717,431, filed on August 10, 2018, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention generally relates to an improved method for scanning bar codes or other patterns. More specifically, it relates to a method for distinguishing or blocking coherent light reflections from incoherent emissions of bar codes and other patterns illuminated by a coherent light source that can scan bar codes and other patterns at an increased offset distance. Background Art

[0004] In recent years, the use of tags (encoded tags) in the form of barcodes and QR tags has increased rapidly in manufacturing environments, where tags were previously used primarily in consumer markets. This form of tagging has been used to identify products or objects to help merchants manage inventory and to identify products at the time of purchase. In order to obtain an accurate scan of the barcodes typically affixed to the label, and more recently, the QR tags, the label must be placed in close proximity to the barcode scanner. If close proximity between the tag and the scanner is not achieved, the scanning process can prove unreliable.

[0005] Recently, the use of markers in manufacturing has proven to be useful for quality control and managing inventory in a factory or manufacturing environment. Ensuring that the proper part has been assembled to the workpiece and signaling to the controller that a part has been removed from inventory has proven to be beneficial. However, the additional step of scanning the marker due to the proximity requirement has proven to be inefficient. In some cases, handheld scanners capable of wireless transmission have been used. However, these handheld scanners are cumbersome and still require proximity to the marker to work effectively. Alternatively, fixed scanners are used which require the operator to move the marker into close proximity with the scanner, which adds a step to the assembly process and reduces efficiency.

[0006] To date, attempts to reduce the inefficiencies of using close proximity scanners have proven futile. Long-range scanning of marks as a method to eliminate the use of handheld scanners or close proximity scanning stations has proven futile. Long-range scanning is particularly useful as a quality control verification of composite component construction, where hundreds or even thousands of individual plies are stacked on a mandrel. These pieces are often not distinguishable by appearance alone. Current attempts to use marks to identify each piece by deciphering marks set on a backing paper have proven to be a hindrance to manufacturing efficiency because of the close proximity scanning required. After a piece is identified, further efficiencies can be achieved when a laser that projects a profile can indicate where the piece is to be placed on the mandrel using a laser projector of the type and process disclosed in U.S. Patent No. 9,200,899 LASER PROJECTOR SYSTEM AND METHOD (the contents of which are incorporated herein by reference).

[0007] Proper confirmation of which piece the operator has selected is critical to meeting quality standards, particularly in aerospace applications. Improper part identification or placement can result in catastrophic failure of an aerospace component. Close proximity mark scanning can be used during the manufacture of small components, such as turbine blades. However, larger components, such as engine cowlings or wings, require that individual pieces be transported to and from scanners in close proximity, resulting in unjustifiable processing delays. Similar situations are known for moving assembly lines in automotive assembly and related plants, where mark scanning is used to verify part selection.

[0008] Ambient light causes additional quality anomalies when attempting to scan marks in a manufacturing environment (not limited to, but especially over long distances). A common method of scanning marks for the purpose of identifying a product or part is with the aid of a flying laser spot. In this example, a laser scans the mark and the return intensity is recorded as it scans. Lasers are useful in scanning in close proximity because the beam from the laser projector can be focused to a very fine focus. The fine focus can be used to overcome high intensity ambient light.

[0009] However, laser beams have an inherent disadvantage in that the typical laser spot of any laser beam destroys the ability to distinguish the contrast of the returning light. Figure 1This is best expressed in , where the laser spot produces a blurred response that is inherently inaccurate for high precision scanning, which is required for long distance bar code deciphering. This problem is compounded when long distance scanning is attempted. Even the integration of a high precision camera cannot overcome the problems associated with the laser spot. Therefore, it is desirable to develop a process for scanning marks at long distances to identify parts without requiring additional steps and processing to ensure accurate scanning. Summary of the invention

[0010] A method for optically scanning a mark on an object includes providing a coherent light source for illuminating the object with coherent light. The object is marked with a mark including a first feature and a second feature. The first feature includes reflection of coherent light and the second feature includes emission of incoherent light. An imaging device capable of distinguishing coherent light from incoherent light is provided. The mark is illuminated with coherent light generated by the coherent light source, so that the mark reflects coherent light and emits incoherent light. Coherent light is distinguished from incoherent light emitted by the mark, thereby identifying a pattern of one of the first feature and the second feature.

[0011] In one embodiment, the barcode or QR logo that constitutes the mark includes two different colors, one that emits light in the fluorescent spectrum when illuminated, and the other that reflects light in the non-fluorescent spectrum. A camera or other imaging device is able to distinguish the difference between coherent features and incoherent features to signal to a controller the finely resolved pattern defined by the mark. The contrast between the detected coherent light reflection and the incoherent light emission overcomes the problems associated with laser spot, even at long distances. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Advantages of the present disclosure will be more readily understood by referring to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0013] Figure 1 An image of laser speckle, which is known to disrupt long-range laser scanning and blur long-range laser images, is shown;

[0014] Figure 2 A first embodiment of the indicia scanner of the present invention is shown;

[0015] Figure 3 A laser projector is shown for identifying a mark projected from a laser template onto a work surface.

[0016] Figure 4 shows a wavelength graph indicating the luminescence of a fluorescent material excited using green laser light;

[0017] Figure 5 A wavelength diagram for distinguishing incoherent light emission using a fluorescent mold in ambient lighting is shown;

[0018] Figure 6 A relative wavelength plot indicating blurred long-distance scanning of a marker using a coherent light source is shown;

[0019] Figure 7 shows a relative wavelength graph indicating enhanced scanning of a tag using coherent to incoherent light conversion;

[0020] Figure 8 An alternative embodiment of the indicia scanner of the present invention is shown; and

[0021] Fig. 9 Another alternative embodiment of the indicia scanner of the present invention is shown;

[0022] Fig.10 Yet another alternative embodiment of the indicia scanner of the present invention is shown. DETAILED DESCRIPTION

[0023] The method of the present invention provides an operator with the ability to scan barcodes, QR logos, etc. at significantly greater distances than currently required by short-range barcode scanners. Generating coherent light illumination and then converting the coherent incident light into incoherent light overcomes the problems associated with, for example, laser spot (which therefore requires the scanner to be in close proximity to the barcode, QR logo, etc.).

[0024] Now refer to Figure 2 , an assembly for implementing the method of the present invention is generally indicated at 10. The assembly includes a laser projector 12 for generating a laser beam 13. The laser beam 13 is directed toward a work surface 14 by a first galvanometer 16 and a second galvanometer 18. The first galvanometer 16 includes a first reflective element 20 driven by a first scanning motor 22, and the second galvanometer 18 includes a second reflective element 24, including a second scanning motor 26. The controller 28 also directs the first scanning motor 22 and the second scanning motor 26 to redirect the laser beam 13 to scan the work surface 14. More specifically, the controller 28 directs the first scanning motor 22 and the second scanning motor 26 to scan the layer piece 30 that has been identified by the mark 32.

[0025] The imaging device 34 images the working surface 14 and the ply 30, and more specifically, the markings 32. The imaging device 34 is a camera, a photogrammetric assembly, an optical sensor array, or an equivalent sensor capable of detecting light in a desired spectrum. In one embodiment, a coherent light filter 36 filters coherent light so that it cannot reach the optical sensor element 38 of the camera 34.

[0026] The indicia 32 includes a first feature 40 and a second feature 42 that is distinguishable from the first feature 40. The first feature 40 and the second feature 42 together form a bar code, a QR logo, or the equivalent. The indicia 32 is unique to each ply 30 so that the controller 28 can identify the ply 30 from the database. In one embodiment, the bars of the bar code form the first feature 40 and the background of the bar code forms the second feature 42. Alternatively, the background forms the first feature 40 and the bars of the bar code form the second feature 42.

[0027] The laser projector 12 provides a coherent light source, which is merely exemplary. Alternative coherent light sources are within the scope of the present invention, including but not limited to light emitting diodes, etc. The first feature 40 includes a fluorescent mold that emits light in a fluorescent spectrum when excited, and more specifically, emits light in an orange spectrum with a peak at about 608nm. However, fluorescent molds that are capable of emitting fluorescence with different fluorescence spectra with different fluorescence peaks when excited are also within the scope of the present invention. It should be understood that the first feature 40 or the second feature 42 can provide fluorescent emission when illuminated. However, only one of the first feature 40 and the second feature 42 can provide fluorescent properties, the purpose of which will become clearer below.

[0028] Figure 6 A graph of reflected coherent light generated by a coherent light source (a laser in this example) scanned over surfaces with widely varying reflectivities is shown. The interference of the coherent light generated by the laser 12 obscures the transition locations of high contrast edges and impedes the detection of low contrast features known to occur in bar codes, QR logos, etc. Figure 1 The laser spot shown in becomes more blurred at long distances, exacerbating the inability to accurately detect transition locations. When the area to be covered by the laser beam 13 is large and the mark 32 is limited, the ability to accurately distinguish, for example, the first feature 40 from the second feature 42 becomes completely insufficient. Therefore, the placement of the mark 32 on a small part placed on a large tool, or in situations where manufacturing features covering wide intervals require additional processing steps to move the mark into close proximity with the scanner, which is precisely the problem solved by the present invention.

[0029] Figure 4 Excitation of a fluorescent material by a green laser emitting coherent light having a peak at about 530 nm is shown. In this example, the fluorescent material produces an incoherent orange fluorescent light in response to the illumination, having a peak response at about 608 nm. Irradiation of the fluorescent material by a light source outside the fluorescent band provides luminescence from the fluorescent material that can be easily separated from the light source. As a non-limiting example, Figure 5Illumination of an orange fluorescent material by an ambient light source is shown, where the orange fluorescent material still produces a luminescent response having a peak at about 608 nm, still providing a distinction from reflected light from a green laser or LED including a peak wavelength of about 530 nm. This differentiated incoherent luminescence result illustrates typical ambient illumination in any manufacturing environment when a laser or LED light source is used for illumination.

[0030] Even when illuminated by coherent light produced by a laser or LED light source, incoherent light is emitted from the fluorescent material. When a pattern is provided having fluorescent first features 40 (e.g., in the orange spectrum) and non-fluorescent second features 42, the first features 40 and the second features 42 can be easily distinguished by the imaging device 34 by Figure 4 This can be clearly seen by the separation of the fluorescent emission and the coherent light reflection produced by the green laser shown in FIG. The sensor element 38 in the imaging device can be a CMOS, CCD or equivalent light sensor depending on the application needs. Further accuracy can be achieved by positioning the filter 36 between the sensor element 38 and the working surface 14 and the layer piece 30 to optically block the coherent excitation energy and / or environmental reflections. The filter 36 is selected to filter the coherent light in the range of about 570nm to about 670nm so that the camera 34 mainly detects the incoherent light emitted by the first feature 40 of the fluorescence, providing a high intensity at the interval or line defined between the first feature 40 and the second feature 42. In this way, the controller 28 is signaled with a high resolution pattern associated with the bar code or QR logo, so that the controller 28 can easily identify the layer piece 30 with the label 32 attached thereto, even at a long distance. It should be understood that the use of green lasers and orange fluorescent materials is merely exemplary, and coherent light produced in different fluorescent emissions at another wavelength is also within the scope of the present invention. Different emission and illumination light ranges may be used in different manufacturing environments and are also within the scope of the present invention. In one embodiment, ambient light may also be eliminated by identifying background level reflections of the mark 32 prior to illumination by the coherent light source. Thus, after the mark 32 is illuminated by the coherent light source, the background light reflections may be subtracted from the image produced by the imaging device 34.

[0031] In one embodiment, filter 44 is selected to block most ambient light in addition to coherent light generated by a coherent light source. Filter 44 may take the form of a passive optical element that can be used to filter light passing through it, or a dichroic mirror that separates one or more ranges of wavelengths, as will be further explained below with respect to alternative embodiments. In yet another embodiment, sensor element 38 may include two sensors, one of which is adapted to detect coherent light from a coherent light source (e.g., a green laser) and a second of which is adapted to detect only incoherent light emitted from a fluorescent material (e.g., an orange fluorescent material).

[0032] The inventors anticipate that there may be some difficulty with the camera 34 initially locating the mark 32 in a large work area (e.g., in an aerospace work cell for manufacturing composite wings) before deciphering the mark. Therefore, the controller 28 directs the coherent light source to scan the work surface 14 while synchronizing the imaging device 34 with the movement of the laser beam 13 on the work surface 14. The imaging device 34 senses when the laser beam 13 scans the fluorescent material, causing and emitting incoherent light. At this time, this high-speed capture does not provide sufficient resolution to decipher the mark 32, but only monitors the intensity of the return as the laser beam 13 scans across the mark 32. The controller 28 correlates the time when the incoherent light is detected within the target range with the location of the laser scan to identify the location of the ply piece 30, thereby identifying the mark 32. Once the mark 32 is located, the controller 28 begins deciphering the mark 32 to identify the piece ply or part 30.

[0033] Alternatively, the imaging device 34 continuously monitors the work surface 14 until the ambient light interacts with the marking 32, and more specifically, with the fluorescent first feature 40. The location of the incoherent light emission from the fluorescent material is signaled to the controller 28 from the imaging device 34. Subsequently, the controller 28 signals the coherent light source where to scan the laser beam 13 to produce a high resolution image of the marking 32 in order to decipher the marking 32 and identify the ply 30. Thus, after the controller 28 determines the location of the marking 32, the imaging device 34 is synchronized with the scanning location of the laser beam 13 on the work surface 14.

[0034] Figure 7 The invention is shown to provide improvements over long-range scanning of bar codes or other indicia where precise demarcations between adjacent features (bars and background) must be discerned for accurate decipherment. Figure 1 As shown in the image above, the laser spot becomes blurrier as the laser focus becomes farther away from the laser. Figure 7 A graph showing coherent light scanning a bar code is scanned across the indicia 32 to emit incoherent light from the indicia 32, including the fluorescence conversion of coherent light to incoherent light. The scan using incoherent light shows a smooth variation in intensity as the curve intersects a reflectivity step, where the reflectivity step represents each edge of a bar contained in a given bar code. The curve represents what a camera would look like as the laser beam scans across the step variation in reflectivity defined by each bar of the bar code, even though the camera lens has limited resolution. Figure 6Each line graph in represents a step in the laser position. Relying on the predictable response, the locations where the reflection steps occur can be accurately inferred, and enables the width of individual barcode lines to be estimated even if they are narrower than the resolution of both the laser and the lens. The dashed line denoting "reflectivity" at 1 on the horizontal axis represents the actual edge that needs to be detected to accurately decipher the barcode. The overlap of the reflectivity at 1 on the horizontal axis is due to the interference of the reflected coherent light caused by the intensity variation of the laser spot, as shown in Figure 1. Figure 6 The result is that the camera cannot detect where the edge of the bar actually is. However, Figure 7 As shown primarily in FIG, converting coherent light (produced by a green laser in this example) into incoherent light provides separation of the coherent light from the incoherent light at the edge of a given bar, allowing a light sensor or camera to clearly identify the edge of the bar even at a long distance.

[0035] In yet another embodiment, the imaging device 34 detects a characteristic spectrum of a tag 32, the tag 32 including a first feature 40 and a second feature 42, wherein at least one of the features 40, 42 is fluorescent, approximating the location of each bar of the bar code. This facilitates the imaging device 34 to quickly scan a high-resolution image based on characteristic ambient light reflected or emitted from the tag 32 when the tag 32 is illuminated using coherent light 13 from a coherent light source. Thus, when the imaging device 34 signals the controller 28 the approximate location of the tag 32, and the controller 28 in turn signals the laser projector where to scan the laser beam 13, the laser projector (coherent light source) does not need to search for the tag 32.

[0036] exist Figure 3 is best shown in (for comparison with Figure 2 In yet another embodiment of the present invention (continuity of the image processing), the laser project and system described in U.S. Patent No. 9,200,899 LASER PROJECTOR AND METHOD is used as a coherent light source. Therefore, the same laser that scans the mark 32 also scans the laser template 44, which is used to guide the operator where to place the ply piece 30 or other part on the work surface 14. Therefore, the controller 28 sends a signal to notify which ply piece 30 has been selected based on the scanning of the mark 32. The controller 28 then guides the operator where to place the ply piece 30 based on the detected mark 32, or sends a signal indicating an error that the ply piece 30 outside the appropriate assembly sequence has been selected. The sequence is formed only by the operator placing the ply piece within the imaging range of the imaging device 34 so that the mark 32 can be scanned after being irradiated with coherent light.

[0037] Figure 8Another alternative embodiment is shown generally at 50 where like elements to the previous embodiment include like element numbers. In this embodiment, fluorescent emissions from the marker 32 return along the same path as the laser beam 13 to be sensed by the imaging device 34.

[0038] The laser 12 (coherent light source) is a green laser that transmits a laser beam 13 having a peak at about 532 nm to a dichroic mirror 52, to a first reflective element 20 and a second reflective element 24, to the location of a mark 32, where the first feature 40 or the second feature 42 includes a fluorescent material. Return light emitted from the fluorescent material is redirected by the first and second reflective elements 20, 24 to the dichroic mirror 52, which transmits only light having a peak at a fluorescent wavelength of about 608 nm to the sensor 54. In this embodiment, the sensor 54 includes collection optics and sensor electronics, such as a photodiode, a photomultiplier, and equivalents, to provide the necessary detection sensitivity.

[0039] Alternatively, yet another embodiment generally Fig. 9 60, includes a non-dichroic (partially reflective) mirror 56 added to the assembly for filtering and directing fluorescent emission 57 to an incoherent light sensor 58, and directing coherent light 59 to a different coherent light sensor 61. This arrangement provides the additional benefit of detecting laser light reflected from a retroreflective target 62 disposed on the work surface 14 in order to accurately locate the work surface 14 in a three-dimensional coordinate system relative to the laser projector 12. Thus, the same laser projector 12 is used to scan the retroreflective target 62, project the laser template 44 ( Figure 3 ) and for scanning the mark 32 with coherent light. Once the mark 32 has been scanned and decoded, the laser projector scans the retroreflective target 62 to locate the work surface 14 in a three-dimensional coordinate system. The retroreflective target 62 returns coherent light to the source in a known manner. This arrangement also provides improved detection of fluorescent emissions by comparing the luminous and reflected coherent light levels, thereby enabling the ratio between the two wavelengths (532nm and 608nm) to be calculated. Therefore, both coherent and incoherent wavelengths pass through the partial reflector 56 to the modified sensor 58, 61. The modified sensor 58, 61 is optionally improved by adding an internal dichroic mirror or beam splitter (not shown) to reflect the emitted light into separate orange and green wavelengths.

[0040] exist Fig.1070 of the drawings, in which similar elements to the first embodiment include similar element numbers. A first camera 72 and a second camera 74 receive light emitted from the work surface 14 and the mark 32, which includes the first feature 40 of fluorescence as described above. The first camera 72 is green filtered and the second camera 74 is orange filtered. Of course, it should be understood that the use of the first camera 72 and the second camera 74 in this manner is intended for detecting the reflected green laser beam and the emitted orange fluorescence. Alternatively, the first camera 72 is green filtered and the second camera 74 is green / orange filtered so that the difference in wavelength is calculated to accurately detect the orange wavelength emitted from the first feature 40. In addition, filters can be used alternatively to detect green laser reflections or orange fluorescence emissions. This alternative arrangement enables the two cameras 72, 74 to triangulate the laser beam 13 when the laser beam 13 is reflected from the retroreflective target 62 fixed to the work surface 14 in the manner set forth in U.S. Patent No. 9,200,899 LASER PROJECTOR SYSTEM AND METHOD for photogrammetry. Thus, the laser projector 12 has the following dual functions: three-dimensional positioning of the object and / or work surface 14 for projection of the laser template 44 ( Figure 3 ) or image, and scanning the bar code or mark 32 with coherent light to verify that the appropriate layer piece has been selected for placement based on the guidance of the laser template.

[0041] The inventors of the present application have determined that synchronization of the emitted energy (light waves) with the motion of the scanning laser beam 13 allows for rapid decoding of the indicia 32, and more specifically, the first features 40 and the second features 42 adhered to the ply 30. In this manner, conventional laser projector systems used to project manufacturing templates can be used to provide bar code scanning functionality.

[0042] Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The foregoing invention has been described in accordance with relevant legal standards; therefore, the description is merely exemplary and not limiting in nature. Variations and modifications to the disclosed embodiments will be apparent to those skilled in the art and fall within the scope of the present invention. Therefore, the scope of legal protection afforded this invention can only be determined by studying the following claims.

Claims

1. A method for optically scanning a mark on an object, comprising the following steps: providing a coherent light source for illuminating an object with coherent light; marking an object with a mark comprising a first characteristic including emission of incoherent light and absorption of coherent light and a second characteristic including reflection of coherent light without emission of incoherent light; Providing an imaging device capable of distinguishing coherent light from incoherent light; scanning a working area with coherent light, and said imaging device locates the mark by detecting emission of incoherent light from said first feature; After detecting emission of incoherent light from the first feature, the imaging device signals the location of the marker to the coherent light source, thereby synchronizing movement of the coherent light with the imaging device for locating the marker in the workspace; illuminating the marker with coherent light generated by a coherent light source, so that the marker reflects the coherent light and emits incoherent light; as well as The presence or absence of incoherent light emitted from the marker is detected to thereby identify the pattern of one of the first feature and the second feature.

2. The method of claim 1, wherein the step of distinguishing coherent light from incoherent light is further defined as filtering coherent light from the imaging device.

3. The method of claim 1, wherein the step of marking the object with a marker comprising a first feature and a second feature is further defined by the first feature being fluorescent and the second feature being non-fluorescent.

4. The method of claim 3, wherein the step of marking the object with a marker comprising a first feature and a second feature is further defined as the first feature emitting incoherent light when illuminated by coherent light and the second feature reflecting coherent light when illuminated by coherent light.

5. The method of claim 1, further comprising the steps of: The imaging device locates the marker by detecting the emission of fluorescent light from the first feature.

6. The method according to claim 5, further comprising the steps of: After detecting emission of fluorescent light from the first feature, the imaging device signals the location of the marker to the coherent light source.

7. The method of claim 1, wherein the step of providing a coherent light source is further defined as providing a laser projector for projecting a coherent light beam.

8. The method of claim 1, wherein the step of illuminating the object with a coherent light source is further defined as scanning the mark with a green laser beam having a wavelength of approximately 532 nm.

9. The method of claim 1, further comprising the steps of: The first feature absorbs light having a wavelength less than about 575 nm and emits light having a peak wavelength of about 608 nm.

10. The method of claim 1, further comprising the steps of: Filters coherent light with wavelengths below approximately 575 nm.

11. The method of claim 1 , wherein the step of distinguishing coherent light from incoherent light is further defined by providing one of a dichroic mirror and a beam splitter for directing coherent light reflected from the second feature to the first light sensor and directing incoherent light emitted from the first feature to the second light sensor.

12. The method of claim 1, wherein the step of providing an imaging device is further defined as providing a camera including a coherent light sensor and an incoherent light sensor.

13. The method of claim 1, wherein the step of providing a coherent light source is further defined as providing a laser projector capable of projecting a laser template onto a work surface defined by the markings disposed on the object.

14. The method of claim 13, wherein the step of projecting a laser template onto a work surface is further defined as interpreting the markings indicating a location on the work surface where the laser template was projected.

15. The method of claim 13, wherein the object is placed on a work surface at a location indicated by the laser template.

16. The method of claim 1, wherein the imaging device comprises two cameras for triangulating the position of the target to determine the position of the target in a three-dimensional coordinate system.

17. The method of claim 16, further comprising the steps of: One of the first camera and the second camera is selectively filtered for reflected coherent light and emitted incoherent light.

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