System and method for illuminating and imaging surfaces in motion

Abstract

This invention provides a system and method for imaging a surface, moving in a motion direction, with a vision system having at least a first camera, defining an optical axis, transmitting acquired images of the surface to a vision system processor. At least a first bar illuminator extends in a direction transverse to the motion direction. The bar illuminator defines opposing, interleaved arrays of localized solid state light sources (e.g. LEDs). Each of the arrays is oriented to propagate light at a respective, opposing oblique angle with respect to the optical axis, which can be independently activated as respective image(s) are acquired. The first bar illuminator is oriented with respect to the surface so as to project arrays that propagate light along a first plane defining a first non-parallel angle versus the optical axis. The two non-parallel angles can each define opposing angles with respect to the optical axis.

Description

SYSTEM AND METHOD FOR ILLUMINATING AND IMAGING SURFACES IN MOTIONRELATED APPLICATION

[0001] This application claims the benefit of co-pending U.S. Provisional Application Serial No. 63 / 653.537, entitled SYSTEM AND METHOD FOR ILLUMINATING AND IMAGING SURFACES IN MOTION, filed May 30, 2024, the teachings of which are expressly incorporated herein by reference.FIELD OF THE INVENTION

[0002] This invention relates to illumination and imaging of moving surfaces for machine vision processes, and more particularly to illumination / imaging systems and methods compatible with photometric stereo techniquesBACKGROUND OF THE INVENTION

[0003] Machine vision systems, also termed “vision systems” herein, are used to perform a variety' of tasks in a manufacturing environment. In general, a vision system consists of one or more cameras with an image sensor (or “imager”) that acquires grayscale or color images of a scene that contains an object or surface of interest. Images of the object / surface can be analyzed to provide data / information to users and associated manufacturing processes. The data produced by the image is ty pically analyzed and processed by the vision system in one or more vision system processors that can be purpose-built, or part of one or more software application(s) using either conventional of deep learning / ALbased processes, instantiated within a general purpose computer (e.g. a PC, laptop, tablet or smartphone), and / or a custom processor. Some types of tasks performed by the vision system can include inspection of objects and surfaces (e.g. web inspection), such as those residing on a moving conveyor arrangement or motion stage, for expected features and / or defects.

[0004] A technique employed by vision systems to inspect moving objects and surfaces is photometric stereo, in which surface normals of objects / surfaces are estimated by observing that object under a plurality' of discrete lighting conditions. Photometric stereo is based upon the principle that light reflected by a surface is dependent on the orientation of the surface in relation to the light source and the observer. By measuring the amount of light reflected into a camera, the space of possible surface orientations isthereby limited. If light is propagated from a sufficient number of discrete angles, then the surface orientation can be constrained to a single orientation, or range of orientations.

[0005] Existing photometric stereo arrangements for imaging large objects or webs in motion typically employ two or more bar lights. These may be conventional bar lights (placed, for example, immediately upstream and dow nstream of the camera), and sometimes also specialized bar lights that produce obliquely angled line illumination to achieve the desired lighting effect for photometric stereo. The use of up to four bar lights (two conventional and two single-oblique) results in a relatively large footprint and cost for the illumination system. However, many production environments are space and / or cost constrained. It is therefore desirable to provide a system and method for imaging and illuminating objects and surfaces (e.g., having a significant widthwise dimension) with a more compact lighting arrangement.SUMMARY OF THE INVENTION

[0006] This invention overcomes disadvantages of the prior art by providing a system and method to illuminate and image the surface of a moving object or surface(e.g. a web) from multiple directions suitable for photometric stereo. This system and method advantageously enhances line-light technology to approximate parallel illumination wavefronts from multiple distant light sources. Whereas distant point sources are inefficient illuminators due to the inverse square law, the system and method provides efficient illumination of scanned surfaces of any width in the presence of one or more cameras that can be triggered by a motion signal associated with the surface.

[0007] In an illustrative embodiment, a system and method for imaging a surface, moving in a motion direction, with a vision system is provided. At least a first camera, defining a first optical axis, can transmit acquired images of the surface to a vision system processor. At least a first bar illuminator can extend in a direction transverse to the motion direction. The bar illuminator can define opposing, interleaved arrays of localized solid state light sources. Each of the arrays can be oriented to propagate light parallel to a line at a respective, opposing oblique angle with respect to the first optical axis, which can be independently activated as respective image(s) are acquired. The first bar illuminator can be oriented with respect to the surface so as to propagate light substantially along a first plane defining a first non-parallel angle with respect to the first optical axis. Illustratively, the system and method can further include a second barilluminator that extends in a direction transverse to the motion direction. The second bar illuminator can also define opposing, interleaved arrays of localized solid state light sources, and each of the arrays can be oriented to propagate light parallel to a line at a respective, opposing oblique angle with respect to the first optical axis. The second bar illuminator can be oriented with respect to the surface so as to propagate light substantially along a second plane defining a second non-parallel angle with respect to the first optical axis. The first bar illuminator and / or the second bar illuminator can be operatively connected to an illumination controller (or other processor arrangement) that independently operates each of the interleaved arrays, in each bar illuminator, as a separate illumination channel (i.e. separate circuits), respectively. The first non-parallel angle and the second non-parallel angle can define opposing angles with respect to the first optical axis. The localized solid state light sources can comprise leaded LEDs, right angle LEDs, MID-style LEDS, LEDs with a prismatic overlay, or LEDs with rotatable mirrors that define a predetermined mirror angle — which, in turn, allows for adjustability of the associated oblique angle of a beam propagated thereby. The prismatic overlay can define a direction turning film configured to bend the light from each of adjacent LEDs into each of the respective, opposing oblique angles. The prismatic / directi on turning film can define two discrete interleaved sets of fingers alternately overlying adjacent LEDs. The leaded LEDs or the MID-style LEDs can be mounted on each of a plurality of adjacent faces of a plurality of risers defining opposing angles on each of the adjacent faces. Illustratively, pairs of the LEDs, can be provided in an array of modules, in which each module includes pairs of the LEDs which propagate the light via the opposing oblique angles. The pairs of the LEDs can be spaced apart by a first spacing distance within the respective module, and the adjacent modules within the array of modules can be further spaced apart by a second spacing distance that is smaller than the first spacing distance. Each of the LEDs can be overlaid by a baffle, which is configured to limit a range of angles of propagation of the light therefrom. The rotatable mirror can be constructed and arranged to allow for (a) adjustment of the predetermined mirror angle during manufacture of the first bar illuminator or the second bar illuminator, and / or (b) field adjustment of the predetermined mirror angle during installation of the first bar illuminator or the second bar illuminator relative to the surface. The vision system processor can be constructed and arranged to acquire, with the first camera, images of the surface in conjunction with predetermined amounts of motion thereof. Each of the arraysof the first bar illuminator and each of the arrays of the second bar illuminator can each, be, respectively, triggered concurrently with each of the predetermined amounts of motion. The predetermined amounts of motion can be signaled by an encoder associated with motion of the surface. The vision system processor can be constructed and arranged to perform a photometric stereo operation on the images and provide results related thereto. The system and method can further include at least one (or two oppositely angled) conventional bar illuminator(s) that propagate(s) light in a line approximately collinear with the line of the first bar illuminator. At least a second camera, adjacent to the first camera, can define a second optical axis. The second camera can be configured to transmit acquired images of the surface to the vision system processor, or to a second vision system processor. Moreover, a plurality of cameras with touching, or overlapping, fields of view (FOVs) can extend across the width of the surface with images thereof provided to the vision system processor(s). Illustratively, the system and method can determine, from the acquired images of the surface, a presence or absence of a three- dimensional (3D — e.g. physical / structural) defect, or a reflectance defect, corresponding to the surface. The 3D defect or the reflectance defect can comprise at least one of: a scratch, a dent, a gouge, debris presence, a buff mark, improper material composition, or a variation in material thickness.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention description below refers to the accompanying drawings, of which:

[0009] Fig. 1 is a diagram showing an exemplary multiple-camera vision system arrangement for acquiring images, in a manner compatible with photometric stereo, relative to a moving surface in the presence of bar light illuminators having a plurality of interleaved lighting source arrays oriented at discrete, differing oblique angles;

[0010] Fig. 2 is an exemplary bar light illuminator in accordance with the example of Fig. 1 showing the dual-angle oblique light source arrangement;

[0011] Fig. 3 is a perspective view showing a pair of oppositely angled bar lights in accordance with the example of Fig. 1;

[0012] Fig. 4 is a plan view showing the arrangement of bar lights in accordance with Fig. 1 illustrating how the four illumination fields produced by a pair of dual-angleoblique bar lights is substantially equivalent to four distant point sources arranged in four quadrants;

[0013] Fig. 5 is a side view of a portion of an array of localized, solid state lighting sources in an interleaved arrangement that propagates light in each of two opposing oblique angles with respect to a vertical / camera optical axis, employing leaded LEDs according to an embodiment;

[0014] Fig. 6 is a perspective view of an exemplary leaded LED for use with the array of Fig. 5;

[0015] Fig. 7 is a side view of a portion of an array of localized, solid state lighting sources in an interleaved arrangement that propagates light in each of two opposing oblique angles with respect to a vertical / camera optical axis, employing rightangle LEDs according to an embodiment;

[0016] Fig. 8 is a perspective view of an exemplary right-angle LED for use with the array of Fig. 7;

[0017] Fig. 9 is a side view of a portion of an array of localized, solid state lighting sources in an interleaved arrangement that propagates light in each of two opposing oblique angles with respect to a vertical / camera optical axis, employing MID- style LEDs according to an embodiment;

[0018] Fig. 10 is a perspective view of exemplary MID-style LEDs for use with the array of Fig. 9;

[0019] Fig. 11 is a side view of a portion of an array of localized, solid state lighting sources in an interleaved arrangement that propagates light in each of two opposing oblique angles with respect to a vertical / camera optical axis, employing surface mount LEDs and a prismatic or direction turning fdm overlay according to an embodiment;

[0020] Fig. 12 is a plan view of two discrete, interleaved direction turning fdm sections overlying each of adjacent, alternating LEDs of Fig. 11;

[0021] Fig. 13 is a side view of a portion of an array of localized, solid state lighting sources in an interleaved arrangement that propagates light in each of two opposing oblique angles with respect to a vertical / camera optical axis, employing surface mount LEDs and discrete, overlying rotatable mirrors according to an embodiment;

[0022] Fig. 14 is a side view of a portion of an array of localized, solid state lighting sources in an interleaved arrangement that propagates light in each of twoopposing oblique angles with respect to a vertical / camera optical axis, employing surface mount LEDs and a prismatic or direction turning film overlay, and in which the LEDs are arranged in modules defining a predetermined spacing between LEDs and an overlying shield or baffle, according to an embodiment;

[0023] Fig. 15 is a side view showing an exemplary camera and a pair of oppositely oriented illumination bars with interleaved, oblique angle arrays, in a first exemplary arrangement, as shown generally in Fig. 1;

[0024] Fig. 16 is a side view showing an exemplary camera and a pair of oppositely oriented illumination bars with interleaved, oblique angle arrays, in a second exemplary arrangement, as shown generally in Fig. 1;

[0025] Fig. 17 is a side view showing an exemplary camera and a pair of oppositely oriented illumination bars with interleaved, oblique angle arrays, in a third exemplary arrangement, as shown generally in Fig. 1;

[0026] Fig. 18 is a side view showing an exemplary camera and one illumination bar with interleaved, oblique angle arrays, and two conventional, oppositely oriented lighting bars, in a fourth exemplary arrangement, as shown generally in Fig. 1;

[0027] Fig. 19 is a side view showing an exemplary camera and one illumination bar with interleaved, oblique angle arrays, and two conventional, oppositely oriented lighting bars, in a fifth exemplary arrangement, as shown generally in Fig. 1; and

[0028] Fig. 20 is a flow diagram of a generalized procedure for acquiring images with illumination bars defining interleaved, oblique angle arrays, and generating results therefrom according to an embodiment.DETAILED DESCRIPTION

[0029] I. System Overview^

[0030] Fig. 1 shows a vison system arrangement 100 according to an illustrative embodiment. In this exemplary system, a moving surface 110 moves in a direction of motion (arrow 112) through an inspection area 114. The surface 110 can be a conveyer having a predetermined width WC carrying objects of one or more sizes / shapes, or a web. The surface of the object or w eb inspected for various defects, details or features that can define a width, length and height / depth (x. y and z dimensions as shown). Thus, such features may require multiple, discrete lighting conditions to be accurately imaged. Theuse of photometric stereo techniques can render such features with sufficient detail to perform classical and / or deep-leaming-based machine vision analysis.

[0031] As shown, a plurality of cameras 120, 122, 124 and 126 are mounted over the surface 110 at the inspection area 114. The cameras can include an appropriate image sensor (e.g. a CMOS sensor) and optics that should be clear to those of skill. These cameras 120-126 each define respective fields of view (FOVs) sufficient to image the entire surface width WC. In this exemplary embodiment, the optical axis OA1, OA2, OA3 and OA4 of each camera 120 is approximately perpendicular to the local plane of the surface 110.

[0032] The cameras 120-126 can include various on board vision system processes / ors and / or can be linked (wired or wirelessly), using an appropriate networking protocol, to a vision system process(or) 130. The vision system processor 130 can be a standalone computing device, and / or instantiated on a general purpose PC, laptop tablet or other device 150 with an appropriate user interface (e.g. keyboard, touchscreen, etc.) 152 and display 154. The vision system process(or) 130 receives image data from each camera 120-126, and provides various controls (131) over the link(s) to the camera(s). Image data is analyzed for features and other information using classical and / or deep- leaming-based tools / processes 132, which can include edge-finding, blob tools, ID readers, etc., as well as image-trained neural networks. The tools / processes 132 can be coordinated with information relative to motion of the surface, which can be derived via an encoder 140 and associated encoder signal 142. The encoder 140 can be operatively connected with the drive components for the surface 110, or otherwise responsive to surface motion (e.g. via mechanical, optical, etc. sensing). Other forms of motion sensing can be employed in alternate embodiments.

[0033] The tools 132 can employ photometric stereo processes on successive images from the camera(s) 120-126. They interoperate with an illumination control process(or) (“illumination controller”) 134 that is interconnected with the tools 132 and provides and / or receives trigger signals 164 to / from a pair of dual-angle oblique bar lights 160 and 162 (also termed herein “bar illuminator(s)”), each oriented at opposing non-parallel angles with respect to the optical axes (OA1-OA4). The bar lights extend across the width WC of the surface 110 so as to provide a continuous illumination pattern to the inspection area 114. The motion signals 142 can be used to trigger different illumination arrays within the overall arrangement of bar lights as described in detailbelow. One or more images are acquired of the inspection area scene in each illumination configuration, and the group of images is analyzed by the tools 132 using photometric stereo and / or other known techniques from which feature information is determined. The feature information is used by further analysis processes 136 to generate results 170. These results can include the surface texture, gradientX / Y, curvature, and / or depth. These results 170 can provide information on object or surface condition, including, but not limited to a presence or absence of a three-dimensional (3D — e.g. physical / structural) defect, or a reflectance defect. The 3D defect or the reflectance defect can be related to one or more of a scratch, a dent, a gouge, debris presence, a buff mark, improper material composition, and / or a variation in material thickness. The results 170 can be transmitted to downstream utilization processes and / or devices to perform desired functions — for example an alarm can be generated, motion can be stopped, a reject action can occur and / or a defective object or surface can be marked. Likewise, analyzed surfaces can be sorted by appropriate gating functions based upon differentiated features.

[0034] II. Dual-Angle Oblique Bar Light Arrangement

[0035] With further reference to Figs. 2-4, the arrangement of the bar lights 160 and 162 (or portions thereof) is shown in further detail. As shown particularly in Fig. 2, the bar lights (a portion of light 160 depicted) define a two-channel arrangement that produces collimated light beams (200 and 202) at two, opposing oblique angles 210 and 220, respectively, with respect to the vertical (e.g. the camera optical axis OA1). The oblique (i.e. non-parallel with the optical axis of the camera) angles 210 and 220 can vary'. In a non-limiting example, the angles 210 and 220 of the opposing oblique light beams each are approximately -35 degrees and +35 degrees, respectively. Notably, each light channel / direction is activated by a separate circuit (that can be directed by the illumination control 134 or another process(or)), so that each channel can independently strobe its array of light sources to propagate light beams 200, 202 at each respective angle. In this example, and as described further below, the two arrays of light sources and associated beams 200, 202 are interleaved across the width (e.g. y-direction) in an alternating manner — i.e. beam 200-beam 202-beam 200-and so forth.

[0036] As described above, and with further reference to Fig. 3, the opposing bar lights 160 and 162 are mounted at opposing angles 310 and 320. The angles are highly variable. By way of non-limiting example, angles 310 and 320 can be approximately -45degrees and +45 degrees, with respect to the optical axis OA1, on opposite sides of the camera (120) to acquire images from the perspective of an upstream and a downstream (relative to the motion direction 112) point of view, respectively.

[0037] Thus, as depicted in Fig. 4, the arrangement of two oppositely angled bar lights 160 and 162, each containing two, interleaved oblique arrays of light sources effectively generates lighting of the scene by four illumination fields that are roughly equivalent to four distant point sources arranged in four quadrants along four discrete directions, respectively that approximate four distant point sources, and associated rays410, 412, 414 and 416, placed at four comers or quadrants Q1-Q4.

[0038] The four depicted illumination channels (quadrants Q1-Q4) are successively strobed to acquire a repeating sequence of four images as the object (or web) surface 1 1 is scanned. The image sequence is then deinterlaced, and used to generate (e.g.) photometric stereo images (texture, gradientX / Y, curvature, and depth).

[0039] III. Interleaved Localized Light Sources

[0040] According to various embodiments, a dual-angle oblique bar light can be constructed with a variety of interleaved light source arrangements. It is contemplated that the light sources are localized within the housing of the bar light(s) 160 and / or 162, meaning that they are electrically powered, light-generating units residing completely within the housing on an appropriate mounting board or other structure. It is also contemplated that the light sources herein are typically solid state units, which employ appropriate semiconductor components and fabrication techniques in their construction, as opposed to filament-based or gas-plasma-based lighting elements. By way of nonlimiting example, each localized solid state light source can comprise an LED (or group of LEDs) of appropriate size, wavelength(s) and configuration.

[0041] Figs. 5 and 6 depict an interleaved dual-angle oblique lighting component with a base 500. The base can be constructed from any appropriate material (e.g. metal, polymer, composite, etc.), and can exhibit heat-dissipation characteristics. The base 500 defines a saw tooth profile as shown, having opposing base platforms 510 and 512 that converge at an angle AL of between approximately 70-90 degrees so as to define the desired oblique angle with respect to the vertical / optical axis for each of a series of leaded LEDs 520. The LEDs in this embodiment include discrete leads 610, 612 (Fig. 6) that interconnect an LED component 620 encapsulated by a lens structure 630. The leads are connected to driver circuitry associated with the base.

[0042] Another arrangement of dual-angle oblique light sources is shown in Figs. 7 and 8. The base 700 includes converging platforms 710 and 172 at an angle AR. which are adapted to mount respective right-angle, surface-mount device (SMD) LEDs 720. An example of such LED components is the PLCC2 (AA4040 Series) available from Kingbright of Taiwan and can include a housing 810 and associated emitter / lens assembly 820. The base 700 can be constructed with a similar angular profile, and heat dissipation function, as the base 500 described above. An appropriate drive can be operatively connected to each LED via an appropriate circuit board.

[0043] Another arrangement of dual-angle oblique light sources is shown in Figs. 9 and 10. The base 900 is similar in form and function as the bases 500 and 700, described above. Thus, the platforms 910 and 912 are disposed at a converging angle AM that allows respective MID-style surface mount risers 920 resulting beams to be directed at the above-described interleaved oblique angles. It is noted that the abovedescribed LED types should be specified to provide a desired current-handling and resulting intensity, which may entail the use of specialized versions of such LEDs, in view of commercially available units currently for sale.

[0044] Higher intensity, commercially available SMD LEDs can be implemented in accordance with the embodiment of Figs. 11 and 12. The arrangement includes a base 1100 that can comprise an appropriate printed circuit board (and associated heat sink / dissipation structure) 1110. The base 1110 is substantially planar, thus simplifying construction and reducing costs. It includes a line of SMD LEDs of sufficient current draw and intensity to provide the desired illumination effect for a given spacing SL therebetw een. The spacing SL can be varied as appropriate to increase or decrease the number / density of LEDs in the array. Notably, the LEDs 1120 can be overlaid by segments of two pieces of direction turning film (or another ID array / structure of prismatic material) 1210 and 1220 that alternate betw een opposing angles of light redirection, which are provided by interleaved fingers 1230 and 1232 with respective, opposing redirection angles. The angle redirection can be within the desired range to provide the desired dual-angle oblique illumination. Note that the direction turning film, or other prismatic structure, can be provided as discrete components overlying the respective LEDs in an alternate embodiment. Appropriate mounting arrangements can be implemented.

[0045] Fig. 13 shows a multiple-oblique angle illumination arrangement using overlying, adjustable (rotatable) mirrors 1330 that allows for a basic printed circuit board (PCB) as a base 1300 and a linear array of high-output SMD LEDs 1310. Each of the rotatable mirrors can be a commercially available unit that is positioned in an appropriate mounting assembly (not shown) along an axis MA overlying a respective LED 1310 that intercepts light received from the LED and propagates the resulting beam at a desired oblique angle direction (arrows 1340 and 1342), with associated, adjacent mirrors rotated (curved double-arrow RM) into opposing orientations. Notably, the mirrors’ functionality allows for fine adjustability of the beam angle to achieve an interleaved set of at least two opposing, oblique-angle beams. It is further contemplated that more than two illumination angles (e.g. 3 angles -35. 0, +35 degrees) can be provided. Thus, the depicted mirror arrangement 1300 of Fig. 13 provided for a high degree of versatility / customization for the bar light, with a straightforward, and high-output LED array.

[0046] Note that the rotatable mirrors provided herein are typically set during manufacturing so as to provide a desired illumination angle. However, it is expressly contemplated that the mirrors can include a modality that allows for field adjustment to repair and / or alter the angle of some or all of the beams in the array.

[0047] The above-described arrangements typically comprise two (or more) interleaved arrays of oblique-angle light sources (e.g. LEDs) disposed along a single line in the widthwise (y-axis) direction. However, any of these arrangements can be modified by placing the opposing-angle light sources / LEDs on separate, adjacent lines within the same bar light housing. This can allow doubling of the density of LEDs for each direction. It is noted that the LEDs would no longer illuminate the same line (collinearly) on the surface, but along displaced lines in the direction of motion (x-axis). Such displacement can be partially compensated by constructing the mounting so as to angle one, or both, of the adjacent arrays toward the other so as to approximate a single line illumination. Other lens arrangements, clear to those of skill, can be used to achieve an approximately collinear illumination effect at the scene.

[0048] Fig. 14 shows another arrangement 1400 of a dual-angle oblique illumination array for a bar light according to an illustrative embodiment, in which the localized solid state light sources (e.g. various types of LEDs above) 1410 are provided in discrete modules 1420 that each consist of two (or more) discrete (e.g.) LEDs mountedon a base 1402 (e.g. a PCB) with vertical separator walls 1404 between modules 1420. Each LED in each module is covered by a prismatic material (or "‘turning film”, as described above) 1430 and 1432 that directs the beam 1440 and 1442, respectively, in each of opposing (i.e. crossing) oblique-angle directions. Notably, the two LEDs are spaced apart by a distance 1450 that is greater than the distance 1452 between LEDs on opposing sides of each module separator wall 1404. This additional spacing distance 1450 allows for a horizontal baffle 1460 on each of opposing sides of the separator wall 1404. The baffles 1460 define openings 1462 along the widthwise direction that limit the relative angle(s) of light propagated from each LED / prism combination to a desired oblique angle range. This eliminates scattered light that is typically produced by such an assembly. Note that this arrangement allows for unlimited expansion of the overall array to accommodate different width bars and also allows for differing oblique and nonoblique angle modules / LED assemblies to be combined in a single line. Note that the configuration of the baffle 1460 can be varied in alternate implementations of this and other embodiments to provide a particular illumination pattern and / or performance characteristic(s).

[0049] Note that the baffles and spacing variation between adjacent light sources can be provided to other embodiments of LEDs and beam-directing components — e.g. angled mounts, rotatable mirrors, etc. — as described above, so as to reduce scattered light outside a desired oblique angle range.

[0050] IV. Alternate Bar Light Configurations

[0051] Figs. 15-19 show7, by way of non-limiting example, a variety7of configurations in w hich one or more dual-angle oblique bar lights 160 and 162, according to the above described embodiments, can be deployed with respect to a surface under inspection 110 by one or more camera(s) C and associated optics O.

[0052] As shown in Fig. 15, the two illustrative bar lights 160 and 1 2 are deployed at opposing angles of approximately 45 degrees (As described above) with respect to the camera optical axis OA. By way of example the opposing far comers are relatively closely spaced at a distance SB1 of approximately 269 mm based upon an exemplary housing height HH of approximately' 150 mm thickness HT of approximately 22 mm. The distance SSI between the light outlet end and the surface 110 in this example is also relatively close at approximately 30 mm (and height HB1 (in the z-axis direction) of approximately 14 mm above the surface 110).

[0053] In the example of Fig. 16, the bar lights 160 and 162 are further spaced apart by an exemplary distance SB2 of approximately 311 mm and an end-to surface spacing SS2 of approximately 60 mm (and height HB2 of approximately 35 mm above the surface 110). In the additional example of the same general configuration in Fig. 17, the bar lights 160, 162 define a spacing SB3 of approximately 396 mm and an end-to- surface spacing SS3 of approximately 120 mm (and height HB3 of approximately 78 mm above the surface 110).

[0054] Fig. 18 shows an alternate, exemplary configuration using a single bar light 160 placed close to the camera optical axis OA and at a relatively small angle (e.g. 10-15 degrees) relative thereto. The end-to-surface spacing SS4 is approximately 134 mm. The single bar light is augments by two conventional non-oblique bar lights 1810 and 1812 oriented at opposing angles (e.g. 45 degrees relative to the optical axis OA) upstream and downstream of the imaged scene. The outer comers are spaced apart by a distance SCI of approximately 352 mm and height HC1 from the outer lower comer to the surface 110 for each bar light 1810, 1812 of approximately 130 mm.

[0055] By way of further example. Fig. 19 shows a minimally compact implementation of the single dual-angle oblique bar light 160 and dual conventional bar lights, as described with reference to Fig. 18 above. In this exemplary embodiment, the dual-angle oblique bar light is located at an end-to-surface distance SS5 of approximately 60 mm. The upstream and downstream conventional bar lights 1910 and 1920 define relative angle of approximately 45 degrees with respect to the optical axis OA and an end-to-surface spacing SSC of approximately 40 mm. The conventional bar lights also define a relatively compact far comer spacing SC2 of approximately 131 mm.

[0056] Note that each of the above exemplary configurations is by way of example and it should be clear that a wide range of possible placements and orientations can be employed to provide the desired illumination effects for a given application. Optimal configurations can be designed empirically using lighting performance specifications and / or by trial and error experimentation by employing different configurations on an imaged scene and acquiring images thereof.

[0057] V. Operational Procedure

[0058] Fig. 20 shows a generalized procedure 2000 for operating an imaging arrangement that employs one or more dual-angle oblique bar lights according to an exemplary embodiment. In step 2010 the system detects motion of the surface underinspection using an encoder signal or other technique and quantifies the degree of motion. When appropriate motion has occurred, the system triggers at least one array of at least one bar light (step 2020). Note that the beams can be provided in one or more wavelengths to achieve different effects, assuming LEDs with a plurality of output wavelengths are provided to one or more arrays are provided. While the surface is illuminated by the array, at least one image is acquired by the associated camera(s) in step 2030. The procedure 2000 then determines if a next array in a given bar light should be triggered as part of the overall image processing task (e.g. photometric stereo) in decision step 2040. If so, then steps 2010-2040 are repeated. Once the last array is triggered (e.g. each opposing angle), then the decision step 2040 branches to decision step 2050, where the procedure 2000 determines whether another bar light is to be illuminated. If so, the procedure repeats steps 2020-2050 until all arrays in all bar lights have been illuminated, and all corresponding images have been acquired and stored in processor memory. Then, in step 2060, the process(or) performs (e.g.) photometric stereo and / or other image processing tasks on the stored images. These processes are used to generate results that are used by downstream processes, as described above.

[0059] In step 2070, as surface motion continues, the procedure 200 repeats 2000 to acquire and analyze another set of images, with which results are generated.

[0060] VI. Conclusion

[0061] It should be clear that the above-described system and method provides consistent illumination across the full width of an object and / or web surface, and is scalable to illuminate moving surfaces of arbitrary size. In a non-limiting example, this illustrative illumination and imaging approach can be used in conjunction with photometric stereo to inspect webs of cathode and anode material that commonly reach 1 .5 meters width. Notably, the dual-angle oblique bar lights of the illustrative embodiments herein can fit into spaces that are too small to accommodate other forms of illumination.

[0062] The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope of this invention. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separateembodiments of the apparatus and method of the present invention, what has been described herein is merely illustrative of the application of the principles of the present invention. For example, as used herein, the terms “process’’ and / or “processor” should be taken broadly to include a variety of electronic hardware and / or software-based functions and components (and can alternatively be termed functional “modules” or “elements”). Moreover, a depicted process or processor can be combined with other processes and / or processors or divided into various sub-processes or processors. Such sub-processes and / or sub-processors can be variously combined according to embodiments herein. Likewise, it is expressly contemplated that any function, process and / or processor herein can be implemented using electronic hardware, software consisting of a non-transitory computer-readable medium of program instructions, or a combination of hardware and software. Additionally, as used herein various directional and dispositional terms such as “vertical”, “horizontal”, “up”, “down”, “bottom”, “top”, “side”, “front”, “rear”, “left”, “right”, and the like, are used only as relative conventions and not as absolute directions / dispositions with respect to a fixed coordinate space, such as the acting direction of gravity. Additionally, where the term “substantially” or “approximately” is employed with respect to a given measurement, value or characteristic, it refers to a quantity' that is within a normal operating range to achieve desired results, but that includes some variability due to inherent inaccuracy and error within the allowed tolerances of the system (e.g. 1-5 percent). Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.

[0063] What is claimed is:

Claims

CLAIMS1. A system for imaging a surface, moving in a motion direction, with a vision system, the system comprising: a first camera, defining a first optical axis, configured to transmit acquired images of the surface to a vision system processor; and a first bar illuminator extending in a direction transverse to the motion direction, the first bar illuminator defining opposing, interleaved arrays of localized solid state light sources, each of the arrays oriented to propagate light in a line at a respective, opposing oblique angle with respect to the first optical axis, and wherein the first bar illuminator is oriented with respect to the surface so as to propagate light substantially along a first plane defining a first non-parallel angle with respect to the first optical axis.

2. The system as set forth in claim 1, further comprising a second bar illuminator extending in a direction transverse to the motion direction, the second bar illuminator defining opposing, interleaved arrays of localized solid state light sources, each of the arrays oriented to propagate light in a line at a respective, opposing oblique angle with respect to the first optical axis, and wherein the second bar illuminator is oriented with respect to the surface so as to propagate light substantially along a second plane defining a second non-parallel angle with respect to the first optical axis.

3. The system as set forth in claim 2, wherein at least one of the first bar illuminator and the second bar illuminator is operatively connected to an illumination controller that independently operates each of the interleaved arrays thereof as a separate illumination channel, respectively.

4. The system as set forth in claim 3, wherein the first non-parallel angle and the second non-parallel angle define opposing angles with respect to the first optical axis.

5. The system as set forth in claim 4, wherein the localized solid state light sources comprise LEDs of at least one of leaded LEDs, right angle LEDs, MID-style LEDS,LEDs with a prismatic overlay, or LEDs with rotatable mirrors defining a predetermined mirror angle.

6. The system as set forth in claim 5, wherein the LEDs comprise the LEDs with the prismatic overlay, and wherein the prismatic overlay defines a direction turning film configured to bend the light from each of adjacent LEDs into each of the respective, opposing oblique angles.

7. The system as set forth in claim 6. wherein the direction turning film defines two discrete interleaved sets of fingers alternately overlying adjacent LEDs.

8. The system as set forth in claim 5, wherein the LEDs comprise at least one of the leaded LEDs or the MID-style LEDs, and wherein the LEDs are mounted on a plurality of adjacent faces of a plurality of risers defining opposing angles on each of the plurality of adjacent faces.

9. The system as set forth in claim 5, further comprising: an array of modules, each module including pairs of the LEDs which propagate the light via the opposing oblique angles, wherein the pairs of the LEDs are spaced apart by a first spacing distance within the respective module, and wherein adjacent modules within the array of modules are spaced apart by a second spacing distance smaller than the first spacing distance.

10. The system as set forth in claim 9, wherein each of the LEDs is overlaid by a baffle configured to limit a range of angles of propagation of the light therefrom.

11. The system as set forth in claim 5, wherein the LEDs comprise the LEDs with rotatable mirrors defining the predetermined mirror angle, and wherein the rotatable mirrors are constructed and arranged to allow for (a) adjustment of the predetermined mirror angle during manufacture of the first bar illuminator or the second bar illuminator, or (b) field adjustment of the predeterminedmirror angle during installation of the first bar illuminator or the second bar illuminator relative to the surface.

12. The system as set forth in claim 4, wherein the vision system processor is constructed and arranged to acquire, with the first camera, images of the surface in conjunction with predetermined amounts of motion thereof, and wherein each of the arrays of the first bar illuminator and each of the arrays of the second bar illuminator are each, respectively, triggered concurrently with each of the predetermined amounts of motion.

13. The system as set forth in claim 12, wherein the predetermined amounts of motion are signaled by an encoder associated with the motion of the surface.

14. The system as set forth in claim 12, wherein the vision system processor is constructed and arranged to perform a photometric stereo operation on the images and provide results related thereto.

15. The system as set forth in claim 1, further comprising a conventional bar illuminator that propagates light in a line approximately collinear with the line of the first bar illuminator.

16. The system as set forth in claim 1, further comprising a second camera adjacent to the first camera, defining a second optical axis, and configured to transmit acquired images of the surface to the vision system processor or a second vision system processor.

17. A method for imaging a surface, moving in a motion direction, with a vision system, the method comprising: transmitting, from a first camera having a first optical axis, acquired images of the surface to a vision system processor; and operating, in a first bar illuminator extending in a direction transverse to the motion direction, opposing, interleaved arrays of localized solid state light sources, so that each of the arrays propagate light in a line at a respective, opposing oblique angle with respect to the first optical axis, andwherein the first bar illuminator is oriented with respect to the surface so as to propagate light substantially along a first plane defining a first non-parallel angle with respect to the first optical axis.

18. The method as set forth in claim 17, further comprising: determining, from the acquired images of the surface, a presence or absence of a 3D defect or a reflectance defect corresponding to the surface.

19. The method as set forth in claim 18, wherein the 3D defect or the reflectance defect comprises at least one of: a scratch, a dent, a gouge, debris presence, a buff mark, improper material composition, or a variation in material thickness20. The method as set forth in claim 17, further comprising, operating, in a second bar illuminator extending in a direction transverse to the motion direction, opposing, interleaved arrays of localized solid state light sources, so that each of the arrays propagate light in a line at a respective, opposing oblique angle with respect to the first optical axis, and wherein the second bar illuminator is oriented with respect to the surface so as to propagate light substantially along a second plane defining a second non-parallel angle with respect to the first optical axis.

21. The method as set forth in claim 20, further comprising independently operating each of the interleaved arrays thereof.

22. The method as set forth in claim 20, wherein the first non-parallel angle and the second non-parallel angle define opposing angles with respect to the first optical axis.

23. The method as set forth in claim 22. further comprising, providing the localized solid state light sources as at least one of leaded LEDs, right angle LEDs, MID-style LEDS, LEDs with a prismatic overlay, or LEDs with rotatable mirrors defining a predetermined mirror angle.

24. The method as set forth in claim 23, further comprising, providing the LEDs with the prismatic overlay, and configuring the prismatic overlay as a direction turning film configured to bend the light from each of adjacent LEDs into each of the respective, opposing oblique angles.

25. The method as set forth in claim 24, further comprising, configuring the direction turning film into two discrete interleaved sets of fingers alternately overlying adjacent LEDs.

26. The method as set forth in claim 24, wherein the LEDs comprise at least one of the leaded LEDs or the MID-style LEDs, and mounting the LEDs on a plurality of adjacent faces of a plurality7of risers defining opposing angles on each of the plurality of adjacent faces.

27. The method as set forth in claim 24, further comprising: configuring an array of modules in which each module thereof includes pairs of the LEDs which propagate the light via the opposing oblique angles, spacing apart the pairs of the LEDs by a first spacing distance within the respective module, and spacing apart adjacent modules within the array of modules by a second spacing distance smaller than the first spacing distance.

28. The method as set forth in claim 27, further comprising, overlaying each of the LEDs with a baffle configured to limit a range of angles of propagation of the light therefrom.

29. The method as set forth in claim 24, further comprising, configuring the LEDs with rotatable mirrors defining the predetermined mirror angle, and configuring the rotatable mirrors to allow for (a) adjustment of the predetermined mirror angle during manufacture of the first bar illuminator or the second bar illuminator, or (b) field adjustment of the predetermined mirror angle during installation of the first bar illuminator or the second bar illuminator relative to the surface.

30. The method as set forth in claim 23, further comprising, acquiring, with the vision system processor, from the first camera, images of the surface in conjunction with predetermined amounts of motion thereof, and triggering each of the arrays of the first bar illuminator and each of the arrays of the second bar illuminator, respectively, concurrently with each of the predetermined amounts of motion.

31. The method as set forth in claim 30, further comprising, signaling the predetermined amounts of motion by an encoder associated with the motion of the surface.

32. The method as set forth in claim 30, further comprising, performing, with the vision system processor, a photometric stereo operation on the images, and providing results related thereto.

33. The method as set forth in claim 20, further comprising, propagating, with a conventional bar illuminator, light in a line approximately collinear with the line of the first bar illuminator.

34. The method as set forth in claim 20, further comprising, configuring a second camera adjacent to the first camera, the second camera defining a second optical axis, and transmitting acquired images of the surface to the vision system processor or a second vision system processor.

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