IL243166B2 - Modification of the optical properties of line-scan illumination depending on the light angle along the line axis - Google Patents

Description

243166/2 MODIFICATION OF THE OPTICAL PROPERTIES OF LINE-SCAN ILLUMINATION DEPENDING ON THE LIGHT ANGLE ALONG THE LINE AXIS BACKGROUND OF THE INVENTION[001] Many optical inspection systems use a line-scan camera to create an image of an inspected article, by moving either the camera or the article in a direction perpendicular to the scan line. Such systems are also fitted with line-illumination devices which move along with the camera and illuminate the part of the article being imaged by the camera. [002] When the inspected article is not flat, e.g. a PCB panel with metal conductors having a trapezoid-like profile, or when looking for surface irregularities, many such systems employ multiple illumination sources, e.g. either dark-field (oblique illumination from the sides) or bright-field (coaxial illumination from above) or both, depending on the application.[003] However, in contrast with area-scan systems, which employ circularly-symmetric concentric rings of illumination, the angular coverage of line-illumination may be inherently anisotropic. So, for example, in applications which require dark-field only illumination (e.g. to find surface irregularities), angular coverage may be incomplete, in particular not covering all surface points along the line axis.[004] Thus, it would be desirable to achieve a more isotropic (i.e. close to circularly- symmetric) angular coverage of both bright- and dark-field illumination in line-scan inspection systems, one which will be closer to that of area-scan systems.

SUMMARY[005] There may be provided systems methods and a beam modifier (also referred to as modifier, beam splitter or modifying module).[006] The system may be for inspecting an object and may include a camera; an illumination module that may be configured to illuminate the object by a first beam, a second beam and a third beam that span over three different angular ranges of incidence; an objective lens that may be configured to (a) receive a reflectance of the first beam, a reflectance of the second beam and a reflectance of the third beam and (b) direct the reflectance of the first beam, the reflectance of the second beam and the reflectance of the 243166/2 third beam towards a sensing module; wherein the sensing module may be configured to sense the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam; wherein the illumination module may include a modifying module that may be configured to perform at least one out of: introduce at least one difference out of color difference and polarization difference between two or more beams of the first, second and third beams; force the first beam to illuminate the object at only one angular range out of (i) a first angular region that may include normal illumination angle and up to a predefined angular deviation from normal illumination; and (ii) a second angular region that surrounds the first angular region; and illuminate the object by a fourth beam that partially overlaps the first beam, when impinging on the object, to form an overlap region that may include the first angular region.[007] The modifying module may include a Fresnel optical component that may be selected from a Fresnel beam splitter and a Fresnel prism.[008] The modifying module may include a beam splitter that may be configured to receive an intermediate beam and to split the intermediate beam to the first beam and a fourth beam thereby causing the first beam and the fourth beam to impinge on the object outside the first angular region.[009] The illumination module may be configured to illuminate the object by the fourth beam at an angular range of incidence that may differ from an angular range of incidence of the first beam; wherein the objective lens may be configured to receive a reflectance of the fourth beam and direct the reflectance of the fourth beam towards the sensing module; wherein the sensing module may be configured to sense the reflectance of the fourth beam.[0010] The beam splitter may include only facets that may be oriented by at least ten degrees to a normal to a propagation axis of the intermediate beam.[0011] The beam splitter may include multiple facets that may be oriented by an angle that does not exceed forty five degrees in relation to a propagation axis of the intermediate beam.[0012] The beam splitter may include multiple facets that may be oriented by an angle that does not exceed twenty degrees in relation to a propagation axis of the intermediate beam. 243166/2 id="p-13" id="p-13" id="p-13" id="p-13" id="p-13" id="p-13"

[0013] The beam splitter may be configured to introduce a color difference between the first and fourth beams.[0014] The beam splitter may be configured to introduce a polarization difference between the first and fourth beams.[0015] The odd facets of the beam splitter and even facets of the Fresnel beam splitter may differ by each other by at least one out of a color filtering property and a polarization property.[0016] The modifying module may include a beam splitter that may be configured to receive an intermediate beam and to split the intermediate beam to the first beam and a fourth beam thereby causing the first beam and the fourth beam to partially overlaps the first beam, when impinging on the object, to form an overlap region that may include the first angular region.[0017] The modifying module may be configured to introduce a color difference between the first and fourth beams.[0018] The modifying module may be configured to introduce a color difference between (a) the first and second beams and (b) the third and fourth beams.[0019] The modifying module may be configured to introduce a polarization difference between the first and fourth beams.[0020] The overlap region may illuminate the object with white light.[0021] The beam splitter may include only facets that may be oriented by at least fifth degrees to a normal to a propagation axis of the intermediate beam.[0022] The modifying module may include a beam splitter that may be configured to receive an intermediate beam and to split the intermediate beam to the first beam, a fourth beam and a fifth beam thereby causing the first beam, the fourth beam and the fifth beam to impinge on the object at different angular ranges.[0023] The first beam may impinge on the object within the first angular range and wherein the fourth and fifth beams impinge on the object outside the first angular range. [0024] The modifying module may be configured to introduce a polarization difference between the first and fourth beams.[0025] The modifying module may be configured to introduce a color difference between the first and fourth beams. 243166/2 id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26"

[0026] The modifying module may include multiple triplets of adjacent facets, wherein each triplets of adjacent facets may include a first fact that may be normal to a propagation axis of the intermediate beam, a second facet that has a positive orientation in relation to the first facet and a third fact that has a negative orientation in relation to the first facet.[0027] The first facet may be coated with a first color filter, the second fact may be coated with a second color filter and the third fact may be coated with a third color filter; wherein at least two color filters out of the first, second and third color filter may differ from each other by spectrum.[0028] The first color filter may differ from the second and third color filters and the second and color filters have a same spectrum.[0029] The first color filter, the second color filter and the third color filter may differ from each other by spectrum.[0030] The first facet may be coated with a first polarizer, the second fact may be coated with a second polarizer and the third fact may be coated with a third polarizer; wherein at least two polarizers out of the first, second and third polarizer may differ from each other by polarization.[0031] The predefined angular deviation may exceed twenty degrees.[0032] The predefined angular deviation may exceed ten degrees.[0033] The method may be for inspecting an object and may include illuminating the object by a first beam, a second beam and a third beam that span over three different angular ranges of incidence; receiving, by an objective lens, a reflectance of the first beam, a reflectance of the second beam and a reflectance of the third beam; directing, by the objective lens, the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam towards a sensing module; sensing, by a sensing module, the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam; wherein the illuminating may include performing, by a modifying module, at least one out of: introducing at least one difference out of color difference and polarization difference between two or more beams of the first, second and third beams; forcing the first beam to illuminate the object at only one angular range out of (i) a first angular region that may include normal illumination angle and up to a 243166/2 predefined angular deviation from normal illumination; and (ii) a second angular region that surrounds the first angular region; and illuminating the object by a fourth beam that partially overlaps the first beam, when impinging on the object, to form an overlap region that may include the first angular region.[0034] The modifying module may include a Fresnel optical component that may be selected from a Fresnel beam splitter and a Fresnel prism.[0035] The modifying module may include a beam splitter; wherein the method may include receiving by the beam splitter an intermediate beam and to splitting the intermediate beam to the first beam and a fourth beam thereby causing the first beam and the fourth beam to impinge on the object outside the first angular region.[0036] The method may include illuminating the object by the fourth beam at an angular range of incidence that may differ from an angular range of incidence of the first beam; receiving by the objective lens a reflectance of the fourth beam and directing the reflectance of the fourth beam towards the sensing module; and sensing, by the sensing module the reflectance of the fourth beam.[0037] The beam splitter may include only facets that may be oriented by at least ten degrees to a normal to a propagation axis of the intermediate beam.[0038] The beam splitter may include multiple facets that may be oriented by an angle that does not exceed forty five degrees in relation to a propagation axis of the intermediate beam.[0039] The beam splitter may include multiple facets that may be oriented by an angle that does not exceed twenty degrees in relation to a propagation axis of the intermediate beam.[0040] The method may include introducing by the beam splitter a color difference between the first and fourth beams.[0041] The method may include introducing by the beam splitter a polarization difference between the first and fourth beams.[0042] The method wherein odd facets of the beam splitter and even facets of the Fresnel beam splitter may differ by each other by at least one out of a color filtering property and a polarization property. 243166/2 id="p-43" id="p-43" id="p-43" id="p-43" id="p-43" id="p-43"

[0043] The modifying module may include a beam splitter; wherein the method may include receiving by the beam splitter an intermediate beam; splitting by the beam splitter the intermediate beam to the first beam and a fourth beam thereby causing the first beam and the fourth beam to partially overlaps the first beam, when impinging on the object, to form an overlap region that may include the first angular region.[0044] The method may include introducing by the modifying module a color difference between the first and fourth beams.[0045] The method may include introducing by the modifying module a color difference between (a) the first and second beams and (b) the third and fourth beams.[0046] The method may include introducing by the modifying module a polarization difference between the first and fourth beams.[0047] The overlap region illuminates the object with white light.[0048] The beam splitter may include only facets that may be oriented by at least fifth degrees to a normal to a propagation axis of the intermediate beam.[0049] The modifying module may include a beam splitter; wherein the method may include receiving by the beam splitter that an intermediate beam and splitting the intermediate beam to the first beam, a fourth beam and a fifth beam thereby causing the first beam, the fourth beam and the fifth beam to impinge on the object at different angular ranges.[0050] The first beam may impinge on the object within the first angular range and wherein the fourth and fifth beams impinge on the object outside the first angular range. [0051] The method may include introducing by the modifying module a polarization difference between the first and fourth beams.[0052] The modifying module may be configured to introduce a color difference between the first and fourth beams.[0053] The modifying module may include multiple triplets of adjacent facets, wherein each triplets of adjacent facets may include a first fact that may be normal to a propagation axis of the intermediate beam, a second facet that has a positive orientation in relation to the first facet and a third fact that has a negative orientation in relation to the first facet. 243166/2 id="p-54" id="p-54" id="p-54" id="p-54" id="p-54" id="p-54"

[0054] The first facet may be coated with a first color filter, the second fact may be coated with a second color filter and the third fact may be coated with a third color filter; wherein at least two color filters out of the first, second and third color filter may differ from each other by spectrum.[0055] The first color filter may differ from the second and third color filters and the second and color filters have a same spectrum.[0056] The first color filter, the second color filter and the third color filter may differ from each other by spectrum.[0057] The first facet may be coated with a first polarizer, the second fact may be coated with a second polarizer and the third fact may be coated with a third polarizer; wherein at least two polarizers out of the first, second and third polarizer may differ from each other by polarization.[0058] The predefined angular deviation may exceed twenty degrees.[0059] The predefined angular deviation may exceed ten degrees.[0060] There may be provided a beam modifier that may include multiple triples of facets; wherein each triplet of facets includes (a) a first facet that may be normal to an input axis of an input light beam and may be coated with a red filter, (b) second and third facets that may be coated with a green filter; wherein the second and third facets of each triplet of facets may be oriented in positive and negative angles to the first facet of the triplet of facets and; wherein the second and third facets of each triplets of facets may be not normal to the input axis.[0061] There may be provided a beam that may include multiple triples of facets; wherein each triplet of facets includes (a) a first facet that may be normal to an input axis of an input light beam and may be coated with a red filter, (b) a second facet that may be coated with a green filter, and (c) a third facet that may be coated with a blue filter; wherein the second and third facets of each triplet of facets may be oriented in positive and negative angles to the first facet of the triplet of facets and; wherein the second and third facets of each triplets of facets may be not normal to the input axis.[0062] There may be provided a beam modifier that may include multiple pairs of facets; wherein the facets of the multiple pairs of facets may be not normal to an input axis of an input light beam; wherein the facets of each pair of facets may be oriented at small angles 243166/2 in relation to a normal to the input axis; wherein each pair of facets may include a first facet that may be coated with a magenta filter and a second facet that may be coated with a green filter.

BRIEF DESCRIPTION OF THE INVENTION[0063] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:[0064] FIG. 1 illustrates an inspection system according to an embodiment of the invention;[0065] FIG. 2 illustrates a prior art illumination pattern formed on a spherical object;[0066] FIG. 3 illustrates a Fresnel beam splitter of the system of FIG.1 according to an embodiment of the invention;[0067] FIG. 4A illustrates a cross sectional view of a Fresnel beam splitter according to an embodiment of the invention;[0068] FIG. 4B illustrates an illumination pattern formed on a spherical object when using the Fresnel beam splitter of FIG. 4A according to an embodiment of the invention;[0069] FIG. 5A illustrates a cross sectional view of a Fresnel beam splitter according to an embodiment of the invention;[0070] FIG. 5B illustrates an illumination pattern formed on a spherical object when using the Fresnel beam splitter of FIG. 5A according to an embodiment of the invention;[0071] FIG. 6A illustrates a cross sectional view of a Fresnel beam splitter according to an embodiment of the invention;[0072] FIG. 6B illustrates an illumination pattern formed on a spherical object when using the Fresnel beam splitter of FIG. 6A according to an embodiment of the invention;[0073] FIG. 7A illustrates a cross sectional view of a Fresnel beam splitter according to an embodiment of the invention;[0074] FIG. 7B illustrates an illumination pattern formed on a spherical object when using the Fresnel beam splitter of FIG. 7A according to an embodiment of the invention;[0075] FIG. 8A illustrates a cross sectional view of a Fresnel beam splitter according to an embodiment of the invention; 243166/2 id="p-76" id="p-76" id="p-76" id="p-76" id="p-76" id="p-76"

[0076] FIG. 8B illustrates an illumination pattern formed on a spherical object when using the Fresnel beam splitter of FIG. 8A according to an embodiment of the invention; [0077] FIG. 9 illustrates a method according to an embodiment of the invention;[0078] FIG. 10 illustrates an illumination path according to an embodiment of the invention; and[0079] FIG. 11 illustrates a relationship between a source angular range and a modified angular range according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION[0080] Because the apparatus implementing the present invention is, for the most part, composed of electronic components and circuits known to those skilled in the art, circuit details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.[0081] In the following specification, the invention will be described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.[0082] In some prior art systems dark-field only line-illumination is anisotropic and particularly does not cover all directions.[0083] According to an embodiment of the invention there is provided a system that exhibits an improved, approximately isotropic, angular coverage of dark-field illumination.[0084] This is achieved by having a Fresnel beam splitter or prism or a similar modifier that is positioned after the bright-field illumination source, such that light rays in normal and small angles are suppressed, leaving only oblique-angle light rays, which, combined with the dark-field illumination sources, create an approximate dark-field illumination ring covering most illumination directions. See, for example, figures 4A and 4B.[0085] In some prior art systems the bright-field only line-illumination is anisotropic, particularly containing unwanted oblique lighting angles. 243166/2 id="p-86" id="p-86" id="p-86" id="p-86" id="p-86" id="p-86"

[0086] According to an embodiment of the invention there is provided a system that exhibits a more concentrated and pure bright-field illumination, covering only normal and small lighting angles.[0087] This is achieved by a Fresnel beam splitter or prism or a similar modifier that is positioned after the bright-field illumination source, such that light rays in oblique angles are suppressed, leaving only normal and small-angle light rays, which create concentrated bright-field illumination spot. See, for example, figures 8A and 8B.[0088] According to an embodiment of the invention there is provided a system that exhibits a better, approximately isotropic, separation of color illumination, with normal and small angles having one color, and oblique angles having the second color.[0089] This is achieved by a Fresnel beam splitter or prism or a similar modifier that is positioned after the bright-field illumination source, such that light rays in normal and small angles are filtered with one color, and oblique-angle light rays are filtered with a second color; and color filters of similar color to that second color applied to the dark­field illumination sources, creating a concentrated bright-field spot of the first color, and an approximate dark-field ring of the second color. . See, for example, figures 5A and 5B. [0090] According to an embodiment of the invention there is provided a system that exhibits a better, approximately isotropic, separation of color illumination, with normal and small angles having one color, and oblique angles having either of the two other colors, depending on the oblique-angle direction.[0091] This is achieved by a Fresnel beam splitter or prism or a similar modifier that is positioned after the bright-field illumination source, such that light rays in normal and small angles are filtered with one color, oblique-angle light rays in one direction along the scan-line are filtered with a second color, and oblique-angle light rays in the opposite direction along the scan-line are filtered with a third color; and color filters of similar colors to those second and third colors applied to the dark-field illumination sources, respectively, creating a concentrated bright-field spot of the first color, and an approximate dark-field ring, half of which having the second color, and the other half having the third color. . See, for example, figures 6A and 6B. The modifier (such as a Fresnel modifier) may be positioned to extend out of the page of the figure. 243166/2 id="p-92" id="p-92" id="p-92" id="p-92" id="p-92" id="p-92"

[0092] Figure 1 illustrates a line-scan inspection system according to an embodiment of the invention.[0093] The system includes:a. A bright-field (BF) illumination source 5 for generating a BF beam.b. A beam splitter 6.c. Objective lens 4.d. Dark-field (DF) illumination sources 71, 72, for generating DF beams.e. Modifier 8 that is positioned between the BF illumination source 5 and the beam splitter 6 and is for modifying the BF beam to provide one or more modified BF beams.f. DF color filters or polarizers 91 and 92 that are positioned between DF illumination sources 71 and 72, respectively, and object 2 for changing the color and/or polarization of the DF beams to provide two modified DF beams that impinge on the article at oblique angles.g. Camera 3.h. Controller 142 for controlling the system.i. Image processor 141 for receiving detection signals from camera 3 and processing the detection signals.j. Table 1 for supporting and/or moving article 2.[0094] Camera 3 may be a polarizing camera. Accordingly – camera 3 may include an analyzer or an adjustable color filter. Thus –camera 3 may receive light of different polarizations and may differentiate between the different polarization components.[0095] Objective lens 4 is positioned between camera 3 and the beam splitter 6. Beam splitter 6 is positioned between the object 2 and the objective lens 4.[0096] The one or more modified BF beams are directed by beam splitter 6 to impinge on object.[0097] A reflectance of each one of the one or more modified BF beams and a reflectance of each one of the modified DF beams pass through the beam splitter 6 and through objective lens 4 and impinges on camera 3.[0098] Modifier 8 and DF color filters or polarizers 91 and 92 form a modifying module. 243166/2 id="p-99" id="p-99" id="p-99" id="p-99" id="p-99" id="p-99"

[0099] An angular coverage map can be generated by illuminating and imaging a shiny metal spherical half-dome, as is often done when calibrating illumination systems in practice- see Figure 2.[00100] The center of the map corresponds to normal lighting and reflection (i.e., from above). Other areas (131 and 132) represent various angles, getting more oblique away from the center.[00101] Figure 2 illustrates a prior art coverage map 11 that is obtained by scanning a spherical shiny surface. Three elongates bright lobes can be observed in the coverage map 11. The central one 12 corresponds to BF, and the top and bottom ones 131, 132 correspond to the two DF sources.[00102] The modifier 8 of Figure 1 can be implemented using a Fresnel array of small prisms, known as beam splitter Fresnel, whose different faces are coated with color-filtering materials of different colors or with different polarizing films, depending on the desired outcome. Each face deflects the light to a different range of angles, thus producing different colors or different polarized rays for different angles of incidence. [00103] Fig. 3 illustrates an example of a modifier 8 according to an embodiment of the invention. The modifier 8 is a Fresnel beam splitter that has multiple facets. None of these facets is normal to the propagation axis (denoted input axis 11).[00104] Figure 4A is a cross sectional view of a modifier 18 which suppresses normal and small angles.[00105] The incoming light rays (propagate along input axis 18) first hit the jagged side of the modifier 18, and then exit through the flat side of modifier 18.[00106] Figure 4B illustrates the resulting angular coverage from applying such a modifier to the BF source. Figure 4B illustrates a coverage map 20 that has four lobes 21, 22, 23 and 24. These lobes do not cover the center of the coverage map 20 – corresponding to a suppression of normal and small angles.[00107] Figure 5A illustrates a modifier 30 which colors small angles with one color Red (R) and oblique angles with a second color Green (G).[00108] Modifier 30 includes multiple triples of facets. Each triplet includes a first facet that is normal to input axis 11 and is coated with a red filter 32 as well as second and third facets that are coated with a green filter 31. The second and third facets are 243166/2 oriented in positive and negative angles to the first facet and both are not normal to input axis 11.[00109] Figure 5B is the resulting coverage map 40 when using this modifier (30) and coloring the DF sources with the same second color G. Coverage map 40 includes four green (G) lobes 41, 42, 43 and 44 – wherein these lobes do not cover the center of the coverage map 40 – corresponding to a suppression of normal and small angles.Coverage map 40 also includes a red (R) lobe – at its center.[00110] Figure 6A illustrates a modifier 50 which colors small angles with one color R and oblique angles with a second color G and third color B.[00111] Modifier 50 includes multiple triples of facets. Each triplet includes a first facet that is normal to input axis 11 and is coated with a red filter 52, a second facet that is coated with a green filter 51 and a third facet that is coated with a blue filter 53. The second and third facets are oriented in positive and negative angles to the first facet and both are not normal to input axis 11.[00112] Figure 6B is the resulting coverage map 60 when using this modifier and coloring the DF sources with the same second and third colors G, B, respectively.[00113] Coverage map 60 of Fig. 6B includes a top green (G) lobe 61, a bottom blue (B) lobe 65, a left green lobe 62, a right blue lobe 64 and a center red lobe 63.[00114] Figure 7A illustrates a modifier 70 which colors leftward angles with one color R and rightward angles with a second color G, such that there is an overlap between the two angle ranges.[00115] Modifier 70 includes multiple pairs of facets. The facets are not normal to input axis 11 and are at relatively small angles in relation to a normal to the input axis 11. Each pair includes a first facet that is coated with a magenta (M) filter 73 and a second facet that is coated with a green (G) filter 71.[00116] Figure 7B is the resulting coverage map when using this modifier 70 and coloring the DF sources with the same first and second colors M, G, respectively. This method effectively creates a tri-color light pattern similar to Fig. 5, but using only two filter colors.[00117] Coverage map 80 includes a top magenta (M) lobe 81, a bottom green (G) lobe 85, and two partially overlapping lobes – left magenta lobe 82 and right green lobe 243166/2 84 – the overlap area between these lobes (82 and 84) is located at the center 83 of coverage map 80 and has a third color which is the combination of the two filter colors (e.g. filter colors magenta and green will generate white in the overlap region). The overlap region is denoted white (W) 83.[00118] There may be provided several types of BF modifiers and optionally combinations thereof with DF color filters or polarizers to achieve various near-isotropic coverage patterns of BF-only, DF-only, dual-color and triple-color. Some are illustrated above.[00119] Any light modification may be of properties other than color. For example, polarizers of different orientations can be applied to the faces of the BF modifier and optionally the DF sources, such that they will be similarly separable when taking multiple polarized images with different analyzer orientations such as polarizing camera, or by using of a liquid crystal optical modulator.[00120] The modifications can be applied to dark-field illumination sources, enabling the creation of even more elaborate angular coverage maps.[00121] There may be provided a method for inspecting an inspected article using a system as illustrated above.[00122] Figure 9 illustrates method 400 according to an embodiment of the invention.[00123] Method 400 may include a sequence of steps 410, 420, 430, 440 and 450.[00124] The method may also include repeating steps 410, 420, 430, 440 and 450while scanning the object. This may include introducing a relative movement between the illumination module and the object.[00125] Step 410 may include illuminating the object by a first beam, a second beam and a third beam that span over three different angular ranges of incidence.[00126] Step 410 may include at least one out of steps 411, 412, 413 and 414.[00127] Step 411 may include introducing at least one difference out of colordifference and polarization difference between two or more beams of the first, second and third beams. See, for example figures 5B, 6B, 7B. 243166/2 id="p-128" id="p-128" id="p-128" id="p-128" id="p-128" id="p-128"

[00128] Step 412 may include forcing the first beam to illuminate the object at only at first angular region that comprises normal illumination angle and up to a predefined angular deviation from normal illumination. See, for example, figure 8B. [00129] Step 413 may include forcing the first beam to illuminate the object at only at second angular region that surrounds the first angular region. See, for example, figure 4B.[00130] Step 414 may include illuminating the object by a fourth beam that partially overlaps the first beam, when impinging on the object, to form an overlap region that comprises the first angular region. See, for example, figure 7A.[00131] Step 420 may include receiving, by an objective lens, a reflectance of the first beam, a reflectance of the second beam and a reflectance of the third beam.[00132] Step 430 may include directing, by the objective lens, the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam towards a sensing module.[00133] Step 440 may include sensing, by a sensing module, the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam.[00134] Step 450 may include processing the detection signals.[00135] Figure 10 shows a whole path from illumination source to the article, to illustrate how it relates to the whole system. In figure 10 (for clarity) the beam-splitter is omitted from the path, as it only folds it without changing the behavior.[00136] It is also noted that illumination line source and the Fresnel modifier of figure 10 should be much longer than the field of view of the article on the table, in order to properly provide the angular illumination.[00137] Figure 11 illustrates that the Fresnel modifier roughly maintains this angular range, but splits the light rays into two wide lobes, which may or may not overlap, depending on the modifier geometry.[00138] Non-limiting examples of ranges of input and output angles.[00139] For the sake of simplicity, only rays at a normal angle (parallel to theoptical axis of the optical components) were considered in the aforementioned figures. However, it is noted that the illumination source outputs light at a significant range of 243166/2 angles (for example between plus and minus thirty degrees to provide an angular range of 60° in total) in the X axis. This is how we get such wide lobes - e.g. in Fig 2.[00140] Non-limiting examples of Fresnel modifiers.[00141] An example of a structure of a fully transparent (without color) modifier is illustrated in http://www.ntkj.co.jp/product_prism_en.html - an actual catalogue of a manufacturer of such Fresnel prism modifiers (without the colors, of course). The various models differ in the geometry of each tiny prism.[00142] We denote the angle at the top of the prism as the apex angle. The above manufacturer offers several choices ranging from 40° to 160°.[00143] Now, some concrete examples using available models, all assuming a 60° spread in input light (as is the actual case with the optical fibers in our system), and a refraction index of about 1.5 for the modifier plastic material:[00144] For the first application as depicted in Fig. 4B (splitting to two separate lobes with a gap in the middle), we calculated that an apex angle of 90° would yield a 14° gap in the middle. An apex angle of 75° would yield a 33° gap.[00145] For the second application as depicted in Figs 5B and 6B (splitting to three lobes), the apex angle should be the same as above, with the addition of horizontal sections between the prisms, as depicted in Fig. 5A and 6A.[00146] For the third application as depicted in Fig. 7B (splitting to two lobes with an overlap), we calculated that an apex angle of 130° would yield a 24° overlap in the middle. An apex angle of 140° would yield a 32° overlap.[00147] Limiting the angular range[00148] In the fourth application, we propose using a modifier which limits the lobe to a narrow spot (Fig 8A and 8B). In this case, a different kind of modifier is needed, one which limits light rays rather than refracting them. Such a modifier is called micro­louver. It is a thin film with a special structure that limits passing light to certain angles along one axis. It is often used for privacy applications such as ATM monitor screens.[00149] An example of such product by 3M can be found here:http://products3.3m.com/catalog/us/en001/electronics_mfg/vikuiti/node_RHGFSQGLQJ be/root_GST1T4S9TCgv/vroot_S6Q2FD9X0Jge/gvel_ZF5G3RNK7Bgl/theme_us_vikui ti_3_0/command_AbcPageHandler/output_html 243166/2 id="p-150" id="p-150" id="p-150" id="p-150" id="p-150" id="p-150"

[00150] Furthermore, those skilled in the art will recognize that boundaries between the functionality of the above described operations are merely illustrative. The functionality of multiple operations may be combined into a single operation, and/or the functionality of a single operation may be distributed in additional operations. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.[00151] Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In an abstract, but still definite sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.[00152] However, other modifications, variations, and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.[00153] The word "comprising" does not exclude the presence of other elements or steps then those listed in a claim. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. Any reference to the terms "comprising", "comprises" should be also be read as a reference to the term "consisting" (excluding the presence of other elements) and/or to the term "essentially consisting" (excluding the presence of other material or important elements).[00154] Furthermore, the terms "a" or "an," as used herein, are defined as one or more than one. Also, the use of introductory phrases such as "at least one" and "one or more" in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing 243166/2 such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe.[00155] Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Claims (50)

1./ WE CLAIM 1. A system for inspecting an object, the system comprises: a camera; an illumination module that is configured to illuminate the object by a first beam, a second beam and a third beam that span over three different angular ranges of incidence; wherein the first beam, the second beam, and the third beam are two dark-field beams and a bright-field beam; an objective lens that is configured to (a) receive a reflectance of the first beam, a reflectance of the second beam and a reflectance of the third beam and (b) direct the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam towards a sensing module; wherein the sensing module is configured to sense the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam; wherein the illumination module comprises a modifying module that is configured to perform at least one out of: (a) introduce at least one difference out of color difference and polarization difference between two or more beams of the first, second and third beams; (b) force the first beam to illuminate the object at only one angular range out of (i) a first angular region that comprises normal illumination angle and up to a predefined angular deviation from normal illumination; and (ii) a second angular region that surrounds the first angular region; and (c) illuminate the object by a fourth beam that partially overlaps the first beam, when impinging on the object, to form an overlap region that comprises the first angular region.

2. The system according to claim 1 wherein the modifying module comprises a Fresnel optical component that is selected from a Fresnel beam splitter and a Fresnel prism.

3. The system according to claim 1 wherein the modifying module comprises a beam splitter that is configured to receive an intermediate beam and to split the intermediate beam to the first beam and a fourth beam thereby causing the first beam and the fourth beam to impinge on the object outside the first angular region. 243166/

4. The system according to claim 3 wherein the illumination module is configured to illuminate the object by the fourth beam at an angular range of incidence that differs from an angular range of incidence of the first beam; wherein the objective lens is configured to receive a reflectance of the fourth beam and direct the reflectance of the fourth beam towards the sensing module; wherein the sensing module is configured to sense the reflectance of the fourth beam.

5. The system according to claim 3 wherein the beam splitter comprises only facets that are oriented by at least ten degrees to a normal to a propagation axis of the intermediate beam.

6. The system according to claim 5 wherein the beam splitter comprises multiple facets that are oriented by an angle that does not exceed forty five degrees in relation to a propagation axis of the intermediate beam.

7. The system according to claim 5 wherein the beam splitter comprises multiple facets that are oriented by an angle that does not exceed twenty degrees in relation to a propagation axis of the intermediate beam.

8. The system according to claim 5 wherein the beam splitter is configured to introduce a color difference between the first and fourth beams.

9. The system according to claim 5 wherein the beam splitter is configured to introduce a polarization difference between the first and fourth beams.

10. The system according to claim 5 wherein odd facets of the beam splitter and even facets of the Fresnel beam splitter differ by each other by at least one out of a color filtering property and a polarization property.

11. The system according to claim 1 wherein the modifying module comprises a beam splitter that is configured to receive an intermediate beam and to split the intermediate beam to the first beam and a fourth beam thereby causing the first beam and the fourth beam to partially overlaps the first beam, when impinging on the object, to form an overlap region that comprises the first angular region.

12. The system according to claim 11 wherein the modifying module is configured to introduce a color difference between the first and fourth beams. 243166/

13. The system according to claim 11 wherein the modifying module is configured to introduce a color difference between (a) the first and second beams and (b) the third and fourth beams.

14. The system according to claim 11 wherein the modifying module is configured to introduce a polarization difference between the first and fourth beams.

15. The system according to claim 11 wherein the overlap region illuminates the object with white light.

16. The system according to claim 11 wherein the beam splitter comprises only facets that are oriented by at least fifth degrees to a normal to a propagation axis of the intermediate beam.

17. The system according to claim 1 wherein the modifying module comprises a beam splitter that is configured to receive an intermediate beam and to split the intermediate beam to the first beam, a fourth beam and a fifth beam thereby causing the first beam, the fourth beam and the fifth beam to impinge on the object at different angular ranges.

18. The system according to claim 17 wherein the first beam impinges on the object within the first angular range and wherein the fourth and fifth beams impinge on the object outside the first angular range.

19. The system according to claim 17 wherein the modifying module is configured to introduce a polarization difference between the first and fourth beams.

20. The system according to claim 17 wherein the modifying module is configured to introduce a color difference between the first and fourth beams.

21. The system according to claim 17 wherein the modifying module comprises multiple triplets of adjacent facets, wherein each triplets of adjacent facets comprises a first fact that is normal to a propagation axis of the intermediate beam, a second facet that has a positive orientation in relation to the first facet and a third fact that has a negative orientation in relation to the first facet.

22. The system according to claim 21 wherein the first facet is coated with a first color filter, the second fact is coated with a second color filter and the third fact is coated with a third color filter; wherein at least two color filters out of the first, second and third color filter differ from each other by spectrum. 243166/

23. The system according to claim 22 wherein the first color filter differs from the second and third color filters and the second and color filters have a same spectrum.

24. The system according to claim 22 wherein the first color filter, the second color filter and the third color filter differ from each other by spectrum.

25. The system according to claim 21 wherein the first facet is coated with a first polarizer, the second fact is coated with a second polarizer and the third fact is coated with a third polarizer; wherein at least two polarizers out of the first, second and third polarizer differ from each other by polarization.

26. The system according to claim 1 wherein the predefined angular deviation exceeds twenty degrees.

27. The system according to claim 1 wherein the predefined angular deviation exceeds ten degrees.

28. A method for inspecting an object, the method comprises: illuminating the object by a first beam, a second beam and a third beam that span over three different angular ranges of incidence; wherein the first beam, the second beam, and the third beam are two dark-field beams and a bright-field beam; receiving, by an objective lens, a reflectance of the first beam, a reflectance of the second beam and a reflectance of the third beam; directing, by the objective lens, the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam towards a sensing module; sensing, by a sensing module, the reflectance of the first beam, the reflectance of the second beam and the reflectance of the third beam; wherein the illuminating comprises performing, by a modifying module, at least one out of: (a) introducing at least one difference out of color difference and polarization difference between two or more beams of the first, second and third beams; (b) forcing the first beam to illuminate the object at only one angular range out of (i) a first angular region that comprises normal illumination angle and up to a predefined angular deviation from normal illumination; and (ii) a second angular region that surrounds the first angular region; and 243166/ (c) illuminating the object by a fourth beam that partially overlaps the first beam, when impinging on the object, to form an overlap region that comprises the first angular region.

29. The method according to claim 28 wherein the modifying module comprises a Fresnel optical component that is selected from a Fresnel beam splitter and a Fresnel prism.

30. The method according to claim 28 wherein the modifying module comprises a beam splitter; wherein the method comprising receiving by the beam splitter an intermediate beam and to splitting the intermediate beam to the first beam and a fourth beam thereby causing the first beam and the fourth beam to impinge on the object outside the first angular region.

31. The method according to claim 30 comprising illuminating the object by the fourth beam at an angular range of incidence that differs from an angular range of incidence of the first beam; receiving by the objective lens a reflectance of the fourth beam and directing the reflectance of the fourth beam towards the sensing module; and sensing, by the sensing module the reflectance of the fourth beam.

32. The method according to claim 30 wherein the beam splitter comprises only facets that are oriented by at least ten degrees to a normal to a propagation axis of the intermediate beam.

33. The method according to claim 32 wherein the beam splitter comprises multiple facets that are oriented by an angle that does not exceed forty five degrees in relation to a propagation axis of the intermediate beam.

34. The method according to claim 32 wherein the beam splitter comprises multiple facets that are oriented by an angle that does not exceed twenty degrees in relation to a propagation axis of the intermediate beam.

35. The method according to claim 32 comprising introducing by the beam splitter a color difference between the first and fourth beams.

36. The method according to claim 32 comprising introducing by the beam splitter a polarization difference between the first and fourth beams. 243166/

37. The method according to claim 32 wherein odd facets of the beam splitter and even facets of the Fresnel beam splitter differ by each other by at least one out of a color filtering property and a polarization property.

38. The method according to claim 28 wherein the modifying module comprises a beam splitter; wherein the method comprises receiving by the beam splitter an intermediate beam; splitting by the beam splitter the intermediate beam to the first beam and a fourth beam thereby causing the first beam and the fourth beam to partially overlaps the first beam, when impinging on the object, to form an overlap region that comprises the first angular region.

39. The method according to claim 38 comprising introducing by the modifying module a color difference between the first and fourth beams.

40. The method according to claim 38 comprising introducing by the modifying module a color difference between (a) the first and second beams and (b) the third and fourth beams.

41. The method according to claim 38 comprising introducing by the modifying module a polarization difference between the first and fourth beams.

42. The method according to claim 38 wherein the overlap region illuminates the object with white light.

43. The method according to claim 38 wherein the beam splitter comprises only facets that are oriented by at least fifth degrees to a normal to a propagation axis of the intermediate beam.

44. The method according to claim 28 wherein the modifying module comprises a beam splitter; wherein the method comprising receiving by the beam splitter that an intermediate beam and splitting the intermediate beam to the first beam, a fourth beam and a fifth beam thereby causing the first beam, the fourth beam and the fifth beam to impinge on the object at different angular ranges.

45. The method according to claim 44 wherein the first beam impinges on the object within the first angular range and wherein the fourth and fifth beams impinge on the object outside the first angular range.

46. The method according to claim 44 comprising introducing by the modifying module a polarization difference between the first and fourth beams. 243166/

47. The method according to claim 44 wherein the modifying module is configured to introduce a color difference between the first and fourth beams.

48. The method according to claim 44 wherein the modifying module comprises multiple triplets of adjacent facets, wherein each triplets of adjacent facets comprises a first fact that is normal to a propagation axis of the intermediate beam, a second facet that has a positive orientation in relation to the first facet and a third fact that has a negative orientation in relation to the first facet.

49. The method according to claim 48 wherein the first facet is coated with a first color filter, the second fact is coated with a second color filter and the third fact is coated with a third color filter; wherein at least two color filters out of the first, second and third color filter differ from each other by spectrum.

50. The method according to claim 49 wherein the first color filter differs from the second and third color filters and the second and color filters have a same spectrum. For the applicant, Oren Reches, Adv.