Sensing system

Abstract

The invention describes a sensing system comprising: a sensor covered by a polarizing filter; and a retroreflective article having a light incident surface. A retroreflective article includes: a non-depolarizing retroreflective layer; a rotation-invariant retardation layer closer to the light incident surface than the retroreflective layer; and an attenuation layer between the light incident surface and the retroreflective layer, substantially absorbing visible wavelengths and substantially transmitting near infrared wavelengths; the retardation layer comprises a quarter-wavelength retardation sheet for at least one wavelength in the near-infrared range, the quarter-wavelength retardation sheet is patterned to encode information and at least comprises a first region and a second region, the first region is a quarter-wavelength retardation sheet for at least one wavelength in the near-infrared range, and the second region is a quarter-wavelength retardation sheet for at least one wavelength in the near-infrared range. The second region has zero delay or absorbs the at least one wavelength for the at least one wavelength; the sensing system is configured to rapidly alternate the rotational directivity of the polarizing filter such that the sensor detects the flash appearance of the retroreflective article to differentiate information near the edge of the encoded information.

Description

[0001] This application is a divisional application of the invention patent application filed on September 27, 2017 (date of entry into the Chinese national phase: August 16, 2019), with the invention name “Retroreflective article including a delay plate” and application number PCT / US2017 / 053657 (national application number: 201780086716X). Technical Field

[0002] The present invention relates to a sensing system. Background Art

[0003] Retroreflective articles are structures that include at least one retroreflective element. Retroreflective elements reflect incident light in substantially the same direction. Retroreflective elements include cube corner prism retroreflectors and bead retroreflectors. Retarder plates cause one of the orthogonal components of incident light that propagate electromagnetic waves to be slower than the other, thereby producing a phase difference, which in turn causes a change in the polarization state of the polarized incident light. Summary of the invention

[0004] In one aspect, the present specification relates to a retroreflective article. In particular, the present specification relates to a retroreflective article having a light incident surface and including a retroreflective layer and a retardation layer, wherein the retardation layer is disposed closer to the light incident surface than the retroreflective layer. The retardation layer includes a retardation plate for a quarter wavelength of at least one wavelength in the near infrared range, the retroreflective layer is non-depolarizing, and the retardation layer is rotationally invariant. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 is a side elevation view of the retroreflective layer.

[0006] Figure 2 is a side elevation view of a retroreflective article.

[0007] Figure 3 It is shown Figure 2 Side elevation view of the general working principle of a retroreflective article.

[0008] Figure 4 is a side elevation view of another retroreflective article.

[0009] Figures 5A to 5B Front elevation views of a retroreflective article illuminated with circularly polarized light of one handedness and another handedness, respectively.

[0010] Figure 6 is a side elevation view showing the range of incidence angles for the retroreflective article.

[0011] Figure 7 is a retroreflective article comprising a randomly aligned film.

[0012] Figure 8 This is the horizontal scan of Example 1.

[0013] Fig. 9 This is the horizontal scan of Example 2.

[0014] Fig.10 This is the vertical scanning of Example 3.

[0015] Fig.11 This is the vertical scanning of Example 4.

[0016] Fig.12 This is the vertical scanning of Example 5.

[0017] Fig.13 This is the vertical scanning of Example 6.

[0018] Fig.14 This is the vertical scanning of Example 7.

[0019] Fig.15 This is the horizontal scan of Example 8.

[0020] Fig.16 This is the vertical scanning of Example 8.

[0021] Fig.17 This is the vertical scanning of Example 8.

[0022] Fig.18 This is the horizontal scan of Example 9.

[0023] Fig.19 This is the vertical scanning of Example 9.

[0024] Fig. 20 This is the vertical scanning of Example 9.

[0025] Fig.21 This is the vertical scanning of Example 10.

[0026] Fig. 22 This is the vertical scanning of Example 11.

[0027] Fig.23 This is the vertical scanning of Example 12.

[0028] Fig.24 This is the vertical scanning of Example 12.

[0029] Fig.25 This is the vertical scanning of Example 12.

[0030] Fig.26 This is the vertical scanning of Example 13.

[0031] Fig. 27 This is the vertical scanning of Example 13.

[0032] Fig.28This is the vertical scanning of Example 13. DETAILED DESCRIPTION

[0033] Retroreflective articles such as those described herein can be used in certain machine vision detection and sensing systems. For example, as transportation infrastructure becomes more complex, vehicles are becoming more autonomous in their driving. To navigate safely and efficiently, these vehicles are incorporating more and more sensing modules to perform tasks ranging from parking assistance, self-adjusting cruise control, lane departure warnings to fully autonomous navigation and driving (including collision avoidance and traffic sign interpretation).

[0034] To sense the world around it, the vehicle uses a set of sensors that emit one or more light points. For example, a lidar system can use a group of light points that move through the environment to detect possible obstacles or information objects. These interrogation beams can use narrow bands, such as 2-20nm, or can use wide bands, such as 100nm or more.

[0035] Figure 1 1 is a side elevation view of a retroreflective layer. The retroreflective layer 100 shown has an incident light ray 110 and a retroreflected light ray 120 that is retroreflected by the retroreflective layer. The retroreflective layer 100 has a certain optical structure so that light is substantially reflected toward its light source. In other words, any incident light ray is substantially reflected 180° from its angle of incidence. For example, the incident light ray 110 is retroreflected into a retroreflected light ray 120 having substantially the same angle as the retroreflective layer 100. Due to the geometry of the optical structure of the retroreflective layer, there may be some slight translation of the retroreflected light ray from the incident light ray. In other words, although the incident light ray and the retroreflected light ray will be substantially parallel, they do not have to coincide.

[0036] Figure 2 2 is a side elevation view of a retroreflective article. Retroreflective article 200 includes a retroreflective layer 210 and a retarder layer 220 having a first region 222 and a second region 224.

[0037] The retroreflective layer 210 may be any suitable retroreflective layer or combination of layers. For the purposes of this specification, suitable retroreflectors include retroreflectors that do not substantially depolarize polarized light. For example, suitable retroreflectors include retroreflectors that maintain the polarization of circularly polarized light or flip the polarization of circularly polarized light. In other words, incident left-handed circularly polarized light that is reflected as left-handed circularly polarized light or right-handed circularly polarized light should all be considered as non-depolarizing retroreflectors. Depending on the application, a certain degree of depolarization may be acceptable and is inevitable to a certain extent based on spatial inhomogeneity, real-world manufacturing conditions, or other situations. Depolarization may also depend to a certain extent on the incident angle of the polarized light. However, in many cases and for the purposes of this specification, a depolarizing retroreflector neither flips nor maintains the polarization of the incident polarized light. For example, incident left-handed circularly polarized light may return a small portion of the left-handed circularly polarized light as part of a larger, substantially random polarization. In other examples using a depolarizing retroreflector, the incident left-handed circularly polarized light may be returned as elliptically polarized light or linearly polarized light. Likewise, for the purposes of this specification, these types of retroreflectors should not be considered non-depolarizing retroreflectors.

[0038] Suitable retroreflectors that do not depolarize polarized light (at least to the extent that may be suitable for the present description) include metal-backed prismatic (cube corner) retroreflectors, metal-backed bead retroreflectors, and bead retroreflectors partially immersed in a binder that optionally includes, for example, pearlescent or other reflective flake materials. Air cavity prisms that rely on total internal reflection to retroreflect incident light have been observed to depolarize incident light, as described in the comparative examples provided herein.

[0039] The retroreflective layer can be of any suitable size and have elements of any suitable size. For example, the size (width or diameter) of the microreplicated prisms or beads used in the retroreflective layer can be microns, tens of microns, hundreds of microns, millimeters, or even centimeters. Beads of a variety of different sizes and size distributions can be used as appropriate and suitable for the application. Depending on the retroreflective wavelength of interest, there may be certain practical minimum feature sizes to prevent diffraction and other sub-wavelength feature effects from affecting or even dominating the desired optical performance.

[0040] For beaded retroreflectors, glass beads are usually used, but any substantially spherical material can be used. The material can be selected based on durability, environmental robustness, manufacturability, refractive index, coatability, or any other physical, optical, or material properties. The beads can be partially immersed in a reflective binder containing, for example, pearlescent or metallic flakes, or they can be partially metallized by vapor coating, sputter coating, or any other suitable process. In some embodiments, the beads can be coated with a dielectric material. In some embodiments, a metal or metallized film can be laminated or otherwise attached to the bead surface. In some embodiments, the coating or layer can be a reflector with spectral selectivity. In some embodiments, the beads can pass through a non-reflective binder to form an optical path between the light incident surface of the retroreflector and a metal or metallized polymer film as a substrate. The binder can have any physical properties and can impart certain desired properties to the retroreflective layer. For example, the binder can include a pigment or dye to impart a coloring effect to the retroreflective article.

[0041] For prismatic retroreflectors, any suitable prism shape can be micro-replicated or otherwise formed on a transparent (at least transparent to the wavelength of interest) medium. In some embodiments, a casting and curing micro-replication process is used to form the prismatic surface. For example, right-angle linear prisms, such as those in brightness enhancement film (BEF), can be used, but such prisms will not reflect back over a very wide angle range. Solid angles are widely used as retroreflective prism shapes, in which each incident ray is reflected three times before returning to the incident direction. Other surfaces with more facets can be used as prismatic retroreflectors. Any suitable micro-replicable resin can be used; in particular, a resin that can be applied in liquid form or in a flowable form, then cured and removed from the tool can be used. The tool can be formed by any suitable process, including etching (chemical or reactive ion etching), diamond turning, etc. In some embodiments, the tool may be a collection of multiple parts that are melted or otherwise attached to cover the entire prismatic sheet surface pattern. Curing can be performed by adding heat or electromagnetic radiation. UV curable resins or resins capable of being cured by atypical environmental conditions may be selected so as to partially or fully cure without accident during handling or pre-curing processes.In some embodiments, additive or subtractive manufacturing processes may be used to form the tool surface for microreplication or the prismatic surface itself.

[0042] The retardation layer 220 may be any suitable retardation layer that selectively slows down one of the orthogonal components of light to change its polarization. In some embodiments, the retardation layer 220 may be configured as a quarter-wave retarder. A quarter-wave retarder has a certain delay, and for a specific wavelength λ of interest, has a delay of λ / 4. A quarter-wave retarder of a given wavelength of light converts light from circularly polarized light to linearly polarized light, and vice versa. In some applications, a quarter-wave retarder may function acceptably without a perfect λ / 4 delay. For some applications, the use of an achromatic retarder may allow a delay of substantially a quarter wavelength to be maintained over a certain wavelength range; for example, a wavelength range spanning 2nm, 10nm, 20nm, 40nm, 50nm, 100nm, 150nm, 200nm, 300nm, 400nm, or even 500nm. In some embodiments, a quarter-wave retarder has a delay of substantially a quarter wavelength over the entire near-infrared wavelength range (e.g., 700nm to 1400nm). In some embodiments, the quarter-wave retarder has substantially a quarter-wavelength retardation over the entire visible wavelength range (e.g., 400 nm to 700 nm). In some embodiments, the quarter-wave retarder has substantially a quarter-wavelength retardation in both the near infrared and visible ranges.

[0043] In some embodiments, the retardation layer 220 can provide substantially similar retardation values ​​over a wide range of incident angles. In some embodiments, the retardation can vary by no more than 10% over a 30 degree half angle cone, can vary by no more than 10% over a 45 degree half angle cone, or can vary by no more than 10% over a 60 degree half angle cone. For some applications, a variation of no more than 20% over a 30 degree, 45 degree, or 60 degree half angle cone may be acceptable.

[0044] The delay layer 220 may include one or more of any suitable delay materials. In some embodiments, the delay layer 220 includes or is a liquid crystal delay plate. In some embodiments, the delay layer 220 includes an oriented birefringent polymer film. Depending on the birefringence of the selected polymer group, a suitable thickness can be selected to obtain the desired delay value. In some embodiments, the delay layer 220 may include a compensation film or other additional film with low delay (e.g., a delay of less than 100nm) to enhance or maintain circularly polarized light over a wide angle range within the wavelength or wavelength range of interest.

[0045] In some embodiments, the retarder layer 220 can be unpatterned, or in some embodiments, it can be patterned, such as Figure 2As shown. The delay layer 220 may include at least a first region 222 and a second region 224 arranged in any spatial pattern, gradient or any other arrangement. The difference between the first region 222 and the second region 224 is at least their incident light delay. For example, in one embodiment, the first region 222 may have a quarter wavelength delay for incident light of a first wavelength. At the same time, the second region 224 may have substantially zero delay for incident light of the first wavelength. In some embodiments, the second region 224 may substantially absorb the light of the first wavelength. In some embodiments, the second region 224 may substantially depolarize the light of the first wavelength. The delay layer 220 (if patterned) may encode or display information. The information may be human-readable, machine-readable, or both readable.

[0046] Retroreflective article 200 can enable certain sensor systems to operate with high fidelity. For example, a sensor that detects circularly polarized light (e.g., a coupled device or CMOS used in conjunction with a filter that passes left-handed circularly polarized light) can be a useful sensor configuration. For example, with left-handed circularly polarized light for interrogation, retroreflective article 200 can provide some portions of retroreflected left-handed circularly polarized light (depending on the configuration and optical properties of retroreflective layer 210 and retardation layer 220). These may appear bright or otherwise be detectable with such a sensor configuration. In other portions of retroreflective article 200, left-handed circularly polarized interrogation light may be depolarized, absorbed, or flipped to right-handed circularly polarized light. Such areas will appear darker or difficult to detect with such a sensor configuration.

[0047] In some embodiments, by utilizing circularly polarized light, several potential advantages can be realized. Specifically, circularly polarized light tends to be rare in nature, thereby reducing the probability of false positive signals or other interferences. In addition, by contrast, the use of linearly polarized light in these applications produces a very high sensitivity to the angle of incidence, thereby rapidly and significantly changing the appearance or intensity of the retroreflected light, depending on the vertical and horizontal translation or viewing angle.

[0048] In some embodiments, the retroreflective article 200 can be configured to operate in the near infrared wavelength range. Certain sensor systems utilize near infrared light in order to operate in wavelengths that are not visible to humans. In some embodiments, the retroreflective article 200 can include a retroreflective layer 210 that retroreflects near infrared light and a retarder layer 220 that is configured as a quarter-wave retarder for at least one wavelength in the near infrared wavelength range.

[0049] Figure 3 It is shown Figure 23. A side elevation view of the general working principle of a retroreflective article of FIG. Retroreflective article 300 includes a retroreflective layer 310 and a retardation layer 320. First incident ray 330, first retroreflected ray 340, second incident ray 350, and second retroreflected ray 360 illustrate the general function of a retroreflective article.

[0050] For example, the first incident light ray 330 and the second incident light ray 350 can each be considered as left-handed circularly polarized light. The first incident light ray 330 and the second incident light ray 350 each strike a region of the retroreflective article 300, specifically a region of the retarder layer 320 having different retarder characteristics. For the purposes of this example, it is assumed that the retroreflective layer 310 has circular polarization flipping properties (although not depolarized); for example, left-handed circularly polarized light is converted into right-handed circularly polarized light, but linearly polarized light is not converted into light having an orthogonal polarization orientation. In addition, it is assumed that the retarder layer 320 is configured, at least in some regions, as a quarter-wave retarder at least for the wavelength of the incident light rays and their angle of incidence.

[0051] The first incident light 330 is incident on the area of ​​the retardation layer 320 configured as a quarter-wavelength retarder, is converted from left-handed circularly polarized light to linearly polarized light, and is maintained in its linear polarization state when retroreflected. After passing through the retardation layer 320 again, it is converted back to circularly polarized light having the same handedness as the incident light. The detector that passes the left-handed circularly polarized light will detect the first retroreflected light 340.

[0052] The second incident light ray 350 is incident on a region of the retardation layer 320 having substantially zero retardation for the retroreflective light. The second incident light ray is not converted into linearly polarized light, and thus its handedness is flipped when retroreflected by the retroreflective layer 310. The second retroreflected light ray 360 is right-handed circularly polarized light, and thus for the same detector as described above (detector for left-handed circularly polarized light), the second retroreflected light ray 360 will not be detected.

[0053] Figure 4 4 is a side elevation view of another retroreflective article. Retroreflective article 400 includes a retroreflective layer 410 , a delay layer 420 , and an attenuation layer 430 .

[0054] In some embodiments, retroreflective article 400 (similar to retroreflective article 300, except that it also includes an attenuation layer) may be useful. Attenuation layer 430 may be any suitable attenuation layer, including a layer that attenuates light by absorbing a specific wavelength. In some embodiments, a broadband absorber such as carbon black may be used. In some embodiments, a selectively absorbing dye or pigment may be used. In some embodiments, a dye or ink that passes light of certain wavelength spectra (i.e., is transparent or highly transmissive within certain wavelength ranges) but absorbs light in different wavelength spectra may be used. In some embodiments, an attenuation layer (i.e., a camouflage layer) that absorbs light in the visible spectrum but substantially transmits light in the near infrared spectrum may be used. For some applications, it may be advantageous to have a retroreflector that is visually imperceptible so as to provide information to the detector without distracting or causing confusion. In some embodiments, attenuation layer 430 may reduce the light reflected from retroreflective article 400 to avoid over-luminescence, highlights, or other detection artifacts due to having too extreme a contrast.

[0055] The attenuation layer 430 may also be or include any surface or bulk scatterer to attenuate light reflected back along a desired retroreflection angle cone. In other words, the attenuation layer 430 may be any suitable material or combination of materials to reduce the well-known retroreflection efficiency R A Measured value. Retroreflectivity (R A ) can use ASTM E810 03(2013) retroreflective sheeting coefficient (R A ) standard test method, using a coplanar geometry with a 0.2° observation angle and a 5° incident angle (i.e., a 0.2 / 5° angle).

[0056] Figures 5A to 5B Front elevation views of a retroreflective article illuminated with circularly polarized light of one handedness and another handedness, respectively. Figure 5A A retroreflective article is shown illuminated with circularly polarized light of one handedness and viewed through a circular polarizing filter. In one example, the retroreflective article appears bright because the handedness of the incident light is preserved and because the handedness of the polarizing filter is the same as the incident light. Thus, other combinations of components, such as incident light polarization, retroreflector type (e.g., handedness preservation or handedness inversion), and handedness of the circular polarizing filter that will be apparent to a skilled artisan, may be employed to obtain a bright appearance of the retroreflective article.

[0057] Figure 5B Similar to Figure 5A, except that the retroreflective article is dark or invisible when viewed through a circular polarizing filter. In one example, the retroreflective article appears dark because the handedness of the incident light is preserved and because the polarizing filter has a transmission handedness opposite to the incident light. Similarly, other combinations of components, such as incident light polarization, retroreflector type, and circular polarizer transmission handedness, can be selected to provide a similar darker appearance. In many cases, the same retroreflective article can be bright under one set of lighting and sensing conditions, but darker under different lighting and sensing conditions.

[0058] Notably, the handedness of the interrogating light (including in some examples using two light sources with different handednesses) or the handedness of the polarizing filter covering the detector or sensor can be rapidly alternated or switched. This will result in a shimmering appearance of the retroreflective article that will help enhance its conspicuity among other objects. Alternatively, two independent detectors for light of each handedness may be able to detect the difference between the images sensed by each detector. This may help to improve the reading accuracy or readability of spatially varying codes or patterns on retroreflective articles. In some embodiments, the alternating effect may help the sensor distinguish information near the edges of the information pattern or code. In some cases, the observed shimmering effect may help further distinguish readable symbols or codes from natural or artificial unreadable objects. In some embodiments, the retroreflective article may provide different or additional information in each state.

[0059] Figure 6 600 includes a retroreflective layer 610 and a range of incident angles 620. As discussed elsewhere in this specification, the retroreflective articles described herein may have a wide range of incident angles available. The range of incident angles 620 may include changes in polar angles (deviations from the normal to the surface of the retroreflective article) and changes in azimuthal angles (rotations around the normal to the surface of the retroreflective article). In some embodiments, the range of incident angles may be described by a cone with a characteristic half-angle. In some embodiments, the range of incident angles may be a position where the retroreflective efficiency is not less than 70% of the maximum value of light of a given circular polarization and wavelength. In some embodiments, the range of incident angles may be a position where the retroreflective efficiency is not less than 80% of the maximum value of a given circular polarization. Of course, the circular polarization used to characterize the range of incident angles should be measurable or detectable by a detector. The retroreflective efficiency of the retroreflective article described herein is both the product of the intrinsic retroreflective efficiency of the retroreflective layer as a function of angle and the ability of the delay layer to maintain a substantially circular polarization within the same angular range.

[0060] Figure 7 The retroreflective article 700 includes a retroreflective layer 710 and a randomly aligned film 720 .

[0061] Another advantage of using circularly polarized light and a quarter-wavelength retarder is that pattern visibility does not vary substantially as a function of azimuthal alignment. In other words, such a retarder can be rotationally invariant relative to the retroreflective layer. In some embodiments, this means that the retroreflective layer has a retroreflective efficiency of not less than 80% of a maximum value as the retarder is rotated about an azimuthal angle. Figure 7 As shown, the retroreflective article 700 includes a film 720 in arbitrary alignment, which includes a patterned delay layer as described elsewhere herein. For the purpose of illustration, it is assumed that the retroreflective article 700 is illuminated and detected under conditions that allow the pattern on the film to be visible (i.e., in certain embodiments, the pattern will be invisible when not illuminated with circularly polarized light, or even completely invisible to the human eye). Applications related to this advantage include stickers or decals that can be placed on signs, clothing, vehicles, horizontal surfaces, infrastructure, buildings, etc. that can be temporarily attached. Because the quarter-wave retarders do not need to be carefully aligned with the polarizer of the detector, such decals can be easily attached without worrying about misalignment or misalignment, resulting in detection errors or incompleteness. Such decals or stickers can be temporarily attached to provide new machine-readable meanings to signs, clothing, or any other attachable surfaces.

[0062] Retroreflective articles as described herein can be used for traffic control signs and orientation / navigation infrastructure. In some embodiments, retroreflective articles as described herein can be used as rigid signs. In some embodiments, these articles can be temporary traffic control devices or included therein, such as cones or signs or portable signs. In some embodiments, these articles can be used for or incorporated into clothing or wearable articles such as reflective vests, helmets or other safety equipment. In some embodiments, retroreflective articles can be conformable, bendable or foldable. In some embodiments, these articles can be attached to any type of vehicle, such as a car, motorcycle, airplane, bicycle, quadcopter (drone), ship or any other means of transportation. In some embodiments, these articles can be used for inventory control in warehouses, train stations, docks or distribution centers, so that the contents of shelves, boxes, shipping containers, etc. can be automatically identified, for example.

[0063] Retroreflective articles as described herein can be any suitable size, ranging from small decals or stickers including pressure-sensitive adhesives to highly visible large traffic signs. A substrate that provides rigidity or ease of adhesion (e.g., pressure-sensitive adhesive) can also be included on the back of the retroreflective layer without affecting the optical properties of the retroreflective article.

[0064] Example

[0065] Example

[0066] Materials / Abbreviations

[0067]

[0068]

[0069] Table 1

[0070] Retardation film manufacturing

[0071] 1. (API) Commercially available, oriented polycarbonate quarter-wave retarder, purchased from

[0072] American Polarizers (APQW92-003-PC)

[0073] 2. (LCPET) A commercially available 2 mil polyester film (DuPont / Teijen) was coated with a liquid crystal polymer retardation coating comprising a first liquid crystal alignment layer and a second liquid crystal polymer. The liquid crystal alignment layer was a linear photopolymer (LPP) type which was slot die coated to a thickness of between 100 nm and 150 nm when dry. The LPP was cured using a Fusion Systems UV lamp through a wire grid polarizer purchased from Moxtek. The polarizer was oriented so that the wire grid was at a 15° angle to the longitudinal direction of the PET substrate to form an oriented alignment layer for the liquid crystal polymer. In a second slot die coating, the liquid crystal polymer (LCP) was applied to the LPP coated polyester film to a dry thickness of approximately 1 μm. Using a Fusions Systems UV

[0074] The LCP is cured by blanket UV radiation from the lamp to lock the orientation of the liquid crystal molecules.

[0075] 3. (LCA1 / LCA2) In each case, an acrylic film coated with a base syrup was prepared by mixing the components in the amounts shown in Table 2 below. Acrylic monomers, crosslinkers, ultraviolet light absorbers (UVA) and photoinitiators were combined in a 1-gallon (3.79-liter) glass jar and mixed using a high shear electric motor to provide a uniform mixture. Next, B60H was added over a period of about three minutes while mixing. Further high-speed mixing was then performed until a uniform viscous solution was obtained. The mixture was then degassed for ten minutes under a vacuum of 9.9 inches (252 mm) of mercury. The base syrup (see Table 2) was applied to a PET film at a thickness of 0.002 inches (51 microns) using a notched bar coater. The base syrup was partially cured by exposing the open surface of the composition to a total UVA energy of about 90 mJ / cm2 in a nitrogen inert environment to obtain an acrylic / PVB film on PET.

[0076] An adhesive slurry was prepared by charging 1784 grams of IOA, 16.2 grams of AA, 360 grams of IBOA, 54 grams of DPA and 0.72 grams of 651 photoinitiator into a one gallon (3.8 liter) jar and stirring until the photoinitiator dissolved and a uniform mixture was obtained. Nitrogen was introduced into the mixture through a tube inserted into the opening on the jar lid and vigorously bubbled for at least 5 minutes to degas the mixture. While stirring, the mixture was exposed to UVA light until the viscosity of the pre-adhesive slurry was deemed suitable for forming a coating. After UV exposure, air was introduced into the jar. Next, 360 grams of IBOA, 4.32 grams of Irg 651, 518.4 grams of Reg 6108 and 1.35 grams of Irg 1076 were added to the pre-adhesive slurry and rolled to mix overnight.

[0077] Use notched scraper coater, with 0.002 inch (51 micron) thickness, adhesive syrup is coated on PET, and the first layer of pressure-sensitive adhesive is provided with this.Use the double-roll coating station with the total gap setting of 0.008 inch (203 micron) and be exposed to the total UVA energy of 958 millijoules / square centimeters, make the PET of irradiated acrylic acid / PVB film / PET combination and be coated with adhesive syrup closely contact.Obtain the structure with PET, PSA, acrylic acid / PVB film and PET successively.Next, remove the PET in contact with acrylic acid film.Use notched scraper coater, with 0.002 inch (51 micron) thickness, adhesive syrup is coated on PET, and use the double-roll coating station with the total gap setting of 0.010 inch (254 micron) to make it closely contact with the exposed surface of acrylic acid / PVB film, and the second layer of pressure-sensitive adhesive is provided with this.By being exposed to the total UVA energy of 958 millijoules / square centimeters, the open surface of the second adhesive is cured in nitrogen inert environment.

[0078]

[0079]

[0080] Table 2: Basic syrup preparation (parts by weight)

[0081]

[0082] Table 3: Adhesive syrup preparation (parts by weight)

[0083] With the thus obtained composite adhesive coated acrylic film, a liquid crystal polymer delay coating is added as an alignment layer and a liquid crystal polymer. The liquid crystal alignment layer is a linear photopolymer (LPP) type, ROP-131EXP 306 from Rolic Technologies, which is coated using a #0K rod to obtain an alignment layer with a thickness between 100 and 150 nm when dry. The LPP is cured using a Fusion Systems UV lamp through a wire grid polarizer UVT240A purchased from Moxtek. The polarizer is oriented so that the wire grid is at a 45° angle to the longitudinal direction of the acrylic substrate to form an oriented alignment layer for the liquid crystal polymer. After curing the LPP, a liquid crystal polymer (LCP) Rolic ROF-5185EXP410 is applied. The LCA1 coating uses a #1K rod for the acrylic film coated with LPP, so that the dry thickness is about 1 μm. The LCA2 coating uses a #4K rod for the acrylic film coated with LPP, so that the dry thickness is about 8 μm. In both cases, the LCP is cured using blanket UV radiation from a Fusions Systems UV lamp to lock in the orientation of the liquid crystal molecules.

[0084] Retardation Plate Test Methods and Results :

[0085] An Axiometrics Mueller matrix polarimeter was used to measure the retardation of each film type. In each case, the axial retardation measurement was performed at 550 nm.

[0086] Retardation Plate Type Measured delay [nm] APIQWF 139.4nm LCPET 134.6nm LCA1 125.0nm LCA2 1270nm*

[0087] *Estimates complicated by higher-order optical measurements

[0088] Table 4: Measured retardation for each retarder type (550nm, normal incidence)

[0089] Retroreflective imaging test method :

[0090] The same test method is used to verify the performance of all combinations of the retroreflective materials and delay plate materials described in these embodiments. In each instance, the test involves (1) illuminating the sample, (2) capturing a camera image of the retroreflective light pattern, and (3) extracting and analyzing the measurement distribution from the captured image. In most cases, the illumination source is circularly polarized light. In this case, the same circular polarizer is placed on both the light source and the camera lens. The circular polarizer consists of a linear polarizer (intrinsic to the ring illuminator), which is covered with an achromatic quarter-wave film (QWF) obtained from American Polarizer (APIQWF), and the polarization direction of the polarizer is at a 45° angle to the optical axis of the APIQWF. In the case of a linear polarization source, a quarter-wave film is not required.

[0091] The following optical setup was common to all retroreflective imaging tests. The retroreflective illumination source was a 3.25" diameter white LED ring light. Visible retroreflective photographs of the samples were taken using a Basler acA2000-165uc (ID 106540-21) camera with an aperture of f / 16 at a distance of 5 feet and a lens (Edmund Optics, 8.5mm / f1.3 (ID 58-000)) with an aperture of f / 8 at a distance of 5 feet. The camera was positioned in the center of the ring light and parallel to the center of the sample, with the incident angle to the sample adhered to a vertical rotation stage ranging from 5° to 60°, as described above. The viewing angle was approximately 1.5 degrees. The camera exposure time was adjusted to 10 ms.

[0092] Each image is loaded into an image processing application and a rectangular region of interest is defined on the image; this is useful for the generation of line scan distributions of the measured intensities. For horizontal cross sections, the pixel grayscale values ​​within the region of interest for each red, green, and blue channel are then averaged by column for each row position and plotted by pixel position. For vertical cross sections, the pixel grayscale values ​​within the region of interest for each red, green, and blue channel are then averaged by row for each column position and plotted by pixel position. The red, green, and blue values ​​thus determined are plotted in the line graph below. A picture is provided to show the location from which the cross sections are derived. The lines represent the center and direction of the rectangular region of interest. Note that the pixels on either side of the line are used to determine the average grayscale value for that pixel position.

[0093] Embodiment Configuration Overview

[0094] The samples were constructed to show the advantageous combination of retroreflector and retarder elements when illuminated with circular or linear polarized light. To provide a measure of contrast, the recorded camera values ​​from the retroreflector area with and without the intervening retarder film were each included in the plate measurement. We define contrast as the ratio of the measured retroreflected light intensity with the retarder divided by the measured light intensity without the retarder element.

[0095]

[0096]

[0097] Table 5: Overview of Examples

[0098] Example 1

[0099] The sample consisted of an API 1 / 4 wave retarder wrapped with Scotchlite 3M Flexible Prismatic Retroreflective Marker Tape (PRXF2340). For this example, the combination was wrapped on a 4 inch diameter cylinder to demonstrate the sensitivity of the material to different incident angles. The purpose of wrapping the cylinder was to produce a range of incident angles and demonstrate the difference in angular uniformity.

[0100] The API retarder shows no fringes at any position, which means that the API retarder returns nearly circularly polarized light regardless of the incident angle.

[0101] Cross sections of the images were analyzed using a line scan procedure for the red, green, and blue channels and are shown in the corresponding figures.

[0102] Figure 8 : Example 1, horizontal pass through APIQWF. The color change here is very smooth, and no color oscillation or fringing is perceived. (Note that the peak between pixels 50 and 65 is due to an object behind the 4-inch roller, and should be ignored).

[0103] Example 2

[0104] A sample consisting of LCOET on Scotchlite 3M Flexible Prismatic Retroreflective Marking Tape (PRXF2340) was wrapped around a 4 inch diameter cylinder to demonstrate the material's sensitivity to different angles of incidence.

[0105] Many color fringes are observed at different locations on the curved LCPET retarder.

[0106] Fig. 9 : Example 2, cross section 1. Horizontal pass through the LCPET retarder. Note that the ripples in the red signal result in the perception of colored fringes near the center of the feature.

[0107] Example 3

[0108] The samples consisted of an APIQWF retarder on Scotchlite PRXF2340 metallized microprismatic retroreflective sheeting.

[0109] In this example, a retroreflector was mounted on a flat surface and illuminated with circularly polarized light. An APIQWF retarder was then used to partially cover the retroreflector and photographs were taken and analyzed.

[0110] Fig.10 : Example 3, the API1 / 4 wavelength delay plate partially covers the PRXF2340 metallized prism.

[0111] High gray values ​​correspond to areas of the sample with a retarder, while low gray values ​​correspond to areas of the sample without a retarder. A high contrast is observed between the two areas.

[0112] Example 4

[0113] The sample is composed of APIQWF covered 6360 high light TIR prism.

[0114] In this example, a retroreflector was mounted on a flat surface and illuminated with circularly polarized light. An APIQWF retarder was then used to partially cover the retroreflector and photographs were taken and analyzed. The angle of incidence was 5 degrees and the observation angle was about 1 degree.

[0115] Fig.11 : Example 4, cross section 2. The edge of the APIQWF retarder partially covers the 6360 high light TIR prism. It shows almost no difference.

[0116] Lower pixel counts, less than 15, correspond to areas of the sample without a retarder, while greater than 15 have a retarder covering. The contrast ratio is close to 1.

[0117] Example 5

[0118] The samples consisted of APIQWF covered with Scotchlite 8830.

[0119] In this example, a retroreflector was mounted on a flat surface and illuminated with circularly polarized light. An API retarder was then used to partially cover the retroreflector and photographs were taken and analyzed. The angle of incidence was 5 degrees and the observation angle was about 1 degree.

[0120] Fig.12 : Example 5, cross section 3. The edges of the API were covered with Scotchlite 8830.

[0121] High gray values ​​correspond to areas of the sample with the retarder, while low gray values ​​correspond to areas of the sample without the retarder. A high contrast is observed.

[0122] Example 6

[0123] The samples consisted of APIQWF covered with Scotchlite 8965.

[0124] In this example, a retroreflector was mounted on a flat surface and illuminated with circularly polarized light. An APIQWF retarder was then used to partially cover the retroreflector and photographs were taken and analyzed. The angle of incidence was 5 degrees and the observation angle was about 1 degree.

[0125] Fig.13: Example 6, cross section 4. The edges of the API were covered with Scotchlite 8965.

[0126] High grayscale values ​​correspond to areas of the sample with a retarder, while low grayscale values ​​correspond to areas of the sample without a retarder.

[0127] Example 7

[0128] The sample consisted of APIQWF covered with Scotchlite 8887.

[0129] In this example, a retroreflector was mounted on a flat surface and illuminated with circularly polarized light. An APIQWF retarder was then used to partially cover the retroreflector and photographs were taken and analyzed. The angle of incidence was 5 degrees and the observation angle was about 1 degree.

[0130] Fig.14 : Example 7. Cross section 5. API partially covered with Scotchlite 8887.

[0131] High grayscale values ​​correspond to areas of the sample with a retarder, while low grayscale values ​​correspond to areas of the sample without a retarder.

[0132] Measurement results of Examples 3 to 7:

[0133] For Examples 3 to 7, the highest contrast channel (red, green or blue) was selected for each sample and reported in the table below, along with an estimate of the contrast with and without the retarder.

[0134] Note that the metal-backed retroreflectors have by far the highest contrast ratio.

[0135] Example Maximum contrast 3 31 4 1 5 25 6 10 7 12

[0136] Table 6: Comparison of contrast ratios of Examples 3 to 7

[0137] Example 8

[0138] The sample consisted of an APIQWF retarder on a Scotchlite 8830 retroreflector. Here is the angular sensitivity observation for the three conditions:

[0139] Horizontal retarder, 5 degree angle of incidence

[0140] Vertical retarder, 5 degree incident angle

[0141] Vertical retarder, 41 degree incident angle

[0142] The API showed no evidence of striation when rotated in any plane.

[0143] Fig.15: Example 8, horizontal, cross section. APIQWF over Scotchlite 8830. Small variations in all signals result in good color uniformity.

[0144] Fig.16 : Example 8, vertical cross section 2. API overlays Scotchlite 8830. Note the good relative color uniformity across the cross section.

[0145] Fig.17 : Example 8, normal, 41 degree angle of incidence. API overlay Scotchlite 8830. Note the relative color uniformity across the cross section.

[0146] Example 9

[0147] The sample consists of LCPET retarder covered with Scotchlite 8830

[0148] Horizontal, 5 degree incident angle

[0149] Vertical, 5 degree incident angle

[0150] Vertical, 41 degree angle of incidence

[0151] When rotated in-plane, PET shows full striations.

[0152] Fig.18 : Example 9, horizontal. LCPET covered with Scotchlite 8830. Note that the variation in the red signal leads to color non-uniformity.

[0153] Fig.19 : Example 9, vertical. LCPET covered with Scotchlite 8830. Note that the color uniformity is poor, especially at higher pixel locations.

[0154] Fig. 20 : Example 9, normal, 41 degree angle of incidence. LCPET covered with Scotchlite 8830. Note that the color uniformity across the cross section is very poor.

[0155] Example 10

[0156] Samples consist of LCA1 covered with Scotchlite 8830. The angle of incidence is 5 degrees and the observation angle is 1 degree. Without the retarder, the 8830 is dim. With the 1 / 4 wave retarder, the retroreflector is bright and colorless.

[0157] Fig.21Example 10. LCA1 retarder coated with Scotchlite 8830. Note that the samples from pixels 1 to 90 have relative color uniformity. 90 to 105 have no coating.

[0158] Embodiment 11

[0159] The sample consists of an LCA2 retarder on a retroreflector Scotchlite 8830. The angle of incidence is 5 degrees and the observation angle is 1 degree. Without the retarder, the 8830 is darker.

[0160] Fig. 22 Example 11. LCA2 retarder coated with Scotchlite 8830. Note that the color of the sample is not uniform from pixel 1 to 80. There is no coating at pixel positions 80 to 105.

[0161] Example 12

[0162] The sample consisted of a Scotchlite 8830 retroreflector covered with an LCA1 retarder.

[0163] The retarder / retroreflector combination was viewed at a range of incident angles and the observation was a bright white received image with no color fringes. This embodiment is angle invariant.

[0164] 5, 30, 60 degrees out-of-plane rotation

[0165] 90 degree plane (vertical orientation)

[0166] Fig.23 : Example 12, vertical cross section 2. QWLC on acrylic covered with Scotchlite 8830. 5 degree angle of incidence.

[0167] Fig.24 : Example 12, vertical cross section 2. LCA1 covered with Scotchlite 8830. 30 degree angle of incidence.

[0168] Fig.25 : Example 12, vertical cross section 2. QWLC on acrylic covered with Scotchlite 8830. 60 degree angle of incidence.

[0169] Example 13

[0170] The samples consisted of LCPET on Scotchlite 8830 retroreflector.

[0171] We observe extreme fringing and high angular sensitivity

[0172] Fig.26: Example 13, vertical cross section 1. LCPET covered with Scotchlite 8830. 5 degree incident angle.

[0173] Fig. 27 Example 13. LCPET covered with Scotchlite 8830. 30 degree incident angle. At this incident angle, the color is very sensitive.

[0174] Fig.28 : Example 13. LCPET covered with Scotchlite 8830. 60 degree incident angle. Compared to the previous incident angle, the color changes again and the color moves on the surface of the retarder.

[0175] Embodiment 14

[0176] The sample consisted of APIQWF on a 3M Scotchlite 8830, where the target response was measured with linearly polarized light. The linear polarizer (on the light source) and the analyzer (linear polarizer on the camera) were aligned.

[0177] The APIQWF was rotated in the plane of the film to approximately 0, 45 and 90 degrees relative to horizontal. The target was also tilted out of plane about a vertical axis to 5, 30 and 60 degrees.

[0178] The biggest change was in brightness, and in some cases, the color was observed to change from bright white to dark purple under different viewing conditions. This is in contrast to previous examples of APIQWF and 8830 observed using circularly polarized light, where angular invariance was observed. The observations are recorded in the table below.

[0179]

[0180]

[0181] Table 7: Visual observation

[0182] Embodiment 15

[0183] The sample consisted of APIQWF on a 3M Scotchlite 8830 and was analyzed using linearly polarized light. In this example, the linear polarizer (on the light source) and the analyzer (linear polarizer on the camera) were crossed.

[0184] The APIQWF was rotated in the plane of the film to approximately 0, 45 and 90 degrees relative to horizontal. The target was also tilted out of plane about a vertical axis to 5, 30 and 60 degrees.

[0185] The biggest change was in brightness, and in some cases, the color was observed to change from bright white to dark purple under different viewing conditions. This is in contrast to previous embodiments of the API and 8830 observed using circularly polarized light, where angular invariance was observed. The observations are recorded in the table below.

[0186]

[0187] Table 8: Additional visual observations

Claims

1. A sensing system, comprising: a sensor, which is covered by a polarizing filter; as well as A retroreflective article having a light incident surface, the retroreflective article comprising: Retroreflective layer; a retardation layer disposed closer to the light incident surface than the retroreflective layer; and an attenuating layer located between the light incident surface and the retroreflective layer, wherein the attenuating layer substantially absorbs visible wavelengths and substantially transmits near infrared wavelengths, wherein the retarder layer comprises a quarter-wave retarder for at least one wavelength in the near infrared range; wherein the retroreflective layer is non-depolarizing by maintaining the polarization of circularly polarized light or flipping the polarization of circularly polarized light; wherein the retardation layer is rotationally invariant; wherein the retarder layer is patterned to encode information and comprises at least a first region and a second region, and wherein the first region of the patterned retarder layer is a quarter-wave retarder for at least one wavelength in the near infrared range, but the second region of the patterned retarder layer has substantially zero retardation for the at least one wavelength in the near infrared range or absorbs the at least one wavelength in the near infrared range; and Wherein the sensing system is configured to rapidly alternate the handedness of the polarizing filter so that the sensor detects the glittering appearance of the retroreflective article to distinguish information near the edge of the encoded information. 2 . The sensing system of claim 1 , wherein the retardation layer comprises a compensation film having a retardation of less than 100 nm. 3 . The sensing system of claim 1 , wherein the retroreflective layer is a metal-backed prismatic retroreflector or a metal-backed bead retroreflector.

4. The sensing system of claim 1, wherein the circularly polarized light of the at least one wavelength incident on the light incident surface corresponding to the first region within the incident angle range is retroreflected by at least 80% because the circularly polarized light has opposite handedness. The sensing system of claim 4 , wherein the range of incident angles comprises at least a 30 degree cone. 6 . The sensing system of claim 1 , wherein the retardation layer is one of a liquid crystal retardation layer and a polycarbonate retardation layer.

7. The sensing system of claim 1, wherein the retarding layer comprises a quarter-wave retarder for a wavelength range that is at least 100 nm wide.

8. The sensing system of claim 7, wherein the wavelength range includes the entire near infrared range. 9 . The sensing system of claim 1 , wherein at least a portion of the retardation layer completely absorbs light of the second wavelength in the near infrared range or the visible range.

10. The sensing system of claim 1, wherein the retroreflective article is conformable.

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