Patent Publication Number: US-2023160838-A1

Title: Low-cost device and method for measuring radar transmission and reflectance of coated articles

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of and priority to U.S. patent application Ser. No. 17/105,191, filed Nov. 25, 2020, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The technical field generally relates to devices and methods for measuring radar transmission and/or reflectance of coated articles, and more particularly relates to the testing of painted automotive panels. 
     BACKGROUND 
     Increasingly, radar sensors are installed and used in automobiles to aid operation of the automobile by the driver or to provide for self-driving operation. Automotive radar sensors are usually installed behind painted bumpers or painted body panels for purposes of aesthetics, aerodynamics, and/or to protect the radar sensors from environmental factors such as rain, snow, debris or wind. The radar sensors may be provided on the front, rear, corners, and sides of an automobile to provide for detecting other vehicles, pedestrians, stationary objects, signs, traffic control devices, or the like. Radar sensors may be deployed in automobiles as blind spot, lane change, collision avoidance, speed regulation, vehicle-following distance, and cross traffic assistants. Typically, a radar sensor includes a transmitter for emitting a radar signal and a receiver for detecting a reflected radar signal. 
     In order for the radar sensors to function reliably, the painted bumper or painted panel material covering the sensors must be sufficiently transparent to radar and homogeneous. If not, radar signals will not pass through as uniformly and unhindered as is necessary for safe operation of the automobile. It is known that the design, shape, and material of the bumper or body panel may negatively affect the phase and amplitude of both emitted and detected radar signals. Specifically, the range of radar detection may be reduced. Further, the angle accuracy of the detection of objects may be degraded. Such effects lead to unacceptable performance of the radar sensors. 
     Design and fabrication processes of articles such as bumpers and body panels may be sufficient in providing suitable radar transparency through uniformly produced substrates having acceptable designs, shapes and materials. However, processes for applying paints or other coatings, including basecoats, topcoats, clearcoats, and the like, to articles may result in variable coating thicknesses between different articles or even within the same article despite best practices. Certain coatings, such as metallic paints or paints including increased amounts of aluminum, exhibit increased levels of radar signal attenuation. Therefore, it may be imperative to ensure that such coatings do not interfere with radar transmission through bumpers or body panels before the bumpers or body panels are installed on automobiles for operation. 
     Accordingly, there is a need for the development of devices and methods for measuring radar transmission through, and reflectance from, coated articles such as automotive bumpers or body panels. Further, there is a need for low-cost devices for measuring radar transmission and reflectance. Also, there is a need for mobile devices for measuring radar transmission and reflectance of coated articles, such as handheld devices. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     SUMMARY 
     Low-cost devices and methods for measuring radar transmission and/or reflectance of coated articles, as well as methods for forming coatings on articles are provided. An exemplary low-cost radar transmission and reflection measurement device includes a radar transmitter that emits a radar signal, a radar target to which the radar signal is directed, and a radar receiver that receives the radar signal. Further, the exemplary low-cost device includes a sample holder located at a prescribed distance between the radar transmitter and the radar target and between the radar target and the radar receiver. The sample holder receives a sample including a coating. The low-cost device also includes a controller connected to the radar transmitter and radar receiver. The controller measures a radar signal loss due to the coating. 
     In another embodiment, a method for measuring radar transmission through or reflectance from a coated article is provided. The exemplary method includes positioning the coated article in a sample holder of a device including a radar transmitter, a radar target, a radar receiver, and a controller connected to the transmitter and receiver. In the device, the sample holder is located at a prescribed distance between the radar transmitter and the radar target and between the radar target and the radar receiver. The method further includes directing a radar signal from the radar transmitter toward the radar target and receiving a portion of the radar signal with the radar receiver. The method also includes measuring a radar signal loss due to a coating on the coated article based on the portion of the radar signal received by the radar receiver. 
     In another embodiment, a method for forming a coating on an article is provided. The method includes applying a layer of a coating composition over the article. The method further includes measuring a radar signal loss due to the coating on the article by measuring radar transmission through and/or radar reflection from the article and the coating with a low-cost radar transmission and reflection measurement device comprising a radar transmitter, a radar target, and a radar receiver. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG.  1    is a schematic diagram of a device for measuring radar transmission through coated articles in accordance with exemplary embodiments; 
         FIG.  2    is a schematic diagram of a device for measuring radar reflectance from coated articles in accordance with exemplary embodiments; 
         FIG.  3    is a schematic diagram of a location for coating articles and for measuring radar transmission and/or reflectance in accordance with exemplary embodiments; 
         FIG.  4    is a flow chart illustrating a method for measuring radar transmission through a coated article in accordance with exemplary embodiments; 
         FIG.  5    is a flow chart illustrating a method for measuring radar reflectance from a coated article in accordance with exemplary embodiments; and 
         FIG.  6    is a flow chart illustrating a method for applying a coating to an article in accordance with exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the devices and methods as described herein. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or in the following detailed description. 
     As used herein, “a,” “an,” or “the” means one or more unless otherwise specified. The term “or” can be conjunctive or disjunctive. Open terms such as “include,” “including,” “contain,” “containing” and the like mean “comprising.” In certain embodiments, numbers in this description indicating amounts, ratios of materials, physical properties of materials, and/or use are may be understood as being modified by the word “about”. The term “about” as used in connection with a numerical value and the claims denotes an interval of accuracy, familiar and acceptable to a person skilled in the art. In general, such interval of accuracy is ±10%. All numbers in this description indicating amounts, ratios of materials, physical properties of materials, and/or use may be understood as being modified by the word “about” or may be understood as being not modified by the word “about”. As used herein, the “%” or “percent” described in the present disclosure refers to the weight percentage unless otherwise indicated. 
     As noted above, error-free radar sensing of the area surrounding an automobile is important both for driver assistance and for autonomous driving. It is known that bumpers and body panels may impair the transmission of radar signals, such that obstacles are detected too late, in the wrong place, or not at all. 
     Radar transmission through articles, such as automotive components like bumpers and body panels, and through coatings, such as primer and/or adhesion promotor, basecoat, clearcoat and/or topcoat layers, is affected by article surface shape, article and coating thickness and compositional material. Specifically, different materials have different permittivity, which is a measure of a material&#39;s ability to be polarized by an applied electric field. Polarizability is related to the distortion of the electron cloud of the atoms comprising a given material when subjected to an applied electric field. High permittivity materials typically have poor radar transmission. 
     Exemplary articles such as bumpers and body panels may be injection molded from plastic in one piece and then coated with several very thin coating layers, such as paint. Inhomogeneous bumper material as well as too thick or unevenly applied paint layers can strongly attenuate the radar signal or change its transmission angle and prevent the radar sensors from functioning properly. 
     Exemplary bumpers and body panels are made of polymer blends with different types and ratios of fillers, such as carbon black and talc. Exemplary coatings include primary pigments, effect pigments such as metallic flake pigments, mica-containing pigments, glass-containing pigments and combinations thereof, functional pigments, as well as numerous additives that may cooperate to improve properties of the coating, such as anti-hangers, pH modifiers, catalysts, surface tension modifiers, solubility modifiers, adhesion promoters and combinations thereof. An exemplary coating layer of primer and/or adhesion promoter has a thickness of from about 4 to about 25 micrometers (μm). An exemplary coating layer of basecoat has a thickness of from about 10 to about 35 μm. An exemplary coating layer of clearcoat has a thickness of from about 25 to about 50 μm. 
     Exemplary metallic pigments may contain different shapes and sizes of metallic flakes depending on the desired visual effect. Metallic pigments are known to particularly inhibit radar transmission. Specifically, electrical susceptibility increases with increasing metal content in the coating layer. 
     Because an exemplary coated article described herein has multiple layers of coatings, reflection of a radar signal transmitted through the coated article is increased. Further, because each material may affect radar transmission, in particular when formed with varying thicknesses. Therefore, while design processing may attempt to predict the level of radar transmission through a finish coated article, such predictions may be unreliable due to myriad factors. Also, such predictions may be non-applicable to non-factory, repaired, and/or repainted articles. 
     As described herein, devices and methods for measuring radar transmission through and/or reflectance from coated articles are provided. Further, exemplary embodiments of such devices are low-cost, lightweight and mobile, such as being handheld, and methods are provided in which coatings are applied on articles and may be measured for radar transmission immediately. For example, radar transmission may be measured during the coating process, between steps of the coating process, immediately after completing the coating process, or during a downstream quality control process. For such methods, a radar transmission and reflectance measurement device may be used on-site at the coating location, such as in a painting chamber or booth. 
     Referring to  FIG.  1   , an exemplary device  100  for measuring radar transmission through coated articles is illustrated. An exemplary device  100  is lightweight, such as having a total weight of less than ten pounds (lbs), such as less than 5 lbs. As shown, an exemplary device  100  may include a housing  110 . Further, the exemplary device  100  includes a radar transmitter  120  that emits a radar signal  121 . An exemplary radar transmitter  120  emits a radar signal with a frequency of from about 76 to about 81 GHz, for example from about 77 GHz to about 79 GHz, such as at a frequency of 77 GHz or 79 GHz. In an exemplary embodiment, the radar transmitter  120  is mounted to the housing at a fixed location. As shown, the exemplary device  100  also includes a radar target  130  to which the radar signal  121  is directed. In an exemplary embodiment, the radar target  130  is mounted to the housing  110  at a fixed location. In the exemplary embodiment of  FIG.  1   , the radar target  130  is a radar reflector that reflects the radar signal  121  that reaches the radar reflector  130  in a transmission mode of the device  100 . As shown, a reflected signal  131  is directed away from the radar target  130 . 
     In  FIG.  1   , the device  100  further includes a radar receiver  140  that receives the reflected radar signal  131 . In an exemplary embodiment, the radar receiver  140  is mounted to the housing  110  at a fixed location. As may be understood, the radar receiver  140  and the radar reflector  130  are aligned so that the reflected signal  131  is directed at the radar receiver  140 . While illustrated as two separate elements, it is contemplated that the radar transmitter  120  and the radar receiver  140  be included or contained in a single radar transceiver unit  150  capable of transmitting and receiving radar signals. In an exemplary embodiment, the radar transceiver unit  150  is mounted to the housing  110  at a fixed location. In certain exemplary embodiments, the device  100  includes an adjustable frame  170  that holds the radar transmitter  120  and radar receiver  140 , or transceiver unit  150 , at a selected position on the housing  110 . 
     As shown, the exemplary device  100  further includes an external sample holder  180 . In the illustrated exemplary embodiment, the sample holder  180  is located between the radar transmitter  120  and the radar target  130 . Further, in the illustrated exemplary embodiment, the sample holder  180  is located between the radar target  130  and the radar receiver  140 . An exemplary sample holder  180  may include a frame and/or arms for holding an article  200  to be tested by the device  100 . In certain embodiments, the sample holder  180  is mounted to the housing  110  at a fixed location. In certain embodiments, the location of the sample holder  180  relative to the housing  110  is adjustable to position the article  200  to be tested at a desirable location and angle relative to the radar transmitter  120 , radar target  130 , and/or radar receiver  140  for optimal radar transmission. 
     While not part of the device  100 , the article  200  is illustrated in  FIG.  1   . An exemplary article  200  includes a coating  210 . An exemplary coating  210  may include a single coating layer or a plurality of layers. For example, the coating  210  may include one or more primer or adhesion promotor, basecoat, clearcoat, and/or topcoat layers, and such layers may include primary pigments, effect pigments such as metallic flake pigments, mica-containing pigments, glass-containing pigments and combinations thereof, functional pigments, and additives. 
     An exemplary article  200  is an automotive part, such as a bumper or body panel. Exemplary articles  200  are comprised of polymer blends with different types and ratios of fillers. Such articles  200  may vary widely in size and shape and an exemplary sample holder  180  may include grasping, frictional, or other functional elements to hold the article  200  in the desired position. Further, while the location of the exemplary sample holder  180  may be adjustable, an exemplary sample holder  180  is adjustable itself to position the article  200  to be tested at a desirable location and angle relative to the radar transmitter  120 , radar target  130 , and/or radar receiver  140 . 
     In  FIG.  1   , the article  200  is distanced from the radar transmitter  120  and radar receiver  140  by a gap  185 . In certain embodiments, gap  185  is an air gap. Further, the article  200  is distanced from the radar reflector  130  by a gap  186 . In certain embodiments, gap  186  is an air gap. In exemplary embodiments, gaps  185  and  186  are formed by a solid structure  184  and  187 , such as a spacer or mechanical fixture that does not impede radar signal path, having a known radar transmission properties. In exemplary embodiments, the article  200  may be positioned on the device  100  to abut the spacer  187 . 
     As further shown, the exemplary device  100  includes a controller  190 . The exemplary controller  190  is connected to the radar transmitter  120  and radar receiver  140 . The controller  190  is configured to measure a radar signal loss due to the coating  210  on the article  200 . The controller  190  may also perform software-implemented calibration of the incident radar signal in order to compensate for geometry or environment-induced measurement error. An exemplary controller  190  includes a circuit board. The controller  190  may utilize techniques, technologies and functions that may be performed by various computing components or devices. Such operations, tasks, and functions are sometimes referred to as being computer-executed, computerized, software-implemented, or computer-implemented. It should be appreciated that the illustrated controller  190  may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. For example, an embodiment of a controller  190  may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. 
     The device  100  of  FIG.  1    may provide for testing the coated article  200  in a transmission mode, i.e., the transmission of a radar signal through the coated article  200  is measured. 
       FIG.  2    illustrates an embodiment for testing a coated article  200  in a reflection mode. As shown in  FIG.  2   , a lightweight device  100  again includes a housing  110 , a radar transmitter  120  mounted to the housing  110  and a radar receiver  140  mounted to the housing  110 , wherein the radar transmitter  120  and radar receiver  140  may in included in an integral radar transceiver unit  150  mounted to the housing. As shown, the radar transmitter  120  and radar receiver  140  are coupled to a controller  190  that controls operation of the device  100  as described above. Further, the radar transmitter  120  and radar receiver  140  may be mounted to an adjustable frame  170  that holds the radar transmitter  120  and radar receiver  140 , or transceiver unit  150 , at a selected position on the housing  110 . 
     In  FIG.  2   , the device  100  includes a radar target  130  that is a radar absorber. An exemplary radar absorber is a carbon foam or lossy foam absorber, though any suitable low-cost, lightweight material may be used provided that the radar absorber absorbs the radar signal that reaches the radar absorber during operation in a reflection mode of the device  100 . 
     As shown, the exemplary device  100  further includes a sample holder  180 . In the illustrated exemplary embodiment, the sample holder  180  is located between the radar transmitter  120  and the radar target  130 . Further, in the illustrated exemplary embodiment, the sample holder  180  is located between the radar target  130  and the radar receiver  140 . Again, the exemplary sample holder  180  may include a frame and/or arms for holding an article  200  with a coating  210  to be tested by the device  100 . In certain embodiments, the sample holder  180  is mounted to the housing  110  at a fixed location. In certain embodiments, the location of the sample holder  180  relative to the housing  110  is adjustable to position the article  200  to be tested at a desirable location and angle relative to the radar transmitter  120 , radar target  130 , and/or radar receiver  140  for optimal radar transmission. In an exemplary embodiment, the sample holder  180  holds the coated article  200  such that the coated article abuts the radar absorber  130 . As shown, the coated article  200  is separated from the radar transmitter  120  and radar receiver  140  by a gap  185 , such as an air gap. 
     As shown in  FIG.  2   , during operation, a radar signal  221  is emitted from the radar transmitter  120 . A portion  231  of the radar signal is reflected by the coating  210  on the article  200  and is received by the radar receiver  140 . The controller  190  interrogates the received signal  231  to measure the radar reflectance by the coating  210 . 
       FIG.  3    provides a schematic overhead view of a paint location  300 , such as an autobody shop, having a plurality of painting chambers, booths or bays  310 . As shown, articles  201 ,  202 ,  203 ,  204 , and  205  are located in each painting chamber  310 . The articles  201 - 205  may be coated or in the process of being coated by coating applicators  320 . In exemplary embodiments, the articles  201 - 205  are automotive bumpers or body panels. 
     As shown, a mobile lightweight low-cost radar transmission and reflection measurement device  100  is provided at the paint location  300 . During use, the device  100  may be carried into a respective painting chamber  310  to measure a respective coated article  201 - 205 . Further, the device  100  may be used to measure a respective coated article  201 - 205  during the painting process, such as during or between painting and/or drying/curing stages. 
     Because the device  100  is mobile and lightweight and can be transported into the painting chambers  310 , coated articles  201 - 205  need not be moved out of the painting chambers  310  for testing. 
       FIG.  4    is a flow chart for a method  400  for measuring radar transmission through a coated article with the device  100  of  FIG.  1    in a radar transmission mode. Cross-referencing  FIGS.  1  and  4   , the method  400  includes, at action block  410 , positioning the coated article  200  at a desired location and orientation with respect to the radar transmitter  120 , radar target/reflector  130 , and radar receiver  140 . For example, the coated article  200  may be positioned in the sample holder  180  of the device  100 . Positioning the coated article at the desired location and orientation may include adjusting the position of the radar transmitter and radar receiver with respect to the housing. 
     The method  400  further includes emitting and directing a radar signal  121  from the radar transmitter  120  toward the radar target  130  at action block  420 . The method  400  includes transmitting, or passing a transmitted portion  121 ′ of, the radar signal  121  through the coating  210  and article  200  at action block  430 . Portions of the radar signal  121  may be reflected or otherwise lost when passing through the coating  210  and article  200 . 
     The exemplary method  400  further includes, at action block  440 , reflecting the transmitted portion  121 ′ of the radar signal that reaches the radar target/reflector  130  to form a reflected signal  131 . As shown, the reflected signal  131  is directed back toward the radar receiver  140  through the coated article  200 . 
     At action block  450 , the method  400  includes transmitting, or passing a transmitted portion  131 ′ of, the reflected radar signal  131  through the coated article  200 . As indicated in  FIG.  4   , the method  400  includes receiving the transmitted portion  131 ′ of the reflected radar signal  131  with the radar receiver  140  at action block  460 . 
     At action block  470 , the method includes measuring a radar signal loss due to a coating  210  on the coated article  200  based on the transmitted portion  131 ′ of the reflected radar signal  131  received by the radar receiver  140 . The processing of action block  470  may be performed by the controller  190  of the device  100  and may include comparing the received portion  131 ′ to the emitted signal  121  and/or to a library of received signals that were transmitted through articles with known levels of radar transmission and reflectance effects. 
       FIG.  5    is a flow chart for a method  500  for measuring radar transmission through a coated article with the device  100  of  FIG.  2    in a radar reflection mode. Cross-referencing  FIGS.  2  and  5   , the method  500  includes, at action block  510 , positioning the coated article  200  at a desired location and orientation with respect to the radar transmitter  120 , radar target/absorber  130 , and radar receiver  140 . For example, the coated article  200  may be positioned in the sample holder  180  of the device  100 . Positioning the coated article at the desired location and orientation may include adjusting the position of the radar transmitter and radar receiver with respect to the housing. 
     The method  500  further includes emitting and directing a radar signal  221  from the radar transmitter  120  toward the radar target  130  at action block  520 . The method  500  includes reflecting a portion of the radar signal  221  off of the coating  210  to form a reflected signal  231  at action block  530 . As shown, the reflected signal  231  is directed back toward the radar receiver  140 . Further, the method  500  includes absorbing a portion  221 ′ of the radar signal  221 , which passes through the coated article  200  and reaches the radar absorber  130 , with the radar absorber  130  at action block  540 . 
     At action block  550 , the method includes measuring a radar signal loss due to the coating  210  on the coated article  200  based on the reflected signal  231  received by the radar receiver  140 . The processing of action block  550  may be performed by the controller  190  of the device  100  and may include comparing the reflected signal  231  to the emitted signal  221  and/or to a library of received signals that were transmitted through articles with known levels of radar transmission and reflectance effects. 
     It is noted that the device  100  as described in relation to the transmission mode of  FIGS.  1  and  4    and the reflectance mode of  FIGS.  2  and  5    may operate in two further modes: contact and non-contact (where the components of the device  100  are set a certain distance from the coated article). In a non-contact configuration, the device  100  can measure the properties of a coating during drying or curing, or after during/drying and before application of an additional layer. 
     As noted above, the methods  400  and/or  500  may be used as techniques or processes during a coating method. For example,  FIG.  6    illustrates a method  600  for applying a coating to an article. Cross-referencing  FIG.  3    and  FIG.  6   , the method  600  includes positioning the article  200  in a painting chamber  310  at action block  610 . Further, the method  600  includes applying a coating to the article  200 , such as with a coating applicator  320 . The method  600  may also include measuring the radar transmission and/or reflection of the coating applied to the article at optional action block  630 . The measuring process of action block  630  may be performed during or after the coating application of action block  620 . In exemplary embodiments, the measuring process of action block  630  occurs without removing the article  200  from the painting chamber  310 , i.e., the device  100  is carried into the painting chamber  310 . 
     The method  600  ascertains whether the radar performance of the coating is acceptable at query  635 . If no, the article is rejected at action block  640 . For example, the coating may be removed or the coating application otherwise adjusted so that only coated articles with acceptable radar performance are produced by the method  600 . 
     If the radar performance is accepted, the method  600  may continue with drying and/or curing the coating at action block  650 . The method  600  may also include measuring the radar transmission and/or reflection of the coating applied to the article at optional action block  660 . The measuring process of action block  660  may be performed during or after the drying and/or curing process of action block  650 . In exemplary embodiments, the measuring process of action block  660  occurs without removing the article  200  from the painting chamber  310 , i.e., the device  100  is carried into the painting chamber  310 . 
     The method  600  ascertains whether the radar performance of the coating is acceptable at query  665 . If no, the article is rejected at action block  670 . For example, the coating may be removed or the coating application otherwise adjusted so that only coated articles with acceptable radar performance are produced by the method  600 . 
     If the radar performance is accepted, the method  600  may continue with ascertaining whether the application is finished, i.e., no more coating layers are to be applied, at query  685 . If the application is not finished, then the method returns to and continues from action block  620  for the application of another coating layer. If the application is finished, then the method may include removing the coated article from the painting booth at action block  690 . 
     As described, methods may be utilized to apply and evaluate applied coatings on newly manufactured articles or on repaired or replacement articles. In case of an OEM coating process the article is typically one made by a serial production process. Automotive plastics articles may be uncoated or they may have a precoating like a conductive primer layer or, an original coating to be repaired. 
     While the method  600  provides for measuring radar transmission and/or reflectance at the time of coating an article, it is also contemplated that the methods of  FIGS.  4  and/or  5    may be performed downstream of the coating application, such as during a quality check or before installation on a vehicle. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims.