Abstract:
A step prismatic retro-reflector includes a main reflective corner having a shared reflective surface of a geometric single plane, a virtual step surface coming into contact with the shared reflective surface at a right angle, and a plurality of sub reflective corners. Each reflective corner has a pair of independent reflective surfaces coming into contact with each other at a right angle, and arranged along the step surface, wherein the retro-reflector elements are arranged to be alternated such that a corner ratio (l/w) of the sub reflective corners is 1.5 or more, a corner orientation of the main reflective corner deviates at an angle of 10 degrees or more with respect to a point of tangency of an incident plane, a reflection orientation thereof deviates at an angle within 10 degrees, and the corner orientations thereof deviate in the opposite direction to each other.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application under 35 U.S.C. §371 of PCT International Application Serial No. PCT/KR2014/008847, which has an international filing date of Sep. 23, 2014, designates the United States of America, which claims priority to Korean Patent Application No. 10-2013-0112922, filed Sep. 23, 2013, the disclosures of both of which are hereby expressly incorporated by reference in their entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates to a step prismatic retro-reflector capable of retro-reflecting incident light toward a light source by using a retro-reflective structure combined with reflective corners, and more particularly, to a step prismatic retro-reflector with both improved retro-reflection efficiency and improved wide-angle performance. 
       BACKGROUND 
       [0003]    Retro-reflectors are installed or attached to various types of traffic safety facilities such as various types of traffic signs, pavement markers, delineators, and traffic tripods, or items such as safety clothing, automobiles, bicycles, hats, and shoes, of which the visibility needs to be ensured at night, and the retro-reflectors may improve visibility of these items by retro-reflecting incident light, which enters from a front side, toward a light source that emits the light. 
         [0004]    As the retro-reflectors applied to these items in the related art, retro-reflectors provided with glass beads or cube corners have been often used. Since the retro-reflectors in the related art have different retro-reflection characteristics varying depending on incident angles of incident light, the retro-reflectors have advantages and disadvantages. 
         [0005]    For example, retro-reflection efficiency of the retro-reflector using the glass beads is uniform regardless of incident angles, but the retro-reflector using the glass beads has problems in that retro-reflection efficiency is low overall, and a reflection function deteriorates in a case in which water is attached to the surface of the retro-reflector. 
         [0006]    Further, the retro-reflector using the cube corners in the related art has high retro-reflectivity for light having a small incident angle, that is, front light, but rapidly degrades brightness for lateral light having a large incident angle, such that a range of incident angles within which retro-reflection is enabled, that is, retro-reflection visibility is very narrow. Moreover, it is very difficult to design and change a direction of retro-reflection visibility in order to mainly retro-reflect light having a large incident angle. 
         [0007]    To solve the problems, the present applicant has developed ‘Retro-Reflection Unit and Retro-Reflector (Korean Patent Application No. 10-2006-7038)’ which have a complex total-reflection prismatic retro-reflective structure in which reflective surfaces, which are orthogonal to each other, are arranged, in a steplike manner, on a reflective surface of two reflective surfaces which are orthogonal to each other, such that overall retro-reflectivity is high, and particularly, a direction of a main reflection orientation, which is defined as an incident direction in which retro-reflectivity is highest, may be very easily changed without limitation on an angle with respect to a normal direction of an incident plane during a design process. 
         [0008]    However, the retro-reflection unit of the retro-reflector includes two reflective surfaces (a shared reflective surface and a step portion), such that there is a problem in that retro-reflection is enabled only for incident light within a particular incident angle range, and thus a retro-reflection range is very narrow. For example, in a case in which the retro-reflector is developed for front light, very high retro-reflection efficiency is implemented for incident light having an incident angle of zero (0) degree, but in a case in which an incident angle becomes 10 degrees or more, the incident light penetrates the shared reflective surface such that a retro-reflection function of some retro-reflection units is degraded, and as a result, there is a problem in that retro-reflection performance is low for lateral light, and in a case in which the retro-reflector is developed for lateral light, there is a problem in that retro-reflection efficiency is very low for front light with compared to lateral light. Accordingly, since the retro-reflector of Korean Patent Application No. 10-2006-7038 has a very narrow reflection range, there is a problem in that applicability to front light or lateral light is restricted. 
       SUMMARY 
       [0009]    The present disclosure has been made in an effort to solve the problems of the retro-reflector in the related art a step prismatic retro-reflector with improved wide-angle performance, which has very high retro-reflection efficiency in respect to front light, and significantly increases a retro-reflection range by enabling retro-reflection for incident light having a large incident angle without degrading a retro-reflection function for the incident light having a large incident angle. 
         [0010]    A step prismatic retro-reflector with improved wide-angle performance according to the present disclosure has retro-reflector elements arranged thereon, the retro-reflector element including: a main reflective corner having a shared reflective surface of a geometric single plane, and a virtual step surface which is in contact with the shared reflective surface at a right angle; and a plurality of sub-reflective corners each having a pair of independent reflective surfaces which are in contact with each other at a right angle, and arranged along the step surface, in which a corner ratio l/w of the sub-reflective corners is 1.5 or more, a corner orientation of the main reflective corner is deflected at 10 degrees or more with respect to a normal line to an incident plane, a reflection orientation is deflected at a deflection angle of 10 degrees or less, and deflection directions of the corner orientations of the main reflective corners are arranged to be alternately staggered in opposite directions to each other. 
         [0011]    In the aforementioned configuration, the corner ratio l/w of the sub-reflective corner may be 3 or more. 
         [0012]    In addition, the deflection angle of the reflection orientation of each of the retro-reflector elements is within a range of 15 to 30 degrees. 
         [0013]    The step prismatic retro-reflector with improved wide-angle performance according to the present disclosure, which is configured as described above, has very high retro-reflection efficiency in respect to front light. Further, the step prismatic retro-reflector particularly has effective retro-reflection efficiency at a predetermined level or higher even in respect to incident light having a large incident angle, and as a result, a range of incident angles is greatly increased, and thus a retro-reflection region within which retro-reflection is enabled is very wide. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The above-mentioned aspects of the present disclosure and the manner of obtaining them will become more apparent and the disclosure itself will be better understood by reference to the following description of the embodiments of the disclosure, taking in conjunction with the accompanying drawings, wherein: 
           [0015]      FIG. 1  is a front view of a step prismatic retro-reflector with improved wide-angle performance according to an exemplary embodiment of the present disclosure; 
           [0016]      FIG. 2A  is a cross-sectional view taken along line II-II of  FIG. 1 ; 
           [0017]      FIG. 2B  is a reflection path view of  FIG. 2A ; 
           [0018]      FIG. 2C  is another reflection path view of  FIG. 2A ; 
           [0019]      FIG. 3  is an exploded schematic view of a retro-reflector element of the step prismatic retro-reflector with improved wide-angle performance according to the present disclosure; 
           [0020]      FIG. 4  is a perspective view of the retro-reflector element of the step prismatic retro-reflector with improved wide-angle performance according to the present disclosure; and 
           [0021]      FIG. 5  is a transverse cross-sectional view of a reflective corner according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. These embodiments are provided so that those skilled in the art can sufficiently understand the present disclosure, but can be modified in various forms and the scope of the present disclosure is not limited to these embodiments. 
         [0023]      FIG. 1  is a front view of a step prismatic retro-reflector with improved wide-angle performance according to an exemplary embodiment of the present disclosure, and  FIG. 2A  is a cross-sectional view taken along line II-II of  FIG. 1 . 
         [0024]    A step prismatic retro-reflector  1  with improved wide-angle performance according to the exemplary embodiment of the present disclosure is a plate-shaped retro-reflector manufactured by using a light transmissive material such as polycarbonate, ultraviolet ray curable resin, acrylic, or glass, and as illustrated, retro-reflector elements  10  are formed to be densely arranged in a predetermined pattern on a rear surface of the retro-reflector. 
         [0025]    The retro-reflector element  10  of the retro-reflector refers to a retro-reflective structure as a smallest unit capable of retro-reflecting incident light, and in the step prismatic retro-reflector  1  with improved wide-angle performance according to the present disclosure, a main reflective corner  11  in the form of a total reflection prism is formed by a shared reflective surface  11   a  and a virtual step surface  11   b  which is in contact with the shared reflective surface  11   a  at a facial angle of 90 degrees, and sub-reflective corners  12 , which are small reflective corners, are formed to be densely arranged on the step surface  11   b,  such that one step prismatic retro-reflector element  10  is formed by the sub-reflective corners  12  and the shared reflective surface  11   a.    
         [0026]    In one configuration, the rear surface of the step prismatic retro-reflector  1  according to the present disclosure may be coated with a reflecting film  14  by a process such as vapor deposition in order to improve reflectivity by blocking light transmission. 
         [0027]      FIGS. 3 and 4  illustrate the step prismatic retro-reflector element which has a retro-reflective structure as a smallest unit of the step prismatic retro-reflector with improved wide-angle performance according to the present disclosure. 
         [0028]    As illustrated, the step prismatic retro-reflector element  10  defines a step prismatic retro-reflective structure, that is, a retro-reflective structure formed in a steplike manner on one surface (the step surface  11   b ) of a total reflection prism (right-angled prism) having two reflective surfaces (the shared reflective surface  11   a  and the step surface  11   b ) which are orthogonal to each other, and the main reflective corner  11  is formed by the shared reflective surface  11   a  and the step surface  11   b  which are in contact with each other at an angle of nearly 90 degrees, and the sub-reflective corner  12  is formed by neighboring independent reflective surfaces  12   a  and  12   b,  which are paired with each other, in the step surface  11   b  of the main reflective corner  11 . Therefore, the independent reflective surfaces  12   a  and  12   b,  which define the sub-reflective corner  12  by being paired with each other, define, together with the shared reflective surface  11   a,  a set of retro-reflective structure as illustrated in  FIG. 3 , and as a result, the respective retro-reflector elements  10  retro-reflect incident light entering the elements  10 . 
         [0029]    For reference, the reflective corner refers to a reflective structure of a total reflection prism, that is, a reflective structure formed by the two reflective surfaces which are orthogonal to each other, and corresponds to the main reflective corner  11  and the sub-reflective corner  12  in the step prismatic retro-reflector with improved wide-angle performance according to the present disclosure. As illustrated in  FIG. 3 , the main reflective corner  11  is a reflective corner formed by the shared reflective surface  11   a  and the virtual step surface  11   b  which is in contact with the shared reflective surface  11   a  at a facial angle of 90 degrees, and the sub-reflective corner  12  is formed by the independent reflective surfaces  12   a  and  12   b  which are arranged to be in contact with each other at a facial angle of 90 degrees along the step surfaces  11   b  by pairing the independent reflective surfaces  12   a  and  12   b  which face to each other. 
         [0030]    In the step prismatic retro-reflector with improved wide-angle performance according to the present disclosure, the sub-reflective corners  12  of the respective retro-reflector elements  10  have a corner ratio l/w of 1.5 or more. Further, the main reflective corner  11  has a corner orientation Dc which is deflected with respect to a normal line N to an incident plane  1   a  at 10 degrees or more, and a reflection orientation Dr which is deflected within a deflection angle of 10 degrees. 
         [0031]    In the step prismatic retro-reflector with improved wide-angle performance, the corner ratio l/w of the sub-reflective corner  12  refers to an aspect ratio l/w of the reflective corner as illustrated in  FIG. 3 , and has a great effect on retro-reflection performance in respect to incident light having a large incident angle, and the retro-reflection efficiency in respect to incident light having a large incident angle is improved as the corner ratio l/w increases. Consequently, the corner ratio l/w of the sub-reflective corner is one design factor of the step prismatic retro-reflector which has a great effect on a reflection range within which retro-reflection may be carried out with effective reflection efficiency. In the case of the step prismatic retro-reflector with improved wide-angle performance according to the present disclosure, the corner ratio l/w of the sub-reflective corner may be set to 1.5 or more in order to ensure an increased reflection range, and in the present exemplary embodiment, the corner ratio l/w of the sub-reflective corner is set to 2.2. 
         [0032]    As illustrated in  FIG. 5 , the corner orientation Dc in the reflective corner  11  is defined as a direction in which the reflective corner  11  is geometrically arranged, that is, a direction of a bisector which bisects a vertical angle A of the corner which is a nearly right angle, and the corner orientation Dc is a factor for determining a direction and a reflection region in which the reflective corner  11  may corner-reflect light. That is, the reflective corner  11  may corner-reflect light entering the corner  11  at an incident angle within approximately 45 degrees in left and right directions based on the corner orientation Dc. In the case of the step prismatic retro-reflector element  10 , the corner orientation Dc of the main reflective corner  11  determines a direction and a region in which the element  10  may retro-reflect light, thereby retro-reflecting light entering the main reflective corner  11  within a range within 45 degrees in the left and right directions of the corner orientation Dc of the main reflective corner  11 . 
         [0033]    The reflection orientation Dr of the reflective corner  11  refers to a direction in which incident light may be corner-reflected with maximum efficiency, and the reflection orientation Dr is defined as a direction of a median line, which connects a corner vertex A and a median point M of a large side  13  (a line that connects two opposite ends of the corner) in view of a transverse cross section of the reflective corner as illustrated in  FIG. 5 . Therefore, in a case in which two reflective surfaces  11   a  and  11   b,  which define the reflective corner  11 , have different widths, the reflection orientation Dr is deflected toward a reflective surface having a greater width. 
         [0034]    As illustrated in  FIG. 2B , in the case of the step prismatic retro-reflector  1  with improved wide-angle performance according to the present exemplary embodiment, the corner orientations Dc of the main reflective corners  11  of the retro-reflector elements  10  which face each other are deflected with respect to the normal line N to the incident plane  1   a  at a deflection angle α c  of 22 degrees in the left and right directions, respectively, and the reflection orientation Dr is deflected at −1 degree, such that even lateral light of which the refraction angle λr at the incident plane  1   a  reaches maximum 42 degrees may be retro-reflected. Consequently, in a case in which a refractive index of a material is 1.5, even lateral light of which the incident angle λi reaches nearly 90 degrees may be retro-reflected. 
         [0035]    Moreover, as illustrated in  FIG. 2C , in the case of the step prismatic retro-reflector  1  with improved wide-angle performance according to the present exemplary embodiment, the reflection orientation Dr of the main reflective corner  11  of the retro-reflector element  10  has a deflection angle α r  of about −1 degree with respect to the normal line N to the incident plane  1   a,  such that front light having an incident angle of 1 degree or less may be retro-reflected with highest efficiency. 
         [0036]    For reference, the 90 degrees, which is mentioned as a facial angle between the respective reflective surfaces in the present exemplary embodiment, refers to an angle which is slightly greater or smaller, within a range of 1 degree or less, than an optical right angle at which the reflective corner is formed by the reflective surfaces, that is, geometric 90 degrees, and this is to retro-reflect incident light by diffusing the incident light in a conical shape. Therefore, the 90 degrees mentioned in the present specification needs to be interpreted as not being geometric 90 degrees, but as being optical 90 degrees, that is, ‘nearly 90 degrees’ which is greater or smaller than 90 degrees within a range of 1 degree or less. 
         [0037]    According to the step prismatic retro-reflector with improved wide-angle performance according to the present disclosure, which is configured as described above, the reflection orientation Dr of the main reflective corner  11  is directed toward a front side, such that the entirety of the front light entering from the front side may be retro-reflected, when ignoring scattering caused by illumination intensity at the incident plane  1   a  or an optical loss caused by light transmittance of a material, and as a result, retro-reflection efficiency is very high. Moreover, the corner orientations Dc of the main reflective corners  11  are deflected at a predetermined angle or larger in opposite directions to each other, such that even lateral light, which is deflected at an incident angle of 60 degrees or more, may be retro-reflected, and a retro-reflection range is also wide. 
         [0038]    While embodiments incorporating the principles of the present disclosure have been described herein, the present disclosure is not limited to the described embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.