Abstract:
A rotational obstruction and beacon signaling apparatus, in which chip-on-board (COB) packaged light emitting diodes (LEDs) are employed to provide a flashed emission pattern with high luminous intensity. The flash sequence of individual LEDs is controlled by an electronic timing circuit to simulate a rotational or other motional signaling effect.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims an invention which was disclosed in Provisional Patent Application No. 60/596,631, filed Oct. 7, 2005, entitled “Rotational Obstruction and Beacon Signaling Based on High Brightness LED”. The benefit under 35 USC §119(e) of the above mentioned United States Provisional Applications is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a signaling apparatus, and more specifically to a rotational obstruction and beacon signaling apparatus based on high intensity light emitting diodes (LEDs). 
     BACKGROUND 
     Light emitting diodes (LEDs) are considered as an ideal replacement for incandescent lamps for warning and guidance signaling applications owing to their high wall-plug efficiency and long lifetime. The LED based warning and guidance signaling apparatus disclosed in prior arts employ traditional T-pack LED units with luminous intensity less than a few tens of candelas. Thus they either are limited in visibility range or require a large number (several hundreds or even thousands) of LEDs to produce the desired luminous intensity. In addition, some mechanical rotating elements are generally used to produce a rotational emission effect, which elements lack in long-term reliability. Those previous disclosures include U.S. Pat. No. 5,608,290 issued to Hutchisson et al., U.S. Pat. No. 5,313,188 issued to Choi et al., and U.S. Pat. No. 6,753,762 issued to Jorba Gonzalez, and U.S. patent application Nos. 2002/0114161 disclosed by Barnett, and 2002/0145533 disclosed by Bushell et al. 
     Recent development in LED technology makes it possible to deliver high lumen power in one LED unit. Such LEDs have been used for maritime signaling applications as disclosed by Trenchard et al. in U.S. patent application No. 2004/0095777. These LED units have large emission area and beam divergence angle. Thus they can not be treated as point light sources. This makes it extremely difficult for LED beam profile control. In the Trenchard patent application, the signaling apparatus comprise twelve high flux LED units and the light beam produced by the entire LED array is controlled by a specially designed Fresnel lens. This lens is both complicated in structure and difficult to manufacture. In addition, such a lens design is not suitable to produce a rotational signaling effect since the divergence angle of the LED units can not be individually controlled. 
     Therefore, there is a need for an improved LED warning and guidance signaling apparatus with high luminous intensity and mechanical reliability, in which the apparatus is modular designed for efficient production, configuration, and installation, as well as for precise beam property control. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, the luminous intensity of the LED signaling apparatus is enhanced by adopting chip-on-board (COB) packaged high intensity LEDs, in which the LED chips are surface mounted on a thermal conductive substrate for improved heat dissipation. The COB approach provides superior thermal control over conventional T-pack devices as the LED chips are directly attached on the substrate with their whole surfaces as the heat dissipation channel. The improved heat-sinking keeps the temperature of the LED PN junction as low as possible, which makes the LED capable of operating at much higher currents or output levels. It also leads to long lifetime as well as wavelength and intensity stability. 
     According to another aspect of the present invention, the light beam produced by each LED unit in the signaling apparatus is controlled individually by an optical beam transformer, which precisely defines its intensity distribution, divergence angle, and other relevant properties. The spatial distribution and angular orientation of the LED units and the corresponding optical beam transformers are precisely controlled so that the LED beams mix in a pre-determined manner to produce an emission pattern with desired intensity distribution. Such a discrete LED beam control method eliminates the need for complex lens design. It also provides the flexibility to produce relatively complex emission patterns. 
     According to yet another aspect of the present invention, the LED units in the signaling apparatus can operate in a time sequenced flashing mode, where the on-off status, intensity, and wavelength of the LED units are modulated in time domain. The flash sequence of the LED units is controlled by an electronic timing circuit to simulate a rotational or other motional emission effect. The flashing frequency, the intensity and wavelength variation pattern of the LED units can be programmed to achieve different motional signaling effects. The signaling apparatus comprises no mechanical moving parts, which enhances it long-term reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. 
         FIG. 1  illustrates the optical and mechanical structure of one exemplary LED obstruction and beacon signaling apparatus. 
         FIG. 2  illustrates one exemplary rotational flash pattern produced by the LED obstruction and beacon signaling apparatus shown in  FIG. 1 . LEDs in different mechanical stacks are represented by different shades in the figure. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
     DETAILED DESCRIPTION 
     Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to an LED based rotational obstruction and beacon signaling apparatus. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
     In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
     One preferred embodiment of the present invention is illustrated in  FIG. 1 . The signaling apparatus comprises twelve high intensity COB LED units  10  mounted in three vertically adjacent stacks. Each stack comprises four LED units separated by 90 degrees (90°) angularly in the horizontal plane. A 30° angular offset is applied between adjacent LED stacks. Thus the twelve LED units can cover a 360° emission angle. Each LED unit  10  comprises one or more LED chips  11  surface mounted on a thermal conductive substrate  12 , and a secondary optical system  13 , preferably a non-imaging optical lens, to collect and collimate the light emitted from the LED chips  11 . The collimated LED beam has a divergence angle of &lt;10° in both the horizontal and vertical direction. The LED unit  10  further comprise a cylindrical lens array or a high-transmission holographic diffuser  14  as described by Lieberman et al. in U.S. Pat. No. 6,446,467 to homogenize and anisotropically expand the LED beam to a divergence angle of 30°×10° in the horizontal and vertical direction, respectively. The optical beam from the twelve LED units  10  thus cover a full 360° emission angle in the horizontal plane, and a small emission angle in the vertical plane. The COB LED unit in combination with the multi-stack structure makes it possible to produce a greatly improved luminous intensity. The LED beam in the present embodiment exhibits a luminous intensity of several hundred or even several thousand candelas, which enhances its visibility by an order of magnitude over the prior arts. The luminous intensity can be further increased by employing more LED units so that each LED unit operates at a smaller horizontal divergence angle. The LED units  10  may have different emission wavelengths (colors), such as red, blue, yellow or even in the infrared wavelength range for special night vision based warning and guidance signaling applications. The LED units  10  are mounted on a cylindrical shaped metal heat sink  15  for improved heat dissipation. The whole LED signaling module is enclosed in a transparent waterproof housing  16 . 
     The signaling apparatus is controlled by an electronic timing circuit  17 , which can be AC, DC or battery powered. The timing circuit  17  is enclosed in an electronic compartment  18  underneath the housing  16 . A base element  19  below the electronic compartment  18  is used to support the whole signaling apparatus. The timing circuit  17  controls the on-off status and intensity of individual LED units, thus generating a flash pattern. A typical flash pattern of the LED signaling apparatus is illustrated in  FIG. 2 , where the LED units  10  are switched on and off in a sequential manner so that a rotational emission effect is realized. LED units in different mechanical stacks are represented by different shades in the figure. Other emission patterns can be easily realized by programming the timing circuit  17  to control the LED flash frequency, duty cycle, average luminous intensity or even intensity variation profile with time. The modular design of the LED signaling apparatus make it possible to realize complex rotational signaling effects since the divergence angle and intensity distribution of each LED unit are precisely defined. The LED signaling apparatus disclosed in the present invention comprises no mechanical moving parts, which enhances its long-term reliability. 
     In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. For example, the signaling apparatus can adopt other mechanical layouts. The holographic diffuser may be replaced by a micro-lens array. Recitations of the numerical values are illustrative rather than limiting. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.